Institute For Nanotechnologie

Eggenstein-Leopoldshafen, Germany

Institute For Nanotechnologie

Eggenstein-Leopoldshafen, Germany
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Clemens O.,University of Birmingham | Clemens O.,TU Darmstadt | Clemens O.,Institute For Nanotechnologie | Berry F.J.,University of Birmingham | And 5 more authors.
Journal of Solid State Chemistry | Year: 2013

We report here a detailed study of the system La1-xSr xFeO3-xFx, by neutron powder diffraction- and magnetic-measurements. All the compounds are robust antiferromagnetics with ordering temperatures well above room temperature. Magnetic moments are shown to align parallel to the c-axis. FC-ZFC measurements indicate a small canting of the magnetic moments, resulting in a ferromagnetic component with a maximum for La0.5Sr0.5FeO2.5F0.5. We show that the system exhibits a composition-driven transition from a phase, for low fluorination levels (x≤0.5), with Pnma symmetry and the usual system of octahedral tiltings, to a phase with space group Imma for higher fluorine contents, where a correlated distortion of the oxygen octahedra plays a significant role. The consistency of the structural models, with respect to the expected continuity of the amplitudes of the different distortion modes and the invariance of their internal form, was monitored through the symmetry mode decomposition of the structures. © 2013 Elsevier Inc.

Clemens O.,Saarland University | Clemens O.,TU Darmstadt | Clemens O.,Institute For Nanotechnologie | Haberkorn R.,Saarland University | And 2 more authors.
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2014

In this paper we report on the possibility of Li substitution by M 2+ to various high degrees in LiMPO4 olivine-type compounds (M = Ni, Co, Fe, Mn), depending on the kind of transition metal M. The experimental studies were carried through by reacting stoichiometric amounts of LiMIIPO4 and MII 1.5PO4 (= MII 3(PO4)2) to form compounds of composition LixMII 1.5-x/2PO4 (0 ≤ x ≤ 1). A complete solid solution over the whole range of x was found for M = Ni (together with a second order structural transition from orthorhombic to monoclinic for decreasing x), whereas far smaller degrees of dopability of the Li site were found for LiCoPO4 and LiFePO4 (up to compositions of approx. (Li0.8Co0.1)CoPO4 and approx. (Li0.9Fe0.05)FeO4. In addition, the nearly stoichiometric monoclinically distorted olivine-type compounds with compositions (Li0.42-0.47Co0.29-0.265)CoPO4 and (Li0.14-0.16Fe0.43-0.42)FePO4 could be identified and are described in this article. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Laudenbach J.,TU Berlin | Hennrich F.,Institute For Nanotechnologie | Telg H.,Los Alamos National Laboratory | Kappes M.,Karlsruhe Institute of Technology | Maultzsch J.,TU Berlin
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We present a resonance Raman study of the disorder-induced D mode in a sample highly enriched with semiconducting (9,7) single-walled carbon nanotubes in the excitation energy range of 1.49-2.05eV. The intensity of the D mode shows a resonance behavior near the optical transition of the (9,7) tube. The well-known dispersion of the D-mode frequency, on the other hand, is not observed at the resonance, but only above a certain excitation energy. We explain our results by numerical simulations of the D-mode spectra. © 2013 American Physical Society.

Greb L.,CNRS Institute of Science and Supramolecular Engineering | Greb L.,Institute For Nanotechnologie | Mutlu H.,Karlsruhe Institute of Technology | Barner-Kowollik C.,Karlsruhe Institute of Technology | And 2 more authors.
Journal of the American Chemical Society | Year: 2016

N-alkyl α-bisimines were employed as main-chain functional groups in acyclic diene metathesis (ADMET)-polymers, conferring dual responsiveness for the controlled switching of the polymeric particle shape with light and metal ions. Photochemical Z/E-isomerization leads to a significant and reversible change in hydrodynamic volume, thus introducing simple imines as novel photoswitches for light-responsive materials. Mild imine-directed CH activation by Pd(OAc)2 is demonstrated as a new single-chain nanoparticle (SCNP) folding process, enabling a controlled atom- and step-economic SCNP synthesis. The combination of light- and metallo-responsiveness in the same polymer provides the ability for orthogonal switching, a valuable tool for advanced functional material design. © 2015 American Chemical Society.

Kriegler C.E.,Karlsruhe Institute of Technology | Kriegler C.E.,Institute For Nanotechnologie | Rill M.S.,Karlsruhe Institute of Technology | Rill M.S.,Institute For Nanotechnologie | And 4 more authors.
IEEE Journal on Selected Topics in Quantum Electronics | Year: 2010

In metamaterials, electric (magnetic) dipoles can be excited by the electric (magnetic) component of the incident light field. Moreover, in the description of bianisotropic metamaterials, cross terms occur, i.e., magnetic dipoles can also be excited by the electric-field component of the incident light and vice versa. For the cross terms, in the general bianisotropic case, the exciting field and dipole vectors include an arbitrary angle. For the special case of chirality, the angle is zero. In the spirit of a brief tutorial, a very simple electric-circuit description of the split-ring resonator is used to give a basic introduction to the cross terms. Mathematical details of the effective parameter retrieval are presented. Furthermore, we briefly review recent experiments on bianisotropic metamaterials operating at optical frequencies. © 2006 IEEE.

Longo P.,Karlsruhe Institute of Technology | Schmitteckert P.,Institute For Nanotechnologie | Busch K.,Karlsruhe Institute of Technology
Physical Review Letters | Year: 2010

We present a detailed analysis of the dynamics of photon transport in waveguiding systems in the presence of a two-level system. In these systems, quantum interference effects generate a strong effective optical nonlinearity on the few-photon level. We clarify the relevant physical mechanisms through an appropriate quantum many-body approach. Based on this, we demonstrate that a single-particle photon-atom bound state with an energy outside the band can be excited via multiparticle scattering processes. We further show that these trapping effects are robust and, therefore, will be useful for the control of photon entanglement in solid-state based quantum-optical systems. © 2010 The American Physical Society.

Thomale R.,Stanford University | Rachel S.,Yale University | Schmitteckert P.,Institute For Nanotechnologie | Schmitteckert P.,Karlsruhe Institute of Technology | Greiter M.,Karlsruhe Institute of Technology
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We investigate a family of spin-S chain Hamiltonians recently introduced by one of us [Greiter, Mapping of Parent Hamiltonians, Springer Tracts in Modern Physics, Vol. 244 (Springer, Berlin, 2011)]. For S=1/2, it corresponds to the Haldane-Shastry model. For general spin S, we find indication that the low-energy theory of these spin chains is described by the SU(2) k Wess-Zumino-Witten model with coupling k=2S. In particular, we investigate the S=1 model whose ground state is given by a Pfaffian for even number of sites N. We reconcile aspects of the spectrum of the Hamiltonian for arbitrary N with trial states obtained by Schwinger projection of two Haldane-Shastry chains. © 2012 American Physical Society.

Klein F.,Karlsruhe Institute of Technology | Striebel T.,Karlsruhe Institute of Technology | Fischer J.,Karlsruhe Institute of Technology | Jiang Z.,Karlsruhe Institute of Technology | And 6 more authors.
Advanced Materials | Year: 2010

(Figure Presented) Elastic 3D scaffolds (see figure) are fabricated into a biocompatible photoresist using direct laser writing. These scaffolds can be rhythmically deformed by single beating cardiomyocytes and calibration with atomic force microscopy indicates that cellular forces down to 1020 nN are detectable with the setup. © 2010 WILEY-VCH Verlag GmbH &, Co. KGaA.

Prati L.,University of Milan | Villa A.,University of Milan | Chan-Thaw C.E.,University of Milan | Arrigo R.,Fritz Haber Institute of the Max Planck Society | And 2 more authors.
Faraday Discussions | Year: 2011

Commercial carbon nanotubes (CNTs) and carbon nanofibers (CNFs) modified in various ways at the surface have been used as supports for gold nanoparticles (AuNPs) in order to study their influence on the activity/selectivity of catalysts in the aqueous oxidation of alcohol. Particularly oxidative treatment was used to introduce carboxylic functionalities, whereas subsequent treatment with NH3 at different temperatures (473 K, 673 K and 873 K) produced N-containing groups leading to an enhancement of basic properties as the NH 3 treatment temperature was increased. The nature of the N-containing groups changed as the temperature increased, leading to an increase in the hydrophobicity of the support surface. Similar Au particle size and similar textural properties of the supports allowed the role of chemical surface groups in both the activity and the selectivity of the reaction of glycerol oxidation to be highlighted. An increase of basic functionalities produced a consistent increase in the activity of the catalyst, which was correlated to the promoting effect of the basic support in the alcoholate formation and the subsequent C-H bond cleavage. The selectivity towards primary oxidation products (C3 compounds) was the highest for the catalysts treated with NH3 at 873 K, which presented the most hydrophobic surface. The same trend in the catalyst activity has been obtained in the aqueous benzyl alcohol base-free oxidation. As in the case of glycerol, the increasing of basicity and/or hydrophobicity increased the consecutive reactions. © 2011 The Royal Society of Chemistry.

Brendler E.,TU Bergakademie Freiberg | Heine T.,Jacobs University Bremen | Seichter W.,TU Bergakademie Freiberg | Wagler J.,TU Bergakademie Freiberg | Witter R.,Institute For Nanotechnologie
Zeitschrift fur Anorganische und Allgemeine Chemie | Year: 2012

29Si NMR shielding tensors of a series of triphenylsilanes Ph 3SiR with R = Ph, Me, F, Cl, Br, OH, OMe, SH, NH 2, SiPh 3, C≡CPh were determined from 29Si CP/MAS spectra recorded at low spinning rates. In addition the principal components of the shielding tensor were calculated employing the DFT-IGLO method. For most silanes experimental and calculated values are in good accordance. Larger differences were observed for systems with hydrogen bridge forming substituents and the halides bromide and chloride. In some of the spectra the shielding information interfered with residual dipolar couplings. The different contributions of the various substituents to the principal components of the shielding tensor and the orientation of the tensor within the molecules are discussed and compared for the compounds under investigation. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

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