Atomic-scale Oxygen-mediated Etching of 2D MoS$_2$ and MoTe$_2$

TL;DR

This study investigates how oxygen causes degradation in 2D transition metal dichalcogenides, revealing that MoTe$_2$ is reactive to oxygen while MoS$_2$ remains inert, with carbon contamination significantly accelerating damage.

Contribution

The paper provides atomic-scale insights into oxygen-induced degradation mechanisms in MoTe$_2$ and MoS$_2$, highlighting the role of carbon contamination and using DFT calculations to elucidate etching processes.

Findings

MoTe$_2$ degrades rapidly above 1×10^{-7} torr oxygen pressure.

MoS$_2$ remains inert under oxygen, with damage caused mainly by electron irradiation.

Carbon contamination accelerates MoTe$_2$ degradation by up to forty times.

Abstract

Some of the materials are more affected by oxidation than others. To elucidate the oxidation-induced degradation mechanisms in transition metal chalcogenides, the chemical effects in single layer MoS$_2$ and MoTe$_2$ were studied in situ in an electron microscope under controlled low-pressure oxygen environments at room temperature.Oxidation is the main cause of degradation of many two-dimensional materials, including transition metal dichalcogenides, under ambient conditions. MoTe$_2$ is found to be reactive to oxygen, leading to significant degradation above a pressure of 1$\times 10^{-7}$ torr. Curiously, the common hydrocarbon contamination found on practically all surfaces accelerates the damage rate significantly, by up to a factor of forty. In contrast to MoTe$_2$, MoS$_2$ is found to be inert under oxygen environment, with all observed structural changes being caused by electron irradiation only, leading to well-defined pores with high proportion of molybdenum nanowire-terminated edges. Using density functional theory calculations, a further atomic-scale mechanism leading to the observed oxygen-related degradation in MoTe$_2$ is proposed and the role of the carbon in the etching is explored. Together, the results provide an important insight into the oxygen-related deterioration of two-dimensional materials under ambient conditions relevant in many fields.