Swift heavy ion induced electronic structure modifications in ZnO thin films: X-ray absorption spectroscopy study

Abstract

ZnO is a potential material for electronic device applications due to its versatile semiconducting properties with a direct band gap of 3.3 eV. This research represents a modification in the electronic structure of ZnO thin films (350 nm) irradiated with swift heavy ions (SHI) at different fluences. ZnO thin films were grown on a silicon substrate (100) using radio-frequency magnetron sputtering, which are highly oriented in a single phase/plane (002). The deposited thin films were subjected to SHI of 100 MeV O-ion with fluence of 3x1012 ions cm-2, 45 MeV Li-ion beams with fluence of 3x1012 ions cm-2 and 120 MeV Au-ion with varying fluence from 1x1011 to 5x1012 ions cm-2. SRIM/TRIM software was utilized to study theoretical effects of SHI like ion ranges, phonon energy, etc. Modifications in the structure and the electrical properties of ZnO thin films were investigated using high-resolution X-ray diffraction (HRXRD), Atomic Force Microscopy and Near Edge X-ray Absorption Fine Structure (NEXAFS) spectroscopy at the O K- and Zn L 3,2 -edges. HRXRD employed for the structure, crystallinity, and phase of the system whereas NEXAFS for the local atom bonding symmetry via the molecular orbital hybridization between Zn and O. Furthermore, Density Functional Theory based on first principles FEFF9.6 has been incorporated for better understanding of NEXAFS while discussing the various parameters and cards. Simulations were performed to support the NEXAFS experimental data for the determination of various physical entities and their interpretations for diverse applications. NEXAFS measurements provide a deeper understanding of the effects of SHI for promising applications through the controlled fluence rate of ion beam irradiations.