Theoretical Study On Epitaxial Growth And Protection Of Phosphorene

The excellent electronic properties,optical properties,and thermal properties of phosphorene make it have a wide range of application prospects in field effect transistors,optoelectronic devices,gas sensors and solar cells.Great efforts have been dedicated to synthesizing phosphorene on transition metal surfaces by vapor deposition,but there is still limited success until now.The main reason is that the strong interaction between phosphorus and most transition metal substrates makes it difficult for phosphorene to exist stably on the surface.Here we studied if functionalizing transition metal surfaces by different phosphorous isomers can assist the epitaxial growth of blue phosphorene.At the same time,as black phosphorene is easy to be oxidized in ambient condition,we also explored the method to stabilize black phosphorene and keep its electronic and optical performance.The specific research contents are as follows:The surface activity of transition metals affects the formation of phosphorous isomers.Using density functional theory（DFT）,we systematically explored five families of phosphorous isomers,including blue phosphorene,modified blue phosphorene,surface phosphide,metal-phosphorus hybrid and blue phosphorene on surface phosphide on five different transition metal surfaces,Au（111）,Cu（111）,Co（0001）,Ni（111）and Pt（111）.It is found that blue phosphorene can be formed by controlling the P coverage on less active transition metal surfaces,such as Au（111）surface.On more active transition metal surfaces,such as Cu（111）,Co（0001）,Ni（111）and Pt（111）substrates,surface phosphides tend to form first and blue phosphorene may be formed on top of the surface phosphide by further increasing the P coverage.Ag（111）surface can form phosphorous chains,pentamers and blue phosphorene.We found that one-dimensional armchair chains have high stability at low P concentration,and five-membered-rings of phosphorus,or phosphorous pentamers are the most stable structures at medium P concentration.The armchair chains and pentamers can not exist on Au（111）,Cu（111）,Co（0001）,Ni（111）and Pt（111）substrates due to instability.We also identified a few patterns of phosphorous pentamers on Ag（111）surface,which agree well with experimental observation.Based on the stable structures of armchair chains and pentamers,we predict the growth mechanism of P isomers on Ag（111）substrate.The armchair chains form first at low P concentration,followed by the pentamers at the medium P concentration by breaking the P-P bond of every five P atoms in chain.At last,the blue phosphorene can be formed by the moving of pentamers to the edge of blue phosphorene.The chemisorption of C₆₀ at the black phosphorene boundary can protect black phosphorene and its excellent properties.We applied first-principles theoretical calculations and found that C₆₀ passivation at its edge can stabilize black phosphorene and keep its excellent properties.It is found that C₆₀ functionalization at the zigzag,armchair andθ₅₄ edges moves the conduction band minimums（CBMs）of BP below the O₂/O₂^-redox potential,preventing the electron transfer from black phosphorene to O₂ under light excitation.Moreover,the CBM of the functionalized BP changes from the edge P atoms to the adsorbed C₆₀ and the valence band maximum（VBM）remains on the BP,leading to charge transfer from BP to C₆₀ under light excitation.Furthermore,the light adsorption of C₆₀ passivated BP is enhanced,which provides better performance for BP’s application in optoelectronics.This study highlights the structural diversity of the transition metal surfaces in an active environment and provides a guidance for the synthesis of phosphorene on transition metal surfaces.In addition,our study provides theoretical mechanism to improve the stability of black phosphorene by edge functionalization.