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 been investigated by surface-enhanced Raman spectroscopy (SERS). An oxygen plasma caused oxidation of adsorbed CN- to Au(CN)4 -, and there was evidence of oxidation of the adsorption site gold atoms at the Au/p-nitrobenzoate surface, while in a hydrogen plasma Au(CN)4 - was reduced back to adsorbed CN-. No adsorbed oxidation or reduction products of thiophenate or p-nitrobenzoate 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 preferentially 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 films were rapidly destroyed.