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58. Three-State Switching of an Fe Spin Crossover Complex

Author

Johannsen, Sven, Schüddekopf, Sascha, Ossinger, Sascha, Grunwald, Jan, Tuczek, Felix, Gruber, Manuel, and Berndt, Richard

Subjects
General Energy, Physical and Theoretical Chemistry, Physik (inkl. Astronomie), Surfaces, Coatings and Films, Electronic, Optical and Magnetic Materials
Published
2022

60. Spin Crossover in a Cobalt Complex on Ag(111)

Author

Johannsen, Sven, primary, Ossinger, Sascha, additional, Grunwald, Jan, additional, Herman, Alexander, additional, Wende, Heiko, additional, Tuczek, Felix, additional, Gruber, Manuel, additional, and Berndt, Richard, additional

Published
2022
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64. Stability of functionalized platform molecules on Au(111).

Author

Jasper-Tönnies, Torben, Poltavsky, Igor, Ulrich, Sandra, Moje, Tobias, Tkatchenko, Alexandre, Herges, Rainer, and Berndt, Richard

Subjects
GOLD nanoparticles, SCANNING tunneling microscopy, LOW temperatures, METHYL groups, GAS phase reactions, ETHYNYL compounds, HYDROGEN
Abstract

Trioxatriangulenium (TOTA) platform molecules were functionalized with methyl, ethyl, ethynyl, propynyl, and hydrogen and sublimated onto Au(111) surfaces. Low-temperature scanning tunneling microscopy data reveal that >99% of ethyl-TOTA and methyl-TOTA remain intact, whereas 60% of H-TOTA and >99% of propynyl-TOTA and ethynyl-TOTA decompose. The observed tendency toward fragmentation on Au(111) is opposite to the sequence of gas-phase stabilities of the molecules. Although Au(111) is the noblest of all metal surfaces, the binding energies of the decomposition products to Au(111) destabilize the functionalized platforms by 2 to 3.9 eV (190–370 kJ/mol) and even render some of them unstable as revealed by density functional theory calculations. Van der Waals forces are important, as they drive the adsorption of the platform molecules. [ABSTRACT FROM AUTHOR]

Published
2018
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69. Current shot noise in atomic contacts:Fe and between Au electrodes

Author

Mohr, Michael, Weismann, Alexander, Li, Dongzhe, Brandbyge, Mads, Berndt, Richard, Mohr, Michael, Weismann, Alexander, Li, Dongzhe, Brandbyge, Mads, and Berndt, Richard

Abstract

Single Fe atoms on Au(111) surfaces were hydrogenated and dehydrogenated with the Au tip of a low-temperature scanning tunneling microscope (STM). Fe and FeH2 were contacted with the tip of the microscope and show distinctly different evolutions of the conductance with the tip-substrate distance. The current shot noise of these contacts has been measured and indicates a single relevant conductance channel with the spin-polarized transmission. For FeH2, the spin polarization reaches values up to 80% for low conductances and is reduced if the tip-surface distance is decreased. These observations are partially reproduced using density functional theory (DFT)-based transport calculations. We suggest that the quantum motion of the hydrogen atoms, which is not taken into account in our DFT modeling, may have a significant effect on the results.

Published
2021

72. Deformation of a 'rigid' molecule in self-assembled nanostructures

Author

Hao Tang, Coudret, Christophe, Maroutian, Thomas, and Berndt, Richard

Subjects
Deformations (Mechanics) -- Analysis, Fluorine compounds -- Chemical properties, Conformational analysis -- Methods, Copper compounds -- Chemical properties, Chemicals, plastics and rubber industries
Abstract

A simple spirobifluorene molecule with pseudotetrahedral structure was investigated for its supposed conformational resilience upon adsorption. The molecule stays 'rigid' by keeping one of the original symmetry elements in the two physisorbed states while in an unexpected state, a strong deformation destroyed definitively any symmetry of the molecule.

Published
2005

84. Reversible coordination-induced spin-state switching in complexes on metal surfaces

Author

Köbke, Alexander, primary, Gutzeit, Florian, additional, Röhricht, Fynn, additional, Schlimm, Alexander, additional, Grunwald, Jan, additional, Tuczek, Felix, additional, Studniarek, Michał, additional, Longo, Danilo, additional, Choueikani, Fadi, additional, Otero, Edwige, additional, Ohresser, Philippe, additional, Rohlf, Sebastian, additional, Johannsen, Sven, additional, Diekmann, Florian, additional, Rossnagel, Kai, additional, Weismann, Alexander, additional, Jasper-Toennies, Torben, additional, Näther, Christian, additional, Herges, Rainer, additional, Berndt, Richard, additional, and Gruber, Manuel, additional

Published
2019
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89. Spin in a closed‐shell organic molecule on a metal substrate generated by a sigmatropic reaction

Author

Ministerio de Economía y Competitividad (España), European Commission, Bocquet, Marie-Laure, Lorente, Nicolás, Berndt, Richard, Gruber, Manuel, Ministerio de Economía y Competitividad (España), European Commission, Bocquet, Marie-Laure, Lorente, Nicolás, Berndt, Richard, and Gruber, Manuel

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.

Published
2019

94. Iron in a Cage: Fixation of a Fe(II)tpy2 Complex by Fourfold Interlinking.

Author

Brandl, Thomas, Johannsen, Sven, Häussinger, Daniel, Suryadevara, Nithin, Prescimone, Alessandro, Bernhard, Stefan, Gruber, Manuel, Ruben, Mario, Berndt, Richard, and Mayor, Marcel

Subjects
SUPERCONDUCTING quantum interference devices, SCANNING tunneling microscopy
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 T2 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. [ABSTRACT FROM AUTHOR]

Published
2020
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95. Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling.

Author

Jasper‐Tönnies, Torben, Gruber, Manuel, Ulrich, Sandra, Herges, Rainer, and Berndt, Richard

Subjects
HONEYCOMB structures, UNIT cell, MOLECULES, CELL size, COMPETITION (Biology), TILES
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 C3 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. [ABSTRACT FROM AUTHOR]

Published
2020
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100. CoPc adsorption on Cu(111): Origin of the C4 to C2 symmetry reduction.

Author

Cuadrado, Ramón, Cerdá, Jorge I., Wang, Yongfeng, Xin, Ge, Berndt, Richard, and Tang, Hao

Subjects
PHTHALOCYANINES, ADSORPTION (Chemistry), COPPER, METALLIC surfaces, SYMMETRY (Physics), SCANNING tunneling microscopy, ELECTRONIC structure, SIMULATION methods & models
Abstract

The adsorption of phthalocyanines (Pc) to various surfaces has recently been reported to lead to a lowering of symmetry from C4 to C2 in scanning tunneling microscope (STM) images. Possible origins of the reduced symmetry involve the electronic structure or geometric deformation of the molecules. Here, the origin of the reduction is clarified from a comprehensive theoretical study of CoPc adsorbed on the Cu(111) surface along with the experimental STM data. Total energy calculations using different schemes for the exchange-correlation energy and STM simulations are compared against experimental data. We find that the symmetry reduction is only reproduced when van der Waals corrections are included into the formalism. It is caused by a deformation along the two perpendicular molecular axes, one of them coming closer to the surface by around 0.2 Å. An electronic structure analysis reveals (i) the relevance of the CoPc interaction with the Cu(111) surface state and (ii) that intramolecular features in dI/dV maps clearly discriminate a Co-derived state from the rest of the Pc states. [ABSTRACT FROM AUTHOR]

Published
2010
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