Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31742 Publications
Bestimmung der Bindungsform des Urans in Mineralwässern
Bernhard, G.; Geipel, G.;
Zum ersten Mal wird über die direkte spektroskopische Bestimmung der Bindungsform des Urans bei niedrigsten originalen Konzentrationen in Mineralwasserproben berichtet.
Zu diesem Zweck wurde ein spezielles laserinduziertes Fluoreszenzspektroskopiesystem eingesetzt und die Proben bei tiefen Temperaturen vermessen. Exemplarisch werden die Ergebnisse der spektroskopischen Bestimmung der Bindungsform des Urans in einer Mineralwasserprobe (Urankonzentration 3,56 μg/L) und im Wasser einer Heilquelle (Urankonzentration 467,0 μg/L) vorgestellt. Die Speziation wird im Mineralwasser durch den Komplex Ca2UO2(CO3)3 und im Heilwasser durch eine Mischung aus den Komplexen Ca2UO2(CO3)3 und UO2 (CO3)34- dominiert. Die Mobilität und Toxizität des Urans sind stark abhängig von seiner Bindungsform.
Keywords: Uran, Speziation, Mineralwasser, Laserinduzierte Kryo-FluoreszenzspektroskopieLaserspektroskopie
  • Vom Wasser 105(2007)3, 7-10

Publ.-Id: 8841 - Permalink


Laser Gain and Intra-cavity Losses of the ELBE Mid-IR FEL
Lehnert, U.; Michel, P.; Seidel, W.; Teichert, J.; Wünsch, R.;
The the U27-FEL of the ELBE radiation source allows to choose between five mirrors with different outcoupling holes. This allows to adapt the optical resonator to the required wavelength range to ensure the needed laser gain and to optimize the outcoupled laser power. Another parameter which influences the achievable laser gain and output power is the detuning length of the optical cavity. While for CW operation often the minimum detuning point is choosen which maximizes the outcoupled power, for pulsed-mode operation about one wavelength of cavity detuning maximizes the laser gain and yields best stability of the laser. To gain some insight into the behavior of the optical resonator we have measured the round-trip losses and the net laser gain and compare both to calulations. For the measurements we have used a fast-readout MCT detector to measure the decay and rise-time of the outcoupled infrared beam caused by a 10μs break in the electron beam micro-pulse train. We show gain and loss for 5, 10 and 20μm wavelength with the typical detuning curves of an FEL.
  • Poster
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
    Proceedings of the 28th International Free Electron Laser Conference, 339-340

Publ.-Id: 8840 - Permalink


The Rossendorf IR-FEL ELBE
Michel, P.; Buettig, H.; Gabriel, F. G.; Helm, M.; Lehnert, U.; Schneider, C.; Schurig, R.; Seidel, W.; Stehr, D.; Teichert, J.; Winnerl, S.; Wünsch, R.;
The radiation source ELBE is the central research facility in the Forschungszentrum Rossendorf. The machine is based on a 40 MeV superconducting RF Linac wich can be operated up to 1mA in cwmode. After commissioning the Bremsstrahlung and the X-ray facilities in 2002, and 2003 respectively, and the first lasing of the mid- IR FEL (4-22 um) in 2004 about 7000 hours user beam-time have been provided. At present a second FEL for long IR waves (15-150 um) using a partial waveguide is under commissioning. Besides in-house users especially the IR beam is available to external users in the FELBE (FEL@ELBE) program witch is a part of the integrated activity on synchrotron and free electron laser science in the EU. In this talk the fundamental features of the ELBE IR FEL’s and the parameters demanded by users are displayed. In addition, an overview about user experimental work and important machine date like availability are shown. Future projects like the combination of the new High Magnetic Field lab with the ELBE-IR beams will be described.
  • Invited lecture (Conferences)
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
    Proceedings of the 28th International Free Electron Laser Conference, 488-491

Publ.-Id: 8838 - Permalink


Cryomodule and Tuning System of the Superconducting RF Photo-Injector
Teichert, J.; Arnold, A.; Buettig, H.; Janssen, D.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Xiang, R.; Kamps, T.; Lipka, D.; Klemz, G.; Lehmann, W.-D.; Stephan, J.; Will, I.;
We present the designs and report on the progress in construction and testing of the cryomodule and the tuning system for the
SRF gun. The SRF gun project, a collaboration of BESSY, DESY, MBI and FZR, aims at the installation of a high average current CW photo injector at the ELBE linac with a Nb cavity. The cryostat consists of a stainless steel vacuum vessel, a warm magnetic shield, a liquid N cooled thermal shield, and a He tank with two-phase supply tube. A heater pot in the He input port will be used for He level control. The 10 kW power coupler is adopted from ELBE module. A cooling and support systemfor the NC photo cathode has been developed and tested. It allows the adjustment of the cathode with respect to the cavity from outside. The cryomodule will be connected with the 220 W He refrigerator of ELBE and will operate at 1.8 to 2 K. The static thermal loss is expected to be less than 20W. Two tuners will be installed for separate tuning of the three TESLA cells and the half-cell. The tuners are dual spindle-lever systems with stepmotors and low-vibration gears outside the cryostat. Functionality, tuning range and accuracy have been tested in cryogenic environment.
  • Poster
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
    Proceedings of the 28th International Free Electron Laser Conference, 575-578

Publ.-Id: 8836 - Permalink


First RF-Measurements at the 3.5-Cell SRF-Photo-Gun Cavity in Rossendorf
Arnold, A.; Buettig, H.; Janssen, D.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Kamps, T.; Lipka, D.; Marhauser, F.; Klemz, G.; Lehmann, W.-D.; Stephan, J.; Volkov, V.; Will, I.;
At the Forschungszentrum Rossendorf the development and the setup of the 2nd superconducting radio frequency photo electron injector (SRF-Photo-Gun) is nearly finished. One of the main attentionwas focussed at the treatment of the cavity. Their RF properties were measured at room temperature. The warm tuning was carried out considering pre-stressing and tuning range of both tuners (half cell and full cells). The adjusted field profiles and pass band frequencies of the four fundamental modes met the requirements. An external Q study of the main coupler yielded to an optimal antenna length and showed very good agreement between simulation and measurement. Furthermore the characteristics of the choke filter and both HOM filters were simulated, measured and tuned at the pi-mode frequency. The preparation (etching and rinsing) and the cold test were successfully done at DESY. The poster presents the setup for the measurements as well as a comparison of the simulated and measured results.
  • Poster
    28th International Free Elektron Laser Conference, 27.08.-01.09.2006, Berlin, Germany
  • Contribution to proceedings
    28th Free Electron Laser Conference 2006, 27.08.-01.09.2006, Berlin, Germany
    Proceedings of the 28th International Free Electron Laser Conference, 567-570

Publ.-Id: 8834 - Permalink


Pulsed RF System for the ELBE Superconducting Accelerator
Buechner, A.; Gabriel, F. G.; Buettig, H.; Lehnert, U.; Michel, P.; Schneider, C.; Schurig, R.;
The RF system for the ELBE accelerator was originally designed for CW mode. Although this works problem-free tests have shown that it is possible to reach higher gradients in the TESLA cavities with a pulsed RF system. The new RF system will be presented together with measurements of the achievable gradients. Roughly 30% higher gradients could now be used in pulsed mode. As positive side effects the radiation by field emission is reduced by the duty cycle and an easy in situ RF conditioning of cavities and coupler windows is possible.
  • Poster
    European Particle Accelerator Conference, 26.-30.09.2006, Edinburgh, Scotland

Publ.-Id: 8833 - Permalink


A Pulsed-RF High-power Processing Effect of Superconducting Niobium Cavities observed at the ELBE Linear Accelerator
Lehnert, U.; Buettig, H.; Michel, P.; Schneider, C.; Schurig, R.; Buechner, A.; Gabriel, F. G.;
The driver LINAC of the ELBE radiation source is built for cw operation. However, in some cases a pulsed-mode operation was desired to extend the otherwise stringent gradient limits. The main restriction results from field emission that decreases the Q of the cavities which was evaluated from measurements of the liquid helium consumption. After pulsed-mode operation with gradients exceeding the maximum cw accelerating gradients by 30–40\% a significant reduction in the field emission was observed. This in turn allows higher accelerating gradients to be used in cw as well. We attribute this behaviour to an rf-processing of the cavity surface which burns off field emitters.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, Scotland
    EPAC 2006 - Proceedings, 413-414

Publ.-Id: 8832 - Permalink


Design of a Superconducting Cavity for a SRF Injector
Janssen, D.; Volkov, V.;
In a collaboration between BESSY, DESY, FZR, MBI and BINP a 3-1/2 cell superconducting RF electron gun is under development at the FZ - Rossendorf. The status of the project and the progress obtained in the last year is reported on this conference. The motivation for the design of a new gun cavity, presented in this paper, is the new FEL project at BESSY. This FEL is designed for a bunch charge of 2.5 nC and the transverse emittance should be comparable with that of the current SRF gun project. In order to compensate the high bunch charge a high electric field on the cavity axis is necessary. In the present paper we will present the design of a 1-1/2 cell cavity for a superconducting RF gun. The active length of the cavity (without beam tube) is 14.4 cm. For the magnetic peak field the conservative value of 130 mT is assumed. The obtained particle energy is 6.6 MeV, corresponding to an accelerating field strength of 45.6 MV/m . In the TESLA cavity the same magnetic peak field is connected with an accelerating field strength of approximately 31 MV/m. Tracking calculation of electron bunches are in progress and will be also reported.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, Scotland
    EPAC 2006 - Proceedings, 2472-2474

Publ.-Id: 8831 - Permalink


Progress of the Rossendorf SRF Gun Project
Janssen, D.; Arnold, A.; Buettig, H.; Hempel, R.; Lehnert, U.; Michel, P.; Moeller, K.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Xiang, R.; Kamps, T.; Lipka, D.; Marhauser, F.; Lehmann, W.-D.; Stephan, J.; Volkov, V.; Will, I.;
In this paper we report the status and the progress of the superconducting RF gun project in Rossendorf. The gun is designed for cw operation mode with 1 mA current and 10 MeV electron energy. The cavity consists of three cells with TESLA geometry, a special designed half-cell in which the photo cathode will be inserted and a choke filter, which prevents the leakage of RF power by the coaxial line between the cathode and the cavity cell. A double tuner allows the tuning of the half-cell and the TESLA cells separately. In 2005 the fabrication of two cavities with RRR300 and RRR40 was finished. We present the results of the field measurement and the warm tuning of the cavity cells as well as the tuning and performance measurement of the choke filter. The fabrication of the double tuner has been also finished. In a test bench we measured the properties of the tuner (tuning range, resolution) at LN2 temperature. Further activities concern the diagnostic beam line of the gun, the new cathode preparation and cathode transfer system, the driver laser and the LHe transfer line.
  • Contribution to proceedings
    European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, Scotland
    EPAC 2006 - Proceedings, 2469-2471
  • Poster
    10th biennal European Particle Accelerator Conference EPAC 2006, 26.-30.06.2006, Edinburgh, Scotland, UK

Publ.-Id: 8830 - Permalink


Study of hydrogen-defect interaction in thin Nb film on Si substrate using positron annihilation
Cizek, J.; Procházka, I.; Brauer, G.; Anwand, W.; Mücklich, A.; Kirchheim, R.; Pundt, A.; Bäthz, C.; Knapp, M.;
Nanocrystalline thin Nb films loaded with hydrogen were studied in the present work. Thin Nb films were prepared on (100) Si substrates at room temperature by cathode beam sputtering. Microstructure observations by transmission elec tron mi cros copy (TEM) revealed that the films exhibit elon gated col umnlike grains. The width of the columns is smaller than 100 nm. Two “generations” of grains can be distinguished in the columns: (i) “first generation” grains at tached directly to the Si substrate, and (ii) “second generation” grains which grow on top of the “first generation” grains. X-ray diffraction (XRD) studies revealed that the Nb films are characterized by a strong (110) texture. However, the lateral orientation of grains (i.e. in the plane of the substrate) is random. Defect studies were performed by variable energy positron annihilation spectroscopy (VEPAS) with measurement of Doppler broadening (DB) of the an ni hi la tion line. The shape of the annihilation line was characterized by the S parameter which represents a frac tion of positrons annihilating with low-momentum electrons. It was found that the virgin Nb films (i.e. free of hy dro gen) con tain a high den sity of defects. Nanocrystalline grain size leads to a sig nif i cant volume frac tion of grain bound aries con tain ing open volume vacancy-like defects. Thus, most of positrons annihilate from a trapped state in the open volume defects at grain boundaries. Subsequently, the films were step-by-step electrochemically charged with hydrogen and the evolution of microstructure with increasing hydrogen concentration was monitored. Hydrogen loading leads to a significant lattice expansion which was measured by XRD. Contrary to free standing bulk metals, the lattice expansion is highly anisotropic in thin films. The inplane expansion is prevented because the films are clamped to an elastically hard substrate. On the other hand, the out-of-plane expansion is substantially larger than in the bulk samples. Moreover, an enhanced hydrogen solubility in the a-phase in the nanocrystalline Nb films is found. Formation of the b-phase (NbH) starts at a hydrogen concentration of xH = 0.25 [H/Nb atomic ra tio], i.e. it is » 4 times higher than in bulk Nb. Using VEPAS it was found that hydrogen is trapped in vacancy-like de fects at grain bound aries. Hydrogen trapping leads to a local increase of the electron density in these defects and is reflected by a pronounced decrease of the S parameter in the hydrogen-loaded samples. Subsequently, when the hydrogen concentration exceeds xH = 0.02 [H/Nb], all available traps at grain bound aries are already filled with hydrogen and the S parameter does not change any more. Formation of the b-phase particles leads to an introduction of new de fects, which is reflected by an increase of the S parameter at xH > 0.25 [H/Nb].
Keywords: variable energy positron annihilation spectroscopy, niobium, hydrogen, vacancy-like defects, phase diagram
  • Open Access LogoMaterials Structure in Chemistry, Biology, Physics and Technology 13(2006), 82-89

Publ.-Id: 8829 - Permalink


Deep acceptor states in ZnO single crystals
von Wenckstern, H.; Pickenhain, R.; Schmidt, H.; Brandt, M.; Biehne, G.; Lorenz, M.; Grundmann, M.; Brauer, G.;
The authors report the observation of both acceptor- and donorlike defects in ZnO by deep level transient spectroscopy. The observation is facilitated by using a p-n junction allowing the injection of holes and electrons. The junction is realized by implanting a n-conducting ZnO wafer grown by pressurized melt growth with nitrogen ions. The authors found the commonly observed donorlike defects E1 and E3 and two acceptorlike defects A2 and A3, as well as a broad acceptorlike defect band. The thermal activation energies of A2 and A3, were determined to be about 150 and 280 meV, respectively.

Publ.-Id: 8827 - Permalink


Basic flow and its 3D linear stability in a small spherical droplet spinning in an alternating magnetic field
Shatrov, V.; Priede, J.; Gerbeth, G.;
We present a numerical analysis of the liquid metal flow and its 3D linear stability in a spherical droplet spinning in an alternating magnetic field. The applied magnetic field is uniform and the droplet spins around an axis parallel to the field. The droplet is assumed to be small so that its deformation by both electromagnetic and centrifugal forces is negligible. We find that a sufficiently fast spinning suppresses and so stabilizes the internal flow in the droplet. However, there is a narrow range of rotation rates corresponding to an Ekman number of E » 10-2 where the spinning can destabilize the internal flow. Our results can be useful for the assessment of melt flow conditions in certain material processing technologies using electromagnetic levitation melting techniques.
  • Physics of Fluids 19(2007)7, 78106

Publ.-Id: 8825 - Permalink


A simple approach to estimate the Performance Ratio of distributed PV plants
Rindelhardt, U.; Bodach, M.; Gasch, S.; Hiller, W.; Mehlich, H.;
The Performance Ratio (PR) is the most frequently used figure to characterize the quality of design and components of a photovoltaic power plant (PVP). It is usually calculated from the measured irradiation in the generator plane and the generated photovoltaic energy (final yield). Unfortunately, at the most PVPs no irradiation sensor is available.
The paper presents a simple approach to estimate the performance ratio from daily energy measurements and terrestrial irradiation measurements in the neighbourhood of the PVP. The approach is verified in Saxony, based on irradiance ground data collected by the Saxon agro-meteorological measuring network.
Keywords: PVP, Performance Ratio, PR
  • Contribution to proceedings
    21st European Photovoltaic Solar Energy Conference and Exhibition, 04.-8.9.2006, Dresden, Germany
    Proceedings, ISBN 3-936338-20-5, 2723-2725
  • Poster
    21st European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Deutschland

Publ.-Id: 8823 - Permalink


Fabrication of ultra-shallow p-n junctions as piezoresistive sensors for AFM deflection sensing
Zier, M.; Schmidt, B.; Rangelow, I.; Ivanov, T.; Sarov, Y.; Dontsov, D.; Schott, W.;
Piezoresistive deflection sensing is a promising approach for massively parallel AFM cantilever arrays. It is well known, that p-type Si exhibits piezoresistivity [1]. We have fabricated boron-doped piezoresistors in n-type Si with pn-junction depths down to 10-20 nm. For p-type Si layers below 10 nm it is known, that the piezoresistive coefficient in <110> direction is much larger than for bulk p-type Si due to quantum confinement effects [2]. This was achieved by a sophisticated process technology called point defect engineering (PDE). Using 400 keV Si+ ion irradiation a vacancy-rich layer near the wafer surface was created [3]. A 10nm thick boron layer was deposited as a solid source for subsequent diffusion using Rapid Thermal Annealing (RTA) at temperatures between 900°C and 1000°C. Secondary ion mass spectrometry (SIMS) analyses were carried out to obtain and compare the boron atomic concentration profiles. These show, that the transient enhanced diffusion of boron can be retarded by this fabrication method, and pn-junction depths of about 10-20 nm can be achieved. In comparison, pn-junctions were fabricated using low energy ion implantation of 1 keV B+ ions and subsequent RTA. SIMS profile analyses show, that the pn-junction depth is larger, but still in the range of <100 nm.
The sheet resistance of the fabricated ultra-thin p-doped layers were measured using a dedicated layout, which allows extracting the sheet resistance using conventional two-point probe measurements of U-I-characteristics. These measurements show, that the PDE fabricated layers exhibit a lower sheet resistance than the B+ implanted layers, even though the conducting layer thickness is smaller. This shows, that the PDE process not only yields very shallow pn-junctions, but also that the boron activation during RTA is improved compared to the ion implanted samples.
Finally we present sensitivity measurements for the completed cantilever chip, which show excellent sub-nm sensitivity.

[1] C. S. Smith, Phys. Rev. 94 (1954) 42
[2] T. Ivanov, PhD Thesis (2004), University of Kassel
[3] K.-H. Heinig and H.-U. Jäger, Proc. of 1st workshop of ENDEASD (European Network on Defect Engin. of Advanced Semiconductor Devices), C. Claeys, (ed.), Santorini, Greece, April 1999, p. 294
Keywords: ultra-shallow junction, point defect engineering, crystalTRIM
  • Poster
    Micro- and Nanoengineering 2006, 17.-20.09.2006, Barcelona, Espana

Publ.-Id: 8821 - Permalink


EXAFS study of the phosphodiester bond cleavage by Mo-containing polyoxometallates
van Deun, R.; Cartuyvels, E.; Nikitenko, S.; Hennig, C.; Parac-Vogt, T.;
- wird nachgereicht
  • Abstract in refereed journal
    Acta Crystallographica Section A 62(2006), 206-206

Publ.-Id: 8820 - Permalink


Electron transfer at the mineral/water interface: Selenium reduction by ferrous iron sorbed on clay
Charlet, L.; Scheinost, A.; Tournassat, C.; Greneche, J.; Géhin, A.; Fernández-Martínez, A.; Coudert, S.; Tisserand, D.; Brendle, J.;
The mobility and availability of the toxic metalloid selenium in the environment is largely controlled by sorption and redox reactions, which may proceed at temporal scales similar to that of subsurface water movement at saturated or unsaturated conditions. Since such waters are often anaerobic and rich in Fe2+, we investigated the long-term (£ 1 month) kinetics of selenite (Se(IV)O3-) sorption to montmorillonite in the presence of Fe2+ at anoxic condition. A synthetic montmorillonite was used to eliminate the influence of structural Fe. In the absence of aqueous Fe2+, selenite was sorbed as outer-sphere sorption complex, covering only part of the positive edge sites, as verified by a structure-based MUSIC model and Se K-edge X-ray absorption spectroscopy. When selenite was added to montmorillonite equilibrated with Fe2+ solution, however, slow reduction of Se and formation of a solid phase was observed with Se K-edge XANES (x-ray absorption near-edge spectroscopy) and EXAFS (extended x-ray absorption fine-structure) spectroscopy. Iterative transformation factor analysis of XANES and EXAFS spectra suggested that only one Se reaction product formed, which was identified as nano-particulate Se(0). Even after one month, only 75 % of the initially sorbed Se(IV) was reduced to this solid species.
Moessbauer spectrometry revealed that before and after addition and reduction of Se, 5 % of total sorbed Fe occurred as Fe(III) species on edge sites of montmorillonite (» 2 mmol kg-1). The only change observed after addition of Se was the formation of a new Fe(II) species (15 %) with d =
1.37 mm s-1 and DEQ = 3.76 mm s-1. The large quadrupolar splitting may indicate formation of an outer-sphere Fe(II)-Se sorption complex. The combined Moessbauer and XAS results hence clearly suggest that the Se and Fe redox reactions are not directly coupled. Based on the results of a companion paper, we hypothesize that the electrons produced in the absence of Se by oxidation of sorbed Fe(II) are stored, e.g. by formation of surface
H2 species, and are then available for the later Se(IV) reduction. The slow reaction rate indicates a diffusion controlled process. Homogeneous precipitation of an iron selenite was thermodynamically predicted and experimentally observed only in the absence of clay. Interestingly, half of Fe was oxidized in this precipitate (Moessbauer). Since DFT calculations predicted the oxidation of Fe at the water-Se solid interface only and not in the bulk phase, the average particle size of this precipitate would not exceed 2 nm. A comparison with the Moessbauer and XAS spectra of the clay samples demonstrates that such homogenous precipitation can be excluded as mechanism for the observed slow Se reduction, emphasizing the role of abiotic, heterogeneous precipitation and reduction for the removal of Se from subsurface waters.
  • Geochimica et Cosmochimica Acta 71(2007), 5731-5749

Publ.-Id: 8818 - Permalink


Synthesis of a new type of 99mTechnetium labeled fatty acids for myocardial metabolism imaging and their Rhenium analogues
Walther, M.; Bergmann, R.; Pietzsch, J.; Rode, K.; Mirtschink, P.; Stehr, S.; Heintz, A.; Wunderlich, G.; Kraus, W.; Pietzsch, H.-J.; Deussen, A.; Spies, H.;
Technetium-labelled fatty acids intended for myocardial metabolism imaging and the respective rhenium model complexes were synthesized according to the “4+1” mixed-ligand approach and investigated in vitro and in vivo. In “4+1” mixed-ligand Tc(III) and Re(III) complexes the metal is coordinated by both a tripodal tetradentate thiolato ligand and by a monodentate isocyano ligand bearing the biomolecule. High heart extraction in perfused heart studies (up to 26% ID) and noticeable heart uptake of the 99mTc tracer in vivo being in the order of 2% ID/g at 5 min p.i., accompanied by a good heart to blood ratio of 8, confirms that the new Tc-compounds are mimics of fatty acids.
  • Poster
    7th International Symposium on Technetium in Chemistry and Nuclear Medicine, 06.-09.09.2006, Bressanone, Italy
  • Contribution to external collection
    U. Mazzi: Technetium, Rhenium and other Metals in Chemistry and Nuclear Medicine, Padova: SGEditoriali, 2006, 88-89884-04-5, 113-114

Publ.-Id: 8817 - Permalink


Fluorescein-labeled stable neurotensin derivatives
Maes, V.; Hultsch, C.; Kohl, S.; Bergmann, R.; Hanke, T.; Tourwé, D.;
Neurotensin(8-13) analogs containing a glycine or 5-aminovaleroyl spacer were labeled with fluorescein through formation of a N-terminal thiourea function. The receptor binding was measured in HT-29 cell cultures and showed a substantial decrease in affinity, especially for the metabolically stabilized[MeArg9, Tle11] analog. Using fluorescence microscopy, the internalization of the fluorescent neurotensin analogs into HT-29 cells was observed.
Keywords: neurotensin; fluorescein; receptor binding; fluorescence microscopy

Publ.-Id: 8816 - Permalink


Hydration of U(VI,V) and Np(VI) Ions Revisited
Tsushima, S.; Scheinost, A.;
Hydration of uranyl(VI) ion has been a subject of both theoretical and experimental interests for many years. Most of recent publications from both theory and experimental sides agree that the uranyl(VI) ion in aqueous solution exists as 5-fold UO2(H2O)52+. In this work, we studied the hydration of uranyl(VI, V) and neptunyl(VI) ions in further accurate way by optimizing structures of AnO2(H2O)n2+/+ (n = 4, 5, 6) clusters at the DFT level in aqueous solution using polarizable continuum model (PCM); with special focus on the conformation of coordinating water molecules. A stable energy minimum with no imaginary vibrational frequency was found for UO2(H2O)52+ having U-Oax distance of 1.756 and 1.757Å, and U-Oeq distance of 2.428, 2.436, 2.441, 2.441, and 2.443Å. Three water planes stay perpendicular to the equatorial plane, while two water planes stay parallel to the equatorial plane. Structures and energies of 4-, and 5-fold uranyl(VI,V) and neptunyl(VI) hydrates were studied and compared with recent experimental data some of which suggest presence of 4-fold actinyl hydrates.
  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, ISBN 978-92-64-99006-7, 313-317
  • Poster
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany

Publ.-Id: 8815 - Permalink


Effect of Ni on the formation of defect-solute clusters in neutron irradiated iron alloys
Bergner, F.; Ulbricht, A.; Kammel, M.;
Irradiation of reactor pressure vessel (RPV) steels induces a degradation of the mechanical properties caused by the formation of nano-scale defect-solute clusters. Impurity Cu plays the major role in cluster formation, whereas the effect of the alloying element Ni depends on the Cu level and is not yet well understood.
The present experiment was devoted to the Ni effect. The SANS results for a Fe-3%Ni alloy, pure Fe and model alloys were reported.
Keywords: Small-angle neutron scattering, iron alloys, irradiation-induced cluster
  • Other report
    Berlin: BENSC Experimental Reports 2006, Hahn-Meitner-Institut, 2007
    1 Seiten

Publ.-Id: 8813 - Permalink


Flammenpyrolytische Oberflächenvorbehandlung von beschichteten Halbzeugen vor dem Kleben
Lebelt, P.; Gehrke, J.; Schütz, A.; Reuther, H.;
Flammenpyrolytische Oberflächenvorbehandlung von beschichteten Halbzeugen vor dem Kleben
  • Poster
    Thüringer Grenz- und Oberflächentage, 13.09.2006, Oberhof, Deutschland

Publ.-Id: 8812 - Permalink


Bio-nanotechnology/Nanocluster dank Bakterien
Raff, J.;
Nanotechnologie gilt als Zukunftstechnologie schlechthin. Auch die Biologie kann hier einen bedeutenden Beitrag leisten, zumal die wichtigsten "Bioobjekte" (DNA, Proteine ...) Nanoobjekte sind und damit die Biologie selbst höchst erfolgreich im Nanobereich "agiert".
Insbesondere die Hüllstrukturen vieler Bakterien, sogenannte S-Layer, bieten aufgrund ihrer Fähigkeit zur Selbstassemblierung und zur Ausbildung monolagiger hochgeordneter Gitterstrukturen neue Möglichkeiten zur Herstellung kleinster metallischer und halbleitender Nanocluster, Nanostrukturen und damit zur Entwicklung neuartiger (Biokomposit-)Materialien.
  • Lecture (others)
    Vortrag zum Besuch der japanischen Nano-Tech-Delegation, 26.09.2006, Dresden, Germany
  • Invited lecture (Conferences)
    Innovationsforum "Nanobasierte Umwelttechnik", 09.-10.11.2006, Jena, Germany
  • Lecture (others)
    Vortrag zum Besuch von Schülern der 11. und 12. Klasse (Chemie-LK) des Gymnasums Radeberg, 18.01.2007, Dresden, Germany

Publ.-Id: 8809 - Permalink


RBE of soft X-rays for chromosomal damage determined for two human mammary epithelial cell lines
Lehnert, A.; Beyreuther, E.; Enghardt, W.; Lessmann, E.; Pawelke, J.; Wagner, W.; Dörr, W.;
There is an ongoing discussion on the relative biological effectiveness (RBE) of low-energy X-rays below about 50 keV. Considering their wide application in diagnostic radiology and particularly in mammography, RBE has to be determined for an appropriate biological object. Further, the dependence on the photon energy distribution of the radiation sources has to be considered.
We have determined the effectiveness of low-energy X-rays by X-ray tube irradiation for two human mammary epithelial cell lines, MCF-12A and 184A1. For the soft X-ray irradiation, a tungsten-anode X-ray tube operated at either 10 kV (no filtration) or 25 kV (0.3 mm Al filter) was used. The reference radiation source was a 200 kV X-ray tube filtered with 0.5 mm Cu. The dose rate for all irradiations was 0.3 -1.9 Gy/min, and doses in the range 0.5 - 5 Gy were applied. The cytokinesis-block micronucleus (MN) test was used to assess chromosomal damage in the cell line MCF-12A. The fraction of binucleated cells (BNC) with MN, the number of MN per BNC and the number of MN per BNC with MN were determined for all radiation qualities. Additionally, chromosomal aberrations were studied by conventional Giemsa-staining in both cell lines. Dicentrics, rings and excess acentric fragments were assessed. In addition, first results will be presented on stable chromosome aberrations studied by whole-chromosome FISH painting of chromosomes 1, 8 and 17 for the cell line 184A1.
All data has been fitted to the linear-quadratic model. The soft X-rays were observed to be more effective in inducing radiation damage, RBE increasing with decreasing photon energy. Whereas the RBE for 25 kV X-rays determined by the MN test resulted in a value of 1.1 - 1.4, values of up to 3 were obtained for the 10 kV X-rays for the cell line MCF-12A. The chromosomal aberration data for both cell lines resulted in an RBE value of up to 2 for both soft X-ray radiation qualities.
The data obtained in the present work confirm the observations of other authors for the photon energy dependence of RBE in this energy range. However, the study of the detailed RBE dependence on photon energy is possible only at a monochromatic X-ray source. The progress in the installation of a quasi-monochromatic channelling radiation source at the ELBE accelerator at Forschungszentrum Rossendorf will be presented.
Keywords: RBE, soft X-rays, micronuclei, chromosomal aberrations, MCF-12A, 184A1, human mammary epithelial cells, ELBE
  • Lecture (Conference)
    The 35th Annual Meeting of the European Radiatiton Research Society, 22.-25.08.06, Kiev, Ukraina
  • Contribution to proceedings
    The 35th Annual Meeting of the European Radiatiton Research Society, 22.-25.08.2006, Kiev, Ukraine
    Book of Abstracts, 32

Publ.-Id: 8808 - Permalink


NMR-study on the structure and stability of 4-substituted aromatic iodosyl compounds
Hiller, A.; Patt, J. T.; Steinbach, J.;
Two 4-substituted aromatic iodosyl compounds were investigated with regard to their solubility, stability and chromatographic behaviour. 1-Iodosyl-4-methoxy- and 1-iodosyl-4-nitro-benzene are soluble in methanol and provide acceptable 1H and 13C NMR spectra; however, gradual oxidation of the solvent was observed. LC-MS analyses suggest that unlike the parent substance, iodosylbenzene, which has a polymeric structure, both compounds rather exist in the monomeric form.
Keywords: NMR; 1H NMR; 13C NMR; aromatic iodosyl compounds; oxidation; HPLC-MS

Publ.-Id: 8806 - Permalink


The use of the GDT based neutron source as driver in a sub-critical burner of minor actinides
Noack, K.;
The lecture is divided in two parts. First, as introduction on the subject, in part I a brief overview is given on the actual state in the area of transmutation of radioactive nuclear waste by means of reactors and driven sub-critical systems. In part II the application of the GDT-based neutron source as driver in a sub-critical system dedicated to the transmutation of minor actinides is discussed. This GDT driven minor actinide burner is compared with the corresponding accelerator driven system, which is presently considered as the favored option.
  • Lecture (others)
    Institutskolloquium des Budker Instituts Novosibirsk, 26.09.2006, Novosibirsk, Russia

Publ.-Id: 8793 - Permalink


A Comparative Study of U(V)O2+- and U(VI)O22+-Carbonato Complexes in Aqueous Solution
Ikeda, A.; Hennig, C.; Rossberg, A.; Scheinost, A.; Bernhard, G.; Mizuoka, K.; Ikeda, Y.;
The properties of pentavalent uranium have not been well understood yet, although a large number of studies have been performed and reported concerning the uranium chemistry up to now, because it is very unstable due to its disproportionation reaction to U(IV) and U(VI). At the moment, the uranyl tricarbonate complex, [UO2(CO3)3]n-, is the only known species that can be stabilized as U(V) in aqueous solution. In order to elucidate the properties of this complex in detail, we performed electrochemical (cyclic voltammetry) and spectroscopic (UV-visible absorption and XAFS) measurement.
From the electrochemical study, it was found that the UVO2+-carbonate complex was stable only in the limited concentration range of 0.8 M < [Na2CO3] < 1.4 M, and a Pt- or Au working electrode is more efficient to reduce UVIO22+ to UVO2+ than a glassy carbon electrode. Therefore, the UVO2+ samples for XAFS measurements were prepared in 1.4 M-Na2CO3 solution by using a Pt-mesh working electrode. The UVO2+ solution was transferred to a glass cuvette that was completely sealed by hot melting to avoid the possibility of any O2-penetration in the cuvette during sample transportation and measurement. The results of XAFS measurement indicated that both uranyl(V) and uranyl(VI) ions form the tricarbonate complex, [UO2(CO3)3]n- (n = 5 for uranyl(V) and 4 for uranyl(VI)). The coordination occurs in a bidentate manner and, in general, all bond lengths for the uranyl(V) complex were longer than those for the uranyl(VI) complex. Additionally, a chemical shift was also observed in the U LI- and LIII-XANES spectra.
  • Poster
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, ISBN 978-92-64-99006-7, 225-231

Publ.-Id: 8792 - Permalink


Investigation of Element Specific Hysteresis Loops of ion-induced Magnetically Patterned Ni81Fe19/Ru/Co90Fe10 Films with Magnetic Soft X-ray Microscopy.
Küpper, K.; Bischoff, L.; Mattheis, R.; Fischer, P.; Kim, D.-H.; Faßbender, J.ORC
We present a layer resolved magnetic soft x-ray microscopy study of a RKKY coupled Ni81Fe19/Ru/Co90Fe10 layered system where magnetic patterns were imprinted by using a 60 keV fine focused Co ion beam so as to change the coupling from antiferromagnetic to ferromagnetic on a micron scale. Thereby artificial structures in form of stripes with locally varying interlayer exchange coupling are generated. Utilizing the elemental specificity of high-resolution full field soft x-ray microscopy at the Co L3 and the Ni L3 edges we determined the magnetic domain configuration during full magnetization reversal processes locally and layer resolved. In addition to the locally varying interlayer exchange coupling across the Ru layer our data verify a direct exchange coupling within each ferromagnetic layer in the magnetically patterned structure. We conclude that the magnetization reversal behaviour of the irradiated
stripes is largely influenced by the surrounding magnetic film for both, the Permalloy and the Co90Fe10 layer.
Keywords: magnetism, RKKY, exchange coupling, magnetic patterning, x-ray microscopy, XMCD
  • Poster
    MRS Fall Meeting 2006, 27.11.-01.12.2006, Boston, USA

Publ.-Id: 8791 - Permalink


Ripple induced modifications of magnetic properties
Liedke, M. O.; Keller, A.; Facsko, S.; Fassbender, J.ORC
Self-organized ripple formation during ion erosion of a Si wafer is used to create a template system with a well defined roughness of uniaxial symmetry. By using special buffer layers subsequent thin magnetic film deposition by molecular beam epitaxy leads to a periodically modulated magnetic thin film with drastically modified magnetic properties with respect to a nominally “flat” film of the same thickness. In the case of Permalloy thin films, an enhancement of the uniaxial in-plane anisotropy by approximately a factor of 20 is observed (see Fig. 2). The enhancement can be explained by a combination of step induced dipolar and magnetocrystalline surface anisotropy contributions.
If a ferromagnet/antiferromagnet-bilayer is deposited a superposition of ripple-induced uniaxial anisotropy and exchange coupling induced unidirectional anisotropy is observed. Since the direction of the unidirectional anisotropy depends only on the magnetic field direction during a field cooling procedure any angle between both anisotropy contributions can be set. The observed angular dependence of the magnetization reversal behavior is in perfect agreement with simulations based on the Stoner-Wolfarth coherent rotation model.
Keywords: magnetism, ripples, ion errosion, magnetic anisotropy, exchange bias
  • Poster
    International Workshop on Nanomagnets by Self-Organization, 08.-11.10.2006, Eisenerz, Österreich
  • Lecture (Conference)
    MRS Fall Meeting 2006, 27.11.-01.12.2006, Boston, USA

Publ.-Id: 8790 - Permalink


Magnetic properties of thin magnetic films on rippled and smooth substrates
Fassbender, J.ORC
A review about the influence of the substrate, buffer layers and the substrate morphology on the magnetic properties of ultrathin films is presented.
Keywords: magnetism, ripple, ion erosion, exchange bias, magnetic anisotropies
  • Invited lecture (Conferences)
    Workshop on Properties of ultrathin magnetic films, 07.-09.09.2006, Bialowieza, Poland

Publ.-Id: 8789 - Permalink


Growth of carbon and carbon nitride thin films by low energy (~150 eV) N2/Ar ion assisted evaporation of C60
Berndt, M.; Vinnichenko, M.; Kreissig, U.; Abrasonis, G.; Kolitsch, A.; Möller, W.;
The influence of assisting low energy (~150 eV) ion bombardment during the deposition of evaporated C60 on the composition and bonding structure is investigated. Thin films were grown on Si (100) substrates by evaporation of C60 with assisting low-energy (~150 eV) N or Ar ion bombardment at different ion to molecule arrival ratios Iion/Imolecule (4-10) and substrate temperatures (RT-300°C). The film composition and areal density was analysed using elastic recoil detection analysis, while the obtained chemical bond structure was analysed by Raman spectroscopy. Spectroscopic ellipsometry was used to determine the film thickness. Raman spectra of the films grown without ion assistance show similar features as the Raman spectrum of initial C60 powder. The additional N or Ar assistance results in a decomposition of the C60 molecules independent of the ion type and Iion/Imolecule, resulting in a bonding structure similar to that observed in a-C or a-CNx. The N and Ar atomic ratios in the films (16-27 at. % for N and 2-4 at.% for Ar) are proportional to Iion/Imolecule and no saturation limit was reached under the present working conditions. The amount of deposited material decreases with increasing Iion/Imolecule for a given substrate temperature for both type of ions. Besides, it is observed that ion bombardment results in a densification of the films compared to the films obtained without ion assistance. The results are discussed on the basis of ion induced displacements of C atoms in the fullerene molecules resulting in a decomposition of the initial fullerene structure.
  • Poster
    Tenth International Conference on Plasma Surface Engineering - PSE 2006, 10.-15.09.2006, Garmisch-Partenkirchen, Germany
  • Contribution to proceedings
    International Doctoral Seminar 2006, 23.-26.04.2006, Smolenice, Slovak
    Proceedings, 14-18

Publ.-Id: 8788 - Permalink


Effect of the growth rate on the morphology and structural properties ofhut-shaped Ge islands in Si(001)
Yakimov, A. I.; Nikiforov, A. I.; Dvurechenskii, A. V.; Ulyanov, V. V.; Volodin, V. A.; Groetzschel, R.;
The effect of Ge deposition rate on the morphology and structural properties of self-assembled Ge/Si(001) islands was studied. Ge/Si(001) layers were grown by solid-source molecular-beam epitaxy at 500 ◦C. We adjusted the Ge coverage, 6 monolayers (ML), and varied the Ge growth rate by a factor of 100, R = 0.02–2 ML s−1, to produce films consisting of hut-shaped Ge islands. The samples were characterized by scanning tunnelling microscopy, Raman spectroscopy, and Rutherford backscattering measurements. The mean lateral size of Ge nanoclusters decreases from 14.1 nm at R = 0.02 ML s−1 to 9.8 nm at R = 2 ML s−1. The normalized width of the size distribution shows non-monotonic behaviour as a function of R and has a
minimum value of 19% at R = 2 ML s−1. Ge nanoclusters fabricated at the highest deposition rate demonstrate the best structural quality and the highest Ge content (∼0.9).
Keywords: Epitaxy; Germanium; Nanoclusters; Quantum dots
  • Nanotechnology 17(2006), 4743-4747

Publ.-Id: 8787 - Permalink


RBS-channeling, ERDA and XRD study of lithium tantalate modified by annealed proton echange (APE)
Mackova, A.; Salavkova, L.; Spirkova, J.; Grötzschel, R.; Eichhorn, F.;
Lithium tantalate (LT) single crystals are very promising substrates for constructing highly sophisticated photonics devices. The used
procedure for fabricating optical waveguides in them was annealed proton exchange (APE). Here we have used Rutherford backscattering
spectrometry (RBS) – channeling analysis, X-ray diffraction (XRD) and elastic recoil detection analysis (ERDA) to study changes in
the surface of the LT wafers caused by the APE treatment and to determine the concentration depth profiles of hydrogen atoms. The
measurements were taken for both virgin (untreated) and APE:LT samples fabricated using various experimental conditions. We have
found that the incorporation of hydrogen during the first step, i.e. the PE procedure (proton exchange), leads to modifications of the
structure of the LT single crystal, which gradually relaxed towards the structure of the original LT during the post-proton-exchange
annealing (A). This study also revealed a substantial dependence of sample behaviour on the crystallographic orientation of the pertinent
substrate wafers (commonly used X-(h1120i) and Z-(h0001i) cuts).
Keywords: RBS-channeling; ERDA; XRD;APE: LiTaO3
  • Nuclear Instruments and Methods in Physics Research B 249(2006), 339-342

Publ.-Id: 8786 - Permalink


How do high energy heavy ions shape Ge nanoparticles embedded in SiO2?
Schmidt, B.; Mücklich, A.; Röntzsch, L.; Heinig, K.-H.;
Crystalline Ge nanospheres embedded in SiO2 where irradiated at room temperature with fluences from 1x1015 to 4x1015 cm-2 of energetic J7+ ions. The spheres transform into amorphous oblate-like Ge nanoparticles, with the short axis aligned to the ion beam direction. This ion beam shaping is similar to that of free silica spheres, but differs from the prolate-like ion beam shaping of Au spheres embedded in SiO2.
Keywords: heavy ion irradiation, ion beam shaping, nanoparticles
  • Nuclear Instruments and Methods in Physics Research B 257(2007), 30-32
    DOI: 10.1016/j.nimb.2006.12.152
  • Lecture (Conference)
    15th International Conference on Ion Beam Modification of Materials, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 8785 - Permalink


X-ray diffraction spot mapping – a tool to study structural properties of semiconductor disk laser devices
Zeimer, U.; Grenzer, J.; Korn, D.; Döring, S.; Zorn, M.; Pittroff, W.; Pietsch, U.; Saas, F.; Weyers, M.;
The local lattice plane curvature of semiconductor disk laser devices were determined by a newly devel-oped X-ray spot mapping technique using white beam synchrotron radiation. This method is suited for in-situ studies of the dependence of both parameters on device temperature and on local heating by optical pumping. The influence of different device mounting procedures on the structural and optical device pa-rameters was investigated as well. This knowledge was used for device optimisation.
Keywords: SCDL laser, white beam synchrotron radiation, wafer mapping
  • Poster
    8th Biennial Conference on High Resolution X-Ray Diffraction and Imaging, 19.-22.09.2006, Baden-Baden/Karlsruhe, Germany
  • Physica Status Solidi (A) 204(2007)8, 2753-2759
    DOI: DOI 10.1002/pssa.200675655

Publ.-Id: 8784 - Permalink


Defect induced nanowire growth by FIB implantation
Bischoff, L.; Akhmadaliev, C.; Schmidt, B.;
In this work a defect induced formation of CoSi2 nanoparticles and nanowires is investigated and discussed. The results show that the defects created in silicon by FIB irradiation can getter Co atoms, solved in the sample before the ion beam treatment. Nanowires and nanoparticles are formed in the defect regions and are stabilized by following Ostwald ripening and can grow due to diffusion of the Co atoms during annealing. The nanowires are oriented in the <110> crystalline directions energetically favored for CoSi2 growth. Presumably this process is initiated by the formation of the well known {311}-extended rod-like defects elongated in those <110> directions.
Keywords: mass separated FIB; implantation, defects, annealing, nanowire growth.
  • Lecture (Conference)
    32nd International Conference on Micro- and Nano-Engineering 2006, 17.-21.09.06, Barcelona, Spain
  • Microelectronic Engineering 84(2007), 1459-1462

Publ.-Id: 8783 - Permalink


A statistical analysis of polarity reversals of the geomagnetic field
Sorriso-Valvo, L.; Carbone, V.; Stefani, F.; Nigro, G.;
We investigate the temporal distribution of polarity reversals of the geomagnetic field. In spite of the commonly assumption that the reversal sequence can be modeled as a realization of a renewal Poisson process with a variable rate, we show that the polarity reversals strongly depart from a local Poisson statistics. The origin of this failure can be attributed to the presence of temporal clustering. We also show that a Lévy function is able to reproduce the distribution of polarity persistence times, thus suggesting the presence of long-range correlations in the underlying dynamo process. In this framework we compare our results with the behavior of some toy models that describe the time evolution of the reversals and with MHD geodynamo numerical simulations.
  • Lecture (Conference)
    AGU 2006 Fall Meeting, 11.-15.12.2006, San Francisco, United States
  • Physics of the Earth and Planetary Interiors 164(2007), 197-207
    DOI: 10.1016/j.pepi.2007.07.001
  • Abstract in refereed journal
    Eos, Transactions, American Geophysical Union 87(2006)52, GP21B-1308

Publ.-Id: 8781 - Permalink


Defect induced formation of CoSi2 nanowires by focused ion beam synthesis
Akhmadaliev, C.; Schmidt, B.; Bischoff, L.;
Cobalt implantation with a focused ion beam (FIB) was applied to study ion beam synthesis of cobalt disilicide nanowires in silicon. Two mechanisms of CoSi2 nanowire formation were investigated: (a) conventional synthesis by Co++ FIB implantation at elevated temperatures into silicon along in-plane <110> Si crystal direction and subsequent annealing, and (b) self-aligned CoSi2 nanowire growth in Co supersaturated silicon on FIB-induced defects at RT during subsequent annealing. The obtained CoSi2 nanowires are 20-100 nm in diameter and several micrometers long.
Keywords: nanowire, cobalt disilicide, focused ion beam, defects

Publ.-Id: 8780 - Permalink


Untersuchungen zur Aufnahme von Organika aus natürlichen Wässern durch Ionenaustauscher mit C-14-markierten Modellsubstanzen
Ender, V.; Schumann, T.; Sachs, S.; Bernhard, G.;
Untersucht wurde die Aufnahme C-14-markierter Modellsubstanzen (beta-Alanin, Stärke und synthetische Huminsäure M42) durch Anionenaustauscher und ihre korrespondierenden nichtfunktionalisierten Copolymere. Die Modellsubstanzen stehen für die TOC-Fraktionen der Neutralstoffe / Amphiphile, Polysaccharide und Huminstoffe enstprechender der LC-OCD-Methode von HUBER. Variiert wurden der Salzgehalt resp. der pH-Wert und die Temperatur bei der Beladung...
  • Contribution to proceedings
    VGB-Konferenz "Chemie im Kraftwerk 2006" mit Fachausstellung, 11.-12.10.2006, Bad Neuenahr, Germany
    Proceedings VGB-Konferenz "Chemie im Kraftwerk 2006", TB 442/P11, 13
  • Lecture (Conference)
    VGB-Konferenz "Chemie im Kraftwerk 2006" mit Fachausstellung, 11.-12.10.2006, Bad Neuenahr, Germany

Publ.-Id: 8779 - Permalink


GaBi liquid metal alloy ion source for the production of ions of interest in microelectronics research
Bischoff, L.; Pilz, W.; Ganetsos, T.; Forbes, R.; Akhmadaliev, C.;
Focused Ion beam (FIB) systems employing liquid metal ion sources (LMISs) have become of increasing importance in the microelectronics research and industry [1]. Applications of LMISs include IC analysis and modification, maskless ion implantation, secondary ion mass spectroscopy, scanning ion microscopy and ion beam lithography [2-3].
Alloy LMISs are the basis of mass separated FIB systems applying a variety of ion species which can be focused into diameters smaller than 10nm with current densities of several A/cm2 [4].
In this work a Ga38Bi62 alloy liquid metal ion source (Tmelt = 222°C), prepared on a mechanical treated Ta - emitter has been studied, which allows to implant in the case of a silicon substrate shallow donor ions (Bi) as well as acceptors (Ga) in the sub micron range without changing the source. A detailed analysis of the mass spectra as a function of emission current, obtained from this source, shown in Fig. 1, was used to investigate the mechanism for the production of single and double-charged ions. The transition metals in the mass spectra result from the re-sputtered extractor stainless steal material. Moreover, we represent the intensity of cluster ions extracted by the source, as function of emission current. Theoretical modeling support the experimental results.
[1]P.D. Prewett, G.L.R. Mair, Focused Ion Beams from Liquid Metal Ion Sources,
Taunton, Somerset, UK: Research Studies Press, 1991, Chap. 2.
[2]J. Orloff et al, High Resolution Focused Ion Beams – FIB and Its Applications,
Kluwer Academic / Plenum Publishers, 2002, Chap. 6.
[3]L. Bischoff, J. Teichert, S. Hausmann, Th. Ganetsos and GLR. Mair, Microelectronic Engineering, 53 (2000) 613.
[4]L. Bischoff, Ultramicroscopy, 103 (2005) 59.
Keywords: Alloy liquid metal ion source, GaBi, mass spectra
  • Lecture (Conference)
    The Joint 19th International Vacuum Nanoelectronics Conference and 50th International Field Emission Symposium, 17.-20.07.2006, Guilin, China
  • Ultramicroscopy 107(2007)9, 865-868

Publ.-Id: 8778 - Permalink


Planar channeling radiation from electrons in quartz
Azadegan, B.; Wagner, W.; Pawelke, J.; Grigoryan, L. S.;
Planar channeling radiation from 32 MeV electrons channeled in quartz has for the first time been measured at the radiation source ELBE. The theory of channeling radiation was applied for the assignment of the observed spectra to the crystal planes. Calculations of the continuum potentials, transverse electron states, transition energies, and radiation intensities have been performed for selected planes of quartz. Specific properties of the hexagonal binary quartz crystal influencing the generation of channeling radiation are discussed.
Keywords: Channeling radiation, X-rays, quartz
  • Contribution to proceedings
    "Channeling 2006", International Conference on Charged and Neutral Particles Channeling Phenomena II, 03.-07.07.2006, Frascati (Rome), Italy
    Proceedings of the International Conference on Charged and Neutral Particles Channeling Phenomena II, Bellingham (USA): SPIE, 9780819467782, 66340S
  • Lecture (Conference)
    "Channeling 2006", International Conference on Charged and Neutral Particles Channeling Phenomena II, 03.-07.07.2006, Rom, Italy

Publ.-Id: 8777 - Permalink


Deposition and Re-emission of Potential Energy - extended dynamical COB simulation -
Kost, D.; Röder, F.; Möller, W.;
We present results of a numerical computer simulation based on the extended dynamical classical over the barrier model (EDCOB). To get an energy balance for the transferred potential energy of the highly charged ions (HCIs) to the solid surface, we apply an additional extension of the model evaluating the energy loss of Auger electrons which are generated during the relaxation of the HCI. From the results of the simulation we can distinguish between the potential energy deposited in the nuclear system due to image charge acceleration of the incoming HCI and the potential energy which is released over Auger processes. Further, we break down this energy into that which is deposited in the solid and that which is re-emitted due to escaping secondary electrons.
  • Open Access LogoJournal of Physics: Conference Series 58(2007), 343
  • Poster
    13th International Conference on the Physics of Highly Charged Ions, 27.08.-01.09.2006, Belfast, Northern Ireland, UK

Publ.-Id: 8776 - Permalink


Subthreshold production of Sigma(1385) baryons in Al+Al collisions at 1.9A GeV
Lopez, X.; Herrmann, N.; Crochet, P.; Andronic, A.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Bühler, P.; Cargnelli, M.; Caplar, R.; Cordier, E.; Dupieux, P.; Dzelalija, M.; Fabietti, L.; Fodor, Z.; Gasparic, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Kim, Y. J.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Marton, J.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zmeskal, J.; Kienle, P.; Yamazaki, T.;
First deep sub-threshold production of the Sigma(1385) hyperon resonance is presented. The measurement was performed in Al+Al collisions at a beam energy of 1.9A GeV with the FOPI detector at GSI-Darmstadt. The result is found to be in relatively good agreement with the statistical model prediction. It allows to better understand strangeness sub-threshold production by leading information on the strangeness exchange reaction which is the dominant process for K- production below and close-to threshold.

Publ.-Id: 8775 - Permalink


Structure and conductivity of self-assembled films of gold nanoparticles
Pelka, J. B.; Brust, M.; Gierlowski, P.; Paszkowicz, W.; Schell, N.;
Self-assembled thin films of gold nanoparticles of 4-5 nm, prepared on glass using aliphatic dithiols of different hydrocarbon chain lengths as interparticle linker molecules, have been studied by x-ray methods and dc conductivity. X-ray data revealed small spacer-dependent cluster size variations in the films. Conductivity, in the temperature range of 4.2-300 K, showed a strong relation with spacer length, indicating that different mechanisms of conduction from metal-like through hopping to tunneling dominate, depending on temperature range and particle spacing. The results demonstrate that the electronic and optical properties of such films can be precisely controlled by interparticle distance.
  • Applied Physics Letters 89(2006), 063110

Publ.-Id: 8774 - Permalink


Nitrogen Plasma Íon Implantation of Al Alloy in the High Voltage Glow Discharge Mode
Oliveira, R. M.; Ueda, M.; Rossi, J. O.; Reuther, H.; Lepienski, C. M.; Beloto, A. F.;
Nitrogen Plasma Íon Implantation of Al Alloy in the High Voltage Glow Discharge Mode
  • Lecture (Conference)
    International Conference on Íon Implantation Technology, 11.-16.06.2006, Marseille, France

Publ.-Id: 8773 - Permalink


Plasma Immersion Ion Implantation with a 4 kV/10kHz Compact High Voltage Pulser
Ueda, M.; Oliveira, R. M.; Rossi, J. O.; Reuther, H.; Silva, G.;
Plasma Immersion Ion Implantation with a 4 kV/10kHz Compact High Voltage Pulser
  • Lecture (Conference)
    6th International Conference on Íon Implantation Technology, 11.-16.06.2006, Marseille, France

Publ.-Id: 8772 - Permalink


Implantação Iônica por Imersão em Plasma de Nitrogênio Usando Baixa Energia
Silva, G.; Ueda, M.; Rossi, J. O.; Reuther, H.;
Implantação Iônica por Imersão em Plasma de Nitrogênio Usando Baixa Energia
  • Contribution to proceedings
    XII Encontro e Exposição Brasileira de Tratamentos de Superfície & II INTERFINISH Latino- Americano, 09.-11.05.2006, Sao Paulo, Brazil
    Proceedings of XII Encontro e Exposição Brasileira de Tratamentos de Superfície & II Interfinish Lat, paper 33

Publ.-Id: 8771 - Permalink


Hybrid Processing of Ti-6Al-4V Using Plasma Immersion Ion Implantation Combined with Plasma Nitriding
Silva, M. M.; Ueda, M.; Otani, C.; Reuther, H.; Lepienski, C. M.; Soares Jr, P. C.; Otubo, J.;
Hybrid Processing of Ti-6Al-4V Using Plasma Immersion Ion
Implantation Combined with Plasma Nitriding
  • Open Access LogoMaterials Research 9(2006)1, 97-100

Publ.-Id: 8770 - Permalink


Numerical and experimental modeling of the melt flow in a traveling magnetic field for Vertical Gradient Freeze crystal growth
Galindo, V.; Grants, I.; Lantzsch, R.; Pätzold, O.; Gerbeth, G.;
A Traveling Magnetic Field (TMF) is attractive for melt crystal growth as it offers a direct flow driving mechanism. We present numerical and experimental results on the TMF driven flow in an isothermal model fluid. The TMF is generated by a system of six equidistant coils, which are fed by a three phase current power supply to create an up- or downward directed traveling field. Special attention is focused on the description of the electromagnetic fields for varying field frequency, and its influence on the resulting melt velocity.
Keywords: Fluid Flows, Magnetic Fields, Stirring, Crystal Growth
  • Journal of Crystal Growth 303(2007), 258-261
    DOI: 10.1016/j.jcrysgro.2006.11.194
  • Lecture (Conference)
    5th International Workshop on Modeling in Crystal Growth, 10.-13.09.2006, Bamberg, Germany

Publ.-Id: 8769 - Permalink


Thin film patterning by surface-plasmon-induced thermocapillarity
Röntzsch, L.; Heinig, K.-H.; Schuller, J. A.; Brongersma, M. L.;
It is reported that standing surface-plasmon-polariton (SPP) waves can cause regular thickness undulations of thin polymethyl methacrylate (PMMA) films above a metallic substrate. Ripples and hillock arrays with long-range order were found. Numerical calculations reveal that periodic in-plane temperature profiles are generated in the PMMA due to the non-radiative damping of SPP interference patterns. Atomistic computer simulations on the temperature-gradient-driven mass transport confirm that thermocapillarity is the dominating mechanism of the observed surface patterning.
Keywords: Thermocapillarity, surface plasmon lithography, ploymer, PMMA, laser irradiation, thin films

Publ.-Id: 8768 - Permalink


The structure of soddyite-exafs shell fitting and wavelet analysis
Funke, H.; Hennig, C.; Scheinost, A.;
Many uranyl (U(VI)) minerals have a characteristic layer structure in the equatorial plane due to the strong electrovalence of the two axial oxygen atoms. For structures containing heavy atoms like U, the XRD patterns are dominated by the backscattering from the heavy atoms, while the positions of light atoms like O or Si may be occasionally inaccurate. The EXAFS spectrum were measured of a soddyite sample of Renaud Vochten’s collection of uranium minerals at 30 K. The local structure determined by shell fitting is fairly consistent with crystallographic data. Wavelet analysis clearly resolved the Si and U atoms at nearly the same distance between 3.6 and 3.9 Å.
  • Poster
    4th Workshop on Speciation, Techniques, and Facilities for Radioactive Materials at Synchrotron Light Sources (Actinide XAS 2006), 18.-20.09.2006, Karlsruhe, Germany
  • Contribution to proceedings
    Actinide XAS 2006, 18.-20.09.2006, Karlsruhe, Germany
    Speciation Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources: OECD, 978-92-64-99006-7, 211

Publ.-Id: 8767 - Permalink


Radioimmunotherapy of solid tumors by targeting extra domain B fibronectin: identification of the best-suited radioimmunoconjugate.
Berndorff, D.; Borkowski, S.; Sieger, S.; Rother, A.; Friebe, M.; Viti, F.; Friebe, M.; Hilger, C. S.; Cyr, J. E.; Dinckelborg, L. M.;
PURPOSE: The expression of extra domain B (ED-B) fibronectin is always associated with angiogenic processes and can be exclusively observed in tissues undergoing growth and/or extensive remodeling. Due to this selective expression, ED-B fibronectin is an interesting target for radioimmunotherapy of malignant diseases. The aim of this study was to identify the most appropriate ED-B-targeting radioimmunoconjugate for the therapy of solid tumors. EXPERIMENTAL DESIGN: Three ED-B fibronectin-binding human antibody formats of L19 were investigated: dimeric single-chain Fv (approximately 50 kDa), "small immunoprotein" (SIP, approximately 80 kDa), and immunoglobulin G1 (IgG1, approximately 150 kDa). These L19 derivatives were either labeled with I-125 or with In-111 (using MX-diethylenetriaminepentaacetic acid, MX-DTPA). Pharmacokinetics and tumor accumulation of the radiolabeled immunoconjugates were investigated in F9 (murine teratocarcinoma) tumor-bearing mice. Subsequently, dosimetry for the corresponding therapeutic isotopes I-13-1 and Y-90 was done. After testing the myelotoxicity of I-131-L19-SIP and I-131-L19-IgG1 in non-tumor-bearing mice, the therapeutic efficacy of these iodinated antibody formats was finally investigated in F9 tumor-bearing mice. RESULTS: The most favorable therapeutic index was found for I-131-L19-SIP followed by I-131-L19-IgG1. The therapeutic index of all In-111-labeled derivatives was significantly inferior. Considering the bone marrow as the dose-limiting organ, it was calculated that activities of 74 MBq I-131-L19-SIP and 25 MBq I-131-L19-IgG1 could be injected per mouse without causing severe myelotoxicity. The best therapeutic efficacy was observed using I-131-L19-SIP, resulting in significant tumor growth delay and prolonged survival after a single injection. CONCLUSION: Compared with other L19-based radioimmunoconjugates, I-131-L19-SIP is characterized by superior antitumor efficacy and toxicity profile in the F9 teratocarcinoma animal model. These results indicate that ED-B fibronectin-targeted radioimmunotherapy using I-131-L19-SIP has potential to be applied to treatment of solid cancers.
  • Clinical Cancer Research 11(2005), 7053s-7063s

Publ.-Id: 8766 - Permalink


In vivo magnetic resonance imaging and spectroscopy of various adipose tissue deposits in mice
Strobel, K.; van den Hoff, J.; Pietzsch, J.;
An emerging paradigm supports the view that adipose tissue (AT) dysregulation might play a crucial role in the pathogenesis of insulin-resistance, atherosclerosis, and other disease states. In the last years, rodent models have played an important role in the investigation of AT biology and disorder. In this line, non-invasive differentiation and characterization of various AT deposits in the living animal is a current challenge. In the present paper, magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques are applied for quantitative in vivo evaluation of superficial and mediastinal brown adipose tissue (BAT), as well as subcutaneous and intra-abdominal white adipose tissue (WAT) deposits in mice.
All experiments were carried out in NMRI mice and nude mice aging from 8 to 24 weeks. Morphological differentiation between various BAT and WAT deposits was obtained by 1H-MRI at 7 Tesla using a Biospec 70/30 (Bruker, Germany). Images were obtained with high spatial resolution of 156 microns (field of view 4 x 4 cm, matrix size 256 x 256; slice thickness 1.5 to 3 mm). Furthermore, 1H-MRS has been performed to quantify in vivo the different lipid patterns in BAT and WAT deposits using a volume selective PRESS sequence on 3 to 8 mm^3 voxels.
In both nude mice and NMRI mice the various BAT and WAT deposits were clearly distinguished from the non-AT tissue with excellent contrast by T1-weighted MSME MRI sequences. Comparison of MR images with corresponding histological whole-animal sections indicated high specificity and sensitivity of the MRI sequences applied. The high resolution spectra obtained at 7 T allow identification of at least 9 different proton resonances specific for lipids, and thus, for calculation of mono- to polyunsaturated fatty acid ratio in vivo. In this study, nude mice showed a 1.5- to 3-fold higher degree of unsaturation and polyunsaturation of triglyceride fatty acid acyl chains in BAT when compared to NMRI mice. No differences were observed in WAT deposits.
High-resolution MRI and MRS are potentially useful tools for studying the biology of different BAT and WAT deposits non-invasively in small experimental animals in vivo.
  • Poster
    ESMRMB 23. Annual Scientific Meeting, European Society for Magnetic Resonance in Medicine and Biology, 21.-23.09.2006, Warsaw, Poland
  • Abstract in refereed journal
    Magnetic Resonance Materials in Physics, Biology and Medicine 19(2006)Suppl. 1, 236

Publ.-Id: 8765 - Permalink


β´´-(ET)2SF5CH2CF2SO3 - a layered 2D metal with vanishing interlayer coupling
Wosnitza, J.;
  • Invited lecture (Conferences)
    International Symposium on Crystalline Organic Metals, Superconductors and Ferromagnets (ISCOM2005), 11.-16.09.2005, Key West, USA

Publ.-Id: 8763 - Permalink


Recent developments at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields - V, 05.-09.08.2005, Tallahassee, USA

Publ.-Id: 8762 - Permalink


Metalle in hohen Magnetfeldern
Wosnitza, J.;
  • Invited lecture (Conferences)
    Physikalisches Kolloquium der Universität Konstanz, 05.07.2005, Konstanz, Deutschland

Publ.-Id: 8761 - Permalink


Coil design for non-destructive pulsed-field magnets targeting 100 T
Zherlitsyn, S.; Bianchi, A. D.; Hermannsdörfer, T.; Pobell, F.; Skourski, Y.; Sytcheva, A.; Zvyagin, S. A.; Wosnitza, J.;
Progress and recent achievements in coil design are presented for the new Dresden High Magnetic Field Laboratory (HLD), which is under construction at the Forschungszentrum Rossendorf. This laboratory is planned to be open for external users in 2007. The facility is placed near a free electron laser which will offer the opportunity to perform infrared spectroscopy in pulsed magnetic fields. Implementation of various experimental techniques, such as transport, magnetization, specific heat, ultrasound, and magnetic resonance in pulsed magnetic fields up to 100 T are planned. Typical pulse durations will be in the range between 10 and 1000 ms with magnet bores ranging from 20 to 40 mm. The pulsed magnets will be energized by a 50 MJ/24 kV modular capacitive pulsed-power supply. With our newly designed coils, so far we were able to reach 65 T in a non-destructive manner. These coils are built using regular copper wire reinforced with an organic fiber (Zylon). Pulse durations for the various coils are between 20 and 50 ms. Different magnet failure modes have been analysed and possible improvements of the magnets are discussed.
We also present numerical simulations of our pulsed magnets.
  • IEEE Transactions on Applied Superconductivity 16(2006), 1660

Publ.-Id: 8760 - Permalink


Metals at high magnetic fields
Wosnitza, J.;
es hat kein Abstract vorgelegen.
  • Invited lecture (Conferences)
    Seminar at the Laboratoire National des Champes Megnétiques Pulsés (CNRS-LNCMP), 15.03.2005, Toulouse, France
  • Invited lecture (Conferences)
    Seminar at the International Max-Planck Research School, Dresden, 13.07.2005, Dresden, Deutschland

Publ.-Id: 8759 - Permalink


Increase of blue electroluminescence from Ce-doped SiO2 layers through sensitization by Gd3+ ions
Sun, J. M.; Prucnal, S.; Skorupa, W.; Helm, M.; Rebohle, L.; Gebel, T.;
Efficient blue electroluminescence peak at around 440 nm with a maximum output power density of 34 mW/cm2 was obtained from Ce and Gd coimplanted metal-oxide-semiconductor light emitting devices. Energy transfer from Gd3+ to Ce3+ ions was observed during the excitation process, leading to a more than threefold increase of the external quantum efficiency of the blue Ce3+ luminescence up to 1.8%. This is evidenced by the increase of the excitation cross section of Ce3+ ions from 4.8x10−13 to 3.5x10−12 cm2 and the simultaneous reduction of the decay time and the impact
cross section of Gd3+ ions.
Keywords: Si light emitter, electroluminescence, rare earth

Publ.-Id: 8758 - Permalink


Extraction of radio-labelled xanthine derivatives by artificial receptors – deep insight into the association behaviour
Bomkamp, M.; Siering, C.; Landrock, K.; Stephan, H.; Fröhlich, R.; Waldvogel, S. R.;
Association constants for the interaction of almost insoluble substrates with triphenylene ketal-based receptors in toluene have been determined by means of an extraction method employing the corresponding radio-labelled substrates. Flexible and more polar receptors tend to aggregate and exhibit inferior extraction qualities. Binding constants in toluene were found to be in the range 105–107M-1 which is significantly higher than in dichloromethane.
X-ray analyses indicate the direct participation of a water molecule in the binding process, which may account for the surprisingly small effect of moisture in the solvent on the stability of the complexes.
Keywords: caffeine · extraction · isotopic labelling · receptors · supramolecular chemistry

Publ.-Id: 8757 - Permalink


The new Seattle-TRIUMF 7Be(p,γ)8B S-factor determination
Junghans, A. R.; Mohrmann, E. C.; Snover, K. A.; Steiger, T. D.; Adelberger, E. G.; Casandjian, J. M.; Swanson, H. E.; Buchmann, L. R.; Laird, A.; Zyuzin, S. P. A. Y.;
We present new measurements of the 7Be(p,γ)8B cross section from ‏‾Ecm = 116 to 2460 keV. Our new measurements lead to S17(0) = 22.1 ± 0.6(expt) ± 0.6(theor) eV b, where the central value is based on the theory of Descouvemont and Baye. We recommend a “best” value, S17(0) = 21.4 ± 0.5(expt) ± 0.6(theor) eV b, based on the mean of all modern direct measurements below the 1+ resonance.

Publ.-Id: 8756 - Permalink


Structure analysis of actinide compounds in solution by X-ray absorption spectroscopy
Hennig, C.;
Actinides with their large number of oxidation states are susceptible to redox conditions, forming different complexes in aqueous solution which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their complex species distribution and thermodynamic metastability. Thermodynamic estimation of species distribution may fail for higher actinide concentrations. In such cases X-ray absorption spectroscopy is able to reveal structural parameters that provide information on the solution species. A spectroelectrochemical cell was developed for the study of structure and speciation of actinide complexes in situ by X-ray absorption spectroscopy, while applying and maintaining a constant potential. This equipment allows the investigation of actinide complexes under different redox conditions. An overview about the actual knowledge of actinides coordination in valence states III, IV, V, VI and VII in aqueous solution will be given.
Keywords: EXAFS, coordination, An(III), An(IV), An(V), An(VI), An(VII)
  • Invited lecture (Conferences)
    23nd European Crystallographic Meeting, 06.-11.08.2006, Leuven, Belgium
  • Abstract in refereed journal
    Acta Crystallographica Section A 62(2006), 61

Publ.-Id: 8749 - Permalink


Mo K-edge EXAFS investigation of the [Mo7O24]6- promoted phosphate ester hydrolysis
van Deun, R.; Hennig, C.; Cartuyvels, E.; Nikitenko, S.; Parac-Vogt, T. N.;
The early transition metals (V, Nb, Ta, Mo, W) in their high oxidation states are able to form metal-oxygen clusters, commonly referred to as polyoxometallates (POMs). The diverse structures and compositions of polyoxometallates offer a wide versatility in terms of shape, polarity, redox potentials, surface charge distribution and acidity, and allow for numerous potential applications of POMs. The first reports describing the antitumoral activity of POMs appeared about ten years ago, and they have revealed that the antitumoral activity of [Mo7O24]6- is even better than that of commercial drugs. We have investigated the potential towards phosphate ester bond cleavage of the [Mo7O24]6- cluster.
Keywords: EXAFS, polyoxometallate, anti-tumor activity
  • Poster
    23nd European Crystallographic Meeting, 06.-11.08.2006, Leuven, Belgium
  • Abstract in refereed journal
    Acta Crystallographica Section A 62(2006), s206

Publ.-Id: 8748 - Permalink


A comparative UV-Vis and EXAFS investigation of the coordination of the uranyl ion UO22+ in solution
Servaes, K.; Hennig, C.; van Deun, R.; Görller-Walrand, C.;
The identification of uranyl complexes in solution is not always straightforward. Unlike crystal structures, which can be revealed by X-ray diffraction, the structure of solution species could only be indicated in the past by means of spectroscopic techniques (UV-Vis absorption spectroscopy, luminescence, magnetic circular dichroism). These methods demonstrated the existence of a uranyl tetrachloro complex [UO2Cl4]2- with D4h coordination symmetry and a uranyl trinitrato complex [UO2(NO3)3]- with D3h symmetry in non-aqueous solution, based on their characteristic absorption spectra.Nowadays, limited structural parameters of solution species can be determined using Extended X-ray Absorption Fine Structure (EXAFS). The complex formation of the uranyl ion UO22+ with small inorganic ligands like Cl- and NO3- in non-aqueous solution was investigated using U LIII EXAFS spectroscopy and UV-Vis absorption spectroscopy. Both techniques confirm the existence of a [UO2Cl4]2- limiting species with D4h symmetry as well as a [UO2(NO3)3]- limiting species with D3h symmetry in acetonitrile solution. The distances in the U(VI) coordination sphere of [UO2Cl4]2- are U-Oax = 1.77 ± 0.01 Ǻ and U-Cl = 2.68 ± 0.01 Ǻ. For [UO2(NO3)3]- the distances in the U(VI) coordination sphere are U-Oax = 1.77 ± 0.01 Ǻ and U-Oeq = 2.49 ± 0.01 Ǻ. The U-N distance of 2.94 ± 0.01 Ǻ points at a bidentate coordination mode of the nitrate group.
Keywords: UV-vis, EXAFS, uranium complexes, nonaqueous solution
  • Poster
    23rd European Crystallographic Meeting, 06.-11.08.2006, Leuven, Belgium
  • Abstract in refereed journal
    Acta Crystallographica Section A 62(2006), 205

Publ.-Id: 8747 - Permalink


Comparison of in vitro and in vivo properties of 99mTc-cRGD peptides labelled using different novel Tc-cores
Decristoforo, C.; Santos, I.; Pietzsch, H.-J.; Duatti, A.; Smith, C. J.; Rey, A.; Alberto, R.; von Guggenberg, E.; Haubner, R.;
The alphavbeta3 integrin is involved in angiogenesis and tumor metastasis. RGD-peptides bind with high affinity to this integrin. This study compares the influence of 99mTc-labelling applying novel Technetium-cores on imaging characteristics of the radiolabelled peptide. Different peptide conjugates based on the cyclic pentapeptide c(RGDyK) (cRGD) were prepared and characterised (HYNIC-, Cys-, L2- and Pz1-cRGD). Radiolabelling experiments using different coligands for HYNIC-cRGD, the 99mTc(CO)3 metal fragment for PZ-1-cRGD (pyrazolyl-derivative), the Tc-nitrido-core using a phosphine-coligand (PNP) for Cys-cRGD and an isonitrile–conjugate (L2-cRGD) together with a NS3-coligand (4+1 concept) were performed and showed labelling yields >90% at high specific activities. A high in vitro stability was observed, plasma protein binding and lipophilicity varied considerably between different radiolabelled cRGD conjugates. Experiments on biological activity of the radiolabelled peptides using alphavbeta3 positive (M21) and negative (M21L) tumour cells did show specific uptake of various conjugates. Studies in tumour bearing animals revealed significant differences between different conjugates concerning pharmacokinetic behaviour (predominant renal excretion to considerable hepatobiliary clearance) as well as tumour uptake (0.2-2.7%ID/g). Highest specific tumour uptake and tumour/background values were found for 99mTc-EDDA/HYNIC-c(RGDyK), 99mTc-Nitrido-PNP-Cys-c(RGDyK) and 99mTc(CO)3-Pz1-c(RGDyK). In conclusion, using novel Tc-cores such as the 99mTc(CO)3 metal fragment, Tc-nitrido- and the 4+1 concept peptides could be labelled with 99mTc-technetium at high specific activities resulting in complexes with high stability, but binding moieties have to be optimized especially concerning hydrophilicity resulting in renal rather than hepatobiliary excretion. This comparative study underlines that peptide labelling strategies using 99mTc have to be properly selected and optimized. Different in vitro assays are necessary to predict targeting properties in vivo.
  • Quarterly Journal of Nuclear Medicine and Molecular Imaging 51(2007), 33-41

Publ.-Id: 8746 - Permalink


Röntgenographische Elektronendichtebestimmung von unterschiedlich synthetisierten YNi2B2C-Einkristallen
Leisegang, T.; Meyer, D. C.; Paufler, P.; Souptel, D.; Behr, G.; Bergk, B.; Ignatchik, O.; Wosnitza, J.; Ormeci, A.; Rosner, H.;
Das Übergangsmetall-Borkarbid YNi2B2C (Raumgruppe 8139) I4/mmm) geht bei Temperaturen unterhalb von ca. 15 K vom normalleitenden in den supraleitenden Zustand über [1]. Das supraleitende Verhalten ist stark von der chemischen Zusammensetzung im schmalen Homogenitätsbereich und von Feinheiten der Struktur abhängig.
Qualitativ hochwertige Einkristalle lassen sich mit dem Zonenschmelzverfahren [2] oder der Flusszüchgung [3] synthetisieren. Zur Bestimmung der elektronischen Bandstruktur sowie zur Charakterisierung der supraleitenden Energielücke wurden von Ignatchik et al. [4] de Haas-van Alphen (dHvA) Messungen an Einkristallen beider Züchungsmethoden durchgeführt. Die dHvA-Oszillationen weisen eine ungewöhnliche Dämpfung in der supraleitenden Phase für die zonengeschnmolzenen Proben auf. Im Unterschied dazu lassen sich für flussgezogene Proben Oszillationen deutlich bis zu tiefen Temperaturen beobachten.
Zur Aufklärung dieser Unterschiede wurden nun an denselben Proben röntgeneinkristalldiffraktometrische Messungen bei Raumtemperatur durchgeführt. Neben der Strukturverfeinerung zur Bestimmung der exakten Kristallstruktur werden verschiedene Fehlordnungsmodelle diskutiert. Die aus den verfeinerten Parametern berechneten Eletronendichteverteilungen werden mit theoretischen Berechnungen verglichen. Erst Ergebnisse weisen auf unterschiedliche Besetzungswahrscheinlichkeiten der C-Lage hin.
Diese Arbeit wurde von der Deutschen Forschungsgemeinschaft im Rahmen des SFB 463 unterstützt.
[1] R. Nagarajan et al. Phys. Rev. Lett. 72, 274-277 (1994).
[2] D. Souptel et al. J. Cryst. Growth 276, 652-662 (2005).
[3] P. Canfield et al. Phys. Today 51 (10), 40-46 (1998).
[4] O. Ignatchik et al. J. Magn. Magn. Mat. 290-291, 424-427 (2005).
  • Poster
    14. Jahrestagung der Deutschen Gesellschaft für Kristallographie 2006, 03.-06.04.2006, Freiburg, Deutschland

Publ.-Id: 8745 - Permalink


Magnetic quantum oscillations in the normal and superconducting state of nonmagnetic borocarbides
Ignatchik, O.; Bergk, B.; Jäckel, M.; Wosnitza, J.; Souptel, D.; Behr, G.; Canfield, P. C.;
We report on de Haas-van Alphen (dHvA) investigations of the non-magnetic borocarbides YNi2B2C and LuNi2B2C. The measurements were carried out on high-quality single crystals by the torque method in magnetic fields up to 30 T. In the normal state the Fermi-surface topology has been analysed. In comparison with band-structure calculations several deviations are determined. Below the upper critical field, Bc2, in the vortex state an additional damping of the dHvA amplitudes appears. This damping is caused by the evolution from of the superconducting gap parameter. Concerning these topics we observe strong differences between differently grown crystals. The crystals produced by a zone-melting method show an abrupt vanishing of the dHvA signal at the upper critical field Bc2. In contrast, the flux grown crystals display a broader phase transition combined with a continuous decrease of the dHvA amplitude.
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8744 - Permalink


Granularity and Spontaneous Vortex State for the Weakly Ferromagnetic Superconductor RuSr2GdCu2O8
Papageorgiou, T.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.;
In the high-Tc cuprate RuSr2GdCu2O8 (Ru1212) weak ferromagnetism (T Ru/N ? 130 K) coexists with superconductivity (Tc,conset ? 50 K). This rises the interesting question concerning the formation of a spontaneous vortex state (SVS) in the case that the internal magnetic field is greater than the first critical field Hc1. Recently, the formation of a SVS has been proposed for Ru1212 after the phase diagram for this compound was constructed from dc-magnetization and resistance measurements [1]. We show, by a comparison of resistance with ac-susceptibility and dc-magnetization measurements, where both the intra- and inter-granular superconducting transition are obvious, that the granular nature of the investigated samples has to be carefully considered in the investigations of possible SVS formation. A particular SVS with vortices pinned in the intergrain area is much more likely. Single crystals would be required to unambiguously demonstrate the formation or non-formation of a spontaneaous vortex state in bulk Ru1212.
[1] C. Y. Yang, B. C. Chang, H. C. Ku, Y. Y. Hsu, cond-mat/0507014
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8743 - Permalink


Single crystal X-ray diffraction analysis and electron density calculation of YNi2B2C
Leisegang, T.; Meyer, D. C.; Paufler, P.; Souptel, D.; Behr, G.; Ignatchik, O.; Ormeci, A.; Rosner, H.; Wosnitza, J.;
The quarternary borocarbide YNi2B2C, space group (139) I4/mmm, exhibits superconductivity (Tc ≈ 15 K) as was first reported in [1]. This superconducting behaviour depends strongly on the crystal composition within the samll homogeneity range and on the crystal growth conditions. Here we report on investigations of two different samples, namely bulk samples grown by a floating zone technique [2] and plate samples grown by a flux-growth method [3]. De Haas-van Alphen (dHvA) measurements were performed to determine the electronic band structure as well as the evolution of a superconducting energy gap at the Fermi surface [4]. To evaluate the exact crystal structure, single-crystal X-ray diffaction measurements at room temperature were performed. Different models of structural disorder were refined and a difference-Fourier analysis was carried out. The experimental electron density will be compared with theoretical calculations. The work was supported by the Deutsche Forschungsgemeinschaft (SFB 463).
[1] Nagarajan et al., Phys. Rev. Lett. 72, 274 (1994).
[2] Souptel et al., J. Cryst. Growth 276, 652 (2005).
[3] Canfield et al., Phys. Today 51, 40 (1998).
[4] Ignatchik et al., J. Magn. Magn. Mat. 290-291, 424 (2005).
  • Lecture (Conference)
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8742 - Permalink


Uranium(VI) complexes with phospholipid model compounds – a laser spectroscopic study
Koban, A.; Bernhard, G.;
We present the complex formation of the uranyl ion (UO22+) in the aqueous system with phosphocholine, O-phosphoethanolamine and O-phosphoserine. These phosphonates (R-O-PO32-) represent the hydrophilic head groups of phospholipids. The complexation was investi-gated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at pH 2 to 6. An increase of the fluorescence intensity, connected with a strong red shift of about 8 nm com-pared to the free uranyl ion, indicates a complex formation between UO22+ and the phospho-nates already at pH 2. Even at pH 6 these complexes prevail over the uranyl hydroxide and carbonate species, which are generated naturally at this pH. At pH 4 and higher a 1 : 2 com-plex between uranyl and O-phosphoserine was found. Complexes with a metal-to-ligand ratio of 1 : 1 were observed for all other ligands. Fluorescence lifetimes, emission maxima and complex stability constants at T = 22 ± 1°C are reported. The TRLFS spectra of uranyl com-plexes with two phosphatidic acids (1,2-dimyristoyl-sn-glycero-3-phosphate and 1,2-dipalmitoyl-sn-glycero-3-phosphate), which represent the apolaric site of phospholipids, show in each case two different species.
Keywords: TRLFS, uranyl, phospholipid fragments, phosphonates, complexation

Publ.-Id: 8741 - Permalink


Spin-zero anomaly in the magnetic quantum oscillatins of a two-dimensional metal
Bergk, B.; Ignatchik, O.; Jäckel, M.; Wosnitza, J.; Gvozdikov, V. M.; Schlueter, J. A.; Mohtasham, J.; Winter, R. W.; Gard, G. L.;
We present de Haas-van Alplhen (dHvA) and Shubnikov-de Haas (SdH) measurements on the quasi-two-dimensional organic superconductor β"-(BEDT-TTF)2SF5CH2CF2SO3. The measurements were carried out by the torque method and by four-point low-frequency ac-resistance measurements in magnetic fields up to 15 T. Unlike theoretical expectations for two-dimensional metals the dHvA signal shows an unconventional sawtooth wave-form, e. e., an 'inversed sawtooth' wave form is observed.In order to investigate the behaviour in more detail we performed angle-dependent dHvA and SdH measurements. The SdH effect displays the behaviour predicted by the grand-canonical Lifshitz-Kosevich theorie. In contrast, the dHvA signal can be explained by a theory, which includes a slightly oscillating chemical potential. Even for simultaneous measurements of both effects the behaviour does not change. This means that the dHvA signal is not affected by an external charge carrier reservoir.
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8740 - Permalink


Electron Spin Resonance in sine-Gordon Spin Chains in the Perturbative Spinon Regime
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A.; Krzystek, J.; Feyerherm, R.;
We report on low-temperature multi-frequency ESR studies of coopper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of S = 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained. Results of the presentation are published in: S.A. Zvyagin et al., Phys. Rev. Lett. 95, 017207, 2005.
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8739 - Permalink


Sample-dependent resistivity profiles in K-(ET)2Cu[N(CN)2]Br organic superconductors - interrelations with other normal- and superconducting-state properties
Strack, C.; Akinci, C.; Paschenko, V.; Wolf, B.; Uhrig, E.; Assmus, W.; Lang, M.; Schreuer, J.; Wiehl, L.; Schlueter, J.; Wosnitza, J.; Schweitzer, D.; Wyckhoff, J.;
The organic superconductor κ-(ET)2Cu[N(CN)2Br shows striking sample-to-sample variations in the electrical resistivity [1]: While most of the crystals reveal a ρ(T) maximum around 90 K with a semiconducting behaviour above, some remain metallic for T < 300 K. In the absence of significant differences in the crystals´structural parameters, chemical composition and ESR spectra, these results indicate that real structure phenomena, i.e. disorder and/or defects, strongly affect the inclastic scattering. [1]. Here we report on a comparative resistivity study on a variety of crystals with quite different ρ(T) profiles. The work aims at seeking out interrelations between the anomalous scattering contributions at intermediate temperatures and features of the normal- and superconducting-state, susch as the glass transition at T9 ≈ 77 K, the temperature T* ≈ 40 K [1], as well as the superconducting transition temperature. [1] C. Strack et al., Phys. Rev. B 72 054511 (2005)
  • Lecture (Conference)
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8737 - Permalink


Untersuchung des Verhaltens von freigesetztem Isolationsmaterial in einer Kühlmittelströmung (Kühlmittelströmung mit Feststoffpartikeln) - Modellentwicklung
Krepper, E.; Grahn, A.;
Die CFD-Modellierung des Fasertransports wurde auf der Basis des Euler/Euler-Ansatzes untersucht. Die Nachbildung des Transportverhaltens der Partikel erfordert die korrekte Beschreibung des Impulsaustausches. Hierfür liefert die Auswertung der Sinkgeschwindigkeiten aus den Experimenten am Versuchsstand „Säule“ die notwendigen Informationen. Über die Vorgabe von Partikeldichte und Partikeldurchmesser kann die Sinkgeschwindigkeit nachgebildet und der Partikeltransport adäquat modelliert werden. Beispielsimulationen einer partikelbeladenen Strömung im Versuchsstand „Ringkanal“ lieferten plausible Resultate.
Das Anlagerungs- bzw. Abtragungsverhalten der Partikel an Hindernissen (z. B. Wehren) wurde über die Modellierung einer vom Feststoffanteil abhängigen Viskosität simuliert. Dieser Zusammenhang wurde an die Ergebnisse der Experimente im Ringkanal angepasst. Erste Demonstrationsrechnungen zur Beschreibung des Partikeltransportes an Hindernissen ergaben plausible Resultate. In anderen Beispielen zeigte die Parametervariation einer feststoffabhängigen Viskosität jedoch einen zu geringen Einfluss auf die berechneten Ablagerungsmengen, um die experimentellen Befunde zu reproduzieren.
Es wurde ein Modell des Differenzdruckaufbaus aus den Kompaktierungseigenschaften der auf dem Sieb abgelagerten Fasern entwickelt und an Experimenten justiert. Damit steht neben den in der Literatur veröffentlichten Korrelationen ein weiteres Verfahren zur Berechnung des Differenzdrucks zur Verfügung. In einer Machbarkeitsstudie wurde die Wirkung eines Siebes auf das Strömungsfeld unter Nutzung des Modellansatzes des porösen Körpers in CFX-4.4 implementiert. Das implementierte Modell liefert qualitativ plausible Resultate.
Keywords: CFD, fibre transport, sedimentation, resuspension, difference pressure at sieves
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-458 2006

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Publ.-Id: 8736 - Permalink


Sound wave anomalies in superconducting compounds
Lüthi, B.; Zherlitsyn, S.; Wolf, B.;
Temperature dependence of the elastic constants in the superconducting state is described on the basis of the Ginsburg-Landau theory. This approach shows very general character and allows to describe quantitative renormalization of the elastic constants in the superconducting state for different materials including non-conventional superconductors. Various examples (A-15 compounds, Chevrel compounds, CeRu2, Ba0.63K0.37BiO3, Yb3Rh4Sn13, Ca3Rh4Sn13, HfV2, some heavy fermion compounds and Sr2RuO4) are given.
  • European Physical Journal B 46(2005), 169-176

Publ.-Id: 8734 - Permalink


Bindungsformen des Urans in umweltrelevanten Kompartimenten
Bernhard, G.;
Ausgehend vom Vorkommen, der physikalisch-chemischen Eigenschaften und der Verwendung werden die Eintragspfade für Uran in die Umwelt behandelt. Hintergrundwissen bilden dabei die zahlreichen Daten zu den Gehalten in den Kompartimenten Boden, Gestein, Mineral, unterschiedlichen Wässern, der Luft und in den Biosystemen.
Nach der Besprechung der Methoden zur Bestimmung der Bindungsform werden die Ergebnisse zur Uranbindungsform in unterschiedlichen Wässern und in Bakterien vorgestellt.
  • Lecture (others)
    Vortrag im Forschungszentrum Jülich GmbH, 13.09.2006, Jülich, Germany

Publ.-Id: 8733 - Permalink


Solitary waves in S = 1/2 quantum spin chains: ESR study in magnetic fields up to 25 T
Zvyagin, S. A.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
We report the low-temperature multifrequency ESR studies of copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic chain with alternating g tensor and the Dzyaloshinskii-Moriya interaction, allowing us to test a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)]. Their theory, based on bosonization and self-energy formalism, can be applied for precise calculation of ESR parameters of S = 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields-V, 05.-09.08.2005, Tallahassee, USA

Publ.-Id: 8732 - Permalink


Tunable-frequency Electron Paramagnetic Resonance - a Novel Tool to Investigate High-Spin Transition Metal Complexes
Krzystek, J.; Ozarowski, A.; Trofimenko, S.; Zvyagin, S. A.; Telser, J.;
Although Electron Paramagnetic Resonance (EPR) has been a very successful method to investigate transition metal ions in coordination complexes and biomolecules, not all such ions can be subject to conventional EPR investigations even if they are paramagnetic. In particular, high-spin (S >1/2) species pose serious challenges to spectroscopists, and of these, the non-Kramers (integer-spin) ions have been long considered ‘EPR-silent’ at conventional frequencies and fields. We propose a novel EPR-related technique that takes an advantage of tunable sources operating in the sub-THz range of frequencies in conjunction with very high magnetic fields (up to 25 Tesla) to determine accurate intrinsic spin Hamiltonian parameters not only for a variety of non-Kramers transition metal ions (such as Ni2+, Mn3+, and Fe2+) that have traditionally been termed ‘EPR-silent’, but also for those Kramers (half-integer) species that are poorly characterized in their high-spin states, such as Co2+. The obtained parameters can serve to better characterize the electronic structure of the ions in question, in combination with other experimental methods.
  • Advances in Coordination, Bioinorganic and Inorganic Chemistry (2005), 143-158

Publ.-Id: 8730 - Permalink


Magnetic excitations in sine-Gordon spin chains: ESR studies
Zvyagin, S. A.;
  • Invited lecture (Conferences)
    Workshop, 15.08.2005, Kharkov, Ukrainian

Publ.-Id: 8729 - Permalink


High-Field Electron Spin Resonance in Quasi-2D Frustrated Spin System SrCu2(BO3)2
Zvyagin, S. A.; Wosnitza, J.; Krzysted, J.; Stern, R.; Dabkowska, H.; Gaulin, B.;
We present results of high-frequency/field Electron Spin Resonance (ESR) studies of the highly frustrated spin system SrCu2(BO3)2,which can be regarded as to the best known realization of the Shastry-Sutherland model for two-dimensional Heisenberg antiferromagnets. The frequency-field diagram of magnetic excitations has been studied in a frequency range of 150-700 GHz, employing unable-frequency ESR technique. Two gapped odes were observed in the excitation spectrum. The size of the quantum spin gaps determined directly is: 708 GHz and 764 GHz (34 K and 36.7 K). The observation of excitations from the ground state (which are normally forbidden) and a double-gap structure of the ESR excitation spectrum in SrCu2(BO3)2 suggest and essential role of the Dzyaloshinski-Moriya interaction. The results are compared with those obtained by Nojiri et al. [J. Phys. Soc. Jpn. 68, 2906 (1999); J.Phys. Soc. Jpn. 72, 3243 (2003)]. The temperature behavior of excited-state transitions in SrCu2(BO3)2 (ESR linewidth and intensity) is presented and discussed.
  • Poster
    Workshop Highly Frustrated Magnetism (HFM), 07.-09.11.2005, Agelonde, La Londe Les Maures, Frankreich

Publ.-Id: 8728 - Permalink


Adhesion Issues in PBO/Epoxy Composites
Liu, J.; Gao, S. L.; Mäder, E.; Bianchi, A. D.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S. A.; Wosnitza, J.;
This study aims to address interfacial adhesion requirements for composites with high electrical insulation properties for extreme high magnetic field and pressure environments. The magnetic field is one fundamental parameter influencing the physics of many systems. Over the recent years, research with high magnetic fields has led to a range of enhanced modern technologies. These efforts were triggered by experiments such as the integer and fractional quantum Hall effect and as a result several high magnetic field facilities were built in the US, Japan, and Europe. The current technology limits the generation of static magnetic fields to 45 T. Magnetic fields of up to about 70 T are only available for experiments with pulse duration in the ms range. The Hochfeld-Magnetlabor Dresden, as well as the Los Alamos branch of the National High Magnetic Field Laboratory, are aiming at generating fields up to 100 T. The access to this magnetic field range possesses a large number of technological issues, particularly abnormal heating and high stress, generated by the Lorentz forces from the electrical current and the magnetic field of the magnet. In a 100 T magnet these forces amount to a pressure of the order of 4 GPa and ordinary steel would burst under the stresses involved in confining the high magnetic field inside the magnet. This problem is circumvented by reinforcing all conductor layers of the coil with high modulus fibre reinforced composites. Because the pulsed field magnets are operated at high voltages and large currents, this demands high electrical insulation properties of the composite and makes the use of electrically conducting carbon fibres problematic. Today, the high ultimate tensile strength of 5 GPa, high heat resistance/service temperature and the good insulation properties make poly p-phenylene-2,6-benzobisoxazole (PBO) fibre of good choice. However, it is challenging to get adequate interfacial adhesion of PBO fibre due to the nonpolar surface nature of PBO preventing any chemical bonding the smooth PBO surface with polymer matrix.
We have characterised the interfacial adhesion strength and critical interphase energy release rate by single fibre pull-out tests. The PBO fibre surfaces were de-sized by extraction of the commercial finish, and sized with different sizings. In addition, both O2 and NH3 gas plasma treatments and plasma modification with Maleic anhydride were used. It was found that the rather low surface free energy of the as-received PBO fibres (34 mJ/m²) could be increased by appropriate surface modification, particularly the oxygen-plasma and Maleic anhydride graft. However, the adhesion strength increased marginally with increasing surface free energy due to induced limited hydrogen and covalent bonds at their interface, which is in the same level like aramid, i.e. below the adhesion strength of glass fibre / epoxy systems. A short time plasma treatment (30s) with NH3 gas results in both reduction of surface energy and interfacial adhesion strength. AFM was used to characterize the surface topography varied by different fibre surface modifications and to evaluate the fracture surfaces. The fractographs are dominated by adhesive failure, that is to say, the interfacial crack propagation occurs primarily in the fibre/matrix interface plane, suggesting a further improvement of chemical bonding/mechanical interlocking is required. Moreover, for the application in a high magnetic field also the temperature change in the coil during operation has to be taken into account. Epoxy resins with different temperature resistance have not shown significant differences in the interfacial shear strength. The micro-mechanical results agree well with those of compression shear tests performed with real composite samples.
  • Lecture (Conference)
    Polymer Fibres 2006 Conference, 12.-14.07.2006, Manchester, UK

Publ.-Id: 8727 - Permalink


Spin excitations in S = 1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
The magnetic excitation spectrum of copper pyrimidine dinitrate, a material containing s = 1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction, and exhibiting a field-induced spin gap, is probed using multi-frequency electron spin resonance spectroscopy in magnetic fields up to 25 T. Signatures of three breather branches an a soliton, as well as those of several multi-particle excitation modes are identified, and their frequency-field dependences are described in frame of the quantum sine-Gordon field theory. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)] ist tested. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of s = 1/2 antiferromagnetic chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained. Results are published in S.A. Zvyagin et al., Phys. Rev. Lett. 93, 027201 (2004);ibid. Phys. Rev. Lett. 95, 012707 (2005).
  • Lecture (Conference)
    APS March Meeting, 13.-17.03.2006, Baltimore, USA

Publ.-Id: 8725 - Permalink


Phase control of Al2O3 thin films grown at low temperatures
Andersson, J. M.; Wallin, E.; Helmersson, U.; Kreissig, U.; Münger, E. P.;
Low-temperature growth (500°C) of alpha-Al2O3 thin films by reactive magnetron sputtering was achieved for the first time. The films were grown onto Cr2O3 nucleation layers and the effects of the total and O2 partial pressures were investigated. At 0.33 Pa total pressure and >16 mPa O2 partial pressure alpha-Al2O3 films formed, while at lower O2 pressure or higher total pressure (0.67 Pa), only gamma phase was detected in the films (which were all stoichiometric). Based on these results we suggest that alpha phase formation was promoted by a high energetic bombardment of the growth surface. This implies that the phase content of Al2O3 films can be controlled by controlling the energy of the depositing species. The effect of residual H2O (approx. 10(-4) Pa) on the films was also studied, showing no change in phase content and no incorporated H (< 0.1%). Overall, these results are of fundamental importance in the further development of low-temperature Al2O3 growth processes.
Keywords: Aluminum oxide; Chromium oxide; Sputtering; Ion bombardment; X-ray diffraction; Phase formation
  • Thin Solid Films 513(2006), 57-59

Publ.-Id: 8724 - Permalink


Dielectron production in 12C+12C collisions at 2 AGeV with HADES
Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Bertini, D.; Bielcik, J.; Bellia, G.; Böhmer, M.; Bokemeyer, H.; Boyard, J. L.; Braun-Munziger, P.; Cabanas, P.; Chernenko, S.; Christ, T.; Coniglione, R.; Cosentino, L.; Diaz, J.; Dohrmann, F.; Duran, I.; Eberl, T.; Enghardt, W.; Fabbietti, L.; Fateev, O.; Fernandez, G.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garabatos, C.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Gonzalez-Diaz, D.; Grosse, E.; Guber, F.; Hennino, T.; Hlavac, S.; Holzmann, R.; Homolka, J.; Ierusalimov, A.; Iori, I.; Ivashkin, A.; Jaskula, M.; Jurkovic, M.; Kargalis, M.; Kajetanowicz, M.; Kämpfer, B.; Kanaki, K.; Karavicheva, T.; Kastenmüller, A.; Kidon, L.; Kienle, P.; Koenig, I.; Koenig, W.; Körner, H. J.; Kolb, B. W.; Kotte, R.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Lang, S.; Lange, S.; Lehnert, J.; Lins, E.; Magestro, D.; Maiolino, C.; Malarz, A.; Markert, J.; Metag, V.; Mousa, J.; Münch, M.; Müntz, C.; Naumann, L.; Nekhaev, A.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Pechenov, V.; Perez, T.; Piattelli, P.; Pietraszko, J.; Pleskac, R.; Ploskon, M.; Pospisil, V.; Prokopovicz, W.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Ritman, J.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Sanchez, M.; Sapienza, P.; Schmah, A.; Schön, H.; Schön, W.; Simon, R. S.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Ströbele, H.; Stroth, J.; Strurm, C.; Sudol, M.; Suk, M.; Taranenko, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vassiliev, D.; Vazquez, A.; Wagner, V.; Walus, W.; Wisniovski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsky, Y.; Zeitelhack, K.; Zoviec, D.; Zumbruch, P.;
The invariant mass spectrum of e^+ e^- pairs produced in ^{12}C+^{12}C collisions at 2 GeV per nucleon incident energy has been measured for the first time with the HADES spectrometer at GSI. The measured pair production probabilities span over five orders of magnitude within the \pi^0\to e^+e^-\gamma to \rho/\omega\to e^+e^- invariant mass region. A thermal model of the dielectron sources underestimates the measured probabilities by a factor of roughly two at intermediate masses (0.2 -- 0.6 GeV/c^2) whereas it overshoots data at the \rho/\omega pole. Transport model calculations assuming vacuum spectral functions of the vector mesons fail to describe the entire invariant mass spectrum, as well.

Publ.-Id: 8723 - Permalink


Fermi Surface of the Half Heusler Compounds Ce1-xLaxBiPt
Bianchi, A. D.; Wosnitza, J.; Kozlova, N.; Eckert, D.; Schultz, L.; Opahle, I.; Elgazzar, S.; Richter, M.; Doerr, M.; Hagel, J.; Goll, G.; von Löhneysen, H.; Zwicknagel, G.; Yoshino, T.; Takabatake, T.;
We report on the Fermi surface in the correlated half-Heusler compound Ce1-xLaxBiPt. In CeBiPt we find a field-induced change of the electronic band structure as discovered by electrical-transport measurements in pulsed magnetic fields. For magnetic fields above ca 25 T, the charge-carrier concentration determined from Hall-effect measurements increases nearly 30%, whereas the Shubnikov-de Haas (SdH) signal disappears at the same field. In the non-4f compound LaBiPt the Fermi surface remains unaffected, suggesting that these features are intimately related to the Ce 4F electrons. Electronic band-structure calculations point to a 4f-polarization-induced change of the Fermi-surfache topology. In order to test this hypothesis, we have measured the (SdH) signal in a Ce0.95La0.05BiPt sample with a low La concentration.
  • Lecture (Conference)
    APS March Meeting, 13.-17.03.2006, Baltimore, USA
  • Poster
    DPG-Frühjahrstagung, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8722 - Permalink


Elementary excitations in the S=1/2 quantum sine-gordon spin chain
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
An isotropic S = 1/2 Heisenberg antiferromagnetic (AFM) chain with uniform nearest-neighbor exchange coupling represents one of the paradigm models of quantum magnetism. Its ground state is a spin singlet and the dynamics are determined by a gapless two-particle continuum of spin- 1/2 excitations, commonly referred to as spinons. Since the S = 1/2 AFM chain is critical, even small perturbations can considerably change fundamental properties of the system. One of the most prominent examples is the S = 1/2 AFM chain perturbed by an alternating g-tensor and the Dzyaloshinskii-Moriya interaction; this situation is realized experimentally in the copper pyrimidine dinitrate, Cu-PM. In the presence of such interactions, application of a uniform external field H induces an effective transverse staggered field h ∝ H, which leads to the opening of an energy gap Δ ∝ H2/3. Here we report on the excitation spectrum in Cu-PM measured using submillimeter wave electron spin resonance (ESR) spectroscopy in fields up to 25 T [1]. Ten excitation modes are resolved in the low-temperature spectrum. The field-induced gap is measured directly. Signatures of three breather branches and a soliton, as well as those of several multi-particle excitation modes are identified. The experimental data are sufficiently detailed to make a very accurate comparison with predictions based on the quantum sine-Gordon field theory [2]. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [3] has been tested. Their theory, based on bosonization and the self-energy formalism, can be applied for precise calculation of ESR parameters of S = 1/2 AFM chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained [4].
[1] S.A. Zvyagin et al., Phys. Rev. Lett. 93 (2004) 027201.
[2] M. Oshikawa and I. Affleck, Phys. Rev. Lett. 79 (1997) 2883; I. Affleck and
M. Oshikawa, Phys. Rev. B 60 (1999) 1038; ibid 62 (2000) 9200.
[3] M. Oshikawa and I. Affleck, Phys. Rev. Lett. 82 (1999) 5136.
[4] S.A. Zvyagin et al., Phys. Rev. Lett. 95 (2005) 017207.
  • Poster
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 8720 - Permalink


Anisotropy and spin-triplet excitions in theS = 1/2 gapped antiferromagnet BaCuSi2O6.
Zvyagin, S. A.; Wosnitza, J.; Krzystek, J.; Stern, R.; Jaime, M.; Sasago, Y.; Uchinokura, K.;
BaCuSi2O6 (also known as Han Purple Pigment) can be regarded as an almost ideal realization of the S = 1/2 system of weakly-interacting spin dimers with the spin-singlet ground state and gapped excitation spectrum [1]. By application of an external magnetic field the gap can be closed, creating a gas of interacting bosonic spin-triplet excitations (triplons). In BaCuSi2O6 this phenomenon can be effectively described in terms of the field-induced Bose-Einstein condensation of triplons [2]. Here, we focus on another interesting phenomenon associated with interacting excited triplets but in the low-field quantum-disordered state. We argue that a fine structure observed in low-temperature EPR spectra of BaCuSi2O6 is a fingerprint of triplet excitations (excitons), which are mobile at low temperatures and getting localized when the temperature is increased. Analyzing the angular dependence of the exciton modes allows us to precisely calculate the zero-field splitting with the triplet state and,correspondingly, the anisotropy parameter, D = 0.07 cm-1. The proposed procedure can be applied for a large number of S = 1/2 gapped quantum antiferromagnets with dimerized or alternating spin structure and might be of particular importance for studying anisotropy effects in S = 1/2 quantum chains (see for instance [3]). In addition, the temperature dependence of the EPR intensity and linewidth has been measured and discussed. The magnitude of the energy spin gap determined by analyzing the temperature dependence of the integrated signal intensity (¢ = 53 K) is in excellent agreement with data obtained from neutron-scattering measurements [1].
[1] Y. Sasago et al., Phys. Rev. B 55 (1997) 8357.
[2] M. Jaime et al., Phys. Rev. Lett. 93 (2004) 087203.
[3] R.D. Somma and A.A. Aligia, Phys. Rev. B 64 (2001) 024410.
  • Poster
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 8719 - Permalink


Untersuchungen zum Flüssigkeits-Holdup und zur Flüssigkeitsverweilzeit in Schüttungen mittels Röntgenradiographie und Gammatomographie
Hampel, U.; Bieberle, A.; Hessel, G.; Zimmermann, W.; Zippe, C.;
Zusammenfassung
Es wurden Verweilzeituntersuchungen und Gasverteilungsmessungen an einer senkrecht mit Wasser durchströmten kiesbefüllten Säule mit vier intermediären Eisengranulatschichten durchgeführt. Zur Messung der Verweilzeitspektren wurde in die Zuleitung der Säule ein 60 ml Bolus BaCl2-Lösung (1,4 mol/l) eingespeist. Der Eintrittszeitpunkt des Bolus an der Säule wurde mittels einer direkt am Eintrittstutzen angebrachten Leitfähigkeitsnadelsonde erfasst. Der Durchgang des Tracerbolus durch verschiedene Messebenen wurde mittels Gammadurchstrahlung aufgezeichnet. Aus dem Schwächungssignal lassen sich Verweilzeitspektren direkt ableiten. Zur Bestimmung der Verweilzeit bzw. der mittleren Strömungsgeschwindigkeit in der Säule wurden zwei charakteristische Zeitpunkte des Verweilzeitspektrums verrechnet. Einmal der Frontzeitpunkt, der den erstmaligen Nachweis von Tracerflüssigkeit in der Messebene bezeichnet, sowie der Boluszeitpunkt, der durch die maximale Tracerkonzentration in der Messebene gegeben ist. Der gammadensitometrische Nachweis des Tracerbolus war aufgrund der starken axialen Dispersion nur in der unteren Hälfte der Säule möglich. Die Ergebnisse gaben keinen Hinweis auf größere gasbedingte hydraulische Obstruktionen in der Säule.
Der Nachweis von Gaseinschlüssen bzw. die Darstellung der Gasverteilung in vier ausgewählten Messebenen wurde mit dem Verfahren der Gammastrahlungstomographie realisiert. Die Messebenen wurden jeweils mittig zwischen den Eisengranulatschichten gewählt. Bezüglich der Verteilung des Bariumtracers wurden keine nennenswerten Konzentrationsgradienten im Messquerschnitt gefunden, so dass von einer homogenen Durchströmung der Säule ausgegangen werden kann. Erkannt wurden Gaseinschlüsse besonders im peripheren Bereich des Säulenquerschnitts. Der globale Gasgehalt ist dabei kleiner als 5%.
Keywords: Gammatomographie, Gammaradiographie, Röntgenradiographie, Flüssigkeitsverweilzeit, Schüttbett
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-456 2006

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Publ.-Id: 8717 - Permalink


Magnetic Excitations in S = 1/2 Spin Chains with Alternating g-tensor and theDzyaloshinskii-Moriya Interaction
Zvyagin, S. A.; Wosnitza, J.; Kolezhuk, A. K.; Krzystek, J.; Feyerherm, R.;
The magnetic excitation spectrum in copper pyrimidine dinitrate, a spin-1/2 antiferromagnetic (AFM) chain system with an alternating g-tensor and the Dzyaloshinskii-Moriya interaction, has been studied using electron-spin resonance (ESR) spectroscopy in magnetic fields up to 25 T. Ten modes were resolved in the spectrum. The data were analyzed in terms of the sine-Gordon quantum field theory [Phys. Rev. Lett. 79, 2883 (1997)]; signatures of three breather branches and a soliton were identified. The field-induced gap was measured directly. In addition, a new theoretical concept proposed recently by Oshikawa and Affleck [Phys. Rev. Lett. 82, 5136 (1999)] has been tested.
Their theory, based on bosonization and the self-energy formalism, can be applied for the precise calculation of ESR parameters of spin-1/2 AFM chains in the perturbative spinon regime. Excellent quantitative agreement between the theoretical predictions and experiment is obtained.
e-mail: s.zvyagin@fz-rossendorf.de
  • Lecture (Conference)
    Yamada Conference LX on Research in High magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 8716 - Permalink


Superconducting Properties of RuSr2RECu2O8
Papageorgiou, T. P.; Casini, E.; Braun, H. F.; Herrmannsdörfer, T.; Bianchi, A. D.; Wosnitza, J.;
The resistance R of the (weakly) ferromagnetic (TM ≈ 133K) superconductor RuSr2EuCu2O8 (Ru1212Eu) shows a maximum at Tmax ≈ 30 K while Tc (R = 0) ≈ 10 K. Using dc-magnetization measurements we were able to identify Tmax as the temperature where the intragrain superconducting transition takes place,whereas Tc fits well with the temperature where intergrain (Josephson)coupling between the grains is established. Our findings suggest that the wide(≈ 20 K) superconducting transition of Ru1212Eu in zero applied magnetic field is most probably due to resistive grain contacts. A similar situation is realised for RuSr2GdCu2O8. These results contradict reports which attribute the wide superconducting transition of these compounds to the movement of spontaneously induced vortices [1]. Spontaneous vortex-state formation at T < Tc cannot be excluded, nevertheless we show that it is more likely that the vortices are pinned in the intergrain area (area between the grains). Single crystals would be required to unambiguously clarify the state of the individual grains. Furthermore, Tmax for Ru1212Eu is shifted to lower temperatures when an external magnetic field is applied. This challenges reports [2], where an increase of the critical temperature with the application of an external magnetic field in specific heat measurements was interpreted as possible evidence for triplet pairing in the ruthenium cuprates.
[1] C. Y. Yang et al., Phys. Rev. B 72, 174508 (2005)
[2] J. L.Tallon et al., Phys. Rev. B 61, R6471 (2000)
  • Poster
    International Conference on Magnetism (ICM), 20.-25.08.2006, Kyoto, Japan

Publ.-Id: 8715 - Permalink


Polyoxometalates – a new class of potent ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) inhibitors
Müller, C. E.; Iqbal, J.; Baqi, Y.; Zimmermann, H.; Röllich, A.; Stephan, H.;
Polyoxotungstates were identified as potent inhibitors of NTPDases1, 2, and 3. The most potent compound was K6H2[TiW11CoO40], exhibiting Ki values of 0.140 µM (NTPDase1), 0.910 µM (NTPDase2), and 0.563 µM (NTPDase3). One of the compounds, (NH4)18[NaSb9W21O86], was selective for NTPDases2 and 3 versus NTPDase1. NTPDase inhibition might contribute to the described biological effects of polyoxometalates, including their anti-cancer activity.

Publ.-Id: 8714 - Permalink


Complexation of curium(III) with L2-aminobutyric acid investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS).
Moll, H.; Bernhard, G.;
The complex formation of curium(III) with L2-Aminobutyric acid was characterized by time-resolved laser-induced fluorescence spectroscopy (TRLFS) at trace Cm(III) concentrations (3x10-7 M).
The different curium(III) species, MpHqLr, identified are characterized by their individual luminescence spectra and luminescence lifetimes. The following formation constants were determined log β101 = 5.17 ± 0.07, log β102 = 9.00 ± 0.07, and log β103 = 11.30 ± 0.09 at ionic strength I = 0.5 M. Possible structures of the curium aminobutyrate species will be discussed on the basis of the luminescence lifetime measurements and the magnitude of the formation constants.
Keywords: Amino acids; L2-Aminobutyric acid; TRLFS; Curium; Complexation

Publ.-Id: 8713 - Permalink


Pulsed-magnet design at the Dresden High Magnetic Field Laboratory
Zherlitsyn, S.; Herrmannsdoerfer, T.; Skourski, Y.; Sytcheva, A.; Wosnitza, J.;
The current status of the pulsed-magnet program of the High Magnetic Field Laboratory at Dresden (HLD) is reported. The non-destructive pulsed magnets for the HLD include a wide spectrum of coils designed for energies between 1 and 46 MJ, magnetic fields of 60 - 100 T, and pulse durations of 10 - 1000 ms. Magnet bores from 20 to 40 mm will accommodate different experimental setups. A universal core design has been developed at the HLD for these pulsed magnets. In spite of a strong external mechanical structure, our magnets are designed in a compact way. That allows to use this design both for inner and outer coils in multi-coil configurations. The core design has been successfully examined for a number of magnets for fields between 60 and 65 T. Already some user magnets for first scientific experiments have been installed and tested. The construction of a 9 MJ / 70 T mono-coil magnet has been accomplished. First test results are presented. The design of a two-coil 46 MJ magnet for magnetic fields above 85 T has been completed. Different aspects of the pulsed-magnet design and coil construction are discussed. Important issues of the coil design are numerical simulations of the pulsed-magnet behavior. Both analytical approximations and finite element analysis are used for these simulations at the HLD. Some simulation results are presented.
e-mail: s.zherlitsyn@fz-rossendorf.de
  • Poster
    Yamada Conference LX on Research in High magnetic Fields (RHMF), 16.-19.08.2006, Sendai, Japan

Publ.-Id: 8712 - Permalink


Fast THz time-domain spectrometer for pulsed magnets
Drachenko, O.; Winnerl, S.; Schneider, H.; Helm, M.; Wosnitza, J.;
  • Poster
    17th International Conference on High Magnetic Fields in Semiconductor Physics (HMF), 20.07.-04.08.2006, Würzburg, Deutschland

Publ.-Id: 8710 - Permalink


Characterization of ZnO single crystals by positron annihilation
Brauer, G.;
  • Lecture (others)
    Seminar an der University of Western Ontario, 31.07.2006, London/Ontario, Canada
  • Lecture (others)
    Seminar an der McMaster University, 03.08.2006, Hamilton/Ontario, Canada
  • Lecture (others)
    Seminar an der University of Texas at Arlington, 31.08.2006, Arlington/Texas, USA
  • Lecture (others)
    Seminar an der Texas Christian University, 01.09.2006, Ft. Worth/Texas, USA
  • Lecture (others)
    Seminar an der University of Texas at Austin, 30.08.2006, Austin/TX, USA
  • Lecture (others)
    Seminar an der University of North Texas, 28.08.2006, Denton/Texas, USA

Publ.-Id: 8708 - Permalink


Positron annihilation-induced Auger electron emission from 6H-SiC surfaces
Mukherjee, S.; Nadesalingam, M.; Davis, B.; Brauer, G.; Kohyama, A.; Nozawa, T.; Weiss, A.;
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada

Publ.-Id: 8707 - Permalink


Positron annihilation in three zirconia polymorphs
Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Anwand, W.; Brauer, G.; Konstantinova, T. E.; Danilenko, I. A.;
Positron lifetimes and high momentum profiles both for the perfect lattice and selected defects are calculated in three (cubic, tetragonal and monoclinic) zirconia polymorphs using the atomic superposition method. Theoretical data are compared with the measured positron lifetime for cubic and tetragonal monocrystals of yttria-stabilized zirconia (YSZ) and coincidence Doppler broadening measurements on tetragonal monocrystals of YSZ. Positron lifetime spectra of YSZ monocrystals exhibit a single component spectrum with lifetimes 178 ps and 174 ps for cubic and tetragonal phases, respectively. Possible interpretations of measured lifetime and Doppler data are discussed.
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada
  • Physica Status Solidi (C) 4(2007), 3831-3834

Publ.-Id: 8706 - Permalink


Positron annihilation spectroscopic study of hydrothermal grown n-type zinc oxide single crystal
Hui, C. W.; Zhang, Z. D.; Taojun, Z.; Ling, C. C.; Beling, C. D.; Fung, S.; Brauer, G.; Anwand, W.; Skorupa, W.;
Positron lifetime and coincidence Doppler broadening spectroscopic (CDBS) measurements were carried out to study the defects in two hydrothermal (HT) grown ZnO single crystal samples (HT1 and HT2) obtained from two companies. Single component model could offer good fittings to the room temperature spectra of HT1 and HT2, with the positron lifetimes equal to 199 ps and 181 ps respectively. These two lifetime components were associated with saturated positron trapping into two VZn-related defects with different microstructures. The positron lifetimes of HT1 was found to be temperature independent. For the HT2 sample, the positron lifetime remained unchanged with T > 200 K and decreased with decreasing temperature as T<200K. This could be explained by the presence of an additional positron trap having similar electronic environment to that of the delocalized state and competing in trapping positrons with the 181 ps component at low temperatures. Positron-electron autocorrelation function, which was the fingerprint of the annihilation site, was extracted from the CDBS spectrum. The obtained autocorrelation functions of HT1 and HT2 at room temperature, and HT2 at 50 K had features consistent with the above postulates that the 181 ps and the 199 ps components had distinct microstructures and the low temperature positron trap existed in HT2.
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada
  • Physica Status Solidi (C) 4(2007), 3672-3675

Publ.-Id: 8704 - Permalink


Influence of hydrogen peroxide treatment on Au/n-ZnO contact
Chen, X. D.; Ling, C. C.; Djurisic, A. B.; Brauer, G.; Anwand, W.; Skorupa, W.; Reuther, H.;
The Au/n-ZnO contact behavior was investigated as a function of hydrogen peroxide pre-treatment of the ZnO sample by current-voltage (IV) measurement. The change from non-rectifying to rectifying performance upon etching was discussed in connection with sample characterization by positron annihilation spectroscopy (PAS), Auger electron spectroscopy (AES) and scanning electron microscopy (SEM). It was concluded that the gain of the rectifying property was properly associated with the formation of a defective interfacial region at the Au/n-ZnO contact.
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada
  • Physica Status Solidi (C) 4(2007), 3633-3636

Publ.-Id: 8703 - Permalink


Defect studies of hydrogen loaded Nb: bulk metals and thin films
Cizek, J.; Prochazka, I.; Danis, S.; Vlach, M.; Zaludova, N.; Brauer, G.; Anwand, W.; Mücklich, A.; Gemma, R.; Nikitin, E.; Kirchheim, R.; Pundt, A.;
Microstructure investigations of Nb loaded with H are presented in this work. The microstructure was examined by positron annihilation spectroscopy (PAS), combined with X-ray diffraction (XRD) and transmission electron microscopy (TEM). The behaviour of H-loaded bulk samples and thin films was compared. First, the microstructure of the virgin (H-free) specimens was characterized. Subsequently, the development of the microstructure during step-by-step electrochemical H charging was studied. The investigations were performed mainly in the low H concentration region (α-phase), where the Nb-H system represents a single phase interstitial solid solution. In bulk samples it was found that new vacancy-like defects are introduced by H loading. Vacancies surrounded by H were detected also in the electron irradiated bulk samples. Nanocrystalline thin films were produced by sputtering at room temperature. They exhibit a significant volume fraction of grain boundaries with open volume defects which trap H.
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada
  • Physica Status Solidi (C) 4(2007), 3485-3488

Publ.-Id: 8702 - Permalink


The pulsed high-brightness positron source EPOS
Krause-Rehberg, R.; Brauer, G.; Krille, A.; Jungmann, M.; Sachert, S.; Rogov, A.; Noack, K.;
  • Lecture (Conference)
    14th International Conference on Positron Annihilation (ICPA-14), 23.-28.07.2006, Hamilton/Ontario, Canada
  • Lecture (Conference)
    19th International Conference on the Application of Accelerators in Research and Industry (CAARI2006), 20.-25.08.2006, Ft. Worth/Texas, USA

Publ.-Id: 8701 - Permalink


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