Preparation and characterization of silica supported Au-Pd model catalysts.

Au-Pd bimetallic model catalysts were synthesized as alloy clusters on SiO2 ultrathin films under ultrahigh vacuum (UHV) conditions. The surface composition and morphology were characterized with low energy ion scattering spectroscopy (LEIS), infrared reflection absorption spectroscopy (IRAS), and temperature programmed desorption (TPD). Relative to the bulk, the surface of the clusters is enriched in Au. With CO as a probe, IRAS and TPD were used to identify isolated Pd sites at the surface of the supported Au-Pd clusters. Ethylene adsorption and dehydrogenation show a clear structure-reactivity correlation with respect to the structure/composition of these Au-Pd model catalysts.

CO-NO and CO-O(2) interactions on Cu(100) between 25 and 200 K studied with infrared reflection absorption spectroscopy.

Infrared reflection absorption spectroscopy (IRAS) has been used to study CO-NO and CO-O(2) interactions on Cu(100) between 25 and 200 K. A strong repulsive interaction between CO and NO on Cu(100) at 25 K causes tilting of the CO molecules away from the surface normal and a blue-shift of the CO vibrational frequency. Upon warming and decomposition of the NO, the CO molecules return to a bonding position normal to the surface plane. The vibrational frequency of CO blue-shifts from 2087 to 2136 cm(-1) upon coadsorption with N and O atoms formed from NO decomposition. On the other hand, the interaction of CO with O(2) at 27 K on Cu(100) in the submonolayer regime induces a red-shift of the CO vibrational frequency. Atomic oxygen, formed on Cu(100) by dissociation of O(2) at 95 K, induces a blue-shift of the vibrational frequency of coadsorbed CO to 2116 cm(-1). The CO vibrational frequency shifts to 2091 cm(-1) when the surface is annealed to 140 K, implying a change in the adsorption geometry of the oxygen atoms on Cu(100).

The growth of silver on an ordered alumina surface.

The growth of Ag on an ordered Al2O3 surface was studied by low energy ion scattering spectroscopy (LEIS), scanning tunneling microscopy (STM), X-ray photoelectron spectroscopy (XPS), and temperature programmed desorption (TPD). Three-dimensional (3D) growth of Ag clusters was observed with STM and LEIS, with the cluster size increasing with Ag coverage. The XPS core level binding energies and the Auger parameters indicate a weak interaction between the Ag clusters and the Al2O3 support. Final state effects are determined to be the primary contribution to the Ag core level binding energy shift. Nonzero order kinetics was observed for Ag desorption in TPD with the Ag sublimation energy decreasing with decreasing cluster size.

The composition and structure of Pd-Au surfaces.

Pd, Au, and Pd-Au mixtures were deposited via physical vapor deposition onto a Mo(110) substrate, and the surface concentration and morphology of the Pd-Au mixtures were determined by low-energy ion scattering spectroscopy (LEISS), infrared absorption spectroscopy (IRAS), temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Pd-Au mixtures form a stable alloy between 700 and 1000 K with substantial enrichment in Au compared to the bulk composition. Annealing a 1:1 Pd-Au mixture at 800 K leads to the formation of a surface alloy with a composition Au(0.8)Pd(0.2) where Pd is predominantly surrounded by Au. The surface concentration of this isolated Pd site can be systematically controlled by altering the bulk Pd-Au alloy concentration.

Resolution analysis of incoherent triangular holography.

We derived the point-spread function (PSF) including the recording and reconstruction systems of the modified triangular interferometer; the modified triangular interferometer forms incoherent holograms without bias and the conjugate image. We also derived and analyzed the resolution of the modified triangular interferometer and compared it with that of the conventional one for amplification factor, wavelength, and hologram size.