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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Bergeron, H., Rougeau, N., Sidis, V., Sizun, M., Teillet-Billy, D., & Aguillon, F. (2008). OH Formation from O and H Atoms Physisorbed on a Graphitic Surface through the Langmuir-Hinshelwood Mechanism: A Quasi-Classical Approach. J. Phys. Chem. A, 112(46), 11921–11930.
Résumé: We study the quasi-classical dynamics of OH formation on a graphitic surface through the Langmuir-Hinshelwood (LH) mechanism when both 0 and H ground-state atoms are initially physisorbed on the surface. The model proceeds from previous theoretical work on the LH formation of the H-2 molecule on graphite [Morisset, S.; Aguillon, F.; Sizun, M.; Sidis, V. J. Chem. Phys. 2004, 121, 6493; ibid 2005, 122, 194704]. The H-graphite system is first revisited with a view to get a tractable DFT-GGA computational prescription for the determination of atom physisorption onto graphitic surfaces. The DZP-RPBE combination is found to perform well; it is thereafter used along with MP2 calculations to determine the physisorption characteristics of atomic oxygen on graphitic surfaces. We also deal with chemisorption. In accordance with previous work, we find that 0 chemisorbs on graphite in a singlet spin state epoxy-like conformation. In the triplet state we find only “metastable” chemisorption with an activation barrier of 0.2 eV. The physisorption results are then used in the LH dynamics calculation. We show that in the [0.15 meV, 12 meV] relative collision energy range of the reacting 0 and H atoms on the surface, the OH molecule is produced with a large amount of internal energy (similar or equal to 4 eV) and a significant translation energy (>= 100 meV) relative to the surface.
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Borisov, A. G., Sametoglu, V., Winkelmann, A., Kubo, A., Pontius, N., Zhao, J., Silkin, V. M., Gauyacq, J. P., Chulkov, E. V., Echenique, P. M., & Petek, H. (2008). Pi resonance of chemisorbed alkali atoms on noble metals. Phys. Rev. Lett., 101(26), 266801.
Résumé: We have performed a joint experimental and theoretical study of the unoccupied electronic structure of alkali adsorbates on the (111) surfaces of Cu and Ag. Combining angle- and time-resolved two-photon photoemission spectroscopy with wave packet propagation calculations we show that, along with the well known sigma resonance oriented along the surface normal, there exist long-lived alkali-localized resonances oriented parallel to the surface (pi symmetry). These new resonances are stabilized by the projected band gap of the substrate and emerge primarily from the mixing of the p and d Rydberg orbitals of the free alkali atom modified by the interaction with the surface.
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Diaz-Tendero, S., Foelsch, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J. - P. (2008). Electron propagation along Cu nanowires supported on a Cu(111) surface. Nano Lett., 8(9), 2712–2717.
Résumé: We present a joint experimental-theoretical study of the one-dimensional band of excited electronic states with sp character localized on Cu nanowires supported on a Cu(111) surface. Energy dispersion and lifetime of these states have been obtained, allowing the determination of the mean distance traveled by an excited electron along the nanowire before it escapes into the substrate. We show that a Cu nanowire supported on a Cu(111) surface can guide a one-dimensional electron flux over a short distance and thus can be considered as a possible component for nanoelectronics devices.
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Diaz-Tendero, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J. - P. (2008). Theoretical study of electron confinement in Cu corrals on a Cu(111) surface. Phys. Rev. B, 77(20), 205403.
Résumé: We present a theoretical study of the energies, lifetimes, wave functions, and decay paths of the excited electronic states in corral structures formed by Cu adatoms on the Cu(111) surface. Three different corrals with 35, 48, and 70 Cu adatoms have been studied within a joint approach including the density functional theory and wave packet propagation. Confinement of the electronic surface state inside the corral structure leads to the formation of well-defined resonances in the density of electronic states. Particular emphasis is given in the present work to the role of excited electronic states localized on the ring of Cu adatoms forming the corral. While never discussed in the past for corral structures, these states are equivalent to the one-dimensional sp band of Cu atomic chains assembled on the Cu(111) surface that has been recently studied thoroughly. The coupling between the confined surface state resonances and the sp state localized on the Cu ring have been studied in detail. It is shown that the sp state localized on the corral wall appears as a strong perturbation in the spectrum of confined states.
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Ferro, Y., Teillet-Billy, D., Rougeau, N., Sidis, V., Morisset, S., & Allouche, A. (2008). Stability and magnetism of hydrogen dimers on graphene. PHYSICAL REVIEW B, 78(8), 085417.
Résumé: We report on the magnetism and stability of H dimers on a graphene sheet. Graphene is used as a simple model to grasp the basics of the H interaction with graphitic systems including graphite, graphene, polyaromatic hydrocarbons, and nanotubes. The dimers investigated here are found to be in ferromagnetic, antiferromagnetic, or nonmagnetic states. Results obtained from DFT calculations on the H dimer adsorption are analyzed with the help of spin-density maps. We thereby show that the dimer stability results from the magnetic properties of the pair of H atoms on graphene. The stability of dimers adsorbed in ortho and para positions is particularly emphasized. In order to rationalize the single and double H atom adsorption mechanisms, the whole pair formation process is divided into theoretical elementary steps to which energetic values are assigned.
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Gauyacq, J. P. (2008). Laser-induced photo-desorption in the Na/Cu(111) system. SURFACE SCIENCE, 602(22), 3477–3483.
Résumé: Desorption in the Na/Cu(111) system induced by an electronic excitation is studied using a quantal approach. The system is excited by a laser pulse in the fs range to the Na state corresponding to the transient capture of an electron by the alkali adsorbate. The present quantal approach describes on an equal footing the laser-induced vibrational excitation of the adsorbate in the adsorption well and the photo-desorption process. It confirms earlier results using a semi-classical input. It also allows a discussion of the photo-desorption probability with the photon energy: the maximum of the desorption probability per absorbed photon occurs off-resonance in the high-energy wing of the electronic transition. This feature is related to the dynamics of the laser-induced process. (C) 2008 Elsevier B.V. All rights reserved.
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M.Wiesenmayer, M. B., S.Mathias, M.Wessendorf, E.V.Chulkov, V.M.Silkin, A.G.Borisov, J.P.Gauyacq, P.M.Echenique et M.Aeschlimann. (2008). Lifetime of an adsorbate excitation modified by a tunable two-dimensional substrate. Phys. Rev. B, 78, 245410.
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Marinica, D. C., Borisov, A. G., & Shabanov, S. V. (2008). Bound States in the continuum in photonics. Phys. Rev. Lett., 100(18), 183902.
Résumé: With examples of two parallel dielectric gratings and two arrays of thin parallel dielectric cylinders, it is shown that the interaction between trapped electromagnetic modes can lead to scattering resonances with practically zero width. Such resonances are the bound states in the radiation continuum first discovered in quantum systems by von Neumann and Wigner. Potential applications of such photonic systems include: large amplification of electromagnetic fields within photonic structures and, hence, enhancement of nonlinear phenomena, biosensing, as well as perfect filters and waveguides for a particular frequency, and impurity detection.
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Morisset, S., & Allouche, A. (2008). Quantum dynamic of sticking of a H atom on a graphite surface. JOURNAL OF CHEMICAL PHYSICS, 129(2).
Résumé: A quantum study of the sticking of a hydrogen atom chemisorbed onto graphite (0001) surface was carried out also including the phonon modes of the system in the collinear scattering approximation. A new model was developed to extract the substrate vibrational modes from density functional theory (DFT) calculation and include them in the total system dynamics. The resulting coupled-channel equations are numerically developed along time using the wave packet methods. The sticking coefficients are calculated for hydrogen atoms incident energies ranging from 0.17 and 1.3 eV for a surface temperature of 10 K and between 0.17 and 0.2 eV for a surface temperature of 150 K. The results are found to be in good agreement with the experimental work. (C) 2008 American Institute of Physics.
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Quijada, M., Borisov, A. G., & Muino, R. D. (2008). Time-dependent density functional calculation of the energy loss of antiprotons colliding with metallic nanoshells. Phys. Status Solidi, 205(6), 1312–1316.
Résumé: Time-dependent density functional theory is used to study the interaction between antiprotons and metallic nanoshells. The ground state electronic proper-ties of the nanoshell are obtained in the jellium approximation. The energy lost by the antiproton during the collision is calculated and compared to that suffered by antiprotons traveling in metal clusters. The resulting energy loss per unit path length of material in thin nanoshells is larger than the corresponding quantity for clusters. It is shown that the collision process can be interpreted as the antiproton crossing of two nearly bi-dimensional independent metallic systems. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
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Teperik, T. V., Garcia de Abajo, F. J., Borisov, A. G., Abdelsalam, M., Bartlett, P. N., Sugawara, Y., & Baumberg, J. J. (2008). Omnidirectional absorption in nanostructured metal surfaces. Nature Photon., 2(5), 299–301.
Résumé: Light absorbers available at present provide far from optimal black-body performance. The need for more efficient absorbers is particularly acute on the microscale, where they can play a significant role in preventing crosstalk between optical interconnects, and also as thermal light-emitting sources. Several efforts have been made in this context to achieve near-total but directionally dependent absorption using periodic grating structures(1-7). However, the ability to absorb light completely for any incident direction of light remains a challenge. Here we show that total omnidirectional absorption of light can be achieved in nanostructured metal surfaces that sustain localized optical excitations. The effect is realized over a full range of incident angles and can be tuned throughout the visible and near-infrared regimes by scaling the nanostructure dimensions. We suggest that surfaces displaying omnidirectional absorption will play a key role in devising efficient photovoltaic cells in which the absorbed light leads to electron-hole pair production.
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Actes de Conférences |
Gauyacq, J. - P., Borisov, A. G., & Kazansky, A. K. (2008). Theoretical study of excited electronic states at surfaces, link with photo-emission and photo-desorption experiments. In 24TH SUMMER SCHOOL AND INTERNATIONAL SYMPOSIUM ON THE PHYSICS OF IONIZED GASES (Vol. 133, 012009).
Résumé: Excited electronic states at surfaces play a very important role in a variety of surface processes. These excited states have a finite lifetime due to electron-transfer processes and their efficiency as reaction intermediates depends crucially on their lifetime. A review of several physical situations, where an excited electronic state localized on an atom interacting with a metal surface intervenes in a surface process, is presented with an emphasis on the way the metal electronic structure influences the excited state dynamics. Examples are chosen among the alkali/metal systems, stressing how the same transient electronic state can influence different dynamical processes.
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