First-principles Study Of Edge Reconstructions Of The Black Phosphorene

Ten years after the successful preparation of graphene,a new single-element two-dimensional material called black phosphorene has been successfully prepared experimentally and has attracted great attention.Its distinctive folded honeycomb-like lattice,similar to corrugated paper,is caused by the sp³hybridization of phosphorus atoms and the presence of lone pair electrons,which results in the highly anisotropic charge transfer properties and optical properties of black phosphorene.Unlike graphene with zero band gap and Mo S₂with low carrier mobility,black phosphorene has a direct band gap that can be adjusted with the number of layers(1.73?2.0 e V for single layer)and very high anisotropic carrier mobility(1000 cm²V^-1s^-1).In addition,the switching current ratio of the FET based on black phosphorene can reach 10⁴.Its tunable electronic band structure,excellent optical,charge transport and thermoelectric properties lay a foundation for the application of black phosphorene in future nano-devices.It is well known that the physical and chemical properties of three-dimensional materials are closely related to their surface structures.Similarly,the edge structures of two-dimensional materials also have an important influence on the stability,magnetism and electronic characteristics.For example,the black phosphorene nanoribbon with zigzag edges are metallic,while the armchair edges show semiconductor properties.In addition,the magnetic properties of the zigzag edge of the black phosphorene nanoribbons are also affected by the position of the atom at the edge.In the experiment,when nanoribbons are prepared by cutting method,there will be dangling bonds at the edge of the nanoribbon,which is not conducive to the stability of the structures.Therefore,the edge atoms need to be rearranged to saturate the dangling bonds,that is,the edge reconstruction.The reconstructed edges result in the electronic,optical and magnetic properties of a two-dimensional material that are different from their bulk phase.Therefore,it is necessary to reveal the possible edge reconstruction of black phosphorene.Most of the reported edge structures of black phosphorene are ideal edges or simple rearrangement of atoms on the basis of ideal edges,but there is no effective search for the potential energy surface of the edge structure of black phosphorene.Although some simple edge structures can be obtained by means of molecular dynamics simulation and manual rearrangement of edge atom positions,the global search of the edge structure of black phosphorene cannot be realized and a truly stable edge cannot be obtained.Up to now,there is still a lack of global search for the edge reconstruction of black phosphorene.In this paper,the first-principles particle swarm optimization(PSO)algorithm is used to search the edge structures of black phosphorene globally in two-dimensional space.The potential edge reconstructions of black phosphorene were predicted and explored.Different from previous studies,the influence of local phosphorus concentrations on the edge of black phosphorene was fully considered in the calculation,and the following innovative research results were obtained:1.For the first time,three typical edges(zigzag,armchair and diagonal edge)of black phosphorene databases were established based on edge formation energy and local phosphorus concentration.A variety of edge structures of the black phosphorene with global stability are determined.2.The relationship between the stability of the edge structures and the local phosphorus concentration was determined.With the increase of local phosphorus concentration,the change trend of edge formation energy shows obvious odd-even effect,especially for the zigzag edge and diagonal edge.The local phosphorus concentration plays an important role in the appearance of specific black phosphorene edge.3.The bonding mechanism of the edge reconstruction of the black phosphorene is revealed.The edge phosphorus atom tends to combine with the three nearest phosphorus atoms by?(sp³,sp³)bond or form a P=P double bond to balance the hanging bond of the edge and thus improve the stability of the black phosphorene edge.In addition,cluster-like and nanotubule-like structures are more easily formed under higher local phosphorus concentration.4.The band structures of the two most stable zigzag edges,armchair edges and diagonal edges are calculated respectively,and it is found that the reconstructed edge can lead to the semiconductor properties of the black phosphorene nanoribbons.Black phosphorene edge databases provide data support in the study of edge-determined properties and practical applications for black phosphorene nanomaterials while serving as useful references for edge studies of other 2D materials with puckered honeycomb structures.