Crystal Structures And Physical Properties Of Potential New Arsenic-phosphorus Alloys Predicted From First-principles Calculations

In 2014,two-dimensional black phosphorene was mechanically exfoliated from layered black phosphorus.It has attracted great research interests for its significant band gap and high carrier mobility.The electronic properties of black phosphorene can be effectively modulated by varies ways,such as geometrical cutting into nanoribbons,chemical modification the surface,stacking into multi-layered hetero-junctions.In fact,elementary doping or alloying is also an alternative way to provide us phosphorus-based 2D materials for nano-electronics application.Very recently,layered alloy of arsenic-phosphorus(PxAs1-x)with tunable property has been synthesized in an alloying strategy and its corresponding 2D counterpart of a few layers has also been mechanically exfoliated.However,the fundamental electronic properties of the 2D alloy of binary PxAs1-x were not reported in the literature due to the lack of unambiguous crystal structures.Nevertheless,identifying the crystal structures of 2D binary PxAs1-x alloys is a significant work.Most of the previous theoretical works about the 2D P0.5As0.5 alloy always take the ?-and ?-configurations of phosphorene to investigate their physical properties.In this work,we systematically predicted the structural stabilities and fundamental electronic properties of 25 potential 2D P0.5As0.5 alloys.Our main results are as follows:(1)Based on the hexagonal honeycomb-like lattice of graphene,twenty-five possible crystal structures of 2D binary P0.5As0.5 alloy are proposed according to the combinations of atomic fluctuation and elementary distribution.First-principles method is employed to investigate the structures,stabilities,fundamental electronic properties of these twenty-five possible 2D binary P0.5As0.5 alloys.We found that the two atomic configurations of ?-and ?-are the most two favorable configurations for atomic fluctuation in 2D P0.5As0.5.In addition,we also found that the predicted structure IV is confirmed slightly more favorable than the previously proposed structure III for elementary distribution.Our results show that elementary doping and alloying are effective ways to modulate the fundamental electronic properties of 2D binary P0.5As0.5 alloys.(2)Two types of van der Waals modifications are considered in calculation of the structures,stabilities and electronic properties of these twenty-five possible 2D binary P0.5As0.5 alloy again.About the structures and stabilities,whether we consider van der Waals modification or not,we found that all the results are in good agreement with those calculated without van der Waals modification.However,the electronic properties(especially the type of band-gap)predicted from different methods show obvious differences for ?-phase and ?-phase with relatively larger thickness.The band-gap types of the other three phases with relatively small thickness calculated from different methods are in accordance with each other.No evidence can confirm that which functional is reasonable for the binary 2D P0.5As0.5 alloy.We just noticed that the differences always appear in the configurations with relatively larger thickness.We expect experimental voice to confirm these results to help us understand the van der Waals interactions in such single layered systems.