State Key Laboratory of Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences, Beijing 100083, China.
Chem Soc Rev. 2015 May 7;44(9):2757-85. doi: 10.1039/c4cs00282b. Epub 2015 Feb 13.
Two-dimensional (2D) transition metal dichalcogenide (TMD) nanosheets exhibit remarkable electronic and optical properties. The 2D features, sizable bandgaps and recent advances in the synthesis, characterization and device fabrication of the representative MoS2, WS2, WSe2 and MoSe2 TMDs make TMDs very attractive in nanoelectronics and optoelectronics. Similar to graphite and graphene, the atoms within each layer in 2D TMDs are joined together by covalent bonds, while van der Waals interactions keep the layers together. This makes the physical and chemical properties of 2D TMDs layer-dependent. In this review, we discuss the basic lattice vibrations of 2D TMDs from monolayer, multilayer to bulk material, including high-frequency optical phonons, interlayer shear and layer breathing phonons, the Raman selection rule, layer-number evolution of phonons, multiple phonon replica and phonons at the edge of the Brillouin zone. The extensive capabilities of Raman spectroscopy in investigating the properties of TMDs are discussed, such as interlayer coupling, spin-orbit splitting and external perturbations. The interlayer vibrational modes are used in rapid and substrate-free characterization of the layer number of multilayer TMDs and in probing interface coupling in TMD heterostructures. The success of Raman spectroscopy in investigating TMD nanosheets paves the way for experiments on other 2D crystals and related van der Waals heterostructures.
二维（2D）过渡金属二卤化物（TMD）纳米片具有显著的电子和光学性能。2D 特征、相当大的带隙以及在合成、表征和器件制造方面的最新进展，使 MoS2、WS2、WSe2 和 MoSe2 TMD 等代表性 TMD 在纳米电子学和光电子学中具有吸引力。与石墨和石墨烯类似，2D TMD 中每层内的原子通过共价键连接在一起，而范德华相互作用使层保持在一起。这使得 2D TMD 的物理和化学性质具有层依赖性。在这篇综述中，我们讨论了 2D TMD 从单层、多层到体材料的基本晶格振动，包括高频光学声子、层间剪切和层呼吸声子、拉曼选择定则、声子的层数演化、多声子副本和声子在布里渊区边缘。讨论了拉曼光谱在研究 TMD 性质方面的广泛能力，如层间耦合、自旋轨道分裂和外部扰动。层间振动模式用于快速、无衬底的多层 TMD 层数表征以及 TMD 异质结构中的界面耦合探测。拉曼光谱在研究 TMD 纳米片方面的成功为其他 2D 晶体和相关范德华异质结构的实验铺平了道路。
