Interface Effect In The Growth Preparation Of Two-dimensional Materials

Based on the spin-polarized first-principles calculations,we investigated the structural models of two-dimensional materials?silicene,germanene and Al-Ge alloyed germanene?on the supporting substrates and the influence of interface effects on the growth and preparation of two-dimensional materials.First of all,the structures of silicene on different metal substrates and the influence of interface interaction on the growth and preparation of two-dimensional Si materials have been studied.Based on the energy stability analysis,SRT7-1T is the most stable configuration of silicene on Cu,Pt and Ir metal substrates.However,the stability of SRT7 silicene configuration is poor on Au,Ag and Al substrates,which is at least 0.12 eV/atom lower than its ground state structure.The ground state configuration of silicene on the Au?111?substrate is SRT13-1T.On Ag?111?and Al?111?substrates,the most stable structure of silicene is BHS-6T,and the stability of its lower isomers?Ag:SRT12-2T,SRT13-1T and Al:SRT13-4T,SRT12-3T?is only less than 19 meV/atom compared with BHS-6T.Therefore,they would probably have roughly equal chance to be fabricated on experiment under well-controlled experimental conditions.In addition,bond lengths and bond energies,charge density differences and the adhesive energies of these silicene/metal system have been calculated and discussed.We find that two-dimensional Si materials have greatly strong interaction with Pt and Ir metal substrates.Secondly,we have studied the structures of germanene on the supporting substrates?metal and alloyed substrates?and the effect of near-surface alloying on the growth and preparation of two-dimensional Ge materials.HL is the most stable configuration of germanene on Cu,Au,Pt,Ir and Al metal substrates,and the stability of HL is at least 40meV/atom higher than its lower isomers.To some sense,these metal substrates hinder the growth of the buckled germanene superlattices?such as BHS,TRP,SRT7 and SRT19?.However,on the pristine Ag?111?substrate,the stability of HL is lower 103 meV/atom than its configuration of ground state SRT19-1T.Surface alloying changes the energy sequence of germanene structure models.BHS-2T,BHS-1T,HL and BHS-1H are the most stable germanene configurations on the Cu₂Ge,Ag₂Ge,Au₂Ge,Ir₂Ge and Al₂Ge alloy substrates,respectively.In addition to the Ir₂Ge alloy substrate,surface alloying facilitates the growth of the buckled germanene superlattices,which makes them have more priorities in energy.Near surface alloying reduces the surface activities of metal?111?and weakens the interaction between the two-dimensional germanene structures and the supporting substrates,which makes it possible for the two-dimensional germanene materials to separate from the supporting substrates.Finally,we have studied the interface effect of the process of germanene alloying on Al?111?and Al₂Ge.The buckled germanene superlattices could be alloyed in the range of low-concentration doping though the one-atomic thick honeycomb and Kagome lattices would remain undoped.The stable BHS,TRP,and SRT7 structures of the pure and alloyed germanenes supported on both Al?111?and Al2Ge surface alloy,except the SRT7 pure germanene on the Al₂Ge,could re-produce the experimental scanning tunneling microscopy images.For the Al-Ge alloy sheets,the relative stable species are the Al₃Ge₅ BHS-2T,Al₃Ge₅TRP-2T,and Al₃Ge₃ SRT7-1T on Al?111?while they are the Al₄Ge₄ BHS-1T,Al₃Ge₅ TRP-2T,and Al₂₇Ge₂₇7 SRT7-?3×3?-9T on Al₂Ge.In addition,the Al₃Ge₅ BHS-2T and Al₄Ge₄ BHS-1T are the most stable alloy sheets on Al?111?and Al2Ge,respectively.There is no structural transition between the alloy structures,which is compared with the experimental reports of the BHS-2T and BHS-1H structural transitions of undoped germanene,indicating that the experimental conditions have an important effect on the selective growth of pure germanene or alloy germanene.At the same time,precisely controlled experimental conditions and processes may also grow and synthesize the theoretical minimum energy structure—the honeycomb monoatomic layer structure adsorbed on the Al?111?substrate.The detailed theoretical and experimental cooperative research still needs to be further developed by the scientific community to promote the exploration of cheap supporting substrate materials for the growth and preparation of two-dimensional materials.