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 angstrom 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 mu(B) on the surface. Our results are helpful for understanding these defects in ZnO nanowires and thus useful for nanodevice design. (c) 2011 American Institute of Physics. [doi:10.1063/1.3549131]