Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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39109 Publications

The chemical potential for the inhomogeneous electron liquid in terms of its kinetic and potential parts with special consideration of the surface potential step and BCS-BEC crossover

Morawetz, K.; March, N. H.; Squire, R. H.

The chemical potential μ of a many-body system is valuable since it carries fingerprints of phase changes. Here, we summarize results for μ
for a three-dimensional electron liquid in terms of average kinetic and potential energies per particle. The difference between μ and the energy
per particle is found to be exactly the electrostatic potential step at the surface. We also present calculations for an integrable one-dimensional
many-body system with delta function interactions, exhibiting a BCS–BEC crossover. It is shown that in the BCS regime the chemical potential
can be expressed solely in terms of the ground-state energy per particle. A brief discussion is also included of the strong coupling BEC limit.

  • Physics Letters A 372(2008), 1707-1711

Publ.-Id: 12108

Transport in OFETs by surface Green functions

Morawetz, K.

Theorieseminar TU Chemnitz

  • Lecture (others)
    Theorieseminar Professur Theorie ungeordneter Systeme, 17.12.2008, Chemnitz, Germany

Publ.-Id: 12106

Bose condensation for attractive interaction?

Maennel, M.; Lipavský, P.; Morawetz, K.; Schreiber, M.

We investigate an interacting Bose gas using a scheme to eliminate successive collisions. For attractive interaction we find a two-particle bound state. When the binding energy of this bound state becomes twice the chemical potential there is a second order phase transition and a gap appears in the dispersion relation. The gap decreases with increasing density. At the critical point the gap vanishes, the dispersion becomes linear for small momenta and a Bose condensate appears. We interpret the appearance of the gap as a sign of structure formation.

  • Poster
    International Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Germany

Publ.-Id: 12105

Phase diagram for interacting Bose systems

Maennel, M.; Morawetz, K.; Schreiber, M.

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.03.2008, Berlin, Germany

Publ.-Id: 12104

Enhancement of Tc due to charge transfer

Morawetz, K.

International Workshop on Physics and Chemistry of FeAs-based Superconductors,
Dresden: Enhancement of Tc due to charge transfer

  • Poster
    International Workshop on Physics and Chemistry of FeAs-based Superconductors, Dresden, 27.-29.10.2008, Dresden, Germany

Publ.-Id: 12103

Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli Potential in Superconductors

Morawetz, K.

  • Lecture (others)
    Interviewtalk for Professorship, 16.11.2008, Loughborogh, Great Britain

Publ.-Id: 12102

Quantum Kinetic Theory beyond Quasiparticle Picture - Bernoulli potential in Superconductors

Morawetz, K.

International Center for Condensed Matter Physics, Bras´ılia:

  • Lecture (others)
    International Center for Condensed Matter Physics, 29.09.2008, Brasilia, Brazil

Publ.-Id: 12101

Nonlocal kinetic theory

Morawetz, K.

Talk for Professorship at University College Dublin

  • Lecture (others)
    Colloquium talk, 14.08.2008, UCD, Ireland

Publ.-Id: 12100

Counter-current flow limitation experiments in a model of the hot leg of a pressurised water reactor - comparison between high pressure steam/water experiments and low pressure air/water experiments

Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Forschungszentrum Dresden-Rossendorf (FZD). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of FZD, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the refluxcondenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.

Furthermore, the flooding characteristic obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, both parameters fail to properly correlate the data: a discrepancy is observed between the air/water and steam/water series. Therefore, a modified Wallis parameter is proposed, which takes into account the effect of the fluid viscosities on the CCFL. The new parameter is validated against comparable data found in the literature, even though no data was found with such a large range of viscosities. This analysis points out that the effect of the dynamic viscosity on flooding has already been observed, but not identified. Furthermore, it is shown that the proposed modification of the Wallis parameter allows a significant improvement for experimental series with variation of the viscosities.

Keywords: two-phase flow; flooding; counter-current flow limitation; hot leg; pressurised water reactor; Wallis parameter; viscosity

  • Contribution to proceedings
    13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan, N13P1107
  • Lecture (Conference)
    13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13), 27.09.-02.10.2009, Kanazawa, Japan

Publ.-Id: 12099

Borverdünnungsanalysen beim Start der ersten HKP - Ergänzende Nachweise

Kliem, S.

In diesem Bericht werden die offenen Punkte OP1 bis OP3 aus der TÜV-Stellungnahme A-Nr.: 5576 vom 24.09.2008 durch ergänzende Nachweise zur von uns vorgelegten Borverdünnungsanalyse abgearbeitet.

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    12 Seiten
    ISSN: 1437-322X

Publ.-Id: 12098

Evaluation Scheme for a Positron Emission Tomography System Used in Monitoring of Radiation Therapy

Shakirin, G.; Fiedler, F.; Enghardt, W.

Positron emission tomography (PET) is used for independent monitoring of dose delivery in ion therapy. An in-beam PET scanner registers the annihilation γ-rays following the decay of β+-radioactive nuclei produced via nuclear reactions between the ions of the therapeutic beam and the irradiated tissue. From a comparison of the reconstructed activity distributions with those predicted from the treatment plan, deviations between the prescribed and the applied dose can be detected. In-beam PET, therefore, allows to verify the physical beam model of the treatment planning, to detect patient dislocations and density changes in the irradiated tissue. Issues related to the image quality and evaluation of a whole PET imaging system are discussed in this paper.

Keywords: in-beam PET; radiation therapy; image quality

  • Contribution to proceedings
    Workshop Bildverarbeitung für die Medizin - Algorithmen, Systeme, Anwendungen (BVM), 22.-25.03.2009, Heidelberg, Germany
    Evaluation Scheme for a Positron Emission Tomography System Used in Monitoring of Radiation Therapy: Springer-Verlag
  • Lecture (Conference)
    Workshop Bildverarbeitung für die Medizin, 22.-25.03.2009, Heidelberg, Germany

Publ.-Id: 12097

Study of the ELBE RF-couplers with a new 1.3 GHz RF- coupler test bench driven by a resonant ring

Büttig, H.; Arnold, A.; Büchner, A.; Freitag, M.; Krätzig, M.; Lehnert, U.; Michel, P.; Schurig, R.; Staats, G.; Teichert, J.; Voigtländer, J.; Winter, A.

To study the performance of the ELBE RF-couplers until their limits a 1.3 GHz resonant ring driven by a 10 kW CW klystron (VKL7811St, CPI) has been built to operate a RF-coupler and RF-window test bench. The ring allows tests with RF power up to 100 kW in continuous wave (CW) mode and 200 kW in pulsed mode.
Details of the resonant ring, the test bench design and results of the ELBE RF-coupler tests will be presented.

Keywords: RF power couplers; Superconducting CW RF; Resonant Ring; Travelling wave resonator; Waveguide window; RF test bench; Linac RF-system

Publ.-Id: 12096

Optimierung optischer und mechnischer Eigenschaften magnetrongesputterter Niobpentoxidschichten

Vinnichenko, M.; Rogozin, A.; Kolitsch, A.; Grambole, D.; Möller, W.; Stenzel, O.; Wilbrandt, S.; Chuvilin, A.; Kaiser, U.

Using high plasma ion density influence during the reactive pulsed magnetron sputtering allowed formation of the dense amorphous Nb2O5 layers with controlled nano-porosity for optical applications. The films possess unique combination of high refractive index (n> 2.5 at wavelength 400 nm), low optical extinction (k<5x10^-4 at 400 nm), low mechanical stress and negligible thermal shift.

Keywords: optical coatings; Nb2O5; nano-sized porosity; optical properties; reactive pulsed magnetron sputtering

  • Lecture (Conference)
    OptoNet Workshop: Funktionale Oberflächen für optische Anwendungen, 12.11.2008, Jena, Germany

Publ.-Id: 12095

Effect of elevated temperature on electrical properties and structure of ZnO:Al films with different dopant concentrations

Vinnichenko, M.; Rogozin, A.; Cornelius, S.; Shevchenko, N.; Gago, R.; Jimenez, I.; Kolitsch, A.; Möller, W.

Al-doped ZnO (ZnO:Al) is a cost-effective alternative to the Sn-doped indium oxide which is widely used as a material for transparent electrodes. To further reduce the production costs, it would be preferable to sputter reactively from a metal alloy target at sufficiently high partial pressure of oxygen. However, under this condition, a sufficiently low resistivity of the films can not readily be obtained, so that a deposition on heated substrates is necessary. The mechanisms of incorporation and electrical activation of the Al doping impurity into ZnO at elevated temperatures are not well understood that makes difficult improvement of reproducibility and long-term stability of the film electrical properties.
In order to have a deeper insight into these processes, polycrystalline ZnO and ZnO:Al films were grown by reactive pulsed magnetron sputtering of Zn and Zn:Al (4.7 and 8.7 at. % of Al) targets, respectively. The O2 partial pressure in Ar-O2 sputtering gas mixture was precisely monitored during deposition using a capacitance gauge. The substrate temperatures (Ts) were spanning in the 40-580 °C range. The films were characterized by Hall effect measurements, spectroscopic ellipsometry (SE), X-ray diffraction (XRD) and X-ray absorption near edge spectroscopy (XANES). At fixed oxygen partial pressure, the electrical resistivity of ZnO:Al films shows a clear minimum at Ts=300 and 350 °C for the films grown using magnetron targets with 8.7 and 4.7 at. % of Al, respectively. The lower resistivity is due to the increased density and mobility of free electrons according to the Hall effect measurements. A maximum of the film crystallinity (grain size) is observed at temperatures of 250 and 300 °C for higher and lower Al concentration, respectively. At Ts>350 °C, the ZnO:Al film crystallinity significantly deteriorates with even stronger temperature effect at higher Al content, leading to formation of nanocrystalline ZnO:Al films at Ts>400 °C in the latter case. It is in contrast to undoped ZnO films grown at identical conditions whose crystallinity always improves by increasing Ts. XANES results show that the poorer film crystallinity and higher resistivity at high Ts can be related to a new homologous phase (ZnO)3(Al2O3) . Further, the electrical properties correlate with changes in the O(1s) absorption edge, whereas the Zn(2p) edge shows no modification with respect to undoped ZnO films.
The authors gratefully acknowledge the financial support of SMWA/SAB under the Project #11815/1854.

Keywords: transparent conducitve oxides; Al-doped ZnO; free electron mobility; reactive pulsed magnetron sputtering

  • Lecture (Conference)
    2nd International Symposium on Transparent Conductive Oxides, 22.-26.10.2008, Hersonissos, Crete, Greece

Publ.-Id: 12094

Formation of light-emitting Si nanostructures in SiO2 by pulsed anneals

Kachurin, G. A.; Cherkova, S. G.; Marin, D. V.; Yankov, R. A.; Deutschmann, M.

Intense excimer laser pulses, flash lamp annealing and rapid thermal annealing were used to form Si nanocrystals in thin SiO2 layers implanted with high doses of Si ions. The pulse durations were 20 ns, 20 ms and 1 s, respectively. Laser annealing produced light sources luminescing in the wavelength range of 400-600 nm. They were attributed to the Si clusters formed as a result of the fast segregation of Si atoms from the SiO2 network. There were no indications of nanocrystal formation in the as-implanted layers after 20 ns laser pulses; however, nanocrystals formed when, before the laser annealing, the amorphous Si nanoprecipitates were prepared in the oxide layers. Evaluations show that the crystallization may proceed via melting. A photoluminescence band near 800 nm, typical of Si nanocrystals, was found after 20 ms and 1 s anneals. Calculations revealed that the annealing times in both cases were too short to provide the diffusion-limited crystal growth if one uses the values of stationary Si diffusivity in SiO2. This points toward the existence of a transient rapid growth process at the very beginning of the anneals.

  • Nanotechnology 19(2008)35, 355305

Publ.-Id: 12093

The Fluorine Effect for High Temperature Oxidation Protection of TiAl-Alloys for Automotive and Aero-Engine Applications

Donchev, A.; Kolitsch, A.; Möller, W.; Schütze, M.; Yankov, R. A.

The insufficient oxidation resistance of TiAl-alloys above roughly 800°C is a major disadvantage for their use in several high temperature applications. This problem can be overcome by small amounts of halogens in the surface zone of the TiAl-material. Especially fluorine has proven to be a beneficial doping element. The fluorine effect is stable at least for one year at temperatures up to 900°C under thermocyclic conditions. Results of fluorine treated and untreated TiAl-coupons, more complex samples and real components are shown in this paper. The specimens were exposed isothermally and thermocyclically in the temperature range from 700 – 1050°C in laboratory air or synthetic air. The specimens can be treated with fluorine in several ways e.g. spraying or ion implantation. Without any treatment some samples were heavily destroyed during high temperature oxidation but after fluorine treatment the components were still intact. Post oxidation investigations revealed the formation of a thin and protective Al2O3-scale confirming the fluorine effect.

  • Lecture (Conference)
    The Minerals, Metals & Materials Society Annual Meeting, 09.-13.03.2008, New Orleans, USA

Publ.-Id: 12092

Self- growing shark skin pattern on the surface of gamma-TiAl alloys

Pflumm, R.; Schütze, M.; Yankov, R.; Kolitsch, A.

This work deals with surface structuring of gamma-titanium aluminide engineering alloy samples by using the oxidation behaviour of the material between 800 and 1000°C. Previous experiments showed that if the pattern of the structures is similar to that of a shark skin, aerodynamical losses due to shear strain at the surface of a solid moving in a flow are decreased. Tiny riblets arranged parallel to the flow direction hamper the cross flow which causes the most of the wall shear stress. Such improvement in the flow conditions is foreseen to be applied to compressor and turbine blades of aero engines for example. These components operate at temperatures between 500 and 1000°C and in strong temperature gradients. Therefore the surface structuring process should not prevent the growth of a protective oxide layer, necessary to protect the material against high temperature corrosion. Several structuring methods leading to self-growing of a shark skin pattern via partial microalloying of halogens (e.g. Fluor) in the first 100 nm of the sample surface were investigated. On the halogen- rich domains a thin protective Al-oxide layer grows slowly at temperatures up to 1000°C (so called “halogen effect”). On the domains free of halogen a thick mixed Al- and Ti-oxide layer grows fastly and builds the riblets. The growth of the non- protective mixed oxide layer should be stopped by lateral diffusion of the halogen from the halogen-rich to the halogen-free domains in order to prevent the spallation of the riblets. The principle and results on the development of such structures including the nucleation process depending on the halogen distribution over the sample surface are shown and discussed for isothermal oxidation at temperatures between 800 and 1000°C.

  • Lecture (Conference)
    Materials Science and Engineering, 01.-04.09.2008, Nürnberg, Germany

Publ.-Id: 12091

High temperature oxidation resistance of fluorine-treated TiAl alloys: Chemical vs. ion beam fluorination techniques

Neve, S.; Masset, P. J.; Yankov, R. A.; Kolitsch, A.; Zschau, H.-E.; Schütze, M.

Surface modification of TiAl alloys by introducing fluorine is known to improve significantly their oxidation behaviour at high temperatures. The effect is based on the preferential reaction of the aluminium with the applied fluorine at the oxide/alloy interface, and is associated with the formation of an adherent and stable protective alumina layer.
Well-defined fluorine profiles beneath the surface of the material can be formed by either fluorine beam line ion implantation (BLI²) or plasma immersion ion implantation (PI3). As an alternative to the implantation-based approach, chemical fluorination techniques such as gas-phase treatment and dipping in F-based solutions have also been investigated in the present work. The fluorine depth profiles have been measured before and after oxidation at 900 °C using non-destructive ion beam analyses (Proton Induced Gamma-ray Emission, Rutherford Backscattering Spectroscopy and Elastic Recoil Detection Analysis). The results of this study enable one to optimize the fluorination conditions and to produce surface-modified technical TiAl alloys suitable for industrial applications.

  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM’08), 31.08.-05.09.2008, Dresden, Germany
  • Nuclear Instruments and Methods in Physics Research B 268(2010), 3381-3385

Publ.-Id: 12090

Plasma immersion ion implantation of fluorine for oxidation-resistant TiAl alloys

Yankov, R. A.; Kolitsch, A.; Munnik, F.; Donchev, A.; Schütze, M.

Titanium aluminides are being used in an expansive variety of advanced applications requiring lightness in weight and retention of strength at elevated temperatures. To date, the upper temperature limit has been at about 700°C because of the poor oxidation resistance of the TiAl alloys at higher temperatures. It has recently been established that the TiAl alloys can be rendered highly resistant to environmental degradation by ion implanting halogens, notably fluorine. In modifying the oxidation properties of the TiAl alloys, strong preference has been given to the technique of plasma immersion ion implantation (PIII) because of the possibility to shorten substantially the implant times as well as to avoid the line-of-sight limitation inherent to the standard beamline implantation process. In this work, various TiAl alloys in the form of either rectangular coupons or actual components have been treated by PIII of fluorine. A cheap, easy-to-handle and environmentally-friendly hydrofluorocarbon (difluoromethane) mixed with argon has been used as the precursor gas to implant fluorine into the TiAl alloys. Energy Dispersive X-ray Analysis, Scanning Electron Microscopy, Rutherford Backscattering Spectrometry and Elastic Recoil Detection Analysis have been undertaken for sample characterization. Optimum processing windows and conditions have been identified under which the modified TiAl alloys acquire a stable, adherent and highly protective alumina scale against high-temperature oxidation. The degree of oxidation protection has been evaluated by testing F-implanted samples under conditions of both isothermal oxidation and thermal cyclic oxidation in air at temperatures up to 1050°C and for times as long as 6000 hours.

  • Poster
    16th International Conference on Ion Beam Modification of Materials (IBMM’08), 31.08.-05.09.2008, Dresden, Germany

Publ.-Id: 12089

Plasma immersion ion implantation of fluorine: an efficient technique for enhancing the oxidation resistance of TiAl alloys

Yankov, R.; Kolitsch, A.; Munnik, F.; Wolfhard, M.; Donchev, A.; Schütze, M.

Titanium aluminides are promising lightweight materials for novel aerospace, automobile and power generation applications. However, because of their insufficient oxidation resistance at temperatures above 700°C, they cannot yet find broader use. The oxidation behaviour of TiAl-alloys can be improved considerably by adding small amounts of fluorine into the subsurface zone of the components (microalloying). The use of TiAl-components after fluorine treatment is feasible up to 1050°C in oxidising environments. One possibility to introduce fluorine into the near-surface of complex TiAl-components is the plasma immersion ion implantation (PI³) technique. The use of an Ar/CH2F2-plasma for the F-PI³ processing leads to a positive halogen effect. The main characterization techniques used in this study have been ERDA and RBS. The oxidation behavior of TiAl samples treated by PI³ of F has been examined using thermogravimetric analysis, and oxidation kinetics curves have been derived. Post-oxidation analyses by SEM reveal a thin protective alumina scale at the surface of the implanted samples as opposed to the thick mixed oxide scale (TiO2/Al2O3) that unavoidably grows upon high temperature oxidation in air.

  • Invited lecture (Conferences)
    11th International Conference on Plasma Surface Engineering, 15.-19.09.2008, Garmisch-Partenkirchen, Germany

Publ.-Id: 12088

Ion implantation of fluorine: towards high-temperature oxidation-resistant TiAl alloys

Yankov, R. A.; Kolitsch, A.; Munnik, F.; Donchev, A.; Schütze, M.

Due to their light weight and high strength, TiAl alloys are of great interest for advanced automobile, aerospace and power generation applications. However, destructive oxidation occurring in these materials in air at temperatures above 700°C has to date hindered their widespread use. In the present study, the high-temperature oxidation behaviour of TiAl has been examined with consideration of the role of ion-implanted fluorine in providing practically useful oxidation protection. Samples of technical TiAl alloys have been treated by either beamline ion implantation of F or plasma immersion ion implantation (PIII) of F using various F-containing precursor gases. The degree of oxidation protection has been evaluated by testing ion implanted samples under conditions of isothermal and thermal cyclic oxidation at temperatures as high as 1050°C. Optimized ion implantation processing has been found to produce marked improvement in the oxidation behaviour of the TiAl alloys. After PIII of F at a bias voltage of 30 kV, broad fluorine implant profiles extending to depths well beyond those predicted by the theory have been identified by elastic recoil detection analysis (ERDA) in the as-implanted samples. The alloys modified in this way acquire a stable, adherent and highly protective alumina scale against environmental oxidation while retaining the bulk mechanical properties of the starting material. Some of the most important process parameters that enable the formation of an efficient protective scale are considered and assessed. PIII of F using suitable F-containing precursor gases has been successfully applied in protecting machine components made of gamma-TiAl and TNB such as turbine blades and turbochargers.

Keywords: Composition and Microstructure; Fluorine; TiAl alloys; Corrosion

  • Lecture (Conference)
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12087

Laser-driven Electron Acceleration in Plasmas with Few-Cycle Pulses

Veisz, L.; Schmid, K.; Tavella, F.; Benavides, S.; Tautz, R.; Herrmann, D.; Buck, A.; Hidding, B.; Marcinkevicius, A.; Schramm, U.; Geissler, M.; Meyer-Ter-Vehn, J.; Habs, D.; Krausz, F.

We report on laser-driven electron acceleration with 8 fs -three optical cycle- long pulses and only 40 mJ energy. This situation constitutes an ideal parameter range for laser wake-¯eld acceleration as prophesied by theory and numerical simulations, which was experimentally not explored before. The produced electron spectra are monoenergetic with a peak in the tens-of-MeV range -up to 50 MeV- and free of low-energy electrons with thermal spectrum. The electron beam has a typical divergence of 5 - 10 mrad. The accelerator is routinely operated at 10 Hz and correspondingly it is a promising source for several applications.

Keywords: bubble regime; bubble; monoenergetic; electron acceleration; ultrashort; few-cycle; laser; laser plasma

  • Comptes Rendus Physique 10(2009)2-3, 140-147

Publ.-Id: 12086

Penning Trap Progress in Munich

Szerypo, J.; Kolhinen, V. S.; Bussmann, M.; Habs, D.; Neumayr, J. B.; Schuermann, C.; Sewtz, M.; Thirolf, P. G.; Schramm, U.

The MLLTRAP, presently under construction at the Maier---Leibnitz Laboratory (Garching), is a Penning trap system designed to decelerate, purify, charge-breed and cool the radioactive ions with the aim to perform the high-accuracy nuclear mass measurements. It involves novel techniques, like sympathetic cooling of highly-charged ions of interest with laser-cooled Mg+ ions. The goal is to reach an accuracy of 10-10, which is required for high precision fundamental physics studies like the determination of fundamental constants and measurement of electron binding energies for QED at strong fields.

Keywords: Penning trap; sympathetic laser cooling; mass measurement

  • Open Access Logo Acta Physica Polonica B 39(2008), 471-476

Publ.-Id: 12085

X-ray investigations off nano structures manufactured by focused ion beam techniques

Grenzer, J.

Nanowires and chains of nanoparticles are of emerging interest in nanoelectronics, nanophotonics and plasmonics. One possible method is the use of a focused ion beam (FIB) that allows to write any pattern directly into the sample to create a particular nano structure. FIB implantation opens the way to manipulate the device structure locally on a length scale of a few 10 nm only and therefore as well as its electronic and optical properties. FIB combines implantation and lithography. The big advantage over other techniques is the reduction of technological steps necessary to make a particular device structure.
We report on strain and defect analysis of lateral nanostructures created in GaAs and Si substrates. The investigations were performed utilizing the method of high resolution X-ray diffraction using grazing incidence and micro focusing techniques at ESRF beamlines.
We have used two different ways to create lateral nanostructures in Si and GaAs, either by creating one or two dimensional patterns by FIB implantation using a liquid metal ion source of Ga or AuGeSi or by focused ion beam synthesis that allows the fabrication of epitaxial CoSi2 layers embedded in silicon. The spot size of the focused ion beam was in the order of 50nm; an ion beam energy in the order of 25keV was used. The whole implanted area had a size of less than 0.2 mm2.

Keywords: ion beam synthesis; X-ray diffraction; nano focussing

  • Lecture (others)
    Seminar on structure analysis, 06.01.2009, Prag, Tschechische Republik

Publ.-Id: 12084

Tuning exchange spring magnets by ion irradiation and annealing: X-ray investigations

Roshchupkina, O.; Grenzer, J.; Fassbender, J.; Choi, Y.; Jiang, J. S.; Bader, S. D.

The coupling effectiveness of the exchange spring effect can be influenced by the interface structure between hard and soft magnetic films. We have investigated the structural and magnetic properties of an Fe/Sm2Co7 exchange spring bilayer system after annealing and after low-energy ion irradiation. To study the interface properties X-ray reflectivity (XRR) measurements were carried out. From the XRR measurements it was shown that annealing influences the roughness of the layer surfaces causing an almost symmetrical broadening of the interfacial layers. Irradiation induces changes in the top three layers and the most pronounced effect upon irradiation is a change in electron density of the first two top layers and an interface broadening between Fe and Sm2Co7. In contrast annealing after irradiation triggers a material flow influencing the whole irradiated layers. The annealing afterwards therefore influences mainly the Fe layer by creating an Fe/Sm2Co7 intermixed region.

Keywords: X-ray reflectivity; magnetic nano structures

  • Lecture (Conference)
    DPG Frühjahrstagung, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12083

MLLTRAP: A Penning trap facility for high-accuracy mass measurements

Kolhinen, V.; Bussmann, M.; Habs, D.; Neumayr, J.; Schramm, U.; Schurmann, C.; Sewtz, M.; Szerypo, J.; Thirolf, P.

The MLLTRAP, presently under construction at the Maier-Leibnitz-Laboratory (Garching), is a Penning trap facility designed to
combine several novel techniques to decelerate, purify, charge breed and cool the reaction products and perform high-accuracy nuclear mass measurements of highly charged, laser-cooled ions.

Keywords: Gas cell; Ion cooling; Mass measurement; Penning trap; RFQ; Sympathetic laser-cooling

Publ.-Id: 12082

Xe+ ion beam induced rippled structures on Si miscut wafers

Hanisch, A.; Grenzer, J.; Biermanns, A.; Pietsch, U.

We report on the influence of the initial roughness and crystallography of the substrate on the formation of self-organized ripple structures on semiconductors surfaces by noble gas ion bombardment. The Bradley-Harper theory predicts that an initial roughness is most important for starting the sputtering process which in the ends leads to the evolution of regular patterns. We produced regular patterns with intermediate Xe+ ion energies (5-70 keV) at different incidence and azimuthal angles which lead to the assumption that also crystallography plays a role at the beginning of ripple evolution. Most of the previous investigations started from the original roughness of a polished silicon wafer. We used (001) silicon wafers with a miscut angle of 1°, 5° and 10° towards [110]. We studied the ripple formation keeping the ion beam parallel to the [111], [-1-11] or [-111] direction, i.e. parallel, antiparallel or prependicular to the miscut direction [110]. The parallel and antiparallel case implies a variation of the incidence angle with increased roughness over the surface step terraces. The perpendicular orientation means almost no roughness. The results were compared to normal Si(001) and Si(111) wafers.

Keywords: rippled structures nanostructures miscut self-organization

  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12081

Transition from smoothing to roughening of ion-eroded GaSb surfaces

Keller, A.; Biermanns, A.; Carbone, G.; Grenzer, J.; Facsko, S.; Plantevin, O.; Gago, R.; Metzger, T. H.

During ion sputtering of GaSb(100) surfaces a transient behavior from initial smoothing to roughening accompanied by self-organized pattern formation has been observed using in-situ x-ray reflectivity and grazing incidence small angle scattering. A characteristic hexagonal dot pattern with a spatial periodicity of 30 nm is observed and the correlation length increases with ion fluence. In the framework of the Bradley-Harper model, where the dot pattern formation results from an interplay of surface roughening due to sputtering and surface smoothing due to diffusion, the initial smoothing behavior results from the same diffusion processes as the pattern formation.

Keywords: ion beam erosion; X-ray scattering; nano strucutures

Publ.-Id: 12080

Ripple structures on surfaces and underlying crystalline layers in ion beam irradiated Si wafers

Grenzer, J.; Biermanns, A.; Mücklich, A.; Grigorian, S. A.; Pietsch, U.

We report on the formation of ion beam induced ripples in Si(001) wafers when bombarded with Ar+ ions at an energy of 60keV. A set of samples varying incidence and azimuthal angles of the ion beam with respect to the crystalline surface orientation was studied by two complementary near surface sensitive techniques, namely atomic force microscopy and depth-resolved X-ray grazing incidence diffraction. Additionally cross-section TEM investigations were carried out. The ripple-like structures are formed at the sample surface as well as at the buried amorphous-crystalline interface. Best quality of the ripple pattern was found when the irradiating ion beam was aligned parallel to the <111> planes. The quality decreases rapidly if the direction of ion beam deviates from <111>.

Keywords: ion beam erosion; nano structures; X-ray diffraction; TEM; AFM

  • Physica Status Solidi (A) 206(2009)8, 1731-1735

Publ.-Id: 12079

Submicron resolution X-ray diffraction from periodically patterned GaAs nanorods grown onto Ge[111]

Davydok, A.; Biermanns, A.; Pietsch, U.; Grenzer, J.; Paetzelt, H.; Gottschalch, V.; Bauer, J.

We present spatially resolved X-ray diffraction pattern of individual GaAs nanorods grown catalyst-free throughout a pre-patterned amorphous SiNx mask onto germanium [111] surfaces. The experiment has been performed using synchrotron radiation using a micro-sized beam prepared by compound refractive lenses. Due to the non-polar character of the substrate the shapes of NR´s appear not uniform and vary between deformed hexagonal and trigonal in symmetry. Because the average diameter of NR´s equals the experimental resolution certain cuts through slightly inclined edges or corners of individual nanorods with lateral size of about 225 nm could be selected using spatially resolved reciprocal space mapping.

Keywords: X-ray diffraction; nano structures

  • Physica Status Solidi (A) 206(2009)8, 1704-1708

Publ.-Id: 12078

Polyedrisierung dreidimensionaler digitaler Objekte mit Mitteln der konvexen Hülle

Schulz, H.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-506 2008
    ISSN: 1437-322X


Publ.-Id: 12077

Annual Report 2007 - Institute of Safety Research

Weiss, F.-P.; Rindelhardt, U.; (Editors)

The Institute of Safety Research (ISR) is one of the six Research Institutes of Forschungszentrum Dresden-Rossendorf e.V. (FZD e.V.), which is a member institution of the Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz (Leibniz Association). Together with the Institute of Radiochemistry, ISR implements the research programme „Safety and Environment“, which is one of the three scientific programmes of FZD. In the framework of this research programme, the institute is responsible for the programme areas “Plant and Reactor Safety” and “Thermal Fluid Dynamics”, respectively (see Table 1). By participating in the development and operation of a pulsed photo-neutron source at the radiation source ELBE (Electron linear accelerator for beams of high brilliance and low emittance), we also contribute to the project “Neutron Induced Processes”, which is part of the FZD programme dedicated to the structure of matter.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; FZD-501 2008
    ISSN: 1437-322X


Publ.-Id: 12076

Large-area Terahertz Emitters based on GaInAsN

Peter, F.; Winnerl, S.; Schneider, H.; Helm, M.; Köhler, K.

The high price and the complexity of commonly used titanium-sapphire lasers hinder a more widespread use of pulsed THz systems. Er-doped fiber lasers can be a promising alternative. Since the band gap of GaAs is larger than the photon energy at 1.55 µm, this material – while being the standard material for photoconductive THz antennas excited with titanium-sapphire lasers – is not suitable for systems driven by fiber lasers. Dipole antennas have been successfully demonstrated on low-temperature grown InGaAs [1] and ion-irradiated InGaAs [2]. However, the resistivity of these small-gap materials is too low for microstructured large-area emitters. Such emitters consist of an interdigitated finger structure on the semiconductor substrate and a second metallization preventing destructive interference from THz wavelets excited in regions with opposite direction of the bias field [3]. Since these microstructured large-area emitters can withstand large excitation power and high bias fields, they show improved efficiency and higher THz power as compared to conventional antennas.
A 1000 nm thick Ga0.89In0.11As0.96N0.04 layer was grown lattice matched on semi-insolating GaAs by molecular beam epitaxy. On top, additional layers of 60 nm AlGaAs and 5 nm GaAs were grown, resulting in a higher resistivity of the substrate. A THz emitter with an active area of 1 mm  1 mm with a microstructure similar to the one described in ref. 3 was produced using standard optical lithography. The emitter was excited with radiation from an optical parametric oscillator (OPO; tuning range: 1.1 - 1.5 µm). The THz radiation was detected by electro-optic sampling in a ZnTe crystal gated with an 800 nm beam from a titanium sapphire laser. Strong THz emission is observed for excitation wavelength below 1.35 µm [4]. No saturation effects occur within the available range of average power (up to 50 mW) of the OPO. Furthermore the GaInAsN emitter was compared with an emitter based on semi-insolating GaAs at an excitation wavelength of 800 nm. The THz field amplitude of the GaAs emitter is eight times higher as compared to the GaInAsN emitter. Again, in the available excitation power range (up to 0.5 W), no saturation effects are observed.
In summary an efficient and easy-to-align microstructured THz emitters based on GaInAsN has been demonstrated. While further improvement of the material is necessary for excitation at 1.55 µm, the material studied here is suitable for fiber lasers operating at 1.1 µm.


[1] M. Suzuki and M. Tounouchi, Appl. Phys. Lett. 86, 163504, (2005).
[2] A. Takazato, et al., Appl. Phys. Lett. 91, 011102, (2007).
[3] A. Dreyhaupt, et al., Appl. Phys. Lett. 86, 121114 (2005).
[4] F. Peter et al., Appl. Phys. Lett. 93, 101102 (2008).

  • Lecture (Conference)
    SPIE Europe Michrotechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    SPIE Europe Michrotechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland, 04.-06.05.2009, Dresden, Deutschland
    Proceedings of SPIE, 73661R-73661R-6

Publ.-Id: 12075

Terahertz Emitters and Detectors for Radially and Azimuthally Polarized Beams

Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.

Typical pulsed terahertz (THz) systems operate with freely propagating THz waves of linear polarization and Gaussian beam profile. In the range of visible light and near-infrared radiation, Bessel-Gauss modes have stimulated great interest over last years. The lowest order Bessel-Gauss modes have a donut-like intensity distribution and are either radially or azimuthally polarized. Radially polarized beams have interesting fundamental properties such as smaller beam waists in the focus as compared to Gaussian modes and strong longitudinal field components in the focus. In the THz range, superior coupling properties for radially polarized light to plasmonic guided modes on wires, so called Sommerfeld modes are predicted. While there are many investigations on these guided THz modes, only little work is done on freely propagating modes of radial polarization [1] and no publications exist for azimuthally polarized THz beams. Here we present a concept that allows creating emitters and detectors for any desired mode. The principle is demonstrated by showing results on radially and azimuthally polarized THz beams.
The photoconductive emitter and detector structures are based on a microstructured electrode pattern on a semiconductor substrate. The electrode pattern is inverse to the desired polarization pattern, i.e. emitters for radially polarized modes consist of equidistant concentric ring electrodes, while emitters for azimuthally polarized modes are a circular structure of metallized sectors. To avoid electric fields pointing in the opposite direction, a second metallization layer is used in a similar way as previously described for emitter of linearly polarized radiation [2]. While the emitters were fabricated on semi-insulating GaAs, detectors were prepared on GaAs substrates implanted with N+. A titanium sapphire laser was used for excitation of the emitters and gating of the detectors. Beam profiles were measured for the divergent beam 25 mm behind the emitters, and for the refocused beam after a path of ~0.5 m. In this experiment the detector was sensitive for a linearly polarized component of the radiation. The observed beam profiles agree well with the ones expected for Bessel-Gauss beams. Furthermore radiation with radial polarization was detected with an antenna optimized for radial polarization and one for azimuthal polarization. With the detector for azimuthal polarization no signal is expected. However, due to imperfections of the beam profile of the near-infrared laser, a residual signal of about 10 % compared to the signal measured with the detector for radial polarization is observed. This experiment serves as a proof of principle that the emitter-detector combination well suited for studying changes of the mode structure.


[1] G. Chang, Ch.J. Divin, C.-H. Liu, S.L. Williamson, A. Galvanauskas, and T.B. Norris, Opt. Lett. 32, 433 (2006).
[2] A. Dreyhaupt, S. Winnerl, T. Dekorsy, and M. Helm, Appl. Phys. Lett. 86, 121114 (2005).

  • Lecture (Conference)
    SPIE Europe Microtechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    SPIE Europe Microtechnologies for the New Millenium, 04.-06.05.2009, Dresden, Deutschland
    Proceedings of SPIE, 73661N-73661N-7

Publ.-Id: 12074

Terahertz Vector Beams

Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.

We present a concept for the design of photoconductive antennas which allows the generation and detection of terahertz radiation pulses of freely selectable modes. We demonstrate the principle by showing electric field distributions for vector beams, namely the lowest order Gaussian-Bessel beams. They have a donut-like intensity distribution and either radial or azimuthal polarization. For comparison, Gaussian beams are investigated.

  • Poster
    33rd International Conference on Infrared, Millimeter, and Terahertz Waves, 14.-19.09.2008, Pasadena, USA
  • Contribution to proceedings
    33rd International Conference on Infrared, Millimeter, and Terahertz Waves, 14.-19.09.2008, Pasadena, USA
    Conference Digest of the 33rd International Conference on Infrared, Millimeter, and Terahertz Waves

Publ.-Id: 12073

Terahertz Bessel-Gauss beams of radial and azimuthal polarization from microstructured photoconductive antennas

Winnerl, S.; Zimmermann, B.; Peter, F.; Schneider, H.; Helm, M.

We report on emission and detection of pulsed terahertz radiation of radial and azimuthal polarization by microstructured photoconductive antennas. To this end the electrode geometry of the emitter is inverse to the desired THz field pattern and a second periodic structure prevents destructive interference effects. Beam profiles of freely propagating THz waves are studied for divergent and refocused beams. They can be well described as the lowest order Bessel-Gauss modes with a divergence comparable to linearly polarized Gaussian beams. Additionally, polarization sensitive detection is demonstrated for radially polarized radiation.

  • Open Access Logo Optics Express 17(2009), 1571-1576

Publ.-Id: 12072

Nanocrystals formation in a –Si/SiO2 layer by ion mixing and plasma immersion ion implantation in different energy ranges

Mello, C. B.; Ueda, M.; Beloto, A. F.; Mücklich, A.; Reuther, H.

Nanocrystals formation in a –Si/SiO2 layer by ion mixing and plasma immersion ion implantation in different energy ranges

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 12071

Nitrogen PIII in SS304 stainless steel using different temperature time-histories

Ueda, M.; Diaz, C.; Lepienski, C. M.; Reuther, H.

  • Poster
    16th International Conference on Ion Beam Modification of Materials, 31.08.-05.09.2008, Dresden, Deutschland

Publ.-Id: 12070

Tribological Effects of Plasma Immersion Ion Implantation Heating Treatments on SS304 Stainless Steel

Mello, C. B.; Ueda, M.; Geraldo, A. S.; Nascimento, D. P.; Lepienski, C. M.; Reuther, H.

  • Poster
    VII Encontro da SBPMat, Symposium C – Mechanical properties of surfaces, thin films and coatings, 28.09.-02.10.2008, Guarujá, Brasilien

Publ.-Id: 12069

Terahertz Si:B blocked-impurity-band detectors defined by nonepitaxial methods

Rauter, P.; Fromherz, T.; Winnerl, S.; Zier, M.; Kolitsch, A.; Helm, M.; Bauer, G.

The molecular beam epitaxial (MBE) fabrication of blocked-impurity-band detectors (BIB) has been a technologically complex and delicate matter ever since its demonstration in silicon, and has not been adapted for other material systems offering detection onsets at lower terahertz frequencies. We report the fabrication and characterization of a vertical Si:B BIB, circumventing the intrinsically troublesome MBE growth of an ultrapure blocking layer by employing ion implantation. We present a thorough characterization of our device, which exhibits highly competitive figures of merits. Our results not only increase the accessibility of BIB fabrication tools for ultrasensitive terahertz detection but also open a road to other material systems.

Keywords: Infrared detector

Publ.-Id: 12068

Contribution of the surface dipole to deformation of superconductors

Lipavský, P.; Morawetz, K.; Kolácek, J.; Brandt, E. H.; Schreiber, M.

The interaction of the ionic lattice with the superconducting condensate is treated in terms of the electrostatic force in superconductors. It is shown that the surface dipole supplies the force responsible for the volume difference of the normal and superconducting states. Assuming this mechanism, we argue that the usual parametrization of the theory of deformable superconductors should be revisited.

  • Physical Review B 77(2008), 014506-1-014506-6

Publ.-Id: 12067

Synthesis report on work package 2.1: Pressureized Thermal Shock (PTS)

Lucas, D.; Bestion, D.; Coste, P.; Pouvreau, J.; Morel, C.; Martin, A.; Boucker, M.; Bodele, E.; Schmidtke, M.; Scheuerer, M.; Smith, B.; Dhotre, M. T.; Niceno, B.; Lakehal, D.; Galassi, M. C.; Mazzini, D.; D’Auria, F.; Bartosiewicz, Y.; Seynhaeve, J.-M.; Tiselj, I.; ŠTrubelj, L.; ProšEk, A.; Ilvonen, M.; Kyrki-Rajamäki, R.; Tanskanen, V.; Laine, M.; Puustinen, J.

This report summarizes the results of the NURESIM project for the work package 2.1 “Pressurized Thermal Shock (PTS)”. It includes summaries of the single tasks done by the partners involved in this work package. In the Introduction chapter some more general information on the PTS issue is given, which should help to clarify the integration of the single activities. Since the PTS scenario involves different flow situations, for which also different modelling approaches are necessary, the tasks are sorted according to these flow situations. The relation of the work done to the general aim of the NURESIM project, which is to establish a new code platform, is indicated by assigning the activities to 6 different types. The results achieved in the PTS work package are in agreement with the expectations to the NURESIM project. The conclusion drawn from the single investigations and recommendations for future work are discussed in a separate chapter. It was shown, that for further improvement of the CFD-code capabilities for the two-phase PTS case new well-instrumented experimental data are needed especially for condensation at the surface of a sub-cooled liquid jet in a steam environment as well as on free surfaces, turbulence production and bubble entrainment below the jet and mixing in a stratified flow. Integral experiments, which reflect the PTS flow situations, are important to test the interplay between all the sub-models. Some of the local flow situations can be already captured quite well by presently available CFD codes, for other still many open questions exist. In general more flexible models are required which allow switching between different approaches within one flow domain but for the different local flow situations. Examples for such model approaches are the Large Scale Simulation (LSS) which should allow the application of a two-fluid model for dispersed flows and Interface Tracking Methods for large surfaces and the Scale Adaptive Simulations (SAS) which allow the simulation of large eddies while modelling the turbulence at the unresolved scales. The work done leads to a clear improvement of the simulation capabilities regarding a two-phase PTS situation, but caused by the complexity of the issue it will still be a long way to enable predictive simulations for all the different phenomena that occur in this application. In the near term, one may envisage a simplified treatment of two-phase PTS transients by neglecting some effects which are not yet controlled.

Keywords: Pressurized Thermal Shock; CFD; two-phase flow

  • Article, self-published (no contribution to HZDR-Annual report)
    Forschungszentrum Rossendorf 2008
    Institutsbericht FZD\FWS\2008\11
    40 Seiten
    ISSN: 1437-322X

Publ.-Id: 12065

Be-10 and Cl-36 interlaboratory comparisons

Merchel, S.; Bremser, W.; Alfimov, V.; Arnold, M.; Aumaître, G.; Benedetti, L.; Bourlès, D. L.; Braucher, R.; Caffee, M.; Christl, M.; Fifield, L. K.; Finkel, R. C.; Freeman, S. P. H. T.; Ruiz-Gómez, A.; Kubik, P. W.; Rood, D. H.; Sasa, K.; Steier, P.; Tims, S. G.; Wallner, A.; Wilcken, K. M.; Xu, S.

Driven by the progress in AMS and its spreading application within geosciences, measurements of increasing numbers of samples with low isotopic ratios will be required in the future. Therefore, we have examined the linearity of 10Be/9Be as a function of isotope ratio by distributing 3 secondary standards (dilutions of NIST4325: 10-12-10-14) to 9 AMS labs. The problem of low ratio samples is even more crucial for 36Cl mainly due to the high volatility of chlorine. Thus, we have prepared large quantities of 3 36Cl/Cl solutions from a certified 36Cl activity (NIST4943) by dilution with NaCl. AgCl precipitated from these solutions (10-11-10-13) has been distributed to 9 AMS labs. Some measurements are still ongoing. First results from 6 labs for each nuclide show that these interlaboratory exercises are very valuable.

Keywords: accelrator mass spectrometry; AMS; round-robin; standards

  • Lecture (Conference)
    73. Jahrestagung der DPG und DPG Frühjahrstagung der Sektion AMOP (SAMOP), 02.-06.03.2009, Hamburg, Deutschland

Publ.-Id: 12064

Intersubband relaxation and dephasing in narrow InGaAs/AlAsSb quantum well structures

Grimm, C. V.-B.; Pfau, C.; Ohser, S.; Winnerl, S.; Schneider, H.; Helm, M.; Biermann, K.; Künzel, H.

The InGaAs/AlAsSb heterostructure has been attractive in recent years due to its high conduction band offsets, which is necessary for intersubband transition (ISBT) based devices at short wavelength (< 3 microns) [1]. To achieve this goal, very thin QWs are required, leading to a particular band configuration where a X or L cross-over takes place. Nevertheless it has been shown that intervalley transfer is rather inefficient for ISBT wavelengths as short as 2.3 m [2], indicating that quantum cascade lasers (QCL) at such short wavelength are feasible. Indeed, QCL with wavelength around 3.0 μm [3], using the same material, were recently demonstrated. Besides the intersubband relaxation time, providing the nonradiative lifetime of the QCL, another important parameter for the design of QCL is the homogeneous linewidth, since it would affect the gain profile of the laser. Therefore the study of the dephasing time, being directly relevant for the homogeneous linewidth, is as important as the intersubband relaxation time.
In this work we present a study of the intersubband relaxation dynamics and dephasing time of QW doped InGaAs /AlAsSb samples grown on InP substrate, through, respectively, degenerate pump-probe and four-wave-mixing (FWM) measurements, at wavelengths around 2 m. The measured intersubband relaxation time constants, between 1 and 1.8 ps, increase with the decrease of the temperature due to the reduced LO phonon scattering. The measured FWM time constant increases by a factor of 4, inferring from the increase of the FWM signal intensity with the decrease of the temperature from 300K to13K.
[1] C. V-B. Grimm, M. Priegnitz, S. Winnerl, H. Schneider, M. Helm, Appl. Phys. Lett. 91, 191121(2007).
[2] C.V-B. Tribuzy, S. Ohser, S. Winnerl, J. Grenzer, H. Schneider, M. Helm, J. Neuhaus, T. Dekorsy, K. Biermann, H. Künzel, Appl. Phys. Lett. 89, 171104 (2006).
[3] D. G. Revin, J. W. Cockburn, M. J. Steer, R. J. Airey, M. Hopkinson, A. B. Krysa, L. R. Wilson, and S. Menzel, Appl. Phys. Lett. 90, 021108 (2007).

Keywords: multiple quantum well; dephasing time; intersubband relaxation

  • Lecture (Conference)
    35th International Symposium on Compound Semiconductors, 21.-24.09.2008, Europa-Park, Rust, Deutschland

Publ.-Id: 12063

Laboratory Underground for Nuclear Astrophysics (LUNA)

Bemmerer, D.

Deep underground in the Gran Sasso national laboratory in Italy, the 400 kV LUNA accelerator supplying up to 0.5 mA H+ and He+ beams has been installed. Due to the 3400 meters (water equivalent) overburden present at Gran Sasso, the cosmic-ray induced laboratory background in gamma-ray detectors is strongly reduced at LUNA. The accelerator is being used for the study of radiative-capture reactions of astrophysical interest, both by in-beam gamma-ray spectrometry and by activation. The features of the site and accelerator will be shown on the poster; some applications and a future outlook will also be presented.

  • Poster
    IEEE-NSS 2008 Nuclear Science Symposium, 19.-25.10.2008, Dresden, Deutschland

Publ.-Id: 12062

Metal-oxide semiconductor light-emitting devices based on Ge nanocrystals co-implanted with Er ions

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

Si nanocrystals (NCs) have widely been used as sensitizers in Er-doped SiO2 layers where following the recombination of excitons (electron-hole pairs) in optically excited Si NCs energy is transferred to the higher energy levels of the 4f shell of Er3+ ions and subsequently decay radiatively via 4I13/2 → 4I15/2 transition. This as a result emits light at ~1.53 m, which coincides well the silica-based optical fibers. However, the temperature and concentration quenching of Er3+ ions in Si-rich SiO2 matrices are the basic obstacles for practical application. In the quest for an alternative host material, Ge-rich SiO2 layers have presently attracted a considerable interest due to strong quantum confinement effect and a better control of the surface oxidation of Ge NCs with respect to Si-NCs. In fact, the growth of Er-doped Ge nanoperticles embedded in a SiO2 layer and the photoluminescence (PL) properties have recently been studied. Despite progress in PL response, electrically pumped light-emitting devices (LEDs) are highly required from the optoelectronic standpoints.
We have investigated Ge NCs embedded in a metal-oxide semiconductor (MOS) structure co-doped with Er3+ ions and the corresponding electroluminescence (EL). Here we follow the two step implantation approach: (i) First, 130 keV Ge ions have been implanted (dose of 2–6E16 ions/cm2) into a thermally grown 200 nm thick SiO2 layer followed by furnace annealing (FA) at 950 C for 60 min, which is followed by (ii) 250 keV Er implantation (dose of 1-5E15 ions/cm2) combined with FA in the range of 800-1100oC for 30 min in nitrogen ambience. The MOS structures have been fabricated by depositing indium-tin-oxide (ITO) and aluminium in the front and rare sides of the samples, respectively, and patterning the ITO layer using photolithography. Interestingly, instead of electrically driven pumping of Er3+ ions by Ge NCs, we found that an EL band ~407 nm associated to the Ge-related oxygen-deficiency centres (GeODCs) have been pumped by Er3+ ions and discuss the observed phenomenon on the ground of an inverse energy transfer process. Concentration and temperature dependent modification of microstructure and the subsequent impact on EL response will also be discussed.

Keywords: GeODC; EL; nanocrystals; Er

  • Lecture (Conference)
    SPIE Europe - Microtechnologies for the New Millennium, 04.-06.05.2009, Dresden, Germany

Publ.-Id: 12061

Strong Er luminescence at 1.53 um in rapid thermal annealed Si-rich SiO2 layers co-implanted with Er

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

The Er-doped SiO2 layers containing Si nanocrystals (Si-ncs) have attracted considerable interest for more than a decade in realizing efficient light sources at 1.54 um, owing to the coincidence of the luminescence wavelength to the absorption minimum of the silicon based optical fibres.1 Although about two orders of magnitude Er luminescence has been noticed in long time annealed sputtered deposited samples,2 observation of such high efficiency in ion implantation processed samples is scarce. Recently, we have succeeded in producing such a system by a combination of sequential Si and Er implantations and rapid thermal annealing (RTA). The processing conditions have been optimized for achieving maximum Er photoluminescence (PL) at 1533 nm at the expense of a broad luminescence band peaking at ~580 nm. Spectral analyses suggest that the appearance of such visible range PL band can be explained in the light of the interfacial state mediated recombination of carriers in the Si-ncs according to the model proposed by Wolkin et al.3. The energy migration from Si-ncs to the nearby Er ions has further been manifested using time-resolved PL measurements.
[1] A. Polman, J. Appl. Phys. 82, 1 (1997).
[2] M. Fujii, M. Yoshida, Y. Kanzawa, S. Hayashi, and K. Yamamoto, Appl. Phys. Lett. 71, 1198 (1997).
[3] M. V. Wolkin, J. Jorne, P. M. Fauchet, G. Allan, and Delerue, Phys. Rev. Lett. 82, 197 (1999).

Keywords: nanocrystals; Er; RTA; PL

  • Poster
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik mit anderen Fachverbänden und den Arbeitskreisen der DPG, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 12060

Strong Er luminescence in rapid thermal annealed Er-doped SiO2 layers containing Si nanoclusters

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

The Er-doped SiO2 layers containing Si nanocrystals (Si-ncs) have attracted considerable interest for more than a decade in realizing efficient light sources at 1.54 um [1,2], owing to the coincidence of the luminescence wavelength to the absorption minimum of the silicon based optical fibers. Although about two orders of magnitude Er luminescence has been noticed in presence of Si-ncs in a long time annealed sputtering deposited samples [3], observation of such high efficiency in ion implantation processed samples is scarce. Recently, we have succeeded in producing such a system by a combination of sequential Si and Er implantations and rapid thermal annealing (RTA). The processing conditions have been optimized for achieving maximum Er photoluminescence (PL) at 1533 nm at the expense of a broad luminescence band peaking at ~580 nm. Spectral analyses suggest that the appearance of such visible range PL band can be explained in the light of the interfacial state mediated recombination of carriers in the Si-ncs according to the quantum-confinement model [4]. The energy migration from Si-ncs to the nearby Er ions has further been manifested using time-resolved PL measurements.

[1] A. Polman, J. Appl. Phys. 82, 1 (1997).
[2] G. Franzò, S. Boninelli, D. Pacifici, F. Priolo, F. Iacona, and C. Bongiorno, Appl. Phys. Lett. 82, 3871 (2003).
[3] M. Fujii, M. Yoshida, Y. Kanzawa, S. Hayashi, and K. Yamamoto, Appl. Phys. Lett. 71, 1198 (1997).
[4] M. V. Wolkin, J. Jorne, P. M. Fauchet, G. Allan, and Delerue, Phys. Rev. Lett. 82, 197 (1999).

Keywords: Nanocrystals; PL; Er

  • Poster
    E-MRS 2008 Spring Meeting, 26.-30.05.2008, Strasbourg, France

Publ.-Id: 12058

Electrically driven reverse energy transfer process in Er-doped SiO2 layers containing Ge nanocrystals

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

Optically active Er3+ ions dispersed in a SiO2 layer are often used for amplifying signals at the wavelength of ~1.5 m that coincides with the maximum transparency window of silica-based optical fibers. In order to enhance the 1.5 m Er luminescence, a sufficient number of Er ions must be in the excited state, and it is only possible by employing a high-power pumped laser. Si nanocrystals (NCs) embedded in an Er-doped SiO2 layer show a new avenue to excite Er3+ ions indirectly, where Si-NC behaves like a sensitizer [1]. The basic mechanism of the above mentioned system relies on three facts: (i) optical excitation of Si-NC, (ii) nonradiative transfer of energy from Si-NC to the neighbouring Er3+, and (iii) subsequent relaxation from the first excited state to the ground state of Er3+ by emitting light at 1.5 m. However, to integrate these photonic systems into current microelectronics, it is essential to fabricate metal-oxide-semiconductor based light-emitting devices. Based on electroluminescence (EL) experiments, some groups have shown the importance of Si-NCs in enhancing the 1.5 µm Er luminescence.
Here we use an experimental approach for evaluating the influence of Ge NCs on the Er EL in Er-doped SiO2 layers. In particular, we demonstrate an increase in intensity of the 400 nm band, characteristic of the Ge-NC related oxygen-deficiency centres (GeODC), at the expense of the Er-related signals with maxima at 522, 550, 660 and 1532 nm during electrical pumping at room-temperature  indicating an energy transfer process from the excited Er ions to the confined carriers in the GeODC, which is just opposite to the concept commonly used for the Er-doped SiO2 layers containing Si-NCs. Formation of Ge-NCs was verified by transmission electron microscopy.

[1] Polman A, Nature Materials 2002;1:10.

Keywords: nanocrystals; Er; EL

  • Lecture (Conference)
    VIIth International Conference: Ion Implantation and Other Applications of Ions and Electrons, 16.-19.06.2008, Kazimierz Dolny, Poland

Publ.-Id: 12056

Energy Transfer from the Er3+ to Ge Nanocrystals During Electroluminescence in MOSLEDs.

Kanjilal, A.; Rebohle, L.; Voelskow, M.; Skorupa, W.; Helm, M.

It is well established that Si nanocrystals (NCs) can act as sensitizers in Er-doped SiO2 during optical pumping [1-4]. In fact, following the recombination of excitons (electron-hole pairs) in optically excited Si NCs transfer their energy to the higher energy levels of the nearest Er3+ ions and subsequently decay to the ground state by intra-4f transitions. Among those, the 4I13/2 → 4I15/2 radiative transition has attracted substantial interest since the respective luminescence at ~ 1.53 m corresponds to the maximum transparency of silica-based optical fibers [2]. Ge is another group-IV element with similar electronic properties to that of Si. We have examined the impact of Ge NCs in Er-doped SiO2 layers by investigating electroluminescence (EL) of the metal-oxide semiconductor (MOS) structures, where the Er-doped Ge-rich SiO2 layers have been prepared by ion implantation technique combined with rapid thermal annealing (RTA). The samples have been prepared by two steps: (i) 130 keV Ge ions have been implanted with a dose of 2  1016 ions/cm2 in a 200 nm thick thermally grown SiO2 layers followed by RTA at 1050 oC for 180 s, and subsequently (ii) 250 keV Er ions have been implanted with a dose of 1  1015 ions/cm2 followed by RTA in the range of 850-1050 oC for 6-150 s in nitrogen ambience. Transmission electron microscopy experiments reveal formation of randomly oriented Ge NCs with average size ~4 nm. The MOS structures have been fabricated by depositing indium-tin-oxide (ITO) and aluminium in the front and rare sides of the samples, respectively, and patterning the ITO layer using photolithography. During EL measurements, in absence of the visible range band correlated to the quantum confinement in Ge NCs a band appears at ~400 nm in Ge-rich SiO2 layer as a consequence of hot electron mediated impact excitation in Ge-related oxygen-deficiency centres (GeODCs) during electrical pumping [5]. We find an increase of the 400 nm EL intensity with a concomitant reduction of the Er-related emission, and discuss the observed phenomenon on the ground of an inverse energy transfer process [4] from excited Er3+ to the GeODCs.

[1] A. Polman, J. Appl. Phys. 82, 1 (1997).
[2] O. Savchyn, F. R. Ruhge, P. G. Kik, R. M. Todi, K. R. Coffey, H. Nukala, and H. Heinrich, Phys. Rev. B 76, 195419 (2007).
[3] M. Fujii, K. Imakita, K. Watanabe, and S. Hayashi, J. Appl. Phys. 95, 272 (2004).
[4] I. Izeddin, A. S. Moskalenko, I. N. Yassievich, M. Fujii, and T. Gregorkiewicz, Phys. Rev. Lett. 97, 207401 (2006).
[5] L. Rebohle, J. von Borany, R. A. Yankov, W. Skorupa, I. E. Tyschenko, H. Fröb, and K. Leo, Appl. Phys. Lett. 71, 2809 (1997).

Keywords: nanocrystals; Er; energy transfer

  • Poster
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, MA, USA

Publ.-Id: 12055

Stabilization of extra dimensions in higher-dimensional cosmological models

Günther, U.

We present an overview over research on higher-dimensional cosmological models carried out from 1997 till 2004. The basic starting point is the problem of stabilizing the sizes of the extra-dimensional factor spaces so that they are kept unobservable at low energies --- as indicated by current data from high-energy collider experiments and astrophysical observations. This problem is well known as the moduli stabilization problem in string theory and M-theory. Stabilizing the scale factors of the extra-dimensional factor spaces by some effective potentials (which are naturally induced via dimensional reduction of the higher-dimensional setups) fixes only the average sizes (moduli) but still allows for small (quantum) fluctuations around the minimum position (radion fluctuations). Once these fluctuations will depend on the coordinates of our external (uncompactified) space they will act as multicomponent scalar fields. Due to their Planck-scale-suppressed coupling to usual standard matter they may be considered as possible candidates for dark matter or UHECR (ultra-high energy cosmic rays).
In the talk, we comment on various dimensional reduction schemes, large extra dimensions (ADD-setups) as well as on orbifold compactification schemes of Randall-Sundrum type. We provide a brief summary about the obtained results published during the 8 years of active research in this field --- including discussions of effective static and dynamic perfect fluid scenarios, relations to reheating, transitions from radiation dominance to matter dominance, quintessence, UHECR, reaction channels with standard matter and possible creation of moduli excitations in ultra-strong background magnetic fields of magnetars. Finally, we give a brief overview about results on higher-dimensional f(R) theories as they are used in 4D as possible explanation for dynamically induced dark energy.

Keywords: string theory; M-theory; phenomenology; cosmology; extra dimensions; moduli stabilization; radion fluctuations; perfect fluids; UHECR; magnetars; f(R) gravity; dark matter; dark energy

  • Invited lecture (Conferences)
    Institutsseminar, 10.12.2008, Jena, Deutschland

Publ.-Id: 12054

Two models of Krein-space related physics: the MHD α2-dynamo and the PT-symmetric Bose-Hubbard model

Günther, U.; Kirillov, O.; Graefe, E.-M.; Korsch, H.-J.; Niederle, A.

In the first part of the talk, the eigenvalue behavior λ(α,β) of the 2×2 matrix differential operator of the spherically symmetric α2-dynamo of magnetohydrodynamics is considered for constant α-profiles and boundary conditions which depend on a parameter β. Specifically, β∈[0,1] acts as parameter in the homotopic interpolation between idealized (Dirichlet) and physically realistic (Robin) boundary conditions (BCs). For the quasi-exactly solvable monopole setup (with spherical mode number l=0) the characteristic equation is derived explicitly. It is shown that the β-homotopy describes an interpolation between spectra of mesh type (idealized BCs) and a countably infinite set of parabolas (physically realistic Robin Bcs). Interestingly, the mesh nodes (semisimple twofold degenerate eigenvalues) are fixed points of the β-homotopy. An underlying ruled-surface structure of the spectrum is uncovered.

In the second part of the talk, we provide a brief summary of recent results on the spectral behavior of the PT-symmetric
Bose-Hubbard system as it is used for the description of quantum Bose-Einstein condensates with balanced gain-loss interactions. For an N-particle system the corresponding Fock-space Hamiltonian reduces to an N×N-matrix which is selfadjoint in an N-dimensional Pontryagin space. The unfolding of higher-order branch-points of the spectrum is considered under parameter perturbations. Numerical as well as analytical results are presented which demonstrate the relevance of the Hessenberg type of the Hamiltonian as defining matrix structure for the occurrence of specific Galois cycles in the eigenvalue rings of the unfolding branch points.
partially based on: J. Phys. A 41 (2008) 255206; arXiv:0802.3164 [math-ph].

Keywords: Krein space; operator theory; boundary values; homotopy; spectral mesh; ruled surface; Bose-Hubbard model; Bose-Einstein condensate; Hessenberg type; spectral degeneration; Jordan block structure

  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12053

J-self-adjoint operators with C-symmetries: extension theory approach

Kuzhel, S.; Günther, U.; Albeverio, S.

A linear densely defined operator A acting in a Krein space with fundamental symmetry J and indefinite metric [.,.]J =(J.,.) is called J-selfadjoint if A*J = JA.  In contrast to self-adjoint operators in Hilbert spaces (which necessarily have a purely real spectrum), J-selfadjoint operators, in general, have a spectrum which is only symmetric with respect to the real axis. However, one can ensure the reality of the spectrum by imposing an extra condition of symmetry. In particular, a J-selfadjoint operator A has the property of C-symmetry if there exists a bounded linear operator C in H such that: (i) C2 =I; (ii) JC > 0; (iii) AC = CA. 
The properties of C are nearly identical to those of the charge conjugation operator in quantum field theory and the existence of C provides an inner product (.,.)C=[C.,.]J whose associated norm is positive definite and the dynamics generated by A is therefore governed by a unitary time evolution. However, the operator C depends on the choice of A and its finding is a nontrivial problem. 
The report deals with the construction of C-symmetries for J-selfadjoint extensions of a symmetric operator Asym with finite deficiency indices . We present a general method allowing us: (i) to describe the set of J-selfadjoint extensions A of Asym with C-symmetries; (ii) to construct the corresponding C-symmetries in a simple explicit form which is closely related to Clifford algebra operator structures; (iii) to establish a Krein-type resolvent formula for J-self adjoint extensions A with C-symmetries. 
The results are exemplified on 1D pseudo-Hermitian Schrödinger and Dirac Hamiltonians with complex point-interaction potentials. 

Keywords: J-selfadjoint operators; Krein space; extension theory; deficiency index; C-symmetry; Clifford algebra

  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12052

Determining role of Krein signature for 3D Arnold tongues of oscillatory dynamos

Kirillov, O.; Günther, U.; Stefani, F.

Using a homotopic family of boundary eigenvalue problems for the meanfield α2-dynamo with helical turbulence parameter α(r)= α0 + γΔα(r) and homotopy parameter β∈[0,1], we show that the underlying network of diabolical points for Dirichlet (idealized, β=0) boundary conditions substantially determines the choreography of eigenvalues and thus the character of the dynamo instability for Robin (physically realistic, β = 1) boundary conditions. In the (α0,β,γ)-space the Arnold tongues of oscillatory solutions at β =1 end up at the diabolical points for β = 0. In the vicinity of the diabolical points the space orientation of the 3D tongues, which are cones in first-order approximation, is determined by the Krein signature of the modes involved in the diabolical crossings at the apexes of the cones. The Krein space induced geometry of the resonance zones explains the subtleties in finding α-profiles leading to spectral exceptional points, which are important ingredients in recent theories of polarity reversals of the geomagnetic field.

Keywords: MHD dynamos; oscillatory dynamos; Krein space; Krein signature; diabolical points; perturbation theory; homotopy; boundary conditions; Arnold tongues; resonance zones

  • Lecture (Conference)
    8th Workshop "Operator Theory in Krein Spaces and Inverse Problems", 18.-21.12.2008, Berlin, Deutschland

Publ.-Id: 12051

The Structure of Polynuclear Uranyl Sorption Complexes at the Gibbsite/Water Interface

Rossberg, A.; Tsushima, S.; Scheinost, A. C.

Up to now only occasionally polynuclear sorption complexes of uranyl have been reported. This is undoubtedly surprising, since polynuclear hydrolysis species dominate aqueous uranyl speciation across a wide pH range and at solution concentrations typically used for sorption studies (10-6 - 10-4 M). Using U-LIII EXAFS spectroscopy at 15 K, we demonstrate here that polynuclear sorption complexes occur consistently at the gibbsite surface. They were observed across a pH range of 5.5 to 7.5 in equilibrium with atmospheric CO2, and at pH 8.5 in absence of CO2.
At these conditions, thermodynamic calculations predict the trimeric (UO2)3(OH)5+ complex to be the predominant hydrolysis species in the aqueous phase. This complex has been investigated recently by EXAFS spectroscopy and DFT calculations [1]. Both methods showed a stoichiometry of (UO2)3O(OH)3+ for this complex with a central oxo bridging, and provided a relatively short U-U distance of 3.8 Å. In contrast, coordination numbers and radial distances found for the sorption complex are 2xOaxial @ 1.8 Å, 6xOequatorial @ 2.4 Å and 1xU @ 4.2 Å. Both EXAFS shell fitting and a newly developed approach for the calculation of the radial pair distribution function achieved the same result. The U-U distance of 4.2 Å together with the coordination number of six for equatorial oxygen are in line with formation of uranyl dimers, where the two uranyl units are linked in edge-sharing configuration. This unusual structure is currently further investigated by DFT calculations.

1. S. Tsushima, A. Rossberg, A. Ikeda, K. Mueller, A. C. Scheinost, Inorganic Chemistry 46, 10819-10826 (2007).

  • Lecture (Conference)
    5th Workshop on Speciation, Techniques and Facilities for Radioactive Materials at Synchrotron Light Sources, Actinide-XAS-2008, 15.-17.07.2008, Saint-Aubin, France

Publ.-Id: 12050

Pair distribution function, Monte Carlo modelling and Factor Analysis: New approaches to EXAFS analysis.

Rossberg, A.; Funke, H.; Scheinost, A. C.

X-ray absorption fine-structure (EXAFS) spectroscopy allows the study of a large number of elements and compounds in different physical and chemical states. The most prominent structural parameters derived from EXAFS are coordination numbers, interatomic distances, static and vibrational disorder expressed by the Debye-Waller factor. These parameters are used in the conventional shell fitting approach to approximate the true radial pair distribution function (PDF). This shell fitting approach has three critical limitations for which we present possible solutions.

a) Due to the approximation of the PDF with Gaussian peak shapes, the conventional shell fitting approaches fails for all systems which show anharmonic contributions to the vibrational or static displacement of atoms, caused for instance by temperature effects or week bonds in adsorbate-adsorbent interactions [1]. To overcome this limitation we present two techniques: (1) a Monte Carlo simulation technique for EXAFS spectra which takes not only the first order scattering, but also higher order scattering into account [2] and (2) a novel application designed for the direct calculation of the PDF from the EXAFS spectrum.

b) Due to the limited resolution in R, the shell fitting approach commonly fails, if the X-ray absorbing atom is present in different chemical environments at the same time, i.e. in case of chemical mixtures. For this case we present a way to isolate the pure spectral components by Iterative Factor Analysis [3] and/or by a mathematical combination of Factor Analysis and Monte Carlo simulation [2].

c) In order to find a unique structural solution, shell fitting tends to be a soft modelling approach, because many structural arrangements may lead to a similar description of the EXAFS signal and have to be tested. Especially for the investigation of the unknown structures of sorption complexes, a hard modelling approach, which can take the complete substrate structure into account, would be much better suited. We show that the Monte Carlo simulation technique can be used as a hard modelling approach to solve the structure of sorption complexes [4].

[1] Crozier, E. D. Impact of the Asymmetric Pair Distribution Function in the Analysis of Xafs. Physica B-Condensed Matter 209, 330-333 (1995).
[2] Rossberg, A. & Scheinost, A. C. Three-dimensional modeling of EXAFS spectral mixtures by combining Monte Carlo Simulations and Target Transformation Factor Analysis. Analytical and Bioanalytical Chemistry 383(1), 56-66 (2005).
[3] Rossberg, A., Reich, T. & Bernhard, G. Complexation of uranium(VI) with protocatechuic acid - application of iterative transformation factor analysis to EXAFS spectroscopy. Analytical and Bioanalytical Chemistry 376, 631-638 (2003).
[4] Ulrich, K.-U., Rossberg, A., Foerstendorf, H., Zänker, H. & Scheinost, A. C. Molecular characterization of uranium(VI) sorption complexes on iron(III)-rich acid mine water colloids. Geochimica Et Cosmochimica Acta 70, 5469-5487 (2006).

  • Invited lecture (Conferences)
    2008 SSRL/LCLS Users' Meeting and Workshops, 15.-18.10.2008, Stanford, USA

Publ.-Id: 12049

Neuartige kapazitive Sensoren für die Visualisierung von Mehrphasenströmungen

Da Silva, M. J.; Thiele, S.; Hampel, U.

In diesem Beitrag werden zwei neuartige, bildgebende Sensoren zur Untersuchung von Mehrphasenströmungen beschrieben - der kapazitive Gittersensor und der kapazitive Flächensensor. Beide Sensoren basieren auf einer matrixförmigen Anordnung von Messelementen, mit denen die elektrische Kapazität eines umgebenden Fluides sehr schnell abgetastet wird. Dadurch sind diese Sensoren in der Lage, zeitlich und räumlich hoch aufgelöste Bilder der Phasenverteilung einer Mehrphasenströmung zu erzeugen. Die Sensoren und die zugehörige Messelektronik werden präsentiert. Darüber hinaus werden ausgewählte Ergebnisse von Strömungsvisualisierungen dargestellt und diskutiert.

In this article, two novel imaging sensors for the investigation of multiphase flows are introduced – the capacitive wire-mesh sensor and the capacitive planar array sensor. Both sensor systems are based on a matrix-type arrangement of sensing elements by which the electrical capacitance of a surrounding fluid is very fast scanned. Thus these sensors are able to produce high temporal and spatial resolution images of the phase distribution in a multiphase flow. The sensors and associated measuring electronics are presented. Furthermore some selected flow visualization results are represented and discussed.

Keywords: flow visualization; multiphase flow; electrical capacitance; electric permittivity; wire-mesh sensor; interdigital sensor


Publ.-Id: 12048

Coupled neutronic thermo-hydraulic analysis of full PWR core with BGCore system

Kotlyar, D.; Fridman, E.; Shwageraus, E.

BGCore reactor analysis system, recently developed at Ben-Gurion University for calculating in-core fuel composition and spent fuel emissions following discharge, couples the Monte Carlo neutronic code (MCNP4C) with an independently developed burnup and decay module SARAF. The BGCore utilizes multi-group approach for generation of one group cross-sections. According to this approach, only multi-group neutron spectrum is calculated by MCNP, while reaction rates are calculated in a separate subroutine using pre-generated multi-group cross-section set and the fine group neutron spectrum obtained from MCNP.
BGCore code system offers a number of advantages over similar MCNP-depletion codes. These include:

  • Multi-group coupling approach significantly reduces the code execution time without compromising the accuracy of the results.
  • Use of the most recent data based on JEFF-3.1 data files,
  • Careful choice of about 1700 isotopes to cover all potentially significant aspects of fuel irradiation and decay. All nuclides are included in the calculation matrix with no asymptotic approximation,
  • The fact that all of the isotopes, and not just the most neutronically important, are tracked in the BGCore throughout all depletion steps, allows calculations of post-irradiation fuel characteristics such as, activity, radiotoxicity, and decay heat with high degree of accuracy.
Substantial reduction in the BGCore code execution time allows consideration of problems with much higher degree of complexity, such as introduction of thermal hydraulic (T-H) feedback into the calculation scheme. Recently, a new T-H feedback module (THERMO) was developed and integrated into the BGCore system. At each computation point, the THERMO module receives as an input the power and the fuel burnup distributions in the core from the neutronic solver (MCNP) and calculates the temperatures distribution in core components and the coolant flow distribution in the core channels. The results of the THERMO calculations can be used for updating the relevant parameters in the MCNP input, such as fuel and moderator temperatures, and moderator density.
This study presents the results of coupled neutronic T-H analysis of full PWR core performed with BGCore system. The verification of BGCore system results against alternative state of the art computer code is also presented.

Keywords: Monte-Carlo burnup; coupled neutronic thermal-hydraulic analysis

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12047

Fracture mechanics characterisation of the WWER-440 reactor pressure vessel beltline welding seam of Greifswald unit 8

Viehrig, H.-W.; Schuhknecht, J.

WWER-400 second generation (V-213) reactor pressure vessels (RPV) were produced by IZHORA in Russia by and SKODA the former Czechoslovakia. The surveillance Charpy-V and SE(B) specimens of both producers have different orientation. The main difference is the crack extension direction which is through the RPV thickness and circumferential for ISHORA and SKODA RPV, respectively. In particular for the investigation of weld metal from multilayer submerged welding seams is the crack extension direction of importance. Depending on the crack extension direction in the specimen there are different welding beads or a uniform structure along the crack front. This is especially important for the fracture toughness determined according to the Master Curve (MC) approach as standardised in the ASTM Standard Test Method E1921-05. This approach was applied on weld metal of the RPV beltline welding seam of Greifswald Unit 8 RPV. Charpy size SE(B) specimens from 13 locations equally spaced over the thickness of the welding seam were tested. The specimens are TL and TS orientation.
The fracture toughness values measured on the SE(B) specimens with both orientations follow the course of the MC. Nearly all values lie within the fracture toughness curves for 5% and 95% fracture probability. There is a strong variation of the reference temperature T0 though the thickness of the welding seam, which can be explained with structural differences. The scatter is more pronounced for the TS SE(B) specimens. It can be shown that specimens with TL and TS orientation in the welding seam have a differentiating and integrating behaviour, respectively. The statistical assumptions behind the MC approach are valid for both specimen orientation even if the structure is not uniform along the crack front.

Keywords: reactor pressure vessel; multilayer welding seam; specimen orientation; structure; fracture toughness; Master Curve approach; reference temperature; integrity assessment of base metal from the Greifswald Unit 8 RPV show large scatter

  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2008, Dresden, Deutschland
    Proceedings Jahrestagung Kerntechnik 2009: INFORUM GmbH

Publ.-Id: 12046

Intense white photoluminescence emission of V-implanted ZnO oxide thin films

Müller, S.; Lorenz, M.; Czekalla, C.; Benndorf, G.; Hochmuth, H.; Grundmann, M.; Schmidt, H.; Ronning, C.

Pulsed laser deposited ZnO films were imlpanted with vanadium ions using ion energies between 30 and 250 keV with different fluences yielding vanadium concentrations in the range between 0.8 and 5 at. %. After annealing under oxygen ambient at 800°C, a broad luminescence band observed by photoluminescence covers nearly the total visible spectral region. This luminescence is a superposition of different bands triggered by the incoporated V and remaining implantation defects. The visual impression of the bright whitish emission of the implanted ZnO has been quantified using the color space map of the Commission internationale de l'Eclairage. Furthermore, the intensity of the white emission strongly increases with increasing V concentration, whereas Ar-implanted reference sample shows only weak white emission.

Keywords: ZnO; white luminescence

Publ.-Id: 12045

Hochdynamische Prozesse im Röntgenblick

Hampel, U.; Fischer, F.

Ein ultraschneller Elektronenstrahl-Tomograph visualisiert strömende Stoffgemische berührungsfrei mit Bildraten von bis zu 7000 Bildern pro Sekunde und einer räumlichen Auflösung von einem Millimeter. Das Gerät kann so Prozesse in Blasensäulenreaktoren sichtbar machen.

Keywords: Elektronenstrahltomographie

  • Nachrichten aus der Chemie (2009)1, 47-49

Publ.-Id: 12044

Influence of air entrainment on the liquid flow field caused by a plunging jet

Krepper, E.; Alt, S.; Renger, S.

During a jet gaseous bubbles are entrained. These bubbles influence the liquid flow field. The liquid flow field transports fibers in a sump geometry. Dependent on the flow situation different flow characteristics might occur. In the paper results of CFD calculations are presented and compared to experiments.

Keywords: plunging jet; two phase flow; gas entrainment; fiber transport

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany
    Proceedings of the Annual Meeting of Nuclear Technology (CD-ROM), paper No. 220
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Germany

Publ.-Id: 12043

Porovnani experimentalnich technik v oblasti dvoufazoveho proudeni (Comparison of experimental techniques in two-phase flow)

Otahal, J.; Hampel, U.; Schleicher, E.

We performed wire-mesh and X-ray micro-tomography studies of the two-phase flow in the mixing chamber of an effervescent atomizer. Flow patterns in the mixing chamber can be revealed by the miniature wire mesh sensor with a temporal resolution of 10 kHz whereas microtomography provides accurate and high-resolution axial-radial gas fraction profiles. The paper describes both measurement techniques and first results of experimental investigation.

Keywords: effervescent atomizer; two-phase flow; wire mesh sensor

  • Contribution to proceedings
    27th International Conference of Fluid Dynamics and Thermodynamics Departments, 24.-27.06.2008, Plzen, Czech Republic
    Proceedings of 27th International Conference of Fluid Dynamics and Thermodynamics Departments, Paper No. SK06

Publ.-Id: 12042

Two-phase flow characteristics in the mixing chamber of the effervescent atomizer

Otahal, J.; Hampel, U.; Schleicher, E.; Jicha, M.

The article deals with the description of two-phase flow in the mixing chamber of an effervescent atomizer. The first observation has been carried out with the use of high-speed records of the flow inside the mixing tube. The flow in the mixing chamber is very fast and inhomogeneous thus the need to use a high-sampling frequency device has arisen in order to describe changes in the flow. Therefore, an experimental technique has been found which is able to describe the liquid-air distributions in small channels. As a two-phase flow measurement instrument, a miniature wire-mesh conductivity sensor to deal with cross-sections of 8 mm in diameter was designed and built. The frame rate of this sensor is 10 000 images per second. In this study, a special model of a transparent nozzle spraying deionized water that makes use of air as the atomizing medium was used. The effervescent nozzle is of "inside-out gas injection" configuration with the internal diameter of the mixing channel 8 mm. During the experiment, the effervescent atomizer was operated at different air pressure levels ranging from 0.1 to 0.5 MPa and mass GLR (Gas-to-liquid- ratio) from 0.1 to 25%. Mass flow rates of water ranged from 5 up to 65 g·s-1. The results reveal the unstable behavior of two-phase flow in the mixing chamber.

Keywords: effervescent atomizer; two-phase flow; wire mesh sensor

  • Contribution to proceedings
    ILASS Europe 2008 - 22nd European Conference on Liquid Atomization and Spray Systems, 08.-10.09.2008, Como Lake, Italy

Publ.-Id: 12041

Empirical and numerical studies on gas entrainment by impinging jets

Schmidtke, M.; Danciu, D.

This work concerns experiments as well as CFD simulations on the gas entrainment for the impinging jet configuration. Impinging jets may occur in different situations related to reactor safety analyses. Many experiments have been carried out on impinging jets. A comprehensive overview by Bin [1993] reveals that the results depend critically on the individual setup (e.g. the nozzle geometry) and it is difficult to draw general conclusions. For the qualification of Computational Fluid Dynamics (CFD) models for such flow situations data with high resolution in space and time are required. Therefore a new experiment with a very simple setup was designed and first CFD simulations were done for these experiments.

Keywords: impinging jet; bubble entrainment

  • Contribution to proceedings
    Jahrestagung Kerntechnik 2009, 12.-14.05.2009, Dresden, Deutschland
    Beitrag 215
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2009, Beitrag 215, 12.-14.05.2009, Dresden, Deutschland

Publ.-Id: 12038

Huge performance increase of Tb-implanted MOS light emitting devices with SiOxNy layers moderating hot carrier effects

Rebohle, L.; Sun, J.; Prucnal, S.; Nazarov, A.; Tyagulskii, I.; Helm, M.; Skorupa, W.

The electrical stability of Tb-implanted SiO2 light emitting devices was drastically improved by using a SiON dielectric buffer layer. For fabrication thermally grown oxide layers on Si were implanted with Tb followed by a thermal treatment and the deposition of a SiON protection layer by plasma-enhanced chemical vapor deposition. The structures were finally provided with an indium tin oxide front contact and an aluminum rear contact. The incorporation of the SiON layer increases the breakdown electric field from 7.5 to 10.5 MV/cm and enhances the operation time of the light emitters up to three orders of magnitude under constant injection currents. By varying the SiO2 and SiON layer thickness it was found that the largest stability enhancements can be achieved if the SiON layer thickness is more than twice the thickness of the SiO2 layer.
The beneficial role of the SiON layer is mainly explained by reducing the chance of destructive avalanche breakdowns in the oxide layer and by an efficient cooling process of hot electrons moving in the conduction band of SiO2. The latter effect is based on the lower electric fields in SiON as compared to SiO2 and the lower band offset of SiON relative to the gate electrode. In addition, the SiON layer acts as a diffusion barrier against moisture from the working ambient and broadens the operation range of the light emitters on the voltage scale.

Keywords: electroluminescence; Terbium implanted MOS device; Si based light emission; silicon oxynitride

  • Lecture (Conference)
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12037

Electroluminescence, Charge Trapping and Clustering in Rare-Earth Implanted SiO2-Si Light-Emitting Diodes

Nazarov, A.; Tyagulskii, I.; Tyagulskiy, S.; Rebohle, L.; Prucnal, S.; Lehmann, J.; Biskupek, J.; Kaiser, U.; Skorupa, W.

In this work a comparative study of charge trapping, electroluminescence intensity (ELI) and clustering in SiO2 implanted by different rare-earth (RE) impurities (Eu, Tb, Gd, Er, Tm) with following high-temperature annealing is performed to clarify the connection between the electrical properties, the structure of the luminescent centers, the ELI and the EL spectra. RE impurities were implanted into the bulk of thermally grown SiO2 on n-type Si. The implanted doses were chosen in such a way that the maximum concentration corresponded to 0.1, 0.5, 1.5 and 3.0 at %. To activate the RE implanted impurities a post implantation furnace anneal in the temperature range of 800-1100 °C for 30 min and flash lamp annealing (FLA) for 20 ms at 1000 °C in a nitrogen ambient have been carried out. The ITO layer was used as a transparent electrode. Charge trapping was studied by the shifting of the high-frequency CV characteristics and the changing of the applied voltage during constant current electron injection from Si into SiO2. The EL signal was recorded at the same injection regime at room temperature in the wavelength range of 300 to 750 nm. Some control structures were studies by transmission electron microscopy with high resolution (XTEM).
It was shown that RE impurities such as Tb, Gd, Er and Tm implanted into SiO2 cause mainly net positive charge trapping in the range of the injected charge from 1x1015 to 2x1017 e/cm2 and stable ELI of their main luminescence lines in green, UV, IR and blue spectral region of the EL spectra, respectively. Above 1x1018 e/cm2 of the injected charge an electron trapping in the bulk of the oxide and a hole trapping at the SiO2-Si interface is observed for all types of the RE impurities. The electron trapping correlates with the EL quenching of the main EL lines for all studied RE implanted structures with the exception of the Eu implanted one. The Eu implanted oxide demonstrates effective electron trapping up to 1x1020 e/cm2 without EL quenching of the main studied EL lines: in red spectral region with a maximum at 618 nm (5D0-7F2 transition for Eu3+ ions); in the blue-green spectral region around 460-470 nm and in blue-violet one at 410 nm (corresponding to a 4f6d-4f7 transition of the Eu2+ ion). The XTEM measurements discovered that the clustering in the Eu-implanted SiO2 is enhanced considerably in comparison with the Tb-implanted one. It is suggested that the enhanced electron trapping in the Eu implanted structures is associated with enhanced clustering, which is partly caused by low valency (2+) oxides existing for the Eu impurity such as EuO and Eu3O4. The use of FLA for the Eu implanted SiO2 results in a decrease of the nanocluster size and an increase of the ELI in the red region of the spectrum.

Keywords: electroluminescence; rare earth implanted MOS devices; charge trapping; clustering

  • Poster
    2008 MRS Fall Meeting, 01.-05.12.2008, Boston, USA

Publ.-Id: 12036

Correlation between electroluminescence and charge trapping in multi-color Eu-implanted Si-based light-emitting diodes

Nazarov, A. N.; Tyagulskii, I. P.; Tyagulskii, S. I.; Rebohle, L.; Skorupa, W.; Biskupek, J.; Kaiser, U.

Electroluminescence (EL) spectra, charge trapping during operation of EL devices and clustering of rare earth oxides in SiO2 have been investigated in Eu-implanted SiO2-Si structures which demonstrate luminescence associated with the light-emitting transitions in Eu2+ and Eu3+. Strong electron trapping in all studied regions of the injected charge (from 1x10E14 to 1x10E18 e/cm2) during operation of the light-emitting devices has been found that considerably differed from the oxides implanted by other rare earth impurities (Ce, Tb, Gd, Er, Tm). It has been shown that the observed strong electron trapping and the low EL intensity in the Eu implanted structures were associated with enhanced clustering of the Eu oxides. The mechanisms of electron trapping in the SiO2 containing a large cluster concentration is discussed, and flash lamp annealing is proposed to decrease the nanocluster size and to enhance the EL intensity.

Keywords: MOSLEDs; rare earth implanted oxide; electroluminescence; charge trapping; clustering

  • Lecture (Conference)
    EMRS 2008 Spring Meeting, 26.-30.05.2008, Strasbourg, France
  • Physica E 41(2009), 902


Publ.-Id: 12035

Entwicklung neuer Chelatsysteme für nuklearmedizinische Anwendungen

Stephan, H.

kein Abstract verfügbar

  • Invited lecture (Conferences)
    Gastvorlesung Fachhochschule Zittau/Görlitz, 11.12.2008, Zittau, Deutschland

Publ.-Id: 12034

Cis-Trans-Isomerie in Bispidinkomplexen

Kraus, W.; Emmerling, F.; Juran, S.; Matterna, M.; Walther, M.; Stephan, H.

Radioaktive Kupferisotope nehmen sowohl für den Einsatz in der nuklearmedizinischen Diagnostik als auch in der Therapie einen besonderen Stellenwert ein. 64Cu und 67Cu sind dabei aufgrund günstiger kernphysikalischer Eigenschaften (Halbwertzeit, Art der Strahlung) von besonderem Interesse. Derivate des Bispidins (3,7-Diazabicyclo[3.3.1]nonan) bilden mit Übergangsmetall-kationen wie Cu2+, Co2+ oder Fe2+, Komplexe hoher Stabilität [1,2].
Für Bispidine ergeben sich drei unterschiedliche Konformationsisomere. Die abgeflachte Doppel-Sessel-Form repräsentiert die thermodynamisch stabilste Konformation. Darin sind die beiden Aminstickstoff-Donoratome N3 und N7 für die Koordination mit Metallionen optimal vororganisiert. Die Stellung von Substitutenten in den Positionen C2 und C4 bezüglich der Ringebene kann zur Bildung von Isomeren einer cis-trans-Konfigurationsisomerie führen. Sterisch anspruchsvolle Reste erzwingen die Bildung von trans-Isomeren. Das gilt in gleicher Weise für die Bindung voluminöser Donoreinheiten – wie Benzimidazolyl-Substituenten – in N3-Position des Bispidin-Gerüsts. Das entsprechende Piperidon (Fig.1) sowie das Bispidon (Fig. 2) zeigen die erwartete trans-Isomerie [3]. Dieser Befund wurde mit Hilfe der Kristallstrukturen nachgewiesen. Der Precursor (C27H25N5O5), a=8.1752(6) Å, b=11.1511(8) Å, c=15.8128(14) Å, V=1260.89(17) Å3, Z=2, R1=0.043 kristallisiert in der Raumgruppe P-1. In der Kristallstruktur des Kupferkomplexes [Cu(C35H33N7O5)(NO2)2] • H2O, P21/n, a=13.242(5) Å, b=17.971(7) Å, c=15.650(6) Å, V=3722.1(2) Å3, Z=4, R1=0.0451 2) ist das Kupferatom verzerrt quadratisch pyramidal koordiniert (dCu−N = 1.947(5) - 2.308(7) Å) und durch den Bispidin-Liganden nahezu vollständig von der Umgebung abgeschirmt.
Erste radiopharmakologische Untersuchungen zeigen, dass die Entwicklung kopplungsfähiger Liganden und deren Anknüpfung an ausgewählte Biomoleküle einen weiteren Schritt in Richtung einer besseren Bioverfügbarkeit von radioaktiv markierten Kupferverbindungen darstellt.

  • Poster
    17. Jahrestagung der Deutschen Gesellschaft für Kristallographie, 09.-12.03.2009, Hannover, Deutschland

Publ.-Id: 12033

Nanopatterning of semiconductor surfaces by sputtering from an inductively coupled plasma

Zhou, J.; Facsko, S.; Keller, A.; Möller, W.

Self-organized dot patterns have been fabricated on GaSb and Si surfaces by sputtering from an inductively coupled plasma. The dependence of the patterns on the ion energy has been investigated. In agreement with previous studies using plasmas or Kaufman sources, the dot wavelength on GaSb increases with energy. On Si surfaces, however, the dot wavelength increases with energy only in the range E < 800 eV. For 800 eV < E < 1500 eV, the dot wavelength is constant.

  • Lecture (Conference)
    Workshop Complex Nanostructures, 06.-07.10.2008, Dresden, Germany

Publ.-Id: 12032

Digital positron lifetime spectroscopy at EPOS

Krille, A.; Krause-Rehberg, R.; Jungmann, M.; Becvar, F.; Brauer, G.

As the digital equipment to measure positron lifetimes gets cheaper and more widely used, it is decided that EPOS, the ELBE positron source will sample the signals from the photomultipliers directly and evaluate it online or offline by digital means. Still using isotope sources, the EPOS lifetime spectrometer results in a timing resolution of around 170 ps (with Co-60), which compares good to analog equipment. A distinct improvement is expected when a coincidence setup will be used at ELBE. However, also the software needs further improvement: while one of the goals is of course to achieve the best time resolution, there is also the aspect of runtime and expandability. Results of evaluations will be presented and compared with results from other groups.

Publ.-Id: 12031

Efforts to verify neutron fluence calculations at pressure vessels of decommissioned reactors by means of retrospective niobium dosimetry

Konheiser, J.; Noack, K.; Mittag, S.; Rindelhardt, U.; Borodkin, G.; Borodkin, P.; Gleisberg, B.

For the first time, trepans from a decommissioned VVER-440 (Greifswald-1) reactor pressure vessel (RPV) have been examined. Activities of a trepan, taken at the RPV weld with the highest fast-neutron load, were measured and estimated on the basis of fluence calculations by the codes TRAMO and DORT. A maximum fluence of 4.05*1019 n/cm2 (E>0.5 MeV) was calculated. The average deviation between the two codes is 2.6 %. Activities resulting from the reaction 93Nb(n,n’)93mNb were measured, niobium being a trace element in the RPV steel. Unfortunately, 93mNb is also produced by neutron capture in the alloy component 92Mo, the built-up 93Mo decaying by electron capture. The ratios of calculated to measured (C/E) 93mNb gamma activities for several trepan samples are between 0.42 and 0.97. The fact that all C/E ratios are below unity suggests that the measured values may have been additionally heightened by activities from other nuclides.

  • Lecture (others)
    8.AAA Meeting Garching(München), 08.12.2008, München, Germany

Publ.-Id: 12030

A biogenic catalyst for hydrogenation, reduction and selective dehalogenation in non-aqueous solvents

Creamer, N. J.; Deplanche, K.; Snape, T. J.; Mikheenko, I. P.; Yong, P.; Samyahumbi, D.; Wood, J.; Pollmann, K.; Selenska-Pobell, S.; Macaskie, L. E.

We report the activity of a new palladium catalyst supported on fundamentally different Gram negative (Desulfovibrio) and Gram positive (Bacillus) bacterial surfaces (bio-Pd). Under H-2 (electron donor), cells of both strains reduced Pd(II) to Pd(0) as discrete nanoparticles located in the periplasmic space of D. desulfuricans or between the peptidoglycan and the proteinaceous surface layer (S-layer) of B. sphaericus. The catalytic activity of the preparations was similar in their ability to reduce Cr(VI) to Cr(III) (aq), and in the hydrogenation of itaconic acid (aq.) Bio-Pd on D. desulfuricans was also an effective catalyst in a range of reactions in methanol, performing comparably to a commercially available catalyst (10% Pd/C) in the conversion of 4-azidoaniline to 1,4-phenytenediamine. In the hydrogenation of 3-nitrostyrene, the bio-Pd showed selectivity for the partly reduced (dehalogenated) product (1-ethyl-3-nitrobenzene -74%, 1-ethyl-3-aminobenzene -7%) whereas the ! commercial catalyst produced only the fully reduced product (1-ethyl-3-aminobenzene -73%). In the case of 1-bromo-2-nitrobenzene, again bio-Pd was selective for the dehalogenated product, nitrobenzene, whereas the commercial catalyst produced the salt aniline hydrobromide.

Publ.-Id: 12029

Activities towards p-type doping of ZnO

Brauer, G.

  • Lecture (Conference)
    Seminar an der University of Hong Kong (Physics Department), 26.11.2008, Hong Kong, China

Publ.-Id: 12028

Potential of mirror-image oligonucleotides as molecular probes for pretargeting

Schlesinger, J.; Közle, I.; Bergmann, R.; Klussmann, S.; Vonhoff, S.; Pietzsch, H.-J.

To explore the potential of complementary mirror-image oligonucleotides as recognition systems for pretargeting, the present work deals with radiopharmacological evaluation of an 86Y-labeled 17mer l-DNA and of a hybrid consisting of the radiolabeled l-DNA and a complementary l-RNA (Figure 1). The 17mer l-DNA was functionalized with DOTA-Nhydroxysuccinimide ester and radiolabeled with 86Y (t1/2 = 14.7 h) resulting in the HPLCpurified [86Y-DOTA]-17mer (31 MBq; 2.0 GBq/μmol). Biodistribution studies with [86Y-DOTA]-17mer in Wistar rats showed high renal excretion and moderate kidney uptake (SUV: 18 ± 2.4, 18 h p. i.). More than 87% of [86Y-DOTA]-17mer were found intact in rat urine 60 min after injection. In thermal denaturation studies, a high melting point of 68°C (32 mM [Na+]) was determined for the hybrid. In conclusion, the high metabolic stability of the l-DNA and the high thermal stability of the l-DNA/l-RNA hybrid suggest the potential of this class of compounds as molecular probes for pretargeting.

  • Poster
    XI Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
  • Contribution to proceedings
    XI Turku PET Symposium New Targets in Molecular Imaging, 24.-27.05.2008, Turku, Finland
    Abstracts of the XI Turku PET Symposium, Kaarina, Finland: Painola, 978-951-29-3563-5, 38

Publ.-Id: 12027

The structure of monomeric and dimeric uranyl adsorption complexes on gibbsite: A combined DFT and EXAFS study

Hattori, T.; Saito, T.; Ishida, K.; Scheinost, A. C.; Tsuneda, T.; Nagasaki, S.; Tanaka, S.

We investigated the structure of uranyl sorption complexes on gibbsite (pH 5.6 - 9.7) by two independent methods, density functional theory (DFT) calculations and extended X-ray absorption fine structure (EXAFS) spectroscopy at the U-LIII edge. To model the gibbsite surface with DFT, we tested two Al (hydr)oxide clusters, a dimer and a hexamer. Based on polarization, structure, and relaxation energies during geometry optimization, the hexamer cluster was found to be the more appropriate model. An additional advantage of the hexamer model is that it represents both edges and basal faces of gibbsite. The DFT calculations of (monomeric) uranyl sorption complexes show an energetic preference for the corner-sharing versus the edge-sharing configuration on gibbsite edges. The energy difference is so small, however, that possibly both surface species may coexist. In contrast to the edge sites, sorption to basal sites was energetically not favorable. EXAFS spectroscopy revealed in all investigated samples the same interatomic distances of the uranyl coordination environment (RU-Oax ≈ 1.80 Å, RU-Oeq ≈ 2.40 Å), and towards the gibbsite surface (RU-O ≈ 2.87 Å, RU-Al ≈ 3.38 Å). In addition, two U-U distances were observed, 3.92 Å at pH 9.7 and 4.30 Å at pH 5.6, both with coordination numbers of ~ 1. The short U-U distance is close to that of the aqueous uranyl hydroxo dimer, UO2(OH)2, reported as 3.875 Å in the literature, but significantly longer than that of aqueous trimers (3.81-3.82 Å), suggesting sorption of uranyl dimers at alkaline pH. The longer U-U distance (4.30 Å) at acidic pH, however, is not in line with known aqueous uranyl polymer complexes. Based on the EXAFS findings we further refined dimeric surface complexes with DFT. We propose two structural models: in the acidic region, the observed long U-U distance can be explained with a distortion of the uranyl dimer to form both a corner-sharing and an edge-sharing linkage to neighboring Al octahedra, leading to RU-U = 4.150 Å. In the alkaline region, a corner-sharing uranyl dimer complex is the most favorable. The U-O path at ~2.87 Å in the EXAFS spectra arises from the oxygen atom linking two Al cations in corner-sharing arrangement. The adsorption structures obtained by DFT calculations are in good agreement with the structural parameters from EXAFS analysis: U-Al (3.394 Å), U-U (3.949 Å), and U-O (2.823 Å) for the alkaline pH model, and U-Al (3.279 Å), U-U (4.150 Å), and U-O (2.743 Å) for the acidic pH model.

Keywords: EXAFS; DFT; uranyl; sorption; gibbsite; dimer; trimer

Related publications

  • Geochimica et Cosmochimica Acta 73(2009)20, 5975-5988

Publ.-Id: 12025

Surface diffusion assisted phase separation during the growth of carbon : transition metal thin films

Abrasonis, G.

Encapsulated nanostructures formed by surface diffusion assisted phase separation during thin film growth are promising candidates for the multifunctional devices, high density magnetic storage media, multifunctional coatings, as large scale templates for nanowire fabrication. In this talk our activities concerning the investigation of the growth mechanisms, structure of the metallic ‘inclusion’ and carbon ‘tissue’ phase as well as their interface structure of carbon: transition metal (TM=V,Co,Ni,Cu) thin films will be summarized. It will be demonstrated that a combined use of laboratory and element selective synchrotron radiation based analytical tools allows identification of the morphology, nearest neighbour coordination as well as the electronic structure of the metallic nanoparticles and the carbon matrix individually and tracking of their changes as a function of the growth temperature, metal type and metal content.

  • Lecture (others)
    Invited seminar, 28.11.2008, Melbourne, Victoria, Australia

Publ.-Id: 12024

A High Resolution Time-of-Flight Spectrometer for Fission fragments and Ion beams

Kosev, K. M.

Thesis For the purpose of fission-fragment detection a double time-of-flight (TOF) spectrometer has been developed. The key component of the spectrometer is a TOF detector consisting of multichannel-plate (MCP) detectors with a position-sensitive readout, a foil for secondary electron production and an electrostatic mirror. The spectrometer performance is tested at tandem and superconducting linear accelerator.

  • Other report
    Dissertation: Technische Universität Dresden, 2009
    119 Seiten

Publ.-Id: 12023

An improved experiment for the investigation of the helical magnetorotational instability

Stefani, F.; Gerbeth, G.; Gundrum, T.; Szklarski, J.; Rüdiger, G.; Hollerbach, R.

The magnetorotational instability (MRI) is widely believed to play an essential role in the formation of stars and black holes. Destabilizing hydrodynamically stable Keplerian flows, the MRI triggers turbulence and enables outward transport of angular momentum in accretion discs which is necessary to explain the mass accumulation rates of central objects. The Potsdam Rossendorf Magnetic InStability Experiment (PROMISE) is intended to study the helical version of MRI which works already at Reynolds numbers of the order of 1000 and Hartmann numbers of the order 10. We focus on the results of an improved experiment in which split end caps are used to minimize the effect of Ekman pumping.

  • Lecture (Conference)
    11th MHD days, 01.-03.12.2008, Ilmenau, Germany

Publ.-Id: 12022

Semiconductor-based spintronics

Schmidt, H.

In the talk the advantages of semiconductor-based spintronics are presented.

  • Lecture (others)
    FZD Lecture, 05.05.2008, Dresden, Deutschland

Publ.-Id: 12021

Room temperature ferromagnetism in Nd- and Mn-codoped ZnO films

Xu, Q.; Schmidt, H.; Hochmuth, H.; Lorenz, M.; Setzer, A.; Meinecke, C.; Grundmann, M.

Nd and Mn were codoped into ZnO films which have been grown on a-plane sapphire substrates by pulsed laser deposition with the thickness ranging between 46 and 971 nm. The room temperature resistivity of the codoped films is independent of the film thickness. Large positive magnetoresistance and clear anomalous Hall effect were observed at 5 K. Ferromagnetism with clear hysteresis up to 290 K was observed. Codoping is suggested to be an efficient method to introduce energy levels in the ZnO band gap to mediate electron spins of the magnetic doping ions.

Keywords: ZnO; ferromagnetism

Publ.-Id: 12020

Vacuum ultraviolet dielectric function and band structure of ZnO

Schmidt-Grund, R.; Rheinländer, B.; Kaidashev, E. M.; Lorenz, M.; Fritsch, D.; Schubert, M.; Schmidt, H.; Herzinger, C. M.

For ZnO, the optical dielectric functions for polarizations parallel and perpendicular to the optical axis were determined in the photon energy range from 4.0 to 9.5 eV by using generalized spectroscopic ellipsometry and the band structure was calculated by means of the empirical pseudopotential method. From the band structure, a theoretical dielectric function was derived. The dielectric functions reveal features that were identified as band-to-band transitions. The energies of those transitions were assigned to band-to-band transition energies of critical points of the calculated band structure.

Keywords: ZnO; empirical pseudopotential; generalized spectroscopic ellipsometry; dielectric function

  • Journal of the Korean Physical Society 53(2008)1, 88-93

Publ.-Id: 12019

Intensity of optical absorption close to the band edge in strained ZnO films

Fritsch, D.; Schmidt, H.; Schmidt-Grund, R.; Grundmann, M.

Besides other one of the remarkable properties making wurtzite ZnO such an interesting material is its large exciton binding energy of about 60 meV, leading to stable excitons at room-temperature. Also, the Curie temperature of this wide-gap material has been predicted to lie above room temperature, making ZnO alloyed with magnetic ions a possible material for spintronics applications. One big challenge in the fabrication of the ZnO-based heterostructure devices is the lattice mismatch between the ZnO films and the substrates and the different thermal expansion coefficient inducing biaxial strain. This work reports on the electronic band structure of biaxially strained ZnO for strains along the a- or c-axis ranging from -1% to 1 %, as calculated by means of the empirical pseudopotential method. Thereby, we also account for relativistic effects in the form of the spin-orbit interaction, as well as for the energy dependence of the crystal potential through the use of nonlocal model potentials. Moreover, the application of a variable plane wave basis set allows us to directly obtain the strain-induced variations of the electronic and the optical properties of wurtzite ZnO.

Keywords: ZnO; emipirical pseudopotential method; dielectric function

  • Journal of the Korean Physical Society 53(2008)1, 123-126

Publ.-Id: 12018

Homoepitaxial ZnO thin films by PLD: Structural properties

Lorenz, M.; Wagner, G.; Rahm, A.; Schmidt, H.; Hochmuth, H.; Schmid, H.; Mader, W.; Brandt, M.; von Wenckstern, H.; Grundmann, M.

Homoepitaxial ZnO films deposited on annealed hydrothermal O-face ZnO single crystals show superior structural quality. This is demonstrated by narrow ZnO(00.2) rocking curves with FWHM of typically 23 to 35 arcsec, and nearly dislocation-free TEM cross sections. Nominally undoped ZnO films indicate a minor in-plane strain of about 250 ppm and no out-of-plane strain. Target doping by 0.01% P2O5 or 0.5% Li3N results in pseudomorphic film growth without in-plane strain. Increasing doping concentration of 0.1 and 1% P2O5 results in both in-plane and out-of-plane strain up to 0.9 % indicating relaxed films. The O-face polarity of the homoepitaxial ZnO films is confirmed by convergent beam electron diffraction.

Keywords: ZnO; pulsed laser deposition

Publ.-Id: 12017

THz sideband generation in multi quantum wells

Wagner, M.; Schneider, H.; Helm, M.; Schartner, S.; Andrews, A. M.; Roch, T.; Strasser, G.

Ac THz electric fields which couple strongly with intraband excitations in semiconductors can lead to spectral sidebands when an interband excitation is present. In this nonlinear mixing process a near-infrared (NIR) laser beam is mixed with a THz beam to generate sidebands around the NIR frequency with a frequency spacing equal to the THz frequency or multiples of it. In the last years this effect has been investigated in various semiconductor systems (i.e. in bulk GaAs or in multi quantum wells).
We investigated the third-order nonlinear mixing process between a near-infrared laser and a free-electron laser in an undoped symmetric AlGaAs/GaAs multi quantum well. Differently from the literature where electronic intersubband transitions were used, we are using the transition between the heavy-hole and light-hole states. This transition around 73 µm is pumped close to normal incidence by FELBE, the free-electron laser (FEL) of the Forschungszentrum Dresden-Rossendorf. The picosecond NIR laser is transmitted through the sample where the GaAs substrate has been etched away. It is focused on the entrance slit of the spectrometer of a Streak-camera system. With the Streak-camera temporal and spectral measurements are possible.
The n=+2 sideband conversion efficiency is of the order of 0,005% with respect to the incoming NIR intensity. Among other things we present the power dependency on NIR and FEL intensity and the resonance behavior with respect to the NIR and FEL wavelengths.

Keywords: THz sidebands; free-electron laser; FEL

  • Poster
    GDRE-THz workshop 2008 Paris, 25.-26.09.08, Paris, Frankreich
  • Poster
    EOS Annual Meeting 2008, 29.09.-02.10.2008, Paris, Frankreich
  • Poster
    Nonna 2008 - Workshop on Nonequilibrium Nanostructures, 01.-06.12.2008, Dresden, Deutschland

Publ.-Id: 12016

High electron mobility of phosphorous-doped homoepitaxial ZnO thin films grown by pulsed-laser deposition

Brandt, M.; von Wenckstern, H.; Schmidt, H.; Rahm, A.; Biehne, G.; Benndorf, G.; Hochmuth, H.; Lorenz, M.; Meinecke, C.; Butz, T.; Grundmann, M.

The transport properties of phosphorous-doped ZnO thin films, grown by pulsed-laser deposition on thermally pretreated hydrothermally grown ZnO single-crystal substrates, are reported. The ZnO:P thin films show very good morphological and structural properties as confirmed by atomic force microscopy (AFM), high resolution x-ray diffraction, and Rutherford backscattering (RBS) channeling. Steps of height c/2 are visible in AFM investigations for all samples. For an oxygen partial pressure of 0.1 mbar, two-dimensional growth was found. RBS channeling of a ZnO:P film shows a minimum yield of 0.034 which is comparable to that of an annealed substrate (0.033). Hall effect measurements revealed that all films are n-type for the present growth conditions. Peak mobilities of 800 cm^2/Vs have been observed around 70 K, in line with the high structural quality of the samples. Room-temperature mobility in ZnO:P is up to 170 cm^2/Vs.

Keywords: ZnO; phosphorous-doping

Publ.-Id: 12015

X-ray scattering and diffraction from Xe-induced ripples in crystalline (001) silicon

Biermanns, A.; Pietsch, U.; Grenzer, J.; Hanisch, A.; Facsko, S.; Carbone, G.; Metzger, H.

The formation of surface-nanostructures with a characteristic size ranging from several nanometer up to microns has attracted significant interest in the last decades in the context of fabrication of novel opto-electronic and storage devices. One kind of those nanostructures are wave-like patterns (ripples) produced by an interplay between a roughening process caused by ion beam erosion (sputtering) of the surface and smoothening processes caused by surface diffusion. In this contribution we report on investigations of patterned Si (001) surfaces after irradiation with Xe-ions using ion-energies up to 70keV. During the sputtering, an amorphous surface-layer is formed followed by a rather sharp interface towards crystalline material, showing the same morphology as the surface. The structures of the amorphous layer and the amorphous-crystalline interface were studied by means of grazing incidence- small angle scattering (GISAXS) and diffraction (GID) using synchrotron-radiation. We found that the crystal structure at the interface is expanded along the ripples, caused by the creation of defects inside the surface region, whereas this expansion is strongly reduced across the ripples, which can be explained by an anisotropic defect distribution close to the amorphous-to-crystalline interface.

Keywords: nanostructures ion-beam patterning GISAXS GID

  • Poster
    16th International Conference on Ion Beam Modification of Materials - IBMM 08, 31.07.-05.09.2008, Dresden, Germany

Publ.-Id: 12014

Paramagnetism in Co-doped ZnO films

Xu, Q.; Zhou, S.; Markó, D.; Potzger, K.; Fassbender, J.; Vinnichenko, M.; Helm, M.; Hochmuth, H.; Lorenz, M.; Grundmann, M.; Schmidt, H.

Co-doped ZnO films with various electron concentrations up to 4.61×1019 cm-3 at room temperature were prepared by pulsed laser deposition on a-plane sapphire substrates. Only paramagnetism was observed down to 2 K for all the samples, which was also confirmed by x-ray magnetic circular dichroism (XMCD) measurements at 30 K. The average magnetic moment per Co2+ ion is significantly smaller than the expected moment for Co2+ ions (L=1.07, S=3/2), mainly due to the antiferromagnetic exchange interaction between the neighbouring Co2+ ions in the ZnO matrix. Also clustering instead of a uniform distribution of Co2+ ions may play a role. The formation of Co clusters is hindered at higher substrate temperature during the thin film growth. Clear anomalous Hall effect was observed in the highly conducting Co-doped ZnO films at low temperatures up to 100 K.

Keywords: diluted magnetic semiconductor; paramagnetism; anomalous Hall effect

Publ.-Id: 12013

X-ray absorption and photoelectron spectroscopy investigation of selenite reduction by FeII-bearing minerals

Funke, H.; Scheinost, A.

Wavelet transform (WT) has been proven as a valuable tool for EXAFS data analysis for structures, where two types of backscattering atoms are at the same distance from the central atom [1-3]. WT provides not only radial distance resolution of the spectra like the Fourier transform, but resolves also the wave vector space permitting to probe the discrimination of atoms by their elemental nature.
A short introduction to the continuous WT will be given. The variation of the parameters of the Morlet mother wavelet will be used to build an adapted wavelet for the analysis of specific EXAFS spectra. Thereby the analysis of the (Heisenberg) uncertainty boxes of the Morlet wavelet is a central point to understand the resolution limitations of the WT as well as the form of the wavelet ridges.
Two examples for the use of WT for EXAFS data analysis will be given.
First, the method is applied to a structural problem of Zn-Al layered double hydroxides, demonstrating the homogeneity of the metal cation distribution in the hydroxide layers. Depending on the specific problem, either the well-known Morlet wavelet was used, or a newly developed FEFF-Morlet wavelet, based on theoretical EXAFS back scattering functions.
Second, the reduction from soluble selenium species to elemental Se and iron selenides by Fe containing minerals is examined in detail [4]. Here, the wavelet analysis is used to answer the question: Is Se coordinated to Se atoms/elemental Se or to the Fe (and Se) atoms? This analysis is performed by comparison to well–known reference spectra.
In the outlook two open questions will be discussed: the k weighting and the destructive interference by phase shifts.


[1] H. Funke, A. C. Scheinost, and M. Chukalina, Phys. Rev B, 71, 094110, 2005.
[2] H. Funke, M. Chukalina, and A. C. Scheinost, J. Synchrotron Rad. 14, 426-432, 2007.
[3] M. Muñoz, P. Argoul, and F. Farges, Am. Mineral. 88, 694, 2003.
[4] A. C. Scheinost, L. Charlet , Environ. Sci. Technol. 42, 1984, 2008.

  • Lecture (Conference)
    Workshop on X-ray absorption spectroscopy and advanced XAS techniques, 06.-10.10.2008, Villigen, Switzerland

Publ.-Id: 12012

S-Layer für neue Nanomaterialien

Pollmann, K.; Raff, J.

Im Rahmen des Vortrags werden die Arbeiten zur Herstellung von Nanopartikeln und Nanomaterialien mit Hilfe von bakteriellen Hüllproteinen vorgestellt und Möglichkeiten einer zukünftigen Zusammerarbeit diskutiert.

  • Lecture (others)
    Koordinierungstreffen mit dem Leibniz-Institut für Katalyse e.V. der Universität Rostock, Außenstelle Berlin, 17.04.2008, Berlin, Deutschland

Publ.-Id: 12009

Tailoring the FePt orientation on amorphous substrates by magnetron sputtering, structural and magnetic investigations

Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.

Towards an increase of the magnetic recording density, materials with a high magnetic anisotropy are strongly recommended to overcome the physical limits due to superparamagnetism. For this reason, FePt alloys are widely studied because of the excellent magnetocrystalline anisotropy (KU ~ 5-8 x 10-7 erg/cm3) and large magnetic moments at 300K. [1] But, for perpendicular recording media, a (001) preferential orientation, perpendicular to the layer surface, is required.
10 and 15 nm Fe55Pt45 layers were deposited by dual magnetron sputtering on amorphous SiO2 / Si (001) substrate, varying the deposition methods, form co-deposition to monolayers sequence deposition, and working gas, from Ar to Xe, at 0.3 Pa.
The Ar plasma is more energetic than the Xe one: it is characterized by sputtered atoms with a mean energy of about 12 eV and Ar reflected neutrals, reaching a mean energy of about 100 eV when backscattered from the Pt target. This energy budget that enhance the surface adatom mobility during deposition (few eV are required), and create vacancies (E > 40 eV), that decrease the phase transition temperature to 450°C for thin layers. [2]
But, the impact of energetic atoms supports a vertical layers intermixing resulting in a randomly oriented FePt A1 structure at RT. Subsequent Rapid Thermal Annealing at 750°C is completely transforming the layer into the L10 phase, with a coercivity field HC = 1 T, but introducing a weak perpendicular magnetic anisotropy, not evidencing any difference between the deposition techniques.
The reduction of the plasma energy, by using Xe as working gas, is not decreasing the layer magnetic properties (HC = 1 T) after annealing, but strongly enhance the (001) preferential orientation, with a dispersion of the (001) direction around the surface normal of 6°, already in the co-deposition experiment.
The layer by layer technique, associated with Xe plasma, supports the (001) layer orientation after RTA at 750°C, underlining the importance to reduce the elements diffusion path to an atomistic scale. [3]

[1] H. Kanazawa, G. Lanhoff, T. Suzuki, J. Appl. Phys. 87 (2000) 6143
[2] V. Cantelli, J. von Borany, A. Mücklich, Shengqiang Zhou, J. Grenzer,
Nucl. Instr. and Meth. B, 257, 1-2 (2007) 406-410.
[3] M. L. Yan, N. Powers, D. J. Sellmyer, J. Appl. Phys. 93, 8292 (2003)

Keywords: FePt; sputtering gas; (001) orientation

  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12007

Experiments on nuclear astrophysics in Dresden

Bemmerer, D.

Recent experimental work on nuclear astrophysics questions at Research Center Dresden-Rossendorf (FZD) is discussed. Several large scale experimental facilities hosted in the city of Dresden/Germany have been used. The ELBE accelerator provides a 40 MeV intensive electron beam driving secondary radiation sources, for example bremsstrahlung and neutron time-of-flight. At the FZD ion beam center, a study on hydrogen burning is underway. The Felsenkeller shallow-underground counting facility in Dresden is used for a study of the astrophysical p-process.

  • Invited lecture (Conferences)
    Seminar, INFN sezione di Padova, 27.11.2008, Padua, Italy
  • Invited lecture (Conferences)
    Nuclear Physics Seminar, 14.05.2009, Legnaro (PD), Italien

Publ.-Id: 12006

MRPC prototype developments for NeuLAND/R3B at FZ Dresden Rossendorf

Bemmerer, D.; Yakorev, D.; Stach, D.; Wagner, A.

Multigap resistive plate chamber detector (MRPC) prototypes for the future NeuLAND detector at R3B/FAIR have been developed and built at Forschungszentrum Dresden-Rossendorf. The prototypes have been submitted to a variety of tests, including highly precise timing measurements at the ELBE electron beam in Dresden. Results and future perspectives of MRPC prototyping for NeuLAND by the Dresden group are discussed.

  • Lecture (Conference)
    Joint R3B/EXL/ELISE Collaboration Meeting, 11.-14.10.2008, Göteborg, Sweden

Publ.-Id: 12005

Präzise Kernphysik für die Sonne

Bemmerer, D.

Neue astronomische Beobachtungen ermöglichen es, ein bisher unerreicht genaues Bild unserer Sonne zu zeichnen. Solch ein Bild ist erforderlich, um den langfristigen Einfluss der Sonne auf das Erdklima zu verstehen, und um aus der Sonne einen kalibrierten Referenzstern zu machen.

Allerdings gibt es beim Verständnis der für die Energieproduktion im Sonneninnern verantwortlichen Kernfusionsreaktionen noch Diskrepanzen. Um sie aufzuklären, sind präzise kernphysikalische Messungen vonnöten. In dem Vortrag werden in Dresden und am Gran Sasso (Italien) untersuchte und für die Sonne relevante Kernreaktionen diskutiert und gezeigt, wie die neu gewonnenen Daten bisher bestehende Genauigkeitslücken schließen.

Abschließend wird auch auf die Auswirkungen der neuen Daten auf das Verständnis der Urknall-Nukleosynthese und der Entstehung der chemischen Elemente in Sternen, die schwerer als die Sonne sind, eingegangen.

  • Invited lecture (Conferences)
    Physikalisches Kolloquium, 02.12.2008, Dresden, Deutschland

Publ.-Id: 12004

The 3He(alpha,gamma)7Be S-factor at solar energies: The prompt gamma experiment at LUNA

Costantini, H.; Bemmerer, D.; Confortola, F.; Formicola, A.; Gyürky, G.; Bezzon, P.; Bonetti, R.; Broggini, C.; Corvisiero, P.; Elekes, Z.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Imbriani, G.; Junker, M.; Laubenstein, M.; Lemut, A.; Limata, B.; Lozza, V.; Marta, M.; Menegazzo, R.; Prati, P.; Roca, V.; Rolfs, C.; Rossi Alvarez, C.; Somorjai, E.; Straniero, O.; Strieder, F.; Terrasi, F.; Trautvetter, H. P.

The 3He(alpha,gamma)7Be process is a key reaction in both Big-Bang nucleosynthesis and p–p chain of Hydrogen Burning in Stars. A new measurement of the 3He(alpha,gamma)7Be cross section has been performed at the INFN Gran Sasso underground laboratory by both the activation and the prompt gamma detection methods. The present work reports full details of the prompt gamma detection experiment, focusing on the determination of the systematic uncertainty. The final data, including activation measurements at LUNA, are compared with the results of the last generation experiments, and two different theoretical models are used to obtain the S -factor at solar energies.

Publ.-Id: 12003

The effect of the sputtering gas (Ar, Xe) on FePt clusters formation. Structural and magnetic properties

Cantelli, V.; Grenzer, J.; von Borany, J.; Fassbender, J.

In this study it will be reported about the effect of the sputtering gases, Ar and Xe, on FePt clusters formation using magnetron sputtering deposition at high working pressures. Two different deposition techniques were investigated, a sequential layer by layer deposition and a co-deposition of Fe and Pt. All layers with bulk equivalent thicknesses between 3 to 5 nm were realized at RT and subsequently rapid thermal annealed in order to induce the A1-L10 ordering transformation at 550°C.
The highest L10 fraction in the annealed samples was found using Xe as sputtering gas: Xe decreases the transformation activation energy and therefore, reduces the critical thickness necessary to obtain the strong ferromagnetic phase.
The Ar assisted depositions give FePt clusters with the L10 phase only if the layer-by-layer growth is used, whereas for Xe no differences in the deposition techniques were observed.

Keywords: FePt; Magnetron sputtering; sputtering gases; clusters

  • Lecture (Conference)
    53th Conference on Magnetism and Magnetic Materials, 10.-14.11.2008, Austin Texas, USA
  • Contribution to proceedings
    53th Conference on Magnetism and Magnetic Materials, 10.11.-14.12.2008, Austin Texas, USA
    Journal of Applied Physics 105(2009), 07B529-07B529-3
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany


Publ.-Id: 12002

Cavity layer introduction in SIMOX technology

Ou, X.; Kögler, R.; Mücklich, A.; Skorupa, W.; Möller, W.; Wang, X.

The oral conference contribution reports about latest results of the improvement of the SIMOX process for fabrication of silicon-on-insulator (SOI) materials by defect engineering.

Keywords: SOI; SIMOX; ion implantation; defect engineering

  • Lecture (Conference)
    72. Jahrestagung der DPG und DPG Frühjahrstagung des Arbeitskreises Festkörperphysik, 25.-29.02.2008, Berlin, Germany

Publ.-Id: 12001

Kelvin probe force microscopy imaging of cross-sections of Si multilayer structures

Baumgart, C.; Müller, A.-D.; Müller, F.; Helm, M.; Möller, A.; Schmidt, H.

Kelvin probe force microscopy (KPFM) is a standard technique for the investigation of surface potentials. We present its applicability to cross-sectionally prepared p-p+ Si multilayer structures. The contact potential difference (CPD) image between tip and sample has been recorded by means of an Anfatec Level-AFM with a 2nd amplifier and NSC15 probes from MikroMash. Using an active mixer, the excitation amplitude of the NSC15 probes is almost independent on the working frequency. The probed CPD signal difference between the layers ranges between 60 meV and 850 meV and can be correlated to the variation of the diffusion potential in the Si multilayer structure. The p-type of majority charge carriers and the corresponding acceptor dopant profile have been pinpointed by scanning capacitance measurements. Starting from the known donor dopant concentration in the NSC15 probe, we simulated the CPD and determined the acceptor concentration in the whole p-p+ Si multilayer structure. From the frequency dependence of the CPD we can clearly distinguish between surface and bulk effects.

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2009, 22.-27.03.2009, Dresden, Germany

Publ.-Id: 12000

Influence of the fluid properties on co-current two-phase flows in a horizontal channel connected to a riser

Vallee, C.; Seidel, T.; Lucas, D.; Beyer, M.; Prasser, H.-M.; Pietruske, H.; Schütz, P.; Carl, H.

0In the event of a loss-of-coolant-accident (LOCA) in a pressurised water reactor (PWR), emergency strategies have to be mapped out in order to guarantee the reliable removal of the decay heat from the reactor core. During a hypothetical small break LOCA with failure of the high pressure emergency core cooling system, the decay heat has to be released to the secondary circuit over the steam generators. Therefore, the primary circuit is designed to forward a natural circulation if the main coolant pumps are not available. Furthermore, if steam is generated in the primary circuit due to its depressurisation, stratified two-phase flow regimes can occur in the main cooling lines, which could be relevant for the reactor safety. It is intended that a computational fluid dynamics (CFD) approach could increase the simulation accuracy of such transient accident scenarios compared to the state of the art system codes.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Forschungszentrum Dresden-Rossendorf (FZD). The hot leg is the line connecting the reactor pressure vessel (RPV) to the steam generator (SG) and is composed of a horizontal pipe, a 50° upward bend and an inclined riser (Figure 1). The hot leg model is operated in the pressure chamber of the TOPFLOW facility of FZD (Figure 1), which is used to perform high-pressure experiments under pressure equilibrium with the inside atmosphere of the chamber. Therefore, the test section does not have to support overpressures and can be designed with thin materials. Consequently, parts of the test section could be equipped with big size windows for the application of optical observation techniques, also at reactor typical boundary conditions. In order to provide optimal observation possibilities, a flat test-section design was chosen with a width of 50 mm.

Co-current flow experiments were performed in the hot leg model, simulating a two-phase natural circulation in the primary circuit of a PWR. The experiments were done with air and water at 3.0 bar and room temperature as well as with steam and water at pressures up to 50 bar and the corresponding saturation temperature (i.e. up to 264°C). Over this range of boundary conditions, the main fluid properties vary significantly. The frequency distribution of the water level measured in the RPV simulator was used to characterise the flow in the hot leg (Figure 2). It was found that the form of the distribution informs about the stationarity of the water flow to the steam generator: the flatter the distribution, the more discontinuous the transport of water over time. This tendency was confirmed by the high-speed video observations (Figure 3), which were also used to identify the flow regime. Furthermore, Figure 2 shows a comparison between the frequency distributions obtained from the air/water and the steam/water experiments. Generally, the distributions are flatter for the cold experiments than for the hot ones. This shows that, due to the lower surface tension and viscosity, the transport of water induced by the gas is more constant in time for the steam/water flow.

Keywords: two-phase flow; co-current flow; fluid properties; hot leg; pressurised water reactor; PWR

  • Contribution to proceedings
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland, Krakow: AGH University of Science and Technology Press, 978-83-7464-235-4, 443-452
  • Lecture (Conference)
    ExHFT-7 - 7th World Conference on Experimental Heat Transfer, Fluid Mechanics and Thermodynamics, 28.06.-03.07.2009, Krakow, Poland

Publ.-Id: 11999

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