Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

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

Permalink: https://www.hzdr.de/publications/Publ-8771
Publ.-Id: 8771


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 Logo Materials Research 9(2006)1, 97-100

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Permalink: https://www.hzdr.de/publications/Publ-8770
Publ.-Id: 8770


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

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Permalink: https://www.hzdr.de/publications/Publ-8769
Publ.-Id: 8769


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

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Permalink: https://www.hzdr.de/publications/Publ-8768
Publ.-Id: 8768


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

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Permalink: https://www.hzdr.de/publications/Publ-8767
Publ.-Id: 8767


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

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Permalink: https://www.hzdr.de/publications/Publ-8766
Publ.-Id: 8766


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

Permalink: https://www.hzdr.de/publications/Publ-8765
Publ.-Id: 8765


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

Permalink: https://www.hzdr.de/publications/Publ-8763
Publ.-Id: 8763


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

Permalink: https://www.hzdr.de/publications/Publ-8762
Publ.-Id: 8762


Metalle in hohen Magnetfeldern

Wosnitza, J.
  • Invited lecture (Conferences)
    Physikalisches Kolloquium der Universität Konstanz, 05.07.2005, Konstanz, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8761
Publ.-Id: 8761


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

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Permalink: https://www.hzdr.de/publications/Publ-8760
Publ.-Id: 8760


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

Permalink: https://www.hzdr.de/publications/Publ-8759
Publ.-Id: 8759


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

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Permalink: https://www.hzdr.de/publications/Publ-8758
Publ.-Id: 8758


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

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Permalink: https://www.hzdr.de/publications/Publ-8757
Publ.-Id: 8757


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.

Permalink: https://www.hzdr.de/publications/Publ-8756
Publ.-Id: 8756


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

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Permalink: https://www.hzdr.de/publications/Publ-8749
Publ.-Id: 8749


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

Permalink: https://www.hzdr.de/publications/Publ-8748
Publ.-Id: 8748


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

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Permalink: https://www.hzdr.de/publications/Publ-8747
Publ.-Id: 8747


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

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Permalink: https://www.hzdr.de/publications/Publ-8746
Publ.-Id: 8746


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

Permalink: https://www.hzdr.de/publications/Publ-8745
Publ.-Id: 8745


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

Permalink: https://www.hzdr.de/publications/Publ-8744
Publ.-Id: 8744


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

Permalink: https://www.hzdr.de/publications/Publ-8743
Publ.-Id: 8743


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

Permalink: https://www.hzdr.de/publications/Publ-8742
Publ.-Id: 8742


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

Permalink: https://www.hzdr.de/publications/Publ-8741
Publ.-Id: 8741


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

Permalink: https://www.hzdr.de/publications/Publ-8740
Publ.-Id: 8740


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

Permalink: https://www.hzdr.de/publications/Publ-8739
Publ.-Id: 8739


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

Permalink: https://www.hzdr.de/publications/Publ-8737
Publ.-Id: 8737


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 Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-458 2006

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Permalink: https://www.hzdr.de/publications/Publ-8736
Publ.-Id: 8736


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

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Permalink: https://www.hzdr.de/publications/Publ-8734
Publ.-Id: 8734


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

Permalink: https://www.hzdr.de/publications/Publ-8733
Publ.-Id: 8733


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

Permalink: https://www.hzdr.de/publications/Publ-8732
Publ.-Id: 8732


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

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Permalink: https://www.hzdr.de/publications/Publ-8730
Publ.-Id: 8730


Magnetic excitations in sine-Gordon spin chains: ESR studies

Zvyagin, S. A.
  • Invited lecture (Conferences)
    Workshop, 15.08.2005, Kharkov, Ukrainian

Permalink: https://www.hzdr.de/publications/Publ-8729
Publ.-Id: 8729


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

Permalink: https://www.hzdr.de/publications/Publ-8728
Publ.-Id: 8728


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

Permalink: https://www.hzdr.de/publications/Publ-8727
Publ.-Id: 8727


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

Permalink: https://www.hzdr.de/publications/Publ-8725
Publ.-Id: 8725


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

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Permalink: https://www.hzdr.de/publications/Publ-8724
Publ.-Id: 8724


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.

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Permalink: https://www.hzdr.de/publications/Publ-8723
Publ.-Id: 8723


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

Permalink: https://www.hzdr.de/publications/Publ-8722
Publ.-Id: 8722


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

Permalink: https://www.hzdr.de/publications/Publ-8720
Publ.-Id: 8720


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

Permalink: https://www.hzdr.de/publications/Publ-8719
Publ.-Id: 8719


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 Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-456 2006

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Permalink: https://www.hzdr.de/publications/Publ-8717
Publ.-Id: 8717


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

Permalink: https://www.hzdr.de/publications/Publ-8716
Publ.-Id: 8716


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

Permalink: https://www.hzdr.de/publications/Publ-8715
Publ.-Id: 8715


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.

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Permalink: https://www.hzdr.de/publications/Publ-8714
Publ.-Id: 8714


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

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Publ.-Id: 8713


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

Permalink: https://www.hzdr.de/publications/Publ-8712
Publ.-Id: 8712


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

Permalink: https://www.hzdr.de/publications/Publ-8710
Publ.-Id: 8710


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

Permalink: https://www.hzdr.de/publications/Publ-8708
Publ.-Id: 8708


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

Permalink: https://www.hzdr.de/publications/Publ-8707
Publ.-Id: 8707


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

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Permalink: https://www.hzdr.de/publications/Publ-8706
Publ.-Id: 8706


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

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Permalink: https://www.hzdr.de/publications/Publ-8704
Publ.-Id: 8704


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

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Publ.-Id: 8703


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

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Permalink: https://www.hzdr.de/publications/Publ-8702
Publ.-Id: 8702


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

Permalink: https://www.hzdr.de/publications/Publ-8701
Publ.-Id: 8701


Copper deposition and dissolution in seemingly parallel electric and magnetic fields: Lorentz force distributions and flow configurations

Cierpka, C.; Weier, T.; Gerbeth, G.; Uhlemann, M.; Eckert, K.
In two different cylindrical electrochemical cells, copper deposition and dissolution in the presence of a magnetic field mostly parallel to the electric field has been investigated. Particle image velocimetry measurements show that even under such a field configuration where Lorentz forces are often a priori neglected in fact they may dominate the flow. Further on, depending on the electrode radius a reversal of the secondary flow has been found. This feature can be explained by the different Lorentz force configurations calculated from the magnetic field and the primary current distributions. The components of the magnetic field have been determined by means of a traversed Hall probe as well as calculated by a commercial finite element package. Experimentally and numerically determined field distributions match very well. A good agreement between the measured and calculated velocity distributions has also been found, suggesting that in the present case the effect of the Lorentz force alone is sufficient to explain the magnetic field influence on the flow.

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Permalink: https://www.hzdr.de/publications/Publ-8700
Publ.-Id: 8700


Electron Imaging Based on Charge Density Potentials and Frozen Lattices

Scheerschmidt, K.; Kuhlmann, V.; Rother, A.; Gemming, S.
Standard potential for the simulation of electron holographic images are based on the superposition of atomic scattering potentials, and thermal effects are included by a Debye-Waller factor. In the present theoretical treatment these limitations have been overcome by the use of MD simulations with atomistic pair potentials, which yield an atom-resolved description of the thermal motion. A further refinement of the scattering potential is possible, if the self-consistently calculated electron distribution from a first-principles calculation on selected MD frames is employed instead of the spherical electronic part of the superposed atomic potentials.
Keywords: Electron scattering, thermal effects, Debye-Waller factor
  • Poster
    IMC 16, 02.-07.09.2006, Sapporo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8699
Publ.-Id: 8699


Modelling ferroic functional elements

Gemming, S.
The modelling concepts of a nanoscale organic field effect transistor on a ferroelectric substrate are presented. The device consists of a ferroelectric substrate with a switchable, macroscopic electric polarisation, an electric-field-sensitive organic molecule, and suitable connectors. The structural and electronic properties of the single components and the major interactions between them are modelled by first-priciples electronic structure calculations. For the influence of the electric field on the optical and the conductivity properties of the larger organic molecules, a related density-functional-based tight-binding scheme was employed, which focusses on the salient features of the electronic system. For the self-assembly of the transistor building blocks, mesoscale approaches based on atomistic pair potentials and on a supramolecular Ising-type modelling have been developped and successfully applied.
Keywords: multi-scale modelling, functional materials, organic field effect transistor, optical properties, conductivity
  • Invited lecture (Conferences)
    MMM 2006 - International Conference on Multiscale Materials Modelling, 17.-22.09.2006, Freiburg, Brsg., Deutschland
  • Contribution to proceedings
    MMM 2006 - Third International Conference on Multiscale Materials Modeling, 18.-22.09.2006, Freiburg, Brsg., Deutschland
    Proceedings of MMM III, Stuttgart: Fraunhofer IRB Verlag, 3-8167-7206-4, 835-842
  • Invited lecture (Conferences)
    SFB 484 - Kooperative Phänomene im Festkörper, 16.10.2007, Augsburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-8698
Publ.-Id: 8698


Simulation and AFM-Measurement Of PTCDA On Ag-supported KBr Films

Gemming, S.; Olbrich, C.; Morawetz, K.; Schreiber, M.; Loppacher, C.; Seifert, G.; Eng, L. M.
On a partially KBr-covered Ag(111) substrate thin films of PTCDA molecules exhibit different growth modes, which depend on the thickness of the KBr layer. If no KBr is present, PTCDA form large islands with a herringbone-type substructure; on 1 ML KBr many small, not well aligned PTCDA islands with a large size distribution are formed. On 2ML KBr, again large flat PTCDA clusters are observed, which exhibit a pile-up of PTCDA molecules at the edges of the KBr islands. These growth modes have been analysed with an anisotropic Ising model for a square lattice including next-nearest neighbour interactions. The coupling constants and the adsorbate-substrate interaction strength were derived from electronic-strcuture calculations. The simulations give evidence that large clusters are formed if either the adsorbate-substrate interactions (no KBr) or the lateral inter-molecular interactions (2 ML KBr) dominate. In the intermediate case of 1 ML KBr on Ag(111), both mechanisms compete and a high number of cluster seeds is generated. The presence of the surface steps between regions of different KBr layer thickness enhances this effect.
Keywords: Monte-Carlo, Ising, 2D square lattice, surface step, pattern formation
  • Lecture (Conference)
    IMC16, 02.-07.09.2006, Sapporo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8697
Publ.-Id: 8697


Structure and stability of Molybdenum Sulfide Fullerenes

Enyashin, A. N.; Gemming, S.; Bar-Sadan, M.; Popovits-Biro, R.; Hong, S. Y.; Prior, Y.; Tenne, R.; Seifert, G.
Atomic models of MoS-based nanoparticles with fullerene-like structures were constructed. Their stability and electronic properties with respect to the particle size and composition have been investigated for the first time using the DF-TB method. The present calculations and MD simulations show that stoichiometric single-walled moS2 fullerenes with octahedral shape are unstable, at least up to sizes of several hundreds of atoms. The instability is attributed to the high strain energies at the corners of the MoS2 nanooctahedra. However, the particles are considerably stabilized if local deviations from the stoichiometry is allowed at the corners. An additional attractive inter-layer interaction enhances this trend, such that multi-wall nanooctahedra with sizes between thousand and ten thousand atoms are stable species, which can be observed experimentally. Larger nanooctahedra are transformed into multiwall particles with a spherical shell.
Keywords: DFTB calculations, MoS2, inorganic fullerenes

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Permalink: https://www.hzdr.de/publications/Publ-8696
Publ.-Id: 8696


Reduction of surface coverage of finite systems due to geometrical steps

Morawetz, K.; Olbrich, C.; Gemming, S.
The coverage of vicinal, stepped surfaces with molecules is simulated with the help of a two-dimensional Ising model including local distortions and a Schwoebel barrie term at the steps. An effective two-spin model is capable to describe the main properties of this distorted Ising model. It is employed to analyze the behavior of the system close to the critical points. Within a well-defined regime of bonding strengths and Schwoebel barriers we find a reduction of coverage (magnetization) due to the presence of the surface step. This results in a second, low-temperature transition besides the standard Ising order-disorder transition. The additional transition is characterized by a divergence of the susceptibility and the magnetization as finite-size effects. Due to the surface step the specific heat diverges with a power law.
Keywords: Monte-Carlo simulation, Ising model, finite-size effects, mean-field model, 2D square lattice, Schwoebel barrier

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Permalink: https://www.hzdr.de/publications/Publ-8695
Publ.-Id: 8695


SrTiO3(001)|LaAlO3(001) multilayers: A density-functional investigation

Gemming, S.; Seifert, G.
SrTiO3(0 0 1)|LaAlO3(0 0 1) (STO|LAO) multilayers were investigated by density-functional band structure calculations. The lattice constant parallel to the interface equals roughly the average of the two constituents (3.81 Angstrom). The system contains two interface terminations: (I) SrO(0 0 1)|AlO2(0 0 1) with a spacing of 1.92 Angstrom as in STO and (II) TiO2(0 0 1)|LaO(0 0 1) with a spacing of 1.89 Angstrom as in LAO.
Additional displacements of the metal atoms close to the boundaries lead to rumplings of up to 0.06 Angstrom. A stoichiometric model is electronically neutral and insulating. Model systems with only termination I exhibit spatially localised holes in the O-based valence band; in systems with termination II the additional electron occupies the Ti-based conduction band. The strongly anisotropic dielectric constants obtained from linear response calculations show that the interface chemistry allows a fine tuning of perovskite multilayers.
Keywords: electronic structure, DFT, interfaces, non-linear dielectric properties, ferroic oxides

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Permalink: https://www.hzdr.de/publications/Publ-8694
Publ.-Id: 8694


Structure and dynamics in the complex ion (UO2)2(CO3)(OH)3–

Szabó, Z.; Moll, H.; Grenthe, I.
The structure and ligand exchange dynamics of the ternary complex (UO2)2(CO3)(OH)3- have been investigatedd by EXAFS and NMR spectroscopy. Very broad signals can be observed in both the 13C and the 17O NMR spectra.
The EXAFS data show the presence of 1.3 ± 0.3 short uranium–oxygen distances at 2.26 Å, consistent with single bonded hydroxide and 3.9 ± 0.6 distances at 2.47 Å for the other ligands in the first co-ordination shell. There is also evidence for a U U interaction at 3.90 Å. Based on the EXAFS and NMR data we suggest the presence of three isomers with different bridge arrangements, the dominant one, C, contains 80% of the uranium and the minor ones A and B, 5 and 15%, respectively. The ligand exchange reactions between these isomers are slow.
The NMR data indicate that the main reactions involve intramolecular exchanges between isomers with different positions of the non-bridging ligands in A, B and C. We suggest that these take place through water exchange as discussed earlier for other ternary uranium() complexes.

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Permalink: https://www.hzdr.de/publications/Publ-8693
Publ.-Id: 8693


Characterization of Nickel induced crystallized Silicon by spectroscopic ellipsometry

Pereira, L.; Águas, H.; Beckers, M.; Martins, R. M. S.; Fortunato, E.; Martins, R.
In this work Spectroscopic Ellipsometry (SE) was used to study metal induced crystallization (MIC) on amorphous silicon films in order to analyze the influence of different annealing conditions on their structural properties. The variation of the metal thickness has shown to be determinant on the time needed to full crystallize silicon films. Films of 100 nm thickness crystallize after 2h at 500ºC using 1 nm of Ni deposited on it. When reducing the average metal thickness down to 0.05 nm the same silicon film will need almost 10 hours to be totally crystallized. Using a new approach on the modelling procedure of the SE data we show to be possible to determine the Ni remaining inside the crystallized films. The method consists in using Ni as reference on the Bruggeman Effective Medium Approximation (BEMA) layer that will simulated the optical response of the crystallized silicon. Silicon samples and metal layers with different thicknesses were analyzed and this new method has shown to be sensible to changes on the initial metal/silicon ratio. The nickel distribution inside the silicon layers was independently measured by Rutherford Backscattering Spectroscopy (RBS) to check the data
obtained from the proposed approach.
  • Materials Research Society Symposium Proceedings 910(2006), 0910-A21-06

Permalink: https://www.hzdr.de/publications/Publ-8692
Publ.-Id: 8692


The geomagnetic dynamo - laboratory experiments

Stefani, F.; Gerbeth, G.; Gailitis, A.
After seven years of successful experimental dynamo work, and after six years work of the DFG Priority Programme 1097 "Geomagnetic field variations", we summarize what has been achieved in the liquid metal laboratories, and what part of this could be of interest for geodynamo researchers. We try to make a compromise between a general survey of the worldwide dynamo scene, and a stock-taking of the activities in the framework of the Priority Programme. Since one project was directly devoted to the Riga dynamo experiment, we discuss this experiment a bit more in detail.
  • Invited lecture (Conferences)
    International Final Colloquium of the German Science Foundation Priority Programme 1097 "Geomagnetic Field Variations: Space-Time Structure, Processes, and Effects on System Earth", 04.-05.10.2006, Braunschweig, Germany
  • Contribution to proceedings
    International Final Colloquium of the German Science Foundation Priority Programme 1097 "Geomagnetic Field Variations: Space-Time Structure, Processes, and Effects on System Earth", 04.-05.10.2006, Braunschweig, Germany
    Terra Nostra 3(2006), Berlin: Selbstverlag der Alfred-Wegener-Stiftung, 0946-8978, 83-93

Permalink: https://www.hzdr.de/publications/Publ-8691
Publ.-Id: 8691


Electron intraband capture and relaxation in self-assembled InAs/GaAsquantum dots

Menzel, S.; Zibik, E. A.; Aivaliotis, P.; Carpenter, B. A.; Stehr, D.; Winnerl, S.; Helm, M.; Steer, M. J.; Hopkinson, M.; Cockburn, J. W.; Wilson, L. R.
We will present a detailed investigation of intraband electron capture and relaxation processes in InAs quantum dots (QDs) using an energy and temperature dependent, mid-infrared pump-probe (PP) measurement. We find that the electron relaxation time is strongly dependent on the photo-excitation energy and varies from ~4 ps for relaxation from the higher energy excited states inside the QDs up to ~10 ps for relaxation from the wetting layer (WL)/barrier states. Although the ‘phonon bottleneck’ effect predicts the capture time to be much longer, the measured times still exceed significantly the typical ~1ps relaxation time for quantum wells. Also our intraband measurements clearly indicate that the electron capture/relaxation occurs directly to the QD ground state, not step-wise between the QD excited states as it was suggested previously. An advantage of the intraband PP measurement is that the electron population is determined by the doping, varying from 0.5 up to >2 electrons per dot, giving a more precise control of the QD population compared with interband excitation.
Our previous studies have shown that the electron relaxation in QDs from the p-like first excited state to s-like ground state (low energy peak in Fig.1) is typically >30ps [1]. Surprisingly, in the present work, the PP signal corresponding to the relaxation of electrons from higher energy excited states (dashed line in Fig.2) decays with time constant τ ~4ps. Such a short decay time allows us to conclude, that electron relaxation occurs directly to the ground state, avoiding the p-state. When we excite into the WL/barrier states the intraband relaxation time increases to ~10ps for the PP energy of ~210meV. Furthermore, at low temperatures a bi-exponential decay of the PP signal corresponding to electron relaxation from WL/barrier states to QD ground state with τ1=(8 ± 2) ps and τ2=(300 ± 100) ps is observed (solid line in Fig.2 and inset). The short decay time is related to electron capture in the same QD from which it was originally excited, whereas the long decay time is strongly dependent on the temperature and originates from the electron capture and thermal re-emission in adjacent QDs.
Additionally, interband pump/intraband probe measurements were performed from which the electron capture times from the GaAs barrier and WL states into the QDs of ~6ps and ~4ps, respectively, has been determined. Since interband excitation creates photo-generated electron-hole pairs, we explain the shortening of the electron capture time by Auger-type carrier-carrier scattering.
Using a combination of these two techniques we have been able to gain detailed insight into the electron relaxation processes in QDs, which are significant for quantum dot based lasers and infrared photodetectors. Our results show that due to longer WL states lifetime (~10ps) QD infrared photodetectors have the potential to be more efficient compared to quantum well analogues.
  • Lecture (Conference)
    International Conference on Superlattices, Nanostructures and Nanodevices 2006, 30.07.-04.08.2006, Instanbul, Turkei

Permalink: https://www.hzdr.de/publications/Publ-8690
Publ.-Id: 8690


Experimental data on a three dimensional flow field around an obstacle in a vertical pipe

Al Issa, S.; Prasser, H.-M.; Beyer, M.
In many industrial applications, i.e. constrictions, expansions and various valves, three dimensional two-phase flows occur. Two-phase flows over an asymmetric obstacle create pronounced 3D structures, including: flow separation at the obstacle edge, recirculation zone and vortex formation in the wake of them as well as strong shear fields with curved streamlines and large angles.
The presentation starts with a description of the test section, the measuring technique and the boundary conditions of the required experiments. Furthermore, algorithms and equations for estimation of the axial liquid and the lateral bubble velocities were given. The results of the data treatment are shown in cross section views of the tube in well defined distances under and above the obstacle. Additionally, comparisons of void fractions and liquid velocities of selected experiments were discussed. In this context it is possible to identify from the plots the stagnant point upstream the obstacle and the flow separation zone as well as recirculation and reattachment phenomena.
The ability to build 3D sets of data makes it useable to validate CFD codes and proof new implemented models. The work will be continued.
Keywords: Two-phase flow, asymmetric obstacle, flow separation, recirculation zone, vortex, lateral bubble velocity, CFD code
  • Lecture (Conference)
    Multiphase Flow Workshop, 27.-29.06.2006, Dresden, Germany
  • Contribution to proceedings
    Multiphase Flow Workshop, 27.-29.06.2006, Dresden, Germany
    CD - Multiphase Flow Workshop: 28.06.2006, paper 05, II-5

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Publ.-Id: 8689


Quantum Well Infrared Photodetector: Physics and Applications

Schneider, H.; Liu, H. C.
Addressed to both students as a learning text and scientists/engineers as a reference, this book discusses the physics and applications of quantum-well infrared photodetectors (QWIPs). It is assumed that the reader has a basic background in quantum mechanics, solid-state physics, and semiconductor devices. To make this book as widely accessible as possible, the treatment and presentation of the materials is simple and straightforward. The topics for the book were chosen by the following criteria: they must be well-established and understood; and they should have been, or potentially will be, used in practical applications. The monograph discusses most aspects relevant for the field but omits, at the same time, detailed discussions of specialized topics such as the valence-band quantum wells.
Keywords: Intersubband, Quantum-well infrared photodetector, QWIP, Thermal Imaging
  • Book (Authorship)
    Heidelberg: Springer-Verlag, 2006
    250 Seiten

Permalink: https://www.hzdr.de/publications/Publ-8688
Publ.-Id: 8688


Quadratic autocorrelation of free-electron laser radiation and photocurrent saturation in two-photon quantum well infrared photodetectors

Schneider, H.; Drachenko, O.; Winnerl, S.; Helm, M.; Walther, M.
Using the free-electron laser facility FELBE, the authors have studied the influence of the intensity on the quadratic autocorrelation measured with two-photon quantum well infrared photodetectors (QWIPs). At high illumination powers, the shape of the autocorrelation trace is affected by photocurrent saturation of the two-photon QWIP. They describe the saturation mechanism by different analytical models taking account of the photocurrent nonlinearity in analogy to linear QWIPs and give conditions where true quadratic behavior can be observed. While these studies were carried out at 77 K, properties of two-photon QWIPs at room temperature will also be addressed.
Keywords: quantum-well infrared photodetector, QWIP, quadratic autocorrelation, GaAs/AlGaAs, free-electron laser

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Publ.-Id: 8687


FELBE: a new infrared free-electron-laser user facility

Helm, M.; Michel, P.
no abstract available
Keywords: free-electron laser
  • Notiziario Neutroni e Luce di Sincrotrone 11(2006)2, 33-35

Permalink: https://www.hzdr.de/publications/Publ-8686
Publ.-Id: 8686


Spectroscopic ellipsometry study of nickel induced crystallization of a-Si

Pereira, L.; Águas, H.; Beckers, M.; Martins, R. M. S.; Fortunato, E.; Martins, R.
The aim of this work is to present a spectroscopic ellipsometry study focused on the annealing time effect on nickel metal induced crystallization of amorphous silicon thin films. For this purpose silicon layers with 80 and 125 nm were used on the top of which a 0.5 nm Ni thick layer was deposited. The ellipsometry simulation using a Bruggemann Effective Medium Approximation shows that films with 80 nm reach a crystalline fraction of 72% after 1 h annealing, appearing to be full crystallized after 2 h. No significant structural improvement is detected for longer annealing times. On the 125 nm samples the crystalline volume fraction after 1 h is only around 7%, requiring 5 h to get a similar crystalline fraction than the one achieved with the thinner film. This means that the time required for full crystallization will be strongly determined by the Si layer thickness. Using a new fitting approach the Ni content within the films was also determined by SE and related to the silicon film thickness.
Keywords: Crystallization; Optical spectroscopy; Rutherford backscattering; Microstructure
  • Journal of Non-Crystalline Solids (2006)352, 1204-1208

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Publ.-Id: 8685


Planar channeling radiation from electrons in quartz

Wagner, W.; Azadegan, B.; Grigoryan, L. S.; Pawelke, J.
The possibility to stimulate channeling radiation by external excitation of ultrasonic waves in a piezoelectric single crystal is predicted by theory. The experimental verification of this effect requires the knowledge of the undisturbed spectrum of channeling radiation. For the first time, planar channeling radiation from 17, 25 and 32 MeV electrons channeled in a quartz crystal has been measured. The analysis performed bases on the application of the theory of channeling radiation. Real planar continuum potentials of quartz, eigenvalues of channeling states and transition energies have been calculated and radiation intensities were evaluated. The corresponding calculations proved to be necessary for the unambiguous identification of the spectra of channeling radiation registered from a hexagonal crystal.
Keywords: channeling radiation, quartz crystal

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Publ.-Id: 8684


Quasi-Particle Description of Strongly Interacting Matter: Towards a Foundation

Bluhm, M.; Kämpfer, B.; Schulze, R.; Seipt, D.
We confront our quasi-particle model for the equation of state of strongly interacting matter with recent first-priciple QCD calculations. In particular, we test its applicability at finite baryon densities by comparing with Taylor expansion coefficients of the pressure for two quark flavours. We outline a chain of approximations starting from the Phi-functional approach to QCD which motivates the quasi-particle picture.
  • Contribution to proceedings
    Hot Quarks 2006, 15.-20.05.2006, Villasimius, Sardinia, Italy
  • European Physical Journal C 49(2007)1, 205-211
    DOI: 10.1140/epjc/s10052-006-0056-y

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Publ.-Id: 8683


Isentropic Equation of State of Two-Flavour QCD in a Quasi-Particle Model

Bluhm, M.; Kämpfer, B.; Schulze, R.; Seipt, D.
We examine the isentropic QCD equation of state within a quasi-particle model being adjusted to first principle QCD calculations of two quark flavours. In particular, we compare with Taylor expansion coefficients of energy and entropy densities and with the isentropic trajectories describing the hydrodynamical expansion of a heavy-ion collision fireball.
Keywords: QCD Equation of State, Quasi-particle model
  • Contribution to proceedings
    International Workshop on Hot and Dense Matter in Relativistic Heavy Ion Collisions, 09.-12.04.2006, Budapest, Hungary
  • Acta Physica Hungarica A 27(2006), 397-402

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Publ.-Id: 8682


An investigation of target poisoning during reactive magnetron sputtering using ion beam analysis and energy resolved mass spectroscopy

Güttler, D.; Abendroth, B.; Möller, W.
The effect of target poisoning is commonly observed in reactive magnetron sputtering, where a metallic target is sputtered in reactive gas atmosphere. This phenomenon can be described quite well in terms of sputter rate, reactive gas pressure and pumping speed, however the details of the processes on the target are not yet understood. In this work, an experimental setup is presented that combines energy resolved mass spectroscopy with quantitative in situ nuclear reaction analysis (NRA) of the reactive species target coverage. By adjusting the position of the magnetron, locally resolved information is obtained across the target surface. Experiments have been performed for the reactive deposition of TiN in an Ar/N2 gas mixture at varying process parameters, with special emphasis on the transition from metallic to poisoned target mode.
In the centre of the race track the nitrogen coverage is significantly smaller than on the remaining part of the target surface. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen.
The energy distribution of the neutral species is clearly composed from particles originating from the gas atmosphere and sputtered particles from the magnetron target. Significant differences in the energy distribution of the sputtered atoms are observed between the centre and the erosion zone of the target. The ratio of sputtered N/Ti atoms reflects characteristically the metallic or compound mode of operation.
  • Lecture (Conference)
    Workshop "Oberflächentechnologie mit Plasma- und Ionenstrahlprozessen", 14.-16.03.2006, Mühlleithen, Deutschland

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Publ.-Id: 8681


Target poisoning during magnetron sputtering: Real-time in-situ analysis and collisional computer simulation

Güttler, D.; Abendroth, B.; Grötzschel, R.; Depla, D.; Möller, W.
The evolution of reactive gas uptake at the target surface has been investigated by real-time in-situ diagnostics during magnetron sputtering. Using a planar circular DC magnetron for reactive sputter deposition of TiN from a Ti target in an argon/nitrogen gas mixture, the target uptake of nitrogen was determined at varying gas flow of nitrogen using the 14N(d,a)12C nuclear reaction, directly demonstrating the target "poisoning" effect. The expected hysteresis behaviour at increasing/decreasing nitrogen gas flow is confirmed. In the centre of the racetrack, the nitrogen uptake is significantly smaller than on the remaining target surface. Within the precision of the measurement, the nitrogen content remains unaltered after switching off the magnetron, indicating the absence of a significant mobile fraction of nitrogen in the target. The maximum amount of retained nitrogen significantly exceeds one adsorbed monolayer, which is attributed to nitrogen ion implantation and recoil implantation of adsorbed nitrogen. This is quantitatively reproduced by TRIDYN collisional computer simulations.
  • Poster
    VEIT 2005, 14th International Summer School on Vacuum, Electron and Ion Technologies, 12.-16.09.2005, Sunny Beach, Bulgaria

Permalink: https://www.hzdr.de/publications/Publ-8680
Publ.-Id: 8680


Relaxation dynamics of interminiband transitions and electron cooling in doped GaAs/AlGaAs superlattices

Stehr, D.; Winnerl, S.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.
Semiconductor superlattices represent a key model system for artificial crystals and are an essential component of novel infrared devices such as detectors and quantum cascade lasers. Hence their optical and transport properties have been investigated extensively during the past two decades. However, unlike for quantum well structures where considerable knowledge on the intersubband relaxation dynamics has been obtained, so far no experimental work has been published on the interminiband relaxation dynamics in superlattices.

We have studied the transient transmission of a doped GaAs/Al0.3Ga0.7As superlattice in pump-probe experiments [1]. The superlattice with thickness of 9.0 nm and 2.5 nm of the wells and barriers, respectively, was n-doped in the center of the wells, resulting in a doping density of 1.51016 cm-3 averaged over one superlattice period. Picosecond infrared pulses in the range from 4 µm to 22 µm were generated at 13 MHz repetition rate by the free-electron laser FELBE at the Forschungszentrum Rossendorf. In particular, the experiments were performed at the absorption maxima of the superlattice at 9.0 µm and 15.8 µm. These wavelengths are the spectral positions of the van Hove singularities of the joint density of states in the center and at the edge of the mini-Brillouin zone, respectively.

The measured pump-probe signals consist of a fast component due to the bleaching of the interminiband transition and subsequent relaxation and thermalization, and a slower component due to cooling of the heated electron system. The fast component decays typically around 2-2.5 ps, in reasonable agreement with published theoretical values [2]. The slower component due to cooling is positive for excitation at 9.0 µm and negative at 15.8 µm and shows a strong temperature and excitation density dependence with cooling times ranging from 5 to 50 ps. This behavior is consistent with the temperature dependence of the linear absorption spectrum, i.e. yielding higher or lower transmission for increasing electron temperature. The effect provides an internal thermometer for the miniband electrons on a picosecond timescale.

We will also report on data from superlattices with higher doping density, which shows the influence of electron-electron scattering.

[1] D. Stehr et al., submitted to Appl. Phys. Lett.
[2] F. Compagnone, A. Di Carlo, and P. Lugli, Appl. Phys. Lett. 80, 920 (2002)
  • Lecture (Conference)
    28th International Conference on the Physics of Semiconductors, 24.-28.07.2006, Wien, Austria
  • Contribution to proceedings
    28th International Conference on the Physics of Semiconductors, 24.-28.07.2006, Wien, Austria
    AIP Conference Proceedings 893, 485-486

Permalink: https://www.hzdr.de/publications/Publ-8679
Publ.-Id: 8679


Theory of impurity states in coupled quantum wells and superlattices and their infrared absorption spectra

Stehr, D.; Helm, M.; Metzner, C.; Wanke, M. C.
The problem of shallow impurities in confined semiconductor systems has been extensively investigated over the past two decades. It is well known that in two dimensions the binding energy is increased and the degeneracy of the states is lifted due to the symmetry breaking. Yet virtually all calculations were based on variational approaches for the impurity levels; some more sophisticated calculations, on the other hand, were mostly done solely for the ground state and other low-lying states.

Here we present an essentially exact calculation, treating the quantum well (QW) and impurity potential on the same footing in a unified framework [1], by diagonalizing the fully three-dimensional Schrödinger equation exactly on a 100 x 100 nm grid (however neglecting electron-electron interaction). This results in some thousand states. To facilitate comparison with existing experiments we calculate the infrared (IR) absorption spectra by properly evaluating the matrix elements between all relevant states, taking into account their proper thermal occupation.

These calculations have lead to some remarkable insights:

In a superlattice (SL; we use 20 QWs for the calculation) we show that there is not only a an excited 2pz state slightly below the second miniband [2], but rather an excited, resonant impurity band which partly overlaps the second miniband [1]. Consequently the low-temperature IR absorption spectrum in not too highly doped SLs exhibits a transition from the 1s ground state to this resonant impurity band, showing two maxima related to the band edges. This implies that there are impurity states not only attached to the lower miniband edge, but also to the higher miniband edge. The localized nature of the high-energy peak can only be identified by analyzing the final-state wavefunction in the xy plane, since it occurs at nearly the same spectral position as the kz=0 interminiband peak. This observation requires re-interpretation of previous interminiband absorption experiments and is important for the experimental diagnostics of the magnetic-field induced metal-insulator transition. Note that the excited impurity band does not result from impurity levels overlapping in the xy plane, but from the state coupling in z-direction, just like the miniband.

By studying the energy levels and IR spectra for systems with a varying number of quantum wells, we can map out the transition from coupled QWs to a SL, i.e. from sharp intersubband and/or impurity lines to band-like spectra including their van Hove singularities. In a coupled double QW, where the 1-3 intersubband transition is symmetry forbidden, the related impurity transition can nevertheless be observed.

A particularly spectacular example is provided by the analysis of previously not understood experimental IR absorption spectra of a quadruple QW system. The complex temperature dependent absorption pattern is reproduced by our theory with a remarkable degree of accuracy.

[1] D. Stehr et al., Phys. Rev. Lett. 95, 257401 (2005)
[2] M. Helm et al., Phys. Rev. B 48, 1601 (1993)
  • Poster
    28th International Conference on the Physics of Semiconductors, 24.-28.07.2006, Wien, Austria
  • Contribution to proceedings
    28th International Conference on the Physics of Semiconductors, 24.-28.07.2006, Wien, Austria
    AIP Conference Proceedings 893, 243-244

Permalink: https://www.hzdr.de/publications/Publ-8678
Publ.-Id: 8678


Use of models for lift, wall and turbulent dispersion forces acting on bubbles for poly-disperse flows

Lucas, D.; Krepper, E.; Prasser, H.-M.
Closure laws are needed for the qualification of CFD codes for two-phase flows. In case of bubbly and slug flow, forces acting on the bubbles usually model the momentum transfer between the phases. These forces depend on the liquid flow field as well as on the size and the shape of the bubbles. The validation of these forces base on a detailed experimental database for vertical pipe flows, which contains data on the radial distribution of bubbles of different size and local bubble size distributions. A one-dimensional model resolving the variables in radial direction and considering a large number of bubble size classes, is used for an analysis of several bubble force models. Results of this model were compared to results of 3D simulations done by the commercial code CFX-5.7 for simplified cases with only one bubble class. The effects of the number of bubbles classes as well as the effect of the lateral extension of the bubbles were analysed. For the validation of bubble force models measured bubble size distributions were taken as an input for the model. On basis of the assumption of equilibrium of the lateral bubble forces, radial volume fraction profiles were calculated separately for each bubble class. In the result of the validation of different models for the bubble forces, a set of Tomiyama lift and wall force, deformation force and Favre averaged turbulent dispersion force was found to reflect the experimental data with best agreement. Some discrepancies remain at high liquid superficial velocities.
Keywords: bubbly flow, bubble forces, CFD, pipe flow

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Publ.-Id: 8677


Off-normal ion erosion of silicon – simultaneous observation of two ripple modes

Keller, A.; Roßbach, S.; Facsko, S.; Möller, W.
It is well known that oblique low and mediate energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelength ranging from 10 to 1000 nm. These structures were found on a large variety of materials, such as semiconductors, metals, and insulating surfaces [1]. The first attempt to describe the formation of surface ripples was made by Bradley and Harper [2]. In their framework the ripples are either parallel or perpendicular to the direction of the ion beam, depending on the angle of incidence. This was also shown experimentally on HOPG [3].
In the presented work we studied the formation of ripples on Si(100) surface under sub-keV Ar+ bombardment using ex-situ AFM. In addition to previous experimental observations two simultaneous ripple modes are found with direction perpendicular and parallel to the ion beam, respectively. The dependence of each mode on ion energy, fluence, flux, and incidence angle is investigated. The two modes have wavelengths of some ten and a few hundred nanometres and show different temporal behaviour. Finally, our observations are compared to simulations based on the damped Kuramoto-Sivashinsky equation [4].

[1] M. A. Makeev et al., Nucl. Inst. Meth. Phys. Res. B 197 (2002), 185
[2] R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6 (1988), 2390
[3] S. Habenicht et al., Phys. Rev. B 60 (1999), R2200
[4] S. Facsko et al., Phys. Rev. B 69 (2004), 153412
  • Lecture (Conference)
    22nd International Conference on Atomic Collisions in Solids, 21.-26.07.2006, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-8676
Publ.-Id: 8676


Computational studies on the design of an electromagnetic pump for the process of aluminum investment casting

Galindo, V.; Eckert, S.; Gerbeth, G.; Willers, B.
The mould filling process of aluminum investment casting consists basically of the liquid metal flow in a U-bend. It shows a high pouring velocity at the beginning and decreasing flow velocity values during the course of the process. The main problem is the occurrence of large velocity values at the beginning of the casting process, leading to an accumulated generation of vortices inside the pouring channel. A high rate of turbulence in the flow is supposed to entail the transported impurities, oxides or gas bubbles from the walls and the free surface, respectively, into the bulk of the casting patterns. As a result, the mechanical properties of the casting products are deteriorated.
We present results on the design and application of electromagnetic pumps to control the velocity of the aluminum melt during the pouring process. The induced electromagnetic force in the melt caused by the coil system were calculated using the commercial finite-element code OPERA-3d (Vector Fields Ltd.). The free surface problem which occurs in the riser of the casting unit was taken into account by a Volume-of-Fluids Method. Three-dimensional transient calculations using the commercial finite-element code FIDAP (FLUENT Inc.) were carried out for a simplified model system. Parallel to the simulations model experiments have been performed using the low melting eutectic GaInSn.
The casting unit was modeled by a perspex model [1], which also allows the monitoring of the filling process. Ultrasonic Doppler velocimetry measurements were applied in the model in order to validate the numerical calculations [2]. A comparison between numerical and experimental results showed an excellent agreement.
The main goal of this study is the optimization of the pump design depending on the geometry of the coil system in oder to achieve the best possible homogeneity in the electromagnetic force distribution with an integral flow rate of sufficient strength. Inhomogeneities in the force distribution can lead to undesirable fluid vortices in the melt, which on this part can induce a detriment of the material properties after solidification.

References

[1] A. Cramer, S. Eckert, V. Galindo, G. Gerbeth, W. Willers, W. Witke,
Liquid metal model experiments on casting and solidification processes
Journal of Materials Science 39 (2004) 7285-7294
[2] S. Eckert, G. Gerbeth, Th. Gundrum, F. Stefani, W. Witke,
New approaches to determine the velocity field in metallic melts,
Proceedings of the 4th Int. Conference on Electromagnetic Processing of
Materials (EPM 2003), Lyon (France), October 14-17, 2003, pp. 601-608
  • Lecture (Conference)
    7th World Congress on Computational Mechanics, 16.-22.07.2006, Los Angeles, California, United States

Permalink: https://www.hzdr.de/publications/Publ-8675
Publ.-Id: 8675


Nanostructures by ion beams

Schmidt, B.
Ion beam techniques, including conventional broad beam ion implantation, ion beam synthesis and ion irradiation of thin layers as well as local ion implantation with fine-focused ion beams (FIB) have been applied in different fields of micro- and nanotechnology. The ion beam synthesis of nanoparticels in high dose ion implanted solids is explained as phase separation of nanostructures from a super-saturated solid state through precipitation and Ostwald–ripening during subsequent thermal treatment of the ion implanted samples. A special topic will be addressed to self-organization processes of nanoparticles during ion irradiation of flat and curved solid state interfaces. As an example of silicon nanocrystal application the fabrication of silicon nanocrystal non-volatile memories will be described. Finally, the fabrication possibilities of nanostructures, like nanowires and chains of nanoparticles (e.g. CoSi2), by ion beam synthesis using a focused Co+ ion beam will be demonstrated and possible applications will be mentioned.
Keywords: Ion implantation, Ion beam synthesis, Ion irradiation, nanoclusters, nanowires
  • Radiation Effects and Defects in Solids 162(2007)3-4, 171-184
    DOI: 10.1080/10420150601132743
  • Invited lecture (Conferences)
    Workshop on Ion Beam Studies of Nanomaterials: Synthesis, Modification and Characterization, 26.06.-01.07.2006, Trieste, Italy

Permalink: https://www.hzdr.de/publications/Publ-8674
Publ.-Id: 8674


In-beam PET measurements of biological half-lives of {12}C irradiation induced beta+-activity

Fiedler, F.; Sellesk, M.; Crespo, P.; Jülich, R.; Parodi, K.; Pawelke, J.; Pönisch, F.; Enghardt, W.
One of the long-standing problems in carbon-ion therapy is the monitoring of the treatment, i.e. of the delivered dose to a given tissue volume within the patient. Over the last 8 years, in-beam positron emission tomography (PET) has been used at the experimental carbon ion treatment facility at the Gesellschaft für Schwerionenforschung (GSI) Darmstadt and has become a valuable quality assurance tool. In order to determine and evaluate the correct delivery of the patient dose, a simulation of the positron emitter distribution has been compared to the measurement. One particular effect is the blurring as well as the reduction of the measured activity distribution via washout. The objective of this study is the investigation of tissue dependent effective half lives from patient data. We find no significant dependence of the effective half life on the Hounsfield unit but on the local dose. The biological half-live within the high dose region is longer than in the low dose region. Furthermore, the influence of the overall treatment time on the kinetics of the positron emitter is reported. There are indications for a metabolic response of the tissue on the irradiation. Taking into account the biological half-life in the simulation leads to an improvement of the quality of the PET-images in some cases.
Keywords: in-beam PET, washout

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Publ.-Id: 8673


Excited and ground state properties of LaSrMnO4: A combined x-ray spectroscopic study

Kuepper, K.; Klingeler, R.; Reutler, P.; Büchner, B.; Neumann, M.
The electronic properties of the parent compound of the single layered manganites La1−xSr1+xMnO4, namely LaSrMnO4 has been investigated in a detailed spectroscopic study.
We apply different complementary x-ray spectroscopic techniques in the soft x-ray regime. X-ray photoelectron spectroscopy and normal like x-ray emission spectroscopy were used to reveal a detailed picture of the total and partial densities of states in this compound. Furthermore we apply resonant x-ray emission spectroscopy to the Mn L2,3 edges. The spectra exhibit a rich multiplet structure. Resonant x-ray emission spectroscopy at the O K edge is used to study the local partial densities of states of the in plane and out of plane oxygen atoms. The results are discussed along available band structure calculations as well as charge transfer multiplet calculations.
Keywords: PACS numbers: 71.20.-b, 75.47.Lx, 78.70.En, 79.60.-i

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Publ.-Id: 8672


One-step reductive etherification of 4-[18F]fluoro-benzaldehyde with decaborane

Funke, U.; Jia, H.; Fischer, S.; Scheunemann, M.; Steinbach, J.
Reductive coulling reactions between 4-[18F]fluoro-benzaldehyde ([18F]19 and different alcoholsby use of decaborane (B10H14)as reducing agent have the potential to synthesize 4-[18F]fluoro-benzylethers in one step. [18F]1 was sythesized from 4-trimethylammonium benzaldehyde (triflate salt) via a standard fluorination procedure (K[18F]F/Kryprofix 222) in dimethylformamide at 90°C for 25 min and purified by solid-phase extraction. Subsequently, reductive etherifications of [18F]1 were performed as one-step reactions with primary and secondary alcohols, mediated by B10H14 in acetonitrile at 60°C. Various 4-[18F]fluorobenzyl ethers (6 examples are shown) were obtained within 1-2h reaction time in decay-corrected radiochemical yields of 12-45%.
Keywords: 4[18F]fluoro-benzylether; fluorine-18; reductive etherification; decarborane; labelling
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 745-755
    DOI: 10.1002/jlcr.1087

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Publ.-Id: 8671


On the efficiency of MHD drag reduction

Gerbeth, G.; Shatrov, V.
Permanent magnets and high electric current densities are often used to achieve reasonable Lorentz forces for a magnetohydrodynamic flow control. This choice, however, usually leads to a low energetic efficiency for the flow control of seawater. We present results of direct numerical simulations of turbulent channel flow [1] drag reduction using electromagnetic forces. The Lorentz force is created by a permanent magnetic field and an electric current from electrodes placed on the bottom wall. The Reynolds number Re, the magnetic interaction parameter N and the load factor k are the control parameters of the problem.
In the first case we used a spanwise oscillating force. The efficiency is the ratio between saved and used power [2]. We found that the efficiency at the load factor k = 4 is about 100 times larger than at k = 1000.
In the second case a streamwise Lorentz force [3] was used. The flow is accelerated near the bottom and the thrust force applied to the bottom wall is directed against the mean flow. The energetic efficiency is the ratio between the mechanical power necessary to move the flat plate with a given velocity and the used electric power. The efficiency is more than 0.9 at k = 0.8.
The main result is that a significant efficiency improvement is possible if load factors k in the order of 1 are used.
References:
1. R.D. Moser, J. Kim and Nagi N. Mansour, "Direct numerical simulation of turbulent channel flow up to Ret = 590," Phys. Fluids, v. 11, no. 4, p. 943-945, 1999.
2. T.W. Berger, J. Kim, C. Lee and L. Lim, "Turbulent boundary layer control utilizing the Lorentz force," Phys. Fluids, v. 12, no. 3, p. 631-649, 2000.
3. A. Gailitis and O. Lielausis, "On the possibility of drag reduction of a flat plate in an electrolyte," Applied Magnetohydrodynamics, Rep. of the Phys. Inst., AN Latv. SSR, v. 12, p. 143-146, (in Russ.), 1961.
Keywords: MHD, drag reduction
  • Lecture (Conference)
    7th World Congress on Computational Mechanics, 17.-22.07.2006, Los Angeles, United States

Permalink: https://www.hzdr.de/publications/Publ-8670
Publ.-Id: 8670


The GDT as neutron source in a sub-critical system for transmutation?

Noack, K.; Rogov, A.; Ivanov, A. A.; Kruglyakov, E. P.
In the last decade, a great progress was made in developing projects of sub-critical fission systems dedicated to transmutation of nuclear waste. In contrast to a fission reactor, such a device is fed with neutrons from an outer source in order to sustain a steady-state power generation. The Budker Institute of Nuclear Physics has made the proposal of a powerful 14 MeV neutron source based on a gas dynamic trap (GDT). This neutron source is primarily thought as irradiation facility for fusion material research. So, the question raises, whether the GDT based neutron source could be a candidate to efficiently drive such a sub-critical system too. The contribution pursues this question using results of first neutron transport calculations. The calculations were made for a simplified model of an actinides burner, which has been developed for an international benchmark exercise performed under the auspices of the Nuclear Energy Agency (NEA) of the Organization for Economic Cooperation and Development (OECD). Important parameters of the burner are compared for two cases - when driven by a spallation or by the GDT neutron source. From this comparison some advices for further improvements of the GDT neutron source are concluded.
Keywords: transmutation of nuclear waste, sub-critical system, minor actinides burner, plasma neutron source, gas dynamic trap
  • Invited lecture (Conferences)
    Open Magnetic Systems for Plasma Confinement, 17.-21.07.2006, Tsukuba, Japan
  • Fusion Science and Technology 51(2007), 65-68

Permalink: https://www.hzdr.de/publications/Publ-8668
Publ.-Id: 8668


Spin-up and spin-down dynamics driven by a single rotating magnetic field pulse

Nikrityuk, P. A.; Eckert, S.; Eckert, K.
This paper presents a study concerning the transient dynamics of the flow field inside a liquid metal column created by an application of a rotating magnetic field (RMF) in form of a single pulse. The flow structure is governde by an impulsive spin-up form the rest state which is followed by a spin-down phase under the inertia of the fluid. A distinctive influence of pulse length the transient fluid flow has been found. Our results reveal that the recirculating flow in the radial-meridional plane shows periodic reversals. This phenomena is especially pronounced if the pulse length of the electromagnetic forcing corresponds to the so-called initial adjustment phase.
Keywords: electromagnetic stirring, rotating magnetic field, UDV flow measurment

Permalink: https://www.hzdr.de/publications/Publ-8667
Publ.-Id: 8667


Synthesis and evaluation of novel multimeric neurotensin(8-13) analogs

Hultsch, C.; Pawelke, B.; Bergmann, R.; Wüst, F.
Neurotensin(8–13) is a hexapeptide with subnanomolar affinity to the neurotensin receptor 1 which is expressed with high incidence in several human tumor entities. Thus, radiolabeled neurotensin(8–13) might be used for tumor targeting. However, its application is limited by insufficient metabolic stability. The present study aims at improving metabolic stability by the synthesis of multimeric neurotensin(8–13) derivatives rather than commonly employed chemical modifications of the peptide itself. Thus, different dimeric and tetrameric peptides carrying C- or N-terminal attached neurotensin(8–13) moieties have been synthesized and their binding affinity toward the neurotensin receptor has been determined. The results demonstrate that branched compounds containing neurotensin(8–13) attached via its C-terminus only show low receptor affinities, whilst derivatives with neurotensin(8–13) attached via the N-terminus show IC50 values in the nanomolar range. Moreover, within the multimeric neurotensin(8–13) derivatives with neurotensin(8–13) attached via the N-terminus an increasing number of branching units lead to higher binding affinities toward the neurotensin receptor.
Keywords: Neurotensin, Multimer, Peptides, Tumor targeting
  • Bioorganic & Medicinal Chemistry 14(2006)17, 5913-5920

Permalink: https://www.hzdr.de/publications/Publ-8666
Publ.-Id: 8666


Flow control in bubble-driven liquid metal flows by means of external magnetic fields

Zhang, C.; Eckert, S.; Gerbeth, G.
In our experiments we investigated the consequences of an application of both DC and AC magnetic fields on the velocity field of bubble plumes. A restructuring of the entire flow field can be observed if a bubble plume is exposed to a DC magnetic field. The application of a transverse field leads not only to a general damping of the flow, but also favours the occurrence of vortices aligned parallel to the magnetic field direction. AC magnetic fields can be applied to generate flow structures being different from the recirculating flow known from classical bubble plumes. A tailoring of the flow using magnetic fields obviously allows a control of the heat and mass transfer in bubble plumes.
Keywords: bubble plume, DC magnetic field, AC travelling magnetic field, electromagnetic stirring, velocity measurements, ultrasound Doppler technique
  • Contribution to proceedings
    EPM2006, 5th International. Conference on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan
    Proceedings: The Iron and Steel Institue of Japan (ISIJ), 4-930980-55-0 C3057, 242-247
  • Lecture (Conference)
    EPM2006, 5th International. Conference on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-8665
Publ.-Id: 8665


Velocity measurements in metallic melts driven by AC magnetic fields in a square vessel

Pal, J.; Eckert, S.; Zhang, C.; Gerbeth, G.
Model experiments are an important tool to understand the details of the flow structure and the transport properties of flows occurring in real-scale metallurgical facilities as well as to validate the multitude of numerical codes for flow simulation. The present study considers the electromagnetic stirring of a liquid metal by a rotating magnetic field (RMF). Measurements of the velocity field in a square column filled with the eutectic GaInSn have been carried out utilising the ultrasound Doppler velocimetry (UDV). In this paper the spatiotemporal properties of both the primary, swirling and the secondary flow arising from a sinusoidal modulation of the RMF will be presented.
Keywords: electromagnetic stirring, rotating magnetic field, velocity measurements, ultrasound Doppler technique
  • Contribution to proceedings
    5th International Conference on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan
    Proceedings: The Iron and Steel Institute of Japan (ISIJ), 4-930980-55-0 C3057, 725-730
  • Lecture (Conference)
    EPM 2006, 23.-27.10.2006, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-8664
Publ.-Id: 8664


The influence of electromagnetically-driven convection on temperature field and solute distribution during directional solidification

Willers, B.; Nikrityuk, P. A.; Eckert, S.; Eckert, K.
Solidification experiments as well as numerical simulations were carried out considering the directional solidification of Pb Sn alloys from a water cooled copper chill. A rotating magnetic field (RMF) was applied for melt agitation. The comparison between numerical simulations and solidification experiments delivered a good agreement. Our results disclose that the forced convection causes distinct modifications of the temperature and concentration field. The electromagnetic stirring promotes the columnar-to-equiaxed transition and causes a considerable grain refinement. Indications for a flow-induced fragmentation have been found in the microstructure of the stirred samples.
Keywords: solidification, fluid flow, electromagnetic stirring, rotating magnetic field
  • Contribution to proceedings
    EPM2006, 5th Int. Conference on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan
    Proceedings: The Iron and Steel Institute of Japan (ISIJ), 4-930980-55-0 C3057, 407-412
  • Lecture (Conference)
    EPM2006, 5th International Symposium on Electromagnetic Processing of Materials, 23.-27.10.2006, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-8663
Publ.-Id: 8663


Buoyancy driven coolant mixing studies of natural circulation flows at the ROCOM test facility using ANSYS CFX

Höhne, T.; Kliem, S.; Rohde, U.; Weiss, F.-P.
Coolant mixing in the cold leg, downcomer and the lower plenum of pressurized water reactors is an important phenomenon mitigating the reactivity insertion into the core. Therefore, mixing of the de-borated slugs with the ambient coolant in the reactor pressure vessel was investigated at the four loop 1:5 scaled ROCOM mixing test facility. Thermal hydraulics analyses showed, that weakly borated condensate can accumulate in particular in the pump loop seal of those loops, which do not receive safety injection. After refilling of the primary circuit, natural circulation in the stagnant loops can re-establish simultaneously and the de-borated slugs are shifted towards the reactor pressure vessel (RPV).
In the ROCOM experiments, the length of the flow ramp and the initial density difference between the slugs and the ambient coolant was varied. From the test matrix experiments with 0 resp. 2% density difference between the de-borated slugs and the ambient coolant were used to validate the CFD software ANSYS CFX. To model the effects of turbulence on the mean flow a higher order Reynolds stress turbulence model was employed and a mesh consisting of 6.4 million hybrid elements was utilized. Only the experiments and CFD calculations with modeled density differences show a stratification in the downcomer. Depending on the degree of density differences the less dense slugs flow around the core barrel at the top of the downcomer. At the opposite side the lower borated coolant is entrained by the colder safety injection water and transported to the core. The va¬li¬¬dation proves that ANSYS CFX is able to simulate appropriately the flow field and mixing effects of coolant with different densities.
Keywords: PWR, Boron Dilution, ROCOM
  • Contribution to proceedings
    14th International Conference on Nuclear Engineering, 16.-20.07.2006, Miami, United States
    CD-ROM, paper ICONE 14- 89120
  • Lecture (Conference)
    14th International Conference on Nuclear Engineering, 16.07.2006, Miami, United States

Permalink: https://www.hzdr.de/publications/Publ-8662
Publ.-Id: 8662


Competition between damage buildup and dynamic annealing in ion implantation into Ge

Posselt, M.; Bischoff, L.; Grambole, D.; Herrmann, F.
Channeling implantation of Ga into Ge is performed at two very different ion fluxes (1011 and 1019 cm-2 s-1), at two temperatures (room temperature and 250 0C), and at five different fluences. The fluence dependence of the range profiles and of the implantation damage is strongly influenced by defect accumulation and dynamic annealing. At 250 0C a significant reduction of the ion-beam-induced defects is already observed 1 s after an ion impact, and the maximum lifetime of the defects is less than 10 s. On the other hand, at room temperature no significant annealing is found within the first 10 s after ion impact. The measured Ga depth profiles are reproduced very well by atomistic computer simulations.
Keywords: Germanium, ion implantation, defects, computer simulation
  • Applied Physics Letters 89(2006), 151918

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Publ.-Id: 8661


Alkaline earth elements in the uranium phosphate system - a TRLFS study

Geipel, G.
wird nachgereicht
  • Lecture (others)
    Kolloquium, 01.08.2006, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8659
Publ.-Id: 8659


Uranium speciation in water - lectures learned from the nature

Geipel, G.
wird nachgereicht
  • Lecture (others)
    Seminar, 31.07.2006, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8658
Publ.-Id: 8658


Interaction of Cu(II) with dendritic ligands studied by TRLFSand some remarks on luminescence of uranium(V)

Geipel, G.
wird nachgereicht
  • Lecture (others)
    Seminar, 01.08.2006, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-8657
Publ.-Id: 8657


Evaluation of Research Institutes in Germany - Basics, Procedures, Results

Joehnk, P.
  • Invited lecture (Conferences)
    Workshop "Mechanism and criteria for efficiency of evaluation of research institutions", 14.07.2006, Moskva, Russia

Permalink: https://www.hzdr.de/publications/Publ-8656
Publ.-Id: 8656


Systematics of pion emission in heavy ion collisions in the 1A GeV regime

Reisdorf, W.; Stockmeier, M.; Andronic, A.; Benabderrahmane, M. L.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Kim, Y. J.; Kis, M.; Koczon, P.; Kress, T.; Leifels, Y.; Lopez, X.; Merschmeyer, M.; Schüttauf, A.; Alard, J. P.; Barret, V.; Basrak, Z.; Bastid, N.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Grishkin, Y.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Korolija, M.; Kotte, R.; Lebedev, A.; Matulewicz, T.; Neubert, W.; Petrovici, M.; Rami, F.; Ryu, M. S.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z.; Xu, H. S.; Yushmanov, I.; Zhilin, A.
Using the large acceptance apparatus FOPI, we study pion emission in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 197Au+197Au (0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include longitudinal and transverse rapidity distributions and stopping, polar anisotropies, pion multiplicities, transverse momentum spectra, ratios (pi+/pi-) of average transverse momenta and of yields, directed flow, elliptic flow. The data are compared to earlier data where possible and to transport model simulations.

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Permalink: https://www.hzdr.de/publications/Publ-8654
Publ.-Id: 8654


Synthesis of metal nanoparticles using bacterial surface layers (S-layers) as biological templates

Pollmann, K.; Merroun, M.; Raff, J.; Fahmy, K.; Hennig, C.; Selenska-Pobell, S.; Herrmannsdörfer, T.
The regular structured paracrystalline surface layers (S-layers), which are one of the most common surface structures found in bacteria and archaea, are promising biological templates for the production of metal nanoclusters. Most of them are composed of protein monomers with the ability to self assemble in two-dimensional arrays. They possess regularly arranged pores of identical size that enable the exchange of ions and small molecules between the living cells and their environment.
In the present work the purified S-layer sheets of the uranium mining waste pile isolate B. sphaericus JG-A12 were used as biological template to produce Pd, Au, and Pt nanoparticles of a size of 0.8-1 nm. Such metal nanoparticles may have strongly altered properties compared to their bulk counterparts making them interesting for the development of new materials and applications in the field of catalysis. The deposition of metal nanoclusters was performed via a two step process, consisting of biosorption by exposition of the S-layer proteins to a hydrolyzed solution of metal salt (I) and of metal reduction (II) by the addition of a strong reducing agent. The interaction of Pd(II) with the S-layer of B. sphaericus JG-A12 and the formed Pd-nanoclusters were analyzed using EXAFS-spectroscopy and ATR-FT-IR-spectroscopy. The analyses demonstrated the complexation of Pd(II) to carboxyl groups. The metal nanoclusters were investigated using EXAFS spectroscopy and SQUID magnetometry. The Pd and Pt nanoclusters reveal interesting magnetic properties in a wide temperature and magnetic field range.
  • Poster
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-8653
Publ.-Id: 8653


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