2017

  • 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}
      }

  • 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}
      }

  • 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}
      }

  • 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}
      }

2016

  • 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 Appl. Mater. 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 Appl. Mater. 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}
      }

  • 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}
      }

  • 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}
      }

  • Thermoelectric properties of nanocarbons: Atomistic modeling
    • T. Lehmann, D. A. Ryndyk, G. Cuniberti
    • Phys. Status Solidi A-Appl. Mat. 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 = {Phys. Status Solidi A-Appl. Mat.},
      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}
      }