Ultrathin metal films and particles on oxide surfaces: structural, electronic and chemisorptive properties

The interaction of isolated Cu, Pd, and Cs atoms on regular and defect sites of the SiO2 surface has been studied with cluster models. Hartree−Fock, density functional theory, and multireference co...

Adsorption of Cu, Pd, and Cs Atoms on Regular and Defect Sites of the SiO2 Surface

Size-dependent oxidation of Pdn (n ⩽ 13) on alumina/NiAl(110): Correlation with Pd core level binding energies

The interaction of O2 with small Pd particles (2−10 nm) supported on an α-Al2O3(0001) single crystal under both ultrahigh vacuum (UHV) and high-pressure conditions has been studied by temperature-programmed desorption (TPD), temperature-programmed low-energy ion scattering (TP-LEIS), and X-ray photoelectron spectroscopy (XPS). A low O2 exposure (30 L) at 500 K leads to surface oxygen adatoms on the Pd nanoparticles, which desorb in TPD as O2 in a peak at ∼880 K. Surface O adatoms on the smallest Pd particles move to subsurface sites starting at 400 K, and they almost all move subsurface by ∼750 K, desorbing mainly at considerably higher temperature. The dominant oxygen species above 700 K is subsurface, implying that it is more stable than oxygen adatoms on Pd. Exposures of the Pd nanoparticles to 25 Torr O2 at 373−473 K readily convert the Pd to a species whose Pd XPS peak shifts by the same amount as the binding energy difference between bulk Pd and bulk PdO. We attribute this to PdO nanoparticles (or a...

Interactions of O2 with Pd Nanoparticles on α-Al2O3(0001) at Low and High O2 Pressures

X-ray absorption near-edge structure (XANES) is commonly used to probe the oxidation state of metal-containing nanomaterials; however, as the particle size in the material drops below a few nanometers, it becomes important to consider inherent size effects on the electronic structure of the materials. In this paper, we analyze a series of size-selected Ptn/SiO2 samples, using X-ray photoelectron spectroscopy (XPS), low energy ion scattering, grazing-incidence small-angle X-ray scattering, and XANES. The oxidation state and morphology are characterized both as-deposited in UHV, and after air/O2 exposure and annealing in H2. The clusters are found to be stable during deposition and upon air exposure, but sinter if heated above ∼150 °C. XANES shows shifts in the Pt L3 edge, relative to bulk Pt, that increase with decreasing cluster size, and the cluster samples show high white line intensity. Reference to bulk standards would suggest that the clusters are oxidized; however, XPS shows that they are not. Inste...

Inherent Size Effects on XANES of Nanometer Metal Clusters: Size-Selected Platinum Clusters on Silica

Atomic Force Microscopy (A.F.M.) and Rutherford back scattering (R.B.S.) have been employed to study the nucleation and growth phenomena of Palladium clusters cattered onto a thin (20 A) layer of SiOx, grown by plasma oxidation onto Si(100) doped B surface. X ray photoemission (XPS) of the 3d core level of palladium has permitted to follow the clusters silica interaction. Intrinsic final state size effect and extrinsic initial chemical state are discussed for clusters in the range of 10 to 104 atoms.

S. Mechken

Papers

Metallic clusters surface interaction: The case of Pd/SiOx/n-Si(100)