Development and characterisation of novel anti-bacterial S-phase based coatings

Highlights: • S-phase co-deposited with Ag/Cu by magnetron sputtering in mono- and multilayer. • The layer architecture and doping concentration of Ag and Cu were tunable. • Long-lasting antibacterial efficacy was achieved by SCu10 and SCu35 coatings. - Abstract: It is well-known that biologically active Ag/Cu ions are strong bactericides and silver or copper nanoparticles have been used in polymer-based antibacterial coatings. However, their poor durability has limited their use in tribological applications. This problem has been largely addressed recently by developing novel plasma co-alloying of austenitic stainless steel surfaces with both nitrogen and Ag/Cu to form wear resistant antibacterial S-phase. However, this technology is only applicable to austenitic stainless steel as the S-phase cannot be formed to other materials. In this study, S-phase based anti-bacterial coatings have been, for the first time, developed using magnetron sputtering through co-deposition of austenitic stainless steel with Ag/Cu to form hard S-phase doped with Ag, Cu or both in monolayer and multilayer structures. These coatings were fully characterised using multiple techniques such as SEM, TEM, XRD, GDOES and anti-bacterial tests. It has been found that it is possible to produce dense Ag and Cu doped S-phase layer with significant anti-bacterial efficacy. This was achieved while preserving the advantageous properties of the S-phase microstructure. As opposed to the popular diffusion based S-phase production such as plasma nitriding, this technology can also be applied on all kinds of surfaces, including low-cost steel surfaces, polymers and ceramics.