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Koch M.,Fritz Haber Institute of the Max Planck Society | Ample F.,Institute of Materials Research and Engineering of Singapore | Joachim C.,Institute of Materials Research and Engineering of Singapore | Joachim C.,CNRS Toulouse Center for Materials Elaboration and Structural Studies | Grill L.,Fritz Haber Institute of the Max Planck Society
Nature Nanotechnology | Year: 2012

Graphene nanoribbons could potentially be used to create molecular wires with tailored conductance properties. However, understanding charge transport through a single molecule requires length-dependent conductance measurements and a systematic variation of the electrode potentials relative to the electronic states of the molecule. Here, we show that the conductance properties of a single molecule can be correlated with its electronic states. Using a scanning tunnelling microscope, the electronic structure of a long and narrow graphene nanoribbon, which is adsorbed on a Au(111) surface, is spatially mapped and its conductance then measured by lifting the molecule off the surface with the tip of the microscope. The tunnelling decay length is measured over a wide range of bias voltages, from the localized Tamm states over the gap up to the delocalized occupied and unoccupied electronic states of the nanoribbon. We also show how the conductance depends on the precise atomic structure and bending of the molecule in the junction, illustrating the importance of the edge states and a planar geometry. © 2012 Macmillan Publishers Limited. All rights reserved.

Wiecha P.R.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Nature Nanotechnology | Year: 2016

The rational design of photonic nanostructures consists of anticipating their optical response from systematic variations of simple models. This strategy, however, has limited success when multiple objectives are simultaneously targeted, because it requires demanding computational schemes. To this end, evolutionary algorithms can drive the morphology of a nano-object towards an optimum through several cycles of selection, mutation and cross-over, mimicking the process of natural selection. Here, we present a numerical technique that can allow the design of photonic nanostructures with optical properties optimized along several arbitrary objectives. In particular, we combine evolutionary multi-objective algorithms with frequency-domain electrodynamical simulations to optimize the design of colour pixels based on silicon nanostructures that resonate at two user-defined, polarization-dependent wavelengths. The scattering spectra of optimized pixels fabricated by electron-beam lithography show excellent agreement with the targeted objectives. The method is self-adaptive to arbitrary constraints and therefore particularly apt for the design of complex structures within predefined technological limits. © 2016 Nature Publishing Group

Caillard D.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Acta Materialia | Year: 2014

We present a complete analysis of the velocity of individual screw dislocations in pure iron, as a function of stress and temperature, by means of in situ straining experiments in a transmission electron microscope. The results show a very pronounced deviation from the classical laws of thermodynamics, which is at the origin of the discrepancy between experimental and calculated deformation stresses at low temperature. This strongly supports the occurrence of large quantum effects proposed in a recent theoretical study. © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Hawkes P.W.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Ultramicroscopy | Year: 2015

The progress of electron lens aberration correction from about 1990 onwards is chronicled. Reasonably complete lists of publications on this and related topics are appended.A present for Max Haider and Ondrej Krivanek in the year of their 65th birthdays.By a happy coincidence, this review was completed in the year that both Max Haider and Ondrej Krivanek reached the age of 65. It is a pleasure to dedicate it to the two leading actors in the saga of aberration corrector design and construction. They would both wish to associate their colleagues with such a tribute but it is the names of Haider and Krivanek (not forgetting Joachim Zach) that will remain in the annals of electron optics, next to that of Harald Rose. I am proud to know that both regard me as a friend as well as a colleague. © 2015 Elsevier B.V.

Soldano C.,CNRS Toulouse Center for Materials Elaboration and Structural Studies | Mahmood A.,CNRS Toulouse Center for Materials Elaboration and Structural Studies | Dujardin E.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Carbon | Year: 2010

This review on graphene, a one-atom thick, two-dimensional sheet of carbon atoms, starts with a general description of the graphene electronic structure as well as a basic experimental toolkit for identifying and handling this material. Owing to the versatility of graphene properties and projected applications, several production techniques are summarized, ranging from the mechanical exfoliation of high-quality graphene to the direct growth on carbides or metal substrates and from the chemical routes using graphene oxide to the newly developed approach at the molecular level. The most promising and appealing properties of graphene are summarized from an exponentially growing literature, with a particular attention to matching production methods to characteristics and to applications. In particular, we report on the high carrier mobility value in suspended and annealed samples for electronic devices, on the thickness-dependent optical transparency and, in the mechanical section, on the high robustness and full integration of graphene in sensing device applications. Finally, we emphasize on the high potential of graphene not only as a post-silicon materials for CMOS device application but more ambitiously as a platform for post-CMOS molecular architecture in electronic information processing. © 2010 Elsevier Ltd. All rights reserved.

Caillard D.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Acta Materialia | Year: 2010

In situ straining experiments have been carried out in pure Fe, in order to determine the geometry and the kinetics of dislocation glide at room temperature. Straight screw dislocations glide slowly in {1 1 0} elemental slip planes, at a velocity proportional to their length, whereas curved non-screw parts are highly mobile. The exact loop shape can yield the local stress as well as the difference of core energy between pure screw and near-screw orientations. The velocity-stress dependence of screws has been measured at the scale of a single dislocation source, and compared with macroscopic activation areas. The results are discussed in terms of the kink-pair mechanism. © 2010 Acta Materialia Inc.

Caillard D.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Acta Materialia | Year: 2010

In situ straining experiments have been carried out at low temperature in pure Fe, in order to study the change of mechanism occurring at around 250 K. The local stress necessary to move individual screw dislocations is in good agreement with the macroscopic yield stress at various temperatures. In the lower temperature range, straight screw segments have a jerky motion in {1 1 0} planes, at variance from the steady motion observed near room temperature. The distributions of waiting times in locked positions, and jump distances, the temperature variation of the average jump distance, and the stress/temperature variation of the macroscopic activation areas, are inconsistent with the kink-pair mechanism observed above 250 K. They have been interpreted in terms of a locking-unlocking mechanism, already proposed in hexagonal-closed-packed metals. Under such conditions, the change of mechanism at 250 K can account for the surprisingly low value of the flow stress extrapolated to 0 K (much lower than the theoretical Peierls stress). © 2010 Acta Materialia Inc.

Launay J.-P.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Coordination Chemistry Reviews | Year: 2013

Intramolecular electron transfer in binuclear mixed valence complexes where the metal atoms are linked by a bridging ligand illustrates a long-known problem: is it a two-step process with a temporary oxidation or reduction of the bridging ligand, or a one-step process best described by the super-exchange mechanism? In the latter case, information on the effective coupling between metal sites, Vab, can be obtained from the intensity of the intervalence transition. It is thus possible to study the decay of the coupling with distance, and also to show the possibility of molecular switching by using a photoactive ligand.However an integrated description of both mechanisms is possible by the explicit introduction of the bridging ligand nuclear degrees of freedom. This is achieved in a three-center model where the usual Hush-Marcus parabolas are replaced by three paraboloids in interaction. It is thus possible to compare different chemical systems and visualize the two limiting mechanisms.An interesting parallel can be made with the case of nanojunctions of the metal-molecule-metal type, which are increasingly available from scanning tunneling microscopy of molecules deposited on a suitable substrate. Such systems present an additional flexibility because the position of one electrode and the potentials can be changed. Thus one can probe again the decay of the electronic effect with distance and the possibility of molecular switching. But in addition, new effects can be observed. A remarkable experiment is the " charge trapping" on a single atom or a single molecule through the application of a voltage pulse. This can be considered as a redox reaction, the charge being stabilized by nuclear relaxation, the same process as the one occurring in polaron formation or in the two-step process invoked above. Finally, by moving the STM tip laterally above a molecule weakly coupled to its substrate, one can image in some cases molecular orbitals. © 2012 Elsevier B.V.

Hawkes P.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Ultramicroscopy | Year: 2014

Recent books and conference proceedings are examined. © 2013 Elsevier B.V.

Mitov M.,CNRS Toulouse Center for Materials Elaboration and Structural Studies
Advanced Materials | Year: 2012

The cholesteric-liquid-crystalline structure, which concerns the organization of chromatin, collagen, chitin, or cellulose, is omnipresent in living matter. In technology, it is found in temperature and pressure sensors, supertwisted nematic liquid crystal displays, optical filters, reflective devices, or cosmetics. A cholesteric liquid crystal reflects light because of its helical structure. The reflection is selective - the bandwidth is limited to a few tens of nanometers and the reflectance is equal to at most 50% for unpolarized incident light, which is a consequence of the polarization- selectivity rule. These limits must be exceeded for innovative applications like polarizer-free reflective displays, broadband polarizers, optical data storage media, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. Novel cholesteric-liquid-crystalline architectures with the related fabrication procedures must therefore be developed. This article reviews solutions found in living matter and laboratories to broaden the bandwidth around a central reflection wavelength, do without the polarization-selectivity rule and go beyond the reflectance limit. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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