A Study On Exfoliation And Magnetic Properties Of Borophenes

Since the first successful experimental preparation of graphene,it has gained extensive attention by researchers.And in recent years,most of the synthesized monolayer two-dimensional（2D）materials have special properties and significant potential applications.Boron,as the close neighbor of carbon,has rich chemical diversity,the monolayer allotrope of which has drawn a lot of attention in the past few years.Recently borophenes were finally experimentally realized on silver substrates.Borophenes have many excellent properties,but the significant interaction between borophenes and silver substrates,and borophenes may turn into another allotrope after exfoliation due to the change in the charge environment.Therefore the exfoliation of borophenes from substrates without phase transition becomes a prerequisite for their further applications.Theoretical studies suggested that β₁₂ borophene may be separated from the substrate in a manner analogous to that of graphene if the interaction is weakened.Previous studies have shown that the interaction between graphene and the substrate could be effectively weakened by atom intercalation between them.On the other hand,borophenes are non-magnetic,which greatly limits their use in spintronic devices.Doping or adsorbing 3d transition metal（TM）atoms is a common method for graphene performance regulation and an effective method to achieve its spin polarization.Inspired by these achievements,in this study,we will use calculations to study the exfoliation and magnetic properties of borophenes.We systematically investigated the exfoliation of β₁₂ borophene from the Ag（111）substrate with and without adsorbed or intercalated Li/Mg atoms using DFT methods.Our results indicated that Li and Mg adatoms tended to separate and distribute evenly on the borophene due to which the low diffusion barriers could be overcome by the Coulomb repulsion between adatoms combined with thermal energy.These Li/Mg adatoms transformed the interaction between borophene and the substrate into van der Waals-like,interaction,which would make the exfoliation much easier.Though it was very difficult for Li/Mg atoms to penetrate through the holes of borophene,it is possible for them to intercalate below borophene from armchair edges below the typical preparation temperature of β₁₂ borophene.The intercalated Li/Mg atoms separated borophene and the substrate,and low-concentration intercalation performed better than the high-concentration intercalation for separation,though it led to Coulomb attraction between borophene and Li/Mg atoms as well as that between Li/Mg atoms and the silver substrate.Our study proposed a preliminary exploration on the exfoliation of borophenes,which would facilitate the exfoliation of borophenes from metal substrates in future experiments,and may promote their application study in Li-ion batteries.We investigated the magnetic of β₁₂ borophene with adsorbed Fe,Co and Ni atoms by using first-principles study.Our results indicated that the Fe and Co modified systems showed magnetic characteristics under the high atomic adsorption concentration（Θ=1）.Although both systems tend to be antiferromagnetic as a whole,they are ferromagnetic along the direction of adjacent holes,which may be useful in spin transport.Ni-modified system is nonmagnetic.Three systems exhibit metal conductivity,which is mainly contributed by the d-orbital of the transition metals.When the atomic adsorption concentration Θ=1/8,the Fe-modified system tends to be ferromagnetic.The Co-modified system tends to be antiferromagnetic but is still ferromagnetic along the vertical hole.The Ni-modified system is still nonmagnetic.The properties exhibited by Fe and Co modified systems will promote the use of borophenes in spintronic devices.