Structural Phase Transition and Interlayer Coupling in Few-Layer 1T' and T MoTe.

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.