Optical Properties of ZnFe₂O₄-SiO₂ Granular Films Prepared by rf Magnetron Sputtering

We report on the optical properties of ZnFe₂O₄-SiO₂ granular films prepared on quartz substrates by the radio frequency magnetron sputtering method. Post-annealing was performed at different temperatures under flow oxygen atmosphere. The morphology and structures of ZnFe₂O₄ nanoparticles were characterized by x-ray diffraction, transmission electron microscopy, and optical absorption spectra. It has been found that there are two different line types in the optical absorption curves of ZnFe₂O₄-SiO₂ granular films. The critical transition of line types occurs when ZnFe₂O₄ changes from amorphous to crystalline, and the transition temperature increases with increasing content of ZnFe₂O₄. There is an obvious blueshift of the optical absorption edge of the granular films with the decreasing annealing temperature.