Tunable Titanium and Tantalum oxide coatings as highly efficient antibacterial agents

This study evaluates the bactericidal efficacy of non-stoichiometric titanium oxide (TiO<inf>x</inf>) and tantalum oxide (Ta<inf>x</inf>O<inf>y</inf>) thin films, synthesized through radio frequency (RF) magnetron sputtering under varying process conditions. Structural and chemical analyses reveal that TiO<inf>x</inf> films undergo a transformation from an amorphous to an anatase crystalline structure when oxygen is incorporated and/or when subsequently heat-treated at 823 K. In contrast, Ta<inf>x</inf>O<inf>y</inf> films retain their amorphous structure regardless of the oxygen content during deposition. However, annealing Ta<inf>x</inf>O<inf>y</inf> films at 1073 K leads to the formation of β-Ta<inf>x</inf>O<inf>y</inf> phases. Despite variations in film thickness, both oxide films exhibit high optical transmittance (∼80 %), making them suitable for aesthetic coatings. These films are tested for bactericidal activity against two bacterial strains, Escherichia coli (Gram-negative) and Staphylococcus aureus (Gram-positive), to assess their effectiveness against different bacterial cell wall types. Here, among these fabricated TiO<inf>x</inf> and Ta<inf>x</inf>O<inf>y</inf> films, the amorphous, non-stoichiometric Ta<inf>x</inf>O<inf>y</inf> films (with a cation-to-anion ratio of 1:2.3) outperform previous reports, achieving a 17.0 % survival rate against E. coli. However, both oxide films demonstrate significant bacterial survival against S. aureus (as low as ∼ 35 % for TiO<inf>x</inf> thin film). The comparable wettability and surface roughness across all films further indicate that intrinsic material properties, such as ion release, are likely responsible for the observed enhancement in bactericidal efficacy.