Mechanical durability, optoelectronic properties and structure tuning of RF sputtered NiO thin films– effect of pressure, temperature, power and bias

The evolution of the nanostructure, surface quality, tribo-mechanical, and optoelectrical properties of nickel oxide (NiO) thin films was systematically investigated to unlock their potential for advanced applications. The films were deposited by RF magnetron sputtering under a wide range of technologically relevant conditions, including process pressure, temperature, power and substrate bias. The XRD analysis confirmed a polycrystalline structure, with a tunable preferential orientation from (111) to (200) or (220). A positive correlation between grain size and surface roughness was established via SEM and 3D laser scanning microscopy. Bandgap values, determined through spectroscopic ellipsometry, could be tuned from 3.6 to 3.9 eV. Nanoindentation revealed a film hardness ranging from 3 to 12 GPa, governed largely by deposition pressure and substrate bias. Scratch resistance and film failure mode were strongly dependent on the technological properties and could be easily investigated by AE signals analysis during scratch testing. This study provides a comprehensive examination of the tribo-mechanical behaviour of thin films, offering detailed insights into their durability and functional performance, an aspect often underexplored in similar research.