We report on the extensive structural and optical studies of Re-doped molybdenum disulfide (MoS 2 ) grown by the chemical vapor transport (CVT) method using Br 2 as a transport agent. To evaluate the influence of Re on the structural properties of crystals, we have conducted X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments. For optical characterization, we carried out piezoreflectance (PzR) and electrolyte electroreflectance (EER) measurements. The Re dopant clearly caused a structural change in MoS 2 from a two-layer hexagonal (2H) structure to a three-layer rhombohedral (3R) structure, which has been clearly verified and identified herein.
A series of MoxW1−xS2 (0 ≤ x ≤ 1) layered mixed crystals was grown by the chemical vapor transport method. A systematic study of these crystals was then conducted using the Raman scattering measurements. The peaks of the two dominant first-order Raman-active modes, A1g and E 1 2g , and of several second-order bands are observed from 150 cm −1 to 500 cm −1 . The peaks corresponding to A1g mode show one-mode type behavior, whereas the peaks of E 1 2g mode demonstrate two-mode type behavior for the entire series. These results can be explained by the atomic displacements of each mode. For A1g mode, only S atoms vibrate, thereby resulting in a one-mode type behavior for the mixed crystals. For E 1 2g mode, metal and S atoms vibrate. The mass difference in the vibrating Mo and W cations causes the two-mode type behavior of E 1 2g mode. In addition, the largest asymmetry and broadening of A1g mode for Mo0.5W0.5S2 is attributed to random alloy scattering.
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