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ABSTRACT: We report on the elaboration of networks of SAM domains. More precisely, we show the feasibility in making arrays of functionalized alkylthiol nanodomains bordered with an alkylthiol matrix. The several step process relies on the replication of a self-organized cobalt array grown on Au(111). The SAM process takes place in solution. The chemical affinity of thiol for gold leads to the selective grafting of molecules on the surface. After having removed the inorganic array, alkylthiol functionalized with a terthiophene unit is grafted in free gold areas. The efficiency of the replication of the initial template depends on the stability of the first SAM. We also investigate electronic tunnel transport through oligothiophene islands with the STM. The variation of the molecular contrast with bias voltage between the two molecular species indicates a potential resonant tunneling mechanism through the orbitals of the aromatic compound.
Langmuir 09/2012; 28(42):15095-105. · 4.19 Impact Factor
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ABSTRACT: Using organic materials in spintronic devices raises a lot of expectation for future applications due to their flexibility, low cost, long spin lifetime, and easy functionalization. However, the interfacial hybridization and spin polarization between the organic layer and the ferromagnetic electrodes still has to be understood at the molecular scale. Coupling state-of-the-art spin-polarized scanning tunneling spectroscopy and spin-resolved ab initio calculations, we give the first experimental evidence of the spin splitting of a molecular orbital on a single non magnetic C(60) molecule in contact with a magnetic material, namely, the Cr(001) surface. This hybridized molecular state is responsible for an inversion of sign of the tunneling magnetoresistance depending on energy. This result opens the way to spin filtering through molecular orbitals.
Nano Letters 07/2012; 12(9):4558-63. · 13.20 Impact Factor
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Frederic Joucken,
Yann Tison,
Jerome Lagoute,
Jacques Dumont,
Damien Cabosart,
Bing Zheng, Vincent Repain,
Cyril Chacon,
Yann Girard,
Andres Rafael Botello-Mendez,
Sylvie Rousset,
Robert Sporken,
Jean-Christophe Charlier,
Luc Henrard
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ABSTRACT: Nitrogen-doped epitaxial graphene grown on SiC(000?1) was prepared by
exposing the surface to an atomic nitrogen flux. Using Scanning Tunneling
Microscopy (STM) and Spectroscopy (STS), supported by Density Functional Theory
(DFT) calculations, the simple substitution of carbon by nitrogen atoms has
been identifi?ed as the most common doping con?guration. High-resolution images
reveal a reduction of local charge density on top of the nitrogen atoms,
indicating a charge transfer to the neighboring carbon atoms. For the fi?rst
time, local STS spectra clearly evidenced the energy levels associated with the
chemical doping by nitrogen, localized in the conduction band. Various other
nitrogen-related defects have been observed. The bias dependence of their
topographic signatures demonstrates the presence of structural con?gurations
more complex than substitution as well as hole-doping.
Phys. Rev. B. 04/2012; 85(16).
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ABSTRACT: Carbon nanotubes are the focus of considerable research efforts due to their fascinating physical properties. They pro-vide an excellent model system for the study of one dimensional materials and molecular electronics. The chirality of nanotubes can lead to very different electronic behaviours, either metallic or semiconducting. Their electronic spec-trum consists of a series of Van Hove singularities defining a bandgap for semiconducting tubes and molecular orbitals at the corresponding energies. A promising way to tune the nanotubes electronic properties for future applications is to use doping by heteroatoms. Here we report on experimental investigation of the role of many-body interactions in nanotube bandgaps, the visualization in direct space of the molecular orbitals of nanotubes and the properties of nitro-gen doped nanotubes using scanning tunneling microscopy and transmission electron microscopy as well as electron energy loss spectroscopy. Résumé Etude couplée par TEM/EELS et STM/STS des propriétés structurales et électroniques des nanotubes C et CN x Les nanotubes de carbone sont l'objet d'importants efforts de recherche en raison de leurs fascinantes propriétés physiques. Ils constituent un système modèle particulièrement intéressant pour l'étude fondamentale de matériaux à une dimension et pour l'électronique moléculaire. En fonction de leur chiralité, les nanotubes peuvent adopter un comportement électronique soit semiconducteur soit métallique. Leur spectre électronique est dominé par une série de singularités de Van Hove qui définit la bande interdite des tubes semiconducteurs et les orbitales moléculaires situées à ces énergies. Pour contrôler et moduler les propriétés électroniques des nanotubes, une voie prometteuse est d'utiliser le dopage par des hétéroatomes. Les travaux présentés ici portent sur l'étude expérimentale de l'influence des interactions à N corps sur la valeur de la bande interdite des tubes semiconducteurs, la visualisation dans l'espace direct des orbitales moléculaires des nanotubes et les propriétés des nanotubes dopés par l'azote en utilisant des mesures de microscopie tunnel, microscopie électronique à balayage et spectroscopie de perte d'énergie des électrons.
11/2011;
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ABSTRACT: The electronic states of self-organized Fe nanoislands on a Au(111) surface have been investigated using low-temperature scanning tunneling microscopy and spectroscopy. We show that the local density of states is dominated by Shockley surface states confined in the nanostructures. Comparing the experimental dispersion diagram with a free-electron model we derive the effective mass m*=0.39 me and the band onset E0=−420 meV of these states. Ab initio calculations show the existence of the Shockley surface states in the Fe layer, in agreement with the experiment, and reveal that they are fully spin polarized.
Phys. Rev. B. 07/2011; 84(3).
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Comptes Rendus Physique 01/2011; 12:909. · 1.36 Impact Factor
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Hong Lin,
Jérôme Lagoute, Vincent Repain,
Cyril Chacon,
Yann Girard,
François Ducastelle,
Hakim Amara,
Annick Loiseau,
Patrick Hermet,
Luc Henrard,
Sylvie Rousset
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ABSTRACT: Carbon nanotubes have attracted considerable interest for their unique electronic properties. They are fascinating candidates for fundamental studies of one dimensional materials as well as for future molecular electronics applications. The molecular orbitals of nanotubes are of particular importance as they govern the transport properties and the chemical reactivity of the system. Here we show for the first time a complete experimental investigation of molecular orbitals of single wall carbon nanotubes using atomically resolved scanning tunneling spectroscopy. Local conductance measurements show spectacular carbon-carbon bond asymmetry at the Van Hove singularities for both semiconducting and metallic tubes, demonstrating the symmetry breaking of molecular orbitals in nanotubes. Whatever the tube, only two types of complementary orbitals are alternatively observed. An analytical tight-binding model describing the interference patterns of ? orbitals confirmed by ab initio calculations, perfectly reproduces the experimental results.
11/2009;
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ABSTRACT: Electron-electron interactions and excitons in carbon nanotubes are locally measured by combining Scanning tunneling spectroscopy and optical absorption in bundles of nanotubes. The largest gap deduced from measurements at the top of the bundle is found to be related to the intrinsic quasi-particle gap. From the difference with optical transitions, we deduced exciton binding energies of 0.4 eV for the gap and 0.7 eV for the second Van Hove singularity. This provides the first experimental evidence of substrate-induced gap renormalization on SWNTs.
07/2009;
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ABSTRACT: We investigate the influence of the native staircase nanostructure of a Au(111) vicinal surface upon the self-assembly of alkylthiols. Through a comparison with standard alkylthiol SAMs deposited on Au(111) flat surfaces, we show that on the vicinal surface the octanethiol monolayer (OT SAM) reproduces the nanopatterned staircase structure, giving rise to a new kind of molecular layer self-ordered on the nanometer scale. The SAM's structure is determined by UHV STM and PM-IRRAS measurements and exhibits a specific behavior relative to the nanostructured substrate. The differences from the film grown on Au(111) are attributed to the influence of step edges on the molecular packing, leading to a specific 2D crystallographic order through the step edges.
Langmuir 04/2008; 24(5):2042-50. · 4.19 Impact Factor
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ABSTRACT: The surface topography of a kinked vicinal surface of Au(111) is characterized by in situ grazing incidence small-angle x-ray scattering and scanning tunneling microscopy. The step edges exhibit a long range ordering of kinks which is attributed to the repulsive interaction between the kinks and the surface reconstruction. The kink size and ordering are revealed by three-dimensional measurements of the reciprocal space close to the origin and by a detailed analysis performed in the framework of the ideal paracrystal model. The growth of Co clusters on this surface gives rise to a long-range ordering induced by the surface reconstruction and revealed by the interferences between the x-ray waves scattered by the steps and/or kinks and by the Co clusters. These results are completed with in situ grazing incidence x-ray diffraction measurements, providing a crystallographic description of the Co clusters.
Phys. Rev. B. 77(4).
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ABSTRACT: We have studied the energetics, relaxation and interactions of steps on the Au(332) vicinal surface, using a combination of grazing incidence X-ray diffraction (GIXD), anisotropic linear elasticity (ALE) theory, and ab initio density functional theory (DFT). We find that the initial force distribution on a bulk-truncated surface, as well as the resulting pattern of atomic relaxations, can be reproduced excellently by a buried dipole elastic model. The close agreement obtained between experimental and calculated X-ray diffraction profiles allows us to precisely determine the value of the elastic dipole density at the steps. We also use these results to obtain an experimental estimate of the surface stress on an unreconstructed Au(111) facet, 2.3+/-0.4 Nm-1, and the value of the step-step elastic interaction energy: 950 +/- 150 meV.Å.
Physical Review B.
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Olivier Fruchart,
Gilles Renaud,
Antoine Barbier,
Marion Noblet,
Olivier Ulrich,
Jean-Paul Deville,
Fabrice Scheurer,
Jeannot Mané-Mané, Vincent Repain,
Grégory Beaudot,
Sylvie Rousset
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ABSTRACT: Hetero-epitaxial growth on a strain-relief vicinal patterned substrate has revealed unprecedented 2D long range ordered growth of uniform cobalt nanostructures. The morphology of a Co sub-monolayer deposit on a Au(111) reconstructed vicinal surface is analyzed by Variable Temperature Scanning Tunneling Microscopy (VT-STM) experiments. A rectangular array of nano-dots (3.8~nm x 7.2 nm) is found for a particularly large deposit temperature range lying from 60 K to 300 K. Although the nanodot lattice is stable at room temperature, this paper focus on the early stage ofordered nucleation and growth at temperatures between 35 K and 480 K. The atomistic mechanisms leading to the nanodots array are elucidated by comparing statistical analysis of VT-STM images withmulti-scaled numerical calculations combining both Molecular Dynamics for the quantitative determination of the activation energies for the atomic motion and the Kinetic Monte Carlo methodfor the simulations of the mesoscopic time and scale evolution of the Co submonolayer.
