Raman studies of anisotropic properties of ReSe₂

ReSe₂ is a van der Waals layered semiconductor with an indirect bandgap of ~ 1.3 eV which is smaller than most transition metal dichalcogenides (TMDCs). ReSe₂ has a distorted octahedral structure (1T') with much lower symmetry and in-plane anisotropy compared to other hexagonal TMDCs such as MoS₂ and WS₂ [1]. Due to the structural in-plane anisotropy resulting in an optical and electrical anisotropy, ReSe₂ can be used as polarization sensitive optoelectronic devices [2]. We studied polarization dependence of Raman response with different excitation energies. The polarization dependence patterns vary dramatically with different excitation energies. In particular, we determined the direction of the rhenium chains with a mode at ~ 160 cm^-1 by using the 1.96 eV-excitation and confirmed it with HRSTEM measurements. In addition, we developed a method to determine front and back sides of a sample.

[1] J. A. Wilson et al., Advances in Physics 18, 193 (1969).
[2] Shengxue Yang et al., Scientific Reports 4, 5442 (2014).