Design, optical and antimicrobial properties of extremely thin alumina films colored with silver nanospecies

In this study, conditions for the fabrication of extremely thin and flexible anodic films decorated with silver nanowire arrays by alternating current treatments for the finishing of high purity and commercial aluminium foils were developed. For characterization of these porous films with a thickness of ≤1.0 μm and encased silver species, inductively coupled plasma optical emission spectroscopy, X-ray diffraction and field emission scanning electron microscopy were used. Variable angle spectroscopic ellipsometry in the wavelength range of 200-1700 nm was also used to determine the influence of the deposited Ag content and the film thickness on the optical constants (n, k) of the fabricated alumina films. It is shown that due to surprisingly low k values of nano-Ag-in-alumina films in the visible and near IR regions these films could be applied as transparent films with an extremely low refractive index. In addition, the antimicrobial activity of the obtained films was assessed for the as-deposited and fully-encapsulated silver nanowire arrays against several widespread fungi and bacteria. The results obtained from in vitro tests indicated that the as-formed Ag-in-alumina films containing ≥19 μg cm(-2) of silver possessed antimicrobial properties and could be promising as foodstuff packaging materials.