Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
A Compton Imager for in-vivo Dosimetry of Proton Beams - A Design Study
Kormoll, T.; Fiedler, F.; Schöne, S.; Wüstemann, J.; Zuber, K.; Enghardt, W.;
In-beam SPECT during therapeutic proton beam irradiation is a novel method for three dimensional in-vivo dose verification. For this purpose a Compton camera design is evaluated with respect to the special requirements and conditions that arise from this application. Different concepts are studied by means of simulation concerning the angular resolution and the efficiency. It was found that a cadmium zinc telluride system can perform sufficiently well. For further evaluation the construction of a semiconductor scintillator hybrid system is under way.
Keywords: in-beam SPECT, in vivo dosimetry, ion beam therapy, proton therapy

Publ.-Id: 14906 - Permalink


Lateral straggling and its influence on lateral diffusion in implantation with a focused ion beam
Batabyal, R.; Roy, A.; Roy, S.; Bischoff, L.; Dev, B. N.;
Ion implantation plays an important role in semiconductor industry. Different kinds of ions are introduced into semiconductors by implantation in order to form n-type and p-type semiconductors. Nanoscale doped structures are required to be fabricated, usually by a focused ion beam (FIB), for applications in nanoelectronics. However, how closely these structures could be fabricated for an effective device performance would be determined by the limitation imposed by the lateral diffusion of the implanted species. For ion implantation, lateral straggling of the ion beam also produces defects surrounding the implanted region. This would produce radiation enhanced lateral diffusion. It is important to understand the lateral diffusion in FIB-fabricated nanostructures. We present a method based on photoemission electron microscopy (PEEM) for the determination of lateral diffusion coefficient in nanostructures. As an example, we present the investigation of lateral diffusion of Ga in FIB-fabricated structures of Ga-implanted n-type Si. For a set of parallel Ga implanted stripes, the diffusion profiles at the end of the stripes along their length obey the standard diffusion equation and the diffusion coefficient is extracted. However, across the stripes the diffusion profile is more complex, due to the presence of defects due to lateral straggling in the neighbouring stripes.
Keywords: photoemission, focused ion beam, diffusion in nanostructures
  • Lecture (Conference)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS, ICACS-24, 18.-23.07.2010, Krakow, Poland

Publ.-Id: 14905 - Permalink


Spectroscopic studies of arsenic retention onto biotite
Chakraborty, S.; Bardelli, F.; Mullet, M.; Greneche, J.-M.; Varma, S.; Ehrhardt, J.-J.; Banerjee, D.; Charlet, L.;
Biotite is a constituent Fe-bearing mineral of Delta subsoils in India and Bangladesh and has been hypothesized as a primary source of arsenic (As). The adsorption behavior of As onto structural Fe(II,III)-bearing biotite fractions (<50 µm) was investigated in the pH range 4-8 under a CO2-free, anoxic condition (O2 <1 ppmv) using X-ray Photoelectron Spectroscopy (XPS) and X-ray Absorption Spectroscopy (XAS). The batch experiments indicate that As adsorption is strongly pH dependent and As(V) adsorbs more efficiently than As(III). X-ray Absorption Near-Edge Structure (XANES) spectra show no oxidation or reduction of As by biotite after 3 days reaction with As(III) or As(V) solutions. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopic results suggest that As(III) forms bidentate mononuclear edge-sharing (2E) and bidentate binuclear corner-sharing (2C) surface complexes at pH 7.7 as indicated by the average As-Fe bond distances at 3.00 ± 0.02 Å and 3.37 ± 0.03 Å respectively. The surface speciation retrieved by XPS does not provide any evidence of reduction of As(V) on biotite after 30 days further confirming the thermodynamic prediction and the XANES results. This study has therefore significant environmental implications for As contaminated areas, where biotite retards the release of As into reducing groundwater. The changes in soil redox condition and weathering of biotite may likely contribute to the occurrence of high As in groundwater.
Keywords: Arsenic, adsorption, biotite, surface complex, reduction
  • Chemical Geology 281(2011), 83-92

Publ.-Id: 14904 - Permalink


On the "yl" bond weakening in uranyl(VI) coordination complexes
Tsushima, S.;
The U–Oyl triple bonds in the UO22+ aquo ion are known to be weakened by replacing the first shell water with organic or inorganic ligands. Weakening of the U–Oyl bond may enhance the reactivity of “yl” oxygens and uranyl(VI) cation–cation interactions. Density functional theory calculations as well as previously published vibrational spectroscopic data have been used to study the origin of the U–Oyl bond weakening in uranyl(VI) coordination complexes. Natural population analyses (NPA) revealed that the electron localization on the Oyl 2p orbital is a direct measure of the U–Oyl bond weakening, indicating that the bond weakening is correlated to the weakening of the U–Oyl covalent bond and not that of the ionic bond. The Mulliken analysis gives poor results for uranium to ligand electron partitioning and is thus unreliable. Further analyses of molecular orbitals near the highest occupied molecular orbital (HOMO) show that both the sigma and pai donating abilities of the ligands may account for the U–Oyl bond weakening. The mechanism of the bond weakening varies with coordinating ligand so that each case needs to be examined independently.

Publ.-Id: 14903 - Permalink


Influence of humic acids on the actinide migration in the environment: Suitable humic acid model substances and their application in studies with uranium – a review
Sachs, S.; Bernhard, G.;
Humic acids (HA) can influence the speciation of metal ions, e.g., actinide ions, and thus their migration in the environment. Therefore, knowledge of the impact of HA on the actinide migration is required to assess their transport in natural systems. However, due to the complex and heterogeneous nature of HA, there are a lot of difficulties in the thermodynamic description of their geochemical interaction behavior. A more basic understanding of the interaction processes of HA can be obtained by investigations applying HA model substances with more defined and specific properties. This work gives a review of selected types of HA model substances (HA-alike melanoidins, synthetic HA with pronounced redox functionality, modified HA with blocked phenolic/acidic OH groups, synthetic humic substance-clay-associates), their synthesis, isotopic labeling, and characterization in comparison to isolated natural HA. Examples for their application in various geochemical studies, such as complexation, redox, sorption and migration studies with uranium as representative for actinides are presented.
Keywords: Humic acids, model substances, synthesis, characterization, labeling, modification, application, uranium, actinides

Publ.-Id: 14902 - Permalink


On the use of different analytical solutions for recalculation of the YALINA-Booster experiment SC3A
Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.;
The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’ is analyzed in detail based on a full HELIOS model for the calculations. The two region design causes unexpected results in the experiments The special problems for the analysis of the experiments are shown. For an improved representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time is used. To model the streaming of neutrons from the thermal area into the fast area an analytical solution for the space-time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. The space-time dependent thermal and fast neutron flux distributions are discussed. The new analytical solution shows very good agreement in the comparison with the experimental results, even for the unexpected behavior at the outermost detector. Thus analytical solutions without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments
Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation

Publ.-Id: 14901 - Permalink


Constraining the S factor of 15N(p,g)16O at Astrophysical Energies
Leblanc, P. J.; Imbriani, G.; Goerres, J.; Junker, M.; Azuma, R.; Beard, M.; Bemmerer, D.; Best, A.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Couder, M.; Deboer, R.; Elekes, Z.; Falahat, S.; Formicola, A.; Fulop, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyurky, G.; Kaeppeler, F.; Kontos, A.; Kuntz, R.; Leiste, H.; Lemut, A.; Li, Q.; Limata, B.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; O'Brien, S.; Palumbo, A.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Stech, E.; Straniero, O.; Strieder, F.; Tan, W.; Terrasi, F.; Trautvetter, H. P.; Uberseder, E.; Wiescher, M.;
The 15N(p,g)16O reaction represents a break out reaction linking the first and second cycle of the CNO cycles redistributing the carbon and nitrogen abundances into the oxygen range. The reaction is dominated by two broad resonances at Ep = 338 keV and 1028 keV and a Direct Capture contribution to the ground state of 16O. Interference effects between these contributions in both the low energy region (Ep < 338 keV) and in between the two resonances (338
  • Physical Review C 82(2010), 055804
    DOI: 10.1103/PhysRevC.82.055804
  • Contribution to WWW
    ArXiV preprint server: http://arxiv.org/abs/1011.2518
  • Publ.-Id: 14900 - Permalink


    Blitzlampentemperung für die Photovoltaik
    Skorupa, W.;
    A review regarding the application of flash lamp annealing for photovoltaic purposes was presented.
    Keywords: Flash lamp annealing, doping, ion implantation, solar cells
    • Lecture (Conference)
      Topical meeting with members of the company Bosch, 10.02.2010, FZ Dresden-Rossendorf, Deutschland

    Publ.-Id: 14899 - Permalink


    Advances in Si & Ge millisecond processing: From SOI to superconducting Ge
    Skorupa, W.; Wündisch, C.; Posselt, M.; Heera, V.; Herrmannsdörfer, T.; Buca, D.; Mantl, D.; Haeberlein, S.; Fendler, R.; Gebel, T.;
    Recently we could demonstrate that advanced SOI material can be treated in advantageous manner regarding USJ formation [1]. Especially, strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. Their successful integration into new device architectures depends on the ability of forming ultra shallow and ultra steep junctions. We present results for dopant activation in SOI, sSOI, HOI and sHOI [2]. FLA allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□ in both, SOI and sSOI. Strained and unstrained SiGe heterostructures indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region. Moreover, we demonstrate that, after diamond and silicon, the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure [3]. For the first time, techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material, i.e. a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. It is shown that superconductivity can be generated and tailored in the Ge host at temperatures as high as 0.5 K. Results of critical-field measurements demonstrate the quasi-two-dimensional character of superconductivity in the 60 nm thick Ge:Ga layer.
    [1] F. Lanzerath, D. Buca, H. Trinkaus, M. Goryll, S. Mantl, J. Knoch, U. Breuer, W. Skorupa, B. Ghyselen, J. Appl. Phys. 104 (2008), 044908
    [2] R. A. Minamisava, W. Heiermann, D. Buca, H. Trinkaus, J. Hartmann, W. Skorupa, U. Breuer, B. Ghyselen, S. Mantl, Proc. 215th ECS Meeting, Vol. 19, Issue 1, May 24-29, 2009
    [3] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W, . Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, J. Wosnitza,
    Phys. Rev. Lett., 102 (2009) 217003, Supercond. Sc. & Techn., 23 (2010) 034007
    Keywords: ion implantation, flash lamp annealing, SOI, superconduction, germanium, silicon
    • Invited lecture (Conferences)
      The VIII-th International Conference on Ion Implantation and other Applications of Ions and Electrons – ION 2010 will be held in Kazimierz Dolny, Poland, between 14-th and 17-th June 2010., 14.-17.06.2010, Kazimierz Dolny, Poland

    Publ.-Id: 14898 - Permalink


    Doping of Vertical Si Nanowires by Ion Implantation
    Skorupa, W.;
    A review of recent work published in:
    ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024
    NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175
    NANOSCALE RESEARCH LETTERS Volume: 5 Issue: 1 Pages: 243-246
    Keywords: ion implantation, silicon nanowires, doping, scanning spreading resistance microscopy
    • Invited lecture (Conferences)
      43.Deutsches Nutzertreffen Ionenimplantation, 06.05.2010, Erlangen, Deutschland

    Publ.-Id: 14897 - Permalink


    Literaturübersicht Temperaturmessung in RTP Mit Augenmerk auf die Blitzlampenausheilung
    Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.;
    No abstract available.
    • Lecture (Conference)
      25. Treffen der Nutzergruppe RTP, 07.05.2009, Erlangen, Deutschland

    Publ.-Id: 14896 - Permalink


    Application of Large-Eddy Simulation to Pressurized Thermal Shock: assessment of the accuracy
    Loginov, M. S.; Komen, E.; Höhne, T.;
    Pressurized Thermal Shock (PTS) is identied as one of the safety issues where Computational Fluid Dynamics (CFD) can bring real benefits. The turbulence modeling may impact overall accuracy of the calculated thermal loads on the vessel walls, therefore advanced methods for turbulent fows are required. The feasibility and mesh resolution of LES for single-phase PTS are assessed earlier in a companion paper. The current investigation deals with the accuracy of LES approach with respect to the experiment. Experimental data from the Rossendorf Coolant Mixing (ROCOM) facility is used as a basis for validation. Three test cases with dierent ow rates are considered. They correspond to a buoyancy-driven, a momentum-driven, and a transitional coolant mixing pattern in the downcomer. Time- and frequency-domain analysis are employed for comparison of the numerical and experimental data.
    Keywords: PTS, CFD, Coolant Mixing, ROCOM

    Publ.-Id: 14895 - Permalink


    Doping Issues of Si Nanowires
    Skorupa, W.;
    A review of recent work published in:
    ADVANCED MATERIALS Volume: 22 Issue: 36 Pages: 4020-4024,
    NANO LETTERS Volume: 10 Issue: 1 Pages: 171-175,
    Keywords: Doping, ion implantation, scanning spreading resistance profiling, silicon nanowire
    • Invited lecture (Conferences)
      27.Deutsches Nutzertreffen RTP und Heissprozesse, 05.05.2010, Erlangen, Deutschland

    Publ.-Id: 14894 - Permalink


    Biaxial optical anisotropy of self aligned silver nanoparticles and nanowires
    Ranjan, M.; Facsko, S.; Möller, W.;
    In the present study ion beam sputtering has been used for prestructuring of a silicon substrate followed deposition of metal by ebeam evaporation. First a low energy ion beam (Ar+, 500 eV) is incident on the substrate surface at an angle of 67∘ to the surface normal to produce well ordered (20-50 nm) ripple patterns. Then physically vaporized Ag atoms are deposited at grazing angle of 70∘ to the surface normal and normal to the ripples direction. Varying deposition parameters, i.e. ripple periodicity, substrate temperature and atomic flux, we were able to produce well ordered nanoparticles and nanowires. Self-aligned Ag nanoparticles and nanowires deposited on pre-patterned ripple surfaces exhibit strong optical anisotropy. Generalised ellipsometry measurements show that off diagonal Jones matrix elements (Ψ_ps, Δ_ps, Ψ_sp, Δ_sp) are non zero and vary with Eulers angle \phi. This indicates that such a medium is biaxial in nature. A biaxial layer model approach is used to calculate dielectric functions for such a system. Tauc-Lorentz oscillators are used along x and y direction independently and Drude model along z-direction for nanoparticles. This approach provides a very good fitting with the measured Jones matrix element Ψ_pp, Δ_pp, Ψ_ps, Δ_ps, Ψ_sp, Δ_sp. Different cases for ordered nanoparticles and wires will be presented.
    • Lecture (Conference)
      DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Germany

    Publ.-Id: 14892 - Permalink


    Self-Organisation of metal nanoparticles and nanowires grown on ripple templates
    Ranjan, M.; Oates, T. W. H.; Facsko, S.;
    Nobel metal nanoparticles exhibit distinct optical properties due to their localized surface plas-mon resonance. Potential applications of these structures can be found in solar cells, nonlinear optical devices, or sensors. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favored.
    Ion beam sputtered surfaces featuring self-organized ripple patterns have proven to be excellent templates for the alignment of these metal nanoparticles [1]. In the continuous sputtering proc-ess, induced by the bombardment with low-energy ions (100 – 2000 eV), periodic surface pat-terns appear in form of ripples or arrays of hexagonally ordered mounds, which show a very high degree of regularity [2]. The dimension of the pattern is related to the size of the typical collision cascade of a single ion event and lies in the range of ten to tens of nanometers. The periodicity and regularity of the pattern is established by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been pro-duced in this way on very different materials including semiconductors, isolators, and metals, demonstrating the universality of the mechanism [3].
    Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostructures align parallel to the ripples, eventually coalesce forming nanowires [4]. Due to the alignment the nanoparticles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the parallel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective directions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon reso-nance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
    This work is partly supported by DFG FOR 845.
    REFERENCES
    1. T.W.H. Oates, A. Keller, S. Facsko , A. Mücklich , Plasmonics 2, 47 (2007).
    2. A. Keller, S. Rossbach, S. Facsko, et al., Nanotechnology 19, 135303 (2008).
    3. A. Keller, S. Facsko, and A. Moller, Jour. Phys. Cond. Matt. 21, 495305 (2009).
    4. T.W. H.Oates, A.Keller, S.Noda, S.Facsko , Appl. Phys. Lett. 93, 063106 (2008
    • Poster
      Nanofair 2010, 06.07.-07.11.2010, Dresden, Germany

    Publ.-Id: 14891 - Permalink


    Self-Organisation of metal nanoparticles on ion beam produced ripple templates
    Ranjan, M.; Facsko, S.; Möller, W.;
    Ion beam sputtering has been used for pre-structuring of the substrate. Low energy ion beam (Ar+, 500 eV) incident on the substrate surface (Si in our case) at an angle of 67o to the surface normal to produce well ordered (20-50 nm) ripple patterns [1, 2]. The periodicity and regularity of the pattern is estab-lished by the effective filtering of a narrow band of spatial frequencies on the surface, which results from the interplay between a surface instability caused by the sputtering and surface diffusion processes. Regular ripple morphologies have been produced in this way on very different materials including semiconductors, iso-lators, and metals, demonstrating the universality of the mechanism [2].
    Depending on deposition angle, substrate temperature, beam flux, and deposition time, the metal nanostruc-tures align parallel to the ripples, eventually coalesce forming nanowires [3,4].A very high degree of align-ment not reported so far using the present technique has been achieved. Due to the alignment the nanoparti-cles exhibit strongly anisotropic optical properties. The difference in the interparticle distance along the paral-lel and perpendicular direction, respectively, leads to different plasmonic coupling in the respective direc-tions. Therefore a red shift of the plasmon-polariton resonance is observed for light polarized parallel to the ripple direction. In addition, the resonance shifts with the aspect ratio of the nanoparticles. Energy shifts of the plasmon resonance of 0.2 eV to 0.7 eV have been determined for aspect ratios in the range of 2 to 5.
    References:
    [1]. Keller.A, Rossbach.S, Facsko.S, Nanotechnology 19(2008) 135303
    [2]. Keller.A, Facsko.S,Möller.W, Jour. Phys. Cond. Matt. 21(2009) 495305
    [3]. Oates.T.W.H, Keller.A, Facsko.S, A. Mücklich, Plasmonics 2(2007) 47
    [4]. Oates.T.W.H, Keller.A, Noda.S, Facsko.S, Appl. Phys. Lett. 93(2008) 063106
    • Poster
      Workshop Ion Beam Physics, 29.-31.03.2010, Dresden, Germany

    Publ.-Id: 14890 - Permalink


    Self-assembled Ag nanoparticles on plasma sputtered hexagonally ordered GaSb nanodots
    Ranjan, M.; Fritzsche, M.; Zhou, J.; Facsko, S.; Möller, W.;
    Low energy ion-irradiation is capable to produce self-organized ripple and dot pattern on surfaces [1, 2].Ion bombardment normal to surface generate hexagonally correlated dot pattern on semiconductor surfaces [2]. Metal film grown on such pre-patterned substrate may lead to highly ordered self-assembled nanoparticles or nanowires [3]. Ordered metal nanoparticles show unique optical properties [4, 5]. In this work negatively biased (-1.2 kV) GaSb substrate was immersed in an inductively coupled RF plasma. Plasma sheath formation around the sample maintained the normal ion incidence. Ion fluence equivalent to 1x1018 cm-2 is sufficient to produce well pronounced hexagonally ordered dot structures. Later oblique incidence PVD growth of silver on such substrate, produce self-assemble nanoparticles fallowing the dots periodicity. Reflection measurement shows a plasmonic splitting and results in two pronounce resonance peak. Such a splitting is arises due to hexagonal arrangement of nanoparticles, not appeared for non-ordered particles. More details study of this work will be presented.

    References:
    [1] A. Keller, S. Facsko, W. Möller, New J. Phys. 10 (2008) 063004
    [2] S.Facsko, T.Dekorsy, C. Koerdt, H. Kurz, A. Vogt, H. Hartnagel, Science 285 (1999)1551
    [3] T.W. H.Oates, A.Keller, S.Noda, S.Facsko, Appl. Phy. Lett., 93(2008) 063106.
    [4] T.W. H.Oates, A.Keller, S.Facsko, A.Mücklich, Plasmonics 2(2007) 47.
    [5] A. Taleb, V. Russier, A. Courty, M. P. Pileni, Phys.Rev.B 59 (1999) 13350
    • Poster
      Plasma Surface Engineering (PSE), 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

    Publ.-Id: 14889 - Permalink


    Radioökologische Forschung als Basis zur Entwicklung neuer Materialien
    Raff, J.;
    wird nachgereicht
    • Lecture (others)
      Besuch ehemaliger IRC-Mitarbeiter, 19.11.2010, Dresden, Deutschland

    Publ.-Id: 14888 - Permalink


    Vortex coupling in magnetic multilayer elements
    Wintz, S.; Puzic, A.; Strache, T.; Bunce, C.; Körner, M.; Schönherr, T.; Neubert, A.; McCord, J.; Moench, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; Erbe, A.; Fassbender, J.ORC
    Spin vortices have attracted much attention due to their chiral nature and the variety of dynamic phenomena associated with them. In this contribution we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic spacer. For such systems the relative configurations of the in-plane flux senses (circulations) as well as the core orientations (polarities) of layered vortices are identified by means of scanning transmission x-ray microscopy (STXM). The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC). Remarkably, a modification of the IEC, which can be induced by noble gas ion irradiation, allows to specifically set the circulation configuration of a layered vortex pair to be either an- tiferromagnetic or ferromagnetic. In addition, time-resolved measurements of the response of interlayer coupled vortices to an excitation by sinusoidal magnetic fields will be shown.
    Keywords: magnetic vortex, coupling, STXM, interlayer exchange coupling
    • Poster
      DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

    Publ.-Id: 14887 - Permalink


    Iodine in alluvial platinum–palladium nuggets
    Cabral, A. R.; Radtke, M.; Munnik, F.; Lehmann, B.; Reinholz, U.; Riesemeier, H.; Tupinambá, M.; Kwitko-Ribeiro, R.;
    Synchrotron radiation-induced X-ray fluorescence (SR-XRF) spectrometry was applied to determine iodine concentrations in alluvial Pt–Pd aggregates with delicate morphological features from Córrego Bom Sucesso, Minas Gerais, Brazil. The millimetre-sized botryoidal and rod-shaped grains of alluvial Pt–Pd–Hg intermetallic compounds have surprisingly high concentrations of iodine, in the range from 10 to ~120 µg/g. Because iodine is a strongly biophile element, known to be enriched in peatlands and plant remains in soils by microbial activity, its concentration in the Pt–Pd nuggets suggests biogenic precious-metal fixation in the aqueous alluvial milieu.
    Keywords: Iodine, Pt–Pd nuggets, Córrego Bom Sucesso, Minas Gerais, Brazil

    Publ.-Id: 14886 - Permalink


    Magnetically induced electric polarization in an organometallic magnet
    Zapf, V. S.; Kenzelmann, M.; Wolff-Fabris, F.; Balakirev, F.; Chen, Y.;
    The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S = 1/2 Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

    Publ.-Id: 14885 - Permalink


    Breaking Translational Invariance by Population Imbalance: The Fulde-Ferrell-Larkin-Ovchinnikov States
    Zwicknagl, G.; Wosnitza, J.;
    An overview is given of our present understanding of superconductivity with spontaneously broken translation symmetry in polarized Fermi systems. The existence of “crystalline” superconducting phases is considered in a wide range of systems, prominent examples being conduction electrons in metals, ultra-cold atoms in a trap, nuclear matter and dense quark systems. The underlying physics is delineated and theoretical approaches to the inhomogeneous phases and their properties are discussed. From the experimental side, it is argued that superconductivity with imbalance-induced order parameters is realized in layered organic compounds and potentially in heavy-fermion systems.

    Publ.-Id: 14884 - Permalink


    On-chip superconductivity via gallium overdoping of silicon
    Skrotzki, R.; Fiedler, J.; Herrmannsdörfer, T.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.;
    We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology

    Publ.-Id: 14883 - Permalink


    Investigation of conducting 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. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 300 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 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 lithography, graphitization, nano structures
    • Poster
      75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Deutschland

    Publ.-Id: 14882 - Permalink


    Freestanding Si nanowires fabricated by Ga+ FIB implantation and subsequent anisotropic etching
    Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.;
    Localized Ga+ ion implantation in silicon-on-insulator substrates (top layer 2 µm) by focused ion beam and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires with reproducible widths between 20 and 200 nm.
    The dependence of the resulting nanowire width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the nanowire width as a function of the implanted fluence. Moreover, the temperature dependence of the nanowires’ resistivity and the activation energy for electrical current flow were investigated before and after direct current annealing in air and in vacuum ambient. Annealed nanowires showed a decrease of their resistivity up to two orders of magnitude, indicating a partial recrystallization of the nanowires through self-heating and a change in the conduction mechanism. The assumption of recrystallization is supported by scanning electron microscopy and Raman spectroscopy.
    The comprehension of the pinpointed fabrication of such Si nanostructures establishes a broad range of application in the field of nano-electro-mechanical systems.
    Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy
    • Poster
      DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

    Publ.-Id: 14881 - Permalink


    Complex formation of trivalent americium with salicylic acid at very low concentrations
    Müller, M.; Acker, M.; Taut, S.; Bernhard, G.;
    For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 9 10-9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log b110 = 2.56 ± 0.08 and log b120 = 3.93 ± 0.19.
    Keywords: Americium, Long path flow cell, UV–vis, Detection limit, Complexation, Salicylic acid

    Publ.-Id: 14880 - Permalink


    Development of a high resolution and high dispersion Thomson Parabola
    Jung, D.; Hoerlein, R.; Kiefer, D.; Letzring, S.; Gautier, D. C.; Schramm, U.; Huebsch, C.; Oehm, R.; Albright, B. J.; Fernandez, J. C.; Habs, D.; Hegelich, B. M.;
    Here we report on the development of a novel high resolution and high dispersion Thomson Parabola for simultaneously resolving protons and low-Z ions of more than 100 MeV/nucleon necessary to explore novel laser-ion-acceleration schemes. High electric and magnetic ¯elds enable energy resolutions of ¢E=E < 5% at 100 MeV/nucleon and impede premature merging of di®erent ion species at low energies on the detector plane. First results from laser driven ion acceleration experiments performed at the Trident Laser facility demonstrate high resolution and superior species and charge state separation of this novel Thomson parabola for ion energies of more than 30 MeV/nucleon.
    Keywords: laser ion acceleration, ino spectrometer

    Publ.-Id: 14879 - Permalink


    Sicherheitstechnische Fragestellungen im Reaktorbetrieb am Beispiel eines DWR
    Schäfer, F.; Tusheva, P.; Weiss, F.-P.;
    Der Vortrag erläutert grundlegende Prinzipien der nuklearen Sicherheit, gibt einen Überblick zu Betriebstransienten und hypothetischen Störfällen in einem DWR und diskutiert die verschiedenen Methoden, welche für Untersuchungen zur Reaktorsicherheit angewendet werden.
    Keywords: Nuclear Reactor, Reactor Safety
    • Invited lecture (Conferences)
      3. VDI-KTG Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

    Publ.-Id: 14878 - Permalink


    Spatial manipulation of magnetic damping in ferromagnetic-antiferromagnetic films by ion irradiation
    McCord, J.; Strache, T.; Mönch, I.; Mattheis, R.; Fassbender, J.ORC
    The effective magnetic damping parameter in ferromagnetic-antiferromagnetic-ferromagnetic NiFe/IrMn/NiFe try-layer structures is set over a wide range. Ultra-thin antiferromagnetic systems in combination with low fluence Ni-ion irradiation are used to control the magnetic damping parameter by two independent mechanisms. Changing the ferromagnetic-antiferromagnetic interface the initially strongly increased damping parameter is reduced. Applying the method locally, results in a magnetic layer with spatially distributed regions of different damping. The overall relaxation time of the mixed property film is found to be a direct superposition of the individual relaxation time contributions and thus determined by the ratio of phases with individual damping parameter.

    Publ.-Id: 14877 - Permalink


    Realization of radiobiological in vitro cell experiments at conventional X-ray tubes and unconventional radiation sources
    Beyreuther, E.;
    More than hundred years after the discovery of X-rays different kinds of ionizing radiation are ubiquitous in medicine, applied to clinical diagnostics and cancer treatment as well. Irrespective of their nature, the widespread application of radiation implies its precise dosimetric characterization and detailed knowledge of the radiobiological effects induced in cancerous and normal tissue. Starting with in vitro cell irradiation experiments, which define basic parameters for the subsequent tissue and animal studies, the whole multi-stage process is completed by clinical trials that translate the results of fundamental research into clinical application. In this context, the present dissertation focuses on the establishment of radiobiological in vitro cell experiments at unconventional, but clinical relevant radiation qualities.
    In the first part of the present work the energy dependent biological effectiveness of photons was studied examining low-energy X-rays (≤ 50 keV), as used for mammography, and high-energy photons (≥ 20 MeV) as proposed for future radiotherapy. Cell irradiation experiments have been performed at conventional X-ray tubes providing low-energy photons and 200 kV reference radiation as well. In parallel, unconventional quasi-monochromatic channeling X-rays and high-energy bremsstrahlung available at the radiation source ELBE of the Forschungszentrum Dresden-Rossendorf were considered for radiobiological experimentation. For their precise dosimetric characterization dosimeters based on the thermally stimulated emission of exoelectrons and on radiochromic films were evaluated, whereas just the latter was found to be suitable for the determination of absolute doses and spatial dose distributions at cell position. Standard ionization chambers were deployed for the online control of cell irradiation experiments. Radiobiological effects were analyzed in human mammary epithelial cells on different subcellular levels revealing an increasing amount of damage for decreasing photon energy. For this reason, the assumed photon energy dependence was reconfirmed for a cell line other than human lymphocytes, an important finding that was discussed on the 2007 Retreat of the German Commission on Radiological Protection.
    After successful finalization of the photon experiments the focus of the present dissertation was directed to the realization of in vitro cell irradiation experiments with laser-accelerated electrons. This research was carried out in the frame of the project onCOOPtics that aims on the development of laser-based particle accelerators, which promise accelerators of potentially compact size and more cost-effectiveness suitable for a widespread medical application, especially for high precision hadron therapy. The unique properties, i.e., the ultrashort bunch length and resultant ultrahigh pulse dose rate, of these unconventional particle accelerators demand for extensive investigations with respect to potential effects on the dosimetric and radiobiological characterization. Based on the experiences gained at ELBE first experiments on the radiobiological characterization of laser-accelerated electrons have been performed at the Jena Titanium:Sapphire laser system. After beam optimization, a sophisticated dosimetry system was established that allow for the online control of the beam parameters and for the controlled delivery of dose to the cell sample. Finally, worldwide first systematic in vitro cell irradiation experiments were carried out resulting in a reduced biological effectiveness for laser-accelerated electrons relative to the 200 kV X-ray reference, irrespectively on the biological effect and cell lines examined. These successful results are the basis for future in vivo studies and experiments with laser-accelerated protons.
    Keywords: X-ray tubes, radiation sources
    • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-540 2010

    Downloads:

    Publ.-Id: 14876 - Permalink


    Time resolved spectroscopy on quantum dots and graphene at the FELBE free-electron laser
    Winnerl, S.; Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Seidel, W.; Michel, P.; Zibik, E. A.; Carpenter, B. A.; Porter, N. E.; Skolnick, M. S.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
    The free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf enables experiments with spectral, temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz pulses in a wavelength range from 5 µm to 280 µm. Operation in a continous pulsing regime and synchronization to various tabletop laser sources allows for two-color pump-probe experiments. Here we review the potential of the laser and focus on two highlight pump-probe experiments. In the first experiments, the relaxation dynamics in self assembled InGaAs quantum dots at energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 2 ps at 30 meV (7 THz). The results are in very good agreement with our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons [1]. In the second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 – 250 meV. For excitations below the phonon energy of the G-mode, long relaxation times (20 – 40 ps) are observed. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).

    [1] E. A. Zibik et al. Nature Materials 8, 803 - 807 (2009).
    Keywords: Quantum dots, graphene, relaxation dynamics, polarons, terahertz, infrared, pump-probe spectroscopy
    • Invited lecture (Conferences)
      SPIE Photonics West, 22.-27.01.2011, San Francisco, USA
    • Proceedings of SPIE 7937(2011), 793708
      DOI: 10.1117/12.873702

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    Publ.-Id: 14875 - Permalink


    Relaxation dynamics in epitaxial graphene probed at low excitation energies
    Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
    The relaxation dynamics of graphene has been investigated in various degenerate as well as two-color pump-probe studies at excitation energies E = 1.6 eV [1-5]. We report on degenerate pump-probe spectroscopy at much lower energies (E = 20 – 250 meV; radiation source: free-electron laser) on graphene multilayers grown by thermal decomposition. Relaxation times between 20 and 40 ps are found for photon energies E < 70 meV, where only acoustic phonons can contribute to the relaxation dynamics. At 245 meV a much faster relaxation with two time constants (tau_1 ≈ 1.2 ps, tau_2 = 4 – 8 ps) is observed and attributed to contributions of optical phonons. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV (Fig. 1). The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).
    [1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
    [2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
    [3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
    [4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
    [5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).
    Keywords: Relaxation dynamics, graphene, infrared, terahertz
    • Poster
      2nd International Symposium on the Science and Technology of Epitaxial Graphene, 14.-17.09.2010, Amelia Island, USA

    Publ.-Id: 14874 - Permalink


    Compositional depth profiling of TaCN thin films
    Adelmann, C.; Conard, T.; Franquet, A.; Brijs, B.; Munnik, F.; Burgess, S.; Witters, T.; Meersschaut, J.; Kittl, J. A.; Vandervorst, W.;
    The composition profiling of thin TaCN films was studied. For the composition profile determination using x-ray photoemission spectrometry (XPS) in combination with Ar sputtering, preferential sputtering effects of N with respect to Ta and C were found to lead to inaccurate elemental concentrations. Sputter yield calculations for the given experimental conditions allowed for the correction of a part of the error, leading to fair accuracy by reference-free measurements. Further improvement of the accuracy was demonstrated by the calibration of the XPS compositions against elastic recoil detection analysis (ERDA) results. For Auger electron spectrometry (AES) in combination with Ar sputtering, accurate results required the calibration against ERDA. Both XPS and AES allowed for a reliable and accurate determination of the compositional profiles of TaCN-based thin films after calibration. Time-of-flight secondary-ion mass spectrometry was also used to assess the composition of the TaCN films. However, the analysis was hampered by large matrix effects due to small unintentional oxygen contents in the films. Energy-dispersive x-ray spectrometry is also discussed, and it is shown that an accurate reference-free measurement of the average film concentration can be achieved.
    Keywords: TaC; TaN; TaCN; XPS; AES; ToF-SIMS; ERDA; EDX; composition profile

    Publ.-Id: 14873 - Permalink


    Speciation of Uranium in Seepage and Pore Waters of Heavy Metal-Contaminated Soil
    Baumann, N.; Arnold, T.; Lonschinski, M.;
    The uranium speciation in natural occurring seepage water samples, and in soil water samples, all samples from test site “Gessenwiese”, were analyzed by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Test site Gessenwiese was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of a recultivated former uranium mining heap close to Ronneburg (Eastern Thuringia).
    Those investigations revealed that the uranium speciation in that seepage water is dominated by the uranium (VI) sulfate species UO2SO4(aq). The analyses were performed to compare presented results in a later stage with the uranium speciation in plants, which grow on the grassland test site Gessenwiese. It was showed that TRFLS is a useful tool for clearing up the speciation of uranium in water, which is affiliated by plants.
    • Book chapter
      Kothe, Erika; Varma, Ajit: Bio-Geo Interactions in Metal-Contaminated Soils, Berlin: Springer, 2012, 978-3-642-23326-5, 131-142

    Publ.-Id: 14872 - Permalink


    Reversals and the turbulent alpha-effect in kinematic simulations of natural and experimental dynamos
    Giesecke, A.; Stefani, F.; Gerbeth, G.;
    From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it is evident that reversing dynamos are a quite common phenomenon. An easy access to the examination of reversing dynamos is provided by simplifying mean field simulations where the induction effects of helical small scale turbulence are parametrized by the so called α-effect.

    In a geodynamo-like α2-model reversing solutions are obtained only for a highly restricted class of radial α-profiles which are characterized by a proximity of oscillating and non-oscillating state. The required properties of the α-effect, indeed, have been found from local simulations of rotating magnetoconvection in a Cartesian box (Giesecke et al. 2005, PEPI 152, 90-102). Essential properties of the field reversals can be assigned to the behavior of so called exceptional points in the spectrum of the dynamo-operator where two different non-oscillatory field eigenmodes merge and continue as one oscillatory eigenmode (Stefani et al. 2005, PRL, 94, 184506). The connection between oscillating solutions and irregular occurring reversals arises from fluctuations of the α-effect, which causes a sporadic switching from steady to the oscillatory regime and vice versa. In this picture a reversal is an inevitable consequence of the behavior of the instantanous growthrate in conjuction with fluctuations of the driving source.

    Recent results of the French von-Kármán-Sodium (VKS) dynamo offer a possibility for detailed investigations of reversing magnetic fields. In the VKS experiment a turbulent flow of liquid sodium is driven by two counter rotating soft iron impellers located close to the endplates of a cylindrical vessel. The geometric structure of the observed magnetic field is dominated by an axisymmetric dipole that exhibits regular and irregular reversals if the impellers rotate with different frequencies. Recent simulations show that the induction process is essentially determined by the material properties of the flow driving impellers (high permeability) because of internal boundary conditions for the magnetic field on the interface between fluid and impeller (Giesecke et al. 2010, PRL 104, 044503). However, only the combined interaction of soft iron disks and a comparatively small α-effect allows to explain the dominating axisymmetric field. Contributions of dipole and quadrupole type fields deduced from the equatorial symmetry show nearly the same growth rate supporting the reversal model presented by Pétrélis & Fauve (2009, PRL 102, 144503) that is based on the coupling between these two modes.
    Keywords: Dynamo Geodynamo alpha-effect Simulations
    • Poster
      AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
    • Contribution to proceedings
      AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
      Reversals and the turbulent α-effect in simulations of natural and experimental dynamos

    Publ.-Id: 14871 - Permalink


    High permeability material and dynamo action
    Giesecke, A.; Stefani, F.; Gerbeth, G.;
    A prescribed flow of liquid sodium provides an energy source for self-generation of a magnetic field. The influences of non-uniform material properties on the dynamo process are examined by means of kinematic simulations of the electromagnetic induction equation.

    High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcement of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.
    Keywords: Dynamo Permeability
    • Poster
      MHDDAYS 2010, 22.-23.11.2010, Dresden, Germany

    Publ.-Id: 14870 - Permalink


    Multiple active mirror concept for high energy short-pulse lasers
    Loeser, M.; Kroll, F.; Röser, F.; Siebold, M.; Schramm, U.; Sauerbrey, R.;
    Ytterbium-doped gain media are preferably utilized in high-energy, diode-pumped lasers due to their comparably long fluorescence lifetime, absence of excited state absorption, and quenching effects. Despite exhibiting a low quantum defect, thermal lensing and stress birefringence within the amplifying medium limits the maximum repetition rate of large aperture lasers. Furthermore, the quasi-three-level scheme of Yb3+ leads to re-absorption losses at room temperature especially when operating at low fluences. Here, we present a novel approach combining longitudinal cooling of a disk-laser design with the energy storage capability of a rod amplifier. Therefore, a multiple active mirror amplifier is presented for improved optical-to-optical conversion efficiency and reduced thermally induced aberrations at high repetition rates. Multi-passing both pump and extraction beams through the gain medium, which is well known from thin-disk lasers, also reduces the re-absorption losses. However, energy scaling of a single thin-disk design is limited by parasitic lasing due to a high aspect ratio between longitudinal and transverse gain. We also introduce simulation results on a multiple active mirror short-pulse amplifier employing various Ytterbium-doped gain media such as Yb:YAG, Yb:CaF2, Yb:glass, and Yb:silica. Furthermore, time resolved measurements of thermally induced aberrations at pulse-pumped operation are illustrated.
    Keywords: Diode-pumped lasers, Ytterbium-doped solid state lasers
    • Lecture (Conference)
      DPG Frühjahrstagung der Sektion AMOP 2010, 08.-12.03.2010, Hannover, Deutschland

    Publ.-Id: 14869 - Permalink


    Ion-beam induced hydrogen redistribution in a-Si:H-based triple layer structures
    Pantchev, B.; Danesh, P.; Schmidt, B.; Grambole, D.; Bischoff, L.;
    Ion-beam induced hydrogen migration has been studied in triple layer structures, a-Si/a-Si:H/a-Si and SiO2/a-Si:H/SiO2. Nuclear reaction analysis has been used for simultaneous irradiation with MeV ions and measurement of hydrogen distribution in the structures. It has been established that there is no hydrogen loss from SiO2/a-Si:H/SiO2 structures, but an asymmetric redistribution due to hydrogen penetration into the bottom SiO2 layer. Hydrogen loss has been observed from the a-Si/a-Si:H/a-Si structures. The inspection of the surface of these samples by means of atomic force microscope has shown that it proceeds by bubble formation and blistering at the inner interface. The observed ion-beam induced selective penetration of hydrogen into the underlying material can be used as a tool for preparation of microcavity and microchannel arrays.
    Keywords: a-Si:H, ion implantation, hydrogen migration
    • Lecture (Conference)
      16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
    • Open Access LogoJournal of Physics: Conference Series 253(2010), 012055
      DOI: 10.1088/1742-6596/253/1/012055

    Publ.-Id: 14868 - Permalink


    Nanoindentation-induced pile-up in hydrogenated amorphous silicon
    Pantchev, B.; Danesh, P.; Wiezorek, J.; Schmidt, B.;
    Nanoindentation-induced material extrusion around the nanoindent (pile-up) leads to an overestimation of elastic modulus, E, and nanohardness, H, when the test results are evaluated using the Oliver and Pharr method. Factors affecting the pile-up during testing are residual stresses in film and ratio of film and substrate mechanical properties. Nanoindentation of hydrogenated amorphous silicon (a-Si:H) films has been carried out with the aim to study the effect of residual compressive stress on the pile-up in this material. To distinguish the contribution of compressive stress to the appearance of pile-up ion implantation has been used as a tool, which reduces the compressive stress in a-Si:H. Scanning probe microscope has been used for the imaging of the indent and evaluation of the pile-up. The values of E and H have been obtained from the experimental load-displacement curves using depth profiling with Berkovich tip, which has created negligible pile-up. A sharper cube corner tip has been used to study the pile-up. It has been established that pile-up is determined by the material plasticity, when the compressive stress is below 200 MPa. The contribution of mechanical stress to the pile-up is essential for the stress as high, as about 500 MPa.
    Keywords: Nanoindentation, silicon hardness, ion implantation
    • Lecture (Conference)
      16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
    • Open Access LogoJournal of Physics: Conference Series 253(2010), 012054
      DOI: 10.1088/1742-6596/253/1/012054

    Publ.-Id: 14867 - Permalink


    Effect of hydrogen on hardness of amorphous silicon
    Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.; Grambole, D.;
    A comparative study of hardness of thin films of hydrogenated amorphous silicon (a-Si:H) and hydrogen-free amorphous silicon (a-Si) was carried out to reveal the role of hydrogen in the plastic properties of amorphous silicon. In addition, the effect of hydrogen on hardness was established by changing hydrogen concentration in the material using post-deposition processing of the samples. The hydrogen concentration in a-Si:H was decreased by thermal annealing. In a-Si hydrogen was introduced by plasma hydrogenation. The values of hardness of the as-prepared a-Si and a-Si:H films were determined by nanoindentation using depth profiling. Low-depth indentation was applied to evaluate the effect of post-hydrogenation. The results obtained show that the presence of hydrogen in the amorphous silicon network leads to the increase in hardness. The conducted experiments demonstrate that plasma hydrogenation can be used as an effective tool to increase the hardness of amorphous silicon. Hardness of a-Si:H of about 12.3–12.7 GPa is as high as of crystalline silicon, suggesting a-Si:H can be a substitute for crystalline silicon in some MEMS.
    Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

    Publ.-Id: 14866 - Permalink


    Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon
    Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.;
    The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0x1013–5.0x1016 cm-2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.
    Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

    Publ.-Id: 14865 - Permalink


    Magnetic hybrid films - magnetic property patterning by ion irradiation
    McCord, J.; Hamann, C.; Strache, T.; Martin, N.; Mönch, I.; Mattheis, R.; Kaltofen, R.; Quandt, E.; Fassbender, J.ORC
    Ion irradiation and implantation allows for a focussed materials modification in the range of a few nanometer. Effects of periodic patterning of the physical properties circumventing topographic patterning in the conventional sense are exploited. Magnetic materials with mixed hybrid magnetic properties are created. An overview over ongoing activities at the FZD will be given.
    • Invited lecture (Conferences)
      „Struktur und Eigenschaften kondensierter Materie“ Seminar der TU Chemnitz, 23.11.2010, TU Chemnitz, Germany

    Publ.-Id: 14864 - Permalink


    Electrical characterization of oxygen vacancies in oxides by means of space charge spectroscopy
    Schmidt, H.;
    The development of new materials for cool devices, e.g. memristive and spintronics devices, needs non-destructive techniques to characterize defects in new materials. The knowledge on defects is strongly desired and will help to prevent device degredation. The non-destructive characterization of certain defects is possible by means of positron annihilation spectroscopy (PAS) if open volume-defects are large and electrically neutral/negatively charged, if segregations are attractive for positrons and change the annihilation rate, and/or if the electron density and with that annihilation rate changes during phase transitions. The complementary, destructive characterization of defects in semiconductors prepared as diodes by means of space charge spectroscopy is possible if the defects are charged/decharged in response to electrical pulses applied to the diode.
    Keywords: defects, space charge spectroscopy, positron annihilation spectroscopy
    • Lecture (Conference)
      Workshop on Positron Annihilation Spectroscopy, 19.10.2010, FZD, Germany

    Publ.-Id: 14862 - Permalink


    Electrical characterization of semiconductors on the mm-nm length scale
    Schmidt, H.;
    The electrical conductivity of semiconductors is controlled by the activated dopant level and the intrinsic carrier concentration. Semiconductor devices are prepared with either holes or electrons as the majority charge carriers. Hall effect measurements yield carrier concentration and mobility and estimates of scattering mechanisms. The use of Hall effect measurements and of capacitance-voltage and deep level transient spectroscopy measurements for profiling depth dependent free carrier concentrations and for identifying deep traps within the forbidden gap of semiconductors, respectively, yields a potent suite of characterization techniques on the mm-mum length scale. Insight into the electrical properties of doped semiconductor nanostructures may be obtained from scanning spreading resistance microscopy and Kelvin probe force microscopy measurement. Dielectric semiconductor conductivities on the nm scale may be obtained from scanning probe microscopy measuremens. Examples of current investigations by means of the presented electrical characterization techniques are given.
    Keywords: space charge spectroscopy, electrical nanometrology
    • Invited lecture (Conferences)
      IZFP-Kolloquium, 25.10.2010, Saarbrücken, Germany

    Publ.-Id: 14861 - Permalink


    Temperature Measurement in Rapid Thermal Annealing
    Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.;
    Microelectronics Industry and consequently semiconductor research have developed into pillars of modern technology. Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds.
    One major application for thermal annealers is to anneal damage caused by ion implantation. For this purpose temperatures above 600 °C are preferred, although a high diffusion rate of the dopants ought to be avoided. Therefore, short heating periods with steep ramp rates are desired.
    This is where Flash Lamp Annealing comes into play. It allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultra-short time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk.
    The applications are numerous, especially in thermal treatment of semiconductor surfaces where doping concentrations far beyond the solubility limit are desired, e.g. for ultra shallow implantation profiles. Similarily, highly doped layers are required when studying small scale effects like superconductivity brought about by the implanted dopant.
    Due to the high energy density on the sample even high melting points can be achieved for defect annealing during recrystallization of the melt.
    The response of various materials to subsecond thermal treatment, however, is not well understood for most cases, especially the temperature dependence of many material parameters is unknown to a large extent. Clearly, for deeper investigation into the subject a real-time temperature measurement with a high temperature resolution (ΔT << 5K), is crucial and is regarded as a key component in order to achieve rapid and reliable processing.
    For this purpose traditional means of temperature measurement, e.g. thermocouples, must be excluded. Not only do they lead to wafer contamination but their long response time contradicts the ultra-fast annealing time of the Flash Lamp Device.
    In the framework of the presentation previous non-contact approaches to rapid temperature measurement will be discussed with special regard to temperature resolution and industrial mass production.
    Keywords: Temperature Measurement, Rapid Thermal Annealing, Flash Lamp Annealing
    • Lecture (Conference)
      9th International Workshop on Subsecond Thermophysics, 22.-24.09.2010, Graz, Österreich

    Publ.-Id: 14860 - Permalink


    Rückbau des Zyklotrons U-120 am Forschungszentrum Dresden-Rossendorf
    Naumann, B.; Friedrich, M.; Matz, W.;
    Der Beitrag gibt einen Überblick über den Stand des Rückbaus des Zyklotrons U-120, das von 1958 bis 1999 eines der größten experimentellen Anlagen im Forschungszentrum Rossendorf war. Der Rückbau der Beschleunigeranlage begann im Jahr 2001. Bis zum November 2010 sind alle Anlagenteile und Experimentaufbauten radiologisch bewertet und größtenteils entsorgt worden. Der Beitrag beschreibt u. a. die Verfahren zur Bewertung der Aktivierung großer Bauteile des Zyklotrons.
    • Invited lecture (Conferences)
      4. Symposium Stilllegung und Rückbau kerntechnischer Anlagen, 02.-03.11.2010, Hannover, Deutschland

    Publ.-Id: 14859 - Permalink


    A trigonal nodal solution approach to the multi-group simplified P3 equations in the reactor code DYN3D
    Duerigen, S.; Grundmann, U.; Mittag, S.; Merk, B.; Fridman, E.; Kliem, S.;
    The neutronics model of the nodal reactor dynamics codeDYN3D developed for 3-D analyses of steady states and transients in light-water reactors has been extended by a simplified P3 (SP3) neutron transport option to overcome the limitations of the diffusion approach. To provide a method being applicable to reactors with hexagonal fuel assemblies and furthermore allowing flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, the derivation of the trigonal SP_3 method is presented and preliminary assessment of the methodology is performed.
    Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal
    • Contribution to proceedings
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, 978-85-63688-00-2
    • Lecture (Conference)
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

    Publ.-Id: 14858 - Permalink


    Preparation of laser-accelerated proton beams for radiobiological applications
    Metzkes, J.; Cowan, T. E.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Richter, T.; Zeil, K.; Schramm, U.;
    This paper presents the concept of transport and filtering of laser-accelerated proton pulses used for the first cell irradiation experiments performed with the Dresden 150 TW laser DRACO. Based on a simple non-focusing magnetic dipole equipped with two apertures the concept makes use of an energy dependent angular asymmetry of the proton spectra. For micron thin target foils protons of interest with energies above 7 MeV are observed to be significantly oset from target normal where low energy emission is dominantly centered. As the eect can be controlled via the target rotation with respect to the incoming light, it can be used to optimize the transport efficiency for high energy protons while simultaneously suppressing background radiation.
    Keywords: laser acceleration of ions, target normal sheath acceleration, magnetic energy filter, radiobiological studies

    Publ.-Id: 14857 - Permalink


    Bispidine-derivatives for radiopharmaceutical applications
    Fähnemann, S.;
    kein Abstract verfügbar
    • Lecture (others)
      Seminarvortrag School of Chemistry, Monash University, 07.10.2010, Melbourne, Australia

    Publ.-Id: 14856 - Permalink


    Correlation between the microstructure and the degradation of rare earth implanted Si-based light emitters
    Rebohle, L.; Nazarov, A.; Tyagulskii, S.; Tyagulskii, I.; Lehmann, J.; Skorupa, W.;
    The degradation of rare earth (RE)-implanted light emitters based on a Si-SiO2-SiON-ITO structure was investigated using the example of Tb and Eu as a function of their microstructural, electrical and electroluminescence (EL) properties. As shown by transmission electron microscopy and Rutherford backscattering spectroscopy the different implantation and annealing conditions lead to two different types of microstructures: devices with small RE oxide clusters and devices with large RE oxide clusters and strong RE agglomerations at the SiO2 interfaces. The electrical and EL properties of the devices were characterized by constant current injection measurements, in which the EL and the applied voltage is monitored with time, and IV, CV and EL spectrum measurements. As a result of these investigations it is shown that devices with small RE oxide clusters normally exhibit a high EL intensity and degrade in a two-step process characterized by a negative and a positive net charge trapping. In contrast to this, devices with large RE oxide clusters have a lower EL intensity, but the first step of degradation is suppressed resulting in lower quenching cross sections and thus a longer operation life time. The degradation is explained by a defect shell model in which the RE oxide clusters are surrounded by defect regions of different extensions leading to the different behavior of devices with small and large RE oxide clusters.
    Keywords: Electroluminescence, rare earth, MOS capacity, charge trapping, ion implantation
    • Lecture (Conference)
      3rd Int. Meeting on Recent Developments in the study of Radiation Effects in Matter, 24.-28.10.2010, Gramado, Brazil

    Publ.-Id: 14855 - Permalink


    Comparison of the stability of Y-90-, Lu-177- and Ga-68- labeled human serum albumin microspheres (DOTA-HSAM)
    Wunderlich, G.; Schiller, E.; Bergmann, R.; Pietzsch, H.-J.;
    Introduction:
    Microparticles derived from denatured human serum albumin (DOTA-derivatized human serum albumin microspheres, or DOTA-HSAM) are attractive carriers of radionuclides for both therapeutic and diagnostic purposes. In this article, we describe a labeling procedure for diagnostic (Ga-68) and therapeutic (Y-90, Lu-177) radionuclides and report on the results of stability studies of these products.

    Methods:
    DOTA-HSAM was labeled in 0.5 M ammonium acetate buffer, pH 5.0, containing 0.02 mg/ml detergent. After adding the radionuclide, the mixture was shaken for 15 min at 90°C. Labeling yields and in vitro stability were determined by thin-layer
    chromatography. For determination of the in vivo stability of Ga-68 and Y-90 DOTA-HSAM, the particles were injected intravenously in Wistar rats.

    Results:
    Labeling yields up to 95% in the case of Ga-68 and Lu-177 were achieved. Ga-68-labeled DOTA-HSAM showed high in vitro and in vivo stability. The amount of particle-bound radioactivity of Lu-177 DOTA-HSAM declines slowly in a linear manner to approximately 72% after 13 days. For Y-90, the labeling yield decreased with increasing radioactivity level. We presume radiolysis as the reason for these findings.

    Conclusion:
    The labeling of DOTA-HSAM with different radionuclides is easy to perform. The radiation-induced cleavage of the labeled chelator together with the rather short half-life of radioactivity fixation in vivo (3.7 days) is, in our opinion, opposed to therapeutic applications of DOTA-HSAM. On the other hand, the high stability of Ga-68 DOTA-HSAM makes them an attractive candidate for the measurement of regional perfusion by PET.
    Keywords: Human serum albumin microspheres; Stability; Radiolabeled particles; Radiolysis; Thiourea bond

    Publ.-Id: 14854 - Permalink


    Production of Lambda and Sigma(0) hyperons in proton-proton collisions
    Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filges, D.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Georgi, J.; Gillitzer, A.; Gottwald, J.; Hesselbarth, D.; Jaeger, H.; Jakob, B.; Jaekel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Marwinski, S.; Mauro, S.; Meyer, W.; Michel, P.; Moeller, K.; Morsch, H. P.; Moertel, H.; Naumann, L.; Paul, N.; Pinna, L.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schoenmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Stinzig, F.; Steinke, M.; Sun, G. Y.; Teufel, A.; Ullrich, W.; Wagner, G. J.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wirth, S.; Wuestner, P.; Zupranski, P.;
    This paper reports results on simultaneous measurements of the reaction channels pp → pK+Λ and pp → pK+Σ0 at excess energies of 204, 239, and 284MeV (Λ) and 127, 162, and 207MeV (Σ0). Total and differential cross-sections are given for both reactions. It is concluded from the measured total cross-sections that the high-energy limit of the cross-section ratio is almost reached at an excess energy of only about 200MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the Λ production mechanism is concluded while resonant Σ0 production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of Λ but an important role for Σ0 production. Thus the peculiar energy dependence of the Λ/Σ0 cross-section ratio appears in a new light as its explanation requires more than mere differences between the pΛ and the pΣ0 final-state interaction. The data provide a benchmark for theoretical models already available or yet to come.

    Publ.-Id: 14853 - Permalink


    Characterization of microstructural defects in melt grown ZnO single crystals
    Anwand, W.; Brauer, G.; Grynszpan, R. I.; Cowan, T. E.; Schulz, D.; Klimm, D.; Čížek, J.; Kuriplach, J.; Procházka, I.; Ling, C. C.; Djurišić, A. B.; Klemm, V.; Schreiber, G.; Rafaja, D.;
    Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis.
    A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 +/- 0.03) at.-% of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the "blue light domain" of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials as well as nitrogen-related defects is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for the observed positron lifetime.
    Keywords: zinc oxide, microstructure defects, positron annihilation, optical transmission, X-ray diffraction, transmission electron microscopy

    Publ.-Id: 14852 - Permalink


    Bakterielle Wechselwirkungen ausgewählter Actinide vor dem Hintergrund der Endlagerung von radioaktivem Abfall
    Moll, H.;
    Bakterien, ubiquitär vorkommende Mikroorganismen, können signifikant die Speziation und damit das Verhalten von Schwermetallen in der Umwelt beeinflussen. Detaillierte Kenntnisse der Wechselwirkungsprozesse von Bakterien mit Actiniden sind z.B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen erforderlich. Das Interesse an mikrobiellen Prozessen der Actinide ist in den letzten Jahren stetig gestiegen. Dennoch sind die Kenntnisse zur mikrobiellen Diversität an möglichen Endlagerstandorten von nuklearem Abfall relativ begrenzt.
    Im Vortrag werden am Beispiel ausgewählter Actinide detaillierte Untersuchungen zur Aufklärung von deren Speziation mit speziellen Bakterien vorgestellt. Ein kurzer Überblick zur Bestimmung der mikrobiellen Diversität in Umweltproben wird gegeben. Der Hauptschwerpunkt liegt auf direkten und indirekten Wechselwirkungsprozessen der Actinide mit Bakterien.
    Keywords: bacteria, actinides, nuclear waste disposal
    • Invited lecture (Conferences)
      Seminar für Kern- und Radiochemie am Institut für Kernchemie der Johannes Gutenberg-Universität Mainz, 29.11.2010, Mainz, Deutschland

    Publ.-Id: 14851 - Permalink


    Surface Modification on KBr (001) with Slow Highly Charged Ions
    Wilhelm, R. A.; Heller, R.; El-Said, A. S.; Facsko, S.;
    Highly Charged Ions (HCI) carry an enormous amount of potential energy (up to 100 keV for Xe50+) which is defined as the sum of the binding energies of all missing electrons. This unique parameter offers new ways of surface modifications without a significant bulk damage.
    During neutralization and de-excitation processes of the HCI the potential energy is released into electronic excitations within the solid (creation of electron hole pairs). These electron hole pairs get rapidly self-trapped due to strong electron-phonon coupling in the ionic lattice and decay into color centers (mainly H, F and F*-centers).
    Finally these color centers lead to a desorption of K and Br neutralized atoms at the surface site, which after a agglomeration of many of these color centers forms a pit-like nanostructure on atomically flat KBr(001) surfaces.
    The influence of kinetic and potential energy effects will be discussed.
    Keywords: HCI, DIET, KBr, electron-hole pair, pit, nanostructures, color center
    • Lecture (Conference)
      International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige
    • Poster
      International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige

    Publ.-Id: 14850 - Permalink


    The traceless Staudinger ligation with fluorine-18: a novel and versatile labeling technique for the synthesis of PET-radiotracers
    Pretze, M.; Wuest, F.; Peppel, T.; Köckerling, M.; Mamat, C.;
    The development of rapid radiolabeling techniques under mild reaction conditions involving the short-lived positron emitter fluorine-18 remains a special challenge in organic PET chemistry. This work describes a novel and facile application of the traceless Staudinger ligation as a mild and versatile labeling method for preparation of various radiotracers labeled with fluorine-18.
    Keywords: Radiolabeling; Traceless Staudinger ligation; Bioorthogonal; Fluorine-18

    Publ.-Id: 14849 - Permalink


    The speciation of U(VI) in aqueous solution and sorbed onto TiO2 studied by in situ vibrational spectroscopy
    Müller, K.; Meusel, T.; Brendler, V.; Foerstendorf, H.; Bernhard, G.;
    The migration behavior of uranium in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
    In the present study, the speciation of uranium(VI) at the TiO2-water interface has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
    • Lecture (others)
      Seminar at the Department of Nuclear Engineering, Kyoto University, 29.06.2010, Kyoto, Japan

    Publ.-Id: 14848 - Permalink


    Speciation of actinyl ions in aqueous solution and at water-mineral interfaces. A vibrational spectroscopic approach
    Müller, K.;
    The migration behavior of actinides in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
    In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral-water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
    Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
    • Lecture (others)
      Jahresseminar des Graduiertenkollegs 826/3, 08.11.2010, Burg Schönburg in Oberwesel, Deutschland

    Publ.-Id: 14847 - Permalink


    Uranium sorption on various forms of titanium dioxide – influence of surface area, surface charge and impurities
    Comarmond, M. J.; Payne, T. E.; Harrison, J. J.; Thiruvoth, S.; Wong, H. K.; Aughterson, R. D.; Lumpkin, G. R.; Müller, K.; Foerstendorf, H.;
    Titanium dioxide (TiO(2)) has often served as a model substrate for experimental sorption studies of environmental contaminants. However, various forms of Ti-oxide have been used, and the different sorption properties of these materials have not been thoroughly studied. We investigated uranium sorption on some thoroughly characterized TiO(2) surfaces with particular attention to the influence of surface area, surface charge, and impurities. The sorption of U(VI) differed significantly between samples. Aggressive pretreatment of one material to remove impurities significantly altered the isoelectric point, determined by an electroacoustic method, but did not significantly impact U sorption. Differences in sorption properties between the various TiO(2) materials were related to the crystallographic form, morphology, surface area, and grain size, rather than to surface impurities or surface charge. In-situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopic studies showed that the spectra of the surface species of the TiO(2) samples are not significantly different, suggesting the formation of similar surface complexes. The data provide insights into the effect of different source materials and surface properties on radionuclide sorption.

    Publ.-Id: 14846 - Permalink


    Preparation, 99mTc-labeling and biodistribution studies of a PNA oligomer containing a new ligand derivative of 2,2′-dipicolylamine
    Gasser, G.; Jäger, K.; Zenker, M.; Bergmann, R.; Steinbach, J.; Stephan, H.; Metzler-Nolte, N.;
    A new azido derivative of 2,2′-dipicolylamine (Dpa), 2-azido-N,N-bis((pyridin-2-yl)methyl)ethanamine, (Dpa-N3) was readily prepared from the known 2-(bis(pyridin-2-ylmethyl)amino)ethanol (Dpa-OH). It was demonstrated that Dpa-N3 could be efficiently labeled with both [Re(CO)3(H2O)3]Br and [99mTc(H2O)3(CO)3]+ to give [Re(CO)3(Dpa-N3)]Br and [99mTc(CO)3(Dpa-N3)]+, respectively. Furthermore, Dpa-N3 was successfully coupled, on the solid phase, to a Peptide Nucleic Acid (PNA) oligomer (H-4-pentynoic acid-spacer-spacer-tgca-tgca-tgca-Lys-NH2; spacer = –NH–(CH2)2–O–(CH2)2–O–CH2–CO–) using the Cu(I)-catalyzed [2 + 3] azide/alkyne cycloaddition (Cu-AAC, often referred to as the prototypical “click” reaction) to give the Dpa-PNA oligomer. Subsequent labeling of Dpa-PNA with [99mTc(H2O)3(CO)3]+ afforded [99mTc(CO)3(Dpa-PNA)] in radiochemical yields > 90%. Partitioning experiments in a 1-octanol/water system were carried out to get more insight on the lipophilicity of [99mTc(CO)3(Dpa-N3)]+ and [99mTc(CO)3(Dpa-PNA)]. Both compounds were found rather hydrophilic (log Do/w values at pH = 7.4 are −0.50: [99mTc(CO)3(Dpa-N3)]+ and −0.85: [99mTc(CO)3(Dpa-PNA)]. Biodistribution studies of [99mTc(CO)3(Dpa-PNA)] in Wistar rats showed a very fast blood clearance (0.26 ± 0.1 SUV, 1 h p.i.) and modest accumulation in the kidneys (5.45 ± 0.45 SUV, 1 h p.i.). There was no significant activity in the thyroid and the stomach, demonstrating a high in vivo stability of the 99mTc-labeled Dpa-PNA conjugate.
    Keywords: Bio-organometallic chemistry; Click chemistry; Nuclear medicine; Peptide nucleic acid (PNA); Rhenium compounds; Technetium compounds

    Publ.-Id: 14845 - Permalink


    Characterization of Si nanowires fabricated by Ga+ FIB implantation and subsequent selective wet etching
    Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.;
    Local gallium (Ga) ion implantation in silicon (Si) by focused ion beam (FIB) and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires (NWs) with reproducible widths between 20 and 200 nm. The dependence of the resulting NW width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the NW width as a function of the implanted fluence. Furthermore, the resistance of the NWs, its temperature response and the activation energy for electrical current flow were investigated before and after direct current (DC) annealing in air and in vacuum. Annealed NWs showed a decrease of their resistivity up to two orders of magnitude, indicating a partial re-crystallization of the NWs through self-heating and a change in the conduction. The assumption of recrystallization is supported by scanning electron microscopy (SEM) and Raman spectroscopy.
    Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy

    Publ.-Id: 14844 - Permalink


    A method to estimate the planar, instantaneous body force distribution from velocity field measurements
    Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.;
    We present a simple method to derive a planar, instantaneous body force distribution from a given 2-D velocity field without knowledge of the pressure field. If the body force consists of one component only, spatial integration completely recovers this component.
    Particle Image Velocimetry and Direct Numerical Simulations of a wall jet induced by a known body force were conducted to validate the method, demonstrating a good agreement of the original and reconstructed force fields.

    Publ.-Id: 14843 - Permalink


    Präzisionsmessung der Photodissoziation des Deuterons bei Energien im Bereich der Big-Bang-Nukleosynthese
    Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Kempe, M.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schwengner, R.; Sobiella, M.; Wagner, A.;
    Die für die primordiale Nukleosynthese wichtige Reaktion d(γ,n)p wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht.
    Der Photonenfluss wurde mit Hilfe der resonanten Streuung an Aluminiumkernen bei Energien von 2,2 und 3,0 MeV bestimmt. Die Effektivität der verwendeten Germanium-Detektoren wurde mit Hilfe von Referenzstrahlern und Simulationsrechnungen ermittelt. Mit beidseitig ausgelesenen Szintillationsdetektoren wurden Flugzeit und -strecke der Neutronen bestimmt. Wegen der niedrigen Nachweisschwelle der Detektoren kann der Wirkungsquerschnitt für Neutronenenergien von 50 keV bis 1,4 MeV bestimmt werden. Die erreichte statistische Unsicherheit beträgt 5 %, die Energieauflösung 4 %. Bisher untersuchte systematische Unsicherheiten werden diskutiert.
    Keywords: Big Bang nucleosynthesis, bremsstrahlung, gamma-ray spectroscopy, neutron time-of-flight, nuclear astrophysics, photon scattering
    • Lecture (Conference)
      74. Jahrestagung der DPG und DPG Frühjahrstagung, 15.-19.03.2010, Bonn, Deutschland

    Publ.-Id: 14842 - Permalink


    Investigation of the beltline welding seam and base metal of the Greifswald WWER-440 Unit 1 reactor pressure vessel
    Schuhknecht, J.; Viehrig, H.-W.; Rindelhardt, U.;
    The investigation of reactor pressure vessel (RPV) materials from decommissioned nuclear power plants (NPPs) offers the unique opportunity to scrutinize the irradiation behavior under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterization. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I); irradiated and recovery annealed (IA); and irradiated, recovery annealed, and reirradiated (IAI). The working program is focused on the characterization of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the American Society for Testing of Materials (ASTM) Test Standard E1921–08 to determine the fracture toughness of the RPV steel in different thickness locations. In a first step, the trepans taken from the RPV Greifswald unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the master curve (MC) approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behavior. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on subsize Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy-V transition temperature TT41J estimated with results of subsize specimens after the recovery annealing was confirmed by the testing of standard Charpy-V-notch specimens. The evaluated TT41J shows a better accordance with the irradiation fluence along the wall thickness than the master curve reference temperature T0. The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The reembrittlement during two campaign operations can be assumed to be low for the weld and base metal.
    Keywords: nuclear power plant, decommisioning, reactor pressure vessel, testing, fracture toughness, Master Curve, integrity assessment
    • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 133(2011)5, 052904
      DOI: 10.1115/1.4000891

    Publ.-Id: 14841 - Permalink


    Experimental and numerical modeling of the steel flow in a continuous casting mould under the influence of a transverse DC magnetic field
    Timmel, K.; Miao, X.; Eckert, S.; Lucas, D.; 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
    • Magnetohydrodynamics 46(2010), 437-448

    Publ.-Id: 14840 - Permalink


    Experimental facility for two- and three-dimensional ultrafast electron beam X-ray computed tomography
    Stürzel, T.; Bieberle, M.; Laurien, E.; Hampel, U.; Barthel, F.; Menz, H.-J.; Mayer, H.-G.;
    An experimental facility is described which has been designed to perform ultrafast two- and three-dimensional electron beam computed tomography. As a novelty a specially designed transparent target enables tomography with no axial offset for 2D imaging and high axial resolution three-dimensional im-aging employing the cone-beam tomography principles. The imaging speed is 10,000 frames per second for planar scanning and more than 1000 frames per second for 3D imaging. The facility serves a broad spectrum of potential applications primarily the study of multiphase flows, but also in principle non-destructive testing or small animal imaging. In order to demonstrate the aptitude for these applications static phantom experiments at a frame rate of 2000 fps were performed. Resulting spatial resolution was found to be 1.2 mm and better for a reduced temporal resolution.
    Keywords: three-dimensional tomography, electron beam tomography, X-ray tomography, multiphase flow measurement

    Publ.-Id: 14839 - Permalink


    Editorial on the special issue on imaging systems and techniques
    Karras, D. A.; Giakos, G. C.; Hampel, U.;
    Imaging systems and techniques have found widespread application in medical and biological imaging, security and surveillance systems, remote sensing, biometrics, non-destructive testing, computer sciences, materials research, and most recently also in various types of customer products. Imaging systems may be based on different physical measuring principles, such as optical, infrared, acoustic, microwave, terahertz, electrical, X-ray and gamma ray sensing techniques, for example. But behind the imaging sensor there is strong common ground in electronics concepts and circuits for signal conversion, processing, acquisition, and storage as well as algorithms for image enhancement, image reconstruction and image analysis. Imaging systems are increasingly complex and therefore challenge electronic engineers and computer scientists. Concurrently to an ongoing trend of increasing the spatial and temporal resolution of such systems, there is a growing demand for hardware-supported image processing, multi-modality imaging, data reduction as well as improved sensitivity, specificity and robustness.
    Keywords: imaging systems and techniques
    • International Journal of Signal and Imaging Systems Engineering 3(2011)3, 145-147

    Publ.-Id: 14837 - Permalink


    Stand und Perspektiven der Kernenergie in Deutschland und „Umgebung“
    Lucas, D.; Weiß, F.-P.;
    In einem Überblicksvortrag werden aktuelle Fakten und Entwicklungen zur Kernenergienutzung in Deutschland und der Welt vorgestellt und diskutiert. Das schließt auch die Darstellung aktueller Forschungsschwerpunkte für gegenwärtige und zukünftige Reaktoren ein.
    Keywords: Nuclear energy
    • Invited lecture (Conferences)
      3. VDI-KTG-Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

    Publ.-Id: 14836 - Permalink


    A moderation layer to improve the safety behavior of sodium cooled fast reactors
    Merk, B.; Weiß, F.-P.;
    The nature of the sodium void effect in an infinite lattice is discussed with all different contributions. In a next step, the insertion of a layer consisting of moderating material for a reduction of the effect is proposed. The effect of three different moderating layers on the sodium void defect, the neutron spectrum, and the kinf over burnup is investigated. Special emphasis is given to the influence of the moderation layer on the feedback effects. Especially the uranium-zirconium hydride UzrH layer causes a strong reduction of the sodium void effect. Additionally this layer improves the fuel temperature effect and the coolant effect of the system significantly. All changes cause by the insertion of the UZrH layer lead to a significant increase in stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides. The insertion of the moderating layer does not imply any constraints on the core design and the power distribution in the fuel element an. Thus the use of a moderation layer gives the opportunity of designable feedback effects in a fast reactor core.
    Keywords: Sodium Void Effect, SFR, Fast Reactor, Uranium-Zirconium Hydride, Boron Carbide
    • Contribution to proceedings
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
    • Lecture (Conference)
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

    Publ.-Id: 14835 - Permalink


    Application of a two energy group analytical solutions to the YALINA experiment SC3A
    Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.;
    The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’is analyzed based on a full HELIOS model for the calculations. The effect of the two region design on the experimental results at different detector positions is leading to unexpected results and the special problems for the analysis of the experiments have been shown. For a more detailed representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time was used. To model the above mentioned streaming of neutrons from the thermal area into the fast area an analytical solution for the time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. In addition to the central source pulse of the external source a source at the boundary of the system has been introduced. The new analytical solution shows very good agreement with the experimental results, even for the unexpected behavior of the outermost deterctor. Thus analytical solution without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments.
    Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation
    • Contribution to proceedings
      The International Conference on Mathematics and Computational Methods applied to Nuclear Science and Engineering (MC 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
    • Lecture (Conference)
      International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

    Publ.-Id: 14834 - Permalink


    Investigation of coolant mixing in reactor VVER-1000
    Lisenkov, A.; Bezrukov, Y. A.; Ulianovskiy, D. V.; Zaytsev, D. V.; Bykov, M. A.; Shishov, A. V.; Höhne, T.; Rohde, U.; Gallori, D.;
    This paper presents arrangement of the problem, methodology of experiment performance and results of experimental investigation of coolant mixing in downcomer and lower plenum of VVER-1000. Three groups of experiments simulating coolant mixing were executed: in conditions of RCP start-up, during natural circulation recovery in the course of SB LOCA and in conditions of stable operation of different amount of RCPs. Results of experiments are used for validation of codes.
    Keywords: CFD, VVER-1000
    • Contribution to proceedings
      ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France
    • Lecture (Conference)
      ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France

    Publ.-Id: 14833 - Permalink


    Experimental investigation of in-vessel mixing phenomena in a VVER-1000 scaled test facility during unsteady asymmetric transients
    Moretti, F.; Melideo, D.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Lisenkov, E.; Bucalossi, A.; Gallori, D.;
    In-vessel turbulent mixing phenomena affect the time and space distribution of coolant properties (e.g. boron concentration and temperature) at the core inlet which impacts consequently the neutron kinetics response. For reactor safety evaluation purposes and to characterize these phenomena it is necessary to set and validate appropriate numerical modelling tools to improve the current conservative predictions. With such purpose, an experimental campaign was carried out by OKB Gidropress, in the framework of the European Commission Project “TACIS R2.02/02 - Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”. The experiments were conducted on a scaled facility representing the primary system of a VVER-1000 including a detailed model of the Reactor Pressure Vessel with its internals. The simulated transients involved perturbations of coolant properties distribution providing a wide validation matrix. The main achievements of the set of experiments featuring transient asymmetric pump behaviour are presented in this paper. The potential of the obtained experimental database for the validation of thermal fluid dynamics numerical simulation tools is also discussed and the role of computational fluid dynamics in supporting the experimental data analysis is highlighted.
    Keywords: CFD, turbulent mixing

    Publ.-Id: 14832 - Permalink


    Highly anisotropic effective dielectric functions of silver nanoparticle arrays
    Oates, T. W. H.; Ranjan, M.; Facsko, S.; Arwin, H.;
    Variable-angle and Mueller matrix spectroscopic ellipsometry measurements of highly anisotropic plasmonic materials composed of random and aligned silver nanoparticles and nanorods are presented. We show that the effective dielectric tensors of randomly dispersed particles are uniaxially anisotropic and those of aligned particles are biaxially anisotropic, with the anisotropy predominantly at the plasmonic resonances. The strong resonances in nanorod arrays result in the real part of the effective in-plane permittivities being opposite in sign over a significant range in the visible, suggesting the potential to design materials that display tunable negative-refraction.
    Keywords: metamaterial, left-handed medium, extreme anisotropy, photonic crystals, indefinite materials
    • Open Access LogoOptics Express 19(2011)3, 2014-2028

    Publ.-Id: 14831 - Permalink


    Pygmy Dipole Strength in Exotic Nuclei and the Equation of State
    Klimkiewicz, A.; Paar, N.; Adrich, P.; Fallot, M.; Le Bleis, T.; Rossi, D.; Boretzky, K.; Aumann, T.; Alvarez-Pol, H.; Aksouh, F.; Benlliure, J.; Berg, T.; Boehmer, M.; Casarejos, E.; Chartier, M.; Chatillon, A.; Cortina-Gil, D.; Datta Pramanik, U.; Elze, T. W.; Emling, H.; Ershova, O.; Fernando-Dominguez, B.; Geissel, H.; Gorska, M.; Heil, M.; Hellstrom, M.; Johansson, H.; Jones, K. L.; Junghans, A.; Kiselev, O.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Labiche, M.; Lemmon, R.; Litvinov, Y.; Mahata, K.; Maierbeck, P.; Nilsson, T.; Nociforo, C.; Palit, R.; Paschalis, S.; Plag, R.; Reifarth, R.; Simon, H.; Summerer, K.; Surowka, G.; Vretenar, D.; Wagner, A.; Walus, W.; Weick, H.; Winkler, M.;
    A concentration of dipole strength at energies below the giant dipole resonance was observed in neutron-rich nuclei around 132Sn in an experiment using the FRS-LAND setup. This so-called “pygmy” dipole strength can be related to the parameters of the symmetry energy and to the neutron skin thickness on the grounds of a relativistic quasiparticle random-phase approximation. Using this ansatz and the experimental findings for 130Sn and 132Sn, we derive a value of the symmetry energy pressure of p-bar0 = 2.2±0.5 MeV/fm3. Neutron skin thicknesses of Rn−Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 132Sn, respectively, have been determined. Preliminary results on 68Ni from a similar experiment using an improved setup indicate an enhanced cross section at low energies, while the results for 58Ni are in accordance with results from photoabsorption measurements.
    Keywords: dipole strength giant dipole resonance neutron-rich nuclei 132Sn FRS-LAND pygmy dipole strength symmetry energy skin thickness quasiparticle random-phase approximation photoabsorption
    • Contribution to proceedings
      NUCLEAR STRUCTURE AND DYNAMICS '09: Proceedings of the International Conference, 04.-08.05.2009, Dubrovnik, Croatia
      Pygmy Dipole Strength in Exotic Nuclei and the Equation of State: AIP Conference Proceedings, 978-0-7354-0702-2, 181-184

    Publ.-Id: 14830 - Permalink


    Influence of hydrogen on the thermally induced phase separation in GeO/SiO2 multilayers
    Sahle, C. J.; Zschintzsch, M.; Sternemann, C.; von Borany, J.; Nyrow, A.; Jeutter, N. M.; Wagner, R.; Frahm, R.; Tolan, M.;
    The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeOx/SiO2 multilayers (x ~ 1) leading to size controlled growth of Ge nanocrystals is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing a complete phase separation at approximately 450 °C using inert N2 ambient. The use of reducing H2 in the annealing atmosphere influences the phase separation even in an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50 °C. At temperatures above 400 °C the sublayer composition and thus the density of the Ge nanocrystals can be altered by making use of the reduction of GeO2 by H2.
    • Nanotechnology 22(2011)12, 125709

    Publ.-Id: 14829 - Permalink


    Simulation der Teilchenbeschleunigung auf mehreren GPUs mittels CUDA
    Knüpfer, A.; Bussmann, M.;
    Präsentation von PIConGPU
    Keywords: particle in cell, pic, gpu
    • Invited lecture (Conferences)
      Herbsttreffen des ZKI-Arbeitskreises "Supercomputing", 27.-28.10.2010, Göttingen, Deutschland

    Publ.-Id: 14828 - Permalink


    pp and ππ intensity interferometry in collisions of Ar+KCl at 1.76A GeV
    Agakishiev, G.; Balanda, A.; Bannier, B.; Bassini, R.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Moriniere, E.; Mousa, J.; Muentz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez-Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.;
    Results on pp, π+π+, and π-π- intensity interferometry are reported for collisions of Ar+KCl at 1.76$A$~GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The experimental correlation functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time extent of the corresponding emission sources. The π π source radii are found significantly larger than the pp emission radius. The present radii do well complement the source-size excitation functions of the collision system of size $A+A \simeq 40+40$. The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants. From this trend, a lower limit of the pp correlation radius is deduced.

    Publ.-Id: 14827 - Permalink


    Irradiation Response of Greifswald Unit 8 RPV Steels
    Viehrig, H.-W.; Gillemot, F.; Horvat, M.; Acosta, B.; Debarberis, L.;
    Base and weld metal and cladding of the not commissioned SKODA reactor pressure vessel of Greifswald Unit 8 was investigated. Tensile, Charpy size SE(B) and 0.5T-C(T) specimens were irradiated at the LYRA and BAGIRA irradiation rigs with different neutron fluxes. The main focus was on fracture toughness testing according to the Mater Curve approach and crack extension curves. With these tests the reference temperature T0 and fracture toughness values for ductile tearing according to the ASTM test standards ASTM E1921 and ASTM E1820, respectively, were determined.
    The irradiation in the LYRA rig with a neutron flux of about 1.57•1012 n/cm2 results in shifts of the reference temperature ΔT0 which correspond with the prediction according to the Russian WWER-440 code. In contrast the BAGIRA irradiation with a neutron flux of about 68.6•1012 n/cm2 results in remarkable higher ΔT0 values then predicted. For weld metal from multilayer welding seams the orientation of the specimens is crucial for the direct measurement of the fracture toughness by using the MC concept. The evaluation of J-R curves measured on Charpy size SE(B) specimens is demanding because of the unsteady developing through the different structures of the cladding.
    Keywords: reactor pressure vessel steel,neutron, neutron irradiation, fracture toughness, Master Curve approach, crack extension curve, neutron embrittlement
    • Lecture (Conference)
      IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

    Publ.-Id: 14826 - Permalink


    Previous results of the investigation on the decommissioned reactor pressure vessels of the Greifswald NPP
    Viehrig, H.-W.; Houska, M.;
    The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated and annealed and irradiated, annealed and re-irradiated.
    The paper presents test results measured on the trepan taken from the beltline welding seam located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The working program comprises chemical analysis, microstructure investigations (by means of metallography and SEM), mechanical testing (hardness and tensile), and fracture mechanics testing. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The KJc values measured on TS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the welding seam approximately follow the course of the Master Curve but with a large scatter. Reference temperatures T0 through the thickness of the RPV beltline welding seam runs almost opposite to the trend predicted by the Russian code for the decrease of the neutron fluence from 5.1•E19 n/cm2 to 1.1•E19 n/cm2 (E>0.5MeV). T0 varies between 6°C from near the welding root at ¼ wall thickness to 117°C at ¾ wall thickness. The scatter of T0 beyond the welding root is about 40 K and depends strongly on the structure at the crack tip. The results are also evaluated according to integrity assessment procedures based on the Master Curve concept.
    Keywords: reactor pressure vessel, welding seam, specimen orientation, fracture toughness, Master Curve approach, integrity assessment
    • Lecture (Conference)
      IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

    Publ.-Id: 14825 - Permalink


    Shaping of submicrometer-structures by swift heavy ion irradiation
    Ferhati, R.; Guilliard, N.; Weishaar, T.; Amirthapandian, S.; Fritzsche, M.; Bischoff, L.; Bolse, W.;
    Processing of small structures on µm- or nm-scales using swift heavy ions of some MeV/u energy (SHI) has become an important research topic because of the unique features of the ion irradiation technique. Each single ion impact in the solid results in a highly excited (some eV per atom), almost one-dimensional excitation, which because of its cold surrounding lasts for only a few tens of picoseconds. In many crystalline materials (especially insulators) this rapidly quenched local excitation manifests itself in a highly disordered or even amorphous cylinder of the above mentioned dimensions. The irradiation was carried out in our new in-situ high resolution scanning electron microscope (HRSEM), which we have recently installed at the new UNILAC accelerator of the Helmholtz Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. This setup enables us to perform sequences of combined ion irradiation and HRSEM analysis steps at one and the same spot on target surface throughout the whole experiment and allows us to investigate the evolution of individual objects during ion irradiation with a lateral resolution of a few nm. The specimen consisted of a 100 nm thick NiO film, which has been deposited onto an oxidized Si substrate by of reactive magnetron sputtering. The film was prestructured with a grid of 50 x 50 right-angled trenches by means of a focused ion beam (FIB) at the Forschungszentrum Dresden-Rossendorf. The trenches extended from the surface down to the NiO/SiO2 interface and had a width of about 100 nm. The distances were varied from 0.2 µm to 5 µm, with always 5 trenches having the same distance. This way NiO-blocks of 100 nm height were created, having quadratic (along the diagonal of the grid) respectively rectangular cross sections (off-grid elements). The specimen was then irradiated with 5.9 MeV/u U-ions under grazing incidence (tilt angle 80) and continuous azimuthal rotation (angular velocity 1.45_/s). We have investigated the reshaping of µm- to nm-sized rectangular NiO-blocks by SHI irradiation under grazing incidence and continuous azimuthal rotation. While initially small blocks form single pillar-like structures, blocks of larger dimensions rearrange into tooth-like objects. Below a certain size (~100 nm in diameter) the structures become instable and start to move and coalesce. The plastic deformation and the formation of the pillars can be understood in terms of the hammering effect (or better: in terms of isotropic tensile in-plane stresses due to the irradiation). The observed saturation effect and the instability until now remain unexplained and need further experiments for their clarification.
    Keywords: oxide films, FIB, swift heavy ions, submicron structures
    • Contribution to external collection
      Prof. Dr. Peter Michler, Prof. Dr. Wolfgang Bolse: Annual Report 2009, Institut für Halbleiteroptik und funktionale Grenzflächen, Universität Stuttgart, Stuttgart: Universität Stuttgart, 2010, 48-49

    Publ.-Id: 14824 - Permalink


    A Common Approach to Image Reconstruction for Different Applications of Compton Cameras
    Schöne, S.; Shakirin, G.; Kormoll, T.; Herbach, C.-M.; Pausch, G.; Enghardt, W.;
    Compton camera imaging is a promising technique for the measuring of high energetic gamma rays. Potential applications of Compton cameras are homeland security and medical imaging.
    Up to now the only method for the monitoring of ion radiation therapy is positron emission tomography (PET). The main disadvantage of the PET technique is the distortion of the measured β+-activity by metabolism and blood flow due to a half-live of up to 20 min for the therapy relevant positron emitters. This problem can be overcome by measuring the prompt photons of wide energies using Compton cameras. Compton cameras can also be used in homeland security for location and nuclide identification of remote radiation sources.
    We developed an application independent method for representation and calculation of the system matrix (SM) for Compton cameras. The method provides a structured approach for the SM creation which simplifies the software development process and the optimization of the computational performance. Additionally, the SM calculation is completely independent of the reconstruction algorithm itself.
    The first reconstruction results based on this unified SM calculation approach for medical imaging and homeland security applications are presented.
    • Poster
      2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
    • Contribution to proceedings
      2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
      Conference Record 2010 Nuclear Science Symposium and Medical Imaging Conference

    Publ.-Id: 14823 - Permalink


    Requirements on the instrumentation of a prompt gamma measuring device
    Fiedler, F.; Kormoll, T.; Müller, A.; Enghardt, W.;
    no abstract available
    Keywords: in-beam SPECT, in vivo dosimetry, Compton camera
    • Lecture (Conference)
      2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA
    • Contribution to proceedings
      2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA, 29.10.-06.11.2010, Knoxville, USA
      Proceedings to NSS MIC 2010

    Publ.-Id: 14822 - Permalink


    Eu3+-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory
    Barkleit, A.; Tsushima, S.; Savchuk, O.; Philipp, J.; Heim, K.; Acker, M.; Taut, S.; Fahmy, K.;
    Thermodynamic parameters for the complexation of Eu3+ with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerisable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 µM Eu3+, <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60°C. At elevated concentrations (>500 µM Eu3+ and BTC) a temperature-dependent polymerization was observed. The two methods lead to consistent thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol-1; ΔS = 152 ± 5/130 J mol-1 K-1; TRLFS/ITC) in the absence of polymerisation. With the onset of polymeristaion, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly monodentate binding of a single carboxylate group in both the monomeric and the polymeric complexes of the polycarboxylate with Eu3+. The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerisation as a crucial factor in determining the effect of humic acids on the mobility of radionuclides in soils.

    Publ.-Id: 14820 - Permalink


    Comparative characterization of two natural humic acids from the Pearl River Basin, China, and their environmental implications
    Liu, J.; Wang, J.; Chen, Y.; Lippold, H.; Lippmann-Pipke, J.;
    Two humic acids (HAs) were isolated from contaminated river sediments present under comparative conditions in the Pearl River Basin, China. YFHA (the HA extracted at an open pyrite mining area in Yunfu) exhibits a lower absorption intensity for certain bands in the Fourier Transform Infrared spectra, a lower E4/E6 value (the UV absorbances at 465 nm (E4) and 665 nm (E6)), a lower apparent molecular weight, a lower polarity index and a lower oxygen functionality in comparison with GZHA (the HA isolated at an urban living area in Guangzhou). All these differences generally indicate a higher degree of humification of YFHA than GZHA. Overall, the enrichment patterns of permanent heavy metals in the studied HAs are similar to those in the corresponding sediments. In particular, YFHA exhibits high enrichment of trace element Tl, a characteristic concomitant from the mining of the pyrite minerals. The adsorption isotherms of two HAs for goethite and pyrolusite--two representative geological materials generally conform to the Langmuir equation. Based on the qualitative relationships between the Langmuir constants of the adsorption isotherms and the chemical characteristics of HAs, the main mechanism of HA adsorption on these materials is suggested to be hydrophobic interaction. This study highlights the promising use of HA as a peculiar bio-indicator of uncommon trace metal contaminations. The HA adsorption mechanism on representative geological materials further provides a theoretical basis for the study on the unusual metal behavior in complex environmental settings.
    Keywords: humic acid; permanent metal load; adsorption; goethite; pyrolusite

    Publ.-Id: 14819 - Permalink


    European activities on cross-cutting nuclear thermal-hydraulics
    Cheng, X.; Boudier, P.; Class, A.; Hampel, U.; Ma, W. M.; Meloni, P.; Papukchiev, A.; Prasser, M.; Roelofs, F.; van Tichelen, K.;
    For the long-term development of nuclear power, innovative nuclear systems such as Gen-IV reactors and transmutation systems need to be developed for meeting future energy challenges. Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of more than 20 institutions of research centers, universities and nuclear industries with the main objectives to identify and to organize research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. A large-scale integrated research project is proposed to FP7 of European Commission and expected to start in the near future.
    The main topics considered in the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project are (a) Advanced reactor core thermal-hydraulics; (b) Single phase mixed convection; (c) Single phase turbulence; (d) Multiphase flow; (e) Numerical code coupling and qualification. The main objectives of the project are:
    • Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena. This data base contains both experimental data and data from direct numerical simulations (DNS).
    • Development of new physical models and modelling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena such as heat transfer and flow mixing, turbulent flow modelling for a wide range of Prandtl numbers, and modelling of flows under strong influence of buoyancy.
    • Improvement of the numerical engineering tools and establishment of a numerical platform for the design analysis of the innovative nuclear systems. This platform contains numerical codes of various classes of spatial scales, i.e. system analysis, sub-channel analysis and CFD codes, their coupling and the guidelines for their applications.
    The project will achieve optimum usage of available European resources in experimental facilities, numerical tools and expertise. It will establish a new common platform of research results and research infrastructure. The main outcomes of the project will be a synergized infrastructure for thermal-hydraulic research of innovative nuclear systems in Europe.
    This paper summarizes some key crosscutting thermal-hydraulics issues and corresponding ongoing research activities in Europe. The technical and management structure of the THINS project will be described. Examples of results achieved so far will be presented.
    Keywords: generation IV nuclear reactors, nuclear thermal hydraulics
    • Contribution to proceedings
      14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-29.09.2011, Toronto, Canada
      Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
    • Lecture (Conference)
      14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada

    Publ.-Id: 14818 - Permalink


    New 18F-labelled alkyl-substituted spirocyclic piperidines for imaging of σ1 receptors: radiolabelling and preliminary biological evaluation
    Maisonial, A.; Fischer, S.; Hiller, A.; Große Maestrup, E.; Deuther-Conrad, W.; Scheunemann, M.; Schepmann, D.; Steinbach, J.; Wünsch, B.; Brust, P.;
    Ziel: It is accepted that at least two σ receptor subtypes exist, termed σ1 and σ2 [1, 2]. Of these, σ1 receptor, the best characterized up to now [3], is assumed to be involved in several neurological diseases. PET imaging using specific σ1 receptor radioligands could be very helpful to obtain a target validation during drug development, a quantitative in vivo mapping of σ1 receptors as well as an improvement of our understanding of all the processes in which σ1 receptors are involved. Recently, a new class of spirocyclic piperidines with high affinity and selectivity for σ1 receptor binding site has been developed. Within this series, [18F]WMS1813 ([18F]1’-benzyl-3-(3-fluoropropyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]) has been successfully developed and used for detection of central σ1 receptors in mice [4]. Further structure-activity relationship studies on the linear ω-fluoroalkyl chain provided three other promising analogues, bearing either fluoromethyl- (WMS1850), fluoroethyl- (WMS1828) or fluorobutyl- (WMS1847) moieties. Herein, we report on the radiosynthesis and preliminary biological evaluation of these new candidates for PET imaging of σ1 receptors.
    Methoden: [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were synthesized by direct aliphatic nucleophilic substitution of the corresponding tosylate precursors by using the K[18F]F-K222-carbonate complex. For each radiotracer studied, solvent, temperature, reaction time and precursor concentration were optimized. Preliminary experiments on lipophilicity, chemical stability, organ distribution and metabolic stability in CD-1 mice were performed.
    Ergebnisse: Optimisation of radiofluorination parameters provided high labelling efficiencies of 61-88% using acetonitrile or DMSO as solvent, at 83 °C or 150°C respectively, with precursor concentrations between 2.0 and 3.0 mg/mL. [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were obtained with radiochemical yields of 43-50%, 35-45%, and 45-53%, respectively, radiochemical purities of >98.5%, and high specific activities, generally ≥150 GBq/µmol. Distribution coefficients determined experimentally (Log D = 2.39-3.16, pH = 7.2), underline the moderate lipophilic character of the three radiotracers. The radiolabeled compounds also show appropriate chemical stabilities in acetonitrile, PBS, TRIS-HCl, and Dulbecco buffer.
    No radiometabolites permeated into the brain of mice up to 60 min p.i. Metabolic profiles in liver, plasma, and urine were also investigated. By ex vivo autoradiography, the highest target (facial nucleus)-to-nontarget (olfactory bulb) tissue ratio has been determined for [18F]WMS1828 with a value of 4.69 at 45 min p.i. [18F]WMS1828 was superior also in organ distribution studies with a value of brain uptake of 4.71 ± 1.39 %ID/g in comparison to [18F]WMS1813 (3.18 ± 0.68 %ID/g), and [18F]WMS1847 (1.78 ± 0.16 %ID/g), and [18F]WMS1850 (2.65 ± 0.68 %ID/g) at 30 min p.i.
    Schlussfolgerungen: For the three radiotracers studied, optimised protocols led to very efficient radiosyntheses. With respect to first biological data, [18F]WMS1828 appears to be the most promising candidate for PET imaging of σ1 receptors, with even better pharmacological profile than the lead compound. Hence, [18F]WMS1828 radiosynthesis is selected for transfer onto an automated radiosynthesis module with a view to further clinical development.
    Referenzen:
    [1] Quirion, R.; Bowen, W. D.; Itzhak, Y.; Junien, J. L.; Musacchio, J. M.; Rothman, R. B.; Su, T. S.; Tam, S. W.; Taylor, D. P. Trends Pharmacol Sci. 1992; 13: 85-86.
    [2] Hayashi, T. ; Su, T. P. Current Neuropharmacology. 2005; 3: 267-280.
    [3] van Waarde, A.; Ramakrishnan, N. K.; Rybczynska, A. A.; Elsinga, P. H.; Ishiwata, K.; Nijholt, I. M.; Luiten, P. G. M.; Dierckx, R. A. Behavioural Brain Research. 2010; doi:10.1016/j.bbr.2009.12.043.
    [4] Maestrup, E. G.; Fischer, S.; Wiese, C.; Schepmann, D.; Hiller, A.; Deuther-Conrad, W.; Steinbach, J.; Wünsch, B.; Brust, P. J. Med. Chem. 2009; 52: 6062-6072.
    Keywords: σ1 receptor, 18F, radiolabelling, imaging
    • Lecture (Conference)
      18. Jahrestagung der Arbeitsgemeinschaft Radiochemie / Radiopharmazie der DGN, 16.-18.09.2010, Bad Boll, Deutschland

    Publ.-Id: 14817 - Permalink


    Synthesis, pharmacological activity and structure affinity relationships of spirocyclic σ1 receptor ligands with a (2-fluoroethyl) residue in 3-position
    Große Maestrup, E.; Wiese, C.; Schepmann, D.; Brust, P.; Wünsch, B.;
    In order to develop a fluorinated radiotracer for imaging of σ1 receptors in the central nervous system a series of (2-fluoroethyl) substituted spirocyclic piperidines 3 has been prepared. In the key step of the synthesis 2-bromocinnamaldehyde acetal 5 was added to piperidones 6 with various substituents at the N-atom. Unexpectedly, this reaction led to 2-benzoxepines 8, which were contracted with acid to afford the spirocyclic 2-benzofuranacetaldehydes 9. The best yields were obtained, when the transformations up to the alcohols 10 were performed without isolation of intermediates. Generally the (2-fluoroethyl) derivatives 3 have higher σ1 affinity and σ1/σ2 selectivity than the corresponding (3-fluoropropyl) derivatives 2. The most promising candidate for the development as radiotracer is the (2-fluoroethyl) derivative 3a (WMS-1828, fluspidine, 1’-benzyl-3-(2-fluoroethyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]), which shows subnanomolar σ1 affinity (Ki = 0.59 nM) and excellent selectivity over the σ2 subtype (1331-fold) as well as some other receptor systems. The novel synthetic strategy also allows the systematic pharmacological evaluation of intermediate alcohols 10. Despite their high σ1 affinity (Ki = 6-32 nM) and selectivity the alcohols 10 are 10-30-fold less potent than the bioisosteric fluoro derivatives 3.
    Keywords: σ1 receptor ligands; spirocyclic piperidines; [18F] radiotracer; neuroimaging; structure affinity relationships; ring contraction.

    Publ.-Id: 14816 - Permalink


    The serotonin transporter availability in untreated early-onset and late-onset patients with obsessive-compulsive disorder
    Hesse, S.; Stengler, K.; Regenthal, R.; Patt, M.; Becker, G.-A.; Franke, A.; Knüpfer, H.; Meyer, P. M.; Luthardt, J.; Jahn, I.; Lobsien, D.; Heinke, W.; Brust, P.; Hegerl, U.; Sabri, O.;
    The pathogenetic role of the central serotonin transporters (SERT) in obsessive-compulsive disorder (OCD) has been investigated in vivo by positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies with inconsistent results. This might reflect methodological differences but possibly also the pathophysiological heterogeneity of the disorder, i.e. the age at onset of OCD. The aim of our study was to compare the SERT availability in patients with OCD to healthy controls (HC) taking into account the onset type, other factors and covariates (e.g. SERT genotype, age, depression level, gender). We studied 19 drug-naïve OCD patients (36±13 years, 8 females) with early onset (EO-OCD, n=6) or with late onset (LO-OCD, n=13), and 21 HC (38±8 years, 9 females) with PET and the SERT-selective radiotracer [11C]DASB. Statistical models indicated that a variety of covariates and their interaction influences SERT availability as measured by distribution volume ratios (DVR). These models revealed significant effects of onset type on DVR with lower values in the LO-OCD (starting at an age of 18 years) compared with EO-OCD and HC in limbic (e.g., the amygdala), paralimbic brain areas (the anterior cingulate cortex), the nucleus accumbens and striatal regions, as well as borderline significance in the thalamus and the hypothalamus. The putamen, the nucleus accumbens and the hypothalamus were found with significant interaction between two SERT gene polymorphisms (SERT-LPR and VNTR). These findings suggest that late but not early onset of OCD is associated with abnormally low SERT availability. In part, functional polymorphisms of the SERT gene might determine the differences.
    Keywords: Serotonin transporter, positron emission tomography, obsessive-compulsive disorder

    Publ.-Id: 14813 - Permalink


    Tailoring the Magnetic Coupling of Fe/Cr/Fe Trilayers by Using Substrates with Nanometer Scale Ripples
    Körner, M.; Liedke, M. O.; Strache, T.; Dzenisevich, S.; Keller, A.; Facsko, S.; Lenz, K.; Fassbender, J.ORC
    Artificial antiferromagnets made from magnetically coupled trilayer structures are the basis for all types of spintronic devices like MRAM, GMR sensors etc. For years major effort lay on adjusting the coupling strength by changing the spacer thickness or material. Today, nanostructures offer a different approach as they add additional coupling mechanisms like proximity effects or Néel orange-peel coupling to the common interlayer exchange coupling (IEC). By means of ion beam erosion techniques it is possible to create well ordered substrate ripples with nanometer periodicity. They are transferred into the films grown on these rippled substrates. Hence, such ripples are a convenient way to induce Néel orange-peel coupling [1] and thus allow for tailoring the magnetic properties [2] as well as the coupling strength by varying the ripple periodicity without adjusting the spacer thickness. We have investigated the influence of rippled vs. flat Si substrates on the interlayer exchange coupling contributions in polycrystalline Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm). The substrate surface was periodically modulated (periods of 23 nm and 37 nm) by Ar+ ion beam erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by longitudinal magneto-optical Kerr effect (MOKE) applying a Stoner-Wohlfarth model on the magnetization reversal loops. Using 23 nm period ripples, we find an orange peel type coupling, predicted by Néel's theory superimposed on the IEC. In addition due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy is induced.
    This work is supported by DFG grant FA 314/6-1.
    REFERENCES
    1. Körner M. et al., Physical Review B 80, 214401, 2009.
    2. Fassbender J. et al., New Journal of Physics 11, 125002, 2009
    • Poster
      Nanofair 2010 - 8th International Nanotechnology Symposium, 06.-07.07.2010, Dresden, Germany

    Publ.-Id: 14812 - Permalink


    Investigating the Magnetic Properties of Tailored Bit Patterned Media Using Ferromagnetic Resonance
    Ball, D.; Faßbender, J.ORC; Lenz, K.; Markó, D.; Körner, M.; Fritzsche, M.; Strache, T.; Mücklich, A.; Albrecht, M.; Makarov, D.; Tibus, S.; Krone, P.
    no abstract available
    Keywords: Vector network analyzer ferrromagnetic resonance, CoCrPt:SiO2, Anisotropy, g-factor, damping phenomena, Gilbert damping, two magnon scattering
    • Lecture (others)
      Group Seminar, 09.06.2010, München, Germany

    Publ.-Id: 14811 - Permalink


    Morphology Induced Magnetic Phenomena
    Körner, M.; Lenz, K.; Liedke, M. O.; Strache, T.; Keller, A.; Facsko, S.; Fassbender, J.ORC
    no abstract available
    • Lecture (others)
      group seminar, 09.06.2010, München, Germany

    Publ.-Id: 14810 - Permalink


    Rational design of nanoparticle arrays using bioinspired mineralisation mediated by peptide-modified bacterial S-layers
    Pollmann, K.; Rothenstein, D.;
    Thema zur Einreichung im DFG-Schwerpunktprogramm
    • Lecture (Conference)
      DFG-SPP 1569 “Generation of Multifunctional Inorganic Materials by Molecular Bionics”, Kick-Off-Meeting, 25.10.2010, Stuttgart, Deutschland

    Publ.-Id: 14809 - Permalink


    Bioinspired nanocomposites based on self-assembling bacterial surface layer proteins
    Pollmann, K.; Günther, T.; Weinert, U.; Marquard, A.; Kutschke, S.; Lehmann, F.; Raff, J.;
    Bio-inorganic materials are very attractive for a variety of technical applications. The use of self-assembling proteins as part of such a hybrid material is an attractive approach for the development of such materials. Especially the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].
    In a current project we use monolayers of the S-layer protein of Lysinibacillus sphaericus for the construction of sensory layers. These S-layers are functionalized by aptamers (oligonucleotides) that work as receptor and two different fluorophores working as donor/acceptor for detection. Appropriate excitation/emission spectra and closest proximity of the fluorophores permit FRET. The binding of the analyte to the aptamer should influence the fluorescence, ideally causing the interruption of the FRET.
    In other projects we used the S-layers for the formation of (photo)catalytic layers. In this approach S-layers work as template for the bioinspired formation of (photo)catalytic particles such as Pd or ZnO. Size, crystallinity, distribution and morphology of the particles are influenced by the proteinaceous template.
    These examples demonstrate the high potential of the S-layers for various applications.

    [1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
    [2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
    [3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244
    Keywords: S-layers nanocomposites bio-inspired
    • Lecture (Conference)
      Euro BioMat 2011, 13.-14.04.2010, Jena, Deutschland

    Publ.-Id: 14808 - Permalink


    Lock and load the SRF gun
    Teichert, J.;
    In a forest close to the city of Dresden, Germany, lies the ELBE radiation source - the largest facility of the Research Centre Dresden-Rossendorf (FZD). After years of research, February saw the first SRF gun beam injected and accelerated in ELBE. Jochen Teichert tells more about the facility, the research and the gun.
    • EuCARD Newsletter 4(2010), 4-6

    Publ.-Id: 14807 - Permalink


    Au and Ge Nanoparticle Shaping by Swift Heavy Ion Irradiation
    Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Akhmadaliev, C.; Ridgeway, M.; Kluth, P.; Vredenberg, A.;
    The driving forces of nanomaterials processing by swift heavy ions as identified by our studies are (i) the mate-rials dependent electronic stopping power, (ii) the vol-ume change upon melting, (iii) the asymmetric hydro-dynamic flow due to stress field hysteresis, as well as (iv) far-from-equilibrium steady-state solubilities and strongly anisotropic diffusion coefficients. Size distributions, shapes and anisotropies of nanoparticles can be tailored by appropriate tuning of these driving forces. The evolution of Au and Ge nanospheres under swift heavy ion irradiation was studied experimentally and by atomistic computer simulations. Ge nanospheres of different sizes embedded in SiO2 show different response to I7+ ion irradiation at 38 MeV. Spheres below a critical size become discus-shaped, very small ones show Ge loss at their equator. Computer simula-tions based on a model which includes the driving forces listed above describe the Ge shaping and the Au shaping, where Au nanospheres of 15 nm diame-ter elongate to rods. Our model describes the ion-induced shape evolution of different elements for different ion species, energies and fluences quantitatively, where only one fit parameter describes all experiments. This is a strong evidence that our model based on classical thermodynamics and hydrodynamics describes the shaping mechanism appropriate. Using critical-size nanospheres with an unimodal size distributions and changing the ion impact angle during irradiation, tailoring of very exotic nanoparticle shapes become feasible.
    Keywords: Swift heavy ions, nanoparticles, ion bem shaping
    • Lecture (Conference)
      Workshop Ion Beam Physics, 29.-31.03.2010, Dresden-Rossendorf, Germany

    Publ.-Id: 14806 - Permalink


    Silicon Sensors realized by KETEK in Co-operation with FZD
    Wiest, F.; Eggert, T.; Fojt, R.; Höllt, L.; Knobloch, J.; Pahlke, A.; Pahlke, S.; Stötter, R.; Schmidt, B.; Lange, H.;
    In 2004 Ketek has established a long term co-operation with the Reasearch Centre Dresden (FZD) and the Universität der Bundeswehr München (UBW) targeted on the development of new silicon radiation detectors as well as on their commerz-ialization.
    Silicon Drift Detectors (SDDs) are widely used in XRF, TXRF, electron micro-probe analysis systems and synchrotron applications. The big benefit of SDDs compared to other x-ray de-tectors as Si(Li)s or pin-diodes is the spectroscopic performance principally being independent of the sen-sitive area. KETEK offers silicon drift detectors with sizes varying from 10 to 100 mm² whereby the large area devices become more and more attractive for most of the applications. Energy resolution below 130 eV for the Manganese Ka line and peak to background values of more than 10.000 can be achieved for devices with active areas of 100 mm² when cooled down to -60°C. This temperature can be already realized by a Peltier element integrated into the detector module, since the thermal budget of this evacuated device is well optimized. Count rate dependency of the energy resolution and the peak position is negligible up to count rates of 100.000 counts per second.
    Silicon Photomultiplier (SiPMs) are single photon sensitive devices built from an avalanche photodiode (APD) array on common Si substrate, whereby the APDs are operated in Geiger modus (above break down voltage). All applications for this sensor are connected with fast low level light sensing like e.g. the indirect gamma radiation detection by a scintillator. The first SiPM prototypes which have been realized by Ketek in co-operation with FZD show promising val-ues for photon detection efficiency, dark rate and opti-cal cross talk. Now this detector shall be further opti-mized for PET application.
    Keywords: Silicon drift detector. Silicon photomultiplier
    • Lecture (Conference)
      Workshop Ion Beam Physics (29th-31st March 2010), 29.-31.03.2010, Dresden-Rossendorf, Germany

    Publ.-Id: 14805 - Permalink


    Tailoring the magnetism of GaMnAs films by ion irradiation
    Li, L.; Zhou, S.; Buerger, D.; Roshchupkina, O.; Rushforth, A.; Campion, R. P.; Yao, S.; Grenzer, J.; Fassbender, J.ORC; Helm, M.
    The properties of magnetic metals such as saturation magnetization and magnetic anisotropy can be modified in a controllable manner by energetic ions [1]. GaMnAs is a well known magnetic semiconductor. The ability to tune the magnetic properties of magnetic semiconductors is an important issue in future semiconductor devices. Here we tailored the magnetism of GaMnAs films by He+ ion irradiation. The GaxMn1-xAs films with a Mn concentration of 5% and the easy axis of magnetization lying in-plane have been grown on GaAs substrates by LT-MBE. He+ ions of 650 keV were used to place the peak of damage into the GaAs substrate, so that the GaMnAs epilayer lies in the relatively uniform part of the damage profile. We show that the coercivity can be increased (Fig.1) from 50 Oe to 165 Oe when the dose reaches 3×1014/cm2 ~ 6×1014/cm2. Meanwhile, the saturation magnetization at 5 K is only reduced slightly to 22 emu/cm3 compared to non-irradiated GaMnAs films with a saturation magnetization amounting to 27 emu/cm3. Magneto-transport results indicate that the sheet resistance is increased by about 4 times compared to the non-irradiated GaMnAs film with a sheet resistance of 103 Ω. The irradiated GaMnAs still has an in-plane easy axis of magnetization at 5 K, but the anisotropy energy is much decreased. When the dose increases to 1×1015/cm2, no M-H hysteresis has been probed. Our study demonstrates the tailoring of magnetism and magnetoresistance in GaMnAs films by He+ ion irradiation.
    [1] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320 (2008) 579–596
    Keywords: magnetism, GaMnAs, ion irradiation
    • Lecture (Conference)
      Trends in Spintronics and Nanomagnetism, 22.05.-27.10.2010, Lecce, Italy
    • Poster
      Ion beam workshop, 29.-31.03.2010, Dresden, Deutschland
    • Journal of Physics D: Applied Physics 44(2011)4, 045001

    Publ.-Id: 14804 - Permalink


    Activation of acceptor levels in Mn implanted Si by pulsed laser annealing
    Li, L.; Zhou, S. Q.; Bürger, D.; Fassbender, J.ORC; Helm, M.; Schmidt, H.; Oesterlin, P.; Yao, S. D.
    The success of GaMnAs ferromagnetic semiconductors stands on two facts: (1) the efficient suppression of Mn-rich precipitates and (2) the large hole concentration created by substitutional Mn ions. If GaMnAs can be a guide, these two prerequisites should be considered when fabricating Si based ferromagnetic semiconductors. In this paper, nearly intrinsic Si wafers were implanted with Mn ions. The implanted Si films were annealed by pulsed laser annealing (PLA) or rapid thermal annealing (RTA). Activation of acceptors was only realized in the PLA films with a free hole concentration of 4×1017 cm-3, compared to the activation of donors in RTA films with a free electron concentration of 6×1015 cm-3. The PLA films reveal negative magnetoresistance with MR= 0.5% at 20 K and 30 K and at 7 T, hinting towards spin polarization of holes. Ferromagnetism was probed for both RTA and PLA films by a SQUID magnetometer at low temperatures. The formation of ferromagnetic MnSi1.7 nanoparticles has been proven in RTA films by synchrotron radiation X-ray (SR-XRD) measurements [1] and could be excluded in Mn implanted Si annealed by PLA.
    [1] S. Zhou et al., Phys. Rev. B 75, 085203 (2007).
    Keywords: Mn,Si, pulsed laser annealing,acceptor level
    • Lecture (Conference)
      DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 21.-26.03.2010, Regensburg, Deutschland

    Publ.-Id: 14803 - Permalink


    Ion Implantation in AFM Cantilever Array Fabrication
    Schmidt, B.; Zier, M.; Potfajova, J.; Philipp, P.;
    Low energy ion implantation has been applied to fabrication of shallow piezoresistive elements for AFM deflection sensing. The corresponding process parameters have been optimized to meet the demands of the electronics (power supply, resistance) connected to the piezoresistors. For the dimension (length x width = 5x20 µm2) of the piezoresistors designed by the University of Ilmenau, the resistance of them is 2.3-2.5 kOhm. The full processing of PRONANO AFM arrays consists additional three ion implantation steps for integrated heater and interconnect fabrication as well as for substrate reverse-biasing.
    Keywords: cantilever, array, piezoresistor, ion implantation, shallow pn-junction, sheet resistance
    • Contribution to external collection
      T. Sulzbach, I. W. Rangelow: PRONANO Proceedings of the Integrated Project on Massively Parallel Intelligent Cantilever Probe Platforms for Nanoscale Analysys and synthesis, Münster: Monsenstein und Vannerdat OHG (MV Wissenschaft), 2010, 978-3-86991-117-9, 111-117

    Publ.-Id: 14802 - Permalink


    Ion patterning of Si studied by kinetic Monte Carlo using ion damage from Molecular Dynamics calculations
    Numazawa, S.; Süle, P.; Heinig, K.-H.;
    During molecular dynamics (MD) simulation of Xe+, 500eV ion bombardment with the incidence angle 67° on Si (001), some dislocation patterns of near surface Si atoms were observed. We focused on the distribution of adatom generation points on Si (001) surface.
    After 500 single ion bombardment MD simulations, the observed distribution shapes Gaussian distribution with different aspect ratio. The center of distribution is around 1.8 nm forward from the impact point. We performed 3 dimensional lattice kinetic Monte-Carlo simulations with this adatom generation distribution and surface diffusion process. In early stage, the surface was simply roughened homogeneously and after around 3 x 1015 ion/cm2 dose, the surface started to form ripple structure perpendicular to the azimuthal incidence angle with wavelength ~15 nm. The ripple moves forward to the incident angle. These processes agree nicely with experimental observation. The mechanism of ripple formation related to surface atomic flows induced by ions, surface damage distribution and Mullin’s diffusion is discussed.
    Keywords: ion erosion, surface pattern, nanostructure, modelling, kinetic Monte Carlo, Molecular Dynamics
    • Poster
      17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-28.08.2010, Montréal, Canada
    • Poster
      17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-28.08.2010, Montréal, Canada

    Publ.-Id: 14801 - Permalink


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