Peer-reviewed Publications |
Bachellerie, D., Sizun, M., Aguillon, F., & Sidis, V. (2009). Effects of a Nonrigid Graphene Surface on the LH Associative Desorption of H Atoms and on the Deexcitation of Nascent H-2 Molecules Colliding with Model Walls of Carbonaceous Porous Material. J. Phys. Chem. A, 113(1), 108–117.
Résumé: A planar slab of 200 C atoms bound by the Brenner potential is used to study the Langmuir-Hinshelwood (LH) recombination of two physisorbed H atoms on a graphene sheet and to simulate afterward successive collisions of the nascent H-2 molecule with pore walls of a carbonaceous dust grain of the interstellar medium. The study is based on successive propagations of classical trajectories for the 200 C + 2 H atoms. The characteristics of H2 molecules formed by the LH reaction on the flexible surface are found to differ but negligibly from those formed on a rigid one. Collisions of those H,, molecules with graphitic pore walls are studied next. Reflection from and “trapping” onto the surface is observed and discussed. The most important energy transfer is from the molecule vibration to its rotation. This conversion mediates the transfer of the molecule internal energy to its translation or to surface heating. It is found that a single H-2-surface impact has little effect on the internal energy of the molecules. The grain absorbs on the average but a very weak energy. Several impacts are required to appreciably cool the molecule. The molecule cooling is accompanied by a significant increase of its translational energy. The swifter the molecules are or get, the larger the number of their impacts on the surface they undergo per unit time and the more efficiently cooled they get.
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Bachellerie, D., Sizun, M., Aguillon, F., Teillet-Billy, D., Rougeau, N., & Sidis, V. (2009). Unrestricted study of the Eley-Rideal formation of H-2 on graphene using a new multidimensional graphene-H-H potential: role of the substrate. Phys. Chem. Chem. Phys., 11(15), 2715–2729.
Résumé: The Brenner potential is adapted to handle chemical interactions and reactions of H atoms at a graphene surface. The adapted potential reproduces several important features of DFT computed data and reveals an extended puckering of the surface upon its adsorption of an H atom. This potential is used to investigate in a much more realistic way than has been done before, the Eley-Rideal abstraction reaction producing H-2 in H + H-graphene collisions at energies E-col <= 0.2 ev. The graphene surface is represented by a slab of 200 carbon atoms and the study is carried out using classical molecular dynamics for vertical incidences in a cylinder centered about the chemisorption axis. A highlight of the present study is that upon the arrival of the gas phase H atom, the adsorbent C atom is attracted and pulls out its surrounding surface atoms. The hillock thus formed remains puckered until the newly formed molecule is released. The range of impact parameters leading to reaction depends on the collision energy and is governed by the shape of the entrance channel potential; the reaction probability in this range is 100%. On average, in the studied E-col range, the available energy (3.92 eV + E-col) is shared as: 69 52% for the internal energy, 11-23% for the translation energy and 20 25% for the energy imparted the surface. Also, the average vibration and rotation energy levels of the nascent H-2 molecule are, respectively, < v > = 5-4 and < i > = 2-4.
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Diaz-Tendero, S., Borisov, A. G., & Gauyacq, J. - P. (2009). Extraordinary electron propagation length in a metallic double chain supported on a metal surface. Phys. Rev. Lett., 102(16), 166807.
Résumé: The present theoretical study shows that a double chain of Cu metal atoms adsorbed on a Cu(111) metal surface can guide an excited electron for distances exceeding 10 nm. The nanostructure appears to be quasi-decoupled from the substrate and thus to act as a nanowire. The origin of the above phenomenon is the interference between the decay of the quasistationary 1D sp-band states localized on each chain. This allows to approach the situation of the formation of bound states in the continuum first discussed in quantum systems by von Neumann and Wigner.
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Diaz-Tendero, S., Olsson, F. E., Borisov, A. G., & Gauyacq, J. - P. (2009). Excited electron dynamics in Cu nanowires supported on a Cu(111) surface. Phys. Rev. B, 79(11), 115438.
Résumé: We present a theoretical study of the excited electron dynamics in infinite Cu monoatomic chains (nanowires) supported on a Cu(111) surface. A joint approach based on the wave packet propagation and the density functional theory is used. The nanowire-induced potential obtained from ab initio density functional theory calculations serves as an input for the wave-packet propagation study of the excited electron dynamics. The energy dispersion and the lifetime of an unoccupied one-dimensional (1D) nanowire-localized electronic band with sp character are obtained. From the group velocity and lifetime of the 1D sp-band states, it follows that an excited electron can travel about four to five atomic sites along the nanowire before its escape into the bulk. We show that the surface projected band gap and the surface Brillouin zone backfolding of the substrate states play a fundamental role in the lifetime of the nanowire-localized states.
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Gauyacq, J. P., Diaz-Tendero, S., & Borisov, A. G. (2009). Mapping of the electron transmission through the wall of a quantum corral. Surf. Sci., 603(13), 2074–2081.
Résumé: We report on a theoretical study of the escape of confined surface states electrons from quantum corrals made of Cu adatoms on a Cu(1 1 1) surface. This study maps electron transmission through the corral wall and provides an extension of our earlier work focused on confinement in Cu corrals [S. Diaz-Tendero, F.E. Olsson, A.G. Borisov, J.P. Gauyacq, Phys. Rev. B 77 (2008) 205403]. The existence of two decay modes for the confined surface state is stressed: (i) non-resonant tunnelling through the corral wall concentrated on the Cu adatoms and (ii) a resonant-induced decay involving the transient formation of a resonant state localized on top of the corral wall. The present mapping of the electron transmission reveals how the interference between the two decay modes works: there exist regions where the electron leaves the corral, balanced by regions where it enters the corral, though the global behaviour of the quasi-stationary states is electron escape from the corral. (C) 2009 Elsevier B.V. All rights reserved.
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Lorente, N., & Gauyacq, J. - P. (2009). Efficient Spin Transitions in Inelastic Electron Tunneling Spectroscopy. Phys. Rev. Lett., 103(17), 176601.
Résumé: The excitation of the spin degrees of freedom of an adsorbed atom by tunneling electrons is computed using strong coupling theory. Recent measurements [Heinrich et al., Science 306, 466 ( 2004)] reveal that electron currents in a magnetic system efficiently excite its magnetic moments. Our theory shows that the incoming electron spin strongly couples with that of the adsorbate so that memory of the initial spin state is lost, leading to large excitation efficiencies. First-principles transmissions are evaluated in quantitative agreement with the experiment.
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M.Ziegler, J. K., R.Berndt, A.G.Borisov et J.P.Gauyacq. (2009). Linewidth of a cesium adatom resonance on Ag(111). Phys. Rev. B, 79, 075401.
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Morisset, S., Ferro, Y., & Allouche, A. (2009). Isotopic effects in the sticking of H and D atoms on the (0001) graphite surface. CHEMICAL PHYSICS LETTERS, 477(1-3), 225–229.
Résumé: A quantum study of the sticking of hydrogen and deuterium atoms chemisorbed onto graphite (0001) surface is carried out in the collinear scattering approximation, taking into account the phonon modes of the system. The sticking coefficients are calculated for hydrogen and deuterium atoms with incident energies ranging from 0.17 to 0.22 eV, for surface temperatures of 10 and 150 K. The calculation of the sticking coefficients of H and D evidenced an isotopic effect which is discussed. (C) 2009 Elsevier B.V. All rights reserved.
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Nave, S., & Jackson, B. (2009). Methane dissociation on Ni(111) and Pt(111): Energetic and dynamical studies. JOURNAL OF CHEMICAL PHYSICS, 130(5).
Résumé: Electronic structure studies and quantum scattering methods are used to elucidate the differing reactivities of methane on Ni(111) and Pt(111). For both surfaces the lowest energy pathway to dissociation is over the top site, where the static surface barrier to reaction is about 0.14 eV lower on Pt(111) than on Ni(111). If allowed to relax, both surfaces exhibit a puckering of the metal atoms in the vicinity of the adsorbates and at the transition state. Thus, motion of the lattice can change the barrier to reaction. A quantum model for dissociation is employed that includes several molecular coordinates, and allows for coupling to the lattice motion and puckering of the lattice. We find that on Ni(111) the lattice has time to pucker, increasing the reactivity relative to the static surface case. The more massive atoms on the Pt(111) surface do not have time to pucker during the reaction. As both lattices become vibrationally excited the reactivity increases significantly, particularly at low incident energies where tunneling dominates. Our model suggests that tunneling is important for these large barrier systems, particularly at the relatively low incident energies of the experiments. Our work also suggests that at the large nozzle temperatures of the experiments, there are contributions to the total reactivity from vibrationally excited molecules, particularly for Ni(111). Our model is in reasonable agreement with the experimental results for Ni(111), while we significantly underestimate the reactivity on Pt(111) as well as the difference in reactivity between Ni(111) and Pt(111). This may result from errors in our total-energy calculations and/or effects due to motion (tunneling) of the methyl group at the transition state.
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Teperik, T. V., & Borisov, A. G. (2009). Optical resonances in the scattering of light from a nanostructured metal surface: A three-dimensional numerical study. Phys. Rev. B, 79(24), 245409.
Résumé: We present the full three-dimensional numerical study of the scattering of light by the gold substrate composed of square periodic array of inverted pyramidal pits. The time-dependent wave-packet-propagation approach was used to extract the complete scattering matrix as well as the near fields. The role of the pit-localized and surface-supported plasmonic modes in resonant reflection spectra and field enhancement is revealed. We show that the resonances in the specular reflection arise because of the excitation of the pit-localized plasmons while resonant absorption is linked with excitation of the surface-plasmon polaritons. For certain structure parameters absorption can reach 100%. Our theoretical results are in a good agreement with recently published experimental data [N. M. B. Perney , Opt. Express 14, 847 (2006); Phys. Rev. B 76, 035426 (2007)]. We also show that present structure allows one to obtain zero specular reflection where all scattered intensity is redirected into the grazing beams.</p>.
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Tiwari, A. K., Nave, S., & Jackson, B. (2009). Methane Dissociation on Ni(111): A New Understanding of the Lattice Effect. PHYSICAL REVIEW LETTERS, 103(25), 253201.
Résumé: The nature of the lattice motion during the dissociation of methane on Ni(111) is analyzed in great detail, and various models for including lattice effects are explored. It is shown that the thermal vibrations of the lattice strongly modify the reactivity, but that the lattice motion is relatively unperturbed by the incident molecule during the collision, in contrast with several earlier predictions. Based on these studies we propose a new model to describe the effects of lattice motion, which agrees well with exact quantum calculations.
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Zugarramurdi, A., Zabala, N., Silkin, V. M., Borisov, A. G., & Chulkov, E. V. (2009). Lifetimes of quantum well states and resonances in Pb overlayers on Cu(111). Phys. Rev. B, 80(11), 115425.
Résumé: We present results of calculations of the lifetimes of excited electrons (holes) in quantum well states and quantum well resonances in Pb overlayers supported on Cu(111). Many-body decay via inelastic energy relaxation and one-electron decay via energy-conserving one-electron transfer into the substrate are considered. One-electron energies and wave functions have been computed for different coverages of the Pb overlayer (from 1 to 18 monolayers) by using a one-dimensional pseudopotential for the entire overlayer-substrate system in the framework of density functional theory within the local density approximation. The elastic (energy-conserving resonant electron transfer) contribution to the total lifetime broadening of quantum well resonances has been calculated within the wave packet propagation method. The inelastic electron-electron (many-body) contribution to the lifetime broadening of both occupied and unoccupied quantum well states has been evaluated using GW approximation. The decay mechanisms of both quantum well states and quantum well resonances in thick overlayers are discussed.
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