No abstract

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.

Supported metal nanoparticles have been fabricated using electron beam lithography (EBL) and pulsed laser deposition (PLD). EBL produced ordered two-dimensional arrays with particle diameters of 40 ± 0.5 nm, uniform interparticle distances (230 ± 2 nm), and uniform height (20 ± 0.5 nm). Due to the narrow size distribution of the particles and the long-range (cm2) order, the arrays produced using EBL were applied as models for supported metal catalysts. Smaller particle sizes can be obtained using PLD, but with larger size and spatial distributions of the particles. Particles fabricated with PLD have mean sizes ranging from 2 to 50 nm, depending on the ambient pressure during deposition. The nanoparticles have been characterized using TEM, AFM, UPS, and SEM. Reaction studies of ethylene hydrogenation on Pt nanoparticle arrays have demonstrated that detectable amounts of ethane are produced, despite the low surface area of the model catalysts.