Size effects on formation energies and electronic structures of oxygen and zinc vacancies in ZnO nanowires: A first-principles study

We investigated the energetic, structural, and electronic properties of neutral O and Zn vacancies in ZnO nanowires with different sizes based on the first-principles calculations using density functional theory. We found that for ZnO nanowire with an O vacancy on the surface the formation energy is not sensitive to the size change. The presence of the surface O vacancy results in the formation of the metal-metal bonds. From the band structure analysis, we predicted that the optical property relating to the O vacancy can be strongly altered with decreasing the nanowire diameter. Moreover, there is a large structural deformation on the surface in the presence of Zn vacancy. The formation of a Zn vacancy in the ZnO nanowire with diameter of 16.4 Å is more favorable than in those with smaller diameters. Furthermore, the O vacancy is nonmagnetic, whereas the Zn vacancy is spin-polarized with a magnetic moment of 2.0 μB on the surface. Our results are helpful for understanding these defects in ZnO nanowires and thus useful for nanodevice design.