Arunprabhu Arunachalam Sugumaran¹, Ethan Muir¹, Ryan Bower², Ming Fu², David Owen¹, Yashodhan Purandare¹, Papken Eh. Hovsepian¹, Peter Petrov², Rupert Oulton², Thomas J. Smith¹, Arutiun P. Ehiasarian^1
1Sheffield Hallam University, Sheffield, United Kingdom
²Imperial College London, London, United Kingdom
Durable antimicrobial surfaces are in high demand in hospitals and public spaces to reduce the transmission of infections and maintain the health of vulnerable patients and the general public. Standard antimicrobial materials work by eluting heavy metal ions, which are toxic to patients in high concentrations. Alternatively, those based on nanoscopic spikes of Si or Ti oxides, are activated by ultraviolet light to produce reactive oxygen species which are harmful to pathogens. Neither of these materials are hard wearing due to immiscibility of the coating matrix with elutants or the low hardness of the active oxides. Plasmonically active transition metal nitrides are promising candidates whose activity is influenced by their purity and structure. High-Power Impulse Magnetron Sputtering (HIPIMS) has been deployed to tailor the microstructure of nanoscale multilayer TiN / NbN coatings and evaluate the effect on their toughness, plasmonic activity and anti-microbial function. Plasma characterisation shows a significant fraction of atomic nitrogen and metal ions in both TiN and NbN deposition conditions. The native oxides on the coating surface analysed by XPS showed that the presence of Nb promoted significant increases in the lifetime of active hot electron species in the films. The bi-layer thickness in nanoscale multilayer films was used to tailor the toughness and hardness as determined from nanoindentation. Nanostructured films showed an excellent resistance to ultra-sonication and wear in pin-on-disk tests, surviving 40 m of dry sliding, and outperforming nano-patterned Si. The coatings required visible light activation to achieve moderate antimicrobial kill rate of ~ 1 log for Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa (P. aeruginosa) and Candida albicans (C. albicans). The antimicrobial efficiency was superior to benchmark coatings of TiCN, CrCN, TiOx and TiO_xN_y as well as patterned Si.