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

Abstract

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.