83 research outputs found
Electronic structure investigation of CoO by means of soft X-ray scattering
The electronic structure of CoO is studied by resonant inelastic soft X-ray
scattering spectroscopy using photon energies across the Co 2p absorption
edges. The different spectral contributions from the energy-loss structures are
identified as Raman scattering due to d-d and charge-transfer excitations. For
excitation energies close to the L3 resonance, the spectral features are
dominated by quartet-quartet and quartet-doublet transitions of the 3d7
configuration. At excitation energies corresponding to the satellites in the Co
2p X-ray absorption spectrum of CoO, the emission features are instead
dominated by charge-transfer transitions to the 3d8L-1 final state. The spectra
are interpreted and discussed with the support of simulations within the single
impurity Anderson model with full multiplet effects which are found to yield
consistent spectral functions to the experimental data.Comment: 8 pages, 2 figures, 2 tables,
http://link.aps.org/doi/10.1103/PhysRevB.65.20510
Interface and electronic characterization of thin epitaxial Co3O4 films
The interface and electronic structure of thin (~20-74 nm) Co3O4(110)
epitaxial films grown by oxygen-assisted molecular beam epitaxy on MgAl2O4(110)
single crystal substrates have been investigated by means of real and
reciprocal space techniques. As-grown film surfaces are found to be relatively
disordered and exhibit an oblique low energy electron diffraction (LEED)
pattern associated with the O-rich CoO2 bulk termination of the (110) surface.
Interface and bulk film structure are found to improve significantly with
post-growth annealing at 820 K in air and display sharp rectangular LEED
patterns, suggesting a surface stoichiometry of the alternative Co2O2 bulk
termination of the (110) surface. Non-contact atomic force microscopy
demonstrates the presence of wide terraces separated by atomic steps in the
annealed films that are not present in the as-grown structures; the step height
of ~ 2.7 A corresponds to two atomic layers and confirms a single termination
for the annealed films, consistent with the LEED results. A model of the (1 *
1) surfaces that allows for compensation of the polar surfaces is presented.Comment: 8 pages, 7 figure
CO-induced lifting of Au (001) surface reconstruction
We report CO-induced lifting of the hexagonal surface reconstruction on Au
(001). Using in-situ surface x-ray scattering, we determined a
pressure-temperature phase diagram for the reconstruction and measured the
dynamical evolution of the surface structure in real time. Our observations
provide evidence that, under certain conditions, even macroscopic Au surfaces,
much larger than catalytic Au nanoparticles [M. Haruta, Catal. Today 36, 153
(1997)], can exhibit some of the reactive properties and surface transitions
observed in systems known to be catalytically active such as Pt (001).Comment: 4 Figures. Accepted as a Letter to Journal of Physical Chemistry
Interfacial chemistry in Al and Cu metallization of untreated and plasma treated polyethylene and polyethyleneterephtalate
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Interfacial chemistry in Al and Cu metallization of untreated and plasma treated polyethylene and polyethyleneterephtalate
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Preferential CO oxidation in a large excess of hydrogen on Pt3Sn surfaces
2 Dupont, C. Delbecq, F. Loffreda, D. Jugnet, Y.An experimental evaluation, under realistic conditions, of the catalytic properties of a Pt3Sn(1 1 1) model catalyst in CO oxidation under excess of hydrogen is reported in this study. From a structural point of view, two different surface terminations are available in this alloy, viz. (2 x 2) and (root 3 x root 3)R30 degrees, differing by their tin concentration and Pt-Sn local structural arrangements in the uppermost layers, thus offering specific active sites for the reaction to proceed. In this study, mass spectrometry and polarization modulation infrared reflection absorption spectroscopy measurements (PM-IRRAS) have been performed at near ambient pressure on both surfaces of the alloy and compared to those obtained on Pt(1 1 1) used as a reference. The presence of hydrogen promotes the rate of CO oxidation on the three surfaces. The influence of tin is remarkable, increasing the catalytic activity of Pt atoms by one order of magnitude. With the exception of CO, no other species such as formyls or carbonates are observed on the surface by IR spectroscopy in the range of temperature (293-425 K) investigated. (C) 2010 Elsevier Inc. All rights reserved
Recent Advances in PROX: Vibrational Characterization and Reactivity on the Pt3Sn(111) Surface
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