Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
Cold quark stars from hot lattice QCD
Schulze, R.; Kämpfer, B.;
Based on a quasiparticle model for \beta stable and electrically neutral deconfined matter we address the possibility of pure quark stars. The model is adjusted to recent hot lattice QCD results for 2+1 flavors with almost physical quark masses. Using stability and binding arguments general statements can be made concerning the existence of such compact stellar objects.
Keywords: QCD, quasiparticle model, quark stars, quark gluon plasma
  • Invited lecture (Conferences)
    Hot and Cold Baryonic Matter 2010, 15.-20.08.2010, Budapest, Hungary

Publ.-Id: 14467 - Permalink


Schlagende Herzen und rasante Strömungen - Schnelle bildgebende Messverfahren in Technik und Medizin
Hampel, U.;
Der Vortrag gibt einen Einblick in die Nutzung schneller tomographischer Bildgebungsverfahren in der Medizin und Technik.
Keywords: fast tomography methods, medicine, engineering
  • Invited lecture (Conferences)
    Dresdner Seniorenakademie, 09.09.2010, Dresden, Germany

Publ.-Id: 14465 - Permalink


Steam bubble condensation in polydispersed flow experiments and CFD simulations
Krepper, E.; Schmidtke, M.; Lucas, D.; Beyer, M.;
Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in a 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a wire mesh sensor. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-2 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapur void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.
Keywords: two phase flow, experiments, CFD simulation, population balance models, mass transfer
  • Contribution to proceedings
    Int. Conf. "Nuclear Energy for New Europe", 06.09.-09.10.2010, Portoz, Slovenien
  • Lecture (Conference)
    Int. Conf. "Nuclear Energy for New Europe", 06.-09.09.2010, Portoz, Slovenien

Publ.-Id: 14464 - Permalink


Computing the KPZ Equation Using GPU Acceleration
Schulz, H.; Odor, G.; Kelling, J.; Heinig, K.-H.; Liedke, B.; Schmeißer, N.;
In this talk we present an approach for fast parallel computation of the Kardar-Parisi-Zhang equation (KPZ). Acceleration of these computations is always a major task since the run time of the simulations representing sequential algorithms is in the range of several months. We developed an implementation for the KPZ equation on graphics processing units (GPU) using the Compute Unified Device Architecture (CUDA). Experimental results show a significant speed-up compared to implementations on conventional processors.
  • Contribution to proceedings
    Innovation Information Technologies - Theory and Practice, 06.-10.09.2010, Dresden, Deutschland
    Computing the KPZ Equation Using GPU Acceleration, Dresden: FZD, 978-3-941405-10-3, 46-48

Publ.-Id: 14463 - Permalink


Raster-Kelvinkraft-Mikroskopie zur quantitativen Dotierprofilierung an dotiertem Silizium und Mn-implantiertem Germanium
Baumgart, C.; Zhou, S.; Helm, M.; Schmidt, H.;
Am Beispiel von dotierten Halbleitern konnte gezeigt werden, dass es mit Hilfe der korrekten Interpretation von KPFM-Daten möglich ist, die gemessene KPFM-Spannung mit der Ladungsträger-Konzentration in den untersuchten Halbleitern zu korrelieren. Die präsentierten Ergebnisse an dotiertem Silizium und Mn-implantiertem Germanium legen nahe, dass die Modellierung der KPFM-Spannung auf alle dotierten Halbleitermaterialien angewandt werden kann, solange die intrinsische Ladungsträgerkonzentration geringer als die Dotierkonzentration ist. Wir erwarten, dass in Zukunft die KPFM-Methode auch zur quantitativen Untersuchung der elektrischen Eigenschaften anderer Materialsysteme eingesetzt wird. Grundlage dafür ist immer das Verständnis der Ursache der mittels KPFM detektierten elektrostatischen Kräfte und die damit verbundene korrekte Interpretation der KPFM-Spannung.

Publ.-Id: 14462 - Permalink


Enhanced nucleation of vortices in soft magnetic disks prepared by silica nanosphere lithography
Martin, N.; Bigall, N. C.; Mönch, I.; Gemming, T.; Eychmüller, A.; Mattheis, R.; Schäfer, R.; Schultz, L.; McCord, J.;
Magnetic vortices show promise as data storage structures, however the vortex formation process imposes a lower limit on the element’s size. In this article a technique is presented, which application increases the probability of nucleating of magnetic vortices in sub-micron sized soft magnetic thin film elements. By tailoring the edge geometry of the elements, the symmetry of their magnetic configuration is broken in a manner which favors vortex nucleation. Micromagnetic simulations are presented, which demonstrate this effect in soft-magnetic disks with beveled edges. The favored edge geometry was realized by applying nanosphere lithography directly on top of a ferromagnetic thin film material. The resulting magnetic reversal loops show that in both magnetically isolated as well as in closely packed arrays of beveled disks, vortex formation takes place. The technique presented facilitates the vortex formation even in closely packed and small elements. The lowering of the minimum critical diameter for vortex formation enables a significant increase of data storage density in devices based on magnetic vortices.
Keywords: nanoparticles, patterned arrays, magnetic materials, thin films, magnetic vortex

Publ.-Id: 14459 - Permalink


Synthesis and Radiofluorination of Iodophenyl Esters as Tool for the Traceless Staudinger Ligation
Pretze, M.; Flemming, A.; Köckerling, M.; Mamat, C.;
A new synthetic pathway for the preparation of ω-functionalized 2-iodophenyl esters as starting materials for the synthesis of substituted phosphanes is described. A radiolabeling of these esters with fluorine-18 has led to building blocks which were reacted with HPPh2 in a Pd-catalyzed P-C cross coupling to establish new phosphanes. These compounds can be applied as mild and bioorthogonal radiolabeling agents by means of the traceless Staudinger ligation. A route to access this class of compounds has been established.
Keywords: Staudinger Ligation, Traceless, Bioorthogonal, Radiofluorination, PET, X-Ray Structure
  • Zeitschrift für Naturforschung Section B - A Journal of Chemical Sciences 65(2010), 1128-1136

Publ.-Id: 14458 - Permalink


A Compton Imager for in-vivo Dosimetry of Proton Beams
Enghardt, W.; Golnik, C.; Kormoll, T.; Wüstemann, J.; Fiedler, F.; Müller, A.; Schöne, S.;
no abstract available
Keywords: in-vivo dosimetry, proton irradiation, ion irradiation
  • Lecture (others)
    WP 3 Meeting, ENVISION, 04.09.2010, Stockholm, Schweden

Publ.-Id: 14457 - Permalink


High-precision ( p,t) reaction to determine 25Al( p,γ )26Si reaction rates
Matic, A.; van den Berg, A. M.; Harakeh, M. N.; Wörtche, H. J.; Berg, G. P. A.; Couder, M.; Görres, J.; Leblanc, P.; O’Brien, S.; Wiescher, M.; Fujita, K.; Hatanaka, K.; Sakemi, Y.; Shimizu, Y.; Tameshige, Y.; Tamii, A.; Yosoi, M.; Adachi, T.; Fujita, Y.; Shimbara, Y.; Fujita, H.; Wakasa, T.; Brown, B. A.; Schatz, H.;
Since the identification of ongoing 26Al production in the universe, the reaction sequence 24Mg(p,γ )25Al(β+ν)25Mg(p,γ )26Al has been studied intensively. At temperatures where the radiative capture on 25Al (t1/2 = 7.2 s) becomes faster than the β+ decay, the production of 26Al can be reduced due to the depletion of 25Al. To determine the resonances relevant for the 25Al(p,γ )26Si bypass reaction, we measured the 28Si(p,t )26Si reaction with high-energy precision using the Grand Raiden spectrometer at the Research Center for Nuclear Physics, Osaka. Several new energy levels were found above the p threshold and for known states excitation energies were determined with smaller uncertainties. The calculated stellar rates of the bypass reaction agree well with previous results, suggesting that these rates are well established.
Keywords: 26Al 24Mg(p,γ )25Al(β+ν)25Mg(p,γ )26Al Grand Raiden spectrometer

Publ.-Id: 14456 - Permalink


Analysis of Design Basis Accidents
Weiss, F.-P.; Schaefer, F.; Kliem, S.; Tusheva, P.;
The safety philosophy of nuclear reactors aims at maintaining the barriers for the retention of radioactivity. The safety functions required to achieve this fundamental protection goal are implemented by the operational and safety systems. All these systems are elements in a staggered safety concept, known as the defence in depth (DiD) concept which is meant to optimize the interaction of the manifold systems in respect to their effect on the safety of the nuclear power plant. On the first two levels of the DiD concept, i.e. at normal and abnormal or disturbed operation, the operational as well as the limitation and protection systems are designed to keep the plant at normal operation or to return to normal operation after a disturbance had occurred. Only in case of a failure of these systems or by effect of external events, an operational disturbance might develop into an accident. Accident scenarios which have been considered in the plant design are called design basis accidents. Safety systems and measures are arranged at level 3 of the DiD concept to control the design basis accidents and to bring the reactor back to a safe state.
  • Lecture (Conference)
    FJOH Summer School 2010, 24.-26.08.2010, Aix-en-Provence, Frankreich
  • Contribution to proceedings
    Analysis of Design Basis Accidents, 24.-26.08.2010, Aix-en Provence, Frankreich

Publ.-Id: 14455 - Permalink


Experiments and numerical simulations of horizontal two-phase flow regimes using an interfacial area density model
Höhne, T.; Vallee, C.;
Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows, which can lead to slug generation. In the last decade, stratified flows have increasingly been modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. Recent improvements of the multiphase flow modelling in the ANSYS CFX code, now make it possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, a high spatial and temporal resolution of measurement data are required. For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model based on the implemented mixture model was introduced, which allows the detection of the morphological form of the two-phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result, this model can distinguish between bubbles, droplets and the free surface using the local value of the volume fraction of the liquid phase. The behaviour of slug generation and propagation was qualitatively reproduced by the simulation, while local deviations require a continuation of the work.
Keywords: CFD, AIAD, TOPFLOW
  • Contribution to proceedings
    ANSYS Conference & 28. CADFEM Users´ Meeting 2010, 03.-05.11.2010, Aachen, Deutschland
    CD-ROM
  • Invited lecture (Conferences)
    ANSYS Conference & 28. CADFEM Users´ Meeting 2010, 03.-05.11.2010, Aachen, Deutschland
  • The Journal of Computational Multiphase Flows 2(2010)3, 131-143

Publ.-Id: 14454 - Permalink


Thermodynamical limits of diluted (magnetic) semiconductors
Bürger, D.; Seeger, M.; Zhou, S.; Skorupa, W.; Helm, M.; Schmidt, H.;
The incorporation of transition metal dopants in semiconductors above their solubility limit is the main challenge for the fabrication of diluted magnetic semiconductors. Dietl et al. have predicted the Curie temperature of different p-type conducting semiconductors alloyed with 5 at. % Mn [1]. This work motivated experimental efforts focused on the fabrication of highly diluted magnetic semiconductors. Unfortunately, such highly diluted magnetic semiconductors are metastable alloys and try to reach their thermodynamical equilibrium by the diffusion of the incorporated magnetic dopants leading to spinodal decomposition and secondary phase formation. There exist classical models which describe the kinetics of phase transitions and secondary phase formation for large clusters consisting of 100, 1000 or more atoms. However, electronic properties like carrier concentration strongly depend on the fraction of unclustered dopant atoms. Especially, in diluted magnetic semiconductors the formation of such clusters has to be prevented and growth techniques far from thermodynamical equilibrium are necessary.
Besides the LT-MBE process, the magnetic dopant implantation followed by pulsed laser annealing (PLA) appears to be a promising route for the fabrication of ferromagnetic semiconductors. The fast temperature quenching during PLA suppresses the diffusion of magnetic dopant atoms, i.e. diffusion via random hopping of these dopants is frozen and metastable diluted magnetic semiconductors are formed.
In this contribution we present the results from combined random-walk simulations and heat-flow calculations to describe the initial cluster formation for different magnetic semiconductors being characterized by a large variation of diffusion coefficients of the magnetic dopants. Under the assumption that the de-clustering probability of neighbouring dopants is lower than the clustering probability, we can explain the successful fabrication of GaAs:Mn and the impossibility to fabricate diluted ferromagnetic Si:Mn with LT-MBE or Mn implantation followed by PLA. Especially, our modelling approach can be used to estimate first clustering events during the re-crystallization after PLA. Within this picture, we conclude that for the preparation of diluted ferromagnetic semiconductors the basic diffusion parameters and the room temperature solubility of the magnetic dopants are reasonable parameters to estimate the chance for a successful preparation of different kinds of diluted systems.
[1] T. Dietl et al. Science 287 1019 (2000)
Keywords: ferromagnetic semiconductors, pulsed laser annealing, metastable, manganese
  • Poster
    30th International Conference on the Physics of Semiconductors (ICPS 2010), 25.-30.07.2010, Seoul, Südkorea

Publ.-Id: 14453 - Permalink


Characterization of mesoporous ZnO:SiO2 films obtained by the sol-gel method
Martins, R. M. S.; Musat, V.; Mücklich, A.; Franco, N.; Fortunato, E.;
ZnO:SiO2 films are intensively investigated for optical and electronic applications. Additionally, porous ZnO:SiO2 films are of great interest as catalyst and gas-sensing materials. The sol–gel method is an efficient and low-cost process for the deposition of meso- and microporous silica-based films. The present paper studies the effect of the withdrawal speed on the microstructure and optical properties of mesoporous ZnO:SiO2 films obtained by the sol–gel method. The morphology of the films was investigated by atomic force microscopy and the overall structure was studied by X-ray diffraction. The structure and size of the zinc oxide nanoparticles embedded in the silica matrix were investigated in more detail by transmission electron microscopy. These techniques showed ZnO:SiO2 films with crack-free mesoporous morphology and highly efficient embedding of ZnO nanoparticles with (100) preferred orientation. Furthermore, the optical transmittance (in the visible and near infrared regions) and the optical band gap value were observed to vary with withdrawal speed. It is shown that ZnO:SiO2 nanocomposites films which possess ZnO particles exhibiting a (100) orientation, with possible special applications in non-linear optics, could be prepared by the low-temperature crystallization sol–gel method.
Keywords: sol–gel, Zinc oxide, nanoparticles, silica matrix, thin films, mesoporous films, optical and electrical properties, X-ray diffraction, atomic force microscopy

Publ.-Id: 14450 - Permalink


3D QSAR study, synthesis and in vitro evaluation of (+)-5-FBVM as potential PET radioligand for the Vesicular AcetylCholine Transporter (VAChT)
Kovac, M.; Mavel, S.; Deuther-Conrad, W.; Méheux, N.; Glöckner, J.; Wenzel, B.; Anderluh, M.; Brust, P.; Guilloteau, D.; Emond, P.;
Located in presynaptic cholinergic nerve terminals, the vesicular acetylcholine transporter (VAChT) represents a potential target for quantitative visualization of early degeneration of cholinergic neurons in Alzheimer´s disease using PET. Benzovesamicol derivatives are proposed as radioligands for this purpose. We report QSAR studies of vesamicol and benzovesamicol derivatives taking into account the stereoselectivity of the VAChT binding site. Use of different data sets and different models in this study revealed that both enantiomers of 5-fluoro-3-(4-phenyl-piperidin-1-yl)-1,2,3,4-tetrahydro-naphthalen-2-ol (5-FBVM) are promising candidates, with predicted VAChT affinities between 6.1 and 0.05 nM. The synthesis of enantiopure (R,R)- and (S,S)-5-FBVM and their corresponding triazene precursors for future radiofluorination is reported. Both enantiomers exhibited high in vitro affinity for VAChT [(+)-5-FBVM: Ki = 6.95 nM and (-)-5-FBVM: Ki = 3.68 nM] and were selective for s2 receptors (~70-fold), only (+)-5-FBVM is selective for s1 receptors (~5-fold). These initial results suggest that (+)-(S,S)-5-FBVM warrants further investigation as a potential radioligand for in vivo PET imaging of cholinergic nerve terminals.
Keywords: Benzovesamicol derivative; VAChT; triazene; fluoro-dediazoniation, 3D QSAR

Publ.-Id: 14449 - Permalink


Actinide Interactions with Bacteria
Moll, H.; Bernhard, G.;
Microbes are widely distributed in nature also under harsh conditions (e.g., high salinity; low permeability; high and low temperatures). They can strongly influence the migration of hazardous actinides in the environment once they have been released. This is demonstrated by an increased interest in studies exploring the interaction processes involving actinides and bacteria during the last years. However, worldwide only little detailed information is available about the biodiversity and microbial influences on radionuclide migration under the conditions of a deep nuclear repository.
The presentation covers the broad topic of actinide interactions with bacteria. A short overview about the determination of the microbial diversity giving the dominant bacterial strains will be given. In more detail, the manifold interaction process of bacteria with actinides will be highlighted based on selected examples.
With this presentation we want to point out the importance of actinide-microbe interactions for the disposal of nuclear waste.
Keywords: microbes, actinides, nuclear waste disposal
  • Lecture (Conference)
    Actinide and Brine Chemistry in a Salt-Based Repository (ABC-SALT) International Workshop, 15.-17.09.2010, Carlsbad, New Mexico, USA

Publ.-Id: 14448 - Permalink


Terahertz nonlinear optics using intraexcitonic quantum well transitions: sideband generation and AC Stark splitting
Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Andrews, A. M.; Schartner, S.; Strasser, G.; Helm, M.;
Intense THz electric fields coupling to intraband excitations can modify the interband absorption of semiconductors. A classical nonlinear mixing process is the sideband generation, where a ps NIR laser beam is mixed with the THz beam to generate sidebands at ωNIR ± n × ωTHz (integer n). In an undoped GaAs/AlGaAs multi quantum well film (substrate etched away) we observe several even-order sidebands using an all-normal-incidence geometry for the NIR and THz laser pulses [1]. Varying THz and NIR frequencies, we identify several resonances, where the intraexciton 1s-2p transition (at ~9 meV) makes the strongest contribution. Fig. 1(a) shows a typical NIR transmission spectrum with the NIR fundamental at the hh(1s) state and the resulting even-order sidebands.
In a second experiment we monitor the sample’s broadband transmission under THz pumping. THz light can couple and “dress” two resonant states, giving rise to the Autler-Townes or AC Stark effect [2, 3]. Fig. 1(b) shows the measured transmission spectra without (dashed line) and with (solid line) THz light at a THz peak intensity of 220 kW/cm² for THz pumping above (14 meV), near (10.5 meV) and below (6.1 meV) resonance. Near resonance (10.5 meV) we observe a distinct line splitting (see arrows), which represents the first clear evidence of the Autler-Townes effect in an intraexcitonic transition. Above and below resonance, low- and high-energy shoulders, respectively, are observed (see arrows). We discuss our findings on the basis of a simple two-level model that describes the situation surprisingly well near resonance up to a THz field strength of 10 kV/cm, corresponding to a Rabi energy of 0.6 times the 1s-2p transition energy. This is already well beyond the rotating-wave approximation of our model. Observed deviations would have to be addressed within a full many-body theory dealing with the complete set of excitonic states as well as with the possibility of exciton field ionization. Note that for the above parameters the ponderomotive energy is 3 meV, comparable to the exciton transition/ionization energy and the Rabi energy, an extremely non-perturbative regime with a Keldysh parameter near unity.

References:
[1] M. Wagner et al., Appl. Phys. Lett. 94, 241105 (2009).
[2] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[3] S. G. Carter et al., Science 310, 651 (2005).
Keywords: AC Stark effect, Autler Townes effect, excitons, terahertz, sideband generation, nonlinear optics
  • Lecture (Conference)
    NOEKS 10 - 10th International workshop on Nonlinear Optics and Excitation Kinetics in Semiconductors, 16.-19.08.2010, Paderborn, Deutschland

Publ.-Id: 14447 - Permalink


Terahertz induced intra-excitonic Autler-Townes effect in semiconductor quantum wells
Wagner, M.; Schneider, H.; Stehr, D.; Winnerl, S.; Helm, M.; Roch, T.; Andrews, A. M.; Schartner, S.; Strasser, G.;
When light is resonant with a material excitation the optical Stark or Autler-Townes (AT) effect couples the involved energy states and alters their energy, i.e. the states get “dressed” by the light-matter interaction. This fundamental quantum-mechanical feature of light-matter interaction was originally observed in atomic spectroscopy [1]. However, despite some theoretical work, it took a long time to the first observation of the AT effect for terahertz (THz) light coupled to hole [2] and electron [3] intersubband transitions in semiconductor quantum wells.
Here, we report clear evidence of the intra-excitonic AT effect. In our experimental work we study the NIR transmission at low temperature of a GaAs/AlGaAs multiple quantum well film (substrate etched away) exposed to strong picosecond THz pulses from the free-electron laser (FEL) at FZD. NIR spectra are recorded for a series of different THz frequencies and intensities. When tuning the THz photon energy in the range from 6 to 17 meV around the 1s-2p intra-excitonic transition energy that lies at ~9 meV, we observe a line splitting when pumping near resonance, and low- and high-energy shoulders, respectively, when pumping off resonance. This behavior is consistent with the AT effect. In Fig. 1 the measured absorption around the heavy-hole 1s exciton is displayed for different THz photon energies, showing the two dressed states and their expected anticrossing behavior. We discuss our experimental evidence of a coupling between the NIR “bright” 1s state and the NIR “dark” 2p state on the basis of a two-level model. Near resonance (10.5 meV) we find that our simplified model describes the situation surprisingly well up to a THz field strength of 10 kV/cm (I = 650 kW/cm2), corresponding to a Rabi energy of 0.6 times the 1s-2p transition energy. This is already well beyond the limits of the rotating-wave approximation. At the highest field strengths, the Rabi sidebands appear to start interacting with other exciton states. A full many-body theory would have to deal with the complete manifold of excitonic states as well as with the possibility of exciton field ionization. Note that for the above parameters in our case the ponderomotive energy is 3 meV and thus of the same order as the exciton transition/ionization energy (i.e. Keldysh parameter near unity) and the Rabi energy, an extremely non-trivial regime.
Using picosecond THz pulses we finally demonstrate that the induced absorption change occurs adiabatically only during the THz pulse. This ultrashort change that corresponds to an up to 20-fold increase in transmission can in principle be exploited in NIR modulators or switches.

[1] S. H. Autler and C. H. Townes, Phys. Rev. 100, 703 (1955).
[2] S. G. Carter et al., Science 310, 651 (2005).
[3] J. F. Dynes, M. D. Frogley, M. Beck, J. Faist, and C. C. Phillips, Phys. Rev. Lett. 94, 157403 (2005).
Keywords: AC Stark effect, Autler Townes effect, excitons, terahertz, sideband generation, nonlinear optics
  • Lecture (Conference)
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
  • Contribution to proceedings
    ICPS 2010, 30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul, Südkorea
    AIP Conference Proceeding 1399 (2011) 479-480; doi: 10.1063/1.3666462

Publ.-Id: 14446 - Permalink


Interaction of U(VI) with Schizophyllum commune
Günther, A.; Roßberg, A.; Raff, J.; Bernhard, G.;
Biosorption processes of heavy metals and actinides like uranium by fungal cells play an important role in the mobilisation or immobilisation of these elements in nature. Different sorption experiments of U(VI) with Schizophyllum commune at different initial uranium concentrations and therewith connected varying initial uranium speciation showed high uranium sorption capacities in the pH range from 4 to 7. Formed uranium complexes were investigated by means of time-resolved laser-induced fluorescence spectroscopic measurements (TRLFS). The obtained spectra show clearly differences between the emissions properties of the uranium species on fungi and the dissolved uranium species in the initial mineral medium. While the oxidation state of uranium remained unchanged during the sorption process, the uranium speciation changes significantly. Extra- and/or intracellular phosphate groups are the predominant binding places of uranium due to our first spectroscopic results. X-ray absorption fine structure spectroscopic measurements (EXAFS) were performed for a structural characterisation of formed uranium-fungi species and a verification of the TRLFS results.
Keywords: Uranium(VI), fungi, TRLFS, EXAFS
  • Lecture (Conference)
    9th Symposium on remediation in Jena, "Jenaer Sanierungskolloquium", 04.-05.10.2010, Jena, BRD

Publ.-Id: 14445 - Permalink


Nanostructuring of BaF2 (111) surfaces by single slow highly charged ions
El-Said, A. S.; Heller, R.; Facsko, S.;
The creation of surface nanostructures in BaF2 (111) surfaces was studied after irradiation with slow highly charged Xe ions from the Dresden-EBIT (Electron Beam Ion Trap). After irradiation, the crystals were investigated by scanning force microscopy (SFM). Using specific ion parameters, the topographic images show nanohillocks emerging from the surface. Additionally, we used the technique of selective chemical etching to reveal the lattice damage created by ion energy deposition below and above threshold needed for surface hillocks formation. The role of both potential and kinetic energy as well as a comparison with results for swift heavy ion irradiations of BaF2 single crystals are presented.
Keywords: highly charged ions, nanostructures
  • Nuclear Instruments and Methods in Physics Research B 269(2011), 901-904

Publ.-Id: 14444 - Permalink


Ion-Induced Nanoscale Ripple Patterns on Si Surfaces - Theory and Experiment
Keller, A.; Facsko, S.;
Nanopatterning solid surfaces by low-energy ion bombardment has received considerable interest in the recent years. This interest was partially motivated by promising applications of nanopatterned substrates in the production of functional surfaces. Especially nanoscale ripple patterns on Si surfaces have attracted attention both from a fundamental and an application related point of view. This paper summarizes the theoretical basics of ion-induced pattern formation and compares the predictions of the various continuum models to experimental observations with special emphasis on the morphology development of Si surfaces during sub-keV ion sputtering.
Keywords: nanopatterning; ion sputtering; surface morphology; continuum theory

Publ.-Id: 14443 - Permalink


Vibrational spectroscopy of actinyl sorption complexes
Gückel, K.;
Information about motivation and objectives as well as first results of the PhD thesis
  • Poster
    FZD PhD Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14442 - Permalink


Stofftransport bei Bergbaufolgeschäden und Altlastensanierung
Wolf, M.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    GEOforum Leipzig, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14441 - Permalink


Geochemische Wechselwirkungen bei Anwesenheit von Huminstoffen in Untertagedeponien
Fellmer, F.;
Es ist kein Abstract vorhanden.
  • Lecture (others)
    GEOforum 2010, 08.06.2010, Leipzig, Deutschland

Publ.-Id: 14439 - Permalink


Ultrafast three-dimensional X-ray computed tomography
Bieberle, M.; Hampel, U.; Barthel, F.; Menz, H.-J.; Mayer, H.-G.;
X-ray computed tomography (CT) is nowadays a well established 2D and 3D visualization technique in medicine and non-destructive testing. An increasing number of scientific and engineering problems requires three-dimensional imaging capabilities, since structures of growing complexity are seldom seizable by a cross-section only. Because CT scanning requires sampling of radiographic projections from different viewing angles around an object, typically mechanical rotation mechanisms, either for the source-detector compound or the object, are employed by common CT systems. Hence, they are quite slow and their application in the study of fast processes, such as multiphase flows or live animals, was so far impossible.
Here we introduce a new ultrafast three-dimensional X-ray CT method based on electron beam scanning, which achieves imaging rates of 500 volume images per second. It represents an extension of a two-dimensional ultrafast electron beam CT modality presented earlier1. Although this 2D CT system reaches cross-sectional frame rates of up to 10,000 images per second, the new system is superior for the analysis of processes and moving objects, where structural changes occur in three dimensions. With an experimental study that is reported here we could demonstrate the capability of this new method to recover the structure of typical gas-solid and gas-liquid two-phase flows. Thus, ultrafast three-dimensional X-ray CT forms a practical alternative to high-speed videometry and furthermore provides non-superimposed density distributions even from opaque media.
Keywords: ultrafast, X-ray, 3D, computed tomography

Publ.-Id: 14437 - Permalink


Molecular and microscopical characterization of the algae mat from the „Gessenhalde“ (Ronneburg/Eastern Thuringia) and the proof of the retention of uranium
Zirnstein, I.; Krawczyk-Bärsch, E.; Arnold, T.; Röske, I.;
Next to the test-field site of the former uranium leaching dump “Gessenhalde” (Ronneburg/Eastern Thuringia), which is part of a research program of the Friedrich-Schiller University, biofilms were sampled from a creek and investigated by PCR and cloning, light microscopy, CLSM and TEM/EDX. The molecular and microscopical characterization of the eukaryote diversity showed a wide spectrum of free living eukaryote microorganism, like the filamentary green algae Microspora and Klebsormidium as the dominant eukaryote. Flagellates, ciliates and rotaroria are present as representatives of the protozoa in minor amount. The water of the creek is characterized by a low pH of 3.3 – 3.9 and a uranium concentration, which ranges seasonally between 1x10-6 M/L and 6x10-6 M/L. Following up the question if the algae mat may have immobilized uranium by biosorption or bioaccumulation the filamentary algae were selected and investigated microscopically and spectroscopically by CLSM and TEM/EDX. Since the results did not provide any microscopic and spectroscopic evidence for the presence of uranium immobilization, the filamentary algae were cultured in rain water with a pH adjusted to 6,0. After the addition of uranium as UO2(ClO4)2 in the ecologically relevant concentration of 1x10-5 M/L the algae showed characteristic fluorescence spectra in the wavelength range of 480-560 nm, which is typical for uranium (VI). The results demonstrated that the actual in-situ geochemical conditions of the creek from the "Gessenhalde" inhibit the retention of uranium by the algae mat. The removal of uranium from the aqueous phase requires the cultivation of algae in a neutral media.
Keywords: biofilm, algae, uranium
  • Poster
    9. Sanierungskolloquium, 04.-05.10.2010, Jena, Deutschland

Publ.-Id: 14436 - Permalink


Interaction of Selected Actinides with Microorganisms Relevant to Nuclear Waste Disposal
Frost, L.; Moll, H.; Krawczyk-Bärsch, E.;
The sorption behavior/ retardation of actinides (uranium) in deep geological formations like clay, granite or salt is determined by the constitution of the host rock material and the presence of bioligands and microbes. To which extent can bioligands and microbes lead to a mobilisation of the respective actinyl ion?
By presenting results of our current research categorical examples for the interaction of uranium(VI) with above mentioned interaction partners are given:
- Interaction with host rock material: the anaerobic sorption of U(VI) onto Opalinus Clay
- Interaction with bioligands: interaction of U(VI) with the model ligand benzoic acid investigated by UV-vis spectroscopy and cryo-TRLFS
- Interaction with microbes: interaction of U(VI) with the Äspö bacterium Pseudomonas fluorescens (HAADF-TEM measurements and uranium accumulation experiments)
Keywords: Uranium, Opalinus Clay, Pseudomonas fluorescens, UV-vis spectroscopy, cryo-TRLFS
  • Poster
    5th FZD Ph.D. Seminar, 22.-24.09.2010, Krögis, Deutschland

Publ.-Id: 14435 - Permalink


Analysis of the influence of different arrangements for ZrH moderator material on the performance of a SFR core
Merk, B.; Weiß, F. P.;
The structure for the development of a fuel element design with reduced sodium void achieved by the use of the moderating material ZrH is investigated. In the study the sodium void effect, as well as the major feedback coefficients are analyzed. Besides the feedback coefficients, the influence on the operational parameters like neutron flux distribution, power distribution, and burnup distribution is investigated for the different possibilities of arranging the moderating material in the fuel element. Additionally, the fuel cycle parameters breeding and minor actinide production are analyzed. For a first evaluation of the behavior during transients the influence of temperature changes in the ZrH and the consequences of dissociation of the ZrH on the fuel element power are studied.
Keywords: Sodium void, fast reactor, zirconium hydride

Publ.-Id: 14434 - Permalink


Electromagnetic induction in non-uniform domains
Giesecke, A.; Stefani, F.; Gerbeth, G.;
Numerical simulations of the electromagnetic induction equation are carried out applying a grid based finite volume method where insulating boundaries are treated by the boundary element method. A prescribed flow of liquid sodium provides the energy source for self-generation of a magnetic field and the influences of non-uniform material properties on the induction process are examined by means of internal assemblies and outer container walls with high conductivity or high permeability.

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 enforcing 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.

The third examined configuration is motivated by an application of the contactless inductive flow tomography (CIFT) in a continuous casting model experiment. Consideration of the finite conductivity of the copper container walls results in a quantitative modification of the current distribution within the solid material. An enhanced current yields an amplified induced magnetic field outside of the container which must be considered in the reconstruction of the fluid velocity field.
Keywords: Dynamo Conductivity Permeability Induction
  • Lecture (Conference)
    Workshop on Numerical Simulations of MHD flows, 18.-20.10.2010, Karlsruhe, Deutschland

Publ.-Id: 14433 - Permalink


Ein Modell zur Beschreibung der Kühlmittelvermischung und seine Anwendung auf die Analyse von Borverdünnungstransienten in Druckwasserreaktoren
Kliem, S.;
Es wurde ein Modell zur realistischen Beschreibung der Kühlmittelvermischung innerhalb des Reaktordruckbehälters eines Druckwasserreaktors entwickelt und validiert. Dieses schnell rechnende Modell basiert auf dem Prinzip der linearen Superposition der Antwortfunktionen auf Dirac-Impuls-ähnliche Störungen der Kühlmittelparameter. Es wurde in den gekoppelten Programmkomplex DYN3D/ATHLET als Schnittstelle zwischen dem eindimensionalen Thermohydraulikprogramm ATHLET und dem dreidimensionalen neutronenkinetischen Kernmodell DYN3D eingebunden und simuliert in effizienter Weise die Vermischung des Kühlmittels innerhalb des RDB.
Für die Analyse von hypothetischen Borverdünnungsstörfallen wurde eine Methodik entwickelt, die auf dem neuen Modell zur Beschreibung der Kühlmittelvermischung basiert. Diese Methodik besteht aus einer Kombination von stationären und transienten Rechnungen, in denen die Vermischung der deborierten Pfropfen auf dem Weg zum Reaktorkern in realistischer Weise simuliert wird. Über die Variation der Größe des deborierten Kühlmittelpfropfens kann der gewünschte Grad an Konservativität für die Analysen vorgegeben werden.
Diese neue Methodik wurde erfolgreich auf zwei verschiedene Borverdünnungsstörfalle angewandt. Neben dem Start der ersten Hauptkühlmittelpumpe bei Vorhandensein eines deborierten Kühlmittelpfropfens im kalten Strang des Primärkreislaufes wurde ein Deborierungsstörfall im Nachkühlbetrieb betrachtet. In beiden Fällen zeigten die Ergebnisse der Parameterstudie für eine generische Kernkonfiguration, dass es selbst bei Annahme des maximal möglichen Pfropfenvolumens zwar zur Rekritikalität des abgeschalteten Reaktors aber nicht zu einer unzulässigen Erhöhung der Hüllrohrtemperatur kommt. Wesentliche Ursache dafür ist die Verwendung realistischer zeitabhängiger Verteilungen der Borkonzentration am Eintritt in jedes Brennelement.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-539 2010
    ISSN: 1437-322X

Downloads:

Publ.-Id: 14432 - Permalink


Aqueous curium(III) phosphate species characterized by time-resolved laser-induced fluorescence spectroscopy
Moll, H.; Brendler, V.; Bernhard, G.;
The formation of aqueous Cm(III) phosphate complexes was studied at room temperature by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in 0.1 M NaClO4 solutions. The experiments were perfomed at a fixed total Cm(III) concentration of 3x10-7 or 2x10-8 M by varying the phosphoric acid concentration (3x10-5 - 0.1 M) and the pH (1.4 - 6.0). The red shift of the excitation and emission spectra, as well as the increase of luminescence lifetimes clearly showed the influence of phosphate on the aqueous Cm(III) speciation. In acidic phosphate solutions ([H3PO4] < 0.1 M, pH 1.4 - 2.6) an increase in luminescence intensity was detected due to complexation with H2PO4 -. At [H3PO4] > 4x10-4 M and between pH 4.0 and 6.0 in general a decrease in luminescence intensity affiliates the complexation with HPO42-. Two Cm(III)-phosphate complexes could be identified from the emission data, CmH2PO4 2+ and CmHPO4+, having peak maxima at 599.6 and 600.8 nm, respectively. TRLFS in combination with ultra-filtration (1 kD) showed that the formation of CmHPO4+ is affiliated by the generation of Cm(III)-phosphate colloids especially at [H3PO4] > 0.002 M and pH > 5. Cm(III)-phosphate colloids formed at pH 5 and 6 are characterized by an emission maximum at 603.1 nm. Based on the factor analysis of the emission data the stability constants of the two complexes were calculated to be log ß121 = 20.23 ± 0.13 and log ß111 = 16.54 ± 0.80 at an ionic strength of 0.1 M (NaClO4).
Keywords: Curium(III), Phosphoric acid, Stability constant, Speciation, Complexation, TRLFS, Ultra-filtration

Publ.-Id: 14431 - Permalink


Test site Gessenwiese: Results in TRLFS investigations on surface water and pore waters, and preliminary results on plant saps concerning uranium speciation
Baumann, N.; Arnold, T.;
Plants may take up uranium from contaminated sites and thus may represent a potential risk. To evaluate the risk of uranium being transferred from the environment into the human food chain knowledge concerning the uranium speciation is essential since reactivity and toxicity of uranium largely depend on its speciation.
Plants take up their nutrients from the soil in dissolved form and thus uranium may enter plants as dissolved species. To study this process the speciation of uranium in a uranium contaminated site, i.e. Gessenheap near Ronneburg in Saxony/Germany was studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) in the aqueous phase, i.e. in surface water (drainage channel on the Gessenheap) and in pore water (approximately 0.5 – 1 m below surface of test site Gessenwiese). In both waters uranium sulfate species dominate the uranium speciation and clearly show that uranium sulfate species are in contact with plant components.
In a second step we determined the uranium concentration in the plants obtained from the test field Gessenheap by ICP-MS. For these analyses cell saps of birch leaves, of a birch boletus, and of compartments of butterbur (leaves, roots, and sprouts) were obtained by ultra centrifugation. The highest uranium concentration was found in sap samples from roots of butterbur with 39.3 ppb uranium (approximately 1.5 • 10-7 M uranium); in the sap samples of birch leaves 18.1 and 16.6 ppb uranium, respectively were detected. In all other sap samples the uranium contents were below 4 ppb uranium. The uranium content in the studied dried plant materials were less than 2.2 ppb, and dried birch leaves contains less than 0.1 ppb uranium.
The above listed uranium concentrations turned out to be too low to be successfully analyzed by TRLFS. In addition, we have to mention that plant sap may contain substances which quench the fluorescence signal of uranium (VI), e. g. some heavy metal ions or organic compounds. For future studies plant samples containing higher uranium concentrations are used for TRLFS investigations, possibly mosses or lichens.
Keywords: TRLFS, uranium speciation
  • Lecture (Conference)
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany
  • Contribution to proceedings
    9th Symposium on remediation in Jena "Jenaer Sanierungskolloqium", 04.-05.10.2010, Jena, Germany

Publ.-Id: 14430 - Permalink


Terahertz activated luminescence of trapped carriers in InGaAs/GaAs quantum dots
Bhattacharyya, J.; Wagner, M.; Helm, M.; Hopkinson, M.; Wilson, L. R.; Schneider, H.;
Optical properties and interdot transfer dynamics of trapped carriers in InGaAs quantum dots (QDs) are investigated. Time resolved photoluminescence (PL) was measured for time-delayed interband and intraband excitations. Terahertz activated luminescence (TAL) from trapped carriers having lifetimes of ~250 ns at 8 K, was observed. Spectral shift of the TAL with respect to the PL showed the trionic nature of the PL in the n-doped QDs. With increasing terahertz excitation intensity, the TAL increased and reached saturation. The activation energy associated with the trapped carrier decay was quite close to the intersublevel transition energy (~20 meV) indicating trapping in the QDs.
Keywords: Quantum dots, Photoluminescence quenching, trapped carriers

Publ.-Id: 14427 - Permalink


Development of the coupled 3D neutron kinetics/thermal-hydraulics code DYN3D-HTR for the simulation of transients in block-type HTGR
Rohde, U.; Baier, S.; Duerigen, S.; Fridman, E.; Merk, B.; Weiss, F.-P.;
At the Forschungszentrum Dresden-Rossendorf (FZD), the Light Water Reactor (LWR) dynamics code DYN3D is extended and adopted for the application to block-type High temperature gas-cooled reactor (HTGR). DYN3D is a two-group diffusion code for 3D steady-state and transient core calculations based on nodal expansion methods. In addition to the neutron kinetics, it disposes of a thermal-hydraulics model for flow in parallel coolant channels. Macroscopic cross section data libraries precalculated with variation of burn-up, reactor poisons concentrations and thermal-hydraulic feedback parameters are linked to the code. Recently, a multi-group version of the code was developed.
In this paper, we give an overview of the latest developments of DYN3D concerning block-type HTGR.
The SP3 transport approximation is implemented into the multi-group DYN3D code to take anisotropy of the neutron flux and heterogeneity of the core more precisely into account. The SP3 method previously implemented into DYN3D for square fuel element geometry of LWR is being extended for hexagonal geometry of the graphite blocks, where the hexagons are subdivided into triangular nodes to be able to perform a systematic mesh refinement.
The main challenge in cross section generation for the HTGR core calculations is the treatment of the so-called “double heterogeneity”. The Reactivity equivalent Physical Transformation (RPT) approach is applied in order to eliminate the double-heterogeneity of HTGR fuel elements in HELIOS calculations. The full core analysis of the reference simplified HTGR core is performed with DYN3D using macroscopic nodal cross sections provided by HELIOS. The DYN3D results are verified against full core Monte Carlo simulations.
A 3D heat conduction module coupled with a channel-type coolant flow model is implemented to take into account the temperature reactivity feedback to neutronics physically correctly. It is shown that there is significant redistribution of the produced heat by heat conduction between the graphite blocks.
Keywords: high temperature reactor, reactor dynamics, computer code, double heterogeneity, SP3 transport approximation, heat conduction, temperature reactivity feedback, computer code
  • Lecture (Conference)
    5th Topical Meeting in High Temperature Reactor Technology, 18.-20.10.2010, Prague, Czech Republic
  • Contribution to proceedings
    5th Topical Meeting on High Temperature Reactor Technology, 18.-20.10.2010, Pargue, Czech Republic
    Conference Website http://www.htr2010.eu/authors-area/upload/docs/htr2010_pdfonly.rar, Paper #036

Publ.-Id: 14426 - Permalink


Very large DPSS lasers are coming
Toepfer, T.; Neukum, J.; Hein, J.; Siebold, M.;
New alcaline-earth fluoride laser materials and ever-improving diode-laser module technology are bringing very high-energy, moderate-to high-repetition-rate DPSS lasers for research closer to reality.
Keywords: High-energy, diode-pumped, solid-state lasers
  • Open Access LogoLaser Focus World 46(2010)10, 64-67

Publ.-Id: 14425 - Permalink


Excitation wavelength dependence of phase matched terahertz emission from a GaAs slab
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.;
We report on phase matched THz emission from GaAs using the anomalous dispersion introduced by optical phonon absorption at the reststrahlenband in GaAs. For this system tunability of the emitted THz frequencies by changing the near infrared excitation wavelength is predicted. We investigate this phenomenon for an oversized double metallized GaAs waveguide. A shift in the THz spectra is observed when the near-infrared wavelength is varied. Enhanced emission is found when phase matching is achieved at 1.4 µm.
Keywords: Terahertz, far infrared, ultrafst nonlinear optics
  • Open Access LogoOptics Express 18(2010)19, 19574-91580

Publ.-Id: 14424 - Permalink


Longitudinal Fields in Focused Radially Polarized Terahertz Beams
Winnerl, S.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.;
We study the spatial and temporal structure of focused THz beams of radial polarization. Strong longitudinal field components localized at the axis of propagation are observed. The phase of the longitudinal field components is shifted by pi/2 with respect to the transverse field components.
Keywords: Terhertz, vector beams
  • Invited lecture (Conferences)
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
  • Contribution to proceedings
    35th International Conference on Infrared, Millimeter and Terahertz Waves, 05.-10.09.2010, Rome, Italy
    Conference Digest of the 35th International Conference on Infrared, Millimeter and Terahertz Waves

Publ.-Id: 14423 - Permalink


Thermal Emittance Measurement of the Cs2Te Photocathode in FZD Superconducting RF Gun, WEPB22
Xiang, R.; Arnold, A.; Michel, P.; Murcek, P.; Teichert, J.;
The thermal emittance of the photocathode is an interesting physical property for the photoinjector, because it decides the minimum emittance the photoinjector can finally achieve. In this paper we will report the latest results of the thermal emittance of the Cs2Te photocathode in FZD Superconducting RF gun. The measurement is performed with solenoid scan method with very low bunch charge and relative large laser spot on cathode, in order to reduce the space charge effect as much as possible, and meanwhile to eliminate the wake fields and the effect from beam halos

http://www.maxlab.lu.se/maxlab/conference/fel2010/index.html
  • Poster
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
  • Contribution to proceedings
    FEL 2010 Conference, 23.-27.08.2010, Malmö, Sweden
    Proceedings of the FEL 2010

Publ.-Id: 14422 - Permalink


QCD sum rules for D mesons in dense and hot nuclear matter
Hilger, T.; Schulze, R.; Kämpfer, B.;
Open charm mesons (pseudo-scalar and scalar as well as axial-vector and vector) propagating or resting in nuclear matter display an enhanced sensitivity to the chiral condensate. This offers new prospects for seeking signals of chiral restoration, in particular in pA and \bar{p}A reactions as envisaged in first-round experiments by the CBM and PANDA collaborations at FAIR. Weinberg-type sum rules for charming chiral partners are presented, and the distinct in-medium modifications of open-charm mesons are discussed. We also address the gluon condensates near Tc and their impact on QCD sum rules.

Publ.-Id: 14420 - Permalink


[18F]NS10743: Characterisation Of A Selective a7 Nicotinic Acetylcholine Receptor (a7 nAChR) Radioligand In Pig Brain By PET
Deuther-Conrad, W.; Fischer, S.; Hiller, A.; Funke, U.; Østergaard Nielsen, E.; Brunicardi Timmermann, D.; Steinbach, J.; Peters, D.; Brust, P.;
Introduction: Alterations of a7 nAChR have been observed in schizophrenia, brain trauma and neurodegenerative diseases. For PET imaging of a7 nAChR [18F]NS10743 has been successfully developed evaluated in mice by tissue distribution and specificity studies. Here we report on baseline and blocking PET studies with [18F]NS10743 in pig brain.
Methods: [18F]NS10743 was synthesized with high specific activity (>150 GBq/μmol) and radiochemical purity (>99%). Dynamic PET scanning was performed in anaesthetized female piglets (13-15 kg), intravenously injected with ~ 330 MBq [18F]NS10743 (total mass ~ 472 ng) for 120 min. Three animals additionally received 3 mg/kg of the a7 nAChR partial antagonist NS6740 at 10 min pre-tracer injection followed by a continuous infusion (1 mg/kg/h). Plasma samples were taken and metabolite-corrected input functions were estimated. Individual regions of interest were defined using an MRI-based template of pig brain. SUV and distribution volume (VT = K1/k2) were estimated. The ratio of specifically bound radioligand and non-displaceable radioligand in brain tissue was calculated from the VT values by BPND = (VT region - VT reference)/VT reference.
Results: [18F]NS10743 readily passed the blood-brain barrier and the uptake of radioactivity peaked with SUV = 2.23 ± 0.71 at 8 min in the baseline scan while in NS6740-blocking studies the radioactivity levels peaked significantly earlier (SUV = 3.02 ± 1.28 at 5 min) and decreased faster. At the end of study (between 90 and 120 min p.i.) SUV was significantly decreased by NS6740 in allinvestigated brain regions except olfactory bulb, which was chosen as reference region for calculation of BPND. At baseline, a VT value of 6.07 ± 1.54 was estimated for the whole brain with the highest radiotracer accumulation in the temporal, parietal, and occipital lobe, thalamus, striatum, and middle cortex (VT = 7.27 ± 1.95 – 7.10 ± 1.58). Intermediate binding was observed in hippocampus, colliculi, midbrain, frontal lobe, and ventral cortex (VT = 6.76 ± 1.71 – 6.09 ± 1.05), and lowest values were assessed in the cerebellum, pons, and olfactory bulb (VT = 5.71 ± 1.18 – 4.11 ± 0.96). Baseline BPND values for high (temporal lobe), median (hippocampus) and low specific binding (cerebellum) were 0.76 ± 0.07, 0.54 ± 0.08, and 0.39 ± 0.08, respectively. NS6740 significantly reduced the binding potential BPND in regions with high [18F]NS10743 binding (temporal lobe: -29 %, p = 0.01; midbrain: -35 %, p = 0.02) while the decrease in regions with low binding was not significant (cerebellum: -16 %, p = 0.2).
Conclusion: These data make [18F]NS10743 a reasonable candidate for further development of in vivo a7 nAChR imaging by PET. The challenge to improve the binding potential of [18F]NS10743, limited mainly by the low density of a7 nAChR expression in the brain and reflected by rather small regional differences in baseline uptake of [18F]NS10743, will be met by further modifications of the NS10743 core structure intended to increase the target affinity of the tracer compound.
the target affinity of the tracer compound.
Keywords: [18F]NS10743; a7 nAChR; PET
  • Lecture (Conference)
    NRM2010 (Neuroreceptor Mapping Congress), 22.-24.07.2010, Glasgow, Großbritannien
  • Abstract in refereed journal
    NeuroImage 52(2010)1
    DOI: 10.1016/j.neuroimage.2010.04.230

Publ.-Id: 14418 - Permalink


Extension of CFD codes - application to two-phase flow safety problems, phase 2
Bestion, D.; Anglart, H.; Mahaffy, J.; Lucas, D.; Song, C. H.; Scheuerer, M.; Zigh, G.; Andreani, M.; Kasahara, F.; Heitsch, M.; Komen, E.; Moretti, F.; Morii, T.; Mühlbauer, P.; Smith, B. L.; Watanabe, T.;
This document is an extension of the NEA/SEN/SIN/AMA(2006)2 report produced by the Writing Group 3 on the extension of CFD to two-phase flow safety problems, which was formed following the recommendations made at the “Exploratory Meeting of Experts to Define an Action Plan on the Application of Computational Fluid Dynamics (CFD) Codes to Nuclear Reactor Safety Problems” held in Aix-en-Provence, in May 2002. Extension of CFD codes to two-phase flow is a chance for safety investigations, by giving some access to smaller scale flow processes which were not seen by present tools. Using such tools as part of a safety demonstration may bring a better understanding of physical situations, more confidence in the results, and an estimation of safety margins. The increasing computer performance allows a more extensive use of 3D modelling of two-phase Thermalhydraulics with finer nodalization. However, models are not as mature as in single phase flows and a lot of work has still to be done on the physical modelling and numerical schemes in such two-phase CFD tools. The Writing Group listed and classified the NRS problems where extension of CFD to two-phase flow may bring real benefit and also classified different modelling approaches. First ideas were reported about the specification and analysis of needs in terms of validation and verification.
Keywords: CFD, two phase flow, nuclear safety research
  • Other report
    OECD: Report NEA/CSNI/R(2010)2, 2010
    137 Seiten

Publ.-Id: 14416 - Permalink


Studies on the patterning effect of copper deposits in magnetic gradient fields
Tschulik, K.; Sueptitz, R.; Koza, J.; Uhlemann, M.; Mutschke, G.; Weier, T.; Gebert, A.; Schultz, L.;
Electrochemical Cu deposition was performed from electrolytes containing 0.1 M to 1 M CuSO4 in a well-defined magnetic gradient field. Patterned deposits resulted in all cases showing a strong correlation to this gradient field. It was observed that with increasing Cu2+ concentration the structuring effect decreases in terms of differences in topography and morphology. An explanation of this effect is presented based on local convection induced by the magnetic field gradient force which is dependent on the concentration gradient established during the deposition. Superimposed effects of Lorentz force driven convection were observed for high Cu2+ concentrations, and their influence on the deposition process is discussed.
Keywords: magnetic gradient field, deposit patterns, Lorentz force

Publ.-Id: 14415 - Permalink


The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf
Krause-Rehberg, R.; Butterling, M.; Jungmann, M.; Krille, A.; Anwand, W.; Brauer, G.; Rogov, A.; Noack, K.; Cowan, T.; Wagner, A.;
The heart of the radiation source ELBE at the Forschungszentrum Dresden-Rossendorf (FZD) is a 40-MeV LINAC with an average current of 1 mA. Due to its superconducting technology, the time structure is different from conventional LINACs. Electron bunches as short as 2 ps with a 26 MHz repetition rate can be used in continuous operation (cw) mode. This is an ideal host for an intense positron source. After organizing SLOPOS-9 in Rossendorf, it was decided to add EPOS (ELBE Positron Source) to the existing experiments at ELBE. EPOS consists of two LINAC-based setups, Gamma-induced Positron Spectroscopy (GiPS) and Monoenergetic Positron Spectroscopy (MePS). The GiPS setup, where positrons are produced inside the whole sample volume by pair production using a pulsed gamma beam, is unique so far. Here, bulky samples such as coarse powders, dispersions, but also liquids or whole devices of non-destructive testing can be investigated by all positron techniques important for materials science (lifetime spectroscopy, age-momentum correlation, and coincidence Doppler broadening spectroscopy). The same techniques will be applied at the MePS setup, where slow, mono-energetic positrons will be generated by moderation to study near-surface layers. This system is still under construction. The EPOS system will be completed by two conventional setups, a continuous slow positron beam and a positron lifetime/ Doppler spectrometer, both operated by 22Na sources.
Keywords: Positron spectroscopy, Positron Annihilation, Monoenergetic Positrons, Gamma-induced Positrons, LINAC-based
  • Contribution to proceedings
    Proceedings of the International School of Physics "E. Fermi" - Physics with many positrons, 07.-17.07.2009, Varenna, Italia
    The EPOS system at the radiation source ELBE at For-schungszentrum Dresden-Rossendorf, Amsterdam: IOS Press Amsterdam

Publ.-Id: 14413 - Permalink


Pu recycling in a full Th-MOX PWR core: Part I - steady state analysis
Fridman, E.; Kliem, S.;
Current practice of Pu recycling in existing LWRs in the form of U-Pu mixed oxide fuel (MOX) is not efficient due to continuous Pu production from U-238. The use of Th-Pu mixed oxide (TOX) fuel will considerably improve Pu consumption rates because virtually no new Pu is generated from thorium. In this study, the feasibility of Pu recycling in a typical pressurized water reactor (PWR) fully loaded with TOX fuel is investigated.
Detailed 3-dimensional 100% TOX and 100% MOX PWR core designs are developed. The full MOX core is considered for comparison purposes. The design stages included determination of Pu loading required to achieve 18-month fuel cycle assuming three-batch fuel management scheme, selection of poison materials, development of the core loading pattern, optimization of burnable poison loadings, evaluation of critical boron concentration requirements, estimation of reactivity coefficients, core kinetic parameters, and shutdown margin.
The performance of the MOX and TOX cores under steady-state condition and during selected reactivity initiated accidents (RIA) is compared with that of the actual uranium oxide (UOX) PWR core.
Part I of this paper describes the full TOX and MOX PWR core designs and reports the results of steady state analysis. The TOX core requires a slightly higher initial Pu loading than the MOX core to achieve the target fuel cycle length. However, the TOX core exhibit superior Pu incineration capabilities.
The significantly degraded worth of control materials in Pu cores is partially addressed by the use of enriched soluble boron and B4C as a control rod absorbing material. Wet annular burnable absorber (WABA) rods are used to flatten radial power distribution. The temperature reactivity coefficients of the TOX core were found to be always negative. The TOX core has a slightly reduced, as compared to UOX core, but still sufficient shutdown margin.
In the TOX core βeff is smaller by about a factor of two in comparison to the UOX core and even lower than that of the MOX core. The combination of small βeff and reduce control materials worth may potentially deteriorate the performance under RIA conditions and requires an additional examination. The behavior of the considered cores during the most limiting RIAs, such as rod ejection, main steam line break, and boron dilution, is further investigated and reported in Part II of the paper.
Keywords: Pu recycling, PWR, Thorium, MOX, three-dimensional core analysis

Publ.-Id: 14412 - Permalink


The superconducting RF photoelectron source for the ELBE accelerator at Rossendorf
Teichert, J.;
Most of the proposed electron accelerator projects for future FELs, ERLs, or 4th generation light sources require electron beams with an unprecedented combination of high-brightness, low emittance and high average current. The ideal candidate for it is the superconducting RF photogun (SRF gun) which can be easily operated in CW like a DC photogun and may reach the beam quality of a normal conducting RF photogun. Challenges are the design of the superconducting cavity, the choice of the photocathode type, its life time, a possible cavity contamination, the difficulty of coupling high-average power into the gun and finally the risk of beam excitation of higher order cavity modes. At the FZ Dresden-Rossendorf a SRF gun has been developed and installed at the ELBE superconducting linac. The SRF gun is designed for an average current of 1 mA and an maximum electron energy of 9 MeV. The 1.3 GHz cavity consists of three full cells with TESLA geometry, a specially designed half-cell where the photocathode is placed. The photocathode with a Cs2Te photoemission layer is normal-conducting and cooled by liquid nitrogen. In the talk an overview of the technical concept, the RF properties, the photo cathode development, and beam parameter measurements will be given.
  • Lecture (others)
    ANKA Seminar, 08.02.2010, Karlsruhe, Deutschland

Publ.-Id: 14411 - Permalink


A new hexanuclear rhenium cluster complex with six terminal acetate ligands: Synthesis, structure, and properties of K4[Re6S8(CH3COO)6]·8H2O
Brylev, K. A.; Mironov, Y. V.; Fedorov, V. E.; Kim, S.-J.; Pietzsch, H.-J.; Stephan, H.; Ito, A.; Kitamura, N.;
A room-temperature reaction between [Re6S8(OH)6]4− and acetic acid in an aqueous solution resulted in the substitution of all terminal hydroxo groups by acetate ligands, affording a new hexanuclear anionic rhenium cluster complex [Re6S8(CH3COO)6]4−. The complex was isolated as a potassium salt with the composition of K4[Re6S8(CH3COO)6]·8H2O (1) and characterized by X-ray single-crystal diffraction and elemental analyses, IR, 1H NMR, UV–Vis, and luminescence spectroscopies.
Keywords: Synthesis; Cluster compounds; Rhenium; Carboxylate ligands; Luminescence

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Publ.-Id: 14409 - Permalink


Traveling-wave Thomson scattering and optical undulators for high-yield EUV and X-ray sources
Debus, A. D.; Bussmann, M.; Siebold, M.; Jochmann, A.; Schramm, U.; Cowan, T. E.; Sauerbrey, R.;
We present a novel high-yield Thomson scattering geometry that takes advantage of compact electron bunches, as available in advanced, low-emittance linear accelerators or laser wakefield accelerators. In order to avoid the restrictions on the X-ray photon yield imposed by the Rayleigh limit, we use ultrashort, pulse-front tilted laser pulses in a side-scattering geometry. Such a traveling-wave setup allows an overlap of electron and laser beams, even after propagating over distances much longer than the Rayleigh length. Experimental designs are discussed and optimized for different scattering angles. Specifically, to minimize group delay dispersion at large scattering angles > 10° degrees, we propose the use of varied-line spacing (VLS) gratings for spatio-temporal laser pulse shaping. Compared to head-on (180° degrees) Thomson scattering, interaction lengths are in the centimeter to meter range and photon numbers for ultrashort X-ray pulses can increase by several orders of magnitudes.
Keywords: Thomson Scattering, Traveling-Wave Thomson Scattering, Xray , EUV, VLS gratings
  • Applied Physics B 100(2010)1, 61-76
    DOI: 10.1007/s00340-010-3990-1
  • Lecture (others)
    WIP Seminar, 21.05.2010, FZD, Deutschland

Publ.-Id: 14408 - Permalink


Novel 99mTc '4 + 1' peptide conjugates: Tuning the biodistribution by variation of coligands
Künstler, J.-U.; Seidel, G.; Bergmann, R.; Gniazdowska, E.; Walther, M.; Schiller, E.; Decristoforo, C.; Stephan, H.; Haubner, R.; Steinbach, J.; Pietzsch, H.-J.;
A sophisticated coligand strategy is presented for peptide-derived radioconjugates based on 99mTc '4 + 1' mixed-ligand complexes. The new pharmacologically active coligands are assessed for 99mTc-labeling of the RGD-peptide cyclo(Arg-Gly-Asp-D-Tyr-Lys) which is an established vehicle to target avß3 integrins playing a crucial part in tumor pathogenesis.
Complexes of the general formula [99mTc(NS3R)X] were synthesized and evaluated, in which Tc(III) is coordinated by NS3R, a derivative of the tetradentate chelator 2,2´,2´´-nitrilotriethanethiol (NS3), and by X, a monodentate binding isocyanide bearing the biomolecule. The novel tetradentate chelators (NS3R = NS3crown, NS3en, NS3(COOH)3) constitute NS3 with a crown ether, an amine or a tricarboxylic acid as pharmacological modifiers. The isocyanides (X = L2-RGD, L2-Lys) contained the linker isocyanobutanoic acid (L2) coupled to N6-Lys of the RGD-peptide and additionally to a single Lys.
The lipophilicity (distribution coefficient log DO/W, pH = 7.4) of the RGD-containing radiotracers decreased in the order of the coligands NS3crown (-1.7 +/- 0.1), NS3en (-2.7 +/- 0.1) and NS3(COOH)3 (-3.3 +/- 0.1). In the same order of the coligands, the biodistribution of the series [99mTc(NS3R)(L2-RGD)] in normal rats showed a decrease of hepatobiliary and an increase of urinary excretion.
The ratio of specifically to unspecifically uptaken activity (sum of surface bound and internalized activity) in avß3 integrin-expressing M21 cells was in the range of approximately 4-5 and comparable for all [99mTc(NS3R)(L2-RGD)] tracers. The biodistribution of [99mTc(NS3en)(L2-RGD)] in v/v mice bearing M21 and M21L (control) tumor xenografts exhibited a specific tumor uptake with a low target-background ratio.
The metabolic stability of the [99mTc(NS3R)(L2-RGD)] tracers in normal rats was high, since 75-87% of the radioactivity in the plasma extract was assigned to the injected radiotracers 60 min after intravenous
application in a rat. The hypothetical metabolites [99mTc(NS3R)(L2-Lys)] were not found.
These results demonstrate a considerable improvement of in vivo properties of 99mTc '4 + 1' peptide conjugates and open up the possibility of applying the labeling approach for further radiodiagnostic peptides.
Keywords: Technetium; '4 + 1' Mixed-ligand complex; Peptide; RGD

Publ.-Id: 14407 - Permalink


Advanced Materials Research - Biennial Scientific Report 2007-2008 / Volume 1
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-507 2010

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Publ.-Id: 14405 - Permalink


Cancer Research - Biennial Scientific Report 2007-2008 / Volume 2
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-508 2010

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Publ.-Id: 14404 - Permalink


Nuclear Safety Research - Biennial Scientific Report 2007-2008 / Volume 3
Bohnet, C.; Bartho, A.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-509 2010

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Publ.-Id: 14403 - Permalink


The sorption of uranium(VI) and neptunium(V) onto surfaces of selected metal oxides and alumosilicates studied by in situ vibrational spectroscopy
Müller, K.;
The migration behavior of actinides and other radioactive contaminants 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 liquid-solid 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, 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.
From the infrared spectra, a significant change of the U(VI) speciation is derived upon lowering the U(VI) concentration from the milli- to the micromolar range, strongly suggesting the dominance of monomeric U(VI) hydrolysis products in the micromolar solutions. In contradiction to the predicted speciation, monomeric hydroxo species are already present at pH ≥ 2.5 and become dominant at pH 3. At higher pH levels (> 6), a complex speciation is evidenced including carbonate containing complexes.
For the first time, spectroscopic results of Np(VI) hydrolysis reactions are provided in the submillimolar concentration range and at pH values up to 5.3, and they are comparatively discussed with U(VI). For both actinides, the formation of similar species is suggested at pH ≤ 4, whereas at higher pH, the infrared spectra evidence structurally different species. At pH 5, the formation of a carbonate-containing dimeric complex, that is (NpO2)2CO3(OH)3^-, is strongly suggested, whereas carbonate complexation occurs only under more alkaline conditions in the U(VI) system.
The results from the experiments of the sorption processes clearly demonstrate the formation of stable U(VI) surface complexes at all investigated mineral phases. This includes several metal oxides, namely TiO2, Al2O3, and SiO2, serving as model systems for the elucidation of more complex mineral systems, and several alumosilicates, such as kaolinite, muscovite and biotite. From a multiplicity of in situ experiments, the impact of sorbent characteristics and variations in the aqueous U(VI) system on the sorption processes was considered.
A preferential formation of an inner-sphere complex is derived from the spectra of the TiO2 and SiO2 phases. In addition, since the in situ FT-IR experiments provide an online monitoring of the absorption changes of the sorption processes, the course of the formation of the U(VI) surface complexes can be observed spectroscopically. It is shown that after prolonged sorption time on TiO2, resulting in a highly covered surface, outer-sphere complexation predominates the sorption processes. The prevailing crystallographic modification, namely anatase and rutile, does not significantly contribute to the spectra, whereas surface specific parameters, e.g. surface area or porosity are important.
A significant different surface complexation is observed for Al2O3. The formation of innerspheric species is assumed at low U(VI) surface coverage which is fostered at low pH, high ionic strength and short contact times. At proceeded sorption the surface complexation changes. From the spectra, an outer-spheric coordination followed by surface precipitation or polymerization is deduced. Moreover, in contrast to TiO2, the appearance of ternary U(VI) carbonate complexes on the γ-Al2O3 surface is suggested.
The first results of the surface reactions on more complex, naturally occurring minerals (kaolinite, muscovite and biotite) show the formation of U(VI) inner-sphere sorption complexes. These findings are supported by the spectral information of the metal oxide surfaces.
In this work, first spectroscopic results from sorption of aqueous Np(V) on solid mineral phases are provided. It is shown that stable inner-sphere surface species of NpO2 ^+ are formed on TiO2. Outer-sphere complexation is found to play a minor role due to the pH independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2, and ZnO indicate structurally similar bidentate surface complexes.
The multiplicity of IR spectroscopic experiments carried out within this study yields a profound collection of spectroscopic data which will be used as references for future investigations of more complex sorption systems in aqueous solution. Furthermore, from a methodological point of view, this study comprehensively extends the application of ATR FT-IR spectroscopic experiments to a wide range in the field of radioecology.
The results obtained in this work contribute to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V/VI), in the environment. Consequently, more reliable predictions of actinides migration which are essential for the safety assessment of nuclear waste repositories can be performed.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-535 2010
    ISSN: 1437-322X

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Publ.-Id: 14401 - Permalink


Self-organization of Ge nanopattern under erosion with heavy Bi monomer and cluster ions
Bischoff, L.; Heinig, K.-H.; Schmidt, B.; Facsko, S.; Pilz, W.;
The self-organisation of periodic pattern on (001)Ge by bombardment with different heavy ion species (Bi+, Bi++, Bi2+, Bi3+, Bi3++) obtained from a liquid metal ion source in a mass separating 30 kV FIB system was studied. Aspect ratios exceeding values reported so far for elemental semiconductors substantially were found after cluster irradiation. An excellent regular self-ordering of dot (40 nm in height, interdistance of ~50 nm) and ripple pattern was achieved. Despite of high ion fluence, Raman measurements prove a crystalline surface layer. This result deviates drastically from monomer irradiation, where similar to former ion irradiation of Ge a spongy amorphous surface layer is formed. For the transition from the usual behaviour to the unexpected pronounced pattern formation a threshold of the energy density deposited by the collision cascade was identified: If the deposited energy density exceeds the melting threshold, dot or ripple pattern appear. In our model we assume that the ion-impact-induced deposition of energy per volume (estimated by SRIM) must exceed the energy needed for melting. Thus, Bi segregation during re-solidification of the melted pool and the 5% volume difference between molten and solid Ge can cause the observed Bi separation and Ge patterning, respectively. A consistent, qualitative model will be discussed.
Keywords: Bi-cluster; germanium; FIB; nanopattern
  • Poster
    17th International Conference on Ion Beam Modification of Material - IBMM 2010, 22.-27.08.2010, Montreal, Canada
  • Nuclear Instruments and Methods in Physics Research B 272(2012), 198-201
    DOI: 10.1016/j.nimb.2011.01.064

Publ.-Id: 14400 - Permalink


FZD intern 57
Bartho, A.; Bohnet, C.;
Hauszeitung des FZD
  • Communication & Media Relations
    Hauszeitung des FZD 06.08.2010
    8 Seiten

Publ.-Id: 14399 - Permalink


The effect of rare-earth clustering on charge trapping and electroluminescence in rare-earth implanted metal-oxide-semiconductor light-emitting devices
Nazarov, A. N.; Tiagulskyi, S. I.; Tyagulskyy, I. P.; Lysenko, V. S.; Rebohle, L.; Lehmann, J.; Prucnal, S.; Voelskow, M.; Skorupa, W.;
The effect of rare-earth clustering in dielectric media on the electroluminescence (EL) intensity, the charge trapping and the EL quenching was investigated using the example of Tb and Eu-implanted SiO2 layers. It was shown that the increase in the REOX cluster size induced by an increase in the furnace annealing temperature resulted in an increase in the concentration of electron traps with capture cross sections from 2 x 10-15 to 2 x 10-18 cm2. This is probably associated with an increase in the concentration of oxygen deficiency centers as well as with strained and dangling bonds in the SiO2 matrix which leads to an enhanced scattering of hot electrons and a decrease in the excitation cross section of the main EL lines of RE3+ ions. For the main EL lines of Tb3+ and Eu3+ ions the relation of the EL quenching to negative and positive charge generation in the SiO2 was considered. It was demonstrated that in case of REOX nanoclusters with small sizes (up to 5 nm) the E!
L quenching process can mainly be explained by a defect shell model which suggests the formation of negatively charged defect shells around the nanoclusters leading to a Coulomb repulsion of hot electrons and a suppression of the RE3+ excitation. At high levels of the injected charge (more than 2 x 1020 e/cm2) a second stage of the EL quenching was observed which was contributed to a positive charge accumulation in the SiO2 at a distance beyond the tunneling distance from the SiO2-Si interface. In case of Eu-implanted SiO2 the quenching of the main EL line of Eu3+ is mostly correlated with positive charge trapping in the bulk of the dielectric. A model of EL quenching of the main Eu3+ line is proposed. (C) 2010 American Institute of Physics.
Keywords: Electroluminescence, rare earth, MOS capacity, charge trapping, ion implantation
  • Journal of Applied Physics 107(2010)12, 123112

Publ.-Id: 14397 - Permalink


New sensors for the velocity measurement in liquid metal processes
Timmel, K.; Eckert, S.; Wondrak, T.; Stefani, F.; Gerbeth, G.;
In many technological processes involving liquid metals or semiconductor melts the velocity fields cannot be measured due to the lack of commercial measuring techniques for opaque melts. We present two measuring techniques which have proven recently as providing reliable velocity measurements in liquid metals, at least in the temperature range up to about 700°C: the ultrasonic Doppler Velocimetry (UDV) and the contactless inductive flow tomography (CIFT). UDV is capable of delivering velocity profiles along the ultrasonic beam with a time-resolution of about 20 Hz. CIFT is based on the flow-induced modification of some externally applied magnetic field, which is measured by some array of magnetic field sensors outside of the melt. We present measurements with both techniques at the small-scale liquid metal model Mini-LIMMCAST of the continuous steel casting process. Both measuring methods give consistent results for the jets evolving from the nozzle outlets.
Keywords: continuous casting, liquid metal model, magnetic field, mould flow, Ultrasound Doppler Method, industrial tomography
  • Lecture (Conference)
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
  • Contribution to proceedings
    2011 TMS Annual Meeting & Exhibition, 27.02.-03.03.2011, San Diego, Californien, USA
    Sensors, Sampling, and Simulation for Process Control: Wiley, 978-1-118-03618-1, 43-50

Publ.-Id: 14396 - Permalink


Competition of two-ion and single-ion anisotropy in rare-earth systems: Large anisotropy example of Tb5Ge3
Doerr, M.; Haase, A.; Loewenhaupt, M.; Rotter, M.; Bartkowiak, M.; Daou, R.; Kampert, E.; Perenboom, J.; Tsutaoka, T.;
The standard model of rare-earth magnetism assumes that magnetic anisotropy is mainly caused by single-ion effects. The importance of two-ion anisotropy is still disputed. For a number of materials this two-ion anisotropy is in the same order of magnitude and strongly influences the magnetic properties. Single crystalline Tb5Ge3 has a high moment and low symmetry and, because of this, a large anisotropy is expected. In the present study the influence of the two-ion interaction was investigated. Magnetization and magnetostriction were measured in high magnetic fields up to 60 T. The magnetic phase diagram constructed for the main crystallographic directions shows antiferromagnetism in zero field and a number of magnetic phases at higher fields. The exchange interaction was evaluated based on a model calculation of these phase diagrams. We conclude that a huge anisotropy in the two-ion interaction is present, which overwhelms the single-ion effects.
  • Physical Review B 82(2010), 024422

Publ.-Id: 14395 - Permalink


Manganese implanted Germanium: from clustering to carrier-mediated ferromagnetism
Zhou, S.; Bürger, D.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.;
Mn doped Ge (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior is entirely different from the GaAs:Mn system [1], the prototype of a ferromagnetic semiconductor.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [1-4]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, flash lamp and pulsed laser annealing (PLA) has been applied. We obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [1]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [2]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [3]. Indeed all samples show p-type conductivity with a hole concentration ranging from 1018 to 1020 cm3. The highest concentrations above 1020 cm3 can only be achieved by PLA. In the sample with the largest hole concentration of 2.1×1020 cm3, we observed a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K [3, 4]. We argue that the hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn [4]. In addition to the compatibility to Si technology, ion implantation followed by PLA is an established scalable chip technology and may have a significant industry impact.

[1] S. Zhou et al., APL, 95, 172103 (2009).
[2] S. Zhou et al., APL, 95, 192505 (2009).
[3] S. Zhou et al., PRB 81, 165204 (2010).
[4] S. Zhou et al., APL, in press (2010).
  • Lecture (Conference)
    The 17th International Conference on Ion Beam Modification of Materials, 22.-27.08.2010, Montreal, Canada

Publ.-Id: 14392 - Permalink


Manganese doped Germanium: from clustering to carrier-mediated ferromagnetism
Zhou, S.; Bürger, D.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.;
Manganese doped Germanium (Ge:Mn) is a promising candidate for a ferromagnetic semiconductor compatible with silicon technology, since Mn acts as a magnetic ion as well as a double acceptor. In recent years, Ge:Mn thin layers as well as nanostructures have been fabricated, mostly by LT-MBE, and analyzed [1-4]. Whereas ferromagnetism above room temperature has been evidenced by magnetization measurements, the transport behavior (magnetoresistance: MR, anomalous Hall effect: AHE) is entirely different from the GaAs:Mn system, the prototype of a ferromagnetic semiconductor. For instance, the previously reported AHE in Ge:Mn (i) was observed at temperatures above 10 K, (ii) but exhibited no hysteresis, and (iii) changed the sign of its slope. This behavior has been ascribed to Mn-diluted Ge [2, 4], Mn-rich spinodal decomposed phases [3] and MnGe precipitates [5], respectively. We argue that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 1019 cm-3.

We have prepared a series of Ge:Mn layer by Mn ion implantation into near-intrinsic, n-type Ge substrates, at 350 °C (resulting in Mn5Ge3 clusters) and -40 °C (without precipitates) [6-8]. The Mn concentration ranges from 0.004% to 10%. For samples with 10% Mn, several annealing procedures have been applied, namely ms flash lamp annealing and nsec pulsed laser annealing with various optical fluences. By this systematic preparation, we obtained three kinds of samples: (1) very dilute Ge:Mn where no ferromagnetic coupling can be expected [6]; (2) nanocrystalline Mn5Ge3 embedded inside the Ge matrix [7]; and (3) diluted Ge:Mn together with Mn-rich spinodal phases [8]. Indeed all samples show p-type conductivity with a hole concentration ranging from 1018 to 1020 cm-3. The highest concentrations above 1020 cm-3 can only be achieved with the help of pulsed laser annealing. A careful characterization of structure, magnetic and transport properties, leads us to the following conclusions.

(1) From 20 to 10 K the resistance of samples with a hole concentration of >1018 cm-3 increases in an activated manner with an activation energy of 4 meV, but below 10 K it saturates, i.e. the sample behaves metallic.
(2) We evoke the consideration of a two-band-like conduction in Ge:Mn. Above 10 K another conducting channel with different mobility is active, resulting in the drop of resistivity and the anomalous Hall resistance. The latter can be well described over a wide of parameters by considering two types of carriers with different mobility and population (see Ref. 6).
(3) In the sample with the largest hole concentration of 2×1020 cm-3, we observed, for the first time to our knowledge, a one-to-one correspondence between the hysteresis in magnetization, magnetoresistance and Hall resistance below 10 K. This is our key result, shown in Fig. 1, and is a strong evidence for carrier-mediated ferromagnetism. Note however that considering mere magnetization data, ferromagnetism remains present up to >100 K.

In summary, we present the magnetic and magnetotransport properties of a series of Ge:Mn samples with hole concentrations ranging from 1018 to 2x1020 cm-3. The hole concentration is the critical parameter to establish carrier mediated ferromagnetism in Ge:Mn, similar as is known for GaAs:Mn. A high-concentration co-doping with a shallow acceptor may allow to increase the hole concentration further, possibly resulting in a dramatically increased Curie temperature. In addition to the compatibility to Si technology, ion implantation followed by pulsed laser annealing is an established scalable chip technology and therefore may have a significant industry impact.

References:
[1] Y. D. Park et al., Science 295, 651 (2002).
[2] F. Tsui et al., Phys. Rev. Lett. 91, 177203 (2003).
[3] M. Jamet et al., Nature Mater. 5, 653 (2006).
[4] C. Zeng, et al., Phys. Rev. Lett. 100, 066101 (2008).
[5] O. Riss, et al., Phys. Rev. B 79, 241202(R) (2009).
[6] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009).
[7] S. Zhou et al., Appl. Phys. Lett. 95, 192505 (2009).
[8] S. Zhou et al., Phys. Rev. B (2010), submitted.
  • Lecture (Conference)
    International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors (PASPS-VI), 01.-04.08.2010, Tokyo, Japan
  • Invited lecture (Conferences)
    Invited talk at the Institute of Physics, Chinese Academy of Sciences, 13.04.2010, Beijing, China

Publ.-Id: 14391 - Permalink


Hysteresis in the magneto-transport of Manganese-doped Germanium: evidence for carrier-mediated ferromagnetism
Zhou, S.; Bürger, D.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.;
The III-V compound GaMnAs is considered as being the prototype diluted ferromagnetic semiconductor (FMS), exhibiting negative magnetoresistance (MR) and anomalous Hall effect (AHE) related to carrier-mediated ferromagnetism. However, it would be very desirable to have a group-IV FMS, being compatible with silicon technology. In particular manganese-doped germanium prepared using low-temperature molecular beam epitaxy (LT-MBE) has proven to be a very promising material [1]. Still, no direct correspondence between transport and magnetization data has been reported yet to date. The reported MR and AHE in Ge:Mn are likely caused by (super)paramagnetic Mn ions or precipitates or by two-band-like conduction [2]. We believe that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 1019 cm-3, which indicates the possible unsuitability of LT-MBE to achieve a large hole concentration in Ge:Mn.

In this contribution, we show that the hole concentration can be increased by two orders of magnitude, from 1018 to 1020 cm-3, through Mn-ion implantation into Ge followed by pulsed laser annealing [3]. In Mn-doped Ge with a hole-concentration of around 2.1×1020 cm-3, we observe that the longitudinal (Fig. 1c) and the Hall (Fig. 1b) resistance exhibit the same hysteresis as the magnetization (Fig. 1a) at temperatures below 10 K. This hysteresis in magneto-transport is usually considered as a direct evidence of carrier-mediated ferromagnetism. In sharp contrast to this, such effects are absent in Mn-doped Ge with a smaller hole-concentration. Below 10 K, the resistance of Ge:Mn films is nearly constant, i.e., quasi metallic, while from 10 to 20 K it decreases steeply with an activation energy of 4 meV. The magnetic and magneto-transport properties can be qualitatively well explained within a picture of dopant segregation and the formation of bound magnetic polarons. We will present a comprehensive correlation between the magnetic, transport and structural properties of Ge:Mn samples with different hole concentrations, as well as a comparison with literature. Note that ion implantation followed by pulsed laser annealing is an established scalable chip technology and may have a significant industry impact.

[1] Y. D. Park et al., Science 295, 651 (2002); M. Jamet et al., Nature Mater. 5, 653 (2006).
[2] S. Zhou et al., Appl. Phys. Lett. 95, 172103 (2009); Appl. Phys. Lett. 95, 192505 (2009).
[3] S. Zhou et al., Phys. Rev. B (2010), submitted.
  • Lecture (Conference)
    30th International Conference on the Physics of Semiconductors, 25.-30.07.2010, Seoul,, korea

Publ.-Id: 14390 - Permalink


Rate theory and SANS study of phase separation in a neutron irradiated Fe-12.5at%Cr model alloy
Gokhman, A. R.; Bergner, F.; Küchler, R.;
Cluster dynamics (CD) is used to study the evolution of the size distributions of vacancy clusters (VC), self-interstitial atom (SIA) clusters (SIAC) and Cr-precipitates in neutron irradiated Fe-12.5at%Cr alloy at the irradiation doses up to 12 dpa, fluence about 140 ndpa/s and T=300 C. Transmission electron microscopy (TEM) and small angle neutron scattering (SANS) data [1,2] on the defect structure of this material irradiated at the doses of 0.6 and 1.5 dpa are used to calibrate the model. It was found the saturation behaviour of free vacancy and free SIA concentrations, number density of SIAC and Cr-precipitates volume fraction for neutron expose great than 0.006 dpa; strong peak of SIAC with the average diameter about 0.5 nm and presence of VC with radius less 0.5 nm.
Keywords: Cluster dynamics, neutron irradiation, chromium iron alloys, defects
  • Invited lecture (Conferences)
    XIV.th Research Workshop Nucleation Theory and Applications, 10.-17.04.2010, Dubna, Russia

Publ.-Id: 14389 - Permalink


The MoS2 nanotubes with defect-controlled electric properties
Remskar, M.; Mrzel, A.; Virsek, M.; Godec, M.; Krause, M.; Kolitsch, A.; Singh, A.; Seabaugh, A.;
We describe a two-step synthesis of pure multiwall MoS2 nanotubes with a high degree of homogeneity in size. The Mo6S4I6 nanowires grown directly from elements under temperature gradient conditions in hedgehog-like assemblies were used as precursor material. Transformation in argon-H2S/H2 mixture leads to the MoS2 nanotubes still grouped in hedgehog-like morphology. The described method enables a large scale production of MoS2 nanotubes and their size control. X-ray diffraction, optical absorption and Raman spectroscopy, scanning electron microscopy with wave dispersive analysis, and transmission electron microscopy were used to characterize the starting Mo6S4I6 nanowires and the MoS2 nanotubes. The unit cell parameters of the Mo6S4I6 phase are proposed. Blue shift in optical absorbance and metallic behaviour of MoS2 nanotubes in two-probe measurement are explained by a high defect concentration.
Keywords: inorganic fullerenes, layered compounds, nanotubes, nanowires

Publ.-Id: 14388 - Permalink


Ultrashort pulse laser accelerated proton beams for first radiobiological applications
Schramm, U.; Zeil, K.; Richter, C.; Beyreuther, E.; Bussmann, M.; Cowan, T. E.; Enghardt, W.; Karsch, L.; Kluge, T.; Kraft, S.; Laschinsky, L.; Metzkes, J.; Naumburger, D.; Pawelke, J.; Sauerbrey, R.;
We report on the generation of proton pulses with maximum energies exceeding 15MeV bymeans of the irradiation of few micron thick metal foils by ultrashort (30 fs) laser pulses at a power level of 100 TW. In contrast to the well known situation for longer laser pulses, here, a near linear scaling of the maximum proton energy with laser power can be found. Aiming for radiobiological applications the long and short term stability of the laser plasma accelerator as well as a compact energy selection and dosimetry system is presented. The first irradiation of in vitro tumour cells showing dose dependent biological damage is demonstrated paving the way for systematic radiobiological studies.
Keywords: laser proton acceleration, first cell irradiation
  • Contribution to proceedings
    14th Workshop on Advanced Accelerator Concepts, 13.-19.06.2010, Annapolis, MD, USA, USA
    AIP Conference Proceedings, Advanced Esselerator Concepts, 1299: AIP, 731

Publ.-Id: 14382 - Permalink


Physikalische Modellierung des Stranggussprozesses mit niedrig schmelzenden Legierungen
Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.;
Die Strömung in der Metallschmelze hat einen wesentlichen Einfluss auf die Produktqualität beim Stranggießen. Probleme entstehen beispielsweise durch Einschlüsse von Oxiden, intermetallischen Verbindungen oder Gasblasen, die durch eine unkontrollierte Strömung in die Erstarrungszone gelangen. Die Optimierung dieser Strömung basierte bisher vor allem auf numerischen Simulationen und Modellexperimenten mit Wasser. Obwohl die Strömungsuntersuchungen an diesen Wassermodellen signifikante Erkenntnisgewinne über die Strömung und die optimale Auslegung z.B. des Tauchrohrs oder der Eintauchtiefe des Tauchrohrs gebracht haben, stoßen diese Modelle für eine Reihe von Fragestellungen an ihre physikalischen Grenzen, da Flüssigmetalle z.B. sehr hohe Oberflächenspannungen und sehr kleine Prandtl-Zahl besitzen, und Wasser offensichtlich für Untersuchungen des Einflusses von Magnetfeldern völlig ungeeignet ist.
In den vergangenen Jahren wurden am Forschungszentrum Dresden-Rossendorf experimentelle Versuchsanlagen mit niedrig schmelzenden Legierungen für die physikalische Modellierung des Stranggussprozesses aufgebaut. Ziel ist die systematische Untersuchung der Flüssigmetallströmungen und Transportprozesse in Verteiler, Tauchrohr und Kokille. Dabei steht insbesondere die Wirkung elektromagnetischer Felder, wie sie in Form von elektromagnetischen Bremsen oder Rührern bereits im industriellen Einsatz sind, im Mittelpunkt. Außerdem bieten die Versuchsanlagen gute Bedingungen für die Erprobung neuer Messtechniken und Anlagenkomponenten. Die Versuchsanlage „CONCAST-LMM“ (Continuous Casting Liquid Metal Model) ist 2009 fertig gestellt worden und arbeitet mit einer Sn60Bi40-Legierung als Modellfluid im Temperaturbereich von 200°C bis 400°C. Ein kleineres Modell mit der eutektischen GaInSn-Legierung wird bei Raumtemperatur betrieben. Die Strömungseigenschaften werden mit Hilfe lokaler Sonden sowie modernen Ultraschall und elektromagnetischen Methoden vermessen.
Im Rahmen dieses Beitrages werden Strömungsmessungen in einer einphasigen Flüssigmetallströmung in der Kokille unter Einwirkung eines statischen Magnetfeldes vorgestellt und mit entsprechenden numerischen Simulationen verglichen. Es zeigt sich, dass das Magnetfeld den aus dem Tauchrohr in die Kokille austretenden Jet ablenkt und lokale Rezirkulationsgebiete verstärkt. Die bremsende Wirkung des Magnetfeldes stellt sich als äußerst komplex dar. Eine gleichmäßige Reduktion der Strömungsgeschwindigkeit im gesamten Volumen wird nicht beobachtet.
Keywords: continuous casting, liquid metal model, magnetic field, mould flow, Ultrasound Doppler Method
  • Lecture (Conference)
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland
  • Contribution to proceedings
    Symposium Stranggießen, 15.-17.11.2010, Neu-Ulm, Deutschland

Publ.-Id: 14381 - Permalink


Structural evolution of magnetron sputtered shape memory alloy Ni–Ti films
Martins, R. M. S.; Schell, N.; von Borany, J.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.;
Near equiatomic and Ti-rich Ni–Ti polycrystalline films have been deposited by magnetron co-sputtering using a chamber installed at a synchrotron radiation beamline. The in situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during film processing.
The depositions on a 140 nm amorphous SiO2 buffer layer heated at 520°C (without applying bias voltage, Vb, to the substrate) led to a preferential growth of <100> oriented grains of the Ni–Ti B2 phase from the beginning of film growth until the end of the deposition.
Films exhibiting a preferential growthof <110> oriented grains of the Ni–Ti B2 phase from the beginning of the deposition were obtained (without and with a Vb of - 45 V) by using a TiN coating with a topmost layer formed by <111> oriented grains. Those trends have been observed for the growth of near equiatomic (~50.0 at.% Ti–Ni) and Ti-rich (~50.8 at.% Ti–Ni) Ni–Ti films.
Additionally, an ion gun had been commissioned, which allows ion bombardment during sputter deposition or post-deposition ion irradiation. In this first series of experiments, a Ni–Ti film was irradiated with He ions after deposition (without exposing the film to the atmosphere, i.e., avoiding surface oxide formation), thus modifying deliberately the microstructure of the film locally.
Keywords: Deposition by sputtering, Ni–Ti Shape memory alloy (SMA), In situ X-ray diffraction (XRD), Texture development, Ion bombardment

Publ.-Id: 14380 - Permalink


Quantitative KPFM Measurements on Silicon Nanowire Structures
Baumgart, C.;
This workshop focus on the electrical characterization of vertical and horizontal Si nanowires.
  • Lecture (others)
    Workshop FZD/FZJ: Silicon Nanowire Structures, 29.04.2010, Dresden, Germany

Publ.-Id: 14379 - Permalink


Quantitative Kelvin probe force microscopy imaging on locally doped Si
Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface
potential. Since KPFM was developed in 1991 the measured KPFM signal was attributed to the contact potential difference (CPD) between conductive probe and sample. We show that the CPD is not suitable to describe the measured Kelvin bias in semiconductors quantitatively and introduce a unique KPFM model [1] which successfully correlates the measured Kelvin bias with the difference between Fermi energy and respective band edge. Quantitative dopant profiling is demonstrated on cross-sectionally prepared Si epilayer structures and on a Si dynamic random access memory cell.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80 (2009) 085305.
  • Poster
    DPG Frühjahrstagung, 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14378 - Permalink


Shallow acceptor and hydrogen impurity in p-type arsenic-doped ZnMgO films grown by radio frequency magnetron sputtering
Fan, J.; Ding, G.; Fung, S.; Xie, Z.; Zhong, Y.; Wong, K.; Brauer, G.; Anwand, W.; Grambole, D.; Ling, C.;
Arsenic-doped ZnMgO films were fabricated on SiO2 by the radio frequency magnetron sputtering technique at different substrate temperatures during growth. The yielded films were characterized by room temperature Hall measurement, x-ray diffraction, x-ray photoelectron spectroscopy, scanning electron microscopy, secondary ion mass spectroscopy, nuclear reaction analysis and low-temperature photoluminescence. As-doped samples grown at low substrate temperature (350 degrees C) were n-type conducting (n similar to 1018 cm-3), with evidence showing that the hydrogen impurity was an important shallow donor associated with the observed n-type conduction. Conversion of n-type to p-type conduction being observed at the substrate temperature of similar to 400 degrees C was associated with the formation of the AsZn(VZn)2 shallow acceptor complex and the drastic reduction of the hydrogen content.

Publ.-Id: 14377 - Permalink


Quantitative Kelvin probe force microscopy on semiconductors
Baumgart, C.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.


[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).
  • Lecture (others)
    2. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 05.08.2010, Dresden, Germany

Publ.-Id: 14375 - Permalink


Quantitative Kelvin probe force microscopy imaging on locally doped semiconductors
Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices demand knowledge of their electrical properties. Especially, quantitative profiling of dopant concentrations is essential for process and device engineering in semiconductor industry. The most straightforward nanometrology technique is the Kelvin probe force microscopy (KPFM) where electrostatic forces are detected.
Quantitative dopant profiling by means of KPFM measurements is successfully shown on a conventional static random access memory (SRAM) cell and on
cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different pulsed laser annealed Mn-implanted Ge samples by revealing a strong variation of the Fermi level position on the micrometer scale in dependence on
the annealing conditions after Mn implantation [2].
In addition, the frequency dependence of the KPFM bias is discussed. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, the frequency dependence is samplespecific and KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor are
probed.

[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm,
and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
  • Lecture (Conference)
    Nano 2010, 13.-17.09.2010, Rome, Italy

Publ.-Id: 14374 - Permalink


Quantitative Kelvin probe force microscopy on semiconductors under ambient conditions
Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Schmidt, H.;
Failure analysis and optimization of nanoelectronic devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of the surface potential. We present its applicability to locally doped semiconductors. Quantitative dopant profiling by means of KPFM is successfully shown on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayer structures by applying a recently introduced new explanation of the measured KPFM signal [1]. The presented KPFM model is also used to explain observed large conductivity differences in different Mn implanted and pulsed laser annealed Ge samples by revealing a strong variation of the Fermi level position on the µm scale in dependence on the annealing conditions [2].
In addition, the frequency dependence of the Kelvin bias above differently doped regions is discussed with respect to surface states and trapped charges in the thin oxide layer on top [3]. Using an active mixer, the excitation amplitude of the cantilever is almost independent of the operation frequency. As a result, KPFM measurements have to be performed at frequencies high enough so that the electrical properties of the locally doped semiconductor and not of the oxide layer are probed.


[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).
[2] S. Zhou, D. Bürger, A. Mücklich, C. Baumgart, W. Skorupa, C. Timm, P. Oesterlin, M. Helm, and H. Schmidt, Phys. Rev. B 81 (2010), 165204.
[3] F. Müller and A.-D. Müller, J. Vac. Sci. Techn. B 27, 969 (2009).
  • Lecture (Conference)
    Nanofair 2010, 06.-07.07.2010, Dresden, Germany

Publ.-Id: 14373 - Permalink


Revealing the role of anchoring groups in the electrical conduction through single-molecule junctions
Zotti, L. A.; Kirchner, T.; Cuevas, J.-C.; Pauly, F.; Huhn, T.; Scheer, E.; Erbe, A.;
A combined experimental and theoretical study is presented revealing the influence of metal-molecule coupling on electronic transport through single-molecule junctions. Transport experiments through tolane molecules attached to gold electrodes via thiol, nitro, and cyano anchoring groups are performed. By fitting the experimental current-voltage characteristics to a single-level tunneling model, we extract both the position of the molecular orbital closest to the Fermi energy and the strength of the metal-molecule coupling. The values found for these parameters are rationalized with the help of density-functional-theory-based transport calculations. In particular, these calculations show that the anchoring groups determine the junction conductance by controlling not only the strength of the coupling to the metal but also the position of the relevant molecular energy levels.
Keywords: anchoring groups, break junctions, density functional theory, molecular electronics, molecular wires

Publ.-Id: 14372 - Permalink


Density reduction and diffusion in driven two-dimensional colloidal systems through microchannels
Henseler, P.; Erbe, A.; Köppl, M.; Leiderer, P.;
The behavior of particles driven through a narrow constriction is investigated in experiment and simulation. The system of particles adapts to the confining potentials and the interaction energies by a self-consistent arrangement of the particles. It results in the formation of layers throughout the channel and of a density gradient along the channel. The particles accommodate to the density gradient by reducing the number of layers one by one when it is energetically favorable. The position of the layer reduction zone fluctuates with time while the particles continuously pass this zone. The flow behavior of the particles is studied in detail. The velocities of the particles and their diffusion behavior reflect the influence of the self-organized order of the system.
Keywords: Colloids, Nonlinear dynamics and chaos, Computer simulation of molecular and particle dynamics, Studies of specific magnetic materials

Publ.-Id: 14370 - Permalink


Observation of negative differential resistance in DNA molecular junctions
Kang, N.; Erbe, A.; Scheer, E.;
The mechanically controllable break junction technique is used to study charge transport through suspended DNA molecules. The current-voltage (I-V) characteristics in an aqueous solution display series of negative differential resistance (NDR) and hysteresis behavior. Under high-vacuum conditions, the peak positions of NDR shift to lower voltage, and the amplitude is reduced dramatically. The observed NDR behavior is consistent with the polarization mechanism in DNA molecular junctions, which demonstrates a change in the coupling of the molecular level to a polaron mode under different environment.
Keywords: DNA electronics, molecular electronics, mechanically controllable break junctions

Publ.-Id: 14369 - Permalink


Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamintransporter-Liganden FP-CIT (DaTSCANTM)
Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.;
Es ist kein Abstract vorhanden.
Keywords: SPECT; 123I; Dopamintransporter Ligand; FP-CIT; DaTSCAN
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners, Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 100-107

Publ.-Id: 14368 - Permalink


Leitlinie für SPECT-Untersuchungen mit dem 123I-markierten Dopamin-D2-Rezeptor Liganden IBZM
Tatsch, K.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Grünwald, F.; Kuwert, T.; Krause, B. J.; Sabri, O.;
Es ist kein Abstract vorhanden.
Keywords: SPECT; 123I; Dopamin-D2-Rezeptor; Ligand; IBZM
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 108-115

Publ.-Id: 14367 - Permalink


Leitlinie für die Hirnperfusions-SPECT mit 99mTc-Radiopharmaka
Menzel, C.; Bartenstein, P.; Brust, P.; Coenen, H. H.; Krause, B. J.; Kuwert, T.; Sabri, O.; Schreckenberger, M.; Tatsch, K.; Grünwald, F.;
Es ist kein Abstract vorhanden.
Keywords: Hirnperfusions-SPECT; 99mTc
  • Contribution to external collection
    Eckardt; Geworski; Lerch; Reiners; Schober: DGN - Empfehlungen zur Qualitätskontrolle in der Nuklearmedizin, Stuttgart: Schattauer GmbH, 2009, 978-3-7945-2572-0, 87-91

Publ.-Id: 14366 - Permalink


Dose-dependent biological damage of tumour cells by laser-accelerated proton beams - online diagnostics
Schramm, U.;
Talk on the status of laser proton acceleration and online dosimetry with respect to radiobiological applications.
  • Invited lecture (Conferences)
    First Workshop on Instrumentation for Diagnostics and Control of Laser Accelerated Proton Beams, 09.-10.08.2010, Abingdon / Oxford, UK

Publ.-Id: 14365 - Permalink


Slip ratio in dispersed viscous oil-water pipe flow
Rodriguez, I. H.; Yamaguti, H. K. B.; de Castro, M. S.; Da Silva, M. J.; Rodriguez, O. M. H.;
In this article, dispersed flow of viscous oil and water is investigated. The experimental work was performed in a 26.2-mm-i.d. 12-m-long horizontal glass pipe using water and oil (viscosity of 100 mPa.s and density of 860 kg/m3) as test fluids. High-speed video recording and a new wire mesh sensor based on capacitance (permittivity) measurements were used to characterize the flow. Furthermore, holdup data were obtained using quick-closing-valves technique (QCV). An interesting finding was the oil-water slip ratio greater than one for dispersed flow at high Reynolds number. Chordal phase fraction distribution diagrams and images of the holdup distribution over the pipe cross-section obtained via wire-mesh sensor indicated a significant amount of water near to the pipe wall for the three different dispersed flow patterns identified in this study: Oil-in-water Homogeneous Dispersion (o/w H), Oil-in-water Non-homogeneous Dispersion (o/w NH) and Dual continuous (Do/w & Dw/o). The phase slip might be explained by the existence of a water film surrounding the homogeneous mixture of oil in water in a hidrofilic-oilfobic pipe.
Keywords: Liquid-liquid flow; oil-water flow; viscous oil; dispersed flow; slip ratio; wire-mesh sensor

Publ.-Id: 14364 - Permalink


Marangoni convection in molten salts - physical modelling toward lower Prandtl numbers
Cramer, A.; Landgraf, S.; Beyer, E.; Gerbeth, G.;
Marangoni convection is involved in many technological processes. The substances of industrial interest are often governed by diffusive heat transport and their physical modelling is limited with respect to the Prandtl number Pr. The present paper addresses this deficiency. Studies were made on molten salts having Pr values in an intermediate range well below that of the typically employed organics. Since some of the selected species have a relatively high melting point, a high-temperature facility which allows studying thermocapillary convection at temperatures in excess of 1000°C was built. The results presented here were obtained in a cylindrical geometry, although the equipment that was built is not restricted to this configuration because of its modular construction. Modelled after some applications, the fluid was heated centrically on top. The bulk was embedded in a large thermostatically controlled reservoir so as to establish the lower ambient reference temperature. A characteristic size of the experimental cell was chosen such that, on the one hand, the dynamic Bond number Bo did not become too high; on the other hand, the liquid had to have a certain depth to allow particle image velocimetry. The complicated balance between body forces and thermocapillary forces in the case of intermediate Bo was found to result in a distinct local separation into a bulk motion governed by natural convection with a recirculating Marangoni flow on top. In contrast to low viscosity organics, the vapour pressure of which increases considerably with decreasing Pr, high values of the Marangoni number can be reached. Comparisons of the topology of Marangoni vortices between molten salts with 2.3 <= Pr <= 6.4 and a silicone oil with Pr typically one order of magnitude higher suggest that the regime of non-negligible heat diffusion is entered.
Keywords: Marangoni convection, surface tension driven flow, molten salts, Prandtl number, physical modelling

Publ.-Id: 14363 - Permalink


On the prediction of boron dilution using the CMFD code TRANSAT: the ROCOM test case
Labois, M.; Panyasantisuk, J.; Lakehal, D.; Höhne, T.; Kliem, S.;
This contribution aims at introducing a new multiscale, multicomponent CFD/CMFD approach for the simulation of thermal-hydraulics flows evolving in complex component-scale configurations. In this novel approach, the flow system could involve one or two fluids, convective and conductive heat transfer in solids, and phase-change heat transfer. This is made possible thanks to the Immersed Surfaces Technology (IST), a methods inspired from Interface Tracking techniques for two-phase flow, whereby solid bodies contained in the system are defined using a solid level set function to describe their surfaces, transcending conventional unstructured and body-fitted grids (BFC). In a typical two-phase flow, material properties of the fluids and the solid are segregated based on the gas-liquid and solid Level-Set functions. The technique helps solve conjugate heat transfer problems without resorting to explicit jump conditions. Selected validation test-cases are presented here. The main application includes steady and transient solutions of the boron dilution in the ROCOM test case.
Keywords: CFD, ASCOMP, FZD, ROCOM, TRANSAT
  • Contribution to proceedings
    CFD4NRS-3, 14.-16.09.2010, Washington, USA
    CD-ROM
  • Lecture (Conference)
    CFD4NRS-3, 14.-16.09.2010, Washington, USA

Publ.-Id: 14362 - Permalink


Controlling blue-violet electroluminescence of Ge-rich Er-doped SiO2 layers by millisecond annealing using flash lamps
Kanjilal, A.; Rebohle, L.; Voelskow, M.; Helm, M.; Skorupa, W.;
Systematic evolution of the 400 nm electroluminescence (EL) with increasing flash lamp annealing (FLA) temperature from 800 to 1100 °C in an Er-doped Ge-rich metal-oxide semiconductor structure is presented. No significant change in the 1535 nm Er EL is observed with increasing FLA temperature. Enhancement of the 400 nm EL decay time with rising FLA temperature is found to be associated with recrystallization of the damaged Ge clusters in the absence of Ge outdiffusion. The 400 nm EL quenching with continuous charge injection process is also discussed within the device operation time.
Keywords: electroluminescence, flash lamp annealing, Er-doped Ge-rich metal-oxide semiconductor

Publ.-Id: 14361 - Permalink


Ultrasound investigations of some frustrated and low-dimensional magnets
Zherlitsyn, S.; Chiatti, O.; Sytcheva, A.; Wosnitza, J.; Zvyagin, A. A.;
The investigation of the correlations between magnetic and lattice degrees of freedom provides a better understanding of the underlying physics of frustrated and low-dimensional spin systems. Ultrasound experiments are proven to be a powerful tool to probe the spin-lattice interactions and lattice instabilities. Here, we will present some recent outcome of our ultrasound studies performed at high magnetic fields. We report results of our investigations of the frustrated spin system CdCr2O4 [1]. This material shows a wide magnetization plateau, from 28 to 58 T, at one half of the full moment of S = 3/2 Cr3+. We further present results for the low-dimensional quantum antiferromagnets Cs2CuCl4 [2] and NiCl2-4SC(NH2)2 [3]. The spin-strain coupling is discussed in frame of the exchange-striction mechanism.
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES 2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14360 - Permalink


Electronic band structure of superconducting PrPt4Ge12
Wosnitza, J.; Bergk, B.; Ignatchik, O.; Polyakov, A.; Gumeniuk, R.; Leithe-Jasper, A.; Schnelle, W.; Nicklas, M.; Rosner, H.; Grin, Y.;
Recently, the new skutterudite superconductor PrPt4Ge12 with the comparably high transition temperature of Tc = 7.9 K was discovered [1]. First experiments gave evidence for strong coupling and hint at point-like nodes of the order parameter [2]. The Sommerfeld coefficient is rather low and indicates that PrPt4Ge12 is not a heavy-fermion superconductor. Here, we present results of a de Haas-van Alphen (dHvA) study performed on a high-quality single crystal. Several dHvA frequencies could be resolved over a broad angular range. The small band-resolved effective masses (less than half the free-electron mass) confirm the non-heavy-fermion character of the electron system. To get insight into the nature of the mass renormalization, the experimental data are compared with state-of-the-art band-structure calculations
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14359 - Permalink


High-field ultrasound investigations of frustrated and low-dimensional magnets
Zherlitsyn, S.;
es hat kein Abstract vorgelegen.
  • Invited lecture (Conferences)
    International Workshop "Perspectives in Highly Frustrated Magnetism", 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14358 - Permalink


Influence of vanadium concentration on the microstructure and magnetic properties of V-doped ZnO thin films
Naydenova, T.; Atanasov, P.; Koleva, M.; Nedialkov, N.; Perriere, J.; Defourneau, D.; Fukuoka, H.; Obara, M.; Baumgart, C.; Zhou, S.; Schmidt, H.;
Vanadium doped ZnO thin films (Zn1−xVxO, where x=0.05 or x=0.13) were grown on c-cut sapphire substrates using pulsed laser deposition technique. Their structure and magnetic properties were examined in relation to the doping concentration. All deposited films were highly oriented along the c-axis and exhibited ferromagnetic behavior with a Curie temperature up to 300 K. The crystal structure was found to be better for layers with lower vanadium concentration. The films had a porous fine-grained microstructure and a column-like character as the V concentration was reduced. A weak dependence of magnetization on temperature was observed. The saturation magnetization was found to be strongly dependent on the crystal structure, grain size and V-ion concentration.
Keywords: ZnO, Vanadium doping, Thin films, PLD, DMS
  • Thin Solid Films 518(2010), 5505-5508

Publ.-Id: 14357 - Permalink


Magnetic properties of the quasi-two-dimensional S = 1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6
Zvyagin, S. A.;
We report on high-field magnetization, specific-heat and electron spin resonance (ESR) studies of the quasi-two-dimensional spin-1/2 Heisenberg antiferromagnet [Cu(pyz)2(HF2)]PF6. The frequency-field diagram of ESR modes below TN \approx 4.38 K is described in the frame of the mean-field theory. The obtained results allowed us to determine the anisotropy/exchange interaction ratio, A/J = 0.003, and the upper limit for the inter/intra-plane exchange-interaction ratio, J'/J = 1/16. It is argued that despite of onset of 3D long-range magnetic ordering the magnetic properties of this material (including high-magnetic-field magnetization and nonmonotonic field dependence of the Neel temperature) are strongly affected by two-dimensional spin correlations.
  • Poster
    International Workshop on "Perspectives in Highly Frustrated Magnetism", 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14356 - Permalink


Room temperature ferromagnetism in Ni-doped HfO2 thin films
Sharma, M.; Kanjilal, A.; Voelskow, M.; Kanjilal, D.; Chatterjee, R.;
In this paper detailed studies on modification of structural and magnetic properties of Ni-doped hafnium oxide (HfO2) thin films are reported. We used 200 keV Ni beam for doping of Ni. For homogeneous dispersion and activation of doped Ni ions, 120 MeV Ni swift heavy ions (SHI) irradiation was used. This unique combination of Ni doping by ion beam and dispersing and activating by Ni SHI irradiation of HfO2 films is reported for the first time. The origin of ferromagnetism in the Ni-doped HfO2 thin films is investigated. We demonstrate the cluster free nature of our film using cross-sectional high resolution transmission microscopy and magnetization versus temperature data. Rutherford backscattering data are used to establish that Ni ions are implanted in the HfO2 matrix at the predicted location. Dispersion of implanted Ni and lattice defects such as oxygen vacancies are attributed to be the main source of ferromagnetism.
Keywords: magnetic clusters, Ni-doped hafnium oxide (HfO2), swift heavy ion irradiation

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Publ.-Id: 14355 - Permalink


Antiferromagnetic resonance in the multiferroic frustrate YMnO3
Kamenskyi, D.;
Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Using THz-range FEL- and BWO-based electron spin resonance (ESR) spectroscopy techniques, the frequency-field dependence of magnetic excitations in the hexagonal multiferroic YMnO3 in the antiferromagnetically (AFM) ordered phase has been studied. A slope of the frequency-field dependences of AFM resonance modes, ~ 0.5 cm−1/T, is explaned in terms of the triangular AFM model. A gap in the excitation spectrum, ~ 42 cm−1, was observed directly. A fine structure of AFM resonance absorption observed by as is a clear signature of a finite interaction between the neighboring Mn3+ layers. The interplane exchange interactions constants, J1 = -510 mK and J2 = -350 mK, have been estimated.
  • Poster
    International Workshop on "Perspectives in Highly Frustrated Magnetism" (PHFM10), 19.-23.04.2010, Dresden, Deutschland

Publ.-Id: 14354 - Permalink


New experimental study of low-energy (p,gamma) resonances in magnesium isotopes
Limata, B.; Strieder, F.; Formicola, A.; Imbriani, G.; Junker, M.; Becker, H. W.; Bemmerer, D.; Best, A.; Bonetti, R.; Broggini, C.; Caciolli, A.; Corvisiero, P.; Costantini, H.; Dileva, A.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Lemut, A.; Marta, M.; Mazzocchi, C.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Salvo, C.; Somorjai, E.; Straniero, O.; Terrasi, F.; Trautvetter, H.-P.;
Proton captures on Mg isotopes play an important role in the Mg-Al cycle active in stellar H shell burning. In particular, the strengths of low-energy resonances with E < 200 keV in 25Mg(p,gamma)26Al determine the production of 26Al and a precise knowledge of these nuclear data is highly desirable. Absolute measurements at such low-energies are often very difficult and hampered by gamma-ray background as well as changing target stoichiometry during the measurements. The latter problem can be partly avoided using higher energy resonances of the same reaction as a normalization reference. Hence the parameters of suitable resonances have to be studied with adequate precision. In the present work we report on new measurements of the resonance strengths omega_gamma of the E = 214, 304, and 326 keV resonances in the reactions 24Mg(p,gamma)25Al, 25Mg(p,gamma)26Al, and 26Mg(p,gamma)27Al, respectively. These studies were performed at the LUNA facility in the Gran Sasso underground laboratory using multiple experimental techniques and provided results with a higher accuracy than previously achieved.

Publ.-Id: 14353 - Permalink


Low-Temperature Elastic Properties of Non-Kramers Doublet Compound PrMg3
Araki, K.; Mitsumoto, K.; Akatsu, M.; Nemoto, Y.; Suzuki, H. S.; Tanida, H.; Takagi, S.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Goto, T.;
We have investigated low-temperature elastic properties of PrMg3 with a non-Kramers Gamma3 doublet ground state using ultrasonic measurements. Although the Gamma3 doublet possesses electric quadrupoles Ou and Ov with Gamma3-symmetry and magnetic octupole Txyz with Gamma2, PrMg3 reveals no sign of symmetry breaking long-range ordering down to 20 mK. [1] The elastic constant of (C11-C12)/2 in PrMg3 exhibits remarkable softening below 8 K, which is well described in terms of a Curie-type quadrupole susceptibility for the Gamma3 doublet. An appreciable upturn in (C11-C12)/2 below 800 mK in PrMg3 may indicate an transition into an exotic ground state due to the quadrupole Kondo state being screened by conduction electrons. Frequency dependence in (C11-C12)/2 and its attenuation coefficients at low temperature in PrMg3 suggests quadrupole fluctuations possessing a characteristic relaxation time tau = tau0exp(E/kT) with tau0 = 6x10-11 sec and an activation energy E = 410 mK. The low-temperature behavior in (C11-C12)/2 of PrMg3 under magnetic fields is also presented.
  • Poster
    Strongly Correlated Electron Systems 2010 (SCES 2010), 27.06.-02.07.2010, Santa Fe, USA

Publ.-Id: 14352 - Permalink


Die Jagd nach dem Feldrekord: Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Lecture (others)
    Eröffnungsvortrag zum Tag des offenen Labors des Forschungszentrum Dresden-Rossendorf, 04.07.2010, Dresden, Deutschland

Publ.-Id: 14351 - Permalink


Research at the Dresden High Magnetic Field Laboratory
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Seminar at the National High Magnetic Field Laboratory, Los Alamos, 25.06.2010, Los Alamos, USA
  • Invited lecture (Conferences)
    Seminar at the Institute for Solid State Physics, University of Tokyo, 17.09.2010, Kashiwa, Japan

Publ.-Id: 14350 - Permalink


Das Hochfeld-Magnetlabor Dresden – Forschung und Infrastruktur
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Klausurtagung des SFB 609 „Elektromagnetische Strömungsbeeinflussung in Metallurgie, Kristallzüchtung und Elektrochemie", 11.-12.03.2010, Schmochtiz, Deutschland

Publ.-Id: 14349 - Permalink


Evidence for a novel superconducting state in layered organic superconductors
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    International Conference of the SFB/TR 49 „Novel states in correlated matter - from model systems to real materials", 02.-04.03.2010, Berlin, Deutschland

Publ.-Id: 14348 - Permalink


Die Jagd nach dem Feldrekord – Forschung in hohen Magnetfeldern
Wosnitza, J.;
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Gemeinsames Kolloquium des KIT und der Universität Heidelberg, 29.01.2010, Karlsruhe, Deutschland

Publ.-Id: 14347 - Permalink


High-frequency and high-field ESR in quantum spin systems
Zvyagin, S. A.;
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Terahertz spectroscopy and its high-field applications & EuroMagNET II user meeting, 14.-16.06.2010, Dresden, Deutschland

Publ.-Id: 14346 - Permalink


Optical conductivity of Ba(Fe0.9Co0.1)2As2 and LuNi2B2C in the terahertz range
Pronin, A. V.; Fischer, T.; Wosnitza, J.; Schachinger, E.; Iida, K.; Kurth, F.; Haindl, S.; Niemeier, T.; Schultz, L.; Holzapfel, B.;
es hat kein Abstract vorgelegen.
  • Poster
    Low-Energy Electrodynamics in Solids 2010 (LEES 2010), 05.-10.07.2010, Les Diablerets, Schweiz

Publ.-Id: 14345 - Permalink


Nuclear data needs for underground accelerators
Bemmerer, D.;
The nuclear data needs for underground accelerators will be reviewed, with a focus on the present and future LUNA program.
  • Lecture (Conference)
    Data needs for nuclear astrophysics, 25.-27.07.2010, Darmstadt, Deutschland

Publ.-Id: 14344 - Permalink


The 14N(p,gamma)15O cross section at 0.5-1.5 MeV
Bemmerer, D.;
The 14N(p,g)15O reaction is the bottleneck of the carbon-nitrogen-oxygen (CNO) cycle, thus determining its speed. The precise knowledge of its cross section is necessary to address the recently discovered discrepancy for elemental abundances in the standard solar model, the so-called solar abundance problem. Several experimental efforts are underway to improve the precision, among them lifetime measurements of excited states in the 15O compound nucleus. The seminar talk will report on a different approach, namely a direct cross section measurement at comparatively high energy, 0.5-1.5 MeV, recently performed at the Dresden Tandetron.
  • Invited lecture (Conferences)
    Seminar INFN Laboratori Nazionali di Legnaro, Italy, 30.07.2010, Legnaro, Italien

Publ.-Id: 14343 - Permalink


Dissipative Taylor-Couette flows under the influence of helical magnetic fields
Rüdiger, G.; Gellert, M.; Schultz, M.; Hollerbach, R.;
The linear stability of magnetohydrodynamic Taylor-Couette flows in axially unbounded cylinders is considered for magnetic Prandtl number unity. Magnetic background fields varying from purely axial to purely azimuthal are imposed, with a general helical field parametrized by beta=B-phi/B-z. We map out the transition from the standard magnetorotational instability (MRI) for beta=0 to the nonaxisymmetric azimuthal magnetorotational instability for beta ->infinity. For finite beta, positive and negative wave numbers m, corresponding to right and left spirals, are no longer degenerate. For the nonaxisymmetric modes, the most unstable mode spirals in the opposite direction to the background field. The standard (beta=0) MRI is axisymmetric for weak fields (including the instability with the lowest Reynolds number) but is nonaxisymmetric for stronger fields. If the azimuthal field is due in part to an axial current flowing through the fluid itself (and not just along the central ax! is), then it is also unstable to the nonaxisymmetric Tayler instability which is most effective without rotation. For purely toroidal fields the solutions for m=+/- 1 are identical so that in this case no preferred helicity results. For large beta the wave number m=-1 is preferred, whereas for beta less than or similar to 1 the mode with m=-2 is most unstable. The most unstable modes always spiral in the same direction as the background field. For background fields with positive and not too large beta the kinetic helicity of the fluctuations proves to be negative for all the magnetic instabilities considered.
  • Physical Review E 82(2010), 016319

Publ.-Id: 14342 - Permalink


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