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Christian Joachim - One of the best experts on this subject based on the ideXlab platform.

  • Single and double valence configuration interactions for recovering the exponential decay law while tunneling through a Molecular Wire
    Nanotechnology, 2016
    Co-Authors: Mathilde Portais, Mohamed Hliwa, Christian Joachim
    Abstract:

    The exponential decay of the electronic transmission through a Molecular Wire with its length is calculated using a configuration interaction elastic scattering quantum chemistry (CI-ESQC) theory [1, 2]. In the HOMO–LUMO gap and in a one-electron approximation, this decay is exponential since the scattering matrix comes from a product of spatial propagators along the Wire. In a valence SD–CI (single and double-configurations interaction) description, such a product does not exist. An effective one was numerically obtained from the CI-ESQC scattering matrix. Fluctuations over the effective CI-exponential decay come from the truncation of the full CI basis set and also from many-body exchange-correlation effects along the Molecular Wire.

  • Conductance of a single flexible Molecular Wire composed of alternating donor and acceptor units
    Nature Communications, 2015
    Co-Authors: Christophe Nacci, Christian Joachim, Francisco Ample, David Bleger, Stefan Hecht, Leonhard Grill
    Abstract:

    Molecular-scale electronics is mainly concerned by understanding charge transport through individual molecules. A key issue here is the charge transport capability through a single—typically linear—molecule, characterized by the current decay with increasing length. To improve the conductance of individual polymers, Molecular design often either involves the use of rigid ribbon/ladder-type structures, thereby sacrificing for flexibility of the Molecular Wire, or a zero band gap, typically associated with chemical instability. Here we show that a conjugated polymer composed of alternating donor and acceptor repeat units, synthesized directly by an on-surface polymerization, exhibits a very high conductance while maintaining both its flexible structure and a finite band gap. Importantly, electronic delocalization along the Wire does not seem to be necessary as proven by spatial mapping of the electronic states along individual Molecular Wires. Our approach should facilitate the realization of flexible ‘soft’ Molecular-scale circuitry, for example, on bendable substrates.

  • The contact conductance on a Molecular Wire
    Chemical Physics Letters, 2005
    Co-Authors: Sladjana Stojkovic, Christian Joachim, Leonhard Grill, Francesca Moresco
    Abstract:

    On a metal–molecule–metal nanojunction, the scanning tunneling microscope (STM) scans at the precise location of the electronic metal–molecule interaction permit a measurement of the contact conductance G0. The conversion curve between the change in the STM contrast Dh due to this interaction and G0 is presented for a series of conjugated Molecular Wires. At chemisorption distances, the two-valued character of the G0(Dh) function is discussed, indicating experimental ways to evaluate G0 as a function of Dh for different metal–molecule interaction ranges. � 2005 Elsevier B.V. All rights reserved.

  • Contacting a single Molecular Wire by STM manipulation
    Applied Physics A, 2005
    Co-Authors: Francesca Moresco, Micol Alemani, Christian Joachim, Andre Gourdon, Leo Gross, L. Grill, Karl-heinz Rieder
    Abstract:

    The Lander molecule (C_90H_98) consists of a long polyaromatic Molecular Wire and four lateral di-tert-butyl-phenyl spacer groups, designed to maintain the Molecular Wire parallel above the substrate. It represents a model system for investigating the electronic contacts of a Molecular Wire to a nanoscale metallic electrode. In this article, some recent manipulation experiments of single Lander molecules by low temperature scanning tunneling microscopy (LT-STM) are presented. The selective adsorption of the molecule, the molecule-induced reconstruction of copper substrates, and their application to the investigation of contacts between molecules and nanostructures or between molecules are discussed. Manipulation experiments are reported, where the Molecular Wire part of a Lander molecule is contacted to a monoatomic step and to a two-atom-wide metallic nanostructure. The contact is characterized by the apparent height of the contact point in STM images and, in case of the Cu(111) substrate, by the perturbation observed in the electronic standing wave patterns.

  • Distance Dependence of the Electronic Contact of a Molecular Wire
    AIP Conference Proceedings, 2005
    Co-Authors: Leonhard Grill, Christian Joachim, Andre Gourdon, Francesca Moresco, P. Jiang, Sladjana Stojkovic, Karl-heinz Rieder
    Abstract:

    The central Molecular Wire of a so‐called Reactive Lander molecule is brought in electronic contact with an atomic scale metallic nanostructure by manipulation with the STM tip. Several stable conformations are obtained in a controlled way, in accordance with calculations. An additional contribution to the tunneling current is observed at the end of the Molecular board, reflecting the electronic interaction between the Molecular Wire and the nanostructure. The characteristic intensity of this electronic contact for different conformations is discussed by means of the vertical interatomic distance between the Molecular Wire and the metal atoms.

Guillaume Schull - One of the best experts on this subject based on the ideXlab platform.

Gaël Reecht - One of the best experts on this subject based on the ideXlab platform.

Jianwei Zhao - One of the best experts on this subject based on the ideXlab platform.

  • first principles study of substituents effect on Molecular junctions towards Molecular rectification
    Computational Materials Science, 2008
    Co-Authors: Geping Yin, Jinhuan Yao, Jianwei Zhao
    Abstract:

    Abstract The nonequilibrium Green’s function technique and density functional theory were used to perform ab initio quantum-mechanical calculations of electronic transport of single polyacetylene (PA) Molecular Wire sandwiched between two gold electrodes. To inspect the substituents effect on the electronic transport properties, both the electron-donating (–NH2) and electron-withdrawing (–NO2) groups were asymmetrically introduced into the conjugated PA Molecular Wire, resembling the semiconductor p–n junction. The results demonstrated the rectification behavior of the substituted PA. The asymmetric evolutions of the energy levels and spatial distributions of the frontier Molecular orbitals with the applied voltage are found to be essential in generating this current–voltage asymmetry.

  • theoretical investigations of oligo phenylene ethylene Molecular Wire effects from substituents and external electric field
    Computational Materials Science, 2007
    Co-Authors: Yanwei Li, Jianwei Zhao
    Abstract:

    Abstract Theoretical investigation of the substituent effect on the Molecular Wire, oligo(phenylene ethynylene) (OPE), has been performed with density functional calculations by considering the influence from the external electric field (EF). Compared to the electron-donating –NH 2 group, the electron-withdrawing –NO 2 group plays more important roles, such as increase of Molecular dipole moment, decrease of LUMO–HOMO gap, and localization of LUMO. Both the geometric and electronic structures of the model Molecular Wires are sensitive to the external EF. In particularly, the –NO 2 substituted OPE yields obvious asymmetrical evolutions of both the frontier Molecular orbital energies and their spatial distribution, which could be used to intuitively interpret the asymmetrical current–voltage behaviors of molecules.

  • ab initio investigations of the electric field dependence of the geometric and electronic structures of Molecular Wires
    Journal of Physical Chemistry A, 2006
    Co-Authors: Yanwei Li, Jianwei Zhao
    Abstract:

    Theoretical investigations on the typical Molecular Wire, polyacetylene, which bridges two chemically inert electrodes, have been carried out at the Hartree−Fock level by incorporating the external electric field into the calculations. The results demonstrate that both the geometric and the electronic structures of the conjugated Molecular Wires are sensitive to the electric field. When the electric field increases, the carbon−carbon single bonds become shorter and the double bonds become longer, leading to a higher conjugation. The electric field reduces the HOMO−LUMO gap and increases the dipole moment. The spatial distributions of the Molecular orbitals are used to analyze the electrical properties of the Molecular Wire. All of these features are more pronounced with increasing conjugation chain length. Quantitative correlations between most of these features and the electric field have been discussed as well.

  • Theoretical analysis of geometry-correlated conductivity of Molecular Wire
    Chemical Physics Letters, 2006
    Co-Authors: Xing Yin, Yan Zhang, Jianwei Zhao
    Abstract:

    Abstract An approach closer to the in situ modeling of the Molecular electronic device is proposed with partial relaxation of the Molecular geometry under the interaction of the external electric field. A typical Molecular Wire (4,4′-(1,4-phenylenedi-2,1-ethynediyl)bis-benzenethiol) has been studied by this methodology using first-principles DFT calculations and non-equilibrium Green’s function formalism. It is found that the optimized Molecular Wire exhibits a different behavior compared with the geometry-frozen one. The HOMO–LUMO gaps, spatial distributions of the frontier Molecular orbitals, and the transmission spectra have been used in the explanation of the observations.

Andre Gourdon - One of the best experts on this subject based on the ideXlab platform.

  • Contacting a single Molecular Wire by STM manipulation
    Applied Physics A, 2005
    Co-Authors: Francesca Moresco, Micol Alemani, Christian Joachim, Andre Gourdon, Leo Gross, L. Grill, Karl-heinz Rieder
    Abstract:

    The Lander molecule (C_90H_98) consists of a long polyaromatic Molecular Wire and four lateral di-tert-butyl-phenyl spacer groups, designed to maintain the Molecular Wire parallel above the substrate. It represents a model system for investigating the electronic contacts of a Molecular Wire to a nanoscale metallic electrode. In this article, some recent manipulation experiments of single Lander molecules by low temperature scanning tunneling microscopy (LT-STM) are presented. The selective adsorption of the molecule, the molecule-induced reconstruction of copper substrates, and their application to the investigation of contacts between molecules and nanostructures or between molecules are discussed. Manipulation experiments are reported, where the Molecular Wire part of a Lander molecule is contacted to a monoatomic step and to a two-atom-wide metallic nanostructure. The contact is characterized by the apparent height of the contact point in STM images and, in case of the Cu(111) substrate, by the perturbation observed in the electronic standing wave patterns.

  • Distance Dependence of the Electronic Contact of a Molecular Wire
    AIP Conference Proceedings, 2005
    Co-Authors: Leonhard Grill, Christian Joachim, Andre Gourdon, Francesca Moresco, P. Jiang, Sladjana Stojkovic, Karl-heinz Rieder
    Abstract:

    The central Molecular Wire of a so‐called Reactive Lander molecule is brought in electronic contact with an atomic scale metallic nanostructure by manipulation with the STM tip. Several stable conformations are obtained in a controlled way, in accordance with calculations. An additional contribution to the tunneling current is observed at the end of the Molecular board, reflecting the electronic interaction between the Molecular Wire and the nanostructure. The characteristic intensity of this electronic contact for different conformations is discussed by means of the vertical interatomic distance between the Molecular Wire and the metal atoms.

  • Controlled manipulation of a single Molecular Wire along a copper atomic nanostructure
    Physical Review B, 2004
    Co-Authors: Leonhard Grill, Christian Joachim, Andre Gourdon, Francesca Moresco, P. Jiang, Karl-heinz Rieder
    Abstract:

    Nanoscience Group, CEMES-CNRS, 29 rue J. Marvig, P.O. Box 4347, 31055 Toulouse, France~Received 28 July 2003; revised manuscript received 10 November 2003; published 29 January 2004!Different stable conformations of a Molecular Wire along a short copper nanostructure are studied by meansof low temperature scanning tunneling microscopy ~STM! and controlled manipulations, with the aim ofinvestigating the electronic contact of a single molecule to a metallic pad. The Molecular Wire is the so-calledLander molecule, a conjugated Wire group supported by four legs. Independent of its position along the coppernanostructure, the central Molecular Wire is always in electronic interaction with the atomic Wire underneath.This effect becomes visible in the STM images depending on the orientation of the legs. By STM manipula-tion, the Molecular Wire can be precisely positioned in an electronic contact conformation at the end of theatomic Wire.DOI: 10.1103/PhysRevB.69.035416 PACS number~s!: 68.37.Ef, 72.80.Le, 68.65.La, 85.65.1hI. INTRODUCTION

  • Probing the different stages in contacting a single Molecular Wire.
    2003
    Co-Authors: Francesca Moresco, Micol Alemani, Andre Gourdon, Karl-heinz Rieder, Leo Gross, Hao Tang, Christian Joachim
    Abstract:

    A crucial problem in Molecular electronics is the control of the electronic contact between a molecule and its electrodes. As a model system, we investigated the contact between the Molecular Wire group of a C90H98 (Lander) molecule and the edge of a Cu(111) monatomic step. The reproducible contact and decontact of the Wire was obtained by manipulating the Lander with a low temperature scanning tunneling microscope. The electronic standing wave patterns on the Cu(111) surface serve to monitor the local electronic perturbation caused by the interaction of the Wire end with the step edge, giving information on the quality of the contact.

  • conformations of a Molecular Wire adsorbed on a metal surface
    Physical Review B, 2002
    Co-Authors: J Kuntze, Andre Gourdon, H Tang, P. Jiang, Richard Berndt, Christian Joachim
    Abstract:

    The conformation changes of a Molecular Wire induced upon adsorption on a Cu(001) surface are investigated by low-temperature scanning tunneling microscopy. Measured images are compared with calculations using the elastic-scattering quantum chemistry technique, allowing the extraction of Molecular adsorption geometries on terraces and at steps. The Molecular bonds prove to be very flexible, resulting in different conformations upon adsorption compared to the Molecular gas-phase structure.