Transformation of TiN to TiNO films via In-situ Temperature-dependent Oxygen Diffusion Process and their Electrochemical Behavior

Titanium oxynitride (TiNO) thin films have attracted a lot of attention as a material system that is beneficial for a wide range of applications including, energy storage devices, solar cells, sensors, durable protective coatings, and electrocatalysis. This study reports the synthesis of TiNO thin films with controlled variation of the oxygen levels followed by a detailed structural investigation using X-ray diffraction (XRD), X-ray reflectivity (XRR), X-ray photon spectroscopy (XPS), X-ray absorption spectroscopy (XAS), and Non-Rutherford backscattering spectrometry (N-RBS). These characterization methods allowed detailed analysis that identified phase, composition, and crystallinity of the films. Structural control was established through temperature dependent oxygen in-diffusion and nitrogen out-diffusion processes and adatom mobility associated nucleation growth processes. Our XPS analysis made it clear that the TiNO films are heterogeneous mixtures of TiN, TiNO, and TiO2 phases. We were able to examine correlations between the structure and electrochemical behavior of the films. Through these observations we noticed that the TiNO films with relatively higher N/O ratio, meaning less oxidized, were more electrochemically active than the films with lower N/O ratio (i.e. TiN films with more oxidized phase). The more oxidized films exhibited an increase in crystallinity and improved stability during electrochemical polarization. These findings underscore the significance of substrate temperature control in tailoring the properties of TiNO film, which is a fundamental part of designing and optimizing an efficient electrode material.