ATOMIC-LEVEL STUDIES OF SELENIUM ELECTRODEPOSITION ON GOLD(111) AND GOLD(110)

Studies of the electrodeposition of Se atomic layers on Au(111) and Au (110) are presented. Three electrochemical methods of forming Se atomi c layers were investigated: reductive deposition, oxidative stripping of bulk Se, and reductive stripping of bulk Se. The resulting Se atomi c layers were studied using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). LEED indicated the formation of Au(111)(root 3 x root 3)R30 degrees-Se and Au(110)(2 x 3)-Se structure s. STM analysis confirmed the presence of those structures along with several others. At low Se coverages on Au(lll), a mosaic structure was formed, composed of a large number of small domains of a (root 3 x ro ot 3)R30 degrees-Se structure, separated by areas void of Se. At highe r coverages, near 1/3, the (root 3 x root 3)R30 degrees structure cove red most of the surface, except for a number of linear phase boundarie s. Commensurate with completion of the (root 3 x root 3)R30 degrees st ructure, some domains of square Se-8 rings were usually evident, as we ll. At still higher coverages, a heterogeneous surface was formed, com posed of a complex network of rings, chains, clusters, and pits. This heterogeneity appears to result from slow deposition kinetics, probabl y the result of both a low exchange current and low Se surface mobilit y. Some of the kinetic sluggishness may have resulted from the need to translate whole domains of Se atoms from one site to another, in orde r to remove phase boundaries. STM studies of the Au(110) surface indic ated that only the (2 x 3) structure was formed at coverages much belo w 1 monolayer and that it was formed homogeneously. At monolayer cover ages and above, a honeycomb structure composed of chains of Se atoms w as observed, which filled in at still higher coverages to complete a s econd Se layer.