Raman spectroscopic investigations of the selenization of MoO3 in the chemical vapor deposition process to form two-dimensional MoSe2

Abstract

The transformation of the precursor MoO3 into two-dimensional MoSe2 in the synthesis using Chemical Vapor Deposition method is monitored using micro-Raman spectroscopy. Broadly, domains with three different morphologies: square, triangular, and hexagonal with variable thickness were obtained in the deposition process. The Raman spectroscopy results reported here demonstrate that MoO3 is selenized to form MoO2, then MoOSe2, and finally to MoSe2 and that the three different morphologies represent different compounds, with the square flakes corresponding to oxide phases, MoO2 and Mo4O11, the hexagonal to oxy- selenide compound MoOSe2, while the triangular domains are purely mono- and few- layers MoSe2 with no detectable traces of oxygen. Further, photoluminescence spectroscopy shows a sharp light emission around 800 nm from only the triangular domains. This work provides insights into the stepwise selenization mechanism of formation of MoSe2.