Theoretical Studies On The Structure And Properties Of Thin Film Influenced By Substrate

In this thesis,by using the first principles calculation methods,we have studied a postgrowth aging mechanism of Bi2Te3(111)films,((?)×(?))stanene growth on Bi(111)surface,the intrinsic interaction between in-plane ferroelectric polarization and surface adsorption.The main conclusions are listed in the following.1.We report a postgrowth aging mechanism of Bi2Te3(111)films.We studied the Bi and Te adatoms(intercalated atoms)on the Bi2Te3(111)surface and vdW gap,as well as the influence of substrate on the stability of BiTe monolayer.The formation of a defective Te atom is less favorable in the vdW gap than on the surface.In comparison,the formation of defective Bi atom is much easier in the gap than on the surface.The diffusion barriers of both Bi and Te atoms in the vdW gap as same as on the surface.We demonstrate a BiTe aging effect on the Bi2Te3(111)surface.The monolayer is unstable against the formation of domains.Considering the common nature of weak bonding between vdW layers,we expect such unusual diffusion and aggregation of the intercalated atoms may be of general importance for most kinds of vdW layered materials.2.We demonstrate an efficient way of tuning the atomic buckling in stanene to open a topologically nontrivial energy gap.The((?)×(?))stanene is more stable than the(1×1)structure on Bi(111)surface.It is interesting to note that the((?)×(?))stanene favors large band inversion at the Γ point,and the spin orbital coupling opens a energy gap,by 0.1 eV.The existence of edge states suggest the topology of the((?)×(?))stanene.This study provides an alternative way to tune the topology of stanene.3.We studied the effect of the ferroelectric polarization on the adsorption of molecules.When the polarization direction is perpendicular to the surface,the depolarization field may induce surface reconstruction and thus change the chemistry of the ferroelectric surface.In contrast,the polarization paralleling to the surface results into neither electronic nor atomic reconstruction on the surface.Therefore the influence of the ferroelectricity on the surface properties can be intrinsically reflected by the interplay between the in-plane polarization and the surface adsorption.In this work,by using first-principles calculations,we studied the effect of the strain-induced in-plane polarization on the adsorption of a series of molecules in both molecular and dissociative states on the reduced rutile TiO2(110)surface.We revealed that it is the surface doping caused by the charge transfer between the adsorbates and the surface that dominates the polarization-induced change of the adsorption energy.