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

Abstract

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.