Emergence of Layer Stacking Disorder in c-axis Confined MoTe$_2$

TL;DR

This study reveals that thin flakes of MoTe$_2$ exhibit highly disordered layer stacking due to confinement effects, contrasting with ordered stacking in WTe$_2$, impacting their quantum properties and device applications.

Contribution

The paper demonstrates that confinement induces stacking disorder in MoTe$_2$, providing new insights into 2D material behavior and potential for stacking control in device engineering.

Findings

MoTe$_2$ shows highly disordered stacking in thin flakes

WTe$_2$ maintains ordered stacking even at thin scales

Thickness influences stacking order in 2D materials

Abstract

The layer stacking order in 2D materials strongly affects functional properties and holds promise for next generation electronic devices. In bulk, octahedral MoTe$_2$ possesses two stacking arrangements, the Weyl semimetal T$_d$ phase, and the higher-order topological insulator 1T' phase; however, it remains unclear if thin exfoliated flakes of MoTe$_2$ follow the T$_d$, 1T', or an alternative stacking sequence. Here, we resolve this debate using atomic-resolution imaging within the transmission electron microscope. We find that the layer stacking in thin flakes of MoTe$_2$ is highly disordered and pseudo-random, which we attribute to intrinsic confinement effects. Conversely, WTe$_2$, which is isostructural and isoelectronic to MoTe$_2$, displays ordered stacking even for thin exfoliated flakes. Our results are important for understanding the quantum properties of MoTe$_2$ devices, and suggest that thickness may be used to alter the layer stacking in other 2D materials.