Structural and optical modifications of RF-sputtered ZnO thin films using low energy Ar ion irradiation

In the present work, the structural and optical properties of the pristine and argon (Ar) ion irradiated RF-sputtered ZnO thin films have been studied using X-ray diffraction (XRD), UV–visible spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). The ion irradiation was performed at a constant fluence of 5 × 1015 ions/cm2, and the incident ion energy was varied from 300 keV to 1 MeV. The XRD pattern of the pristine ZnO film shows amorphous-like behavior, whereas ion irradiated films exhibit the evolution of hexagonal wurtzite structure along c-axis (002) orientation at higher energies. The crystallinity of the films was found to improve with the ion irradiation at increased energy, and the crystallite size varies from 5.4 to 23.0 nm. The surface features of the pristine and ion irradiated films were recorded by SEM and AFM both. The 3 D images show growth of cone-like structure with enhanced energy-dependent ion irradiation. However, beyond 800 keV, dissolution of grains was noticed. With UV–visible spectroscopy, the transparency of the films was noticed to decrease with increasing the incident ion energy, and the optical band gap as measured using Tauc plots was found to vary from 3.31 to 3.26 eV. With chosen incident ion energies, viz. 300 keV, 550 keV, 800 keV, and 1 MeV, the ratio of the electronic to nuclear energy loss (Se/Sn) takes the value of 1, 2, 3, and 4 as deduced using SRIM Monte-Carlo simulation program and, and this provides us a probe to verify the synergistic effect of ion irradiation in tailoring the properties of ZnO. The ion-induced tunability of the structural and optical properties in such oxide films facilitates the wide range of applications mainly the piezoelectric transduction mechanism and fabrication of optoelectronics devices.