Cu oxidation mechanism on Cu-Zr(O)N coatings: Role on functional properties

Zirconium oxynitride (Zr(O)N) and Copper-Zirconium oxynitrides (Cu-Zr(O)N) were deposited by a DC reactive magnetron sputtering technique on stainless steel substrates. A duty cycle controller was used to obtain different oxygen contents in the developed films and a chemical activation procedure was carried out to obtain copper oxides. The samples were chemical and structurally characterized by SEM, EDS, XRD and XPS. Additional functional features were evaluated according to colour variation and inhibition halo tests. Zr(O)N and Cu-Zr(O)N surfaces showed a wide colour variation from golden to black tones, progressing through intermediate tones such as purple, blue and ‘bluish’ grey. An antibacterial effect was only obtained after the chemical activation of Cu-ZrON-DC100, which showed a Zr(O)N matrix incapable of catching more oxygen from deposition. After, with the additional availability of O2− ions, the Cu present in the coating reacted with these ions forming CuO. The antibacterial mechanism was associated with the aforementioned characterizations and ICP-OES spectroscopy. The Cu2+ ions release had no influence on the antibacterial effect although the presence of CuO was decisive in obtaining an antibacterial behaviour. The acquired results demonstrated a potential multifunctionality of Cu-Zr(O)N coatings, joining an aesthetical surface with an antibacterial effect.