Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Setting the REE Industry-Specific Criteria and their Significant Role in the Viability of Rare Earth Underground Mining Projects - Festlegung der für die SEE-Industrie spezifischen Kriterien und ihre bedeutende Rolle bei der Durchführbarkeit von Tiefbauprojekten für seltene Erden

Barakos, G.; Mischo, H.

To evaluate the feasibility of a future underground mining operation is a complex problem in itself, with several different parameters to be accounted for and evaluated to secure investment decisions over the viability of any potential underground mining project. This procedure gets even more complicated when it comes to exploiting rare earth deposits. Various concerns are expressed regarding the environmental impacts that an underground mining operation may cause due to the radioactivity of the rare earth elements during mining and in waste treatment. Furthermore, the fragile market and the diversified supply and demand of the different rare earth elements can significantly affect the viability of such a venture, among other factors. This paper deals with the definition and classification of the specific criteria that govern the REE mining industry. Moreover, a thorough investigation is made of how these criteria can determine not only the selection of the underground mining method to be applied, but also of the impact that they may have to the overall feasibility of any given potential project. This paper was presented by the author´s at the SOMP conference on 24th June 2015 at the TU Bergakademie Freiberg, Freiberg, Germany.

Keywords: rare earth elements; underground mining; viability of mining projects

  • Open Access Logo Mining Report 151(2015)4, 5


Publ.-Id: 22408

Rare Earth Underground Mining Approaches with Respect to Radioactivity Control and Monitoring Strategies

Barakos, G.; Mischo, H.; Gutzmer, J.

All rare earth deposits contain Natural Occurring Radioactive Materials (NORMs), which primarily comprise radionuclides from the decay series of elements like Uranium (U) and Thorium (Th), especially products like radon. The contents of these materials are variable, and often occupational and environmental radiation exposures during mining need to be carefully assessed during the selection of appropriate technologies. The restriction of exposure to radon is the main target to help maintain a safe underground working environment. Mine ventilation is the primary technique of controlling ambient concentrations of radon progeny. In this paper, an attempt is made to determine the radon dispersion sources and the risks related to radiation exposure. Evaluations are made of the boundary conditions and the technologies that can contribute to the restriction and removal of radon from the underground mine air.

Keywords: Rare earth elements; underground mining; radon; occupational exposure; ventilation; tailings; mine water; radiation monitoring; dust suppression

  • Book chapter
    Ismar Borges de Lima, Walter Leal Filho: Rare Earths Industry: Technological, Economic, and Environmental Implications, Amsterdam, Netherlands: Elsevier, 2015, 978-0-12-802328-0, 121-138

Publ.-Id: 22407

Ultrasonic and other Techniques for Measuring Liquid Metal Multiphase Flows

Eckert, S.; Vogt, T.; Wondrak, T.; Gundrum, T.; Boden, S.; Gerbeth, G.

Gas-liquid metal two-phase flows are widespread in many technical fields such as metallurgy or energy and nuclear engineering. In general, the gas injection leads to highly turbulent and complex two-phase flows, which are difficult to predict by numerical simulations. The injected gas bubbles have a distinct influence on the flow pattern and may trigger instabilities in the liquid metal flow. However, almost all experimental investigations are limited to water models so far. This restriction is mainly attributed to the non-availability of suitable diagnostic technique which allow for a satisfactory characterization of the gas bubbles inside the liquid metal. We present laboratory experiments using the eutectic alloy GaInSn which is liquid at room temperature. As an example, ultrasonic techniques were used to investigate the vortex activated entrainment of air at the free surface of a rotating flow. The X-ray radioscopy was applied to visualize the behaviour of Argon bubbles rising in the liquid metal. The measurements reveal distinct differences between water and GaInSn especially with respect to the process of bubble formation, the coalescence and the breakup of bubbles.

Keywords: Liquid metal two-phase flow; bubbles; ultrasound Doppler method; Mutual Inductance Tomography; X-ray radioscopy

  • Invited lecture (Conferences)
    9th International Symposium on Measurement Techniques for Multiphase Flow, 22.-25.09.2015, Sapporo, Japan

Publ.-Id: 22406

Recycling of black dross containing rare earths originating from melting and recycling of magnesium alloys

Scharf, C.; Ditze, A.

The process of melting and recycling magnesium alloys using fluxes produces a residue termed black dross. The black dross investigated contained metal and non-metallic phases with a considerable content of rare earth metals (REEs). The black dross was separated by crushing and screening into metal and non-metallic fractions. The non-metallic fraction was further processed by water and acid leaching. In the water leach, NaCl, KCl and CaCl2 were separated for crystallisation. In the acid leach the residue was treated with hydrochloric acid in order to dissolve the rare earth elements Ce, La, Nd and Pr. Selective precipitation by oxalic acid and solvent extraction using D2EHPA or PC88A enables a recovery of up to 92.6% of the REEs from the oxide-salt-fraction. The equilibrium isotherms of the solvent extraction operation indicate the potential for further separating the rare earth elements. A flow sheet of the whole processes was developed in order to guide industrial application.

Keywords: Dross; Leaching; Magnesium; Rare earth; Residue; Solvent extraction

Publ.-Id: 22405

Single-crystal X-ray diffraction and resonant X-ray magnetic scattering at helium-3 temperatures in high magnetic fields at beamline P09 at PETRA III

Francoual, S.; Strempfer, J.; Warren, J.; Liu, Y.; Skaugen, A.; Poli, S.; Blume, J.; Wolff-Fabris, F.; Canfield, P. C.; Lograsso, T.

The resonant scattering and diffraction beamline P09 at PETRA III at DESY is equipped with a 14 T vertical field split-pair magnet. A helium-3 refrigerator is available that can be fitted inside the magnet's variable-temperature insert. Here the results of a series of experiments aimed at determining the beam conditions permitting operations with the He-3 insert are presented. By measuring the tetragonal-to-orthorhombic phase transition occurring at 2.1 K in the Jahn-Teller compound TmVO4, it is found that the photon flux at P09 must be attenuated down to 1.5 x 109 photons s-1 for the sample to remain at temperatures below 800 mK. Despite such a reduction of the incident flux and the subsequent use of a Cu(111) analyzer, the resonant X-ray magnetic scattering signal at the Tm LIII absorption edge associated with the spin-density wave in TmNi2B2C below 1.5 K is intense enough to permit a complete study in magnetic field and at sub-Kelvin temperatures to be carried out.

Publ.-Id: 22404

A new Particle-Induced X-ray Emission set-up for laterally resolved analysis over wide areas

Hanf, D.; Buchriegler, J.; Merchel, S.; Munnik, F.; Renno, A.; Ziegenrücker, R.; Scharf, O.; Nowak, S. H.; von Borany, J.

The recently installed and unique PIXE (particle-induced X-ray emission) set-up at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) is mainly dedicated to applications for a detailed overview of elemental composition over large sample areas within a short time even at trace level. The so-called High-Speed-PIXE (HS-PIXE), a combination of a pnCCD based pixel-detector with polycapillary X-ray optics, offers simultaneous imaging of sample areas up to 12 x 12 mm² with a lateral resolution better than 100 µm. Each of the 264 x 264 individual pixels detects X-ray photons in an energy range from 2 keV to 20 keV with an energy resolution of 156 eV (@Mn-Kα). A high precision sample manipulator offers the inspection of areas up to 250 x 250 mm². During first experiments the lateral resolution could be determined to (76 ± 23) µm using a sample of well-known sharp-edged chromium patterns. Trace element analysis has been performed using a geological sample, a tin ore, with an average Ta-concentration below 0.1 at.%. Fine-zoned structures became visible in the Ta-Lα intensity map within only 45 min. The High-Speed-PIXE closes a gap in the analytic process flow chain especially for geoanalytical characterisations. It is a unique and fast detection system to identify areas of interest in comparably short time at large-area scale for further analysis.

Keywords: PIXE; Lateral Resolution; Imaging; Geometallurgy

Publ.-Id: 22403

Mikrobielle Laugung von Seltenen Erden aus Leuchtpulver

Hopfe, S.; Kutschke, S.; Pollmann, K.

Seltene Erden (SE) werden in fast allen neuen Technologien eingesetzt, dennoch gibt es bis heute kein umweltfreundliches Recycling-Verfahren. Bei Verwertung von Energiesparlampen und Leuchtstoffröhren fallen in Deutschland jährlich rund 175 Tonnen Leuchtpulver an [1, 2], die aufgrund der Quecksilber-Belastung als Sondermüll gelagert werden müssen. Gebunden in den schwer wasser-löslichen Drei¬banden-Farbstoffen enthält das Leuchtpulver ca. 10% SE-Oxide [3]. Bei voll-ständigem Recycling könnten aus den Leuchtstoffabfällen folglich 17,5 Tonnen SE Oxide gewonnen werden. Bei den derzeit niedrigen SE-Preisen [4] entspräche das einem Wert von einer halben Million Dollar.
In dieser Arbeit wurde deshalb die mögliche Rückgewinnung von SE aus Leucht-pulver mithilfe von biohydro¬metallurgischen Techniken untersucht. Aufgrund der elektrochemischen Rand¬bedingungen, erscheint die Laugung mit organischen Säuren und metallbindenden Proteinen erfolgversprechender als Oxidations- oder Reduktions¬reaktionen [5, 6] Auf dieser Grundlage und der Literatur [7] wurden verschiedene hetero- und autotrophe aerobe Mikroorganismen (MO) als Rein- und Mischkultur ausgewählt. Mit den MO-Stämmen wurden zwei-wöchige Laugungs-experimente im Batch-Verfahren durchgeführt. Zur Bestimmung des Einflusses der MO wurden außerdem Experimente mit Kulturüberständen ohne MO gestartet. Mittels ICP-MS wurden die Konzentrationen von verschiedenen Metallionen der Dreibanden-Farbstoffe im Überstand bestimmt. Die gebildeten organischen Säuren wurden durch HPLC analysiert.
Erfolgversprechende Ergebnisse konnten mit den chemoorgano-heterotrophen MO Yarrowia lipolytica, Komatogateibacter xylinus und Lactobacillus casei sowie mit der Mischkultur Kombucha erzielt werden. Allen gemeinsam ist die Absenkung des pH-Wertes während der Kultivierung infolge der Bildung von organischen Säuren. Der Mechanismus für die Auflösung der Dreibanden-Farbstoffe ist daher wahrscheinlich mit der Carboxyl-Funktionalität verknüpft. Dennoch schienen auch die MO einen Einfluss auf die Solubilisierung zu haben, da bei den Experimenten mit Kultur¬überständen niedrigere Laugungsraten erzielt wurden. Diese Arbeiten zeigen erstmals, dass eine Biolaugung von Seltenen Erden aus technischen Produkten prinzipiell möglich ist.

[1] Gallenkemper, B. and J. Breer, Analyse der Datenerhebung nach ElektroG über die Berichtsjahre 2009 und 2010 zur Vorbereitung der EU-Berichtspflicht 2012, in Fachgebiet III 1.6, D. Hörig (Editor) 2012, Umweltbundesamt: Dessau-Rosslau, Ahlen.
[2] Lightcycle, Verwertbare Bestandteile von Altlampen, 2014, Riemann, Stephan.
[3] Haucke, E., T. Huckenbeck, and R. Otto, Verfahren zur Rückgewinnung seltener Erden aus Leuchtstofflampen, Osram AG, 2011: Germany.
[4] Argus Media: Metal-Pages, URL: (Stand 29.07.2015)
[5] Evans, C.H., Biochemistry of the Lanthanides. Biochemistry of the Elements, Editor. E. Frieden. Vol. 1. 1990, New York, London: Plenum Press.
[6] Morss, L.R., Yttrium, Lanthanum, and the Lanthanide Elements, in Standard Potentials in Aqueous Solution, Editoren: A.J. Bard, R. Parsons, and J. Jordan. 1985, Marcel Dekker, Ink.: New York, Basel. p. 587-629.
[7] Krebs, W., et al., Microbial recovery of metals from solids. FEMS Microbiology Reviews, 1997. 20 (3-4): p. 605–617.

Keywords: Seltene Erden; Biologische Laugung; Leuchtpulver

  • Poster
    Aufbereitung und Recycling, 11.-12.11.2015, Freiberg, Deutschland

Publ.-Id: 22402

Bioleaching of rare earth elements from fluorescent phosphor with the tea fungus Kombucha

Hopfe, S.; Kutschke, S.; Möckel, R.; Pollmann, K.

Rare earth elements (REE) are used in mostly all new technologies and until now, there is nearly no recycling of REE containing end-of-life products [1]. Furthermore, only poor information is available regarding interactions of microorganisms with REE and there are almost no studies describing the bioleaching of REE. However, it can be assumed that microorganisms play an important role in the biogeochemistry of REE. This study investigates the potential of organic acid producing microbes to extract REE from technical waste.
During recycling of energy-saving bulbs fluorescent phosphor (FP) is collected as a distinct fraction. It contains about 10% REE-oxides bound in the hardly water-soluble triband dyes as oxides, phosphates and aluminates [2]. In the present, the feasibility of the mixed culture Kombucha to dissolve the REE-compounds from FP was examined. Kombucha is a symbiosis of acetic bacteria and yeasts that grows on green tea with sucrose producing organic acids. Besides batch- and fed-batch approaches with the whole culture, also experiments with single Kombucha-organisms and culture supernatant were performed. The concentrations of the solubilised metal ions in the supernatant were measured with ICP-MS and the produced organic acids were analysed by HPLC. Futhermore, we tried to determine the microbial diversity trough DNA-analysis.
It could be shown, that the production of organic acids by the microoganisms of Kombucha lead to considerable higher concentrations of REE in the supernatant than in the control. These results show that it is possible to dissolve the REE compounds of FP by the help of microbial processes. Moreover, it provides the basis for the development of an eco-friendly alternative to the currently applied methods.

[1] European Commission (2014) On the review of the list of critical raw materials for the EU and the implementation of the Raw Materials Initiative, Brüssel. [2] Haucke et al. (2011) Verfahren zur Rückgewinnung seltener Erden aus Leuchtstofflampen, Osram AG.

Keywords: Bioleaching; Kombucha; Rare Earth Elements; Fluorescent Phosphor

  • Lecture (Conference)
    Goldschmidt 2015, 16.-21.08.2015, Prague, Česká republika

Publ.-Id: 22401

Screening of different microorganisms for the biological leaching of rare earth elements from fluorescent phosphor

Hopfe, S.; Kutschke, S.; Möckel, R.; Pollmann, K.

Rare earth elements (REE) are used in mostly all new technologies and until now, there exists no environmentally friendly recycling-process for fluorescent phosphor (FP). Furthermore, China has with a worldwide market share of 94 % (Roskill, 2011) a virtual monopoly in the production of REE. Therefore, there is increasing demand for novel recycling technologies to secure the supply of REE. During recycling of energy-saving bulbs annually 175 tons of FP are collected as a distinct fraction (Gallenkemper and Breer 2012, Riemann 2014). It contains about 10% of REE-oxides, which are bound in the hardly water-soluble triband dyes as oxides, phosphates and aluminates (Hauke et al., 2014).
In this study the feasibility of the solubilisation of triband dyes by bio-hydrometal¬lurgical techniques is examined. Due to electrochemical restrictions, leaching with organic acids and metal binding molecules is more promising, than oxidation or reduction reactions (Evans 1990, Morss 1985). On this basis and the literature (e.g. Krebs et al., 1997), different auto- and heterotrophic aerobic microorganisms are selected. With these strains two weeks lasting batch-experiments were performed. The concentrations of several metal ions of the triband dyes in the supernatants were measured by ICP MS. Furthermore, the produced organic acids were analysed by HPLC.
With “classical” bio-leaching organisms no relevant leaching success could be achieved, since the pH-value in the media was increased by the FP, thus inhibiting the growth of microorganisms. In contrast, some chemo-organoheterotrophic species were able to solubilize REE-compounds. Particularly the bacteria Komatogateibacter xylinus, Lactobacillus casei and the yeast Yarrowia lipolytica turned out to be suitable. Common for all these strains is the lowering of the pH-value during the cultivation due to the production of organic acids (e.g. acetic, lactic or citric acid). Therefore, the underlying mechanism of triband dye solubilisation is probably connected with the carboxyl-functionality. Additionally it is conspicuous, that in all approaches especially the red dye yttrium europium oxide is affected. This is presumably because of the higher solubility of oxides in comparison to phosphates and aluminates in general.
These results show that it is possible to dissolve the REE-compunds of FP by the help of microbial processes. Moreover, it provides the basis for the development of an eco-friendly alternative to the currently applied methods.

Keywords: Bioleaching; Rare earth elements; Fluorescent phosphor

  • Lecture (Conference)
    ICBB 2015 BARCELONA, International Conference on Bioengineering and Biotechnology, 15.07.2015, Barcelona, España

Publ.-Id: 22400

Epitaxial Post-Implant Recrystallization in Germanium Nanowires

Kelly, R. A.; Liedke, B.; Baldauf, S.; Gangnaik, A.; Biswas, S.; Georgiev, Y.; Holmes, J. D.; Posselt, M.; Petkov, N.

As transistor dimensions continue to diminish, techniques for fabrication need to be adapted. In particular, crystal recovery post ion implantation is required due to destructive ion bombardment inducing crystal damage including amorphization. Here, we report a study on the post-implant recrystallization in germanium (Ge) nanowires (NWs) following gallium (Ga) ion doping. In this work a variation of NW diameters and orientations were irradiated and annealed in situ to investigate the mechanism of recrystallization. An added complication of misorientation of crystal grains increases the complexity of crystal recovery for suspended NWs. We show that when the misorientation is prevented, by leaving a crystal link between two seeds and providing a rigid support, recrystallization occurs primarily via solid phase epitaxial growth (SPEG). Finally, we demonstrate that topdown fabricated Ge NWs on insulator can be recovered with no extended defects. This work highlights both experimentally and through molecular dynamic simulations the importance of engineering crystal recovery in Ge NWs which may have potential for next-generation complementary metal-oxide semiconductor (CMOS) devices.

Keywords: Ge nanowires; post-implant recrystallization

Publ.-Id: 22399

Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium

Radek, M.; Bracht, H.; Johnson, B. C.; McCallum, J. C.; Posselt, M.; Liedke, B.

The atomic mixing of matrix atoms during solid-phase epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures that were amorphized by Ge ion implantation up to a depth of 1.5 micrometer. Recrystallization of the amorphous structure is performed at temperatures between 350 °C and 450 °C. Secondary-ion-mass-spectrometry is used to determine the concentration-depth profiles of the Ge isotope before and after SPE. An upper limit of 0.5 nm is deduced for the displacement length of the Ge matrix atoms by the SPE process. This small displacement length is consistent with theoretical models and atomistic simulations of SPE, indicating that the SPE mechanism consists of bond-switching with nearest-neighbours across the amorphous-crystalline (a/c) interface.

Keywords: solid-phase epitaxial recrystallization; Ge; atomic transport

Publ.-Id: 22398

New “green” biotechnical concepts for the recovery of metals from primary and secondary resources

Pollmann, K.; Raff, J.; Hopfe, S.; Kostudis, S.; Matys, S.; Bertheau, R.; Lehmann, F.; Suhr, M.; Vogel, M.; Flemming, K.; Schönberger, N.; Kutschke, S.

Novel environmental-friendly technologies are required in order to secure the demand of industrial relevant metals, covering the fields of exploitation, beneficiation and recycling of rare elements.
Nature itself offers promising approaches in these fields. In our group we develop bio-based technologies for extracting, treating and recycling metals such as copper or rare earths using microbes, microbial metabolites or biomolecules. The presentation gives an overview of current research activities that are performed in our group.
Natural processes such as microbial weathering, biomineralization, or biosorption are highly attractive for biotechnological applications that intend the recovery of metals from primary and secondary resources.
Currently applied bioleaching concepts use acidophilic bacteria such as Acidithiobacillus ferrooxidans for the extraction of metals from sulfidic ores. This approach is already used for the extraction of copper especially in ores with low metal content. Other concepts use metabolic products from microorganisms for indirect bioleaching processes. For example, in our group we investigate the use of heterotrophic bacteria for the extraction of strategic relevant elements such as copper and Rare Earth Elements from different sources.
Biosorption uses the metal binding capabilities of biomass or biomolecules for the recovery of metals from solutions. Such compounds can be immobilized on materials to construct metal selective filter materials. These materials enable an efficient removal of specific metals, are relatively cheap, and can be regenerated. In our group we use bacterial surface layer proteins (S-layers) for the construction of metal selective biocomposites. In other projects we select metal binding peptides using phage surface display technology. In a third approach we use metabolic products, e.g. metallophores, as complexing agents.
In conclusion, in combination with established physical and chemical processes, such biotechnological approaches have a high potential to improve metal beneficiation and recycling and contribute to environmentally friendly and sustainable processes.

Keywords: biomining; biosorption; bioleaching; metal recovery

  • Lecture (Conference)
    Green & Sustainable Chemistry, 04.-06.04.2016, Berlin, Deutschland

Publ.-Id: 22397

Pobibilities and challenges of remote sensing for exploration of carbonatite-hosted REE deposits

Zimmermann, R.; Brandmeier, M.; Gloaguen, R.

Remote sensing data can provide valuable information about ore deposits and their alteration zones at surface level. However, small-scale, structurally controlled ore deposits require remotely sensed data with a very high spatial and spectral resolution. Due to their economic importance, carbonatite-hosted HREE deposits have become a focus of interest and provide a challenge for traditional remote sensing methods. Thus, in this study we focus on developing and testing new remote sensing exploration methods to detect carbonatites as potential host rocks in a well known deposit: Lofdal/Bergville Farm in the northern part of Namibia. The HREE-hosting carbonatite dykes have widths of 0.5 to 3 m. HREE got enriched within these small dykes and fractures during a post-carbonatite intrusion hydrothermal mineralization stage [1].

Several classification and unmixing algorithms were tested on airborne HyMap data. We observe a significant improvement of classification results by using a combination of spectral, textural and geomorphometric information in an expert-based approach compared to "traditional" classification algorithms. The extent of major dykes and the main intrusion could be reproduced very accurately. Thus, we recognize that carbonatites are associated with specific geometric patterns that help to improve classification results. Furthermore, the structures found by Automated lineament extraction (TecLines Toolbox [2]) agree with the orientation of mapped structures in the area and provide more detail to the original mapping.

However, a major difficulty that arised during this study was the still inadequate spatial resolution of 5 m for mapping most of the dykes. Small-scale alteration zones and narrow dykes cannot be detected or mapped correctly. Furthermore, the spectral signature of the surrounding host rocks is similar to the carbonatites and the fenitization zone. Including geometric information into the classification does not lead to significant improvement.

High spatial and spectral resolution is essential for accurate mapping of those narrow mineralized structures. Therefore, we hope to handle these problems by using high-resolution drone-borne systems for hyperspectral imaging, geophysics and 3D photogrammetry.

[1] Anthony-Jones, W., Bau, M. and Wall, F. (2014): Rare Earth Element deposits. Proceedings of the 13th Freiberg Short Course in Economic Geology, TU Bergakademie Freiberg

[2] Rahnama, M. and Gloaguen, R. (2014): TecLines: A MATLAB-Based Toolbox for Tectonic Lineament Analysis from Satellite Images and DEMs, Part 1: Line Segment Detection and Extraction, Remote Sensing 6: 5938–5958

  • Lecture (Conference)
    IAMG 2015 - The 17th annual conference of the International Association for Mathematical Geosciences, 08.09.2015, Freiberg, Deutschland
  • Contribution to proceedings
    IAMG 2015 - The 17th annual conference of the International Association for Mathematical Geosciences, 05.-13.09.2015, Freiberg, Deutschland
    Proceedings of IAMG 2015, 978-3-00-050337-5, 773-783

Publ.-Id: 22396

On the burning of Plutonium originating from Light Water Reactor use in a fast molten salt reactor – A neutron physical study

Merk, B.; Litskevich, D.

An efficient burning of the plutonium produced during light water reactor (LWR) operation has the potential to significantly improve the sustainability indices of LWR operation. The work offers a comparison of the efficiency of the Pu burning in different reactor configurations - a molten salt fast reactor, a LWR with MOX fuel, and a sodium cooled fast reactor. The calculations are performed using the HELIOS 2 code. All results are evaluated against the plutonium burning efficiency determined in the CAPRA project. The results are discussed with special view on the increased sustainability of LWR use in the case of successful avoidance of an accumulation of Pu which otherwise would have to be forwarded to a final disposal. A strategic discussion is given about the unavoidable plutonium production, the possibility to burn the plutonium to avoid a burden for the future generations which would have to be controlled.

Keywords: Plutonium; Plutonium Management; Plutonium Burning; Nuclear Reactors; Molten Salt Reactor; Fast Reactor; Light Water Reactor; MOX Fuel

Publ.-Id: 22395

Assisted dynamical Schwinger effect: pair production in a pulsed bifrequent field

Panferov, A. D.; Smolyansky, S. A.; Otto, A.; Kämpfer, B.; Blaschke, D.; Juchnowski, L.

Electron-positron pair production by the superposition of two laser pulses with different frequencies and amplitudes is analyzed as a particular realization of the assisted dynamic Schwinger effect. It is demonstrated that, within a non-perturbative kinetic equation framework, an amplification effect is conceivable for certain parameters. When both pulses have wavelengths longer than the Compton wavelength, the residual net density of produced pairs is determined by the resultant field strength. The number of pairs starts to grow rapidly if the wavelength of the high-frequency laser component gets close to the Compton wavelength.

Publ.-Id: 22394

Spectral caustics in laser assisted Breit-Wheeler process

Nousch, T.; Seipt, D.; Kämpfer, B.; Titov, A. I.

Electron-positron pair production by the Breit-Wheeler process embedded in a strong laser pulse is analyzed. The transverse momentum spectrum displays prominent peaks which are interpreted as caustics, the positions of which are accessible by the stationary phases. Examples are given for the superposition of an XFEL beam with an optical high-intensity laser beam. Such a configuration is available, e.g., at LCLS at present and at European XFEL in near future. It requires a counter propagating probe photon beam with high energy which can be generated by synchronized inverse Compton backscattering.


Publ.-Id: 22393

Addendum to “Determination of gamma-ray widths in 15N using nuclear resonance fluorescence”

Szücs, T.; Mohr, P.

The determination of absolute widths of two observed levels above the proton threshold in 15N has been improved by a combined analysis of our recent 15N(gamma,gamma′)15N∗ photon scattering data, resonance strengths omegagamma of the 14C(p,gamma)15N reaction, and gamma-ray branchings b_gamma,i in 15N. The revised data are compared to the adopted values, and some inconsistencies in the adopted values are illustrated.

Keywords: 15N; gamma-ray widths; proton widths

Publ.-Id: 22392

Gamma background studies in 45 m and 150 m deep mines

Szücs, T.

A very low background level is a key requirement for low-energy nuclear astrophysics experiments. A detailed high energy (E_gamma > 3 MeV) gamma-background study with two escape-suppressed HPGe detectors has been performed at a medium deep underground site, in the Reiche Zeche mine (150 m) in Freiberg, Germany [1]. The new data complement a data set with the same detector at the Earth's surface, shallow underground (45 m) in the Felsenkeller laboratory in Dresden, Germany [2], and deep underground (1400 m) in LNGS in Gran Sasso, Italy [3]. The detailed background data from one and the same escape-suppressed HPGe detector at different underground depths allows the investigation of the effect of the active and passive shielding on the high energy (E_gamma > 3 MeV) laboratory background. A detailed interpretation of the behaviour of different background components as a function of the underground depth will be presented. The data show that already a shallow underground site has sufficiently low gamma-background for many nuclear astrophysics studies when an additional active shield is used to veto the remaining muon flux. Benefiting from these low background conditions, a used 5MV Pelletron tandem accelerator is currently being refurbished for installation at the Dresden Felsenkeller [4].
[1] T. Szücs et al., Eur. Phys. J. A 51, 33 (2015).
[2] T. Szücs et al., Eur. Phys. J. A 48, 8 (2012).
[3] T. Szücs et al., Eur. Phys. J. A 44, 513 (2010).
[4] D. Bemmerer et al., Proc. of Sciences NIC XIII, 044 (2015).

Keywords: background; underground; active shielding

  • Lecture (Conference)
    European Nuclear Physics Conference (EuNPC2015), 31.08.-04.09.2015, Groningen, The Netherlands

Publ.-Id: 22391

Analysis and applications of a generalized multi-field two fluid approach for plunging jet configuration

Krepper, E.; Zidouni, F.; Lucas, D.

The paper describes the simulation of a plunging jet. A generalized approach developed for the simulation of two-phase flow problems with multi-scale interfacial structures is applied for this problem. The GEneralized TwO Phase flow (GENTOP) modeling approach considers different scales in term of interfacial structure. The explicit statistical simulation of the interface between continuous gas and fluid is combined with the Euler/Euler simulation of dispersed gas. For the dispersed gas the Multiple Size Group (MUSIG) approach simulates different bubble sizes. The mass transfer between the bubble sizes is considered by bubble breakup and coalescence models. The gas entrainment during the plunging jet is described by the transition between continuous gas and dispersed gas. Here for a special sub grid model is applied.
This set of models is applied for the simulation of plunging jet experiments performed by Chanson et al. (2004). In the tests different geometric scale of plunging jet were investigated and here analyzed. The paper shows the capabilities of this approach and identifies weak points which need further development.

Keywords: CFD; two phase flow; Euler/Euler approach; interfacial area; plunging jet

  • Lecture (Conference)
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA
  • Contribution to proceedings
    The 16th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-16), 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 22390

Concepts for the development of new biosorbents

Matys, S.

In this contribution new approaches for the development of alternative, selectively binding biosorption materials for metal recyclables on the basis of bacterial surface proteins and peptides are presented and discussed.

  • Lecture (Conference)
    Freiberger Forschungsforum, 66. Berg-und Hüttenmännischer Tag (BHT), 17.-19.06.2015, Freiberg, Deutschland

Publ.-Id: 22389

Low-energy enhancement in the gamma-ray strength functions of 73,74Ge

Renstrøm, T.; Nyhus, H.-T.; Utsunomiya, H.; Schwengner, R.; Goriely, S.; Larsen, A. C.; Filipescu, A. D. M.; Gheorghe, I.; Bernstein, L. A.; Bleuel, D. L.; Glodariu, T.; Görgen, A.; Guttormsen, M.; Hagen, T. W.; Kheswa, B. V.; Lui, Y.-W.; Negi, D.; Ruud, I. E.; Shima, T.; Siem, S.; Takahisa, K.; Tesileanu, O.; Tornyi, T. G.; Tveten, G. M.; Wiedeking, M.

The gamma-ray strength functions and level densities of 73,74Ge have been extracted up to the neutron separation energy Sn from particle- coincidence data using the Oslo method. Moreover, the gamma-ray strength function of 74Ge above Sn has been determined from photo-neutron measurements; hence these two experiments cover the range of E = 1 - 13 MeV for 74 Ge. The obtained data show that both 73,74 Ge display an increase in strength at low energies. The experimental strength functions are compared with M1 strength functions deduced from average B(M1) values calculated within the shell model for a large number of transitions. The observed low-energy enhancements in 73,74 Geare adopted in the calculations of the 72,73Ge(n,gamma) cross sections, where there are no direct experimental data. Reaction rate calculations for more neutron-rich germanium isotopes are shown to be sensitive to a low-energy enhancement.

Keywords: Nuclear structure; nuclear reactions; strength functiopns; level densities

Publ.-Id: 22388

PIConGPU: Unleashing the Full Computational Potential for the Many-Core Era

Huebl, A.; Widera, R.; Pausch, R.; Worpitz, B.; Eckert, C.; Burau, H.; Garten, M.; Debus, A.; Kluge, T.; Bussmann, M.

Since its release as open source in 2013, PIConGPU is the fastest published 3D3V Particle-in-Cell (PIC) code in the world in terms of sustained peak performance with 7.2 Pflop/s scaling up to 18'432 GPUs on Titan (ORNL). Accelerator hardware is the key technology enabling an order-of-magnitude increase in computational power over conventional CPUs, but on the same time requires a general rethinking of particle-mesh and particle-particle algorithms in terms of multi-level parallelism.
We present the challenges that are common to all PIC codes in a heterogeneous computing environment and possible solutions in PIConGPU. Starting from a general description of mesh-based operations over communication and latency hiding down to efficient caching and register usage, a sustainable programming technique is explained that is both interchangeable in algorithms and performance portable.
The continuing trend of steady increase in theoretical peak performance for the world's leading machines diverges significantly from the bandwidths that are available for high-performance file systems, causing substantial change in established imulation and analysis chains. In-situ and staged processing are approaches to bridge that gap and will be presented on routines that are either memory limited, computationally highly expensive or communication bound.
Quantitatively, a dramatically lowered time-to-solution is the direct advantage of a many-core accelerated based PIC code. The former is indispensable for an equally significant, qualitative scientific improvement that allows to incorporate multi-physics models that are beyond the simple averaging over ensembles, e.g., kinetic collision and non-LTE ionization models. The potential impact for laser-ion acceleration on solid density targets will be illustrated in an example.

Keywords: HPC; PIConGPU; LPA; GPU; Simulation; PIC

  • Invited lecture (Conferences)
    ICNSP 2015 - International Conference on Numerical Simulation of Plasmas, 12.-14.08.2015, Golden (CO), USA

Publ.-Id: 22387

A treatment planning study to assess the feasibility of laser-driven proton therapy using a compact gantry design

Hofmann, K. M.; Masood, U.; Pawelke, J.; Wilkens, J. J.

Purpose: Laser-driven proton acceleration is suggested as a cost- and space-efficient alternative for future radiation therapy centers, although the properties of these beams are fairly different compared to conventionally accelerated proton beams. The laser-driven proton beam is extremely pulsed containing a very high proton number within ultrashort bunches at low bunch repetition rates of few Hz and the energy spectrum of the protons per bunch is very broad. Moreover, these laser accelerated bunches are subject to shot-to-shot fluctuations. Therefore, the aim of this study was to investigate the feasibility of a compact gantry design for laser-driven proton therapy and to determine limitations to comply with. Methods: Based on a published gantry beam line design which can filter parabolic spectra from an exponentially decaying broad initial spectrum, a treatment planning study was performed on real patient data sets. All potential parabolic spectra were fed into a treatment planning system and numerous spot scanning proton plans were calculated. To investigate limitations in the fluence per bunch, the proton number of the initial spectrum and the beam width at patient entrance were varied. A scenario where only integer shots are delivered as well as an intensity modulation from shot to shot was studied. The resulting plans were evaluated depending on their dosimetric quality and in terms of required treatment time. In addition, the influence of random shot-to-shot fluctuations on the plan quality was analyzed. Results: The study showed that clinically relevant dose distributions can be produced with the system under investigation even with integer shots. For small target volumes receiving high doses per fraction, the initial proton number per bunch must remain between 1.4×108 and 8.3×109 to achieve acceptable delivery times as well as plan qualities. For larger target volumes and standard doses per fraction, the initial proton number is even more restricted to stay between 1.4×109 and 2.9×109. The lowest delivery time that could be reached for such a case was 16 min for a 10 Hz system. When modulating the intensity from shot to shot, the delivery time can be reduced to 6 min for this scenario. Since the shot-to-shot fluctuations are of random nature, a compensation effect can be observed, especially for higher laser shot numbers. Therefore, a fluctuation of ±30% within the proton number does not translate into a dosimetric deviation of the same size. However, for plans with short delivery times these fluctuations cannot cancel out sufficiently, even for ±10% fluctuations. Conclusions: Under the analyzed terms, it is feasible to achieve clinically relevant dose distributions with laser-driven proton beams. However, to keep the delivery times of the proton plans comparable to conventional proton plans for typical target volumes, a device is required which can modulate the bunch intensity from shot to shot. From the laser acceleration point of view, the proton number per bunch must be kept under control as well as the reproducibility of the bunches.

Keywords: laser accelerated protons; novel accelerators; proton beam therapy; treatment planning

Publ.-Id: 22386

The influence of the beam charge state on the analytical calculation of RBS and ERDA spectra

Baradas, N. P.; Kosmata, M.; Hanf, D.; Munnik, F.

Analytical codes dedicated to the analysis of Ion Beam Analysis data rely on the accuracy of both the calculations and of basic data such as scattering cross sections and stopping powers. So far, the effect of the beam charge state of the incoming beam has been disregard by general purpose analytical codes such as NDF. In fact, the codes implicitly assume that the beam is always in the equilibrium charge state, by using tabulated stopping power values e.g. from SRIM, which are in principle valid for the equilibrium charge state. The dependence of the stopping power with the charge state is ignored. This assumption is reasonable in most cases, but for high resolution studies the actual change of the charge state from the beam charge state towards equilibrium as it enters and traverses the sample must be taken into account, as it influences the shape of the observed data. In this work, we present an analytical calculation, implemented in NDF, that takes this effect into account. For elastic recoil detection analysis (ERDA), the changing charge state of the recoils can also be taken into account. We apply the calculation to the analysis of experimental high depth resolution ERDA data for various oxide layers collected using a magnetic spectrometer.

Keywords: NDF; RBS; ERDA; beam charge state

Publ.-Id: 22385

High-temperature scintillation of alumina under 32 MeV 63Cu5+ heavy-ion irradiation

Lederer, S.; Akhmadaliev, S.; von Borany, J.; Gütlich, E.; Lieberwirth, A.; Zimmermann, J.; Ensinger, W.

Polycrystalline alumina samples (α-Al2O3, purity: 99.8%) were irradiated with 63Cu5+63Cu5+ ions of 32 MeV kinetic energy (≈0.5 MeV/u) up to fluences of 1E14 ions/cm2 at various temperatures ranging from 295 to 973 K. Ion beam induced luminescence and emission spectra were monitored at wavelengths from 320 to 800 nm. Optical absorption measurements were performed to deduce color center formation. Results were evaluated by the Birks model to determine the material’s radiation hardness. The applicability of alumina as scintillation screens for ion beam diagnostics could be extended by enhanced temperature operation. Analysis of the emission spectra shows a complex color center formation behavior as a function of fluence and temperature.

Keywords: Alumina; Heavy-ion irradiation; Scintillation yield decrease; High-temperature scintillation; Thermal annealing

Publ.-Id: 22384

MHz Repetion Rate Yb:YAG and Yb:CaF2 Regenerative Picosecond Laser Amplifiers with a BBO Pockels Cell

Bergmann, F.; Siebold, M.; Loeser, M.; Röser, F.; Albach, D.; Schramm, U.

We present picosecond Yb:YAG and Yb:CaF2 regenerative laser amplifiers with ultra-high repetition rates in the MHz range. A maximum pulse energy of 40 uJ was obtained at 20 kHz while we achieved around 1 uJ at 1 MHz. We demonstrated a pulse duration of 2.1 ps for Yb:YAG and 4.8 ps for Yb:CaF2 when seeded by a mode-locked Yb:KGW fs-oscillator without pulse stretching or phase compensation.

Keywords: high repetition rate; regenerative amplifiers; picosecond lasers; ytterbium-doped laser materials

Publ.-Id: 22383

Structural Characterization of Aluminum (Oxy)hydroxide Films at the Muscovite (001)−Water Interface

Lee, S. S.; Schmidt, M.; Fister, T. T.; Nagy, K. L.; Sturchio, N. C.; Fenter, P.

The formation of Al (oxy)hydroxide on the basal surface of muscovite mica was investigated to understand how the structure of the substrate controls the nucleation and growth of secondary phases. Atomic force microscopy images showed that solid phases nucleated on the surface initially as two-dimensional islands that were ≤10 Å in height and 100–200 Å in diameter after 16–50 h of reaction in a 100 μM AlCl3 solution at pH 4.2 at room temperature. High-resolution X-ray reflectivity data indicated that these islands had an internal atomic structure that resembles a single gibbsite layer, i.e., a plane of Al ions octahedrally coordinated to oxygen or hydroxyl groups. The formation of a gibbsite layer is likely favored because of the structural similarity between its basal plane and the underlying mica surface. After 700–2000 h of reaction, thicker and continuous films formed on top of the gibbsite-layer coated mica surface. X-ray diffraction data showed that these films were composed of diaspore whose formation was predicted by thermodynamic calculations. This diaspore film grew predominantly with its (040) and (140) crystallographic directions oriented along the muscovite (001) direction, indicating that the preformed metastable gibbsite layer acted as a structural anchor for the subsequent growth of thermodynamically stable diaspore.

Publ.-Id: 22382

Solidification characteristics of Fe-Ni peritectic alloy thin strips under a near-rapid solidification condition

Song, C.-J.; Yang, Y.; Guo, Y.-Y.; Zhang, Y.-H.; Lu, W.; Zhai, Q.-J.

This paper is an experimental investigation of the structure evolution and the solute distribution of 2 mm thick strips of Fe-(2.6, 4.2, 4.7, 7.9wt.%)Ni peritectic alloy under a near-rapid solidification condition, which were in the regions of d-ferrite single-phase, hypo-peritectic, hyper-peritectic and γ-austenite single-phase, respectively. The highest area ratio of equiaxed grain zone in the hyper-peritectic of Fe-4.7wt.%Ni alloy strip was observed, while other strips were mainly columnar grains. The lowest micro-segregation was obtained in the Fe7.9wt.%Ni alloy strip, while micro-segregation in the Fe-4.7wt.%Ni alloy was the highest. As opposed to the microsegregation, the macro-segregation of all the Fe-Ni strips was suppressed due to the rapid solidification rate. Finally, the structure formation mechanism of Fe-Ni alloy strips was analyzed.

Keywords: Fe-Ni peritectic alloy; Near-rapid solidification; Solidification characteristics

  • Open Access Logo China Foundry 12(2015)3, 189-195

Publ.-Id: 22381

Resistance fluctuations in insulating silicon films with superconducting nanopreciptitates – superconductor-to-metal or vortex matter phase transition?

Heera, V.; Fiedler, J.; Skorupa, J.; Skorupa, W.

Silicon films with Ga-rich nanoprecipitates are superconductors or insulators in dependence on their normal state resistance. Even in the insulating state of the film superconducting nanoprecipitates exist below the critical temperature of 7 K and determine its complex transport behavior. In this range sometimes large, random resistance jumps appear that are accompanied by little temperature changes. The resistance fluctuates between a well-defined low-resistance value and a broader band of higher resistances. Jumps to higher resistance are associated with a temperature decrease and vice versa. We present experimental results on these fluctuations and suppose a first order phase transition in the film as probable origin.

Keywords: resistance fluctuations; silicon film; superconducting nanoprecipitates; first order phase transition; vortex matter

Publ.-Id: 22380

Ion implantation of the 4H SiC epitaxial layers and substrates with 2MeV Se+ and 1MeV Al+ ions

Wierzchowski, W.; Turos, A.; Wieteska, K.; Stonert, A.; Ratajczak, R.; Jóźwik, P.; Wilhelm, R.; Akhamadaliev, S.; Mazur, K.; Paulmann, C.

The implantations were performed in 4H silicon carbide homoepitaxial layers deposited on (00.1) substrates with 8° offcut, and reference 4H-SiC substrates. The 2MeV Se+ ions and 1MeV Al+ ions were implanted with four fluences subsequently increased by the factor of 4-5×. The samples were studied by means of X-ray diffraction topography, high-resolution diffractometry, specular X-ray reflectometry, and Rutherford backscattering spectrometry\channeling method. The dislocation density in the samples evaluated from the diffraction topographs did not exceed 5×103cm-2. The representative roughness values evaluated from the reflectometric measurements was 2.3±0.1nm for the substrates and less than 1.4±0.1nm for the epitaxial layers. A significantly higher damage level in the case of 2MeV Se+ ions in comparison with 1MeV Al+ ion and a linear increase of the strain with the fluence was indicated, but the highest doses of selenium ions caused the amorphization of the implanted layer. It was also possible to obtain a good fitting of the theoretical and experimental diffraction curves approximating the strain profiles by the distribution of the point defects calculated with the SRIM 2008 code. It was confirmed that the maximum coming from surface damages observed in channeling spectra of the virgin substrate wafers was significantly higher than in the case of epitaxial layers.

Publ.-Id: 22379

Effect of pressure and high magnetic field on phase transitions and magnetic properties of Ni1.92Mn1.56Sn0.52 and Ni2MnSn Heusler compounds

Kastil, J.; Kamarad, J.; Isnard, O.; Skourski, Y.; Misek, M.; Arnold, Z.

Complex study of magnetic, magnetocaloric and structural properties of the Ni2MnSn and Ni1.92Mn1.56Sn0.52 compounds was performed. The stoichiometric single-crystal of Ni2MnSn was prepared by Czochralski method. The remarkable pressure effect on the martensitic magnetization and the martensite-austenite transition temperature TM–A was observed in the Ni1.92Mn1.56Sn0.52 compound. The coefficient dTM–A/dp reached value of 18 K/GPa. The already low value of martensite magnetization of Ni1.92Mn1.56Sn0.52 was further substantially decreased by external pressure, in contrast with pressure almost insensitive magnetization of the stoichiometric Ni2MnSn single-crystal. The pulse magnetic field of 58 T invoked the structural transition at temperature 180 K that is of about 100 K below TM–A of Ni1.92Mn1.56Sn0.52 at zero field. An anomalous increase of resistivity of the compound has been observed at temperature range below TM–A, however, it does not copy the sharp change of magnetization at TM–A. The obtained results indicate the important role of interatomic distances on the magnetic ordering and electronic structure of the studied Heusler alloys and are in agreement with the Jahn-Teller mechanism of the martensitic transition in these compounds.

Publ.-Id: 22378

ISPT 7 - Book of Proceedings

Bieberle, A.; Schlessiger, H.; Hampel, U.; (Editors)

Process tomography aims at non-invasive dynamic imaging and measurement of industrial processes and multiphase flows. In recent years different modalities, based on e.g. electrical measurements, X-ray, gamma ray or neutron transmission, positron emission, ultrasound and visible light, have been developed into technical solutions and stimulated the work of scientists and engineers in many application fields, such as chemical and process engineering, oil and gas production, power engineering, fundamental research on flow mechanics as well as CFD code development.

The symposium provides a platform for scientists and engineers to introduce and discuss recent advances in process tomography and its application in industrial process analysis and control, multiphase flow measurement and dynamic non-destructive testing. It continues a series of preceding events in Jurata 2000, Wroclaw 2002, Lodz 2004, Warzaw 2006, Zakopane 2008, and Cape Town 2011.

Keywords: Process tomography systems and Hardware; Inverse problems and reconstruction methods; Image processing and data visualization; Multi-modality and multi-sensor approaches; Mathematical modeling; Multiphase flow studies; Data generation for computational fluid Dynamics; Industrial application; Dynamic non-destructive testing

  • Book (Editorship)
    Dresden: HZDR, 2015

Publ.-Id: 22377

ISPT7 - Book of Abstracts

Bieberle, A.; Schlessiger, H.; Hampel, U.; (Editors)

Process tomography aims at non-invasive dynamic imaging and measurement of industrial processes and multiphase flows. In recent years different modalities, based on e.g. electrical measurements, X-ray, gamma ray or neutron transmission, positron emission, ultrasound and visible light, have been developed into technical solutions and stimulated the work of scientists and engineers in many application fields, such as chemical and process engineering, oil and gas production, power engineering, fundamental research on flow mechanics as well as CFD code development.

The symposium provides a platform for scientists and engineers to introduce and discuss recent advances in process tomography and its application in industrial process analysis and control, multiphase flow measurement and dynamic non-destructive testing. It continues a series of preceding events in Jurata 2000, Wroclaw 2002, Lodz 2004, Warzaw 2006, Zakopane 2008, and Cape Town 2011.

Keywords: Process tomography systems and Hardware; Inverse problems and reconstruction methods; Image processing and data visualization; Multi-modality and multi-sensor approaches; Mathematical modeling; Multiphase flow studies; Data generation for computational fluid Dynamics; Industrial application; Dynamic non-destructive testing

  • Book (Editorship)
    Dresden: HZDR, 2015

Publ.-Id: 22376

Investigation into the Formation of Nanoparticles of Tetravalent Neptunium in Slightly Alkaline Aqueous Solution

Husar, R.

Considering the worldwide growing discharge of minor actinides and the current need for geological disposal facilities for radioactive waste, this work provides a contribution to the safety case concerning Np transport if it would be released from deep repository sites and moving from alkaline cement conditions (near-field) to more neutral environmental conditions (far-field). The reducing conditions in a nuclear waste repository render neptunium tetravalent, which is assumed to be immobile in aqueous environment due to the low solubility solution of Np(IV). For tetravalent actinide nuclides, the most significant transport should occur via colloidal particles. This work demonstrates the formation of intrinsic neptunium dioxide nanocrystals and amorphous Np(IV) silica colloids under environmentally relevant conditions.

The dissociation of the initial soluble Np(IV) complex (i.e. [Np(IV)(CO3)5]6-) induces the intrinsic formation of nanocrystalline NpO2 in the solution phase. The resulting irregularly shaped nanocrystals with an average size of 4 nm exhibit a face-centered cubic (fcc), fluorite-type structure (space group ). The NCs tend to agglomerate under ambient conditions due to the weakly charged hydrodynamic surface at neutral pH (zetapotential ~0 mV). The formation of micron-sized agglomerates, composed of nanocrystals of 2-5 nm in size, and the subsequent precipitation cause immobilization of the major amount of Np(IV) in the Np carbonate system. Agglomeration of NpO2 nanocrystals in dependence on time was indicated by PCS and UV-vis absorption spectroscopy with the changes of baseline characteristics and absorption maximum at 742 nm.

Hitherto, unknown polynuclear species as intermediate species of NpO2 nanocrystal formation were isolated from solution and observed by HR-TEM. These polynuclear Np species appear as dimers, trimers and hexanuclear compounds in analogy with those reported for other actinides.

Intrinsic formation of NpO2 (fcc) nanocrystals under ambient environmental conditions is prevented by admixing silicic acid: amorphous Np(IV) silica colloids are formed when silicate is present in carbonate solution.

Herein, the initial molar ratio of Si to Np in solution lead to the formation of Np(IV) silica particles of different composition and size where Si content determines the structure and stability of resulting colloids. Implications for different electronic structures of Np(IV) in dependence on Si content in the solid phase are given by the shift of the absorption maximum at 742 nm characteristic for Np(IV) colloids, silica excess of 5 times the magnitude of Si to Np reveal a redshift up to 6 nm in the colloidal UV-vis spectrum. Precipitation of Np(IV) particles in the ternary system results in a different coordination sphere of Np(IV) compared to the binary system, and the incorporation of Si into internal structure of Np(IV) silica colloids in coffinite-like structure is confirmed by EXAFS. TEM confirms different kinds of particle morphologies in dependence on the silica content. Silica-poor systems reveal porous particles in the micron-range which consist of irregular cross-linked hydrolyzed Np(IV) silica compartments with pores <15 nm.

In contrast, long-term stabilized and silica-enriched systems are characterized by isolated particles with an average particle size of 45 nm. Agglomerates of such isolated Np(IV) silica particles appear as consolidated amorphous solids with a densely closed surface and exhibit no internal fractures. The latter mentioned morphology of Np(IV) silica particles might facilitate the migration behavior of Np(IV) in a stabilized colloidal form under environmental conditions. The silica-enriched particles with densely closed surface are long-term stabilized as colloidal dispersion (>1 year) due to repulsion effects caused by significant surface charge. Particles synthesized from Si/Np = 9/1 carry exclusively negative surface charge in nearly the whole pH range from pH 3 to pH 10 with zetapotential = (-) 5 to (-) 30 mV. The zeta potentials of all particle systems containing silica are significantly shifted to more negative values below pH 7 where the isoelectrical point shifts from pH = 8.0 to 2.6 effecting negative charge under ambient conditions which supports electrostatic stabilization of Np(IV) particles. Particle surface charge at the slipping plane, particle size and shape necessarily depend on the initial magnitude of Si content in solution during particle formation. Particular changes of the morphology and internal structure of different Np(IV) silica colloids by aging are indicated by TEM and XPS. The composition and the crystallinity state of the initially formed amorphous phases partially changed into well-ordered nanocrystalline units characterized with fcc structure.

The presence of silicate under conditions expected in a nuclear waste repository significantly influences the solubility of Np(IV) and provoke the stabilization of waterborne Np(IV) up to concentrations of 10-3 M, exceeding Np´s solubility limit by a factor of up 10.000.

Neptunium and silicate significantly interact with each other, and thereby changing their individual hydrolysis and polymerization behavior. Silicate prevents the intrinsic formation of NpO2 NCs in fcc-structure, and at the same time, Np(IV) prevents the polymerization of silicate. Both processes result in the formation of Np(IV) silica colloids which possibly influence the migration behavior and fate of Np in the waste repositories and surrounding environments. For tetravalent actinides in general, the most significant transport in the environment would occur by colloidal particles. Therefore, Np(IV) silica colloids could have a significant implication in the migration of Np, the important minor actinide in the waste repositories, via colloidal transport.

Keywords: Actinides; neptunium; nanoparticles; nanocrystals; environmental chemistry

  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Dr. Thorsten Stumpf
    113 Seiten

Publ.-Id: 22375

Remote sensing based improvement of the geological map of the Neoproterozoic Ras Gharib segment in the Eastern Desert (NE-Egypt) using texture features

Jakob, S.; Bühler, B.; Gloaguen, R.; Breitkreuz, C.; Eliwa, H. A.; El Gameel, K.

Geological mapping in the Eastern Desert is impeded by difficult accessibility. We improve the existing geological maps by including texture features in a classification scheme of ASTER and Landsat 8 data. We tested the improvement of support vector machine classification using band ratios, principal component analysis (PCA) and texture analysis in the Ras Gharib segment (NE Egypt). A very high classification overall accuracy of 99.85% was achieved. We demonstrate that the input of textures provide valuable additional data for lithological mapping. With the gained information, the existing geological map of the study area was improved distinctly in precision and resolution, but also in terms of correction of yet wrong or inaccurate locations and of lithological unit extents.

Keywords: Remote sensing; North Eastern Desert of Egypt; Texture analysis; Lithological mapping; ASTER and Landsat 8 image analysis; Support vector machine classification

Publ.-Id: 22374

Actinide oxidation state and O/M ratio in hypostoichiometric uranium-plutonium-americium U0.750Pu0.246Am0.004O2-x mixed oxides

Vauchy, R.; Belin, R. C.; Robisson, A.-C.; Lebreton, F.; Scheinost, A. C.; Aufore, L.; Martin, P. M.

Innovative americium-bearing uranium-plutonium mixed oxides U1-yPuyO2-x are envisioned as nuclear fuel for next generation Sodium-cooled Fast neutron Reactors (SFRs). The Oxygen-to-Metal (O/M) ratio, directly related to the oxidation state of cations, affects many of the fuel properties. Thus, a thorough knowledge of its variation with the sintering conditions is essential. The aim of this work is to follow the oxidation state of uranium, plutonium and americium, and so the O/M ratio, in U0.750Pu0.246Am0.004O2-x samples sintered for 4 h at 2023 K in various Ar + 5% H2 + z vpm H2O (z = ~15, ~90 and ~200) gas mixtures. The O/M ratios were determined by gravimetry, XAS and XRD and evidenced a partial oxidation of the samples at room temperature. Finally, by comparing XANES and EXAFS results to that of a previous study, we demonstrate that the presence of uranium does not influence the interactions between americium and plutonium and that the differences in the O/M ratio between the investigated conditions is controlled by the reduction of plutonium. We also discuss the role of the homogeneity of cation distribution on the mechanisms involved into the reduction process.

Keywords: Nuclear fuel; Sodium-cooled fast-neutron reactors; actinide oxide; Americium; Plutonium; Uranium; EXAFS; XANES

Publ.-Id: 22373

Interstellar 60Fe on the surface of the Moon

Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez-Guzmán, J. M.; Hain, K.; Herzog, G.; Knie, K.; Korschinek, G.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.

A dying massive star ends in a supernova explosion ejecting a large fraction of its mass into the interstellar medium. If this happens nearby, part of the ejecta might end on Solar System bodies and, in fact, radioactive 60Fe has been detected on the Pacific ocean floor in about 2 Ma old layers. Here, we report on the detection of this isotope also in lunar samples, originating presumably from the same event. The concentration of the cosmic ray produced isotope 53Mn, measured in the same samples, proves the supernova origin of the 60Fe. From the 60Fe concentrations found we deduce a reliable value for the local interstellar fluence in the range of 1 × 108 at/cm2. Thus, we obtain constraints on the recent and nearby supernova(e).

Keywords: AMS; Fe-60; Moon; Supernova

Publ.-Id: 22371

Simulation of the Secondary Radiation Field at Proton Therapy Facilities Modelling of the IBA Universal Nozzle at the University Hospital Carl Gustav Carus with the TOPAS Software

Lutz, B.; Enghardt, W.; Swanson, R.; Fiedler, F.

no abstract available

  • Lecture (Conference)
    PPRIG Proton Therapy Physics Workshop, 01.-02.10.2015, London, United Kingdom

Publ.-Id: 22370

Modelling of turbulence modulation in bubbly flows with the aid of direct numerical simulation

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

a new BIT model dependent on bubble Reynolds number is proposed and validated in a more complex bi-dispersed bubbly channel flow.

Keywords: Direct Numerical Simulations; RANS

  • Lecture (Conference)
    9th International Conference on Multiphase Flow - ICMF 2016, 22.-27.05.2016, Firenze, Italy

Publ.-Id: 22369

Large eddy simulations of the gas–liquid flow in a rectangular bubble column

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

The paper presents Euler-Euler Large Eddy Simulations of dispersed bubbly flow in a rectangular bubble column at a low Reynolds number. The physical models describing the momentum exchange between the phases including drag, lift and wall force were chosen according to previous experiences of the authors. The emphasis of the study is the analysis of bubbly flows concerning the investigation of the influence of the bubble-induced turbulence model. It is found that the presented modeling combination provides fairly good agreement with experimental data for the mean flow. The impact of the modeling on the liquid velocity fluctuations is investigated and the energy spectrum obtained from the resolved velocity is discussed.

Keywords: LES; bubble column; energy spectrum

Publ.-Id: 22368

Large Eddy Simulation of a rectangular bubble column

Ma, T.; Lucas, D.

Prediction of mean flow and turbulent parameter with Euler-Euler-LES

Keywords: Two-fluid model; LES

  • Poster
    Dynamics of bubbly flow, 08.-12.06.2015, Udine, Italy

Publ.-Id: 22367

lll-V integration in Si and Ge by ion beam synthesis and flash lamp annealing

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

In order to follow Moore’s law on the path to smaller and smaller devices, more and more materials have to be integrated into Si technology. Current research activities focus on the integration of Ge and binary III-V compounds into Si, as these materials promise a further transistor performance increase due to their high hole and electron mobility, respectively. In addition, the direct band gap of most of the compound semiconductors is of great interest for optoelectronic applications. However, the integration into Si generates a lot of challenges regarding both the quality of the III-V material itself and the quality of its interfaces. At present, most integration technologies rely on molecular beam epitaxy or similar growth mechanisms. Recently, we showed that III-V nanocrystals (NC) in Si can also be fabricated by sequential ion implantation followed by flash lamp annealing (FLA) [1]. Moreover, the use of a patterned implantation mask allows the fabrication of III-V NCs in a Si nanowire at defined positions [2].

In this presentation we extend our previous investigations to the case of Ge. In order to get a better understanding of the NC formation process, InAs and GaAs NCs were fabricated in Si and Ge by ion implantation and FLA, and their structural and electric properties were compared to each other. It will be shown that the recrystallization of the near-surface layer of amorphous substrate material (Si or Ge), together with the NC formation, is rather governed by liquid phase than by solid phase epitaxy. This scenario is supported by the evaluation of the corresponding segregation and diffusion coefficients, the temperature profile during FLA and the final size distribution of the NCs.

[1] S. Prucnal, S. Facsko, C. Baumgart, H. Schmidt, M.O. Liedke, L. Rebohle, A. Shalimov, H. Reuther, A. Kanjilal, A. Mucklich, M. Helm, J. Zuk, and W. Skorupa, Nano Lett. 11, Issue 7, 2814-2818 (2011)
[2] S. Prucnal, M. Glaser, A. Lugstein, E. Bertagnolli, M. Stöger-Pollach, S. Zhou, M. Helm, D. Reichel, L. Rebohle, M. Turek, J. Zuk, and W. Skorupa, Nano Res. 7, 1769 (2014)

Keywords: III-V integration; ion implantation; flash lamp annealing; silicon; germanium

  • Lecture (Conference)
    Gettering and Defect Engineering in Semiconductor Technology (GADEST) 2015, 20.-25.09.2015, Bad Staffelstein, Deutschland

Publ.-Id: 22366

High-temperature photon-noise-limited performance terahertz quantum-well photodetectors

Jia, J. Y.; Wang, T. M.; Zhang, Y. H.; Shen, W. Z.; Schneider, H.

In this paper, we propose using a terahertz quantumwell photodetector (THz QWP) in combination with a terahertz source to realize a detection system with photon-noise limited performance (PLIP) at high temperatures. Systematical investigations on the high-temperature performances of THz QWPs, including required signal power density for PLIP, detectivity, and the signal-to-noise ratio, have been carried out by elaborating their dark current mechanism and photocurrent response both experimentally and theoretically. We also present the optimal doping concentration of THz QWPs designed for different peak wavelengths and the resulting optimum performance regarding the above three key parameters. Numerical results show that optimal designed QWP with peak response frequency of 5.5 THz is expected to achieve PLIP at 77 K at signal power density at 819 W/cm and above. This work gives a precise description of PLIP performance of THz QWPs and will open ways for new applications for high-temperature detection in the THz regime.

Keywords: High temperature; detectivity; photon-noise limited; quantum-well photodetector (QWP); Terahertz (THz)

Publ.-Id: 22365

Nanoscale femtosecond imaging of transient hot solid density plasmas with elemental and charge state sensitivity using resonant coherent diffraction

Kluge, T.; Bussmann, M.; Chung, H.-K.; Gutt, C.; Huang, L. G.; Zacharias, M.; Schramm, U.; Cowan, T. E.

Here we propose to exploit the low energy bandwidth, small wavelength and penetration power of ultrashort pulses from XFELs for resonant Small Angle Scattering (SAXS) on plasma structures in laser excited plasmas. Small angle scattering allows to detect nanoscale density fluctuations in forward scattering direction. Typically, the SAXS signal from laser excited plasmas is expected to be dominated by the free electron distribution. We propose that the ionic scattering signal becomes visible when the X-ray energy is in resonance with an electron transition between two bound states (Resonant coherent X-ray diffraction, RCXD). In this case the scattering cross-section dramatically increases so that the signal of X-ray scattering from ions silhouettes against the free electron scattering background which allows to measure the opacity and derived quantities with high spatial and temporal resolution, being fundamentally limited only by the X-ray wavelength and timing. Deriving quantities such as ion spatial distribution, charge state distribution and plasma temperature with such high spatial and temporal resolution will make a vast number of processes in shortpulse laser-solid interaction accessible for direct experimental observation e.g. hole-boring and shock propagation, filamentation and instability dynamics, electron transport, heating and ultrafast ionization dynamics.

Publ.-Id: 22364

Tunneling breakdown of a strongly correlated insulating state in VO2 induced by intense multiterahertz excitation

Mayer, B.; Schmidt, C.; Grupp, A.; Bühler, J.; Oelmann, J.; Marvel, R. E.; Haglund, R. F.; Oka, T.; Brida, D.; Leitenstorfer, A.; Pashkin, A.

We directly trace the near- and midinfrared transmission change of a VO2 thin film during an ultrafast insulator-to-metal transition triggered by high-field multiterahertz transients. Nonthermal switching into a metastable metallic state is governed solely by the amplitude of the applied terahertz field. In contrast to resonant excitation below the threshold fluence, no signatures of excitonic self-trapping are observed. Our findings are consistent with the generation of spatially separated charge pairs and a cooperative transition into a delocalized metallic state by THz field-induced tunneling. The tunneling process is a condensed-matter analog of the Schwinger effect in nonlinear quantum electrodynamics. We find good agreement with the pair production formula by replacing the Compton wavelength with an electronic correlation length of 2.1 A° .

Publ.-Id: 22363

Probing ultrafast, transient plasma dynamics at solid density with X-ray lasers

Bussmann, M.; Kluge, T.; Huang, L.; Cowan, T. E.; Chung, H.-K.

Combining high power lasers with x-ray lasers provides unique opportunities to study ultrafast, transient processes in solid-density plasmas. We present simulation studies of probing ionization dynamics, electron transport and heating of solid-density targets driven by high power lasers with state-of-the-art X-ray lasers. We show that a precise understanding of the underlying atomic physics processes is necessary and needs to be implemented in kinetic simulations of the laser plasma interaction. Our results show that albeit the complexity of atomic processes happening during the laser plasma interaction, the very same processes can be exploited to understand the temporal evolution of the plasma.

  • Lecture (Conference)
    Radiative Properties of Hot Dense Matter, 29.09.-03.10.2014, Wien, Österreich

Publ.-Id: 22362

Bispecific antibody releasing-mesenchymal stromal cell machinery for retargeting T cells towards acute myeloid leukemia blasts

Aliperta, R.; Cartellieri, M.; Feldmann, A.; Arndt, C.; Koristka, S.; Michalk, I.; von Bonin, M.; Ehninger, A.; Bachmann, J.; Ehninger, G.; Bornhäuser, M.; Bachmann, M. P.

Bispecific antibodies (bsAbs) engaging T cells are emerging as a promising immunotherapeutic tool for the treatment of hematologic malignancies. Because their low molecular mass, bsAbs have short half-lives. To achieve clinical responses, they have to be infused into patients continously, for a long period of time. As a valid alternative we examined the use of mesenchymal stromal cells (MSCs) as autonomous cellular machines for the constant production of a recently described, fully humanized anti-CD33-anti-CD3 bsAb, which is capable of redirecting human T cells against CD33-expressing leukemic cells. The immortalized human MSC line SCP-1 was genetically modified into expressing bsAb at sufficient amounts to redirect T cells efficiently against CD33 presenting target cells, both in vitro and in an immunodeficient mouse model. Moreover, T cells of patients suffering from acute myeloid leukemia (AML) in blast crisis eliminated autologous leukemic cells in the presence of the bsAb secreting MSCs over time. The immune response against AML cells could be enhanced further by providing T cells an additional co-stimulus via the
CD137-CD137 ligand axis through CD137L expression on MSCs. This study demonstrates that MSCs have the potential to be used as cellular production machines for bsAb-based tumor immunotherapy in the future.

Publ.-Id: 22361

Surface Modificationwith heavy Mon- and Polyatomic Ions

Bischoff, L.; Böttger, R.; Heinig, K.-H.

Self-organization of nanopatterns on solid surfaces by ion irradiation is a well-established technique to create regular and ordered structures like ripples or dots. Characteristics of patterns can be controlled selecting different ion species as well as by varying their energy, fluence, incidence angle or the sample temperature during irradiation. To date, mostly monatomic ions with masses between 40 (Ar) and 131 amu (Xe) were used for self-organized nanopatterning or contrary for surface smoothing. A comprehensive review is given.Here, self-organization of periodic patterns by bombardment with polyatomic/cluster ion species with masses of up to ~835 amu is studied – a regime not explored so far. Each impact of a very heavy polyatomic projectile deposits within femtoseconds an extremely high energy density into a local, near-surface volume. The achieved energy density exceeds that of irradiation with monatomic ions of medium mass considerably, it is of the order of femtosecond laser irradiation or swift heavy ion bombardment. Therefore, compared to former ion-induced pattern formation, different pattern based on different mechanisms can be expected.A new quality of pattern on Ge surfaces are obtained by Bi2, Bi3, Bi4 and Au2, Au3 ion irradiation. Polyatomic ions are provided by liquid metal (alloy) ion sources (LM(A)IS) in a mass-separating 30 kV focused ion beam (FIB) system. Results are compared to monatomic Bi and Au ion irradiation using otherwise equivalent irradiation parameters. For this, SEM and AFM were applied to investigate the pattern formation in dependence on ion species, energy per projectile atom, fluence, incidence angle and target temperature. Finally, a consistent, qualitative model for the surface evolution relating on energy density deposition sufficient for localized, transient nano melt pool formation is discussed.

Keywords: Self-organization; ripples; dots; mon- and polyatomic ions; FIB

  • Invited lecture (Conferences)
    The 22nd International Conference on Ion-Surface Interactions, ISI - 2015, 20.-24.08.2015, Moscow, Russia

Publ.-Id: 22360

Denudation rates across the Pamir based on 10Be concentrations in fluvial sediments: dominance of topographic over climatic factors

Fuchs, M. C.; Gloaguen, R.; Merchel, S.; Pohl, E.; Sulaymonova, V. A.; Andermann, C.; Rugel, G.

A clear understanding of erosion processes is fundamental in order to comprehend the evolution of actively deforming mountain ranges. However, the relative contributions of tectonic and climatic factors and their feedbacks remain highly debated. In order to contribute to the debate, we quantify basin-wide denudation rates from cosmogenic 10Be concentrations in modern river sediments in the Pamir. This mountain range is a unique natural laboratory because the ongoing India–Eurasia collision sustains high deformation rates and, on account of its position at the transition between Westerlies and monsoon, a strong regional climatic variability arises. Sample acquisition and preparation for accelerator mass spectrometry measurements were challenging due to difficult field accessibility, low quartz and high feldspar concentrations and crystal coating. Six samples along the main draining river, the Panj, and five samples within the major, east–west elongated tributary basins allow us to quantify basin-wide denudation rates for the first time in this orogen. An average denudation rate of 0.64 mm yr-1 reveals a rapid evolution of the entire Pamir. Denudation rates of tributary sub-basins highlight the strong contrast between the Pamir Plateau (0.05 to 0.16 mm yr-1) and its margins (0.54 to 1.45 mm -1). The intensity of denudation is primarily correlated with geometric properties of the surface, such as slope steepness (0.75 quartiles; R2 of 0.81), and to a lesser extent to climatic factors such as precipitation. We thus argue that either tectonic uplift or base-level lowering are the main contributors to denudation processes. Multiple linear regression analysis (best R2of 0.93) suggests that precipitation may act as a limiting factor to denudation.
The highest denudation rates coincide with areas of the northwestern Pamir margin that receive precipitation predominantly from the Westerlies during winter. There, the concentrated discharge during spring and early summer may sustain the pronounced denudation and allow the rapid sediment transport out of the basins. Low slope angles and dry conditions hamper the sediment flux on the plateau and, consequently, denudation. The magnitude of denudation in the Pamir is similar to rates determined in the southern Himalaya despite very different climatic and tectonic conditions. The discrepancy between rates of basin-wide denudation and the fluvial incision that is up to 10 times higher evidences a transient landscape in the Pamir. This underpins the hypothesis that river captures may have caused the strong base-level lowering that drives the enhanced incision of the Panj and its main tributaries.

Keywords: erosion; geomorphology; accelerator mass spectrometry; AMS; cosmogenic nuclide

Publ.-Id: 22359

Quantitative analysis of sulphides and sulphates by WD-XRF: Capability and constraints

Uhlig, S.; Möckel, R.; Pleßow, A.

Geochemical characterisations are implemented to get information about the composition of unknown samples but some elements occur in different oxidation states that can not be determined by established techniques without special efforts like sample dissolution or extra equipment. One example is sulphur with its most common species, sulphide and sulphate. Different approaches, based on WD-XRF routine measurements, provide simple alternatives for a quantitative speciation. A set of 100 synthetic samples has been prepared in different concentrations and were measured by a Panalytical Axios minerals spectrometer. The first approach is based on the shift of the Kα1,2 doublet. Sulphide peaks are located at 2309 eV, sulphates at 2310 eV and mixtures can be found on a linear regression of energy and sulphide amount. As opposed to sulphides, sulphates show sulphur Kβ’ satellite peaks. Another procedure is based on this difference because the intensity of S Kβ’ increases with increasing sulphate content. The amount of sulphide can be calculated by a linear regression based the quotient Kβ’/Kβ of the sulphur peak height or area. However, this method has two limitations: low sulphide concentrations (<10 g/kg sulphide in the sample) and interferences with lead (Pb Mβ peak). The WD-XRF based strategies provide simple and reliable methodologies for a quantitative speciation of sulphides and sulphates whereupon the matrix influence can be neglected. These approaches have been implemented in investigations of ore-containing samples from mining dumps in Saxony/Germany. These procedures can be applied to give previously not measurable data on solid samples containing different sulphur species.

Keywords: Sulphur speciation; Satellite lines; Fluorescence peak shift

Publ.-Id: 22358

Particle acceleration with the Dresden PW lasers

Schramm, U.

Invited review talk on particle acceleration and PW laser development in Dresden

  • Invited lecture (Conferences)
    SPIE optics and optoelectronics, 13.-16.04.2015, Prague, Czech Republic

Publ.-Id: 22357

Single-pulse picking at kHz repetition rates using a Ge plasma switch at the free-electron laser FELBE

Schmidt, J.; Winnerl, S.; Seidel, W.; Bauer, C.; Gensch, M.; Schneider, H.; Helm, M.

We demonstrate a system for picking of mid-infrared and terahertz (THz) radiation pulses from the free-electron laser (FEL) FELBE operating at a repetition rate of 13 MHz. Single pulses are reflected by a dense electron-hole plasma in a Ge slab that is photoexcited by amplified near-infrared (NIR) laser systems operating at repetition rates of 1 kHz and 100 kHz, respectively. The peak intensity of picked pulses is up to 400 times larger than the peak intensity of residual pulses. The required NIR fluence for picking pulses at wavelengths in the range from 5 μm to 30μm is discussed. In addition, we show that the reflectivity of the plasma decays on a time scale from 100 ps to 1 ns dependent on the wavelengths of the FEL and the NIR laser. The plasma switch enables experiments with the FEL that require high peak power but lower average power. Furthermore, the system is well suited to investigate processes with decay times in the μs to ms regime, i.e., much longer than the 77 ns long pulse repetition period of FELBE.

Keywords: Pulse picking; plasma switch

Publ.-Id: 22356

Erbium-ion implantation into various crystallographic cuts of Al2O3

Nekvindova, P.; Mackova, A.; Malinsky, P.; Cajzl, J.; Svecova, B.; Oswald, J.; Wilhelm, R. A.

This paper reports on the importance of crystallographic cuts with a different orientation on the luminescent properties and structural changes of Al2O3 implanted with Er+ ions at 190 keV and with a fluence of 1.0 × 1016 cm−2. Post-implantation annealing at 1000 °C in oxygen atmosphere was also done. The chemical compositions and erbium concentration-depth profiles of implanted layers were studied by Rutherford Backscattering Spectrometry (RBS) and compared to SRIM simulations. The same value of the maximum erbium concentration (up to 2 at.%) was observed at a depth of about 40 nm for all crystallographic cuts. The structural properties of the prepared layers were characterised by RBS/channelling. The relative amount of disordered atoms of 70–80% was observed in the prepared implanted layers and discussed for various cuts. It has been found that erbium is positioned randomly in the Al2O3 crystalline matrix, and no preferential positions appeared even after the annealing procedure. Erbium luminescence properties were measured in the wavelength range of 1440–1650 nm for all samples. As-implanted Al2O3 samples had a significant luminescence band at 1530 nm. The best luminescence was repeatedly observed in the 〈0 0 0 1〉 cut of Al2O3. The annealing procedure significantly improved the luminescent properties.

Keywords: Sapphire; Erbium; Ion implantation; Luminescence

Publ.-Id: 22355

Magnetoelectricity of the spin-ice compound Ho2Ti2O7

Herrmannsdörfer, T.; Schönemann, R.; Green, E.; Opherden, L.; Skrotzki, R.; Wang, Z.; Kaneko, H.; Suzuki, H.; Wosnitza, J.

  • Lecture (Conference)
    ICM2015 - 20th International Conference on Magnetism, 05.-10.07.2015, Barcelona, Espana

Publ.-Id: 22354

Recent near-Earth supernovae probed by global deposition of interstellar radioactive 60Fe

Wallner, A.; Feige, J.; Kinoshita, N.; Paul, M.; Fifield, L. K.; Golser, R.; Honda, M.; Linnemann, U.; Matsuzaki, H.; Merchel, S.; Rugel, G.; Tims, S.; Steier, P.; Yamagata, T.; Winkler, S. R.

The rate of supernovae (SNe) in our local galactic neighborhood within a distance of ~100 parsec from Earth (1 parsec (pc)=3.26 light years) is estimated at 1 SN every 2-4 million years (Myr), based on the total SN-rate in the Milky Way (2.0±0.7 per century). Recent massive-star and SN activity in Earth’s vicinity may be evidenced by traces of radionuclides with half-lives t1/2 ≤ 100 Myr, if trapped in interstellar dust grains that penetrate the Solar System (SS). One such radionuclide is 60Fe (t1/2=2.6 Myr) which is ejected in supernova explosions and winds from massive stars. Here we report that the 60Fe signal observed previously in deep-sea crusts, is global, extended in time and of interstellar origin from multiple events. Deep-sea archives from all major oceans were analyzed for 60Fe deposition via accretion of interstellar dust particles. Our results, based on 60Fe atom-counting at state-of-the-art sensitivity, reveal 60Fe interstellar influxes onto Earth 1.7–3.2 Myr and 6.5–8.7 Myr ago. The measured signal implies that a few percent of fresh 60Fe was captured in dust and deposited on Earth. Our findings indicate multiple supernova and massive-star events during the last ~10 Myr at nearby distances ≤100 pc.

Keywords: accelerator mass spectrometry; AMS; supernova; cosmogenic radionuclide

Publ.-Id: 22353

Separation of Diastereomeric Flubatine Metabolites using Sciex’ SelexION™ Technology

Fabritz, S.; Smits, R.; Ludwig, F.-A.

Es ist kein Abstract vorhanden.

Publ.-Id: 22352

Synthese, 18F-Markierung und radiopharmakologische Charakterisierung eines 30mer-Peptids als potentieller Radiotracer für die molekulare Bildgebung von Claudin-4 mittels PET

Bader, M.; Kuchar, M.; Wodtke, R.; Lenk, J.; Bergmann, R.; Pufe, J.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.

Der Zelloberflächenrezeptor Claudin-4 (Cld-4) wird in verschiedenen Tumoren überexprimiert und stellt daher ein potentielles Target sowohl für die Diagnose als auch die Therapie von Tumoren epithelialen Ursprungs dar. Dies lässt die Entwicklung von Sonden, die das in vivo-Imaging dieses Proteins ermöglichen, attraktiv erscheinen. Im Rahmen dieser Arbeit sollte untersucht werden, inwiefern sich das C-terminale Fragment der C-terminalen Domäne des Clostridium perfringens-Enterotoxins cCPE(290-319) für die PET-Bildgebung von Cld-4 eignet. Dieses Fragment besteht aus 30 Aminsäuren und weist die Sequenz SLDAGQYVLVMKANSSYSGNYPYSILFQKF auf, was den Positionen 290-319 im cCPE entspricht.
Die Synthese des cCPE(290-319) und davon abgeleiteter Analoga, insbesondere N-terminal fluorbenzoylierter und FITC-konjugierter Derivate sowie Varianten, in denen kritische Aminosäuren (Tyr 306 und Leu 315) ausgetauscht wurden, sollte durch Festphasenpeptidsynthese erfolgen. Unter verschiedenen erprobten Strategien erwies sich die sequentielle Festphasenpeptidsynthese unter Einsatz von drei Pseudoprolin-Dipeptiden am effizientesten, um cCPE(290-319) und dessen Derivate zugänglich zu machen. Die Affinität der erhaltenen Peptide zu einem artifiziellen Proteinkonstrukt bestehend aus beiden extrazellulären Domänen des Cld-4 wurde mit Hilfe der Oberflächen-Plasmonenresonanz (SPR) untersucht, wodurch ein Kd-Wert von 1.4 µM für das N-terminal 4-fluorbenzoylierte cCPE(290-319) ermittelt wurde. Die Markierung von CPE(290-319) mit Fluor-18 erfolgte an fester Phase mit Hilfe von N-Succinimidyl-4-[18F]fluorbenzoat ([18F]SFB) und 4-[18F]Fluorobenzoylchlorid. Dabei wurden die besten Resultate erzielt, wenn harzgebundenes cCPE(290-319) mit N-terminalem 6-Aminohexansäure-Spacer mit [18F]SFB zur Reaktion gebracht wurde. Die Inkubation des auf diese Weise erhaltenen Radiotracers mit Zellüberstand und Blutplasma ließ keine Anzeichen von Instabilität in diesen physiologischen Medien erkennen. Die Zellbindung von 18F-markiertem cCPE(290-319) wurde mit den Tumorzelllinien HT29, A375 und A431 untersucht. Dabei konnte die zeitabhängige Bindung des radiomarkierten Peptids an Cld-4-positive A375- und A431-Zellen beobachtet werden, die stärker war als im Fall der Cld-4-negativen HT29-Zellen. Dieses Ergebnis wird gestützt durch konfokale Fluoreszenzmikroskopie mit FITC-konjugiertem cCPE(290-319) an A431-Zellen. Das in vivo-Verhalten von 18F-markiertem cCPE(290-319) wurde durch dynamisches PET-Imaging und Radiometabolit-Analysen in NMRI nu/nu-Mäusen bzw. Wistar-Ratten evaluiert. Dabei hat sich gezeigt, dass 18F-markiertes cCPE(290-319) schnell metabolisiert wird und einer deutlichen Aufnahme in die Leber unterliegt.

  • Poster
    GDCh-Wissenschaftsforum 2015, 30.08.-02.09.2015, Dresden, Deutschland

Publ.-Id: 22351

Targeting of tissue transglutaminase for functional tumour imaging: Studies on novel assay methods and inhibitors for this enzyme

Wodtke, R.; Hauser, C.; Jäckel, E.; Ruiz-Gómez, G.; Wong, A.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.

An increased activity of tissue transglutaminase (TGase 2) in tumours correlates with enhanced invasive potential as well as resistance to chemo- and radiotherapy. Therefore, this enzyme represents an interesting target for the development of PET tracers for functional in vivo imaging of tumours.
One important prerequisite for the identification and characterisation of TGase 2-binding compounds are reliable assay methods to measure the enzymatic activity. For this, a continuous fluorimetric activity assay was established, which allows the detection of the TGase 2-activity through the measurement of an increase in fluorescence. In this context, six novel water-soluble fluorogenic acyl donors containing either 7-hydroxycoumarin or 7-hydroxy-4-methylcoumarin (HMC) as fluorogenic leaving groups were developed and extensively characterised concerning their enzymatic hydrolysis and aminolysis. Within these substrates, the dipeptide Z-Glu(HMC)-Gly-OH exhibits not only the most favourable substrate properties of all compounds in this study but also within the peptidic acyl donors described for TGase 2 so far. In addition to that, a fluorescence anisotropy-based assay method was established where the TGase 2-mediated incorporation of either fluorescein- or rhodamine-conjugated cadaverine into N,N-dimethylcasein is quantified.
For the development of PET tracers for molecular imaging of TGase 2, different approaches are pursued. One of those exploits the use of irreversible inhibitors for this enzyme. Among the TGase 2 inhibitors described in the literature, the recently reported Nα-acyl-Nε-acryloyl-lysine-4-pyridylpiperazides seem to be most suitable for radiotracer development as these compounds exhibit strong inhibitory potential and selectivity towards TGase 2 as well as favourable pharmacokinetic properties. Hence, derivatives based on this class of compounds that allow the labelling with radionuclides such as fluorine-18 and iodine-124 were prepared and their inhibitory potential towards TGase 2 was evaluated by the two independent assay methods outlined above. The kinetic characterisation of the compounds revealed interesting structure-activity relationships. Particularly, the introduction of iodine into the C-terminal pyridyl moiety resulted in a significantly increased inhibitory potential towards TGase 2 compared to the lead structure. This was further illustrated by investigations on covalent docking of the lysine-derived inhibitors within the catalytic centre of TGase 2 which simultaneously will open strategies for the design of even more potent inhibitors.

  • Lecture (Conference)
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22350

III-V nanocrystals in Silicon via Liquid Phase Epitaxy: Microstructure and related properties

Wutzler, R.; Rebohle, L.; Prucnal, S.; Böttger, R.; Hübner, R.; Grenzer, J.; Helm, M.; Skorupa, W.

The integration of III-V compound semiconductors into existing semiconductor technology is a milestone in future development of micro- and opto-electronics. However, one of the main problems is the presence of defects both inside the III-V semiconductor and at its interfaces. In the present case, III-V compound semiconductor nanocrystals (NCs) were fabricated in Si based systems. For NC formation ion implantation and short-time flash lamp annealing (FLA) were used. After the implanted Si is molten by FLA, the NCs grow via liquid phase epitaxy (LPE) in a millisecond regime. Several binary and ternary III-V compounds have been produced using this approach. While binary compounds are fabricated stoichiometrically, ternary compounds can be achieved with varying compositions. Raman spectroscopy measurements confirmed the formation of III-V NCs within the particular, recrystallized matrices and Si doping. Microstructural properties were investigated by scanning electron microscopy (SEM), cross-sectional transmission electron microscopy (TEM) and X-ray diffraction analysis. SEM and TEM images show crystalline, strained III-V nanocrystals in recrystallized Si layers.

Keywords: ion implantation; flash lamp annealing; III-V integration; silicon; liquid phase epitaxy

  • Poster
    28th International Conference on Defects in Semiconductors (ICDS), 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22349

Experimental investigations on the influence of adhesive oxides on the metal-ceramic bond

Enghardt, S.; Richter, G.; Richter, E.; Reitemeier, B.; Walter, M. H.

The objective of this study was to test the influence of selected base metals, which act as oxide formers, on the metal-ceramic bond of dental veneer systems. Using ion implantation techniques, ions of Al, In and Cu were introduced into near-surface layers of a noble metal alloy containing no base metals. A noble metal alloy with base metals added for oxide formation was used as a reference. Both alloys were coated with a low-temperature fusing dental ceramic. Specimens without ion implantation or with Al2O3air abrasion were used as controls. The test procedures comprised the Schwickerath shear bond strength test (ISO 9693-1), profile height (surface roughness) measurements (ISO 4287; ISO 4288; ISO 25178), scanning electron microscopy (SEM) imaging, auger electron spectroscopy (AES) and energy dispersive X-ray analysis (EDX). Ion implantation resulted in no increase in bond strength. The highest shear bond strengths were achieved after oxidation in air and air abrasion with Al2O3 (41.5 MPa and 47.8 MPa respectively). There was a positive correlation between shear bond strength and profile height. After air abrasion, a pronounced structuring of the surface occurred compared to ion implantation. The established concentration shifts in alloy and ceramic could be reproduced. However, their positive effects on shear bond strength were not confirmed. The mechanical bond appears to be of greater importance for metal-ceramic bonding.

Keywords: Alloy; Chemical bond; Ion implantation; Mechanical bond; Metal-ceramic bond; Shear bond strength

Publ.-Id: 22348

III-V nanocrystal formation in ion-implanted Ge and Si via liquid phase epitaxy during short-time flash lamp annealing

Wutzler, R.; Rebohle, L.; Prucnal, S.; Hübner, R.; Facsko, S.; Böttger, R.; Helm, M.; Skorupa, W.

A combination of n-type III-V compound semiconductors and p-type Ge for future CMOS device technology is a possible way to satisfy the demand for higher device performance. In this work, an alternative method to integrate III-V’s into Ge is achieved by using a combination of ion implantation and short-time flash lamp annealing. With this process InAs nanocrystals are formed within a Ge substrate for the first time. Raman spectroscopy, scanning electron microscopy, Auger electron spectroscopy element mapping as well as transmission electron microscopy are performed to investigate these nanocrystal regarding size, shape and crystalline quality. Experiments show epitaxial growth of the III-V compound within the Ge matrix and a liquid phase epitaxy mechanism is used to describe the nanocrystal formation. Finally, the microstructural properties are compared for InAs nanocrystals in a Ge and a Si matrix.

Keywords: ion implantation; flash lamp annealing; III-V integration; germanium; liquid phase epitaxy

Publ.-Id: 22347

Linear magnetoresistance in mosaic-like bilayer graphene

Kisslinger, F.; Ott, C.; Heide, C.; Kampert, E.; Butz, B.; Spiecker, E.; Shallcross, S.; Weber, H. B.

The magnetoresistance of conductors usually has a quadratic dependence on magnetic field, however, examples exist of non-saturating linear behaviour in diverse materials. Assigning a specific microscopic mechanism to this unusual phenomenon is obscured by the co-occurrence and interplay of doping, mobility fluctuations and a polycrystalline structure. Bilayer graphene has virtually no doping fluctuations, yet provides a built-in mosaic tiling due to the dense network of partial dislocations. We present magnetotransport measurements of epitaxial bilayer graphene that exhibits a strong and reproducible linear magnetoresistance that persists to B = 62 T at and above room temperature, decorated by quantum interference effects at low temperatures. Partial dislocations thus have a profound impact on the transport properties in bilayer graphene, a system that is frequently assumed to be dislocation-free. It further provides a clear and tractable model system for studying the unusual properties of mosaic conductors.

Publ.-Id: 22346

Solid-phase synthesis of selectively monofluorobenzoylated polyamines for targeting of transglutaminases and polyamine transporters in tumours

Wodtke, R.; Steinbach, J.; Pietzsch, J.; Pietsch, M.; Löser, R.

Transglutaminases and polyamine transporters are promising targets for functional imaging of tumours. Therefore, our aim is to synthesise polyamine-based radiotracers that allow the in vivo imaging of the aforementioned targets by positron emission tomography (PET). Labelling with the radionuclide fluorine-18 can be accomplished via attaching a [18F]fluorobenzoyl group with the prosthetic labelling reagent N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). To access the required non- radioactive analogues, a solid-phase synthesis was developed that enables selective fluorobenzoylation at distinct amino groups of various polyamines (e.g. cadaverine, spermidine, spermine) on the basis of a recently described synthetic concept for the selective functionalisation of polyamines. The established route can be directly applied to synthesise the 18F-labelled analogues.
The mono-fluorobenzoylated polyamines were obtained by solidphase synthesis of the corresponding oxopolyamines and subsequent reduction of the amide bond with BH3-THF. By applying Dde and Boc as orthogonal protecting groups and taking advantage of the selective reaction of 2-acetyldimedone with primary amino groups in the presence of secondary amines, the selective fluorobenzoylation (FBz) of different amino groups becomes possible.
Additionally, the selective mono-fluorobenzylation (FBn) of selected diamines by reaction with 4-fluorobenzaldehyde and subsequent reduction of the resulting imine using sodium triacetoxyborohydride was performed. Based on the established methodology, the following compounds among others were obtained in good yields: N-FBzcadaverine, N-FBn-cadaverine, N1-FBz- spermidine, N4-FBz-spermidine, N8-FBz-spermidine and N1-FBz-spermine. Furthermore, the naturally occurring diamine cadaverine was conjugated to different reporter groups such as biotin. The identity of the compounds was confirmed by NMR spectroscopy and mass spectrometry. The kinetic parameters towards transglutaminase 2-catalysed acyl transfer were determined for selected compounds with an in-house fluorimetric assay using the fluorogenic acyl donor Cbz–Glu(HMC)–Gly–OH.

  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22345

Synthesis, 18F-labeling and radiopharmacological characterization of a 30mer peptide as potential radiotracer for PET imaging of claudin-4

Kuchar, M.; Bader, M.; Wodtke, R.; Lenk, J.; Pufe, J.; Bergmann, R.; Haase-Kohn, C.; Steinbach, J.; Pietzsch, J.; Löser, R.

The cell surface receptor claudin-4 (Cld-4) represents a single-chain protein containing four transmembrane domains and constitutes cell–cell contacts of the tight-junction type by engaging in homophilic interactions. Cld-4 is upregulated in various tumors and represents a promising target for both diagnosis and treatment of solid tumors of epithelial origin. Therefore, the development of agents that allow imaging of Cld-4 in vivo such as 18F-labeled compounds for positron emission tomography (PET) appears to be attractive. A suitable ligand to target Cld-4 in vivo seems to be the C-terminal peptidic fragment of the C-terminal domain of the Clostridium perfringens enterotoxin cCPE(290-319). This fragment is of 30 amino acids in length and has the sequence SLDAGQYVLVMKANSSYSGNYPYSILFQKF corresponding to positions 290-319 of cCPE.
The synthesis of cCPE(290–319) and analogues derived thereof, such as N-terminally modified derivatives (fluorobenzoylated and FITC-conjugated) and variants in which critical amino acids (Tyr 306 and Leu 315) have been replaced, was envisaged to be accomplished by solid-phase peptide synthesis (SPPS). Among several approaches, sequential SPPS using three pseudoproline-dipeptide building blocks revealed to be the most efficient one to afford cCPE(290–319) and its derivatives. The affinity of the furnished peptides to a soluble protein construct that contains both extracellular loops of Cld-4 was studied by surface plasmon resonance (SPR), which allowed determining a Kd value of 1.4 lM for the N-terminally fluorobenzoylated cCPE(290-319). Labeling of cCPE(290–319) with fluorine-18 was achieved on solid phase using N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB) and 4-[18F]fluorobenzoyl chloride as 18F-acylating agents. Most advantageous results were obtained when [18F]SFB was reacted with resin-bound cCPE(290–319) containing an N-terminal 6-aminohexanoic spacer. Stability assays in cell supernatants and plasma indicated no degradation of the resulting radiotracer in these physiological media. Cell binding of 18F-labeled cCPE(290–319) was investigated using the HT29, A375 and A431 tumor cell lines. Timedependent binding of the radiolabeled peptide to the Cld-4-positive A375 and A431 cells was observed, which was stronger than for the Cld-4-negative HT29 cell line. These findings are in accordance with results of confocal microscopy studies using FITC-conjugated cCPE(290–319) and A431 cells. The in vivo behavior of 18F-labeled cCPE(290–319) was studied in NMRI nu/nu mice and Wistar rats by dynamic PET imaging and radiometabolite analyses, respectively. These investigations have shown that 18F-labeled cCPE(290–319) is subject to substantial liver uptake and rapid metabolic degradation in vivo.
In conclusion, the synthesis and 18F-labeling of cCPE(290-319) were successfully established. Its binding to Cld-4 in vitro and in cellulo has been demonstrated. Initial radiopharmacological studies suggest the limited suitability of this peptide in its current non-stabilized form to target Cld-4 in vivo.

  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629-1630
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22344

A new fluorescence anisotropy-based assay for activity determination of tissue transglutaminase

Hauser, C.; Wodtke, R.; Löser, R.; Pietsch, M.

Considerable evidence for the implication of tissue transglutaminase (TGase 2) in a variety of pathological processes, such as neurodegenerative diseases, disorders related to autoimmunity and inflammation as well as tumor progression, has been revealed over the recent years. This renders TGase 2 attractive for developing agents which allow the enzyme’s targeting for both therapeutic and imaging purposes. The development of such molecules requires the establishment of reliable methods to assess the interaction with TGase 2, which can be done most conveniently in continuous kinetic assays.
Several assays have been published over the last decades to determine TGase 2 activity, with only very few using the method of fluorescence anisotropy. Measurement of fluorescence anisotropy offers a better signal to noise ratio than other techniques, such as those based solely on fluorescence emission and does not need washing or separation of unbound fluorescent substance.
Here, we report a fluorescence anisotropy-based approach for the determination of TGase 2’s transamidase activity, established and validated by using fluorescein- and rhodamine B-labeled cadaverines as acyl acceptor substrates. The synthesis of the cadaverine derivatives has been accomplished in a solid-phase approach. To allow efficient conjugation of the rhodamine B moiety, different linkers providing secondary amine functions have been introduced between the cadaverine and xanthenyl entities.
The increase in fluorescence anisotropy resulting from covalent binding of the relatively small cadaverine derivatives to the much larger acyl donor substrate N,N-dimethylated casein was followed over time and enzyme activities were derived thereof. The assay was found to be highly reproducible and shows no background signal in the absence of the enzyme for all synthesized cadaverine derivatives. After characterization of the enzyme–substrate interaction by determination of the Michaelis constants, Km, and the maximum velocities of substrate conversion, Vmax, the assay was validated for screening of non-covalent and covalent inhibitors by using the literature-known substances GTP and iodoacetamide, respectively, as well as a recently reported L-lysine acrylamide derivative.

  • Abstract in refereed journal
    Amino Acids 47(2015)8, 1629
  • Poster
    14th International Congress on Amino Acids, Peptides and Proteins, 03.-07.08.2015, Wien, Österreich

Publ.-Id: 22343

18F-Labeled 1,4-Dioxa-8-azaspiro[4.5]decane Derivative: Synthesis and Biological Evaluation of a σ1 Receptor Radioligand with Low Lipophilicity as Potent Tumor Imaging Agent

Xie, F.; Bergmann, R.; Kniess, T.; Deuther-Conrad, W.; Mamat, C.; Neuber, C.; Liu, B.; Steinbach, J.; Brust, P.; Pietzsch, J.; Jia, H.

We report the syntheses and evaluation of series of novel piperidine compounds with low lipophilicity as σ1 receptor ligands. 8-(4-(2-Fluoroethoxy)benzyl)-1,4-dioxa-8-azaspiro[4.5]decane (5a) possessed high affinity (Ki = 5.4 ± 0.4 nM) for σ1 receptors and selectivity for σ2 receptors (30-fold) and the vesicular acetylcholine transporter (1404-fold). [18F]5a was prepared using a one-pot, two-step labeling procedure in an automated synthesis module, with a radiochemical purity of >95%, and a specific activity of 25−45 GBq/μmol. Cellular association, biodistribution, and autoradiography with blocking experiments indicated specific binding of [18F]5a to σ1 receptors in vitro and in vivo. Small animal positron emission tomography (PET) imaging using mouse tumor xenograft models demonstrated a high accumulation in human carcinoma and melanoma. Treatment with haloperidol significantly reduced the accumulation of the radiotracer in tumors. These findings suggest that radiotracer with suitable lipophilicity and appropriate affinity for σ1 receptors could be used for tumor imaging.

Keywords: 8 [4 (2 fluoroethoxy)benzyl) 1,4 dioxa 8 azaspiro[4.5]decane f 18; fluorine 18; haloperidol; piperidine derivative; radioligand; radiopharmaceutical agent; sigma 1 opiate receptor; sigma 2 opiate receptor; unclassified drug; vesicular acetylcholine transporter

Publ.-Id: 22342

Complex antiferromagnetic structure in the intermediate-valence intermetallic Ce2RuZn4

Hartwig, S.; Prokes, K.; Hansen, T.; Ritter, C.; Gerke, B.; Pöttgen, R.; Mydosh, J. A.; Förster, T.

Neutron powder diffraction experiments were performed on the intermediate-valence Ce2RuZn4 intermetallic compound and combined with magnetic bulk measurements including high magnetic field experiments up to 58 T. Previous theoretical studies suggest that only one (here Ce1) out of two inequivalent Ce sites ismagnetically active. Ce2RuZn4 orders antiferromagnetically at TN = 2.3 K. The magnetic structure is characterized by an incommensurate propagation vector qm = (0.384, 0.384, 1/2). Assuming that the Ce2 site does not carry any substantial moment, Ce1 magnetic moments are confined to the (110)-type planes and transversely modulated with an amplitude of 1.77(3) μB.

Publ.-Id: 22341

Atomic scale interface design and characterisation

Bittencourt, C.; Ewels, C.; Krasheninnikov, A. V.

There is no abstract

Keywords: nanotechnology

Publ.-Id: 22339

Development and Validation of Advanced Theoretical Modeling for Churn-Turbulent Flows and Subsequent Transitions

Montoya Zabala, G. A.

The applicability of CFD codes for two-phase flows has always been limited to special cases due to the very complex nature of its interface. Due to its tremendous computational cost, methods based on direct resolution of the interface are not applicable to most problems of practical relevance. Instead, averaging procedures are commonly used for these applications, such as the Eulerian-Eulerian approach, which necessarily means losing detailed information on the interfacial structure. In order to allow widespread application of the two-fluid approach, closure models are required to reintroduce in the simulations the correct interfacial mass, momentum, and heat transfer.
It is evident that such closure models will strongly depend on the specific flow pattern. When considering vertical pipe flow with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking.
The purpose of this dissertation is the development, testing, and validation of a multifield model for adiabatic gas-liquid flows at high gas volume fractions, for which a multiple-size bubble approach has been implemented by separating the gas structures into a specified number of groups, each of which represents a prescribed range of sizes. A fully-resolved continuous gas phase is also computed, and represents all the gas structures which are large enough to be resolved within the computational mesh. The concept, known as GENeralized TwO Phase flow or GENTOP, is formulated as an extension to the bubble population balance approach known as the inhomogeneous MUltiple SIze Group (iMUSIG). Within the polydispersed gas, bubble coalescence and breakup allow the transfer between different size structures, while the modeling of mass transfer between the polydispersed and continuous gas allows including transitions between different gas morphologies depending on the flow situations. The calculations were performed using the computational fluid dynamic code from ANSYS, CFX 14.5, with the support of STAR-CCM+ v8.06 and v9.02. A complete three-field and four-field model, including a continuous liquid field and two to three gas fields representing bubbles of different sizes, were first tested for numerical convergence and then validated against experimental data from the TOPFLOW and MT-Loop facilities.

Keywords: CFD; GENTOP; Surface Tension; MT-Loop; TOPFLOW

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-063 2015
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 22338

Solubility of boron, carbon, and nitrogen in transition metals: getting insight into trends from first-principles calculations

Hu, X.; Björkman, T.; Lipsanen, H.; Sun, L.; Krasheninnikov, A. V.

Efficient chemical vapor deposition synthesis of two-dimensional (2D) materials such as graphene, boron nitride, and mixed BCN systems with tunable band gaps requires precise knowledge of the solubility and mobility of B/C/N atoms in the transition metals (TMs) used as substrates for the growth. Yet, surprisingly little is known about these quantities either from experiments or simulations. Using first-principles calculations, we systematically study the behavior of B/C/N impurity atoms in a wide range of TMs. We compute formation energies of B/C/N interstitials and demonstrate that they exhibit a peculiar but common behavior for TMs in different rows of the periodic table, as experimentally observed for C. Our simulations indicate that this behavior originates from an interplay between the unit cell volume and filling of the d- shell electronic states of the metals. We further assess the vibrational and electronic entropic contributions to the solubility, as well as the role of anharmonic effects. Finally, we calculate the migration barriers, an important parameter in the growth kinetics. Our results not only unravel the fundamental behavior of interstitials in TMs but also provide a large body of reference data, which can be used for optimizing the growth of 2D BCN materials.

Keywords: graphene; solubility; interstitials

Publ.-Id: 22337

Implementation and Validation of a Surface Tension Model for the Multi-scale approach GENTOP

Montoya Zabala, G. A.; Baglietto, E.; Lucas, D.

Multiphase flows encountered in the nuclear industry are largely of a complex nature, and knowledge of the accurate distribution of the void fraction is of utmost importance for operation of the reactor under steady, transient, and accident conditions. At high void fractions, strong coalescence leads to the formation of large deformable bubbles. An appropriate multiphase CFD modeling of these flow regimes should be able to account for both, large and small interfacial structures, also including the effect on closure modeling of the large structures. A concept known as GEneralized TwO Phase flow or GENTOP, has been developed at the Helmholtz-Zentrum Dresden-Rossendorf in order to address such flow configurations, by dealing with a resolved potentially-continuous gas field, one or more polydispersed gas fields, and a continuous liquid phase. Application of the model to churn-turbulent and slug flow in vertical pipes [1], have evidenced an important limitation related to the lack of a surface tension modeling within the free surface, which leads to an unphysical accumulation of void near the pipe wall. This work discusses the implementation of surface tension and contact angle within the GENTOP approach, as well as the validation of these models against analytical and experimental results. The validation of the surface tension has been performed against analytically calculated oscillating periods of different shapes of ethanol droplets suspended in air. Furthermore, different contact angles are analyzed for a drop of water residing on a smooth surface. Rising velocities and deformation of a single large bubble rising in a vertical pipe were finally validated against analytical solutions. The implementation of the surface tension model in the GENTOP approach demonstrated improvements on the resolution of the bubble and stability of the interface, with considerable reduction of the numerical diffusion.

Keywords: CFD; GENTOP; Surface Tension; Contact Angle; MT-Loop

  • Contribution to proceedings
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA
    Proceedings of the 16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, Chicago, USA
  • Lecture (Conference)
    16th International Topical Meeting on Nuclear Reactor Thermalhydraulics, 30.08.-04.09.2015, Chicago, USA

Publ.-Id: 22336

A review on mechanisms and models for the churn-turbulent flow regime

Montoya Zabala, G. A.; Lucas, D.; Baglietto, E.; Liao, Y.

The modeling of two-phase flows has always been limited to special cases due to the very complex nature of its interface. When considering vertical pipe flows with low gas volume flow rates, bubbly flow occurs. With increasing gas volume flow rates larger bubbles are generated by bubble coalescence, which further leads to transition to slug, churn-turbulent, and annular flow. Considering, as an example, a heated tube producing steam by evaporation, as in the case of a vertical steam generator, all these flow patterns including transitions are expected to occur in the system. Despite extensive attempts, robust and accurate simulations approaches for such conditions are still lacking. This paper summarizes the state-of-the-art on the understanding of the physics behind churnturbulent flow, and transitions to and from this flow pattern. Both, benefits and limitations of the existent experimental approaches and their usefulness for model development and validation at these high void fraction conditions are discussed. Limitation of both, low-dimensional approaches (0D, 1D, and 2D), and high resolution approaches such as Direct Numerical Simulations (DNS) are analyzed. Averaging procedures, such as the Eulerian-Eulerian approach including the interfacial momentum closures which has been used in the past for simulating churn flow, are review thoroughly. Finally, possible improvements are proposed.

Keywords: churn-turbulent; CFD; multiphase; review

Publ.-Id: 22335

Broadband THz detection from 0.1 to 22 THz with large area field-effect transistors

Regensburger, S.; Mittendorff, M.; Winnerl, S.; Lu, H.; Gossard, A. C.; Preu, S.

We report on ultrafast detection of radiation between 100 GHz and 22 THz by field-effect transistors in a large area configuration. With the exception of the Reststrahlenband of GaAs, the spectral coverage of the GaAs-based detectors is more than two orders of magnitude, covering the entire THz range (100 GHz - 10 THz). The temporal resolution of the robust devices is yet limited by the 30GHz oscilloscope used for read out. The responsivity roll-off towards higher frequencies is weaker than expected from an RC-roll-off model. Terahertz pulses with peak powers of up to 65 kW have been recorded without damaging the devices.

Keywords: terahertz detetector; field-effect transistor; braodband and fast THz detection

Publ.-Id: 22334

From a non-magnet to a ferromagnet: Mn implantation into different TiO2 structures

Yildirim, O.; Cornelius, S.; Butterling, M.; Anwand, W.; Wagner, A.; Smekhova, A.; Fiedler, J.; Böttger, R.; Bähtz, C.; Potzger, K.

We study effect of the initial structural order on the resulting magnetic properties of the manganese implanted TiO2 films. Different microstructures of as-grown TiO2 films, namely amorphous, polycrystalline anatase and epitaxial anatase, have been implant-doped with Mn+ up to a concentration of 5 at.%. We found that the different initial structures lead to different defect and charge carrier concentrations, and as a result, strongly influence the magnetic properties upon implantation. Depending on the initial microstructure, paramagnetism, secondary phases related magnetic properties as well as ferromagnetism could be observed in the films.


Publ.-Id: 22333

X-ray Absorption Spectroscopy for Actinide Chemistry - Basics, Experiments and Applications

Ikeda-Ohno, A.

Synchrotron-based X-ray spectroscopy is an emerging and powerful tool for actinide chemistry. This lecture focuses particularly on X-ray absorption spectroscopy, and will provide a comprehensive overview of the basics and experiments of this technique, as well as their applications to actinide chemistry.

Keywords: X-ray absorption spectroscopy; XAS; XANES; EXAFS; synchrotron; actinide; chemistry; overview; introduction

  • Invited lecture (Conferences)
    The ThUL School in Actinide Chemistry, 28.09.-02.10.2015, Karlsruhe, Germany

Publ.-Id: 22332

Targeting lysyl oxidase for molecular imaging in breast cancer

Wuest, M.; Kuchar, M.; Sharma, S. K.; Richter, S.; Hamann, I.; Wang, M.; Vos, L.; Mackey, J. R.; Wuest, F.; Löser, R.

Introduction: Lysyl oxidase (LOX; ExPASy ENZYME entry: EC and members of the LOX-like family, LOXL1–LOXL4, are copper-dependent enzymes that can modify proteins of the extracellular matrix. Expression of LOX is elevated in many human cancers, including breast cancer. LOX expression correlates with the level of tissue hypoxia, and it is known to play a critical role in breast cancer metastasis. The goal of the present study was to target LOX with (1) molecular probe fluorescent labeling to visualize LOX in vitro and (2) a radiolabeled peptide to target LOX in vivo in three different preclinical models of breast cancer.
Methods: Gene expression of all five members of the LOX family was analyzed at the transcript level via microarray analysis using tissue biopsy samples from 176 patients with breast cancer. An oligopeptide sequence (GGGDPKGGGGG) was selected as a substrate-based, LOX-targeting structure. The peptide was labeled with fluorescein isothiocyanate (FITC) for confocal microscopy experiments with the murine breast cancer cell line EMT-6. In vivo molecular imaging experiments were performed using a C-terminal amidated peptide, GGGDPKGGGGG, labeled with a short-lived positron emitter, fluorine-18 (18F), for positron emission tomography (PET) in three different breast cancer models: EMT6, MCF-7 and MDA-MB-231. The PET experiments were carried out in the presence or absence of β-aminopropionitrile (BAPN), an irreversible inhibitor of LOX.
Results: Immunostaining experiments using a LOX-specific antibody on EMT-6 cells cultured under hypoxic conditions confirmed the elevation of LOX expression in these cells. An FITC-labeled oligopeptide, FITC-Ava- GGGDPKGGGGG-NH2, was found to be localized in different cellular compartments under these conditions. After injection of [18F]fluorobenzoate-GGGDPKGGGGG-NH2, radioactivity uptake was visible in all three breast cancer models in vivo. Tumor uptake was reduced by predosing the animals with 2 mg of BAPN 4 h or 24 h before injection of the radiotracer.
Conclusions: The present data support further investigation into the development of LOX-binding radiolabeled peptides as molecular probes for molecular imaging of LOX expression in cancer.

Publ.-Id: 22331

Ultrasound Doppler flow measurements in a liquid metal column under the influence of a strong axial electric current

Starace, M.; Weber, N.; Seilmayer, M.; Kasprzyk, C.; Weier, T.; Stefani, F.; Eckert, S.

Magnetohydrodynamic instabilities can constitute a serious hazard to the functionality of liquid metal batteries. Here we consider the Tayler instability, which appears when the electric current, passing through a conducting fluid, reaches a critical value. The experiment discussed in this article involves a column of a eutectic GaInSn alloy, along whose axis an electric current passes. Ultrasound transducers encased in a copper electrode bounding the top of the column were used to obtain the vertical component of fluid flow, once a noise suppression system had been devised. The data thus retrieved will be discussed here.

  • Magnetohydrodynamics 51(2015)2, 249-256

Publ.-Id: 22330

Ion acceleration enhanced by target ablation

Zhao, S.; Lin, C.; Wang, H. Y.; Lu, H.; Tu He, X.; Chen, J.; Cowan, T. E.; Q. Yan, X.

Laser proton acceleration can be enhanced by using target ablation, due to the energetic electrons generated in the ablation preplasma. When the ablation pulse matches main pulse, the enhancement gets optimized because the electrons' energy density is highest. A scaling law between the ablation pulse and main pulse is confirmed by the simulation, showing that for given CPA pulse and target, proton energy improvement can be achieved several times by adjusting the target ablation.

Publ.-Id: 22329

Caustic structures in the spectrum of x-ray Compton scattering off electrons driven by a short intense laser pulse

Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.

We study the Compton scattering of x-rays off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons. Special emphasis is placed on how the shape of the short assisting laser pulse affects the spectrum of the scattered x-rays. In particular, we observe sharp peak structures in the plateau region, whose number and locations are highly sensitive to the laser pulse shape. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element.


Publ.-Id: 22328

Directional Spin Wave Emission From Topological Spin Textures

Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.; Raabe, J.; Wintz, S.

In the present contribution we will show that in a stacked vortex pair system with uniaxial magnetic anisotropy, directional spin waves of different symmetries and dimensionalities can be excited.

Keywords: spin waves; multilayers; dipole-exchange; non-reciprocity

  • Lecture (Conference)
    13th Joint MMM/Intermag Conference, 11.-15.01.2016, San Diego, USA

Publ.-Id: 22327

Parameter-free determination of the exchange constant in thin films using magnonic patterning

Langer, M.; Wagner, K.; Sebastian, T.; Hübner, R.; Grenzer, J.; Wang, Y.; Kubota, T.; Schneider, T.; Stienen, S.; Linder, J.; Lenz, K.; Linder, J.; Takanashi, K.; Arias, R.; Fassbender, J.

An all-electrical method is presented to determine the exchange constant of magnetic thin films using ferromagnetic resonance. For films of 20 nm thickness and below, the determination of the exchange constant A, a fundamental magnetic quantity, is anything but straightforward. Among others, the most common methods are based on the characterization of perpendicular standing spin-waves. These approaches are however challenging, due to (i) very high energies and (ii) rather small intensities in this thickness regime. In the presented approach, surface patterning is applied to a permalloy (Ni80Fe20) film and a CFMS (Co2Fe0.4Mn0.6Si) Heusler compound. Acting as a magnonic crystal, such structures enable the coupling of backward volume spin-waves to the uniform mode. Subsequent ferromagnetic resonance measurements give access to the spin-wave spectra free of unquantifiable parameters, and thus, to the exchange constant A with high accuracy.

Publ.-Id: 22326

Breaking of axial symmetry in excited heavy nuclei as identified in GDR data

Grosse, E.; Junghans, A. R.; Massarczyk, R.

A recent theoretical prediction of a breaking of axial symmetry in quasi all heavy nuclei is confronted to a new critical analysis of photon strength functions of nuclei in the valley of stability. For the photon strength in the isovector giant dipole resonance (IVGDR) regime a parameterization of GDR shapes by the sum of three Lorentzians (TLO) is extrapolated to energies below and above the IVGDR. The impact of non-GDR modes adding to the low energy slope of photon strength is discussed including recent data on photon scattering and other radiative processes. These are shown to be concentrated in energy regions where various model calculations predict intermediate collective strength; thus they are obviously separate from the IVGDR tail. The triple Lorentzian (TLO) ansatz for giant dipole resonances is normalized in accordance to the dipole sum rule. The nuclear droplet model with surface dissipation accounts well for positions and widths without local, nuclide specific, parameters. Very few and only global parameters are needed when a breaking of axial symmetry already in the valley of stability is admitted; a reliable prediction for electric dipole strength functions also outside of it is expected.


Publ.-Id: 22325

Post-test calculations of UPTF experiments with ANSYS CFX

Höhne, T.

The last decade has seen an increasing use of three-dimensional CFD codes to predict steady state and transient flows in nuclear reactors because a number of important phenomena such as pressurized thermal shocks, coolant mixing, and thermal striping cannot be predicted by traditional one-dimensional system codes with the required accuracy and spatial resolution.
The nuclear industry now also recognizes that CFD codes have reached the desired level of maturity (at least for single-phase applications) for them to be used as part of the Nuclear Power Plant (NPP) design process, and it is the objective the research and development teams to assess the current capabilities of such codes in this regard, and contribute to the technology advance in respect to their verification and validation. CFD is already well-established in addressing certain safety issues in NPPs, as reported and discussed at various international workshops. The development, verification and validation of CFD codes in respect to NPP design necessitates further work on the complex physical modelling processes involved, and on the development of efficient numerical schemes needed to solve the basic equations. In parallel, it remains an overriding necessity to benchmark the performance of the CFD codes, and for this experimental databases need to be established, first for separate-effect tests but especially for full-size integral tests.
In order to validate the CFD Code ANSYS CFX for reactor safety relevant flow phenomena it is essential to use the UPTF experiments, since they are full scale tests. All other separate effect test rigs and test facilities like ROCOM (Höhne, 2000) are scaled. Scaling parameters of flow conditions are one of the still open topics for the use of CFD codes in nuclear reactor safety. Three UPTF tests were selected and post-test calculation were performed. The major focus was analyzing the qualitative flow behavior.

Keywords: UPTF; CFX; LOCA; PTS

  • Other report
    Dresden: HZDR, 2015
    25 Seiten

Publ.-Id: 22324

H trapping and mobility in nanostructured tungsten grain boundaries: A combined experimental and theoretical approach

González, C.; Panizo-Laiz, M.; Gordillo, N.; Tejado, E.; Munnik, F.; Guerrero, C.; Piaggi, P.; Iglesias, R.; Perlado, J. M.; González-Arrabal, R.

The H trapping and mobility in nanostructured W grain boundaries has been studied by combining experimental and density functional theory (DFT) data. Experimental results show that nanostructured W coatings with a columnar structure and a large number of (110)/(211) interfaces retain more H than the coarsed grained W tungsten samples do. To investigate the possible influence of grain boundaries on the H retention, a complete energetic analysis has been done in a semi-coherent W(110)/W(112) interface built by DFT. Our results show that this kind of non-coherent interface largely attract points defects (both H atom and metallic monovacancy separately) and that the presence of these interfaces contribute to decrease the migration energy of the H atoms with respect to the bulk. When both W monovacancy and H atom are introduced together into the system, the HV complex results the most stable configuration suggesting an explanation to the H retention in the GB observed experimentally.

Keywords: Fusion; H trapping

Publ.-Id: 22323

The first four years of the AMS-facility DREAMS: Status and developments for more accurate radionuclide data

Rugel, G.; Pavetich, S.; Akhmadaliev, S.; Enamorado Baez, S. M.; Scharf, A.; Ziegenrücker, R.; Merchel, S.

DREAMS, the DREsden AMS-facility, is performing routine accelerator mass spectrometry of 10Be, 26Al, 36Cl, 41Ca, and 129I for diverse kinds of applications. All DREAMS data is normalised directly to primary standards or traceable via cross-calibration of secondary standards to those.
Recent technical developments such as a low-memory ion source for 36Cl and 129I and sophisticated tuning strategies for 129I led to improved accuracy data.Tests of ion source output have been performed with different metal binders, sample-to-binder mixing ratios, and compaction pressures in order to find optimal parameters. The highest and most stable outputs have been obtained for 10Be, 26Al, and 41Ca for the following binders and mixing ratios (by weight): BeO:Nb, 1:4; Al2O3:Ag, 1:1; CaF2:Ag, 1:4. Higher beam currents generally result in reduced statistical uncertainty. Cross-contamination and long-term memory seem to be underestimated problems asking for further tests and improvements such as the development of low-level in-house-standards.

Keywords: accelerator mass spectrometry; cosmogenic nuclides

Publ.-Id: 22322

Terahertz spectroscopy of 0D and 2D semiconductors with a free-electron laser

Schneider, H.

This talk reviews recent experimental studies carried out using the free-electron laser (FEL) facility FELBE in Dresden, Germany. Intense, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes provide unique research opportunities to study novel materials and devices.

Keywords: free-electron laser; terahertz spectroscopy

  • Lecture (others)
    Seminar, Xi'an University of Technology, 04.05.2015, Xi'an, China
  • Lecture (others)
    Seminar, CAEP, 07.05.2015, Mianyang, China

Publ.-Id: 22321

Spin-based nanoelectronic devices for mobile Information-Communication Technology

Deac, A. M.

Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn its discoverers a Nobel price [1]. More recently, it has been demonstrated that non-volatile, ultra-fast spin-based memory bit devices can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [2]. Other spin-based nanoelectronics devices currently under consideration - which will be discussed here - range from tuneable radio-frequency oscillators to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. [1] [2]

Alina Deac is currently the leader of the Spintronics Group at the Helmholtz-Zentrum Dresden - Rossendorf in Dresden, Germany. During the last 15 years, her research has been focused on spin-torque induced phenomena and their potential applications for mobile ICT devices. After obtaining her PhD in Physics at the Universite Joseph Fourier Grenoble, France in 2005, she pursued her career by working with top-notch institutions in Japan, US and Switzerland. She is a Senior Member of the IEEE Magnetics Society and an expert in the field of spintronics for the EU.

Keywords: spintronics; magnetic storage; information-communication technology

  • Invited lecture (Conferences)
    SEMICON Europa 2015, 06.-08.10.2015, Dresden, Germany

Publ.-Id: 22317

In Situ Tuning the Conductance of Single Molecular Diarylethene Switches

Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Huhn, T.; Scheer, E.; Kerbusch, J.; Gemming, S.; Erbe, A.

A major goal of molecular electronics is the development and implementation of molecular electronic devices such as single molecular switches. In this work we present a detailed study of single diarylethene molecules that were in situ switched from their non-conductive to conductive state in the presence of gold nanoelectrodes via controlled light irradiation. The molecules were dissolved in two different solvents and measured with two different side-groups. Histograms of conductance traces were taken and complemented by extracting the relative position of the current carrying molecular level and its level broadening from current-voltage characteristics by means of the single level transport model. The obtained results show a clear light-induced ring forming isomerization, which is almost independent of the side-groups, while electron withdrawing side groups lead to a reduction of conductance, a decrease of the level broadening and an increased difference between the molecular level and the Fermi energy of the metals. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by the electron-withdrawing substituents.

  • Poster
    Annual Workshop IHRS NanoNet 2014, 29.-30.09.2014, Lohmen/Bastei, Deutschland
  • Poster
    DCCMS Annual Workshop and General Assembly 2014, 20.10.2014, Dresden, Deutschland

Publ.-Id: 22316

Spin-based nanoelectronic devices for mobile Information-Communication Technology

Deac, A. M.

Perhaps the best known (or most successfully implemented) spin-based device is the hard-disk read-head. Indeed, the discovery of giant magnetoresistance enabled a paradigm shift in the miniaturization of magnetic storage technology, which was disruptive enough to earn a Nobel for the two researchers who carried out the initial studies [1]. In a nutshell, giant magnetoresistance refers to the fact that the electrical properties of a multilayer containing at least two magnetic layers depend on the orientation of their magnetic moment. For instance, if the magnetic layers are cobalt, iron or nickel (or their alloys), the resistance of the structure is maximum when the magnetic moments are antiparallel to each other, and minimum when they are parallel.

More recently, it has been demonstrated the inverse phenomenon can also be observed: the relative orientation of the magnetic moments of two ferromagnetic layers can be manipulated by applying an electrical bias (i.e. a current or a voltage) across the structure. This is a consequence of spin-momentum transfer between the conduction electrons and the magnetization of the layer they are travelling across, which effectively induces a torque on the magnetization, the so-called ‘spin-transfer torque’ or ‘spin-torque’ [2-6]. Two main effects can be induced exploiting this torque: the magnetic moment of a given layer can be switched to a chosen direction – for instance, from parallel to antiparallel to the magnetization of the second layer – or it can be induced to gyrate around a given direction for as long as the electrical bias is applied.

Spin-transfer switching as the first spin-transfer induced phenomenon to be demonstrated experimentally, with the first report published at the end of 2000 [5]. Today, spin-transfer switching is the write scheme for non-volatile, ultra-fast Spin-Transfer Torque Random Access Memory (STT-RAM) bit devices. STT-RAM can be designed so that they can scale down to more than one fifth of all other available technologies, including SRAM [7,8]. Spin-transfer driven precession, first demonstrated in 2003 [6], has been suggested as working principle for other spin-based nanoelectronics devices currently under consideration, which range from tuneable, low input power radio-frequency oscillators wireless communication, to magnetic field sensors, negative resistors, amplifiers, write heads and random number generators. Indeed, the frequency of such devices can be adjusted simply by changing the applied bias, and they provide sufficient power [9] while at the same time being about 50 times smaller than present devices used in mobile telecommunication [10]. Moreover, novel materials hold the promise of pushing the frequency limit beyond what present-day technology can achieve [11]. Possible applications include anti-collision systems for cars, remote hospitals and immersive audio-video entertainment systems.

[2] J. C. Slonczewski, J. Magn. Magn. Mater. 159, L1 (1996).
[3] L. Berger, Phys. Rev. B 54, 9353 (1996).
[4] M. D. Stiles, A. Zangwill, Phys. Rev. B 66, 014407 (2002).
[5] J. A. Katine, F. J. Albert, R. A. Buhrman et al., Phys. Rev. Lett. 84, 3149 (2000).
[6] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov et al., Nature (London) 425, 380 (2003).
[9] A. Deac, A. Fukushima, H. Kubota, et al., Nature Phys. 4, 803 (2008).
[10] P. Villard, U. Ebels, D. Houssameddine, et al., IEEE J. Solid-State Circuits 45, 214
[11] S. Mizukami, F. Wu, A. Sakuma, et al., Phys. Rev. Lett. 106, 117201 (2011).

Keywords: spintronics; wireless communication; magnetic data storage

  • Invited lecture (Conferences)
    The 12th Japanese-German Frontiers of Science (JGFoS) Symposium, 01.-04.10.2015, Kyoto, Japan

Publ.-Id: 22315

Spin-Torque Devices Based on MgO-Based Magnetic Tunnel Junctions

Deac, A. M.

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism; magnetic tunnel junctions; spin-transfer torque

  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures Gordon Research Conference Nanoscale Spintronics with Magnons, Phonons, and Photons, 26.-31.07.2015, The Hong Kong University of Science and Technology, China

Publ.-Id: 22314

International research environment and career development

Deac, A. M.

This talk provides mentoring for students seeking an international career.

Keywords: carrer development

  • Invited lecture (Conferences)
    Spin Dynamics in Nanostructures (GRS) Gordon Research Seminar Interplay of Spin, Charge and Lattice Dynamics, 25.-26.07.2015, The Hong Kong University of Science and Technology, China

Publ.-Id: 22313

Zero-field precession and suppression of the output power due to the biasdependence of the TMR in MgO-based spin-torque oscillators Alina Maria Deac

Kowalska, E.; Sluka, V.; Fowley, C.; Kakay, A.; Aleksandrov, Y.; Lindner, J.; Deac, A. M.; Fassbender, J.

Spin-torque nano-oscillators (STNOs) are novel devices which may be exploited for wireless
communication applications [1-3]. In particular, it has recently been demonstrated that STNOs utilizing an in-plane magnetized polarizer (also acting as read-out layer) and out-of-plane magnetized free layer allow for the full parallel-to-antiparallel resistance variation to be exploited in the limit of 90° precession angle, thereby maximizing the output power [1]. However, for this specific geometry, steady-state precession can only be sustained if the spin-transfer torque exhibits an asymmetric dependence on the angle between the free and the polarizing layer, such as in the case of fully metallic devices [1]. Nevertheless, it has recently been reported that dynamics have been experimentally observed in similarly designed MgO-based magnetic tunnel junctions (MTJs) under constant applied electrical current, in spite of the fact that such devices do not exhibit any asymmetry in the spin-torque angular dependence [4,5]. These results have so far been interpreted based on the formalism for metallic devices.

Here, we explore potential mechanisms for sustaining steady-state precession in MgO-based STNOs with this specific geometry. To this end, we analytically and numerically solve the Landau-Lifshitz-Gilbert-Slonczewski equation under a constant perpendicular applied current and field. We take into account both the angular and the bias dependence of the resistance of the nanopillar in order to convert the current into voltage, which is the relevant parameter in an MgO-MTJ. The field-like torque is neglected. We demonstrate that the angular dependence of the resistance introduces sufficient asymmetry of the in-plane spin-torque term to sustain precession in this system, but the bias dependence of the resistance gradually quenches this asymmetry as the current is increased and consequently suppresses precession above a given threshold. We furthermore prove that in an STNO with circular cross-section an external field is required to observe steady-state dynamics, but this constraint is lifted when introducing an in-plane easy axis, which opens new avenues to be explored for designing devices for mobile communication.

[1] W. H. Rippard, A. M. Deac, M. R. Pufall, et al., Physical Review B 81, 014426 (2010).
[2] A. M. Deac, A. Fukushima, H. Kubota, et al., Nature Physics 4, 308 (2008).
[3] S. I. Kiselev, J. C. Sankey, I. N. Krivorotov, et al., Nature 425, 380 (2003).
[4] H. Kubota, K. Yakushiji, A. Fukushima, et al., Applied Physics Express 6, 103003 (2013).
[5] T. Taniguchi, H. Arai, S. Tsunegi, et al., Applied Physics Express 6, 123003 (2013).

Keywords: magnetism; spin-transfer torque; magnetic tunnel junction

  • Invited lecture (Conferences)
    20th International Conference on Magnetism, 06.-10.07.2015, Barcelona, Spain
  • Poster
    12th Japanese-German Frontiers of Science Symposium 2015, 01.-04.10.2015, Kyoto, Japan

Publ.-Id: 22312

Atomic transport during solid-phase epitaxial recrystallization of amorphous germanium

Radek, M.; Bracht, H.; Mccallum, J. C.; Johnson, B. C.; Posselt, M.; Liedke, B.

The atomic mixing of matrix atoms during solid-phase-epitaxy (SPE) is studied by means of isotopically enriched germanium (Ge) multilayer structures grown by molecular beam epitaxy on natural Ge wafers. The entire isotope structure and parts of the natural Ge wafer were preamorphized by Ge implantation. Recrystallization of the amorphous Ge layer is performed at temperatures between 350 ˚C and 450 ˚C. The position of the amorphous/crystalline (a/c) interface was monitored during SPE regrowth using a time-resolved-reflectivity (TRR) system. The SPE process was stopped before the a/c interface reached the surface, i.e, before the recrystallization of the amorphous layer was completed. Secondary-ion-mass-spectrometry (SIMS) was applied to determine the self-atom distribution within the amorphous and recrystallized part of each sample. An upper limit of 0.5 nm is determined for the displacement length of the matrix atoms. This small displacement length is consistent with theoretical models and atomistic simulations of SPE predicting that bond-switching with nearest-neighbours across the a/c interface controls the SPE regrowth.

Keywords: Germanium; Solid-phase epitaxial recrystallization; atomic transport; isotope multilayers

  • Poster
    28th International Conference on Defects in Semiconductors (ICDS 2015), 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22311

Characterisation and properties of f-element complexes with amide and amidine ligands

März, J.; Schmid, M.; Ikeda-Ohno, A.

The lanthanide (Ln) complexes with N-chelating ligands have attracted considerable attentions because of their unique tuneable steric and electronic properties.[1] Amongst such Ln complexes with N-chelating ligands, amide-based complexes are known to offer a wide range of applications, e.g., as efficient luminescent agents employed in bio-analytical fields.[2] Furthermore, amidine-based complexes enable the Ln metals to stabilise in exotic oxidation states (i.e., di- and tetravalent) with remarkable catalytic activity.[3]
These unique properties of amide- and amidine-based complexes of f-elements motivate us to perform the present study focusing on the synthesis and characterisation of the f-element complexes with newly synthesised amide- and amidine ligands shown in Figure 1. The aim of this study is to investigate the physical/chemical properties (e.g., optical properties) of f-elements (i.e., Ln and actinides (An)) complexed with the amide- and amidine ligands and compare their properties between Ln and An, and between solid and solution states, by means of single-crystal X-ray diffraction, X-ray absorption spectroscopy, etc. A comprehensive overview of the amide- and amidine complexes of f-elements will be presented particularly in terms of structural point of view.

1 A. A. Trifonov, Coord. Chem. Rev. 2010, 254, 1327 –1347.
2 e.g., Y. Tang et al., Inorg. Chem. Commun. 2005, 8, 1018-1021; J. Xu et al., J. Am. Chem. Soc. 2011, 133, 19900–19910.
3 F. T. Edelmann, Chem. Soc. Rev. 2009, 38, 2253-2268.

Keywords: lanthanide; actinide; complex; amide; amidine; single-crystal XRD

  • Poster
    International conference on f-elements, 06.-09.09.2015, Oxford, United Kingdom

Publ.-Id: 22310

Dilute ferromagnetic InMnP

Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.

We have synthesized a new magnetic semiconductor,InMnP, by Mn ion implantation and pulsed laser annealing [1, 2]. Clear ferromagnetic hysteresis loops and a perpendicular magnetic anisotropy are observed up to a Curie temperature of 42 K. Large values of negative magnetoresistance and magnetic circular dichroism as well as anomalous Hall effect are further evidences of a ferromagnetic order in InMnP. An effort is made to understand the transport mechanism in InMnP using the theoretical models. We find that the valence band of InP does not merge with the impurity band of the heavily doped InMnP (8 %). Our results suggest that impurity band conduction is a characteristic of Mn‐doped InP and GaP which have deep Mn‐ cceptor levels. [1] M. Khalid, et al., Phys. Rev. B 89, 121301(R) (2014) [2] M. Khalid, et al., J. Appl. Phys. 117, 043906 (2015).

  • Poster
    20th International Conference on Mangetism, 05.-10.07.2015, Barcelona, Spain

Publ.-Id: 22309

Mid-infrared ridge waveguide in MgO:LiNbO3 crystal produced by combination of swift O5+ ion irradiation and precise diamond blade dicing

Cheng, Y.; Lv, J.; Akhmadaliev, S.; Zhou, S.; Kong, Y.; Chen, F.

We report on the fabrication of ridge waveguide operating at mid-infrared wavelength in MgO:LiNbO3 crystal by using O5+ ion irradiation and precise diamond blade dicing. The waveguide shows good guiding properties at the wavelength of 4 μm along the TM polarization. Thermal annealing has been implemented to improve the waveguiding performances. The propagation loss of the ridge waveguide has been reduced to be 1.0 dB/cm at 4 μm after annealing at 310 °C. The micro-Raman spectra indicate that the microstructure of the MgO:LiNbO3 crystal has no significant change along the ion track after swift O5+ ion irradiation.

Keywords: Optical waveguide; MgO:LiNbO3 crystal; Ion irradiation; Diamond blade dicing; Mid-infrared waveguides

Publ.-Id: 22308

Enhancing Robustness and Applicability of Contactless Inductive Flow Tomography

Ratajczak, M.; Wondrak, T.; Zürner, T.; Stefani, F.

Measuring the flow velocity in hot, chemically aggressive and opaque melts is a challenging task even for today’s measurement techniques. The contactless inductive flow tomography (CIFT) could provide a solution by applying magnetic fields to an electrically conducting melt and measuring the small flow-induced magnetic perturbances outside of the container. In this paper we will demonstrate how the robustness of CIFT can be enhanced by means of excitation with time-harmonic magnetic fields, making it more insensitive to the ubiquitous changes of the environmental magnetic field. Further we will show how the problem of an electrically conducting container can be treated, which is necessary, e.g., for industrial application in continuous casting.

  • Contribution to proceedings
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea
    Proceedings of IEEE Sensors 2015, 662-665
  • Lecture (Conference)
    IEEE Sensors 2015, 01.-04.11.2015, Busan, Südkorea

Publ.-Id: 22307

Ferromagnetism induced by vacancy clusters in Silicon

Liu, Y.; Zhang, X. H.; Yuan, Q.; Han, J. C.; Zhou, S. Q.; Song, B.

Defect-induced ferromagnetism provides an alternative for organic and semiconductor spintronics. Though it is weak, it can be stable above room temperature. Till now it has been confirmed at least in oxides [1, 2] and carbon based materials [3, 4]. Interestingly, the relation between magnetism and defects in Silicon was demonstrated decades ago [5]. Since then, some progresses were made [6-9] and push forward the research of magnetic Mn doped Si a lot but it is drawn little attention itself. Here, with the latest growth purifying technique and sensitive measurements, we investigated the magnetism in Silicon after neutron irradiation and try to correlate the observed magnetism to particular defects in Si.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors

  • Poster
    28th International Conference on Defects in Semiconductors, 27.-31.07.2015, Espoo, Finland

Publ.-Id: 22306

Strong Auger scattering in Landau-quantized graphene evidenced by circularly polarized pump-probe spectroscopy

Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.

While the carrier dynamics in graphene in absence of magnetic fields is well researched in a large spectral range ranging from UV to THz, the dynamics in Landau quantized graphene is almost unexplored. We investigate the carrier dynamics within the system of Landau levels (LLs) of index n = -1, n = 0 and n = 1 by pump-probe experiments complemented by microscopic modelling. Using circularly polarized terahertz radiation (at 18 THz) allows one to selectively excite the two energetically degenerate transitions LL-1 → LL0 and LL0 → LL1, respectively (at B  4 T). While three of the four possible configurations give intuitive results (bleaching, when pumping and probing with the same polarization, induced absorption with opposite polarizations), surprisingly, one configuration counterintuitively leads to bleaching while pumping and probing with opposite polarizations (Fig. 1 lower panel). This implies that even though LL0 is being optically pumped, its population decreases [1] ! Calculations show that LL0 is actually depleted by strong Auger scattering. Note that the two configurations shown in the Figure are distinguishable only because of the slight (n-type) doping of the graphene sample.
We discuss the role of carrier-carrier and carrier-phonon scattering in Landau quantized graphene and provide an outlook on the application potential of this system for tunable THz lasers.

Keywords: Graphene; Landau levels; carrier relaxation; pump-probe; free electron laser

  • Lecture (Conference)
    Electronic Properties Of Two-Dimensional Electron Systems (EP2DS-21), 26.-31.07.2015, Sendai, Japan

Publ.-Id: 22305

Effect of an upward magnetic field on nanosized sulfide precipitation in ultra-low carbon steel

Duan, K. J.; Zhang, L.; Yuan, X. Z.; Han, S. S.; Liu, Y.; Huang, Q. S.

An induction levitation melting (ILM) refining process is performed to remove most microsized inclusions in ultra-low carbon steel (UCS). Nanosized, spheroid shaped sulfide precipitates remain dispersed in the UCS. During the ILM process, the UCS is molten and is rotated under an upward magnetic field. With the addition of Ti additives, the spinning molten steel under the upward magnetic field ejects particles because of resultant centrifugal, floating, and magnetic forces. Magnetic force plays a key role in removing sub-micrometer-sized particles, composed of porous aluminum titanate enwrapping alumina nuclei. Consequently, sulfide precipitates with sizes less than 50 nm remain dispersed in the steel matrix. These findings open a path to the fabrication of clean steel or steel bearing only a nanosized strengthening phase.

Keywords: ultra-low carbon steel; magnetic field; sulfide precipitation; induction levitation; titanium

Publ.-Id: 22304

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