title: Controlled growth of high-quality monolayer WS2 layers on sapphire and imaging its grain boundary.
abstract: Atomically thin tungsten disulfide (WS2), a structural analogue to MoS2, has attracted great interest due to its indirect-to-direct band-gap tunability, giant spin splitting, and valley-related physics. However, the batch production of layered WS2 is underdeveloped (as compared with that of MoS2) for exploring these fundamental issues and developing its applications. Here, using a low-pressure chemical vapor deposition method, we demonstrate that high-crystalline mono- and few-layer WS2 flakes and even complete layers can be synthesized on sapphire with the domain size exceeding 50 × 50 μm(2). Intriguingly, we show that, with adding minor H2 carrier gas, the shape of monolayer WS2 flakes can be tailored from jagged to straight edge triangles and still single crystalline. Meanwhile, some intersecting triangle shape flakes are concomitantly evolved from more than one nucleus to show a polycrystalline nature. It is interesting to see that, only through a mild sample oxidation process, the grain boundaries are easily recognizable by scanning electron microscopy due to its altered contrasts. Hereby, controlling the initial nucleation state is crucial for synthesizing large-scale single-crystalline flakes. We believe that this work would benefit the controlled growth of high-quality transition metal dichalcogenide, as well as in their future applications in nanoelectronics, optoelectronics, and solar energy conversions.
authors.affiliation: Department of Materials Science and Engineering, College of Engineering, Peking University , Beijing 100871, People's Republic of China.
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhang
authors.forename: Yanfeng
authors.initials: Y
authors.lastname: Zhang
authors.forename: Qingqing
authors.initials: Q
authors.lastname: Ji
authors.forename: Jing
authors.initials: J
authors.lastname: Ju
authors.forename: Hongtao
authors.initials: H
authors.lastname: Yuan
authors.forename: Jianping
authors.initials: J
authors.lastname: Shi
authors.forename: Teng
authors.initials: T
authors.lastname: Gao
authors.forename: Donglin
authors.initials: D
authors.lastname: Ma
authors.forename: Mengxi
authors.initials: M
authors.lastname: Liu
authors.forename: Yubin
authors.initials: Y
authors.lastname: Chen
authors.forename: Xiuju
authors.initials: X
authors.lastname: Song
authors.forename: Harold Y
authors.initials: HY
authors.lastname: Hwang
authors.forename: Yi
authors.initials: Y
authors.lastname: Cui
authors.forename: Zhongfan
authors.initials: Z
authors.lastname: Liu