Stoichiometry-Led Electronic Structure Reconstruction Finetunes the Color Characteristics of Titanium Nitride Thin Films

Abstract

Atomic-vapor-deposited nitride thin films attract considerable interest as decorative coatings in various industrial applications. Recent research efforts in the process-structure relationship for such films have converged on the need to develop electronic characteristics-led design principles. Here, we varied substrate-temperature (180, 450 °C) for deposition of titanium nitride (TiN x ) thin films in a rocksalt structure with varying stoichiometry (x: 0.98−0.87). Reciprocity of the varying color characteristics of the deposited TiN x thin films was studied against their structural and electronic details by employing combined methods of experiments and simulations. The long-range and local structural order of the thin films were studied using grazing incidence X-ray diffraction analysis and Ti K-edge extended X-ray absorption fine structure spectroscopy (EXAFS), respectively. N K-edge X-ray absorption near-edge spectroscopy (XANES) and simulation of the spectrum using Green formalism (multiple scattering) delineated electronic reconstruction occurring during the atomic-level structural changes. In a key finding, no change in the density of states (DOS) was observed in the simulation carried out on a single NTi 6 octahedra extracted from the long-range structure of TiN x thin films. The axial compression of the octahedra under varying stoichiometry did not cause significant change electronically and therefore did not contribute to the varying color characteristics. Long-range structural characteristics led by substoichiometry of the TiN x thin films induced electron localization near the conduction band edge. Small change produced in the band gap thus tuned the color characteristics of the thin films.