Strain-induced phonon shifts in tungsten disulfide nanoplatelets and nanotubes
Strain-induced phonon shifts in tungsten disulfide nanoplatelets and nanotubes
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DOI：
10.1088/2053-1583/4/1/015007
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发表时间：
2017-03-01
期刊：
影响因子：
5.5
通讯作者：
Young, Robert J.
中科院分区：
文献类型：
--
作者：
Wang, Fang;Kinloch, Ian A.;Young, Robert J.
结构和性能之间的关系已遵循不同的纳米级形式的二硫化钨（2 H-WS 2），即剥离单层和少层纳米片，和纳米管。这些纳米结构材料之间的相似性和差异已被检查使用光学显微镜，扫描和高分辨率透射电子显微镜和原子力显微镜的组合。光致发光和拉曼光谱也被用来区分单层和少层材料。从单轴形变过程中A（1g）和E-2g（1）拉曼带位置的变化，跟踪了应变引起的声子位移。这已被建模为单层使用密度泛函理论与测量和预测的行为之间的良好协议。已经发现，对于少层晶体或纳米管，随着WS 2层数的增加，A（1g）模式变硬，而E-2g（1）模式变软。这被认为是由于A（1g）模式，其涉及面外原子运动，受到WS 2层数量增加的限制，而容易滑动减少了E-2g（1）模式的应力传递到各个层，仅涉及面内振动。这一发现使得早期压力测量中WS 2的异常声子位移行为得以解决，以及其他过渡金属二硫属化物（如二硫化钼）中的类似效应得到解释。
The relationship between structure and properties has been followed for different nanoscale forms of tungsten disulfide (2H-WS2) namely exfoliated monolayer and few-layer nanoplatelets, and nanotubes. The similarities and differences between these nanostructured materials have been examined using a combination of optical microscopy, scanning and high-resolution transmission electron microscopy and atomic force microscopy. Photoluminescence and Raman spectroscopy have also been used to distinguish between monolayer and few-layer material. Strain induced phonon shifts have been followed from the changes in the positions of the A(1g) and E-2g(1) Raman bands during uniaxial deformation. This has been modelled for monolayer using density functional theory with excellent agreement between the measured and predicted behaviour. It has been found that as the number of WS2 layers increases for few-layer crystals or nanotubes, theA(1g) mode hardens whereas the E-2g(1) mode softens. This is believed to be due to the A(1g) mode, which involves out of plane atomic movements, being constrained by the increasing number of WS2 layers whereas easy sliding reduces stress transfer to the individual layers for the E-2g(1) mode, involving only in-plane vibrations. This finding has enabled the anomalous phonon shift behaviour in earlier pressure measurements on WS2 to be resolved, as well as similar effects in other transition metal dichalcogenides, such as molybdenum disulfide, to be explained.