Conformal Growth of Stable 1T-Phase WS2 by Alkali Metal-Halide-Assisted Chemical Vapor Deposition.

The potential exploitation of two-dimensional transition metal dichalcogenides (TMDs) like WS2 in nanotechnology applications still require the development of efficient synthesis protocols for their large-scale growth as well as their polymorphic phase selection. Indeed, in the former framework, the growth protocols developed for chemical vapor deposition (CVD) typically use seeding promoters and/or salts (e.g., alkali metal halides) to enhance the adhesion to the substrate and lower the temperature for metal oxide precursor (e.g., WO3) dissociation. In the latter framework, the wealth of electronic properties of WS2 make it semiconducting or metallic depending on the crystallographic phase. In this work, we use potassium chloride-assisted CVD to produce the metastable 1T phase of WS2 without the need of additional seeding promoter even on patterned substrates demonstrating conformal and stable (over months and up to 200 °C) deposition. Furthermore, thermal Raman spectroscopy measurements were carried out determining the temperature coefficients, even for the specific 1T-phase sensitive Raman mode. Our findings demonstrate that the chemistry of salt-assisted CVD growth process can be exploited for TMDs phase filtration without constraints on the large-scale and conformal growth.