Composition dependent lattice dynamics in MoS<i>x</i>Se(2–<i>x</i>) alloys

Abstract

We report on room temperature, polarization-resolved Raman scattering measurements on layered crystals of the series MoSxSe(2–x) (0 ≤ x ≤ 2) grown by chemical vapor transport technique. The results reveal two distinct sets of features related to the E2g1 and A1g modes of pure members of series. As composition x changes, the in-plane E2g1 mode shows two-mode behavior, whereas the out-of-plane A1g mode presents more complex evolution. The MoSe2-like branch reveals the splitting associated with the altering arrangement of S and Se atoms around Mo and the resulting changes in the dipole moment of the molecule. The X-ray diffraction measurements confirm that the samples are single-phase materials of 2H-type structure over the entire range of the sulfide composition x, while the scanning transmission electron microscopy imaging reveals a random arrangement of the S and Se atoms. Modified random-element-isodisplacement model is adopted to predict the behavior of the individual modes in the alloys. The model successfully confirms the two-mode behavior exhibited by the MoSxSe(2–x) series.