Showing papers by "Gérard Tourillon published in 1995"

Adsorption of Acrylonitrile on Pt(111) and Au(111) at 95 K in the Monolayer and Multilayer Ranges Studied by NEXAFS, UPS, and FT-IR

Abstract: published in Advance ACS Absrrucrs, March 1, 1995 0022-3654/95/2099-5058$0900/0 without any influence of the substrate; it is thus a reference for the monolayer spectra We also present UPS experiments which probe the valence bands of the adsorbed layer In our case, UPS will give information on the chemical activity of the nitrogen lone pair and on the n orbitals of the molecule, which cannot be seen with NEXAFS spectroscopy which probes only the unfilled states We have also used XPS (X-ray photoelectron spectroscopy) experiments to determine the carbon and the nitrogen 1s binding energies They are needed for the inter- pretation of the NEWS transitions: indeed, there are three nonequivalent carbon atoms in acrylonitrile, giving three non- equivalent C( 1s) levels from where the photoelectrons could be excited to the same final state At last, FT-IR experiments on the adsorbates will provide information about the bond strength modifications upon adsorption

An EELS and XAS Study of Cubic Boron Nitride Synthesized under High Pressure - High Temperature Conditions

Abstract: Cubic Boron Nitride (c-BN) single-crystals have been synthesized under high pressure and high temperature conditions (HP - HT) using hexagonal Boron Nitride (h-BN) precursors. We have performed a study of both phases with electron (EELS) and X-ray (XAS) spectroscopy that are compared. The c-BN ELNES spectra at B-K and N-K edges are found to be consistent with the XANES (XAS) data, although the energy resolution achieved with X-rays is better than that obtained by EELS with a LaB 6 filament. However, XAS is at a disadvantage by comparison with EELS owing to the presence of the N-K edge second order. Attempts were made to dope c-BN with carbon atoms. The examination of the EELS spectra reveals that the incorporation of carbon species in the BN material is always accompanied by the addition of oxygen. Several samples were analyzed both with selected area electron diffraction and energy loss spectroscopy. Most probed crystals containing C (and therefore O) were found to be hexagonal. These results emphasized that the range of existence of the cubic phase is very narrow around the binary composition

MS-Xα approach of near edge X-ray absorption spectra of the acrylonitrile molecule (CH2CHCN)

Abstract: The C and N K-edge NEXAFS spectra of oriented acrylonitrile multilayers have been recorded at normal and grazing incidence. Calculated spectra using the multiple scattering Xα approach (MS-Xα) are used to interpret the different resonances observed from each excited atom of the molecule.

Adsorption study of ethylene derivatives on Pt(111) at 95 K as probed by NEXAFS

Abstract: The interactions of unsaturated molecules with a metallic surface is of great interest both from a theoretical point of view (charge transfer mechanisms, surface reactivity, etc.) and from a practical point of view (catalysis, adhesion, corrosion, etc.). We have recently shown that the substitution of one or two hydrogen atoms by CH3 groups on ehtylene (butene, propylene) has no effect on the interaction mode of the molecule on Pt(111): chemisorption with the formation of a di-σ bond. We report in this paper some C K-edge NEXAFS experiments performed on substituted ethylene adsorbed on Pt(111) at 95 K where one hydrogen atom is replaced by a chemical function (acid, aldehyde). Acrylic acid (CH2  CHCOOH) is strongly chemisorbed on Pt(111) at 95 K (di-σ bond) whereas acrolein (CH2  CHCOH) is π-bonded. These results combined with XPS and UPS data reveal that the differences in the interactions come from differences in molecular orbitals conjugations which make possible (or impossible) an overlapping of the molecular orbitals with the metal d band.