Direct Visualization of Electric Field induced Structural Dynamics in Monolayer Transition Metal Dichalcogenides

TL;DR

This study uses in situ transmission electron microscopy to visualize how electric fields induce structural changes in monolayer MoS2, revealing mass transport and defect dynamics relevant for device stability.

Contribution

It provides the first direct visualization of electric field-induced structural dynamics at interfaces and defects in monolayer TMDs using in situ TEM.

Findings

Electric field causes mass transport at grain boundaries.

Void formation and structural deformation observed under bias.

Structural stability improves after initial biasing cycles.

Abstract

Layered transition metal dichalcogenides (TMDs) offer many attractive features for next-generation low-dimensional device geometries. Due to the practical and fabrication challenges related to in situ methods, the atomistic dynamics that give rise to realizable macroscopic device properties are often unclear. In this study, in situ transmission electron microscopy techniques are utilized in order to understand the structural dynamics at play, especially at interfaces and defects, in the prototypical film of monolayer MoS2 under electrical bias. Through our sample fabrication process, we clearly identify the presence of mass transport in the presence of a lateral electric field. In particular, we observe that the voids present at grain boundaries combine to induce structural deformation. The electric field mediates a net vacancy flux from the grain boundary interior to the exposed surface edge sites that leaves molybdenum clusters in its wake. Following the initial biasing cycles, however, the mass flow is largely diminished, and the resultant structure remains stable over repeated biasing. We believe insights from this work can help explain observations of non-uniform heating and preferential oxidation at grain boundary sites in these materials.