Structural characteristic correlated to bandgap properties in MoS2

Figure Caption: Correlations of electronic band gap properties with the observed bond angles with pressure in MoS<sub>2</sub>. The filled symbols with error bars are from our XRD experiments; the solid lines are the linear regressions. The dashed lines are extrapolations of the fitted lines to expanded lattice (or negative pressure). The open symbols in the negative pressure regime are the bond angles of monolayer MoS<sub>2</sub> from previous theoretical works.
Figure Caption: Correlations of electronic band gap properties with the observed bond angles with pressure in MoS2. The filled symbols with error bars are from our XRD experiments; the solid lines are the linear regressions. The dashed lines are extrapolations of the fitted lines to expanded lattice (or negative pressure). The open symbols in the negative pressure regime are the bond angles of monolayer MoS2 from previous theoretical works.

Molybdenum disulfide (MoS2) attracts extensive interests because of its peculiar bandgap properties and the two-dimensional structure. The layer-dependent band structure has been studied by many theoretical calculations, including its evolution with pressure, e.g., the increase of the direct band gap by applying pressures. It is believed that the band-gap behavior is closely related to lattice strains. However, no general description has been established. A recent study conducted at HPCAT reveals a structural characteristic that is strongly correlated to bandgap behavior, regardless of its form as monolayer or bulk.  There are two unique structural parameters describing the strain of MoS2: in-plane S-Mo-S bond-angle φ and its out-of-plane pair θ. The trends in φ and θ have been determined as a function of external pressure using high-pressure X-ray powder diffraction for bulk MoS2. The results reveal surprisingly simple relationships between q orf and the bandgap properties of MoS2 (Figure).  The extrapolated results to expanded lattice (or negative pressure) coincide with the properties observed in samples from mechanical exfoliation. More details can be found in S. Chu, C. Park, and G. Shen. (2016) Phys. Rev. B 94, 020101(R).