The environmental instability of single- or few-layer black phosphorus (BP) has become a major hurdle for BP-based devices. The degradation mechanism remains unclear and finding ways to protect BP from degradation is still highly challenging. Based on ab initio electronic structure calculations and molecular dynamics simulations, a three-step picture on the ambient degradation of BP is provided: generation of superoxide under light, dissociation of the superoxide, and eventual breakdown under the action of water. The well-matched band gap and band-edge positions for the redox potential accelerates the degradation of thinner BP. Furthermore, it was found that the formation of P-O-P bonds can greatly stabilize the BP framework. A possible protection strategy using a fully oxidized BP layer as the native capping is thus proposed. Such a fully oxidization layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.

The environmental instability of single-or few-layer black phosphorus (BP) has become am ajor hurdle for BPbased devices.T he degradation mechanism remains unclear and finding ways to protect BP from degradation is still highly challenging.Based on ab initio electronic structure calculations and molecular dynamics simulations,athree-step picture on the ambient degradation of BP is provided:g eneration of superoxide under light, dissociation of the superoxide,a nd eventual breakdown under the action of water.T he wellmatched band gap and band-edge positions for the redox potential accelerates the degradation of thinner BP.F urthermore,i tw as found that the formation of P-O-P bonds can greatly stabilizet he BP framework. Ap ossible protection strategy using afully oxidized BP layer as the native capping is thus proposed. Suchafully oxidization layer can resist corrosion from water and leave the BP underneath intact with simultaneous high hole mobility.

In zero-gap semimetallic silicene, introducing a sizable band gap without degrading its high carrier mobility is vital to its application in optoelectronic devices. Herein, we design a novel atomically thin system based on silicene and arsenene nanocomposites (Si/As heterostructure), which could open a direct band gap of about 125 meV at the K point in silicene. Moreover, its band gap is linearly controllable over a wide range even with a semiconductor-metal transition by the external electric field (E), with an impressive band gap of up to 328 meV at E = -0.9 V Å. Additionally, the Si/As heterostructure can exhibit pronounced optical absorption in the far infrared range. The binding energy of the first bright exciton is as large as 623 meV, which can be significantly increased with an enhanced E. The tunable bandgap together with a superior optical absorption makes the Si/As heterostructure a potential candidate for nanoelectronic and optoelectronic applications.