Tungsten film as a hard and compatible carrier for antibacterial agent of silver

Abstract

Silver-containing tungsten (W–Ag) films for antibacterial applications were deposited on glass, silicon, and 316L stainless-steel substrates by magnetron sputtering with the silver target current of 0–2.0 A. The addition of silver improves adhesion of the films on glass substrate due to the reduced residual stress in the films. SEM and EDX analyses reveal Ag-rich tiny dots (~ 20 nm) at the surface of W–Ag films with high silver contents. In XRD patterns, silver peaks are present for the samples deposited at 1.5 and 2.0 A, and tungsten grain size is decreased from ~ 23 to 10 nm by silver addition. XPS analysis shows that tungsten is slightly oxidized (WO3) at the top surface of the film, and silver presents mainly in metallic state. The low Ag/W ratios and the small surface roughness (< 8 nm) indicate that silver segregation at the film surface is not obvious. Microhardness of the samples with ≤ 6.7 at.% silver is nearly seven times that of the stainless steel (~ 250 HV). The coated samples are hydrophobic tested by contact angle measurement. The potentiodynamic polarization and the soaking test simulating the inflammatory state show that even corrosion occurs and silver addition decreases corrosion resistance of the films. The antibacterial ratio of the coated samples increases with silver content, being 91% at 4.2 at.% silver content tested by agar plate counting method. In agar disk diffusion assay, no inhibition zone is observed for all samples. The antibacterial property of the W–Ag films is localized, long-lasting, and reusable, which would be beneficial for their potential biomedical and environmental applications.