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

The ambient environmental instability and degradation mechanism of single- and few-layer WTe₂ are investigated. Oxidation of W and Te atoms appears to be a main reason for degradation. Single-layer samples' Raman signals disappear within 20 min in air. Few-layer WTe₂ exhibits saturating degradation behavior: only the top layer WTe₂ is oxidized; the degraded layer can protect inner layers from further degradation.