title: Thermal Oxidation of WSe2 Nanosheets Adhered on SiO2/Si Substrates.
abstract: Because of the drastically different intralayer versus interlayer bonding strengths, the mechanical, thermal, and electrical properties of two-dimensional (2D) materials are highly anisotropic between the in-plane and out-of-plane directions. The structural anisotropy may also play a role in chemical reactions, such as oxidation, reduction, and etching. Here, the composition, structure, and electrical properties of mechanically exfoliated WSe2 nanosheets on SiO2/Si substrates were studied as a function of the extent of thermal oxidation. A major component of the oxidation, as indicated from optical and Raman data, starts from the nanosheet edges and propagates laterally toward the center. Partial oxidation also occurs in certain areas at the surface of the flakes, which are shown to be highly conductive by microwave impedance microscopy. Using secondary ion mass spectroscopy, we also observed extensive oxidation at the WSe2-SiO2 interface. The combination of multiple microcopy methods can thus provide vital information on the spatial evolution of chemical reactions on 2D materials and the nanoscale electrical properties of the reaction products.
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Yingnan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: ‡Microelectronics Research Center, University of Texas at Austin, Austin, Texas 78758, United States.|§Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Cheng
authors.initials: C
authors.lastname: Tan
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Harry
authors.initials: H
authors.lastname: Chou
authors.affiliation: ‡Microelectronics Research Center, University of Texas at Austin, Austin, Texas 78758, United States.
authors.forename: Avinash
authors.initials: A
authors.lastname: Nayak
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Di
authors.initials: D
authors.lastname: Wu
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Rudresh
authors.initials: R
authors.lastname: Ghosh
authors.affiliation: ‡Microelectronics Research Center, University of Texas at Austin, Austin, Texas 78758, United States.
authors.forename: Hsiao-Yu
authors.initials: HY
authors.lastname: Chang
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Yufeng
authors.initials: Y
authors.lastname: Hao
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Xiaohan
authors.initials: X
authors.lastname: Wang
authors.affiliation: ‡Microelectronics Research Center, University of Texas at Austin, Austin, Texas 78758, United States.
authors.forename: Joon-Seok
authors.initials: JS
authors.lastname: Kim
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Richard
authors.initials: R
authors.lastname: Piner
authors.affiliation: §Department of Mechanical Engineering and the Materials Science and Engineering Program, University of Texas at Austin, Austin, Texas 78712, United States.|∥Center for Multidimensional Carbon Materials, Institute for Basic Science (IBS), Ulsan 689-798, Republic of Korea.|⊥Department of Chemistry, Ulsan National Institute of Science and Technology (UNIST), Ulsan 689-798, Republic of Korea.
authors.forename: Rodney S
authors.initials: RS
authors.lastname: Ruoff
authors.affiliation: ‡Microelectronics Research Center, University of Texas at Austin, Austin, Texas 78758, United States.
authors.forename: Deji
authors.initials: D
authors.lastname: Akinwande
authors.affiliation: †Department of Physics, University of Texas at Austin, Austin, Texas 78712, United States.
authors.forename: Keji
authors.initials: K
authors.lastname: Lai
keywords: 2D materials; Tungsten diselenide; microwave impedance microscopy; secondary ion mass spectroscopy; thermal oxidation