UV-Vis Spectroscopic and NEXAFS Studies of Polycrystalline Zinc Ferrite Films

In this study, zinc ferrite films with thicknesses about 270nm are deposited using radio frequency sputtering method on fused quartz substrates under a base pressure of 5x10(-6)Torr and an oxygen pressure of 40mTorr during deposition. Films are annealed at 200, 400, and 600 degrees C for 1h. X-ray diffraction studies envisage the polycrystalline nature of as-grown film. With the increase of annealing temperature, the crystallinity of these films improves. The optical band-gap of these films increases with the increase of annealing temperature. Fe L-edge and Zn L-edge near-edge X-ray absorption fine-structure (NEXAFS) measurements envisage that Fe and Zn ions remain in 3+ and 2+ state, respectively, in the deep of these films, however, the valence state of Fe ions at the surface of these films is modified. O K-edge NEXAFS measurements reveal the improvement of metal-oxygen hybridized states. Therefore, it can be proposed that the optical band-gap of these films is influenced by the improved crystallization and metal-oxygen hybridization with annealing temperature.