报告人：Kazuhito Tsukagoshi 研究员 （National Institute forMaterials Science, Japan）

报告题目：Self-assembled hetero-structure based on two-dimensionaltransition metal dichalcogenides

报告时间：2017年11月30日（星期四）上午09:30

报告地点：独墅湖校区909号楼一楼B会议室

摘要

Growth of auniform oxide film with a tunable thickness on two-dimensionaltransition metal dichalcogenides is of great importance for electronic and optoelectronicapplications in next generation atomically-controlled hetero semiconductingstructure. Here we demonstrate homogeneous surface oxidation of atomically thinWSe₂ with a self-limiting thickness from single- to trilayers.Exposure to ozone (O₃) below 100 °C leads to the lateral growth oftungsten oxide selectively along selenium zigzag-edge orientations on WSe₂.With further O₃ exposure, the oxide regions coalesce and oxidationterminates leaving a uniform thickness oxide film on top ofunoxidized WSe₂. At higher temperatures, oxidation evolves in thelayer-by-layer regime up to trilayers. The oxide films formed onWSe₂ are nearly atomically flat. Usingphotoluminescence and Raman spectroscopy, we find that theunderlying single-layer WSe₂ is decoupled from the top oxide buthole-doped. The hole-doping by the under-stoichiometric tungsten oxides (WO_x with x < 3) grown on WSe₂ can be used as both controlled chargetransfer dopants and low-barrier contacts for p-type WSe₂ transistors. WO_x-covered WSe₂ is highly hole-doped due tosurface electron transfer from the underlying WSe₂ to the highelectron affinity WO_x. The dopant concentration can be reduced bysuppressing the electron affinity of WO_x by air exposure, butexposure to O₃ at room temperature leads to the recovery of theelectron affinity. Hence, surface transfer doping with WO_x isvirtually controllable. Transistors based on WSe₂ covered with WO_x show only p-type conductions with orders of magnitude better on-current, on-offcurrent ratio, and carrier mobility than without WO_x, suggestingthat the surface WO_x serves as a p-type contact with a low holeSchottky barrier. Our findings point to a simple and effective strategy forcreating p-type devices based on two-dimensional transition metal dichalcogenideswith controlled dopant concentrations.

References

1.Self-limiting surface oxidation of atomically thin WSe₂, M.Yamamoto,S.Dutta, K. Wakabayashi, M. S. Fuhrer, K.Ueno, K.Tsukagoshi, Nano Letters 15, 2067�2073 (2015).

2. Surface Oxides on Single- and Few-layer WSe₂ as Controlled Dopants and Low-Barrier Contacts, M.Yamamoto,S.Nakaharai, K.Ueno, K.Tsukagoshi, Nano Letters, 16,2720�2727 (2016).

个人简介

Dr. KazuhitoTsukagoshi, Principal Investigator of National Institute for Materials Science(NIMS). He studied experimental research on transport physics in semiconductormicrostructure, completing his PhD in 1995. After that he worked as a visitingassociate in Cavendish laboratory (University of Cambridge, U.K.) and then inHitachi Cambridge Laboratory (Hitachi Europe Ltd, U.K.). In 1999, he joined RIKEN (Japan) where he carriedout research on carbon nanotube and organic electronics. He continued thisresearch in AIST in 2008, and moved to WPI-MANA, NIMS in 2009. His currentresearch focuses on ultra-thin functional devices to realize the nextgeneration electronics. He was awarded The MEXT Young Scientists' Prize (2006)and JSPS prize (2013).

联系人：王穗东 教授

责任编辑：杨娟