The Effects of Substrate on the Contact Resistance of Tarnish Films

Studies were made of the contact resistance of Ag2S films on pure silver, and on gold-silver and palladium-silver alloys. Although relatively thick films of Ag2S on silver gave low contact resistance, equivalent film thicknesses on other substrates gave contact resistance values that were orders of magnitude higher. These results were attributed to mechanical rather than electrical-property differences of either the films, the substrates, or an interaction of both. Data clearly indicate that the "desirable" properties of silver sulfide are unique only to films on pure silver.