Effects of rapid thermal annealing on structural, magnetic and optical properties of Ni-doped ZnO thin films

XPS depth profiles were used to investigate the effects of rapid thermal annealing under varying conditions on the structural, magnetic and optical properties of Ni-doped ZnO thin films. Oxidization of metallic Ni from its metallic state to two-valence oxidation state occurred in the film annealed in air at 600 C, while reduction of Ni2þ from its two-valence oxidation state to metallic state occurred in the film annealed in Ar at 600 and 800 C. In addition, there appeared to be significant diffusion of Ni from the bottom to the top surface of the film during annealing in Ar at 800 C. Both as-deposited and annealed thin films displayed obvious room temperature ferromagnetism (RTFM) which was frommetallic Ni, Ni2þ or both with two distinct mechanisms. Furthermore, a significant improvement in saturation magnetization (Ms) in the films was observed after annealing in air (Ms1⁄4 0.036 mB/Ni) or Ar (Ms1⁄4 0.033 mB/Ni) at 600 C compared to that in as-deposited film (Ms1⁄4 0.017 mB/Ni). An even higherMs value was observed in the film annealed in Ar at 800 C (Ms1⁄4 0.055 mB/Ni) compared to that at 600 C mainly due to the diffusion of Ni. The ultraviolet emission of the Ni-doped ZnO thin film was restored during annealing in Ar at 800 C, which was also attributed to the diffusion of Ni. 2011 Elsevier B.V. All rights reserved.