Electroless deposition of silver by galvanic displacement on aluminum alloyed with copper

In this paper, a procedure is described for the electroless deposition of silver on films containing 99.5% aluminum and 0.5% copper. The deposition proceeds in the absence of external reducing agents via the galvanic displacement mechanism by which silver cations are reduced and copper is oxidized. Although aluminum is a stronger reducing agent than copper, the galvanic displacement of aluminum by silver is not observed with pure (99.997%) aluminum substrates. By alloying aluminum with copper, aluminum films are made amenable to electroless deposition of silver by galvanic displacement. To generate a clean surface for electroless deposition with a controlled and minimal thickness of surface oxide, the aluminum films alloyed with copper are anodized in oxalic acid and etched in a mixture of chromic and phosphoric acids. Thinning of the barrier aluminum oxide during etching and deposition of silver particles are monitored with electrochemical impedance spectroscopy (EIS). Analysis of EIS data indicates that deposition of silver particles for 3 h dramatically increases the interfacial capacitance from 5 to 6 muF/cm(2), characteristic for a thin layer of barrier aluminum oxide, to 30-40 muF/cm(2), typical for metal electrode surfaces. Scanning electron micrographs show that electroless deposition results in the formation of films composed of silver particles. These films can be employed for the fabrication of miniature silver-zinc batteries, optical devices for surface enhanced Raman scattering and FT-IR spectroscopy, composite materials with photocatalytic properties, and surfaces with anti-microbial properties.