Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

32227 Publications
Pairs of Effective Spin Merons in Ferromagnetic Multilayer Elements
Wintz, S.; Bunce, C.; Neudert, A.; Körner, M.; Strache, T.; Buhl, M.; Erbe, A.; Gemming, S.; Raabe, J.; Quitmann, C.; Fassbender, J.ORC
We report on pairs of diverging/converging spin vortices in Co/Rh/Ni81Fe19 disks. The lateral magnetization distribution of these effective spin merons [1] is directly imaged by means of element-selective x-ray microscopy. By this method, both the circulation and divergence states of the individual layers are identified as antisymmetric [2] (see Figure 1). Magnetization reversal measurements of corresponding continuous films reveal that biquadratic interlayer exchange coupling is the origin for the formation of such effective meron pairs. Furthermore, the effective meron pair’s three-dimensional magnetic structure is determined via micromagnetic simulations. We find that the perpendicular magnetization component is distributed nonhomogeneously, namely M is partially circulating on a flux-closing torus. This toroidal topology enforces a symmetry break, which ties the core polarities to the divergence configuration. Upon excitation, such topology-induced core stabilization could lead to enhanced maximum amplitudes of steady gyration compared to single layer vortices, as the meron pair’s core switching onset velocity is expected to be higher than that of a single vortex.
  • Lecture (Conference)
    58th Conference on Magnetism and Magnetic Materials (MMM), 04.-08.11.2013, Denver, USA

Publ.-Id: 18911 - Permalink


Economic surface treatment of Ti-alloys to improve their resistance against environmental high temperature attack
Donchev, A.; Schütze, M.; Kolitsch, A.; Yankov, R.;
High temperature Ti-alloys are usually sophisticated and hence expensive. To allow the use of cheaper alloys at elevated temperatures an economic and easy to apply procedure was developed to improve their high temperature capability. The treatment consists of a combination of Alenrichment in a shallow surface region plus additional fluorination. The Al-enrichment at elevated temperatures leads to the formation of intermetallic TiAl-phases. These phases improve the oxidation resistance of Ti-alloys but not to a sufficient extent. An additional fluorine treatment of the Al-enriched surface leads to the formation of a protective alumina scale due to the fluorine effect. In this paper results from high temperature exposure tests performed on different Ti-alloys without any treatment and with a combination of Al-treatment plus fluorination are presented. The results are discussed in the view of the use of the optimized Ti-components for several high temperature applications.
Keywords: titanium, embrittlement, oxidation

Publ.-Id: 18910 - Permalink


Precise study of the supernova reaction 40Ca(α,γ) 44Ti by activation and in-beam γ-spectroscopy
Schmidt, K.; Akhmadaliev, C.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Degering, D.; Dietz, M.; Dressler, R.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Munnik, F.; Schumann, D.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.;
The radioactive nuclide 44Ti is believed to be produced in the α-rich freezeout preceding supernova explosions. The γ-rays from its decay have been observed in space-based γ-observatories for the Cassiopeia A and very recently also SN 1987A supernova remnants. The rates of the nuclear reactions governing the production and destruction of 44Ti should therefore be known with high precision. Over the last years there have been various studies of the 40Ca(α,γ)44Ti reaction, which is dominating the 44Ti production in supernovae. Those studies have been performed using in-beam γ-spectroscopy, activation, accelerator mass spectrometry (AMS), and recoil mass spectrometry via inverse kinematics. However, there are still discrepancies in the resulting reaction rates. Using an α-beam of 1-2 A intensity the strengths of the strongest 40Ca(α,γ)44Ti resonances from 3.5 to 4.5 MeV laboratory α-energy have been studied by in-beam γ-counting and activation. The samples have been analyzed in the ultra-low-background underground γ-counting facility "Felsenkeller Dresden". The target stoichiometry has been determined by nuclear reactions and by elastic recoil detection analysis (ERDA). An AMS measurement of the activated samples is in preparation.
Keywords: alpha rich freeze-out, capture reaction, hydrogen depth profiling
  • Lecture (Conference)
    Workshop on "Open problems and future directions in heavy element nucleosynthesis", 10.-12.04.2013, Debrecen, Hungary
  • Lecture (Conference)
    25th International Nuclear Physics Conference (INPC 2013), 02.-07.06.2013, Firenze, Italy

Publ.-Id: 18909 - Permalink


Electron-induced damage of biotin studied in the gas phase and in the condensed phase at a single-molecule level
Keller, A.; Kopyra, J.; Gothelf, K.; Bald, I.;
Biotin is an essential vitamin that is on the one hand relevant for the metabolism, gene expression, and in the cellular response to DNA damage, and on the other hand finds numerous applications in biotechnology. The functionality of biotin is due to two particular sub-structures, the ring structure and the side chain with carboxyl group. The heterocyclic ring structure results in the capability of biotin to form strong intermolecular hydrogen and van-der-Waals bonds with proteins such as streptavidin, whereas the carboxyl group can be employed to covalently bind biotin to other complex molecules. Dissociative electron attachment (DEA) to biotin results in a decomposition of the ring structure and the carboxyl group, respectively, within resonant features in the energy range 0-12 eV, thereby preventing the capability of biotin for intermolecular binding and covalent coupling to other molecules. Specifically, the fragment anions (M-H)-, (M-O)-, C3N2O-, CH2O2-, OCN-, CN-, OH- and O- are observed, and exemplarily the DEA cross section of OCN- formation is determined to be 3·10-19 cm2. To study the response of biotin to electrons within a complex condensed environment we use the DNA origami technique and determine a dissociation yield of (1.1 ± 0.2)·10-14 cm2 at 18 eV electron energy, which represents the most relevant energy for biomolecular damage induced by secondary electrons. The present results thus have important implications for the use of biotin as a label in radiation experiments.

Publ.-Id: 18908 - Permalink


Bildung Zn-haltiger Korrosionsprodukte bei einem Kühlmittelverluststörfall
Hoffmann, W.; Kryk, H.;
Im Kühlmittel eines DWR können nach einem Störfall mit Kühlmittelverlust während des Sumpfumwälzbetriebs höhere Konzentrationen an gelöstem Zink auftreten, die durch Korrosion verzinkter Einbauten des Containments verursacht werden. Bei höheren Temperaturen werden feste Korrosionsprodukte ausgeschieden. Die Ausscheidung lief im Batchversuch mit einer Verzögerung ab, was auf komplexe Vorgänge bei der Partikelbildung hinweist. Unterschiede in der chemischen Zusammensetzung zu Produkten, die an Heizelementen entstehen, lassen einen Einfluss der Bildungsbedingungen auf den Reaktionsmechanismus erkennen. Durch die im Notkühlkreislauf vorliegenden Temperaturgradienten können die korrosionsbedingte Zn-Auflösung und Partikelbildung gleichzeitig ablaufen. Die Bildung und Ablagerung von Zn-Korrosionsprodukten im Kern soll durch weiterführende Arbeiten im Rahmen des Projektes untersucht werden.
Keywords: LOCA, Zn corrosion, boric acid, deposition of corrosion products
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2013, 14.-16.05.2013, Berlin, Deutschland
    CD-ROM

Publ.-Id: 18907 - Permalink


Simulation of particle deposition and multilayer formation between periodic steps
Lecrivain, G.; Drapeau-Martin, S.; Barth, T.; Hampel, U.;
In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 8,000. Particles in the size range d = 1...100μm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site
  • Lecture (Conference)
    Cluster Workshop on Thermal Hydraulics of Innovative Nuclear Systems, 06.-07.02.2013, Stockholm, Sweden

Publ.-Id: 18906 - Permalink


Simulation of particle bed formation between obstacles
Lecrivain, G.; Hampel, U.;
In a pebble-bed high temperature reactor core where thousands of pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust eventually deposits in the primary circuit of the reactor. The numerical prediction of graphite dust deposition is therefore a key safety issue and needs investigation. The deposition of aerosol graphite particles in a turbulent channel flow obstructed by periodic steps is here numerically investigated at Reynolds number Re = 10,000. Particles in the size range d = 1...20µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. A two dimensional quasi-static simulation is performed. The quasi-static assumption is motivated by the time duration of the experimental test which lasts several hours. The iterative process is decomposed as follows: a Reynolds Averaged Navier Stokes turbulence model is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After sufficient deposition of the particulate matter, the build-up of the dust layer is computed using mechanics of dry granular material. The wall boundaries of the computational domain are then updated prior to the next flow simulation. The procedure is repeated until the dust layer reaches appropriate growth. The result of the multi-layer deposition matches reasonably well that of the experimental test performed on-site
  • Lecture (others)
    2nd Ph.D. Reactive Transport Modeling Meeting, 26.03.2013, Leipzig, Dresden

Publ.-Id: 18905 - Permalink


Simulation of graphite dust resuspension in a turbulent square dust flow
Lecrivain, G.; Loyseau, X.; Hampel, U.;
In a pebble-bed High Temperature Reactor (HTR) core where thousands of graphite pebbles are amassed, the friction between the outer graphite layers of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the coolant gas and deposits in the primary circuit of the reactor. In the event of a Loss of Coolant Accident (LOCA) radioactive carbonaceous dust may be resuspended and escape the system boundaries. There is therefore a need to predict the dust resuspension during a LOCA.
A resuspension model is here presented and coupled with computational fluid dynamics. A Reynolds-averaged Navier–Stokes is employed to simulate the turbulent flow in a wall-bounded channel flow. Micro-sized graphite particles are initially placed on the bottom wall surface of the virtual channel flow. The gas velocity is gradually increased and the resuspended fraction is plotted as a function of the wall shear velocity. The number of reentrained particles increases with gas velocity. The overall resuspended fraction matches experimental data available from the literature. It is found that particles far from the side walls reenter the turbulent flow much faster than those near the corner.
Findings from this study can be used for the prediction of carbonaceous dust resuspension in a HTR during a LOCA.
  • Open Access LogoContribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-15.05.2013, Pisa, Italy

Publ.-Id: 18904 - Permalink


Infrared ellipsometry for improved laterally resolved analysis of thin films
Hinrichs, K.; Furchner, A.; Sun, G.; Gensch, M.; Rappich, J.; Oates, T.;
In the present article we discuss developments towards increasing the spatial resolution of infrared ellipsometry and ellipsometric microscopy for the study of thin films. Relevant aspects in the interpretation of observed peaks in the infrared (ellipsometric) spectra are discussed. In particular anisotropic effects in dependence of molecular orientations in organic films and the excitation of a macroscopic wave, the Berreman mode, in thin silicon oxide films are addressed. For correct interpretation of measured data optical simulations are essential to avoid incorrect conclusions on band frequency and assignments.
Keywords: FTIR-microscopy, Infrared spectroscopic ellipsometry, molecular orientation, thickness, polymer film, silicon oxide

Publ.-Id: 18903 - Permalink


Speciation of iodine isotopes inside and outside of a contaminant plume at the Savannah River Site
Schwehr, K. A.; Otosaka, S.; Merchel, S.; Kaplan, D. I.; Zhang, S.; Xu, C.; Li, H.-P.; Ho, Y.-F.; Yeager, C. M.; Santschi, P. H.; Aster, T.;
A primary obstacle to understanding the fate and transport of the toxic radionuclide 129I (a thyroid seeker) is an accurate method to distinguish it from its stable isotope, 127I, and to quantify its various species at environmentally relevant concentrations (~10-8 M). A pH-dependent solvent extraction and combustion method was paired with accelerator mass spectrometry (AMS) to measure ambient levels of 129I/127I isotope ratios and iodine speciation (iodide (I-), iodate (IO3-), and organo-I (OI)) in aquatic systems. The method exhibits an overall uncertainty of 10% or less for iodide and iodate, and less than 20% for organo-I species concentrations and enabled 129I measurements as low as 0.5 Bq/L in groundwater from the Savannah River Site (SRS) in South Carolina, USA along a pH, redox potential (Eh), and organic carbon gradient. The data confirmed that the 129I/127I ratios and species distribution were strongly pH dependent, consistent with our knowledge that the 129I was emanating from a strongly acidic source. Low 129I concentrations detected in samples collected outside the known 129I plume, as delineated by the Maximum Contaminant Level (MCL) of 1 pCi/L129I (0.037 Bq/L), were still orders of magnitude higher than ambient 129I concentration typically found in the USA groundwater. This is likely due to past atmospheric releases of volatile 129I species by SRS nuclear reprocessing facilities near the study site. The results confirmed the existence of 129I as not only iodide, but as organic iodine and iodate species. This study underscores the importance of understanding a contaminant’s biogeochemistry at multiple concentrations, concentrations below and above regulatory MCLs.
Keywords: Radioiodine (I-129), Iodide, Iodate, Organo-iodine, Accelerator mass spectrometry, AMS, Iodine speciation

Publ.-Id: 18902 - Permalink


Crystallization induced by thermal annealing with millisecond pulses in silicon-on-insulator films implanted with high doses of hydrogen ions
Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.;
The crystallization of silicon-on-insulator films, implanted with high doses of hydrogen ions, upon annealing with millisecond pulses is studied. Immediately after hydrogen-ion implantation, the formation of a three-phase structure composed of silicon nanocrystals, amorphous silicon, and hydrogen bubbles is detected. It is shown that the nanocrystalline structure of the films is retained upon pulsed annealing at temperatures of up to similar to 1000A degrees C. As the temperature of the millisecond annealing is increased, the nanocrystal dimensions increase from 2 to 5 nm and the fraction of the nanocrystalline phase increases to similar to 70%. From an analysis of the activation energy of crystal phase growth, it is inferred that the process of the crystallization of silicon films with a high (similar to 50 at %) hydrogen content is limited by atomic-hydrogen diffusion.
Keywords: Crystallization, Flash Lamp Annealing, Hydrogen Implantation, SOI

Publ.-Id: 18901 - Permalink


A new approach to chemical imaging with PIXE using an X-ray colour camera
Munnik, F.; Hanf, D.; Ziegenrücker, R.; Renno, A. D.;
Summary:
A new approach using poly-capillaries has been used for laterally resolved PIXE.
Promising for large area surveys.
The experimental setup is ready and works.

Outlook:
Start of a Ph.D. student in the framework of the Marie-Cure project SPRITE.
Some technical extensions have still to be installed.
Development data-reduction protocols and image reconstruction.
Development of integrated control and analysis software.
Keywords: PIXE, CCD camera
  • Lecture (Conference)
    Workshop „Ionenstrahlen – Forschung und Anwendung“, 12.-13.06.2013, Leipzig, Deutschland

Publ.-Id: 18900 - Permalink


Prozessführung und Echtzeit-Monitoring von Grignard-Reaktionen
Kryk, H.;
Als Grignard-Reaktionen werden chemische Reaktionen zwischen einem organischen Halogenid und Magnesium zur entsprechenden magnesium-organischen Verbindung (Grignard-Reagenz) bezeichnet, welche große Bedeutung als Zwischenprodukte für organische Synthesen in der Feinchemie und der pharmazeutischen Industrie haben. Grignard-Reaktionen besitzen aufgrund des spezifischen Prozessverhaltens der stark exothermen Bildungsreaktionen und der hohen Reaktivität der Grignard-Reagenzien ein erhöhtes Gefahrenpotenzial. Hauptgefahrenquellen sind das verzögerte Starten der Reaktion bei unzulässig hoher Halogenid-Konzentration und Halogenid-Akkumulationen im Rührkesselreaktor während des Semibatch-Prozesses durch hohe Dosierraten und/ oder sinkende Reaktionsgeschwindigkeiten. Von großer Bedeutung für die Prozesssicherheit sind deshalb industriell anwendbare Methoden für eine objektive Detektion des Reaktionsstarts und für die Echtzeit-Verfolgung von Edukt-Akkumulationen im Reaktionsgemisch.
In Form eines Übersichtsvortrages werden online-spektroskopische Methoden zur Reaktionsverfolgung mittels FTIR sowie am HZDR entwickelte, auf gekoppelten Energie- und Stoffbilanzen basierende echtzeitfähige Verfahren zur Reaktionsstart-Detektion und zur Verfolgung der Edukt- und Produktkonzentrationen im Reaktionsgemisch eines Rührkesselreaktors vorgestellt und im Detail erläutert. Weiterhin erfolgt der Vergleich zwischen industriell etablierten Detektionsmethoden unter Nutzung konventioneller Prozesssignale sowie analytik- und bilanzbasierten Verfahren, wobei die Vor- und Nachteile der einzelnen Methoden dargestellt werden. Aus den Ergebnissen der bilanzbasierten Reaktionsverfolgung können sicherheitstechnische Kenngrößen abgeleitet werden, die eine inhärent sichere Prozessführung bei gleichzeitiger Erhöhung der Prozesseffizienz ermöglichen.
Keywords: Grignard, process control, FTIR, real-time monitoring, heat balance, process safety, inherent safety
  • Invited lecture (Conferences)
    Firmen-Kolloquium der Saltigo GmbH, 13.06.2013, Leverkusen, Deutschland

Publ.-Id: 18899 - Permalink


Impact of Triaxiality on the Emission and Absorption of Neutrons and Gamma Rays in Heavy Nuclei
Grosse, E.; Junghans, A. R.; Massarczyk, R.;
For many spin-0 target nuclei neutron capture measurements yield information on level densities at the neutron separation energy. Also the average photon width has been determined from capture data as well as Maxwellian average cross sections for the energy range of unresolved resonances. Thus it is challenging to use this data set for a test of phenomenological prescriptions for the prediction of radiative processes. An important ingredient for respective calculations is the photon strength function for which a parameterization was proposed using a fit to giant dipole resonance shapes on the basis of theoretically determined ground state deformations including triaxiality. Deviations from spherical and axial symmetry also influence level densities and it is suggested to use a combined parameterization for both, level density and photon strength. The formulae presented give a good description of the data for low spin capture into 124 nuclei with 72 Keywords: Nuclear triaxiality; level density; average radiative width; Maxwellian averaged cross sections; nuclear waste transmtation

Publ.-Id: 18898 - Permalink


Geometallurgical Classification of REE Mineralisation in Alkaline Complexes
Atanasova, P.; Gutzmer, J.; Leijd, M.;
Alkaline complexes comprise one of the most promising future sources for future rare earth element supply. They are particularly enriched in heavy rare earth elements. However, the often complex and highly unusual mineralogy of REE-enriched ores from alkaline complexes pose particular challenges for beneficiation. A geometallurgical approach is required to quantify mineralogical and textural diversity and variability. Based on a geometallurgical model, a suitable approach to beneficiation can be developed. SEM-based image analysis can be used to characterize ores as well as beneficiation products. A wide range of tangible mineralogical and textural parameters are constrained for every ore type, including mineral abundance, grain size, and liberation. The use of such an approach is illustrated here for the case of the Norra Kärr alkaline complex, Sweden. The complex is highly deformed and metamorphosed and known currently to contain resources of 41.6 Mt @ 0.57 % TREO with 51 % HREO/TREO and 1.7 % ZrO2 (indicated) and 16.5 Mt @ 0.64 % TREO with 49% HREO/TREO and 1.7 % Zr2O (inferred). Mineralization is hosted by aegirine nepheline-syenites that show a considerable textural and compositional diversity. REE-bearing minerals include eudialyte group minerals and very minor mosandrite and cerite. Zr is hosted by Zr-silicates catapleiite and eudialyte. Current research focuses to provide quantitative mineralogical and textural constraints for different lithological domains recognized in the HREE-Zr-mineralized zones of the complex. Based on the results, a geometallurgical model will be developed that will be based on the processing characteristics rather of the different portions of the mineralized zones.
Keywords: rare earth elements, alkaline complex, geometallurgy
  • Lecture (Conference)
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
  • Contribution to proceedings
    Critical Minerals 2013, 04.-05.06.2013, Perth, Australia
    Critical Minerals Conference 2013 - Conference Proceedings, Australia: Australasian Institute of Mining and Metallurgy, 978 1 921522 88 8

Publ.-Id: 18897 - Permalink


Transient increase of the energy gap in superconducting NbN thin Films excited by resonant narrow-band terahertz pulses
Beck, M.; Rousseau, I.; Klammer, M.; Leiderer, P.; Mittendorff, M.; Winnerl, S.; Helm, M.; Gol’tsman, G. N.; Demsar, J.;
Observations of radiation-enhanced superconductivity have thus far been limited to a few type-I superconductors (Al, Sn) excited at frequencies between the inelastic scattering rate and the superconducting gap frequency 2Δ=h. Utilizing intense, narrowband picosecond THz pulses, tuned to just below and above 2Δ=h of a BCS superconductor NbN, we demonstrate that superconducting gap can be transiently increased also in a type-II dirty-limit superconductor. The effect is particularly pronounced at higher temperatures and is attributed to radiation induced non-thermal electron distribution persisting on a 100 ps timescale.
Keywords: radiation-enhanced superconductivity, NbN, Time resolved spectroscopy

Publ.-Id: 18896 - Permalink


Fast relaxation of free carriers in compensated n- and p-type germanium
Deßmann, N.; Pavlov, S.; Mittendorff, M.; Winnerl, S.; Zhukavin, R.; Tsyplenkov, V.; Shengurov, V.; Shastin, V.; Abrosimov, N.; Riemann, H.; Hübers, H.-W.;
The relaxation of free holes and electrons in compensated germanium doped by gallium (p-Ge:Ga:Sb) and antimony (n-Ge:Sb:Ga) has been studied by a pump-probe experiment with the free-electron laser FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. The relaxation times vary between 20-300 ps and depend on the incident THz intensity and compensation level. The relaxation times are about five times shorter than previously obtained results for uncompensated n-Ge:Sb and p-Ge:Ga. The results support the development of fast photoconductive detectors in the THz frequency range.
Keywords: Time resolved spectroscopy, THz
  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665867

Publ.-Id: 18895 - Permalink


The computation of lipophilicities of 64Cu PET systems based on a novel approach for fluctuating charges
Comba, P.; Martin, B.; Sanyal, A.; Stephan, H.;
A QSPR scheme for the computation of lipophilicities of 64Cu complexes was developed with a training set of 24 tetraazamacrocylic and bispidine-based CuII compunds and their experimentally available 1-octanol/water distribution coefficients. A minimum number of physically meaningful parameters was used in the scheme, and these are primarily based on data available from molecular mechanics calculations, using an established force field for CuII complexes and a recently developed scheme for the calculation of fluctuating atomic charges. The developed model was also applied to an independent validation set and found to accurately predict distribution coefficients of potential 64Cu PET (positron emission tomography) systems. A possible next step would be the development of a QSAR-based biodistribution model to track the uptake of imaging agents in different organs and tissues of the body. It is expected that such simple, empirical models of lipophilicity and biodistribution will be very useful in the design and virtual screening of positron emission tomography (PET) imaging agents.

Publ.-Id: 18894 - Permalink


Ultra-fast transistor-based detectors for precise timing of near infrared and THz signals
Preu, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Weber, H. B.;
A whole class of two-color experiments involves intense, short Terahertz radiation pulses. A fast and moderately sensitive detector capable to resolve both near-infrared and Terahertz pulses at the same time is highly desirable. Here we present the first detector of this kind. The detector element is a GaAs-based field effect transistor operated at room temperature. THz detection is successfully demonstrated at frequencies up to 4.9 Hz. The THz detection time constant is shorter than 30 ps, the optical time constant is 150 ps. This detector is ideally suited for precise, simultaneous resolution of optical and THz pulses and for pulse characterization of high-power THz pulses up to tens of kW peak power levels. The dynamic range of the detector is as large as 65 ± 3 dB/√Hz, enabling applications in a large variety of experiments and setups, also including table-top systems.
Keywords: ultrafast detector, THz detection

Publ.-Id: 18893 - Permalink


Resonance triplet at Eα = 4.5 MeV in the 40Ca(α,γ)44Ti reaction
Schmidt, K.; Akhmadaliev, S.; Anders, M.; Bemmerer, D.; Boretzky, K.; Caciolli, A.; Degering, D.; Dietz, M.; Dressler, R.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Hannaske, R.; Junghans, A. R.; Marta, M.; Menzel, M.-L.; Munnik, F.; Schumann, D.; Schwengner, R.; Szücs, T.; Wagner, A.; Yakorev, D.; Zuber, K.;
The 40Ca(α,γ)44Ti reaction is believed to be the main production channel for the radioactive nuclide 44Ti in core-collapse supernovae. Radiation from decaying 44Ti has been observed so far for two supernova remnants, and a precise knowledge of the 44Ti production rate may help improve supernova models. The 40Ca(α,γ)44Ti astrophysical reaction rate is determined by a number of narrow resonances. Here, the resonance triplet at Eα = 4497, 4510, and 4523 keV is studied both by activation, using an underground laboratory for the counting, and by in-beam spectrometry. The target properties are determined by elastic recoil detection analysis and by nuclear reactions. The strengths of the three resonances are determined to ωγ = (0.92 ± 0.20), (6.2 ± 0.5), and (1.31 ± 0.24) eV, respectively, a factor of two more precise than before. The strengths of this resonance triplet may be used in future works as a point of reference. In addition, the present new data directly affect the astrophysical reaction rate at relatively high temperatures, above 3.5GK.
Keywords: alpha rich freeze-out, capture reaction, hydrogen depth profiling

Publ.-Id: 18892 - Permalink


InGaAs-based Large Area Photoconductive Emitters For 1.55 µm Excitation
Xu, M.; Mittendorff, M.; Dietz, R.; Göbel, T.; Schneider, H.; Helm, M.; Winnerl, S.;
We present a scalable large-area terahertz (THz) emitter designed for excitation with 1.55 µm pump radiation. It is based on an InGaAs heterostructure combined with a microstructured electrode pattern. Electric fields of more than 2.5 V/cm in the THz focus are reached, the spectrum of the pulses extends up to 3 THz.
Keywords: photoconductive THz emitter, 1.55 µm excitation, InGaAs-based THz emitter
  • Poster
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665436

Publ.-Id: 18891 - Permalink


Ultrafast graphene-based THz detection at room temperature
Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.;
We present an ultrafast terahertz detector suitable for wavelengths from 30 μm to 220 μm, which is based on a graphene flake. A logarithmic-periodic antenna is used to couple the radiation to the flake. The detector, characterized by a fast rise time combined with room temperature operation, is well suited for determining timing differences of THz laser pulses.
Keywords: graphene, ultrafast detector, THz detection
  • Lecture (Conference)
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves, 01.-06.09.2013, Mainz, Deutschland
    DOI: 10.1109/IRMMW-THz.2013.6665851

Publ.-Id: 18890 - Permalink


Surface patterning by heavy-ion induced melting
Böttger, R.; Bischoff, L.; Heinig, K.-H.; Liedke, B.; Anders, C.; Urbassek, H. M.;
The driving forces for surface patterning by ion bombardment have been under discus-sion for many years. At first, a continuum theory based on competition between the sur-face instability due to curvature dependent sputtering and surface smoothing by Mul-lins-Herring diffusion was proposed [1]. Later, a continuum theory with a surface destabilizing term based on ion impact-induced mass-drift was published [2]. Recently, this momentum transfer to target atoms by ion impacts has been proven to be the dominating driving force for pattern formation in many cases [3]. In case that collision-induced defects cannot reach the surface to form a crater, defect diffusion induced pat-terns like pits and sponges can form. It should be noted that the manifold of beautiful patterns on Si and Ge published recently are caused by metal impurities [4]. Thus, it is now commonly accepted that at normal ion incidence on elemental, amorphous targets no surface patterns should evolve. However, we recently found well-ordered dot patterns at normal irradiation of Ge with polyatomic Bi ions of 10-20 keV kinetic energy per atom [5]. Similar patterns were found with monatomic Bi ion irradiation of heated Ge substrates, when the deposited energy per Ge atom exceeds a critical value within a larger volume [6].
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been combined with modeling based on molecular dynamics and kinetic Monte-Carlo simulations. The studies prove that these patterns appear only, if nanomelt pools form at the surface of irradiated Ge or Si.
It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology, which evolves as . The competing surface roughening term results from the missing material due to intense sputtering by Bi ions. This leads to a depression of the melt pool surface. For off-normal incidence, the meniscus is shifted with respect to the ion impact point in dependence on the surface slope, which leads to a surface destabilizing up-hill mass drift.
[1] R. M. Bradley and J. M. E. Harper, J. Vac. Sci. Technol. A 6 (1988) 2390.
[2] G. Carter and V. Vishnyakov, Phys. Rev. B 54 (1996) 17647.
[3] C. S. Madi, H. B. George, and M. J. Aziz, J. Phys. Condens. Matter 21 (2009) 224010.
[4] B. Ziberi, M. Cornejo, F. Frost, and B. Rauschenbach, J. Phys. Condens. Matter 21 (2009) 224003.
[5] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko, and W. Pilz, Nucl. Instr. Meth. Phys Res. B 272 (2012) 198.
[6] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz, and B. Schmidt, J. Vac. Sci. Technol. B 30 (2012) 06FF12.
Keywords: silicon, germanium, nanodots, polyatomic ions, melting
  • Lecture (Conference)
    The 17th International Conference on Radiation Effects in Insulators 2013 (REI-17), 30.06.-05.07.2013, Helsinki, Finland

Publ.-Id: 18889 - Permalink


Condensation of the dianion of ethyl acetoacetate with perfluoroalkyl iodides. Application to the synthesis of 3-perfluoroalkylsalicylic acids
Mamat, C.; Langer, P.;
3-Perfluoroalkylsalicylic esters and acids were prepared based on the condensation of the dianion of ethyl acetoacetate with various perfluoroalkyl iodides.
Keywords: Dianions Condensation; Organofluorine compounds Arenes; Cyclizations Regioselectivity

Publ.-Id: 18888 - Permalink


Surface Patterning by heavy-ion induced melt pools
Böttger, R.; Bischoff, L.; Liedke, B.; Heinig, K.-H.; Anders, C.; Urbassek, H. M.;
The driving forces for surface patterning by ion bombardment have been under discussion for many years. Bradley and Harper developed a continuum theory based on the competition between the surface instability due to curvature dependent sputtering and surface smoothing by Mullins-Herring diffusion [1]. Later, a continuum theory with a surface destabilizing term based on ion impact induced mass drift was published [2]. Recently, this momentum transfer to target atoms by ion impacts has been proven to be the dominating driving force for pattern formation in many cases [3], it can be treated by a neat crater function formalism. In case that the collision-induced defects cannot reach the surface to form a crater function, nonlinear diffusion induced pattern like holes and sponges can form. However, it should be noted that the manifold of beautiful patterns on Si and Ge published recently are dominated by metal impurities [4].
Thus, currently the community arrived at the consensus that at normal ion incidence on elemental, amorphous targets no surface pattern should evolve. However, we recently found well-ordered dot patterns at normal irradiation of Ge with polyatomic Bi ions of ~10…20 keV kinetic energy per atom [5]. Similar patterns (Figure 1) were found with monoatomic Bi ions at elevated Ge substrate temperatures [6], where the energy per Ge atom exceeds a critical value within a larger volume (Figure 2).
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been combined with modeling based on molecular dynamics and kinetic Monte-Carlo simulations. The studies prove that these patterns appear only, if nanomelt pools form at the Ge surface.
It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology, which evolves as . The competing surface destabilizing term results from the missing material due to intense sputtering by Bi ions. This leads to a depression of the melt pool surface, a meniscus, which is visualized in Figure 3 due to amorphous resolidification after Bi3+ ion impact into c-Ge. For off-normal incidence, the meniscus is shifted with respect to the ion impact point in dependence on the surface slope, which leads to a surface destabilizing up-hill mass drift.
Keywords: self-organized surface patterns, ion irradiation, germanium, silicon, bismuth, polyatomic ions, melting
  • Invited lecture (Conferences)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark
  • Lecture (others)
    Symposium TU Vienna, 28.02.2013, Vienna, Austria

Publ.-Id: 18887 - Permalink


Automated preparation of [18F]AFP and [18F]BFP: Two novel bifunctional 18F-labeling building blocks for Huisgen-click
Pretze, M.; Mamat, C.;
A bioorthogonal labeling approach based on the Huisgen-click reaction including the one-step radiosynthesis of two novel versatile and bifunctional labeling building blocks ([18F]AFP) [18F]12 and ([18F]BFP) [18F]6 with the PET radionuclide fluorine-18 is described. Optimized reaction conditions for the fully automated synthesis procedure using the TRACERlab FxFN module gave both piperazine derivatives [18F]6 and [18F]12 with radiochemical yields of 31 9% (S.D., n = 8, d.c.) and 29 5% (S.D., n = 19, d.c.), respectively, within 40 min synthesis time and high specific activities after convenient purification using silica gel cartdridges. First biological studies of both building blocks revealed a remarkable in vitro stability in rat blood as well as rat plasma over more than 60 min. Sample ligation reactions of [18F]6 and [18F]12 with azide and alkyne functionalized amino acid derivatives yielded the corresponding labeled triazoles in good to high RCYs. Moreover, the azide functionalized peptide 17, which is highly affine to the EphB2 receptor due to its SNEW sequence, was synthesized and successfully radiolabeled with [18F]BFP [18F]6 under relatively mild conditions yielding the corresponding triazolyl-peptide [18F]18.
Keywords: Click chemistry; Bioorthogonal; Building block; Automated synthesis; Eph receptor

Publ.-Id: 18886 - Permalink


An Efficient Bioorthogonal Strategy Using CuAAC Click Chemistry for Radiofluorinations of SNEW Peptides and the Role of Copper Depletion
Pretze, M.; Kuchar, M.; Bergmann, R.; Steinbach, J.; Pietzsch, J.; Mamat, C.;
The EphB2 receptor is known to be overexpressed in various types of cancer and is therefore a promising target for tumor cell imaging by positron emission tomography (PET). In this regard, imaging could facilitate the early detection of EphB2-overexpressing tumors, monitoring responses to therapy directed toward EphB2, and thus improvement in patient outcomes. We report the synthesis and evaluation of several fluorine-18-labeled peptides containing the SNEW amino acid motif, with high affinity for the EphB2 receptor, for their potential as radiotracers in the non-invasive imaging of cancer using PET. For the purposes of radiofluorination, EphB2-antagonistic SNEW peptides were varied at the C terminus by the introduction of l-cysteine, and further by alkyne- or azide-modified amino acids. In addition, two novel bifunctional and bioorthogonal labeling building blocks [18F]AFP and [18F]BFP were applied, and their capacity to introduce fluorine-18 was compared with that of the established building block [18F]FBAM. Copper-assisted Huisgen 1,3-dipolar cycloaddition, which belongs to the set of bioorthogonal click chemistry reactions, was used to introduce both novel building blocks into azideor alkyne-modified SNEW peptides under mild conditions. Finally, the depletion of copper immediately after radiolabeling is a highly important step of this novel methodology.

Publ.-Id: 18885 - Permalink


Design and Development of 99mTc-‘4 + 1’-Labeled Dextran-Mannose Derivatives as Potential Radiopharmaceuticals for Sentinel Lymph Node Detection
Giglio, J.; Fernandez, S.; Jentschel, C.; Pietzsch, H.-J.; Papadopoulos, M.; Pelecanou, M.; Pirmettis, I.; Paolino, A.; Rey, A.;
The synthesis, labeling, and biological evaluation of a dextran derivative (DCM-30-iso) as potential radiopharmaceutical for sentinel lymph node imaging is presented. DCM-30-iso bears mannose as active moiety and isocyanide as ligand for technetium through the formation of a ‘4 + 1’ Tc(III) mixed-ligand complex. A second derivative without mannose (DC-25-iso) was also prepared and evaluated as control. DCM-30-iso and DC-25-iso were synthesized from dextran in four steps (>50% overall yield) and characterized by spectroscopic methods. Labeling with 99mTc was achieved by reaction with 2,2¢,2¢¢-nitrilotris(ethanethiol) and 99mTc-EDTA. Radiochemical purity was above 90% and was stable for at least 4 hours postlabeling at 37C. The identity of the 99mTc complex was established through comparative HPLC studies using the well-characterized analogous Re-DC-25-iso complex. Biodistribution and imaging experiments of 99mTc-DCM-30-iso showed high uptake in the popliteal lymph node, which could be blocked with preinjection of mannose, and very low uptake in other nodes and organs. The nonmannosylated 99mTc-DC-25-iso derivative showed negligible uptake in all lymph nodes. The novel dextran-mannose derivative DCM-30-iso can be successfully labeled with 99mTc to give a well-characterized ‘4 + 1’ complex with favorable biological properties as sentinel lymph node imaging agent.
Keywords: ‘4 + 1’ Tc(III) mixed-ligand complexes, dextran, mannose, rhenium, sentinel lymph node imaging, Technetium-99m

Publ.-Id: 18883 - Permalink


The PET-derived tumor-to-blood standard uptake ratio (SUR) is superior to tumor SUV as a surrogate parameter of the metabolic rate of FDG
van den Hoff, J.; Oehme, L.; Schramm, G.; Langner, J.; Lougovski, A.; Petr, P.; Beuthien-Baumann, B.; Hofheinz, F.;
The Standard Uptake Value (SUV) approach in oncological PET has known shortcomings all of which affect the reliability of the SUV as a surrogate of the targeted quantity, the metabolic rate of FDG ([18F]fluorodeoxyglucose), Km. Among the shortcomings are time dependence, susceptibility to errors in scanner and dose calibration, insufficient correlation between systemic distribution volume and body weight, and, consequentially, residual inter-study variability of the arterial input function (AIF) despite SUV normalization. Especially the latter turns out to be a crucial factor adversely affecting the correlation between SUV and Km and causing inter-study variations of tumor SUVs that do not reflect actual changes of the metabolic uptake rate. In this work, we propose to replace tumor SUV by the tumor to blood standard uptake ratio (SUR) in order to distinctly improve the linear correlation with Km.
Methods: Assuming irreversible FDG kinetics, SUR can be expected to exhibit a much better linear correlation to Km than SUV. The theoretical derivation for this prediction is given and evaluated in a group of 9 patients with liver metastases of colorectal cancer for which 15 fully dynamic investigations were available and Km could thus be derived from conventional Patlak analysis.
Results: For any fixed time point T at sufficiently late times p.i. the Patlak equation predicts a linear correlation between SUR and Km under the following assumptions: 1.) approximate shapeinvariance (but arbitrary scale) of the AIF across scans/patients and 2.) low variability of the apparent distribution volume Vr (the intercept of the Patlak Plot). This prediction – and validity of the underlying assumptions – has been verified in the investigated patient group. Replacing tumor SUVs by SURs does improve the linear correlation of the respective parameter with Km from r = 0:61 to r = 0:98.
Conclusion: SUR is an easily measurable parameter that is highly correlated to Km. In this respect it is clearly superior to SUV. Therefore, SUR should be seriously considered as a drop-in replacement for SUV-based approaches.
Keywords: SUV, tumor to blood ratio, PET, PET/CT, therapy response control, FDG

Publ.-Id: 18882 - Permalink


Effects of implantation temperature and thermal annealing on the Ga+ ion beam induced optical contrast formation in a-SiC:H
Tsvetkova, T.; Wright, C. D.; Kitova, S.; Bischoff, L.; Zuk, J.;
The effects of implantation temperature and post-implantation thermal annealing on the Ga+ ion beam induced optical contrast formation in hydrogenated silicon–carbon alloy films have been studied. As a result of the implantation a well-expressed ‘‘darkening’’ effect (i.e. absorption edge shift to the longerwavelength/lower-photon-energy region) has been registered. It is accompanied by a remarkable increase of the absorption coefficient up to 2 orders of magnitude in the measured photon energy range (1.5–3.1 eV). The optical contrast thus obtained (between implanted and unimplanted regions of the film material) has been made use of in the form of optical pattern formation by computer-operated Ga+-focused ion beam. Possible applications of this effect in the area of submicron lithography and high-density optical data storage have been suggested with regard to the most widely spread focused micro-beam systems based on Ga+ liquid metal ion sources. The fact that Ga has a very low melting point (Tm = 29.8 C) and an unusual feature of volume contraction on melting are factors which favour Ga incorporation upon ion-implantation as dispersed clusters, or small nanoparticles. It has been previously noted that Ga precipitation into nanoparticles can vary dramatically (in terms of particle size) with Ga concentration and small changes in surface implant temperature, thus affecting the optical properties of the target. The precise role of implantation temperature effects, i.e. the target temperature during Ga+ ion irradiation, on the optical contrast obtainable, has been therefore a key part of this study. Appropriate post-implantation annealing treatments were also studied, since these are expected to offer further benefits in reducing the required ion dose and enhancing contrast, thus increasing the cost-effectiveness of the bit-writing method.
Keywords: Focused ion beams; Optical data storage; Near-field techniques

Publ.-Id: 18881 - Permalink


Surface morphologies of Ge and Si under heavy single-atom and poly-atom ion irradiation
Bischoff, L.; Böttger, R.; Heinig, K.-H.;
Well-ordered dot patterns can be obtained at normal irradiation on Ge and Si with polyatomic Bi ions of ~10…20 keV kinetic energy per atom. Similar patterns were found with monoatomic Bi ions at elevated Ge substrate temperatures, when the energy per Ge atom exceeds a critical value.
To identify the driving force for this unexpected dot pattern formation, focused ion beam and broad beam studies have been performed in parallel with molecular dynamics and kinetic Monte-Carlo simulations. This investigation proves that these patterns appear only, if nanomelt pools form at the surface of irradiated Ge or Si. It will be shown that melt pools induce a surface smoothing process like in the well-known laser polishing technology. Contrary, surface destabilization results from the shift of the center of the melt pool meniscus with respect to the ion impact point, where the meniscus arises from the missing material due to sputtering.
Keywords: polyatomic Bi ions; germanium; silicon; melt pool
  • Lecture (Conference)
    Workshop „Ionenstrahlen in Forschung und Anwendung“ & Treffen der DFG-Forschergruppe FOR 845, 12.-14.06.2013, Leipzig, Germany

Publ.-Id: 18880 - Permalink


A methodology for highly accurate results of direct numerical simulations: Drag force in dense gas-solid flows at intermediate Reynolds number
Tang, Y.; Kriebitzsch, S. H. L.; Peters, E. A. J. F.; van der Hoef, M. A.; Kuipers, J. A. M.;
Simulations with an iterative immersed boundary method (IBM) are performed to predict the drag force for gas–solid flows at intermediate Reynolds number (Re). A methodology is developed to obtain highly accurate IBM results at relatively low computational cost. First of all, “resolution-free” gas–solid forces are estimated for a face-centered-cubic (FCC) array of monodisperse spheres in terms of the resolution convergence. This data is subsequently used to compute the relocation of the marker points, so as to correct for the resolution dependence of the simulated force on coarser grids. We then assume that the relocation derived from FCC arrays is also valid for the simulations of random arrays. As a result, the accurate gas–solid forces on random arrays can be obtained from the simulations at a relatively low resolution. We have applied this methodology to predict the gas–solid force at Re = 100 and 50, with ϕ varying from 0.1 up to the close-pack limit. The results are consistent with the recently published correlations. A new fit has been proposed for the interaction force at these two specific Reynolds numbers. This methodology makes it feasible to model the dense granular flows of large assemblies at high Re by direct numerical simulations at relatively low computational cost.
Keywords: direct numerical simulation, immersed boundary method, methodology, gas-solid drag, resolution-free

Publ.-Id: 18879 - Permalink


Lighting Up the Inner Workings of LWFA – How Radiative Particle-in-Cell Simulations can Shed New Light into the Dynamics of Laser-Accelerated Electrons
Pausch, R.; Debus, A.; Steiniger, K.; Hübl, A.; Burau, H.; Widera, R.; Bussmann, M.; Schramm, U.;
We present simulations of angularly resolved radiation spectra from laser-wakefield accelerated electrons (LWFA) based on classical Liénard-Wiechert potentials ranging from infrared to the X-ray wavelengths.
These radiation spectra give insight into the momentum distribution with a spatial resolution small enough to study in detail the electron dynamics during the formation of the wakefield, the injection of electrons into the wakefield and in the coherent motion of electrons during acceleration. As spectral information is accessible in experiments, our results can serve as a valuable input to new diagnostics. A quantitative comparison of measured and simulated spectra poses a unique method to determine the phase space distribution of electrons in the LWFA process. Our code is capable of computing the spectra of all particles in the simulation and fully accounts for coherent effects. We thus can quantitatively predict the spectral intensities observed in experiment and are able to link them to specific phase space regions much smaller than the plasma wavelength. We show that radiation diagnostics can serve as a powerful tool to understand a large variety of plasma phenomena and how large-scale simulations of Petaflop performance can in the future help to optimize LWFA.
Keywords: radiation spectra, Liénard-Wiechert potentials, LWFA, laser wakefield acceleration, large-scale simulations, Petaflop, plasma phenomena, coherent radiation
  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Isola d'Elba, Italy

Publ.-Id: 18878 - Permalink


Publication fees for Open Access journals - work flows at Helmholtz Centres
Reschke, E.; Köhler, M.; Wagner, A.; Grosse, K.;
Open Access is a new way of publishing. The presentation aims to show how the golden way of Open Access Publishing has to be funding. Based on the "Berlin Declaration to Knowledge in the Science and Humanities" and the "Agreement of the Assembly of Members" (assembly of the directors of the Helmholtz Centres) the Helmholtz Research Centres organized the publishing and funding process in different ways. The presentation shows 4 examples for it: DESY, Forschungszentrum Jülich, GSI Darmstadt and HZDR.
Keywords: Open Access, Funding, Author fees, Publication fees
  • Lecture (others)
    Open Access to Publications and Data in the Research Field "Structure of Matter" of the Helmholtz Association, 10.-11.06.2013, Hamburg, Deutschland

Publ.-Id: 18877 - Permalink


Traveling-Wave Thomson-Scattering and optical FELs
Steiniger, K.; Pausch, R.; Widera, R.; Debus, A.; Kluge, T.; Bussmann, M.; Cowan, T.; Schramm, U.; Sauerbrey, R.;
We show that optical free electron lasers in the X-ray range can be realized using Traveling-Wave Thomson-scattering (TWTS). TWTS provides long interaction lengths in the centimeter to meter range with undulator periods in the micron range. These can be accomplished with existing petawatt class lasers as optical wigglers in a side scattering geometry by tilting the laser pulse front. TWTS circumvents both the nonlinear Thomson intensity threshold and the Rayleigh-length limit which in head-on Thomson-scattering prevents the SASE process to occur. Furthermore TWTS offers tuneability in the scattered wavelength via the incidence angle and flexibility in the optical undulator length.
In this talk we discuss the FEL dynamics of relativistic electrons in TWTS and quantify the influence of dispersion effects on the laser pulse properties and showing that they can be suppressed effectively. We present a self-consistent 1.5D FEL-theory which accounts for the oblique incident laser pulse and give scaling laws on the interaction geometry and FEL-amplification with respect to incidence angle and electron beam parameters. We finally present numbers on expected experimental performance for laser and electron beam parameters that will be available at HZDR.
Keywords: traveling-wave, thomson scattering, x-ray, free electron laser, laser pulse
  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Isola d'Elba, Italy

Publ.-Id: 18876 - Permalink


Resistive Switching in thermally oxidized Titanium Films
Blaschke, D.; Zahn, P.; Skorupa, I.; Scheumann, B.; Scholz, A.; Gemming, S.; Potzger, K.;
Polycrystalline rutile TiO2 thin films were prepared on Pt/Ti/SiO2/Si substrates by thermal oxidation of a 100nm thick titanium film at temperatures between 500°C and 800°C. We observed stable nonvolatile unipolar switching in the films oxidized at 600-800°C. Retention measurements showed stable ON and OFF states for a time of at least 24h at room temperature, if there was a sufficient relaxation period between the switching event and the start of the read out process. Without any relaxation time, we observed an increase in resistance in the high resistance state (HRS) after the RESET process. In contrast, the LRS did not show a time dependent resistance change after the SET process.
Keywords: TiO2; resistive switching; thermal oxidation; retention
  • Contribution to proceedings
    Semiconductor Conference Dresden-Grenoble (ISCDG), 2013 International, 26.-27.09.2013, Dresden, Germany
    Semiconductor Conference Dresden-Grenoble (ISCDG), 2013 International: IEEE, 978-1-4799-1250-6
    DOI: 10.1109/ISCDG.2013.6656318
  • Lecture (Conference)
    International Semiconductor Conference Dresden-Grenoble, 26.-27.09.2013, Dresden, Germany

Publ.-Id: 18875 - Permalink


Gated phantom irradiation for 4D in-beam and 4D off-beam PET comparison
Laube, K.; Bert, C.; Enghardt, W.; Helmbrecht, S.; Kaderka, R.; Kurz, C.; Parodi, K.; Saito, N.; Tian, Y.; Fiedler, F.;
no abstract available
Keywords: ion beam therapy, intra-fractional motion, in vivo dose monitoring, 4D PET
  • Open Access LogoContribution to external collection
    Katrin Große: GSI Scientific Report 2012, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2013, 486

Publ.-Id: 18873 - Permalink


The Helmholtz SIMS Network: Cooperation at Multiple Scales
Renno, A. D.; Merchel, S.; Akhmadaliev, S.; Rugel, G.; Ziegenrücker, R.; Döbeli, M.; Richnow, H.-H.; Wiedenbeck, M.;
Super-SIMS - also called Accelerator-SIMS or Trace Element Accelerator Mass Spectrometry (TEAMS) - is an ultrasensitive analytical method for the determination of stable elements and isotopes. A Super-SIMS-Set-up is now under installation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) ion beam centre where we are connecting a conventional SIMS-source (Cameca IMS 6f, formerly installed at the GFZ Potsdam, currently upgraded to a 7f-Auto) to a 6 MV tandem accelerator (Akhmadaliev et al., 2013). A similar set-up has been operated by the ETH Zurich for several years (Maden, 2003).
Due to the acceleration of the extracted sample ions to MeV-energies and their charge reversal from negative to positive ions, Super-SIMS can reach about 2 to 3 orders of magnitude lower detection limits (down to 10-12 or ppt, highly depending on analyte and matrix) as conventional SIMS.
The HZDR Super-SIMS will be part of the Helmholtz-SIMS-Network, called SIGMA, which is currently being developed. Other partners are the Helmholtz Centre for Environmental Research in Leipzig (NanoSIMS & TOF-SIMS currently under installation) and the GFZ Potsdam (High-resolution 1280-HR SIMS under installation). Thus, extensive knowledge exchange will assure the optimal environment for optimizing our highly sophisticated accelerator set-up running. Later, easy access for international users from research institutes from e.g. Brazil, India, Russia and South Africa is planned within SIGMA.
Funding from an Integrated Infrastructure Initiative (I3) from the European Commission within Horizon 2020 will be applied for; this would allow Trans-National Access (TNA) to both Super-SIMS facilities in Dresden and Zurich. An independent User Selection Panel will examine user proposals for TNA. After receiving a positive evaluation, European users can obtain free access to the Super-SIMS-facilities including logistical, scientific and technical support, and travel and accommodation grants. ETH Zurich and HZDR will widen their already established joint research activities from the I3-project SPIRIT (Möller, 2011) to reach the ultimate detection limits, which are possible using the Super-SIMS technique.
Keywords: Super-SIMS, AMS, accelerator-based mass spectrometry
  • Invited lecture (Conferences)
    7th Biennial Geo-SIMS Workshop, Lecture Series "SIMS: Current Strengths and Future Potential", 20.-22.08.2013, Potsdam, Deutschland

Publ.-Id: 18872 - Permalink


Ion-guided microstructure evolution of carbon-nickel nanocomposite films during ion beam assisted deposition: 3D sculpting at the nanoscale
Krause, M.; Buljan, M.; Oates, T. W. H.; Mücklich, A.; Fritzsche, M.; Facsko, S.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.; Abrasonis, G.;
Ion assistance during film growth provides unique opportunities to influence the microstructure due to energy transfer and imposed directionality. During nanocomposite film growth at low temperatures (RT to 300°C), phase separation occurs at the growing film surface. A systematic study of ion irradiation as a pure energy and momentum transfer agent in the context of surface diffusion assisted phase separations is, however, lacking. Here the influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 50 at.% Ni) thin films will be reported. Two types of ordered nanostructures, - tilted columns and self-organized 3D patterns with well-defined surface periodicity - are identified and characterized. For a given composition of the depositing flux, the transition from the column to the self-organized 3D pattern formation regime as a function of the assisting ion energy is demonstrated. Tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. The effects of the metal content and the assisting ion current on the self-organized 3D patterns and surface periodicity are studied. Mechanical and tribological properties of both types of nanostructures will be reported.

Acknowledgement: The work is funded by the European Union, LEI Folgeprojekt D1, "C-basierte Funktionsschichten für tribologische Anwendungen (CarboFunctCoat)", No. 7310000211.
Keywords: Nanocomposites, Ion assistance, pattern formation, microstructure
  • Lecture (Conference)
    E-MRS 2013 SPRING MEETING - Symposium W - Ion beam applications: new and innovative approaches, 26.-31.05.2013, Strasbourg, Frankreich

Publ.-Id: 18871 - Permalink


SWCNT growth from C:Ni nanocomposite templates
Krause, M.; Haluska, M.; Kunze, T.; Mücklich, A.; Hübner, R.; Melkhanova, S.; Bayrak, T.; Abrasonis, G.; Gemming, S.;
Single walled carbon nanotubes (SWCNT) grown from C:Ni nanocomposite thin film templates are studied by Raman mapping, scanning, and transmission electron microscopy. The templates consist of few nm thick films of Ni nanoparticles embedded in a protective matrix of amorphous carbon. They are prepared by ion beam sputtering, which allows a precise control of the particle size, shape, and arrangement in a sub nanometer length scale. SWCNT growth is performed by low pressure chemical vapour deposition in C2H2/ H2 at temperatures of about 735°C. The electron micrographs show that a large part of the nanoparticles preserves its initial geometry. The effect of the different particle morphologies on the mean SWCNT diameter and diameter distribution is demonstrated and discussed in the framework of current growth models.
Keywords: Nanocomposites, Single-walled carbon nanotube growth, diameter control, Raman mapping, electron microscopy
  • Poster
    27th International Winterschool on Electronic Properties of Novel Materials (IWEPNM), 02.-09.03.2013, Kirchberg, Österreich
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18870 - Permalink


Microbial Diversity in Opalinus Clay and Interaction of Dominant Microbial Strains with Actinides (Final Report BMWi Project No.: 02 E 10618)
Moll, H.; Lütke, L.; Bachvarova, V.; Steudtner, R.; Geißler, A.; Krawczyk-Bärsch, E.; Selenska-Pobell, S.; Bernhard, G.;
For the first time microbial tDNA could be isolated from 50 g unperturbed Mont Terri Opalinus Clay. Based on the analysis of the tDNA the bacterial diversity of the unperturbed clay is dominated by representatives of Firmicutes, Betaproteobacteria, and Bacteriodetes. Firmicutes also dominate after treatment of the clay with R2A medium. Bacteria isolated from Mont Terri Opalinus Clay on R2A medium were related to Sporomusa spp., Paenibacillus spp., and Clostridium spp.. All further investigations are concentrated on the unique isolates Sporomusa sp. MT-2 and Paenibacillus sp. MT-2. Cells of the type Sporomusa sp. MT-2 and Paenibacillus sp. MT-2 were comprehensively analyzed in terms of growing, morphology, functional groups of the cell envelope, and cell membrane structure.
Strong actinide(An)/lanthanide(Ln)-interactions with the Opalinus Clay isolates and the Äspö-strain Pseudomonas fluorescens (CCUG 32456) could be determined within a broad pH range (2-8). The metals bind as a function of pH on protonated phosphoryl, carboxyl and deprotonated phosphoryl sites of the respective cell membrane. The thermodynamic surface complexation constants of bacterial An/Ln-species were determined and can be used in modeling programs. Depending on the used An different interaction mechanisms were found (U(VI): biosorption, partly biomineralisation; Cm(III): biosorption, indications for embedded Cm(III); Pu: biosorption, bioreduction and indications for embedded Pu). Different strategies of coping with U(VI) were observed comparing P. fluorescens planktonic cells and biofilms under the chosen experimental conditions. An enhanced capability of the biofilm to form meta-autunite in comparison to the planktonic cells was proven. Conclusively, the P. fluorescens biofilm is more efficient in U(VI) detoxification.
In conclusion, Mont Terri Opalinus Clay contains bacterial communities, that may influence the speciation and hence the migration behavior of selected An/Ln under environmental conditions.
Keywords: Actinides, uranium, curium, plutonium, Opalinus Clay, microbial interactions, bacteria, speciation, repository
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-036 2013

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Publ.-Id: 18869 - Permalink


Simple transport system for solid targets
Franke, K.; Hauser, J.;
Reduction of the radiation dose during transfer of solid targets from the irradiation position of the cyclotron Cyclone 18/9
Keywords: cyclotron, target, transport system, radiation dose
  • Poster
    IBA User's Meeting 2013, 17.-19.06.2013, Hillerød, Denmark

Publ.-Id: 18868 - Permalink


Closure models for turbulent bubbly flows: a CFD study
Rzehak, R.; Krepper, E.;
For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, bubble-induced turbulence is one such process for which a satisfactory model is still not available. A common approach to its solution is to add source terms to the single phase two-equation turbulence models. Here we report a comparison of different models of this type some of which have been used previously, some of which are new. To qualify the validity of the different models a set of reference data has been selected from the literature. Together with a suitable model for the bubble forces the most promising variants can be identified. Special attention in this respect is given to the wall force. Guidelines for modeling bubbly turbulence are proposed and needs for further research identified.
Keywords: dispersed gas liquid multiphase flow, bubble-induced turbulence, Euler-Euler two-fluid model, closure relations, CFD simulation, model validation

Publ.-Id: 18867 - Permalink


Polarized Photocathode SRF Guns
Teichert, J.;
The talk gives an overview of development and test of superconducting RF photo guns with GaAs photocathodes.
Keywords: Superconducting RF, photo electron injector, photocathode, GaAs, polarized electrons
  • Invited lecture (Conferences)
    EuCARD´13, 10.-14.06.2013, Geneva, Schweiz

Publ.-Id: 18866 - Permalink


Thermodynamic study of the complexation of protactinium(V) with diethylenetriaminepentaacetic acid
Mendes, M.; Leguay, S.; Le Naour, C.; Hamadi, S.; Roques, J.; Moisy, P.; Guillaumont, D.; Topin, S.; Aupiais, J.; Den Auwer, C.; Hennig, C.;
The complex formation of protactinium(V) with DTPA was studied at different temperatures (25−50 °C) and ionic strengths (0.1−1 M) with the element at tracer scale. Irrespective of the temperature and ionic strength studied, only one neutral complex with (1:1) stoichiometry was identified from solvent extraction and capillary electrophoresis coupled to ICP-MS (CEICP-MS) experiments. Density Functional Theory (DFT) calculations revealed that two complexes can be considered: Pa(DTPA) and PaO(H2DTPA). The associated formation constants were determined from solvent extraction data at different ionic strengths and temperatures and then extrapolated to zero ionic strength by SIT methodology. These constants are valid, regardless of complex form, Pa(DTPA) or PaO(H2DTPA). The standard thermodynamic data determined with these extrapolated constants revealed a very stable complex formed energetically by an endothermic contribution which is counter balanced by a strong entropic contribution. Both, the positive enthalpy and entropy energy terms suggest the formation of an inner sphere complex.
Keywords: Protactinium, Pa(V), diethylenetriaminepentaacetic acid

Publ.-Id: 18865 - Permalink


Raman spectroscopy and power diffraction study of synthetic Coffinite (USiO4) at high pressures
Bauer, J. D.; Labs, S.; Weiss, S.; Bayarjargal, L.; Curtis, H.; Morgenroth, W.; Bosbach, D.; Hennig, C.; Winkler, B.;
Coffinite, USiO4, can form under reducing conditions from UO2 in contact with silica-rich waters (Langmuir’s criterion) [1]. Spent nuclear fuel (SNF) consists to > 90% of UO2, so coffinite needs to be taken into account in the safety assessment as a potential secondary phase. While high pressures are not of specific relevance for a possible final repository for SNF, its structural behaviour at high pressures is of general interest to understand the phase stabilities and to benchmark model calculations. The high pressure behaviour of coffinite has been studied before on natural samples [2,3]. A pressure-induced irreversible phase transformation from the zircon- to the scheelite-type structure was found at about 15 GPa using an alcohol-water mixtures as a pressure medium [3].
Here, synthetic coffinite was studied under high pressure conditions in the diamond anvil cell with neon as quasi-hydrostatic pressure medium up to pressures of 35 GPa. The samples are free of impurities of UO2, as characterized by XRD and HRTEM. Powder diffraction experiments with synchrotron radiation indicate a pressure-induced phase transformation at 18-20 GPa. In contrast to the earlier high pressure study [3], this transformation is reversible on pressure release and no UO2 is formed during the process. A detailed data analysis is currently in progress.
Raman spectra were obtained up to a pressure of 18 GPa. The study of the Raman spectra at higher pressures is on-going.

[1] Langmuir (1978), Geochim. Cosmochim. Acta 42, 547-569
[2] Liu (1982), Earth Plan. Sci. Lett. 57, 110-116
[3] Zhang et al. (2009), Am. Min. 94, 916-920
Keywords: Spent nuclear fuel, Coffinite, USiO4, phase transition zircon-scheelite
  • Lecture (Conference)
    Goldschmidt Conference 2013, 25.-30.08.2013, Florence, Italy

Publ.-Id: 18864 - Permalink


Closure models for turbulent bubbly flows: a CFD study
Rzehak, R.; Krepper, E.;
For practical applications the Euler-Euler two-fluid model relies on suitable closure relations describing interfacial exchange processes. In dispersed gas-liquid multiphase flow, bubble-induced turbulence is one such process for which a satisfactory model is still not available. A common approach to its solution is to add source terms to the single phase two-equation turbulence models. We here report a comparison of different models of this type some of which have been used previously, some of which are new. To qualify the validity of the different models a set of reference data has been selected from the literature. Together with a suitable model for the bubble forces the most promising variants can be identified. Special attention in this respect is given to the wall force. Conclusions towards best practice guidelines for modeling bubbly turbulence are drawn and needs for further research identified.
Keywords: dispersed gas liquid multiphase flow, bubble induced turbulence, Euler Euler two fluid model, closure relations, CFD simulation, model validation
  • Contribution to proceedings
    8th International Conference on Multiphase Flow, ICMF2013, 26.-31.05.2013, Jeju, Korea
    Closure models for turbulent bubbly flows: a CFD study
  • Lecture (Conference)
    8th International Conference on Multiphase Flow, ICMF2013, 26.-31.05.2013, Jeju, Korea

Publ.-Id: 18863 - Permalink


CFD Simulation of Counter-current Flow Limitations in a Full Scale Pressurized Water Reactor (PWR) Hot Leg
Darlianto, D.; Agung, R.; Höhne, T.; Prayitno, S.; Lucas, D.;
The counter-current gas-liquid two-phase flow in the hot leg of a pressurized water reactor (PWR) has received a special attention for safety regulation in the nuclear industry. One hypothetical scenario is a loss-of-coolant-accident (LOCA) in a PWR, which is caused by the damage at any position of the primary circuit. The analytical simulation of this phenomenon is an essential element to understand safety-related issues in nuclear power plants. It is expected that the introduction of computational fluid dynamics (CFD) tools will enhance the accuracy of the simulation predictions compared to the established one-dimensional thermal hydraulic analyses. Here CFD allows substituting geometry-dependent empirical closure relations with more physically justified closure laws that are formulated at the scale of the structures of the gas–liquid interface.
This paper presents a CFD simulation on the counter-current flow limitation (CCFL) phenomena in a full scale PWR hot leg of Upper Plenum Test Facility (UPTF) Test case No 11 by using a commercial CFD code of ANSYS CFX 13.0, based on the finite volume method for an Euler-Euler model. The grid consist 29,100 hexahedral elements and 30,102 nodes. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a shear stress transport (SST) turbulence model. A new formulation of an interfacial drag coefficient was implemented inside the Algebraic Interfacial Area Density (AIAD) model (Höhne, 2010) into the three-dimensional (3-D) computational fluid dynamics (CFD) code.
To demonstrate the feasibility of the developed drag coefficient in AIAD model, the computed main parameters of the selected test case were compared with experimental data. The results indicated that the quantitative agreement between calculation and experimental data was obtained. This means that the AIAD model combined with the new drag force formulation is a promising way to simulate the phenomena in the frame of an Euler-Euler approach.
Keywords: counter-current flow limitations, AIAD, pressurized water reactor, hot leg, CFD, Upper Plenum Test Facility (UPTF)
  • Contribution to proceedings
    8th International Conference on Multiphase Flow, ICMF 2013, 26.-31.05.2013, Jeju, Korea
    CD-ROM
  • Lecture (Conference)
    8th International Conference on Multiphase Flow ICMF 2013, 26.-31.05.2013, Jeju, Korea

Publ.-Id: 18862 - Permalink


Baseline Model For CFD Of Dispersed Bubbly Flow
Rzehak, R.; Liao, Y.; Lucas, D.; Krepper, E.;
A set of closure relations for adiabatic bubbly flow has been collected that represents the best available knowledge and may serve as a baseline for further improvements and extensions to more general situations. Submodels for bubble forces, bubble-induced turbulence and bubble coalescence and breakup are considered. A preliminary validation of the model is presented by comparison to selected tests from the TOPFLOW database. Specific attention is paid to effects of polydispersity. Issues to be addressed in future work are discussed.
Keywords: dispersed gas liquid multiphase flow, bubble induced turbulence, bubble coalecence and breakup, Euler Euler two fluid model, closure relations, CFD simulation
  • Contribution to proceedings
    15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-16.05.2013, Pisa, Italy
  • Poster
    15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-15, 12.-16.05.2013, Pisa, Italy

Publ.-Id: 18861 - Permalink


Numerical simulation of multilayer deposition in an obstructed channel flow
Lecrivain, G.; Drapeau-Martin, S.; Barth, T.; Hampel, U.;
Simulation of multilayer deposition of dry aerosol particles in turbulent flows has gained a growing interest in various industrial and research applications. The multilayer deposition of carbonaceous aerosol particles in a turbulent channel flow obstructed by a succession of square ribs is here numerically investigated. The multilayer particle bed growth on the various wall surfaces affects the air flow, which in turn affects the overall deposition rate. An iterative numerical procedure is therefore suggested to simulate the evolution of the graphite layer. The iterative process used to reproduce the layer build-up is decomposed as follows: Reynolds-Avergared Navier Stokes is employed to generate the flow field. The turbulent dispersion of the particles is reproduced through the use of a continuous random walk model. After statistically sufficient deposition of particulate matter, the layer build-up is computed using mechanics of dry granular material. The layer build-up model shows good agreement with data obtained from experimental tests carried out on-site.

Publ.-Id: 18860 - Permalink


Swift carbon ion irradiated Nd:YAG ceramic optical waveguide amplifier
Tan, Y.; Luan, Q.; Liu, F.; Akhmadaliev, S.; Zhou, S.; Chen, F.;
A high-gain optical waveguide amplifier has been realized in a channel waveguide platform of Nd:YAG ceramic produced by swift carbon ion irradiation with metal masking. The waveguide is single mode at wavelength of 810 and 1064 nm, and with the enhanced fluorescence intensity at around 1064 nm due to the Nd3+ ion emissions. In conjunction with the low propagation loss of the waveguide, about 26.3 dB/cm of the small signal gain at 1064 nm is achieved with an 18 ns pulse laser as the seeder under the 810-nm laser excitation. This work suggests the carbon ion irradiated Nd:YAG waveguides could serve as efficient integrated amplifiers for the signal amplification.
Keywords: Optical amplifiers, Rare-earth-doped materials, Waveguides

Publ.-Id: 18859 - Permalink


Transport in ZnCoO thin films with stable bound magnetic polarons
Kaspar, T.; Fiedler, J.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.;
Diluted magnetic ZnCoO films with 5 at.% Co have been fabricated by pulsed laser deposition on c-plane sapphire substrates and Schottky and Ohmic contacts have been prepared in top-top configuration. The diode current is significantly reduced after the diode has been subjected to an external magnetic field. In the reverse bias range the corresponding positive magnetoresistance is persistent and amounts to more than 1800% (50 K), 240% (30 K), and 50% (5 K). This huge magnetoresistance can be attributed to the large internal magnetic field in depleted ZnCoO with ferromagnetic exchange between stable bound magnetic polarons.
Keywords: magnetic semiconductors; spintronics; Schottky contact; depletion layer

Publ.-Id: 18858 - Permalink


CFD modeling for subcooled flow boiling: Actual state and parametric variations
Krepper, E.; Rzehak, R.;
For CFD modeling of subcooled flow boiling the Euler/Euler two-phase flow description with heat flux partitioning has been proven to be very successful to analyse experimental data. Robust predictive capabilities of the modeling however require that it is validated for a wide range of parameters. Suitable experiments should yield sufficient information for the verification of the microscopic details of the models. In the presented investigations experiments at the CEA facility DEBORA were investigated in which a vertical pipe was heated from the side wall. Measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size were performed. A comprehensive sensitive study of the wall boiling model showed that quantities with a strong influence on the amount of produced steam are the bubble size at detachment and the nucleation site density. In the paper the potential of the application of a population balance model is demonstrated. The measured gas bubble size profiles show an increase of the bubble size with increased distance from the heated wall caused by bubble coalescence. Furthermore the model framework is shown to be able to describe a shift from wall peak to core peak in the radial gas volume fraction profiles with increasing inlet temperature respective decreasing subcooling temperature.
Keywords: CFD, two phase flow, subcooled boiling, population balance model, DEBORA experiments, model validation
  • Contribution to proceedings
    International Conference on Multiphase Flow 2013, 26.-31.05.2013, Jeju, Südkorea
  • Lecture (Conference)
    International Conference on Multiphase Flow 2013, 26.-31.05.2013, Jeju, Südkorea

Publ.-Id: 18857 - Permalink


Countercurrent flow limitation in a PWR hot leg
Murase, M.; Kinoshita, I.; Utanohara, Y.; Lucas, D.; Tomiyama, A.;
In order to evaluate countercurrent flow limitation (CCFL) characteristics in a PWR hot leg under reflux condensation, numerical simulations have been done for pressures of 0.1 MPa < P < 8 MPa using a VOF (volume of fluid) method implemented in the computational fluid dynamics software, FLUENT6.3.26. In this paper, first Wallis-type CCFL correlations for air-water and steam-water conditions were derived using the previously measured data and calculated results. The slope m was 0.70 and CCFL constants were C = 0.63 ± 0.02 and C = 0.655 ± 0.025 for air-water and steam-water conditions, respectively. Then, numerical simulations were additionally done by using the VOF method to evaluate the effect of fluid properties at a pressure of 16 MPa, and it was shown that the Wallis-type CCFL correlation for steam-water conditions could be used in the pressure range of 0.1 MPa < P <16 MPa. Finally, effects of fluid properties on CCFL characteristics were discussed.
Keywords: CCFL, reflux
  • Contribution to proceedings
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy
    Paper NURETH15-008
  • Lecture (Conference)
    NURETH-15 - 15th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18856 - Permalink


Low-energy M1 strength within the shell model
Schwengner, R.;
Magnetic dipole strength functions have been deduced from a large number of M1 transition strengths calculated within the shell model for the nuclides 94Mo, 95Mo, and 90Zr. An enhancement of M1 strength toward low energy has been found for all nuclides considered. This enhancement supports results of recent (3He,3He') and (d,p) experiments, but is at variance with analytical M1 strength functions currently given in reaction-data libraries and used in statistical-reaction codes.
Keywords: Nuclear structure, transition strengths, strength functions, shell model.
  • Invited lecture (Conferences)
    4th Workshop on Nuclear Level Density and Gamma Strength, 27.-31.05.2013, Oslo, Norwegen

Publ.-Id: 18855 - Permalink


Mean-field modeling of the interaction of soft iron with helical flows
Giesecke, A.; Stefani, F.;
We have performed kinematic simulations of dynamo action of a helical flow of a conducting fluid with a flow geometry in the style of the G.O. Roberts flow. As an extension to the original model, we have taken into account internal rods and/or walls that lie in the center of individual eddies and/or provide a separation of the eddies from each other. These flow guiding fixtures can be made of soft iron with a relative permeability much larger than one and the associated inhomogeneity significantly alters the behavior of the leading dynamo eigenmodes. The investigations are motivated from the roughly unknown induction effects of the forced helical flow that is used in fast reactors to remove the heat from the reactor core and from the supporting impact for dynamo action caused by the presence of soft iron impellers in the von-Karman-Sodium (VKS) dynamo.

Applying the testfield method we have computed the elements of the alpha tensor from direct simulations of a restricted number of helical eddies. The results may be extrapolated to model the combined induction effect of an extremely large number of individual helical eddies that cannot be resolved in direct simulations.

We will show which properties of the small scale induction in principle can be reproduced in a simplified mean-field model and where discrepancies/inconsistencies might arise. Furthermore, we investigate the possibility to include spatial "fluctuations" of the permeability into the framework of simple mean-field simulations.
Keywords: Dynamo
  • Lecture (Conference)
    International Symposium on Geophysical and Astrophysical Dynamos, 07.-12.07.2013, Zürich, Schweiz

Publ.-Id: 18854 - Permalink


Ga Implantation Induced Atomic Mixing in Crystalline and Amorphous Ge Isotope Multilayers
Radek, M.; Bracht, H.; Schmidt, B.; Bougeard, D.; Haller, E. E.;
Self-atom mixing induced by Gallium (Ga) implantation in crystalline and amorphous germanium (Ge) is investigated using an isotopic multilayer structure of alternating 73 Ge and nat Ge layers grown by molecular beam epitaxy. The distribution of the implanted Ga atoms and ion-beam induced depth-dependent mixing was determined by means of the secondary ion mass spectroscopy (SIMS). The position and form of the implanted Ga peak is very similar in the amorphous and crystalline Ge and can be reproduced accurately by SRIM simulations, whereas the ion-beam induced self-atom mixing strongly depends on the state of the Ge structure. The data from SIMS-measurements reveal a stronger mixing of the crystalline compared to amorphous structure. Molecular dynamics simulations suggest a higher mixing efficiency in the amorphous structure due to the lower thermal transport capacity. The kinetic energy of the implanted ions cause thermal spikes characterized by localized melted regions. Because of the lower thermal transport capacity of the amorphous structure the thermal spike lasts longer and leads to a higher mixing efficiency. The experimentally observed disparity in the ion-beam mixing efficiency of crystalline and amorphous Ge in comparison with the simulation indicates different mixing mechanisms.
Keywords: ion-beam mixing, Ge, SIMS
  • Lecture (Conference)
    E-MRS 2013 Spring Meeting, Symposium W, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18853 - Permalink


Atomistic modeling of solid phase recrystallization of amorphous Si and Ge
Posselt, M.;
Recrystallization of amorphous Si and Ge continues to be an important issue in nanoelectronic technologies. In order to obtain high dopant concentrations in the nanoscale regions ion implantation at relatively high fluence is required which causes the amorphization of the host material. Subsequently, thermal processing must be used to restore the semiconductor crystal. In planar structures this can be fully achieved by solid-phase epitaxial recrystallization whereas more complex processes take place in fins and nanowires due to the significant influence of surfaces and interfaces. It is highly desirable to understand the recrystallization phenomena on the atomic level. This work presents results of molecular dynamics simulations of solid phase recrystallization in Si and Ge. At first the process of epitaxial recrystallization of amorphous layers is considered and the influence of accuracy of the interatomic potential used in the simulations is discussed. Then the method is ap plied to solid phase recrystallization of fins and nanowires. The incomplete restoration of the host crystal is characterized by the occurrence of defects, stacking faults and polycrystallization.
Keywords: solid phase recrystallization, Si, Ge, molecular dynamics simulations
  • Invited lecture (Conferences)
    E-MRS 2013 Spring Meeting, Symposium K, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18852 - Permalink


In vivo dose response studies for laser driven particle beams
Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Reuter, M.; Sävert, A.; Schnell, M.; Schürer, M.; Pawelke, J.;
Purpose. The novel technology of proton and ion acceleration by ultra high intensity lasers promises the realization of compact and economic particle accelerators for cancer therapy that can be integrated in already existing clinics. Before potential clinical application possible biological consequences of laser accelerated and therewith ultra-short pulsed particle beams with high pulse dose have to be investigated. As first step in the chain of translational research extensive in vitro dose response studies with laser driven electron and proton beams were performed within the joint research project “onCOOPtics”. We now report on first experiments comparing laser and conventional accelerated particle beams in vivo.
Material and methods. A mouse tumor model suitable for the currently available still low energy (up to ~30 MeV) of laser accelerated protons was established and successfully implemented using laser accelerated electrons, likewise providing information about biological consequences of ultra-short pulsed beams. To apply a prescribed dose to each tumor the prior established laser based 2D in vitro irradiation technology was enhanced for the 3D animal model in terms of beam transport, beam monitoring, dose delivery and dosimetry. A system for mouse fixation, precise tumor positioning and verification at the irradiation site was realized (Schürer et al. 2012). In vivo tumor irradiation was performed at the 30 TW Jena Titanium: Sapphire (JeTi) laser system. Electron pulses of energies up to a few 10 MeV were generated focusing laser pulses of 28 fs duration into a hydrogen gas jet. Murine sarcoma KHT and human squamous cell carcinoma FaDu tumors were irradiated with doses up to 14 Gy at mean dose rates of 1–2 Gy/min. Reference electron irradiation was performed with the same setup and dosimetry system at a conventional therapy LINAC. The radiation induced tumor growth delay was investigated for several hundred mice.
Results. The irradiation campaign was conducted over a period of several months proving the reliability and stability of all implemented setup components and methods. Dose response curves of both beam qualities have been obtained for the direct comparison of ultra-short pulsed laser accelerated and conventional continuous electron beams. The current status of the ongoing data evaluation gives no evidence for a different RBE of laser driven electrons.
Conclusion. The successful establishment of all technical requirements for and the world wide first performance of systematic animal studies with laser accelerated electrons mark an important step towards the clinical application of laser accelerated particle beams. The realization of in vivo studies with laser driven proton beams is now feasible.
1. M Schürer et al (2012) Irradiation system for pre-clinical studies with laser accelerated electrons. Biomed Tech 57(Suppl. 1):62–65
Supported by BMBF grant nr. 03ZIK455 and 03Z1N511.
  • Abstract in refereed journal
    Strahlentherapie und Onkologie 189(2013)Suppl 1, 12-12
  • Lecture (Conference)
    19. Jahreskongress der Deutschen Gesellschaft für Radioonkologie, 09.-12.05.2013, Berlin, Deutschland

Publ.-Id: 18851 - Permalink


Mobile uranium(IV)-bearing colloids in a mining-impacted wetland
Wang, Y.; Frutschi, M.; Suvorova, E.; Phrommavanh, V.; Descostes, M.; Osman, A. A. A.; Geipel, G.; Bernier-Latmani, R.;
Uranium is known to accumulate in wetland soils, where the precipitation of the sparingly soluble U(IV) mineral uraninite (UO2) under reducing conditions is considered a promising strategy for U immobilization. Here, we investigate the mobility of U in a mining impacted wetland in France that exhibited locations harboring U concentrations of up to 4,000 ppm. A distinct release of U into the stream passing through the wetland is observable. We examine soil and porewater composition as a function of depth at two U hotspots to assess the geochemical conditions leading to this release. The analyses show that U is present in soil as a non-crystalline U(IV) species sorbed onto amorphous Fe-Al-P-Si aggregates through phosphate groups, and that high U(IV) concentrations in porewater are due to the association of U with Fe- and organic matter-containing colloids. These results show that tetravalent U in soil is labile and releases U(IV) to form mobile colloids that ultimately result release of U into the stream. This is the first report of mobile U(IV) colloids in the environment and strongly brings into question the common assumption that U is immobile when present in a tetravalent oxidation state.
Keywords: Uranium, wetland, transport

Publ.-Id: 18850 - Permalink


Using XFELs for Probing of Complex Interaction Dynamics of Ultra-Intense Lasers with Solid Matter
Kluge, T.; Gutt, C.; Huang, L.; Metzkes, J.; Schramm, U.; Bussmann, M.; Cowan, T. E.;
We demonstrate the potential of X-ray free-electron lasers (XFEL) to advancethe understanding of complex plasma dynamics by allowing for the first time nanometer and femtosecond resolution at the same time in plasma diagnostics. Plasma phenomena on such short timescales are of high relevance for many fields of physics, in particular in the ultra-intense ultra-short laser interaction with matter. Highly relevant yet only partially understood phenomena may become directly accessible in experiment. These include relativistic laser absorption at solid targets, creation of energetic electrons and electron transport in warm dense matter, including the seeding and development of surface and beam instabilities, ambipolar expansion, shock formation, and dynamics at the surfaces or at buried layers.
We demonstrate the potentials of XFEL plasma probing for high power laser matter interactions using exemplary the small angle X-ray scattering technique, focusing on general considerations for XFEL probing.
  • Physics of Plasmas 21(2014), 033110
    DOI: 10.1063/1.4869331
  • Lecture (Conference)
    HIBEF Kickoff Meeting, 02.-05.06.2013, Hamburg, Deutschland
  • Poster
    HIBEF Kickoff Meeting, 02.-05.06.2013, Hamburg, Deutschland
  • Contribution to WWW
    arXiv:1306.0420: http://arxiv.org/pdf/1306.0420v1.pdf
  • Poster
    OncoRay Retreat, 27.-28.03.2014, Dresden, Deutschland
  • Lecture (others)
    Group-Semininar, 6.1.2015, Osaka, Japan

Publ.-Id: 18849 - Permalink


Practical guide for validated memristance measurements
Du, N.; Shuai, Y.; Luo, W.; Mayr, C.; Schueffny, R.; Schmidt, O. G.; Schmidt, H.;
Chua [IEEE Trans. Circuit Theory 18, 507-519 (1971)] predicted rather simple charge-flux curves for active and passive memristors (short for memory resistors) and presented active memristor circuit realizations already in the 1970 s. The first passive memristor has been presented in 2008 [D. B. Strukov, G. S. Snider, and D. R. Williams, Nature (London) 453, 80-83 (2008)]. Typically, memristors are traced in complicated hysteretic current-voltage curves. Therefore, the true essence of many new memristive devices has not been discovered so far. Here, we give a practical guide on how to use normalized charge-flux curves for the prediction of hysteretic current-voltage characteristics of memristors. In the case of memristive BiFeO3 thin film capacitor structures, the normalized charge-flux curves superimpose for different numbers of measurement points Ns and a different measurement time per measurement point Ts. Such normalized charge-flux curves can be used for the prediction of current-voltage characteristics for input signals with arbitrarily chosen Ns and Ts.
Keywords: memristance

Publ.-Id: 18848 - Permalink


Three-dimensional simulation of multiphase flows in porous solid foam structures
Subramanian, K.; Schubert, M.; Krepper, E.; Lucas, D.; Hampel, U.;
1 Introduction
Ceramic foam packings, due to their high porosity, high specific surface area and low pressure drop are promising alternatives for packing internals used in chemical engineering processes. Photograph of the sponges can be seen in Figure 1. The applications of foam packing as burners and heat exchangers have been widely studied, but as catalyst carriers particularly for gas-liquid systems solid foam behaviour is not yet well understood. Due to its highly porous nature, it is very tough to understand the influence of hydrodynamics on the process performance. The long term goal of this work is to perform three dimensional Computational Fluid Dynamics (CFD) simulations of the evolving gas-liquid patterns considering ceramic foams as column internals and to validate them with experimental X-ray tomographic studies. It is noteworthy to mention that no 3D CFD simulations have been performed considering Ceramic foams as column internals in pilot scale. On the other hand, detailed studies are available considering spherical particles as internals in Trickle bed reactors. The closures will be modified according to the ceramic foam specifications.

2 Modeling Details
To simulate the column with ceramic foam as internals, there are two major requirements. One is the more precise information regarding the geometry and other is the appropriate closures.

The major challenge to grasp the ceramic foam packing as representative ‘porous body’ is to characterize the geometrical parameters such as pore diameter, strut diameter, pores per inch, porosity accurately and to understand the relationship with specific surface and pressure drop. Different empirical correlations are already available in the literature [2, 3]. Some of the correlations proposed in the literature will be used initially in this work.

A two phase Eulerian model is used considering the flow domain as porous. The influence of the liquid and gas drag is added as external source term to liquid and gas momentum equations separately. The drag force between the phases have been taken into account using relative permeability approach which was developed by Saez and Carbonell [4] for packed beds using capillary pressure and relative permeabilities of two phase flows.

As a first step, simulations are performed considering 2 mm spherical particles with porosity of 0.41 as column internals. Column has diameter of 0.3 m and height of 1.3 m. Air and Water is used as test substance. Single orifice with 25mm ID is used as inlet distributor. These simulation results are compared with experimental investigation studies of Marcandelli et. al. [5]. As next, this validated model is transferred to solid foams by mimicking high solid foam porosity of 0.93 with different ppi’s and to validate with in-house experiments performed using X-ray tomographic studies.

References
[1] Calvo. S., Beugre. D., Crine. M., Leonard. A., Marchot. P., Toye. D., Phase distribution measurements in metallic foam packing using X-ray radiography and micro-tomography, Chemical Engineering and Processing, Vol. 48, pp. no. 1030–1039, (2009).
[2] Dietrich, B., Pressure drop correlation for ceramic and metal sponges, Chemical Engineering Science, Vol. 74, pp. no. 192 – 199, (2012).
[3] Inayat, A., Freund,H., Zeiser, T., Schwieger, W., Determining the specific surface area of ceramic foams : The tetrakaidecahedron model revisited, Chemical Engineering Science, Vol. 66, pp. no. 1179 – 1188, (2011).
[4] Saez, A.E., Carbonell, R.G., Hydrodynamic Parameters for Gas-Liquid Cocurrent Flow in Packed Beds, AIChE Journal, Vol. 31, No.1, pp no. 52- 62, 1985.
[5] Marcandelli, C., Lamine, A.S., Bernard, J.R., Wild, G., Liquid Distribution in Trickle-Bed Reactor, Oil & Gas Science and Technology – Rev. IFP, Vol. 55, No.4, pp no. 407 - 415, 2000.

Acknowledgement
This work was funded by the Helmholtz Association within the frame of the Helmholtz Energy Alliance "Energy Efficient Chemical Multiphase Processes".
Keywords: CFD, Ceramic foams, Relative permeability, Multiphase flow
  • Poster
    Interpore - 5th International Conference on Porous Media & Annual Meeting, 21.-24.05.2013, Prague, Czech Republic

Publ.-Id: 18847 - Permalink


Numerical simulation of horizontal two-phase flow experiments using a morphology detection model
Höhne, T.;
One limitation today in simulating horizontal two phase flow is that there is no special turbulence treatment at the free surface. For self generating waves and slugs, the interfacial momentum exchange and the turbulence parameters have to be modelled correctly. Without any special treatment of the free surface, the high velocity gradients at the free surface generate too high turbulence when using eddy viscosity models like the k-ε or the k-ω model. In the past turbulence damping (symmetric damping procedures for the solid wall-like damping of turbulence in both gas and liquid phases) were introduced within the Algebraic Interfacial Area Density (AIAD) model into the three-dimensional (3-D) computational fluid dynamics (CFD) code ANSYS-CFX. The AIAD approach allows the use of different models depending on the local morphology. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered for instance in the interfacial drag formulation.
A further step of improvement of modelling the turbulence is the consideration of small wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. So fare in the present code versions they are neglected. However, the influence on the turbulence kinetic energy of the liquid side can be significantly large. A region of marginal breaking is defined according Brocchini and Peregrine and added as a source term in the turbulent kinetic energy equation.
This paper presents first CFD-simulations on horizontal multiphase flows using the new modelling approach.
Keywords: CFD, horizontal flow, AIAD, ANSYS-CFX
  • Lecture (Conference)
    ANSYS Conference & 31. CADFEM Users' Meeting, 19.-21.06.2013, Mannheim, Deutschland
  • Contribution to proceedings
    ANSYS Conference & 31. CADFEM Users' Meeting, 19.-21.06.2013, Mannheim, Deutschland
    CD-ROM

Publ.-Id: 18846 - Permalink


Supraleitende Schichten in Halbleitern
Fiedler, J.;
  • Lecture (Conference)
    Ionenstrahlen in Forschung und Anwendung, 12.-14.06.2013, Leipzig, Deutschland

Publ.-Id: 18845 - Permalink


Application of gamma-ray tomography for the development of flow regime maps of an inclined rotating fixed-bed reactor
Härting, H.-U.; Bieberle, A.; Schubert, M.; Hampel, U.;
This contribution presents the inclined rotating fixed-bed reactor as a new chemical reactor concept for heterogeneous multiphase reactions. Combining the inclined and rotating operation of the fixed-bed, this new process intensification equipment allows for flow regime adjustment at fixed flow rates and overcomes liquid maldistribution. A highly integrated, compact gamma-ray computed tomography system for the non-invasive investigation of the flow regimes in the new reactor is presented, as well. Based on systematic flow experiments, flow regime maps for the inclined rotating fixed-bed reactor are generated for the first time and the effects of varying physico-chemical properties of the liquid phase on the flow regimes are discussed.
Keywords: Gamma-ray computed tomography, process intensification, multiphase flow, fixed-bed reactor, flow regime maps
  • Open Access LogoContribution to proceedings
    7th World Congress on Industrial Process Tomography, WCIPT7, 02.-05.09.2013, Krakow, Poland, 336-344

Publ.-Id: 18844 - Permalink


Reaktionstechnische und hydrodynamische Untersuchungen an einem geneigt rotierenden Festbettreaktor
Härting, H.-U.; Schubert, M.;
Kontinuierlich betriebene Festbettreaktoren mit regellos gepackten Formkatalysa-toren in Rieselfahrweise werden für viele katalytische Gas/Flüssig-Reaktionen einge-setzt. Anwendungen sind beispielsweise die Hydrierung von Alkenen, die Hydro-desulfurierung von Mineralöl oder die Abwasseraufbereitung.
Stellt die Stoffübertragung der Gasphase an die aktiven Zentren des Katalysators den geschwindigkeitsbestimmenden Teilschritt der Reaktion dar, kann die periodische Betriebsweise, z. B. in Form von Strömungsmodulation, eine Erhöhung der Raum-Zeit-Ausbeute bewirken. Weitere Vorteile der periodischen Betriebsweise sind die Verringerung von Fehlverteilungen und die Vermeidung von lokal überhitzten Stellen in der Katalysatorschüttung. Als Nachteile sind die Abnahme der positiven Effekte mit der Reaktorlänge sowie höhere Anforderungen an die Umsetzung im industriellen Maßstab, hervorgerufen durch die transienten Strömungsvorgänge im Reaktor und deren Auswirkungen auf den Anlagenverbund, bekannt.
Durch ein neuartiges periodisches Reaktorkonzept kann der Festbettreaktor unter quasi-stationären Bedingungen betrieben werden. Dabei ist der Reaktor geneigt und rotiert zusätzlich um seine Längsachse.
Durch die Neigung wird die Phasenseparation begünstigt, während die Rotation die periodische Be- und Entnetzung der Katalysatorschüttung hervorruft und somit den Zugang der Gasphase an die aktiven Zentren des Katalysators verbessert.
Mittels Gamma-Computertomographie wurden hydrodynamische Studien unter Variation von Reaktordrehzahl und -neigung sowie Variation von Flüssigphase, Durchsätzen und Packungsmaterial zur Aufklärung der Strömungsformen in einem Rohrreaktor (DI = 0,1 m und L = 1,2 m) durchgeführt.
Zur Bewertung des neuartigen Reaktorkonzepts wurde der Einfluss der Strömungs-formen auf die Raum-Zeit-Ausbeute der Hydrierung von α-Methylstyrol zu Cumol an Palladium auf kugelförmigem γ-Al2O3 untersucht.
Im Beitrag werden ausführlich hydrodynamische Studien und die darauf aufbauenden reaktionstechnischen Untersuchungen vorgestellt.
Keywords: Process Intensification, inclined rotating fixed-bed reactor, gamma-ray computed tomography
  • Poster
    Jahrestreffen Reaktionstechnik 2013, 06.-08.05.2013, Würzburg, Deutschland
  • Open Access LogoContribution to proceedings
    Jahrestreffen Reaktionstechnik 2013, 06.-08.05.2013, Würzburg, Deutschland
    Tagungshandbuch Jahrestreffen Reaktionstechnik 2013

Publ.-Id: 18843 - Permalink


PT-symmetries in physics and some operator-theoretic challenges
Günther, U.;
In the first half of the talk, a brief overview is given about basic results obtained in PT-symmetry related physics since 1998: early numerical indications on the reality of the spectrum of certain non-Hermitian effective Hamiltonians in quantum mechanics, the concrete reality condition for the spectrum, PT phase transitions, self-adjointness in Krein spaces, as well as most recent physical applications in optical waveguide systems, threshold lasers and coherent perfect absorbers.
In the second half of the presentation, we discuss some operator-theoretic challenges like the general structure of the so-called C-operator and its specific Lie group structures. Finally, we comment on the unboundedness of the C-operator for model Hamiltonians with ix^3 potential and possible group-theoretic implications.
Keywords: PT symmetry, quantum mechanics, phase transitions, optical wave guides, threshold lasers, coherent perfect absorbers, microwave cavities, Krein space, C operator, Lie group structures, unbounded operators
  • Lecture (Conference)
    5th Anniversary Workshop of the GAMM Activity Group Applied Operator Theory, 30.-31.05.2013, Berlin, Deutschland

Publ.-Id: 18842 - Permalink


Uranium contents in plants and mushrooms grown on a uranium contaminated site near Ronneburg in Eastern Thuringia/Germany
Baumann, N.; Arnold, T.; Haferburg, G.;
Uranium concentrations in cultivated (sunflower, sunchoke, potato) and native plants, plant compartment specimens and mushrooms, grown on a test site within a uranium contaminated area in Eastern Thuringia, were analyzed and compared. This test site belongs to the Friedrich-Schiller University Jena, and is situated on the ground of a former, but now removed uranium mine waste leaching heap. For determination of the U concentrations in the biomaterials, the saps of the samples were squeezed out by using an ultra-centrifuge, after that the uranium concentrations in the saps and the remaining residue were measured, using ICP-MS.
The study further showed that uranium concentrations observed in plant compartment and mushroom fruiting bodies sap samples were always higher than their associated solid residue sample. Also it was found that the detected uranium concentration in the root samples were always higher than were observed in their associated above ground biomass, e.g. in shoots, leaves, blossoms etc.
The highest uranium concentration was measured with almost 40 ppb U in a fruiting body of a mushroom and in roots of butterbur. However, the detected uranium concentrations in plants and mushrooms collected in this study were always lower than in the associated surface and soil water of the test site, indicating that under the encountered natural conditions none of the studied plant and mushroom species turned out to be a hyper-accumulator for uranium, which could have extracted uranium in sufficient amounts out of the uranium contaminated soil.
In addition, it was found that the detected uranium concentrations in the sap samples, despite being above the sensitivity limit, proved to be too low – in combination with the presence of fluorescence quenching substances, e.g. iron and manganese ions, and/or organic quenchers – to extract a useful fluorescence signal, which could have helped to identify the uranium speciation in plants.
Keywords: Uranium (VI) • Phytoremediation • Heavy metal contaminated soil • TRLFS

Publ.-Id: 18841 - Permalink


Free-Electron Laser Operation with a Superconducting Radio-Frequency Photoinjector at ELBE
Teichert, J.; Arnold, A.; Büttig, H.; Justus, M.; Kamps, T.; Lehnert, U.; Lu, P.; Michel, P.; Murcek, P.; Rudolph, J.; Schurig, R.; Seidel, W.; Vennekate, H.; Will, I.; Xiang, R.;
At the radiation source ELBE a superconducting radio-frequency photoinjector (SRF gun) was developed and put into operation. Since 2010 the gun has delivered beam into the ELBE linac. A new driver laser with 13 MHz pulse repetition rate allows now to operate the free-electron lasers (FELs) with the SRF gun. This paper reports on the first lasing experiment with the far-infrared FEL at ELBE, describes the hardware, the electron beam parameters and the measurement of the FEL infrared radiation output.
Keywords: Superconducting RF, SRF gun, Photo injector, Free-electron laser, Linear accelerator

Publ.-Id: 18840 - Permalink


Atomic Layer Deposition of LiF Thin Films from Lithd and TiF4 Precursors
Mäntymäki, M.; Hämäläinen, J.; Puukilainen, E.; Munnik, F.; Ritala, M.; Leskelä, M.;
Lithium fluoride (LiF) is an important optical material with a low refractive index and a large band gap. In this study, thin films of LiF are deposited using atomic layer deposition (ALD). Lithd and TiF4 are used as precursors, and they produce crystalline LiF in the temperature range 250–350 °C. The films are studied with UV-Vis spectrometry, field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), atomic force microscopy (AFM) and elastic recoil detection analysis (ERDA). Adhesion of the films is tested by a Scotch tape test. This ALD process results in LiF films with a growth rate of approximately 1 Å per cycle at 325 °C. According to ERDA measurements, the films are pure LiF with only small O, C, and H impurities.
Keywords: Atomic layer deposition; Lithium fluoride; Thin films

Publ.-Id: 18839 - Permalink


Mapping the local elastic properties of nanopatterned Ge
Bischoff, L.; Böttger, R.; Keller, A.; Facsko, S.;
Due to their reduced dimensions, the mechanical properties of nanostructures may differ substantially from those of bulk materials. Quantifying and understanding the nanomechanical properties of individual nanostructures is thus of tremendous importance both from a fundamental and a technological point of view. We employed a recently introduced atomic force microscopy (AFM) mode, i.e., peak-force quantitative nanomechanical imaging, to map the local elastic properties of nanostructured germanium surfaces. This imaging mode allows for the quantitative determination of the Young’s modulus with nanometer resolution. Heavy-ion irradiation was used to fabricate different self-organized nanostructures on Ge surfaces. Depending on the sample temperature during irradiation, nanoporous sponge-like structures and hexagonally ordered nanodots are obtained. The sponge-like Ge surface is found to exhibit a surprisingly low Young’s modulus well below 10 GPa which furthermore depends on the ion energy. For the nanodot patterns, local variations in the Young’s modulus are observed: at moderate sample temperatures, the dot crests have a lower modulus than the dot valley whereas this situation is reversed at high temperatures. These observations are explained by vacancy dynamics in the amorphous Ge matrix during irradiation. Our results furthermore offer the possibility to tune the local elastic properties of nanostructured Ge surfaces by adjusting the ion energy and sample temperature.
Keywords: Nanostructures, Germanium, Youngs Modulus
  • Lecture (Conference)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark

Publ.-Id: 18838 - Permalink


Spin anisotropy in Cu(en)(H2O)2SO4: A quasi-two-dimensional S = 1/2 spatially anisotropic triangular-lattice antiferromagnet
Tarasenko, R.; Orendácová, A.; Cizmár, E.; Matas, S.; Orendác, M.; Potocnák, I.; Siemensmeyer, K.; Zvyagin, S.; Wosnitza, J.; Feher, A.;
We have studied in detail the effect of the spin anisotropy on the electron paramagnetic resonance spectra and magnetic properties of Cu(en)(H2O)2SO4, an S = 1/2 spatially anisotropic triangular lattice antiferromagnet. The angular and temperature dependence of the resonance fields as well as the magnetization and magnetic susceptibility reflect the exchange and g-factor anisotropy with Jz/Jx,y < 1 and gz/gx,y > 1, respectively. The exchange anisotropy and Dzyaloshinskii-Moriya interaction are responsible for the main broadening mechanism at higher temperatures while spin-diffusion effects prevail at helium temperatures. The ratio of the uniform susceptibilities calculated along the three crystal directions suggests an easy-axis anisotropy with the a axis as the magnetic easy axis. Its impact on the physical properties of the title compound is discussed.

Publ.-Id: 18837 - Permalink


Observation of an intersublattice exchange magnon in CoCr2O4 and analysis of magnetic ordering
Kamenskyi, D.; Engelkamp, H.; Fischer, T.; Uhlarz, M.; Wosnitza, J.; Gorshunov, B. P.; Komandin, G. A.; Prokhorov, A. S.; Dressel, M.; Bush, A. A.; Torgashev, V. I.; Pronin, A. V.;
We report on an investigation of optical properties of multiferroic CoCr2O4 at terahertz frequencies in magnetic fields up to 30 T. Below the ferrimagnetic transition (94 K), the terahertz response of CoCr2O4 is dominated by a magnon mode, which shows a steep magnetic-field dependence. We ascribe this mode to an exchange resonance between two magnetic sublattices with different g factors. In the framework of a simple two-sublattice model (the sublattices are formed by Co2+ and Cr3+ ions), we find the inter-sublattice coupling constant, λ = −(18 ± 1) K, and trace the magnetization for each sublattice as a function of field. We show that the Curie temperature of the Cr3+ sublattice, θ2 = (49 ± 2) K, coincides with the temperature range, where anomalies of the dielectric and magnetic properties of CoCr2O4 have been reported in literature.

Publ.-Id: 18836 - Permalink


Evidence of d-wave superconductivity in K1−xNaxFe2As2 (x = 0,0.1) single crystals from low-temperature specific-heat measurements
Abdel-Hafiez, M.; Grinenko, V.; Aswartham, S.; Morozov, I.; Roslova, M.; Vakaliuk, O.; Johnston, S.; Efremov, D. V.; van den Brink, J.; Rosner, H.; Kumar, M.; Hess, C.; Wurmehl, S.; Wolter, A. U. B.; Büchner, B.; Green, E. L.; Wosnitza, J.; Vogt, P.; Reifenberger, A.; Enss, C.; Hempel, M.; Klingeler, R.; Drechsler, S.-L.;
From the measurement and analysis of the specific heat of high-quality K1−xNaxFe2As2 single crystals we establish the presence of large T2 contributions with coefficients αsc ≈ 30 mJ/mol K3 at low T for both x = 0 and x = 0.1. Together with the observed √B behavior of the specific heat in the superconducting state both findings give evidence of d-wave superconductivity on almost all Fermi-surface sheets with an average gap amplitude of Δ0 in the range of 0.4–0.8 meV. The derived 0 and observed Tc agree well with the values calculated within Eliashberg theory, adopting a spin-fluctuation mediated pairing in the intermediate coupling regime.

Publ.-Id: 18835 - Permalink


Vortex lock-in transition and evidence for transitions among commensurate kinked vortex configurations in single-layered Fe arsenides
Li, G.; Grissonnanche, G.; Conner, B. S.; Wolff-Fabris, F.; Putzke, C.; Zhigadlo, N. D.; Katrych, S.; Bukowski, Z.; Karpinski, J.; Balicas, L.;
We report an angle-dependent study of the magnetic torque τ (θ) within the vortex state of single-crystalline LaO0.9F0.1FeAs and SmO0.9F0.1FeAs as a function of both temperature T and magnetic field H. Sharp peaks are observed at a critical angle θc at either side of θ = 90◦, where θ is the angle between H and the interplanar c axis. θc is interpreted as the critical depinning angle where the vortex lattice, pinned and locked by the intrinsic planar structure, unlocks and acquires a component perpendicular to the planes. We observe a series of smaller replica peaks as a function of θ and as θ is swept away from the planar direction. These suggest commensurability effects between the period of the vortex lattice and the interplanar distance leading to additional kinked vortex configurations.

Publ.-Id: 18834 - Permalink


Slow spin relaxation induced by magnetic field in [NdCo(bpdo)(H2O)4(CN)6].3H2O
Vrábel, P.; Orendác, M.; Orendácová, A.; Cizmár, E.; Tarasenko, R.; Zvyagin, S.; Wosnitza, J.; Prokleska, J.; Sechovský, V.; Pavlík, V.; Gao, S.;
We report on a comprehensive investigation of the magnetic properties of [NdCo(bpdo)(Hsub2O)4(CN)6] . 3H2O (bpdo = 4, 4´-bipyridine-N,N´-dioxide) by use of electron paramagnetic resonance, magnetization, specific heat and susceptibility measurements. The studied material was identified as a magnet with an effective spin S D 1=2 and a weak exchange interaction J/kB = 25 mK. The ac susceptibility studies conducted at audio frequencies and at temperatures from 1.8 to 9 K revealed that the application of a static magnetic field induces a slow spin relaxation. It is suggested that the relaxation in the magnetic field appears due to an Orbach-like process between the two lowest doublet energy states of the magnetic Nd3+ ion. The appearance of the slow relaxation in a magnetic field cannot be associated with a resonant phonon trapping. The obtained results suggest that the relaxation is influenced by nuclear spin driven quantum tunnelling which is suppressed by external magnetic field.

Publ.-Id: 18833 - Permalink


Fabrication of Si1-xGex Alloy on Silicon by Ge-Ion-Implantation and Short-Time-Annealing
Gao, K.; Prucnal, S.; Mücklich, A.; Skorupa, W.; Zhou, S.;
In our contribution we present the fabrication of Si1-xGex alloy by ion-implantation and millisecond flash lamp annealing. The 100 keV Ge ions at the fluence of 10×1016, 5×1016, and 3×1016 cm-2 were implanted into monocrystalline (100)-oriented Si wafers covered by 50 nm thermal oxide. In the consequence, the 50 nm amorphous Ge rich Si layers were obtained. The recrystallization of the implanted layers and the Si1-xGex alloying were accomplished by flash lamp annealing with the pulse duration of 20 ms. Flash lamp treatment at high energy densities leads to local melting of the Ge-rich silicon layer. Then the recrystallization takes place due to the millisecond range liquid phase epitaxy. Formation of the high quality monocrystalline Si1-xGex layer was confirmed by the μ-Raman spectroscopy, the Rutherford backscattering channeling and cross-sectional transmission electron microscopy investigation. The μ-Raman spectra reveal three phonon modes located at around 293, 404, and 432 cm-1 corresponding to the Ge-Ge, Si-Ge and Si-Si in the Si1-xGex alloy vibrational modes, respectively. Due to much higher carrier mobility in the Si1-xGex layers than in silicon such system can be used for the fabrication of advanced microelectronic devices.
Keywords: SiGe, ion-implantation, flash lamp annealing

Publ.-Id: 18831 - Permalink


Geological variations in the Merensky Reef at Bafokeng Rasimone 4 Platinum Mine and its influence on flotation performance
Smith, A. J. B.; Viljoen, K. S.; Schouwstra, R.; Roberts, J.; Schalkwyk, C.; Gutzmer, J.;
The Merensky Reef of the Bushveld Complex of South Africa is marked by prominent lateral and vertical variations in its geology, platinum group element grade distribution and platinum group mineralogy. At Bafokeng Rasimone Platinum Mine on the western limb of the complex eleven distinct Merensky Reef facies have been identified. The reef facies show different mineral processing behaviour. Detailed geo-metallurgical characterisation of three reef facies (FW 1A contact, FW 3 pothole and pothole edge reef facies) at Bafokeng Rasimone Platinum Mine has been carried out in an attempt to understand differences in flotation performance. Results illustrate that the FW1A contact facies has the best Pt and Pd grades and recoveries in the flotation concentrates and the pothole edge facies has the worst. The differences are related not only to mineralogical and textural characteristics of the platinum group minerals and base metal sulphides in the different facies, but also pertain to the geological position and the mineralogy of the host rocks that are introduced as dilution to achieve a realistic mining cut.
Keywords: Precious metal ores Froth flotation Liberation analysis Ore mineralogy

Publ.-Id: 18830 - Permalink


Structural analysis of ternary actinyl(V/VI) sorption complexes on gibbsite – A combined quantum chemical and spectroscopic approach
Gückel, K.;
For the safety assessment of high-level nuclear waste repositories, it is mandatory to know the transportation paths of contaminants, e.g. actinyl ions (UO22+, NpO2+), in the geological barrier. The most attention needs to be focused on the transport in aquifers, because water contamination, depending on retention and migration processes of radionuclides in the geosphere, is of primary environmental concern. The migration behavior of actinides in ground water is mainly controlled by aquatic speciations and sorption processes at water-mineral interfaces. Hence, the investigation of complex species in aqueous solutions and at mineral surfaces becomes essential for the safety assessment in the near and far field of nuclear repositories.

For deep ground repositories, clay and clay minerals are considered as possible host rocks, because they show a low permeability and are expected to have a high retention capacity towards actinyl ions. But the complexity of naturally occurring minerals in particular their surface often hampers the unequivocal interpretation of results obtained from sorption experiments. The use of model phases only showing one particular functional group at the surfaces with a well defined surface topology is an appropriate approach for the understanding of the basic sorption processes. Aluminum oxide and hydroxides are of special interest because they represent main components in clays and clay minerals. In particular, gibbsite is widely used as a model system because it represents not only the most common crystalline aluminum hydroxide but also a ubiquitous weathering product of alumosilicates. Furthermore, the elemental structural unit of gibbsite, that is the Al(OH)6 octahedron, occurs ubiquitously as part of the structure of common clay minerals like kaolinite.

In the present study, the sorption processes of U(VI) and Np(V) on gibbsite were studied under consideration of the aqueous speciation. First, the structural data of an aqueous dimeric U(VI)-carbonato species were revisited and refined by a combined approach of quantum chemical calculations and vibrational spectroscopy. The combination of these techniques is expected to provide progress in the identification of the molecular structures of the aqueous uranyl species, which in turn are needed for a reliable prediction of surface complexes. The results show that an isomer with a carbonate ligand bridging the two uranyl units is most likely the predominant structure. Second, the sorption processes and the influence of atmospherically derived carbonate on them were analyzed by a combined spectroscopic approach using vibrational and X ray absorption spectroscopy. From results provided, complementary molecular information can be obtained because of the different molecular scales probed by each technique.

In the absence of atmospherically derived CO2, the relevant interface processes can be described by the formation of stable U(VI) surface complexes at trace concentrations which continuously change to surface precipitates with ongoing U(VI) accumulation at the surface. In contrast, in the presence of carbonate ions the surface speciation on gibbsite is significantly changed due to the formation of dimeric uranyl carbonato surface complexes inhibiting the formation of insoluble polymeric species in the micromolar concentration range. The interatomic distances and coordination numbers obtained by EXAFS spectroscopy are concordant with the values calculated for the aquatic dimeric U(VI)-carbonato species.

From the in situ sorption experiments of Np(V) on gibbsite probed by vibrational spectroscopy, the formation of only monomeric inner sphere complexes is derived from experiments in inert gas and in the presence of atmospheric equivalent added carbonate. These findings are supported by results from EXAFS spectroscopy providing evidence for Np–C and Np–Al interactions. Additionally, the values of interatomic distances and coordination numbers are concordant with values for an inner-sphere complex.

From the results of this study, it can be proposed that Al-hydroxides effectively retard the dissemination of actinyl ions at micromolar concentrations in water-bearing host rocks at near neutral pH values, where gibbsite shows the lowest solubility. Furthermore, this work contributes to a better understanding of the geochemical interactions of actinides, in particular U(VI) and Np(V), in the environment and are of relevance for the assessment of the migration behavior of actinyl ions in groundwater systems. The multiplicity of spectroscopic experiments and quantum chemical calculations carried out within this study yields a profound collection of data which can be used as reference for future radioecological investigations of more complex sorption systems in aqueous solution.
  • Doctoral thesis
    TU Dresden, 2013
    91 Seiten

Publ.-Id: 18828 - Permalink


Numerical simulations of the condensing steam-water flow
Apanasevich, P.; Lucas, D.; Seidel, T.;
Gas-liquid two-phase flows including heat and mass transfer across a moving interface have become increasingly important in engineering equipment and technology. In recent decades, experimental and numerical investigations of condensation heat transfer have also been of major importance in connection with the safety analysis of nuclear reactors. Some scenarios for Small Break Loss Of Coolant Accidents (SB-LOCA) lead to an Emergency Core Cooling (ECC) water injection into the cold leg of a Pressurized Water Reactor (PWR). The cold water mixes there with the hot coolant present in the primary circuit. The mixture flows to the downcomer where further mixing of fluids takes place. Such a scenario may result in high thermal loads on the Reactor Pressure Vessel (RPV) wall, while the system pressure is still high. Such a situation is known as Pressurized Thermal Shock (PTS). In context of two-phase PTS situations direct contact condensation occurring in the cold leg and downcomer is one of the most important phenomena. Improvement and validation of CFD models for two-phase stratified condensing flows require high-resolution data in both space and time for the whole domain of interest. For this purpose, the TOPFLOW DENISE experimental program has been conceived at the Helmholtz-Zentrum Dresden-Rossendorf. Its objective is to provide an experimental database for both the validation of CFD modeling of the two-phase condensing flow and to improve the understanding of the direct contact condensation phenomena involved. The paper focuses on condensation of the steam on a subcooled water interface and describes the pre-test CFD simulations of the DENISE steam/water experiments. The simulations were performed to support the definition of the experimental test matrix and the procedure of experiments.
Keywords: Direct Contact Condensation, Stratified Two-phase flow, CFD
  • Contribution to proceedings
    The 15th International Topical Meeting on Nuclear Reactor Thermal - Hydraulics (NURETH-15), 12.-17.05.2013, Pisa, Italy
    Proceedings of NURETH-15
  • Poster
    The 15th International Topical Meeting on Nuclear Reactor Thermal - Hydraulics (NURETH-15), 12.-17.05.2013, Pisa, Italy

Publ.-Id: 18827 - Permalink


Dynamics of ion heating and ionization in high power ultrashort laser pulses interacting with solid density plasmas
Huang, L.; Kluge, T.; Gutt, C.; Bussmann, M.; Cowan, T. E.;
Plasma heating and ionization are important processes during the interaction of high power ultra-short laser pulses with solid density targets. In order to understand the relevant physics, particle-in-cell simulations including collisions and ionization were run to study ion heating dynamics in buried layer targets illuminated by high-intensity, ultra-short laser pulses. Our results show that bulk ions can be heated to above 1keV temperature. When studying the ionization dynamics strong filaments have been observed which depend on preplasma on the target front side, laser pulse duration and intensity. In order to study the evolution of ionization and ion bulk heating in experiment, ultra-bright X-ray free electron lasers - such as the European XFEL - are a very promising and strong tool to resolve the spatial and temporal scales of these processes inside the solid target.
Keywords: ion heating,ionization dynamics, high power laser
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Germany

Publ.-Id: 18824 - Permalink


Experimental investigation on the electromagnetically controlled buoyancy-induced flow in a model of a Czochralski puller
Pal, J.; Cramer, A.; Gerbeth, G.;
A great deal of work with respect to both physical and numerical modelling of Czochralski crystal growth has been conducted in the generic Rayleigh-Bénard system. In order to come closer to the conditions in a real Czochralski puller, specific effects such as the influence of a rounded crucible bottom, deviations of the thermal boundary conditions from the generic case, crucible and/or crystal rotation, and the influence of magnetic fields are often studied separately. Within this paper we present a model experiment focusing on investigations of the impact of magnetic fields on the flow in a Czochralski puller. To achieve similar thermal boundary conditions as in an industrial growth facility, a double-walled rounded bottom glass crucible was chosen to hold the fluid. Similarity of the heat transfer conditions was guaranteed by selecting the ternary alloy GaInSn as the model fluid. Measurements of the fluid flow have been conducted by means of the ultrasound Doppler velocimetry. The results reveal the complex flow structure of natural convection in a Czochralski crucible. Because the growth of high quality mono-crystalline crystals is impeded by such a non-axisymmetric flow, rotating magnetic fields (RMF) are often proposed to render the flow more axisymmetric. To study the effect of an RMF on the natural convection in a Czochralski system the experimental apparatus was mounted inside the home-made MULTIpurpose MAGnetic field facility (MULTIMAG). In the present contribution the three-dimensional convective patterns as well as the resulting temperature fluctuations will be discussed both for the pure buoyant case and for the application of an RMF.
  • Contribution to proceedings
    International Conference on Heating by Electromagnetic Sources (HES-13), 21.-24.05.2013, Padova, Italy
    Proceedings of HES-13, 978-88-89884-25-6, 37-44
  • Lecture (Conference)
    International Conference on Heating by Electromagnetic Sources (HES-13), 21.-24.05.2013, Padova, Italia
  • International Journal of Applied Electromagnetics and Mechanics 44(2014), 163-170
    DOI: 10.3233/JAE-141756

Publ.-Id: 18823 - Permalink


Synthesis and sructure investigation of USiO4 - comparison between local structure and bulk
Labs, S.; Weiss, S.; Hennig, C.; Hübner, R.; Curtis, H.; Bosbach, D.;
Coffinite is a natural mineral with general composition USiO4 [1]. The structure (SG I 41/a m d) with tetravalent uranium in an eightfold coordination with oxygen and isolated silicate tetrahedra is isostructural to zircon, ZrSiO4, and thorite, ThSiO4. Coffinite is the second most important uranium ore. Under reducing conditions with high silica concentrations (c(SiO4) ≧10 -4 mol/L) the reaction of UO2 to USiO4 is favoured (Langmuir's criterion) [2]. Coffinite therefore may be a potential secondary phase in a deep geological repository for spent nuclear fuel. Estimates on the solubility of coffinite indicate a significantly lower uranium solubility compared to that of UO2, thus reducing the uranium source term significantly. Unfortunately, reliable and valdidated thermodynamic data are missing. However, the use of natural samples is not feasible, as these always are associated with significant amounts of impurities like ThO2, UO2, selenides, oxides of REE and organic matter. Because of the high alpha radiation damage, natural coffinit is also usually amorphous. The synthesis of coffinite proves to be rather challenging. Recently Pointeau et al. [3] reported the successful synthesis of coffinite by applying the protocol developed by Hoekstra and Fuchs [4]. However, the obtained products always contained amounts of nanocrystalline UO2. In contrast to recent studies [3,5] we were able to synthesize coffinite, USiO4, without impurities of UO2.

[1] L.R. Stieff, T.W. Stern, and A.M. Sherwood, Coffinite, a Uranous Silicat e with Hydroxyl Substitutions: A New Mineral, Amer. Min., 41 (1956) 675-689. [2] D. Langmuir, Uranium solution-mineral
equilibria at low t emperatures with applications to sedimentary ore deposits, Geochim.Cos mochim.Ac ta 42, 547-569, 1978. [3] V. Pointeau et al. Synthesis and characterization of coffinite, J. Nuc.
Mat. 393 (2009) 449-458. [4] L.H. Fuchs H.R. Hoekstra, The preparation and properties of uranium (IV) silicate, Amer. Min., 44 (1959) 1057-1063. [5] D. Costin et al., How to explain the difficulties in the coff inite synthesis from the study of uranothorite?, Inorg. Chem. 50(21), (2011) 11117-111126.
Keywords: Coffinite, XRD, EXAFS, TEM, SEM, IR, Raman
  • Poster
    EMRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18822 - Permalink


Spectroscopic investigation of heavy metals
Hennig, C.;
Overview on spectroscopic investigation of heavy metals. Physical background of the spectroscopic methods will be discussed and typical applications will be demonstrated.
Keywords: XANES, EXAFS, UV-Vis, IR, UV-Vis, XPS, X-ray scattering, X-ray diffraction (powder and single-crystal), WAXS, LAXS, Neutron scattering
  • Lecture (others)
    Universidad de Granada, Facultad de Ciencias, Departamento de Micobiologia, 21.05.2013, Granada, Spain

Publ.-Id: 18821 - Permalink


U1-xAmxO2±δ solid solution study
Lebreton, F.; Martin, P. M.; Belin, R. C.; Horlait, D.; Dardenne, K.; Rothe, J.; Rossberg, A.; Scheinost, A. C.; Delahaye, T.; Blanchart, P.;
Americium isotopes are produced in nuclear fuels in low amounts (< 0.1 wt.%) by successive neutron captures during irradiation in power reactors. Due to its high activity and long half-life, this element is responsible for the second highest contribution (after plutonium isotopes) to the radiotoxicity and heat load of spent fuels after a hundred years. In order to lower this radiotoxicity and decrease the ecological footprint of ultimate nuclear wastes, transmutation of americium in fast neutron reactors appears to be a possible solution, notably in heterogeneous mode, i.e., through the use of (U,Am)O2 MABB (Minor Actinide Bearing Blanket) fuels destined for the periphery of the core.
In this context, research is being conducted at the Atalante facility not only on the development of fabrication processes for such fuels, but also on the acquisition of data on their fundamental properties. In this work, we report recent experiments performed notably by HT-XRD (high-temperature X-ray diffraction) and XAS (X-ray absorption spectroscopy) which seek a better understanding of the U1-xAmxO2 solid solution over a wide range of compositions (up to x = 0.5). The discussion is mainly focused on: (1) the specific cationic charge distribution in these materials, (2) its influence on the solid solution formation via solid state reaction and (3) on their oxidation behaviour when in contact with different atmospheres (reducing, neutral).
Keywords: Fourth generation nuclear fuel Americium oxidation state ROBL XANES
  • Lecture (Conference)
    E-MRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 18820 - Permalink


Ultrafast graphene-based broadband THz detector
Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.; Schneider, H.; Helm, M.;
We present an ultrafast graphene-based detector, working in the THz range at room temperature. A logarithmic-periodic antenna is coupled to a graphene flake that is produced by exfoliation on SiO2. The detector was characterized with the free-electron laser FELBE for wavelengths from 8 µm to 220 µm. The detector rise time is 50 ps in the wavelength range from 30 µm to 220 µm. Autocorrelation measurements exploiting the nonlinear photocurrent response at high intensities reveal an intrinsic response time below 10 ps. This detector has a high potential for characterizing temporal overlaps, e. g. in two-color pump-probe experiments.
Keywords: graphene, ultrafast detector, THz detection

Publ.-Id: 18819 - Permalink


Switchable zero-bias anomaly in individual C60 molecules contacted with tunable aluminum electrodes
Scheer, E.; Böhler, T.; Edtbauer, A.; Egle, S.; Erbe, A.; Pietsch, T.;
We report the observation of strong resonances at zero bias in the differential conductance through Al–C60–Al junctions with tunable electrode distance, measured above T 1⁄4 10 K. The conductance value at resonance ranges from a few percent up to eighty percent of the quantum of conductance. The resonances may disappear or reoccur completely and discontinuously upon very small changes of the electrode distance. However, once they are formed they are very robust with respect to changes of the electrode distance. We discuss similarities and differences to the common theories of the Kondo screening of a spontaneous spin polarization of the C60 molecule. We deduce Kondo temperatures in the range from 35 to 160 K and demonstrate that the temperature dependence is in agreement with the scaling behavior of the Kondo effect in the temperature range of our experiment.
Keywords: molecular electronics, mechanically controllable break junctions, Kondo effect

Publ.-Id: 18818 - Permalink


Fracture mechanics and mechanical characterization of the beltline welding seam of the decommissioned WWER-440 reactor pressure vessels of nuclear power plant Greifswald Unit 4
Viehrig, H.-W.; Altstadt, E.; Houska, M.; Valo, M.;
The paper presents data measured for two trepans sampled from the beltline welding seam of the decommissioned WWER-440/V-230 reactor pressure vessel (RPV) of the nuclear power plant Greifswald Unit 4. Greifswald Unit 4 representing the first generation of this reactor type was shut down after 11 operating cycles in 1990. The aging of the RPV steels was not monitored by any surveillance program. The main focus of this work is put on fracture toughness characterization according to test standard ASTM E1921. Charpy size SE(B)-specimens were machined from different locations through the thickness of the multilayer beltline welding seam. SE(B) specimens machined from the same thickness are a set of specimens for which one reference temperature T0 was defined according to ASTM E1921. The pre-cracked and side-grooved Charpy-size SE(B) specimens were monotonically loaded until they failed by cleavage instability. T0 values were evaluated with the measured cleavage fracture toughness values, KJc, by applying the multi-temperature procedure. The neutron fluence at the RPV outer and inner RPV wall was determined with 4.1•1019 und 0.87•1019, respectively. That is a decrease for about 80% over the RPV wall.
Large variations in the evaluated T0 values across the wall of the multilayer beltline welding seams were observed. At the inner wall just beyond the cladding and in the welding root region comparatively low a T0 were evaluated with 28°C and 6°C, respectively. After the welding root towards the outer wall the average T0 amounts 81°C with a span (maximum value minus minimum value) of 57 K. It is demonstrated that the ductile-to-brittle transition temperature shift predicted by the Russian code for the existing content of deleterious elements P and Cu and the accumulated neutron fluences lies within the scatter of the measured T0 values. The irradiation induced shift of T0 expected due to the decrease of the neutron fluence by about 80% from the inner to the outer RPV wall is not visible. It is overlapped by the strong variation of KJc values caused by the intrinsic weld bead structure and the different filling materials used for weld root and the main weld.
In addition Charpy-V tests were performed to compare the results of fracture mechanics testing with the current integrity assessment code practice. The transition temperatures TT47J vary also through the thickness of the multilayer welding seam. At the inner wall just beyond the cladding and in the welding root region TT47J was measured with 73°C and 40°C, respectively. After the welding root the average TT47J amounts to 124°C with a span of 16 K. Compared with T0 the variation of TT47J within the filling layers after the welding root is considerably smaller.
Compact and reconstituted Charpy-V and SE(B) specimens were thermally annealed at 475°C for 152 h. This temperature time regime corresponds to the one applied to the Greifswald Units 1 to 3. The comparison of test of thermally annealed and non-annealed specimens provides irradiation induced shifts of 114 K for TT47J and 86 K for T0. The testing of annealed specimens confirms the results measured with samples from thermally annealed RPV of Greifswald Unit 2.
Keywords: decommissioned nuclear power plant, reactor pressure vessel, welding seam, annealing, fracture toughness, ductile-to-brittle transition, neutron embrittlement
  • Lecture (Conference)
    26th Symposium on the Effects of Radiation on Nuclear Materials, 12.-13.06.2013, Indianapolis, USA

Publ.-Id: 18817 - Permalink


Spheroid Control Probability as Analytical Endpoint for the Evaluation of a Radio-chemo-therapeutic Approach Combining External and Internal Irradiation
Ingargiola, M.; Runge, R.; Heldt, J.-M.; Pietzsch, H.-J.; Kotzerke, J.; Cordes, N.; Steinbach, J.; Baumann, M.; Kunz-Schughart, L. A.;
kein Abstract verfügbar
  • Abstract in refereed journal
    European Journal of Cancer 48(2012), S272
  • Poster
    22nd Biennial Congress of the European Association for Cancer Research, 07.-10.07.2012, Barcelona, Spain

Publ.-Id: 18816 - Permalink


From holes to sponge at irradiated Ge surfaces with increasing ion energy - an effect of defect kinetics?
Böttger, R.; Heinig, K.-H.; Bischoff, L.; Liedke, B.; Facsko, S.;
We show that hole patterns and sponge-like layers at irradiated Ge surfaces originate from the same driving force, namely the kinetics of ion beam induced defects in the amorphous Ge surface layer. Ge hole Patterns reported earlier for irradiation with low energy (5 keV) Ga+ ions were reproduced for low energy Bi+ but also for Ge+ selfirradiation, which proves that the dominating driving force for morphology evolution cannot originate from the implanted impurities. At higher ion energies the well-known formation of sponge-like Ge surface layers after heavy ion irradiation was found for Bi+ irradiation and Ge+ self-irradiation too. The transition from smooth surfaces via hole patterns to sponge-like morphologies with increasing ion energies was studied in detail. A model based on the kinetics of ion beam induced defects was developed and implemented in 3D kinetic Monte Carlo simulations, which reproduce the transition from hole patterns to sponge-like layers with increasing ion energy.
Keywords: germanium, ion Irradiation, defect accumulation, self-organization, kinetic Monte Carlo simulations

Publ.-Id: 18815 - Permalink


Optical Synchronization and Electron Bunch Diagnostic at ELBE
Kuntzsch, M.; Gensch, M.; Lehnert, U.; Roeser, F.; Schurig, R.; Bousonville, M.; Czwalinna, M. K.; Schlarb, H.; Schulz, S.; Vilcins, S.;
The continuous wave electron accelerator ELBE is upgraded to generate short and highly charged electron bunches (~100fs duration, up to 1 nC) . In the last years a prototype of an optical synchronization system using a mode locked fiber laser has been build up which is now in commissioning phase. The stabilized pulse train can be used for new methods of electron bunch diagnostics like bunch arrival time measurements with femtosecond resolution. At ELBE a Bunch arrival time monitor (BAM) has been designed and tested at the accelerator. The contribution will show the design of the BAM and some measurement results.
Keywords: Synchronization
  • Poster
    IPAC2013 - The 4th International Particle Accelerator Conference, 12.-17.05.2013, Shanghai, China
  • Open Access LogoContribution to proceedings
    IPAC2013 - The 4th International Particle Accelerator Conference, 12.-17.05.2013, Shanghai, China
    Proceedings of the 4th International Particle Accelerator Conference, 978-3-95450-122-9, 2932-2934

Publ.-Id: 18814 - Permalink


Optische Synchronisation an der Strahlenquelle ELBE mit Femtosekunden Präzision
Kuntzsch, M.;
Dieses wissenschaftliche Seminar an der Hochschule für Technik und Wirtschaft Dresden gibt einen Überblick zu der Strahlerzeugung und Diagnose am supraleitenden Elektronenbschleuniger ELBE im Helmholtz-Zentrum Dresden-Rossendorf. Besonders wird dabei auf die im Bau befindlichen Röntgenstrahlungs- und THz- Quellen eingegangen, die erhöhte Anforderungen an die Synchronisation und die Strahldiagnose stellen.
Um stabile Experimentierbedingungen zu schaffen, wird ein Synchronisationssystem mit einer Stabilität von mindestens 100 fs benötigt. Es wird beschrieben, wie dieses System funktioniert und erste Ergebnisse vom Betrieb des Prototyps vorgestellt.
Basierend auf dem optischen Synchronisationssystem wurde ein Gerät für die exakte Ermittlung der Ankunftszeit der Elektronenpulse an einer Stelle im Beschleuniger entwickelt. Es werden erste Messergebnisse dieser Einrichtung und deren Aufbau präsentiert.
  • Invited lecture (Conferences)
    158. Wissenschaftliches Seminar, 19.03.2013, Dresden, Germany

Publ.-Id: 18813 - Permalink


Optical Synchronization and Electron Bunch Diagnostic at the quasi-CW accelerator ELBE
Kuntzsch, M.; Lehnert, U.; Röser, F.; Czwalinna, M. K.; Schulz, S.; Schlarb, H.; Vilcins, S.;
The continuous wave electron accelerator ELBE is upgraded to generate short and highly charged electron bunches (~200fs duration, up to 1 nC) with an energy of up to 40 MeV. In the last years a prototype of an optical synchronization system using a mode locked fiber laser has been build up which is now in commissioning phase. The stabilized pulse train can be used for new methods of electron bunch diagnostics like bunch arrival time measurement with the resolution down to a few femtoseconds. At ELBE a bunch arrival time monitor (BAM) has been designed and tested at the accelerator. The contribution will show the concept of the femtosecond synchronization system, the design of the BAM and first measurement results.
Keywords: Synchronization ELBE
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Germany

Publ.-Id: 18812 - Permalink


Semiconductor quantum well excitons in strong, narrowband terahertz fields
Teich, M.; Wagner, M.; Schneider, H.; Helm, M.;
Optical transitions between exciton states in semiconductors – intraexcitonic transitions – usually fall into the terahertz (THz) range and can be resonantly excited with narrowband, intense THz radiation as provided by a free-electron laser. We investigate this situation for two different quantum well structures by probing the near-infrared excitonic absorption spectrum near the band edge. We observe the dynamical Stark – or Autler Townes – splitting of the 1s exciton ground state and follow its evolution for various THz photon energies and field strengths. The behavior is considerably more complex than in atomic systems. At the highest field strengths, where the Rabi energy is of the same order of magnitude as the exciton level separation, the system cannot be described within the standard framework of a two-level system in rotating wave approximation. When the ponderomotive energy approaches the exciton binding energy, signatures of exciton field ionization are observed.
Keywords: terahertz, Stark effect, quantum well, exciton, Autler-Townes, free electron laser

Publ.-Id: 18811 - Permalink


Rare earth implanted MOS structures: Advantages and drawbacks for optoelectronic applications
Rebohle, L.;
Integrated photonics is a key technology of the 21st century, and Si-based photonic components are of special interest as they propose an easy integration into the CMOS platform. An essential building block is the electrically driven light emitter (LE) which, however, is difficult to realize. Among the different approaches rare earth (RE) implanted MOS structures feature a high conformity with standard CMOS processes combined with the excellent optical properties of RE elements.
However, despite an intense research for more than 20 years in the field of Si-based light emission, the results are mixed. With respect to important key parameters like power efficien-cy, Si-based LE are not yet able to compete with their counterparts based on compound or organic semiconductors. The following contribution is focused on RE implanted MOS structures and discusses the different problems to turn them into long-living, efficient LE.
Such a LE typically consists of a Si substrate, a dielectric stack and a transparent electrode (Abb. 1). The layers of the dielectric stack fulfil several tasks like hosting the luminescence centres or providing a buffer against early electrical breakdowns. Usually, the injected charge carriers have to overcome substantial potential barriers requiring high electric fields for operation. The electroluminescence (EL) is based on radiative 4f intrashell transitions within the trivalent RE ion, although there are exceptions involving a 5d electron (e.g. Ce). For this reason oxidic materials, especially SiO2, are suitable as host matrices, but there are also successful reports where RE elements are embedded in other materials, e.g. silicon nitride.



Fig. 1: Basic scheme of a RE-implanted MOS device

At the beginning, a short view to the EL excitation mechanism may be helpful. From the physical point of view, there are two main types of excitation. At first, under favourable conditions electrons can be accelerated to high energies which can be transferred by inelastic scattering to the lumines¬cence centres. This mode can be fairly efficient, depending on the fraction of hot electrons in the average electron energy distribution, but inherently contains the seed of destruction: hot electrons are also efficient in creating new defects and degrading oxides. Different to this, charge carrier recombination releases the band gap energy of the host semiconductor at maximum, which prevents degradation and limits the different types of potential luminescence centres. In case of Si-based LE the efficiency is often less than in case of hot electron excitation, but there are ongoing research activities to improve the situation.
Starting the discussion with the quest for the most efficient RE-implanted MOS device, there are at least three strategies to be pursued: (i) to increase the excitation cross section, (ii) to increase the internal quantum efficiency, and (iii) to increase the outcoupling efficiency.
In most cases the first strategy was pursued, and indeed, this strategy probably offers the greatest potential if the efficiency is far away from reasonable levels. Among the most popular ideas is the use of Si nanoclusters to enhance the excitation cross section of RE ions, especially of Er. Although this recipe was quite successful in case of photoluminescence, it was found that often only a small percentage of Er is excited [1]. The problem was partially solved in the last years by substantial changes in the composition of the dielectric stack. The use of Ge nanoclusters gave the unexpected result that the RE ions were pumping the Ge nanoclusters instead vice versa [2]. At present, in case of EL the use of a second RE element pumping the first one was more efficient, as demonstrated for Gd pumping the EL of Ce [3].
In case of hot electron excitation another problem appears, namely the existence of a dark zone close to the injecting interface. This is the region where electrons are already accelerated but not yet have enough energy to excite the RE ions. In case of Tb-implanted MOS devices it was found that this zone extends up to 20 nm into the gate oxide [4] which limits the scalability to thinner devices and to lower operation voltages.
To improve operation lifetime, the use of LOCOS (LOCal Oxidation of Silicon) structures and dielectric buffer layers made of SiON [5] can prevent early electric breakdowns. However, these strategies cannot solve the fundamental problem of oxide degradation by hot electrons. In addition, the EL often exhibits degradation over lifetime due to the charging of defects and RE clusters [6]. Experiments with MOS structures, where SiO2 is replaced by materials with less hot electrons, show that in fact the operation lifetime is strongly enhanced, but unfortunately at the expense of efficiency. A possible solution could be the shift of the excitation mode to charge carrier recombination, e.g. if electrons and holes are both injected during AC excitation.
In summary, the advantages and drawbacks of RE-implanted MOS devices were discussed. At present, the current status of these devices allows only a few applications where efficiency and operation lifetime is not of major importance, as for some sensor applications. However, some possible solutions to reduce or overcome these problems were addressed.
References
[1] B. Garrido, C. García, P. Pellegrino, D. Navarro-Urrios, N. Daldosso, L. Pavesi, F. Gourbilleau, and R. Rizk, Appl. Phys. Lett. 89 (2006) 163103
[2] L. Rebohle, A. Kanjilal, W. Skorupa, and M. Helm, Opt. Mat. 33, Issue 7 (2011) 1075.
[3] J.M. Sun, S. Prucnal, W. Skorupa, M. Helm, L. Rebohle, and T. Gebel, Appl. Phys. Lett. 89, 091908 (2006)
[4] L. Rebohle, J. Lehmann, S. Prucnal, J. M. Sun, M. Helm and W. Skorupa, App. Phys. B 98:2 (2010) 439
[5] J.M. Sun, L. Rebohle, S. Prucnal, M. Helm, W. Skorupa, Appl. Phys. Lett. 92, 071103 (2008)
[6] A. N. Nazarov, S. I. Tiagulskyi, I. P. Tyagulskyy, V. S. Lysenko, L. Rebohle, J. Lehmann, S. Prucnal, M. Voelskow, and W. Skorupa, J. Appl. Phys. 107, 123112 (2010)
Keywords: electroluminescence, rare earth implantation, erbium
  • Invited lecture (Conferences)
    7th International Workshop “Functional Nanomaterials and Devices”, 08.-11.04.2013, Kyiv, Ukraine
  • Book chapter
    Nazarov, A., Francis, B., Valeriya, K., Flandre, D: Functional Nanomaterials and Devices for Electronics, Sensors and Energy Harvesting, Berlin: Springer, 2014, 978-3-319-08803-7, 349-364
    DOI: 10.1007/978-3-319-08804-4_16

Publ.-Id: 18810 - Permalink


Interaction of uranium(VI) and neptunium(V) with Äspö diorite under anoxic conditions
Schmeide, K.; Gürtler, S.; Bok, F.; Brendler, V.;
The interaction of uranium(VI) and neptunium(V) with diorite obtained from Äspö Hard Rock Laboratory (HRL, Sweden) has been studied by means of batch sorption experiments under anoxic conditions (N2) as a function of contact time (5 to 108 d) applying a synthetic Äspö groundwater (pH 7.8, I = 0.18 M) as background electrolyte. In the case of uranium(VI), sorption isotherms have been recorded by varying the total uranium(VI) concentration between 3•10−9 and 2•10−5 M. Distribution coefficients, Kd values, were determined. Desorption experiments have been performed using synthetic Äspö groundwater. For redox speciation of actinides in sample solution or desorbed from the diorite, solvent extraction has been applied.
Keywords: sorption, reduction, U(VI), Np(V), Np(IV)
  • Lecture (Conference)
    Final Workshop of the Project "Crystalline rock retention processes" (CROCK), 14.-16.05.2013, Karlsruhe, Germany
  • Poster
    Final Workshop of the Project "Crystalline rock retention processes" (CROCK), 14.-16.05.2013, Karlsruhe, Germany
  • Contribution to proceedings
    Final Workshop of the Project "Crystalline Rock Retention Processes" (CROCK), 14.-16.05.2013, Karlsruhe, Germany
    Final Workshop Proceedings of the Collaborative Project "Crystalline Rock Retention Processes" (7th EC FP CP CROCK), KIT Scientific Reports 7656, Karlsruhe: KIT Scientific Publishing, 211-223 (2014)

Publ.-Id: 18809 - Permalink


Accelerator based super-radiant THz sources: Challenges and opportunities
Gensch, M.;
The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrowbandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges will be discussed on the example of recent pilot experiments.
[1] G.L. Carr et. al., High power terahertz radiation from relativistic electrons, Nature 420 (2002), 153.
[2] M. Gensch et. al., New infrared undulator beamline at FLASH, Infrared Phys. Technol. 51 (2008), 423.
[3] U. Fruehling et. al., Single-Shot THz-field-driven X-ray streak camera, Nat. Photon. 3 (2009), 523.
[4] F. Tavella, N. Stojanovic, G. Geloni, M. Gensch, Few-Femtosecond timing at Fourth-Generation X-ray Light sources, Nat. Photon. 5 (2011), 162.
[5] D. Daranciang et. al., Single-cycle terahertz pulses with > 0.2 V/angstrom field amplitudes via coherent transition radiation, Appl. Phys. Lett. 99 (2011), 141117.
  • Invited lecture (Conferences)
    Seminar, Lehrstuhl für Angewandte und Experimentelle Physik, Universität Regensburg, 28.05.2013, Universität Regensburg, Deutschland

Publ.-Id: 18808 - Permalink


A biochemical approach to single particle X-FEL studies on membrane proteins
Oertel, J.; Keller, A.; Weiss, S.; Stellato, F.; Barty, A.; Fahmy, K.;
Membrane proteins are vital for making cells responsive to environmental stimuli as well as in controlling the exchange of ions between the cytoplasm and the extracellular space. Both processes depend on proteins containing multiple transmembrane helices that rearrange during function. The development of a technology that allows resolving structural transitions in single membrane proteins by the use of ultra-short X-ray pulses from X-ray free electron lasers (X-FELs) will represent a significant advance in studies of membrane protein structure and dynamics. The successful use of X-FEL radiation for Structural Biology has been proven for nanocrystals. In contrast, the potential for a fully crystallization-independent analysis of large protein structures at the single molecule level has not been explored experimentally.
Engineered phospholipid nanodiscs (NDs), which are lipid-protein complexes surrounded by a helical protein belt of two membrane scaffold proteins (MSPs) provide a completely soluble nanoscale section of a lipid bilayer designed for functional investigations of membrane proteins. Exploring their suitability for single particle X-ray diffraction will have a strong impact on X-FEL applications in Structural Biology, particular for the crystallization-independent structure determination of membrane proteins. Additionally, NDs will be labelled with small gold spheres of ~1.4nm diameter to aid particle identification and orientation. Sufficiently high concentrations of NDs have been obtained for preliminary X-ray diffraction experiments and aggregation can be prevented even at high concentrations (mg/ml).
Keywords: membrane proteins, structural biology, X-FEL
  • Poster
    Kick-off meeting for the HIBEF User Consortium, 02.-05.06.2013, Hamburg, Deutschland

Publ.-Id: 18807 - Permalink


Low-electrical resistivity polycrystalline TiO2-based transparent conductors by millisecond flash lamp annealing of magnetron sputtered films
Neubert, M.; Vinnichenko, M.; Cornelius, S.; Gebel, T.; Liepack, H.;
Transparent conductive oxides (TCO), mainly In2O3:Sn (ITO), ZnO:Al (AZO) and SnO2:F (FTO) are widely used as transparent electrodes in flat panel displays, thin film solar cells and solid state lighting. In contrast to these TCOs, TiO2 –based films offer unique combination of low cost, high refractive index, stability against humidity, the high chemical stability and the non-toxicity. The Nb or Ta doped TiO2 films epitaxially grown on crystalline substrates already show electrical and optical properties which are comparable to those of conventional TCOs. However, it is still a challenge to achieve low electrical resistivity polycrystalline TiO2 - based films as required for most of applications. Furthermore, it is not possible to get low resistivity in polycrystalline films by direct growth at elevated substrate temperatures. Only a two-step approach, i.e. the deposition of amorphous films followed by annealing for minutes up to hours in vacuum or hydrogen delivers films with resistivity values in the range of 1•10-3 Ωcm. Both, the direct growth on crystalline substrates and the post deposition annealing of the amorphous films require substrate temperatures of about 400°C to ensure desired resistivity, which drastically limits applications. Furthermore, the high demand for energy for an annealing time of several minutes or even hour is almost unacceptable for a cost-efficient and environmental friendly replacement of conventional by TiO2 - based TCOs, especially for large area applications. In order to address this problem, we studied the films formed on glass substrates without heating by direct current magnetron sputtering (DC MS) of reduced TiO2:Ta ceramic targets followed by flash lamp annealing (FLA) in the millisecond range to crystallize as-deposited amorphous films. The Ti/O ratio of the as-deposited films was varied using a DC MS process in conjunction with a plasma feedback system to achieve an oxygen fine-tuning. Using FLA, the heat treatment is confined to the film and the substrate is only partly heated (several µm at the surface) which drastically lowers the energy consumption and allows the use of temperature sensitive substrates. In addition, the short annealing enables the film processing at atmospheric pressure in argon or even in air. The emerging electrical, optical and structural properties are strongly affected by the Ti/O ratio in the as-deposited films adjusted by the plasma feeback system Our approach delivered films with an electrical resistivity in the range of 1•10-3 Ωcm, optical transmittance above 80% for 400nm thick films and electrical activation of Ta dopants up to 60%. The reference films obtained combining deposition onto unheated substrate and subsequent conventional annealing in vacuum at 425°C for 1 hour show almost the same electrical and optical properties.
Keywords: transparent conductive oxide, TCO, titania, tantalum, flash lamp annealing
  • Lecture (Conference)
    2013 MRS Spring Meeting & Exhibit, 01.-05.04.2013, San Francisco, United States of America

Publ.-Id: 18806 - Permalink


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