1
|
Nibhanupudi SST, Roy A, Chowdhury S, Schalip R, Coupin MJ, Matthews KC, Alam MH, Satpati B, Movva HCP, Luth CJ, Wu S, Warner JH, Banerjee SK. Low-Temperature Synthesis of WSe 2 by the Selenization Process under Ultrahigh Vacuum for BEOL Compatible Reconfigurable Neurons. ACS APPLIED MATERIALS & INTERFACES 2024; 16:22326-22333. [PMID: 38635965 DOI: 10.1021/acsami.3c18446] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/20/2024]
Abstract
Low-temperature large-area growth of two-dimensional (2D) transition-metal dichalcogenides (TMDs) is critical for their integration with silicon chips. Especially, if the growth temperatures can be lowered below the back-end-of-line (BEOL) processing temperatures, the Si transistors can interface with 2D devices (in the back end) to enable high-density heterogeneous circuits. Such configurations are particularly useful for neuromorphic computing applications where a dense network of neurons interacts to compute the output. In this work, we present low-temperature synthesis (400 °C) of 2D tungsten diselenide (WSe2) via the selenization of the W film under ultrahigh vacuum (UHV) conditions. This simple yet effective process yields large-area, homogeneous films of 2D TMDs, as confirmed by several characterization techniques, including reflection high-energy electron diffraction, atomic force microscopy, transmission electron microscopy, and different spectroscopy methods. Memristors fabricated using the grown WSe2 film are leveraged to realize a novel compact neuron circuit that can be reconfigured to enable homeostasis.
Collapse
Affiliation(s)
- S S Teja Nibhanupudi
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Anupam Roy
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
- Department of Physics, Birla Institute of Technology Mesra, Ranchi, Jharkhand 835215, India
| | - Sayema Chowdhury
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Ryan Schalip
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Matthew J Coupin
- Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Kevin C Matthews
- Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Md Hasibul Alam
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Biswarup Satpati
- Surface Physics and Material Science Division, Saha Institute of Nuclear Physics, 1/AF, Bidhannagar, Kolkata 700 064, India
| | - Hema C P Movva
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Christopher J Luth
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Siyu Wu
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| | - Jamie H Warner
- Texas Materials Institute, The University of Texas at Austin, Austin, Texas 78712, United States
| | - Sanjay K Banerjee
- Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, Texas 78758, United States
| |
Collapse
|
2
|
Laukkanen P, Punkkinen M, Kuzmin M, Kokko K, Liu X, Radfar B, Vähänissi V, Savin H, Tukiainen A, Hakkarainen T, Viheriälä J, Guina M. Bridging the gap between surface physics and photonics. REPORTS ON PROGRESS IN PHYSICS. PHYSICAL SOCIETY (GREAT BRITAIN) 2024; 87:044501. [PMID: 38373354 DOI: 10.1088/1361-6633/ad2ac9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/18/2023] [Accepted: 02/19/2024] [Indexed: 02/21/2024]
Abstract
Use and performance criteria of photonic devices increase in various application areas such as information and communication, lighting, and photovoltaics. In many current and future photonic devices, surfaces of a semiconductor crystal are a weak part causing significant photo-electric losses and malfunctions in applications. These surface challenges, many of which arise from material defects at semiconductor surfaces, include signal attenuation in waveguides, light absorption in light emitting diodes, non-radiative recombination of carriers in solar cells, leakage (dark) current of photodiodes, and light reflection at solar cell interfaces for instance. To reduce harmful surface effects, the optical and electrical passivation of devices has been developed for several decades, especially with the methods of semiconductor technology. Because atomic scale control and knowledge of surface-related phenomena have become relevant to increase the performance of different devices, it might be useful to enhance the bridging of surface physics to photonics. Toward that target, we review some evolving research subjects with open questions and possible solutions, which hopefully provide example connecting points between photonic device passivation and surface physics. One question is related to the properties of the wet chemically cleaned semiconductor surfaces which are typically utilized in device manufacturing processes, but which appear to be different from crystalline surfaces studied in ultrahigh vacuum by physicists. In devices, a defective semiconductor surface often lies at an embedded interface formed by a thin metal or insulator film grown on the semiconductor crystal, which makes the measurements of its atomic and electronic structures difficult. To understand these interface properties, it is essential to combine quantum mechanical simulation methods. This review also covers metal-semiconductor interfaces which are included in most photonic devices to transmit electric carriers to the semiconductor structure. Low-resistive and passivated contacts with an ultrathin tunneling barrier are an emergent solution to control electrical losses in photonic devices.
Collapse
Affiliation(s)
- Pekka Laukkanen
- Department of Physics and Astronomy, University of Turku, Turku, Finland
| | - Marko Punkkinen
- Department of Physics and Astronomy, University of Turku, Turku, Finland
| | - Mikhail Kuzmin
- Department of Physics and Astronomy, University of Turku, Turku, Finland
| | - Kalevi Kokko
- Department of Physics and Astronomy, University of Turku, Turku, Finland
| | - Xiaolong Liu
- Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland
| | - Behrad Radfar
- Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland
| | - Ville Vähänissi
- Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland
| | - Hele Savin
- Department of Electronics and Nanoengineering, Aalto University, Espoo, Finland
| | - Antti Tukiainen
- Optoelectronics Research Centre, Tampere University, Tampere, Finland
| | - Teemu Hakkarainen
- Optoelectronics Research Centre, Tampere University, Tampere, Finland
| | - Jukka Viheriälä
- Optoelectronics Research Centre, Tampere University, Tampere, Finland
| | - Mircea Guina
- Optoelectronics Research Centre, Tampere University, Tampere, Finland
| |
Collapse
|
3
|
Wang X, Hu Y, Kim SY, Addou R, Cho K, Wallace RM. Origins of Fermi Level Pinning for Ni and Ag Metal Contacts on Tungsten Dichalcogenides. ACS NANO 2023; 17:20353-20365. [PMID: 37788682 DOI: 10.1021/acsnano.3c06494] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/05/2023]
Abstract
Tungsten transition metal dichalcogenides (W-TMDs) are intriguing due to their properties and potential for application in next-generation electronic devices. However, strong Fermi level (EF) pinning manifests at the metal/W-TMD interfaces, which could tremendously restrain the carrier injection into the channel. In this work, we illustrate the origins of EF pinning for Ni and Ag contacts on W-TMDs by considering interface chemistry, band alignment, impurities, and imperfections of W-TMDs, contact metal adsorption mechanism, and the resultant electronic structure. We conclude that the origins of EF pinning at a covalent contact metal/W-TMD interface, such as Ni/W-TMDs, can be attributed to defects, impurities, and interface reaction products. In contrast, for a van der Waals contact metal/TMD system such as Ag/W-TMDs, the primary factor responsible for EF pinning is the electronic modification of the TMDs resulting from the defects and impurities with the minor impact of metal-induced gap states. The potential strategies for carefully engineering the metal deposition approach are also discussed. This work unveils the origins of EF pinning at metal/TMD interfaces experimentally and theoretically and provides guidance on further enhancing and improving the device performance.
Collapse
Affiliation(s)
- Xinglu Wang
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Yaoqiao Hu
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Seong Yeoul Kim
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Rafik Addou
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Kyeongjae Cho
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| | - Robert M Wallace
- Department of Materials Science and Engineering, The University of Texas at Dallas, Richardson, Texas 75080, United States
| |
Collapse
|
4
|
Liu S, Liu Y, Holtzman L, Li B, Holbrook M, Pack J, Taniguchi T, Watanabe K, Dean CR, Pasupathy AN, Barmak K, Rhodes DA, Hone J. Two-Step Flux Synthesis of Ultrapure Transition-Metal Dichalcogenides. ACS NANO 2023; 17:16587-16596. [PMID: 37610237 DOI: 10.1021/acsnano.3c02511] [Citation(s) in RCA: 5] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
Two-dimensional transition-metal dichalcogenides (TMDs) have attracted tremendous interest due to the unusual electronic and optoelectronic properties of isolated monolayers and the ability to assemble diverse monolayers into complex heterostructures. To understand the intrinsic properties of TMDs and fully realize their potential in applications and fundamental studies, high-purity materials are required. Here, we describe the synthesis of TMD crystals using a two-step flux growth method that eliminates a major potential source of contamination. Detailed characterization of TMDs grown by this two-step method reveals charged and isovalent defects with densities an order of magnitude lower than those in TMDs grown by a single-step flux technique. For WSe2, we show that increasing the Se/W ratio during growth reduces point defect density, with crystals grown at 100:1 ratio achieving charged and isovalent defect densities below 1010 and 1011 cm-2, respectively. Initial temperature-dependent electrical transport measurements of monolayer WSe2 yield room-temperature hole mobility above 840 cm2/(V s) and low-temperature disorder-limited mobility above 44,000 cm2/(V s). Electrical transport measurements of graphene-WSe2 heterostructures fabricated from the two-step flux grown WSe2 also show superior performance: higher graphene mobility, lower charged impurity density, and well-resolved integer quantum Hall states. Finally, we demonstrate that the two-step flux technique can be used to synthesize other TMDs with similar defect densities, including semiconducting 2H-MoSe2 and 2H-MoTe2 and semimetallic Td-WTe2 and 1T'-MoTe2.
Collapse
Affiliation(s)
- Song Liu
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Yang Liu
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Luke Holtzman
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, United States
| | - Baichang Li
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Madisen Holbrook
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - Jordan Pack
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Takashi Taniguchi
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Kenji Watanabe
- National Institute for Materials Science, Tsukuba, Ibaraki 305-0044, Japan
| | - Cory R Dean
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Abhay N Pasupathy
- Department of Physics, Columbia University, New York, New York 10027, United States
| | - Katayun Barmak
- Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, United States
| | - Daniel A Rhodes
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, New York 10027, United States
| |
Collapse
|
5
|
Giri A, Park G, Jeong U. Layer-Structured Anisotropic Metal Chalcogenides: Recent Advances in Synthesis, Modulation, and Applications. Chem Rev 2023; 123:3329-3442. [PMID: 36719999 PMCID: PMC10103142 DOI: 10.1021/acs.chemrev.2c00455] [Citation(s) in RCA: 11] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The unique electronic and catalytic properties emerging from low symmetry anisotropic (1D and 2D) metal chalcogenides (MCs) have generated tremendous interest for use in next generation electronics, optoelectronics, electrochemical energy storage devices, and chemical sensing devices. Despite many proof-of-concept demonstrations so far, the full potential of anisotropic chalcogenides has yet to be investigated. This article provides a comprehensive overview of the recent progress made in the synthesis, mechanistic understanding, property modulation strategies, and applications of the anisotropic chalcogenides. It begins with an introduction to the basic crystal structures, and then the unique physical and chemical properties of 1D and 2D MCs. Controlled synthetic routes for anisotropic MC crystals are summarized with example advances in the solution-phase synthesis, vapor-phase synthesis, and exfoliation. Several important approaches to modulate dimensions, phases, compositions, defects, and heterostructures of anisotropic MCs are discussed. Recent significant advances in applications are highlighted for electronics, optoelectronic devices, catalysts, batteries, supercapacitors, sensing platforms, and thermoelectric devices. The article ends with prospects for future opportunities and challenges to be addressed in the academic research and practical engineering of anisotropic MCs.
Collapse
Affiliation(s)
- Anupam Giri
- Department of Chemistry, Faculty of Science, University of Allahabad, Prayagraj, UP-211002, India
| | - Gyeongbae Park
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Cheongam-Ro 77, Nam-Gu, Pohang, Gyeongbuk790-784, Korea.,Functional Materials and Components R&D Group, Korea Institute of Industrial Technology, Gwahakdanji-ro 137-41, Sacheon-myeon, Gangneung, Gangwon-do25440, Republic of Korea
| | - Unyong Jeong
- Department of Materials Science and Engineering, Pohang University of Science and Technology, Cheongam-Ro 77, Nam-Gu, Pohang, Gyeongbuk790-784, Korea
| |
Collapse
|
6
|
Och M, Anastasiou K, Leontis I, Zemignani GZ, Palczynski P, Mostaed A, Sokolikova MS, Alexeev EM, Bai H, Tartakovskii AI, Lischner J, Nellist PD, Russo S, Mattevi C. Synthesis of mono- and few-layered n-type WSe 2 from solid state inorganic precursors. NANOSCALE 2022; 14:15651-15662. [PMID: 36189726 PMCID: PMC9631355 DOI: 10.1039/d2nr03233c] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 06/12/2022] [Accepted: 09/05/2022] [Indexed: 06/16/2023]
Abstract
Tuning the charge transport properties of two-dimensional transition metal dichalcogenides (TMDs) is pivotal to their future device integration in post-silicon technologies. To date, co-doping of TMDs during growth still proves to be challenging, and the synthesis of doped WSe2, an otherwise ambipolar material, has been mainly limited to p-doping. Here, we demonstrate the synthesis of high-quality n-type monolayered WSe2 flakes using a solid-state precursor for Se, zinc selenide. n-Type transport has been reported with prime electron mobilities of up to 10 cm2 V-1 s-1. We also demonstrate the tuneability of doping to p-type transport with hole mobilities of 50 cm2 V-1 s-1 after annealing in air. n-Doping has been attributed to the presence of Zn adatoms on the WSe2 flakes as revealed by X-ray photoelectron spectroscopy (XPS), spatially resolved time of flight secondary ion mass spectroscopy (SIMS) and angular dark-field scanning transmission electron microscopy (AD-STEM) characterization of WSe2 flakes. Monolayer WSe2 flakes exhibit a sharp photoluminescence (PL) peak at room temperature and highly uniform emission across the entire flake area, indicating a high degree of crystallinity of the material. This work provides new insight into the synthesis of TMDs with charge carrier control, to pave the way towards post-silicon electronics.
Collapse
Affiliation(s)
- Mauro Och
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
| | | | - Ioannis Leontis
- Department of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, UK
| | - Giulia Zoe Zemignani
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
- Center for Nano Science and Technology, Milan, Italy
| | - Pawel Palczynski
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
| | - Ali Mostaed
- Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
| | | | - Evgeny M Alexeev
- Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH, UK
| | - Haoyu Bai
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
| | | | - Johannes Lischner
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
- Thomas Young Centre for Theory and Simulation of Materials, Imperial College London, London, SW7 2AZ, UK
| | - Peter D Nellist
- Department of Materials, University of Oxford, Oxford, OX1 3PH, UK
| | - Saverio Russo
- Department of Physics and Astronomy, University of Exeter, Exeter, EX4 4QL, UK
| | - Cecilia Mattevi
- Department of Materials, Imperial College London, London, SW7 2AZ, UK.
| |
Collapse
|
7
|
Noh S, Lee S, Lee J, Jo H, Lee H, Kim M, Kim H, Kim YA, Yoon H. All-Gas-Phase Synthesis of Heterolayered Two-Dimensional Nanohybrids Decorated with Metallic Nanocatalysts for Water Splitting. SMALL (WEINHEIM AN DER BERGSTRASSE, GERMANY) 2022; 18:e2203633. [PMID: 36108130 DOI: 10.1002/smll.202203633] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2022] [Revised: 08/07/2022] [Indexed: 06/15/2023]
Abstract
Herein, a sequential gas-phase process involving air jet milling followed by chemical vapor deposition (CVD), is demonstrated to be an efficient strategy for the fabrication of heterolayered 2D nanohybrids (2DNHs) decorated with nanocatalysts. Tens of grams of the nanohybrids, which is a substantial quantity at the laboratory scale, are produced in the absence of solvents and water, and without the need for an extra purification procedure. Air jet milling enables the development of binary/ternary heterolayered structures consisting of graphene, WSe2 , and/or MoS2 via the gas-phase co-exfoliation of their bulk counterparts. Based on the X-ray photoelectron and Raman spectroscopy data, the heterolayers of the 2DNHs exert chemical and electronic effects on each other, while diminishing the interactions between same-component layers. Moreover, the electrochemically active surface area increases by >190% and the charge transfer resistance decreases by >35%. CVD is performed to introduce Pt and Ru nanoparticles with diameters of a few nanometers as additional electrocatalysts into the 2DNHs. The nanocatalyst-decorated 2DNHs show excellent performance for the production of hydrogen and oxygen gases in water-splitting cells. Notably, the proposed all-gas-phase processes allow for the large-scale production of functional 2DNHs with minimal negative environmental impact, which is crucial for the commercialization of nanomaterials.
Collapse
Affiliation(s)
- Seonmyeong Noh
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Seungmin Lee
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Jisun Lee
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Hyemi Jo
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Haney Lee
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Minjin Kim
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Hyungwoo Kim
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
- School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Yoong Ahm Kim
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
- School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| | - Hyeonseok Yoon
- Department of Polymer Engineering, Graduate School, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
- School of Polymer Science and Engineering, Chonnam National University, 77 Yongbong-ro, Buk-gu, Gwangju, 61186, South Korea
| |
Collapse
|
8
|
Peña Román RJ, Auad Y, Grasso L, Padilha LA, Alvarez F, Barcelos ID, Kociak M, Zagonel LF. Design and implementation of a device based on an off-axis parabolic mirror to perform luminescence experiments in a scanning tunneling microscope. THE REVIEW OF SCIENTIFIC INSTRUMENTS 2022; 93:043704. [PMID: 35489916 DOI: 10.1063/5.0078423] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2021] [Accepted: 02/27/2022] [Indexed: 06/14/2023]
Abstract
We present the design, implementation, and illustrative results of a light collection/injection strategy based on an off-axis parabolic mirror collector for a low-temperature Scanning Tunneling Microscope (STM). This device allows us to perform STM induced Light Emission (STM-LE) and Cathodoluminescence (STM-CL) experiments and in situ Photoluminescence (PL) and Raman spectroscopy as complementary techniques. Considering the Étendue conservation and using an off-axis parabolic mirror, it is possible to design a light collection and injection system that displays 72% of collection efficiency (considering the hemisphere above the sample surface) while maintaining high spectral resolution and minimizing signal loss. The performance of the STM is tested by atomically resolved images and scanning tunneling spectroscopy results on standard sample surfaces. The capabilities of our system are demonstrated by performing STM-LE on metallic surfaces and two-dimensional semiconducting samples, observing both plasmonic and excitonic emissions. In addition, we carried out in situ PL measurements on semiconducting monolayers and quantum dots and in situ Raman on graphite and hexagonal boron nitride (h-BN) samples. Additionally, STM-CL and PL were obtained on monolayer h-BN gathering luminescence spectra that are typically associated with intragap states related to carbon defects. The results show that the flexible and efficient light injection and collection device based on an off-axis parabolic mirror is a powerful tool to study several types of nanostructures with multiple spectroscopic techniques in correlation with their morphology at the atomic scale and electronic structure.
Collapse
Affiliation(s)
- Ricardo Javier Peña Román
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Yves Auad
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Lucas Grasso
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Lazaro A Padilha
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Fernando Alvarez
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| | - Ingrid David Barcelos
- Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970 Campinas, SP, Brazil
| | - Mathieu Kociak
- Université Paris-Saclay, CNRS, Laboratoire de Physique des Solides, 91405 Orsay, France
| | - Luiz Fernando Zagonel
- "Gleb Wataghin" Institute of Physics, University of Campinas-UNICAMP, 13083-859 Campinas, SP, Brazil
| |
Collapse
|
9
|
Coexistence of electron whispering-gallery modes and atomic collapse states in graphene/WSe 2 heterostructure quantum dots. Nat Commun 2022; 13:1597. [PMID: 35332128 PMCID: PMC8948210 DOI: 10.1038/s41467-022-29251-2] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Accepted: 02/11/2022] [Indexed: 11/08/2022] Open
Abstract
The relativistic massless charge carriers with a Fermi velocity of about c/300 in graphene enable us to realize two distinct types of resonances (here, c is the speed of light in vacuum). One is the electron whispering-gallery mode in graphene quantum dots arising from the Klein tunneling of the massless Dirac fermions. The other is the atomic collapse state, which has never been observed in experiment with real atoms due to the difficulty of producing heavy nuclei with charge Z > 170; however, they can be realized near a Coulomb impurity in graphene with a charge Z ≥ 1 because of the "small" velocity of the Dirac excitations. Here we demonstrate that both the electron whispering-gallery modes and atomic collapse states coexist in graphene/WSe2 heterostructure quantum dots due to the Coulomb-like potential near their edges. By applying a perpendicular magnetic field, we explore the evolution from the atomic collapse states to unusual Landau levels in the collapse regime.
Collapse
|
10
|
Peña Román RJ, Auad Y, Grasso L, Alvarez F, Barcelos ID, Zagonel LF. Tunneling-current-induced local excitonic luminescence in p-doped WSe 2 monolayers. NANOSCALE 2020; 12:13460-13470. [PMID: 32614018 DOI: 10.1039/d0nr03400b] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/11/2023]
Abstract
We have studied the excitonic properties of exfoliated tungsten diselenide (WSe2) monolayers transferred to gold substrates using the tunneling current in a Scanning Tunneling Microscope (STM) operated in air to excite the light emission locally. In obtained spectra, emission energies are independent of the applied bias voltage and resemble photoluminescence (PL) results, indicating that, in both cases, the light emission is due to neutral and charged exciton recombination. Interestingly, the electron injection rate, that is, the tunneling current, can be used to control the ratio of charged to neutral exciton emission. The obtained quantum yield in the transition metal dichalcogenide (TMD) is ∼5 × 10-7 photons per electron. The proposed excitation mechanism is the direct injection of carriers into the conduction band. The monolayer WSe2 presents bright and dark defects spotted by STM images performed under UHV. STS confirms the sample as p-doped, possibly as a net result of the observed defects. The presence of an interfacial water layer decouples the monolayer from the gold support and allows excitonic emission from the WSe2 monolayer. The creation of a water layer is an inherent feature of the sample transferring process due to the ubiquitous air moisture. Consequently, vacuum thermal annealing, which removes the water layer, quenches excitonic luminescence from the TMD. The tunneling current can locally displace water molecules leading to excitonic emission quenching and to plasmonic emission due to the gold substrate. The present findings extend the use and the understanding of STM induced light emission (STM-LE) on semiconducting TMDs to probe exciton emission and dynamics with high spatial resolution.
Collapse
Affiliation(s)
- Ricardo Javier Peña Román
- Applied Physics Department, "Gleb Wataghin" Institute of Physics, University of Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil.
| | - Yves Auad
- Applied Physics Department, "Gleb Wataghin" Institute of Physics, University of Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil.
| | - Lucas Grasso
- Applied Physics Department, "Gleb Wataghin" Institute of Physics, University of Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil.
| | - Fernando Alvarez
- Applied Physics Department, "Gleb Wataghin" Institute of Physics, University of Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil.
| | - Ingrid David Barcelos
- Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM), 13083-970, Campinas, SP, Brazil
| | - Luiz Fernando Zagonel
- Applied Physics Department, "Gleb Wataghin" Institute of Physics, University of Campinas - UNICAMP, 13083-859, Campinas, SP, Brazil.
| |
Collapse
|
11
|
Karthick Kannan P, Shankar P, Blackman C, Chung CH. Recent Advances in 2D Inorganic Nanomaterials for SERS Sensing. ADVANCED MATERIALS (DEERFIELD BEACH, FLA.) 2019; 31:e1803432. [PMID: 30773698 DOI: 10.1002/adma.201803432] [Citation(s) in RCA: 94] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2018] [Revised: 01/02/2019] [Indexed: 05/23/2023]
Abstract
Surface-enhanced Raman spectroscopy is a powerful and sensitive analytical tool that has found application in chemical and biomolecule analysis and environmental monitoring. Since its discovery in the early 1970s, a variety of materials ranging from noble metals to nanostructured materials have been employed as surface enhanced Raman scattering (SERS) substrates. In recent years, 2D inorganic materials have found wide use in the development of SERS-based chemical sensors owing to their unique thickness dependent physico-chemical properties with enhanced chemical-based charge-transfer processes. Here, recent advances in the application of various 2D inorganic nanomaterials, including graphene, boron nitride, semiconducting metal oxides, and transition metal chalcogenides, in chemical detection via SERS are presented. The background of the SERS concept, including its basic theory and sensing mechanism, along with the salient features of different nanomaterials used as substrates in SERS, extending from monometallic nanoparticles to nanometal oxides, is comprehensively discussed. The importance of 2D inorganic nanomaterials in SERS enhancement, along with their application toward chemical detection, is explained in detail with suitable examples and illustrations. In conclusion, some guidelines are presented for the development of this promising field in the future.
Collapse
Affiliation(s)
| | - Prabakaran Shankar
- School of Advanced Materials Science and Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
- Institute of Innovative Science and Technology, Tokai University, Hiratsuka, Kanagawa, 259 1292, Japan
| | - Chris Blackman
- Department of Chemistry, University College London, London, WC1H 0AJ, UK
| | - Chan-Hwa Chung
- School of Chemical Engineering, Sungkyunkwan University, Suwon, 16419, Republic of Korea
| |
Collapse
|
12
|
Rhodes D, Chae SH, Ribeiro-Palau R, Hone J. Disorder in van der Waals heterostructures of 2D materials. NATURE MATERIALS 2019; 18:541-549. [PMID: 31114069 DOI: 10.1038/s41563-019-0366-8] [Citation(s) in RCA: 188] [Impact Index Per Article: 37.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/26/2018] [Accepted: 04/09/2019] [Indexed: 05/25/2023]
Abstract
Realizing the full potential of any materials system requires understanding and controlling disorder, which can obscure intrinsic properties and hinder device performance. Here we examine both intrinsic and extrinsic disorder in two-dimensional (2D) materials, in particular graphene and transition metal dichalcogenides (TMDs). Minimizing disorder is crucial for realizing desired properties in 2D materials and improving device performance and repeatability for practical applications. We discuss the progress in disorder control for graphene and TMDs, as well as in van der Waals heterostructures realized by combining these materials with hexagonal boron nitride. Furthermore, we showcase how atomic defects or disorder can also be harnessed to provide useful electronic, optical, chemical and magnetic functions.
Collapse
Affiliation(s)
- Daniel Rhodes
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Sang Hoon Chae
- Department of Mechanical Engineering, Columbia University, New York, NY, USA
| | - Rebeca Ribeiro-Palau
- Centre de Nanosciences et de Nanotechnologies (C2N), CNRS, Université Paris Sud, Université Paris-Saclay, Palaiseau, France
| | - James Hone
- Department of Mechanical Engineering, Columbia University, New York, NY, USA.
| |
Collapse
|
13
|
Yin X, Tang CS, Wu D, Kong W, Li C, Wang Q, Cao L, Yang M, Chang Y, Qi D, Ouyang F, Pennycook SJ, Feng YP, Breese MBH, Wang SJ, Zhang W, Rusydi A, Wee ATS. Unraveling High-Yield Phase-Transition Dynamics in Transition Metal Dichalcogenides on Metallic Substrates. ADVANCED SCIENCE (WEINHEIM, BADEN-WURTTEMBERG, GERMANY) 2019; 6:1802093. [PMID: 30989029 PMCID: PMC6446595 DOI: 10.1002/advs.201802093] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2018] [Indexed: 05/23/2023]
Abstract
2D transition metal dichalcogenides (2D-TMDs) and their unique polymorphic features such as the semiconducting 1H and quasi-metallic 1T' phases exhibit intriguing optical and electronic properties, which can be used in novel electronic and photonic device applications. With the favorable quasi-metallic nature of 1T'-phase 2D-TMDs, the 1H-to-1T' phase engineering processes are an immensely vital discipline exploited for novel device applications. Here, a high-yield 1H-to-1T' phase transition of monolayer-MoS2 on Cu and monolayer-WSe2 on Au via an annealing-based process is reported. A comprehensive experimental and first-principles study is performed to unravel the underlying mechanism and derive the general trends for the high-yield phase transition process of 2D-TMDs on metallic substrates. While each 2D-TMD possesses different intrinsic 1H-1T' energy barriers, the option of metallic substrates with higher chemical reactivity plays a significantly pivotal role in enhancing the 1H-1T' phase transition yield. The yield increase is achieved via the enhancement of the interfacial hybridizations by the means of increased interfacial binding energy, larger charge transfer, shorter interfacial spacing, and weaker bond strength. Fundamentally, this study opens up the field of 2D-TMD/metal-like systems to further scientific investigation and research, thereby creating new possibilities for 2D-TMDs-based device applications.
Collapse
Affiliation(s)
- Xinmao Yin
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
| | - Chi Sin Tang
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
| | - Di Wu
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyShenzhen UniversityShenzhen518060China
- Hunan Key Laboratory of Super‐microstructure and Ultrafast ProcessSchool of Physics and ElectronicsCentral South UniversityNo. 932, South Lushan RoadChangshaHunan Province410083China
| | - Weilong Kong
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
| | - Changjian Li
- Department of Materials Science and EngineeringNational University of Singapore9 Engineering Drive 1Singapore117575Singapore
| | - Qixing Wang
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
| | - Liang Cao
- Anhui Province Key Laboratory of Condensed Matter Physics at Extreme ConditionsHigh Magnetic Field Laboratory of the Chinese Academy of SciencesHefei230031China
| | - Ming Yang
- Institute of Materials Research and EngineeringA∗STAR (Agency for Science, Technology and Research)2 Fusionopolis WaySingapore138634Singapore
| | - Yung‐Huang Chang
- Bachelor Program in Interdisciplinary StudiesNational Yunlin University of Science and TechnologyYunlin640Taiwan
| | - Dianyu Qi
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyShenzhen UniversityShenzhen518060China
| | - Fangping Ouyang
- Hunan Key Laboratory of Super‐microstructure and Ultrafast ProcessSchool of Physics and ElectronicsCentral South UniversityNo. 932, South Lushan RoadChangshaHunan Province410083China
| | - Stephen J. Pennycook
- Department of Materials Science and EngineeringNational University of Singapore9 Engineering Drive 1Singapore117575Singapore
| | - Yuan Ping Feng
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
| | - Mark B. H. Breese
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
| | - Shi Jie Wang
- Institute of Materials Research and EngineeringA∗STAR (Agency for Science, Technology and Research)2 Fusionopolis WaySingapore138634Singapore
| | - Wenjing Zhang
- International Collaborative Laboratory of 2D Materials for Optoelectronics Science and TechnologyShenzhen UniversityShenzhen518060China
| | - Andrivo Rusydi
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
| | - Andrew T. S. Wee
- Department of PhysicsFaculty of ScienceNational University of SingaporeSingapore117542Singapore
- Singapore Synchrotron Light Source (SSLS)National University of SingaporeSingapore117603Singapore
- NUS Graduate School for Integrative Sciences and EngineeringNational University of SingaporeSingapore117456Singapore
| |
Collapse
|
14
|
Sotthewes K, van Bremen R, Dollekamp E, Boulogne T, Nowakowski K, Kas D, Zandvliet HJW, Bampoulis P. Universal Fermi-Level Pinning in Transition-Metal Dichalcogenides. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2019; 123:5411-5420. [PMID: 30873255 PMCID: PMC6410613 DOI: 10.1021/acs.jpcc.8b10971] [Citation(s) in RCA: 43] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/12/2018] [Revised: 02/13/2019] [Indexed: 05/26/2023]
Abstract
Understanding the electron transport through transition-metal dichalcogenide (TMDC)-based semiconductor/metal junctions is vital for the realization of future TMDC-based (opto-)electronic devices. Despite the bonding in TMDCs being largely constrained within the layers, strong Fermi-level pinning (FLP) was observed in TMDC-based devices, reducing the tunability of the Schottky barrier height. We present evidence that metal-induced gap states (MIGS) are the origin for the large FLP similar to conventional semiconductors. A variety of TMDCs (MoSe2, WSe2, WS2, and MoTe2) were investigated using high-spatial-resolution surface characterization techniques, permitting us to distinguish between defected and pristine regions. The Schottky barrier heights on the pristine regions can be explained by MIGS, inducing partial FLP. The FLP strength is further enhanced by disorder-induced gap states induced by transition-metal vacancies or substitutionals at the defected regions. Our findings emphasize the importance of defects on the electron transport properties in TMDC-based devices and confirm the origin of FLP in TMDC-based metal/semiconductor junctions.
Collapse
Affiliation(s)
- Kai Sotthewes
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
- II.
Institute of Physics B and JARA-FIT, RWTH-Aachen
University, 52056 Aachen, Germany
| | - Rik van Bremen
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Edwin Dollekamp
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Tim Boulogne
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Krystian Nowakowski
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Daan Kas
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Harold J. W. Zandvliet
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Pantelis Bampoulis
- Physics
of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| |
Collapse
|
15
|
Yao Q, Zhang L, Bampoulis P, Zandvliet HJW. Nanoscale Investigation of Defects and Oxidation of HfSe 2. THE JOURNAL OF PHYSICAL CHEMISTRY. C, NANOMATERIALS AND INTERFACES 2018; 122:25498-25505. [PMID: 30450151 PMCID: PMC6231157 DOI: 10.1021/acs.jpcc.8b08713] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 10/17/2018] [Indexed: 05/24/2023]
Abstract
HfSe2 is a very good candidate for a transition metal dichalcogenide-based field-effect transistor owing to its moderate band gap of about 1 eV and its high-κ dielectric native oxide. Unfortunately, the experimentally determined charge carrier mobility is about 3 orders of magnitude lower than the theoretically predicted value. This strong deviation calls for a detailed investigation of the physical and electronic properties of HfSe2. Here, we have studied the structure, density, and density of states of several types of defects that are abundant on the HfSe2 surface using scanning tunneling microscopy and spectroscopy. Compared to MoS2 and WSe2, HfSe2 exhibits similar type of defects, albeit with a substantially higher density of 9 × 1011 cm-2. The most abundant defect is a subsurface defect, which shows up as a dim feature in scanning tunneling microscopy images. These dim dark defects have a substantially larger band gap (1.25 eV) than the pristine surface (1 eV), suggesting a substitution of the Hf atom by another atom. The high density of defects on the HfSe2 surface leads to very low Schottky barrier heights. Conductive atomic force microscopy measurements reveal a very small dependence of the Schottky barrier height on the work function of the metals, suggesting a strong Fermi-level pinning. We attribute the observed Fermi-level pinning (pinning factor ∼0.1) to surface distortions and Se/Hf defects. In addition, we have also studied the HfSe2 surface after the exposure to air by scanning tunneling microscopy and conductive atomic force microscopy. Partly oxidized layers with band gaps of 2 eV and Schottky barrier heights of ∼0.6 eV were readily found on the surface. Our experiments reveal that HfSe2 is very air-sensitive, implying that capping or encapsulating of HfSe2, in order to protect it against oxidation, is a necessity for technological applications.
Collapse
Affiliation(s)
- Qirong Yao
- Physics
of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Lijie Zhang
- School
of Physics and Electronics, Hunan University, 410082 Changsha, China
| | - Pantelis Bampoulis
- Physics
of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Harold J. W. Zandvliet
- Physics
of Interfaces and Nanomaterials, MESA Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500AE Enschede, The Netherlands
| |
Collapse
|
16
|
Hoffman AN, Stanford MG, Zhang C, Ivanov IN, Oyedele AD, Sales MG, McDonnell SJ, Koehler MR, Mandrus DG, Liang L, Sumpter BG, Xiao K, Rack PD. Atmospheric and Long-term Aging Effects on the Electrical Properties of Variable Thickness WSe 2 Transistors. ACS APPLIED MATERIALS & INTERFACES 2018; 10:36540-36548. [PMID: 30256093 DOI: 10.1021/acsami.8b12545] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/08/2023]
Abstract
Atmospheric and long-term aging effects on electrical properties of WSe2 transistors with various thicknesses are examined. Although countless published studies report electrical properties of transition-metal dichalcogenide materials, many are not attentive to testing environment or to age of samples, which we have found significantly impacts results. Our as-fabricated exfoliated WSe2 pristine devices are predominantly n-type, which is attributed to selenium vacancies. Transfer characteristics of as-fabricated devices measured in air then vacuum reveal physisorbed atmospheric molecules significantly reduced n-type conduction in air. First-principles calculations suggest this short-term reversible atmospheric effect can be attributed primarily to physisorbed H2O on pristine WSe2, which is easily removed from the pristine surface in vacuum due to the low adsorption energy. Devices aged in air for over 300 h demonstrate irreversibly increased p-type conduction and decreased n-type conduction. Additionally, they develop an extended time constant for recovery of the atmospheric adsorbents effect. Short-term atmospheric aging (up to approximately 900 h) is attributed to O2 and H2O molecules physisorbed to selenium vacancies where electron transfer from the bulk and adsorbed binding energies are higher than the H2O-pristine WSe2. The residual/permanent aging component is attributed to electron trapping molecular O2 and isoelectronic O chemisorption at selenium vacancies, which also passivates the near-conduction band gap state, p-doping the material, with very high binding energy. All effects demonstrated have the expected thickness dependence, namely, thinner devices are more sensitive to atmospheric and long-term aging effects.
Collapse
Affiliation(s)
| | | | | | | | | | - Maria Gabriela Sales
- Department of Materials Science & Engineering , University of Virginia , Charlottesville , Virginia 22904 , United States
| | - Stephen J McDonnell
- Department of Materials Science & Engineering , University of Virginia , Charlottesville , Virginia 22904 , United States
| | | | | | | | | | | | | |
Collapse
|
17
|
Bampoulis P, Sotthewes K, Siekman MH, Zandvliet HJW. Local Conduction in Mo xW 1- xSe 2: The Role of Stacking Faults, Defects, and Alloying. ACS APPLIED MATERIALS & INTERFACES 2018; 10:13218-13225. [PMID: 29578328 PMCID: PMC5909175 DOI: 10.1021/acsami.8b01506] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/26/2018] [Accepted: 03/26/2018] [Indexed: 05/26/2023]
Abstract
Here, we report on the surface conductivity of WSe2 and Mo xW1- xSe2 (0 ≤ x ≤ 1) crystals investigated with conductive atomic force microscopy. We found that stacking faults, defects, and chemical heterogeneities form distinct two-dimensional and one-dimensional conduction paths on the transition metal dichalcogenide surface. In the case of WSe2, in addition to step edges, we find a significant amount of stacking faults (formed during the cleaving process) that strongly influence the surface conductivity. These regions are attributed to the alternation of the 2H and 3R polytypism. The stacking faults form regular 2D patterns by alternation of the underlying stacking order, with a periodicity that varies significantly between different regions and samples. In the case of Mo xW1- xSe2, its conductivity has a localized nature, which depends on the underlying chemical composition and the Mo/W ratio. Segregation to W-rich and Mo-rich regions during the growth process leads to nonuniform conduction paths on the surface of the alloy. We found a gradual change of the conductivity moving from one region to the other, reminiscent of lateral band bending. Our results demonstrate the use of C-AFM as a nanoscopic tool to probe the electrical properties of largely inhomogeneous samples and show the complicated nature of the surface conductivity of TMDC alloys.
Collapse
|
18
|
Lin YC, Jariwala B, Bersch BM, Xu K, Nie Y, Wang B, Eichfeld SM, Zhang X, Choudhury TH, Pan Y, Addou R, Smyth CM, Li J, Zhang K, Haque MA, Fölsch S, Feenstra RM, Wallace RM, Cho K, Fullerton-Shirey SK, Redwing JM, Robinson JA. Realizing Large-Scale, Electronic-Grade Two-Dimensional Semiconductors. ACS NANO 2018; 12:965-975. [PMID: 29360349 DOI: 10.1021/acsnano.7b07059] [Citation(s) in RCA: 79] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Atomically thin transition metal dichalcogenides (TMDs) are of interest for next-generation electronics and optoelectronics. Here, we demonstrate device-ready synthetic tungsten diselenide (WSe2) via metal-organic chemical vapor deposition and provide key insights into the phenomena that control the properties of large-area, epitaxial TMDs. When epitaxy is achieved, the sapphire surface reconstructs, leading to strong 2D/3D (i.e., TMD/substrate) interactions that impact carrier transport. Furthermore, we demonstrate that substrate step edges are a major source of carrier doping and scattering. Even with 2D/3D coupling, transistors utilizing transfer-free epitaxial WSe2/sapphire exhibit ambipolar behavior with excellent on/off ratios (∼107), high current density (1-10 μA·μm-1), and good field-effect transistor mobility (∼30 cm2·V-1·s-1) at room temperature. This work establishes that realization of electronic-grade epitaxial TMDs must consider the impact of the TMD precursors, substrate, and the 2D/3D interface as leading factors in electronic performance.
Collapse
Affiliation(s)
- Yu-Chuan Lin
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Bhakti Jariwala
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Brian M Bersch
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Ke Xu
- Department of Chemical and Petroleum Engineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Yifan Nie
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
| | - Baoming Wang
- Department of Mechanical Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Sarah M Eichfeld
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Xiaotian Zhang
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Tanushree H Choudhury
- Two-Dimensional Crystal Consortium (2DCC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Yi Pan
- Paul-Drude-Institut für Festkörperelektronik , Hausvogteiplatz 5-7, Berlin 10117, Germany
| | - Rafik Addou
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
| | - Christopher M Smyth
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
| | - Jun Li
- Department of Physics, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Kehao Zhang
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - M Aman Haque
- Department of Mechanical Engineering, The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Stefan Fölsch
- Paul-Drude-Institut für Festkörperelektronik , Hausvogteiplatz 5-7, Berlin 10117, Germany
| | - Randall M Feenstra
- Department of Physics, Carnegie Mellon University , Pittsburgh, Pennsylvania 15213, United States
| | - Robert M Wallace
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
| | - Kyeongjae Cho
- Department of Materials Science and Engineering, The University of Texas at Dallas , Richardson, Texas 75080, United States
| | - Susan K Fullerton-Shirey
- Department of Chemical and Petroleum Engineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
- Department of Electrical and Computer Engineering, University of Pittsburgh , Pittsburgh, Pennsylvania 15213, United States
| | - Joan M Redwing
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Two-Dimensional Crystal Consortium (2DCC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| | - Joshua A Robinson
- Department of Materials Science and Engineering, Materials Research Institute, and Center for 2D and Layered Materials (2DLM), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
- Two-Dimensional Crystal Consortium (2DCC), The Pennsylvania State University , University Park, Pennsylvania 16802, United States
| |
Collapse
|
19
|
An B, Liu Y, Xu C, Wang H, Wan J. Novel magnetically separable Fe3O4–WSe2/NG photocatalysts: synthesis and photocatalytic performance under visible-light irradiation. NEW J CHEM 2018. [DOI: 10.1039/c8nj00406d] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Visible light responsive Fe3O4–WSe2/NG (nitrogen doped graphene oxide) heterojunction nanocomposites were synthesized by a hydrothermal synthesis route, in which Fe3O4 and WSe2 particles were coated on the surface of NG.
Collapse
Affiliation(s)
- Baihong An
- College of Environment and Safety Engineering
- Key Laboratory of Eco-chemical Engineering
- Ministry of Education
- Qingdao University of Science and Technology
- Qingdao 266042
| | - Yanan Liu
- College of Environment and Safety Engineering
- Key Laboratory of Eco-chemical Engineering
- Ministry of Education
- Qingdao University of Science and Technology
- Qingdao 266042
| | - Chengcheng Xu
- College of Environment and Safety Engineering
- Key Laboratory of Eco-chemical Engineering
- Ministry of Education
- Qingdao University of Science and Technology
- Qingdao 266042
| | - Han Wang
- Center of Chemical Examination of Qingdao Customs District of PRC
- Qingdao
- China
| | - Jun Wan
- College of Environment and Safety Engineering
- Key Laboratory of Eco-chemical Engineering
- Ministry of Education
- Qingdao University of Science and Technology
- Qingdao 266042
| |
Collapse
|
20
|
Zhu H, Wang Q, Cheng L, Addou R, Kim J, Kim MJ, Wallace RM. Defects and Surface Structural Stability of MoTe 2 Under Vacuum Annealing. ACS NANO 2017; 11:11005-11014. [PMID: 29116754 DOI: 10.1021/acsnano.7b04984] [Citation(s) in RCA: 57] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
Understanding the structural stability of transition-metal dichalcogenides is necessary to avoid surface/interface degradation. In this work, the structural stability of 2H-MoTe2 with thermal treatments up to 500 °C is studied using scanning tunneling microscopy and scanning transmission electron microscopy. On the exfoliated sample surface at room temperature, atomic subsurface donors originating from excess Te atoms are observed and presented as nanometer-sized, electronically-induced protrusions superimposed with the hexagonal lattice structure of MoTe2. Under a thermal treatment as low as 200 °C, the surface decomposition-induced cluster defects and Te vacancies are readily detected and increase in extent with the increasing temperature. Driven by Te vacancies and thermal energy, intense 60° inversion domain boundaries form resulting in a "wagon wheel" morphology after 400 °C annealing for 15 min. Scanning tunneling spectroscopy identified the electronic states at the domain boundaries and the domain centers. To prevent extensive Te loss at higher temperatures, where Mo6Te6 nanowire formation and substantial desorption-induced etching effects will take place simultaneously, surface and edge passivation with a monolayer graphene coverage on MoTe2 is tested. With this passivation strategy, the structural stability of MoTe2 is greatly enhanced up to 500 °C without apparent structural defects.
Collapse
Affiliation(s)
- Hui Zhu
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Qingxiao Wang
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Lanxia Cheng
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Rafik Addou
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Jiyoung Kim
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Moon J Kim
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| | - Robert M Wallace
- Department of Materials Science and Engineering, The University of Texas at Dallas , 800 West Campbell Road, Richardson, Texas 75080, United States
| |
Collapse
|
21
|
Bampoulis P, van Bremen R, Yao Q, Poelsema B, Zandvliet HJW, Sotthewes K. Defect Dominated Charge Transport and Fermi Level Pinning in MoS 2/Metal Contacts. ACS APPLIED MATERIALS & INTERFACES 2017; 9:19278-19286. [PMID: 28508628 PMCID: PMC5465510 DOI: 10.1021/acsami.7b02739] [Citation(s) in RCA: 88] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/24/2017] [Accepted: 05/16/2017] [Indexed: 05/19/2023]
Abstract
Understanding the electronic contact between molybdenum disulfide (MoS2) and metal electrodes is vital for the realization of future MoS2-based electronic devices. Natural MoS2 has the drawback of a high density of both metal and sulfur defects and impurities. We present evidence that subsurface metal-like defects with a density of ∼1011 cm-2 induce negative ionization of the outermost S atom complex. We investigate with high-spatial-resolution surface characterization techniques the effect of these defects on the local conductance of MoS2. Using metal nanocontacts (contact area < 6 nm2), we find that subsurface metal-like defects (and not S-vacancies) drastically decrease the metal/MoS2 Schottky barrier height as compared to that in the pristine regions. The magnitude of this decrease depends on the contact metal. The decrease of the Schottky barrier height is attributed to strong Fermi level pinning at the defects. Indeed, this is demonstrated in the measured pinning factor, which is equal to ∼0.1 at defect locations and ∼0.3 at pristine regions. Our findings are in good agreement with the theoretically predicted values. These defects provide low-resistance conduction paths in MoS2-based nanodevices and will play a prominent role as the device junction contact area decreases in size.
Collapse
Affiliation(s)
- Pantelis Bampoulis
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
- E-mail: (P.B.)
| | - Rik van Bremen
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Qirong Yao
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Bene Poelsema
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Harold J. W. Zandvliet
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
| | - Kai Sotthewes
- Physics
of Interfaces and Nanomaterials and Physics of Fluids and J.M. Burgers Centre
for Fluid Mechanics, MESA+ Institute for
Nanotechnology, University of Twente,
P.O. Box 217, 7500AE Enschede, The Netherlands
- E-mail: (K.S.)
| |
Collapse
|