Density Functional Study On The Hybrid Phases Composed By Germanene And Alkali Metal Atoms

Germanene and silicene are both new type of graphene analogue two-dimensional crystal materials with honeycomb structure.They are two-dimensional single-atom thin films with buckled structure.The difference is that the buckled height of germanene is0.737?,which is greater than 0.44? as that in silicone.For this reason the germanene behaves stronger spin-orbit coupling(SOC)effects than silicene.Recently,monolayer germanene has been successfully fabricated on Pt(111)surface and Au(111)surface.In order to make better use of the electronic properties of germanene,various methods have been applied to modulate its electronic structure.In this work,we performed first principles pseudopotential calculations on the basis of density functional theory to investigated the new hybrid phase and their electronic properties of germanene combined with alkali metal atoms.The following conclusions are obtained.1.Considering the SOC effects,the new hybrid phase of germanene with saturated adsorption of alkali metal adatoms,Ge2X2(X=Li、Na、K、Rb),were studied by exploring the stability of these new hybrid phase with germanene.The studied formation energies indicate that all of them could form stable hybrid structures at room temperature.Furthermore,the formation energies of Li、Na、K are smaller than that of germanene,indicating a higher stability of the new phase than monolayer germanene.By comparsion the formation energy between Ge2Li2 hybrid phase and the saturated hydrogenation structure of germanene,we found that the stability of the Ge2Li2 new hybrid phase is even more stable than the complex formed by the saturated hydrogenation of germanene.With the recent successful preparation of hydrogen saturated germanene on experiments,our calculations predict the possibility of the preparation of germanene saturated lithium compounds.Bader charge analysis shows that charge transfer is significant between the alkali metal atoms and Ge atoms,but some covalent components are still existed.The calculated band structure indicated that the saturated adsorption of Li atoms in germanene presents a direct band gap of 0.14 eV,exhibiting the nature of direct band gap semiconductor.But the new phases formed by other alkali metal atoms and germanene exhibit metallic property.2.Considering the spin polarization effect in our calculations,the new hybrid phases formed by half saturated adsorption of alkali metal atoms on germanene,Ge2X1(X=Li、Na、K、Rb),were studied.By the comparison of their stability,charge transfer and bonding character,we found that there are very similar charater between Ge2X2(X=Li、Na、K、Rb)and Ge2X1(X=Li、Na、K、Rb)hybrid phases.However,the half saturated germanene with alkali metal atoms exhibit metallic property.It also shows weak polarization near the fermi level.Our calculations predict that the half saturated lithiumation structure behaves a local magnetic moment of 0.48μB on Geatoms adjacent to Li adatom.It implies that half saturated germanene with alkali metal adatoms has potential application in the aspect of spin elecreonics.