• Title, Summary, Keyword: Transition Metal Dichalcogenide

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Phase Transformation of Two-Dimensional Transition Metal Dichalcogenides

  • Kim, Jaemin;Lee, Zonghoon
    • Applied Microscopy
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    • v.48 no.2
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    • pp.43-48
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    • 2018
  • Transition metal dichalcogenide (TMD) materials have distinctive structures in comparison with other two-dimensional materials. TMD materials' structure is held together by van der Waals and covalent intralayer interactions; consequently, TMDs exhibit multiple phases and properties depending on their structure. This article reviews some of the research currently being undertaken to control TMD phases to utilize their different properties. This review introduces some trials for changing the phase of TMDs.

Transition Metal Dichalcogenide Nanocatalyst for Solar-Driven Photoelectrochemical Water Splitting (전이금속 디칼코제나이드 나노촉매를 이용한 태양광 흡수 광화학적 물분해 연구)

  • Yoo, Jisun;Cha, Eunhee;Park, Jeunghee;Lim, Soo A
    • Journal of the Korean Electrochemical Society
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    • v.23 no.2
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    • pp.25-38
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    • 2020
  • Photoelectrochemical water splitting has been considered as the most promising technology for generating hydrogen energy. Transition metal dichalcogenide (TMD) compounds have currently attracted tremendous attention due to their outstanding ability towards the catalytic water-splitting hydrogen evolution reaction (HER). Herein, we report the synthesis method of various transition metal dichalcogenide including MoS2, MoSe2, WS2, and WSe2 nanosheets as excellent catalysts for solar-driven photoelectrochemical (PEC) hydrogen evolution. Photocathodes were fabricated by growing the nanosheets directly onto Si nanowire (NW) arrays, with a thickness of 20 nm. The metal ion layers were formed by soaking the metal chloride ethanol solution and subsequent sulfurization or selenization produced the transition metal chalcogenide. They all exhibit excellent PEC performance in 0.5 M H2SO4; the photocurrent reaches to 20 mA cm-2 (at 0 V vs. RHE) and the onset potential is 0.2 V under AM1.5 condition. The quantum efficiency of hydrogen generation is avg. 90%. The stability of MoS2 and MoSe2 is 90% for 3h, which is higher than that (80%) of WS2 and WSe2. Detailed structure analysis using X-ray photoelectron spectroscopy for before/after HER reveals that the Si-WS2 and Si-WSe2 experience more oxidation of Si NWs than Si-MoS2 and Si-MoSe2. This can be explained by the less protection of Si NW surface by their flake shape morphology. The high catalytic activity of TMDs should be the main cause of this enhanced PEC performance, promising efficient water-splitting Si-based PEC cells.

Semi-analytical Modeling of Transition Metal Dichalcogenide (TMD)-based Tunneling Field-effect Transistors (TFETs)

  • Huh, In
    • Proceeding of EDISON Challenge
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    • pp.368-372
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    • 2016
  • In this paper, the physics-based analytical model of transition metal dichalcogenide (TMD)-based double-gate (DG) tunneling field-effect transistors (TFETs) is proposed. The proposed model is derived by using the two-dimensional (2-D) Landauer formula and the Wentzel-Kramers-Brillouin (WKB) approximation. For improving the accuracy, nonlinear and continuous lateral energy band profile is applied to the model. 2-D density of states (DOS) and two-band effective Hamiltonian for TMD materials are also used in order to consider the 2-D nature of TMD-based TFETs. The model is validated by using the tight-binding non-equilibrium Green's function (NEGF)-based quantum transport simulation in the case of monolayer molybdenum disulfide ($MoS_2$)-based TFETs.

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2D transition-metal dichalcogenide (WSe2) doping methods for hydrochloric acid

  • Nam, Hyo-Jik;Park, Jin-Hong
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.291.2-291.2
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    • 2016
  • 3D semiconductor material of silicon that is used throughout the semiconductor industry currently faces a physical limitation of the development of semiconductor process technology. The research into the next generation of nano-semiconductor materials such as semiconductor properties superior to replace silicon in order to overcome the physical limitations, such as the 2-dimensional graphene material in 2D transition-metal dichalcogenide (TMD) has been researched. In particular, 2D TMD doping without severely damage of crystal structure is required different conventional methods such as ion implantation in 3D semiconductor device. Here, we study a p-type doping technique on tungsten diselenide (WSe2) for p-channel 2D transistors by adjusting the concentration of hydrochloric acid through Raman spectroscopy and electrical/optical measurements. Where the performance parameters of WSe2 - based electronic device can be properly designed or optimized. (on currents increasing and threshold voltage positive shift.) We expect that our p-doping method will make it possible to successfully integrate future layered semiconductor devices.

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Comparison of Device Characteristics Between Transition-Metal Dichalcogenide and 2-D Silicon Single-Layer Field-Effect Transistors (전이 금속 이칼코겐화합물 전계효과 트랜지스터와 2차원 단층 실리콘 전계효과 트랜지스터의 소자 특성 비교 연구)

  • Yoo, Tae Kyun;Hwang, Shin Ae;Jang, Moon Gyu
    • New Physics: Sae Mulli
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    • v.67 no.10
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    • pp.1200-1204
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    • 2017
  • We performed simulations to analyze the characteristics of a transition-metal dichalcogenide field-effect transistor (TMD FET) and an ultra-thin-body field-effect transistor (UTB FET) using a $MoS_2$ mono layer and a silicon mono layer as channel materials. The gate voltage, the characteristics of the drain current, and the subthreshold swing were analyzed by varying the channel thickness and the oxide thickness, and the channel thickness and the oxide thickness became smaller with decreasing short-channel effect. Based on the simulation result that the thicknesses of the channel and the oxide layers should be about 1 nm, we compared the optimal characteristics of the transistor using a thin channel with each other for the TMD FET and the UTB FET. The subthreshold swing value of the TMD FET is better than that of the UTB FET.

Transparent Photovoltaic Device using Two-dimensional Transition-metal Dichalcogenides (이차원 반도체 소재를 이용한 투명 태양전지 특성에 관한 연구)

  • Jwa, Tae-Hun;Hyun, Chul-Min;Kim, Min-Sik;Lee, Hyeok-ju;Ahn, Ji-Hoon
    • Journal of the Korean institute of surface engineering
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    • v.49 no.2
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    • pp.186-190
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    • 2016
  • In this study, we fabricated the transparent photovoltaic device using 2-dimensional transition-metal dichalcogenides and investigated the transparency and photovoltaic characteristics. P-n heterojunction was formed by mechanical exfoliation and aligned transfer method on the transparent sheet using n-type $MoS_2$ and p-type $WSe_2$. Our transparent photovoltaic device exhibited the open-circuit voltage of ~ 0.15 V and the short-circuit current of 0.48 nA under illumination of white light.

Investigation on 2D Transition Metal Chalcogenide Using Angular-Resolved Photoelectron Spectroscopy (각도분해 광전자 분광법을 이용한 2차원 전이금속 칼코겐 화합물의 전자구조 연구)

  • Park, Soohyung
    • Ceramist
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    • v.22 no.4
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    • pp.350-356
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    • 2019
  • Recently, transition metal dichalcogenide (TMDC) monolayers have been the subject of research exploring the physical phenomenon generated by low dimensionality and high symmetry. One of the keys to understanding new physical observations is the electronic band structure of 2D TMDCs. Angle-resolved photoelectron spectroscopy (ARPES) is, to this point, the best technique for obtaining information on the electronic structure of 2D TMDCs. However, through ARPES research, obtaining the long-range well-ordered single crystal samples always proves a challenging and obstacle presenting issue, which has been limiting towards measuring the electronic band structures of samples. This is particularly true in general 2D TMDCs cases. Here, we introduce the approach, with a mathematical framework, to overcome such ARPES limitations by employing the high level of symmetry of 2D TMDCs. Their high symmetry enables measurement of the clear and sharp electronic band dispersion, which is dominated by the band dispersion of single-crystal TMDCs along the two high symmetry directions Γ-K and Γ-M. In addition, we present two important studies and observations for the direct measuring of the exciton binding energy and charge transfer of 2D TMDCs, both being established by the above novel approach.

Synthesis and Characterization of Large-Area and Highly Crystalline Molybdenum Disulphide Atomic Layer by Chemical Vapor Deposition

  • Park, Seung-Ho;Kim, Yooseok;Kim, Ji Sun;Lee, Su-Il;Cha, Myoung-Jun;Park, Chong-Yun
    • Proceedings of the Korean Vacuum Society Conference
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    • pp.287.1-287.1
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    • 2013
  • The Isolation of few-layered transition metal dichalcogenides has mainly been performed by mechanical and chemical exfoliation with very low yields. in particular, the two-dimensional layer of molybdenum disulfide (MoS2) has recently attracted much interest due to its direct-gap property and potential application in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS2 atomic thin layers is still rare. In this account, a controlled thermal reductionsulfurization method is used to synthesize large-MoOx thin films are first deposited on Si/SiO2 substrates, which are then sulfurized (under vacuum) at high temperatures. Samples with different thicknesses have been analyzed by Raman spectroscopy and TEM, and their photoluminescence properties have been evaluated. We demonstrated the presence of single-, bi-, and few-layered MoS2 on as-grown samples. It is well known that the electronic structure of these materials is very sensitive to the number of layer, ranging from indirect band gap semiconductor in the bulk phase to direct band gap semiconductor in monolayers. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.

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Research Trends of Two Dimensional Transition Metal Dichalcogenide Semiconductor Materials and Devices (이차원 전이금속 칼코겐화합물 반도체 소재 및 소자 기술개발 동향)

  • Yun, S.J.;Lim, J.W.;Cho, D.H.;Chung, Y.D.
    • Electronics and Telecommunications Trends
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    • v.29 no.6
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    • pp.43-52
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    • 2014
  • 수 원자층 두께의 전이금속 칼코겐화물 이차원 반도체 소재는 스위칭 소자 등에 활용하기에 적합한 밴드갭 에너지를 가지며, 높은 이동도와 우수한 광반응성으로 인해 최근 큰 관심을 끌고 있다. 특히 이차원 소재이므로 dangling bond가 없다는 점, 구조적 안정성, 실리콘에 뒤지지 않는 고이동도, 직접천이 특성 등으로 인해 차세대 전자소자용, 더 나아가 실리콘 반도체 대체 소재로써의 가능성도 점쳐지고 있다. 본고에서는 전이금속 칼코겐화물 이차원 반도체의 소재 특성과 제조방법, 소자 응용면에서의 기술개발 동향, 시장전망 등에 대해 소개하고, 이 소재가 현재 기대하는 만큼 중요하게 활용되고 기술이 발전하기 위해서 반드시 해결해야 할 숙제 등에 대해 논의하고자 한다.

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