Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Biokinetics, metabolism and PET imaging with Cu-64 and Ga-68 labeled ghrelin analogues in rats

Bergmann, R.; Chollet, C.; Pietzsch, J.; Beck-Sickinger, A. G.; Steinbach, J.

Ghrelin is a gastric peptide involved in food intake control, and growth hormone release. Besides its well-defined orexigenic role, ghrelin is likely involved in tumor development and growth. Therefore, non-invasive imaging agents for determining ghrelin receptors are desirable. However, ghrelin receptors are expressed in low level making detection via imaging difficult. The labeling using activated esters like 4-(F-18-fluoro)benzoyl-succinimide (2) was not possible due to the existence of three primary amino groups per peptide. Therefore, human ghrelin1-28 [Lys16(NODAGA)]-ghrelin1-28 and a short ghrelin inverse agonist NODAGA-KwFwLL-NH2 were synthesised on solid-phase. Subsequently, radiolabeling yielded Cu-64- and Ga-68-NODAGA-peptides in high radiochemical purity (>98%) with a specific activity >10 GBq/Gmol. For basic radiopharmacological characterization biodistribution, small animal PET, and metabolite analysis in arterial blood plasma were carried out in Wistar rats with all 4 radiotracers. The ghrelin analogues were in high amounts taken up by the kidneys. The Cu-64- and Ga-68-NODAGA-KwFwLL-NH2 were for the most part hepathobilliary eliminated. The metabolite analysis showed the well-known des acyl ghrelin as the main metabolite in vivo reaching 90% in blood plasma after one hour. On the other site the NODAGAKwFwLL-NH2 peptides were highly stabile; only 5% metabolites were observed after one hour in rat plasma. Interestingly, the biodistribution and kinetics were similar for the pairs of peptide labeled ether with Cu-64 or Ga-68. This shows the small effect of the different ionization of the Ga-68 (neutral) or Cu-64 (one negative charge) NODAGA complexes on the biodistribution. The blood clearance of these peptides was relative low, with about 50% of starting amount after one hour. The high stability and low blood clearance are important prerequisites for further studies of ghrelin receptor imaging. These results indicate that further in vivo evaluation of radiolabeled ghrelin inverse agonists as potential PET tracers for ghrelin receptors is warranted.

Reference: (1) Holst, B., et al. (2003) High constitutive signaling of the ghrelin receptor--identification of a potent inverse agonist. Mol Endocrinol 17, 2201-10. (2) Bergmann, R., et al. (2002) Biodistribution and catabolism of (18)F-labeled neurotensin(8-13) analogs. Nucl Med Biol 29, 61-72.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057

  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Publ.-Id: 15243

Dual-labeled Cetuximab-based imaging agent for NIR Fluorescence and PET

Bergmann, R.; Zenker, M.; Walther, M.; Pietzsch, H.-J.; Hofheinz, F.; van den Hoff, J.; Pietzsch, J.; Steinbach, J.

Cetuximab (C225) as a chimeric monoclonal antibody specifically targets the epidermal growth factor receptor (EGFR) that often is overexpressed in human malignancies. This phenotype is associated with tumor aggressiveness, treatment resistance, and biological heterogeneity with potential to bypass the blockade of the EGFR signaling pathways. The aim of this work was to prepare and characterize the C225 for near infrared fluorescence (NIRF) and PET imaging using a X-SIGHT Large Stokes Shift Dye (X-SIGHT 670 LSS Dye) and [64Cu]Cu-NOTA as a prerequisite for combination of both imaging methods. C225 was conjugated with the bifunctional chelator 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bz-NOTA) and the X-SIGHT 670 Large Stokes Shift Dye, TFP Ester (XS670). The EGFR-affinity of the immunoconjugate resulted in 94% versus 100% of the unmodified C225 measured with specific enzyme-linked immunosorbent assay (ELISA) on EGFR-positive tumor cell line A431. C225-SCNBz-NOTA was labeled with 64Cu within 30 min with high radiolabeling yield and radiochemical purity. The [64Cu]Cu-NOTA-C225-XS670 showed high accumulation in xenotransplanted squamous cell carcinoma tumors in mice after 24 hours imaged with small animal PET and NIRF. The comparison of both methods in living animals showed the high signal intensity and accumulation of the probe in tumors; however only PET allowed the quantitative characterization of the probe distribution in vivo. The subsequent whole body cryosectioning of the animals into 40 µm sections permitted the direct comparison of the autoradiograms and NIRF images of the tissue cuts. The quantitative comparison of the autoradiograms and the NIRF images after coregistration of the corresponding images yielded a good correlation of the pixel intensities, but the different geometric resolution did not allow a pixel vise comparison. The NIRF images showed a higher differentiation than the autoradiograms. The dual-labeled C225 demonstrated the higher resolution and comparable concentration values of the antibody distribution in whole body cryosections of tumor bearing mice using the combination of 64Cu-radioluminography and NIRF imaging. The dual labeling of antibodies is a promising tool for quantitative evaluation of the long time distribution in animals using NIRF of cryosections beyond the decay of the radionuclide used.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057

  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Publ.-Id: 15242

Multimodality imaging in preclinical cancer research

Bergmann, R.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    4th Bioscan Imaging Users Meeting (European part), 10.10.2010, Vienna, Austria

Publ.-Id: 15241

Identification of transport processes in bioirrigated muddy sediments by [18F]fluoride PET (Positron Emission Tomography)

Roskosch, A.; Lewandowski, J.; Bergmann, R.; Wilke, F.; Brenner, W.; Burchert, R.

In aquatic environments transport processes across the sediment–water interface are intensified by bioirrigating macrozoobenthos. Transport processes caused by Chironomus plumosus larvae dwelling in U-tubes were investigated by dynamic small animal Positron Emission Tomography (PET) with [18F]fluoride. Significant tracer transport from the burrows into the sediment was detected; penetration was deeper at the outlet branch of the burrow than at the inlet branch. Hence, advection plays a significant role in exchange between water in the burrows and muddy sediment.

Publ.-Id: 15240

Small animal PET for evaluation of tumor therapy

Bergmann, R.

kein Abstract verfügbar

  • Lecture (others)
    Oncoray Retreat, 28.01.2010, Bautzen, D

Publ.-Id: 15239

Biodistribution, -kinetics, metabolic stability, and imaging with radioactive ghrelin analogues

Bergmann, R.

kein Abstract verfügbar

  • Lecture (Conference)
    2nd GIPIO meeting, 02.-03.06.2010, Copenhagen, Danmark

Publ.-Id: 15238

Small animal molecular imaging in cancer research

Bergmann, R.

Quantitative small animal imaging plays a key role in preclinical research and drug development. However, no single imaging modality is perfect and sufficient to gain all the necessary morphologic, physiologic, metabolic or genetic information. For instance, optical fluorescence imaging is difficult to quantify - especially in tissue more than a few millimetres in depth within a subject; magnetic resonance imaging of protons (MRI) has superb resolution but low sensitivity, positron emission tomography (PET) has very high sensitivity but poor resolution, single photon emission tomography (SPECT) has good resolution but low sensitivity and X-ray tomography (CT) has good resolution of bones but cannot good resolve tissues. The combination of multiple molecular imaging techniques can therefore offer synergistic advantages over any modality alone. The multimodal approach by combination of the methods and development of multimodal probes is far from trivial and a challenge for the interdisciplinary work and collaboration of scientists.
In the presentation we provide an overview of the small animal imaging in the Forschungszentrum Dresden-Rossendorf, recent developments of probes and applications in multimodal cancer research. We will show examples of quantitative imaging using low and high molecular weight probes and microspheres labeled for PET, SPECT and optical imaging. The especial developed animal bed system helps us to register the 3D data from different dedicated modalities for combining and comparing the methods. The development of imaging probes is embedded a combination of in vitro and ex vivo evaluation of gene expression, cell uptake and binding studies.
The molecular imaging in mouse and rat models allows us to ‘see’ the biological complexities of tumors for the treatment of this disease. This is one of the most exciting and growing areas in our research.

  • Invited lecture (Conferences)
    International workshop on bio-medical applications of micro-PET, 20.-21.09.2010, Seville, Spain

Publ.-Id: 15237

Small animal imaging in Cancer Research

Bergmann, R.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Budapest, 28.04.2010, Budapest, Hungary
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Veterinärmedizinische und Pharmazeutische Universität Brno, 27.04.2010, Brno, Czech Republic
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Karls-University Prague, 26.04.2010, Prague, Czech Republic

Publ.-Id: 15236

Multimodality small animal imaging in tumor biology

Bergmann, R.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Seminar Semmelweis University of Medicine, Faculty of Medicine, Institute of Human Physiology and Clinical Experimental Research, 28.04.2010, Budapest, Hungary

Publ.-Id: 15235

Synthesis and biological evaluation of novel 4-benzylpiperazine ligands for sigma-1 receptor imaging

Li, Z.-J.; Ren, H.-Y.; Cui, M.-C.; Deuther-Conrad, W.; Tang, R.-K.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.

We report the synthesis and evaluation of 4-benzylpiperazine ligands (BP-CH3, BP-F, BP-Br, BP-I, and BPNO2) as potential r1 receptor ligands. The X-ray crystal structure of BP-Br, which crystallized with monoclinic space group P21/c, has been determined. In vitro competition binding assays showed that all the five ligands exhibit low nanomolar affinity for r1 receptors (Ki = 0.43–0.91 nM) and high subtype selectivity (r2 receptor: Ki = 40–61 nM; Kir2/Kir1 = 52–94). [125I]BP-I (1-(1,3-benzodioxol-5-ylmethyl)-4-(4-iodobenzyl)piperazine) was prepared in 53 ± 10% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via iododestannylation of the corresponding tributyltin precursor. The log D value of [125I]BP-I was found to be 2.98 ± 0.17, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiolabeled substances in organs known to contain r1 receptors, including the brain, lung, kidney, heart, and spleen. Administration of haloperidol 5 min prior to injection of [125I]BP-I significantly reduced the concentration of radioactivity in the above-mentioned organs. The accumulation of radiolabeled substance in the thyroid was quite low suggesting that [125I]BP-I is relatively stable to in vivo deiodination. These findings suggest that the binding of [125I]BP-I to r1 receptors in vivo is specific.

Publ.-Id: 15234

Micro-structured copper electrodeposition in inhomogeneous magnetic fields

Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Fröhlich, J.

It is well known that in various electrochemical systems the mass transfer and also the morphology and the structure of the electrodeposits can be influenced by the proper application of magnetic fields. One of the main reasons seems to be the convection induced by the resulting magnetic forces. Lorentz forces have been used to tailor the electrodeposition of metals for quite a while. Only recently, an improved understanding of the convection forced was gained that turned out to be more complex than expected, even in simple geometries [1]. Additionally, the influence of magnetic gradient forces on the preparation of micro-structured metal deposits on field-gradient electrodes has been discussed in the literature [2]. These electrodes consist of magnetic elements such as permanent magnets or magnetized ferromagnetic materials which are arranged beneath the surface of the working electrode. Here, however, besides the magnetic gradient force, also the Lorentz force might influence the deposition process. The presentation will summarize new numerical simulations, analytical findings and experimental results in order to discuss the influence of the different magnetic forces involved and will discuss the prospects towards smaller deposition structures [3,4].

[1] G. Mutschke et al., Electrochim. Acta 55 (2010) 1543.

[2] K. Tschulik et al., Electrochem. Comm. 11 (2009) 2241.

[3] G. Mutschke et al., Electrochim. Acta 55 (2010) 9060.

[4] K. Tschulik et al., Electrochim. Acta 56 (2010) 297.

Keywords: Magnetoelectrochemistry; electrodeposition

  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15233

Future aspects of X-ray emission from crystalline undulators at positron channeling

Backe, H.; Krambrich, D.; Lauth, W.; Buonomo, B.; Dabagov, S. B.; Mazzitelli, G.; Quintieri, L.; Lundsgaard Hansen, J.; Uggerhoj, U. I.; Azadegan, B.; Dizdar, A.; Wagner, W.

In connection with ideas to produce undulator-like radiation in the hundreds of keV up to the MeV region by means of positron and electron channeling, there is renewed interest to study various channeling phenomena also experimentally. With electrons experiments have been performed at the Mainz Microtron MAMI to explore channeling-radiation emission by a 4-period epitaxially grown strained layer SiGe undulator. Unfortunately, high quality positron beams of sufficient intensity are not easily accessible. The only serious candidate in Europe seems to be the Beam Test Facility at INFN LNF Frascati, Italy. Some requirements to extend BTF in a facility which is also well suited for positron channeling-radiation experiments will be outlined.

Keywords: undulator radiation; crystal undulator; positron channeling; channeling radiation

  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Future aspects of X-ray emission from crystalline undulators at positron channeling, Bologna: Societa Italiana di Fisica, 175-180
  • Nuovo Cimento C 34(2011)04, 175-180
    DOI: 10.1393/ncc/i2011-10983-9

Publ.-Id: 15232

Simulation of axial channeling radiation on a thin Ge single crystal

Azadegan, B.; Dabagov, S. B.; Wagner, W.

Based on classical electrodynamics the radiation emitted by axially channeled electrons has been investigated by means of computer simulations. Using the Doyle-Turner approximation for the atomic scattering factor and taking thermal vibrations of atoms into account, we calculated the two-dimensional continuum potential of the <110> crystallographic axis of a thin Ge single crystal. The trajectories, velocities and accelerations of electrons are obtained by solving the equations of motion in three dimensions, and the spectral-angular distribution of radiation has been calculated in the classical way.

Keywords: axial channeling; channeling radiation; Germanium single crystal

  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Simulation of axial channeling radiation on a thin Ge single crystal, Bologna: Societa Italiana di Fisica, 149-156
  • Nuovo Cimento C 34(2011)04, 149-156
    DOI: 10.1393/ncc/i2011-10919-5

Publ.-Id: 15231

Ion erosion induced surface patterning studied by combined trim and kinetic monte-carlo simulations

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

Understanding of surface morphology evolution induced by ion erosion is still limited. Continuum models cannot explain microscopic processes. On the other hand, so far atomistic simulations could not describe pattern evolution on experimental spatiotemporal scales. Therefore, recently continuum equations were feeded with MD simulation results, which allows the understanding of smoothing mechanisms like an effective mass ‘downhill’ current induced by ballistic drift.

We developed a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. This allows a fully atomistic description on experimental spatiotemporal scales. 3D atom relocations were calculated using the binary collision approximation, whereas the thermally activated relaxation as well as diffusive processes were simulated by a bit-coded kinetic 3D Monte Carlo program. Effects like ballistic mass drift or dependence of local morphology on sputtering yield are automatically included by this approach.

The mechanism of ripple formation induced by a local surface currents is studied. The quantitative description of current vectors for different environmental parameters, and initial surface condition of sinusoidal structure, can be analized in time and space, following the local atomic drift. Different driving forces can be distinguished. Without ion irradiation the mass current vectors are always parallel to the surface plane with down-hill direction. Collision-cascade-induced defects change the mass currents significantly. Up-hill currents induce self-organization for certain obligue ion incidence angles. This driving forces causes patterning even without sputtering events.

Keywords: ripples; ion beam sputtering; pattern formation; kinetic Monte-Carlo; TRIM; crater formation; surface mass current

  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Publ.-Id: 15230

Channeling radiation on quartz stimulated by acoustic waves

Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Mkrtchyan, A. R.; Pawelke, J.

The stimulation of channeling radiation by acoustic waves excited in the single crystal has been predicted in early works of the 1980's. Based on quantum calculations, the described experiment aimed at verification of theoretical considerations. Making use of the reverse piezoelectric effect, hypersonic waves of frequency 12 GHz, which corresponds to a dedicated transition between bound states of planar channelled relativistic electrons, were excited in a single-crystal quartz plate. The spectrum of channeling radiation measured under the influence of acoustic waves reveals enhanced radiation intensity. The obtained results are discussed and may be phenomenologically understood assuming electron diffraction on an acoustic superlattice.

Keywords: channeling radiation; quartz single crystal; ultrasound

  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Channeling radiation on quartz stimulated by acoustic waves, Bologna: Societa Italiana di Fisica, 133-140
  • Nuovo Cimento C 34(2011)04, 133-140
    DOI: 10.1393/ncc/i2011-10899-4

Publ.-Id: 15229

Ion-beam-induced interface mixing: unified atomistic simulations of collisional and thermal processes

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.

Ion beam processing of materials at elevated temperature, which can be room temperature for metals, is controlled simultaneously by both, collisional and thermally activated processes. So far, large scale process simulations separate these processes, calculating all collision cascades of the complete ion irradiation in the binary collision approximation like the TRIDYN code, and simulating then the defect relaxation/impurity nucleation by kinetic Monte Carlo.

Here we present and apply a unified computer simulation program package which unifies both programs, i.e. after each calculated 3D collisional cascade some kinetic Monte Carlo steps allow relaxation, diffusion, phase separation etc. in the whole volume. Contrary to molecular dynamics simulations, our approach allows studies on experimental spatiotemporal scales. In this presentation we focus on the evolution of interfaces under ion irradiation, where collisional mixing is in competition with thermally activated diffusion and phase separation. He+ irradiations for two extreme cases were studied: (i) Irradiation of interfaces made by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters form and show self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces made by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co, resulting in a stepwise changing Pt/Co concentration depth profile. Novel magnetic properties of such sandwiched phases are predicted and can explain the transition between out of plane and in-plane magnetic anisotropy caused by ion irradiation.

Keywords: interface; mixing; bi-layer; kinetic monte-carlo; KMC; TRIM; TRIDYN; phase transition; crystal ordering

  • Lecture (Conference)
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Publ.-Id: 15228

Quantum uncertainties in the energy of transverse oscillations of planar channeled particle

Mkrtchyan, A. R.; Grigoryan, L. S.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Azadegan, B.

It is shown that quantum uncertainties in the energy of transverse oscillations of planar channeled particle become significant at definite values of the crystal period in the direction of channeling. The possibility of producing superlattices with periodical potential is discussed.

Keywords: channeling radiation; quantum uncertainties

  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Quantum uncertainties in the energy of transverse oscillations of planar channeled particle, Yerevan, Armenia, 978-99941-2-486-2

Publ.-Id: 15226

Channeling radiation on quartz influenced by acoustic waves

Wagner, W.; Azadegan, B.; Büttig, H.; Mkrtchyan, A. R.; Grigoryan, L. S.; Pawelke, J.

The influence of acoustic waves excited in a single quartz crystal on the emission of channeling radiation by relativistic electrons has been proved experimentally.

Keywords: channeling radiation; quartz single crystal; ultrasound

  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Proceedings of the International conference on electrons, positrons, neutrons and X-rays scattering under external influences, Yerevan, Armenia, 978-99941-2-486-2

Publ.-Id: 15225

Warum Ge und Si durch Ionenimplantation zu Supraleitern werden

Fiedler, J.

Es konnte gezeigt werden, dass neben Diamant auch die technologisch relevanten Gruppe-IV-Halbleiter Si und Ge im extrem hochdotierten Zustand supraleitend werden. Am Helmholtz – Zentrum Dresden – Rossendorf ist es erstmalig gelungen, supraleitfähige Ge-Schichten in einem zu Fertigungsverfahren der Mikroelektronik kompatiblen Dotierprozess, bestehend aus Ga-Ionenimplantation und Kurzzeitausheilung, herzustellen. Die hochdotierten Ge-Schichten zeigen intrinsische Supraleitung mit kritischen Temperaturen bis zu 1 K. Eine weitere Erhöhung der Dotierkonzentration und damit der kritischen Temperatur ist aufgrund der begrenzten Löslichkeit von Ga in Ge (1 at.%) sehr schwierig. Um dennoch höhere Sprungtemperaturen zu erreichen, wurden die geringe Löslichkeit von Ga in Si (0.1 at.%) sowie die supraleitenden Eigenschaften von Ga ausgenutzt. In Ga implantiertem Si bilden sich Ausscheidungen, wodurch vergrabene, extrinsisch supraleitende Ga reiche Schichten hergestellt werden können. Die kritische Temperatur ist mit 7 K deutlich höher als in dotiertem Ge.
Die Struktur der Proben wurde mit Rutherford Rückstreuspektrometrie (RBS), Transmissionselektronenmikroskopie (TEM) sowie Sekundärionen-Massenspektrometrie (SIMS) untersucht. Für die elektrische Charakterisierung wurden Temperaturen zwischen 100 mK und 400 K sowie Magnetfelder bis 9 T verwendet. Im Vortrag werden die Grundzüge der Dotierung mittels Ionenimplantation sowie die Ergebnisse elektrischer und struktureller Untersuchung beider Materialsysteme vorgestellt.

  • Lecture (others)
    Institutsseminar SS 2011, Institut für Physik, TU Ilmenau, 18.05.2011, Ilmenau, Deutschland

Publ.-Id: 15224

ROBL: The first European actinide XAS beamline in its second decade of operation

Scheinost, A. C.; Hennig, C.; Rossberg, A.; Banerjee, D.

The Rossendorf Beamline at ESRF (ROBL) in operation since 1998 [1] is together with the INE Beamline at ANKA and the micro-XAS beamline at SLS one of three dedicated radionuclide XAS beamlines in Europe. ROBL is specialized in handling actinide nuclides up to Cf with a total activity to 185 MBq. The wide energy range (5 to 35 keV) permits to run actinide L1, L2 and L3 edges, important for the investigation of mixed actinide systems. Both the high photon flux (6 1011 ph/s on the sample) and the high-performance fluorescence detection makes ROBL suited for very low concentrations (according to XAS standards,  1 ppm XANES,  20 ppm EXAFS). Research at ROBL encompasses basic actinide chemistry, biogeochemistry, environmental chemistry and materials sciences, with applications for the improvement of nuclear waste repositories, remediation of uranium mining areas and other contaminated sites, development of fourth generation nuclear fuels, minor actinide waste forms and transmutation targets. The ROBL team supports users before, during and after the experiments. Own research specializes on the development of new data analysis tools (statistical tools, wavelets, Monte-Carlo simulations, PDF) as well as on actinide redox chemistry (structure of aqueous and non-aqueous complexes, redox mechanisms at water/mineral interfaces). From 2012 on, a major upgrade of the ROBL optics will further increase photon flux, energy range, and spectral resolution; and reduce spot size and data acquisition time; while maintaining reliable and relatively easy operation.

[1] W. Matz et al., Journal of Synchrotron Radiation 6, 1076-1085 (1999).

Keywords: xafs; robl; xanes; xas; synchrotron; beamline

  • Invited lecture (Conferences)
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan

Publ.-Id: 15223

AcXAS, a reference data base for XAS spectra of actinides and other radionuclides

Scheinost, A. C.; Schmeisser, N.; Denecke, M.; Banerjee, D.; Dardenne, K.; Hennig, C.; Rossberg, A.; Rothe, J.; Daehn, R.

Reference spectra of well characterized samples are crucial for the analysis of x-ray absorption spectra (XAS). In order to avoid that experimentalists have to repeat XAS measurements of standard actinide compounds/species, thereby making more efficient use of costly radionculides, sample preparation, beamtime, radioprotection measures, transport, administration, etc., we are in the process of establishing a public database of actinide XAS reference spectra. The spectra are retrieved from the large data inventory of the three current European radionuclide beamlines, the Rossendorf Beamline at ESRF (France), the INE beamline at ANKA (Germany), and the micro-XAS beamline at SLS (Switzerland), but will also include data from other beamlines. This effort is supported by the European Commission through the ACTINET-I3 project. An overview on data base structure, criteria for data entry and use, as well as on the current status of data will be given.

Keywords: actinides; xas; xanes; exafs; data base

  • Poster
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan
  • Invited lecture (Conferences)
    ACTINET Plenary Meeting, 01.02.2011, Marcoule, France

Publ.-Id: 15222

Probing redox reactions at the mineral/water interface by X-ray absorption spectroscopy: Reduction of Se, Sn, Sb and Pu by Fe(II)-bearing minerals

Scheinost, A. C.

Fe(II)-bearing phases are naturally occuring in most anoxic aquifers, and form also at the surface of corroding steel containers under typical nuclear waste repository conditions. Due to their ability to reduce metal and metalloid contaminants, they are expected to play a key role for the migration behaviour of a wide range of radionuclides, including actinides and fission products. Using X-ray absorption spectroscopy as main tool, we have studied reaction end products, mechanisms and kinetics of redox processes at a range of water/mineral interfaces, including magnetite, green rust, mackinawite, siderite and Fe2+-sorbed clays. Our results show that the electron transport within mineral structures and at the surface is controlling the extent and the kinetics of multi-electron redox reactions. Examples that I will show include: (1) The fast reduction of Se(IV) to Se and Se(-II) nanoparticles, a reaction which was previously thought to be extremely slow. (2) The reduction of Pu(V) to Pu(III), which then forms a highly ordered inner-sphere sorption complex at the 111 face of magnetite, instead of the expected precipitation of PuO2 clusters. (3) The oxidation of Sn(II) to Sn(IV), which then forms inner-sphere sorption complexes, instead of the expected precipitation of SnO2. The results highlight the need for direct spectroscopic investigation of such processes, which are difficult to predict by thermodynamic methods, in order to provide reliable risk assessments.

Keywords: Redox; interfaces; XAFS; XANES

  • Lecture (Conference)
    LES Seminar, 15.03.2011, Villigen, Switzerland

Publ.-Id: 15221

Experiments on electromagnetic control of a backward facing step flow

Weier, T.; Wittwer, S.; Albrecht, T.; Gerbeth, G.

The flow over a backward-facing step is a prototype of a separating and reattaching shear flow and has therefore received a considerable amount of interest. We focus here on the excitation of the separated shear layer since it is often understood as the basic mechanism in active flow control. Forcing frequencies and amplitudes are obviously major parameters of influence, but different signal forms can have a profound impact as well, albeit the physical mechanism behind the latter is still not fully understood.

Electromagnetic body forces offer a simple and direct way to provide excitation by different wave forms. Particle image velocimetry measurements have been performed in a free surface electrolyte channel. We will discuss spatial amplification rates in the unforced shear layer, which show a fair agreement with results obtained by others in free shear layers. Compared to the natural flow, forcing near the optimal excitation frequency St=0.012 leads to a much earlier vortex roll-up and, consequently, the reattachment length is reduced. For the first subharmonic of the optimal excitation frequency, vortex roll up starts later but produces larger vortices. Excitation with the relatively high frequency of St=0.03 has only a very small effect on the flow. Keeping the excitation frequency at St=0.012 and increasing the forcing amplitude leads to earlier vortex roll up, larger vortices, and shorter reattachment lengths.

Keywords: flow control; Lorentz force; backward facing step

  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Publ.-Id: 15220

Elektrische Kontaktierung vertikaler Nanostrukturen

Wieser, M.

Diese Arbeit beschreibt die Herstellung, Kontaktierung und Charakterisierung vertikaler Nanostrukturen in Form von Pfeilern der Höhe 50 nm mit einer elliptischen Querschnittsfläche von 100 × 150 nm. Die hergestellte Gesamtstruktur besteht dabei aus mehreren Metallebenen, so dass der Pfeiler an der Unterseite von einer Grundelektrode und an der Oberseite von einer Deckelektrode kontaktiert wird. Zur Fertigung der Metallebenen wird die Elektronenstrahllithographie mit anschließendem thermischen Bedampfen und Lift-Off genutzt. Die Isolation der Grundelektrode von der obersten Metallebene erfolgt mit einem durch Rotationsbeschichtung aufgetragenen Negativ-Lack aus dem Bereich der Elektronenstrahllithographie, der bei Erwärmung in Siliziumoxid transformiert.
Nach dem Ausarbeiten und Optimieren des Herstellungsprozesses dieser Strukturen sollten erste Nanostrukturen mit integrierter Tunnelbarriere erstellt und charakterisiert werden. Aufgrund von unvorhergesehenen Verzögerungen bei der Herstellung konnten diese Strukturen allerdings nicht fertiggestellt werden, so dass für die Charakterisierungsmessungen auf eine aus einem anderen Projekt bereitgestellte Probe zurückgegriffen werden musste, die einen ähnlichen Strukturaufbau besitzt. Die während der Charakterisierung dieser Probe aufgenommenen Strom-Spannungs-Kennlinien werden mit bekannten quantenmechanischen Tunnelmodellen verglichen.

Keywords: Electrical contacting vertical nanostructures

  • Diploma thesis
    Otto-von-Guericke-Universität Magdeburg, 2010
    79 Seiten

Publ.-Id: 15219

Electrical Contacting of Vertical Nanostructures

Wieser, M.; Grebing, J.; Höwler, M.; Bernert, K.; Schmidt, B.; Fassbender, J.; Erbe, A.

The aim of this new approach is the contacting and characterization of small vertical nanostructures. Therefore, in contrast to conventional lateral contacting a vertical pillar with a height of about 70 nm and an elliptic size of 100 nm × 150 nm is contacted using a bottom electrode, a via with the same height as the pillar and two top electrodes for tipcontacting of measurement devices. The structuring of the different layers is done using electron beam lithography (EBL). A resist layer is used as an insulator between the bottom and the top electrodes. In the center of the pillar an Al2O3 tunnel barrier will be integrated. The current voltage (IV) characteristics of the system will be investigated and compared to the direct tunneling and the Fowler-Nordheim tunneling model. Using this technique we will characterize the electrical properties of oxides with varying thickness.

Keywords: Electrical contacting vertical nanostructures

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 15218

3D vector magnetooptical ellipsometry investigations on magnetic thin film samples at room temperature

Mok, K. M.; Schmidt, H.

We present the set-up of a vector-magneto-optical generalized ellipsometer (VMOGE) which allows to perform generalized Mueller matrix ellipsometry in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. Using VMOGE measurements, we measured the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni and extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions via model analysis.

Keywords: Magnetic semiconductors; spin poalrization; magnetooptical response

  • Lecture (others)
    Halbleiterphysik-Seminar (AG Zahn), TU Chemnitz, 21.01.2011, Chemnitz, Germany

Publ.-Id: 15217

Magnetic characterization of Bi(Fe1 − xMnx)O3

Xu, Q.; Zhou, S.; Wen, Z.; Wu, D.; Qiu, T.; Xu, M.; Potzger, K.; Schmidt, H.

Bi(Fe1 − xMnx)O3 ceramics (x up to 0.3) were prepared by rapid sintering. Weak ferromagnetism with two magnetic anomalies at low temperatures was observed for Bi(Fe0.95Mn0.05)O3 and Bi(Fe0.9Mn0.1)O3. From temperature-dependent magnetic relaxation measurements, the anomalies at 20 K and 100 K are related to the freezing of cluster spin glass.

Keywords: Multiferroic; Spin glass; Ferromagnetism; Cluster

Publ.-Id: 15216

Synthesis and characterization of nickel cobalt oxide thin films

Calin, G.; Irimia, M.; Scarlat, C.; Purica, M.; Comanescu, F.; Iacomi, F.

p-Type transparent and conductive cobalt–nickel oxide films of 130 nm thickness, have been deposited by spin coating method on glass substrates. The electrical and optical properties of the oxides have been studied as a function of the x=Co/(Co+Ni) ratio. A combination of x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectroscopy was used in order to investigate thin film structures. Thin films of mixed oxides: NiCo2O4, Ni1.71 Co1.29 O4; NiO were obtained for x>0.60. The electrical conductivity of these films reaches a maximum conductivity at this stoichiometry.

Keywords: p-type TCO; structure; optical properties; electrical properties; Raman spectroscopy

  • Contribution to proceedings
    International Semiconductor Conference (CAS 2010), 11.-13.10.2010, Sinaia, Romania
    Semiconductor Conference (CAS), 2010 International, Sinaia, 978-1-4244-5783-0, 387-390

Publ.-Id: 15215

Experimental realisation of homogeneous dynamo action

Giesecke, A.; Stefani, F.; Gerbeth, G.

From the technical point of view the realisation of dynamo action under laboratory conditions is a demanding task because it requires magnetic Reynolds numbers of the order of Rm ~100. So far only three experiments have been able to demonstrate fluid flow driven self-excitation of magnetic fields.

The dynamo experiments in Karlsruhe and Riga, based on an optimized flow geometry, have demonstrated the principal possibility of the magnetic field generation process and its saturation as it occurs e.g. in stars or planets. Both dynamos are characterized by a non-axisymmetric field mode and are theoretically very well understood.

In contrast to this the mechanism responsible for the dynamo process in the von Karman sodium (VKS) experiment is still subject of intense discussion, in particular due to the obscure influence of the flow driving soft iron impellers. Recently, it could be shown numerically that the (localized) high relative permeability of the impellers is responsible for the rather low value of the critical magnetic Reynolds number as well as for the selection of the dominating axisymmetric dynamo mode observed in the experiment (Giesecke et al. 2010, PRL 104). However, to explain a growing axisymmetric field an alpha-effect is required for which the theoretical or experimental justifications remain only vague.

Further progress in the experimental examination of dynamo action is expected from the future dynamo facility that is scheduled at the Helmholtz-Zentrum Dresden-Rossendorf. In order to avoid the influence of internal components or artificial driving mechanisms a precession driven flow of liquid sodium in a cylinder shall provide the necessary energy to exhibit dynamo action. A precession driven dynamo operating in a sphere has been presented by A. Tilgner (2005, Phys. Fl. 17). However, it remains to be shown that precessional flow driving will be possible with sufficient efficiency to overcome the dynamo threshold in a cylindrical geometry as well.

Keywords: Dynamo; Simulations; Experiments; Precession; VKS dynamo

  • Lecture (Conference)
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Wien, Oesterreich
  • Contribution to proceedings
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Vienna, Austria
    Experimental realisation of homogeneous dynamo action

Publ.-Id: 15214

Oscillating alpha-square dynamos

Giesecke, A.; Stefani, F.; Gerbeth, G.

A simple way to interpretate the reversal mechanism of the Earth's magnetic field has been achieved in theoretical models based on the interplay between very few magnetic modes.

Motivated by the temporal behavior of elementary multipolar components of the Earth's magnetic field during the last reversal 780ka ago, (Leonhardt & Fabian 2007) the possibility of interacting magnetic modes is examined in a simple mean field model.

Field modes that are suitable canditates to be involved in the reversal process are oscillating eigenfunctions of the linear eigenvalue problem for geodynamo models of alpha2 type.

Regarding the spectrum of the dynamo operator time-dependent solutions arise at so called exceptional points where two stationary modes merge and continue at a single oscillating eigenfunction. In the present model this behavior essentially involves dipolar and octupolar modes. The spectrum exhibits further time-dependent modes of higher order that appear at coupling points of different radial field modes.

In order to couple odd ("dipolar-like") and even ("quadrupolar-like") modes equatorial symmetry breaking is required. However, instead of oscillating eigenfunctions an equatorial asymmetry results in stationary hemispherical dynamos. This behavior can be explained by the approximate dipole-quadrupole degeneration for the unperturbed problem.

More complicated scenarios occur in case of (more realistic) anisotropies of alpha- and beta-effect or through non-linearities caused by the backreaction of the magnetic field (magnetic quenching).

Keywords: Dynamo; linear eigenvalue problem; alpha-effect; reversal; geodynamo

  • Lecture (Conference)
    RädlerFest: Alpha Effect and Beyond, 14.-18.02.2011, Stockholm, Sweden

Publ.-Id: 15213

Ga ion irradiation induced spin reorientations in Co films

Mazalski, P.; Maziewski, A.; Tekielak, M.; Ferré, J.; Jaworowicz, J.; Mougin, A.; Liedke, B.; Liedke, M. O.; Fassbender, J.

Some years ago, it has been demonstrated that after submitting Pt/Co/Pt films to increasing ion irradiation dose, one observes a decrease of: (i) perpendicular magnetic anisotropy (up to reach a spin reorientation transition (SRT) towards an in-plane magnetisation state); (ii) coercive field; (iii) Curie temperature (see e.g. [1-3]). In thicker Co films, by increasing the Ga ion dose, two successive inverse SRTs take place [4].
Pt(4.5nm)/Co(2.6nm)/Pt(3.5nm) films were deposited by sputtering on a sapphire substrate. 1mm wide strip regions were irradiated by 30 keV Ga ions under different doses D ranging from 2x1013 to 3x1014 Ga ions/cm2. Samples were studied by polar Kerr PMOKE (out-of-plane magnetization component sensitive), magneto-optical microscopy and local scanning magnetometry using a focused light beam. In-plane magnetized domains were studied using longitudinal magneto-optical Kerr effect, LMOKE. Magnetic Force Microscopy (MFM) was used to image domain patterns at higher spatial resolution. TRIDYN simulations were performed to estimate irradiation driven changes of the in-depth ion distributions. The irradiation driven SRTs are illustrated in Fig.1. Magnetization lies in-plane in the non-irradiated (NI) region. When increasing D, two successive SRTs undergo between planar to perpendicular magnetization states, and again back to a planar state (through a canted magnetization state, as shown from the magnetization curve obtained for D=3x1014 Ga ions/cm2).

This work was partly supported by the EU-“Research Infrastructures Transnational Access” program “Center for Application of Ion Beams in Materials Research” under contract no. 025646 and DAAD.

[1] C. Chappert, H. Bernas, et al., Science 280, 1919 (1998)
[2] J. Ferré and J.-P. Jamet, in Handbook on Magnetism and Advanced Materials. Eds H. Kronmüller and S. Parkin Vol. 3, 1710 (2007).
[3] Fassbender and J. McCord, J. Magn. Magn. Mat. 320 (2008).
[4] J. Jaworowicz, A. Maziewski, P.Mazalski, M.Kisielewski, I. Sveklo, M. Tekielak, V. Zablotski, J. Ferré, N. Vernier, A. Mougin, A. Henschke, J. Fassbender, Appl. Phys. Lett., 95, 022502 (2009).

Keywords: irradiation; SRT; TRIDYN

  • Poster
    IV Euro-Asian Symposium “Trends in MAGnetism”: Nanospintronics. EASTMAG – 2010, 28.06.-02.07.2010, Ekaterinburg, Russia

Publ.-Id: 15212

Magnetooptical Spectroscopy Of Ga+ Irradiated Pt/Co/Pt Sandwiches

Lišková, E.; Veis, M.; Višpovský, Š.; Maziewski, A.; Mazalski, P.; Ferré, J.; Mougin, A.; Liedke, M. O.; Fassbender, J.

The magnetic properties of ultrathin Pt/Co/Pt sandwiches depend on the interface structure and can thus be controlled by ion irradiation [1]. In the present work, we study the magneto-optic properties by polar Kerr rotation upon Ga+ irradiation of Pt(3.5 nm)/Co(2.6 nm) /Pt(4.5 nm) trilayers which have been sputter deposited on (001) Al2O3 substrates. In Figure 1 the MO spectra at saturation before and after irradiation are compared. The enhanced MO amplitude after irradiation results from an increased thickness of the alloyed PtxCo1-x interface layer [2]. The MO spectra were modeled assuming interface PtxCo1-x layers with a monotonous x gradient using the data of ref. [3]. The curves in Fig. 1 were obtained assuming the structure shown in Fig. 2, i.e., Pt(2.8 nm)/ PtxCo1-x(1.1 nm)/Co(2.3 nm) /PtxCo1-x(1.1 nm)/Pt(4.0 nm) and Pt(1.2 nm)/ PtxCo1-x(4.0 nm)/ Co(1.0 nm)/PtxCo1-x(3.0 nm) /Pt(1.5 nm)/Al2O3 for the non-irradiated sample and the sample irradiated with a dose of 1014 Ga+/cm2, respectively. The changes in the MO spectra after irradiation confirm the expected high sensitivity of the coupled 3d levels of Co and 5d levels of Pt (with high spin-orbit interaction) to the interface geometry [2]. Partially supported by NSF (DMR 0605629 and DMR 0907053), Research Corporation (CC6471), CU-NIST Joint Project and by Ministry of Education, Youth and Sport of the Czech Republic (MSM 6198910016, 0021520834 and ME09045), Grant Agency of Charles University (3146/2008), Czech Science Foundation (P204/10/P346), EU-“Research Infra-structures Transnational Access” program “Center for Appli-cation of Ion Beams in Materials Research” (025646) and DAAD.
[1] J. Jaworowicz et al., Appl. Phys. Lett. 95, 022502 (2009)
[2] D. Weller et al. J. Magn. Magn. Mat. 93, 183 (1991)
[3] S. Visnovsky et al., IEEE Trans Magn. 29, 3390 (1993)

Keywords: irradiation; Co; Pt; MOKE

  • Poster
    IEEE 7th International Symposium on Metallic Multilayers (MML2010), 19.-24.09.2010, Berkeley, CA, USA

Publ.-Id: 15211

Influence of Ga+ irradiation on MO spectra of Pt/Co/Pt films

Liskova, E.; Veis, M.; Visnovsky, S.; Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Wawro, A.; Baczewski, L. T.

The magnetic anisotropy of Pt/Co/Pt sandwiches transforms from in-plane to out-of-plane and back as a function of uniform Ga+ ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett. 95 (2009)]. We study the effect of the irradiation on magneto-optical (MO) Kerr spectra between 1 and 5 eV in Pt(5nm)/Co(3.3nm)/Pt(20nm)/Mo(20nm). In the range up to an irradiation fluence of 1e15 ions/cm2 the MO amplitudes gradually increase and at 6e15 ions/cm2 it falls below that of the non-irradiated sample. The results are explained assuming the model system Pt/PtxCo1-x/Co/PtxCo1-x/Pt which accounts for increased PtCo alloy thicknesses at the interfaces. At 6e15 ions/cm2, the reduction in MO amplitudes is explained by the circumstance that a significant part of the sample is ablated and the sandwich reduces to a single alloy layer.

Keywords: irradiation; MOKE

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15210

Modifications of magnetic properties of Pt/Co/Pt layers induced by Ga irradiations

Gieniusz, R.; Mazalski, P.; Kurant, Z.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Wawro, A.; Baczewski, L. T.

The influence of Ga irradiation dose D on the magnetic properties of Pt/Co(d=3.3nm)/Pt trilayers grown by molecular beam epitaxy have been studied by both ferromagnetic resonance (FMR) and magnetooptical magnetometry (PMOKE). A broadening of Co-Pt interfaces induced by irradiation was deduced from X-ray reflectivity. For the nonirradiated sample the magnetisation was in-plane with negligible remanence ThetaR PMOKE hysteresis loops. Increasing D ThetaR(D) displays a maximum in irradiated samples for a dose DM ~ 2,8e14 ions/cm2. FMR study showed a similar behaviour (occurence of a maximum in a function of dose) both effective uniaxial magnetic anisotropy and FMR linewidth. For DM the increase of a uniaxial anisotropy field up to 0.3T was estimated from FMR data. Similar effects have been recently reported for Ga irradiated Co films deposited by sputtering which showed a double spin reorientation [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502].

Keywords: SRT; FMR; irradiation

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15209

X-ray reflectivity investigations of Ga+ ion irradiated Pt/Co/Pt films

Kanak, J.; Stobiecki, T.; Powroznik, W.; Mazalski, P.; Sveklo, I.; Maziewski, A.; Liedke, M. O.; Fassbender, J.; Wawro, A.; Baczewski, L. T.

The effects of Ga+ ion implantation in MBE grown Mo20nm/Pt20nm/Co3.3nm/Pt5nm films were investigated by low and high angle x-ray diffraction methods. The reflectivity measurements were used for characterization of changes in layer thickness and interface Pt/Co structure upon 30 keV Ga ion irradiation in a fluence range between 0 and 6e15 ions/cm2. The layer stack thickness was found to decrease with increase of Ga+ fluence. Mixing of Pt and Co at interfaces leads to a change of interface roughness of the top layers. The results were compared with high-fluence ion implantation simulations, of the dynamic changes of thickness and composition of layers, obtained using TRIDYN.

Keywords: TRIDYN; irradiation; Co; Pt; SRT

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15208

Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Tripathia, J. K.; Satpatib, B.; Liedke, M. O.; Guptad, A.; Som, T.

Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K

Keywords: Pt/Cr/Co multilayer; Structural property; Magnetic property; Thermal annealing

Publ.-Id: 15207

Quenched-in vacancies in Fe-Al alloys

Melikhova, O.; Cizek, J.; Lukac, F.; Procházka, I.; Kuriplach, J.; Anwand, W.; Brauer, G.

Quenched-in vacancies in Fe-Al alloys with Al content ranging from 24 to 49 at.% were investigated employing two complementary techniques of positron annihilation: slow positron implantation spectroscopy and positron lifetime measurements. It was found that quenched alloys exhibit a very high concentration of vacancies. Although the free positron component cannot be resolved in positron lifetime spectrum in majority of samples, the concentration of quenched-in vacancies can be still determined from the positron diffusion length measured by a variable energy positron beam. The lowest concentration of vacancies was found in a stoichiometric (SM) Fe3Al alloy. The concentration of defects increases with increasing degree of non-stoichiometry with respect to Fe3Al, i.e. in alloys with under-SM and over-SM Al concentration. However, the increase in concentration of quenched-in defects is more pronounced in Al-rich alloys, i.e. alloys containing more than 25 at.% of Al.

Publ.-Id: 15204

Use of superconducting linacs for positron generation: the EPOS system at the Forschungszentrum Dresden-Rossendorf (FZD)

Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.

Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting LINACbased accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system (ELBE Positron Source) at the Forschungszentrum Dresden-Rossendorf (FZD), is described.

Publ.-Id: 15203

Surface nanostructures induced by slow highly charged ions

Facsko, S.; Wilhelm, R. A.; El-Said, A. S.; Heller, R.

Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear or electronic sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation in the surface can thus induce various modifications [1]. Recently, it has been shown that hillock structures are formed on CaF2 by HCI due to a localized phase transition [2].
In the case of the alkali halide crystal KBr we observed the formation of nanostructures resulting by desorption of surface atoms from a single ion impact site [3]. For high enough charge states each ion produces a mono-atomic deep pit with a diameter of 10-30 nm (depending on the charge state) on the atomically flat surface. The desorption of such a high amount of material can not be induced by kinetic sputtering alone, which dominates in this kinetic energy regime, but is induced by the excitation due to the potential energy. For a kinetic energy of 40 keV a threshold in the potential energy of the HCI is found for the formation of these structures between Xe15+ and Xe20+ around 3 keV. Above this threshold the volume of the pits and therewith the potential sputtering yield exhibits a linear dependence on the potential energy. However, the kinetic energy also plays an important role. For higher kinetic energies the threshold shifts to lower values of the potential energy.

Keywords: highly charged ions; nanostructures; surface modifications

  • Invited lecture (Conferences)
    EMMI Workshop "Physics prospects at the ESR and HITRAP", 27.-30.06.2010, Eisenach, Deutschland

Publ.-Id: 15202

SQUID investigations of Ga+ irradiated epitaxial Pt/Co/Pt trilayers

Liedke, M. O.; Shalimov, A.; Fassbender, J.; Mazalski, P.; Maziewski, A.; Wawro, A.; Baczewski, L. T.

Spin reorientation transition in polycrystalline Pt/Co/Pt trilayers, i.e. rotation of the magnetization from an in-plane to out-of-plane orientation and vice versa can be precisely controlled by ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502], similarly to the epitaxial Pt/Co/Pt trilayers exposed to 30 keV Ga+ ions in the fluence range of 1014-1016 ion·cm−2. Magnetic properties of a such irradiated system are studied by means of SQUID magnetometry. Zero field cooling and field cooling dependencies and also magnetization reversal curves are measured and analyzed in the frame of the Preisach model. The model explains structural and magnetic modifications occurring due to ion irradiation. A key magnetic properties, i.e. distribution of coercive and interaction fields, reversible and irreversible magnetic contributions are addressed. The interpretation of the results is also supported by the XRD synchrotron studies.

Keywords: SQUID; spin reorientation transition; Co; Pt; magnetization

  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15201

Magnetic anisotropy engineering: ultrathin Fe films on single crystalline rippled surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Ranjan, M.; Fassbender, S.; Facsko, J.

Ultrathin Fe films exhibit an excellent epitaxial relation to MgO(100) substrates because of a very low lattice mismatch (~3.8%). Due to a cubic symmetry of the Fe crystal an in-plane fourfold magnetic anisotropy is induced. By means of ion erosion coherently aligned single crystalline patterns (ripples) are created at the MgO surface, which induce an additional uniaxial magnetic anisotropy in the afterwards deposited Fe film. The uniaxial magnetic anisotropy direction and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ion energy dependent ripple wavelength, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance and magneto-optic Kerr effect techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in a perfect agreement with the experiment.

Keywords: magnetic anisotropy; ripples; MgO; Fe; single crystalline; ion erosion

  • Lecture (Conference)
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Publ.-Id: 15200

Ions for Nanotechnology

Kolitsch, A.

The aim of the nanocenter slovakion is its integration into university research (e.g. STU/MtF, materials research), which is highly required by professional public This will enable university to bring its research closer to the needs of industry and shift it to up-to-date topics on one side, and raise funds from private sources in the industry on the other side, which altogether represents a unique chance to train young qualified researchers in the field of contemporary materials research. The activities of the centre will be equally utilised by both in-house and external research and in a wide scale of services oriented on the support in introducing nanostructures using plasma and ion technologies into production processes for external industrial and other users.
The subject of the research, both basic and applied, will be focused on the modification of surface properties, such as hardness, friction, wear, fatigue, adhesion, as well as electrical, magnetic and optical properties, along with corrosion and bio-compatibility using ion beams technologies in the nanometer range. The research will employ the technologies, such as ion implantation (II), ion beam mixing (IBM) and ion beam assisted deposition (IBAD), as well as plasma assisted pulsing, non-pulsing, reactive and non-reactive processes where energetic ions form a decisive component of this process implementation. Highly topical is the research dealing with the development of nanostructures via ion beams.
Typical fields of utilisation are as follows:
• Exposed parts in automotive and mechanical engineering industry (injection nozzles, camshafts, bearings, valves and others);
• Medical and biomedical applications (prosthetics with interesting alloys, even those with the surfaces not sufficiently wear-resistant);
• Surface nitration of stainless steels via ion implantation with the purpose to improve wear resistance of stainless steels while preserving their high corrosion resistance;
• Stents (endoluminal catheter protheses), nano-porous stents for additional controlled administration of drugs, biocompatible and blood-compatible materials, etc. for modern medicine;
• Further possibilities of ion implantation in industry in the fields other than microelectronics, such as precise mechanics, special construction parts of expensive watches;
• High thermal oxidation protection (Ti AL – alloys, turbine construction);
• Mould injection of plastics (improvement of safety in the removing of injection-made plastic parts from the mould, as well as wear protection of highly exposed parts of forming tools);
• Ion implantation of polymers surfaces for the improvement of certain surface properties, such as printability for electric conductivity, biocompatibility, etc.

The important areas of ion beams technology application can be found in the field of ion beam analysis in a nanometer scale as well as in research and industry. Planned procedures are as follows:
• Rutherford Backscattering (RBS)
• Elastic Recoil Detection (ERD)
• Nuclear reaction Analysis (NRA)
• Proton Induced X-ray Emission (PIXE)
• Proton Induced Gamma-ray Emission (PIGE)

They provide a possibility of a non-standard depth profile analysis with high precision of nearly all chemical elements. In special cases, such as hydrogen depth profile analysis or light elements (B, C, N, O) analysis in heavy matrix (steel), they are unequalled when compared to other procedures.
Three groups of devices suggested as basic equipment for various uses of ion implantation are as follows:
• PBII equipment (three machines with various chamber volumes, basic vacuum and pulse voltage);
• Two linear ion implanters in the energetic range up to 500 kV (standard equipment) and 200 kV as a so-called high current implanter;
• 6 MV Tandetron Accelerator with experimental stations for high energy ion implantation and ion beam analysis.

The basic equipment for plasma and ion beam assisted separation processes is as follows:
• IBAD instrumentation with different low energy ion sources;
• Combination of PBII and thin film deposition
• Universal magnetron sputtering application systems with possible reactive middle frequency pulsed dual magnetron sputtering and the possibility of choice for typical plasma diagnostics and thin layers diagnostics.
Along with the implantation processes for micro-electronic development of nano-clusters, nano-wires, and nano-arrays, typical surface processes aiming at nano-scale ordered structures such as surface design created by ion erosion, nano-porosity for bio-medicine usage, blistering, etc., play an important role. Anyway, the magnetic nano-scale order of a structure as an indication of ferro-magnetic phases in non-magnetic materials or magnetic domain configuration using ion beams is of certain interest. Ion-beam-assisted separation process or special reactive processes of magnetron sputtering contributed to a significant achievement in the field of fullerene materials, nano-crystalline highly refracting optical materials or in transparent electrical conductive oxides, which play an important role in solar technology and technology of displays. Coating by super hard substances such as a-C or c-BN is impossible without energetic ions.

Keywords: ion implantation; plasma; ion assisted deposition; plasma based implantation; plasma immersion ion implantation; nanotechnology; hard coatings; doping; accelerator; implanter

  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic

Publ.-Id: 15199

Exploring uranyl(VI) photochemistry by DFT calculations (in Japanese)

Tsushima, S.

no abstract for this publication

  • Lecture (Conference)
    Seminar talk at the Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 08.03.2011, Tokyo, Japan

Publ.-Id: 15198

Time-resolved photoluminescence from GaAs/AlGaAs multiquantum wells quenched by pulsed mid-infrared radiation

Zybell, S.; Schneider, H.; Winnerl, S.; Helm, M.

Several groups have demonstrated the suppression of photoluminescence (PL) from semiconductor quantum wells (QWs) by intense midinfrared radiation (MIR). Since most of the previous studies are done on time-integrated PL the ultrafast changes in the radiative state population are not well understood. We present a detailed study on time-resolved PL from an undoped GaAs/AlGaAs QW sample quenched by MIR pulses from a free-electron laser, which was tuned to the intersubband transition (ISBT) energy. At the arrival time of the MIR pulse a clear sharp dip appears in the PL transient. Free carrier absorption and ISBT are the two processes that take place under MIR excitation and result in an abrupt drop of the radiative state population and consequently in an ultrafast quenching of the PL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free carrier absorption from that of ISBT. A quantitative analysis of the PL dip depth and recovery time as a function of MIR fluence was done using a model based on rate equations.

Keywords: time-resolved photoluminescence; semiconductor quantum wells; intersubband transition

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 15197

Voruntersuchungen am HZDR für Filmdickenmessungen an der thermohydraulischen Versuchsanlage KATHY (Karlstein, AREVA NP) mit Gamma-CT

Bieberle, A.; Hoppe, D.; Hampel, U.

Für die Überprüfung des Strömungsregimes im sogenannten Kaminrohr, das in Kernkraftwerken der AREVA NP zur Anwendung kommen soll, müssen zur Überprüfung des Systems im thermohydraulischen Versuchsstand KATHY in Karlstein (AREVA NP) authentische Betriebsszenarien nachgebildet und getestet werden. Grundlage hierfür sind Simulationen und Berechnungen, die mit direkt am Versuchstand gewonnenen Messwerten überprüft werden müssen. Aus diesem Grund soll der mögliche Einsatz des am HZDR entwickelten hochauflösenden Gamma-Computertomographie-Messsystems (Gamma-CT) zur Bestimmung von Wasserfilmdicken überprüft werden.

Keywords: Gamma-CT; Wasser-Dampf Strömung

  • Other report
    HZDR: HZDR, 2011
    20 Seiten

Publ.-Id: 15196

Optimierung des Energiefensters für I-124 anhand von Monte-Carlo Simulationen und PET-Messungen an Kleintier- und Human-Tomographen

Sauerzapf, S.; Zakhnini, A.; Behe, M.; Thomas, L.; Axer, M.; Weber, W.; Pietrzyk, U.; Mix, M.

Die Verwendung des nichtreinen Positronenstrahlers I-124 bietet aufgrund seiner Halbwertszeit von 4,18 Tagen Vorteile bei der Quantifizierung von langsamen biochemischen Prozessen. Nachteilig bei I-124 ist das komplexe Zerfallsschema. Der Anteil an Positronen liegt nur bei 22,8%. Zusätzlich werden koinzidente g -Linien mit Energien emittiert, die innerhalb des am PET-Scanner verwendeten Energiefensters liegen. Ziel dieser Arbeit ist es, das Energiefenster für die PET-Akquisition so zu optimieren, dass ein möglichst geringer Anteil an falschen Koinzidenzen auftritt. Dazu wurden Monte-Carlo Simulationen gerechnet, und Phantome an verschiedenen Kleintier- und Humanscannern gemessen.

Methodik/ Methods:
Die Monte-Carlo Simulationen wurden mit Hilfe von GATE (1) für die Scanner ClearPET (Raytest) und Gemini TF (Philips) sowie für unterschiedliche Phantome durchgeführt. Um die zusätzlich zum Positronenzerfall auftretenden koinzidenten g -Linien im Energiespektrum zu unterscheiden, wurde die I-124 Aktivität nicht als Ionenquelle, sondern alle g -Linien als reine Gammaemitter und die Positronenemission als quasikontinuierliches Energiehistogramm definiert. F-18 wurde als Ionenquelle definiert und als Vergleichsstandard verwendet. Die
Energiespektren wurden für die verschiedenen Bereiche im Phantom hinsichtlich der wahren und gestreuten Koinzidenzen unterschieden. Neben den Messungen mit den o.g. Phantomen für I-124 und F-18 am ClearPET und PET/CT Gemini TF 64 wurden vergleichende Messungen am MicroPET Focus 120 (Concorde) und am ECAT EXACT (Siemens) gemacht.

Ergebnisse/ Results:
Die Simulationen zeigen, dass im Vergleich zu F-18 die I-124 Energiespektren mehr Counts speziell im niederenergetischen Bereich (<350keV) aufweisen. Dies resultiert aus den zusätzlich koinzidenten g -Linien, die als wahre Koinzidenzen gewertet werden. Da die Energieverteilung der g -Linien exponentiell verläuft, wird durch die Wahl einer höheren unteren Energieschwelle (450keV anstatt 250 bzw. 350keV) ein Großteil der falschen
Koinzidenzen herausgefiltert. Die Energieauflösung des PET-Scanners bestimmt dabei die Qualität dieser Maßnahme, was sich in den Phantommessungen an den unterschiedlichen Scannern bestätigt. Besonders deutlich wird dies zwischen dem BGO- und dem LYSOHumanscanner. Durch das engere Energiefenster am Gemini TF wird mit I-124 im Phantom eine auf 10% genaue Quantifizierung sowie annähernd keine Streuanteile in kalten Phantombereichen festgestellt.

Schlussfolgerungen/ Conclusions:
Die Simulationen erlauben eine sehr gute Abschätzung, inwieweit sich bei den PET-Scannern die Akquisition mit dem Isotop I-124 durch Einschränkung des Energiefensters verbessern lässt. Die Phantommessungen zeigen, dass gute quantitative Ergebnisse mit I-124 erreicht werden können.

(1) S. Jan /et al /2004 GATE: a simulation toolkit for PET and SPECT. Phys. Med. Biol. 49

  • Poster
    NuklearMedizin2011, 13.-16.04.2011, Bregenz, Österreich

Publ.-Id: 15195

Surface nanostructures induced by low energy ion sputtering

Facsko, S.

Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth.
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].

[1]W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2]R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3]R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Keywords: ion sputtering; surface patterns; ripple patterns

  • Lecture (others)
    Birck Nanoscience Center Seminar, 28.04.201, West Lafayette, Indiana, USA

Publ.-Id: 15194

Comprehensive study of the p-type conductivity formation in radio frequency magnetron sputtered arsenic-doped ZnO film

Fan, J. C.; Zhu, C. Y.; Yang, B.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Wong, K. S.; Zhong, Y. C.; Xie, Z.; Ling, C. C.

Arsenic doped ZnO and ZnMgO films were deposited on SiO2 using radio frequency magnetron sputtering and ZnO–Zn3As2 and ZnO–Zn3As2–MgO targets, respectively. It was found that thermal activation is required to activate the formation of p-type conductivity. Hall measurements showed that p-type films with a hole concentration of ∼ 1017 cm−3 and mobility of ∼ 8 cm2 V−1 s−1 were obtained at substrate temperatures of 400–500 °C. The shallow acceptor formation mechanism was investigated using x-ray photoelectron spectroscopy, positron annihilation, low temperature photoluminescence, and nuclear reaction analysis. The authors suggest that the thermal annealing activates the formation of the AsZn-2VZn shallow acceptor complex and removes the compensating hydrogen center.

Keywords: zinc oxide; positron annihilation; ZnMgO; p-type conductivity; nuclear reaction analysis; XPS; PL; AsZn-2VZn shallow acceptor complex

Publ.-Id: 15193

Time-resolved photoluminescence from undoped GaAs/Al0.35Ga0.65As quantum wells quenched by pulsed midinfrared radiation

Zybell, S.; Schneider, H.; Wagner, M.; Winnerl, S.; Köhler, K.; Helm, M.

There is much interest in the development of ultrafast devices with possible applications in optoelectronics. An important goal consists in ultrafast control of luminescence in light-emitting devices; it is therefore interesting to investigate the effect of abrupt changes in the carrier distribution on the luminescence signal. We present an experimental study of the effects of mid-infrared radiation (MIR) on the photoluminescence (PL) from undoped AlGaAs/GaAs quantum wells. Electron-hole pairs, created by weak near-infrared light pulses, were excited in the system while a delayed MIR pulse induces an ultrafast redistribution of free carriers that results in abrupt quenching of the PL with a subsequent PL recovery. The source of the MIR laser pulses was the free-electron laser facility FELBE at the Forschungszentrum Dresden-Rossendorf. In combination with the synchroscan streak camera, collecting the PL from the electron-hole recombination, it turned out to be a great spectroscopic tool for time-resolved measurements. Using a simple fit function we found PL recovery times between 40 and 150 ps depending on the MIR intensity.

Keywords: quantum wells; time-resolved photoluminescence; streak camera; FELBE

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.03.2010, Regensburg, Deutschland

Publ.-Id: 15192

Ordered Ag nanocluster structures by vapor deposition on pre-patterned SiO2

Numazawa, S.; Ranjan, M.; Heinig, K.-H.; Facsko, S.; Smith, R.

Highly ordered Ag nanocluster structures have been grown on pre-patterned amorphous SiO2 surfaces by oblique angle physical vapor deposition at room temperature. Despite the small undulation of the rippled surface, the stripe-like Ag nanoclusters are very pronounced, reproducible and well-separated. Computer modeling of the growth has been performed with a lattice-based kinetic Monte-Carlo (KMC) method using a combination of a simplified inter-atomic potential and experimental transition barriers taken from the literature. An effective transition event classification method is introduced which allows a boost factor of several thousand compared to a traditional KMC approach, thus allowing experimental time scales to be modeled. The simulation predicts a low sticking probability for the arriving atoms, millisecond order lifetimes for single Ag monomers and ~1 nm square surface migration ranges of Ag monomers. It is also shown that metal nucleations can trigger even on defect free surfaces. The simulations give excellent reproduction of the experimentally observed nanocluster growth patterns.

Keywords: Kinetic Monte-Carlo; Physical vapor deposition; nanopatterning

Publ.-Id: 15191

Impact of Slow Highly Charged Ions on Insulating Surfaces

Facsko, S.

Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation can thus induce various effects, like secondary electron emission, potential sputtering, and finally also permanent surfaces modifications [1].
Systematic investigations of surface modifications induced by highly charged ion on different materials have revealed many interesting mechanisms. On CaF2 surfaces hillock structures are formed by the impact of HCI due to a localized phase transition [2]. In the case of the alkali halide crystal KBr the formation of nanostructures results from the desorption of surface atoms from a single ion impact site [3]. In both cases a threshold in the potential energy for the formation of the structure has been identified and could be interpreted in the frame of the applied models. However, still a unified picture of these effects is missing.
This work has been supported by the European Project ITSLEIF (RII3#026015).
[1] S. Facsko, R. Heller, A. S. El-Said, W. Meissl and F. Aumayr, J. Phys.: Cond. Matter 21, 2240122 (2009) .
[2] A. S. El-Said, R. Heller, W. Meissl, R. Ritter, S. Facsko, C. Lemell, B. Solleder, I. C. Gebeshuber, G. Betz, M. Toulemonde, W. Moller, J. Burgdorfer and F. Aumayr, Phys. Rev. Lett. 100 237601 (2008).
[3] R. Heller, S. Facsko, R. Wilhelm, and W. Möller, Phys. Rev. Lett. 101, 096102 (2008).

Keywords: highly charged ions; surface modifications; nanostructures

  • Invited lecture (Conferences)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS ICACS-24, 18.-23.07.2010, Krakow, Polen

Publ.-Id: 15190

Ion-Induced Surface Patterns as Templates for Thin Film Growth

Facsko, S.; Ranjan, M.; Keller, A.; Oates, T. W. H.; Faßbender, J.; Möller, W.

Nanostructured thin films are of growing relevance for all kind of applications in photovol-taics, plasmonics, or as magnetic materials. Various methods have been used to fabricate these nanostructured thin films with well defined morphology. Besides the top-down ap-proaches using lithographic methods, bottom-up, self-organized methods have been used ex-tensively in the last years because of their fast and easy way of producing patterns with struc-tures down to 10 nm.
Ion beam sputtering has proven to be a promising way to produce self-organized patterns on various surfaces. Depending on the ion incidence angle hexagonally ordered dot patterns as well as ripple patterns oriented perpendicular or parallel to the ion beam direction are formed during the continuous sputtering (see Fig. 1 left). These patterns are excellent templates for the growth of metal thin films. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography (Fig. 1 right top) or as nanoparticles on the substrate surface (Fig. 1 right bottom). Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires [1].
Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favoured. Because of alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [2]. In addition, the magnetic properties of ferromagnetic thin films are drastically change by the presence of the interface and surface periodic roughness [3].

[1] T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[2] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[3] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).

Keywords: ripple patterns; nanostructured thin films; magnetic films; plasmonic material

  • Invited lecture (Conferences)
    PSE 2010, Twelfth International Conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 15189

Cross-Coupling Reactions as Valuable Tool for the Preparation of PET Radiotracers

Pretze, M.; Große-Gehling, P.; Mamat, C.

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of new radiotracers and novel radiolabeling procedures with the most prominent short-lived positron emitters carbon-11 and fluorine-18. Radiolabeling with these radionuclides represents a remarkable challenge. Special attention has to be paid to synthesis time and specific labeling techniques due to the short physical half life of the respective radionuclides 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). In the past, numerous transition metalcatalyzed reactions were employed in organic chemistry, even though only a handful of these coupling reactions were adopted in radiochemical practice. Thus, the implementation of modern synthesis methods like cross-coupling reactions offers the possibility to develop a wide variety of novel radiotracers. The introduction of catalysts based on transition metal complexes bears a high potential for rapid, efficient, highly selective and functional group-tolerating incorporation of carbon-11 and fluorine-18 into target molecules. This review deals with design, application and improvement of transition metal-mediated carbon-carbon as well as carbon-heteroatom cross-coupling reactions as a labeling feature with the focus on the preparation of radiolabeled compounds for molecular imaging.

Keywords: cross-coupling; radiolabeling; carbon-11; fluorine-18

Publ.-Id: 15188

Surface patterning by low energy ion sputtering

Facsko, S.

The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as templates for nanostructured thin film deposition [3]. On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion processes. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is dissipated mainly kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.

[1] A. Keller, S. Rossbach, S. Facsko and W. Möller, Nanotechnology 19, 135303 (2008).
[2] S. Facsko et al., Science 285, 1551 (1999), F. Frost et al., Phys. Rev. Lett. 85, 4116 (2000).
[3] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mucklich, S. Facsko and J. Fassbender

Keywords: Nanostructures; ion sputtering; ripple patterns

  • Lecture (others)
    Seminar der Physikfakultät, 25.11.2010, Cosenza, Italia

Publ.-Id: 15187

In vitro binding profile and radiosynthesis of a novel 18F-labeled azaspirovesamicol analog as potential ligand for imaging of the vesicular acetylcholine transporter

Wenzel, B.; Hiller, A.; Fischer, S.; Sorger, D.; Deuther-Conrad, W.; Scheunemann, M.; Brust, P.; Sabri, O.; Steinbach, J.

Radiolabeled vesamicol analogues are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of early cholinergic degenerations in brain. The 4-fluorobenzoyl substituted azaspirovesamicol derivative FBASV is one out of six novel vesamicol analogs and demonstrated most appropriate in vitro binding data. 18F-radiolabeling was performed by microwave assisted nucleophilic aromatic substitution of the corresponding nitro precursor and two methods were developed for the purification of [18F]FBASV. Utilizing method A, the remaining nitro precursor was reduced to its corresponding amine, which was separated via semi-preparative HPLC on a conventional RP column. In method B a phenyl column was used for the direct separation of [18F]FBASV and its nitro precursor, resulting in a change of the elution order and better separation parameters. Thus, [18F]FBASV was synthesized with a RCY of 16-18%, a specific activity > 300 GBq/µmol, and a radiochemical purity of > 99.5% suitable for future in vivo studies.

Keywords: azaspirovesamicol; [18F]FBASV; VAChT; PET; 18F-labeling; vesamicol; nitro precursor

  • Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 426-432
    DOI: 10.1002/jlcr.1891

Publ.-Id: 15186

Transition metal implanted ZnO: Have we obtained a diluted magnetic semiconductor?

in Chinese

Zhou, S.

Ferromagnetic semiconductor, exhibiting properties of a ferromagnet and a semiconductor simultaneously, is a key material for semiconductor spintronics. To realize diluted ferromagnetic semiconductors, one has to dope semiconductors with transition metal up to several percents. H. Ohno et al. obtained ferromagnetic GaAs:Mn by decreasing the growth temperature in molecular beam epitaxy [1]. In 2000, T. Dietl et al. successfully interpreted the ferromagnetism in GaAs:Mn based on mean-field theory and predicted that p-type wide bandgap semiconductors (ZnO and GaN) can be ferromagnetic above room temperature given the Mn concentration of 5 at.% [2]. This prediction pushed the research on mining for room-temperature ferromagnetic semiconductors as one of the most active topics in the last decade. In this talk, I will present the magnetic and structure properties of transition metal implanted ZnO as well as the opinions from other research groups [3, 4].

1. H. Ohno, et al., Appl. Phys. Lett. 69, 363 (1996).
2. T. Dietl, et al., Science 287, 1019 (2000).
3. K. Potzger, S. Zhou, et al., Appl. Phys. Lett. 88, 052508 (2006).
4. S. Zhou, et al., Phys. Rev. B 77, 035209 (2008).

  • Invited lecture (Conferences)
    Invited talk at Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 08.11.2010, Shanghai, China

Publ.-Id: 15185

On the role of americium in the reduction process in plutonium-americium oxides

Belin, R. C.; Martin, P. M.; Gavilan, E.; Reynaud, M.; Scheinost, A. C.

Innovative mixed oxide (MOX) (U,Pu)O2-x fuels for sodium fast neutron reactors (SFRs) systems are currently studied within the framework of the fourth generation (GEN-IV) nuclear reactors development. SFRs will be able to burn long-lived minor actinides (MA) such as Americium by adding them homogeneously to the fuel in a small amount (2 to 6%). Because oxygen to metal ratio (O/M) has a direct impact on irradiation performance, a thorough knowledge of its correlation with oxygen potential during manufacturing and especially sintering is of major concern.
A study by Osaka et al. [ ] highlights a conflicting redox behaviour of Am and Pu cations responsible for an unusual oxygen potential vs. O/M ratio relationship in Am-doped MOX. The reason might be that interactions between U and Am predominate and those between Pu and Am can be neglected [ ]. According to the authors, this should result in U being oxidized to a pentavalent state since Am is likely to be trivalent [ ].
We recently performed a coupled X-Ray Diffraction (XRD) and X-Ray Absorption Spectroscopy (XAS) characterization on substoichiometric Am-containing MOX [ ]. Our results show that Am reduction to Am+III is completed before any reduction of Pu is yet observed. Surprisingly, no pentavalent U was evidenced and the behaviour of Am tends to solely influence that of Pu.

In the present work, to go deeper into the underlying phenomenon involved in the correlated redox behavior of Pu and Am, we focused on U-free sub-stoichiometric (Pu,Am)O2-x compounds. Three compositions were prepared via conventional solid-state reaction under Ar/5%H2 (1800K; 50h): (Pu0.992Am0.008)O2-x, (Pu0.9Am0.1)O2-x and (Pu0.8Am0.2)O2-x. XRD and XAS analyses were combined to selectively probe the long-range and the short-range order and the local environment of both cations. In particular, X-ray Absorption Near Edge Structure (XANES) allows to quantitatively determining the oxidation states for each cation. XRD shows a monophasic system for each composition. Interestingly, the variation of the cell parameter vs. Am concentration is not linear.
In the presentation, we shall detail and compare XRD and XAS results. Especially, we will focus on the correlation between Am content, cell parameter and ratios of Am+3/Am+4 and of Pu+3/Pu+4. We believe our results will improve comprehension of the role of Americium in the overall reduction process occuring in Americium-doped MOX fuels. They may also contribute to the development of the chemical thermodynamic models used to describe such materials.

Keywords: americium; plutonium; MOX; nuclear fuel; SFR; XAS; XRD

  • Lecture (Conference)
    GLOBAL 2011, 04.-09.09.2011, Nagoya, Japan

Publ.-Id: 15184

CFD simulation of fibre material transport in a PWR under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Weiss, F.-P.

During a postulated cold leg LOCA with hot leg ECC injection, a limited amount of small fractions of the insulation material after passing the sump strainers can enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling. The CFD simulations show that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “brake through channels” located at the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that at the beginning the fibers are not uniformly deposited over the core cross section.

Keywords: CFD; LOCA; PWR

  • Kerntechnik 76(2011), 39-45

Publ.-Id: 15183

Structural characterization of thermodynamically predicted U(VI)-tartrate complexes: Combing Factor Analysis with Landweber inversion method

Rossberg, A.; Lucks, C.; Tsushima, S.; Scheinost, A. C.

An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (PDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not yield a unique solution. The shell fit analysis of complicated spectra, as in the case of thermodynamically predicted aqueous complexes of U(VI) with tartaric acid, is much more eased if the PDF for the first shells are computed precisely and independently. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the PDF for the aqueous mono-, bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the PDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes were determined. Depending on the pH the U(VI)-tartaric acid complexes coexist, hence the EXAFS signal is a mixture of the spectral contributions of the complexes. In order to accomplish this special structural analysis we measured an EXAFS pH-series and isolated the spectra of the single complexes from their mixtures by using factor analysis [2].

[1] A. Rossberg, et al., Journal of Synchrotron Radiation, 17, 280-288 (2010).
[2] A. Rossberg, et al., Analytical and Bioanalytical Chemistry, 376, 631-638 (2003).

Keywords: EXAFS; metal complex; inverse method; Landweber iteration

  • Poster
    Actinide XAS 2011, 02.-04.03.2011, Hyogo, Japan

Publ.-Id: 15182

Numerical simulations of counter-current two-phase flow experiments in a PWR hot leg model using an interfacial area density model

Höhne, T.; Deen, D.; Lucas, D.

In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz–Zentrum Dresden–Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler–Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a k-x turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all Code users, with the possibility of the implementation of their own correlations.

Keywords: Slug flow; CFD; AIAD

Publ.-Id: 15181

Herstellung und magnetische Charakterisierung von Co-Nanopartikel auf ionenstrahlerodierten Siliziumsubstraten

Buhl, M.; Körner, M.; Fritzsche, M.; Wiesenhütter, U.; Liedke, O.; Fassbender, J.

Co-Nanopartikel wurden auf den selbstorganisierten Ripplen ionenstrahlerodierter Si-Substrate mittels Molekularstrahlepitaxie deponiert. Im Rahmen der Untersuchung sind Substrattemperatur und nominelle Beschichtungsdicke gezielt variiert worden. Mit Hilfe der longitudinalen magneto-optischen Kerr-Effekt Magnetometrie wurde der Einfluss der Ripple-Oberfläche auf das magnetische Verhalten der Co-Partikel analysiert. Die Auswertung der Messergebnisse von normierter remaneter Kerr-Drehung und Koerzitivfeldstärke zeigt eine uniaxiale magnetische Anisotropie. Die leichte Richtung der Magnetisierbarkeit liegt parallel zu den Ripple-Wellenfronten.

Keywords: Ripple; Co-nanoparticle; MOKE; Co-particle; Kerr Effect; Selforganisation; Magnetism; Anisotropy

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 15180

The trigonal nodal SP3 method of the reactor code DYN3D

Duerigen, S.; Fridman, E.; Kliem, S.

DYN3D is a 3D nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option for square geometry as well as a multi-group diffusion version for hexagonal geometry.
In this work, the multi-group SP3 method based on a trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs).
In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of two VVER-440 single assembly test examples with different material compositions. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are shown for 2 and 8 energy groups, respectively, and are in good agreement to the reference solutions. The maximum deviation in the nodal power distribution is about 1%.

Keywords: simplified P3; SP3; nodal; trigonal; triangular; hexagonal; DYN3D

  • Contribution to proceedings
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan
  • Lecture (Conference)
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan

Publ.-Id: 15179

Numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field

Miao, X.; Lucas, D.; Gerbeth, G.

The numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field is presented. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model.

Keywords: continuous casting; electromagnetic brake; numerical simulation

  • Lecture (Conference)
    Symposium zur Simulation metallurgischer Strömungen an österreichischen und deutschen Universitäten, 17.-18.06.2010, Kirnitzschtal, Germany

Publ.-Id: 15178

Structural characterisation of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy

Anwand, W.; Kanjilal, A.; Brauer, G.; Wagner, A.; Butterling, M.; Cowan, T. E.; Rebohle, L.; Skorupa, W.

Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, leading to the formation of Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, can lead to an improvement of the luminescent properties. However, the intensity of electroluminescence was found to decrease drastically after exceeding an optimum concentration of the Er doping.
Slow positron implantation spectroscopy (SPIS), both in single (DB) and coincidence (CDB) Doppler broadening mode, was applied to probe processes at a microscopic level which might have an impact on the optical response. It shows that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and also with the improved reverse energy transfer process between Er and Ge.

Keywords: Er doped Ge-rich SiO2; electroluminescence; positron annihilation; Doppler broadening; structural changes

Publ.-Id: 15177

Cu diffusion-induced vacancy-like defects in freestanding GaN

Elsayed, M.; Krause-Rehberg, R.; Moutanabbir, O.; Anwand, W.; Richter, S.; Hagendorf, C.

Positron annihilation spectroscopy was employed to elucidate the nature and thermal behavior of defects induced by Cu in freestanding GaN crystals. Cu atoms were intentionally introduced in GaN lattice through thermally activated diffusion from an ultrathin Cu capping layer. During isochronal annealing of the obtained Cu-doped GaN in the temperature range of 450–850 K, vacancy clusters were found to form, grow and finally vanish. Doppler broadening measurements demonstrate the presence of vacancy-like defects across the 600 nm-thick layer below the surface corresponding to the Cu-diffused layer as evidenced by secondary ion mass spectrometry. A more qualitative characterization of these defects was accomplished by positron lifetime measurements. We found that annealing at 450K triggers the formation of divacancies, whereas further increase of the annealing temperature up to 550K leads to the formation of large clusters of about 60 vacancies. Our observations suggest that the formation of these vacancy-like defects in bulk GaN is related to the out-diffusion of Cu.

Keywords: Cu diffusion-induced vacancy-like defects; GaN; positron annihilation spectroscopy

  • Open Access Logo New Journal of Physics 13(2011), 013029

Publ.-Id: 15176

The DRESDYN project at FZD

Gerbeth, G.; Eckert, S.; Gundrum, T.; Stefani, F.

The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is intended to become a platform both for large scale experiments related to geo- and astrophysics as well as for safety and thermohydraulic studies related to liquid metal batteries and sodium fast reactors. The most ambitious parts of DRESDYN are a homogeneous dynamo driven solely by precession and a large Tayler-Couette like experiment for the combined investigation of the magnetorotational instability and the Tayler instability.
In the talk we give a short summary of the previous achievements, and we delineate the next steps for the realization of DRESDYN.

  • Lecture (Conference)
    13th MHD-days, 22.-23.11.2010, Dresden, Germany

Publ.-Id: 15175

Experimental and numerical modeling of the steel flow in a continuous casting mould exposed to a transverse DC magnetic field

Timmel, K.; Miao, X.; Lucas, D.; Eckert, S.; Gerbeth, G.

This paper is concerned with numerical and experimental investigations focusing on the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Systematic measurements of the mould flow were carried out using the eutectic alloy GaInSn inside a plexiglass model at room temperature. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mould. The ultrasound Doppler velocimetry (UDV) was applied to obtain a detailed experimental data base with respect to the mean values and transient properties of the velocity fields occurring in the mould. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The comparison between our numerical calculations and the experimental results displays a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a smooth reduction of the velocity fluctuations at the nozzle outlet.

Keywords: continuous casting; electromagnetic brake; experimental modeling; numerical simulation

  • Lecture (Conference)
    Workshop "Modelling for Material Processing", 16.-17.09.2010, Riga, Latvia

Publ.-Id: 15174

How to circumvent the size limitation of liquid metal batteries due to the Tayler instability

Stefani, F.; Weier, T.; Gundrum, T.; Gerbeth, G.

Recently, a new type of battery has been proposed that relies on the principle of self-assembling of a liquid metalloid positive electrode, a liquid electrolyte, and a liquid metal negative electrode. While this configuration has been claimed to allow arbitrary up-scaling, there is a size limitation of such a system due to a current-driven kink-type instability that is known as the Tayler instability. We characterize this instability in large-scale self-assembled liquid metal batteries and discuss various technical means how it can be avoided.

Publ.-Id: 15173

VGF - type buoyant flow under a Travelling Magnetic Field - Numerical and experimental modelling

Galindo, V.; Niemietz, K.; Paetzold, O.; Gerbeth, G.; Stelter, M.

The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The application of a travelling magnetic field (TMF) allows the temperature and concentration fields to be tailored during growth by introducing an additional melt flow. Detailed knowledge about the flow pattern and stability resulting from the superposition of buoyant and electromagnetic forces is necessary to achieve VGF-TMF growth under optimal convective conditions. Direct measurements of the melt flow in real conditions, however, are extremely difficult because of the enclosed, high-temperature growth environment. In this lecture experimental and numerical modelling of a VGF-type flow under the influence of a TMF are presented. Low-temperature flow experiments at around 70°C were carried out using a GaInSn alloy (melting point: 10.5°C) as the model fluid. Radial heating and cooling of the melt leading to a double vortex buoyant flow like in typical VGF growth, was introduced by means of a model furnace with separately adjustable resistance heaters. The flow was characterized by means of Ultrasonic Doppler Velocimetry (UDV) giving the velocity profile perpendicular to the UDV probe face. The turbulent flow and the temperature distribution in the melt due to the combined action of a travelling magnetic field and the thermal convection were simulated numerically using a finite volume code based on the open source code library OpenFOAM. The k-omega SST RAS turbulence model was used. The distribution of the amplitude of the kinetic energy k, as an expression for the velocity fluctuations, was calculated for different values of the strength and frequency of the applied magnetic field and different heating regimes. The melt flow is systematically studied as a function of axial and radial temperature gradients as well as of strength and frequency of the magnetic field. Particular attention is paid on the effect of the thermal and TMF parameters on the transition to time-dependent melt flow which is a crucial problem in VGF crystal growth. The stability limit is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. It is shown that the TMF-induced flow can be stabilized by natural buoyancy and vice versa, and the conclusions to be drawn for real VGF growth are discussed.

Keywords: crystal growth; vertical gradient freeze; travelling magnetic field

  • Lecture (Conference)
    7. Workshop Angewandte Simulation in der Kristallzüchtung, 23.-24.11.2010, Burghausen, Deutschalnd

Publ.-Id: 15172

Bakterien als Lieferanten für neue Recycling-Technologien: Rückgewinnung von Metallen aus Wässern mit neuen Biokompositmaterialien

Pollmann, K.

Potenzial von Bakterien für neue Technologien

  • Invited lecture (Conferences)
    1. Freiberger Ressourcen-Technologie Symposium, 14.-15.02.2011, Freiberg, Deutschland

Publ.-Id: 15171

Combination of internal and external irradiation: Binding of the monoclonal EGFR-antibody C225 in irradiated tumors

Koi, L.; Brüchner, K.; Bergmann, R.; Helbig, L.; Steinbach, J.; Baumann, M.; Zips, D.

kein Abstract verfügbar

  • Poster
    European Society for Therapeutic Radiology and Oncology (ESTRO), 12.-16.09.2010, Barcelona, Spain

Publ.-Id: 15170

Fundamental and application oriented research on bacterial S-layers from uranium mining waste pile isolates

Weinert, U.; Raff, J.; Günther, T.; Pollmann, K.

Übersicht des Instiutes für Radiochemie und Vorstellung aktueller Forschungsthemen der Nachwuchsgruppe NanoBio

  • Lecture (others)
    Besuch der Arbeitsgruppe von Prof. Betzel, 26.01.2011, DESY Hamburg, Deutschland

Publ.-Id: 15169

Monte-Carlo simulations for timing-system of EPOS at ELBE in Research Centre Dresden-Rossendorf

Butterling, M.; Jungmann, M.; Bondarenko, V.; Sachert, S.; Brauer, G.; Anwand, W.; Krause-Rehberg, R.

Most of the monoenergetic slow-positron beam systems capable for positron lifetime spectroscopy are bunched from a continuous beam (e.g., the PLEPS system in Munich). The EPOS system at the ELBE radiation source will use the original time structure of the 40-MeV electron beam which is utilized for pair production. This is an infinite repetition of very short electron pulses (< 5 ps) with an adjustable repetition rate (typical 77 ns). In both cases, the time structure of the positron beam needs sharpening so that the time focus is located at the sample position. This is realized by the bunching system. Usually, double-slit bunchers are used. They are operated by a sinusoidal RF-voltage. This bunching requires an adjustment according to the final positron energy (0.5...30 keV), since the acceleration of the positrons shifts their time focus. Monte-Carlo simulations were done to investigate the effect of different methods of time focusing. One method is the variation of amplitude of the buncher RF-voltage. Another improvement is the combination of such a buncher voltage variation with a variable drift path acceleration short before the final acceleration which is operated by a DC voltage. Our simulations show that indeed a combination of a buncher variation with a drift path gives the sharpest positron pulses when both devices are supplied with individual voltages for each positron implantation energy.

Keywords: Monte-Carlo simulations for timing-system

Publ.-Id: 15168

Single-magnet rotary flowmeter for liquid metals

Priede, J.; Buchenau, D.; Gerbeth, G.

We present a novel design of a contactless flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis, about which it can freely rotate, and placed close to a duct with a liquid metal flow. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation.
The equilibrium rotation rate, which is attained at a vanishing net electromagnetic torque on the magnet, depends only on the flow rate and the geometry of the system while it is independent of the electromagnetic torque itself.
A laboratory model of such a flowmeter has been built and tested on a liquid metal flow.

  • Journal of Applied Physics 110(2011)3, 034512
    DOI: 10.1063/1.3610440
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 575-579

Publ.-Id: 15167

Quenched-in vacancies in Fe3Al based alloys: a positron annihilation study

Melikhova, O.; Čížek, J.; Kuriplach, J.; Procházka, I.; Lukáč, F.; Cieslar, M.; Anwand, W.; Brauer, G.

In the present contribution, high-resolution positron lifetime spectroscopy and slow positron implantation spectroscopy are used to characterize defects in Fe75.99Al24.01 and Fe71.98Al28.02 alloys. In order to facilitate defect identification, we also perform a theoretical study of basic vacancy-like defects in three phases of the Fe3Al system: ordered (D03), shortrange ordered (B2) and disordered (A2). Positron characteristics, i.e. positron lifetime and positron binding energy to defects are calculated from the first principles for various defect configurations. The results are discussed in the context of experimental data obtained here and available in literature.

Keywords: Fe-Al alloys; defects; positron annihihaltion spectroscopy

Publ.-Id: 15166

Contactless electromagnetic phase-shift flowmeter for liquid metals

Priede, J.; Buchenau, D.; Gerbeth, G.

We present a concept and test results of an induction flowmeter for liquid metals.
The flow rate is determined by applying a weak AC magnetic field to a liquid metal flow and measuring the flow-induced phase disturbance in the external electromagnetic field. The phase disturbance is found to be more robust than that of the amplitude used in conventional AC flowmeters. The basic characteristics of this type of flowmeter are analysed using simple theoretical models where the flow is approximated by a solid body motion. Design of such a flowmeter is presented and its test results reported.

  • Measurement Science and Technology 22(2011)5, 055402

Publ.-Id: 15165

Digital positron lifetime: the influence of noise

Krille, A.; Anwand, W.; Krause-Rehberg, R.

In contrast to the world around where everything seems to go digital as soon as possible, positron lifetime spectrometers are kind of a “last sanctuary” for analog measurements. Only a few of the newer spectrometers use the analog-digital-converters directly after the photomultipliers and extract the timing information via computer. Judging from their results it seems as if the current available converters and the timing mathematics are only as good as the conventional analog setup in the timing resolution. As it is decided that EPOS [1] will use digital positron lifetime, we try to find some reasons for limited timing resolution by simulating anode pulses from the photomultipliers and measuring the FWHM. We create pulses similar to current state-of-the-art 4GS/s digitizers but can control the level of noise and the bit-depth independently. We found that especially the noise (that would come from the analog electronics in/before the converters) has a great influence on the timing resolution. Also we try to use lowpass filtering to reduce that influence with great success.

Keywords: digital positron lifetime spectroscopy

Publ.-Id: 15164

The sensitivity of a travelling magnetic field driven flow to axial alignment

Cramer, A.; Pal, J.; Koal, K.; Tschisgale, S.; Stiller, J.; Gerbeth, G.

The sensitivity of a flow that is driven by a travelling magnetic field (TMF) with respect to a shift between the axes of the cylindrical liquid metal column and of the TMF was studied both experimentally and by numerical simulation. In the physical modelling, the generation of the TMF comprised six equidistantly spaced cylindrical coils loaded with ac current having a phase shift of 60 degree, respectively, between them. Ultrasound Doppler velocimetry was used to acquire vertical sections of the vertical velocity component along the beam axis in the centre and at various azimuthal positions for a fixed radial coordinate. The measurements are compared to the according flow data from large eddy simulations. These computations were based on the usual approximations to simplify the magnetohydrodynamical equations, which are low frequency and low induction, and on an analytical expression for the Lorentz force considering the shift between the fluid volume and the field. It is shown that even a small shift between the axes may result in a distinct three-dimensional constituent of the flow structure, and thus changing completely the usually assumed axisymmetric torus-type flow.

Keywords: Fluid flows; Magnetic fields; Stirring; Growth from melt

  • Journal of Crystal Growth 321(2011)1, 142-150

Publ.-Id: 15163

Optimization of the Electron Beam Properties of Dresden EBIT for Charge Breeding

Thorn, A.; Ritter, E.; Sokolov, A.; Vorobjev, G.; Bischoff, L.; Herfurth, F.; Kester, O.; Pilz, W.; Thorn, D. B.; Ullmann, F.; Zschornack, G.

This paper summarizes the results of studies to enhance the performance of Dresden Electron Beam Ion Traps (EBIT) regarding aspects which are important for charge breeding, i.e. injection of externally produced low charged ions and their conversion to highly charged ions. The properties of the electron beam of this compact room-temperature operated EBIT were investigated via position sensitive Xray detection. A detailed analysis of the spatial distribution as well as the energy of the X-ray photons emitted from the electron beam region allowed for the determination of the source parameters needed to guarantee optimal ion trapping conditions and ionization rates. The parameters found in this investigation were applied for the successful realization of charge breeding with the Dresden EBIT.

Keywords: EBIT; charge breeding; X-ray

  • Lecture (Conference)
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 18.-23.07.2010, Stockholm, Sweden
  • Open Access Logo Journal of Instrumentation 5(2010), C09006-1-C09006-10
    DOI: 10.1088/1748-0221/5/09/C09006

Publ.-Id: 15162

Some thermophysical properties of the intermetallic Ti40Al60 alloy in the melting-solidification temperature range

Plevachuk, Y.; Sklyarchuk, V.; Hermann, R.; Gerbeth, G.

TiAl intermetallic alloys are being developed as potential materials for applications in aerospace and automotive industries and also for chemical and biomedical applications because of their excellent chemical and physical properties such as low density, high modulus and corrosion resistance at high temperatures. The thermophysical properties (electrical conductivity, thermoelectric power and thermal conductivity) of the solid and liquid intermetallic alloy Ti40Al60 have been measured during melting and solidification processes in order to supply necessary information for crystal growth and casting processes. Good reproducibility of the results has been obtained.

Publ.-Id: 15161

Raising the temper - μ-spot analysis of temper inclusions in experimental ceramics

Sterba, J. H.; Munnik, F.; Pearce, N. J. G.

Provenancing of ancient ceramics is a highly important scientific tool for archaeological studies. In general, ceramics are not made from the original clay, as it can be found in deposits. To produce the needed physical properties in the finished product, the clay has to be either tempered by adding sands or biological materials or levigated, to remove the coarse fraction. Thus, the chemical composition of the finished ceramic differs from the composition of the original clay bed. To overcome this obfuscation, any information that can be gained about the temper used is useful. In a small series, several pieces of ceramic were produced from known clay and tempers and the resulting ceramics analysed by INAA. As many attempts to physically separate the temper from the clay matrix have failed, μ-spot analysis of temper inclusions were performed at the μ-PIXE (Particle induced X-Ray Emission) facility in Rossendorf and by LA-ICPMS (Laser ablation Inductively coupled plasma mass spectroscopy) in Aberystwyth. It could be shown that from a small number of measurements, a general impression of the temper used could be gained, showing if the temper consists mainly of quartz, feldspars or other main components. With this information, dilution calculations can be greatly facilitated, and a close resemblance of the chemical composition of the clay matrix can be calculated.

  • Poster
    13th International Conference on Modern Trends in Activation Analysis, 13.-18.03.2011, Texas, USA
  • Journal of Radioanalytical and Nuclear Chemistry 291(2012), 25-35
    DOI: 10.1007/s10967-011-1208-6

Publ.-Id: 15160

E. coli filament formation induced by heterologous S-layer expression

Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.

Escherichia coli is a rod-shaped intestinal bacterium which has a size of 1.1-1.5 µm x 2.0-6.0 µm. The fast cell division process and the uncomplicated living conditions turn E. coli into a widely used host in genetic engineering and into one of the best studied microorganism at all. We used E. coli BL21(DE3) as host for heterologous expression of S-layer proteins of Lysinibacillus sphaericus JG-A12 in order to enable a fast and high efficient protein production. The S-layer expression induced in E. coli an unusual elongation of the cells, thus producing filaments with >100 µm in length. In the stationary growth phase, E. coli filaments develop tube-like structures that contain E. coli single cells. Fluorescence microscopic analyses of S-layer expressing E. coli cells that were stained with membrane stain FM® 5-95 verify the membrane origin of the tubes. Analyses of DAPI stained GFP-S-layer expressing E. coli support the assumption of a disordered cell division that is induced by the huge amount of recombinant S-layer proteins. However, the underlying mechanism is still not characterized in detail. These results describe the occurrence of a novel stable cell form of E. coli as a result of a disordered cell division process.

Keywords: Heterologous expression; S-layer; E. coli; morphology; cell division; tube-like structures; Outer membrane; membrane stain; DAPI

Publ.-Id: 15159

GATE goes Material Sciences - ClearPET in Environmental Research

Zakhnini, A.

Es existiert kein Abstract.

  • Lecture (others)
    OpenGATE technical meeting, 17.05.2010, Köln, Deutschland

Publ.-Id: 15158

Reactive Transport Division - scopes and aims

Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    PSI/IRC Meeting, 28.-29.09.2010, Rossendorf, Deutschland

Publ.-Id: 15156

Reactive transport investigations by means of radiotracer applications

Lippmann-Pipke, J.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    Kolloquium der Friedrich-Schiller Universität Jena, 07.12.2010, Jena, Deutschland

Publ.-Id: 15155

PET imaging of σ1 receptors: New F-18-labelled alkyl-substituted spirocyclic piperidine radiotracers

Maisonial, A.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Große Maestrup, E.; Steinbach, J.; Wünsch, B.; Brust, P.

There is evidence that σ1 receptors are involved in the cognitive impairment found in neurodegenerative diseases. Because of considerable drawbacks of the currently used PET ligand for neuroimaging of σ1 receptors, [C-11]SA4503, we have recently developed a new spirocyclic piperidine derivative: [F-18]WMS1813 ([F-18]1'-benzyl-3-(3-fluoropropyl)-3H-spiro[[2]benzofuran-1,4'-piperidine]) with high affinity and selectivity for σ1 receptor binding site (1). Further SAR studies on the fluoroalkyl chain provided three other promising analogues, bearing either fluoromethyl- (WMS1850), fluoroethyl- (WMS1828) or fluorobutyl-(WMS1847) moieties. Herein, we report on radiosyntheses and biological evaluation of these candidates for PET imaging of σ1 receptors.

Radiosyntheses of [F-18]WMS1850, [F-18]WMS1828, and [F-18]WMS1847 were performed by direct nucleophilic substitution of corresponding aliphatic tosylate precursors, using the K[F-18]F-K222-carbonate complex. Biodistribution studies and ex vivo brain autoradiography of the radiotracers were performed in female CD-1 mice. Target specificity was validated by pre-treatment with 1 mg/kg i.p. of the σ1 receptor antagonist haloperidol. In vivo metabolism of each radiotracer was evaluated by radio- TLC/-HPLC.

The three radiotracers were obtained with radiochemical yields of 35-53%, radiochemical purities >98.5%, and high specific activities ≥150 GBq/μmol. In mice, they rapidly accumulated in brain tissue. [F-18]WMS1828 was superior with a brain uptake value of 4.71 ± 1.39 %ID/g (30 min p.i.) in comparison to [F-18]WMS1813, [F-18]WMS1847 and [F-18]WMS1850 (3.18±0.68; 1.78±0.16; 2.65±0.68 %ID/g respectively). For all radiotracers, uptake in brain as well as in peripheral σ1 receptor expressing organs was significantly inhibited by haloperidol. At 30 min p.i., more than 75% of the radioactivity detected in plasma samples corresponded to native [F-18]WMS1850, [F-18]WMS1828 and [F-18]WMS1847. None of the radiometabolites observed crossed the blood-brain barrier. Results of ex vivo autoradiography of brain slices revealed resemblance between radioactivity distribution pattern of all radiotracers and regions with known high σ1 receptors density. The highest target (facial nucleus)-to-nontarget (olfactory bulb) tissue ratio was determined for [F-18]WMS1828 (4.69 at 45 min p.i.).

Within the series of σ1 receptor-specific radiotracers studied, [F-18]WMS1828 ([F-18]fluspidine) appears to be the most promising candidate for PET imaging with even better pharmacological profile than the lead compound WMS1813. Hence, [F-18]fluspidine radiosynthesis is selected for transfer onto an automated radiosynthesis module for further (pre)clinical development.

(1) Maestrup E G et al. J Med Chem 2009; 52, 6062-6072.

Keywords: PET; imaging; F-18; σ1 receptor

  • Lecture (Conference)
    NuklearMedizin2011, 13.-16.04.2011, Bregenz, Österreich
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A39

Publ.-Id: 15154

The Tayler instability of toroidal magnetic fields in a columnar gallium experiment

Rüdiger, G.; Schultz, M.; Gellert, M.

The nonaxisymmetric Tayler instability of toroidal magnetic fields due to axial electric currents is studied for conducting incompressible fluids between two coaxial cylinders without endplates. The inner cylinder is considered as so thin that the limit of Rin → 0 can be computed. The magnetic Prandtl number is varied over many orders of magnitudes but the azimuthal mode number of the perturbations is fixed to m = 1. In the linear approximation the critical magnetic field amplitudes and the growth rates of the instability are determined for both resting and rotating cylinders. Without rotation the critical Hartmann numbers do not depend on the magnetic Prandtl number but this is not true for the corresponding growth rates. For given product of viscosity and magnetic diffusivity the growth rates for small and large magnetic Prandtl number are much smaller than those for Pm = 1. For gallium under the influence of a magnetic field at the outer cylinder of 1 kG the resulting growth time is 5 s. The minimum electric current through a container of 10 cm diameter to excite the instability is 3.20 kA. For a rotating container both the critical magnetic field and the related growth times are larger than for the resting column.

Publ.-Id: 15153

Radiosynthese und physikochemische Bewertung eines 7-(2-[F-18]Fluorethoxy)-6-methoxychinazolin-Derivates für die Darstellung der PDE10A mit PET

Funke, U.; Schwan, G.; Scheunemann, M.; Maisonial, A.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Sträter, N.; Nieber, K.; Briel, D.; Brust, P.

Neurologische und psychiatrische Erkrankungen, wie Schizophrenie und Psychosen werden in Zusammenhang mit Beeinträchtigungen der Aktivität der Phosphodiesterease 10A (PDE10A) gebracht. Selektive und hirngängige PDE10A-Inhibitoren sind daher Ziel der Entwicklung hochwirksamer Therapeutika (1) und geeigneter Diagnostika für die molekulare Bildgebung (2).
Ein Papaverin-basierter chiraler 6,7-Dimethoxychinazolin-Ligand diente in den vorliegenden Arbeiten als Leitstruktur für die Entwicklung eines 7-(2-[F-18]Fluorethoxy)-Analogons [F-18]I zur Darstellung der PDE10A mit PET.

Die Referenzverbindung I sowie die Markierungsvorläufer II und III wurden in Mehrstufen-Synthesen dargestellt und der logD7,0 mittels HPLC ermittelt. Für eine zweistufige Radiosynthese wurde 1,2-Bistosyloxyethan nach einem Standardverfahren zu 2-[F-18]Fluorethyltosylat [F-18]IV umgesetzt und [F-18]IV ohne Aufarbeitung weiterverwendet. Deprotonierung des 7-Hydroxy-Synthesevorläufers II mittels K.222/K2CO3 (2-3 h, 50-60°C, MeCN) und anschließende Veretherung (2 mg; K.222/K2CO3, MeCN/80°C) mit [F-18]IV führten zur Zielverbindung [F-18]I. Die direkte Radiofluorierung erfolgte über Substitution des 7-(2-Tosyloxyethyl)-Präkursors III mit n.c.a. [F-18]F- (2-3 mg; K.222/K2CO3, MeCN/80°C). Nach Aufarbeitung mit FPE (RP-18, MeCN) folgte semipräparative Radio-HPLC (RP-18, 45-50% MeCN, 20 mM NH4OAc) und Formulierung in MeCN, MeOH, EtOH oder wässrigem Puffer. Mit [F-18]I-Lösungen wurde die Stabilität bei 40 und 80°C untersucht sowie der logD7,2-7,4 mittels Extraktion in n-Octanol/Puffer-Systemen bestimmt.

[F-18]IV konnte in 5 min mit Markierungsausbeuten (MA, DC/HPLC) von 50-76% dargestellt werden. Hiermit wurde II in 15-20 min zu 30-45% MA an [F-18]I umgesetzt. Die radiochemische Ausbeute (RCA) betrug nach 2-3 h ohne Aufarbeitung 18-29%.
Mittels Tosylat III wurde n.c.a. [F-18]I in 15 min mit MA von 42-72%, einer chemischen und radiochemischen Reinheit ≥99% (DC/HPLC) sowie spezifischen Aktivität von 110-1110 GBq/μmol (HPLC) erhalten. Die RCA betrug nach 3-4 h Gesamtsynthesedauer 17-40%. Für die Zielverbindung I/[F-18]I wurden ein logD7,0 von 2,63±0,01 mittels HPLC und ein logD7,2-7,4 von 2,59±0,46 mittels Extraktion ermittelt. [F-18]I ist bei 40°C nur in ethanolischer KOH labil und erweist sich in EtOH und MeCN bei 80°C auch nach 120 min als stabil.

Die Zielverbindung konnte sowohl in einer zweistufigen als auch direkten Radiofluorierung dargestellt werden, wobei letztere eine höhere radiochemische Ausbeute lieferte. Ein logD von ∼ 2,6 stellt eine gute Voraussetzung für eine gute Hirnaufnahme des Radioliganden bei ausreichend niedriger unspezifischer Bindung dar. Weiterführende Experimente sind geplant, um die Organverteilung des Radioliganden sowie Bindung in vitro und in vivo zu untersuchen.

(1) Chappie T A et al. J Med Chem 2007; 50: 182-185
(2) Celen S et al. J Nucl Med 2010; 51: 1584-1591

Keywords: PDE10A; PET; 7-(2-[F-18]Fluorethoxy)-6-methoxychinazolin-Derivat

  • Lecture (Conference)
    NulearMedizin2011, 13.-16.04.2011, Bregenz, Österreich
  • Abstract in refereed journal
    Nuklearmedizin 50(2011), A38-A39

Publ.-Id: 15152

Investigation of conductive nanostructures on ta-C films made by FIB lithography

Philipp, P.; Bischoff, L.

Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 1016 cm-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 1017 cm-2. Investigations of the conduction mechanism were done by Hall-mobility measurements on Van der Pauw and Hall test structures. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 200 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 0.3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
[1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.

Keywords: tetrahedral amorphous carbon; ta-C; FIB; nanostructures; graphitization; sheet resistance

  • Lecture (Conference)
    E-MRS 2011 Spring Meeting, 09.-13.05.2011, Strassburg, France
  • Nuclear Instruments and Methods in Physics Research B 282(2012), 121-124
    DOI: 10.1016/j.nimb.2011.08.057

Publ.-Id: 15151

Ein neuer mit Fluor-18 markierter Radioligand für die molekulare Bildgebung der Phosphodieesterase 10A im Gehirn

Funke, U.; Schwan, G.; Scheunemann, M.; Fischer, S.; Hiller, A.; Donat, C.; Sträter, N.; Nieber, K.; Briel, D.; Brust, P.

Die Phosphodiesterase 10A (PDE10A) terminiert die Signalübertragung der Second messenger cAMP und cGMP durch Hydrolyse und wird vorrangig in Gehirn (Striatum) und Schilddrüse exprimiert. Veränderungen der Aktivität der PDE10A werden in Zusammenhang mit Schizophrenie und Psychosen gebracht. Selektive und hirngängige PDE10A-Inhibitoren sind daher Ziel der Entwicklung hochwirksamer Therapeutika und geeigneter Diagnostika für die molekulare Bildgebung, wie unser 7-(2-[18F]Fluorethoxy)-6-methoxychinazolin-Derivat zur Visualisierung der PDE10A mit Positronen-Emissions-Tomographie (PET). Die zur Analytik erforderliche nichtradioaktive Referenzverbindung und die Ausgangsverbindungen für die 18F-Markierung wurden in Mehrstufen-Synthesen dargestellt. Für die 18F-Markierung wurde zunächst ein schneller zugängliches zweistufiges Verfahren entwickelt. Eine verbesserte Darstellung erfolgte anschließend im Einstufenverfahren über die direkte Umsetzung des entsprechenden 7-(2-Tosyloxyethyl)-Präkursors mit trägerfreiem [18F]F-. Die Markierungsausbeute betrug 42-72%, die chemische und radiochemische Reinheit ≥99% und die spezifische Aktivität 110-1110 GBq/µmol. Die zerfallskorrigierte radiochemische Ausbeute lag nach 3-4 h Gesamtsynthesedauer bei 17-40%. Als Kriterium für die Qualität der Hirnaufnahme wurde die Lipophilie des Radioliganden bei pH 7 bis 7,4 mittels HPLC und extraktiven Methoden bestimmt. Ein logD7,0-7,4  2,6 weist auf eine gute Hirnaufnahme bei ausreichend niedriger unspezifischer Bindung hin. Weiterführende Experimente sind geplant, um die Organverteilung des Radioliganden sowie Bindung in vitro und in vivo zu untersuchen.

Keywords: Fluor-18; Phosphodieesterase; molekulare Bildgebung

  • Poster
    9th Research Festival for Life Sciences, 07.12.2010, Leipzig, Deutschland

Publ.-Id: 15150

Fabrication of highly ordered magnetic bio-Au nanoclusters by using SlaA-layer ghosts of Sulfolobus acidocaldarius as a template

Selenska-Pobell, S.; Reitz, T.; Geissler, A.; Herrmannsdörfer, T.; Merroun, M.

The regularly structured paracrystalline surface layers (S-layers) of prokaryotic microorganisms are promising biological templates for production of metal nanoclusters for biotechnological applications. Formerly, we have demonstrated that some bacterial S-layers can effectively bind noble metals and can be used for preparation of palladium, platinum, and gold nanoclusters by using different reduction agents (1, 2) or electron beam (3).
In this work Au-nanoclusters were produced on the extremely stable (against high temperatures, acidity, proteases, and mechanic stress) S-layer of the acidothermophilic Archaeon Sulfolobus acidocaldarius. One additional important characteristic feature of this S-layer, called recently SlaA (4) is the presence of the sulfur containing amino acid cystein in its primary structure. This is in contrast to the above mentioned bacterial S-layers and is of great importance for the effective binding and deposition of Au cations. The purified SlaA-layer fraction was treated initially with tetrachloroauric (III) acid solution. Afterwards the deposited Au(III) cations were reduced to Au(0) by using dimethylaminoburane. The analysis of the obtained Au-nanoclusters by using Transmission Electron Microscopy combined with Energy Dispersive X-ray analyses (TEM-EDX) demonstrated that the nanoclusters have a size in the range of 2-3.5 nm and that they are associated with sulfur atoms (Fig. 1). As measured via SQUID Magnetometer they possess magnetic properties (Fig. 2). No magnetic properties were observed in the case of the Au-nanoparticles formed on the bacterial S-layers possessing no sulfur. We suggest that the sulfur atoms are possibly contributing to the observed magnetic properties. However, the number of sulfur atoms implicated in the Au complexation is extremely low (only a few atoms per nano-particle). On the other hand, the size of the nanoparticles formed on the archaeal SlaA-layer is significantly bigger (about 3 nm) in comparison to those formed on the bacterial S-layer (less then 1 nm). The size difference in the two kinds of nano-particles can be explained with the different size of the pores of the two S-layer lattices, where the initial deposition of the metal cations occurs. The archaeal SlaA-layer possesses p3 lattice symmetry and significantly larger pores (4) then the bacterial S-layer which has p4 symmetry (1, 2). The size of the Au-nanoclusters may play also a role for their magnetic properties. Efforts to understand the reasons for the observed unexpected magnetic behavior of the newly constructed bio-Au nanoparticles are in progress.
To our knowledge, this is the first report on constructing of highly ordered Au nanoparticles on an archaeal S-layer. These bio-Au structures possess some advantageous properties, such as high stability to high temperatures, acidic and mechanical stress, in comparison to those formerly constructed on bacterial S-layers. Moreover, in contrast to Au as a bulk noble metal and to bacterial bio-Au, the archaeal bio-Au nanoparticles possess unique magnetic properties.
1. Fahmy K, Merroun M, Raff J, Pollmann K, Hennig Ch, Savchuk O, Selenska-Pobell S (2006) Biophys J 91:996-1007.
2. Merroun M, Rossberg A, Hennig C, Scheinost A, Selenska-Pobell S (2007) Mater Sci & Engin C27, 188-192
3. Wahl R, Mertig M, Raff J, Selenska-Pobell S, Pompe W (2001) Adv Mater 13, 736-740
4. Veith A, Klingl A, Zolghadr B, Lauber K, Mentele R, Lottspeich F, Rachel R, Alberts S-V, Kletzin A (2009) Mol Microbiol 73, 58-72

  • Contribution to proceedings
    Nano Tech Conference, 13.-16.06.2011, Boston, USA
    Nanotechnology 2011, Vol. 3: NSTI, 978-1-4398-7138-6, 189-192

Publ.-Id: 15149

Dosimetric system for quantitative cell irradiation experiments with laser-accelerated protons

Richter, C.; Karsch, L.; Dammene, Y.; Metzkes, J.; Schramm, U.; Sobiella, M.; Schürer, M.; Weber, A.; Zeil, K.; Pawelke, J.

An Integrated DOsimetry and Cell Irradiation System (IDOCIS) with laser-accelerated proton beams was developed, characterized, calibrated and successfully used for systematic in vitro experiments. Due to the broad exponentially shaped energy spectrum, the low energy range of the protons (< 20 MeV) and the high pulse dose, the absolute dosimetry for this beam quality is challenging. Therefore, a dedicated Faraday cup is used as an energy and dose rate independent absolute dosimeter that has been calibrated consistently with three independent methods. A transmission ionization chamber providing online relative dose information is cross-calibrated against the Faraday cup. Providing both online and absolute dose information the IDOCIS allows for quantitative dosimetric and radiobiological studies at current low-energy laser-accelerated proton beams. Finally, first dosimetric characterizations of a laser-accelerated proton beam with the IDOCIS are presented.

Keywords: laser particle acceleration; proton; dosimetry; faraday cup; radiochromic films

Publ.-Id: 15148

Formation of a ternary neptunyl(V) biscarbonato inner-sphere sorption complex inhibits calcite growth rate

Heberling, F.; Scheinost, A. C.; Bosbach, D.

Neptunyl, Np(V)O2+, along with the other actinyl ions U(VI)O22+ and Pu(V,VI)O2+,2+, is considered to be highly mobile in the geosphere, while interaction with mineral surfaces (inner- or outer-sphere adsorption, ion-exchange, coprecipitation/structural incorporation) may retard its migration. Detailed information about the exact interaction mechanisms including the structure and stoichiometry of the adsorption complexes is crucial to predict the retention behavior in diverse geochemical environments. Here, we investigated the structure of the neptunyl adsorption complex at the calcite-water interface at pH 8.3 in equilibrium with air by means of low-temperature (15 K) EXAFS spectroscopy at the Np-LIII edge. The coordination environment of neptunyl consists of two axial oxygen atoms at 1.87(±0.01) Å, and an equatorial oxygen shell of six atoms at 2.51(±0.01) Å. Two oxygen backscatterers at 3.50(±0.04) Å along with calcium backscatterers at 3.95(±0.03) Å suggest that neptunyl is linked to the calcite surface through two monodentate bonds towards carbonate groups of the calcite surface. Two additional carbon backscatterers at 2.94(±0.02) Å are attributed to two carbonate ions in bidentate coordination. This structural environment is conclusively interpreted as a ternary surface complex, where a neptunyl biscarbonato complex sorbs through two monodentate carbonate bonds to steps at the calcite (104) face, while the two bidentately coordinated carbonate groups point away from the surface. This structural information is further supported by Mixed Flow Reactor (MFR) experiments. They show a significant decrease of the calcite growth rate in the presence of neptunyl(V), in line with blockage of the most active crystal growth sites, step and kink sites, by adsorption of neptunyl. Formation of this sorption complex constitutes an important retention mechanism for neptunyl in calcite-rich environments.

Keywords: EXAFS; Neptunium; Sorption; Calcite

Publ.-Id: 15147

Bioinspred hybrid nanomaterials based on self-assembling proteins

Raff, J.; Weinert, U.; Günther, T.; Marquard, A.; Lehmann, F.; Kutschke, S.; Pollmann, K.

Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (figure 1) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements and their compounds. On other cells, S-layers may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defense of host organism, by other bacteria or by lytic enzymes. These properties makes S-layer, together with their capability to self-assemble in suspension, on surfaces and at interfaces, very interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and multiple functionalized by a layer-by-layer technique. This interdisdisciplinary approach allows the design of novel bio-inorganic hybrid materials. Currently under development are three kinds of materials, namely metal filters, nanocatalysts and sensors. Regarding metal filters the aim is the development of selective materials for the removal of toxic metals and metalloids or the recovery of precious metals. In the case of nanocatalysts, the research is focused on the development of highly efficient catalysts or photocatalysts on the basis of immobilized and regular arranged metal or metal oxide nanoparticles for organic synthesis or the elimination of organic pollutants. S-layer based biosensors were under development to detect chemicals or pharmaceuticals by combining highly specific receptors like aptamers with stable fluorescence dyes.

Keywords: S-layer; biocomposites; nanomaterials

  • Poster
    DFG-NSF Research Conference, 22.-25.03.2011, New York, USA

Publ.-Id: 15146

Advances in Si & Ge millisecond processing: From SOI to superconductivity and carrier-mediated ferromagnetism

Skorupa, W.

This paper reviews the advances that millisecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, namely silicon and germanium, thus enabling the fabrication of novel microelectronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Opportunities in ultra-shallow junction formation for silicon-on-insulator, superconducting Ge and Si, and diluted ferromagnetic Ge, along with the technical reasons for using annealing times in the ms range are discussed in the context of state-of-the-art materials processing. Whereas these examples base on solid phase processing, the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. As a recent example the controlled surface melting of a Ge enriched silicon substrate is reported.

Keywords: flash lamp annealing; millisecond thermal processing; silicon germanium; ion implantation; silicon-on-insulator; diluted semiconductors; ferromagnetism; superconduction; liquid phase; surface melting; laser annealing

  • Invited lecture (Conferences)
    219th Electrochemical Society Meeting, SYMPOSIUM E1 Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications, 01.-06.05.2011, Montreal, Kanada
  • Contribution to proceedings
    219th Electrochemical Society Meeting, SYMPOSIUM E1 "Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications", 01.-06.05.2011, Montreal, Kanada
    Silicon compatible materials, processes and technologies for Advanced Integrated Circuits and Emerging Applications, Pennington, New Jersey, USA: Electrochemical Society, 978-1-56677-863-3, 193-204

Publ.-Id: 15145

In-vivo dosimetry for proton and ion therapy

Fiedler, F.

Abstract not available.

  • Invited lecture (Conferences)
    Retreat - Oncoray Seminar, 11.-12.01.2011, Riesa, Germany

Publ.-Id: 15144

High regiocontrol in the nucleophilic ring opening of 1-aralkyl-3,4-epoxypiperidines with amines – A short-step synthesis of 4-fluorobenzyltrozamicol and novel anilidopiperidines

Scheunemann, M.; Hennig, L.; Funke, U.; Steinbach, J.

Nucleophilic ring-opening reactions of three 1-aralkyl-3,4-epoxy piperidines with a series of aliphatic and aromatic amines have been investigated. Reactions in protic solvents, preferably 2-propanol, gave rise to 3-amino-piperidin-4-ols in ratios up to 20:1. Accordingly, the highly VAChT affine 4-fluorobenzyltrozamicol was obtained directly from an epoxide ring opening in one step, without the need of chromatographic separation. Reactions in acetonitrile assisted by Li-salts, most suitable with LiBr, led regioselectively to trans-4-amino-piperidin-3-ols in high yields. N-Phenethyl substituted anilino-piperidinols as easily obtained by this method were converted into a series of new β-hydroxy substituted anilidopiperidines.

Keywords: 1-aralkyl-3; 4-epoxy piperidines; 4-fluorobenzyltrozamicol; anilidopiperidines

Publ.-Id: 15143

Entwicklung von Radiotracern zur Untersuchung des cholinergen Systems mittels Positronen-Emissions-Tomografie

Brust, P.

Es ist kein Abstract vorhanden.

  • Lecture (others)
    Universität Leipzig - Kolloquium des Paul-Flechsig-Instituts für Hirnforschung, 31.03.2011, Leipzig, Deutschland

Publ.-Id: 15142

Design radioaktiver Sonden zur molekularen Bildgebung bei Hirnerkrankungen

Brust, P.

Es ist kein Abstract vorhanden.

  • Invited lecture (Conferences)
    24. Tagung der KTG-Fachgruppe Nutzen der Kerntechnik, 05.11.2010, Leipzig, Deutschland

Publ.-Id: 15141

Microstructure-property relations of reactively magnetron sputtered VCxNy films

Mitterer, C.; Fateh, N.; Munnik, F.

VCxNy films with a wide range of chemical composition were grown onto silicon and high-speed steel substrates using reactive unbalanced magnetron sputtering from V targets in an Ar/N2/C2H2 atmosphere at a substrate temperature of 500°C. A solid solution of VN and VC is formed for N2 and C2H2 addition, with increasing fractions of an additional amorphous carbon phase for increasing C2H2 flow ratios. While an increase in hardness is observed for low carbon contents due to solid solution hardening, raising the amorphous carbon phase fraction results in a hardness reduction. Dry-sliding ball-on-disc tests yield low friction coefficients with values of 0.22 for those films with the highest content of amorphous carbon phase, while the lowest wear is observed for films with dominating vanadium carbonitride solid solution. The low friction behavior is attributed to the formation of tribo-layers with easy-shearable C-H bonds formed in humid atmospheres, and is not observed in dry nitrogen and synthetic air.

Keywords: Vanadium carbonitride; amorphous carbon; sputtered films; low friction

Publ.-Id: 15140

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