Raman study of 2H-Mo1−xWxS2 layered mixed crystals

A systematic study of a series of Mo1−xWxS2 layered mixed crystals, with 0 ≤ x ≤ 1, grown by the chemical-vapor transport method were carried out by using Raman scattering measurements. The peaks of the two dominant first-order Raman-active modes, A1g and E2g1, and several second-order bands have been observed in the range of 200–1000 cm−1. The peaks corresponding to A1g mode show one-mode type behavior while the peaks of E2g1 mode demonstrate two-mode type behavior for the entire series. The results can be explained on the basis of the atomic displacements for each mode. For A1g mode only sulfur atoms vibrate and this give rise to a one-mode type behavior for the mixed crystals. For E2g1 mode metal atoms also vibrate as well as sulfur atoms, the mass difference of the vibrating Mo and W cations causes the two-mode type behavior of E2g1 mode. In addition, the observation of largest asymmetry and broadening of A1g mode for Mo0.5W0.5S2 has been attributed to random alloy scattering.

Research highlightsIn this report, a systematic study of a series of Mo1−xWxS2 layered mixed crystals, with 0 ≤ x ≤ 1, grown by the chemical-vapor transport method were carried out by using Raman scattering measurements. The peaks of the two dominant first-order Raman-active modes, A1g and E2g1, and several second-order bands have been observed in the range of 200–1000 cm−1. The peaks corresponding to A1g mode show one-mode type behavior while the peaks of E2g1 mode demonstrate two-mode type behavior for the entire series. The results can be explained on the basis of the atomic displacements for each mode. For A1g mode only sulfur atoms vibrate and this give rise to a one-mode type behavior for the mixed crystals. For E2g1 mode metal atoms also vibrate as well as sulfur atoms, the mass difference of the vibrating Mo and W cations causes the two-mode type behavior of E2g1 mode. In addition, the observation of largest asymmetry and broadening of A1g mode for Mo0.5W0.5S2 has been attributed to random alloy scattering.