Shaping tungsten dichalcogenides properties by chemical vapor deposition of alloys and polytypes

Two-dimensional (2D) transition metal dichalcogenides (TMDs) present varied optical and electronic properties, each associated to a different crystal structure. We optimize the chemical vapor deposition (CVD) of tungsten-based TMDs, such as hexagonal (1H) WSe₂ and WS₂ monolayers, as well as monoclinic (1T’) WTe₂. While 1H WSe₂ and WS₂ are typically direct band-gap semiconductors in the monolayer form [1], the anisotropic 1T' WTe₂ is a small band gap topological insulator. Our purpose is to study the structural and electronic phase transition of the ternary alloy WSe_2xTe22_(1-x) between the 1H and 1T' crystal structures. We further optimize our CVD growth methods to maximize the yield of bilayer (2ML) hexagonal WSe₂ and WS₂, for which the available polytype combinations and the relative physical properties are even richer [2]. In addition

to Raman and photoluminescence spectroscopies, we employ various other experimental techniques, including second harmonic generation and selective area electron diffraction, to discern between the 2ML polytypes.

[1] Mahmoudi A. et al., Phys. Rev. B 108, 045417 (2023).

[2] Di Berardino G. et al., Phys. Rev. B 111, 125403 (2025).