Role of surface adsorption in tuning the properties of black phosphorus

H₂O and O₂ are believed to be key factors that influence the structural stability of black phosphorus (BP) in ambient conditions. In this work, the interactions of H₂O and/or O₂ with BP are investigated using first-principles calculations. The results indicate that water molecules prefer to adsorb on the BP surface and form a six-member water ring. The dissociation barrier of O₂ is significantly reduced in the presence of H₂O, which dramatically promotes the degradation of BP. Moreover, the introduction of O₂ also facilitates the adsorption of water on the surface. The effects of H₂O and/or O₂ on the quasiparticle band gap and exciton binding energy of BP are also investigated. The results suggest that water adsorption has only a slight influence on the electronic properties and exciton binding energy, while O₂ adsorption causes obvious changes in the properties of BP, which results in a direct-to-indirect band gap transition in BP.