Raman study of ion beam irradiation damage on nanostructured TiO2 thin film

90 MeV Xe and 25.78 MeV Cu ion irradiation effect on nanostructured anatase TiO2 thin film, prepared by sol-gel method, was investigated by Raman spectroscopy. The nonirradiated films show five Raman modes corresponding to the anatase phase. Raman spectra of irradiated films reveal crystalline-amorphous phase transition, fact evidenced by a progressive vanishing of Raman peaks correlated by emergence of a novel broad band at higher fluence, attributed to the amorphous structure. The broadening and blue shift of Raman peaks after irradiation indicate the generation of non-stoichiometric oxygen deficiency caused eventually by a preferential sputtering upon irradiation. A compressive stress was thus developed in the lattice which leads to the shortening of Ti-O bonds and the reduction of the crystallinity. The strain calculations reveal a correlation between the amorphization process and lattice strain enhancement. At higher fluence, the relaxation of the compressive stress may occur and results in volume expansion and hillocks formation. The strain and disorder calculations indicate that Xe irradiated films are completely amorphous, whereas, the anatase phase may still be present in Cu irradiated films. This behavior is explained by the difference in the electronic stopping power, which is manifested also in the disorder damage cross section. This latter is similar to that obtained by strain calculations and previously by XRD analysis.