E. Coli Inactivation on Ag-Surfaces: High Power Impulse Magnetron Sputtering (HIPIMS) and Traditional Pulsed Sputtering (DCMSP)

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This study addresses the deposition of Ag-nanoparticle films on polyester using high power impulse magnetron sputtering (HIPIMS), and the comparison between the films deposited by HIPIMS and direct current pulsed magnetron sputtering (DCMSP).

Experimental Results

The initial results were provided for the inactivation of E.coli bacteria by HIPIMS sputtered polyester (Figure 1) over Ag-polyester sputtered by DCMSP. The HIPIMS layers are significantly thinner than the DCMSP sputtered layers, meaning HIPIMS require lower Ag- loading for E.coli inactivation within the same period of time.

Figure 1. Schematic of the HIPIMS setup, the cathode used was Ag and the substrate polyester

The first evidence is presented for the E. 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.coli within the same time scale. The Ag-nanoparticle films sputtered by DCMSP at 300 mA for 160s was observed to inactivate completely E. coli within 2 hours having a content of 0.205% Ag wt%/polyester wt%. HIPIMS-sputtered at 5 Amp for 75s led to complete E. coli bacterial inactivation also within 2 hours having a content Ag 0.031% Ag wt%/polyester wt%. The atomic rate of deposition with DCMSP is 6.2x1015 atoms Ag/cm²s while with HPIMS this rate was 2.7x1015 atoms Ag/cm²s.

Figure 2. Transmission electron microscopy of Ag-polyester fibers sputtered by HIPIMS at 5 Amps for 150s

The degree of ionization of Ag⁺/Ag²⁺ and Ar⁺/Ar²⁺ is proportional to the target current applied during HIPIMS-sputtering. As demonstrated by the ion-flux composition, these experiments have shown considerable differences at the higher end of the currents applied during HIPIMS sputtering.

The surface atomic concentration of C, Ag and O on the Ag-polyester was determined using X-ray photoelectron spectroscopy (XPS). The surface atomic concentrations were followed during the E. coli inactivation, which indicate the E. coli oxidation on the Ag- polyester.

X-ray diffraction studies have revealed Ag-metallic character for DCMSP sputtered samples for longer times compared to the Ag-clusters sputtered by HIPIMS leading to Ag-clusters aggregates. When compared to Ag-nanoparticle films sputtered by DCMSP, Ag-nanoparticle films on polyester sputtered by HIPIMS are thinner and consist of lower quantities of Ag. Using a Hiden mass spectrometer linked with the DC-magnetron gas chamber, the ions in the chamber were analyzed. The Ar⁺, Ar²⁺ and Ag⁺ and Ag²⁺ ions were also characterized.

The Ag⁺ gas phase increases and Ar⁺ decreases with increasing current. With increasing current the Ar+ decreases and the Ag+ gas phase increases. The most interesting result is that HIPIMS discharges at 10 A peak current produced high quantities of Ag⁺-ions along a small amount of Ag²⁺-ions.

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This information has been sourced, reviewed and adapted from materials provided by Hiden Analytical.

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