少层ReSe $_2$的光学特性
The optical signature of few-layer ReSe$_2$
摘要：
本文研究了从单层（1 ML）到九层（9 ML）厚度范围内的稀土二硒化物（ReSe $_2$）薄层的光学性质。分别在低温（$T$ =5 K）和室温（$T$ =300 K）下测量了光致发光（PL）和拉曼散射。ReSe $_2$层的PL光谱显示两条分辨良好的发射线，当层厚度从9 ML减小到单层时，其蓝移约120 meV。所观察到的低能量拉曼散射模式的丰富结构可以在线性链模型内解释。在大约120 cm $^{-1}$处的拉曼散射光谱中观察到的层内振动的两个声子模式，表现出非常敏感和相反的演化作为层厚度的函数。结果表明，它们的能量差可以作为一个方便和可靠的工具来确定ReSe $_2$薄片的厚度在几层的限制。
英文摘要：
Optical properties of thin layers of rhenium diselenide (ReSe$_2$) with thickness ranging from mono- (1 ML) to nona-layer (9 MLs) are demonstrated. The photoluminescence (PL) and Raman scattering were measured at low ($T$=5 K) and room ($T$=300 K) temperature, respectively. The PL spectra of ReSe$_2$ layers display two well-resolved emission lines, which blueshift by about 120 meV when the layer thickness decreases from 9 MLs to a monolayer. A rich structure of the observed low-energy Raman scattering modes can be explained within a linear chain model. The two phonon modes of intralayer vibrations, observed in Raman scattering spectra at about 120 cm$^{-1}$, exhibit very sensitive and opposite evolution as a function of layer thickness. It is shown that their energy difference can serve as a convenient and reliable tool to determine the thickness of ReSe$_2$ flakes in the few-layer limit.
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