High power impulse magnetron sputtering (HIPIMS) and traditional pulsed sputtering (DCMSP) Ag-surfaces leading to E. coli inactivation
This study addresses the high power impulse magnetron sputtering (HIPIMS) deposition of Ag-nanoparticle films on polyester and the comparison with films deposited by direct current pulsed magnetron sputtering (DCMSP). The first evidence is presented for the Escherichia coli bacterial inactivation by HIPIMS sputtered polyester compared to Ag-polyester sputtered by DCMSP. HIPIMS layers were significantly thinner than the DCMSP sputtered layers needing a much lower Ag-loading to inactivate E. coil within the same time scale. The Ag-nanoparticle films sputtered by DCMSP at 300 mA for 160 s was observed to inactivate completely E. coil within 2 h having a content of 0.205% Ag wt%/polyester wt%. HIPIMS-sputtered at 5 A for 75 s led to complete E. colt bacterial inactivation also within 2 h having a content Ag 0.031% Ag wt%/polyester wt%. The atomic rate of deposition with DCMSP is 6.2 x 10(15) atoms Ag/cm(2) s while with HPIMS this rate was 2.7 x 10(15) atoms Ag/cm(2) s. The degree of ionization of Ag+/Ag2+ and Ar+/Ar2+ was proportional to the target current applied during HIPIMS-sputtering as determined by mass spectroscopy. These experiments reveal significant differences at the higher end of the currents applied during HIPIMS sputtering as illustrated by the ion-flux composition. X-ray photoelectron spectroscopy (XPS) was used to determine the surface atomic concentration of 0, Ag, and C on the Ag-polyester. These surface atomic concentrations were followed during the E. colt inactivation time providing the evidence for the E. coli oxidation on the Ag-polyester. X-ray diffraction shows Ag-metallic character for DCMSP sputtered samples for longer times compared to the Ag-clusters sputtered by HIPIMS leading to Ag-clusters aggregates. Ag-nanoparticle films on polyester sputtered by HIPIMS contain less Ag and are thinner compared to Ag-nanoparticle films sputtered by DCMSP. (C) 2011 Elsevier B.V. All rights reserved.