Nanosize gold particles were prepared by Ar(+) ion implantation of 10-nm thick gold film deposited onto a SiO(2)/Si(100) wafer possessing no catalytic activity in the CO oxidation. Along with size reduction the valence band of the gold particles and the actual size were determined by ultraviolet- and X-ray photoelectron spectroscopy (UPS, XPS) and by transmission electron microscopy (TEM) as well as atomic force microscopy (AFM), respectively. The catalytic activity was determined in the CO oxidation. Energy distribution of the photoelectrons excited from 5d valence band of gold was strongly affected by Ar(+) implantation. This variation was interpreted by the redistribution of the valence band density of states (DOS). The intrinsic catalytic activity of the gold particles increased with decreasing size. When an Au/FeO(x) interface was created by FeO(x) deposition on large gold nanoparticles, a significant increase in the rate of the CO oxidation was observed. These data can be regarded as an experimental verification of the correlation between the catalytic activity and valence band density of states of gold.

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A neutron-scattering measurement was performed on pure amorphous Si. The radial distribution function was derived from the wide momentum-transfer range spectra. These data are compared to 0 theoretical models in the 0 -10-A real-space interval.Despite more than 15 years of investigation, one of the main problems concerning amorphous silicon remained the determination of its microscopic structure. Since Polk' made the first so-called continuous-randomnetwork (CRN) model in 1971, many models have been constructed in different ways. ' In the relaxed CRN models the Keating, the Stillinger-Weber, the Weber bond-charge potential, and the Lifson-Warshel force field were used as assumptions for the interatomic interaction to minimize the total energy. Four models' ' were obtained by molecular-dynamics techniques. The number

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Morphology, electron structure, and catalytic activity in CO oxidation over a Au/FeO x /SiO2/Si(100) model sample prepared by pulsed laser deposition (PLD) have been investigated by X-ray photoelectron spectroscopy (XPS), UV photoelectron spectroscopy (UPS), and transmission electron microscopy (TEM). Two types of sample were prepared denoted by PLD I and PLD II, the latter being prepared by multiple laser deposition alternatively by iron and gold. PLD I was characterized in “as prepared” oxidized and reduced states, the respective gold particle sizes being 3.8, 4.1, and 5 nm; the iron oxide support was amorphous after the first two treatments while it was partially crystallized after reduction. The activity in CO oxidation increased after oxidation of the sample, whereas it was diminished after subsequent reduction. XPS studies showed that higher activity was associated with amorphous iron oxide with Fe 2p binding energy = 711.3 eV. It was established that in developing the catalytic activity the gold should be metallic and the support should be amorphous with high binding energy and the reaction occurs at the perimeter of gold particles. PLD II has a slightly lower activity which might be the result of more crystalline phase in the iron oxide.

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