Structural and optical properties of dysprosium oxide thin films

Thin films of dysprosium oxide were deposited by thermal evaporation using two techniques. In the first technique, dysprosium was reactively evaporated in an oxygen atmosphere. In the second technique, dysprosium thin films were evaporated in vacuum and then annealed in air in the 200-800 °C temperature range; where the oxide films were obtained upon annealing at 400 °C or higher. Structural and morphological analyses were employed to assess the quality of the films. The oxide films were polycrystalline, with surfaces that were characterized by columnar growth. The dispersion relations for the refractive index and the extinction coefficient were determined using the spectrophotometric technique. The oxide films were highly transparent, and possessed optical properties that showed significant variation with the preparation conditions. The refractive indices increased with annealing up 600 °C, but decreased when the films were annealed at 800 °C. The direct and indirect band gaps were determined, and both showed a significant reduction as a result of annealing.