Madhavi Thakurdesai

Substrate dependence in the formation of TiO2 nanophases by dense electronic excitation

Irradiation by swift heavy ion (SHI) is an excellent tool for the nanostructuring of thin films. During SHI irradiation, the energy of the projectile is transferred to the target mainly via electronic energy loss (Se). If the value of Se is more than a threshold value Seth, then latent tracks are formed in the target and a large amount of deposited energy gets confined in narrow dimensions. This leads the system to a non-equilibrium state and it then relaxes dynamically by inducing nucleation of nanocrystallites along the latent tracks. In the present investigation, amorphous thin films of TiO2 are deposited on substrates of fused silica and that of single crystal sapphire. The films are then irradiated by a 100 MeV Au ion beam. Atomic force microscopy is employed for the surface study. The structural phase change induced by SHI irradiation is identified by glancing angle x-ray diffraction. Optical characterization is carried out by UV?vis absorption spectroscopy. Defects created during irradiation are studied by electron spin resonance spectroscopy studies. The role of a substrate in the SHI-induced nanocrystallization process is studied.

Study of Swift Heavy Ion Irradiation Induced Nanophases of TiO2

Ion beam irradiation is a unique non-equilibrium technique for phase formation and material modification. Localized rise in temperature and ultra fast (~1012 s) dissipations of impinging energy make it an attractive tool for nanostructure synthesize. Dense electronic excitation induced spatial and temporal confinement of high energy in a narrow dimension leads the system to a highly non-equilibrium state and the system then relaxes dynamically inducing nucleation of nanocrystals along the latent track. In the present investigation, amorphous thin films of TiO2 are irradiated by 100 MeV Ag ion beam. These irradiated thin films are characterized by Atomic Force Microscopy (AFM), Glancing Angle X-ray Diffraction (GAXRD), Transmission Electron Microscopy (TEM) and UV-VIS absorption spectroscopy. AFM and TEM studies indicate formation of circular nanoparticles of size 10±2 nm in a film irradiated at a fluence of 1×1012 ions.cm-2. Nanophase formation is also inferred from the blueshift observed in UV-VIS absorption band edge.