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Kittelmann M.,Johannes Gutenberg University Mainz | Nimmrich M.,Johannes Gutenberg University Mainz | Lindner R.,Johannes Gutenberg University Mainz | Gourdon A.,Nanoscience Group | Kuhnle A.,Johannes Gutenberg University Mainz
ACS Nano | Year: 2013

The bottom-up construction of functional devices from molecular building blocks offers great potential in tailoring materials properties and functionality with utmost control. An important step toward exploiting bottom-up construction for real-life applications is the creation of covalently bonded structures that provide sufficient stability as well as superior charge transport properties over reversibly linked self-assembled structures. On-surface synthesis has emerged as a promising strategy for fabricating stable, covalently bound molecular structure on surfaces. So far, a majority of the structures created by this method have been obtained from a rather simple one-step processing approach. But the on-surface preparation of complex structures will require the possibility to carry out various reaction steps in a sequential manner as done in solution chemistry. Only one example exists in literature in which a hierarchical strategy is followed to enhance structural complexity and reliability on a metallic surface. Future molecular electronic application will, however, require transferring these strategies to nonconducting surfaces. Bulk insulating substrates are known to pose significant challenges to on-surface synthesis due to the absence of a metal catalyst and their low surface energy, frequently resulting in molecule desorption rather than reaction activation. By carefully selecting a suitable precursor molecule, we succeeded in performing a two-step linking reaction on a bulk insulating surface. Besides a firm anchoring toward the substrate surface, the reaction sites and sequential order are encoded in the molecular structure, providing so far unmatched reaction control in on-surface synthesis on a bulk insulating substrate. © 2013 American Chemical Society. Source


Renaud N.,Northwestern University | Ratner M.A.,Northwestern University | Joachim C.,Nanoscience Group
Journal of Physical Chemistry B | Year: 2011

We present a simple method to compute the transmission coefficient of a quantum system embedded between two conducting electrodes. Starting from the solution of the time-dependent Schrodinger equation, we demonstrate the relationship between the temporal evolution of the state vector,ψ(t), initially localized on oneelectrode and the electronic transmission coefficient, T(E). We particularly emphasize the role of the oscillation frequency and the decay rate of ψ(t)in the line shape of T(E). This method is applied to the well-known problems ofthe single impurity, two-site systems and the benzene ring, where it agrees with well-accepted time-independent methods and gives new physical insight to the resonance and interference patterns widely observed in molecular junctions. © 2011 American Chemical Society. Source


Kittelmann M.,Johannes Gutenberg University Mainz | Rahe P.,Johannes Gutenberg University Mainz | Nimmrich M.,Johannes Gutenberg University Mainz | Hauke C.M.,Johannes Gutenberg University Mainz | And 2 more authors.
ACS Nano | Year: 2011

On-surface synthesis in ultrahigh vacuum provides a promising strategy for creating thermally and chemically stable molecular structures at surfaces. The two-dimensional confinement of the educts, the possibility of working at higher (or lower) temperatures in the absence of solvent, and the templating effect of the surface bear the potential of preparing compounds that cannot be obtained in solution. Moreover, covalently linked conjugated molecules allow for efficient electron transport and are, thus, particularly interesting for future molecular electronics applications. When having these applications in mind, electrically insulating substrates are mandatory to provide sufficient decoupling of the molecular structure from the substrate surface. So far, however, on-surface synthesis has been achieved only on metallic substrates. Here we demonstrate the covalent linking of organic molecules on a bulk insulator, namely, calcite. We deliberately employ the strong electrostatic interaction between the carboxylate groups of halide-substituted benzoic acids and the surface calcium cations to prevent molecular desorption and to reach homolytic cleavage temperatures. This allows for the formation of aryl radicals and intermolecular coupling. By varying the number and position of the halide substitution, we rationally design the resulting structures, revealing straight lines, zigzag structures, and dimers, thus providing clear evidence for the covalent linking. Our results constitute an important step toward exploiting on-surface synthesis for molecular electronics and optics applications, which require electrically insulating rather than metallic supporting substrates. © 2011 American Chemical Society. Source


Kadu B.S.,Nanoscience Group | Chikate R.C.,Nanoscience Group
Journal of Environmental Chemical Engineering | Year: 2013

The reductive removal of Cr(VI) is investigated with zero-valent iron, Fe-Ni bimetallic nanoparticles and Fe-Ni bimetallic-montmorillonite nanocomposites. XRD and TEM studies reveal generation of active sites on nanocomposites possessing increased surface area.The removal of Cr(VI) follows pseudo-second order rate model with 2 g L-1 composite loading with sorption capacity (qe) in the range of 30-50 mg g-1 for the composites. Employing adsorption isotherms like Langmuir, Freundlich, Redlich-Peterson, Dubinin-Radushkevich (D-R), Temkin and Flory-Huggins (F-H), it is observed that adsorption process essentially follows pseudo-multilayer exothermic chemisorption process with free energy of adsorption (DG) in the range of -10 to -15 KJ mol-1. Pore diffusion is predominant as compared to film diffusion process; evaluated from intra-particle diffusion models, augurs well for stronger ionic interactions between Cr(VI) ions and adsorbents. The improved efficiency of composites may be attributed to the large number of available surface Fe0 atoms that significantly contributes towards reduction of adsorbed Cr(VI) on the surface. XPS measurements of composites after last cycle clearly establish the fact that formation of surface hydroxides mediates efficient flow of electron from bulk to Cr(VI) suggesting their potential usage for continuous removal capabilities. © 2013 Elsevier Ltd. All rights reserved. Source


Lindner R.,Johannes Gutenberg University Mainz | Rahe P.,Johannes Gutenberg University Mainz | Rahe P.,University of Utah | Kittelmann M.,Johannes Gutenberg University Mainz | And 3 more authors.
Angewandte Chemie - International Edition | Year: 2014

A substrate-guided photochemical reaction of C60 fullerenes on calcite, a bulk insulator, investigated by non-contact atomic force microscopy is presented. The success of the covalent linkage is evident from a shortening of the intermolecular distances, which is clearly expressed by the disappearance of the moiré pattern. Furthermore, UV/Vis spectroscopy and mass spectrometry measurements carried out on thick films demonstrate the ability of our setup for initiating the photoinduced reaction. The irradiation of C 60 results in well-oriented covalently linked domains. The orientation of these domains is dictated by the lattice dimensions of the underlying calcite substrate. Using the lattice mismatch to deliberately steer the direction of the chemical reaction is expected to constitute a general design principle for on-surface synthesis. This work thus provides a strategy for controlled fabrication of oriented, covalent networks on bulk insulators. Reactions on insulators: C60 fullerenes undergo a photochemical reaction on calcite, a bulk insulator. The irradiated structures are investigated by non-contact atomic force microscopy. Domains of covalently linked molecules form along specific substrate directions. The observed directional reaction is readily explained by a model based on lattice mismatch minimization. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

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