ADSORBATE-INDUCED ETCHING OF AU(111) SURFACES - A COMBINED IN-SITU INFRARED-SPECTROSCOPY AND SCANNING-TUNNELING-MICROSCOPY STUDY

In this paper the initial stages of the etching of Au(lll) electrode s urfaces in the presence of adsorbed tetramethylthiourea (TMTU) are inv estigated using the complementary methods of in-situ IR spectroscopy a nd STM. Scanning tunneling microscopy (STM)has been used in-situ to ex amine changes in surface topography associated with the surface etchin g. STM images show that the etching process proceeds from step edges a nd eventually leads to the exposure of monatomic steps which are orien tated at 60 degrees/120 degrees with respect to each other. This indic ates that the more lowly co-ordinated kink atoms are more readily etch ed than ''straight'' steps, leading to an appearance of anisotropic et ching of steps. Iri-situ IR spectroscopy confirms that etching leads t o the formation of gold-TMTU complexes, which are soluble in the elect rolyte solution. It is also apparent from these spectroscopic data tha t no significant TMTU decomposition occurs during the anodic surface e tching. The potential dependence of the IR band intensity of the Au-TM TU complex indicates the important role which adsorbed TMTU plays in t he etching process. Upon subsequently lowering the electrode potential a slow growth of the step edges is seen by in-situ STM. Deductions co ncerning the growth could be made by following the development of the surface topography with in-situ STM. Growth preceded two-dimensionally from substrate step edges and gradually gave rise to semicircular ste p edges which advanced slowly across the surface. This can be interpre ted as the nucleation and growth of gold islands by electrodeposition of the TMTU-complexed gold.