Annealing effect on the structural and optical properties of Co/TiO2 multilayer thin films prepared by e-beam evaporation

The Co/TiO2 multilayer thin films were prepared by e-beam evaporation on glass substrate. Each film was consisting of three alternative bilayer of Co and TiO2 and the top layer of the films were TiO2. Films were annealed in open air at different temperatures. The crystal structure, optical transmittance, absorption, absorption coefficient, optical band gap, and surface morphology were studied. It was observed that the average crystallite size of the annealed films is lower than that of the as deposited films and annealing samples exhibited higher transmittance compare to the as-deposited one. Absorption was maximum in the UV (300 nm) range and decreases continuously till 350 nm. From 350 nm to 800 nm, absorption was almost constant with increasing wavelength and the value is very small. Absorption and absorption coefficient decreased with annealed temperature increased. Optical band gap decreased with annealed temperature increased. Surface roughness of annealed films were higher than as deposited films.