Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31735 Publications
Mechanism of electrical properties degradation of ZnO:Al films during growth at elevated temperatures
Vinnichenko, M.; Gago, R.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Kolitsch, A.; Möller, W.;
Resistivity of ZnO:Al (AZO) films is known to increase significantly during annealing or growth at temperatures higher than certain optimum value that is a problem during preparation of thin film solar cells. To understand this process, AZO films with different Al concentrations grown by reactive pulsed magnetron sputtering were studied. The electrical resistivity of the films shows a minimum at an optimum substrate temperature, which shifts from 400 °C to 200 °C with increasing Zn/O flux ratio. At higher temperatures, resistivity increases due to simultaneous decrease of the free electron density and mobility. It is accompanied by a significant deterioration of the film crystallinity, increase of Al concentration and drop of the growth rate. X-ray absorption near edge structures (XANES) excludes formation of aluminum oxides in this case. It shows formation of homologous phase (ZnO)3(Al2O3) whose formation is triggered by an increase of the Al/Zn ratio in the film. Therefore, at growth temperatures above the optimum value Al preferentially forms this phase instead of occupying Zn site in the lattice.
Keywords: Al-doped ZnO, transparent conductive oxides, homologous metastable phase, (ZnO)3(Al2O3)
  • Lecture (Conference)
    5th Forum on New Materials (in the framework of 12th International Conference on Modern Materials and Technologies - CIMTEC 2010), 13.-18.06.2010, Montecatini Terme, Italy

Publ.-Id: 14205 - Permalink


Biosensing for the Environment and Defence: Aqueous Uranyl Detection Using Bacterial Surface Layer Proteins
Conroy, D. J. R.; Millner, P. A.; Stewart, D. I.; Pollmann, K.;
The fabrication of novel uranyl (UO2 2+) binding protein based sensors is reported. The new biosensor responds to picomolar levels of aqueous uranyl ions within minutes using Lysinibacillus sphaericus JG-A12 S-layer protein tethered to gold electrodes. In comparison to traditional self assembled monolayer based biosensors the porous bioconjugated layer gave greater stability, longer electrode life span and a denser protein layer. Biosensors responded specifically to UO2 2+ ions and showed minor interference from Ni2+, Cs+, Cd2+ and Co2+. Chemical modification of JG-A12 protein phosphate and carboxyl groups prevented UO2 2+ binding, showing that both moieties are involved in the recognition to UO2 2+.
Keywords: S-layer; surface layer; protein biosensor; uranium; uranyl; metal ion; sequestering; impedance spectroscopy

Publ.-Id: 14204 - Permalink


Effect of secondary phase formation on electrical and optical properties of Al-doped ZnO
Vinnichenko, M.; Cornelius, S.; Gago, R.; Krause, M.; Shevchenko, N.; Rogozin, A.; Munnik, F.; Kolitsch, A.; Möller, W.;
It has been shown that increasing substrate temperature above its optimum value leads to an increase of Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. The formation of (ZnO)3Al2O3 is established for the AZO films grown in a given range of deposition conditions, while the films grown at substantially different conditions may show formation of other secondary phases (e.g. aluminium oxide or spinel). This (ZnO)3Al2O3 impedes crystal growth and causes a significant increase of free electron scattering. In turn, it leads to an increase of electrical resistivity of the films. This phase has been observed by XANES even in the films with the lowest Al concentration and the best crystallinity. Increase of this phase volume fraction with increasing Al concentration correlates with observed changes in the film Raman and optical constants spectra.
Keywords: Al-doped ZnO, homologous metastable phase, (ZnO)3Al2O3
  • Lecture (Conference)
    EFDS-Workshop „Transparente leitfähige Oxide - Festkörperphysikalische Grundlagen und Technologie“, 01.-02.06.2010, Dresden, Germany

Publ.-Id: 14203 - Permalink


Capabilities and limitations of spectroscopic ellipsometry for characterization of functional thin films
Vinnichenko, M.;
An overview of different configurations of spectroscopic ellipsometers was given. The approaches for data acquisition and analysis in case of high refractive index materials and transparent conductive oxides were discussed.
  • Lecture (others)
    Invited lecture during visit to "Next Energy" EWE-Forschungszentrum für Energietechnologie e.V., 10.-11.02.2010, Oldenburg, Germany

Publ.-Id: 14202 - Permalink


Properties, structure and phase composition of transparent conductive oxide thin films grown by magnetron sputtering
Vinnichenko, M.; Cornelius, S.; Rogozin, A.; Shevchenko, N.; Gago, R.; Kolitsch, A.; Möller, W.;
Understanding of the mechanisms of donor impurity incorporation, its electrical activation and charge carrier transport in transparent conducting oxides (TCO) is required for further improvement of functionality of this class of materials. The present work focuses on investigation of indium oxide (IO), Sn-doped indium oxide (ITO), ZnO, and ZnO:Al (AZO) films grown by reactive pulsed magnetron sputtering (RPMS) with a precise control of the oxygen partial pressure at substrate temperatures, Ts, ranging from RT to 550°C. In order to explore potential advantages of RPMS, the relationship between the deposition parameters and structure, phase composition and physical properties of these TCOs was investigated. The films were characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and AZO films, by X-ray absorption near edge structures (XANES). The Sn concentration in ITO was determined by Auger analysis, while the Al concentration in ZnO matrix was estimated by elastic recoil detection analysis and Rutherford back scattering.
The comparison of the real-time behavior of the IO and ITO film structure and electrical properties during annealing provides a direct evidence of Sn donor activation (with an estimated efficiency of 40%) in ITO due to amorphous-to-crystalline transition. The ITO film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. In contrast, the electrical resistivity of AZO films shows a clear minimum at an optimum substrate temperature (200-400 °C), which depends on metal/oxygen flux ratio and correlates with a maximum in crystallinity (grain size). In this case, the highest mobility value of 46 cm2 V-1 s-1 is comparable to the best values achieved in AZO films grown by less cost-efficient techniques. This value is achieved at the free electron density of 6x1020 cm-3 which corresponds to maximum ~30% electrical activation of Al impurity. At higher temperatures, the AZO electrical properties and crystalline quality deteriorate abruptly according to the following mechanism. Increasing Ts above its optimum value leads to a higher Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth and causes a significant increase of free electron scattering both at grain boundaries and inclusions of this phase. In order to enable the growth of low-resistivity AZO films in a wider range of TS, lower metal/oxygen flux ratios should be used. The proposed approach to minimizing the influence of this undesirable phase may also be applied to other deposition methods of AZO involving high-energy particle bombardment.
Keywords: Al-doped ZnO, transparent conductive oxides, electrical properties, optical properties, phase composition
  • Lecture (others)
    Invited talk during visit to "Next Energy" EWE-Forschungszentrum für Energietechnologie e.V., 10.-11.02.2010, Oldenburg, Germany

Publ.-Id: 14201 - Permalink


RBS\channeling and TEM study of damage buildup in ion bombarded GaN
Pagowska, K.; Ratajczak, R.; Stonert, A.; Turos, A.; Nowicki, L.; Sathish, N.; Jozwik, P.; Muecklich, A.;
A systematic study on structural defect buildup in 320 keV Ar-ion bombarded GaN epitaxial layers has been reported, by varying ion fluences ranged from 5x1012 to 1x1017 at/cm2. 1μm thick GaN epitaxial layers were grown on sapphire substrates using the MOVPE technique. RBS\channeling with 1.7 MeV 4He beam was applied for analysis. As a complementary method High Resolution Transmission Electron Microscopy (HRTEM) has been used. The later has revealed the presence of extended defects like dislocations, faulted loops and stacking faults. New version of the Monte Carlo simulation code McChasy has been developed that makes it possible to analyze such defects on the basis of the Bent Channel (BC) model. Damage accumulation curves for two distinct types of defects, i.e. Randomly Displaced Atoms (RDA) and extended defects (i.e BC) have been determined. They were evaluated in the frame of the MultiStep Damage Accumulation (MSDA) model, allowing numerical parameterization of defect transformations occurring upon ion bombardment. Displaced atoms buildup is a three step process for GaN and whereas extended defect buildup is always a two step process.
Keywords: GaN, ion bombardment, ion channeling, TEM, defect transformations
  • Lecture (Conference)
    VIII-th International Conference Ion Implantation and Other Applications of Ions and Electrons, 14.-17.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14200 - Permalink


Bildgebende Messverfahren und CFD-Simulation für die Energieverfahrenstechnik
Hampel, U.; Lucas, D.; Vallée, C.; Höhne, T.; Beyer, M.; Fischer, F.; Weiß, F.-P.;
In diesem Beitrag werden ausgewählte tomographische Bildgebungsverfahren vorgestellt, die in den zurückliegenden Jahren am Forschungszentrum Dresden-Rossendorf für die Untersuchung von Mehrphasenströmungen entwickelt wurden. Neben einer Beschreibung der Messverfahren wird ihre Anwendung in der experimentellen Thermofluiddynamik und ihr Bezug zur Entwicklung und Validierung von CFD-Modellen für Zweiphasenströmungen diskutiert.
Keywords: multiphase flow, flow imaging techniques, CFD simulation
  • Contribution to external collection
    M. Beckmann, A. Hurtado: Kraftwerkstechnik - Sichere und nachhaltige Energieversorgung - Band 2,, Neuruppin: TK Verlag Karl Thomé-Kozmienski, 2010, 978-3-935317-57-3, 769-786
  • Lecture (Conference)
    42. Kraftwerkstechnisches Kolloquium, 12.-13.10.2010, Dresden, Germany

Publ.-Id: 14199 - Permalink


Synthesis of neurotensin(8-13)-phosphopeptide heterodimers via click chemistry
Richter, S.; Ramenda, T.; Bergmann, R.; Knieß, T.; Steinbach, J.; Pietzsch, J.; Wuest, F.;
Two neurotensin(8-13)-containing peptide heterodimers were prepared via copper(I)-mediated click chemistry. The resulting peptide dimers could be obtained in 28-31% yield after HPLC purification. Neurotensin( 8-13)-containing peptide dimers were used in an in vitro binding assay to determine binding affinity towards the neurotensin receptor-1 (NTR1). The determined IC50 values of 8.3 µM and 0.7 µM indicate only very low binding affinity of the neurotensin(8-13)-containing peptide heterodimers towards the NTR1.
Keywords: Click chemistry, Neurotensin receptor, Phosphopeptide, Peptide heterodimer

Publ.-Id: 14198 - Permalink


Ferromagnetic resonance on metal nanocrystals in Fe and Ni implanted ZnO
Ankiewicz, A. O.; Martins, J. S.; Carmo, M. C.; Grundmann, M.; Zhou, S.; Schmidt, H.; Sobolev, N. A.;
We studied the angular dependence of the ferromagnetic resonance (FMR) spectra of (0001)ZnO single crystals implanted with Ni and Fe ions and compared the results to the data obtained by other experimental techniques, especially, x-ray diffraction (XRD) and superconducting quantum interference device magnetometry. The FMR revealed the formation of metal nanocrystals (NCs) embedded in the ZnO lattice in an oriented way. Whereas in the case of Ni, the conclusions drawn from the FMR studies corroborated the XRD and magnetometry results with respect to the alignment of the NCs in the host lattice, in the case of the Fe NCs, the FMR clearly shows that the hard magnetization axis (which is < 111 > in bcc Fe) is oriented perpendicular to the sample surface (parallel to the [0001]ZnO axis), at variance with the former XRD observations.
Keywords: ferromagnetic resonance, II-VI semiconductors, ion implantation, iron, magnetisation, nanostructured materials, nickel, X-ray diffraction, zinc compounds

Publ.-Id: 14196 - Permalink


Encapsulation of Fluorescent Cluster Complexes into Dendritic Nanocontainer
Kuhlmann, M.;
kein Abstract verfügbar
  • Lecture (Conference)
    7th Supraphone Meeting, 28.04.-01.05.2010, Maria Laach, D

Publ.-Id: 14195 - Permalink


Personen- und Produktschutz bei der Herstellung von PET Radiopharmaka
Füchtner, F.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    2. NZW Dresden - Onkologisch-Pharmazeutischer Fachkongress, 18.-19.06.2010, Dresden, D

Publ.-Id: 14194 - Permalink


Water repartitioning at the water lipid protein interface controls receptor activation in G-Protein coupled receptors
Eichler, S.; Fahmy, K.;
G-Protein coupled receptors (GPCRs) play a fundamental role in many physiological processes. High ligand specifity of rhodopsin-like GPCRs in contrast to the highly conserved and class defining D(E)RY motif undergoing a protonation upon receptor activation suggests a general local activation mechanism acting as an autonomous functional module.
It has been shown that the D(E)RY motif positioned at the phase boundary acts as a pH-dependent switch which is governed by side chain partitioning between the aqueous and lipidic phase [1].
Here we have addressed the putative reverse effect, i.e. restructuring of the water lipid interface upon side chain protonation to elucidate the functional implication of water lipid protein interactions in the control of protein conformation. We have studied a TM3 derived transmembrane segment where a fluorescence reporter resides below the D(E)RY motif inside the helix. By fluorescence spectroscopy, FRET studies and FTIR-Fluorescence cross correlation experiments we show the pH dependent hydration site N-terminally of the D(E)RY motif. Thus the ionized D(E) side chain attracts water that dissolves the TM-sequence even beyond the two preceding hydrophobic residues.
These results argue for a key role of the rearrangement of the water lipid protein microstructure upon GPCR activation as it effects not only the phase boundary but even more hydrophobic environment inside the lipidic phase.
[1] S. Madathil, K.Fahmy, J Biol Chem 284, 28801-28809 (2009)
Keywords: membrane transport, protonation, FTIR spectroscopy, fluorescence spectroscopy, FRET, charge stabilization, bilayer, water reorganization
  • Lecture (Conference)
    Annual Meeting of the German Biophysical Society, 03.-06.10.2010, Bochum, Deutschland

Publ.-Id: 14193 - Permalink


Experiments and numerical simulations of horizontal two phase flow regimes using an interfacial area density model
Höhne, T.; Vallée, C.;
Stratified two-phase flow regimes can occur in the main cooling lines of Pressurized Water Reactors, Chemical plants and Oil pipelines. A relevant problem occurring is the development of wavy stratified flows which can lead to slug generation. In the last decade, 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. 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 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 at other superficial velocities.
Keywords: CFD, AIAD, multiphase flow
  • The Journal of Computational Multiphase Flows 2(2010)3, 131-143

Publ.-Id: 14192 - Permalink


Blending magnetic properties - hybrid magnetic thin films
McCord, J.;
The control of the effective magnetic anisotropy, saturation magnetization, as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for most applications in spin electronics. Usually the magnetic anisotropy, e.g. uniaxial anisotropy or unidirectional anisotropy, in ferromagnetic single or multi-layers is initialized by applying a magnetic field during film deposition or by a magnetic field anneal, which results in an anisotropy aligned along the applied field direction. The saturation magnetization is mainly determined by the film's composition. Whereas anisotropy and saturation magnetization together determine the precessional frequency of the films, the magnetic damping parameter cannot easily be varied in a controlled way.
Here we give a summary on different ways to pattern magnetic films in terms of laterally varying magnetic properties and not by shape patterning [1]. Different samples of anisotropy [1,2], exchange bias [1,3], and saturation magnetization [4] modulated thin films are prepared by local oxidation, introducing local stress variation [5], and local ion irradiation or implantation. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from multilayer samples. The main emphasis of the investigations is on the role of magnetic domain formation and domain wall effects in stripe-like magnetic hybrid structures on the overall static and dynamic magnetic properties.
The presented paths of film preparation provide an additional degree of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films.
  • Invited lecture (Conferences)
    Colloquium of the "Sonderforschungsbereich 855" - Magnetoelektrische Verbundwerkstoffe - biomagnetische Schnittstellen der Zukunft, 01.07.2010, Kiel, Deutschland

Publ.-Id: 14191 - Permalink


Effects of lateral fluid percussion injury on cholinergic markers in the newborn piglet brain
Donat, C. K.; Walter, B.; Kayser, T.; Deuther-Conrad, W.; Schliebs, R.; Nieber, K.; Bauer, R.; Haertig, W.; Brust, P.;
Traumatic brain injury is a leading cause of death and disability in children. Studies using adult animal models showed alterations of the central cholinergic neurotransmission as a result of trauma. However, there is a lack of knowledge about consequences of brain trauma on cholinergic function in the immature brain. It is hypothesized that trauma affects the relative acetylcholine esterase activity and causes a loss of cholinergic neurons in the immature brain. Severe fluid percussion trauma (FP-TBI, 3.8 0.3 atm) was induced in 15 female newborn piglets, monitored for 6 h and compared with 12 control animals. The hemispheres ipsilateral to FP-TBI obtained from seven piglets were used for acetylcholine esterase istochemistry on frozen sagittal slices, while regional cerebral blood flow and oxygen availability was determined in the remaining eight FP-TBI animals. Post-fixed slices were immunohistochemically labelled for choline acetyltransferase as well as for lowaffinity neurotrophin receptor in order to characterize cholinergic neurons in the basal forebrain. Regional cerebral blood flow and brain oxygen availability were reduced during the first 2 h after FPTBI (P < 0.05). In addition, acetylcholine esterase activity was significantly increased in the neocortex, basal forebrain, hypothalamus and medulla after trauma (P < 0.05), whereas the number of choline acetyltransferase and low-affinity neurotrophin receptor positive cells in the basal forebrain were unaffected by the injury. Thus, traumatic brain injury evoked an increased relative activity of the acetylcholine esterase in the immature brain early after injury, without loss of cholinergic neurons in the basal forebrain. These changes may contribute to developmental impairments after immature traumatic brain injury.
Keywords: Traumatic brain injury Immature brain Cholinergic system Acetylcholine esterase

Publ.-Id: 14190 - Permalink


Alterations of cholinergic receptors and the vesicular acetylcholine transporter after lateral fluid percussion injury in newborn piglets
Donat, C. K.; Walter, B.; Deuther-Conrad, W.; Nieber, K.; Brust, R.; Bauer, P.;
Aims: Traumatic brain injury (TBI) is one of the leading causes of death and disability in children. Adult animal models of TBI showed cholinergic alterations. However, there is no comparable data on immature animals. Therefore, this study investigates cholinergic markers in a large animal model of juvenile TBI. Methods: Twenty-seven female newborn piglets were subjected to lateral fluid percussion (FP) injury and compared with 12 untreated animals. After 6 h, animals were sacrificed and the brains removed.The hemispheres ipsilateral to FP-TBI from seven piglets and corresponding hemispheres from six control animals were used for autoradiography. Receptor density was determined with [3H]epibatidine (nicotinic acetylcholine receptors) or [3H]QNB (muscarinic acetylcholine receptors). The density of the vesicular acetylcholine transporter (vAChT) was assessed with (-)-[3H]vesamicol. Cerebral blood flow was measured by coloured microsphere method. Results: Cerebral blood flow and brain oxygen delivery were transiently reduced early after FP-TBI (P < 0.05). TBI caused reductions of muscarinic acetylcholine receptor density (fmol/mg) in the basal forebrain (sham: 10797 1339, TBI: 8791 1031), while nicotinic acetylcholine receptor remained stable. Significant increases in vAChT density (fmol/mg) were observed in the basal forebrain (sham: 2347 171, TBI: 2884 544), putamen (sham: 2276 181, TBI: 2961 386), cortex (sham: 1928 262, TBI: 2377 294), thalamic areas (sham: 2133 272, TBI: 2659 413), hippocampus (sham: 2712 145, TBI: 3391 501) and hypothalamus (sham: 2659 139, TBI: 3084 304). Conclusions: Cholinergic markers are altered after mildto- moderate TBI in the immature brain.Whereas the ACh receptors are stable in almost any brain region after TBI, vAChT expression increases after trauma at the employed severity of this specific trauma model.
Keywords: muscarinic, newborn pig, nicotinic, receptor, traumatic brain injury, vesicular transporter

Publ.-Id: 14189 - Permalink


Neue fluoreszenzspektroskopische Untersuchungen zur Huminstoff-Komplexbildung konkurrierender Metalle und aktuelle Ergebnisse von Transportstudien mittels PET
Lippold, H.; Kulenkampff, J.; Gründig, M.; Eidner, S.; Kumke, M.;
Für die Veranstaltung wurden keine Abstracts eingereicht.

Vorgestellt wurden TRLFS-Studien mittels Eu(III) an Systemen aus Huminstoff und Al(III) verschiedenen Alters. Innerhalb des untersuchten Zeitraums von ca. 2 Tagen wurde eine Zunahme im Konkurrenzeffekt von Al(III) bezüglich der Huminstoff-Komplexbildung anderer Metalle festgestellt. Ziel der spektroskopischen Messungen war ein Nachweis struktureller Veränderungen am Huminstoff, die den beobachteten Effekt erklären. Zwar konnte gezeigt werden, dass durch die Komplexbildung von Al(III) erhebliche Veränderungen in der Mikroumgebung des Sondenmetalls Eu(III) induziert werden. Diese entsprachen jedoch nicht dem zeitlichen Trend im Konkurrenzeffekt. Aus Spektrenanalysen ging hervor, dass ein solcher Trend bei der relativ hohen Konzentration des Sondenmetalls gar nicht auftritt.
Gezeigt wurden auch erste PET-Untersuchungen zum diffusiven Transport in einem Opalinuston-Bohrkern. Mit Hilfe verbesserter Korrekturverfahren und neuer Visualisierungstechniken konnte die Methodik erheblich voran gebracht werden. Bereits nach einer Versuchsdauer von 2 Wochen konnte ein Diffusionskoeffizient abgeschätzt werden, der in Übereinstimmung mit Literaturdaten stand. Die Erfassung räumlicher Inhomogenitäten im Ausbreitungsverhalten erfordert jedoch längere Messzeiten und einen modifizierten Versuchsaufbau, welcher ebenfalls vorgestellt wurde.
  • Lecture (others)
    8. Workshop zum Verbundvorhaben "Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika", 13.-14.04.2010, Dresden-Rossendorf, Deutschland

Publ.-Id: 14188 - Permalink


Novel Indole Derivatives as Potential Imaging Agents for Alzheimer’s Disease
Yu, L.; Scheunemann, M.; Deuther-Conrad, W.; Hiller, A.; Fischer, S.; Sorger, D.; Sabri, O.; Jia, H.; Steinbach, J.; Brust, P.; Liu, B.;
kein Abstract verfügbar
Keywords: β-Amyloid, Indole, Positron emission tomography, Senile plaques

Publ.-Id: 14187 - Permalink


On the action of magnetic gradient forces in micro-structured copper deposition
Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Fröhlich, J.;
In order to shed more light on the role of magnetic gradient forces and Lorentz forces on the deposition pattern found recently at copper electrodes, experiments and numerical simulations have been performed in a generic geometry that consists of a single small cylindrical permanent magnet which is placed behind the cathode. The cylinder axis coincides with the magnetization direction and points normal to the electrode surface. The electrode is oriented vertically which allows a separate discussion of the influence of both forces.

Experiments and numerical simulations are found to give very good agreement with respect to the deposition pattern. Our analysis clearly shows that the major influence is due to the action of the magnetic gradient force. Numerical simulations prove that the separate action of the Lorentz force does not reproduce the deposition structure. A detailed analytical discussion of the motion forced by the different magnetic forces in superposition with natural convection is given.
Keywords: Lorentz force, field gradient force, magnetoelectrochemistry

Publ.-Id: 14186 - Permalink


Tomographische Radiotraceruntersuchungen zu Transportprozessen im Salinar und seinem Deckgestein in Staßfurt Tomographic Investigations of Transport Processes with Radiotracers in Evaporitic Rock and its Hanging Wall in Staßfurt
Kulenkampff, J.; Wolf, M.; Gründig, M.; Mittmann, H.; Richter, M.;
Positronen-Emissions-Tomographie (PET) wurde als Methode zur Untersuchung von Transportvorgängen in Bohrkernen aus dem Salinargestein und seinem Deckgebirge in Staßfurt eingesetzt. Die Ergebnisse dienen der Verbesserung des Verständnisses der hydraulischen und chemischen Prozesse im heterogenen, teils dichten Material. Es kann anhand von Beispielen gezeigt werden, dass diese Prozesse sich nicht allgemein durch einfache Modelle beschreiben lassen.
  • Exkursionsführer und Veröffentlichungen der Deutschen Gesellschaft für Geowissenschaften 242(2010), 95-97

Publ.-Id: 14185 - Permalink


Surface modeling and chemical solution deposition of SrO(SrTiO3)n Ruddlesden–Popper phases
Zschornak, M.; Gemming, S.; Gutmann, E.; Weißbach, T.; Stöcker, H.; Leisegang, T.; Riedl, T.; Tränkner, M.; Gemming, T.; Meyer, D. C.;
Strontium titanate (STO) is a preferred substrate material for functional oxide growth, whose surface properties can be adjusted through the presence of Ruddlesden–Popper (RP) phases. Here, density functional theory (DFT) is used to model the (1 0 0) and (0 0 1) surfaces of SrO(SrTiO3)n RP phases. Relaxed surface structures, electronic properties and stability relations have been determined. In contrast to pure STO, the near-surface SrO–OSr stacking fault can be employed to control surface roughness by adjusting SrO and TiO2 surface rumpling, to stabilize SrO termination in an SrO-rich surrounding or to increase the band gap in the case of TiO2 termination. RP thin films have been epitaxially grown on (0 0 1) STO substrates by chemical solution deposition. In agreement with DFT results, the fraction of particular RP phases n = 1–3 changes with varying heating rate and molar ratio Sr:Ti. This is discussed in terms of bulk formation energy.
Keywords: functional oxide, oxide, DFT, Ruddlesden-Popper, TEM, X ray, surfaces

Publ.-Id: 14184 - Permalink


EXAFS, XANES, and DFT study of the mixed-valence compound YMn 2O 5: Site-selective substitution of Fe for Mn
Wunderlich, F.; Leisegang, T.; Weissbach, T.; Zschornak, M.; Dshemuchadse, J.; Lubk, A.; Führlich, T.; Welter, E.; Souptel, D.; Gemming, S.; Seifert, G.; Meyer, D. C.;
In YMn2O5 the Mn atoms occupy two non-equivalent Wyckoff sites within the unit cell exhibiting different oxygen coordinations, i. e. the system can be characterized as a mixed-valence compound. For the formation of the orthorhombic crystal structure Jahn-Teller distortions are assumed to play an important role. In this study, we aimed at the investigation of the crystal structure on the substitution of Mn by the non-Jahn-Teller cation Fe+3. Therefore, we synthesized a series of YMn(2-x)FexO5 powder samples with x = 0; 0:5; 1 by a citrate technique. We utilized extended x-ray absorption fine structure (EXAFS), x-ray absorption near edge structure (XANES) analysis and Density Functional Theory to investigate the two non-equivalent Wyckoff sites within the orthorhombic crystal structure (confirmed for all compositions) occupied by transition-metal atoms. For quantitative determination of structural short-range order firstly all plausible options of substitution of Fe for Mn were discussed. On basis of these evaluations the EXAFS and XANES behavior was analyzed and appropriate crystallographic weights were assigned to the subset of structural models in accordance with the experimental data. From EXAFS analysis, using multiple scattering theory, we concluded only the 4h Wyckoff site to be occupied by Fe (occupancy refined was (100 +- 3)% in case of x = 1). Furthermore, taking the XANES spectra into account, we could verify the EXAFS results and additionally explain the differences in the Mn-K XANES spectra in dependence on x to be caused by changes of the dipole transitions to 4p final states. Since only one Wyckoff site is involved the experimentally observed limit to a maximum amount of x = 1 is explained. Additionally, a possible disorder, discussed in the literature, was not proven for our samples. With DFT calculations the experimental findings were verified on base of the total energy of the different possible electronic configurations. Crystal field effects were identified to be responsible for the site selective substitution of Fe for Mn.
Keywords: multiferroic, oxide, functional, DFT, XANES, XAFS, X-ray, ferrimagnet, antiferromagnet

Publ.-Id: 14183 - Permalink


Measurement of K*(892)0 and K0 mesons in Al+Al collisions at 1.9A GeV
Lopez, X.; Herrmann, N.; Piasecki, K.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Buehler, P.; Cargnelli, M.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fabbietti, L.; Fijal-Kirejczyk, I.; Fodor, Z.; Gasik, P.; Gasparic, I.; Grishkin, Y.; Hartmann, O.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kirejczyk, M.; Kim, Y. J.; Kis, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Suzuki, K.; Tyminski, Z.; Wagner, P.; Widmann, E.; Wisniewski, K.; Xiao, Z. G.; Yushmanov, I.; Zhang, X. Y.; Zhilin, A.; Zmeskal, J.; Kienle, P.; Yamazaki, T.;
A new measurement of subthreshold K∗(892)0 and K0 production is presented. The experimental data complete the measurement of strange particles produced in Al + Al collisions at 1.9AGeV measured with the FOPI detector at SIS at GSI (Darmstadt). The K∗(892)0/K0 yield ratio is found to be 0.0315 ± 0.006(stat.) ± 0.012(syst.) and is in good agreement with the transport model prediction. These measurements provide information on the in-medium cross section of K+-π− fusion, which is the dominant process in subthreshold K∗(892)0 production.

Publ.-Id: 14182 - Permalink


Experimental investigation of horizontal gas-liquid flow by means of wire-mesh sensor
Da Silva, M. J.; Hampel, U.; Arruda, L. V. R.; Amaral, C. E. F.; Morales, R. E. M.;
The monitoring and visualization of two-phase flow is of great importance either from technical/practical point of view for process control and supervision or from scientific/theoretical point of view, for the understanding of physical phenomenon. A wire-mesh sensor was applied to experimentally investigate two-phase horizontal pipe flow. Furthermore, some physical flow parameters were extracted based on the raw measured data obtained by the sensor. In this article, first the work principle of wire-mesh sensors is revised and second the methodology of flow parameter extraction is described. A horizontal flow test section comprising of a pipe of 26 mm i.d. 9 m long was employed to generate slug flows under controlled conditions. A 8 × 8 wire-mesh sensor installed at the end of the test section delivers cross-sectional images of void fraction. Based on the raw data, mean void fraction, time series of void fraction and characteristic slug frequency are extracted and analyzed.
Keywords: oil-gas flow, horizontal two-phase flow, wire-mesh sensor
  • Open Access LogoJournal of the Brazilian Society of Mechanical Science and Engineering XXXIII(2011)3, 237-242

Publ.-Id: 14181 - Permalink


Validation Training with ANSYS CFX
Höhne, T.;
Course in Mixing, Multiphase flow, and Turbulence modelling
Keywords: CFD, Mixing, Multiphase flow
  • Invited lecture (Conferences)
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
  • Contribution to proceedings
    CFD Validation Training, Malaysia, KLCC, KL, 10.-12.07.2010, Kualar Lumpur, Malaysia
    CD-ROM, Hand-out

Publ.-Id: 14180 - Permalink


Numerische Strömungsberechnung/Computational Fluid Dynamics
Höhne, T.;
Sektion 2 Thermo- und Fluiddynamik / Thermodynamics and Fluid Dynamics
Sitzung: Numerische Strömungsberechnung
Die Leitung der Sitzung hatte Herr Dr. Th. Höhne vom Forschungszentrum Dresden- Rossendorf e.V., Dresden inne.
Keywords: CFD, FZD
  • atw - International Journal for Nuclear Power (2010)10, 648-655

Publ.-Id: 14178 - Permalink


In-situ X-ray diffraction studies during deposition of Ni-Ti films
Martins, R. M. S.; Schell, N.; Mahesh, K. K.; Silva, R. J. C.; Braz Fernandes, F. M.;
The deposition of Ni-Ti films with definite stoichiometry and high purity remains still a challenge. Furthermore, important issues like the formation of film texture and its control are not yet resolved. Near equiatomic (~ 50.0 at.% Ti¨CNi) and Ti-rich (~ 50.8 at.% Ti¨CNi) Ni-Ti polycrystalline films (thickness values ¡Ü 800 nm) have been deposited by magnetron co-sputtering using a chamber installed into the six-circle diffractometer of the Rossendorf beamline at the European Synchrotron Radiation Facility. The in-situ X-ray diffraction studies enabled the identification of different steps of the structural evolution during films processing. Films exhibiting a (100) preferential orientation for the B2 phase have been successfully produced. A continuous increase of the B2(200) diffraction peak intensity has been observed for depositions on a 140 nm amorphous SiO2 buffer layer heated at 520¡ãC (without substrate bias voltage, Vb). A (100) texture has been observed for films as thick as 800 nm. Films deposited without and with Vb on a TiN coating with a topmost layer formed by <111> oriented grains have shown a preferential growth of <110> oriented grains of the B2 phase from the beginning of the deposition. Those trends have been observed for the growth of near equiatomic and Ti-rich films.
  • Lecture (Conference)
    E-MRS 2010 - Spring Meeting, 07.-10.06.2010, Strasbourg, France

Publ.-Id: 14177 - Permalink


Direct quantitative observation of transport processes with Positron-Emission-Tomography
Kulenkampff, J.; Gründig, M.; Wolf, M.; Lippmann-Pipke, J.; Richter, M.; Enzmann, F.;
Positron-Emission-Tomography (PET) enables direct and quantitative monitoring of the spatio-temporal distributions of dissolved inert and/or reactive PET-nuclides and PET-nuclide-labeled colloids during their passage through decimeter-scaled material samples. We apply PET exclusively to geomaterial samples and reach the physical resolution limit of about 1 mm with our small-animal-PET scanner (ClearPET, Raytest). We suggest our GeoPET has unrivalled sensitivity and selectivity for our tracer concentrations to some 107 tracer atoms/µl and thus is ideally suited for direct flow and transport process observations in geomaterials. This lower limit of the tracer concentration in the order of about 1 kBq/µl outranges other process observation methods (e.g. NMR or resistivity tomography) by many orders of magnitude. Like in the common medical practice, a combination with µCT for structural imaging would be advantageous for improving the spatial significance.
In the past we demonstrated the feasibility of the method, applying in-house developed and medical PET-scanners (Richter et al., 2003, Gründig et al., 2007). The installation of ClearPET in our controlled area made possible long-term experiments, like diffusion of long-living PET-tracers (like 58Co, decay time 71 days) and flow observations over several days (with 124I-labelled compounds, decay time 4 days) (Kulenkampff et al. 2008, Wolf 2010). The installation of a new cyclotrone will extend the availability of short-living PET-isotopes for fast process observations (e.g. 11C, decay time 20 min).
The density of geomaterials may cause more than 50% of Compton-scattered events, which degrade image quality mainly by inhomogeneous reconstruction artifacts. These artifacts caused explicitly by geomaterials (and only insignificantly in medical applications) are currently being addressed by model-based scatter-correction procedures.
Application examples include the fluid flow visualization in saliniferous rock cores. Different types of flow regimes are identified: in rather dense and low porous rock samples we observe slowly propagating diffuse “clouds of tracer”, whereas in fractured halite and sandstone samples (Fig. 1) we identified networks of extremely localized pathways, each with locally varying propagation velocities (Fig. 2). Quantitative parameterization of pathway and velocity distributions is possible, but still pending. However, with GeoPET-process observations we are capable of evaluating the results of Lattice-Boltzmann simulations, based on structural information from voxel-wise segmented µCT of the same sample. With respect to localized pathways in the fracture system of the halite, the model yields comparable results.
Nevertheless, even the high resolution of µCT may be insufficient to visualize the pore-space characteristics in tighter material, and more complex compositions may impair segmentation results from µCT-images. Then, stochastic models which are generated from other information, like pore-size distributions (with missing network information) and integral transport parameters (with missing distribution information), can still be validated by comparing model results with GeoPET-observations.
Keywords: PET, transport, tracer, geomaterial, tomography
  • Lecture (Conference)
    Transport in porous materials, 19.-20.8.2010, Villigen, Schweiz

Publ.-Id: 14176 - Permalink


Ni-Ti surface modification for enhanced biocompatibility and corrosion performance in biomedical applications
Martins, R. M. S.; Barradas, N.; Alves, E.; Henke, D.; Reuther, H.; Carmezim, M. J.; Silva, T. M.; Fernandes, J. C. S.;
The plasma-immersion ion implantation (PIII) technique was used to modify and improve the surface of a Ni-Ti alloy (» 50.2 at.% Ni) for biomedical applications. The main goal has been the formation of a Ni-depleted surface, which should serve as a barrier to out-diffusion of Ni ions from the bulk material. Ion implantation of oxygen was carried out. The depth profiles of the elemental distribution in the alloy surface region, obtained by Auger electron spectroscopy (AES), confirm the formation of a Ti-rich oxide layer. The working plan also comprised ion implantation of nitrogen. In this case, the formation of titanium oxynitride (TiNxOy) was observed. The AES depth profiles clearly show a Ni-depleted fraction for experiments performed with 40 keV.
Keywords: plasma-immersion ion implantation, Ni-Ti surface modification
  • Poster
    E-MRS 2010 - Spring Meeting (Symposium S: Shape Memory Materials for smart systems III);, 07.-10.06.2010, Strasbourg, France

Publ.-Id: 14175 - Permalink


The ternary system U(VI) / humic acid / Opalinus Clay
Joseph, C.; Schmeide, K.; Sachs, S.; Brendler, V.; Bernhard, G.;
Beside salt dome and granite rock, also clay rock is discussed as a possible host rock for siting a nuclear waste repository in Germany. The focus of the present work is the investigation of the U(VI) interaction with Opalinus Clay from Mont Terri, Switzerland, used here as a generic test case for studying radionuclide-clay interaction. The influence of humic acid (HA), a representative of natural organic complexing agents, on the migration of U(VI) is studied in addition.
U(VI) sorption experiments with ground Opalinus Clay and U(VI) diffusion experiments with intact clay rock were performed in the absence and presence of HA using synthetic Opalinus Clay pore water (I = 0.36 M, pH 7.6; [1]) as the background electrolyte. It was found that the U(VI) sorption onto Opalinus Clay is low and it is not influenced by HA. Speciation calculations showed that, under pore water conditions, Ca2UO2(CO3)3(aq) [2] is the dominant U(VI) species in solution both in the absence and presence of HA. The U(VI) speciation is not influenced by HA, which is predominantly present as a Ca complex [3]. It can be concluded, that calcium ions released by the dissolution of calcite (13% of Opalinus Clay [4]) play an important role in the investigated system.


[1] F.J. Pearson, PSI Internal report TM-44-98-07, Paul Scherrer Institut, Villigen PSI, Switzerland, 1998.
[2] G. Bernhard, G. Geipel, T. Reich, V. Brendler, S. Amayri, H. Nitsche, Radiochim. Acta 89 (2001) 511.
[3] A. Paulenová, P. Rajec, M. Žemberyová, G. Sasköiová, V. Višacký, J. Radioanal. Nucl. Chem. 246 (2000) 623.
[4] Nagra, Nagra Technical Report NTB 02-03, Wettingen, Switzerland, 2002, p. 230.
Keywords: uranium(VI), humic acid, Opalinus Clay, pore water, sorption, diffusion, speciation, calcium
  • Lecture (others)
    Seminar at the Institute of Laboratory for Waste Management (LES) - Paul Scherrer Institut (PSI), 28.-30.06.2010, Villigen, Switzerland

Publ.-Id: 14174 - Permalink


Identifizierung von 11C-Radiotracern mittels 13C-NMR
Mamat, C.;
kein Abstract verfügbar
  • Lecture (others)
    Dresdner NMR-Seminar, 30.03.2010, Dresden, D

Publ.-Id: 14173 - Permalink


Crystal structure of N-benzyl-4-fluorobenzamide, C14H12FNO, at 173 K
Mamat, C.; Flemming, A.; Köckerling, M.;
C14H12FNO, monoclinic, P21/n (no. 14), a = 5.6653(2) Å,
b = 25.305(1) Å, c = 8.2832(3) Å, ß = 92.237(3)°,
V = 1186.6 Å3, Z = 4, Rgt(F) = 0.047, wRref(F2) = 0.123,
T = 173 K.

Publ.-Id: 14172 - Permalink


Recent Application of Click Chemistry for the Synthesis of Radiotracers for Molecular Imaging
Mamat, C.; Ramenda, T.; Wuest, F.;
Click chemistry has received considerable attention as powerful modular synthesis approach, which has found numerous applications in many areas of modern organic chemistry, drug discovery and material science. Recently, click chemistry, and in particular the copper-mediated 1,3-dipolar [3+2] cycloaddition between azides and alkynes, has also entered the field of radiopharmaceutical sciences. This review addresses the recent developments of click chemistry for the synthesis of various radiotracers for molecular imaging purposes. Click chemistry-based radiotracers that will be covered include peptides and small organic molecules containing the short-lived positron emitters fluorine-18, and the gamma-emitters technetium-99m, indium-111, and iodine-125.
Keywords: Click chemistry, radiopharmaceutical science, radiotracer
  • Mini-Reviews in Organic Chemistry 6(2009), 21-34

Publ.-Id: 14171 - Permalink


Studying Obsidians from Milos by Complementary Techniques: An Application of Ion Beam and Instrumental Neutron Activation Analysis
Eder, F.; Neelmeijer, C.; Bichler, M.; Merchel, S.;
The natural volcanic glass obsidian was an important raw material for tools and arms during prehistoric time and has been found by researchers at great distances from potential natural sources. Reliable provenancing can provide evidence of contacts over a certain dis-tance and information about exchange patterns and mobility of prehistoric people.
Instrumental Neutron Activation Analysis (INAA) is one of the major analytical techniques to solve the problem of obsidian provenancing by means of its highly specific chemical composition, the “chemical fingerprint” [1-4]. The advantages of bulk INAA are the absence of matrix effects, the large number of ele-ments simultaneoulsy detectable, its sensitivity and accuracy. However, INAA is limited as being destruc-tive and inclusions cannot be distinguished from the matrix applying routine analytical practice.
Additional application of non-destructive Ion Beam Analysis (IBA), consisting of Proton Induced X-ray Emission (PIXE), Proton Induced Gamma-ray Emission (PIGE) and Rutherford Backscattering Spectrometry (RBS), supplement INAA measurements by enabling systematic spatially resolved surface investigations and adding a complementary element spectrum [5-9]. Furthermore, a comparison of chemical compositions obtained by different analytical methods provide the actual degree of the reliability of the analytical results [10].
For this study, both INAA and IBA measurements have been applied to the same samples to gain a more complete set of elements and to check the self-consistency of the analytical results. The samples originate from the obsidian sources Demenegakion and Agia Nychia (Cape Bombarda) on the island of Melos (Greece) (Fig. 1). Our INAA studies have been performed at the TRIGA MkII 250 kW research reactor of the Atominstitut in Vienna, where 150 mg of ground aliquots have been irradiated for 1 min at a thermal neutron flux of 3.3x1012cm-2s-1. IBA measurements have been carried out using the 4 MeV proton beam in-air of the 5 MV tandem accelerator of the Ion Beam Centre of FZD [9,11].

Fig. 1: Geographical situation of obsidian sources on the island of Melos (after [12]).

Our investigations are part of a joint project to apply selected analytical methods, in particular INAA, IBA and Inductively Coupled Plasma-Mass Spec-trometry (ICP-MS), to reveal a maximum of compositional differences between easily available samples of the natural obsidian sources in Europe. This knowledge should enable to decide, which least invasive analytical method should be chosen for the analysis of a specific highly valuable archaeological artefact, on a case by case basis.

References: [1] Meloni S. et al. J. Radioanal. Nucl. Chem. 271 (2007) 533-539. [2] Arias A. et al. J. Radioanal. Nucl. Chem. 268 (2006) 371-386. [3] Kilikoglou V. et al. J. Archaeol. Sci. 23 (1996) 343–349. [4] Aspinall. A. et al. Nature 237 (1972) 333–334. [5] Bellot-Gurlet L. et al. C. R. Palevol 7 (2008) 419–427. [6] Calligaro T. X-Ray Spectrometry 37 (2008) 169–177. [7] Lugliè C. et al. C. R. Palevol 5 (2006) 995–1003. [8] Kim J.C. et al. IPPA Bull. 27 (2005) 122–128. [9] Bugoi R. and Neelmeijer C. NIMB 226 (2004) 136-146. [10] Hancock R.G.V. and Carter T. J. Archaeol. Sci. 37 (2010) 243–250. [11] Saminger S. et al. J. Radioanal. Nucl. Chem. 245 (2000) 375-383. [12] Higgins M. and Higgins R. (1996) A geological companion to Greece and the Aegean Cornell University Press.
Keywords: archaeometry, PIXE, PIGE, INAA
  • Lecture (Conference)
    6. Workshop RCA (Radiochemische Analytik bei Betrieb und Rückbau kerntechnischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz) & 23. SAAGAS (Seminar Aktivierungsanalyse und Gammaspektroskopie), 06.-08.09.2010, Dresden, Deutschland

Publ.-Id: 14170 - Permalink


Cs2Te normal conducting photocathodes in the superconducting RF gun
Xiang, R.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schamlott, A.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.;
The superconducting radio frequency photo-injector (SRF gun) is one of the latest applications of superconducting RF technology in the accelerator field. Since superconducting photocathodes with high quantum efficiency are still unavailable, normal conducting cathode material is the main choice for SRF photo-injectors. However, the compatibility between the photocathode and the cavity is one of the challenges for this concept. Recently, a SRF gun with Cs2Te cathode has been successfully operated in Forschungszentrum Dresden-Rossendorf (FZD). In this paper, we will present the physical properties of Cs2Te photocathodes in the SC cavity, such as the quantum efficiency, the life time, the rejuvenation, the charge saturation and the dark current.
Keywords: Cs2Te, photocathode, SRF gun, QE, life time, rejuvenation, dark current

Publ.-Id: 14169 - Permalink


Quantitative Tiefenprofilelementanalyse mit Subnanometer Tiefenauflösung
Kosmata, M.; Munnik, F.; Heller, R.; Neelmeijer, C.;
Einleitung: Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich we-niger Nanometer ist in den letzten Jahren in den Fokus aktueller Forschung gerückt. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch spezielle Abscheidever-fahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination in den Schichten. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
Ionenstrahlanalyse: Mittels Ionenstrahlanalyseverfahren kann die Zusammensetzung einer Probe angefangen von der Oberfläche bis in eine bestimmte Tiefe des Materials quantitativ untersucht werden. Hierzu werden auf die zu untersuchende Probe Ionen mit einer definierten Energie (2-40 MeV) geschossen und die Streuprozesse zur Analyse genutzt. Da die Wahrscheinlichkeit für einen bestimmten Prozess (Wirkungsquerschnitt) bekannt ist, ergibt sich aus deren absoluten Häufigkeit die Konzentration aller Elemente. Im Gegensatz zu den meisten konventionellen (nicht nuklearen) Analyseverfahren sind daher zur Quantifizierung der Ergebnisse keine Messungen gegen Referenzmaterialien gleicher Matrix notwendig.
Auf dem Weg durch die Probe verlieren die Ionen durch inelastische Stöße mit Elektronen und Kernen der Atome der Matrix kontinuierlich Energie. Diese weglängenabhängige Energieabgabe (Bremsvermögen) kann berechnet und damit die chemische Zusammensetzung der Probe tiefenabhängig bestimmt werden. Abhängig von der Anfangsenergie und Art der Ionen können Tiefen bis zu wenigen Mikrometern untersucht werden.
Subnanometer Tiefenauflösung: Mit konventionellen Ionenstrahlanalysemethoden sind Tiefenauflösungen im Bereich von Atommonolagen (< 1 nm) nicht zu erreichen. Hierzu ist eine Modifizierung des klassischen Messaufbaus notwendig. Am Forschungszentrum Dresden-Rossendorf (FZD) kommen hierbei Magnetspektrometer in Kombination mit den Ionenstrahlanalyseverfahren Rutherford-Rückstreu-Spektrometrie (RBS) und Elastische Rück-streuanalyse (ERD) zum Einsatz. Mittels dieser Erweiterung muss die tiefenbestimmende Energie nicht mit einem limitierenden Energiedetektor gemessen werden, sondern kann aufgrund der Lorentzkraft aus dem Flugradius im Magnetfeld der Magnetspektrometer ermittelt werden. Allein mittels dieser Erweiterung können oberflächennah Monolagen verschiedener Elemente bestimmt werden (s. Abb. 1).

Abb. 1: Sauerstoffkonzentration eines SiO2-Multischicht-systems bestimmt mittels konventioneller ERD und ERD im “high-resolution”-Mode (HR-ERD).

Wasserstoff: Eine Ausnahme bildet das leichteste Element: Wasserstoff. Dieses Element kann mittels Kernreaktionsanalyse (NRA) über die resonante Kernreaktion 1H(15N,αγ)12C ermittelt werden. Die Tiefenabhängigkeit ergibt sich hierbei ebenfalls aus inelastischen Stößen beim Durchqueren der Stickstoffionen durch die Probe bis zum Ort der Kernreaktion.
Performance: RBS, ERD und NRA können in der Regel zerstörungsarm durchgeführt werden. Bei einigen Matrices kann allerdings der Ionenbeschuss bei hohen Fluenzen durch Diffusionsverlust oder Sputtering zum Verlust des Analyten führen und limi-tiert so die Nachweisgrenze (s. Tab. 1). Bei der Durch-führung der RBS und ERD im „high-resolution“-Mode (HR-RBS / HR-ERD) muss zur exakten Quantifizierung das Auftreten wechselnder Ionenladungszustände berücksichtigt werden. Alle Ionenstrahlanalysemethoden können zudem mit lateraler Auflösung im Mikrometerbereich (Mikrosonde) durchgeführt werden.

Tab. 1: Performance der Ionenstrahlanalysemethoden mit und ohne „high-resolution“-Mode (HR) am FZD.
Analyt Tiefen-auflösung [nm] Nachweis-grenze [at%] max.
Analysen-tiefe [nm]
RBS > Si ≈ 15 0,01 1000
HR-RBS > Si < 1 1 20
ERD ≤ Si ≈ 20 0,01 500
HR-ERD ≤ Si < 1 1 20
NRA H (F) ≈ 1 0,02 2000
Keywords: High Resolution, ERD, ERDA, RBS, HR-ERD, HR-RBS, NRA, ubnanometer Tiefenauflösung, Magnetspektrometer, high-resolution, Mikrosonde
  • Lecture (Conference)
    6. Workshop RCA (Radiochemische Analytik bei Betrieb und Rückbau kerntechnischer Anlagen, der Deklaration von Abfällen und im Strahlenschutz) & 23. SAAGAS (Seminar Aktivierungsanalyse und Gammaspektroskopie), 06.-08.09.2010, FZD, Deutschland

Publ.-Id: 14168 - Permalink


All-optical Laser Cooling and Beam Diagnostics for Relativistic C3+ Ion Beams at ESR
Bussmann, M.; Kroll, F.; Loeser, M.; Siebold, M.; Schramm, U.; Wen, W.; Winters, D. F.; Walther, T.; Beck, T.; Rein, B.; Birkl, G.; Kruse, J.; Nörtershäuser, W.; Kühl, T.; Novotny, C.; Kozhuharov, C.; Geppert, C.; Steck, M.; Nolden, F.; Dimopoulou, C.; Ma, X.; Stöhlker, T.;
We present the current status of the laser cooling experiment using relativistic C3+ ion beams at the Experimental Storage Ring (ESR) at GSI.
Based on the results of two previous beam times we show that with modern laser systems and new optical diagnostics all-optical cooling of an ion beam can be achieved and ion beam properties can be measured with high accuracy. Laser cooling can become an important tool for high-energy storage rings, because, unlike other beam cooling methods, laser cooling provides a cooling force that grows stronger for increasing beam energy.
Keywords: laser cooling, ion beam, relativistic, esr, optical, diagnostic
  • Invited lecture (Conferences)
    EMMI Workshop on Physics Prospects at the ESR and HiTrap, 27.-30.06.2010, Eisenach, Deutschland

Publ.-Id: 14167 - Permalink


Defect characterization of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy
Anwand, W.; Kanjilal, A.; Wagner, A.; Butterling, M.; Brauer, G.; Cowan, T. E.; Rebohle, L.; Skorupa, W.;
Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, which forms Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, led to an improvement of the luminescence properties. However, with exceeding an optimum concentration of the Er doping the intensity of the electro-luminescence was found to be drastically decreased.
Slow positron spectroscopy (single Doppler broadening (DB) and coincidence DB) was applied in order to probe ongoing processes at a microscopic level and, in particular an impact on the optical response depending on the concentration of rare earth Er. It could be shown that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and the improved reverse energy transfer process between Er and Ge. Obtained positron annihilation results will be compared with Transmission Electron Microscopy investigations [1] and with conclusions in recently published papers [2, 3].

[1] A. Kanjilal, L. Rebohle, M. Voelskow, W. Skorupa, M. Helm
J. Appl. Phys. 106, 026104 (2009)
[2] C.L. Heng, E. Chelomentsev, Z.L. Peng, P. Mascher, P.J. Simpson
J Appl. Phys. 105, 014312 (2009)
[3] R.S. Yu, M. Maekawa, A. Kawasuso, T. Sekiguchi, B.Y. Wang, X.B. Qin, Q.Z. Wang
NIMB 267, 3097 (2009)
Keywords: Ge, Er doped SiO2, electro-luminescence, positron annihilation spectroscopy
  • Lecture (Conference)
    39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14166 - Permalink


Complex defect structure of oxides studied by positrons
Kuriplach, J.; Melikhova, O.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.;
Transition metal oxides show a variety of interesting properties and attract wide attention because of a broad application potential. At the same time, oxides often exhibit a complex defect structure comprising vacancy-like defects and positron annihilation can be effectively used to investigate and, thereby, to understand such structures. In this contribution, we concentrate on two oxides, namely these are zinc oxide (ZnO) and yttria stabilized zirconia (YSZ), the latter being a solid solution of an appropriate amount of yttria (Y2O3) in zirconia (ZrO2). As hydrogen has been detected in both these oxides and its content is not negligible [1,2], we also deal with positron characteristics of H-related defects, in addition to ‘bare’ vacancies. The structure of studied defects is obtained using an ab initio computational technique. Since there is a large charge transfer between oxygen and transition metal atoms in oxides, self-consistent calculations including positron induced forces are necessary to determine reliably positron characteristics.
As for ZnO, we discuss briefly the structure of studied vacancy-like defects. Then, the results of positron lifetime calculations are shown and compared with experimental data. Next, we present calculated formation energies of the same defects. We conclude that all calculated data support idea that in hydrothermally grown ZnO positrons annihilate in Zn vacancy-hydrogen complexes. Concerning YSZ, due to yttria doping a significant amount of O vacancy-yttrium complexes is present. Despite of earlier assumptions our calculations indicate that such complexes do not constitute positron traps. We further concentrate on the Zr vacancy and its complexes with hydrogen. First results for positron calculations with positron induced forces are presented. Calculated positron lifetimes are compared with experimental data, which suggests that the Zr vacancy and its complexes with hydrogen could be responsible for positron trapping in YSZ. Finally, further prospects of positron studies of defects in oxides are outlined.

[1] G. Brauer et al., Phys. Rev. B 79, 115212 (2009)
[2] O. Melikhova et al., Mat. Res. Symp. Proc. 1216, W07-10 (2010)
Keywords: ZnO, yttria stabilized zirconia, H-related defects, ab initio computational technique, positron annihilation
  • Lecture (Conference)
    39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14165 - Permalink


Positron defect studies in oxides
Kuriplach, J.; Cizek, J.; Melikhova, O.; Prochazka, I.; Brauer, G.; Anwand, W.; Egger, W.; Sperr, P.;
Transition metal oxides show a variety of interesting properties and attract wide attention because of a broad application potential. Oxides often exhibit a complex defect structure and understanding such defect structures is of primary importance for planned applications. Defects in oxides involve vacancy-like defects and positron annihilation can be effectively used to investigate them. In this lecture, we summarize results of our recent theoretical and experimental investigations carried out for zinc oxide (ZnO) and yttria stabilized zirconia (YSZ), the latter being a solid solution of an appropriate amount of yttria (Y2O3) in zirconia (ZrO2). Hydrogen-related defects in these two oxides are also considered as hydrogen is existing in a non-negligible amount in both these oxides [1,2]. The structure of defects expected to be present in the studied materials is obtained using an ab initio computational technique. Since there is a large charge transfer between oxygen and transition metal sublattices in oxides, self-consistent calculations including positron induced forces are necessary to determine reliably positron characteristics.

First, we report on positron lifetime measurements performed with a pulsed low energy positron beam system and a conventional setup on as-grown and hydrogen plasma treated single crystal ZnO samples produced under hydrothermal conditions. The results of lifetime measurements are compared with lifetimes calculated for various configurations of vacancy-like defects taking into account also defects’ formation energies. We conclude that all calculated data support the idea that in as-grown ZnO samples positrons far from the surface annihilate in Zn vacancy-hydrogen complexes. In hydrogen plasma treated samples the situation is similar, but a component originating from delocalized positrons appears, which is attributed to a reduced concentration of vacancy-like defects capable of positron trapping because of the hydrogen plasma treatment. Vacancy agglomerates are also found in the subsurface region of both types of samples.

As for YSZ, due to yttria doping a significant amount of O vacancy-yttrium complexes is present. Despite of earlier assumptions our calculations indicate that such complexes do not constitute positron traps. We further concentrate on the Zr vacancy and its complexes with hydrogen. First results for positron calculations with positron induced forces are presented. Calculated positron lifetimes are compared with experimental data obtained for YSZ single crystals, which suggests that the Zr vacancy and its complexes with hydrogen could be responsible for positron trapping in YSZ.

[1] G. Brauer et al., Phys. Rev. B 79, 115212 (2009)
[2] O. Melikhova et al., Mat. Res. Soc. Symp. Proc. 1216, W07-10 (2010)
Keywords: Transition metal oxides, defect structure, positron lifetime measurements and calculations
  • Invited lecture (Conferences)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia

Publ.-Id: 14164 - Permalink


A Generic Approach for Developing Highly Scalable Particle-Mesh Codes for GPUs
Hönig, W.; Schmitt, F.; Widera, R.; Burau, H.; Juckeland, G.; Mueller, M. S.; Bussmann, M.;
We present a general framework for GPU-based low-latency data transfer schemes that can be used for a variety of particlemesh algorithms [9]. This framework allows to hide the latency of the data transfer between GPU-accelerated computing nodes by interleaving it with the kernel execution on the GPU. We discuss as an example the fully relativistic particle-in-cell (PiC) code PIConGPU [6] currently used to simulate particle acceleration by extremely short high-energy laser pulses. The PiC algorithm is a versatile algorithm used frequently in plasma physics—especially for large-scale simulations of fusion plasmas [14]—, in astrophysics [10], or for the simulation of particle accelerators [12]. A special Cell processor version is used as a benchmark code for the Roadrunner system at Los Alamos National Lab [5]. The presented hybrid GPU-CPU data transfer and access framework can, furthermore, be used for general particle-mesh schemes. GPU memory access to particle data and mesh data are efficiently separated, while data that has to be exchanged between domains located on different GPUs is transferred during computing steps using GPU-CPU memory copy and MPI. A simulation of laser-wakefield acceleration of electrons in an underdense plasma serves as a real-world benchmark for the performance of the framework.
Keywords: gpu, gpgpu, performance, particle-mesh, particle-in-cell, pic, simulation, algorithm, communication, framework, laser, plasma

Publ.-Id: 14163 - Permalink


Divacancy-hydrogen complexes in zinc oxide
Kuriplach, J.; Brauer, G.; Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.;
In the present work we study Zn+O divacancies filled up with varying amount of hydrogen atoms. Besides the structure and energy-related properties of such defects, we also investigate their capability to trap positrons taking into account positron induced forces. We show that the Zn+O divacancy may trap positrons when up to two hydrogen atoms are located inside the divacancy. The calculated properties are discussed in the context of other computational and experimental studies of ZnO.
Keywords: ZnO, Zn+O divacancies, hydrogen, computational and experimental studies
  • Contribution to proceedings
    Mater. Res. Soc. Symp., 30.11.-04.12.2009, Boston, MA, USA
    Zinc Oxide and Related Materials - 2009, edited by Steve Durbin, Martin Allen, and Holger von Wenckstern, Mater. Res. Soc. Symp. Proc. 1201, Warrendale, PA, 2010), 1201-H02-03 (6 pp)

Publ.-Id: 14162 - Permalink


Investigation of interaction of hydrogen with defects in zirconia
Melikhova, O.; Kuriplach, J.; Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.;
In the present work we study theoretically hydrogen incorporated into several positions in the zirconia cubic and tetragonal lattices. These are positions in the interstitial space and in the zirconium vacancy (VZr). We examine the structure of such configurations and for VZr-related defects we also calculate selected positron characteristics in order to assess their capability of trapping positrons. It is shown that hydrogen atoms do not prefer to stay in the center of the largest interstitial space nor of VZr and they rather tend to create bonds with neighboring oxygen atoms. The positron lifetime of the VZr+1H complex is shorter than that for non-decorated VZr and positron trapping in VZr+1H complexes could, in principle, explain experimental lifetime data.
Keywords: zirconia, zirconium vacancy, theoretically incorporated hydrogen
  • Contribution to proceedings
    Mater. Res. Soc. Symp., 30.11.-04.12.2009, Boston, MA, USA
    Hydrogen Storage Materials, edited by E. Akiba, W. Tumas, P. Chen, M. Fichtner, and S. Zhang, (Mater. Res. Soc. Symp. Proc. 1216, Warrendale, PA, 2010), 1216-W07-10 (6 pp)

Publ.-Id: 14161 - Permalink


Quenched-in vacancies in Fe-Al alloys
Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.; Brauer, G.;
Intermetallic Fe-Al alloys are perspective materials for industrial applications at elevated temperatures. A high concentration of vacancies is a specific feature of such alloys. The equilibrium concentration of thermal vacancies in these alloys is considerably higher than in pure metals and may be as high as several at.%. Moreover, a high concentration of thermal vacancies existing at elevated temperatures can be quenched-in down to room temperature. Hence, a detailed investigation of vacancies and other vacancy-like defects in Fe-Al based alloys is necessary for a deeper understanding of the physical properties of these materials.

Quenched-in vacancies in Fe-Al alloys were investigated in this work employing three complementary techniques of positron annihilation: Doppler broadening spectroscopy performed using a variable energy slow positron beam (SPIS = slow positron implantation spectroscopy), coincidence Doppler broadening (CDB) spectroscopy and positron lifetime (LT) measurements. It was found that quenched alloys exhibit a high concentration of vacancies. Although a free positron component cannot be resolved in our LT spectra, the concentration of quenched-in vacancies can still be determined from the shortening of the positron diffusion length measured by SPIS. Hence, SPIS is a very important technique for the investigation of defect-rich materials, like quenched Fe-Al alloys.

In the present work, the concentration of quenched-in vacancies was determined in Fe-Al based alloys at various Al content ranging from 24 up to 45 at.-%. The lowest concentration of quenched-in vacancies was found in the stoichiometric Fe3Al alloy, i.e. an alloy with an Al concentration of 25 at.-%. This concentration increases with an increasing degree of non-stoichiometry with respect to Fe3Al. Hence, the concentration of quenched-in vacancies increases both in alloys with under-stoichiometric as well as in those with over-stoichiometric Al content. However, the increase in concentration is more pronounced in the Al-rich alloys, i.e. alloys containing more than 25 at.% of Al. CDB revealed that quenched-in vacancies are surrounded predominantly by Al atoms which indicates that they occupy predominantly the Fe sub-lattice.
Keywords: Fe-Al alloys, quenched-in vacancies, slow positron implantation spectroscopy, positron lifetime measurements
  • Poster
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia

Publ.-Id: 14160 - Permalink


Characterization of point defects in yttria stabilized zirconia single crystals
Melikhova, O.; Cizek, J.; Kuriplach, J.; Prochazka, I.; Anwand, W.; Brauer, G.; Grambole, D.;
Yttria stabilized zirconia (YSZ) has a big potential of use in a wide area of high-temperature applications. Although pure zirconia is monoclinic at room temperature and exhibits relatively poor mechanical properties, high temperature tetragonal or cubic zirconia phases with superior properties can be stabilized down to room temperature by the addition of an appropriate amount of yttria (Y2O3). The deviation from stoichiometry caused by the addition of trivalent yttrium ions leads to the formation of a high density of point defects in YSZ. These defects are believed to influence significantly not only phase stabilization itself but also material characteristics of YSZ’s important for their practical use. Hence, the detailed characterization of defects in YSZ is a very important task.
In this work we performed a thorough investigation of point defects in tetragonal and cubic YSZ single crystals. Experimental data were obtained by three complementary techniques of positron annihilation spectroscopy (PAS), namely slow positron implantation spectroscopy, positron lifetime measurements, and coincidence Doppler broadening. The interpretation of PAS data was performed with the help of state-of-the-art ab-inito theoretical calculations of positron parameters for various types of vacancy-like defects.
Present experimental data suggest that both tetragonal and cubic YSZ single crystals contain a high concentration of vacancy-like defects. Theoretical calculations showed that neither oxygen vacancies nor their neutral complexes with substitute yttrium atoms are capable of positron trapping. On the other hand, zirconium vacancies are deep positron traps and most probably responsible for positron trapping observed in YSZ single crystals. However, the calculated positron lifetime for a zirconium vacancy is apparently longer than the experimental value estimated for YSZ single crystals. We argue that this effect could be explained by hydrogen atoms trapped at zirconium vacancies. On the basis of structure relaxations, we found that zirconium vacancy – hydrogen complexes represent positron traps with the calculated lifetimes close to the experimental ones. In the vicinity of a zirconium vacancy the hydrogen atom forms an O-H bond with one of the nearest neighbour oxygen atoms. This result testifies that hydrogen is an important impurity in YSZ which strongly interacts with vacancies. Hence, the hydrogen content in YSZ materials should be considered as a very important parameter. In this work, therefore, we employed also nuclear reaction analysis for a determination of the hydrogen content in YSZ single crystals. It was found that the hydrogen content in our studied samples is in a range of 0.1-0.3 at.-%, which is sufficient for the formation of hydrogen complexes with zirconium vacancies capable of saturated positron trapping.
Keywords: Yttria stabilized zirconia, zirconium vacancy – hydrogen complexes, positron annihilation spectroscopy
  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia
  • Open Access LogoJournal of Physics: Conference Series 262(2011), 012038
    DOI: 10.1088/1742-6596/262/1/012038

Publ.-Id: 14159 - Permalink


Hydrogen-induced surface modifications of ZnO single crystals
Prochazka, I.; Cizek, J.; Anwand, W.; Brauer, G.; Grambole, D.; Schmidt, H.;
ZnO is a wide band gap semiconductor with a variety of applications including UV light emitting diodes and lasers, optoelectronic devices, and gas sensors. Due to a progress in crystal growth, high quality single crystals are nowadays available. However, properties which are essential for any of the applications mentioned are significantly influenced by the presence of lattice defects. A detailed characterization of lattice defects in ZnO crystals is, therefore, a key task in order to understand their physical properties. Defect studies of hydrothermally grown ZnO single crystals revealed that hydrogen is the most important impurity in ZnO crystals [1]. It was found that hydrogen is coupled with zinc vacancies in the form of vacancy-hydrogen complexes. Moreover, it has been demonstrated that a huge amount of hydrogen (30 at.-%) can be introduced into ZnO crystals by electrochemical loading [2].

Surface changes in ZnO crystals electrochemically doped with hydrogen were investigated in this work using slow positron implantation spectroscopy (SPIS) combined with atomic force microscopy (AFM) and optical microscopy (OM). It was found that hexagonally shaped pyramids were formed on the surface (Fig. 1). All these pyramids have the same crystallographic orientation as the ZnO matrix. The formation of pyramids can be explained by hydrogen-induced plastic deformation which is realized by slip in the [0001] direction. Such a picture is supported (i) by AFM where terraces of a height comparable with the c-lattice parameter were found at the base of the pyramids, and (ii) by SPIS which revealed a defected subsurface layer, being formed by the hydrogen-induced plastic deformation and exhibiting an enhanced concentration of open-volume defects.

Fig. 1 Optical microscopy image (taken using oblique light) of the surface of a ZnO crystal electrochemically loaded with hydrogen.


References
[1] G. Brauer, et al., Phys. Rev. B 79, 115212 (2009).
[2] J. Čížek, et al., J. Appl. Phys. 103, 053508 (2008).
Keywords: ZnO, vacancy-hydrogen complexes, hydrogen-induced plastic deformation, positron annihilation spectroscopy, atomic force microscopy
  • Lecture (Conference)
    12th International Workshop on Slow Positron Beam Techniques for Solids and Surfaces (SLOPOS-12), 01.-06.08.2010, Magnetic Island/North Queensland, Australia
  • Open Access LogoJournal of Physics: Conference Series 262(2011), 012050
    DOI: 10.1088/1742-6596/262/1/012050

Publ.-Id: 14158 - Permalink


Zur Bindungsform des Urans in Umweltkompartimenten
Bernhard, G.;
- wird nachgereicht
  • Invited lecture (Conferences)
    GDCh-Kolloquien im Sommersemester 2010, 03.06.2010, Dresden, Deutschland

Publ.-Id: 14157 - Permalink


Functional role of protonation and hydration at the lipid protein interface in membrane receptors
Eichler, S.; Madathil, S.; Fahmy, K.;
The visual photoreceptor rhodopsin is a proto¬typical 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 trans¬membrane helix-3 promotes the formation of the G-protein-activating state. Using trans¬mem¬brane segments derived from helix-3 of bovine rhodopsin, we show that lipid protein interactions play a key role in this cytosolic "proton switch". Infra¬red- and fluo¬res¬cence-spectroscopic pKa deter¬minations reveal that the D(E)RY motif is an auto¬no¬mous functional module coupling side chain neu¬trali¬za¬tion to conformation and helix positio¬ning as evidenced by side chain to lipid headgroup Foerster-re¬so¬nance-energy-transfer. Using rapid scan FTIR spectroscopy, we show that the motif is also a local protonein hydration site. This dual function renders the proton acceptor group a key residue in conformational control by positioning helix-3 at the water lipid protein interface.
Keywords: membrane transport protonation FTIR spectroscopy fluorescence spectroscopy FRET charge stabilization bilayer
  • Contribution to proceedings
    Annual Meeting of the German Biophysical Society, 03.-06.10.2010, Ruhr-Universität-Bochum, Germany

Publ.-Id: 14156 - Permalink


The ELBE accelerator facility starts operation with the superconducting RF gun
Xiang, R.; Arnold, A.; Buettig, H.; Janssen, D.; Justus, M.; Lehnert, U.; Michel, P.; Murcek, P.; Schneider, C.; Schurig, R.; Staufenbiel, F.; Teichert, J.; Kamps, T.; Rudolph, J.; Schenk, M.; Klemz, G.; Will, I.;
As the first superconducting rf photo-injector (SRF gun) in practice, the FZD 3+1/2 cell SRF gun is successfully connected to the superconducting linac ELBE. This setting will improve the beam quality for ELBE users. It is the first example for an accelerator facility fully based on superconducting RF technology. For high average power FEL and ERL sources, the combination of SRF linac and SRF gun provides a new chance to produce beams of high average current and low emittance with relative low power consumption.
The main parameters achieved from the present SRF gun are the final electron energy of 3 MeV, 16 μA average current, and rms transverse normalized emittances of 3 mm mrad at 77 pC bunch charge. A modified 3+1/2 cell niobium cavity has been fabricated and tested, which will increase the rf gradient in the gun and thus better the beam parameters further. In this paper the status of the integration of the SRF gun with the ELBE linac will be presented, and the latest results of the beam experiments will be discussed.
Keywords: SRF gun, superconducting linac ELBE
  • Poster
    IPAC10, 23.-28.05.2010, Kyoto, Japan
  • Contribution to proceedings
    IPAC'10, 23.-28.05.2010, Kyoto, Japan
    Proceedings of IPAC'10, 1710-1712

Publ.-Id: 14155 - Permalink


Recent status of the GiPS facility at ELBE and first measurements
Butterling, M.; Anwand, W.; Brauer, G.; Cowan, T. E.; Hartmann, A.; Jungmann, M.; Kosev, K.; Krause-Rehberg, R.; Krille, A.; Schwengner, R.; Wagner, A.;
At the superconducting LINAC ELBE [1] at Research Centre Dresden-Rossendorf the new facility for Gamma-induced Positron Spectroscopy (GiPS) is successfully running [2] and first measurements were done. Two AMOC (Age Momentum Correlation) spectrometers (each consisting of a barium fluoride timing detector and a high purity germanium detector for measuring the energy) and a detector setup for Coincidence Doppler Broadening Spectroscopy allow to measure standard positron techniques simultaneously.
Influences from the surroundings (e.g. randomly scattered photons) disturb the recorded energy and lifetime spectra (increase of background, several peaks in lifetime spectra). Therefore it is of great importance to avoid such disturbing influences and to get clear and corrected spectra.
Recent efforts to optimize the setup and to eliminate the negative influences of the surroundings are presented. Selected results of first measurements with GiPS show the great potential of this unique facility.
Keywords: Positron annihilation, Electron and positron beams, Positrons, Positron-induced reactions, Gamma-induced Positron Spectroscopy
  • Poster
    PSPA10 - 39th Polish Seminar on Positron Annihilation, 20.-25.06.2010, Kazimierz Dolny, Poland

Publ.-Id: 14154 - Permalink


Bispidine Derivatives for Dual-Modality Imaging
Fähnemann, S.;
kein Abstract verfügbar
  • Lecture (Conference)
    7th Supraphone Meeting, 28.04.-01.05.2010, Maria Laach, Deutschland

Publ.-Id: 14153 - Permalink


Nuclear structure study of 19,20,21N nuclei by gamma spectroscopy
Elekes, Z.; Vajta, Z.; Dombradi, Z.; Aiba, T.; Aoi, N.; Baba, H.; Bemmerer, D.; Fulop, Z.; Iwasa, N.; Kiss, A.; Kobayashi, T.; Kondo, Y.; Motobayashi, T.; Nakabayashi, T.; Nannichi, T.; Sakurai, H.; Sohler, D.; Takeuchi, S.; Tanaka, K.; Togano, Y.; Yamada, K.; Yamaguchi, M.; Yoneda, K.;
The structure of neutron rich nitrogen nuclei has been studied by use of neutron removal reaction and inelastic scattering. Mass and charge deformations have been deduced for the first excited state of 21N, which indicates the partial persitence of the N=14 subshell closure in nitrogen isotopes. The spectroscopic information obtained on the structure of 19,20,21N confirms the results from a previous experiment.
Keywords: nuclear structure, radioactive ion beam, nuclear astrophysics

Publ.-Id: 14152 - Permalink


From Molecular Chemistry to Solid State Physics – Chemical Concepts in Material Science
Gemming, S.;
no abstract available
Keywords: density-functional, material science
  • Lecture (others)
    Institutskolloquium - Institut für Chemie und Biochemie / Physikalische und Theoretische Chemie der Freien Universität Berlin und Kolloquium des Graduiertenkollegs 788, 03.06.2010, Berlin, Deutschland

Publ.-Id: 14151 - Permalink


Irradiation damage and embrittlement in RPV steels under the aspect of long term operation – overview of the FP7 project LONGLIFE
Altstadt, E.; Bergner, F.; Hein, H.;
The increasing age of the European NPPs and envisaged lifetime extensions up to 80 years require an improved understanding of RPV irradiation embrittlement effects connected with long term operation (LTO). Phenomena which might become important at high neutron fluences (such as late blooming effects and flux effects) must be considered adequately in the safety assessments. Therefore the project LONGLIFE was initiated within the 7th Framework Programme of the European Commission. The project aims at: i) improved knowledge on LTO phenomena relevant for European reactors; ii) assessment of prediction tools, codes, standards and surveillance guidelines. In the paper, we give an overview of the project structure and the related tasks. Furthermore we present two examples for the experimental evidence of LTO relevant phenomena: the first example is related to the flux dependence of defect cluster formation in a neutron irradiated weld material. We have found that the size of the irradiation induced defects exhibits a flux effect whereas the mechanical properties are almost independent of the flux. The second example refers to the acceleration of irradiation hardening after exceeding a threshold fluence. This effect was observed by means of both small angle neutron scattering (SANS) and tensile testing for low Cu RPV steels irradiated at a temperature of 255°C. These examples demonstrate that LTO irradiation effects have to be investigated in more detail to guarantee the applicability of the embrittlement surveillance guidelines beyond 40 years of operation.
Keywords: neutron irradiation embrittlement, reactor pressure vessel, long term operation, small angle neutron scattering, flux effect, late blooming effect
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering ICONE18, 17.-21.05.2010, Xian, China
    Proceedings of the 18th International Conference on Nuclear Engineering ICONE18
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering ICONE18, 17.-21.05.2010, Xian, China

Publ.-Id: 14150 - Permalink


Binary and Ternary Uranium(VI) Humate Complexes Studied by Attenuated Total Reflection Fourier-transform Infrared Spectroscopy
Steudtner, R.; Müller, K.; Schmeide, K.; Sachs, S.; Bernhard, G.;
The complexation of U(VI) with humic acid (HA) in aqueous solution has been investigated at an ionic strength of 0.1 M (NaCl) in the pH range between pH 2 and 10 at different carbonate concentrations by attenuated total reflection Fourier-transform infrared (ATR FT IR) spectroscopy. For the first time, the formation of binary and ternary U(VI) humate complexes was directly verified by in-situ spectroscopic measurements. The complex formation constants for the binary U(VI) humate complex (UO2HA(II)) and the for ternary U(VI) mono hydroxo humate complex (UO2(OH)HA(I)) as well as the ternary U(VI) dicarbonato humate complex (UO2(CO3)2HA(II)4−) determined from the spectroscopic data amount to log β0.1 M = 6.70 ± 0.25, log β0.1 M = 15.14 ± 0.25 and log β0.1 M = 24.47 ± 0.70, respectively and verify literature data.
Keywords: Actinides, Vibrational spectroscopy, Metal-organic frameworks, Radiochemistry

Publ.-Id: 14149 - Permalink


Iodine-124: A Promising Positron Emitter for Organic PET Chemistry
Koehler, L.; Gagnon, K.; Mcquarrie, S.; Wuest, F.;
The use of radiopharmaceuticals for molecular imaging of biochemical and physiological processes in vivo has evolved into an important diagnostic tool in modern nuclear medicine and medical research. Positron emission tomography (PET) is currently the most sophisticated molecular imaging methodology, mainly due to the unrivalled high sensitivity which allows for the studying of biochemistry in vivo on the molecular level. The most frequently used radionuclides for PET have relatively short half-lives (e. g. C-11: 20.4 min; F-18: 109.8 min) which may limit both the synthesis procedures and the time frame of PET studies. Iodine-124 (I-124, t(1/2) = 4.2 d) is an alternative long-lived PET radionuclide attracting increasing interest for long term clinical and small animal PET studies. The present review gives a survey on the use of I-124 as promising PET radionuclide for molecular imaging. The first part describes the production of I-124. The second part covers basic radiochemistry with I-124 focused on the synthesis of I-124-labeled compounds for molecular imaging purposes. The review concludes with a summary and an outlook on the future prospective of using the long-lived positron emitter I-124 in the field of organic PET chemistry and molecular imaging.

Publ.-Id: 14148 - Permalink


Efficient preparation of 99mTc(III) ‘4+1’ mixed-ligand complexes for peptide labeling with high specific activity
Künstler, J.-U.; Seidel, G.; Pietzsch, H.-J.;
An improved labeling procedure for peptides attached to organometallic 99mTc(III) ‘4+1’ mixed-ligand complexes in which the radiometal is coordinated by a tripodal tetradentate chelator 2,2',2''-nitrilotriethanethiol (NS3) and a monodentate isocyanide ligand is presented. The labeling procedure was evaluated by the synthesis of [99mTc(NS3)(L2-RGD)]. The containing radiopharmaceutically interesting RGD-peptide cyclo[Arg-Gly-Asp-D-Tyr-Lys] was modified with 4-isocyanobutanoic acid (L2) as linker conjugated to N6-Lys to get the monodentate ligand L2-RGD. The structural identity of the 99mTc-conjugate was confirmed by comparison to a Re reference compound. The Tc- and Re-conjugates had matching retention times under identical HPLC conditions. The 99mTc-labeling was performed in a novel one-step procedure using the eluate of a 99Mo/99mTc generator, NS3, the isocyanide modified peptide, SnCl2, Na2EDTA, mannitol and ascorbic acid in the reaction mixture. Using optimized reagents it is possible to label 50 nmol peptide with 99mTc within 60 min at room temperature with a radiochemical yield higher than 95% and a specific activity of ~20 GBq/mmol.
Keywords: Technetium-99m; ‘4+1’ mixed-ligand complexes; Peptide labeling; Specific activity

Publ.-Id: 14147 - Permalink


The impact of interstitials on diffusion in germanium under proton irradiation
Schneider, S.; Bracht, H.; Klug, J.; Lundsgaard Hansen, J.; Nylandsted Larsen, A.; Bougeard, D.; Haller, E.; Posselt, M.; Wündisch, C.;
Experiments on the influence of 2.5 MeV proton irradiation on self- and dopant diffusion in germanium (Ge) were performed at 600 and 570°C, respectively. Ge isotope heterostructures consisting of 20 layers were used for the self-diffusion study. Ge with boron (B) doped multilayers and samples implanted with phosphorus (P) were utilized for the investigation of irradiation mediated dopant diffusion. Self-diffusion under irradiation reveals an unusual homogenous broadening of the isotope structure. This behaviour and the enhanced diffusion of B and retarded diffusion of P under irradiation demonstrates that an interstitial-mediated diffusion process dominates in Ge under irradiation. This discovery establishes new ways to suppress vacancy-mediated diffusion in Ge and to solve the donor deactivation problem that limits Ge-based nanoelectronics.
Keywords: germanium, diffusion, interstitials
  • Lecture (Conference)
    Gemeinsame DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM), den Fachverbänden Kristallographe (KR), Strahlen und Medizinphysik (ST), Physik sozio-ökonomischer Systeme (SOE) und des Arbeitskreises Industrie und Wirtschaft (AIW), 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14146 - Permalink


Experimentelle und theoretische Untersuchungen zur elektrischen Aktivierung von Dotanden und zur Festphasenepitaxie in Ge
Posselt, M.;
Review of recent results on electrical doping of Ge by ion implantation and ms flash lamp annealing, overview on atomistic simulation of solid phase epitaxial recrystallization of amorphous Ge
Keywords: germanium, electrical doping, ion implantation, flash lamp annealing, solid phase epitaxial recrystallization, computer simulation
  • Lecture (others)
    Seminar des Instituts für Materialphysik der Universität Münster, 01.06.2010, Münster, Deutschland

Publ.-Id: 14145 - Permalink


Interaction between molten corium UO2+x-ZrO2-FeOy and VVER vessel steel
Bechta, S. V.; Granovsky, V. S.; Khabensky, V. B.; Krushinov, E. V.; Vitol, S. A.; Sulatsky, A. A.; Gusarov, V. V.; Almiashev, V. I.; Lopukh, D. B.; Bottomley, D.; Fischer, M.; Piluso, P.; Miassoedov, A.; Tromm, W.; Altstadt, E.; Fichot, F.; Kymalainen, O.;
In case of in-vessel corium retention during a severe accident in a light water reactor, weakening of the vessel wall and deterioration of the vessel steel properties can be caused both by the melting of the steel and by its physicochemical interaction with corium. The interaction behavior has been studied in medium-scale experiments with prototypic corium. The experiments yielded data for the steel corrosion rate during interaction with UO2+X - ZrO2 - FeOy melt in air and steam at different steel surface temperatures and heat fluxes from the corium to the steel. It has been observed that the corrosion rates in air and steam atmosphere are almost the same. Further, if the temperature at the interface increases beyond a certain level, corrosion intensifies. This is explained by the formation of liquid phases in the interaction zone. The available experimental data have been used to develop a correlation for the corrosion rate as a function of temperature and heat flux.
Keywords: severe accident, in-vessel, retention, vessel steel corrosion
  • Nuclear Technology 157(2010)4, 210-218

Publ.-Id: 14144 - Permalink


Evolution of Ion-Induced Ripple Patterns - Anisotropy, nonlinearity, and scaling
Keller, A.;
This thesis addresses the evolution of nanoscale ripple patterns on solid surfaces during low-energy ion sputtering. Particular attention is paid to the long-time regime in which the surface evolution is dominated by nonlinear processes. This is explored in simulation and experiment.
In numerical simulations, the influence of anisotropy on the evolution of the surface patterns in the anisotropic stochastic Kuramoto-Sivashinsky (KS) equation with and without damping is studied. For a strong nonlinear anisotropy, a 90 rotation of the initial ripple pattern is observed and explained by anisotropic renormalization properties of the anisotropic KS equation. This explanation is supported by comparison with analytical predictions. In contrast to the isotropic stochastic KS equation, interrupted ripple coarsening is found in the presence of low damping. This coarsening seems to be a nonlinear anisotropy effect that occurs only in a narrow range of the nonlinear anisotropy parameter.
Ex-situ atomic force microscopy (AFM) investigations of Si(100) surfaces sputtered with sub-keV Ar ions under oblique ion incidence show the formation of a periodic ripple pattern. This pattern is oriented normal to the direction of the ion beam and has a periodicity well below 100 nm. With increasing ion fluence, the ripple pattern is superposed by larger corrugations that form another quasi-periodic pattern at high fluences.
This ripple-like pattern is oriented parallel to the direction of the ion beam and has a periodicity of around one micrometer. Interrupted wavelength coarsening is observed for both patterns. A dynamic scaling analysis of the AFM images shows the appearance of anisotropic scaling at large lateral scales and high fluences. Based on comparison with the predictions of different nonlinear continuum models, the recent hydrodynamic model of ion erosion, a generalization of the anisotropic KS equation, is considered as a potentially powerful continuum description of this experiment.
In further in-situ experiments, the dependence of the dynamic scaling behavior of the sputtered Si surface on small variations of the angle of incidence is investigated by grazing incidence small angle X-ray scattering (GISAXS). A transition from strongly anisotropic to isotropic scaling is observed. This indicates the presence of at least two fixed points in the system, an anisotropic and an isotropic one. The dynamic scaling exponents of the isotropic fixed point are in reasonable agreement with those of the Kardar-Parisi-Zhang (KPZ) equation. It remains to be seen whether the hydrodynamic model is able to show such a transition from anisotropic to isotropic KPZ-like scaling.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-519 2009

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Publ.-Id: 14143 - Permalink


Bi-Annual Report 2007/08 - Rossendorf Beamline at ESRF (ROBL-CRG)
Scheinost, A. C.; Baehtz, C.; (Editors)
The Rossendorf Beamline (ROBL) - located at BM20 of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France - is in operation since 1998. This 6th report covers the period from January 2007 to December 2008. In these two years, 50 peerreviewed papers have been published based on experiments done at the beamline. The average citation index, which increased constantly over the years, has now reached 3.5 (RCH) and 3.0 (MRH), indicating that papers are predominately published in journals with high impact factors. Six exemplary highlight reports on the following pages should demonstrate the scientific strength and diversity of the experiments performed on the two end-stations of the beamline, dedicated to Radiochemistry (RCH) and Materials Research (MRH).
Demand for beamtime remains very high as in the previous years, with an average oversubscription rate of 1.8 for ESRF experiments. The attractiveness of our beamline is based upon the high specialization of its two end-stations. RCH is one of only two stations in Europe dedicated to x-ray absorption spectroscopy of actinides and other radionuclides. The INE beamline at ANKA provides superior experimental flexibility and extends to lower energies, including important elements like P and S. In contrast, ROBL-RCH provides a much higher photon flux, hence lower detection limits crucial for environmental samples, and a higher energy range extending to elements like Sb and I. Therefore, both beamlines are highly complementary, covering different aspects of radiochemistry research. Once the MARS beamline at SOLEIL is ready to run radionuclides (>2010), it will cover a third niche (Materials Science of actinides, including irradiated fuel) not accessible for the two other beamlines.
The Materials Research Hutch MRH has realized an increasing number of in-situ investigations in the last years. On the one hand thin film systems were characterized during magnetron sputtering. On the other hand diffraction experiments under controlled atmosphere were performed. A high variety of experimental parameters was covered by varying pressure, temperature and atmospheric compositions including highly reactive gases. Furthermore structural investigations were combined with electrical conductivity measurements. These kind of in-situ experiments are the key to monitor and understand reaction mechanism or the influence of process parameters, which are again the basis to tailor materials properties on demand. The core competences of MRH are these experimental possibilities, which make it unique among other diffraction beamlines. In fall 2007, ROBL was reviewed by an international panel on behalf of the ESRF. The very positive panel report recommended a renewal of the contract between ESRF and FZD for the next five years, and a major upgrade of critical optical components of the beamline to keep ROBL competitive for the next decade. The FZD will provide 2 Mio € from 2009 to 2011 for this upgrade, which will be performed in parallel to the major upgrade of the ESRF to minimize the downtime. According to the current plans of the ESRF, our users have to expect that ROBL will have only limited or no operation for several months from August 2011 on.
Since July 2004 the beamline is a member of the pooled facilities of ACTINET – European Network of Excellence. In the reported period, RCH has provided 27 % of its inhouse beamtime to perform 11 ACTINET experiments. The success of ACTINET within FP-6 has now led to a renewal of ACTINET within FP-7, running until end of 2011.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-517 2009

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Publ.-Id: 14142 - Permalink


Annual Report 2009 - Institute of Ion Beam Physics and Materials Research
von Borany, J.; Heera, V.; Faßbender, J.ORC; Helm, M.; Möller, W.
The Institute of Ion Beam Physics and Materials Research (IIM) is one of the six institutes of the Forschungszentrum Dresden-Rossendorf (FZD), and contributes the largest part to its Research Program "Advanced Materials", mainly in the fields of semiconductor physics and materials research using ion beams. The institute operates a national and international Ion Beam Center, which, in addition to its own scientific activities, makes available fast ion technologies to universities, other research institutes, and industry. Parts of its activities are also dedicated to exploit the infrared/THz free-electron laser at the 40 MeV superconducting electron accelerator ELBE for condensed matter research. For both facilities the institute holds EU grants for funding access of external users.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-528 2010
    ISSN: 1437-322X

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Publ.-Id: 14141 - Permalink


The formation of near surface SiGe layers with combined high-dose ion implantation and flash-lamp annealing
Voelskow, M.; Stoimenos, I.; Rebohle, L.; Skorupa, W.;
The formation of near surface SiGe layers by means of combined high dose Ge ion implantation and flash lamp annealing will be addressed. Furthermore, we show that the formation of an undesirable facetted liquid/solid in-terface, which is well known for pulse melting in the mil-lisecond time regime, is less pronounced due to the de-creasing melting temperature of Si with increasing Ge concentration at the SiGe/Si interface. A dislocation net-work, which is observed by using transmission electron microscopy, is expected to play an important role to form these thin SiGe layers. We will demonstrate the depth profiles of Ge by Rutherford backscattering spectrometry and discuss the concerned mechanism.
Keywords: flash lamp annealing, ion implantation, SiGe, TEM, RBS
  • Poster
    E-MRS 2010 Spring Meeting Symp I, 07.-11.06.2010, Strasbourg, France
  • Physica Status Solidi (C) C 8(2011)3, 960-963
    DOI: 10.1002/pssc.201000159

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Publ.-Id: 14140 - Permalink


Temperature dependence of lattice parameters of langasite single crystals
Krausslich, J.; Hofer, S.; Zastrau, U.; Jeutter, N.; Baehtz, C.;
To determine the coefficient of thermal expansion of trigonal langasite (La3Ga5SiO14) the two independent lattice parameters a and c are measured over a temperature range of 800 degrees C using X-ray diffraction on single crystal samples. From the given nonlinear temperature dependence the linear and quadratic thermal coefficients of expansion alpha(11), beta(11) and alpha(33), beta(33) for the two lattice parameters a and c could be deduced.

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Publ.-Id: 14139 - Permalink


Proton mu-PIXE mapping, AFM imaging and size statistics of mineral granules in a dental composite
Preoteasa, E.; Preoteasa, E.; Harangus, L.; Moldovan, A.; Dinescu, M.; Grambole, D.; Herrmann, F.;
We applied proton microbeam particle-induced X-ray emission (mu-PIXE) for mapping Ca, Zr, Ba and Yb, and atomic force microscopy (AFM) for imaging the surface landscape of a dental composite which releases Ca2+ and F- for the protection of hard dental tissues. Three areas,similar to 250 x 250 mu m(2) located similar to 0.5-2 mm apart on a smooth surface specimen were mapped with 3.1 MeV protons focused to a similar to 3.0 mu m spot and at similar to 3.9 mu m pixel size sampling. The maps evidenced particles with diameters of 3.2-32 mu m (Ca), 20-60 mu m (Zr), <= 4 mu m (Ba) and 10-50 mu m (Yb). Cross-section area histograms of Ca-rich particles fitted with 2-6 Poisson functions revealed a polydisperse size distribution and substantial differences from an area to another, possibly implying large local variations of Ca2+ released in the hard tissue near a dental filling of a few millimeters in diameter. Such imbalances may lead to low local Ca2+ protection of the dental tissue!
, favoring the onset of secondary caries. Similarly, AFM images showed high zone-dependent differences in the distributions of grains with apparent diameters of 1-4 mu m, plausibly recognized as Ca- and Ba-containing particles. In a simple model based on demineralization data, lateral diffusion of Ca2+ between adjacent domains containing high- and low-area Ca-rich grains is described by exponential concentration gradients. These gradients may generate appreciable electromotive forces, which may enhance electrochemically the local tissue demineralization. Similar effects are to be expected in the protective action of F- ions released from microgranules of YbF3 and of Ba fluoroaluminosilicate glass.
  • X-Ray Spectrometry 39(2010)3, 208-215

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Publ.-Id: 14138 - Permalink


PiConGPU
Bussmann, M.;
We present details on the implementation of the particle-in-cell algorithm on a single GPU and a GPU cluster.
Keywords: gpu, gpgpu, pic, particle-in-cell, cluster, simulation, algorithm, communication, laser, plasma
  • Lecture (others)
    Institutsvortrag FWK, 01.06.2010, Dresden, Deutschland

Publ.-Id: 14137 - Permalink


Work hard, play harder - Skalierbare GPGPU Programmierung, große Laser und warum ich die Crysis Spiele-Engine liebe
Bussmann, M.;
Aktuelle Grafikkarten können eine Fließkomma-Leistung von mehreren TFLOPS liefern. Sie sind daher eine interressante Plattform für preiswertes, energieeffizientes Höchstleistungsrechnen. Eine GPU-getriebene Simulations-Software für echte Physikanwendungen benötigt eine hierarchische Strukturierung der Berechnungs- und Kommunikationsaufgaben, welche weit über die einfache Meldungsübergabe im heutzutage weit verbreiteten Hochleistungsrechnen (HPC) hinausgeht. Ich werde eine GPGPU Implementierung für eine Laser Plasma Simulation präsentieren, die auch auf große Rechencluster skaliert und führe Performancewerkzeuge ein, die gleichzeitig Informationen über die Prozessausführung auf CPUs und GPUs liefern. Zuletzt werde ich vorstellen, warum ein hierarchisches Algorithmen-Design unumgänglich ist, wenn man auf stark skalierbare Simulationen abzielt und wie dies in Zukunft die Softwareentwicklung in der Wissenschaft beeinflussen wird.
Keywords: gpgpu, gpu, pic, particle-in-cell, simulation, algorithm, communication, scaling, high-performance computing, hpc
  • Invited lecture (Conferences)
    Big Techday 3, 28.05.2010, München, Deutschland

Publ.-Id: 14136 - Permalink


A Bismuth Liquid Metal Ion Source for mass separated FIB Applications
Bischoff, L.; Pilz, W.; Schmidt, B.;
A bismuth liquid metal ion sources (LMIS) is investigated with respect to the emission behaviour as a function of current and temperature, the mass spectra and the energy distribution of the individual ion species [1]. For this Bi-LMIS the sputtering yields for monomer Bi ions as well as Bi-clusters (Bi2+, Bi3+, Bi4+, Bi3++) on Si, SiO2 and Ge substrates were compared with that of Ga projectile ions applied in a mass separating focused ion beam system (CANION 31Mplus). Additionally, a self-organisation of very regular, high-amplitude dot and ripple patterns depending on the angle of incidence on (001)Ge has been found under bombardment with heavy ions of bismuth dimers and trimers. Some applications in surface modification will be presented and discussed.

[1] L. Bischoff, W. Pilz, P. Mazarov, A.D.Wieck, Comparison of bismuth emitting liquid metal ion sources, Appl. Phys. A 99 (2010)145.
Keywords: Bi-LMIS, mass separating FIB, surface modification
  • Lecture (Conference)
    Arbeitskreis FIB 5. FIB Workshop, 28.-29.06.2010, Wien, Österreich

Publ.-Id: 14135 - Permalink


Optimisation of induction heating for container-less melt extraction from a metallic sheet
Cramer, A.; Park, J.-S.; Gerbeth, G.;
This work is concerned with induction heating of a metal sheet going to be used for multiple instance melt extraction from the lower edge. The task formulation of heating the edge in first place while keeping the release of Joule’s heat along that edge as homogeneous as possible, i.e. the avoidance of end effects, is solved numerically with a parametric study. A set of factors is also physically modeled in the framework of an experimental series. Subject to variation are (i) the extension of the substrate, which simulates the extraction wheel, in both directions parallel and perpendicular to the inductor, and (ii) the protrusion depth of the edge of the sheet below the lower face of the inductor. Reasonable conformity may be stated between the calculated and the experimental results.
Keywords: Melt extraction, Metallic fibres, Induction heating, Tailored magnetic fields
  • Lecture (Conference)
    Int. Symp. Heating by Electromagnetic Sources, 18.-21.05.2010, Padova, Italia
  • Contribution to proceedings
    Int. Symp. on Heating by Electromagnetic Sources, 18.-21.05.2010, Padova, Italia
    Int. Symp. on Heating by Electromagnetic Sources Induction, Dielectric and Microwaves, Condunction & Electromagnetic Processing, Padova: SGE Ditoriali, 241-248

Publ.-Id: 14134 - Permalink


Terahertz optical sideband emission in self-assembled quantum dots
Sandall, I. C.; Porter, N. E.; Wagner, M.; Schneider, H.; Winnerl, S.; Helm, M.; Wilson, L.;
A multilayer quantum dot sample has been excited with a strong terahertz (THz) electric field and probed with a near-infrared (NIR) laser. First- and second-order THz optical sidebands are generated on the NIR probe beam by driving quantum dot intersublevel resonances with the THz fields. A conversion efficiency of 3×10−6 was obtained for the conversion of NIR power into sideband emission at 4 K, decreasing by a factor of 20 up to room temperature. The sideband emission wavelength can be tuned over ∼ 20 nm by selection of appropriate NIR and THz frequencies, due to the inhomogeneous broadening of the dot ensemble.
Keywords: quantum dots, free-electron laser, terahertz sidebands

Publ.-Id: 14133 - Permalink


Simultaneous diagnostics of laser-accelerated protons and electrons
Metzkes, J.; Zeil, K.; Kraft, S.; Richter, T.; Cowan, T.; Schramm, U.;
Pulses of energetic protons with energies of several MeV can be produced by focusing an ultra-short intense laser pulse onto a solid target. The protons stem from the target rear side where they gain energy in an electric field that builds up due to charge separation effects triggered by electrons that are accelerated during the interaction of the laser with the target.
In order to investigate the acceleration of protons at solid targets which is expected to be strongly correlated to the properties of the electrons that set up the electric field at the target rear side we have set up a diagnostic which allows for the simultaneous online analysis of the accelerated protons as well as electrons. Here we are going to present first experimental results that have been measured at a table-top Ti:Sapphire laser with a pulse length of 30 fs and a peak intensity exceeding 1021 W/cm2. From these data fundamental parameters can be derived that allow for a testing of theoretical scaling laws for the proton acceleration mechanism.
  • Lecture (Conference)
    DPG-Frühjahrstagung 2010 Hannover, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 14132 - Permalink


g-factor measurements at RISING: The cases of 127Sn and 128Sn
Atanasova, L.; Balabanski, D. L.; Chamoli, S. K.; Hass, M.; Simpson, G.; Bazzacco, D.; Becker, F.; Bednarczyk, P.; Benzoni, G.; Blasi, N.; Blazhev, A.; Bracco, A.; Brandau, C.; Caceres, L.; Camera, F.; Crespi, F. C. L.; Detistov, P.; Doornenbal, P.; Fahlander, C.; Farnea, E.; Georgiev, G.; Gerl, J.; Gladnishki, K. A.; Gorska, M.; Grebosz, J.; Hoischen, R.; Ilie, G.; Ionescu-Bujor, M.; Iordachescu, A.; Jungclaus, A.; Lo Bianco, G.; Kmiecik, M.; Kojouharov, I.; Kurz, N.; Lakshmi, S.; Lozeva, R.; Maj, A.; Montanari, D.; Neyens, G.; Pfutzner, M.; Pietri, S.; Podolyak, Z.; Prokopowicz, W.; Rudolph, D.; Rusev, G.; Saito, T. R.; Saltarelli, A.; Schaffner, H.; Schwengner, R.; Tashenov, S.; Valiente-Dobon, J. J.; Vermeulen, N.; Walker, J.; Werner-Malento, E.; Wieland, O.; Wollersheim, H. J.; Grawe, H.; Hjorth-Jensen, M.;
We report g-factor measurements for the 19/2+ T1/2 = 4.5(3) µs isomer in 127 Sn and the 10+ T1/2 = 2.69(23) µs isomer in 128 Sn. The experiment was carried out on isomers which were produced and spin-aligned in relativistic heavy-ion fragmentation at GSI and were selected and separated by the GSI fragment separator (FRS). The gamma-rays of the isomer decay were detected by the RISING array. The method of time-differential perturbed angular distribution was utilized. The measured g factors, g(19/2+ ;127 Sn) = -0.17(2) and g(10+ ;128 Sn) = -0.20(4), are compared with shell model calculations. The results demonstrate the feasibility of the method for similar measurements in exotic neutron-rich nuclei.
Keywords: Nuclear structure, nuclear spectroscopy, time-differential perturbed angular distribution, g-factors, shell model.

Publ.-Id: 14131 - Permalink


Liquid metal experiments on dynamo action and related magnetic instabilities
Stefani, F.;
The talk starts with a short summary of liquid metal experiments on dynamo action that have been carried out during the last decade. Its main focus, however, is on recent experiments on the magnetorotational instability (MRI). The prospects for future experiments on dynamo action, MRI, and the Tayler instability, as well as for possible combinations will also be discussed.
  • Invited lecture (Conferences)
    International Summer School and Workshop on Self-Organization in Turbulent Plasmas and Fluids, 03.-14.05.2010, Dresden, Germany

Publ.-Id: 14130 - Permalink


Helical magnetorotational instability in theory and experiment
Stefani, F.; Gerbeth, G.; Gundrum, T.; Hollerbach, R.; Kirillov, O.; Priede, J.; Rüdiger, G.; Szklarski, J.;
The magnetorotational instability (MRI) is widely believed to play a key role in cosmic structure formation by maintaining turbulence and enabling angular momentum transport in accretion disks. The helical version of MRI (HMRI) was recently shown to have a scaling behaviour that is quite different to that of the standard version of MRI. Yet both types are continuously connected. We solve this apparent paradox by showing the emergence of an exceptional spectral point at which the slow magneto-Coriolis wave and one inertial wave coalesce and exchange their branches. Further, we compare the results of the PROMISE experiment on HMRI with various numerical predictions.
  • Lecture (Conference)
    AIMS 8th International Conference, 25.-28.05.2010, Dresden, Germany

Publ.-Id: 14129 - Permalink


Wie die Natur die Forscher inspirieren kann
Raff, J.;
Unter dem Motto „Lernen von der Natur" gibt der Vortrag einen Überblick über die radioökologische Grundlagenforschung zur Wechselwirkung bakterieller Haldenisolate mit Uran und anderen Metallen, sowie darüber, welche Möglichkeiten sich daraus ergeben, neue Materialien für technische Anwendungen zu entwickeln.
  • Lecture (others)
    Tag des offenen Labors 2010, 04.07.2010, Dresden-Rossendorf, Deutschland

Publ.-Id: 14128 - Permalink


Wie Bakterien einer Uranabfallhalde zur Entwicklung neuer Materialien beitragen können.
Raff, J.;
Vorgestellt werden die radioökologischen Arbeiten des Instituts mit Bakterien und deren Potenzial zur Entwicklung neuartiger Materialien für technische Anwendungen.
  • Invited lecture (Conferences)
    "Tage der Wissenschaften", 16.06.2010, Radebeul, Deutschland

Publ.-Id: 14127 - Permalink


Bioinspired nanocomposite materials for technical applications
Raff, J.; Weinert, U.; Günther, T.; Marquard, A.; Matys, S.; Kutschke, S.; Pollmann, K.;
Bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example, intensively studied at the Institute of Radiochemistry of the Forschungszentrum Dresden-Rossendorf, is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins prevent the uptake and any sustainable damage of the cell by toxic and/or radioactive metals. The S-layers itself form highly ordered and mono-molecular envelopes around bacterial cells. Noteworthy is their ability to self-assemble in suspension, on surfaces and at interfaces. Furthermore S-layers of different bacteria are able to fulfil different functions and thus may act as immobilization matrix for exoenzymes, as molecular sieve, as ion and molecule trap or they protect the cell from being affected by the immune defence of host organism, by other bacteria or by lytic enzymes. By using and combining these unique features of S-layer proteins, smart coatings on many different surface can be realized. Currently at the Institute of Radiochemistry, S-layer based functional coatings are under development for the production of (photo)catalytic active materials, metal selective filters or highly specific biosensors. Therefore possible applications are the elimination of pharmaceuticals and germs, the detoxification of metals, the recovery of noble metals or the detection of pharmaceuticals and other organic matter in water. Additionally, combinations of functionalities are possible using a layer-by-layer technique, offering a wide field for the development of new nanostructured biocomposites for many different applications.
  • Lecture (Conference)
    Materials Science and Engineering 2010, 24.-26.08.2010, Darmstadt, Deutschland

Publ.-Id: 14126 - Permalink


Dipole strength in 139La below the neutron-separation energy
Makinaga, A.; Schwengner, R.; Rusev, G.; Dönau, F.; Bemmerer, D.; Junghans, A. R.; Klug, J.; Beyer, R.; Crespo, P.; Erhard, M.; Kosev, K.; Nair, C.; Schilling, K. D.; Wagner, A.;
The -ray strength function is an important input quantity for the determination of the photoreaction rate and the neutron capture rate for astrophysics as well as for nuclear technologies. To test model predictions, the photoabsorption cross section of 139La up to the neutron-separation energy was measured using bremsstrahlung produced at the electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf with an electron beam of 11.5 MeV kinetic energy. The experimental data were analyzed by applying Monte Carlo simulations of -ray cascades to obtain the intensities of the ground-state transitions and their branching ratios. We found a large enhancement of electric dipole strength in the energy range from 6 to 8 MeV that may be related with a pygmy dipole resonance. The present data are combined with photoneutron cross sections for 139La and compared with results of ISS-QRPA calculations.
Keywords: Nuclear structure, gamma-ray spectroscopy, gamma-ray strength functions, quasiparticle random phase approximation, instantaneous-shape sampling.

Publ.-Id: 14125 - Permalink


Electrical conductivity and P-wave velocity in rock samples from high-temperature Icelandic geothermal fields
Kristinsdóttir, L. H.; Flóvenz, Ó. G.; Árnason, K.; Bruhn, D.; Milsch, H.; Spangenberg, E.; Kulenkampff, J.;
Measurements of electrical conductivity and P-wave velocity of seven rock samples were made in the laboratory under inferred in situ conditions. The samples were collected from smectite and chlorite alteration zones in boreholes from the Krafla and Hengill, Iceland, geothermal areas. The measurements were done in the 25–250°C range, with pore pressure and confining pressure equal to inferred in situ hydrostatic and lithostatic pressures, respectively. Conductivity increases linearly with temperature over the 30–170°C range; that rise is considerably smaller above 170°C. Time-dependent effects on conductivity occur above approximately 100°C. These effects may be related to ion exchange between the clay minerals or the Stern layer, and the pore fluid. The temperature coefficient of conductivity is found to be considerably higher than attributed to pore fluid conduction alone, indicating interface conduction in an electrical double layer on the mineral-water interface in the pores. The results also show that there is no distinction in electrical conduction mechanism in the smectite and chlorite alteration zones; both are dominated by interface conductivity under in situ conditions. The sharp decrease in conductivity at the top of the chlorite alteration zone, commonly observed in resistivity surveys in high-temperature geothermal systems, is most likely due to the lower cation exchange capacity of chlorite compared to that of smectite.
Keywords: Keywords: Geothermal Petrophysics Electrical conductivity Temperature Hydrothermal alteration

Publ.-Id: 14124 - Permalink


Influence of an impinging jet on sedimented debris
Kratzsch, A.; Renger, S.; Kaestner, W.; Hampel, R.; Krepper, E.;
The presented work is part of a joint research project performed in cooperation between the Forschungszentrum Dresden and University of Applied Sciences Zittau/Goerlitz.
The paper deals with experimental investigations concerning the influence of an impinging jet on sedimented insulation material in a building sump of the reactor containment.
To investigate the influence of an impinging jet a special test facility was designed. The test facility "Tank" was build up with acrylic glass. Thereby it is possible to use laser PIV to measure the flow field and high-speed video to analyze the jet-structure in the test facility. With help of this instrumentation the following experiments were performed:
- Experiments without air entrainment and different distances between pipe outlet and water surface in the test facility.
- Experiments with air entrainment, different distances between pipe outlet and water surface in the test facility and different flow velocities of the impinging jet.
- Experiments with a cold impinging jet and hot water in the test facility for a defined distance between pipe outlet and water surface and a defined jet velocity of the jet.
The main goal of the experiments is to study the physical phenomena of the impinging jet and provide experimental data for verification of CFD models.
Keywords: water, air, fibres, experiments
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, ICONE18, 17.-21.05.2010, Xi'an, China

Publ.-Id: 14123 - Permalink


Temperaturabhängigkeit der Komplexbildung und Sorption von Am(III)/ Eu(III) im System Ac(III)-NOM-Tongestein
Müller, M.; Acker, M.; Barkleit, A.; Taut, S.; Bernhard, G.;
Im Vortrag werden Ergebnisse zur Temperaturabhängigkeit der Eu(III)-Sorption an Opalinuston sowie zum Einfluss kleiner organischer Moleküle auf das Sorptionsverhalten vorgestellt. Außerdem wird die Komplexierung von Am(III) mit Weinsäure, untersucht bei Raumtemperatur mit UV-vis mittels LWCC, präsentiert. Des weiteren werden die Temperaturabhängigkeit des Eu(III)-Pyromellitsäure-Komplexsystems, untersucht mit TRLFS und Mikrokalorimetrie, und strukturelle Aspekte dieses Systems, ermittelt mit FT-IR und DFT, diskutiert.
Keywords: actinides, lanthanides, complexation, sorption, opalinus clay, small organic molecules
  • Lecture (others)
    Workshop zum Verbundprojekt „Wechselwirkung und Transport von Actiniden im natürlichen Tongestein unter Berücksichtigung von Huminstoffen und Tonorganika“, 13.-14.04.2010, Dresden, Deutschland

Publ.-Id: 14122 - Permalink


Use of Zirconium-Based Moderators to Enhance Feedback Coefficients in a MOX-Fueled Sodium-Cooled Fast Reactor
Merk, B.; Weiß, F.-P.; Fridman, E.; Kliem, S.;
This work shows the effect of the use of moderating layers on the sodium void effect in sodium cooled, MOX fuelled fast breeder reactors. The moderating layers are consisting of either zirconium boride ZrB2 or zirconium hydride ZrH2. The two investigated ZrH2 layers (0.1mm and 0.2 mm thick) cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system significantly. All changes caused by the insertion of the ZrH2 layers cause a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides.
Keywords: Sodium Void Effect, SFR, Fast Reactor, Zirconium Hydride, Zirconium boride
  • Nuclear Science and Engineering 171(2012)2, 136-149

Publ.-Id: 14120 - Permalink


On the use of a moderation layer to improve the safety behavior in sodium cooled fast reactors
Merk, B.; Fridman, E.; Weiß, F.-P.;
This work shows the effect of the use of moderating layers on the sodium void effect in sodium cooled fast breeder reactors. The moderating layers consisting of either boron carbide B4C or uranium-zirconium hydride UzrH cause a strong reduction of the sodium void effect. Additionally these layers improve the fuel temperature effect and the coolant effect of the system. The use of the UZrH is significantly more effective for the reduction of the sodium void effect as well as for the improvement of the fuel temperature and the coolant effect. All changes cause by the insertion of the UZrH layer cause a significantly increased stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides.
Keywords: Sodium Void Effect, SFR, Fast Reactor, Uranium-Zirconium Hydride, Boron Carbide
  • Annals of Nuclear Energy 38(2011)5, 921-929

Publ.-Id: 14119 - Permalink


The inverse energy transfer between Ge nanocrystals and erbium in SiO2 and its dependence on microstructure
Rebohle, L.; Kanjilal, A.; Skorupa, W.; Helm, M.;
The electroluminescence (EL) of Er-implanted SiO2 layers containing Ge nanocrystals (NCs) was investigated and correlated with microstructural results obtained by transmission electron microscopy, Raman spectroscopy and x-ray diffraction. In case of EL, and in contrast to the behaviour of Er-doped Si-rich SiO2 known from literature it appears that there is an inverse energy transfer from Er to Ge-related oxygen deficiency centres which are located at the surface of the Ge NCs or in the transition region between the NC and the SiO2 matrix. This is indicated by the increase of the blue-violet, Ge-related EL in presence of Er, although the Ge-related photoluminescence, which was excited by UV wavelengths non-resonant to Er, decreases at the same time. The microstructural results reveal that the maximum increase of the Ge-related EL occurs when the Ge NCs are not amorphized and/or fragmented by the Er implantation but surrounded by an Er shell. Possible mechanisms for this unexpected behaviour will be discussed.
Keywords: Electroluminescence, Ge nanocluster, Rare Earth, Optoelectronic Device, Si-based light emission
  • Optical Materials 33(2011)7, 1075-1078
  • Lecture (Conference)
    E-MRS 2010 Spring Meeting Symp K, 07.-11.06.2010, Strasbourg, France

Publ.-Id: 14118 - Permalink


High-Field ESR in Low-Dimensional Spin Systems
Zvyagin, S.;
Quantum fluctuations in low-dimensional magnets give rise to a variety of exotic strongly correlated states, making those systems an extremely attractive ground for testing various theoretical concepts. In this presentation I will focus on high-field ESR studies of two spin-chain systems. The first system is copper pyrimidine dinitrate, a material containing S=1/2 antiferromagnetic chains with alternating g-tensor and the Dzyaloshinskii-Moriya interaction and exhibiting a field-induced spin gap. Signatures of three breather branches and a soliton excitation have been identified [1,2], which is in excellent agreement with predictions of the sine-Gordon quantum field theory. In addition, a field-induced crossover from the soliton-breather to the magnon state was observed in this material in higher magnetic field [3]. The second material is NiCl2-4SC(NH2)2 (DTN), a quantum spin-1 chain system with strong easy-pane anisotropy. Using high-field ESR data, a revised set of spin-Hamiltonian parameters has been obtained [4]. These values were used to calculate the antiferromagnetic phase boundary, magnetization and the frequency-field dependence of two-magnon bound-state excitations predicted by theory and observed in DTN for the first time. Excellent quantitative agreement with experimental data was obtained.
  • Invited lecture (Conferences)
    Fakultät für Physik und Geowissenschaften Universität Leipzig, 25.05.2010, Leipzig, Deutschland

Publ.-Id: 14117 - Permalink


Enantioseparation of vesamicol and novel vesamicol analogs by high-performance liquid chromatography on different chiral stationary phases
Wenzel, B.; Fischer, S.; Brust, P.; Steinbach, J.;
High-performance liquid chromatography enantioseparation of vesamicol and six novel azaspirovesamicols (amino alcohols) was accomplished on different chiral stationary phases (CSPs) by using an optical rotation based chiral detector for identification of the resolved enantiomers. The Pirkle-type column Reprosil Chiral-NR was found to be most suitable for chiral resolution in normal phase (NP) mode; all compounds could be enantioseparated successfully. Also the cellulose-based column Reprosil Chiral-OM showed appropriate separation properties by using NP conditions. The amylose-type column Reprosil Chiral-AM-RP was most suitable for enantioseparation in reversed phase (RP) mode; five out of seven compounds were resolved. This CSP showed a considerably higher capability for chiral recognition of vesamicol derivatives in RP mode than the corresponding cellulose-based column Reprosil Chiral-OM-RP. Enantioseparation with the teicoplanin aglycone-based column Reprosil Chiral-AA was successful under polar ionic mobile phase conditions.
Keywords: Vesamicol Azaspirovesamicol Chiral separation Chiral stationary phases Polysaccharide-type CSP Pirkle-type CSP Teicoplanin aglycone CSP Chiral detector

Publ.-Id: 14116 - Permalink


Optical properties of Si+ implanted PMMA
Balabanov, S.; Tsvetkova, T.; Borisova, E.; Avramov, L.; Bischoff, L.; Zuk, J.;
In the present work, low energy ion beam irradiation was used for surface modification of polymethyl-methacrylate (PMMA) using silicon (Si+) as the ion species. After high doses ion implantation of Si+ in the polymer material, a characterization of the optical properties was performed using optical transmission measurements in the visible and near infra-red (IR) wavelength range. The optical absorption increase observed with the ion dose was attributed to ion beam induced structural changes in the modified material.
Keywords: PMMA; ion implantation; optical absorption
  • Lecture (Conference)
    16th Int. Summer School on Vacuum, Electron and Ion Technologies VEIT2009, 28.09.-02.10.2009, Sunny Beach, Bulgaria
  • Open Access LogoJournal of Physics: Conference Series 233(2010), 012032_1-012032_4
    DOI: doi:10.1088/1742-6596/223/1/012032

Publ.-Id: 14115 - Permalink


Application of the Master Curve approach to fracture mechanics characterisation of reactor pressure vessel steel
Viehrig, H.-W.; Zurbuchen, C.; Schindler, H.-J.; Kalkhof, D.;
The paper presents results of a research project founded by the Swiss Federal Nuclear Inspectorate concerning the application of the Master Curve approach in nuclear reactor pressure vessels integrity assessment. The main focus is put on the applicability of pre-cracked 0.4T-SE(B) specimens with short cracks, the verification of transferability of MC reference temperatures T0 from 0.4T thick specimens to larger specimens, ascertaining the influence of the specimen type and the test temperature on T0, investigation of the applicability of specimens with electroerosive notches for the fracture toughness testing, and the quantification of the loading rate and specimen type on T0. The test material is a forged ring of steel 22 NiMoCr 3 7 of the uncommissioned German pressurized water reactor Biblis C.
SE(B) specimens with different overall sizes (specimen thickness B=0.4T, 0.8T, 1.6T, 3T, fatigue pre-cracked to a/W=0.5 and 20% side-grooved) have comparable T0. T0 varies within the 1σ scatter band. The testing of C(T) specimens results in higher T0 compared to SE(B) specimens. It can be stated that except for the lowest test temperature allowed by ASTM E1921-09a, the T0 values evaluated with specimens tested at different test temperatures are consistent. The testing in the temperature range of T0 ± 20 K is recommended because it gave the highest accuracy. Specimens with a/W=0.3 and a/W=0.5 crack length ratios yield comparable T0. The T0 of EDM notched specimens lie 41 K up to 54 K below the T0 of fatigue pre-cracked specimens. A significant influence of the loading rate on the MC T0 was observed. The HSK AN 425 test procedure is a suitable method to evaluate dynamic MC tests. The reference temperature T0 is eligible to define a reference temperature RTTo for the ASME-KIC reference curve as recommended in the ASME Code Case N-629. An additional margin has to be defined for the specific type of transient to be considered in the RPV integrity assessment. This margin also takes into account the level of available information of the RPV to be assessed.
Keywords: reactor pressure vessel steel, fracture toughness, Master Curve approach, specimen size, constraint, loading rate, reactor pressure vessel integrity assessment
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-536 2010
    ISSN: 1437-322X

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Publ.-Id: 14114 - Permalink


Photoluminescence of Si+ and C+ implanted polymers
Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Angelov, I.; Bischoff, L.;
Visible photo luminescence (PL) of ion implanted polymers was studied. Different polymer materials were used for the purpose: polypropylene (PP), poly-tetrafluor-ethylene (Teflon), ultra-high-molecular-weight-polyethylene (UHMWPE) and UHMWPE+Bi. Ion implantation with Si+ and C+ was performed at energies of 30 keV with doses in the range 1013 – 1017 cm−2. The results show that a PL enhancement (PLE) effect may occur for some polymer materials if proper implantation energy and doses are employed, the effect in the case of some polymer materials implanted with Si+ and C+ being considerable. While the effect is observed for all doses of C+ implanted in UHMWPE, PLE is only observed for the lowest dose of Si+ (D=1×1015 cm−2) implanted in Teflon, the further dose increase resulting in PL quenching only, presumably due to processes of structural degradation The appearance of ultra-violet (UV) range PL in the case of Si+ implanted UHMWPE could be originating from the formation of Si-related new defect sites, but more data are needed to explore this effect further into the deeper UV range (λ<350 nm).
Keywords: photo luminescence; polymers; implantation
  • Lecture (Conference)
    16th Int. Summer School on Vacuum, Electron and ion Technologies VEIT2009, 28.09.-02.10.2009, Sunny Beach, Bulgaria
  • Open Access LogoJournal of Physics: Conference Series 223(2010), 012033_1-012033_5
    DOI: doi:10.1088/1742-6596/223/1/012033

Publ.-Id: 14113 - Permalink


Dynamics of magnetic objects and ultra-fast phase transitions in RhFe
Quitmann, C.; Raabe, J.; Puzic, A.; Wintz, S.; Fassbender, J.ORC; Marriager, S.; Ingold, G.; Johnson, S.; Beaud, P.; Feidenhans'L, R.; Pressacco, F.; Back, C.
In the first part we report on progress in measuring and understanding the dynamics of mesoscopic magnetic objects. These are studied in a scanning transmission x-ray microscope (STXM) which provides information about the space- and time resolved magnetization. We study individual objects, arrays and multilayer samples. The multilayer samples are of particular interest because the coupling between the layers can be tuned from anti-ferromagnetic to ferromagnetic using ion-beam irradiation. In a second part we present results on the unusual magnetic phase transition in RhFe taking place above room temperature. Here an anti-ferromagnetic low-temperature phase changes to a ferromagnetic high-temperature phase. This phase transition can be initiated using an ultra-fast laser pulse. We have studied the evolution of the crystal lattice in this transition using a pump-probe scheme. The pump-pulse is a fs laser pulse, the probe pulse is an x-ray pulse (width ~200 fs) produced by laser slicing of the stored electron beam. The data provide quantitative information about the time evolution of the lattice constants and the domain sizes. These data can be compared to optical MOKE data which measure the time dependant magnetization.
Keywords: mesoscopic magnetic objects, ultrafast RhFe phase transition, magnetization dynamics, domain imaging, x-ray microscopy
  • Invited lecture (Conferences)
    International Workshop on X-Ray spectroscopy of Magnetic Solids (XRMS10), 10.-11.06.2010, Oxfordshire, United Kingdom

Publ.-Id: 14112 - Permalink


Advanced emitters and detectors for terahertz time-domain spectroscopy
Peter, F.;
The idea of terahertz-time-domain spectroscopy (THz-TDS) is to exploit a single cycle, spectrally broad THz radiation pulse to gain insight into the response of matter. Photoconductive devices and nonlinear crystals are utilized in both the generation as well as the coherent detection of THz radiation. The relatively high cost and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems for commercial applications. Er-doped femtosecond fiber lasers operating at 1.55 μm could offer a viable alternative. In this thesis nonlinear crystals and photoconductive emitters are discussed for excitation in the near infrared (NIR) window of between 800 nm to 1550 nm. The main focus of this thesis is a detailed study of substrate materials for an interdigitated photoconductive antenna. Photoconductive antennas with microstructured electrodes provide high electric acceleration fields at moderate voltages because of small electrode separations. The scalability of these devices allows for large active areas in the mm^2 range, which are sufficient for excitation at large optical powers. In comparison with conventional emitter structures, these antennas have more favourable characteristics regarding THz power, spectral properties, and ease of handling. Depending on the utilized substrate material, photoconductive antennas can then be operated using different excitation wavelengths. By employing substrates with short carrier trapping times these antennas can be operated as THz-detectors. Moreover the design of electrode structures for generating radially and azimuthally polarized THz waves are presented. A second topic deals with the signal analysis and signal interpretation of THz pulses transmitted through several material systems. These experiments show the potential for tomographic and spectroscopic applications. The third part deals with THz emission by frequency mixing in nonlinear organic and inorganic crystals. Hereby the focus is on polaritonic phase matching in GaAs. Furthermore, indications of THz tunability by the excitation wavelength were found by utilizing waveguide structures. However, the observed tuning range is much lower then theoretically predicted. Specific reasons for this are discussed.
Keywords: infrared spectroscopy, terahertz, photoconductive devices, nonlinear optics
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-538 2010
    ISSN: 1437-322X

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Publ.-Id: 14111 - Permalink


Field and stress induced twin boundary motion in NiMnGa
Neudert, A.; Lai, Y. W.; Schäfer, R.; McCord, J.;
Twin boundaries in NiMnGa can be moved by applying either magnetic fields or mechanical stresses, which favour one of the two variants next to the twin boundary. We have used polarized light microscopy to study the two different ways of twin boundary motion in bulk NiMnGa. By placing magnetic indicator films on top of the sample surface we were able to detect the magnetic domain structure of the sample. Without the indicator films, the different variants can be seen by using polarized light illumination.
We found qualitative differences in the resulting magnetic state after a twin boundary has been moved by magnetic field or mechanical stress. By applying a magnetic field along the easy axis of one variant this variant is magnetically saturated and upon reducing the magnetic field the domain state consists of wide anti-parallel domains with 180° domain walls. Moving the twin boundary by applying mechanical stress results in a different domain state. Here the magnetization rotates by about 90° as the twin boundary passes through the area and we found the domain state to consist mainly of smaller patchy domains. The domain state with wide anti-parallel domains can be reached by demagnetizing the sample in an ac magnetic field. This suggests that the magnetic state after stress induced twin boundary motion is not in its global energy minima but rather trapped in a higher energy state
Keywords: magnetic shape memory alloy, field induced twin boundary motion, stress induced twin boundary motion, magnetization process
  • Lecture (Conference)
    EMRS Strasbourg, 07.06.2010, Strasbourg, France

Publ.-Id: 14110 - Permalink


Twin boundary motion in NiMnGa upon pulsed field excitation
Neudert, A.; Lai, Y. W.; McCord, J.;
We studied the motion of twin boundaries in NiMnGa shape memory alloy bulk samples using time-resolved optical polarisation microscopy. The sample was excited by pulsed magnetic fields with variable rise-time. The restoring force to reset the sample, necessary for stroboscopic imaging, was set by applying mechanical stress along the long axis of the bulk sample perpendicular to the magnetic field. Upon decreasing the rise-time from 10 to 1 ms we found an increase of the twin boundary motion. This dependency of the actuation range on the pulsed field rise-time can be used in actuation devices to improve the magnetic field-induced strain by changing the field rise-time without having to change the repetition rate of the magnetic field.
Keywords: magnetic shape memory alloy, twin boundary motion
  • Poster
    Actuator 2010 Bremen, 14.-16.06.2010, Bremen, Deutschland
  • Contribution to proceedings
    Actuator 2010, 15.06.2010, Bremen, Germany
    Actuator 2010 Conference Proceedings, 978-3-933339-13-3

Publ.-Id: 14109 - Permalink


Systematics of central heavy ion collisions in the 1A GeV regime
Reisdorf, W.; Andronic, A.; Averbeck, R.; Benabderrahmane, M. L.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Kang, T. I.; Kim, Y. J.; Kis, M.; Koczon, P.; Kress, T.; Leifels, Y.; Merschmeyer, M.; Piasecki, K.; Schuettauf, A.; Stockmeier, M.; Barret, V.; Basrak, Z.; Bastid, N.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasik, P.; Grishkin, Y.; Hong, B.; Kecskemeti, J.; Kirejczyk, M.; Korolija, M.; Kotte, R.; Lebedev, A.; Lopez, X.; Matulewicz, T.; Neubert, W.; Petrovici, M.; Rami, F.; Ryu, M. S.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhilin, A.;
Using the large acceptance apparatus FOPI, we study central collisions in the reactions (energies in A GeV are given in parentheses): 40Ca+40Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), 58Ni+58Ni (0.15, 0.25, 0.4), 96Ru+96Ru (0.4, 1.0, 1.5), 96Zr+96Zr (0.4, 1.0, 1.5), 129Xe+CsI (0.15, 0.25, 0.4), 197Au+197Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include cluster multiplicities, longitudinal and transverse rapidity distributions and stopping, and radial flow. The data are compared to earlier data where possible and to transport model simulations.

Publ.-Id: 14108 - Permalink


Energy dependence of the pp -> K(+)n Sigma(+) reaction close to threshold
Valdau, Y.; Barsov, S.; Buscher, M.; Chiladze, D.; Dymov, S.; Dzyuba, A.; Hartmann, M.; Kacharava, A.; Keshelashvili, I.; Khoukaz, A.; Koptev, V.; Kulessa, P.; Merzliakov, S.; Mielke, M.; Mikirtychiants, S.; Nekipelov, M.; Ohm, H.; Papenbrock, M.; Rathmann, F.; Serdyuk, V.; Stroher, H.; Trusov, S.; Wilkin, C.;
Production of the Sigma(+) hyperon through the pp -> K(+)n Sigma(+) reaction has been investigated at four energies close to threshold, 1.826, 1.920, 1.958, and 2.020 GeV. At low energies, correlated K+pi(+) pairs can only originate from Sigma(+) production so their measurement allows the total cross section for the reaction to be determined. The results obtained are completely consistent with the values extracted from the study of the K+-proton correlation spectra obtained in the same experiment. These spectra, as well as the inclusive K+ momentum distributions, also provide conservative upper limits on Sigma(+) production rates. The measurements show a Sigma(+) production cross section that varies roughly like phase space, and, in particular, none of the three experimental approaches used supports the anomalously high, near-threshold pp -> K(+)n Sigma(+) total cross section previously reported [T. Rozek et al., Phys. Lett. B 643, 251 (2006)].

Publ.-Id: 14107 - Permalink


The microstructure of neutron-irradiated Fe-Cr alloys: A small-angle neutron scattering study
Heintze, C.; Bergner, F.; Ulbricht, A.; Eckerlebe, H.;
The effect of Cr on the microstructures of neutron-irradiated Fe-Cr alloys is not yet known in all details including types, sizes, concentrations and compositions of irradiation-induced features on the nanoscale. Such details are needed in order to develop and validate models devoted to the long-term evolution of microstructures. Among other techniques, small-angle neutron scattering (SANS) can contribute to this task. Results obtained for a set of Fe-Cr alloys of Cr levels of 2.5, 5, 9 and 12.5 at%, irradiated at 300°C up to neutron exposures of 0.6 and 1.5 dpa are reported. We have found that the incoherent magnetic scattering of the unirradiated alloys exhibits a systematic variation with the Cr content and that there is an irradiation-induced increase of the coherent magnetic scattering for each of the irradiated conditions. The effect of Cr on size and type of irradiation-induced scatterers is discussed.

Publ.-Id: 14106 - Permalink


Small-angle neutron scattering investigation of as-irradiated, annealed and reirradiated reactor pressure vessel weld material of decommissioned reactor
Ulbricht, A.; Altstadt, E.; Bergner, F.; Viehrig, H.-W.; Keiderling, U.;
Small-angle neutron scattering (SANS) was applied to characterize the microstructure of weld material taken from the reactor pressure vessel (RPV) of the decommissioned VVER440(230)-type nuclear power plant (NPP) Greifswald, units 1, 2 and 4. The welding seam of highest neutron exposure of unit 1 was subject to a large-scale annealing treatment in 1988 after about 11.5 effective years of operation. The same type of annealing was applied to unit 2 in 1990 after about 11 effective years of operation. After final decommissioning of NPP Greifswald in 1990, RPV material was left in the reirradiated condition (unit 1), in the as-annealed condition (unit 2) and in the as-irradiated condition (unit 4). Trepans of material from the highly irradiated RPV welds of these units have recently become available for examination. The results of the SANS investigation are reported and compared with published results obtained for asirradiated, post-irradiation annealed and reirradiated surveillance material of the same type. We have found general agreement indicating in particular the formation of irradiation-induced Cu-enriched clusters and efficient recovery as a result of the largescale annealing treatments. The only essential difference was observed for the ratio of magnetic and nuclear scattering indicating differences of the cluster composition for the RPV wall and surveillance material.

Publ.-Id: 14105 - Permalink


SANS investigation of RPV weld material from the decommissioned NPP Greifswald
Bergner, F.; Ulbricht, A.; Viehrig, H.-W.; Keiderling, U.;
Nuclear plant operators must demonstrate that the structural integrity of a nuclear reactor pressure vessel (RPV) is assured during routine operations or under postulated accident conditions. The aging of the RPV steels is monitored with surveillance program results or predicted by trend curves. Embrittlement forecast with trend curves and surveillance specimens may not reflect the reality. Accordingly, the most realistic evaluation of the toughness response of RPV material to irradiation is done directly on RPV wall samples from decommissioned nuclear power plants (NPP). Such a unique opportunity is now offered with material from the decommissioned Greifswald NPP. The four Greifswald NPP units representing the first generation of WWER-440/V-230 reactors were shut down in 1990 after 11–17 years of operation. Material from RPVs in three different conditions is available: Unit 1 is irradiated, annealed and reirradiated. Unit 2 is irradiated and annealed. Unit 4 is in the as-irradiated condition. Small-angle neutron scattering (SANS) was applied in order to characterize the microstructure of weld material taken from the core-belt regions of Units 1, 2 and 4. Furthermore, material from Unit 4 exposed to post-irradiation annealing corresponding to the large-scale annealings of Units 1 and 2 was also investigated. The results of the SANS experiments are reported and compared with mechanical properties as well as results obtained for surveillance material of the same type.
  • Lecture (Conference)
    E-MRS 2010 Spring Meeting, 06.-11.06.2010, Strasbourg, Frankreich

Publ.-Id: 14104 - Permalink


Microstructure of oxide dispersion strengthened Eurofer and iron–chromium alloys investigated by means of small-angle neutron scattering and transmission electron microscopy
Heintze, C.; Bergner, F.; Ulbricht, A.; Hernandez-Mayoral, M.; Keiderling, U.; Lindau, R.; Weißgärber, T.;
Oxide dispersion strengthening of ferritic/martensitic chromium steels is a promising route for the extension of the range of operation temperatures for nuclear applications. The investigation of dedicated model alloys is an important means in order to separate individual effects contributing to the mechanical behaviour under irradiation and to improve mechanistic understanding. A powder metallurgy route based on spark plasma sintering was applied to fabricate oxide dispersion strengthened (ODS) Fe9Cr model materials. These materials along with Eurofer97 and ODS-Eurofer were investigated by means of small-angle neutron scattering (SANS) and TEM. For Fe9Cr–0.6 wt.%Y2O3, TEM results indicate a peak radius of the size distribution of Y2O3 particles of 4.2 nm with radii ranging up to 15 nm, and a volume fraction of 0.7%, whereas SANS indicates a peak radius of 3.8 nm and a volume fraction of 0.6%. It was found that the non-ODS Fe9Cr and Eurofer97 are suitable reference materials for ODS-Fe9Cr and ODS-Eurofer, respectively, and that the ODS-Fe9Cr variants are suitable model materials for the separated investigation of irradiation-Y2O3 particle interaction effects.

Publ.-Id: 14103 - Permalink


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