ICMCTF 2025 Session KYL-MoKYL: Keynote Lecture I

Plasmonic catalysis enabled by visible light is vital to enhancing the activity of surfaces in promoting a broad range of chemical reactions including water splitting and associated production of bioactive reactive oxygen species.However standard catalysts that rely on nanoparticles are not sufficiently robust for deployment in the environment.Transition metal nitrides are promising candidates whose function is highly dependent on their purity and structure.High-Power Impulse Magnetron Sputtering has been deployed to tailor the texture and morphology of nanoscale multilayer TiN / NbN coatings and evaluate the effect of their plasmonic activity.Plasma characterisation show a significant fractions of dissociated nitrogen and double-charged metal ions in both TiN and NbN deposition conditions.Time-resolved ion energy distribution functions obtained from energy-resolved mass spectroscopy indicate that 30% of dissociated nitrogen possesses a high-energy tail and originates from sputtering from the target surface alongside Ti and Nb thereby increasing adatom mobility and intergranular density and promoting a strong (200) fibre texture as observed in pole figures.Nevertheless oxidation of the surface detected through XPS deteriorated the plasmonic performance of the films as observed through ellipsometry.Pump-probe laser measurements showed significant increases in the lifetime of active electron species in the films due to trapping of hot carriers in oxygen vacancies such as Nb³⁺ and Ti³⁺., with Nb being more sensitive due to a higher enthalpy of its oxide. Nanoscale multilayer films deposited with small bi-layer thickness of 1.7 nm exhibited strong intermixing between the TiN and NbN layers which led to small grain size observed by AFM and longer hot carrier lifetime.Bilayer thickness of 2.4 and 3.5 nm led to doubling of the grain size and shorter hot carrier lifetimes.A graded structure, starting from a bilayer thickness of 2.4 and reducing to 1.7 nm exhibited a large grain size and increased hardness and toughness as determined from nanoindentation. Ellipsometric measurements of the real component of the dielectric permittivity confirmed an excellent plasmonic activity.The effects of carrier lifetime on photocatalytic activity are discussed.The results pave the way to using nanosale multilayer coatings for catalysis.