Scanning Tunneling Microscopy of Galena (100) Surface Oxidation and Sorption of Aqueous Gold

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Science  15 Nov 1991:
Vol. 254, Issue 5034, pp. 983-986
DOI: 10.1126/science.254.5034.983


Scanning tunneling microscopy was used to characterize the growth of oxidized areas on galena (100) surfaces and the formation of gold islands by the reductive adsorption of AuCl4 from aqueous solution. The gold islands and galena substrate were distinguished by atomic resolution imaging and tunneling spectroscopy. Oxidized areas on galena have [110]-trending boundaries; gold islands elongate along [110] directions. However, there are no obvious structural registry considerations that would lead to elongation of gold islands in a [110] direction. Instead, it is probable that a direct coupling of gold reduction and sulfide surface oxidation controls the initial formation of gold islands. Gold islands grow less quickly on preoxidized galena surfaces and show no preferred direction of growth.