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.