Narrow Results

The Free-energy Concentration Expansion Method (FCEM) was utilized for the prediction of compositional structures in Ni–Cu–Rh cubo-octahedron nanoclusters in comparison to recently reported Ni–Cu–Pd data. While both systems exhibit site-specific, sequentially competitive surface segregation (and resultant core separations), remarkable differences governed by the opposite heteronuclear effective interactions, were noted in the surface compositional patterns. Thus, at relatively low temperatures "mixed" Cu/Pd ordering takes place at the Ni–Cu–Pd cluster surface, whereas in the Ni–Cu–Rh cluster Cu and Ni populate separate low and high-coordinated surface sites, thus forming a kind of "demixed surface order". Dissimilarities in the temperature dependence are discussed in terms of the interplay of segregation and compositional order. Such findings may have implications in heterogeneous catalysis and other technologies based on highly dispersed alloyed particles.

Nickel films electrodeposited from chloride and sulfate baths at pH 3.8 have been investigated. The influence of the plating baths on the electrochemical growth and the characteristics of nickel were studied by means of cyclic voltammetry, potentiostatic steps (chronoamperometry), atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques. The electrocrystallization mechanism was analyzed using the Scharifker and Hills model. The nucleation mechanism was found to be progressive at -1.1 V versus SCE, while at elevated overpotentials (more negative than -1.2 V versus SCE) instantaneous nucleation behavior was obtained. AFM characterization of the deposits indicated that the baths composition influences greatly the morphology of the deposits. XRD analysis indicated polycrystalline growth of the Ni film with a preferred (111) orientation with the fcc structure for both baths. The Ni crystallite sizes are 19–31 nm for the sulfate bath and 14–33 nm for the chloride one.