Investigation by surface-enhanced Raman spectroscopy of the effect of oxygen and hydrogen plasmas on adsorbate-covered gold and silver island films

The effects of radio-frequency-excited oxygen and hydrogen plasmas on gold island films with adsorbed CN-, thiophenate, or p-nitrobenzoate ions have b een investigated by surface-enhanced Raman spectroscopy (SERS). An oxygen p lasma caused oxidation of adsorbed CN- to Au(CN)(4)(-), and there was evide nce of oxidation of the adsorption site gold atoms at the Au/p-nitrobenzoat e surface, while in a hydrogen plasma Au(CN)(4)(-) was reduced back to adso rbed CN-. No adsorbed oxidation or reduction products of thiophenate or p-n itrobenzoate were detected, however. Exposure of gold films to an oxygen or hydrogen plasma also caused partial removal of the adsorbates, though with some loss of SERS activity, and in a hydrogen plasma thiophenate was prefe rentially removed from a gold film with coadsorbed thiophenate and CN-. On silver films, hydrogen plasma treatment almost completely removed adsorbed CN- with only a small loss of SERS activity, but in an oxygen plasma the fi lms were rapidly destroyed.