Structural characteristic correlated to the electronic band gap inMoS2

Abstract

The structural evolution with pressure in bulk $\mathrm{Mo}{\mathrm{S}}_{2}$ has been investigated by high-pressure x-ray diffraction using synchrotron radiation. We found that the out-of-plane S-Mo-S bond angle \ensuremath{\theta} increases and that in in-plane angle $\ensuremath{\phi}$ decreases linearly with increasing pressure across the known semiconducting-to-metal phase transition, whereas the Mo-S bond length and the S-Mo-S trilayer thickness display only little change. Extrapolating the experimental result along the in-plane lattice parameter with pressure, both S-Mo-S bond angles trend to those found in monolayer $\mathrm{Mo}{\mathrm{S}}_{2}$, which manifests as a structural characteristic closely correlating the electronic band gap of $\mathrm{Mo}{\mathrm{S}}_{2}$ to its physical forms and phases, e.g., monolayer as direct band gap semiconductor, multilayer or bulk as indirect band gap semiconductor, and high-pressure $(g19\phantom{\rule{0.16em}{0ex}}\mathrm{GPa})$ bulk form as metal. Combined with the effects of bond strength and van der Waals interlayer interactions, the structural correlations between the characteristic bond angle and electronic band gaps are readily extendible to other transition metal dichalcogenide systems ($M{X}_{2}$, where $M=\mathrm{Mo}$, W and $X=\mathrm{S}$, Se, Te).