Formation of metallic/oxide composites of Sn from SnO2 thin films with swift heavy ion irradiation

The present work reports the effects of 120 MeV Au9+ on structural and electronic properties of polycrystalline SnO2 films of about 170 nm thickness prepared by spin-coating. 119Sn Mössbauer measurements are used to probe the electronic properties. The observed isomer-shift values clearly indicate Sn4+ for the pristine sample and its progressive reduction to Sn2+ and eventually to the metallic Sn state at higher fluence values. These observations are corroborated by x-ray diffraction, Raman, and x-ray photo-electron spectroscopy measurements. The x-ray diffraction measurements indicate the complete amorphization of the tin oxide phase, while the recrystallization of the metallic Sn phase with irradiation. The optical bandgap is observed to vary with ion beam irradiation. The observations indicate the possibility of tuning the electronic configuration of Sn in tin oxide thin films with swift heavy ion beam irradiation, and the results are explained in terms of the thermal-spike model of swift heavy ion irradiation.