Measurement of the chemical and morphological changes that occur on gold surfaces following thermal desorption and acid dissolution of adsorbed mercury Original Research Article

We have studied the chemical and morphological changes that occur in mercury-covered polycrystalline gold films after thermal annealing and acid dissolution. Atomic force microscopy images show that acid etching causes significant morphological changes in the gold films. The morphological changes following acid dissolution can be explained by the preferential dissolution of Hg at grain boundaries in polycrystalline films, which causes the nucleation of larger gold islands and creation of voids. X-ray photoelectron spectroscopy indicates that not all of the Hg can be dissolved from the polycrystalline gold films with concentrated nitric acid, but heating above 500 K is sufficient to remove the Hg. Thermal desorption of Hg from a Au(1 1 1) single crystal was also studied under ultrahigh vacuum conditions. Desorption peaks were observed at ∼240 and ∼380 K and were assigned to the multilayer and monolayer, respectively. These findings are important since they suggest mercury cannot be completely removed from polycrystalline gold surfaces (i.e. electrodes) by acid dissolution. The implications of cleaning gold-based mercury sensors are discussed.