29 results on '"Manuel Gruber"'
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2. Spin-Crossover Complexes in Direct Contact with Surfaces
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Manuel Gruber and Richard Berndt
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spin crossover ,single molecule ,surfaces ,scanning tunneling spectroscopy ,near-edge X-ray absorption fine structure ,Chemistry ,QD1-999 - Abstract
The transfer of the inherent bistability of spin crossover compounds to surfaces has attracted considerable interest in recent years. The deposition of the complexes on surfaces allows investigating them individually and to further understand the microscopic mechanisms at play. Moreover, it offers the prospect of engineering switchable functional surfaces. We review recent progress in the field with a particular focus on the challenges and limits associated with the dominant experimental techniques used, namely near-edge X-ray absorption fine structure (NEXAFS) spectroscopy and scanning tunneling microscopy (STM). One of the main difficulties in NEXAFS-based experiments is to ascertain that the complexes are in direct contact with the surfaces. We show that molecular coverage determination based on the amplitude of the edge-jump of interest is challenging because the latter quantity depends on the substrate. Furthermore, NEXAFS averages the signals of a large number of molecules, which may be in different states. In particular, we highlight that the signal of fragmented molecules is difficult to distinguish from that of intact and functional ones. In contrast, STM allows investigating individual complexes, but the identification of the spin states is at best done indirectly. As quite some of the limits of the techniques are becoming apparent as the field is gaining maturity, their detailed descriptions will be useful for future investigations and for taking a fresh look at earlier reports.
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- 2020
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3. Feasibility study on electrically conductive joining of MoSi 2 electrodes for spark plugs
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Manuel Gruber, Anton Tilz, Walter Harrer, Roman Papsik, Wolfgang Fimml, and Michael Engelmayer
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Marketing ,Materials Chemistry ,Ceramics and Composites ,Condensed Matter Physics - Published
- 2023
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4. Iron in a Cage: Fixation of a Fe(II)tpy 2 Complex by Fourfold Interlinking
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Thomas Brandl, Sven Johannsen, Daniel Häussinger, Nithin Suryadevara, Alessandro Prescimone, Stefan Bernhard, Manuel Gruber, Mario Ruben, Richard Berndt, and Marcel Mayor
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02 engineering and technology ,General Medicine ,010402 general chemistry ,021001 nanoscience & nanotechnology ,0210 nano-technology ,01 natural sciences ,0104 chemical sciences - Published
- 2020
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5. Coverage‐Controlled Superstructures of C 3 ‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling
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Richard Berndt, Manuel Gruber, Torben Jasper-Tönnies, Rainer Herges, and Sandra Ulrich
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Materials science ,Surface Coverage ,Pattern formation ,010402 general chemistry ,01 natural sciences ,Catalysis ,law.invention ,law ,coverage control ,Molecule ,Research Articles ,Hexagonal tiling ,Mesoscopic physics ,010405 organic chemistry ,Honeycomb (geometry) ,General Medicine ,General Chemistry ,molecular tiling model ,C3-symmetric molecules ,0104 chemical sciences ,Template ,Chemical physics ,scanning tunneling microscopy ,Scanning tunneling microscope ,honeycomb superstructure ,Order of magnitude ,Research Article - Abstract
The competition between honeycomb and hexagonal tiling of molecular units can lead to large honeycomb superstructures on surfaces. Such superstructures exhibit pores that may be used as 2D templates for functional guest molecules. Honeycomb superstructures of molecules that comprise a C3 symmetric platform on Au(111) and Ag(111) surfaces are presented. The superstructures cover nearly mesoscopic areas with unit cells containing up to 3000 molecules, more than an order of magnitude larger than previously reported. The unit cell size may be controlled by the coverage. A fairly general model was developed to describe the energetics of honeycomb superstructures built from C 3 symmetric units. Based on three parameters that characterize two competing bonding arrangements, the model is consistent with the present experimental data and also reproduces various published results. The model identifies the relevant driving force, mostly related to geometric aspects, of the pattern formation., Molecular honeycomb superstructures were investigated using scanning tunneling microscopy, covering nearly mesoscopic areas and with unit cells containing up to 3000 molecules. A fairly general model was developed that describes the energetics of such structures and show that their sizes can be controlled by coverage.
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- 2020
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6. Spin Crossover in a Cobalt Complex on Ag(111)
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Sven Johannsen, Sascha Ossinger, Jan Grunwald, Alexander Herman, Heiko Wende, Felix Tuczek, Manuel Gruber, and Richard Berndt
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General Chemistry ,General Medicine ,Physik (inkl. Astronomie) ,Catalysis - Abstract
The Co-based complex [Co(H
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- 2021
7. Probing the Spin State of Spin-Crossover Complexes on Surfaces with Vacuum Ultraviolet Angle-Resolved Photoemission Spectroscopy
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Jan Grunwald, Felix Tuczek, M. Kalläne, Benedikt M. Flöser, Jana Kähler, Florian Diekmann, Kai Rossnagel, Manuel Gruber, Sascha Ossinger, and Sebastian Rohlf
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Materials science ,Spin states ,Angle-resolved photoemission spectroscopy ,Physik (inkl. Astronomie) ,Molecular physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,Vacuum ultraviolet ,General Energy ,Spin crossover ,Condensed Matter::Strongly Correlated Electrons ,ddc:530 ,Physical and Theoretical Chemistry - Abstract
The journal of physical chemistry / C 125(25), 14105-14116 (2021). doi:10.1021/acs.jpcc.1c03527, Spin-crossover complexes in direct contact with substrates have sparked considerable interest, in particular, in view of their potential applications in molecular electronics. While a huge number of spin-crossover complexes is available, many of them are not robust enough to withstand the sample preparation and/or the interaction with the substrate. The techniques usually employed for these investigations, namely, near-edge X-ray absorption fine structure spectroscopy and low-temperature scanning tunneling microscopy, are not adapted for systematic studies because of the limited access to synchrotron-radiation facilities and complexity of the (indirect) spin determination, respectively. Here, we detail a methodology using a (more) commonly available technique, namely, vacuum ultraviolet (angle-resolved) photoemission spectroscopy, to determine the spin state of layers of three different spin-crossover complexes with thicknesses down to the submonolayer regime. We present an approach to determine the thicknesses of the investigated layers, relying on the inelastic mean free path of electrons determined from combined photoemission and X-ray absorption measurements. We report on the high-spin to low-spin relaxation dynamics of spin-crossover (SCO) layers and the influence of the ultraviolet light on these dynamics. While the observed relaxation processes occur on a timescale on the order of minutes, probing spin-state dynamics on the picosecond timescale is foreseeable with pump–probe photoemission spectroscopy., Published by Soc., Washington, DC
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- 2021
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8. Frontispiz: Coverage‐Controlled Superstructures of C 3 ‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling
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Manuel Gruber, Rainer Herges, Richard Berndt, Torben Jasper-Tönnies, and Sandra Ulrich
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Materials science ,Condensed matter physics ,law ,Coverage control ,Honeycomb (geometry) ,Molecule ,General Medicine ,Scanning tunneling microscope ,Hexagonal tiling ,law.invention - Published
- 2020
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9. Frontispiece: Coverage‐Controlled Superstructures of C 3 ‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling
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Torben Jasper‐Tönnies, Manuel Gruber, Sandra Ulrich, Rainer Herges, and Richard Berndt
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General Chemistry ,Catalysis - Published
- 2020
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10. Spin dependent transmission of nickelocene-Cu contacts probed with shot noise
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Manuel Gruber, Alexander Weismann, Michael Mohr, Nicolás Lorente, David Jacob, P. N. Abufager, Richard Berndt, German Research Foundation, Agencia Estatal de Investigación (España), Ministerio de Ciencia, Innovación y Universidades (España), Universidad del País Vasco, and Eusko Jaurlaritza
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transmissiion ,Nickelocene ,FOS: Physical sciences ,02 engineering and technology ,spin ,01 natural sciences ,nickelocene ,law.invention ,purl.org/becyt/ford/1 [https] ,Condensed Matter - Strongly Correlated Electrons ,chemistry.chemical_compound ,law ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,0103 physical sciences ,010306 general physics ,Spin-½ ,Physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,Strongly Correlated Electrons (cond-mat.str-el) ,Condensed matter physics ,Spin polarization ,Shot noise ,purl.org/becyt/ford/1.3 [https] ,021001 nanoscience & nanotechnology ,Coupling (probability) ,chemistry ,Condensed Matter::Strongly Correlated Electrons ,Density functional theory ,Scanning tunneling microscope ,0210 nano-technology ,Noise (radio) - Abstract
The current I through nickelocene molecules and its noise are measured with a low-temperature scanning tunneling microscope on a Cu(100) substrate. Density functional theory calculations and many-body modeling are used to analyze the data. During contact formation, two types of current evolution are observed, namely an abrupt jump to contact and a smooth transition. These data along with conductance spectra (dI/dV) recorded deep in the contact range are interpreted in terms of a transition from a spin-1 to a spin-12 state that is Kondo-screened. Many-body calculations show that the smooth transition is also consistent with a renormalization of spin excitations of a spin-1 molecule by Kondo exchange coupling. The shot noise is significantly reduced compared to the Schottky value of 2eI. The noise can be described in the Landauer picture in terms of the spin polarization of the transmission of ≈35% through two degenerate dπ-orbitals of the nickelocene molecule., This work has been supported by the Deutsche Forschungsgemeinschaft, project BE 2132/8. N.L. is grateful for the financial support from MICINN (RTI2018- 097895-B-C44). D.J. acknowledges funding by the grant “Grupos Consolidados UPV/EHU del Gobierno Vasco” (IT1249-19).
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- 2020
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11. Incipient plasticity and surface damage in LiTaO3 and LiNbO3 single crystals
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Manuel Gruber, Alexander Leitner, Raul Bermejo, Daniel Kiener, and Peter Supancic
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010302 applied physics ,Materials science ,Mechanical Engineering ,Cleavage (crystal) ,02 engineering and technology ,Nanoindentation ,Plasticity ,021001 nanoscience & nanotechnology ,01 natural sciences ,Focused ion beam ,Brittleness ,Mechanics of Materials ,0103 physical sciences ,lcsh:TA401-492 ,General Materials Science ,lcsh:Materials of engineering and construction. Mechanics of materials ,Composite material ,0210 nano-technology ,Crystal twinning ,Anisotropy ,Single crystal - Abstract
The outstanding functional properties of single crystals used in many engineering applications often rely on their surface quality. The associated grinding process in single crystals is known to introduce surface or sub-surface defects (cracks), which may compromise the functionality and/or structural integrity of the final device. The small size of such defects often yields relatively high strength values, but also usually large scatter which implies low reliability. The aim of this work is to analyze the onset of surface contact damage in single crystals with respect to crystal orientation and elastic properties. LiTaO3 and LiNbO3 anisotropic single crystal samples are investigated using nanoindentation techniques and focused ion beam based sub-surface analyses. Experimental findings show that the onset of damage is correlated to weaker cleavage planes. At this stage also traces of plastic deformation on the contact surface due to twinning are observed. Further load increase revealed contact cracks in both materials; their morphology and extension being related to the orientation of the cleavage planes and elastic properties of the crystals. Our results advance the understanding of damage in anisotropic materials such as LiTaO3 and LiNbO3, and can generally be utilized to assess the onset of damage in other brittle materials. Keywords: Nanoindentation, Single crystals, Anisotropy, Pop-in, Twinning, Cracking
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- 2018
12. Understanding the effect of surface flaws on the strength distribution of brittle single crystals
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Peter Hans Supancic, Raul Bermejo, Irina Kraleva, Manuel Gruber, Alexander Leitner, and Daniel Kiener
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010302 applied physics ,Surface (mathematics) ,Materials science ,Distribution (number theory) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Brittleness ,0103 physical sciences ,Materials Chemistry ,Ceramics and Composites ,Fracture (geology) ,Surface modification ,Composite material ,0210 nano-technology - Published
- 2018
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13. Atomistic origins of the differences in anisotropic fracture behaviour of LiTaO3 and LiNbO3 single crystals
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Peter Supancic, Raul Bermejo, Manuel Gruber, Maxim N. Popov, Ruth Konetschnik, Daniel Kiener, and Jürgen Spitaler
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010302 applied physics ,Toughness ,Materials science ,Polymers and Plastics ,Metals and Alloys ,Cleavage (crystal) ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Piezoelectricity ,Electronic, Optical and Magnetic Materials ,Brittleness ,0103 physical sciences ,Ceramics and Composites ,Wafer ,Density functional theory ,Composite material ,0210 nano-technology ,Anisotropy ,Single crystal - Abstract
The search of new designs for communication technologies is driven by the required high data transfer rates. Piezoelectric single crystals such as LiTaO3 and LiNbO3 have qualified as materials for efficient and precise frequency filters also considered for the new 5G standards. To ensure optimal high frequency functionality, single crystal wafers are grown and cut in particular directions. However, due to the high anisotropic physical properties of these brittle materials, the structural integrity and reliability of devices are affected by the crystal orientation with respect to the occurring thermo-mechanical stresses. In this work, the anisotropic fracture response of LiTaO3 and LiNbO3 single crystals is investigated through combination of (i) toughness measurements in notched micro-cantilevers along weak cleavage planes and (ii) atomistic modelling of cleavage fracture energies using density functional theory. It is demonstrated that differences in fracture behaviour between LiTaO3 and LiNbO3 can be explained by the stronger chemical bonding in LiTaO3 as compared to LiNbO3 within the loaded crystallographic planes. The knowledge on the alignment of tough as well as weak planes (i.e. cleavage planes) can be used to tailor the design of single crystal based functional components, aiming to exhibit enhanced mechanical reliability without compromising the functionality.
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- 2018
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14. Power-to-Gas through High Temperature Electrolysis and Carbon Dioxide Methanation: Reactor Design and Process Modeling
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Stefan Harth, Raffaele Pirone, Emanuele Giglio, Manuel Gruber, Fabio Alessandro Deorsola, Dimosthenis Trimis, Eduard Alexandru Morosanu, and Samir Bensaid
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Power to gas ,Work (thermodynamics) ,Substitute natural gas ,Process modeling ,Materials science ,020209 energy ,General Chemical Engineering ,Oxide ,02 engineering and technology ,General Chemistry ,7. Clean energy ,Industrial and Manufacturing Engineering ,chemistry.chemical_compound ,Chemical engineering ,chemistry ,High-temperature electrolysis ,Methanation ,Carbon dioxide ,0202 electrical engineering, electronic engineering, information engineering - Abstract
This work deals with the coupling between high temperature steam electrolysis using solid oxide cells (SOEC) and carbon dioxide methanation to produce a synthetic natural gas (SNG) directly injecta...
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- 2018
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15. Light-Induced Spin Crossover in an Fe(II) Low-Spin Complex Enabled by Surface Adsorption
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Kai Rossnagel, Manuel Gruber, Torben Jasper-Toennies, M. Kalläne, Simon Jarausch, Winfried Plass, Felix Tuczek, Jan Grunwald, Sebastian Rohlf, Benedikt M. Flöser, Florian Diekmann, Axel Buchholz, and Richard Berndt
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Materials science ,Spintronics ,Analytical chemistry ,02 engineering and technology ,Atmospheric temperature range ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,0104 chemical sciences ,Adsorption ,Spin crossover ,Excited state ,ddc:530 ,General Materials Science ,Physical and Theoretical Chemistry ,Thin film ,Absorption (chemistry) ,0210 nano-technology ,Spectroscopy - Abstract
The journal of physical chemistry letters 9(7), 1491 - 1496 (2018). doi:10.1021/acs.jpclett.8b00338, Understanding and controlling the spin-crossover properties of molecular complexes can be of particular interest for potential applications in molecular spintronics. Using near-edge X-ray absorption fine structure spectroscopy, we investigated these properties for a new vacuum-evaporable Fe(II) complex, namely [Fe(pypyr(CF$_3$)$_2$)$_2$(phen)] (pypyr = 2-(2′-pyridyl)pyrrolide, phen = 1,10-phenanthroline). We find that the spin-transition temperature, well above room temperature for the bulk compound, is drastically lowered for molecules arranged in thin films. Furthermore, while within the experimentally accessible temperature range (2 K < T < 410 K) the bulk material shows indication of neither light-induced excited spin-state trapping nor soft X-ray-induced excited spin-state trapping, these effects are observed for molecules within thin films up to temperatures around 100 K. Thus, by arranging the molecules into thin films, a nominal low-spin complex is effectively transformed into a spin-crossover complex., Published by ACS, Washington, DC
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- 2018
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16. Influence of Ring Contraction on the Electronic Structure of Nickel Tetrapyrrole Complexes: Corrole vs Porphyrin
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Martin Bröring, Jan Herritsch, Jan-Niclas Luy, Kai Rossnagel, M. Kalläne, Manuel Gruber, Ralf Tonner, Peter Schweyen, Sebastian Rohlf, Benedikt P. Klein, and J. Michael Gottfried
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Materials science ,Electronic structure ,Porphyrin ,XANES ,Electronic, Optical and Magnetic Materials ,chemistry.chemical_compound ,Crystallography ,chemistry ,X-ray photoelectron spectroscopy ,ddc:660 ,Density functional theory ,Valence bond theory ,Corrole ,Ultraviolet photoelectron spectroscopy - Abstract
ECS journal of solid state science and technology 9(6), 061005 - (2020). doi:10.1149/2162-8777/ab9e18, The influence of the contracted corrole macrocycle, in comparison to the larger porphyrin macrocycle, on the electronic structure of nickel was studied with X-ray and ultraviolet photoelectron spectroscopy (XPS, UPS) and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy. Synthesis and in situ characterization of the Ni complexes of octaethylporphyrin (NiOEP) and hexaethyldimethylcorrole (NiHEDMC) were performed in ultra-high vacuum. XPS and NEXAFS spectra reveal a +2 oxidation state and a low-spin d8 electron configuration of Ni in both complexes, despite the formal trianionic nature of the corrole ligand. UPS, in combination with density functional theory (DFT) calculations, support the electronic structure of a Ni(II) corrole with a π-radical character of the ligand. The NEXAFS spectra also reveal differences in the valence electronic structure, which are attributed to the size mismatch between the small Ni(II) center and the larger central cavity of NiOEP. Analysis of the gas-phase structures shows that the Ni−N bonds in NiOEP are 4%–6% longer than those in NiHEDMC, even when NiOEP adopts a ruffled conformation. The individual interactions that constitute the Ni−ligand bond are altogether stronger in the corrole complex, according to bonding analysis within the energy decomposition analysis and the natural orbitals for chemical valence theory (EDA-NOCV)., Published by ECS, Pennington, NJ
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- 2020
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17. Iron in a Cage: Fixation of a Fe(II)tpy2 Complex by Fourfold Interlinking
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Alessandro Prescimone, Stefan Bernhard, Marcel Mayor, Mario Ruben, Daniel Häussinger, Nithin Suryadevara, Manuel Gruber, Richard Berndt, Sven Johannsen, Thomas Brandl, Institut de Physique et Chimie des Matériaux de Strasbourg (IPCMS), Université de Strasbourg (UNISTRA)-Matériaux et nanosciences d'Alsace (FMNGE), Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Institut de Chimie du CNRS (INC)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS)-Réseau nanophotonique et optique, Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA)-Université de Haute-Alsace (UHA) Mulhouse - Colmar (Université de Haute-Alsace (UHA))-Centre National de la Recherche Scientifique (CNRS)-Université de Strasbourg (UNISTRA), and Université Louis Pasteur - Strasbourg I-Centre National de la Recherche Scientifique (CNRS)
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Technology ,Coordination sphere ,Materials science ,010405 organic chemistry ,Ligand ,Temperature independent ,General Chemistry ,010402 general chemistry ,01 natural sciences ,Catalysis ,0104 chemical sciences ,3. Good health ,law.invention ,SQUID ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,chemistry.chemical_compound ,Crystallography ,chemistry ,law ,Wittig reaction ,Terpyridine ,Scanning tunneling microscope ,Cage ,ddc:600 - Abstract
The coordination sphere of the Fe(II) terpyridine complex 1 is rigidified by fourfold interlinking of both terpyridine ligands. Profiting from an octa‐aldehyde precursor complex, the ideal dimensions of the interlinking structures are determined by reversible Schiff‐base formation, before irreversible Wittig olefination provided the rigidified complex. Reversed‐phase HPLC enables the isolation of the all‐trans isomer of the Fe(II) terpyridine complex 1, which is fully characterized. While temperature independent low‐spin states were recorded with superconducting quantum interference device (SQUID) measurements for both, the open precursor 8 and the interlinked complex 1, evidence of the increased rigidity of the ligand sphere in 1 was provided by proton T$_{2}$ relaxation NMR experiments. The ligand sphere fixation in the macrocyclized complex 1 even reaches a level resisting substantial deformation upon deposition on an Au(111) surface, as demonstrated by its pristine form in a low temperature ultra‐high vacuum scanning tunneling microscope experiment.
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- 2020
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18. Reversible coordination-induced spin-state switching in complexes on metal surfaces
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Edwige Otero, Felix Tuczek, Alexander Köbke, Alexander Weismann, Kai Rossnagel, Sebastian Rohlf, Sven Johannsen, Manuel Gruber, Torben Jasper-Toennies, Richard Berndt, Michał Studniarek, Rainer Herges, Philippe Ohresser, Florian Gutzeit, Christian Näther, Florian Diekmann, Fadi Choueikani, Danilo Longo, Fynn Röhricht, Alexander Schlimm, Jan Grunwald, Institut für Experimentelle und Angewandte Physik [Kiel] (IEAP), Christian-Albrechts-Universität zu Kiel (CAU), Otto-Diels-Institut für Organische Chemie, Paul Scherrer Institute (PSI), Synchrotron SOLEIL (SSOLEIL), Centre National de la Recherche Scientifique (CNRS), Christian-Albrechts University of Kiel, COSMICS, European Project: 766726,211587,COSMICS(2017), Institut fur Anorganische Chemie, The Swiss Light Source (SLS) (SLS-PSI), and Deutsches Elektronen-Synchrotron [Hamburg] (DESY)
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Materials science ,Spin states ,Biomedical Engineering ,Bioengineering ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,Metal ,chemistry.chemical_compound ,Molecule ,General Materials Science ,Electrical and Electronic Engineering ,[PHYS.COND]Physics [physics]/Condensed Matter [cond-mat] ,[PHYS]Physics [physics] ,Spin polarization ,Spintronics ,Ligand ,[CHIM.ORGA]Chemical Sciences/Organic chemistry ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Porphyrin ,Atomic and Molecular Physics, and Optics ,3. Good health ,0104 chemical sciences ,chemistry ,Chemical physics ,Intramolecular force ,visual_art ,visual_art.visual_art_medium ,Condensed Matter::Strongly Correlated Electrons ,[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph] ,0210 nano-technology ,ddc:600 - Abstract
Molecular spin switches are attractive candidates for controlling the spin polarization developing at the interface between molecules and magnetic metal surfaces1,2, which is relevant for molecular spintronics devices3–5. However, so far, intrinsic spin switches such as spin-crossover complexes have suffered from fragmentation or loss of functionality following adsorption on metal surfaces, with rare exceptions6–9. Robust metal–organic platforms, on the other hand, rely on external axial ligands to induce spin switching10–14. Here we integrate a spin switching functionality into robust complexes, relying on the mechanical movement of an axial ligand strapped to the porphyrin ring. Reversible interlocked switching of spin and coordination, induced by electron injection, is demonstrated on Ag(111) for this class of compounds. The stability of the two spin and coordination states of the molecules exceeds days at 4 K. The potential applications of this switching concept go beyond the spin functionality, and may turn out to be useful for controlling the catalytic activity of surfaces15. Spin-crossover complexes often lose their functionality upon adsorption on metal surfaces. Here, a metal–organic complex adsorbed on a silver surface undergoes reversible interlocked spin and coordination switching, which is enabled by an intramolecular feedback mechanism controlling the position of an axial ligand strapped to the complex.
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- 2020
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19. Insights into the catalytic CO2 methanation of a boiling water cooled fixed-bed reactor: Simulation-based analysis
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Stefan Harth, Manuel Gruber, A. Loukou, Manuel Haas, Dimosthenis Trimis, and Denis Wiedmann
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Materials science ,General Chemical Engineering ,02 engineering and technology ,General Chemistry ,Mechanics ,Heat transfer coefficient ,010402 general chemistry ,021001 nanoscience & nanotechnology ,01 natural sciences ,Industrial and Manufacturing Engineering ,0104 chemical sciences ,Carbide ,Reaction rate ,chemistry.chemical_compound ,Thermal conductivity ,chemistry ,Thermocouple ,Methanation ,Boiling ,Silicon carbide ,Environmental Chemistry ,0210 nano-technology - Abstract
This article presents the simulation-based analysis of experimental results from a catalytic fixed-bed reactor for the methanation of CO2. During previously published experiments, temperature profiles inside bidisperse catalyst-silicon carbide fixed-beds were gathered and reactant conversions at the reactor outlet measured. On the basis of the temperature profiles along the fixed-bed length and outlet reactant conversions, a procedure for the numerical characterisation of these results was developed. Primary parameters like the inserted multipoint thermocouple and the heat transfer coefficient between reactor wall and surrounding boiling water cooling are systematically investigated. Concerning the binary bidisperse fixed-beds of porous catalyst cylinders and highly thermal conductive silicon carbide, a simple numerical method for the determination of the effective heat conductivity of the bed is presented. The modelling of effective reaction rates within an industrial sized catalyst and reactor is a non-trivial task, due to interlinking aspects like intrinsic reaction rate and internal and external transport limitations. Intrinsic reaction rate, internal and external transport limitations are linked, what makes a separate investigation challenging. Thus, a step by step analysis is presented and the single effects investigated in detail. From the results of the stepwise numerical characterisation, an excellent agreement between experiments and numerics was reached. Additionally, a novel partially resolved 3D fixed-bed reactor model is presented and selected results like particle overheating presented. Overall the present numerical investigations provided a deep insight into the methanation of CO2 in a cooled fixed-bed reactor.
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- 2021
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20. Inactivation of vegetative microorganisms by ohmic heating in the kilohertz range – Evaluation of experimental setups and non-thermal effects
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Henry Jaeger, Maximilian Gratz, Manuel Gruber, Christoph Schoenher, Nicole Burghardt, Felix Schottroff, Joane Schelling, and Dominik Biebl
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Range (particle radiation) ,Materials science ,Microorganism ,Kinetics ,04 agricultural and veterinary sciences ,General Chemistry ,040401 food science ,Industrial and Manufacturing Engineering ,0404 agricultural biotechnology ,Chemical engineering ,Scientific method ,Electric field ,Heat transfer ,Thermal ,Joule heating ,Food Science - Abstract
The present study highlighted the importance of equipment design for the experimental differentiation of thermal and electric field effects during ohmic heating. Based on these findings, a specifically designed setup was capable of reducing temperature inhomogeneities of conventional and ohmic heating, thus allowing for a maximum comparability of the processes. The effects of the treatments were evaluated by determination of inactivation kinetics, using different microorganisms, i.e. Microbacterium lacticum, Escherichia coli, Listeria innocua, Staphylococcus carnosus, Saccharomyces cerevisiae, and Rhodotorula glutinis in neutral as well as acidic (pH 3.8) solutions. Selected kinetics were further analyzed by flow cytometry, using SYBR green and propidium iodide staining. Based on comparable T, t-profiles and plate counts, conventional and ohmic heating were shown to be capable of effectively inactivating all tested microorganisms (max. 2.5–6.5 log), depending on treatment intensity (2.5 kW, up to 140 s) and pH level. No additional, non-thermal inactivation effects were determined for ohmic heating treatments, independent of the used matrix, pulse repetition rate/frequency, or waveform. Industrial relevance Ohmic heating is an alternative thermal preservation treatment increasingly used in the food and biotechnological industries for sensitive matrices, which are otherwise difficult to thermally process. It is able to overcome heat transfer limitations usually present in conventional thermal treatments, by application of an electric current flow through the product. The present paper contributes to better understand preservation by electrotechnologies and to the elucidation of inactivation mechanisms by ohmic heating. Thus, the understanding of the effects of ohmic heating on microorganisms is increased, which is crucial for industrial implementation of the technology and the corresponding process design.
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- 2020
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21. Fragmentation and Distortion of Terpyridine-Based Spin-Crossover Complexes on Au(111)
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Marcel Mayor, Gero D. Harzmann, Thomas Knaak, Manuel Gruber, César González, Thomas Brandl, Yannick J. Dappe, Richard Berndt, Christian-Albrechts-Universität zu Kiel (CAU), Universidad Autonoma de Madrid (UAM), Groupe Modélisation et Théorie (GMT), Institut Rayonnement Matière de Saclay (IRAMIS), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Service de physique de l'état condensé (SPEC - UMR3680), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Centre National de la Recherche Scientifique (CNRS), University of Basel (Unibas), Karlsruhe Institute of Technology (KIT), European Project: 766726,211587,COSMICS(2017), Universidad Autónoma de Madrid (UAM), Service de physique de l'état condensé (SPEC - UMR3680), Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Institut Rayonnement Matière de Saclay (IRAMIS), and Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université Paris-Saclay
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Materials science ,Electrospray ionization ,02 engineering and technology ,010402 general chemistry ,01 natural sciences ,law.invention ,Metal ,chemistry.chemical_compound ,Fragmentation (mass spectrometry) ,law ,Spin crossover ,[CHIM.COOR]Chemical Sciences/Coordination chemistry ,Physical and Theoretical Chemistry ,021001 nanoscience & nanotechnology ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Crystallography ,General Energy ,chemistry ,visual_art ,visual_art.visual_art_medium ,Density functional theory ,Condensed Matter::Strongly Correlated Electrons ,[PHYS.PHYS.PHYS-CHEM-PH]Physics [physics]/Physics [physics]/Chemical Physics [physics.chem-ph] ,Scanning tunneling microscope ,Terpyridine ,0210 nano-technology - Abstract
International audience; Spin-crossover complexes are attractive for their spin-switching functionality. However, only a few compounds have been found to remain intact in direct contact to metal surfaces. For the design of new spin-crossover complexes, it is important to understand the mechanisms leading to fragmentation. Here, we investigate, using low-temperature scanning tunneling microscopy along with density functional theory calculations, two Fe-(terpyridine) 2 complexes deposited on Au(111) by electro-spray ionization with in-line mass selection. Only fragments of the first compound are observed on the surface, while the second compound is strongly flattened. On the basis of a detailed analysis of the adsorbates on the surface, possible mechanisms for the fragmentation and molecular distortion are proposed.
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- 2019
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22. Influence of Substrate Electronic Properties on the Integrity and Functionality of an Adsorbed Fe(II) Spin-Crossover Compound
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Michał Studniarek, Kai Rossnagel, Manuel Gruber, Richard Berndt, Torben Jasper-Toennies, Sebastian Rohlf, Jan Grunwald, Sven Johannsen, Felix Tuczek, and Florian Diekmann
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Materials science ,Absorption spectroscopy ,Bistability ,Substrate (chemistry) ,02 engineering and technology ,010402 general chemistry ,021001 nanoscience & nanotechnology ,Photochemistry ,01 natural sciences ,3. Good health ,0104 chemical sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,General Energy ,Adsorption ,Spin crossover ,ddc:530 ,Physical and Theoretical Chemistry ,0210 nano-technology ,Electronic properties - Abstract
The bistability of spin-crossover complexes on surfaces is of great interest for potential applications. Using X-ray absorption spectroscopy, we investigated the properties of [Fe(pypyr(CF$_3$)$_2$)$_2$(phen)] (pypyr = 2-(2′-pyridyl)pyrrolide, phen = 1,10-phenanthroline), a vacuum-evaporable Fe(II) complex, in direct contact to a set of substrates. The electronic properties of these substrates range from metallic to semiconducting. While dissociation is observed on metal surfaces, efficient light-induced switching is realized on semimetallic and semiconducting surfaces. This indicates that the density of states of the substrate at the Fermi level plays a role for the integrity and functionality of the adsorbed compound. In an intermediate case, namely, [Fe(pypyr(CF$_3$)$_2$)$_2$(phen)] on graphene/Ni(111), functional and dissociated species are found to coexist. This result indicates that some previous studies may deserve to be reconsidered because the possibility of coexisting intact and fragmented spin-crossover complexes was neglected.
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- 2019
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23. Spin in a closed‐shell organic molecule on a metal substrate generated by a sigmatropic reaction
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Richard Berndt, Nicolás Lorente, Marie-Laure Bocquet, Manuel Gruber, Ministerio de Economía y Competitividad (España), European Commission, Processus d'Activation Sélective par Transfert d'Energie Uni-électronique ou Radiatif (UMR 8640) (PASTEUR), Département de Chimie - ENS Paris, École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS Paris), Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-Institut de Chimie du CNRS (INC)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Universidad Pública de Navarra [Espagne] = Public University of Navarra (UPNA), Christian-Albrechts-Universität zu Kiel (CAU), European Project: 766726,211587,COSMICS(2017), Université Paris sciences et lettres (PSL), École normale supérieure - Paris (ENS-PSL), and Université Paris sciences et lettres (PSL)-Université Paris sciences et lettres (PSL)-École normale supérieure - Paris (ENS-PSL)
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Materials science ,Radical ,Allene ,Sigmatropy ,02 engineering and technology ,Conjugated system ,010402 general chemistry ,01 natural sciences ,Catalysis ,law.invention ,Delocalized electron ,chemistry.chemical_compound ,law ,Metal surfaces ,Moiety ,Molecule ,[CHIM]Chemical Sciences ,Physics::Chemical Physics ,Scanning tunneling microscopy ,Open shell ,General Chemistry ,General Medicine ,021001 nanoscience & nanotechnology ,3. Good health ,0104 chemical sciences ,[CHIM.THEO]Chemical Sciences/Theoretical and/or physical chemistry ,Density functional calculations ,chemistry ,Organic radicals ,Chemical physics ,Scanning tunneling microscope ,0210 nano-technology - Abstract
Inert metal surfaces present more chances of hosting organic intact radicals than other substrates, but large amounts of delocalized electronic states favor charge transfer and thus spin quenching. Lowering the molecule-substrate interaction is a usual strategy to stabilize radicals on surfaces. In some works, thin insulating layers were introduced to provide a controllable degree of electronic decoupling. Recently, retinoid molecules adsorbed on gold have been manipulated with a scanning tunneling microscope (STM) to exhibit a localized spin, but calculations failed to find a radical derivative of the molecule on the surface. Now the formation of a neutral radical spatially localized in a tilted and lifted cyclic end of the molecule is presented. An allene moiety provokes a perpendicular tilt of the cyclic end relative to the rest of the conjugated chain, thus localizing the spin of the dehydrogenated allene in its lifted subpart. DFT calculations and STM manipulations give support to the proposed mechanism., M.‐L.B. thanks the national computational center CINES, and TGCC (Grant 2017‐ [GENCI project: A0010807364]) for a computer grant and acknowledges the Mercator fellowship of SFB 677 in CAU Kiel. N.L. acknowledges financial support from MINECO (MAT2015‐66888‐C3‐2‐R) and FEDER funds, and he is thankful to the Mercator fellowship of SFB 677 in CAU Kiel. M.G. acknowledges financial support of SFB 677. This project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement No. 766726.
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- 2019
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24. The Kondo resonance line shape in scanning tunnelling spectroscopy: instrumental aspects
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Manuel Gruber, Richard Berndt, and Alexander Weismann
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Physics ,Microscope ,Condensed matter physics ,Condensed Matter - Mesoscale and Nanoscale Physics ,FOS: Physical sciences ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,01 natural sciences ,Resonance (particle physics) ,Noise (electronics) ,Spectral line ,law.invention ,Modulation ,law ,0103 physical sciences ,Mesoscale and Nanoscale Physics (cond-mat.mes-hall) ,General Materials Science ,Kondo effect ,010306 general physics ,0210 nano-technology ,Quantum tunnelling ,Line (formation) - Abstract
In the scanning tunnelling microscope, the many-body Kondo effect leads to a zero-bias feature of the differential conductance spectra of magnetic adsorbates on surfaces. The intrinsic line shape of this Kondo resonance and its temperature dependence in principle contain valuable information. We use measurements on a molecular Kondo system, all- trans retinoic acid on Au(1 1 1), and model calculations to discuss the role of instrumental broadening. The modulation voltage used for the lock-in detection, noise on the sample voltage, and the temperature of the microscope tip are considered. These sources of broadening affect the apparent line shapes and render difficult a determination of the intrinsic line width, in particular when variable temperatures are involved.
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- 2018
25. Disentangling Magnetic Hardening and Molecular Spin Chain Contributions to Exchange Bias in Ferromagnet/Molecule Bilayers
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Eric Beaurepaire, Hashim Jabbar, Jacek Arabski, Guy Schmerber, Manuel Gruber, Victor Da Costa, Garen Avedissian, Prashanth Rengasamy, Martin Bowen, Samy Boukari, F. Schleicher, Wolfgang Weber, and Bertrand Vileno
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Materials science ,Magnetometer ,FOS: Physical sciences ,Bioengineering ,02 engineering and technology ,01 natural sciences ,law.invention ,Condensed Matter::Materials Science ,law ,0103 physical sciences ,Molecular film ,General Materials Science ,010306 general physics ,Quantum tunnelling ,Condensed Matter - Materials Science ,Spintronics ,Magnetic moment ,Mechanical Engineering ,Materials Science (cond-mat.mtrl-sci) ,General Chemistry ,equipment and supplies ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,Ferromagnetic resonance ,Exchange bias ,Ferromagnetism ,Chemical physics ,0210 nano-technology ,human activities - Abstract
We performed SQUID and FMR magnetometry experiments to clarify the relationship between two reported magnetic exchange effects arising from interfacial spin-polarized charge transfer within ferromagnetic metal (FM)/molecule bilayers: the magnetic hardening effect, and spinterface-stabilized molecular spin chains. To disentangle these effects, both of which can affect the FM magnetization reversal, we tuned the metal phthalocyanine molecule central site's magnetic moment to selectively enhance or suppress the formation of spin chains within the molecular film. We find that both effects are distinct, and additive. In the process, we 1) extended the list of FM/molecule candidate pairs that are known to generate magnetic exchange effects, 2) experimentally confirmed the predicted increase in anisotropy upon molecular adsorption; and 3) showed that spin chains within the molecular film can enhance magnetic exchange. This magnetic ordering within the organic layer implies a structural ordering. Thus, by distengangling the magnetic hardening and exchange bias contributions, our results confirm, as an echo to progress regarding inorganic spintronic tunnelling, that the milestone of spintronic tunnelling across structurally ordered organic barriers has been reached through previous magnetotransport experiments. This paves the way for solid-state devices studies that exploit the quantum physical properties of spin chains, notably through external stimuli., None
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- 2018
26. Scale‐Up of Innovative Honeycomb Reactors for Power‐to‐Gas Applications – The Project Store&Go
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Manuel Gruber, Thomas Kolb, Dominik Schollenberger, Siegfried Bajohr, and Rainer Reimert
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Engineering ,Energy storage ,020209 energy ,General Chemical Engineering ,Catalyst carriers ,02 engineering and technology ,Formal kinetics ,7. Clean energy ,Industrial and Manufacturing Engineering ,Chemical engineering ,Thermal conductivity ,0202 electrical engineering, electronic engineering, information engineering ,Process engineering ,Simulation ,Power to gas ,Substitute natural gas ,Power-to-X ,Electrolysis of water ,business.industry ,Communication ,Methanation ,Power‐to‐X ,General Chemistry ,Communications ,Renewable energy ,Energiewende ,Heat transfer ,ddc:660 ,Electric power ,business - Abstract
The German ‘‘Energiewende’’ is heavily based on electric power and, therefore, requests solutions to serve non-electric energy uses and to store electric energy in large scale. Synthetic natural gas (SNG) produced with hydrogen from water electrolysis and with CO2 from mainly renewable sources is one approach. For the catalytic SNG production efficient removal and utilization of the reaction heat is the main issue. A metallic honeycomb-like carrier-based reactor proved in laboratory scale to match this challenge. This type of reactor shows good heat conductivity and enables optimized operation. In the EU-funded project Store&Go the honeycomb methanation is scaled up to MW-scale. For this, heat transfer and kinetic data were determined experimentally and used in CFD calculations for the reactor design. Finally a SNG plant with 1MW feed-in will be built and fully integrated operation will be shown.
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- 2018
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27. First glimpse of the soft x-ray induced excited spin-state trapping effect dynamics on spin cross-over molecules
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Philippe Ohresser, V. Davesne, V. Da Costa, Manuel Gruber, Martin Bowen, Ana B. Gaspar, S. Boukari, Toshio Miyamachi, Wulf Wulfhekel, Fadi Choueikani, Laurent Joly, E. Otero, Eric Beaurepaire, F. Scheurer, and José Antonio Real
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Absorption spectroscopy ,Spin states ,Chemistry ,Chimie/Matériaux ,Metastability ,Excited state ,Transition temperature ,General Physics and Astronomy ,Physical and Theoretical Chemistry ,Atmospheric temperature range ,Atomic physics ,LIESST ,Spin-½ - Abstract
The dynamics of the soft x-ray induced excited spin state trapping (SOXIESST) effect of Fe(phen)(2)(NCS)(2) (Fe-phen) powder have been investigated by x-ray absorption spectroscopy (XAS) using the total electron yield method, in a wide temperature range. The low-spin (LS) state is excited into the metastable high-spin (HS) state at a rate that depends on the intensity of the x-ray illumination it receives, and both the temperature and the intensity of the x-ray illumination will affect the maximum HS proportion that is reached. We find that the SOXIESST HS spin state transforms back to the LS state at a rate that is similar to that found for the light induced excited spin state trapping (LIESST) effect. We show that it is possible to use the SOXIESST effect in combination with the LIESST effect to investigate the influence of cooperative behavior on the dynamics of both effects. To investigate the impact of molecular cooperativity, we compare our results on Fe-phen with those obtained for Fe[Me(2)Pyrz](3)BH(2) (Fe-pyrz) powder, which exhibits a similar thermal transition temperature but with a hysteresis. We find that, while the time constant of the dynamic is identical for both molecules, the SOXIESST effect is less efficient at exciting the HS state in Fe-pyrz than in Fe-phen. (C) 2013 AIP Publishing LLC.
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- 2013
28. Robust spin crossover and memristance across a single molecule
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Eric Beaurepaire, Wulf Wulfhekel, Martin Bowen, Manuel Gruber, Loïc Joly, Fabrice Scheurer, Guillaume Rogez, V. Davesne, Toyo Kazu Yamada, Philippe Ohresser, T. Miyamachi, and Samy Boukari
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Multidisciplinary ,Materials science ,Condensed matter physics ,Spin states ,Basis (linear algebra) ,Aucun ,General Physics and Astronomy ,Molecular electronics ,Nanotechnology ,General Chemistry ,General Biochemistry, Genetics and Molecular Biology ,Spin crossover ,Molecule ,Condensed Matter::Strongly Correlated Electrons ,Layer (electronics) ,Metallic substrate - Abstract
A nanoscale molecular switch can be used to store information in a single molecule. Although the switching process can be detected electrically in the form of a change in the molecule's conductance, adding spin functionality to molecular switches is a key concept for realizing molecular spintronic devices. Here we show that iron-based spin-crossover molecules can be individually and reproducibly switched between a combined high-spin, high-conduction state and a low-spin, low-conduction state, provided the individual molecule is decoupled from a metallic substrate by a thin insulating layer. These results represent a step to achieving combined spin and conduction switching functionality on the level of individual molecules.
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- 2012
29. Large Orbital Moment of Two Coupled Spin-Half Co Ions in a Complex on Gold
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Chao Li, Roberto Robles, Nicolas Lorente, Sanjoy Kr Mahatha, Sebastian Rohlf, Kai Rossnagel, Alessandro Barla, Boris V. Sorokin, Stefano Rusponi, Philippe Ohresser, Sara Realista, Paulo N. Martinho, Torben Jasper-Toennies, Alexander Weismann, Richard Berndt, and Manuel Gruber
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atoms ,ray circular-dichroism ,exchange ,General Engineering ,General Physics and Astronomy ,exchange coupling ,Physik (inkl. Astronomie) ,ligand ,field ,magneticanisotropy ,scanning tunnelingmicroscopy ,x-ray magnetic circular dichroism ,densityfunctional theory ,magnetic-anisotropy ,General Materials Science ,orbital moment ,dinuclear complex - Abstract
in press The magnetic properties of transition-metal ions are generally described by the atomic spins of the ions and their exchange coupling. The orbital moment, usually largely quenched due the ligand field, is then seen as a perturbation. In such a scheme, S = 1/2 ions are predicted to be isotropic. We investigate a Co(II) complex with two antiferromagnetically coupled 1/2 spins on Au(111) using low-temperature scanning tunneling microscopy, X-ray magnetic circular dichroism, and density functional theory. We find that each of the Co ions has an orbital moment comparable to that of the spin, leading to magnetic anisotropy, with the spins preferentially oriented along the Co–Co axis. The orbital moment and the associated magnetic anisotropy is tuned by varying the electronic coupling of the molecule to the substrate and the microscope tip. These findings show the need to consider the orbital moment even in systems with strong ligand fields. As a consequence, the description of S = 1/2 ions becomes strongly modified, which have important consequences for these prototypical systems for quantum operations.
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