Peer-reviewed Publications |
Bulard, E., Guo, Z., Zheng, W., Dubost, H., Fontaine-Aupart, M. - P., Bellon-Fontaine, M. - N., Herry, J. - M., Briandet, R., & Bourguignon, B. (2011). Non-Invasive Vibrational SFG Spectroscopy Reveals That Bacterial Adhesion Can Alter the Conformation of Grafted “Brush” Chains on SAM. Langmuir, 27(8), 4928–4935.
Résumé: Understanding bacterial adhesion on a surface is a crucial step to design new materials with improved properties or to control biofilm formation and eradication. Sum Frequency Generation (SFG) vibrational spectroscopy has been employed to study in situ the conformational response of a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film to the adhesion of hydrophilic and hydrophobic ovococcoid model bacteria. The present work highlights vibrational SFG spectroscopy as a powerful and unique non-invasive biophysical technique to probe and control bacteria interaction with ordered surfaces. Indeed, the SFG vibrational spectral changes reveal different ODT SAM conformations in air and upon exposure to aqueous solution or bacterial adhesion. Furthermore, this effect depends on the bacterial cell surface properties. The SFG spectral modeling demonstrates that hydrophobic bacteria flatten the ODT SAM alkyl chain terminal part, whereas the hydrophilic ones raise this ODT SAM terminal part. Microorganism-induced alteration of grafted chains can thus affect the desired interfacial functionality, a result that should be considered for the design of new reactive materials.
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Bundaleski, N., Soulisse, P., Momeni, A., Khemliche, H., & Roncin, P. (2011). Decoherence in fast atom diffraction from surfaces. Nucl. Instrum. Methods Phys. Res., B, 269(11), 1216–1220.
Résumé: Diffraction of fast atoms from crystal surfaces at grazing incidence (GIFAD) has now been observed on all types of materials, from wide band gap insulators to metals, including semiconductors. Since mainly the (slow) motion normal to the surface is important diffraction patterns are comparable to those obtained in thermal energies atomic diffraction (TEAS), however, the specific scattering geometry of GIFAD has a strong influence on decoherence phenomena. The contribution of atomic vibrations is much less pronounced than in TEAS but other sources of decoherence such as electronic excitations, clearly observed on metals, can participate due to the comparatively large projectile velocity parallel to the surface. We present here simple models that describe these decoherence effects. The results are in good agreement with the experimental results. (C) 2010 Elsevier B.V. All rights reserved.
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Chiaravalloti, F., Dujardin, G., Riedel, D., Pinto, H. P., & Foster, A. S. (2011). Atomic-scale study of the adsorption of calcium fluoride on Si(100) at low-coverage regime. PHYSICAL REVIEW B, 84(15), 155433.
Résumé: We investigate, experimentally and theoretically, the initial stage of the formation of Ca/Si and Si/F structures that occurs during the adsorption of CaF(2) molecules onto a bare Si(100) surface heated to 1000 Kin a low-coverage regime (0.3 monolayer). A low-temperature (5 K) scanning tunneling microscope (STM) is used to observe the topographies and the electronic properties of the exposed silicon surfaces. Our atomic-scale study reveals that several chemical reactions arise during CaF(2) deposition, such as dissociation of the CaF(2) molecules and etching of the surface silicon dimers. The experimental and calculated STM topographies are compared using the density functional theory, and this comparison enables us to identify two types of reacted structures on the Si(100) surface. The first type of observed complex surface structure consists of large islands formed with a semiperiodic sequence of 3 x 2 unit cells. The second one is made of isolated Ca adatoms adsorbed at specific sites on the Si(100)-2 x 1 surface.
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Diaz-Tendero, S., Borisov, A. G., & Gauyacq, J. - P. (2011). Theoretical study of the electronic excited states in ultrathin ionic layers supported on metal surfaces: NaCl/Cu(111). Phys. Rev. B, 83(11), 115453.
Résumé: We present a theoretical study of the electronic excited states in ultrathin ionic layers supported on metal surfaces. We have studied 1, 2, 3, and 4 monolayers of NaCl on a Cu(111) surface. Energies, lifetimes, and associated wave functions of the excited states have been obtained with a joint, model potential-wave packet propagation approach. The excited state with the lowest energy has the character of an image potential state repelled from the surface by the NaCl layer. The next two states present a mixed character of image potential states and NaCl layer states corresponding to the quantization of the conduction band in the finite-size layer. We discuss the role of the layer thickness in decoupling these states from the metal surface and how it affects their lifetime.
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Fan, C., Poumellec, B., Zeng, H., Lancry, M., Yang, W., Bourguignon, B., & Chen, G. (2011). Directional Writing Dependence of Birefringence in Multicomponent Silica-based Glasses with Ultrashort Laser Irradiation. JOURNAL OF LASER MICRO NANOENGINEERING, 6(2), 158–163.
Résumé: We reveal laser-induced high birefringence in multicomponent silica-based glass by means of ultrashort laser irradiation. It is attributed to the residual stress. A systematic study of birefringence variation is carried out according to laser parameters such as pulse energy, writing speed and direction, and laser polarization. Strong writing directional dependence is clearly observed when the writing direction is perpendicular to the laser polarization at the writing speeds of 20 μm/s – 120 μm/s, which was likely due to an asymmetry of the laser beam or an asymmetry of interaction mechanism. DOI: 10.2961/jlmn.2011.02.0011
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Ouvrard, A., Niebauer, J., Ghalgaoui, A., Barth, C., Henry, C. R., & Bourguignon, B. (2011). Characterization of Thin MgO Films on Ag(001) by Low-Energy Electron Diffraction and Scanning Tunneling Microscopy. J. Phys. Chem. C, 115(16), 8034–8041.
Résumé: The evolution of the MgO(001) film morphology on Ag(001) was studied in dependence on the growth temperature (373-673 K) and grown MgO quantity (0.2-2 ML) by low-energy electron diffraction and scanning tunneling microscopy. We evidence an island growth mode of MgO for all temperatures. At 373 K, the MgO film exhibits a high island density, which is due to a too small surface mobility of the film compounds during the film growth. At a growth temperature of 673 K, silver hampers a perfect growth of MgO islands due to its high mobility, which leads to dendrites of MgO. The flattest and. largest MgO islands are obtained at a growth temperature of around 573 K, which is a compromise guaranteeing a sufficiently high Mg or MgO mobility but also an enough low diffusion of silver.
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Park, C., Yang, H., Mayne, A. J., Dujardin, G., Seo, S., Kuk, Y., Ihm, J., & Kim, G. (2011). Formation of unconventional standing waves at graphene edges by valley mixing and pseudospin rotation. PNAS, 108(46), 18622–18625.
Résumé: We investigate the roles of the pseudospin and the valley degeneracy in electron scattering at graphene edges. It is found that they are strongly correlated with charge density modulations of short-wavelength oscillations and slowly decaying beat patterns in the electronic density profile. Theoretical analyses using nearest-neighbor tight-binding methods and first-principles density-functional theory calculations agree well with our experimental data from scanning tunneling microscopy. The armchair edge shows almost perfect intervalley scattering with pseudospin invariance regardless of the presence of the hydrogen atom at the edge, whereas the zigzag edge only allows for intravalley scattering with the change in the pseudospin orientation. The effect of structural defects at the graphene edges is also discussed.
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Stepanow, S., Mugarza, A., Ceballos, G., Gambardella, P., Aldazabal, I., Borisov, A. G., & Arnau, A. (2011). Localization, splitting, and mixing of field emission resonances induced by alkali metal clusters on Cu(100). Phys. Rev. B, 83(11), 115101.
Résumé: We report on a joint scanning tunneling microscopy (STM) and theoretical wave packet propagation study of field emission resonances (FER's) of nanosized alkali metal clusters deposited on a Cu(100) surface. In addition to FER's of the pristine Cu(100) surface, we observe the appearance of island-induced resonances that are particularly well resolved for STM bias voltage values corresponding to electron energies inside the projected band gap of the substrate. The corresponding dI/dV maps reveal island-induced resonances of different nature. Their electronic densities are localized either inside the alkali cluster or on its boundaries. Our model calculations allow us to explain the experimental results as due to the coexistence and mixing of two kinds of island-induced states. On the one side, since the alkali work function is lower than that of the substrate, the nanosized alkali metal clusters introduce intrinsic localized electronic states pinned to the vacuum level above the cluster. These states can be seen as the FER's of the complete alkali overlayer quantized by the cluster boundaries. On the other side, the attractive potential well due to the alkali metal cluster leads to two-dimensional (2D) localization of the FER's of the Cu(100) surface, the corresponding split component of the resonances appearing below the bottom of the parent continuum. Our main conclusions are based on the attractive nature of the alkali ad-island potential. They are of general validity and, therefore, significant to understand electron confinement in 2D.
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Wang, T., Boer-Duchemin, E., Tranvouez, E., Cartwright, R., Comtet, G., Dujardin, G., & Mayne, A. J. (2011). Low voltage fabrication of sub-nanometer insulating layers on hydrogenated diamond. JOURNAL OF APPLIED PHYSICS, 110(3), 034311.
Résumé: A new regime of electrochemical anodic oxidation with an atomic force microscope (AFM) is introduced for producing insulating layers on a hydrogenated diamond surface. In this new regime, when a low surface voltage (V(S) < +2 V) is applied to the sample, an insulating layer is created without any measurable change in the topography. Insulating layers created in this fashion are shown to preserve the high sub-surface conductance of hydrogenated diamond surfaces, contrary to the oxide layers accompanied by a topographic change, which destroy sub-surface conductance. (C) 2011 American Institute of Physics. [doi:10.1063/1.3615956]
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Wang, T., Boer-Duchemin, E., Zhang, Y., Comtet, G., & Dujardin, G. (2011). Excitation of propagating surface plasmons with a scanning tunnelling microscope. NANOTECHNOLOGY, 22(17), 175201.
Résumé: Inelastic electron tunnelling excitation of propagating surface plasmon polaritons (SPPs) on a thin gold film is demonstrated. This is done by combining a scanning tunnelling microscope (STM) with an inverted optical microscope. Analysis of the leakage radiation in both the image and Fourier planes unambiguously shows that the majority (up to 99.5%) of the detected photons originate from propagating SPPs with propagation lengths of the order of 10 μm. The remaining photon emission is localized under the STM tip and is attributed to a tip-gold film coupled plasmon resonance as evidenced by the bimodal spectral distribution and enhanced emission intensity observed using a silver STM tip for excitation.
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Zugarramurdi, A., Borisov, A. G., Zabala, N., Chulkov, E. V., & Puska, M. J. (2011). Clustering and conductance in breakage of sodium nanowires. Phys. Rev. B, 83(3), 035402.
Résumé: We study the conductance during the elongation and breakage of Na nanowires described with the ultimate jellium model. A combined approach is used where the nanowire breakage is simulated self-consistently within the density-functional theory, and the wave packet propagation technique is applied for ballistic electron transport. For certain conditions the breakage of the nanowire is preceded by formation of clusters of magic size in the break junction. This affects the conductance G, in particular the shape of the G = 3G(0) to G = G(0) (=2e(2)/h) step upon elongation. The observed trends can be explained as due to the transient trapping of ballistic electrons inside the cluster, leading to a resonant character of the electron transport through the break junction. The cluster-derived resonances appear as peak structures in the differential conductance which may serve as an experimental signature of clustering.
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Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Comment on “Phase Contribution of Image Potential on Empty Quantum Well States in Pb Islands on the Cu(111) Surface”. Phys. Rev. Lett., 106(24), 249601.
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Zugarramurdi, A., Zabala, N., Borisov, A. G., & Chulkov, E. V. (2011). Theoretical study of constant current scanning tunneling spectroscopy in Pb overlayers. Phys. Rev. B, 84(11), 115422.
Résumé: We present a theoretical study of the constant current scanning tunneling spectroscopy of quantum well states localized in Pb(111) overlayers on Cu(111) surfaces. The distance-voltage characteristic of the tunneling junction is obtained with a mixed approach. The wave packet propagation technique is applied to describe electron tunneling from the tip into the sample, and the density functional calculations provide the necessary inputs for the one-dimensional model potential representation of the system. The excited-state population decay mechanisms via inelastic electron-electron and electron-phonon interactions are taken into account with a bias-dependent absorbing potential introduced in the metal. Our results are in good agreement with recent experimental studies [Phys. Rev. Lett. 102, 196102 (2009), Phys. Rev. B 81, 205438 (2010)] over the energy range where the free-electron description of the Pb overlayer used here applies. We find that at high bias the quantum well states experience a Stark energy shift and partially acquire a character of field emission resonances. The present model study also sheds light at the experimentally observed departure of the energies of the quantum well states from the particle-in-a-box prediction for the bias above 4 eV. The measured trend can be consistently explained as due to the departure of the realistic Pb band structure in the Gamma-L direction from free-electron parabola when the electron momentum approaches the Gamma point.
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Actes de Conférences |
Bulard, E., Dubost, H., Fontaine-Aupart, M. - P., Zheng, W., Herry, J. - M., Bellon-Fontaine, M. - N., Briandet, R., & Bourguignon, B. (2011). Non invasive SFG spectroscopy: a tool to reveal the conformational change of grafted chains due to bacterial adhesion. In CLINICAL AND BIOMEDICAL SPECTROSCOPY AND IMAGING II (Vol. 8087).
Résumé: In many fields such as biomedical or food industry, surface colonization by micro-organisms leads to biofilms formation that are tridimentional biostructures highly resistant to the action of antimicrobials, by mechanisms still unclear. In order to deepen our understanding of the initial interaction of bacteria cells with a solid surface, we analyze by in situ vibrational Sum Frequency Generation (SFG) spectroscopy the effect of the adhesion of hydrophilic Lactoccocus lactis bacteria and its hydrophobic mutants in distilled water on a self-assembled monolayer (SAM) of octadecanethiol (ODT) on a gold film. When a homogeneous bacterial monolayer is deposited on this ordered surface, SFG spectrum of the ODT SAM shows significant intensity changes from that in air or in water. Its modelling as a function of conformation allows to distinguish optical effects due to the water solution surrounding bacteria from conformational changes of the ODT SAM due to the presence of the bacteria cells. Futhermore, bacterial adhesion induces different measurable effects on the ODT SAM conformation, depending on the hydrophobic / hydrophilic character of the bacterial surface. Such a result deserves to be taken into account for the design of new materials with improved properties or to control biofilm formation.
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Monographies |
Mayne, A. J., & Dujardin, G. (2011). Atomic and Molecular Manipulation (Vol. 2). Frontiers in Nanoscience. A.J. Mayne, G. Dujardin.
Résumé: Work with individual atoms and molecules aims to demonstrate that miniaturized electronic, optical, magnetic, and mechanical devices can operate ultimately even at the level of a single atom or molecule. As such, atomic and molecular manipulation has played an emblematic role in the development of the field of nanoscience. New methods based on the use of the scanning tunnelling microscope (STM) have been developed to characterize and manipulate all the degrees of freedom of individual atoms and molecules with an unprecedented precision. In the meantime, new concepts have emerged to design molecules and substrates having specific optical, mechanical and electronic functions, thus opening the way to the fabrication of real nano-machines. Manipulation of individual atoms and molecules has also opened up completely new areas of research and knowledge, raising fundamental questions of “Optics at the atomic scale”, “Mechanics at the atomic scale”, Electronics at the atomic scale“, ”Quantum physics at the atomic scale“, and ”Chemistry at the atomic scale“. This book aims to illustrate the main aspects of this ongoing scientific adventure and to anticipate the major challenges for the future in ”Atomic and molecular manipulation" from fundamental knowledge to the fabrication of atomic-scale devices.
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Chapitres de Livres |
Mayne, A. J., Riedel, D., Comtet, G., & Dujardin, G. (2011). Electronic Control of Single Molecule Nanomachines. In Current-Driven Phenomena in Nanoelectronics (pp. 156–188). T. Seideman.
Résumé: Consisting of ten chapters written by some of the world’s leaders in the field, this book combines experimental, theoretical and numerical studies of current-driven phenomena in the nanoscale. The topics covered range from single-molecule, site-specific nanochemistry induced by a scanning tunneling microscope, through inelastic tunneling spectroscopy and current-induced heating, to current-triggered molecular machines. The various chapters focus on experimental and numerical method development, the description of specific systems, and new ideas and novel phenomena.
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