Excimer-Laser Induced Structural Transformations of TiO2 Thin Films

Thin films of TiO2 are deposited by magnetron sputtering on glass substrate and are irradiated by UV radiation using a KrF excimer laser (? = 248 nm). The present works deals with the ablation regime. In order to characterize the structural transformations occurring in the process, the morphology of the films are studied as a function of the laser fluence (F), by means of profilometry and atomic force microscopy (AFM). As deposited films are measured to be amorphous. After one pulse, when the laser fluence, F, is varied, various regimes are observed. We show thanks to this process, it is possible to remove a layer in a predefined thickness by choosing F. More over, we observe a linear dependence of the ablated depth with F. It is shown that the morphology of the surfaces depends strongly of F, as evidenced from AFM images, roughness measurements and the fractal dimension. In order to interpret these results, temperature evaluations are performed. The ablation rate may not be explained by purely thermal effects. It is argued that electronic effects play a major role in excimer-laser induced structural transformations of TiO2 thin films.