Ferroelasticity and domain physics in two-dimensional transition metal dichalcogenide monolayers.

Wenbin Li,Ju Li

doi:10.1038/ncomms10843

Abstract

Monolayers of transition metal dichalcogenides can exist in several structural polymorphs, including 2H, 1T and 1T′. The low-symmetry 1T′ phase has three orientation variants, resulting from the three equivalent directions of Peierls distortion in the parental 1T phase. Using first-principles calculations, we predict that mechanical strain can switch the relative thermodynamic stability between the orientation variants of the 1T′ phase. We find that such strain-induced variant switching only requires a few percent elastic strain, which is eminently achievable experimentally with transition metal dichalcogenide monolayers. Calculations indicate that the transformation barrier associated with such variant switching is small (<0.2 eV per chemical formula unit), suggesting that strain-induced variant switching can happen under laboratory conditions. Monolayers of transition metal dichalcogenides with 1T′ structure therefore have the potential to be ferroelastic and shape memory materials with interesting domain physics.

Highlights

Monolayers of transition metal dichalcogenides can exist in several structural polymorphs, including 2H, 1T and 1T0
A ferroelastic material is defined by the existence of two or more stable orientation variants, which can be switched from one variant to another without diffusion by the application of external stress[26,27]
In the 1T phase, the W atoms arrange in 2D triangular lattice, which is sandwiched between two Te atomic layers

Summary

Introduction

Monolayers of transition metal dichalcogenides can exist in several structural polymorphs, including 2H, 1T and 1T0. Using first-principles calculations, we predict that mechanical strain can switch the relative thermodynamic stability between the orientation variants of the 1T0 phase We find that such strain-induced variant switching only requires a few percent elastic strain, which is eminently achievable experimentally with transition metal dichalcogenide monolayers. Monolayers of group VI transition metal dichalcogenides (TMDs) with chemical formula MX2, where M is Mo or W and X stands for S, Se or Te, have in particular attracted much recent attention due to their semiconducting, optical and valleytronic properties[4,7,8,9]. The low-symmetry ferroelastic phase possesses several orientation states (domain variants) with different spontaneous strain[28], that is, the distortion of the unit cell relative to that in the prototype phase. On activation by appropriate external stress, those twin boundaries can move in a glissile fashion, resulting in the growth of one orientation state at the expense of another, as well as hysteretic stress–strain response[27]

Methods

Results

Conclusion