Peer-reviewed Publications |
Abouaf, R., & Teillet-Billy, D. (2008). Low energy electron collisions in H2S and H2Se: Structure in dissociative attachment cross-sections. INTERNATIONAL JOURNAL OF MASS SPECTROMETRY, 277(1-3), 79–83.
Résumé: Dissociative electron attachment between 0 and 4 eV has been investigated in hydrogen sulfide and hydrogen selenide with an improved electron resolution (0.040 eV). HS- and HSe- cross-sections versus electron energy present vertical onsets revealing that the potential surfaces of the resonances which are reached around 2 eV are bound. A well-developed and intriguing structure is observed in HS-, S-, HSe- and Se- cross-sections. It could reveal interferences due to an attractive resonance having a lifetime of the order of one vibrational period. The strong similarity between the anion behaviour in H2S and H2Se is in contrast with H2O where no dissociative attachment process occurs in this energy range. (C) 2008 Elsevier B.V. All rights reserved.
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Abouaf, R., Ptasinska, S., & Teillet-Billy, D. (2008). Low energy electron impact on gas phase 5-nitrouracil. CHEMICAL PHYSICS LETTERS, 455(4-6), 169–173.
Résumé: Excitation of the first electronic states, vibrational excitation between 1 and 3 eV, and negative ion formation (0-2 eV) in gas phase 5-nitrouracil are presented. Five singlet states are clearly identified at 4.76; 5.72; 6.82; 7.82 and 9.2 eV. A band at 3.7 eV could be assigned to a triplet state. The vibrational modes observed indicate resonant states having both pi* and sigma* character. The most intense anions (M-NO2) , (M-H) appear at zero energy with huge cross sections (>= 10 18 m(2)). Anion cross sections versus electron energy reveal structures interpreted using the anion energy thresholds found by DFT calculations. (C) 2008 Elsevier B.V. All rights reserved.
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Amiaud, L., Momeni, A., Dulieu, F., Fillion, J. H., Matar, E., & Lemaire, J. L. (2008). Measurement of the adsorption energy difference between ortho- and para-D(2) on an amorphous ice surface. Phys. Rev. Lett., 100(5), 056101.
Résumé: Molecular hydrogen interaction on water ice surfaces is a major process taking place in interstellar dense clouds. By coupling laser detection and classical thermal desorption spectroscopy, it is possible to study the effect of rotation of D(2) on adsorption on amorphous solid water ice surfaces. The desorption profiles of ortho- and para-D(2) are different. This difference is due to a shift in the adsorption energy distribution of the two lowest rotational states. Molecules in J('')=1 rotational state are on average more strongly bound to the ice surface than those in J('')=0 rotational state. This energy difference is estimated to be 1.4 +/- 0.3 meV. This value is in agreement with previous calculation and interpretation. The nonspherical wave function J('')=1 has an interaction with the asymmetric part of the adsorption potential and contributes positively in the binding energy.
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Bobrov, K., & Guillemot, L. (2008). Interplay between adsorbate-induced reconstruction and local strain: Formation of phases on the Cu(110)-(2x1): O surface. PHYSICAL REVIEW B, 78(12), 121408.
Résumé: We present an STM study on the interplay between adsorbate-induced reconstruction and local strain on the oxygen adsorbed Cu(110) surface. Thermal annealing of the surface resulted in surface terrace ripening revealing larger terraces, uniformly covered by the (2x1)-O reconstructed phase, separated by step bunches. The largest terrace was found to be partially splitted by emerging dislocations inducing strong inhomogeneous strain in their close vicinity. This extra strain caused local conversion of the dominating (2x1)-O phase into oxygen chemisorbed phases drastically different from the dominating phase. A meaningful correlation between lateral evolution of the extra strain and structure of these phases has been found. The symmetry of the discovered phases has been determined and their structural models have been elaborated.
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Bundaleski, N., Khemliche, H., Soulisse, P., & Roncin, P. (2008). Grazing incidence diffraction of keV helium atoms on a Ag(110) surface. Phys. Rev. Lett., 101(17), 177601.
Résumé: Diffraction of fast atoms at grazing incidence has been recently demonstrated on the surface of alkali halides and wide band gap semiconductors, opening applications for the online monitoring of surface processes such as growth of ultrathin layers. This Letter reports energy resolved diffraction of helium on Ag(110) metal surface showing that a band gap is not mandatory to restrict the decoherence due to electron-hole pair excitations by the keV projectile. Measurement of the energy loss, which is in the eV range, sheds light on the scattering process.
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Burean, E., Abouaf, R., Lafosse, A., Azria, R., & Swiderek, P. (2008). High-resolution vibrational electron-energy-loss spectroscopy of gaseous and solid glycine. JOURNAL OF PHYSICAL CHEMISTRY C, 112(25), 9405–9411.
Résumé: The vibrational spectra of thin solid films of glycine deposited at temperatures between 12 and 130 K, as well as gaseous glycine, have been measured by high-resolution electron-energy-loss (HREEL) spectroscopy. The spectra are dominated by hydrogen-bonded glycine dimers when the films are deposited at low temperatures. The HREEL spectra of films deposited at higher temperature (130 K) have a different habitus that can be explained on the basis of a proton transfer reaction leading to the formation of zwitterionic glycine. Gas-phase HREEL spectra show bands characteristic of the neutral monomer of glycine. The results are discussed in relation to a previous study aiming at glycine synthesis in mixed ices under the effect of low-energy electrons.
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Dablemont, C., Lang, P., Mangeney, C., Piquemal, J. Y., Petkov, V., Herbst, F., & Viau, G. (2008). FTIR and XPS study of Pt nanoparticle functionalization and interaction with alumina. LANGMUIR, 24(11), 5832–5841.
Résumé: Platinum nanoparticles with a mean size of 1.7 nm were synthesized by reduction in sodium acetate solution in 1,2-ethanediol. The particles were then functionalized with dodecylamine, dodecanethiol, and omega-mercapto-undecanoic acid (MUDA). Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) showed important variations of the particle surface state with functionalization whereas their structure differs only slightly. Platinum-to-sulfur charge transfer inferred front XPS of thiol-coated particles enabled the identification of the formation of Pt delta+-S delta- bonds. The native carbon monoxide (CO) at the surface of the particles was a very efficient probe for following the functionalization of the particles by FTIR. The red shift of nu(CO) accounts for the nature of the ligands at the surface of the particles and also for their degree of functionalization. Immobilization on alumina substrates of particles functionalized with MUDA was realized by immersion in colloidal solutions. Free molecules, isolated particles, and aggregates of particles interconnected by hydrogen bonds at the surface of alumina were evidenced by FTIR. With successive washings, the energy variation of the CO stretch of carbon monoxide and of carboxylic acid groups and the relative intensity nu(CH2)/nu(CO) showed that the free molecules are eliminated first, followed by aggregates and less-functionalized particles. Particles presenting a high degree of functionalization by MUDA remain and interact strongly with alumina.
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Guillemot, L., Bandurin, Y., Bobrov, K., & Esaulov, V. A. (2008). Electron transfer processes between sputtered O atoms and Ag(110): O(n x 1) reconstructed surfaces. JOURNAL OF PHYSICS-CONDENSED MATTER, 20(35).
Résumé: We present results of a study of sputtered oxygen atom outgoing trajectory dependence of the electron transfers with oxidized Ag(110) surfaces reconstructed in different (n x 1) added row structures. With a charge state resolved time-of-flight-direct recoil spectroscopy investigation using 4 keV Ar(+) incident ions, we determine relative yields of sputtered O and Ag atoms as well as the fraction of sputtered O-ions, for different incident polar and azimuthal angles. The relative yields of sputtered O atoms are satisfactorily reproduced by a classical dynamics simulation. No sputtered Ag-ions were detected. A qualitative discussion of the features of the oxygen negative ion fractions suggests that its description needs, in general, to take into account both capture and loss of electrons as the oxygen atom leaves the surface. The experimental data also suggest that one needs to correctly describe the corrugation of the surface and that the electron loss rates should be site-specific.
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Guo, Z., Zheng, W., Hamoudi, H., Dablemont, C., Esaulov, V. A., & Bourguignon, B. (2008). On the chain length dependence of CH3 vibrational mode relative intensities in sum frequency generation spectra of self assembled alkanethiols. SURFACE SCIENCE, 602(23), 3551–3559.
Résumé: A global modelling of Sum Frequency Generation (SFG) spectra of the self assembly of alkanethiols is presented. All CH modes are modelled together. CH2 modes are assumed local to allow easy calculation of the spectrum as a function of molecular conformation. Ab initio molecular hyperpolarizabilities are used. A phenomenological approach is used to include the Fermi resonance in the model: the calculated intensity of the CH3 symmetric stretch is redistributed according to intensity borrowing by the Fermi resonance. The model is applied to octadecanethiol (ODT) and pentadecanethiol (PDT). The even/odd intensity alternation of SFG CH3 vibrational bands as a function of chainlength is used to test the model. It is found that the relative magnitudes of the hyperpolarizability tensors of the CH3 asymmetric and symmetric modes need to be adjusted. The model provides tilt and twist angles of the alkyl chain in agreement with the literature. It shows that the all trans conformation does not imply the absence of CH2 bands in SFG spectra. In addition, new information is obtained. In particular, if two types of molecular conformations are assumed, the C planes of the two molecules must be perpendicular to each other. (C) 2008 Elsevier B.V. All rights reserved.
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Hamoudi, H., Dablemont, C., & Esaulov, V. A. (2008). Interaction of Li+ with a Au(100) surface. SURFACE SCIENCE, 602(14), 2486–2490.
Résumé: Results of a study of Li+ neutralisation on Au(1 0 0) are presented and compared with an earlier study of neutralisation on Au(1 1 1), where anomalously high neutralisation had been tentatively related to the existence of the L-bandgap and occupied surface state. Neutralisation probability on Au(1 0 0) has a similar magnitude to that on Au(1 1 1) and a similar incident energy dependence, though the electronic structure is different. These results for surfaces with high workfunctions are very unexpected, since significantly smaller values may be expected in a “traditional” picture of a Li+ ion departing from the surface. We can account for the relatively large value of the neutral fraction by considering that the Li(2s) level lies below the Fermi level at short atom-surface separations as this has been shown to be the case for the Cu surface by Goldberg et al. This allows electron capture at small distances and the surviving neutrals account well for the behaviour of the neutral fraction at energies above 500 eV but not at lower energies. This could be due to various reasons including intermediate Li- formation and non-adiabatic effects. (C) 2008 Published by Elsevier B.V.
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Hamoudi, H., Guo, Z., Prato, M., Dablemont, C., Zheng, W. Q., Bourguignon, B., Canepa, M., & Esaulov, V. A. (2008). On the self assembly of short chain alkanedithiols. PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 10(45), 6836–6841.
Résumé: A study of the self-assembly of nonane-alkanedithiol monolayers on gold in n-hexane and ethanol solvents is presented. Self-assembled monolayers (SAMs) are characterised by reflection-absorption infrared spectroscopy (RAIRS), sum frequency generation (SFG) and spectroscopic ellipsometry (SE) measurements. Data obtained for alkanethiols SAMs are also shown for comparison. The measurements show that nicely organized HSC(9)SH SAMs can be obtained in n-hexane provided that N(2)-degassed solutions are used and all preparation steps are performed in the absence of ambient light. SFG measurements show that these SAMs have free standing SH groups. Use of an un-degassed and/or light-exposed n-hexane solutions leads to a worse layer organization. Preparation in ethanol, even in degassed solutions with processing in the dark, leads to poorly organized layers and no sign of free-SH groups was observed.
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Hoffman, A., Lafosse, A., Michaelson, S., Bertin, M., & Azria, R. (2008). Nano size effects in the high resolution electron energy loss spectra and excitation function of hydrogenated diamond films. SURFACE SCIENCE, 602(18), 3026–3032.
Résumé: The present work studies the high resolution electron energy loss spectra (HR-EELS) and excitation function of hydrogenated diamond films composed of diamond grains of varying size of similar to 300, similar to 20 nm and similar to 5 nm. It is reported that HR-EELS modes associated with C-C lattice phonons are comparably more intense than modes associated with the C-H surface vibrational modes in the case of nano-crystal line compared to micro-crystalline diamond films. Excitation function measurements of the different modes show a pronounced maximum at similar to 8 eV for the nano-diamond films, whereas for micro-crystalline films similar modes showed maximum intensities at 13 eV with a smaller contribution at 8 eV. It is reported that the elastic electron reflectivity is substantially larger for the nano-diamond films, showing broad maxima at similar to 8 and similar to 13 eV in both cases. It is suggested that these effects are associated with the larger probability for inelastic scattering of electrons by lattice phonons mediated by scattering with internal grain boundaries and defects in the case of nano-crystalline diamond films. (C) 2008 Elsevier B.V. All rights reserved.
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Lafosse, A., Bertin, M., Michaelson, S., Azria, R., Akhvlediani, R., & Hoffman, A. (2008). Surface defects induced by in-situ annealing of hydrogenated polycrystalline diamond studied by high resolution electron energy loss spectroscopy. DIAMOND AND RELATED MATERIALS, 17(6), 949–953.
Résumé: Plasma hydrogenation of polycrystalline diamond films results in a fully hydrogenated well-ordered diamond surface and etching of the amorphous phase located at grain boundaries. Vacuum annealing to 1000 degrees C followed by in-situ hydrogenation by thermal activated hydrogen of the bared diamond surface results in the formation of sp(3)-CH(x) adsorbed groups located on the top surface. Annealing of the in-situ hydrogenated surface to 600 degrees C results in desorption of these species and partial reconstruction of the film surface. Some irreversible surface degradation was detected in the in-situ annealed and hydrogenated surface compared to the state of the surface obtained upon plasma hydrogenation. (C) 2008 Elsevier B.V. All rights reserved.
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Lemaire, J. L., Fillion, J. H., Dulieu, F., Momeni, A., Baouche, S., Amiaud, L., & Cobut, V. (2008). Formation of molecules in the interstellar medium. In search for formation mechanisms of molecular H2 on the interstellar dust grains: the FORMOLISM experiment. Actual Chim., (315), III-IX.
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Manson, J. R., Khemliche, H., & Roncin, P. (2008). Theory of grazing incidence diffraction of fast atoms and molecules from surfaces. Phys. Rev. B, 78(15), 155408.
Résumé: Prompted by recent experimental developments, a theory of surface scattering of fast atoms at grazing incidence is developed. The theory gives rise to a quantum-mechanical limit for ordered surfaces that describes coherent diffraction peaks whose thermal attenuation is governed by a Debye-Waller factor, however, this Debye-Waller factor has values much larger than would be calculated using simple models. A classical limit for incoherent scattering is obtained for high energies and temperatures. Between these limiting classical and quantum cases is another regime in which diffraction features appear that are broadened by the motion in the fast direction of the scattered beam but whose intensity is not governed by a Debye-Waller factor. All of these limits appear to be accessible within the range of currently available experimental conditions.
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Valdes, J. E., Vargas, P., Celedon, C., Sanchez, E., Guillemot, L., & Esaulov, V. A. (2008). Electronic density corrugation and crystal azimuthal orientation effects on energy losses of hydrogen ions in grazing scattering on a Ag(110) surface. PHYSICAL REVIEW A, 78(3).
Résumé: We present a detailed study of the energy losses of hydrogen ions that are scattered off an Ag (110) single-crystal surface for primary energies between 1 and 4 keV. We performed measurements for grazing angles as a function of crystal azimuthal orientation, which show large differences in energy losses. Experimental results are discussed by means of trajectory calculations of protons scattered under grazing-incidence conditions on the surface. Using nonlinear models for the stopping power, ab initio crystal structure calculations of the electronic density, and semiclassical simulations, we obtain data that are in very good agreement with experimental results. These simulations allow us to properly take into account the variations of the surface electronic density and hence obtain an accurate description of the energy loss processes for ion scattering along various azimuthal orientations of the target.
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Actes de Conférences |
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Bundaleski, N., Khemliche, H., Rousseau, P., Cassimi, A., Soulisse, P., & Roncin, P. (2008). COLLISIONS OF IONS WITH INSULATOR SURFACES: CHARGING AND DISCHARGING DYNAMICS. In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012016).
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Khemliche, H., Soulisse, P., Bundaleski, N., & Roncin, P. (2008). SURFACE AND THIN FILM ANALYSIS USING GRAZING INCIDENCE FAST ATOM DIFFRACTION (GIFAD). In Publications of the Astronomical Observatory of Belgrade (Vol. 84, p. 142).
Résumé: Grazing collisions at surfaces offer rather contrasted conditions. For well ordered flat surfaces, the scattering is spread among several lattice sites, each of which produces only a tiny elementary deflection. If, in addition, the atomic projectile is aligned along a crystallographic direction, the surface appears as made of parallel furrows which act as a diffraction grating for the atomic wave. We will show that the analysis of characteristic diffraction pattern recorded on the position sensitive detector located downstream allow a sensitive measure of the shape of the surface electronic density. At variance, if a terrace edge or an ad-atom is sitting on the surface along the trajectory, a quasi-binary collision will follow in which energy and momentum conservation allow identification of the mass of the collision partner.
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Rousseau, P., Khemliche, H., Bundaleski, N., Soulisse, P., Momeni, A., & Roncin, P. (2008). Surface analysis with grazing incidence fast atom diffraction (GIFAD). In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012013).
Résumé: Grazing collisions at surfaces offer rather contrasted conditions. For well ordered flat surfaces, the scattering is spread among several lattice sites, each of which produces only a tiny elementary deflection. If, in addition, the atomic projectile is aligned along a crystallographic direction, the surface appears as made of parallel furrows or as a washboard which act as a diffraction grating for the atomic wave. We will show that the analysis of characteristic diffraction pattern recorded on a position sensitive detector located downstream allows a sensitive measure of the shape of the surface electronic density. A modified Debye Waller factor is proposed to explain the observed diffraction signal.
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