Nickel nanoparticle assembly on single-crystal support:: formation, composition and stability

A nickel nanoparticle assembly was formed by vapour deposition on various single-crystal supports. The nanoparticle structure, distribution, composition and charge transfer properties were examined simultaneously by atomic force microscopy (AFM), x-ray photoelectron spectroscopy (XPS), mass spectroscopy (MS) and electrochemistry. The data obtained by applied analytical techniques were correlated. X-ray photoelectron spectroscopy (XPS) of nanoparticle assemblies deposited at ambient temperature revealed the Ni(II) oxidation state, while metallic Ni was found in nanoparticles grown at 300 degrees C. The amount of nickel deposited on highly ordered pyrolytic graphite (HOPG) estimated by AFM was found to be an order of magnitude higher than that obtained from XPS analysis, while AFM and XPS data for silicon agree well. The discrepancy was discussed in terms of differences in support elastic properties and AFM-tip/surface interactions. Current-potential measurements of nanoparticle charge transfer reaction point to the high stability and low resistant Ohmic character of the nanoparticle/HOPG interface.