Atomic-scale mechanisms of defect- and light-induced oxidation and degradation of InSe

Abstract

Layered indium selenide (InSe), a new two-dimensional (2D) material with a hexagonal structure and semiconducting characteristics, is gaining increasing attention owing to its intriguing electronic properties. Here, by using first-principles calculations, we reveal that perfect InSe possesses high chemical stability against oxidation, superior to MoS₂. However, the presence of intrinsic Se vacancy (V_Se) and light illumination can markedly affect its surface activity. In particular, the excess electrons associated with the exposed In atoms at the V_Se site under illumination are able to remarkably reduce the dissociation barrier of O₂ to ∼0.2 eV. Moreover, under ambient conditions, the splitting of O₂ enables the formation of substitutional (apical) oxygen atomic species, which further cause the trapping and subsequent rapid splitting of H₂O molecules and ultimately the formation of hydroxyl groups. Our findings uncover the causes and underlying mechanisms of InSe surface degradation via defect-photo-promoted oxidations. Such results will be beneficial in developing strategies for the storage of the InSe material and its applications for surface passivation with boron nitride, graphene or In-based oxide layers.