High-energy 120 MeV Au9+ ion beam-induced modifications and evaluation of craters in surface morphology of SnO2 and TiO2 nanocomposite thin films

Abstract

The electronic excitation and modification in the properties of the target material occur due to the kinetic energy loss of incident ions mainly through the inelastic collision with atomic electrons in the process of electronic energy stopping. Nanocomposite tin oxide (SnO2) and titanium dioxide (TiO2) thin film were grown on silicon and ITO substrates using RF magnetron-sputtering process. These thin films were irradiated by 120 MeV Au9+ Swift Heavy Ion (SHI) beam with varying fluence from 5 × 1011 ions cm−2 to 2 × 1013 ions cm−2 to induce modifications in thin films by dense electronic excitation. Surface morphology and depth profile of craters (approx. 85 nm) have been characterized by multimode atomic force microscopy (AFM). Grain mapping of AFM images provided the variation in grain size in the range of 72–279 nm and RMS roughness increased (4.01–23.6 nm) with increasing the ion fluence. Scanning Electron Microscopy (SEM) was also carried out to confirm the formation of craters in the irradiated film. X-ray diffraction (XRD) technique has been used for the structural analysis of virgin and irradiated thin films. XRD patterns established the formation of film in mixed (rutile and gamma) phase. Further, the crystallite size was evaluated using the Debye–Scherrer and Williamson–Hall method. It was found that crystallite size lie in the range of 36–54 nm which increased for the lower fluence and then decreased for higher fluence. The ion irradiation-induced strain has been explained by Thermal spike and Coulomb explosion model. UV–Vis study showed that the optical band gap reduced from 3.87 to 3.72 eV with increasing the ion fluence which can be ascribed to the formation of intermediate states and free radicals between the valance and band conduction band. Rutherford Backscattering Spectrometry (RBS) ensured that the film thickness decreased from 210 to 183 nm with increasing the ion fluence. The simulation of the RBS spectra provides the elemental composition of Sn (0.37), Ti (0.65) and O (0.85) in SnO2 and TiO2 nanocomposite thin films.