Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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30097 Publications
Experimental investigations and rate-based modeling of CO₂ absorption with sandwich packings
Flechsig, S.; Sohr, J.; Schubert, M.; Hampel, U.; Kenig, E. Y.
In the process industry, packed columns are used in a variety of fluid separation operations, e.g. in distillation and absorption, in order to create a desirable flow pattern of two-phase systems. Due to the high energy requirements of separation processes, the interest on their optimization is vital. In particular, column internals have permanently been the focus of investigations.
An improvement of the separation efficiency can be achieved by the application of sandwich packings. The latter consist of two alternating layers of industrially available standard packings with different specific surface areas, one with lower (the so-called holdup layer) and another with higher (the so-called de-entrainment layer) capacity. Sandwich packings are typically used at operating conditions between the flooding points of holdup layer and de-entrainment layer. Above the holdup layer, a froth sublayer is formed, which reveals high separation efficiency due to intensified phase mixing. In the upper section of the de-entrainment layer, film-like flow patterns can be observed [1]. Under certain conditions, this intensive heterogeneous flow pattern can be used in a beneficial way for fluid separation processes. However, the application of this integrated packing type is hindered by lacking validated design methods [2].
An accurate prediction of the performance characteristics is essential for the design of sandwich packings. In our project, the effects of the individual flow regimes on fluid dynamics and mass transfer are investigated complementarily with both experimental and theoretical studies. In order to determine the impact of each individual flow regime, experiments on an absorption/desorption plant are supplemented by flow imaging measurements of sandwich packings. At the Paderborn University, CO2 absorption is examined in a pilot plant for various design and operating parameters. This plant allows measuring temperature profiles of the gas phase as well as concentration profiles of both phases. At the Helmholtz-Zentrum Dresden-Rosendorf, a detailed view on the phase distribution within the sandwich packings is realized bymeans of an ultrafast X-ray tomography. The measured data from both experimental methods are used to establish correlations for mass transfer coefficients, interfacial area, holdup and pressure drop, which are applied in a rate-based stage model for CO2 absorption processes with aqueous amine solutions.
The absorption experiments were performed under ambient conditions in a column with an inner diameter of 0,1 m and 3,2 m packing height. The influence of different operating and design parameters on the separation characteristics in sandwich packings was studied in order to identify appropriate operating conditions and to provide a sufficient basis for the experimental validation of a model, which is able to describe the heterogeneous flow patterns. In particular, we investigated the impact of the holdup-layer height and its corresponding specific surface area. In addition, the inclination angle of the flow channels in the de-entrainment layer was varied.
The rate-based approach, which accounts for the specifics of different column internals via correlations, was applied. We expected that different fluid dynamic regimes would have different impacts on the mass transfer. Therefore, each fluid dynamic regime was considered individually. The column was represented as a sequence of alternating segments, and each segment was described by a corresponding set of correlations. Experimental data of the CO2 absorption with sandwich packings were then compared with simulation results.
The authors are grateful to the Deutsche Forschungsgemeinschaft (DFG) for financial support (KE 837/26-1, HA 3088/10-1).
[1] U. Brinkmann, B. Kaibel, M. Jödecke, J. Mackowiak, E.Y. Kenig: Beschreibung der Fluiddynamik von Anstaupackungen, Chemie Ingenieur Technik 84, 36-45 (2012).
[2] Ö. Yildirim, E.Y. Kenig: Rate-based modelling and simulation of distillation columns with sandwich packings, Chemical Engineering and Processing: Process Intensification 98, 147-154 (2015).
  • Lecture (Conference)
    ACHEMA Congress 2018, 11.-15.06.2018, Frankfurt am Main, Deutschland

Publ.-Id: 27815 - Permalink

Three-Dimensional Composition and Electric Potential Mapping of III−V Core−Multishell Nanowires by Correlative STEM and Holographic Tomography
Wolf, D.; Hübner, R.; Niermann, T.; Sturm, S.; Prete, P.; Lovergine, N.; Büchner, B.; Lubk, A.
The nondestructive characterization of nanoscale devices, such as those based on semiconductor nanowires, in terms of functional potentials is crucial for correlating device properties with their morphological/materials features, as well as for precisely tuning and optimizing their growth process. Electron holographic tomography (EHT) has been used in the past to reconstruct the total potential distribution in three dimension but hitherto lacked a quantitative approach to separate potential variations due to chemical composition changes (mean inner potential, MIP) and space charges. In this letter, we combine and correlate EHT and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) tomography on an individual ⟨111⟩ oriented GaAs-AlGaAs core-multishell nanowire (NW). We obtain excellent agreement between both methods in terms of the determined Al concentration within the AlGaAs shell, as well as thickness variations of the few nanometer thin GaAs shell acting as quantum well tube. Subtracting the MIP determined from the STEM tomogram enables us to observe functional potentials at the NW surfaces and at the Au-NW interface, both ascribed to surface/interface pinning of the semiconductor Fermi level.
Keywords: GaAs-AlGaAs, III−V nanowire, 3D elemental mapping, functional potential, quantum well tube, tomography, holography

Publ.-Id: 27807 - Permalink

Terahertz pump-induced anisotropy and nonlinear susceptibility in graphene
Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.
We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.
Keywords: graphene, nonlinear terahertz spectroscopy, nonlinear susceptibility, pump-probe
  • Poster
    34-th International Conference on the Physics of Semiconductors (ICPS 2018), 29.07.-03.08.2018, Montpellier, Frankreich

Publ.-Id: 27805 - Permalink

High-performance and room-temperature QWIPs & terahertz spectroscopy
Schneider, H.
The topic of this seminar talk is high-performance and room-temperature quantum well photodetectors and terahertz spectroscopy.
Keywords: quantum well infrared photodetector, terahertz spectroscopy
  • Lecture (others)
    Seminarvortrag, Yunnan University, 03.05.2018, Kunming, China

Publ.-Id: 27804 - Permalink

Nonlinear THz spectroscopy of graphene and GaAs quantum wells using a free-electron laser
Schneider, H.
This talk reviews some recent experiments using FEL-based intense narrow-band terahertz fields, in particular pump-induced optical anisotropy and nonlinear four-wave mixing in graphene, and dressing of excitons, exciton-polaritons, and intersubband transitions in GaAs quantum wells.
Keywords: nonlinear terahertz spectroscopy, graphene, interaubband, exciton
  • Invited lecture (Conferences)
    The 9th International Symposium on Ultrafast Phenomena and Terahertz Waves (ISUPTW 2018), 23.-26.04.2018, Changsha, China
  • Invited lecture (Conferences)
    International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2018), Budker Institute of Nuclear Physics, 25.-28.06.2018, Novosibirsk, Russische Föderation

Publ.-Id: 27803 - Permalink

Nonlinear THz free-electron laser spectroscopy of graphene and GaAs quantum wells
Schneider, H.
This talk reviews some recent experiments on graphene and on GaAs quantum wells using FEL-based strong THz fields.
In graphene, we have investigated the pump-induced anisotropy of the carrier distribution upon excitation with linearly polarized light. Since optical-phonon scattering is suppressed at THz frequencies and low temperatures, we observe the decay of this anisotropy to be very slow, as long as several ps, which is theoretically explained by non-collinear Coulomb scattering. We also report on degenerate four-wave mixing experiments in Landau-quantized graphene to investigate the induced coherent polarization. In GaAs quantum wells, intense narrow-band THz fields are exploited for dressing elementary electronic excitations. We will address THz-induced dressing of excitons, exciton-polaritons, and intersubband transitions.
Keywords: Graphene, intersubband, nonlinear terahertz spectroscopy,
  • Lecture (others)
    Seminarvortrag, University of California at Santa Barbara (UCSB), 05.02.2018, Santa Barbara, USA
  • Lecture (others)
    Physikalisches Kolloquium der TU Chemnitz, 13.06.2018, Chemnitz, Deutschland
  • Lecture (others)
    Seminar, Chengdu Campus of CAEP, 23.07.2018, Chengdu, China

Publ.-Id: 27802 - Permalink

Terahertz orientational relaxation and phase relaxation in graphene
Schneider, H.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Wang, Y.; Belyanin, A.; Pashkin, A.; Helm, M.; Winnerl, S.
We report on investigations of the carrier dynamics in graphene close to the Dirac point by nonlinear terahertz spectroscopy. At terahertz frequencies and low temperatures, optical-phonon scattering is suppressed. In this case, the decay of the pump-induced anisotropy in the carrier distribution is observed to be very slow, long as several ps, which is theoretically explained by non-collinear Coulomb scattering. In Landau-quantized graphene, degenerate four-wave mixing experiments in resonance to the lowest Landau level transition allow us to investigate the induced coherent polarization and to compare its dependence on THz field strength and B-field detuning with theoretical expectations.
Keywords: graphene, nonlinear terahertz spectroscopy, nonlinear susceptibility, four-wave mixing, pump-probe
  • Lecture (Conference)
    SPIE Photonics West, Symposium on "Ultrafast Phenomena and Nanophotonics XXII", 27.01.-01.02.2018, San Francisco, USA

Publ.-Id: 27801 - Permalink

Halbleitertechnik im Osten der Republik
Skorupa, W.
Eingeladener Vortrag anlässlich des Workshops zum 60. Gründungsjubiläum des Institutes für Halbleitertechnik an der Universität Stuttgart mit Bezug zur Ionenstrahlphysik und -technologie am Forschungsstandort Dresden-Rossendorf, jetzt Helmholtzzentrum Dresden-Rossendorf
Keywords: Halbleitertechnik, Chiptechnologie, DDR, Geschichte, Ionenstrahlphysik, Ionenstrahltechnologie
  • Invited lecture (Conferences)
    Workshop anlässlich des 60. Jahrestages des Institutes für Halbleitertechnik an der Universität Stuttgart, 01.08.2018, Stuttgart, Deutschland

Publ.-Id: 27800 - Permalink

All-optical quantum thermometry based on spin-level cross-relaxation and multicenter entanglement under ambient conditions in SiC
Anisimov, A. N.; Soltamov, V. A.; Breev, I. D.; Babunts, R. A.; Mokhov, E. N.; Astakhov, G. V.; Dyakonov, V.; Yakovlev, D. R.; Suter, D.; Baranov, P. G.
All-optical thermometry technique based on the energy level cross-relaxation in atomic-scale spin centers in SiC is demonstrated. This technique exploits a giant thermal shift of the zero-field splitting for centers in the triplet ground state, S=1, undetected by photoluminescence (so called “dark” centers) coupling to neighbour- ing spin-3/2 centers which can be optically polarized and read out (“bright” centers), and does not require radiofrequency fields. EPR was used to identify defects. The width of the cross-relaxation line is almost an order of magnitude smaller than the width of the excited state level-anticrossing line, which was used in all-optical ther- mometry and which can not be significantly reduced since determined by the lifetime of the excited state. With approximately the same temperature shift and the same sig- nal intensities as for excited state level-anticrossing, cross-relaxation signal makes it possible to increase the sensitivity of the temperature measurement by more than an order of magnitude. Temperature sensitivity is estimated to be approximately 10 mK/Hz1/2 within a volume about 1 μ3, allocated by focused laser excitation in a scanning confocal microscope. Using cross-relaxation in the ground states of “bright” spin-3/2 centers and “dark” S=1 centers for temperature sensing and ground state level anti-crossing of “bright” spin-3/2 centers an integrated magnetic field and tempera- ture sensor with submicron space resolution can be implemented using the same spin system. The coupling of individually addressable “bright” spin-3/2 centers connected by a chain of “dark” S=1 spins, could be considered in quantum information pro- cessing and multicenter entanglement under ambient conditions.
Keywords: Defects, Quantum Technology, Thermometry, Silicon Carbide

Publ.-Id: 27798 - Permalink

Detailed study of the Fermi surfaces of the type-II Dirac semimetallic candidates XTe2 (X = Pd, Pt)
Zheng, W.; Schönemann, R.; Aryal, N.; Zhou, Q.; Rhodes, D.; Chiu, Y.-C.; Chen, K.-W.; Kampert, E.; Förster, T.; Martin, T. M.; Mccandless, G. T.; Chan, J. Y.; Manousaki, E.; Balicas, L.
We present a detailed quantum oscillatory study on the Dirac type-II semimetallic candidates PdTe2 and PtTe2 via the temperature and the angular dependence of the de Haas–van Alphen and Shubnikov–de Haas effects. In high-quality single crystals of both compounds, i.e., displaying carrier mobilities between 103 and 104 cm2/ Vs, we observed a large nonsaturating magnetoresistivity which in PtTe2 at a temperature T = 1.3 K leads to an increase in the resistivity up to (5×104)% under a magnetic field μ0H = 62 T. These high mobilities correlate with their light effective masses in the range of 0.04 to 1 bare electron mass according to our measurements. For PdTe2 the experimentally determined Fermi surface cross-sectional areas show excellent agreement with those resulting from band structure calculations. Surprisingly, this is not the case for PtTe2, whose agreement between calculations and experiments is relatively poor even when electronic correlations are included in the calculations. Therefore, our study provides strong support for the existence of a Dirac type-II node in PdTe2 and probably also for PtTe2. Band structure calculations indicate that the topologically nontrivial bands of PtTe2 do not cross the Fermi level ɛF. In contrast, for PdTe2 the Dirac type-II cone does intersect ɛF, although our calculations also indicate that the associated cyclotron orbit on the Fermi surface is located in a distinct kz plane with respect to that of the Dirac type-II node. Therefore, it should yield a trivial Berry phase.

Publ.-Id: 27795 - Permalink

Experimental evidence for the microscopic mechanism of the unusual spin-induced electric polarization in GdMn2O5
Yahia, G.; Damay, F.; Chattopadhyay, S.; Baledent, V.; Peng, W.; Kim, S. W.; Greenblatt, M.; Lepetit, M.-B.; Foury-Leylekian, P.
We report in this paper the temperature evolution of the magnetic structure of GdMn2O5, in the range 2–40 K, studied by neutron diffraction on an isotope-enriched powder. We detail a thorough analysis of the microscopic mechanisms needed to release the different magnetic frustrations that are at the origin of the polarization. In addition to the usual exchange-striction term, known to be at the origin of the polarization in this family, an additional exchange-striction effect between the Gd3+ and Mn3+ spins is found to be responsible for the very large polarization in the Gd compound.

Publ.-Id: 27794 - Permalink

Pressure-induced commensurate order in TbMn2O5 and DyMn2O5: Influence of rare-earth anisotropy and 3d-4 f exchange
Deutsch, M.; Peng, W.; Foury-Leylekian, P.; Baledent, V.; Chattopadhyay, S.; Fernandez-Diaz, M. T.; Hansen, T. C.; Forget, A.; Colson, D.; Greenblatt, M.; Lepetit, M.-B.; Petit, S.; Mirebeau, I.
The magnetic structure of TbMn2O5 and DyMn2O5 multiferroics has been studied by high-pressure neutron diffraction in a large pressure range up to 6.6 GPa. In both cases, we observe a pressure-induced commensurate magnetic phase with propagation vector ( 1/2 0 1/2 ), growing with pressure at the expense of the ambient pressure phases. Being previously observed in YMn2O5 and PrMn2O5, this phase is most likely a generic feature of the RMn2O5 multiferroic family. A simple model is proposed to explain qualitatively the emergence of this pressure-induced phase. Differences between TbMn2O5 and DyMn2O5 behaviors at ambient and low pressures provide clues on the interaction scheme.

Publ.-Id: 27793 - Permalink

Probing the Jeff = 0 ground state and the Van Vleck paramagnetism of the Ir5+ ions in layered Sr2Co0.5Ir0.5O4
Agrestini, S.; Kuo, C.-Y.; Chen, K.; Utsumi, Y.; Mikhailova, D.; Rogalev, A.; Wilhelm, F.; Förster, T.; Matsumoto, A.; Takayama, T.; Takagi, H.; Haverkort, M. W.; Hu, Z.; Tjeng, L. H.
We report a combined experimental and theoretical x-ray magnetic circular dichroism (XMCD) spectroscopy study at the Ir-L2,3 edges on the Ir5+ ions of the layered hybrid solid state oxide Sr2Co0.5Ir0.5O4 with the K2NiF4 structure. From theoretical simulation of the experimental Ir-L2,3 XMCD spectrum, we found a deviation from a pure Jeff = 0 ground state with an anisotropic orbital-to-spin moment ratio (Lx/2Sx = 0.43 and Lz/2S = 0.78). This deviation is mainly due to multiplet interactions being not small compared to the cubic crystal field and due to the presence of a large tetragonal crystal field associated with the crystal structure. Nevertheless, our calculations show that the energy gap between the singlet ground state and the triplet excited state is still large and that the magnetic properties of the Ir5+ ions can be well described in terms of singlet Van Vleck paramagnetism.

Publ.-Id: 27792 - Permalink

Short-range quasistatic order and critical spin correlations in α-Ru1−xIrxCl3
Do, S.-H.; Lee, W.-J.; Lee, S.; Choi, Y. S.; Lee, K.-J.; Gorbunov, D. I.; Wosnitza, J.; Suh, B. J.; Choi, K.-Y.
The magnetic ground states of the diluted α-Ru1−x IrxCl3 are systematically investigated by magnetization, specific heat, and muon spin rotation measurements. Introduction of moderate spin vacancies leads to a destabilization of the zigzag antiferromagnetic order towards a short-range ordered state. It is remarkable that the x = 0.2 sample located near a quantum critical point shows an extremely short correlation length of the magnitude of magnetic moments ζmag ∼ 1.2a (a = lattice spacing) and a power-law behavior of the magnetic susceptibility χ(T ) ∼ T−p below 14 K for μ0HIIab and below 30 K for μ0HIIc. Our work demonstrates that the α-Ru1−x IrxCl3 system hosts a short-range, quasistatic order characterized by critical spin correlations.

Publ.-Id: 27790 - Permalink

The electronic structure and band interface of cesium bismuth iodide on a titania heterostructure using hard X-ray spectroscopy
Phuyal, D.; Jain, S. M.; Philippe, B.; Johansson, M. B.; Pazoki, M.; Kullgren, J.; Kvashnina, K. O.; Klintenberg, M.; Johansson, E. M. J.; Butorin, S. M.; Karis, O.; Rensmo, H.
Bismuth halide compounds as a non-toxic alternative are increasingly investigated because of their potential in optoelectronic devices and their rich structural chemistry. Hard X-ray spectroscopy was applied to the ternary bismuth halide Cs3Bi2I9 and its related precursors BiI3 and CsI to understand its electronic structure at an atomic level. We specifically investigated the core levels and valence band using X-ray photoemission spectroscopy (PES), high-resolution X-ray absorption (HERFD-XAS), and resonant inelastic X-ray scattering (RIXS) to get insight into the chemistry and the band edge properties of the two bismuth compounds. Using these element specific X-ray techniques, our experimental electronic structures show that the primary differences between the two bismuth samples are the position of the iodine states in the valence and conduction bands and the degree of hybridization with bismuth lone pair (6s2) states. The crystal structure of the two layered quasiperovskite compounds plays a minor role in modifying the overall electronic structure, with variations in bismuth lone pair states and iodine band edge states. Density Functional Theory (DFT) calculations are used to compare with experimental data. The results demonstrate the effectiveness of hard X-ray spectroscopies to identify element specific bulk electronic structures and their use in optoelectronic devices

Publ.-Id: 27782 - Permalink

Entwicklung und Synthese neuartiger fluorhaltiger Liganden zur molekularen Bildgebung des Adenosin A2B-Rezeptors im Gehirn mittels Positronen-Emissions-Tomographie
Lindemann, M.ORC
Der G-Protein-gekoppelte A2B-Rezeptor unterscheidet sich von den anderen Adenosinrezeptorsubtypen (A1, A2A, A3) durch die niedrige Affinität zu seinem endogenen Liganden Adenosin. Es wird beschrieben, dass der Rezeptor in verschiedenen pathologischen Prozessen, die durch eine erhöhte Adenosinkonzentration ausgezeichnet sind, wie beispielsweise bei Entzündungen (Inflammation), Hypoxie oder auch Krebs, eine wichtige Rolle spielt. Ziel dieser Arbeit ist die Entwicklung eines Fluor-18 markierten Radioliganden für die molekulare Bildgebung des A2B-Rezeptors im Organismus bzw. im speziellen des Gehirns mittels PET. Es soll damit der Einfluss des Rezeptors bei neurodegenerativen, neuroinflammatorischen und neuroonkologischen Erkrankungen untersucht werden. Die hier erstellte Arbeit basiert auf drei verschiedenen Leitstrukturen: den Pyrazinen (PA), Pyrimidinen (PYM) und Xanthinen (PXS). Für die ersten beiden Strukturklassen wurden zunächst die Leitverbindung und verschiedene fluorierte Derivate dargestellt. Für die Xanthine wurden zwei verschiedene Derivate synthetisiert. Alle Verbindungen wurden hinsichtlich ihrer Affinität und Selektivität gegenüber den Adenosinrezeptorsubtypen untersucht. Für die Klasse der Pyrazine wurde die bis dahin beste Verbindung PA51 ausgewählt. Trotz geringer Defizite gegenüber der Selektivität zu den anderen Adenosinrezeptorsubtypen, sollte PA51 zur Untersuchung der Hirngängigkeit der Verbindungsklasse genutzt werden. Nach erfolgreicher manueller Radiomarkierung und Transfer in eine automatisierte Radiosynthese, wurde die In-vivo-Gehirnaufnahme (Autoradiographie, PET) und der In-vivo-Metabolismus von [18F]PA51 in Mäusen untersucht. Bei In-vivo- Verteilungsstudien in Mäusen wurde eine homogene Verteilung des Radiotracers im Gehirn bestimmt. Des Weiteren wurden Gehirn- und Plasmaproben zu unterschiedlichen Zeitpunkten mit verschiedenen Methoden (RP-HPLC und MLC) auf enthaltene Radiometabolite untersucht. Nach 30 min p.i. konnten 70% an intaktem Radiotracer und ein Hauptradiometabolit mit einem Anteil von 30% im Gehirn nachgewiesen werden. Dessen Struktur konnte durch Synthese einer nichtradioaktiven Vergleichssubstanz aufgeklärt werden. Auf Grund dieser Ergebnisse ist die Substanzklasse der Pyrazine nicht geeignet als PET Radiotracer. Im Vergleich zu den Pyrazinen sind die Pyrimidinderivate in der Literatur als metabolisch stabiler beschrieben. Aus diesem Grund wurde zunächst die Leitverbindung PYM80, unter leichter Modifizierung der beschriebenen siebenstufigen Syntheseroute, dargestellt. Die fluorierte Verbindung PYM81 wurde über eine neu entwickelte sechsstufige Syntheseroute dargestellt. Diese weist eine hohe Affinität und Selektivität zum A2B-Rezeptor auf, weshalb PYM81 großes Potential für die Anwendung als neuartiger fluorierter Radioligand für die molekulare Darstellung des A2B-Rezeptors mittels PET besitzt. Als dritte Strukturklasse wurden zwei Xanthinderivate PXS7-1 und PXS7-2 dargestellt. Diese Strukturen basieren auf dem literaturbekannten, hochaffinen und selektiven Liganden PSB-603. Durch Reduzierung des sterisch anspruchsvollen Sulfonamidrestes sollten die molare Masse und die stark polaren Eigenschaften dieser Verbindungsklasse gesenkt werden. An Stelle der sterisch anspruchsvollen Sulfonamidreste sollten kleine Substituenten wie 4-Fluorpiperidin oder 4-Amino-2-fluorpyridin eingeführt werden. Diese beiden Verbindungen zeigten moderate Affinitäten und Selektivitäten gegenüber dem A2B-Rezeptor, weshalb weitere strukturelle Modifizierungen, zur Steigerung der Affinität und Selektivität zum A2B-Rezeptor, folgen sollen.

The G protein-coupled A2B receptor differs from other adenosine receptor subtypes (A1, A2A, A3) by its low affinity towards the endogenous ligand adenosine. It is suggested to be involved in various pathological processes accompanied by increased levels of adenosine, e.g. inflammation, hypoxia, and cancer. In this work, the development and synthesis of a fluorine-18 labelled radioligand with the particular aim for the imaging of the A2B receptor is described, to enable the investigation of the function and expression of A2B receptor in the organism and the influence of neurodegenerative, neuroinflammatory and neurooncological processes with PET. This work is based on three different lead structures: pyrazines (PA), pyrimidines (PYM), and xanthines (PXS). For the first two structure classes, the syntheses of the lead and different fluorinated compounds were performed. For the xanthines two different molecules were synthesized. The binding affinities for the different adenosine receptor subtypes were determined for each compound. To check the brain penetration of the pyrazine class, the best candidate so far, PA51 (although lacking selectivity), was labeled with 18-fluorine. After transfer of the manual radiolabeling procedure to the automated synthesis module, the in vivo brain uptake and the in vivo metabolism studies of [18F]PA51 in mice were performed. The in vivo brain uptake studies (brain sampling, autoradiography and PET) showed a homogeneous distribution of [18F]PA51. After different time intervals, brain and plasma samples were investigated by using different methods for metabolite analytics, showing only 70% of intact radiotracer in the brain 30 min p.i. A main brain radiometabolite with an amount of 30% after 30 min p.i. was structurally identified by use of a synthesized nonradioactive reference compound. In summary, this compound class is not suitable for the use as PET radiotracer, because of the fast metabolism of the compound and the formation of a brain-penetrable radiometabolite. The pyrimidine derivatives are described in literature as more metabolically stable as the pyrazines. For this compound class, the lead compound PYM80 was synthesized in a slightly modified seven-step synthesic route. A fluorinated derivative, PYM81, was synthesized over a newly developed six-step synthesic route. The compound showed good affinity and selectivity towards the A2B receptor. Therefor PYM81 has a high potential as a novel fluorinated radioligand for the molecular imaging of the A2B receptor with PET. As third class, xanthine derivatives were synthesized because of the highly affine and selective lead compound PSB-603. Due to the high molar mass and high polarity of these compounds the sulfonamide group was modified. Instead of this group, a small 4-amino-2-fluoropyridine or 4-fluoropiperidine groups was introduced to form derivatives PXS7-1 and PXS7-2. The compounds showed moderate affinities and selectivities for the A2B receptor. In conclusion, various fluorinated compounds were synthesized and showed different affinities and selectivities for the A2B receptor and its subtypes. Furthermore, the synthesis of additional fluorinated structures with the pyrimidine lead structure is required to enhance affinity and selectivity. For a first checkup of the brain uptake of this compound class, PYM81 needs to be radiolabeled with fluorine-18 because of the literature described higher metabolic stability in comparison to the pyrazine derivatives. PYM81 and the class of pyrimidines had a high potential as novel ligands for imaging the A2B receptor with PET in the brain.
Keywords: A2B-Rezeptor, 18-Fluor, Pyrazine, Pyrimidine, Xanthine, Pyrido[2,3-d]pyrimidin-2,4(1H,3H)dione, Positronen-Emissions-Tomographie
  • Doctoral thesis
    Universität Leipzig, 2018
    Mentor: Prof. Dr. P. Brust, Dr. B. Wenzel
    274 Seiten

Publ.-Id: 27776 - Permalink

Modification of magnetic properties of Pt/Co/Pt Films by Ga+ Ion irradiation: Focused versus uniform irradiation
Sveklo, I.; Mazalski, P.; Jaworowicz, J.; Jamet, J.-P.; Vernier, N.; Mougin, A.; Ferre, J.; Kisielewski, M.; Zablotskii, V.; Bourhis, E.; Gierak, J.; Postava, K.; Fassbender, J.; Kanak, J.; Maziewski, A.
30 keV Ga+ irradiation-induced changes of magnetic and magneto-optical properties of sputtered Pt/Co/Pt ultrathin trilayers films have been studied as a function of the ion fluence. Out-of-plane magnetic anisotropy states with enhanced magneto-optical e ects were evidenced for specific values of cobalt thickness and irradiation fluence. Results obtained after uniform or quasi-uniform focused ion beam irradiation on either out-of-plane or in-plane magnetized sputtered pristine trilayers are compared. Similar irradiation-induced magnetic changes are evidenced in quasi-uniformly focused ion beam or uniformly irradiated films, grown either by sputtering or molecular beam epitaxy. We discuss on plausible common mechanisms underlying the observed effects.
Keywords: ion irradiation, magnetism, perpendicular anisotropy

Publ.-Id: 27774 - Permalink

64Cu-labeled bioconjugates based on triazacyclononane bifunctional chelators for radiopharmaceutical applications
Stephan, H.; Pant, K.; Joshi, T.; Zarschler, K.
The development of multi-functional complexing agents for radiometal nuclides for nuclear medical application represents an intensively studied and rapidly evolving field of research. In this context, multifunctionalisable ligands that can form highly stable metal complexes are of particular interest. Their use enables the simultaneous introduction of radiolabels for nuclear imaging and vector molecules for pharmaceutical targeting.1-2
The tridentate azamacrocycle 1,4,7-triazacyclononane (TACN) is one such ligand that is of special interest for the development of bifunctional chelating agents (BFCAs), TACN forms stable Cu(II)complexes and the azamacrocyclic ligand structure can be easily modified. The introduction of further donor groups on the ligand scaffold, such as pyridine units, significantly enhances the thermodynamic stability as well as the kinetic inertness of the Cu(II) complexes formed. These ligands mostly form Cu(II) complexes with square-pyramidal and distorted octahedral coordination geometry.
Examples of target-specific conjugates (peptides, antibody fragments) and bio(nano)materials equipped with appropriate BFCAs based on TACN (Figure 1), suitable for labeling with 64Cu, will be presented. This enables tumor imaging and biodistribution studies of the materials over a period of days via positron emission tomography (PET).

1. E.W. Price, C. Orvig, Chem. Soc. Rev. 2014, 43, 260. 2. G. Singh, M.D. Gott, H.-J. Pietzsch, H. Stephan, Nuclearmedicine, 2016, 55, 41.
  • Lecture (Conference)
    43rd International Conference on Coordination Chemistry, 30.07.-04.08.2018, Sendai, Japan

Publ.-Id: 27769 - Permalink

Radiolabelled Nanomaterials for Imaging and Treatment of Cancer
Stephan, H.
Novel nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. Thanks to their structural variability, which facilitates setting up the basic structure, modifying the periphery as well as creating complex structures, their properties allow being tailored to both diagnosis and treatment of diseases (theranostic approach) [1]. Provided with special functionalities, NMs allow the simultaneous application of different molecular imaging methods. In the field of cancer medicine, the combination of different imaging techniques such as nuclear (PET: positron emission tomography and SPECT: single-photon emission computed tomography) and near-infrared fluorescence (NIRF) imaging for tracking down tumors and metastases is particularly attractive [2].
This lecture will focus on the development and application of very small radiolabeled NMs, embracing polymeric structures [3] and inorganic particles [4]. Novel strategies will be discussed to develop stealth NMs capable of avoiding biomolecular corona formation and thus evading scavenging of NMs by the mononuclear phagocyte system, leading to eventual accumulation in the liver and spleen [5].

[1] J. A. Barreto, W. O’Malley, M. Kubeil, B. Graham, H. Stephan, L. Spiccia, Adv Mater 23 (2011) H18-H40.
[2] G. Singh, M. D. Gott, H.-J. Pietzsch, H. Stephan, Nuklearmedizin 55 (2016) 41-50.
[3] K. Pant, O. Sedláček, R. A. Nadar, M. Hrubý, H. Stephan, Adv Healthcare Mat 6 (2017) 1601115.
[4] K. Zarschler, L. Rocks, N. Licciardello, L. Boselli, E. Polo, K. Pombo Garcia, L. De Cola, H. Stephan, K. A. Dawson, Nanomed-Nanotechnol 12 (2016) 1663-1701.
[5] K. Pombo-García, K. Zarschler, L. Barbaro, J. A. Barreto, W. O’ Malley, L. Spiccia, H. Stephan, B. Graham
Small 10 (2014) 2516-2529.
  • Lecture (others)
    Kolloquium, 26.07.2018, Tokyo, Japan

Publ.-Id: 27768 - Permalink

Union of light ion therapy centers in Europe (ULICE EC FP7) - Objectives and achievements of joint research activities
Pötter, R.; Balosso, J.; Baumann, M.; Bert, C.; Davies, J.; Enghardt, W.; Fossati, P.; Harris, S.; Jones, B.; Krämer, M.; Mayer, R.; Mock, U.; Pullia, M.; Schreiner, T.; Dosanjh, M.; Debus, J.; Orecchia, R.; Georg, D.
Under the umbrella of the European Network for Light Ion Therapy (ENLIGHT), the project on Union of Light Ion Centers in Europe (ULICE), which was funded by the European Commission (EC/FP7), was carried out from 2009 to 2014. Besides the two pillars on Transnational Access (TNA) and Networking Activities (NA), six work packages formed the pillar on Joint Research Activities (JRA). The current manuscript focuses on the objectives and results achieved within these research work packages: "Clinical Research Infrastructure", "Biologically Based Expert System for Individualized Patient Allocation", "Ion Therapy for Intra-Fractional Moving Targets", "Adaptive Treatment Planning for Ion Radiotherapy", "Carbon Ion Gantry", "Common Database and Grid Infrastructures for Improving Access to Research Infrastructures". The objectives and main achievements are summarized. References to either publications or open access deliverables from the five year project work are given. Overall, carbon ion radiotherapy is still not as mature as photon or proton radiotherapy. Achieved results and open questions are reflected and discussed in the context of the current status of carbon ion therapy and particle and photon beam therapy. Most research topics covered in the ULICE JRA pillar are topical. Future research activities can build upon these ULICE results. Together with the continuous increase in the number of particle therapy centers in the last years ULICE results and proposals may contribute to the further growth of the overall particle therapy field as foreseen with ENLIGHT and new joint initiatives such as the European Particle Therapy Network (EPTN) within the overall radiotherapy community.
Keywords: Particle therapy; Proton; Carbon ion; EC project

Publ.-Id: 27766 - Permalink

A coronene-based semiconducting two-dimensional metal-organic framework with ferromagnetic behavior
Dong, R.; Zhang, Z.; Tranca, D. C.; Zhou, S.; Wang, M.; Adler, P.; Liao, Z.; Liu, F.; Sun, Y.; Shi, W.; Zhang, Z.; Zschech, E.; Mannsfeld, S.; Felser, C.; Feng, X.
Metal–organic frameworks (MOFs) have so far been highlighted for their potential roles in catalysis, gas storage and separation. However, the realization of high electrical conductivity (>10^−3  S cm^−1) and magnetic ordering in MOFs will afford them new functions for spintronics, which remains relatively unexplored. Here, we demonstrate the synthesis of a two-dimensional MOF by solvothermal methods using perthiolated coronene as a ligand and planar iron-bis(dithiolene) as linkages enabling a full π-d conjugation. This 2D MOF exhibits a high electrical conductivity of ~10 S cm−1 at 300 K, which decreases upon cooling, suggesting a typical semiconductor nature. Magnetization and 57Fe Mössbauer experiments reveal the evolution of ferromagnetism within nanoscale magnetic clusters below 20 K, thus evidencing exchange interactions between the intermediate spin S = 3/2 iron(III) centers via the delocalized π electrons. Our results illustrate that conjugated 2D MOFs have potential as ferromagnetic semiconductors for application in spintronics.

Publ.-Id: 27760 - Permalink

Protracted river recovery from medieval earthquakes
Stolle, A.; Schwanghart, W.; Andermann, C.; Bernhardt, A.; Fort, M.; Wittmann, H.; Merchel, S.ORC; Rugel, G.; Adhikary, B. R.; Korup, O.
Mountain rivers respond to strong earthquakes by rapidly aggrading to accommodate excess sediment delivered by co-seismic landslides. Detailed sediment budgets indicate that rivers need several years to decades to recover from such seismic disturbances, depending on how recovery is defined. We examine several proxies of river recovery around Pokhara, Nepal’s second largest city. We use a freshly exhumed cohort of floodplain trees in growth position as a geomorphic marker of rapid sedimentation that formed a fan covering 148 km² in a Lesser Himalayan basin with tens of meters of debris. Radiocarbon dates of these buried trees are consistent with those of nearby valley fills linked to major Himalayan earthquakes during medieval times, and offer benchmarks for estimating average rates of sedimentation and re-incision. We combine high-resolution digital elevation data, geodetic field surveys, aerial photos documenting historic channel changes, estimated removed volumes, calculated long-term denudation rates, and dated re-exhumed tree trunks to reconstruct dated geomorphic marker surfaces. The volumes of sediment lost from these surfaces require net sediment yields of up to 4200 t km² yr¹, averaged over some 650 years since the last inferred earthquake. These rates exceed density-adjusted rates of catchment-wide denudation derived from concentrations of cosmogenic ¹⁰Be in river sands. The lithological composition of active channel-bed load differs from that of local bedrock, confirming that rivers are still mainly evacuating medieval valley fills, locally incising at rates of 160 to 220 mm yr¹ in the past 50 years. Pronounced knickpoints and epigenetic gorges at tributary junctions add to the picture of a protracted fluvial response; only the distal portions of the earthquake-derived sediment wedge have been incised to near their base. Our results challenge the notion that mountain rivers recover from earthquakes within years to decades. The valley fills around Pokhara document that even highly erosive Himalayan rivers need at least centuries to millennia to adjust. Our results motivate some rethinking of post-seismic hazard appraisals and infrastructural planning in mountain regions.
Keywords: accelerator mass spectrometry, cosmogenic nuclide, geomorphological risk assessment, Earthquake
  • Poster
    4th Central European Geomorphology Conference, 09.-13.10.2017, Bayreuth, Deutschland

Publ.-Id: 27757 - Permalink

Dynamics of nanoparticle morphology under low energy ion irradiation
Holland-Moritz, H.; Graupner, J.; Möller, W.; Pacholski, C.; Ronning, C.
If nanostructures are irradiated with energetic ions, the mechanism of sputtering becomes important when the ion range matches about the size of the nanoparticle. Gold nanoparticles with diameters of ∼50 nm on top of silicon substrates with a native oxide layer were irradiated by gallium ions with energies ranging from 1 to 30 keV in a focused ion beam system. High resolution in situ scanning electron microscopy imaging permits detailed insights in the dynamics of the morphology change and sputter yield. Compared to bulk-like structures or thin films, a pronounced shaping and enhanced sputtering in the nanostructures occurs, which enables a specific shaping of these structures using ion beams. This effect depends on the ratio of nanoparticle size and ion energy. In the investigated energy regime, the sputter yield increases at increasing ion energy and shows a distinct dependence on the nanoparticle size. The experimental findings are directly compared to Monte Carlo simulations obtained from iradina and TRI3DYN, where the latter takes into account dynamic morphological and compositional changes of the target.
Keywords: in situ ion beam, Monte Carlo, nanoparticles, sputtering

Publ.-Id: 27756 - Permalink

The role of incidence angle in the morphology evolution of Ge surfaces irradiated by medium-energy Au ions
Dell’Anna, R.; Iacob, E.; Barozzi, M.; Vanzetti, L.; Hübner, R.; Böttger, R.; Giubertoni, D.; Pepponi, G.
Germanium (Ge) surfaces have been irradiated with 26 keV gold (Au) ions at a constant fluence and at incidence angles varying from 0° to 85°. The evolution of the emerging nanostructures is studied by atomic force microscopy (AFM), scanning electron microscopy, x-ray photoelectron spectroscopy (XPS), and cross-sectional transmission electron microscopy. The obtained results are compared with findings reported in the literature. Periodic rippled patterns with the wave vector parallel to the projection of the ion beam direction onto the Ge surface develop between 30° and 45°. From 75° the morphology changes from parallel-mode ripples to parallel-mode terraces, and by further increasing the incidence angle the terraces coarsen and show a progressive break-up of the front facing the ion beam. No perpendicular-mode ripples or terraces have been observed. The analysis of the AFM height profiles and slope distributions shows in the 45°-85° range an angular dependence of the temporal scale for the onset of nonlinear processes. For incidence angles below 45°, the surface develops a sponge-like structure, which persists at higher incidence angles on the top and partially on the face of the facets facing the ion beam. The XPS and the energy-dispersive x-ray spectroscopy evidence the presence of Au nano-aggregates of different sizes for the different incidence angles. This study points out the peculiar behavior of Ge surfaces irradiated with medium-energy Au ions and warns about the differences to be faced when trying to build a universal framework for the description of semiconductor pattern evolution under ion-beam irradiation.
Keywords: ion beam irradiation, germanium, gold ions, binary system, ripples, terraces, sponge-like structures

Publ.-Id: 27746 - Permalink

A versatile ion beam spectrometer for studies of ion interaction with 2D materials
Schwestka, J.; Melinc, D.; Heller, R.; Niggas, A.; Leonhartsberger, L.; Winter, H.; Facsko, S.; Aumayr, F.ORC; Wilhelm, R. A.ORC
We present an ultra-high vacuum setup for ion spectroscopy of freestanding two-dimensional solid targets. An ion beam of different ion species (e.g. Xe with charge states from 1 to 44 and Ar with charge states from 1 to 18) and kinetic energies ranging from a few 10 eV to 400 keV is produced in an electron beam ion source. Ions are detected after their transmission through the 2D target with a position sensitive microchannel plate detector allowing the determination of the ions exit charge state as well as the scattering angle with a resolution of approx. 0.04◦. Further, the spectrometer is mounted on a swiveling frame covering a scattering angle of ±8° with respect to the incoming beam direction. By utilizing a beam chopper we measure the time-of-flight of the projectiles and determine the energy loss when passing a 2D target with an energy uncertainty of about 2%. Additional detectors are mounted close to the target to observe emitted secondary particles and are read-out in coincidence with the position and time information of the ion detector. A signal in these detectors can also be used as a start trigger for time-of-flight measurements, which then yield an energy resolution of 1% and an approx. 1000-fold larger duty cycle. First results on the interaction of slow Xe30+ ions with a freestanding single layer of graphene obtained with the new setup are compared to recently published data where charge exchange and energy were measured by means of an electrostatic analyzer.
Keywords: slow highly charged ions, 2D materials, ion spectrometer, single layer graphene


  • Secondary publication expected

Publ.-Id: 27743 - Permalink

Neutralization Dynamics of Slow Highly Charged Ions in 2D Materials
Wilhelm, R.ORC; Gruber, E.ORC; Schwestka, J.; Heller, R.; Fascko, S.; Aumayr, F.ORC
We review experimental and theoretical work on the interaction of slow highly charged ions with two-dimensional materials. Earlier work in the field is summarized and more recent studies on 1 nm thick amorphous carbon nanomembranes and freestanding single layer graphene by the authors are reviewed. To explain the findings, models for energy loss determination as well as qualitative model descriptions for the observed ultrafast neutralization dynamics are discussed. The results shown in this paper will be put into context with findings of nanostructure formation on two-dimensional materials, both freestanding and on substrate, as well as on surfaces of bulk insulators.
Keywords: low energy ions; highly charged ions; 2D materials

Publ.-Id: 27742 - Permalink

Nonlinear THz Spectroscopy of Two-Dimensional Systems
Helm, M.; König-Otto, J.; Schmidt, J.; Dimakis, E.; Winnerl, S.; Schneider, H.
Nonlinear THz experiments using a free-electron laser are presented on Landau quantized graphene as well as on intersubband transitions in a single GaAs quantum well.
Keywords: terahertz, free electron laser, graphene, Landau Levels, intersubband, GaAs, quantum well
  • Invited lecture (Conferences)
    Frontiers of photonics, plasmonics and electronics with 2D nanosystems, 14.-20.07.2018, Erice, Italy
  • Invited lecture (Conferences)
    Advanced Electromagnetics Symposium (AES 2018), 24.06.-01.07.2018, Marseille, France

Publ.-Id: 27737 - Permalink

Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides AlyTi1-y(OxN1-x). Part 2: Experimental validation and durability tests at high temperature
Escobar-Galindo, R.; Guillén, E.; Heras, I.; Rincón-Llorente, G.; Alcón-Camas, M.; Lungwitz, F.; Munnik, F.; Schumann, E.; Azkona, I.; Krause, M.
The durability of two solar-selective aluminium titanium oxynitride multilayer coatings was studied under conditions simulating realistic operation of central receiver power plants. The coatings were deposited by cathodic vacuum arc applying an optimized design concept for complete solar-selective coating (SSC) stacks. Compositional, structural and optical characterization of initial and final stacks was performed by scanning electron microscopy, elastic recoil detection, UV-Vis-NIR-IR spectrophotometry and X-Ray diffraction. The design concept of the solar selective coatings was validated by an excellent agreement between simulated and initial experimental stacking order, composition and optical properties.

Both SSC stacks were stable in single stage tests of 12 hours at 650°C. At 800°C, they underwent a structural transformation by full oxidation and they lost their solar selectivity. During cyclic durability tests, multilayer 1, comprised of TiN, Al0.64Ti0.36N and an Al1.37Ti0.54O top layer, fulfilled the performance criterion (PC) ≤ 5% for 300 symmetric, 3 hours long cycles at 600°C in air. Multilayer 2, which was constituted of four AlyTi1-y(OxN1-x) layers, met the performance criterion for 250 cycles (750 hours), but was more sensitive to these harsh conditions. With regard to the degradation mechanisms, the coarser microstructure of multilayer 1 is more resistant against oxidation than multilayer 2 with its graded oxygen content. These results confirm that the designed SSCs based on AlyTi1-y(OxN1-x) materials withstand breakdown at 600ºC in air. Therefore, they can be an exciting candidate material for concentrated solar power applications at high temperature.
Keywords: Solar selective coatings, thermal stability, optical properties, concentrated solar power, optical simulation, oxynitrides


  • Secondary publication expected from 23.04.2019

Publ.-Id: 27734 - Permalink

Cluster tool for in situ processing and comprehensive characterization of thin films at high temperatures
Wenisch, R.; Lungwitz, F.; Hanf, D.; Heller, R.; Zscharschuch, J.; Hübner, R.; von Borany, J.; Abrasonis, G.; Gemming, S.; Escobar Galindo, R.; Krause, M.
A new cluster tool for in situ real-time processing and depth-resolved compositional, structural and optical characterization of thin films at temperatures from -100 to 800 °C is described. The implemented techniques comprise magnetron sputtering, ion irradiation, Rutherford backscattering spectrometry, Raman spectroscopy and spectroscopic ellipsometry. The capability of the cluster tool is demonstrated for a layer stack MgO/ amorphous Si (~60 nm)/ Ag (~30 nm), deposited at room temperature and crystallized with partial layer exchange by heating up to 650°C. Its initial and final composition, stacking order and structure were monitored in situ in real time and a reaction progress was defined as a function of time and temperature.
Keywords: Cluster tool, thin films, in situ, high temperature, Rutherford backscattering, Raman spectroscopy, ellipsometry, metal-induced crystallization


  • Secondary publication expected from 31.05.2019

Publ.-Id: 27732 - Permalink

Phytotoxicity of polymetallic mine wastes from southern Tuscany and Saxony
Franzaring⁠⁠, J.; Ancora⁠, S.; Paoli⁠, L.; Fongoh⁠, A. H.; Büttner⁠, P.; Fangmeier⁠, A.; Schlosser⁠, S.; Monaci, F.
Restoration potential of mine wastes or approaches to improve soil conditions and to ameliorate phytotoxicity on these sites may be simulated in standardized greenhouse experiments. Plants can be cultivated side by side on materials from different origins in dilution series with defined admixtures of certain aggregates. Mine wastes used in the present study originated from Fenice Capanne (FC, Tuscany, Italy) and Altenberg (ALT, Saxony, Germany). Tailings of the Italian site contain high concentrations of lead, zinc, arsenic and sulphur while tin, wolfram, molybdenum and lithium are highly elevated in the German mine waste. We tested growth responses of five crop species and analyzed concentrations of various metals and nutrients in the shoot to evaluate the toxicity of the FC mine waste and found oilseed rape being the most and corn the least resistant crop. Interestingly, oilseed rape accumulated seven times higher levels of lead than corn without showing adverse effects on productivity. In a subsequent comparison of FC and ALT mine waste, we cultivated different species of buckwheat (Fagopyrum spec.), a fast growing genus that evolved in mountain areas and that has been shown to be tolerant to low pH and high concentrations of metals. We found that the FC mine waste was more toxic than the ALT substrate in F. tataricum and F. esculentum. However, lower admixtures of FC material (10%) resulted in stronger growth reductions than higher proportions (25%) of the mine waste which was primarily related to the slightly lower pH and higher availability of essential metals due to the admixture of sand. These results confirm the importance of managing the soil chemical and physical characteristics of wastelands and call for the development of assisted reclamation to prepare sites for regular biomass production.
Keywords: Mine wastes, Phytoremediation, Heavy metals, Oilseed rape, Buckwheat, Soil amendment

Publ.-Id: 27721 - Permalink

Stability of melt flow during magnetic sonication in a floating zone configuration
Grants, I.; Gerbeth, G.
This paper considers the linear stability of a liquid metal flow driven by superimposed alternating and static axial magnetic fields in the floating zone configuration. A simple model is constructed that assumes a slight axial variation of the flow-driving radial magnetic force and a low-to-moderate skin effect. This force drives two symmetrical flow tori. Formation of the field-parallel layer is observed for a strong static field. In this regime the instability sets in as a standing azimuthal wave around the circumference of the cylindrical melt volume near its midplane. The length of this wave scales with the thickness of the parallel layer. The instability criterion may be formulated in terms of an interaction parameter reaching its critical value at around 525.
Keywords: -

Publ.-Id: 27720 - Permalink

High-speed X-ray CT imaging of a strongly cavitating nozzle flow
Bauer, D.; Barthel, F.; Hampel, U.
Examining or imaging of internal structures in flows with cavitation is still one of the greatest challenges in this field of research. In a specially designed nozzle, a strong cavitation region (CR) is generated with a liquid core (LC) in the center, surrounded by vapour. While it is almost not feasible to visualize the inside of the CR with visible light, it is shown that with high-speed X-ray computed tomography it is possible to visualize the dynamics of the unsteady cavitational flow structures inside the CR. The observed phenomena start with a ring of cavitation and small amounts of vapour inside the LC at / near the entrance of the cavitation channel. Further downstream the cavitation is growing rapidly and cavitation structures, as string cavitation can be identified inside the LC. In addition the results are compared with former time averaged CT images of the same nozzle and with results obtained with high-speed videography.
Keywords: Cavitation Flow, ROFEX, Ultrafast X-ray CT

Publ.-Id: 27719 - Permalink

A baseline closure concept for simulating bubbly flow with phase change: interfacial heat transfer coefficient
Liao, Y.; Krepper, E.; Lucas, D.
In line with the best practice guidelines for computational fluid dynamics in nuclear reactor safety, Helmholtz-Zentrum Dresden – Rossendorf proposed an Euler-Euler baseline closure concept some years ago. Simulations with a fixed set of closures may help to identify model inadequacy and facilitate the further improvement. Currently, the baseline model concerns interfacial momentum and turbulent kinetic energy exchange as well as bubble coalescence and breakup. It has been tested for a wide range of isothermal applications with different geometrical configurations and material systems. In the present work, the baseline model is extended to non-isothermal flows by including a heuristic model for interfacial heat transfer coefficient. The extended baseline model is validated for both bubble-growing in superheated liquid and -condensing in sub-cooled liquid. The baseline model proposal is independent on the use of a certain CFD code. The presented simulation is carried out with the commercial software ANSYS CFX by employing the best practice guidelines. The simulated liquid temperature, gas volume fraction, vapor bubble size and velocity are compared with the measured ones. The effectivity of the model is demonstrated by the general good agreement.
  • Contribution to proceedings
    CFD4NRS-7 OECD-NEA & IAEA Workshop, 04.-06.09.2018, Shanghai, China

Publ.-Id: 27711 - Permalink

Cfd modelling of flashing instability in natural circulation cooling systems
Liao, Y.; Schuster, C.; Hu, S.; Lucas, D.
Passive cooling systems driven by natural circulation are common design features of proposals for advanced reactors. The natural circulation systems are inherently more unstable than forced circulation ones due to its nonlinear nature and low driving force. Any disturbance, e.g. flashing or boiling inception, in the driving force will affect the flow which in turn will influence the driving force leading to an oscillatory behavior. Owing to safety concerns, flashing instability particularly for advanced boiling water reactors has been broadly investigated, and many test facilities have been constructed in the past. A number of numerical analyses of experimental test cases are available. Nevertheless, there exists a need to update the method from one-dimensional system codes to high-resolution computational fluid dynamics (CFD). In the present work flashing-induced instability behavior and flow pattern in the riser of the GENEVA facility, which is a downscale of a reactor containment passive cooling system, is investigated using the commercial CFD code ANSYS CFX. A two-fluid model is adopted for the unstable turbulent gas-liquid flow, and the HZDR baseline closure is used to model interphase mass, momentum, heat transfer as well as bubble-induced turbulence. The simulated fluid temperature, pressure and local void fraction at different heights of the riser are compared with the measured ones. The limitation and possibility of the CFD technique for such complex two-phase scenarios are discussed, and suggestions for improving the predictability of simulations are made.
  • Contribution to proceedings
    26th International Conference on Nuclear Engineering, ICONE26, 23.-26.07.2018, Hammersmith, London, England

Publ.-Id: 27710 - Permalink

Reprocessing of a southern Chilean Zn tailing by flotation - a case study
Babel, B.; Penz, M.; Schach, E.; Böhme, S.; Rudolph, M.
The reprocessing of tailings can have economic and environmental benefits compared to the processing of primary ore deposits. In this paper we present the characterization of a tailings dam in southern Chile by means of mineralogical and geochemical investigations focusing on sphalerite and trace elements with the aim to investigate a potential reprocessing. The assessment is followed by a flotation study, focusing on the recovery of sphalerite with a high selectivity towards sulfidic and non-sulfidic gangue minerals. An in-depth analysis of a selected test based on mineral liberation analysis data is used to refine the liberation, concentration and flotation weighting function for future investigations.
Keywords: Geometallurgy; Flotation; Sphalerite; Tailings; Reprocessing

Publ.-Id: 27707 - Permalink

Bioremediation of uranium contaminated sites from former mining activities by microorganisms – a microscopic and spectroscopic approach.
Krawczyk-Bärsch, E.; Gerber, U.; Steudtner, R.; Müller, K.; Moll, H.; Rossberg, A.; Merroun, M. L.
Environmental pollution by metals and radionuclides is one of the biggest challenges which have to be solved globally. For in situ remediation of uranium contaminated waste waters and environments from activities such as uranium mining and uranium processing, microorganisms could be important due to their ability to immobilize radionuclides and heavy metals. To improve bioremediation strategies based on a better understanding of binding mechanisms on the molecular level we applied uranium interaction experiments with selected microorganisms from the former uranium mining site Königstein (Germany). Acidovorax facilis, the Gram-negative Betaproteobacteria, was one of the microorganisms used for our experiments. It is an aerobic and widely distributed strain in nature and commonly found in soils but also in the mine water of uranium mines. The present work describes a multidisciplinary approach combining wet chemistry, transmission electron microscopy, and spectroscopy .The results reveal that the local coordination of uranium associated with the cells of A. facilis depends upon time of incubation. Uranium biosorption by outer membrane lipopolysaccharides containing phosphoryl residues was observed within the first hours of contact between the cells and uranium. By increasing the incubation time up to 24 h the implication of carboxyl groups within the cell wall peptidoglycan was proved in addition to phosphoryl groups. To a lower extend, uranium is also coordinated to phosphoryl groups of the intracellular polyphosphate granules. This study showed that different cell compartments play a major role in the sequestration of uranium. Our findings contribute to a better understanding of the mechanisms of microbial response to uranium and demonstrate that A. facilis may play an important role in predicting the fate and transport of uranium in uranium-contaminated sites by being a suitable candidate for bioremediation purposes.
Keywords: Uranium, A. facilis, sorption, TRLFS, ATR FT-IR, TEM
  • Lecture (Conference)
    19th International Conference on Heavy Metals in the Environment (ICHMET 2018),, 22.-25.07.2018, Athens, U.S.

Publ.-Id: 27706 - Permalink

Why do secondary cracks preferentially form in hot-rolled ODS steels in comparison with hot-extruded ODS steels?
Das, A.ORC; Viehrig, H. W.; Altstadt, E.ORC; Bergner, F.ORC; Hoffmann, J.ORC
Secondary cracks are known to absorb energy, retard primary crack propagation and initiate at lower loads than primary cracks. They are observed more often in hot-rolled than in hot extruded ODS steels. In this work, the microstructural factors responsible for this observation are investigated. Better understanding of these factors can lead to tailoring of im-proved ODS steels. Fracture toughness testing of two batches of 13Cr ODS steel, one hot-rolled and the other hot-extruded, was carried out. The fracture behaviour of secondary cracks was investigated using scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). Crystallographic texture and grain morphology play a predominant role in preventing secondary cracks in hot-extruded ODS steels. At lower temperatures, secondary cracks occur predominantly via transgranular cleavage. The fracture mode changes to ductile and intergranular at higher temperatures.
Keywords: ODS steel, fracture behaviour, anisotropy, intergranular fracture, secondary cracking, delamination

Publ.-Id: 27705 - Permalink

Real space bonding and stability analysis of tetravalent f-element complexes with N-, O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.
N-/O-donor ligands are promising complexing ligands for actinides in high-level liquid wastes. Especially the covalency of the An–N/O bonds and a comparison to lanthanides, e.g. Ce, is of interest for these complexes. Thus, the bond character for [M(salen)2] with M = Ce, Th, Pa, U, Np, Pu was investigated. Furthermore the stability of the complexes is compared and correlated with the bonding character.
Keywords: real-space bonding analysis, stability analysis, DFT, actinides, Schiff bases
  • Poster
    16th International Congress of Quantum Chemistry, 18.-23.06.2018, Menton, Frankreich

Publ.-Id: 27690 - Permalink

Investigation of a wetland contaminated by uranium mine tailings in Central France
Fichtner, A.; Sachs, S.; Rossberg, A.; Scheinost, A. C.; Arnold, T.; Montavon, G.; Stumpf, T.
The release of uranium from mine tailings may present a hazard to the environment, which is the reason for the monitoring of the relevant storage sites in many countries. Studying the behavior of released radionuclides at these sites serves to better estimate the local risk and can help to improve the understanding of the geochemistry of the involved contaminants, e.g. for the application in transport modelling.
The storage site Roffin, located in the Region of Auvergne, France, contains approximately 30 000 t of mill tailings from the adjacent processing plant of the same name, which operated from 1947 to 1956. After the shutdown of the plant, the responsible operator has remodeled the site several times over the decades, in order to meet updated environmental standards [1].
Recent gamma-ray surveys have shown elevated radiation levels alongside a creek downstream of the storage site, especially in a wetland area in some two hundred meters distance of the site. Drill cores taken in this area show uranium concentrations up to 2000 ppm in the upper 30 cm, with peak concentrations in a whitish,clayey layer with a thickness of about 5 cm at a depth of 20 cm. Besides this anomalous layer, the soil is of the histosol type, with very high contents of organic matter and mostly saturated with water. The goal of our study is to identify the involved uranium species in the solid and aqueous phases, in order to understand the influence of discharge history and geochemistry on the risk presented by this contamination.
Sequential extractions performed on the different layers of the soil following the protocol of Tessier et al. [2] indicate a majority of the uranium to be bound to soil organic matter. Yet scanning electron microscopy analysis (SEM) of the white layer shows the presence of particles containing high uranium concentrations with sizes around 10 μm. Energy dispersive X-ray spectra (EDS) of some of these particles give compositions corresponding to a specific mineral processed in the plant, which is Parsonsite [Pb2(UO2)(PO4)2]. Dating the soil with the C-14 of the soil organic matter and the depth profile of Cs-137 from nuclear fallout further suggests that the origin of the white layer is connected to the active period of the site. X-ray absorption spectroscopy performed on the soil shows a variable distribution of U(IV) and U(VI) in the different layers. Porewater obtained by centrifugation contains uranium concentrations up to 1000 ppb.
Further studies aim to quantify the distribution of uranium between the different solid phases of the soil, as well as the identification of the main species in the porewater.

[1] Himeur, N., Andres, C.: Bilan environnemental - Sites miniers du Puy-de-Dôme. AREVA Operational Report (2010).
[2] Tessier, A., Campbell, P.G.C., Bisson, M.: Sequential Extraction Procedure for the Speciation of Particulate Trace Metals. Anal. Chem. (1979) Issue 51, pp. 844-851.
Keywords: Uranium, wetland, mine tailing, speciation, characterization
  • Contribution to proceedings
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
    Czech Chemical Society Symposium Series, 18th Radiochemical Conference, Mariánské Lázně, Czech Republic, 13-18 May 2018, Booklet of Abstracts, 214
  • Poster
    RadChem 2018-18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czech Republic
  • Poster
    8. RCA-Workshop, 12.-14.06.2018, Dresden, Deutschland

Publ.-Id: 27689 - Permalink

Zero Overhead Modern C++ for Mapping to Any Programming Model
Huebl, A.ORC; Matthes, A.ORC; Worpitz, B.; Zenker, E.ORC; Widera, R.ORC; Juckeland, G.ORC; Bussmann, M.ORC
Towards exascale computing, today's HPC systems have become heterogeneous and diverse. Accounting for both host and accelerator, the TOP10 supercomputers in 11/2017 alone provided as much as 11 different computing architectures. On top of the hardware follow the accompanying programming models: from directive based, implicit and explicit descriptions up to task-based. Scientific code developers are facing a tough choice as commitment to a specific hardware and/or programming model narrows down potential target systems. With limited development resources but usually multi-decade long project lifetimes, maintaining multiple implementations of the same algorithms to widen platform support is unfeasible for most teams. Alpaka is a standard C++, compile-time meta-programming library providing a unified, explicit, parallel programming model. On typical MPI+X parallelized applications, Alpaka enables developers to describe shared-memory, in-node parallelism. Zero-overhead abstraction is achieved by compile-time specializing C++ templates to native backends (e.g. CUDA, OpenMP, TBB, ...). Alpaka stays with modern C++ as a standardized, widely supported language without introducing pre-processor or pragma-based annotations to the user directly. It naturally allows inlining, kernel fusion and code-reuse on a single-source programming paradigm. With such, abstractions and control within the final software stack are achievable without duplicating implementations leading to a maintainable code base even for large applications.
Keywords: HPC, performance portability, programming model, open source, alpaka, cuda, gpu, openpower, portability, high performance computing
  • Invited lecture (Conferences)
    Platform for Advanced Scientific Computing (PASC) Conference 2018, 02.-04.07.2018, Basel, Switzerland
    DOI: 10.5281/zenodo.1304272

Publ.-Id: 27685 - Permalink

Wide acceptance measurement of K/K+ ratio from Ni+Ni collisions at 1.91A GeV
Piasecki, K.; Herrmann, N.; Averbeck, R.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Berger, M.; Buehler, P.; Cargnelli, M.; Čaplar, R.; Cordier, E.; Crochet, P.; Czerwiakowa, O.; Deppner, I.; Dupieux, P.; Dželalija, M.; Fabbietti, L.; Fodor, Z.; Gasik, P.; Gašparić, I.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Hong, B.; Kang, T. I.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Kiš, M.; Koczon, P.; Korolija, M.; Kotte, R.; Lebedev, A.; Leifels, Y.; Le Fèvre, A.; Liu, J. L.; Lopez, X.; Mangiarotti, A.; Manko, V.; Marton, J.; Matulewicz, T.; Merschmeyer, M.; Münzer, R.; Pelte, D.; Petrovici, M.; Rami, F.; Reischl, A.; Reisdorf, W.; Ryu, M. S.; Schmidt, P.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczyńska, K.; Smolyankin, V.; Stoicea, G.; Suzuki, K.; Tymiński, Z.; Wagner, P.; Weber, I.; Widmann, E.; Wiśniewski, K.; Xiao, Z. G.; Xu, H. S.; Yushmanov, I.; Zhang, Y.; Zhilin, A.; Zinyuk, V.; Zmeskal, J.
The FOPI Collaboration at GSI SIS-18 synchrotron measured the charged kaons from central and semi-central collisions of Ni+Ni at the beam energy of 1.91A GeV. We present the distribution of K−/K+ ratio on the plane of energy vs polar angle in the nucleon-nucleon centre-of-mass frame, with and without the subtraction of the contribution of φ(1020) meson decays to the K− yield. The acceptance of the current experiment is substantially wider compared to the previous measurement of the same colliding system. The K−/K+ ratio is expected to be sensitive to the in-medium modifications of basic kaon properties like mass. Recent results obtained by the HADES Collaboration at 1.23A and 1.76A GeV indicate, that no mass-shift effect is needed to explain the difference between energy slopes of charged kaon spectra within uncertainties. The K−/K+ ratios obtained in this experiment, even after correction for the contribution due to the φ(1020) meson decays, decrease with increasing kinetic energy, as generally predicted in models assuming mass modifications.


Publ.-Id: 27681 - Permalink

Precise nuclear data of the 14N(p,γ)15O reaction for solar neutrino predictions
Wagner, L.
The 14N(p,γ)15O reaction is the slowest stage of the carbon-nitrogen-oxygen cycle of hydrogen burning and thus determines its reaction rate. Precise knowledge of its rate is required to improve the model of hydrogen burning in our sun. The reaction rate is a necessary ingredient for a possible solution of the solar abundance problem that led to discrepancies between predictions of the solar standard model and helioseismology. The solar 13N and 15O neutrino fluxes are used as independent observables that probe the carbon and nitrogen abundances in the solar core. This could settle the disagreement, if the 14N(p,γ)15O reaction rate is known with high precision. After a review of several measurements its cross section was revised downward due to a much lower contribution by one particular transition, capture to the ground state in 15O. The evaluated total relative uncertainty is still 7.5%, in part due to an unsatisfactory knowledge of the excitation function over a wide energy range.
The present work reports experimentally determined cross sections as astrophysical S- factor data at twelve energies between 0.357 – 1.292 MeV for the strongest transition, capture to the 6.79MeV excited state in 15O with lower uncertainties than before and at ten energies between 0.479 – 1.202 MeV for the second strongest transition, capture to the ground state in 15O.
In addition, an R-matrix fit is performed to estimate the impact of the new data on the astrophysical relevant energy range. The recently suggested slight S-factor enhancement at the Gamow window could not be confirmed and differences to previous measurements at energies around 1 MeV were observed. The present extrapolated zero-energy S-factors are S679(0) = (1.19±0.10) keV b and SGS(0) = (0.25±0.05) keV b and they are within the uncertainties consistent with values recommended by the latest review.
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-092 2018


Publ.-Id: 27680 - Permalink

Two-phase flow experiments and measuring techniques @ HZDR
Lucas, D.
TOPFLOW-experiments on vertical pipes and within the TOPFLOW pressure chamber are presented. Innovative measuring techniques as wire-mesh sensors and ultrafast X-ray tomography provide detailed information on the interfacial structure in gas-liquid flows. Details on these measuring techniques are discussed and experiments on flows under adiabatic conditions as well as flows with phase transfer are presented.
Keywords: wire-mesh sensor, ultrafast X-ray tomography, pipe flow, pressure chamber, TOPFLOW
  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.-08.06.2018, Changsha, China

Publ.-Id: 27676 - Permalink

The Institute of Fluid Dynamics at HZDR
Lucas, D.
The Institute of Fluid Dynamics within the HZDR was introduced in frame of a lecture series at Central South University inn Changsha, China. Special focus was on the activities of the CFD-department.
Keywords: HZDR, multiphase flow, CFD
  • Invited lecture (Conferences)
    Lectures on multiphase CFD at Central South University, School of Energy Science and Engineering, 06.06.2018, Changsha, China

Publ.-Id: 27675 - Permalink

CFD-modelling for bubbly flows in medium and large scales
Lucas, D.; Liao, Y.; Ma, T.; Krepper, E.; Ziegenhein, T.
For gas-liquid flows in large and medium scale industrial applications the Euler-Euler approach is frequently used and for many problems it is the only feasible one. During the derivation of the basic conservation equations the information on the interface gets lost and all interfacial exchange between gas and liquid has to be reflected by appropriate closure models. They have to reflect local phenomena that usually are similar in different global flow situations as bubble columns, pipe flows and others. For this reason a unified setup for closure models should be applicable without any modification for such a spectrum of flow situations. The HZDR baseline model for bubbly flows defines such a set of closures. It was applied to more than 150 different cases indicating a good overall performance, but showing also the limits of the present model. For this reason the model has to be improved continuously.
Recently a new model for bubble-induced turbulence in the RANS framework was included into the baseline model. It was developed basing on DNS of a bubbly channel flow. Other activities aim on the lateral lift force, which is closely connected to the bubble shape. Weak points in the present setup are the near wall simulation and the consideration of swarm effects. For these issues more basic research is required to improve the understanding of the phenomena and to derive better closure models. The present model also shows clear deviations from experimental findings for cases with high liquid superficial velocities which are connected with large gradients in the liquid flow field and a high turbulence level.
The focus of the presentation is on recent and ongoing activities to improve closure models and on the requirements for further improvements.
Keywords: CFD, bubbly flow, Euler-Euler, baseline
  • Lecture (Conference)
    8th European-Japanese Two-Phase Flow Group Meeting, 22.-26.04.2018, New York, USA

Publ.-Id: 27672 - Permalink

Rohstoff-Forschung in Freiberg: „Excellent with the potential to become outstanding“
Gutzmer, J.
The presentation is an invited keynote for the 12. Sächsischer Rohstofftag organised by the Geokompetenzzentrum Freiberg. The presentation focused on the interaction of different stakeholders in the resource technology landscape in Freiberg, including research, education and public institutions such as geological survey or the mining authority. Case studies were presented to illustrate the process and success of interaction. Recommendations were given to illustrate how the stakeholders could collaborate even more effectively.
Keywords: Freiberg, Saxony, resource technology
  • Invited lecture (Conferences)
    12. Sächsischer Rohstofftag, 21.-22.06.2018, Dresden, Germany

Publ.-Id: 27666 - Permalink

Attachment of colloidal particles to a fluidic interface – Aplication to the flotation process
Lecrivain, G.; Yamamoto, R.; Taniguchi, T.; Hampel, U.
The attachment of colloidal particles to the fluidic surface of immersed fluid droplets is central to a wide variety of industrial applications, among which stand out the stabilisation of emulsion (Jansen et al., 2011) and the recovery of minerals by gas bubbles (Albijanic et al., 2010), a process known as forth flotation. Flotation, which is here of primary interest, is a separation process which plays a major role in the mining industry. It is employed to recover a vast array of different valuable commodities such as rare earth minerals essential to the manufacture of high-tech products. The process essentially involves the attachment of hydrophobised colloidal particles to the surface of rising air bubbles. The commercially valueless hydrophilic material settles down the flotation. Experimental and numerical works dealing with the attachment of spherical and non-spherical particles to a fluidic interface are here presented (See Figure 1). Using an optical microbubble sensor the various microprocesses (Lecrivain et al, 2015) associated with the colloidal attachment of elongated fibres are first investigated. In a second stage, direct numerical simulations are used to simulate the dynamics of such particles at a fluidic interface. Unlike spherical colloidal particles, it is found that plate-like particles attach more rapidly to a fluidic interface and are subsequently harder to dislodge when subject to an external force.
  • Lecture (Conference)
    Jahrestreffen Merseburg / Jahrestreffen der ProcessNet-Fachgruppen Mechanische Flüssigkeitsabtrennung, Trocknung und Grenzflächenbestimmte Systeme und Prozesse, 26.-28.02.2018, Halle-Merseburg, Germany

Publ.-Id: 27664 - Permalink

Inelastische Streuung schneller Neutronen an 56 Fe
Beyer, R.ORC
An der Neutronen-Flugzeit-Anlage nELBE des Helmholtz-Zentrums Dresden-Rossendorf sollen Reaktionsquerschnitte mit Relevanz für die nukleare Transmutation bestimmt werden. Die Transmutation hochradioaktiver Abfälle aus abgebrannten Brennelementen thermischer Kernreaktoren in schnellen Neutronenspektren hat das Potential die langlebige Radiotoxizität der Abfälle deutlich zu reduzieren. Zum grundlegenden Verständnis der Physik der Transmutation müssen sowohl Spalt- und Neutroneneinfang-Wahrscheinlichkeiten von Brennelementbestandteilen als auch inelastische Streuquerschnitte an Konstruktionsmaterialien im schnellen Neutronenspektrum mit möglichst kleinen Unsicherheiten bekannt sein.
Diese Arbeit beschäftigt sich mit der Messung des inelastischen Neutronen-Streuquerschnittes mit Hilfe einer neu entwickelten Doppel-Flugzeit-Methode. Mit einem kombinierten Aufbau aus Plastik- und BaF 2 -Szintillationsdetektoren werden die beim Streuprozess emittierten Neutronen und Photonen in Koinzidenz erstmalig nachgewiesen und dadurch der bei der Streuung angeregte Zustand des Zielkerns identifiziert.
An nELBE wird weltweit einzigartig der Elektronenstrahl eines supraleitenden Linearbeschleunigers, des ELBE-Beschleunigers, zur Erzeugung schneller Neutronen benutzt. Dieser wird auf einen Kreislauf flüssigen Bleis fokussiert, in dem die Elektronen Bremsstrahlung erzeugen, die wiederum Neutronen aus Bleikernen herauslöst. Durch die kurze Zeitdauer der Elektronenstrahlimpulse von ca. 5 ps kann mit einem kompakten Neutronenquellvolumen auch mit einer kurzen Flugstrecke eine gute Zeitauflösung erzielt werden. Das emittierte Neutronenspektrum hat eine einem Maxwell-Boltzmann-Spektrum ähnliche Verteilung und reicht von etwa 10 keV bis etwa 10 MeV. Bei einem verwendbaren Elektronenstrom von 15 μA beträgt die Quell-Stärke etwa 1,6 · 10 11 n/s.
Die Neutronen werden kollimiert und auf eine Probe natürlichen Eisens geschossen, die bei einer Flugstrecke von etwa 6 m positioniert war. Die Probenposition ist von einem Array von bis zu 42 BaF 2 -Szintillationsdetektoren zur Photonendetektion umgeben. In einem Abstand von 1 m sind fünf 1 m lange Plastik-Szintillationsdetektoren zum Neutronennachweis aufgebaut. Zur Bestimmung des einfallenden Neutronenflusses wurde eine 235 U-Spaltkammer verwendet, die bei einer Flugstrecke von etwa 4,3 m zwischen Neutronenquelle und Probe aufgestellt war. Die Signale aller Detektoren werden von einer speziell dafür entworfenen VME basierten Datenaufnahmeelektronik verarbeitet und die Zeit- und Ladungs-Werte bestimmt.
Aus dem Detektionszeitpunkt des Photons wird die Flugzeit und damit die Energie des einfallenden Neutrons bestimmt. Aus der Zeitdifferenz zwischen der Photonen- und Neutronendetektion ergibt sich die Flugzeit bzw. Energie des gestreuten Neutrons. Mit Hilfe von Kinematik-Rechnungen können die Ereignisse herausgefiltert werden, die der inelastischen Streuung unter Anregung eines bestimmten Kernniveaus eines bestimmten Isotops entsprechen. Aus dem Verhältnis von eingefallenem Neutronenstrom und nachgewiesenen Streuereignissen jeder Kombination aus einem Plastik- und einem BaF 2 -Szintillationsdetektor wurde entsprechend der Raumwinkelabdeckung der Detektoren der winkel- und energiedifferentielle inelastische Streuquerschnitt d 3 σ/dE n dΩ n ′ dΩ γ bestimmt.
Keywords: nELBE, inelastic scattering, Fe-56, fast neutrons, double-time-of-flight
  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Dr. A.R. Junghans


Publ.-Id: 27660 - Permalink

Silver Accumulation in the Green Microalga Coccomyxa actinabiotis: Toxicity, in Situ Speciation, and Localization Investigated Using Synchrotron XAS, XRD, and TEM
Leonardo, T.; Farhi, E.; Pouget, S.; Motellier, S.; Boisson, A. M.; Banerjee, D.; Rebeille, F.; Den Auwer, C.; Rivasseau, C.
Microalgae are good candidates for toxic metal remediation biotechnologies.
This study explores the cellular processes implemented by the green microalga Coccomyxa actinabiotis to take up and cope with silver over the concentration range of 10−7 to 10−2 M Ag+. Understanding these processes enables us to assess the potential of this microalga for applications for bioremediation. Silver in situ speciation and localization were investigated using X-ray absorption spectroscopy, X-ray diffraction, and transmission electron microscopy. Silver toxicity was evaluated by monitoring microalgal growth and photochemical parameters. Different accumulation mechanisms were brought out depending on silver concentration. At low micromolar concentration, microalgae fixed all silver initially present in solution, trapping it inside the cells into the cytosol, mainly as unreduced Ag(I) bound with molecules containing sulfur. Silver was efficiently detoxified. When concentration increased, silver spread throughout the cell and particularly entered the chloroplast, where it damaged the photosystem. Most silver was reduced to Ag(0) and aggregated to form crystalline silver nanoparticles of face-centered cubic structure with a mean size of 10 nm. An additional minor interaction of silver with molecules containing sulfur indicated the concomitant existence of the mechanism observed at low concentration or nanoparticle capping. Nanoparticles were observed in chloroplasts, in mitochondria, on the plasma membrane, on cytosolic membrane structures, and in vacuoles. Above 10−4MAg+, damages were irreversible, and photosynthesis and growth were definitely inhibited. However, high silver amounts remained confined inside microalgae, showing their potential for the bioremediation of contaminated water.
Keywords: Algae Ag Coccomyxa actinabiotis EXAFS


Publ.-Id: 27656 - Permalink

A novel fluorescence anisotropy‐based assay to investigate the GTP-binding site of human tissue transglutaminase
Hauser, C.; Kasprzyk, R.; Wodtke, R.; Kowalska, J.; Löser, R.; Jemielity, J.; Pietsch, M.
Tissue transglutaminase (TGase 2) is a multifunctional enzyme that catalyzes the formation of covalent crosslinks between protein-bound glutamine and primary amine substrates (transamidase activity) but also functions as a GTP-binding protein (Gh protein). These two functions are associated with an “open” and a “closed” conformation, respectively, being tightly regulated by Ca2+ and GDP/GTP levels. In recent years, several assays for the transamidase activity have been published [1], leaving the GTP-binding function virtually untouched.
Here, we report a novel assay to quantify the GTP-binding activity of human TGase 2, which follows the increase in fluorescence anisotropy of an optimized fluorescein-labeled GTP probe upon binding to the protein. Validity of the assay was ensured by means of the (endogenous) ligands GTP, GTPγS and GDP showing inhibitory potencies (IC50) for displacement of the new probe comparable to reported values [2]. ATP, commonly not considered as being an inhibitor of TGase 2, was found to diminish binding of the probe to TGase 2 at unphysiologically high concentrations. The binding assay was then applied for the characterization of a small library of GDP and GTP analogs to obtain structure-activity relationships.
In addition, assays quantifying the transamidase [3] and GTP-binding activities, respectively, were subjected to a titration with calcium chloride (Ca2+) to elucidate its influence on the conformation of TGase 2. Exclusive interaction of ligands/substrates with the GTP binding site and with the active site were found in the absence of Ca2+ and at [Ca2+] > 10 mM, respectively. Both assays exhibit an activity of ~60% at [Ca2+] = 0.5 mM, with this intermediate calcium concentration being applicable to identify ligands of both the active and the GTP-binding site at the same time. This finding was confirmed in both assays by means of GTPγS and recently reported N6-acryloyllysine piperazides [4,5] shown to irreversibly interact with the active-site cysteine residue.

[1] Pietsch et al., Bioorg. Med. Chem. Lett. 2013, 23, 6528.
[2] Schaertl et al., J. Biomol. Screen. 2010, 15, 478.
[3] Hauser et al., Amino Acids 2017, 49, 567.
[4] Wityak et al., ACS Med. Chem. Lett. 2012, 3, 1024.
[5] Wodtke et al., J. Med. Chem. 2018, accepted.
  • Lecture (Conference)
    Transglutaminases in Human Disease Processes, 17.-21.06.2018, Les Diablerets, Schweiz

Publ.-Id: 27652 - Permalink

Advanced thermal processing of group-IV materials and beyond
Rebohle, L.; Skorupa, W.; Prucnal, S.; Berencén, Y.; Zhou, S.; Helm, M.
One of the main issues in semiconductor research is doping and crystallization. To meet the high standards of today’s microelectronic industry, especially in the context of nanostructures, more and more non-equilibrium processing technologies has been entered. This applies, above all, to thermal processing which usually has to activate dopants and anneal out defects, but has to suppress diffusion and segregation at the same time. This presentation is focused on the use of millisecond flash lamp annealing (FLA) for advanced thermal processing of group-IV materials including Si, Ge and GeSn alloys. FLA is able to exceed the solid solubility limit of dopants which is discussed for the cases of P and Sn in thin Ge films as well as for Se in Si nanowires. Moreover, the specific conditions of FLA determine whether a thin amorphous film on a crystalline substrate, e.g. an amorphous Ge layer on Ge after ion implantation, recrystallizes in a poly- or monocrystalline way. Finally, perspectives of FLA for other materials will be presented.
Keywords: flash lamp annealing, ion implantation, hyperdoping of silicon, Sn doping of germanium, silicon nanowire
  • Invited lecture (Conferences)
    European Materials Research Society Spring Meeting 2018, 18.-22.06.2018, Strasbourg, France

Publ.-Id: 27648 - Permalink

Crystallization of thin amorphous silicon films on glass by magnetron sputtering and flash lamp annealing
Rebohle, L.; Neubert, M.; Schumann, T.; Skorupa, W.
Flash lamp annealing (FLA) is an innovative annealing method already used in semiconductor industry, for flexible electronics and for thin, functional coatings on glass. Due to the short time scale of milliseconds, FLA is cost and time effective, suitable for temperature-sensible substrates and allows the exploitation of non-equilibrium crystallization processes.
In this contribution we present a new approach in which magnetron sputtering is combined with FLA. In detail, thin polycrystalline Si films have been fabricated and characterized with respect to their structural, optical and electrical properties. Special focus is set on the non-equilibrium crystallization process within the millisecond time scale. Furthermore, strategies to avoid thermal stress, to minimize defects and to obtain layers with a low electrical resistivity are discussed.
Keywords: flash lamp annealing, magnetron sputtering, amorphous silicon
  • Lecture (Conference)
    European Materials Research Society Spring Meeting 2018, 18.-22.06.2018, Strasbourg, France

Publ.-Id: 27647 - Permalink

Sputtering in combination with flash lamp annealing for thin film deposition on glass
Rebohle, L.; Neubert, M.; Schumann, T.; Skorupa, W.
Flash lamp annealing (FLA) is an innovative annealing method already used in semiconductor industry, for flexible electronics and for thin, functional coatings on glass. Due to the short time scale of milliseconds, FLA is cost and time effective, suitable for temperature-sensible substrates and allows the exploitation of non-equilibrium processes. Recently, FLA was combined with atomic layer deposition to improve the properties and functionality of thin films by in-situ annealing.
In this contribution we present a new approach in which magnetron sputtering is combined with FLA. Whereas the first part covers technological aspects of this new approach, the second part reports on first experiments to fabricate thin films (e.g. polycrystalline silicon) on glass carriers and thin glass foils. The improvement of sputtered films by post-deposition treatment is a general issue in order to achieve the desired structural, optical and electrical properties. In detail, the functionalization process on the millisecond time scale and strategies to avoid thermal stress, to minimize defects and to obtain layers with a low electrical resistivity are discussed.
Keywords: Flash lamp annealing, magnetron sputtering, amorphes Silicon,
  • Poster
    ICCG 12 – Conference on Coatings on Glass and Plastics, 11.-15.06.2018, Würzburg, Deutschland

Publ.-Id: 27646 - Permalink

The Precession Dynamo Experiment at HZDR
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.
Cosmic magnetic fields are ubiquitous phenomena that are observed on all scales, from planets and stars to galaxies and clusters of galaxies. The origin of these fields involves the formation of electrical currents by means of complex flows of conducting fluids or plasmas.
Fluid flow induced magnetic fields via this dynamo effect have also been observed in experiments, which, however, require considerable technical efforts due to the significantly smaller scales available in the laboratory. The project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) conducted at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) provides a new platform for a variety of liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. The most ambitious experiment within this project is a precession driven dynamo experiment that currently is under construction and will consist of a cylinder filled with liquid sodium that simultaneously rotates around two axes. The experiment is motivated by the idea of a precession-driven flow as a complementary energy source for the geodynamo or the ancient lunar dynamo.
In our presentation we will address corresponding numerical and experimental examinations aimed at an optimization of the precession driven flow with regard to improve the dynamo process in the planned experiment. Both approaches show that in the strongly nonlinear regime the flow is essentially composed of the directly forced primary Kelvin mode and higher modes in terms of standing inertial waves that arise from nonlinear self-interactions. A peculiarity is the resonance-like emergence of an axisymmetric mode that represents a double roll structure in the meridional plane. Kinematic simulations of the magnetic field evolution induced by the time-averaged flow yield dynamo action at critical magnetic Reynolds numbers around Rm_crit ∼430, which is well within the range of the planned liquid sodium experiment.
Keywords: Dynamo Precession DRESDYN
  • Lecture (Conference)
    The Third Russian Conference on Magnetohydrodynamics, 18.-21.06.2018, Perm, Russia

Publ.-Id: 27645 - Permalink

Sensitive, Selective and Biodegradable – New biosorbents for metal recovery
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Low concentrated heavy metal ions are causing diverse problems for conventional metal processing. Artificial peptides with metal binding affinities are a new, innovative challenger for conventional metal recovery. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential for geobiotechnology.
Here, we aimed for the development of novel peptidic bio-materials for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and genetically optimized for heterologous expression and production. Methods used for characterizing the peptide metal interaction, were e.g. quartz crystal microbalance with dissipation monitoring (QCM-D) and UV/Vis spectroscopy. Our system can be adapted to many different purposes/materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, leading to the discovery of novel metal-interacting biomolecules.
Introduction. With biomining first applie
Keywords: phage display; biosorption; peptide; biohydrometallurgy; metallopeptide; metal binding, bioremediation
  • Lecture (Conference)
    Sustainable Minerals '19, 14.-15.06.2018, Windhoek, Namibia

Publ.-Id: 27644 - Permalink

Heavy metal binding peptides – biosorbents with economic and ecological potential
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Critical heavy metal concentrations can be found in environmental and/or industrial systems. Removal of metals for detoxification (bioremediation) and recovery of metals (geobiotechnology) from natural water bodies or waste waters is challenging because of low concentrated metal ions. Artificial peptides, that are able to bind metal ions, are of great potential as they combine unique sensitivity and high specificity.
Here we present the development of peptide-based biosorptive materials for heavy metal removal, including identification, adaptation and characterization of specific peptides binding nickel and cobalt. Using Phage Surface Display (PSD) and deep sequencing we identified and produced metal binding peptides. Metal-peptide interactions were studied using e.g. quartz crystal microbalance with dissipation monitoring (QCM-D), and UV/Vis spectroscopy. With this study we provide a system that can be adapted to other materials and knowledge about the nature of metal-peptide interaction, which may lead to the discovery of novel metal-interacting biomolecules, e.g. enzymes and peptides.
Keywords: phage display; biosorption; peptide; biohydrometallurgy; metallopeptide; metal binding, bioremediation
  • Lecture (Conference)
    Biohydrometallurgy '18, 12.-13.06.2018, Windhoek, Namibia

Publ.-Id: 27643 - Permalink

Sensitive, selective and biodegradable – new biosorbents for metal recovery
Braun, R.ORC; Matys, S.ORC; Schoenberger, N.; Jain, R.; Lederer, F.ORC; Pollmann, K.ORC
Low concentrated heavy metal ions are causing diverse problems for conventional metal processing. Artificial peptides with metal binding affinities are a new, innovative challenger for conventional metal recovery. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential for geobiotechnology.
Here, we aimed for the development of novel peptidic bio-materials for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and genetically optimized for heterologous expression and production. Methods used for characterizing the peptide metal interaction, were e.g. quartz crystal microbalance with dissipation monitoring (QCM-D) and UV/Vis spectroscopy. Our system can be adapted to many different purposes/materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, leading to the discovery of novel metal-interacting biomolecules.
  • Lecture (Conference)
    69. BHT - Freiberger Universitätsforum, 06.-08.06.2018, Freiberg, Germany

Publ.-Id: 27642 - Permalink

Heavy metal biosorbents – New approaches for old problems
Braun, R.ORC; Matys, S.ORC; Jain, R.; Schoenberger, N.; Lederer, F.ORC; Pollmann, K.
Low concentrations of heavy metal ions are causing diverse problems from the environmental and economic viewpoints. Conventional metal processing is complicated, both from a technical and economic perspective with low heavy metal concentrations e.g. in mine tailing waste waters. Additionally, even in low concentrations particular heavy metal ions are highly toxic and do have a severe influence on environmental systems. Artificial peptides with special metal binding affinities are therefore a new, innovative challenger for conventional metal recovery methods. They combine high specificity and sensitivity and being biodegradable, they do not add additional environmental pressure, therefore they are of high potential both for geobiotechnology and bioremediation.
In the present study we aimed for the development of novel bio-based materials of peptidic nature for the recovery of cobalt and nickel. Combining Phage Surface Display Technology (PSD) with deep sequencing approaches, suitable sequences were identified and subsequently genetically optimized for heterologous expression, production and purification. Different methods were used for characterizing the peptide metal interaction, e.g. quartz crystal microbalance with dissipation monitoring (QCM-D), fast protein liquid chromatography (FPLC) and UV/Vis spectroscopy. The developed system can be adapted to many different purposes and desired materials and the identified motifs can provide information for a deeper understanding of bio-inorganic interactions, potentially leading to the discovery of novel metal-interacting biomolecules, e.g. enzymes and peptides.
  • Lecture (Conference)
    3rd Green & Sustainable Chemistry Conference, 13.-16.05.2018, Berlin, Germany

Publ.-Id: 27641 - Permalink

A simple route to synchronized nucleation of self-catalyzed GaAs nanowires on Si for sub-Poissonian length distributions
Tauchnitz, T.ORC; Berdnikov, Y.; Dubrovskii, V. G.ORC; Schneider, H.; Helm, M.; Dimakis, E.ORC
The achievement of sub-Poissonian length distributions (LDs) in VLS-grown III-V nanowire (NW) ensembles, as theoretically predicted by Glas and Dubrovskii, requires synchronized nucleation of all NWs on their substrate. This is especially challenging for self-catalyzed GaAs NWs on a natively-oxidized Si(111) substrate because their nucleation involves a sequence of different physical mechanisms: the formation of Ga droplets at random positions on the substrate, their interaction with SiOx and the formation of nano-sized holes, and finally the droplet-assisted nucleation of GaAs inside these holes.
Here, we demonstrate that it is possible to achieve highly-synchronized nucleation of MBE-grown GaAs NWs and, thus, very narrow LDs if a simple in situ procedure is employed prior to the growth in order to decouple the formation of SiOx holes from the subsequent nucleation of NWs. This procedure consists of three steps (substrate annealing – Ga deposition – substrate annealing) and produces SiOx holes (free of Ga droplets) of controlled size and number density.
Our study compares the LD of GaAs NWs grown on Si substrates with different size or number density of SiOx holes. The results were fitted with a continuum-growth theoretical model that accounts for nucleation fluctuations, kinetic fluctuations and nucleation antibunching in individual NWs. We have found that the formation of large-enough holes before the initiation of the NW growth can shorten the characteristic nucleation time of the NWs by one order of magnitude and narrow the LD by a factor of 2. The LD was further improved by decreasing the number density of SiOx holes/GaAs NWs, which is attributed to the suppression of beam-shadowing effects. In the best case, we obtained GaAs NWs that exhibit a remarkably short characteristic nucleation time of 10 ms and a sub-Poissonian LD. All in all, our results (unpublished) not only prove the validity of theoretical considerations about the sub-Poissonian LD for self-catalyzed NWs, but also demonstrate a simple route to low-cost fabrication (without substrate patterning) of GaAs NW-based devices with controllable number density and length uniformity.
Keywords: surface modification, SiOx holes, synchronized nucleation
  • Lecture (Conference)
    Nanowire Week 2018, 11.-15.06.2018, Hamilton, Ontario, Kanada

Publ.-Id: 27640 - Permalink

Preparation of nanowire cross-sections by ultramicrotomy
Formanek, P.; Hübner, R.; Balaghi, L.; Wagner, J.; Dimakis, E.
Preparation of nanowire cross-sections by ultramicrotomy
  • Lecture (others)
    6. Sächsisches TEM-Präparatorentreffen, 10.04.2018, Dresden, Deutschland

Publ.-Id: 27639 - Permalink

Thermodynamic Reference Database - Recent and present activities in THEREDA
Moog, H. C.; Bok, F.; Marquardt, C.; Thoenen, T.; Voigt, W.; Yalçintaş, E.
Five institutions joined efforts to create a common thermodynamic reference database (THEREDA), dedicated to the calculation of radionuclide solubility in high-saline solutions in underground nuclear disposal sites. The principal output of the project are ready-to-use parameter files for thermodynamic equilibrium codes, among them ChemApp.
The presentation will give an account on the development of the project in the past ten years. Results from recent and upcoming releases will be given. Some emphasis will be given to lessons learnt in recent activities, where redox equilibria were involved.
The presentation will conclude on the long-term perspective of THEREDA and an outlook to the envisaged support of another Gibb energy minimizer.
Keywords: THEREDA, Thermodynamic reference database, ChemApp, Gibb energy minimizer
  • Lecture (Conference)
    GTT Users' Meeting 2018, 27.-29.06.2018, Herzogenrath-Kohlscheid, Deutschland

Publ.-Id: 27637 - Permalink

DFT studies on the nature of Y-Ti-O nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.; Faßbender, J.
Nanostructured Ferritic Alloys (NFA) are promising candidates for structural materials of future fusion and fission reactors. They consist of a ferritic or ferritic/martensitic Fe-Cr matrix with a high dispersion of nanometer-size yttria-based oxide particles. In this research project the nature of the yttria-based oxide nanoclusters in a bcc Fe matrix is investigated by Density Functional Theory (DFT). The main goal of the studies is the better understanding of structure, energetics and composition of the clusters.
In the first part of the work three types of structures are considered: (i) clusters consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe, (ii) clusters with Y, Ti, and O on bcc sites, and (iii) clusters with of Y, Ti, on bcc sites and O on octahedral interstitial sites of the bcc lattice. Simulation cells containing the three different structures but the same composition of atoms (Fe, Y, Ti, O) are considered, and relaxation calculations are performed using the DFT code VASP. It is found that in the three cases the energetics, i.e. the total binding energy of the clusters, is very similar. This contradicts the statement of Barnard et al. [1] that type (i) structures are most favorable. Further alternative cluster models with a core similar to the NaCl structure and an oxygen atom in the center are constructed and investigated in the second part of the work. For the compositions considered some of these clusters are more stable than those investigated before. Finally, the binding energy of O, Y, Ti atoms, and of the vacancy to selected cluster structures was studied. Oxygen and the vacancy are strongly attracted by the nanoclusters, while the interaction with metal atoms is weaker.
[1] L. Barnard et al. Acta Mater. 60, 935 (2012)
Keywords: Y-Ti-O nanoclusters in Fe, Density Functional Theory
  • Poster
    The 14th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2018), 18.-22.06.2018, Shanghai, China

Publ.-Id: 27634 - Permalink

Diffusion of oxygen in bcc Fe under the influence of other foreign atoms
Wang, X.; Posselt, M.; Faßbender, J.
Density Functional Theory (DFT) and Atomistic Kinetic Monte Carlo (AKMC) simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of substitutional foreign atoms, such as Al, Si, P, S, Ti, Cr, Mn, Ni, Y, Mo, and W. These atoms are assumed to be immobile since their diffusion coefficient is much smaller than that of oxygen.
In the first part of the work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites are investigated by DFT. It is found that the first-neighbor jump is most relevant with the tetrahedral site as the saddle point. The second-neighbor jump consists of two consecutive first-neighbor jumps whereas the barrier of the third-neighbor jump is too high to be significant for the diffusion process. In the second part DFT is applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of the substitutional foreign atom, etc. Si, P, Ni, Mo and W influence the migration barriers of oxygen and their interaction energy with O is mainly repulsive. While Al, Cr and Mn have also a significant influence on the barriers they show strong attractive interactions. The strongest modification of the barriers is found for S, Ti, and Y where deep attractive states exist. At large distance from the solutes the O migration barriers converge to the value for pure Fe. The most relevant migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Finally, the diffusion coefficient of oxygen is determined by AKMC simulations on a rigid lattice, considering a dilute iron alloy and using the migration barriers calculated by DFT. Si, P, Ni, Mo, and W have almost no influence on the diffusivity of O, i.e. it is nearly identical to that in pure bcc Fe. The presence of Al, Cr, Mn, S, Ti, and Y causes a reduction of the mobility of oxygen. The strongest decrease of the diffusion coefficient is obtained for the foreign atoms S, Ti, and Y.
Keywords: Diffusion of oxygen in iron, Density Functional Theory, Atomistic Monte Carlo simulations
  • Poster
    The 14th International Conference on Computer Simulation of Radiation Effects in Solids (COSIRES 2018), 18.-22.06.2018, Shanghai, China

Publ.-Id: 27633 - Permalink

Nanoindentation and nanoscratching of a ferrite/austenite iron bi-crystal: An atomistic study
Al Motasem, A. T.; Posselt, M.; Bergström, J.
Molecular dynamics simulations are applied to investigate the wear/friction behavior of a ferrite/austenite iron bi-crystal, as a model system for duplex stainless steels. The plasticity of the ferrite phase is dominated by dislocations while both dislocations and stacking faults are the primary cause of plastic deformation of the austenite phase. Interestingly, the responses of tribological parameters vary depending on the scratch direction. For instance, the scratch hardness is increased by about 46% whereas the friction coefficient is reduced by about 22% when scratch starts from austenite to ferrite. At the interface, a local softening/hardening occurs because of dislocation-interface interaction. The present results demonstrate that martensitic phase transformation is responsible for experimentally observed high amount of ferrite of the pile-up.
Keywords: Atomistic simulation Ferrite Austenite Wear

Publ.-Id: 27632 - Permalink

Comparison of FIB Resolution for Different Ion Species in Imaging and Writing Mode
Bischoff, L.; Pilz, W.; Hlawacek, G.; Mazarov, P.; Bauerdick, S.; Gierak, J.
Focused Ion Beam (FIB) processing, which is nearly exclusively based on gallium Liquid Metal Ion Sources (LMIS) [1] expands more and more to other ion species also by implementation of other types of ion sources. Many applications in nano-technology could benefit from ion species other than gallium, like local doping by ion implantation, ion beam mixing, ion beam synthesis [2], or direct milling using various ions [3]. The application of Gas Field Ion Sources (GFIS) opens the sub-nm range for ion microscopy in the case of He [4].
A key parameter of FIB applications is the spatial resolution in terms of full width at half maximum (FWHM) of the beam profile, which can be described by e.g. two Gaussian functions or a Holtsmark distribution. Three main parts contribute to the obtainable resolution: a source term containing the virtual source size and the magnification, the spherical aberration, describing geometrical effects and the chromatic aberration depending on the energy spread of the ion source [5]. All contents are influenced by the ion source itself as well as the performance of the ion optics. For an optimum image resolution another shape of the beam profile with a sharp tip should be chosen by a suited alignment than for surface patterning by ion milling where more parallel slopes of the distribution a preferred. For a minimum feature size the beam interaction with the surface as well as the combination of ion species and target material must be put into consideration.
In this contribution the beam resolution will be basic discussed for a broad spectrum of ions beginning for light species, Helium Ion Microscope (Fig. 1) and Be from an AuSiBe LMAIS in a mass separated FIB (Fig. 2) up to very heavy ones, like Au, Bi and polyatomic clusters from them. The obtainable FIB resolution in the image and the patterning mode will be compared and discussed.

[1] J. Gierak; Focused ion beam technology and ultimate applications, Sem. Sci. Technol. 24 (2009), 1.
[2] L. Bischoff, P. Mazarov, L. Bruchhaus and J. Gierak; Liquid metal alloy ion sources – An alternative for focused ion beam technology, Appl. Phys. Rev. 3 (2016), 021101.
[3] S. Bauerdick et al.; Multispecies focused ion beam lithography system and its applications, J. Vac. Sci. Technol. B 31 (2013), 06F404-1.
[4] G. Hlawacek, V. Veligura, R. van Gastel, and B. Poelsema; Helium ion microscopy, J. Vac. Sci. Technol. B 32 (2014), 020801-1.
[5] R.G. Forbes in Charged Particle Optics, ed. J. Orloff, CRC Press (2009).
Keywords: Focused ion beam, Liquid Metal Alloy Ion Source, Helium microscope
  • Lecture (Conference)
    2nd EUFN Workshop 2018, 19.-20.06.2018, Grenoble, France

Publ.-Id: 27627 - Permalink

Rayleigh–Ritz based expansion method for wakefields in dielectrically lined rectangular waveguides
Reimann, F.; Michel, P.; Lehnert, U.; van Rienen, U.
n this work, a semi-analytical method for determining wakefields in dielectrically lined rectangular waveguides is presented. This approach is based on a Rayleigh–Ritz method to analytically identify the eigenmodes of the structure, which is currently studied for the application as a so-called ‘wakefield dechirper’. The electric field is subsequently determined through an eigenmode expansion, and the wakefield is calculated from the electric field. By virtue of using an analytic ansatz throughout the wakefield determination, an expression for the Green's function wakefield is found.

The semi-analytical method is then benchmarked against simulations using purely numerical approaches. Compared to numerical approaches, the advantages of the presented method are the independence from any need of discretisation, the computational efficiency of the method's presented Python-based implementation and finally the opportunity to calculate a true Green's function wakefield. From this Green's function, the wake potentials of different bunch shapes can be obtained via convolution.
Keywords: Wakefields Wakefield dechirping Eigenmode expansion Green's function

Publ.-Id: 27626 - Permalink

Magnetic-field-induced quadrupolar ordering and the crystal electric field effect in the distorted kagome lattice antiferromagnet Dy3Ru4Al12
Ishii, I.; Mizuno, T.; Takezawa, K.; Kumano, S.; Kawamoto, Y.; Suzuki, T.; Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.
To investigate the 4f -electronic states under a crystal electric field (CEF) and the phase transition inDy3Ru4Al12
with the antiferromagnetic transition temperature TN = 7 K, we performed ultrasonic measurements on a single-crystalline sample at zero magnetic field and under fields. The transverse elastic modulus C44 shows a characteristic elastic softening. The CEF analyses indicate that the softening is caused by an interlevel quadrupole interaction between the ground and excited Kramers doublets. Under fields, we found a magnetic-field-induced phase transition along both the [100] and [001] directions in addition to the antiferromagnetic ordering. A plausible origin of the field-induced transition is quadrupolar ordering, which is estimated from our CEF calculation. These results and the negative sign of a quadrupole-quadrupole coupling constant suggest that the effect of geometrical frustration alignment due to the kagome lattice also appears on the electric quadrupoles of the Dy ions with the antiferroquadrupolar-type interaction.

Publ.-Id: 27625 - Permalink

OC-0594: Postoperative [11C]MET-PET predicts radiochemotherapy outcome in glioblastoma: a prospective trial
Krause, M.; Seidlitz, A.; Löck, S.; Jentsch, C.; Platzek, I.; Zöphel, K.; Petr, J.; van den Hoff, J.; Steinbach, J.; Krex, D.; Schackert, G.; Falk, M.; Baumann, M.; Beuthien-Baumann, B.
Despite combined modality treatment involving surgery and adjuvant radiotherapy, a relevant percentage of chordoma and chondrosarcoma patients develop a local recurrence. In a previous study, we identified optic apparatus and/or brainstem compression, histology and GTV volume as prognostic factors for the risk of local failure. The present study aims to analyze patterns of recurrence and correlate local control with a detailed dosimetric analysis.

Publ.-Id: 27624 - Permalink

EP-2137: Development of a modular MRI processing workflow for volumetric analysis of healthy brain tissue
Gommlich, A.; Petr, J.; Raschke, F.; van den Hoff, J.; Krause, M.; Troost, E.
An inherent problem of magnetic resonance imaging (MRI)-based analyses of morphological tissue changes is the absence of a ground truth. A particular issue in cerebral imaging is the lack of consensus regarding the order and manner, in which registration and segmentation algorithms are employed to evaluate volumes and longitudinal changes of different tissue types, e.g., grey and white matter (GM and WM).
Considering shortcomings of a procedure widely applied for global segmentation of the entire brain we developed a modular MRI processing workflow particularly suitable for volumetric analysis of the contralateral hemisphere in brain tumor patients.

Publ.-Id: 27623 - Permalink

Electron mobility and lifetime in GaAs/In𝑥Ga1−𝑥As core/shell nanowires studied by optical pump – THz probe spectroscopy
Fotev, I.; Balaghi, L.; Hübner, R.; Schmidt, J.; Hähnel, M.; Schneider, H.; Helm, M.; Dimakis, E.; Pashkin, A.
We utilize ultrafast optical pump – terahertz probe spectroscopy in order to investigate charge carrier response of GaAs/In𝑥Ga1−𝑥As core/shell nanowires (NWs) produced by molecular beam epitaxy. The NWs were ≈2 𝜇m long. The GaAs core diameter was 25nm and the InGaAs shell thickness was 80 nm. We studied the shells with different compositions, from 𝑥 = 0.20 to 𝑥 = 0.44.
From the pump-probe measurements we extracted terahertz photoconductivity of NWs and used the localized surface plasmon model to fit the results. The charge carrier lifetimes were estimated to be around 80–100 ps while the extracted electron mobilities reach 3700 cm2V−1s−1 at room temperature. Even without a surface passivation shell, these values are higher than those in previously studied GaAs/AlGaAs core/shell nanowires, but still lower than the ones for bulk InGaAs. Possible reasons (sources of electron scattering) which affect the mobility will be discussed.
Keywords: nanowires; terahertz; mobility
  • Lecture (Conference)
    DPG Spring Meeting 2018, 11.-16.03.2018, Berlin, Germany

Publ.-Id: 27620 - Permalink

Nonlinear Plasmonic Response of Doped GaAs Nanowires Observed in sSNIM
Lang, D.; Balaghi, L.; Dimakis, E.; Hübner, R.; Kehr, S. C.; Eng, L. M.; Pashkin, A.; Winnerl, S.; Schneider, H.; Helm, M.
We present nanoscopic infrared-optical investigations on highly n-type doped GaAs-based nanowires, revealing interesting nonlinear phenomena such as a pronounced redshift of the plasma resonance by the strong THz fields of a free-electron laser.
Keywords: nanowires, nonlinear plasmonics, free-electron laser, terahertz, s-SNOM, nanoscopy
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO), 14.05.2018, San José, USA
    Conference on Lasers and Electro-Optics
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO), 14.-18.05.2018, San José, USA

Publ.-Id: 27619 - Permalink

Enhancing the Magnetic Moment of Ferrimagnetic NiCo2O4 via Ion Irradiation driven Oxygen Vacancies
Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Meyer, D. C.; Chin, Y. Y.; Lin, H. J.; Chen, C. T.; Gemming, S.; Helm, M.; Chu, Y. H.; Zhou, S.ORC
Ion irradiation has emerged as a powerful tool for the efficient control of uniaxial lattice expansion to fine tune and modulate the otherwise inaccessible complex correlated phases in oxide thin-films. We report the fine tuning of the magnetic moment, ferromagneticparamagnetic and metal-insulator transition temperatures in the NiCo2O4 inverse-spinel oxide by creating oxygen deficiencies, employing high energy He-ion irradiation. Tailoring of oxygen vacancies and consequently a uniaxial lattice expansion in the out-of-plane direction drives the system towards the increase of the magnetic moment by two-times in magnitude.
The magnetic moment increases with the He-ion irradiation fluence up to 2.5×1016/cm2 . Our results are corroborated well by spin-polarized electronic structure calculations with density functional theory and X-ray absorption spectroscopic data which show peak-height change and energy shift of Co-L2,3 and Ni-L2,3 edges driven by the oxygen vacancies. These results demonstrate a new pathway of tailoring oxygen vacancies via He-ion irradiation, useful for designing new functionalities in other complex oxide thin-films.

Publ.-Id: 27617 - Permalink

Vergleich der Wirkung von Alpha- und Protonenstrahlung an Normal- und Tumorzellen
Maucksch, U.; Runge, R.; Wetzig, K.; Naumann, A.; Freudenberg, R.; Lühr, A.; Beyreuther, E.; von Neubeck, C.; Kotzerke, J.
Für Alpha-Strahler ist bekannt, dass diese aufgrund eines hohen linearer Energietransfers (LET) bei gleicher Dosis eine höhere relative biologische Wirksamkeit (RBE) im Vergleich zu Gammastrahlern zeigen. Als Ursache werden die hohe lokale Dosisdeposition sowie die erhöhte Wahrscheinlichkeit für DNA-Doppelstrangbrüche (DSB) angenommen. Für Protonenstrahlung ist eine RBE von 1,1 zu erwarten. Untersucht wurde die Wirksamkeit von 150 MeV Protonenbestrahlung im Vergleich zum Alpha-Emitter Ra-223 auf das verwendete Zellsystem.
Die Wirkung der Protonenbestrahlung und des Alpha-Emitters Ra-223 wurde durch Bestrahlung der Schilddrüsennormalgewebszelllinie FRTL-5 sowie der Tumorzelllinie FaDu überprüft. Die Protonenbestrahlung im Dosisbereich von 0,5 bis 10 Gy erfolgte mit 3 Gy/min am Protonenstrahl der Universitätsprotonentherapie Dresden. Um Dosispunkte zwischen 0,125 und 2 Gy des Alpha-Strahlers Ra-223 zu applizieren, wurden die Zellen mit verschiedene Aktivitätskonzentrationen über 24 h inkubiert. Das klonogene Zellüberleben und die Anzahl der residualen DNA-DSB (H2AX-Assay) wurden 24 h nach Bestrahlung untersucht.
Aus den Dosiswirkungskurven des Koloniebildungsassays wurde die Dosis für 37 % Überleben (D37) für die Normalzelllinie FRTL-5 nach Protonenbestrahlung mit 2,96 Gy und für Ra-223 mit 0,35 Gy bestimmt. Die Tumorzelllinie FaDu zeigte nach Protonenbestrahlung eine D37 von 2,32 Gy und nach Inkubation von Ra-223 eine D37 von 0,31 Gy. Für beide Zelllinien war die Anzahl an residualen DNA-DSB (H2AX-Assay) nach Protonenbestrahlung signifikant geringer als bei Bestrahlung mit Ra-223.
Der erhöhte LET des Alpha-Strahlers Ra-223 (max. 250 keV/µm) führt zu einem geringenen Zellüberleben und zu einer höheren Anzahl der residualen DNA-DSB im Vergleich zur Protonenbestrahlung (LET ca. 2 keV/µm).
  • Lecture (Conference)
    56. Jahrestagung der Deutschen gesellschaft für Nuklearmedizin, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 27616 - Permalink

Best Practices in Running Collaborative GPU Hackathons: Advancing Scientific Applications with a Sustained Impact
Chandrasekaran, S.ORC; Juckeland, G.ORC; Lin, M.ORC; Otten, M.ORC; Pleiter, D.ORC; Stone, J. E.; Lucio-Vega, J.; Zingale, M.ORC; Foertter, F.ORC
The OLCF GPU Hackathons are a one-week code-development/learning event to better enable attendees to utilize GPUs. It only took three years to grow from a ``Let's give this a try''-event to a repeatedly copied format with several spin-offs that inspired HPC centers around the world.
Sticking to a few fundamental principles---work on your own code, learn from your mentors just what you need and when you need it, stay flexible in achieving your goal---the week-long hackathon format created at Oak Ridge Leadership Computing Facility (OLCF) has been just the spark needed by many groups of scientists to light the fire of a wider GPU adoption in leading-edge as well as university-scale HPC environments. Most interestingly, the format enabled both ends of the experience spectrum---graduate students vs. postdoc fellows---the same kind of progress and chance of success.
Keywords: B.1.4.b Languages and compilers D.1 Programming Techniques M.12.0.b Case Studies in Scientific Applications


Publ.-Id: 27612 - Permalink

Local probe of irradiation induced structural changes and orbital magnetism in Fe60Al40 thin films via order-disorder phase transition
La Torre, E.; Smekhova, A.; Schmitz-Antoniak, C.; Ollefs, K.; Eggert, B.; Cöster, B.; Walecki, D.; Wilhelm, F.; Rogalev, A.; Lindner, J.; Bali, R.; Banerjee, R.; Sanyal, B.; Wende, H.
Hard X-ray absorption and magnetic circular dichroism spectroscopy have been applied to study the consequential changes of the local environment around Fe atoms and their orbital polarizations in Fe60Al40 thin films of 40 nm thickness along the order-disorder (B2→A2) phase transition initiated by 20keV Ne+ ion-irradiation with fluences of (0.75 - 6) × 1014 ions cm-2. The analysis of the extended X-ray absorption fine structure spectra measured at the Fe K-edge at room temperature revealed an increased number of Fe-Fe nearest-neighbors from 3.47(7) to 5.0(1) and ~ 1% of volume expansion through the transition. The visualization of the Fe and Al nearest neighbors rearrangement in the first coordination shell of Fe absorbers via the transition was carried out by wavelet transformations. The obtained changes in Fe coordination are evidently reflected in the XMCD spectra which show an increased orbital magnetic moment of Fe atoms and a pronounced magnetic multi-electronic excitations peak at ~60 eV above the edge. The amplitudes of both peaks demonstrated similar dependencies on the irradiation fluence. The results of self-consistent DFT calculations on relaxed Fe60Al40 model structures for the ordered (B2) and the disordered (A2) phases are consistent with the experimental findings and point to the formation of Fe-rich regions in the films studied.
Keywords: Chemical disorder, ion-irradiation, magnetism, EXAFS, wavelet transform, XMCD, DFT


Publ.-Id: 27611 - Permalink

Large-scale self-organized gold nanostructures with bidirectional plasmon resonances for SERS
Schreiber, B.; Gkogkou, D.; Dedelaite, L.; Kerbusch, J.; Hübner, R.; Sheremet, E.; Zahn, D. R. T.; Ramanavicius, A.; Facsko, S.; Rodriguez, R. D.
Efficient substrates for surface-enhanced Raman spectroscopy (SERS) are under constant development, since time-consuming and costly fabrication routines are often an issue for high-throughput spectroscopy applications. In this research, we use a two-step fabrication method to produce self- organized parallel-oriented plasmonic gold nanostructures. The fabrication routine is ready for wafer-scale production involving only low-energy ion beam irradiation and metal deposition. The optical spectroscopy features of the resulting structures show a successful bidirectional plasmonic response. The localized surface plasmon resonances (LSPRs) of each direction are independent from each other and can be tuned by the fabrication parameters. This ability to tune the LSPR characteristics allows the development of optimized plasmonic nanostructures to match different laser excitations and optical transitions for any arbitrary analyte. Moreover, in this study, we probe the polarization and wavelength dependence of such bidirectional plasmonic nanostructures by a complementary spectroscopic ellipsometry and Raman spectroscopy analysis. We observe a significant signal amplification by the SERS substrates and determine enhancement factors of over a thousand times. We also perform finite element method-based calculations of the electromagnetic enhancement for the SERS signal provided by the plasmonic nanostructures. The calculations are based on realistic models constructed using the same particle sizes and shapes experimentally determined by scanning electron microscopy. The spatial distribution of electric field enhancement shows some dispersion in the LSPR, which is a direct consequence of the semi-random distribution of hotspots. The signal enhancement is highly efficient, making our SERS substrates attractive candidates for high-throughput chemical sensing applications in which directionality, chemical stability, and large-scale fabrication are essential requirements.

Publ.-Id: 27608 - Permalink

Strain engineering in lattice-mismatched core/shell nanowires: extending the properties of GaAs
Balaghi, L.; Bussone, G.; Grifone, R.; Hübner, R.; Grenzer, J.; Shan, S.; Fotev, I.; Pashkin, A.; Ghorbani-Asl, M.; Krasheninnikov, A.; Wolf, D.; Hlawacek, G.; Schneider, H.; Helm, M.; Dimakis, E.
Strain engineering in core/shell nanowires (NWs) can be an alternative route to tailor the properties of III-V semiconductors without changing their chemical composition. In particular, we demonstrate that the GaAs core in GaAs/InxGa1-xAs or GaAs/InxAl1-xAs core/shell NWs can sustain unusually large misfit strains that would have been impossible in equivalent thin-film heterostructures, and undergoes a significant modification of its electronic properties.
Self-catalyzed core/shell NWs were grown on SiOx/Si(111) by MBE (Fig. 1a). The growth conditions were optimized in order to minimize the bending of the NWs, a phenomenon that originates from the large misfit between the core and the shell. Synchrotron X-ray diffraction and Raman scattering measurements showed that for a given core diameter, the magnitude and the spatial distribution of the built-in misfit strain can be regulated via the composition and the thickness of the shell. Beyond a critical shell thickness (Fig. 1b), we obtain a heavily tensile-strained core and a strain-free shell. The tensile strain of the core exhibits a quasi-hydrostatic character and causes the reduction of the GaAs band gap energy in accordance with our theoretical predictions (deformation potential theory and first principle calculations), reaching the remarkable value of 40% (0.87 eV at 300 K) for 7% of strain (x = 0.54). Signatures of valence-band splitting were also identified in polarization-resolved photoluminescence measurements, as a result of the strain anisotropy in GaAs. Presuming a reduced effective mass of electrons in the tensile-strained core of GaAs/InxAl1-xAs NWs (core diameter = 22 nm, x = 0.39–0.49), the corresponding electron mobility was measured by optical-pump THz-probe spectroscopy to be in the range of 4000 cm2/V·s at 300 K. These values are the highest reported, even in comparison to GaAs/AlxGa1-xAs NWs with double the core thickness.
In conclusion, our results (unpublished) demonstrate the possibility to resemble to a large extent the fundamental properties of InxGa1-xAs alloys using strained GaAs NWs grown epitaxially on Si (Fig. 1c). This could open a new dimension in the design of nano-photonics and nano-electronics, surmounting issues with phase separation, surface segregation or alloy disorder that typically exist in ternary alloys and limit the device performance.
Keywords: optoelectronics, band gap reduction, InxGa1-xAs
  • Lecture (Conference)
    Nanowire Week, 11.-15.06.2018, Hamilton, Ontario, Canada

Publ.-Id: 27606 - Permalink

Implanting Germanium into Graphene
Tripathi, M.; Markevich, A.; Böttger, R.; Facsko, S.; Besley, E.; Kotakoski, J.; Susi, T.
Incorporating heteroatoms into the graphene lattice may be used to tailor its electronic, mechanical and chemical properties, although directly observed substitutions have thus far been limited to incidental Si impurities and P, N and B dopants introduced using low-energy ion implantation. We present here the heaviest impurity to date, namely 74Ge+ ions implanted into monolayer graphene. Although sample contamination remains an issue, atomic resolution scanning transmission electron microscopy imaging and quantitative image simulations show that Ge can either directly substitute single atoms, bonding to three carbon neighbors in a buckled out-of-plane configuration, or occupy an in-plane position in a divacancy. First-principles molecular dynamics provides further atomistic insight into the implantation process, revealing a strong chemical effect that enables implantation below the graphene displacement threshold energy. Our results demonstrate that heavy atoms can be implanted into the graphene lattice, pointing a way toward advanced applications such as single-atom catalysis with graphene as the template.
Keywords: heteroatom doping; ion implantation; molecular dynamics; scanning transmission electron microscopy


Publ.-Id: 27605 - Permalink

Wechselwirkungs- und Transportuntersuchungen dreiwertiger Radiometalle in Ton unter Berücksichtigung des Einflusses von Fulvinsäure und erhöhten Salinitäten
Poetsch, M.
The storage of radioactive waste demands for evidence of security over a long period. Mainly because of its high sorption capacity as well as favourable geomechanical properties, clay is being explored as one of the potential host rocks for a final repository. This work contributes to the understanding of interactions between trivalent lanthanides (as analogues for trivalent actinides), fulvic acid and Opalinus clay regarding high ionic strength. High salinity and natural organic matter are both known to facilitate migration of toxic or radioactive metals in geochemical systems, but little is known on their combined effect.
The complex system was split into three binary systems with the following interactions: lanthanides (Tb, Eu) and Opalinus clay, lanthanides and fulvic acid, Opalinus clay and fulvic acid.
The binary systems were investigated at pH of 5 and 7 with variable amounts of NaCl, MgCl2 or CaCl2 within a range of 0 - 4 mol L-1. The sorption of the lanthanides and fulvic acid onto the Opalinus clay was investigated in batch experiments, employing 160Tb, 152Eu and 14C as radiotracers. For the investigation of the complexation behaviour of Tb(III) and Eu(III) with fulvic acid, time-resolved laser-induced fluorescence spectroscopy was used.
A combined Kd approach (Linear Additive Model) was tested for suitability in predicting solid-liquid distribution of metals in the presence of organic matter based on the interactions in the constituent subsystems. The metal-ion interactions with fulvic acid were modelled by using the NICA-Donnan approach. To reproduce the migration behaviour of lanthanides in clay, a diffusion-based process was modelled.
This study has shown that there is no synergism in the mobilising effects of fulvic acid and electrolytes at in-situ pH. On the contrary, a mitigating effect of ionic strength was evidenced, based on the fact that metal binding is suppressed while adsorption of humic matter is hardly influenced.
  • Doctoral thesis
    Universität Leipzig, 2018
    Mentor: Lippold, Holger
    106 Seiten

Publ.-Id: 27603 - Permalink

THz spectroscopy of solids with a free-electron laser
Helm, M.
I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. If time permits, I will also introduce the new superradiant THz radiation source TELBE.
Keywords: free electron laser, terahertz, graphene
  • Lecture (others)
    Kolloquium am Max-Born-Institut Berlin, 13.06.2018, Berlin, Germany
  • Lecture (others)
    Vortrag am Paul-Drude-Institut, 23.07.2018, Berlin, Germany

Publ.-Id: 27602 - Permalink

Isolated Proton Bunch Acceleration by a Petawatt Laser Pulse
Hilz, P.ORC; Ostermayr, T. M.ORC; Huebl, A.ORC; Bagnoud, V.; Borm, B.; Bussmann, M.ORC; Gallei, M.; Gebhard, J.; Haffa, D.; Hartmann, J.; Kluge, T.ORC; Lindner, F. H.; Neumayr, P.; Schaefer, C. G.; Schramm, U.ORC; Thirolf, P. G.; Rösch, T. F.; Wagner, F.; Zielbauer, B.; Schreiber, J.ORC
Often, the interpretation of experiments concerning the manipulation of the energy distribution of laser-accelerated ion bunches is complicated by the multitude of competing dynamic processes simultaneously contributing to recorded ion signals. Here we demonstrate experimentally the acceleration of a clean proton bunch. This was achieved with a microscopic and three-dimensionally confined near critical density plasma, which evolves from a 1μm diameter plastic sphere, which is levitated and positioned with micrometer precision in the focus of a Petawatt laser pulse. The emitted proton bunch is reproducibly observed with central energies between 20 and 40 MeV and narrow energy spread (down to 25%) showing almost no low-energetic background. Together with three-dimensional particle-in-cell simulations we track the complete acceleration process, evidencing the transition from organized acceleration to Coulomb repulsion. This reveals limitations of current high power lasers and viable paths to optimize laser-driven ion sources.
Keywords: laser-plasma interaction, laser-ion acceleration, accelerator research, paul trap, experiment, HPC, simulation, PIConGPU

Publ.-Id: 27599 - Permalink

cupla - C++ User interface for the Platform independent Library Alpaka
Widera, R.ORC
cupla [qχɑpˈlɑʔ] is a simple user interface for the platform independent parallel kernel acceleration library alpaka. It follows a similar concept as the NVIDIA® CUDA® API by providing a software layer to manage accelerator devices. alpaka is used as backend for cupla.
  • Software in the HZDR data repository RODARE
    Publication date: 2018-06-10
    DOI: 10.14278/rodare.29
    License: LGPL-3.0


Publ.-Id: 27585 - Permalink

Explicit decay heat calculation in the nodal diffusion code DYN3D
Bilodid, Y.ORC; Fridman, E.ORC; Kotlyar, D.ORC; Shwageraus, E.ORC
The residual radioactive decay heat plays an important role in some accident scenarios and, therefore, needs to be accurately calculated when performing accident analyses. The current reactor simulation codes used for accident analysis account for the residual decay heat by means of simplified models. Typically, these models rely on semi-empirical correlations which are defined over a limited range of burnup and fuel types. Therefore, the applicability of such correlations is limited and any deviation from the definition range may lead to high uncertainties, which is detrimental in evaluating safety margins.
Reactor dynamic code DYN3D was originally developed for transient and accident analysis of LWRs. In DYN3D, the residual radioactive decay heat calculation is based on the German national standard DIN Norm 25463 model. The applicability of this model is limited to a low enriched uranium dioxide fuel for light water reactors.
This paper describes a new general decay heat calculation model implemented in DYN3D. The radioactive decay rate of each nuclide in each spatial node is calculated by recently implemented depletion module and the cumulative released heat is used to obtain the spatial distribution of the decay power for every time step. Such explicit approach is based on first principles and is free from approximations and, thus, can be applied to any reactor system (e.g. thermal and fast) and fuel type. The proposed method is verified against the reference Serpent 2 Monte Carlo solutions for a range of reactor types.
Keywords: DYN3D, Decay heat, Microdepletion


Publ.-Id: 27581 - Permalink

C++ & Python API for Scientific I/O with openPMD
Koller, F.ORC; Huebl, A.ORC

openPMD is an open metadata format for open data workflows in open science. This library provides a common high-level API for openPMD writing and reading. It provides a common interface to I/O libraries and file formats such as HDF5 and ADIOS. Where supported, openPMD-api implements both serial and MPI parallel I/O capabilities.

Keywords: openPMD; Open Science; Open Data; HDF5; ADIOS; data; MPI; HPC; research; file-format; file-handling
  • Software in the HZDR data repository RODARE
    Publication date: 2018-06-18
    DOI: 10.14278/rodare.27
    License: LGPL-3.0


Publ.-Id: 27579 - Permalink

Amphiphilic Siderophore Marinobactin for Froth Flotation Process
Schrader, S.; Kutschke, S.; Rudolph, M.; Pollmann, K.
The consumption of metallic raw materials increased in the last years. The coverage of demand is getting more difficult, because both primary and secondary raw materials become more and more complex. To find a solution, some new ways have to be gone, like the combination of biotechnology with classic processing methods.
The idea of this work is the biotechnological production of siderophores for the application in the classic froth flotation process. Siderophores are small organic molecules with a high affinity for binding Fe(III) and to form strong complexes also with other metals. They are produced by microorganisms (aerobic bacteria and fungi) and some plants to equalize the low bioavailability of iron in their environment. Especially the group of amphiphilic siderophores are very interesting. The hydrophilic part, carrying hydroxamate groups, is responsible for the binding of the metals. Flotation agents produced by the chemical industry with the same functional groups have already been applied successfully in this processing method. It can be suggested siderophores carrying the same functional groups, also work well as collectors. The fatty acid tail, that is representing the hydrophobic part, gets in contact with the bubble and spares additional chemicals and further working steps for making the target mineral particles hydrophobic.
This work includes on the one hand the biotechnological production of the marine siderophore marinobactin for the first time using a bioreactor and optimized conditions to make the production more efficient. On the other hand, the produced siderophore is tested in different froth flotation micro scale experiments like “Bubble-pick-up-test” and micro flotation in the Halimond Tube. These results show for the first time that amphiphilic siderophores are working in the froth flotation process and supply first concepts about the required concentration of siderophores in this processing process. In addition, the results also include interaction studies of different metals.
The application of amphiphilic siderophores as biochemicals in the froth flotation process can change the classic processing method in a more sustainable process – the bioflotation process. This will reduce the usage of other chemical agents. Moreover the specific metal binding of siderophores changes flotation in a more purposeful and efficient process.
Keywords: Bioflotation, Flotation, Siderophore, Marinobactin
  • Lecture (Conference)
    Applied Biotechnology in Mining, 25.-27.04.2018, Dnipro, Ukraine

Publ.-Id: 27577 - Permalink

Re-irradiation of recurrent gliomas: pooled analysis and validation of an established prognostic score-report of the Radiation Oncology Group (ROG) of the German Cancer Consortium (DKTK)
Combs, S.; Niyazi, M.; Adeberg, S.; Bougatf, N.; Kaul, D.; Fleischmann, D.; Gruen, A.; Fokas, E.; Rodel, C.; Eckert, F.; Paulsen, F.; Oehlke, O.; Grosu, A.; Seidlitz, A.; Lattermann, A.; Krause, M.; Baumann, M.; Guberina, M.; Stuschke, M.; Budach, V.; Belka, C.; Debus, J.; Kessel, K.
The heterogeneity of high-grade glioma recurrences remains an ongoing challenge for the interdisciplinary neurooncology team. Response to re-irradiation (re-RT) is heterogeneous, and survival data depend on prognostic factors such as tumor volume, primary histology, age, the possibility of reresection, or time between primary diagnosis and initial RT and re-RT. in the present pooled analysis, we gathered data from radiooncology centers of the DKTK Consortium and used it to validate the established prognostic score by Combs et al. and its modification by Kessel et al. Data consisted of a large independent, multicenter cohort of 565 high-grade glioma patients treated with re-RT from 1997 to 2016 and a median dose of 36 Gy. Primary RT was between 1986 and 2015 with a median dose of 60 Gy. Median age was 54 years; median follow-up was 7.1 months. Median OS after re-RT was 7.5, 9.5, and 13.8 months for WHO IV, III, and I/II gliomas, respectively. All six prognostic factors were tested for their significance on OS. Aside from the time from primary RT to re-RT (P = 0.074) and the reresection status (P = 0.101), all factors (primary histology, age, KPS, and tumor volume) were significant. Both the original and new score showed a highly significant influence on survival with P < 0.001. Both prognostic scores successfully predict survival after re-RT and can easily be applied in the routine clinical workflow. Now, further prognostic features need to be found to even improve treatment decisions regarding neurooncological interventions for recurrent glioma patients.
Keywords: Outcome, prognostic score, recurrent glioma, re-irradiation

Publ.-Id: 27576 - Permalink

Atomic scale reversible opto-structural switching of few atom luminescent silver clusters confined in LTA zeolites
Aghakhani, S.; Grandjean, D.; Baekelant, W.; Coutiño-Gonzalez, E.; Fron, E.; Kvashnina, K.; Roeffaers, M. B. J.; Hofkens, J.; Lievens, B. F.; Sels, P.
Luminescent silver clusters (AgCLs) stabilized inside partially Ag exchanged Na LTA zeolites show a remarkable reversible on–off switching of their green-yellowish luminescence that is easily tuned by a hydration and dehydration cycle, making them very promising materials for sensing applications. We have used a unique combination of photoluminescence (PL), UV-visible-NIR Diffuse Reflectance (DRS), X-ray absorption fine structure (XAFS), Fourier Transform-Infrared (FTIR) and electron spin resonance (ESR) spectroscopies to unravel the atomic-scale structural changes responsible for the reversible optical behavior of the confined AgCLs in LTA zeolites. Water coordinated, diamagnetic, tetrahedral AgCLs [Ag4(H2O)4]2+ with Ag atoms positioned along the axis of the sodalite six-membered rings are at the origin of the broad and intense green-yellowish luminescence in the hydrated sample. Upon dehydration, the luminescent [Ag4(H2O)4]2+ clusters are transformed into non-luminescent (dark), diamagnetic, octahedral AgCLs [Ag6(OF)14]2+ with Ag atoms interacting strongly with zeolite framework oxygen (OF) of the sodalite four-membered rings. This highly responsive on–off switching reveals that besides quantum confinement and molecular-size, coordinated water and framework oxygen ligands strongly affect the organization of AgCLs valence electrons and play a crucial role in the opto-structural properties of AgCLs.


  • Secondary publication expected from 04.06.2019

Publ.-Id: 27571 - Permalink

Flow Structures in a Weakly Turbulent Rayleigh-Bénard Convection affected by a Horizontal Magnetic Field
Vogt, T.; Yanagisawa, T.; Ishimi, W.; Tasaka, Y.; Eckert, S.
MHD Rayleigh-Bénard convection was studied experimentally using the eutectic metal alloy GaInSn inside a box having a square horizontal cross section and an aspect ratio of 5. Flow measurements were performed by means of ultrasound Doppler velocimetry that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field [1], [2]. If the Rayleigh number (Ra) is increased over a certain threshold Ra/Q, whereby Q is the Chandrasekhar number, the flow undergoes a transition to turbulence. Besides the primary convection rolls the measurements reveal regular flow oscillations arising from 2D and 3D deformations of the rolls, Ekman-pumping induced flow as well as smaller side vortices that develop around the convection rolls [3]. Our findings demonstrate the importance to take 3D flow effects into account in order to explain the observed flow structures, which are often considered as quasi 2D. The comparison between the experiments and accompanying direct numerical simulations shows a very good agreement.
  • Lecture (Conference)
  • Open Access LogoContribution to proceedings

Publ.-Id: 27570 - Permalink

Large-scale circulations of turbulent Rayleigh-Bénard convection in a finite liquid metal layer
Akashi, M.; Tasaka, Y.; Yanagisawa, T.; Vogt, T.; Murai, Y.; Eckert, S.
Large-scale circulations of Rayleigh-Bénard convection in a finite liquid metal layer were examined experimentally by means of ultrasonic Doppler velocimetry. The fluid layer with aspect ratio of five and L = 40 mm in height was filled with eutectic alloy of GaInSn (Prandtl number, Pr = 0.03), and multiple ultrasonic transducers for the velocimetry were mounted in the side wall of the vessel to capture 3D structures of the convection.
  • Lecture (Conference)

Publ.-Id: 27569 - Permalink

LSC Oscillations in a Liquid Metal
Vogt, T.; Horn, S.; Grannan, A.; Aurnou, J.
We present experimental results of liquid metal Rayleigh Bénard convection in a Gamma = D/H = 2 cylindrical tank. The tank is filled with liquid gallium that has a Prandtl-number Pr = 0.03. Ultrasound Doppler velocimetry is used in this study to measure the instantaneous velocity distribution along four different measuring lines. This technique is a useful tool to measure the velocities in opaque fluids, such as liquid metals non-invasively. Furthermore, a total number of 29 thermocouples is used to monitor the temperature in the experiment. Thus, the experimental set-up allows for a simultaneous analysis of the velocity and temperature field. We observed a strong oscillatory behaviour of the LSC in both, the velocity and temperature signal whose characteristic behaviour remains unchanged over the investigated range of 7x10^4 < Ra < 6x10^6. We analysed the three dimensional structure of the oscillation and compare the results to direct numerical simulation, which are in excellent agreement to the experimental observation.
  • Lecture (Conference)
  • Open Access LogoContribution to proceedings

Publ.-Id: 27568 - Permalink

Architecture and mineral potential of the Paleoproterozoic Karrat Group, West Greenland - Results of the 2017 Season
Rosa, D.; Bernstein, S.; Dewolfe, M. Y.; Dziggel, A.; Grocott, J.; Guarnieri, P.; Kolb, J.; Partin, C. A.; Sørensen, E.-V.; Zimmermann, R.
The main goal of the 2017 field season was to revise the geological maps of the southern area of Karrat Group exposures. This revision will encompass the 1:100 000 sheets of Maarmorilik 71V.2 Syd, Nuugaatsiaq 71V.2 Nord, Pannertooq 72V.2 Syd, and Svartenhuk 71V.1 Nord, originally compiled between 1980 and 1991. This third field season followed up on fieldwork carried out in 2015 and 2016 and, as the other two field seasons, was jointly financed by the Geological Survey of Denmark and Greenland (GEUS) and the Ministry of Mineral Resources of Greenland (MMR).
Within this framework, and since the focus of the first two seasons had been on the Paleo- proterozoic Karrat Group, the 2017 fieldwork targeted Archean rocks, namely in Panner- tooq (head of Ukkusissat Fjord), Upernivik Ø, Kigarsima/Tornit and the area south of Maarmorilik. This work led to the identification, in what was originally mapped as Archean orthogneiss, of significant paragneiss and quartzite sequences, of uncertain age. These supracrustal sequences often appear infolded with Archean orthogneiss, so some of them could possibly be unrelated to the stratigraphy of the Karrat Group. Similar infolding ob- served in the Qeqertarssuaq Formation, mapped in Kangilleq Fjord, suggests that this for- mation could possibly also be unrelated to the Karrat Group, as traditionally defined. Cor- roborating this interpretation is the fact that higher-P metamorphic assemblages, evi- denced by garnet amphibolite and kyanite micaschist, were documented in the Qeqertars- suaq Formation, but not in overlying formations. This contrasting metamorphic evolution can be interpreted as evidence for an early thermal event, prior to Qaarsukassak Formation deposition. Alternatively, the disparate metamorphic conditions could be accounted for by juxtaposition of different tectonic units during the Rinkian orogeny. T o further constrain the depositional ages of the paragneiss and quartzite (including those of the Qeqertarssuaq Formation), follow up detrital zircon geochronology is warranted. However, regardless of what the subsequent analytical work reveals, these findings appear to already imply signifi- cant revisions to the existing maps.
Within the Paleoproterozoic volcano-sedimentary succession, fieldwork allowed for the identification of the presence of the Qaarsukassak Formation (informal) in Kussinersuaq (Umiammakku Isbræ), Rinks Isbræ, Qingaarssuaq (Kangerlussuaq Fjord), Kigarsima/T ornit (Kangerluarsuk Fjord) and Kangerluarsuup Sermia. This formation hosts the stratabound mineralisation in the Rio Tinto Zinc (RTZ) Discovery area (Kangerluarsuk Fjord), where it was first defined. While no primary Zn mineralisation was observed at the defined localities, with only faint zinc zap responses obtained at Kussinersuaq, and other localities not tested for mineralisation, these findings significantly stretch the areal extent of the stratabound Zn- hosting Qaarsukassak Formation, and are therefore of economic significance. Detailed follow up photogeological mapping and interpretation of hyperspectral scenes of this min- eralisation host should consequently be carried out. Further work within the Paleoprotero- zoic Karrat Group, included the study of the mafic volcanic rocks of the Kangilleq Fm (in- formal), was aimed at recognising horizons with distinct geochemical signatures (alkaline vs. subalkaline), as identified in samples collected in previous seasons, in order to elucidate petrogenesis of the volcanic rocks.
The structural setting and metamorphism of the Prøven Igneous Complex (PIC) is key to understanding the geological evolution of the region and its lower contacts and some internal structures were studied. This work demonstrated that the PIC comprises one or more tabular intrusions. In the west, near Upernavik, the complex was emplaced close to the basement-cover contact. Farther to the east and south, it seems to have been emplaced at a higher stratigraphic position within the Paleoproterozoic sedimentary sequence. Subse- quently, the complex was displaced to the NW (north side of the PIC) and SE (south side of the PIC). Wherever it was studied, both North and South, this contact is a shear zone. The PIC contains abundant enclaves of meta-sedimentary rocks, particularly near the lower contact. The enclaves are most likely to be from a Paleoproterozoic sequence - the Karrat Group - although this assumption is unproven. In the instances where possible cross- cutting intrusive relations are found with meta-sedimentary rocks at the base of the PIC, the cross-cutting igneous rocks are late syn-tectonic biotite granite and leucogranites, rather than elements of the PIC proper. Earlier workers assumed that these late syn-tectonic granites and the PIC were part of the same magmatic event and were both late syn- tectonic. Our new field evidence from the northern contact of the PIC, consistent with re- cently published geochronology (Sanborn-Barrie et al. 2017), shows that the PIC was af- fected by intense fabric formation and folding and that its contacts with its host rocks, where we have seen them, are always concordant as a consequence of intense defor- mation. We conclude that the published interpretation that the PIC was emplaced relatively late during Rinkian orogenic evolution should be rejected (Grocott & Pulvertaft, 1990 and references therein).
  • Other report
    København, Danmark: Danmarks of Grønlands geologiske undersøgelse, 2018
    102 Seiten

Publ.-Id: 27564 - Permalink

Parametric resonances in periodically perturbed dynamo models
Giesecke, A.; Stefani, F.
I present results on kinematic dynsamo models driven by an axisymmetric large scale flow impacted by periodic perturbations due to azimuthally propagating vortices. I found a strong impact on growth rates and frequencies with regimes of parametric resonances whenn the frequency of the perturbation is twice the frequency of the unperturbed case. These models behave similar to rotating mechanical systems subject to periodic distortions that are described by the Matthieu equation. A possible application are dynamo experiments like VKS dynamo in Cadarache or convection driven planetary dynamos that are influenced by tidal forces.
Keywords: dynamo DRESDYN
  • Lecture (Conference)
    Planetary-Stellar Connection: The Sun's Lesson, 07.-09.05.2018, Freiburg, Deutschland

Publ.-Id: 27559 - Permalink

Local structural effects of Eu3+ incorporation into xenotime-type solid solutions with different host cations
Xiao, B.; Lösch, H.; Huittinen, N.ORC; Schmidt, M.ORC
In this study, the effect of host cations on the local structure around the dopant site of materials from the xenotime family is systematically studied on the molecular level. A series of six Eu3+-doped xenotime-type single crystals (Tb, Y, Ho, Er Yb, and LuPO4) have been grown and spectroscopically analyzed using polarization−dependent laser−induced luminescence spectroscopy (p−TRLFS). Our results demonstrate that the structural disorder changes in a non-linear manner with a structural break between Yb3+ and Lu3+. Despite adopting identical crystal structures, the solid solutions of these materials vary significantly, and differ from monazite solid solutions. Similar Eu3+ incorporation behavior with a strongly distorted dopant site is found for the early members of the xenotime family, while LuPO4 with the largest host vs. dopant radii mismatch is anomalous in that it contains the most symmetrical lattice site. This goes along with a significantly stronger crystal field, indicating a shorter Eu – O bond distance, as well as a strong vibronic coupling to external translational lattice vibrations. The p−TRLFS analysis confirms the breakdown of the crystallographic site symmetry from D2d to C1 in YPO4, whereas a small distortion of the crystallographic site in LuPO4 results in an S4 point symmetry for the Eu3+ cation. The lattice with the smallest cation host site is no longer sufficiently flexible to make room for Eu3+ and instead “forces” the guest ion to occupy a less distorted Lu3+ site.
Keywords: Xenotime, Incorporation, TRLFS, Luminescence, Eu3+

Publ.-Id: 27557 - Permalink

Temporal Evolution of Calcite Surface Dissolution Kinetics
Bibi, I.; Arvidson, R. S.; Fischer, C.; Luttge, A.
This brief paper presents a rare dataset: a set of quantitative, topographic measurements of a dissolving calcite crystal over a relatively large and fixed field of view (~400 μm) and long total reaction time (>6h). Using a vertical scanning interferometer and patented fluid flow cell, surface height maps of a dissolving calcite crystal were produced by periodically and repetitively removing reactant fluid, rapidly acquiring a height dataset, and returning the sample to a wetted, reacting state. These reaction-measurement cycles were accomplished without changing the crystal surface position relative to the instrument’s optic axis, with an approximate frequency of one data acquisition per six minutes’ reaction (~10/h). In the standard fashion, computed differences in surface height over time yield a detailed velocity map of the retreating surface as a function of time. This dataset thus constitutes a near-continuous record of reaction, and can be used to both understand the relationship between changes in the overall dissolution rate of the surface and the morphology of the surface itself, particularly the relationship of a) large, persistent features (e.g., etch pits related to screw dislocations; b) small, short-lived features (e.g., so-called pancake pits probably related to point defects); c) complex features that reflect organization on a large scale over a long period of time (i.e., coalescent “super” steps), to surface normal retreat and stepwave formation. Although roughly similar in frequency of observation to anin situ AFM fluid cell, this VSI method reveals details of the interaction of surface features over a significantly larger scale, yielding insight into the role of various components in terms of their contribution to the cumulative dissolution rate as a function of space and time.

Publ.-Id: 27556 - Permalink

Self-Diffusion in Amorphous Silicon by Local Bond Rearrangements
Kirschbaum, J.; Teuber, T.; Donner, A.; Radek, M.; Bougeard, D.; Lundsgaard Hansen, J.; Nylandsted Larsen, A.; Posselt, M.; Bracht, H.; Böttger, R.
Experiments on self-diffusion in amorphous silicon (Si) were performed at temperatures between 460 to 600° C. The amorphous structure was prepared by Si ion implantation of single crystalline Si isotope multilayers epitaxially grown on a silicon-on-insulator wafer. The Si isotope profiles before and after annealing were determined by means of secondary ion mass spectrometry. Isothermal diffusion experiments reveal that structural relaxation does not cause any significant intermixing of the isotope interfaces whereas self-diffusion is significant before the structure recrystallizes. The temperature dependence of self-diffusion is described by an Arrhenius law with an activation enthalpy Q =2.70 +- 0.11eV and preexponential factor D0=5.5(+11.1 -3.7) × 10−2 cm2 s−1. Remarkably, Q equals the activation enthalpy of hydrogen diffusion in amorphous Si, the migration of bond defects determining boron diffusion, and the activation enthalpy of solid phase epitaxial recrystallization reported in the literature. This close agreement provides strong evidence that self-diffusion is mediated by local bond rearrangements rather than by the migration of extended defects as suggested by Strauß et al. (Phys. Rev. Lett. 116, 025901 (2016)).
Keywords: amorphous Si, self-diffusion, isotope multilayers

Publ.-Id: 27555 - Permalink

Design, validation and testing of new receiver coatings for concentrated solar power
Krause, M.; Heras, I.; Lungwitz, F.; Wenisch, R.; Schumann, E.; Janke, D.; Guillén, E.; Munnik, F.; Azkona, I.; Gemming, S.; Escobar-Galindo, R.
Increasing central receiver solar plant’s operation temperature from 550°C to about 800°C would improve the energy conversion efficiency by 15 to 20%. Absorber coatings appropriate for such conditions have to outperform the state-of-the-art pigment paint Pyromark® that has an absorptivity α > 95% but a high emittance (ε ~ 80%). The development of environmentally stable solar-selective coatings (SSC) for these temperatures requires new concepts of design and thermal testing. Multilayer SSC based on [AlyTi1-y(OxN1-x)] absorbers were designed after an extensive microstructural characterization and optical simulations. Based on excellent simulation performance values of α = 88-94% and εRT = 4.8-13.6%, complete coating stacks were experimentally validated and tested in vacuum and in air up to temperatures of 800°C [1]. Thermal stability in vacuum up to 800°C is shown by in situ Rutherford backscattering spectrometry (RBS), Raman spectroscopy and spectroscopic ellipsometry (SE) for individual layers as well as for complete SSC. Regarding in-air stability, the most stable SSC fulfilled the standard performance criterion PC ≤ 5% for 300 symmetric, 3 hours long cyclic tests between 300°C and 600°C. Another promising and simpler coating concept to be presented is based on a metal-doped transparent conductive oxide acting as solar-selective transmitter on top of a blackbody. The onset of the infrared reflectivity is tuneable by variation of the parameters during reactive magnetron sputtering deposition, thus matching the specific temperature requirements during solar applications. Thermal stability up to 800°C in vacuum is demonstrated by in situ RBS and SE.

Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.

[1] I. Heras, et al. , Design of high-temperature solar-selective coatings based on aluminium titanium oxynitrides [AlyTi1-y(OxN1-x)]. Part 1: Advanced microstructural characterisation and optical simulation. Solar Energy Materials and Solar Cells 176 (2018) 81-92
Keywords: Solar selective coatings, oxynitrides, TCO's, thermosolar energy, in situ analysis, cluster tool
  • Invited lecture (Conferences)
    5th European Conference in Nanofilms (ECNF), 20.-22.03.2018, Cranfield, United Kingdom

Publ.-Id: 27553 - Permalink

Percolated Si:SiO2 Nanocomposites: Oven- vs. Millisecond Laser-induced Crystallization of SiOx Thin Films
Schumann, E.; Hübner, R.; Grenzer, J.; Gemming, S.; Krause, M.ORC
Three-dimensional nanocomposite networks consisting of percolated Si nanowires in a SiOx matrix, Si:SiO2, were studied. The structures were obtained by reactive ion beam sputter deposition of SiOx (x~0.6) thin films at 450 °C and subsequent crystallization using conventional oven as well as millisecond line focus laser annealing. Rutherford backscattering spectrometry, Raman spectroscopy, X-ray diffraction, cross-sectional and energy-filtered transmission electron microscopy were applied for sample characterization. While oven annealing resulted in a mean Si wire diameter of 10 nm and a crystallinity of 72 % within the Si volume, almost single-domain Si structures with 30 nm in diameter and almost free of amorphous Si were obtained by millisecond laser application. The structural differences are attributed to the different crystallization processes: Conventional oven tempering proceeds via solid state, millisecond laser application via liquid phase crystallization of Si. The 5 orders of magnitude larger diffusion constant in the liquid phase is responsible for the three times larger Si nanostructure diameter. In conclusion, laser annealing offers not only significantly shorter process times but moreover a superior structural order of nano-Si compared to conventional heating.
Keywords: silicon; nanostructures; percolated networks; nanocomposites; thin films; laser processing; phase separation; liquid phase crystallization

Publ.-Id: 27552 - Permalink

Synthesis and radiofluorination of a novel monocarboxylate transporter 1 inhibitor for tumor imaging by PET
Sadeghzadeh, M.; Moldovan, R.-P.; Wenzel, B.; Fischer, S.; Teodoro, R.; Ludwig, F.-A.; Gurrapu, S.; Drewes, L. R.; Brust, P.
Monocarboxylate transporter 1 (MCT1) is an integral plasma membrane protein that bi-directionally transports lactate and ketone bodies and is highly expressed in non-hypoxic regions of human colon, brain, breast, lung and other tumors. Accordingly, MCT1 inhibitors are regarded to be of potential clinical use. In the current study we developed a new 18F-labeled radioligand for in vivo imaging of MCT1-overexpressing brain tumors by PET.
A new fluorinated analogue of α-cyano-4-hydroxycinnamic acid (RM231) was synthesized from m-anisidine via alkylation, ortho formylation and Knoevenagel condensation in 50% overall yield. Its MCT1 inhibition activity was evaluated via [14C]lactate uptake assay on rat brain endothelial 4 cells. The mesylated precursor was similarly prepared in 52% overall yield. Radiosynthesis of [18F]RM231 was achieved by a two-step reaction, starting with the radiofluorination using [18F]-K2CO3-K222 complex followed by protective group removal via hydrolysis under optimized reaction conditions.
RM231 showed relatively high MCT1 inhibition activity (IC50 = 12 nM). The radiolabeled intermediate was obtained by an optimized procedure (acetonitrile, 5.5 mg of K222, 0.7 mg of K2CO3, 12-15 GBq of K18F, 100 ̊C, 8 min) with 44-50% yield determined by radio-HPLC analysis (N=3, non-isolated). The final product was obtained by hydrolysis with TFA in dry dichloromethane at room temperature for 10 minutes with 29% yield (radio-HPLC, non-isolated).[18F]RM231 could be obtained after separation using semi-preparative HPLC (RP C18 column; 30% ACN, 20 mM NH4CO2H). Currently, attempts are made to stabilize and formulate the final product appropriately for biological investigation. The newly developed MCT1 radioligand is anticipated to be a useful agent for imaging of the tumors with PET. Accordingly, animal studies on the new radiotracer are currently under investigation.
Keywords: Monocarboxylate transporter 1, α-Cyanocinnamic acid derivatives, Radiofluorination, Fluorine-18, Brain tumors.
  • Lecture (Conference)
    18th Radiochemical Conference, 13.-18.05.2018, Mariánské Lázně, Czeck Republic

Publ.-Id: 27549 - Permalink

Erratum: Three new low-energy resonances in the 22Ne(p,γ)23Na reaction
Cavanna, F.; Depalo, R.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Böltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Prati, P.; Scott, D. A.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.
Reported strengths of newly discovered resonances in [F. Cavanna et al., Phys. Rev. Lett. 115, 252501 (2015)] were affected by an error in the analysis. The energy straggling of the ion beam was erroneously neglected. When taking this effect into account, 18-19% higher values are found for the resonance strengths. The astrophysical implications are unchanged.

Publ.-Id: 27547 - Permalink

Inductive System for Reliable Magnesium Level Detection in a Titanium Reduction Reactor
Krauter, N.; Eckert, S.; Gundrum, T.; Stefani, F.; Wondrak, T.; Frick, P.; Khalilov, R.; Teimurazov, A.
The determination of the Magnesium level in a Titanium reduction retort by inductive methods is often hampered by the formation of Titanium sponge rings which disturb the propagation of electromagnetic signals between excitation and receiver coils. We present a new method for the reliable identification of the Magnesium level which explicitly takes into account the presence of sponge rings with unknown geometry and conductivity. The inverse problem is solved by a look-up-table method, based on the solution of the inductive forward problems for several tens of thousands parameter combinations.
Keywords: titanium, Kroll process, level detection, inductive measurements


Publ.-Id: 27532 - Permalink

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