Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

Inter-sublevel dephasing in quantum dots

Teich, M.; Schneider, H.; Bhattacharyya, J.; Winnerl, S.; Wilson, L.; Helm, M.

We use the Dresden Free-Electron-Laser (FELBE) to investigate intersublevel coherence times in semiconductor quantum dots (QDs) by degenerate four-wave mixing (DFWM) spectroscopy. We know from pump-probe measurements1 on a series of quantum dot samples with varying intersublevel energy that intersublevel relaxation times of the s-p intersublevel transition can become very long (up to 1.5 ns). Due to the discrete nature of these sublevels, intersublevel coherence times should exhibit similar time constants at low temperatures where “pure dephasing” is suppressed.

Keywords: semiconductor quantum dot; inter-sublevel transition; terahertz free-electron laser; degenerate four-wave mixing; homogeneous and inhomogeneous broadening

  • Contribution to proceedings
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665455
  • Poster
    38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland

Publ.-Id: 19666

Extra-long hole spin relaxation time in InGaAs/GaAs quantum wells probed by cyclotron resonance spectroscopy

Drachenko, O.; Kozlov, D.; Ikonnikov, A.; Spirin, K.; Gavrilenko, V.; Schneider, H.; Helm, M.; Wosnitza, J.

We report a long, ms range, spin relaxation time of holes in InGaAs/GaAs quantum wells probed by cyclotronresonance spectroscopy in pulsed magnetic fields up to 60 Tesla. We found a strong hysteresis in the spectral weights of the cyclotron resonance absorption when a rapidly changing magnetic field is used for the experiment, while the hysteresis vanishes when a much slower changing magnetic field is used. We attribute this behavior to a long, comparable to the magnetic-field rise time, energy relaxation time between the two lowest spin-split hole Landau levels, i.e., a long hole spin relaxation time.

Keywords: cyclotron resonance spectroscopy; hole spin relaxation; pulsed magnetic fields; InGaAs/GaAs quantum well

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665921

Publ.-Id: 19665

Plasmonic focusing on metal and semiconductor disks under radially polarized terahertz illumination

Kaltenecker, K. J.; Wallauer, J.; Waselikowski, S.; Hodapp, J.; Fischer, C.; Winnerl, S.; Schneider, H.; Fischer, B. M.; Walther, M.

Optimal focusing of surface plasmon polaritons in the center of a metal disc illuminated by radially polarized terahertz pulses is demonstrated. Due to the cylinder symmetrical structure surface plasmons can be excited along the entire circumference, which interfere constructively in the center of the disk forming a sharp frequency-depended focal spot. We map the field distribution on the disk by THz near-field microscopy and compare our result to numerical simulations. For comparison, behavior under linearly polarized THz illumination is characterized. Furthermore, first results of semiconducting plasmonic lenses are presented.

Keywords: Terhertz radiation; plasmon polaritons; radial polarization

  • Lecture (Conference)
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland
  • Contribution to proceedings
    2013 38th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2013), 01.-06.09.2013, Mainz, Deutschland: IEEE Xplore Digital Library
    DOI: 10.1109/IRMMW-THz.2013.6665612

Publ.-Id: 19664

Krein space related physics: from mathematical structures towards experiments

Günther, U.

A compact overview is given about physical systems with antilinear symmetries as they have been intensively studied during the past 15 years and as they are currently still under intensive investigation worldwide. Starting from a few comments on the historical background, the underlying basic mathematical structures are sketched. This especially concerns the properties of the corresponding effective Hamiltonians, their non-selfadjointness in usual Hilbert spaces with positive definite (Euclidean type) inner products and their selfadjointness in Hilbert spaces with indefinite inner products, so called Krein spaces. Specific properties of these Hamiltonians like non-diagonalizability at spectral branch-points, hidden Jordan block structures, perturbation theory in terms of Puisseux series expansions instead of Taylor expansions as well as related group structures will be briefly discussed. Realizations of the antilinear symmetries are demonstrated for physical systems with simultaneous time-reversal and parity-inversion symmetries (PT symmetries). Specific physical effects like PT phase transitions and exciting new features of these systems are illustrated on simulations for various optical waveguide systems, Bose-Einstein condensates (BECs), microwave cavities, systems of coupled oscillators etc. Finally, a brief overview is given about recent experimental implementations as well as about a couple of promising new directions of research with interconnections to other areas of active research in theoretical and experimental physics.

Keywords: PT physics; PT phase transitions; operator theory; Krein spaces; branch points; Jordan blocks; Puisseux series expansions; Bose-Einstein condensates; optical waveguide systems; microwave cavities

  • Lecture (others)
    Lecture presented at the Physics Department, College of Sciences, Koc University, Istanbul, 16.12.2013, Istanbul, Turkey

Publ.-Id: 19663

Stabilite des systemes non conservatifs et algebra lineaire

Lerbet, J.; Aldowaji, M.; Challamel, N.; Kirillov, O.; Nicot, F.; Darve, F.

Investigations about linear stability of nonconservative systems with non symmetric stiness matrices lead to linear algebra results that are unusual in mechanics. It may also lead to original linear algebra developments. It is illustrated about linear divergence stability when adding kinematic constraints on the nonconservative system. The original concept of m-positive definite matrices is proposed, the main result is given and some mathematical open problems are suggested.

Keywords: nonconservative systems; kinematic constraints

  • Open Access Logo Contribution to proceedings
    21eme Congres Francais de Mecanique, 26.-30.08.2013, Bordeaux, France
    Congrès Francais de Mécanique, 39/41 rue Louis Blanc, 92400 Courbevoie, France: AFM, Maison de la Mécanique

Publ.-Id: 19662

Robust stability at the swallowtail singularity

Kirillov, O. N.; Overton, M. L.

Consider the set of monic fourth-order real polynomials transformed so that the constant term is one. In the three-dimensional space of the coefficients describing this set, the domain of asymptotic stability is bounded by a surface with the Whitney umbrella singularity. The maximum of the real parts of the roots of these polynomials is globally minimized at the Swallowtail singular point of the discriminant surface of the set corresponding to a negative real root of multiplicity four. Motivated by this example, we review recent works on robust stability, abscissa optimization, heavily damped systems, dissipation-induced instabilities, and eigenvalue dynamics in order to point out some connections that appear to be not widely known.

Keywords: abscissa; optimization; overdamping; asymptotic stability; Whitney umbrella; Swallowtail; caustic; eigenvalue dynamics

Publ.-Id: 19661

In Vivo Imaging of Microglia Cells Activated by LPS-Induced Systemic Inflammation in Mouse

Mathe, D.; Futo, I.; Veres, D.; Horvath, I.; Semjeni, M.; Kovacs, N.; Tóth, M.; Bergmann, R. K.; Szigeti, K.

Introduction: The role of microglia cells in the pathogenesis of inflammations and chronic neurodegenerative disorders in the central nervous system (CNS) is an active research field in recent years. The ramified form of microglia cells is activated via inflammation markers (e.g. IL-1b, TNF-alpha). The activated form of microglia cells as a key player of the innate immune system in the CNS present MHC II and release antiinflammatory agents. The activation status of the microglial benzodiazepine (BZD) receptor system could be used to monitor the process of neuroinflammation. Methods: Healthy (n=6) and LPS induced inflamed (n=4) C57BL/6 mice were used. The activation of the microglia cells was induced by systemic injection of 0.3 g/bw kg lipopolysaccharide (LPS) 5h before the in vivo measurements. We used NanoSPECT/CT Plus and nanoScan PET/MRI (Mediso Ltd, Hungary) multimodal in vivo imaging systems. To detect dynamics and localization of microglia activation we used a micro dose partial inverse BZD agonist ( 125-I - Iomazenil). The change of the general metabolic state in the CNS was monitored by 18-F-FDG PET. 99m-Tc-HMPAO (hexamethylpropylene-amino-oxime) was used for the detection of altered regional cerebral perfusion. The segmentation of different mouse regions was first based on MRI measurements of the animals and for aims of standardization coregistered with an MRI atlas. Results: FDG uptake was increased by systemic LPS in every region of the brain (p<5%). HMPAO uptake was decreased in several brain regions (p<5%). We found that the activity concentration of 125-I-Iomazenil was increased in the hippocampus and cerebellum but not in the cortex after systemic induction of neuroinflammation. Conclusions: FDG uptake increase indicates an increased metabolic rate due to induced brain inflammation. HMPAO uptake change could show glutathione depletion generated decrease of HMPAO fixation induced by reactive oxygen species (ROS) generated by activated inflammatory cells. The surprising result of selective Iomazenil uptake increase could be attributed to a higher amount of an activated but already resident microglia cell pool in the hippocampus as an early step of acute systemic inflammation in the brain. Based on our results the LPS induced changes in the BZD system should be further monitored in neuroinflammation in concordance with ROS status and the time course of the inflammatory changes in this general neuroinflammatory model in mice. A multi-modal imaging approach combining detailed structural and functional approaches elucidates important unknown details of neuroinflammation monitoring. This work was supported in part by INMiND (HEALTH.2011.2.2.1-2 No.278850) of FP7.

  • Poster
    World Molecular Imaging Congress, 18.-21.09.2013, Savannah, USA

Publ.-Id: 19660

Preparation of PW-class laser driven radiation sources for radiation oncology and structural analysis

Schramm, U.

Over the last decade laser particle acceleration has made such progress that first applications in special fields can be envisioned. Prominent examples are radiation therapy with laser accelerated ion beams as well as the generation of pulsed X-ray sources.
In this presentation the status of the joint activities of the Dresden groups at HZDR running the high power laser Draco and at Oncoray, the national center for radiation research in oncology, will be discussed. Emphasis will be given to the energy scaling of proton bunches accelerated in the TNSA regime with and during ultra-short pulses, potential instabilities in the process, methods for online monitoring, and to the status of the ongoing upgrade of Draco to PW power level. This topic will be complemented by a presentation of the recently achieved results on X-ray generation via Thomson back-scattering.

Keywords: Laser plasma acceleration

  • Invited lecture (Conferences)
    Institutsseminar HI Jena, 11.12.2013, Jena, Deutschland

Publ.-Id: 19659

Status of the PW laser at the HZDR Dresden

Schramm, U.

Status of the HZDR PW laser project with respect to the upcoming installations in Salamanca.

Keywords: PW laser

  • Invited lecture (Conferences)
    Third User Meeting of the Spanish Pulsed Laser Center CLPU, 02.-03.12.2013, Salamanca, Spanien

Publ.-Id: 19658

Diffusion Processes in the Sintering of Zirconia-Based Nanomaterials

Melikhova, O.; Cizek, J.; Prochazka, I.; Anwand, W.; Konstantinova, T.; Danilenko, I.

In the present work, zirconia-based nanomaterials with various stabilizers were prepared by a co-precipitation technique. Defects in these nanomaterials were characterized by positron annihilation spectroscopy which is a non-destructive technique with a high sensitivity to open volume defects and atomic scale resolution. It was found that zirconia-based nanomaterials contain vacancies and also nano-scale and meso-scale pores. Diffusion processes which occur in the nanomaterials sintered at elevated temperatures were investigated by depth sensitive positron annihilation studies on a variable energy slow positron beam. It was found that sintering causes intensive grain growth and residual porosity is removed from samples by diffusion to the surface.

Keywords: Yttria-stabilised zirconia; nanopowders; sintering; porosity; positron annihilation

Publ.-Id: 19657

Hydrogen absorption in thin ZnO films prepared by pulsed laser deposition

Melikhova, O.; Cizek, J.; Lukac, F.; Vlcek, M.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Connolly, J.; Mccarthy, E.; Krishnamurthy, S.; Mosnier, J.-P.

ZnO films with thickness of ~80 nm were grown by pulsed laser deposition (PLD) on MgO(100) single crystal and amorphous fused silica (FS) substrates. Structural studies of ZnO films and a high quality reference ZnO single crystal were performed by slow positron implantation spectroscopy (SPIS). It was found that ZnO films exhibit significantly higher density of defects than the reference ZnO crystal. Moreover, the ZnO film deposited on MgO substrate exhibits higher concentration of defects than the film deposited on amorphous FS substrate most probably due to a dense network of misfit dislocations. The ZnO films and the reference ZnO crystal were subsequently loaded with hydrogen by electrochemical cathodic charging. SPIS characterizations revealed that absorbed hydrogen introduces new defects into ZnO.

Keywords: ZnO; thin films; hydrogen; positron annihilation; defects

Publ.-Id: 19656

GISAXS Messungen am Labor-Diffraktometer

Grenzer, J.; Gateshki, M.; Holz, T.; Kharchenko, A.

Die Entwicklung neuer Materialien geht meistens einher mit der Schaffung neuer funktionalisierter Nanostrukturen. Strukturuntersuchungen sind dabei der Schlüssel, um eine Verbindung zwischen der Funktion und den strukturellen Eigenschaften, welche diese Funktion generieren, herstellen zu können. Dieses Wissen macht es möglich neuartige Materialien mit genau vorbestimmten Eigen-schaften zu entwerfen. Dünne nanostrukturierte Schichten können Ober- und Grenzflächen-eigenschaften derart beeinflussen, dass die Materialeigenschaften von konventionellen Werkstoffen optimal an die jeweilige Aufgabe angepasst werden können. Dabei wird die Funktion von Nanostrukturen nicht nur von deren innerer Struktur sondern zu einem großen Teil durch Ihre Morphologie und Oberfläche bestimmt.
Kleinwinkel-Röntgenstreuung im streifenden Einfall (GISAXS - Grazing incidence small angle scattering) hat den Vorteil gegenüber bildgebenden mikroskopischen Methoden (TEM, SEM), dass in der Regel keine aufwendige Probenpräparation notwendig ist und größere Probenvolumina untersucht werden können. GISAXS erlaubt es die Morphologie von oberflächennahen Strukturen als auch deren (innere) Elektronendichteverteilung zu ermitteln. GISAXS-Untersuchungen wurden lange fast ausschließlich an spezialisierten Synchrotronstrahllinien durchgeführt, da die Anforderungen an die Strahlqualität, Detektor und Experimentierfläche (sehr lange Strahllinie) mit konventionellen Laborgeräten gar nicht oder nur schlecht zu erfüllen waren. Seit einigen Jahren kann man beobachten, dass die Kleinwinkelstreuung Einzug in das Labor hält. Die Entwicklung von Mikrofokusquellen in der Kombination von leistungsfähigen Optiken und vor allem die Entwicklung neuer Halbleiter-flächendetektoren etabliert GISAXS-Untersuchungen zunehmend an Laborgeräten.

  • Invited lecture (Conferences)
    7. PRORA 2013 - Fachtagung Prozessnahe Röntgenanalytik, 21.-22.11.2013, Berlin, Germany

Publ.-Id: 19655

New structural constraints on the southern Provence thrust belt (France): evidences for an Eocene shortening event linked to the Corsica-Sardinia subduction

Andreani, L.; Loget, N.; Rangin, C.; Pichon, X. L.

We reply to the comments of J. Philip regarding the structure of La Nerthe range (southern Provence, France) and the timing of the deformation. We first agree with J. Philip on the structural independence of La Nerthe and L’Etoile ranges. We then discuss the allochthonous and autochthonous models. The allochthonous model mainly relies on a reactivation of a N-verging thrust during the Oligocene. There are no evidences for a Middle Rupelian thrusting event and the interpretation of the Oligocene series in southern Provence area was entirely revised. J. Philip’s Argumentation is solely based on the existence of steep dipping Rupelian limestones. However we demonstrate that they could be tilted along normal faults as it is the case in the Marseille basin. Recent works clearly show that the Oligocene Marseille and Saint-Pierre basins have a similar tectonic history resulting from two main extensional events. The last point debated by J. Philip is the age of the strike-slip faults. As it is pointed in our contribution the strike-slip fault planes cut folded strata and were reactivated during an extensional event. This strike-slip faulting event occurred between the latest stages of the main Bartonian compressional event and the beginning of the Early Rupelian extensional tectonics. As pointed by J. Philip the E-trending faults of Saint-Pierre basin acted as normal faults during the Oligocene. We however suggest that these faults were inherited from the Late Eocene strike-slip tectonics and reactivated during the Oligocene.

Keywords: Tectonics; Southern Provence; La Nerthe range; Paleogene; Neogene

Publ.-Id: 19654

Deep-Sea Astronomy with Accelerator Mass Spectrometry

Feige, J.; Wallner, A.; Fifield, L. K.; Korschinek, G.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S.; Winkler, S. R.; Golser, R.

Accelerator Mass Spectrometry (AMS) is a highly sensitive method to measure extremely low isotopic ratios of long-lived radionuclides relative to its stable isotope. Inspired by findings of an excess of 60Fe in a ferromanganese crust approximately 2 Myr ago, which was interpreted to be of supernova-origin, we use this method to determine concentrations of a variety of radionuclides in deep-sea sediment samples covering a time range from 1.7 to 3.2 Myr.
An international collaboration of different AMS facilities is utilized to search for signatures of 26Al, 53Mn, and 60Fe above terrestrial background production and extraterrestrial influx. In addition, the cosmogenic radionuclide 10Be is measured to confirm existing magnetostratigraphic dating of the samples and for comparison with atmospheric production ratios of 26Al/10Be. All 10Be and 26Al measurements arefinished, 53Mn and 60Fe is in progress. Measurement results and the influence of different background sources on a potential supernova signature will be presented and discussed.

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

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19653

Hydrogen interaction with defects in nanocrystalline, polycrystalline and epitaxial Pd films

Čížek, J.; Melikhova, O.; Vlček, M.; Lukáč, F.; Vlach, M.; Dobroň, P.; Procházka, I.; Anwand, W.; Brauer, G.; Wagner, S.; Uchida, H.; Gemma, R.; Pundt, A.

Hydrogen interaction with defects and structural development of Pd films with various microstructures were investigated. Nanocrystalline, polycrystalline and epitaxial Pd films were prepared and electrochemically loaded with hydrogen. Structural changes of Pd films caused by absorbed hydrogen were studied by in-situ X-ray diffraction combined with acoustic emission and measurement of electromotorical force. Development of defects during hydrogen loading was investigated by positron annihilation spectroscopy. It was found that hydrogen firstly fills open volume defects existing already in the films ans subsequently it occupies also interstitial sites in Pd lattice. Absorbed hydrogen causes volume expansion, which is strongly anisotropic in thin films. This introduces high stress into the films loaded with hydrogen. Acoustic emission measurements revealed that when hydrogen-induced stress achieves certain critical level rearrangement of misfit dislocations takes place. The stress which grows with increasing hydrogen concentration can be further released by plastic deformation and also by detachment of the film from the substrate.

Keywords: hydrogen; palladium; thin films; defects; positron annihilation; acoustic emission; X-ray diffraction

Publ.-Id: 19652

Forschungsprojekt am Helmholtz-Institut Freiberg für Ressourcentechnologie zum Rohstoffrecycling in der GaAs-Waferfertigung

Eichler, S.; Reinhold, T.; Zeidler, O.

Der Vortrag gibt einen Überblick zur Fertigung und Anwendung von GaAs Wafern. Durch den hohen Preisdruck für Wafer bei gleichzeitig schwankenden Gallium-Preisen und einer begrenzter Rohstoffverfügbarkeit ist das Unternehmen auf die Erschließung bisher ungenutzter Recyclingpotentiale angewiesen. Zusammen mit dem Helmholtz-Institut Freiberg wurde ein umfassendes Konzept für ein ökonomisches Recycling auf Grundlage von Membranverfahren entwickelt.

  • Invited lecture (Conferences)
    9. Sächsischer Kreislaufwirtschaftstag, 21.-22.11.2013, Freiberg, Deutschland

Publ.-Id: 19651

Revisiting magnetic stripe domains - anisotropy gradient and stripe asymmetry

McCord, J.; Erkartal, B.; von Hofe, T.; Kienle, L.; Quandt, E.; Grenzer, J.; Roshchupkina, O.

The thickness dependent generation of magnetic stripe domains in NiFe films is investigated by in-depth magnetic domain and micromagnetic analysis, as well as complementary analysis of the microstructure by x-ray diffraction and transmission electron microscopy. A gradient of perpendicular magnetic anisotropy with film thickness is found. Micromagnetic simulations show that the anisotropy gradient results in an asymmetric stripe domain configuration. Columnar grain coarsening and texture development with thickness are derived from the microstructural investigations. The variations correspondingly lead to the gradient of magnetic anisotropy and to an asymmetric magnetic stripe domain structure.

Publ.-Id: 19650

Neutron capture cross section measurements for 197Au from 4 to 80 keV at GELINA

Massimi, C.; Becker, B.; Dupont, E.; Kopecky, S.; Lampoudis, C.; Massarczyk, R.; Moxon, M.; Pronyaev, V.; Schillebeeckx, P.; Sirakov, I.; Volev, K.; Wynants, R.

Neutron induced capture cross section measurements for 197Au have been performed in the energy region between 4 keV and 80 keV. The experiments have been carried out at the time-of-flight facility GELINA. The prompt capture gamma-rays were detected by two C6D6 liquid scintillators, placed at 12.5 m distance from the neutron source. The shape of the neutron flux was measured with a 10B-loaded double Frisch-gridded ionization chamber based on the 10B(n,alpha) reaction. The total energy detection principle in combination with the pulse height weighting technique was applied. The data have been normalized to the well-isolated and saturated 197Au resonance at 4.9 eV. Special procedures have been applied to reduce bias effects due to the weighting function, normalization, dead time and background corrections. Uncertainties due to normalization, neutron flux and weighting function are 1.0 %. An additional uncertainty of 0.5 % results from the correction for self-shielding and multiple interactions, which have been verified by experiment. Resonance fluctuations have been studied by additional measurements at a 30 m flight path station. The results reported in this work deviate systematically by more than 5% from the cross section that is recommended as a reference for astrophysical applications. They are about 2% lower compared to a standard evaluation of the 197Au(n,gamma) cross section that was based on a least squares fit of experimental data available in the literature prior to this work and are fully consistent with the latest average capture cross section obtained in a quasi-Maxwellian spectrum at 25 keV.

Keywords: neutron capture; neutron resonances; neutron cross section

Publ.-Id: 19649

Novel scintillators - new ways at ELBE

Massarczyk, R.; Schwengner, R.; Junghans, A.; Wagner, A.

Nuclear resonance fluorescence experiments are a suitable tool to measure photo-absorption cross sections, from which one can determine the electromagnetic photon-strength functions. These strength functions are one of the main ingredients in network calculations for the nucleosynthesis in supernovae as well as in simulations concerning future nuclear power facilities. However, with the new orientation of these power plants from pure power production to a site where the transmutation of nuclear waste becomes more and more important, new kinds of data sets are needed.
The talk will show how we started to use the unique characteristics of LaBr3 detectors in experiments at the ELBE accelerator in Dresden-Rossendorf.
Experiments with positrons, neutrons and photons are presented and potential improvements are pointed out, which show how these experiments can benefit from the developments in the field of novel scintillators.

Keywords: LaBr3; detector techniques; nuclear structure; dipole strength functions

  • Invited lecture (Conferences)
    Physics with Large Arrays of Novel Scintillators, 15.-16.01.2014, Dublin, Ireland

Publ.-Id: 19648

Dose enhancement and localisation by combining reduced mass targets and a pulsed solenoid for radiobiological effectiveness studies of laser accelerated protons

Kroll, F.; Kluge, T.; Bussmann, M.; Cowan, T. E.; Herrmannsdörfer, T.; Kraft, S. D.; Metzkes, J.; Sauerbrey, R.; Schmidt, B.; Schramm, U.; Zeil, K.; Zier, M.; Zherlitsyn, S.

Proton beams by means of the well-confined dose deposition in matter are a promising tool for improving radiotherapy of cancer. Wider clinical use, however, is limited by the complexity and expense of current proton accelerators. Compact laser-driven proton therapy accelerators are a potential alternative, yet require substantial development in reliable beam generation, transport and dosimetric monitoring as well as validation in radiobiological studies.

In vitro cell irradiations with laser-accelerated protons show radiobiological effectiveness similar to conventionally accelerated protons. In vivo animal irradiations – the next step in the translational research chain towards laser-driven proton therapy of cancer – are currently restricted by the low proton yield and energy at the irradiation site.

We report on systematic investigations of the ultrashort pulse laser-driven acceleration of protons from thin targets of narrow lateral dimension, so-called reduced mass targets (RMTs). A robust maximum energy enhancement (almost doubled) was found when compared to reference irradiations of plain foils of same thickness and material. Combining RMTs with a pulsed high-field solenoid for particle capturing, as developed at Helmholtz-Zentrum Dresden-Rossendorf, gives the potential to enhance and localise the dose per pulse applied to the tumour, thus making further radiobiological studies on volumetric tumours feasible in the future.

  • Lecture (Conference)
    1st European Advanced Accelerator Concepts Workshop, 02.-07.06.2013, La Biodola, Elba, Italien

Publ.-Id: 19647

Nuclear structure - photon strength functions and nuclear level densities

Massarczyk, R.

Overview talk on investigations in nuclear structure today and their relation to astrophysical topics.

Keywords: nuclear structure; dipole strength

  • Invited lecture (Conferences)
    XLIV Arbeitstreffen Kernphysik in Schleching, 21.-28.02.2013, Schleching, Deutschland

Publ.-Id: 19646

Neutrons and Photons at ELBE - Contribution to the transmutation Project ERINDA

Massarczyk, R.; Schwengner, R.; Beyer, R.; Elekes, Z.; Ferrari, A.; Grosse, E.; Hannaske, R.; Junghans, A. R.; Kempe, M.; Kögler, T.; Wagner, A.

Contribution of experiments with neutrons and gamma rays at the radiation source ELBE to transmutation related projects like ERINDA

Keywords: transmutation; nuclear reaction

  • Poster
    11th International Topical Meeting on Nuclear Applications on Accelerators, 05.-08.08.2013, Brugge, Belgien

Publ.-Id: 19645

Depth profiling of Fe-implanted Si(100) by means of X-ray reflectivity and extremely asymmetric X-ray diffraction

Khanbabaee, B.; Biermanns, A.; Pietsch, U.; Grenzer, J.; Facsko, S.

This article reports on surface density variations that are accompanied by ion-beam-induced pattern formation processes on Si. The density profiles perpendicular to Si(100) surfaces were investigated after off-normal implantation with 5 keV Fe+ ions at fluences ranging from 1 x 10(16) to 5 x 10(17) ions cm(-2). Ripple formation was observed for ion fluences above 1 x 10(16) ions cm(-2). X-ray reflectivity (XRR) revealed the formation of a nanometre subsurface layer with incorporated Fe. Using XRR, no major dependence of the surface density on the ion fluence could be found. In order to improve the surface sensitivity, extremely asymmetric X-ray diffraction was applied. Depth profiling was achieved by measuring X-ray rocking curves as a function of the decreasing incidence angle down to 0 degrees using this noncoplanar scattering geometry. The density information was extracted from the dynamical Bragg shift of the diffraction peak caused by refraction of the X-ray beam at the air-sample interface.
Simulations based on the dynamical theory of X-ray diffraction revealed a decrease of density for increasing ion fluence in a region close to the surface, caused by the amorphization and surface roughening.

Publ.-Id: 19644

Broadband, diode pumped Yb:SiO2 multicomponent glass laser

Roeser, F.; Loeser, M.; Reichelt, A.; Albach, D.; Siebold, M.; Schwuchow, A.; Litzkendorf, D.; Grimm, S.; Schramm, U.

The spectroscopic properties and laser performance of a Yb:SiO2 multicomponent glass has been investigated. A maximum slope efficiency of 51%, an optical to optical efficiency of 42% and a tuning range of 80nm was realized.

Keywords: Lasers, solid-state; Laser materials; Lasers, ytterbium

  • Poster
    Ultrafast Optics 2013, 04.-08.03.2013, Davos, Switzerland

Publ.-Id: 19643

Progress at DREsden AMS

Rugel, G.; Akhmadaliev, S.; Merchel, S.; Pavetich, S.; Renno, A. D.; Ziegenrücker, R.

The combination of a mass spectrometer with an accelerator allows very sensitive detection limits for many applications. At the Helmholtz-Zentrum Dresden-Rossendorf an AMS (accelerator mass spectrometry) facility, DREsden AMS (DREAMS), with a 6-MV tandem accelerator has been successfully installed [1]. DREAMS has its applications in many scientic fields by determining 10Be, 26Al, 36Cl and 41Ca. We made progress to develop a negative ion source for volatile elements like chlorine or iodine by reducing the memory effect [2]. The range of isotopes is broaden to higher masses by the first experiments with actinides. A time-of-flight beam line will enable the measurement at higher count rates and of additional isotopes. Another focus is the combination of a commercial SIMS (CAMECA 7f Auto) with the accelerator. For this so called Super-SIMS the CAMECA 7f is utilized as ion source and low energy mass spectrometer. By complete destruction of molecules in the stripping process at the terminal of the accelerator detection limits some orders of magnitude better than for traditional dynamic SIMS are expected, i.e. ~10-9-10-12, see e.g. [3]. The Focus of applications will be geological samples in the framework of resource technology research. Ref.: [1] S. Akhmadaliev et al., NIMB 294 (2013) 5. [2] S. Pavetich et al., this conference. [3] C. Maden, Dissertation ETH Zürich 2003.

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 19642

HZDR pulsed power developments for laser plasma applications and the LIGHT collaboration

Kroll, F.; Cowan, T. E.; Herrmannsdörfer, T.; Masood, U.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Schlenvoigt, H.-P.; Schramm, U.; Zherlitsyn, S.

Since the mid-1950s, pulsed (iron-free) high-field magnets have become a common, versatile research tool. Applications in solid state physics have promoted the development of sophisticated magnets that nowadays can achieve fields above 90 T repeatedly.

We report here another area of application for pulsed power magnet technology in combination with high-intensity lasers; namely the use of pulsed magnets as research tools in laser-based laboratory astrophysics and as effective optical devices for laser-accelerated particle beams. Pulsed power solenoids for focusing of laser-accelerated particle beams might allow for the use of these new radiation qualities in medical radiation therapy or could function as a crucial part of a compact, laser-based ion source.

The talk gives a survey of developments at Helmholtz-Zentrum Dresden-Rossendorf in portable pulse generator technology and pulsed high-field magnets, especially designed to match the requirements of different laser-plasma physics environments. The beam optical properties of a capacitor-driven air core solenoid are derived from experimental data and most recent experimental results collected within the LIGHT collaboration at the PHELIX laser system at GSI, Darmstadt are presented.

Keywords: High-field magnet; laser; plasmas; beam optics; astrophysics

  • Lecture (Conference)
    LaB 2013 - Exploring the coupling between intense magnetic fields and high-power lasers, 02.-04.12.2013, Palaiseau, France

Publ.-Id: 19641

Algorithm for fluid velocity field quantification from image sequences in complex geomaterials

Korn, N.; Lippmann-Pipke, J.

For reactive transport modelling in geosciences a velocity field v(xi,t) with i = 1, 2, or 3 is required. This velocity field can be a) obtained by definition, b) calculated on the basis of a given geometry, a set of partial differential equations and initial and boundary conditions or, c) obtained from observations:
By now, various tomographic methods have been applied to observe fluid flow also in dense geological material under realistic conditions. These are magnetic resonance imaging (MRI, e.g. (Greiner et al., 1997), neutron transmission tomography (e.g. (Pleinert and Degueldre, 1995), X-ray computed tomography (CT) (e.g. (Goldstein et al., 2007; Klise et al., 2008), electrical resistivity tomography (ERT), e.g. (Bowling et al., 2006; Gheith and Schwartz, 1998) and last but not least positron emission tomography (PET), e.g. (Khalili et al., 1998; Kulenkampff et al., 2008; Richter et al., 2005). Still, the extraction of quantitative velocity fields from observed concentrations fronts that pass through complex geological media is not a trivial task.
One option to solve this kind of problem is to inject a tracer pulse into a sample, record image sequences of the tracer's flow through the sample and generate local break through curves (BTC). Numerical simulations – e.g. on the basis of finite difference methods (e.g. (Yoon et al., 2008) – may then vary hydraulic conductivity, porosity and dispersivity values within appropriate ranges and evaluate the model fits of the data over different scales. The authors conclude that predicting water flow at fine scales (relative to permeability variations) is very challenging and that this may have large implications for modelling reactive transport, where reactant residence time and mixing can be greatly impacted by water flowpaths.

To overcome such problems that accompany the fitting of parameter values such as hydraulic conductivity, porosity or dispersivity in 3D numerical flow models, we designed, implemented and tested a new algorithm. It is conceptualized for application to real-world 3D PET image series of transport process observation in geological media that may be affected to some degree by noise, image artifacts and detection limits. Our algorithm does not need prior information about the internal geometry of the sample, but only the global flow rate and the geometric boundaries of the sample.
Still, the foundation of the algorithm is the continuity equation. Its validity serves as an optimization criterion to fit segments of flow paths to the images. In this way, the network of flow paths is recovered and the velocity can be computed using a robust and universal approach.
We model the flow path network inside a rock sample as a network of flow path segments. Each segment is a straight and typically a short part of a single flow path. For these segments, we assume that the fluid is incompressible and that there are no sinks and sources within a segment. These assumptions are typically true for water in a closed flow path.
As a first step, the algorithm identifies regions that show a significant increase in mass at some point in time (maxima in a BTC). At such regions nodes are placed, that are to be connected later with segments of the flow path network.
For each straight flow path segment, it is sufficient to use a 1D model, which greatly reduces computation time without sacrificing much accuracy, and makes the algorithm more robust against noise. For the algorithm, a segment is represented by a cylindrical tube that completely covers the flow path. Because there are no sinks and sources, the flow rate is constant when the tube covers exactly one flow path, but varies when it does not. Therefore, we can use the variation of the flow rate as an optimization criterion to decide where to place a tube, i.e. which of the aforementioned nodes to connect.
Finally, we can compute the velocity field from the flow rate and cross-sectional area of the tube.

Results & Discussion
For validating the algorithm we simulated a non-reactive tracer experiment in COMSOL Multiphysics® on a synthetic fracture network as a benchmark model for the algorithm. (Later, the image sequences obtained from the transport simulation are to be replaced by the PET image sequences). A velocity field (derived using the cubic law) was used to simulate transport of a conservative tracer. The resulting image sequence was provided to our new algorithm, which then computed the underlying velocity field.

Here we introduced our new algorithm (work in progress) that estimates velocity distributions from image sequences. It is robust against noise and static image artefacts, and requires no prior knowledge about the, possibly complex geometry of the sample. The current run-time for the example shown is well under ten seconds . These properties make the new algorithm universally suitable for tracer experiments for a wide range of applications.
The obtained velocity distributions (fig. 2, left) can directly be used for further reactive transport modelling.

Bowling, J.C., Zheng, C., Rodriguez, A.B. and Harry, D.L., 2006. Geophysical constraints on contaminant transport modeling in a heterogeneous fluvial aquifer. Journal of Contaminant Hydrology, 85(1–2): 72-88.
Gheith, H.M. and Schwartz, F.W., 1998. Electrical and visual monitoring of small scale three-dimensional experiments. Journal of Contaminant Hydrology, 34(3): 191-205.
Goldstein, L., Prasher, S.O. and Ghoshal, S., 2007. Three-dimensional visualization and quantification of non-aqueous phase liquid volumes in natural porous media using a medical X-ray Computed Tomography scanner. Journal of Contaminant Hydrology, 93(1–4): 96-110.
Greiner, A., Schreiber, W., Brix, G. and Kinzelbach, W., 1997. Magnetic resonance imaging of paramagnetic tracers in porous media: Quantification of flow and transport parameters. Water Resources Research, 33(6): 1461-1473.
Khalili, A., Basu, A.J. and Pietrzyk, U., 1998. Flow visualization in porous media via positron emission tomography. Physics of Fluids, 10: 1031-1033.
Klise, K.A., Tidwell, V.C. and McKenna, S.A., 2008. Comparison of laboratory-scale solute transport visualization experiments with numerical simulation using cross-bedded sandstone. Advances in Water Resources, 31(12): 1731-1741.
Kulenkampff, J., Richter, M., Gründig, M. and Seese, A., 2008. Observation of transport processes in soils and rocks with Positron Emission Tomography. Geophysical Research Abstracts, 9: 02754.
Pleinert, H. and Degueldre, C., 1995. Neutron radiographic measurement of porosity of crystalline rock samples: a feasibility study. Journal of Contaminant Hydrology, 19(1): 29-46.
Richter, M., Gründig, M., Zieger, K., Seese, A. and Sabri, O., 2005. Positron Emission Tomography for modelling of geochmical transport processes in clay. Radiochimica Acta, 93: 643-651.
Yoon, H., Zhang, C., Werth, C.J., Valocchi, A.J. and Webb, A.G., 2008. Numerical simulation of water flow in three dimensional heterogeneous porous media observed in a magnetic resonance imaging experiment. Water Resources Research, 44: W06405.

  • Lecture (Conference)
    TRePro III 2014, 05.-07.03.2014, Karlsruhe, Deutschland

Publ.-Id: 19640

AER Working Group D on VVER safety analysis – report of the 2013 meeting

Kliem, S.

The AER Working Group D on VVER reactor safety analysis held its 22th meeting in Paris, France, during the period April 10-11, 2013. The meeting was hosted by the OECD/NEA and was held in conjunction with the fifth workshop on the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and the seventh workshop on the OECD Benchmark for Uncertainty Analysis in Best-Estimate Modeling (UAM) for Design, Operation and Safety Analysis of LWRs. Altogether 17 participants attended the meeting of the working group D, 12 from AER member organizations and 5 guests from non-member organization. The co-ordinator of the working group, Mr. S. Kliem, served as chairman of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given presentations and the discussions can be attributed to the following topics:
• Code development and benchmarking including the calculation of the OECD/NEA Benchmark for the Kalinin-3 VVER-1000 NPP and 7th AER Dynamic Benchmark
• Safety analyses methods and results
• Future activities
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairman.

  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, Budapest: MTA Energoatom, 417-422
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia

Publ.-Id: 19639

Charakterisierung von Mineralen, Laugungsüberständen und Mikroorganismen mittels Raman-Spektroskopie

Kostudis, S.; Kutschke, S.; Pollmann, K.

Heute erfahren die regionalen Kupferschiefervorkommen nach dem Ende der 800jährigen Bergbauära im Jahr 1990 eine Wiederentdeckung. Der moderate Kupfergehalt fordert den Einsatz alternativer umweltschonender und effizienter Abbauprozesse. Ziel unserer Arbeit ist daher die Etablierung von Biolaugungsprozessen mit heterotrophen Mikroorganismen zu Kupfergewinnung. Bio-induzierte Veränderungen auf Mineraloberflächen, der Laugungsüberstände sowie Veränderungen der Biomasse durch Wechselwirkungen mit dem Laugungsmaterial sollen unter anderem mithilfe von Raman-Spektroskopie analysiert werden.
Als Grundlage für die Zuordnung der Minerale zu den Raman-Spektren wird die Polarisationsmikroskopie genutzt. Dasselbe mikroskopierte Areal wird mithilfe der zweidimensionalen Scanfunktion des mit einem Mikroskop gekoppelten Raman-Spektrometers analysiert. Aus den erhaltenen Daten ist die bildgebende Differenzierung zwischen den Hauptmineralen Chalkopyrit (CuFeS2) und Bornit (Cu5FeS4) im Kupferschiefer unter Verwendung univariater Datenanalyse möglich. Der Vergleich der Spektren von Chalkopyrit und Bornit zeigt, dass sich die verschiedenen Kristallgitter und Anteile von Kupfer, Schwefel und Eisen in unterschiedlichen Bandenintensitäten widerspiegeln.
Bei der Untersuchung der Laugungsüberstände können die von der Probe erhaltenen Spektren mithilfe von Referenzmessungen zugeordnet werden. Im Vergleich zu den abiotischen Komponenten des Laugungssystems sind deutliche Unterschiede in den Spektren der eingesetzten Biomasse sichtbar.

  • Poster
    Aufbereitung und Recycling, 13.-14.11.2013, Freiberg, Deutschland

Publ.-Id: 19638

Investigation of the hydrophobization of silicate ore minerals using a Force Mapping Method combining Non contact Atomic Force Microscopy and Raman Spectroscopy

Rudolph, M.; Peuker, U. A.

The Helmholtz-Institute Freiberg (HIF) founded in 2011 conducts research on innovative techniques for the enhanced processing of strategic metal containing resources. Flotation has been identified as the most essential process in the minerals processing department to be focusing research on. In this paper we introduce a force mapping technique based on non-contact colloidal probe atomic force microscopy where a cantilever with an attached hydrophobic sphere is oscillating above a planarized ore sample in the aqueous environment including dissolved collector molecules. The physical background of force-distance conversion from amplitude- and phase-distance evaluations is presented to point out the opportunities when compared to conventional AFM force spectroscopy. Raman spectroscopy is used in combination to identify the mineral phase localized at the cantilever position. The method is applied on samples of a rare earth containing silicate ore from southern Sweden made up of feldspars, aegirine, nepheline and the rare earth containing eudialyte.

  • Lecture (Conference)
    Flotation '13, 18.-21.11.2013, Cape Town, South Africa

Publ.-Id: 19637

Highly efficient all diode pumped burst mode laser system for ultra-short pulses

Körner, J.; Hein, J.; Liebtrau, H.; Seifert, R.; Klöpfel, D.; Kahle, M.; Loeser, M.; Siebold, M.; Schramm, U.; Kaluza, M.

Concept and first results on an all diode pumped cryogenically cooled Yb:CaF2 based burst mode laser system are presented. Output parameters are designed to be 5J per burst of 1000 350fs pulses at 1MHz.

  • Contribution to proceedings
    Advanced Solid State Lasers (ASSL), 27.10.-01.11.2013, Paris, France
    Conference Papers ASSL, 978-1-55752-982-4, ATu3A.63
    DOI: 10.1364/ASSL.2013.ATu3A.63

Publ.-Id: 19636

Direct Observation of Waterglass Impregnation of Fractured Salt Rock with Positron Emission Tomography

Bittner, L.; Kulenkampff, J.; Gründig, M.; Lippmann-Pipke, J.; Enzmann, F.

Sealing with waterglass is one option of technical improvement of the geological barrier. The process of injection is rather involved, because it depends on the kinetics of reaction of the injected waterglass with salt and brines, on the nature of the fractures and the injection velocity. Generally, up to now only the final result of this impregnation could be tested with injection tests and tomographic methods.
We already applied PET process monitoring as laboratory method in a large number of studies of conservative and reactive flow, as well as diffusion experiments, in different geological materials. PET enables to observe the propagation of radiolabelled substances with ultimate sensitivity and with a reasonable spatial resolution of 1 mm. We now developed a method to observe the process of waterglass impregnation into salt rock with PET. Labelling of waterglass is possible by simply adding a small portion of [18F]KF solution, with an activity of around 100 MBq. During the injection of the labelled waterglass into the salt rock we acquire a sequence of PET scans which yield a sequence of the spatial activity distribution in the sample. The activity per voxel is proportional to the volume fraction of waterglass.
The method was tested on small volumes of salt grit and a drill core, which was previously damaged with a geomechanical test and characterized with CT-imaging. These first examples were conducted at a low entry pressure, which limited the achievable depth of penetration and thus the achieved permeability reduction. However, PET-monitoring of the flow process before and after the waterglass injection showed significant alterations of the flow field.
Generally, this method is applicable also with other impregnation agents and matrices. Our approach, where we combine numerical process simulation based on CT-imaging with direct experimental process observation with PET is suited to improve fundamental process understanding and to verify the underlying assumptions and model codes.

Keywords: PET; pet; reactive transport; tracer; flow experiments; geological barrier; nuclear waste disposal

  • Lecture (Conference)
    International Conference on the Performance of Engineered Barriers: Backfill, Plugs & Seals, 06.-07.02.2014, Hannover, Deutschland

Publ.-Id: 19635

Ressourcentechnologie ‚Made in Germany‘ -Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF)-

Birtel, S.; Klossek, A.; Gutzmer, J.

Die exportorientierte Industrie in der Bundesrepublik Deutschland ist in ihrer derzeitigen Ausrichtung nahezu vollständig abhängig von metallischen und mineralischen Rohstoffen, die auf dem Weltmarkt erworben und importiert werden müssen. Die Gründung des Helmholtz-Instituts Freiberg für Ressourcentechnologie im August 2011 war daher motiviert durch den raschen Anstieg und die starke Fluktuation der Rohstoffpreise des letzten Jahrzehnts und der damit einhergehenden Sorge möglicher Versorgungsengpässe. Das Helmholtz-Institut ist organisatorisch an das Helmholtz-Zentrum Dresden-Rossendorf angegliedert und wird von diesem gemeinsam mit der Technischen Universität Bergakademie Freiberg aufgebaut. Die Forschung im Helmholtz-Institut fokussiert sich hauptsächlich auf interdisziplinäre und tech-nologieorientierte Projekte zur energie- und ressourceneffizienten Nutzung einer Auswahl von Hochtechnologierohstoffen (insbes. Seltene Erden, Indium, Germanium und Gallium), aber auch die Nutzung von anderen Hochtechnologiemetallen. Es werden sowohl Technologien zur primären Rohstoffnutzung als auch für das Recycling erforscht. Forschungsprojekte werden gemeinsam mit Partnern in Konsortien auf regionaler, nationaler und internationaler Ebene initiiert und durchgeführt. Nicht zuletzt leistet das Helmholtz-Institut einen signifikanten Beitrag zur Ausbildung einer neuen Generation hochqualifizierter Wissenschaftler und Techniker für die deutsche Industrie und den Hochschulsektor.

Keywords: Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF); Rohstoffstrategie; Rohstoffabkommen; Zusammenarbeit mit Industrie und Forschung

  • Other report
    Santiago: AHK Chile, 2014

Publ.-Id: 19634

Effect of compounding principles on thermal, mechanical and magnetic performance of soft magnetic polymethylmethacrylate/Fe3O4 nanocomposites

Xie, L.; Kirchberg, S.; Rudolph, M.; Ziegmann, G.; Peuker, U.

In this study, the effect of compounding principles on the properties of Polymer Bonded Soft Magnetic Nanocomposites (PBSMNs) was discussed. The polymethylmethacrylate /Fe3O4 magnetic nanocomposites (Fe3O4: 30 wt%) were prepared by the in situ process based on the solution and spray drying method, as well as by the ex situ process based on the kneading machine. As reference, the process combining these two compounding principles was also carried out for the PBSMN preparation, named as in-between process. The morphology structures, thermal, mechanical and magnetic properties of the magnetic nanocomposites achieved with different compounding principles were characterized. The results show that compounding principles have significant influence on the properties of the magnetic polymer nanocomposites. In the end, their contributions to the power electronic applications were discussed as well.

Keywords: compounding process; in situ polymerization; Polymer composites; soft magnetic composites

Publ.-Id: 19633

Start of user operation of the Mono-energetic Positron Source MePS

Butterling, M.; Anwand, W.; Büttig, H.; Cowan, T. E.; Jungmann, M.; Keßler, C.; Müller, A.; Krause-Rehberg, R.; Staats, G.; Wagner, A.

The Mono-energetic Positron Source MePS is an intense positron source for depth-resolving defect characterization at the superconducting accelerator ELBE (Electron LINAC for beams with high Brilliance and low Emittance) at Helmholtz-Zentrum Dresden-Rossendorf. In 2013 the chopper was added to improve timing resolution (before about 400 ps) and shape of positron lifetime spectra (by removing distortions). We also started user operation with investigations of porous samples. First measurements and results as well as the effect of the chopper will be presented.

Keywords: mono-energetic positrons; defect characterization; positron lifetime; accelerator

  • Lecture (others)
    13th International Workshop on Slow Positron Beam Techniques and Applications, 15.-20.09.2013, München, Deutschland

Publ.-Id: 19632

Radiolabeled cetuximab conjugates for EGFR targeted cancer diagnostics and therapy

Sihver, W.; Pietzsch, J.; Krause, M.; Baumann, M.; Steinbach, J.; Pietzsch, H. J.

The epidermal growth factor receptor (EGFR) evolved over years one main molecular target for treatment of different cancer entities. The anti-EGFR antibody cetuximab has been approved alone or in combination with chemotherapy for palliative colorectal and head and neck squamous cell carcinoma therapy, or in combination with radiotherapy for head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab might increase the intrinsic activity in combination with the specific targeting properties of cetuximab. The article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and / or treatment on different tumor models. A promising theranostic approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. The therapeutic effect of this treatment method will be discussed. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important goal is the reduction of nonspecific uptake of radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized treatment.

Keywords: EGFR; radiolabeled cetuximab conjugates; radioimmunotherapy; cancer theranostics; external beam radiotherapy; endoradionuclide therapy

Publ.-Id: 19631

Investigation of the effective mass in GaAsN

Lomakina, F.; Drachenko, O.; Schneider, H.; Patanè, A.; Hopkinson, M.; Helm, M.

Dilute nitride semiconductors (DNS), such as GaAsN, with a nitrogen content y of a few percent or even less, have recently attracted considerable interest due to the giant bowing effect. That, in turn, offers the possibility to tailor the band structure of new devices, like LEDs, lasers, solar cells, and infrared photodetectors by varying the nitrogen content [1]. Determining proper values of the effective mass (EM) of DNS is a topic of interest because of the inconsistency of previous results (e.g. [2, 3]). To clarify the conflict we study a series of GaAsN samples (y = 0%-1%) by cyclotron resonance (CR) spectroscopy, Fourier spectroscopy and photoluminescence spectroscopy in magnetic fields in order to deduce the EM via the CR frequency, plasma frequency and the dielectric shift, respectively. So far, we are able to show that the discrepancies of former publications are most likely caused by the particular choice of the experimental technique. Probably the most direct and reliable method is the CR spectroscopy, which has rarely been used due to the low electron mobility in GaAsN. The CR does not signicantly change with different N contents and thus the EM. Our Magneto-PL spectroscopy results exhibit a completely dierent behavior. We use the same method as e.g. [2] and see a huge increase of the EM with the N content which is even bigger than in previous publications. On the other hand, the slope of ΔE, which is the key parameter in the calculation of the EM in this method, strongly depends on the region of interest. In our opinion, this method is not accurate enough for the EM determination.

[1] A. Erol, Dilute III-V Nitride Semiconductors and Material Systems, Springer-Verlag Berlin Heidelberg (2008).
[2] F. Masia et. al., Appl. Phys. Lett. 82, 4474 (2003).
[3] Y. J. Wang et. al., Appl. Phys. Lett. 82, 4453 (2003).

  • Poster
    20th International Conference on Electronic Properties of Two-Dimensional Systems (EP2DS-20) and 16th International Conference on Modulated Semiconductor Structures (MSS-16), 01.-05.07.2013, Wroclaw, Polska

Publ.-Id: 19630

Baseline Closure Model for Dispersed Bubbly Flow: Bubble Coalescence and Breakup

Liao, Y.; Rzehak, R.; Lucas, D.; Krepper, E.

A set of closures for two-fluid modelling of adiabatic bubbly flows has been defined as baseline model, which provides a common basis for further improvement and development. It includes closures for bubble forces, bubble-induced turbulence as well as bubble coalescence and breakup. In this work, the baseline model is applied to the case of adiabatic upward vertical pipe flows and validated with aid of the MTLoop database. Special attention is paid to the performance of the newly proposed coalescence and breakup model. The comparison with measurements shows that the baseline model is able to capture the evolution of bubble size distribution, gas volume fraction and velocity profiles along the pipe over a wide range of flow conditions.

Keywords: baseline model; bubble coalescence and breakup; MUSIG, poly-dispersed bubbly flow; vertical pipe

Publ.-Id: 19629

Investigation of the effective mass in dilute nitride semiconductors

Lomakina, F.; Drachenko, O.; Schneider, H.; Patanè, A.; Hopkinson, M.; Helm, M.

Dilute nitride semiconductors (DNS), such as GaAsN, with a nitrogen content y of a few percent or even less, have attracted considerable current interest due to the giant bowing effect. That, in turn, offers the possibility to tailor the band structure of new devices, like LEDs, lasers, solar cells, and infrared photodetectors by varying the nitrogen content [1]. Determining proper values of the effective mass (EM) of DNS is a topic of interest because of the inconsistency of previous results (e.g. [2,3]). To clarify the conflict we study a series of GaAsN and InAsN samples (y=0%-1.9%) by cyclotron resonance (CR) spectroscopy, Fourier spectroscopy and photoluminescence spectroscopy in magnetic fields in order to deduce the EM via the CR frequency, plasma frequency and the dielectric shift, respectively. First results of CR measurements indicate that the EM is not significantly affected by the nitrogen doping in contrast to previous publications.

[1] A. Erol, Dilute III-V Nitride semiconductors and Material Systems, Springer-Verlag Berlin Heidelberg (2008)
[2] F. Masia et al. Appl. Phys. Lett. 82, 4474 (2003)
[3] Y. J. Wang et al. Appl. Phys. Lett. 82, 4453 (2003)

  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 19628

Broadband THz detection and homodyne mixing using GaAs high-electron-mobility transistor rectifiers

Preu, S.; Regensburger, S.; Kim, S.; Mittendorff, M.; Winnerl, S.; Malzer, S.; Lu, H.; Burke, P. G.; Gossard, A. C.; Weber, H. B.; Sherwin, M. S.

We report on Terahertz (THz) detectors based on III-V high-electron-mobility field-effect transistors (FET). The detection results from a rectification process that is still highly efficient far above frequencies where the transistor provides gain. Several detector layouts have been optimized for specific applications at room temperature: we show a broadband detector layout, where the rectifying FET is coupled to a broadband logarithmic-periodic antenna. Another layout is optimized for mixing of two orthogonal THz beams at 370 GHz or, alternatively, 570 GHz. A third version uses a large array of FETs with very low access resistance allowing for detection of very short high-power THz pulses. We reached a time resolution of 20 ps.

Keywords: THz detection; field effect transistor; ultrafast detector; mixing

  • Contribution to proceedings
    6th International Conference on Millimetre Wave and Terahertz Sensors and Technology, 24.-25.09.2013, Dresden, Deutschland
    Proceedings of SPIE 8900 (2013), 89000R
    DOI: 10.1117/12.2029478
  • Invited lecture (Conferences)
    6th International Conference on Millimetre Wave and Terahertz Sensors and Technology, 24.-25.09.2013, Dresden, Deutschland

Publ.-Id: 19627

Experimental investigations of single and two-phase flow in a heated rod bundle

Barthel, F.; Franz, R.; Hampel, U.

Within the frame of the coordinated project "Modeling, simulation and experiments for boiling phenomena in pressurized water reactors" (BMBF FZK 02NUK010) an experimental facility for the study of boiling flows in a 3 · 3 rod bundle geometry was setup. The bundle resembles in essential geometrical parts the geometry in a pressurized water reactor fuel element. The facility is operated with a refrigerant fluid. Beside Standard instrumentation for temperature, pressure and flow rate we employed particle image velocimetry for single phase flow studies, gamma ray densitometry for integral gas fraction measurement sand ultrafast X-ray tomography for the study of the void Dynamics in the cross-section. Moreover extensive thermo-Instrumentation allows axial rod surface temperature measurements for the central heated rod. First experimental results have been achieved and will be introduced and discussed in this article.

Publ.-Id: 19626

Strategies for Contacting Single Molecule Devices

Wieser, M.; Sendler, T.; Kilibarda, F.; Teshome, B.; Keller, A.; Grebing, J.; Erbe, A.

Single molecules have been under investigation in terms of their suitability as building blocks for future electronics for more than a decade now. But the ultimate goal of molecular electronics is the (controlled) creation of functional electric circuits, i.e., networks, rather than individual devices. This requires two aspects to be addressed: The properties of the devices themselves and the properties of the contacts between individual devices as well as to the molecules forming the devices.

Traditionally, top-down methods are used to form these contacts. Here, results of measurements on PEEB (P-Ethoxy Ethyl Benzoate) molecules using the technique of mechanically controllable break junctions will be presented.

However, a bottom-up approach is favorable because of the reduced effort in fabrication. Therefore, in the second part an intermediate, hybrid approach using DNA double helix bundles as templates for leads and top-down fabricated contacts to establish a connection to the macroscopic world will be discussed.

Keywords: Molecular Electronics; Electronic Transport; Mesoscopic Physics; DNA

  • Invited lecture (Conferences)
    IHRS NANONET Annual Workshop 2013, 10.10.2013, Dresden, Deutschland

Publ.-Id: 19625

Cosmic ray exposure and pre-atmospheric size of the Gebel Kamil iron meteorite

Ott, U.; Merchel, S.; Herrmann, S.; Pavetich, S.; Rugel, G.; Faestermann, T.; Fimiani, L.; Gomez-Guzman, J. M.; Hain, K.; Korschinek, G.; Ludwig, P.; D’Orazio, M.; Folco, L.

Cosmogenic He Ne and, Ar as well as the radionuclides 10Be, 26Al, 36Cl, 41Ca, 53Mn and 60Fe have been determined on samples from the Gebel Kamil ungrouped Ni-rich iron meteorite by noble gas mass spectrometry and accelerator mass spectrometry (AMS), respectively. The meteorite is associated with the ~45 m diameter Kamil crater in southern Egypt. Samples originate from an individual large fragment (“Individual”) as well as shrapnel. Concentrations of all cosmogenic nuclides – stable and radioactive - are a factor ~4x lower in the shrapnel samples than in the Individual. Assuming negligible 36Cl decay during terrestrial residence (indicated by the young crater age <5000 a; Folco et al. 2011), data are consistent with a simple exposure history and a 36Cl-36Ar cosmic ray exposure age (CRE) of ~(366 +- 18) Ma (systematic errors not included). Both noble gases and radionuclides point to a pre-atmospheric radius >85 cm, i.e. a pre-atmospheric mass >20 tons, with a preferred radius of 115-120 cm (50-60 tons). The analyzed samples came from a depth of ~20 cm (Individual) and ~50-80 cm (shrapnel). The size of the Gebel Kamil meteoroid determined in this work is close to estimates based on impact cratering models combined with expectations for ablation during passage through the atmosphere (Folco et al. 2010, 2011).

Keywords: accelerator mass spectrometry; AMS; cosmogenic nuclides; cosmochemsitry; meteorite

Publ.-Id: 19624

Green up-conversion of swift C5+ ion irradiated planar waveguide in Er3+, MgO codoped nearly stoichiometric LiNbO3 crystal

Liu, H.; Jia, Y.; Ren, Y.; Akhmadaliev, S.; Zhou, S.; Chen, F.

We report on the green up-conversion emission from Er3+, MgO codoped nearly stoichiometric LiNbO3 planar waveguides fabricated by the swift C5+ ion irradiation. The characteristics of the waveguides are investigated by using a continuous wave laser at wavelength of 800 nm. The reconstructed distribution of the refractive index of the C ion irradiated waveguides shows a “barrier and well” profile. The up-conversion emissions of green light, corresponding to the transition of 4H11/2→4I15/2 and 4S3/2→4I15/2 bands, have been observed in the waveguides with intensity of 40% of that from the bulk.

Keywords: Optical waveguides; Swift heavy ion irradiation; Green up-conversion emission; LiNbO3 crystal

Publ.-Id: 19623

Channel waveguide lasers at 1064  nm in Nd:YAG crystal produced by C5+ ion irradiation with shadow masking

Yao, Y.; Jia, Y.; Chen, F.; Akhmadaliev, S.; Zhou, S.

We report on the fabrication of channel waveguides in Nd:YAG crystals, using swift C5+ ion irradiation with ion energy of 15 MeV and fluence at 5×10^15  ions/cm2. A laser-cut shadow mask of a number of open stripes with varied width was covered on the sample surface during the ion irradiation. Channel waveguides were formed in the Nd:YAG crystal due to the refractive index increase along the ion trajectory. Room temperature waveguide laser oscillations at 1064 nm have been observed under 808 nm optical pumping, with laser slope efficiency at 38% and a maximum output power of 36 mW.

Publ.-Id: 19622

Is silicide formation the decisive factor in impurity induced ion beam pattern formation?

Engler, M.; Müller, S.; Will, M.; Frost, F.; Feder, R.; Spemann, D.; Hübner, R.; Facsko, S.; Michely, T.

Recent experiments showed that metal deposition during ion beam erosion causes the pattern formation at low incidence angles.
We performed 2 keV Kr+ ion beam erosion of Si(001) experiments using a scanned fine focus ion source with simultaneous deposition of metal atoms. After ion beam erosion we analyzed our samples in-situ with scanning tunneling microscopy and ex-situ with atomic force microscopy and transmission electron microscopy. The metal concentration on the Si surface was analyzed ex-situ with Rutherford backscattering spectrometry.
To distinguish the effects of collision kinetics versus chemical interaction in metal co-deposition induced pattern formation on Si(001) we conducted Ag and Pd sputter co-deposition from a target mounted on the Si sample. This setup results in a flux and concentration gradient of the co-deposited metals on the Si sample. While for Pd a concentration dependent ripple pattern is observed, no pattern evolves for Ag co-deposition under ultra high vaccum conditions. Since Ag and Pd possess nearly the same nuclear charge and atomic mass, their different ability to form a pattern must be attributed to their different ability to form silicides. While Pd forms a variety of silicides, Ag forms none. Silicide formation of the co-deposited metal appears thus to be a necessary condition to induce a pattern on Si during ion exposure.

  • Lecture (Conference)
    Nanocale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark

Publ.-Id: 19621

Enhanced growth and Cu diffusion barrier properties of thermal ALD TaNC films in Cu/low-k interconnects

Wojcik, H.; Hossbach, C.; Kubasch, C.; Verdonck, P.; Barbarin, Y.; Merkel, U.; Bartha, J. W.; Hübner, R.; Engelmann, H.-J.; Friedemann, M.

For thermal ALD TaxNyCz films improved growth behaviour and Cu diffusion barrier performance are demonstrated by applying a plasma treatment prior to film deposition, in particular on low-k dielectrics. Two different kinds of ALD processes for depositing thermal ALD TaxNyCz films are applied in this study, involving either TBTDET or PDMAT as a precursor. Ammonia is used as a reactant and Ar as a purging gas in both processes. Within the experiment, two types of pre-treatments prior to ALD are investigated: a wet-chemical pre-treatment using diluted (0.5%) HF, and plasma pre-treatments using Ar/H2 or N2 plasmas. It is examined by transmission electron microscopy (TEM) from a microstuctural perspective whether improved growth behaviour of thermal ALD TaxNyCz films can be achieved by applying a plasma treatment prior to film deposition. The Cu diffusion barrier properties of 10-15 nm ALD TaNC films are then evaluated by bias temperature stress (BTS) and triangular voltage sweep (TVS) measurements on metal-insulator-semiconductor (MIS) test structures, after annealing at up to 600 °C under H2/N2 atmosphere. The results imply that, from a process side, thermal ALD TaNC films can intrinsically achieve a Cu diffusion barrier performance similar to PVD TaN. However, if no treatment was applied, Cu drift occurred.

Keywords: ALD TaN; Cu diffusion barrier; Triangular voltage sweep; Plasma treatment; Low-k

Publ.-Id: 19620

The giant Shakhdara migmatitic gneiss dome, Pamir, India–Asia collision zone, II:Timing of dome formation, Tectonics

Stübner, K.; Ratschbacher, L.; Weise, C.; Chow, J.; Hofmann, J.; Khan, J.; Rutte, D.; Sperner, B.; Pfänder, J. A.; Hacker, B. R.; Dunkl, I.; Tichomirowa, M.; Stearns, M. A.; Bahram, I.; Gadoev, M.; Gloaguen, R.; Jonckheere, R.; Kanaev, E.; Minaev, V.; Oimahmadoc, I.; Rajabov, N.; Stanek, K. P.

Cenozoic gneiss domes—exposing middle-lower crustal rocks—cover ~30% of the surface exposure of the Pamir, western India-Asia collision zone; they allow an unparalleled view into the deep crust of the Asian plate. We use titanite, monazite, and zircon U/Th-Pb, mica Rb-Sr and 40Ar/39Ar, zircon and apatite fission track, and zircon (U-Th)/He ages to constrain the exhumation history of the ~350 × 90 km Shakhdara-Alichur dome, southwestern Pamir. Doming started at 21–20 Ma along the Gunt top-to-N normal-shear zone of the northern Shakhdara dome. The bulk of the exhumation occurred by ~NNW-ward extrusion of the footwall of the crustal-scale South Pamir normal-shear zone along the southern Shakhdara dome boundary. Footwall extrusion was active from ~18–15 Ma to ~2 Ma at ~10 mm/yr slip and with vertical exhumation rates of 1–3 mm/yr; it resulted in up to 90 km ~N-S extension, coeval with ~N-S convergence between India and Asia. Erosion rates were 0.3–0.5 mm/yr within the domes and 0.1–0.3 mm/yr in the horst separating the Shakhdara and Alichur domes and in the southeastern Pamir plateau; rates were highest along the dome axis in the southern part of the Shakhdara dome. Incision along the major drainages was up to 1.0 mm/yr. Thermal modeling suggests geothermal gradients as high as 60°C/km along the trace of the South Pamir shear zone and their strong N-S variation across the dome; the gradients relaxed to ≤40–45°C/km since the end of doming.

Keywords: Pamir; gneiss dome; synorogenic extension; low-angle detachment

Publ.-Id: 19619

The giant Shakhdara migmatitic gneiss dome, Pamir, India–Asia collision zone, I: Geometry and kinematics

Stübner, K.; Ratschbacher, L.; Rutte, D.; Stanek, K.; Minaev, V.; Wiesinger, M.; Gloaguen, R.; Bahram, I.; Gadoev, M.; Gordon, S. M.; Hacker, B. R.; Hofmann, J.; Kanaev, E.; Oimahmadoc, I.; Rajabov, N.

Cenozoic gneiss domes comprise one third of the surface exposure of the Pamir and provide a window into the deep crustal processes of the India-Asia collision. The largest of these are the doubly vergent, composite Shakhdara-Alichur domes of the southwestern Pamir, Tajikistan, and Afghanistan; they are separated by a low-strain horst. Top-to-SSE, noncoaxial pervasive flow over the up to 4 km thick South Pamir shear zone exhumed crust from 30–40 km depth in the ~250 × 80 km Shakhdara dome; the top-to-NNE Alichur shear zone exposed upper crustal rocks in the ~125 × 25 km Alichur dome. The Gunt shear zone bounds the Shakhdara dome in the north and records alternations of normal shear and dextral transpression; it contributed little to bulk exhumation. Footwall exhumation along two low-angle, normal-sense detachments resulted in up to 90 km syn-orogenic ~N-S extension. Extension in the southwestern Pamir opposes shortening in a fold-thrust belt north of the domes and in particular in the Tajik depression, where an evaporitic décollement facilitated upper crustal shortening. Gravitational collapse of the Pamir-plateau margin drove core-complex formation in the southwestern Pamir and shortening of the weak foreland adjacent to the plateau. Overall, this geometry defines a “vertical extrusion” scenario, comprising frontal and basal underthrusting and thickening, and hanging gravitationally driven normal shear. In contrast to the Himalayan vertical extrusion scenario, erosion in the Pamir was minor, preserving most of the extruded deep crust, including the top of the South Pamir shear zone at peak elevations throughout the dome.

Keywords: Pamir; gneiss dome; synorogenic extension; low-angle detachment

Publ.-Id: 19618

Remote Sensing Analysis of Lake Dynamics in Semi-Arid Regions: Implication for Water Resource Management. Lake Manyara, East African Rift, Northern Tanzania

Deus, D.; Gloaguen, R.

We show here that a remote sensing (RS) approach is a cost-efficient and accurate method to study water resource dynamics in semi-arid areas. We use a MODIS surface reflectance dataset and a Modified Normalized Difference Water Index (MNDWI) to map the variability of Lake Manyara’s water surface area using a histogram segmentation technique. The results indicate that Lake Manyara’s water surface coverage has been decreasing from 520.25 km2 to 30.5 km2 in 2000 and 2011 respectively. We observe that the lake water surface and the lake water balance displayed a similar pattern from 2006 to 2009, probably initiated by heavy rainfall and low temperature in 2006. Lake water surface area appears to have an inverse relationship with MODIS evapotranspiration (ET) and MODIS land surface temperature (LST). We imply that recent fluctuations of Lake Manyara’s surface water area are a direct consequence of global and regional climate fluctuations. We therefore conclude that, by means of RS it is possible to provide timely and up-to-date water resource information to managers and hence enable optimized and operational decisions for sustainable management and conservation. We suggest that the method employed in this research should be applied to monitor water resource dynamics provided that remotely sensed datasets are available.

Keywords: water resource management; lake dynamics; climate variability; lake extraction; water index; remote sensing

Publ.-Id: 19617

Tectonic and Climatic Forcing on the Panj River System During the Quaternary

Fuchs, M.; Gloaguen, R.; Pohl, E.

Surface processes involve complex feedback effects between tectonic and climatic influences in the high mountains of Pamir. The ongoing India–Asia collision provokes the development of east–west-trending mountain ranges that impose structural control on flow directions of the Pamir rivers. The evolving relief is further controlled by strong moisture gradients. The decreasing precipitations from the southern and western margins of the Pamir Plateau to its center, in their turn, control the emplacement of glaciers. Chronologies of glacial records from the Pamir Plateau attest for strong climatic variability during the Quaternary. Corresponding remnants of glacial advances suggest glacial morphodynamic restricted to 4,000 m a.s.l. since marine isotope stage 4. The Panj, the trunk river of Pamir, deflects from the predominant westward drainage, connecting its main tributaries at the western margin of the drainage basin. The geometry of the river network and the pattern of incision characterize the Panj as a composite river. River reaches of indicated low incision coincide with west-trending valleys, parallel to domes and their bounding faults. Valley shape ratios reflect increased incision in north-trending sections, but do not match with changes in the catchment geometry or erodibility of rock types. Modelled riverbed profiles distinguish three Panj reaches. The upstream increase in convexity suggests successive river captures in response to local base-level changes. The northward-deflected river reaches link the local base levels, which coincide with the southern boundaries of the Shakhdara and Yazgulom Dome and Darvaz Range. We argue that tectonics plays a large role controlling the drainage system of the Panj and hence surface processes in the Pamir mountains.

Keywords: Pamir; Panj river network; Tectonic; geomorphology; Glacial chronology; Fluvial incision; River profiles

Publ.-Id: 19616

Automatic Extraction and Size Distribution of Landslides in Kurdistan Region, NE Iraq.

Othman, A. A.; Gloaguen, R.

This study aims to assess the localization and size distribution of landslides using automatic remote sensing techniques in (semi-) arid, non-vegetated, mountainous environments. The study area is located in the Kurdistan region (NE Iraq), within the Zagros orogenic belt, which is characterized by the High Folded Zone (HFZ), the Imbricated Zone and the Zagros Suture Zone (ZSZ). The available reference inventory includes 3,190 landslides mapped from sixty QuickBird scenes using manual delineation. The landslide types involve rock falls, translational slides and slumps, which occurred in different lithological units. Two hundred and ninety of these landslides lie within the ZSZ, representing a cumulated surface of 32 km2. The HFZ implicates 2,900 landslides with an overall coverage of about 26 km2. We first analyzed cumulative landslide number-size distributions using the inventory map. We then proposed a very simple and robust algorithm for automatic landslide extraction using specific band ratios selected upon the spectral signatures of bare surfaces as well as posteriori slope and the normalized difference vegetation index (NDVI) thresholds. The index is based on the contrast between landslides and their background, whereas the landslides have high reflections in the green and red bands. We applied the slope threshold map to remove low slope areas, which have high reflectance in red and green bands. The algorithm was able to detect ~96% of the recent landslides known from the reference inventory on a test site. The cumulative landslide number-size distribution of automatically extracted landslide is very similar to the one based on visual mapping. The automatic extraction is therefore adapted for the quantitative analysis of landslides and thus can contribute to the assessment of hazards in similar regions.

Keywords: brightness Indicator; landslide; automatic extraction; landslide index; remote sensing; GIS; number-size distribution; Zagros

Publ.-Id: 19615

Water Balance Modeling in a Semi-Arid Environment with Limited in situ Data Using Remote Sensing in Lake Manyara, East African Rift, Tanzania.

Deus, D.; Gloaguen, R.; Krause, P.

The purpose of this paper is to estimate the water balance in a semi-arid environment with limited in situ data using a remote sensing approach. We focus on the Lake Manyara catchment, located within the East African Rift of northern Tanzania. We use a distributed conceptual hydrological model driven by remote sensing data to study the spatial and temporal variability of water balance parameters within the catchment. Satellite gravimetry GRACE data is used to verify the trends of the inferred lake level changes. The results show that the lake undergoes high spatial and temporal variations, characteristic of a semi-arid climate with high evaporation and low rainfall. We observe that the Lake Manyara water balance and GRACE equivalent water depth show comparable trends; a decrease after 2002 followed by a sharp increase in 2006–2007. Our modeling confirms the importance of the 2006–2007 Indian Ocean Dipole fluctuation in replenishing the groundwater reservoirs of East Africa. We thus demonstrate that water balance modeling can be performed successfully using remote sensing data even in complex climatic settings. Despite the small size of Lake Manyara, GRACE data showed great potential for hydrological research on smaller un-gauged lakes and catchments in similar semi-arid environments worldwide. The water balance information can be used for further analysis of lake variations in relation to soil erosion, climate and land cover/land use change as well as different lake management and conservation scenarios.

Keywords: semi-arid; water balance; remote sensing; rainfall; evapotranspiration; runoff; GRACE

Publ.-Id: 19614

River Courses Affected by Landslides and Implications for Hazard Assessment: A High Resolution Remote Sensing Case Study in NE Iraq–W Iran

Othman, A. A.; Gloaguen, R.

The objective of this study is to understand the effect of landslides on the drainage network within the area of interest. We thus test the potential of rivers to record the intensity of landslides that affected their courses. The study area is located within the Zagros orogenic belt along the border between Iraq and Iran. We identified 280 landslides through nine QuickBird scenes using visual photo-interpretation. The total landslide area of 40.05 km2 and their distribution follows a NW–SE trend due to the tectonic control of main thrust faults. We observe a strong control of the landslides on the river course. We quantify the relationship between riverbed displacement and mass wasting occurrences using landslide sizes versus river offset and hypsometric integrals. Many valleys and river channels are curved around the toe of landslides, thus producing an offset of the stream which increases with the landslide area. The river offsets were quantified using two geomorphic indices: the river with respect to the basin midline (Fb); and the offset from the main river direction (Fd). Hypsometry and stream offset seem to be correlated. In addition; the analysis of selected river courses may give some information on the sizes of the past landslide events and therefore contribute to the hazard assessment.

Keywords: landslides; river offset; hypsometry; remote sensing; GIS; Zagros

Publ.-Id: 19613

Geothermal activities in the Main Ethiopian Rift: Hydrogeochemical characterization of geothermal waters and geothermometry applications

Pürschel, M.; Gloaguen, R.; Stadler, S.

Ethiopia holds an enormous capacity to generate geothermal energy in the volcano-tectonically active zones of the East African Rift System. In this study, we investigate the potential of three geothermal prospect areas in the Main Ethiopian Rift (Dofan-Fantale, Gergede-Sodere, Aluto-Langano). We examine existing and new data from a water sampling campaign, both of which are evaluated in terms of geochemistry and applicability for the estimation of geothermal subsurface temperatures. Several solute geothermometers, Cl–SO4–HCO3 and Na–K–Mg ternary diagrams as well as silica-enthalpy and chloride-enthalpy mixing models were applied to the prevailing alkaline and Na–HCO3 or Na–Cl–HCO3 dominated waters. Mixing was most pronounced in the individual subregions of Dofan-Fantale and Gergede-Sodere, yet these areas still indicate high heat-generating capabilities. The applied enthalpy-chloride mixing model suggests a subsurface temperature of 190 ± 20 °C for these hot springs. This temperature estimate is in good agreement with those obtained from the Na–K and Na–K–Ca geothermometers (185 ± 20 °C) for both geothermal areas. Additionally, for Gergede-Sodere it agreed well with the silica-enthalpy mixing model hot spring water results with the assumption that steam loss occurs before mixing (170 ± 20 °C). Furthermore, the enthalpy-chloride mixing model refers to reservoir temperatures between 300 °C and 370 °C for the Aluto-Langano geothermal fluids, which are in the same magnitude than the ones obtained by the silica-enthalpy mixing model for hot springs, if no steam loss occurs before mixing (270 ± 30 °C). In addition, they are comparable with few known data collected in drilled wells in the Aluto-Langano geothermal field (231–282 °C for LA-4 and LA-8 as well as 315–363 °C for LA-3 and LA-6).

Keywords: Subsurface temperatures; Groundwater; Thermal waters; Geothermometry; Geothermal energy; Ethiopia

Publ.-Id: 19612

Environmental change detection in the central part of Iraq using remote sensing data and GIS

Othman, A. A.; Al-Saady, Y. I.; Al-Khafaji, A. K.; Gloaguen, R.

This study aims to assess the potential of sev-eral ancillary input data for the improvement of unsuper-vised land cover change detection in arid environments. The study area is located in Central Iraq where deserti-fication has been observed. We develop a new scheme based on known robust indices. We employ Landsat (multispectral scanner, thematic mapper, and enhanced thematic mapper) satellite data acquired in 1976, 1990, and 2002. We use the Normalized Deferential Vegetation Index, Normalized Differential Water Index (NDWI), Salinity Index (SI), and Eolian Mapping Index. Two new equations were applied for the SI and the NDWI indices. Validation was performed using ground truth data collected in 16 days. We show that such an ap-proach allows a robust and low-cost alternative for pre-liminary and large-scale assessments. This study shows that desertification has increased in the study area since 1990.

Keywords: Remote sensing; changes detection; NDVI; NDWI; SI; EMI; MSS; TM; ETM; Land cover; Iraq

Publ.-Id: 19611

Influence of rigid coregistration of PET and CT data on metabolic volumetry: a user's perspective

Steffen, I. G.; Hofheinz, F.; Rogasch, J. M. M.; Furth, C.; Amthauer, H.; Ruf, J.

While non-rigid fusion is by definition expected to alter the information of positron emission tomography (PET) data, we assessed whether rigid transformation also influences metabolic tumor volume (MTV) determination.

The PET/computed tomography (CT) data of 28 solid pulmonary lesions of 20 tumor patients examined with 18 F-Fluordeoxyglucose (FDG) was retrospectively analyzed. The original (OR) hardware-coregistered PET images were fused with contrast-enhanced diagnostic CT (CT1, 1 mm slices) and low dose CT (CT5, 5 mm slices). After automatic rigid transformation (Mirada Fusion7D) using two algorithms (rigid fast (RF), rigid slow (RS)), MTV and maximal standardized uptake value (SUVmax) were determined applying four different segmentation methods with either fixed or background-adapted thresholding and compared to OR-PET data.

Relative differences in SUVmax compared to OR data revealed no significant differences for RF (median, -0.1%; interquartile range (IQR), -1.1% to 0.9%; p = 0.75) and RS (median, 0.5%; IQR, -0.6% to 1.3%; p = 0.19) in CT1, whereas in CT5 significant deviations were observed for RF (median, -9.0%; IQR, -10.9 to -6.1; p < 0.001) and RS (median, -8.4%; IQR, -11.1 to -5.6; p < 0.001). Relative MTV differences were 0.7% (IQR, -3.0% to 2.7%; p = 0.76) for RF and -1.3% (IQR, -3.6% to 0.9%; p = 0.12) for RS in CT1. Coregistration led to significant MTV differences in RF (median, 10.4%; IQR, 7.4% to 16.7%; p < 0.001) and RS (median, 10.6%; IQR, 5.4% to 17.7%; p < 0.001) in CT5.

Rigid coregistration of PET data allows a quantitative evaluation with reasonable accuracy in most cases. However, in some cases, it can result in substantial deviations of MTV and SUVmax. Therefore, it is recommended to perform quantitative evaluation in the original PET data rather than in coregistered PET data.

Publ.-Id: 19610

Evaluating SAR polarization modes at L-band for forest classification purposes in Eastern Amazon, Brazil

Liesenberg, V.; Gloaguen, R.

Single, interferometric dual, and quad-polarization mode data were evaluated for the characterization and classification of seven land use classes in an area with shifting cultivation practices located in the Eastern Amazon (Brazil). The Advanced Land-Observing Satellite (ALOS) Phased Array L-band Synthetic Aperture Radar (PALSAR) data were acquired during a six month interval. A clear-sky Landsat-5/TM image acquired at the same period was used as additional ground reference and as ancillary input data in the classification scheme. We evaluated backscattering intensity, polarimetric features, interferometric coherence and texture parameters for classification purposes using support vector machines (SVM) and feature selection. Results showed that the forest classes were characterized by low temporal backscatter-ing intensity variability, low coherence and high entropy. Quad polarization mode performed better than dual and single polarizations but overall accuracies remain low and were affected by precipitation events on the date and prior SAR date acquisition. Misclassifications were reduced by integrating Landsat data and an overall accuracy of 85% was attained. The integration of Landsat to both quad and dual polarization modes showed similarity at the 5% significance level. SVM was not affected by SAR dimensionality and feature selection technique reveals that co-polarized channels as well as SAR derived parameters such as Alpha-Entropy decomposition were important ranked features after Landsat' near-infrared and green bands. We show that in absence of Landsat data, polarimetric features extracted from quad-polarization L-band increase classification accuracies when compared to single and dual polarization alone. We argue that the joint analysis of SAR and their derived parameters with optical data performs even better and thus encourage the further development of joint techniques under the Reducing Emissions from Deforestation and Degradation (REDD) mechanism.

Keywords: Polarization modes; secondary forest; successional forest; ALOS/PALSAR; SVM; Eastern Amazon

Publ.-Id: 19609

Beneficiation potential of low-grade iron ore from the Manganore Iron Formation through gravity concentration

Beyeme-Zogo, J. C.; Beukes, N. J.; Gutzmer, J.

About 84% of the high-grade iron ore produced in South Africa is hosted by the Manganore Iron Formation of the Ghaap Group of the Asbestos Hills Subgroup, Transvaal Supergroup. The Manganore Iron Formation (MIF) is slumped into sinkhole structures of the Campbellrand Subgroup and occurs exclusively on the Maremane Dome, an arcuate structure located between Postmasburg in the south and Sishen/Kathu in the north, in the Northern Cape Province of South Africa. In the absence of major discoveries of new high-grade iron ore deposits around the world, mining companies have to turn to materials that were once classified as waste. This study was initiated to assess the beneficiation potential of banded MIF and brecciated MIF, two texturally distinct types of partly ferruginized iron formation that occur along the contact of the MIF with the immediately underlying Wolhaarkop Breccia and the Campbellrand Subgroup. The stratigraphic thickness of the partly ferruginized materials in drill core varied between from 23.2 m to 101.9 m. Both material types were sampled in drill cores, and Hand specimen samples were also collected from dump stockpiles and open pits at the Beeshoek and Khumani mines.
Partly ferruginized banded MIF consists of alternating bands of haematite and microbanded chert varying in thickness from the millimetre to the centimetre scale, with specularite filling fissures and pore spaces. The brecciated and partly ferruginized MIF comprises angular fragments of chert, quartz, iron formation, jasper, and high-grade haematite ore with or without matrix. Light microscopy and X-ray diffraction studies revealed that haematite is the principal ore mineral and quartz (chert) the main gangue mineral. Iron- and silica-rich bands were separated using a diamond saw for density measurements and for major element geochemistry by X-ray fluorescence spectrometry. The bulk density varies between 2.7 and 5.2 , and correlates well with the iron concentration, which range from 13.5 to 69.4 wt.% Fe. Bulk samples of both raw material types were crushed using a jaw crusher, then sieved in different size ranges and a particle size range (-5.6+1.4 mm) was selected for gravity concentration. This crushed material was found to contain 35.9 wt% Fe (brecciated MIF) and 33.7 wt% Fe (banded MIF). The beneficiation potential of the Manganore low-grade raw material type was assessed using a mineral density separator. The Mintek fixed trailer jig was used with input parameters of 200 kpa pressure. Separation success was monitored by determining the iron concentration of different beds using X-ray fluorescence spectrometry (XRF). The best separation was observed for brecciated MIF, which yielded a gravity concentrate containing 60.7 wt.% Fe (1.69 enrichment ratio), while processing of banded MIF yielded gravity concentrates of up to 52.2 wt.% Fe (1.72 enrichment ratio). The results d e m o n s t r a t e clearly that partly ferruginized MIF holds potential to be processed into a high-grade iron ore concentrate. However, the texture of the low-grade iron formation impacts significantly on separation success.

Keywords: Manganore Iron Formation; Gravity Concentration; Beneficiation Potential; Iron Ore

  • Contribution to proceedings
    SAIMM Physical Beneficiation Conference, 19.-21.11.2013, Misty Hills, South Africa
    Physical Beneficiation 2013, Johannesburg: SAIMM, 1 919783 50 4, 1-28

Publ.-Id: 19608

Lithium-Erkundung in Zinnwald, Osterzgebirge

Neßler, J.; Seifert, T.; Gutzmer, J.; Müller, A.; Stute, S.; Henker, J.; Kühn, K.

Nach einem beinahe 70-jährigen Stillstand der bergmännischen Tätigkeiten im Revier der Li-Sn-W-Lagerstätte Zinnwald im Osterzgebirge gehen die Erkundungsbemühungen in die nächste Runde. Die Freiberger Firma SolarWorld Solicium GmbH, einhundertprozentige Tochter der SolarWorld AG, erkundet seit der Erteilung der Aufsuchungsgenehmigung durch das Sächsische Oberbergamt im Februar 2011 gemeinsam mit der TU Bergakademie Freiberg und der GEOS Ingenieurgesellschaft mbH Mitteleuropas größtes bekanntes Li-Vorkommen.

Keywords: exploration; Saxony; resource technology

  • Acamonta 20(2013), 33-35

Publ.-Id: 19607

"Erzminerale sehen heißt verstehen" - automatisierte Mineralogie und ihre Anwendung

Schulz, B.; Gutzmer, J.

Die von der Industrie benötigten Rohstoffe, insbesondere Metalle und Halbmetalle liegen in der Natur nur selten in einer elementaren und unmittelbar nutzbaren Form vor. Metalle wie beispielsweise Kupfer (Cu), Chrom (Cr) und Platin (Pt) finden sich vielmehr in vielfältigen molekularen Verbindungen mit Schwefel (S), Sauerstoff (O) und vielen weiteren Elementen in Erzmineralen wie Chalkopyrit (CuFeS2), Chromit ((Mg,Fe)Cr2O4) oder Braggit ((Pt,Pd,Ni)S. Diese Wertminerale treten wiederum oftmals in nur geringen Anteilen in den dazugehörigen Erzen.

Keywords: automated mineralogy; geometallurgy; mineral liberation analysis; resource technology

  • Acamonta 20(2013), 30-33

Publ.-Id: 19606

Heimische Geopotenziale II - E3 - Rohstofferkundung im Erzgebirge mittels Geophysik

Osbahr, I.; Buske, S.; Spitzer, K.; Eiermann, M.; Siemon, B.; Meyer, U.; Gutzmer, J.; Gloaguen, R.; Stein, S.; Lehmann, U.

Im Januar dieses Jahres hat das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) in Kooperation mit der Technischen Universität Bergakademie Freiberg, der Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), sowie dem Landesamt für Umwelt, Landwirtschaft und Geologie (LfULG) einen Antrag auf eine wissenschaftliche Aufsuchungsgenehmigung für ein Gebiet im Raum Geyer im Erzgebirgskreis beantragt. Das damit einhergehende Forschungsprojekt hat das Ziel, mittels geophysikalischer Verfahren das Rohstoffpotenzial des geologischen Untergrundes bis in eine Tiefe von ca. 500 m zu erfassen. Alle relevanten Daten, die im Rahmen dieser Aufsuchung erhoben werden, sollen genutzt werden, um ein 3D-Modell des geologischen Untergrunds im Aufsuchungsgebiet zu erstellen. Sowohl dieses Modell als auch die ihm zugrundeliegenden Daten sollen mit Abschluss des auf drei Jahre ausgelegten Projekts veröffentlicht werden.

Keywords: geophysics; exploration; Saxony; resource technology

  • Acamonta 20(2013), 28-30

Publ.-Id: 19605

Heimische Geopotenziale I - Wertstoffe aus Bergbauhalden

Osbahr, I.; Buettner, P.; Gutzmer, J.; Bertau, M.; Fritze, M.; Heide, G.; Janneck, E.; Kleeberg, R.; Leißner, T.; Luhmer, R.

Im Erzgebirge wurde über Jahrhunderte hinweg Erzbergbau betrieben. Abhängig vom Stand der Technik wurden nicht auszubringende oder nicht verwertbare Bestandteile des geförderten Gesteins aufgehaldet. Daher existieren als Hinterlassenschaft des Erzbergbaus des vorigen Jahrhunderts auch heutzutage noch etliche große Bergehalden, Spülhalden und Waschsandhalden aus der Aufbereitung sowie Schlacke- und Flugstaubablagerungen aus der Verhüttung. Diese Halden enthalten noch für die damalige Aufbereitung zu fein verwachsenes Material bzw. Restkonzentrationen der abgebauten Erzmetalle – z. B. Zinn, Zink, Silber oder Wolfram – und Begleitelemente, wie Lithium oder Indium. Einige der Metalle, die bei der historischen Gewinnung wirtschaftlich von wenig Interesse waren, sind heute von wirtschaftsstrategischer Relevanz.

Keywords: resource technology; resource efficiency; mine tailings; Saxony

  • Acamonta 20(2013), 25-27

Publ.-Id: 19604

Printing Nearly-Discrete Magnetic Patterns Using Chemical Disorder Induced Ferromagnetism

Bali, R.; Wintz, S.; Meutzner, F.; Hübner, R.; Boucher, R.; Ünal, A. A.; Valencia, S.; Neudert, A.; Potzger, K.; Bauch, J.; Kronast, F.; Facsko, S.; Lindner, J.; Fassbender, J.

Ferromagnetism in certain alloys consisting of magnetic and non-magnetic species can be activated by the presence of chemical disorder. This phenomenon is linked to an increase in the number of nearest-neighbour magnetic atoms and local variations in the electronic band structure due to the existence of disorder sites. An approach to induce disorder is through exposure of the chemically ordered alloy to energetic ions; collision cascades formed by the ions knock atoms from their ordered sites and the concomitant vacancies are filled randomly via thermal diffusion of atoms at room temperature. The ordered structure thereby undergoes a transition into a metastable solid solution. Here we demonstrate the patterning of highly resolved magnetic structures by taking advantage of the large increase in the saturation magnetization of Fe60Al40 alloy triggered by subtle atomic displacements. The sigmoidal characteristic and sensitive dependence of the induced magnetization on the atomic displacements manifests a sub-50 nm patterning resolution. Patterning of magnetic regions in the form of stripes separated by ~ 40 nm wide spacers was performed, wherein the magnet/spacer/magnet structure exhibits re-programmable parallel (↑/spacer/↑) and antiparallel (↑/spacer/↓) magnetization configurations in zero field. Materials in which the magnetic behavior can be tuned via ion-induced phase transitions may allow the fabrication of novel spin-transport and memory devices using existing lateral patterning tools.

Keywords: phase-transitions; chemical disorder; magnetic patterning; magnetic nanostructures; memory devices

Publ.-Id: 19603

Preclinical PET/MRI – First time use and validation of a potential tool for image based dosimetry

Kranz, M.; Sattler, B.; Patt, M.; Donat, C. K.; Deuther-Conrad, W.; Hiller, A.; Smits, R.; Hoepping, A.; Sabri, O.; Brust, P.

Objectives :
PET image based preclinical dosimetry (ibPD) allows the dose assessment for new radiotracers. However, most of the small animal systems are combined with CT. The low soft tissue contrast results in poor organ delineation. Therefore, we like to evaluate a new preclinical PET/MRI system by comparing a recent ibPD in female mice (M) with a post mortem biodistribution (PMB) and previous PET/CT based studies in piglets (P) and humans (H), after i.v. injection of [18F]flubatine.

Methods :
Whole body ibPD was performed in 3 M (11 w, 27.8 g), 3 P (7 w, 14.0 kg) and 3 H (59.6 y, 74.3 kg). The anesthetized animals and the H were PET-imaged (M: MEDISO nanoScan PET/MRI; P, H: SIEMENS Biograph16 PET/CT) up to 7h post i.v. injection of 13.1 MBq, 183.5. MBq, 353.7 MBq [18F]flubatine, followed by iterative reconstruction including MR- and CT-based attenuation correction respectively. Exponential curves were fitted to the time-activity-data (%ID/organ). In M and P, time and mass were adapted to the human scale. The activity data from the PMB study was obtained by organ counting of 27 M (11 w, 28.2 g) in a γ-counter. The ODs were calculated with OLINDA and the ED using tissue weighting factors (ICRP103).

Based on preclinical PET/MRI, the highest OD (μSv/MBq) was in kidneys (47.5) and urinary bladder (33.4). The highest contribution to the ED (μSv/MBq) was by stomach (1.8) and lungs (1.7), resulting in an ED of 12.1 which is almost identical with the results of the PMB (12.5). The ED based on the PET/CT data is 14.3 (P) and 22.6 in H.

Conclusions :
It was proven, exemplary for [18F]flubatine, that ibPD studies with a preclinical PET/MRI in mice for dose assessment to humans are possible, taking into account an underestimation of the ED of about 40% as shown by earlier studies[1]. The investigation of further radiotracers is required to confirm the reliability of this study.

[1] B. Sattler, M. Kranz, M. Patt et al. Incorporation dosimetry of F-18-Flubatine - Comparison of animal model data with first-in-man results. Journal of Nuclear Medicine 2012; 53(suppl): 1503.

  • Poster
    SNMMI 2014 Annual Meeting, 07.-11.06.2014, St. Louis, Missouri, USA
  • Abstract in refereed journal
    Journal of Nuclear Medicine 55(2014)1, 1140

Publ.-Id: 19602

Triaryl-olefine based nitric oxide-releasing selective cyclooxygenase-2 inhibitors as potential radiosensitizers

Bechmann, N.; Sehn, F.; Tondera, C.; Mosch, B.; Kniess, T.; Pietzsch, J.

kein Abstract verfügbar

  • Poster
    40th Annual Meeting of the Europoean Radiation Research Society, 01.-05.09.2013, Dublin, Ireland
  • Contribution to proceedings
    40th Annual Meeting of the European Radiation Research Society, 01.-05.09.2013, Dublin, Ireland
    Congress Program and Abstracts, Dublin: ERR conference partner

Publ.-Id: 19601

Near-room-temperature photon-noise-limited quantum well infrared photodetector

Hao, M. R.; Yang, Y.; Zhang, S.; Shen, W. Z.; Schneider, H.; Liu, H. C.

With the modern development of infrared laser sources such as broadly tunable quantum cascade lasers and frequency combs, applications of infrared laser spectroscopy are expected to become widespread. Consequently, convenient infrared detectors are needed, having properties such as fast response, high efficiency, and room-temperature operation. This work investigated conditions to achieve near-room-temperature photon-noise-limited performance of quantum well infrared photodetectors (QWIPs), in particular the laser power requirement. Both model simulation and experimental verification were carried out. At 300 K, it is shown that the ideal performance can be reached for typical QWIP designs up to a detection wavelength of 10 μm. At 250 K, which is easily reachable with a thermoelectric Peltier cooler, the ideal performance can be reached up to 12 μm. QWIPs are therefore suitable for detection and sensing applications with devices operating up to or near room temperature.

Keywords: Quantum well infrared photodetector; QWIP; background limited performance; detectivity; signal-to-noise ratio

Publ.-Id: 19600

Strong Quadrupole-Strain Interaction of Vacancy Orbital in Boron-Doped Czochralski Silicon

Okabe, K.; Akatsu, M.; Baba, S.; Mitsumoto, K.; Nemoto, Y.; Yamada-Kaneta, H.; Goto, T.; Saito, H.; Kashima, K.; Saito, Y.

We have carried out ultrasonic measurements of a boron-doped silicon ingot grown by the Czochralski method in order to determine the quadrupole-strain interaction constant of a vacancy orbital. The low-temperature softening of the elastic constant C44 shows a remarkable variation depending on positions of the ingot, which reflects the distribution of vacancy concentration N in the ingot. An infrared laser scattering tomograph was employed to measure the density and size of voids in the silicon wafers by determining the vacancy concentration Ncons consumed in void formation. Using a combination of laser scattering tomography and low-temperature softening, we have found a sum rule in which the initially created vacancy concentration Ntotal corresponds to the sum of the residual vacancy concentration N and the consumed vacancy concentration Ncons as Ntotal = N + Ncons. Taking account of the sum rule, we deduce the interaction constant gΓ5 = (2.8±0.2)×105 K for the quadrupole-strain interaction HQS = -gΓ5Ozxεzx of the vacancy orbital. The huge deformation energy of 1.6×105 K per vacancy with the Γ8 ground state for unit strain εzx = 1 verified the strong electron–lattice interaction of the vacancy orbital. Employing the one-to-one correspondence between the softening of ΔC44/C44 = 1.0×10-4 down to 30 mK and the vacancy concentration of N = 1.5 ×1013 cm-3, we can determine the vacancy concentration by low-temperature ultrasonic measurements. The present work surely puts forward a novel semiconductor technology based on low-temperature ultrasonic measurements for evaluating vacancy concentration in silicon wafers.

Keywords: vacancy; boron-doped silicon wafer; ultrasound; quadrupole; softening

Publ.-Id: 19599

Chemical reactions between poly(carbonate) and poly(vinyl amine) thermally induced by a high magnetic field pulse

Zimmerer, C.; Heinrich, G.; Wolff-Fabris, F.; Koch, E.; Steiner, G.

A high magnetic field pulse with a magnetic flux density of Bmax = 60.5 T was used to induce chemical reactions between poly(carbonate) (PC) and poly(vinyl amine) (PVAm). PC and PVAm were prepared as a thin film composite onto calcium fluoride substrate. A silver ring structure of 30 am thickness and a mean diameter of 4.5 mm was embedded in the PC/PVAm interface. The applied magnetic pulse induced an Eddy current in the silver ring which results in a temperature of approx. 90 degrees C. Chemical reactions between PC and PVAm were investigated by Fourier transform infrared spectroscopic imaging and principal component data analysis. The spectroscopic results point to a formation of urethane bonds and degraded PC chains with phenolic end groups in the vicinity of the silver ring structure. The results are in accordance with differential scanning calorimetric experiments and demonstrate a thermally induced chemical reaction between PC and PVAm.

Publ.-Id: 19598

ESR of coupled spin-1/2 chains in copper pyrazine dinitrate: unveiling geometrical frustration

Validov, A. A.; Ozerov, M.; Wosnitza, J.; Zvyagin, S. A.; Turnbull, M. M.; Landee, C. P.; Teitel’Baum, G. B.

The spin dynamics of copper pyrazine dinitrate (Cu(C4H4N2)(NO3)2), a model spin-1/2 Heisenberg antiferromagnetic (AF) chain system, was investigated by means of electron spin resonance (ESR). Using the high-field ESR we evidenced the inequivalence of Cu sites belonging to adjacent spin chains in the ac planes of this compound. It was revealed that the dominating interchain interaction is of zig-zag-type. This interaction gives rise to geometrical frustration strongly affecting the character of AF ordering. Combining our experimental findings with the results of a quasiclassical approach we predict that at low temperatures the system orders in an incommensurate spiral state.

Publ.-Id: 19597

Magnetization, magnetic susceptibility and ESR in Tb3Ga5O12

Löw, U.; Zvyagin, S.; Ozerov, M.; Schaufuss, U.; Kataev, V.; Wolf, B.; Lüthi, B.

We report on the measurement of the magnetic susceptibility and of ESR transitions in the garnet substance Tb3Ga5O12 (TGG). The results are compared with a calculation in the framework of crystal field theory for the orthorhombic surroundings of the six inequivalent Tb ions of TGG. We also present a calculation of the magnetization for the three main crystal directions.

Publ.-Id: 19596

The "quiet" Goldschmidt reaction 2Al + α-Fe2O3 → 2Fe + α-Al2O3

Stӧßer, R.; Feist, M.; Willgeroth, C.; Emmerling, F.; Menzel, M.; Reuther, H.

The well-known Goldschmidt reaction, i.e. the reaction of (2 Al + α-Fe2O3), was investigated upon mechanochemical activation by employing Mössbauer and ESR spectroscopy in combination with thermal analysis (TA), magnetic susceptibility measurements and X-ray powder diffraction (XRD).

  • Poster
    International Conference on the Applications of the Mossbauer Effect - 2013, 01.-06.09.2013, Opatija, Kroatien

Publ.-Id: 19595

Thin layer analysis with electrons - AES, XPS, Mössbauer spectroscopy

Reuther, H.

Thin surface layers on a solid may refine properties like corrosion, friction or wear of the whole workpiece. There are a lot of methods for modification and the analysis of such layers is often based on different kinds of electron spectroscopy.

  • Invited lecture (Conferences)
    XXXIV Brazilian Congress of Vacuum Applications in Industry and Science, 21.-25.10.2013, Ilheus, Brasilien

Publ.-Id: 19594

Evidence of formation of the tridymite form of AlPO4 in some municipal sewage sludge ashes

Peplinski, B.; Adam, C.; Adamczyk, B.; Muller, R.; Schadrack, R.; Michaelis, M.; Emmerling, F.; Reuther, H.; Menzel, M.

Evidence is provided that the tridymite component observed in the X-ray diffraction patterns of some sewage sludge ashes (SSAs) should not be interpreted as the tridymite modification of SiO2 but as the tridymite form of AlPO4. This proof is based on a combined X-ray Powder Diffraction (XRD), X-ray fluorescence (XRF) and Mossbauer spectroscopy investigation of two SSAs produced at two fluidized bed incineration facilities, located in different municipalities and operated differently. The structural and chemical characterization was carried out on the 'as received' SSA samples as well as on the residues of these two SSAs pretreated by leaching in citric acid. In addition, direct proof is presented that the tridymite form of AlPO4 does crystallize from X-ray amorphous precursors under conditions that mimic the huge heating rate and short retention time (just seconds at T approximate to 850 °) typical for fluidized bed incinerators.

  • Powder Diffraction 28(2013), S425-S435
    DOI: 10.1017/S0885715613000869
  • Lecture (Conference)
    13. European Powder Diffraction Conference, 28.-31.10.2013, Grenoble, Frankreich

Publ.-Id: 19593

Comparison of CFD simulations on two-phase Pressurized Thermal Shock scenarios

Apanasevich, P.; Coste, P.; Ničeno, B.; Heib, C.; Lucas, D.

Small Break Loss of Coolant Accident (SB LOCA) is one of the most severe transients which may lead to pressurized thermal shock (PTS) on the reactor pressure vessel (RPV) wall. During postulated SB LOCA emergency core cooling (ECC) water is injected into the cold leg, where it mixes with the hot coolant. The mixture of cold and hot coolants flows towards the downcomer. Knowledge of transient temperature distribution in the downcomer is necessary to predict thermal gradients in the structural components of the RPV wall. For the prediction of the temperature fields and heat transfer coefficient between the fluid and wall in the cold leg and the downcomer, reliable computational fluid dynamics (CFD) simulations are needed. To validate CFD models for two-phase PTS scenarios numerical simulations of the TOPFLOW-PTS experiments were performed in the framework of the EU NURISP (NUclear Reactor Integrated Simulation Project) project. The paper presents the post CFD simulations of a steady-state TOPFLOW-PTS air/water experiment and the pre-test blind simulations of a steady-state TOPFLOW-PTS steam/water case with condensation. CFD simulations were performed with ANSYS FLUENT, ANSYS CFX and NEPTUNE_CFD. The simulations of the air/water test have shown that correct modeling of the ECC jet behavior is essential for the temperature prediction in the cold leg. For modeling these two-phase flows with rather smooth large free surfaces, Reynolds Averaged Navier-Stokes approach seems to be appropriate. The pre-test simulations of steam/water flow predicted a thermal stratification at the entrance of the downcomer. Finally, the simulations of the TOPFLOW-PTS experiments have depicted considerable differences between the codes and the models.

Keywords: Computational fluid dynamics (CFD); Stratified two-phase flow; Pressurized thermal shock (PTS); Direct contact condensation (DCC); TOPFLOW-PTS experiments

Publ.-Id: 19592

Depositional environment and lithostratigraphy of the Paleoproterozoic Mooidraai Formation, Kalahari Manganese Field, South Africa

Kunzmann, M.; Gutzmer, J.; Beukes, N. J.; Halverson, G. P.

The Paleoproterozoic Mooidraai Formation is an up to 220 m-thick succession of marine carbonate rocks that caps the Fe- and Mn-bearing Hotazel Formation in the Kalahari Manganese Field, South Africa. Although it occupies an important stratigraphic position within the upper Transvaal Supergroup, which records major perturbations of the early Paleoproterozoic biosphere, a detailed sedimentological study on the Mooidraai Formation has never been conducted. Here we present a detailed facies analysis that distinguishes eight carbonate and two iron formation lithofacies types. The lower Mooidraai Formation is dominated by carbonate rhythmites and slope breccias deposited on a foreslope, occasionally interbedded with oxide or carbonate facies iron formation. The upper part of the formation reflects various shelf and peritidal environments arranged in shallowing-upward parasequences. Clastic-textured massive dolarenites deposited in shelf and lagoonal environments typically form the base of parasequences and are overlain by subtidal thrombolites, lagoonal to intertidal microbialaminites, and upper intertidal to supratidal smoothly laminated stromatolites. Supratidal intraclast breccias cap shallowing-upward parasequences. Strong base level rise in the lower Mooidraai Formation reflects a transgressive systems tract tied to rapid early subsidence. Together with considerable lateral thickness variation in the following regressive systems tract, this suggests deposition in a basin with significant seafloor relief.

Keywords: no keywords required

Publ.-Id: 19591

Experimental study of the 14N(p,γ)15O reaction for solar fusion at 0.5-1.5 MeV

Wagner, L.; Bemmerer, D.; Anders, M.; Elekes, Z.; Junghans, A.; Marta, M.; Reinhardt, T.; Reinicke, S.; Schmidt, K.; Röder, M.; Schwengner, R.; Wagner, A.; Zuber, K.; Takács, M.; Szücs, T.

Die 14N(p,γ)15O-Reaktion bestimmt als langsamste Kernreaktion die Rate des Bethe-Weizsäcker-Zyklus. Für eine präzise Extrapolation des Wirkungsquerschnitts zu niedrigen Energien ist die genaue Kenntnis der Anregungsfunktion über einen weiten Energiebereich notwendig. Am 3 MV Tandetron des Helmholtz-Zentrums Dresden-Rossendorf wurde der nichtresonante Wirkungsquerschnitt der 14N(p,γ)15O-Reaktion im Bereich von 0,5-1,5 MeV Strahlenergie neu untersucht. In dem Vortrag werden vorbereitende Simulationen, die experimentellen Daten und die resultierenden S Faktoren präsentiert.

Keywords: Nuclear Astrophysics; solar fusion; CNO cycle; 3MV Tandetron; non resonant cross sections; 14N(p; γ)15O

  • Lecture (Conference)
    NAVI annual meeting, 16.-17.12.2013, Darmstadt, Deutschland

Publ.-Id: 19590

Durchführung von Sorptions- und Desorptionsversuchen von Uran(VI) an Montmorillonit

Zehlike, L.

In dieser Arbeit wurde die Sorption und Desorption von U(VI) an dem Tonmineral Montmorillonit untersucht. Dies geschah zum einen in Abhängigkeit vom pH-Wert, welcher im Bereich 5 - 7 lag und zum anderen in Abhängigkeit von der Ionenstärke. Als Hintergrundelektrolyten wurden NaCl und CaCl2 verwendet.
Die Ergebnisse zeigen, dass das Sorptionsmaximum in beiden Systemen bei ca. pH 6 liegt, obwohl im NaCl-System bei der Ionenstärke 3,0 mol/kg eine Verschiebung des Sorptionsmaximums zu pH-Wert 7 auftritt. Bei pH 7 nimmt die Sorption im CaCl2-System auf Grund des stabilen Ca2UO2(CO3)3(aq)-Komplexes stark ab, im NaCl-System bleibt sie dagegen annähernd konstant. Außerdem ist im CaCl2-System bei pH 6 und 7 eine Ionenstärkeabhängigkeit zu beobachten, welche im NaCl-System nicht gegeben ist. Des Weiteren scheinen verschiedene Ausfällungen wie z. B. Silikatniederschläge im CaCl2-System eine wichtige Rolle zu spielen.
Die Desorptionsuntersuchungen zeigten, dass die Desorption dieselbe pH-Abhängigkeit wie die sorption aufweist. Bei pH 5 konnte bei beiden Systemen die stärkste Desorption festgestellt werden, bei pH 6 die geringste. Die Desorptionsvorgänge laufen überwiegend reversiebl ab, was darauf schließen lassen könte, dass die Komplexierungsmechanismen vorrangig an den schwachen Bindungsstellen des Montmorillonit auftreten. Im CaCl2-System sind jedoch große Unterschiede in den logKd-Werten zwischen Sorption und Desorption zu verzeichnen, was mit den schon genannten Ausfällungen in Verbindung gebracht werden kann. Im NaCl-System scheint der Desorptionsvorgang abhängig von der Ionenstärke reversibel oder irreversibel zu verlaufen.
Von den getätigten Untersuchungen ausgehend, ist der Montmorillonit besonders für ein Endlagersystem mit pH-Werten im Bereich 6-7 geeignet, wobei sich allerdings hohe Calciumkonzentration in Gegenwart von Carbonat-Ionen nachteilig auf das sorptionsverhalten auswirken. Hohe NaCl-Konzentrationen haben keinen erheblichen negativen Einfluss auf die Sorptions- und Deosprtionsfähigkeit des Montmorillonits.

Keywords: nuclear waste repositories; uranium sorption; argillaceous rock; clay; uranium; montmorillonite; high ionic strength; desorption

  • Bachelor thesis
    TU Dresden, 2013
    0048 Seiten

Publ.-Id: 19588

Hyperdoping semiconductors by ion implantation

Zhou, S.

Ion implantation followed by annealing is a well-established method to dope Si and has been maturely integrated with the IC industry production line. Nowadays, the demands for functional materials require a supersaturated doping of semiconductors, i.e., the dopant concentration should be in the percent range. For instance for spintronic applications one needs to prepare magnetic semiconductors which are doped with up to 5-10% Mn [1]. For multiband solar cells one needs to dope semiconductors with deep levels at a concentration large enough to form impurity bands in the bandgap of the semiconductor host material [2]. In this talk, I will make an overview of the activities in my group utilizing ion implantation and short time annealing. These activities include synthesizing full spectrum of III-V:Mn diluted magnetic semiconductors [3-5], optical property modification of GaAs [6-7] and metal-insulator transition in Se/S doped Si.

1. T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000).
2. A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).
3. D. Bürger, S. Zhou, et al., Application of pulsed laser annealing to ferromagnetic GaMnAs, Phys. Rev. B 81, 115202 (2010).
4. S. Zhou, et al., The importance of hole concentration in establishing carrier-mediated ferromagnetism in Mn doped Ge, Appl. Phys. Lett. 96, 202105 (2010).
5. S. Zhou, et al. Ferromagnetic InMnAs on InAs Prepared by Ion Implantation and Pulsed Laser Annealing, Appl. Phys. Express 5, 093007 (2012)
6. S. Prucnal, …, S. Zhou, Temperature stable 1.3 μm emission from GaAs, Optics Express, 20, 26075-26081 (2012).
7. K. Gao, …, S. Zhou, Origin and enhancement of the 1.3 μm luminescence from GaAs treated by ion-implantation and flash lamp annealing, J. Appl. Phys. 114, 093511 (2013).

  • Lecture (others)
    Invited seminar at Southeast University and Nanjing University, Nanjing, China, 07.-08.10.2013, Nanjing, China

Publ.-Id: 19587

Ion beam synthesis of ferromagnetic semiconductors

Zhou, S.

Ferromagnetic semiconductors are under intensive investigation in last decade. Until now, III-Mn-V based compound semiconductors are the only well accepted family. The prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. To prepare ferromagnetic semiconductors, one needs to dope the host with up to 5-10% Mn, which is far beyond the solid solubility of Mn in III-V compounds. As a non-equilibrium process, ion implantation can introduce enough dopants as required. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. The mature development and commercialization of ion implantation promise the versatility. The approach combining ion implantation and pulsed laser melting allows us to prepare ferromagnetic semiconductors covering the full spectrum of III-V compound semiconductors. We have successfully synthesized ferromagnetic Mn doped III-V from InAs to GaP with different bandgaps. The results of magnetization, magnetic anisotropy, resistivity, anomalous Hall effect, magnetoresistance and x-ray magnetic circular dichroism obtained from the synthesized samples confirm the intrinsic origin and the carrier-mediated nature of the ferromagnetism. These results could allow a panorama-like understanding of III-V:Mn based ferromagnetic semiconductors.

  • Invited lecture (Conferences)
    7th Symposium on Vacuum based Science and Technology, 19.-21.11.2013, Kołobrzeg, Poland

Publ.-Id: 19586

Structural and magnetic properties of irradiated SiC

Wang, Y.; Chen, X.; Li, L.; Shalimov, A.; Tong, W.; Prucnal, S.; Munnik, F.; Yang, Z.; Skorupa, W.; Helm, M.; Zhou, S.

We present a comprehensive structural characterization of ferromagnetic SiC single crystals induced by Ne ion irradiation. The ferromagnetism has been confirmed by electron spin resonance and possible transition metal impurities can be excluded to be the origin of the observed ferromagnetism. Using X-ray diffraction and Rutherford backscattering/channeling spectroscopy, we estimate the damage to the crystallinity of SiC which mutually influences the ferromagnetism in SiC.

  • Journal of Applied Physics 115(2014), 17C104
    DOI: 10.1063/1.4860659
  • Lecture (Conference)
    The 58th Annual Magnetism and Magnetic Materials (MMM) Conference, 04.-08.11.2013, Denver, USA

Publ.-Id: 19585

Defect-induced ferromagnetism in semiconductors: a controllable approach by particle irradiation

Zhou, S.

Making semiconductors ferromagnetic has been a long dream. One approach is to dope semiconductors with transition metals (TM). TM ions act as local moments and they couple with free carriers to develop collective magnetism. However, there are no fundamental reasons against the possibility of local moment formation from localized sp states. Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators including ZnO and TiO2. This kind of observation challenges the conventional understanding of ferromagnetism. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accident or by mistake. Therefore, in this field theory goes much ahead of experimental investigation. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in ZnO, TiO2 and SiC. In this short review, we also summarize some results by other groups using energetic ions to introduce defects, and thereby magnetism in various materials. Ion Irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Keywords: Ion irradiation; Defects; Magnetism

  • Nuclear Instruments and Methods in Physics Research B 326(2014), 55-60
    DOI: 10.1016/j.nimb.2013.10.049
  • Invited lecture (Conferences)
    The 17th International Conference on Radiation Effects in Insulators, 30.06.-05.07.2013, Helsinki, Finland

Publ.-Id: 19584

Transport phenomena and dynamics of externally and self-propelled colloids in confined geometry

Kreuter, C.; Siems, U.; Nielaba, P.; Leiderer, P.; Erbe, A.

Over the last decades, colloidal suspensions have been proven as powerful model systems to reveal fundamental questions in soft matter or general physics. In this work, we will focus on the influ- ence of interaction and confinement to the mobility of colloidal particles as well as to the transport behavior of particles over obstacles placed in a micro-channel. Both experiments are supported with Brownian dynamics simulations to complete the experimental work. The paper concludes with the investigation of the behavior of single active swim- mers close to a wall.

Keywords: colloidal model systems; active swimmers; transport phenomena

Publ.-Id: 19583

Formation of radiation damage and helium release in yttria-stabilized zirconia

Ou, X.; Kögler, R.; Zhou, H.; Anwand, W.; Grenzer, J.; Hübner, R.; Voelskow, M.; Butterling, M.; Zhou, S.; Skorupa, W.

The radiation damage induced by neutrons and α-decay in YSZ (yttria-stabilized zirconia) was simulated using synchronized Zr+ & He+ dual ion beam implantation. [1] The measured damage profiles consist of two peaks which agree well with the calculated profiles of excess point defects generated by the collision cascade. The spatial separation of vacancy and interstitial defects is known as the “½Rp” effect describing the vacancy accumulation in the region at half of the projected ion range. This special implantation-related effect has to be considered carefully during the evaluation of experimental investigations which simulate isotropic irradiation effects caused by α-decay. Comparing the amount and type of radiation defects in single and dual beam implanted YSZ reveals that the implanted helium is released from the sample during simultaneous dual beam irradiation instead to be trapped by the created open volume defects at ½Rp region. According to first-principles total energy calculations, helium is mobilized and released via a vacancy-assisted trapping/detrapping mechanism induced by the simultaneous Zr+ ion implantation. The release of helium during room temperature dual beam irradiation demonstrates one of the suitable characteristics of YSZ that contributes to its excellent radiation hardness, since helium in YSZ can accumulate in undesirable helium bubbles and results in local surface swelling and lift-off.
[1] Xin Ou et al. PHYSICAL REVIEW B 86, 224103 (2012)

Keywords: radiation damage; dual ion beam implantation

  • Poster
    E-MRS 2013 Spring Meeting, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19582

Tuning the resistive switching characteristics of BiFeO3 by Ar+ irradiation (Best Poster Award)

Ou, X.; Shuai, Y.; Luo, W.; Kögler, R.; Fiedler, J.; Reuther, H.; Zhou, S.; Hübner, R.; Facsko, S.; Helm, M.; Schmidt, H.

Sufficient and stable read current is critical for the scalability of RRAM devices and designing of multilevel resistive switching devices.
Here, we report that a remarkable increase of the current density and retention stability of Au/BiFeO3/Pt/Ti resistance random access memory (RRAM) devices can be achieved by low-energy (≤ 1 keV) Ar+ ion irradiation of BiFeO3 films.
According to dynamic simulations and microstructure characterizations, oxygen atoms are preferentially sputtered from the BiFeO3 surface by Ar+ ion irradiation. The generation of oxygen vacancies acting as "dopants" modifies the Schottky contact of the Au/BiFeO3 interface and also may contribute to the formation of highly conductive "shunt" channels. These two effects are proposed as the reasons for the increased current density by more than two orders of magnitude and the improved retention stability. After Ar+ irradiation the retention stability was increased as the current density remaining after the retention time is improved from 7% to 85% of the initial value.

Keywords: RRAM; ion irradiation

  • Poster
    European Materials Research Society Conference, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19581

Reverse Epitaxy of Ge Surface for Nanopattern Formation

Ou, X.; Mücklich, A.; Fassbender, J.; Facsko, S.

Periodical semiconductor nanostructure arrays have the potential for nano-electronic and nano-optoelectronic application. Besides the conventional low efficiency lithographic techniques broad ion beam erosion is a simple and potentially mass productive technique to fabricate nanostructure patterns on semiconductor surfaces.[1] Based on a “self-organized” erosion process, periodic ripple, hole, dot or tip arrays can be created on various semiconductor surfaces due to the interplay of different processes.[2] However, the main drawback of this method is that the irradiated semiconductor surfaces are amorphized. In this work we report the recent discovery of single crystal Ge nanopattern formation based on a “reverse epitaxy” process. The vacancies created during the ion beam irradiation distribute according to the crystallographic anisotropy, which results in orientation-dependent pattern formation on single crystal Ge surface. The formation of these patterns is interpreted as the result of a surface instability due to an Ehrlich-Schwoebel barrier for ion induced surface vacancies. The simulation of the pattern formation is performed by a continuum equation accounting for the effective surface currents.

[1] Stefan Facsko et al. Science 285, 1551 (1999).

Keywords: Nanopattern; ion irradiation

  • Lecture (Conference)
    European Materials Research Society Conference, 27.-31.05.2013, Strasbourg, France

Publ.-Id: 19580

Formation of radiation damage and helium release in yttria-stabilized zirconia under dual ion beam irradiation

Ou, X.; Kögler, R.; Zhou, H. B.; Anwand, W.; Grenzer, J.; Hübner, R.; Voelskow, M.; Butterling, M.; Zhou, S.; Skorupa, W.; Facsko, S.

Fission gas retention or release has a critical impact on the function of advanced nuclear materials. Helium trapping in, and release from, radiation defects induced by neutrons and by α decay in YSZ (yttria-stabilized zirconia) is experimentally simulated using synchronized Zr+ and He+ dual ion beam irradiation. The measured damage profiles consist of two peaks which agree well with the calculated profiles of implantation induced excess point defects. This special implantation related effect has to be carefully considered in the Evaluation of experimental investigations which simulate isotropic irradiation effects such as α decay. First-principles calculations show that helium is energetically favorable to be trapped by Zr vacancies in YSZ. Implanted helium alone in YSZ is accumulated in undesirable helium bubbles and results in local surface swelling and lift-off. However, under dual beam irradiation helium is released from vacancy defects and is out-diffused at room temperature. Helium is mobilized by a vacancy-assisted trapping/detrapping mechanism induced by the simultaneous Zr+ ion implantation. This behavior avoids the deleterious helium bubble formation and contributes to the suitable application characteristics of YSZ which result in its excellent radiation hardness.

Keywords: radiation defects; ZrO2

  • Lecture (Conference)
    German workshop on Ion Beam Research and Application, 12.-14.06.2013, Leipzig, Germany

Publ.-Id: 19579

Ion beam irradiation and doping effect on 1D and 2D materials

Ou, X.

In this lecture, I will give a brief review on the doping of the nanostructure by ion beam implantation and irradiation. Because of the high surface to volume ratio of the low-dimensional materials, the doping behavior is quite different from the bulk materials. Some examples on doping of nanowire1,2 and graphene by ion beam will be discussed. Meanwhile, ion beam irradiation can create the oxygen vacancy in functional oxide in a controllable way. The generation of oxygen vacancies acting as "dopants" modifies the properties of the oxide. An example of tuning the resistive switching characteristics of resistive switching oxide 3 by low energy ion irradiation will be discussed.4

Keywords: doping of the nanostructure; ion beam implantation and irradiation

  • Invited lecture (Conferences)
    International School on Ion Beams in Material Science, 21.-22.10.2013, Jaipur, India

Publ.-Id: 19578

Nanopatterning of semidonductor surfaces by ion beam irradiation

Ou, X.; Keller, A.; Helm, M.; Fassbender, J.; Facsko, S.

Periodic semiconductor nanostructure arrays have the potential for nanoelectronic and optoelectronic application. Besides the conventional low efficiency lithographic techniques broad ion beam irradiation is a simple and potentially mass productive technique to fabricate nanostructure patterns on semiconductor surfaces.[1] Based on a “self-organized” erosion process, periodic ripple, hole, or dot arrays can be produced on various semiconductor surfaces. Moreover, an array of isolated nanostructures on insulator substrate can be fabricated by ion beam erosion of a thin Si or Ge layer deposited on insulator and precisely stopping the sputtering as soon the nanopattern meets the interface of the buried oxide layer.[2]
However, the main drawback of this method is that the irradiated semiconductor surfaces are amorphized. In this work we report the recent discovery of single crystal Ge nanopattern formation based on a “reverse epitaxy” process.[3] The vacancies created during ion beam irradiation distribute according to the crystallographic anisotropy, which results in an orientation-dependent pattern formation on single crystal Ge surface. The formation of these patterns is interpreted as the result of a surface instability due to an Ehrlich-Schwoebel barrier for ion induced surface vacancies. The simulation of the pattern formation is performed by a continuum equation accounting for the effective surface currents.

[1] Stefan Facsko et al. Science 285, 1551 (1999).
[2] Xin Ou et al., AIP Advances, 1, 042174 (2011).
[3] Xin Ou et al., Physical Review Letters 111, 016101 (2013).

Keywords: nanopatterning

  • Invited lecture (Conferences)
    International Conference on Nanostructuring by Ion Beams, 23.-25.10.2013, Jaipur, India

Publ.-Id: 19577

Investigation of a packed bed in a mini channel with a low channel-to-particle diameter ratio: Flow regimes and mass transfer in gas–liquid operation

Langsch, R.; Zalucky, J.; Haase, S.; Lange, R.

This work analyzes flow regimes and mass transfer in a miniaturized packed bed reactor under reacting conditions. The reactor consisted of a cylindrical channel with an inner diameter of 2 mm which was filled with spherical catalyst particles having an outer diameter of 0.8 mm. The liquid phase hydrogenation of α-methylstyrene over a Pd/γ-Al2O3 catalyst was employed as reaction system. Based on experimental reaction rates, overall (gas–liquid–solid) volumetric mass transfer coefficients of hydrogen, which were between 0.5 s−1 and 6.0 s−1, were computed. Detailed discussions focus on the impact of the flow regime, the gas and liquid superficial velocities and, consequently, their ratio, as well as system pressure on overall mass transfer rates.

Keywords: Mass transfer; Multiphase reactors; Hydrodynamics; Packed bed; Catalysis; Gas–liquid–solid reaction

Publ.-Id: 19576

Dissolution and diffusion behaviors of hydrogen in copper: A first-principles investigation Dissolution and diffusion behaviors of hydrogen in copper: A first-principles investigation

Zhou, H. B.; Zhang, Y.; Ou, X.

We have investigated the dissolution and diffusion behaviors of hydrogen (H) in copper (Cu) based on first-principles calculations in combination with the classical thermodynamics models. A single H atom energetically prefers to occupy the octahedral interstitial site (OIS) instead of the tetrahedral interstitial site (TIS). This can be confirmed by the charge density results. The dissolved equilibrium concentration of H is 8.98 × 10−7 at a typical temperature 600 K. We demonstrate that the OIS → TIS → OIS path is the optimal diffusion path of H in Cu with diffusion barrier of 0.23 eV. Double H atoms tend to be paired up at the two neighboring OIS’s along the 〈1 1 0〉 direction with a distance of 2.59 Å and a binding energy of 0.07 eV. This suggests a weak attractive interaction between H atoms, with the implication that self-trapping of H and thus formation of the H2 molecules are quite difficult in the bulk Cu.

Keywords: first-principles calculations; diffusion behaviors

  • Computational Materials Science 79(2013), 923

Publ.-Id: 19575

Effect of carbon on helium trapping in tungsten: a first-principles investigation

Zhou, H.; Ou, X.; Zhang, Y.; Shu, X.; Liu, Y.; Lu, G.

We investigate the effect of carbon (C) on helium (He) trapping in tungsten (W) using a first-principles method. We show C can effectively reduce the solution energy of He in the bulk W originated from the charge density redistribution. This leads to a strong attraction between He and C in W. We demonstrate the C–vacancy (C–V) complex can serve as a trapping center by reducing charge density in its vicinity to induce He nucleation in comparison with the defect-free W. The maximal number of He atoms that can be trapped by such C–V complex is 5, and He diffusion into the C–V complex is kinetically feasible. Further, it is found the binding energy of He to a C–V complex is weaker than that to a C-free vacancy, suggesting C will decrease the He trapping capability of vacancy. We thus propose that C plays a key role in He trapping behavior.

Keywords: tungsten; first-principles method; trapping

Publ.-Id: 19574

A Si-based nanocomposite absorber for thin film solar cells

Heinig, K.-H.; Aydinli, A.; Turan, R.; Hauschild, D.

Si-based thin film solar cells suffer from a rather low efficiency. This leads to a relative small market share, although their module prices are comparably low. RainbowEnergy aims at a novel nanostructured Si-based thin film PV cell absorber, which increases the efficiency substantially without increasing the module costs.
If after phase separation SiOx --> 0.5SiO2 + (1-0.5x)Si the volume fraction of Si exceeds ~30%, then Si forms a percolated nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on kinetic Monte-Carlo.
As the wire diameters coarsens with time of heat treatment like d~t1/3, and because the Si bandgap opens for nm-structures by quantum confinement, a band gap engineering for PV cell optimization becomes feasible. It will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way with industrial partners.

Keywords: Solar Energy; thin film; nanocomposite; Si; SiO2; atomistic simulation; EFTEM

  • Invited lecture (Conferences)
    2013 Energy Materials Nanotechnology (EMN Spring), 08.-11.04.2013, Orlando, USA

Publ.-Id: 19573

Key concepts behind forming-free resistive switching incorporated with rectifying transport properties

Shuai, Y.; Ou, X.; Luo, W.; Mücklich, A.; Bürger, D.; Zhou, S.; Wu, C.; Chen, Y.; Zhang, W.; Helm, M.; Mikolajick, T.; Schmidt, O.; Schmidt, H.

This work reports the effect of Ti diffusion on the bipolar resistive switching in Au/BiFeO3/Pt/Ti capacitor-like structures. Polycrystalline BiFeO3 thin films are deposited by pulsed laser deposition at different temperatures on Pt/Ti/SiO2/Si substrates. From the energy filtered transmission electron microscopy and Rutherford backscattering spectrometry it is observed that Ti diffusion occurs if the deposition temperature is above 600°C. The current-voltage (I–V) curves indicate that resistive switching can only be achieved in Au/BiFeO3/Pt/Ti capacitor-like structures where this Ti diffusion occurs. The effect of Ti diffusion is confirmed by the BiFeO3 thin films deposited on Pt/sapphire and Pt/Ti/sapphire substrates. The resistive switching needs no electroforming process, and is incorporated with rectifying properties which is potentially useful to suppress the sneak current in a crossbar architecture. Those specific features open a promising alternative concept for nonvolatile memory devices as well as for other memristive devices like synapses in neuromorphic circuits.

Keywords: resistive switching; BiFeO3; Ti diffusion

Publ.-Id: 19572

Forming-free resistive switching in multiferroic BiFeO3 thin films with enhanced nanoscale shunts

Ou, X.; Shuai, Y.; Luo, W.; Siles, P. F.; Kögler, R.; Fiedler, J.; Reuther, H.; Zhou, S.; Hübner, R.; Facsko, S.; Helm, M.; Mikolajick, T.; Schmidt, O. G.; Schmidt, H.

A controlled shunting of polycrystalline oxide thin films on the nanometer length scale opens the door to significantly modify their transport properties. In this paper, the low energy Ar(+) irradiation induced shunting effect of forming-free, non-volatile resistive switching in polycrystalline BiFeO3 thin film capacitor-like structures with macroscopic bottom and top contacts was investigated. Oxygen atoms at the BiFeO3 surface are preferentially sputtered by Ar(+) ion irradiation and oxygen vacancies and a metallic Bi phase are formed at the surface of the BiFeO3 thin film before deposition of the top contacts. A phenomenological model is that of nanoscale shunt resistors formed in parallel to the actual BiFeO3 thin film capacitor-like structure. This model fits the noticeable increase of the retention stability and current density after irradiation. The formation of stable and conductive shunts is further evidenced by conductive atomic force microscopy measurements.

Keywords: resistive switching; Ar irradiation; shunting; oxygen vacancy; current retention; BiFeO3

Publ.-Id: 19571

Hollandite-type TiO2: a new negative electrode material for sodium-ion batteries

Perez-Flores, J. C.; Baehtz, C.; Kuhna, A.; Garcia-Alvaradoa, F.

The electrochemical properties of TiO2 with the hollandite structure (TiO2(H)) as a negative electrodematerial for sodium-ion batteries are reported. TiO2(H) was obtained from hollandite K0.21TiO2 by an oxidation–ion extraction process. Na/TiO2(H) cells exhibit a large first discharge capacity of 280 mA h g1 down to 0.2 V. After the first discharge the Na/TiO2(H) cells develop a reversible charge–discharge capacity of 85 mA h g1 at C/8 rate in the 2.5–0.2 V voltage range; this corresponds to the reversible insertion of 0.25 Na per TiO2(H) formula unit. Chronoamperometry and potentiostatic intermittent titration techniques were used to further characterize the electrochemical reaction mechanism. Structural changes in the TiO2(H) electrode upon sodium insertion and extraction have been studied by ex situ XRD and high resolution in situ synchrotron diffraction techniques, for which appropriately modified coin-type cells were used. It is seen that sodium insertion into TiO2(H) is commenced with a single-phase solid solution followed by a structural transition from tetragonal I4/m to monoclinic I2/m symmetry, in which the skeleton framework is retained. The reversible transition includes few structural changes with a small volume change of only 1.1%. Fourier difference maps deduced from SXRD patterns revealed the location of Na ions in 4i sites in the tunnel space. The coordination arrangement around Na ions is distorted capped trigonal prisms formed by seven oxygen atoms. Although still far from the theoretical capacity (335 mA h g1), the cycling properties at a low insertion potential together with the host framework stability indicate the feasibility of TiO2 with the hollandite structure as a negative electrode material for Na-ion batteries.

Keywords: sodium-ion batterie; in-situ XRD; hollandite

Publ.-Id: 19570

Unusual crystallization behavior in Ga-Sb phase change alloys

Putero, M.; Coulet, M.-V.; Ouled-Khachroum, T.; Muller, C.; Baehtz, C.; Raoux, S.

Combined in situ X-ray scattering techniques using synchrotron radiation were applied to investigate the crystallization behavior of Sb-rich Ga-Sb alloys. Measurements of the sheet resistance during heating indicated a reduced crystallization temperature with increased Sb content, which was confirmed by in situ X-ray diffraction. The electrical contrast increased with increasing Sb content and the resistivities in both the amorphous and crystalline phases decreased. It was found that by tuning the composition between Ga:Sb = 9:91 (in at.%) and Ga:Sb = 45:55, the change in mass density upon crystallization changes from an increase in mass density which is typical for most phase change materials to a decrease in mass density. At the composition of Ga:Sb = 30:70, no mass density change is observed which should be very beneficial for phase change random access memory (PCRAM) applications where a change in mass density during cycling is assumed to cause void formation and PCRAM device failure.

Keywords: PCRAM; XRD; XRR; phase change material

Publ.-Id: 19569

Phase transition in stoichiometric GaSb thin films: Anomalous density change and phase segregation

Putero, M.; Coulet, M.-V.; Ouled-Khachroum, T.; Muller, C.; Baehtz, C.; Raoux, S.

The crystallization of stoichiometric GaSb thin films was studied by combined in situ synchrotron techniques and static laser testing. It is demonstrated that upon crystallization, GaSb thin films exhibit an unusual behaviour with increasing thickness and concomitant decreasing mass density while its electrical resistance drops as commonly observed in phase change materials. Furthermore, beyond GaSb amorphous-to-crystalline phase transition, an elemental segregation and a separate crystallization of a pure Sb phase is evidenced.

Keywords: PCRAM; XRD; XRR; synchrotron

Publ.-Id: 19568

Observing Graphene Grow: Catalyst−Graphene Interactions during Scalable Graphene Growth on Polycrystalline Copper

Kidambi, P. R.; Bayer, B. C.; Blume, R.; Wang, Z.-J.; Baehtz, C.; Weatherup, R. S.; Willinger, M.-G.; Schloegl, R.; Hofmann, S.

Complementary in situ X-ray photoelectron spectroscopy (XPS), X-ray diffractometry, and environmental scanning electron microscopy are used to fingerprint the entire graphene chemical vapor deposition process on technologically important polycrystalline Cu catalysts to address the current lack of understanding of the underlying fundamental growth mechanisms and catalyst interactions. Graphene forms directly on metallic Cu during the high-temperature hydrocarbon exposure, whereby an upshift in the binding energies of the corresponding C1s XPS core level signatures is indicative of coupling between the Cu catalyst and the growing graphene. Minor carbon uptake into Cu can under certain conditions manifest itself as carbon precipitation upon cooling. Postgrowth, ambient air exposure even at room temperature decouples the graphene from Cu by (reversible) oxygen intercalation. The importance of these dynamic interactions is discussed for graphene growth, processing, and device integration.

Keywords: Graphene; chemical vapor deposition (CVD); polycrystalline copper (Cu); in situ X-ray photoelectron spectroscopy; in situ X-ray diffractometry; environmental scanning electron microscopy; intercalation

Publ.-Id: 19567

Introducing Carbon Diffusion Barriers for Uniform, High-Quality Graphene Growth from Solid Sources

Weatherup, R. S.; Baehtz, C.; Dlubak, B.; Bayer, B. C.; Kidambi, P. R.; Blume, R.; Schloegl, R.; Hofmann, S.

Carbon diffusion barriers are introduced as a general and simple method to prevent premature carbon dissolution and thereby to significantly improve graphene formation from the catalytic transformation of solid carbon sources. A thin Al2O3 barrier inserted into an amorphous-C/Ni bilayer stack is demonstrated to enable growth of uniform monolayer graphene at 600 °C with domain sizes exceeding 50 μm, and an average Raman D/G ratio of <0.07. A detailed growth rationale is established via in situ measurements, relevant to solid-state growth of a wide range of layered materials, as well as layer-by-layer control in these systems.

Keywords: Graphene; solid carbon; low temperature; diffusion barrier; in situ; XPS; XRD

Publ.-Id: 19566

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