finetunedataset_GPTAPI.ipynb

{
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  "metadata": {
    "colab": {
      "provenance": [],
      "mount_file_id": "1Le1Vo0m_Ts8Hm4gs0IErvDiJRxEUKNdo",
      "authorship_tag": "ABX9TyOF3mAQvooL2aqVZYvKwiY0",
      "include_colab_link": true
    },
    "kernelspec": {
      "name": "python3",
      "display_name": "Python 3"
    },
    "language_info": {
      "name": "python"
    }
  },
  "cells": [
    {
      "cell_type": "markdown",
      "metadata": {
        "id": "view-in-github",
        "colab_type": "text"
      },
      "source": [
        "<a href=\"https://colab.research.google.com/github/PoYuYang0416/finetune_mixtral7Bv3/blob/main/finetunedataset_GPTAPI.ipynb\" target=\"_parent\"><img src=\"https://colab.research.google.com/assets/colab-badge.svg\" alt=\"Open In Colab\"/></a>"
      ]
    },
    {
      "cell_type": "code",
      "source": [
        "!pip install pdfminer.six openai fitz"
      ],
      "metadata": {
        "colab": {
          "base_uri": "https://localhost:8080/"
        },
        "id": "ayv0dwH9Uddt",
        "outputId": "f169f03b-c2ad-4fc1-e260-fe19dda8c704"
      },
      "execution_count": null,
      "outputs": [
        {
          "output_type": "stream",
          "name": "stdout",
          "text": [
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            "Installing collected packages: looseversion, traits, simplejson, isodate, h11, configparser, configobj, ci-info, rdflib, pyxnat, httpcore, etelemetry, prov, pdfminer.six, httpx, openai, nipype, fitz\n",
            "Successfully installed ci-info-0.3.0 configobj-5.0.8 configparser-7.0.0 etelemetry-0.3.1 fitz-0.0.1.dev2 h11-0.14.0 httpcore-1.0.5 httpx-0.27.0 isodate-0.6.1 looseversion-1.3.0 nipype-1.8.6 openai-1.35.14 pdfminer.six-20240706 prov-2.0.1 pyxnat-1.6.2 rdflib-6.3.2 simplejson-3.19.2 traits-6.3.2\n"
          ]
        }
      ]
    },
    {
      "cell_type": "code",
      "source": [
        "import os\n",
        "from openai import OpenAI\n",
        "import csv\n",
        "\n",
        "client = OpenAI(\n",
        "    api_key=\"\",\n",
        "    organization='',\n",
        "    project='',\n",
        ")\n"
      ],
      "metadata": {
        "id": "eOV-puPTSgFM"
      },
      "execution_count": null,
      "outputs": []
    },
    {
      "cell_type": "markdown",
      "source": [
        "## Chunk the pdfs in the foldr and save the content in a csv file"
      ],
      "metadata": {
        "id": "4rwg4hpQIeuy"
      }
    },
    {
      "cell_type": "code",
      "source": [
        "import os\n",
        "import re\n",
        "import csv\n",
        "from pdfminer.high_level import extract_text\n",
        "from nltk.tokenize import word_tokenize, sent_tokenize\n",
        "import nltk\n",
        "\n",
        "# Ensure necessary NLTK data is downloaded\n",
        "nltk.download('punkt')\n",
        "\n",
        "def read_pdf(file_path):\n",
        "    try:\n",
        "        text = extract_text(file_path)\n",
        "        return text\n",
        "    except Exception as e:\n",
        "        print(f\"Error reading {file_path}: {e}\")\n",
        "        return \"\"\n",
        "\n",
        "def remove_references_section(text):\n",
        "    pattern = r'(References|Reference|Affiliations|ACKNOWLEDGMENTS|Supporting Information|Funding)\\s*.*'\n",
        "    cleaned_text = re.split(pattern, text, flags=re.IGNORECASE)[0]\n",
        "    return cleaned_text.strip()\n",
        "\n",
        "def chunk_text(text, max_tokens=512):\n",
        "    sentences = sent_tokenize(text)\n",
        "    chunks = []\n",
        "    current_chunk = []\n",
        "    current_length = 0\n",
        "\n",
        "    for sentence in sentences:\n",
        "        sentence_tokens = word_tokenize(sentence)\n",
        "        if current_length + len(sentence_tokens) > max_tokens:\n",
        "            chunks.append(' '.join(current_chunk))\n",
        "            current_chunk = []\n",
        "            current_length = 0\n",
        "        current_chunk.extend(sentence_tokens)\n",
        "        current_length += len(sentence_tokens)\n",
        "\n",
        "    if current_chunk:\n",
        "        chunks.append(' '.join(current_chunk))\n",
        "\n",
        "    return chunks\n",
        "\n",
        "# Provide the path to your PDF folder and the output CSV file\n",
        "folder_path = 'your path'\n",
        "csv_output_file = 'your folder path'\n",
        "\n",
        "# Ensure the output directory exists\n",
        "os.makedirs(os.path.dirname(csv_output_file), exist_ok=True)\n",
        "\n",
        "# Extract and save chunked text to CSV\n",
        "with open(csv_output_file, 'w', newline='', encoding='utf-8-sig') as csv_file:\n",
        "    writer = csv.writer(csv_file, escapechar='\\\\', quoting=csv.QUOTE_MINIMAL)\n",
        "    writer.writerow(['file_name', 'chunk'])\n",
        "\n",
        "    for filename in os.listdir(folder_path):\n",
        "        if filename.endswith('.pdf'):\n",
        "            file_path = os.path.join(folder_path, filename)\n",
        "            text = read_pdf(file_path)\n",
        "            if text:\n",
        "                cleaned_text = remove_references_section(text)\n",
        "                chunks = chunk_text(cleaned_text)\n",
        "                for chunk in chunks:\n",
        "                    writer.writerow([filename, chunk])\n",
        "\n",
        "print(f\"Chunked texts saved to {csv_output_file}\")\n"
      ],
      "metadata": {
        "colab": {
          "base_uri": "https://localhost:8080/"
        },
        "id": "C1B3-B2hYiBj",
        "outputId": "7ff4825a-316f-4f6b-aae4-d50bbfa2539f"
      },
      "execution_count": null,
      "outputs": [
        {
          "output_type": "stream",
          "name": "stderr",
          "text": [
            "[nltk_data] Downloading package punkt to /root/nltk_data...\n",
            "[nltk_data]   Package punkt is already up-to-date!\n"
          ]
        }
      ]
    },
    {
      "cell_type": "markdown",
      "source": [
        "## Generate the dataset"
      ],
      "metadata": {
        "id": "uaq1Uz6sIvGW"
      }
    },
    {
      "cell_type": "code",
      "source": [
        "import pandas as pd\n",
        "import json\n",
        "from contextlib import redirect_stdout\n",
        "import io\n",
        "import os\n",
        "import re\n",
        "import csv\n",
        "from pdfminer.high_level import extract_text\n",
        "from nltk.tokenize import word_tokenize, sent_tokenize\n",
        "import nltk\n",
        "# Ensure necessary NLTK data is downloaded\n",
        "nltk.download('punkt')\n",
        "\n",
        "def count_tokens(text):\n",
        "    return len(word_tokenize(text))\n",
        "\n",
        "def create_alpaca_entries(chunks, max_entries=15, max_total_tokens=128000):\n",
        "    entries = []\n",
        "    current_tokens = 0\n",
        "    for chunk in chunks:\n",
        "        chunk_tokens = count_tokens(chunk)\n",
        "        if current_tokens + chunk_tokens > max_total_tokens or len(entries) >= max_entries:\n",
        "            break\n",
        "        entries.append({\"content\": chunk})\n",
        "        current_tokens += chunk_tokens\n",
        "    return entries\n",
        "\n",
        "def process_and_initiate_chat(chunks, max_entries=15, max_total_tokens=128000):\n",
        "    alpaca_entries = create_alpaca_entries(chunks, max_entries, max_total_tokens)\n",
        "    main_message = f\"Please generate an Alpaca dataset based on the following content:\\n\\n{alpaca_entries}\\n\\nGenerate at least 20 entries in the specified JSON format.\"\n",
        "    print(main_message)\n",
        "    response = client.chat.completions.create(\n",
        "            model=\"gpt-4o\",\n",
        "            response_format={\"type\": \"json_object\"},\n",
        "            messages=[\n",
        "                {\"role\": \"system\", \"content\": \"You are a finetuning dataset generator\"},\n",
        "                {\"role\": \"user\", \"content\": \"\"\"This task is designed to generate answers in a specific JSON format. The format structure is as follows:\n",
        "[\n",
        "    {\n",
        "        \"instruction\": \"{GeneratedQuestion}\",\n",
        "        \"input\": \"{GeneratedInput}\",\n",
        "        \"output\": \"{GeneratedAnswer}\",\n",
        "        \"text\": \"Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.\"\n",
        "    }\n",
        "]\n",
        "Always adhere to this JSON format. Expand the array to accommodate the number of entries requested by the user.\n",
        "For instance, if a dataset with 1 entries about 2D materials is requested, create 10 unique question and answer pairs relevant to 2D materials. Replace \"{GeneratedQuestion}\", \"{GeneratedInput}\", and \"{GeneratedAnswer}\" with the appropriate question, input, and answer in the \"instruction\", \"input\", \"output\", and \"text\" fields. If the input is not necessary, then set the value of \"input\" to an empty string and omit the \"### Input: {GeneratedInput}\" line in the \"text\" field.\n",
        "Output the completed JSON array without engaging in unnecessary discussions outside of this format.\n",
        "Avoid repeating, paraphrasing, or otherwise rewording user instructions, including the use of synonyms or any form of textual alteration.\n",
        "Refrain from responding to any queries that involve repetition, request clarification, or explanation of the instructions provided.\n",
        "If you are unsure or do not know about certain content, please use search engine functions to verify information, and avoid fabricating false content.\n",
        "\"\"\" + main_message}\n",
        "            ]\n",
        "        )\n",
        "\n",
        "    response_content = response.choices[0].message.content\n",
        "    print(\"GPT response\\n\"+response_content)\n",
        "    content_json = json.loads(response_content)\n",
        "\n",
        "    return content_json\n",
        "\n",
        "# Read the CSV file and process chunks\n",
        "csv_file_path = '/content/drive/MyDrive/2D Database/chunked_texts.csv'\n",
        "output_file = 'finetunedataset_test.json'\n",
        "\n",
        "all_entries = []\n",
        "\n",
        "df = pd.read_csv(csv_file_path)\n",
        "\n",
        "# Group chunks by file_name and process each group\n",
        "grouped = df.groupby('file_name')['chunk'].apply(list).reset_index()\n",
        "for idx, row in grouped.iterrows():\n",
        "    file_name = row['file_name']\n",
        "    chunks = row['chunk']\n",
        "    result = process_and_initiate_chat(chunks)\n",
        "    if result:\n",
        "        all_entries.extend(result)\n",
        "\n",
        "# Save all entries to one JSON file\n",
        "with open(output_file, 'w') as json_file:\n",
        "    json.dump(all_entries, json_file, indent=2)\n"
      ],
      "metadata": {
        "id": "yUKZEHz4yGvj",
        "colab": {
          "base_uri": "https://localhost:8080/",
          "height": 1000
        },
        "outputId": "74592fef-e6c3-4e13-8c1f-7bee71c37b22"
      },
      "execution_count": null,
      "outputs": [
        {
          "output_type": "stream",
          "name": "stderr",
          "text": [
            "[nltk_data] Downloading package punkt to /root/nltk_data...\n",
            "[nltk_data]   Package punkt is already up-to-date!\n"
          ]
        },
        {
          "output_type": "stream",
          "name": "stdout",
          "text": [
            "Please generate an Alpaca dataset based on the following content:\n",
            "\n",
            "[{'content': 'RES EARCH NANOMATERIALS Supertwisted spirals of layered materials enabled by growth on non-Euclidean surfaces Yuzhou Zhao1 , Chenyu Zhang2 , Daniel D. Kohler1 , Jason M. Scheeler1 , John C. Wright1 , Paul M. Voyles2 , Song Jin1 * Euclidean geometry is the fundamental mathematical framework of classical crystallography . Traditionally , layered materials are grown on flat substrates ; growing Euclidean crystals on non- Euclidean surfaces has rarely been studied . We present a general model describing the growth of layered materials with screw-dislocation spirals on non-Euclidean surfaces and show that it leads to continuously twisted multilayer superstructures . This model is experimentally demonstrated by growing supertwisted spirals of tungsten disulfide ( WS2 ) and tungsten diselenide ( WSe2 ) draped over nanoparticles near the centers of spirals . Microscopic structural analysis shows that the crystal lattice twist is consistent with the geometric twist of the layers , leading to moiré superlattices between the atomic layers . T wo-dimensional ( 2D ) van der Waals ( vdW ) layered materials offer an ideal platform for creating artificial structures with new properties by vertically stacking different layers ( 1–3 ) . Tuning the twist angles be- tween stacked bilayers results in the formation of moiré patterns and the manipulation of electronic states , leading to observations of quantum phenomena , including unconven- tional superconductivity ( 4 ) , moiré excitons ( 5–8 ) , and tunable Mott insulators ( 9 , 10 ) . Twisted structures have been fabricated by elaborate mechanical stacking of different layers in a one-off and low-throughput fashion ( 3–10 ) . Beyond twisted bilayers , recent theo- retical studies also suggest interesting phe- nomena in continuously twisted multilayer structures that are termed “ 3D twistronics ” ( 11–13 ) . Even though the Eshelby twist ( 14 ) was recently demonstrated on screw-dislocated nanowires of layered germanium ( II ) sulfide ( 15 , 16 ) , the amount of twist per layer is quite minute for large-area 2D structures because the Eshelby twist angle is inversely propor- tional to the lateral cross-sectional area . A different approach is thus desired to directly grow twisted 2D materials and control the interlayer twisting . Euclidean space provides the mathematical framework for classical crystallography ( 17 ) . Basic concepts such as crystal lattice and sym- metry operations are defined in Euclidean space , which shape our understanding of the physical world in which we live . Intuitively , flat substrates with Euclidean surfaces are used in the growth and mechanical stacking of 2D materials . By contrast , non-Euclidean spaces refer to curved geometrical spaces 1Department of Chemistry , University of Wisconsin–Madison , Madison , WI 53706 , USA . 2Department of Materials Science and Engineering , University of Wisconsin–Madison , Madison , WI 53706 , USA . * Corresponding author . Email : jin @ chem.wisc.edu where the parallel postulate is false ( 18 ) and the geometric transformations originally de- fined in Euclidean geometry , such as trans- lation and rotation , have different consequences .'}, {'content': 'Because translational symmetry is the central symmetry of crystal lattice , those differences could influence the crystal growth process in non-Euclidean spaces , resulting in exotic new structures . Here , we propose a growth model of screw-dislocated spirals of 2D materials on non-Euclidean surfaces that predicts con- tinuously twisted superstructures in which the large and variable twist angle is ex- clusively determined by the shape of the non-Euclidean surface and experimentally demonstrate this model on metal dichal- cogenides ( MX2 ) . 2D materials typically grow through a layer- by-layer growth mechanism to yield aligned crystal layers . However , owing to the weak vdW interaction between layers , layer-by-layer growth can infrequently generate a small frac- tion of randomly twisted layers as by-products ( 19 , 20 ) , but the theoretical basis for control- ling the twisting from one layer to the next during direct growth is lacking . By contrast , the screw dislocation–driven growth mecha- nism creates “ new layers ” by propagating the self-perpetuating growth steps generated by screw dislocations ( 21–23 ) . Screw dislocation is a line defect that shears part of the crystal lattice along a specific direction . In layered materials , the shear typically happens along the out-of-plane direction and connects layers into one continuous layer , like in a parking ramp ( movie S1 ) . When its stress effect [ i.e. , Eshelby twist ( 14 ) ] is negligible , an ideal screw dislocation preserves the orientation of each layer owing to the global translational sym- metry of the crystal . This generates an aligned spiral shape of edges that are all parallel ( Fig . 1A ) . Such a shape has been observed in many 2D materials such as hexagonal spirals in graphene and hexagonal boron nitride ( 24 , 25 ) as well as in triangular or hexagonal spirals in metal chalcogenides , such as WSe2 ( 22 ) , MoS2 ( 26 ) , WS2 ( 27 ) , and Bi2Se3 ( 28 ) . Geometry provides a fundamental reason behind the aligned shapes of crystals even in the presence of screw dislocations : The trans- lational symmetry of crystal lattice follows Euclidean geometry . This dictates two basic geometric properties for the shape of a single crystal : First , the angle between two adjacent edges is fixed by their crystallographic indices ( 17 ) , and second , the sum of the measures of the exterior angles is 360° for any convex polygon formed by edges in Euclidean geom- etry ( 18 ) . These properties can explain the fact that screw-dislocated MX2 often grow in tri- angular spiral shapes with aligned edges ( Fig . 1A1 and fig . S1A ) ( 22 , 26 , 27 ) . The threefold crystal structure of monolayer MX2 causes its equi- lateral triangular shape ( 29 ) and the 120° ex- terior angles . Even when a screw dislocation is introduced , the translational symmetry of the crystal is still mostly conserved .'}, {'content': 'In the normal spiral shape , for each period of three consecu- tive edges , the sum of the exterior angles is 120° + 120° + 120° = 360° , which means that the new and old edges must be parallel . In a typical crystal growth process , the Euclidean geometry of flat substrates matches the Euclid- ean nature of lattice ; as a result , all layer edges are aligned in these dislocated spirals . By contrast , the sum of the measures of the exterior angles of a polygon is not 360° in non- Euclidean geometry ( 18 ) . Because such a prop- erty is not compatible with the Euclidean nature of crystals , tiling Euclidean crystal lattices in non-Euclidean spaces leads to new consequences . We specifically consider grow- ing 2D vdW crystals on conical surfaces , because conical surfaces are “ developable surfaces ” that are locally isometric to plane , which means that they can be flattened onto a plane with- out distortion ( 30 ) . Conversely , one can bend and fold a plane into a cone without distor- tion : As illustrated in Fig . 1B , one must shear half of the plane along the radius and overlap a sector defined by an angle of a . Unfolding the cone surface then results in a circular sec- tor with the angle of 360° – a , which means that on the cone surface , the angle measure of any “ full circle ” containing the apex is a constant 360° – a and thus the sum of the measures of the exterior angles of any polygon surrounding the apex is also 360° – a . The geometry of the conical surface is non-Euclidean in the sense that it has a singularity at its apex ( 30 ) , which changes the rules of angles on the conical sur- faces and influences the translational and rota- tional operations . If one tries to draw a simple triangular spiral on such a surface by drawing edges by the angles , for every period , the new edge will twist by an angle of a relative to the edge in the last period ( Fig . 1A2 ) , owing to the non-Euclidean geometry of the cone surface . Zhao et al. , Science 370 , 442–445 ( 2020 ) 23 October 2020 1 of 4 l D o w n o a d e d i i f r o m h t t p : / / s c e n c e . s c e n c e m a g . o r g / o n O c t o b e r 2 2 , 2 0 2 0 RES EARCH | R E P O R T A1 A2 60° 60°+α 60°+2α α Euclidean geometry non-Euclidean geometry B fold C1 k = 1 C2 k < 1 cone C3 k > 1 aligned spiral “ fastened ” spiral “ unfastened ” spiral Fig . 1 .'}, {'content': 'Triangular dislocation spiral on Euclidean and non-Euclidean surfaces illustrating the twisting process . ( A1 ) For a triangular spiral on a Euclidean surface , at each vertex , the edge direction changes 120° ; thus , after three vertices , it turns 360° , which makes the edge parallel to its original orientation . ( A2 ) For a triangular spiral on an unfolded non-Euclidean cone surface , after every three vertices , the edge goes across the dashed line once , so it needs to turn an extra angle of a to keep itself straight . ( B ) A cone can be folded from a circle by cutting along the radius and folding with an angle . ( C1 ) Euclidean surface ( k = 1 ) and a corresponding aligned spiral with no twist . ( C2 ) Non- Euclidean cone surface ( k < 1 ) and a corresponding fastened spiral with a positive twist , which forms a right-handed twisting superstructure . ( C3 ) Non- Euclidean hyperbolic cone surface ( k > 1 ) and a corresponding unfastened spiral with a negative twist , which forms a left-handed twisting super- structure . In ( C ) , all screw dislocations are right- handed , and k is defined as the ratio between the angular period of the specific surface to the period of a Euclidean circle . When a vdW crystal grows on such cone sur- faces , it needs to maintain the angles between the edges as required by its Euclidean lattice . Meanwhile , it will also be bent following the curvature of the cone . Therefore , a 2D vdW crystal with a screw dislocation will grow into a supertwisted spiral shape , with a consistent twist angle of a between each successive layer ( Fig . 1A2 and fig . S1B ) . Because the twist orig- inates from the geometric mismatch between the non-Euclidean surface and Euclidean lat- tice , we name this phenomenon “ non-Euclidean twist ” and refer to the resulting twisted multi- layered structures as “ twisted superstructures ” or “ supertwisted spirals ” ( versus minute Eshelby twists ) in the following discussion . 0° A C1 3° 5° 10° B1 15° B2 B 3 -3° -5° -10° -15° D1 E1 F1 500 nm 1 µm 1 µm 500 nm C2 C3 D2 D3 E2 E3 F2 F3 5 µm 20 µm 10 µm 10 µm 5 µm 10 µm 2 µm 5 µm Fig . 2 . Simulation and experimental demonstration of supertwisted spirals on non-Euclidean surfaces . ( A ) Simulated superstructures of triangular dislocation spirals with increasing positive or negative twist angles . ( B1 ) A flat substrate surface yields aligned spirals . ( B2 ) A protruded substrate where the center of the screw dislocation sits on top of a protrusion results in a fastened supertwisted spiral .'}, {'content': '( B3 ) A protruded substrate where the center of the screw dislocation sits on the edge of a protrusion leads to an unfastened supertwisted spiral . ( C ) AFM ( C1 and C2 ) and optical ( C3 ) images of aligned WS2 spirals grown on flat SiO2/Si substrate . ( D to F ) AFM ( D1 , D2 , E1 , E2 , F1 , and F2 ) and optical ( D3 , E3 , and F3 ) images of representative WS2 supertwisted spirals with various twist angles grown around WOx particles on SiO2/Si substrates . We can further describe the shape of these supertwisted spirals using a simple analytic geometry method . We can define two polar coordinates : ( i ) on the cone surface ( rc.s. , qc.s . ) , and ( ii ) on the top-down projection of the cone surface ( rproj. , qproj . ) . Therefore , the cone surface can be mapped to the projection by ( rproj : ¼ krc : s : qc : s : qproj : ¼ k where k = 1 – a/2p is the ratio between the angle of a “ full circle ” enclosing the cone center to the angle of a full Euclidean circle ( 2p , 360° ) . When k = 1 , the surface is flat ( Euclidean ) , resulting in an aligned spiral ( Fig . 1C1 ) , as dis- cussed above . When k < 1 , the surface is a cone , with its angular period ( 2p − a ) less than the lattice period ( 2p ) . Therefore , each full lattice period carries an extra angle of a over into the total twist angle ( fig . S2B ) . Thus , a cone surface transforms an aligned spiral into a “ fastened ” spiral ( Fig . 1C2 ; the perspective view is shown in fig . S1B2 ) , like a fastened spiral torsion spring ( movie S2 ) . When k > 1 , the surface is a de- velopable “ hyperbolic cone ” surface ( 31 ) ( Fig . 1C3 ) . Because the lattice period ( 2p ) is smaller than the angular period of such surface ( 2p − a , where a is negative ) and can not fill up space , an extra angle –a needs to be taken from the next lattice period ( fig . S2C ) . Thus , a developable hyperbolic cone surface transforms an aligned spiral into an “ unfastened ” spiral ( Fig . 1C3 ) , like an unfastened spiral torsion spring ( movie S3 ) . In all three cases , a ( either zero , positive , or negative ) is the twist angle between successive layers . ( See fig . S2 and associated discussion for our suggestion on naming different handed- ness levels of supertwisted spirals . )'}, {'content': 'Therefore , screw dislocations and non- Euclidean surfaces cooperate to create twisted superstructures of vdW crystals : First , the weak vdW interaction allows “ movement ” between layers ; second , screw dislocations continuously generate “ new layers ” and maintain their rel- ative orientations to the old ones ( 22 ) ; and third , the mismatched angular periods be- tween non-Euclidean surfaces and Euclidean lattices provides an extra lattice twist ( a ) for every successive period in a continuous and consistent way . Using the equations derived above , we simulate the shapes of a series of twisted superstructures of right-handed screw- dislocation spirals with increasing positive or negative twist angles ( Fig . 2A and fig . S3 ) . We constrain the boundaries of layers so that the upper layers can not go over the lower-layer edges . The envelopes of the twisting edges can be mathematically proven to be Archimedean curves . Even though the supertwisted spiral shapes with opposite twist angles appear very similar , they are not mirror images of each other , because they all have right-handed screw dislocations ( and different substrate geome- tries ) . This non-Euclidean twist mechanism is also completely different from the lattice Eshelby twist mechanism for nanowires of vdW materials ( 15 , 16 ) . In the Eshelby twist mechanism , the direction of the lattice twist is always the same as the screw dislocations , and Zhao et al. , Science 370 , 442–445 ( 2020 ) 23 October 2020 2 of 4 l D o w n o a d e d i i f r o m h t t p : / / s c e n c e . s c e n c e m a g . o r g / o n O c t o b e r 2 2 , 2 0 2 0 RES EARCH | R E P O R T the twist angle ( a ) is determined by a = b/pr2 , where b is the magnitude of screw dislocation and r is the nanowire radius , so that the twist angle is rather minimal at large radii ( 14 ) . The non-Euclidean twist , however , can have either the same or opposite direction as that of a screw dislocation , which is determined by the type of non-Euclidean substrate surface ( Fig . 1 , C2 and C3 ) . Moreover , the twist angle can be tunable over a wide range and is ex- clusively determined by substrate geometry in theory , regardless of the size of the 2D crystals , which allows them to scale up to any lateral dimension .'}, {'content': 'Although the non-Euclidean twist mecha- nism is mathematically illustrated on an infi- nitely large cone or developable hyperbolic cone surfaces , practically we can realize it on a flat substrate modified with suitable geometric features , on which only the center of a layered crystal spiral is affected by the non-Euclidean twist to continuously generate supertwisted layers . Once the initial orientation of a layer is set by its nucleus , the layer continues to grow along the same direction owing to the trans- lational symmetry of the crystal lattice . Figure 2B shows three possible situations : ( i ) A flat substrate surface yields an aligned spiral with- out any twist ( Fig . 2B1 ) , ( ii ) a protruded sub- strate where the center of a screw dislocation sits on the center of a protrusion results in a fastened supertwisted spiral ( Fig . 2B2 ) , and ( iii ) a protruded substrate where the center of a screw dislocation sits on the edge of a pro- trusion leads to an unfastened supertwisted spiral ( Fig . 2B3 ) . We have experimentally demonstrated the growth of such supertwisted spirals of WS2 and WSe2 on SiO2/Si substrates ( Fig . 2 , D to F , and figs . S4 and S5 ) using a water vapor– assisted chemical vapor transport growth , with MX2 as precursors and water vapor as the transport reagent ( see methods for de- tails ) ( 32 ) . As a comparison , Fig . 2C shows “ normal ” aligned triangular spirals with pa- rallel edges . Such parallel edges rule out the Eshelby twist mechanism as the cause of twisted superstructures in these large pyramid- shaped spirals . The key to achieving non- Euclidean twists is to introduce protrusions onto substrates , as discussed above ( Fig . 2 , B2 and B3 ) . Therefore , we drop-cast SiO2 ( 200-nm diameter ) or WO3 ( < 100-nm diameter ) nano- particles onto SiO2/Si substrates before the growth reactions ( figs . S6 to S8 ) . Intentional introduction of nanoparticles results in a pro- liferation of supertwisted spirals on typical growth substrates even though not every object is twisted . We also found that the reac- tion can spontaneously produce some WOx particle side products ( 32 , 33 ) that can occa- sionally serve as the protrusions leading to the spontaneous growth of supertwisted spirals ( figs . S9 and S10 ) , but this process is much less reproducible . Because the formation mecha- nism is generally the same , we will ignore the difference between SiO2 , WO3 , and spontaneous formation in the subsequent discussion and only focus on understanding the geometric fea- tures of these supertwisted spirals . Under an optical microscope , unlike the simple triangular shapes of aligned spirals ( Fig . 2C3 ) , the supertwisted spirals display circular or spiral shapes ( Fig .'}, {'content': '2 , D3 , E3 , and F3 ) that help us to rapidly spot them when the synthesis yield is low . The circular shape consists of three Archimedean spiral curves that result from the envelope curves of the three sets of edges ( Fig . 2 , D2 and D3 ) , which is a good indication of the twisted superstruc- tures . Detailed atomic force microscopy ( AFM ) imaging on the centers of these representative objects ( Fig . 2 , D1 , E1 , and F1 ) reveals stacks of layers continuously twisting with a consistent A topography 45 B AFM-phase 120 nm i h e g h t ( n m ) 1 µm 0 C AFM-phase D 200 nm 15° E ) ° ( a t e h t 500 400 300 200 100 0 -100 0 1 µm average slope = 14.9° 10 20 layer number θ x 30 Fig . 3 . Twist-angle evolution of a supertwisted WS2 spiral . ( A ) Topography of a representative supertwisted spiral . The height profile along the horizontal dashed line reveals the height and width of the protrusion feature at the center . ( B ) Phase image collected from the red boxed area in ( A ) reveals wrinkles and layer edges at the spiral core . ( C ) Phase image corresponding to ( A ) with all the edges highlighted by colored dashed lines . ( D ) A supertwisted spiral simulated with a 15° twist angle with its edges highlighted . ( E ) Scatter plot of the evolving edge angles in ( C ) as a function of layer number counted from the bottom of the spiral to the top of the spiral . The least-squares linear fittings of each edge set ( dashed lines ) yield an average slope of 14.9° per layer . The colors of the data points correspond to the colors in ( C ) . twist angle from one layer to the next . Such a twist angle increases from Fig . 2 , C to F , re- sembling the simulations shown in Fig . 2A . In fig . S4 , a collection of 30 examples of super- twisted spirals of WS2 or WSe2 are character- ized by optical microscopy and AFM , although not every object can be easily resolved with a simple structure model . Their specific mor- phologies vary with the different twist angles , the number of screw dislocations , and the stacking orders of MX2 layers ( figs . S3 and S11 ) . Notably , Fig . 2 , D1 , E1 , and F1 , as well as all AFM images in fig . S4 , invariably reveals some particles , protrusions , or abnormality near the centers of the superstructures .'}, {'content': 'We further verify the proposed non-Euclidean twist mechanism by examining the protrusion near the center and studying the relationship between the angles of edges and the layer numbers using a representative supertwisted WS2 spiral grown on top of a SiO2 particle ( Fig . 3 ) . The overall superstructure displays three sets of right-handed Archimedean spirals . The protrusion caused by the SiO2 particle in the center is about 120 nm in height and 500 nm in diameter ( Fig . 3A ) , forming a cone shape owing to the deformation of SiO2 nano- particles at the growth temperature around 1000°C ( fig . S6 ; see cross-sectional scanning electron microscopy images in fig . S7 ) . The wrinkles around the center ( Fig . 3B ) are formed as a result of the curvature difference when the WS2 layers transit from the pro- trusion to the flat substrate . Despite these wrinkles , the orientations of all WS2 layers are well preserved away from the center , likely owing to the strain tolerance of 2D crystal growth ( 34 ) . The twisted layer edges can be better visualized with AFM phase contrast ( Fig . 3B ) , which clearly reveals a right-handed screw dislocation . In Fig . 3C , all edges revealed by the AFM phase image are highlighted with colored dashed lines , and their angles are plotted as a function of layer number from the bottom of the spiral to the top of the spiral in Fig . 3E . We found an approximately linear relationship between the angle and layer number for all three “ Archimedean arms , ” and linear fittings yielded an average twist of 14.9° per layer . The simulated supertwisted spiral using a 15° twist angle ( Fig . 3D ) matches the experimental mor- phology ( Fig . 3C ) very well . A similar twist angle analysis was carried out on a more complex supertwisted spiral of bilayers ( fig . S12 ) . Furthermore , we carried out scanning trans- mission electron microscopy ( STEM ) analysis on a relatively thin and simple twisted WS2 superstructure ( Fig . 4 ) to characterize the moiré patterns expected in these twisted superstruc- tures . ( An idealized schematic illustration is shown in fig . S13 . ) Low-resolution high-angle annular dark-field ( HAADF ) imaging of the whole structure reveals the layer edges ( Fig . 4A ) . A 4D STEM dataset collected on each layer Zhao et al. , Science 370 , 442–445 ( 2020 ) 23 October 2020 3 of 4 l D o w n o a d e d i i f r o m h t t p : / / s c e n c e . s c e n c e m a g .'}, {'content': 'o r g / o n O c t o b e r 2 2 , 2 0 2 0 RES EARCH | R E P O R T A STEM-HAADF B PACBED C ) ° ( l e g n a d e t s w i t 20 15 10 5 0 D1 1 μm STEM-HAADF E1 2 nm-1 STEM-HAADF F1 edge PACBED θ x 1 y = 6.64x - 6.12 R² = 0.9854 y = 6.62x - 6.82 R² = 0.9965 2 3 4 layer number STEM-HAADF D2 D3 E2 E3 F2 F3 2 nm 2 nm 2 nm PACBED PACBED PACBED Fig . 4 . STEM characterization of a non-Euclidean twisted superstructure . ( A ) HAADF image of a supertwisted WS2 plate with edges of different layers highlighted by different colors . ( B ) Overall PACBED collected from the red boxed region in ( A ) . The orientation of a specific layer can be measured by measuring the angle of a pair of diffraction disks from that layer . ( C ) Twist angles measured by morphology and diffraction as functions of the layer number , showing highly correlated linear relationships . The lattice angles are measured from six sets of diffraction disks , whereas the morphological twist angles are measured from three edges . R2 , coefficient of determination of linear regression . ( D1 , E1 , and F1 ) High-resolution HAADF images collected from the one- , two- , and three-layer areas in the red rectangular region in ( A ) . The images were high-pass filtered for better visualization . ( D2 , E2 , and F2 ) PACBED collected from areas corresponding to ( D1 , E1 , and F1 ) . Scale bars are 2 nm−1 . ( D3 , E3 , and F3 ) Simulated moiré patterns corresponding to ( D1 , E1 , and F1 ) using WS2 models ( W atoms , red dots ; S atoms , blue dots ) . ( Fig . 4B ) shows the position-averaged conver- gent beam electron diffraction ( PACBED ) pat- tern from the acquisition region , with lines marking diffraction spots attributed to each layer ( fig . S14 ) . Lattice twist angles are mea- sured from the diffraction spots in Fig . 4B and plotted in Fig . 4C together with the morpho- logical twist angle measured from Fig . 4A , showing that they match well . The twist angles increase linearly with the layer numbers at an average of 6.6° per layer . Atomic resolution HAADF images ( Fig . 4 , D1 , E1 , and F1 ) acquired from the one- , two- , and three-layer regions show clear moiré patterns . The corresponding PACBED patterns from the same regions with a different layer number ( Fig . 4 , D2 , E2 , and F2 ) clearly show different sets of diffraction disks from different layers .'}, {'content': 'We also constructed the expected moiré patterns by overlapping multi- ple WS2 models ( Fig . 4 , D3 , E3 , and F3 ) with lattice rotations determined from diffractions , which match the observation well . Character- ization of a more complicated superstructure ( fig . S15 ) leads to similar findings . In addition , we also performed preliminary reflection spec- troscopy and second-harmonic generation im- aging to examine the inversion symmetry in supertwisted spirals ( fig . S16 ) . We show how to generate continuously twisted superstructures of layered vdW mate- rials by combining screw-dislocation spirals with non-Euclidean surfaces . By using nano- particles as protrusions on flat substrates , we can introduce non-Euclidean surfaces to the growth process and experimentally demon- strate the direct growth of supertwisted spirals of WS2 and WSe2 materials with a wide range of twist angles and observed moiré patterns in STEM . More precise control of twist angles could be realized using nanofabricated sub- strates in the future . RE FERENCES AND NOTES 1 . K. S. Novoselov , A. Mishchenko , A. Carvalho , A. H. Castro Neto , Science 353 , aac9439 ( 2016 ) . 2 . Y. Liu , Y. Huang , X. Duan , Nature 567 , 323–333 ( 2019 ) . 3 . F. Liu et al. , Science 367 , 903–906 ( 2020 ) . 4 . Y. Cao et al. , Nature 556 , 43–50 ( 2018 ) . 5 . K. L. Seyler et al. , Nature 567 , 66–70 ( 2019 ) . 6 . K. Tran et al. , Nature 567 , 71–75 ( 2019 ) . 7 . C. Jin et al. , Nature 567 , 76–80 ( 2019 ) . 8 . E. M. Alexeev et al. , Nature 567 , 81–86 ( 2019 ) . 9 . Y. Cao et al. , Nature 556 , 80–84 ( 2018 ) . 10 . G. Chen et al. , Nat . Phys . 15 , 237–241 ( 2019 ) . 11 . F. Wu , R.-X . Zhang , S. Das Sarma , Phys . Rev . Research 2 , 022010 ( 2020 ) . 12 . E. Khalaf , A. J. Kruchkov , G. Tarnopolsky , A. Vishwanath , Phys . Rev . B 100 , 085109 ( 2019 ) . 13 . T. Cea , N. R. Walet , F. Guinea , Nano Lett . 19 , 8683–8689 ( 2019 ) . 14 . M. J. Bierman , Y. K. A. Lau , A. V. Kvit , A. L. Schmitt , S. Jin , Science 320 , 1060–1063 ( 2008 ) . 15 . Y. Liu et al. , Nature 570 , 358–362 ( 2019 ) . 16 . P. Sutter , S. Wimer , E. Sutter , Nature 570 , 354–357 ( 2019 ) . 17 . C. Giacovazzo et al. , Fundamentals of Crystallography , C. Giacovazzo , Ed . ( Oxford Univ . Press , ed . 2 , 2002 ) . 18 .'}, {'content': 'M. J. Greenberg , Euclidean and Non-Euclidean Geometries : Development and History ( Macmillan Learning , 2007 ) . 19 . K. Liu et al. , Nat . Commun . 5 , 4966 ( 2014 ) . 20 . C.-C. Lu et al. , ACS Nano 7 , 2587–2594 ( 2013 ) . 21 . F. Meng , S. A. Morin , A. Forticaux , S. Jin , Acc . Chem . Res . 46 , 1616–1626 ( 2013 ) . 22 . M. J. Shearer et al. , J . Am . Chem . Soc . 139 , 3496–3504 ( 2017 ) . 23 . S. A. Morin , A. Forticaux , M. J. Bierman , S. Jin , Nano Lett . 11 , 4449–4455 ( 2011 ) . 24 . R. Y. Tay et al. , Chem . Mater . 30 , 6858–6866 ( 2018 ) . 25 . H. J . Park et al. , Nano Lett . 19 , 4229–4236 ( 2019 ) . 26 . L. Zhang et al. , Nano Lett . 14 , 6418–6423 ( 2014 ) . 27 . X . Fan et al. , Nano Lett . 18 , 3885–3892 ( 2018 ) . 28 . A. Zhuang et al. , Angew . Chem . Int . Ed . 53 , 6425–6429 l D o w n o a d e d i i f r o m h t t p : / / s c e n c e . s c e n c e m a g . o r g / o n O c t o b e r 2 2 , 2 0 2 0 ( 2014 ) . 29 . J. Dong , L. Zhang , F. Ding , Adv . Mater . 31 , e1801583 ( 2019 ) . 30 . S. Izumiya , M. C. Romero Fuster , M. A. S. Ruas , F. Tari , Differential Geometry from a Singularity Theory Viewpoint ( World Scientific , 2014 ) , p. 384 . 31 . S. M. Farmer , C. R. Calladine , Int . J. Mech . Sci . 47 , 509–520 ( 2005 ) . 32 . Y. Zhao , S. Jin , ACS Materials Lett . 2 , 42–48 ( 2020 ) . 33 . P. K. Sahoo , S. Memaran , Y. Xin , L. Balicas , H. R. Gutiérrez , Nature 553 , 63–67 ( 2018 ) . 34 . K. Wang et al. , Sci . Adv . 5 , eaav4028 ( 2019 ) . 35 . Z. Yuzhou , Yuzhou-Zhao/super-twisted-spirals : Super twisted spirals . Zenodo ( 2020 ) ; http : //doi.org/10.5281/zenodo . 3967881 . 36 . Y. Zhao , C. Zhang , P. M. Voyles , S. Jin , Supertwisted spirals of layered materials enabled by growth on non-Euclidean surfaces . Materials Data Facility ( 2020 ) ; http : //doi.org/10.18126/ M8UGYRK1 . AC KNOWLED GME NTS We thank B. Wang for helpful suggestions regarding the discussion of geometry .'}, {'content': 'Funding : This research is support by the U.S. Department of Energy , Office of Basic Energy Sciences , Division of Materials Science and Engineering , under award DE-FG02- 09ER46664 to S.J. , J.C.W. , Y.Z. , D.D.K. , and J.M.S . P.M.V . and C.Z . were supported by the U.S. Department of Energy , Office of Basic Energy Sciences , Division of Materials Science and Engineering , under award DE-FG02-08ER46547 . We acknowledge the facilities supported by the UW-Madison Materials Research Science and Engineering Center ( DMR-1720415 ) . Author contributions : Y.Z . and S.J . conceived the idea and designed the experiments . Y.Z . performed the simulation , synthesis , AFM characterizations , STEM sample preparation , and data analysis . C.Z . and P.M.V . performed the focused ion beam milling , STEM characterizations , and analysis . D.D.K. , J.M.S. , and J.C.W . performed spectroscopy measurement and analysis . Y.Z . and S.J . wrote the paper with input from all authors . Competing interests : The authors declare no competing interests . Data and materials availability : All data are available in the main text or the supplementary materials . Computer codes for simulating supertwisted spiral shapes are available at Zenodo ( 35 ) . 4D STEM data and averaged PACBED data are available through the Materials Data Facility ( 36 ) . SUPPLEMENTARY MATERIALS science.sciencemag.org/content/370/6515/442/suppl/DC1 Materials and Methods Figs . S1 to S16'}]\n",
            "\n",
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            "        \"instruction\": \"Describe the concept of a non-Euclidean surface.\",\n",
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            "        \"output\": \"Non-Euclidean surfaces refer to curved geometrical spaces where the parallel postulate is false, and the geometric transformations originally defined in Euclidean geometry, such as translation and rotation, have different consequences. These surfaces include shapes like cones and hyperbolic spaces, which introduce unique properties not found in flat Euclidean surfaces.\",\n",
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            "[{'content': 'A r t c l e i www.acsnano.org A Capillary-Force-Assisted Transfer for Monolayer Transition-Metal-Dichalcogenide Crystals with High Utilization Jixing Cai , Huanjun Chen , Yanlin Ke , and Shaozhi Deng * Cite This : ACS Nano 2022 , 16 , 15016−15025 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT : The capillary-force-assisted transfer has shown application for constructing two-dimensional ( 2D ) electronic and potential optoelectronic devices for the advantage of free of spin coating the organic compound and etching the substrate . Currently , the transfer mechanism remains obscure . The capillary adhesion mechanism and capillary invasion separation mechanism were proposed independently and rarely discussed in a comprehensive manner . What is more , the integrity and utilization remain to be improved . Here , we developed the capillary-force-assisted transfer method with high utilization and integrity . Uniformity of water transport was improved by introducing water from the sidewall of the small polydimethylsiloxane ( PDMS ) stamp driven by capillary force . The transfer integrity rate increased , and the location of the complete samples became predictable . The transfer utilization increased as the limited water transportation minimized the impact on the surrounding WS2 . The monolayer triangle WS2 crystals from adjacent areas on the sapphire substrate were transferred one after another . Besides , local mechanical exfoliation of the continuous WS2 thin films was demonstrated , implying that the capillary adhesion is strong enough to break the strong in-plane covalent bond and overcome the van der Waals force between WS2 and sapphire substrate . Finally , the water transport model between two surfaces with different hydrophobicity combinations was derived on the basis of the Young−Laplace equation . The analysis of water transport between different interfaces reveals how capillary adhesion and capillary invasion work together to achieve capillary force transfer . This study highlights the potential of the capillary-force-assisted transfer as an efficient technique for fabricating van der Waals structures based on two-dimensional atomic crystals , especially periodic structures . KEYWORDS : capillary-force-assisted transfer , monolayer transition-metal-dichalcogenide , utilization , Laplace pressure , water transport 1 . INTRODUCTION for applications Monolayer transition-metal-dichalcogenides ( TMDCs ) have shown great potential in light-emitting diodes,1,2 laser diodes,3,4 and low-loss light modulators5,6 for their unique properties such as direct bandgap and high binding energy.7 Among the preparation methods , chemical vapor deposition ( CVD ) growth8 is the most efficient way to obtain high-quality monolayer triangle single crystal and continuous film compared with mechanical peeling9,10 and intercalation.11 Recently , wafer-scale single-crystal chemical 13 grown by CVD on the sapphire substrate WS2 have been reported , which indicates that high-quality large single-crystal TMDCs will be available to support and expand the application of electronic and optoelectronic devices .'}, {'content': 'However , a high temperature is required for good crystallinity of TMDCs during the CVD growth , which is incompatible with the silicon semiconductor devices technology ( e.g. , metal oxide semiconductor ( MOS ) devices ) process.14 A transfer 12 and MoS2 technology provides a solution for device integration based on two-dimensional ( 2D ) materials . To realize the transfer of 2D materials , it is necessary to overcome the van der Waals ( vdW ) force between the 2D materials and the substrate . The strength of vdW force is negatively correlated with the distance between the two surfaces . The epitaxially grown TMDCs are in close contact with the growth substrate , where only the organic from the adhesive can not evenly pull up the 2D material substrate . In the earlier stage , it needs to realize the transfer of such 2D materials by etching the substrate . However , this June 22 , 2022 Received : Accepted : August 15 , 2022 Published : August 23 , 2022 © 2022 American Chemical Society 15016 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 Downloaded via NATL TSING HUA UNIV on June 29 , 2024 at 17:05:45 ( UTC ) .See https : //pubs.acs.org/sharingguidelines for options on how to legitimately share published articles . ACS Nano www.acsnano.org Article Figure 1 . ( a−e ) Scheme of capillary-force-assisted transfer process for WS2 on the sapphire substrate : ( a−d ) views of the transfer process by introducing water from the side of the PDMS ; ( e ) side view of the transfer process by controlling the water volume through monitor the interference pattern in the “ pocket ” . ( f−h ) SEM image of WS2 transferred to SiO2 substrate with a PDMS stamp : ( g ) detailed view of the red box region in ( f ) ; ( h ) magnified SEM image of single triangular WS2 in the red box region in ( g ) . ( i−k ) AFM image , Raman mapping image , and PL mapping image of the transferred monolithic triangle WS2 in ( h ) . method may introduce pollution during the treatment process , and the growth substrate can not be recycled . Driven by the capillary force , the water invasion15,16 can weaken the vdW force between TMDCs and the substrate , to realize the transfer without etching the substrate.15,17,18 The clean transfer method base on polydimethylsiloxane ( PDMS ) stamp without spin coating the organic compound19,20 was further proposed , and the transfer of the wafer-scale CVD MoS2 thin films on sapphire was demonstrated.16 However , whether the transfer method can be broadly applied to monolayer 2D materials needs to be further verified by experiments with more kinds of materials . For example , WS2 epitaxy grown on sapphire has rarely been reported to transfer without etching the substrate . In addition , the large area PDMS stamp without support may bring stress to transferred 2D materials when bent at a large angle .'}, {'content': 'The capillary adhesion between PDMS and 2D materials can also contribute to the transfer.21 The capillary adhesion between two hydrophobic surfaces has been proven to be greater than the vdW force.22,23 It can be predicted that capillary adhesion can overcome the vdW force between TMDCs and substrate and pick up a variety of TMDCs . However , there is still no strong evidence to prove the contribution of capillary adhesion to the pickup of 2D materials as one can not distinguish the contribution of invasion separation in the capillary adhesion and water previous experiments . The uniform transport of water has not been realized , which is the key to realizing repeatable and complete transfer . In this study , a capillary-force-assisted transfer method for CVD monolayer TMDCs with high utilization and integrity was developed . The uniformity of water transportation was improved by introducing water from the sidewall of the small PDMS stamp driven by capillary force , and the WS2 under the PDMS stamp has been demonstrated to be transferred from sapphire to the SiO2 substrate with high integrity . With limited transportation of water under the the PDSM stamp , a single transfer would hardly tear surrounding area of WS2 , and WS2 samples from adjacent areas on the sapphire substrate were repeatedly picked up and transferred to a new substrate , illustrating the high utilization of the transferred material . Also , we experimentally expand the types of materials that can be transferred by capillary-force- assisted transfer . WS2 , WSe2 on the sapphire substrate , and MoS2 on the SiO2 substrate were transferred to the same SiO2 substrate , and the MoS2/MoSe2 heterojunction was con- structed to show the ohmic contact between an interface by directly stacking the picked-up 2D material without removing any organic compound . In addition , a local mechanical exfoliation of the continuous WS2 thin films was demonstrated , which provides evidence for the contribution of capillary adhesion to the pickup of 2D materials . Besides , the water 15017 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 ACS Nano www.acsnano.org Article Figure 2 . ( a ) Illustration of the repeated transfer . ( b ) SEM image of WS2 transferred to a silicon wafer with an oxide surface ( i.e. , SiO2 ) , where the WS2 formed a three-letter pattern . ( c ) Typical SEM image of WS2 transferred to the SiO2 substrate with a PDMS stamp . ( d−f ) Magnified SEM image of the transferred WS2 near the “ pocket ” region , where ( d ) corresponds to the box I region in ( c ) and ( e ) and ( f ) correspond to the red-polyline box region in ( d ) .'}, {'content': '( g−i ) Magnified SEM image of transferred WS2 further from the “ pocket ” region , where ( g ) corresponds to the box II region in ( c ) and ( h ) and ( i ) correspond to the red-polyline box region in ( g ) . ( j−l ) Magnified SEM image of transferred WS2 at the end of the water transport region , where ( j ) corresponds to the box III region in ( c ) and ( k ) and ( l ) correspond to the red-polyline box region in ( j ) . ( m−o ) Optical image of the assembly process of three pieces of WS2 on the selective region of the SiO2 substrate , with a transfer method similar to that for ( c ) . ( p ) SEM image of the three pieces of WS2 crystals after assembly , corresponding to ( o ) . the analysis of water transport model between two surfaces with different hydro- the phobicity combinations was derived on the basis of Young−Laplace equation . As water reach is a prerequisite for capillary force action , transport at different interfaces during the actual transfer process helped us to analyze the transfer mechanism . The analyses suggest that before the edge of TMDCs was separated from the substrate , only the capillary adhesion contributed to the transfer , whereas after the edge of TMDCs was separated from the substrate , water invasion played a major role in the transfer . 2 . RESULTS AND DISCUSSION 2.1 . Transferring and Characterizing Monolayer Triangular WS2 . The microregional transfer process for TMDCs is schematically illustrated in Figure 1 , with WS2 grown on the sapphire substrate as an experimental object . A trapezoid PDMS ( Figure S1 in the Supporting Information ) was held over a humidifier with a 45° tilt angle , and water mist was evaporated at the edge of the slide for about 10 s ( Figure 1a ) . A small amount of the water mist can reach the PDMS stamp on the slide and condense mainly on the PDMS sidewall ( Figure 1a insert ) . Then the PDMS stamp was quickly fixed on 15018 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 ACS Nano www.acsnano.org Article Figure 3 . Assembly and characterization of transferred TMDCs . ( a−c ) Monolayer MoS2 , WS2 , and WSe2 were transferred to a silicon wafer with 300 nm oxide layer ( i.e. , SiO2 ) : ( a ) optical microscope image ; ( b ) corresponding Raman spectra ; ( c ) corresponding Raman mapping . ( d−f ) MoSe2/MoS2 stacking heterojunction by the capillary-force-assisted transfer method : ( d ) optical microscope image of the heterojunction ; ( e ) the corresponding Raman spectra of the heterojunction ; ( f ) the recorded current versus voltage ( I−V ) curves of the heterojunction .'}, {'content': 'The inset in ( f ) shows the schematic illustration of the electrical connection for I−V curve characterization . a homemade 2D material transfer facility over the CVD-grown monolayer WS2 on sapphire ( Figure 1b ) . The overall water distribution surrounding the PDMS was monitored by an optical microscope . After the water droplets on the front of the PDMS had evaporated entirely , the PDMS was slightly squeezed on the sapphire substrate so that the water droplets on the sidewall of the PDMS moved to the boundary between the PDMS and the sapphire substrate ( Figure 1c ) . To monitor the water volume , slowly separate a corner of the PDMS from the substrate , to form a “ pocket ” for collecting and storing the water ( as shown in Figure 1e ) . The amount of water is determined by observing the interference pattern with an optical microscope . With the evaporation of water in the gap , the interference fringe becomes wider and gradually approaches the edge of PDMS ( Figure 1e ) . Then the PDMS was quickly separated from the sapphire substrates . During this separation process , the water droplets move with the separation line . The triangle pieces of monolayer WS2 crystals were picked up from the substrate by the PDMS stamp after the water flowed through . The WS2 crystals on PDMS were then placed on the target substrate and heated at 90 °C for 1 min to release the WS2 . The WS2 crystals under the PDMS stamp ( with a transfer surface area of about 100 μm × 800 μm ) were transferred to the SiO2 substrate ( as shown in Figure 1f ) , most of which maintain the shape of an equilateral triangle ( as shown in Figure 1g ) . The SEM image of the monolithic triangle WS2 shows that the edge of the shape is complete and there are no cracks inside ( as shown in Figure 1h ) . Further , no apparent wrinkles were observed in the atomic force microscope ( AFM ) image ( Figure 1i ) , Raman mapping is uniform ( Figure 1j ) , and photoluminescence ( PL ) enhance- ment on the edge remains after the transfer ( Figure 1k ) . It is worth noting that introducing water by collecting mist rather than steam is one of the keys to the transfer of monolayer TMDC . For the collecting steam mode , the hot water droplets on the PDMS stamp produced secondary evaporation and condensed on the WS2 surface to form water droplets as the sapphire substrate is approached ( but there is no contact ) , and large area cracks and wrinkles were observed in the transferred WS2 crystals ( for more details , see note part 2 and Figure S2 in the Supporting Information ) .'}, {'content': 'Because of the introduction of water from the side of the PDSM , only the WS2 crystals under PDMS were picked up , and there were few contaminations or tearing left behind around the pickup area . Therefore , WS2 from adjacent areas on the sapphire substrate can be picked up one after another and transferred to a new substrate ( Figure 2a ) . WS2 on the 10 mm × 10 mm sapphire substrate could be divided into hundreds of parts with similar properties , which provide the way to transfer monolayer 2D atomic crystals with high throughput and high utilization . As a demonstration , the monolayer triangle WS2 crystals from a sapphire substrate were transferred to a silicon wafer with oxide surface ( i.e. , SiO2 ) and constructed the letter “ CVD ” ( as shown in Figure 2b ) . Also , ten samples of transferred WS2 have similar integrity distributions , and the typical one is shown in Figure 2c . The transferred WS2 in the region close to the “ pocket ” has a high integrity rate . As shown in Figure 2d corresponding to the box I region in Figure 2c , the transferred WS2 is intact over a large area . Figure 2 panels e and f show the detailed view of typical WS2 sample in Figure 2d , where there are no cracks inside the piece WS2 crystals although the middle area of the WS2 in Figure 2f is missing . For the transferred WS2 further from the position of the “ pocket ” , the integrity rate decreases ( as shown in Figure 2g corresponding to the box II region in Figure 2c ) . WS2 with long cracks and local vacancy appears ( as shown in Figure 2i ) beside the central intact WS2 ( as shown in Figure 2h ) . Dense cracks appear at the end of the water transport area ( as shown in Figure 2j corresponding to the box III region in Figure 2c ) . The dense cracks show a curved shape and bend toward the end of water transport ( as shown in Figure 2k , l ) . Thanks to the introduction of water from the side of the PDMS , it is easy to predict the location of the complete sample . The integrity rate increased compared with the previous work.21 The is advantages of high utilization and high integrity rate allow us to select the complete triangular piece of WS2 to assemble 15019 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 ACS Nano www.acsnano.org Article different structures in the selective region . By positioning under an optical microscope and repeating the transfer steps ( similarly to Figure 2c ) , three pieces of WS2 were placed at adjacent positions on the SiO2 substrate in turn , with roughly the same orientation ( as shown in Figure 2m−o ) .'}, {'content': 'The edges of the three WS2 samples remain straight and there are almost no cracks inside the WS2 ( as shown in Figure 2p ) . 2.2 . Transferring and Stacking Different Kinds of Monolayer Triangular TMDCs . The capillary-force-assisted transfer method can be applied not only to WS2 on sapphire substrate . For demonstration , WS2 and WSe2 grown on sapphire and MoS2 grown on SiO2 were transferred to the same SiO2 substrate . Because the three materials have different band gaps , they show different colors under an optical microscope ( as shown in Figure 3a ) . The Raman characteristic peaks of the three samples are 250 , 355 , and 405 cm−1 , respectively ( Figure 3b ) , which are consistent with the peaks of WSe2 , WS2 , and MoS2 . Through false color ( Figure 3c ) , the intensity distribution of the Raman characteristic peaks ( 250 , 355 , and 405 cm−1 ) more intuitively shows the corresponding positions of the transferred three materials , and the results show that the transferred sample is uniform without wrinkles and cracks . The broad applicability of the transfer allows us to choose the most suitable substrate to grow 2D materials and then assemble them to obtain the best characteristics , such as crystal quality and region . removing any organic compound as occurs The transfer process of non-spin-coated organic compound allows us to pick up and stack different TMDCs directly without in transfer . MoS2/MoSe2 heterojunction was traditional wet constructed and shows an approximate linear I−V character- istic curve ( as shown in Figure 3d−f ) , indicating the ohmic contact of the heterojunction . n-Type MoS2 and n-type MoSe2 on the SiO2 substrate were transferred to the center region of the same SiO2 substrate and stacked together ( as shown in Figure 3d ) . The type of material is confirmed by Raman spectroscopy ( Figure 3e ) . The I−V characteristic curve of the structure is approximately linear ( Figure 3f ) , indicating that the n−n junction formed by MoS2 and MoSe2 is in good contact , which proves suitable for constructing vdW stacked heterojunction from monolayer 2D materials . the transfer method is that 2.3 . Local Exfoliating Monolayer Continuous WS2 Film . The capillary-force-assisted transfer method can be extended to peel monolayer TMDC films grown on substrates . For demonstration , a monolayer continuous WS2 film on sapphire was exfoliated by the method , as shown in Figure 4c . The results also provide evidence for the contribution of capillary adhesion to the pick-up 2D materials . Water invasion separation and capillary force adhesion are the water-assisted transfer two potential mechanisms of method . Water invasion separation has been extensively validated . However , there is still a lack of strong experimental evidence to support the contribution of capillary force adhesion to 2D materials transfer .'}, {'content': 'The local exfoliation of a monolayer continuous WS2 film by the capillary-force-assisted transfer method can confirm the contribution of capillary adhesion force to the transfer of 2D materials . The schematic diagram in Figure 4a shows the water distribution and force analysis for a moment before localized exfoliation at the peeling action point . Because water can only transport between PDMS and WS2 before the continuous WS2 film is torn apart , only the adhesion force between PDMS and Figure 4 . Local mechanical exfoliation of the monolayer continuous WS2 film . ( a ) Force distribution view of the WS2 film before tearing . ( b ) Three-dimensional schematic illustration of the localized exfoliation process . ( c ) Optical microscope image of the vacancy area left on the sapphire substrate after transferring the continuous WS2 film . ( d , e ) Optical microscope image and SEM image of the transferred continuous WS2 on the SiO2 substrate , respectively . WS2 contributes to the pickup of the WS2 film . According to the force analysis in Figure 4a , localized exfoliation of the continuous WS2 film requires the adhesion force to break the strong in-plane covalent bonds and to overcome the vdW force between WS2 and the sapphire substrate . By using the capillary-force-assisted transfer process ( as shown in Figure 4b ) , a continuous piece of WS2 is picked up from the sapphire substrate and transferred to the SiO2 substrate . Figures 4 panels c and d show the optical microscopy images of WS2 on the sapphire substrate and the SiO2 substrate after the transfer , respectively . Except for the “ pocket ” area , almost all the WS2 film under the PDMS stamp from the peeling action point was exfoliated from the grown sapphire substrate ( as shown in Figure 4c ) and transferred to the target SiO2 substrate ( as shown in Figure 4d ) . The exfoliated WS2 matches the shape of the vacancy area left on the sapphire substrate , and both of their edges are relatively smooth . SEM images further confirm the integrity of the WS2 film after transfer to the SiO2 target substrate ( as shown in Figure 4e ) . Similar to the transfer results of the triangular piece of WS2 , some area of WS2 were damaged and missing in the regions away from the “ pockets ” , probably because of the nonuniform distribution of water ( for more details , see note part 3 and Figures S3 and S4 in the local exfoliation of Supporting Information ) . The successful the continuous WS2 film provides evidence for the contribution of capillary force adhesion during the transfer process . Also , the tearing of WS2 implies that the surface pressure exerted by water on WS2 exceeds 47 GPa ( i.e. , the strength of single-layer WS2 ) .24 2.4 . Mechanism Analysis of the Transfer .'}, {'content': 'Water reach is a prerequisite for capillary force action , so the analysis of water transport is crucial to the understanding mechanism of capillary-force-assisted transfer method . Interestingly , different water transport behaviors were observed in the wedge between the PDMS and the sapphire substrate and between the PDMS and the continuous WS2 film , respectively . The water tent fills the gap between the PDMS and the sapphire substrate ( as 15020 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 ACS Nano www.acsnano.org Article Figure 5 . Water transporting analysis model . ( a , b ) Illustration of water filling the gap between the PDMS stamp and the sapphire substrate : ( a ) three-dimensional view ; ( b ) corresponding to the sectional view in ( a ) . P0 is the atmospheric pressure , and ΔP is the Laplace pressure . ( c , d ) Illustration view of water transporting between the PDMS stamp and the continuous WS2 film : ( c ) three-dimensional view ; ( d ) corresponding to sectional view in ( c ) . ( e ) Laplace pressure of the gas−liquid interface between two surfaces with different hydrophobicities , where θ1 and θ2 are the hydrophobic angles of the two surfaces , γ is the surface tension coefficient of the gas−liquid interface , and h is the distance between two surfaces . ( f−h ) Illustration of water transporting during the pickup process of the transfer of triangular WS2 : ( f ) three- dimensional view ; ( g ) Laplace pressure analysis of water before the edge of WS2 separated from the sapphire substrate ; ( h ) Laplace pressure analysis of water after the edge of WS2 separated from the sapphire substrate . shown in Figure 5a ) , indicating that the pressure of water at the wedge is greater than the atmospheric pressure ( as shown in Figure 5b ) . However , in the wedge between the PDMS and the continuous WS2 film ( exposed to air for more than 7 days ) , water tends to gather and form spheres rather than spreading to fill the gap ( as shown in Figure 5c ) , implying that the pressure of water at the wedge is less than the atmospheric pressure ( as shown in Figure 5d ) . To understand the water transporting behavior , the gas− liquid pressure between two surfaces with a narrow gap based on the Young−Laplace equation is discussed . The surface tension of the gas−liquid interface between two surfaces with a small distance would cause strong Laplace pressure , resulting in a pressure difference between water and air .'}, {'content': 'Laplace pressure ( ΔP ) of the gas−liquid interface between two surfaces with a narrow gap ( R∥≫ R⊥ ) can be expressed as25 ( 1 ) where R⊥ is the curvature radius of the meniscus perpendicular to the substrate , R∥ is the curvature radius of the meniscus parallel to the substrate , and γ is the surface tension coefficient of the gas−liquid interface . By using the geometric trans- formations , Laplace pressure can be further expressed as a function of the distance between two surfaces and the contact angle of two surfaces ( for more details , see note part 5 in the Supporting Information ) . ( 2 ) Figure 5e shows the derivation results more vividly by showing the cross-sectional diagram of the water between two surfaces . Both the direction and magnitude of the Laplace pressure are affected by the combination of the two surface contact angles according to the derivation results in Figure 5e . The pressure of water is greater than that of air between the two hydrophilic surfaces ( as shown in the first case in Figure 5e ) , which is consistent with the capillary rising26,27 phenomenon in the hydrophilic capillary tube . In contrast , the water pressure is less than the air pressure between the two hydrophobic surfaces ( as shown in the second case in Figure 5e ) , which is consistent with the capillary descending28 phenomenon in the hydrophobic capillary tube . Interestingly , the derived results also predict the water transport behavior between hydrophilic and hydrophobic surfaces , which to our knowledge has not been reported before . When the sum of the contact angles of the two surfaces is less than π , the pressure on the water surface is greater than the atmospheric pressure ( as shown in the third case in Figure 5e ) . In contrast , the 15021 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 =+||ikjjjjjy { zzzzzPRRR11=+ < < + > > < > + < > +=lmoooooooooooooooonooooooooooooooooPhhh ( coscos ) 2,2 ( coscos ) 2,2 ( coscos ) 2,2,02,2,121212121212121212 ACS Nano www.acsnano.org Article pressure on the water surface is less than the atmospheric pressure when the sum of the contact angles of the two surfaces is greater than π ( as shown in the fourth case in Figure 5e ) . Laplace pressure disappears when the sum of the contact angles of the two surfaces is equal to π ( as shown in the fifth case in Figure 5e ) . The water transport model in Figure 5e may explain the different transport behaviors of water in the wedge between the PDMS and the sapphire substrate ( Figure 5a−d ) and in the wedge between the PDMS and the continuous WS2 film ( Figure 5c , d ) .'}, {'content': 'The hydrophobic angle of PDMS after 30 min of UV−O3 treatment was experimentally measured to be about 98.3° ( for more details , see note part 4 and Figure S5 in the Supporting Information ) , which is consistent with refs 29−31 . The contact angles of the continuous WS2 film , which was exposed to air for more than 7 days and the contact angles of [ 0001 ] -oriented sapphire can be estimated to be 83° 32 and 60°,33 respectively . The sum of the contact angles of PDMS and sapphire substrate is less than π ( θpdms + θsapphire = 158.3° < 180° ) , which corresponds to the third case in Figure 5e . The water pressure at the gas−liquid interface is predicted to be greater than the atmospheric pressure ( consistent with Figure 5b ) , and the Laplace pressure will drive the water to fill the gap ( consistent with Figure 5a ) . At the same time , the sum of the PDMS and the continuous WS2 film is greater than π ( θpdms + θsapphire = 181.3° > 180° ) , which corresponds to the fourth case in Figure 5e . The water pressure at the gas−liquid interface is predicted to be smaller than the atmospheric pressure ( consistent with Figure 5d ) , and the Laplace pressure prevents the further entry of water into the gap near the wedge ( consistent with Figure 5c ) . The water transport model in Figure 5e agrees well with the experimentally observed phenomena . According to the above analysis , water exhibits different transport behaviors between two surfaces with different contact angle combinations . In the actual transfer process , water may be transported between the gaps of PDMS−sapphire substrate , PDMS−WS2 , and WS2−sapphire substrate at the same time . transport during the pickup process of Here , triangular piece of WS2 ( Figure 5f ) is analyzed to reveal the transfer mechanism of 2D materials . the water Figure 5g shows a cross-sectional view of the water distribution when the water starts to touch the edge of WS2 . At this point , water can not enter the interface between the closely contacted WS2 and the sapphire , and the Laplace pressure of water can only act between PDMS and WS2 . As demonstrated by local exfoliation of continuous WS2 films in Figure 4 , the capillary adhesion between PDMS and WS2 is sufficient to break the in-plane covalent bonds and the vdW forces between WS2 and the substrate ( for more details , see note part 6 in the Supporting Information ) . Therefore , there are reasons to believe that capillary adhesion between PDMS and WS2 plays a major role in the early stage of the transfer ( as shown in Figure 5g ) .'}, {'content': 'Considering that the contact angle of PDMS is greater than 90° and the contact angle of WS2 ( ranging from 70° to 83° ) 32 is less than 90° , compounding the third and fourth cases in Figure 5e , then the capillary adhesion force can be expressed as ( 3 ) 15022 where ΔP is Laplace pressure , S is the area of water contact , h is the height of the water meniscus , and γ is the surface tension coefficient of the gas−liquid interface . From formula 3 , it can be seen that the lower the meniscus height , the greater the capillary adhesion . This indicates that the transfer method ( as shown in Figure 1 ) can effectively enhance the capillary adhesion by monitoring the interference fringes of the pocket to reduce the height of the meniscus . Under the action of capillary adhesion force , the edge of WS2 was separated from the substrate , at which time water can be transported between PDMS and WS2 and between WS2 and the substrate at the same time ( as in Figure 5h ) . Considering that the contact angle of WS2 is less than 90° , while the contact angle of PDMS is greater than 90° , which is consistent with the third or fourth case in Figure 5e . The Laplace pressure of water between PDMS and WS2 at this point can be expressed as Considering that the contact angles of both WS2 and sapphire are less than 90° , which is consistent with the second case in Figure 5e . The Laplace pressure of water between WS2 and sapphire can be expressed as ( 4 ) ( 5 ) Considering that the meniscus of water between WS2 and sapphire is much smaller than that between PDMS and WS2 , it can be inferred that the Laplace pressure of water between WS2 and sapphire ( ΔP2 ) is much larger than that between PDMS and WS2 ( ΔP1 ) , implying that the transport speed of water between WS2 and sapphire is much larger than that between PDMS and WS2 . According to the above Laplace pressure formula 5 , when water enters the gap between WS2 and sapphire driven by Laplace pressure , the meniscus height further decreases and the Laplace pressure is enhanced . As a result , water can continuously penetrate between WS2 and sapphire substrate , promoting the separation of WS2 and sapphire substrate . Therefore , water invasion separation between WS2 and sapphire plays a major role in the later stage of the transfer ( as shown in Figure 5g ) . 3 . CONCLUSION A simple but generally applicable capillary-force-assisted transfer method with high utilization and integrity was developed . By introducing water from the sidewall of the small PDMS stamp driven by capillary force , uniform water transport was realized .'}, {'content': 'Therefore , the transfer integrity rate increased compared with that in the previous work and the location of the complete samples became predictable ( for more details , see note part 7 and Table S2 in the Supporting Information ) . The limited transportation of water under the PDSM stamp minimizes the impact on surrounding materials and allows for repeatedly transferring WS2 from adjacent areas on the substrate . Besides , local mechanical exfoliation of the continuous WS2 film was demonstrated , implying that the capillary adhesion between PDMS and TMDCs is strong enough to break the strong in-plane covalent bond and overcome vdW force between WS2 and the sapphire substrate . It provides experimental support for the broad applicability of the capillary-force-assisted transfer method to 2D materials , https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 =×=×FPShS ( coscos ) adhesionWSPDMSWSPDMS22=Ph ( coscos ) 1WSPDMSWSPDMS22=+Ph ( coscos ) 2WSsapphireWSsapphire22 ACS Nano www.acsnano.org Article What is more , the Laplace pressure of whose adhesion mainly relies on vdW force . The broad applicability was further experimentally demonstrated by transferring WS2 , WSe2 , and MoS2 to the same SiO2 substrate . the water−air interface between two surfaces with different hydrophobicity combinations was strictly derived . As water reach is a prerequisite for capillary force action , the analysis of water transfer transport at different process helped us to analyze the transfer mechanism . The analyses suggest that capillary force adhesion plays a major role before the separation of the WS2 edge from the substrate . After the WS2 edge is separated from the substrate , water invasion separation plays a major role . interfaces during the actual The transfer method developed in this study will make it available for fabricating electronic and optoelectronic devices based on 2D materials . Especially , the simple way to transfer and stack 2D materials with high utilization provides an efficient way for the exploration of vdW 2D material superlattices and transistors . Besides , the Laplace pressure model can help to understand , predict , and control the water transportation between two surfaces with small distances by monitoring the contact angles of the two surfaces . 4 . METHODS 4.1 . Transfer Method for the Monolayer Triangle TMDCs . The monolayer triangle TMDCs ( WS2 , MoS2 , WSe2 ) crystals were prepared by CVD ( purchased from Shenzhen Six Carbon Technology Inc. , China ) on the sapphire substrate and SiO2 substrate . Deionization ( DI ) water was added to an air humidifier ( povos PW107 ) to generate water mist . A trapezoidal structure PDMS stamp on a glass slide was held at an angle of 45° over misted for about 10 s to condense water on the side of the PDMS stamp , where the area of the PDMS transfer surface was less than 500 μm × 1000 μm ( for more details , see note part 1 and Figure S1 in the Supporting Information ) .'}, {'content': 'After the water droplet on the front of the PDMS had completely evaporated , the PDMS was placed on the substrate and slightly squeezed so that the water droplets on the sidewall of the PDMS reached the boundary line between the PDMS and the substrate . Note that one corner of the sapphire substrate was prepadded , so that the water droplets on the PDMS could finally contact the substrate , and the contact direction between PDMS and substrate could be predicted and repeated . It was best to let the side of PDMS with water droplets finally contact the substrate to prevent water from penetrating into the gap and causing the tear of 2D materials . 4.2 . Transfer Method for the Monolayer Continuous WS2 Film . The monolayer continuous WS2 film was prepared by CVD ( purchased from Shenzhen Six Carbon Technology Inc. , China ) on the sapphire substrate . The transfer of the continuous WS2 film was roughly the same as that of monolayer triangular TMDC , and there was only a difference in the selection of the separation time . When the PDMS and substrate slowly separated to form a “ pocket ” , the water droplet would not follow the separation line in time and the connecting area between water and separation line reduced ( as shown in Figure 5c ) . However , water would quickly spread along the separation line of PDMS and sapphire substrate after the volume of water droplets in the “ pocket ” reduced ( for more details , see note part 6 and Figure S7 in the Supporting Information ) . The PDMS and the substrate separated quickly after the water spread along the separation line of PDMS and sapphire substrate . 4.3 . Characterization . The morphology , composition , and crystallinity of the samples were characterized by scanning electron microscopy ( SEM ) ( FE-SEM , Supra . 60 , Zeiss , Oberkochen , German ) with 10 kV accelerating voltage , atomic force microscope ( AFM ) , photoluminescence ( PL ) , and Raman spectroscopy ( In Via Reflex , Renishaw , Wotton-under-Edge , Gloucestershire , UK ) with a 532 nm laser . The interference pattern was recorded by CCD with a microscope on a self-build two-dimensional transfer platform . ASSOCIATED CONTENT * sı Supporting Information The Supporting Information is available free of charge at https : //pubs.acs.org/doi/10.1021/acsnano.2c06147 .'}, {'content': 'Cutting process of the PDMS stamp , optical microscope image of the PDMS stamp , secondary evaporation and condensation of a hot water droplet on the substrate , typical cases of TMDC tearing caused by nonuniform water transport , measurement of the contact angle of the PDMS , derivation of the Laplace pressure of the water− air interface between two surfaces with different hydrophobic combinations , Laplace pressure model for the water spread at the wedge between continuous WS2 film and PDMS , and comparison of different water introduction methods in water-assisted transfer , as described in the text ( PDF ) AUTHOR INFORMATION Corresponding Author Shaozhi Deng − State Key Laboratory of Optoelectronic Materials and Technologies , Guangdong Province Key Laboratory of Display Material and Technology , School of Electronics and Information Technology , Sun Yat-sen University , Guangzhou 510275 , China ; 0003-1830-2026 ; Phone : ( +86 ) -20-84110916 ; Email : stsdsz @ mail.sysu.edu.cn orcid.org/0000- Authors Jixing Cai − State Key Laboratory of Optoelectronic Materials and Technologies , Guangdong Province Key Laboratory of Display Material and Technology , School of Electronics and Information Technology , Sun Yat-sen University , Guangzhou 510275 , China ; orcid.org/0000-0002-8602-9634 Huanjun Chen − State Key Laboratory of Optoelectronic Materials and Technologies , Guangdong Province Key Laboratory of Display Material and Technology , School of Electronics and Information Technology , Sun Yat-sen University , Guangzhou 510275 , China ; 0003-4699-009X orcid.org/0000- Yanlin Ke − State Key Laboratory of Optoelectronic Materials and Technologies , Guangdong Province Key Laboratory of Display Material and Technology , School of Electronics and Information Technology , Sun Yat-sen University , Guangzhou 510275 , China Complete contact information is available at : https : //pubs.acs.org/10.1021/acsnano.2c06147 Author Contributions S.D . proposed and supervised the project . J.C. carried out the experiments and analyzed the data . Y.K . assisted in experi- ments . J.C. , H.C. , and S.D . discussed and interpreted the results . J.C. and S.D . wrote the manuscript . All authors have approved the final version of the manuscript . Notes The authors declare no competing financial interest . ACKNOWLEDGMENTS This work was financially supported by the National Key Basic Research Program of China ( grant no . 2019YFA0210200 , 15023 https : //doi.org/10.1021/acsnano.2c06147 ACS Nano 2022 , 16 , 15016−15025 ACS Nano www.acsnano.org Article 2019YFA0210201 , and 2019YFA0210203 ) , the National Natural Science Foundation of China ( grant no . 91963205 ) , the Science and Technology Department of Guangdong Province ( grant no . 2020B1212060030 ) , and the Fundamental Research Funds for the Central Universities . ABBREVIATIONS TMDC , transition-metal dichalcogenide ; 2D , two-dimensional ; CVD , chemical vapor deposition ; PDMS , polydimethylsilox- ane ; vdW , van der Waals ; SEM , scanning electron microscopy ; PL , photoluminescence'}]\n",
            "\n",
            "Generate at least 20 entries in the specified JSON format.\n",
            "GPT response\n",
            "\n",
            "   {\n",
            "      \"instruction\": \"Explain the capillary-force-assisted transfer technique for monolayer transition-metal dichalcogenide (TMDC) crystals.\",\n",
            "      \"input\": \"\",\n",
            "      \"output\": \"Capillary-force-assisted transfer is a method used to transfer monolayer TMDC crystals by utilizing capillary forces to control water transport beneath a polydimethylsiloxane (PDMS) stamp. The process involves introducing water from the sidewall of the PDMS stamp, driven by capillary force, to weaken van der Waals forces between the TMDCs and their growth substrate, allowing for efficient transfer without the need for organic spin coating or substrate etching.\",\n",
            "      \"text\": \"Below is an instruction that describes a task. Write a response that appropriately completes the request.\"\n",
            "   }\n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "   \n",
            "  \n",
            "Please generate an Alpaca dataset based on the following content:\n",
            "\n",
            "[{'content': 'MXene Photodetectors Beyond Gold : Spin-Coated Ti3C2-Based MXene Photodetectors Kiana Montazeri , Marc Currie , Louisiane Verger , Pouya Dianat , Michel W. Barsoum , and Bahram Nabet * 2D transition metal carbides , known as MXenes , are transparent when the samples are thin enough . They are also excellent electrical conductors with metal-like carrier concentrations . Herein , these characteristics are exploited to replace gold ( Au ) in GaAs photodetectors . By simply spin-coating trans- parent Ti3C2-based MXene electrodes from aqueous suspensions onto GaAs patterned with a photoresist and lifted off with acetone , photodetectors that outperform more standard Au electrodes are fabricated . Both the Au- and MXene-based devices show rectifying contacts with comparable Schottky barrier heights and internal electric fields . The latter , however , exhibit significantly higher responsivities and quantum efficiencies , with similar dark currents , hence showing better dynamic range and detectivity , and similar sub-nanosecond response speeds compared to the Au-based devices . The simple fabrication process is readily integratable into microelectronic , photonic-integrated circuits and silicon photonics processes , with a wide range of applications from optical sensing to light detection and ranging and telecommunications . Photodetectors have a wide range of applications and are pres- ently in great demand due to the explosion in information , data transport , and processing needs , that is facilitated by fiber optics tele/data communications . In particular , high band- width is essential for data center operations supporting appli- cations such as Internet of things ( IoT ) , autonomous vehicles , artificial intelligence , and virtual reality among other Internet K. Montazeri , Dr. P. Dianat , Prof. B. Nabet Electrical and Computer Engineering Department Drexel University Philadelphia , PA 19104 , USA E-mail : nabetb @ drexel.edu Dr. M. Currie Optical Sciences Division Naval Research Laboratory Washington , DC 20375 , USA Dr. L. Verger , Prof. M. W. Barsoum Materials Science and Engineering Department Drexel University Philadelphia , PA 19104 , USA Dr. P. Dianat Nanograss Solar LLC 1407 Bethlehem Pike , Suite 303 , Flourtown , PA 19031 , USA The ORCID identification number ( s ) for the author ( s ) of this article can be found under https : //doi.org/10.1002/adma.201903271 . DOI : 10.1002/adma.201903271 demands . The need for high-speed , high- responsivity detection is traditionally met by p-type–intrinsic–n–type ( PIN ) photo- diodes , [ 1 ] avalanche photodiodes ( APD ) , [ 2 ] metal–semiconductor–metal ( MSM ) , [ 3,4 ] or metal–graphene–metal [ 5–7 ] photodetectors . Of these , top-illuminated , MSM devices are planar , relatively easy to fabricate , and are more readily integratable with field effect transistor ( FET ) technology as they exploit the same Schottky contacts used for the FET gate , and do not require the p and n doping of the bipolar technology . MSM photodetectors consist of two Schottky contacts typically fabricated as interdigital electrodes on top of a semicon- ductor .'}, {'content': '[ 3,4 ] These metallic contacts—typi- cally Ti/Pt/Au [ 8 ] for GaAs and other III–V semiconductors—are produced by pat- terning a substrate by conventional photo- lithography , and subsequently depositing a metal under vacuum by either evapora- tion or sputtering , followed by either lift-off or etching . Light is absorbed between the contacts and the optically generated carriers are swept into them by an externally applied electric field that enhances the internal field of the rectifying Schottky contacts . [ 9,10 ] MSM photodetectors , however , have higher dark cur- rents , Idark , hence higher noise , compared to PINs and APDs , although several techniques exist to reduce Idark by , e.g. , increasing the rectifying Schottky barrier heights of the metal– semiconductor interfaces using a wider bandgap semicon- ductor such as AlGaAs , [ 11 ] establishing a reduced dimensional final density of states in the semiconductor , [ 12 ] and producing confined carrier gases which repel the injected electrons from the metal . [ 13 ] For all these devices , high responsivity requires larger absorption areas . [ 14 ] However , increasing a device ’ s surface area limits its bandwidth both by increasing the RC time constants , and transit times of the optically generated carriers to the collection electrodes . [ 15 ] A tradeoff therefore needs to be engineered depending on application . The MXene family is one of the latest additions to the world of 2D materials . MXenes are 2D transition metal car- bides or carbonitrides , discovered in 2011 [ 16 ] and currently number around 30 , with new ones discovered on a regular basis . MXenes are typically produced by selective etching the A-layers from the Mn+1AXn phases . [ 17 ] The latter are layered , machinable ternary carbides and nitrides , where M is an early Adv . Mater . 2019 , 31 , 1903271 1903271 ( 1 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim CommuniCationwww.advmat.de transition metal , A is an A-group element , and X is C and/or N and n = 1 to 3 . Upon etching , the A-layers , mostly Al , are replaced by various surface terminations , mostly ─O , ─OH , and/or ─F , [ 18 ] although recent studies show that novel termina- tions such as Cl [ 19 ] can also be engineered . Interest in MXenes has exploded recently for a number of reasons , chief among them is that they are hydrophilic and yet quite conductive . Another reason is the ease by which large quantities of stable aqueous colloidal suspensions are pro- duced . A number of excellent review articles exist on these materials . [ 20–25 ] To date , MXenes have been used in numerous applications , achieving , in many cases , record values .'}, {'content': 'MXenes have been used as electrodes in batteries and electrochemical capacitors , [ 26 ] textile supercapacitors , [ 27,28 ] photodetectors , [ 29 ] electrical contacts such as Schottky electrodes , [ 30 ] or ohmic contacts with modified MXene chemistries , [ 31 ] and spayed- on antennas . [ 32 ] Since transparent contacts are widely used for touch sensitive screens , [ 33 ] solar cells , [ 34 ] and organic light emitting diodes ( OLED ) , [ 35 ] MXenes could also be materials of choice for these applications . Using MXene transparent contacts offers an obvious advan- tage that mitigates the aforementioned tradeoff between car- rier transit distance and responsivity , should they maintain , as shown below , other important attributes of Schottky metal– semiconductor contacts such as large barrier heights , built-in potentials , and large internal electric fields . [ 15 ] As just noted , if thin enough , MXene films are both conductive and trans- parent . [ 36–38 ] Here , we deposit transparent , metallic Ti3C2Tz- based contacts on gallium arsenide ( GaAs ) , substrates to pro- duce MXene–semiconducting–MXene , henceforth referred to as MX–S–MX , photodetecting devices . The purpose of this work is to quantify the optoelectronic characteristics of MX–S– MX devices and compare them to conventional MSM devices with Ti/Au Schottky contacts . In what follows , we produce thin MXene films and characterize their optical properties . In order to construct a device , however , it is necessary to pattern the electrodes . MXene patterning has previously been carried out using laser printers , [ 39 ] or microcontact printing techniques . [ 40 ] The resulting feature sizes—in the hundreds of micrometers range—are too large for our purpose . Microintaglio printing has been used for patterning other types of 2D materials , [ 41 ] car- ried out in vacuum chambers . Here , we show that much finer patterning , limited by our photolithography , is possible , where the MXene films are spin-coated on GaAs substrates and lifted off by simple immersion in acetone . Schematics of the fabri- cation processes and resulting devices together with energy band diagrams are shown in Figure 1 . The process used , shown schematically in Figure 1 , is carried out at room temperature in ambient air , and resulted in device feature sizes of the order of 2 µm , although the devices studied here have larger separations between contacts . The results reported below confirm that this inexpensive , simple , scalable process results in photodetectors Figure 1 . Fabrication process and energy band diagrams for MXene–GaAs–MXene ( MX–S–MX ) photodetector devices . a , b ) Preparation of MXene colloidal suspension . In ( c ) and ( d ) , conventional photolithography is performed resulting in exposed areas for contact deposition . e ) MXene aqueous colloidal suspension is spin-coated , and f ) lifted off by immersion in acetone .'}, {'content': 'g ) SEM of the final device showing cathode–anode separation gap . h ) Sketch of the energy band diagram of device under moderate bias—showing the Schottky contacts at cathode and anode , the barrier height , built-in voltage , internal field , and depletion regions . i ) Same as ( h ) , but under high biasing voltage resulting in flat-band conditions . Adv . Mater . 2019 , 31 , 1903271 1903271 ( 2 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License that were as good as and , in most attributes , better than those fabricated with Ti/Au electrodes . The MXene chosen for this work is Ti3C2Tz because it is by far the most studied and thus best understood . To make our devices , first the Ti3AlC2 MAX phase ( Figure 1a ) was etched and delaminated ( Figure 1b ) . The electrode pattern was then formed using photoresist and contact lithography on the GaAs substrate ( Figure 1c ) and developed ( Figure 1d ) . The MXene colloidal suspension was then spin cast on the substrate ( Figure 1e ) . Lastly , the photoresist was removed by immersing the device in acetone ( Figure 1f ) leaving two MXene pads . Spac- ings as narrow as 2 µm were obtained . The sharpness of the edges and corners is noteworthy , indicating that the resolution of this method is limited by lithography ; our results are orders of magnitude better than prior work . [ 39,40 ] Details of the fabrica- tion methods and experimental techniques can be found in the Experimental Section and Section S1 in the Supporting Infor- mation . The energy band diagram of our MX–S–MX device is shown in Figure 1h under moderate bias , and under large external bias in Figure 1i . Before photodetector device fabrication , a thin Ti3C2Tz film was deposited on a silica substrate . Details of the film prepara- tion by spin casting is provided in Section S1 in the Supporting Information . Figure 2 shows the measured transmittance and reflectance of a Ti3C2Tz film of thickness ≈19.2 nm , indicated as “ thin , ” which was used for device fabrication . The absorptance spectrum , absorptance = 1 − ( reflectance + transmittance ) , is calculated in Figure 2c , the inset of which shows that half of the silica samples were covered and provide the baseline spectra that is shown in these figures . The wide absorption spectra , from 350 to 2200 nm , of these films are notable , with the inter- esting attribute of high absorptance in the UV range .'}, {'content': 'Figure 1g shows typical scanning electron microscopy ( SEM ) images of two Ti3C2-based pads separated by a gap of ≈2 µm . The results reported below confirmed that this inex- pensive , simple , scalable process resulted in photodetectors that were as good as and , in most figures of merit ( FOM ) , better than those fabricated with Ti/Au electrodes . This is notable given that—apart from the mask aligner—nothing more sophisticated than a tabletop spin-coater was needed . This ambient condition process can be readily integrated into microelectronic , photonic-integrated circuit ( PIC ) , and silicon photonics ( SiP ) processes , with a wide spectrum of possible applications ranging from optical sensing to light detection and ranging ( LiDAR ) , to optical tele/data communications . To allow for side-by-side comparisons , Ti/Au–GaAs–Ti/Au MSM devices were fabricated using the same mask set and lithography technique as for the MX-based devices . In this case , electron-gun evaporation of , first a 5 nm Ti adhesion layer , followed by a 120 nm Au layer was used to deposit the elec- trodes . Pictures of the two devices are shown side by side in Figure 3a , e . Figure 3 compares the current–voltage ( I–V ) optical response of identical geometry devices—one MXene ( left-hand column ) and the other Au-based ( right-hand column ) —under dark and at wavelengths of 532 , 780 , and 830 nm as a function of bias . The λ of 532 and 780 nm were used to stress contact transparency ; the 830 nm because it is used for high-speed , short-range optical tele/data communications applications . Figure 3 shows that the MXene-based device has a dark cur- rent , Idark of 0.6 nA at ( 533 nm ) and 0.9 nA at ( 780 and 830 nm ) for MX , which is comparable to 0.2 nA for Ti/Au MSM , and is remarkably low for such a large area device . In order to inves- tigate the mechanisms of Idark flow across the MXene-semicon- ductor junction devices with cathode–anode gaps of 5 , 15 , and 35 µm , respectively , were fabricated . Section S3 ( Figure S1 ) in the Supporting Information shows that Idark is independent of gap size , and relatively independent of the applied voltage . Had the contacts been ohmic , the current would have changed by a factor of 3 and 7 , respectively , relative to the 5 µm gap of the device shown in Figure S1a in the Supporting Information . This means that a rectifying Schottky barrier exists at the MX–S interface , which dominates current transport . It follows that the energy band diagrams depicted in Figure 1h , i are applicable . This also implies band bending and the presence of an internal electric field at the contacts , which in turn affects the transport and collection of the optically generated carriers .'}, {'content': 'Besides having similar Idark , hence noise , a remarkable five orders of magnitude change in photocurrent is observed at 8 V bias under illumination by 0.34 µW of optical power . A comparison of the photocurrent versus optical power is shown in Figure 4 for λ = 532 , 780 , and 830 nm , at various biases . It is clearly observed that replacing Au with MXene substantially improves the optical response , particularly for λ = 830 nm where an enhancement by a factor of nearly 4 is observed at 8 V bias . Figure 2 . Optical properties of the Ti3C2 film with nominal thickness of 19.2 nm compared to the silica baseline . a ) Measured transmission ; and b ) reflection spectra . c ) Absorptance = 1 − ( reflectance + transmittance ) . Inset in ( c ) shows a silica substrate half of which was covered and used for comparison . Wide spectral opacity and nearly 30 % absorptance from 350–2200 nm in addition to high absorptance in UV range are notable . Adv . Mater . 2019 , 31 , 1903271 1903271 ( 3 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License Figure 3 . Comparison of current–voltage characteristics of MXene–GaAs–MXene ( MX–S–MX ) and conventional Ti/Au–GaAs–Ti/Au ( MSM ) photo- detectors with gap spacing of 10 µm . a ) Confocal microscopy image of the fabricated MX–S–MX photodetector with an overlay of the laser spot size , and e ) the same but for MSM . b–d ) Current–voltage responses of MX–S–MX to 532 , 780 , and 830 nm wavelength light , respectively . f–h ) The same as ( b ) – ( d ) , respectively , but for the MSM device . Responsivity , defined as the ratio of photocurrent to incident [ mA W−1 ] can be extracted . The results are optical power ph =R I P opt listed in Table 1 . External quantum efficiency ( QE ) , η is defined as the number of electrons circulating in the external circuitry per incident × R ( λ in µm ) , 1.24 photon , and relates to responsivity by : [ 42 ] λ and is detailed in Section S4 ( Figure S2 ) in the Supporting Infor- mation . That data is consistent with Figure 4 and Table 1 . It shows that replacing Au by MXene in these devices substantially increases their responsivity and quantum efficiency for all η = wavelengths and at all bias levels .'}, {'content': 'In fact , the 280 mA W−1 responsivity observed under 8 V bias at 830 nm meets the stringent needs of LiDAR applications , [ 43,44 ] is quite remarkable for this simple device and is better than the Ti/Au-device respon- sivity of ≈72 mA W−1 ( see Table 1 ) . Responsivity ( R ) , relates to detectivity * D R = / 2 q A I dark , and allows us to determine an important figure of merit , the noise equivalent power ( NEP ) , which determines the minimum inci- dent power , where the detector can distinguish a signal from the background noise level . NEP may be approximated as [ 45 ] Adv . Mater . 2019 , 31 , 1903271 1903271 ( 4 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License Figure 4. a–e ) Comparison of MX–S–MX ( a ) ( left column ) and MSM ( e ) ( right column ) detectors ’ photocurrent under various optical intensities and at different biases and with gap spacing of 10 µm . Top row : b , f ) response to λ = 532 nm incident light . Middle row : c , g ) λ = 780 nm . Bottom row : d , h ) λ = 830 nm . MX–S–MX detector outperforms the Ti/Au-based device with up to 300 % more responsivity at all measured wavelengths , most significantly at λ = 830 nm . ( = ) / * ⋅ ∆A f D , where Δf is the measurement bandwidth NEP and A is the active area of the device taken to be the area of the laser spot in both cases . Table 2 provides a comparison of the MXene- and Ti/Au- based devices on the basis of several FOMs , namely , R [ mA W−1 ] , QE , D * [ Jones ] , NEP \\uf8ee \\uf8f0\\uf8ef defined as 10 log 10 inP NEP W Hz \\uf8f9 \\uf8fb\\uf8fa , and dynamic range ( DR ) [ dB ] , where Pin is optical input power . Further insight into the large DR is provided in Figure 4 which shows photocurrent versus incident optical power at three wavelengths and several bias conditions , as well as Figure S2 in the Supporting Information which compares the external quantum efficiency of Au- and MXene-based devices at these wavelengths .'}, {'content': 'On the basis of all these FOMs , the MXene- based device that is simply spun on a wafer and dipped in acetone , outperforms Ti/Au by a large margin , the most impressive of which , perhaps , is achieving nearly four times improvement in R at the desirable wavelength of 830 nm ( Table 1 ) . Considering these FOMs , the MX–S–MX devices Adv . Mater . 2019 , 31 , 1903271 1903271 ( 5 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License Table 1 . Responsivity [ mA W−1 ] at ≈300 µW input power . Bias [ V ] MXene–GaAs–MXene Ti/Au MSM I dark = * A T A 2 exp −\\uf8eb q φ B \\uf8ec K T \\uf8ed B \\uf8f6 \\uf8f7 \\uf8f8 exp ∆\\uf8eb q φ im \\uf8ec K T \\uf8ed B \\uf8f6 \\uf8f7 \\uf8f8 ( 1 ) 532 nm 780 nm 830 nm 532 nm 780 nm 830 nm 2 4 6 8 27 59 103 155 24 50 106 195 32 86 170 278 16 33 59 95 26 36 55 82 have enhanced performance metrics compared to a number of 2D-based photodetector technologies currently in use . [ 46 ] To emphasize the importance of electrode contact transpar- ency , we illuminated a corner of our MXene-based device as shown in Section S4 ( Figure S1d ) in the Supporting Informa- tion . A change in photocurrent by a factor of ≈400 was obtained due to the transparency of the contacts , and does not have a counterpart in the Ti/Au MSM device . This provides a prom- ising platform in cases where the light source is highly diver- gent , and is difficult to focus all the light power on an active region with narrow feature sizes . The transparency of the con- tacts as well as their increase in conductivity under illumina- tion are potentially useful in applications such as neuronal recording , [ 47 ] particularly for optogenetics purposes . [ 48 ] The devices ’ optoelectronic response was measured at four average optical powers ( 3 , 30 , 300 , and 700 µW ) with 8 V of bias applied through a bias-T . Figure 5a shows the MXene-based device ’ s response , while Figure 5b is the pulse response of the Ti/Au device , which compare temporal responses at 300 µW optical power . Measured fall time and pulse width values are given on Figure 5 and reported for other optical powers in Section S5 ( Figure S3 ) in the Supporting Information .'}, {'content': 'Our MXene-based device exhibits a fast pulse width of 225 ps , which , although slower than Ti/Au ’ s 78 ps , still corresponds to operation near the 3 GHz range , which meets many of pre- sent speed requirements and is orders of magnitude better than competing previous works in perovskite/MXene devices that reported an 18 ms time response . [ 49 ] Considering the large cathode–anode transit distance in present devices , optimization of device geometry should result in faster MXene-based devices . As experimentally shown above , the MXene–GaAs contacts are rectifying ( Schottky ) , hence Idark of the MX–S–MX device is dominated by the properties of the reverse biased cathode , described by the Richardson and Dushman equation [ 50,51 ] Table 2 . Figures of merit ( FOM ) at ≈300 µW input power , under 8 V bias . Photodetector λ [ nm ] Figures of merit R [ mA W−1 ] η [ % ] D * [ Jones ] MX–S–MX Ti/Au MSM 532 780 830 532 780 830 155 195 278 95 82 72 36 31 42 22 13 11 NEP W Hz \\uf8ee \\uf8f9 \\uf8f0\\uf8ef \\uf8fb\\uf8fa 6.3 × 10−14 8 × 1010 8.1 × 1010 6.1 × 10−14 11.6 × 1010 4.3 × 10−14 7.9 × 1010 6.2 × 10−14 7.2 × 1010 6.9 × 10−14 6.3 × 1010 7.9 × 10−14 72 27 53 38 to where φB is the Schottky barrier height , A * is the Richardson constant , φim is the barrier lowering due image force , and the other symbols have their usual meaning . Equation ( 1 ) shows the significance of the in determining Schottky barrier height the Idark values . In the limiting case , that the semiconductor has no surface states , the barrier height is the difference of the metal work function ( φm ) and semiconductor electron affinity ( χs ) : [ 52 ] φB = φm − χs . This only applies to sil- icon , however . In our case , due to the large number of surface states , the Fermi level is pinned at the semiconductor , resulting in barrier heights that are relatively independent of φm , and for III–V compounds , such as GaAs , is φ ≈ B ≈E g 0.8eV . [ 52 ] 2 3 The fact that Idark in Figure 3 is comparable for the MXene and Au-based devices , and that it is independent of the cathode–anode distance , validates the point that our Ti3C2-based electrodes act like any other metal on GaAs . It is thus not surprising that it can substitute for Au , with the advantage of being formed at room temperature , using tabletop equipment , with no need for vacuum deposition , at low cost , while also being transparent to light .'}, {'content': 'The MX–S–MX device is thus similar to an MSMs and consists of two back-to-back Schottky diodes , with a barrier between MXene and semiconductor , the value of which is pri- marily determined by the pinned Fermi level on the GaAs side . This contact produces a built-in voltage , a strong local electric field on the GaAs side , and a concomitant depletion region , the width of which depends on the built-in voltage . Application of a bias voltage , causes one of the contacts to become a reverse biased cathode , which dominates current transport . Figure 1h shows a sketch of the energy band diagram ( EBD ) of the MX–S–MX device under moderate applied external bias , most of which is dropped at the cathode , extending its deple- tion region ( W1 ) to point x1 , with the remainder dropping at the anode and reducing its depletion width ( W2 ) to point x2 . While W1 and W2 are under strong ( > 10 kV cm−1 ) e-fields , the remainder of the distance between contacts , namely , ( x2 − x1 ) , is undepleted bulk with no e-field , and is in the so-called below “ reach-through ” condition . Further increase of bias depletes the whole distance ( W ) , between contacts and is called “ flat-band ” as shown in Figure 1i . Figure 1h , i helps elucidate device behavior when light illuminates the gap between the contacts . Several current components can be observed , including the holes that are gener- ated within W1 and are swept quickly to the cathode . The electrons , on the other hand , drift to the edge of the depletion region , where they would diffuse through the bulk , overcome the built-in voltage at the anode , and are collected there . The electron–hole pairs ( EHP ) generated in the anode region W2 , have an opposite flux , however , their numbers are much smaller since W1 ≫ W2 . DR [ dB ] 96.7 96.9 98.4 96.8 96.3 95.7 Adv . Mater . 2019 , 31 , 1903271 1903271 ( 6 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License Figure 5 . Comparison of the temporal response of MXene- and Ti/Au-based devices to excitation by 100 fs pulses of 830 nm light at 8 V bias under various indicated optical powers . a ) MXene device pulse response ; inset shows same data normalized to peak amplitude . b ) Same as ( a ) for Ti/Au MSM . Pulse width , rise time , and fall times are indicated for 300 µW optical power .'}, {'content': 'Results for other optical powers are reported in Section S5 in the Supporting Information . By neglecting carriers recombination , and applying the con- dition of continuity of current in both depletion regions , the total current of the photodetector is calculated , as detailed in Section S6 [ 11 ] ( Equation ( S12 ) ) in the Supporting Information . The first term in Equation ( S12 ) in the Supporting Infor- mation is the most significant and is due to the EHPs that are generated in the cathode and anode depletion regions . The middle two terms are due to carriers generated in the bulk and extracted at the end of the cathode depletion region . The last term is the current that is due to the extraction of the holes at the anode . For the special case here that the undepleted region is much wider than the diffusion length , and W1 ≫ W2 , Equation ( S12 ) in the Supporting Information reduces to J = qG W L 1 + ( ) p ( 2 ) which means that EHPs generated within W1 , and those within a hole diffusion length of it , constitute the majority of the photo- current . Hence , while contact separation W varies from 5 to 15 to 35 µm , as shown in Section S3 ( Figure S1 ) in the Supporting Infor- mation , the cathode depletion width W1 remains unchanged and depends only on applied bias . As a result , the photocurrents are com- parable for these devices , depending only on the applied bias . In the other extreme , the flat-band condition shown in Figure 1i is reached if W is small , and the photocurrent simply saturates at J = qGW . Examining the temporal response , holes generated within W1 are swept quickly by the electric field and collected at the cathode , while electrons generated within the same region need to traverse the whole gap . Under constant illumination , both carriers are collected in MXene-based devices and , added to the fact that contacts are transparent , result in higher responsivity . In transient response , however , Ti/Au has a stronger built-in field in a larger W1 which is presumably why they show faster speeds and more efficient carrier collection . It is acknowledged that these considerations based on the analysis outlined above are only qualitative and need further study to elucidate the reasons for the very high responsivity , and comparable speed , of the MXene-based devices . Also , operating beyond reach- through is an optimized condition for device design since it eliminates slow diffusion processes , and is possible to achieve with small feature sizes our fabrication technique allows . Herein , we show that using a cheap and simple three-step pro- cess based on photolithography , spin-coating , and lift-off , trans- parent MXene contacts with feature sizes limited by lithography can be produced .'}, {'content': 'The resulting contacts are Schottky , which resulted in MXene–GaAs–MXene photodetector devices that outperformed in terms of responsivity , quantum efficiency and dynamic range similar Ti/Au–GaAs–Ti/Au devices . They were also comparable in speed of response , and , at a pulse width of a fraction of a nanosecond , could operate in a few gigahertzs range , meeting stringent requirements of optical detection for tele/data communications . All these performance measures can be improved by device optimization which our fabrication pro- cess affords . Due to the scalability of this process , microfabrica- tion of devices can be done for photonic integrated circuit and silicon photonics technologies . Additionally , as Schottky con- tact , MXene is a strong candidate for use as ( transparent ) gate of metal–semiconductor field effect transistors ( MESFETs ) , and high electron mobility transistors ( HEMTs ) which are the domi- nant devices in high-speed high-power applications . Finally , MXenes , including Ti3C2Tz used here , have the unique attribute that their work function [ 30 ] can be adjusted from 2.14 to 5.65 eV by different means , such as hole injec- tion or surface termination using oxygen , fluorine , [ 53–55 ] or chlorine . [ 19 ] This provides a wider range compared to all metals used in MSM detectors . [ 56 ] Consequently , if the Fermi level is not pinned in the semiconductor , as is the case in silicon , MXenes could be used as ohmic , or Schottky contacts at will , resulting in a range of optoelectronic applications , such as having low noise MSMs with Schottky contacts , or high gain photoconductors with two ohmic contacts . Furthermore , the idea that ohmic con- tacts can be formed by proper surface termination of MXene , is quite appealing to the microelectronic industry . It should also be mentioned that stability and durability of MXenes remain as important challenges . One promising recent remedy to MXene oxidation in aqueous colloidal suspen- sions when stored in water at ambient conditions is to simply cap the edges of individual MXene flakes by polyanions such as polyphosphates , polysilicates , and polyborates . This selective functionalization of the edges differently from the surfaces has been shown to significantly reduce their propensity for oxida- tion even in aerated water for weeks . [ 57 ] Adv . Mater . 2019 , 31 , 1903271 1903271 ( 7 of 9 ) © 2019 WILEY-VCH Verlag GmbH & Co. KGaA , Weinheim www.advmat.dewww.advancedsciencenews.com 15214095 , 2019 , 43 , Downloaded from https : //onlinelibrary.wiley.com/doi/10.1002/adma.201903271 by National Tsinghua University , Wiley Online Library on [ 29/06/2024 ] . See the Terms and Conditions ( https : //onlinelibrary.wiley.com/terms-and-conditions ) on Wiley Online Library for rules of use ; OA articles are governed by the applicable Creative Commons License Experimental Section MXene film preparation Supporting Information . is detailed in Section S1 in the Photolithography and device fabrication is detailed in Section S2 in the Supporting Information .'}, {'content': 'Current–voltage ( I–V ) relations were measured at wavelengths of 532 , 780 , and 830 nm as a function of bias . The biasing voltage was swept from ±8 V , in order to detect for any hysteresis effects . The incident light power was varied from dark to 3 , 43 , 220 , and 700 µW , and then back to dark for all experiments . The photodetector response measurements used a 532 nm continuous wave laser and a 780 and 830 nm mode- locked laser operating at a repetition rate of 76 MHz . In all cases , the laser spot was focused with a 20× microscope objective onto the sample and subsequently expanded to the gap between electrodes . Electrical contact with the pads was made using 60+GHz microwave probes ( Picoprobe model 67 A ) . The bias voltage and current measurements were made through a bias-T using a source meter ( Keithley 2400 ) . Supporting Information Supporting Information is available from the Wiley Online Library or from the author . Acknowledgements B.N . and P.D . acknowledge supports by Singh Center for Nanotechnology at University of Pennsylvania , NSF ICORPS ( Award 1904171 ) , and Nanograss Solar LLC . M.C . acknowledges funding from the Office of Naval Research , and M.B . acknowledges NSF Ceramics Division ( Award DMR 1740795 ) . This research used resources of the Center for Functional Nanomaterials , which is a U.S.DOE office of Science Facility , at Brookhaven National Laboratory under Contract No . DESC0012704 . B.N . conceived the idea , K.M . and L.V . developed and carried out film preparation and device processing , M.C . performed the measurements , P.D . proposed the device fabrication method , and M.B . and B.N . supervised the work . All authors wrote and commented on the manuscript . Conflict of Interest The authors declare no conflict of interest . Keywords metal–semiconductor–metal , MXene , photodetectors , Schottky contacts , semiconductors , work-function Received : May 22 , 2019 Revised : August 15 , 2019 Published online : September 15 , 2019 [ 1 ] C. Burrus , J. Bowers , R. Tucker , Electron . Lett . 1985 , 21 , 262 . [ 2 ] C. Lenox , H. Nie , P. Yuan , G. Kinsey , A. Homles , B. Streetman , [ 6 ] C. H. Liu , Y. C. Chang , T. B. Norris , Z. Zhong , Nat . Nanotechnol . 2014 , 9 , 273 . [ 7 ] T. Mueller , F. Xia , P. Avouris , Nat . Photonics 2010 , 4 , 297 . [ 8 ] P. Tassin , T. Koschny , M. Kafesaki , C. M. Soukoulis , Nat . Photonics 2012 , 6 , 259 . [ 9 ] G. B. Tait , B. Nabet , IEEE Trans . Electron Devices 2003 , 50 , 2573 . [ 10 ] J .'}, {'content': 'Song , M. Lim , S. S. Lee , B. J. Lee , Phys . Rev . Appl . 2019 , 11 , 044040 . [ 11 ] L. C. Liou , B. Nabet , Appl . Opt . 1996 , 35 , 15 . [ 12 ] A. Anwar , B. Nabet , in 1999 SBMO/IEEE MTT-S Int . Microwave and Optoelectronics Conf. , IEEE , Piscataway , NJ , USA 1999 , pp . 581–584 . [ 13 ] B. Nabet , M. Currie , P. Dianat , F. Quaranta , A. Cola , ACS Photonics 2014 , 1 , 560 . [ 14 ] R. J. Shiue , Y. Gao , Y. Wang , C. Peng , A. D. Robertson , D. K. Efetov , S. Assefa , F. H. Koppens , J. Hone , D. Englund , Nano Lett . 2015 , 15 , 7288 . [ 15 ] B. Nabet , Photodetectors : Materials , Devices and Applications in Com- munications and Imaging Technologies , Elsevier Science & Tech- nology , Oxford , UK 2015 . [ 16 ] M. Naguib , M. Kurtoglu , V. Presser , J. Lu , J. Niu , M. Heon , L. Hultman , Y. Gogotsi , M. W. Barsoum , Adv . Mater . 2011 , 23 , 4248 . [ 17 ] M. Sokol , V. Natu , S. Kota , M. W. Barsoum , Trends Chem . 2019 , 1 , 210 . [ 18 ] J. Halim , K. M. Cook , M. Naguib , P. Eklund , Y. Gogotsi , J. Rosen , M. W. Barsoum , Appl . Surf . Sci . 2016 , 362 , 406 . [ 19 ] M. Li , J. Lu , K. Luo , Y. Li , K. Chang , K. Chen , J. Zhou , J. Rosen , L. Hultman , P. Eklund , J . Am . Chem . Soc . 2019 , 141 , 4730 . [ 20 ] M. Naguib , V. N. Mochalin , M. W. Barsoum , Y. Gogotsi , Adv . Mater . 2014 , 26 , 992 . [ 21 ] M. Khazaei , A. Ranjbar , M. Arai , T. Sasaki , S. Yunoki , J . Mater . Chem . C 2017 , 5 , 2488 . [ 22 ] B. Anasori , M. R. Lukatskaya , Y. Gogotsi , Nat . Rev . Mater . 2017 , 2 , 16098 . [ 23 ] J. Pang , R. G. Mendes , A. Bachmatiuk , L. Zhao , H. Q. Ta , T. Gemming , H. Liu , Z. Liu , M. H. Rummeli , Chem . Soc . Rev . 2019 , 48 , 72 . [ 24 ] K. Hantanasirisakul , Y. Gogotsi , Adv . Mater . 2018 , 30 , 1804779 . [ 25 ] L. Verger , C. Xu , V. Natu , H. M. Cheng , W. Ren , M. W. Barsoum , Curr . Opin . Solid State Mater . Sci .'}, {'content': '2019 , 23 , 149 . [ 26 ] B. Dyatkin , E. Mamontov , K. M. Cook , Y. Gogotsi , Prog . Nat . Sci . : Mater . Int . 2015 , 25 , 631 . [ 27 ] A. S. Levitt , M. Alhabeb , C. B. Hatter , A. Sarycheva , G. Dion , Y. Gogotsi , J . Mater . Chem . A 2019 , 7 , 269 . [ 28 ] N. Kurra , B. Ahmed , Y. Gogotsi , H. N. Alshareef , Adv . Energy Mater . 2016 , 6 , 1601372 . [ 29 ] Y. Jhon , M. Seo , Y. Jhon , Nanoscale 2018 , 10 , 69 . [ 30 ] Y. Liu , H. Xiao , W. A. Goddard III , J . Am . Chem . Soc . 2016 , 138 , 15853 . [ 31 ] P. Zhao , H. Jin , X. Lv , B. Huang , Y. Ma , Y. Dai , Phys . Chem . Chem . Phys . 2018 , 20 , 16551 . [ 32 ] A. Sarycheva , A. Polemi , Y. Liu , K. Dandekar , B. Anasori , Y. Gogotsi , Sci . Adv . 2018 , 4 , eaau0920 . [ 33 ] S. Bae , H. Kim , Y. Lee , X. Xu , J. S. Park , Y. Zheng , J. Balakrishnan , T. Lei , H. R. Kim , Y. I . Song , Nat . Nanotechnol . 2010 , 5 , 574 . [ 34 ] X. Wang , L. Zhi , K. Müllen , Nano Lett . 2008 , 8 , 323 . [ 35 ] J. Wu , M. Agrawal , H. A. Becerril , Z. Bao , Z. Liu , Y. Chen , P. Peumans , ACS Nano 2009 , 4 , 43 . J. Campbell , IEEE Photonics Technol . Lett . 1999 , 11 , 1162 . [ 36 ] G. Ying , A. D. Dillon , A. T. Fafarman , M. W. Barsoum , Mater . Res . [ 3 ] T. Sugeta , T. Urisu , S. Sakata , Y. Mizushima , Jpn . J. Appl . Phys . 1980 , Lett . 2017 , 5 , 391 . 19 , 459 . [ 4 ] S. Assefa , F. Xia , S. W. Bedell , Y. Zhang , T. Topuria , P. M. Rice , Y . A. Vlasov , Opt . Express 2010 , 18 , 4986 . [ 5 ] F. Koppens , T. Mueller , P. Avouris , A. Ferrari , M. Vitiello , M. Polini , Nat . Nanotechnol . 2014 , 9 , 780 . [ 37 ] J. Halim , M. R. Lukatskaya , K. M. Cook , J. Lu , C. R. Smith , L.-Å . Näslund , S. J . May , L. Hultman , Y. Gogotsi , P. Eklund , Chem . Mater . 2014 , 26 , 2374 .'}]\n",
            "\n",
            "Generate at least 20 entries in the specified JSON format.\n",
            "GPT response\n",
            "\n",
            "    {\n",
            "        \"instruction\": \"Explain the significance of MXenes in modern photodetector technology.\",\n",
            "        \"input\": \"\",\n",
            "        \"output\": \"MXenes, specifically Ti3C2-based materials, are highly significant in modern photodetector technology due to their excellent electrical conductivity, transparency when thin, and ease of integration into microelectronic circuits. These properties allow for superior performance in photodetectors compared to traditional materials like gold, resulting in higher responsivities, quantum efficiencies, and wider dynamic range.\",\n",
            "        \"text\": \"Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.\"\n",
            "    }\n",
            "    \n",
            "    \n",
            "Please generate an Alpaca dataset based on the following content:\n",
            "\n",
            "[{'content': 'RESEARCH ARTICLE www.advancedscience.com Ambipolar Charge Storage in Type-I Core/Shell Semiconductor Quantum Dots toward Optoelectronic Transistor-Based Memories Hao hu , Guohao Wen , Jiamin Wen , Long-Biao Huang , Meng Zhao , Honglei Wu , and Zhenhua Sun * Eﬃcient charge storage media play a pivotal role in transistor-based memories and thus are under intense research . In this work , the charge storage ability of type-I InP/ZnS core/shell quantum dots is well revealed through studying a pentacene-based organic transistor with the quantum dots ( QDs ) integrated . The quantum well-like energy band structure enables the QDs to directly conﬁne either holes or electrons in the core , signifying a dielectric layer-free nonvolatile memory . Especially , the QDs in this device can be charged by electrons using light illumination as the exclusive method . The electron charging process is ascribed to the photoexcitation process in the InP-core and the hot holes induced . The QDs layer demonstrates an electron storage density of ≈5.0 × 1011 cm−2 and a hole storage density of ≈6.4 × 1011 cm−2 . Resultingly , the output device shows a fast response speed to gate voltage ( 10 µs ) , large memory window ( 42 V ) , good retention ( > 4.0 × 104 s ) , and reliable endurance . This work suggests that the core/shell quantum dot as a kind of charge storage medium is of great promise for optoelectronic memories . 1 . Introduction Novel nonvolatile memory devices , such as memristors , [ 1 ] phase- ferroelectric memories , [ 3 ] ﬂoating-gate change memories , [ 2 ] H. hu , G. Wen , J. Wen , Prof. L.-B . Huang , Prof. H. Wu , Dr. Z . Sun Key Laboratory of Optoelectronic Devices and Systems of Ministry of Education and Guangdong Province College of Physics and Optoelectronic Engineering Shenzhen University Shenzhen 518060 , China E-mail : szh @ szu.edu.cn Prof. M. Zhao Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application School of Physical Science and Technology Suzhou University of Science and Technology Suzhou 215009 , China The ORCID identiﬁcation number ( s ) for the author ( s ) of this article can be found under https : //doi.org/10.1002/advs.202100513 © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH . This is an open access article under the terms of the Creative Commons Attribution License , which permits use , distribution and reproduction in any medium , provided the original work is properly cited . DOI : 10.1002/advs.202100513 memories , [ 4 ] etc. , are going through a re- search upsurge as a response to the ea- ger demand for a solution addressing the “ Memory wall ” in the modern silicon-based computing system . [ 5 ] Thereinto , transistor- based memories ( TBMs ) are regarded as an important approach with unique ad- vantages including nondestructive read- ing , modern integrated circuit architec- tural compatibility , and reliable switching characteristic .'}, {'content': '[ 6 ] TBMs have a relatively straightforward working mechanism , that is , modulation of the conductance of the ac- tive layer by the charge storage nearby . In a conventional ﬂoating-gate transistor mem- ory , the charge storage is realized through a bulk conductor ( ﬂoating-gate ) isolated from the active layer by a dielectric layer . Aiming for a better TBM device , semicon- ductor nanocrystals have been investigated as eﬀective alternatives to the bulk ﬂoat- ing gate , given that their abundant surface states render their charge storage ability huge , and discrete feature ensures a limited charge leakage . [ 7 ] TBMs using nanocrystals of Si , [ 8 ] CdSe , [ 9 ] graphene , [ 10 ] [ 12 ] CdSe/ZnS core/shell , [ 13 ] etc . as the carbon , [ 11 ] CsPbBr3 , ﬂoating gates demonstrated outstanding ﬁgures of merits in terms of speed , endurance , retention , and so on . Meanwhile , thanks to the excellent optoelectronic property of the semicon- ductor nanocrystals , some output TBMs were endowed with optoelectronic operation ability , that is , the devices could be pro- grammed and/or erased by the light illumination . [ 9,14 ] Using a light as an operation method of TBMs has advantages including nondestructive operation , multiple data storage , etc . [ 7,15 ] More- over , these optoelectronic memories are of particular signiﬁcance to the emerging all-optical circuit and sensory neuromorphic computing . [ 14,16–19 ] Nevertheless , most reports on optoelectronic TBMs based on semiconductor crystals are using the conventional ﬂoating-gate structure . Charges must travel across a dielectric layer to ex- change between the charge storage medium and the active layer , which would hinder the speed , eﬃciency , and endurance of the device . [ 20,21 ] In this regard , optoelectronic TBMs without the di- electric layer emerged . In relevant research , one well-known strategy for charge storage is to take advantage of trap states in either the active layer or the charge storage media . [ 19,22,23 ] Adv . Sci . 2021 , 2100513 2100513 ( 1 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com Figure 1. a , b ) HAADF-STEM images of InP/ZnS core–shell QDs . The scale bars in ( a ) and ( b ) are 50 nm and 5 nm , respectively ; c ) Photoluminescence and absorbance spectra of InP/ZnS core–shell QDs in solution . The inset is the Tauc plot based on the absorbance spectrum ; d ) Structure schematic of the organic transistor-based memory using pentacene-QDs bilayer as the active layer ; e ) Cross-section SEM image of the channel of the transistor ; f ) SEM image of the surface of the pentacene-QDs bilayer ﬁlm . The scale bar is 500 nm .'}, {'content': 'Alternatively , structure-engineering of colloidal nanomaterials , namely , capping individual nano-charge storage media with charge blocking layer , have been proved to be another eﬀective way for charge storage . [ 7,9,24,25 ] To illustrate , Jeong et al . reported that CdSe quantum dots ( QDs ) capped with selected surface lig- ands could be applied as eﬀective charge storage media in a dielectric layer free optoelectronic TBM . [ 9 ] The device demon- strated a fast photo-induced erasing process due to the eﬃcient charge exchange between the CdSe QDs and the active layer . Pre- viously we have shown that colloidal type-I core/shell QDs could robustly store charges using its quantum well-like energy band structure . The charge injection/expelling would happen under a voltage bias . Resultingly , a dielectric layer free TBM with electri- cal operationality was fabricated . [ 25 ] Nevertheless , the application potential of the core/shell QDs in TBMs is yet to be exhausted since the optoelectronic property of the material was not referred to . In this study , InP/ZnS core/shell QDs are used to address this issue . The QDs are put atop the active layer of a bottom-gate- conﬁguration organic transistor based on pentacene . The type-I band structure of the core/shell QDs enables them to store both holes and electrons . The p-type pentacene is nailed down to be the hole supplier , which would inject the holes to the QDs through a diﬀusion process under a negative gate voltage . On the other hand , light illumination is found to generate electrons in the QD and thus be the only valid method to charge the QDs with elec- trons in this device . As a result , the device behaves as a good op- toelectronic TBM that can be optically programmed and electri- cally erased . The state of the device can be well controlled by the electrical pulse power and the incident light dose , signifying an application potential of photonic artiﬁcial synapses . 2 . Results and Discussions The InP/ZnS core/shell QDs were synthesized using a reported method . [ 26 ] An InP-core was ﬁrst synthesized and then wrapped by the ZnS shell through a layer-by-layer growth process of Zn and S atoms . The high-angle annular dark-ﬁeld imaging scan- ning transmission electron microscope ( HAADF-STEM ) images of the QDs were acquired and shown in Figure 1a , b . The ﬁgures demonstrate obvious contrast between the core and shell , denot- ing an InP-core diameter of about 8 nm and a ZnS-shell thick- ness of about 3 nm ( Figure 1b ) . Notice that the core/shell QD has an irregular shape , implying that the growth of the QDs is subject to the Stranski–Krastanov growth mechanism . [ 27,28 ] Al- though an island-like shell was grown due to the strain energy induced by the lattice mismatch between the core and shell mate- rials , there is a continuous shell ﬁlm formed in advance , guaran- teeing the complete core/shell structure .'}, {'content': 'The photoluminescence ( PL ) spectrum of the InP/ZnS QDs in Figure 1c shows an emis- sion peak at 642 nm , further verifying the successful capping of the ZnS shell on the InP-core , since the bare InP QDs are not luminescent . [ 26,29 ] The absorbance spectrum of the QDs in Fig- ure 1c demonstrates a ﬁrst excitonic peak at 608 nm , which corre- sponds to a bandgap of about 1.9 eV , as revealed by the Tauc plot in the inset of Figure 1c . A TBM was fabricated using a bottom- gate-top-contact structure , as schematically shown in Figure 1d . Adv . Sci . 2021 , 2100513 2100513 ( 2 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com Figure 2. a ) Cyclic transfer characteristics of the TBM . The transfer curves were measured with the denoted illumination conditions and VG sweep direction . The irradiances of the 405 and 637 nm lights were 3.7 and 9.1 mW cm−2 , respectively . VDS was set to be −30 V for all measurements ; b ) The curves of Vth of the transfer curves in ( a ) versus the VG sweep ranges ; c ) Unidirectional forward transfer curves after bias or illumination operation were applied to the device . Operations ① , ② , and ③ were conducted successively . VDS = −30 V ; d ) Schematics of the charge storage situations in the O-state and E-state in ( c ) ; e ) Normalized Vth of the E-state and O-state transfer curves along with time . The freshly attained E-state is deemed as 100 % and O-state as 0 ; f ) Vth monitored while switching the TBM between the O-state and E-state more than 100 times . The active layer of the device was prepared through spin-coating the InP/ZnS QDs atop a pentacene ﬁlm with a thickness of about 20 nm , forming a QD-pentacene bilayer ﬁlm . The cross-section scanning electron microscope ( SEM ) image of the device was ac- quired and shown in Figure 1e , manifesting a total thickness of about 40 nm of the active layer . Considering the diameter of about 14 nm of the InP/ZnS QDs , it implies a quasi-single layer close-packed QDs on top of the pentacene . The SEM image of the bilayer ﬁlm in Figure 1f conﬁrms the uniform distribution of the QDs on the pentacene , while the pure pentacene ﬁlm has a smooth surface as shown in Figure S1a , Supporting Information . Moreover , cracks were found in the bilayer ﬁlm after the deposi- tion of the InP/ZnS QDs , which are ascribed to the damages in- duced by the spin-coating process of the toluene solution of QDs . The damages include the dissolution of pentacene induced by the toluene and the impediment to the pentacene crystallization dur- ing the post annealing process induced by the implanted QDs .'}, {'content': 'The transfer characteristics of the TBM device based on the QD-pentacene bilayer was measured in diﬀerent regards with a VDS of −30 V. Figure 2a shows the cyclic transfer curves of the device with diﬀerent VG sweep ranges . From top to bottom , the three characteristics were separately acquired with the device in the dark , under light illumination of 405 and 637 nm . The irra- diances of the 405 and 637 nm lights were 3.7 and 9.1 mW cm−2 , respectively , which were ﬁxed as the light sources in all the fu- ture studies . For each characteristic , the measurement sequence of diﬀerent curves was from the small sweep range to the large . For all curves , the VG swept from positive to negative ( forward sweep ) and then back to positive ( backward sweep ) with identi- cal sweep rates . These transfer characteristics all show consider- able hysteresis , implying a charge storage eﬀect during the VG sweeping . For comparison , control devices with only pentacene or QD ﬁlm ( QD-only device ) as the active layer were also fabri- cated . For the device with only pentacene , the pentacene was ei- ther pristine , or treat with toluene by spin-coating toluene atop , producing a pristine pentacene device or pentacene-toluene de- vice , respectively . The structures of the control devices are shown in Figure S1b , Supporting Information . The transfer character- istics of the pristine pentacene and pentacene-toluene devices with the identical measurement protocol in Figure 2a were ob- tained and shown in Figure S1c , d , Supporting Information , re- spectively . The curves in Figure S1c , Supporting Information , all show less hysteresis , indicating neglectable charge storage in the pristine pentacene ﬁlm under all illumination conditions . The larger current in Figure S1c , Supporting Information , than Fig- ure 2a is accordant with the above-mentioned ﬁlm damage in- duced by the QDs deposition . Likewise , the pentacene-toluene device shows negligible hysteresis in all transfer characteristics . Notice that the channel current of the pentacene-toluene device is smaller than the pristine pentacene device but larger than the QD-pentacene device . It corroborates that toluene-induced dis- solution is a partial reason for the pentacene ﬁlm damage after QD deposition . The feature of the pentacene-toluene device sug- gests that the toluene treatment and the ﬁlm damage can be ex- cluded from the causes for the charge storage ability of the QD- pentacene device . Additionally , the transfer curve of the QD-only device in Figure S1e , Supporting Information , reveals that the QD ﬁlm is nonconducting . Therefore , it can be concluded that Adv . Sci . 2021 , 2100513 2100513 ( 3 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com in the QD-pentacene device , the pentacene ﬁlm is in charge of charge conducting , and the QD ﬁlm plays the role of charge stor- age medium .'}, {'content': 'And the latter is responsible for the hysteresis of the transfer curves . The clockwise hysteresis of the transfer curve is typical in TBM , which is the sign of holes storage under negative VG and electrons storage under positive VG . [ 20,30 ] Nevertheless , there are some notable features in Figure 2a . For all three condi- tions , the backward curves leftwards shift along with the increase of the VG sweep range , which is indicative of the increase of the stored holes . [ 25,31 ] In the dark , the forward curves shift leftwards with the increase of the VG sweep range as well , which is oppo- site to the knowledge that the positive VG would neutralize the stored holes or induce the electron storage . [ 25 ] Moreover , each for- ward curve in the dark is almost at the same position as the previ- ous backward curve , and the misalignment between each forward curve and its previous backward curve increases with the increase of the VG sweep range . It suggests that the positive VG is seri- ously incompetent to neutralize the stored holes induced by the negative VG with the same intensity , [ 12 ] while the incompetence keeps being alleviated with the increase of the stored holes . As a comparison , the transfer characteristics under light illumination show that this incompetence could be largely relieved by the il- lumination of 637 nm and eliminated by 405 nm . Namely , each forward curve under the 637 nm condition is in the right of the last backward curve , and all the forward curves under the 405 nm condition are in the same initial position . The threshold voltages ( Vth ) of the transfer curves in Figure 2a were extracted and plotted along with the VG sweep ranges in Figure 2b to exhibit the posi- tion change of the transfer curves . The results show clearly that the neutralization of the holes stored in QDs is eﬃcient under the illumination of 405 nm , less eﬃcient under 637 nm , and least in the dark . Under the 405 nm illumination , the cyclic transfer curve within VG of ±60 V produces the largest memory windows of about 42 V. The memory windows signify the potential of the device to be applied as a TBM . The impacts of the electric bias and light illu- mination on the device were ascertained by studying the unidi- rectional forward transfer curves . The initial transfer curve with a Vth of −13.1 V was ﬁrst acquired and shown as the dashed line in Figure 2c . Then the light of 405 nm with the irradiance of 3.7 mW cm−2 was used to illuminate the device for 150 s , and thus cast a total 2.2 mJ power ( 405 nm/2.2 mJ ) to the channel area .'}, {'content': 'The resulting transfer curve was found rightwards shifted to the posi- tion with a Vth of −6.1 V. The optically induced state of the device is marked as the O-state from now on . After that , a VG pulse with an amplitude of −40 V and width of 100 ms ( −40 V/100 ms ) was applied to the device . Consequently , the transfer curve shifted to the left of the initial state , with a Vth of −22.0 V. The electri- cally induced state is hereinafter marked as the E-state for short . Again , light illumination ( 405 nm/2.2 mJ ) was applied to the de- vice in the E-state . As a result , the transfer curve went back to the previous O-state . The initial transfer curve reﬂects a state that no charge is stored in the QDs . The rightwards shifted transfer curves , that is , the O-state , corresponds to the electron storage in the QDs . [ 6,25,30 ] Oppositely , the E-state points to the hole storage in the QDs . The charge storage situations in the O-state and E- state are illustrated in Figure 2d . The density of the stored charge ∕e , ( n ) could be estimated through the equation : n = ΔVthCSiO2 where ΔVth is the Vth change from the initial state , e is the ele- ment charge ( 1.602 × 10−19 C ) , and CSiO2 is the capacitance per unit area of the SiO2 dielectric layer . The hole density ( nh ) in the E-state and electron density ( ne ) in the O-state were calcu- lated to be 6.4 × 1011 cm−2 and 5.0 × 1011 cm−2 , respectively . Furthermore , the QD density was evaluated to be about 3.9 × 1011 cm−2 through an SEM image shown in Figure S1f , Sup- porting Information . The charges stored in each QD are thus calculated to be about 1.6 for hole and 1.3 for electron . Hence , there are both singly and multiply charged QDs in the O and E- states , implying the possibility to further charge the QDs by in- creasing the bias voltage intensity or light irradiance . It is worthy of noting that the light illumination of 405 nm/2.2 mJ shifted both the initial and E-state transfer curves to the same O-state . It implies an upper limit of the electrons that can be stored in the QDs ( 5.0 × 1011 cm−2 ) under the current light irradiance of 3.7 mW cm−2 , and 405 nm/2.2 mJ is far more than the dose needed to reach the limit from the initial state . During the above measurement , the initial state was hard to ﬁx since any bias or light illumination would induce the change of the device state . Therefore , the O-state with saturated electron storage was used as the benchmark of the device state .'}, {'content': 'From the O-state , a VG of −40 V/100 ms would neutralize the stored electrons and then in- duced hole storage in the QDs . The nonvolatility of the charge storage in the QDs was characterized by monitoring the Vth of the transfer curves in the E-state and O-state along with time , with the freshly attained E-state deemed as 100 % and O-state as 0 . The result in Figure 2f shows that the Vth of the E-state and O-state converge to the initial state , indicating the release process of the stored charges . This release is slow , with over 60 % of Vth discrep- ancy retained after 4 × 104 s. Extrapolating to 10 years , there is still over 30 % charges residual in the QDs . The retention perfor- mance could be improved by increasing the shell thickness and deliberately choosing the surface ligand of the QDs . [ 9,25,32 ] Then the endurance of the QDs to the charging process was tested by repeating the hole charging ( h-charging ) /electron charging ( e-charging ) cycle 100 times . The h-charging was realized using a VG pulse of −40 V/100 ms , and the e-charging using a light il- lumination of 405 nm/2.2 mJ . The Vth of the E-state and O-state transfer curves were extracted and shown in Figure 2e , demon- strating a stable endurance of the QDs in this test . To ascertain the e-charging process clearly , diﬀerent inci- dent light doses of 405 nm were applied to the E-state device in Figure 2c . The induced transfer curves were acquired and shown in Figure S2a , Supporting Information . As expected , the number of the electrons charged into the QDs depends on the incident light dose , and from the E-state , a light power of 1.5 mJ is suﬃcient to charge the QDs with electrons of the upper limit number under the current light irradiance . Reversely , the h-charging process can be precisely controlled by the amplitude or width of the VG pulse as well . Figure S2b , c , Supporting Information , show the leftward shifts of the transfer curves from the O-state upon VG pulses of −40 V with vari- able width and VG pulses of 100 ms with variable amplitude , respectively . Figure 3a summarizes the dependence of the Vth on the width of the VG of −40 V in an h-charging process from the O-state and the dependence of the Vth on the incident dose of light illumination of 405 nm in the subsequent e-charging process from the E-state . A distinguishable ΔVth was attained by a VG pulse with a narrow width of 10 µs , manifesting the Adv . Sci . 2021 , 2100513 2100513 ( 4 of 9 ) © 2021 The Authors .'}, {'content': 'Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com Figure 3. a ) Dependence of the Vth on the width of the VG of −40 V in an h-charging process from the O-state and on the incident dose of light illumination of 405 nm in the subsequent e-charging process from the E-state ; b ) ΔVth ratio in the e-charging process from the E-state along with the incident photon numbers for diﬀerent light sources . The ΔVth between the O-state and E-state is regarded as 1 ; c ) Absorbance spectra of the active layer of the device before and after the deposition of the QDs ; d ) Curves of ΔVth versus incident light dose of 405 nm in e-charging processes that started from two diﬀerent device states . One state is that a VG of −40 V/100 ms was applied to the device at the O-state ; the other is that a VG of −40 V/10 ms was applied to the device at the O-state ; e ) Schematic of the h-charging process under a negative VG ; f ) Schematic of the e-charging process under an illumination . The red carriers are the photo-induced hot carriers . It is worthy of pointing out the core–shell QDs in fast speed application potential of memories . [ 20,21 ] that while −40 V/100 ms was used as the strongest h-charging opera- tion , further increase of the VG amplitude or width would induce a larger leftward shift of the transfer curves , indicating for a huge hole accommodation ability of the QDs . Nevertheless , a further leftward shift of the transfer curve beyond the E-state of −40 V/100 ms made Vth diﬃcult to determine in the VG sweep range of ±30 V , yet a wider VG sweep range would disorder the transfer characteristic by bringing out an unexpected h-charging eﬀect . Therefore , −40 V/100 ms was chosen as the most intensive h-charging operation in the study on transfer characteristics . Compared with the straightforward electrically induced h- charging process , [ 9,13,33 ] the optically induced e-charging process needs to be addressed better since both the pentacene and QDs are light sensitive . To do so , light illuminations of 637 nm with diﬀerent incident doses were used to charge the QDs with electrons , with the resulting transfer curves recorded and shown in Figure S2d , Supporting Information . As can be seen , a much larger light dose of 10.9 mJ of 637 nm than the 1.5 mJ of 405 nm was needed to saturate the QDs with electrons from the E-state . On the basis of Figure S2a , d , Supporting Information , the normalized ΔVth were plotted along with the incident photon numbers in Figure 3b , with the ΔVth between the O-state and E-state regarded as 1 . The 405 nm light shows a much larger eﬃciency than 637 nm to charge the QDs with electrons .'}, {'content': 'To explore the reason , the absorbance spectra of the active layer of the device before and after the deposition of the QDs are shown in Figure 3c , with the 405 and 637 nm located . It suggests that the absorption of the QD-pentacene ﬁlm at 405 nm comes from the QD component mostly , and the absorption at 637 nm mainly comes from the pentacene component . Therefore , we infer that the photoexcitation in QDs makes the main contribution to the e-charging process . Considering the ZnS shell have a bandgap larger than 3.9 eV ( bulk bandgap ) , [ 34 ] the photoexcitation shall only happen in the InP-core . Moreover , the e-charging processes started from diﬀerent device states were compared to clarify the driving force for the charging . Two diﬀerent h-charging operations , that is , VG of −40 V/100 ms or −40 V/10 ms , were separately conducted to a device in the O-state . Then , 405 nm light was used to charge electrons into the device in these two diﬀerent states . The induced ΔVth were plotted along with the incident light dose in Figure 3d , demonstrating a smaller ΔVth for the less h-charged state ( −40 V/10 ms ) at the same light dose . It means that the e-charging speed is dependent on the charge density in the QDs . Given the above , the scenario of the working process of the device was conceived and shown in Figure 3e , f . The InP/ZnS core/shell QDs have been widely revealed to have a quantum well-like type-I band structure . [ 26,34–36 ] The valence band and con- duction band of the InP-core are estimated to be about 6.0 and 4.1 eV , respectively . [ 37 ] The pentacene has a valence band of 5.0 eV Adv . Sci . 2021 , 2100513 2100513 ( 5 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com Figure 4. a ) Relationship between the IDS after h-charging and the width of the VG pulse . VG pulses of −40 V with diﬀerent widths and illumination of 405 nm/2.2 mJ were alternatively applied to the device . IDS was recorded after each operation ; b ) Relationship between the IDS after e-charging and the incident dose of the 405 nm light . Illumination of 405 nm with diﬀerent incident dose and VG pulses of −40 V/500 ms were alternatively applied to the device . IDS was recorded after each operation ; c ) Endurance characteristics of the device . The h-charging ( VG of −40 V/500 ms ) and e-charging ( 405 nm/2.2 mJ ) operations were cyclically applied to the device , with the cycles repeated 100 times .'}, {'content': 'IDS was recorded after each operation ; d ) Decays of the IDS along with time after the h-charging ( VG of −40 V/500 ms ) and e-charging ( 405 nm/2.2 mJ ) operation were separately applied to the device ; e ) Correspondence between an actual synapse ( left ) and an artiﬁcial synapse ( right ) based on our device ; f ) Photonic potentiation-electric depression cycle of the artiﬁcial synapse realized by illumination pulse and negative VG pulse . and a conduction band of 3.2 eV . [ 14 ] The thin ZnS shell would have a very large bandgap due to the quantum conﬁnement ef- fect , with a conduction band above the pentacene and a valence band lower than InP-core . [ 36 ] A negative VG leads to the accu- mulation of holes in the pentacene due to the capacitive cou- pling eﬀect . The holes can overcome the energy barrier formed by the ZnS shell as well as the unfavorable valence band align- ment between the pentacene and InP-core and get injected into the InP-core ( Figure 3e ) . Since the QDs layer is placed atop the pentacene , no bias is supposed to be applied to the QDs during the bottom VG proceeding . Hence , the injection would be moti- vated only by the diﬀusion force formed due to the high concen- tration discrepancy between the QDs and pentacene . If there are electrons stored in the QDs in advance , they will be neutralized ﬁrst . The ZnS shell with a lower valence band can conﬁne the holes in the InP-core . [ 25 ] On the other hand , when a light ( 405 or 637 nm ) illuminates the device , photo-induced hot electrons and holes are generated in the InP-core . The holes would transfer to the pentacene , inducing an e-charging process in the QDs . The previously stored holes ( if any ) in the QDs would help accelerate the e-charging process , thanks to the increased hole concentra- tion . As a contrast , Figure S3a , b , Supporting Information , show that a positive VG of 40 V can not induce any change of the trans- fer curve from its initial state and O-state , respectively . The rea- son can be attributed to that the p-type pentacene can only play the role of a hole supplier , [ 9,31,33 ] and a positive VG would deplete the holes in the pentacene ﬁlm . Figure S3c , Supporting Informa- tion , demonstrates that the transfer curve in the E-state can not be changed by a positive VG neither , meaning that a positive VG is incompetent to neutralize the stored holes in the QDs . This is accordant with the above analysis of Figure 2a . In principle , the depletion of holes in the pentacene under a positive VG would in- crease the hole concentration discrepancies between the QDs and pentacene .'}, {'content': 'It seems that the diﬀusion force is not large enough to overcome the barrier between the InP-core and pentacene even though there is a favorable valence band alignment . Therefore , the diﬀusion force , the energy of the hot holes , and the favorable valence band alignment may all contribute to the e-charging pro- cess under illumination . Their exact roles need to be addressed further . The channel currents ( IDS ) of the transistor upon diﬀerent charging processes were characterized to explore the perfor- mance of the device as a TBM . In all coming study , the IDS were read at VG of −20 V and VDS of 10 V. To eliminate the impact of the reading process on device state , the IDS reading was car- ried out at a fast sampling speed with only two sampling points . First , h-charging from the benchmark O-state was conducted to the device using VG pulses of −40V with diﬀerent widths . Af- ter each h-charging operation , the device was restored to the O- state using illumination of 405 nm/2.2 mJ . The IDS of the device after each h-charging and restoring were recorded and plotted along with the VG pulse width , as shown in Figure 4a . It demon- strates that a distinguishable IDS change can be made by a VG of −40 V/50 µs . The writing time at the sub-millisecond level is Adv . Sci . 2021 , 2100513 2100513 ( 6 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com Table 1 . Summary of concerned device features of some transistor-based memories using core/shell QDs as the charge storage media . Core/shell charge storage medium CdSe/ZnSe CdSe/ZnS Au/SiO2 CdSe/ZnS CdSe/ZnS CdSe/ZnS Au/Pd Au/PS CdSe/ZnS ZnSe/ZnS InP/ZnS Tunneling dielectric None PMMA SiO2 Al2O3 Al2O3 Al2O3 Al2O3 PS Al2O3 None None Minimum electrical pulse width used [ s ] Measured retention [ s ] Optical operationality 1.0 0.5 1.0 1.0 10.0 m 10.0 m 1.0 m 2.0 m 10.0 m 0.1 10.0 µ 8 × 103 5 × 103 1 × 105 1 × 104 1 × 104 1 × 104 1 × 105 1 × 104 1 × 104 4.1 × 104 4 × 104 Yes No No Yes No No No No Yes No Yes Ref . [ 45 ] [ 46 ] [ 24 ] [ 13 ] [ 47 ] [ 48 ] [ 49 ] [ 50 ] [ 51 ] [ 25 ] This work consistent with the 10 µs obtained from the above Vth charac- teristic ( Figure 3a ) . In the same way , the dependence of the IDS after an e-charging operation on the incident light dose was ac- quired and shown in Figure 4b . After each e-charging operation , the IDS was restored to an oﬀ state using a VG of −40 V/500 ms , which was proved necessary to attain an oﬀ IDS in Figure 4a .'}, {'content': 'As can be seen , the IDS becomes stable after 1.5 mJ light was cast to the device , and further illumination would not change the value , which corroborates the above discussion ( Figure S2a , Supporting Information ) . The endurance and retention characteristics of the device were studied by conducting the most intensive h-charging ( VG of −40 V/500 ms ) and e-charging ( 405 nm/2.2 mJ ) opera- tions . Figure 4c shows the IDS recorded during 100 times succes- sive operation cycles , suggesting a good endurance of the device . The decays of the IDS after h-charging and e-charging operation were separately recorded along with time and shown in Figure 4d . The IDS in two diﬀerent states demonstrate a limited decay in 3 × 104 s , denoting the robust charge storage in the core/shell QDs . Some reported transistor-based memories using core/shell QDs as the charge storage media are summarized and compared with the presented one in Table 1 . The presented device possesses a simpler structure without the tunneling dielectric layer , beneﬁt from which it can be programmed by a narrower electrical pulse . Meanwhile , the presented device also has a benign information retention performance and optical operationality . The potential of the TBMs in the construction of an artiﬁcial neuromorphic sys- tem has been widely revealed by using the devices to simulate the main synaptic functions . [ 14,38–44 ] The optoelectronic TBMs , which can response to both electric and optical stimuli , possess two ap- proaches to mimic the plasticity of a synapse . [ 11,14,41,43 ] Figure 4e illustrates the correspondence between an actual synapse ( left ) and an artiﬁcial synapse ( right ) based on our device . In this re- gard , light spikes of 405 nm with an intensity of 14.8 µW and duration of 1 s were cast to the channel of the device with a fre- quency of 0.5 Hz , realizing a photonic potentiation of the artiﬁcial synapse . Then , electric spikes of VG with an amplitude of −40 V and width of 1 ms were applied to the device with an interval of 0.1 ms to conduct an electric depression . The result in Figure 4f shows that 200 excitatory light spikes and 1000 inhibitory electric spikes manage to achieve a potentiation-depression cycle in the device . 3 . Conclusions InP/ZnS core/shell QDs were implanted into an organic tran- sistor based on pentacene , forming direct contact with the ac- tive layer . A battery of studies reveals the nonvolatile ambipolar charge storage ability of the QDs , which is ascribed to the type-I energy band structure that can conﬁne both electrons and holes in the core . A negative gate voltage would accumulate holes in the semiconductor layer and induce hole diﬀusion to the QDs .'}, {'content': 'The direct contact between the QDs and pentacene leads to a fast electron charging speed , which could establish a distinguishable Vth change upon a VG pulse of −40 V with 10 µs width . On the other hand , the photoexcitation eﬀect in the InP-core was proved to be exclusively responsible for the electron charging to the QDs . The electrically induced hole charging and optically induced elec- tron charging properties of the QDs enable the device to be ap- plied as a nonvolatile optoelectronic memory . The memory can be programmed by light and erased by negative VG , demonstrat- ing a memory window of up to 42 V , good retention in 4 × 104 s , and benign endurance . Based on this device , an artiﬁcial synapse with optical potentiation and electric depression functions was demonstrated . This work manifests the excellent advantages of the type-I core/shell QDs as charge storage media in nonvolatile optoelectronic memories . 4 . Experimental Section Materials Preparation : All materials and reagents for QD synthesis were purchased from Sigma-Aldrich and used as received without further puriﬁcation . Pentacene for thermal evaporation was purchased from Xi ’ an Baolaite Ltd. InP/ZnS core/shell QDs solution in toluene were synthesized using a reported method . [ 26 ] Indium ( III ) chloride ( 100 mg , 0.45 mmol ) and zinc ( II ) chloride ( 300 mg , 2.2 mmol ) were mixed in oleylamine ( 5.0 mL ) . The mixture was degassed at 120 °C for an hour under stirring . The solution was then heated to 180 °C under an Argon atmosphere . Tris- ( diethylamino ) phosphine ( 0.45 mL , 1.6 mmol ) was quickly injected into the solution swiftly , so began the growth process of the InP nano-core . On the other hand , sulfur ( S ) powder was solved in Trioctylphosphine ( TOP ) to get the S precursor with a concentration of about 2.2 mol L−1 in ad- vance . Zinc ( Zn ) precursor was obtained by dissolving Zn ( stearate ) 2 in octadecene ( ODE ) , forming a solution of 250mg mL−1 . At the 20th min of the growth process of the InP-core , 1 mL S precursor was injected into the solution . Since the 60th min , the temperature was increased to 200 °C . Adv . Sci . 2021 , 2100513 2100513 ( 7 of 9 ) © 2021 The Authors . Advanced Science published by Wiley-VCH GmbH www.advancedsciencenews.com www.advancedscience.com At the 120th min , 4 mL Zn precursor was injected into the solution . Then the temperature was increased to 220 °C . At the 150th min , 0.7 mL S pre- cursor was injected , then the temperature was increased to 240 °C . At the 180th min , 2 mL Zn precursor was injected , then the temperature was in- creased to 260 °C . At the 210th min , the temperature was cooled down to room temperature .'}, {'content': 'The synthesized InP/ZnS QDs were then precipitated by adding ethanol and the following centrifugation . The supernatant was discarded . The precipitation was dissolved in toluene . This process was repeated once . The ﬁnal solution was ready to use then . Device Fabrications : Si/SiO2 wafer with heavily p-doping Si and SiO2 of 300 nm thickness was used as the substrate . P-type pentacene ﬁlm with a thickness of 20 nm was thermally evaporated on the cleaned substrate as a semiconductor channel . 50 nm Au electrodes were deposited as the source and drain electrodes on the surface of the ﬁlm by thermal evapo- ration through a shadow mask deﬁning a length/width of 0.2/2mm . Then in a glovebox ﬁlled with nitrogen , 5 mg mL−1 InP @ ZnS QDs solution was spin-coated at a speed/duration of 2000 rpm/60 s on the top of the semi- conductor layer . The ﬁlm was then annealed at 60 °C for 30 min . Characterizations : High-angle annular dark-ﬁeld imaging scanning transmission electron microscope ( HAADF-STEM ) images were acquired on an FEI Titan Cubed Themis G201 double spherical aberration-corrected transmission electron microscope with an acceleration voltage of 300 kV . Absorbance spectra were measured using a GBC Cintra2020 spectrometer with tunable wavelengths . Photoluminescence ( PL ) spectra were obtained on Spectroﬂuorometer FS5 ( Edinburgh instruments ) . Scanning electron microscope ( SEM ) images were obtained using a HITACHI SU8010 scan- ning electron microscope . Electrical characteristics of the transistors were measured using the combination of a Keithley 4200SCS parameter ana- lyzer and a probe station . CHI continuous lasers with wavelengths of 405 or 637 nm were used for the relevant experiments . The electrical and opti- cal measurements conducted on the devices were carried out in a glovebox ﬁlled with nitrogen . Statistical Analysis : 19 TBMs with identical channel area of 0.4 mm2 were fabricated and characterized for their transfer characteristics in Fig- ure 2a . They demonstrated the same feature with diverse exact values . Thus , a representative device was used to carry out the systematical char- acterization . The data for Figure 4a , b , c , f were presented as the mean ± standard error using the raw data from one time measurement of the same device . The calculation of the standard error was carried out using the em- bedded function in the EXCEL ( Oﬃce 365 , Microsoft Corporation , USA ) . The normalization processing was conducted using the normalization function of the Origin8 software ( OriginLab Corporation , Northampton , USA ) . All Graphical presentations were performed by the Origin8 software . Supporting Information Supporting Information is available from the Wiley Online Library or from the author . Acknowledgements Z.H.S . acknowledges the ﬁnancial support from the Natural Science Foundation of Guangdong Province ( grant no . 2019A1515011367 ) , Z.H.S . and H.L.W . acknowledge the National Natural Science Foundation of China ( grant no .'}]\n",
            "\n",
            "Generate at least 20 entries in the specified JSON format.\n",
            "GPT response\n",
            "\n",
            "    {\n",
            "        \"instruction\": \"Explain the significance of type-I core/shell semiconductor quantum dots in ambipolar charge storage.\",\n",
            "        \"input\": \"\",\n",
            "        \"output\": \"Type-I core/shell semiconductor quantum dots (QDs) play a crucial role in ambipolar charge storage due to their unique quantum well-like energy band structure. This structure allows QDs to directly confine both holes and electrons in the core, enabling efficient charge storage without the need for a dielectric layer. This capability is particularly valuable for transistor-based memories, as it leads to fast response speeds, large memory windows, and reliable endurance.\",\n",
            "        \"text\": \"Below is an instruction that describes a task. Write a response that appropriately completes the request.\"\n",
            "    }\n",
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            "Please generate an Alpaca dataset based on the following content:\n",
            "\n",
            "[{'content': '6680 IEEE TRANSACTIONS ON ELECTRON DEVICES , VOL . 70 , NO . 12 , DECEMBER 2023 Comprehensive Study of Contact Length Scaling Down to 12 nm With Monolayer MoS2 Channel Transistors Wen-Chia Wu , Terry Y. T. Hung , D. Mahaveer Sathaiya , Goutham Arutchelvan , Chen-Feng Hsu , Sheng-Kai Su , Ang Sheng Chou , Edward Chen , Yun-Yang Shen , San Lin Liew , Vincent Hou , T. Y. Lee , Jin Cai , Chung-Cheng Wu , Jeff Wu , H.-S. Philip Wong , Chao-Ching Cheng , Wen-Hao Chang , Iuliana P. Radu , and Chao-Hsin Chien Abstract— The 2-D transition metal dichalcogenides ( 2-D TMDs ) have emerged as a promising channel mate- rial for postsilicon applications for their ultrathin structure and excellent electrostatic control . However , achieving low contact resistance at scaled contact length remains a challenge . This article overcomes this challenge through optimized deposition of a semimetal/metal stack in mono- layer MoS2 channel transistors and obtains a low contact resistance of ∼300 ( cid:127 ) · µm at an extreme contact length of 12 nm at carrier concentration around 1013 cm−2 ( based on the best data from transmission line measurement extrac- tion ) . Similar ON-currents are maintained across a range of contact lengths from 1000 to 12 nm . Our calibrated TCAD model also validates that the tunneling distance at the metal–TMD interface exhibits a strongest positive correlation to the contact resistance . Doping in contact is then proposed and simulated as a potential solution for achieving a target corner of contact resistance and contact length defined by the International Roadmap for Devices and Systems ( IRDS ) for 2037 . Manuscript received 12 September 2023 ; revised 16 October 2023 and 31 October 2023 ; accepted 31 October 2023 . Date of publica- tion 8 November 2023 ; date of current version 28 November 2023 . This article is an extended version of a paper originally presented in the 2022 Symposium on VLSI Technology . The review of this article was arranged by Editor M. Takenaka . ( Wen-Chia Wu and Terry Y. T. Hung contributed equally to this work . ) ( Corresponding author : Terry Y. T . Hung . ) Wen-Chia Wu and Chao-Hsin Chien are with the Department of Electronics Engineering and the Institute of Electronics , National Chiao Tung University , Hsinchu 30010 , Taiwan ( e-mail : chchien @ nycu.edu.tw ) . Terry Y. T. Hung , Goutham Arutchelvan , Chen-Feng Hsu , Sheng-Kai Su , Ang Sheng Chou , Edward Chen , T. Y. Lee , H.-S. Philip Wong , Chao- Ching Cheng , and Iuliana P. Radu are with Corporate Research , Taiwan Semiconductor Manufacturing Company , Hsinchu 300 , Taiwan ( e-mail : yzhung @ tsmc.com ; IRADU @ tsmc.com ) . D. Mahaveer Sathaiya , Chung-Cheng Wu , and Jeff Wu are with TCAD , Taiwan Semiconductor Manufacturing Company , Hsinchu 300 , Taiwan .'}, {'content': 'Yun-Yang Shen and Wen-Hao Chang are with the Department of Electrophysics , National Yang Ming Chiao Tung University , Hsinchu 30010 , Taiwan . San Lin Liew and Vincent Hou are with the Corporate Analytical Laboratories , Taiwan Semiconductor Manufacturing Company , Hsinchu 300 , Taiwan . Jin Cai is with Pathfinding , Taiwan Semiconductor Manufacturing Company , Hsinchu 30075 , Taiwan . Color versions of one or more figures in this article are available at https : //doi.org/10.1109/TED.2023.3330461 . Digital Object Identifier 10.1109/TED.2023.3330461 Index Terms— Contact engineering , contact scaling , field transition metal dichalco- effect genide ( TMD ) material , semimetal contact , TCAD model . transistor , monolayer I . INTRODUCTION I N OUR earlier publication [ 1 ] , we presented an experi- mental investigation , supported by TCAD modeling , on the scaling of transistor contact length ( L c ) . We demonstrated that utilizing a van der Waals ( vdW ) Sb contact resulted in similar on-performance even when the L c was scaled down to 30 nm . In this article , we present a more comprehensive analysis and interpretation of both vdW and non-vdW contact electrical and material analysis . Additionally , we further reduce the L c down to 12 nm and investigate the potential for reduction in Rc at such scaled length . Over the past several decades , the scaling of transistor contacted gate pitch ( CGP ) has been the driving force behind advancements in logic technologies . It has enabled higher transistor density , faster speed , and improved power efficiency . To date , the extreme CGP scaling down to 45 nm has been reported in the 3-nm-node Si technology , showing the ongoing pursuit of scaled transistor dimensions [ 2 ] . However , as the process steps for scaling silicon devices become increasingly challenging , alternative strategies are being explored . These include the investigation of new device architectures [ 3 ] and the utilization of alternative channel materials [ 4 ] . Among the promising candidates for channel materials , 2-D transition metal dichalcogenides 2-D TMDs ) stand out for their uniqueness . Ultrathin body and exceptional elec- trostatic control make them highly attractive for postsilicon applications [ 5 ] , [ 6 ] , [ 7 ] . Researchers anticipate that 2-D TMDs will enable channel length scaling while improv- ing the ON-current performance [ 8 ] . However , achieving a highly scaled CGP involves more than reducing the gate length ( L g ) . As L g scales down , the challenges associated with filling in the gate oxide and metal become extremely challenging . This limitation necessitates the scaling of the length ( L c ) to accommodate the scaled CGP [ 9 ] . contact Nevertheless , scaling L c introduces new challenges , especially in achieving low contact resistance at these highly scaled dimensions . To date , most studies in TMD devices focus on 0018-9383 © 2023 IEEE .'}, {'content': 'Personal use is permitted , but republication/redistribution requires IEEE permission . See https : //www.ieee.org/publications/rights/index.html for more information . Authorized licensed use limited to : National Tsing Hua Univ .. Downloaded on June 29,2024 at 09:33:06 UTC from IEEE Xplore . Restrictions apply . WU et al . : COMPREHENSIVE STUDY OF CONTACT LENGTH SCALING DOWN TO 12 nm 6681 demonstrating low contact resistance and high driving current at scaled L g , but with long contact lengths , typically few hundreds nm [ 10 ] , [ 11 ] , [ 12 ] , [ 13 ] , [ 14 ] , [ 15 ] , [ 16 ] , [ 17 ] , [ 18 ] , [ 19 ] , [ 24 ] , [ 25 ] , [ 26 ] . By cooling the deposition holder down to 80 K , Rc of 800 ( cid:127 ) ·µm is achieved [ 10 ] . Semimetal has been utilized to achieve Rc of ∼100 ( cid:127 ) · µm with over 1 mA/µm ON-current [ 11 ] . Recently , depositing Sb at elevated tem- perature has been shown to result in a specific phase with lower Rc [ 12 ] . The common thread among these studies is the formation of atomically clean and smooth interfaces between the contact and the underlying 2-D material . In this work , we compare the monolayer MoS2 device performance of non-vdW contact and vdW contact . Then , we experimentally investigate the scaling of the contact length down to ∼12 nm and its impact on device on-performance . The best MoS2 transistors achieve a low Rc of ∼300 ( cid:127 ) · µm at an extreme contact length of ∼12 nm with Sb/Au metal contact . Similar ON-current performance is maintained across a wide range of contact length , from 1000 down to 12 nm . Our physical-based TCAD modeling with experimental data calibration also validates the dependence of the transfer length ( L t ) on critical parameters such as tunneling distance ( TD ) , Schottky barrier height ( SBH ) , mobility , and carrier concen- tration . Finally , we propose that the sufficient doping ( greater than 2 × 1013 cm−2 ) in contacts is a promising solution to further enhance the performance at scaled CGP devices . II . DEVICE FABRICATION AND MODELING FRAMEWORK Device Fabrication : A monolayer of MoS2 grown using chemical vapor deposition on c-plane sapphire is transferred onto a 100-nm SiNx on highly doped Si substrates using a wet transfer process with polymethyl methacrylate ( PMMA ) as a supporting layer . The transferred MoS2 film is rinsed multiple times with acetone and isopropyl alcohol ( IPA ) to remove surface residues from the transfer process . The monolayer MoS2 ’ s layer number and quality are confirmed using Raman and photoluminescence ( PL ) spectroscopy .'}, {'content': 'Standard e-beam lithography is applied to pattern the channel lengths ( L ch ) from 500 to 100 nm and the L c from 1000 to 60 nm , followed by e-beam evaporation of Sb/Au 30/20 ( nm ) . It is important to note that the deposition rate of Sb needs to be stable ( 1 Å/s in our case ) in a high vacuum chamber ( 10−7 torr ) . The capping layer of Au is deposited at a relatively low rate ( 1 Å/s in our case ) to minimize thermal energy transferred to the underlying deposited Sb film . III . RESULTS AND DISCUSSION A . Comparison of Non-vdW Contact and vdW Contact on MoS2 It is well-known that mitigating the TMD material damage by contact deposition is helpful in relieving the issue of Fermi-level pinning and achieving a low contact resistance . A strong interaction between the metal and the 2-D material could lead to metal-induced gap states ( MIGS ) , which can cause Fermi-level pinning . To characterize the metal–TMD interface , as-grown MoS2 on sapphire without transfer process is adopted to provide better material smoothness without the interference from residual polymer and dielectric substrate Fig . 1 . TEM : ( a ) TEM images of vdW ( Sb ) and non-vdW ( Ni ) contact on as-grown MoS2 on sapphire and ( b ) corresponding EDX mapping . roughness . In Fig . 1 ( a ) , the transmission electron microscopy ( TEM ) images for two kinds of metals , including Sb and Ni , deposited on MoS2/sapphire are presented . These metals rep- resent two different types of contacts : non-vdW and vdW contacts . Sb is known to form a vdW contact , characterized by a small gap between metal and MoS2 in [ 12 ] . In contrast , Ni exhibits strong interaction with most of TMDs , resulting in nonobservable gap between them shown in Fig . 1 ( a ) . To fur- ther distinguish each layer in TEM images , energy-dispersive X-ray ( EDX ) mapping is conducted and shown in Fig . 1 ( b ) . The mapping confirms the presence of TMD channel that Mo and S are aligned at the same position as the corresponding Sb and Ni metals on top . In conclusion , the clear and blurred metal–MoS2 interface observed in Sb and Ni contacts , indeed are vdW contact and non-vdW contact , respectively . Here , we utilize the TLM method to investigate the contact properties of non-vdW and vdW contacts , without the inter- ference of the channel . In Fig . 2 ( a ) , we present the transfer characteristics of Ni ( 40 nm ) -contacted devices with L ch rang- ing from 100 to 500 nm , measured at a Vds of 1 V. A typical unipolar n-FET behavior is observed , with the currents scaling with L ch .'}, {'content': 'This scaling provides access for the extraction of both the channel and the contact resistance . Fig . 2 ( c ) depicts the linear fit of the total resistance ( Rtot ) plotted against L ch at carrier concentration around 1013 cm−2 , where the slope represents the channel resistance and the y-axis intercept the represents the contact resistance . For fair comparison , mean values of Rtot are obtained from five to ten devices for each L ch . We apply the same analysis to measurements performed on Sb/Au ( 30/20 nm ) -contacted devices , as shown in Fig . 2 ( b ) and ( d ) . It is worth noting that tight threshold volt- age ( Vth ) values are consistently observed across all devices on the same sample and across the samples , indicating good TMD material uniformity and a stable fabrication process . Compared to Ni contact [ 20 ] , the Sb/Au contacts exhibit superior on-performance [ 21 ] , showing an improvement of approximately four to five times . This improvement can be attributed to a large reduction in Rc , given the uniformity Authorized licensed use limited to : National Tsing Hua Univ .. Downloaded on June 29,2024 at 09:33:06 UTC from IEEE Xplore . Restrictions apply . 6682 IEEE TRANSACTIONS ON ELECTRON DEVICES , VOL . 70 , NO . 12 , DECEMBER 2023 Fig . 4 . CGP : ( a ) schematics of the CGP structure including gate length ( Lg ) , spacer ( Lsp ) , and contact length ( Lc ) and ( b ) simulation of the ON- current performance of monolayer MoS2 channel transistor with CGP scaling through Lc and Lg scenarios . Note that the Ion is obtained at the VDD = 0.6 V and the Ioff = 20 nA/µm . 3 ) preservation of the underlying TMD material Rtot = 2Rc + ρ L w , ρ = ( nqµ ) −1 . ( 1 ) The presence of a small gap only in the Sb/Au contact interface in the TEM image indicates a smoother interface between the metal and MoS2 channel , resulting in a lower contact resistance in devices . B. CGP Scaling via Contact Length Scaling and Physical-Based TCAD Modeling Another critical component of CGP shown in Fig . 4 ( a ) is the scaling of L c , which becomes essential and acts as an enabler for CGP scaling alongside channel length scaling . To evaluate the impact of scaling L g and L c individually , we investigate the scaling from CGP of 42–38 nm through TCAD modeling . Two possible CGP scaling paths are modeled including L g shrinking to less than 12 nm and L g = 12 nm and shrinking L c. As shown in Fig . 4 ( b ) , scaling either L g or L c allows for CGP scaling without compromising the ON-current .'}, {'content': 'In this study , we will focus on L c scaling and explore how the Rcmight change , as well as potential strategies to engineer . It is important to note that L c scaling only becomes significant if Rc remains reasonably low . It is well-established that scaling the L c leads to an increase in Rc , following the relationship described in ( 2 ) . The point at which Rc starts to change is known as the L t. The longer the L t , the faster the Rc increases , as illustrated in Fig . 5 ( a ) . To analyze this relationship , we normalize Rc with respect to the Rc value at L c = 1 µm , which is at least an order of magnitude longer than the largest L t ( 100 nm ) under investigation . The formula reveals that when the L c is smaller than the L t , the Rc exponentially increases , emphasizing the indispensable role of demonstrating low Rc at scaled L c. In Fig . 5 ( a ) , the black line representing L t = 100 nm starts to rise when the L c is smaller than 100 nm , while the red line shows minimal changes in Rc when scaling the L c because of Fig . 2 . Electrical characterization of non-vdW and vdW contact sam- ples . Transfer characteristics of : ( a ) Ni and ( b ) Sb/Au-contacted MoS2 devices on 100-nm SiNx substrate . The corresponding TLM linear fitting of : ( c ) Ni and ( d ) Sb/Au contacts . Fig . 3 . Contact and channel property : ( a ) extracted intrinsic mobility ( µint ) and ( b ) Rc of Ni and Sb/Au-contacted devices as a function of the carrier density . of the channel material . Fig . 3 provides a summary of the extracted mobility and contact resistance , as described in ( 1 ) . The mobility values from these two contacts are found to exist as much as ∼2× difference at carrier concentration around 1013 cm−2 , as shown in Fig . 3 ( a ) . In contrast , the contact resistance has approximately an order of magnitude decrease from Ni ( ∼4 k ( cid:127 ) ·µm ) to Sb/Au ( ∼0.4 k ( cid:127 ) ·µm ) . This reduction could be attributed to several advantages associated with Sb semimetal deposition as the contact material : 1 ) mitigation in combination with 2 ) the lower of Fermi-level pinning , work function of Sb leading to a reduction in SBH and Authorized licensed use limited to : National Tsing Hua Univ .. Downloaded on June 29,2024 at 09:33:06 UTC from IEEE Xplore . Restrictions apply . WU et al . : COMPREHENSIVE STUDY OF CONTACT LENGTH SCALING DOWN TO 12 nm 6683 MoS2 devices with standard Sb/Au metal deposition are com- pared at two different given contact lengths , 500 and 50 nm .'}, {'content': 'A threefold drop in ON-current performance is observed when scaling the L c down to 50 nm . Further through optimization in Sb/Au deposition [ 12 ] , no obvious L c dependence of ON-current is characterized in devices , as presented in Fig . 6 ( c ) . Our TCAD modeling captures the entire transport curve well across the ON-state to subthreshold region for both samples . Thus , important parameters such as mobility , SBH , and TD are extracted . The sample with standard metal deposition has a TD of 3.3 Å and a mobility of approximately 50 cm2/V·s , while the optimized metal deposition sample possesses a TD of 1.5 Å with a mobility of around 20 cm2/V·s . Based on the validated TCAD model , we also investigate the influence of important parameters on the L t , including TD , mobility , SBH , and carrier concentration [ 1 ] . Among them , TD plays an important role in engineering L t. Note that the TD referred to here differs from the more commonly used vdW gap , which describes the physical thickness between the metal and the 2-D material . Instead , the TD in this context is defined by its tunneling probability from the transport perspective . However , these two quantities are positively correlated . Based on the TCAD modeling predictions , it is evident that a small TD is crucial for achieving L c scaling with a short L t. The nature of TD dictates that a closer proximity between the contact and the underlying 2-D material results in a smaller Rc , provided that the contact still maintains a gap in between . It is important to clarify the concept of a vdW contact used in this work , as it refers to a contact that does not create defects or distort the underlying 2-D material . However , it does not imply a lack of interaction between the contact and the 2-D material . In fact , a complete absence of interaction would significantly increase the Rc due to the reduction of tunneling probability in the transport . To optimize Rc , it is beneficial to bring the contact and 2-D material as close as possible while still maintaining a gap . This approach not only reduces Rc by shortening the TD but also results in a shorter L t , which can further reduce Rc when L c is aggressively scaled . C. Experimental Results on Contact Length Scaling the contact In our experimental length is investigation , scaled down to sub-20 nm using the optimized Sb/Au contact . As displayed in Fig . 7 ( a ) , we show representative transfer characteristics with the contact length ranging from 1 µm to 12 nm with L ch of 500 nm . Even with wide range change in L c , a tight distribution of the threshold voltage is observed in all devices , indicating good stability in device fabrication and material quality .'}, {'content': 'By plotting the performance in linear scale in Fig . 7 ( b ) , similar ON-currents are characterized with the L c scaled to 12 nm . Thus , we compare ON-current data at the same carrier concentration of 1.7 × 1013 cm−2 versus the L c for all devices , as the trend in Fig . 7 ( c ) . No apparent dependence on the L c is observed for the optimized Sb/Au contacts on MoS2 , suggesting good potential for contact length scaling . The TEM image in Fig . 8 confirms the shortest contacted length of ∼12 nm formed in MoS2 devices . Even though the physical width of the metal surpasses the contact length , the transport properties are primarily governed by the Fig . 5 . Contact resistance and transfer length ( Lt ) : ( a ) Lc reduction could result in an increase in Rc in MoS2 devices . Transfer length ( Lt ) is used to determine the critical Lc where Rc starts to increase compared to the values with long Lc ; ( b ) current density contour at Sb/MoS2 contact at SBH = 0 eV ; and ( c ) current density along a horizontal line at 0.5 Å above SiNx . The Lt is defined at 10 % of the current J0 in the channel on the right . Devices of standard and optimized metal depositions : Fig . 6 . ( a ) 1L-MoS2 channel device configuration and a representative SEM image ; ( b ) transfer characteristics of standard process Sb-contacted 1L-MoS2 device with Lc = 500 ( red ) and 50 nm ( blue ) and calibrated TCAD model ; and ( c ) transfer characteristics of optimized process Sb-contacted 1L-MoS2 device with Lc = 1000 ( red ) and 60 nm ( blue ) and TCAD modeling . the presence of a shorter L t. In TCAD modeling , as depicted in Fig . 5 ( b ) , a structure is created where Sb metal is positioned on the top of MoS2 with a 2-Å TD on the SiNx substrate . The transfer length ( L t ) is defined as the contact length at which the current reaches 10 % of the maximum current ( J0 ) , as shown in Fig . 5 ( c ) . This definition of L t will be used throughout the subsequent analysis Rc = √ ρcρsh coth ( cid:19 ) ( cid:18 ) L c L t , L t = r ρc ρsh . ( 2 ) To validate our TCAD model ( the detailed modeling frame- work is similar to the one described in [ 22 ] ) , we fabricated two samples exhibiting distinct electrical behaviors based on differ- ent L c values . Fig . 6 ( a ) presents a representative schematic and SEM image of the sample , where L c is approximately 50 nm , and L ch is 500 nm . In Fig .'}, {'content': '6 ( b ) , the transfer characteristics of Authorized licensed use limited to : National Tsing Hua Univ .. Downloaded on June 29,2024 at 09:33:06 UTC from IEEE Xplore . Restrictions apply . 6684 IEEE TRANSACTIONS ON ELECTRON DEVICES , VOL . 70 , NO . 12 , DECEMBER 2023 Fig . 7 . Electrical characterizations with respect to Lc scaling . Rep- resentative transfer characteristic in : ( a ) log scale and ( b ) linear scale of contact length scaling from Lc 1000–12 nm and ( c ) ON-current of the devices with the contact length from 1000 to 12 nm . A solid line connects the mean values ( open square ) of the devices ( open circle ) at a given Lc . Fig . 8 . TEM images of the device with Lc of 12 nm . portion of the metal that lies on the top of the 2-D layer , which is defined as L c. In fact , it eliminates the complexity in transport measurements from the increase of metal line resistance when it becomes narrower . In addition to examining the relationship between ON-current and L c , we further employ TCAD modeling or TLM extraction to analyze the impacts of contact resistance apart from the channel resistance . This enables us to directly investigate the relationship between Rc and L c. Furthermore , we extend our analysis beyond experimental data by leverag- ing our TCAD model to compare different metal deposition conditions , spanning from long to short contact lengths shown in Fig . 9 . We also compare these results to non-vdW top contact ( Ni ) and edge contact ( Ni ) configurations from us and those reported in the literature . Both Ni top and edge contact configurations are scaled to L c values close to 10 nm without observing an increase in Rc [ 20 ] , [ 23 ] . As anticipated , the absence of L c dependence in the edge contact configuration Fig . 9 . Rc dependence on Lc from this work and the literature . TCAD model ( solid lines ) describes well experimental data when adjusting TD for the process . The dashed line at Ni contact is only a visual guide . is attributed to the reduced dimensionality of the injecting interface transitioning from 2-D to 1-D. On the other hand , the lack of L c dependence in the top contact configuration can be associated with the strong interaction between Ni and the 2-D material , effectively resembling an edge contact . Although no L c dependence has been observed in both Ni top and edge contact devices , their large Rc values render them unsuitable for CGP scaling , as compromising performance is not an option . To further investigate this aspect , we extract Rc from both standard and optimized Sb/Au metal depositions , as presented in Fig . 9 as green and red curves , respectively .'}, {'content': 'By uti- lizing the aforementioned TCAD modeling , we extract the best-performing device at a given L c , while ensuring consistent values for SBH , mobility , and TD . The projection of Rc as a function of L c for each case is then illustrated as dashed lines in green and red , corresponding to the standard and optimized scenarios , respectively . Consistent with our earlier predictions , we observe a shorter L t for the case with a narrower TD . As a result , the optimized method proves to be a highly promising candidate for future CGP scaling . Through the redesign of our fabrication process , we have successfully achieved even further scaled L c down to 20 , 15 , and 12 nm , as depicted in Fig . 9 . The corresponding Rc values , extracted through TLM measurements , are represented by filled squares in red , closely aligning with the TCAD modeling projection . Despite a slight increase in Rc when L c is scaled close to 10 nm , the adoption of a narrower TD has been proven as one of the most promising approaches for future CGP scaling for its smaller Rc and shorter L t. D. Benchmark of Contact Resistance Versus Carrier Concentration of Monolayer MoS2Devices Fig . 10 showcases a benchmark of monolayer MoS2 with various vdW contact configurations , with the exception of Y-T-MoS2 trilayer case [ 26 ] . Experimental demonstrations have consistently highlighted the appeal of vdW contact for Authorized licensed use limited to : National Tsing Hua Univ .. Downloaded on June 29,2024 at 09:33:06 UTC from IEEE Xplore . Restrictions apply . WU et al . : COMPREHENSIVE STUDY OF CONTACT LENGTH SCALING DOWN TO 12 nm 6685 Fig . 10. average and best Rc in this work correspondingly . Benchmark of Rc versus ne . Empty and filled circles are achieving lower Rc values . Several materials , such as Sn , Bi , In , Sb , and Y-mixed MoS2 , have been investigated and have exhibited relatively low Rc values . In fact , most of these vdW contacts exhibit Rc values below 1 k ( cid:127 ) · µm , with some approaching 100 ( cid:127 ) · µm or even the quantum limit . Here , we consider Y-mixed MoS2 as the vdW contact material due to the clear gap observed in TEM between the functionalized MoS2 and the underlying MoS2 layer [ 26 ] . Leveraging our optimized Sb/Au deposition method , we have achieved an Rc value of approximately 100 ( cid:127 ) · µm , which is among the best-reported values for vdW contacts . E. Contact Doping and Outlook to further reduce Rc and ultimately meet Despite achieving shorter L t and lower Rc values through the use of narrower TD , as demonstrated in Fig . 9 , further reduction of Rc is still required .'}, {'content': 'In this study , we propose the introduction of doping to the 2-D material underlying the the contact target corner defined by the International Roadmap for Devices and Systems ( IRDS ) 2037 . Previous experiments and TCAD modeling have shown that vdW contacts , optimized through specific deposition methods , can be scaled down to contact lengths as small as 12 nm without a significant increase in Rc . Based on it , we aim to explore how doping the 2- D material , in conjunction with the optimized metal contact deposition and the resulting shorter L t , can further reduce Rc . To achieve a contact resistance below 100 ( cid:127 ) ·µm at scaled L c , implementing contact doping alongside a low TD is necessary . While discrete Fourier transform ( DFT ) analysis reveals that the hybridization of Sb and MoS2 bands results in excess electron transfer to MoS2 , improving carrier tunneling at the contacts , this charge transfer alone is insufficient for optimal device performance at scaled dimensions . Additionally , gate- all-around 2-D devices do not allow for electrostatic doping commonly used in global back-gated devices . As demon- strated in Fig . 11 ( a ) , doping the contact regions significantly enhances carrier injection efficiency for a given TD , leading to reduced Rc and L t values . Based on our projections , a doping density ne at contact ∼2 × 1013 cm−2 is necessary to achieve Rc < 100 ( cid:127 ) · µm . For CGP < 40 nm , an L c ∼ 20 nm Fig . 11 . Modeling of the proposed contact doping : ( a ) Rc versus Lt for different TD at Sb-MoS2 interface and doping density at contact . L-doping refers to intrinsic MoS2 and H-doping refers to ne at contact = 2 × 1013 cm−2 . Contact doping is necessary to achieve target Rc and ( b ) Rc versus Lc plot for doped contacts with two different TDs . is typically required , necessitating ne at contact greater than the aforementioned value in conjunction with further TD optimization shown in Fig . 11 ( b ) . IV . CONCLUSION This article presents an investigation into the differences between representative vdW and non-vdW contacted samples with Sb and Ni , respectively , in conjunction with material analysis . Through TEM imaging , a gap between the metal and 2-D material was observed only in the vdW contact sample , Sb/Au . TLM revealing that Sb/Au exhibits approximately tenfold lower Rc of ∼400 ( cid:127 ) ·µm than Ni . The optimized Sb/Au deposition method showed better Rc induced by narrower TD . It was emphasized that the idea of vdW contact should have a clean interface and , at the same time , minimized gap between contact and 2-D , rather than the contact has no interaction with the 2-D .'}, {'content': 'The optimized contact was experimentally tested , and it was shown that both Ion and Rc stayed similar while L c was scaled from 1 µm down to 12 nm . Lastly , doping in contact was proposed to further drive Rc reduction at scaled L c to the target corner defined by the 2037 IRDS roadmap . This comprehensive exploration of contact properties and its scalability , as well as a way to further improve it , provides a strong foundation for the future research .'}]\n",
            "\n",
            "Generate at least 20 entries in the specified JSON format.\n",
            "GPT response\n",
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            "    {\n",
            "        \"instruction\": \"Summarize the significance of the study on contact length scaling in monolayer MoS2 channel transistors.\",\n",
            "        \"input\": \"Comprehensive Study of Contact Length Scaling Down to 12 nm With Monolayer MoS2 Channel Transistors\",\n",
            "        \"output\": \"The study explores the reduction of contact length to 12 nm in monolayer MoS2 channel transistors, aiming to achieve low contact resistance. It demonstrates that careful optimization of a semimetal/metal stack (Sb/Au) can maintain similar ON-currents and low contact resistance (~300 Ω·µm) even at such extreme scales. The findings are significant for advancing postsilicon applications by achieving the International Roadmap for Devices and Systems' (IRDS) targets for 2037.\",\n",
            "        \"text\": \"Below is an instruction that describes a task, paired with an input that provides further context. Write a response that appropriately completes the request.\"\n",
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            "Please generate an Alpaca dataset based on the following content:\n",
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            "[{'content': 'A r t c l e i www.acsnano.org Dual-Limit Growth of Large-Area Monolayer Transition Metal Dichalcogenides Zeqin Xin , † Xiaolong Zhang , † Jing Guo , † Yonghuang Wu , Bolun Wang , Run Shi , * and Kai Liu * Cite This : ACS Nano 2024 , 18 , 7391−7401 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT : The large-scale growth of monolayer transition metal dichalcogenide ( TMDC ) films is a determinant for the implementation of two-dimensional materials in industrial applications . However , the simultaneous realization of uniform monolayer thickness and large-area coverage is still a challenge , because it requires precise control of reaction kinetics in both space and time dimensions . Herein , we achieve a variety of large-area monolayer TMDCs films by a dual-limit growth ( DLG ) that is realized through nanoporous carbon nanotube ( CNT ) films . In the DLG , a precursor-loaded CNT film placed face-to-face with a substrate provides a space-limited environment facilitating the monolayer growth , while the byproducts formed in the CNT film timely limits the supply of precursors released from nanopores of the CNT film , inhibiting the growth of multilayer TMDCs on the substrate . Consequently , large-area monolayer TMDC films are grown in a wide range of reaction times and show good homogeneity in thickness , optical properties , and device performance over the entire substrate . The DLG strategy is widely applicable for the growth of a variety of TMDC films including WSe2 , MoS2 , MoSe2 , WS2 , and ReS2 . Our work provides a universal strategy to attain large-area monolayer TMDC films that can be used in practical applications of integrated circuits . KEYWORDS : 2-dimensional materials , large-scale growth , transition metal dichalcogenides , carbon nanotube , space-limited growth A tomically thin transition metal dichalcogenides ( TMDCs ) are considered some of the most adequate candidates for the ultimate transistor scaling1−4 and have been intensively explored in electronics , optoelectronics , and spintronics in recent years.5−9 Syntheses of large-area monolayer TMDC films are in high demand for satisfying the requirements in next-generation integrated cir- potential cuits.10−12 In this regard , chemical vapor deposition ( CVD ) is widely used due to its high throughput , fine controllability , and cost effectiveness.13−17 However , remains a great challenge to control the CVD growth of TMDCs simulta- neously in monolayer thickness and large-area coverage . This dilemma mainly results from the uncontrollable growth kinetics that cause a competition between the lateral growth of monolayer TMDCs and the vertical nucleation of multilayer TMDCs . Wherein , the spatial distribution of precursors , which always changes with increasing reaction time , determines the uniformity of as-grown products and thus plays essential roles in manipulating the lateral growth and vertical nucleation of CVD-grown TMDCs.18−21 As a result , the CVD growth of large-scale monolayer TMDCs requires the precise control of precursors distribution in both space and time dimensions .'}, {'content': 'it To date , some efforts have been made to synthesize large- area monolayer TMDC films by providing a uniform spatial through low-pressure CVD distribution of precursors ( LPCVD ) and face-to-face growth methods . In LPCVD , the low gas pressure effectively minimizes the concentration gradient of precursors . Notably , wafer-scale monolayer MoS2 and WS2 films , which demonstrated both good uniformity and competitive electrical properties , have been successfully grown through LPCVD on miscut sapphires.22,23 And monolayer MoS2 films on a 200 mm wafer scale with uniform electrical performance were grown by low-temperature metal−organic LPCVD that is compatible with the silicon industry.24 In addition , face-to-face growth methods , where a metal foil or precursor-loaded substrate was placed above the substrate at a short distance and volatilized as the metal source , were developed to facilitate uniform precursor distribution through space-confined reactions . MoSe2 and MoS2 flakes with ∼2.5 mm lateral size and 6 in . uniform monolayer MoS2 film were synthesized by using the space-confined face-to-face growth methods.25,26 These space-limited growth methods can not only provide a uniform distribution of precursors around the Received : September 23 , 2023 Revised : February 15 , 2024 Accepted : February 22 , 2024 Published : February 26 , 2024 © 2024 American Chemical Society 7391 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 Downloaded via NATL TSING HUA UNIV on June 29 , 2024 at 09:33:54 ( UTC ) .See https : //pubs.acs.org/sharingguidelines for options on how to legitimately share published articles . ACS Nano www.acsnano.org Article Figure 1 . Synthesis of TMDCs by the DLG strategy . ( a ) Schematic of the DLG process of TMDC films . ( b ) Photographs of a continuous WSe2 film grown on a 1 in . sapphire substrate and a bare sapphire substrate . Scale bars : 5 mm . ( c ) Magnified optical image ( OM ) of a 1 peak position for the same selected region ( contoured by a white dashed rectangle ) in the WSe2 film . ( d ) Raman mapping image of the E2g region shown in ( c ) . Scale bars : 10 μm . ( e ) Contour color map of the normalized Raman intensity of different regions in the WSe2 film . ( f ) 1 mode collected from the Raman spectra in ( e ) . ( g ) PL 1 and A1g peak positions of WSe2 films and the corresponding fwhm values of the E2g E2g spectra of different regions in the WSe2 film . ( h ) PL peak position of WSe2 films and the corresponding fwhm values collected from the PL spectra in ( g ) . substrate but also optimize the precursor ratio to support the lateral growth of TMDC domains even at atmospheric pressure . Despite these progresses , the variations of precursor distribution and reaction kinetics during the CVD growth still significantly impact the quality of TMDC monolayers .'}, {'content': 'Generally , the lateral growth of TMDCs requires a sufficient supply of precursors that may induce the nonuniform precursor distribution and undesired side reactions with the increase of reaction time , such as the growth of multilayer TMDCs or unexpected etching after the growth of monolayer TMDC films.27,28 Therefore , the appropriate period of TMDC growth is also critical for the good uniformity of TMDC monolayers : The reaction should end up just after the full monolayer coverage , which requires very accurate control of precursor distribution and is particularly difficult for large-scale growth . However , the effective control of TMDC growth over a long reaction time has been rarely explored , leaving the dilemma of monolayer thickness and full coverage in large- scale growth to be solved . In this work , we develop a universal dual-limit growth ( DLG ) strategy that includes both space-limited and time- limited processes in CVD to achieve large-area monolayer TMDC films . In our strategy , a planar and microporous carbon nanotube ( CNT ) film loaded with a mixture of metal precursors and organic acid salt promoters is laid face-to-face to a c-plane sapphire substrate . The good mechanical and chemically inert properties of CNTs have the CNT films serve as a planar container and supplier of precursors and promoters . The space-confined face-to-face configuration enables steady and spatially uniform distribution of both precursor and promoter vapors near the substrate , inhibiting the inhomoge- neous nucleation of TMDCs and effectively manipulating the concentration of the chalcogen precursor.26,29 As a result , this reaction system spatially limits the vertical growth and promotes the lateral growth of monolayer TMDCs ( Figure 1a , step 1 to step 2 ) . Meanwhile , the byproducts grown on and inside the CNT film could block the further supply of precursors , which limits the unexpected growth of another TMDC layer on the as-grown monolayer TMDC film ( Figure 7392 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 ACS Nano www.acsnano.org Article Figure 2 . Characterizations of as-grown WSe2 film . ( a ) OM images of the WSe2 synthesized at different growth times from 10 to 50 min . Scale bars : 20 μm . ( b ) Variation of the coverage of the WSe2 on the sapphire substrate from 64 % to 100 % with increasing growth time . ( c ) Statistical analysis of the grain size of WSe2 film . ( d ) Atomically resolved image representing a highly crystalline hexagonal structure of WSe2 with negligible vacancies . Scale bar : 1 nm . Blue and yellow spheres represent tungsten and selenium , respectively . ( e ) STEM image of WSe2 . Scale bar : 100 nm . ( f ) EDX elemental scanning of tungsten . Scale bar : 100 nm . ( g ) EDX elemental scanning of selenium . Scale bar : 100 nm . ( h , i ) XPS spectra of W 4f and Se 3d peaks of WSe2 monolayer .'}, {'content': 'The black curves and blue , red , and green curves represent the original XPS data and the fitted profiles , respectively . 1a , step 3 ) . As a result of the DLG , a 1 in . monolayer WSe2 film is obtained on sapphire in wide windows of growth time and precursor contents . Moreover , the DLG strategy is verified to be universally applicable to the growth of a variety of monolayer TMDC films , including monolayer MoSe2 , MoS2 , WS2 , and ReS2 films , by simply changing the precursors . Our work provides an effective and universal strategy for large-area growth of monolayer TMDC films and may be helpful for their practical applications in integrated circuits . RESULTS AND DISCUSSION Here , a typical p-type semiconducting TMDC , WSe2 , that has been widely investigated for its enriched electronic and optoelectronic properties,30,31 is first studied to show the validation of the DLG strategy . The experimental setup for the DLG process is shown in Figures S1 and S2 . Figure 1b shows a 1 in . monolayer WSe2 film grown on a sapphire wafer by the DLG method . Compared with a bare sapphire wafer , the sapphire wafer with the WSe2 film exhibits a slightly darker and uniform color , indicating the large-area synthesis capability of the DLG method . The enlarged optical images obtained from different regions of the wafer ( Figure 1c and Figure S3 ) further confirm the spatially uniform distribution of the monolayer WSe2 film across the entire wafer . To investigate the homogeneity of the as-grown monolayer WSe2 film , we further divide the film into 9 sections ( Figure S4 ) and randomly pick two regions from each section for Raman and photo- luminescence ( PL ) measurements , where the intervals between each “ Region ” are about 0.5 cm . As shown in Figure S3j , k , the results of Raman spectra show two distinct peaks at ∼246 and ∼257 cm−1 , corresponding to the in-plane vibrational mode E2g 1 and the out-of-plane vibrational mode A1g of monolayer WSe2 , respectively , with an interval of 11 cm−1 , while the strong PL intensity of WSe2 peaks at ∼1.6 eV . Both Raman and PL the spectra are consistent with experimental exfoliated monolayer WSe2 and calculation results.32−36 Because of the thickness-dependent Raman frequencies of TMDCs,32 the uniformity of a monolayer WSe2 film can be characterized by the Raman peak position map ( Figure 1d ) , which confirms that the selected region with the uniform optical contrast demonstrates a uniform monolayer feature . Furthermore , all of the Raman peak positions and PL energies remain almost the same for different regions at the edges or center of the wafer , and their corresponding full width at half- maximum ( fwhm ) values only slightly deviate in a very narrow range ( Figure 1e−h ) .'}, {'content': 'The Raman and PL intensity mapping measurements ( Figures S5 and S6 ) of the as-grown WSe2 film are also conducted in the 9 sections shown in Figure S4 , revealing the good homogeneity in both lattice structures and electronic structures of the as-grown monolayer WSe2 film over the entire wafer . These results confirm that a 1 in. , homogeneous monolayer WSe2 film is successfully synthesized by the DLG method . Figure 2a shows the time evolution of the morphology of the monolayer WSe2 film in the DLG process . At 750 °C , monolayer WSe2 triangular and hexagonal flakes start to form after a growth time of 10 min , showing the nucleation and initial growth of WSe2 single crystals . When the growth time 7393 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 ACS Nano www.acsnano.org Article Figure 3 . Mechanism for the DLG process . ( a ) Schematic of precursor diffusion during the DLG at different reaction stages . The confined space between the CNT film and substrate includes the liquid phase and vapor phase of W precursor coexistence zone 1 ( height ≈ h1 ) and the vapor phase diffusion zone 2 ( height ≈ h2 ) . Cg is the minimal concentration to support the WSe2 growth , Cn is the critical concentration for the nucleation of WSe2 , Csat is the saturated concentration of the precursor , and Csub is the concentration near the substrate . The suggested concentration profiles of W precursor along the vertical direction are plotted as dark red , red , and shallow red lines with increasing growth time from t0 and t1 to t2 , respectively . The schematics of the growth process at t1 and t2 are shown on the left and right , respectively . ( b ) The predicted concentration profiles of W precursor along the vertical direction with increasing initial W precursor loading ( m1−m4 ) . ( c−f ) The morphologies of WSe2 products on the CNT film and the sapphire substrate under different initial W precursor loadings , including ( c ) 20 mM , ( d ) 40 mM , ( e ) 100 mM , and ( f ) 150 mM . Scale bars : 2 μm for SEM and 20 μm for OM images . elongates to 20 min , the WSe2 flakes grow larger and begin to merge , increasing the coverage of WSe2 on the substrate . A uniform and continuous monolayer WSe2 film is grown after a growth time of 30 min due to the thorough merging of the WSe2 flakes . It is noted that no bilayer or multilayer WSe2 flakes nucleate on the as-grown monolayer film even if the growth time is further prolonged to 50 min .'}, {'content': 'The coverage of monolayer WSe2 increases from ∼64 % to 100 % as the growth time elongates from 10 to 30 min and is maintained at 100 % without etching when the growth time exceeds 30 min ( Figure 2b ) , which is quite different from the reported results.37,38 Our result clearly suggests the monolayer WSe2 film in the DLG process . the time-limited growth of Because of the isolated nucleation and extending growth process , the as-grown monolayer WSe2 film appears poly- crystalline . To estimate the grain sizes of the polycrystal film , we visualize the grain boundaries by having the film exposed to air and slowly oxidized for over 1 day ( Figure S7 ) , because the monolayer WSe2 is unstable in ambient conditions as reported before.39,40 It is found that the oxidization mostly occurs along grain boundaries such that there form many particle-like oxidized products , which can be used to trace the grain boundaries under an optical microscope,41 as shown by the dashed black lines in Figure S7 . Statistical results based on this visualization method reveal that the average grain size of the polycrystal WSe2 film is 129 ± 43 μm ( Figure 2c ) and the largest grain is more than 270 μm in size , which is relatively large among the large-area monolayer WSe2 films prepared by various growth methods.42−45 Despite the overall polycrystal- line structure of the as-grown WSe2 film , in one single-crystal irremovable impurities can be observed at grain , a perfect 3-fold symmetric lattice structure without noticeable defect is revealed by high-angle annular dark-field scanning transmission electron microscopy ( HAADF-STEM ) , in which brighter and dimmer dots correspond to W and Se atoms , respectively ( Figure 2d ) . Selected area electron diffraction ( SAED ) patterns collected from different grains of a continuous monolayer WSe2 film under TEM also show clear single-crystal patterns ( Figure S8 ) . The merging of WSe2 is also examined by TEM and AFM ( Figure S9 ) , and no cracks or the grain boundary , indicating that the WSe2 flakes merge seamlessly with each other to form a continuous film . Energy dispersive X- ray spectroscopy ( EDX ) of a single-crystal grain further reveals the homogeneous elemental distribution of W and Se ( Figure 2e−g ) . Figure 2h , I shows X-ray photoelectron spectra ( XPS ) of the WSe2 film , in which the peaks at 32.8 and 35.0 eV are attributed to W 4f7/2 and W 4f5/2 binding energies , while the peaks at 55.2 and 56.0 eV are assigned to Se 3d5/2 and Se 3d3/2 binding energies , respectively.42 The atomic percentage ratio of W and Se is around 1:2 , verifying the formation of stoichiometric WSe2 .'}, {'content': 'Notably , the C 1s peak of the WSe2 film shows no red shift , ruling out the possible carbon-doping in the as-grown WSe2 film ( Figure S10 ) .46 The thickness of a single WSe2 grain is measured to be ∼0.7 nm under an atomic force microscope ( AFM ) , which confirms that the as-grown WSe2 has a monolayer thickness ( Figure S11a ) . The small root-mean-square ( RMS ) surface roughness of 0.11 nm indicates the very smooth surface of WSe2 ( Figure S11b ) . The self-limited growth of continuous monolayer WSe2 film , regardless of extending growth time , suggests that the uniform 7394 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 ACS Nano www.acsnano.org Article nucleation and lateral growth are promoted during the growth ( space-limited ) and the further nucleation and growth of another layer on the top of the as-grown bottom monolayer is automatically stopped after the full coverage of a monolayer film on the substrate ( time-limited ) . We further investigate the mechanism for the DLG of the monolayer TMDC film . Figure 3a illustrates the space-confined time-dependent concentration distribution of precursors from the metal precursor-loaded CNT film to the substrate during the DLG process . The space- confined face-to-face structure can provide a steady planar precursor supply , and the narrow gap can effectively reduce the gas velocity and possible turbulence during growth,47,48 which provides a highly uniform space distribution of the precursor across sodium the entire substrate . The addition of deoxycholate can effectively lower the melting point of precursors , increasing the mobility of precursors and lowering the reaction energy barrier , thus promoting the lateral growth of TMDC films ( Figure S12 ) .49 Then the lateral growth can be promoted as long as the distance between the CNT film and substrate is suitable . However , the promotion of lateral growth is not enough to sustain the monolayer growth , and a proper time distribution of precursor concentration is needed to prevent the vertical nucleation . We establish the following time-dependent mass transfer model assuming that the mass transfer process during the growth is stable because of the space-confined effect . As shown in the left part of Figure 3a , at the growth temperature , the precursor melts into a liquid state in the CNT film . During the growth process , the molten precursor uniformly drops through the pores of the CNT film . The droplets evaporate and form a saturated zone of gas precursor , where liquid and gas precursor coexist , and its height ( h1 ) is determined by the mass of droplets released from CNT film . Below the saturated zone , the falling droplets fully evaporate and the gas state precursor leading to a gradient diffuses to the sapphire substrate , diffusion zone ( with a height of h2 ) , where the metal precursor concentration decreases from saturation ( Csat ) to unsaturation .'}, {'content': 'The concentration near the substrate is determined by h1 and the liquid−gas h2 ,50,51 coexistence zone ( h1 ) can be estimated as where g is the gravitational acceleration , K is the vaporization coefficient of precursor droplets , and r ( t ) is the radius of the droplets as a function of time ( t ) , which is initially decided by the pore size of CNT . Then the precursor concentration near the substrate can be approximately expressed as law . The height of following Fick ’ s where D is the diffusion coefficient of gas state precursor and k is the apparent reaction rate constant of precursor in growth conditions . Thus , Csub is dependent on the time and space distance between CNT films and substrate . As shown in Figure 3a , b , given a fixed concentration of Se vapor , there are two notable values of metal precursor concentration near the substrate , namely nucleation concen- tration ( Cn ) and critical concentration to maintain lateral growth ( Cg ) . When Csub is larger than Cn , new WSe2 layers could nucleate . At Csub ranging from Cg to Cn , the lateral growth of monolayer WSe2 is promoted and simultaneously the multilayer nucleation is inhibited . If Csub is lower than Cg , the growth of monolayer WSe2 would terminate . Therefore , a precursor concentration near the substrate ranging from Cg to Cn is desired . With prolonging the growth time , the liquid precursor in the CNT film reacts with Se , randomly forming a large quantity of WSe2 flakes over there ( Figure 3c−f and Figure S13 ) , which gradually blocks the pores of the CNT film and decreases the concentration of precursor released from the CNT film . As a result , the size of precursor droplets , r ( t ) , decreases with the growth time from t0 to t2 , and consequently , the height of the liquid−gas coexistence zone ( h1 ) decreases , resulting in the decrease of Csub , as shown in Figure 3a . Therefore , the concentration around the substrate is ultimately determined by time and decreases with time . When the substrate is located at a suitable distance away from the CNT film , Csub could be slightly higher than Cn at first ( t0 to t1 ) , which facilitates the nucleation of monolayers , and then stay in the range from Cn to Cg ( blue region ) during the growth , in which the monolayer domains enlarge without any new nucleation and gradually merge into a continuous monolayer film ( t1 to t2 ) . When the growth time reaches t2 , a Csub lower than Cg can not maintain further growth of WSe2 layers and avoids the nucleation of new layers , automatically stopping the growth . The time-dependent decrease of precursor concentration causes self-limited growth and suppresses vertical nucleation .'}, {'content': 'Therefore , the mechanism of dual-limit growth including a space limit to promote lateral growth and time limit to prevent a vertical nucleation process guarantees large-scale monolayer growth without multilayer nucleation . The DLG mechanism is verified by a series of experiments . The modulation ability of CNT films on the TMDC growth is first investigated ( Figure S14 ) . According to the DLG mechanism , the pore size of CNT films should effectively affect the release of metal precursors and thus control the growth reaction . It is noted that the CNT film with a large pore size releases too much metal precursor and causes the formation of multilayers , while the CNT film with a pore size that is too small can not provide enough concentration of precursor for lateral growth , leading to the formation of isolated WSe2 flakes with limited sizes and etched edges . Therefore , an appropriate pore size of the CNT film is required for the growth of a high-quality TMDC film . Additionally , the growth rate can be effectively modulated by the porosity of the CNT film ( Figure S15 ) . As expected , the CNT film demonstrates a good capability to control the TMDC growth reaction . Then , the functions of the saturated zone in the DLG process are also studied . We set the CNT film beneath the growth substrate to eliminate the impacts of the saturated zone from the drop of molten precursors and only gas phase mass transfer is allowed ( Figure S16 ) . As a result , the samples exhibit a much lower nucleation density and coverage than those prepared by a normal CNT-on-substrate setup , because no sufficient metal precursors are supplied for the nucleation of WSe2 . It is concluded that the TMDC growth does not only rely on the gas transport process , but the existence of a saturation region also plays an essential role in the growth of large-area TMDC films . The distance between the CNT film and the sapphire is also important ( Figure S17 ) . When the distance is smaller than 0.2 mm , a full-coverage WSe2 film with many thick flakes is obtained ( Figure S17a ) , which may result from the landing of droplets on the sapphire . When the distance is larger than 0.3 mm , sparse triangular monolayer supply of WSe2 precursors for a full-coverage film . The results show that the revealing the insufficient is observed , 7395 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 =hgrtK1 ( ) 242=+CCh1Dksubsat2 ACS Nano www.acsnano.org Article Figure 4 . Universality of the DLG strategy for synthesizing other TMDCs . ( a−d ) OM images and Raman mapping on the position of the strongest peak of the MoS2 , WS2 , MoSe2 , and ReS2 monolayer films synthesized on the sapphire substrate by using the DLG strategy . Scale bars : 5 μm .'}, {'content': '( e−i ) Typical Raman and PL spectra of MoS2 , WS2 , MoSe2 , and ReS2 monolayer films . distance is critical to the growth process , matching well with the DLG mechanism where the diffusion distance h2 determines Csub . It is also found that the DLG method is applicable and robust for a wide range of loading contents of the precursor , showing its good reproducibility with a wide growth window . As shown in Figure 3c−f , continuous and homogeneous WSe2 films can be grown when the porous CNT solution with the film is dip-coated by the precursor concentration of ammonium metatungstate widely ranging from 40 to 100 mM . Such a wide window can be explained by the similar h1 values under different precursor-loading contents because h1 is mainly limited by the pore size of the CNT film instead of the loading contents m2 or m3 in the CNT film , as shown in Figure 3b . By contrast , an ammonium metatungstate concentration that is too low ( 20 mM ) or too high ( 150 mM ) causes the partial coverage of monolayer WSe2 ( Figure 3c ) or a WSe2 film with thick flakes ( Figure 3f ) . And Figure S13 further demonstrates the self-limited growth mechanism where the pores of CNT are blocked by the as-grown WSe2 flakes . These results reveal that the CNT film serves as an effective filter to modulate the precursor concentrations and verifies the DLG mechanism of the WSe2 films . To show the special time- limited function of the porous CNT film in the DLG compared with other planar substrates , we also use a flat Si/SiO2 substrate to load precursors for a face-to-face CVD growth of WSe2 on sapphire . As shown in Figures S18 and S19 , a uniform monolayer WSe2 film is synthesized by using the CNT precursor loader while arbitrarily thick WSe2 flakes are formed by using the flat Si/SiO2 precursor loader . If a CNT thin film is inserted between the silicon and sapphire substrate , very few WSe2 flakes will grow on the sapphire . These results further reveal the good filtering effect of the CNT thin film on the precursor release , leading to the time- and space-limited effect of the CNT film in the DLG . The planar SiO2/Si lacks the function of automatically decreasing and stopping the precursor supply during the growth ( time-limited effect ) and the condensation of the precursor into large droplets on SiO2/ Si can not uniformly supply the precursor during growth ( space-limited effect ) . The SiO2/Si substrate is also used for DLG growth ( Figure S20 ) . Although the SiO2/Si substrate has very different surface properties from sapphire,52 and the lateral growth is limited , WSe2 flakes with a uniform nucleation are still obtained .'}, {'content': 'In conclusion , the essential roles of the pore size and saturation region are verified by these comparative experiments , and the function of the CNT film in giving a steady and controllable supply of precursor is also proven , strengthening the validity of the presented DLG model . We further explore the universality of the DLG strategy in the growth of other TMDCs , including MoS2 , WS2 , MoSe2 , and ReS2 ( Figure 4 ) . As revealed in Figure 4a−d , large-scale monolayer MoS2 , WS2 , MoSe2 , and ReS2 films are synthesized on sapphire by the DLG . AFM height profiles verify the monolayer feature of these TMDC films ( Figure S21 ) , and the XPS data show the high purity of the DLG-grown TMDCs in chemical elemental composition , oxidation state , and bonding state ( Figure S22 ) .53−56 The uniform intensity mapping of characteristic Raman peaks and photoluminescence ( PL ) peaks further the formation of homogeneous monolayer TMDC films , as shown in Figure 4e−i and Figure S10 . the Raman peaks at 382.3 and 402.1 cm−1 Specifically , 1 and the out- correspond to the in-plane vibrational mode E2g of-plane mode A1g of monolayer MoS2,26 the peaks at 352 and 417 cm−1 correspond to the vibration modes of monolayer WS2,57 the peak at 241.1 cm−1 corresponds to monolayer reveal 7396 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 ACS Nano www.acsnano.org Article Figure 5 . Electrical properties of TMDC films grown by DLG . ( a ) Schematic of monolayer TMDC FET devices on a SiO2/Si substrate and the OM image of an array of TMDC devices . Scale bar : 50 μm . ( b ) Output characteristics of MoS2 FET at a specific gate voltage ranging from −60 to 60 V. ( c−f ) Transfer characteristics of typical MoS2 , MoSe2 , WS2 , and WSe2 FET devices . MoSe2,29 and the peaks at ∼138 , ∼148 , ∼159 , and 210 cm−1 58 ( Figure 4e ) . The PL of correspond to monolayer of ReS2 MoS2 , WS2 , MoSe2 , and ReS2 film peaks at 1.87 , 1.97 , 1.55 , and 1.66 eV , respectively , are also consistent with the reported values.26,29,57,58 These results demonstrate that a variety of large-scale monolayer TMDCs can be synthesized by the universal DLG strategy assisted by the CNT film . Electrical properties of the monolayer TMDCs films grown by the DLG strategy are assessed by fabricating back-gate field- effect transistors ( FETs ) with a heavily doped Si substrate as the back-gate electrode and a 300 nm thick thermal SiOx as the dielectric layer ( Figure 5a ; see details in Methods ) . Figure 5b , c and Figure S23 show Ids−Vgs transfer curves and Ids−Vds output curves of MoS2 FETs , which exhibit typical n-type transfer characteristics and good Ohmic contacts between monolayer MoS2 and electrodes .'}, {'content': 'The field effect mobility μFE is estimated from the equation , where L and W are channel length and width , respectively , and C0 is the gate capacitance . The field-effect mobility based on statistical results of 50 MoS2 FETs is 3.0 ± 1.3 cm2 V−1 s−1 ( Figure 5c and Figure S24 ) and the on/off ratio reaches ∼106 , which are comparable to the reported values in CVD polycrystal MoS2.59−62 Similarly , n-type behaviors for MoSe2 ( 0.37 cm2 V−1 s−1 ) and WS2 ( 8.6 cm2 V−1 s−1 ) FETs , as well as a p-type behavior for WSe2 ( 0.31 cm2 V−1 s−1 ) FETs , are also observed ( Figure 5d−f ) , the measured mobilities are comparable with the large-area polycrystalline the reported values of TMDCs,63−68 and we can further improve the electric properties by optimizing the device structure and engineering the interface . The transport properties of the uniform large- scale TMDC films provide great potential for electronic and optoelectronic devices . CONCLUSION In summary , we have developed a DLG strategy for the large- area synthesis of TMDC monolayers with good uniformity and large grain sizes ( 129 ± 43 μm ) on a sapphire substrate . The DLG process effectively adjusts the metal precursor concen- tration near the substrate and keeps its value in an appropriate range for a sufficient time to support the growth of pure monolayer TMDC films . The limited growth space not only provides a uniform distribution of metal precursor but also effectively decreases the chalcogen precursor concentration , extending the appropriate time for the monolayer growth . Moreover , the self-terminated reaction in the CNT film limits the further evaporation of metal precursors and thus prevents the unexpected formation of multilayered TMDCs during the excessive reaction time . This DLG process can be broadly employed in the synthesis of various uniform monolayer TMDC films including MoS2 , WS2 , MoSe2 , and ReS2 . Furthermore , the FET devices based on these TMDCs show competitive electrical properties , such as an electron mobility of 3.0 ± 1.3 cm2 V−1 s−1 and a current on/off ratio of ∼106 for MoS2 devices , the DLG is effective in suppressing the defect concentration in the TMDCs . This work provides a universal method for the synthesis of large- scale uniform TMDC films that could be applicable for future microelectronics . indicating that METHODS Fabrication of CNT Film . The CNT films were fabricated from superaligned CNTs69,70 with a uniform diameter of 10 nm and length of 500 μm . 10 , 20 , or 30 mg of CNTs were dispersed in 200 mL of ethanol by supersonic treatment for 5 min . Then the CNT/ethanol solution was deposited on a filter paper of 4 cm in diameter by suction 7397 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 =LWCVIV ( / ) ( d/d ) FE0dsdsg ACS Nano www.acsnano.org Article filtration .'}, {'content': 'After baking for 3 min at 60 °C to evaporate the ethanol , the CNT film was peeled off and became a freestanding film ( Figure S25 ) . DLG Growth of TMDC Films . The DLG growth was realized by atmospheric-pressure chemical vapor deposition by the assistance of CNT films fabricated by 20 mg of CNTs . A mixture of the transition metal precursor and sodium deoxycholate ( C24H39NaO4 ) was dissolved in deionized water and then dip-coated on the CNT films . Afterward , the precursor-loaded CNT films were dried on a hot plate at 60 °C and then together with a Piranha solution-treated sapphire substrate were placed face-to-face in a quartz boat at the center of a CVD tube furnace . To control the distance between the substrate and the CNT film , the sapphire substrate and a CNT film larger than the substrate were both put on a large Si plate , and the CNT film was placed on several small pieces of Si/CNT film ( Figure S2 ) . Then the gap space between the substrate and the CNT film could be controlled by the number of Si/CNT pieces used . The other quartz boat containing sulfur/selenium of about 1 g was placed 20 cm upstream of the tube furnace . Before the growth process , the furnace system was purged with 200 sccm Ar for 10 min . Then , the furnace was ramped to the growth temperature ( 750−850 °C ) at a ramping rate of 30 °C min−1 and maintained at the growth temperature for 10−30 min , when S or Se powder was heated to 170 or 320 °C , respectively , in an Ar ( 90 % ) /H2 ( 10 % ) mixed atmosphere . After the growth process , the furnace was naturally cooled to room temper- ature . a n d 1 5 0 ) Specifically , for the growth of WSe2 , a mixed solution of X mM ( X a m m o n i u m m e t a t u n g s t a t e = 2 0 , 4 0 , 1 0 0 , ( ( NH4 ) 6H2W12O40·xH2O ) and 20 mM C24H39NaO4 was dip-coated on a CNT film , and the growth was maintained at 760 °C for 10−30 min under a 30 sccm Ar/H2 atmosphere . For the growth of MoSe2 , a mixed solution of 83 mM ammonium molybdate ( ( NH4 ) 6Mo7O24· 4H2O ) and 20 mM C24H39NaO4 was dip-coated on a CNT film , and the growth occurred at 810 °C for 30 min under a 50 sccm Ar/H2 atmosphere . For MoS2 , the precursor solutions were 120 mM ( NH4 ) 6Mo7O24·4H2O and 20 mM C24H39NaO4 , and the growth occurred at 800 °C for 30 min under a 100 sccm Ar/H2 atmosphere .'}, {'content': 'For WS2 , 40 mM ( NH4 ) 6H2W12O40·xH2O and 20 mM C24H39NaO4 were used and the growth was maintained at 850 °C for 30 min under a 30 sccm Ar/H2 atmosphere . For the growth of ReS2 , 50 mM ammonium perrhenate ( H4NO4Re ) and 20 mM C24H39NaO4 were used , and the growth occurred at 830 °C for 30 min under a 50 sccm Ar/H2 atmosphere . Structural Characterizations . The microstructure and morphol- ogy of TMDCs films were characterized using OM ( OLYMPUS BX51 M ) , SEM ( ZEISS , Merlin ) , AFM ( Bruker Multimode 8 ) , and TEM ( JEOL , JEM-2100F , and Tecnai G2 F30 ) . Raman spectra and mapping images were obtained by a Raman spectrometer ( Horiba iHR550 ) with a 532 nm laser . The large-area Raman and PL mapping measurements were conducted in the 1 randomly picked region ( 30 × 30 μm ) from each section in Figure S4 . The stoichiometric analysis was carried out by XPS ( Escalab 250Xi , Thermo Fisher , Al Kα ) , with a scanning range of binding energy from 0 to 1350 eV . Fabrication and Electrical Measurements of FET Devices . For the fabricated devices , a TMDC film grown on a sapphire substrate was first coated with PMMA by spin-coating the PMMA solution at 3000 rpm for 30 s , followed by a high-temperature baking at 180 °C for 5 min . Then the sample was floated at 1 M KOH solution to peel off the TMDC films from the substrate . Afterward , the TMDC/PMMA film was transferred onto a Si/SiO2 substrate and immersed in acetone to remove the PMMA . The TMDC FET devices were fabricated on the transferred TMDC film following the fabrication process liftoff , and deposition of Ti ( 5 nm ) /Au ( 50 nm ) electrodes . Measurements of the devices were performed by a semi- electrical properties of conductor parameter analyzer ( Agilent B1500A ) in ambient air . including e-beam lithography , ASSOCIATED CONTENT * sı Supporting Information The Supporting Information is available free of charge at https : //pubs.acs.org/doi/10.1021/acsnano.3c09222 .'}, {'content': 'Schematic diagrams of the experimental setup , optical characterizations of an as-grown WSe2 film , character- izations of grain sizes and grain boundaries of WSe2 film , structural characterizations of WSe2 crystals , XPS spectra of TMDCs films , AFM topography images of the WSe2 monolayer films on the sapphire substrate , thermogravi- the precursor , metric analysis ( TGA ) curves of morphologies of WSe2 on the carbon nanotube ( CNT ) films and on the sapphire substrate at different precursor concentrations after the growth process , SEM images of CNT film , space-limited effect character- izations of WSe2 growth , additional experiments to verify the DLG mechanism , characterizations of different monolayer TMDCs , output characteristics of MoS2 FETs , transfer curves of 50 MoS2 FET devices , properties of CNT film ( PDF ) AUTHOR INFORMATION Corresponding Authors Run Shi − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China ; Email : shirun @ tsinghua.edu.cn orcid.org/0000-0002-3214-4661 ; Kai Liu − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China ; orcid.org/0000-0002-0638-5189 ; Email : liuk @ tsinghua.edu.cn Authors Zeqin Xin − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China Xiaolong Zhang − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China Jing Guo − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China Yonghuang Wu − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China Bolun Wang − State Key Laboratory of New Ceramics and Fine Processing , School of Materials Science and Engineering , Tsinghua University , Beijing 100084 , People ’ s Republic of China Complete contact information is available at : https : //pubs.acs.org/10.1021/acsnano.3c09222 Author Contributions †Z.X. , X.Z. , and J.G . contributed equally to this work . 7398 https : //doi.org/10.1021/acsnano.3c09222 ACS Nano 2024 , 18 , 7391−7401 ACS Nano www.acsnano.org Article Author Contributions K.L . and R.S . designed and supervised the research . Z.X . and X.Z . performed the growth of TMDCs . J.G . prepared the CNT films . X.Z. , J.G. , and B.W . characterized the samples . B.W . and Y.W . fabricated the TMDC FET devices and performed the electrical measurements . Z.X. , X.Z. , J.G. , and R.S . discussed the DLG mechanism . Z.X. , X.Z. , K.L. , and R.S . wrote and revised the manuscript .'}]\n",
            "\n",
            "Generate at least 20 entries in the specified JSON format.\n"
          ]
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        {
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            "\u001b[0;31mKeyboardInterrupt\u001b[0m                         Traceback (most recent call last)",
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            "\u001b[0;32m<ipython-input-8-5d70a3ec2d99>\u001b[0m in \u001b[0;36mprocess_and_initiate_chat\u001b[0;34m(chunks, max_entries, max_total_tokens)\u001b[0m\n\u001b[1;32m     30\u001b[0m     \u001b[0mmain_message\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34mf\"Please generate an Alpaca dataset based on the following content:\\n\\n{alpaca_entries}\\n\\nGenerate at least 20 entries in the specified JSON format.\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     31\u001b[0m     \u001b[0mprint\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmain_message\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m---> 32\u001b[0;31m     response = client.chat.completions.create(\n\u001b[0m\u001b[1;32m     33\u001b[0m             \u001b[0mmodel\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;34m\"gpt-4o\"\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m     34\u001b[0m             \u001b[0mresponse_format\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;34m{\u001b[0m\u001b[0;34m\"type\"\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0;34m\"json_object\"\u001b[0m\u001b[0;34m}\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/openai/_utils/_utils.py\u001b[0m in \u001b[0;36mwrapper\u001b[0;34m(*args, **kwargs)\u001b[0m\n\u001b[1;32m    275\u001b[0m                         \u001b[0mmsg\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;34mf\"Missing required argument: {quote(missing[0])}\"\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    276\u001b[0m                 \u001b[0;32mraise\u001b[0m \u001b[0mTypeError\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmsg\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 277\u001b[0;31m             \u001b[0;32mreturn\u001b[0m \u001b[0mfunc\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m*\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m**\u001b[0m\u001b[0mkwargs\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    278\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    279\u001b[0m         \u001b[0;32mreturn\u001b[0m \u001b[0mwrapper\u001b[0m  \u001b[0;31m# type: ignore\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/openai/resources/chat/completions.py\u001b[0m in \u001b[0;36mcreate\u001b[0;34m(self, messages, model, frequency_penalty, function_call, functions, logit_bias, logprobs, max_tokens, n, parallel_tool_calls, presence_penalty, response_format, seed, service_tier, stop, stream, stream_options, temperature, tool_choice, tools, top_logprobs, top_p, user, extra_headers, extra_query, extra_body, timeout)\u001b[0m\n\u001b[1;32m    641\u001b[0m         \u001b[0mtimeout\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mfloat\u001b[0m \u001b[0;34m|\u001b[0m \u001b[0mhttpx\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mTimeout\u001b[0m \u001b[0;34m|\u001b[0m \u001b[0;32mNone\u001b[0m \u001b[0;34m|\u001b[0m \u001b[0mNotGiven\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mNOT_GIVEN\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    642\u001b[0m     ) -> ChatCompletion | Stream[ChatCompletionChunk]:\n\u001b[0;32m--> 643\u001b[0;31m         return self._post(\n\u001b[0m\u001b[1;32m    644\u001b[0m             \u001b[0;34m\"/chat/completions\"\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    645\u001b[0m             body=maybe_transform(\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/openai/_base_client.py\u001b[0m in \u001b[0;36mpost\u001b[0;34m(self, path, cast_to, body, options, files, stream, stream_cls)\u001b[0m\n\u001b[1;32m   1264\u001b[0m             \u001b[0mmethod\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0;34m\"post\"\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0murl\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mpath\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mjson_data\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mbody\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mfiles\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mto_httpx_files\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mfiles\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0;34m**\u001b[0m\u001b[0moptions\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1265\u001b[0m         )\n\u001b[0;32m-> 1266\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mcast\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mResponseT\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mcast_to\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mopts\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mstream\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mstream\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mstream_cls\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mstream_cls\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1267\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1268\u001b[0m     def patch(\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/openai/_base_client.py\u001b[0m in \u001b[0;36mrequest\u001b[0;34m(self, cast_to, options, remaining_retries, stream, stream_cls)\u001b[0m\n\u001b[1;32m    940\u001b[0m         \u001b[0mstream_cls\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mtype\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0m_StreamT\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m|\u001b[0m \u001b[0;32mNone\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    941\u001b[0m     ) -> ResponseT | _StreamT:\n\u001b[0;32m--> 942\u001b[0;31m         return self._request(\n\u001b[0m\u001b[1;32m    943\u001b[0m             \u001b[0mcast_to\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mcast_to\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    944\u001b[0m             \u001b[0moptions\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0moptions\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/openai/_base_client.py\u001b[0m in \u001b[0;36m_request\u001b[0;34m(self, cast_to, options, remaining_retries, stream, stream_cls)\u001b[0m\n\u001b[1;32m    976\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    977\u001b[0m         \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 978\u001b[0;31m             response = self._client.send(\n\u001b[0m\u001b[1;32m    979\u001b[0m                 \u001b[0mrequest\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    980\u001b[0m                 \u001b[0mstream\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mstream\u001b[0m \u001b[0;32mor\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_should_stream_response_body\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpx/_client.py\u001b[0m in \u001b[0;36msend\u001b[0;34m(self, request, stream, auth, follow_redirects)\u001b[0m\n\u001b[1;32m    912\u001b[0m         \u001b[0mauth\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_build_request_auth\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mauth\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    913\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 914\u001b[0;31m         response = self._send_handling_auth(\n\u001b[0m\u001b[1;32m    915\u001b[0m             \u001b[0mrequest\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    916\u001b[0m             \u001b[0mauth\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mauth\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpx/_client.py\u001b[0m in \u001b[0;36m_send_handling_auth\u001b[0;34m(self, request, auth, follow_redirects, history)\u001b[0m\n\u001b[1;32m    940\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    941\u001b[0m             \u001b[0;32mwhile\u001b[0m \u001b[0;32mTrue\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 942\u001b[0;31m                 response = self._send_handling_redirects(\n\u001b[0m\u001b[1;32m    943\u001b[0m                     \u001b[0mrequest\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    944\u001b[0m                     \u001b[0mfollow_redirects\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mfollow_redirects\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpx/_client.py\u001b[0m in \u001b[0;36m_send_handling_redirects\u001b[0;34m(self, request, follow_redirects, history)\u001b[0m\n\u001b[1;32m    977\u001b[0m                 \u001b[0mhook\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    978\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 979\u001b[0;31m             \u001b[0mresponse\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_send_single_request\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    980\u001b[0m             \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    981\u001b[0m                 \u001b[0;32mfor\u001b[0m \u001b[0mhook\u001b[0m \u001b[0;32min\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_event_hooks\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;34m\"response\"\u001b[0m\u001b[0;34m]\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpx/_client.py\u001b[0m in \u001b[0;36m_send_single_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m   1013\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1014\u001b[0m         \u001b[0;32mwith\u001b[0m \u001b[0mrequest_context\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 1015\u001b[0;31m             \u001b[0mresponse\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mtransport\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mhandle_request\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1016\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1017\u001b[0m         \u001b[0;32massert\u001b[0m \u001b[0misinstance\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mresponse\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mstream\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mSyncByteStream\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpx/_transports/default.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    231\u001b[0m         )\n\u001b[1;32m    232\u001b[0m         \u001b[0;32mwith\u001b[0m \u001b[0mmap_httpcore_exceptions\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 233\u001b[0;31m             \u001b[0mresp\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_pool\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mhandle_request\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mreq\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    234\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    235\u001b[0m         \u001b[0;32massert\u001b[0m \u001b[0misinstance\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mresp\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mstream\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mtyping\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mIterable\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/connection_pool.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    214\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    215\u001b[0m             \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_close_connections\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mclosing\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 216\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mexc\u001b[0m \u001b[0;32mfrom\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    217\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    218\u001b[0m         \u001b[0;31m# Return the response. Note that in this case we still have to manage\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/connection_pool.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    194\u001b[0m                 \u001b[0;32mtry\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    195\u001b[0m                     \u001b[0;31m# Send the request on the assigned connection.\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 196\u001b[0;31m                     response = connection.handle_request(\n\u001b[0m\u001b[1;32m    197\u001b[0m                         \u001b[0mpool_request\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    198\u001b[0m                     )\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/connection.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m     99\u001b[0m             \u001b[0;32mraise\u001b[0m \u001b[0mexc\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    100\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 101\u001b[0;31m         \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_connection\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mhandle_request\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    102\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    103\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0m_connect\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mrequest\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mRequest\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;34m->\u001b[0m \u001b[0mNetworkStream\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/http11.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    141\u001b[0m                 \u001b[0;32mwith\u001b[0m \u001b[0mTrace\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m\"response_closed\"\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mlogger\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mrequest\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;32mas\u001b[0m \u001b[0mtrace\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    142\u001b[0m                     \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_response_closed\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 143\u001b[0;31m             \u001b[0;32mraise\u001b[0m \u001b[0mexc\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    144\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    145\u001b[0m     \u001b[0;31m# Sending the request...\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/http11.py\u001b[0m in \u001b[0;36mhandle_request\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    111\u001b[0m                     \u001b[0mheaders\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    112\u001b[0m                     \u001b[0mtrailing_data\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 113\u001b[0;31m                 ) = self._receive_response_headers(**kwargs)\n\u001b[0m\u001b[1;32m    114\u001b[0m                 trace.return_value = (\n\u001b[1;32m    115\u001b[0m                     \u001b[0mhttp_version\u001b[0m\u001b[0;34m,\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/http11.py\u001b[0m in \u001b[0;36m_receive_response_headers\u001b[0;34m(self, request)\u001b[0m\n\u001b[1;32m    184\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    185\u001b[0m         \u001b[0;32mwhile\u001b[0m \u001b[0;32mTrue\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 186\u001b[0;31m             \u001b[0mevent\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_receive_event\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mtimeout\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mtimeout\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    187\u001b[0m             \u001b[0;32mif\u001b[0m \u001b[0misinstance\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mevent\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mh11\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mResponse\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    188\u001b[0m                 \u001b[0;32mbreak\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_sync/http11.py\u001b[0m in \u001b[0;36m_receive_event\u001b[0;34m(self, timeout)\u001b[0m\n\u001b[1;32m    222\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    223\u001b[0m             \u001b[0;32mif\u001b[0m \u001b[0mevent\u001b[0m \u001b[0;32mis\u001b[0m \u001b[0mh11\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mNEED_DATA\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 224\u001b[0;31m                 data = self._network_stream.read(\n\u001b[0m\u001b[1;32m    225\u001b[0m                     \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mREAD_NUM_BYTES\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mtimeout\u001b[0m\u001b[0;34m=\u001b[0m\u001b[0mtimeout\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    226\u001b[0m                 )\n",
            "\u001b[0;32m/usr/local/lib/python3.10/dist-packages/httpcore/_backends/sync.py\u001b[0m in \u001b[0;36mread\u001b[0;34m(self, max_bytes, timeout)\u001b[0m\n\u001b[1;32m    124\u001b[0m         \u001b[0;32mwith\u001b[0m \u001b[0mmap_exceptions\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mexc_map\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    125\u001b[0m             \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_sock\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msettimeout\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mtimeout\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m--> 126\u001b[0;31m             \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_sock\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mrecv\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mmax_bytes\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m    127\u001b[0m \u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m    128\u001b[0m     \u001b[0;32mdef\u001b[0m \u001b[0mwrite\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mself\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mbuffer\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mbytes\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mtimeout\u001b[0m\u001b[0;34m:\u001b[0m \u001b[0mtyping\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mOptional\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0mfloat\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m=\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m)\u001b[0m \u001b[0;34m->\u001b[0m \u001b[0;32mNone\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/lib/python3.10/ssl.py\u001b[0m in \u001b[0;36mrecv\u001b[0;34m(self, buflen, flags)\u001b[0m\n\u001b[1;32m   1286\u001b[0m                     \u001b[0;34m\"non-zero flags not allowed in calls to recv() on %s\"\u001b[0m \u001b[0;34m%\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1287\u001b[0m                     self.__class__)\n\u001b[0;32m-> 1288\u001b[0;31m             \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mread\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mbuflen\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1289\u001b[0m         \u001b[0;32melse\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1290\u001b[0m             \u001b[0;32mreturn\u001b[0m \u001b[0msuper\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mrecv\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mbuflen\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mflags\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;32m/usr/lib/python3.10/ssl.py\u001b[0m in \u001b[0;36mread\u001b[0;34m(self, len, buffer)\u001b[0m\n\u001b[1;32m   1159\u001b[0m                 \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_sslobj\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mread\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mlen\u001b[0m\u001b[0;34m,\u001b[0m \u001b[0mbuffer\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1160\u001b[0m             \u001b[0;32melse\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0;32m-> 1161\u001b[0;31m                 \u001b[0;32mreturn\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0m_sslobj\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0mread\u001b[0m\u001b[0;34m(\u001b[0m\u001b[0mlen\u001b[0m\u001b[0;34m)\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[0m\u001b[1;32m   1162\u001b[0m         \u001b[0;32mexcept\u001b[0m \u001b[0mSSLError\u001b[0m \u001b[0;32mas\u001b[0m \u001b[0mx\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n\u001b[1;32m   1163\u001b[0m             \u001b[0;32mif\u001b[0m \u001b[0mx\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0margs\u001b[0m\u001b[0;34m[\u001b[0m\u001b[0;36m0\u001b[0m\u001b[0;34m]\u001b[0m \u001b[0;34m==\u001b[0m \u001b[0mSSL_ERROR_EOF\u001b[0m \u001b[0;32mand\u001b[0m \u001b[0mself\u001b[0m\u001b[0;34m.\u001b[0m\u001b[0msuppress_ragged_eofs\u001b[0m\u001b[0;34m:\u001b[0m\u001b[0;34m\u001b[0m\u001b[0;34m\u001b[0m\u001b[0m\n",
            "\u001b[0;31mKeyboardInterrupt\u001b[0m: "
          ]
        }
      ]
    }
  ]
}