  Layered indium selenide (InSe), a new two-dimensional (2D) material with a
hexagonal structure and semiconducting characteristic, is gaining increasing
attention owing to its intriguing electronic properties. Here, by using
first-principles calculations, we reveal that perfect InSe possesses a high
chemical stability against oxidation, superior to MoS2. However, the presence
of intrinsic Se vacancy (VSe) and light illumination can markedly affect the
surface activity. In particular, the excess electrons associated with the
exposed In atoms at the VSe site under illumination are able to remarkably
reduce the dissociation barrier of O2 to ~0.2 eV. Moreover, at 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 the defect-photo promoted oxidations. Such results will
be beneficial in developing strategies for the storage of InSe material and its
applications for surface passivation with boron nitride, graphene or In-based
oxide layers.
