Electronic structures of a Zn vacancy on the ZnO(10(1)over-bar-0) surface: Density functional theory calculations

Abstract

We perform spin-polarized density functional theory calculations for a Zn vacancy on the ZnO(100) surface. Two stable configurations of the surface Zn vacancy are found, and the activation energy barrier is estimated to be similar to 0.01 eV. The lower energy configuration has a newly formed surface Zn-O bond to restore the bulk-like structure on the surface. Due to the newly formed bond, the vacancy state in the band gap is characterized by a complicated hybridization of neighboring surface and subsurface atoms and by a more extended electron density. Despite such a hybridization, the surface Zn vacancy is found to have a robust magnetic moment of 1 mu (B) , implying that surface Zn vacancies may be responsible for the ferromagnetism observed in ZnO thin films and nanoparticles. Simulated scanning tunneling microscope images show that the two structures of the surface Zn vacancy can be distinguished in the filled-state images.