Surface modification nanoporous titanium oxide films using continuous wave CO₂ laser

This study investigated the characteristics of titanium dioxide (TiO₂) films modified through laser annealing by using a CO₂ laser source (CSS 500 AIR, Spectral Inc., Italy) with a wavelength of 10,600 nm and a continuous wave mode. Commercial TiO₂ thin films with a thickness of 100 nm were prepared through radio-frequency magnetron sputtering on soda-lime glass substrates. The optical properties (optical absorption and transmittance spectra), surface morphology, and surface chemical composition characteristics of the TiO₂ films depended on the laser irradiation conditions. The characteristics of the films were systematically analyzed using a ultraviolet–visible near-infrared spectrophotometer, an X-ray photoelectron spectroscope, and a field emission scanning electron microscope. The experimental results demonstrated that the experimental transmittance spectra exhibited slight changes caused by laser annealing and a maximum transmittance in the visible region of approximately 91.4 %. The absorbance of all annealed TiO₂ films exceeded that of as-deposited films. Moreover, the absorption band edge moved toward the long-wavelength side (red shift) as the annealing speed decreased because the heat applied during annealing caused the TiO₂ film grains to grow. Diffusion and mobility between the films and glass substrates during laser annealing segregated elemental Ag.