700 keV Ni+2 ions induced modification in structural, surface, magneto-optic and optical properties of ZnO thin films

Abstract

We investigate the effect of 700keV Ni+2 ions irradiation at different ion fluences (1×1013, 1×1014, 2×1014, 5×1014ions/cm2) on the structural, surface, magneto-optic and optical properties of ZnO thin films. The X-ray diffraction (XRD) results show improved crystallinity when ion fluence is increased to 2×1014ions/cm2, while deterioration is observed at the highest ion fluence of 5×1014ions/cm2. Scanning electron micrographs (SEM) show the formation of small grains at ion fluence 1×1013ions/cm2, micro-rods at fluences 1×1014 and 2×1014ions/cm2 and ultimate fracturing of thin film surface at ion fluence 5×1014ions/cm2. Faraday rotation measurements are also performed and show a decrease in Verdet constant from 53 to 31rad/(T-m) when irradiated at 1×1013ions/cm2, increasing up to 45rad/(T-m) at 2×1014ions/cm2, and then decreasing again to 36rad/(T-m) at 5×1014ions/cm2. The optical band gap energy of the films is determined using spectroscopic ellipsometry, which shows an increase in optical band gap energy (Eg) from 3.04eV to 3.19eV when the fluence increases to 2×1014ions/cm2 and a decrease to 3eV at fluence 5×1014ions/cm2. We argue that these properties can be explained using ion heating effect of thin films.