Published in 2D Materials 5, 025017 (2018).

One Dimensional Metallic Edges in Atomically Thin WSe2 Induced by Air Exposure

Rafik Addou1, Christopher M. Smyth1, Ji-Young Noh1, Yu-Chuan Lin2, Yi Pan3, Sarah M. Eichfeld2, Stefan Fölsch3, Randall M. Feenstra4, Joshua A. Robinson2, Kyeongjae Cho1, and Robert M. Wallace1
1 Department of Materials Science and Engineering, University of Texas, Dallas, Richardson, TX 75080, USA
2Department of Materials Science and Engineering and Center for 2-Dimensional and Layered Materials, The Pennsylvania State University, University Park, PA 16802, USA
3Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin, Germany
4Department of Physics, Carnegie Mellon University, Pittsburgh, PA 15213, USA

Abstract

Transition metal dichalcogenides are a unique class of layered two-dimensional (2D) crystals with extensive promising applications. Tuning the electronic properties of low-dimensional materials is vital for engineering new functionalities. Surface oxidation is of particular interest because it is a relatively simple method of functionalization. By means of scanning probe microscopy and X-ray photoelectron spectroscopy, we report the observation of metallic edges in atomically thin WSe2 monolayers grown by chemical vapor deposition on epitaxial graphene. Scanning tunneling microscopy shows structural details of WSe2 edges and scanning tunneling spectroscopy reveals the metallic nature of the oxidized edges. Photoemission demonstrates that the formation of metallic sub-stoichiometric tungsten oxide (WO2.7) is responsible for the high conductivity measured along the edges. Ab initio calculations validate the susceptibility of WSe2 nanoribbon edges to oxidation. The zigzag terminated edge exhibits metallic behavior prior the air-exposure and remains metallic after oxidation. Comprehending and exploiting this property opens a new opportunity for application in advanced electronic devices.

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