The present study probes into the transition from anatase to rutile phase of TiO2 in 100 nm thick nanocrystalline thin films under thermal annealing and swift heavy ion (SHI) irradiation. The films were prepared using sol-gel and spin coating techniques on silicon (100) substrates. The as-deposited films are found to be amorphous by glancing angle x-ray diffraction and Raman spectroscopy. Though thermal annealing is known to cause transformation from anatase to rutile phase of TiO2 in a temperature interval of 700–900 °C, in nanoparticle thin films, we found that a sizable volume fraction of anatase still remains even after annealing at 1000 °C. Irradiations by 200 MeV Ag ions on the other hand suppressed the anatase phase and almost phase pure rutile TiO2 could be obtained at a fluence of 3×1012 ions cm−2. A mechanism based on the competing effect of grain growth and conversion of anatase to rutile at the grain boundary of the anatase on annealing and conversion of anatase to rutile in the grains of the anatase due to SHI induced thermal spike is proposed to explain the observed result.

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Sensitivity of the anatase and rutile phases of titanium dioxide to Swift Heavy Ion (SHI) irradiation was experimentally probed and compared with the predictions of the Coulomb explosion, analytical and inelastic thermal spike models of ion-matter interaction. Conforming to the predictions of all these models, our study indicated higher sensitivity of anatase to these ions than the rutile phase. A detailed examination however revealed that Coulomb explosion model cannot explain either the nature of variation of the interaction cross section of SHI with the energy deposited by these ions, Se to the target electrons, or the relative values of the threshold electronic energy loss, Seth of anatase and rutile. The analytical thermal spike (a-TS) model, using the available physicochemical data for this oxide, predicted that tracks cannot form either in anatase or in rutile by 297 MeV and 511 MeV Ni ions, while inelastic thermal spike (i-TS) model predicted formation of ion tracks by 297 MeV Ni ions and their absence with 511 MeV Ni ions in both anatase and rutile. Our observation agreed with the predictions of i-TS model albeit with a difference in the radius of the tracks. In addition, we observed halo of defect ridden crystalline region of much larger radius around the ion track. Interestingly, the radius of the halo scales with the velocity of the ions, which is opposite to the conventionally observed velocity effect.

Nanostructured TiO 2 thin films have been prepared through chemical route using sol-gel and spin coating techniques. The deposited films were annealed in the temperature range 400-1000°C for 1 h. The structure and microstructure of the annealed films were characterized by GAXRD, micro-Raman spectroscopy and AFM. The as-deposited TiO 2 thin films are found to be amorphous. Micro-Raman and GAXRD results confirm the presence of the anatase phase and absence of the rutile phase for films annealed up to 700°C. The diffraction pattern of the film annealed at 800 to 1000°C contains peaks of both anatase and rutile reflections. The intensity of all peaks in micro-Raman and GAXRD patterns increased and their width (FWHM) decreased with increasing annealing temperature, demonstrating the improvement in the crystallinity of the annealed films. Phase transformation at higher annealing temperature involves a competition among three events such as : grain growth of anatase phase, conversion of anatase to rutile and grain growth of rutile phase. AFM image of the asdeposited films and annealed films indicated exponential grain growth at higher temperature.