State Key Lab for Mesoscopic Physics and School of Physics, Peking University, Beijing, 100871, China.
Collaborative Innovation Center of Quantum Matter, Beijing, 100871, China.
Sci Rep. 2016 Jul 11;6:29254. doi: 10.1038/srep29254.
Tungsten ditelluride (WTe2) is a semi-metallic layered transition metal dichalcogenide with a stable distorted 1T phase. The reduced symmetry of this system leads to in-plane anisotropy in various materials properties. We have systemically studied the in-plane anisotropy of Raman modes in few-layer and bulk WTe2 by angle-dependent and polarized Raman spectroscopy (ADPRS). Ten Raman modes are clearly resolved. Their intensities show periodic variation with sample rotating. We identify the symmetries of the detected modes by quantitatively analyzing the ADPRS results based on the symmetry selection rules. Material absorption effect on the phonon modes with high vibration frequencies is investigated by considering complex Raman tensor elements. We also provide a rapid and nondestructive method to identify the crystallographic orientation of WTe2. The crystallographic orientation is further confirmed by the quantitative atomic-resolution force image. Finally, we find that the atomic vibrational tendency and complexity of detected modes are also reflected in the shrinkage degree defined based on ADPRS, which is confirmed by corresponding density functional calculation. Our work provides a deep understanding of the interaction between WTe2 and light, which will benefit in future studies about the anisotropic physical properties of WTe2 and other in-plane anisotropic materials.
二碲化钨（WTe2）是一种具有稳定扭曲 1T 相的半金属层状过渡金属二卤化物。该体系的对称性降低导致各向异性在各种材料性能。我们通过角相关和偏振拉曼光谱（ADPRS）系统地研究了少层和块状 WTe2 中面内各向异性的拉曼模。清晰分辨出了 10 个拉曼模。它们的强度随样品旋转而呈周期性变化。我们通过基于对称选择定则的定量分析 ADPRS 结果来确定所检测模式的对称性。通过考虑高振动频率的声子模式的复拉曼张量元素来研究材料对声子模式的吸收效应。我们还提供了一种快速、无损的方法来识别 WTe2 的晶体取向。通过定量原子分辨率力像进一步证实了晶体取向。最后，我们发现基于 ADPRS 定义的收缩度也反映了所检测模式的原子振动趋势和复杂性，这通过相应的密度泛函计算得到了证实。我们的工作提供了对 WTe2 与光相互作用的深入理解，这将有利于未来对 WTe2 和其他面内各向异性材料的各向异性物理性质的研究。
