Environmental Instability and Degradation of Single- and Few-Layer WTe2 Nanosheets in Ambient Conditions

TL;DR

This study investigates the degradation mechanisms of single- and few-layer WTe2 nanosheets in ambient conditions, revealing oxidation processes and layer-dependent stability through spectroscopic analyses.

Contribution

It provides detailed experimental insights into the degradation process of WTe2 nanosheets, highlighting oxidation effects and the protective role of surface oxidation.

Findings

1L WTe2 degrades faster than 2L and 3L flakes.

Oxidation of Te and W atoms causes degradation.

Oxidation occurs within 0.5nm of the surface.

Abstract

Since the discovery of large, non-saturating magnetoresistance in bulk WTe2 which allows microexfoliation, single- and few-layer WTe2 crystals have attracted increasing interests. However, as it mentioned in existing studies, WTe2 flakes appear to degrade in ambient conditions. Here we report experimental observations of saturating degradation in few-layer WTe2 through Raman spectroscopy characterization and careful monitoring of the degradation of single-, bi- and tri-layer (1L, 2L & 3L) WTe2 over long time. Raman peak intensity decreases during WTe2 degradation and 1L flakes degrade faster than 2L and 3L flakes. The relatively faster degradation in 1L WTe2 could be attributed to low energy barrier of oxygen reaction with WTe2. We further investigate the degradation mechanisms of WTe2 using XPS and AES and find that oxidation of Te and W atoms is the main reason of WTe2 degradation. In addition, we observe oxidation occurs only in the depth of 0.5nm near the surface, and the oxidized WTe2 surface could help prevent inner layers from further degradation.