2018

  • Time-dependent framework for energy and charge currents in nanoscale systems
    • T. Lehmann, A. Croy, R. GutiĆ©rrez, G. Cuniberti
    • Chemical Physics (2018)
    • DOI   Abstract  

      The calculation of time-dependent charge and energy currents in nanoscale systems is a challenging task. Nevertheless it is crucial for gaining a deep understanding of the relevant processes at the nanoscale. We extend the auxiliary-mode approach for time-dependent charge transport to allow for the calculation of energy currents for arbitrary time dependencies. We apply the approach to two illustrative examples, a single-level system and a benzene ring, demonstrating its usefulness for a wide range of problems beyond simple toy models, such as molecular devices.

      @article{,
      author = {Thomas Lehmann and Alexander Croy and Rafael GutiƩrrez and Gianaurelio Cuniberti},
      title = {Time-dependent framework for energy and charge currents in nanoscale systems},
      journal = {Chemical Physics},
      abstract = {The calculation of time-dependent charge and energy currents in nanoscale systems is a challenging task. Nevertheless it is crucial for gaining a deep understanding of the relevant processes at the nanoscale. We extend the auxiliary-mode approach for time-dependent charge transport to allow for the calculation of energy currents for arbitrary time dependencies. We apply the approach to two illustrative examples, a single-level system and a benzene ring, demonstrating its usefulness for a wide range of problems beyond simple toy models, such as molecular devices.},
      year = {2018},
      url = http://dx.doi.org/{10.1016/j.chemphys.2018.01.011},
      doi = {10.1016/j.chemphys.2018.01.011},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Electronic Resonances and Gap Stabilization of Higher Acenes on a Gold Surface
    • J. Kruger, F. Eisenhut, D. Skidin, T. Lehmann, D. A. Ryndyk, G. Cuniberti, F. Garcia, J. M. Alonso, E. Guitian, D. Perez, D. Pena, G. Trinquier, J. Malrieu, F. Moresco, C. Joachim
    • ACS nano 12, 8506-8511 (2018)
    • DOI   Abstract  

      On-surface synthesis provides a powerful method for the generation of long acene molecules, making possible the detailed investigation of the electronic properties of single higher acenes on a surface. By means of scanning tunneling microscopy and spectroscopy combined with theoretical considerations, we discuss the polyradical character of the ground state of higher acenes as a function of the number of linearly fused benzene rings. We present energy and spatial mapping of the tunneling resonances of hexacene, heptacene, and decacene, and discuss the role of molecular orbitals in the observed tunneling conductance maps. We show that the energy gap between the first electronic tunneling resonances below and above the Fermi energy stabilizes to a finite value, determined by a first diradical electronic perturbative contribution to the polyacene electronic ground state. Up to decacene, the main contributor to the ground state of acenes remains the lowest-energy closed-shell electronic configuration.

      @article{,
      author = {Justus Kruger and Frank Eisenhut and Dmitry Skidin and Thomas Lehmann and Dmitry A. Ryndyk and Gianaurelio Cuniberti and Fatima Garcia and Jose M. Alonso and Enrique Guitian and Dolores Perez and Diego Pena and Georges Trinquier and Jean-Paul Malrieu and Francesca Moresco and Christian Joachim},
      title = {Electronic Resonances and Gap Stabilization of Higher Acenes on a Gold Surface},
      journal = {ACS nano},
      volume = {12},
      number = {8},
      pages = {8506-8511},
      abstract = {On-surface synthesis provides a powerful method for the generation of long acene molecules, making possible the detailed investigation of the electronic properties of single higher acenes on a surface. By means of scanning tunneling microscopy and spectroscopy combined with theoretical considerations, we discuss the polyradical character of the ground state of higher acenes as a function of the number of linearly fused benzene rings. We present energy and spatial mapping of the tunneling resonances of hexacene, heptacene, and decacene, and discuss the role of molecular orbitals in the observed tunneling conductance maps. We show that the energy gap between the first electronic tunneling resonances below and above the Fermi energy stabilizes to a finite value, determined by a first diradical electronic perturbative contribution to the polyacene electronic ground state. Up to decacene, the main contributor to the ground state of acenes remains the lowest-energy closed-shell electronic configuration.},
      year = {2018},
      url = http://dx.doi.org/{10.1021/acsnano.8b04046},
      doi = {10.1021/acsnano.8b04046},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Plasmonic Biosensor Based on Vertical Arrays of Gold Nanoantennas
    • S. Klinghammer, T. Uhlig, F. Patrovsky, M. Boehm, J. Schuett, N. Puetz, L. Baraban, L. M. Eng, G. Cuniberti
    • Acs Sensors 3, 1392-1400 (2018)
    • DOI   Abstract  

      Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detection of biomolecules, relying on localized surface plasmon resonances. Large arrays (similar to 1 cm(2)) of vertically aligned and densely packed gold nanorods to receive, locally confine, and amplify the external optical signal are used to allow for reliable biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance in the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into functional understanding and technical implementation of a large array of gold nanowires for future medical applications.

      @article{,
      author = {Stephanie Klinghammer and Tino Uhlig and Fabian Patrovsky and Matthias Boehm and Julian Schuett and Nils Puetz and Larysa Baraban and Lukas M. Eng and Gianaurelio Cuniberti},
      title = {Plasmonic Biosensor Based on Vertical Arrays of Gold Nanoantennas},
      journal = {Acs Sensors},
      volume = {3},
      number = {7},
      pages = {1392-1400},
      abstract = {Implementing large arrays of gold nanowires as functional elements of a plasmonic biosensor is an important task for future medical diagnostic applications. Here we present a microfluidic-channel-integrated sensor for the label-free detection of biomolecules, relying on localized surface plasmon resonances. Large arrays (similar to 1 cm(2)) of vertically aligned and densely packed gold nanorods to receive, locally confine, and amplify the external optical signal are used to allow for reliable biosensing. We accomplish this by monitoring the change of the optical nanostructure resonance in the presence of biomolecules within the tight focus area above the nanoantennas, combined with a surface treatment of the nanowires for a specific binding of the target molecules. As a first application, we detect the binding kinetics of two distinct DNA strands as well as the following hybridization of two complementary strands (cDNA) with different lengths (25 and 100 bp). Upon immobilization, a redshift of 1 nm was detected; further backfilling and hybridization led to a peak shift of additional 2 and 5 nm for 25 and 100 bp, respectively. We believe that this work gives deeper insight into functional understanding and technical implementation of a large array of gold nanowires for future medical applications.},
      year = {2018},
      url = http://dx.doi.org/{10.1021/acssensors.8b00315},
      doi = {10.1021/acssensors.8b00315},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

2017

  • Absolute Energy Level Positions in CdSe Nanostructures from Potential-Modulated Absorption Spectroscopy (EMAS)
    • D. Spittel, J. Poppe, C. Meerbach, C. Ziegler, S. G. Hickey, A. Eychmueller
    • Acs Nano 11, 12174-12184 (2017)
    • DOI   Abstract  

      Semiconductor nanostructures such as CdSe quantum dots and colloidal nanoplatelets exhibit remarkable optical properties, making them interesting for applications in optoelectronics and photocatalysis. For both areas of application a detailed understanding of the electronic structure is essential to achieve highly efficient devices. The electronic structure can be probed using the fact that optical properties of semiconductor nanoparticles are found to be extremely sensitive to the presence of excess charges that can for instance be generated by means of an electrochemical charge transfer via an electrode. Here we present the use of EMAS as a versatile spectroelectrochemical method to obtain absolute band edge positions of CdSe nanostructures versus a well-defined reference electrode under ambient conditions. In this, the spectral properties of the nanoparticles are monitored with respect to an applied electrochemical potential. We developed a bleaching model that yields the lowest electronic state in the conduction band of the nanostructures. A change in the band edge positions caused by quantum confinement is shown both for CdSe quantum dots and for colloidal nanoplatelets. In the case of CdSe quantum dots these findings are in good agreement with tight binding calculations. The method presented is not limited to CdSe nanostructures but can be used as a universal tool. Hence, this technique allows the determination of absolute band edge positions of a large variety of materials used in various applications.

      @article{,
      author = {Daniel Spittel and Jan Poppe and Christian Meerbach and Christoph Ziegler and Stephen G. Hickey and Alexander Eychmueller},
      title = {Absolute Energy Level Positions in CdSe Nanostructures from Potential-Modulated Absorption Spectroscopy (EMAS)},
      journal = {Acs Nano},
      volume = {11},
      number = {12},
      pages = {12174-12184},
      abstract = {Semiconductor nanostructures such as CdSe quantum dots and colloidal nanoplatelets exhibit remarkable optical properties, making them interesting for applications in optoelectronics and photocatalysis. For both areas of application a detailed understanding of the electronic structure is essential to achieve highly efficient devices. The electronic structure can be probed using the fact that optical properties of semiconductor nanoparticles are found to be extremely sensitive to the presence of excess charges that can for instance be generated by means of an electrochemical charge transfer via an electrode. Here we present the use of EMAS as a versatile spectroelectrochemical method to obtain absolute band edge positions of CdSe nanostructures versus a well-defined reference electrode under ambient conditions. In this, the spectral properties of the nanoparticles are monitored with respect to an applied electrochemical potential. We developed a bleaching model that yields the lowest electronic state in the conduction band of the nanostructures. A change in the band edge positions caused by quantum confinement is shown both for CdSe quantum dots and for colloidal nanoplatelets. In the case of CdSe quantum dots these findings are in good agreement with tight binding calculations. The method presented is not limited to CdSe nanostructures but can be used as a universal tool. Hence, this technique allows the determination of absolute band edge positions of a large variety of materials used in various applications.},
      year = {2017},
      url = http://dx.doi.org/{10.1021/acsnano.7b05300},
      doi = {10.1021/acsnano.7b05300},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Micropatterning kinetics of different glass-forming systems investigated by thermoplastic net-shaping
    • B. Sarac, S. Bera, F. Spieckermann, S. Balakin, M. Stoica, M. Calin, J. Eckert
    • Scripta Materialia 137, 127-131 (2017)
    • DOI   Abstract  

      The formability difference between good and marginal glass-forming systems is investigated by micro-surface patterning of hierarchical features using thermoplastic net-shaping (TPN). For each alloy, a remarkable change in the flow behaviour is observed as the applied force along with the pressing time and temperature are optimized. The flow kinetics of glassy alloys with different glass-forming abilities is best described by the formability parameter S, which is defined by the ratio of the width of the supercooled to undercooled liquid region (T-1 – T-g)/(T-x – T-g). Reproducible micro-engineered surfaces with high uniformity can be established by controlled TPN processing. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

      @article{,
      author = {Baran Sarac and Supriya Bera and Florian Spieckermann and Sascha Balakin and Mihai Stoica and Mariana Calin and Juergen Eckert},
      title = {Micropatterning kinetics of different glass-forming systems investigated by thermoplastic net-shaping},
      journal = {Scripta Materialia},
      volume = {137},
      pages = {127-131},
      abstract = {The formability difference between good and marginal glass-forming systems is investigated by micro-surface patterning of hierarchical features using thermoplastic net-shaping (TPN). For each alloy, a remarkable change in the flow behaviour is observed as the applied force along with the pressing time and temperature are optimized. The flow kinetics of glassy alloys with different glass-forming abilities is best described by the formability parameter S, which is defined by the ratio of the width of the supercooled to undercooled liquid region (T-1 - T-g)/(T-x - T-g). Reproducible micro-engineered surfaces with high uniformity can be established by controlled TPN processing. (C) 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.},
      year = {2017},
      url = http://dx.doi.org/{10.1016/j.scriptamat.2017.02.038},
      doi = {10.1016/j.scriptamat.2017.02.038},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Hierarchical surface patterning of Ni- and Be-free Ti- and Zr-based bulk metallic glasses by thermoplastic net-shaping
    • B. Sarac, S. Bera, S. Balakin, M. Stoica, M. Calin, J. Eckert
    • Materials Science & Engineering C-Materials for Biological Applications 73, 398-405 (2017)
    • DOI   Abstract  

      In order to establish a strong cell-material interaction, the surface topography of the implant material plays an important role. This contribution aims to analyze the formation kinetics of nickel and beryllium-free Ti- and Zr-based Bulk Metallic Glasses (BMGs) with potential biomedical applications. The surface patterning of the BMGs is achieved by thermoplastic net-shaping (TPN) into anisotropically etched cavities of silicon chips. The forming kinetics of the BMG alloys is assessed by thermal and mechanical measurements to determine the most suitable processing temperature and time, and load applied. Array of pyramidal micropattems with a tip resolution down to 50 nm is achievable for the Zr-BMG, where the generated hierarchical features are crucial for surface furtctionalization, acting as topographic cues for cell attachment The unique processability and intrinsic properties of this new class of amorphous alloys make them competitive with the conventional biomaterials. (C) 2016 Elsevier B.V. All rights reserved.

      @article{,
      author = {B. Sarac and S. Bera and S. Balakin and M. Stoica and M. Calin and J. Eckert},
      title = {Hierarchical surface patterning of Ni- and Be-free Ti- and Zr-based bulk metallic glasses by thermoplastic net-shaping},
      journal = {Materials Science & Engineering C-Materials for Biological Applications},
      volume = {73},
      pages = {398-405},
      abstract = {In order to establish a strong cell-material interaction, the surface topography of the implant material plays an important role. This contribution aims to analyze the formation kinetics of nickel and beryllium-free Ti- and Zr-based Bulk Metallic Glasses (BMGs) with potential biomedical applications. The surface patterning of the BMGs is achieved by thermoplastic net-shaping (TPN) into anisotropically etched cavities of silicon chips. The forming kinetics of the BMG alloys is assessed by thermal and mechanical measurements to determine the most suitable processing temperature and time, and load applied. Array of pyramidal micropattems with a tip resolution down to 50 nm is achievable for the Zr-BMG, where the generated hierarchical features are crucial for surface furtctionalization, acting as topographic cues for cell attachment The unique processability and intrinsic properties of this new class of amorphous alloys make them competitive with the conventional biomaterials. (C) 2016 Elsevier B.V. All rights reserved.},
      year = {2017},
      url = http://dx.doi.org/{10.1016/j.msec.2016.12.059},
      doi = {10.1016/j.msec.2016.12.059},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Molecular Self-Assembly Driven by On-Surface Reduction: Anthracene and Tetracene on Au(111)
    • J. Krueger, F. Eisenhut, T. Lehmann, J. M. Alonso, J. Meyer, D. Skidin, R. Ohmann, D. A. Ryndyk, D. Perez, E. Guitian, D. Pena, F. Moresco, G. Cuniberti
    • Journal of Physical Chemistry C 121, 20353-20358 (2017)
    • DOI   Abstract  

      Epoxyacenes adsorbed on metal surfaces form acenes during thermally induced reduction in ultrahigh vacuum conditions. The incorporation of oxygen bridges into a hydrocarbon backbone leads to an enhanced stability of these molecular precursors under ambient condition; however, it has also a distinct influence on their adsorption and self assembly on metal surfaces. Here, a low-temperature scanning tunneling microscopy (LT-STM) study of two different epoxyacenes on the Au(111) surface at submonolayer coverage is presented. Both molecules show self-assembly based on hydrogen bonding. While for the molecules with a single epoxy moiety nanostructures of three molecules are formed, extended molecular networks are achieved with two epoxy moieties and a slightly higher surface coverage. Upon annealing at 390 K, the molecules are reduced to the respective acene; however, both systems keep a similar assembled structure. The experimental STM images supported by theoretical calculations show that the self-assembly of the on-surface fabricated acenes is greatly influenced by the on-surface reaction and strongly differs from the adsorption pattern of directly deposited acenes, highlighting the importance of the cleaved oxygen in the self-assembly.

      @article{,
      author = {Justus Krueger and Frank Eisenhut and Thomas Lehmann and Jose M. Alonso and Joerg Meyer and Dmitry Skidin and Robin Ohmann and Dmitry A. Ryndyk and Dolores Perez and Enrique Guitian and Diego Pena and Francesca Moresco and Gianaurelio Cuniberti},
      title = {Molecular Self-Assembly Driven by On-Surface Reduction: Anthracene and Tetracene on Au(111)},
      journal = {Journal of Physical Chemistry C},
      volume = {121},
      number = {37},
      pages = {20353-20358},
      abstract = {Epoxyacenes adsorbed on metal surfaces form acenes during thermally induced reduction in ultrahigh vacuum conditions. The incorporation of oxygen bridges into a hydrocarbon backbone leads to an enhanced stability of these molecular precursors under ambient condition; however, it has also a distinct influence on their adsorption and self assembly on metal surfaces. Here, a low-temperature scanning tunneling microscopy (LT-STM) study of two different epoxyacenes on the Au(111) surface at submonolayer coverage is presented. Both molecules show self-assembly based on hydrogen bonding. While for the molecules with a single epoxy moiety nanostructures of three molecules are formed, extended molecular networks are achieved with two epoxy moieties and a slightly higher surface coverage. Upon annealing at 390 K, the molecules are reduced to the respective acene; however, both systems keep a similar assembled structure. The experimental STM images supported by theoretical calculations show that the self-assembly of the on-surface fabricated acenes is greatly influenced by the on-surface reaction and strongly differs from the adsorption pattern of directly deposited acenes, highlighting the importance of the cleaved oxygen in the self-assembly.},
      year = {2017},
      url = http://dx.doi.org/{10.1021/acs.jpcc.7b06131},
      doi = {10.1021/acs.jpcc.7b06131},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Imaging the electronic structure of on-surface generated hexacene
    • J. Krueger, F. Eisenhut, J. M. Alonso, T. Lehmann, E. Guitian, D. Perez, D. Skidin, F. Gamaleja, D. A. Ryndyk, C. Joachim, D. Pena, F. Moresco, G. Cuniberti
    • Chemical Communications 53, 1583-1586 (2017)
    • DOI   Abstract  

      Surface-assisted reduction of specially designed air-stable precursors allows us to study single hexacene molecules on Au(111) by scanning tunneling microscopy and spectroscopy, mapping with intramolecular resolution their extended electronic eigenstates.

      @article{,
      author = {Justus Krueger and Frank Eisenhut and Jose M. Alonso and Thomas Lehmann and Enrique Guitian and Dolores Perez and Dmitry Skidin and Florian Gamaleja and Dmitry A. Ryndyk and Christian Joachim and Diego Pena and Francesca Moresco and Gianaurelio Cuniberti},
      title = {Imaging the electronic structure of on-surface generated hexacene},
      journal = {Chemical Communications},
      volume = {53},
      number = {10},
      pages = {1583-1586},
      abstract = {Surface-assisted reduction of specially designed air-stable precursors allows us to study single hexacene molecules on Au(111) by scanning tunneling microscopy and spectroscopy, mapping with intramolecular resolution their extended electronic eigenstates.},
      year = {2017},
      url = http://dx.doi.org/{10.1039/c6cc09327b},
      doi = {10.1039/c6cc09327b},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • On-Surface Annulation Reaction Cascade for the Selective Synthesis of Diindenopyrene
    • F. Eisenhut, T. Lehmann, A. Viertel, D. Skidin, J. Kruger, S. Nikipar, D. A. Ryndyk, C. Joachim, S. Hecht, F. Moresco, G. Cuniberti
    • Acs Nano 11, 12419-12425 (2017)
    • DOI   Abstract  

      We investigated the thermally induced on surface cyclization of 4,10-bis(2′-bromo-4′-methylpheny1)1,3-dimethylpyrene to form the previously unknown, nonalternant polyaromatic hydrocarbon diindeno[1,2,3-cd:1′,2′,3′-mn]pyrene on Au(111) using scanning tunneling microscopy and spectroscopy. The observed unimolecular reaction involves thermally induced debromination followed by selective ring closure to fuse the neighboring benzene moieties via a five-membered ring. The structure of the product has been verified experimentally as well as theoretically. Our results demonstrate that on-surface reactions give rise to unusual chemical reactivities and selectivities and provide access to nonalternant polyaromatic molecules.

      @article{,
      author = {Frank Eisenhut and Thomas Lehmann and Andreas Viertel and Dmitry Skidin and Justus Kruger and Seddigheh Nikipar and Dmitry A. Ryndyk and Christian Joachim and Stefan Hecht and Francesca Moresco and Gianaurelio Cuniberti},
      title = {On-Surface Annulation Reaction Cascade for the Selective Synthesis of Diindenopyrene},
      journal = {Acs Nano},
      volume = {11},
      number = {12},
      pages = {12419-12425},
      abstract = {We investigated the thermally induced on surface cyclization of 4,10-bis(2'-bromo-4'-methylpheny1)1,3-dimethylpyrene to form the previously unknown, nonalternant polyaromatic hydrocarbon diindeno[1,2,3-cd:1',2',3'-mn]pyrene on Au(111) using scanning tunneling microscopy and spectroscopy. The observed unimolecular reaction involves thermally induced debromination followed by selective ring closure to fuse the neighboring benzene moieties via a five-membered ring. The structure of the product has been verified experimentally as well as theoretically. Our results demonstrate that on-surface reactions give rise to unusual chemical reactivities and selectivities and provide access to nonalternant polyaromatic molecules.},
      year = {2017},
      url = http://dx.doi.org/{10.1021/acsnano.7b06459},
      doi = {10.1021/acsnano.7b06459},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Micro-patterning by thermoplastic forming of Ni-free Ti-based bulk metallic glasses
    • S. Bera, B. Sarac, S. Balakin, P. Ramasamy, M. Stoica, M. Calin, J. Eckert
    • Materials & Design 120, 204-211 (2017)
    • DOI   Abstract  

      The development of bulk metallic glasses for biomedical applications has become the focus of intense research interest. In this work, we report on the unique thermoplastic behavior of two Ni-free Ti-based bulk metallic glasses by utilizing the dramatic softening of the amorphous structure in the super cooled liquid region. Ti(40)Zr(10)Cu(34)Ed(14)Ga(2) and Ti40Zr10Cu34Pd14Sn2 bulk glassy alloys were produced by copper mold casting. Ga and Sn micro-alloying (2 at%) improve the glass-forming ability and mechanical properties of Ti40Zr10Cu36Pd14 alloy effectively. The cast rods were thermo-mechanically characterized to determine the most suitable processing temperature and time, and the load that has to be applied for thermoplastic net-shaping of the BMGs into anisotropically etched cavities of silicon chips. Periodic features with high surface smoothness and uniform height (24 mu m high circular bumps with sub-pm roughness) were created on the surface of the BMGs. The surface patterning with controllable roughness of Ti-based BMGs can be useful in biomedical studies by mediating material – cell interactions. (C) 2017 Elsevier Ltd. All rights reserved.

      @article{,
      author = {S. Bera and B. Sarac and S. Balakin and P. Ramasamy and M. Stoica and M. Calin and J. Eckert},
      title = {Micro-patterning by thermoplastic forming of Ni-free Ti-based bulk metallic glasses},
      journal = {Materials & Design},
      volume = {120},
      pages = {204-211},
      abstract = {The development of bulk metallic glasses for biomedical applications has become the focus of intense research interest. In this work, we report on the unique thermoplastic behavior of two Ni-free Ti-based bulk metallic glasses by utilizing the dramatic softening of the amorphous structure in the super cooled liquid region. Ti(40)Zr(10)Cu(34)Ed(14)Ga(2) and Ti40Zr10Cu34Pd14Sn2 bulk glassy alloys were produced by copper mold casting. Ga and Sn micro-alloying (2 at%) improve the glass-forming ability and mechanical properties of Ti40Zr10Cu36Pd14 alloy effectively. The cast rods were thermo-mechanically characterized to determine the most suitable processing temperature and time, and the load that has to be applied for thermoplastic net-shaping of the BMGs into anisotropically etched cavities of silicon chips. Periodic features with high surface smoothness and uniform height (24 mu m high circular bumps with sub-pm roughness) were created on the surface of the BMGs. The surface patterning with controllable roughness of Ti-based BMGs can be useful in biomedical studies by mediating material - cell interactions. (C) 2017 Elsevier Ltd. All rights reserved.},
      year = {2017},
      url = http://dx.doi.org/{10.1016/j.matdes.2017.01.080},
      doi = {10.1016/j.matdes.2017.01.080},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

2016

  • Electronically Driven Single-Molecule Switch on Silicon Dangling Bonds
    • A. Nickel, T. Lehmann, J. Meyer, F. Eisenhut, R. Ohmann, D. A. Ryndyk, C. Joachim, F. Moresco, G. Cuniberti
    • Journal of Physical Chemistry C 120, 27027-27032 (2016)
    • DOI   Abstract  

      We demonstrate that a single 4-acetylbiphenyl molecule adsorbed along the dimer row of a Si(100)-(2 X 1) surface can be reversibly switched between two stable conformations using the tunneling current of a scanning tunneling microscope. The experiment supported by density functional theory calculations demonstrates that the molecule by switching selectively passivates and depassivates a dangling-bond pair on the silicon surface, opening new routes for the logical input in dangling-bond-based atomic-scale circuits.

      @article{,
      author = {Anja Nickel and Thomas Lehmann and Jorg Meyer and Frank Eisenhut and Robin Ohmann and Dmitry A. Ryndyk and Christian Joachim and Francesca Moresco and Gianaurelio Cuniberti},
      title = {Electronically Driven Single-Molecule Switch on Silicon Dangling Bonds},
      journal = {Journal of Physical Chemistry C},
      volume = {120},
      number = {47},
      pages = {27027-27032},
      abstract = {We demonstrate that a single 4-acetylbiphenyl molecule adsorbed along the dimer row of a Si(100)-(2 X 1) surface can be reversibly switched between two stable conformations using the tunneling current of a scanning tunneling microscope. The experiment supported by density functional theory calculations demonstrates that the molecule by switching selectively passivates and depassivates a dangling-bond pair on the silicon surface, opening new routes for the logical input in dangling-bond-based atomic-scale circuits.},
      year = {2016},
      url = http://dx.doi.org/{10.1021/acs.jpcc.6b05680},
      doi = {10.1021/acs.jpcc.6b05680},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Thermoelectric properties of nanocarbons: Atomistic modeling
    • T. Lehmann, D. A. Ryndyk, G. Cuniberti
    • Physica Status Solidi a-Applications and Materials Science 213, 591-602 (2016)
    • DOI   Abstract  

      We present a general atomistic ab initio-based modeling approach and numerical implementation for the calculation of thermoelectric properties of carbon nanomaterials. The approach is based on density functional theory calculations of electronic and vibrational properties in combination with quantum transport theory in the Green function formalism. It allows to calculate charge and heat transport, and therefore electrical conductance, thermopower (Seebeck coefficient), electron thermal conductance, phonon thermal conductance, and thermoelectric efficiency, i.e., figure of merit. We systematically investigated temperature, doping, and disorder dependence of the thermoelectric properties of the fundamental types of nanocarbons, such as graphene, metallic and semiconducting nanoribbons, as well as metallic and semiconducting nanotubes. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

      @article{,
      author = {Thomas Lehmann and Dmitry A. Ryndyk and Gianaurelio Cuniberti},
      title = {Thermoelectric properties of nanocarbons: Atomistic modeling},
      journal = {Physica Status Solidi a-Applications and Materials Science},
      volume = {213},
      number = {3},
      pages = {591-602},
      abstract = {We present a general atomistic ab initio-based modeling approach and numerical implementation for the calculation of thermoelectric properties of carbon nanomaterials. The approach is based on density functional theory calculations of electronic and vibrational properties in combination with quantum transport theory in the Green function formalism. It allows to calculate charge and heat transport, and therefore electrical conductance, thermopower (Seebeck coefficient), electron thermal conductance, phonon thermal conductance, and thermoelectric efficiency, i.e., figure of merit. We systematically investigated temperature, doping, and disorder dependence of the thermoelectric properties of the fundamental types of nanocarbons, such as graphene, metallic and semiconducting nanoribbons, as well as metallic and semiconducting nanotubes. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim},
      year = {2016},
      url = http://dx.doi.org/{10.1002/pssa.201532610},
      doi = {10.1002/pssa.201532610},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Tetracene Formation by On-Surface Reduction
    • J. Krueger, N. Pavlicek, J. M. Alonso, D. Perez, E. Guitian, T. Lehmann, G. Cuniberti, A. Gourdon, G. Meyer, L. Gross, F. Moresco, D. Pena
    • Acs Nano 10, 4538-4542 (2016)
    • DOI   Abstract  

      We present the on-surface reduction of diepoxytetracenes to form genuine tetracene on Cu(111). The conversion is achieved by scanning tunneling microscopy (STM) tip-induced manipulation as well as thermal activation and is conclusively demonstrated by means of atomic force microscopy (AFM) with atomic resolution. We observe that the metallic surface plays an important role in the deoxygenation and for the planarization after bond cleavage.

      @article{,
      author = {Justus Krueger and Niko Pavlicek and Jose M. Alonso and Dolores Perez and Enrique Guitian and Thomas Lehmann and Gianaurelio Cuniberti and Andre Gourdon and Gerhard Meyer and Leo Gross and Francesca Moresco and Diego Pena},
      title = {Tetracene Formation by On-Surface Reduction},
      journal = {Acs Nano},
      volume = {10},
      number = {4},
      pages = {4538-4542},
      abstract = {We present the on-surface reduction of diepoxytetracenes to form genuine tetracene on Cu(111). The conversion is achieved by scanning tunneling microscopy (STM) tip-induced manipulation as well as thermal activation and is conclusively demonstrated by means of atomic force microscopy (AFM) with atomic resolution. We observe that the metallic surface plays an important role in the deoxygenation and for the planarization after bond cleavage.},
      year = {2016},
      url = http://dx.doi.org/{10.1021/acsnano.6b00505},
      doi = {10.1021/acsnano.6b00505},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }

  • Cold Flow as Versatile Approach for Stable and Highly Luminescent Quantum Dot-Salt Composites
    • A. Benad, C. Guhrenz, C. Bauer, F. Eichler, M. Adam, C. Ziegler, N. Gaponik, A. Eychmueller
    • Acs Applied Materials & Interfaces 8, 21570-21575 (2016)
    • DOI   Abstract  

      Since the beginning of the 1980s, colloidally synthesized quantum dots (QDs) have been in the focus of interest due to their possible implementation for color conversion, luminescent light concentrators, and lasing. For all these applications, the QDs benefit from being embedded into a host matrix to ensure stability and usability. Many different host materials used for this purpose still have their individual shortcomings. Here, we present a universal, fast, and flexible approach for the direct incorporation of a wide range of QDs into inorganic ionic crystals using cold flow. The QD solution is mixed with a finely milled salt, followed by the removal of the solvent under vacuum. Under high pressure (GPa), the salt powder loaded with QDs transforms into transparent pellets. This effect is well-known for many inorganic salts (e.g., KCl, KBr, KI, NaCl, CsI, AgCl) from, e.g., sample preparation for IR spectroscopy. With this approach, we are able to obtain strongly luminescent QD-salt composites, have precise control over the loading, and provide a chemically robust matrix ensuring long-term stability of the embedded QDs. Furthermore, we show the photo-, chemical, and thermal stability of the composite materials and their use as color conversion layers for a white light-emitting diode (w-LED). The method presented can potentially be used for all kinds of nanoparticles synthesized in organic as well as in aqueous media.

      @article{,
      author = {Albrecht Benad and Chris Guhrenz and Christoph Bauer and Franziska Eichler and Marcus Adam and Christoph Ziegler and Nikolai Gaponik and Alexander Eychmueller},
      title = {Cold Flow as Versatile Approach for Stable and Highly Luminescent Quantum Dot-Salt Composites},
      journal = {Acs Applied Materials & Interfaces},
      volume = {8},
      number = {33},
      pages = {21570-21575},
      abstract = {Since the beginning of the 1980s, colloidally synthesized quantum dots (QDs) have been in the focus of interest due to their possible implementation for color conversion, luminescent light concentrators, and lasing. For all these applications, the QDs benefit from being embedded into a host matrix to ensure stability and usability. Many different host materials used for this purpose still have their individual shortcomings. Here, we present a universal, fast, and flexible approach for the direct incorporation of a wide range of QDs into inorganic ionic crystals using cold flow. The QD solution is mixed with a finely milled salt, followed by the removal of the solvent under vacuum. Under high pressure (GPa), the salt powder loaded with QDs transforms into transparent pellets. This effect is well-known for many inorganic salts (e.g., KCl, KBr, KI, NaCl, CsI, AgCl) from, e.g., sample preparation for IR spectroscopy. With this approach, we are able to obtain strongly luminescent QD-salt composites, have precise control over the loading, and provide a chemically robust matrix ensuring long-term stability of the embedded QDs. Furthermore, we show the photo-, chemical, and thermal stability of the composite materials and their use as color conversion layers for a white light-emitting diode (w-LED). The method presented can potentially be used for all kinds of nanoparticles synthesized in organic as well as in aqueous media.},
      year = {2016},
      url = http://dx.doi.org/{10.1021/acsami.6b06452},
      doi = {10.1021/acsami.6b06452},
      openaccess = yes,
      peerreview = yes,
      keywords = {nanotechnology}
      }