Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2
Identifying light impurities in transition metal dichalcogenides: the local vibrational modes of S and O in ReSe2 and MoSe2
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DOI：
10.1038/s41699-017-0043-1
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发表时间：
2017-11
影响因子：
9.7
通讯作者：
L. Hart;J. Webb;Stephen Murkin;D. Wolverson;D. Lin
中科院分区：
文献类型：
--
作者：
L. Hart;J. Webb;Stephen Murkin;D. Wolverson;D. Lin
过渡金属二硫属化合物为二维材料的研究提供了丰富的领域，已知有金属、半导体、超导体和电荷密度波材料。这个家族的成员通常是六方晶系，但那些基于ReSe 2和ReS 2的合金及其三元合金由于其三斜晶系结构和由此产生的强面内各向异性而引起关注。为了研究ReSe 2晶胞中硫原子在非等效硫族元素位置上的分布，获得了低硫含量（x≤ 0.25）的稀ReSe 2-xSx合金的拉曼光谱.观察到四个不同的拉曼谱带产生的硫原子的本地振动模式，对应于这四个网站。一个局部振动模式具有硫原子的基本上面内位移，两个是部分面外的，一个是完全面外的。实验数据的解释是基于晶格动力学和非共振拉曼张量的模型合金通过密度泛函理论的计算。为了比较，还提出了纯ReS 2的偏振相关的拉曼光谱;当激发偏振垂直于层并且光在层平面中传播时，发现面外模式的拉曼截面急剧增加。类似的增加横截面的实验发现，在稀ReSe 2-xSx合金中的硫的局部振动模式，并预测稀含硫合金的基础上MoSe 2。计算研究了ReSe_2中置换型氧杂质的类似局域振动模式。
The transition metal dichalcogenides provide a rich field for the study of two-dimensional materials, with metals, semiconductors, superconductors and charge density wave materials being known. Members of this family are typically hexagonal, but those based on rhenium (ReSe2and ReS2) and their ternary alloys are attracting attention due to their triclinic structure and their resulting, strong in-plane anisotropy. Here, Raman spectra of dilute ReSe2-xSxalloys containing low levels of sulfur (x≤ 0.25) were obtained in order to investigate the distribution of substitutional sulfur atoms over the non-equivalent chalcogen sites of the ReSe2unit cell. Four different Raman bands arising from the local vibrational modes of sulfur atoms were observed, corresponding to these four sites. One local vibrational mode has a substantially in-plane displacement of the sulfur atom, two are partially out-of-plane and one is completely out-of-plane. The interpretation of the experimental data is based on calculations of the lattice dynamics and non-resonant Raman tensors of a model alloy via density functional theory. For comparison, polarization-dependent Raman spectra of pure ReS2are also presented; a dramatic increase in the Raman cross-section is found for the out-of-plane modes when the excitation polarization is normal to the layers and the light propagates in the layer plane. A similar increase in cross-section is found experimentally for the local vibrational modes of sulfur in dilute ReSe2 -xSxalloys and is predicted for dilute sulfur-containing alloys based on MoSe2. The analogous local vibrational modes of substitutional oxygen impurities in ReSe2were also investigated computationally.