In-situ Raman analysis of hydrogenation in well-defined ultrathin molybdenum diselenide deposits synthesized through vapor phase deposition

We report on the synthesis, characterization and in-situ Raman spectroscopy analysis of hydrogenation in ultrathin crystalline MoSe(2) deposits. We use a controllable vapor phase synthesis method using MoSe(2) powder as the only precursor, to fabricate nano- to micro-size few layer thick MoSe(2) deposits with tunable number densities on SiO(2)/Si substrates. We employ this controllable synthesis method to correlate characteristic Raman spectroscopy response of MoSe(2) at ca. 242 cm(−1) (A(1g)) and ca. 280 cm(−1) (E(2g)(1)) with the thickness of the deposits acquired from atomic force microscopy (AFM). We also use this array of well-defined atomically thin MoSe(2) deposits to study possible hydrogenation effects on select architectures using in-situ Raman spectroscopy. Interestingly, our analysis indicates that ultrathin MoSe(2) deposits with exposed edges show a blue shift of 1–2 cm(−1) when exposed to H(2) flow at 150–250 sccm for 2–4 hours in a sealed reaction cell. Exposure to Ar flow under same condition reverses the observed shift in the A(1g) mode of the select MoSe(2) deposits. Our measurements provide in-situ evidence for hydrogen adsorption on MoSe(2) deposits at room temperature and insight into the possible active sites for hydrogen reactions on layered dichalcogenides at lower dimensions.