C. Trautmann

Search for superfluid Josephson effect

Abstract The superfluid Josephson effect is based on the weak coupling between two adjacent superfluid reservoirs, relates their pressure difference to a frequency and promises the realization of high-precision sensors for pressure and rotation. Ion tracks provide obstacles sufficiently small to interfere with superfluids. These so-called “weak links” represent potential barriers through which tunneling occurs between the two neighboring superfluid reservoirs. The experimental status is described.

Sensitization of track etching in CR-39 by copolymerization with methacryloyl-L-alanine methyl ester

Abstract Copolymer films of diethyleneglycol-bis-allylcarbonate (monomer of CR-39) and selected volume percentages of methacryloyl- L -alanine methyl ester (MA- L -AlaOMe) between 5 and 60% were irradiated with Au ions of 13 MeV nucl -1 and etched in NaOH solution at 60°C. Sensitization of track etching was observed for NaOH concentrations of 4 and 6 N. The maximum reduced etch-rate ratio, V t / V b -1, was obtained for the copolymer of 90% of CR-39 monomer and 10% of MA- L -AlaOMe at 4 N NaOH, which was 3.6 times higher than that for pure CR-39. The sensitization was accompanied by an increase in V b so that the etching time could be reduced to ca 1/30 in comparison with that for pure CR-39.

Metal-organic frameworks shaped into one-dimensional nanostructures via templated electrodeposition

Metal-organic frameworks (MOFs) are a relatively new class of hybrid materials, which consist of metal ions or clusters as the secondary building unit and organic linkers connecting the metallic building units via coordination bonds of moderate strength [1]. Thereby, MOFs combine the robustness and crystallinity of inorganic materials with the flexibility of organic molecules. This opens up the possibility for MOFs to be used in a wide range of applications ranging from gas storage and gas separation to sensors and photocatalysis [1-3]. In this study, MOF nanowires were made via electrodeposition inside etched ion-track membranes in order to precisely control the size, shape and location of the resulting MOF crystals. By controlled oxidation of Cu nanowires in a solution containing 1,3,5-benzenetricarboxylate (BTC) molecules, we synthesised nanowires of the well-known MOF Cu3(BTC)2, which consists of Cu ions as the metallic core linked together by BTC ligands. To the best of our knowledge, this is the first time that templated electrodeposition was used for the synthesis of one-dimensional MOF nanostructures.

Synthesis of Au

In this work, three dimensional AuAg-alloy-nanowirenetworks with controlled composition and defined wire diameter were fabricated by electrodeposition in ion-trac k etched polymer templates. These structures are very interesting for applications in sensorics and catalysis since th ey exhibit a very high surface area and are mechanically stable due to their interconnected nanowires. For the synthesis of the nanowire-networks, we have irradiated 30μm-thin polymer foils at the GSI linear accelerator UNILAC with swift heavy ions of initial energy 11.4 MeV/u. Each foil is sequentially irradiated four times under an angle of 45 ◦ respective to the polymer surface. The ions damage molecular bonding in the foils and create cylindrical damage tracks. By chemical etching with aqueous 6-M NaOH solution at 50 ◦ C these ion tracks are transformed into nanochannels. Under these etching conditions, the etching rate amounts 23 nm/min. By varying the etching time between 2 min and 5 min nanochannels with defined diameter between 60-150 nm were fabricated. After creating a conductive cathode layer by sputtering gold on one side of the foil, nanowires are electrodeposited in the pores. We have deposited AuAg-nanowires using an electrolyte consisting of 50 mmol KAu(CN) 2 and 50 mmol KAg(CN)2 in a three-electrode set-up. A Ag/AgCl electrode was used as reference electrode and a platinum coil as anode. All deposition potentials are given here vs. Ag/AgCl reference. Wet-chemical dissolution of the polymer leads to free-standing stable nanowire-networks. Fig. 1 shows the SEM image of a network with 100 nm wire diameter.

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Bi2Te3 belongs to a recently discovered new class of materials, called topological insulators (TI), which form conductive surface states while their bulk material is an ordinary band insulator. These exotic surface states are generated by strong spin-orbit coupling and feature spinmomentum locking of the charge carriers due to time reversal symmetry. For this reason TI materials are of high interest for future electronic applications like dissipat onless transport and spintronics [1, 2]. The major challenge to address the surface states is the reduction of the concentration of residual bulk carriers dominating over the signal. Nanowires (NWs) of high surface-to-volume ratio combined with controllable geometric, crystallograph ic and morphologic properties are excellent model systems to investigate the TI surface states. Here, we present x-ray photoelectron spectroscopy (XPS) studies with sub-micron resolution on individual 100 nm diameter Bi 2Te3 NWs. The NWs are synthesized by electrodeposition in etched ion-track templates fabricated by irradiating 30μm thick polycarbonate foils with GeV heavy ions at the UNILAC accelerator and selective chemical etching of the ion tracks in 6 M NaOH at 50 ◦C. Subsequently, NWs are electrodeposited within the channels at an applied potential of 0 V vs. SCE at 30 ◦C. Details on the fabrication and characterization are reported in [3]. After deposition, the NWs were released from the membrane and randomly distributed onto a silicon wafer. Figure 1 displays XPS spectra recorded with an unfocused beam, i.e. from the entire substrate, as prepared (red), aft er 15 s (blue) and 15 min (black) of Ar plasma cleaning in UHV. The O and C signals indicating contamination of the Bi2Te3 surface by i.e. oxidation, polymer residual, etc., decrease with increasing cleaning time. After surface prepa-