Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Das prätherapeutische hypoxische Tumorvolumen und nicht der SUVmax hat eine prognostische Wertigkeit im F18-MISO-PET für die Heilungswahrscheinlichkeit nach Einzeitbestrahlung im Tiermodell
Beuthien-Baumann, B.; Schütze, C.; Bergmann, R.; Yaromina, A.; Hessel, F.; Mäding, P.; Krause, M.; Zips, D.; Baumann, M.;
Untersuchung zur prognostischen Wertigkeit von F18-Misonidazol-PET (F18-MISO) bezüglich der Heilungswahrcheinlichkeit im Tumor-Xenograft-Model des humanen Plattenepithel-Karzionms (hSCC) FaDu auf Nacktmäusen vor Einzeitbestrahlung.

Das humane Plattenepithel-Karzinom wurde subcutan auf das Hinterbein von 70 Nacktmäusen transplantiert. Bei einem Tumordurchmesser von 7-9mm wurde eine F18-MISO-PET (11MBq i.v., Micro-PET P4, CTI Molecular Imaging Inc., gemessene Schwächungskorrektur, Emission in Anaesthesie über 30min ab 210min p.i.) durchgeführt. Die Auswertung erfolgte mittels 3D-regions of interest über dem Tumor ("ROIFinder automatic mode", ROVER software ABX Radeberg, Germany). Bestimmt wurden das hypoxische Volumen (HV) und der maximale standard uptake value (SUVmax). Nach dem PET wurde eine Einzeitbestrahlung von 25 Gy oder 35 Gy unter normalem Blutfluß appliziert (200 kV Röntgenstrahlung, 0,5mm Cu, ca. 1,2 Gy/min). Der Studienendpunkt waren lokale Tumorkontrolle bzw. Zeitpunkt des Rezidivs.

Tumorkontrollraten nach 25 Gy waren geringer als nach 35 Gy (22% versus 69%, log rank p<0,0001). Der mediane SUVmax betrug 2,54 (range: 0,19-6,83). Das HV reichte von 38 mm3 bis 353 mm3 (median 112 mm3, 95%CI: 92-128 mm3). In Tumoren mit einem HV geringer als dem Median betrug die Tumorkontrolle 33% nach 25 Gy und 82% nach 35 Gy. In Tumoren mit einem HV größer als dem Median betrug die Tumorkontrolle 15% nach 25 Gy und 53% nach 35 Gy. In der multivariaten COX Analyse ergab sich nach Korrektur für Dosis und Tumorvolumen eine signifikante prognostische Aussage bezüglich des HV für die Tumorkontrolle. Die Bestrahlungsdosis hatte einen signifikanten Einfluß auf die Rezidivwahrscheinlichkeit (p<0,0005), das Tumorvolumen und der SUVmax waren bezüglich der Prognose der Heilungswahrscheinlichkeit nicht relevant.

Das F-18-MISO HV ist eine signifikanter Prädiktor für das outcome nach Bestrahlung mit hoher Einzeldosis im FaDu hSCC Tumormodell in der Nacktmaus. Von der Intensität der F18-MISO-Anreicherung, gemessen als SUVmax, konnte in dieser Studie keine prognostische Aussage abgeleitet werden.

Diese Arbeit wurde im 6.EU-Rahmenprogrammes Projekt BioCare proposal#505785 durchgeführt.
  • Lecture (Conference)
    47. Jahrtestagung der Deutschen Gesellschaft für Nuklearmedizin, 22.-25.04.2009, Leipzig, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 48(2009)2, A16

Publ.-Id: 12634 - Permalink

An Investigation of Target Poisoning during Reactive Magnetron Sputtering
Güttler, D.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-515 2009


Publ.-Id: 12633 - Permalink

Highly dense amorphous Nb2O5 films with closed nano-sized pores
Vinnichenko, M.; Rogozin, A.; Grambole, D.; Munnik, F.; Kolitsch, A.; Möller, W.; Stenzel, O.; Wilbrandt, S.; Chuvilin, A.; Kaiser, U.;
This study is focused on tailoring Nb2O5 film porosity during reactive pulsed magnetron sputtering. Dense amorphous films with closed nanopores have been formed onto unheated substrates at high growth rates. The films have a high refractive index n_400=2.54, a low extinction coefficient, k_400~6x10-4, a low mechanical stress (-90 MPa) and a negligible thermal shift. The specific depth distribution of the nanopores is believed to be the reason for the high film density combined with a low mechanical stress.
Keywords: reactive pulsed magnetron sputtering, high refractive index materials, Nb2O5, nano-sized pores, optical properties
  • Applied Physics Letters 95(2009), 081904-1-081904-3
    DOI: 10.1063/1.3212731
  • Lecture (Conference)
    EMRS Spring Meeting, 08.-12.06.2009, Strasbourg, France

Publ.-Id: 12632 - Permalink

Interlayer Exchange Coupling of Fe/Cr/Fe Thin Films on Rippled Substrates
Körner, M.; Lenz, K.; Liedke, M. O.; Strache, T.; Mücklich, A.; Keller, A.; Facsko, S.; Fassbender, J.ORC
The influence of rippled vs. flat Si substrates on the interlayer exchange coupling of polycrystalline Fe/Cr/Fe thin films is studied. The rippled substrates with ripple wavelengths of 22 and 37 nm where created by means of ion beam erosion. Using lambda=22 nm ripple substrates we find a Néel coupling superimposed on the interlayer exchange coupling in Fe/Cr/Fe trilayers associated with a strong uniaxial anisotropy induced by the substrate topography. These results are obtained by applying a Stoner-Wolfarth model on magnetic reversal loops obtained via longitudinal magneto-optical Kerr effect magnetometry.
Keywords: Interlayer Exchange Coupling Magneto-optical Kerr effect Rippled Substrates Néel coupling

Publ.-Id: 12631 - Permalink

Modelling of polydispersed flows using two population balance approaches
Cheung, S. C. P.; Duan, X.; Yeoh, G. H.; Tu, J.; Krepper, E.; Lucas, D.;
Polydispersed bubbly flows with wide range of bubble size are commonly encountered in many industrial fields. The use of population balance models coupled with the two-fluid model presents the most viable way of handling such complex flow structures. The main focus of this paper is to access the capabilities of two population balance models – namely Average Bubble Number Density (ABND) and Inhomogeneous MUlti-SIze-Group (MUSIG) model; in resolving the dynamical changes of void fraction and bubble size distribution under polydispersed flow conditions. Numerical predictions are validated against two polydispersed flow measurements. Special attentions are directed towards the performance of the two models in capturing the behavioral transition of “wall peak” to “core peak” void fraction profile. Applicability and drawbacks of the two population balance models for industrial applications are also discussed.
Keywords: Population balance, Turbulence, Polydispersed, Bubbly flow, ABND
  • Contribution to proceedings
    6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion, 11.-15.07.2009, Xi’an, China
  • Lecture (Conference)
    6th International Symposium on Multiphase Flow, Heat Mass Transfer and Energy Conversion, 11.-15.07.2009, Xi’an, China

Publ.-Id: 12630 - Permalink

Toward physical modeling of laser welding: thermophysics revisited
Cramer, A.; Lange, A.; Plevachuk, Y.; Sklyarchuk, V.;
Experimental determination of the thermophysical properties conductivity, viscosity, and surface tension of lithium iodide was carried out in the temperature range starting slightly above the melting point and up to about 950~K. These measurements are motivated by the search for a transparent substance, the Prandtl number Pr of which approaches or is even less than unity, and which shows a stable Marangoni effect with respect to a potential pollution of the melt. Such a combination of material properties is mandatory in the attempt of a physical modelling of laser welding processes where optical access to the bulk of the fluid is needed in order to measure the flow field. In an extension to these basic studies, also the electrical conductivity and the influence of the admixture of other iodides on Pr was studied exemplarily.
Keywords: Electrical conductivity, Lithium iodide, Prandtl number, Surface tension, Thermal conductivity, Viscosity

Publ.-Id: 12629 - Permalink

Clusters in Cobalt implanted Boron pre-doped ZnO
Mücklich, A.; Potzger, K.;
Clusters in Cobalt implanted Boron pre-doped ZnO
Keywords: diluted magnetic semiconductor, structural characterization
  • Poster
    Microscopy Conference 2009, 30.08.-04.09.2009, Graz, Österreich

Publ.-Id: 12628 - Permalink

Thermodynamics and Structure of Actinide(IV) Complexes with Nitrilotriacetic Acid
Bonin, L.; Guillaumont, D.; Jeanson, A.; Den Auwer, C.; Grigoriev, M.; Berthet, J.-C.; Hennig, C.; Scheinost, A.; Moisy, P.;
Nitrilotriacetic acid, commonly known as NTA (N(CH2CO2H)3), can be considered a representative of the polyaminocarboxylic family. The results presented in this paper describe the thermodynamical complexation and structural investigation of An(IV) complexes with NTA in aqueous solution. In the first part, the stability constants of the An(IV) complexes (An ) Pu, Np, U, and Th) have been determined by spectrophotometry. In the second part, the coordination spheres of the actinide cation in these complexes have been described using extended X-ray absorption fine structure spectroscopy and compared to the solid-state structure of (Hpy)2[U(NTA)2] · (H2O). These data are further compared to quantum chemical calculations, and their evolution across the actinide series is discussed. In particular, an interpretation of the role of the nitrogen atom in the coordination mode is proposed. These results are considered to be model behavior of polyaminocarboxylic ligands such as diethylenetriamine pentaacetic acid, which is nowadays the best candidate for a chelating agent in the framework of actinide decorporation for the human body.
Keywords: Nitrilotriacetic acid, UV-Vis , XRD, EXAFS

Publ.-Id: 12627 - Permalink

Numerical study on population balance approaches in modeling of isothermal vertical bubbly flows
Cheung, C. P.; Yeoh, G. H.; Tu, J. Y.; Krepper, E.; Lucas, D.;
Practicing engineers are constantly confronted with the prospect of solving complex gas-liquid bubbly flow problems in real industrial systems. The use of population balance models coupled with the two-fluid model presents the most viable way of handling such flows. The homogeneous MUltiple-SIze-Group (MUSIG) model has recently become a widely adopted population balance approach whereby the continuous bubbles size range can be represented by a series of discrete classes. The improved inhomogeneous MUSIG model extends the capability of accounting different bubble shapes and travelling gas velocities. Conversely, the Average Bubble Number Density (ABND) model represents another simpler approach in handling bubble interactions in complex gas-liquid bubbly flow. The capability of these three population balance models is assessed. Particular emphasis is directed towards the possible handling of bubbly-to-slug transition flow conditions. Numerical predictions are compared against experimental data obtained from Lucas et al. [1] and Hibiki et al. [2]. Shortcomings and applicability of these models for industrial applications are also discussed.
Keywords: CFD, Multiphase flows, population balance
  • Contribution to proceedings
    The 5th International Conference on Computational Fluid Dynamics, ICCFD5, 07.-11.07.2008, Seoul, Korea
  • Lecture (Conference)
    The 5th International Conference on Computational Fluid Dynamics, ICCFD5, 07.-11.07.2008, Seoul, Korea

Publ.-Id: 12626 - Permalink

Photoluminescensia plenok Si3N4 implantirovannich ionami Ge+ i Ar+
in Russian
Tyschenko, I. E.; Volodin, V. A.; Rebohle, L.; Voelskow, M.; Skorupa, W.;
Spektri emissii i wosbuschdenia photoluminescencii pri komnatnoi temperature plenok Si3N4 implantirovannich plenok Ge+ i Ar+, issledovanui v savisimosti ot dosui ionov i temperaturui posledujuschego otschiga.
Keywords: photoluminescence Si3N4 ion implantation annealing
  • Fizika i Tekhnika Poluprovodnikov 33(1999)5, 559-566

Publ.-Id: 12625 - Permalink

Experimental investigations on air entrainment by means of impinging jets
Danciu, D. V.; Da Silva, M. J.; Schmidtke, M.; Lucas, D.;
The phenomenon of air entrainment as a result of an impinging water jet was experimentally studied by means of videometry and image processing methods. A series of experiments at different conditions was performed and evaluated. Each experiment consisted of a 10s recorded sequence with a frequency of 200Hz. Jet lengths varied between 0.01m and 0.2m and jet exit velocities ranged between 0.8m/s and 2.5m/s. Image processing algorithms were applied to extract information about jet penetration depth, width of the bubble plume and bubble size distribution. Therefore, images were subdued to background subtraction, binarization and averaging. Bubble sizes were estimated from single images by subsequent background subtraction, cell segmentation, bubble detection and bubble size calculation by means of a Hough-transform based algorithm. It was found that the bubble sizes were in accordance to the data present in the literature. The penetration depth of the plume was compared to an empirical formula presented by Bin in the literature. It was established that in addition to the impact velocity, the amount of entrained gas has a significant effect on the penetration depth.
Keywords: air entrainment, impinging jet, image processing, penetration depth, bubble size
  • Contribution to proceedings
    ExHFT-7, 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland
    ExHFT-7 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics 28 June - 03 July 2009, Krakow, Poland Proceedings, ISBN 978-83-7464-235-4, 761-768
  • Lecture (Conference)
    ExHFT-7, 28.06.-03.07.2009, Krakow, Polen

Publ.-Id: 12624 - Permalink

Development and validation of a Multifield Model of churn-turbulent gas/liquid flows
Tselishcheva, E. A.; Antal, S. P.; Podowski, M. Z.; Post Guillen, D.; Beyer, M.; Lucas, D.;
The accuracy of numerical predictions for gas/liquid two phase flows using Computational Multiphase Fluid Dynamics (CMFD) methods strongly depends on the formulation of models governing the interaction between the continuous liquid field and bubbles of different sizes. The purpose of this paper is to develop, test and validate a multifield model of adiabatic gas/liquid flows at intermediate gas concentrations (e.g., churn turbulent flow regime), in which multiple-size bubbles are divided into a specified number of groups, each representing a prescribed range of sizes. The proposed modeling concept uses transport equations for the continuous liquid field and for each bubble field. The overall model has been implemented in the NPHASE-CMFD computer code. The results of NPHASE-CMFD simulations have been validated against the experimental data from the TOPFLOW test facility. Also, a parametric analysis on the effect of various modeling assumptions has been performed.
Keywords: Computational Multiphase Fluid Dynamics, adiabatic gas/liquid flows, churn turbulent flow regime, transport equations, NPHASE-CMFD, TOPFLOW test facility
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering (ICONE-17), 12.-16.07.2009, Brussels, Belgium
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering (ICONE-17), 12.-16.07.2009, Brussels, Belgium

Publ.-Id: 12623 - Permalink

Formirovanie zentrov photolumineszensii pri otschige sloev SiO2 implantirovannich ionami Ge
in Russian
Kachurin, G. A.; Rebohle, L.; Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.; Skorupa, W.; Fröb, H.;
Metodami photolumineszensii, kombinirovannove rassejania i spektroskopii obratnogo rasseania alpha tschastiz issledovano formirovanie zentrov rekombinationnogo uslutschenia pri otschige sloev SiO2, implantirovannich ionami Ge.
Keywords: photoluminescence ge ion implantation SiO2 annealing
  • Fizika i Tekhnika Poluprovodnikov 34(2000)1, 23-27
  • Semiconductors 34(2000)1, 21-26

Publ.-Id: 12622 - Permalink

Experimental investigation on air entrainment below impinging jets by means of video observations and image processing
Danciu, D. V.; Da Silva, M. J.; Schmidtke, M.; Lucas, D.; Hampel, U.;
Air entrainment as a result of a water jet plunging into a pool of water was studied by means of visualization techniques. Image processing algorithms were used to analyze the recorded sequences of the phenomenon. Data regarding the penetration depth and bubble size distribution was gathered for different jet impact velocities and jet lengths. The accumulated results are further used to validate the models implemented in computational fluid dynamics (CFD) codes.
Keywords: air entrainment, plunging jet, penetration depth, image processing, bubbles size distribution
  • Contribution to proceedings
    Multiphase Flow 2009 Fifth International Conference on Computational and Experimental Methods in Multiphase and Complex Flow, 15.-17.06.2009, New Forest, England
    Computational Methods in Multiphase Flow V: WIT Press, ISSN 1743-3533, 481-491
  • Lecture (Conference)
    Multiphase Flow 2009 Fifth International Conference on Computational and Experimental Methods in Multiphase and Complex Flow, 15.-17.06.2009, New Forest, England

Publ.-Id: 12621 - Permalink

Optimization of a two-fluid hydrodynamic model of churn turbulent flow
Post Guillen, D.; Shelley, J. K.; Antal, S. P.; Tselishcheva, E. A.; Podowski, M. Z.; Lucas, D.; Beyer, M.;
A hydrodynamic model of two-phase, churn-turbulent flows is being developed using the computational multiphase fluid dynamics (CMFD) code, NPHASE-CMFD. The numerical solutions obtained by this model are compared with experimental data obtained at the TOPFLOW facility of the Institute of Safety Research at the Forschungszentrum Dresden-Rossendorf. The TOPFLOW data is a high quality experimental database of upward, co-current air-water flows in a vertical pipe suitable for validation of computational fluid dynamics (CFD) codes. A five-field CMFD model was developed for the continuous liquid phase and four bubble size groups using mechanistic closure models for the ensemble-averaged Navier-Stokes equations. Mechanistic models for the drag and non-drag interfacial forces are implemented to include the governing physics to describe the hydrodynamic forces controlling the gas distribution. The closure models provide the functional form of the interfacial forces, with user defined coefficients to adjust the force magnitude. An optimization strategy was devised for these coefficients using commercial design optimization software. This paper demonstrates an approach to optimizing CMFD model parameters using a design optimization approach. Computed radial void fraction profiles predicted by the NPHASE-CMFD code are compared to experimental data for four bubble size groups.
Keywords: CFD validation, churn turbulent flow, two-fluid model, design optimization, NPHASE-CMFD, multiphase flow
  • Contribution to proceedings
    17th International Conference on Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium
    Optimization of a two-fluid hydrodynamic model of churn turbulent flow
  • Lecture (Conference)
    17th International Conference on Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium

Publ.-Id: 12620 - Permalink

A new model for bubble coalescence and breakup in poly-disperse bubbly flows
Liao, Y.; Lucas, D.;
A basis model was proposed in this work, which considers bubble coalescence and breakup due to different mechanisms, including coalescence due to turbulence, laminar shear, wake entrainment and eddy capture, and breakup due to turbulent fluctuation, laminar shear and interfacial slip velocity. The basis model was implemented into an efficient 1D Test Solver, which is developed specially for bubbly flows in a round vertical pipe. For the first step, the new model was validated with the high quality experimental data for the case of air-water mixtures, which were obtained at the TOPFLOW facility. Simulation results showed that at relatively low superficial gas velocities, the initial bubble size was small and had a narrow distribution, and coalescence dominates the evolution; with the increase in the superficial gas velocity, large bubbles appear near injection position, and result in a much wider bubble size distribution, and breakup became predominant. The radial air volume fraction was redistributed from the injection position at wall to the whole cross section, and the stable peak remains near the wall for small bubbles while migrating towards the pipe centre for large bubbles. The comparison of simulation results with experimental data showed encouraging agreements, which affirmed the feasibility and capability of the basis model and indicated also the requirements for adjustments and improvements.
Keywords: Basis Model, Air-Water Bubbly Flow, Bubble Coalescence and Breakup, TOPFLOW facility
  • Contribution to proceedings
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa City, Ishikawa Prefecture, Japan
  • Lecture (Conference)
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa City, Ishikawa Prefecture, Japan

Publ.-Id: 12619 - Permalink

Condensation of Steam Bubbles Injected into Sub-Cooled Water
Lucas, D.; Beyer, M.; Frank, T.; Zwart, P.; Burns, A.;
Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. In a previous work a simplified test solver, developed especially to test models for vertical pipe flow was used to simulate these effects. Now the results will be transferred to the CFD code CFX from ANSYS. Recently the Inhomogeneous MUSIG model was implemented into the code enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Now an extension of the model is proposed to include the effects due to phase transfer. The paper discusses the necessary extensions of the Inhomogeneous MUSIG model and presents the new experimental setup for the investigation on steam bubble condensation.
Keywords: two-phase flow, condensation, bubble, CFD
  • Contribution to proceedings
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), Paper N13P1097, 27.09.-02.10.2009, Kanazawa City, Japan
  • Lecture (Conference)
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa City, Japan

Publ.-Id: 12618 - Permalink

Lipid Protein Interactions Couple Protonation to Conformation in a Conserved Cytosolic Domain of G-Protein-Coupled Receptors
Madathil, S.; Fahmy, K.;
The visual photoreceptor rhodopsin is a prototypical class-I (rhodopsin-like) G protein-coupled receptor (GPCR). Photoisomerization of the covalently bound ligand 11-cis-retinal leads to restructuring of the cytosolic face of rhodopsin. The ensuing protonation of Glu-134 in the class-conserved D(E)RY motif at the C-terminal end of transmembrane helix-3 promotes the formation of the G-protein-activating state. Using transmembrane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch". Infrared- and fluorescence-spectroscopic pKa determinations reveal that the D(E)RY motif is an autonomous functional module coupling side chain neutralization to conformation and helix positioning as evidenced by side chain to lipid headgroup Förster-resonance-energy-transfer. The free enthalpies of helix stabilization and hydrophobic burial of the neutral carboxyl shift the side chain pKa into the range typical of Glu-134 in photoactivated rhodopsin. The lipid-mediated coupling mechanism is independent of interhelical contacts allowing its conservation without interference with the diversity of ligand-specific interactions in class-I GPCRs.
Keywords: membrane, lipids, infrared, fluorescence, GPCR, biophysics
  • Journal of Biological Chemistry 284(2009)42, 28801-28809

Publ.-Id: 12617 - Permalink

Uranium accumulation and tolerance in Arabidopsis halleri under native versus hydroponic conditions
Viehweger, K.; Geipel, G.;
Comparisons of uranium (U) accumulation and tolerance were conducted in terrestrial versus laboratory trials using an endemic, on a former U mining site growing Arabidopsis halleri.
Sequential extractions combined with ICP-MS measurements were used for determining the soil content of different metals and the U accumulation in plants, respectively. Root elongation tests, investigations of photosynthetic traits via absorption and fluorescence spectroscopy enabled estimations of U tolerance.
Hydroponically grown plants accumulated 100 fold more U in roots and 10 fold more in shoots compared with plants growing in their native habitat. Despite this elevated U uptake, the root elongation was not affected. However, impairments of the photosynthetic machinery could clearly be proven.
These facts are important indications for a pronounced decreasing U tolerance under laboratory conditions. The occasional different bioavailability of U and essential metals such as iron in the two approaches is one of the key factors affecting U accumulation, transport, tolerance or toxicity development. The described “uranophyte” Arabidopsis halleri could be a versatile tool for such unequal objects.
Keywords: uranium, bioavailability, soil, sequential extraction, hydroponics, accumulation, photosynthesis

Publ.-Id: 12616 - Permalink

Systematics of electric dipole strength in the stable even-mass Mo isotopes
Schwengner, R.; Rusev, G.; Beyer, R.; Erhard, M.; Grosse, E.; Junghans, A. R.; Kosev, K.; Nair, C.; Schilling, K. D.; Wagner, A.; Zhang, S. Q.; Dönau, F.; Frauendorf, S.; Kämpfer, B.;
Photoabsorption cross sections sigma_gamma up to the neutron-separation energy S_n were measured for the stable even-mass isotopes 92-100Mo in photon-scattering experiments at the ELBE accelerator. As a consequence of the high level density at excitation energies close to S_n a huge number of resolved transitions and in addition an even greater intensity portion in an unresolved continuum have been observed. Simulations of gamma-ray cascades were performed to estimate the intensity distribution of inelastic transitions to low-lying levels and, hence, to deduce intensities and branching ratios of the ground-state transitions needed for the determination of sigma_gamma. The combination of the present data with (gamma,n) data allows us to obtain sigma_gamma in the energy range from about 4 MeV up to the giant dipole resonance. The experimental cross sections are compared with predictions of a new approach called Instantaneous Shape Sampling that calculates dipole strengths by means of QRPA for instantaneous shapes of the nucleus with probabilities obtained from IBA. The calculated sigma_gamma reproduce very well the experimental values around S_n.
Keywords: Nuclear structure, transitional nuclei, photon scattering, strength function, absorption cross section, random-phase-approximation, interacting boson approximation, nuclear deformation, shape sampling
  • Lecture (Conference)
    Frühjahrstagung des Fachverbandes Hadronen und Kerne, 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12615 - Permalink

Komplexierung von Am(III) mit organischen Säuren
Müller, M.; Acker, M.; Barkleit, A.; Taut, S.; Bernhard, G.;
Vorgestellt werden aktuelle Ergebnisse zur Komplexierung von dreiwertigem Americium mit den Liganden Pyromellitsäure, Citronensäure und Salicylsäure. Mit TRLFS und UV-vis-Spektroskopie konnten für die Systeme belastbare Komplexbildungskonstanten bestimmt werden. Erste Ergebnisse zu temperaturabhängigen Messungen und Sorptionexperimenten werden präsentiert.
Keywords: Americium, Complexation, Thermodynamics, Sorption
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 07.-08.04.09, Leipzig, Deutschland

Publ.-Id: 12614 - Permalink

Structural and optical properties of nitrogen doped ZnO films
Alves, E.; Franco, N.; Barradas, N. P.; Munnik, F.; Monteiro, T.; Peres, M.; Wang, J.; Martins, R.; Fortunato, E.;
Zinc oxide is getting an enormous attention due to its potential applications in a variety of fields such as optoelectronics, spintronics and sensors. The renewed interest in this wide band gap oxide semiconductor relies on its direct high energy gap (Eg~3.437 eV at low temperatures) and large exciton binding energy. However to reach the stage of device production the difficulty to produce in a reproducible way p-type doping must be overcome.
In this study we discuss the structural and optical properties of ZnO films doped with nitrogen, a potential p-type dopant. The films were deposited by magnetron sputtering using different conditions and substrates. The composition and structural properties of the films were studied combining X-ray diffraction (XRD), Rutherford backscattering (RBS), and heavy ion elastic recoil detection analysis (HI-ERDA). The results show an improvement of the quality of the films deposited on sapphire with increasing radio-frequency (RF) power with a preferentially growth along the c-axis. The ERDA analysis reveals the presence of H in the films and a homogeneous composition over the entire thickness. The photoluminescence of annealed samples evidences an improvement on the optical quality as identified by the well structured near band edge recombination.
Keywords: ZnO films; Nitrogen doping; RF magnetron sputtering

Publ.-Id: 12611 - Permalink

Spin reorientation transitions in Pt/Co/Pt films under low dose Ga+ ion irradiation
Jaworowicz, J.; Maziewski, A.; Mazalski, P.; Kisielewski, M.; Sveklo, I.; Tekielak, M.; Zablotskii, V.; Ferre, J.; Vernier, N.; Mougin, A.; Henschke, A.; Fassbender, J.ORC
A new route for tuning the magnetic anisotropy of ultrathin Co films by Ga+ ion irradiation is presented. The magnetic anisotropy of a Pt/Co(2.6 nm)/Pt film is first changed from in-plane to out-of-plane by uniform low dose Ga+ ion irradiation at 30 keV. When increasing the dose, a second spin reorientation transition towards the sample plane is also evidenced. This could be an elegant way to design magnetic nanowires with perpendicular anisotropy, embedded in an in-plane magnetized environment, either by uniform irradiation through a mask or focused ion beam. Tentative explanations
on the origin of these two successive spin reorientations are proposed.
Keywords: magnetism, ion irradiation, spin reorientation transition, magnetic anisotropy
  • Applied Physics Letters 95(2009)2, 022502

Publ.-Id: 12610 - Permalink

Atomistic simulation of ion-beam-induced defect formation
Posselt, M.;
Using a combination of computer simulations based on the binary collision approximation and molecular dynamics simulations the (meta)stable defect structure formed after a single ion impact into single crystalline silicon is obtained. Characteristics of the defect morphology such as the ratio between isolated and clustered defects are mainly determined by mass of the incident ion.
Keywords: computer simulation defects ion implantation molecular dynamics
  • Lecture (Conference)
    Int. Workshop Dresden ENLITE 09, 01.-03.04.2009, Dresden, Germany

Publ.-Id: 12609 - Permalink

Flash Lamp Activation of n- and p-type Dopants in Strained and Unstrained SOI and HOI
Minamisawa, R. A.; Buca, D.; Heiermann, W.; Lanzerath, F.; Mantl, S.; Skorupa, W.; Hartmann, J. M.; Ghyselen, B.; Kernevez, N.; Breuer, U.;
Strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. The successful integration of these materials into new MOSFETs architectures depends on the ability of forming ultra shallow and ultra steep junctions for the source/drain regions. Here, we present results using flash lamp annealing for dopant activation in SOI, sSOI, HOI and sHOI. Flash lamp annealing technique allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□, in both, SOI and sSOI. First investigations of strained and unstrained SiGe heterostructures after flash lamp annealing indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region.
Keywords: strained Si and SiGe/Si heterostructures on insulator, nanoelectronics devices, ultra shallow and ultra steep junctions, flash lamp annealing, dopant activation in SOI, sSOI, HOI and sHOI, suppression of diffusionantimony, boron
  • Contribution to proceedings
    215th ECS Meeting - Symposium on Advanced Gate Stack, Source/Drain, and Channel Engineering for Si-Based CMOS: New Materials, Processes, and Equipment, 24.-29.05.2009, San Francisco, USA
    ECS Transactions, 19(2009)1, 79-86, Pennington, NJ, USA: The Electrochemical Society

Publ.-Id: 12608 - Permalink

Magnetism of La0.875Sr0.125MnO3 by means of magnetometry and XMCD
Kuepper, K.; Raekers, M.; Taubitz, C.; Prinz, M.; Uhlarz, M.; Galakhov, V. R.; Mukovskii, Y. M.; Neumann, M.;
The manganites La1-xSrxMnO3 exhibit a remarkable rich phase diagram as function of temperature, doping concentration and magnetic field, accompanied by attractive properties like colossal magneto resistance (CMR). Furthermore lightly doped La1-xSrxMnO3 (around x = 0.125) shows an unusual ferromagnetic insulating (FMI) ground state which can not be explained by the conventional double exchange model. We studied the magnetic properties of a La0.875Sr0.125MnO3 single crystal by means of temperature dependent magnetometry and applied x-ray circular magnetic dichroism (XMCD) at the Mn L2,3 edges. In contrast to previous results reported [1] we do not find a significant Mn orbital moment, neither in the FMI phase (T < 180 K) nor in the high temperature paramagnetic insulating phases (T > 180 K). The experimental XMCD results are compared with charge transfer multiplet calculations.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12607 - Permalink

Neue Untersuchungen zum Einfluss von Huminsäure-Schwefelfunktionalitäten auf die Uran(VI)-Komplexierung und zur Uran(VI)-Sorption an Opalinuston
Sachs, S.; Joseph, C.;
Im Vortrag werden die Synthese und Charakterisierung schwefelhaltiger Huminsäure-Modellverbindungen sowie Ergebnisse zur Untersuchung des Einflusses von Huminsäureschwefelfunktionalitäten auf die U(VI)-Komplexierung diskutiert. Weiterhin werden Ergebnisse zur U(VI)-Sorption an Opalinuston vorgestellt.
Keywords: Humic substances, model compounds, sulfur functionalities, synthesis, characterization, complexation, uranium(VI), sorption, Opalinus clay
  • Lecture (others)
    Workshop zum Forschungsvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 07.-08.04.2009, Leipzig, Germany

Publ.-Id: 12606 - Permalink

Superconducting properties of boron-doped diamond
Uhlarz, M.; Skrotzki, R.; Papageorgiou, T.; Wosnitza, J.; Dubrovinskaia, N.; Dubrovinsky, L.; Miyajima, N.; Bosak, A.; Krisch, M.; Braun, H. F.; Wirth, R.;
The question of the nature of superconductivity in boron-doped diamond (synthesized at high pressures and high temperatures) is still open. Here we present consistent measurements of resistivity and specific-heat on two samples containing pure 13C and 12C, revealing a 0.2 K shift of the superconducting transition temperature Tc. Hallcoefficient measurements confirm equal charge-carrier concentrations in both samples. The results are interpreted as a carbon-isotope effect more than two times larger than expected from the most simple BCS model for phonon-mediated superconductivity. Additional analyses of microstructure and exact boron content of the superconducting material show the presence of highly boron-enriched amorphous boundaries between the grains. For these investigations highresolution transmission-electron microscopy and electron-energy-loss spectroscopy were used.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland
  • Poster
    9th Conference on Materials and Mechanisms of Superconductivity (M2S), 07.-12.09.2009, Tokyo, Japan

Publ.-Id: 12605 - Permalink

Ultrasonic investigation of the quasi-2D quantum antiferromagnet Cs2CuCl4
Sytcheva, A.; Zherlitsyn, S.; Wosnitza, J.; Chiatti, O.; Zvyagin, A. A.; Coldea, R.;
We report on results of sound-velocity and sound-attenuation measurements in the triangular-lattice quasi-2D spin-1/2 antiferromagnet (AFM) Cs2CuCl4 (TN = 0.6 K), in magnetic fields up to 18 T applied along the a axis and at low temperatures from 5 down to 0.3 K. Below TN this material displays a 3D incommensurate spiral longrange AFM order, which is stable up to Bs ≈ 8.5 T for fields applied along the a axis. Above this field all spins are polarized. For the AFM phase a possibility for the Bose-Einstein condensation of magnons has been suggested whereas beyond the AFM phase at low temperatures a proximity to the spin liquid (SL) state is considered in this compound. The longitudinal c11 acoustic mode, which has a propagation direction along the a axis, shows pronounced anomalies in sound velocity and attenuation in discussed temperature and field range indicating spinstrain interaction. It also demonstrates frequency-dependent effects indicating the presence of relaxation processes. The ultrasonic results are analyzed with a theory based on exchange-striction coupling. There is a good qualitative agreement between theory and experiment.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12604 - Permalink

Magnetic dipole sequences in 83Rb
Schwengner, R.; Rainovski, G.; Schnare, H.; Wagner, A.; Frauendorf, S.; Dönau, F.; Jungclaus, A.; Hausmann, M.; Iordanov, O.; Lieb, K. P.; Napoli, D. R.; de Angelis, G.; Axiotis, M.; Marginean, N.; Brandolini, F.; Rossi Alvarez, C.;
High-spin states in 83Rb were populated in the reaction 11B + 76Ge at beam energies of 45 and 50 MeV. Gamma rays were detected with the spectrometer GASP. The level scheme of 83Rb was extended up to 13.9 MeV. Mean lifetimes of 23 levels were determined using the Doppler-shift-attenuation method. Among the bands newly established is a sequence including intense M1 transitions and cross-over E2 transitions. This sequence turns out to be irregular and thus shows that magnetic rotation observed in the neighboring odd-odd isotopes cannot be sustained in this odd-even nuclide. Excited states in 83Rb were interpreted in terms of the shell model using the model space pi (0f5/2, 1p3/2, 1p1/2, 0g9/2) nu (1p1/2, 0g9/2). The configuration predicted for the M1 sequence is analogous to the one predicted for the M1 band in the neighbor 84Rb and reproduces the transition strengths at high spin.
Keywords: Nuclear structure, gamma-ray spectroscopy, angular correlations, Doppler-shift attenuation, Tilted-Axis Cranking Model, Shell Model.

Publ.-Id: 12603 - Permalink

Ion Irradiation Induced Modification of Magnetic Properties in Py-Ta-Multilayers
Markó, D.; Strache, T.; Lenz, K.; Fassbender, J.ORC; Kaltofen, R.
We have investigated Py-Ta thin film systems with varying numbers of interfaces, but a constant overall thickness of 20 nm Py and 38 nm Ta. The samples have been irradiated with Ne+ ions at various fluences in order to modify their magnetic properties, that have been probed using ferromagnetic resonance (FMR), magneto-optical Kerr effect (MOKE), and SQUID magnetometry. The saturation magnetization Ms decreases both with increasing number of Py-Ta inferfaces and with increasing ion fluences. The uniaxial anisotropy of the samples is only of small magnitude and remains almost unaffected. There is a critical fluence depending on the number of interfaces for which ferromagnetism vanishes.
Keywords: magnetism, magnetization dynamics, damping, ion irradaition, thin fims, multilayers
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12602 - Permalink

Energy pulse modification of electronic materials: from electronics via photonics to other advanced materials
Skorupa, W.; Anwand, W.; Gebel, T.;
Regarding electronic materials there is a clear and increasing interest in energy pulse modification of materials, especially also thermal processing far below one second, i.e. the lower limit of RTP (Rapid Thermal Processing) called spike annealing. It is the world of processing in the millisecond or nanosecond range. In the past, this was mainly driven by the need of suppressing the so-called Transient Enhanced Diffusion for advanced boron-implanted shallow pn-junctions in the front-end silicon chip technology. Meanwhile the interest in flash lamp annealing (FLA) in the millisecond range spread out into other fields than just “classical” silicon electronics. This paper reports shortly about the restart in flash lamp annealing and further on recent experiments regarding shallow junction engineering in germanium and SOI (silicon-on-insulator), annealing of ITO (Indium Tin Oxide) layers on glass and plastic foil interesting for low cost electronics as well as investigations which we did during the last years in the field of wide band gap semiconductor materials (SiC, ZnO). Moreover recent achievements in the field of silicon-based light emission basing on Metal-Oxide-Semiconductor Light Emitting Devices will be reported. Finally it will be demonstrated that the basic principle of short time thermal processing, i.e. surface heating on a colder bulk, features also advantages regarding the casting of lead sheets to produce organ pipes in the spirit of the 17th century.
Keywords: millisecond processing, flash lamp annealing, silicon, germanium, indium tin oxide, silicon carbide, zinc oxide, low cost electronics, photonics, light emission, electroluminescence
  • Contribution to proceedings
    ASME International Manufacturing Science & Engineering Conference (MSEC) Symp. 22: High Power Density Surface Treatments, 04.-07.10.2009, West Lafayette, IN, USA
    Proceedings of the ASME International Manufacturing Science & Engineering Conference (MSEC) Symp. 22: High Power Density Surface Treatments, New York
  • Invited lecture (Conferences)
    Seminar at the Univ. of Hongkong, 08.05.2009, Hongkong, China
  • Lecture (others)
    European Project Mtg. "Teramagstor", 28.-29.05.2009, Santorini, Greece
  • Lecture (Conference)
    Energy pulse modification of electronic materials: from electronics via photonics to other advanced materials, 06.10.2009, West Lafayette, IN, USA

Publ.-Id: 12601 - Permalink

Annual Report 2008 - Institute of Radiochemistry
Foerstendorf, H.; Richter, A.; Viehweger, K.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-511 2009


Publ.-Id: 12600 - Permalink

Photocapacitance measurements on MOS light emitting devices
Seeger, M.; Bürger, D.; Rebohle, L.; Skorupa, W.; Helm, M.; Schmidt, H.;
The photocapacitance (PC) has been probed on MOS diodes with an Eu-implanted SiO2 layer. In general, rare earth implanted SiO2 layers in MOS diodes are of great interest for possible applications in integrated metal-oxide-semiconductor light emitting devices (MOSLEDs). For example, green and ultraviolet electroluminescence has been probed on SiO2:Tb-MOSLEDs and SiO2:Gd-MOSLEDs, respectively. MOSLEDs reach external quantum efficiencies between 1% and 16%, and the electroluminescence peaks are typically ascribed to 4f-intrashell transitions of trivalent rare earth ions. A clear capacitance change has been observed for different wavelengths under monochromatic illumination. Some of the detected peaks correspond to the energies of 4f-intrashell transitions of the Eu ions. According to this, the number of active luminescence centers in MOSLEDs may be determined from PC measurements. Some 4f-intrashell transitions have been also observed by means of electroluminescence measurements on the same MOSLEDs. To emphasize the physical significance of the PC data recorded on SiO2:Eu-MOSLEDs, we also compare PC data recorded on different MOSLEDs implanted with other rare earth ions.
Keywords: photocapacitance, MOS, implanted, rare earth
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.09, Dresden, Germany

Publ.-Id: 12599 - Permalink

Measurements in Voigt configuration on PLD grown NiO thin films
Mok, K. M.; Scarlat, C.; Hartmann, L.; Zhou, S.; Vinnichenko, M.; Lorenz, M.; Grundmann, M.; Helm, M.; Schubert, M.; Schmidt, H.;
NiO has great potential applications in gas sensors, optical fibers, solar thermal absorbers, or in non-volatile resistive random memories. In our study NiO, NiMnO, and NiMnLiO have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition. In contrast to the antiferromagnetic behaviour of bulk NiO, we probed weak ferromagnetism with a coercivity ranging between 150 and 250 Oe by means of SQUID magnetometry. We measured the complex Voigt angle using a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 and two LockIns. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic and diamagnetic NiO thin films on diamagnetic r-plane sapphire substrates has been modelled using the 4*4 matrix formalism in dependence of an external magnetic field applied in-plane. The modelling results revealed that for the bare diamagnetic substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic and diamagnetic NiO thin films changed the parabolic dependence of the Voigt angle in the range of ±0.1 T to a flat-top shape in agreement with the experimentally determined Voigt angle.
  • Contribution to proceedings
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12598 - Permalink

Influence of Rippled Substrate Morphology on the Interlayer Exchange Coupling in Fe/Cr/Fe Thin Films
Körner, M.; Liedke, M. O.; Strache, T.; Dzenisevich, S.; Keller, A.; Facsko, S.; Fassbender, J.ORC
We have investigated the interlayer exchange coupling in Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm) deposited on rippled armorphous silicon substrates. The substrate surface was periodically modulated (periods of 20 nm, 35 nm, and 50 nm) by Ar+ ion erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by magneto-optical Kerr effect (MOKE). We found an orange peel type coupling, predicted by Néel’s theory and, due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy in the system.
This work is supported by DFG grant FA 314/6-1.
Keywords: interlayer exchange coupling, Néel coupling, iron, chromium, ripple
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 23.03.2009, Dresden, Deutschland

Publ.-Id: 12597 - Permalink

Numerical prediction of horizontal two phase flow using an interfacial area density model
Höhne, T.; Vallee, C.;
During a Lost of Coolant Accident (LOCA) cold Emergency Core Cooling (ECC) water can be injected into the cold leg of the primary loop of PWR. A relevant problem occurring in this situation is the development of wavy stratified flows which can lead to slug generation. Because slug flow cannot be predicted with the required accuracy and spatial resolution by the one-dimensional system codes, the stratified flows are increasingly modelled with computational fluid dynamics (CFD) codes. In CFD, closure models are required that must be validated. The recent improvements of the multiphase flow modelling in the ANSYS CFX code make it now possible to simulate these mechanisms in detail. In order to validate existing and further developed multiphase flow models, high-resolution measurement data is needed in time and also in space.

For the experimental investigation of co-current air/water flows, the HAWAC (Horizontal Air/Water Channel) was built. The channel allows in particular the study of air/water slug flow under atmospheric pressure. Parallel to the experiments, CFD calculations were carried out. A picture sequence recorded during slug flow was compared with the equivalent CFD simulation made. The two-fluid model was applied with a special turbulence damping procedure at the free surface. An Algebraic Interfacial Area Density (AIAD) model on the basis of the implemented mixture model was introduced, which allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value.

The behaviour of slug generation and propagation at the experimental setup was qualitatively reproduced by the simulation, while local deviations require a continuation of the work. The creation of small instabilities due to pressure surge or an increase of interfacial momentum should be analysed in the future. Furthermore, experiments with pressure and velocity measurements are planned and will allow quantitative comparisons, also at other superficial velocities.
Keywords: CFD, stratified flow, slug flow, HAWAC
  • Lecture (Conference)
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa City, Japan
  • Contribution to proceedings
    The 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa City, Japan

Publ.-Id: 12596 - Permalink

Ion implantation and cluster formation in silica
Salh, R.; Fitting-Kourkoutis, L.; Zamoryanskaya, M. V.; Schmidt, B.; Fitting, H.-J.;
Cathodoluminescence (CL), scanning transmission electron microscopy (STEM), and energy dispersive X-ray analysis (EDX) have been used to investigate Si and Ge cluster formation in amorphous silicon dioxide layers and their respective luminescence behavior.
Commonly, CL emission spectra of pure SiO2 are identified with particular defect centers within the atomic network of silica including the non-bridging oxygen-hole center (NBOHC) associated with the red luminescence (R) at 650 nm (1.9 eV) and the oxygen deficient centers (ODC) with the blue (B) (460 nm; 2.7 eV) and ultraviolet UV (295 nm; 4.2 eV) bands. In GeC ion implanted SiO2 an additional violet (V) Ge related emission band is identified at (410 nm; 3.1 eV). A post-implantation thermal annealing at temperatures Ta = 700-1100 °C in dry nitrogen leads up to 900 °C to a huge increase of the violet luminescence, followed by a decrease towards 1100 °C. The strong increase of the violet luminescence is associated with formation of low-dimension Ge aggregates like dimers, trimers and higher formations; the following decay of luminescence is due to further growing to Ge nanoclusters.
Keywords: Silica, Ion implantation, Cathodoluminescence, Cluster formation

Publ.-Id: 12595 - Permalink

Blue electroluminescence of ytterbium clusters in SiO2 by co-operative up-conversion.
Prucnal, S.; Rebohle, L.; Skorupa, W.;
Metal-oxynitride-oxide-silicon (MONOS) structures containing SiO2 layer implanted with different concentrations of ytterbium atoms were investigated. The electroluminescence (EL) measurements show that the MONOS:Yb devices can operate as blue or near infrared light emitters depending on the Yb concentration and annealing time. For an Yb concentration of up to 1.5% and annealing times of 30 min the near infrared EL with a peak at 975 nm corresponding to the 2F5/2→2F7/2 transition dominates. The short time annealed (6 s) sample containing 3% of Yb atoms exhibits mainly the blue EL due to co-operative up-conversion emission in the Yb3+-Yb3+ system. An enhancement of the red EL at 650 nm due to up-conversion energy transfer from the 2F5/2 excited state to the nonbridging oxygen hole center (NBOHC) is also presented.
Keywords: co-operative up-conversion, electroluminescence, MOSLED, rare earth
  • Applied Physics B 98(2010)2-3, 451-454

Publ.-Id: 12594 - Permalink

Structural and magnetic properties of pulsed laser annealed GaMnAs
Bürger, D.; Pandey, M.; Zhou, S.; Grenzer, J.; Reuther, H.; Anwand, W.; Helm, M.; Schmidt, H.;
Magnetic semiconductors with high Curie temperatures and large coercivity are very promising materials for spintronic applications. An approach to fabricate GaMnAs is the Mn-implantation of GaAs followed by pulsed laser annealing (PLA). We investigated the influence of Mn concentration and PLA conditions, e.g. number of pulses, pulse length, and pulse energy, on the structural and magnetic properties of GaMnAs. Using SQUID magnetometry, we revealed a strong decrease of the saturation magnetization with increasing number of pulses. HRXRD-measurements revealed a lattice expansion normal to the surface after implantation. PLA leads either to a strain decrease (1 pulse) or even to a strain over compensation (10 pulses). We conclude that Mn implantation into GaAs followed by PLA is not sufficient for increasing the Curie temperature in GaMnAs. In addition, the drawback of the Mn implantation is the loss of As from the GaAs surface as detected by means of Auger electron spectroscopy. Heat transfer calculations and coimplantation with suitable elements are possible approaches to enhance the properties of GaMnAs.
Keywords: pulsed laser annealing, DMS, GaMnAs, implantation, ferromagnetism
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12593 - Permalink

On the formation of secondary phases in Fe implanted GaN
Talut, G.; Reuther, H.; Grenzer, J.; Baehtz, C.; Novikov, D.; Walz, B.;
The request for room-temperature diluted magnetic semiconductors resulted in a large interest in GaN containing transition metals. Recent investigations have shown that beside of the real dilute state spinodal decomposition as well as the formation of secondary phases may play an important role in the discussion of the origin of the ferromagnetism [1, 2].
In this study, the dynamics of formation of secondary phases is investigated on GaN epilayers deposited on sapphire and implanted with 57Fe+ ions (3, 8 and16 • 1016 cm−2) at room temperature. Samples were annealed at 750° – 1200° C in N2 and Ar flow for durations between some ms and some minutes.
The formation of secondary phases in Fe implanted GaN upon annealing a N2-flow was detected ex-situ by means of x-ray diffraction and Mössbauer spectroscopy and supported by SQUID magnetometry. During annealing in reduced N2 atmosphere the reversal phase change from Fe3N at room temperature to Fe2.4N at 1023 K was observed by means of in-situ x-ray diffraction. Samples, annealed by a flash lamp in an Ar flow show the formation of different secondary phases depending on annealing time and temperature.

[1] Bonanni et al., PRL 101, (2008) 135502
[2] Li et al., Journal of Crystal Growth 310, (2008) 3294–3298
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12592 - Permalink

Radiolabeled human serum albumin microspheres for radiotherapeutical treatment of liver malignancies
Förster, C.; Schiller, E.; Pietzsch, H.-J.; Bergmann, R.; Pietzsch, J.; Noll, B.; Drews, A.; Johannsen, B.; Wunderlich, G.;
Radiolabelled particles are an attractive tool in the therapy of malignancies of the liver. Hepatic tumours receive their blood supply mainly from the arterial circulation, unlike normal liver tissue which is supplied by the portal vein. The intra-arterial application of microspheres with particle size > 10 m are trapped in the capillary bed and release a local radiotoxic dose with low levels of toxicity to the normal liver (1). The aim of this study was to determine the in vitro (incubation in human plasma and DTPA-Challenge) and in vivo characteristics of radiolabelled human serum albumin (HSA) microspheres and the valuation of suitability for radiotherapeutical treatment of liver malignancies. Covalent attachment of DOTA chelators onto the surface of the spheres opens up an easy access to Y-86-radiolabelled HSA microspheres. For in vivo experiments the labelled spheres were injected into the tail vein of Wistar rats. After 1, 12, 24 and 48 h the animals were sacrificed and the radioactivity concentration of isolated organs and tissue was determined. Furthermore, to investigate the influence of the surface structure we have used three different batches of HSA microspheres (smooth to rough; diameter 20-30 µm).

Approximately 25 DOTA molecules per molecule HSA could be attached as estimated from elemental analysis of DOTA-HSA microspheres, independently of the surface characteristics of the spheres. They were Y-86 labelled under optimized conditions in 96 ± 1 % yield. No significant differences between smooth- and rough-surfaced spheres were found. In DTPA challenge experiments 98 % of the radioactivity was still particle-associated after 24 hours incubation at 37 °C. In vitro studies in human plasma resulted in 95 ± 4 % particle-associated radioactivity after 48 h incubation at 37 °C. In the in vivo experiments radiolabelled smooth and rough microspheres were completely trapped in the lungs, which served in our experiments as model for the vascular system of a solid tumour. Biodistribution of radioactivity was determined up to 48 h p.i. The estimated activity in the urine was below 1 %ID at 1 and 12 h p.i., and below 9 %ID at 24 and 48 h. Radioactivity level of other organs and tissues was marginal (< 2 %ID at all time points). The three batches of particles differed considerably in their radioactivity recovery in the lungs. For the clearance of radioactivity from the lungs decay-corrected half-lives of 85 h (rough microspheres) and 187 h (smooth microspheres) were calculated (2).
We found a strong dependency between the in vivo stability of radiolabel fixation on the surface and the roughness of the particle. We concluded that for the preparation of HSA-derived microspheres for radiotherapeutic application smooth-surfaced spheres are superior to rough spheres due to their higher in vivo stability.

1. Murthy R et al., Yttrium-90 microsphere therapy for hepatic malignancy: devices, indications, technical considerations, and potential complications. Radiographics 25 (2005), 41-55.
2. Schiller E, Bergmann R, Pietzsch J, Noll B, Sterger A, Johannsen B, Wunderlich G, Pietzsch H-J, Yttrium-86-labelled human serum albumin microspheres: relation of surface structure with in vivo stability, Nucl. Med. Biol., doi: 10.1016/j.nucmedbio.2007.10.008.
  • Poster
    7th International Symposium on Polymer Therapeutics: From Lab to Clinic, 26.-28.05.2008, Valencia, Spain

Publ.-Id: 12591 - Permalink

Vanadium:Silicon - an ion-beam generated diluted magnetic semiconductor? - Integration of Vanadium into the Silicon host crystal
Thieme, M.; Gemming, S.; Potzger, K.;
The generation of dilute magnetic semiconductors (DMS) by ion-beam implantation of magnetic centres into semiconducting materials has experienced renewed interest since the generation of magnetic thin films from the Cobalt-doped wide-gap semiconductor TiO2. Since the magnitude of the magnetic moment in such films is strongly varying and since the implementation in a standard, Silicon-based semicon ductor device is challenging, we have concentrated on the binary and fully integrable system Vanadium:Silicon. At higher doping concentrations, Vanadium and Silicon form several binary compounds; the most well characterised structures have the compositions V:Si= 3:1, 5:3, 6:5, 1:2, and bear the potential to exhibit magnetism. At higher dilution, Vanadium may form point defects in the crystalline Silicon host matrix. Here, we investigate different combinations of substitutional and interstitial vanadium atoms in a silicon crystal matrix.
Keywords: Magnetism, Spintronic
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM)2009, 25.03.09, Dresden, Deutschland

Publ.-Id: 12590 - Permalink

Extraction of nitride trap density distribution in SONOS structures based on an advanced thermal emission model
Bernert, K.; Schönlebe, J.; Oestreich, C.; Mikolajick, T.;
As a result of continued scaling and the emphasis on low power and low voltage operation, silicon-oxide-nitride-oxide-silicon (SONOS) nonvolatile memory has received more attention recently. In this talk we investigate the charge decay characteristics of SONOS devices at elevated temperatures. Based on the thermal emission model as the dominant charge loss mechanism, the trap density energy distribution is determined. Furthermore we present an advanced model which includes the influence of subsequent tunneling through the bottom oxide after thermal excitation in the conduction band of the nitride.
Keywords: charge trapping memory, charge decay characteristics, thermal emission
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 26.03.2009, Dresden, Deutschland

Publ.-Id: 12589 - Permalink

The morphology of amorphous SiO2 surfaces during low energy ion sputtering
Keller, A.; Facsko, S.; Möller, W.;
The morphology of different amorphous or amorphized SiO2 surfaces, including thermally grown films, fused silica, and single crystalline quartz, during low energy ion sputtering has been investigated by means of atomic force microscopy. For all three materials, the formation of periodic ripple patterns oriented normal to the direction of the ion beam is observed at intermediate incident angles. At near-normal incidence, the SiO2 surfaces remain flat, whereas a rotation of the ripple patterns is observed at grazing incidence. At intermediate angles, the patterns on the different surfaces exhibit wavelength coarsening of different strengths, which can be attributed to different amounts of near-surface mass transport by the surface-confined ion-enhanced viscous flow. In the framework of the recent hydrodynamic model of ion erosion, the observed differences in ripple coarsening are consistent with this interpretation and indicate that the surface energies of thermally grown SiO2 and amorphized quartz are lower and higher than that of fused silica, respectively.
  • Journal of Physics: Condensed Matter 21(2009), 495305

Publ.-Id: 12588 - Permalink

Silicon based light emitters: from rare-earth doped MOS devices to resonant-cavity LEDs
Helm, M.;
no abstract available
Keywords: light emitter, silicon, rare earth, microcavity
  • Lecture (others)
    Seminar am van der Waals - Zeeman Institut der Universität Amsterdam, 27.03.2009, Amsterdam, Niederlande

Publ.-Id: 12587 - Permalink

Kelvin probe force and scanning capacitance microscopy on MOS structures
Baumgart, C.; Jaensch, S.; Helm, M.; Schmidt, H.;
As the size of semiconductor devices is decreasing permanently, new techniques are required to probe their dopant profile reliably on a nanometer scale. Kelvin probe force microscopy (KPFM) and scanning capacitance microscopy (SCM) are the most promising techniques for this demand. KPFM (LevelAFM from Anfatec) enables the detection of the contact potential difference (CPD) between tip and sample and SCM (DI3100 from Veeco Instruments) probes the capacitance of the metal oxide structures formed in contact. In order to demonstrate the complementary information obtained by KPFM and SCM measurements, we used the pn junction in a static random access memory integrated circuit device where the n-well with a donor concentration of 2E17 cm−3 has been fabricated by implanting the p-epi with a nominal acceptor concentration of 2E16 cm−3 with P+ ions of energy 900 keV and a fluence of 1.7E13 cm−2 [1]. As expected, KPFM yields a smooth variation of the CPD between the p-epi and the n-well amounting to 230 meV. SCM clearly shows the boxlike doping profile of this pn junction. The CPD variation can be modelled by assuming a partially compensated donor concentration in the n-well.
[1] M.W. Nelson et al., Electrochemical and Solid-State Letters 2 (1999) 475.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12586 - Permalink

Terahertz emission from an InGaAsN large area emitter
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.;
The simple operability of stable and compact fiber lasers motivated research on photoconductive THz emitters based on substrates that allow interband excitation with wavelengths up to 1.55 μm. Low-temperature grown InGaAs and ion-irradiated InGaAs, both grown lattice-matched on InP, have been used as substrate materials for dipole emitter antennas [1,2]. However, the resistivity of these materials is still too low for large-area emitters with interdigitated electrodes [3]. These structures prevent carrier excitation in every second spacing by an additional metallization or by etching of the substrate [4]. Hereby the excited elementary THz waves interfere constructive in the far field. These emitter designs combine the advantages of high bias fields and large active areas. Furthermore detection with elements of similar electrode geometry based on GaAs substrates with sub-picosecond carrier lifetimes and resistivity in the 106 Ω cm range has been demonstrated [5]. Here we present such large-area emitters based on InGaAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm.
The substrate material consists of a 1000 nm Ga1-yInyAs1-xNx (y=0.11 and x=0.04) layer grown by molecular-beam epitaxy on semi-insulating GaAs. On top there is an additional 60 nm thick Al0.3Ga0.7As barrier layer followed by a 5 nm GaAs cap layer. Transmission measurements with a Fourier spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The esistance of a complete device with an active area of 1 mm2 is 0.3 MΩ. This allows operation with high bias fields (30 kV/cm) without being limited by heating. For excitation an optical parametric oscillator (OPO), tunable between 1.1 μm and 1.5 μm, is used. The pulse duration is 280 fs. The THz signal is detected by electro-optical sampling using a 1 mm thick ZnTe crystal. The gating beam (λ = 820 nm) for detection is split off from a Ti:sapphire oscillator which drives the OPO.
The THz transient is measured with lock-in technique and has a signal-to-noise ratio of 400 obtained with 100 ms integration time constant. The bandwidth of the emitted radiation is 2.5 THz and is limited by the pulse duration of the OPO. Varying the OPO wavelength at fixed excitation power results in constant THz signals for wavelengths below 1.3 μm. For excitation wavelengths of 1.4 μm the signals are about 5 times smaller as compared to the shorter wavelengths. Furthermore we compare the InGaAsN emitter with an emitter based on semi-insulating (SI) GaAs when both are excited at 800 nm. Here the SI-GaAs emitter shows an 8 time higher THz field then the InGaAsN emitter at the same excited carrier density. We attribute this to the high electron obility in the SI-GaAs substrate.
In summary the THz emission indicates a high transient conductance of the InGaAsN material. The high resistivity makes it suitable for large area antennas with interdigitated electrode geometry.
[1] M. Suzuki and M. Tounouchi, Appl. Phys. Lett. 86, 163504, 2005
[2] A. Takazato, M. Kamakura, T. Matsui, J. Kitagawa, and Y. Kadoya, Appl. Phys. Lett. 91, 011102 ,2007
[3] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 86, 121114, 2005
[4] M. Awad, M. Nagel, and H. Kurz, Appl. Phys. Lett. 91, 181124, 2007
[5] F. Peter, S. Winnerl, S. Nitsche, A. Dreyhaupt, H. Schneider, and M. Helm, Appl. Phys. Lett. 91, 081109, 2007
  • Poster
    International Workshop on Optical Terahertz Science and Technology, 07.-11.03.2009, Santa Barbara, USA

Publ.-Id: 12584 - Permalink

Terahertz wave emission from InGaAsN large area emitter
Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.;
We present large-area emitters [1] based on InGaAsN which show efficient THz emission for excitation wavelengths up to 1.35 μm [2].
The substrate material consists of a 1000 nm GayIn1-yAs1-xNx (y=0.11 and x=0.04) layer grown by molecular-beam epitaxy on semi-insulating GaAs. On top there is an additional GaAs/Al0.3Ga0.7As heterostructure with thicknesses of 5 nm for the GaAs and 60 nm for the AlGaAs layer, respectively. Transmission measurements with a Fourier spectrometer reveal a bandgap corresponding to a wavelength of 1.5 μm. The resistance of a complete device with an active area of 1 mm2 is 0.3 MΩ. This allows operation with high bias fields (30 kV/cm) without being limited by heating. For excitation an optical parametric oscillator (OPO), tunable between 1.1 μm and 1.5 μm, is used. The pulse duration is 280 fs (FWHM). The THz signal is detected using electro-optical sampling with a 1 mm thick ZnTe crystal. The gating beam (λ = 820 nm) for detection is split off from a Ti:sapphire oscillator which drives the OPO.

[1] A. Dreyhaupt, et al., Appl. Phys. Lett. 86, 121114 (2005).
[2] F. Peter et al., Appl. Phys. Lett. 93, 101102 (2008).
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM)2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12583 - Permalink

Novel concepts for anisotropic Heisenberg modelling of multiferroic oxides
Kunze, T.; Gemming, S.;
Hexagonal manganites are oxides, in which structural, electronic, and magnetic degrees of freedom are coupled in a complex manner. Therefore, such materials have the potential for novel, nanoscale sensing and switching applications. Manganites are composed of dense-packed hexagonal manganese oxide layers with strong in-plane and weak interlayer coupling, thus the possible spin configurations may be studied with the help of a two-dimensional model Hamiltonian. Special focus is directed to the efficient sampling of the configuration space at low temperatures and concepts for improved importance sampling will be discussed.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12582 - Permalink

Conductivity through an organic field-effect transistor with ferroelectric gating
Kunze, T.; Gemming, S.; Luschtinetz, R.; Pankoke, V.; Morawetz, K.; Schreiber, M.;
The electronic transport of electrons and holes through stacks of functionalized quaterthiophene molecules as part of a novel organic ferroic field-effect transistor is investigated. The novel application of a ferroelectric instead of a dielectric substrate provides a bit-wise switching of the ferroelectric domains and enables the opportunity of employing the polarization field of these domains as a gate field in an organic semiconducting device. An already established phenomenological model called multilayer organic light-emitting diodes (MOLED) [1] is extended to transverse fields and numerical results are discussed. Model-specific parameters are determined with the help of experimental and theoretical methods.

[1] Houili et al., Comp. Phys. Comm. 156, 103-122 (2003)
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12581 - Permalink

Modelling the transport through organic layers on a ferroelectric substrate
Kunze, T.; Gemming, S.; Luschtinetz, R.; Pankoke, V.; Morawetz, K.; Schreiber, M.; Eng, L.; Seifert, G.;
Organic semiconductors, which might be suitable for logical as well as optical applications, have attracted a lot of scientific effort in recent years. This includes the understanding of the underlying transport mechanisms, the improvement of the transport characteristics and possible fields of application. The electronic transport through stacks of functionalized quaterthiophene molecules as part of a novel organic device is presented and investigated by means of a phenomenological approach called multilayer organic light-emitting diode (MOLED) [1]. Numerical results including the tuning of carrier injection and optical activity will be discussed.

[1] Houili et al., Comp. Phys. Comm. 156, 103-122 (2003)
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12580 - Permalink

Field induced phases in the antiferromagnet UPt2Si2
Bleckmann, M.; Schulze Grachtrup, D.; Süllow, S.; Willenberg, B.; Bartkowiak, M.; Rakoto, H.; Mydosh, J. A.;
Previously, UPt2Si2 has been described as a moderately mass enhanced antiferromagnet with a transition temperature of TN = 32K [1]. In contrast, and more recently, it has been demonstrated that UPt2Si2 closely resembles the tetragonal heavy fermion superconductor/hidden order material URu2Si2 in various physical properties [2,3]. We present a detailed study of high field magnetization and resistivity on single crystalline UPt2Si2. While up to now the high field behavior of UPt2Si2 was discussed in terms of a crystalline electric field scheme applied to an f electron local moment system [4], we show that the high field behavior is much more complex than previously thought. In particular, the magnetic phase diagrams derived from our measurements contain various field induced phases, again analougous to URu2Si2. We compare the phase diagrams of both systems and discuss possible scenarios accounting for such behavior in UPt2Si2.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12579 - Permalink

Superconductivity in Ga-doped Germanium
Skrotzki, R.; Herrmannsdörfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Wosnitza, J.;
We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced a series of Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga concentrations up to 6%, i.e., a doping level which is clearly larger than the solubility limit and not accessible to any other method so far. Transport measurements reveal superconducting transitions with Tc up to 0.5 K. In more detail, we observe a strong dependence of the superconducting critical parameters on the annealing conditions. Further, we find a strong anisotropy of the superconducting critical field reflecting the two-dimensional character of the superconducting state in the thin Ge:Ga layer having an effective depth of only 60 nm. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], our work reports another unexpected obervation of superconductivity in doped elemental semiconductors.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12578 - Permalink

High Magnetic Field Measurements on single crystalline (5-MAP)2CuBr4
Rauch, D.; Kreitlow, J.; Skourski, Y.; Turnbull, M. M.; Süllow, S.;
(2-amino-5-methylpyridinium)2CuBr4, abbreviated as (5-MAP)2CuBr4, has been characterized as a square S=1/2 Heisenberg antiferromagnetic lattice [1,2]. The compound consists of two-dimensional sheets of highly distorted CuBr4 tetrahedra separated by the organic cations. The magnetic coupling constants are 6.5 K for the intra-sheet coupling, 1.5 K for a residual inter-sheet coupling, with both interactions in effect resulting in an antiferromagnetic transition occurring at TN = 3.8 K. Here we report a single crystal high magnetic field study on (5-MAP)2CuBr4, with magnetic fields up to 40 T at temperatures down to 1.5 K. From the data additional information on local anisotropies such as of the g-factor can be obtained and will be discussed.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12577 - Permalink

Specific heat of the highly anisotropic antiferromagnet [Cu(pyz)2(HF2)]PF6
Beyer, R.; Uhlarz, M.; Wosnitza, J.; Schlueter, J. A.;
The metal-organic compound [Cu(pyz)2(HF2)]X with X = PF6 exhibits a quasi-cubic lattice of copper ions (S = 1/2), but the magnetic properties show a predominantly two-dimensional (2D) nature due to a large anisotropy in the exchange couplings. The magnetic entropy and the antiferromagnetic ordering, eventually occurring at about 4 K, were investigated by specific-heat measurements. For this we established a continuous relaxation-time technique, using a single relaxation process to get specific heat data over a wide temperature range. The calorimetric investigations, performed between 2 and 100 K and in magnetic fields up to 14 T, have revealed a non-monotonic field dependence of the ordering temperature. The results are as expected from the model for a S = 1/2 2D square-lattice quantum Heisenberg antiferromagnet with an additional weak interlayer exchange (via Cu-F-H-F-Cu bonds). In comparison to the X = BF4 compound, the antiferromagnetically ordered phase extends to much higher temperatures. In a more detailed analysis, we can extract all exchange interactions with an interlayer coupling ten times larger than in X = BF4. Thus, the 2D character is significantly reduced in X = PF6.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12576 - Permalink

The Superconducting Phase Diagram of Ba1−xKxFeAs Single Crystals
Bartkowiak, M.; Sun, G. L.; Lin, C. T.; Keimer, B.; Wosnitza, J.;
The discovery of superconductivity in iron pnictides has opened up a new class of high-Tc superconductors. It is quite remarkable that superconductivity is induced in layers of FeAs. These layers are separated by either rare-earth oxides or barium, which when doped act as charge-carrier reservoir. Single crystals of the (122) phase are currently available. We have determined the temperature dependence of the critical field Hc2, for various single crystals of K-doped BaFe2As2 using ac-transport measurements. The experiments were done at the pulsed-field facility in Dresden in fields up to 60 T applied parallel and perpendicular to the superconducting planes. The obtained phase diagram serves as an excellent benchmark for theoretical models of the order parameter.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12575 - Permalink

Antiferromagnetic resonance in multiferroic YMnO3 and LuMnO3
Kamensky, D.; Ozerov, M.; Cizmar, E.; Wosnitza, J.; Zvyagin, S.;
Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic order. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) techniques, magnetic excitations in the hexagonal multiferroic materials YMnO3 and LuMnO3 have been studied. In the antiferromagnetically (AFM) ordered phase the gap in the excitation spectrum (~ 42 and ~ 48 cm−1 for YMnO3 and LuMnO3, respectively) was observed directly. Similar slope of the frequency-field dependences of the AFM resonance modes, ~ 0.5 cm−1/T, was found for both compounds. A fine structure of the AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn3+ layers.
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12574 - Permalink

Multiband superconductivity in YNi2B2C single crystals studied by use of specific-heat measurements
Bekkali, A.; Wosnitza, J.; Uhlarz, M.; Beyer, R.; Schneider, M.; Behr, G.; Drechsler, S.-L.; Fuchs, G.;
We present new specific-heat data for two different YNi2B2C single crystals grown by a zone-melting method. The two samples (Tc,A = 15.26(4) K, Tc,B = 15.6(1) K) were studied in magnetic fields up to B = 9 T in the temperature range from T = 0.35 . . . 20 K, using both a relaxation and a heat-pulse method. In the superconducting state (B = 0) we find an uncommon dependence of the electronic contribution to the specific heat, Cel(T), strenghtening the assumption of a multiband nature of the superconducting state of YNi2B2C. A quantitative analysis of Cel(T) evidences multiple electronic contributions from electrons with very different electron-phonon coupling strengths, thus exhibiting several different superconducting energy gaps Δ(T,B = 0). This feature is in agreement with recent de Haas – van Alphen results [1] and point-contact spectroscopy data [2].
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12573 - Permalink

Antiferromagnetic resonance in multiferroic YMnO3 and LuMnO3
Zvyagin, S. A.;
Multiferroic rare-earth manganites have attracted much attention because of the coexistence of ferroelectric and magnetic orders. Combining conventional far-infrared Fourier-transform and THz-range free electron laser electron spin resonance (ESR) spectroscopy techniques, magnetic excitations in hexagonal multiferroic YMnO3 and LuMnO3 in the antiferromagnetically (AFM) ordered phase have been studied. The gap in the excitation spectrum (˜42 and ˜48 cm-1 for YMnO3 and LuMnO3, respectively) was observed directly. Similar slope of the frequency-field dependences of AFM resonance modes, ˜ 0.5 cm-1/T, was revealed for both compounds. A fine structure of AFM resonance absorption has been revealed by means of high-resolution ESR techniques, which can be explained taking into account a finite interaction between the neighboring Mn^3+ layers. The work was done in collaboration with M. Ozerov, D. Kamensky, E. Cizm'ar, J. Wosnitza, A.K. Kolezhuk, D. Smirnov, H.D. Zhou, and C.R. Wiebe.
  • Invited lecture (Conferences)
    APS March Meeting, 16.-20.03.2009, Pittsburgh, USA

Publ.-Id: 12572 - Permalink

Magnetic interactions and high-field properties of Ag2VOP2O7: frustrated alternating chain close to the dimer limit
Tsirlin, A. A.; Nath, R.; Weickert, F.; Skourski, Y.; Geibel, C.; Rosner, H.;
We report on high field magnetic properties of the silver vanadium phosphate Ag2VOP2O7. This compound has a layered crystal structure, but the specific topology of the V-P-O framework gives rise to a one-dimensional spin system, a frustrated alternating chain. Low-field magnetization measurements and band structure calculations show that Ag2VOP2O7 is close to the dimer limit with the largest nearest-neighbor interaction of about 30 K. High-field magnetization data reveal the critical fields µ0Hc1 = 23 T (closing of the spin gap) and µ0Hc2 = 30 T (saturation by full alignment of the magnetic moments). From Hc1 to Hc2 the magnetization increases sharply similar to the system of isolated dimers. Thus, the magnetic frustration in Ag2VOP2O7 bears little influence on the high-field properties of this compound.
  • Open Access LogoJournal of Physics: Conference Series 145(2009), 012067

Publ.-Id: 12571 - Permalink

White electroluminescence from a gadolinium doped Si nanocluster enriched SiO2-SiON interface region
Prucnal, S.; Rebohle, L.; Kanjilal, A.; Krzyzanowska, H.; Skorupa, W.;
Efficient white electroluminescence is obtained from metal-oxynitride-oxide-silicon (MONOS) structures with a silicon rich SiO2/SiON interface as an active layer. Samples containing only silicon show white electroluminescence (EL) under constant current excitation of 500 A. The EL spectra consist of three main bands associated with the neutral oxygen vacancy at 430 nm (NOV), E’ centers at about 550 nm and nonbridging oxygen hole centers (NBOHC) peaking at 650 nm. After Gd codoping into the SiO2:Si-nc layer the light emitted from the MONOS structure observed by naked eye is clearly white but the constant current needed for the EL excitation is reduced five times. Additionally, a fourfold increase of the electroluminescence power efficiency after Gd codoping was observed.
Keywords: Electroluminescence, MOSLED, Silicon nanoclusters, Rare earth
  • Electrochemical and Solid State Letters 12(2009)9, H333-H335

Publ.-Id: 12570 - Permalink

Investigation of the beltline welding seam and base metal of the Greifswald WWER-440 Unit 1 reactor pressure vessel
Schuhknecht, J.; Viehrig, H.-W.; Rindelhardt, U.;
The investigation of reactor pressure vessel (RPV) materials from decommissioned NPPs offers the unique opportunity to scrutinize the irradiation behaviour under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterisation. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I), irradiated and recovery annealed (IA) and irradiated, recovery annealed and re-irradiated (IAI). The working program is focussed on the characterisation of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the ASTM Test Standard E1921-05 to determine the fracture toughness of the RPV steel in different thickness locations.
In a first step the trepans taken from the RPV Greifswald Unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the Master Curve approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behaviour. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on sub size Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy transition temperature TT41J estimated with results of sub size specimens after the recovery annealing was confirmed by the testing of standard Charpy V-notch specimens.
The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. T0 increases from -120°C at the inner surface to -104°C at a distance of 33 mm from it and again to -115°C at the outer RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The re-embrittlement during 2 campaigns operation can be assumed to be low for the weld and base metal.
Keywords: Russian WWER-type reactor, WWER, reactor pressure vessel, multilayer welding seam, SE(B) specimen, specimen orientation, fracture toughness, Master Curve approach
  • Lecture (Conference)
    Proceedings of the 17th International Conference on Nuclear Engineering ICONE17 July 12-16, 2009, Brussels, Belgium, 12.07.2009, Brussels, Belgium
  • Contribution to proceedings
    Proceedings of the 17th International Conference on Nuclear Engineering ICONE 17, 12.-16.07.2009, Brussels, Belgium
    Proceedings of the 17th International Conference on Nuclear Engineering, CDROM, paper 75063: ASME, 978-0-7918-3852-5

Publ.-Id: 12569 - Permalink

Multimodale Bildgebung an Kleintieren - eine Informationsbasis für die Dosimetrie
Bergmann, R.;
kein Abstract verfügbar
  • Lecture (others)
    70. Sitzung Arbeitskreis Dosimetrie, 30.-31.03.2009, Dresden, Deutschland

Publ.-Id: 12568 - Permalink

Transition metal implanted ZnO: a correlation between structure and magnetism
Zhou, S.;
Nowadays ferromagnetism is often found in potential diluted magnetic semiconductor systems. However, many authors question the origin of this ferromagnetism, i.e. if the observed ferromagnetism stems from ferromagnetic precipitates rather than from carrier-mediated magnetic coupling of ionic impurities, as required for a diluted magnetic semiconductor. In this thesis, this question will be answered for transition-metal implanted ZnO single crystals. Magnetic secondary phases, namely metallic Fe, Co and Ni nanocrystals, are formed inside ZnO. They are - although difficult to detect by common approaches of structural analysis - responsible for the observed ferromagnetism. Particularly Co and Ni nanocrystals are crystallographically oriented with respect to the ZnO matrix. Their structure phase transformation and corresponding evolution of magnetic properties upon annealing have been established. Finally, an approach, pre-annealing ZnO crystals at high temperature before implantation, has been demonstrated to sufficiently suppress the formation of metallic secondary phases.
  • Lecture (Conference)
    ThyssenKrupp Electrical Steel Dissertationspreis der AG Magnetismus 2009 DPG Spring Meeting, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12567 - Permalink

A Multi-Radionuclide Approach for in-situ produced Terrestrial Cosmogenic Nuclides 10Be, 26Al, 36Cl and 41Ca
Merchel, S.; Benedetti, L.; Bourlès, D. L.; Braucher, R.; Dewald, A.; Faestermann, T.; Finkel, R. C.; Korschinek, G.; Masarik, J.; Poutivtsev, M.; Rochette, P.; Rugel, G.; Zell, K.-O.;
In-situ produced cosmogenic nuclides have proved to be valuable tools for quantifying Earth's surface processes. Here, the work-horses are 10Be and 26Al in quartz-rich minerals, and 36Cl in Ca- or K-rich minerals. Several attempts to find new matrix-product-pairs have been yet performed, especially with respect to broaden the time-scale to both more ancient [1] and more recent (historic) times. Thus, we have investigated other nuclides than 36Cl as possible dating tools by cross-calibration in accompanied calcite- and quartz-rich samples from Antarctica (DV3 & Joh) and Southern France (Ciot).
AMS measurements of 10Be and 26Al have been performed at the French 5 MV-AMS facility ASTER, 36Cl at CAMS, LLNL, USA, and 41Ca at the Maier-Leibnitz-Laboratory. As we could only perform a single run for 41Ca measurements, all results can be regarded as preliminary.
Ratios between different nuclides from the same matrix (CaCO3) and ratios of 10Be or 26Al from CaCO3 and SiO2 can be compared with pure physical model calculations [2] giving us experimental terrestrial production rates for 10Be, 26Al and 41Ca from Ca and CaCO3.
As shown earlier [3], cosmogenic 10Be is highly contaminated with atmospheric 10Be and cannot be removed quantitatively from calcite samples, even by an improved chemical cleaning procedure [4]. Only working on clay-free calcite provides correct 10Be data, giving a 2.7 times higher production rate of 10Be from CaCO3 than from SiO2. Though, the production rate of 26Al is only ~4.6% (CaCO3 relative to SiO2), 26Al can be easily determined in calcite, as the low intrinsic 26Al concentration yields to nearly as high 26Al/27Al as within corresponding quartz.
The measurement of 41Ca, mainly produced via thermal-neutron-capture, is hindered by very low 41Ca/Ca: <2.9x10-15. Of course, 41Ca counting statistics are poor: Measured 41Ca/Ca values are based on total counts of 1-5. Nevertheless, the reproducibility (Joh & Joh-WC) is excellent. All our data are lower than the already published one from rock samples, i.e. lower than the six surface samples (3-63 x 10-15) of Henning et al. [5] and Kutschera et al. [6] and lower than the surface and strongly shielded sample at 11 m depth (3.4-7.6 x 10-15) of Middleton et al. [7].
The low 41Ca/Ca ratios make it very unlikely that 41Ca could be generally used for in-situ dating of calcareous environments, especially as there is little hope that background level for CaF2-targets will improve, thus asking for very sophisticated and time-consuming CaH2-target preparation and handling [9].

We appreciate the help of D. Lal (UCSD), M. Arnold and G. Aumaître (CEREGE), J. Lachner and I. Dillmann (TU Munich), S. Nardon (ENI S.p.A., Milan) and J. Borgomano (U Marseille). This work was partially funded within the framework of CRONUS-EU (Marie-Curie Action 6th FP; #511927).
[1] J.M. Schaefer et al., EPSL 251 (2006) 334.
[2] J. Masarik et al., NIMB 259 (2007) 642.
[3] S. Merchel et al., Quat. Geochronol. 3 (2008) 299.
[4] S. Merchel et al., NIMB, in review.
[5] W. Henning et al., Science 236 (1987) 725.
[6] W. Kutschera et al., Radiocarbon 31 (1989) 311.
[7] R. Middleton et al., Radiocarbon 30 (1989) 305.
[8] G. Korschinek and W. Kutschera, NIM144 (1977) 343.
Keywords: cosmogenic radionuclides, AMS, accelerator mass spectrometry
  • Contribution to external collection
    in: Annual report of the Maier-Leibnitz-Laboratorium für Kern- und Teilchenphysik der Ludwig- Maximilians-Universität München und der Technischen Universität München (MLL), München: Maier-Leibnitz-Laboratorium, 2008, 26

Publ.-Id: 12566 - Permalink

Cosmogenic nuclides: Endless opportunities?
Merchel, S.;
The Forschungszentrum Dresden-Rossendorf expands its measurement capability by another highly-sensitive analytical method: accelerator mass spectrometry (AMS). The method will be mainly used for the determination of long-lived cosmogenic radionuclides. In contrast to ordinary decay counting, AMS scientists do not wait for the disintegration of a radioactive nucleus. In fact, they determine directly the not-yet-decayed radionuclides by mass spectrometry, which is much more efficient.
There is a main advantage of using a high-energy accelerator for mass spectrometry: The background and interfering signals, resulting from molecular ions and ions with similar masses e.g. isobars, are nearly completely eliminated. Thus, AMS generally provides much lower detection limits in comparison to conventional mass spectrometry. Our AMS system offers excellent measurement capabilities also for external users. In contrary to common low-energy AMS facilities in Europe, which have mainly specialized in radiocarbon analyses (14C), the FZD-AMS is the first modern-type facility in the EU that will run at a terminal voltage of 6 MV.
The benefits from using AMS for radiation protection, nuclear safety, nuclear waste, radioecology, phytology, nutrition, toxicology, and pharmacology research are obvious and manifold: Smaller sample sizes, easier and faster sample preparation, higher sample throughput and the redundancy for radiochemistry laboratories will largely reduce costs. Lower detection limits will widen applications to shorter and longer time-scales and to sample types that could never been investigated before.
In environmental and geosciences, the determination of long-lived cosmogenic radionuclides like 10Be, 26Al, and 36Cl became more and more important within the last twenty years. Using these nuclides dating of suddenly occurring mass movements, e.g. volcanic eruptions, rock avalanches, tsunamis, meteor impacts, earth quakes and glacier movements, is possible. The so-called in-situ produced cosmogenic nuclides have proved to be valuable tools for quantifying Earth's surface processes also on longer time-scales and wider areas, e.g for the determination of basin-wide erosion rates. Additionally, glacier movements and data from ice cores containing atmospherically produced nuclides give hints for the reconstruction of historic climate changes and providing information for the validation of climate model predicting future changes.
Within the project CRONUS-EU the European-wide interdisciplinary network has focussed on basic data problems, that could strongly influence the quality of applications in geosciences. We have e.g. performed round-robin exercises and lowest-level measurements at different AMS facilities and cross-calibrations, searched for explanations for discrepancies in published production rates, explored new nuclide-matrix possibilities, and investigated in detail other sources of errors like scaling and nuclear reaction models.
Keywords: accelerator mass spectrometry, cosmogenic nuclides, AMS
  • Invited lecture (Conferences)
    GeoKolloquium - Geowissenschaftliches Kolloquium der Fakultät für Geowissenschaften, Geotechnik & Bergbau, TU Bergakademie Freiberg, 08.04.2009, TU Bergakademie Freiberg, Germany
  • Contribution to external collection
    in:, Freiberg: TU Bergakademie Freiberg, 2009

Publ.-Id: 12565 - Permalink

Phenol biodegradation by two xenobiotics tolerant bacteria immobilized in polyethylene oxide cryogels
Satchanska, G.; Topalova, J.; Dimkov, R.; Petrov, P.; Tsvetanov, C.; Selenska-Pobell, S.; Gorbovska, A.; Bogdanov, V.; Glovinsky, E.;
Biofilms were formed on poly(ethylene oxide) (PEO) cryogels by using bacteria cultured from xenobiotics polluted environments in order to investigate their phenol biodegradation capability. PEO cryogels were synthesized via UV irradiation cross linking of moderately frozen aqueous system. Two xenobiotics tolerant bacterial isolates KCM R5 and KCM RG5 were used to construct the biofilms on the surfaces of the cryogels. Obtained PEO-biofilms were assessed for their ability to remove phenol at concentrations – 300, 400, 600 and 1 000 mg L-1 for 28 days. The biofilm PEO-KCM RG5 removed phenol up to 600 mg L-1/24h, whereas the biofilm PEO-KCM R5 was able to degrade up to 1 000 mg L-1/24h. The high content of free-water in the cryogels allowed reproduction of the used bacteria. Short initial adaptation of the PEO-biofilms with 100 mg L-1/24h phenol was crucial for protecting the bacterial cells forming the biofilm from dead. The obtained results showed that the liquid debit through the biofilms at the 28-th day was lower if compared to the initial one. Cryogels demonstrated non-toxicity, high biocompatibility with bacteria and excellent mechanical characteristics. After the aggressive phenol treatment the PEO-biofilms remained compact, porous and elastic. The investigated new biological materials demonstrate potential for application in the industrial wastewater treatment technologies.
  • Open Access LogoComptes Rendues de l'Academie bulgare des Sciences 62(2009)8, 957-964

Publ.-Id: 12564 - Permalink

Lattice Location Determination of Ge in SiC by ALCHEMI
Kups, T.; Voelskow, M.; Skorupa, W.; Soueidan, M.; Ferro, G.; Pezoldt, J.;
The incorporation of Ge into cubic and hexagonal silicon carbide is compared for three different doping methods: ion-implantation; molecular beam epitaxy and liquid phase epitaxy.
Keywords: MBE; ALCHEMI; Ge; doping methods
  • Contribution to external collection
    A.G. Cullis; P.A. Midgley: Microscopy of semiconductor materials, Netherlands: Springer Netherlands, 2008, 978-1-4020-8615-1, 353-358

Publ.-Id: 12563 - Permalink

Electronic bandstructure of the ZnTe absorber material
Fritsch, D.; Schmidt, H.;
Due to its large absorption coefficient, zinc telluride proved to be useful for the production of high-efficiency multi-junction solar cells. Nowadays ZnTe with a mixture of zincblende and wurtzite phases is fabricated by thin film growth techniques. The optical properties of both phases have been extensively studied by ab initio density functional methods [1]. Here we focus on the question whether the effective electron and hole mass in ZnTe are small enough to meet the high-efficiency expectation of the ZnTe absorber material in solar cells and present direction dependent effective mass and Luttinger and Luttinger-like parameters of cubic and wurtzite ZnTe, respectively. Making use of the transferability of ionic model potential parameters [2] and the experimentally known transition energies of different II-VI compounds ZnX (X=O, S, Se, Te), we obtained one single set of cationic model parameters for the Zn atom. The calculations have been performed by means of the empirical pseudopotential method using a simple empty core model potential.
[1] S. Zh. Krazhanov, P. Ravindran, A. Kjekshus, H. Fjellvag, and B.G. Svensson, Phys. Rev. B 75, 155104 (2007).
[2] D. Fritsch, H. Schmidt, M. Grundmann, Appl. Phys. Lett. 88, 124104 (2006), Phys. Rev. B 69, 165204 (2004).
Keywords: absorber material, ZnTe
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12562 - Permalink

Tuning the static and dynamic magnetization properties of exchange bias modulated thin films
Hamann, C.; McCord, J.; Fassbender, J.ORC; Mattheis, R.; Kaltofen, R.; Schäfer, R.; Schultz, L.
Aiming for new magnetic properties, the lateral combination of different magnetic properties into hybrid magnetic thin film structures are of increasing interest. We investigated exchange bias patterned thin NiFe/IrMn films to correlate the static and dynamic magnetization processes of the artificial hybrid material to the intrinsic material properties. Arrays of stripes with modulated exchange bias, i.e. exchange bias strength and direction, and a periodicity of a few micrometers were created. Inductive magnetometry revealed a distinct influence of geometry and orientation on the magnetization loop yielding either single-step shifted hysteresis loops or two-step loops with exchange spring effect. By means of high resolution Kerr microscopy, this could be attributed to either coherently or separately reversed stripe magnetization. As for the dynamics, the films exhibited either multiple resonance frequencies (as superposition of the input properties) or a single hybrid resonance frequency. The acquired frequencies at zero bias field as well as according damping parameters could be varied by a factor of about two. The different phenomena are discussed in terms of direct exchange coupling via the extended NiFe film as well as quasi-magnetostatic interactions at the stripe interfaces.
Keywords: magnetism, exchange bias, patterning, hybrid structures, microscopy, magnetization dynamics
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12561 - Permalink

Local setting of magnetic anisotropy in FeCoSiB thin films by means of indirect ion implantation
Martin, N.; McCord, J.; Gerber, A.; Strache, T.; Gemming, T.; Mönch, I.; Schäfer, R.; Fassbender, J.ORC; Quandt, E.; Schultz, L.
The magnetic anisotropy direction and strength of amorphous FeCoSiB thin films was modified locally by masked ion implantation without alteration of the magnetic material’s structure and the intrinsic magnetic properties of the ferromagnetic film. The changes were introduced by local ion implantation in a SiO2 covering and protection layer, inducing additional stress-induced magnetic anisotropy to the magnetostrictive ferromagnetic layer. Hybrid hysteresis curves combining switching and rotational processes were measured and the underlying local variation of magnetic anisotropy was confirmed by magnetic domain observations. A good agreement between the calculated stress distribution and the experimentally obtained magnetic data was found. The described indirect method, relying purely on magneto-elastics, introduces a new path to the creation or alteration of magnetic properties subsequent to magnetic film preparation in structured magnetic samples without introducing any structural changes to the ferromagnetic layers.
Keywords: magnetism, ion irradiation, amorphous films, strain, stress, patterning, anisotropy
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12560 - Permalink

Determining role of Krein signature for 3D Arnold tongues of oscillatory dynamos
Kirillov, O.; Günther, U.; Stefani, F.;
Using a homotopic family of boundary eigenvalue problems for the meanfield α2-dynamo with helical turbulence parameter α(r)= α0 + γΔα(r) and homotopy parameter β∈[0,1], we show that the underlying network of diabolical points for Dirichlet (idealized, β=0) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, β = 1) boundary conditions. In the (α0,β,γ)-space the Arnold tongues of oscillatory solutions at β =1 end up at the diabolical points for β = 0. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to spectral exceptional points, which are important ingredients in recent theories of polarity reversals of the geomagnetic field.
Keywords: MHD dynamos, oscillatory dynamos, Krein space, Krein signature, diabolical points, perturbation theory, homotopy, boundary conditions, Arnold tongues, resonance zones
  • Lecture (Conference)
    Verhandlungen der Deutschen Physikalischen Gesellschaft e.V., 22.-27.03.2009, Dresden, Deutschland

Publ.-Id: 12559 - Permalink

Fano Signatures in the Intersubband Terahertz Response of Optically Excited Semiconductor Quantum Wells
Golde, D.; Wagner, M.; Stehr, D.; Schneider, H.; Helm, M.; Andrews, A. M.; Roch, T.; Strasser, G.; Kira, M.; Koch, S. W.;
Absorption and transmission spectra of broadband terahertz pulses are measured to probe the intersubband response of an optically excited quantum-well heterostructure. While the terahertz absorption shows the single peak of the resonant intersubband transition, the transmission spectra display strong Fano signatures due to the phase sensitive superposition of ponderomotive and terahertz currents as predicted by our microscopic theory.
Keywords: ponderomotive, intersubband, THz, Fano

Publ.-Id: 12558 - Permalink

Sorption of Np(V) onto TiO2, SiO2, and ZnO: An in situ ATR FT-IR spectroscopic study.
Müller, K.; Foerstendorf, H.; Brendler, V.; Bernhard, G.;
The migration of hazardous neptunium is strongly affected by sorption processes at the solid-water interface. Up to now, almost no spectroscopic data are available to characterize Np(V) species on a molecular level. For the first time, the speciation in aqueous solution and the sorption of Np(V) at a micromolar concentration level onto metal oxides were studied using NIR and in situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy providing reference data for future investigations of neptunyl(V) sorption processes on natural mineral phases under environmental conditions.
The obtained spectra of aqueous Np(V) solutions confirmed the predominance of the fully hydrated species NpO2+ up to pH 7.7, predicted by the updated NEA TDB. From the Np(V) sorption studies on TiO2, stable surface species of NpO2+ are derived. The type of the sorbed species can be elucidated by a spectral shift (~ 30 cm−1) to lower wavenumbers of the antisymmetric stretching vibration ν3(NpO2+) compared to the aqueous species suggesting an inner-sphere complexation. Outer-sphere complexation is found to play a minor role due to the independence of the sorption species throughout the pH range 4 – 7.6. The comparative spectroscopic experiments of Np(V) sorption onto TiO2, SiO2 and ZnO indicate structurally similar bidentate surface complexes.
  • Environmental Science & Technology 43(2009)20, 7665-7670

Publ.-Id: 12557 - Permalink

THz sideband generation in GaAs/AlGaAs multi quantum wells
Wagner, M.; Schneider, H.; Helm, M.; Schartner, S.; Andrews, A. M.; Roch, T.; Strasser, G.;
THz sideband generation is a nonlinear mixing process where a near-infrared (NIR) laser beam is mixed with a THz beam to generate new frequencies (sidebands) ω around the NIR frequency: ω = ω_NIR ± n × ω_THz (with integer n). This effect has been investigated in various semiconductor systems (e. g., in bulk GaAs [1] and in multi quantum wells [2]).
We report on third-order nonlinear mixing between a NIR laser and a free-electron laser (FEL) in an undoped AlGaAs/GaAs multi quantum well. Differently from the literature where electronic and heavy-hole intersubband transitions were used, we are covering different transitions by tuning the FEL wavelength. We directly compare the n=+2 sideband generation efficiency when the FEL pumps the heavy-hole light-hole transition with the efficiency when the intraexcitonic 1s-2p transition of the heavy-hole is pumped. In the latter case the efficiency increases up to 0.2%, which is comparable to the best values achieved for an even stronger n=+1 sideband process [2].

[1] M. A. Zudov et al., Phys. Rev. B 64, 121204, 2001
[2] S. G. Carter et al., Appl. Phys. Lett. 84, 840, 2004
Keywords: THz sidebands, free-electron laser
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12556 - Permalink

Measurements of an unsteady liquid metal flow during spin-up driven by a rotating magnetic field
Räbiger, D.; Eckert, S.; Gerbeth, G.;
This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. The flow measurements confirm a theoretical study by Nikrityuk et al. (2005) who suggested the existence of two stages during the RMF-driven spin-up, in particular the so-called initial adjustment phase followed by an inertial phase which is dominated by inertial oscillations of the secondary flow. Evolving instabilities of the double-vortex structure of the secondary flow have been detected at a Taylor number of 1.24´105 confirming the predictions of Grants and Gerbeth (2002). Perturbations in form of Taylor-Görtler vortices have been observed just above the instability threshold.
Keywords: Liquid metal flow, Rotating magnetic field, Spin-up, Ultrasound Doppler velocimetry
  • Experiments in Fluids 48(2010), 233-244

Publ.-Id: 12555 - Permalink

Thermophysical properties of liquid tin-bismuth alloys
Plevachuk, Y.; Sklyarchuk, V.; Gerbeth, G.; Eckert, S.;
Tin-bismuth alloys are under intense consideration as favourable lead-free solders for consumer electronics and telecommunications. The electrical and thermal conductivity, viscosity, surface tension and density were studied in a wide temperature range above the liquidus. The scaling relations have been proposed. A comparison with data available in the literature is given.
Keywords: lead-free alloys, liquid metal properties, tin-bismuth
  • International Journal of Materials Research 101(2010), 839-844

Publ.-Id: 12554 - Permalink

CONCAST – a liquid metal experimental facility for modeling the continuous casting process of steel
Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.;
The pursuit of better product quality and higher productivity of the continuous casting of steel makes the flow control in tundish and mould and the initial solidification control in the mould to important issues. Numerous sophisticated numerical simulations concerned with the metal flow during the casting process need a fundamental experimental validation. The use of water models gives the advantage to save expense and to be able to apply a number of well-proofed measuring methods. However, a generalisation of these results to liquid metal flows has to be considered as questionable because the true values of flow parameters (Re, Pr, Gr, Ha, etc.) are difficult to meet. In many cases, for instance liquid metal flows with strong temperature gradients, two-phase flows or applications of electromagnetic fields, the flow phenomena cannot be modelled correctly by means of water experiments.
In this paper we present a new experimental facility CONCAST for modeling the continuous casting process by using the low melting point alloy BiSn. The facility operates at temperatures of 200°C-300°C. Main parameters of the facility and dimensions of the test sections will be shown. The resultant possibilities with respect to flow investigations in tundish, submerged entry nozzle and mould will be discussed. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic or electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range until 300°C.
First experimental results will be presented which have been obtained using a small-scale preliminary set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. The application of electromagnetic fields for flow and solidification control in steelmaking will be a crucial point of the future working program.
Keywords: Continuous casting of steel, Liquid metal model experiments, Flow measurements, Electromagnetic flow control
  • Lecture (Conference)
    3rd International Conference on Simulation and Modelling of Metallurgical Processes in Steelmaking, 08.-10.09.2009, Leoben, Austria
  • Contribution to proceedings
    3rd International Conference on Simulation and Modelling of Metallurgical Processes in Steelmaking, 08.-10.09.2009, Leoben, Austria

Publ.-Id: 12553 - Permalink

Solidification of a binary metal alloy in a turbulent melt flow driven by AC fields
Nikrityuk, P. A.; Eckert, K.; Eckert, S.;
The application of an RMF during the solidification of a metal alloy may cause macrosegregations, which are the result of the secondary flow in the form of a double vortex structure appearing in a rotating flow due to the Ekman pumping effect. The aim of this work is to improve the understanding of the influence of turbulent RMF-driven flows on the final macrosegregation during unidirectional columnar and equiaxed solidification of a binary metal alloy. The weakly turbulent flow was modeled by means of direct numerical simulations in an axisymmetric approach, where the transient heat and mass transfer was simulated by means of a standard mixture model. Both types of solidification, columnar and equiaxed, were considered by the application of both a permeability and a hybrid model to treat the fluid flow in the mushy zone. Our analysis shows that the oscillations of the radial flow are damped by the rather high viscosity of the slurry region formed by the mixture of equiaxed dendrites and interdendritic liquid. The transport of the equiaxed dendrites towards the axis of the cylinder results in a faster cooling of the melt and a convex shape of the mushy zone. The final macrosegregation is significantly smaller in comparison with the columnar solidification. An increase of the Taylor number leads to a further decrease of the macrosegregation in the middle of the sample for two reasons. First, the enhancement of turbulent mixing of the rejected solute and floating dendrites with the bulk liquid mediated by the T-G vortices, and second, the transport of floating dendrites by the flow reduces the ‘washing’ effect, given by the convective transport of the rejected solute from the solid interface, in comparison with non-movable dendrites.
Keywords: solidification, melt flow, rotating magnetic field, turbulence, macrosegregation
  • Lecture (Conference)
    6th International Symposium on Turbulence, Heat and Mass Transfer, 14.-18.09.2009, Rome, Italy

Publ.-Id: 12552 - Permalink

High energy electron crystal spectrometer
Kudyakov, T.; Jochmann, A.; Zeil, K.; Kraft, S.; Finken, K. H.; Schramm, U.; Willi, O.;
A spectrometer has been developed to measure relativistic electrons produced in di®erent types of plasmas, like: tokamak plasmas, laser produced plasmas. The spectrometer consists of 9 YSO (Y2SiO5 : Ce) crystals, which are shielded by stainless steel ¯lters. The absolute calibration of the spectrometer was performed at the superconducting electron linear accelerator ELBE. The spectrometer can provide information about energy distribution of electrons and their numbers for the energy range between 4 and 30 MeV. The spectrum is analyzed by means of the Monte Carlo 3D Geant4 code.
Keywords: electron spectrometer
  • Review of Scientific Instruments 80(2009)7, 076106

Publ.-Id: 12549 - Permalink

Kinematic dynamo simulations in cylindrical geometry
Giesecke, A.; Stefani, F.; Gerbeth, G.;
In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.
A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.
An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.
Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.
Keywords: Dynamo Experiment MHD Kinematic Simulations
  • Lecture (Conference)
    Astrophysical Magnetohydrodynamics, 06.-10.04.2009, Nurmijärvi, Finnland

Publ.-Id: 12548 - Permalink

4D in-beam PET Datenauswertung für bewegte Phantome bei Bestrahlung mit einem getrackten 12C6+-Strahl
Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.;
In-beam PET has become a quality assurance tool providing valuable clinical feedback for static tumor entities and shall be extended to monitor the treatment of intra-fractional moving tumors like in the lung or
liver which are subjected to respiratory motion. The potential of 4D in-beam PET for the detection of possible malfunction of the motion compensated beam delivery has been investigated by means of systematic phantom experiments at the clinical in-beam PET installation at GSI Darmstadt. The new system for tracking moving targets with the scanned ion beam at GSI Darmstadt was used to adapt the Bragg peak positions laterally and in depth. The pencil beam has been rescanned on a horizontal line in a phantom placed at the central plane of the double head PET scanner with an energy corresponding to 60mm penetration depth while the target was performing a one dimensional periodic motion perpendicular to the beam direction. 4D PET data were compared with an appropriate 3D PET measurement which followed immediately after the dynamic acquisition. It is shown for different irradiation scenarios that in-beam PET is capable for detecting treatment errors for moving target irradiation.
Keywords: in-beam PET, moving targets, ion therapy
  • Lecture (Conference)
    DPG Frühjahrstagung 2009, 09.-13.03.2009, München, Deutschland

Publ.-Id: 12546 - Permalink

Performance of the new drift chambers for HADES @ FAIR
Göbel, K.; Kämpfer, B.; Kotte, R.; Naumann, L.; Palka, M.; Tarantola, T.; Traxler, M.; Wüstenfeld, J.;
Seven new Multiwire Drift Chambers of plane 1 for the High - Acceptance Di - Elektron Spectrometer (HADES) are assembled in the Detector workshop of the Forschungszentrum Dresden - Rossendorf.
We present the results of test performed on the first chamber in comparison with the main design parameters .
End of 2008 one detector was completely equipped with the new generation of the readout system designed for the high multiplicity environment as provided in collisions of heavy systems at HADES @ FAIR.
The chamber was investigated with cosmic rays and β 90Sr source. The obtained results show that the new design fulfills the equirements with respect to efficiency, accuracy and rate capability.
These chambers will be installed in 2009 to be armed for the upcoming heavy ion program.
Keywords: HADES, FAIR, detector development
  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC) 2009, 16.-20.3.2009, Bochum, Deutschland

Publ.-Id: 12544 - Permalink

Fluorescence spectroscopic study on complexation of uranium(VI) by glucose - a comparison of room and low temperature measurements
Steudtner, R.; Arnold, T.; Geipel, G.; Bernhard, G.;
The complexation of uranium(VI) with glucose was studied in the pH range from pH 2 to 6 by time resolved laser-induced fluorescence spectroscopy (TRLFS) at room temperature (RT) and for the first time under cryogenic conditions of 153 K (cryo-TRLFS). A uranyl(VI) glucose complex was spectroscopically identified by cryo-TRLFS measurements at pH 5. At lower pH values only the free uranyl(VI) ion was identified. The study revealed that quenching effects severely influenced the TRLFS measurements conducted at RT and significantly reduced the uranium(VI) fluorescence signal. This decrease in U(VI) fluorescence intensity is usually used to calculate complex formation constants of non-fluorescent uranyl(VI) organic complexes. However, our cryo-TRLFS results clearly showed that the observed decrease in U(VI) fluorescence intensity at RT for the samples at pH 2 to 4 is not attributed to the formation of such a non-fluorescent U(VI) glucose complex, i.e. to static quenching, but related to dynamic quenching of glucose on the uranyl(VI) fluorescence. At higher pH values the formation of uranyl(VI) glucose complexes were suppressed by the formation of uranyl(VI) carbonate species. The detected uranyl(VI) glucose complex was characterized by five emission bands at 499.0, 512.1, 525.2, 541.7, and 559.3 nm. The respective fluorescence lifetime determined at 153 K was 20.9 ± 2.9 µs. The uranyl(VI) glucose complex formation constant was calculated for the first time to be logßI = 0.1 M = 15.35 ± 0.91. Comparing this constant with formation constants of other important environmentally relevant inorganic ligands, in particular carbonate, it became evident that glucose only may influence the transport behaviour of uranium in a very small pH region of about 5. Our cryo-TRLFS investigation opens up new possibilities for the determination of complex formation constants since interfering quenching effects often encounter at RT are suppressed by measurements at cryogenic conditions.
Keywords: uranyl, glucose, Laser fluorescence spectroscopy, TRLFS, cryogenic conditions

Publ.-Id: 12543 - Permalink

Complex Formation and Molecular Structure of Np(VI) and Np(V) Acetates
Takao, K.; Takao, S.; Scheinost, A. C.; Bernhard, G.; Hennig, C.;
Neptunium is one of the most problematic actinides for long-term storage of the radioactive waste. Acetate (AcO-) is one of the important organic ligands occurring in natural environment. To study complexation reactions of Np(V) and Np(VI) with AcO-, we performed titration experiments based on UV-Vis-NIR spectroscopy. Furthermore, we used cyclic voltammetry to obtain information on the stability field of the individual solution species. However, it is difficult to extract structural information solely from these techniques. Therefore, we additionally adopted X-ray absorption fine structure (XAFS) spectroscopy to detect complexation reaction and molecular structure of Np(VI)- and Np(V)-AcO- complexes in aqueous solution.
The UV-Vis-NIR absorption spectra of the Np(VI)-AcO- system as a function of pH do not show any isosbestic points, indicating the presence of more than two equilibria. As a result of stability constant refinement, the spectral change is indicated as a 3-step complexation reaction of NpVIO2(AcO)n2-n (n = 1, 2, 3). The evaluated stability constants are log K1 = 2.98 ± 0.01, log b2 = 4.60 ± 0.01, and log b3 = 6.34 ± 0.01, which are comparable with the values reported previously. For comparison reasons the complex formation of Np(VI)-AcO- was investigated by XAFS spectroscopy (XANES and EXAFS). The refinement analysis of the XAFS spectra revealed similar stability constants (log K1 = 2.87 ± 0.03, log b2 = 4.20 ± 0.06, and log b3 = 6.00 ± 0.01). The k3-weighted EXAFS spectra of NpVIO2(AcO)n2-n (n = 0, 1, 3) provided structural data consistent with the complex stoichiometry, being well-explained by bidentate coordination of AcO- (Np-Oax: 1.76-1.77 Å, Np-Oeq: 2.43-2.47 Å, Np-Ccarbo: 2.87 Å, Np-Cterm: 4.38 Å) which are consistent with the crystal structure of NaNpVIO2(AcO)3.
Also in the UV-Vis-NIR spectrum of a pH series of the Np(V)-AcO- system, no isosbestic points were detected. The refinement analysis resulted also in 3-step complexation equilibrium of NpVO2(AcO)n1-n (n = 1, 2, 3) with the stability constants log K1 = 1.93 ± 0.01, log b2 = 3.11 ± 0.01, and log b3 = 3.56 ± 0.01. This result is corroborated by the structural data obtained from EXAFS (Np-Oax: 1.83-1.85 Å, Np-Oeq: 2.51 Å, Np-Ccarbo: 2.90-2.93 Å) which are comparable with the crystal structure of BaNpVO2(AcO)3.
The observed stability constants were used to calculate a Paurbaix diagram. The validity of the assumed complexation reactions was confirmed by comparing the boundary of the stability field between Np(V) and Np(VI) species with experimental Np(V/VI) redox potentials.
Keywords: Neptunyl, UV-Vis-NIR, XAFS, Stability Constant, Molecular Structure
  • Lecture (Conference)
    Migration'09, 20.-25.09.2009, Kennewick, Washington, USA
  • Inorganic Chemistry 48(2009), 8803-8810
    DOI: 10.1021/ic900981q

Publ.-Id: 12542 - Permalink

Structural properties of MoS2 “mama”- tubes and related materials
Virsek, M.; Krause, M.; Kolitsch, A.; Mrzel, A.; Iskra, I.; Remskar, M.;
MoS2 nanomaterials synthesized by sulphurization of Mo6S2I8 nanowires were studied by wavelength dependent Raman spectroscopy, X-ray diffraction, and high resolution transmission electron microscopy (HRTEM). The transformation process leads to a variety of selective morphologies of the MoS2 product, like coaxial nanotubes, i.e. nanotubes with split walls, “mama”- tubes with encapsulated MoS2 fullerene-like particles, or other hybrid nanostructures. The temperature inside our horizontal fluidized-bed reactor directly determines the final morphology of the product. A temperature above 850°C leads to a formation of MoS2 “mama”– tubes, while below 850°C the growth of coaxial MoS2 nanotubes in which a number of multiwall nanotubes grow coaxially separated by gaps is favored. HRTEM was used to study how MoS2 layers form from outside of precursor nanowires toward inside and to observe the nucleation of fullerene-like particles. Results of a possible oxidation during the Raman experiments are correlated with partially or fully oxidized Mo6S2I8 nanowires of the composition MoO3-x, which can be afterwards also sulphurized resulting in MoS2 polycrystalline nanowires.
By the means of Raman and X-ray diffraction spectroscopies we have studied effect of temperature and duration of the sulphurization process. We followed the stages of the transformation to explore the chemical reaction kinetics.
  • Poster
    XXIIIrd International Winterschool on Electronic Properties of Novel Materials(IWEPNM 2009), 07.-14.03.2009, Kirchberg, Austria

Publ.-Id: 12541 - Permalink

Size and shape dependent Raman scattering of WS2 nanomaterials
Krause, M.; ViršEk, M.; Salacan, N.; Chen, L.; Abrasonis, G.; Kolitsch, A.; RemšKar, M.; Fleischer, N.; Hatto, P.; Möller, W.;
Fullerene-like WS2 nanoparticles and WS2 nanotubes are studied by wavelength dependent Raman spectroscopy. The response from the nanomaterials is compared to that of 2H-WS2 crystals and microcrystalline 2H-WS2 powder. The Raman signatures point to a hexagonal 2H stacking of the WS2 layers in all nanostructures. While the wave numbers of 1st and 2nd order Raman scattering show only little dependence, the line widths and the intensity ratios exhibit a systematic evolution with respect to the specific WS2 nanostructure. The sulfur-sulfur stretching mode range is particularly sensitive to the different stages of disorder and is suitable for the diagnostic classification of the WS2 nanostructures. Raman mapping across the nanoparticles is used to distinguish between disorder and surface effects on the vibrational spectra. All the experiments were performed at low laser power, since the transformation into WO3 is induced already at moderate illumination due to the limited photo- and thermal stability of the materials.

This work is supported by the European Union sixth Framework Program (FOREMOST project under contract NMP3-CT-2005-515840).
  • Poster
    XXIIIrd International Winterschool on Electronic Properties of Novel Materials (IWEPNM 2009), 07.-14.03.2009, Kirchberg, Austria

Publ.-Id: 12540 - Permalink

Speciation of Rare-Earth Metal Complexes in Ionic Liquids: A Multiple-Technique Approach
Nockemann, P.; Thijs, B.; Lunstroot, K.; Parac-Vogt, T. N.; Görller-Walrand, C.; Binnemans, K.; van Hecke, K.; van Meervelt, L.; Nikitenko, S.; Daniels, J.; Hennig, C.; van Deun, R.;
Abstract: The dissolution process of metal complexes in ionic liquids was investigated by a multiple-technique approach to reveal the solvate species
of the metal in solution. The task-specific ionic liquid betainium bis(trifluoromethylsulfonyl) imide ([Hbet][Tf2N]) is able to dissolve stoichiometric amounts of the oxides of the rare-earth elements. The crystal structures of the compounds [Eu2(bet)8(H2O)4][Tf2N]6,
[Eu2(bet)8(H2O)2][Tf2N]6·2H2O, and [Y2(bet)6(H2O)4][Tf2N]6 were found to
consist of dimers. These rare-earth complexes are well soluble in the ionic
liquids [Hbet][Tf2N] and [C4mim]- [Tf2N] (C4mim=1-butyl-3-methylimidazolium). The speciation of the metal complexes after dissolution in these ionic liquids was investigated by luminescence spectroscopy, 1H, 13C, and 89Y NMR spectroscopy, and by the synchrotron techniques EXAFS (extended X-ray absorption fine structure) and HEXS (high-energy X-ray scattering). The combination of these complementary analytical techniques reveals that the cationic dimers decompose into monomers after dissolution of the complexes in the ionic liquids. Deeper insight into the solution processes of metal compounds is desirable for applications of ionic liquids in the field of electrochemistry, catalysis, and materials chemistry.

Publ.-Id: 12539 - Permalink

Neue Materialien zur Eliminierung von Arzneimittelreststoffen durch Nano-Biotechnologie
Pollmann, K.; Marquard, A.; Günther, T.; Lehmann, F.; Richter, L.; Raff, J.;
- wird nachgereicht
  • Poster
    4. Dresdner Symposium "Endokrin aktive Stoffe in Abwasser, Klärschlamm und Abfällen, 25.03.2009, Dresden, Deutschland

Publ.-Id: 12537 - Permalink

Fluorine-18-radiolabeled S100A12: a potential probe for functional characterization of inflammatory processes in vivo
Hoppmann, S.; Richter, S.; Steinbach, J.; Pietzsch, J.;
S100A12 has been implicated in inflammation. However, the role of extracellular S100A12 in vivo is still unclear. We report a novel methodology using radiolabeling of human recombinant S100A12 with the positron-emitter fluorine-18 and the use of 18F-S100A12 in cell assays in vitro and in small animal positron emission tomography (PET) studies in rats in vivo. For S100A12 radiolabeling N-succinimidyl-4-(18F)fluorobenzoate was used. S100A12 was shown to stimulate secretion of cytokines by macrophages and endothelial cells. In vitro assays revealed specific binding of 18F-S100A12 to the soluble receptor for advanced glycation endproducts (sRAGE) and, furthermore, to membrane RAGE on both cell types. Cell interaction of 18F-S100A12 was inhibited by RAGE inhibitors like glycated LDL and, interestingly, also by scavenger receptor ligands, e.g., maleylated albumin, and by lectines. PET data showed sustained temporary association of 18F-S100A12 with tissues expressing RAGE, e.g., lung and endothelium in vivo. Moreover, specific accumulation of 18F-S100A12 in tissues enriched in cells expressing scavenger receptors, e.g., liver and spleen, was observed. Concluding, 18F-radiolabeling of S100A12 and the use of PET allow discrimination of the kinetics and the metabolic fate of S100A12 in vivo. The approach provides a novel probe for functional characterization of inflammation in rodent models of disease.
  • Poster
    9th World Congress on Inflammation, 06.-10.07.2009, Tokyo, Japan
  • Inflammation Research 58(2009)Suppl. 2, S145-S146

Publ.-Id: 12536 - Permalink

Combined UV-vis and EXAFS study on the complex formation of uranium(VI) with several carboxylic acids
Lucks, C.; Roßberg, A.; Scheinost, A.;
Natural organic matter (NOM) released by microorganisms and plants is ubiquitous in waters, soils and sediments. NOM can form relatively stable aqueous complexes with U(VI) and may interact like U(VI) with mineral surfaces. In systems containing U(VI), NOM and mineral surfaces binary and ternary sorption complexes have to be considered. These intricate interactions may profoundly influence the mobility of U(VI). However, the study of such a ternary system requires first its decomposition into simpler binary subsystems. Here we show the interaction of U(VI) with relatively simple carboxylic acids. Acetic, succinic and DL-tartaric acid were used as model compounds to simulate the different -COOH and -OH functionalities of the structurally more complicated, polyelectrolytic NOM.

Aqueous complexes of U(VI) with the model compounds were investigated by applying UV-VIS and EXAFS measurements. UV-VIS pH titration experiments were performed to identify the binary complexes formed in large excess of organic ligands and to derive their speciation. Uranium LIII-edge EXAFS spectra of pH series were then measured. Based on the speciation derived from UV-VIS spectroscopy, we were able to derive the EXAFS spectra of the pure U(VI) complexes from the EXAFS spectral mixtures by means of iterative target transform factor analysis [1]. Shell fit and an inversion method was then applied to validate their structures.
The uranium acetate and succinate complexes are characterized by a bidentate coordination of the carboxylic group. Furthermore, the formation of seven-membered rings can be rejected in the uranium succinate system. In contrast, the tartaric acid system is much more complicated because tartaric acid is able to form tridentate chelates with uranium using two carboxylic and one alcoholic groups. These chelates were identified to be dimeric at lower pH (3-5) and trimeric at higher pH (6-7). In addition, the structure of the trimer is also validated by the U-O radial pair distribution function (PDF) which is directly calculated from the EXAFS spectrum by an inversion method. The PDF of the oxygen atoms in the equatorial plane of U(VI) is asymmetric and gives evidence for one central oxygen atom linking the three uranyl ions of the trimer in a much shorter U-O distance than the remaining equatorial U-O distances.
In conclusion, we can provide structural models for the aqueous complexes of U(VI) with acetate, succinate and tartrate – the substances used as model compounds for NOM in this study.

[1] A. Rossberg, T. Reich, G. Bernhard, Anal. and Bioanal. Chem. 376, 631 (2003).
Keywords: uranium, complex formation, EXAFS
  • Poster
    PhD-Seminar 2009, 16.-18.09.2009, Krögis, Deutschland
  • Poster
    Migration Conference 2009, 20.-25.09.2009, Kennewick, Washington, USA

Publ.-Id: 12534 - Permalink

Microbial communities in extreme environments and their interactions with uranium and other xenobiotics
Selenska-Pobell, S.; Merroun, M.; Satchanska, G.; Golovinski, E.;
Bacteria are the most ubiquitous organisms in all terrestrial and aquatic environments. The talk will focus on cell wall dependent accumulation and biomineralization of uranium by particular Gram-positive and Gram-negative bacteria recovered from different extreme habitats. By using TEM, EXAFS and TRLF we were able to demonstrate that the Gram-negative and most of the Gram-positive bacteria inhabiting oligotrophic environments such as deep subsurface layers or heavy metal and pesticides polluted industrial sites immobilize U(VI) at their cell walls or extracellularly in a form of uranyl phosphate compounds. Some of the isolates demonstrated high capability to utilize phenol compounds as well. These properties of the studied extremophile bacterial isolates are promising for development of bioremediation approaches for heavy metal and phenol polluted environments
  • Invited lecture (Conferences)
    Ecology Seminar of the ECOLOGICAL ENGINERING AND ENVIRONMENTAL PROTECTION Society, 23.-24.04.2009, Sofia, Bulgaria

Publ.-Id: 12533 - Permalink

In-beam PET für die Therapie mit hochenergetischen Photonen
Kunath, D.; Kluge, T.; Pawelke, J.; Enghardt, W.;
Poster über die Integration von PET in die Strahlentherapie mit hochenergetischen Photonen
  • Poster
    Strategie-Meeting des OncoRay, 14.-15.01.2009, Bautzen, Deutschland

Publ.-Id: 12532 - Permalink

Determining the radial pair distribution function from EXAFS spectra by use of the Landweber iteration method
Rossberg, A.; Funke, H.;
The Landweber iteration method (1) is used to construct the radial pair distribution function (PDF) from an EXAFS spectrum. The PDF as solution of the fundamental EXAFS integral equation is determined in a stable way without additional supplementary conditions due to the semi-convergent behaviour of the Landweber iteration.
For the correct determination of the PDF it is important to know the energy shift dE0. If dE0 is unknown then usually it is determined by a shell fit of the spectrum before an inversion method is applied. If the shell fit model is incorrect then the determined dE0 is erroneous and an inverse method would give a wrong PDF. This leads in turn to the conclusion that the recent inversion procedures are only applicable if the structural model for the investigated system is already known; hence they are not “stand-alone” methods.

We developed an algorithm based on the Landweber iteration for deriving the appropriate dE0. The performance was tested by several theoretical and experimental EXAFS spectra of metal hydrates (U(IV), Np(IV), Th(IV), Cm(III)). For the estimation of the optimum number of iterations we adopted the L-curve concept which was recently used for the determination of the optimal regularization parameter in Tichonov’s method [2]. The examples show that the Landweber iteration in combination with the simultaneous determination of dE0 and the L-curve concept for the estimation of the optimum number of iterations is a robust way to calculate the PDF. The approach enables the calculation of the PDF even for strong overlapping shells like for Cm(III) hydrate.

(1) Landweber, L. Am. J. Math. 73, 615-624 (1951).
(2) Kunicke, M., et al. Physica Scripta T115, 237–239 (2005).
  • Lecture (Conference)
    The 14th International Conference on X-ray Absorption Fine Structure (XAFS14), 26.-31.07.2009, Camerino, Italy

Publ.-Id: 12531 - Permalink

The potential of in-beam positron emission tomography within image-guided radiation therapy
Kunath, D.; Fiedler, F.; Kluge, T.; Kormoll, T.; Laube, K.; Pawelke, J.; Priegnitz, M.; Shakirin, G.; Enghardt, W.;
Abstract about the potential of in-beam PET within IGRT
  • Abstract in refereed journal
    Radiotherapy and Oncology 90(2009)Suppl. 3, S77-S78

Publ.-Id: 12530 - Permalink

In-Beam and Off-Beam PET Measurements of Target Activation by Megavolt X-Ray Beams
Kunath, D.; Kluge, T.; Pawelke, J.; Priegnitz, M.; Enghardt, W.;
In-beam positron emission tomography (in-beam PET) is a valuable in situ method for quality assurance in radiation therapy. It is well investigated for therapy with carbon ions and has been successfully implemented clinically at the Gesellschaft für Schwerionenforschung (GSI), Darmstadt, Germany. The extension of this efficient technique to other radiation treatment modalities may be worthwhile. For protons, 3-He, 7-Li, and 16-O the feasibility has already been experimentally shown. Furthermore, it seems to be feasible for the case of radiotherapy with high-energy photons, since positron emitters are generated by photons with energies above 20 MeV due to (gamma, n) photo-nuclear reactions (predominantly 11-C and 15-O in tissue). In this regard, promising conclusions have been obtained by Geant4 simulations as well as by off-beam PET experiments using a conventional PET scanner. The next step was the installation of a small double head positron camera consisting of two bismuth germanate (BGO) block detectors at the irradiation site to measure the generated beta+ activity distribution simultaneously to the irradiation. The relation between deposited dose and beta+ activity density was quantified. The obtained results are presented and compared to that of off-beam PET experiments. Higher activities as well as an improved contrast between materials of different stoichiometry are achieved by measuring in-beam, showing the advantage of in-beam PET over off-beam PET. Thus, the application of in-beam PET to radiation therapy with high-energy photons can be useful for quality assurance, comprising monitoring of dose delivery, patient positioning and tumor response.
Keywords: Dose monitoring, high-energy photon therapy, positron emission tomography.

Publ.-Id: 12529 - Permalink

A two group analytical approximation solution for an external source problem without separation of space and time
Merk, B.; Weiß, F. P.;
This work presents the development of analytical approximation solutions for a space-time dependent neutron transport problem in two energy groups for a one dimensional system consisting of a homogenized medium with a central external source. The approximation solutions are developed using Green's functions, the influence of the delayed neutrons is not considered. Qualitative results for a given system are analyzed. A detailed comparison of the developed analytical approximation solutions with solutions with one energy group and with results gained by the time dependent diffusion equation without separation of space and time is given.
Keywords: Time dependet neutron diffusion, Accelerator driven system, Experimental analysis, Green's funtion expansion
  • Annals of Nuclear Energy 37(2010), 942-952

Publ.-Id: 12528 - Permalink

Pu Bestimmung von 242Pu in Plutoniumnuklidgemischen mittels Flüssigszintillation
Nebelung, C.;
Für Speziations- und Sorptionsuntersuchungen mit Plutonium steht am Institut für Radiochemie des FZ Dresden-Rossendorf 242Pu (T1/2 3,755*105 Jahre) zur Verfügung, das eine Reinheit von 99,93 Atom% hat. Da die übrigen enthaltenen Plutoniumisotope zum Teil wesentlich kürzere Halbwertszeiten haben (240Pu: T1/2 6563 Jahre, 238Pu: T1/2 87,7 Jahre, 241Pu: T1/2 14,35 Jahre), ist der Aktivitätsanteil dieser Isotope erheblich. Das Material wurde vor 29 Jahren hergestellt, so dass zusätzlich zu den Plutoniumisotopen die Tochter von 241Pu, das 241Am, zu beachten ist. Es besteht die Aufgabe, schnell für eine Vielzahl von Proben den Gehalt des 242Pu zu bestimmen. Das wird durch Flüssigszintillation erreicht, bei der zunächst eine alpha/beta Separation durchgeführt wird und anschließend durch Spektrenentfaltung [1] der Peak des 242Pu vom gemeinsamen 238Pu/241Am-Peak getrennt wird.

[1] Nebelung, C., Baraniak, L., 2007. Simultaneous Determination of 226Ra, 233U and 237Np by Liquid Scintillation Spectrometry. Applied Radiation and Isotopes, 65, 209-217.
Keywords: liquid scintillation, alpha/beta separation, Pu nuclide, spectra deconvolution
  • Lecture (Conference)
    5. LSC Anwendertreffen „Aktivitätsbestimmung mit Hilfe der Flüssigszintillationsmesstechnik“, 23.-24.04.2009, Karlsruhe, Deutschland

Publ.-Id: 12527 - Permalink

Flavonoids – natural phenolic complexing agents towards uranium
Geipel, G.; Viehweger, K.; Bernhard, G.;
Flavonoids belong to a class of secondary plant metabolites. They are one of the largest classes of plant phenolics. All flavonoids consist of a 15 carbon skeleton. Flavonoids are most commonly known at least for four main properties: colored (to attract animals), absorbing ultraviolet light (to protect against damage), antimicrobial activity (to protect against bacterial or fungal infection) and antioxidant activity (which may be responsible for anticancer benefits) [1].
The structure of flavonoids is dominated by phenolic hydroxyl groups.

We studied the complex formation of the flavonoid kaempferol with uranium. Kaempferol is a 3,5,7-Trihydroxy-2- (4-hydroxyphenyl)-4H-1- benzopyran-4-on. As stated already flavonoids show strong absorption spectra in the UV-range. The change in their spectroscopic data was used to determine the stability constants. Spectra were evaluated with the factor analysis program Specfit [2]. All spectra of flavonoids show isosbestic points indicating a clear interaction between kaempferol and uranium(VI).
A strong interaction was found for kaempferol. The derived stability constant was assigned to be log β121 = 31.7 ± 0.4 at an ionic strength of 0.1 M for the reaction

UO22+ + C15H5O64- + 2 H+ → UO2C15H7O6 (1)

Data derived from studies with quercetin and hesperetin show an analogue stability constant for the non-charged complex.
We assume that the complex formation occur by a ring formation, whereas the flavonoids form rings between the phenolic group in position 3 or 5 respectively and the ketone oxygen in the benzopyran-4-one ring [3].

[1] Tiaz L, Zeiger E Plant Physiology 2006 4. Edition, Sinauer Associates Inc.
[2] Binstead R A, Jung B, Zuberbühler A D Specfit Global analysis system Spectrum Software Associates 2000-2003
[3] Malesev D, Kuntic V 2007 J. Serb. Chem. Soc. 72 921
Keywords: flavonoids, actinides, uranium, complex formation
  • Contribution to proceedings
    Migration Conference 2009, 20.-25.09.2009, Kennewick, Washington,, USA
  • Poster
    Migration 2009, 20.-25.09.2009, Kennewick, Washington,, USA

Publ.-Id: 12526 - Permalink

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