Peer-reviewed Publications |
Anouchah Momeni, P. S., Patrick Rousseau, Hocine Khemliche, and Philippe Roncin. (2010). Grazing Incidence Fast Atom Diffraction (GIFAD): Doing RHEED with Atoms. e-J. Surf. Sci. Nanotech, 8, 101–104.
Résumé: We describe a new diffraction technique to investigate the surface of single crystal surfaces. Its geometry is the
same as that of the RHEED technique. In GIFAD, instead of 10-30 keV electrons, the projectiles are neutral atoms
(mainly helium) with energies in the keV range. We present few results obtained with GIFAD highlighting the
simplicity of interpretation.
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Bellec, A., Riedel, D., Dujardin, G., Boudrioua, O., Chaput, L., Stauffer, L., & Sonnet, P. (2010). Nonlocal Activation of a Bistable Atom through a Surface State Charge-Transfer Process on Si(100)-(2 x 1):H. Phys. Rev. Lett., 105(4), 048302.
Résumé: The reversible hopping of a bistable atom on the Si(100)-(2 x 1):H surface is activated nonlocally by hole injection into Si-Si bond surface states with a low temperature (5 K) scanning tunneling microscope. In the contact region, at short distances (<1.5 nm) between the hole injection site and the bistable atom, the hopping yield of the bistable atom exhibits remarkable variations as a function of the hole injection site. It is explained by the density of state distribution along the silicon bond network that shows charge-transfer pathways between the injection sites and the bistable atom.
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Boer-Duchemin, E., Tranvouez, E., & Dujardin, G. (2010). The interaction of an atomic force microscope tip with a nano-object: a model for determining the lateral force. Nanotechnology, 21(45), 455704.
Résumé: A calculation of the lateral force interaction between an atomic force microscope (AFM) tip and a nano-object on a substrate is presented. In particular, the case where the AFM tip is used to manipulate the nano-object is considered; i.e., the tip is displaced across the nano-object with the feedback off. The Hamaker equations are used to calculate the force when the tip and sample are not in contact and the Johnson, Kendall and Roberts (JKR) or Derjaguin, Muller and Toporov (DMT) formalisms are used for the contact force. The effect of the material parameters, the choice of contact theory and the shape of the nano-object on the resulting lateral forces are explored. The calculation is applied to an experimental system consisting of a cadmium selenide nanorod on graphite.
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Gauyacq, J. - P., Novaes, F. D., & Lorente, N. (2010). Magnetic transitions induced by tunneling electrons in individual adsorbed M-phthalocyanine molecules (M=Fe and Co). Phys. Rev. B, 81(16), 165423.
Résumé: We report on a theoretical study of magnetic transitions induced by tunneling electrons in individual adsorbed M-Phthalocyanine (M-Pc) molecules where M is a metal atom: Fe-Pc on a Cu(110)(2 x 1)-O surface and Co-Pc layers on Pb(111) islands. The magnetic transitions correspond to the change in orientation of the spin angular momentum of the metal ion with respect to the surroundings and possibly an applied magnetic field. The adsorbed Fe-Pc system is studied with a density-functional-theory-transport approach showing that (i) the magnetic structure of the Fe atom in the adsorbed Fe-Pc is quite different from that of the free Fe atom or of other adsorbed Fe systems and (ii) that injection of electrons (holes) into the Fe atom in the adsorbed Fe-Pc molecule dominantly involves the Fe 3d(z)2 orbital. These results fully specify the magnetic structure of the system and the process responsible for magnetic transitions. The dynamics of the magnetic transitions induced by tunneling electrons is treated in a strong-coupling approach. The Fe-Pc treatment is extended to the Co-Pc case. The present calculations accurately reproduce the strength of the magnetic transitions as observed by magnetic inelastic electron tunneling spectroscopy experiments; in particular, the dominance of the inelastic current in the conduction of the adsorbed M-Pc molecule is accounted for.
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Nimmrich, M., Kittelmann, M., Rahe, P., Mayne, A. J., Dujardin, G., von Schmidsfeld, A., Reichling, M., Harneit, W., & Kuhnle, A. (2010). Atomic-resolution imaging of clean and hydrogen-terminated C(100)-(2x1) diamond surfaces using noncontact AFM. Phys. Rev. B, 81(20), 201403.
Résumé: High-purity, type IIa diamond is investigated by noncontact atomic force microscopy (NC-AFM). We present atomic-resolution images of both the electrically conducting hydrogen-terminated C(100)-(2 x 1) : H surface and the insulating C(100)-(2 x 1) surface. For the hydrogen-terminated surface, a nearly square unit cell is imaged. In contrast to previous scanning tunneling microscopy experiments, NC-AFM imaging allows both hydrogen atoms within the unit cell to be resolved individually, indicating a symmetric dimer alignment. Upon removing the surface hydrogen, the diamond sample becomes insulating. We present atomic-resolution images, revealing individual C-C dimers. Our results provide real-space experimental evidence for a (2 x 1) dimer reconstruction of the truly insulating C(100) surface.
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Novaes, F. D., Lorente, N., & Gauyacq, J. - P. (2010). Quenching of magnetic excitations in single adsorbates at surfaces: Mn on CuN/Cu(100). Phys. Rev. B, 82(15), 155401.
Résumé: The lifetimes of spin excitations of Mn adsorbates on CuN/Cu(100) are computed from first principles. The theory is based on a strong-coupling approach that evaluates the decay of a spin excitation due to electron-hole pair creation. Using a previously developed theory [Phys. Rev. Lett. 103, 176601 (2009) and Phys. Rev. B 81, 165423 (2010)], we compute the excitation rates by a tunneling current for all the Mn spin states. A rate equation approach permits us to simulate the experimental results by Loth and co-workers (Nat. Phys. 6, 340 (2010)] for large tunneling currents, taking into account the finite population of excited states. Our simulations give us insight into the spin dynamics, in particular, in the way polarized electrons can reveal the existence of an excited-state population. In addition, it reveals that the excitation process occurs in a way very different from the deexcitation one. Indeed, while excitation by tunneling electrons proceeds via the s and p electrons of the adsorbate, deexcitation mainly involves the d electrons.
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Perez-Gonzalez, O., Zabala, N., Borisov, A. G., Halas, N. J., Nordlander, P., & Aizpurua, J. (2010). Optical Spectroscopy of Conductive Junctions in Plasmonic Cavities. Nano Lett., 10(8), 3090–3095.
Résumé: The optical properties of a nanoparticle dimer bridged by a conductive junction depend strongly on the junction conductivity. As the conductivity increases, the bonding dimer plasmon blueshifts and broadens. For large conductance, a low energy charge transfer plasmon also appears in the spectra with a line width that decreases with increasing conductance. A simple physical model for the understanding of the spectral feature is presented. Our finding of a strong influence of junction conductivity on the optical spectrum suggests that plasmonic cavities might serve as probes of molecular conductance at elevated frequencies not accessible through electrical measurements.
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Quijada, M., Diez Muino, R., Borisov, A. G., Alonso, J. A., & Echenique, P. M. (2010). Lifetime of electronic excitations in metal nanoparticles. New J. Phys., 12, 053023.
Résumé: Electronic excitations in metal particles with sizes up to a few nanometers are shown to have a one-electron character when a laser pulse is applied off the plasmon resonance. The calculated lifetimes of these excitations are in the femtosecond timescale but their values are substantially different from those in bulk. This deviation can be explained from the large weight of the excitation wave function in the nanoparticle surface region, where dynamic screening is significantly reduced. The well-known quadratic dependence of the lifetime with the excitation energy in bulk breaks down in these finite-size systems.
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Raseev, G., & Bejan, D. (2010). Multipole surface plasmon resonance of an aluminium surface. Opt. Commun., 283(20), 3976–3984.
Résumé: The surface photoelectric effect and the surface plasmon resonances appear when a p/transverse magnetic polarized laser hits a gas-solid interface. We model this effect in the long wave length (LWL) domain (lambda(vac)>10 nm, (h) over cap omega<124 eV) by combining the Ampere-Maxwell equation, written in classical approximation, with the material equation for the susceptibility. The resulting model, called the vector potential from the electron density (VPED), calculates the susceptibility as a product of the bulk susceptibility and the electron density of the actual system. The bulk susceptibility is a sum of the bound electron scalar susceptibility taken from the experiment and of the conduction electron non-local isotropic susceptibility tensor in a jellium metal (Lindhard, 1954 [1]). The electron density is the square of the wave function solution of the Schrodinger equation. The analysis of observables, the reflectance R and the photoelectron yield Y as well as the induced charge density permits to identify and characterize the multipole surface plasmon resonance of Al(111) appearing at omega(m) similar to 0.8 omega(p), or 11-12 eV. (c) 2010 Elsevier B.V. All rights reserved.
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Riedel, D., Delattre, R., Borisov, A. G., & Teperik, T. V. (2010). A Scanning Tunneling Microscope as a Tunable Nanoantenna for Atomic Scale Control of Optical-Field Enhancement. Nano Lett., 10(10), 3857–3862.
Résumé: The high stability of a low temperature (9 K) scanning tunneling microscope junction is used to precisely adjust the enhancement of an external pulsed vacuum ultraviolet (VUV) laser The ensuing VUV optical-field strength is mapped on an hydrogenated Si(100) surface by imprinting locally one-photon atomic scale hydrogen desorption Subsequent to irradiation, topography of the Si(100) H surface at the reacted area revealed a desorption spot with unprecedented atomic precision Our results show that the shapes. positions. and sizes of the desorption spots are correlated to the calculated optical-field structure, offering real control of the optical-held distribution at molecular scale
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Sizun, M., Bachellerie, D., Aguillon, F., & Sidis, V. (2010). Investigation of ZPE and temperature effects on the Eley-Rideal recombination of hydrogen atoms on graphene using a multidimensional graphene-H-H potential. Chem. Phys. Lett., 498(1-3), 32–37.
Résumé: We study the Eley-Rideal recombination of H atoms on graphene under the physical conditions of the interstellar medium. Effects of the ZPE motions of the chemisorbed H atom and of the graphene thermal motions are investigated. Classical molecular dynamics calculations undertaken with the multidimensional potential of Bachellerie et al. [Phys. Chem. Chem. Phys. 11 (2009) 2715] are reported. The ZPE effects are the strongest. The closer the collision energy is to the classical reaction threshold the more sizeable the effects. The quantum reaction cross section is also estimated below and above the classical threshold using a capture model. (C) 2010 Elsevier B.V. All rights reserved.
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Yang, H., Mayne, A. J., Boucherit, M., Comtet, G., Dujardin, G., & Kuk, Y. (2010). Quantum Interference Channeling at Graphene Edges. Nano Lett., 10(3), 943–947.
Résumé: Electron scattering at graphene edges is expected to make a crucial contribution to the electron transport in graphene nanodevices by producing quantum interferences. Atomic-scale scanning tunneling microscopy (STM) topographies of different edge structures of monolayer graphene show that the localization of the electronic density of states along the C-C bonds, a property unique to monolayer graphene, results in quantum interference patterns along the graphene carbon bond network, whose shapes depend only on the edge structure and not on the electron energy.
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