Antibacterial Ag-Cu coatings deposited using an asymmetric bipolar high-power impulse magnetron sputtering technique

High-power impulse magnetron sputtering was used to deposit bimetallic Ag-Cu coatings using an asymmetric bipolar mode. The frequency used for the Ag-Cu deposition was 250 Hz and the pulse on-times were 100 and 150 is for the Ag and Cu targets, respectively. The peak current to the Ag target was 50 A while that to the Cu target was varied from 80 to 200 A. The mean power (Pmean) and peak power (P-max) of the Ag target were 1.2 and 47.5 kW, respectively. The P-mem, of the Cu target varied from 1.8 to 6.0 kW and the P-max from 50.9 to 162.4 kW. It was found that the Cu/Ag ratio in the coating increases from 1.9 to 4.4 with increasing Cu target current. Optical emission spectroscopy analysis shows that the intensities of all the ions in the plasma are much higher adjacent to the Cu target than that adjacent to the Ag target. Furthermore, the HiPIMS process not only leads to the ionization of the sputtered Cu and the sputtering gas Ar but also helps the ionization of the sputtered Ag. Disk diffusion test shows that Ag-Cu coatings having appropriate Cu/Ag ratios give better inactivation of E. colt, while a lower Cu/Ag ratio gives better inactivation of P. aerllginosa.