Effects of atomic defects of α-Al2O3(0001) on ZnO adsorption

The Al and O atomic vacancies on α-Al2O3(0001) surface an d the adsorption o f ZnO are calculated theoretically by using a plane wave ultrasoft pseudo-potent ial method based on density functional theory. The electron localization functio n(ELF) shows the electronic density changes at the atomic vacancies. There is an obvious absence of electronic areas where the vacancies of Al have the dangling bonds of oxygen, which are favourable for the adsorption of Zn atoms. In contra st, at the vacancies of O, there are more electron distribution(ELF:005—03) , forming lone electron pairs which are profitably available to combine O atoms or O2- ions. Through the dynamics calculation, we find that surface d efect s can significantly strengthen particle adsorption, and the vacancies are filled by adatoms(Al or O), with the adsorption energy much higher than the case of th e adsorption on a perfect surface. The surface Al-vacancies where the ZnO adsorp tion clearly breaks the hexagonal symmetry of oxygen on the α-Al2O3(0001) s urface because of the formation of the O double bonds, which apparently weakens the reaction diffusivity of O, and has a further negative impact on the regular ZnO films formation. Accordingly, more defects and dislocations in films growth might be produced. Contrarily, the O-vacancies on the α-Al2O3(0001) surface , the chemisorption and dissociation of ZnO do not have an effect on the surface hexagonal symmetry.