I. Alber

GSI Helmholtzzentrum für Schwerionenforschung, Jena, Thuringia, Germany

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Publications (12)47.33 Total impact

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    ABSTRACT: We have optimized the fabrication of sharp copper nanocones (Cu-NCs) for flat patch-structured field emission (FE) cathodes. Polycarbonate (PC) foils were irradiated through a shadow mask with swift Xe or U ions. The ion tracks were asymmetrically etched in a mixture of NaOH and methanol. These membranes were metallized, fixed on an Al plate, and electrochemically filled with Cu through the small pore openings. Flat cathodes of 25 mm2 size with mechanically stable Cu-NCs of ~28 μm height, ~3 μm base, and ~130 nm tip diameter were obtained. Fairly distributed FE with at least 8 (10) emitters per patch was achieved for the bare (60-nm Au-coated) Cu-NCs. Integral measurements of selected patches yielded average stable FE currents up to 30 (151) μA at 32 (50) V/μm, respectively.
    Vacuum Nanoelectronics Conference (IVNC), 2013 26th International; 01/2013
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    ABSTRACT: We report on the experimental and the theoretical investigation of multipole surface plasmon resonances in metal nanowires conductively connected by small junctions. The influence of a conductive junction on the resonance energies of nanowire dimers was simulated using the finite element method based software CST Microwave Studio and experimentally measured by electron energy-loss spectroscopy in a transmission electron microscope. We extend the analysis of conductively connected structures to higher order multipole modes up to third order, including dark modes. Our results reveal that an increase in junction size does not shift significantly the antibonding modes, but causes a strong blue shift of the bonding modes, leading to an energetic rearrangement of the modes compared to those of a capacitively coupled dimer with similar dimensions.
    ACS Nano 10/2012; · 12.03 Impact Factor
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    ABSTRACT: Field emission (FE) properties of unstructured and patch-structured cathodes with randomly distributed and vertically aligned copper nanocones (Cu-NCs) are reported. The cones of ~28 μm height, 2.4 μm base diameter and 95-220 nm tip radius were fabricated by electrochemical deposition of Cu into conical channels of heavy-ion-irradiated and asymmetrically etched polycarbonate membranes. FE measurements of the unstructured cathodes with slowly-grown Cu-NCs of high number density (107 cm-2) and excellent mechanical stability yield stable currents up to 280 μA from an emission spot of 30 μm. For the structured cathodes with a triangular patch array of less dense Cu-NCs (<106 cm-2), well-aligned FE with ~90% efficiency is reproducibly achieved. A trade-off between low onset field (~22 V/μm) for sparsely grown Cu-NCs with sharp tips and high current limit (~100 μA) for densely grown ones with broader tips is observed. Possibilities for further optimization of such field emitters for cold cathode applications are discussed.
    The European Physical Journal Applied Physics 04/2012; 58(1):10402-. · 0.71 Impact Factor
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    ABSTRACT: We report the fabrication of Bi2Te3 nanowires with diameters as small as 15 nm, which is comparable to the size theoretically estimated for the onset of improvement of the thermoelectric figure of merit ZT by quantum-size effects. The versatility of the template-assisted growth, combining self-prepared ion-track etched membranes and electrochemical deposition, has been employed to synthesize Bi2Te3 nanowires with controlled diameters in 10, 30, and 60 μm thick membranes and with large aspect ratios (length over diameter) of up to 1000. SEM, HRTEM, and XRD investigations reveal how morphology, surface roughness, and crystalline orientation of the Bi2Te3 nanowires depend on deposition potential, temperature, and channel diameter.
    The Journal of Physical Chemistry C 02/2012; 116(9):5367–5375. · 4.84 Impact Factor
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    ABSTRACT: We present the synthesis of Bi1−xSbx nanowires with controlled composition between x = 0.05 and x = 0.40 over a wide range of diameters (20−100 nm) interesting for the investigation of the enhancement of thermoelectric efficiency via quantum size effects. We find that the relative concentration of Bi and Sb ions in the electrolyte, together with the deposition potential, determines the resulting nanowire composition. Morphology and composition were analyzed using X-ray diffraction, electron microscopy, and energy dispersive X-ray analysis. Two different templates were fabricated to enable the synthesis of nanowires with smooth and rough contour.
    Crystal Growth & Design 01/2012; 12:615. · 4.69 Impact Factor
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    ABSTRACT: We have fabricated patch-structured nanocone (NC) cathodes by using asymmetrically etched ion-track membranes which were metallized and fixed on flat holders. The conical channels of these templates were filled by potentiostatic copper deposition resulting in freestanding Cu-NC of ~ 28 μm length, ~ 3 μm base, and 160-240 nm tip diameter. Fairly homogeneous and well-aligned field emission from all patches was obtained due to the high NC (105 cm-2) and emitter densities (~ 3/patch). Local measurements of selected spots and patches show distinct current jumps at μA levels. SEM images of the processed areas reveal morphological changes proving a successive destruction of single Cu-NCs. Nevertheless, improved current values of ~ 300 μA at reduced fields of 30-50 V/μm have been achieved for the best Cu-NC patches.
    Vacuum Nanoelectronics Conference (IVNC), 2012 25th International; 01/2012
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    ABSTRACT: We study the transversal and longitudinal localized surface plasmon resonances in single nanowires and nanowire dimers excited by the fast traveling electron beam in a transmission electron microscope equipped with high-resolution electron energy-loss spectroscopy. Bright and dark longitudinal modes up to the fifth order are resolved on individual metallic nanowires. On nanowire dimers, mode splitting into bonding and antibonding is measured up to the third order for several dimers with various aspect ratio and controlled gap size. We observe that the electric field maxima of the bonding modes are shifted toward the gap, while the electric field maxima of the antibonding modes are shifted toward the dimer ends. Finally, we observe that the transversal mode is not detected in the region of the dimer gap and decays away from the rod more rapidly than the longitudinal modes.
    ACS Nano 11/2011; 5(12):9845-53. · 12.03 Impact Factor
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    ABSTRACT: Copper nanocones (Cu-NCs) of about 30 μm length and of ~2.4 μm in base and ~380 nm in tip diameter were grown in polymer ion-track membranes. Field emission (FE) properties of two types of cathodes with randomly distributed Cu-NCs were investigated. The unstructured cathode with high number density (107 cm<sup>-2</sup>) and excellent mechanical stability of Cu-NCs yielded stable currents up to 100 μA at electric fields of about 100 V/μm as measured with an anode of 30 μm in diameter. The structured cathode with triangular patch array of less Cu-NCs (<; 10<sup>6</sup> cm<sup>-2</sup>) provided well-aligned FE with about 90% efficiency at much reduced onset field levels (~20 V/μm) but lower current limits, too. SEM images of the random Cu-NCs after current processing revealed only slight changes of the tip morphology. The actual status and further optimization steps of structured Cu-NC cathodes for device applications will be discussed.
    Vacuum Nanoelectronics Conference (IVNC), 2011 24th International; 08/2011
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    ABSTRACT: Freestanding copper nanocones (Cu-NC) are fabricated by electrodeposition in etched ion-track membranes for field emission investigations. Different deposition conditions of the Cu-NC were studied in order to get mechanically stable cones with good electrical contact to the substrate. Electrodeposition at -40 mV lead to a slow growth rate, resulting in uniform and mechanically stabile Cu-NC of about 28 μm length, 1.2 μm base radius, and 190 nm tip radius. The deposition process was monitored via current-vs-time curves.
    Vacuum Nanoelectronics Conference (IVNC), 2011 24th International; 08/2011
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    ABSTRACT: The fabrication of three-dimensional assemblies consisting of large quantities of nanowires is of great technological importance for various applications including (electro-)catalysis, sensitive sensing, and improvement of electronic devices. Because the spatial distribution of the nanostructured material can strongly influence the properties, architectural design is required in order to use assembled nanowires to their full potential. In addition, special effort has to be dedicated to the development of efficient methods that allow precise control over structural parameters of the nanoscale building blocks as a means of tuning their characteristics. This paper reports the direct synthesis of highly ordered large-area nanowire networks by a method based on hard templates using electrodeposition within nanochannels of ion track-etched polymer membranes. Control over the complexity of the networks and the dimensions of the integrated nanostructures are achieved by a modified template fabrication. The networks possess high surface area and excellent transport properties, turning them into a promising electrocatalyst material as demonstrated by cyclic voltammetry studies on platinum nanowire networks catalyzing methanol oxidation. Our method opens up a new general route for interconnecting nanowires to stable macroscopic network structures of very high integration level that allow easy handling of nanowires while maintaining their connectivity.
    Nano Letters 06/2011; 11(6):2304-10. · 13.03 Impact Factor
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    ABSTRACT: We report on the investigation of field emission (FE) properties of gold nanowire patch arrays as well as on the observation of morphology changes of the nanowires in selected patches due to FE operation. The actual current limits in the μA range are caused by heating and successive destruction of nanowires. SEM images reveal geometrical constrictions in the contact region to the substrate. Appropriate modifications of the fabrication are suggested.
    Vacuum Nanoelectronics Conference (IVNC), 2010 23rd International; 08/2010