Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Simultaneous STXM imaging and resistance measurements of trilayer vortices
Banholzer, A.; Wintz, S.; Fowley, C.; Deac, A.; Raabe, J.; Lenz, K.; Lindner, J.; Fassbender, J.ORC
We investigate a trilayer vortex system by simultaneous scanning transmission X-ray microscopy (STXM) and in-situ giant magnetoresistance (GMR) measurements. Our aim is to correlate the magnetic configuration of both magnetic layers with the corresponding magneto-resistance effects.
The sample is a Co/Cu/Ni80Fe20 cylindrical trilayer, with 2 µm diameter [1]. Top and bottom contacts allow to apply a perpendicular DC current to measure the resistance. Simultaneously the magnetic configuration of each element of the disc is imaged using STXM. This is performed at the Paul Scherrer Institute. The vortex core formation in both magnetic layers and the position of the vortex core can be controlled by applying an in-plane external magnetic field. When the cores are at the edge, and the magnetization state resembles that of two in-plane magnetized disks, the GMR is low, as both cores move towards the center. With decreasing field the resistance increases, as the cores move beyond the center and towards the opposite side, the resistance decreases again. We investigate the resistance at different DC currents in dependency on the swept magnetic fields.
REFERENCES
[1] S. Wintz, Appl. Phys. Lett. 98, 232511 (2011)
Keywords: Vortex, STXM
  • Lecture (Conference)
    Joint European Magnetic Symposia (JEMS) 2013, 25.-30.08.2013, Rhodos, Greece

Publ.-Id: 19211 - Permalink


Direct Condensation and Entrainment Installation for Steam Experiments TOPFLOW-DENISE: Stratified Steam Condensation Experiments
Seidel, T.; Beyer, M.;
1. MOTIVATION
In a hypothetical Small Break Loss of Coolant Accident (SB-LOCA) in a Pressurized Water Reactor (PWR), the Reactor Pressure Vessel wall (RPV) may be exposed to thermal stress, since Emergency Core Cooling Systems (ECCS) injects cold water. The loads on the primary loop and RPV walls are determined by mixing processes with the surrounding hot water and by the condensation of steam on the surface (see Bestion 2010 and Lucas 2005)
For the development and validation of CFD-models, experiments have to meet a high standard of reproducibility, measurement certainty and temporal and local resolution. The pressure tank technology of the TOPFLOW facility allows conducting such experiments at reasonable effort.
2. TOPFLOW-DENISE FACILITY
The Direct Condensation and Entrainment Installation for Steam Experiments (DENISE) is made for CFD-grade condensation experiments at up to 50 bars pressure (see Figure 1). Subcooled water is injected into the DENISE-basin in three different configurations for experimental investigation:
A) Stratified flow
B) Subcooled water Jet
C) steam bubble entrainment with a jet falling on a stratified surface
The experimental facility is equipped with a dense instrumentation. The flow inside is observed and controlled with a high speed camera and an infrared camera, coriolis flow meters and a set of micro thermocouples. The facility is supplied with a 4 MW electrical boiler, saturated water pumps, a 30 kW electrical heater and a 2 MW water cooler.
3. FIRST EXPERIMENTAL SERIES
The first series contains stratified flow experiments comparable to non-adiabatic flow inside hot and cold legs of PWRs. Measurement results can be compared to CFD simulations. Recently 56 experiments have been carried out according to the test matrix in Table 1.
The observed high speed and infrared images from the reference experiment are shown in Figure 2. The surface is slightly wavy and a small increase of water temperature is observable between inlet (left) and outlet (right). Processed data from these measurements, like the temperature plots shown in Figure 3 will provide comparable results for the development and validation of CFD-models.
4. OUTLOOK
Experiments with stratified steam-water surfaces have been carried out in August 2013. They are being analyzed till end of 2013. For the next experiments, a jet injector will be added to the facility and plunging jet experiments with bubble entrainment will be measured. Finally, there will be experiments with a subcooled water jet falling through the steam atmosphere. A special movable thermo sensor will be used to measure temperature profiles inside the jet.
  • Lecture (Conference)
    150 Jahre - Richard Mollier, Internationales Kolloquium zum 150. Geburtstag von Richard Mollier, 21.-23.11.2013, Dresden, Germany

Publ.-Id: 19210 - Permalink


Lateral spin transfer torque induced magnetic switching at room temperature demonstrated by x-ray microscopy.
Buhl, M.; Erbe, A.; Grebing, J.; Wintz, S.; Raabe, J.; Fassbender, J.ORC
Changing and detecting the orientation of nanomagnetic structures, which can be used for durable information storage, needs to be developed towards true nanoscale dimensions for keeping up the miniaturization speed of modern nanoelectronic compo- nents. Therefore, new concepts for controlling the state of nanomagnets are currently in the focus of research in the field of nanoelectronics. Here, we demonstrate re- producible switching of a purely metallic nanopillar placed on a lead that conducts a spin-polarized current at room temperature. Spin diffusion across the metal-metal (Cu to CoFe) interface between the pillar and the lead causes spin accumulation in the pillar, which may then be used to set the magnetic orientation of the pillar. In our experiments, the detection of the magnetic state of the nanopillar is performed by direct imaging via scanning transmission x-ray microscopy (STXM).
Keywords: Magnetic Materials and Devices, Nanosensors and other Devices, Surface Patterning and Imaging

Publ.-Id: 19209 - Permalink


Entwicklung von CFD-Modellen für Wandsieden und Entwicklung hochauflösender, schneller Röntgentomographie für die Analyse von Zweiphasenströmungen in Brennstabbündeln
Krepper, E.; Rzehak, R.; Barthel, F.; Franz, R.; Hampel, U.;
In einem Verbundprojekt im Rahmen des Programms „Energie 2020+“ gefördert durch das BMBF koordiniert durch das HZDR arbeiteten 4 Universitäten, 2 Forschungszentren und ANSYS zusammen. Der vorliegende Bericht beschreibt die Arbeiten des HZDR, die im Zeitraum September 2009 bis Januar 2013 durchgeführt wurden. Das Vorhaben war auf die Entwicklung und Validierung von CFD-Modellen von unterkühltem Sieden bis zu Filmsieden gerichtet.
Im Bericht werden die entwickelten und verwendeten Modelle dargestellt. Anhand der Nachanalyse von Experimenten wird auf die vorgeschlagene Kalibrierung der Modelle eingegangen. Wichtig ist hierbei eine genauere Beschreibung der Zwischenphasengrenzfläche, die durch Kopplung des Wandsiedemodells mit einem Populationsmodell erreicht werden kann. Anhand der Analyse von Bündelexperimenten konnte gezeigt werden, dass die gemessenen querschnittsgemittelten Messwerte mit einem Satz im Rahmen der Modellunsicherheiten kalibrierter Modellparameter reproduziert werden kann. Für die Berechnung der Verteilungsmuster des Dampfgehaltes im Kanalquerschnitt muss die Modellierung der Turbulenz beachtet werden.
Die experimentellen Arbeiten waren auf die Untersuchung eines Brennelementbündels gerichtet. An einer Versuchsanordnung zu einem Brennelementbündel werden die turbulente einphasige Geschwindigkeit (PIV), der mittlere Gasgehalt (Gamma-Densitometrie) sowie der zeitlich und räumlich aufgelöste Gasgehalt (Hochgeschwindigkeits-Röntgentomographie) gemessen. Letztere Methode wurde in Rossendorf entwickelt.
Keywords: boiling, CFD, bubbly flow, momentum exchange, mass exchange, population balance model, experiments, PIV, gamma densitometry, fast x-ray tomography
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-040 2013
    ISSN: 2191-8708

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Publ.-Id: 19208 - Permalink


Laser assisted Compton scattering of X-ray photons
Seipt, D.; Kämpfer, B.;
The Compton scattering of X-ray photons, assisted by a short intense optical laser pulse is discussed. The differential scattering cross section reveals the interesting feature that the main Klein-Nishina line is accompanied by a series of side-lines forming a broad plateau where up to ${\cal O} (10^3)$ laser photons participate simultaneously in a single scattering event. Due to the non-linear mixing of X-ray and laser photons a frequency dependent rotation of the polarization of the final state photons relative to the scattering plane emerges. A consistent description of the scattering process with short laser pulses requires to work with X-ray pulses. An experimental investigation can be accomplished, e.g., at LCLS or the European XFEL in the near future.

Publ.-Id: 19207 - Permalink


Magnetic properties of granular CoCrPt:SiO2 thin films deposited on GaSb nanocones
Ball, D. K.; Lenz, K.; Fritzsche, M.; Varvaro, G.; Günther, S.; Krone, P.; Makarov, D.; Mücklich, A.; Facsko, S.; Fassbender, J.ORC; Albrecht, M.
We report on the effect of microstructure on the magnetic properties of granular CoCrPt:SiO2 films with weakly interacting magnetic grains deposited on pre-structured GaSb nanocone templates fabricated by ion erosion technique. By tuning the irradiation conditions, nanocone patterns of different cone size were prepared (from 28 to 120 nm in diameter and 32 to 330 nm high, respectively). The influence of the intergranular exchange coupling was also investigated by varying the SiO2 content from 8 to 12 at.\%. Deposition of CoCrPt:SiO2 on samples with small nanocones leads to a close magnetic grain packing, which results in the formation of extended magnetic domains larger than the average distance between the GaSb cones. In contrast, on larger nanocones, the magnetic coating grows on the side-walls with large separation between neighbouring cones leading to magnetic single-domain regions, which are correlated to the underlying structure. Magnetometry measurements indicate that both remanence and coercivity decrease with increasing cone size and/or SiO2 content due to the combined effect of the angular distribution of the magnetic easy axis of the grains and the intergranular exchange coupling strength.
Keywords: Magnetic granular films, Ion beam erosion, nanocones

Publ.-Id: 19206 - Permalink


Origin and enhancement of the 1.3 mu m luminescence from GaAs treated by ion-implantation and flash lamp annealing
Gao, K.; Prucnal, S.; Skorupa, W.; Helm, M.; Zhou, S.;
GaAs and GaAs based materials have outstanding optoelectronic properties and are widely used as light emitting media in devices. Many approaches have been applied to GaAs to generate luminescence at 0.88, 1.30, 1.55 µm which are transmission windows of optical fibers. In this paper we present the photoluminescence at 1.30 µm from deep level defects in GaAs treated by ion-implantation and flash lamp annealing (FLA). Such emission, which exhibits superior temperature stability, can be obtained from FLA treated virgin GaAs as well as doped GaAs. Indium-doping in GaAs can greatly enhance the luminescence. By photoluminescence, Raman measurements, and positron annihilation spectroscopy, we conclude that the origin of the 1.30 µm emission is from transitions between the VAs-donor and X-acceptor pairs.
Keywords: GaAs, 1.3 µm photoluminescence, ion-implantation, flash lamp annealing

Publ.-Id: 19205 - Permalink


Structure and energetics of oxidic nanoclusters in bcc-iron
Posselt, M.; Devaraj, M.;
Nanostructured ferritic alloys (NFA) or Oxide Dispersion Strengthened (ODS) steels consist of an iron-based matrix with dispersed nanometer-size oxide particles. Compared to conventional steels these materials exhibit two remarkable properties that are not fully understood yet: (i) Stability: Up to rather high temperatures the number and size of the oxygen-rich nanoparticles do not change significantly. (ii) Tolerance: The nanoclusters act as sinks for transmutation helium, vacancies and self-interstitial. The first property is the reason for the improved creep strength at high temperature, whereas the second property is related to the radiation resistance of these materials. Therefore, NFA or ODS are promising candidates for applications as structural materials in extreme environments, i.e. at high temperature and intense particle irradiation, such as in advanced nuclear fission and fusion reactors.
The detailed structure and composition of the oxidic nanoclusters containing Y, Ti, O along with other minor alloying and impurity elements is still under discussion. In this work simulated annealing (SA) based on the Metropolis Monte Carlo method is used in order to determine the structure of the oxidic nanoclusters with the lowest formation energy. Since cluster sizes up to a few nm are of interest, first-principle methods cannot be used throughout since they are computationally too expensive. In contrast to previous theoretical investigations both pair and triple interactions between the different atomic species are employed in the SA method. The corresponding interaction parameters are obtained from comprehensive first-principle calculations on the structure and energetics of point defects and small clusters. SA is performed for various oxidic clusters and the results are compared with available experimental and theoretical data from literature. The binding energy of the nanoclusters obtained in this work can be used as input parameters of coarse-grained method such as Object Kinetic Monte Carlo simulations and Rate Theory.
Keywords: ODS alloy, oxide nanocluster, structure and energetics, simulated annealing
  • Poster
    EUROMAT 2013, 08.-13.09.2013, Sevilla, Spain
  • Poster
    GETMAT Int. Workshop, 17.-19.09.2013, Berlin, Deutschland

Publ.-Id: 19204 - Permalink


Temperature-dependent free formation energies of Y, Ti and O in bcc Fe: A first principles study
Devaraj, M.; Posselt, M.;
The dispersion of thermally stable nanosized oxide particles in the ferritic matrix remarkably increases the high temperature mechanical strength of these alloys. These alloys are referred to as Nanostructured ferritic alloys (NFA) or Oxide Dispersion Strengthened (ODS) steels and are potential candidate for use as structural materials in advanced fast breeder and fusion nuclear reactors. NFA possess excellent creep strength compared to conventional ferritic/martensitic steels. These alloys are also found to be highly resistant against long term neutron and radiation fluxes and act as sinks for transmutation helium, vacancies and self-interstitial. The physical mechanisms leading to the formation of these oxide nanoclusters in ferritic matrix is not yet fully understood. The basic properties of these clusters containing Y, Ti, O and vacancies are investigated by Density Functional Theory (DFT). Further, the formation and binding energies obtained from DFT calculations are being used as input for Monte Carlo simulations. In this multiscale approach, the results of calculations crucially depend on the input parameters obtained from DFT calculations. In previous studies only DFT data determined at T=0 have been used as inputs. The main objective of present work is to calculate the temperature-dependent free formation energies of Y, Ti and O point defects in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The present work is motivated by the assumption that the knowledge of the temperature dependence of free formation and binding energies is very important to understand the thermodynamics of the formation of the oxide nanoclusters at high consolidation temperatures. The results obtained in this work are compared with recent theoretical calculations and discussed in relation to experimental solubility data.
Keywords: iron, foreign atoms, free formation energy, DFT
  • Lecture (Conference)
    EUROMAT 2013, 08.-13.09.2013, Sevilla, Spain

Publ.-Id: 19203 - Permalink


Compositionally modulated ripples during composite film growth: three-dimensional pattern formation at the nanoscale
Krause, M.; Buljan, M.; Mücklich, A.; Möller, W.; Fritzsche, M.; Facsko, S.; Heller, R.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.; Abrasonis, G.;
Three-dimensional, ion-induced nano-scale pattern formation in the growth mode is studied for a bi-component thin film. C:Ni films were grown by dual ion beam co-sputtering applying an assisting oblique incidence low energy Ar+ ion beam. Their microstructure was determined by scanning electron, atomic force, and transmission electron microscopy, as well as by grazing incidence small angle X-ray scattering. The role of ion-induced collisional effects was investigated by binary collision computer simulations. The formation of compositionally modulated ripples on the C:Ni film surface is demonstrated. They consist of metal enriched topographic crests and carbon enriched valleys. Since the surface is constantly covered by incoming species, this pattern is transferred into the bulk as a periodic array of Ni3C nanoparticles in a carbon matrix. Lateral ripple propagation is shown to be one of the crucial phenomena for the film morphology. The essential experimental features are reproduced by the computer simulations. The results reveal the importance of ion-induced preferential displacements as driving factor for an surface instability, which gives rise to the observed pattern formation. The physical nature of the approach holds potential for the growth of functional nanocomposites with tunable properties independently of the nature of the materials.
Keywords: Nanoscale pattern formation; 3D nanoparticle arrays; Ion beam assisted deposition; Nanocomposites; Thin film morphology

Publ.-Id: 19202 - Permalink


Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis
Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Ferrari, A.; Grosse, E.; Junghans, A. R.; Kempe, M.; Kögler, T.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schramm, G.; Schwengner, R.; Wagner, A.; Yakorev, D.;
At energies relevant to Big Bang nucleosynthesis there is only scarce experimental data for the reaction p(n,gamma)d. Its reaction rate used in nuclear network calculations relies on theoretical models constrained by nucleon-nucleon scattering data, the capture cross section for thermal neutrons and experimental data of the photodissociation of the deuteron d(gamma,n)p, which as well is investigated sparsely at Big-Bang energies. Large experimental uncertainties make a comparison of measurements with precise theoretical calculations difficult.
We have studied the reaction d(gamma,n)p at the superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf using bremsstrahlung with an endpoint energy of 5.0 MeV. The target consisted of alternating layers of aluminum and deuterated polyethylen. Nuclear-resonance-fluorescence spectroscopy on 27Al with high-purity Germanium detectors allowed us to measure the photon flux at 2.2 and 3.0 MeV. ELBE offers a pulse length of some ps and an adjustable repetition rate making time-of-flight experiments even at a small flight path of 1 m possible. Neutrons with a kinetic energy from 20 to 1400 keV have been measured with six 1-meter-long plastic scintillators read out on two sides by high-gain photomultipliers.
Interactions of the emitted neutrons with components of the experimental setup (target, detectors, collimators, beam dump, walls) have a non-negligible influence and have been simulated using the FLUKA code. In combination with the neutron detection efficiency, which was experimentally determined at Physikalisch-Technische Bundesanstalt Braunschweig, we calculated a time-of-flight-dependent correction factor to the measured neutron spectrum.
We will present the experimental setup, the data analysis, the results of the simulation and the cross section.
Keywords: Big Bang nucleosynthesis, bremsstrahlung, gamma-ray spectroscopy, neutron time-of-flight, nuclear astrophysics, photon scattering, neutron detector, efficiency, FLUKA
  • Lecture (Conference)
    Nuclear Physics in Astrophysics VI, 19.-24.05.2013, Lisbon, Portugal
  • Open Access LogoJournal of Physics: Conference Series 665(2016), 012003
    DOI: 10.1088/1742-6596/665/1/012003

Publ.-Id: 19201 - Permalink


Clay mineral characterization and nano-pores evaluation - Arcabuco zone (Colombia)
Palacio, C. A.; Parra Vargas, C. A.; Anwand, W.; Mejía, J. A.; Martínez Ovalle, S. A.;
Colombian mining is usually done without any proper scientific methodology, and therefore, without knowing if there is more potential for the mineral resource being mined. For a scientific insight, this work presents the analysis of clay mineral characterization and nano-pores evaluation. The samples were obtained from the Arcabuco zone, a region located in Boyacá-Colombia. The techniques used to identify the minerals, the crystal structure, the chemical composition and the thermal properties were X-ray Diffraction (XRD), Scanning Electron Microscopy and Energy-dispersive X-ray Spectroscopy (SEM - EDX), Thermogravimetry and Differential Thermal Analysis (TG-DTA), Mössbauer Spectroscopy (MS), and finally Positron Annihilation Spectroscopy.
The XRD data were analyzed by means of the Rietveld refinement method, finding phases like Montmorillonite, Quartz, Illite and Kaolinite. These phases were corroborated using the characterization techniques previously described. Positron annihilation data were used to detect and evaluate the size of the nano-pores and to correlate them with the behavior of the dehydration and hydration kinetics in these measurements obtained by TG-DTA.
Keywords: Clay Minerals, Geological environment, Positron Annihilation, Positronium; Open space, nano-pores, Interlayer space, Hydration
  • Lecture (Conference)
    21st Latin American Symposium On Solid State Physics (SLAFES XXI), 30.09.-04.10.2013, Villa de Leyva, Colombia

Publ.-Id: 19200 - Permalink


Isotope exchange investigation of nitrogen redistribution in expanded austenite
Christiansen, T. L.; Drouet, M.; Martinaviciusc, A.; Somers, M. A. J.;
Sequential plasma and gaseous nitriding of Fe–18Cr–10Ni–3Mo stainless steel at 390 C with 14N and 15N isotopes followed by denitriding in flowing hydrogen was investigated. Redistribution of plasma-inserted nitrogen atoms (15N) by subsequent gaseous nitriding (14N) was observed. Denitriding after plasma- and gaseous nitriding resulted in predominant retraction of 14N, and only a minor amount of 15N. The nitrogen isotope diffusion behaviour is explained by two different states of nitrogen bonding and shortrange ordering between nitrogen and chromium.
Keywords: Nitriding; Nuclear reaction analysis; X-ray diffraction (XRD); Stainless steel
  • Scripta Materialia 69(2013), 582-585

Publ.-Id: 19199 - Permalink


Development of Cannabinoid Receptor (CB2R) Ligands for Application in PET Studies - Where to Attach the Radiolabel?
Günther, R.; Moldovan, R.; Lueg, C.; Deuther-Conrad, W.; Wünsch, B.; Brust, P.;
The cannabinoid receptors type 2 (CB2R) are involved in many physiological processes but their expression level in healthy and diseased brain has not been unravelled. With positron emission tomography (PET) it is possible to monitor quantitatively very low amounts of compounds labelled with positron emitting isotopes like 18F in living organisms at high spatial resolution. For application in clinical research, such radiotracers have to show high selectivity and affinity to the target protein.
A series of fluorinated N-carbazolyl-oxadiazolyl-propionamides [1] was synthesised and the affinity towards the human CB2R was measured in receptor binding studies. Here, we combine our CB2R receptor model with 3D-QSAR data [2] to support molecular docking studies employing the MOE software (Version 2012.12 Chemical Computing Group Inc. Montreal. http://www.chemcomp.com). The studies revealed that both the primarily investigated compound 2 and the 2-fluoroethyl substituted carbazole derivative 1 (Ki = 3.6 nM) fits well into the binding pocket. Attachment of the fluorine at different positions of the structure does not lead to significantly different poses in accordance with the experimental data. Organ distribution studies on CD1-mice verified our prediction, [4] that [18F]1 and [18F]2 can cross the blood-brain barrier.
[1] Rühl T, Deuther-Conrad W, Fischer S, Günther R, Hennig L, Krautscheid L, Brust P: Cannabinoid Receptor Type 2 (CB2)-Selective N-Aryl-Oxadiazolyl-Propionamides: Synthesis, Radiolabelling, Molecular Modelling and Biological Evaluation. Org Med Chem Lett 2012, 2: 32
[2] Günther R, Brust P: Synergistic approach of structure- based and ligand-based drug design for the development of selective cannabinoid receptor ligands. J Cheminform 2012, 4(Suppl 1): P11
[4] Gerebtzoff G, Seelig A: In Silico Prediction of Blood-Brain Barrier Permeation Using the Calculated Molecular Cross-Sectional Area as Main Parameter. J Chem Inf Model 46 2006, 6: 2638–2650
  • Lecture (Conference)
    9th German Conference on Chemoinformatics 2013, 10.-12.11.2013, Fulda, Deutschland
  • Open Access LogoAbstract in refereed journal
    Journal of Cheminformatics 6(2014)1, O9
    DOI: 10.1186/1758-2946-6-S1-O9

Publ.-Id: 19198 - Permalink


Intense green-yellow electroluminescence from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices
Berencen, Y.; Wutzler, R.; Rebohle, L.; Hiller, D.; Ramirez, J. M.; Rodriguez, J. A.; Skorupa, W.; Garrido, B.;
High optical power density of 0.5 mW/cm2, external quantum efficiency of 0.1%, and population inversion of 7% are reported from Tb+-implanted silicon-rich silicon nitride/oxide light emitting devices. Electrical and electroluminescence mechanisms in these devices were investigated. The excitation cross section for the 543 nm Tb3+ emission was estimated under electrical pumping, resulting in a value of 8.2E-14 cm2, which is one order of magnitude larger than one reported for Tb3+:SiO2 light emitting devices. These results demonstrate the potentiality of Tb+-implanted silicon nitride material for the development of integrated light sources compatible with Si technology.
Keywords: electroluminescence, MOS devices, Terbium, Si-rich nitride

Publ.-Id: 19195 - Permalink


Correlation between efficiency and stability in Er- and Si-implanted MOS light emitting devices
Rebohle, L.; Wutzler, R.; Germer, S.; Helm, M.; Skorupa, W.; Berencén, Y.; Garrido, B.; Hiller, D.;
Er-based light emitters, which can be electrically driven and easily integrated into Si-based circuitries, are of great interest for a broad palette of applications, especially in the field of telecommunication and sensing. Among the different approaches Er-implanted MOS devices feature their excellent compatibility to standard CMOS processes and the reproducibility of the implantation process. However, at present such devices do achieve neither the efficiency nor the operation lifetime usually required for such applications.
In this study we compare various designs of Er-implanted MOS devices with respect to their electroluminescence efficiency and electrical operation lifetime. The different designs comprise devices implanted with Er alone or co-implanted with Si and Er, various single and multilayer systems and different host matrices for Er, namely SiO2 or Si-rich Si3N4. Despite the different design parameters, a strong correlation between efficiency and operation lifetime is found. This behavior is explained by the ambivalent role of hot electrons which play a key role both for the efficient excitation of erbium and for the oxide degradation.
Keywords: electroluminescence, MOS devices, Erbium, Si-rich SiO2
  • Lecture (Conference)
    EMRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19194 - Permalink


Surface exposure dating of the Veliki vrh rock avalanche in Slovenia associated with the 1348 earthquake
Merchel, S.; Mrak, I.; Braucher, R.; Benedetti, L.; Repe, B.; Bourlès, D. L.; Reitner, J. M.;
Over 30 samples from bedrock and boulders from theVeliki vrh rock avalanche have been collected for surface exposure dating. The limestone rocks have been radiochemically treated to isolate and determine long-lived 36Cl by accelerator mass spectrometry. It could be shown that the Veliki vrh rock avalanche from the Košuta Mountain (Slovenia) event can be very likely linked to one of the major historical Earth-quakes in Europe happening on the 25th of January 1348. Taken into account independently determined denudation rates, inherited 36Cl originating from pre-exposure at shallow depths (20-55 m) could be calculated. The high amount of inherited 36Cl, i.e. 17-46% of the total 36Cl, makes this site not suitable for a precise determination of the 36Cl production rate as it was originally anticipated. Velikhi vrh is a “classic” rock avalanche of high velocity. The slope failed in the upper part with a translational slide, whereas dynamic fragmentation is the cause for further crushing of the material and the long runout.
Keywords: terrestrial cosmogenic nuclides (TCN); exposure dating; accelerator mass spectrometry, earthquake; rock avalanche; 36Cl; Slovenia

Publ.-Id: 19193 - Permalink


Volume-doped cobalt titanates for ethanol sensing: an impedance and X-ray absorption spectroscopy study
Belle, C. J.; Wesch, G. E.; Neumeier, S.; Lozano-Rodríguez, M. J.; Scheinost, A. C.; Simon, U.;
The dynamic C2H5OH sensitivity of ilmenite-type cobalt titanates volume-doped by 2 at% Li, Na, K, Sb, La, Sm, Gd, Ho and Pb was systematically studied with respect to exhaust monitoring. Therefore, the p-type semiconducting CoTiO3 materials were characterized as resistive gas sensors via high-throughput impedance spectroscopy toward 5-200 ppm C2H5OH at 300-500 °C. The best performing materials were tested further by time-resolved and long-term measurements whereby the CoTiO3 volume-doped with K exhibited an outstanding overall performance. X-ray absorption spectroscopy on this particular material gave evidence that the local structure around Co and Ti remains unaffected by the doping despite of a slight increase in static disorder. Hence, the effect of K doping does not originate from alteration in the metal-to-oxygen interaction as expected from previous findings
Keywords: EXAFS Cobalt titanates sensors

Publ.-Id: 19192 - Permalink


Nonlinear Geostatistics for Geometallurgical Optimisation
van den Boogaart, K. G.; Konsulke, S.; Tolosana Delgado, R.;
Adaptive mineral processing has to rely on spatially predicted information on primary geometallurgical parameters, like phase composition, size and shape distributions of grains from various phases, portions of value elements in different grain types. Naively, one would predict these parameters geostatistically and select an optimal processing for the predicted structure. This is suboptimal, due to various kinds of nonlinearities in the problem. First, some primary geometallurgical quantities themselves are measured in non-real scales, like compositional or stereologically distorted geometric information. Standard geostatistics has to be replaced by compositional and geometric geostatistics, involving complex transforms and restrictions. Further, only partial and uncertain information is available, introducing a stochastic character to the optimisation problem. Moreover, many response variables leading to costs, outcomes, and eventual effects of later processing depend nonlinearly on the primary geometallurgical parameters, which implies that the final monetary value is not estimated unbiasedly by kriging. Finally unbiased linear prediction (such as kriging) is not the best method of prediction for decision making. The conditional expectation of the monetary values is needed instead. The impact of these problems is explained in this paper with simplified examples and a first approach to a general solution is proposed.
Keywords: geometallurgy, nonlinear geostatistics, adaptive processing
  • Contribution to proceedings
    GeoMet 2013, The second AusIMM International Geometallurgy Conference 2013, 30.09.-2.10.2013, Brisbane, Australia
    Proceedings of GeoMet 2013, 253-258

Publ.-Id: 19191 - Permalink


Millennial erosion rates across the Pamir based on 10Be concentrations in fluvial sediments: Dominance of topographic over climatic factors
Fuchs, M. C.; Gloaguen, R.; Merchel, S.; Pohl, E.; Sulaiman, V.; Andermann, C.; Rugel, G.;
The understanding of erosion processes is fundamental to study the evolution of actively deforming mountain ranges, whereas the relative contributions tectonic and climatic factors and their feedbacks are debated. The Pamir is peculiar in both, high deformation rates induced by the India-Eurasia collision and its position at the transition between Westerlies and Monsoon. In order to contribute to this debate we quantify basin-wide erosion rates from cosmogenic 10Be concentrations in modern river sediments measured by accelerator mass spectrometry. Sample locations represent the Panj basin at six sites along its trunk stream, and the major, east-west elongated tributary basins at five sites. An average erosion of 0.64 mm/yr for the entire Pamir reveals a rapid landscape evolution.
Erosion rates of tributary sub-basins highlight the strong contrast between the plateau (0.05 mm/yr to 0.16 mm/yr) and the Pamir margins (0.54 mm/yr to 1.45 mm/yr). The intensity of erosion is primarily (R2 of 0.81) correlated to slope steepness (0.75 quartiles) suggesting either tectonic uplift or base level lowering. Multiple linear regression reveals that precipitation may contribute also to the efficiency of erosion (R2 of 0.93) to a lesser extent. Dry conditions and low slopes hinders sediment transport and consequently, erosion on the plateau. The highest erosion coincides with the predominant winter precipitation from the Westerlies. The concentrated discharge during spring and early summer favors pronounced erosion along the north-western Pamir margin by driving the sediment flux out of the basins. The magnitude of erosion in Pamir is similar to rates determined in the south Himalayan escarpment, whereas climatic and tectonic conditions are very different. Millennial erosion does not balance the roughly ten times higher fluvial incision implying a transient landscape. We propose that river captures are responsible for the strong base level drop driving the incision along the Panj and consequently, initiate steep hillslopes that will contribute to high erosion at the Pamir margins. Precipitation may act as limiting factor to hillslope adjustment and consequently to erosion processes.
Keywords: accelerator mass spectrometry, erosion rate, Pamir, cosmogenic nuclides, fluvial sediments

Publ.-Id: 19190 - Permalink


Untersuchungen zur Abtrennung von Uranverbindungen aus Grubenwässern
Zabelt, D.;
Im Rahmen der vorliegenden Arbeit konnten sowohl erste Ergebnisse zur Abtrennung von Uran(VI)-Spezies aus Grubenwässern der Standorte Königstein und Schlema mittels Membrantrenntechnik, als auch eine Verknüpfung von Speziationsmessung und Modellierung erreicht werden. Die Speziation des gelösten Urans wurde zum einen über direkte Messung mittels TRLFS bestimmt und zum anderen mit einer Gleichgewichtsmodellierung berechnet. Dadurch lassen sich die Speziationen der komplex zusammengesetzten Lösungen mit zusätzlicher Sicherheit bestimmen. Im Vergleich zu bestehenden Untersuchungen, die sich aufgrund der Nichtverfügbarkeit von TRLFS auf sehr einfache synthetische Lösungen beschränken mussten, wurden in dieser Arbeit erste spektroskopische Untersuchungen realer Probenwässer durchgeführt, um eine gesicherte Datenlage für die Membrantrennung liefern zu können.
Ziel der Arbeit war die Untersuchung verschiedener Nanofiltrations- und Umkehrosmosemembranen auf ihre Eignung zur Abtrennung verschiedener Uranverbindungen. Im Rahmen dieser Arbeit sollten die Membranen zunächst anhand des Reinwasserfluxes und Magnesiumsulfat-Rückhaltes charakterisiert werden. Im Anschluss daran fanden Batch- und Cross-Flow-Versuche mit realen Grubenwässern aus Königstein und Schlema statt. Dabei wurden die Rückhalte der Membranen für Uran, sowie die Selektivitäten der Membranen für Uran gegenüber Calcium und Magnesium bestimmt.
  • Bachelor thesis
    Technische Universität Bergakademie Freiberg, 2013
    66 Seiten

Publ.-Id: 19189 - Permalink


Spektroskopische Untersuchungen von Uran(VI) und Uran(IV) - Redoxprozesse und Komplexierungsverhalten in Gegenwart organischer Säuren
Jäckel, E.;
In dieser Arbeit wird das Verhalten des natürlich auftretenden radioaktiven Isotops Uran-238 gegenüber verschiedenen organischen Säuren, genauer Citronensäure und Oxalsäure, untersucht. Dabei wird auf die Komplexierung sowie auf mögliche Redoxreaktionen in Abhängigkeit vom pH-Wert eingegangen.
  • Bachelor thesis
    Hochschule Zittau/Görlitz, 2013
    93 Seiten

Publ.-Id: 19188 - Permalink


Robust Regression with Compositional Response: Applications to Geosciences
Hron, K.; Filzmoser, P.; Templ, M.; van den Boogaart, K. G.; Tolosana-Delgado, R.;
Compositional data are multivariate observations describing quantitatively the relative importance or weight of a set of parts on a whole. Compositions frequently occur in geochemistry and they are popularly expressed in relative units, like proportions or percentages (i.e. as data with constant sum constraint 1 or 100, respectively).
The aim of multivariate regression is to quantify relations between a multivariate response and one or more explanatory variables, and to use these identied relations for prediction. The standard theory on linear regression models - the least squares methodology - is appropriate if the data do not include outlying observations, deviating from the main linear trend. Although robust regression tolerates a certain amount of deviating data points, it may lead to distorted results if it is directly applied to compositional data.
The isometric logratio (ilr) transformation is used to develop classical least-squares regression, where a compositional response depends on (non-compositional) explanatory variables. For several reasons it exists no straightforward solution for the robust robust regression problem with compositional response. Similarly as in the classical case, the step from the multivariate to the multiple model is not possible if the response ilr coordinates are not independent. Even more, in the robust case, to regress the response variables separately would result in ignoring the multivariate outliers. An additional challange is the proper choice of the ilr transformation that is crucial for an appropriate interpretation of results. Finally, a simplied approach to implement robust methods to ilr transformed data may produce transformationdependent results, an undesirable characteristic.
A solution is provided by the multivariate least trimmed squares (MLTS) method that fullls all required concepts of robustness for regression with compositional data. The robust regression model with compositional response can be used also for testing on subcompositional independence. Theoretical results are applied to a real-world problem from geosciences.
Keywords: compositional data, robust regression, least trimmed squares
  • Contribution to proceedings
    15th Annual Conference of the International Association for Mathematical Geosciences, IAMG 2013, 02.-6.9.2013, Madrid, Espana
    Mathematics of Planet Earth, Proceedings of the 15th Annual Conference of the International Association for Mathematical Geosciences, Lecture Notes in Earth System Science, Heidelberg: Springer, 978-3-642-32407-9, 87-90
    DOI: 10.1007/978-3-642-32408-6

Publ.-Id: 19187 - Permalink


Stochastic differential equations with fuzzy drift and diffusion
Sprungk, B.; van den Boogaart, K. G.;
A new framework for the fuzzification of stochastic differential equations is presented. It allows for a detailed description of the model uncertainty and the non-predictable stochastic law of natural systems, e.g. in ecosystems even the probability law of the random dynamic changes due to unobservable influences like anthropogenic disturbances or climate variation. The fuzziness of the stochastic system is modelled by a fuzzy set of stochastic differential equations which is identified with a fuzzy set of initial conditions, time-dependent drift and diffusion functions. Using appropriate function spaces the extension principle leads to a consistent theory providing fuzzy solutions in terms of fuzzy sets of processes, fuzzy states, fuzzy moments and fuzzy probabilities.
Keywords: Fuzzy stochastic differential equations; Fuzzy stochastic processes; Model uncertainty

Publ.-Id: 19186 - Permalink


Inertial wave dynamics in a rotating liquid metal
Vogt, T.; Raebiger, D.; Eckert, S.;
The dynamics of free and forced inertial waves inside cylinders of different aspect ratios A = H0/2R0 are studied experimentally. The liquid metal GaInSn was choosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of AC electromagnetic fields. The ultrasound Doppler velocimetry was used to record the flow structure and the inertial waves. Our experiments demonstrate the capability for selective excitation of different inertial wave modes by deliberate variations of the magnetic field parameters. The application of time-modulated AC fields turned out to be an efficient method for triggering inertial waves. Furthermore, it was found that turbulent fluctuations in a swirling flow driven by a rotating magnetic field are able to provoke one specific inertial wave mode inside the cylinder and that such an inertial wave is able to survive over a distinct time. Experiments at the fundamental resonance have shown that multiple harmonic oscillation modes appeared simultaneously. The measured inertial wave frequencies were compared to the predictions of the linear inviscid theory.

Publ.-Id: 19185 - Permalink


Spin-up of a magnetically driven tornado-like vortex
Vogt, T.; Grants, I.; Eckert, S.; Gerbeth, G.;
The spin-up of a concentrated vortex in a liquid metal cylinder with a free surface is considered experimentally and numerically. The vortex is driven by two flow-independent magnetic body forces. A continuously applied rotating magnetic field provides source of the angular momentum. A pulse of about one order of magnitude stronger travelling magnetic field drives a converging flow that temporarily focuses this angular momentum towards the axis of the container. A highly concentrated vortex forms that produces a funnel-shaped surface depression. We explore experimentally the duration, the depth and the conditions of formation of this funnel. Additionally, we measure the axial velocity and calculate the axi-symmetric flow field of such transient vortex at a lower force magnitude. The spin-up vortex is similar to the corresponding developed time-averaged turbulent vortex driven by the same magnetic forces (Grants et al. 2008). There are two main differences. First, the maximum swirl concentration condition does not express as a constant ratio of the both driving forces. Second, a much higher degree of swirl concentration is feasible. We explain those differences by a much lower turbulence during the spin-up.

Publ.-Id: 19184 - Permalink


Eine Ausleseelektronik für CZT-Detektoren mit dem RENA-3 IC von Nova R&D
Födisch, P.; Lange, B.; Kaever, P.;
Vorgestellt wird die Entwicklung einer kompakten Ausleseeinheit für CZT-Detektoren (Cadmiumzinktellurid) für die energieauflösende Spektroskopie von Gammastrahlung. Der von NOVA R&D verfügbare RENA-3 ASIC (Readout Electronics for Nuclear Applications) ist für den direkten Anschluss an die Detektoren vorgesehen und deckt so einen Großteil der analogen Funktionen ab. Im ASIC sind 36 konfigurierbare Eingangskanäle integriert, die mit ladungsempfindlichen Vorverstärkern und analoger Signalverarbeitung (pulse shaping) für CZT-Detektoren optimiert sind. Für die Ansteuerung des ASICs und die Verarbeitung der Ausgangssignale wurde eine digitale, FPGA-basierte Elektronik entwickelt. Die Konfiguration der Hardware wird mittels eines synthetischen Prozessors durch Software im FPGA und auf einem PC unterstützt. Gezeigt werden die Instrumentierung des Prototyps und die Ergebnisse der Kalibrierung des Gesamtsystems durch synthetische Detektorsignale in einer automatisierten Testumgebung. Mit dem entwickelten System werden der Messbereich, die Energieauflösung und das Zeitverhalten des ASICs untersucht und auf die geplante Anwendung mit CZT-Detektoren hin überprüft.
  • Open Access LogoContribution to proceedings
    104. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2013, 11.-13.03.2013, Jülich, Deutschland, Hamburg: Verlag Deutsches Elektronen-Synchrotron, 978-3-935702-72-0, 135-143

Publ.-Id: 19183 - Permalink


High Resolution Energy-Angle Correlation Measurement of Hard X Rays from Laser-Thomson Backscattering
Jochmann, A.; Irman, A.; Bussmann, M.; Couperus, J. P.; Cowan, T. E.; Debus, A. D.; Kuntzsch, M.; Ledingham, K. W. D.; Lehnert, U.; Sauerbrey, R.; Schlenvoigt, H. P.; Seipt, D.; Stöhlker, T.; Thorn, D. B.; Trotsenko, S.; Wagner, A.; Schramm, U.;
Thomson backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses but also for the investigation of the complex particle dynamics at the interaction point. For this purpose a complete spectral characterization of a Thomson source powered by a compact linear electron accelerator was performed with unprecedented angular and energy resolution. A rigorous statistical analysis comparing experimental data to 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential gamma-ray sources.
Keywords: Laser Thomson Backscattering Linear Accelerator ELBE X-Ray Emittance

Publ.-Id: 19182 - Permalink


Elektrische und strukturelle Eigenschaften von supraleitenden Schichten in Gallium-implantiertem Silizium und Germanium
Fiedler, J.;
Zielstellung der Dissertation ist die detaillierte Analyse der Auswirkungen von supraleitenden Galliumausscheidungen auf das elektrische Transportverhalten hochdotierter Silizium- und Germaniumschichten. Dafür wird ein neues Verfahren zur Herstellung von supraleitenden Schichten in kommerziellen Silizium- und Germanium-Wafern mit Hilfe von Ionenimplantation und Kurzzeitausheilung entwickelt. Mittels Ionenimplantation durch eine dünne dielektrische Deckschicht wurden Galliumkonzentrationen weit über der Gleichgewichtslöslichkeit in die Silizium- und Germaniumsubstrate eingebracht. Kurzzeitausheilverfahren wurden verwendet, um die die Umverteilung des Galliums anzuregen. Die resultierende Galliumverteilung wurde analysiert und es konnte ein Modell entwickelt werden, welches die Ursache für die Ausbildung einer 10 nm dünnen Gallium-reichen Schichten an der Deckschicht/Halbleiter-Grenzfläche beschreibt. Übersteigt die Galliumkonzentration an der Grenzfläche den kritischen Wert von 15 at.%, können die Schichten bei Temperaturen unterhalb von 6 – 7 K supraleitend werden und zeigen damit eine ähnlich kritische Temperatur wie bereits untersuchte dünne amorphe Galliumfilme. Es wird somit erstmalig gezeigt, dass Gallium-reiche Ausscheidungen eine mit reinem Gallium vergleichbare kritische Temperatur haben. Der bisher häufig als Funktion der Schichtdicke erforschte Supraleiter-Isolator-Übergang konnte in den Schichten durch die Variation der Ausheilzeit hervorgerufen werden. Der normalleitende Schichtwiderstand ist als entscheidender Parameter für den Phasenübergang anzusehen. Da sich Gallium-reiche Ausscheidungen in Germanium wegen der geringen Differenz in Masse und Elektronenstruktur nur schwer nachweisen lassen, erfolgten die Strukturuntersuchungen hauptsächlich an Siliziumschichten. Die Ergebnisse dieses Modellsystems lassen sich zum großen Teil auf das Verhalten von Gallium in Germanium übertragen. Dieser Vergleich zeigt, dass außer der kritischen Temperatur alle elektrischen Eigenschaften der Gallium-reichen Schichten vom Substratmaterial abhängen. Supraleitung in Gallium-dotiertem Germanium wurde bisher nur bei Temperaturen unterhalb von 1 K beobachtet. Deshalb ist die kritische Temperatur ein geeigneter Parameter, um durch Dotierung hervorgerufene Supraleitung in Germanium von supraleitenden Ausscheidungen zu unterscheiden.
  • Doctoral thesis
    TU Ilmenau, 2013
    126 Seiten

Publ.-Id: 19181 - Permalink


Semiconductor spectroscopy using THz free-electron lasers
Helm, M.;
I will briefly review the history of THz free-electron lasers (FEL) as versatile sources for semiconductor spectroscopy and present some recent experiments using the FEL in Dresden.
Keywords: free-electron laser, terahertz, semiconductors
  • Invited lecture (Conferences)
    38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW_THz 2013), 01.-06.09.2013, Mainz, Germany
  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW_THz 2013), 01.-06.09.2013, Mainz, Germany

Publ.-Id: 19180 - Permalink


Effects of inlet condition on flows structure of bubbly flow in a rectangular column
Akbar, M. H. B. M.; Hayashi, K.; Lucas, D.; Tomiyama, A.;
Experiments on bubbly flows in a rectangular column are carried out to investigate effects of inlet condition on flow structure. An air diffuser having 35 nozzles is used. The inlet gas flow rates from 34 nozzles are uniform and the lift coefficients of bubbles are small at this flow rate, whereas the gas inflow from the remaining one nozzle is varied to change the sign and magnitude of lift coefficients. The main conclusions obtained are as follows: (1) bubbly flow in a bubble column is apt to be heterogeneous even with small non-uniformity in the distribution of gas inflow, (2) when the nozzle causing non-uniform gas inflow is located in the center of the diffuser plate and the inflow distribution is symmetric, heterogeneous structure is formed due to the lift-induced flow instability pointed out by Lucas et al., (3) when the nozzle causing non-uniform gas inflow is located near the side wall of the column and the inflow distribution is asymmetric, heterogeneous structure is induced by the Coanda effect, and (4) the effects of inlet condition on flow structure in a bubble column can be predicted using a multi-fluid model.
Keywords: Instability, Bubble, Bubble column, Inlet condition, Lift force, Multi-fluid model

Publ.-Id: 19179 - Permalink


New insights into the dynamics of adsorption equilibria of humic matter as revealed by radiotracer studies
Lippold, H.; Lippmann-Pipke, J.;
The mobility of contaminants in the subsurface hydrosphere can be governed by their interaction with aquatic humic substances, which may act as carriers. For modelling migration processes, retardation of humic molecules at mineral surfaces must be considered. There is, however, a lack of clarity concerning the reversibility of adsorption of these natural polyelectrolytes. In this work, evidence was provided that a dynamic adsorption equilibrium exists. For this purpose, adsorption of humic substances (purified Aldrich humic acid and an aquatic fulvic acid) onto kaolinite was examined in tracer exchange studies by means of 14C-labelled humic material. In addition, the kinetics of adsorption and desorption were investigated in batch experiments.
Attaining the equilibrium state of adsorption took considerably longer for the humic acid than for the fulvic acid (24 h and 4 h, respectively). In desorption experiments, initiated by diluting the supernatant at constant pH, no net release was observed for both substances within a time frame of 4 weeks. However, when introducing radiolabelled humic or fulvic acid as a tracer into pre-equilibrated adsorption systems in the state of surface saturation, quantitative exchange was found to take place. This indicates that adsorption of humic matter is in fact a reversible process, albeit an exchange time of more than 4 weeks was required for both humic materials. Models for humic-bound contaminant transport (presuming dynamic equilibria) are thus applicable under appropriate conditions.

Publ.-Id: 19178 - Permalink


Microbially mediated immobilization of radionuclide in subsurface crystalline rock environments
Krawczyk-Bärsch, E.;
In the underground rock characterization facility tunnel ONKALO in Finland, and in the Äspö Hard Rock Laboratory (HRL) in Sweden massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures. The main goal of the study was to evaluate the relevance of microbial processes for the immobilization of radionuclides in a deep crystalline repository for high-level radioactive waste. In laboratory experiments the effect of uranium on biofilms was studied on site in the ONKALO tunnel by adding uranium to the fracture water in a self constructed flow cell by using detached biofilm samples. Biofilm specimens collected for transmission electron microscopy studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms as needle-shaped uranyl phosphate minerals, similar to meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O).
Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) from the Äspö HRL were used for laboratory experiments, in which uranium and neptunium, respectively, were added to the BIOS biofilms. The biofilms were submerged in Äspö groundwater in a flow cell under aerobic conditions. The results showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85% and 95%, respectively. Thermodynamic calculation of the theoretical predominant fields of uranium species showed that the formation of an aqueous uranium carbonate species Ca2UO2(CO3)3 was predicted due to the high concentration of carbonate in the groundwater. Under the given pH conditions the uptake of uranium and neptunium in the BIOS biofilm depends predominantly on the high amount of ferrihydrite, which precipitated onto the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea. Consequently, the combination of the biological material and iron oxides created an abundant surface area for bioaccumulation and adsorption of radionuclides.
Keywords: biofilm, uranium, neptunium, nuclear waste repository
  • Invited lecture (Conferences)
    12th Symposium on remediation, 26.-27.09.2013, Jena, Germany

Publ.-Id: 19177 - Permalink


Industrial applicability of microbial interaction with metals and metalloids
Suhr, M.; Vogel, M.; Matys, S.; Raff, J.; Pollmann, K.;
Many processes in nature are highly efficient and very fast. Therefore it is an obvious idea to screen natural structures and processes for applicability in related industrial processes. Especially microorganisms are known to be highly efficient in what they do. We thusly use microbes or microbial structures for metal removal and metal recovery, the development of novel catalysts and the development of biosensors [1, 2]. In our group we investigated different processes to fix dissolved metals and ecotoxic substances and how they can be used for metal filtering and nanoparticle (NP) synthesis. One scientific topic is the reduction of soluble selenium oxyanion selenit to elemental selenium by Azospirillum brasilense. The formation of hardly soluble Se(0) nanoparticles during this process might be of interest for both bioremediation of selenium contaminated water and for nanotechnology (photovoltaic/ semiconducting industry).
Furthermore, we intensively study self-assembling biomolecules, namely S-layers, which represents the outermost cell envelope of many bacteria and archaea. This highly ordered protein polymers are an attractive matrix to functionalize all kinds of materials. Their surface with its numerous functional groups and their regular distributed pores offers ideal binding and nucleation sites for various metals e.g. gold, palladium and platinum as well as for metal oxide nanoparticles e.g. composed of titanium dioxide or zinc oxide. By reducing bound metals, well defined and regularly arranged nanoparticles were obtained [3, 4]. These nanoparticle lattices can be used as catalysts for organic synthesis like homogeneous and heterogeneous hydrogenation and for metallization of surfaces (Pd-NP), improved photo catalysts with higher degradation rates (TiO2-, ZnO-NP), for defined synthesis of single and multi-walled carbon nanotubes (CNT’s) in case of Pt-NP and the development of bio sensory layer systems (Au-NP).
To increase the efficiency of the resulting nanoparticle lattice, we have introduced adhesion promoter between the technical surfaces and living microorganisms or S-layers by using the layer by layer technique [5]. This results in higher layer stability and a fully covered technical surface.

[1] Raff, J. et al. (2003), Chem. Mat. 15, 240-244.
[2] Sleytr, U.B. et al. (1999), Angew. Chem.-Int. Edit. 38, 1035-1054.
[3] Wahl, R. et al. (2001), Adv. Materials 13, 736-740.
[4] Pollmann, K. et al. (2006), Biotechnol. Adv. 24, 58-68.
[5] Decher, G. et al. (1994), Biosensors & Bioelectronics 9, 677-684.
Keywords: Bioremediation, Sorption, Nanoparticles, Gold, Selen, Bacteria, Microorganisms, Polyelectrolytes
  • Poster
    Engineering Life 2013: Bio-molecular principles for novel methods and materials, 17.-18.09.2013, Dresden, Deutschland

Publ.-Id: 19176 - Permalink


Adsorption behavior and heavy metal interaction processes of cellular components of Gram-positive bacteria investigated by QCM-D
Suhr, M.; Matys, S.; Viacava Romo, K. E.; Raff, J.; Pollmann, K.;
Sorption processes based on biological materials like biomass itself or cell fragments become more and more attractive for biotechnological applications. In our group we work with isolated bacteria from the uranium mining waste pile Haberland (Johanngeorgenstadt, Saxony) that have high affinities for heavy metals [1]. The metal binding sites are predominantly provided by the bacterial cell wall, mainly by surface layer proteins, but also by other parts of the cell wall e.g. membrane lipids and peptidoglycan. Such biological structures and vital bacterial cells can be used to develop biosorptive materials that are of interest for a broad range of applications. Examples are bioremediation, for a specific and efficient removal and recovery of heavy, precious or actinide metals and as templates for synthesis of bio-based sensory layers or chemical catalysts [2, 3].
In our investigations surface layer proteins (S-layers) are one major research topic. They represent the outermost cell envelope of many eubacteria and archaea forming highly ordered paracrystalline lattices not only on the living cell, but also after isolation on various technical surfaces by self-assembling processes [4]. In previous work these proteins were immobilized in sol-gel ceramics for the successful removal of uranium and chromium [5, 6]. The highly ordered proteins allow a specific metal binding in the pores of the protein lattice. This property can be used for the arrangement of highly structured nanoparticles (e.g. Au, Pd, Pt). Thus investigation of the interaction of isolated cell wall components, like S-layer, peptidoglycan, lipids and secondary cell wall polymers (SCWP) or intact composites with metals and nanoparticles is important. But the deeper understanding of these processes on a molecular level remains challenging. Besides standard analytical methods the quartz crystal microbalance with dissipation monitoring (QCM-D) is used as versatile tool to track and control the biological layer formation, metal interaction and nanoparticle deposition as well as adsorption kinetics. This method allows the real time detection of sorption processes on a molecular level and gives further information of viscoelastic properties, layer stabilities and the total adsorbed mass [7]. Aim of our work is to study metal sorption behavior of cells and single cell wall fragments from Gram-positive bacteria to get more information about multilevel processes in complex natural systems. Therefore it is necessary to examine different immobilization strategies for the used biological components on various technical surfaces [8, 9]. The sorption behavior of metals and nanoparticles with the biological material will be studied by batch experiments and QCM-D [9]. The results were partially evaluated by supporting atomic force microscopy (AFM).

[1] Raff, J., Selenska-Pobell, S. (2006), Nuclear Engineering International 51 (619), 34-36.
[2] Das, N. (2010), Hydrometallurgy 105, 180-189.
[3] Pollmann, K. et al. (2006), Biotechnol. Adv. 24, 58-68.
[4] Sleytr, U. B. et al. (2007), FEMS Microbiology Letters 267(2), 131-144.
[5] Carreo, D. M. et al. (2011), The Canadian Journal of Chemical Engineering 89, 1281-1287.
[6] Raff, J. et al. (2003), Chem. Mater. 15, 240-244.
[7] Lopez, A.E. et al. (2010), Small 6 (3), 396-403.
[8] Günther, T. J., Suhr, M. et al. (2013), submitted.
[9] Suhr, M. et al. (2013), in preparation.
Keywords: Biosorption, Bacteria, S-Layer, Heavy metals, Actinides, Lipids, Bioremediation, Nanoparticles
  • Poster
    International Soft Matter Conference 2013, 15.-19.09.2013, Rome, Italy

Publ.-Id: 19175 - Permalink


Spectroscopic investigations of actinides for ecological risk assessment in the context of nuclear waste disposal
Foerstendorf, H.;
In the aftermath of the Fukushima Daiichi incident, the federal government of Germany terminated the civil use of nuclear power within the next decade. Hence, a solution for the long term storage of the nuclear waste from the power plants becomes more and more mandatory. In fact, up to now, the frame conditions for the search of an appropriate repository are still not defined much less accepted by the general public. In this lecture, aspects of the applied research in the field of nuclear waste disposal at the Institute of Resource Ecology of the Helmholtz-Zentrum Dresden-Rossendorf, Germany, are introduced. The focus is set on spectroscopic investigations on radionuclides including their speciation in aqueous solution and as well on mineral surfaces. The multi-spectroscopic approach, namely vibrational, X-ray absorption and luminescence spectroscopy, potentially provides complementary information on a molecular scale which is indispensable for the verification of current surface complex modeling calculations for a long term risk assessment of a deep ground waste repository.
  • Lecture (others)
    Seminar of Quantum Beam Science Directorate, JAEA, 30.09.2013, Tokai, Ibaraki, Japan
  • Lecture (others)
    Seminar of Department of Nuclear Engineering, Kyoto University, 02.10.2013, Kyoto, Japan

Publ.-Id: 19173 - Permalink


Präklinische Fortschritte in der Alpha7-Nikotinrezeptor-PET
Deuther-Conrad, W.;
Es ist kein Abstract vorhanden.
  • Invited lecture (Conferences)
    iPET.4 Forschung und Diagnostik, 07.09.2013, Ostrau, Deutschland

Publ.-Id: 19172 - Permalink


1D Two-Fluid Model simulations of Flashing Flows in TOPFLOW Facility
Mikuz, B.; Tiselj, I.; Beyer, M.;
The decompression experiment performed at TOPFLOW (acronym for Transient twO Phase FLOW) in 2011 has been reproduced using an in-house code WAHA as well as the latest bestestimate thermohydraulic system code TRACE. The evaporation of liquid water to steam caused by depressurization was simulated in about 8 m long vertical tube with an inner diameter of 195.3 mm. The liquid water was almost saturated at initial pressure value of 6.5 MPa. Simulations successfully reproduced the main features of the experiment’s pressure and temperature history.
Keywords: TOPFLOW, WAHA, TRACE, depressurization
  • Lecture (Conference)
    NENE 2013, 22nd International Conference Nuclear Energy for New Europe, 09.-12.09.2013, Bled, Slovenia
  • Contribution to proceedings
    NENE 2013, 22nd International Conference Nuclear Energy for New Europe, 09.-12.09.2013, Bled, Slovenia
    Proceedings of NENE 2013

Publ.-Id: 19171 - Permalink


Fine distributed moderating material with improved thermal stability applied to enhance the feedback effects in SFR cores
Merk, B.;
The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effect in sodium cooled fast reactor cores is described. The influence of the moderating material on the fuel assembly geometry, the neutron spectrum, the feedback effects, the power and burnup distribution, and the transmutation performance is given. An overview on possible materials is provided and the relationship between hydrogen content and thermal stability is described. A solution for the problem of the limited thermal stability of primarily proposed hydrogen bearing moderating material ZrH1.6 is developed by the use of Yttrium-mono-hydride. The similarity in the effects reached by ZrH and YH is demonstrated by comparison calculations. The topic is closed by an overview on material properties, manufacturing issues, experience in fast reactors and a comparison of raw material costs.
Keywords: Nuclear, Nuclear reactors, Fast reactors, Innovative reactors, enhanced feedback, moderating material, Yttrium hydride, thermal stability

Publ.-Id: 19170 - Permalink


Electron Bunch Diagnostic at the Upgraded ELBE Accelerator: Status and Challenges
Kuntzsch, M.; Findeisen, S.; Gensch, M.; Green, B. W.; Hauser, J.; Kovalev, S.; Lehnert, U.; Michel, P.; Roeser, F.; Schneider, C.; Schurig, R.; Kaya, C.; Al-Shemmary, A.; Bousonville, M.; Czwalinna, M. K.; Golz, T.; Schlarb, H.; Schmidt, B.; Schulz, S.; Stojanovic, N.; Vilcins, S.; Hass, E.;
Within the ELBE upgrade towards a Center for High Power Radiation Sources (HSQ), a mono energetic positron, a liquid lead photo neutron source and two new THz sources have been installed at the superconducting electron linac at ELBE. A variety of established as well as newly developed electron beam diagnostics were installed and tested. In this paper we want to present first results achieved with the currently existing prototype beam arrival time and bunch compression monitors (BAM, BCM) as well as one versatile EOS set-up. Based on these future developements and upgrades are discussed.
Keywords: ELBE Bunch Diagnostic
  • Lecture (Conference)
    International Beam Instrumentation Conference IBIC 2013, 16.-19.09.2013, Oxford, United Kingdom
  • Open Access LogoContribution to proceedings
    International Beam Instrumentation Conference IBIC 2013, 16.-19.09.2013, Oxford, United Kingdom
    Proceedings of IBIC 2013

Publ.-Id: 19169 - Permalink


The Structural changes of Y2O3 in ferritic ODS alloys during milling
Hilger, I.; Tegel, M.; Gorley, M. J.; Grant, P. S.; Weißgärber, T.; Kieback, B.;
Oxide dispersion strengthened (ODS) ferritic steels are usually fabricated via mechanical alloying and subsequent consolidation via hot extrusion or hot isostatic pressing. During the individual process steps, a complex evolution of the nanoparticle structure is taking place. Powders with different Y2O3 contents were milled and examined by means of X-ray diffraction (XRD) and atom probe tomography (APT). It has been observed that the Y2O3 is fragmented and becomes partially X-ray amorphous upon milling. This effect is due to the grain refinement of Y2O3 during the milling process and not because of its dissociation in the steel matrix.
Keywords: X-ray diffraction, XRD, ODS, ferritic steels, GenIV, dissolution, Y2O3, Atom Probe tomography, amorphous, mechanical alloying, milling

Publ.-Id: 19168 - Permalink


Advantages and dynamics features of liquid fueled MSR
Krepel, J.; Fiorina, C.; Kliem, S.;
Nuclear reactors operated with liquid fuel may have several remarkable advantages and features. The most developed reactor system in this category is the Molten Salt Reactor (MSR). It represents an old concept, but its properties are qualifying it for the advance utilization: inherent safety, excellent neutron economy, continuous or batch reprocessing possibility. The focus of this paper is to characterize the MSR physics, highlighting its unique advantages and investigating its specific dynamics.
  • Contribution to proceedings
    Conference on Molten Salts in Nuclear Technology, 09.-11.01.2013, Mumbai, India
    Proceedings of the conference on Molten Salts in Nuclear Technology CMSNT-2013, Mumbai

Publ.-Id: 19167 - Permalink


Fuel cycle advantages and dynamics features of liquid fueled MSR
Krepel, J.; Hombourger, B.; Fiorina, C.; Mikityuk, K.; Rohde, U.; Kliem, S.; Pautz, A.;
Nuclear reactors operated with liquid fuel may have several remarkable advantages and features. The most developed reactor system in this category is the Molten Salt Reactor. It represents an old concept, but its properties are qualifying it for the advanced utilization: inherent safety, excellent neutron economy, continuous or batch reprocessing possibility without fuel fabrication. The focus has currently moved from the graphite moderated MSR studied in the past towards the fast MSR. The aim of this study is to characterize the MSR physics, highlighting its unique fuel cycle advantages using ERANOS-based EQL3D procedure and investigating its specific dynamics features by the dedicated DYN3D-MSR code.

Publ.-Id: 19166 - Permalink


RIA Fuel Codes Benchmark Volume 1
OECD / NEA, Committee On The Safety Of Nuclear Installations, Working Group On Fuel Safety; Holt, L.;
Reactivity-initiated accident (RIA) fuel rod codes have been developed for a significant period of time and they all have shown their ability to reproduce some experimental results with a certain degree of adequacy. However, they sometimes rely on different specific modeling assumptions the influence of which on the final results of the calculations is difficult to evaluate.

A conclusion from the 2009 CSNI workshop on RIA was that RIA fuel rod codes are now heavily used, within the industry as well as the technical safety organizations (TSOs), in the process of setting up and assessing revised safety criteria for the RIA design basis accident.

It is then very important to master the use of such codes for reactor accident studies, particularly those involving safety analyses. It is essential to identify and understand real accident conditions that deviate from those of experiments. As a conclusion of the workshop, it was recommended that a benchmark between these codes be organized in order to give a sound basis for their comparison and assessment.

In order to maximize the benefits from this exercise, it was decided to use a consistent set of four experiments on very similar highly irradiated fuel rods tested under different experimental conditions:

- low temperature, low pressure, stagnant water coolant, very short power pulse (NSRR VA-1),
- high temperature, medium pressure, stagnant water coolant, very short power pulse (NSRR VA-3),
- high temperature, low pressure, flowing sodium coolant, larger power pulse (CABRI CIP0-1),
- high temperature, high pressure, flowing water coolant, medium width power pulse (CABRI CIP3-1).

Each of these four sibling rods are of identical fuel design and cladding material. Each experienced essentially the same pre-test irradiation history. For most practical purposes, the experiments are identical except for test conditions. The intent was to examine the so-called “temperature” effect (i.e. how to transpose results from experiments at low temperature to reactor conditions at high temperature?) in various RIA test programs.

The participation to the benchmark has been very important: 17 organizations representing 14 countries provided solutions for some or all the cases that were defined. In terms of computer codes used, the spectrum was also large as solutions were provided with FALCON, FEMAXI coupled to TRACE, FRAPTRAN, RANNS, RAPTA, SCANAIR, TESPAROD and TRANSURANUS.

The first noticeable fact is that, nearly all the participants used code that rely on simplified geometrical representation usually referred to as 1.5D codes. Although some 3D calculations may be done (one example was shown by one participant), it appears that given the conclusions below, the detailed geometrical description is not a priority. Rather, it looks more important at this stage to put the efforts and continue working on physical modeling.

During the benchmark, one source of differences between the results of the participants was identified to be due to the way input data, in particular the power pulse, are interpreted within the different codes. It is recommended that the code developers carefully examine the way the input data are used because this source of difference, that appeared to be significant, should be completely removed.

It was not possible during this benchmark to assess the influence of the initial state (resulting from base irradiation) of the fuel on the behavior during RIA. Nevertheless, this would be an important thing to do in the future in order to evaluate how much it accounts for on the scatter of the results.

With respect to the thermal behavior, the general conclusion is that the differences in the evaluation of fuel temperatures remain limited, although significant in some cases. The situation is very different for the cladding temperatures that exhibited considerable scatter, in particular for the cases when water boiling occurs. The film boiling heat transfer model was responsible for large differences between the calculations.

With respect to mechanical behavior, when compared to the (known) results of an experiment that involved only PCMI, the predictions of the cladding hoop strain from the different participants appeared acceptable, even though there was a factor of 2 between the highest and the lowest calculations. The conclusion is not as favorable for a case for which both the experimental results are unknown and water boiling is predicted to appear because then a factor of 10 on the hoop strain between the calculations was exhibited. This is due for a large part to the differences on the cladding temperatures.

In this benchmark, the fission gas release evaluations were also compared. The ratio of the maximum to the minimum values appears to be roughly 2, which is estimated to be relatively moderate given the complexity of fission gas release processes.

Finally, failure predictions that may appear as the ultimate goal of fuel code dedicated to the behavior under RIA conditions were compared. When looking at predictions in terms of enthalpy at failure, which is of interest in practical reactor applications, typical variations between calculations were found to be within a +/- 50 % range. Although major causes of the differences were identified, it is recommended to perform more systematic sensitivity and uncertainty analyses in a new phase of the benchmark to further assess the significance of the results produced.

It has been possible to evaluate the so-called user effect for the FRAPTRAN and SCANAIR codes. For both of them, it was found to be very limited on the cases of this benchmark, nearly negligible if compared to the differences between the results of the different codes. To generalize this conclusion would require more case to be studied.

The broader objective of the benchmark was to assess the possibility of evaluating the “temperature effect” that can be stated as: is it realistic to use the RIA fuel codes to transpose results, in particular enthalpy at failure, from experiments performed at low temperature to typical reactor conditions? Based on the conclusions formulated above, it appears obvious that it should be done with caution given the scatter that exists between the predictions of the different codes mainly due to the different approaches used to assess the rod failure level.
  • Other report
    Paris: OECD / NEA, 2013
    56 Seiten

Publ.-Id: 19165 - Permalink


Development of a General Coupling Interface for the Fuel Performance Code TRANSURANUS Tested with the Reactor Dynamic Code DYN3D
Holt, L.; Rohde, U.; Seidl, M.; Schubert, A.; van Uffelen, P.;
Several institutions plan to couple the fuel performance code TRANSURANUS developed by the European Institute for Transuranium Elements with their own codes. One of these codes is the reactor dynamic code DYN3D maintained by the Helmholtz-Zentrum Dresden - Rossendorf. DYN3D was developed originally for VVER type reactors and was extended later to western type reactors. Usually, the fuel rod behavior is modeled in thermal hydraulics and neutronic codes in a simplified manner. The main idea of this coupling is to describe the fuel rod behavior in the frame of core safety analysis in a more detailed way, e.g. including the influence of the high burn-up structure, geometry changes and fission gas release. It allows to take benefit from the improved computational power and software achieved over the last two decades.

The coupling interface was developed in a general way from the beginning. Thence it can be easily used also by other codes for a coupling with TRANSURANUS. The user can choose between a one-way as well as a two-way online coupling option. For a one-way online coupling, DYN3D provides only the time-dependent rod power and thermal hydraulics conditions to TRANSURANUS, but the fuel performance code doesn’t transfer any variable back to DYN3D. In a two-way online coupling, TRANSURANUS in addition transfers parameters like fuel temperature and cladding temperature back to DYN3D. This list of variables can be extended easily by geometric and further variables of interest.

First results of the code system DYN3D-TRANSURANUS will be presented for a control rod ejection transient in a modern western type reactor. Pre-analyses show already that a detailed fuel rod behavior modeling will influence the thermal hydraulics and thence also the neutronics due to the Doppler reactivity effect of the fuel temperature. The coupled code system has therefore a potential to improve the assessment of safety criteria. The developed code system DYN3D-TRANSURANUS can be used also for VVER type reactors. For this purpose, only the DYN3D and TRANSURANUS input files have to be modified.
  • Contribution to proceedings
    10th International Conference on WWER Fuel Performance, Modelling and Experimental Support, 07.-14.09.2013, Sandanski, Bulgaria
    Proceedings of 10th International Conference on WWER Fuel Performance, Modelling and Experimental Support
  • Lecture (Conference)
    10th International Conference on WWER Fuel Performance, Modelling and Experimental Support, 07.-14.09.2013, Sandanski, Bulgaria

Publ.-Id: 19164 - Permalink


Kurzzeittemperung zur Herstellung TiO2-basierter TCOs
Neubert, M.; Vinnichenko, M.; Gemming, S.; Gebel, T.; Liepack, H.; Kolitsch, A.;
Die vielfältigen Anwendungen transparenter leitfähiger Oxide (TCO), wie zum Beispiel in Flachbildschirmen, Solarzellen und der Beleuchtungstechnik erfordern die Entwicklung neuartiger TCO-Materialien. Darüber hinaus ist der Einsatz der etablierten TCOs, wie Indiumzinnoxid (ITO) oder Fluor dotiertes Zinnoxid (FTO) zukünftig nur bedingt fortzuführen. Die Verwendung von ITO ist aufgrund des kontinuierlich steigenden Indiumpreises sehr kostenintensiv, während der Einsatz von FTO-Dünnschichten aufgrund des hochgradig toxischen Herstellungsprozesses weltweit umstritten ist. Es konnte gezeigt werden, dass Titandioxid dotiert mit Tantal (TTO) vergleichbare elektrische und optische Eigenschaften, verglichen mit den etablierten TCOs aufweist. Eine wesentliche Herausforderung besteht allerdings darin, TTO-Dünnschichten mittels eines industrienahen kostengünstigen Prozess abzuscheiden. Diese Problemstellung wurde gelöst, indem TTO-Schichten mittels eines 2-stufigen Prozesses, bestehend aus Sputterabscheidung und anschließender Blitzlampentemperung, hergestellt wurden. Die dabei erreichten spezifischen Widerstände im Bereich von 0,001 Ohmcm entsprechen denen, bei Nutzung konventioneller Ofentemperung und sind für zahlreiche Anwendung ausreichend.
Keywords: transparent conductive oxide, TCO, tantalum, titania, titanium dioxide
  • Lecture (Conference)
    Workshop "Transparente leitfähige Materialien (TCO / TCM) – Festkörperphysikalische Grundlagen und Technologien", 04.-05.06.2013, Dresden, Deutschland

Publ.-Id: 19163 - Permalink


Nuclear deformation and neutron excess as competing effects for dipole strength in the pygmy region
Massarczyk, R.; Schwengner, R.; Dönau, F.; Frauendorf, S.; Anders, M.; Bemmerer, D.; Beyer, R.; Bhatia, C.; Birgersson, E.; Butterling, M.; Elekes, Z.; Ferrari, A.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kelley, J. H.; Kögler, T.; Matic, A.; Menzel, M. L.; Müller, S.; Reinhardt, T. P.; Röder, M.; Rusev, G.; Schilling, K. D.; Schmidt, K.; Schramm, G.; Tonchev, A. P.; Tornow, W.; Wagner, A.; Gooden, M. E.;
The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132 and 134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIgS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.
Keywords: nuclear resonance flourescene, dipole strength, pygmy strength, statistical analysis, photo-nuclear reactions

Publ.-Id: 19162 - Permalink


Wave optical description of the Traveling-Wave Thomson-Scattering optical undulator field and its application to the TWTS-FEL
Steiniger, K.; Widera, R.; Pausch, R.; Debus, A.; Bussmann, M.; Schramm, U.;
We show that X-ray optical free-electron lasers (OFELs) can be realized using Traveling-Wave Thomson-Scattering (TWTS).
In TWTS pulse front tilted laser pulses are scattered off relativistic electron bunches in a side-scattering geometry.
The pulse-front tilt guarantees overlap between laser and electrons over distances in the meter range while both are traveling in different directions.
An interaction distance of 90 cm is obtained in a setup were 590 MeV electrons scatter off a petawatt class laser incident under an angle of 4.5°.
The amplification of the 1.5 Å radiation saturates at the end of the interaction.
In order to account for spatial and temporal dispersion introduced with the pulse front tilt, we develop an exact three-dimensional analytical description of TWTS pulses that can be used in three-dimensional simulations of the radiation amplification process.
The wave-optical formulation of the TWTS pulse includes dispersion to all orders and provides a general description of laser pulses diffracted at VLS gratings.
Keywords: traveling-wave, thomson scattering, optical FEL, VLS grating
  • Contribution to proceedings
    1st European Advanced Accelerator Concepts, 02.-06.06.2013, La Biodola, Isola d'Elba, Italy
    Proceedings of the 1st European Advanced Accelerator Concepts, Amsterdam: Elsevier, 147-152
    DOI: 10.1016/j.nima.2013.10.091
  • Nuclear Instruments and Methods in Physics Research A 740(2014), 147-152
    DOI: 10.1016/j.nima.2013.10.091

Publ.-Id: 19161 - Permalink


Excitation of the Delta(1232) isobar in deuteron charge exchange on hydrogen at 1.6, 1.8, and 2.3 GeV
Mchedlishvili, D.; Barsov, S.; Carbonell, J.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Engels, R.; Gebel, R.; Glagolev, V.; Grigoryev, K.; Goslawski, P.; Hartmann, M.; Imambekov, O.; Kacharava, A.; Kamerdzhiev, V.; Keshelashvili, I.; Khoukaz, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Lehrach, A.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Merzliakov, S.; Mielke, M.; Mikirtychyants, M.; Mikirtychyants, S.; Nioradze, M.; Ohm, H.; Papenbrock, M.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Stein, H. J.; Steffens, E.; Stockhorst, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Uzikov, Y.; Valdau, Y.; Wilkin, C.;
The charge-exchange break-up of polarised deuterons pol{d}p -> {pp}n, where the final {pp} diproton system has a very low excitation energy and hence is mainly in the 1S0 state, is a powerful tool to probe the spin-flip terms in the proton-neutron charge-exchange scattering. Recent measurements with the ANKE spectrometer at the COSY storage ring at 1.6, 1.8, and 2.27 GeV have extended these studies into the pion-production regime in order to investigate the mechanism for the excitation of the Delta(1232) isobar in the pol{d}p -> {pp}X reaction. Values of the differential cross section and two deuteron tensor analysing powers, A_{xx} and A_{yy}, have been extracted in terms of the momentum transfer to the diproton or the invariant mass Mx of the unobserved system X. The unpolarised cross section in the high Mx region is well described in a model that includes only direct excitation of the Delta isobar through undistorted one pion exchange. However, the cross section is grossly underestimated for low Mx, even when Delta excitation in the projectile deuteron is included in the calculation. Furthermore, direct Delta production through one pion exchange only reproduces the angular dependence of the difference between the two tensor analysing powers.

Publ.-Id: 19160 - Permalink


First measurements of spin correlations in the np -> d pi0 reaction
Shmakova, V.; Mchedlishvili, D.; Dymov, S.; Azaryan, T.; Barsov, S.; Chiladze, D.; Engels, R.; Gebel, R.; Gou, B.; Grigoryev, K.; Hartmann, M.; Kacharava, A.; Komarov, V.; Kulessa, P.; Kulikov, A.; Kurbatov, V.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Merzliakov, S.; Mikirtytchiants, M.; Mikirtytchiants, S.; Nioradze, M.; Ohm, H.; Prasuhn, D.; Rathmann, F.; Serdyuk, V.; Seyfarth, H.; Ströher, H.; Tabidze, M.; Trusov, S.; Tsirkov, D.; Uzikov, Y.; Valdau, Y.; Wilkin, C.;
The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have been measured for the first time in quasi-free kinematics at the COSY-ANKE facility using a polarised deuteron beam incident on a polarised hydrogen cell target. The results obtained for neutron energies close to 353 MeV and 600 MeV are in good agreement with the partial wave analysis of data on the isospin-related pp-> d pi^+ reaction, though the present results cover also the small-angle region, which was largely absent from these data.

Publ.-Id: 19159 - Permalink


Terahertz interlevel spectroscopy of quantum well excitons
Schneider, H.; Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Helm, M.;
According to the proceedings of the first conference on intersubband transitions in quantum wells (ITQW), which took place in 1991 in Cargèse [1], research on this topic in the early 90s concentrated mostly on mid-infrared detectors (quantum well infrared photodetectors, QWIPs) for applications in thermal imaging. The following reasons make ITQW quite interesting for infrared optoelectronics: (a) III-V semiconductor technology supply a mature technological basis, (b) spectral properties of ITQW are determined basically by layer thicknesses and not by material bandgaps, and (c) theoretically engineered layer structures enable novel device concepts and huge resonant optical nonlinearities [2]. In 1994, the invention of the quantum cascade laser (QCL) [3] has marked the birth of another exciting research field and paved the way for a wide range of new applications for ITQW. Later on, both the QWIP and QCL concepts have been applied to longer wavelengths beyond the Reststrahlen band [4,5], thus giving rise to important devices in the emerging field of terahertz (THz) technology.
Going from the 2D quantum well (QW) system to 1D quantum wires, and even 0D quantum dots (QD), there has been a long debate whether device performance, in particular at high operation temperatures, will become superior due to the restricted phase space for electron scattering. Most importantly, a phonon bottleneck has been predicted [6], which gave rise to the expectation that quantum dot infrared photodetectors (QDIP) [7] and QD-based QCLs could exhibit improved device properties. Even though the formation of a "true" phonon bottleneck is prevented by polaron effects, very long relaxation times up to ~ 1 ns have in fact been observed for intersublevel transitions in n-type QD systems at appropriate transition energies [8]. Nevertheless, the performance of QD-based infrared devices is limited as yet mainly by technological difficulties to realize QD ensembles with sufficient homogeneity, spatial density, and, in particular, optimized QD shape.
Besides QD and QW, yet another interesting system is the quantum well exciton (QWE), which is caused by the Coulomb attraction between a – usually photogenerated – electron and hole inside a QW. This results in a hydrogen-like quasi atom with discrete bound states. In contrast to ITQW, interlevel transitions in QWEs have their dipole matrix elements in the QW plane, such that optical transitions between QWE levels occur under normal incidence. Since QWE can move freely in the QW, the center-of-mass momentum gives rise to a 2D continuum, which is in close analogy to the in-plane dispersion of QW subbands. Being a two-particle molecule, the QWE exhibits more complex physics than an electron in a QW or QD, including angular momentum as a new degree of freedom, finite recombination lifetime, and various optically active (bright) or inactive (dark) exciton states. For possible applications, an intriguing property of QWE is the opportunity of controlling near-infrared (NIR) interband processes (eV range) via intra-exciton transitions (few meV range) between bright and dark exciton states [9-11].
This talk will focus on the internal dynamics of quantum well excitons, which are excited into higher levels using a THz free-electron laser, by monitoring intra-exciton relaxation via time-resolved interband photoluminescence.
Acknowledgements – The authors thank E. Rosencher for initiating the ITQW conference series. We are also indebted to L. Schneebeli, C. N. Böttge, B. Breddermann, S. Chatterjee, M. Kira, and S. W. Koch (U. Marburg, Germany) for fruitful discussions and collaboration, to A.M. Andrews and G. Strasser (TU Vienna) for sample growth, and to P. Michel, W. Seidel (HZDR Dresden) and the ELBE team for their dedicated support.
References
[1] E. Rosencher, B. Vinter, B. F. Levine, Eds., "Intersubband Transitions in Quantum Wells", NATO ASI, Series B: Physics, Vol. 188 (Plenum Press, New York, 1992).
[2] E. Rosencher, A. Fiore, B. Vinter, V. Berger, Ph. Bois, J. Nagle, "Quantum Engineering of Optical Nonlinearities ", Science 271, 168 (1995).
[3] J. Faist, F. Capasso, D. L. Sivco, C. Sirtori, A. L. Hutchinson, A. Y. Cho, "Quantum Cascade Laser", Science 264, 553 (1994).
[4] H. C. Liu, C. Y. Song, A. J. SpringThorpe, J. C. Cao, "Terahertz quantum-well photodetector", Appl. Phys. Lett. 84, 4068 (2004).
[5] R. Köhler, A. Tredicucci, F. Beltram, H. E. Beere, E. H. Linfield, A. G. Davies, D. A. Ritchie, R. C. Iotti, F. Rossi, "Terahertz semiconductor heterostructure laser", Nature 417, 156 (2002).
[6] U. Bockelmann and G. Bastard, "Phonon scattering and energy relaxation in two-, one-, and zero-dimensional electron gases" Phys. Rev. B 42, 8947 (1990).
[7] H. C. Liu, M. Gao, J. McCaffrey, Z. R. Wasilewski, S. Fafard, "Quantum dot infrared photodetectors", Appl. Phys. Lett. 78, 79 (2001).
[8] E. A. Zibik, T. Grange, B. A. Carpenter, N. E. Porter, R. Ferreira, G. Bastard, D. Stehr, S.Winnerl, M. Helm, H. Y. Liu, M. S. Skolnick, L. R. Wilson, "Long lifetimes of quantum-dot intersublevel transitions in the terahertz range", Nature Mat. 8, 803 - 807 (2009).
[9] M. Kira and S. W. Koch, "Exciton-Population Inversion and Terahertz Gain in Semiconductors Excited to Resonance", Phys. Rev. Lett. 93, 076402 (2004).
[10] W. D. Rice, J. Kono, S. Zybell, S. Winnerl, J. Bhattacharyya, H. Schneider, M. Helm, B. Ewers, A. Chernikov, M. Koch, S. Chatterjee, G. Khitrova, H. M. Gibbs, L. Schneebeli, B. Breddermann, M. Kira, S. W. Koch, "Observation of Forbidden Exciton Transitions Mediated by Coulomb Interactions in Photoexcited Semiconductor Quantum Wells", Phys. Rev. Lett. 110, 137404 (2013).
[11] J. Bhattacharyya, M. Wagner, S. Zybell, S. Winnerl, D. Stehr, M. Helm, H. Schneider, "Simultaneous time and wavelength resolved spectroscopy under two-color near infrared and terahertz excitation", Rev. Sci. Instr. 82, 103107 (2011).
Keywords: Terahertz free-electron laser, semiconductor quantum wells, excitons, Coulomb scattering
  • Invited lecture (Conferences)
    The 12th International Conference on Intersubband Transitions in Quantum Wells - ITQW 2013, 15.-20.09.2013, Bolton Landing, NY, USA

Publ.-Id: 19158 - Permalink


THz free-electron laser spectroscopy of magnetoexcitons in semiconductor quantum wells
Bhattacharyya, J.; Zybell, S.; Eßer, F.; Winnerl, S.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.; Helm, M.; Schneider, H.;
Transitions between the 1s and 2p levels of the fundamental heavy-hole exciton in GaAs quantum wells, followed by scattering into the 2s state, are investigated by resonant THz excitations using a free-electron laser. We report on the external control of this intra-excitonic population transfer by an external magnetic field.
Keywords: terahertz free electron laser, semiconductor quantum wells, exciton, interlevel transition
  • Invited lecture (Conferences)
    The 38th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz'2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665864

Publ.-Id: 19157 - Permalink


Spectroscopy of low-dimensional semiconductors with a terahertz free-electron laser
Schneider, H.;
This talk reviews recent experimental studies which we carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning the FEL in resonance with the transtion between the excitonic 2s and 2p states (at about 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where far-infrared absorption by single electrons produces sufficient contrast to map individual quantum dots. In graphene, FEL-based pump-probe spectroscopy reveals different relaxation times for excitation energies above and below the optical phonons. At even smaller photon energies, this two-dimensional semiconductor material exhibits a transition from induced transmission to induced absorption, which is indicative for possible applications as an optical modulator.
Keywords: Terahertz spectroscopy, quantum well, quantum dot, exciton
  • Invited lecture (Conferences)
    9th National Conference on Nanoscience and Nanotechnology (NanoTR-9), 14.-28.07.2013, Ataturk University, Erzurum Province, Turkey

Publ.-Id: 19156 - Permalink


In vivo comparison of DOTA based 68Ga-labelled bisphosphonates for bone imaging in non-tumour models
Meckel, M.; Fellner, M.; Thieme, N.; Bergmann, R.; Kubicek, V.; Rösch, F.;
Bone metastases are a class of cancerous metastases that result from the invasion of a tumor into bone. The solid mass which forms inside the bone is often associated with a constant dull ache and severe spikes in pain, which greatly reduce the quality of life of the patient. Numerous 99mTc-labeled bisphosphonate functionalised complexes are well established tracers for bone metastases imaging. The objective of this research was to evaluate the pharmacokinetics and behaviour of three DOTA based bisphosphonate functionalised ligands (BPAMD, BPAPD and BPPED), using both 68Ga μ-PET in vivo imaging and ex vivo biodistribution studies in healthy Wistar rats. The compounds were labelled with 68Ga in high yields using an ammonium acetate buffer, and subsequently purified using a cation exchange resin. High bone uptake values were observed for all 68Ga-labelled bisphosphonates at 60 minutes p.i. The highest uptake was observed for [68Ga]BPPED (2.6 ± 0.3% ID/g) which compares favourably with that of [99mTc]MDP (2.7 ± 0.1 ID/g) and [18F]fluoride (2.4 ± 0.2% ID/g). The 68Ga-labelled DOTA-bisphosphonates showed rapid clearance from the blood and renal system, as well as low binding to soft tissue, resulting in a high bone to blood ratio (9.9 at 60 minutes p.i. for [68Ga]BPPED, for example). Although further studies are required to assess their performance in tumor models, the results obtained suggest that these ligands could be useful both in imaging (68Ga) and therapeutic treatment (177Lu) of bone metastases.
Keywords: Bone metastases; 68Ga; PET; 177Lu; DOTA; Bisphosphonates

Publ.-Id: 19155 - Permalink


Synthesis and radiopharmacological evaluation of a high-affinity and metabolically stabilized 18F-labeled bombesin analogue for molecular imaging of gastrin-releasing peptide receptor-expressing prostate cancer
Richter, S.; Wuest, M.; Krieger, S. S.; Rogers, B. E.; Friebe, M.; Bergmann, R.; Wuest, F.;
Introduction: Bombesin (BBN) and BBN analogues have attracted much attention as high-affinity ligands for selective targeting of the gastrin-releasing peptide (GRP) receptor. GRP receptors are overexpressed in a variety of human cancers including prostate cancer. Radiolabeled BBN derivatives are promising diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of various metabolically stabilized fluorobenzoylated bombesin analogues (BBN-1, BBN-2, BBN-3).

Methods: Three fluorobenzoylated BBN analogues containing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against 125I-[Tyr4]-BBN for their binding potency to the GRP receptor. Intracellular calcium release in human prostate cancer cells (PC3) was measured to determine agonistic or antagonistic profiles of fluorobenzoylated BBN derivatives. Bombesin derivative BBN-2 displayed the highest inhibitory potency toward GRP receptor (IC50 = 8.7 ± 2.2 nM) and was subsequently selected for radiolabeling with fluorine-18 (18F) through acylation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radiopharmacological profile of 18F-labeled bombesin [18F]BBN-2 was evaluated in PC3 tumor-bearing NMRI nude mice involving metabolic stability studies, biodistribution experiments and dynamic small-animal PET studies.

Results: All fluorobenzoylated BBN derivatives displayed high inhibitory potency toward the GRP receptor (IC50 = 8.7–16.7 nM), and all compounds exhibited antagonistic profiles as determined in an intracellular calcium release assay. The 18F-labeled BBN analogue [18F]BBN-2 was obtained in 30% decay-corrected radiochemical yield with high radiochemical purity N95% after semi-preparative HPLC purification. [18F]BBN-2 showed high metabolic stability in vivo with 65% of the radiolabeled peptide remaining intact after 60 min p.i. in mouse plasma. Biodistribution experiments and dynamic small-animal PET studies demonstrated high
tumor uptake of [18F]BBN-2 in PC3 xenografts (2.75 ± 1.82 %ID/g after 5 min and 2.45 ± 1.25 %ID/g after 60 min p.i.). Specificity of radiotracer uptake in PC3 tumors was confirmed by blocking experiments.

Conclusion: The present study demonstrates that 18F-labeled BBN analogue [18F]BBN-2 is a suitable PET radiotracer with favorable metabolic stability in vivo for molecular imaging of GRP receptor-positive
prostate cancer.
Keywords: 18F; Bombesin (BBN); Gastrin-releasing peptide (GRP) receptor; Prostate cancer; N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB); Positron emission tomography (PET)

Publ.-Id: 19154 - Permalink


Quantitative Structure Property Relationship of logP for Radiopharmaceutical Technetium and Rhenium Complexes by using Molecular Dynamics Calculations
Yoshizuka, K.; Pietzsch, H.-J.; Seifert, S.; Stephan, H.;
We have developed a novel molecular modelling technique for radiopharmaceutical Tc and Re complexes combined with molecular mechanics (MM) and molecular dynamics (MD) for estimating the partition coefficient of these complexes between water and l-octanol (logP). The field force parameters developed with a MM program, "MOMEC" were fitted to all relevant X-ray crystal structures of [99mTcO(DMSA)2]- and [188ReO(DMSA)2]- (DMSA: dimercaptosuccinic acid). The force field parameters were transferred to those in a MD program, "Material Explorer". The MD simulations also indicate that a quantitative structure property relationship (QSPR) was optained, which relates the internal energy difference between the Tc/Re-DMSA derivatives in the water phase and that in l-octanol phase with the experimental logP value.
  • Open Access LogoSolvent Extraction Research and Development 20(2013), 15-27

Publ.-Id: 19153 - Permalink


Depth-resolved transport measurements and atom-probe tomography of heterogeneous, superconducting Ge:Ga films
Heera, V.; Fiedler, J.; Naumann, M.; Skrotzki, R.; Kölling, S.; Wilde, L.; Herrmannsdörfer, T.; Skorupa, W.; Wosnitza, J.; Helm, M.;
Ge films with a mean Ga content of about 8 at.% and 1 at.% hole concentration can be fabricated by ion implantation and subsequent flash-lamp annealing. The Ge:Ga films become superconducting below critical temperatures in the range between 1 and 2 K depending on the film resistance. The change of the macroscopic transport properties during step-wise surface etching can be described by a homogeneously doped layer model. However, the Ga distribution is extremely heterogeneous on the nanoscale. Atom-probe tomography analyses reveal the presence of Ga-rich precipitates with Ga clusters up to 10,000 atoms. Since no percolating Ga cluster exists, it can be supposed that the heavy doping of Ge enables a coherent superconducting state via the proximity effect.
Keywords: Ga ion implantation, flash-lamp annealing, superconducting Ge:Ga, inhomogeneous superconductor, hole doping, Ga cluster

Publ.-Id: 19152 - Permalink


PET-Bildgebung von α7 Nikotinrezeptoren: Einfacher Zugang zu einem Markierungsvorläufer für [18F]NS14490
Scheunemann, M.; Rötering, S.; Fischer, S.; Hiller, A.; Peters, D.; Steinbach, J.; Deuther-Conrad, W.; Brust, P.;
Das 1-(2-Fluorethylindol-6-yl)-oxadiazolylamin NS14490 ist ein hoch affiner α7-Subtyp-spezifischer Ligand für den nikotinischen Acetylcholinrezeptor (nAChR, Ki,α7 = 2,5 nM), für dessen 18F-markierte Form wir ein Syntheseverfahren entwickelt haben [1]. Das Potential dieses neuen Radiotracers für die molekulare PET-Bildgebung von α7 nAChR bei neurodegenerativen und Tumorerkrankungen wird gegenwärtig von uns untersucht.
Da die Herstellung des zur Radiosynthese von [18F]NS14490 benötigten Tosylates 1 nach einer ursprünglich verfolgten Methode [1], ausgehend vom N-unsubstituierten NS14490-Derivat unbefriedigende Ergebnisse erbrachte, wurde ein verbessertes Syntheseverfahren aus dem Ester 3 über eine 6-stufige Sequenz, mit BOP-Kupplung zu 7 als Schlüsselschritt [2] entwickelt, das eine Gesamtausbeute von 32% ermöglichte. Die Darstellung von [18F]NS14490 erfolgt mit [18F]Fluorid [18O(p,n)18F-Reaktion am Cyclone 18/9, Leipzig] in Gegenwart von Kryptofix K2.2.2 in einem Schritt aus 1. Die Isolierung und Reinigung des Radiotracers (radiochemisch ≥95%) ist umfassend optimiert und erfolgt durch semipräparative RP-HPLC mit anschließender Festphasenextraktion (RCA: 36%, spezifische Aktivität: 150 GBq/μmol, Synthesedauer: 2-2,5 h).
Weiterführende In-vitro- und In-vivo-Studien, insbesondere zur Hirn-Aufnahme und zur Selektivität der Bindung von [18F]NS14490 an α7 nAChR im Gehirn belegen die potentielle Eignung des Radioliganden für die molekularen Bildgebung [1].
(Unterstützt durch die Deutsche Forschungsgemeinschaft, Ref. DE1165/2-1)
Literatur:
[1] S. Rötering et al. Bioorg. Med. Chem. (im Druck). [2] C. G. Levins et al. Org. Lett. 2008, 10, 1755.
  • Lecture (Conference)
    GDCh Wissenschaftsforum Chemie, 01.-04.09.2013, Darmstadt, Deutschland

Publ.-Id: 19151 - Permalink


Hydrogen-induced microstructural changes of Pd films
Cizek, J.; Melikhova, O.; Vlcek, M.; Lukac, F.; Vlach, M.; Prochazka, I.; Anwand, W.; Brauer, G.; Mücklich, A.; Wagner, S.; Uchida, H.; Pundt, A.;
The development of the microstructure in nanocrystalline, polycrystalline and epitaxial Pd films loaded with hydrogen is investigated. Structural changes in Pd films loaded with hydrogen were characterized by positron annihilation spectroscopy combined with electron microscopy and X-ray diffraction. It was found that hydrogen charging causes plastic deformation which leads to an increase of the defect density in all Pd films studied. Moreover, the formation of buckles was observed in nanocrystalline and polycrystalline Pd films loaded above a certain critical hydrogen concentration. Buckling leads to detachment of the film from the substrate and this is accompanied with in-plane stress relaxation and plastic deformation of the film.
Keywords: Palladium films, Hydrogen, Positron annihilation spectroscopy, X-ray diffraction

Publ.-Id: 19149 - Permalink


Electron transfer processes at the mineral/water interface in the context of anoxic radioactive waste disposal
Scheinost, A.C.;
Se, Pu in the context of radioactive waste disposal
FeII-driven interfacial redox reactions
Se interfacial redox reactions
Pu interfacial redox reactions
Keywords: EXAFS XAFS redox
  • Invited lecture (Conferences)
    Goldschmidt 2013, Workshop: Redox-active Minerals: Properties, Reactions and Applications in Clean Technologies, 25.-30.08.2013, Florence, Italy

Publ.-Id: 19148 - Permalink


Dynamic behavior of selected PET tracers in embryonated chicken eggs
Gebhardt, P.; Würbach, L.; Heidrich, A.; Heinrich, L.; Walther, M.; Opfermann, T.; Sørensen, B.; Saluz, H. P.;
Positron emission tomography/computer tomography (PET/CT) is an established method in the preclinical research of small animal disease models and in the clinical diagnosis of cancer. It combines the functional information of the positron-emitting biomarker with the anatomical data from the CT image, thereby allowing for the 4D in vivo investigation of biological processes of interest. Recently, the bone growth of chicken embryos was monitored using [18F]fluoride as a bone-seeking tracer. We are interested to investigate additional PET/CT tracers in embryonated chicken eggs as in vivo model system. The properties of 18F-, 68Ga-labelled tracers and 64Cu-chloride were studied in catheterised eggs via small animal microPET/CT. [18F]FDG was primarily absorbed at sites of bone growth. 64Cu chloride and a 68Ga-labelled amyloid-fibril-binding antibody accumulated in the liver, while 68Ga-albumin desferrioxamine conjugate was rapidly cleared. The method potentially can be utilised to monitor biological processes in chicken eggs.

Publ.-Id: 19147 - Permalink


Low Energy Proton Radiation Impact on 4H-SiC nMOSFET Electrical Parameters
Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Godignon, P.;
In this work, the effect of 180 keV proton radiation in lateral 4H-SiC nMOSFETs with rapid thermally processed (RTP) gate oxides is investigated before and after radiation. Comparison with non-irradiated (NI) samples allows the study of hole trap effects in the oxide and of generated interface traps. It has been observed that for the two lower fluences, the threshold voltage (VTH) shifts toward lower values, reaching a minimum for a fluence of 5x1012 cm-2. The effective channel mobility (µEFF) and the maximum drain current (IDSAT_MAX) reach maximum values for 5x1012 cm-2 as well; the µEFF gets 6 times superior, while the IDSAT_MAX doubles in accordance with the NI sample values.
Keywords: SiC, low energy proton irradiation, threshold voltage shift, channel mobility
  • Lecture (Conference)
    International Conference on Silicon Carbide and Related Materials, 29.09.-04.10.2013, Phoenix Seagaia Resort, Miyazaki, Japan

Publ.-Id: 19146 - Permalink


5MeV Proton and 15MeV Electron Radiation Effects Study on 4H-SiC nMOSFET Electrical Parameters
Alexandru, M.; Florentin, M.; Constant, A.; Schmidt, B.; Michel, P.; Godignon, P.;
The impact of proton and electron irradiation on the electrical parameters of 4H-SiC nMOSFETs has been
investigated by using time bias stress instability method. This study has allowed observing the effect of holes trapped in the
oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage,
the effective mobility and the maximum drain current were observed. These amendments could be connected with the
Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These
atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of
passivated Carbon atoms is increasing, hence the interface quality getting improved.
Keywords: Charge Trapping, Electron Irradiation, Mobility, Proton irradiation, SiC MOSFET, SiO2/SiC Interface, Time Bias Stress Instability, Threshold Voltage Shift
  • Lecture (Conference)
    Radiation Effects on Components and Systems 2013, 23.-27.09.2013, Oxford, England

Publ.-Id: 19145 - Permalink


10 MeV Proton Irradiation Effect on 4H-SiC nMOSFET Electrical Parameters
Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Godignon, P.;
This work presents the 10 MeV proton irradiation effects on 4H-SiC MOSFETs at different fluences. MOSFETs main electrical parameters, such as the channel mobility (µEFF), threshold voltage (VTH), transconductance (gm) and subthreshold current, were analyzed using the time bias stress instability (BSI) technique. Applying this method allowed us to study the effect of carrier interaction with proton induced defects (traps), whether in the bulk or at the interface. Improvements, such as VTH stabilization in time and a significant increase of the µEFF at high fluencies, have been noticed. We assume that this behavior is connected with the atomic diffusion from the SiO2/SiC interface, towards the epilayer during proton irradiation. These atoms, mainly Nitrogen, may create other bonds by occupying various vacancies coming from Silicon and Carbon’s dangling bond. Therefore, by increasing the number of passivated Carbon atoms, we show that high irradiation proton could be a way to improve the SiO2/SiC interface quality.
Keywords: Silicon carbide, MOSFET devices, proton irradiation
  • Lecture (Conference)
    HeteroSiC-WASMPE, 17.-19.07.2013, Nice, France
  • Materials Science Forum 806(2015), 121-125

Publ.-Id: 19144 - Permalink


Deceleration of Ar9+ ions within a tapered glass capillary
Kreller, M.; Zschornack, G.; Kentsch, U.;
We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. In the experiments we have chosen an incident ion energy of q x 8.5 keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7 kV. Hence, the ion beam was decelerated and compressed to a diameter of 150 µm without using any additional decelerating lens systems.
Keywords: Ion guiding Highly charged ion Tapered macro-capillary Ion beam deceleration

Publ.-Id: 19143 - Permalink


Quantitative imaging of the magnetic configuration of modulated nanostructures by electron holography
Körner, M.; Röder, F.; Lenz, K.; Fritzsche, M.; Lindner, J.; Lichte, H.; Fassbender, J.ORC
Regarding magnetic nanostructures, dipolar stray fields start to evolve with ongoing miniaturization, that grossly alter the magnetic properties. Besides, these fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals.
Hence, a detailed knowledge of the magnetic configuration under geometric confinements on the nanoscale is mandatory.
We present a study of the magnetic fields arising from thin Permalloy films deposited on periodically modulated surfaces (ripples).
These ripples were prepared using a self-organized ion beam erosion process generating modulations on the nanoscale.
Cross-sectional transmission electron holography nowadays offers the necessary sensitivity and nanoscale lateral resolution to probe the magnetic configuration of such rippled films quantitatively.
The imaging allows for an absolute analysis of the local magnetization inside the film as well as the accompanying stray fields outside.
In addition, the evolving stray fields above the sample's surface were investigated by magnetic force microscopy.

Publ.-Id: 19142 - Permalink


Two-Magnon Scattering in the Transition from Periodical Perturbations to Magnonic Crystals
Lenz, K.; Körner, M.; Gallardo, R. A.; Banholzer, A.; Facsko, S.; Lindner, J.; Landeros, P.; Fassbender, J.ORC
Two-magnon scattering is a well-known effect e.g. in ferromagnetic resonance (FMR) experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in periodically perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the resonance response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments [2,3]. The scattering potential of the defects builds up due to the dipolar stray fields at the edges of the defects. Within the perturbation theory this leads on the one hand to a shift of the resonance peak and on the other hand also to a splitting of the uniform resonance mode. Both effects are clearly visible in the FMR experiments. The mode splitting due to the two-magnon scattering finally is also responsible for the opening of magnonic band gaps in the dispersion relation of magnonic crystals. The splitting can be tailored by the geometric and magnetic sample parameters. Experimental data for magnetically patterned stripe samples as well as for ripple samples [3] is presented and compared to calculations by the analytical model (see e.g. Fig. 1).
This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, K. Lenz, A. Banholzer, M. Körner, J. Lindner, J. Fassbender, P. Landeros, Phys Rev. B (2013) submitted
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner, P. Landeros, J. Fassbender, Phys. Rev. B (2013) submitted
Keywords: magnonic crystals, two-magnon scattering
  • Poster
    3rd international conference on magnonics 2013, 04.-08.08.2013, Varberg, Schweden

Publ.-Id: 19141 - Permalink


Establishment of a small animal tumour model for in vivo studies with low energy laser accelerated particles
Brüchner, K.; Beyreuther, E.; Baumann, M.; Krause, M.; Oppelt, M.; Pawelke, J.;
Background: The long-term aim of developing a laser based acceleration of protons and ions towards clinical application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short pulsed particle beams. Recent in-vitro data showed similar effects of laser-accelerated versus “conventional” protons on clonogenic cell survival. As the proton energies currently achieved by laser driven acceleration are too low to penetrate standard tumour models on mice legs, the aim of the present work was to establish a tumour model allowing for the penetration of low energy protons (~ 20 MeV) to further verify their effects in vivo.
Methods: KHT mouse sarcoma cells were injected subcutaneously in the right ear of NMRI (nu/nu) mice and the growing tumours were characterized with respect to growth parameters, histology and radiation response. In parallel, the laser system JETI was prepared for animal experimentation, i.e. a new irradiation setup was implemented and the laser parameters were carefully adjusted. Finally, a proof-of-principle experiment with laser accelerated electrons was performed to validate the tumour model under realistic conditions, i.e. altered environment and horizontal beam delivery.
Results: KHT sarcoma on mice ears expressed a high take rate and showed continuous tumour growth after reaching a volume of ~ 5 mm³. The first irradiation experiment using laser accelerated electrons versus 200 kV X-rays was successfully performed and tumour growth delay was evaluated. Comparable tumour growth delay was found between X-ray and laser accelerated electron irradiation. Moreover, experimental influences, like anaesthesia and positioning at JETI, were found to be negligible.
Conclusion: A small animal tumour model suitable for the irradiation with low energy protons was established and validated at a laser based particle accelerator. For this reason, the translation from in vitro to in vivo experimentation was for the first time realized and an important milestone towards the clinical application of laser driven particle accelerators was achieved.

Publ.-Id: 19140 - Permalink


Laser Induced Sponge-like Si in Si-rich Oxides for Photovoltaics
Gundogdu, S.; Sungur Ozen, E.; Hübner, R.; Heinig, K.-H.; Aydinli, A.;
We show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3rd generation thin-film solar cells. Well passivated by the SiO2 dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar+ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon.

Publ.-Id: 19139 - Permalink


Neutron transport in hexagonal reactor cores modeled by trigonal-geometry diffusion and simplified P3 nodal methods
Duerigen, S.;
The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P3 (or SP3) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP3 transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance.
The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP3 and diffusion equations, which guarantees high accuracy.
The SP3 equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP3 transport problem.
The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP3 transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.
Keywords: DYN3D, trigonal, triangular, hexagonal, nodal, diffusion, simplified P3, SP3
  • Doctoral thesis
    Karlsruhe Institute of Technology, 2013
    175 Seiten
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-035 2013

Downloads:

Publ.-Id: 19137 - Permalink


The DYN3D trigonal-geometry diffusion model – verification using the AER-FCM-101 benchmark
Duerigen, S.; Kliem, S.;
DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of light-water reactors with square and hexagonal fuel assembly geometries as well as of innovative reactor concepts, which is undergoing continuous development.
In this work, the trigonal-geometry DYN3D diffusion model is verified by means of the AER-FCM-101 benchmark. With increasing trigonal mesh refinement, both effective multiplication factor and power distribution converge well to the extrapolated finite-element reference solution. In addition, a comparison to the hexagonal DYN3D diffusion models HEXNEM1 and HEXNEM2 is given.
Keywords: DYN3D trigonal nodal diffusion triangles AER-FCM-101
  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia

Publ.-Id: 19136 - Permalink


A micro-structured ion-implanted magnonic crystal
Obry, B.; Pirro, P.; Braecher, T.; Chumak, A. V.; Osten, J.; Ciubotaru, F.; Serga, A. A.; Fassbender, J.ORC; Hillebrands, B.
We investigate spin-wave propagation in a microstructured magnonic-crystal waveguide fabricated by localized ion implantation. The irradiation caused a periodic variation in the saturation magnetization along the waveguide. As a consequence, the spin-wave transmission spectrum exhibits a set of frequency bands, where spin-wave propagation is suppressed. A weak modification of the saturation magnetization by 7% is sufficient to decrease the spin-wave transmission in the band gaps by a factor of 10. These results evidence the applicability of localized ion implantation for the fabrication of efficient micron- and nano-sized magnonic crystals for magnon spintronic applications.
Keywords: magnonic-crystal waveguide ion implantation

Publ.-Id: 19135 - Permalink


Positron annihilation studies of zirconia doped with metal cations of different valence
Prochazka, I.; Cizek, J.; Melikhova, O.; Konstantinova, T. E.; Danilenko, I. A.; Yashchishyn, I. A.; Anwand, W.; Brauer, G.;
New results obtained by applying positron annihilation spectroscopy to the investigation of zirconia-based nanomaterials doped with metal cations of different valence are reported. The slow-positron implantation spectroscopy combined with Doppler broadening measurements was employed to study the sintering of pressure-compacted nanopowders of tetragonal yttria-stabilised zirconia (t-YSZ) and t-YSZ with chromia additive. Positronium (Ps) formation in t-YSZ was proven by detecting 3γ-annihilations of ortho-Ps and was found to gradually decrease with increasing sintering temperature. A subsurface layer with enhanced 3γ-annihilations, compared to the deeper regions, could be identified. Addition of chromia was found to inhibit Ps formation. In addition, first results of positron lifetime measurements on nanopowders of zirconia phase-stabilised with MgO and CeO2 are presented.
Keywords: positron annihilation spectroscopy, zirconia-based nanomaterials, positronium formation

Publ.-Id: 19134 - Permalink


Technical concepts for the operation of a Cameca 7f-Auto as ion source for the HZDR Super-SIMS
Ziegenrücker, R.; Merchel, S.; Renno, A. D.; Rugel, G.; Akhmadaliev, S.; Wustmann, B.;
Super-SIMS - also called Accelerator-SIMS - is an ultrasensitive analytical method (Döbeli et al., 2013; Renno et al., 2013). A Super-SIMS-Set-up is now under installation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) by connecting a conventional SIMS-source (Cameca 7f-Auto) to a 6 MV tandem accelerator (Akhmadaliev et al., 2013). The operation of a classical SIMS demands strong structural and building technological efforts [Cameca, 2012]. The requirements for the 6 MV tandem accelerator at the HZDR are of the same complexity.

Requirements # Cameca 7f-Auto # 6 MV tandem accelerator
vibrations # very strict # -
temperature | fluctuation # 19°C < T < 23°C|< 1°C•h-1 # max. 25°C
relative humidity | fluctuation # 30% < RH < 75% | < 10%•h-1 # 30%< RH < 75%
spurious magnetic field # < 3•10-7 Tesla # < 10-4 Tesla
vacuum # 10-9 mbar # 10-6 mbar
cooling | fluctuation # 17°C – 19°C | < 1°C•h-1 # 20°C – 25°C
nitrogen # N4.8 # N4.8
compressed air # dry | 5 – 7 bar | 35 – 50 L•min-1 # dry | 5 – 7 bar
uninterruptible power supply # 10 min # only for PC
radiation safety # - # very strict

The original specifications to optimally run both machines are in many cases incompatible. An additional challenge originates from the fact that a pre-acceleration voltage of 30 kV to inject negative secondary ions into the accelerator is needed. To guarantee the compliance with all specifications and safety regulations a specific concept for the housing of the Cameca 7f-Auto following a house-in-house-principle was developed. This concept guarantees the following operational options:
• independent operation of the 6 MV tandem accelerator
• independent operation of the Cameca 7f-Auto
• combined operation as a Super-SIMS by remote control
• operation of the Super-SIMS by remote control from outside the HZDR in the framework of the planned Helmholtz-SIMS network SIGMA
The most critical issue is the complete separation of all electric circuits in- and outside the SIMS housing by an insulating transformer, demanding the supply of electricity, gases, cooling, the intranet broadband network as well as all HVACR (heating, ventilation, air conditioning and refrigeration) without the use of electrically conductive materials. The strong vibrations in the accelerator hall are asking for further precautions. To follow all laboratory specifications for the Cameca instrument, the SIMS will be fixed on a cuboid made of natural gabbro (weight 6.4 t, size: 1.4 m x 1.8 m x 0.86 m) and all peripheral instruments on a frame vibrationally decoupled from the cuboid. This construction ensures the isolation of the SIMS and guarantees the compliance with all high-voltage safety regulations.

References
Döbeli et al., 2013, this meeting.
Renno et al., 2013, this meeting.
Akhmadaliev S., Heller R., Hanf D., Rugel G., Merchel S. (2013) The new 6 MV AMS-facility DREAMS at Dresden. Nucl. Instr. Meth. Phys. Res. B, 294, 5-10.
CAMECA (2012) IMS 7F Auto Installation & Delivery Conditions
Keywords: 6 MV Tandemaccelerator; SIMS; CAMECA 7f-Auto; Super-SIMS; Housing; Gabro; SIGMA
  • Poster
    Seventh Biennial Geo-SIMS Workshop, 20.-22.08.2013, Potsdam, Deutschland

Publ.-Id: 19133 - Permalink


Application of a new concept for multi-scale interfacial structures to the dam-break case with an obstacle
Hänsch, S.; Lucas, D.; Höhne, T.; Krepper, E.;
New results of a generalized concept developed for the simulation of two-phase flows with multi-scale interfacial structures are presented in this paper. By extending the inhomogeneus Multiple Size Group-model, the concept enables transitions between dispersed and continuous gas morphologies, including the appearance and evanescence of one of these particular gas phases. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for interfacial area density and drag. A new drag-formulation considers shear stresses occurring within the free surface area.
The application of the concept to a collapsing water column demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The simulations have been performed with the CFD-code CFX 14.0 and will be compared with experimental images.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.
Keywords: multi-scale, flow regime transitions, air entrainment, dam-break, MUSIG, AIAD

Publ.-Id: 19132 - Permalink


Osteoblast responses to novel titanium-based surfaces produced by plasma- and ion beam technologies
Tsyganov, I.; Lode, A.; Hanke, T.; Kolitsch, A.; Gelinsky, M.;
Plasma and ion beam technologies have been proven to be effective approaches for modification of surface properties of different materials. In the present work, structure, phase composition, hydrophilicity and microhardness of titanium oxynitride TiNxOy, and pure and phosphorus ions implanted TiO2 coatings produced by metal plasma immersion ion implantation and deposition were investigated. The mixed, highly amorphous TiN0.4O1.6 surface has maximal hydrophilicity and microhardness. P implantation in a TiO2 layer consisting mainly of rutile phase leads to disorder in the crystal lattice, slight amorphisation, and increasing hydrophilicity as well as microhardness of the surface. To evaluate the correlation between the structure of the layers and their cytocompatibility, the influence of the surfaces on the behavior of osteoblast-like SaOS-2 cells was studied in vitro. The cells were cultured on the three Ti-based coatings, both on the bare surfaces as well as on the surfaces biomineralised from simulated body fluid. No statistically significant differences were observed for cell adhesion to all bare Ti-based surfaces. Cell proliferation and osteogenic differentiation were surface sensitive and showed an opposite effect:
osteogenic differentiation, indicated by an increase of alkaline phosphatase (ALP) activity, on the P-implanted TiO2 and TiNxOy surfaces was reduced whereas the proliferation increased in comparison to TiO2.
Attachment and proliferation of cells were significantly lower on biomineralised surfaces.
Keywords: Plasma and ion beam technologies, cytocompatibility

Publ.-Id: 19131 - Permalink


Eph-Rezeptoren und Ephrin-Liganden als molekulare Schnittstelle zwischen Melanomzellen und Tumor-assoziierten inflammatorischen Zellen
Neuber, C.;
  • Doctoral thesis
    TU Dresden, Fakultät Mathematik und Naturwissenschaften, 2013
    174 Seiten

Publ.-Id: 19130 - Permalink


Magnetic and Structural Properties of Equiatomic FeRh thin films
Heidarian, A.; Potzger, K.; Lindner, J.; Heller, R.; Wilhelm, R.; Grenzer, J.; Reuther, H.; Bali, R.;
Equiatomic FeRh thin films with varying thickness have been prepared on MgO (100) substrates via molecular beam epitaxy (MBE). The optimization of the stoichiometry was monitored using XRD, RBS and AES while the magnetic properties were probed using SQUID magnetometry. XRD results evidence a well ordered CsCl-type crystal structure. By increasing the annealing temperature of the films, the structural quality of the films also increases. Moreover, the known first order phase transition at ~350 K from an antiferromagnetic (AF) to a ferromagnetic (FM) state slightly shifts towards higher temperatures. M-H loops of films annealed at 800 ∘C or 850 ∘C recorded at 300 K show an opening, which is likely related to the magnetic field-induced AFM-FM phase transition. Residual low-temperature ferromagnetic moments are of unknown origin, but likely related to strain or diffusion effects at the surface or interface.
Keywords: FeRh thin films, Magnetic properties, Lattice structure, SQUID
  • Poster
    The IEEE Magnetics Society Summer School, 09.-14.06.2013, Assisi, Italy
  • Poster
    Joint European Magnetic Symposia (JEMS 2013), 25.-30.08.2013, Rhodes, Greece
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft (DPG 2014), 30.03.-04.04.2014, Dresden, Germany
  • Lecture (Conference)
    IEEE International Magnetics Conference (INTERMAG 2014), 04.-08.05.2014, Dresden, Germany

Publ.-Id: 19129 - Permalink


Atom probe tomography characterization of CrN precipitation in low temperature 15N-enriched plasma nitrided 316L austenitic stainless steel.
Martinavičius, A.; Danoix, R.; Drouet, M.; Abrasonis, G.; Hannoyer, B.; Danoix, F.;
Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400°C) leads to the formation of a modified surface layer which shows increased hardness and induced magnetism, without compromising the corrosion resistance. The exact nature of this layer is still a matter of debate.

In this study, ASS 316L has been plasma nitrided with a mixture of 14N and 15N for 30 min at 400°C. Only a single phase, usually called the S phase or expanded austenite, is detected by X-ray diffraction. Transmission electron microscopy shows a high density of stacking faults and lattice distortions in this S phase, but does not provide any direct information regarding its composition, in particular regarding nitrogen and chromium distributions at the nanometer scale. Atom probe tomography and field ion microscopy reveal the presence of nanometric chromium nitride precipitates, with irregular oblate-spheroid-like shape. The preferential precipitation of chromium nitride at grain boundaries and/or stacking faults is investigated. These observations suggest that incorporation of large amounts of N provides strong driving force for chromium nitride formation, even at such a short nitriding time and rather low temperature.

Because of the presence of silicon and obviously iron in this industrial stainless steel, direct composition measurement of these chromium nitrides, in particular their nitrogen content, is not possible. In order to solve this classical analytical issue, specimens were nitrided using different 14N/15N ratios. Possible N+/Si2+ and N2+/Fe2+ overlaps at 14 and 28 Da respectively are investigated in order to estimate the actual chromium nitride composition. Results will be compared with the one obtained with the newly developed high mass resolution Flextap, potentially allowing N+/Si2+ and N2+/Fe2+ peak discrimination.
  • Poster
    53rd International Field Emission Symposium (IFES 2012), 21.-25.05.2012, Tuscaloosa, Alabama, United States of America

Publ.-Id: 19128 - Permalink


Low-energy enhancement of magnetic dipole radiation
Schwengner, R.; Frauendorf, S.; Larsen, A. C.;
Magnetic dipole strength functions have been deduced from averages of 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 transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M1 strength function deduced from the calculated M1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents for the first time an explanation of the experimental findings.
Keywords: Magnetic dipole radiation, gamma-ray strength functions, shell model.

Publ.-Id: 19127 - Permalink


Extending the Range of the Inductionless Magnetorotational Instability
Kirillov, O.; Stefani, F.;
The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is its questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile. This way we further show how the formerly known lower Liu limit of the critical Rossby number connects naturally with the upper Liu limit.
Keywords: MHD waves, magnetorotational instability, accretion disk, WKB approximation, stability

Publ.-Id: 19126 - Permalink


Validation of closure models for interfacial drag and turbulence in numerical simulations of horizontal stratified gas-liquid flows
Höhne, T.; Mehlhoop, J.-P.;
The development of general models closer to physics and including less empiricism is a long-term objective of the activities of the HZDR research programs. Such models are an essential precondition for the application of CFD codes to the modelling of flow related phenomena in the chemical and nuclear industries. The Algebraic Interfacial Area Density (AIAD) approach allows the use of different physical models depending on the local morphology inside a macroscale multi-fluid framework. A further step of improvement of modelling the turbulence at the free surface is the consideration of sub-grid wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. In fact, the influence on the turbulence kinetic energy of the liquid side can be significantly large. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth and wavy stratified flow experiments of a different rectangular channel. The results approve the ability of the AIAD model to predict key flow features like liquid hold-up and free surface waviness. Furthermore an evaluation of the velocity and turbulence fields predicted by the AIAD model against experimental data was done. The results are promising and show potential for further model improvement.
Keywords: CFD, horizontal flow, AIAD, two-phase flow, HAWAC, HZDR

Publ.-Id: 19125 - Permalink


Ion-irradiation induced damage in Fe-Cr alloys characterized by nanoindentation
Heintze, C.; Bergner, F.; Hernandez Mayoral, M.;
Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe-9at%Cr and Fe-12.5at%Cr irradiated at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles and exploitation of the full load dependence of hardness. The effects of Cr content, fluence and irradiation temperature are discussed. Hardening features were characterized by means of transmission electron microscopy. A tentative multi-feature hardening model was applied, to this end APT data published for the same alloys ion-irradiated under the same nominal conditions are taken into account.
Keywords: Ion irradiation, nanoindentation, TEM, Fe-Cr-alloys
  • Poster
    Getmat International Workshop, 17.-19.09.2013, Berlin, Deutschland

Publ.-Id: 19124 - Permalink


Nanoindentation of ion-irradiated Fe-Cr alloys
Heintze, C.; Bergner, F.; Hernandez Mayoral, M.;
The structural materials of particular components in nuclear applications like fission or fusion reactors are exposed to high neutron fluxes giving rise to the formation of irradiation-induced defects and subsequent changes of the mechanical properties. Ion-irradiation is a well-recognized tool to simulate damage caused by fast neutron irradiation in a wide range of irradiation temperature and fluence and allows for an efficient screening of potential structural materials for nuclear application due to short irradiation times. The limited depth of penetration of the ions into the material (up to few µm) demands characterization methods suitable for thin layers. In the present work, nanoindentation is applied to deduce the irradiation-induced hardness changes. The approach is based on the generation of an approximately rectangular dpa-profile by means of multi-step irradiations with ions of different energies and the exploitation of the depth dependence of the hardness. Results will be reported for ferritic/martensitic Cr-steels considered as candidate structural materials for future application in Generation IV fission reactors and for Fe-Cr binary alloys with emphasis on the effect of irradiation temperature and fluence. Transmission electron microscopy results on the formation of irradiation-induced defects will be taken into account.
Keywords: ion-irradiation, nanoindentation, TEM, Fe-Cr-alloys
  • Poster
    Nano Measure 2013, 25.-26.06.2013, Warsawa, Polska

Publ.-Id: 19123 - Permalink


On the homogenization of the thickness of Cu deposits by means of MHD convection within small dimension cells
Mühlenhoff, S.; Mutschke, G.; Uhlemann, M.; Yang, X.; Odenbach, S.; Fröhlich, J.; Eckert, K.;
The influence of magnetohydrodynamic (MHD) convection on the thickness of an electrochemically deposited copper layer along a vertical plane cathode is examined. A magnetic gradient field, that induces a Lorentz force, establishes a vortical motion of the electrolyte which can be oriented either antiparallel or parallel to the natural convection. For the latter case, we show both experimentally and numerically that a sufficiently strong Lorentz force levels the inhomogeneities of the deposit thickness characteristic for deposition under pure natural convection.
Keywords: electrochemical deposition, magnetoelectrochemistry, Lorentz force, forced convection, mass transport, MHD

Publ.-Id: 19122 - Permalink


Growth of carbon-tungsten nanocomposites by high power impulse magnetron sputtering from compound targets
Yadav, R. K.; Abrasonis, G.; Munnik, F.; Heller, R.; Hübner, R.; Möller, W.; Neidhardt, J.;
High-power impulse magnetron sputtering (HiPIMS, also known as high-power pulsed magnetron sputtering, HPPMS) is a method for physical vapour deposition of thin lms which is based on magnetron sputter deposition. HiPIMS utilises extremely high power densities of the order of kW cm-2 in short pulses (impulses). A distinguishing feature of HiPIMS is its high degree of ionization of the sputtered metal and high rate of molecular gas dissociation. In this poster we present the study on the growth of C-W nanocomposite lms grown in DC (MS) and HiPIMS modes. For deposition, we have used 3 in C and C-W (90 to 10 at%) substrates. In order to prevent arcing, the depositions were carried out with three-pulse sequence followed by a long off-time. Film areal density was determined by Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA). Film microstructure was determined by Raman spectroscopy, X-Ray diraction, and transmission electron microscopy. Film mechanical properties were studied by nanoindentation and scratch test. We got extensive arcing with pure carbon. In contrast, for the compound target we got stable plasma condition with duty cycle as low as 1 %. Deposited films consist of WC nanoparticles embedded in a carbon matrix. From NRA and RBS, the film areal density of tungsten shows a small decrease concomitantly with the duty cycle (transition from pulsed DC to HiPIMS). In contrast, the film areal density of carbon remains constant. This implies that in different sputtering modes like Ar + dominated in the pulsed DC mode or a mixture of Ar/W ions in the HiPIMS mode the average sputtering rate of carbon is not affected. A collisional computer simulation using TRIDYN was carried out to show a considerable sputter yield amplication of carbon when irradiated with a mixture of Ar/W ions. This is in-line with the observed stable carbon film areal density, which can be attributed to the compensation of the change in sputtering ion composition by sputter yield amplication due to W-enrichment of the target surface. Film characterization shows that there is no signicant change between the films grown in DC and HiPIMS modes.
  • Poster
    537th Wilhelm and Else Heraeus Seminar Physics of Ionized and Ion-Assisted PVD: Principles and Current Trends, 26.-28.06.2013, Dreseden, Deutschland

Publ.-Id: 19121 - Permalink


Optical Selectivity Enhancement of Carbon-based nanocomposites: Simulation and Experiments
Guillén, E.; Heras, I.; Abrasonis, G.; Pardo, A.; Krause, M.; Endrino, J. L.;
Carbon-based metal nanocomposites have been shown to be good material candidates for applications requiring optical selectivity. However their true potential usage largely depends on the optimization of their composition and microstructure. Diamond Like Carbon with different transition metals were grown on stainless steel and Inconel substrates using pulse filtered cathodic arc deposition from two repetitively pulsed cathodic arc sources with separate macroparticle filters. The influence of several transition metals (Ti, Zr, Cr, W, Mo, V and Nb) on their optical selectivity was investigated. Carbon metal-containing samples were prepared using two cathodic arc sources provided with a carbon cathode and a pure transition metal cathode. Different metal concentrations in the coatings were obtained by varying the average arc current of the metal pulsed cathodic arc source (Imetal). The volume fraction of metal was determined by combined Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) measurements. The structure of the deposited films was analyzed by Transmission Electron Microscopy (TEM), X-ray diraction (XRD) and Raman spectroscopy. In this study, the computer simulation program Coating Design (CODE) has been used to calculate optical properties of the different carbon-transition metal nanocomposites. The optical constants of various carbon-based nanocomposites were simulated using a physical model proposed by Bruggeman and Maxwell Garnett which averages the dielectric function of the components of the composite, which allows treating the composite system as an effective medium. The performed simulations allowed calculating the solar absorptance and thermal emittance of the nanocomposites. Varying the nanocomposite material configurations such as layer thickness, volume metal fraction, number of layers and multilayer stack resulted in new configurations that enhance the optical selectivity of these materials. Simulated reflectance was compared with spectrophotometry measurements of the deposited films with good agreement between them.
  • Poster
    537th Wilhelm and Else Heraeus Seminar Physics of Ionized and Ion-Assisted PVD: Principles and Current Trends, 26.-28.06.2013, Dresden, Deutschland

Publ.-Id: 19120 - Permalink


Ion induced compositionally modulated ripples during composite film growth: 3D sculpting at the nanoscale
Abrasonis, G.; Krause, M.; Buljan, M.; Mücklich, A.; Fritzsche, M.; Facsko, S.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.;
Ion irradiation of multielement surfaces can induce regular compositionally modulated surface roughness nanopattern formation such as ripples or nanodots. This kind of bottom-up nanopatterning can provide means to not only structure the solid surfaces but also to create ordered heterogeneous structures in three dimensions (3D) when performed in growth mode: the compositional surface nanopattern is continuously buried by incoming species while the surface is again restructured due to ion irradiation.
The present work is an experimental demonstration of this concept: 3D ordered nanocomposites are grown via ion induced two dimensional (2D, surface) nanopattern formation during bi-component film growth. The influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 30 at.% Ni) thin films will be reported. It will be shown that for certain growth conditions surface ripples form during oblique incidence low energy ion beam assisted deposition of C:Ni films. These surface ripples are compositionally modulated: Ni is located on the crests and carbon in the valleys. The film cross sections show periodic distribution of metal nanoparticles in a carbon matrix with the same periodicity as the surface ripples. As this 3D patterning effect has a physical origin, it can be expected to occur in many material systems. Such an approach holds high potential for the growth of functional nanocomposite films for a wide range of applications.
  • Lecture (Conference)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark

Publ.-Id: 19119 - Permalink


Konzeptioneller Entwurf und prototypische Realisierung einer automatisierten Berichtserstellung für statistische Auswertungen des HZDR
Likerski, A.;
Die vorliegende Arbeit zeigt, wie innerbetriebliche Berichtserstellungsprozesse durch Unterstützung von IT-Systemen verbessert werden können. Im Speziellen geht es dabei um die prototypische Realisierung eines Berichtssystems am Helmholtz-Zentrum Dresden-Rossendorf e.V., wobei es den Mitarbeitern mithilfe des SharePoint-Add-In der Microsoft Reporting Services möglich ist, Berichte im SharePoint zu erstellen und diese dort zu hinterlegen.
Zur Umsetzung dieser Zielstellung wurde zunächst die Ausgangssituation anhand des Geschäftsprozesses sowie die Quelle der benötigten Informationen analysiert, um daraufhin ein entsprechendes Konzept zu erarbeiten. Dabei wurde eine, dem System zur Datenbeschaffung, nachgelagerte Datenbank erstellt, welche zur Sammlung aller berichtsrelevanten Informationen dienen soll und danach, nach vorheriger Beschreibung verschiedener Möglichkeiten, die oben genannte Realisierung ausgewählt wurde.
Im Anschluss daran wurde eine Kosten-Nutzen-Analyse durchgeführt, welche die Vorteile der durchgeführten Teilautomatisierung verdeutlicht.
Keywords: Reporting Services, Reporting
  • Bachelor thesis
    BA Dresden, 2013
    69 Seiten

Publ.-Id: 19118 - Permalink


Special Issue: Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications, Geophysical and Astrophysical Fluid Dynamics, 107, Issue 4 (2013)
Ferriz-Mas, A.; Hollerbach, R.; Stefani, F.; Tilgner, A.; (Editors)
This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.
  • Book (Editorship)
    London, UK: Taylor and Francis, 2013
    98 Seiten

Publ.-Id: 19117 - Permalink


GEANT4 Simulationen zur Optimierung einer Compton Kamera für die In-vivo Dosimetrie
Rohling, H.; Enghardt, W.; Hertel, N.; Kormoll, T.; Pausch, G.; Fiedler, F.;
Fragestellungen: Zur Qualitätssicherung der Partikelbestrahlungen von Tumorpatienten ist eine nicht-invasive, in-vivo Überwachung wünschenswert. Am OncoRay / TU Dresden / HZDR wird zur Zeit ein Prototyp einer Compton Kamera für die klinische Anwendung entwickelt, die eine solche Überwachung anhand der bildgebenden Messung prompter Gammastrahlung ermöglichen soll [1]. Aufgrund der Vielzahl der zu optimierenden Parameter wie Größe, Abstände und Material der Detektoren, zur Analyse der auftretenden Wechselwirkungen und zur Selektion von Ereignissen sind Monte Carlo Simulationen dabei unerlässlich.

Material und Methoden: Die betrachtete Compton Kamera ist aus einer Streuebene (CZT) und einer Absorberebene (CZT oder LSO) aufgebaut (Abb.1). Das Funktionsprinzip einer Compton Kamera basiert auf der Berechnung des Streuwinkels und damit der Eintreffrichtung des Photons mithilfe der gemessenen Energiedepositionen.
Zur Optimierung des Detektorsystems wurden Simulationen mit dem Monte Carlo Code GEANT4 Version 9.5 [2] durchgeführt. Neben der Untersuchung der Zählraten war die Charakterisierung der auftretenden Ereignisse das Ziel dieser Simulationen. Dabei wird eine koinzidente Energiedeposition in beiden Detektorebenen genau dann als nutzbares Ereignis angesehen, wenn in der Streuebene genau eine Compton Streuung und in der Absorptionsebene eine vollständige Absorption des Photons stattfand. Außer einer Punktquelle wurden Emissionen aus einer kugelförmigen Quelle mit 10 cm Durchmesser simuliert. Verschiedene Abstände des Detektors zur Quelle sowie unterschiedliche Anordnungen von Streuebene zur Absorptionsebene wurden angenommen. Des Weiteren wurden die Simulationen mit experimentellen Daten verglichen. Ferner wurde der Fehler, der durch die Abweichung zwischen simuliertem Schwerpunkt, der dem experimentellen Messpunkt nahe kommt, und dem Ort der Comptonstreuung im Streuer bzw. der Einfallsrichtung im Absorber untersucht.

Ergebnisse: Die Konfiguration aus CZT und LSO weist erwartungsgemäß eine höhere Ansprechwahrscheinlichkeit als der CZT-CZT Detektor auf (Abb.2), außerdem ist die Rate an nutzbaren Ereignissen deutlich höher (Abb.3). Die Abstände zwischen den Detektorebenen und der Abstand zur Quelle haben kaum Einfluss auf die Güte der Ereignisse. Eine Selektion von Ereignissen zur Minimierung des Rauschens anhand der Wechselwirkungstiefe in der Streuebene erscheint sinnvoll.

Zusammenfassung: Es wurden umfassende Simulationen mit GEANT4 zur Bewertung und Optimierung von möglichen Compton Kamera Systemen durchgeführt. Um die Güte der Simulationen zu bewerten wurden die Simulationsergebnisse mit experimentellen Daten verglichen.

Literatur

[1] Kormoll, T.: A Compton Camera for In-vivo Dosimetry in Ion-beam Radiotherapy. Diss.,
Technische Universität Dresden, Mathematik und Naturwissenschaften. Dresden, 2013

[2] Agostinelli, S. et al 2003 GEANT4 - a simulation toolkit Nucl. Instr. Meth. A 506(3) 250-303
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland
  • Abstract in refereed journal
    Medizinische Physik 2013 (2013), 710

Publ.-Id: 19116 - Permalink


Introduction
Ferriz-Mas, A.; Hollerbach, R.; Stefani, F.; Tilgner, A.;
This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.

Publ.-Id: 19115 - Permalink


Radio-colouration of diamond: a spectroscopic study
Nasdala, L.; Grambole, D.; Wildner, M.; Gigler, A. M.; Heinschwang, T.; Zaitsev, A. M.; Harris, J. W.; Milledge, J.; Schulze, D. J.; Hofmeister, W.; Balmer, W. A.;
We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with a parts per thousand yen10(15) He ions per cm(2). The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 x 10(-3) (-3) (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 A degrees C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of similar to 2.4 +/- A 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10(-6) (-3) (or 0.000006 dpa) and is suppressed at moderate defect densities of similar to 5 x 10(-4) (-3) (or similar to 0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 A degrees C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.
Keywords: Diamond; Radiation damage; Radiocolouration; Defect luminescence; Volume swelling

Publ.-Id: 19114 - Permalink


Energetic ion-assisted nanocomposite film growth: sculpting matter in 3D at the nanoscale
Abrasonis, G.;
Nanostructures dramatically influence materials properties due to size, shape and interface effects. Thus the control over the structure at the nanoscale is a key issue in nanomaterials science. The growth of nanostructured thin films is governed by the atomistic processes at the very surface of the growing film. The interaction range of hyperthermal ions with solid surface is confined to some nanometers. Therefore energetic ion assistance during film deposition is of primary relevance in the context of the thin film nanostructuring.
Our recent activities in the field of ion-assisted physical vapor deposition (PVD) of nanocomposite films will be summarized with the focus on the growth-structure relationship of carbon-transition metal films. This class of materials is relevant in the context of tribology, sensing, fusion, electrochemistry, information storage, spintronics, solar-thermal energy conversion or as metamaterials. We have employed two paradigms involving the use of energetic ions:
• ion assisted PVD (ia-PVD), where the growing film is irradiate with assisting ion beam
• ionized PVD (i-PVD), where the depositing species are energetic ions themselves.
The nanocomposite film growth is determined by surface diffusion assisted phase separation of immiscible species adsorbed from homogeneous mixture in the vapor phase. Ion irradiation intervenes with the interplay of thermodynamic forces and kinetic constraints as a third competing factor and has a dramatic effect on the film morphology. A large variety of structures is observed such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays (see Fig 1.). In addition, the ion induced atomic mobility is not isotropic, as it would be in the case of thermally excited migration, but conserves to a large extent the initial direction of the incoming ions. Independently of the growth regime, it results in the morphology tilt: metal nanopatterns no longer align with the advancing surface but with the incoming ions. Such effects allow 3D sculpting of nanocomposites which is due to ion irradiation effects and does not require any glancing incidence conditions.
As the observed effects are of physical origin (ion-solid interactions), we believe that the presented results are applicable to other immiscible or partially miscible systems as well. This presents a possible path towards a material design approach based on material system independent tools to sculpt the morphology at the nanoscale in order to match the requirements of a wide range of applications.
  • Invited lecture (Conferences)
    2013 Energy Materials Nanotechnology (ENM Spring), 08.-11.04.2013, Orlando, United States of America

Publ.-Id: 19113 - Permalink


Advanced Solar Absorber Coatings Based on Nanocomposites
Heras, I.; Escobar Galindo, R.; Abrasonis, G.; Pardo, A.; Vinnichenko, M.; Endrino, J. L.;
The design of an efficient and stable solar selective coating for photo-thermal conversion plants requires a complex study of the materials that composed the coating. The optimal optical properties for those absorber coatings are high solar absorptance in the wavelength range of 0.3 to 2.5 μm which corresponds to solar spectrum under atmospheric conditions and low thermal emittance in the infrared wavelength range.
Carbon-transition metal nanocomposites have been selected as absorber materials because they show appropriate optical properties as well as thermal and mechanical stability at high temperatures. The refractory metal carbide nanoparticles have been experimentally shown to stabilize the surrounding carbon matrix at least up to 700°C.
The computer simulation program CODE has been used to calculate solar absorptance and thermal emittance of various multilayers coatings material combinations of carbon - metal nanocomposites (NCTM). The optical properties of the inhomogeneous composite material were simulated with a physical model proposed by Bruggeman and Maxwell Garnett which average the dielectric function of the components of the composite. This allows treating the composite system as an effective medium.
This contribution compares simulated optical properties for different nanocomposite structural configurations (layer thickness, metal to carbon ratio). The calculated results are in the range of 0.91-0.97 for solar absorptance and 0.02 - 0.07 for thermal emittance at 300K.
  • Poster
    2013 MRS Spring Meeting & Exhibit, 01.-05.04.2013, San Francisco, CA, United States of America

Publ.-Id: 19112 - Permalink


Ion Assistance Effects on the Morphology of Carbon-Nickel Composite Films Grown by Physical Vapor Deposition at Various Metal Contents
Abrasonis, G.; Krause, M.; Muecklich, A.; Baehtz, C.; Shalimov, A.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Gemming, S.;
Phase separation occurring on the surface of growing films provides unique means to influence the microstructure of composite materials. Here, the influence of ion assistance on the morphology of carbon-nickel nanocomposite thin films for different metal contents is investigated. Carbon-transition metal nanocomposites are relevant in the context of solar-thermal energy conversion, fusion, fuel cells, tribology or sensing. The films were grown by dual ion beam sputtering in a temperature range of RT-300°C. The growing films were irradiated by an assisting Ar ion beam with energies ranging from 50 to 130 eV. It is found that the nickel content drastically influences the morphology of the films: while films with low Ni contents show regular self-organized structures consisting of ordered Ni nanoparticles embedded in the carbon matrix, higher Ni contents predominantly exhibit a columnar morphology. The results are discussed on the basis of the interplay of ion-induced effects and phase separation modes.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379 is gratefully acknowledged.
  • Lecture (Conference)
    2013 MRS Spring Meeting & Exhibit, 01.-05.04.2013, San Francisco, CA, United States of America

Publ.-Id: 19111 - Permalink


Interference effects in super-radiant THz sources
Asgekar, V.; Geloni, G. A.; Kocharyan, V.; Stojanovice, N.; Michel, P.; Gensch, M.;
A new class of linear accelerator (linac) based THz facilities, aiming to provide peak THz fields in the GV/m regime from highly charged, ultra-short relativistic electron bunches is currently studied and developed worldwide. These facilities are based on low emittance, electron beams delivered by a linear radio frequency (RF) driven accelerator followed by one or several magnetic chicanes that act as bunch compressor. THz radiation is then emitted coherently for wavelengths appropriately longer than the longitudinal electron bunch length upon one single pass through any of the typical sources of synchrotron radiation. This allows for an enormous flexibility in the generated spectral, spatial and temporal properties of the THz pulses. Together with the theoretically large scalability and simplicity of these sources, they are discussed as extension of the THz pulses from laser-based THz sources towards extreme transient THz fields and high repetition rates with more than 10 projects currently being pursued worldwide. In this respect it is timely to investigate if current idealized theoretical descriptions can be technically fully realized. As our contribution to this effort, in this paper it is shown by numerical and analytical calculations that the interference effects between different THz radiators, intrinsically emitting in the forward direction of a linac can crucially affect radiation properties.
Keywords: super-radiant THz sources, coherent THz sources

Publ.-Id: 19110 - Permalink


Multiphase CFD @ HZDR - Strategy and research topics of the CFD department
Lucas, D.; Montoya, G.;
CFD Workshop about the different projects and modelling strategies inside the Computational Fluid Dynamics Department of the Institute of Fluid Dynamics of HZDR, along with a brief introduction of other different institutes such as Resource Ecology, Material Research, Cancer Research, among others.
Keywords: CFD, HZDR, Fluid Dynamics, Workshop
  • Invited lecture (Conferences)
    21st International Conference on Nuclear Engineering (ICONE21), 29.07.-02.08.2013, Chengdu, China

Publ.-Id: 19109 - Permalink


Comparison of PHITS, GEANT4, and HIBRAC simulations of depth-dependent yields of beta+-emitting nuclei during therapeutic particle irradiation to measured data
Rohling, H.; Sihver, L.; Priegnitz, M.; Enghardt, W.; Fiedler, F.;
For quality assurance in particle therapy, a non-invasive, in-vivo range verification is highly desired. Particle Therapy Positron-Emission-Tomography (PT-PET) is the only clinically proven method up to now for this purpose. It makes use of the beta+-activity produced during the irradiation by the nuclear fragmentation processes between the therapeutic beam and the irradiated tissue. Since a direct comparison of beta+-activity and dose is not feasible, a simulation of the expected beta+-activity distribution is required. For this reason it is essential to have a quantitatively reliable code for the simulation of the yields of the beta+-emitting nuclei at every position of the beam path. In this paper results of the three-dimensional Monte-Carlo simulation codes PHITS, GEANT4, and the one-dimensional deterministic simulation code HIBRAC are compared to measurements of the yields of the most abundant beta+-emitting nuclei for carbon, lithium, helium, and proton beams. In general, PHITS underestimates the yields of positron-emitters. With GEANT4 the overall most accurate results are obtained. HIBRAC and GEANT4 provide comparable results for carbon and proton beams. HIBRAC is considered as a good candidate for the implementation to clinical routine PT-PET.

Publ.-Id: 19108 - Permalink


Review of effects of radiation damage on the luminescence emission of minerals, and the example of He-irradiated CePO4
Nasdala, L.; Grambole, D.; Ruschel, K.;
The accumulation of structural damage that is created in minerals upon corpuscular irradiation, has two apparently contrarious effects on their luminescence behaviour. First, irradiation may cause the generation of luminescent defect centres, which typically results in broad-band emissions. Such defect emissions are characteristic of low levels of radiation damage. Second, radiation damage depletes in general the luminescence of minerals, which is associated with broadenings and intensity losses of individual emission lines. Minerals that have suffered elevated levels of irradiation hence tend to be virtually non-luminescent. This review paper aims at giving an overview of the possible correlations of radiation damage and emission characteristics of minerals. After a brief, introductory summary of the damage-accumulation process and its causal corpuscular radiation, an array of examples is presented for how internal and/or external irradiation may change appreciably the emission of rock-forming and accessory minerals. As a detailed example for the complexity of changes of emissions upon damage accumulation, preliminary results of a case study of the photoluminescence (PL) of synthetic CePO4 irradiated with 8.8 MeV He ions are presented. Irradiation-induced spectral changes include (i) the initial creation, and subsequent depletion, of a broad-band, defect-related PL emission of orange colour, and (ii) gradual broadenings and intensity losses of PL lines related to electronic transitions of rare-earth elements, eventually leading to gradual loss of their splitting into multiple Stark levels (shown for the 4F3/2 → 4I9/2 transition of Nd3+).

Publ.-Id: 19107 - Permalink


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