Structure characterization and antibacterial properties of Ag-DLC films fabricated by dual-targets HiPIMS

Silver doped diamond-like carbon (DLC) films were prepared on Si (111) substrates by dual-targets high power impulse magnetron sputtering (HiPIMS), and the chemical composition, microstructure, mechanical properties and antibacterial properties of the as-deposited films were obtained. When the sputtering voltage of the Ag target was varied from 450 to 580 V, X-ray photoelectron spectroscopy results revealed that the concentration of Ag in the as-deposited films was increased from 19.1 to 32.0 at. %. High resolution transmission electron microscopy images depicted that the as-deposited films were composed of Ag nanoparticles (AgNPs) embedded in DLC matrix. Along the cross-section of the film, the size of silver nanocrystals was varied from 5–12 (in the middle) to 2–5 nm (in the top surface). When the sputtering voltage was increased, the density of AgNPs was raised also. In addition, when the bias was increased from −50 to −100 V, the size of AgNPs in the top surface was reduced from 5–12 to 2–5 nm. AgNPs with a small size benefited the release of silver ions and improved the antibacterial ability, and the samples fabricated with the sputtering voltage (Ag target) of 500–560 V and a larger bias (-100 V) obtained an excellent antibacterial efficiency (> 99.5%) against Escherichia coli and Staphylococcus aureus.