The First-Principle Research Of Half-Metallicity In Zigzag Silicene Nanoribbons With Aluminum And Phosphorus Doping

Half-metallicity always plays an extremely important role in spintronics.In recent years,more and more attention has been attracted to achieve half-metallicity in 2D materials and many schemes have been proposed to realize this goal.However,all these chemical doping schemes have the same problem that the energy difference between the ferromagnetic(FM)state and anti-ferromagnetic(AFM)state is negligibly small after doping,which means that the half-metallicity can hardly be observed practically since a negligible or too small energy difference((?)E_FM-AFM)between the AFM and FM states means that a finite temperature can easily turn nanoribbons into a paramagnetic state and break the half-metallicity obtained.Therefore,schemes for achieving stable half-metallicity and having good compatibility with conventional semiconductor industry are highly expected.In this thesis,we investigate the possibility of realizing stable half-metallicity in zigzag silicene nanoribbons(ZSiNRs)with chemical doping.Using density functional theory(DFT)calculations,we will show that this goal is achieved by the substitution of Al-P chains/atoms in dihydrogenated ZSiNR unit cell(H2-H2 ZSiNR)and monohydrogenated ZSiNRs super cell(H-H ZSiNR).The main contents and results are listed as follows:(1)We have systematically investigated the Al-P chains doping effects on the electronic structure of the H2-H2 ZSiNRs using first-principles calculations,in which the half-metallicity can be successfully achieved.Most notably,the H2-H2 6-ZSiNR with two Al-P chains at the middle not only becomes half-metallic but also the(?)E_FM-AFMincreases to 5.41me V/unitcell compared with the H-H cases,indicating that dihydrogenation is beneficial for the obtaining the half-metallicity and stabilizing the AFM ground state.With the analysis of the wave functions and electrostatic potential,it is found that,due to the different potential at two edges of the H2-H2 ZSiNR after Al-P doping,the edge states with different spins are shifted towards opposite directions in energy,which makes the full half-metallicity a reality in H2-H2 ZSiNRs.(2)We have investigated the Al and P doping effects on the electronic structure of H-H ZSiNRs super cell using first principles calculations.It is found that doping Al or P atoms affects the localized edge states on the two sides differently,and depending on the doping sites,ZSiNRs can be tuned to be either semiconductors,metals,or nearly half-metals.By jointly applying electron(P)doping and hole(Al)doping at different parts/edges of the ribbon,we can directly control the electron occupation of specific edge states and half-metallicity can always be produced irrespective of the ribbon width.More importantly,the doping sites of the impurity atoms are not necessarily symmetrical but can also be random.