Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

31745 Publications
Coexistence of ferromagnetism and superconductivity in single-phase Bi3Ni nanostructures
Herrmannsdörfer, T.; Skrotzki, R.; Schönemann, R.; Wosnitza, J.; Köhler, D.; Boldt, R.; Ruck, M.;
  • Invited lecture (Conferences)
    Seminar an der TU Chemnitz, 08.11.2011, Chemnitz, Deutschland
  • Poster
    26th International Conference on Low Temperature Physics (LT26), 10.-17.08.2011, Beijing, China
  • Invited lecture (Conferences)
    Workshop on “Magnetic Materials under Extreme Conditions" und ESRF Users´Meeting, 06.-08.02.2012, Grenoble, France

Publ.-Id: 16593 - Permalink

Fermi-Surface Topology of Ce1-xYbxCoIn5
Ignatchik, O.; Polyakov, A.; Wosnitza, J.; Bianchi, A. D.; Prevost, B.; Blackburn, S.; Coté, M.; Capan, C.; Hurt, D.; Fisk, Z.;
  • Poster
    Moscow International Symposium on Magnetism (MISM) 2011, 20.-25.08.2011, Moscow, Russia

Publ.-Id: 16592 - Permalink

Magneto-acoustic study of UCuGe
Zherlitsyn, S.; Andreev, A. V.; Yasin, S.; Skourski, Y.; Wosnitza, J.; Zvyagin, A. A.;
We present results of a magneto-acoustic study of single crystalline UCu0.95Ge in static (up to 18 T) and pulsed (up to 60 T) magnetic fields. This intermetallic compound exhibits antiferromagnetic (AF) ordering at TN = 48 K. The magnetic structure of UCuGe, characterized by the AF arrangement of the magnetic moments in the basal plane of the hexagonal lattice is determined by competing intra- and inter-layer exchange interactions. In magnetic fields applied along the c direction this material shows a phase transition at 38 T to a spin-polarized state with an U magnetic moment of 1.3µB. This phase transition is seen as a jump in the magnetization, accompanied by a hysteresis. The sound velocity and sound attenuation demonstrate pronounced anomalies in the vicinity of both the antiferromagnetic ordering and the field-induced phase transition proving the important role of magneto-elastic interactions in the physics of this actinide compound. We discuss our results in frame of a phenomenological model, which describes qualitatively the main experimental observations. In addition to the features accompanying the magnetic phase transitions, a broad and frequency-dependent step-like change of the sound velocity together with a broad maximum of the sound attenuation have been observed for the ultrasound wave propagating along the c axis at temperatures above TN. We discuss these anomalies in relation to vacancy dynamics in the nonstoichiometric UCu0.95Ge.
  • Poster
    SCES 2011, 29.08.-03.09.2011, Cambridge, United Kingdom

Publ.-Id: 16591 - Permalink

Abschlussbericht Reaktorsicherheitsforschung - Vorhaben-Nr.: 150 1331 Wissenschaftlich-technische Zusammenarbeit mit Russland: Untersuchungen zu Mechanismen der Strahlenversprödung und des Ausheilverfahrens sowie Fluenzberechnungen für Reaktordruckbehälter von WWER-Reaktoren
Viehrig, H.-W.; Houska, M.; Ulbricht, A.; Konheiser, J.; Altstadt, E.; Noack, K.;
The project was performed in the framework of the scientific technical cooperation in the scope of nuclear safety research between Germany and Russia. Objects of the investiga-tions are the decommissioned reactor pressure vessels (RPV) of the Greifswald nuclear power plant. The Greifswald WWER-440/V-230 nuclear reactors represent the first genera-tion of this reactor type. The investigation of these RPV’s enable the assessment of the aging and the effect of an industrial thermal annealing of serial RPVs for the first time. The main focus of the investigations was not on the application of mechanical-technological test methods on which the Russian technical regulation is based, but on the application of ad-vanced fracture mechanics test methods. This enables a fracture mechanics RPV integrity assessment which is based on direct measured fracture toughness values. With the investi-gations it is shown that real neutron induce embrittlement of the beltline welding seam and the forged base metal ring cannot be predicted by the Russian technical regulation. The direct measured KJC values and the resulting Master Curve T0 values, which characterise the ductile-to-brittle transition, differ fundamentally of those which were determined on mechani-cal technological values.
A further topic is the investigation of irradiation induced microstructural defects which origi-nates the embrittlement and their mitigation by the thermal annealing. Within separate sub-projects neutron fluence calculations were performed for the investigated WWER-440/V-230 RPVs and their support constructions.
Keywords: nuclear reactors, Russian WWER type ,reactor pressure vessel, reactor pressure vessel steels, base metal, welding seam, fracture toughness, microstructure, integrity assessment, neutron fluence
  • Other report
    Dresden: Abschlussbericht HZDR\FWS\2011\06, 2011
    161 Seiten

Publ.-Id: 16590 - Permalink

Ion-assisted bottom-up nanostructuring of carbon-transition metal nanocomposite films: a GISAXS study
Abrasonis, G.; Krause, M.; Buljan, M.; Wintz, S.; Zschornak, M.; Grenzer, J.;
Nanocomposite materials become of ever increasing importance in numerous fields of science and technology such as tribology, plasmonics, spintronics, sensing, catalysis, including the strategic quest for renewable energies regarding photovoltaics, solar collectors or thermoelectrics. The macroscale properties of nanocomposite materials are strongly influenced by their nanoscale morphology. Therefore a control of this nanoscale morphology is of major importance.

Here we present a GISAXS study of C:Ni nanocomposite thin films grown by ion beam assisted deposition (IBAD). IBAD combines Ar+ ion beam co-sputtering of a C-Ni target to produce film forming species with a simultaneous irradiation of the growing film with low energy (50-140 eV) Ar+ ions. Depending on the ion energy and metal content this leads to different 3D morphologies such as dispersed nanoparticles, tilted nanocolumns or spatially ordered compositional nanopatterns. These structures show their characteristic fingerprints in GISAXS patterns. A theoretical approach to reproduce such patterns will be presented. The results show that low energy ions provide a powerful means to induce the self-organizion leading to the formation of 3D compositional nanopatterns.
  • Poster
    GISAXS 2011, 10.-12.10.2011, Hamburg, Germany

Publ.-Id: 16589 - Permalink

Spin transfer oscillators with different geometries
Fowley, C.; Sluka, V.; Bernert, K.; Deac, A.;
For applications one requires high power, narrow line-width oscillators which can operate ideally at zero field. Spin transfer torque can induce precession in GMR and TMR spin valves.
There are recent demonstrations of out of plane precession in both in-plane and perpendicular magnetic free layers. Here, we calculate the outputs by solving the LLGS equations for these two geometries. We find that the system with perpendicular free layer is advantageous for two reasons: a further reference layer is not required as the polarising layer itself acts as a reference layer for the GMR effect; precession is independent of the initial magnetisation state, that is various magnetisation directions can be excited into precession at specific fields and currents.
Keywords: spin-transfer torque, spin-torque oscillators, giant magnetoresistance, perpendicular anisotropy
  • Poster
    Spin Master Voice, 13.-16.12.2011, Paris, France

Publ.-Id: 16588 - Permalink

Commissioning Results of the SRF Gun with Lead Cathode
Barday, R.; Anders, W.; Jankowiak, A.; Kamps, T.; Knobloch, J.; Kugeler, O.; Matveenko, A.; Neumann, A.; Quast, T.; Rudolph, J.; Schenk, M.; Völker, J.; Sekutowicz, J.; Smedley, J.; Kneisel, P.; Nietubyc, R.; Teichert, J.;
A superconducting radio-frequency (SRF) gun with a superconducting Pb photocathode was build up for the first stage of the BERLinPro gun. We report on the activities on the gun and measurements of the beam parameters like beam energy and beam current. Improvement of the quantum efficiency after the laser cleaning treatments is discussed.
Keywords: Superconducting Radio Frequency, Photo Injector, Electron Source, Photo Cathode, Pb Cathode, Quantum Efficiency, Laser Cleaning
  • Open Access LogoContribution to proceedings
    PSTP 2011, XIV International Workshop on Polarized Sources, Targets and Polarimetry, 12.-16.09.2011, St. Petersburg, Russia
    Proceedings of the PSTP 2011

Publ.-Id: 16587 - Permalink

Incorporation of N in TiO2 films grown by DC-reactive magnetron sputtering
Sério, S.; Melo Jorge, M. E.; Nunes, Y.; Barradas, N. P.; Alves, E.; Munnik, F.;
Photocatalytic properties of TiO2 are expected to play an important role on emerging technologies based on OH radicals to destroy harmful nonbiodegradable organic and inorganic contaminants in water. The drawback is the wide band gap of TiO2 (3.2 eV) limiting its use to the UV part of electromagnetic spectrum under sunlight. Therefore, modifications of TiO2 are needed to tune the gap in order to allow an efficient use of the entire solar spectrum. One possibility is N-doping of TiO2 to make the photocatalytic activity possible under visible light and more suitable for water treatment.
In our study nitrogen-doped TiO2 (TiO2-xNx) films were deposited by DC-reactive magnetron sputtering using a dual-magnetron co-deposition apparatus on unheated glass and silicon substrates using a pure titanium target. The depth profile of nitrogen was measured with heavy ion elastic recoil detection analysis combined with Rutherford backscattering spectrometry (RBS) and correlated with the optical and structural properties obtained by UV–VIS spectroscopy and X-ray diffraction (XRD).
Keywords: N-doping TiO2, Band gap tuning, Sputtering, Ion beam analysis

Publ.-Id: 16586 - Permalink

Modified SRF photoinjector for the ELBE at HZDR
Murcek, P.; Arnold, A.; Büttig, H.; Michel, P.; Teichert, J.; Xiang, R.; Kneisel, P.;
The superconducting radio frequency photoinjector (SRF photoinjector) with Cs2Te cathode has been successfully
operated under the collaboration of HZB, DESY, HZDR, and MBI. In order to improve the gradient of the gun cavity and the beam quality, a new modified SRF gun (SRF-gun 2008) has been designed. The main updates of the new cavity design for the new photoinjector were published before (SRF09 Conference Berlin). This cavity is being fabricated in Jefferson Lab.
In this paper the new ideas of the further parts of the SRF-gun 2008 will be presented. The most important issue is the special design of half-cell and choke filter. The cathode cooler is also slightly changed, which simplifies the installation of the cathode cooler in the cavity. The next update is the separation of input and output of the liquid nitrogen supply, for the purpose of the stability of the nitrogen pressure as well as the better possibility of temperature measurement. Another key point is the implementation of the superconducting solenoid inside the cryomodule. The position of the solenoid can be accurately adjusted with two step motors, which are thermally isolated to the solenoid itself.
Keywords: Superconducting Radio Frequency, Photo Injector, Electron Source, Superconducting Cavity, Superconducting Solenoid, Cryomodule
  • Poster
    SRF 2011, 15th International Conference on RF Superconductivity, 25.-29.07.2011, Chicago, USA
  • Open Access LogoContribution to proceedings
    SRF 2011, 15th International Conference on RF Superconductivity, 25.-29.07.2011, Chicago, USA
    SRF2011 Proceedings: JACoW

Publ.-Id: 16585 - Permalink

Ion beam analysis of as-received, H-implanted and post implanted annealed fusion steels
Gonzalez-Arrabal, R.; Munnik, F.; González, M.; Romero, P.; Heller, R.; Leardini, F.; Perlado, J. M.;
The elemental distribution for as-received (AR), H implanted (AI) and post-implanted annealed (A) Eurofer and ODS-Eurofer steels has been characterized by means of micro Particle Induced X-ray Emission (µ-PIXE), micro Elastic Recoil Detection (µ-ERD) and Secondary Ion Mass Spectrometry (SIMS). The temperature and time-induced H diffusion has been analyzed by Resonance Nuclear Reaction Analysis (RNRA), Thermal Desorption Spectroscopy (TDS), ERDA and SIMS techniques. µ-PIXE measurements point out the presence of inhomogeneities in the Y distribution for ODS-Eurofer samples. RNRA and SIMS experiments evidence that hydrogen easily outdiffuses in these steels even at room temperature. ERD data show that annealing at temperatures as low as 300 °C strongly accelerates the hydrogen diffusion process, driving out up to the 90% of the initial hydrogen.
Keywords: Fusion reactor steels, ODS-Eurofer, Hydrogen depletion, Elemental composition, Ion beam analysis, Nuclear microprobe

Publ.-Id: 16584 - Permalink

Beam Loss Monitoring and Machine Protection at the ELBE CW Accelerator
Teichert, J.; Büchner; A.; Justus, M.; Lehnert, U.; Michel, P.; Schurig, R.;
The superconducting CW linac of the ELBE facility produces an electron beam up to 40 MeV and 1 mA average current. The beam is used to drive two IR FELs and target stations for production of bremsstrahlung, neutrons, and positrons. An upgrade of the ELBE facility is ongoing which includes an increase of beam current as well as new experimental opportunities such as the production of broadband THz radiation and the interaction of electrons with high power laser beams. The high beam power requires a fast and safe machine protection system. It was found that a continuous beam loss of about 10 µA or a total beam loss for longer than 2 ms produce damage. The beam loss at ELBE is monitored by two systems: beam loss monitors measuring the radiation in cable-like ionization chambers along the beamline, and beam current difference measurement system based on stripe line beam position monitors.
Keywords: Superconducting Linac, Beam Loss, Machine Protection, Ionization Chamber, Beam Position Monitor
  • Lecture (Conference)
    ERL 2011, The 50th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 16.-21.10.2011, Tsukuba, Japan

Publ.-Id: 16583 - Permalink

Structure and Formation of hexanuclear Actinide(IV) complexes
Hennig, C.;
The structure and the formation of Actinide(IV) complexes in aq. solution and related crystal structures will be discussed.
Keywords: EXAFS, XRD, Actinide(IV)
  • Invited lecture (Conferences)
    Johannes Gutenberg Universität Mainz, Institut für Kernchemie, 23.1.2012, Mainz, Germany

Publ.-Id: 16582 - Permalink

ERL2011 Summary of Working Group 1: Progress with RF injectors
Rao, T.; Arnold, A.; Belomestnykh, S.; Nguyen, D.;
This paper summarizes the progress made in the past two years, with RF injectors as electron sources for high average power Energy Recovery Linac-based light sources (ERL) and Free Electron Lasers (FEL).
Keywords: RF injectors
  • Open Access LogoContribution to proceedings
    The 50th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 16.-21.10.2011, Tsukuba, Ibaraki, Japan: Joint Accelerator Conferences Web Site (JACoW), 10-29

Publ.-Id: 16581 - Permalink

Interactions of U(VI) with archaea: what is different than with bacteria?
Selenska-Pobell, S.; Reitz, T.; Merroun, M.;
Archaea, in contrast to the diverse and dense bacterial populations, occur in uranium mining wastes in low numbers and belong mostly to particular crenarchaeal groups, some of them not yet cultured [1,2].
On the example of the termoacidophilic crenarchaeon Sulfolobus acidocaldarius, indigenous for many uranium contaminated wastes [3,4], we demonstrate that archaea tolerate substantially lower concentrations of U(VI) than bacteria and that they interact with this radionuclide in a significantly different way. One of the reasons for this behaviour is the unusual cell wall structure of the representatives of Crenarchaeota which is restricted to a single proteinaceous surface layer (S-layer), that is in contrary to the complex, rather thick, and rich on metal-binding ligands cell wall structure of bacteria. Due to the extreme acidic and mechanic stability of the S. acidocaldarius S-layer, it was possible to produce empty cells (ghosts) consisting only of the outermost S-layer membrane and to study their interactions with U(VI) at highly acidic (pH 1.5 and 3.0) and at moderate acidic (pH 4.5 and 6.0) conditions. Applying a set of modern spectroscopic techniques such as Time-Resolved Laser-induced Fluorescence (TRLF), X-ray Absorption, and Fourier-Transformed Infrared (FT-IR) we were able to clearly demonstrate that at highly acidic conditions the S. acidocaldarius S-layer does not play any protective role against the toxic U(VI). At these conditions low amounts of uranium are bound mainly by the phosphate groups of the cytoplasma membrane [5]. This finding is in distinction to the results obtained with S-layers of the bacterial isolates recovered from uranium mining wastes. The S-layers of the latter bind significant amounts of U(VI) and strongly contribute to the remarkable uranium resistance of their hosts [6]. The high capability of the mentioned bacterial S-layers to bind U(VI) was contributed to the fact that they are phosphorylated [6]. This feature is unusual for both bacterial and archaeal S-layers and is not the case for the S-layer of S. acidocaldarius [6, 7]. At moderate acidic conditions (pH 4.5), typical for most uranium mining wastes, the studied archaeal S-layer ghosts, again in contrast to the bacterial ones, bind insufficient amounts of U(VI) exclusively via the carboxylic groups of their carboxylated amino acid residues [7]. At pH 6.0, which is substantially above the growth optimum of S. acidocaldarius, the permeability of its cells is increased due to the pH stress and possibly also to the presence of U(VI). As a result uncontrolled uptake of U(VI) as well as release of phosphorylated biomolecules and also of orthophosphate occurs. These processes result initially in formation and precipitation of mixed uranyl phosphate phases. With the time the most part of U(VI) is bio-mineralized in inorganic mineral phases. The efficacy of these biomineralization processes is, however, much lower then those published for bacteria, possibly due to the lower amount of polyphosphatic granules in the studied archaeon [8].
We suggest that the limited presence of archaea in uranium wastes is related to their lower resistance to U(VI) which is determined by their cell wall structure and possibly also by some particular physiological and biochemical characteristics.

[1] Rastogi (2009) Microbial Ecology 58, 129-139. [2] Reitz (2007) FZR-Report 459, 42. [3] Marsh (1983] FEMS Microb. Lett., 17, 311-315. [4] Groudev (1993) FEMS Microb. Rev., 11, 260-268. [5] Reitz (2010) Radiochim Acta 98, 249-257. [6] Merroun (2005) Appl. Environ. Microbiol. 71, 5532-5543. [7] Reitz (2011] Radiochim Acta 99, 543-553. [8] Remonselez (2006) Microbiology, 152, 59-66.
Keywords: U(VI) binding, archaea, S-layers, biomineralization
  • Lecture (Conference)
    Goldschmidt 2012, 24.-29.06.2012, Montreal, Canada
  • Abstract in refereed journal
    Mineralogical Magazine 76(2012), 2352

Publ.-Id: 16580 - Permalink

Dipole strength in 78 Se below the neutron separation energy from a combined analysis of 77 Se(n, γ) and 78 Se(γ , γ') experiments
Schramm, G.; Massarczyk, R.; Junghans, A. R.; Belgya, T.; Beyer, R.; Birgersson, E.; Grosse, E.; Kempe, M.; Kis, Z.; Kosev, K.; Krticka, M.; Matic, A.; Schilling, K. D.; Schwengner, R.; Szentmiklosi, L.; Wagner, A.; Weil, J. L.;
The dipole strength function and the nuclear level density of the compound nucleus 78Se were studied in a combined analysis of a cold neutron capture experiment on 77Se performed at the research reactor in Budapest and a photon-scattering experiment on 78Se performed at the electron linear accelerator ELBE with bremsstrahlung produced at a kinetic electron energy of 11.5 MeV. In the combined analysis we developed the extreme statistical code γ DEX for the simulation of radiative cascade deexcitations occurring in neutron capture and photon scattering. Comparisons of experimental and simulated neutron capture spectra allow us to estimate a temperature of T = 900 keV for the level density according to the constant-temperature model for 78Se. Using γ DEX, we were also able to estimate ground-state branching ratios and intensities of inelastic transitions for states in 78Se excited via photon scattering. In this way, we derived the photoabsorption cross section from 4 MeV up to the neutron separation energy from the measured photon-scattering data. The results obtained match the photoabsorption cross section derived from (γ , n) measurements and show an enhancement of dipole strength around 9 MeV.
Keywords: Nuclear level density, Strength functions, Statistical model

Publ.-Id: 16578 - Permalink

The Superconducting RF Photoinjector at ELBE
Arnold, A.;
A superconducting RF photo-injector (SRF gun) has been installed at the ELBE linac. It is the first SRF gun which is in operation at an accelerator up to now. The SRF gun consists of a 3½ cell, 1.3 GHz superconducting cavity with normal conducting photocathode in it. At present, the gun delivers electron bunches with kinetic energies of 3 MeV in CW mode and up to 4 MeV in pulsed mode operation. The Cs2Te photo cathodes used in the gun exhibit a very long life time, e.g. a cathode was in use for more than one year and delivers a charge of 35 C. A degradation of the cavity performance due the normal conducting photo cathode was no found. The electron beam delivered to ELBE was used for beam transport optimization, longitudinal parameter and slice emittance measurements. The performance of the gun is mainly limited by the low gradient of the present cavity. For that reason two new and slightly modified cavities have been fabricated and tested at Jlab. The results of the vertical tests are very promising.
Keywords: superconducting RF photo-injector, SRF-Gun, ELBE
  • Invited lecture (Conferences)
    The 50th ICFA Advanced Beam Dynamics Workshop on Energy Recovery Linacs, 16.-21.10.2011, Tsukuba, Ibaraki, Japan


Publ.-Id: 16577 - Permalink

Formation and structure of hexanuclear Actinide(IV) carboxylates
Hennig, C.;
Recent insights into formation and structure of hexanuclear Actinide(IV) carboxylates will be discussed
Keywords: EXAFS, XRD, Uranium, Thorium, Neptunium
  • Invited lecture (Conferences)
    University of Grenoble I, Institute of Earth Science, 17.01.2012, Grenoble, France

Publ.-Id: 16576 - Permalink

Contactless flowrate sensors for Na, PbBi and Pb flows
Buchenau, D.; Gerbeth, G.; Priede, J.;
Accurate and reliable flow rate measurements are required for various liquid metal systems such as the Na or Lead-flows in fast reactors, the PbBi-flows in transmutation systems, or the flows in liquid metal targets. Commercial flow meters are typically based on the flow-induced electrical voltage, which is measured by electrodes in direct contact to the melt, in a steady magnetic field. For liquid metal flows, a contactless measurement is preferable. We report on the recent development of two types of such flow meters. The former operates by detecting the flow-induced disturbance in the phase distribution of an externally applied AC magnetic field. Such a phase-shift flow meter was developed with an emitting coil at one side of the duct and two sensing coils at the opposite side. The second approach uses a rotatable single cylindrical permanent magnet, which is placed close to the liquid metal duct. The rotation rate of this magnet is proportional to the flow rate. The signal of this sensor is independent on the electrical conductivity of the flowing melt, thus independent on temperature. Both flow rate sensors have been tested at several liquid metal loops: a Na- and a Lead-loop at HZDR, and a PbBi-loop at SCK-CEN Mol (Belgium). In all cases, both sensors show a very good linearity of their signal with the true flow rate in the pipe. For the sodium flow at the NATAN facility of HZDR, the measured flow rates were also compared with measurements of the local velocity profile in the duct performed by ultrasonic Doppler velocimetry.
Keywords: Contactless flowrate measurement, Phase-shift sensor, Rotating magnet, Ultrasonic Doppler Velocimetry, Na, Pb, PbBi
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14 , 25.-30.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14 , 25.-30.09.2011, Toronto, Canada

Publ.-Id: 16575 - Permalink

Quo vadis, Partikeltherapie?
Enghardt, W.; Hodapp, N.; Schreiber, L.; Zink, K.;

Publ.-Id: 16574 - Permalink

Selected research topics on nuclear reactor thermal hydraulics
Lucas, D.; Schäfer, F.; Tusheva, P.;
In the presentation some aspects of nuclear reactor thermal hydraulics are discussed. It focusses on accident analyses for loss of coolant accidents (LOCA) and demonstrates the capabilities of system codes. In a second part recent research on the qualification of CFD codes for nuclear reactor safety issues is presented. Special attention is paid to experimental work done at HZDR to obtain CFD-grade experimental data. The TOPFLOW facility is combined with innovative measuring techniques to obtain such data.
Keywords: nuclear reactor thermal hydraulics, LOCA, CFD, experiment
  • Invited lecture (Conferences)
    International Seminar Series of the Universitas Gadjah Mada, Faculty of Engineering, 30.01.-03.02.2012, Yogyakarta, Indonesia

Publ.-Id: 16573 - Permalink

Innovative Pressure Tube Light Water Reactor with Variable Moderator Control
Rachamin, R.; Galperin, A.; Fridman, E.;
The features of a reactor based on multiple pressure tubes, rather than a single pressure vessel, provide the reactor with considerable flexibility for continuous design improvements and developments. This paper presents the development of innovative pressure tube light water reactor, which has the ability to advance the current pressure tubes reactors. The proposed design is aimed to simplify the pressure tubes reactors by:
• replacing heavy water by a light water as a coolant and moderator,
• adopting batch refueling instead of on-line refueling.
Furthermore, the design is based on proven technologies, existing fuel and structure materials. Therefore, it is reasonable to expect significant capital cost savings, short licensing and introduction period of the proposed concept into the power production grid.
The basic novelty of the proposed design is based on an idea of variable moderator content in the core and “breed & burn” mode of operation. In order to achieve a practical reactor design build on proven technology, several features of the advanced CANDU reactor (ACR-1000) were adopted. It should be stressed however, that while some of the ACR-1000 mechanical design features are adopted, the core design basics of the reactor proposed here are completely different. First, the inter fuel channels spacing, surrounded by the calandria tank, contains a low pressure gas instead of heavy water moderator. Second, the fuel channel design features an additional/external tube (designated as moderator tube) connected to a separate moderator management system. The proposed design is basically pressure tube light water reactor with variable moderator Control (PTVM LWR).
This paper presents a detailed description of the PTVM core design and demonstrates the reactivity control and the “breed & burn” mode of operation, which are implemented by the variation of the moderator in the core, from a neutronics point of view.
Keywords: pressure tube reactor, moderator variation, “breed & burn”, reactivity control
  • Lecture (Conference)
    The 26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel
  • Contribution to proceedings
    The 26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel

Publ.-Id: 16572 - Permalink

Loss of Coolant Accident Analysis for IRR 1
Rachamin, R.; Elias, E.; Galperin, A.;
Detailed LOCA analysis has been performed for the 5MWth swimming pool type IRR-1, which utilizing highly enriched uranium fuel. The analysis was aimed to assess the possibility of passively cooling the exposed reactor core by natural convection of air and thermal radiation. The core uncover time was estimated by assuming that the LOCA was induced by a guillotine break of a 10 inch water pipe at the bottom of the pool, causing the core to uncover about 20 min after reactor SCRAM.
The effect of the reflector on the core cooling was studied by comparing the total heat transfer from the core with and without considering the thermal contact between the core and the graphite reflector elements. It has been shown that for uncover time of 20 min the core may reach melting point if thermal contact with the graphite is neglected. On the other hand, considering perfect thermal contact between the core and the graphite reflector, the core temperature is predicted to remain below the clad melting point.
Keywords: Loss of Coolant Accident (LOCA), Decay heat, Natural convection, Thermal radiation, IRR-1
  • Lecture (Conference)
    The 26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel
  • Open Access LogoContribution to proceedings
    The 26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel

Publ.-Id: 16571 - Permalink

Entwicklung und Validierung von CFD-Modellen für polydisperse Blasenströmungen auf der Basis von TOPFLOW-Experimenten
Lucas, D.; Krepper, E.; Beyer, M.;
In Rahmen der Qualifizierung von CFD-Methoden für Fragestellungen der nuklearen Sicherheitsforschung werden am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) CFD-Modellkonzepte und Schließungsmodelle entwickelt. Für die Modellentwicklung und deren Validierung werden experimentelle Daten in hoher Orts- und Zeitauflösung benötigt. Die TOPFLOW-Anlage des HZDR verbindet Experimente bei anwendungsnahen Parametern mit innovativer Messtechnik, die solche Daten in der erforderlichen Qualität liefert. Am Beispiel der Modellentwicklung für polydisperse Blasenströmungen werden entsprechende Experimente an der TOPFLOW-Anlage vorgestellt und die Verwendung der Resultate für die CFD-Code-Entwicklung und Validierung demonstriert.
Keywords: bubbly flow, experiment, CFD, measuring technique
  • Invited lecture (Conferences)
    Garchinger Seminare, 19.01.2012, Garching, Deutschland

Publ.-Id: 16570 - Permalink

Conceptual Design of a Pressure Tube Light Water Reactor with Variable Moderator Control
Rachamin, R.; Galperin, A.; Fridman, E.;
This paper presents the development of innovative pressure tube light water reactor with variable moderator control. The core layout is derived from a CANDU line of reactors in general, and advanced ACR-1000 design in particular. It should be stressed however, that while some of the ACR-1000 mechanical design features are adopted, the core design basics of the reactor proposed here are completely different. First, the inter fuel channels spacing, surrounded by the calandria tank, contains a low pressure gas instead of heavy water moderator. Second, the fuel channel design features an additional/external tube (designated as moderator tube) connected to a separate moderator management system. The moderator management system is design to vary the moderator tube content from “dry” (gas) to “flooded” (light water filled). The dynamic variation of the moderator is a unique and very important feature of the proposed design. The moderator variation allows an implementation of the “breed & burn” mode of operation. The “breed & burn” mode of operation is implemented by keeping the moderator tube empty (“dry” filled with gas) during the breed part of the fuel depletion and subsequently introducing the moderator by “flooding” the moderator tube for the “burn” part. This paper assesses the conceptual feasibility of the proposed concept from a neutronics point of view. The variation of the moderator in the fuel channels has been modeled and shown to have a potential to increase the discharged burnup and improve the reactivity control.
Keywords: pressure tube reactor, moderator variation, “breed & burn”, reactivity control
  • Lecture (Conference)
    PHYSOR 2012 - Advances in Reactor Physics, 15.-20.04.2012, Knoxville, Tennessee, USA
  • Open Access LogoContribution to proceedings
    PHYSOR 2012 – Advances in Reactor Physics, 15.-20.04.2012, Knoxville, Tennessee, USA

Publ.-Id: 16569 - Permalink

Demonstration of the Serpent Monte-Carlo code applicability to Few-group Constants Generation for Existing and Advanced Reactor concepts
Fridman, E.; Shwageraus, E.;
Serpent is a continuous-energy Monte Carlo (MC) reactor physics code recently developed at VTT Technical Research Centre of Finland. Serpent can be used for 2D fuel lattice calculations as well as for 3D full core simulations. Due to its built-in decay and burnup routine Serpent can perform depletion and decay analysis to provide time-dependent isotopic compositions and spent fuel characteristics including radioactivity and decay heat. Serpent uses matrix exponential method to solve the Bateman decay and depletion equations while the solution of the matrix exponential relies on the Chebyshev Rational Approximation Method (CRAM). Serpent runs significantly faster than other MC codes due to the two main reasons: 1) the use of the Woodcock delta-tracking in a combination with a typical surface-to-surface ray-tracing in a geometry routine, and 2) the use of the unionized energy grid for all point-wise reaction cross sections. The later, however, considerably increases the memory requirements and can be a bottleneck in simulations with a large number of involved nuclides.
Serpent is especially designed to generate homogenized constants for deterministic 3D core analysis. For any region of interest the code automatically calculates homogenized few-group cross sections, group-to-group scattering matrices, diffusion coefficients, assembly discontinuity factors, kinetics parameters, etc. More details can be found in Serpent User's Manual. Recently some new calculation methods related to the production of homogenized few-group constants were implemented in the Serpent code including homogenization in leakage-corrected criticality spectrum, group constant generation in reflectors and other non-fissile regions, and improved treatment of neutron-multiplying scattering reactions.
The capability to generate homogenized few-group constants can be considered as one of the most attractive features of Serpent. Being a MC code, Serpent is capable of handling complex geometries without any major approximations and can be used for producing cross section data for virtually any fuel or reactor type. The demonstration of the Serpent capability to generate few-group cross sections for different reactor systems is the main topic of this paper.
  • Lecture (Conference)
    26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel
  • Contribution to proceedings
    26th Conference of the Nuclear Societies in Israel, 21.-23.02.2012, Dead Sea, Israel

Publ.-Id: 16568 - Permalink

Liquid metal experiments on the creation and action of cosmic magnetic fields
Stefani, F.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Seilmayer, M.; Gailitis, A.; Gellert, M.; Rüdiger, G.;
The success of the large-scale dynamo experiments in Riga and Karlsruhe at the end of 1999 has boosted a strong worldwide activity to simulate the creation and action of cosmic magnetic fields in the liquid metal laboratory. With some focus on our own projects, we review the recent efforts to study hydromagnetic dynamo action and related magnetic instabilities, such as the magnetorotational instability (MRI) and the Tayler instability (TI). We sketch our plans to set-up the new liquid sodium facility DRESDYN that will include a dynamo experiment based on precession, and a Taylor-Couette experiment for the combined investigation of MRI and TI.
  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.03.2012, Stuttgart, Germany

Publ.-Id: 16567 - Permalink

Kosmische Magnetfelder im Experiment
Stefani, F.;
Seit langem schon ist bekannt, dass die Magnetfelder von Planeten, Sternen und Galaxien durch den sogenannten Dynamoeffekt, also durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden erzeugt werden. Weniger bekannt ist hingegen, dass Magnetfelder eine ganz entscheidende Rolle in der kosmischen Strukturbildung spielen. So ist das beobachtete schnelle Wachstum von Sternen und Schwarzen Löchern nur erklärbar, wenn die Akkretionsscheiben, aus denen sie gefüttert werden, turbulent sind und damit Drehimpuls effektiv nach außen transportieren können. Die Ursache dieser Turbulenz liegt in der destabilisierenden Wirkung von Magnetfeldern auf rotierende Strömungen, welche als Magneto-Rotationsinstabilität bezeichnet wird.
Der Vortrag gibt zunächst eine leicht verständliche Einführung in die Theorien zur Entstehung und Wirkung kosmischer Magnetfelder. Im Mittelpunkt stehen dann die Flüssigmetall-Experimente der letzten Jahre, in denen sowohl der Dynamoeffekt als auch die Magneto-Rotationsinstabiliät untersucht worden sind. Im Detail werden insbesondere das Rigaer Dynamo-Experiment und das PROMISE-Experiment am Helmholtz-Zentrum Dresden-Rossendorf (HZDR) besprochen.
Zum Schluss werden die Pläne für ein neues großes Dynamoexperiment am HZDR vorgestellt, in dem Selbsterregung in einer nur durch Präzession getriebenen Strömung von flüssigem Natrium nachgewiesen werden soll.
  • Invited lecture (Conferences)
    Hauptvorträge der Olbers-Gesellschaft Bremen, 10.01.2012, Bremen, Germany
  • Invited lecture (Conferences)
    Hauptvorträge der Sternfreunde Nordenham, 11.01.2012, Nordenham, Germany

Publ.-Id: 16566 - Permalink

Physical properties and valence state of cerium in the filled skutterudite CePt4Ge12
Gumeniuk, R.; Kvashnina, K. O.; Schnelle, W.; Nicklas, M.; Borrmann, H.; Rosner, H.; Skourski, Y.; Tsirlin, A. A.; Leithe-Jasper, A.; Grin, Y.;
Electronic, magnetic, and transport properties of the filled platinum-germanium skutterudite CePt4Ge12 are investigated. High resolution x-ray absorption spectroscopy measurements at the cerium L(III) edge demonstrate that Ce in this compound has a temperature-independent valence close to three. However, magnetic susceptibility, thermopower, Hall effect, and electronic specific heat reveal a broad maximum at Tmax = 65-80 K, suggesting the presence of valence fluctuations. The Sommerfeld coefficient gamma = 105 mJmol-1K-2, deduced from specific heat, indicates moderately enhanced band masses for CePt4Ge12. We discuss these findings and conclude that CePt4Ge12 represents a system at the border between intermediate valence (IV) and Kondo lattice behavior. In addition, the lattice specific heat and the thermal conductivity are discussed with respect to the vibrational dynamics of Ce in the [Pt4Ge12] framework.

Publ.-Id: 16565 - Permalink

Recent and future liquid metal experiments on homogeneous dynamo action and magnetic instabilities
Stefani, F.; Gerbeth, G.; Giesecke, A.; Gundrum, T.; Kirillov, O.; Seilmayer, M.; Gailitis, A.; Gellert, M.; Rüdiger, G.;
The present status of the Riga dynamo experiment is summarized and the prospects for its future exploitation are evaluated. We further discuss the plans for a large-scale precession driven dynamo experiment to be set-up in the framework of the new installation DRESDYN (DREsden Sodium facility for dynamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf. We report recent investigations of the magnetorotational instability and the Tayler instability and sketch the plans for another large-scale liquid sodium facility devoted to the combined study of both effects.
  • Invited lecture (Conferences)
    53rd Annual Meeting of the APS Division of Plasma Physics, 14.-18.11.2011, Salt Lake City, USA
  • Open Access LogoAbstract in refereed journal
    Bulletin of the American Physical Society 56(2011)12, 275-275

Publ.-Id: 16564 - Permalink

High-Field Magnetization Study of R2Fe17H3 (R = Tb, Dy, Ho and Er) Single-Crystalline Hydrides
Tereshina, I. S.; Doerr, M.; Skourski, Y.; Tereshina, E. A.; Watanabe, K.; Telegina, I. V.; Drulis, H.;
The high-field magnetization process in the hydrogen-charged R2Fe17H3 (R = Tb, Dy, Ho and Er) single crystals is studied along principal crystallographic directions at T = 4.2 K and compared with that of the known parent R2Fe17 compounds. Substantial changes of the magnetic anisotropy behavior induced by hydrogenation are found. Depending on the rare earth atom, the R2Fe17H3 compounds possess the "easy-axes", "easy-cone" and "easy-plane" types of magnetocrystalline anisotropy (MCA), whereas the precursors R2Fe17 have the easy-plane type of MCA only. The various observed types of the field-induced phase transitions in R2Fe17H3 are discussed and information on the effect of hydrogen on the strength of R-Fe coupling is obtained.

Publ.-Id: 16563 - Permalink

Magnetoconductance of carbon nanotubes probed in parallel magnetic fields up to 60 T
Jhang, S. H.; Marganska, M.; Del Valle, M.; Skourski, Y.; Grifoni, M.; Wosnitza, J.; Strunk, C.;
Magnetoconductance of carbon nanotubes (CNTs) is investigated. We clearly show that a semiconducting CNT can be converted into a metallic one, or vice versa, with the application of a large magnetic field parallel to the tube axis, providing a consistent confirmation of the Aharonov–Bohm (AB) effect on the band structure of CNTs. We also demonstrate that magnetic-field values where the semiconductor-to-metal transition occurs can be tuned by mechanical strain. Combined control of both the strain and the AB effect may open up new possibilities for CNT devices. In addition, we propose an idea to manipulate spin-split subbands of CNTs, resulting from spin–orbit interaction (SOI), by using the magnetic field to generate sizeable spin-polarized currents.

Publ.-Id: 16562 - Permalink

Intrinsic and extrinsic nonstationary field-driven processes in the spin-ice compound Dy2Ti2O7
Erfanifam, S.; Zherlitsyn, S.; Wosnitza, J.; Moessner, R.; Petrenko, O. A.; Balakrishnan, G.; Zvyagin, A. A.;
Nonequilibrium processes are probed by ultrasound waves in the spin-ice material Dy2Ti2O7 at low temperatures. The sound velocity and the sound attenuation exhibit a number of anomalies versus applied magnetic field for temperatures below the “freezing” temperature of ∼500 mK. These robust anomalies can be seen for longitudinal and transverse acoustic modes for different field directions. The anomalies show a broad hysteresis.Most notable are peaks in the sound velocity,which exhibit two distinct regimes: an intrinsic (extrinsic) one in which the data collapse for different sweep rates when plotted as function of field strength (time). We discuss our observations in context of the emergent quasiparticles which govern the low-temperature dynamics of the spin ice.

Publ.-Id: 16561 - Permalink

DRESDYN - A new liquid sodium facility for experimental studies of dynamo action and related instabilities
Stefani, F.; Gerbeth, G.; Gundrum, T.;
The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) will comprise large scale liquid sodium experiments related to geo- and astrophysics as well as experiments for safety and thermohydraulic studies related to sodium fast reactors and liquid metal batteries. The most ambitious parts of DRESDYN are a homogeneous dynamo driven solely by precession, and a large Tayler-Couette type experiment for the combined investigation of the magnetorotational instability and the Tayler instability. After a short summary of our previous achievements we delineate the next steps for the realization of DRESDYN.
  • Invited lecture (Conferences)
    Dyanamo iGDR Meeting, 12.-17.09.2011, Cargese, France

Publ.-Id: 16560 - Permalink

Integral equations in MHD: theory and application
Stefani, F.; Xu, M.; Gerbeth, G.; Wondrak, T.;
The induction equation of kinematic magnetohydrodynamics is mathematically equivalent to a system of integral equations for the magnetic field in the bulk of the fluid and for the electric potential at its boundary. We summarize the recent developments concerning the numerical implementation of this scheme and its applications to various forward and inverse problems in dynamo theory and applied MHD.

Publ.-Id: 16559 - Permalink

DRESDYN - A new platform for sodium related thermohydraulic studies and measurement developments
Gundrum, T.; Eckert, S.; Stefani, F.; Gerbeth, G.;
The safe and reliable operation of liquid metal systems in innovative reactor concepts like sodium cooled fast breeder reactors or lead-bismuth targets in transmutation systems requires appropriate measuring systems and control units, both for the liquid metal single-phase flow as well as for gas bubble liquid metal two-phase flows. We report on the liquid sodium facility DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies), presently under construction, that will comprise experiments with geo- and astrophysical background as well as experiments for thermohydraulic studies and for the development and the test of measurement techniques for sodium flows.
  • Lecture (Conference)
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.09.-30.11.2011, Toronto, Canada
  • Contribution to proceedings
    The 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 25.-30.09.2011, Toronto, Canada
    Proceedinngs of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics, NURETH-14, 223

Publ.-Id: 16558 - Permalink

Development of an ion source for volatile elements at DREAMS
Pavetich, S.; Akhmadaliev, S.; Merchel, S.; Rugel, G.;
After successful measurements of 10Be, 26Al and 41Ca [1] at DREAMS (DResden Accelerator Mass Spectrometry), extensive test measurements of 36Cl started. Besides the challenge of separating the stable isobar 36S, which at DREAMS is accomplished by post-stripping and a split-anode-ionization-chamber, the problem of ion source memory must be solved [2]. To characterize this effect we use 35Cl/37Cl samples of natural composition and 35Cl-enriched samples with a 35Cl/37Cl-ratio > 100. Similar measurements at the French AMS facility ASTER [3] showed differences of 2-4% in the 35Cl/37Cl ratios of the highly enriched samples after 24 h of sputtering samples with natural isotopic ratios [3]. To minimize the long-term-memory effect, two modified designs of the original source (HVEE) were constructed at DREAMS. A more open geometry was used to improve the vacuum level, and parts of the target loading system were modified to allow the exchange of the individual cathode aperture with each target.
[1] G. Rugel, these proceedings.
[2] K.M. Wilcken et al. NIM B, 268 (2010) 748-751
[3] M. Arnold et al. The French accelerator mass spectrometry facility ASTER after 4 years: Status and recent developments on 36Cl and 129I, article submitted NIM B
Keywords: AMS, DREAMS, 36Cl, long-term-memory-effect, ion source
  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.03.2012, Stuttgart, Deutschland

Publ.-Id: 16557 - Permalink

Self-assembling of Ge quantum dots in an alumina matrix
Buljan, M.; Pinto, S. R. C.; Rolo, A. G.; Martin-Sanchez, J.; Gomes, M. J. M.; Grenzer, J.; Mücklich, A.; Bernstorff, S.; Holy, V.;
In this work we report on a self-assembled growth of a Ge quantum dot lattice in a single 600-nm-thick Ge+Al(2)O(3) layer during magnetron sputtering deposition of a Ge+Al(2)O(3) mixture at an elevated substrate temperature. The self-assembly results in the formation of a well-ordered three-dimensional body-centered tetragonal quantum dot lattice within the whole deposited volume. The quantum dots formed are very small in size (less than 4.0 nm), have a narrow size distribution and a large packing density. The parameters of the quantum dot lattice can be tuned by changing the deposition parameters. The self-ordering of the quantum dots is explained by diffusion-mediated nucleation and surface-morphology effects and simulated by a kinetic Monte Carlo model.

Publ.-Id: 16556 - Permalink

Ion-Irradiated Laterally Graded Ni/C Multilayers: A Combined X-ray Standing Wave and X-ray Reflectivity Analysis
Dev, B. N.; Roy, S.; Bera, S.; Tawara, Y.; Schell, N.; Grenzer, J.; von Borany, J.; Grötzschel, R.;
An X-ray standing wave (XSW) experimental facility was set up at the Rossendorf Beam Line (ROBL) at the European Synchrotron Radiation Facility (ESRF). Using this facility, the microstructures and ion-beam induced microstructural modifications of a nanoscale laterally graded Ni/C multilayer systems have been studied by the combined X-ray reflectivity (XRR) and XSW technique. The multilayer stack with 15 Ni/C layer pairs was fabricated on a glass substrate by ion beam sputtering. A 2MeV Cu(2+) ion beam was rastered on the samples to obtain uniformly irradiated strips with fluences from 1 x 10(14) to 7 x 10(14) ions/cm(2). We have observed that X-ray reflectivity at the first order Bragg peak gradually increases due to increase in multilayer period in the virgin samples. The multilayer period has expanded and interfaces broadened due to ion irradiation. Xray standing wave analysis indicates that, during deposition, a significant amount of Ni diffuses into C layers. Up to a certain fluence, we have observed that more and more Ni atoms are incorporated into C layers. At higher fluences, Ni is progressively segregated from the C layers. These mixing and demixing phenomena of Ni in C layers as a function of ion fluence have been explained in terms of two competitive processes including ballistic mixing and chemically guided atomic movements. (C) 2011 The Japan Society of Applied Physics

Publ.-Id: 16555 - Permalink

Phenomenology of iron-assisted ion beam pattern formation on Si(001)
Macko, S.; Frost, F.; Engler, M.; Hirsch, D.; Hoche, T.; Grenzer, J.; Michely, T.;
Pattern formation on Si(001) through 2 keV Kr(+) ion beam erosion of Si(001) at an incident angle of v = 30 degrees and in the presence of sputter co-deposition or co-evaporation of Fe is investigated by using in situ scanning tunneling microscopy, ex situ atomic force microscopy and electron microscopy. The phenomenology of pattern formation is presented, and experiments are conducted to rule out or determine the processes of relevance in ion beam pattern formation on Si(001) with impurities. Special attention is given to the determination of morphological phase boundaries and their origin. Height fluctuations, local flux variations, induced chemical inhomogeneities, silicide formation and ensuing composition-dependent sputtering are found to be of relevance for pattern formation.

Publ.-Id: 16554 - Permalink

Acclerator Mass Spectrometry
Rugel, G.;
Accelerator Mass Spectrometry (AMS) is presently one of the most sensitive techniques for the detection of long-lived radioisotopes at very low abundances. In recent years more isotopes can be measured via AMS and many isotopes ratios can be determined relatively precise. The main fields of applications are climate history and environmental processes where radioisotopes act as natural tracers. In earth sciences and archaeology AMS provides valuable dating tools. Radioisotopes commonly measured are 10Be, 14C, and 26Al. Accelerators with intermediate energies of 3–6 MeV also allow sensitive detection of 36Cl and 41Ca. More exotic isotopes like 44Ti, 53Mn, 55Fe, 59Ni, 60Fe, 63Ni, 79Se have been measured for astrophysical reasons.
An overview on recent AMS measurements with a focus on nuclear astrophysics will be given.
The technique of AMS at different laboratories will be shown. The new facility DREAMS at the Helmholtz–Zentrum Dresden–Rossendorf with an 6 MV tandem accelererator and the unique facility at Munich of the Technische Universit¨at M¨unchen and the Ludwig Maximilians Universit¨at M¨unchen will be described in more detail.
  • Invited lecture (Conferences)
    496. Wilhelm und Else Heraeus-Seminar - Astrophysics with modern small-scale accelerators, 06.-10.02.2012, Bad Honnef, Deutschland

Publ.-Id: 16553 - Permalink

Determining the C60 molecular arrangement in thin films by means of X-ray diffraction
Elschner, C.; Levin, A. A.; Wilde, L.; Grenzer, J.; Schroer, C.; Leo, K.; Riede, M.;
The electrical and optical properties of molecular thin films are widely used, for instance in organic electronics, and depend strongly on the molecular arrangement of the organic layers. It is shown here how atomic structural information can be obtained from molecular films without further knowledge of the single-crystal structure. C60 fullerene was chosen as a representative test material. A 250 nm C60 film was investigated by grazing-incidence X-ray diffraction and the data compared with a Bragg-Brentano X-ray diffraction measurement of the corresponding C60 powder. The diffraction patterns of both powder and film were used to calculate the pair distribution function (PDF), which allowed an investigation of the short-range order of the structures. With the help of the PDF, a structure model for the C60 molecular arrangement was determined for both C60 powder and thin film. The results agree very well with a classical whole-pattern fitting approach for the C60 diffraction patterns.

Publ.-Id: 16552 - Permalink

Complex formation of Np(V) with fulvic acid at tracer metal concentration
Mueller, K.; Sasaki, T.;
Apparent formation constants of pentavalent Np with fulvic acid were determined in 0.1 M NaClO4, at 25 °C using a solvent extraction technique with thenoyltrifluoroacetone and phenanthroline in an isoamyl alcohol solution. The metal concentration was set constant to a tracer level of 10-15 M Np(V), relevant for the far field safety assessment of a nuclear waste disposal site. The impact of several solution conditions, namely pH, ionic strength, the initial fulvic acid concentration and the presence of Ca2+, on the complex formation were studied. Similar to the sodium system, the divalent calcium ion effectively prevents complexation of the neptunyl ion with humic substance. Furthermore, the derived apparent formation constants were comparatively discussed with literature values obtained at very similar solution conditions.
Keywords: humic substances, apparent formation constant, pentavalent neptunium, solvent extraction, TTA

Publ.-Id: 16551 - Permalink

Evaluation of radiation damage using nonlinear ultrasound
Matlak, K.; Wall, J.; Kim, J.-Y.; Qu, J.; Jacobs, L. J.; Viehrig, H.-W.;
Nonlinear ultrasound was used to monitor radiation damage in two reactor pressure vessel (RPV) steels. The microstructural changes associated with radiation damage include an increase in dislocation density and the formation of precipitates, and nonlinear ultrasonic waves are known to be sensitive to such changes. Six samples each of two different types of RPV steel were previously irradiated in the Rheinsberg power reactor to two fluence levels, up to 1020 n/cm2. Longitudinal waves were used to measure the acoustic nonlinearity in these samples, and the results show a clear increase in the measured acoustic nonlinearity from the unirradiated state to the medium dose, and then a decrease from medium dose to high dose.
Keywords: reactor pressure vessel steel, neutron irradiation, embrittlement, nonlinear ultrasound, microstructural changes

Publ.-Id: 16550 - Permalink

PT brachistochrone and state discrimination
Günther, U.;
In recent work by Bender, Brody, Caldeira and Meister it was shown that the brachistochrone solution of PT Quantum Mechanics (PTQM) can be used to orthogonalize a set of two originally non-orthogonal quantum states. The still remaining draw-back of the proposed technique is in its use of a non-Hermitian PT-symmetric Hamiltonian to achieve the PTQM brachistochrone evolution --- a Hamiltonian which up to now for quantum systems is beyond experimental reach.

We demonstrate that the Bender-Brody-Caldeira-Meister approach can be naturally extended into a higher-dimensional Hilbert space. This allows to interpret the PTQM setup as a very special subsystem of a larger Hermitian system. Moreover we show that this extension can be connected with the standard text-book scheme of unambiguous quantum state discrimination. Technical details of the extension procedure are discussed and ways toward a time-optimal unambiguous state discrimination scheme are indicated.
Keywords: PT quantum mechanics, unambiguous state discrimination, time-optimal state discrimination, PT brachistochrone, extension scheme
  • Invited lecture (Conferences)
    PTQM 2011 symposium, 25.-28.09.2011, Heidelberg, Deutschland

Publ.-Id: 16549 - Permalink

Mineral dusts - a valuable resource or only dust in the wind?
Renno, A. D.;
Rock dust from quarries and from mining operations is a potential valuable resource. Well known and unconventional ways of using are shown. The base for a sustainable use is a very precise chemical and mineralogical characterization of the different dust types.
Keywords: rock dust, sustainable usage of resources, quarry, tailing, mieral dust
  • Invited lecture (Conferences)
    Workshop Internacional Encuentro Alumni DAAD 2012 Geociencias y Energía Desarrollo y Perspectivas de la Cooperación Chileno-Alemana, 18.-21.01.2012, Concepcion, Chile

Publ.-Id: 16548 - Permalink

On the use of fine distributed moderating material to enhance feedback coefficients in fast reactors
Merk, B.; Weiß, F.-P.;
Recently, the use of moderating materials in fuel assemblies for Sodium cooled fast reactors has been investigated and published in several papers (Annals of Nuclear Energy 38, 5, Annals of Nuclear Energy 38, 11 (2011)). Especially the fine distribution of the moderating material in a layer inside the fuel rod or inside the wire spacer has shown very promising results for the enhancement of the feedback coefficients. The validity of the HELIOS results has been demonstrated in a comparison with MCNP and the transferability of the effect to full core calculations has been shown. The fine distribution of the moderating material is very attractive since it causes only a very limited influence on the safety relevant fuel assembly structure and on the operational parameters like power distribution and end of life burnup distribution. In extension to this published work the influence of the use of moderating materials on systems containing fuels for Minor Actinide transmutation (3% Am, 5% Am, and 2% Np – 2% Am) is examined on the basis of detailed lattice calculations based on 112 energy groups and an unstructured mesh geometry modeling of all fuel assembly details. The influence of the insertion of the Minor Actinides on the fuel temperature and the coolant coefficient is investigated for a reference case and the possibilities of enhancing the feedback coefficients by the insertion of ZrH moderating material are analyzed. The changes in the power and burnup distribution due to the use of the moderating material ZrH will be discussed. Further on, the transmutation potential is compared for the cases with and without moderating material. Neptunium and Americium is slightly more reduced during burnup of the fuel with moderating material only the Curium production rises slightly. A detailed analysis demonstrates that the increase of Cm breeding due to the use of moderating material is lower than the additional amount of destroyed Np and Am. Thus, the results demonstrate that even more Am is burnt with the investigated fuel assembly containing moderating material inside the wire wrapper.
Additionally, a first test of the effect of the use of fine distributed moderating material in a lead cooled fast reactor will be shown. The test is based on preliminary data of the fuel assembly in the GUINEVERE facility. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback of the zero power facility is shown and discussed.
Over all, the use of fine distributed moderating material has the potential to open the stage for designable feedback coefficients in fast reactors without creating a major influence on the operational parameters and core coolability.
Keywords: Sodium void effect, SFR, Fast reactor, Zirconium hydride, designable feedback coefficient, transmutation, GUINEVERE, LFR
  • Contribution to proceedings
    Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features, 27.-29.02.2012, Wien, Österreich
  • Lecture (Conference)
    Innovative Fast Reactor Designs with Enhanced Negative Reactivity Feedback Features, 27.-29.02.2012, Wien, Österreich

Publ.-Id: 16547 - Permalink

On the use of moderating material to enhance the feedback coefficients in SFR cores with high minor actinide content
Merk, B.; Weiß, F.-P.;
The use of fine distributed moderating material to enhance the feedback effects and to reduce the sodium void effect is described. The consequences of the introduction of fine distributed moderating material into fuel assemblies with fuel configurations foreseen for minor actinide transmutation is analyzed. The degradation of the feedback effects due to the insertion of minor actinides and the compensation by the use of moderating materials is discussed.
Keywords: Sodium void effect, SFR, Fast reactor, Zirconium hydride, designable feedback coefficient, transmutation
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA
  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP'12), 24.-28.06.2012, Chicago, USA

Publ.-Id: 16546 - Permalink

Solutions without space-time separation for ADS experiments: Overview on Developments and Applications
Merk, B.; Glivici-Cotruţă, V.;
The different analytical solutions without space-time separation foreseen for the analysis of ADS experiments are described. The SC3A experiment in the YALINA-Booster facility is described and investigated. For this investigation the very special configuration of YALINA-Booster is analyzed based on HELIOS calculations. The results for the time dependent diffusion and the time dependent P1 equation are compared with the experimental results for the SC3A configuration. A comparison is given for the deviation between the analytical solution and the experimental results versus the different transport approximations. To improve the representation to the special configuration of YALINA- Booster, a new analytical solution for two energy groups with two sources (central external and boundary source) has been developed starting form the Green’s function solution. Very good agreement has been found for these improved analytical solutions.
Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation

Publ.-Id: 16545 - Permalink

An analytical solution for the consideration of the effect of adjacent fuel assemblies; extension to hexagonal VVER-440 type fuel assemblies
Merk, B.; Rohde, U.;
A new analytical method is described to deal with the Leakage Environmental Effect. The method is based on the one dimensional analytical solution of the two-group diffusion equation for two adjacent fuel assemblies. The quality of the results for this highly efficient method is demonstrated for quadratic fuel assemblies. In additional tests the transferability of the concept to hexagonal VVER-440 type fuel assemblies is shown.
Keywords: VVER, Analytical Solution, Homogenization, Cross Section Preparation, Leakage Assembly Environmental Effect
  • Kerntechnik 4(2012), 230-239

Publ.-Id: 16544 - Permalink

Overview of major HZDR developments for fast reactor analysis
Merk, B.; Glivici-Cotruţă, V.; Duerigen, S.; Rohde, U.; Kliem, S.;
The upgrading of the DYN3D code for the application for fast reactors is described. After validation, a diverse code with the possibility for steady state and transient core analysis on the basis of coupled thermal hydraulics/neutronics calculations is available. The work on the use of fine distributed moderating material in SFR cores is discussed with the target on enhancing the feedback coefficients in SFR cores without influencing the operational. Newly developed analytical solutions without separation of space and time for the analysis of ADS experiments are shown with good agreement for the YALINA experiment. The analytical solutions are a very promising tool for the development of a new method for the analysis of ADS experiments.
Keywords: DYN3D, coupled thermalhydraulics/neutronics calculations, Sodium void effect, designable feedback coefficient, analytical solutions, ADS experiments

Publ.-Id: 16543 - Permalink

Curium(III) and europium(III) speciation studies with Mont Terri Opalinus clay isolates
Moll, H.; Bachvarova, V.; Lütke, L.; Geissler, A.; Selenska-Pobell, S.; Bernhard, G.;
Microorganisms are ubiquitous also in host rocks of potential nuclear waste disposal sites. In this talk, some results will be presented from the current project about the microbial diversity in Opalinus clay and the interactions of dominant microorganisms with actinides. Especially the interactions of a Sporomusa sp. clay isolate with curium(III) and europium(III) will be shown and discussed.
Keywords: Curium. Europium, Bacteria, TRLFS, Speciation
  • Lecture (others)
    Mont Terri Project: Joint HT-MA-BN-GD-PCC Meeting, 06.-07.02.2012, St. Ursanne, Switzerland

Publ.-Id: 16542 - Permalink

DRESDYN: A large scale liquid sodium facility for experiments on dynamo action and related magnetic instabilities
Giesecke, A.; Gerbeth, G.; Gundrum, T.; Kirillov, O.; Seilmayer, M.; Stefani, F.;
The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN), which is presently in the design phase, will comprise a number of large scale liquid sodium experiments devoted to problems of geo- and astrophysical magnetohydrodynamics. A homogeneous dynamo, driven exclusively by precession, will represent the most ambitious compound of DRESDYN.
Another experiment, a sodium filled Taylor-Couette cell, will allow the combined investigation of various versions of the magnetorotational instability and of the Tayler instability. For both experiments, recent results of preparatory studies are presented, and the scientific prospects for the final set-ups are delineated.
Keywords: DRESDYN Dynamo MHD-Instabilities Magnetohydrodynamics Precession Magnetorotational Instability
  • Poster
    European Geosciences Union General Assembly 2012, 23.-27.04.2012, Wien, Austria
  • Open Access LogoAbstract in refereed journal
    Geophysical Research Abstracts 14(2012), EGU2012-2824

Publ.-Id: 16541 - Permalink

Shallow-underground accelerator sites for nuclear astrophysics: Is the background low enough?
Szücs, T.; Bemmerer, D.; Cowan, T.; Degering, D.; Elekes, Z.; Fülöp, Z.; Gyürky, G.; Junghans, A.; Köhler, M.; Marta, M.; Schwengner, R.; Wagner, A.; Zuber, K.;
In order to reliably estimate the rate of a charged particle induced nuclear reaction in a non-explosive astrophysical scenario, its cross section must be measured far below the Coulomb barrier. However, at the corresponding energies the cross section values are very low, so that the experimental counting rate is dominated by cosmic-ray induced background, even if a suitable anticoincidence shield is applied. This problem can be overcome by performing an accelerator-based experiment in a deep underground site, as has been done with great success at the LUNA 0.4 MV accelerator in Gran Sasso, Italy. Several underground accelerators with higher beam energy are in the planning phase worldwide. All of them are shielded by over 1000 m of rock, a depth at which cosmic-ray effects are negligible for the purposes of nuclear astrophysics experiments. It is shown here that a combined approach, using a shallow underground laboratory below 47 m of rock and an active shield to veto surviving muons in simple detectors, results in a background level that is not far from that of deep underground sites. Data have been obtained using two ”traveling” gamma-detectors. They have been transported both shallow underground, to the Dresden Felsenkeller in Germany, and deep underground, to the Gran Sasso laboratory in Italy. As shallow-underground facilities are more easily accessible than deep-underground ones, the present finding holds the promise of greatly accelerated progress in the field of cross section measurements for nuclear astrophysics.

Publ.-Id: 16539 - Permalink

Dose rate dependence for different dosimeters and detectors: TLD, OSL, EBT films, and diamond detectors
Karsch, L.; Beyreuther, E.; Burris-Mog, T.; Kraft, S.; Richter, C.; Zeil, K.; Pawelke, J.;
Purpose: The use of laser accelerators in radiation therapy can perhaps increase the low number of proton and ion therapy facilities in some years due to the low investment costs and small size. The laser-based acceleration technology leads to a very high peak dose rate of about 1011 Gy/s. A first dosimetric task is the evaluation of dose rate dependence of clinical dosimeters and other detectors.
Methods: The measurements were done at ELBE, a superconductive linear electron accelerator which generates electron pulses with 5 ps length at 20 MeV. The different dose rates are reached by adjusting the number of electrons in one beam pulse. Three clinical dosimeters (TLD, OSL and EBT radiochromic films) were irradiated with four different dose rates and nearly the same dose. A faraday cup, an integrating current transformer and an ionization chamber were used to control the particle flux on the dosimeters. Furthermore two diamond detectors were testet.
Results: The dosimeters are dose rate independent up to 4•109 Gy/s within 2 % (OSL and TLD) and up to 15•109 Gy/s within 5 % (EBT films). The diamond detectors show strong dose rate dependence.
Conlusion: TLD, OSL dosimeters and EBT films are suitable for pulsed beams with a very high pulse dose rate like laser accelerated particle beams.

Publ.-Id: 16538 - Permalink

A Tapered Undulator Experiment At The ELBE Far Infrared Hybrid-Resonator Oscillator Free Electron Laser
Lehnert, U.; Michel, P.; Asgekar, V.;
A tapered undulator experiment was carried out at the Helmholtz Forschungszentrum Dresden-Rossendorf (ELBE) far-infrared FEL. The oscillator FEL makes use of a hybrid optical resonator. The main motivation was to see whether the presence of a dispersive medium in the form of a waveguide in the resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering proves beneficial for the output power we observe an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicate a maximum small-signal gain for zero taper while the output peak power is highest for negative taper. Whereas the saturated power output and the detuning curve characteristics agree with the known theoretical predictions, the wavelength shifts showed deviations from the expected values. Details of the experiment are presented.
Keywords: undulator; hybrid optical resonator; waveguide effect on the outcome; saturated power; positive and negative undulator field; detuning curves

Publ.-Id: 16537 - Permalink

Studies on Boiling Water Reactor design with reduced moderation and analysis of reactivity accidents using the code DYN3D-MG
Rohde, U.; Pivovarov, V. A.; Matveev, Y. A.;
The multi-group version of the DYN3D reactor dynamics code was used for calculations for a new concept of a boiling water reactor with tight lattice of fuel rods and reduced neutron moderation. For that purpose, a 5-group cross section library was prepared and connected to the DYN3D code. Comparison calculations with the steady-state finite-difference code ACADEM showed a very good agreement.
The capability of the DYN3D multi-group code in modeling transients in boiling water reactors with tight fuel element lattices was demonstrated by the analysis of two reactivity accidents initiated by the ejection of one control rod and unauthorized withdrawal of a control rod bank from the reactor core. The corresponding analyses were performed for begin of cycle conditions, when the considered control rods are at their maximum insertion depth.
Keywords: high conversion reactor, boiling water reactor, tight fuel lattice, core design, reactor dynamics, reactivity-initiated accidents
  • Kerntechnik 77(2012)4, 240-248

Publ.-Id: 16536 - Permalink

XAS/XMCD studies of Ga+ irradiation driven magnetization reorientation in Pt/Co/Pt nanostructures
Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Ferré, J.; Mougin, A.; Baczewski, L. T.; Wawro, A.; Rogalev, A.; Wilhelm, F.
The magnetic properties of ultrathin films are usually tuned by the varying film thickness, chemical composition or structure (see e.g. [1,2]). It has been demonstrated that the magnetic properties of thin films with perpendicular magnetic anisotropy of interfacial origin may be also tuned by ions irradiation [3]. A Pt/Co/Pt trilayer irradiated by different ions exhibits an out-of-plane to in-plane magnetization reorientation phase transition. Moreover, an ion irradiation-driven intermixing and disordering at the Co–Pt interfaces was shown to lead to a reduction of the anisotropy, coercivity, and Curie temperature.
In our recent paper [4] we presented new effect - remarkable oscillation of the magnetic anisotropy in the Pt/Co(2.6 nm)/Pt (deposited by sputtering technique) induced by an uniform low fluence Ga+ ion irradiation at 30 keV. Increasing fluence F magnetization rotates from in-plane to out-of-plane state and then back to in-plane state. Similar effect, driven by Ga+ ion irradiation, has been recently observed in Pt/Co/Pt deposited by molecular beam epitaxy.
The key question is the origin of observed out-of-plane magnetization state induced by ions irradiation. Ion irradiation driven creation of strongly anisotropic Co-Pt L10 phase is proposed. This hypothesis is supported by measurement of K-edge X-ray absorption (XAS) and X-ray magnetic circular dichroism (XMCD) on the ID12 ERSF beamline. The study was done on: Pt/Co/Pt samples both as deposited film and irradiated one with fluence creating out-of-plane magnetization state, reference sample - L10 Co0.5Pt0.5 thin film. The XMCD spectrum of the irradiated sample is interpreted as the superposition of pure Co and L10 CoPt alloy contributions. TRIDYN [5] simulations, for different Ga ion fluence, were performed for results discussion.
This work was supported by the following projects: SPINLAB - EU programme Innovative Economy, Priority 2.2, SPIRIT European Community - contract no. 227012, ESRF/73/2006.
[1] - M. Kisielewski et al., Phys. Rev. Lett. 89, 87203 (2002)
[2] - A. Stupakiewicz et al., Phys. Rev. Lett. 101, 217202 (2008)
[3] - C. Chappert et al., SCIENCE 280, 1919 (1998)
[4] - J. Jaworowicz et al., Appl. Phys. Lett. 95, 022502 (2009)
[5] - W. Möller et al., Comp. Phys. Commun. 51, 355 (1988).
Keywords: XAS/XMCD studies of Ga+ irradiation driven magnetization reorientation in Pt/Co/Pt nanostructures
  • Lecture (Conference)
    ESRF Users' Meeting 2012, 06.-09.02.2012, Grenoble, France

Publ.-Id: 16535 - Permalink

Interaction of dislocationswith Cu-Ni-vacancy clusters in Fe
Terentyev, D.; Malerba, L.; Bonny, G.; Al-Motasem, A. T.; Posselt, M.;
not available, please contact authors
Keywords: dislocations, iron, Cu-Ni-vacancy clusters, Monte Carlo simulations, molecular dynamics
  • Lecture (Conference)
    16th Meeting of International Group on Radiation Damage Mechanisms in Pressure Vessel Steels (IGRDM-16), 04.-09.12.2011, Santa Barbara, USA

Publ.-Id: 16534 - Permalink

X-ray investigations on CoSi2 nano wires manufactured by focused ion beam synthesis
Grenzer, J.; Roshchupkina, O.; Fritzsche, M.; Mücklich, A.; Bischoff, L.;
Nanowires and chains of nanoparticles are of emerging interest in nanoelectronics, nano-optics and plasmonics as well as for their monolithic integration into microelectronic devices. Epitaxial buried or surface CoSi2 layers in silicon can be formed by implanting Co in stoichiometric concentration and subsequent annealing. Ion beam synthesis allows the fabrication of submicron pattern, which can be formed either directly by a mass separated writing Co focused ion beam (FIB) or indirectly by a Ga FIB in combination with a thin Co film on the rear side of the Si wafer, providing the Co for the nanowire formation by diffusion.

We have studied the strain of the Si host lattice around a single nanostructure depending on their crystallographic orientation using high-resolution x-ray diffraction and TEM. The X-ray experiment was carried out using a highly focused beam (~0.5µm) at the beam line ID01 at ESRF. Surrounding a wire a peak was found indicating a tensile strain of approx. -1.4%.

The CoSi2 peak intensity is strongly modulated by moving from one wire to another. Moreover the diffuse scattered intensity around the Si bulk reflection is increased and is getting even more enhanced between the wires. A possible mechanism lying behind the CoSi2 structure formation is the lattice relaxation by stable dislocation loops. A zigzag like defect structure, characteristic for the formation of 311 defects, was identified by TEM at the grain boundary between the CoSi2 nanowires and the Si bulk.
  • Poster
    E-MRS 2011 SPRING MEETING, 09.-13.05.2011, Nice, France

Publ.-Id: 16533 - Permalink

Material science towards the fs range: What we can do?
Grenzer, J.;
Material science towards the fs range:
What we can do?
  • Lecture (others)
    Workshop on Petawatt-Lasers at Hard X-Ray Light Sources, 05.-09.09.2011, Helmholtz-Zentrum Dresden-Rossendorf, Deutschland

Publ.-Id: 16532 - Permalink

The ROBL Upgrade: in-situ investigations for material science
Grenzer, J.; Baehtz, C.; von Borany, J.;
Werkstoffcharakterisierung mit Strahllinien
  • Lecture (others)
    DGM Fachausschusssitzung, BAM Berlin, 27.05.2011, Berlin, Deutschland

Publ.-Id: 16531 - Permalink

Material science towards the fs range: Experimental challanges using an XFEL
Grenzer, J.;
Seminar Series:
"Understanding advanced materials and processes on the atomic level:
Materials research with ultrashort, intense and coherent X-ray pulses and high-power lasers"
  • Lecture (others)
    Seminar Serie - HZDR, 04.11.2011, Helmholtz-Zentrum Dresden-Rossendorf, Deutschland

Publ.-Id: 16530 - Permalink

High-Electron-Mobility InN Layers Grown by Boundary-Temperature-Controlled Epitaxy
Wang, X.; Liu, S.; Ma, N.; Feng, L.; Chen, G.; Xu, F.; Tang, N.; Huang, S.; Chen, K. J.; Zhou, S.; Shen, B.;
A boundary-temperature-controlled epitaxy, where the growth temperature of InN is controlled at its maximum, is used to obtain high-electron-mobility InN layers on sapphire substrates by molecular beam epitaxy. The Hall-effect measurement shows a recorded electron mobility of 3280 cm^2 V^-1 s^-1 and a residual electron concentration of 1.47×10^17 cm^-3 at room temperature. The enhanced electron mobility and reduced residual electron concentration are mainly due to the reduction of threading dislocation density. The obtained Hall mobilities are in good agreement with the theoretical modelling by the ensemble Monte Carlo simulation.
  • Applied Physics Express 5(2012), 015502
    DOI: 10.1143/APEX.5.015502
  • Communication & Media Relations
    News release at Semiconductor Today 30.01.2012

Publ.-Id: 16529 - Permalink

Actinide(IV)-silica colloids and their potential geochemical implications
Zänker, H.; Weiss, S.; Hennig, C.; Dreissig, I.;
Due to their low solubility, tetravalent actinides, An(IV), are usually assumed to be immobile in natural waters. However, it is also well known that insoluble precipitation products can be mobile if they occur as colloids. For An(IV) oxyhydroxides this phenomenon has thoroughly been studied [1-3]. Here (see also [4]) we describe the formation of a new type of An(IV) colloids.
Evidence is provided by photon correlation spectroscopy (PCS), ultrafiltration and ultracentrifugation that uranium(IV) and Th(IV) can form silicate-containing colloids. The An(IV)-silica particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne An(IV) was observed which is a concentration significantly higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. The size of the < 20 nm particles depends on silicate concentration and pH. The higher the silicate concentration and the pH, the smaller (and obviously the more stable) are the particles that are formed (however, silicate at the concentrations tested does not form particles in the absence of the actinides).
Laser Doppler velocimetry reveals that the nanoparticles are stabilized in solution by electrostatic repulsion due to a negative zeta potential caused by the silicate. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate.
The mechanism of colloidal stabilization can be regarded as “sequestration” by silicate, a phenomenon well known from trivalent heavy metal ions of high ion potential such as iron(III) [5, 6) or curium(III) [7], but never reported for tetravalent actinides so far. Extended X-ray absorption fine structure (EXAFS) spectroscopy on the U(IV)-silica nanoparticles showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids. The next-neighbor coordination of U(IV) in the U(IV)-silica colloids is comparable with that of coffinite, USiO4.
The assessment of actinide behavior in the aquatic environment should take the possible existence of An(IV)-silica colloids into consideration. Their occurrence might influence actinide migration in anoxic waters.
[1] Neck, V. et al., Radiochim. Acta 90, 485 (2002).
[2] Bitea, C. et al., Colloids Surf., A 217, 63 (2003).
[3] Altmaier, M. et al., Radiochim. Acta 92, 537 (2004).
[4] Dreissig, I. et al., Geochim. Cosmochim. Acta 75, 352 (2011).
[5] Browman, M. G. et al., Environ. Sci. Technol. 23, 566 (1989).
[6] Robinson, R. B. et al., J. Am. Water Works Assn. 84, 77 (1992).
[7] Panak, P. J. et al., Radiochim. Acta 93, 133 (2005).
Keywords: Colloids, nanoparticles, uranium, thorium, silica, anoxic groundwater
  • Lecture (Conference)
    E-MRS 2012 SPRING MEETING, 15.-17.05.2012, Strasbourg, France

Publ.-Id: 16528 - Permalink

Pyrrolovesamicols - Synthesis, structure and VAChT binding of two 4-fluorobenzoyl regioisomers
Wenzel, B.; Li, Y.; Kraus, W.; Sorger, D.; Sabri, O.; Brust, P.; Steinbach, J.;
This letter describes the synthesis of two regioisomers of a new class of vesamicol analogs as possible ligands for imaging the vesicular acetylcholine transporter in future PET studies. The reaction mechanism of the synthesis of these two pyrrolovesamicols was studied by HPLC and the molecular structures were determined by X-Ray structure analysis. Binding affinities to VAChT were evaluated by competitive binding analysis using a cell line stably transfected with ratVAChT.
Keywords: Pyrrolovesamicol Vesamicol VAChT Pyrrole

Publ.-Id: 16527 - Permalink

Scalable Microstructured Photoconductive Terahertz Emitters
Winnerl, S.;
The development of scalable emitters for pulsed broadband terahertz (THz) radiation is reviewed. Their large active area in the 1 – 100 mm^2 range allows for using the full power of state-of-the-art femtosecond lasers for excitation of charge carriers. Large fields for acceleration of the photogenerated carriers are achieved at moderate voltages by interdigitated electrodes. This results in efficient emission of single-cycle THz waves. THz field amplitudes in the range of 300 V/cm and 17 kV/cm are reached for excitation with 10 nJ pulses from Ti:sapphire oscillators and for excitation with 5 μJ pulses from amplified lasers, respectively. The corresponding efficiencies for conversion of near-infrared to THz radiation are 2.5 × 10^-4 (oscillator excitation) and 2 × 10^-3 (amplifier excitation). In this article the principle of operation of scalable emitters is explained and different technical realizations are described. We demonstrate that the scalable concept provides freedom for designing optimized antenna patterns for different polarization modes. In particular emitters for linearly, radially and azimuthally polarized radiation are discussed. The success story of photoconductive THz emitters is closely linked to the development of mode-locked Ti:sapphire lasers. GaAs is an ideal photoconductive material for THz emitters excited with Ti:sapphire lasers, which are widely used in research laboratories. For many applications, especially in industrial environments, however, fiber-based lasers are strongly preferred due to their lower cost, compactness and extremely stable operation. Designing photoconductive emitters on InGaAs materials, which have a low enough energy gap for excitation with fiber lasers, is challenging due to the electrical properties of the materials. We discuss why the challenges are even larger for microstructured THz emitters as compared to conventional photoconductive antennas and present first results of emitters suitable for excitation with ytterbium-based fiber lasers. Furthermore an alternative concept, namely the lateral photo-Dember emitter, is presented. Due to the strong THz output scalable emitters are well suited for THz systems with fast data acquisition. Here the application of scalable emitters in THz spectrometers without mechanical delay stages, providing THz spectra with 1 GHz spectral resolution and a signal-to-noise ratio of 37 dB within 1 s, is presented. Finally a few highlight experiments with radiation from scalable THz emitters are reviewed. This includes a brief discussion of near-field microscopy experiments as well as an overview over gain studies of quantum-cascade lasers.
Keywords: Terahertz, scalable emitter

Publ.-Id: 16526 - Permalink

Elastische Rückstoßatomspektrometrie leichter Elemente mit Subnanometer-Tiefenauflösung
Kosmata, M.;
In der vorliegenden Arbeit wird erstmals das QQDS-Magnetspektrometer für die höchstauflösende Ionenstrahlanalytik leichter Elemente am Helmholtz-Zentrum Dresden-Rossendorf umfassend vorgestellt. Zusätzlich werden sowohl alle auf die Analytik Einfluss nehmenden Parameter untersucht als auch Methoden und Modelle vorgestellt, wie deren Einfluss vermieden oder rechnerisch kompensiert werden kann.
Die Schwerpunkte dieser Arbeit gliedern sich in fünf Bereiche.
Der Erste ist der Aufbau und die Inbetriebnahme des QQDS-Magnetspektrometers, der zugehörige Streukammer mit allen Peripheriegeräten und des eigens für die höchstauflösende elastische Rückstoßanalyse entwickelten Detektors. Sowohl das umgebaute Spektrometer als auch der im Rahmen dieser Arbeit gebaute Detektor wurden speziell an experimentelle Bedingungen für die höchstauflösende Ionenstrahlanalytik leichter Elemente angepasst und erstmalig auf einen routinemäßigen Einsatz hin getestet. Der Detektor besteht aus zwei Komponenten. Zum einen befindet sich am hinteren Ende des Detektors eine Bragg-Ionisationskammer, die zur Teilchenidentifikation genutzt wird. Zum anderen dient ein Proportionalzähler, der eine Hochwiderstandsanode besitzt und direkt hinter dem Eintrittsfenster montiert ist, zur Teilchenpositionsbestimmung im Detektor.
Die folgenden zwei Schwerpunkte beinhalten grundlegende Untersuchungen zur Ionen-Festkörper-Wechselwirkung. Durch die Verwendung eines Magnetspektrometers ist die Messung der Ladungszustandsverteilung der herausgestreuten Teilchen direkt nach einem binären Stoß sowohl möglich als auch für die Analyse notwendig. Aus diesem Grund werden zum einen die Ladungszustände gemessen und zum anderen mit existierenden Modellen verglichen. Außerdem wird ein eigens entwickeltes Modell vorgestellt und erstmals im Rahmen dieser Arbeit angewendet, welches den ladungszustandsabhängigen Energieverlust bei der Tiefenprofilierung berücksichtigt. Es wird gezeigt, dass ohne die Anwendung dieses Modells die Tiefenprofile nicht mit den quantitativen Messungen mittels konventioneller Ionenstrahlanalytikmethoden und mit der Dickenmessung mittels Transmissionselektronenmikroskopie übereinstimmen, und damit falsche Werte liefern würden. Der zweite für die Thematik wesentliche Aspekt der Ionen-Festkörper-Wechselwirkung, sind die Probenschäden und -modifikationen, die während einer Schwerionenbestrahlung auftreten. Dabei wird gezeigt, dass bei den hier verwendeten Energien sowohl elektronisches Sputtern als auch elektronisch verursachtes Grenzflächendurchmischen eintreten. Das elektronische Sputtern kann durch geeignete Strahlparameter für die meisten Proben ausreichend minimiert werden. Dagegen ist der Einfluss der Grenzflächendurchmischung meist signifikant, so dass dieser analysiert und in der Auswertung berücksichtigt werden muss. Schlussfolgernd aus diesen Untersuchungen ergibt sich für die höchstauflösende Ionenstrahlanalytik leichter Elemente am Rossendorfer 5-MV Tandembeschleuniger, dass die geeignetsten Primärionen Chlor mit einer Energie von 20 MeV sind. In Einzelfällen, wie zum Beispiel der Analyse von Bor, muss die Energie jedoch auf 6,5 MeV reduziert werden, um das elektronische Sputtern bei der notwendigen Fluenz unterhalb der Nachweisgrenze zu halten.
Der vierte Schwerpunkt ist die Untersuchung von sowohl qualitativen als auch quantitativen Einflüssen bestimmter Probeneigenschaften, wie beispielsweise Oberflächenrauheit, auf die Form des gemessenen Energiespektrums beziehungsweise auf das analysierte Tiefenprofil. Die Kenntnis der Rauheit einer Probe an der Oberfläche und an den Grenzflächen ist für die Analytik unabdingbar. Als Resultat der genannten Betrachtungen werden die Einflüsse von Probeneigenschaften und Ionen-Festkörper-Wechselwirkungen auf die Energie- beziehungsweise Tiefenauflösung des Gesamtsystems beschrieben, berechnet und mit der konventionellen Ionenstrahlanalytik verglichen. Die Möglichkeiten der höchstauflösenden Ionenstrahlanalytik werden zudem mit den von anderen Gruppen veröffentlichten Komplementärmethoden gegenübergestellt.
Der fünfte und letzte Schwerpunkt ist die Analytik leichter Elemente in ultradünnen Schichten unter Berücksichtigung aller in dieser Arbeit vorgestellten Modelle, wie die Reduzierung des Einflusses von Strahlschäden oder die Quantifizierung der Elemente im dynamischen Ladungszustandsnichtgleichgewicht. Es wird die Tiefenprofilierung von Mehrschichtsystemen, bestehend aus SiO2-Si3N4Ox-SiO2 auf Silizium, von Ultra-Shallow-Junction Bor-Implantationsprofilen und von ultradünnen Oxidschichten, wie zum Beispiel High-k-Materialien, demonstriert.
Keywords: ERD, IBA, mass spectrometry, high resolution, charge state
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-016 2012
    ISSN: 2191-8708


Publ.-Id: 16525 - Permalink

High precision X-ray polarimetry
Marx, B.; Schulze, K. S.; Uschmann, I.; Kämpfer, T.; Lötzsch, R.; Wehrhan, O.; Wagner, W.; Detlefs, C.; Roth, T.; Härtwig, J.; Förster, E.; Stöhlker, T.; Paulus, G. G.;
The polarization purity of 6.457- and 12.914-keV X- rays has been improved to the level of 2.4E-10 and 5.7E-10. The polarizers are channel-cut silicon crystals using six 90° reflections. Their performance and possible applications are demonstrated in the measurement of the optical activity of a sucrose solution.
Keywords: X-ray polarimetry, diffraction, channel-cut silicon crystal

Publ.-Id: 16524 - Permalink

Channeling radiation at impact of resonant acoustic waves
Azadegan, B.; Grigoryan, L. S.; Wagner, W.;
A consistent classical approach is presented which permits to reveal the influence of acoustic lattice vibrations on important features of planar positron channeling radiation. It is shown that a resonance effect occurs if the wave number of the acoustic field approaches dedicated values corresponding to the wave number of the oscillatory motion of the channeled particle. Modulation of its trajectory and velocity causes an enhancement of the radiation intensity.
Keywords: channeling radiation, positron channeling, acoustic superlattice
  • Invited lecture (Conferences)
    International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, 16.-22.10.2011, Yerevan-Meghri, Armenia
  • Contribution to proceedings
    International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, 16.-22.10.2011, Yerevan-Meghri, Armenia
    Proceedings of the International Conference on Electron, Positron, Neutron and X-ray Scattering under External Influences, Yerevan: IAPP Print, 978-99941-2-710-8, 44-51

Publ.-Id: 16523 - Permalink

Relaxation dynamics in graphene close to the Dirac point
Winnerl, S.; Schneider, H.; Helm, M.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Winzer, T.; Malic, E.; Knorr, A.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
The carrier dynamics in epitaxially grown graphene is studied in pump-probe experiments with photon energies in the range from 10 – 250 meV. A strong increase of the relaxation time is observed as the photon energy is decreased to values below the optical phonon energy. The underlying processes dominating the relaxation are identified by a comparison of the experimental results with microscopic calculations. Variation of the photon energy between 20 meV and 30 meV results in a change from induced transmission for larger photon energies to induced absorption for lower photon energies. An interplay of interband and intraband processes is responsible for this behavior.
  • Invited lecture (Conferences)
    International Symposium on THz nanoscience (TeraNano 2011), 24.-25.11.2011, Osaka, Japan

Publ.-Id: 16522 - Permalink

Planar positron channeling radiation on an acoustic superlattice
Azadegan, B.; Grigoryan, L. S.; Wagner, W.;
Planar positron channeling in an acoustic superlattice and the stimulation of the emission of channeling radiation at resonance of the particle motion with the acoustic field excited in a PbTiO3 single crystal is considered in the framework of classical mechanics and electrodynamics. Based on computed particle trajectories, spectral-angular distributions of channeling radiation influenced by resonant ultrasound have been simulated. The presented method explains the influence of ultrasonic waves on the intensity of channeling radiation in a rather simple and descriptive manner.
Keywords: channeling radiation, superlattice, hypersound
  • Lecture (Conference)
    Radiation from Relativistic Electrons in Periodic Structures (RREPS-11), 12.-16.09.2011, Egham, United Kingdom
  • Open Access LogoJournal of Physics: Conference Series 357(2012), 012025
    DOI: 10.1088/1742-6596/357/1/012025

Publ.-Id: 16521 - Permalink

Planar channeling radiation by relativistic electrons in different structures of silicon carbide
Azadegan, B.; Dabagov, S. B.; Wagner, W.;
Spectral distributions of channelling radiation by relativistic electrons in different planes of different types of polytype silicon carbide crystals such as hexagonal, zincblende, and rombohedral are presented. For every structure we have found the planes from which channeling radiation of relativistic electrons is possible. Using Doyle-Turner approximation to the atomic scattering factor and taking in to account thermal vibrations of atoms, the continuum potentials for different planes of different structure of polytype SiC single crystal were calculated. In the frame of quantum mechanic, the theory of channeling radiation has been applied to calculate the transverse electron states in the continuum potential of the planes and to study transition energies, linewidths, depth dependence for population of quantum states and spectral radiation distributions. At electron energies higher than 100 MeV the spectral distributions of radiation are calculated by classical calculations. The trajectories, velocities and accelerations of electrons are obtained and in the frame of classical electrodynamics. The spectral-angular distribution of radiation has been calculated using real trajectories, velocities and acceleration of electrons. Specific properties of planar channeling radiation in different structures of SiC are discussed.
Keywords: channeling radiation, relativistic electrons, X-rays

Publ.-Id: 16520 - Permalink

Novel unipolar nanodiodes for room-temperature THz detection
Balocco, C.; Kasjoo, S. R.; Lu, X. F.; Zhang, L. Q.; Alimi, Y.; Winnerl, S.; Song, A. M.;
We report on the room-temperature electrical rectification at 1.5 THz with novel non-linear asymmetric nanochannels. The planar layout facilitates the integration of microfabricated THz antennas without introducing parasitic elements, and enables ultra-high operation frequencies. This is the highest speed reported for nanorectifiers to date.
Keywords: Nanodetector, terahertz
  • Lecture (Conference)
    36th International Conference on Infrared, Millimeter, and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA
  • Contribution to proceedings
    36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz 2011), 02.-07.10.2011, Houston, USA
    Proceedings of the 36th International Conference on Infrared, Millimeter and Terahertz Waves (IRMMW-THz 2011)

Publ.-Id: 16519 - Permalink

Self-amplified Cherenkov radiation from a relativistic electron in a waveguide partially filled with a laminated material
Grigoryan, L. S.; Mkrtchyan, A. R.; Khachatryan, H. F.; Arzumanyan, S. R.; Wagner, W.;
The radiation from a relativistic electron uniformly moving along the axis of cylindrical waveguide filled with laminated material of finite length is investigated. Expressions for the spectral distribution of radiation passing throw the transverse section of waveguide at large distances from the laminated material are derived with no limitations on the amplitude and variation profile of the layered medium permittivity and permeability.
Numerical results for layered material consisting of dielectric plates alternated with vacuum gaps are given. It is shown that at a special choice of problem parameters, Cherenkov radiation generated by the relativistic electron inside the plates is self-amplified. The visual explanation
of this effect is given and a possible application is discussed.
Keywords: Cherenkov radiation, relativistic particle, waveguide, periodic medium

Publ.-Id: 16518 - Permalink

Adsorption kinetics of cell wall components of gram positive bacteria on technical surfaces studied by QCM-D
Suhr, M.; Günther, T.; Raff, J.; Pollmann, K.;
In general, the cell wall components of gram-positive bacteria e.g. single lipid bilayer, peptidoglycan, Surface-layer proteins (S-layer) and other biopolymers are well studied. These cell wall components are interesting for several bio-induced technical applications such as biosorptive materials. Although biosorption processes have been intensively investigated, the investigation of metal interaction with biomolecules as well as adsorption processes on substrates on molecular level remains challenging.
In our work we used the quartz crystal microbalance with dissipation monitoring (QCM-D) in order to study the layer formation of cell wall compounds and interaction processes on the nano scale range.
This analytical method allows the detailed detection of array formation of bacterial S-layer proteins and gives a better understanding of the self-assembling processes. S-layer proteins as a part of the outer cell envelope of many eubacteria and archaea form paracrystalline protein lattices in strain depended geometrical structures [1]. Once isolated the proteins exhibit the ability to form these lattices on different kinds of interfaces and possesses equal to the bacteria cells high metal binding capacities. These properties open a wide spectrum of applications e.g. ultrafiltration membranes for organic and inorganic ions and molecules, templates for the synthesis of catalytic nanoparticles and other bio-engineered materials [2, 3].
By performing different experiments with and without modification of technical surfaces with adhesive promoters e.g. polyelectrolytes it is possible to make exact statements regarding coating kinetics, layer stability and interaction with metals. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties. Aim of these investigations is the assembly of a simplified biological multilayer based on cell compounds of gram positive bacteria in order to clarify sorption processes in a complex system. The understanding of coating, biological and biological-metal interaction processes is interesting for different technical applications.

1. U.B. Sleytr et al., Prog. Surf. Sci. 68 (2001), 231-278.
2. K. Pollmann et al., Biotechnology Advances 24 (2006), 58– 68.
3. J. Raff et al., Chem. Mater. 15 (2003), 240-244.
Keywords: QCM-D, S-Layer, bacteria, multi layer, AFM
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 18.-21.03.2012, Tübingen, Deutschland

Publ.-Id: 16517 - Permalink

ASL perfusion quantification: a comparison with PET and Optical Imaging techniques using double labeled microspheres
Bos, A.; Bergmann, R.; Hofheinz, F.; van den Hoff, J.;
Purpose/Introduction: Regional tissue perfusion is a fundamental physiological parameter controlling delivery of oxygen and nutrients to tissue which provides valuable information for cancer research and radiation therapy planning. There do exist established methods in nuclear medicine for perfusion assessment and quantification (e.g. O-15 PET), however, the truly quantitative procedures in general require arterial blood sampling making them ill-suited for routine clinical application.. In contrast, the Arterial Spin Labeling (ASL) MRI technique is absolutely non- invasive, but its quantitative accuracy in small animals is not well investigated. The purpose of this work was to assess accuracy of ASL perfusion measurements in rat brain by a comparison with microspheres derived regional perfusion information using dedicated small animal Positron Emission Tomography (PET) and ex vivo Optical imaging (OI).

Subjects and Methods: 20 µm microspheres were double-labeled with either Cu-64 or Ga-68 for PET and X-sight 670 LSS for OI. They were administered through a catheter to the left ventricle of the heart and a reference blood sample was extracted from the left femoral artery. ASL measurements were performed in a 7T animal system (Bruker Biospin 70/30), using a Flow-sensitive Alternating Inversion Recovery (FAIR) sequence with an adiabatic hyperbolic secant inversion pulse (sech120) and Echo Planar Imaging (EPI) acquisition. Global and selective T1 maps of two measured slices (Hemisphere in caudate putamen region and Cerebellum), PET data and correspondingly cut brain sections were used for calculation of the perfusion. All relevant physiological parameters were monitored. Perfusion of the whole brain (PET, OI) and two dedicated slices (PET, OI, MRI) were analyzed. The results of the different methods were compared.

Results: The perfusion dependency of PET vs. OI was fitted with a linear model resulting in a slope of 0.96 and a Pearson correlation factor (PCF) of 0.97. Since water cannot be considered freely diffusible at elevated perfusion levels, Renkin-Crone formula (y = 1- exp(- PS / x) was used for the fitting of MRI vs. PET data. For the model being used, the sensible value for the surface area product (PS) of 182mL/g/min for water in brain tissue was yielded. .

Discussion/Conclusion: The results of this study show that it is possible to obtain quantitative perfusion values with ASL in the brain of the rat using the EPI-FAIR technique .
Keywords: ASL, PET, IO, perfusion, microspheres
  • Lecture (Conference)
    European Society for Magnetic Resonance in Medicine and Biology 2011, 06.-8.10.2011, Leipzig, Germany

Publ.-Id: 16516 - Permalink

Quantitative Perfusion Measurements: A Comparison of MRI Using Arterial Spin Labeling (ASL) with Radioactive and Fluorescence Microspheres
Bos, A.; Bergmann, R.; van den Hoff, J.;
Aim: Arterial Spin Labeling (ASL) is a Magnetic Resonance Imaging (MRI) technique for perfusion evaluation, which is based on spin inversion in the arterial blood and observation of relaxation effects. However, quantitative accuracy of ASL measurements in small animals is not well investigated. The purpose of this work was to assess accuracy of quantitative ASL perfusion measurements in rat brain by comparison with microspheres derived regional perfusion information using dedicated micro Positron Emission Tomography (PET) and ex vivo Optical imaging (OI).
Methods: Catheters were implanted through the right carotid artery in the left ventricle of the heart for administration of labeled microspheres (diameter 20 µm) and in the left femoral artery for blood sampling. Microspheres were double-labeled with either Cu-64 or Ga-68 for PET and X-sight 670 LSS for OI. ASL measurements were performed in a 7T small animal system using a Flow-sensitive Alternating Inversion Recovery (FAIR) sequence with an adiabatic hyperbolic secant inversion pulse (length-bandwidth product: 80) and Echo Planar Imaging (EPI) acquisition. Global and selective T1 images, correspondingly cut brain sections, and PET data were used for perfusion values calculation. All the crucial physiological parameters were monitored. Perfusion of the whole brain (PET, OI) and two dedicated slices (PET, OI, MRI) were estimated independently with specified methods. The consistency of OI compared to PET for whole brain was used as criterion for inclusion of the respective animal into further data evaluation.
Results: A mean perfusion of the whole brain was 88.8 mL/100g/min. In slices measured with ASL (cerebellum with pons and hemispheres in caudate putamen region) perfusion was calculated with each technique separately. Results from MRI and PET were considered for Cu-64, Ga-68 and for whole data set. The estimated correlation factor for MRI vs. PET is 0.91 and Renkin-Crone model fitting yields a plausible Permeability Surface product (PS) for water (182 mL/g/min). The same data was fitted also with linear regression forced to zero-point (y=0.76x). The left-right disparity in Cortex, Thalamus and Cerebellum was observed because of catheter implantation, namely for 73% of animals perfusion in the left part of the brain was higher.
Conclusions: The quantitative perfusion measurements in the rat brain using ASL are possible but require thorough data analysis. Overall regional contrast provided by ASL is concordant with regional distribution of microspheres in the rat brain. However, deviations from linear correlation are visible and are the subject of further investigations. In order to be useful for routine application in small animal imaging, ASL data acquisition and data evaluation needs to be further optimized. A final calibration via a quantitative comparison with radio- and fluorescent-labeled microspheres seems mandatory.
Keywords: Perfusion, ASL, PET, OI, microspheres
  • Poster
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
  • Contribution to proceedings
    World Molecular Imaging Congress 2011, 02.-10.09.2011, San Diego, USA
    Proceedings of the World Molecular Imaging Congress 2011, S721

Publ.-Id: 16515 - Permalink

Physical characterization of PECVD and PEALD Ru(-C) films and comparison with PVD Ruthenium film properties
Wojcik, H.; Junige, M.; Bartha, W.; Albert, M.; Neumann, V.; Merkel, U.; Peeva, A.; Gluch, J.; Menzel, S.; Munnik, F.; Liske, R.; Utess, D.; Richter, I.; Klein, C.; Engelmann, H. J.; Ho, P.; Hossbach, C.; Wenzel, C.;
PECVD and PEALD of ruthenium films using RuEtcp2 as a precursor andN2/H2/Ar plasma as a reducing agent were characterized. A self-adjusting process to overcome the previously reported inhibition of Ru PEALD on TaN substrates was investigated. Ellipsometric modelling of Ru films was demonstrated providing information on both film thickness and estimated Ru content. The physical properties of PECVD/PEALD Ru films were compared to characteristics of sputtered Ru films within the categories resistivity, impurites, crystal structure, conformity and Cu plating. As a result, ToFSIMS, ERDA and 3D atomprobe revealed the presence of carbon impurities in PECVD and PEALD Ru films, dependent on deposition temperature and plasma power. Nevertheless, highly conductive Ru-C films were produced via PECVD and PEALD achieving resistivities equal to PVD Ru. For all types of Ru films, the size effect played a significant role at thicknesses below 10 nm; Cu plating and crystallization behaviour appeared similar. Direct Cu fill potential of different Ru films was discussed for damascene structures and through silicon vias.

Publ.-Id: 16514 - Permalink

Recombinant production of genetically modified S-layer proteins in different expression systems
Lederer, F.; Kutschke, S.; Pollmann, K.;
Surface layer (S-layer) are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelope. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as ultrafiltration membranes, drug microcontainers, filter materials or patterning structures in nanotechnology.
Heterologous expression of S-layer proteins is not simple and depends on the used vector and the expression system. Equally the S-layer protein size, genetic specifics, and the existence of adapted signal peptides influence the expression. To enable an efficient and economical protein production protein secretion is the most favoured method.
In this work we describe the recombinant production of different S-layer variants and characterize the differences of the used protein expression systems.
We used four different S-layer genes of Lysinibacillus sphaericus JG-A12, Bacillus spec. JG-B12 and Lactobacillus acidophilus and expressed their proteins in Escherichia coli, Pichia pastoris and Lactococcus lactis. Some of these proteins were genetically modified to adapt the construct to the used S-layer expression system.
Our work identified Lactococcus lactis as the best expression system for the used S-layer genes.
  • Poster
    Annual Conference of the Association for General and Applied Microbiology (VAAM), 18.-21.03.2012, Tübingen, Deutschland

Publ.-Id: 16513 - Permalink

On the feasibility of automatic detection of range deviations from in-beam PET data
Helmbrecht, S.; Santiago, A.; Enghardt, W.; Kuess, P.; Fiedler, F.;
In-beam PET is a clinically proven method for monitoring ion beam cancer treatment. The objective is predominantly the verication of the range of the primary particles. Due to dierent processes leading to dose and activity, evaluation is done by comparing measured data to simulated. Up to now, the comparison is performed by well trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. However, an automatic method is desirable. A one dimensional algorithm for range comparison has been enhanced and extended to three dimensions. System inherent uncertainties are handled by means of a statistical approach. To test the method a set of data was prepared. Distributions of +-activity calculated from treatment plans were compared to measurements performed in the framework of the German Heavy Ion Tumor Therapy Project at GSI Helmholtz Centre for Heavy Ion Research Darmstadt, Germany. Articial range deviations in the simulations served as test objects for the algorithm. Range modications of dierent depth (4 mm, 6mm and 10mm water equivalent path length) can be detected. Even though sensitivity and specicity of a visual evaluation is higher, the method is feasible as basis for the selection of patients from the data pool for retrospective evaluation of treatment and treatment plans and correlation with follow up data. Furthermore, it can be used for the development of an assistance tool for a clinical application.
Keywords: in-beam PET, dose monitoring in ion therapy, in-vivo dosimetry, ion therapy

Publ.-Id: 16512 - Permalink

Development Strategies for Creating a Suite of Reference Materials for the In-situ Microanalysis of Non-conventional Raw Materials
Renno, A. D.; Merchel, S.; Michalak, P. P.; Munnik, F.; Wiedenbeck, M.;
The availability of reference materials (RM) for microanalytical methods is decreasing. According to currently exist no materials for which the chemical composition has been certified at the μm sampling scale. Many labs use in-house „standards“ as a temporary measure.
Recent economic trends regarding the supply of rare metals readily justify scientific research into non-conventional raw materials, where a particular need is a better understanding of the relationship between mineralogy, microstructure and the distribution of key metals within ore deposits (geometallurgy). Non-conventional raw materials include everything different from what most people consider to be usual or normal, the geometallurgy concept aims to close the gap between ore body exploration/ exploitation (mining) on the one hand, and mineral processing and metallurgy on the other hand. This interface is widely regarded as an interdisciplinary divide that holds significant potential to utilize non-renewable mineral resources more efficiently and sustainably. Achieving these goals will require an extensive usage of in-situ microanalytical techniques capable of spatially resolving material heterogeneities which can be key for understanding better resource utilization. The availability of certified reference materials (CRMs) is an essential prerequisite for
(1) validating new analytical methods,
(2) demonstrating data quality to the contracting authorities,
(3) supporting method development and instrument calibration, and
(4) establishing traceability between new analytical approaches and existing data sets.
This need has led to the granting of funding by the European Union and the German Free State of Saxony for a program to develop such reference materials .
This effort will apply the following strategies during the selection of the future CRMs:
(1) We will use exclusively synthetic minerals, thereby providing large volumes of homogeneous starting material, following the idea “one CRM for all methods”.
(2) We will focus on matrices which are capable of incorporating many ‘important’ elements while avoid exotic compositions which would not be optimal matrix matches.
(3) We will prefer those phases which remain stable during the various microanalytical procedures.
We decided to synthesize a Fe-S phase, a mineral of the feldspar group, and a phase of the columbite-tantalite solid solution series. As far as possible, both definitive methods as well as methods involving matrix corrections will be used for determining the compositions of the individual materials.
The following methods are considered in our planned studies thus far:
- Electron microprobe analysis (EPMA)
- Laser ablation - ICP-MS (LA-ICP-MS)
- Secondary Ion Mass Spectrometry (SIMS)
- Micro-XRF (μ-XRF)
- Synchrotron-based XRF (S-XRF)
- Particle-induced X-Ray Emission analysis (PIXE)
- Particle-induced γ-Ray-Emission (PIGE)
- Rutherford Backscattering Spectrometry (RBS)
- Elastic Recoil Detection Analysis (ERDA)
- Nuclear Reaction Analysis (NRA)
A critical challenge for the certification process will be the validation of the determination of analytes concentrations as sub-μg sampling masses.
This initiative will assess the homogeneity of the reference materials at sampling sizes ranging between 50 and 1 μm. It is intended to document crystal structural and crystal chemical homogeneity too, knowing that these features may potentially impact specific analytical methods, by affecting diffusion, ion conductivity, and subsurface charging. Both spectroscopic and diffractometric methods will be used, like Raman microspectroscopy, FT-IR microspectroscopy, cathodoluminescence spectroscopy, as well as Electron backscatter diffraction (EBSD).
It is planned to cooperate with those who are interested in the development of such reference materials and we invite them to take part in round-robin exercises.
Keywords: Reference Materials, Geochemistry
  • Invited lecture (Conferences)
    Microscopy and Microanalysis 2011, 07.-11.08.2011, Nashville, USA

Publ.-Id: 16511 - Permalink

Structure and electrical properties of transparent conductive doped ZnO grown by reactive magnetron sputtering
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
No abstract available.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Invited lecture (Conferences)
    IOP Workshop "Plasmas, Surfaces and Thin Films", 08.06.2011, London, England

Publ.-Id: 16510 - Permalink

The Rossendorf beamline BM20 at the ESRF: overview and perspectives
Shalimov, A.; Baehtz, C.; Grenzer, J.; von Borany, J.;
The Rossendorf beamline (ROBL) BM20 at the European Synchrotron Radiation Facility in Grenoble is operated by Helmholtz Zentrum Dresden Rossendorf since 1999. ROBL belongs to Collaborative Research Group (CRG) of beamlines and provides two third parts of beamtime for users from HZDR, while the one third of beamtime is offered to external users selected by ESRF advisory committee. Two experimental stations are placed at the beamline: one is dedicated to materials research, while the second station is designed for spectroscopic investigations of actinides and other radionuclide’s. Material Research Hutch (MRH) is equipped with high precision heavy duty 6-circle diffractometer used for structural characterization of thin layers, nanoparticles, interfaces and analysis of other structural properties of solid state materials. Experimental installations allow users to perform different types of complex experiments including in-situ deposition, annealing in vacuum or gas environment, spectroscopic measurements, following (electro) chemical reactions or morphology transformations using available fast detectors and supplementary devices. Radiochemistry Hutch (RCH) possesses highly specialized safety system making possible investigations of alpha-emitting radionuclides by x-ray absorption spectroscopy (XAS) methods. (More information at
Extensive upgrade of beamline optics, which assets in gain of beam brilliance, homogeneity and accessible energy range is scheduled in 2011. According to our calculation, new monochromator combined with toroidal x-ray mirrors will increase beam intensity up to 3 orders of magnitude in respect to the present value. Energy tunable in the range from 6 up to 35 keV allows users to realize element sensitive spectroscopic measurements like XANES and EXAFS, as well as x-ray scattering investigations (XRD, XRR, GID or GISAX) in anomalous mode. MRH detector installations include novel 1D position sensitive and 2D image Dectris detectors, two modern energy dispersive detectors from KETEK and Bruker Axes, as well as traditional scintillator counters. Besides of that, experimental setup can be tailored with equipment loaned from ESRF instrument pool.
Summarizing the overview of Rossendorf beamline, we would admit broad spectrum of research feasible at ROBL stations: all possible diffraction measurements combined with spectroscopic analysis can be performed during in-situ experiments involving film deposition, different types of annealing, chemical reactions etc. Upcoming modernization of x-ray optics will significantly improve brilliance of the beam, giving outstanding possibilities for researchers in their most challenging experiments.
  • Poster
    IX Krajowe Sympozjum Użytkowników Promieniowania Synchrotronowego, KSUPS 2011, 26.-27.09.2011, Warsaw, Poland

Publ.-Id: 16509 - Permalink

Aktivierung des Al Donators in reaktiv Magnetron-gesputterten ZnO Schichten
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
Al dotiertes ZnO ist eines der am häufigsten untersuchten Ersatzmaterialien für Sn dotiertes In2O3 (ITO) für transparente leitfähige Elektroden. Jedoch wurde bisher nur in wenigen Publikationen versucht zu messen, welcher Anteil des eindotierten Al tatsächlich elektrisch aktiv ist. Basierend auf systematischer Variation von Substrattemperatur und Targetzusammensetzung wurden in dieser Arbeit die elektrischen Eigenschaften aus Hall-Messungen und die mittels Ionenstrahlanalytik bestimmte Zusammensetzung der AZO-Schichten zueinander in Beziehung gesetzt.
Es konnte gezeigt werden, dass für geringe Al Konzentrationen eine maximale effektive Al Aktivierung erreicht wird. Während ab einer gewissen kritischen Al Konzentration die Aktivierung schnell abfällt und die elektrische Leitfähigkeit der Schichten abnimmt.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Lecture (Conference)
    EFDS Workshop "Transparente leitfähige Oxide; Festkörperphysikalische Grundlagen, Materialien und Technologie", 16.05.2011, Dresden, Germany

Publ.-Id: 16508 - Permalink

Self – organized FePt nanoparticles in MgO synthesized by ion-implantation and high-temperature annealing
Shalimov, A.; Akhmadaliev, S.; Baehtz, C.; Potzger, K.;
The formation of FePt nanoparticles (NPs) in MgO crystals after sequential ion implantation and high temperature annealing has been observed and analyzed by means of structural and magnetic characterization. Self-organized FePt NPs were synthesized by an implantation of Fe and Pt ions to the depth of ~90 nm under the MgO surface and post-implantation annealing at 800°C. Structural and magnetic properties of produced NPs have been investigated using x-ray diffraction (XRD), magetometry measurements, and theoretical calculations of ion distributions and magnetization behavior. FePt NPs represent preferential orientation to MgO matrix with a relation of FePt[001]||MgO[001] and FePt[110]||MgO[100]. Using the Preisach formalism of magnetization, the spontaneous moment of FePt was estimated to be in a range ~600 – 3500 mu_B depending on the ion fluences, and corresponds to the NP’s size of 3.5 – 20 nm obtained from XRD study. Several structural phases of FePt NPs, such as, FePt3, disordered fcc and ordered L10 phase were observed in different samples. The evident tendency of L10 ordering after high fluence ion implantation and high-temperature annealing is demonstrated. Optimized regimes of implantation and annealing processes are reported in addition to physical properties of FePt NPs.
  • Poster
    E-MRS 2011 Fall Meeting - Symposium A, 19.-23.09.2011, Warsaw, Poland

Publ.-Id: 16507 - Permalink

Incorporation of Al in ZnO by reactive pulsed magnetron sputtering: electrical properties and dopant activation
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
Al-doped ZnO (AZO) films which combine maximum carrier mobility (μe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg =1.11 eV), and enable a superior light trapping behaviour. A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. The present work focuses on investigation of the influence of Al concentration on the electrical properties of AZO and on establishing performance limits with respect to carrier mobility and resistivity (ρ). Polycrystalline and epitaxial AZO films are grown on fused silica and c-axis oriented sapphire substrates, respectively, by reactive pulsed magnetron sputtering using several sets of Zn/Al alloy targets with an Al concentration (cAl) between 0.7 and 8.7 at%. A systematic variation of process parameters such as substrate temperature (Ts) and oxygen partial pressure results in polycrystalline films with μe>45 cm2V-1s-1 and
<2.3x10-4 Ωcm at optimum conditions, whereas μe~55 cm2V-1s-1 could be obtained for epitaxial films. It is observed that cAl has a strong influence on the optimum value of Ts, the maximum μe and Ne values and also on film structure and surface roughness. The observed dependence of carrier mobility Ne in AZO is discussed in the framework of ionized impurity scattering and clustering as well as grain boundary limited transport which predicts a fundamental physical limit of μe.
Rutherford Backscattering (RBS) and elastic recoil detection analysis (ERDA) confirm a considerable Al enrichment in the films when Ts is increased above its optimum value which correlates with the deterioration of their electrical properties. Combining ion beam analysis and Hall-effect measurements allows to estimate the fraction of electrically active Al dopants, which is rarely reported in a quantitative and systematic manner. The influence of intrinsic defects and charge compensation complicate the interpretation of the results. Nevertheless the target Al concentration as well as the substrate temperature are shown to have an impact on the dopant activation.
Keywords: Al-doped ZnO transparent conductive oxide zinc oxide magnetron sputtering doping activation
  • Lecture (Conference)
    MRS Spring Meeting 2011 (Symposium S: Plasma-assisted Materials Processing and Synthesis), 25.-29.04.2011, San Francisco, USA

Publ.-Id: 16506 - Permalink

Determination of the electrically active Al fraction in Al doped ZnO grown by pulsed reactive magnetron sputtering
Cornelius, S.; Vinnichenko, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.;
Al-doped ZnO (AZO) films which combine maximum carrier mobility (µe), moderate free electron densities (Ne) and high surface roughness are of special interest for application as transparent front electrode in thin film solar cells. They posses high transmission in the near infrared region, close to the bandgap energy of absorber materials like Si (Eg=1.11 eV), and enable a superior light trapping behaviour.
A key to tailor AZO film properties is understanding the mechanisms and effects of the Al-dopant incorporation into the ZnO matrix. It is well accepted that the mobilities in degenerately doped AZO are limited by ionized impurity scattering. A way to overcome this limitation would be to reduce the density of ionized impurities which either don’t donate electrons themselves or compensate the Al donor. This is equivalent to increasing the fraction of electrically active Al in the ZnO host material. Systematic and quantitative investigations on this topic are rarely reported in literature. Therefore this work focuses on quantification of the Al concentration by ion beam analysis methods in conjuction with Hall-effect measurements for AZO films grown by reactive pulsed magnetron sputtering. The influence of parameters like target composition and substrate temperature on the Al activation will be discussed.
Keywords: Al-doped ZnO transparent conductive oxide magnetron sputtering activation doping
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16505 - Permalink

Nonlinear terahertz spectroscopy of semiconductor quantum structures
Schneider, H.;
There is no abstract.
Keywords: infrared/terahertz spectroscopy, nonlinear quadratic detection, semiconductor quantum wells, intersubband transsitions
  • Invited lecture (Conferences)
    2. IR-ON Symposium: InfraRed Optical Nanostructures, 10.03.2011, Wien, Österreich

Publ.-Id: 16504 - Permalink

Voigt effect measurements on PLD grown nickel oxide thin films
Scarlat, C.; Mok, K. M.; Zhou, S.; Lorenz, M.; Grundmann, M.; Helm, M.; Schubert, M.; Schmidt, H.;
NiO has great potential applications in spin valves, magnetooptical sensors, optical fibers, solar thermal absorbers, or in non-volatile resistive random memories [1]. In our study NiO, NiMnO, and NiMnLiO thin films have been grown on double-side polished r-plane sapphire substrates by pulsed laser deposition. We measured the complex Voigt angle using the polarized light from a HeCd laser, a Glan Taylor polarizer, a Hinds PEM-100 and two LockIns [2]. The Voigt effect is a second-order magneto-optic effect [3]. The polarization state of light after transmission through a sample consisting of ca. 1 μm thick, weak ferromagnetic and diamagnetic NiO thin films on purely diamagnetic r-plane sapphire substrates has been modelled using the 4x4 matrix formalism [2] in dependence of an external magnetic field applied in-plane, i.e. in Voigt configuration. The modelling results revealed that for the bare diamagnetic substrate the Voigt angle depends parabolically on the external magnetic field and that the weak ferromagnetic and diamagnetic NiO thin films changed the parabolic dependence of the Voigt angle in the range of ±0.3 T to a flat-top shape in agreement with the experimentally determined Voigt angle. Furthermore, due to the NiO thin films the Voigt angle increased ca. (1±i)10-5 deg for an external in-plane field of ±0.3 T.
[1] U. Russo, D. Ielmini, A.L. Lacaita, A. Pirovano, F. Pellizer and R. Bez, IEEE Electron Device Lett. 25 (2004) 507-509.
[2] C. Scarlat, K. M. Mok, S. Zhou, M. Vinnichenko, M. Lorenz, M. Grundmann, M. Helm, M. Schubert, H. Schmidt, Phys. Stat. Sol. (C) 7 (2010) 334-337.
[3] R. Carey and B.W.J. Thomas, J. Phys.: D: Appl. Phys. 7 (1974) 2362-2368.
  • Lecture (Conference)
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16503 - Permalink

Optical and magnetic properties of Cr-implanted indium oxides thin films
Scarlat, C.; Zhou, S.; Vinnichenko, M.; Kolitsch, A.; Helm, M.; Schmidt, H.;
Dilute magnetic oxides using the electron spin rather than its charge as information carrier are expected to play a key role in the development of spinelectronics. As it has been shown recently, indium oxide (IO), a transparent conducting material, is of potential importance also as a material for spintronics. Polycrystalline and amorphous (ca. 300 nm thick) n-type conductive IO films were grown on SiO2/Si substrates using reactive magnetron sputtering. The films were implanted with Cr+ ions in order to reach Cr concentrations of 1, 2, 3, 4 and 5 at%. The implantation energy was 120 keV. Cr is chosen as a dopant because of its large magnetic moment in the ionic state, and the antiferomagnetic nature of Cr metal segregations. It is non-trivial to form any ferromagnetic secondary phase of Cr oxide. Highly oxygen deficient 2%Cr:IO co-evaporated films revealed ferromagnetism. Here we study the effect of the post-growth treatment on the structural, electrical, magnetic, and optical properties of Cr-implanted IO films. It is shown that only the 2%Cr:IO implanted film is weakly ferromagnetic at 5 K. A reasonable model for the Cr:IO implanted films has been developed to extract optical constants from spectroscopic ellipsometry data below 3 eV in dependence on the Cr concentration.
  • Poster
    DPG Spring Meeting, 13.-18.03.2011, Dresden, Germany

Publ.-Id: 16502 - Permalink

Infrared photodetectors based on quantum wells
Schneider, H.;
There is no abstract.
Keywords: infrared/terahertz detector, semiconductor quantum well, GaAs/AlGaAs, thermal imaging
  • Invited lecture (Conferences)
    Workshop on Infrared Technology, 05.-09.12.2011, Rio de Janeiro, Brasil

Publ.-Id: 16501 - Permalink

Annealed, stress-free, and ferromagnetic Mn-doped indium tin oxide films
Scarlat, C.; Xu, Q.; Zhou, S.; Potzger, K.; Salvan, G.; Helm, M.; Schmidt, H.; Iacomi, F.;
Indium tin oxide (ITO) is a transparent semiconductor and can be highly conductive at room temperature (RT) when doped, making ferromagnetic ITO films attractive candidates for magnetooptical and spintronic devices. Undoped and Mn doped indium tin oxide (ITO) thin films have been grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) technique using targets with the atomic ratio In:Sn:Mn=114:12:13, 109:12:7, 122:12:4 and 122:12:0. In order to have practically stress-free samples [1] all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements revealed negative magnetoresistance and no anomalous Hall effect is observed. The ITO doped films exhibit RT ferromagnetism after annealing. The samples were investigated by magnetooptical Kerr effect (MOKE) spectroscopy measurements.

[1] L Kerkache et al, J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    subtherm 2011, 25.-27.10.2011, Dresden, Germany

Publ.-Id: 16500 - Permalink

Magnetic Mn-doped indium tin oxide films prepared by vacuum thermal evaporation
Scarlat, C.; Xu, Q.; Mok, K.; Shalimov, A.; Fronk, M.; Salvan, G.; Zahn, D. R. T.; Helm, M.; Schmidt, H.; Iacomi, F.;
Indium tin oxide (ITO) can be made a highly conductive transparent coating contact in photovoltaics by doping. Undoped and Mn doped indium tin oxide (ITO) thin films were grown on SiO2/Si substrates by vacuum thermal evaporation (VTE) using sources with atomic ratios of In:Sn:Mn=114:12:13, 109:12:7, 122:12:4, and 122:12:0. In order to have practically stress-free ITO films [1], all the samples were annealed at 450 oC for 2 hours in air. Magnetotransport measurements reveal negative magnetoresistance while no anomalous Hall effect is observed. The Mn-doped ITO films exhibit room temperature ferromagnetism after annealing. We analyzed the magnetization data from SQUID measurements using simulations based on the Preisach approach and derived the magnetic parameters of nanoparticles in the Mn-doped ITO films, namely, the magnetization of individual particles and the distributions of coercive and interparticle interaction fields. The samples were also investigated by magneto-optical Kerr effect spectroscopy and Vector Magnetooptical Generalized Ellipsometry measurements to explore possible combined functionalities in photovoltaics and magnetooptics.

[1] L Kerkache et al., J. Phys. D: Appl. Phys. 39 184–189, (2006).
  • Poster
    Next Generation Solar Energy From Fundamentals to Applications, 12.-14.12.2011, Erlangen, Germany

Publ.-Id: 16499 - Permalink

ROssendorf BeamLine II - New experimental possibilities for in-situ diffraction experiments
Baehtz, C.; Shalimov, A.; Grenzer, J.; von Borany, J.;
New experimental possibilities of the upgraded ROBL-beamline will be represented as well as results of the in-situ growth investigation of carbon nano tubes and graphene.
Keywords: Synchrotron radiation, in-situ diffracton, carbon nano tubes
  • Lecture (others)
    7. Wissenschaftliches Seminar des Dresdner Fraunhofer-Clusters Nanoanalytik, 27.01.2012, Dresden, Deutschland

Publ.-Id: 16498 - Permalink

Bildung von Nanolöchern auf KBr-Oberflächen durch Beschuss mit hochgeladenen Ionen
Wilhelm, R. A.;
Hochgeladene Ionen tragen eine große Menge potentieller Energie (bis zu 100 keV), die als Summe der Bindungsenergien der fehlenden Elektronen definiert ist. Mit Hilfe dieser potentiellen Energie können auf Festkörperoberflächen Strukturen im Bereich von einigen Nanometern erzeugt werden, wobei durch geringe kinetische Energien der Ionen (weniger als 100 eV) Schaden im Festkörpervolumen vermieden werden kann. Die Produktion von Nanolöchern auf KBr(001)-Oberflächen durch den Beschuss mit einzelnen hochgeladenen Ionen wurde bereits untersucht. Diese Arbeit befasst sich aufbauend auf bekannten Ergebnissen mit des Einflusses hoher Fluenzen hoch- und niedriggeladener Ionen auf den Lochbildungsprozess. Diese Untersuchungen sind von Bedeutung um den Mechanismus der defektinduzierten Desorption als treibende Kraft für die Bildung von Nanolöchern zu identifizieren. Ergebnisse von Bestrahlungen von KBr(001)-Oberflächen mit hoch- und niedriggeladenen (4 ≤ q ≤ 54) Ionen bei hohen Fluenzen von (10^10..10^15) cm^−2 und verschiedenen Temperaturen werden in dieser Arbeit vorgestellt. Das zugrunde liegende Modell der defektinduzierten Desorption wird anhand der vorliegenden Ergebnisse diskutiert.

Highly charged ions carry a large amount of potential energy (up to 100 keV), which is defined as the sum of the binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale, and due to very low kinetic energies (less than 100 eV), significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was previously studied in detail. Therefore, investigations of high fluence effects of highly and lowly charged ions are important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations in range of (10^10..10^15) cm^−2 with highly charged ions (4 ≤ q ≤ 54) and the influence of the temperature on the nanostructure production on KBr(001) surfaces are shown. Moreover, the defect mediated desorption model is discussed.
  • Thesis / Students' report
    TU Dresden, 2010
    58 Seiten

Publ.-Id: 16497 - Permalink

In-Situ Analysis of Nanostructures Induced by Slow Highly Charged Ions
Wilhelm, R. A.; Heller, R.; Facsko, S.;
The sum of the binding energies of all missing electrons (potential energy) of highly charged ions can induce surface modifications on the nanometer scale. We present results of a set-up for slow highly charged ion irradiations and scanning probe microscopy studies under in-situ conditions. A Dresden-EBIT is used to provide ions of different species with charge states up to q=40 (e.g. for Xe). An electrostatic deceleration lens system allows to vary the kinetic energies of the ions in the range of 10eV· q up to 5keV· q. Furthermore, we studied surface nanostructures on various substrates by an Omicron ultra high vacuum (UHV) scanning probe microscope, which is directly connected to the ion source. The size and the shape of nanostructures created by the deposition of potential energy and analyzed in-situ under UHV conditions are discussed and compared to those observed by recent studies under ex-situ conditions.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 25.-30.03.2012, Berlin, Deutschland

Publ.-Id: 16496 - Permalink

Surface Modification on KBr(001) with Slow Highly Charged Ions in High Fluence and High Potential Energy Regime
Wilhelm, R. A.; Heller, R.; Facsko, S.;
Highly charged ions (HCI) have an unique property, their potential energy, which can induce modifications on surfaces on the nano-scale without a significant bulk damage. The potential energy, defined as the sum of the binding energies of all missing electrons, can exceed 100 keV, e.g. for Xe50+ or Au60+. This amount of energy is mainly released by the emission of electrons with energies of several 10 eV as described by the classical over the barrier model. The release of the HCI’s potential energy as emission of electrons right in front of the surface or in the first nanometers of the solid leads to a strong interaction with the electronic system of the solid. Especially in ionic crystals like KBr many electron-hole pairs are created near the impact site of the HCI. Due to a strong electronphonon coupling in ionic crystals these excitons become self-trapped and can either recombine or decay into so called colour centres. In KBr F and H-centres are created. H-centres are defined as an interstitial molecular halide atom and a F-center is an electron at an anion site. F-centres, which were produced near the surface, can recombine with surface ions (K+) and lead to their neutralisation and desorption. Also a Br-atom desorption occurs when the H-centre recombines with the surface.
Recently nano-pits on KBr surfaces induced by single ion impacts were investigated and a potential as well as a kinetic energy-threshold for their formation was found. The depths of the pits produced by a single ion impact was found to be one atomic monolayer for Xe charge states up to q = 40 and various kinetic energies. Low charge state (q>10) irradiations, in contrast, show pits as well, but only for much higher fluences (several 10^13 cm^-2). We present studies of high fluence irradiations with highly (q>10) and lowly (q<10) charged Xe ions. For high charge states a deepening of the pits (with increasing fluence) was found, while for low charge state irradiations a depletion region close to low coordinated sites like step edges has been observed. For irradiations with highest charges states, i.e. Au54+ ions and low fluences (<10^10 cm^-2) pit structures could be observed with double monolayer depths for single impacts. This indicates a second energy-threshold for the desorption of the second monolayer by a single ion impact. A qualitative model will be discussed to describe and identify the observed potential and kinetic energy effects.
  • Poster
    XXVII International Conference on Photonic, Electronic and Atomic Collisions, 27.07.-02.08.2011, Belfast, United Kingdom

Publ.-Id: 16495 - Permalink

Nanostructures induced by slow highly charged ions on KBr(001) surfaces
Wilhelm, R. A.; Heller, R.; Facsko, S.;
Highly charged ions carry a large amount of potential energy (up to 100 keV) which is defined as the sum of all binding energies of all missing electrons. This energy can be used to modify surfaces on the nano-scale and due to very low kinetic energies (less than 100 eV) significant bulk damage can be avoided. The production of nanometer sized pit-like structures on KBr(001) surfaces by the impact of single highly charged ions was studied in detail previously. The investigation of high fluence effects of highly and lowly charged ions is important to clearly identify the mechanism of defect mediated desorption as the driving force for the creation of pit-like nanostructures on ionic crystals like KBr. Results of high fluence compared to low fluence irradiations will be shown and kinetic and potential energy effects will be discussed.
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 17.03.2011, Dresden, Deutschland

Publ.-Id: 16494 - Permalink

Pit formation on poly(methyl methacrylate) due to ablation induced by individual slow highly charged ion impact
Ritter, R.; Wilhelm, R. A.; Ginzel, R.; Kowarik, G.; Heller, R.; El-Said, A. S.; Papaléo, R. M.; Rupp, W.; Crespo López-Urrutia, J. R.; Ullrich, J.; Facsko, S.; Aumayr, F.;
We report the formation of nano-sized pits on poly(methyl methacrylate) after exposure to slow highly charged ion beams. The pits are formed on the polymer surface as a direct result of individual ion impacts. Intermittent contact mode atomic-force microscopy was employed to study the size evolution of the pits in dependence of potential and kinetic energies of the incident ions. A potential energy threshold value of approximately 7 keV was found for pit formation. Above this value an increase in potential energy results in an increasing pit volume, while the pit shape can be tuned by varying the kinetic energy.

Publ.-Id: 16493 - Permalink

Ferromagnetic Ge:Mn prepared by ion implantation and pulsed laser annealing
Zhou, S.; Bürger, D.; Li, L.; Skorupa, W.; Helm, M.; Oesterlin, P.; Schmidt, H.;
We report the fabrication of Ge:Mn ferromagnetic semiconductors by Mn-ion implantation into Ge followed by
pulsed laser annealing. The implanted Ge layer was recrystallized during annealing. We observed that the longitudinal and
Hall resistances exhibit the same hysteresis as the magnetization, which is usually considered as a sign of carrier-mediated
Keywords: Magnetic semiconductors, Spin polarized transport in semiconductors, Elemental semiconductors, Magnetotransport phenomena; materials for magnetotransport

Publ.-Id: 16492 - Permalink

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