Growth of TiO2/Cu films by HiPIMS for accelerated bacterial loss of viability

This study shows the first complete report on ultrathin TiO2/Cu nano-particulate films sputtered by highly ionized pulsed plasma magnetron sputtering (HIPIMS) leading to fast bacterial loss of viability. The Cu- and the TiO2/Cu sputtered films induced complete Escherichia coli inactivation in the dark, which was not observed in the case of TiO2. When Cu was present, the bacterial inactivation was accelerated under low intensity solar simulated light and this has implications for a potential for a practical technology. The design, preparation, testing and surface characterization of these innovative films are described in this study. The HIPIMS sputtered composite films present an appreciable savings in metals compared to films obtained by conventional sputtering methods. HIPIMS sputtering induces a strong interaction with the rugous polyester 3-D structure due to the higher fraction of the Cu-ions (M+) attained in the magnetron chamber. The Cu-leaching during the bacterial inactivation was monitored by ion-coupled plasma mass spectrometry (ICP-MS) and found to be in the ppb range. The amounts found were below the cytotoxicity level allowed by the standards related to human health. The immiscibility of Cu and TiO2 in the TiO2/Cu films is shown by High Angular Dark Field (HAADF) microscopy. A mechanism for the photo-induced interfacial charge transfer (IFCT) between TiO2 and Cu is suggested.