Computational and experimental approach for investigation of epsilon-near-zero response in nitrogenated TiO2

Abstract

This study presents simulation and experimental investigations on electronic and optical properties of titanium oxynitride. The computational studies were performed using the full potential-linearized augmented plane wave method (FP-LAPW) based on density-functional-theory (DFT) with the generalized gradient approximation on WIEN2k software. From the DFT simulations, electronic and optical properties such as band structure, density of states, refraction, extinction coefficient, absorption coefficient, epsilon, optical conductivity and reflectivity were extracted. Furthermore, titanium oxynitride thin films were fabricated using reactive magnetron sputtering. The films were grown using bottom-up approach under varying pressure ratios of oxygen and nitrogen gases working in the background vacuum. Various parameters such as thin films thickness and substrate temperature were changed with the target of achieving near-zero-epsilon behavior. X-ray diffraction and scanning electron microscopy were carried out to investigate the crystallinity, phases, and surface morphology of these films. Spectroscopic ellipsometry was employed to extract the various optical parameters specifically the epsilon-near-zero response of the thin films. This phenomenon is attributed to the mixture of phases. The composition dependence of the parameters observed in the grown films is in close agreement with what is predicted by the ab-initio calculations.