Y. Jugnet

CO chemisorption on Au(1 1 0) investigated under elevated pressures by polarized reflection absorption infrared spectroscopy and scanning tunneling microscopy

Abstract CO chemisorption on Au(1xa01xa00) at 300 K is observed under pressures in the range 10 −1 –10 +2 Torr. This is identified by an infrared band at 2110 cm −1 , whose intensity depends on the pressure. Scanning tunneling microscopy reveals deep restructuring of the surface.

Surface characterization and reactivity of Pd8Ni92 (111) and (110) alloys

Abstract Pd 8 Ni 92 (111) and (110) surfaces have been investigated using X-ray photoelectron spectroscopy and low energy ion scattering. As expected, a high rate of Pd segregation is observed on both faces leading to Pd surface concentrations of 76 and 81xa0at.% on the (111) and (110) surfaces, respectively. The catalytic performances of these surfaces have been studied for the 1,3-butadiene hydrogenation reaction. The catalytic activity of these alloys is greatly enhanced relative to that of the pure Pd(111) and (110) surfaces.

A comparative study of 1,3-butadiene and 1-butene chemisorbed on Pt(111), and Pd(111)

Abstract The adsorption of 1,3-butadiene and 1-butene on Pt(111), and Pd(111) was studied by near edge X-ray absorption fine structure (NEXAFS). It is found that at 95 K, 1-butene is π-bonded to Pd(111), while it is di-σ bonded to Pt(111). At 95 K, 1,3-butadiene is loosely bonded on both Pd(111) and Pt(111). However, at 300 K, 1,3-butadiene adsorption differs, depending on the substrate. A di-σ bonding is observed on Pd(111) while on Pt(111), a di-σ interaction, keeping one central carbon-carbon double bond, is proposed. In the butadiene molecule half of the carbon atoms undergo a large rehybridization from sp 2 to sp 3 , as evidenced by high resolution electron energy loss spectroscopy (HREELS). These differences between 1,3-butadiene adsorption on Pt(111) and Pd(111) are discussed in terms of differences in catalytic activities and selectivities in the 1,3-butadiene hydrogenation reaction.

Interaction of Self-Assembled Monolayers of DNA with Electrons: HREELS and XPS Studies

We present results from high-resolution electron energy loss spectroscopy (HREELS) and XPS studies of self-assembled monolayers of DNA. The monolayers are well-organized and display sharp vibrational peaks in the HREEL spectra. The electrons interact mainly with the backbone of the DNA. The XPS results indicate that, in most of the samples studied, the phosphates on the DNA are not charged.

Vibrational identification of the surface reaction intermediates for the dehalogenation of trichloroethene on PdCu(110) alloy

Abstract The adsorption and dissociation of trichloroethene (TCE) on PdCu(1xa01xa00) have been investigated under the view of high resolution electron energy loss spectroscopy (HREELS) and first-principle quantum chemical calculations. At 180 K and after an exposure of 10 L, TCE is physisorbed on the surface. The HREELS spectrum is similar to the gas-phase one, measured by infrared spectroscopy. There are small shifts in the bands of the HREELS spectrum, which also indicate a weak interaction between the molecule and the surface. The chemistry of the TCE dissociation on PdCu(1xa01xa00) is more complex than the one on Cu(1xa01xa00). By increasing the surface temperature, a great variety of surface species occurs, as shown by the experimental spectra and confirmed by the calculations. This reaction seems to occur relatively early, at 200 K. At 280 K most of the CCl bonds have been already broken. The decrease of the intensity of the ν CCl stretching vibration and the increase of the intensity of the metalue5f8Cl vibration are shown to be fingerprints of this process.

Identification of reaction intermediates and products in the dehalogenation of trichloroethene on Cu(110)

Abstract The decomposition of trichloroethene, C 2 HCl 3 , on Cu(110) has been investigated as a function of temperature by RAIRS, HREELS and TPD. This has provided a detailed identification of intermediate surface species involved in the dechlorination reaction. Multilayers form readily at 85xa0K, desorbing at 140xa0K. A weakly perturbed molecular species exists at 150xa0K that is converted, with increasing temperature, to a CCH intermediate at the surface. This ethynyl intermediate subsequently disproportionates to produce C 2 H 2 and a carbon deposit at the surface. At T >300xa0K, C 2 H 2 desorption competes with the trimerisation reaction that leads to benzene evolution at 370xa0K. Cl atoms are retained at the surface up to high temperatures.

Interfacial chemistry in Al and Cu metallization of untreated and plasma treated polyethylene and polyethyleneterephthalate

The growth of Cu and Al films thermally evaporated onto polyethylene (PE) and polyethyleneterephthalate (PET) surfaces is followed in situ by XPS (X-ray Photoelectron Spectroscopy) and XAES (X-ray Auger Electron Spectroscopy) from the early submonolayer stages up to the completion of a metallic film. PE and PET surfaces were metallized first without any preliminary treatment. A second series of metallization experiments were run on the polymer surfaces but pretreated by a remote O2 microwave plasma (2.45 GHz). These metal films have also been investigated by AFM (Atomic Force Microscopy) in air. Both metals are shown not to undergo chemical interaction with low surface energy polyolefin such as PE. While an abrupt interface is seen with A1, a diffusion of Cu into the bulk of the polymer is demonstrated. Large size clusters are evidenced by AFM in the initial steps of deposition. Cu and A1 are both shown to react with PET, but not in the same way. In the case of A1, the chemical interaction across the meta...

HREELS characterisation of polymer surfaces using new generation spectrometers

Abstract Spectra of polystyrene film surfaces achieving a resolution of 2.55 meV (20.4 cm−1) were recorded using new generation high resolution electron energy loss spectroscopy spectrometers. Spectra show a high number of characteristic energy losses corresponding to infrared- and Raman-active modes. Mechanisms involved in the electron interaction with the film surface were unraveled through their energy dependence. Impact is the predominant mechanism revealing an analysis depth of some angstroms. Absence of dipole mechanisms is related to a surface conformation where phenyl rings are mostly perpendicular to the substrate.

New advances on the characterisation of polymer surfaces by HREELS

Self assembled monolayers (SAMs) of thiols functionalised with oligothiophene functions were used as models for polymer surfaces. Thienyl functionalisation simulates the surface region and demonstrates that the analysed depth is of the order of 10 A. Spectra of polystyrene (PS) films were recorded and show that impact mechanism dominates, which corroborates the high sensitivity of HREELS applied to polymer surfaces. Different orientation of phenyl groups is unravel for PS films deposited on platinum and silicon substrates, which is here related to a different conformation of the PS chains in the surface region of the film. To illustrate the state of the art of HREELS applied to organic films, spectra were recorded with old and new generation spectrometers.