Origin of Oxidation\nVariations in Ambient-Stable β‑InSe

Understanding and controlling the oxidation of layered\nmaterials\nremain critical issues in the final stages of their practical application\nin devices. Layered materials achieve a band gap by removing inversion\nsymmetry. However, the oxidation process becomes complex, and the\noxidation of these materials is not yet fully understood. As a representative\nexample, InSe has attracted considerable attention due to its high\ncharge mobility and Si-like band gap. However, conflicting observations\nsuch as oxidation by Se and In have been reported, including contrasting\nassessments of the oxidation susceptibility. In this study, we report\nin situ spectroscopy results detailing the origins of various oxidation\npathways. We observed that at low defect densities the reduced reaction\nbarrier of InSe due to Se vacancies leads to oxygen adsorption, while\nas defects increase, the lower electronegativity of In rises as a\nnew pathway for oxidation. At low defect density, the bulk layer was\nmore energetically favored for oxygen adsorption, allowing oxygen\nto diffuse to a depth sufficient to form pseudoheterojunctions and\nmaking the surface layer seemingly resistant to oxidation. Our results\nprovide an answer to why the resulting diversity of optical responses\nis expected to increase as well as strategies to achieve gas stability.