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 atomic layers were investigated: reductive deposition, oxidative stripping of bulk Se, and reductive stripping of bulk Se. The resulting Se atomic layers were studied using low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM). LEED indicated the formation of Au(111)(√3x√3)R30°-Se and Au(110)(2x3)-Se structures. STM analysis confirmed the presence of those structures along with several others. At low Se coverages on Au(111), a mosaic structure was formed, composed of a large number of small domains of a (√3x√3)R30°-Se structure, separated by areas void of Se. At higher coverages, near 1/3, the (√3x√3)R30° structure covered most of the surface, except for a number of linear phase boundaries. Commensurate with completion of the (√3x√3)R30° structure, some domains of square Se₈ rings were usually evident, as well. At still higher coverages, a heterogeneous surface was formed, composed of a complex network of rings, chains, clusters, and pits. This heterogeneity appears to result from slow deposition kinetics, probably the result of both a low exchange current and low Se surface mobility. Some of the kinetic sluggishness may have resulted from the need to translate whole domains of Se atoms from one site to another, in order to remove phase boundaries. STM studies of the Au(110) surface indicated that only the (2x3) structure was formed at coverages much below 1 monolayer and that it was formed homogeneously. At monolayer coverages and above, a honeycomb structure composed of chains of Se atoms was observed, which filled in at still higher coverages to complete a second Se layer.