Kinetics of Vacancy-Assisted Reversible Phase Transition in Monolayer MoTe$_2$

TL;DR

This study uses atomistic simulations and kinetic theory to elucidate the vacancy-assisted reversible phase transition mechanisms between 2H and 1T' phases in monolayer MoTe2, revealing both diffusive and diffusionless pathways.

Contribution

It introduces a detailed atomistic and kinetic analysis of phase transition mechanisms in monolayer MoTe2, highlighting the role of vacancies and reversible pathways.

Findings

Vacancy coalescence initiates phase nucleation.

Growth involves vacancy incorporation or divacancy absorption.

Reversion to 2H is rapid and diffusionless.

Abstract

We investigate the kinetics of phase transition between the 2H and 1T$^\prime$ phases in monolayer MoTe$_2$ using atomistic simulations based on a machine learning interatomic potential trained on SCAN-DFT data, combined with mean field kinetic theory to interpret the underlying mechanisms. The transition is found to involve both diffusive and diffusionless mechanisms. Nucleation of 1T$^\prime$ phase is initiated by the coalescence of neighboring Te monovacancies into divacancies, which are found to be mobile and can interact with other Te vacancies to form small triangular 1T$^\prime$ islands. Growth of these islands proceeds either by incorporating pre-existing vacancies at the phase boundaries or, in their absence, by absorbing divacancies that migrate from the surrounding lattice. Once a critical island size is reached, vacancy-free growth becomes possible although with a higher activation barrier. Upon removal of external stimuli, the system reverts to 2H phase, during which Te vacancies reorganize into three-fold spoke-like vacancy lines at the island center. This reverse process and the subsequent 1T$^\prime$$\leftrightarrow$2H reversible transitions are diffusionless, rapid, do not require additional vacancies and can be driven by mild external stimuli. Although our analysis focuses on strain-induced transitions, the kinetic mechanisms are expected to be generalizable to other types of stimuli.