Nanotechnology

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Nanoporous membranes are fabricated by heavy ion irradiation and chemical etching. Pore density and pore arrangement are selected by the irradiation conditions. Pore size and geometry are controlled by the etching parameters. By electrodeposition inside the nanopores, micro- and nanowires with controlled geometry and crystallinity can be fabricated. Nanowires fabricated by the template method are excellent objects to investigate size-effects on technologically relevant properties such as optical, electrical, and thermal. Single nanopore membranes developed at GSI are employed by many groups around the world to investigate ionic transport through confined nanochannels, and develop novel chemical- and bio sensors.

Nanowires

Synthesis novel nanostructures Thermoelectrics Plasmonic nanoantennas Reliability of nanostructures

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Synthesis novel nanostructures

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The combination of etched ion-track membranes and electrodeposition allows us to synthesize nanowires with simultaneous and independent control on their dimension, geometry, morphology and crystallinity.Poly- and single-crystalline nanowires, with diameter ranging between few nm and several micrometers, and aspect ratio (length over diameter) as high as 1000, are created by electrochemical deposition in etched ion track templates. The wires can remain in the membrane or can be transfered to another substrate after removal of the membrane. This technique has enabled the synthesis of nanowires of different materials such as copper, gold, nickel, bismuth, platinum, silver, alloys such as Bi1-xSbx and Bi2Te3, and heterostructures such as Co/Cu multilayers.Novel nanostructures such as nanogaps for plasmonics, conical nanowires, and nanowire networks are currently under development and investigation Sabine, this part I just added

By Recent publications:Tuning the Geometrical and Crystallographic Characteristics of Bi2Te3 Nanowires by Electrodeposition in Ion-Track Membranes, O. Picht, S. Müller, I. Alber , Rauber M, Lensch-Falk J, Medlin DL, Neumann R, Toimil-Molares ME J. Phys. Chem. C, 2012, 116 (9), pp 5367–5375 Electrochemical Synthesis of Bi1 xSbx Nanowires with Simultaneous Control on Size Composition and Surface RoughnessMüller S, Schötz C, Picht O, Sigle W, Kopold P, Rauber M, Alber I, Neumann R, Toimil-Molares MECrystal Growth and Design, 12 (2), (2012) 615–621P. Serbun, F. Jordan, A. Navitski, G. Müller, I. Alber, M.E. Toimil-Molares, C. Trautmann, Copper nanocones grown in polymer ion-track membranes as field emitters The European Physical Journal Applied Physics 58 (2012) 58 10402

Thermoelectrics

As it is currently but adding the recent publications:

Tuning the Geometrical and Crystallographic Characteristics of Bi2Te3 Nanowires by Electrodeposition in Ion-Track Membranes, O. Picht, S. Müller, I. Alber , Rauber M, Lensch-Falk J, Medlin DL, Neumann R, Toimil-Molares ME J. Phys. Chem. C, 2012, 116 (9), pp 5367–5375 Electrochemical Synthesis of Bi1 xSbx Nanowires with Simultaneous Control on Size Composition and Surface RoughnessMüller S, Schötz C, Picht O, Sigle W, Kopold P, Rauber M, Alber I, Neumann R, Toimil-Molares MECrystal Growth and Design, 12 (2), (2012) 615–621

Plasmonic nanoantennas

Here the web-link should not be called any more Au-Ag nanowires but plasmonic nano-antennas

Poly- and single-crystalline Au nanowires with diameters down to 25 nm as well as nanowire dimers, are electrochemically synthesized. With infrared spectroscopic microscopy using synchrotron light, the resonant light scattering from single metal nanowires with diameters in the 100 nm range and with lengths of a few microns was investigated in collaboration with the group of Prof. A.M. Pucci at the University of Heidelberg. Significant antenna-like plasmon resonances were observed in good agreement with exact light-scattering calculations. The resonances depend not only on length and diameter but also on the dielectric surrounding of the nanowire. The observed maximum extinction at resonance corresponds to an electromagnetic far-field enhancement by a factor of about 5. In collaboration with MPI for Intelligent Systems, scanning transmission electron microscopy (STEM) imaging combined with electron energy-loss spectroscopy (EELS) is employed to investigate longitudinal surface plasmon resonance coupling in metallic nanowire dimers with gap sizes down to about 7 nm. Applying this method, we investigate bright and dark longitudinal as well as transversal modes with a very high spatial resolution of a few nanometers, and study the influence of gap size, aspect ratio, and multipole order on mode splitting. A high-energy resolution of 0.12 eV enabled the study of mode splitting into bonding and antibonding modes, amounting to 0.23 eV for a gap of about 8 nm. These investigations continue to characterize the plasmonic properties of further novel nanostructures.

1. Visualization of Multipolar Longitudinal and Transversal Surface Plasmon Modes in Nanowire DimersAlber I, Sigle W, Müller S, Neumann R, Picht O, Rauber M, van Aken PA,Toimil-Molares MEACS NANO, 5 (12) (2011) 9845–98532. Resonant Plasmonic and Vibrational Coupling in a Tailored Nanoantenna for Infrared Detection F. Neubrech, A. Pucci, T.W. Cornelius, S. Karim, A. Garcia-Etxarri, J. Aizpurua, Phy. Rev. Lett. 101 (2008) 157403 3. Resonances of individual metal nanowires in the infrared, F. Neubrech, T. Kolb, R. Lovrincic, G. Fahsold, A. Pucci, J. Aizpurua, T.W. Cornelius, M.E. Toimil-Molares, R. Neumann, S. Karim, Appl. Phys. Lett. 89 (2006) 253104 4. Synthesis of gold nanowires with controlled crystallographic characteristics, S. Karim, M.E. Toimil-Molares, F. Maurer, G. Miehe, W. Ensinger, J. Liu, T.W. Cornelius, R. Neumann, Appl. Phys. A 84 (2006) 403-407 5. Electrochemical fabrication of single-crystalline and polycrystalline Au nanowires: The influence of deposition parameters, J. Liu, J.L. Duan, M.E. Toimil-Molares, S. Karim, T.W. Cornelius, D. Dobrev, H.J. Yao, Y.M. Sun, M.D. Hou, D. Mo, Z.G. Wang, R. Neumann, Nanotechnology 17 (2006) 1922-1926

Reliability of Nanostructures

On the way to physical nanowire implementation and device fabrication, both chemical and thermal stability of the nanowires should be carefully analyzed. Due to their extremely high surface-to-volume-ratio, nanowire properties are expected to be influenced by adsorbates, surface chemical modifications, and morphological changes at elevated temperatures.

Our group demonstrated that metal nanowires are transformed into chains of nanospheres during annealing due to the Rayleigh instability. The driving force of this process is the minimization of surface energy of the initial wire. Both sphere size and spacing between adjacent spheres depend on the initial wire diameter, material, and crystallinity of the wire.

Recently, we reported the geometrical transformation of metallic copper nanowires, confined in graphitic coating, into crystalline nanoparticles of up to tenfold increased diameter. In situ transmission electron microscopy images at 500 ° C, recorded as movies, provided an exceptional real-time visualization of Cu draining out of the carbon coating. The solid content of the carbon tube is effectively evacuated over micrometer distances towards the open end, transforming each nanowire into a single monocrystalline, facetted Cu particle. Kinetic Monte Carlo simulationspropose that this dramatic morphological transformation is driven by surface diffusion of Cu atoms along the wire/tube interface, thus minimizing the total free energy of the system. These investigations are relevant for applications of nanotubes including their use as storage media for atoms and small molecules, as nanoscale capsules for chemical reactions, and as nanopipettes for material delivery.Recent Publications1. M.E. Toimil-Molares, xxx.. Adv. Functional materials…2. Influence of crystallinity on the Rayleigh instability of gold nanowires S. Karim, M.E. Toimil-Molares, W. Ensinger, A.G. Balogh, T.W. Cornelius, E.U. Khan, R. Neumann Journal of Physics D- Applied Physics 40 (2007) 3767 3. Morphological evolution of Au nanowires controlled by Rayleigh instability S. Karim, M.E. Toimil-Molares, A.G. Balogh, W. Ensinger, T.W. Cornelius, E.U. Khan, R. Neumann Nanotechnology 17 (2006) 5954 4. Fragmentation of nanowires driven by Rayleigh instability M.E. Toimil-Molares, A.G. Balogh, T.W. Cornelius, R. Neumann, C. Trautmann Appl. Phys. Lett. 85 (2004) 5337

Single nanopores

Single nanopore membranes are fabricated at GSI by single ion irradiation and chemical etching.

Single nanopore membranes are fabricated at GSI by single ion irradiation and chemical etching.

To produce single-nanopore membranes it is necessary to control the exact number of ions hitting the polymer foil. To achieve this, a small circular aperture (diameter ~ 200 μm) is placed in front of the sample, and the ion beam is strongly defocused and adjusted in such a way that single ions pass through the aperture with a

frequency of about 1 Hz. The ions are detected by a solid-state particle detector placed behind the sample. As soon as the detector has registered a single ion impact, the ion beam is deflected by an electrostatic chopper system. The single-ion irradiation system is world-wide unique at GSI.

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After irradiation, the polymer foil is introduced in a two-compartment electrochemical cell. The ion track created by the ion is selectively etched. The etching process is monitored by recording the current-time characteristics, using two electrodes immersed each in one of the two compartents. Geometry and size of the resulting

nanopore are controlled by the etching conditions (solution, concentration, temperature).

Using the same electrochemical cell, two Ag/AgCl electrodes and corresponding electronic devies, the ionic transport through the single nanopore is investigated. These solid state polymeric nanopores are employed as model systems to study the controlled passage of ions through nanochannels. To understand the ionic flow through natural ion channels and artificial nanopores is of fundamental interest in biology, physics and chemistry.

Single nanopore membranes are also used as sensors to detect the pass of a single molecules, viruses, or particles. In these experiments, the current through the single nanopore at a given potential is monitored. Variations of the current (events) are then correlated to the single objects blocking partly the nanopore on their way through.

Another strategy to develop responsive systems and single nanopore sensors rely in incorporating sensing elements into polymer nanochannels.