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For Cu-on-Ag film contact, good boundary lubricating property of LP108 allows sliding with low friction coefficient, burnished worn surface and high load-bearing capacity. Under current-loading condition, mechanical separation and recontact of contacting surface produces electric arc and electric arc-induced damage on Ag film depends on polarity of pin and disk. For positive Cu pin against negative Ag film disk, rainbow-like film and transparent LP108 on Ag film are observed. While, for negative Cu pin against positive Ag film disk, removal of Ag film is observed and this produces dark ionic liquid-Ag suspension. In both cases, electric arc does not degrade LP108. Electric arc and electric arc-induced damage on Ag film can be eliminated by ensuring good contacting surface conformity.

Two kinds of plating solutions, i.e. a standard plating solution and a commercially available plating solution, are employed for the preparation of electroless Ag film. The commercially available plating solution enables fast film deposition within several minutes and is highly selective for deposition onto Cu substrate, and cost-effective (reusable solution, and much less Ag consumption) compared to the standard plating solution. Both electroless Ag films prepared have distinct microstructure, surface chemistry, and bulk chemistry. The film from standard plating solution is composed of nano-grains with an average grain size of 300 nm and homogeneity. The film prepared with commercially available plating solution is composed of equiaxed grains (140 nm in size), and ribbon fish-like grains (80 nm in size and 0.5-2 μm in length) and shows microstructural inhomogeneity. The tribological properties of these electroless Ag films in presence of flooded 1-methyl-3-octylimidazolium hexafluorophosphate are investigated on a reciprocating tribometer with a pin-on-disk configuration under electrical contact. The results demonstrate that both electroless Ag films show better tribological property than Cu-on-Cu contact. Due to their dissimilar microstructure the tribological properties of the two electroless Ag films are quite different. For the standard plated film, local adhesion and tear-up in an annular shape on pin result in many plate-like wear debris in the early stage of the sliding test. For commercially the plated film from a commercial solution, compact and thin tribo-film on the worn surfaces of pin and disk as well as little or no wear debris are observed. The microstructural effect also has an influence on the design of the tribo-interface.