Role of molecular electronic structure in inelastic electron tunneling spectroscopy: O2 on Ag(110)

10 páginas, 8 figuras, 2 tablas.-- PACS number(s): 68.37.-d, 72.10.-d, 72.25.-b, 79.20.RfDensity-functional theory (DFT) simulations corrected by the intramolecular Coulomb repulsion U are performed to evaluate the vibrational inelastic electron tunneling spectroscopy (IETS) of O2 on Ag(110). In contrast to DFT calculations that predict a spinless adsorbed molecule, the inclusion of the U correction leads to the polarization of the molecule by shifting a spin-polarized molecular orbital toward the Fermi level. Hence, DFT+U characterizes O2 on Ag(110) as a mixed-valent system. This has an important implication in IETS because a molecular resonance at the Fermi level can imply a decrease in conductance while in the off-resonance case, an increase in conductance is the expected IETS signal. We use the lowest-order expansion on the electron-vibration coupling in order to evaluate the magnitude and spatial distribution of the inelastic signal. The final IET spectra are evaluated with the help of the self-consistent Born approximation and the effect of temperature and modulation-voltage broadening are explored. Our simulations reproduce the experimental data of O2 on Ag(110) [ J. R. Hahn, H. J. Lee and W. Ho Phys. Rev. Lett. 85 1914 (2000)] and give extra insight of the electronic and vibrational symmetries at play. This ensemble of results reveals that the IETS of O2 is more complicated that a simple decrease in conductance and cannot be ascribed to the effect of a single molecular-orbital resonance.We acknowledge financial support from the Spanish MICINN (Grants No. FIS2007-066711-CO2-00 and No. FIS2009-12721-C04-01), and the Basque Government-UPV/ EHU (Grant No. IT-366-07).Peer reviewe

Elastic transport through dangling-bond silicon wires on H passivated Si(100)

We evaluate the electron transmission through a dangling-bond wire on Si(100)-H (2x1). Finite wires are modelled by decoupling semi-infinite Si electrodes from the dangling-bond wire with passivating H atoms. The calculations are performed using density functional theory in a non-periodic geometry along the conduction direction. We also use Wannier functions to analyze our results and to build an effective tight-binding Hamiltonian that gives us enhanced insight in the electron scattering processes. We evaluate the transmission to the different solutions that are possible for the dangling-bond wires: Jahn-Teller distorted ones, as well as antiferromagnetic and ferromagnetic ones. The discretization of the electronic structure of the wires due to their finite size leads to interesting transmission properties that are fingerprints of the wire nature

Effets inélastiques dans les courants électroniques à l'échelle nanométrique

This thesis deals with inelastic effects in electronic currents. We developed a time-dependent technique and show that this approach gives rich insight into electron-phonon coupling during transport. We compare our results with a time-independent technique and analyse the validity of our model. Finally, the results of a quantum chemistry calculation are presented in the framework of scanning tunneling miscroscopy (STM). We study the chemisorption of a tetrathiafulvalene molecule on a gold surface by performing the calculation of the charge transfer, the induced dipole, and the STM images using the density functional theory.Cette thèse traite des effets inélastiques qui ont lieu au sein des courants électroniques. En utilisant un formalisme dépendant du temps, nous avons obtenu des résultats qui apportent une vision riche en renseignements au sujet du couplage électron-phonon. Nous avons pu comparer cette méthode à une approche indépendante du temps, pour en analyser les avantages et inconvénients. Finalement, une étude de chimie quantique est présentée dans le cadre de la microscopie à effet tunnel (STM). Nous avons étudié la chimisorption d'une molécule de tétrathiafulvalène sur une surface d'or: le calcul du transfert de charge vers la surface, du dipôle induit, puis la simulation d'images STM ont été effectués sur la base de la théorie de la fonctionnelle de la densité

Role of molecular electronic structure in inelastic electron tunneling spectroscopy: O2 on Ag(110)

10 páginas, 8 figuras, 2 tablas.-- PACS number(s): 68.37.-d, 72.10.-d, 72.25.-b, 79.20.RfDensity-functional theory (DFT) simulations corrected by the intramolecular Coulomb repulsion U are performed to evaluate the vibrational inelastic electron tunneling spectroscopy (IETS) of O2 on Ag(110). In contrast to DFT calculations that predict a spinless adsorbed molecule, the inclusion of the U correction leads to the polarization of the molecule by shifting a spin-polarized molecular orbital toward the Fermi level. Hence, DFT+U characterizes O2 on Ag(110) as a mixed-valent system. This has an important implication in IETS because a molecular resonance at the Fermi level can imply a decrease in conductance while in the off-resonance case, an increase in conductance is the expected IETS signal. We use the lowest-order expansion on the electron-vibration coupling in order to evaluate the magnitude and spatial distribution of the inelastic signal. The final IET spectra are evaluated with the help of the self-consistent Born approximation and the effect of temperature and modulation-voltage broadening are explored. Our simulations reproduce the experimental data of O2 on Ag(110) [ J. R. Hahn, H. J. Lee and W. Ho Phys. Rev. Lett. 85 1914 (2000)] and give extra insight of the electronic and vibrational symmetries at play. This ensemble of results reveals that the IETS of O2 is more complicated that a simple decrease in conductance and cannot be ascribed to the effect of a single molecular-orbital resonance.We acknowledge financial support from the Spanish MICINN (Grants No. FIS2007-066711-CO2-00 and No. FIS2009-12721-C04-01), and the Basque Government-UPV/ EHU (Grant No. IT-366-07).Peer reviewe

Effets inélastiques dans les courants électroniques à l'échelle nanométrique

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

One-way rotation of a molecule-rotor driven by a shot noise

cited By 6International audienceThe shot noise of a tunneling current passing through a molecule-motor can sustain a one-way rotation when populating the molecular excited states by tunneling inelastic excitations. We demonstrate that a ratchet-like ground state rotation potential energy curve is not necessary for the rotation to occur. A relative shift in energy difference between the maxima of this ground state and the minima of the excited states is the necessary condition to get to a unidirectional rotation. The rotor speed of rotation and its rotation direction are both controlled by this shift, indicating the necessity of a careful design of both the ground and excited states of the next generation of molecule-motors to be able to generate a motive power at the nanoscale

Iniciativas desde el Sur y hacia el Sur. La proyección argentina, desde su retorno a la democracia, hacia el África subsahariana

En este artículo nos proponemos examinar los cambios y continuidades en materia de política exterior argentina con relación al África subsahariana, resaltando que estos responden no sólo a una dinámica interna, sino también a una nutrida irrupción de variables explicativas de carácter exógeno, fundamentalmente en los primeros años en que se gestó un nuevo orden unipolar. Al focalizar y profundizar muestro análisis en el período 1983-2007, podemos observar más fácilmente –en un contexto signado por la sucesión de gobiernos democráticos– visibles contrastes entre los diseños de agenda exterior hacia el África subsahariana identificando como consecuencia de ello aumentos o retracciones en los flujos de vinculación horizontales. Reflexionar a través de este estudio de caso sobre las vinculaciones Sur-Sur nos permite incursionar sobre un terreno poco transitado e incluso marginal en los principales centros académicos, estimulando con ello el desarrollo de nuevos enfoques que nos posibiliten tomar distancia de un pensamiento hegemónico de tipo eurocentrista, para comenzar a gestar un corpus conceptual alternativo a la narrativa convencional