Photothermoelectric Detection of Gold Oxide Nonthermal Decomposition

A thin coating of gold oxide, metastable at room temperature, can be formed by placing gold in a strongly oxidizing environment such as an oxygen plasma. We report scanning photovoltage measurements of lithographically defined gold nanowires subsequent to oxygen plasma exposure. Photovoltages are detected during the first optical scan of the devices that are several times larger than those mapped on subsequent scans. The first-scan enhanced photovoltage correlates with a reduction of the electrical resistance of the nanostructure back to preoxygen-exposure levels. Repeating oxygen plasma exposure "reinitializes" the devices. These combined photovoltage and transport measurements imply that the enhanced photovoltage results from the photothermoelectric response of a junction between Au and oxidized Au, with an optically driven decomposition of the oxide. Comparisons with the known temperature-dependent kinetics of AuOx decomposition suggest that the light-driven decomposition is not a purely thermal effect. These experiments demonstrate that combined optical and electronic measurements can provide a window on surface-sensitive photochemical processes.