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.
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
Graphene covered metal nanoparticles constitute a novel type of hybrid materials, which provide a unique platform to study plasmonic effects, surface-enhanced Raman scattering (SERS), and metal-graphene interactions at the nanoscale. Such a hybrid material is fabricated by transferring 2 graphene grown by chemical vapor deposition onto closely spaced gold nanoparticles produced on a silica wafer. The morphology and physical properties of nanoparticle-supported graphene is investigated by atomic force microscopy, optical reflectance spectroscopy, scanning tunneling microscopy and spectroscopy (STM/STS), and confocal Raman spectroscopy. This study shows that the graphene Raman peaks are enhanced by a factor which depends on the excitation wavelength, in accordance with the surface plasmon resonance of the gold nanoparticles, and also on the graphene-nanoparticle distance which is tuned by annealing at moderate temperatures. The observed SERS activity is correlated to the nanoscale corrugation of graphene.STM and STS measurements show that the local density of electronic states in graphene is modulated by the underlying gold nanoparticles.
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