Lateral growth of WSe2 monolayer film in a confined reaction environment via an Au vapor-assisted CVD: A systematic and comparative study with a NaCl-assisted CVD

Abstract

Two-dimensional (2D) monolayer tungsten diselenide (WSe₂) is of great interest in optoelectronic and photo(electro)catalytic applications due to its direct optical band gap characteristic which is highly dependent on the number of layers. Achieving uniform, high-purity, large-area monolayer WSe₂ with the traditional salt-assisted chemical vapor deposition method (CVD) remains challenging due to the issues controlling the growth mechanisms and number of layers. Recent studies have demonstrated that metal vapor-assisted CVD can achieve uniform development of large-scale WSe₂ monolayers. It is critical to comprehensively examine the influence of metal vapor-assisted CVD parameters on lateral WSe₂ growth relative to salt-assisted CVD and to analyze the underlying mechanisms. Here, we carried out a systematic and comparable study assessing the effect of several CVD parameters on lateral WSe₂ monolayer growth in the presence of a NaCl and an Au vapor catalyst, respectively. Detailed characterization of the grown WSe₂ materials confirmed that using only a gold vapor catalyst in a confined micro-reactor space of sapphires allows for the ultrafast growth of highly crystalline, uniform, and sub-centimeter-sized monolayer WSe₂ films without any residual ions, which can be scalable for reliable high-performance device fabrication and photocatalytic applications. Moreover, we observed that in-situ etching could occur on the film by the increased reaction time. Overall, this study paves the way for future research on fabricating large-area monolayer transition metal dichalcogenides and reaction mechanisms using gold or other metal vapor-assisted CVD in a confined reaction environment.