Impact of ion beam irradiation on optical and structural properties of nanocomposite ZnO thin films

Pristine ZnO and nanocomposite ZnO–TiO2 thin films were synthesized using the sol–gel spin-coating method on glass substrates. The thin films of ZnO and ZnO–TiO2 so obtained were calcined at 500°C in order to eliminate the volatile materials and to enhance their crystallinity. The ZnO and ZnO–TiO2 thin films were characterized by UV-Vis spectroscopy, XRD, Raman, FESEM, and FTIR for optical and structural properties. After characterization, the films were irradiated with a beam of 100 MeV Ag7+ ions at a fluence of 2 × 1013 ions/cm2. Both ZnO and nanocomposite ZnO–TiO2 thin films were again characterized after irradiation, and the data was analysed. The XRD results substantiated the preparation of ZnO–TiO2 thin films with peaks corresponding to both wurtzite ZnO and anatase TiO2, thereby verifying the synthesis of nanocomposites. Raman spectra revealed the presence of Raman-active modes at 332 and 438 cm−1, which occur due to optical phonons of ZnO in the synthesized films. The crystallite size was observed to decrease from 22.70 nm to 20.45 nm with TiO2 doping and from 22.7 nm to 16.90 nm for ZnO and 20.45 nm to 13.32 nm for ZnO–TiO2 films on ion beam irradiation. FESEM micrographs reveal a decrease in grain size with both doping and irradiation. The UV–Vis results showed a shift toward the red end of the absorption spectra and consequently the decrease in band gap from 3.32 eV to 3.24 eV and 3.20 eV to 3.14 eV for the ZnO film and the ZnO–TiO2 film, respectively, after the samples were exposed to 100 MeV Ag7+ ion beam at a fluence of 2 × 1013 ions/cm2.