Structural Phase Transition and Interlayer Coupling in Few-Layer 1T' and Td MoTe2

TL;DR

This study uses polarized Raman spectroscopy to investigate phase transitions and interlayer coupling in few-layer MoTe2, revealing strong anisotropy, suppressed phase transition in thin layers, and multiple metastable phases.

Contribution

It provides new insights into the interlayer coupling, phase transition behavior, and metastable phases of few-layer MoTe2, which were not well understood before.

Findings

Interlayer coupling strengths were quantified using the linear chain model.

Temperature-driven phase transition to Td phase is suppressed in thinner samples.

Multiple metastable phases with similar energies exist in few-layer MoTe2.

Abstract

We performed polarized Raman spectroscopy on mechanically exfoliated few-layer MoTe2 samples and observed both 1T' and Td phases at room temperature. Few-layer 1T' and Td MoTe2 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' MoTe2. In contrast to bulk 1T' MoTe2 crystals where the phase transition to the Td phase occurs at ~250 K, the temperature-driven phase transition to the Td 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 Td phase with different interlayer vibration modes were observed, which suggests that several metastable phases exist with similar total energies.