Cheon Yeryun, Lim Soo Yeon, Kim Kangwon, Cheong Hyeonsik
Department of Physics, Sogang University, Seoul 04107, Korea.
ACS Nano. 2021 Feb 23;15(2):2962-2970. doi: 10.1021/acsnano.0c09162. Epub 2021 Jan 22.
We performed polarized Raman spectroscopy on mechanically exfoliated few-layer MoTe samples and observed both 1T' and T phases at room temperature. Few-layer 1T' and T MoTe exhibited a significant difference especially in interlayer vibration modes, from which the interlayer coupling strengths were extracted using the linear chain model: strong in-plane anisotropy was observed in both phases. Furthermore, temperature-dependent Raman measurements revealed a peculiar phase transition behavior in few-layer 1T' MoTe. In contrast to bulk 1T' MoTe crystals, where the phase transition to the T phase occurs at ∼250 K, the temperature-driven phase transition to the T phase is increasingly suppressed as the thickness is reduced, and the transition and the critical temperature varied dramatically from sample to sample even for the same thickness. Raman spectra of intermediate phases that correspond to neither 1T' nor T phase with different interlayer vibration modes were observed, which suggests that several metastable phases exist with similar total energies.
我们对机械剥离的少层MoTe样品进行了偏振拉曼光谱分析，在室温下观察到了1T'相和T相。少层1T'和T相的MoTe表现出显著差异，尤其是在层间振动模式方面，利用线性链模型从中提取了层间耦合强度：在两个相中均观察到强烈的面内各向异性。此外，温度相关的拉曼测量揭示了少层1T'相MoTe中一种特殊的相变行为。与块状1T'相MoTe晶体不同，块状晶体中向T相的相变发生在约250 K，随着厚度减小，温度驱动的向T相的相变越来越受到抑制，即使对于相同厚度的样品，相变和临界温度在不同样品之间也有很大差异。观察到了对应于既非1T'相也非T相且具有不同层间振动模式的中间相的拉曼光谱，这表明存在几个具有相似总能量的亚稳相。
