Control of Oxidation during the Self-Assembling Process in Nitride-Based Nanocomposite Films

Nitride-based vertically aligned nanocomposites (VANs), including both nitride-metal and nitride-oxide VAN systems, have demonstrated unique vertical structures with multifunctionalities, such as enhanced second harmonic generation, plasmonic resonance, hyperbolic optical response, magnetic anisotropy, and magneto-optical coupling. However, the control on the growth of the nitride-metal and nitride-oxide VANs is challenging due to the potential oxidation issues during the cogrowth of nitrides and metals. In this work, the oxidation behavior of TiN–Cu nanocomposite thin films was investigated by introducing different oxygen partial pressures during the pulsed laser deposition (PLD) process to underpin the fundamental oxidation process and the phase/morphology tuning. Precise control of the oxygen partial pressure enabled tunable stoichiometry and phase compositions within the film, transitioning from metallic TiN and Cu phases to their oxidized phases, TiOxN and CuO. Our results reveal that the oxidation process initiated in the Cu phase before the TiN phase. This sequential oxidation behavior leads to gradual changes in the overall film morphology and thus tailorable optical properties, from metallic to dielectric behavior, as confirmed by spectroscopic ellipsometry and UV–vis spectrometry measurements. The incorporation of CuO aids in controlling the oxidation process of TiN and enables significant modulation of the optical properties, with potential applications in electrochemical catalysis, water splitting, and others.