Heterogeneous Defect Domains in Single-Crystalline Hexagonal WS2

Abstract

Although intricate defects are inevitably generated during the synthesis of transition metal dichalcogenides (TMdCs) by chemical vapor deposition (CVD), the related discussions are mostly limited to chalcogen vacancies.[1–3] Here, we report the prevailing role of metal vacancies determining macroscopic material properties using a single-crystalline monolayer 2H-WS2 grown by CVD. The hexagonal shape of the WS2 flake is segmented into alternating triangular domains without forming explicit defective grain boundaries: sulfur-vacancy (SV)-rich and tungsten-vacancy (WV)-rich domains. The WV-rich domain with deep-trap states[4–6] revealed an electron-dedoping effect, and its electron mobility and photoluminescence were lower by one order of magnitude than those of the SV-rich domain with shallow-donor states.[7] The vacancy-induced strain and doping effects in such domains were investigated by analyzing spectral changes via Raman spectroscopy and the core-level shift via scanning photoelectron microscopy. Our work sheds light on tailoring macroscopic physical properties of 2D materials via native defect engineering. 2D layered materials such as monolayer graphene and TMdCs can be obtained on a wafer scale by CVD,[8] which could be a direct route for realizing various heterostructures for practical applications.[9] The electrical and optical properties of TMdCs are generally determined by crystal imperfections such as grain boundaries (GBs),[10–12] vacancies,[1,13] and impurities.[14,15] Intrinsic defects are likely more abundant in CVD-grown samples than mechanically exfoliated (ME) ones. In polycrystalline CVD-grown films, GBs are inevitably generated via the coalescence of individual grains and have been well characterized because of their critical influence on electrical transport.[10,11] Vacancies are unavoidably formed inside grains and can also be a key factor in determining the carrier. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim