Antibacterial Ag–ZrN surfaces promoted by subnanometric ZrN-clusters deposited by reactive pulsed magnetron sputtering

Ag–ZrN films were deposited on polyester by direct current pulsed magnetron sputtering (from now on DCMSP) in Ar + N2 atmosphere. ZrN on the polyester surface interacts with Ag leading to Ag–ZrN films. These composite films were more active in Escherichia coli inactivation compared to the Ag-films by themselves. The E. coli inactivation kinetics on Ag–ZrN polyester surfaces was accelerated >4 times compared to samples sputtering only Ag. Sputtering Zr in N2 atmosphere presented no antibacterial activity by itself when applied for short times (< one min). The Ag–ZrN polyester sample sputtered for 20 s at 300 mA led to the fastest antibacterial E. coli inactivation kinetics within 11/2 h. This sample consisted of Ag-particles with sizes of 15–40 nm, within a layer thickness of 30–45 nm covering ∼60–70% of the polyester fiber in the direction of the Ago/Ag-ion-flux from the Ag-target. An Ag sputtering time of 20 s lead to the optimal ratio of Ag-loading/Ag cluster size with the highest amount of Ag-sites held in exposed positions on the polyester surface. The Ag-nanoparticles sputtered for times >20 s agglomerated to bigger units leading to longer bacterial inactivation times. The Ag-atoms are shown to be immiscible with the ZrN-layer. The increase in thickness of the Ag–ZrN at longer sputtering times lead to a concomitant increase in rugosity and hydrophobic character of the Ag–ZrN sputtered layers. Several up-to date techniques have been used to characterize the catalytic Ag–ZrN film providing a full description of its structure. The Ag–ZrN films showed a uniform metal distribution and a semi-transparent gray-brown color.