All electron full-potential linearized augmented plane wave plus local orbitals method was used to investigate the structural and electronic properties of polar (00•1) and non-polar (10•0) surfaces of ZnO in terms of the defect formation energy, charge density, and electronic band structure with the supercell-slab models. The calculations supported the size-dependent structural phase transformation of wurtzite lattice to graphite-like structure which was a result of the termination of hexagonal ZnO at the (00•1) basal plane, when the stacking of ZnO primitive cell along the hexagonal principle c-axis was less than 16 atomic layers of Zn and O atoms. This structural phase transformation was studied in terms of Coulomb energy, nature of the bond, energy due to macroscopic electric field in the [00•1] direction, and the surface to volume ratio for the smaller supercell-slab. It was shown that the size-dependent phase transformation was completely absent for surfaces with a non-basal plane termination, and the resulting structure was less stable. Similarly, elimination of this size-dependent graphite-like structural phase transformation also occurred on the creation of O-vacancy which was investigated in terms of Coulomb attraction at the surface. Furthermore, the defect formation energy at the (10•0)/(¯10•0) and (00•1)/(00•¯1) surfaces was correlated with the slab-like structures elongation in the hexagonal a- and c-axis. Electronic structure of the neutral O-vacancy at the (00•1)/(00•¯1) surfaces was calculated and the effect of charge transfer between the two sides of the polar surfaces (00•1)/(00•¯1) on the mixing of conduction band through the 4s orbitals of the surface Zn atoms was elaborated. An insulating band structure profile for the non-polar (10•0)/(¯10•0) surfaces and for the smaller polar (00•1)/(00•¯1) supercell-slab without O-vacancy was also considered. The results were expected to be useful for the tuning of the structural and electronic properties of the (00•1) and (10•0) ZnO nanosheets by varying their size.

First-Principles Investigation of the Size-Dependent Structural Stability and Electronic Properties of O-Vacancies at the ZnO Polar and Non-Polar Surfaces. Mun Wong, K., Alay-E-Abbas, S.M., Shaukat, A., Fang, Y., Lei, Y.: Journal of Applied Physics, 2013, 113[1], 014304