Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32227 Publications
CFD-modeling of insulation debris transport phenomena in water flow
Krepper, E.; Cartland-Glover, G.; Grahn, A.; Weiss, F.-P.; Alt, S.; Hampel, R.; Kästner, W.; Seeliger, A.;
The investigation of insulation debris generation, transport and sedimentation becomes important with regard to reactor safety research for PWR and BWR, when considering the long-term behavior of emergency core cooling systems during all types of loss of coolant accidents (LOCA). The insulation debris released near the break during a LOCA incident consists of a mixture of disparate particle population that varies with size, shape, consistency and other properties. Some fractions of the released insulation debris can be transported into the reactor sump, where it may perturb/impinge on the emergency core cooling systems.
Open questions of generic interest are the sedimentation of the insulation debris in a water pool, its possible re-suspension and transport in the sump water flow and the particle load on strainers and corresponding pressure drop. A joint research project on such questions is being performed in cooperation between the University of Applied Sciences Zittau/Görlitz and the Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow and the development of CFD models for its description. While the experiments are performed at the University at Zittau/Görlitz, the theoretical modeling efforts are concentrated at Forschungszentrum Dresden-Rossendorf.
In the current paper the basic concepts for CFD modeling are described and feasibility studies including the conceptual design of the experiments are presented.
Keywords: CFD, two-fluid approach, fiber flow

Publ.-Id: 12962 - Permalink


Electromagnetic control of local temperature gradients in a Czochralski crystal growth model
Pal, J.; Röder, M.; Cramer, A.; Gerbeth, G.;
This experimental work is concerned with optimisation of the Czochralski crystal growth process. With respect to the shape of the solidification front and the related mono-crystalline growth, the ratio of the horizontal and the vertical temperature gradient r* = DTh /DTv at the triple point liquid-solid-atmosphere is thought of being a crucial magnitude, which desirably should be in the order of unity. A liquid metal model experiment was therefore built that allows studying this ratio under the influence of magnetic fields applied to the melt. The cylindrical liquid metal column was homogeneously heated from below, whereas on top the heat was extracted in a concentrical region covering only about one third of the surface in order to simulate the growing crystal. It was shown that the native, i. e. without flow control, r* ≈ 3 is far removed from unity. In a first series of measurements, it was then possible to reach the target value r* = 1 for any temperature difference between the bottom and the top at a moderate field strength while applying a rotating magnetic field.
Keywords: Czochralski crystal growth, Stirring, Convection
  • Contribution to proceedings
    Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Deutschland
    Electromagnetic control of local temperature gradients in a Czochralski crystal growth model, 9783936104653, 591-594
  • Lecture (Conference)
    Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Deutschland

Publ.-Id: 12961 - Permalink


Estimation of the solubility limit of Cr in Fe at 300°C from small angle neutron scattering in neutron-irradiated Fe-Cr alloys
Bergner, F.; Ulbricht, A.; Heintze, C.;
The solubility limit of Cr in Fe (a-Fe-Cr) at lower temperatures is a matter of debate. We report a direct estimation of the solubility limit at 300°C from SANS data obtained for neutron-irradiated Fe-Cr alloys. The SANS results indicate that the equilibrium concentration of a’ was reached via irradiation-enhanced diffusion. The solubility limit was estimated using an iterative approach based on the SANS invariant and the lever rule of phase equilibrium
Keywords: Small angle neutron scattering (SANS); Fe-Cr alloys; Phase diagram

Publ.-Id: 12960 - Permalink


Defects in zinc-implanted ZnO thin films
Schmidt, M.; Ellguth, M.; Czekalla, C.; von Wenckstern, H.; Pickenhain, R.; Grundmann, M.; Brauer, G.; Skorupa, W.; Helm, M.; Gu, Q.; Ling, C. C.;
Defects in zinc-implanted and thermally annealed ZnO thin films were investigated by means of capacitance-voltage spectroscopy (C-V), thermal admittance spectroscopy (TAS), deep level transient spectroscopy (DLTS), and photoluminescence (PL) spectroscopy. The authors report on the formation of two donor states approximately 35 and 190 meV below the conduction band edge, observed by TAS and DLTS, respectively. In the PL spectra of a reference sample a peak at 3.366 eV was present, which diminished after the implantation, while a new peak at 3.364 eV was observed only in the spectrum of the implanted sample. Since only intrinsic ions were implanted, the authors consider the defects formed by the zinc implantation and annealing to be intrinsic.
  • Journal of Vacuum Science & Technology B 27(2009)3, 1597-1600

Publ.-Id: 12959 - Permalink


Effect of melt convection on the secondary dendritic arm spacing in peritectic Nd-Fe-B alloy
Biswas, K.; Hermann, R.; Wendrock, H.; Priede, J.; Gerbeth, G.; Büchner, B.;
Dendritic microstructure is one of the major microstructural constituents of peritectic alloys. In the present work, the effect of melt convection on the secondary dendritic arm spacing (SDAS) and volume fraction of properitectic alpha-Fe was investigated during solidification of stoichiometric Nd-Fe-B alloys under forced crucible rotation technique. The resulting microstructure of the alloy in consideration of melt convection has been investigated using scanning electron microscopy and optical microscopy. The average SDAS was determined for each sample from the whole cross-section of the cylindrical test samples using image analyzing software LEICA QWIN. A detailed statistical analysis of the spacing distribution was performed on the basis of the variation of SDAS values averaged from about 80 to 120 dendrites in different zones. The a-Fe volume fraction measured by vibrating sample magnetometer (VSM) reduces with increasing crucible rotation frequency. Similarly, the SDAS values decrease with increasing rotation frequency. These results are explained from the viewpoint of a reduced melt convection state under steady forced crucible rotation leading to a reduced effective mass transfer coefficient.
  • Journal of Alloys and Compounds 480(2009), 295-298

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Publ.-Id: 12958 - Permalink


Phase stability of AlYB14 sputtered thin films
Kölpin, H.; Music, D.; Emmerlich, J.; Munnik, F.; Schneider, J. M.;
AlYB14 (Imma) thin films were synthesized by magnetron sputtering. Based on X-ray diffraction, no phases other than crystalline AlYB14 could be identified. According to electron probe microanalysis, energy dispersive X-ray analysis and elastic recoil detection analysis, the Al and Y occupancy varies in the range of 0.73 to 1.0 and 0.29 to 0.45, respectively. Density functional theory based calculations were carried out to investigate the effect of occupancy on the stability of AlxYyB14 (x, y = 0.25, 0.75, 1). The mean effective charge per icosahedron and the bulk moduli were also calculated. It is shown that the most stable configuration is Al0.5YB14, corresponding to a charge transfer of 2 electrons to the boron icosahedra. Furthermore, it is found that the stability of a configuration is increased if the charge is homogeneously distributed within the icosahedra. The bulk moduli for all investigated configurations are in the range between 196 and 220 GPa, rather close to known hard phases such as α-Al2O3.
Keywords: PACS numbers: 62.20.D-, 71.20.Ps, 81.15.Cd
  • Journal of Physics: Condensed Matter 21(2009)35, 355006

Publ.-Id: 12957 - Permalink


Deviations from the conventional BCS behavior in the penetration depth of LuNi2B2C films at THz frequencies
Fischer, T.; Pronin, A. V.; Wosnitza, J.; Lobo, R. P. S. M.; Niemeier, T.; Holzapfel, B.;
We have measured the temperature and frequency-dependant transmission and phase shift through LuNi2B2C thin films on MgO substrates at terahertz frequencies. From the measured data, we could accurately determine the complex dielectric constant, epsilon, the complex optical conductivity, sigma, and the penetration depth, gamma. Comparing our measured results with theory, we find strong deviations from the standard one-band BCS predictions. These deviations can be attributed to the multiband nature of the superconducting state in LuNi2B2C.
  • Poster
    2009 ICAM-I2CAM Cargèse Summer Workshop, 06.-18.07.2009, Cargèse, France

Publ.-Id: 12956 - Permalink


Nanostructures induced by highly charged ions on CaF2 and KBr
Facsko, S.; Meissl, W.; Heller, R.; Wilhelm, R.; El-Said, A. S.; Kowarik, G.; Ritter, R.; Aumayr, F.;
Impact of a highly charged ion upon a solid surface can induce dramatic changes in the morphology only by the release of its potential energy. Hillocks and mono-atomic deep pits have been observed on the surfaces of CaF2 and KBr, respectively. For both processes a threshold in the potential energy exists for the creation of these nanostructures. Above this threshold the structure size increases linearly with potential energy. The mechanisms for the formation of hillocks and pits are discussed and a rst attempt to present a unied microscopic picture is made.
Keywords: Highly Charged Ions, Naostructures, KBr
  • Contribution to proceedings
    International Conference on Photonic, Electronic, and Atomic Collisions, 22.-28.07.2009, Kalamazoo, USA
    Nanostructures induced by highly charged ions on CaF2 and KBr: IOP

Publ.-Id: 12955 - Permalink


Beschleunigermassenspektrometrie und Ionenstrahlanalytik
Merchel, S.; Munnik, F.;
In diesem Vortrag wird Beschleunigermassenspektrometrie am FZD vorgestellt.
  • Lecture (others)
    Seminarreihe "Moderne analytische Methoden der Physik", 14.07.2009, Berlin, Deutschland

Publ.-Id: 12954 - Permalink


Ion Beam Analysis (IBA) for thin film studies
Munnik, F.; Merchel, S.;
Outline
Ion – Solid interaction
Experimental
RBS + high resolution
ERDA + high resolution
H analysis
Summary
  • Lecture (others)
    Seminarreihe "Moderne analytische Methoden der Physik", 14.07.2009, Berlin, Deutschland

Publ.-Id: 12953 - Permalink


Dosimetrische und physikalische Charakterisierung Laser beschleunigter Teilchen
Richter, C.;
Abstract is not available
  • Lecture (others)
    Verbundprojekttreffen OncoOptics 2009, 30.03.2009, Dresden, Deutschland

Publ.-Id: 12952 - Permalink


Dosimetric characterization of laser-accelerated particles
Richter, C.;
Abstract is not available
  • Lecture (others)
    4th Meeting of the Scientific Advisory Board of OncoRay, 26.02.2009, Dresden, Deutschland

Publ.-Id: 12951 - Permalink


Dosimetric Characterization of an Laser-Accelerated Electron Beam for Precise Cell Irradiation Experiments
Richter, C.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
not available. will be published later
  • Poster
    Advanced Lectures on Protection of Humans and Their Environment Against Ionising Radiation, 09.-18.02.2009, Bad Honnef, Deutschland

Publ.-Id: 12950 - Permalink


Worldwide first systematic in vitro cell irradiation experiments with laser accelerated electrons
Richter, C.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Laschinsky, L.; Leßmann, E.; Naumburger, D.; Nicolai, M.; Pawelke, J.; Sauerbrey, R.; Schlenvoigt, H.-P.; Baumann, M.;
The novel technology of particle acceleration based on high intensity laser systems promises accelerators of compact size and reasonable costs and may significantly contribute to a widespread use of high precision hadron radiotherapy. Although some basic properties of laser acceleration are reasonably well known from theory, simulations and fundamental physical experiments, several further requests have to be fulfilled for its medical application such as supply of a stable and reliable particle beam with reproducible properties and precise delivery of dose in an appropriate irradiation time with required exposure of a desired irradiation field. Moreover, the ultra-short pulsed (in the region of 100 fs) particle beams with resulting high pulse dose-rate (in the order of 1012 Gy/min) have to be characterized with regard to their radiobiological properties.
First in-vitro cell irradiations with laser accelerated electrons have been performed at the Jena Titanium:Sapphire (JeTi) 10 terawatt laser system and dose-effect-curves were obtained for four cell lines and two endpoints. Laser pulses (80 fs duration, 2.5 Hz repetition rate) were focused into a helium gas jet, accelerating electrons to energies of up to 20 MeV. Before irradiation, the JeTi system was optimized for cell experiments: the electron spectrum was limited to a minimum energy of 3 MeV, the beam spot size was adjusted and the dose rate and homogeneity were improved. Each cell sample was equipped with two Gafchromic EBT radiochromic films, one in front and one behind the cell monolayer, used for retrospective precise dose determination. A Roos ionization chamber and a Faraday Cup monitored the beam providing on-line dose information necessary for irradiation control. Moreover the energy spectrum was measured both with an electromagnetic spectrometer and by analyzing film stack measurements. Following to the irradiation the cell survival fraction was determined using clonogenic survival assay. In addition, DNA double strand breaks present in cell 24 h after irradiation were analyzed.
Normally used for physical single-shot experiments, the JeTi was customized for a long-time cell irradiation. 163 Samples were irradiated at 13 experiment days over a period of 10 weeks with doses between 0.3 and 10 Gy. A reasonably stable and reproducible beam was achieved. Dose homogeneity was examined for all samples within the target area and the inhomogeneity obtained was less than 10 % for all days and all applied doses. Although still preliminary, the dose-effect-curves obtained show in general a lower biological effectiveness for the laser accelerated electron beams in comparison with conventional x-rays.
  • Poster
    Workshop on Hadron Beam Therapy of Cancer, 24.04.-01.05.2009, Erice, Italia

Publ.-Id: 12949 - Permalink


Liquid metal tornado
Grants, I.; Zhang, C.; Eckert, S.; Gerbeth, G.;
A concentrated vortex with properties similar to a tornado may be created by magnetic body forces. We study this phenomenon experimentally by applying combined travelling and rotating magnetic fields to a liquid metal cylinder. The bulk velocity is measured by ultrasound Doppler velocimetry and the surface velocity is reconstructed by particle image velocimetry. The travelling magnetic field (TMF) creates an axial body force with a parabolic radial profile. The induced meridional flow follows the field at the rim and returns through the central part. Thus an intense converging flow is created at one end of the cylinder. The additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. The swirl intensification is limited by the centrifugal force which stops the radial inflow at some equilibrium radius. The resulting concentrated vortex is unstable but persistent. We determine conditions of its formation in terms of the ratio of the two magnetic body forces. It turns out that the maximum strength of the vortex is determined by the TMF but its structure is governed by a much weaker RMF. The maximum time-averaged swirl is observed at a force ratio of about 100. A pronounced two-cell vortex with a reversed meridional circulation in the inner core is observed at a force ratio of about 50. The inner core is encircled then by a number of smaller vortices resembling a large wedge-shaped tornado or eye of a tropical cyclone. As the force ratio is further increased the inner core expands until it occupies the entire cylinder. The flow is then essentially controlled by the RMF despite the TMF might be still much stronger. The phenomenon may be useful to stir floating particles into the melt. A related sink-vortex may occur over a drain-hole in various technological processes. Magnetic body forces can be used to alter or eliminate it.
Keywords: liquid metal, rotating magnetic field, traveling magnetic field, swirl intensification, tornado
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, 978-3-936104-65-3, 102-105

Publ.-Id: 12947 - Permalink


Investigation of a bubble-driven liquid metal flow under the influence of a travelling magnetic field
Zhang, C.; Eckert, S.; Gerebth, G.;
This paper describes laboratory experiments for investigations of flow structures in liquid metal bubbly flows under the influence of a travelling magnetic field (TMF). The melt flow is driven by central gas injection into a cylindrical container filled with the low melting point alloy GaInSn. Velocity fields of the liquid were measured non-intrusively using the ultrasound Doppler method. Depending on the travelling direction of the magnetic field, the TMF mainly imposes either a co-current or counter flow with respect to the original bubble-driven circulation. The application of a downward TMF significantly increases the liquid velocity all over the fluid volume. An upward TMF gives rise to more complex structures of the velocity field resulting in alternately arranged up- and downstream regions. Both the upward and downward TMF promote the occurrence of non-steady motions with distinct velocity fluctuations leading to an intensification of related transport processes in the melt and providing the perspective of enhanced mixing efficiencies.
Keywords: liquid metal, bubble plume, traveling magnetic field, Ultrasound Doppler method
  • Poster
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Germany, 978-3-936104-65-3, 127-130

Publ.-Id: 12946 - Permalink


Studies of the radiobiological response of human cell samples irradiated with laser-accelerated electron pulses
Schlenvoigt, H.-P.; Nicolai, M.; Weber, S.; Kaluza, M. C.; Baumann, M.; Beyreuther, E.; Enghardt, W.; Karsch, L.; Laschinsky, L.; Lessmann, E.; Naumburger, D.; Pawelke, J.; Richter, C.; Sauerbrey, R.;
Radiotherapy is a mainstay of cancer treatment. More than 50 % of tumour patients in developed countries receive radiotherapy, either as the only method of treatment or as a crucial component in combination with surgery and/or systemic treatment. However, in many cases, especially for compact, deep-seated, radiation-resistant tumours growing in close vicinity to organs at risk, state-of-the-art radiotherapy which is based on photon or electron beams delivered by compact electron linear accelerators comes to its limits. Considerably improved conformance of radiation dose to the tumour volume with simultaneous preservation of surrounding healthy tissue will derive from utilization of ions whose favourable physical and radiobiological properties have already been demonstrated in clinical application [1, 2]. However, only a few ion therapy facilities are running worldwide, due to their complexity, large scale and high investment cost linked to present radiofrequency accelerator technology. Laser-based particle acceleration is a rapidly evolving new technology [3-9]. It promises the development of compact ion accelerators with reasonable costs, which may be integrated into existing hospitals since they are based on compact table-top multi-terawatt laser systems and the acceleration process takes place within micrometer distances. This novel technology appears to be a key that many more patients could benefit from ion radiotherapy and its favourable properties.
  • Contribution to external collection
    in: Jahresbericht des Instituts für Optik und Quantenelektronik, Friedrich-Schiller-Universität Jena, http://www.physik.uni-jena.de/ioq/Jahresbericht/: Friedrich-Schiller-Universität Jena, 2009

Publ.-Id: 12945 - Permalink


Status of the Penning trap project in Munich
Szerypo, J.; Kolhinen, V.; Bussmann, M.; Gartzke, E.; Habs, D.; Neumayr, J.; Schramm, U.; Schürmann, C.; Sewtz, M.; Thirolf, P.;
The MLLTRAP at the Maier-Leibnitz-Laboratory (Garching) is a new Penning trap facility designed to combine several novel technologies to decelerate, charge breed, cool, bunch and purify the reaction products and perform high-accuracy nuclear and atomic mass measurements. It is now in the commissioning phase, achieving a mass-resolving power of about 105 in the purification trap for stable ions.
Keywords: penning trap, cooling, purification, mass spectrometry, highly charged ions

Publ.-Id: 12944 - Permalink


Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern
Wosnitza, J.;
Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abge-deckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.
  • Invited lecture (Conferences)
    Physikalisches Kolloquium der Universität Kaiserslautern, 15.06.2009, Kaiserslautern, Deutschland

Publ.-Id: 12943 - Permalink


Magnetic quantum oscillations in strongly correlated metals
Wosnitza, J.;
One of the most powerful methods to determine important bulk band-structure parameters in metals is the measurement of magnetic quantum oscillations. By applying high magnetic fields, this can be done e.g. by detecting the oscillations in the field-dependent magnetization, called de Haas-van Alphen (dHvA) effect, or by resolving Shubnikov-de Haas (SdH) oscilla-tions in the field-dependent resistivity. The combination of such kind of experimental data with sophisticated band-structure calculations often is a necessary prerequisite to gain a deeper understanding of the electronic properties of metals. One example for such a joint ef-fort of experimental and theoretical work is the finding and explanation of the field-induced band-structure change in CeBiPt [1]. In this material, a drastic change of the electronic band structure, as seen in the SdH and Hall signals, is found above about 25 T. This field-induced Lifshitz transition can be understood by the splitting of the Ce-5d bands close to the Fermi energy due to the exchange interaction with the polarized Ce-4f states. Another example where dHvA measurements were successfully combined with highly precise full-potential local-orbital calculations is the borocarbide superconductor LuNi2B2C [2]. By carefully com-paring the experimentally extracted effective masses with the calculated bare masses the many-body mass enhancements could be determined independently for several bands and for different directions.
  • Invited lecture (Conferences)
    2nd Bilateral Estonian-German Workshop Strong Nonlinear Vibronic and Electronic Interactions in Solids, 21.-23.05.2009, Cottbus, Deutschland
  • Invited lecture (Conferences)
    10th German-Japanese Symposium "New Quantum States and Phenomena in Condensed Matter", 13.-16.09.2010, Hiroshima, Japan

Publ.-Id: 12942 - Permalink


DC and high-frequency conductivity of the organic metals β"-(BEDT-TT)2SF5RSO3 (R=CH2CF2 and CHF)
Glied, M.; Yasin, S.; Kaiser, S.; Drichko, N.; Dressel, M.; Wosnitza, J.; Schlueter, J. A.; Gard, G. L.;
The temperature dependences of the electric-transport properties of the two-dimensional organic conductors β"--(BEDT-TTF)2SF5CH2CF2SO3, β"-(d8-BEDT-TTF)2SF5CH2CF2SO3, and β"-(d8-BEDTTTF)2SF5CH2CF2SO3 are measured by dc methods in and perpendicular to the highly conducting plane. Microwave measurements are performed at 24 and 33.5GHz to probe the high-frequency behavior from room temperature down to 2 K. Superconductivity is observed in β"-(BEDT-TTF)2SF5CH2CF2SO3 and its deuterated analogue. Although all the compounds remain metallic down to low-temperatures, they are close to a charge-order transition. This leads to deviations from a simple Drude behavior of the optical conductivity which become obvious already in the microwave range. In β"-(BEDT-TTF)2SF5CH2CF2SO3, for instance, charge fluctuations cause an increase in microwave resistivity for T < 20K which is not detected in dc measurements. β"-(BEDT-TTF)2SF5CHFSO3 exhibits a simple metallic behavior at all frequencies. In the dc transport, however, we observe indications of localization in the perpendicular direction.

Publ.-Id: 12941 - Permalink


Violation of Critical Universality at the Antiferromagnetic Phase Transition of YbRh2Si2
Krellner, C.; Hartmann, S.; Pikul, A.; Oeschler, N.; Donath, J. G.; Geibel, C.; Steglich, F.; Wosnitza, J.;
We report on precise low-temperature specific-heat measurements, C(T), of YbRh2Si2 in the vicinity of the antiferromagnetic phase transition on a single crystal of superior quality (residual resistivity ratio of ~150).We observe a very sharp peak at TN = 72 mK with absolute values as high as C/T = 8 J/molK2. A detailed analysis of the critical exponent α around TN reveals α ≤ 0.38 which differs significantly from those of the conventional universality classes in the Ginzburg-Landau theory, where α ≤ 0.11. Thermal-expansion measurements corroborate this large positive critical exponent. These results provide insight into the nature of the critical magnetic fluctuations at a temperature-driven phase transition close to a quantum critical point.
  • Physical Review Letters 102(2009), 196402

Publ.-Id: 12940 - Permalink


Superconducting State in a Gallium-Doped Germanium Layer at Low Temperatures
Herrmannsdörfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Skrotzki, R.; Helm, M.; Wosnitza, J.;
We demonstrate that the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure. Using advanced doping and annealing techniques of state-of-the-art semiconductor processing, we have fabricated a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the ~60 nm thick Ge:Ga layer. The Cooper-pair density in Ge:Ga appears to be exceptionally low.
  • Physical Review Letters 102(2009), 217003

Publ.-Id: 12939 - Permalink


Defect-Enhanced Charge Transfer by Ion-Solid Interactions in SiC using Large-Scale Ab Initio Molecular Dynamics Simulations
Gao, F.; Xiao, H.; Posselt, M.; Weber, W. J.;
Large-scale ab initio molecular dynamics simulations of ion-solid interactions in SiC reveal that significant charge transfer occurs between atoms, and defects can enhance charge transfer to surrounding atoms. The results demonstrate that charge transfer to and from recoiling atoms can alter the energy barriers and dynamics for stable defect formation. The present simulations illustrate in detail the dynamic processes for charged defect formation. The averaged values of displacement threshold energies along four main crystallographic directions are smaller than those determined by empirical potentials due to charge-transfer effects on recoil atoms.
Keywords: silicon carbide, defects, first principle calculations, charge transfer
  • Physical Review Letters 103(2009), 027405

Publ.-Id: 12938 - Permalink


Impact of Biostimulated Redox Processes on Metal Dynamics in an Iron-rich Creek Soil of a former Uranium Mining Area
Burkhardt, E.-M.; Akob, D. M.; Bischoff, S.; Sitte, J.; Kostka, J. E.; Banerjee, D.; Scheinost, A. C.; Kuesel, K.;
Understanding the dynamics of metals and radionuclides in soil environments is necessary for evaluating risks to pristine sites. An iron-rich creek soil of a former uranium-mining district (Ronneburg, Germany) showed high porewater concentrations of heavy metals and radionuclides. Thus, this study aims i) to evaluate metal dynamics during terminal electron accepting processes (TEAPs) and ii) to characterize the active microbial populations in biostimulated soil microcosms using a stable isotope probing (SIP) approach. In biostimulated soil slurries, concentrations of soluble Co, Ni, Zn, As, and unexpectedly U increased during Fe(III)-reduction. This suggests that there was a direct reduction of As and a release of sorbed metals during reductive dissolution of Fe(III)-oxides. Subsequent sulfate-reduction was concurrent with a decrease of U, Co, Ni, and Zn concentrations. The relative contribution of U(IV) in the solid phase changed from 18.5 to 88.7% after incubation. The active Fe(III)-reducing population was dominated by δ-Proteobacteria (Geobacter) in 13C-ethanol amended microcosms. A more diverse community was present in 13C lactate amended microcosms including taxa related to Acidobacteria, Firmicutes, δ- Proteobacteria, and β-Proteobacteria. Our results suggested that biostimulated Fe(III)-reducing communities facilitated the release of metals including U to groundwater which is in contrast to other studies.
Keywords: Uranium-mining, heavy metal and arsenic contamination, iron-reduction, sulfate-reduction, metal dynamics, stable isotope probing, bioremediation
  • Environmental Science & Technology 44(2010), 177-183

Publ.-Id: 12937 - Permalink


Terahertz-range free-electron laser electron spin resonance spectroscopy: Techniques and applications in high magnetic fields
Zvyagin, S. A.; Ozerov, M.; Cizmar, E.; Kamneskyi, D.; Zherlitsyn, S.; Herrmannsdörfer, T.; Wosnitza, J.; Wünsch, R.; Seidel, W.;
The successful use of picosecond-pulse free-electron-laser (FEL) radiation for the continuous-wave terahertz-range electron spin resonance (ESR) spectroscopy has been demonstrated. The combination of two linac-based FELs (covering the wavelength range of 4–250 µm) with pulsed magnetic fields up to 70 T allows for multifrequency ESR spectroscopy in a frequency range of 1.2–75 THz with a spectral resolution better than 1%. The performance of the spectrometer is illustrated with ESR spectra obtained in the 2,2-diphenyl-1-picrylhydrazyl and the low-dimensional organic material (C6H9N2)CuCl3
  • Review of Scientific Instruments 80(2009), 073102

Publ.-Id: 12936 - Permalink


Is there alpha-assisted annealing of radiation damage? A helium implantation study of radiation-damaged zircon and monazite
Nasdala, L.; Grambole, D.; Váczi, T.; Götze, J.;
The stopping of high-energy light ions in a host solid is characterised by a very high ratio of electronic to nuclear stopping powers. Consequently, alpha particles (4He cores whose energies range between 3.9 and 8.8 MeV) penetrating into a host mineral cause tremendous amounts of lattice ionisation, whereas they are rather marginally efficient in generating atomic displacements. Radiohaloes in rock-forming minerals are therefore mostly characterised by relatively low levels of structural radiation damage [1,2]. It is well known, however, that ion-beam irradiation may not only create defects, but it may also cause structural reconstitution [3-5]. It has been suspected that the electronic excitation by the alpha particles may result in radiation-enhanced annealing of pre-existing radiation damage, as for instance the bulk metamictization or fission tracks [6] in minerals.
The present study aimed at checking the principal effect of alpha particles on the self-irradiation damage (i.e., predominantly alpha-recoil damage) in U- and Th-bearing accessory minerals. Three hypothetical possibilities had to be considered, namely, (i) the creation of additional damage, (ii) structural reconstitution of the pre-existing damage, or (iii) insignificant effects on the structural state. For this, a suite of well-characterised zircon and monazite samples, covering the entire range from well-crystallised to fully metamict, were irradiated with 8.8 MeV 4He2+ ions (which are the analogue of alpha particles generated in the 212Po ---> 208Pb decay in the Th chain). Fluences were varied in the range 1012 - 1017 He ions/cm2. In the case of He-irradiated metamict (i.e., amorphous) samples, no indication of recrystallisation or nucleation was found. For all non-amorphous starting materials, we found that the degree of structural damage has always notably increased after the He irradiation. Consequently, alpha particles do create structural damage not only in well-crystallised but also in mildly to highly radiation-damaged zircon and monazite. In contrast, the hypothetical ability of alpha particles to assist damage annealing is not supported.
Our observations do not seem to confirm results of dual-beam ion irradiation experiments (i.e., the simultaneous irradiation of a solid with a heavy ion beam with relatively high nuclear excitation, and a second beam with high electronic excitation, such as high-energy light ions or electrons). Such experiments suggested that the simultaneous, intense electronic excitation may retard or prevent amorphisation by heavy ions [7]. The apparent contrast to our results may perhaps be explained by the consideration that self-irradiating minerals do virtually never experience genuine dual irradiation. Due to their generally low irradiation rates (averaging a few events per minute and mm3), alpha recoils and alpha particle irradiation in the very same volume area do not occur simultaneously but successively.

References:
[1] Nasdala, L., Wildner, M., Wirth, R., Groschopf, N., Pal, D.C., Möller, A. (2006) Mineral. Petrol. 86, 1-27
[2] Krickl, R., Nasdala, L., Götze, J., Grambole, D., Wirth, R. (2008) Eur. J. Mineral. 20, 517-522
[3] Priolo, F., Spinella, C., Rimini, E. (1990) Phys. Rev. B 41, 5235-5242
[4] Heera, V., Kögler, R., Skorupa, W., Grötzschel, R. (1993) Nucl. Instr. Meth. Phys. Res. B80/81, 538-542
[5] Som, T., Ghatak, J., Sinha, O.P., Sivakumar, R., Kanjilal, D. (2008) J. Appl. Phys. 103, 123532
[6] Hendricks B.W.H., Redfield, T.F. (2005) Earth Plan. Sci. Lett. 236, 443-458
[7] Devanathan, R., Sickafus, K.E., Weber, W.J., Nastasi, M. (1998) J. Nucl. Mat. 253, 113-119
  • Poster
    Annual Meeting 2009 of the Mineralogical Society of Great Britain and Ireland: Micro-Analysis, Processes, Time (MAPT), 31.08.-02.09.2009, Edinburgh, United Kingdom
  • Contribution to proceedings
    Annual Meeting 2009 of the Mineralogical Society of Great Britain and Ireland: Micro-Analysis, Processes, Time (MAPT), 31.08.-02.09.2009, Edinburgh, United Kingdom
    Programme and abstracts, 167

Publ.-Id: 12934 - Permalink


Reactive DC Magnetron Sputtering of (GeOx-SiO2) Superlattices for Ge Nanocrystal Formation
Zschintzsch, M.; Jeutter, N. M.; von Borany, J.; Krause, M.; Mücklich, A.;
The underlying motivation of this work is the tailored growth of Ge nanocrystals (NC) for photovoltaic applications. The use of superlattices (SL) delivers a reliable method to control the Ge NC size after phase separation. In this contribution we report the deposition of (GeOx-SiO2) SL via reactive dc magnetron sputtering and the self-ordered Ge NC formation during subsequent annealing. Main attention is directed to define proper deposition conditions for tuning the GeOx composition between elemental Ge (x = 0) and GeO2 (x = 2) by the variation of the deposition temperature and the oxygen partial pressure. A convenient process window has been found which allows sequential GeOx-SiO2 deposition without changing the oxygen partial pressure during deposition. The phase separation and Ge NC formation after subsequent annealing were investigated with in−situ X-ray scattering, Raman spectroscopy and electron microscopy. By these methods the existence of 2-5 nm Ge NC at annealing temperatures of 600-750°C has been confirmed which is within the SL stability range. The used technique allows to produce SL stacks with very smooth interfaces (roughness <1 nm), thus the Ge NC layers could be separated by very thin SiO2 films (d > 3 nm) which offers interesting possibilities for charge transport via direct tunneling.
Keywords: Ge nanoparticles, superlattices, reactive magnetron sputtering, in-situ X-ray diagnostics

Publ.-Id: 12933 - Permalink


Al1-xInxN/GaN bilayers: structure, morphology and optical properties
Lorenz, K.; Magalhães, S.; Franco, N.; Darakchieva, V.; Barradas, N. P.; Alves, E.; Pereira, S.; Correia, M. R.; Munnik, F.; Martin, R. W.; O’Donnell, K. P.; Watson, I. M.;
High quality Al1-xInxN/GaN bilayers, grown by Metal Organic Chemical Vapour Deposition (MOCVD), were characterized using structural and optical techniques. Compositional analysis was performed using Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA). The InN molar fraction x decreased approximately linearly with increasing growth temperature and ranged from x=0.13 to 0.24. Up to x=0.20 the layers grow pseudomorphically to GaN with good crystalline quality. These layers show a smooth surface with V-shaped pits. Two layers with InN contents around 24% showed partial strain relaxation. However, the mechanisms leading to relaxation of compressive strain are very different in the two samples grown both at low temperature but with different growth rate. One sample shows a decreased c/a ratio, as expected for relaxation of the compressive strain, while In was shown to be homogeneously distributed with depth. Another sample started to grow with x=0.24 but relaxed mainly by reduction of the incorporated InN content towards the lattice-match composition of x~0.17. Both samples have an increased surface roughness. All samples show strong Al1-xInxN band edge luminescence with large bowing parameter and Stokes’ shifts.
  • Invited lecture (Conferences)
    International conference on Nitride Semiconductors, ICNS-8, 18.-23.10.2009, JeJu, South Korea
  • Physica Status Solidi (B) 247(2010)7, 1740-1746
    DOI: 10.1002/pssb.200983656

Publ.-Id: 12932 - Permalink


Raman characterisation of MoS2 microtube
Virsek, M.; Krause, M.; Kolitsch, A.; Remskar, M.;
A MoS2 microtube synthesized by chemical transport reaction was studied by Raman line scan mapping. The Raman spectrum of the MoS2 microtube closely resembles that of a MoS2 single crystal. In both, first order A1g and E2g Raman lines are observed with equal wave numbers, while line widths are slightly larger in the microtube spectrum, which can be attributed to defects. In the line scan along the tube axis the wave numbers of first order peaks are constant, while a slight up-shift of the Raman lines is observed in a line scan perpendicular to the tube. Possible mechanisms are discussed and the heating effect is proposed. Line scan approach over the edge of an object thus enables accurate determination of positions of first order peaks in highly absorbing materials.
Keywords: Inorganic nanotubes, layered materials, Raman spectroscopy

Publ.-Id: 12931 - Permalink


Diameter dependent Raman scattering of WS2 nanotubes
Krause, M.; Virsek, M.; Remskar, M.; Kolitsch, A.; Möller, W.;
The effect of the tube diameter and of the surface layer on the Raman spectra of WS2 nanotubes is investigated. With decreasing diameter, a disorder-induced line in the A1g mode range, the D-A1g line, is selectively enhanced. This enhancement is attributed to an increasing structural disorder in smaller nanotubes. On the other hand, no significant effect on the D-A1g / A1g intensity ratio is observed for a Raman scan perpendicular to a 290 nm diameter tube. Therefore the enhancement of the disorder induced line is an intrinsic property of WS2 nanostructures and not a surface layer effect.
Keywords: Inorganic Nanotubes, Layered Compounds, Raman spectroscopy

Publ.-Id: 12929 - Permalink


Experimental study of the electric dipole strength in the even Mo nuclei and its deformation dependence
Erhard, M.; Junghans, A. R.; Nair, C.; Schwengner, R.; Beyer, R.; Kosev, K.; Klug, J.; Wagner, A.; Grosse, E.;
Two methods based on bremsstrahlung were applied to the stable even Mo isotopes for the experimental determination of the photon strength function covering the high excitation energy range above 4 MeV with its increasing level density. Photon scattering was used up to the neutron separation energies Sn and data up to the maximum of the isovector giant resonance(GDR) were obtained by photo-activation. After a proper correction for multi-step processes the observed quasi-continuous spectra of scattered photons show a remarkably good match to the photon strengths derived from nuclear photo effect data obtained previously by neutron detection and corrected in absolute scale using the new activation results. The combined data form an excellent basis to derive a shape dependence of the E1 strength in the even Mo isotopes with increasing deviation from the N = 50 neutron shell, i.e. with the impact of quadrupole deformation and triaxiality. The wide energy coverage of the data allows for a stringent assessment of the dipole sum-rule, and a test of a novel parameterization developed previously which is based upon. This parameterization for the electric dipole strength function in nuclei with A>80 deviates significantly from prescriptions generally used previously. In astrophysical network calculations it may help to quantify the role the p-process plays in the cosmic nucleosynthesis. It also has impact on the accurate analysis of neutron capture data of importance for future nuclear energy systems and waste transmutation.

Publ.-Id: 12928 - Permalink


Laser accelerated ion beams for future medical applications
Kraft, S.;
Recent success in laser-driven particle acceleration has increased interest in laser-generated “accelerator-quality” beams, for example, protons and ions have been produced with up to several tens of MeV per nucleon, and with extremely low emittance (<0.01 mm mrad, normalized). Compact, high-gradient laser-accelerators are therefore now being discussed as a potentially viable technology for a host of particle-beam applications, including future compact medical accelerators for medical diagnostics and therapy. After commissioning of a 150 TW laser system at the FZD, a joint research center for radiation therapy with laser-accelerator ions is being established together with the OncoRay Center for Radiation Research in Oncology, and the University Clinic of the Technical University of Dresden. The present status and future plans of the center, and the results from first proton acceleration experiments at FZD will be presented.
  • Lecture (Conference)
    Laser and Plasma Accelerators Workshop 2009, 22.-26.06.2009, Kardamyli, Griechenland

Publ.-Id: 12927 - Permalink


Characterisation of thin films using ion beams
Munnik, F.;
Introduction to Ion Beam Materials Analysis (IBA)
Characterisation of thin films by Ion Beam Materials Analysis (IBA)
Research topics for Ion Beam Materials Analysis (IBA)
Keywords: Ion Beam Analysis
  • Lecture (others)
    Materials Science Workshop II, 23.-25.03.2009, Sohag, Ägypten

Publ.-Id: 12926 - Permalink


Ion beam analysis of ancient Egyptian wall paintings
Abd El Aal, S.; Korman, A.; Stonert, A.; Munnik, F.; Turos, A.;
Polychromatic decorations of ancient Egyptians tombs and temples have a long tradition over three millennia but are hard to identify because many pigments have been subjected to severe chemical reactions, which have entirely changed their original colours. Optical microscopy, PIXE and microbeam-PIXE have been used for determination of the nature of pigments, their chronology, and identification of domestic and imported materials. Paint flakes from various archeological sites in Egypt were analyzed: we report the results of the analysis of samples which were collected at the Mortuary Temple of Ramesses III (Habu Town), and the tombs of Tuthmosis III (Valley of the Kings) and Sennefer (Valley of the Noblemen). The paint is composed of grains of sizes typically ranging from 50 μm to 300 μm embedded in binding material and has great non-uniformity of pigment depth and lateral distributions and discontinuity of the paint layers. Qualitative analysis using broad beam PIXE has been performed to allow determination of the average composition of both support and pigments. Microbeam-PIXE has been used for mapping of selected grains. Goethite FeO(OH) (yellow), orpiment As2S3 (green), and the two blues: Egyptian Blue CaCuSi4O10 and Green Frit CaCuSiO3 (mixed with the red haematite Fe2O3) were identified, and interesting details of the painting technique of ancient masters, like blending of pigments and the use of multilayer structures, were revealed.
Keywords: Egyptian wall painting, pigments, PIXE, optical microscopy

Publ.-Id: 12925 - Permalink


New versatile bifunctional chelators for stable binding of 68Ga and Cu(II) radioisotopes
Pietzsch, H.-J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Universität Lissabon, 19.06.2009, Lissabon, Portugal

Publ.-Id: 12924 - Permalink


Dextran mannose conjugates with modifiable 99mTc(III) mixed-ligand complexes as potential tracers for sentinel lymph node detection
Pietzsch, H.-J.;
kein Abstract verfügbar
  • Lecture (Conference)
    IAEA-Meeting, 17.-22.05.2009, Athen, Greece

Publ.-Id: 12923 - Permalink


Radio-labeled DOTA-glycodendrimers for potential tumor imaging and therapy
Appelhans, D.; Stephan, H.; Bergmann, R.; Voit, B.;
kein Abstract verfügbar
  • Poster
    6th International Dendrimer Symposium, 14.-18.06.2009, Stockholm, Sweden
  • Contribution to proceedings
    6th International Dendrimer Symposium, 14.-18.06.2009, Stockholm, Sweden

Publ.-Id: 12922 - Permalink


Forschungseinrichtungen als Partner der Wirtschaft - Der Wissenschaftsstandort Dresden
Joehnk, P.;
Rossendorf als lebendiger und attraktiver Standort für Wissenschaft und Wirtschaft
  • Lecture (others)
    BWA Frühjahrsempfang 2009, 30.04.2009, Dresden, Deutschland

Publ.-Id: 12920 - Permalink


Synthesis of new bifunctional chelators for conjugation to vector molecules for tumor targeting
Heldt, J.-M.; Ruffani, A.; Zenker, M.; Walther, M.; Stephan, H.; Pietzsch, H.-J.; Steinbach, J.;
Problem: The goal of this study is to prepare novel chelators suitable for conjugation to vector molecules which can be labeled by yttrium or copper in order to achieve high specific activities and to improve pharmacokinetics. In this context, new water soluble bifunctional DOTA- and bis (2-pyridylmethyl)triazacyclocyclononane (DMPTACN)-based chelators have been synthesized and conjugated to the monoclonal antibody Cetuximab which binds to HER2 of the epithelial growth factor receptor (EGFR) family which is over-expressed by various tumors.

Material and Method: Both chelators have been conjugated to Cetuximab via thiourea-bridging. Radiolabeling of DOTA derivatives has been performed in aqueous ammonium acetate solution at r.t. using 86YCl3 or 90YCl3. Radiolabeling of DMPTACN conjugates with 64Cu was achieved in MES buffer solution at 50°C using 64CuCl2. The affinity of the bioconjugates towards EGFR was determined by ELISA.

Results: The ELISA test showed that the affinity of the bioconjugates has decreased compared to native Cetuximab. A chelator/antibody molar ratio of 4 was achieved as determined by MALDI-TOF-MS for the DOTA-Cetuximab conjugate. Radiolabeling of DOTA-conjugates with 86Y and 90Y at 37°C requires optimization to improve radiochemical yield. DMPTACN-Cetuximab conjugates can be rapidly labeled with 64Cu under mild conditions in almost quantitative yield.

Conclusions: DMPTACN- and DOTA-ligands are attractive bifunctional chelating agents which can be conjugated to vector molecules for PET-imaging and radiotherapy. In the near future, the work with the ligands investigated will be extended using the pre-labeling approach.
  • Lecture (Conference)
    1st TARCC international Workshop on targeted Radionuclide therapy: “Advances in targeted radionuclide therapy”, 25.-26.05.2009, Nantes, France

Publ.-Id: 12918 - Permalink


Thermoelectromagnetic stirring in Metallurgy
Cramer, A.; Zhang, X.; Gerbeth, G.;
Thermoelectromagnetic convection in cubic containers was studied experimentally. Two opposing side walls were cooled and heated, respectively, to produce an uniform temperature gradient. Inhomogeneous magnetic field distributions were achieved either with a permanent magnet or with specifically shaped pole shoes of an electromagnetic system. Ultrasonic Doppler velocimetry demonstrated that even a moderate temperature gradient may drive distinct convection. Two different flow regimes were investigated with the permanent magnet. Located at an isothermal wall, it produced a single vortex spreading the whole container while the flow was relatively stable. Moving the magnet to the center altered the flow structure. Four vortices developed and the velocity fluctuations were intensified. The more generic case realised with the electromagnet provided a gradient of the magnetic field only in one direction. Since the field strength and the area of impact on the melt were larger, developed turbulent regimes were accomplished.
  • Invited lecture (Conferences)
    54th IWK - Internationales Wissenschaftliches Kolloquium, 07.-11.09.2009, Ilmenau, Deutschland
  • Contribution to proceedings
    54th IWK - Internationales Wissenschaftliches Kolloquium, 07.-11.09.2009, Ilmenau, Germany
    "Thermoelectromagnetic Stirring in Metallurgy", Ilmenau: ISLE, 978-3-938843-45-1

Publ.-Id: 12917 - Permalink


Study on Atomic Layer Deposition of Amorphous Rhodium Oxide Thin Films
Hämäläinen, J.; Munnik, F.; Ritala, M.; Leskelä, M.;
Atomic layer deposition (ALD) of rhodium oxide thin films has been studied using Rh(acac)3 (acac = acetylacetonato) and ozone as precursors. Amorphous Rh2O3 thin films were deposited between 160 and 180 °C. The sublimation temperature of Rh(acac)3 set the low temperature limit for the oxide film deposition, while the high temperature limit was governed by the partial reduction of the film to metallic rhodium. The rhodium oxide films were successfully deposited on Al2O3 nucleation layers, soda lime glasses, and native oxide covered silicon substrates. The films demonstrated excellent conformality as characteristic for ALD. The films were not uniform across the substrate, which was most likely due to the catalyzing effect of Rh2O3 for ozone decomposition. The nonuniformity was repeatable and could be simply compensated in the cross-flow reactor. By splitting the deposition in two stages with 180° substrate rotation in between, good uniformity across the substrate was accomplished. The resistivities of about 80 nm thick Rh2O3 films were from 5 to 8 mΩcm.
Keywords: atomic layer deposition, ALD, rhodium oxide, Rh₂O₃, thin film
  • Journal of the Electrochemical Society 156(2009)10, D418-D423
    DOI: 10.1149/1.3190157

Publ.-Id: 12916 - Permalink


Repeatable phase change in Fe implanted GaN Induced by multi-annealing in reduced atmosphere
Talut, G.; Grenzer, J.; Reuther, H.; Baehtz, C.; Novikov, D.; Walz, B.;
Wurtzite GaN(001)-films were implanted with 195 keV 57Fe ions with a fluence Φ = 4*1016 cm-2 at room temperature. No secondary phase was detected in as implanted state. In order to reduce the implantation damage and to investigate the formation of secondary phases the implanted samples were annealed at 1073 K in a reduced N2-atmosphere (0.5 bar) for several cycles in a minute range. The formation of secondary phases in Fe implanted GaN upon annealing was detected by means of in-situ x-ray diffraction and conversion electron Mössbauer spectroscopy (CEMS). In contrast to our previous experiments with the annealing in a N2-flow at 1.1 bar pressure [3] no α-Fe cluster were found, but Fe3N. The repeatable phase change from Fe3N at room temperature and Fe3-xN at 1023 K was observed by means of in-situ x-ray diffraction. The diffusion of Fe during the annealing process limits the availability of secondary phase and hence the repeatability. The annealing process is accompanied by a strong diffusion of Fe and dissolution of GaN. Oxygen contamination promotes the dissolution of GaN and the formation of β-Ga2O3. The oxidation is confirmed by CEMS. The ferromagnetism in the samples is related to the presence of Fe3-xN. No DMS related phenomena have been observed. The results demonstrate that by variation of pressure phase compositions, other than α-Fe, are possible. It is expected that by the proper choice of annealing conditions specific secondary phases can be created, leading to different electronic, magnetic and other properties.
Keywords: GaN, Fe, CEMS, Magnetism
  • Poster
    International Conference on the Applications of the Mössbauer effect ICAME 09, 19.-24.07.2009, Wien, Österreich

Publ.-Id: 12913 - Permalink


Mode-locked pulses from mid-infrared Quantum Cascade Lasers
Wang, C. Y.; Kuznetsova, L.; Gkortsas, V. M.; Diehl, L.; Kärtner, F. X.; Belkin, M. A.; Belyanin, A.; Li, X.; Ham, D.; Schneider, H.; Grant, P.; Song, C. Y.; Haffouz, S.; Wasilewski, Z. R.; Liu, H. C.; Capasso, F.;
In this study, we report the unequivocal demonstration of midinfrared mode-locked pulses from quantum cascade lasers. The train of short pulses was generated by actively modulating the current and hence the gain of an edge-emitting quantum cascade laser (QCL). Pulses with duration of about 3 ps at full-width-at-half-maxima and energy of 0.5 pJ were characterized using a second-order interferometric autocorrelation technique based on a nonlinear quantum well infrared photodetector. The modelocking dynamics in the QCLs was modeled based on the Maxwell-Bloch equations in an open two-level system. Our model reproduces the overall shape of the measured autocorrelation traces and predicts that the short pulses are accompanied by substantial wings as a result of strong spatial hole burning. The range of parameters where short mode-locked pulses can be formed is found.
Keywords: Infrared and far-infrared lasers; Mode-locked lasers; Quantum cascade lasers

Publ.-Id: 12912 - Permalink


Photodisintegration of p-process nuclei
Wagner, A.;
The neutron deficient p-nuclei are shielded from the s- or r-process by stable isotopes. P-nuclei are likely to be formed in high temperature cosmic scenarios like exploding supernovae by photodisintegration reactions on heavy r- or s- seed nuclei. The lack of experimental information on energy-dependent cross sections especially for (gamma,p) and (gamma,gamma) reactions reduces the applicability of nucleosynthesis models. Using intense bremsstrahlung produced at the superconducting electron linear accelereator ELBE at Forschungszentrum Dresden-Rossendorf we investigated (gamma,n), (gamma,p) and (gamma,alpha) reactions for the medium-mass p-nuclei 92Mo and 144Sm, as well as (gamma,n) reactions for 100Mo and 154Sm by photo-activation. The lowest photoactivation yields have been measured in an underground laboratory. The photodisintegration of 197Au serves as a benchmark and it is compared to data measured previously with the positron annihilation technique.
Keywords: p-nuclei nuclear astrophysics disintegration photonuclear
  • Lecture (Conference)
    Spring Meeting of the German and the European Physical Society, 16.-20.03.2009, Bochum, Deutschland

Publ.-Id: 12911 - Permalink


Time-resolved infrared and Terahertz spectroscopy of semiconductor quantum structures
Schneider, H.;
This talk summarizes our activities in nonlinear laser spectroscopy using the free-electron laser at FZD and tabletop lasers. Our research concentrates on III-V semiconductor quantum wells and superlattices. In particular, I will focus on pump-probe spectroscopy, two-photon absorption, and photocurrent autocorrelation involving intersubband transitions in quantum wells at mid-infrared wavelengths, and discuss a concept for scalable photoconductive Terahertz emitters.
Keywords: intersubband transition, two-photon detection, terahertz
  • Lecture (others)
    Seminar, Xi’an University of Technology, 22.06.2009, Xi'an, China
  • Lecture (others)
    Seminar, Xi'an Institute of Optics and Precision Mechanics (Chinese Academy of Sciences), 22.06.2009, Xi'an, China

Publ.-Id: 12910 - Permalink


Quantum well infrared photodetectors for dual-band thermal imaging and two-photon detection
Schneider, H.;
Quantum well infrared photodetectors (QWIPs) provide unique opportunities for high-performance thermal imaging. Due to their narrow absorption bands with relative spectral widths of the order of 10%, QWIPs are particularly suitable for thermal imaging applications involving several atmospheric transmission bands or several colors within the same band. For dual-band/dual-color FPAs, QWIP technology has the unique property that the active region for the long-wavelength band is transparent for the short-wavelength band. Narrow intersubband transition linewidths also enable us to enhance resonantly the cross section for two-photon-absorption by several orders of magnitude. This approach results in particularly sensitive quadratic two-photon detectors, which are useful for pulse diagnostics and photon correlation measurements of mid-infrared laser sources. In the first part of this talk, I will report on QWIP structures optimized for thermal imaging applications and on the performance of QWIP thermal imagers which were jointly realized by the Fraunhofer-Institute for Applied Solid State Physics (Freiburg, Germany) and AIM Infrarot-Module GmbH (Heilbronn, Germany). In particular, a dual-band QWIP FPA with 384x288 pixels detecting simultaneously in the 8 – 12 µm long-wavelength infrared (LWIR) and 3 – 5 µm mid-wavelength infrared (MWIR) regimes was found to exhibit a noise-equivalent temperature difference as low as 20.6 mK in the LWIR and 26.7 mK in the MWIR spectral bands. The array, which is based on a photoconductive QWIP for the MWIR and a photovoltaic "low-noise" QWIP for the LWIR, allows for synchronous and pixel-registered image acquisition in both bands. This functionality yields several advantages, including better distinction between target and background clutter, operation in a much wider range of ambient conditions, and the ability of remote absolute temperature measurement. The second part of my talk will address quadratic detection involving two-photon transitions in specially designed QWIP structures. These two-photon QWIPs are exploited in autocorrelation measurements of pulsed infrared sources including the free-electron laser FELBE in Dresden.
Keywords: quantum well infrared photodetector, dual-band QWIP focal plane array, intersubband transition, two-photon detection, quadratic autocorrelation
  • Invited lecture (Conferences)
    3rd International Symposium on Photoelectronic Detection and Imaging (ISPDI 2009), 17.-19.06.2009, Beijing, China

Publ.-Id: 12909 - Permalink


Comparison of detector systems for the separation of 36Cl and 36S with a 3-MV tandem
Orlowski, T.; Forstner, O.; Golser, R.; Kutschera, W.; Merchel, S.; Martschini, M.; Priller, A.; Steier, P.; Vockenhuber, C.; Wallner, A.;
The possibility of detecting 36Cl for geological exposure dating has been explored for several years at VERA (the Vienna Environmental Research Accelerator). First results on real samples were obtained with an ionization chamber (developed at the ETH/PSI, Zürich, Switzerland) with two anodes. To improve the suppression of 36S, we equipped the ionization chamber with an exit window and added a Time-of-Flight (TOF) system with a double-sided silicon strip detector (50x50 mm2) as stop detector. We optimized the TOF setup by using silicon nitride foils to reduce scattering tails in the energy spectra.
At 3 MV terminal voltage, corresponding to a particle energy of 24 MeV of 36Cl7+, we achieved a 36S7+-suppression of 21500 (50% 36Cl-detector-efficiency).
Keywords: accelerator mass spectrometry, surface exposure dating, AMS

Publ.-Id: 12908 - Permalink


The SPIRIT project: Fast ions for everybody in Europe
Möller, W.; Kolitsch, A.; Merchel, S.; Zier, M.; The Spirit Consortium, W. S.-I. E.;
The EC-funded project SPIRIT (Support of Public and Industrial Research using Ion beam Technology) [1] started in March 2009. It will provide free transnational access to European ion beam infrastructures for users from research and industry. Besides we will improve the methods and tools for ion-beam based analysis and processing of materials by helping European researchers to carry out state-of-the-art multidisciplinary scientific and technological research.
SPRIT partners are eleven leading ion beam facilities, i.e.
• FZD Dresden-Rossendorf (management), Germany*
• Centre d’Etudes Nucléaires de Bordeaux-Gradignan, France*
• Centre de Recherche sur les Ions, les Matériaux et la Photonique, Caen & Service de Recherche en Métallurgie Physique, Saclay, France*
• Instituto Tecnológico e Nuclear, Portugal
• Jožef Stefan Institute, Ljubljana, Slovenia*
• Katholieke Universitet Leuven, Belgium*
• Ruđer Bošković Institute, Zagreb, Croatia
• Surrey Ion Beam Centre, University of Surrey, Great Britain*
• Swiss Federal Institute of Technology, Zurich, Switzerland
• Universität der Bundeswehr, München, Germany*
• Université de Pierre et Marie Curie, Paris, France
Within the project the partners use and provide fast ions (10 keV-100 MeV) for the purpose of modification and analysis of surfaces, interfaces, thin films and nanostructured systems. The partners themselves and their external users focus on fundamental and applied research spanning from material sciences over life, environmental and Earth sciences to investigations of objects from art and cultural heritage.
For example, element distributions can be determined non-destructively and standard-free by mean of ion beam analysis (IBA) including Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA), Elastic Recoil Detection Analysis (ERDA), Particle-Induced X-Ray (PIXE) and Gamma-Emission (PIGE) [2]. All natural-occurring elements are accessible; most elements with lateral, some in 3-D resolution (depth-range: nm-µm; depth-resolution: 0.5-30 nm). Typical detection limits are 10 µg/g (H), 500 µg/g - 1% (He-O), 1 µg/g (F), 10-100 µg/g (Na-U).
Seven SPIRIT partners – those marked above with a * – provide transnational access to researchers from the European Community. Help is provided to external users during planning, performance and evaluation of their research projects. Proposals [3] for running experiments in person (“hands-on”) or remote services are selected after a formal reviewing and ranking following scientific criteria as innovation/originality by an international expert panel. All costs including travel for external users are covered by the EC.
References: [1] www.spirit-ion.eu, contract number 227012. [2] C. Neelmeijer et al., this meeting. [3] http://www.spirit-ion.eu/Project/Transnational-Access/Application-Form.html.
Keywords: PIXE, PIGE, ion beam analysis, RBS, ERDA, NRA
  • Poster
    GDCh-Wissenschaftsforum Chemie 2009, 30.08.-02.09.2009, Frankfurt am Main, Deutschland

Publ.-Id: 12907 - Permalink


Optimized Detector Configurations for Particle Emission Tomography
Fiedler, F.; Braess, H.; Kunath, D.; Laube, K.; Parodi, K.; Priegnitz, M.; Shakirin, G.; Enghardt, W.;
no abstract available
Keywords: PT PET, ion therapy
  • Lecture (Conference)
    Heavy Ions in Therapy and Space Symposium 2009, 06.-10.07.2009, Köln, Deutschland

Publ.-Id: 12906 - Permalink


Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 μm
Yang, K.; Ruf, H.; Neuhaus, J.; Dekorsy, T.; Villas-Boas Grimm, C.; Helm, M.; Heumann, E.; Huber, G.; Biermann´, K.; Künzel, H.;
Saturable absorption mode-locking based on intersubband transitions in quantum wells at 2 μm.
Keywords: intersubband, laser, mode locking
  • Lecture (Conference)
    CLEO Europe, 14.-19.06.2009, München, Deutschland

Publ.-Id: 12905 - Permalink


Investigation of the Formation of Fe-filled Carbon Nanotubes
Reuther, H.; Müller, C.; Leonhardt, A.; Kutz, M. C.;
The formation of Fe-filled carbon nanotubes by thermal decomposition of ferrocene combined with a Fe-catalyst-nanostructuring on an oxidized Si substrate is investigated in the temperature range of 1015 – 1200 K. The optimal growth conditions for aligned and homogeneous carbon nanotubes are found at 1100 K. Mössbauer spectroscopy (both in transmission geometry and CEMS) was used to analyze and quantify the different formed Fe-phases. In general, a-Fe, g-Fe and Fe3C are found to form within the carbon nanotubes. Depending on the growth conditions their fractions vary strongly. Moreover, an alignment of the a-Fe in the tubes could be detected.
  • Open Access LogoJournal of Physics: Conference Series 217(2010), 012098
  • Poster
    International Conference on the Applications of the Mössbauer Effect, 19.-24.07.2009, Wien, Österreich

Publ.-Id: 12904 - Permalink


Kaons and Antikaons in Nuclear Matter: AA vs. pA Collisions
Schade, H.;
Kaons and Antikaons in Nuclear Matter: AA vs. pA Collisions
  • Lecture (Conference)
    Gemeinsame DPG Frühjahrstagung mit der European Physical Society (EuNPC) Frühjahrstagung 2009, 18.03.2009, Bochum, Deutschland

Publ.-Id: 12903 - Permalink


Transport model calculations for HADES
Schade, H.;
Transport model calculations for HADES
  • Lecture (others)
    WIP, 30.01.2009, Dresden, Deutschland

Publ.-Id: 12902 - Permalink


Transport Models for Heavy-Ion Collisions
Schade, H.;
Transport Models for Heavy-Ion Collisions
  • Lecture (Conference)
    ENLITE 2009, 03.04.2009, Dresden, Deutschland

Publ.-Id: 12901 - Permalink


Comparative investigation of the limiting solution species [U(CO3)5]6- and the crystal structure of Na6[U(CO3)5]•12H2O
Hennig, C.; Ikeda-Ohno, A.; Emmerling, F.; Kraus, W.; Bernhard, G.;
The coordination of the limiting U(IV) carbonate species in aqueous solution was investigated by comparing its structure parameters with those of the complex preserved in a crystal structure. The solution species was obtained in a aqueous solution of 0.05 M U(IV) and 1 M NaHCO3. Single crystals of Na6[U(CO3)5]•12H2O were obtained directly from this mother solution. The U(IV) carbonate complex in the crystal structure was identified as [U(CO3)5]6 anionic complex. This monomeric complex forms a network with charge compensating Na+ cations and H2O ligands. The interatomic distances around the U(IV) coordination polyhedron show average distances of U-O = 2.461(8) Å, U-C = 2.912(4) Å and U-Odist = 4.164(6) Å. U L3edge EXAFS spectra were collected from the solid Na6[U(CO3)5]•12H2O and the corresponding solution. In both samples, the first shell of the Fourier transforms (FTs) revealed ten oxygen atoms at an average distance of 2.450.02 Å, the second shell originates from five carbon atoms with a U-C distance of 2.910.02 Å, and the third shell was fit with single and multiple scattering paths of the distal oxygen at 4.170.02 Å. These data indicate the identity of the [U(CO3)5]6 complex in solid and solution state. The high negative charge of the [U(CO3)5]6 anion is compensated by Na+ cations. In solid state the Na+ cations form a bridging network between the [U(CO3)5]6 units, while in liquid state they seem to be located closer at the anionic complex. The average metal-oxygen distances of the coordination polyhedron show a linear correlation to the radius contraction of the neighbour actinide(IV) ions and indicate the equivalence of the [An(CO3)5]6 coordination within the series of thorium, uranium, neptunium and plutonium.
Keywords: U(IV) carbonate species, EXAFS, XRD

Publ.-Id: 12900 - Permalink


Double photoexcitation of 2p and 4f electrons in curium
Hennig, C.; Skanthakumar, S.; Soderholm, L.;
The L3-edge x-ray absorption spectrum of the aqua trivalent Cm ion in aqueous solution exhibits a double photoexcitation involving 2p and 4f electrons. The sharp resonance structure of the multielectron excitation reveals a shake-up process at 508.110 eV. The data indicate a monotonic increase of the [2p4f] excitation energy between elements of sixth period (Au, Hg, Pb, and Bi) and the early actinides (Th, Pa, U, Np, Pu, Am and Cm).
Keywords: Curium, EXAFS, multielectron excitation

Publ.-Id: 12899 - Permalink


Proceedings of the 16th International Conference on Ion Beam Modification of Materials
Möller, W.; Rauschenbach, B.; (Editors)
It is our pleasure to publish the Proceedings of the 16th International Conference on Ion Beam Modification of Materials (IBMM 2008), which was held at the Lecture Hall Centre of the Technische Universität at Dresden, Germany, from August 31 to September 5, 2008, under the common organization by the Forschungszentrum Dresden-Rossendorf, Dresden, Germany and the Leibniz-Institut für Oberflächenmodifizierung, Leipzig, Germany.
The biannual IBMM International Conference Series looks back on a 30-years history starting in 1978, being considered as the major international forum to present and discuss recent results in ion-related materials research and to point into the future of the field. It assembles physicists, chemists, material scientists and engineers from all over the world and along the whole chain from basic research to industrial production.
  • Book (Editorship)
    Amsterdam: Elsevier B.V. in Nuclear Instruments and Methods in Physics Research B, 2009
    544 Seiten

Publ.-Id: 12898 - Permalink


A Comparative Complexation Study on Np(V) Interactions with Bacterial Cell Wall Compartments and Bioligands Secreted by Microbes
Moll, H.; Barkleit, A.; Bernhard, G.;
Microorganisms, microbial components, biopolymers and bioligands secreted by microbes have a great potential to influence the behavior of actinides in the environment. Functional groups provided by both lipopolysaccharide (LPS: main part of the cell wall of Gram-negative bacteria), and peptidoglycan (PG: main part of the cell wall of Gram-positive bacteria) are very effective in complexing uranium(VI) over a wide pH range (2.0 to 9.0) [1, 2]. The main functionalities for uranyl binding are phosphoryl and carboxyl groups of LPS and carboxyl groups of PG. The aerobic soil bacterium Pseudomonas fluorescens (CCUG 32456 A) isolated from the aquifers at the Äspö Hard Rock Laboratory, Sweden secretes pyoverdins. These unique bioligands have a high potential to bind uranium(VI) and curium(III) mainly due to their hydroxamate and catecholate functionalities [3, 4]. However, the interaction of neptunium(V) with both microbial cell wall components (LPS, PG) and secreted bioligands (PYO) are unknown. To address this lack, we thus present findings regarding the complexation of neptunium(V) with LPS, PG, and P. fluorescens (CCUG 32456) pyoverdins (PYO) obtained using near-infrared (NIR) absorption spectroscopy.
The spectrophotometric titrations of the Np(V)-LPS system showed a dominant neptunyl(V) coordination to phosphoryl groups between pH 4 and 8 followed by hydroxyl interactions in the alkaline pH range. A very low affinity of Np(V) to interact with the carboxyl groups of PG was measured. Strong Np(V)-pyoverdin species of the type MxLyHz could be identified from the spectrophotometric titrations. Remarkable was that the influence of Np(V)-pyoverdin species could already be detected under equimolar conditions.
Estimates are possible, on the basis of the determined stability constants, if neptunium(V) prefers to interact with the microbial cell wall (LPS), with biopolymers (PG) or with the secreted pyoverdin bioligands (PYO). The calculations were performed using nearly equimolar conditions of Np(V) and functional groups of the biosystems. More than 80% of all Np(V) is bound to pyoverdin species at pH 8 compared to ~37% bound to LPS and less than 1% bound to PG. This shows both the high affinity of neptunium(V) to bioligands containing hydroxamate and catecholate groups and the importance of indirect interaction processes between neptunium(V) and bioligands secreted by resident microbes.

[1] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. 2879-2886 (2008).
[2] A. Barkleit, H. Moll, G. Bernhard, Dalton Trans. published online: DOI 10.1039/b818702a (2009).
[3] H. Moll, M. Glorius, G. Bernhard, A. Johnsson, K. Pedersen, M. Schäfer, H. Budzikiewicz, Geomicrobiol. J. 25, 157-166 (2008).
[4] H. Moll, A. Johnsson, M. Schäfer, K. Pedersen, H. Budzikiewicz, G. Bernhard, Biometals 21, 219-228 (2008).

This work was funded by the BMWi under contract number: 02E9985.
Keywords: Neptunium, NIR, Spectroscopy, Bioligands, Pyoverdins, LPS, PG, Complexation
  • Contribution to proceedings
    4th Asia-Pacific Symposium on Radiochemistry (APSORC' 09), 29.11.-04.12.2009, Napa, California, USA
  • Lecture (Conference)
    4th Asia-Pacific Symposium on Radiochemistry (APSORC' 09), 29.11.-04.12.2009, Napa, California, USA

Publ.-Id: 12897 - Permalink


Wie man schwarze Löcher füttert - Theorien und Experimente zur Magnetorotationsinstabilität
Stefani, F.;
Seit langem ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch den hydromagnetischen Dynamoeffekt erzeugt werden. Weniger bekannt ist die erstaunlich aktive Rolle, die Magnetfelder in der kosmischen Strukturbildung spielen. So sind die hohen Wachstumsraten von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, die als Magnetorotationsinstabilität (MRI) bezeichnet wird. Der Vortrag gibt eine kurze Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen aber die Flüssigmetall-Experimente der letzten zehn Jahre, in denen Dynamoeffekt bzw. MRI untersucht worden sind, insbesondere das PROMISE-Experiment am Forschungszentrum Dresden-Rossendorf.
  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 23.06.2009, Ilmenau, Deutschland

Publ.-Id: 12895 - Permalink


The influence of bottom oxide thickness on the extraction of the trap energy distribution in SONOS (silicon-oxide-nitride-oxide-silicon) structures
Bernert, K.; Oestreich, C.; Bollmann, J.; Mikolajick, T.;
The charge retention characteristics of SONOS (silicon-oxide-nitride-oxide-silicon) nonvolatile memory cells at elevated temperatures were investigated. Assuming the thermal excitation model to be the dominant charge loss mechanism, the trap energy distribution in the nitride was determined. We present an improved model which includes the influence of subsequent tunneling of the charge carriers through the bottom oxide after being thermally emitted into the conduction band of the silicon nitride. The trap energy distribution was evaluated from samples with different bottom oxide thicknesses. Using this model it was found that the detected trap energy distribution is nearly identical despite the different tunneling probabilities from the various bottom oxide thicknesses.
Keywords: SONOS memory devices, defect levels, trap energy distribution, silicon nitride

Publ.-Id: 12894 - Permalink


SIMS measurement of oxygen content in gamma-TiAl single crystals and polycrystalline alloys with Nb addition
Oswald, S.; Hermanna, R.; Schmidt, B.;
The oxygen content of binary Ti45Al55 and ternary Ti44Al52Nb4 single crystals and polycrystalline alloys
was quantified with secondary ion mass spectrometry (SIMS) using Cs+ primary ions. The SIMS measurements
were calibrated with respect to concentration and depth scale using oxygen implanted samples.
The measurements revealed considerably lower oxygen content in the ternary alloy indicating a protecting
impact of the Nb addition in grain boundaries against oxygen contamination. The relative strong
surface oxide layer thickness of the investigated samples was determined to about 1µm.
Keywords: Ti aluminides, Single crystals, Impurities

Publ.-Id: 12893 - Permalink


Boundary condition for Ginzburg-Landau theory of superconducting layers
Kolacek, J.; Lipavský, P.; Morawetz, K.; Brandt, E. H.;
Electrostatic charging changes the critical temperature of superconducting thin layers. To understand the basic mechanism, it is possible to use the Ginzburg-Landau theory with the boundary condition derived by de Gennes from the BCS theory. Here we show that a similar boundary condition can be obtained from the principle of minimum free energy.
We compare the two boundary conditions and use the Budd-Vannimenus theorem as a test of approximations.
  • Physical Review B 79(2009), 174510-1-174510-6

Publ.-Id: 12892 - Permalink


Magnetic measurements as a sensitive tool for studying dehydrogenation processes in hydrogen storage materials
Menendez, E.; Garroni, S.; Lopez Ortega, A.; Estrader, M.; Liedke, M. O.; Fassbender, J.ORC; Solsona, P.; Surinach, S.; Baro, M. D.; Nogues, J.
Magnetic characterization is shown to be a highly effective, nondestructive, and commonly available method to accurately assess dehydrogenation temperatures and further clarify the reaction mechanisms during dehydrogenation in systems with superconducting or ferromagnetic constituents. As examples, the dehydrogenation temperature of NaBH4 in a nanostructured NaBH4/MgH2 system and the dehydrogenation process of nanostructured Mg2CoH5, based on the superconducting and ferromagnetic properties of MO, and Co, respectively, are determined.
Keywords: hydrogen storage, superconductivity, ball-milling, nanocrystals, SQUID
  • Journal of Physical Chemistry C 114(2010)39, 16818-16822

Publ.-Id: 12891 - Permalink


Conserving T-matrix theory of superconductivity
Sopik, B.; Lipavský, P.; Männel, M.; Morawetz, K.;
A selfconsistent T-matrix theory of many-Fermion systems is proposed. In the normal state the theory agrees with the Galitskii-Feynmann approximation, in the superconducting state it has the form of the renormalized Kadanoff-Martin approximation. The two-particle propagator satisfies the Baym-Kadanoff symmetry condition which guarantees that the theory conserves the number of particles, momentum and energy. The theory is developed for retarded interactions leading to the Eliashberg theory in the approximation of a single pairing channel.

Publ.-Id: 12890 - Permalink


Hydrogen micro-kinetics in titanium under mechanical stress studied by ion beam analysis
Wang, T. S.; Lv, H. Y.; Grambole, D.; Yang, Z.; Peng, H. B.; Han, Y. C.;
Hydrogen (H) is continuously produced by the large dose fast neutron irradiation on fusion reactor material. The concentration, diffusion and evolution of H in the structure material may cause H-embrittlement. Ion beam analysis is one of the most useful methods for studying the micro-kinetics of H in solids. In this work, the H-distribution in titanium (Ti) has been studied by resonance nuclear reaction analysis (resonance-NRA) and micro-elastic recoil detection analysis (micro-ERDA). The evolution of H-depth-profile in titanium samples has been studied versus the change of normal stress. Evident H diffusion has been observed, while a normal stress is changed in the range of 107-963 MPa. The H diffusion is related to the concentration of H in samples.

Publ.-Id: 12889 - Permalink


Self-organized ripple patterns by ion erosion - experiment, theory, and application
Keller, A.; Facsko, S.; Möller, W.;
It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces can lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. These ripple structures have been found on a large variety of materials, including semiconductors, metals, and insulators. The formation and early evolution of the ripple patterns can be described by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account, leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
This talk will provide an overview of ion-induced pattern formation and summarize the theoretical basics. Recent experimental results on the evolution of nanoscale ripple patterns on silicon surfaces during high-fluence ion sputtering will be presented and compared to the predictions of different continuum models. In addition, promising applications of nanorippled substrates as templates in thin film growth will be discussed.
  • Lecture (others)
    Seminar, 16.06.2009, Wien, Austria

Publ.-Id: 12888 - Permalink


Photoluminescence enhancement in Si+ implanted PMMA
Tsvetkova, T.; Balabanov, S.; Avramov, L.; Borisova, E.; Angelov, I.; Sinning, S.; Bischoff, L.;
Silicon ion implantation effects on the optical and photoluminescence (PL) properties of polymethylmethacrylate (PMMA) have been studied. Low-energy ion implantation (E = 30-50 keV) was carried out over a range of different ion fluences (D = 10(13)-10(17) cm(-2)). Visible PL and optical transmission spectra in the range (330-800 nm) have been measured. The existing visible range PL emission in the unimplanted PMMA samples is clearly affected by the Si+ ion implantation and the observed modification effect of photoluminescence enhancement (PLE) is essentially dependent on the implantation fluence. For certain fluences, dependent on the ion energy, the overall amplitude of the PL emission has a several times (similar to 5 times) increase. Optical absorption also gradually increases with the fluence.
Keywords: Si -implantation; PMMA; Photoluminescence

Publ.-Id: 12887 - Permalink


The correlation between mechanical stress, thermal shift and refractive index in HfO2, Nb2O5, Ta2O5 and SiO2 layers and its relation to the layer porosity
Stenzel, O.; Wilbrandt, S.; Kaiser, N.; Vinnichenko, M.; Munnik, F.; Kolitsch, A.; Chuvilin, A.; Kaiser, U.; Ebert, J.; Jakobs, S.; Kaless, A.; Wüthrich, S.; Treichel, O.; Wunderlich, B.; Bitzer, M.; Grössl, M.;
We present extended experimental material about optical and mechanical properties of oxide optical coating materials, deposited by electron beam evaporation, ion and plasma ion assisted evaporation, sputtering and ion plating. A clear correlation between these experimental data is established and understood as being caused by the different degree of the porosity of the films. This assumption has been verified by investigation of the layer structure and accompanying simulations of the effect of porosity on refractive index, layer stress and thermal shift. As a practical conclusion, we find that a certain pore fraction in the films is essential in order to get a valuable balance between optical and mechanical coating properties.
Keywords: metal oxide films, electron beam evaporation, ion and plasma assisted evaporation, magnetron sputtering, ion plating, high-refractive index, low extinction, mechanical properties

Publ.-Id: 12886 - Permalink


Sorption properties of the NaBH4/MgH2 system: dehydrogenation mechanism and pathway
Garroni, S.; Menendez, E.; Lopez Ortega, A.; Estrader, M.; Milanese, C.; Nolis, P.; Nogues, J.; Surinach, S.; Baro, M. D.;
Nanostructured NaBH4/MgH2 composites have established themselves as promising materials for hydrogen storage applications due to their high gravimetric capacity, large hydrogen volumetric density and rather low dehydrogenation temperature compared to that one corresponding to the single compounds. Actually, further research on the NaBH4/MgH2 system could lead to an enhanced understanding of more complex reactive hydride composites, such as Ca(BH4)2/MgH2 or LiBH4/MgH2.

As-received NaBH4 and MgH2 powders were mixed, in a 2 to 1 molar ratio (2NaBH4/MgH2) and ball-milled to obtain nanostructured composites. The milling processes were carried out for diverse times, under Ar atmosphere, in a Spex mill with a ball-to-powder mass ratio of 10:1.

In-situ synchrotron x-ray powder diffraction indicates that the dehydrogenation process starts at around 210 C, with the desorption of the MgH2 to Mg, and rpoceeds with the chemical dismutation of NaBH4 in NaH and a possible intermediate specie, such as Na2B12H12. In fact, solid-NMR seems to confirm the existence of the transitional compound. However, the temperature onset of the dehydrogenation process of the NaBH4 counterpart has not yet been fully elucidated and, since it is difficutls to establish from either x-ray diffraction or thermogravimetric analyiss, magnetic hcaracterization is proposed as an alternative technique, which takes advantage of the superconducting nature of the MgB2 phase, to further study dehydrogenation processes.
Keywords: hydrogen storage, XRD, magnetic characterization, ball-milling
  • Lecture (Conference)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Publ.-Id: 12885 - Permalink


Verfahren zur Bewegungskorrektur
van den Hoff, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    19. Jahrestagung der Gesellschaft für Nuklearmedizin Sachsens, 19.-20.06.2009, Nimbschen, Deutschland

Publ.-Id: 12884 - Permalink


Neue Radiotracer für die Tumorbildgebung
Pietzsch, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    19. Jahrestagung der Gesellschaft für Nuklearmedizin Sachsens, 19.-20.06.2009, Nimbschen, Deutschland

Publ.-Id: 12883 - Permalink


Onkologische Pharmazie versus Radiopharmazie
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Onkologisch-pharmazeutischer Fachkongress, 12.-13.06.2009, Dresden, Deutschland

Publ.-Id: 12882 - Permalink


Labelling of bio-macromolecules: Challenge in radiolabelling for radiopharmacy
Steinbach, J.;
Over the last two decades, radiolabeled antibodies and peptides have been introduced in research and in clinical application of nuclear medicine. Such substances are utilized for tumor targeting as radiotracers and for therapeutic purposes as well. Labelling of such substances with PET radionuclides such as F-18 offers the chance of introduction the label without drastic changes of the molecular properties in conjunction with highest image quality, i.e. high diagnostic value. Radiometal-labeled bioactive substances offer both: The possibility of diagnostics and therapeutic intervention as well. However, the labelling procedure is a considerable alteration of the molecules radiopharmacological properties. This is due to the need of introducing a chelating moiety to bind the radiometals kinetically and thermodynamically inert. Beside this geometric impact, the labelling conditions are of highest importance. Whereas peptides may withstand rather drastic conditions, proteins e.g. antibodies need ambient labelling conditions such as aqueous solution, room temperature, near physiological pH. Furthermore, various proteins tend to coagulate in the presence of heavy metals as radio-copper.
The talk will present such results of scientific investigations at the Institute of Radiopharmacy during the last five years. This involves the application of established methods such as the use of [18F]SFB (N-succinimidyl-4-[18F]fluorobenzoate) for labelling of biomolecules, the development of alternative labelling agents/prosthetic groups as well as current efforts to establish methods for pre- and postlabelling with radiometals. All these investigations are directed to corresponding applications with biomolecules and bioactive compounds, respectively.
  • Invited lecture (Conferences)
    16th Biennial Congress of the György Hevesy Hungarian Society of Nuclear Medicine (MONT), 02.-04.07.2009, Debrecen, Hungary
  • Open Access LogoAbstract in refereed journal
    Nuclear Medicine Review 12(2009)1, 31

Publ.-Id: 12881 - Permalink


18F-Radiotracer: Von der Grundlagenchemie zur Anwendungsrelevanz
Steinbach, J.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Pharmazeutisch-lebensmittelchemisches Kolloquium, Westfälische Wilhelms-Universität Münster, 23.09.2009, Münster, Deutschland

Publ.-Id: 12880 - Permalink


Electromagnetic flow control during solidification of AlSi-alloys using time-modulated AC magnetic fields
Räbiger, D.; Nikrityuk, P. A.; Leonhardt, M.; Eckert, S.; Eckert, K.;
This paper considers the directional solidification of Al-Si alloys from a water cooled copper chill. Melt stirring during solidification has been realised by utilising time-modulated AC magnetic fields in two different variants: (1) an RMF applied in form of a pulse sequence with a periodic inversion of the direction of rotation between two consecutive pulses and (2) a combination of rotating (RMF) and travelling magnetic fields (TMF), whereas both fields are implemented subsequently in form of rectangular pulses. Our results demonstrate that the melt agitation using modulated magnetic fields offers a considerable potential for a well-aimed modification of casting properties by an effective control of the flow field, but, this goal requires an optimisation of the magnetic field onfiguration with respect to the particular solidification parameters.
Keywords: electromagnetic melt stirring, rotating magnetic field (RMF), travelling magnetic field (TMF), solidification, grain refinement
  • Contribution to proceedings
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 624-627
  • Lecture (Conference)
    EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

Publ.-Id: 12879 - Permalink


Comparison of the structural developments in the C:Ni films grown by ion beam sputtering and pulsed filtered cathodic vacuum arc
Abrasonis, G.; Kovacs, G. J.; Ryves, L.; Mücklich, A.; Krause, M.; Munnik, F.; Oates, T. W. H.; Bilek, M. M. M.; Kolitsch, A.; Möller, V.;
he structure of C:Ni nanocomposite thin films grown by ion beam sputtering (IBS) and pulsed filtered cathodic vacuum arc (PFCVA) is compared. The films were grown in the temperature (T) and Ni concentration ranges of RT-500C and 7-40 at.%, respectively. The composition of the films and elemental depth profiles were determined by elastic recoil detection analysis (ERDA). The morphology and phase composition were investigated by transmission electron microscopy and x-ray diffraction, respectively. Independent of the growth method the Ni dispersed phase is carbidic for T<=300C and mostly fcc metallic at higher deposition temperatures. In the C:Ni films grown by IBS the transition from globular towards columnar growth occurs at 200
  • Lecture (Conference)
    E-MRS 2009 Spring Meeting,, 08.-12.06.2009, Strasbourg, France
  • Publ.-Id: 12878 - Permalink


    Grain refinement in Al-Si Alloys by inoculation and electromagnetic stirring
    Räbiger, D.; Metan, V.; Leonhardt, M.; Eigenfeld, K.; Eckert, S.;
    The present study concerns the directional solidification of grain-refined and non-refined AlSi7 alloys under the influence of a travelling magnetic field (TMF). An upwards travelling field has been applied to provide a forced convection within the solidifying melt. The formation of a fine equiaxed structure is favoured by both the addition of grain refining AlTi5B1-particles and electromagnetic stirring as well, whereas the addition of grain refiners into the melt appears to be more efficient for achieving a reduction of the mean grain size. A minimum grain size has been observed of the electromagnetic agitation of a grain-refined alloy. A melt stirring by a sufficiently high magnetic field provides a homogeneous grain size distribution in the sample volume.
    Keywords: grain refinement, solidification, electromagnetic stirring, travelling magnetic field (TMF)
    • Contribution to proceedings
      EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 334-337
    • Poster
      EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

    Publ.-Id: 12877 - Permalink


    Liquid metal flow in a cylinder during the spin-up of a rotating magnetic field
    Räbiger, D.; Eckert, S.; Gerbeth, G.;
    This experimental study is concerned with the secondary meridional flow during the time if the fluid spins up from rest. A cylindrical cavity with an aspect ratio of unity is filled with liquid metal and suddenly exposed to an azimuthal body force generated by a rotating magnetic field (RMF). Vertical profiles of the axial velocity have been measured by means of the ultrasound Doppler velocimetry. Our experimental results show an excellent agreement with recently published numerical results with respect to the laminar spin-up and the onset of linear three-dimensional instabilities in RMFdriven flows.
    Keywords: spin-up, rotating magnetic field (RMF), time-modulated RMF
    • Contribution to proceedings
      EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany, pp. 69-72
    • Lecture (Conference)
      EPM 2009, 6th International Conference on Electromagnetic Processing of Materials, 20.-22.10.2009, Dresden, Germany

    Publ.-Id: 12876 - Permalink


    Quantitative ion beam analysis of ultra thin films with magnetic spectrometers using heavy MeV ions
    Kosmata, M.; Grötzschel, R.; Munnik, F.; Vieluf, M.; Möller, W.;
    The aim of a combination of magnetic spectrometers with ion beam analysis techniques is to measure concentration profiles in thin layers with sub-nanometer depth resolution. For these measurements heavy ions from a MV-ion accelerator are directed to the sample. Scattered primary ions or ejected recoil atoms are detected and energy analysed under forward angles. The depth resolution depends directly on the energy resolution of the spectrometer. High energy resolution can only be obtained using magnetic particle spectrometers, where the energy measurement is transformed into a position measurement at the focal plane.
    The depth scale is provided by the stopping power of energetic heavy ions moving in matter. The yet produced data are only valid for dynamic charge state equilibrium due to electron loss and capture along the ion trajectory. In the case of ultra thin layers the path length of the particles are too short to achieve this equilibrium. Since magnetic spectrometers separate particles with identical energy but different charge states, it is necessary to consider charge state dependent stopping cross sections for quantitative data analysis. Here only very few data are available in the literature.
    In this work, we introduce quantitative ion beam analysis of ultra thin films with magnetic spectrometers.
    1. the Quadruple-Quadrupole-Dipole-Sextupole spectrometer “Little John” to measure concentration profiles and charge state distribution of light ions.
    2. The Browne-Buechner spectrometer, which is designed to measure samples with heavy atoms.
    Keywords: magnetic spectrometer, ion beam analysis, concentration profile, thin layer, high resolution, nonequilibrium charge state, QQDS, Little John
    • Invited lecture (Conferences)
      5th International Workshop on High-Resolution Depth Profiling, 15.-19.11.2009, Kyoto, Japan

    Publ.-Id: 12875 - Permalink


    Ionenstrahlanalyse ultradünner Schichten mit Nanometertiefenauflösung
    Kosmata, M.; Grambole, D.; Grötzschel, R.; Möller, W.; Munnik, F.; Neelmeijer, C.; Vieluf, M.;
    Die quantitative Elementanalytik von Schichten und Schichtabfolgen im Dickenbereich weniger Nanometer ist in den letzten Jahren in den Fokus aktueller Forschung gerückt. Im Mittelpunkt dieser materialwissenschaftlichen Fragestellungen steht die Bestimmung von Tiefenverteilungen von Elementen in dünnen Schichten, die durch spezielle Abscheideverfahren oder nachfolgende Prozessschritte wie Temperung erzielt werden, aber auch der Nachweis unbeabsichtigter Kontamination in den Schichten. Daraus können Informationen im Hinblick auf gezielte Materialentwicklung gewonnen werden und die Qualität bestehender Prozessführungen lässt sich bewerten.
    Die meisten konventionellen (nicht nuklearen) Analyseverfahren sind zur Quantifizierung ihrer Ergebnisse in der Regel auf Referenzmaterialien (gleicher Matrix) angewiesen. Im Gegensatz dazu kann die Ionenstrahlanalyse (ion beam analysis, IBA) standardfrei betrieben werden. Der physikalische Prozess, auf der alle Methoden der IBA beruhen, ist die binäre Wechselwirkung von MeV-Ionen mit den Atomkernen in den Schichten. Diese Wechselwirkung, elastische Streuung oder Kernreaktion, ist einfach und genau beschreibbar; kollektive Matrixeffekte treten dabei nicht auf.
    Am Ionenstrahlzentrum des Forschungszentrums Dresden-Rossendorf kommen hauptsächlich drei Analysemethoden zur Anwendung:
    • Kernreaktionsanalyse (Nuclear Reaction Analysis, NRA) zum tiefenabhängigen Nachweis von Wasserstoff über die resonante Kernreaktion 1H(15N,αγ)12C*
    • Rutherford-Rückstreuspektrometrie (Rutherford Backscattering Spectrometry, RBS) insbesondere zur Detektion von Elementen mit Ordnungszahlen Z > 14
    • Detektion elastisch rückgestossener Atome (Elastic Recoil Detection Analysis, ERDA) zum Nachweis leichter Elemente mit Z = 2-14 (He-Si)
    Die zur Messung ultradünner Schichten mit RBS und ERDA erforderliche Tiefenauflösung (< 1 nm) kann mit Teilchenspektrometern mit höchster Energieauflösung erreicht werden.
    .
    Keywords: Nanometer, subnanometer, ultradünn, ultra dünn, ultra thin, standardfrei, Ionenstrahlanalyse, ion beam analysis, IBA, Kernreaktionsanalyse, muclear reaction analysis, NRA, Wasserstoff, Wasserstoffnachweis, 1H(15N,αγ)12C, Rutherford-Rückstreuspektrometrie, Rutherford Backscattering Spectrometry, RBS, Elastic Recoil Detection Analysis, ERDA, Tiefenauflösung, Spektrometer, Massenspektrometer, QQDS, Little John, Browne Buechner
    • Lecture (Conference)
      15. Tagung Festkörperanalytik, 12.-16.07.2009, Chemnitz, Deutschland
    • Poster
      15. Tagung Festkörperanalytik, 12.-16.07.2009, Chemnitz, Germany

    Publ.-Id: 12874 - Permalink


    Release of light elements from ultra thin films during high resolution depth profiling using heavy ion ERDA
    Kosmata, M.; Grötzschel, R.; Munnik, F.; Vieluf, M.; Möller, W.;
    The modified QQDS magnetic spectrometer “Little John” [1] at the Forschungszentrum Dresden-Rossendorf is aimed to measure concentration profiles of light elements in thin layers with sub-nanometre depth resolution by Elastic Recoil Detection Analysis (ERDA). Of particular interest are various ultra thin films of metal oxides, nitrides and of carbon compounds. For these measurements heavy ions from the 5 MV-Tandem accelerator are directed to the sample. The ejected recoil atoms are detected and their energy is analysed under forward angles (15°, 30°, 45°, or 60°). Due to the low solid angle of the QQDS spectrometer of about 0.5 msr rather high fluences of initial heavy ions have to be applied. Therefore, special care must be taken to minimize layer deterioration and decomposition by preferential release of elements from the film. To identify optimum measurement conditions and perform final corrections for quantification of high resolution results, we studied the release of oxygen as a function of beam fluence. Thus, different oxides have been irradiated with Cl-, Cu- and I-ions in the energy range from 15 to 40 MeV. We could validate the earlier reported [2] dependency of oxygen loss on
    • angle of incidence
    • kind and energy of incoming ion
    • stopping power
    • layer thickness
    for SiO2. Similar results have been yet found for La2O3. Further experiments on materials relevant for microelectronics as e.g. high k-dielectrics as HfO2 or ZrO2 are foreseen for the very near future and, thus, will be presented.

    References: [1] H.J. Gils et al., Nucl. Instr. and Meth. A276 (1989) 151. [2] W.M. Arnoldbik et al., Nucl. Inst. and Meth. B203 (2003) 151.
    .
    Keywords: magnetic spectrometer, thin layers, thin films, high depth resolution, ERDA, elastic recoil detection, Little John, QQDS, quantification, release of oxygen, irradiation, electronic sputtering
    • Poster
      19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, United Kingdom

    Publ.-Id: 12873 - Permalink


    CONCAST: A liquid metal model for continuous steel casting
    Timmel, K.; Eckert, S.; Gerbeth, G.; Claussner, J.; Schlenk, R.; Voigtländer, J.;
    Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows being relevant for metallurgical applications. In this paper we present the new experimental facility CONCAST for modeling the continuous casting process of steel by using the low melting point alloy SnBi. The facility operates at temperatures of 200°C-400°C. Main parameters of the facility and dimensions of the test sections will be shown. The resultant possibilities with respect to flow investigations in tundish, submerged entry
    nozzle and mould will be discussed.
    Keywords: continuous casting, liquid metal model, flow investigation
    • Poster
      6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland
    • Contribution to proceedings
      6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, 251-254

    Publ.-Id: 12872 - Permalink


    Flow investigations in an isothermal liquid metal model of the continuous casting process
    Timmel, K.; Galindo, V.; Miao, X.; Eckert, S.; Gerbeth, G.;
    The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. First experimental results will be presented which have been obtained using a small-scale experimental set-up with the room temperature alloy GaInSn. Measurements of the liquid flow in the mold will be compared with accompanying numerical calculations. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied.
    Keywords: continuous casting, liquid metal model, flow measurement, ultrasound doppler velocimetry, electromagnetic brake
    • Lecture (Conference)
      6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland
    • Contribution to proceedings
      6th International Conference on Electromagnetic Processing of Materials, 19.-23.10.2009, Dresden, Deutschland, 231-234

    Publ.-Id: 12871 - Permalink


    Fluorine-18 radiolabeling of native and oxidized proteins: An important tool in the pathophysiologists’ toolbox
    Pietzsch, J.; Wuest, F.;
    The systematic development and improvement of a methodology for mild radiolabeling of both native and modified proteins with the short-lived positron emitter fluorine-18 (18F) under physiological conditions is reported. The presented methodology is an attractive alternative to protein and lipoprotein radiolabeling methods using iodine or metal radionuclides and, particularly, can be applied for functional characterization of both native and oxidized protein species in vivo by means of positron emission tomography (PET).
    • Chimica Oggi - Chemistry Today 27(2009), 12-14

    Publ.-Id: 12869 - Permalink


    Sorption of Np(V) and Np(IV) onto kaolinite: Effects of pH, ionic strength, carbonate and humic acid
    Schmeide, K.; Bernhard, G.;
    The sorption of Np(V) and Np(IV) onto kaolinite has been studied in the absence and presence of humic acid (HA) in a series of batch equilibrium experiments under different experimental conditions: [Np]0: 1.0x10-6 or 1.0x10-5 M, [HA]0: 0 or 50 mg/L, I: 0.01 or 0.1 M NaClO4, solid to liquid ratio: 4 g/L, pH: 6-11, anaerobic or aerobic conditions.
    The results showed that the Np(V) sorption onto kaolinite is effected by solution pH, ionic strength, Np concentration, presence of carbonate and HA. In the absence of carbonate, the Np(V) uptake increased with pH up to ~ 96% at pH 11. HA further increased the Np(V) sorption between pH 6 and 9 but decreased the Np(V) sorption between pH 9 and 11. In the presence of carbonate, the Np(V) sorption increased with pH and reached a maximum of 54% between pH 8.5 and 9. At higher pH values, the Np(V) sorption decreased due to the presence of dissolved neptunyl carbonate species with a higher negative charge that were not sorbed onto the kaolinite surface which is negatively charged in this pH range. HA again decreased the Np(V) uptake in the near-neutral to alkaline pH range due to formation of aqueous neptunyl humate complexes. The decrease of the initial Np(V) concentration from 1.0x10-5 M to 1.0x10-6 M led to a shift of the Np(V) adsorption edge to lower pH values. A higher ionic strength increased the Np(V) uptake onto kaolinite in the presence of carbonate but had no effect on Np(V) uptake in the absence of carbonate.
    To the best of the author`s knowledge, the sorption of Np(IV) onto kaolinite in the presence of HA was studied the first time. For this, a synthetic HA with pronounced reducing properties was applied. This HA effectively reduced Np(V) to Np(IV) and stabilized the tetravalent oxidation state during sorption experiments over a wide pH range. The Np(IV) uptake onto kaolinite is strongly effected by HA. Especially in the near-neutral pH range the Np(IV) uptake was found to be very low in the presence of HA which was attributed to the strong Np(IV) humate complexation in solution.
    Thus, depending on the prevailing geochemical conditions, HA has an immobilizing as well as a mobilizing effect on Np(V). In case of Np(IV), the mobilizing effect predominates.
    Keywords: Neptunium, Adsorption, Tetravalent, Humic matter, Clay, Kaolinite

    Publ.-Id: 12868 - Permalink


    Resonant enhancement of second order sideband generation for intraexcitonic transitions in GaAs/AlGaAs multiple quantum wells
    Wagner, M.; Schneider, H.; Winnerl, S.; Helm, M.; Roch, T.; Andrews, A. M.; Schartner, S.; Strasser, G.;
    We present an experimental study on efficient second order sideband generation in symmetric undoped GaAs/AlGaAs multiple quantum wells. A near-infrared laser tuned to excitonic interband transitions is mixed with an in-plane polarized terahertz beam from a free-electron laser. The terahertz beam is tuned either to the intraexcitonic heavy-hole 1s-2p transition or to the interexcitonic heavy-hole light-hole transition. We find strong evidence that the intraexcitonic transition is of paramount influence on n=+-2 sideband generation, leading to an order-of-magnitude resonant enhancement of the conversion efficiency up to 0.1% at low temperature. At room temperature, the efficiency drops only by a factor of 7 for low terahertz powers.
    Keywords: THz sidebands, nonlinear mixing, free-electron laser, FEL

    Publ.-Id: 12867 - Permalink


    High-resolution gas-oil two-phase flow visualization with a capacitance wire-mesh sensor
    Da Silva, M. J.; Thiele, S.; Abdulkareem, L.; Azzopardi, B. J.; Hampel, U.;
    The application of a novel wire-mesh sensor based on electrical capacitance (permittivity) measurements for the investigation of gas-oil two-phase flow in a vertical pipe of 67 mm diameter under industrial operating conditions is reported in this article. The employed wire-mesh sensor can be operated at up to 5,000 frames per second acquisition speed and at a spatial resolution of 2.8 mm. By varying gas and liquid flow rates different flow patterns, such as bubbly, slug and churn flow, were produced and investigated. From the images of gas void fraction distribution quantitative flow structure information, such as time series of cross-sectional void fraction, radial void fraction profiles and bubble size distributions, was extracted by special image processing algorithms.
    Keywords: wire-mesh sensor, phase distribution, two-phase flow, flow visualization, void fraction

    Publ.-Id: 12866 - Permalink


    Bedeutung von Experimenten für die Reaktorsicherheit
    Teschendorff, V.; Glaeser, H.; Kliem, S.;
    Experimente waren von Beginn der Reaktortechnik an bis heute Grundlage der Sicherheit und können auch durch weiterentwickelte Rechenmethoden nicht vollständig ersetzt werden. Der Weiterbetrieb unserer laufenden Reaktoren muss von aktiver Sicherheitsforschung begleitet werden, die Experimente mit innovativer Messtechnik einschließt. Der Wirksamkeitsnachweis passiver Sicherheitseinrichtungen bei Gen-III Reaktoren basiert auf spezifischen Experimenten. Neue Experimente zur Sicherheit von Gen-IV-Reaktoren sind parallel zum Design durchzuführen. Deutsche Versuchsanlagen sind unverzichtbar zum Kompetenzerhalt und als Beitrag im internationalen Verbund.
    • Invited lecture (Conferences)
      Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    • Contribution to proceedings
      Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
      Tagungsband der Jahrestagung Kerntechnik 2009; Fachsitzung: Thermohydraulische Experimente für Reaktoren der Generation II - III, Berlin: INFORUM GmbH
    • atw - International Journal for Nuclear Power 55(2010)03, 163-173

    Publ.-Id: 12865 - Permalink


    Ultra fast electron beam x-ray CT scanner for two phase flow measurement
    Fischer, F.; Hampel, U.;
    Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm x 1.5 mm active pixel area. X-ray radiation is produced on a circular water cooled tungsten target The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. On the basis of these data we developed image processing algorithms which enable to extract information on bubble shapes, bubble size distributions and interfacial area density distribution. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.
    Keywords: Two-phase flow, electron beam tomography, CFD code validation
    • Lecture (Conference)
      Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    • atw - International Journal for Nuclear Power (2009)7, 461-464

    Publ.-Id: 12864 - Permalink


    Correlation between morphology and bonding structure in titanium oxide films produced by reactive pulsed magnetron sputtering
    Gago, R.; Redondo-Cubero, A.; Vinnichenko, M.; Jiménez, I.; Czigány, Z.; Vázquez, L.;
    Titanium dioxide (TiO2) thin films have been grown by reactive pulsed magnetron sputtering (PMS) under different O2 partial pressures in an O2/Ar atmosphere. The films were analyzed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), X-ray absorption near edge structure (XANES), grazingincidence X-ray diffraction (GIXRD) and transmission electron microscopy (TEM). RBS shows that stoichiometric TiO2 films are obtained even at low O2 fraction in the process gas (O2/Ar > 0.05). The formation of mixed or dominant amorphous, rutile and anatase atomic arrangements during PMS has been assessed by XANES and GIXRD as a function of the O2 partial pressure. Further, a clear structural evolution with film thickness (derived by SE) has been detected by AFM and TEM, its dynamics driven by the O2 availability in the gas. Interestingly, this evolution leads to a correlation between the surface morphology and the relative content of the rutile phase, resulting in a nanoscale lateral modulation of the surface properties. Growth experiments varying substrate temperature and bias voltage have been also conducted for further control over the film evolution and to deepen in the growth mechanisms.
    Keywords: reactive pulsed magnetron sputtering, TiO2, rutile, anataze
    • Poster
      EMRS Spring Meeting 2009, 08.-12.06.2009, Strasbourg, France

    Publ.-Id: 12863 - Permalink


    Optical and magnetic properties of indium oxides implanted with Cr
    Scarlat, C.; Zhou, S.; Vinnichenko, M.; Kolitsch, A.; Bürger, D.; Fassbender, J.ORC; Potzger, K.; Shalimov, A.; Grenzer, J.; Helm, M.; Schmidt, H.
    Dilute magnetic oxides are expected to play a key role in the development of electronics using the electron spin rather than its charge as information carrier. Indium oxide (IO), a transparent conductive material, is of potential interest for spintronics [1] due to its unique combination of magnetic, electrical, and optical properties. Highly oxygen deficient Cr:IO co-evaporated films revealed ferromagnetism [2]. In present work, we report the post-growth treatment effect on the structural, electrical, magnetic, and optical properties of Cr-implanted IO films. Cr is chosen as a dopant because of its large magnetic moment in the ionic state, and its antiferomagnetic nature in the bulk, ruling out the extrinsic origin of the ferromagnetism if Cr metal segregation occurs. It is non-trivial to form any ferromagnetic secondary phase of Cr oxide. Polycrystalline and amorphous, ca. 300 nm thick IO films were grown on SiO2/Si substrates using reactive pulsed magnetron sputtering and then implanted with Cr+ ions (1, 2, 3, 4 and 5 at% of Cr). The implantation energy was 120 keV. The magnetic-field dependence of magnetization of 2%Cr:IO showed a weak ferromagnetic behavior at 5K. A reasonable model for the Cr implanted IO films has been developed to extract optical constants from spectroscopic ellipsometry data below 3 eV. [1] C. Scarlat et al., Proceedings IBMM 2008, August 31- September 05, 2008, Dresden, Germany [2] J. Philip et al., Nature materials 5, 298 (2006).
    • Poster
      E-MRS 2009 Spring Meeting, 08.-12.06.2009, Strasbourg, France

    Publ.-Id: 12862 - Permalink


    Ultrasound Doppler array measurement system for two-dimensional flow investigations in liquid metals
    Franke, S.; Büttner, L.; Czarske, J.; Räbiger, D.; Eckert, S.;
    This paper presents a specific ultrasound Doppler measurement system for investigations of the velocity field in electromagnetically driven liquid metal flows. Two orthogonally arranged ultrasound sensor line arrays facilitate a two-dimensional measurement of two velocity components (2d/2c) within a square area of 70 x 70 mm². The line array elements are controlled by a specific multiplex mode to achieve both a high spatial and a high temporal resolution. The sensor design, the control electronics and the mode of operation of the measurement system are described. Preliminary results of velocity measurements in a liquid metal flow driven by a rotating magnetic field (RMF) are presented.
    Keywords: Liquid metal, flow measurement, Ultrasound Doppler method, Sensor array
    • Lecture (Conference)
      6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland
    • Contribution to proceedings
      6th International Conference on Electromagnetic Processing of Materials (EPM 2009), 19.-23.10.2009, Dresden, Deutschland, 978-3-936104-65-3, 411-414

    Publ.-Id: 12861 - Permalink


    Impact of wetting on velocity measurements in liquid metal flows
    Eckert, S.; Buchenau, D.; Gerbeth, G.; Stefani, F.; Weiß, F.-P.; Wondrak, T.;
    Flow measurements are an important issue to ensure the safe and reliable operation of liquid metal systems. In many cases the measuring apparatus is influenced by the wetting between the metal melt to be measured and the sensor or the inner wall of the fluid vessel. In this presentation we report about specific experiences obtained from laboratory experiments using different measuring techniques in various liquid metal flows.
    Keywords: Liquid metal, Wetting, Flow measurement, Ultrasound Doppler Method, Electromagnetic flow meter, Inductive flow tomography
    • Lecture (Conference)
      3rd International Seminar "Coolants and Innovative Reactor Technologies", 06.-07.07.2009, Aix-en-Provence, France

    Publ.-Id: 12860 - Permalink


    Micro-ERDA measurements of hydrogen distribution in natural Pd–Pt compounds
    Munnik, F.; Cabral, A. R.; Lehmann, B.;
    Micro-ERDA is a unique technique for the measurement of the 2.5D distribution of hydrogen. In this work, this technique is applied to geological samples and in particular Pd–Pt-containing compounds found at the Serra Pelada Au–Pd–Pt deposit. This deposit triggered the most spectacular gold rush in the Amazon region of Brazil in recent history. The sample material is especially important because it represents a novel mineralization style of platinum-group elements.
    The sample material was taken from a drill core, filled with resin since it was porous rock, cut and polished. The samples were analysed by simultaneous measurements of PIXE and ERDA with the Dresden-Rossendorf Nuclear Microprobe using a 2 MeV He ion beam. The angle of incidence between beam and sample surface was 15°. The PIXE maps were used to locate the areas of interest because the exact beam position on the target is very critical with this incidence angle. PIXE was also used to determine the matrix composition that is needed for the stopping power calculation in the ERDA analysis.
    The results of the measurements and its interpretation are presented. The measurements confirm the presence of hydrogen in the Pd–Pt compounds (either as hydroxide, or hydrated oxide), so far only suspected, and help to better understand the formation process of Pd–Pt mineralization in oxic near-surface environments.
    • Poster
      19th International Conference on Ion Beam Analysis, 07.-11.09.2009, Cambridge, United Kingdom

    Publ.-Id: 12859 - Permalink


    Investigation of luminescence properties of dendritic ligands, molecular clips and flavylium salts by time resolved spectroscopy
    Raditzky, B.;
    Photochemical and photophysical characterization of novel supramolecular host compounds: Dendritic cyclams, molecular clips and flavylium salts. Result overview of working group collaborations within the COST Action D31.
    • Poster
      COST Action D31 4th Workshop, 28.-30.05.2009, Warszawa, Poland

    Publ.-Id: 12858 - Permalink


    NanoFoto - Neue Wege zur verwertungsorientierten Netzwerkbildung in der Nanobiotechnologie (Schlussbericht)
    Raff, J.; Günther, T.; Marquard, A.; Kutschke, S.; Pollmann, K.; Roos, S.; Hofinger, J.; Meyer, A.;
    Wissenschaftliches Ziel des Vorhabens ist die Entwicklung von fotokatalytisch aktiven Verbundmaterialien zum Abbau von organischen Verbindungen (z. B. Arzneistoffen) in Wasser. Diese Verbundmaterialien beruhen auf der Beschichtung von Trägermaterialien mit ZnO/TiO2-Nanopartikeln, die mit Hilfe von selbstorganisierenden bakteriellen Hüllproteinen (S-Layern) als Matrix hergestellt werden. Vorgesehen sind ein Up-Scaling der Biomasseproduktion, Entwicklung und Optimierung von Syntheseverfahren von ZnO-Nanopartikeln, Beschichtung von Trägermaterialien mit ZnO-Nanopartikeln, katalytische Tests. Durch die Beteiligung der Firmen Namos GmbH und UMEX GmbH wird die Überführung der Nanokatalysatoren in eine technische Nutzung vorbereitet, eine kontinuierliche Biomassegewinnung etabliert und optimiert. Weiteres Ziel des Vorhabens ist die Bildung eines verwertungsorientierten Netzwerks.
    • Other report
      Dresden: Schlussbericht, BMBF-Vorhaben 01SF0717 2009, 2009
      70 Seiten

    Publ.-Id: 12857 - Permalink


    Dynamic surface barrier effects on hydrogen storage capacity in Mg-Ni films
    Wirth, E.; Munnik, F.; Pranevicius, L. L.; Milcius, D.;
    Hydrogen distribution profiles in Mg-Ni films deposited on quartz substrate by the magnetron-sputter co-deposition of Mg and Ni atoms have been investigated after hydrogenation at 8 x 105 Pa hydrogen pressure at temperatures 210,230 and 250 degrees C during 1, 3,6 and 72 h using elastic recoil detection analysis (ERDA) and nuclear reaction analysis (NRA) methods. Oxygen distribution profiles in the near-surface region have been measured by ERDA. It is shown that hydrogen storage capacity decreases as hydrogenation temperature increases from 210 to 250 degrees C for fixed hydrogenation duration and changes not monotonously as function of hydrogenation time for a fixed temperature. To explain variations of storage capacity as function of hydrogenation temperature and time, the structural film changes have been studied by X-ray diffraction technique, and surface topography was analysed using scanning electron microscopy. We suggest that registered results may be explained on the basis of assumption about the dynamic properties of surfaces which modify the hydrogen uptake mechanism.

    Publ.-Id: 12856 - Permalink


    Ion implantation enhanced formation of 3C-SiC grains at the SiO2/Si interface after annealing in CO gas
    Pécz, B.; Stoemenos, J.; Voelskow, M.; Skorupa, W.; Dobos, L.; Pongrácz, A.; Battistig, G.;
    Silicon carbide with its hexagonal and cubic polytypes is one of the wide band-gap semiconductors used for high temperature applications. Obviously the growth of cubic SiC on Si would be very advantageous, because very large, high quality substrates would then be available at relatively low cost.
    Keywords: 3C-SiC formation of carbide, ion implantation, annealing in CO
    • Contribution to proceedings
      16th International Conference on Microscopy of Semiconducting Materials, 17.03.2009, Oxford, United Kingdom
      Ion implantation enhanced formation of 3C-SiC grains at the SiO2/Si interface after annealing in CO gas
    • Open Access LogoJournal of Physics: Conference Series 209(2010), 012045-1-012045-2
      DOI: 10.1088/1742-6596/209/1/012045

    Downloads:

    Publ.-Id: 12855 - Permalink


    Crossbeam processing for nano-structures on SOI substrates
    Bischoff, L.; Schmidt, B.; Lange, H.; Donzev, D.;
    The further miniaturization of silicon nanomechanical structures in combination with the highly developed microelectronic technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). A modern technique to fabricate such three-dimensional structures is the combination of high-concentration p-type doping of silicon by high resolution writing implantation using a focused ion beam (FIB) and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale thickness and width have been fabricated using 30 keV Ga+ ion implantation (CANION 31Mplus and NVision40) followed by an anisotropic etching in KOH/H2O solution on Silicon-On-Insulator (SOI) substrates. This technology is combined with classical microelectronic techniques, like lithography and broad beam implantation working on a 4 inch wafer to increase the fabrication efficiency especially for the contact areas. Design, performance and fabrication considerations to achieve freestanding Si structures, like nanowires (NW) and -bridges are discussed and some typical structures are shown. Static electrical measurements are demonstrated among others a nano-thermometer, which reveal a broad spectrum in the field of sensor applications. To reduce the resistance the amorphous Si-NWs were covered by electron beam assisted deposition of a 30 nm Platinum film. The dynamic behaviour like resonance frequency was determined by AC excitation and laser interferometer measurements.
    Keywords: FIB; etching; SOI wafer; nanowire; NEMS
    • Lecture (others)
      4. FIB-Workshop, Focused Ion Beams in Research, Science and Technology, 29.-30.06.2009, Halle/Saale, Deutschland

    Publ.-Id: 12854 - Permalink


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