Department of Physics, University of Bath , Bath BA2 7AY, U.K.
ACS Nano. 2014 Nov 25;8(11):11154-64. doi: 10.1021/nn5053926. Epub 2014 Nov 5.
Rhenium diselenide (ReSe2) is a layered indirect gap semiconductor for which micromechanical cleavage can produce monolayers consisting of a plane of rhenium atoms with selenium atoms above and below. ReSe2 is unusual among the transition-metal dichalcogenides in having a low symmetry; it is triclinic, with four formula units per unit cell, and has the bulk space group P1̅. Experimental studies of Raman scattering in monolayer, few-layer, and bulk ReSe2 show a rich spectrum consisting of up to 16 of the 18 expected lines with good signal strength, pronounced in-plane anisotropy of the intensities, and no evidence of degradation of the sample during typical measurements. No changes in the frequencies of the Raman bands with layer thickness down to one monolayer are observed, but significant changes in relative intensity of the bands allow the determination of crystal orientation and of monolayer regions. Supporting theory includes calculations of the electronic band structure and Brillouin zone center phonon modes of bulk and monolayer ReSe2 as well as the Raman tensors determining the scattering intensity of each mode. It is found that, as for other transition-metal dichalcogenides, Raman scattering provides a powerful diagnostic tool for studying layer thickness and also layer orientation in few-layer ReSe2.
二硒化铼（ReSe2）是一种层状间接带隙半导体，其微机械劈裂可产生由一层铼原子组成的单层，硒原子位于其上下方。在过渡金属二卤化物中，ReSe2 具有低对称性，这很不寻常；它是三斜晶系，每个晶胞中有四个分子式单位，具有体心空间群 P1̅。对单层、少层和体相 ReSe2 的拉曼散射实验研究表明，该光谱包含多达 16 条预期线中的 18 条，具有良好的信号强度、明显的各向异性和在典型测量过程中没有样品降解的迹象。观察到拉曼带的频率随层厚降低至单层没有变化，但带的相对强度的显著变化允许确定晶体取向和单层区域。理论支持包括体相和单层 ReSe2 的电子能带结构和布里渊区中心声子模式以及确定各模式散射强度的拉曼张量的计算。结果表明，与其他过渡金属二卤化物一样，拉曼散射为研究少层 ReSe2 的层厚度和层取向提供了一种强大的诊断工具。
