Tarnished silver–copper surfaces reduction using remote helium plasma at atmospheric pressure studied by means of high-resolution synchrotron x-ray photoelectron microscopy

Abstract Previous investigations suggested that sulphide layers on pure silver surfaces were easily removed with a reducing plasma afterglow at atmospheric pressure, but were harder to remove on silver-copper alloys. In this study we investigated by synchrotron x-ray photoelectron spectroscopy the effect of plasma afterglow on tarnished pure silver, pure copper and sterling silver alloy. The results confirmed that plasma was able to reduce in depth all sulphides except Cu2S. The process was explained by standard reduction potentials and allowed to draw a detailed picture of the submicrometric evolution of the tarnished layers.