Raman Spectroscopy of Few-Layers TaS₂ and Mo-Doped TaS₂ with Enhanced Superconductivity

The use of simple, fast, and economic experimental tools to characterize low-dimensional materials is an important step in the process of democratizing their use. Raman spectroscopy has arisen as a way of indirectly determining the thickness of nanolayers of transition metal dichalcogenides (TMDs), avoiding the use of more expensive tools such as atomic force microscopy, and it is therefore a widely used technique in the study of semiconducting TMDs. However, the study of many metallic TMDs in the limit of few atomic layers is still behind when compared to their semiconducting counterparts, partly due to the lack of similar alternative characterization studies. In this work the characterization of the Raman spectrum, specifically of the E (Formula presented.) - and A_1g-modes, of mechanically exfoliated Ta_1−xMo_xS₂, a metallic TMD which exhibits charge density wave (CDW) formation and superconductivity, is presented. The clear identification of contributions coming from the SiO₂/Si substrate allowed the isolation of the individual E (Formula presented.) - and A_1g-modes of the samples and, for the first time, the observation of a clear evolution of their Raman shifts as a function of sample thickness. This provides a way of indirectly determining sample thickness in the limit of few atomic layers in Ta_1−xMo_xS₂.