Advantages of highly ionized pulse plasma magnetron sputtering (HIPIMS) of silver for improved E. coli inactivation

This study addresses the DC-magnetron sputtering (DCMS) of Ag-films on polyester and compares the results found for the E. coli inactivation with the inactivation obtained when applying highly ionized pulse plasma power magnetron sputtering (HIPIMS). The amounts of Ag needed to inactivate E. coli by HIPIMS sputtering were an order of magnitude lower than with DCMS indicating a significant saving of noble metal and concomitantly a faster E. coli inactivation was observed compared to samples sputtered with DCMS. Higher current densities applied with DCMS led to shorter E. coli inactivation times and this trend was observed also for HIPIMS sputtered samples. By DCMS the thicker layers needed to inactivate E. coli comprised slightly larger Ag-aggregates compared to the thinner Ag-layers sputtered by HIPIMS to inactivate E. coli within short times. Longer sputtering times by DCMS and HIPIMS lead to optically darker Ag-deposits reaching the absorption edge of silver absorption of ~ 1000 nm. Mass spectroscopic analyses indicated that HIPIMS produced a much higher amount of Ag¹⁺ and Ag²⁺ compared to DCMS due to the higher peak discharge current employed in the former case.