Electron-irradiation effects on monolayer MoS2 at elevated temperatures

TL;DR

This study investigates how temperature influences defect creation and dynamics in monolayer MoS2 under electron irradiation, revealing temperature-dependent effects on defect visibility and migration energy barriers.

Contribution

It provides the first quantitative analysis of temperature effects on defect formation and migration in MoS2 during electron irradiation, combining experimental data with theoretical models.

Findings

Increased defect creation probability up to 150°C

Higher temperatures cause rapid defect diffusion, hiding damage

Estimated sulfur vacancy migration energy barrier as 0.26 eV

Abstract

The effect of electron irradiation on 2D materials is an important topic, both for the correct interpretation of electron microscopy experiments and for possible applications in electron lithography. After the importance of including inelastic scattering damage in theoretical models describing beam damage, and the lack of oxygen-sensitivity under electron irradiation in 2D MoS2 were recently shown, the role of temperature has remained unexplored on a quantitative level. Here we show the effect of temperature on both the creation of individual defects as well as the effect of temperature on defect dynamics. Based on the measured displacement cross section of sulphur atoms in MoS2 by atomic resolution scanning transmission electron microscopy, we find an increased probability for defect creation for temperatures up to 150{\deg}C, in accordance with theoretical predictions. However, higher temperatures lead to a decrease of the observed cross sections. Despite this apparent decrease, we find that the elevated temperature does not mitigate the creation of defects as this observation would suggest, but rather hides the created damage due to rapid thermal diffusion of the created vacancies before their detection, leading to the formation of vacancy lines and pores outside the measurement's field of view. Using the experimental data in combination with previously reported theoretical models for the displacement cross section, we estimate the migration energy barrier of sulphur vacancies in MoS2 to be 0.26 +- 0.13 eV. These results mark another step towards the complete understanding of electron beam damage in MoS2.