Conventional Pulsed Sputtering (DCMSP) and High Power Impulse Magnetron Sputtering (HIPIMS) Ag-Surfaces Resulting in E. Coli Inactivation

This article addresses the high power impulse magnetron sputtering (HIPIMS) deposition of silver (Ag)- nanoparticle films on polyester and draws comparison with films deposited through a direct current pulsed magnetron sputtering (DCMSP) method. Figure 1 shows a diagram of the HIPIMS setup, where Ag and the substrate polyester were used as a cathode.

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

Inactivation of E. coli Bacteria

The first evidence is given for the E. coli bacterial inactivation by HIPIMS sputtered polyester in comparison to Ag-polyester sputtered by the DCMSP method. When compared to the DCMSP sputtered layers, HIPIMS layers were considerably thinner and required a relatively lower Ag-loading in order to inactivate E. coli within the same time scale.

DCMSP-sputtered Ag-nanoparticle films were found to completely inactivate E. coli within a period of 2 hours having a content of 0.205% Ag wt%/polyester wt%. This sputtering was performed at 300mA for 160s. HIPIMS-sputtered at 5A for a period of 75s also resulted in complete inactivation of E. coli bacteria within 2 hours having a content of Ag 0.031% Ag wt%/polyester wt%. It was observed that the atomic rate of deposition with the HPIMS method was 2.7x10¹⁵ atoms Ag/cm²s, while the atomic rate of deposition through the DCMSP method was 6.2x10¹⁵ atoms Ag/cm²s.

During HIPIMS-sputtering, the scale of ionization of Ar⁺/Ar²⁺ and Ag⁺/Ag²⁺ was proportional to the applied target current, as established by mass spectroscopy. These experiments show considerable variations at the higher end of the currents applied during the course of HIPIMS sputtering, as shown by the ion-flux composition.

In order to ascertain the surface atomic concentration of C, O, and Ag on the Ag-polyester, X-ray photoelectron spectroscopy or XPS technique were used. During the E. coli inactivation time, such surface atomic concentrations were followed to gain the evidence for the oxidation of E. coli on the Ag-polyester. X-ray diffraction revealed that when compared to HIPIMS-sputtered Ag-clusters, Ag-metallic character for DCMSP appeared to sputter samples for a longer period of time, which resulted in Ag-clusters aggregates. HIPIMS-sputtered Ag-nanoparticle films on polyester include a lower amount of Ag and are thinner in comparison to DCMSP-sputtered Ag-nanoparticle films.

EQP Mass and Energy Analyzer

The Hiden mass spectrometer connected to the DC-magnetron gas chamber was used to perform mass spectroscopy analysis of ions within the chamber. This was followed by determining the Ag⁺, Ag²⁺ Ar^+, and Ar²⁺ ions. With increasing current, the Ag⁺ gas phase increases, and the Ar⁺ decreases, but Ag⁺-ions surpassed the amount of Ar⁺-ions at higher discharge currents. Figure 2 shows a transmission electron microscopy of Ag-polyester fibers sputtered by HIPIMS at 5A for a period of 150s.

Figure 2. Transmission electron microscopy of Ag-polyester fibers sputtered by HIPIMS at 5A for 150s. E in stands for epoxide used during the preparation.

The outcome of this analysis is that HIPIMS discharges at 10A peak current, generating large amounts of Ag⁺-ions along with a small number of Ag²⁺-ions.

Conclusion

This article has discussed how Ag-surfaces sputtered by both HIPIMS and standard DCMSP methods lead to complete inactivation of E. coli bacteria as well as the benefits of the HIPIMS method over the DCMSP method.

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

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