Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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35836 Publications

Test of Compton camera components for prompt gamma imaging at the ELBE bremsstrahlung beam

Hueso-González, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Heidel, K.; Kormoll, T.; Rohling, H.; Schöne, S.; Schwengner, R.; Wagner, A.; Pausch, G.

In the context of ion beam therapy, particle range verification is a major challenge for the quality assurance of the treatment. One approach is the measurement of the prompt gamma rays resulting from the tissue irradiation. A Compton camera based on several position sensitive gamma ray detectors, together with an imaging algorithm, is expected to reconstruct the prompt gamma ray emission density map, which is correlated with the dose distribution. At OncoRay and Helmholtz-Zentrum Dresden-Rossendorf (HZDR), a Compton camera setup is being developed consisting of two scatter planes: two CdZnTe (CZT) cross strip detectors, and an absorber consisting of one Lu2SiO5 (LSO) block detector. The data acquisition is based on VME electronics and handled by software developed on the ROOT framework.

The setup has been tested at the linear electron accelerator ELBE at HZDR, which is used in this experiment to produce bunched bremsstrahlung photons with up to 12.5 MeV energy and a repetition rate of 13 MHz. Their spectrum has similarities with the shape expected from prompt gamma rays in the clinical environment, and the flux is also bunched with the accelerator frequency.

The charge sharing effect of the CZT detector is studied qualitatively for different energy ranges. The LSO detector pixel discrimination resolution is analyzed and it shows a trend to improve for high energy depositions.

The time correlation between the pulsed prompt photons and the measured detector signals, to be used for background suppression, exhibits a time resolution of 3 ns FWHM for the CZT detector and of 2 ns for the LSO detector. A time walk correction and pixel-wise calibration is applied for the LSO detector, whose resolution improves up to 630 ps. In conclusion, the detector setup is suitable for time-resolved background suppression in pulsed clinical particle accelerators. Ongoing tasks are the quantitative comparison with simulations and the test of imaging algorithms. Experiments at proton accelerators have also been performed and are currently under analysis.

Keywords: Compton imaging; Instrumentation for hadron therapy

Publ.-Id: 20471

S-layer proteins as an immobilization matrix for aptamers on different sensor surfaces

Weinert, U.; Vogel, M.; Reinemann, C.; Strehlitz, B.; Pollmann, K.; Raff, J.

In this work, S-layer proteins were used as an immobilization matrix to link aptamers on different solid supports. In nature, S layers operate amongst others as an immobilization matrix for exoenzymes. Consequently, they provide a biocompatible environment with different kinds of chemical groups perfect for the sequential coupling of any kind of biofunctional molecules. In addition, their nanostructure ensures a regular arrangement of these biomolecules. In biosensors, different biological recognition molecules are used. In this study, aptamers were chosen as bio-receptors. Aptamers are oligonucleotide ligands that are especially selected for high-affinity binding to target molecules. Because of their small size and stability, they exhibit a high potential as biological sensing molecules. By coupling aptamers to different surfaces or combining them with other biofunctional molecules, target binding can be detected for example optically or gravimetrically. In this work, a thrombin-binding aptamer and an ofloxacin-binding aptamer were immobilized by different chemical crosslinkers to surfaces modified with S-layer proteins. To verify the functionality of immobilized aptamers, the aptamer-target-binding was proven by Laser Induced Fluorescence Spectroscopy (LIFS), a Resonant Mirror Sensor (IAsys) and a Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D), respectively. Due to their properties of building up a physiological environment on their surface, their high content of modifiable functional groups on their surface and their ability to crystallize in a nanometer thick monolayer on surfaces, S-layer proteins are suitable as biotemplates for various recognition biomolecules like enzymes, antibodies and aptamers. Hence, this paper presents with S-layer proteins an interesting alternative to existing immobilization matrices for recognition biomolecules.

Keywords: S-layer; aptamer; QCM-D; Resonant mirror sensor; LIFS

Publ.-Id: 20470

The nature of chemical bonding in actinide and lanthanide ferrocyanides determined by X-ray absorption spectroscopy and density functional theory

Dumas, T.; Guillaumont, D.; Fillaux, C.; Scheinost, A.; Moisy, P.; Petit, S.; Shuh, D. K.; Tyliszczak, T.; Den Auwer, C.

The electronic properties of actinide cations are of fundamental interest to describe intramolecular interactions and chemical bonding in the context of nuclear waste reprocessing or direct storage. The 5f and 6d orbitals are the first partially or totally vacant states in these elements, and the nature of the actinide ligand bonds is related to their ability to overlap with ligand orbitals. Because of its chemical and orbital selectivities, X-ray absorption spectroscopy (XAS) is an effective probe of actinide species frontier orbitals and for understanding actinide cation reactivity toward chelating ligands. The soft X-ray probes of the light elements provide better resolution than actinide L3-edges to obtain electronic information from the ligand. Thus coupling simulations to experimental soft X-ray spectral measurements and complementary quantum chemical calculations yields quantitative information on chemical bonding. In this study, soft X-ray XAS at the K-edges of C and N, and the L2,3-edges of Fe was used to investigate the electronic structures of the well-known ferrocyanide complexes K4FeII(CN)6, thorium hexacyanoferrate ThIVFeII(CN)6, and neodymium hexacyanoferrate KNdIIIFeII(CN)6. The soft X-ray spectra were simulated based on quantum chemical calculations. Our results highlight the orbital overlapping effects and atomic effective charges in the FeII(CN)6 building block. In addition to providing a detailed description of the electronic structure of the ferrocyanide complex (K4FeII(CN)6), the results strongly contribute to confirming the actinide 5f and 6d orbital oddity in comparison to lanthanide 4f and 5d.

Keywords: XANES; DFT

  • Physical Chemistry Chemical Physics 18(2016), 2887-2895
    Online First (2016) DOI: 10.1039/C5CP05820A

Publ.-Id: 20469

Spectral History Modeling in the Reactor Dynamics Code DYN3D

Bilodid, Y.

A new method of treating spectral history effects in reactor core calculations was developed and verified in this dissertation. The nature of history effects is a dependence of fuel properties not only on the burnup, but also on the local spectral conditions during burnup. The basic idea of the proposed method is the use of the plutonium-239 concentration as the spectral history indicator. The method was implemented in the reactor dynamics code DYN3D and provides a correction for nodal cross sections according to the local spectral history.
A verification of the new method was performed by single-assembly calculations in comparison with results of the lattice code HELIOS. The application of plutonium-based history correction significantly improves the cross section estimation accuracy both for UOX and MOX fuel, with quadratic and hexagonal geometry.
The new method was applied to evaluate the influence of history effects on full-core calculation results. Analysis of a PWR equilibrium fuel cycle has shown a significant effect on the axial power distribution during a whole cycle, which causes axial temperature and burnup redistributions. The observed neutron flux redistribution improves neutron economy, so the fuel cycle is longer than in calculations without history corrections. Analyses of hypothetical control rod ejection accidents have shown a minor influence of history effects on the transient course and safety relevant parameters.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-051 2014
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 20468

Time-resolved laser-fluorescence spectroscopy (TRLFS) – A spectroscopic tool to investigate f-element interactions in solids and solutions on the molecular level

Huittinen, N.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Baumann, N.; Stumpf, T.

Time-resolved laser-fluorescence spectroscopy (TRLFS) is a spectroscopic technique with outstanding sensitivity, based on the spontaneous emission of light. Spontaneous emission of light or luminescence describes the process of radiative decay where an excited substance emits electromagnetic radiation upon relaxation. Some f-elements, such as the actinides U4+, and Cm3+, and the lanthanide Eu3+, relax through intense luminescence emission from an excited f-state to the ground f-level. These f-f transitions are sensitive to changes in the ligand field, thus, making TRLFS an extremely useful tool to account for the complex speciation of these elements. Depending on the f-element, the recorded emission spectra can provide information on e.g. the complexation mechanism of the ion on a solid surface or the symmetry of the adsorption/incorporation site of the metal. Information about the hydration state of the f-element cation can be gained from the fluorescence lifetime, i.e. the residence time in the excited state. In aquatic environments f-element spectroscopy is characterized by relatively short fluorescence lifetimes due to the transfer of electronic energy from an excited f-level to the vibrational levels of water molecules in the first coordination sphere of the metal. When some of these quenching entities are lost upon inner sphere surface complexation a longer lifetime is acquired, thus, providing information on the sorption mechanism. If incorporation occurs, the complete hydration sphere is replaced by the ligands of the crystal lattice and the lifetimes become very long.

In the present work we have used site-selective TRLFS to investigate the structural incorporation of Eu3+, as an analogue for Pu3+, Am3+ and Cm3+ found in spent nuclear fuel, in rare earth phosphate ceramics. These crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes due to their stability over geological time scales [1] and their tolerance to high radiation doses [2]. The REPO4 crystallize in two distinct structures, depending on the ionic radius of the cation: the larger lanthanides (La3+ to Gd3+) crystallize in the nine-fold coordinated monazite structure, the smaller ones as Lu3+ form eight-fold coordinated xenotime structures. Here, we present results on the influence of the ionic radius of the host cation and the crystalline structure of the REPO4 on Eu3+ substitution in the ceramic.

  • Poster
    8th European Summer School on supramolecular, intermolecular, interaggregate interactions and separation chemistry, 07.-09.07.2014, Bonn - Bad Godesberg, Deutschland

Publ.-Id: 20467

P1226 - Funktionalisierte Festkörperoberflächen aus Zwei- und Mehrstoffsystemen mit Komposit-Nanostrukturen aus Metallen, Halbleitern und Isolatoren

Schmidt, H.; Bürger, D.; Skorupa, I.

Die Erfindung betrifft funktionalisierte Festkörperoberflächen mit Kompositen aus Zwei- und Mehrstoffsystemen aus Metallen, Halbleitern und Isolatoren, welche eine definierte chemische Komposition auf der Nanometer und Mikrometer-Längenskala aufweisen für neuartige Komposit-Nano- und Mikrostrukturen.

  • Patent
    DE102012221409 - Offenlegung 22.05.2014

Publ.-Id: 20466

Magnetization states and magnetization processes in nanostructures: From a single layer to multilayers

Maziewski, A.; Fassbender, J.; Kisielewski, J.; Kisielewski, M.; Kurant, Z.; Mazalski, P.; Stobiecki, F.; Stupakiewicz, A.; Sveklo, I.; Tekielak, M.; Wawro, A.; Zablotskii, V.

The results of combined (experimental, analytical, and micromagnetic simulations) studies on the evolution of magnetization states and processes in ultrathin films and multilayered systems are presented. We show ways to manipulate magnetization distributions in ultrathin magnetic single or multilayers by tuning: the thickness of the magnetic layer, the thickness of either the non-magnetic cap or spacer layer, the magnetic anisotropy, and the geometrical constrictions of the system. In ultrathin magnetic films, both the magnetization distribution and the critical thickness of the magnetization reorientation phase transition (RPT) between perpendicular and in-plane states can be also controlled by post-growth treatments, e.g., by either ion or light irradiation. By changing the geometrical parameters of the nanostructure, as well as by an applied external magnetic field, one can tune magnetic domain sizes in a giant range (of a few orders of magnitude) and induce the RPT. Transitions between two- and three-dimensional magnetization distributions are discussed. The authors present possibilities of the engineering of magnetic properties (e.g. magnetic anisotropy and coercivity field) of nanostructures during deposition processes and post growth treatments, e.g. by ion irradiation and laser annealing. Magnetization distributions in single ultrathin layer and multilayers have been studied both experimentally (using Co films sandwiched between Au, Pt or Mo layers) and theoretically. These huge distribution changes, driven by nanostructure geometry or magnetic field, are shown.

Keywords: light and ions irradiation effects; magnetic anisotropy; magnetic domains; magnetic ordering; magnetic ultrathin films and multilayers

Publ.-Id: 20465

Study of growth kinetics and depth resolved composition of a-SiN x:H thin films by resonant soft X-ray reflectivity at the Si L 2,3-edge

Bommali, R. K.; Modi, M. H.; Zhou, S.; Ghosh, S.; Srivastava, P.

Angle dependent resonant soft X-ray reflectivity (R-SoXR) measurements in the energy range (82.67-206.7 eV) were performed on PECVD grown amorphous hydrogenated silicon nitride (a-SiNx:H) thin films of different compositions near the Si-L2,3 edge (∼100 eV). The compositional difference is reflected in the optical density (δ) of the two films. It is demonstrated that R-SoXR can non-destructively distinguish between the compositional variations through the depth of a given thin film, whereby it becomes possible to differentiate between the growth kinetics of the films prepared under different conditions. The compositions determined from R-SoXR, are in qualitative agreement with those determined from Rutherford back scattering (RBS) and elastic recoil detection analysis (ERDA).

Keywords: Optical constant; Reflectivity; Silicon nitride; Soft X-Ray; Thin film

Publ.-Id: 20464

Detecting Ferromagnetic Resonance of Single Nanostructures with the Microresonator

Banholzer, A.; Narkowicz, R.; Lenz, K.; Grebing, J.; Fassbender, J.; Lindner, J.

Nowadays the magnetic characterization of nanosized objects is of major interest, as they are used in the field of nanosized magnetic recording [1] and spintronic devices. With conventional resonance methods, e.g. in an X-band cavity, the minimum number of spins, which can be detected, is about 1012 for permalloy [2]. Therefore, only large arrays of small nanoobjects can be detected. Here, the specific characteristics of small nanoobjects disappear in the averaged signal [3]. Hence, for the analysis of single nanoobjects a much higher sensitivity is required.
We developed a microresonator to measure the ferromagnetic resonance (FMR) of single nanosized objects [4], [5]. We optimized the device for different sample sizes. We show that it is possible to measure FMR on a single Cobalt nanodot with a diameter of 139 nm and 25 nm thickness. Taking the signal-to-noise ratio into account, we extrapolate the detection limit to 105 spins. Not only the uniform excitation mode, but also signals of standing spinwaves like e.g. edgemodes can be observed. Their state can be visualized and interpreted with micromagnetic simulations (OOMMF) [6]. We show results of a variety of nanosized samples and their interpretation.

[1]C. T. Rettner, et. al., IEEE Trans. Magn., 38, 4 (2002).
[2] Poole, Electron Spin Resonance, New York: Wiley, (1983).
[3] J. M. Shaw,, J. Appl. Phys. 108, 093922 (2010).
[4] A. Banholzer, et al., Nanotechnology 22, 295713 (2011).
[5] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).

Keywords: ferromagnetic resonance; nanodot

  • Poster
    IEEE International Conference on Microwave Magnetics (ICMM), 29.06.-02.07.2014, Sendai, Japan

Publ.-Id: 20463

Influence of ionic strength on U(VI) sorption on montmorillonite at high salinities

Fritsch, K.; Schmeide, K.

Clay and clay minerals are potentially suitable as host rock for nuclear waste disposals due to their high sorption capacities and low permeability. In Germany, there are two types of clay that in principle are eligible to be used for the construction of deep geological disposals: South German Opalinus clay with low ionic strength pore waters and north German clay deposits with high ionic strength pore waters, e. g. with sodium chloride concentrations of up to 4 mol/l in the depths relevant for nuclear waste disposal. [1] The present work focuses on U(VI) sorption onto the clay mineral montmorillonite under high ionic strength conditions, with the Konrad mine serving as reference site for experimental conditions. The experiments are conducted in sodium and calcium chloride as well as in a mixed electrolyte that resembles the groundwater at the Konrad site.
The classic ionic strength effect, where sorption decreases with increasing ionic strength, can only be observed in the acidic pH range where cation exchange is the predominant sorption mechanism for U(VI). However, natural groundwaters at the Konrad site have pH values from 5.75 to 6.85, where the ionic strength has an already diminished influence on sorption. The sorption maxima for U(VI) in the different salt systems lie slightly below the neutral point and well within the pH range of groundwaters of the reference site. For high ionic strengths like those in north German groundwaters, U(VI) retention becomes partly irreversible. [2] Furthermore, in the calcium chloride system, U(VI) retention increases strongly with ionic strength in the alkaline pH range. Both these effects are attributed to secondary phase formation, which is promoted by increasing ionic strength.

[1] Brewitz, W. et al. (1982) Eignungsprüfung der Schachtanlage Konrad für die Endlagerung radioaktiver Abfälle. GSF-T 136.
[2] Zehlike, L. (2013) Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit, Bachelor thesis, TU Dresden.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength

  • Poster
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn-Bad Godesberg, Deutschland
  • Open Access Logo Contribution to proceedings
    8th European Summer School on Separation Chemistry and Conditioning as well as Supramolecular, Intermolecular, Interaggregate Interactions, 07.-09.07.2014, Bonn-Bad Godesberg, Deutschland
    Berichte des Forschungszentrums Jülich, Jül-4376, Institut für Energie- und Klimaforschung, Nukleare Entsorgung und Reaktorsicherheit (S. Neumeier, P. Kegler, D. Bosbach, eds.), 24

Publ.-Id: 20462

Montmorillonite as barrier material for uranium(VI) at high ionic strengths

Fritsch, K.; Schmeide, K.

Clay and clay minerals are potential host rocks for nuclear waste disposal due to their high sorption capacities and low permeability. Thus far, research of radionuclide retention by clays has been focused on low ionic strength systems. The present work addresses North German clay deposits whose groundwaters show ionic strengths up to 4 mol/l in depths relevant for nuclear waste disposal.[1] The experimental set-up is modelled on conditions found in the Konrad mine, which serves as reference site. Montmorillonite is used as model clay for uranium sorption and diffusion experiments in sodium and calcium chloride as well as in a mixed electrolyte that resembles the groundwater at the Konrad site.
Ionic strengths effects, where sorption decreases with increasing ionic strength, can generally only be observed in the acidic pH range because they depend on cation exchange. Natural groundwaters at the Konrad site have pH values > 5.5, where cation exchange has ceased to be the predominant sorption mechanism for U(VI), which in turn diminishes ionic strength influence. The sorption maxima in different salt systems lie slightly below the neutral point and within the pH range of groundwaters of the reference site. When approaching the ionic strength of North German groundwaters, sorption becomes partly irreversible.[2] Furthermore, uranium retention greatly increases with ionic strength in the alkaline pH range in the calcium chloride system. Both effects are attributed to secondary phase formation, which is promoted by increasing ionic strength. Additionally, spectroscopic results and surface complexation modelling of the system will be presented.
[1] Brewitz, W. et al. (1982) Eignungsprüfung der Schachtanlage Konrad für die Endlagerung radioaktiver Abfälle. GSF-T 136.
[2] Zehlike, L. (2013) Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit, Bachelor thesis, TU Dresden.

Keywords: uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength

  • Contribution to proceedings
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland
    Proceedings of the 7th Mid-European Clay Conference
  • Lecture (Conference)
    7th Mid-European Clay Conference, 16.-19.09.2014, Radebeul, Deutschland

Publ.-Id: 20461

Gamma-ray CT for multi-phase flow investigation

Bieberle, A.; Schäfer, T.; Hampel, H.

Recently, gamma-ray computed tomography (GCT) has been established at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) for the investigation of two- or multiphase flows in technical apparatuses. The GCT systems at HZDR are operated with collimated 137Cs isotopic sources emitting gamma photons with an energy of 662 keV. This gamma radiation is able to penetrate dense housings and delivers sufficient phase contrast between, e.g., liquid and gas. The radiation detector arcs consist of in-house developed gamma-ray detector modules based on scintillation detector technology. Special effort has been spent on their thermal design. With a thermal stabilisation of better than 1 K for each detector element, a high repeat measuring accuracy could be achieved for varying environmental temperatures within a temperature range of 20 K. A current project is engaged in gas phase distribution determination within industrial centrifugal pumps at various operating states. Because the application of those pumps is limited to single liquid phase flow, gas entrainment reduces its delivery performance as well as the process efficiency. For detailed studies, a thermo hydraulic test facility was assembled at HZDR replicating authentic operating conditions for industrial centrifugal pumps. Defined gas volume fractions can be injectect in form of two different flow regimes, disperse and tubular. Thus, effects onto delivery perfomance and corresponding gas fraction distribution and gas holdup within the impeller region could be determined.

Keywords: gamma-ray computed tomography; process efficiency; centrifugal pump; gas entrainment; multi-phase flow

  • Contribution to proceedings
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea
  • Lecture (Conference)
    5th International Workshop on Process Tomography (IWPT-5), 16.-18.09.2014, Jeju, Korea

Publ.-Id: 20460

Hydrogen accumulation in nanostructured as compared to coarse-grained tungsten

Gonzalez-Arrabal, R.; Panizo-Laiz, M.; Gordillo, N.; Tejado, E.; Munnik, F.; Rivera, A.; Perlado, J. M.

We report on the influence of sample microstructure and of irradiation conditions on the H behaviour in Tungsten (W). For this purpose, commercial coarse grained (CGW) and nanostructured W (NW) samples were implanted with (i) H at room temperature (RT), (ii) sequentially with C and H at RT, and (iii) simultaneously (co-implanted) with C and H at RT. To study the possible effect of implantation temperature on H behaviour, a CGW sample and a NW sample were sequentially implanted with C at RT and with H at 673 K. The H and C implantation fluence was 5×1020 cm−2 and the implantation energies were 160 keV for H and 650 keV for C which are above the displacement damage threshold. Scanning electron microscopy images show that nanostructured samples consist of columns with an average diameter of about 100 nm. These nanocolumns are stable under the studied implantations conditions. Moreover, blistering is absent in all studied samples. X-ray diffraction data illustrate that all samples are mono-phase (α-W phase) and that none of the implantations led to the appearance of secondary phases. Resonant nuclear reaction analysis data show that the H retention in NW samples is larger than in CGW and that synergistic effect has a significant influence on the H retention in CGW samples but not in NW samples.

Keywords: Nanostructured materials; radiation response; hydrogen behaviour; nuclear fusion

Publ.-Id: 20459

Advanced Materials in Extreme Environments

Bertolus, M.; Chichester, H.-M.; Edmondson, P.; Gao, F.; Posselt, M.; Stanek, C.; Trocellier, P.; Zhang, X.; (Editors)

Keywords: advanced materials; extreme environments

  • Contribution to proceedings
    MRS 2013 Fall Meeting, 01.-06.12.2013, Boston, USA

Publ.-Id: 20458

Nonlinear photoresponse of field effect transistors terahertz detectors at high irradiation intensities

But, D. B.; Drexler, C.; Sakhno, M. V.; Dyakonova, N.; Drachenko, O.; Sizov, F. F.; Gutin, A.; Ganichev, S. D.; Knap, W.

Terahertz power dependence of the photoresponse of field effect transistors, operating at frequencies from 0.1 to 3 THz for incident radiation power density up to 100 kW/cm(2) was studied for Si metal-oxide-semiconductor field-effect transistors and InGaAs high electron mobility transistors. The photoresponse increased linearly with increasing radiation intensity up to the kW/cm(2) range. Nonlinearity followed by saturation of the photoresponse was observed for all investigated field effect transistors for intensities above several kW/cm(2). The observed photoresponse nonlinearity is explained by nonlinearity and saturation of the transistor channel current. A theoretical model of terahertz field effect transistor photoresponse at high intensity was developed. The model explains quantitative experimental data both in linear and nonlinear regions. Our results show that dynamic range of field effect transistors is very high and can extend over more than six orders of magnitudes of power densities (from similar to 0.5 mW/cm(2) to similar to 5 kW/cm(2)).

Keywords: Tunneling ionization; Radiation; Fluid

Publ.-Id: 20457

Liquid metal batteries

Weier, T.; Barry, L.; Galindo, V.; Gerbeth, G.; Seilmayer, M.; Starace, M.; Stefani, F.; Weber, N.

Liquid metal batteries are discussed with a focus on the role of fluid dynamics in large-scale cells.

Keywords: Liquid metal batteries; magnetohydrodynamics; Tayler instability

  • Invited lecture (Conferences)
    IKM-Seminar, 04.06.2014, Dresden, Deutschland

Publ.-Id: 20456

Platinum-group element distribution in base-metal sulfides of the UG2, Bushveld Complex, South Africa – a reconnaissance study

Osbahr, I.; Oberthür, T.; Klemd, R.; Josties, A.

The UG2 chromitite of the Bushveld Complex in South Africa contains the world’s largest resources of platinum-group elements (PGE). However, only limited work has been conducted on the distribution of PGE and platinum-group minerals (PGM) within the UG2. In the present study, earlier work on the PGE distribution within the Merensky Reef (Osbahr et al. 2013) is followed up and extended to the UG2. Two drill cores of the UG2 chromitite from the eastern and western Bushveld Complex were studied by whole rock analysis, ore microscopy and SEM/MLA. The PGE, Au and Ag contents of pentlandite, pyrrhotite and chalcopyrite were determined using LA-ICP-MS analysis. Whole-rock analyses of the two profiles reveal highest Pd and Pt concentrations at the top and at the base of the UG2 main seam. Sulfides mostly occur as aggregates of pentlandite, chalcopyrite and rare pyrrhotite and pyrite or as individual grains associated mostly with chromite grains.
In-situ LA-ICP-MS analyses reveal that pentlandite carries distinctly elevated PGE contents. In contrast, pyrrhotite and chalcopyrite contain very low PGE concentrations. Pentlandite shows average maximum values of 350-1000 ppm Pd, 200 ppm Rh, 130-175 ppm Ru, 20 ppm Os and 150 ppm Ir and therefore, is the principal host of Pd and Rh in the studied ores of the UG2.
Mass balance calculations were conducted for samples representing the UG2 main seam of the drill core DT46, eastern Bushveld. Accordingly, pentlandite constantly hosts elevated contents of the whole rock Pd (up to 55 %) and Rh (up to 46 %), and erratic contents of Os (up to 50 %), Ir (2 to 17 %) and Ru (1 - 39 %). PGM investigations support these mass balance results, most of the PGM are Pt-dominant PGM like braggite/cooperite and Pt-Fe alloys or laurite, (carrying elevated concentrations of Os and Ir). Palladium and Rh-bearing PGM are rare.
PGE concentrations and their distribution in BMS in the UG2 largely resemble that of the Merensky Reef, as most of the Pd and Rh are incorporated in pentlandite whereas pyrrhotite, chalcopyrite and pyrite are almost devoid of PGE. Consequently, similar mineralization processes are responsible for the PGE enrichment in the UG2 and in the Merensky Reef.

Keywords: platinum-group elements (PGE); UG2; Bushveld Complex; South Africa; LA-ICP-MS; MLA

Publ.-Id: 20455

Repeated large-magnitude earthquakes in a tectonically active, low-strain continental interior: The northern Tien Shan, Kyrgyzstan

Landgraf, A.; Dzhumabaeva, A.; Abdrakhmatov, K. E.; Strecker, M.; Macaulay, E. A.; Arrowsmith, J. R.; Sudhaus, H.; Preusser, F.; Rugel, G.; Merchel, S.

The northern Tien Shan of Kyrgyzstan and Kazakhstan has been affected by a series of major earthquakes in the late 19th and early 20th centuries. To assess the significance of such a major pulse of strain release in a continental interior, it is important to analyze and quantify strain release over multiple time scales. We have undertaken paleoseismological investigations at two geomorphically distinct sites (Panfilovkoe and Rot Front) near the Kyrgyz capital Bishkek. Although located near the historic epicenters, both sites were not affected by these earthquakes. Trenching was accompanied by dating stratigraphy and offset surfaces using luminescence, radiocarbon, and 10Be terrestrial cosmogenic nuclide methods. At Rot Front, trenching of a small scarp did not reveal evidence for surface rupture during the last five thousand years. The scarp rather resembles an extensive debris-flow lobe. At Panfilovkoe, we estimate a late Pleistocene minimum slip rate of 0.2 +- 0.1 mm/a, averaged over at least two, probably three earthquake cycles. Dip-slip motion along segmented, moderately steep faults resulted in hanging-wall collapse scarps during different events. The most recent earth quake occurred around 1.8 +- 0.2 kyr ago (1 sigma), with dip-slip off sets between 1.2 and 1.4 m. We calculate a probabilistic paleomagnitude to be between 6.7 and 7.1, which is in agreement with regional data from the Kyrgyz range. The morphotectonic signals in the northern Tien Shan are a prime example of deformation in a tectonically active intracontinental mountain belt and as such can help understand the longer-term co-evolution of topography and seismogenic processes in similar structural settings worldwide.

Keywords: earthquake; paleoseismic record; Tien Shan; Kyrgyzstan; TCN; accelerator mass spectrometry; cosmogenic nuclide

  • Journal of Geophysical Research - Solid Earth 121(2016), 3888-3910
    Online First (2016) DOI: 10.1002/2015JB012714

Publ.-Id: 20454

Actinide(IV) colloids at near-neutral pH due to reaction with dissolved silicic acid

Zänker, H.; Weiss, S.; Hennig, C.; Husar, R.

A new type of actinide(IV) colloids - silica-containing U(IV), Th(IV) and Np(IV) colloids formed in near-neutral solutions of background chemicals of geogenic nature (carbonate, silicic acid, Na+) - was studied. Whereas the radiocolloids hitherto addressed in the BELBaR project are formed by the adsorption of radionuclides onto pre-existing particles, the colloids here under discussion result from a reaction of dissolved actinide(IV), An(IV), with dissolved silicic acid. An-O-Si bonds, which increasingly replace the An-O-An bonds of the amorphous actinide(IV) oxyhydroxide with increasing silica concentration, make up the internal structure of these colloids. The particles remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) and a particle size of < 20 nm was observed. The question if such An(IV) colloids may contribute to the mobility of the actinides in the near-field or the far-field of a nuclear waste repository is discussed.

Keywords: Tetravalent actinides; silicic acid; silica; colloids; nanoparticle; nuclear waste repositories; BELBaR

  • Lecture (Conference)
    2nd Annual Workshop CP BELBaR (Bentonite erosion effects on the long term performance of the engineered barrier and radionuclide transport), 16.-18.06.2014, Meiringen, Schweiz

Publ.-Id: 20453

P1227 - Verfahren zur kostengünstigeren Herstellung von Silizium Solarzellen, und mit diesem Verfahren hergestellte Solarzellen

Prucnal, S.; Voelskow, M.; Skorupa, W.

Die Erfindung beschreibt ein einfaches und vor allem kostengünstiges und damit umweltverträgliches Verfahren zur Herstellung von Solarzellen auf der Basis von Silizium, basierend auf einem einzigen, kurzen Millisekunden-Ausheilschritt unter Verwendung der effektiven Plasma-Immersions-Ion-Implantations-Technologie (PIII). Dadurch wird der Energie- und Zeitaufwand und damit die Kosten zur Herstellung einer Silizium-Solarzelle drastisch reduziert werden.

  • Patent
    DE102012221811 - Offenlegung 28.05.2014

Publ.-Id: 20452

The influence of naturally occurring microorganisms on the sorption of uranium

Richter, C.

The influence of naturally occurring microorganisms on the sorption of uranium, the Institute of Resource Ecology and the WEIMAR-project were presented.

  • Lecture (others)
    LLNL intern seminar, 23.-24.06.2014, Livermore, USA

Publ.-Id: 20451

The Influence of Mineral-Originated Microorganisms on the Sorption of Uranium

Richter, C.; Großmann, K.; Brendler, V.

Experiments on commercially available quartz, orthoclase and muscovite showed the presence of microorganisms in these minerals. So the question arose, if and how these microbes affect the sorption of uranium onto them.

Experimental work
To promote the bacterial growth 0.2 g of the minerals were incubated with 10 ml of two different culture media (NB and R2A). Directly after adding the culture media and after three weeks shaking in an incubator at 30°C, the optical density at 600 nm (OD600) was measured.
To estimate the influence of the microorganisms on the uranium sorption, batch experiments were performed under conditions inhibiting growth, e.g. darkness, autoclaving; use of laminar flow boxes; or addition of sodium azide. The amount of uranium sorbed at pH 7 was determined by ICP-MS.

All three minerals show an increase in OD600 during incubation. This increase varies for the three minerals and two nutrients, pointing to different microbial communities.
The batch experiments indicate that the various treatments clearly affect the microbial influence on uranium sorption. In the case of orthoclase, the biggest change is induced by the sodium azide treatment. For quartz, the use of laminar flow boxes has the largest consequences. But in both cases the changes have the same direction: destroying the microbes also stops them actively suppressing uranium sorption. In case of muscovite, the combination of autoclaving, laminar flow box and darkness affects sorption the most – but in the opposite direction. Here, the microbes obviously enhance sorption (dead or alive).
This findings show that on the three investigated minerals different microorganisms are present, and that their effect is difficult to predict. Thus, a separate investigation of microbial effects is recommended for each mineral. In addition, any autoclaving may directly change the mineral surface, e.g. by creating new or altering existing sorption sites.

  • Poster
    Goldschmidt 2014, 09.-13.06.2014, Sacramento, USA

Publ.-Id: 20450

Euler-Euler Scale-Adaptive Simulation of a square cross-sectional bubble column

Ma, T.; Lucas, D.; Fröhlich, J.; Ziegenhein, T.

In this paper we present detailed Euler-Euler Scale-Adaptive Simulation (SAS) of dispersed bubbly flow in a square cross-sectioned bubble column. The main objective of this study is to investigate potential of this approach for the prediction of the bubbly flows with anisotropic liquid velocity fluctuations, in terms of mean quantities. The set of physical models describing the momentum exchange between the phases was chosen according to previous experiences of the authors. Experimental data, Euler-Euler Large Eddy Simulation (LES) are used for comparison. It was found that the presented modelling combination provides very good agreement with experimental data for the mean flow and liquid velocity fluctuations. The energy spectrum made from the resolved velocity from Euler-Euler SAS and LES is presented and discussed.

  • Contribution to proceedings
    10th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 17.-19.09.2014, Marbella, Spain
  • Lecture (Conference)
    10th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements, 17.-19.09.2014, Marbella, Spain
  • Chemical Engineering Science 131(2015), 101-108
    DOI: 10.1016/j.ces.2015.03.047

Publ.-Id: 20449

Euler-Euler Large Eddy Simulations for dispersed bubbly flows

Ma, T.; Ziegenhein, T.; Lucas, D.; Krepper, E.; Fröhlich, J.

A bubble column provides a good experimental system for the study of turbulent phenomena in bubbly flows. It has a wide range of length and time scales on which turbulent mixing takes place. The largest turbulence scales are comparable in size to the characteristic length of the mean flow and depend on reactor geometry and boundary conditions. The small scales depend more on the bubble dynamics and hence are proportional to the bubble diameter. In bubbly flows, the small scales are responsible for the dissipation of the turbulent kinetic energy as in single-phase flow, but the bubbles can also generate back-scatter, i.e. energy transfer from smaller to larger scales. The combination of the both effects and yields an overall enhancement or attenuation of the turbulence intensity.
In the present paper the effect of turbulence modelling is investigated. In the CFD simulations of bubble columns RANS models are used for turbulence modeling traditionally, but the turbulence is modeled only isotropic and without resolved turbulence length scales. Large Eddy Simulation (LES) offers the opportunity to resolve the large-scale anisotropic turbulence directly and to model the small scales with a Subgrid-Scale (SGS) model. The filtering is mostly based directly on the grid width.
In the present work, Euler – Euler modelling of bubbly flow is performed using two types of turbulence modelling, (unsteady) RANS and LES. The simulations are carried out for two rectangular bubble columns with different inlet designs, the ones of (Pfleger et al. 1999) and (Akbar et al. 2012) and compared with the respective experimental data and previous own results of URANS simulations. During all the calculations the bubble coalescence and breakup are neglected. For the Akbar experiment with a low gas superficial velocity, the bubble size distribution is assumed to be monodispersed. The bubbles induced turbulence is dominant in this case. For such a case, LES may not represent the best option for turbulence prediction, since the largest fluctuations are close to the bubble surface and cannot be resolved, but instead are modeled with a very simple SGS model. However, good results are obtained in the same experiment with a much higher gas superficial velocity, since large-scale turbulence is present and mostly resolved. For the other configuration, LES shows a more plausible amplitude and period in liquid velocity fluctuation in the measure point than the results of URANS. The SGS turbulent kinetic energy will also be considered using two methods of estimation for zero-equation SGS models to improve the prediction.

  • Contribution to proceedings
    CFD4NRS-5 - Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 09.-11.09.2014, Zürich, Schweiz
  • Lecture (Conference)
    CFD4NRS-5 - Application of CFD/CMFD Codes to Nuclear Reactor Safety and Design and their Experimental Validation, 09.-11.09.2014, Zürich, Schweiz
  • International Journal of Heat and Fluid Flow 56(2015), 51-59
    Online First (2015) DOI: 10.1016/j.ijheatfluidflow.2015.06.009

Publ.-Id: 20448

Large Eddy Simulation for a rectangular bubble column

Ma, T.; Ziegenhein, T.; Lucas, D.; Fröhlich, J.; Krepper, E.

In vielen verfahrenstechnischen Apparaten wird mit Mehrphasenströmungen gearbeitet, bei denen eine kontinuierliche Flüssigkeitsphase und eine disperse gasförmige Phase vorliegen. Die Turbulenz in der Flüssigkeitsphase ist ein wichtiges Phänomen in Mehrphasenströmungen. Sie hat einen starken Einfluss auf die lokale Verteilung der dispersen Phasen.
Eine Blasensäule stellt eine gute Experimentiereinrichtung für die Untersuchung von turbulenten Phänomen in Mehrphasenströmungen dar. In den CFD Simulationen für Blasensäulen werden traditionell RANS Modelle zur Turbulenzmodellierung verwendet, allerdings wird die Turbulenz nur isotrop modelliert.
LES bietet die Möglichkeit die großskaligen anisotropen Turbulenzen direkt aufzulösen und die kleinskaligen mit einem Subgrid-Scale (SGS) Model zu modellieren. Die Filterung basiert meistens direkt auf der Gitterweite. In dieser Arbeit wird die Euler-Euler Large Eddy Simulation (LES) für eine rechteckige Blasensäule durchgeführt und mit experimentellen Daten von (Akbar 2012) verglichen. Der Euler-Euler Ansatz verlangt eine Gitterweite größer als die Blasengröße, sodass die Gitterweite in den LES Rechnungen für Blasenströmungen in der Meso-Skala bzw. im Blasengrößen Bereich liegt. Für Blasenströmungen mit geringen Leerrohrgeschwindigkeiten ist die Blasen induzierte Turbulenz dominant. Für solche Fälle stellt die LES nicht die optimale Option zur Turbulenzvorhersage dar. Die Ursache besteht darin, dass die größte Fluktuation in der Nähe der Blasenoberfläche liegt und zum Großteil nicht aufgelöst, sondern mit einem sehr einfachen SGS Modell modelliert wird. Hingegen werden für die Blasenströmung mit höheren Leerrohrgeschwindigkeiten gute Ergebnisse erzielt, da großskalige Turbulenzen vorhanden und aufgelöst werden. In der Auswertung wird die SGS turbulente kinetische Energie mit zwei Methoden zur Abschätzung ebenfalls berücksichtigt.

[Akbar 2012] Akbar MHM, Hayashi K, Hosokawa S, Tomiyama A. Bubble tracking Simulation of Bubble-induced Pseudo Turbulence. 6th Japanese-European Two-Phase Flow Group Meeting, 2012

  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics, Mischvorgänge und Rheologie, 24.-25.02.2014, Würzburg, Deutschland

Publ.-Id: 20447

Novel wire-mesh sensor for visualization of threephase flows

E., S.; M., S.; R., M.; S., R.; E., S.; U., H.

For the investigation of three-phase flows, for instance as commonly found in oil and gas production, there are only few suitable measuring techniques. For this reason, in this paper a new multichannel complex impedance measuring system using wire-mesh sensors is presented. The system measures amplitude and phase componets of impedance (at single frequency) and is thus able to determine simultaneously the conductive and the capacitive parts of a fluid (complex permittivity). In the future this system can be employed for the investigation of dynamic processes in multiphase flow. The performance in measuring the complex permittivity is evaluated. First promising results for the three-phase flow are presented

Keywords: Complex impedance measurement; multiphase flow; wire-mesh sensor

  • Contribution to proceedings
    15th Brazilian Congress of Thermal Sciences and Engineering, November 10-13, 2014, Belém, PA, Brazil, 10.-13.11.2014, Belém, Brazil
    Proceedings of ENCIT 2014: ABCM
  • Lecture (Conference)
    15th Brazilian Congress of Thermal Sciences and Engineering, November 10-13, 2014, Belém, PA, Brazil, 10.-13.11.2014, Belém, Brazil, 10.-13.11.2014, Belém, Brasilien

Publ.-Id: 20446

Transient simulation for large scale flow in bubble columns

Ziegenhein, T.; Rzehak, R.; Lucas, D.

The transient simulation of large scale bubbly flow in bubble columns using the unsteady Reynolds averaged Navier Stockes (URANS) equations is investigated in the present paper. An extensive set of bubble forces is used with different models for the bubble induced turbulence. Criteria are given to assess the independence of the simulation time and the time step length. Using these criteria it is shown that a simulation time, time step length and mesh independent solution can be obtained for complex bubbly flows using URANS equations under certain requirements. With the obtained setup the contribution of the resolved turbulence to the total turbulence and the influence of the bubble induced turbulence modeling on the resolved turbulence is investigated. Further, it is pointed out that the virtual mass force is not negligible. The simulations are compared to data from the literature at two different superficial velocities, which cover monodisperse and polydisperse bubbly flows.

Keywords: bubble columns; bubble induced turbulence; transient multiphase flow; Euler-Euler modeling; CFD simulation; model validation

Publ.-Id: 20445

Turbulence modeling of polydispersed bubbly flow for large scale applications

Ziegenhein, T.; Rzehak, R.; Lucas, D.

Aeration of reactors is a wide used concept in biotechnology and chemical engineering to intensify processes. Beside enlarging the interface between liquid and gas phase, enhancement of mixing plays an important role. Turbulence affects these processes strongly. It is a main parameter for mixing and an important parameter for coalescence and break up processes.
Two main turbulence scales can be identified in bubbly flows. The small scale depends on the bubble itself and has a length scale in the magnitude of the bubble diameter. The large scale depends on the reactor geometry and has a length scale in the magnitude of the reactor. To characterize aerated Systems both scales are vital, but the modeling is difficult because of the multiscale problem.
A concept to describe both scales based on Euler-Euler unsteady RANS simulation with a two equation turbulence model is shown. The small scales are modeled with a new bubble induced turbulence model [Rzehak 2013][Ziegenhein 2013] and the large scales are directly computed. The contribution of the modeled and the directly computed turbulence to the total turbulence is shown and discussed on the bases of experimental data.
The aim of this approach is to model a complete reactor. The results can be used to formulate dispersion models for the specific reactor geometry, to support compartment modeling or to simulate different operating modes directly with CFD.

[Rzehak 2013] R. Rzehak and E. Krepper CFD modeling of bubble-induced turbulence, International Journal of Multiphase Flow 2013, 55, 138–155.
[Ziegenhein 2013] T. Ziegenhein, D. Lucas, R. Rzehak, E. Krepper Closure relations for CFD simulation of bubble columns, In proceeding of: International Conference on Multiphase Flow, Jeju, Korea, Volume: 8th

Keywords: Bubble column; two-fluid model; bubble forces; bubble induced turbulence; turbulence; multiscale modeling

  • Poster
    Jahrestreffen der Fachgruppen Computational Fluid Dynamics, Mischvorgänge und Rheologie, 24.-26.02.2014, Würzburg, Deutschland

Publ.-Id: 20444

The electroluminescence of Er-implanted MOS structures with different silicon oxide and silicon nitride environments

Rebohle, L.; Wutzler, R.; Braun, M.; Helm, M.; Skorupa, W.; Berencén, Y.; Garrido, B.; Hiller, D.

Er-based, electrically driven light emitters, which can easily be integrated into Si-based circuitries, are of great interest for a broad range of applications, especially in the field of telecommunication and sensing. This work investigates the electrical and electroluminescence (EL) properties of Er-implanted MOS structures with different designs of the dielectric stack. The dielectric stack is essentially composed of a 30 nm thick SiO2 layer and a 40 nm thick host matrix for the Er ions made of Si-rich SiO2, silicon nitride or Si-rich silicon nitride. All structures implanted with Er show intense EL around 1550 nm which is excited by impact excitation of hot electrons. We compare the different host matrices regarding the EL efficiency, the EL excitation cross section, the EL decay time, the fraction of excited Er ions, the EL quenching cross section and the operation lifetime. This comparison reveals fundamental properties of the EL mechanism and addresses the current problems of this type of Si-based light emitter to achieve the performance level of compound semiconductors with a direct bandgap.

Keywords: Electroluminescence; rare earth; MOS structure; decay time

  • Lecture (Conference)
    E-MRS Spring Meeting 2014, 26.-30.05.2014, Lille, France

Publ.-Id: 20443

Nanocrystallisation of III-V compound semiconductors in Si by ion beam implantation and thermal annealing

Wutzler, R.; Rebohle, L.; Prucnal, S.; Bregolin, F.; Helm, M.; Skorupa, W.

III-V integration into Si is a milestone in the future development of micro- and optoelectronics. Based on SiO2 capped silicon and silicon-on-insulator (SOI) substrates, we fabricated various III-V compound semiconductor nanocrystals (NCs) in Si by high fluence ion beam implantation and short-time annealing. Due to implantation, the surrounding Si material is amorphized. Recrystallization and III-V NC growth by liquid phase epitaxy are achieved through millisecond flash lamp annealing (FLA). By using lithographically patterned cover layers during implantation we were able to obtain single-crystalline GaAs, GaP, InAs, and InP NCs at defined positions.

For the investigation of the microstructure, transmission electron microscopy (TEM), Raman spectroscopy, atomic force microscopy (AFM) and Rutherford Backscattering (RBS) spectroscopy have been performed. Raman measurements confirmed the formation of III-V NCs within the recrystallized Si matrix; TEM images show distinct, single-crystalline NCs of various shapes. Depending on the processing conditions, shape and size range from large dome-like structures over spherical precipitates to nano-pyramids. AFM and RBS were used to control and monitor the fabrication process.

Keywords: Ion Implantation; Flash Lamp Annealing; III-V integration; SOI; heterojunction

  • Lecture (Conference)
    E-MRS 2014 Spring Meeting, 26.-30.05.2014, Lille, France

Publ.-Id: 20442

Instabilities of rotational flows in azimuthal magnetic fields of arbitrary radial dependence

Kirillov, O.; Stefani, F.; Fukumoto, Y.

Using the Wentzel–Kramers–Brillouin (WKB) approximation we perform a linear stability analysis for a rotational flow of a viscous and electrically conducting fluid in an external azimuthal magnetic field that has an arbitrary radial profile Bφ(R). In the inductionless approximation, we find the growth rate of the three-dimensional perturbation in a closed form and demonstrate in particular that it can be positive when the velocity profile is Keplerian and the magnetic field profile is slightly shallower than 1/R.

Keywords: Asymptotic methods; stability; magnetohydrodynamics; magnetorotational instability; azimuthal field

Publ.-Id: 20441

Retention of selenium by cementitious materials under reducing radioactive waste repository conditions

Rojo, H.; Tits, J.; Scheinost, A. C.; Wieland, E.

Cementitious materials play a crucial role as barrier for radionuclide transport in low and intermediate level radioactive waste repositories, where 79Se is an important redox-sensitive and dose-determining radionuclide. In current sorption databases for the cementitious near-field, only sorption data for Se(IV/VI) have been considered. Robust sorption data on reduced Se species in general, and a sufficiently detailed mechanistic understanding of their retention in cementitious environment are, however, lacking.
The aim of this work is to investigate the immobilisation of Se under the reducing conditions existing in a cement-based, deep-underground repository (-230mV < Eh < -750 mV). Under these conditions, Se(IV) and Se(-II) are the dominant redox states. We obtained Se(-II) by electrochemical reduction of Se(IV) in solution. Completion of the reduction process was determined by UV-vis spectroscopy. Se(IV) and Se(-II) sorption kinetic studies were carried out on various synthetic cement components, such as calcium silicate hydrates (C-S-H) and hydrated calcium aluminates (AFm), the principal host phases for radionuclides in hydrated cement. In addition, Se(IV) and Se(-II) sorption experiments were performed with TiO2 as reference solid, stable under alkaline conditions, at pH = 10.0 and 13.3, in the absence and presence of 10-3 M Ca. XANES studies allowed the determination of the redox state of sorbed selenium.
The sorption tests revealed that the uptake of Se(IV) by C-S-H phases is much stronger than expected. Rd values measured on C-S-H phases are approximately two orders of magnitude higher than Rd values measured on TiO2. This high affinity of the C-S-H phases for Se(IV) anions is partially explained by the high specific surface area of these solids. Furthermore, Rd values for Se(IV) on various AFm phases are correlated with their interlayer spacing. The sorption of Se(-II) on the different cementitious materials was found to be weaker than the sorption of Se(IV).

Keywords: XANES; selenium; cement; radioactive waste disposal

  • Poster
    Goldschmidt 2014, 08.-13.06.2014, Sacramento, USA

Publ.-Id: 20440

Synthesis of calix[4]arene-based polycarboxylate ligands and their chemical immobilization onto controlled-pore glass

Haupt, S.; Handke, M.; Kuhnert, R.; Poetsch, M.; Kersting, B.

Three new calix[4]arene-based carboxylate ligands with an appended allyl function have been synthesized, chemically immobilized onto a controlled-pore glass (CPG), and the extracting ability of selected materials towards Sr2+ in solid-liquid extraction was examined.
The calixarenes were characterized by elemental analysis, mass spectrometry, IR and NMR spectroscopy, and where appropriate by X-ray crystallography. Four functionalized CPGs were prepared by radical thiol addition of the corresponding 5-allylcalix[4]arenes to γ-mercaptopropyl-modified CPG. Analysis by 13C and 29Si cross polarization/magic angle spinning (CP/MAS) NMR spectroscopy clearly showed the covalent fixation of the calix[4]arenes to CPG. The calix[4]arene phases were found to be stable up to 200° C by simultaneous thermal analysis (STA). The extraction performance of the modified CPGs towards Sr2+ were found to be superior over the unmodified CPGs as demonstrated by radiotracing using the short-lived radio nuclide 85Sr.

Keywords: calix[4]arene; controlled-pore glass; CP/MAS NMR; solid-liquid extraction; strontium

Publ.-Id: 20437

Low-temperature transport properties of Si and Ge films with Ga-rich nanoprecipitates

Heera, V.; Fiedler, J.; Skrotzki, R.; Naumann, M.; Herrmannsdörfer, T.; Skorupa, W.

Ga-rich (~ 10 at.%) Si and Ge films were fabricated by high-fluence Ga+ ion implantation through a SiO2 capping layer. The structure and the electrical transport properties of these films have been studied after flash-lamp [1-3] and rapid thermal annealing [4, 5]. Amorphous, Ga-rich nanoprecipitates are embedded in a heavily p-type doped semiconductor matrix [3, 4].
These nanoprecipitates become superconducting below critical temperatures up to 7 K. They can interact due to the proximity effect in the degenerately doped semiconductor matrix and form a random network of Josephson junctions. Small modifications of the junction properties, e.g. by annealing or current pulses, can dramatically change the electronic transport in the film. In particular, Ga-rich Si films show a wealth of low-temperature transport phenomena which have been known until now only from granular metals or high-temperature superconductors: superconductor-insulator transition, quasi-reentrant superconductivity and current-controlled sheet resistance [6, 7] .
The possibility to prepare and modify Ga-rich Si and Ge films with microelectronics-compatible technology makes them interesting for both fundamental research on transport phenomena in nanostructured, disordered superconductors as well as for the integration of superconducting circuits into Si devices.

[1] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, et al., Phys. Rev. Lett.,2009, 102, 217003.
[2] R. Skrotzki, T. Herrmannsdörfer, V. Heera, J. Fiedler, et. al., Low Temp. Phys., 2011, 37, 1098.
[3] V. Heera, J. Fiedler, M. Naumann, R. Skrotzki, et al., Supercond. Sci. Technol., 2014, 27, 055025.
[4] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2011, 83, 214504.
[5] J. Fiedler, V. Heera, R. Skrotzki, T. Herrmannsdörfer, et. al., Phys. Rev. B, 2012, 85, 134530.
[6] V. Heera, J. Fiedler, M. Voelskow, A. Mücklich, et al., Appl. Phys. Lett., 2012, 100, 262602
[7] V. Heera, J. Fiedler, R. Hübner, B. Schmidt, et al., New. J. Phys., 2013, 15, 083022

Keywords: Low-temperature transport; Si and Ge films; Ga implantation; Ga nanopreciptates; superconductor-insulator transition

  • Lecture (Conference)
    Workshop "Ionenstrahlen und Nanostrukturen" Paderborn 2014, 20.-22.07.2014, Paderborn, Deutschland

Publ.-Id: 20436

The relevance of melt convection to grain refinement in Al-Si alloys solidified under the impact of electric currents

Räbiger, D.; Zhang, Y.; Galindo, V.; Franke, S.; Willers, B.; Eckert, S.

The present paper considers the directional solidification of Al-7wt%Si alloys under the influence of strong electric currents for the configuration of two parallel electrodes immersed from the free surface into the solidifying alloy. Solidification experiments were performed under the influence of both direct currents (DC) and rectangular electric current pulses (ECP). The interaction between the applied current and its own induced magnetic field causes a Lorentz force which produces an electro-vortex flow covering the entire melt area. Numerical simulations of the magnetohydrodynamic (MHD) problem were conducted to calculate the Lorentz force, the Joule heating and the induced melt flow. The numerical predictions were confirmed by isothermal flow measurements in eutectic Ga-20wt%In-12wt%Sn. The application of the electric current during solidification leads to the formation of refined equiaxed grain structures. There are no remarkable differences with respect to the influence of DC or ECP treatment on the mean grain size and the area of equiaxed zone in the solidified samples provided the effective values of the current strength are identical. The results demonstrate that the grain refining effect observed in our experiments can be ascribed solely to the forced melt flow driven by the Lorentz force.

Keywords: Al-Si alloys; solidification; melt convection; grain refinement

Publ.-Id: 20435

P1316 - Anordnung zur Kontaktierung eines CZT-Kristalls für das Detektormodul einer Compton-Kamera

Heidel, K.; Sobiella, M.; Dersch, U.; Berthel, M.; Golnik, C.

Offenbart wird die Kontaktierung eines quaderförmigen CZT-Kristalls zur Detektierung von Gammastrahlung in einer Compton-Kamera, wobei der CZT-Kristall eine der einfallenden Strahlung zugewandte, vollflächige Vorderseitenelektrode und auf der der Vorderseite gegenüberliegenden Rückseite mehrere, voneinander beabstandete rechteckige und als Elektroden ausgeführte Pixelflächen aufweist, wobei die zu den Pixelflächen komplementären Anschlussflächen eines oder mehrerer Flachbandkabel mit diesen Pixelflächen elektrisch leitfähig mittels eines leitfähigen Klebstoffs verbunden sind.

  • Patent
    DE102013210082 - Erteilung 15.05.2014

Publ.-Id: 20434

Compact Optical Free Electron Laser with Traveling-Wave Thomson Scattering

Steiniger, K.; Bussmann, M.; Debus, A.; Irman, A.; Jochmann, A.; Pausch, R.; Schramm, U.; Widera, R.

We present a fully analytical description of the field and the electrons in an optical free electron laser in the Travelling-Wave Thomson Scattering (TWTS) configuration. This scheme allows for long interaction lengths of an ultra-short, high-intensity pulsed laser with an electron bunch. The latter can be either provided by laser-accelerated electrons or by a conventional accelerator. TWTS provides for high peak brightness, high brilliance pulses from the EUV to the gamma spectrum with high flexibility in the wavelength and bandwidth of the emitted radiation.

Keywords: X-ray; optical FEL; traveling-wave; Thomson scattering

  • Lecture (Conference)
    DPG Frühjahrstagung Dresden 2014, 30.03.-05.04.2014, Dresden, Deutschland

Publ.-Id: 20432

Scaling of Optical Free-Electron Lasers in Traveling-Wave Geometries

Steiniger, K.; Debus, A.; Bussmann, M.; Sauerbrey, R.

Optical free electron lasers in the X-ray range using high power lasers are difficult to realize in the standard head-on Thomson-scattering geometry. Problems arise from the nonlinear Thomson intensity threshold and the Rayleigh-length limiting the interaction distance which prevent the SASE process to occur.

These limits can be circumvented in a Travelling-wave Thomson-scattering (TWTS) geometry, in which ultrashort and narrow-band light pulses in the X-Ray region of the spectrum are created by scattering high intensity laser pulses from relativistic electron bunches. TWTS uses lasers with a pulse front tilt in a sidescattering geometry to scale the interaction length into the centimeter to meter range with undulator periods in the region of one hundred to a few hundred micrometer.

Starting from a fully 3D, wave-optical representation of the TWTS pulse, including its dispersion properties, we present a self-consistent 1.5D FEL-theory which accounts for the coupling of the obliquely incident laser pulse to the electron dynamics. Furthermore, we give scaling laws on the interaction geometry and FEL-amplification with respect to incidence angle and electron beam parameters. Using these findings we discuss possible experimental scenarios and its requirements on laser pulses and electron beams.

Keywords: Optical FEL; Traveling-wave; thomson-scattering; X-ray

  • Lecture (Conference)
    DPG Frühjarstagung Berlin 2014, 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 20431

Two Years Experience with the upgraded ELBE RF-System driven by 20 kW Solid State Amplifier Blocks

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.

Since January 2012 the Superconducting CW Linac ELBE is equipped and in permanent operation with four 20 kW Solid State Amplifier Blocks. The poster gives an overview on the design of the new RF system and the experience gained within the first two years of operation.

Keywords: Solid State Power Amplifiers; Superconducting RF; ELBE-RF System

  • Poster
    IPAC 2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
  • Open Access Logo Contribution to proceedings
    IPAC 2014 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
    Proceedings of IPAC'14, CERN: JaCoW, MOPME067


Publ.-Id: 20430

Status and Operating Experience of the ELBE RF System based on 10kW SSPAs

Büttig, H.; Arnold, A.; Büchner, A.; Justus, M.; Kuntsch, M.; Lehnert, U.; Michel, P.; Staats, G.; Teichert, J.; Schurig, R.

In January 2012 the 10 kW klystrons of the CW LINAC ELBE were replaced by pairs of 10kW solid state power amplifiers (SSPA).
The talk gives an overview on the SSPA based ELBE RF system. The experience gained during the first two years of operation is reviewed.

Keywords: SSPA; Solid State Power Amplifier; Superconducting Radio Frequency; Superconducting LINAC; RF-System for Particle Accelerators; 1.3GHz Power Aplifier

  • Lecture (Conference)
    Continuous Wave and High Power RF Workshop 2014 (CWRF2014), 13.-16.05.2014, Trieste, Italy

Publ.-Id: 20429

Process-Based Forward Numerical Modelling SIMSAFADIM-CLASTIC: The Vilomara Composite Sequence case

Clavera-Gispert, R.; Gratacós, O.; López-Blanco, M.; Tolosana-Delgado, R.

SIMSAFADIM-CLASTIC is a 3D process-based forward numerical model that simulates the stratigraphic infill and evolution of a marine sedimentary basin (Bitzer and Salas, 2001, 2002; Gratacós et al., 2009a, 2009b; Carmona et al., 2010; Clavera et al., 2013). The program is designed to model processes of transport and sedimentation for clastic terrigenous and clastic carbonate sediments. The program, also include the interaction between carbonate producing organisms and clastic sediments in suspension. Considering that, the objective of the program is to model and to represent the spatial and temporal interplay of the generated sedimentary bodies, obtaining realistic depositional architectures in order to reproduce the 3D sediment distribution and the complex heterogeneity present in the sedimentary record.

The model for siliciclastic transport and sedimentation is based on a potential fluid flow. This fluid flow model can establish the general trend of the flow system to determine the sediment transport in the basin over a geological time scale at basin scale (hundred meters to kilometres) with an acceptable computational time. Regarding to the sediment transport, the fluid flow model can determine the movement of solid particles in suspension due to fluid movement processes that include advection, diffusion, and dispersion. The carbonate production model is based in the generalized equation of Lotka-Volterra ecological modelling. The program takes into account the influence of environmental factors to model the carbonate producing organisms associations (water depth, nutrients, clastic sediment concentration is suspension, fluid flow velocity and bottom slope), and the interaction among them (predation, prey, mutualism, competition...). Other processes are modelled to generate (or reduce) accommodation space in the marine basin, including sea level variations, compaction, and isostasy.

In order to show the application and possibilities of the code, the Vilomara Composite Sequence (VCS) of Sant Llorenç del Munt (SLM) fan delta complex (NE Iberian Peninsula) is modelled.

  • Contribution to proceedings
    GeoMod, 31.08.-05.09.2014, Potsdam, Deutschland
    Proceedings of GeoMod2014 - Modelling in Geosciences: Programme and Extended Abstracts, 80-83
    DOI: 10.2312/GFZ.geomod.2014.001

Publ.-Id: 20428

Analysis of self‑assembly of S‑layer protein slp‑B53 from Lysinibacillus sphaericus

Liu, J.; Falke, S.; Drobot, B.; Oberthuer, D.; Kikhney, A.; Guenther, T.; Fahmy, K.; Svergun, D.; Betzel, C.; Raff, J.

The formation of stable and functional surface layers (S-layers) via self-assembly of surface-layer proteins on the cell surface is a dynamic and complex process. S-layers facilitate a number of important biological functions, e.g., providing protection and mediating selective exchange of molecules and thereby functioning as molecular sieves. Furthermore, S-layers selectively bind several metal ions including uranium, palladium, gold, and europium, some of them with high affinity. Most current research on surface layers focuses on investigating crystalline arrays of protein subunits in Archaea and bacteria. In this work, several complementary analytical techniques and methods have been applied to examine structure–function relationships and dynamics for assembly of S-layer protein slp-B53 from Lysinibacillus sphaericus: (1) The secondary structure of the S-layer protein was analyzed by circular dichroism spectroscopy; (2) Small-angle X-ray scattering was applied to gain insights into the three-dimensional structure in solution; (3) The interaction with bivalent cations was followed by differential scanning calorimetry; (4) The dynamics and time-dependent assembly of S-layers were followed by applying dynamic light scattering; (5) The two-dimensional structure of the paracrystalline S-layer lattice was examined by atomic force microscopy. The data obtained provide essential structural insights into the mechanism of S-layer self-assembly, particularly with respect to binding of bivalent cations, i.e., Mg2+ and Ca2+. Furthermore, the results obtained highlight potential applications of S-layers in the fields of micromaterials and nanobiotechnology by providing engineered or individual symmetric thin protein layers, e.g., for protective, antimicrobial, or otherwise functionalized surfaces.

Keywords: Surface-layer protein; Self-assembly; Bivalent cations; AFM; DSC; SAXS


Publ.-Id: 20427

P1303 - Bauteil mit metallhaltiger, selbstorganisierter Schicht, Verfahren zu dessen Herstellung sowie Verwendung

Raff, J.; Günther, T.; Wengrzik, S.

Die Erfindung beschreibt ein Bauteil, welches eine nicht-leitende Oberfläche aufweist und mit einer selbstorganisierten Schicht sowie einer metallischen Deckschicht versehen ist. Die Erfindung beschreibt ferner ein kostengünstiges und industriell serientaugliches Verfahren zur Herstellung eines solchen Bauteils sowie die Verwendung eines solchen Bauteils als Ersatz von metallischen Bauteilen in Fahrzeugen, Haushaltsgeräten, Sanitärausstattungen sowie als gedruckte elektronische Schaltung.
In dem erfindungsgemäßen Verfahren wird die nicht-leitende Oberfläche eines Substrates mit einem Katalysator belegt, anschließend mit einer Poren enthaltenden, selbstorganisierten Schicht belegt und schließlich in einem chemischen Metallisierungsbad mit Metallen beschichtet, wobei das Metallisierungsbad die poröse selbstorganisierte Schicht durchdringt und dadurch auf der nicht-leitende Oberfläche besser mechanisch verankert wird als nach dem Stand der Technik.
Das erfindungsgemäße Bauteil wird bevorzugt hergestellt mit dem erfindungsgemäßen Verfahren und enthält:
a. eine nicht-leitende Oberfläche,
b. auf der Katalysatorpartikel aufgebracht sind
c. wobei auf und um die Katalysatorpartikel eine Poren enthaltende, selbstorganisierte Schicht aufgebracht ist,
d. wobei die selbstorganisierte Schicht mit Metallen beschichtet ist, wobei die aufgebrachte Metallschicht die Poren der selbstorganisierten Schicht durchdringt.

  • Patent
    DE102013208395 - Erteilung 12.05.2014, Nachanmeldung: WO

Publ.-Id: 20426

Nuclear deformation and neutron excess as competing effects for the pygmy dipole strength

Massarczyk, R.; Schwengner, R.; Dönau, F.; Frauendorf, S.

The electromagnetic dipole strength below the neutron-separation energy has been studied for the xenon isotopes with mass numbers A = 124, 128, 132, and 134 in nuclear resonance fluorescence experiments using the ELBE bremsstrahlung facility at Helmholtz-Zentrum Dresden-Rossendorf and the HIS facility at Triangle Universities Nuclear Laboratory Durham. The systematic study gained new information about the influence of the neutron excess as well as of nuclear deformation on the strength in the region of the pygmy dipole resonance. The results are compared with those obtained for the chain of molybdenum isotopes and with predictions of a random-phase approximation in a deformed basis. It turned out that the effect of nuclear deformation plays a minor role compared with the one caused by neutron excess. A global parametrization of the strength in terms of neutron and proton numbers allowed us to derive a formula capable of predicting the summed E1 strengths in the pygmy region for a wide mass range of nuclides.

Keywords: nuclear structure; pygmy strength; photo-absorption; photo-nuclear experiments

  • Lecture (Conference)
    11th INTERNATIONAL SPRING SEMINAR ON NUCLEAR PHYSICS, 12.-16.05.2014, Ischia, Italien
  • Lecture (others)
    Seminar on Nuclear Deformation / telphone presentation, 20.05.2014, Los Alamos, USA

Publ.-Id: 20424

Resource potential of REE as by-product of an existing mining operation – A geometallurgical assessment

Birtel, S.; Kern, M.; Höfig, T. W.; Krause, J.; Gutzmer, J.

A systematic geometallurgical study of the rare earth mineralogy and beneficiation potential as by-product was performed, based on a currently operating flow sheet of an existing large-scale industrial mining and beneficiation operation. For this purpose, a representative suite of samples was collected from a single mining block prior to blasting. The material derived from this mining block was then tracked through beneficiation by comminution and a sequence of flotation steps. Samples were collected at all crucial steps of the beneficiation plant. Whole rock geochemical analyses and quantitative mineralogical and microstructural analyses (by MLA), complemented by mineral chemistry data for relevant REE minerals, were obtained for a suite of more than 60 samples. These data were then used to assess the deportment of REE and to track the route of REE-minerals within the beneficiation process.
Apatite was found to be the most important primary host mineral for REE. Postdepositional alteration evidently led to the breakdown of apatite, resulting in the formation of microcrystalline xenotime and monazite of secondary origin. The latter are the two most abundant rare earth minerals identified in the mining block studied. Additionally identified rare earth minerals occur only in minor or trace amounts. Other minerals were found to contribute only limited amounts to the total REE content of the ore.
Process samples from the flotation circuit illustrate that the material from the cleaner circuit tailing, being usually considered as waste, is strongly enriched in monazite and xenotime, i.e., the two most common REE minerals. The REE minerals are well liberated, thus leading to the conclusion that it may be feasible to produce REE minerals as a future by-product by only slight modification of the current flow sheet.

Keywords: geometallurgy; REE; process optimization

  • Contribution to proceedings
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Deutschland
    Minerals at Focal Point, 126
  • Poster
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft, 21.-24.09.2014, Jena, Deutschland

Publ.-Id: 20423

Towards a novel THz-based monitor for sub picosecond electron bunches working at MHz repetition rates and low bunch charges

Gensch, M.; Green, B.; Kovalev, S.; Kuntzsch, M.; Golz, T.; Stojanovic, N.; Fisher, A.

The control and measurement of electron bunch properties at the femtosecond (fs) level has become an important field in modern accelerator physics, in particular since these became crucial parameters for the operation of 4th Generation X-ray Light-sources. In order to operate modern-day photon factories such as LCLS and the future European X-FEL reliably, a number of novel approaches have been developed that allow the noninvasive measurement of electron bunch form and arrival time. Some of those are based on the electro-optic detection of the coulomb field of the electron bunches in the electron beamline; some detect the super-radiant THz pulses from the electron bunch. However, none of these concepts allows for pulse-to-pulse detection on a quasi-CW accelerator operating at the MHz repetition rates planned for the next generation of X-ray free electron lasers. In this contribution we present first results from a new monitor concept, based on the single-shot electro-optic detection of super-radiant THz pulses, that has the potential to operate at MHz repetition rates.

  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Publ.-Id: 20422

Ионный синтез нанокристаллов InSb в захороненном слое SiO2 структуры кремний-на-изоляторе
Ion-beam synthesis of InSb nanocrystals in the buried SiO2 layer of a silicon-on-insulator structure

Tyschenko, I. E.; Voelskow, M.; Tscherkov, A. G.; Popov, V. P.

Исследован ионный синтез нанокристаллов InSb в слое захороненного SiO2 структуры кремний-на-изоляторе. Изучены профили распределения атомов индия и сурьмы после отжига при температуре Ta = 500−1100◦C. Установлено, что перераспределение имплантированных атомов имеет немонотонный характер в зависимости от температуры отжига. Формирование нанокристаллов InSb происходит при Ta ≥ 800◦C вблизи границы Si/SiO2 и на глубине средних пробегов Rp. Анализ профилей имплантированных атомов и структуры и распределения по глубине формирующихся нанокристаллов позволил сделать предположение о двухстадийном характере образования фазы InSb: на первой стадии происходит формирование преципитатов сурьмы, которые играют роль зародышей для дальнейшего стока на них атомов In и Sb.

The ion-beam synthesis of InSb nanocrystals in the buried SiO2 layer of a silicon-on-insulator structure is investigated. The distributions of In and Sb atoms after annealing at a temperature of T a = 500–1100°C are studied. It is established that the redistribution of implanted atoms is unsteadily dependent on the annealing temperature. The formation of InSb nanocrystals occurs at Ta ≥ 800°C near the Si/SiO2 interface and at a depth corresponding to the mean paths R p . Analysis of the profiles of implanted atoms and of the structure and depth distribution of nanocrystals formed allows an inference regarding the two-stage character of formation of the InSb phase. In the initial stage, antimony precipitates are formed; further the precipitates serve as nuclei for indium and antimony to flow to them.

Keywords: Ion beam Synthesis; InSb; SOI; RBS

  • Fizika i Tekhnika Poluprovodnikov 48(2014)9, 1228-1233
  • Semiconductors 48(2014)9, 1196-1201

Publ.-Id: 20421

Enhanced wear resistance of high-speed steel by pulsed electron-beam melting

Ivanov, Y.; Matz, W.; Rotshtein, V.; Guenzel, V.; Shevchenko, N.

  • Contribution to proceedings
    3rd International Conference on Surface Engineering, 09.-11.03.1993, Bremen, Germany
    Contributions of surface engineering to modern manufacturing and remanufacturing, Chengdu, China: Southwest Jiaotong University Press, 7810576615, 397-402

Publ.-Id: 20420

Ion beam synthesis by tungsten implantation into 6H-silicon carbide at elevated temperatures

Weishart, H.; Matz, W.; Skorupa, W.

  • Contribution to proceedings
    1995 MRS Fall Meeting & Exhibit, 27.11.-1.12.1995, Massachusetts, USA
    MRS Symposium Proceedings Series: III-Nitride, SiC, and Diamond Materials for Electronic Devices: Cambridge University Press, 9781558993266, 195-200

Publ.-Id: 20419

Electron bunch form monitoring at quasi-cw SRF accelerators: Status at the ELBE accelerator

Gensch, M.; Green, B.; Hauser, J.; Kuntzsch, M.; Lehnert, U.; Michel, P.; Schurig, R.; Golz, T.; Stojanovic, N.; Mueller, A. S.; Schwarz, M.; Fisher, A. S.; Neumann, N.; Plettemeier, D.; Bauer, C.

In the past few years the quasi-cw SRF electron accelerator ELBE has been upgraded so that it now allows to compress electron bunches to the sub-picosecond regime at repetition rates of up to 13 MHz and bunch charges up to 100 pC. The actual optimization and control of the electron bunch form represents one of the largest challenges of the coming years at ELBE. In particular with respect to the midterm goal to utilize the ultra-short electron bunches for Laser-Thomson scattering experiments or high field THz experiments. Since 2012, the ELBE accelerator, together with its recently established super-radiant THz facility TELBE serves as a unique test facility for the development of novel diagnostic for quasi-cw electron beams. In this contribution different diagnostic approaches for the online determination of the electron bunch form are presented. The results of the different techniques, ranging from adapted classical laser-based and interferometer-based concepts to novel on-chip THz spectrometers are compared. The merits of the different concepts: e.g. pulse to pulse diagnostics at few 100 kHz repetition rates or a sensitivity for charges down to the few 100 femto coulomb regime are discussed based on the results of recent commissioning campaigns by a multi-institutional collaboration. A careful analysis of simultaneous measurements with the different techniques allows an educated guess for the presently shortest electron bunch duration achieved at ELBE of 1.2 ps (FWHM). It is also shown that interferometric concepts at this moderately short bunch durations systematically underestimate the bunch length due to diffraction effects at low THz frequencies.

  • Poster
    IBIC 2014 - 3rd International Beam Instrumentation Conference, 14.-18.09.2014, Monterey, USA

Publ.-Id: 20418

How magnetic fields can be used for controlling the electrochemical deposition of metal

Mutschke, G.; Mühlenhoff, S.; Yang, X.; Eckert, K.; Tschulik, K.; Uhlemann, M.; Fröhlich, J.; Bund, A.

The contribution attempts to give an overview of recent results regarding the influence of magnetic fields on the electrochemical deposition of metal. Magnetic fields give rise to forces on the electrolyte which, if properly applied, can be useful. Lorentz forces have been known long-since for causing convection of the electrolyte, and thus, to affect mass transfer. In case of homogeneous magnetic fields at vertical electrodes, a short detour to fluid mechanics helps to better understand the resulting changes in mass transfer and the convection pattern. Two different ways of achieving desired properties by tailored magnetic fields are discussed. For vertical electrodes, despite of the influence of buoyancy, inhomogeneous magnetic fields can be utilized for improving the uniformity of the metal deposit [1]. On the contrary, magnetic fields can also be beneficial for obtaining a desired non-uniform deposition at length scales down to the micrometer range. Here, the magnetic Kelvin force becomes important if para- or diamagnetic ions are exposed to inhomogeneous magnetic fields. In both examples, simulations and experimental results will be presented which elucidate the interplay of forces, the electrolyte flow and the effect on mass transfer [2,3].
[1] Mühlenhoff, S.; Mutschke, G.; Uhlemann, M.; Yang, X.; Odenbach, S.; Fröhlich, J.; Eckert, K.; On the homogenization of the thickness of Cu deposits by means of MHD convection within small dimension cells. Electrochem. Comm. 36 (2013) 80–83.
[2] Mutschke, G.; Tschulik, K.; Uhlemann, M.; Bund, M.; Fröhlich, J.: Comment on "Magnetic Structuring of Electrodeposits". Phys. Rev. Lett. 109 (2012) 229401.
[3] Uhlemann, M.; Tschulik, K.; Gebert, A.; Mutschke, G.; Fröhlich, J.; Bund, A.; Yang, X.; Eckert, K.: Structured Electrodeposition in Magnetic Gradient Fields. Eur. Phys. J. Spec. Top. 220 (2013) 287-302.

Keywords: Electrodeposition; magnetic field; layer thickness; Lorentz force; Kelvin force; numerical simulation

  • Lecture (Conference)
    Electrochemistry 2014, 22.-24.09.2014, Mainz, Deutschland

Publ.-Id: 20417

Magnetohydrodynamic Effects in Electrodeposition Reactions

Bund, A.; Ispas, A.; Mutschke, G.

This paper will discuss the effect of magnetic fields in electrodeposition reactions. The best studied effect is the magnetohydrodynamic effect which is due to the Lorentz force. In general Lorentz forces are generated in the electrolyte where the cross product of current density and magnetic flux density is different from zero. At places where the curl of this force density does not vanish a flow is driven. This in turn causes an increased mass transport and thus higher deposition rates in an electroplating cell. Of course the magnetically driven flow will always interact with other types of convective flows in the cell, e.g. the natural convection.
By tailoring the magnetic field (e.g. via its gradient) the uniformity of electroplated layers can be enhanced [1]. Also the structure of deposits (e.g. in the case of nickel fine-grained vs. coarse-grained) can be affected by the magnetic field [2]. Corresponding examples from the author's labs will be discussed in this paper.
In this contribution we will also show that numerical simulation is a powerful tool if one wants to harvest the full potential of magnetic flow control in electrochemical reactions.
[1] S. Mühlenhoff, G. Mutschke, M. Uhlemann, X. Yang, S. Odenbach, J. Fröhlich, K. Eckert. Electrochem. Commun. 36 (2013) 80.
[2] A. Ispas, H. Matsushima, A. Bund, B. Bozzini. J. Electroanal. Chem. 626 (2009) 174.

Keywords: Electrodeposition; Electrolysis; Magnetic field; Lorentz force; numerical simulation

  • Lecture (Conference)
    226th Meeting of The Electrochemical Society (ECS), 05.-10.10.2014, Cancun, Mexico

Publ.-Id: 20416

Modelling the Hydrogen evolution during water electrolysis

Mutschke, G.; Arndt, F.; Gerke, S.; Yang, X.; Fröhlich, J.; Eckert, K.

Hydrogen produced from wind or solar power can be used easily for storing energy, also at large scale, thus allowing to bridge the gap between offer and demand of green energy with respect to time and place. When splitting water by electrolysis, a deeper look at local phenomena near single bubbles at the electrode might be helpful to improve our understanding of the process. The presentation will first introduce a numerical model based on a phase field method to simulate growth and departure of gas bubbles from the electrode. The modelling is supported by detailed data of recent experiments on hydrogen single bubbles evolving at a platinum electrode. The numerical method is then validated by test cases. Work is still in progress at the time of writing this abstract. The simulation results will provide first insight into the local and temporal behaviour of species concentrations, current density and electrolyte velocity during growth and departure of a hydrogen bubble from the electrode.

Keywords: Water electrolysis; hydrogen evolution; bubble growth and departure; phase-field method; numerical simulation

  • Lecture (Conference)
    85th Annual Meeting of the International Association of Applied Mathematics and Mechanics (GAMM), 10.-14.03.2014, Erlangen, Deutschland

Publ.-Id: 20415

How to improve the uniformity of metal deposition at vertical electrodes by electromagnetic forces

Mutschke, G.; Mühlenhoff, S.; Selent, R.; Yang, X.; Uhlemann, M.; Fröhlich, J.; Odenbach, S.; Eckert, K.

In electrochemical plating often a uniform deposition is desirable allowing to reduce both energy and material costs. Magnetic fields are well known to influence the mass transfer during electrolysis and offer easy control of the deposition process. In this paper, first, time-constant Lorentz forces are considered which, if properly designed, may considerably improve the uniformity of the deposit. Second, time-dependent Lorentz forces are investigated. It is demonstrated that pulsed deposition offers a comparable enhancement of the uniformity.

Keywords: Electrolysis; Metal deposition; magnetic field; Lorentz force; pulsed deposition

  • Contribution to proceedings
    9th PAMIR International Conference on Fundamental and Applied MHD, 16.-20.06.2014, Riga, Lettland
    Proceedings of the 9th PAMIR International Conference on Fundamental and Applied MHD, Vol. 2, 164-168

Publ.-Id: 20414

Numerical simulation of the mass transfer of magnetic species at electrodes exposed to small-scale gradients of the magnetic field

Mutschke, G.; Tschulik, K.; Uhlemann, M.; Fröhlich, J.

The mechanisms responsible for the spatially inhomogeneous thickness of metal layers obtained by electrochemical deposition in magnetic gradient fields at small scale are controversially discussed in the literature. The paper presents the results of numerical simulations which support the reasoning that local convection at the electrode, driven by the curl of the magnetic gradient force, is responsible for the effects observed. The deposition of paramagnetic and of diamagnetic ions is discussed, and the influence of electrically inert magnetic ions present in the electrolyte is enlighted.

Keywords: Electrolysis; Magnetic field; Metal deposition; Kelvin force; Numerical simulation

  • Contribution to proceedings
    9th PAMIR International Conference on Fundamental and Applied MHD, 16.-20.06.2014, Riga, Lettland
    Proceedings of the 9th PAMIR International Conference on Fundamental and Applied MHD, Vol. 2, 169-171
  • Magnetohydrodynamics 51(2015)2, 369-374

Publ.-Id: 20413

MaterialVis: Material visualization tool using direct volume and surface rendering techniques

Okuyan, E.; Güdükbay, U.; Bulutay, C.; Heinig, K.-H.

Visualization of the materials is an indispensable part of their structural analysis. We developed a visualization tool for amorphous as well as crystalline structures, called MaterialVis. Unlike the existing tools, MaterialVis represents material structures as a volume and a surface manifold, in addition to plain atomic coordinates. Both amorphous and crystalline structures exhibit topological features as well as various defects. MaterialVis provides a wide range of functionality to visualize such topological structures and crystal defects interactively. Direct volume Rendering techniques are used to visualize the volumetric features of materials, such as crystal defects, which are responsible for the distinct fingerprints of a specific sample. In addition, the tool provides surface visualization to extract hidden topological features within the material. Together with the rich set of parameters and options to control the visualization, MaterialVis allows users to visualize various aspects of materials very efficiently as generated by modern analytical techniques such as the Atom Probe Tomography.

Keywords: Material visualisation; Embedded nanostructure visualisation; Direct volume rendering; Unstructured tetrahedral meshes; Crystal defects

Publ.-Id: 20412

High-field electron spin resonance spectroscopy of singlet-triplet transitions in the spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8

Wang, Z.; Kamenskyi, D.; Cépas, O.; Schmidt, M.; Quintero-Castro, D. L.; Islam, A. T. M. N.; Lake, B.; Aczel, A. A.; Dabkowska, A. B.; Dabkowski, A. B.; Luke, G. M.; Wan, Y.; Loidl, A.; Ozerov, M.; Wosnitza, J.; Zvyagin, S. A.; Deisenhofer, J.

Magnetic excitations in the isostructural spin-dimer systems Sr3Cr2O8 and Ba3Cr2O8 are probed by means of high-field electron spin resonance at subterahertz frequencies. Three types of magnetic modes were observed. One mode is gapless and corresponds to transitions within excited states, while two other sets of modes are gapped and correspond to transitions from the ground to the first excited states. The selection rules of the gapped modes are analyzed in terms of a dynamical Dzyaloshinskii-Moriya interaction, suggesting the presence of phonon-assisted effects in the low-temperature spin dynamics of Sr3Cr2O8 and Ba3Cr2O8.

Publ.-Id: 20411

Spontaneous and field-induced phase transitions inTbFe5Al7

Gorbunov, D. I.; Yasin, S.; Andreev, A. V.; Mushnikov, N. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.

Magnetization and ultrasound measurements have been performed on a TbFe5Al7 single crystal (tetragonal crystal structure) in the temperature range from 2 to 260 K in steady magnetic fields up to 18 T and in pulsed magnetic fields up to 60 T. The compound is a ferrimagnet (TC = 242 K) having an easy-plane anisotropy. Strong anisotropy is also present within the basal plane. At 2K, the easy magnetization direction is the [100] axis. In the vicinity of the compensation temperature, Tcomp = 84 K, TbFe5Al7 displays a spin-reorientation transition from [100] to the [110] axis accompanied by pronounced anomalies in the relative sound-velocity change and sound attenuation. Further, field-induced magnetic transitions have been observed in TbFe5Al7 by magnetization and acoustic measurements. Step-wise rotationof the magnetic moments with a wide hysteresis occurs for fields applied along the [100] axis at T < Tcomp and along the [110] axis at T > Tcomp. The relative sound-velocity change displays sharp minima and the sound attenuation sharp maxima at the transitions. The critical field of the transitions tends to zero near the compensation point and grows sharply away from it reaching 19 and 33 T for fields applied along the [100] and [110] directions, respectively. The Tb–Fe inter-sublattice exchange constant has been determined directly from the high-field data and using molecular-field theory.

Publ.-Id: 20410

Radiolabelling of nanoparticles and its use for transport studies

Franke, K.; Schymura, S.; Hildebrand, H.; Kulenkampff, J.; Lippmann-Pipke, J.

Hundreds of products containing nanoparticles (NP) are already in use. Nanotechnological innovation is identified in many sectors, including public health, employment and occupational health and safety, information society, industry, environmental protection, fuel and energy generation, transportation, security and space exploration. But the new materials may also pose risks to the environment and raise health and safety concerns. These risks have been addressed in several ongoing research projects. The overall conclusion so far is that, even though NP are not per se dangerous, there still is scientific uncertainty about the safety of NP in many aspects and therefore the safety assessment of the substances must be done on a case-by-case basis.
A key factor for the fate of NP in the environment and their introduction into the food chain is the bioavailability and thereby the mobility of the NP. Multiple factors control the migration behaviour of the NP in water and water saturated/unsaturated soils. Reversible and irreversible physical and chemical interactions cause a complex scenario with a great variety of boundary conditions. The transport of NP through soil, water and sediments is influenced by advection, diffusion, retardation due to sedimentation, filtration, staining, size exclusion effects, aging due to chemical corrosion, sorption and aggregation.
The experimental access to transport studies requires the observation of NP in complex environmental media at naturally relevant concentrations. This is a major challenge in laboratory work which can be overcome by the use of radiotracers.
In this work we present different techniques for the introduction of the radiotracers into the NP (Ag0, TiO2, MWCNT) including activation of NP, radiosynthesis of NP, radiolabelling of NP, self-diffusion of radioisotopes into NP and recoil labeling. The radiolabelled NP were used for 1D and 4D (time resolved Positron Emission Tomography (PET)) transport studies. The first results of the transport studies (BTC- break through curves and PET images) will be given as prove of principle.

Keywords: nanoparticle; radiolabelling; transport studies

  • Poster
    4th International Nuclear Chemistry Congress (INCC), 14.-19.09.2014, Maresias, Brasil

Publ.-Id: 20409

Transport system for solid targets of the COSTIS-system mounted at the BTL of the Cyclone 18/9

Franke, K.

The COSTIS system is a commercially available target station for the irradiation of solid targets. Up to 3 targets can be provided for irradiation by a slot system. In standard setup the target can be ejected via a pneumatically driven piston system. The target is then allowed to drop down into an open lead container, which can be closed remotely afterwards. The described procedure is well established and reliable. But the concept is limited to low dose targets and environments. The required entering of the cyclotron vault for manual pick up of the container at the cyclotron and the light 18 mm Pb lead shielding of the container itself cause exposure risk for the per-sonnel after long term irradiations with highly activated cyclotron parts and target. The purpose of this work was the design of an alternative for the pickup and the transport of irradiated targets to minimize the radiation dosage of the personnel during manual handling of the COSTIS-lead container.

Keywords: transport system; solid target; cyclotron

  • Poster
    15th International Workshop on Targetry and Target Chemistry (WTTC15), 18.-21.08.2014, Prague, Czech Republic

Publ.-Id: 20408

Metamagnetic transitions in U2Ni2Sn probed by high-field magnetization and acoustic measurements

Yasin, S.; Andreev, A. V.; Skourski, Y.; Zherlitsyn, S.; Wosnitza, J.

  • Poster
    DPG Frühjahrstagung, 31.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 20407

Magneto-acoustic quantum oscillations in YNi2B2C

Nössler, J.; Yasin, S.; Erfanifam, S.; Seerig, R.; Behr, G.; Zherlitsyn, S.; Wosnitza, J.

  • Poster
    DPG Frühjahrstagung, 31.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 20406

Modification of the COSTIS-system mounted at the Cyclone 18/9

Franke, K.

A widely distributed commercially available target station for the irradiation of solid targets is the COSTIS system. The system is specified for beams up to 500 W and is equipped with a front side He-cooling and water cooling on the back side. The target itself has a coin shape with a diameter of 24 mm and thickness of 2 mm. This recommends the system for irradiation of thin targets like foils but it is also useable for irradiation of metal and oxide powders. However the irradiation of powders and granulates is limited due to the dimension of the target cap-sule. A setup of a capped closed target is hardly achievable. The purpose of this work was the modification of the COSTIS target station for the use of thicker target capsules. This shall enable the more easy and safe handling and irradiation of powdery targets and the use of lockable target capsules.

Keywords: solid tagert; COSTIS; cyclotron

  • Poster
    15th International Workshop on Targetry and Target Chemistry (WTTC15), 18.-21.08.2014, Prague, Czech Republic

Publ.-Id: 20405

Superconductivity and ferromagnetism in nanostructured Bi3Ni

Schönemann, R.; Herrmannsdörfer, T.; Naumann, M.; Skrotzki, R.; Kaiser, M.; Heise, M.; Ruck, M.; Kummer, K.; Graf, D.; Wosnitza, J.

es hat kein Abstract vorgelegen

  • Poster
    DPG Frühjahrstagung, 31.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 20404

Magnetic-field-dependent reentrant superconductivity in Ga-implanted Si

Skrotzki, R.; Herrmannsdörfer, T.; Schönemann, R.; Heera, V.; Fiedler, J.; Kampert, E.; Wolff-Fabris, F.; Förster, T.; Völskow, A.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Helm, M.; Wosnitza, J.

  • Poster
    DPG Frühjahrstagung, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 20403

Magneto-elastic effects in Tb3Ga5O12

Löw, U.; Zherlitsyn, S.; Araki, K.; Akatsu, M.; Nemoto, Y.; Goto, T.; Zeitler, U.; Lüthi, B.

We report new results for the elastic constants studied in Faraday and Cotton-Mouton geometry in Tb3Ga5O12 (TGG), a frustrated magnetic substance with strong spin-phonon interaction and remarkable crystal-electric-field (CEF) effects. We analyze the data in the framework of CEF theory taking into account the individual surroundings of the six inequivalent Tb3+-ion positions. This theory describes both, elastic constants in the magnetic field and as a function of temperature. Moreover we present sound-attenuation data for the acoustic Cotton-Mouton effect in TGG.

Publ.-Id: 20402

Ultra high hole mobilities in a pure strained Ge quantum well

Mironov, O. A.; Hassan, A. H. A.; Morris, R. J. H.; Dobbie, A.; Uhlarz, M.; Chrastina, D.; Hague, J. P.; Kiatgamolchai, S.; Beanland, R.; Gabani, S.; Berkutov, I. B.; Helm, M.; Drachenko, O.; Myronov, M.; Leadley, D. R.

Hole mobilities at low and room temperature (RT) have been studied for a strained sGe/SiGe heterostructure using standard Van der Pauw resistivity and Hall effect measurements. The range of magnetic field and temperatures used were - 14 T < B < + 14 T and 1.5 K < T < 300 K respectively. Using maximum entropy-mobility spectrum analysis (ME-MSA) and Bryan's algorithm mobility spectrum (BAMS) analysis, a RT two dimensional hole gas drift mobility of (3.9 ± 0.4) × 103 cm2/V s was determined for a sheet density (ps) 9.8 × 1010 cm− 2 (by ME-MSA) and (3.9 ± 0.2) × 103 cm2/V s for a sheet density (ps) 5.9 × 1010 cm− 2 (by BAMS).

Publ.-Id: 20401

Crystal structure and magnetic properties of FeSeO3F - Alternating antiferromagnetic S = 5/2 chains

Hu, S.; Johnsson, M.; Law, J. M.; Bettis, J. L.; Whangbo, M.-H.; Kremer, R. K.

The new oxofluoride FeSeO3F, which is isostructural with FeTeO3F and GaTeO3F, was prepared by hydrothermal synthesis, and its structure was determined by X-ray diffraction. The magnetic properties of FeSeO3F were characterized by magnetic susceptibility and specific heat measurements, by evaluating its spin exchanges on the basis of density functional theory (DFT) calculations, and by performing a quantum Monte Carlo simulation of the magnetic susceptibility. FeSeO3F crystallizes in the monoclinic space group P21/n and has one unique Se4+ ion and one unique Fe3+ ion. The building blocks of FeSeO3F are [SeO3] trigonal pyramids and cis-[FeO 4F2] distorted octahedra. The cis-[FeO4F2] octahedra are condensed by sharing the O-O and F-F edges alternatingly to form [FeO3F]∞ chains, which are interconnected via the [SeO3] pyramids by corner-sharing. The magnetic susceptibility of FeSeO3F is characterized by a broad maximum at 75(2) K and a long-range antiferromagnetic order below ∼45 K. The latter is observed by magnetic susceptibility and specific heat measurements. DFT calculations show that the Fe-F-Fe spin exchange is stronger than the Fe-O-Fe exchange, so each [FeO3F]∞ chain is a Heisenberg antiferromagnetic chain with alternating antiferromagnetic spin exchanges. The temperature dependence of the magnetic susceptibility is well-reproduced by a quantum-Monte Carlo simulation.

Publ.-Id: 20400

Direct measurements of the magnetocaloric affect in the Heusler alloy Ni50Mn35In15 in pulsed magnetic fields

Ghorbani Zavareh, M.; Salazar Mejia, C.; Nayak, A.; Nicklas, M.; Skourski, Y.; Felser, C.; Wosnitza, J.

  • Poster
    Intermag 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 20399

Magnetic, thermal, and transport properties of single crystalline U3Cu4Ge4

Skourski, Y.; Andreev, A. V.; Gorbunov, D. I.; Henriques, M. S.; Havela, L.; Wosnitza, J.; Goncalves, A. P.

  • Poster
    Intermag 2014, 04.-08.05.2014, Dresden, Deutschland

Publ.-Id: 20398

Precision measurement of Timing RPC gas mixtures with laser-beam induced electrons

Naumann, L.; Siebold, M.; Kaspar, M.; Kämpfer, B.; Kotte, R.; Laso Garcia, A.; Loeser, M.; Schramm, U.; Wüstenfeld, J.

The main goals of a new test facility at Helmholtz-Zentrum Dresden-Rossendorf are precision measurements of the electron drift velocity and the Townsend coefficient of gases at atmospheric pressure in the strongest ever used homogenous electrical fields and the search for new RPC gas mixtures to substitute the climate harmful Freon. Picosecond UV laser pulses in the UV were focused into a sub-millimeter gas gap to initialize a defined tiny charge. These gaps are formed by electrodes of low-resistive ceramics or high-resistive float glass. The charge multiplication occurs in a strong homogeneous electric field of up to 100\,kV/cm. Electron-ion pairs were generated in a cylindrical micro-volume by multi-photon ionization. The laser-pulse repetition rate ranges from 1\,Hz to a few kHz. The RPC time resolution has been measured for different gases. First results of the Townsend coefficient at 100\,kV/cm show a strong disagreement between the present measurement and Magboltz simulations for the typical Timing RPC gas mixture C2F4H2/SF6/i-C4H{10}, while the measured electron drift velocities are in a good agreement with the model predictions.

Publ.-Id: 20397

Phylogenetic diversity of archaea and the archaeal ammonia monooxygenase gene in uranium mining-impacted locations in Bulgaria

Radeva, G.; Kenarova, A.; Bachvarova, V.; Flemming, K.; Popov, I.; Vassilev, D.; Selenska-Pobell, S.

Uranium mining and milling activities adversely affect the microbial populations of impacted sites. The negative effects of uranium on soil bacteria and fungi are well studied, but little is known about the effects of radionuclides and heavy metals on archaea. The composition and diversity of archaeal communities inhabiting the waste pile of the Sliven uranium mine and the soil of the Buhovo uranium mine were investigated using 16S rRNA gene retrieval. A total of 355 archaeal clones were selected, and their 16S rDNA inserts were analysed by restriction fragment length polymorphism (RFLP) discriminating 14 different RFLP types. All evaluated archaeal 16S rRNA gene sequences belong to the 1.1b/Nitrososphaera cluster of Crenarchaeota. The composition of the archaeal community is distinct for each site of interest and dependent on environmental characteristics, including pollution levels. Since the members of 1.1b/Nitrososphaera cluster have been implicated in the nitrogen cycle, the archaeal communities from these sites were probed for the presence of the ammonia monooxygenase gene (amoA). Our data indicate that amoA gene sequences are distributed in a similar manner as in Crenarchaeota, suggesting that archaeal nitrification processes in uranium mining-impacted locations are under the control of the same key factors controlling archaeal diversity.

Publ.-Id: 20396

EGF receptor-targeting peptide conjugate incorporating a near-IR fluorescent dye and a novel 1,4,7-triazacyclononane-based 64Cu(II) chelator assembled via click chemistry

Viehweger, K.; Barbaro, L.; Pombo García, K.; Joshi, T.; Geipel, G.; Steinbach, J.; Stephan, H.; Spiccia, L.; Graham, B.

A new Boc-protected 1,4,7-triazacyclononane (TACN)-based pro-chelator compound featuring a “clickable” azidomethylpyridine pendant has been developed as a building block for the construction of multimodal imaging agents. Conjugation to a model alkyne (propargyl alcohol), followed by deprotection, generates a pentadentate ligand, as confirmed by X-ray crystallographic analysis of the corresponding distorted square-pyramidal Cu(II) complex. The ligand exhibits rapid 64Cu2+-binding kinetics (> 95% radiochemical yield in < 1 min) and a high resistance to demetallation. It may thus prove suitable for use in 64Cu-based in vivo positron emission tomography (PET). The new chelating building block has been applied to the construction of a bimodal (PET/fluorescence) peptide-based imaging probe targeting the epidermal growth factor (EGF) receptor, which is highly over-expressed on the surface of several types of cancer cells. The probe consists of a hexapeptide sequence, Leu-Ala-Arg-Leu-Leu-Thr (designated “D4”), coupled to a β-homopropargylglycine residue with the TACN-based chelator “clicked” to its side chain, followed by a Cys-β-Ala-β-Ala spacer. A sulfonated near-infrared (NIR) fluorescent cyanine dye (sulfo-Cy5) was introduced at the N-terminus to study the EGF receptor-binding ability of the probe by laser-fluorescence spectroscopy. Binding was also confirmed by co-immunoprecipitation methods, and an apparent dissociation constant (Kd) of ca. 10 nM was determined from radioactivity-based measurements of probe binding to two EGF receptor-expressing cell lines (FaDu and A431). The probe is shown to be a biased or partial allosteric agonist of the EGF receptor, inducing phosphorylation of Thr669 and Tyr992, but not the Tyr845, Tyr998, Tyr1045, Tyr1068 or Tyr1148 residues of the receptor, in the absence of the orthosteric EGF ligand. Additionally, the probe was found to suppress the EGF-stimulated autophosphorylation of these latter residues, indicating that it is also a non-competitive antagonist.

  • Bioconjugate Chemistry 25(2014)5, 1011-1022
    Online First (2014) DOI: 10.1021/bc5001388

Publ.-Id: 20395

Diagnostic nanoparticle targeting of the EGF-receptor in complex biological conditions using single-domain antibodies

Zarschler, K.; Prapainop, K.; Mahon, E.; Rocks, L.; Bramini, M.; Kelly, P.; Stephan, H.; Dawson, K. A.

For effective localization of functionalized nanoparticles at diseased tissues such as solid tumours or metastases through biorecognition, appropriate targeting vectors directed against selected tumour biomarkers are a key prerequisite. The diversity of such vector molecules ranges from proteins, including antibodies and fragments thereof, through aptamers and glycans to short peptides and small molecules. Here, we analyse the specific nanoparticle targeting capabilities of two previously suggested peptides (D4 and GE11) and a small camelid single-domain antibody (sdAb), representing potential recognition agents for the epidermal growth factor receptor (EGFR). We investigate specificity by way of receptor RNA silencing techniques and look at increasing complexity in vitro by introducing increasing concentrations of human or bovine serum. Peptides D4 and GE11 proved problematic to employ and conjugation resulted in non-receptor specific uptake into cells. Our results show that sdAb functionalised particles can effectively target the EGFR, even in more complex bovine and human serum conditions where targeting specificity is largely conserved for increasing serum concentration. In human serum however, an inhibition of overall nanoparticle uptake is observed with increasing protein concentration. For highly affine targeting ligands such as sdAbs, targeting a receptor such as EGFR with low serum competitor abundance, receptor recognition function can still be partially realised in complex conditions. Here, we stress the value of evaluating the targeting efficiency of nanoparticle constructs in realistic biological milieu, prior to more extensive in vivo studies.

Publ.-Id: 20394

What next?

Baumann, M.; Overgaard, J.

Publ.-Id: 20393

A new drag correlation from fully resolved simulations of flow past monodisperse static arrays of spheres

Tang, Y.; Kriebitzsch, S.; Peters, E. A. J. F.; van der Hoef, M. A.; Kuipers, J. A. M.

We performed fully resolved simulations of flows past fixed assemblies of monodisperse spheres using an iterative Immersed Boundary (IB) Method, for both face-centered-cubic (FCC) array and random configurations. For the latter, a methodology has been applied such that the computed gas-solid force is almost independent of the grid resolution. Simulations in this work extend the previously similar studies to a wider range of solids volume fraction (φ ∈ [0.1, 0.6]) and Reynolds number (Re ∈ [50, 1000]). We propose a new drag correlation combining the existed drag correlations for low-Re flows and single-sphere flows, which fits the entire data set with an average relative deviation of 4%. This correlation is so-far the best possible expression for the drag force in monodisperse static arrays of spheres, and is the most accurate basis to introduce the particle mobility for dynamic gas-solid systems, such as in fluidized beds.

Keywords: Immersed Boundary Method; fully resolved simulations; drag correlation

Publ.-Id: 20392

Early increase of cannabinoid receptor density after experimental traumatic brain injury in the newborn piglet

Donat, C. K.; Fischer, F.; Walter, B.; Deuther-Conrad, W.; Brodhun, M.; Bauer, R.; Brust, P.

Paediatric traumatic brain injury (TBI) is a leading cause of death and disability. Previous studies showed neuroprotection after TBI by (endo)cannabinoid mechanisms, suggesting involvement of cannabinoid receptors (CBR). We therefore determined CBR densities and expression of the translocator protein 18 kDA(TSPO) in newborn piglets after experimental TBI. Newborn female piglets were subjected to sham operation (n=6) or fluid-percussion (FP)injury (n=7) under controlled physiological conditions. After six hours, brains were frozen, sagittally cut and incubated with radioligands for CBR ([3H]CP-55,940, [3H]SR141716A) and TSPO ([3H]PK11195), an indicator of gliosis/brain injury. Early after injury, FP-TBI elicited a significant ICP increase at a temporary reduced cerebral perfusion pressure; however, CBF and CMRO2 remained within physiological range.
At 6 hours post injury, we found a statistically significant increase in binding of the non-selective agonist [3H]CP-55,940 in 15 of the 24 investigated brain regions of injured animals. By contrast, no significant changes in binding of the CB1R-selective antagonist [3H]SR141716A were observed. A non-significant trend towards increased binding of [3H]PK11195 was observed, suggesting an incipient microglial activation. We therefore conclude that in this model and time span after injury, the increase in [3H]CP-55,940 binding reflects changes in CB2R density, while CB1R density is not affected. The results may provide explanation for the neuroprotective properties of cannabinoid ligands and future therapeutic strategies of TBI.

Keywords: traumatic brain injury; autoradiography; cannabinoid receptors; neuroprotection

  • Open Access Logo Acta Neurobiologiae Experimentalis 74(2014), 197-210

Publ.-Id: 20391

Sputtered Si-containing low-friction carbon coatings for elevated temperatures

Jantschner, O.; Field, S. K.; Music, D.; Terziyska, V. L.; Schneider, J. M.; Munnik, F.; Zorn, K.; Mitterer, C.

This work presents a tribological study on three sputtered amorphous carbon-based coatings containing Si and Cr (a-C, a-C:Cr and a-C:Si). Molecular dynamics simulations predict tetrahedral bonds between C and Si in the a-C matrix. Ball-on-disk-tests against Al2O3 carried out at room temperature revealed a coefficient of friction of 0.08–0.1 for all films. Between 250 and 325 °C, Si decreases the COF and wear rate to <0.05 and <5×10-17m3/N×laps, respectively. The a-C reference shows a COF of 0.15±0.05 and a wear rate of 1×10-16m3/N×laps, whereas the a-C:Cr film failed. The improved tribological performance of a-C:Si expands its application temperature to 450 °C and is most probably related to formation of Si-compounds on the film surface, as evidenced by X-ray photoelectron spectroscopy.

Keywords: Amorphous carbon; Elevated temperatures; Thermal stability; Temperature induced lubrication

Publ.-Id: 20390

Mapping Hydrophobicity combining AFM and Raman Spectroscopy

Rudolph, M.; Peuker, U. A.

A new concept to evaluate the floatability of individual minerals in an ore specimen is presented. The method is based on the combination of colloidal probe atomic force microscopy to determine hydrophobic interactions responsible for the flotation of fine mineral particles and Raman spectroscopy to identify the mineral phase at the same location. Both methods show a high spatial resolution and allow investigating even small individual minerals. The ore sample of this study is a syenite rock from south Sweden containing the valuable rare earth mineral eudialyte and gangue minerals mainly comprising feldspars, nepheline, aegirine and zeolites. Using the poor selective collector sodium oleate we demonstrate how hydrophobic interactions become apparent conducting force distance measurements in the aqueous environment. We discuss different parameters of the force spectroscopy in static and dynamic mode to be used to define a measure for floatability. In contrast to other studies on the hydrophobic interactions in flotation we propose to draw Information from the detachment of the hydrophobic probe particle of the atomic force microscope from the mineral surface in contrast to the approach force distance spectroscopy. All the hydrophobic interactions identified can be contributed to the appearance of gas layers on the surfaces leading to capillary interactions.

Keywords: Floatability; Flotation; Nanobubbles; Eudialyte; Rare Earth Elements

Publ.-Id: 20389

Magnetic films tailored by ion irradiation

Fassbender, J.

In recent years the tailoring of magnetic properties by means of ion irradiation and implantation techniques has become fashionable. Early investigations relied on the fact that the perpendicular magnetic anisotropy of Co/Pt multilayers depend sensitively on the interface sharpness [1]. Subsequently also the ion induced modification of exchange bias phenomena as well as interlayer exchange coupling has been investigated [2]. For single magnetic films ion implantation has been used to reduce the Curie temperature and hence the saturation magnetization [3]. Nowadays also the reverse process, i.e. the creation of nanomagnets within special binary alloys is employed [4,5]. In combination with lithography a pure magnetic patterning becomes possible [6] leading to hybrid magnetic materials [7] with properties different from both, the ion irradiated as well as the untreated material. Even ion induced chemical reduction can be employed to create a nanomagnetic pattern [8,9].

In an alternative route to design magnetic properties periodically modulated substrates are used. Low energy ion erosion provides an easy technology to create modulated surfaces with periods ranging from 20 to 200 nm. Due to the broken translational invariance new anisotropy contributions appear [10] and additional relaxation channels are opened [11].

An overview of the present status in this research field will be given.

1. C. Chappert et al., Science 280, 1919 (1998).
2. J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
3. J. Fassbender, J. McCord, Appl. Phys. Lett. 88, 252501 (2006).
4. E. Menendez et al., Small 5, 229 (2009).
5. R. Bali et al., Nano Lett. in press.(2014).
6. J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320, 579 (2008).
7. J. McCord, L. Schultz, J. Fassbender, Adv. Mater. 20, 2090 (2008).
8. S. Kim et al., Nature Nanotechnology 7, 567 (2012).
9. J. Fassbender, Nature Nanotechnology 7, 554 (2012).
10. M. O. Liedke, et al., Phys. Rev. B 75, 220407(R) (2007).
11. M. Körner et al., Phys. Rev. B 88, 054405 (2013).

Keywords: magnetism; ion irradiation; patterning

  • Invited lecture (Conferences)
    Physics of Surfaces and Interfaces, 24.-28.02.2014, Puri, Indien

Publ.-Id: 20388

Form follows function - neue Funktionalitäten durch Nanostrukturierung

Fassbender, J.

Festvortrag anlässlich des 10-jährigen Jubiläums des Nano Structuring Center Kaiserslautern

Keywords: nano; patterning; ion irradiation; magnetism

  • Invited lecture (Conferences)
    10 Jahre Nano Structuring Centre Kaiserslautern, 08.07.2014, Kaiserslautern, Deutschland

Publ.-Id: 20387

Biosorption and Biomineralization of U(VI) by the Marine Bacterium Idiomarina loihiensis MAH1: Effect of Background Electrolyte and pH

Morcillo, F.; Gonzalez-Munoz, M. T.; Reitz, T.; Romero-Gonzalez, M. E.; Arias, J. M.; Merroun, M. L.

The main goal of this study is to compare the effects of pH, uranium concentration, and background electrolyte (seawater and NaClO4 solution) on the speciation of uranium(VI) associated with the marine bacterium Idiomarina loihiensis MAH1. This was done at the molecular level using a multidisciplinary approach combining X-ray Absorption Spectroscopy (XAS), Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS), and High Resolution Transmission Electron Microscopy (HRTEM). We showed that the U(VI)/bacterium interaction mechanism is highly dependent upon pH but also the nature of the used background electrolyte played a role.
At neutral conditions and a U concentration ranging from 5-10(-4) to 10(-5) M (environmentally relevant concentrations), XAS analysis revealed that uranyl phosphate mineral phases, structurally resembling meta-autunite [Ca(UO2)(2)(PO4)(2) 2-6H(2)O] are precipitated at the cell surfaces of the strain MAH1. The formation of this mineral phase is independent of the background solution but U(VI) luminescence lifetime analyses demonstrated that the U(VI) speciation in seawater samples is more intricate, i. e., different complexes were formed under natural conditions. At acidic conditions, pH 2, 3 and 4.3 ([U] = 5 . 10(-4) M, background electrolyte = 0.1 M NaClO4), the removal of U from solution was due to biosorption to Extracellular Polysaccharides (EPS) and cell wall components as evident from TEM analysis. The LIII-edge XAS and TRLFS studies showed that the biosorption process observed is dependent of pH. The bacterial cell forms a complex with U through organic phosphate groups at pH 2 and via phosphate and carboxyl groups at pH 3 and 4.3, respectively. The differences in the complexes formed between uranium and bacteria on seawater compared to NaClO4 solution demonstrates that the actinide/microbe interactions are influenced by the three studied factors, i.e., the pH, the uranium concentration and the chemical composition of the solution.

Publ.-Id: 20386

Realization of a spin-wave multiplexer

Vogt, K.; Fradin, F. Y.; Pearson, J. E.; Sebastian, T.; Bader, S. D.; Hillebrands, B.; Hoffmann, A.; Schultheiss, H.

Recent developments in the field of spin dynamics—like the interaction of charge and heat currents with magnons, the quasi-particles of spin waves—opens the perspective for novel information processing concepts and potential applications purely based on magnons without the need of charge transport. The challenges related to the realization of advanced concepts are the spin-wave transport in two-dimensional structures and the transfer of existing demonstrators to the micro- or even nanoscale. Here we present the experimental realization of a microstructured spin-wave multiplexer as a fundamental building block of a magnon-based logic. Our concept relies on the generation of local Oersted fields to control the magnetization configuration as well as the spin-wave dispersion relation to steer the spin-wave propagation in a Y-shaped structure. Thus, the present work illustrates unique features of magnonic transport as well as their possible utilization for potential technical applications.

Keywords: Magnonics; Spintronics; Spin Waves; Brillouin Light Scattering Microscopy

  • Nature Communications 5(2014), 3727
    Online First (2014) DOI: 10.1038/ncomms4727
  • Invited lecture (Conferences)
    Magnetism and Magnetic Materials, 7.11.2014, Honolulu, Hawaii, USA

Publ.-Id: 20385

Ultrafast detection from 0.6 THz to 33 THz employing graphene flakes

Mittendorff, M.; Winnerl, S.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S.; Schneider, H.; Helm, M.

Graphene can serve as an excellent active material for the development of ultrafast electro-optic devices. With the vanishing bandgap, photons can be absorbed via interband processes over an extremely wide spectral range (from ultraviolet to far-infrared). However, in the regime of non-zero Fermi energy and very low photon energies, interband absorption can be prohibited. In this case intraband absorption is an efficient process. T. Müller et al. [1] presented an ultrafast detector for the near-infrared range. Their device was operated at room temperature and reached frequencies of up to 16 GHz. Field-effect transistors made of graphene flakes have been employed for the detection of THz radiation. Vicarelli et al. [2] developed a very sensitive detector for cw radiation at room temperature, while Yan et al. [3] presented an ultrafast bolometer which was cooled to 4 K.
We present a detector based on a graphene flake for a very broad spectral range from 0.6 THz to 33 THz, corresponding to wavelengths of 500 µm to 9 µm, respectively. To couple the far-infrared radiation efficiently to the flake, which is orders of magnitude smaller than the largest wavelengths, a logarithmic periodic antenna [5] is patterned on top of the substrate. The antenna is connected to the graphene flake by an interdigitated structure (see fig. 1). A coaxial cable, bonded to the outer part of the two antenna arms, serves as signal line. The signal is amplified by a high-frequency amplifier and recorded with a fast sampling oscilloscope with a bandwidth of 30 GHz.
The free-electron laser (FEL) FELBE at the Dresden lab served as radiation source for the characterizing the detectors at wavelengths of up to 220 µm. Additional data were obtained using a THz gas laser at the University of Regensburg providing radiation pulses with wavelengths of up to 500 µm. The response time of the devices is about 50 ps, which highlights the potential of this detector for timing measurements of intense THz pulses. The signal of two FEL pulses with a temporal delay of 500 ps is shown in fig. 2. The pulse energy of each of the pulses was about 40 nJ, which lead to a signal amplitude of 30 mV. Despite a low responsivity of about 5 nA/W, pulses with energies down to 1 nJ can be resolved. For high pulse energies, the signal amplitude saturates strongly. While this saturation limits the dynamic range for linear detection, it can be exploited in autocorrelation measurements [6]. In this regime the response time is not limited by the RC time constant but by the intrinsic response time of the graphene flake (< 10 ps).
Furthermore we demonstrate the important role of the substrate for these devices. Our first devices were produced on SiO2 on Si [7]. When a low-resistivity substrate is used, the high-speed performance of the device is strongly deteriorated. The antenna forms a capacitor with the conductive substrate material and therefore increases the RC time constant of the detector. Devices on high-resistive Si could resolve fast signals only for wavelengths above 20 µm. This can be attributed to phonon-related absorption in the Si substrate resulting in higher substrate conductivity due to thermally activated carriers. To overcome this restriction, a new set of detectors has been fabricated on semi-insulating SiC. As graphene is nearly invisible on top of SiC, graphene grown by chemical vapor deposition on copper was transferred to the new substrate and located by Raman mapping. With these new devices FEL pulses can be measured down to a wavelength of 9 µm.


[1] T. Müller et al., Nature Photon. 4, 297 (2010).
[3] L. Vicarelli et al., Nature Mat. 11, 865 (2012).
[4] J. Yan et al., Nature Nanotechnol. 7, 472 (2012).
[5] R. Mendis et al., IEEE Antennas and Propag. Lett. 4, 85 (2005).
[6] S. Winnerl et al., Appl. Phys. Lett. 73, 2983 (1998).
[7] M. Mittendorff et al. Appl. Phys. Lett. 103, 021113 (2013).

  • Lecture (Conference)
    Graphene 2014, 06.-09.05.2014, Toulouse, France

Publ.-Id: 20384

Positron annihilation in flight: experiment with slow and fast positrons

Cizek, J.; Vlcek, M.; Lukac, F.; Melikhova, O.; Prochazka, I.; Anwand, W.; Wagner, A.; Butterling, M.; Krause-Rehberg, R.

A novel digital coincidence Doppler broadening (D-CDB) spectrometer was employed for energy resolved investigations of two-quantum annihilation-in-flight (TQAF). The TQAF phenomenon was studied using monoenergetic positrons produced in a slow positron beam and also using fast positrons. Because of a low background the measurements on the slow positron beam could be performed in a close geometry and the TQAF contribution in the two-dimensional gamma ray energy spectra fills a ‘bowl-like’ area delimited by a hyperbolic curve and a kinematical cut-off determined by the kinetic energy of positrons. With decreasing positron energy the area of TQAF contribution becomes smaller and disappears completely for slow positrons with energies below ~ 100 eV. The measurements with fast positrons were restricted to a limited range of angles between the annihilation gamma rays and the TQAF events contribute to a hyperbolic band in gamma ray energy spectrum.

Keywords: positron annihilation in flight; fast and slow positrons

Publ.-Id: 20383

Optical ridge waveguides in 4H-SiC single crystal produced by combination of carbon ion irradiation and femtosecond laser ablation

Luan, Q.; Jia, Y.; Wang, Y.; Akhmadaliev, S.; Zhou, S.; de Aldana, J.; Tan, Y.; Chen, F.

Optical ridge waveguides were fabricated in 4H-SiC single crystal by combination of 15 MeV C5+ ion irradiation and femtosecond laser ablation. The near-field modal intensity distributions exhibit the well-confined light propagation in the waveguides. A propagation loss as low as 5.1 dB/cm has been achieved at 632.8 nm for the ridge waveguide. The investigation of confocal micro-Raman spectra suggests partial transition of 4H-SiC to 6H-SiC in the irradiated region.

Keywords: Waveguides; SiC; Ion irradiation

Publ.-Id: 20382

Commissioning of a compact laser-based proton beam line for high intensity bunches around 10 MeV

Busold, S.; Schumacher, D.; Deppert, O.; Brabetz, C.; Kroll, F.; Blažević, A.; Bagnoud, V.; Roth, M.

We report on the first results of experiments with a new laser-based proton beam line at the GSI accelerator facility in Darmstadt. It delivers high current bunches at proton energies around 9.6 MeV, containing more than 10^9 particles in less than 10 ns and with tunable energy spread down to 2.7% (ΔE/E0 at FWHM). A target normal sheath acceleration stage serves as a proton source and a pulsed solenoid provides for beam collimation and energy selection. Finally a synchronous radio frequency (rf) field is applied via a rf cavity for energy compression at a synchronous phase of −90 deg. The proton bunch is characterized at the end of the very compact beam line, only 3 m behind the laser matter interaction point, which defines the particle source.

Publ.-Id: 20381

Effect of Waveform of ac Voltage on the Morphology and Crystallinity of Electrochemically Assembled Platinum Nanowires

Nerowski, A.; Pötschke, M.; Wiesenhütter, U.; Nicolai, J.; Cikalova, U.; Dianat, A.; Erbe, A.; Opitz, J.; Bobeth, M.; Baraban, L.; Cuniberi, G.

Here we present electrochemically grown ultrathin platinum nanowires and demonstrate that their morphology and crystalline structure can be tuned by the waveform of the alternating voltage applied to the microelectrodes. The structure of the nanowires was analyzed by scanning and transmission electron microscopy. The voltage signal, applied to grow the nanowires, consisted of several Fourier components of a square-shaped wave. We observed that, depending on the number of Fourier components, the morphology of the nanowires changed from branched dendritic-like patterns to straight wires and the wire crystallinity changed from polycrystalline to highly oriented growth with the [111] direction of platinum crystallites along the nanowire axis. We propose a simple model to explain this intriguing observation.

Keywords: directed electrochemical nanowire growth; dielectrophoresis

Publ.-Id: 20380

Defects Studies of ZnO Single Crystals Prepared by Various Techniques

Lukac, F.; Cizek, J.; Prochazka, I.; Melikhova, O.; Anwand, W.; Brauer, G.

The aim of the present work was a comparison of defects in ZnO crystals grown by various techniques available nowadays, namely hydrothermal growth, pressurized melt, Bridgman method growth and vapor phase growth. Positron annihilation spectroscopy was employed as a principal tool for characterization of defects in ZnO crystals grown by above mentioned various techniques. ZnO crystals can be divided into two groups: (i) hydrothermal grown crystals, which exhibit positron lifetime of 179-182 ps and (ii) ZnO crystals grown by the other techniques (pressurized melt, Bridgman method, vapor phase growth) which are characterized by the lower lifetimes falling in the range of 160-173 ps. Comparison of experimental data with ab initio theoretical calculations revealed that HT grown ZnO crystals contains Zn vacancies associated with hydrogen atom in a bond-centered site. On the other hand, ZnO crystals prepared by other techniques contain most probably stacking faults created by stresses induced by temperature gradients in the melt.

Keywords: Crystal defects; Positron annihilation spectroscopy; Ab initio theoretical calculations; Hydrogen; Hydrothermal growth; Vapor phase growth; Zn vacancies; ZnO single crystals

Publ.-Id: 20379

Uranium redox processes and uptake by plant cells

Geipel, G.; Viehweger, K.

Recently we have shown that uranium can be taken up by plant cells. Fractionation studies showed that the uranium was present in nearly all cell compartments. Nevertheless, luminescence measurements showed that the speciation of the uranium in the several cell compartments differs from each other.
One of the major remaining questions concerns to the ways of uranium uptake. Recently published work /1,2/ proposed that the uranium uptake is influenced by the iron uptake. As it is known that the iron uptake occurs via reduction of the iron(III) into iron(II), we conclude that uranium uptake should also by accompanied by a redox process. First measurements by laser-induced photo-acoustic spectroscopy gave evidence for the presence of uranium(IV) inside the cells.
The formation of uranium(IV) from uranium(VI) is a more complicated redox process, as the oxo-cation uranium(VI) has to be transformed into an oxo-hydrate form. Electrochemically this process is irreversibly. In systems existing at nearly neutral pH additionally hydrolysis or complex formation of the uranium ions occur.
On the other hand the formed uranium(IV) can also be formed by a disproportionation step from uranium(V).

2UO2+ + 4H2O  UO2(OH)2 + U(OH)4 + 2H+

From electrochemical point of view the formation of uranium(V) is a reversible process and the redox potential uranium(VI)/uranium(V) is of the same order as the redox potential iron(III)/iron(II) (values for acidic solution).

UO22+ + e-  UO2+ E0 = - 0.16 V
Fe3+ + e-  Fe2+ E0 = - 0.77 V

However, these values are strongly influenced by pH and complex formation. Uranium(VI) as well as uranium(IV) was detected in cells of Brassica napus.
Therefore we tried to prove the oxidation state uranium(V) by electrochemical and spectroscopic methods.

Keywords: Uranium; Plant cells; redox chemistry

  • Contribution to proceedings
    Biometals 2014, 13.-18.07.2014, Durham, USA
    Proceedings of Biometals 2014

Publ.-Id: 20378

Cross-section measurements at astrophysically relevant energies: The LUNA experiment

Formicola, A.; Bruno, C. G.; Caciolli, A.; Cavanna, F.; Depalo, R.; Di Leva, A.; Scott, D. A.; Trezzi, D.; Aliotta, M.; Anders, M.; Bemmerer, D.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Prati, P.; Somorjai, E.; Straniero, O.; Strieder, F.; Szücs, T.

Accurate knowledge of thermonuclear reaction rates is important in understanding the generation of energy, the luminosity of neutrinos, and the synthesis of elements in stars. Cross-section measurements for quiescent stellar H-burning are mainly hampered by extremely low counting rate and cosmic background. The LUNA Collaboration has shown that, by going underground and by using the typical techniques of low background physics, it is possible to measure nuclear cross-sections down to the energy of the nucleosynthesis inside stars. This paper reports an overview of the experimental techniques adopted in underground nuclear astrophysics through a summary of the main recent results and achievements. The future developments of the LUNA experiment are also given.

Keywords: Nuclear astrophysics; LUNA; Underground accelerator; Solar fusion; Big Bang nucleosynthesis

Publ.-Id: 20377

First-principles study of the free energy of point defects and their clusters in bcc-Fe

Devaraj, M.; Posselt, M.; Schiwarth, M.

No abstract available. For informations please contact the authors.

Keywords: DFT calculations; point defects; foreign atoms; embedded clusters; bcc-Fe

  • Lecture (Conference)
    n-FAME Workshop, 06.-07.05.2014, Stockholm, Sweden

Publ.-Id: 20376

Ain films obtained by a broad energy Nitrogen ion Implantation and rapid thermal anealing process

Grigorov, K. G.; Nedkov, I.; Beshkov, G.; Angelov, C.; Maciel, H. S.; Matz, W.; Groetzchel, R.; Velchev, N.

The paper describes structural, morphological and electrical investigations of thin AlN films. The films were obtained by broad energy range ion bombardment (BERIB) of aluminium, with doses ranging from 1.5 × 1017 cm-2 to 6 × 1017 cm-2. This technique, to our knowledge, has not been described previously in the literature. The ion implantation was carried out with two species - nitrogen atoms with energies from 50, 30, and 20 keV and nitrogen ions with energies of 50 and 30 keV. These energy values were chosen in order to ensure a continuous and wide nitride layer, at least of 150 nm thick.

Keywords: Aluminium nitrides; RTA; PECVD; Ion implantation and characterization

  • Journal of Optoelectronics and Advanced Materials 7(2005)1, 381-384

Publ.-Id: 20375

Summary of the investigations on the decommissioned WWER-440 reactor pressure vessel of the NPP Greifswald

Viehrig, H.-W.; Houska, M.; Altstadt, E.; Valo, M.

The Greifswald WWER-440/V-230 nuclear reactors represent the first generation of this reactor type. The four units of the Greifswald NPP were eternity shut down in 1990 after 11 –15 years of operation and represent different material conditions as follows:

  • Irradiated (Unit 4),
  • irradiated and recovery annealed (Units 2 and 3), and
  • irradiated, recovery annealed and re-irradiated (Unit1).
The recovery annealing of the RPV was performed at a temperature of 475° for about 152 hours and included a region covering ±0.70 m above and below the core beltline welding seam.
Material samples of a diameter of 119 mm called trepans were extracted from the RPV walls. The research program is focused on the characterisation of the RPV steels (base and weld metal) across the thickness of the RPV wall.
This paper presents test results measured on the trepans of the beltline welding seam and base metal of the Units 1, 2 and 4 RPV. The key part of the testing is focussed on the determination of the reference temperature T0 following the ASTM standard E1921 to determine the facture toughness, and how it degrades under neutron irradiation and is recovered by thermal annealing. Other than that the mentioned test results include Charpy-V and tensile test results. Following results have been determined:
  • The results represent the material conditions within the multilayer beltline welding seams and base metals aged under real operating conditions.
  • The fracture toughness values at cleavage failure, KJc, of the weld metals generally follow the course of the MC though with a large scatter. A strong scatter of the KJc values of the irradiated and recovery annealed base metal of Unit 1 and Unit 4 RPV, respectively, is observed with clearly more than 2% of the values below the fracture toughness curve for 2% fracture probability.
  • There is a large variation in the T0 values evaluated across the thickness of the multilayered welding seams from the investigated RPV’s.
  • For the beltline welding seam of the Unit 4 RPV it is demonstrated that the ductile-to-brittle transition temperature (TT) shift predicted by the Russian code [PNAE G-7-008-86] for the present content of deleterious elements P and Cu and the accumulated neutron fluences lies within the scatter of the measured T0 values. The expected shift of T0 is not visible because of the strong variation of toughness caused by the intrinsic weld bead structure and the different filling materials used for weld root and the main weld within the multilayer welding seam. Hence, the position of the crack tip of the specimen in the multilayer welding seam is crucial and defines the cleavage fracture toughness.
  • The mitigation of the neutron embrittlement of the weld and base metal by recovery annealing could be confirmed.
  • For both weld and base metal the highest value of ductile-to-brittle transition temperatures (MC T0 and and Charpy-V TT47J) were not measured directly at the inner surface of the RPV. This points to the fact that the fracture toughness values measured on specimens machined from the “templates” taken directly at the inner RPV wall may not represent the conservative condition.
  • The orientation of the specimens from a multilayer RPV welding seam is of essence for the fracture toughness testing according to ASTM E1921. For TS oriented specimens, the crack propagation across the thickness of the welding seam results in a uniform structure along the crack front, whereas for the T-L specimens with crack propagation in the circumferential direction, the structure along the crack front varies. This influences the KJc values and their scatter as also the MC reference temperature T0. Strictly speaking T-L specimens of weld metal do not fulfil the essential pre-assumption of the MC approach, because of the macroscopically non homogenous structure along the crack front length.

Keywords: nuclear reactor pressure vessel; irradiation behaviour; thermal annealing; fracture toughness; Master Curve; integrity assessment

  • Contribution to proceedings
    Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment The Thirteenth International Conference, 02.-06.06.2014, St. Petersburg, Russia
    Proceedings of the Thirteenth International Conference on "Material Issues in Design, Manufacturing and Operation of Nuclear Power Plants Equipment", St. Petersburg: Prometey Institute

Publ.-Id: 20374

Effects of high-temperature treatment on the hydrogen distribution in silicon oxynitride/silicon nitride stacks for crystalline silicon surface passivation

Schwab, C.; Hofmann, M.; Heller, R.; Seiffe, J.; Rentsch, J.; Preu, R.

This work investigates a double layer stack system that can be used for surface passivation of crystalline silicon. The stack consists of amorphous silicon-rich silicon oxynitride and amorphous silicon nitride on top. Both layers are fabricated by means of plasma-enhanced chemical vapour deposition. We investigate the stack in terms of changes in the hydrogen content and distribution within the different stack layers due to a high temperature treatment. For that purpose the stack is studied by Fourier-transformed infrared spectroscopy and nuclear reaction analysis before and after fast firing at 850 degrees C. Our results determine the bottom silicon oxynitride layer as very hydrogen-rich.
Furthermore, we identify the silicon nitride capping layer as diffusion barrier to atomic hydrogen but still allowing an effusion of molecular hydrogen. We present a qualitative model that explains our findings and distinguishes between atomic and molecular hydrogen.

Keywords: Nuclear reaction analysis; Hydrogen depth profiling; silicon oxynitride; surface passivation

Publ.-Id: 20373

Radiation and annealing response of WWER 440 beltline welding seams

Viehrig, H.-W.; Houska, M.; Altstadt, E.

The focus of this paper is on the irradiation response and the effect of thermal annealing in weld materials extracted from decommissioned WWER 440 reactor pressure vessels of the nuclear power plant Greifswald. The characterisation is based on the measurement of the hardness, the yield stress, the Master Curve reference temperature, T0, and the Charpy-V transition temperature through the thickness of multi-layer beltline welding seams in the irradiated and the thermally annealed condition. Additionally, irradiation-induced defect/solute clusters were measured by small angle neutron scattering.
We observed a large variation in the through thickness T0 values in the irradiated as well as in thermally annealed condition. The T0 values measured with the T-S-oriented Charpy size SE(B) specimens cut from different thickness locations of the multilayer welding seams strongly depend on the intrinsic weld bead structure along the crack tip. The Master Curve, T0, and Charpy-V, TT47J, based ductile-to-brittle transition temperature progressions through the thickness of the multi-layer welding seam do not correspond to the forecast according to the Russian code.
Thermal annealing at 475°C for 152 h results in the expected decrease of the tensile strength and the shift of Master Curve and Charpy-V based ductile-to-brittle transition temperatures to lower temperatures.

Keywords: reactor pressure vessel; multi-layer welding seam; neutron irradiation; fracture toughness; Master Curve approach; Charpy-V

Publ.-Id: 20372

Absence of spin dependence in the final state interaction of the d(pol) p --> 3He eta reaction

Papenbrock, M.; Barsov, S.; Burmeister, I.; Chiladze, D.; Dymov, S.; Fritzsch, C.; Gebel, R.; Goslawski, P.; Hartmann, M.; Kacharava, A.; Keshelashvili, I.; Khoukaz, A.; Kulessa, P.; Kulikov, A.; Lorentz, B.; Mchedlishvili, D.; Mersmann, T.; Merzliakov, S.; Mielke, M.; Mikirtychiants, S.; Ohm, H.; Prasuhn, D.; Rathmann, F.; Rausmann, T.; Serdyuk, V.; Ströher, H.; Täschner, A.; Trusov, S.; Valdau, Y.; Wilkin, C.

The deuteron tensor analysing power t_{20} of the d(pol) p --> 3He eta reaction has been measured at the COSY-ANKE facility in small steps in excess energy Q up to Q = 11 MeV. Despite the square of the production amplitude varying by over a factor of five through this range, t_{20} shows little or no energy dependence. This is evidence that the final state interaction causing the energy variation is not influenced by the spin configuration in the entrance channel. The weak angular dependence observed for t_{20} provides useful insight into the amplitude structure near threshold.

Publ.-Id: 20371

Functional lipid–protein interactions at the single amino acid level in experiment and simulation

Eichler, S.; Sandoval-Perez, A.; Böckmann, R.; Reeves, P.; Fahmy, K.

Membrane proteins such as receptors and channels fulfil vital functions in cellular signalling and ion exchange across cell membranes. Their function involves structural transitions of transmembrane and extramembraneous protein domains. The latter experience aqueous and hydrophobic solvation forces, respectively. We have used time-resolved FTIR spectroscopy coupled to static fluorescence measurements to study how this solvation balance at the membrane water interface affects membrane protein structure. Transmembrane peptides derived from rhodopsin, a prototypical G protein-coupled receptor (GPCRs), exhibit solvent-accessible stretches which couple protonation and hydration to local helical structure: protonation of a conserved cytosolic site in helix 3 (Glu-134) causes side chain partitioning at the water lipid interface [1]. Vice versa, the side chain charge affects structural transitions that are induced by transients (seconds) of interfacial water potential. These local processes depend on the hydrophobic context of the amino acid sequence. Opsin mutants containing amino acid replacements of the same carboxyl side chain also exhibit altered responses of their structure to water potential. The data indicate that the conserved carboxyl in helix 3 of GPCRs is a protonation-controlled hydration site that regulates the partial entry of water at the protein lipid interface, thereby contributing to the free enthalpy difference between active and inactive structures of the receptor. MD simulations agree with the experimental evidence that side chain partitioning can be a driving force for local proton-induced structural changes in membrane proteins.

Keywords: g protein-coupled receptor; rhodopsin; infrared; fluorescence

  • Poster
    Physics of Biological Systems, 24.-27.06.2014, Gif-sur-Yvette, Frankreich

Publ.-Id: 20370

"Bumble Bee Jasper" - Jaspis oder nicht?

Götze, J.; Mavris, C.; Möckel, R.

„Bumble Bee Jasper" ist ein attraktiver Schmuckstein, welcher seit einigen Jahren auf dem Markt ist und vor allem durch seine intensive Farbgebung besticht. Dabei handelt es sich jedoch nicht um Jaspis; die Matrix wird durch Calcit aufgebaut. Die gelb-orange Farbe der Bänderung wird durch Realgar hervorgerufen. Zudem wurde in den dunkleren Bereichen Pyrit nachgewiesen, der z.T. in Form von Framboiden vorliegt.

Keywords: Bumble Bee Jasper

  • Mineralien-Welt 25(2014)3

Publ.-Id: 20369

Identifying and fixing methodical weaknesses by participating the Reynolds Cup competition in quantitative mineral analysis

Kleeberg, R.; Möckel, R.; Kempe, U.

The Reynolds Cup does not only pose a scientific challenge for mineralogists but offers also an independent sight on the weaknesses of the techniques applied in an individual laboratory. Some of the errors seem to be related to well known problems, but nevertheless these mistakes are common in routine as well as in intensive competitive analytical work. The aim of this talk is to highlight problems of mineral analysis using the data of the 7th Reynolds Cup competition. Some exemplary conclusions will be drawn and ideas for methodic improvements will be drafted.
Qualitative identification of minor non-clay minerals in complex mixtures by X-ray powder diffraction techniques is known to be limited due to low peak intensity and peak overlap. Successful strategies are (i) applying mineral enrichment or even single grain separation for XRD and SEM, (ii) performing low-noise measurements, (iii) applying peak identification from difference plots of preliminary Rietveld refinements, and (iv), more unconventional, running measurements on just coarsely powdered samples to enhance peak intensities. Such techniques were successfully applied to identify of < 1 wt% of tourmaline in samples 1 and 3 as well as for the identification of amphibole and its compositional constraint. On the other hand, SEM-EDX analysis can give valuable information for the presence of phases which could not be identified in any XRD pattern, as demonstrated for apatite and nahcolite.
The correct identification of clay minerals from basal reflections measured on oriented samples seems to be straightforward, but practical limitations arise from the limited amount of sample, complicating the application of standard particle size separation techniques. Nevertheless, it is important to apply standard procedures commonly used in clay mineralogy like controlling the interlayer cation occupation, as demonstrated by the improved detection limit for I/S in sample 2.
In fact all quantification procedures successful in the RC competition are based on XRPD patterns but suffer from profile overlap. Especially, the differentiation of disordered 2:1 minerals needs for improved modeling of the diffraction profiles, including the basal reflections in randomly oriented samples. Some minerals call for the application of other techniques than XRD.

Keywords: Reynolds Cup; X-ray diffraction; analytics

  • Lecture (Conference)
    7th Mid-European Clay Conference, 16.-19.09.2014, Dresden, Deutschland

Publ.-Id: 20368

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