Surface oxidation of pristine and defective T_d-WTe₂ semimetals

The chemical instability of semimetallic transition metal dichalcogenides (TMDs) under ambient conditions poses a major challenge for their integration into spintronic and quantum devices. Here, we establish a quantitative framework to elucidate their oxidation mechanism by combining photoelectron spectroscopy with defect engineering via controlled ion irradiation. Freshly cleaved and defect-enriched T_d-WTe₂ single crystals were exposed to air at controlled temperatures, enabling direct evaluation of oxidation kinetics by monitoring the time evolution of the oxide-related X-ray photoelectron signal. The introduction of up to ∼4% concentration of Te vacancies by ion sputtering leads to only moderate enhancement of the surface oxidation rate (by a factor of ∼2-3), despite pronounced modifications of the surface electronic structure revealed by angle-resolved photoelectron spectroscopy. Arrhenius model-based analysis indicates that the apparent activation energy for oxidation (∼0.11 eV) remains essentially unaffected following the ∼4% defect generation. Notably, theoretical calculations demonstrate that oxidation at Te vacancy sites is comparable with that on defect-free regions, which predominantly govern the ambient degradation of semimetallic WTe₂, in contrast to previous reports for semiconducting TMDs. The higher oxidation rate is therefore attributed to surface structural disorder induced by defect formation, which likely promotes adsorption of atmospheric species without altering the intrinsic oxidation energetics. Collectively, these results show that chalcogen vacancies in T_d-WTe₂ do not play a dominant role in controlling oxidation energetics through direct gas-defect interactions, thereby refining the understanding of its environmental stability which is crucial for synthesis and device fabrication strategies under ambient conditions.