Two-Dimensional Transition Metal Dichalcogenides: Controlled Synthesis and Optical Characterization

Chemical vapor deposition (CVD) is a bottom-up approach suitable for the synthesis of MoS$_{2}$ and WS$_{2}$ monolayers. In order to extend the application of CVD, we modified the precursors used during the deposition. We show that by using mixed transition metal precursors of MoS$_{2}$/WO$_{3}$ powders, alloyed monolayers of Mo$_{x}$W$_{1-x}$S$_{2}$ islands can be synthesized exhibiting a compositional gradient and a tunable optical band gap, as confirmed by Raman and photoluminescence measurements. We further show that adding tellurium powders into the transition metal precursors can lead to a 200 $^{o}$C reduction in the synthesis temperature for MoS$_{2}$ and WS$_{2}$ monolayers. The materials synthesized at a reduced temperature maintain a high degree of crystallinity and optical properties.