Structural and Morphological study of ZnO-Ag thin films synthesized by reactive magnetron co-sputtering

Zinc oxide (ZnO) is well-known to present, among other properties, a good antibacterial activity which could be enhanced by the addition of Ag. The efficiency of ZnO-Ag films is correlated to the Ag concentration which should not exceed a threshold of a few atomic percent. Therefore it is necessary to develop a synthesis method allowing a perfect control of the film properties which can be easily transferred to the industry. In this context, we have developed a reactive magnetron co-sputtering process, in which, a Zn and an Ag metallic targets are co-sputtered in Ar-O2 gas mixtures. ZnO-Ag thin films were successfully grown, in which the Ag concentration can be tuned with a precision of 0.2%. The experimental data reveal that the incorporation of Ag disturbs the ZnO crystalline structure, and that Ag migrates to the film surface and agglomerates as a function of time for at.%Ag > 1.5%. The latter phenomenon takes place several days after the film synthesis when they are stored under ambient conditions, and is associated to oxydo-reduction reactions between oxygen and silver atoms.