Imaging Atomic-Level Random Walk of a Point Defect in Graphene

TL;DR

This study demonstrates direct imaging of a point defect's atomic-level diffusion in graphene using a specialized electron microscope, revealing detailed defect migration pathways in real time.

Contribution

First direct observation of a point defect's diffusion in a crystal at atomic resolution using low-voltage electron microscopy.

Findings

Successful real-time tracking of a divacancy in graphene

Stable imaging conditions enabled long sequence capture

Insights into defect migration mechanisms in 2D materials

Abstract

Deviations from the perfect atomic arrangements in crystals play an important role in affecting their properties. Similarly, diffusion of such deviations is behind many microstructural changes in solids. However, observation of point defect diffusion is hindered both by the difficulties related to direct imaging of non-periodic structures and by the time scales involved in the diffusion process. Here, instead of imaging thermal diffusion, we stimulate and follow the migration of a divacancy through graphene lattice using a scanning transmission electron microscope operated at 60 kV. The beam-activated process happens on a timescale that allows us to capture a significant part of the structural transformations and trajectory of the defect. The low voltage combined with ultra-high vacuum conditions ensure that the defect remains stable over long image sequences, which allows us for the first time to directly follow the diffusion of a point defect in a crystalline material.