Peer-reviewed Publications |
Baffou, G., Mayne, A. J., Comtet, G., & Dujardin, G. (2008). State selective electron transport through electronic surface states of 6H-SiC(0001)-3 x 3. Phys. Rev. B, 77(16), 165320.
Résumé: We investigate charge transport through electronic surface states of the 6H-SiC(0001)-3 x 3 surface. Three intrinsic surface states are located within the wide bulk band gap, in which two (S(1) and U(1)) arise from strongly correlated electronic states and the third (S(2)) has negligible electron correlation effects. Combined conductance and luminescence experiments with the scanning tunneling microscope show that the Mott-Hubbard surface states (S(1) and U(1)) have a high resistance (1.0 G Omega), while the noncorrelated state (S(2)) has a negligible resistance. Consequently, current can be selectively transported through any of these three surface states.
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Bellec, A., Riedel, D., Dujardin, G., Rompotis, N., & Kantorovich, L. N. (2008). Dihydride dimer structures on the Si(100):H surface studied by low-temperature scanning tunneling microscopy. Phys. Rev. B, 78(16), 165302.
Résumé: Surface reconstructions on the hydrogenated Si(100):H surface are observed and investigated by using a low-temperature (5 K) scanning tunneling microscope (STM). In addition to the well established 2x1 and 3x1 phases, linear structures extending over one to six silicon dimers along the same dimer row are observed. After a careful analysis of the corresponding STM topographies for both n-type and p-type doped silicon substrates, we conclude that these structures are dihydride dimers. This assignment is supported by ab initio density-functional calculations of the local density of states of dihydride structures of one or two dimers long. Furthermore, the calculation of the free-energy formation of our observed structure shows that their creation is closely linked with the hydrogenation process. These results demonstrate that the previous assignments of “split dimer” and “bow-tie” structures to dihydride dimers and dopant pairs, respectively, need to be reconsidered.
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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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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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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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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., 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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Lastapis, M., Martin, M., Riedel, D., & Dujardin, G. (2008). Role of the dopant in silicon on the dynamics of a single adsorbed molecule. Phys. Rev. B, 77(12), 125316.
Résumé: We investigate the role of the dopant in silicon on the dynamics of a single adsorbed molecule. We demonstrate that the dynamics of a single bistable molecule, a biphenyl molecule, adsorbed on a Si (100)-(2x1) surface is markedly dependent on the silicon type of doping (p or n) even though the electronic excitation and relaxation processes are unchanged. Both strongly and weakly chemisorbed individual biphenyl molecules are shown to interact differently with p- or n-doped Si (100) surfaces, thus inducing different stabilities of the adsorption configurations and different molecular dynamics. These effects rely on electrostatic interactions between distributed charges inside the molecule and charged surface states. The described phenomenon, which is a priori general, should be applicable to most of the molecules adsorbed on doped semiconductors having surface states in their band gap. This result is anticipated to have important applications in molecular electronic for positioning individual molecules with precision.
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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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Mamatkulov, M., Stauffer, L., Sonnet, P., Mayne, A. J., Comtet, G., & Dujardin, G. (2008). Theoretical simulations of the tip-induced configuration changes of the 4,4 '-diacetyl-p-terphenyl molecule chemisorbed on Si(001). J. Chem. Phys., 128(24), 244710.
Résumé: We have investigated from a theoretical point of view modifications of the 4,4'-diacetyl-p-terphenyl molecule chemisorbed on Si(001) induced by the scanning tunneling microscope (STM). In previous experiments, these modifications were observed to occur preferentially at the end of the molecule after a +4.0 V voltage pulse and at the center after a +4.5 V voltage pulse. In the framework of ab initio simulations, we have realized a systematic energetic study of the dissociative chemisorption of one, two, or three phenyl rings of the substituted p-terphenyl molecule. Charge densities were then calculated for the investigated configurations and compared to the STM topographies. Before manipulation with the STM tip, the substituted p-terphenyl molecule is preferentially adsorbed without phenyl ring dissociation, allowing a partial rotation of the central phenyl ring. Our results show that the STM induced modifications observed at the end of the molecule might originate from the dissociation of two phenyl rings (one central and one external ring), while the modifications occurring at the central part of the molecule can be interpreted as a dissociation of the two external rings. (c) 2008 American Institute of Physics.
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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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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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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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Yang, H., Baffou, G., Mayne, A. J., Comtet, G., Dujardin, G., & Kuk, Y. (2008). Topology and electron scattering properties of the electronic interfaces in epitaxial graphene probed by resonant tunneling spectroscopy. Phys. Rev. B, 78(4), 041408.
Résumé: Z-V scanning tunneling spectroscopy is used to probe the topology and electron scattering properties of the electronic interfaces of monolayer and bilayer graphenes, expitaxially grown on SiC(0001). The dZ/dV spectra validate existing calculations of the interface topology and provide evidence for new electron scattering properties due to changes in the electronic character of the bonding. Two sharp boundaries are observed: between the vacuum and the graphene pi state lying above the graphene atom plane and a subsurface barrier between the carbon-rich layer and the bulk SiC.
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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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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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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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Chapitres de Livres |
Mayne, A. J., & Dujardin, G. (2008). STM manipulation and Dynamics. In Dynamics (Vol. 3, pp. 681–759). Handbook of Surface Science. E. Hasselbrink and B.I. Lundqvist.
Résumé: This volume of the Handbook of Surface Science covers all aspects of the dynamics of surface processes. Two dozen world leading experts in this field address the subjects of energy exchange in gas atoms, surface collisions, the rules governing dissociative adsorption on surfaces, the formation of nanostructures on surfaces by self-assembly, and the study of surface phenomena using ultra-fast lasers. The chapters are written for both newcomers to the field as well as researchers.
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