Peer-reviewed Publications |
Bellec, A., Chaput, L., Dujardin, G., Riedel, D., Stauffer, L., & Sonnet, P. (2013). Reversible charge storage in a single silicon atom. Phys. Rev. B, 88(24), 241406.
Résumé: The ultimate miniaturization of electronic devices at the atomic scale with single electrons requires controlling the reversible charge storage in a single atom. However, reversible charge storage is difficult to control as usually only one charge state can be stabilized. Here, combining scanning tunneling microscopy (STM) and density functional theory (DFT), we demonstrate that a single silicon dangling bond of a hydrogenated p-type doped Si(100) surface has two stable charge states (neutral and negatively charged) at low temperature (5 K). Reversible charge storage is achieved using a gate electric field between the STM tip and the surface.
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Borisov, A. G., Sanchez-Portal, D., Kazansky, A. K., & Echenique, P. M. (2013). Resonant and nonresonant processes in attosecond streaking from metals. Phys. Rev. B, 87(12), 121110.
Résumé: We report on the theoretical study of laser-assisted attosecond photoemission from metals. The full time-dependent quantum approach reveals the role of the resonant interband and nonresonant surface emission processes in formation of final atto-streaking spectra. The present results explain recent experimental data on magnesium and show that the valence band streaking essentially reflects the respective weight of surface and resonant bulk electron ejection. DOI: 10.1103/PhysRevB.87.121110
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Koval, N. E., Sánchez-Portal, D., Borisov, A. G., & Díez Muiño, R. (2013). Dynamic screening and energy loss of antiprotons colliding with excited Al clusters. Nucl. Instrum. Methods Phys. Res., B, 317, 56–60.
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Labidi, H., Sonnet, P., & Riedel, D. (2013). Electronic Control of the Tip-Induced Hopping of an Hexaphenyl-Benzene Molecule Physisorbed on a Bare Si(100) Surface at 9 K. JOURNAL OF PHYSICAL CHEMISTRY C, 117(26), 13663–13675.
Résumé: In this work, we show that the hopping directivity of individual hexaphenyl-benzene (HPB) molecules physisorbed along the SA step edge of a bare Si(100)-2×1 surface can be reversibly controlled with a periodic hopping length. This is achieved by using the tunnel electrons of a low temperature (9 K) scanning tunneling microscope (STM). A statistical analysis of the electronic excitations applied at various positions on the HPB molecule reveals that the hopping process is related to a strong decrease of the tunnel junction conductance. This process is associated with a charge transfer from the silicon surface to the HPB molecule leading to a hopping mechanism that occurs in two sequential steps. The first step of the hopping process involves the formation of an HPB− anion that triggers the molecular motion into a metastable state. The second step is related to the neutralization of the HPB− anion which provokes the manipulation of the molecule to its final steady position. Our experimental data are supported by the calculations of the relaxed molecule using the density functional theory on the Si(100) surface that takes the van der Waals forces interactions into account. Additional calculations of the HPB− anion orbitals depict the spatial localization of the extra charge inside the HPB molecule and the relative energies of the HPB− molecular orbitals. Finally, our study shows that the hopping direction can be optimized by positioning the STM tip at specific locations along the hopping pathway.
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Le Moal, E., Marguet, S., Rogez, B., Mukherjee, S., Dos Santos, P., Boer-Duchemin, E., Comtet, G., & Dujardin, G. (2013). An electrically excited nanoscale light source with active angular control of the emitted light. Nano Lett., 13(9), 4198–4205.
Résumé: The angular distribution, polarization, and spectrum of the light emitted from an electrically controlled nanoscale light source arises from the local, low-energy, electrical excitation of localized surface plasmons (LSP) on individual gold nanoparticles induced by a scanning tunneling microscope (STM). The gold nanoparticles (NP) are chemically synthesized truncated bitetrahedrons. The emitted light is collected through the transparent substrate The angular distribution, polarization, and spectrum are found to strongly depend on the lateral position of the STM tip with respect to the upper triangular face of the gold NP. The resulting light emission changes orientation when the electrical excitation via the STM tip is moved from the base to the vertex of the triangular face. Comparison with an analytical dipole model and finite-difference time-domain (FDTD) calculations shows that this behavior is linked to the selective excitation of the out-of-plane and in-plane dipolar LSP modes of the NP.
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Marinica, D. C., Lourenco-Martins, H., Aizpurua, J., & Borisov, A. G. (2013). Plexciton quenching by resonant electron transfer from quantum emitter to metallic nanoantenna. Nano Lett., 13(12), 5972–5978.
Résumé: Coupling molecular excitons and localized surface plasmons in hybrid nanostructures leads to appealing, tunable optical properties. In this respect, the knowledge about the excitation dynamics of a quantum emitter close to a plasmonic nanoantenna is of importance from fundamental and practical points of view. We address here the effect of the excited electron tunneling from the emitter into a metallic nanoparticle(s) in the optical response. When close to a plasmonic nanoparticle, the excited state localized on a quantum emitter becomes short-lived because of the electronic coupling with metal conduction band states. We show that as a consequence, the characteristic features associated with the quantum emitter disappear from the optical absorption spectrum. Thus, for the hybrid nanostructure studied here and comprising quantum emitter in the narrow gap of a plasmonic dimer nanoantenna, the quantum tunneling might quench the plexcitonic states. Under certain conditions the optical response of the system approaches that of the individual plasmonic dimer. Excitation decay via resonant electron transfer can play an important role in many situations of interest such as in surface-enhanced spectroscopies, photovoltaics, catalysis, or quantum information, among others.
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Ovramenko, T., Spillebout, F., Bocquet, F. C., Mayne, A. J., Dujardin, G., Sonnet, P., Stauffer, L., Ksari, Y., & Themlin, J. M. (2013). STM imagery and density functional calculations of C-60 fullerene adsorption on the 6H-SiC(0001)-3x3 surface. Phys. Rev. B, 87(15), 155421.
Résumé: Scanning tunneling microscopy (STM) studies of the fullerene C-60 molecule adsorbed on the silicon carbide SiC(0001)-3 x 3 surface, combined with density functional theory (DFT) calculations, show that chemisorption of individual C-60 molecules occurs through the formation of one bond to one silicon adatom only in contrast to multiple bond formation on other semiconducting surfaces. We observe three stable adsorption sites with respect to the Si adatoms of the surface unit cell. Comprehensive DFT calculations give different adsorption energies for the three most abundant sites showing that van der Waals forces between the C-60 molecule and the neighboring surface atoms need to be considered. The C-60 molecules are observed to form small clusters even at low coverage indicating the presence of a mobile molecular precursor state and nonnegligible intermolecular interactions. DOI: 10.1103/PhysRevB.87.155421
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Raseev, G. (2013). Plasmon resonances of Ag(001) and Ag(111) studied by power density absorption and photoyield. Surf. Sci., 615, 6–20.
Résumé: This paper models the surface and bulk plasmon resonances in photoabsorption and photoelectron spectra (PES) of the Ag(001) and the Ag(111) surfaces in the region of 2.8-10 eV excited with a p or transverse magnetic linearly polarized laser incident at 45 degrees. Using the recently developed vector potential from electron density-coupled integro-differential equations (VPED-CIDE, [1,2]) model, we calculate the electron escaping probability from the power density absorption, Feibelman's parameter d(perpendicular to), the reflectance and the Fermi PE cross section. In the PES experiment the work function is lowered from 45 to 2.8 eV by adsorption of sodium. In our model, this lowering is introduced by adding a phenomenological term to the DFT-LDA model potential of Chulkov et al. [3]. For both Ag(001) and Ag(111), the calculated observables display two plasmon resonances, the multipole surface at 3.70 eV and the bulk at 3.90 eV, in fair agreement with the experimental PES of Barman et al. [4,5] and the reflectance. Except for the Fermi PE cross section of Ag(001) which does not display the multipole surface plasmon resonance at 3.70 eV. This poor result is probably due to a poor calculation of the conduction band wave functions obtained from the Schrodinger equation using the modified DFT-LDA model potential of Chulkov et at (C) 2013 Elsevier B.V. All rights reserved.
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Rios Rubiano, C. A., Bocan, G. A., Gravielle, M. S., Bundaleski, N., Khemliche, H., & Roncin, P. (2013). Ab initio potential for the He-Ag(110) interaction investigated using grazing-incidence fast-atom diffraction. Phys. Rev. B, 87(1), 012903.
Résumé: Experimental diffraction patterns produced by grazing scattering of fast helium atoms from a Ag(110) surface are used as a sensitive tool to test an ab initio potential model derived from accurate density-functional theory (DFT) calculations. The scattering process is described by means of the surface eikonal approximation, which is a distorted-wave method that includes the quantum interference between contributions coming from different projectile paths, taking into account the complete corrugation of the three-dimensional projectile-surface potential. A fairly good agreement between the theoretical and experimental momentum distributions is found for incidence along different low-indexed crystallographic directions. This agreement is indicative of the quality of the DFT potential. The effective corrugation of the interaction potential across the incidence channel is also investigated. DOI: 10.1103/PhysRevA.87.012903
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Schaffert, J., Cottin, M. C., Sonntag, A., Bobisch, C. A., Moeller, R., Gauyacq, J. - P., & Lorente, N. (2013). Tunneling electron induced rotation of a copper phthalocyanine molecule on Cu(111). Phys. Rev. B, 88(7), 075410.
Résumé: The rates of a hindered molecular rotation induced by tunneling electrons are evaluated using scattering theory within the sudden approximation. Our approach explains the excitation of copper phthalocyanine molecules (CuPc) on Cu(111) as revealed in a recent measurement of telegraph noise in a scanning tunneling microscopy experiment [Schaffert et al., Nat. Mater. 12, 223 (2013)]. A complete explanation of the experimental data is performed by computing the geometry of the adsorbed system, its electronic structure, and the energy transfer between tunneling electrons and the molecule's rotational degree of freedom. The results unambiguously show that tunneling electrons induce a frustrated rotation of the molecule. In addition, the theory determines the spatial distribution of the frustrated rotation excitation, confirming the striking dominance of two out of four molecular lobes in the observed excitation process. This lobe selectivity is attributed to the different hybridizations with the underlying substrate.
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Schaffert, J., Cottin, M. C., Sonntag, A., Karacuban, H., Bobisch, C. A., Lorente, N., Gauyacq, J. - P., & Möller, R. (2013). Imaging the dynamics of individually adsorbed molecules. Nat. Mater., 12(3), 223–227.
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Teperik, T. V., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2013). Quantum effects and nonlocality in strongly coupled plasmonic nanowire dimers. Opt. Express, 21(22), 27306.
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Teperik, T. V., Nordlander, P., Aizpurua, J., & Borisov, A. G. (2013). Robust Subnanometric Plasmon Ruler by Rescaling of the Nonlocal Optical Response. Phys. Rev. Lett., 110(26), 263901.
Résumé: We present the optical response of two interacting metallic nanowires calculated for separation distances down to angstrom range. State-of-the-art local and nonlocal approaches are compared with full quantum time-dependent density functional theory calculations that give an exact account of nonlocal and tunneling effects. We find that the quantum results are equivalent to those from classical approaches when the nanoparticle separation is defined as the separation between centroids of the screening charges. This establishes a universal plasmon ruler for subnanometric distances. Such a ruler not only impacts the basis of many applications of plasmonics, but also provides a robust rule for subnanometric metrology.
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Thon, R., Chin, W., Galaup, J. - P., Ouvrard, A., Bourguignon, B., & Crepin, C. (2013). Vibrational Perturbations of W(CO)(6) Trapped in a Molecular Lattice Probed by Linear and Nonlinear Spectroscopy. J. Phys. Chem. A, 117(34), 8145–8156.
Résumé: Vibrational dynamics of the T-1u CO stretching mode of tungsten hexacarbonyl is explored when the molecule is embedded in a nitrogen matrix at low temperature. Experiments combined infrared (IR) absorption spectroscopy and IR stimulated photon echoes at the femtosecond time scale. W(CO)(6) is found to be trapped in two main families of sites differing by their symmetry (called hereafter O-h and D-2h sites). In O-h sites, the vibrational coherence is strongly temperature dependent, exhibiting a coupling with librational phonons of the nitrogen lattice. Perturbation in D-2h sites results in the splitting of the T-1u band in three components. Each component is inhomogeneously broadened, with dephasing times in the tens of picoseconds, and is weakly coupled to the lattice phonons. Experiments in solid krypton are performed to compare the effect of atomic and diatomic host lattices. Dephasing time in Kr does not depend on temperature and remains in the hundreds of picoseconds, highlighting the molecular origin of the dephasing process in N-2. Additionally, nonlinear signals show oscillations due to quantum beats and polarization interferences between different frequency components of the induced third order polarization, giving information, in particular, on the overtone vibrational transition.
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Tsirkin, S. S., Borisov, A. G., & Chulkov, E. V. (2013). Green's function approach to the lifetimes of image potential resonances at metal surfaces. Phys. Rev. B, 88(3), 035449.
Résumé: We present a theoretical study of the image potential resonances (IPRs) at metal surfaces. We develop the Green's functions approach allowing us to calculate binding energies E-n and lifetimes tau(n) of IPRs with high quantum numbers n (up to 10 in this work). A systematic study is performed at the (Gamma) over bar point for the close-packed metal surfaces: Cu(111), Ag(111), Au(111), Al(001), Al(111), Be(0001), Mg(0001), Na(110), Li(110), and also at the (Y) over bar point on Cu(110). The calculated lifetimes of IPRs on close-packed surfaces demonstrate the scaling law tau(n) proportional to n(3). Our results are in agreement with available experimental data. We show that at the (Y) over bar point on Cu(110) each quantum number n corresponds to a pair of IPRs n(+) and n(-), where the energy difference En+ – En- is proportional to n(-3). The lifetimes tau(n+) and tau(n-) differ significantly, however, they both obey the scaling law tau(n +/-) proportional to n(3). Since the electrons trapped in the long-lived IPRs are strongly localized on the vacuum side, we argue that the inelastic electron-electron and electron-phonon scattering have a small contribution to the decay rate of these IPRs. The latter is dominated by the resonant electron transfer into the bulk.
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Yang, H., Mayne, A. J., Cejas, C., Dujardin, G., & Kuk, Y. (2013). Manipulation at a distance: Atomic-scale observation of ballistic electron transport in single layer graphene. Appl. Phys. Lett., 102(22), 223104.
Résumé: We present scanning tunneling microscopy manipulation experiments on epitaxial graphene and the carbon buffer layer grown on hexagonal silicon carbide. Low voltage pulses applied to the graphene layer with the microscope tip induce nonlocal modifications of a bare carbon buffer region 10 nm away. The graphene itself is not affected. This is direct evidence for ballistic hot electrons propagating along the graphene layer to the graphene edge. High energy states in the graphene band structure (Van Hove Singularities) may explain both the electron transport and the coupling of the graphene edge to the adjacent bare carbon buffer region.
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Yang, H., Mayne, A. J., Comtet, G., Dujardin, G., Kuk, Y., Sonnet, P., Stauffer, L., Nagarajan, S., & Gourdon, A. (2013). STM imaging, spectroscopy and manipulation of a self-assembled PTCDI monolayer on epitaxial graphene. Phys. Chem. Chem. Phys., 15(14), 4939–4946.
Résumé: Scanning Tunneling Microscopy (STM), Scanning Tunneling Spectroscopy (STS), and manipulation studies were performed on an ordered self-assembled monolayer (SAM) of N,N'-bis(1-hexylheptyl)perylene-3,4: 9,10-bis(dicarboximide) molecules on epitaxial graphene on hexagonal silicon carbide – SiC(0001). Four novel aspects of the molecular SAM on graphene are presented. Molecules adsorb in both armchair and zig-zag configurations, giving rise to six orientations of the molecular layer with respect to the underlying substrate. The interaction between the molecules and the graphene surface shifts the LUMO towards the Fermi level, inducing a charge transfer and the opening of a band gap in the graphene, with the LUMO inside. This decouples the LUMO from the surface rendering it invisible in the dI/dV spectroscopy. The HOMO only becomes visible at short tip-surface distances, as its energy lies within the band gap of the SiC substrate. Finally, the observed molecular defects are very particular, being composed exclusively of molecular dimers. These molecular dimers have a stronger interaction with the graphene than other molecules.
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Zhang, Y., Boer-Duchemin, E., Wang, T., Rogez, B., Comtet, G., Le Moal, E., Dujardin, G., Hohenau, A., Gruber, C., & Krenn, J. R. (2013). Edge scattering of surface plasmons excited by scanning tunneling microscopy. Opt. Express, 21(12), 13938–13948.
Résumé: The scattering of electrically excited surface plasmon polaritons (SPPs) into photons at the edges of gold metal stripes is investigated. The SPPs are locally generated by the inelastic tunneling current of a scanning tunneling microscope (STM). The majority of the collected light arising from the scattering of SPPs at the stripe edges is emitted in the forward direction and is collected at large angle (close to the air-glass critical angle, θc). A much weaker isotropic component of the scattered light gives rise to an interference pattern in the Fourier plane images, demonstrating that plasmons may be scattered coherently. From these results, we interpret the directional, large angle scattering to be mainly from plasmons on the air-gold interface, and the diffuse scattering forming interference fringes to be dominantly from plasmons on the gold-substrate interface.
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Zugarramurdi, A., & Borisov, A. G. (2013). Theoretical study of the effect of beam misalignment in fast-atom diffraction at surfaces. Phys. Rev. A, 87(6), 062902.
Résumé: Typical applications of the fast-atom diffraction technique exploit incidence along low-index directions to extract accurate structural information on surfaces from the diffraction pattern. The data interpretation in this case is well developed and simplified by the axial channeling conditions, where the three-dimensional projectile-surface interaction appears effectively averaged over the fast-motion direction. We study theoretically the diffraction of fast-atom beams that are significantly misaligned with respect to a low-index direction at the surface. With full quantum wave-packet calculations, we address He atom scattering from the LiF(001) surface within a wide range of azimuthal and polar incidence angles. In particular, we are interested in the transitions between low-index directions upon the azimuthal rotation of the beam, and in the question of the choice of an adequate axial channeling approximation. We make use of the energy criterion to analyze the diffraction patterns and to discuss how the momentum exchange projected on the beam direction affects the diffraction.
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Zugarramurdi, A., & Borisov, A. G. (2013). When fast atom diffraction turns 3D. Nucl. Instrum. Methods Phys. Res., B, 317, 83–89.
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Zugarramurdi, A., Debiossac, M., Lunca-Popa, P., Alarcon, L. S., Momeni, A., Khemliche, H., Roncin, P., & Borisov, A. G. (2013). Surface-grating deflection of fast atom beams. Phys. Rev. A, 88(1), 0129074.
Résumé: For energetic atomic beams grazingly incident at the surface along the low index directions, fast motion parallel to the surface and slow motion perpendicular to the surface lead to the quantum diffraction pattern in the scattered beam. In this experimental and theoretical joint study we show that when the incident beam is misaligned with respect to an axial channel, the characteristic deformation of the diffraction pattern reflects an overall deflection of the scattered beam from the specular direction. The deflection is maximum for the azimuthal misalignment angles close to the rainbow angle and we show how this effect can be explained with the detailed balance principle relating diffraction of misaligned and perfectly aligned beams. We also demonstrate that using the detailed balance principle the diffraction charts for the incident beams aligned along the axial channel can be reconstructed from the azimuthal incidence angle dependence of the data obtained with misaligned beams.
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