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Vitali L.,Max Planck Institute fuer Festkoerperforschung | Ohmann R.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Ecole Polytechnique Federale de Lausanne | And 5 more authors.
Nano Letters | Year: 2010

Molecular junctions have been characterized to determine the influence of the metal contact formation in the electron transport process through a single molecule. With inelastic electron tunneling spectroscopy and first-principles calculations, the vibration modes of a carbon monoxide molecule have been surveyed as a function of the distance from a copper electrode with unprecedented accuracy. We observe a continuous but nonlinear blue shift of the frustrated rotation mode in tunneling with decreasing distance followed by an abrupt softening upon contact formation. This indicates that the presence of the metal electrode sensibly alters the structural and conductive properties of the junction even without the formation of a strong chemical bond. © 2010 American Chemical Society.


Kim J.S.,Pohang University of Science and Technology | Kremer R.K.,Max Planck Institute fuer Festkoerperforschung
Journal of the Korea Institute of Applied Superconductivity and Cryogenics | Year: 2013

We investigate the electrical and thermal transport properties of a sesquicarbide superconductor La2C3, including electrical resistivity, thermoelectric power, and thermal conductivity. The electrical resistivity exhibits a typical metallic character with a saturation behavior at high temperatures. The thermoelectric power shows a metallic behavior with pronounced phonon-drag effect, comparable with pure metals. The broad peak of the thermal conductivity is observed in the superconducting state, which is rapidly suppressed by magnetic fields. These observations suggest that the electron-phonon scattering is significant in La2C3, which is relevant with the relatively high-Tc in La2C3 through strong electron-phonon coupling with low frequency phonon modes.


PubMed | CAS Shanghai Institute of Microsystem and Information Technology, University of Houston, Rice University, CAS Shanghai Institute of Ceramics and 2 more.
Type: | Journal: Journal of physics. Condensed matter : an Institute of Physics journal | Year: 2016

Using the angle-resolved photoemission spectroscopy and band structure calculations we study the electronic structure of KFeCoAs2, which is isoelectronic to the parent material of 122 series of iron-based superconductors BaFe2As2. Although band structure calculations predict nearly identical dispersions of the electronic states in both compounds, experiment reveals drastic differences in both the global renormalization and Fermi surfaces. On the basis of the comparison of electronic structures of these two isoelectronic compounds, we demonstrate local magnetic correlations as a vital role for the peculiar low-energy electron dynamics of iron-based superconductors.


Goler S.,Italian Institute of Technology | Goler S.,CNR Institute of Neuroscience | Coletti C.,Italian Institute of Technology | Coletti C.,Max Planck Institute fuer Festkoerperforschung | And 10 more authors.
Carbon | Year: 2013

On the SiC(0 0 0 1) surface (the silicon face of SiC), epitaxial graphene is obtained by sublimation of Si from the substrate. The graphene film is separated from the bulk by a carbon-rich interface layer (hereafter called the buffer layer) which in part covalently binds to the substrate. Its structural and electronic properties are currently under debate. In the present work we report scanning tunneling microscopy (STM) studies of the buffer layer and of quasi-free-standing monolayer graphene (QFMLG) that is obtained by decoupling the buffer layer from the SiC(0 0 0 1) substrate by means of hydrogen intercalation. Atomic resolution STM images of the buffer layer reveal that, within the periodic structural corrugation of this interfacial layer, the arrangement of atoms is topologically identical to that of graphene. After hydrogen intercalation, we show that the resulting QFMLG is relieved from the periodic corrugation and presents no detectable defect sites. © 2012 Published by Elsevier Ltd.


Dufaux T.,Max Planck Institute fuer Festkoerperforschung | Boettcher J.,Max Planck Institute fuer Festkoerperforschung | Burghard M.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Ecole Polytechnique Federale de Lausanne
Small | Year: 2010

In order to realize solar cells with technologically useful performance, intensive efforts are being directed towards the development of novel device architectures and components. So far, high power conversion effi ciencies exceeding 5% have been reached with dye-sensitized[1] or polymer blend-based solar cells,[2] wherein very fast interfacial charge transfer occurs. However, charge transport is often limiting the performance of these devices. In particular for blendbased solar cells, the photocurrent depends strongly on the properties of the percolation network.[3] A promising strategy to overcome this limitation involves nano-structured solar cells which provide well-defi ned, separate pathways for carrier transport, thus minimizing recombination losses. Examples include vertically aligned arrays of ZnO,[4] TiO2 ,[5] Si nanowires,[6] or TiO2 functionalized CNTs.[7] Especially promising are CNTs decorated with semiconductor nanoparticles, since the former provide a close-to-ideal transport pathway for carriers. However, it is diffi cult to obtain a high quality electrical connection between nanotube and semiconductor without disrupting the carbon framework of the nanotubes. Accordingly, studying the interface between sp 2 -bonded carbon materials and semiconductors is important for further improving the performance of CNT based solar cells. More recently, also the closely related graphene has attracted increasing interest toward photovoltaic applications.[8] It has been chemically modifi ed by the attachment of TiO2 nanoparticles[9] or CdS quantum dots,[10] albeit only little is known about the interface between graphene and inorganic or organic semiconductors, in contrast to the metal-graphene interaction.[11-13] In fact, while ultrafast electron transfer from CdS dots to graphene has been detected by time-resolved photoluminescence spectroscopy,[14] the suitability of these nanocomposites for light harvesting applications remains to be evaluated.Copyright © 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.


Peters E.C.,Max Planck Institute fuer Festkoerperforschung | Lee E.J.H.,Max Planck Institute fuer Festkoerperforschung | Burghard M.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Max Planck Institute fuer Festkoerperforschung | Kern K.,Ecole Polytechnique Federale de Lausanne
Applied Physics Letters | Year: 2010

We have used scanning photocurrent microscopy to explore the electronic characteristics of a graphene p-n junction fabricated by local chemical doping of a graphene sheet. The photocurrent signal at the junction was found to be most prominent for gate voltages between the two Dirac points of the oppositely doped graphene regions. The gate dependence of this signal agrees well with simulations based upon the Fermi level difference between the two differently doped sections. It is concluded that the photocurrent maps are dominated by the built-in electric field, with only a minor photothermoelectric contribution. © 2010 American Institute of Physics.


Dufaux T.,Max Planck Institute fuer Festkoerperforschung | Dorfmuller J.,Max Planck Institute fuer Festkoerperforschung | Vogelgesang R.,Max Planck Institute fuer Festkoerperforschung | Burghard M.,Max Planck Institute fuer Festkoerperforschung | And 2 more authors.
Applied Physics Letters | Year: 2010

We have investigated the near-field coupling of surface plasmons to a titanium/CdS nanowire interface for two different device configurations. A bare aluminum grating on an underlying aluminum layer exhibited the expected stronger electrical signal for perpendicular versus parallel light polarization. An opposite intensity ratio was detected when the grating and the Schottky contact are connected via an aluminum-silica-aluminum sandwich structure. Based upon finite difference time domain device simulations, the enhanced coupling for parallel polarization is attributed to the emergence of a transversal electric wave within the metal-insulator-metal structure. © 2010 American Institute of Physics.


PubMed | Max Planck Institute fuer Festkoerperforschung
Type: Journal Article | Journal: Nano letters | Year: 2010

Molecular junctions have been characterized to determine the influence of the metal contact formation in the electron transport process through a single molecule. With inelastic electron tunneling spectroscopy and first-principles calculations, the vibration modes of a carbon monoxide molecule have been surveyed as a function of the distance from a copper electrode with unprecedented accuracy. We observe a continuous but nonlinear blue shift of the frustrated rotation mode in tunneling with decreasing distance followed by an abrupt softening upon contact formation. This indicates that the presence of the metal electrode sensibly alters the structural and conductive properties of the junction even without the formation of a strong chemical bond.

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