Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

31742 Publications
Self-assembled Ag nanoparticles on plasma sputtered hexagonally ordered GaSb nanodots
Ranjan, M.; Fritzsche, M.; Zhou, J.; Facsko, S.; Möller, W.;
Low energy ion-irradiation is capable to produce self-organized ripple and dot pattern on surfaces [1, 2].Ion bombardment normal to surface generate hexagonally correlated dot pattern on semiconductor surfaces [2]. Metal film grown on such pre-patterned substrate may lead to highly ordered self-assembled nanoparticles or nanowires [3]. Ordered metal nanoparticles show unique optical properties [4, 5]. In this work negatively biased (-1.2 kV) GaSb substrate was immersed in an inductively coupled RF plasma. Plasma sheath formation around the sample maintained the normal ion incidence. Ion fluence equivalent to 1x1018 cm-2 is sufficient to produce well pronounced hexagonally ordered dot structures. Later oblique incidence PVD growth of silver on such substrate, produce self-assemble nanoparticles fallowing the dots periodicity. Reflection measurement shows a plasmonic splitting and results in two pronounce resonance peak. Such a splitting is arises due to hexagonal arrangement of nanoparticles, not appeared for non-ordered particles. More details study of this work will be presented.

[1] A. Keller, S. Facsko, W. Möller, New J. Phys. 10 (2008) 063004
[2] S.Facsko, T.Dekorsy, C. Koerdt, H. Kurz, A. Vogt, H. Hartnagel, Science 285 (1999)1551
[3] T.W. H.Oates, A.Keller, S.Noda, S.Facsko, Appl. Phy. Lett., 93(2008) 063106.
[4] T.W. H.Oates, A.Keller, S.Facsko, A.Mücklich, Plasmonics 2(2007) 47.
[5] A. Taleb, V. Russier, A. Courty, M. P. Pileni, Phys.Rev.B 59 (1999) 13350
  • Poster
    Plasma Surface Engineering (PSE), 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 14889 - Permalink

Radioökologische Forschung als Basis zur Entwicklung neuer Materialien
Raff, J.;
wird nachgereicht
  • Lecture (others)
    Besuch ehemaliger IRC-Mitarbeiter, 19.11.2010, Dresden, Deutschland

Publ.-Id: 14888 - Permalink

Vortex coupling in magnetic multilayer elements
Wintz, S.; Puzic, A.; Strache, T.; Bunce, C.; Körner, M.; Schönherr, T.; Neubert, A.; McCord, J.; Moench, I.; Mattheis, R.; Raabe, J.; Quitmann, C.; Erbe, A.; Fassbender, J.ORC
Spin vortices have attracted much attention due to their chiral nature and the variety of dynamic phenomena associated with them. In this contribution we present experimental findings on vortex coupling in trilayer elements, where two ferromagnetic layers are separated by a nonmagnetic spacer. For such systems the relative configurations of the in-plane flux senses (circulations) as well as the core orientations (polarities) of layered vortices are identified by means of scanning transmission x-ray microscopy (STXM). The dominant coupling mechanisms here are the magneto-dipolar interaction and interlayer exchange coupling (IEC). Remarkably, a modification of the IEC, which can be induced by noble gas ion irradiation, allows to specifically set the circulation configuration of a layered vortex pair to be either an- tiferromagnetic or ferromagnetic. In addition, time-resolved measurements of the response of interlayer coupled vortices to an excitation by sinusoidal magnetic fields will be shown.
Keywords: magnetic vortex, coupling, STXM, interlayer exchange coupling
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 14887 - Permalink

Iodine in alluvial platinum–palladium nuggets
Cabral, A. R.; Radtke, M.; Munnik, F.; Lehmann, B.; Reinholz, U.; Riesemeier, H.; Tupinambá, M.; Kwitko-Ribeiro, R.;
Synchrotron radiation-induced X-ray fluorescence (SR-XRF) spectrometry was applied to determine iodine concentrations in alluvial Pt–Pd aggregates with delicate morphological features from Córrego Bom Sucesso, Minas Gerais, Brazil. The millimetre-sized botryoidal and rod-shaped grains of alluvial Pt–Pd–Hg intermetallic compounds have surprisingly high concentrations of iodine, in the range from 10 to ~120 µg/g. Because iodine is a strongly biophile element, known to be enriched in peatlands and plant remains in soils by microbial activity, its concentration in the Pt–Pd nuggets suggests biogenic precious-metal fixation in the aqueous alluvial milieu.
Keywords: Iodine, Pt–Pd nuggets, Córrego Bom Sucesso, Minas Gerais, Brazil

Publ.-Id: 14886 - Permalink

Magnetically induced electric polarization in an organometallic magnet
Zapf, V. S.; Kenzelmann, M.; Wolff-Fabris, F.; Balakirev, F.; Chen, Y.;
The coupling between magnetic order and ferroelectricity has been under intense investigation in a wide range of transition-metal oxides. The most direct coupling is obtained in so-called magnetically induced multiferroics where ferroelectricity arises directly from magnetic order that breaks spatial inversion symmetry. However, it has been difficult to find nonoxide-based materials in which these effects occur. Here we present a study of copper dimethyl sulfoxide dichloride (CDC), an organometallic quantum magnet containing S = 1/2 Cu spins, in which electric polarization arises from noncollinear magnetic order. We show that the electric polarization can be switched in a stunning hysteretic fashion. Because the magnetic order in CDC is mediated by large organic molecules, our study shows that magnetoelectric interactions can exist in this important class of materials, opening the road to designing magnetoelectrics and multiferroics using large molecules as building blocks. Further, we demonstrate that CDC undergoes a magnetoelectric quantum phase transition where both ferroelectric and magnetic order emerge simultaneously as a function of magnetic field at very low temperatures

Publ.-Id: 14885 - Permalink

Breaking Translational Invariance by Population Imbalance: The Fulde-Ferrell-Larkin-Ovchinnikov States
Zwicknagl, G.; Wosnitza, J.;
An overview is given of our present understanding of superconductivity with spontaneously broken translation symmetry in polarized Fermi systems. The existence of “crystalline” superconducting phases is considered in a wide range of systems, prominent examples being conduction electrons in metals, ultra-cold atoms in a trap, nuclear matter and dense quark systems. The underlying physics is delineated and theoretical approaches to the inhomogeneous phases and their properties are discussed. From the experimental side, it is argued that superconductivity with imbalance-induced order parameters is realized in layered organic compounds and potentially in heavy-fermion systems.

Publ.-Id: 14884 - Permalink

On-chip superconductivity via gallium overdoping of silicon
Skrotzki, R.; Fiedler, J.; Herrmannsdörfer, T.; Heera, V.; Voelskow, M.; Mücklich, A.; Schmidt, B.; Skorupa, W.; Gobsch, G.; Helm, M.; Wosnitza, J.;
We report on superconducting properties of gallium-enriched silicon layers in commercial (100) oriented silicon wafers. Ion implantation and subsequent rapid thermal annealing have been applied for realizing gallium precipitation beneath a silicon-dioxide cover layer. Depending on the preparation parameters, we observe a sharp drop to zero resistance at 7 K. The critical-field anisotropy proofs the thin-film character of superconductivity. In addition, out-of-plane critical fields of above 9 T and critical current densities exceeding 2 kA/cm2 promote these structures to be possible playgrounds for future microelectronic technology

Publ.-Id: 14883 - Permalink

Investigation of conducting nanostructures on ta-C films made by FIB lithography
Philipp, P.; Bischoff, L.;
Tetrahedral amorphous carbon (ta-C) films with high sp3 content produced by mass filtered vacuum arc deposition were modified by Ga+ FIB irradiation. Surface swelling occurs as a function of fluence, caused by ion induced conversion of sp3 to sp2 hybridized carbon atoms. A model [1] for diamond swelling was applied to ta-C films to estimate the swelling for fluences up to 1 x 1016 cm-2. For higher fluences data from TRIDYN simulations were included due to sputtering in a good agreement with the experiments. Van der Pauw structures were produced by means of Ga+ FIB lithography. A decrease of the sheet resistance with increasing fluence due to the evolution of graphitic regions was observed. The lowest value of 290 Ohm/sq was achieved at 1.6 x 1017 cm-2. Additionally, conducting graphitic wires were produced (length: 10 µm, width: 300 nm to 5 µm). The wire resistivity was measured within 130 kOhm (5 µm width) and 3 GOhm (300 nm width). Ion induced graphitization of ta-C films by FIB offers prospective applications in nano technology to fabricate conductive nanostructures in an insulating thin film.
[1] F. Bosia et al. Nucl. Instrum. Meth. B 268 (2010) 2991.
Keywords: tetrahedral amorphous carbon, ta-C, FIB lithography, graphitization, nano structures
  • Poster
    75. Jahrestagung der DPG und DPG Frühjahrstagung, 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 14882 - Permalink

Freestanding Si nanowires fabricated by Ga+ FIB implantation and subsequent anisotropic etching
Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.;
Localized Ga+ ion implantation in silicon-on-insulator substrates (top layer 2 µm) by focused ion beam and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires with reproducible widths between 20 and 200 nm.
The dependence of the resulting nanowire width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the nanowire width as a function of the implanted fluence. Moreover, the temperature dependence of the nanowires’ resistivity and the activation energy for electrical current flow were investigated before and after direct current annealing in air and in vacuum ambient. Annealed nanowires showed a decrease of their resistivity up to two orders of magnitude, indicating a partial recrystallization of the nanowires through self-heating and a change in the conduction mechanism. The assumption of recrystallization is supported by scanning electron microscopy and Raman spectroscopy.
The comprehension of the pinpointed fabrication of such Si nanostructures establishes a broad range of application in the field of nano-electro-mechanical systems.
Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy
  • Poster
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Publ.-Id: 14881 - Permalink

Complex formation of trivalent americium with salicylic acid at very low concentrations
Müller, M.; Acker, M.; Taut, S.; Bernhard, G.;
For the first time, the complexation of americium(III) with salicylic acid was studied at trace metal concentrations using a 2.0 m Long Path Flow Cell for UV–vis spectroscopy. The detection limit of Am(III) in aqueous solution at pH 3.0 was found to be 5 9 10-9 M. Two Am(III)-salicylate complexes were formed at pH 5.0 in 0.1 M NaClO4, indicated by a clear red shift of the absorption maximum. The absorption spectra obtained from spectrophotometric titration were analyzed by means of factor analysis and complex stabilities were calculated to be log b110 = 2.56 ± 0.08 and log b120 = 3.93 ± 0.19.
Keywords: Americium, Long path flow cell, UV–vis, Detection limit, Complexation, Salicylic acid

Publ.-Id: 14880 - Permalink

Development of a high resolution and high dispersion Thomson Parabola
Jung, D.; Hoerlein, R.; Kiefer, D.; Letzring, S.; Gautier, D. C.; Schramm, U.; Huebsch, C.; Oehm, R.; Albright, B. J.; Fernandez, J. C.; Habs, D.; Hegelich, B. M.;
Here we report on the development of a novel high resolution and high dispersion Thomson Parabola for simultaneously resolving protons and low-Z ions of more than 100 MeV/nucleon necessary to explore novel laser-ion-acceleration schemes. High electric and magnetic ¯elds enable energy resolutions of ¢E=E < 5% at 100 MeV/nucleon and impede premature merging of di®erent ion species at low energies on the detector plane. First results from laser driven ion acceleration experiments performed at the Trident Laser facility demonstrate high resolution and superior species and charge state separation of this novel Thomson parabola for ion energies of more than 30 MeV/nucleon.
Keywords: laser ion acceleration, ino spectrometer

Publ.-Id: 14879 - Permalink

Sicherheitstechnische Fragestellungen im Reaktorbetrieb am Beispiel eines DWR
Schäfer, F.; Tusheva, P.; Weiss, F.-P.;
Der Vortrag erläutert grundlegende Prinzipien der nuklearen Sicherheit, gibt einen Überblick zu Betriebstransienten und hypothetischen Störfällen in einem DWR und diskutiert die verschiedenen Methoden, welche für Untersuchungen zur Reaktorsicherheit angewendet werden.
Keywords: Nuclear Reactor, Reactor Safety
  • Invited lecture (Conferences)
    3. VDI-KTG Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

Publ.-Id: 14878 - Permalink

Spatial manipulation of magnetic damping in ferromagnetic-antiferromagnetic films by ion irradiation
McCord, J.; Strache, T.; Mönch, I.; Mattheis, R.; Fassbender, J.ORC
The effective magnetic damping parameter in ferromagnetic-antiferromagnetic-ferromagnetic NiFe/IrMn/NiFe try-layer structures is set over a wide range. Ultra-thin antiferromagnetic systems in combination with low fluence Ni-ion irradiation are used to control the magnetic damping parameter by two independent mechanisms. Changing the ferromagnetic-antiferromagnetic interface the initially strongly increased damping parameter is reduced. Applying the method locally, results in a magnetic layer with spatially distributed regions of different damping. The overall relaxation time of the mixed property film is found to be a direct superposition of the individual relaxation time contributions and thus determined by the ratio of phases with individual damping parameter.

Publ.-Id: 14877 - Permalink

Realization of radiobiological in vitro cell experiments at conventional X-ray tubes and unconventional radiation sources
Beyreuther, E.;
More than hundred years after the discovery of X-rays different kinds of ionizing radiation are ubiquitous in medicine, applied to clinical diagnostics and cancer treatment as well. Irrespective of their nature, the widespread application of radiation implies its precise dosimetric characterization and detailed knowledge of the radiobiological effects induced in cancerous and normal tissue. Starting with in vitro cell irradiation experiments, which define basic parameters for the subsequent tissue and animal studies, the whole multi-stage process is completed by clinical trials that translate the results of fundamental research into clinical application. In this context, the present dissertation focuses on the establishment of radiobiological in vitro cell experiments at unconventional, but clinical relevant radiation qualities.
In the first part of the present work the energy dependent biological effectiveness of photons was studied examining low-energy X-rays (≤ 50 keV), as used for mammography, and high-energy photons (≥ 20 MeV) as proposed for future radiotherapy. Cell irradiation experiments have been performed at conventional X-ray tubes providing low-energy photons and 200 kV reference radiation as well. In parallel, unconventional quasi-monochromatic channeling X-rays and high-energy bremsstrahlung available at the radiation source ELBE of the Forschungszentrum Dresden-Rossendorf were considered for radiobiological experimentation. For their precise dosimetric characterization dosimeters based on the thermally stimulated emission of exoelectrons and on radiochromic films were evaluated, whereas just the latter was found to be suitable for the determination of absolute doses and spatial dose distributions at cell position. Standard ionization chambers were deployed for the online control of cell irradiation experiments. Radiobiological effects were analyzed in human mammary epithelial cells on different subcellular levels revealing an increasing amount of damage for decreasing photon energy. For this reason, the assumed photon energy dependence was reconfirmed for a cell line other than human lymphocytes, an important finding that was discussed on the 2007 Retreat of the German Commission on Radiological Protection.
After successful finalization of the photon experiments the focus of the present dissertation was directed to the realization of in vitro cell irradiation experiments with laser-accelerated electrons. This research was carried out in the frame of the project onCOOPtics that aims on the development of laser-based particle accelerators, which promise accelerators of potentially compact size and more cost-effectiveness suitable for a widespread medical application, especially for high precision hadron therapy. The unique properties, i.e., the ultrashort bunch length and resultant ultrahigh pulse dose rate, of these unconventional particle accelerators demand for extensive investigations with respect to potential effects on the dosimetric and radiobiological characterization. Based on the experiences gained at ELBE first experiments on the radiobiological characterization of laser-accelerated electrons have been performed at the Jena Titanium:Sapphire laser system. After beam optimization, a sophisticated dosimetry system was established that allow for the online control of the beam parameters and for the controlled delivery of dose to the cell sample. Finally, worldwide first systematic in vitro cell irradiation experiments were carried out resulting in a reduced biological effectiveness for laser-accelerated electrons relative to the 200 kV X-ray reference, irrespectively on the biological effect and cell lines examined. These successful results are the basis for future in vivo studies and experiments with laser-accelerated protons.
Keywords: X-ray tubes, radiation sources
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Dresden-Rossendorf; FZD-540 2010


Publ.-Id: 14876 - Permalink

Time resolved spectroscopy on quantum dots and graphene at the FELBE free-electron laser
Winnerl, S.; Stehr, D.; Wagner, M.; Schneider, H.; Helm, M.; Seidel, W.; Michel, P.; Zibik, E. A.; Carpenter, B. A.; Porter, N. E.; Skolnick, M. S.; Wilson, L. R.; Grange, T.; Ferreira, R.; Bastard, G.; Orlita, M.; Plochocka, P.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
The free-electron laser FELBE at the Forschungszentrum Dresden-Rossendorf enables experiments with spectral, temporal, and, by means of near-field microscopy, also high spatial resolution. FELBE delivers picosecond IR and THz pulses in a wavelength range from 5 µm to 280 µm. Operation in a continous pulsing regime and synchronization to various tabletop laser sources allows for two-color pump-probe experiments. Here we review the potential of the laser and focus on two highlight pump-probe experiments. In the first experiments, the relaxation dynamics in self assembled InGaAs quantum dots at energies below the Reststrahlen band is studied. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 2 ps at 30 meV (7 THz). The results are in very good agreement with our microscopic theory of the carrier relaxation process, taking into account polaron decay via acoustic phonons [1]. In the second experiment, the relaxation dynamics in graphene is investigated at photon energies E = 20 – 250 meV. For excitations below the phonon energy of the G-mode, long relaxation times (20 – 40 ps) are observed. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV. The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).

[1] E. A. Zibik et al. Nature Materials 8, 803 - 807 (2009).
Keywords: Quantum dots, graphene, relaxation dynamics, polarons, terahertz, infrared, pump-probe spectroscopy
  • Invited lecture (Conferences)
    SPIE Photonics West, 22.-27.01.2011, San Francisco, USA
  • Proceedings of SPIE 7937(2011), 793708
    DOI: 10.1117/12.873702


Publ.-Id: 14875 - Permalink

Relaxation dynamics in epitaxial graphene probed at low excitation energies
Winnerl, S.; Orlita, M.; Plochocka, P.; Schneider, H.; Helm, M.; Kossacki, P.; Potemski, M.; Sprinkle, M.; Berger, C.; de Heer, W. A.;
The relaxation dynamics of graphene has been investigated in various degenerate as well as two-color pump-probe studies at excitation energies E = 1.6 eV [1-5]. We report on degenerate pump-probe spectroscopy at much lower energies (E = 20 – 250 meV; radiation source: free-electron laser) on graphene multilayers grown by thermal decomposition. Relaxation times between 20 and 40 ps are found for photon energies E < 70 meV, where only acoustic phonons can contribute to the relaxation dynamics. At 245 meV a much faster relaxation with two time constants (tau_1 ≈ 1.2 ps, tau_2 = 4 – 8 ps) is observed and attributed to contributions of optical phonons. While the pump-induced transmission is positive for E > 30 meV, pump-induced absorption occurred for E < 20 meV (Fig. 1). The increased transmission for E > 30 meV is caused by bleaching of the interband transition. We attribute the induced absorption to heating of carriers by intraband free-carrier absorption for E < 2E_F (E_F: Fermi energy).
[1] J.M. Dawlaty et al., Appl. Phys. Lett. 92, 042116 (2008).
[2] D. Song et al., Phys. Rev. Lett. 101, 157402 (2008).
[3] P.A. George et al., Nano Lett. 8 ,4248 (2008).
[4] H. Wang et al., Appl. Phys. Lett., 96, 081917 (2010).
[5] D. Sun et al., Phys. Rev. Lett. 104, 136802 (2010).
Keywords: Relaxation dynamics, graphene, infrared, terahertz
  • Poster
    2nd International Symposium on the Science and Technology of Epitaxial Graphene, 14.-17.09.2010, Amelia Island, USA

Publ.-Id: 14874 - Permalink

Compositional depth profiling of TaCN thin films
Adelmann, C.; Conard, T.; Franquet, A.; Brijs, B.; Munnik, F.; Burgess, S.; Witters, T.; Meersschaut, J.; Kittl, J. A.; Vandervorst, W.;
The composition profiling of thin TaCN films was studied. For the composition profile determination using x-ray photoemission spectrometry (XPS) in combination with Ar sputtering, preferential sputtering effects of N with respect to Ta and C were found to lead to inaccurate elemental concentrations. Sputter yield calculations for the given experimental conditions allowed for the correction of a part of the error, leading to fair accuracy by reference-free measurements. Further improvement of the accuracy was demonstrated by the calibration of the XPS compositions against elastic recoil detection analysis (ERDA) results. For Auger electron spectrometry (AES) in combination with Ar sputtering, accurate results required the calibration against ERDA. Both XPS and AES allowed for a reliable and accurate determination of the compositional profiles of TaCN-based thin films after calibration. Time-of-flight secondary-ion mass spectrometry was also used to assess the composition of the TaCN films. However, the analysis was hampered by large matrix effects due to small unintentional oxygen contents in the films. Energy-dispersive x-ray spectrometry is also discussed, and it is shown that an accurate reference-free measurement of the average film concentration can be achieved.
Keywords: TaC; TaN; TaCN; XPS; AES; ToF-SIMS; ERDA; EDX; composition profile

Publ.-Id: 14873 - Permalink

Speciation of Uranium in Seepage and Pore Waters of Heavy Metal-Contaminated Soil
Baumann, N.; Arnold, T.; Lonschinski, M.;
The uranium speciation in natural occurring seepage water samples, and in soil water samples, all samples from test site “Gessenwiese”, were analyzed by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). Test site Gessenwiese was installed as a part of a research program of the Friedrich Schiller University Jena for investigations within the area of a recultivated former uranium mining heap close to Ronneburg (Eastern Thuringia).
Those investigations revealed that the uranium speciation in that seepage water is dominated by the uranium (VI) sulfate species UO2SO4(aq). The analyses were performed to compare presented results in a later stage with the uranium speciation in plants, which grow on the grassland test site Gessenwiese. It was showed that TRFLS is a useful tool for clearing up the speciation of uranium in water, which is affiliated by plants.
  • Book chapter
    Kothe, Erika; Varma, Ajit: Bio-Geo Interactions in Metal-Contaminated Soils, Berlin: Springer, 2012, 978-3-642-23326-5, 131-142

Publ.-Id: 14872 - Permalink

Reversals and the turbulent alpha-effect in kinematic simulations of natural and experimental dynamos
Giesecke, A.; Stefani, F.; Gerbeth, G.;
From paleomagnetic observations, numerical simulations and -- meanwhile -- also experiments, it is evident that reversing dynamos are a quite common phenomenon. An easy access to the examination of reversing dynamos is provided by simplifying mean field simulations where the induction effects of helical small scale turbulence are parametrized by the so called α-effect.

In a geodynamo-like α2-model reversing solutions are obtained only for a highly restricted class of radial α-profiles which are characterized by a proximity of oscillating and non-oscillating state. The required properties of the α-effect, indeed, have been found from local simulations of rotating magnetoconvection in a Cartesian box (Giesecke et al. 2005, PEPI 152, 90-102). Essential properties of the field reversals can be assigned to the behavior of so called exceptional points in the spectrum of the dynamo-operator where two different non-oscillatory field eigenmodes merge and continue as one oscillatory eigenmode (Stefani et al. 2005, PRL, 94, 184506). The connection between oscillating solutions and irregular occurring reversals arises from fluctuations of the α-effect, which causes a sporadic switching from steady to the oscillatory regime and vice versa. In this picture a reversal is an inevitable consequence of the behavior of the instantanous growthrate in conjuction with fluctuations of the driving source.

Recent results of the French von-Kármán-Sodium (VKS) dynamo offer a possibility for detailed investigations of reversing magnetic fields. In the VKS experiment a turbulent flow of liquid sodium is driven by two counter rotating soft iron impellers located close to the endplates of a cylindrical vessel. The geometric structure of the observed magnetic field is dominated by an axisymmetric dipole that exhibits regular and irregular reversals if the impellers rotate with different frequencies. Recent simulations show that the induction process is essentially determined by the material properties of the flow driving impellers (high permeability) because of internal boundary conditions for the magnetic field on the interface between fluid and impeller (Giesecke et al. 2010, PRL 104, 044503). However, only the combined interaction of soft iron disks and a comparatively small α-effect allows to explain the dominating axisymmetric field. Contributions of dipole and quadrupole type fields deduced from the equatorial symmetry show nearly the same growth rate supporting the reversal model presented by Pétrélis & Fauve (2009, PRL 102, 144503) that is based on the coupling between these two modes.
Keywords: Dynamo Geodynamo alpha-effect Simulations
  • Poster
    AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
  • Contribution to proceedings
    AGU Fall Meeting 2010, 13.-17.12.2010, San Francisco, USA
    Reversals and the turbulent α-effect in simulations of natural and experimental dynamos

Publ.-Id: 14871 - Permalink

High permeability material and dynamo action
Giesecke, A.; Stefani, F.; Gerbeth, G.;
A prescribed flow of liquid sodium provides an energy source for self-generation of a magnetic field. The influences of non-uniform material properties on the dynamo process are examined by means of kinematic simulations of the electromagnetic induction equation.

High permeability material even if localized in a small volume like the flow driving impellers in the French VKS dynamo experiment, essentially determines the field generation process (decrease of the effective critical magnetic Reynolds number and enforcement of internal boundary conditions on material interfaces). Permeability caused facilitation of dynamo action might be important as well for the helical flow in cooling circuits of fast breeders. Preliminary simulations for a model flow in and around soft-iron sub-assemblies (that comprise the nuclear fuel pins) show a reduction of the critical magnetic Reynolds number for the onset of dynamo action by a factor of 2.
Keywords: Dynamo Permeability
  • Poster
    MHDDAYS 2010, 22.-23.11.2010, Dresden, Germany

Publ.-Id: 14870 - Permalink

Multiple active mirror concept for high energy short-pulse lasers
Loeser, M.; Kroll, F.; Röser, F.; Siebold, M.; Schramm, U.; Sauerbrey, R.;
Ytterbium-doped gain media are preferably utilized in high-energy, diode-pumped lasers due to their comparably long fluorescence lifetime, absence of excited state absorption, and quenching effects. Despite exhibiting a low quantum defect, thermal lensing and stress birefringence within the amplifying medium limits the maximum repetition rate of large aperture lasers. Furthermore, the quasi-three-level scheme of Yb3+ leads to re-absorption losses at room temperature especially when operating at low fluences. Here, we present a novel approach combining longitudinal cooling of a disk-laser design with the energy storage capability of a rod amplifier. Therefore, a multiple active mirror amplifier is presented for improved optical-to-optical conversion efficiency and reduced thermally induced aberrations at high repetition rates. Multi-passing both pump and extraction beams through the gain medium, which is well known from thin-disk lasers, also reduces the re-absorption losses. However, energy scaling of a single thin-disk design is limited by parasitic lasing due to a high aspect ratio between longitudinal and transverse gain. We also introduce simulation results on a multiple active mirror short-pulse amplifier employing various Ytterbium-doped gain media such as Yb:YAG, Yb:CaF2, Yb:glass, and Yb:silica. Furthermore, time resolved measurements of thermally induced aberrations at pulse-pumped operation are illustrated.
Keywords: Diode-pumped lasers, Ytterbium-doped solid state lasers
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP 2010, 08.-12.03.2010, Hannover, Deutschland

Publ.-Id: 14869 - Permalink

Ion-beam induced hydrogen redistribution in a-Si:H-based triple layer structures
Pantchev, B.; Danesh, P.; Schmidt, B.; Grambole, D.; Bischoff, L.;
Ion-beam induced hydrogen migration has been studied in triple layer structures, a-Si/a-Si:H/a-Si and SiO2/a-Si:H/SiO2. Nuclear reaction analysis has been used for simultaneous irradiation with MeV ions and measurement of hydrogen distribution in the structures. It has been established that there is no hydrogen loss from SiO2/a-Si:H/SiO2 structures, but an asymmetric redistribution due to hydrogen penetration into the bottom SiO2 layer. Hydrogen loss has been observed from the a-Si/a-Si:H/a-Si structures. The inspection of the surface of these samples by means of atomic force microscope has shown that it proceeds by bubble formation and blistering at the inner interface. The observed ion-beam induced selective penetration of hydrogen into the underlying material can be used as a tool for preparation of microcavity and microchannel arrays.
Keywords: a-Si:H, ion implantation, hydrogen migration
  • Lecture (Conference)
    16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
  • Open Access LogoJournal of Physics: Conference Series 253(2010), 012055
    DOI: 10.1088/1742-6596/253/1/012055

Publ.-Id: 14868 - Permalink

Nanoindentation-induced pile-up in hydrogenated amorphous silicon
Pantchev, B.; Danesh, P.; Wiezorek, J.; Schmidt, B.;
Nanoindentation-induced material extrusion around the nanoindent (pile-up) leads to an overestimation of elastic modulus, E, and nanohardness, H, when the test results are evaluated using the Oliver and Pharr method. Factors affecting the pile-up during testing are residual stresses in film and ratio of film and substrate mechanical properties. Nanoindentation of hydrogenated amorphous silicon (a-Si:H) films has been carried out with the aim to study the effect of residual compressive stress on the pile-up in this material. To distinguish the contribution of compressive stress to the appearance of pile-up ion implantation has been used as a tool, which reduces the compressive stress in a-Si:H. Scanning probe microscope has been used for the imaging of the indent and evaluation of the pile-up. The values of E and H have been obtained from the experimental load-displacement curves using depth profiling with Berkovich tip, which has created negligible pile-up. A sharper cube corner tip has been used to study the pile-up. It has been established that pile-up is determined by the material plasticity, when the compressive stress is below 200 MPa. The contribution of mechanical stress to the pile-up is essential for the stress as high, as about 500 MPa.
Keywords: Nanoindentation, silicon hardness, ion implantation
  • Lecture (Conference)
    16 th International School on Condensed Matter Physics “Progress in Solid State and Molecular Electronics, Ionics and Photonics”, 29.08.-03.09.2010, Varna, Bulgaria
  • Open Access LogoJournal of Physics: Conference Series 253(2010), 012054
    DOI: 10.1088/1742-6596/253/1/012054

Publ.-Id: 14867 - Permalink

Effect of hydrogen on hardness of amorphous silicon
Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.; Grambole, D.;
A comparative study of hardness of thin films of hydrogenated amorphous silicon (a-Si:H) and hydrogen-free amorphous silicon (a-Si) was carried out to reveal the role of hydrogen in the plastic properties of amorphous silicon. In addition, the effect of hydrogen on hardness was established by changing hydrogen concentration in the material using post-deposition processing of the samples. The hydrogen concentration in a-Si:H was decreased by thermal annealing. In a-Si hydrogen was introduced by plasma hydrogenation. The values of hardness of the as-prepared a-Si and a-Si:H films were determined by nanoindentation using depth profiling. Low-depth indentation was applied to evaluate the effect of post-hydrogenation. The results obtained show that the presence of hydrogen in the amorphous silicon network leads to the increase in hardness. The conducted experiments demonstrate that plasma hydrogenation can be used as an effective tool to increase the hardness of amorphous silicon. Hardness of a-Si:H of about 12.3–12.7 GPa is as high as of crystalline silicon, suggesting a-Si:H can be a substitute for crystalline silicon in some MEMS.
Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

Publ.-Id: 14866 - Permalink

Effect of keV ion irradiation on mechanical properties of hydrogenated amorphous silicon
Danesh, P.; Pantchev, B.; Wiezorek, J.; Schmidt, B.;
The susceptibility of mechanical properties of hydrogenated amorphous silicon (a-Si:H) to the implantation-enhanced disorder has been studied with the aim to extend the application field of this material in the technology of micro-electromechanical systems. Effect of keV ion irradiation on the elastic modulus, E, of hardness, H, and of root-mean-squared roughness to silicon ion implantation has been determined. The mechanical properties were evaluated by nanoindentation testing. E of 119 GPa and H of 12.3 GPa were determined for the as-prepared a-Si:H film. The implantation of silicon ions leads to a decrease in E and H, evaluated for a series of the implantation fluences in the range of 1.0x1013–5.0x1016 cm-2. Surface smoothing has been observed at high fluences and low ion energy of 18 keV, suggesting that ion beam may be used as a tool to reduce the roughness of the a-Si:H surface, while keeping intact the mechanical properties inside the film. The conducted experiments show that it is possible to prepare a-Si:H films with hardness and smoothness comparable to crystalline silicon.
Keywords: Hydrogenated amorphous silicon, Ion implantation, Elastic modulus, Hardness

Publ.-Id: 14865 - Permalink

Magnetic hybrid films - magnetic property patterning by ion irradiation
McCord, J.; Hamann, C.; Strache, T.; Martin, N.; Mönch, I.; Mattheis, R.; Kaltofen, R.; Quandt, E.; Fassbender, J.ORC
Ion irradiation and implantation allows for a focussed materials modification in the range of a few nanometer. Effects of periodic patterning of the physical properties circumventing topographic patterning in the conventional sense are exploited. Magnetic materials with mixed hybrid magnetic properties are created. An overview over ongoing activities at the FZD will be given.
  • Invited lecture (Conferences)
    „Struktur und Eigenschaften kondensierter Materie“ Seminar der TU Chemnitz, 23.11.2010, TU Chemnitz, Germany

Publ.-Id: 14864 - Permalink

Electrical characterization of oxygen vacancies in oxides by means of space charge spectroscopy
Schmidt, H.;
The development of new materials for cool devices, e.g. memristive and spintronics devices, needs non-destructive techniques to characterize defects in new materials. The knowledge on defects is strongly desired and will help to prevent device degredation. The non-destructive characterization of certain defects is possible by means of positron annihilation spectroscopy (PAS) if open volume-defects are large and electrically neutral/negatively charged, if segregations are attractive for positrons and change the annihilation rate, and/or if the electron density and with that annihilation rate changes during phase transitions. The complementary, destructive characterization of defects in semiconductors prepared as diodes by means of space charge spectroscopy is possible if the defects are charged/decharged in response to electrical pulses applied to the diode.
Keywords: defects, space charge spectroscopy, positron annihilation spectroscopy
  • Lecture (Conference)
    Workshop on Positron Annihilation Spectroscopy, 19.10.2010, FZD, Germany

Publ.-Id: 14862 - Permalink

Electrical characterization of semiconductors on the mm-nm length scale
Schmidt, H.;
The electrical conductivity of semiconductors is controlled by the activated dopant level and the intrinsic carrier concentration. Semiconductor devices are prepared with either holes or electrons as the majority charge carriers. Hall effect measurements yield carrier concentration and mobility and estimates of scattering mechanisms. The use of Hall effect measurements and of capacitance-voltage and deep level transient spectroscopy measurements for profiling depth dependent free carrier concentrations and for identifying deep traps within the forbidden gap of semiconductors, respectively, yields a potent suite of characterization techniques on the mm-mum length scale. Insight into the electrical properties of doped semiconductor nanostructures may be obtained from scanning spreading resistance microscopy and Kelvin probe force microscopy measurement. Dielectric semiconductor conductivities on the nm scale may be obtained from scanning probe microscopy measuremens. Examples of current investigations by means of the presented electrical characterization techniques are given.
Keywords: space charge spectroscopy, electrical nanometrology
  • Invited lecture (Conferences)
    IZFP-Kolloquium, 25.10.2010, Saarbrücken, Germany

Publ.-Id: 14861 - Permalink

Temperature Measurement in Rapid Thermal Annealing
Reichel, D.; Skorupa, W.; Lerch, W.; Gelpey, J.;
Microelectronics Industry and consequently semiconductor research have developed into pillars of modern technology. Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds.
One major application for thermal annealers is to anneal damage caused by ion implantation. For this purpose temperatures above 600 °C are preferred, although a high diffusion rate of the dopants ought to be avoided. Therefore, short heating periods with steep ramp rates are desired.
This is where Flash Lamp Annealing comes into play. It allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultra-short time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk.
The applications are numerous, especially in thermal treatment of semiconductor surfaces where doping concentrations far beyond the solubility limit are desired, e.g. for ultra shallow implantation profiles. Similarily, highly doped layers are required when studying small scale effects like superconductivity brought about by the implanted dopant.
Due to the high energy density on the sample even high melting points can be achieved for defect annealing during recrystallization of the melt.
The response of various materials to subsecond thermal treatment, however, is not well understood for most cases, especially the temperature dependence of many material parameters is unknown to a large extent. Clearly, for deeper investigation into the subject a real-time temperature measurement with a high temperature resolution (ΔT << 5K), is crucial and is regarded as a key component in order to achieve rapid and reliable processing.
For this purpose traditional means of temperature measurement, e.g. thermocouples, must be excluded. Not only do they lead to wafer contamination but their long response time contradicts the ultra-fast annealing time of the Flash Lamp Device.
In the framework of the presentation previous non-contact approaches to rapid temperature measurement will be discussed with special regard to temperature resolution and industrial mass production.
Keywords: Temperature Measurement, Rapid Thermal Annealing, Flash Lamp Annealing
  • Lecture (Conference)
    9th International Workshop on Subsecond Thermophysics, 22.-24.09.2010, Graz, Österreich

Publ.-Id: 14860 - Permalink

Rückbau des Zyklotrons U-120 am Forschungszentrum Dresden-Rossendorf
Naumann, B.; Friedrich, M.; Matz, W.;
Der Beitrag gibt einen Überblick über den Stand des Rückbaus des Zyklotrons U-120, das von 1958 bis 1999 eines der größten experimentellen Anlagen im Forschungszentrum Rossendorf war. Der Rückbau der Beschleunigeranlage begann im Jahr 2001. Bis zum November 2010 sind alle Anlagenteile und Experimentaufbauten radiologisch bewertet und größtenteils entsorgt worden. Der Beitrag beschreibt u. a. die Verfahren zur Bewertung der Aktivierung großer Bauteile des Zyklotrons.
  • Invited lecture (Conferences)
    4. Symposium Stilllegung und Rückbau kerntechnischer Anlagen, 02.-03.11.2010, Hannover, Deutschland

Publ.-Id: 14859 - Permalink

A trigonal nodal solution approach to the multi-group simplified P3 equations in the reactor code DYN3D
Duerigen, S.; Grundmann, U.; Mittag, S.; Merk, B.; Fridman, E.; Kliem, S.;
The neutronics model of the nodal reactor dynamics codeDYN3D developed for 3-D analyses of steady states and transients in light-water reactors has been extended by a simplified P3 (SP3) neutron transport option to overcome the limitations of the diffusion approach. To provide a method being applicable to reactors with hexagonal fuel assemblies and furthermore allowing flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, the derivation of the trigonal SP_3 method is presented and preliminary assessment of the methodology is performed.
Keywords: simplified P3, SP3, nodal method, trigonal, triangular, hexagonal
  • Contribution to proceedings
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14858 - Permalink

Preparation of laser-accelerated proton beams for radiobiological applications
Metzkes, J.; Cowan, T. E.; Karsch, L.; Kraft, S. D.; Pawelke, J.; Richter, C.; Richter, T.; Zeil, K.; Schramm, U.;
This paper presents the concept of transport and filtering of laser-accelerated proton pulses used for the first cell irradiation experiments performed with the Dresden 150 TW laser DRACO. Based on a simple non-focusing magnetic dipole equipped with two apertures the concept makes use of an energy dependent angular asymmetry of the proton spectra. For micron thin target foils protons of interest with energies above 7 MeV are observed to be significantly oset from target normal where low energy emission is dominantly centered. As the eect can be controlled via the target rotation with respect to the incoming light, it can be used to optimize the transport efficiency for high energy protons while simultaneously suppressing background radiation.
Keywords: laser acceleration of ions, target normal sheath acceleration, magnetic energy filter, radiobiological studies

Publ.-Id: 14857 - Permalink

Bispidine-derivatives for radiopharmaceutical applications
Fähnemann, S.;
kein Abstract verfügbar
  • Lecture (others)
    Seminarvortrag School of Chemistry, Monash University, 07.10.2010, Melbourne, Australia

Publ.-Id: 14856 - Permalink

Correlation between the microstructure and the degradation of rare earth implanted Si-based light emitters
Rebohle, L.; Nazarov, A.; Tyagulskii, S.; Tyagulskii, I.; Lehmann, J.; Skorupa, W.;
The degradation of rare earth (RE)-implanted light emitters based on a Si-SiO2-SiON-ITO structure was investigated using the example of Tb and Eu as a function of their microstructural, electrical and electroluminescence (EL) properties. As shown by transmission electron microscopy and Rutherford backscattering spectroscopy the different implantation and annealing conditions lead to two different types of microstructures: devices with small RE oxide clusters and devices with large RE oxide clusters and strong RE agglomerations at the SiO2 interfaces. The electrical and EL properties of the devices were characterized by constant current injection measurements, in which the EL and the applied voltage is monitored with time, and IV, CV and EL spectrum measurements. As a result of these investigations it is shown that devices with small RE oxide clusters normally exhibit a high EL intensity and degrade in a two-step process characterized by a negative and a positive net charge trapping. In contrast to this, devices with large RE oxide clusters have a lower EL intensity, but the first step of degradation is suppressed resulting in lower quenching cross sections and thus a longer operation life time. The degradation is explained by a defect shell model in which the RE oxide clusters are surrounded by defect regions of different extensions leading to the different behavior of devices with small and large RE oxide clusters.
Keywords: Electroluminescence, rare earth, MOS capacity, charge trapping, ion implantation
  • Lecture (Conference)
    3rd Int. Meeting on Recent Developments in the study of Radiation Effects in Matter, 24.-28.10.2010, Gramado, Brazil

Publ.-Id: 14855 - Permalink

Comparison of the stability of Y-90-, Lu-177- and Ga-68- labeled human serum albumin microspheres (DOTA-HSAM)
Wunderlich, G.; Schiller, E.; Bergmann, R.; Pietzsch, H.-J.;
Microparticles derived from denatured human serum albumin (DOTA-derivatized human serum albumin microspheres, or DOTA-HSAM) are attractive carriers of radionuclides for both therapeutic and diagnostic purposes. In this article, we describe a labeling procedure for diagnostic (Ga-68) and therapeutic (Y-90, Lu-177) radionuclides and report on the results of stability studies of these products.

DOTA-HSAM was labeled in 0.5 M ammonium acetate buffer, pH 5.0, containing 0.02 mg/ml detergent. After adding the radionuclide, the mixture was shaken for 15 min at 90°C. Labeling yields and in vitro stability were determined by thin-layer
chromatography. For determination of the in vivo stability of Ga-68 and Y-90 DOTA-HSAM, the particles were injected intravenously in Wistar rats.

Labeling yields up to 95% in the case of Ga-68 and Lu-177 were achieved. Ga-68-labeled DOTA-HSAM showed high in vitro and in vivo stability. The amount of particle-bound radioactivity of Lu-177 DOTA-HSAM declines slowly in a linear manner to approximately 72% after 13 days. For Y-90, the labeling yield decreased with increasing radioactivity level. We presume radiolysis as the reason for these findings.

The labeling of DOTA-HSAM with different radionuclides is easy to perform. The radiation-induced cleavage of the labeled chelator together with the rather short half-life of radioactivity fixation in vivo (3.7 days) is, in our opinion, opposed to therapeutic applications of DOTA-HSAM. On the other hand, the high stability of Ga-68 DOTA-HSAM makes them an attractive candidate for the measurement of regional perfusion by PET.
Keywords: Human serum albumin microspheres; Stability; Radiolabeled particles; Radiolysis; Thiourea bond

Publ.-Id: 14854 - Permalink

Production of Lambda and Sigma(0) hyperons in proton-proton collisions
Abdel-Bary, M.; Abdel-Samad, S.; Brinkmann, K.-T.; Clement, H.; Dietrich, J.; Doroshkevich, E.; Dshemuchadse, S.; Ehrhardt, K.; Erhardt, A.; Eyrich, W.; Filges, D.; Filippi, A.; Freiesleben, H.; Fritsch, M.; Gast, W.; Georgi, J.; Gillitzer, A.; Gottwald, J.; Hesselbarth, D.; Jaeger, H.; Jakob, B.; Jaekel, R.; Karsch, L.; Kilian, K.; Koch, H.; Krapp, M.; Kress, J.; Kuhlmann, E.; Lehmann, A.; Marcello, S.; Marwinski, S.; Mauro, S.; Meyer, W.; Michel, P.; Moeller, K.; Morsch, H. P.; Moertel, H.; Naumann, L.; Paul, N.; Pinna, L.; Pizzolotto, C.; Plettner, C.; Reimann, S.; Richter, M.; Ritman, J.; Roderburg, E.; Schamlott, A.; Schoenmeier, P.; Schroeder, W.; Schulte-Wissermann, M.; Sefzick, T.; Stinzig, F.; Steinke, M.; Sun, G. Y.; Teufel, A.; Ullrich, W.; Wagner, G. J.; Wagner, M.; Wenzel, R.; Wilms, A.; Wintz, P.; Wirth, S.; Wuestner, P.; Zupranski, P.;
This paper reports results on simultaneous measurements of the reaction channels pp → pK+Λ and pp → pK+Σ0 at excess energies of 204, 239, and 284MeV (Λ) and 127, 162, and 207MeV (Σ0). Total and differential cross-sections are given for both reactions. It is concluded from the measured total cross-sections that the high-energy limit of the cross-section ratio is almost reached at an excess energy of only about 200MeV. From the differential distributions observed in the overall CMS as well as in the Jackson and helicity frames, a significant contribution of interfering nucleon resonances to the Λ production mechanism is concluded while resonant Σ0 production seems to be of lesser importance and takes place only through specific partial waves of the entrance channel. The data also indicate that kaon exchange plays a minor role in the case of Λ but an important role for Σ0 production. Thus the peculiar energy dependence of the Λ/Σ0 cross-section ratio appears in a new light as its explanation requires more than mere differences between the pΛ and the pΣ0 final-state interaction. The data provide a benchmark for theoretical models already available or yet to come.

Publ.-Id: 14853 - Permalink

Characterization of microstructural defects in melt grown ZnO single crystals
Anwand, W.; Brauer, G.; Grynszpan, R. I.; Cowan, T. E.; Schulz, D.; Klimm, D.; Čížek, J.; Kuriplach, J.; Procházka, I.; Ling, C. C.; Djurišić, A. B.; Klemm, V.; Schreiber, G.; Rafaja, D.;
Various nominally undoped, hydrothermally or melt grown (MG) ZnO single crystals have been investigated by standard positron lifetime measurements. Furthermore, optical transmission measurements and structural characterizations have been performed; the content of hydrogen in the bound state was determined by nuclear reaction analysis.
A positron lifetime of 165-167 ps, measured for a brownish MG ZnO sample containing (0.30 +/- 0.03) at.-% of bound hydrogen, matches perfectly the value found for colorless MG ZnO crystals. The edge shift, observed in the "blue light domain" of the optical absorption for the former sample with respect to the latter samples, is estimated to be 0.70 eV, and found equal to a value reported previously. The possible role of zinc interstitials as well as nitrogen-related defects is considered and discussed. Microstructure analysis by X-ray diffraction and transmission electron microscopy revealed the presence of stacking faults in MG crystals in a high concentration, which suggests these defects to be responsible for the observed positron lifetime.
Keywords: zinc oxide, microstructure defects, positron annihilation, optical transmission, X-ray diffraction, transmission electron microscopy

Publ.-Id: 14852 - Permalink

Bakterielle Wechselwirkungen ausgewählter Actinide vor dem Hintergrund der Endlagerung von radioaktivem Abfall
Moll, H.;
Bakterien, ubiquitär vorkommende Mikroorganismen, können signifikant die Speziation und damit das Verhalten von Schwermetallen in der Umwelt beeinflussen. Detaillierte Kenntnisse der Wechselwirkungsprozesse von Bakterien mit Actiniden sind z.B. für Langzeitsicherheitsanalysen für zukünftige Endlager hochradioaktiver Abfälle sowie zur Sanierung kontaminierter Flächen und Einrichtungen erforderlich. Das Interesse an mikrobiellen Prozessen der Actinide ist in den letzten Jahren stetig gestiegen. Dennoch sind die Kenntnisse zur mikrobiellen Diversität an möglichen Endlagerstandorten von nuklearem Abfall relativ begrenzt.
Im Vortrag werden am Beispiel ausgewählter Actinide detaillierte Untersuchungen zur Aufklärung von deren Speziation mit speziellen Bakterien vorgestellt. Ein kurzer Überblick zur Bestimmung der mikrobiellen Diversität in Umweltproben wird gegeben. Der Hauptschwerpunkt liegt auf direkten und indirekten Wechselwirkungsprozessen der Actinide mit Bakterien.
Keywords: bacteria, actinides, nuclear waste disposal
  • Invited lecture (Conferences)
    Seminar für Kern- und Radiochemie am Institut für Kernchemie der Johannes Gutenberg-Universität Mainz, 29.11.2010, Mainz, Deutschland

Publ.-Id: 14851 - Permalink

Surface Modification on KBr (001) with Slow Highly Charged Ions
Wilhelm, R. A.; Heller, R.; El-Said, A. S.; Facsko, S.;
Highly Charged Ions (HCI) carry an enormous amount of potential energy (up to 100 keV for Xe50+) which is defined as the sum of the binding energies of all missing electrons. This unique parameter offers new ways of surface modifications without a significant bulk damage.
During neutralization and de-excitation processes of the HCI the potential energy is released into electronic excitations within the solid (creation of electron hole pairs). These electron hole pairs get rapidly self-trapped due to strong electron-phonon coupling in the ionic lattice and decay into color centers (mainly H, F and F*-centers).
Finally these color centers lead to a desorption of K and Br neutralized atoms at the surface site, which after a agglomeration of many of these color centers forms a pit-like nanostructure on atomically flat KBr(001) surfaces.
The influence of kinetic and potential energy effects will be discussed.
Keywords: HCI, DIET, KBr, electron-hole pair, pit, nanostructures, color center
  • Lecture (Conference)
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige
  • Poster
    International Symposium on Electron Beam Ion Sources and Traps, EBIST2010, 07.-10.04.2010, Stockholm, Sverige

Publ.-Id: 14850 - Permalink

The traceless Staudinger ligation with fluorine-18: a novel and versatile labeling technique for the synthesis of PET-radiotracers
Pretze, M.; Wuest, F.; Peppel, T.; Köckerling, M.; Mamat, C.;
The development of rapid radiolabeling techniques under mild reaction conditions involving the short-lived positron emitter fluorine-18 remains a special challenge in organic PET chemistry. This work describes a novel and facile application of the traceless Staudinger ligation as a mild and versatile labeling method for preparation of various radiotracers labeled with fluorine-18.
Keywords: Radiolabeling; Traceless Staudinger ligation; Bioorthogonal; Fluorine-18

Publ.-Id: 14849 - Permalink

The speciation of U(VI) in aqueous solution and sorbed onto TiO2 studied by in situ vibrational spectroscopy
Müller, K.; Meusel, T.; Brendler, V.; Foerstendorf, H.; Bernhard, G.;
The migration behavior of uranium in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) at the TiO2-water interface has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy. Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
  • Lecture (others)
    Seminar at the Department of Nuclear Engineering, Kyoto University, 29.06.2010, Kyoto, Japan

Publ.-Id: 14848 - Permalink

Speciation of actinyl ions in aqueous solution and at water-mineral interfaces. A vibrational spectroscopic approach
Müller, K.;
The migration behavior of actinides in the environment is controlled by prominent molecular phenomena such as hydrolysis and complexation reactions in aqueous solutions as well as the diffusion and sorption onto minerals present along groundwater flow paths. These reactions significantly influence the mobility and bioavailability of the metal ions in the environment, in particular at water-mineral interfaces. Hence, for the assessment of migration processes the knowledge of the mechanisms occurring at interfaces is crucial. The required structural information can be obtained using various spectroscopic techniques.
In the present study, the speciation of uranium(VI) and neptunium(V) at environmentally relevant mineral-water interfaces of oxides of titania, alumina, silica, iron, zinc, and alumosilicates has been investigated by the application of attenuated total reflection Fouriertransform infrared (ATR FT-IR) spectroscopy.
Moreover, the distribution of the hydrolysis products in micromolar aqueous solutions of U(VI) and Np(V/VI) at ambient atmosphere has been characterized for the first time, by a combination of ATR FT-IR spectroscopy, near infrared (NIR) absorption spectroscopy, and speciation modeling applying updated thermodynamic databases.
  • Lecture (others)
    Jahresseminar des Graduiertenkollegs 826/3, 08.11.2010, Burg Schönburg in Oberwesel, Deutschland

Publ.-Id: 14847 - Permalink

Uranium sorption on various forms of titanium dioxide – influence of surface area, surface charge and impurities
Comarmond, M. J.; Payne, T. E.; Harrison, J. J.; Thiruvoth, S.; Wong, H. K.; Aughterson, R. D.; Lumpkin, G. R.; Müller, K.; Foerstendorf, H.;
Titanium dioxide (TiO(2)) has often served as a model substrate for experimental sorption studies of environmental contaminants. However, various forms of Ti-oxide have been used, and the different sorption properties of these materials have not been thoroughly studied. We investigated uranium sorption on some thoroughly characterized TiO(2) surfaces with particular attention to the influence of surface area, surface charge, and impurities. The sorption of U(VI) differed significantly between samples. Aggressive pretreatment of one material to remove impurities significantly altered the isoelectric point, determined by an electroacoustic method, but did not significantly impact U sorption. Differences in sorption properties between the various TiO(2) materials were related to the crystallographic form, morphology, surface area, and grain size, rather than to surface impurities or surface charge. In-situ attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopic studies showed that the spectra of the surface species of the TiO(2) samples are not significantly different, suggesting the formation of similar surface complexes. The data provide insights into the effect of different source materials and surface properties on radionuclide sorption.

Publ.-Id: 14846 - Permalink

Preparation, 99mTc-labeling and biodistribution studies of a PNA oligomer containing a new ligand derivative of 2,2′-dipicolylamine
Gasser, G.; Jäger, K.; Zenker, M.; Bergmann, R.; Steinbach, J.; Stephan, H.; Metzler-Nolte, N.;
A new azido derivative of 2,2′-dipicolylamine (Dpa), 2-azido-N,N-bis((pyridin-2-yl)methyl)ethanamine, (Dpa-N3) was readily prepared from the known 2-(bis(pyridin-2-ylmethyl)amino)ethanol (Dpa-OH). It was demonstrated that Dpa-N3 could be efficiently labeled with both [Re(CO)3(H2O)3]Br and [99mTc(H2O)3(CO)3]+ to give [Re(CO)3(Dpa-N3)]Br and [99mTc(CO)3(Dpa-N3)]+, respectively. Furthermore, Dpa-N3 was successfully coupled, on the solid phase, to a Peptide Nucleic Acid (PNA) oligomer (H-4-pentynoic acid-spacer-spacer-tgca-tgca-tgca-Lys-NH2; spacer = –NH–(CH2)2–O–(CH2)2–O–CH2–CO–) using the Cu(I)-catalyzed [2 + 3] azide/alkyne cycloaddition (Cu-AAC, often referred to as the prototypical “click” reaction) to give the Dpa-PNA oligomer. Subsequent labeling of Dpa-PNA with [99mTc(H2O)3(CO)3]+ afforded [99mTc(CO)3(Dpa-PNA)] in radiochemical yields > 90%. Partitioning experiments in a 1-octanol/water system were carried out to get more insight on the lipophilicity of [99mTc(CO)3(Dpa-N3)]+ and [99mTc(CO)3(Dpa-PNA)]. Both compounds were found rather hydrophilic (log Do/w values at pH = 7.4 are −0.50: [99mTc(CO)3(Dpa-N3)]+ and −0.85: [99mTc(CO)3(Dpa-PNA)]. Biodistribution studies of [99mTc(CO)3(Dpa-PNA)] in Wistar rats showed a very fast blood clearance (0.26 ± 0.1 SUV, 1 h p.i.) and modest accumulation in the kidneys (5.45 ± 0.45 SUV, 1 h p.i.). There was no significant activity in the thyroid and the stomach, demonstrating a high in vivo stability of the 99mTc-labeled Dpa-PNA conjugate.
Keywords: Bio-organometallic chemistry; Click chemistry; Nuclear medicine; Peptide nucleic acid (PNA); Rhenium compounds; Technetium compounds

Publ.-Id: 14845 - Permalink

Characterization of Si nanowires fabricated by Ga+ FIB implantation and subsequent selective wet etching
Böttger, R.; Bischoff, L.; Schmidt, B.; Krause, M.;
Local gallium (Ga) ion implantation in silicon (Si) by focused ion beam (FIB) and subsequent anisotropic and selective wet etching has been used to fabricate freely suspended nanowires (NWs) with reproducible widths between 20 and 200 nm. The dependence of the resulting NW width on the implanted fluence has been investigated and is supported by a numerical model reproducing the experimental data and enabling an a priori estimation of the NW width as a function of the implanted fluence. Furthermore, the resistance of the NWs, its temperature response and the activation energy for electrical current flow were investigated before and after direct current (DC) annealing in air and in vacuum. Annealed NWs showed a decrease of their resistivity up to two orders of magnitude, indicating a partial re-crystallization of the NWs through self-heating and a change in the conduction. The assumption of recrystallization is supported by scanning electron microscopy (SEM) and Raman spectroscopy.
Keywords: silicon-on-insulator, Ga focused ion beam implantation, nanowire, anisotropic etching, width, resistivity, phase change, annealing, Raman spectroscopy

Publ.-Id: 14844 - Permalink

A method to estimate the planar, instantaneous body force distribution from velocity field measurements
Albrecht, T.; Weier, T.; Gerbeth, G.; Metzkes, H.; Stiller, J.;
We present a simple method to derive a planar, instantaneous body force distribution from a given 2-D velocity field without knowledge of the pressure field. If the body force consists of one component only, spatial integration completely recovers this component.
Particle Image Velocimetry and Direct Numerical Simulations of a wall jet induced by a known body force were conducted to validate the method, demonstrating a good agreement of the original and reconstructed force fields.

Publ.-Id: 14843 - Permalink

Präzisionsmessung der Photodissoziation des Deuterons bei Energien im Bereich der Big-Bang-Nukleosynthese
Hannaske, R.; Bemmerer, D.; Beyer, R.; Birgersson, E.; Grosse, E.; Hartmann, A.; Junghans, A. R.; Kempe, M.; Kosev, K.; Marta, M.; Massarczyk, R.; Matic, A.; Schilling, K.-D.; Schwengner, R.; Sobiella, M.; Wagner, A.;
Die für die primordiale Nukleosynthese wichtige Reaktion d(γ,n)p wurde am supraleitenden Elektronen-Linearbeschleuniger ELBE mit Bremsstrahlung bei einer Endpunktenergie von 5,0 MeV untersucht.
Der Photonenfluss wurde mit Hilfe der resonanten Streuung an Aluminiumkernen bei Energien von 2,2 und 3,0 MeV bestimmt. Die Effektivität der verwendeten Germanium-Detektoren wurde mit Hilfe von Referenzstrahlern und Simulationsrechnungen ermittelt. Mit beidseitig ausgelesenen Szintillationsdetektoren wurden Flugzeit und -strecke der Neutronen bestimmt. Wegen der niedrigen Nachweisschwelle der Detektoren kann der Wirkungsquerschnitt für Neutronenenergien von 50 keV bis 1,4 MeV bestimmt werden. Die erreichte statistische Unsicherheit beträgt 5 %, die Energieauflösung 4 %. Bisher untersuchte systematische Unsicherheiten werden diskutiert.
Keywords: Big Bang nucleosynthesis, bremsstrahlung, gamma-ray spectroscopy, neutron time-of-flight, nuclear astrophysics, photon scattering
  • Lecture (Conference)
    74. Jahrestagung der DPG und DPG Frühjahrstagung, 15.-19.03.2010, Bonn, Deutschland

Publ.-Id: 14842 - Permalink

Investigation of the beltline welding seam and base metal of the Greifswald WWER-440 Unit 1 reactor pressure vessel
Schuhknecht, J.; Viehrig, H.-W.; Rindelhardt, U.;
The investigation of reactor pressure vessel (RPV) materials from decommissioned nuclear power plants (NPPs) offers the unique opportunity to scrutinize the irradiation behavior under real conditions. Material samples taken from the RPV wall enable a comprehensive material characterization. The paper describes the investigation of trepans taken from the decommissioned WWER-440 first generation RPVs of the Greifswald NPP. Those RPVs represent different material conditions such as irradiated (I); irradiated and recovery annealed (IA); and irradiated, recovery annealed, and reirradiated (IAI). The working program is focused on the characterization of the RPV steels (base and weld metal) through the RPV wall. The key part of the testing is aimed at the determination of the reference temperature T0 following the American Society for Testing of Materials (ASTM) Test Standard E1921–08 to determine the fracture toughness of the RPV steel in different thickness locations. In a first step, the trepans taken from the RPV Greifswald unit 1 containing the X-butt multilayer submerged welding seam and from base metal ring 0.3.1 both located in the beltline region were investigated. Unit 1 represents the IAI condition. It is shown that the master curve (MC) approach as adopted in ASTM E1921 is applicable to the investigated original WWER-440 weld metal. The evaluated T0 varies through the thickness of the welding seam. The lowest T0 value was measured in the root region of the welding seam representing a uniform fine grain ferritic structure. Beyond the welding root T0 shows a wavelike behavior. The highest T0 of the weld seam was not measured at the inner wall surface. This is important for the assessment of ductile-to-brittle temperatures measured on subsize Charpy specimens made of weld metal compact samples removed from the inner RPV wall. Our findings imply that these samples do not represent the most conservative condition. Nevertheless, the Charpy-V transition temperature TT41J estimated with results of subsize specimens after the recovery annealing was confirmed by the testing of standard Charpy-V-notch specimens. The evaluated TT41J shows a better accordance with the irradiation fluence along the wall thickness than the master curve reference temperature T0. The evaluated T0 from the trepan of base metal ring 0.3.1 varies through the thickness of the RPV wall. The KJc values generally follow the course of the MC, although the scatter is large. The reembrittlement during two campaign operations can be assumed to be low for the weld and base metal.
Keywords: nuclear power plant, decommisioning, reactor pressure vessel, testing, fracture toughness, Master Curve, integrity assessment
  • Journal of Engineering for Gas Turbines and Power - Transactions of the ASME 133(2011)5, 052904
    DOI: 10.1115/1.4000891

Publ.-Id: 14841 - Permalink

Experimental and numerical modeling of the steel flow in a continuous casting mould under the influence of a transverse DC magnetic field
Timmel, K.; Miao, X.; Eckert, S.; Lucas, D.; Gerbeth, G.;
This paper is concerned with numerical and experimental investigations focusing on the fluid flow in the continuous casting process under the influence of an external DC magnetic field. Systematic measurements of the mould flow were carried out using the eutectic alloy GaInSn inside a plexiglass model at room temperature. The jet flow discharging from the submerged entry nozzle was exposed to a level magnetic field spanning across the entire wide side of the mould. The ultrasound Doppler velocimetry (UDV) was applied to obtain a detailed experimental data base with respect to the mean values and transient properties of the velocity fields occurring in the mould. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model. The comparison between our numerical calculations and the experimental results displays a very well agreement. An important outcome of this study is the feature that the magnetic field does not provide a smooth reduction of the velocity fluctuations at the nozzle outlet.
Keywords: continuous casting, electromagnetic brake, experimental modeling, numerical simulation
  • Magnetohydrodynamics 46(2010), 437-448

Publ.-Id: 14840 - Permalink

Experimental facility for two- and three-dimensional ultrafast electron beam X-ray computed tomography
Stürzel, T.; Bieberle, M.; Laurien, E.; Hampel, U.; Barthel, F.; Menz, H.-J.; Mayer, H.-G.;
An experimental facility is described which has been designed to perform ultrafast two- and three-dimensional electron beam computed tomography. As a novelty a specially designed transparent target enables tomography with no axial offset for 2D imaging and high axial resolution three-dimensional im-aging employing the cone-beam tomography principles. The imaging speed is 10,000 frames per second for planar scanning and more than 1000 frames per second for 3D imaging. The facility serves a broad spectrum of potential applications primarily the study of multiphase flows, but also in principle non-destructive testing or small animal imaging. In order to demonstrate the aptitude for these applications static phantom experiments at a frame rate of 2000 fps were performed. Resulting spatial resolution was found to be 1.2 mm and better for a reduced temporal resolution.
Keywords: three-dimensional tomography, electron beam tomography, X-ray tomography, multiphase flow measurement

Publ.-Id: 14839 - Permalink

Editorial on the special issue on imaging systems and techniques
Karras, D. A.; Giakos, G. C.; Hampel, U.;
Imaging systems and techniques have found widespread application in medical and biological imaging, security and surveillance systems, remote sensing, biometrics, non-destructive testing, computer sciences, materials research, and most recently also in various types of customer products. Imaging systems may be based on different physical measuring principles, such as optical, infrared, acoustic, microwave, terahertz, electrical, X-ray and gamma ray sensing techniques, for example. But behind the imaging sensor there is strong common ground in electronics concepts and circuits for signal conversion, processing, acquisition, and storage as well as algorithms for image enhancement, image reconstruction and image analysis. Imaging systems are increasingly complex and therefore challenge electronic engineers and computer scientists. Concurrently to an ongoing trend of increasing the spatial and temporal resolution of such systems, there is a growing demand for hardware-supported image processing, multi-modality imaging, data reduction as well as improved sensitivity, specificity and robustness.
Keywords: imaging systems and techniques
  • International Journal of Signal and Imaging Systems Engineering 3(2011)3, 145-147

Publ.-Id: 14837 - Permalink

Stand und Perspektiven der Kernenergie in Deutschland und „Umgebung“
Lucas, D.; Weiß, F.-P.;
In einem Überblicksvortrag werden aktuelle Fakten und Entwicklungen zur Kernenergienutzung in Deutschland und der Welt vorgestellt und diskutiert. Das schließt auch die Darstellung aktueller Forschungsschwerpunkte für gegenwärtige und zukünftige Reaktoren ein.
Keywords: Nuclear energy
  • Invited lecture (Conferences)
    3. VDI-KTG-Kolloquium "Perspektiven der Kernenergie", 26.10.2010, Dresden, Deutschland

Publ.-Id: 14836 - Permalink

A moderation layer to improve the safety behavior of sodium cooled fast reactors
Merk, B.; Weiß, F.-P.;
The nature of the sodium void effect in an infinite lattice is discussed with all different contributions. In a next step, the insertion of a layer consisting of moderating material for a reduction of the effect is proposed. The effect of three different moderating layers on the sodium void defect, the neutron spectrum, and the kinf over burnup is investigated. Special emphasis is given to the influence of the moderation layer on the feedback effects. Especially the uranium-zirconium hydride UzrH layer causes a strong reduction of the sodium void effect. Additionally this layer improves the fuel temperature effect and the coolant effect of the system significantly. All changes cause by the insertion of the UZrH layer lead to a significant increase in stability of the fast reactor system against transients. The moderating layers have only a small influence on the breeding effect and on the production of minor actinides. The insertion of the moderating layer does not imply any constraints on the core design and the power distribution in the fuel element an. Thus the use of a moderation layer gives the opportunity of designable feedback effects in a fast reactor core.
Keywords: Sodium Void Effect, SFR, Fast Reactor, Uranium-Zirconium Hydride, Boron Carbide
  • Contribution to proceedings
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14835 - Permalink

Application of a two energy group analytical solutions to the YALINA experiment SC3A
Merk, B.; Glivici-Cotruţă, V.; Weiß, F.-P.;
The SC3A experiment in the YALINA-Booster facility in Belarus is described and investigated. For this investigation the very special configuration of YALINA-Booster core, consisting of a fast and a thermal zone, decoupled with a neutron ‘valve’is analyzed based on a full HELIOS model for the calculations. The effect of the two region design on the experimental results at different detector positions is leading to unexpected results and the special problems for the analysis of the experiments have been shown. For a more detailed representation, a recently developed two group analytical solution for the time dependent diffusion equation obtained by Green’s function method without separation of space and time was used. To model the above mentioned streaming of neutrons from the thermal area into the fast area an analytical solution for the time dependent neutron flux with two sources has been developed from the available Green’s functions for two groups. In addition to the central source pulse of the external source a source at the boundary of the system has been introduced. The new analytical solution shows very good agreement with the experimental results, even for the unexpected behavior of the outermost deterctor. Thus analytical solution without separation of space and time are a very promising tool to develop a new method for the analysis of ADS experiments.
Keywords: Yalina, experimental analysis, Green’s function, Two group diffusion equation
  • Contribution to proceedings
    The International Conference on Mathematics and Computational Methods applied to Nuclear Science and Engineering (MC 2011), 08.-12.05.2011, Rio de Janeiro, Brazil, ISBN 978-85-63688-00-2
  • Lecture (Conference)
    International Conference on Mathematics and Computational Methods Applied to Nuclear Science and Engineering (M&C 2011), 08.-12.05.2011, Rio de Janeiro, Brazil

Publ.-Id: 14834 - Permalink

Investigation of coolant mixing in reactor VVER-1000
Lisenkov, A.; Bezrukov, Y. A.; Ulianovskiy, D. V.; Zaytsev, D. V.; Bykov, M. A.; Shishov, A. V.; Höhne, T.; Rohde, U.; Gallori, D.;
This paper presents arrangement of the problem, methodology of experiment performance and results of experimental investigation of coolant mixing in downcomer and lower plenum of VVER-1000. Three groups of experiments simulating coolant mixing were executed: in conditions of RCP start-up, during natural circulation recovery in the course of SB LOCA and in conditions of stable operation of different amount of RCPs. Results of experiments are used for validation of codes.
Keywords: CFD, VVER-1000
  • Contribution to proceedings
    ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France
  • Lecture (Conference)
    ICAPP11 (2011 International Congress on Advances in Nuclear Power Plants "Performance & Flexibility: The Power of Innovation"), 02.-05.05.2011, Nice, France

Publ.-Id: 14833 - Permalink

Experimental investigation of in-vessel mixing phenomena in a VVER-1000 scaled test facility during unsteady asymmetric transients
Moretti, F.; Melideo, D.; Del Nevo, A.; D’Auria, F.; Höhne, T.; Lisenkov, E.; Bucalossi, A.; Gallori, D.;
In-vessel turbulent mixing phenomena affect the time and space distribution of coolant properties (e.g. boron concentration and temperature) at the core inlet which impacts consequently the neutron kinetics response. For reactor safety evaluation purposes and to characterize these phenomena it is necessary to set and validate appropriate numerical modelling tools to improve the current conservative predictions. With such purpose, an experimental campaign was carried out by OKB Gidropress, in the framework of the European Commission Project “TACIS R2.02/02 - Development of safety analysis capabilities for VVER-1000 transients involving spatial variations of coolant properties (temperature or boron concentration) at core inlet”. The experiments were conducted on a scaled facility representing the primary system of a VVER-1000 including a detailed model of the Reactor Pressure Vessel with its internals. The simulated transients involved perturbations of coolant properties distribution providing a wide validation matrix. The main achievements of the set of experiments featuring transient asymmetric pump behaviour are presented in this paper. The potential of the obtained experimental database for the validation of thermal fluid dynamics numerical simulation tools is also discussed and the role of computational fluid dynamics in supporting the experimental data analysis is highlighted.
Keywords: CFD, turbulent mixing

Publ.-Id: 14832 - Permalink

Highly anisotropic effective dielectric functions of silver nanoparticle arrays
Oates, T. W. H.; Ranjan, M.; Facsko, S.; Arwin, H.;
Variable-angle and Mueller matrix spectroscopic ellipsometry measurements of highly anisotropic plasmonic materials composed of random and aligned silver nanoparticles and nanorods are presented. We show that the effective dielectric tensors of randomly dispersed particles are uniaxially anisotropic and those of aligned particles are biaxially anisotropic, with the anisotropy predominantly at the plasmonic resonances. The strong resonances in nanorod arrays result in the real part of the effective in-plane permittivities being opposite in sign over a significant range in the visible, suggesting the potential to design materials that display tunable negative-refraction.
Keywords: metamaterial, left-handed medium, extreme anisotropy, photonic crystals, indefinite materials
  • Open Access LogoOptics Express 19(2011)3, 2014-2028

Publ.-Id: 14831 - Permalink

Pygmy Dipole Strength in Exotic Nuclei and the Equation of State
Klimkiewicz, A.; Paar, N.; Adrich, P.; Fallot, M.; Le Bleis, T.; Rossi, D.; Boretzky, K.; Aumann, T.; Alvarez-Pol, H.; Aksouh, F.; Benlliure, J.; Berg, T.; Boehmer, M.; Casarejos, E.; Chartier, M.; Chatillon, A.; Cortina-Gil, D.; Datta Pramanik, U.; Elze, T. W.; Emling, H.; Ershova, O.; Fernando-Dominguez, B.; Geissel, H.; Gorska, M.; Heil, M.; Hellstrom, M.; Johansson, H.; Jones, K. L.; Junghans, A.; Kiselev, O.; Kratz, J. V.; Kulessa, R.; Kurz, N.; Labiche, M.; Lemmon, R.; Litvinov, Y.; Mahata, K.; Maierbeck, P.; Nilsson, T.; Nociforo, C.; Palit, R.; Paschalis, S.; Plag, R.; Reifarth, R.; Simon, H.; Summerer, K.; Surowka, G.; Vretenar, D.; Wagner, A.; Walus, W.; Weick, H.; Winkler, M.;
A concentration of dipole strength at energies below the giant dipole resonance was observed in neutron-rich nuclei around 132Sn in an experiment using the FRS-LAND setup. This so-called “pygmy” dipole strength can be related to the parameters of the symmetry energy and to the neutron skin thickness on the grounds of a relativistic quasiparticle random-phase approximation. Using this ansatz and the experimental findings for 130Sn and 132Sn, we derive a value of the symmetry energy pressure of p-bar0 = 2.2±0.5 MeV/fm3. Neutron skin thicknesses of Rn−Rp = 0.23±0.03 fm and 0.24±0.03 fm for 130Sn and 132Sn, respectively, have been determined. Preliminary results on 68Ni from a similar experiment using an improved setup indicate an enhanced cross section at low energies, while the results for 58Ni are in accordance with results from photoabsorption measurements.
Keywords: dipole strength giant dipole resonance neutron-rich nuclei 132Sn FRS-LAND pygmy dipole strength symmetry energy skin thickness quasiparticle random-phase approximation photoabsorption
  • Contribution to proceedings
    NUCLEAR STRUCTURE AND DYNAMICS '09: Proceedings of the International Conference, 04.-08.05.2009, Dubrovnik, Croatia
    Pygmy Dipole Strength in Exotic Nuclei and the Equation of State: AIP Conference Proceedings, 978-0-7354-0702-2, 181-184

Publ.-Id: 14830 - Permalink

Influence of hydrogen on the thermally induced phase separation in GeO/SiO2 multilayers
Sahle, C. J.; Zschintzsch, M.; Sternemann, C.; von Borany, J.; Nyrow, A.; Jeutter, N. M.; Wagner, R.; Frahm, R.; Tolan, M.;
The influence of the annealing atmosphere on the temperature induced phase separation of Ge oxide in GeOx/SiO2 multilayers (x ~ 1) leading to size controlled growth of Ge nanocrystals is explored by means of x-ray absorption spectroscopy at the Ge K-edge. Ge sub-oxides contained in the as-deposited multilayers diminish with increasing annealing temperature, showing a complete phase separation at approximately 450 °C using inert N2 ambient. The use of reducing H2 in the annealing atmosphere influences the phase separation even in an early stage of the disproportionation. In particular, the temperature regime where the phase separation occurs is lowered by at least 50 °C. At temperatures above 400 °C the sublayer composition and thus the density of the Ge nanocrystals can be altered by making use of the reduction of GeO2 by H2.
  • Nanotechnology 22(2011)12, 125709

Publ.-Id: 14829 - Permalink

Simulation der Teilchenbeschleunigung auf mehreren GPUs mittels CUDA
Knüpfer, A.; Bussmann, M.;
Präsentation von PIConGPU
Keywords: particle in cell, pic, gpu
  • Invited lecture (Conferences)
    Herbsttreffen des ZKI-Arbeitskreises "Supercomputing", 27.-28.10.2010, Göttingen, Deutschland

Publ.-Id: 14828 - Permalink

pp and ππ intensity interferometry in collisions of Ar+KCl at 1.76A GeV
Agakishiev, G.; Balanda, A.; Bannier, B.; Bassini, R.; Belver, D.; Belyaev, A.; Blanco, A.; Böhmer, M.; Boyard, J. L.; Cabanelas, P.; Castro, E.; Chernenko, S.; Christ, T.; Destefanis, M.; Diaz, J.; Dohrmann, F.; Dybczak, A.; Eberl, T.; Epple, E.; Fabbietti, L.; Fateev, O.; Finocchiaro, P.; Fonte, P.; Friese, J.; Froehlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhaeuser, R.; Gil, A.; Gilardi, C.; Golubeva, M.; Gonzalez-Diaz, D.; Guber, F.; Gumberidze, M.; Heilmann, M.; Heinz, T.; Hennino, T.; Holzmann, R.; Huck, P.; Iori, I.; Ivashkin, A.; Jurkovic, M.; Kaempfer, B.; Kanaki, K.; Karavicheva, T.; Kirschner, D.; Koenig, I.; Koenig, W.; Kolb, B. W.; Kotte, R.; Krizek, F.; Kruecken, R.; Kuehn, W.; Kugler, A.; Kurepin, A.; Lang, S.; Lange, J. S.; Lapidus, K.; Liu, T.; Lopes, L.; Lorenz, M.; Maier, L.; Mangiarotti, A.; Markert, J.; Metag, V.; Michalska, B.; Michel, J.; Mishra, D.; Moriniere, E.; Mousa, J.; Muentz, C.; Naumann, L.; Otwinowski, J.; Pachmayer, Y. C.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Perez-Cavalcanti, T.; Pietraszko, J.; Przygoda, W.; Ramstein, B.; Reshetin, A.; Roy-Stephan, M.; Rustamov, A.; Sadovsky, A.; Sailer, B.; Salabura, P.; Schmah, A.; Schwab, E.; Siebenson, J.; Sobolev, Y. G.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroth, J.; Sturm, C.; Tarantola, A.; Teilab, K.; Tlusty, P.; Traxler, M.; Trebacz, R.; Tsertos, H.; Wagner, V.; Weber, M.; Wendisch, C.; Wisniowski, M.; Wojcik, T.; Wuestenfeld, J.; Yurevich, S.; Zanevsky, Y.; Zhou, P.; Zumbruch, P.;
Results on pp, π+π+, and π-π- intensity interferometry are reported for collisions of Ar+KCl at 1.76$A$~GeV beam energy, studied with the High Acceptance Di-Electron Spectrometer (HADES) at SIS18/GSI. The experimental correlation functions as a function of the relative momentum are compared to model calculations allowing the determination of the space-time extent of the corresponding emission sources. The π π source radii are found significantly larger than the pp emission radius. The present radii do well complement the source-size excitation functions of the collision system of size $A+A \simeq 40+40$. The pp source radius at fixed beam energy is found to increase linearly with the cube root of the number of participants. From this trend, a lower limit of the pp correlation radius is deduced.

Publ.-Id: 14827 - Permalink

Irradiation Response of Greifswald Unit 8 RPV Steels
Viehrig, H.-W.; Gillemot, F.; Horvat, M.; Acosta, B.; Debarberis, L.;
Base and weld metal and cladding of the not commissioned SKODA reactor pressure vessel of Greifswald Unit 8 was investigated. Tensile, Charpy size SE(B) and 0.5T-C(T) specimens were irradiated at the LYRA and BAGIRA irradiation rigs with different neutron fluxes. The main focus was on fracture toughness testing according to the Mater Curve approach and crack extension curves. With these tests the reference temperature T0 and fracture toughness values for ductile tearing according to the ASTM test standards ASTM E1921 and ASTM E1820, respectively, were determined.
The irradiation in the LYRA rig with a neutron flux of about 1.57•1012 n/cm2 results in shifts of the reference temperature ΔT0 which correspond with the prediction according to the Russian WWER-440 code. In contrast the BAGIRA irradiation with a neutron flux of about 68.6•1012 n/cm2 results in remarkable higher ΔT0 values then predicted. For weld metal from multilayer welding seams the orientation of the specimens is crucial for the direct measurement of the fracture toughness by using the MC concept. The evaluation of J-R curves measured on Charpy size SE(B) specimens is demanding because of the unsteady developing through the different structures of the cladding.
Keywords: reactor pressure vessel steel,neutron, neutron irradiation, fracture toughness, Master Curve approach, crack extension curve, neutron embrittlement
  • Lecture (Conference)
    IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

Publ.-Id: 14826 - Permalink

Previous results of the investigation on the decommissioned reactor pressure vessels of the Greifswald NPP
Viehrig, H.-W.; Houska, M.;
The investigation of reactor pressure vessel (RPV) material from the decommissioned Greifswald NPP representing the first generation of Russian type WWER-440/V-230 reactors offers the opportunity to evaluate the real toughness response. The Greifswald RPVs represent different material conditions viz. irradiated, irradiated and annealed and irradiated, annealed and re-irradiated.
The paper presents test results measured on the trepan taken from the beltline welding seam located in the reactor core region of the Unit 4 RPV. This unit was shut down after 11 years of operation and represents the irradiated condition. The working program comprises chemical analysis, microstructure investigations (by means of metallography and SEM), mechanical testing (hardness and tensile), and fracture mechanics testing. The key part of the testing is focused on the determination of the reference temperature T0 following the ASTM test standard E1921-10. The KJc values measured on TS oriented pre-cracked and side-grooved Charpy size SE(B) specimens from defined thickness locations of the welding seam approximately follow the course of the Master Curve but with a large scatter. Reference temperatures T0 through the thickness of the RPV beltline welding seam runs almost opposite to the trend predicted by the Russian code for the decrease of the neutron fluence from 5.1•E19 n/cm2 to 1.1•E19 n/cm2 (E>0.5MeV). T0 varies between 6°C from near the welding root at ¼ wall thickness to 117°C at ¾ wall thickness. The scatter of T0 beyond the welding root is about 40 K and depends strongly on the structure at the crack tip. The results are also evaluated according to integrity assessment procedures based on the Master Curve concept.
Keywords: reactor pressure vessel, welding seam, specimen orientation, fracture toughness, Master Curve approach, integrity assessment
  • Lecture (Conference)
    IAEA Specialists’ Meeting on Irradiation Embrittlement and Life Management of Reactor Pressure Vessels, 18.-22.10.2010, Znojmo, Czech Republic

Publ.-Id: 14825 - Permalink

Shaping of submicrometer-structures by swift heavy ion irradiation
Ferhati, R.; Guilliard, N.; Weishaar, T.; Amirthapandian, S.; Fritzsche, M.; Bischoff, L.; Bolse, W.;
Processing of small structures on µm- or nm-scales using swift heavy ions of some MeV/u energy (SHI) has become an important research topic because of the unique features of the ion irradiation technique. Each single ion impact in the solid results in a highly excited (some eV per atom), almost one-dimensional excitation, which because of its cold surrounding lasts for only a few tens of picoseconds. In many crystalline materials (especially insulators) this rapidly quenched local excitation manifests itself in a highly disordered or even amorphous cylinder of the above mentioned dimensions. The irradiation was carried out in our new in-situ high resolution scanning electron microscope (HRSEM), which we have recently installed at the new UNILAC accelerator of the Helmholtz Gesellschaft für Schwerionenforschung (GSI) in Darmstadt. This setup enables us to perform sequences of combined ion irradiation and HRSEM analysis steps at one and the same spot on target surface throughout the whole experiment and allows us to investigate the evolution of individual objects during ion irradiation with a lateral resolution of a few nm. The specimen consisted of a 100 nm thick NiO film, which has been deposited onto an oxidized Si substrate by of reactive magnetron sputtering. The film was prestructured with a grid of 50 x 50 right-angled trenches by means of a focused ion beam (FIB) at the Forschungszentrum Dresden-Rossendorf. The trenches extended from the surface down to the NiO/SiO2 interface and had a width of about 100 nm. The distances were varied from 0.2 µm to 5 µm, with always 5 trenches having the same distance. This way NiO-blocks of 100 nm height were created, having quadratic (along the diagonal of the grid) respectively rectangular cross sections (off-grid elements). The specimen was then irradiated with 5.9 MeV/u U-ions under grazing incidence (tilt angle 80) and continuous azimuthal rotation (angular velocity 1.45_/s). We have investigated the reshaping of µm- to nm-sized rectangular NiO-blocks by SHI irradiation under grazing incidence and continuous azimuthal rotation. While initially small blocks form single pillar-like structures, blocks of larger dimensions rearrange into tooth-like objects. Below a certain size (~100 nm in diameter) the structures become instable and start to move and coalesce. The plastic deformation and the formation of the pillars can be understood in terms of the hammering effect (or better: in terms of isotropic tensile in-plane stresses due to the irradiation). The observed saturation effect and the instability until now remain unexplained and need further experiments for their clarification.
Keywords: oxide films, FIB, swift heavy ions, submicron structures
  • Contribution to external collection
    Prof. Dr. Peter Michler, Prof. Dr. Wolfgang Bolse: Annual Report 2009, Institut für Halbleiteroptik und funktionale Grenzflächen, Universität Stuttgart, Stuttgart: Universität Stuttgart, 2010, 48-49

Publ.-Id: 14824 - Permalink

A Common Approach to Image Reconstruction for Different Applications of Compton Cameras
Schöne, S.; Shakirin, G.; Kormoll, T.; Herbach, C.-M.; Pausch, G.; Enghardt, W.;
Compton camera imaging is a promising technique for the measuring of high energetic gamma rays. Potential applications of Compton cameras are homeland security and medical imaging.
Up to now the only method for the monitoring of ion radiation therapy is positron emission tomography (PET). The main disadvantage of the PET technique is the distortion of the measured β+-activity by metabolism and blood flow due to a half-live of up to 20 min for the therapy relevant positron emitters. This problem can be overcome by measuring the prompt photons of wide energies using Compton cameras. Compton cameras can also be used in homeland security for location and nuclide identification of remote radiation sources.
We developed an application independent method for representation and calculation of the system matrix (SM) for Compton cameras. The method provides a structured approach for the SM creation which simplifies the software development process and the optimization of the computational performance. Additionally, the SM calculation is completely independent of the reconstruction algorithm itself.
The first reconstruction results based on this unified SM calculation approach for medical imaging and homeland security applications are presented.
  • Poster
    2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
  • Contribution to proceedings
    2010 Nuclear Science Symposium and Medical Imaging Conference, 30.10.-06.11.2010, Knoxville TN, USA
    Conference Record 2010 Nuclear Science Symposium and Medical Imaging Conference

Publ.-Id: 14823 - Permalink

Requirements on the instrumentation of a prompt gamma measuring device
Fiedler, F.; Kormoll, T.; Müller, A.; Enghardt, W.;
no abstract available
Keywords: in-beam SPECT, in vivo dosimetry, Compton camera
  • Lecture (Conference)
    2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA
  • Contribution to proceedings
    2010 Nuclear Science Symposium and Medical Imaging Conference, 29.10.-06.11.2010, Knoxville, USA, 29.10.-06.11.2010, Knoxville, USA
    Proceedings to NSS MIC 2010

Publ.-Id: 14822 - Permalink

Eu3+-Mediated Polymerization of Benzenetetracarboxylic Acid Studied by Spectroscopy, Temperature-Dependent Calorimetry, and Density Functional Theory
Barkleit, A.; Tsushima, S.; Savchuk, O.; Philipp, J.; Heim, K.; Acker, M.; Taut, S.; Fahmy, K.;
Thermodynamic parameters for the complexation of Eu3+ with pyromellitic acid (1,2,4,5-benzenetetracarboxylic acid, BTC) as a model system for polymerisable metal-complexing humic acids were determined using temperature-dependent time-resolved laser-induced fluorescence spectroscopy (TRLFS) and isothermal titration calorimetry (ITC). At low metal and ligand concentrations (<50 µM Eu3+, <1 mM BTC), a 1:1 monomeric Eu-BTC complex was identified in the range of 25-60°C. At elevated concentrations (>500 µM Eu3+ and BTC) a temperature-dependent polymerization was observed. The two methods lead to consistent thermodynamic data (ΔH = 18.5 ± 1.5/16.5 ± 0.1 kJ mol-1; ΔS = 152 ± 5/130 J mol-1 K-1; TRLFS/ITC) in the absence of polymerisation. With the onset of polymeristaion, TRLFS reveals the water coordination number of the lanthanide, whereas calorimetry is superior in determining the thermodynamic data in this regime. Evaluating the heat uptake kinetics, the monomer and polymer formation steps could be separated by "time-resolved" ITC, revealing almost identical binding enthalpies for the sequential reactions. Structural features of the complexes were studied by Fourier-transform infrared (FTIR) spectroscopy in combination with density functional theory (DFT) calculations showing predominantly monodentate binding of a single carboxylate group in both the monomeric and the polymeric complexes of the polycarboxylate with Eu3+. The data show that pyromellitic acid is a suitable model for the study of metal-mediated polymerisation as a crucial factor in determining the effect of humic acids on the mobility of radionuclides in soils.

Publ.-Id: 14820 - Permalink

Comparative characterization of two natural humic acids from the Pearl River Basin, China, and their environmental implications
Liu, J.; Wang, J.; Chen, Y.; Lippold, H.; Lippmann-Pipke, J.;
Two humic acids (HAs) were isolated from contaminated river sediments present under comparative conditions in the Pearl River Basin, China. YFHA (the HA extracted at an open pyrite mining area in Yunfu) exhibits a lower absorption intensity for certain bands in the Fourier Transform Infrared spectra, a lower E4/E6 value (the UV absorbances at 465 nm (E4) and 665 nm (E6)), a lower apparent molecular weight, a lower polarity index and a lower oxygen functionality in comparison with GZHA (the HA isolated at an urban living area in Guangzhou). All these differences generally indicate a higher degree of humification of YFHA than GZHA. Overall, the enrichment patterns of permanent heavy metals in the studied HAs are similar to those in the corresponding sediments. In particular, YFHA exhibits high enrichment of trace element Tl, a characteristic concomitant from the mining of the pyrite minerals. The adsorption isotherms of two HAs for goethite and pyrolusite--two representative geological materials generally conform to the Langmuir equation. Based on the qualitative relationships between the Langmuir constants of the adsorption isotherms and the chemical characteristics of HAs, the main mechanism of HA adsorption on these materials is suggested to be hydrophobic interaction. This study highlights the promising use of HA as a peculiar bio-indicator of uncommon trace metal contaminations. The HA adsorption mechanism on representative geological materials further provides a theoretical basis for the study on the unusual metal behavior in complex environmental settings.
Keywords: humic acid; permanent metal load; adsorption; goethite; pyrolusite

Publ.-Id: 14819 - Permalink

European activities on cross-cutting nuclear thermal-hydraulics
Cheng, X.; Boudier, P.; Class, A.; Hampel, U.; Ma, W. M.; Meloni, P.; Papukchiev, A.; Prasser, M.; Roelofs, F.; van Tichelen, K.;
For the long-term development of nuclear power, innovative nuclear systems such as Gen-IV reactors and transmutation systems need to be developed for meeting future energy challenges. Thermal-hydraulics is recognized as a key scientific subject in the development of innovative reactor systems. In Europe, a consortium is established consisting of more than 20 institutions of research centers, universities and nuclear industries with the main objectives to identify and to organize research activities on important crosscutting thermal-hydraulic issues encountered in various innovative nuclear systems. A large-scale integrated research project is proposed to FP7 of European Commission and expected to start in the near future.
The main topics considered in the THINS (Thermal-Hydraulics of Innovative Nuclear Systems) project are (a) Advanced reactor core thermal-hydraulics; (b) Single phase mixed convection; (c) Single phase turbulence; (d) Multiphase flow; (e) Numerical code coupling and qualification. The main objectives of the project are:
• Generation of a data base for the development and validation of new models and codes describing the selected crosscutting thermal-hydraulic phenomena. This data base contains both experimental data and data from direct numerical simulations (DNS).
• Development of new physical models and modelling approaches for more accurate description of the crosscutting thermal-hydraulic phenomena such as heat transfer and flow mixing, turbulent flow modelling for a wide range of Prandtl numbers, and modelling of flows under strong influence of buoyancy.
• Improvement of the numerical engineering tools and establishment of a numerical platform for the design analysis of the innovative nuclear systems. This platform contains numerical codes of various classes of spatial scales, i.e. system analysis, sub-channel analysis and CFD codes, their coupling and the guidelines for their applications.
The project will achieve optimum usage of available European resources in experimental facilities, numerical tools and expertise. It will establish a new common platform of research results and research infrastructure. The main outcomes of the project will be a synergized infrastructure for thermal-hydraulic research of innovative nuclear systems in Europe.
This paper summarizes some key crosscutting thermal-hydraulics issues and corresponding ongoing research activities in Europe. The technical and management structure of the THINS project will be described. Examples of results achieved so far will be presented.
Keywords: generation IV nuclear reactors, nuclear thermal hydraulics
  • Contribution to proceedings
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-29.09.2011, Toronto, Canada
    Proceedings of the 14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14)
  • Lecture (Conference)
    14th International Topical Meeting on Nuclear Reactor Thermalhydraulics (NURETH-14), 25.-30.09.2011, Toronto, Canada

Publ.-Id: 14818 - Permalink

New 18F-labelled alkyl-substituted spirocyclic piperidines for imaging of σ1 receptors: radiolabelling and preliminary biological evaluation
Maisonial, A.; Fischer, S.; Hiller, A.; Große Maestrup, E.; Deuther-Conrad, W.; Scheunemann, M.; Schepmann, D.; Steinbach, J.; Wünsch, B.; Brust, P.;
Ziel: It is accepted that at least two σ receptor subtypes exist, termed σ1 and σ2 [1, 2]. Of these, σ1 receptor, the best characterized up to now [3], is assumed to be involved in several neurological diseases. PET imaging using specific σ1 receptor radioligands could be very helpful to obtain a target validation during drug development, a quantitative in vivo mapping of σ1 receptors as well as an improvement of our understanding of all the processes in which σ1 receptors are involved. Recently, a new class of spirocyclic piperidines with high affinity and selectivity for σ1 receptor binding site has been developed. Within this series, [18F]WMS1813 ([18F]1’-benzyl-3-(3-fluoropropyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]) has been successfully developed and used for detection of central σ1 receptors in mice [4]. Further structure-activity relationship studies on the linear ω-fluoroalkyl chain provided three other promising analogues, bearing either fluoromethyl- (WMS1850), fluoroethyl- (WMS1828) or fluorobutyl- (WMS1847) moieties. Herein, we report on the radiosynthesis and preliminary biological evaluation of these new candidates for PET imaging of σ1 receptors.
Methoden: [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were synthesized by direct aliphatic nucleophilic substitution of the corresponding tosylate precursors by using the K[18F]F-K222-carbonate complex. For each radiotracer studied, solvent, temperature, reaction time and precursor concentration were optimized. Preliminary experiments on lipophilicity, chemical stability, organ distribution and metabolic stability in CD-1 mice were performed.
Ergebnisse: Optimisation of radiofluorination parameters provided high labelling efficiencies of 61-88% using acetonitrile or DMSO as solvent, at 83 °C or 150°C respectively, with precursor concentrations between 2.0 and 3.0 mg/mL. [18F]WMS1850, [18F]WMS1828, and [18F]WMS1847 were obtained with radiochemical yields of 43-50%, 35-45%, and 45-53%, respectively, radiochemical purities of >98.5%, and high specific activities, generally ≥150 GBq/µmol. Distribution coefficients determined experimentally (Log D = 2.39-3.16, pH = 7.2), underline the moderate lipophilic character of the three radiotracers. The radiolabeled compounds also show appropriate chemical stabilities in acetonitrile, PBS, TRIS-HCl, and Dulbecco buffer.
No radiometabolites permeated into the brain of mice up to 60 min p.i. Metabolic profiles in liver, plasma, and urine were also investigated. By ex vivo autoradiography, the highest target (facial nucleus)-to-nontarget (olfactory bulb) tissue ratio has been determined for [18F]WMS1828 with a value of 4.69 at 45 min p.i. [18F]WMS1828 was superior also in organ distribution studies with a value of brain uptake of 4.71 ± 1.39 %ID/g in comparison to [18F]WMS1813 (3.18 ± 0.68 %ID/g), and [18F]WMS1847 (1.78 ± 0.16 %ID/g), and [18F]WMS1850 (2.65 ± 0.68 %ID/g) at 30 min p.i.
Schlussfolgerungen: For the three radiotracers studied, optimised protocols led to very efficient radiosyntheses. With respect to first biological data, [18F]WMS1828 appears to be the most promising candidate for PET imaging of σ1 receptors, with even better pharmacological profile than the lead compound. Hence, [18F]WMS1828 radiosynthesis is selected for transfer onto an automated radiosynthesis module with a view to further clinical development.
[1] Quirion, R.; Bowen, W. D.; Itzhak, Y.; Junien, J. L.; Musacchio, J. M.; Rothman, R. B.; Su, T. S.; Tam, S. W.; Taylor, D. P. Trends Pharmacol Sci. 1992; 13: 85-86.
[2] Hayashi, T. ; Su, T. P. Current Neuropharmacology. 2005; 3: 267-280.
[3] van Waarde, A.; Ramakrishnan, N. K.; Rybczynska, A. A.; Elsinga, P. H.; Ishiwata, K.; Nijholt, I. M.; Luiten, P. G. M.; Dierckx, R. A. Behavioural Brain Research. 2010; doi:10.1016/j.bbr.2009.12.043.
[4] Maestrup, E. G.; Fischer, S.; Wiese, C.; Schepmann, D.; Hiller, A.; Deuther-Conrad, W.; Steinbach, J.; Wünsch, B.; Brust, P. J. Med. Chem. 2009; 52: 6062-6072.
Keywords: σ1 receptor, 18F, radiolabelling, imaging
  • Lecture (Conference)
    18. Jahrestagung der Arbeitsgemeinschaft Radiochemie / Radiopharmazie der DGN, 16.-18.09.2010, Bad Boll, Deutschland

Publ.-Id: 14817 - Permalink

Synthesis, pharmacological activity and structure affinity relationships of spirocyclic σ1 receptor ligands with a (2-fluoroethyl) residue in 3-position
Große Maestrup, E.; Wiese, C.; Schepmann, D.; Brust, P.; Wünsch, B.;
In order to develop a fluorinated radiotracer for imaging of σ1 receptors in the central nervous system a series of (2-fluoroethyl) substituted spirocyclic piperidines 3 has been prepared. In the key step of the synthesis 2-bromocinnamaldehyde acetal 5 was added to piperidones 6 with various substituents at the N-atom. Unexpectedly, this reaction led to 2-benzoxepines 8, which were contracted with acid to afford the spirocyclic 2-benzofuranacetaldehydes 9. The best yields were obtained, when the transformations up to the alcohols 10 were performed without isolation of intermediates. Generally the (2-fluoroethyl) derivatives 3 have higher σ1 affinity and σ1/σ2 selectivity than the corresponding (3-fluoropropyl) derivatives 2. The most promising candidate for the development as radiotracer is the (2-fluoroethyl) derivative 3a (WMS-1828, fluspidine, 1’-benzyl-3-(2-fluoroethyl)-3H-spiro[[2]benzofuran-1,4’-piperidine]), which shows subnanomolar σ1 affinity (Ki = 0.59 nM) and excellent selectivity over the σ2 subtype (1331-fold) as well as some other receptor systems. The novel synthetic strategy also allows the systematic pharmacological evaluation of intermediate alcohols 10. Despite their high σ1 affinity (Ki = 6-32 nM) and selectivity the alcohols 10 are 10-30-fold less potent than the bioisosteric fluoro derivatives 3.
Keywords: σ1 receptor ligands; spirocyclic piperidines; [18F] radiotracer; neuroimaging; structure affinity relationships; ring contraction.

Publ.-Id: 14816 - Permalink

The serotonin transporter availability in untreated early-onset and late-onset patients with obsessive-compulsive disorder
Hesse, S.; Stengler, K.; Regenthal, R.; Patt, M.; Becker, G.-A.; Franke, A.; Knüpfer, H.; Meyer, P. M.; Luthardt, J.; Jahn, I.; Lobsien, D.; Heinke, W.; Brust, P.; Hegerl, U.; Sabri, O.;
The pathogenetic role of the central serotonin transporters (SERT) in obsessive-compulsive disorder (OCD) has been investigated in vivo by positron emission tomography (PET) or single-photon emission computed tomography (SPECT) studies with inconsistent results. This might reflect methodological differences but possibly also the pathophysiological heterogeneity of the disorder, i.e. the age at onset of OCD. The aim of our study was to compare the SERT availability in patients with OCD to healthy controls (HC) taking into account the onset type, other factors and covariates (e.g. SERT genotype, age, depression level, gender). We studied 19 drug-naïve OCD patients (36±13 years, 8 females) with early onset (EO-OCD, n=6) or with late onset (LO-OCD, n=13), and 21 HC (38±8 years, 9 females) with PET and the SERT-selective radiotracer [11C]DASB. Statistical models indicated that a variety of covariates and their interaction influences SERT availability as measured by distribution volume ratios (DVR). These models revealed significant effects of onset type on DVR with lower values in the LO-OCD (starting at an age of 18 years) compared with EO-OCD and HC in limbic (e.g., the amygdala), paralimbic brain areas (the anterior cingulate cortex), the nucleus accumbens and striatal regions, as well as borderline significance in the thalamus and the hypothalamus. The putamen, the nucleus accumbens and the hypothalamus were found with significant interaction between two SERT gene polymorphisms (SERT-LPR and VNTR). These findings suggest that late but not early onset of OCD is associated with abnormally low SERT availability. In part, functional polymorphisms of the SERT gene might determine the differences.
Keywords: Serotonin transporter, positron emission tomography, obsessive-compulsive disorder

Publ.-Id: 14813 - Permalink

Tailoring the Magnetic Coupling of Fe/Cr/Fe Trilayers by Using Substrates with Nanometer Scale Ripples
Körner, M.; Liedke, M. O.; Strache, T.; Dzenisevich, S.; Keller, A.; Facsko, S.; Lenz, K.; Fassbender, J.ORC
Artificial antiferromagnets made from magnetically coupled trilayer structures are the basis for all types of spintronic devices like MRAM, GMR sensors etc. For years major effort lay on adjusting the coupling strength by changing the spacer thickness or material. Today, nanostructures offer a different approach as they add additional coupling mechanisms like proximity effects or Néel orange-peel coupling to the common interlayer exchange coupling (IEC). By means of ion beam erosion techniques it is possible to create well ordered substrate ripples with nanometer periodicity. They are transferred into the films grown on these rippled substrates. Hence, such ripples are a convenient way to induce Néel orange-peel coupling [1] and thus allow for tailoring the magnetic properties [2] as well as the coupling strength by varying the ripple periodicity without adjusting the spacer thickness. We have investigated the influence of rippled vs. flat Si substrates on the interlayer exchange coupling contributions in polycrystalline Fe (4nm)/Cr (x nm)/Fe (4nm) thin film trilayers (x=0–5 nm). The substrate surface was periodically modulated (periods of 23 nm and 37 nm) by Ar+ ion beam erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by longitudinal magneto-optical Kerr effect (MOKE) applying a Stoner-Wohlfarth model on the magnetization reversal loops. Using 23 nm period ripples, we find an orange peel type coupling, predicted by Néel's theory superimposed on the IEC. In addition due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy is induced.
This work is supported by DFG grant FA 314/6-1.
1. Körner M. et al., Physical Review B 80, 214401, 2009.
2. Fassbender J. et al., New Journal of Physics 11, 125002, 2009
  • Poster
    Nanofair 2010 - 8th International Nanotechnology Symposium, 06.-07.07.2010, Dresden, Germany

Publ.-Id: 14812 - Permalink

Investigating the Magnetic Properties of Tailored Bit Patterned Media Using Ferromagnetic Resonance
Ball, D.; Faßbender, J.ORC; Lenz, K.; Markó, D.; Körner, M.; Fritzsche, M.; Strache, T.; Mücklich, A.; Albrecht, M.; Makarov, D.; Tibus, S.; Krone, P.
no abstract available
Keywords: Vector network analyzer ferrromagnetic resonance, CoCrPt:SiO2, Anisotropy, g-factor, damping phenomena, Gilbert damping, two magnon scattering
  • Lecture (others)
    Group Seminar, 09.06.2010, München, Germany

Publ.-Id: 14811 - Permalink

Morphology Induced Magnetic Phenomena
Körner, M.; Lenz, K.; Liedke, M. O.; Strache, T.; Keller, A.; Facsko, S.; Fassbender, J.ORC
no abstract available
  • Lecture (others)
    group seminar, 09.06.2010, München, Germany

Publ.-Id: 14810 - Permalink

Rational design of nanoparticle arrays using bioinspired mineralisation mediated by peptide-modified bacterial S-layers
Pollmann, K.; Rothenstein, D.;
Thema zur Einreichung im DFG-Schwerpunktprogramm
  • Lecture (Conference)
    DFG-SPP 1569 “Generation of Multifunctional Inorganic Materials by Molecular Bionics”, Kick-Off-Meeting, 25.10.2010, Stuttgart, Deutschland

Publ.-Id: 14809 - Permalink

Bioinspired nanocomposites based on self-assembling bacterial surface layer proteins
Pollmann, K.; Günther, T.; Weinert, U.; Marquard, A.; Kutschke, S.; Lehmann, F.; Raff, J.;
Bio-inorganic materials are very attractive for a variety of technical applications. The use of self-assembling proteins as part of such a hybrid material is an attractive approach for the development of such materials. Especially the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].
In a current project we use monolayers of the S-layer protein of Lysinibacillus sphaericus for the construction of sensory layers. These S-layers are functionalized by aptamers (oligonucleotides) that work as receptor and two different fluorophores working as donor/acceptor for detection. Appropriate excitation/emission spectra and closest proximity of the fluorophores permit FRET. The binding of the analyte to the aptamer should influence the fluorescence, ideally causing the interruption of the FRET.
In other projects we used the S-layers for the formation of (photo)catalytic layers. In this approach S-layers work as template for the bioinspired formation of (photo)catalytic particles such as Pd or ZnO. Size, crystallinity, distribution and morphology of the particles are influenced by the proteinaceous template.
These examples demonstrate the high potential of the S-layers for various applications.

[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
[3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244
Keywords: S-layers nanocomposites bio-inspired
  • Lecture (Conference)
    Euro BioMat 2011, 13.-14.04.2010, Jena, Deutschland

Publ.-Id: 14808 - Permalink

Lock and load the SRF gun
Teichert, J.;
In a forest close to the city of Dresden, Germany, lies the ELBE radiation source - the largest facility of the Research Centre Dresden-Rossendorf (FZD). After years of research, February saw the first SRF gun beam injected and accelerated in ELBE. Jochen Teichert tells more about the facility, the research and the gun.
  • EuCARD Newsletter 4(2010), 4-6

Publ.-Id: 14807 - Permalink

Au and Ge Nanoparticle Shaping by Swift Heavy Ion Irradiation
Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Akhmadaliev, C.; Ridgeway, M.; Kluth, P.; Vredenberg, A.;
The driving forces of nanomaterials processing by swift heavy ions as identified by our studies are (i) the mate-rials dependent electronic stopping power, (ii) the vol-ume change upon melting, (iii) the asymmetric hydro-dynamic flow due to stress field hysteresis, as well as (iv) far-from-equilibrium steady-state solubilities and strongly anisotropic diffusion coefficients. Size distributions, shapes and anisotropies of nanoparticles can be tailored by appropriate tuning of these driving forces. The evolution of Au and Ge nanospheres under swift heavy ion irradiation was studied experimentally and by atomistic computer simulations. Ge nanospheres of different sizes embedded in SiO2 show different response to I7+ ion irradiation at 38 MeV. Spheres below a critical size become discus-shaped, very small ones show Ge loss at their equator. Computer simula-tions based on a model which includes the driving forces listed above describe the Ge shaping and the Au shaping, where Au nanospheres of 15 nm diame-ter elongate to rods. Our model describes the ion-induced shape evolution of different elements for different ion species, energies and fluences quantitatively, where only one fit parameter describes all experiments. This is a strong evidence that our model based on classical thermodynamics and hydrodynamics describes the shaping mechanism appropriate. Using critical-size nanospheres with an unimodal size distributions and changing the ion impact angle during irradiation, tailoring of very exotic nanoparticle shapes become feasible.
Keywords: Swift heavy ions, nanoparticles, ion bem shaping
  • Lecture (Conference)
    Workshop Ion Beam Physics, 29.-31.03.2010, Dresden-Rossendorf, Germany

Publ.-Id: 14806 - Permalink

Silicon Sensors realized by KETEK in Co-operation with FZD
Wiest, F.; Eggert, T.; Fojt, R.; Höllt, L.; Knobloch, J.; Pahlke, A.; Pahlke, S.; Stötter, R.; Schmidt, B.; Lange, H.;
In 2004 Ketek has established a long term co-operation with the Reasearch Centre Dresden (FZD) and the Universität der Bundeswehr München (UBW) targeted on the development of new silicon radiation detectors as well as on their commerz-ialization.
Silicon Drift Detectors (SDDs) are widely used in XRF, TXRF, electron micro-probe analysis systems and synchrotron applications. The big benefit of SDDs compared to other x-ray de-tectors as Si(Li)s or pin-diodes is the spectroscopic performance principally being independent of the sen-sitive area. KETEK offers silicon drift detectors with sizes varying from 10 to 100 mm² whereby the large area devices become more and more attractive for most of the applications. Energy resolution below 130 eV for the Manganese Ka line and peak to background values of more than 10.000 can be achieved for devices with active areas of 100 mm² when cooled down to -60°C. This temperature can be already realized by a Peltier element integrated into the detector module, since the thermal budget of this evacuated device is well optimized. Count rate dependency of the energy resolution and the peak position is negligible up to count rates of 100.000 counts per second.
Silicon Photomultiplier (SiPMs) are single photon sensitive devices built from an avalanche photodiode (APD) array on common Si substrate, whereby the APDs are operated in Geiger modus (above break down voltage). All applications for this sensor are connected with fast low level light sensing like e.g. the indirect gamma radiation detection by a scintillator. The first SiPM prototypes which have been realized by Ketek in co-operation with FZD show promising val-ues for photon detection efficiency, dark rate and opti-cal cross talk. Now this detector shall be further opti-mized for PET application.
Keywords: Silicon drift detector. Silicon photomultiplier
  • Lecture (Conference)
    Workshop Ion Beam Physics (29th-31st March 2010), 29.-31.03.2010, Dresden-Rossendorf, Germany

Publ.-Id: 14805 - Permalink

Tailoring the magnetism of GaMnAs films by ion irradiation
Li, L.; Zhou, S.; Buerger, D.; Roshchupkina, O.; Rushforth, A.; Campion, R. P.; Yao, S.; Grenzer, J.; Fassbender, J.ORC; Helm, M.
The properties of magnetic metals such as saturation magnetization and magnetic anisotropy can be modified in a controllable manner by energetic ions [1]. GaMnAs is a well known magnetic semiconductor. The ability to tune the magnetic properties of magnetic semiconductors is an important issue in future semiconductor devices. Here we tailored the magnetism of GaMnAs films by He+ ion irradiation. The GaxMn1-xAs films with a Mn concentration of 5% and the easy axis of magnetization lying in-plane have been grown on GaAs substrates by LT-MBE. He+ ions of 650 keV were used to place the peak of damage into the GaAs substrate, so that the GaMnAs epilayer lies in the relatively uniform part of the damage profile. We show that the coercivity can be increased (Fig.1) from 50 Oe to 165 Oe when the dose reaches 3×1014/cm2 ~ 6×1014/cm2. Meanwhile, the saturation magnetization at 5 K is only reduced slightly to 22 emu/cm3 compared to non-irradiated GaMnAs films with a saturation magnetization amounting to 27 emu/cm3. Magneto-transport results indicate that the sheet resistance is increased by about 4 times compared to the non-irradiated GaMnAs film with a sheet resistance of 103 Ω. The irradiated GaMnAs still has an in-plane easy axis of magnetization at 5 K, but the anisotropy energy is much decreased. When the dose increases to 1×1015/cm2, no M-H hysteresis has been probed. Our study demonstrates the tailoring of magnetism and magnetoresistance in GaMnAs films by He+ ion irradiation.
[1] J. Fassbender and J. McCord, J. Magn. Magn. Mater. 320 (2008) 579–596
Keywords: magnetism, GaMnAs, ion irradiation
  • Lecture (Conference)
    Trends in Spintronics and Nanomagnetism, 22.05.-27.10.2010, Lecce, Italy
  • Poster
    Ion beam workshop, 29.-31.03.2010, Dresden, Deutschland
  • Journal of Physics D: Applied Physics 44(2011)4, 045001

Publ.-Id: 14804 - Permalink

Activation of acceptor levels in Mn implanted Si by pulsed laser annealing
Li, L.; Zhou, S. Q.; Bürger, D.; Fassbender, J.ORC; Helm, M.; Schmidt, H.; Oesterlin, P.; Yao, S. D.
The success of GaMnAs ferromagnetic semiconductors stands on two facts: (1) the efficient suppression of Mn-rich precipitates and (2) the large hole concentration created by substitutional Mn ions. If GaMnAs can be a guide, these two prerequisites should be considered when fabricating Si based ferromagnetic semiconductors. In this paper, nearly intrinsic Si wafers were implanted with Mn ions. The implanted Si films were annealed by pulsed laser annealing (PLA) or rapid thermal annealing (RTA). Activation of acceptors was only realized in the PLA films with a free hole concentration of 4×1017 cm-3, compared to the activation of donors in RTA films with a free electron concentration of 6×1015 cm-3. The PLA films reveal negative magnetoresistance with MR= 0.5% at 20 K and 30 K and at 7 T, hinting towards spin polarization of holes. Ferromagnetism was probed for both RTA and PLA films by a SQUID magnetometer at low temperatures. The formation of ferromagnetic MnSi1.7 nanoparticles has been proven in RTA films by synchrotron radiation X-ray (SR-XRD) measurements [1] and could be excluded in Mn implanted Si annealed by PLA.
[1] S. Zhou et al., Phys. Rev. B 75, 085203 (2007).
Keywords: Mn,Si, pulsed laser annealing,acceptor level
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 21.-26.03.2010, Regensburg, Deutschland

Publ.-Id: 14803 - Permalink

Ion Implantation in AFM Cantilever Array Fabrication
Schmidt, B.; Zier, M.; Potfajova, J.; Philipp, P.;
Low energy ion implantation has been applied to fabrication of shallow piezoresistive elements for AFM deflection sensing. The corresponding process parameters have been optimized to meet the demands of the electronics (power supply, resistance) connected to the piezoresistors. For the dimension (length x width = 5x20 µm2) of the piezoresistors designed by the University of Ilmenau, the resistance of them is 2.3-2.5 kOhm. The full processing of PRONANO AFM arrays consists additional three ion implantation steps for integrated heater and interconnect fabrication as well as for substrate reverse-biasing.
Keywords: cantilever, array, piezoresistor, ion implantation, shallow pn-junction, sheet resistance
  • Contribution to external collection
    T. Sulzbach, I. W. Rangelow: PRONANO Proceedings of the Integrated Project on Massively Parallel Intelligent Cantilever Probe Platforms for Nanoscale Analysys and synthesis, Münster: Monsenstein und Vannerdat OHG (MV Wissenschaft), 2010, 978-3-86991-117-9, 111-117

Publ.-Id: 14802 - Permalink

Ion patterning of Si studied by kinetic Monte Carlo using ion damage from Molecular Dynamics calculations
Numazawa, S.; Süle, P.; Heinig, K.-H.;
During molecular dynamics (MD) simulation of Xe+, 500eV ion bombardment with the incidence angle 67° on Si (001), some dislocation patterns of near surface Si atoms were observed. We focused on the distribution of adatom generation points on Si (001) surface.
After 500 single ion bombardment MD simulations, the observed distribution shapes Gaussian distribution with different aspect ratio. The center of distribution is around 1.8 nm forward from the impact point. We performed 3 dimensional lattice kinetic Monte-Carlo simulations with this adatom generation distribution and surface diffusion process. In early stage, the surface was simply roughened homogeneously and after around 3 x 1015 ion/cm2 dose, the surface started to form ripple structure perpendicular to the azimuthal incidence angle with wavelength ~15 nm. The ripple moves forward to the incident angle. These processes agree nicely with experimental observation. The mechanism of ripple formation related to surface atomic flows induced by ions, surface damage distribution and Mullin’s diffusion is discussed.
Keywords: ion erosion, surface pattern, nanostructure, modelling, kinetic Monte Carlo, Molecular Dynamics
  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-28.08.2010, Montréal, Canada
  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-28.08.2010, Montréal, Canada

Publ.-Id: 14801 - Permalink

Silicon nanocluster aggregation in SiO2:Si layers
Fitting, H.-J.; Fitting Kourkoutis, L.; Roushdey, S.; Zamoryanskaya, M. V.; Schmidt, B.;
Energy-filtered transmission electron microscopy (EFTEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters. Therefore, amorphous, thermally grown SiO2 layers on Si substrate were implanted by Siþ ions with an energy of 150 keV and a dose of 5x1016 ions/cm2 leading to an atomic dopant fraction of about 4 at%. Afterwards a post-implantation thermal annealing has been performed at temperatures Ta=700–1300 °C, for 60 min in vacuum. This thermal annealing leads to Si cluster formation and a change of the SiOx matrix from about x=1.923 to 1.929 connected with additional visible luminescence bands in the green-yellow region. CL spectra in the near infrared (NIR) region indicate such Si aggregation by appearance of an additional band in extension of the common NBOHC band at 1.9 eV towards the NIR region. This band shifts with increasing annealing temperatures of the implanted sample to lower energies, probably, due to cluster growth and quantum confinement effects.
Keywords: ion implantation, SiO2, silivium nanocluster, EFTEM

Publ.-Id: 14800 - Permalink

Mechanism of selective nano structure formation on pre-patterned surfaces
Numazawa, S.; Heinig, K.-H.;
A self-alignment of metal nanoclusters has been observed on ripple like pre-patterned oxidized Si surfaces by oblique angle electron-beam evaporation. During the metal deposition perpendicular to ripples the metal nanoclusters are grown on the slopes which point towards the evaporation source.The self-ordering of metal nanoclusters has not been observed for normal deposition and for low-angle deposition parallel to the ripple direction. This indicates that the features of the metal nanostructure depend strongly on the local deposition angle. With the 3D lattice kinetic Monte Carlo simulations we studied the process of silver deposition on pre-patterned surfaces. The experimentally observed Ag nanostructures could be reproduced by using the many-body potential to estimate the atomistic migration barriers. It was shown that the extremely short range of surface adatom migration causing low sticking probability together with a slope-dependent deposition rate promotes the localization of the Ag nanocluster nucleation distribution. Consequently, the observed selective Ag nano structure formation can be understood by the separation of the Volmer-Weber growth mode and the layer-by-layer growth mode due to the localized coalescence of clusters.
Keywords: Kinetic Monte-Carlo, nanopatterning
  • Lecture (Conference)
    10th International Conference on Computer Simulations of Radiation Effects in Solids COSIRES 2010, 19.-23.07.2010, Krakow, Poland

Publ.-Id: 14799 - Permalink

Ion induced surface pattern evolution described by combined TRIM and kinetic Monte-Carlo simulation
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
Atomistic understanding of surface morphology evolution induced by ion beam sputtering is still strongly limited. Available continuum models cannot explain microscopic processes during ion beam irra-diation. On the other hand, so far atomistic simula-tions could not describe pattern dynamics in the spa-tiotemporal scales of experiments.
However, combined atomistic single ion impacts with continuum equations [1] gives a better under-standing of additional smoothing mechanisms, like an effective mass ‘downhill’ current induced by ballistic atomic drift [2][3].
We developed a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of ener-getic atomic configurations as well as diffusive proc-esses were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Effects like ballistic mass drift or dependence of local morphology on sputtering yield are automati-cally included in the BCA approach. Distributions presented in Figure 1 show the mean preferential lo-cation of ad-atoms creation and the sputtering re-gions.
Low energy (up to 5 keV) ion a sputtering simula-tions have been performed on the simulation cell of about 17 million atoms, where irradiation fluence goes up to few 1018 cm-2. The pattern topography has been study by means of various intensive parameters like incidence angle (Fig. 2), ion beam energy, ion fluence, and migration energy of defects. Moreover, the scaling behaviour of surface roughness and pat-tern periodicity has been analysed.
Finally, we compare our results with experiments as well as with continuum theory.
[1] S. A. Norris and M. P. Brenner and M. J. Aziz J. Phys. Condens. Matter 21 (2009) 224017.
[2] G. Carter and V. Vishnyakov PRB 54 (1996) 17647.
[3] M. Moseler and P. Gumbsch and C. Casiraghi and A. C. Ferrari and J. Robertson Science 309 (2005) 1545.
Keywords: TRIM, kinetic Monte-Carlo, ion irradiation, ripple formation, scaling, crater function, surface mass current
  • Poster
    Workshop Ion Beam Physics, 29.-31.03.2010, FZD, Germany

Publ.-Id: 14798 - Permalink

Multiphysics program for ion-induced collision cascades and thermally activated phase separation: intermetallic nanolayers by interface mixing
Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.;
Recent developments in computational materials modelling methods have to provide a qualitatively new level of predictive power and insight into materials design. In nature, different physical processes govern simultaneously the evolution of systems. Due to the complexity of the individual processes, so far their simulations are performed separately. One key to computational progress is the multiphysical treatment in a single computer program package.
Here, we consider the evolution of interfaces under energetic ion irradiation. There, the physical process of collisional mixing is in competition with thermally activated diffusion and phase separation. We developed a novel program which treats both physical processes simultaneously. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic, atomic configurations as well as diffusive processes, were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code. Contrary to molecular dynamics simulations, our approach allows studies on experimental spatiotemporal scales.
As applications we present two extremes of interface mixing: (i) Irradiation of interfaces made by immiscible elements, here Al and Pb, with He ions causes ballistic interface mixing accompanied by phase separation. Al and Pb clusters, which form in the interface region, show self-ordering. (ii) Irradiation of interfaces made by metals which form intermetallics, here Pt and Co, with He ions causes the formation of nanometric intermetallic layers with the sequence Pt/Pt3Co/PtCo/PtCo3/Co across the former interface. In the element mapping perpendicular to the interface (e.g. by RBS measurements), this results in step-wise changes of Pt/Co concentrations. Novel magnetic properties of such sandwiched phases are expected. In particular, a very interesting magnetic behaviour of irradiated Pt/Co/Pt multilayers has been observed. It can be shown that the transition between out of plane and in-plane magnetic anisotropy can be triggered by ion beam irradiation, whereas computer experiment can be useful for understanding the physical mechanism.
Keywords: BCA, kinetic Monte-Carlo, collision cascade, ion irradiation, interface mixing, phase seperation, phase ordering, intermetallics
  • Lecture (Conference)
    COSIRES 2010, 19.-23.07.2010, Collegium Maximum Auditorium in Kraków, Poland

Publ.-Id: 14797 - Permalink

Mechanism of metal nanostructure self-ordering during oblique deposition on pre-patterned surfaces
Numazawa, S.; Heinig, K.-H.; Ranjan, M.; Facsko, S.;
By utilizing electron-beam evaporation, metal nanoclusters have been produced on pre-patterned oxidized Si surfaces. During the oblique deposition perpendicular to ripples the metal nanoclusters are grown on the slopes which point towards the evaporation source.The self-ordering of metal nanoclusters has not been observed for normal deposition and for low-angle deposition parallel to the ripple direction. This indicates that the features of the metal nanostructure depend strongly on the local deposition angle. Here, by means of 3D lattice kinetic Monte Carlo simulations, we studied the process of silver deposition on pre-patterned surfaces. The experimentally observed Ag nanostructures could be reproduced by using the many-body potential to estimate the atomistic migration barriers. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent local deposition rate leads to a strongly localized Ag nanocluster nucleation distribution on the surface because the nucleation rate depends approximately on the dimer adatom concentration.
Keywords: Kinetic Monte-Carlo, nanopatterninig
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Germany

Publ.-Id: 14796 - Permalink

Influence of corrosion processes on the head loss across ECCS sump strainers
Kryk, H.; Hoffmann, W.; Waas, U.;
Corrosion of hot-dip galvanized grating treads, installed in the containment, may exacerbate ECCS strainer clogging problems during LOCA incidents in LWR. In order to identify the corrosion mechanisms as well as the nature of particulate corrosion products formed, corrosion investigations were carried out in boric acid solutions as well as in demineralized water using hot-dip galvanized steel samples. For the related experiments, tailored bench-scale facilities have been constructed. The results of batch experiments as well as of long-time corrosion investigations in the KorrVA test facility at FZD suggest that there is a multi-stage corrosion process. The first stage comprises the dissolution of the Zn layer in the acidic coolant forming zinc ions, which can generate crystalline zinc borate in boric acid solutions, if the ion concentration exceeds the saturation concentration. The base material (steel) is cathodically protected as long as the zinc layer is present. During the second stage, a slight head loss rise may occur due to the release of hard zinc (Zn/Fe) particles. After the complete removal of the hard zinc layer, the base material dissolves forming insoluble corrosion particles similarly to a flow accelerated corrosion process, which can subsequently lead to acceleration of the strainer clogging. The main influences on corrosion were identified as jet impact, water chemistry and Zn surface / coolant volume ratio.
  • Kerntechnik 76(2011)1, 46-53

Publ.-Id: 14795 - Permalink

Einfluss von Korrosionsprozessen auf den Differenzdruck über die Sumpfansaugsiebe von Notkühlsystemen
Kryk, H.; Hoffmann, W.; Waas, U.;
Zur Aufklärung von Korrosionsprozessen und deren Auswirkungen auf die Verstopfung von mit Isoliermaterialfasern belegten Sumpfansaugsieben bei Kühlmittelverluststörfällen in Leichtwasserreaktoren wurden Korrosionsuntersuchungen in speziellen Laboranlagen unter Nutzung von feuerverzinkten Stahlproben durchgeführt. Die Ergebnisse der Batch- sowie der Langzeit-Korrosionsexperimente mit borsäurehaltigen Lösungen lassen auf einen mehrstufigen Korrosionsmechanismus schließen, wobei im ersten Schritt die Auflösung der Reinzinkschicht erfolgt. Die dabei entstehenden Zink-Ionen gehen in Lösung und tragen somit nicht signifikant zur Verstopfung der Sumpfansaugsiebe bei. Im weiteren Verlauf kann es zu einer leichten Differenzdruckerhöhung an den Sumpfsieben durch Ablösung von Partikeln aus der herstellungsbedingten darunterliegenden Hartzinkschicht (Zn/Fe-Legierung) kommen. Nach der kompletten Entfernung der Hartzinkschicht erfolgt eine strömungsinduzierte Korrosion des Basismaterials (Stahl), die zur Bildung unlöslicher Korrosionsprodukte des Eisens in Form kleiner Partikel führt. Diese Partikel lagern sich in die Isoliermaterialfasern an den Sumpfansaugsieben ein, was zu einer starken Erhöhung des Strömungswiderstandes führt. Der Differenzdruckanstieg beginnt, abhängig von den hydrodynamischen Bedingungen, 6 bis 15 Stunden nach Beginn der Beaufschlagung der Proben mit dem Leckwasserstrahl. Eine zweite (theoretische) Quelle für die Bildung partikelförmiger Produkte stellt die Kristallisation von Zinkborat aus einer übersättigten Lösung bei Temperaturerhöhung und/oder Verdampfung des Kühlmittels dar. Haupteinflussfaktoren des Gesamtprozesses sind die Aufprallkraft des Leckstrahls auf die Materialoberfläche, die Wasserchemie (Borsäurekonzentration, pH-Wert) sowie das Verhältnis der Korrosions-Oberfläche zum Kühlmittel-Volumen.
  • Lecture (Conference)
    KTG-Fachtagung „Aktuelle Themen der Reaktorsicherheitsforschung in Deutschland“, 07.-08.10.2010, Dresden, Deutschland

Publ.-Id: 14794 - Permalink

Ion-implanted Silicon detectors ­ - Silicon Strip Detectors
Schmidt, B.; Haberjahn, M.; Lange, H.; Hanf, D.;
Demands on modern silicon detector technology and the detector development for improving analysis in the frame of the EU-Project SPIRIT will be described. For high energy resolution RBS and ERDA experiments large area silicon strip detector with increased sensitivity and energy resolution down to 10 keV FWHM (He+ at max. 2MeV) are required. By applying such strip detectors with certain position resolution kinematic correction procedures will be possible.
Keywords: Silicon radiation detectors, ion implantation, high resolution IBA
  • Lecture (Conference)
    1st SPIRIT Workshop on New detector technologies for advanced materials research using ion beam analysis, 25.-26.10.2010, Plitvice Lakes National Park, Croatia

Publ.-Id: 14793 - Permalink

Transition metal diffusion in diluted magnetic Si and GaAs prepared by pulsed laser processing
Bürger, D.; Seeger, M.; Zhou, S.; Skorupa, W.; Schmidt, H.;
Starting from a random or ordered distribution of 0.8, 1.6, 3.7 and 12.5 % dopants over the lattice sites of a simple cubic host lattice, we estimate the fraction of unclustered dopants after pulsed laser quenching of different host:dopant systems. Initial clustering events are simulated with a greedy algorithm implemented in a Monte-Carlo study. The greedy algorithm gives adequate results for dopants with low diffusity and low solubility.
The absolute initial dopant concentration and declustering strongly in influence the kinetics of clustering. Particularly, we consider transition metal doped Si and GaAs after pulsed laser annealing, which are of interest for spintronics applications. An uncritical integral diffusion of Mn in GaAs:Mn and a tendency of Mn to form silicides in Si:Mn are simulated. These results are in good agreement with experimental observations.
Keywords: diluted magnetic semiconductor, implantation, pulsed laser annealing, ferromagnetism, secondary phase formation, nanoscale clustering

Publ.-Id: 14792 - Permalink

Channeling as a means to obtain information on crystal quality and structure
Munnik, F.; Heller, R.;
Rutherford Backscattering Spectrometry (RBS) is an analysis technique that uses fast ions like He+ to obtain information about the chemical composition in the surface region. In case of crystalline samples, the ion beam can be aligned with the crystal orientation thereby allowing the ions to penetrate the sample much deeper than in a random direction. This results in a large reduction of the yield of backscattered ions, the so-called channeling dip. Information about crystal quality can be obtained from the width and the depth of the channeling dip. The position of atoms of a certain species in the crystal can de deduced from the yield reduction in various crystal orientations.

In this presentation, the basic principles of channeling are explained. Channeling can be used to obtain information about the position of impurities in a crystal and to assess damage caused by implantation and the quality of the crystal after subsequent annealing. Examples of these types of analysis are presented. Complementary PIXE (Particle Induced X-ray Emission) channeling can be applied to obtain information about elements that have a mass similar to the main elements, which cannot be measured with RBS. An example of PIXE channeling is also presented.
  • Invited lecture (Conferences)
    New detector technologies for advanced materials research using ion beam analysis, 25.-26.10.2010, Plitvice Lakes, Croatia

Publ.-Id: 14790 - Permalink

Hysteresis in the magneto-transport of Manganese-doped Germanium: evidence for carrier-mediated ferromagnetism
Bürger, D.; Zhou, S.; Baumgart, C.; Skorupa, W.; Timm, C.; Oesterlin, P.; Helm, M.; Schmidt, H.;
The III-V compound GaMnAs is considered as being the prototype diluted ferromagnetic semiconductor (FMS), exhibiting negative magneto-resistance (MR) and anomalous Hall-effect (AHE) related to carrier-mediated ferromagnetism. However, it would be very desirable to have a group-IV FMS, being compatible with silicon technology. In particular manganese-doped germanium prepared using low-temperature molecular beam epitaxy (LT-MBE) has been proven to be a very promising material [1]. Still, no direct correspondence between transport and magnetization data has been reported yet to date. We believe that the origin of these observations lies in the less effective substitution of Mn at Ge sites, which results in too low a hole concentration, making carrier-mediated ferromagnetism impossible. The hole concentrations realized in Ge:Mn grown by LT-MBE are mostly well below 1019 cm-3, which indicates the possible unsuitability of LT-MBE to achieve a large hole concentration in Ge:Mn.
In this contribution, we show that the hole concentration can be increased by two orders of magnitude, from 1018 to 1020 cm-3, through Mn-ion implantation into Ge followed by pulsed laser annealing [2]. This non-equilibrium technique allows the preparation of metastable materials with interesting material properties, e.g. diluted ferromagnetic GaMnAs [3]. In Mn-doped Ge with a hole-concentration of around 2.1×1020 cm-3, we observe that the longitudinal and the Hall resistance exhibit the same hysteresis as the magnetization at temperatures below 10 K. This hysteresis in magneto-transport is usually considered as a direct evidence of carrier-mediated ferromagnetism. We will present a comprehensive correlation between the magnetic, transport and structural properties of Ge:Mn samples with different hole concentrations, as well as a comparison with literature. Note that ion implantation followed by pulsed laser annealing is an established scalable chip technology and may have a significant industry impact.

[1] Y. D. Park et al., Science 295, 651 (2002); M. Jamet et al., Nature Mater. 5, 653 (2006).
[2] S. Zhou et al., Phys. Rev. B 81, 165204 (2010).
[3] D. Bürger et al., Phys. Rev. B 81, 115202 (2010).
  • Lecture (others)
    47. Punktdefekttreffen, 07.-08.10.2010, Dresden, Deutschland

Publ.-Id: 14789 - Permalink

Synchrotron Radiation in Materials Science
Baehtz, C.;
In Material Science (powder) diffraction methods are a common sample characterisation tool. Beside the laboratory sources synchrotron radiation offers the advantages of high brilliance and tuneable wavelength. As an example for high resolution diffraction the localisation of incorporated guest molecule in zeolites faujasite by crystal structure refinement will be presented.
Heavy load goniometer allows also experiments with high sophisticated sample environments to perform in-situ investigations. Hereby solid state reactions can be monitored or catalyst characterized. Carbon nano tubes (CNT) are synthesized by chemical vapour deposition and the use of iron nano particles. The catalyst processing and CNT synthesis was observed by XRD and the catalytic active species determinated.
By the use of hard X-rays absorption effects are minimized and more complex system like a secondary lithium ion battery can be investigated. Hereby the diffraction pattern of the system in operation can be collected. The charge-discharge behaviour of lithium manganese oxide will be discussed.
In general in-situ investigations have the advantage to monitor different processes directly and being more time efficient. Misleading results of ex-situ measurements by metastable phases, subsequent reactions or aging of the material are avoided.
Keywords: synchrotron radiation, in-situ investigation, zeolites, carbon nano tubes, lithium ion battery
  • Lecture (Conference)
    Seminarvortrag an der TU BA Freiberg, 03.05.2010, Freiberg, Germany

Publ.-Id: 14787 - Permalink

In-situ investigations at ROBL-MRH
Baehtz, C.; von Borany, J.; Wirth, C. T.; Bayer, B. C.; Hofmann, S.;
The last few years have seen an increasing interest in in-situ investigations using different diffraction methods. This is one of the main applications of the Material Research Station of the Rossendorf Beamline (ROBL) at the ESRF. The beamline operates with a monochromatic beam in the energy range of 6 to 36 keV and an energy resolution of ΔE/E of 5*10-4. Equipped with a six circle goniometer, different high temperature chambers can be mounted and various diffraction experiments can be performed, e.g. under controlled reaction conditions. A detector bank behind the goniometer allows the use of additional heavy weight detectors. One field of interest is the synthesis of carbon nanotubes (CNT) by chemical vapor deposition. Here, CNTs were grown from iron nanoparticles acting as the catalyst. The particles were formed by annealing Fe thin films with thicknesses ranging from 1-10 nm. The Fe films were evaporated on Si substrates covered with a SiO2 or Al2O3 buffer layer respectively. The splitting was initiated by annealing the initial Fe films at a temperature of up to 760°C in an Argon/Hydrogen atmosphere at ~200 mbar. The reducing atmosphere also removed initially amorphous iron oxide layers. The splitting temperature depends on the buffer layer, and the particle size of the formed nanocrystals depends on the initial film thickness of the pristine material. Adding acetylene (C2H2) to the gas stream initiated CNT-growth. Two different reaction pathways were observed. A very high α/γ iron ratio at high temperature under reducing atmosphere led to the formation of iron carbide when acetylene is added. If the ratio is around 1, no carbide was observed during CNT synthesis. SEM images show a comparable yield of CNTs in both scenarios. Therefore, the catalytic activity of iron carbide in this process is doubtful [1]. The influence of the buffer layer will be discussed. Thick Ni films (>170 nm) can be used to synthesize graphene also by chemical vapour deposition [2]. Compared with the usual increase of the lattice parameter with temperature due thermal expansion (measured at 5*10-6 mbar), an unusual increase of the the lattice parameter is observed when acetylene is introduced (at 2*10-3 mbar). Also, Rietveld refinement does not reveal any structural changes. This effect can only be explained by cracking of the acetylene molecules on the surface and subsequent carbon storage on interstitials. Upon cooling to room temperature, the differences in lattice parameter are negligible. These examples show that in-situ investigations are a powerful and versatile tool to monitor the deposition of nanosized materials from chemical processes.
Keywords: synchrotron radiation, carbon nano tubes
  • Lecture (Conference)
    12th European Powder Diffraction Conference, 27.-30.08.2010, Darmstadt, Germany

Publ.-Id: 14786 - Permalink

Interstitial nitrogen induced decomposition of austenitic stainless steel
Martinavičius, A.; Abrasonis, G.; Möller, W.;
The nature of the S phase in austenitic stainless steel (ASS) produced by incorporation of large amounts of nitrogen is investigated. The S phase has been produced by plasma nitriding of AISI 304L ASS at 400 °C for 30 h. The S phase structure was studied using a combination of global (X-ray diffraction (XRD), nuclear reaction analysis, glow discharge optical emission spectroscopy) and local (Conversion Electron Mössbauer, X-ray absorption near edge structure, extended X-ray absorption fine structure (EXAFS) spectroscopies) probe techniques. This combination of analytical methods allows direct comparison of the data obtained from atomic up to macroscopic levels. The results show that Fe, Cr and Ni have different local chemical environments: Cr is very similar to CrN, Fe is in a phase similar to Fe4N, while Ni stays metallic. The N coordination is by a factor of 3 higher around than around Fe while negligible around Ni. Three lattice parameters for Fe, Cr and Ni, and a large disorder have been detected by EXAFS analysis. None of these phases could be identified by XRD, except a set of broad peaks which are commonly attributed to the supersaturated nitrogen solid solution in the literature. It is suggested that the incorporation of interstitial nitrogen destabilizes homogeneous distribution of ASS constituents and leads to the segregation of elements with the zones rich in Cr and Ni being small and coherent with the Fe-rich matrix. The data provide strong evidence that the decomposition of the nitrogen saturated ASS is of spinodal nature. The findings of this work on S phase microstructure are correlated to mechanical, magnetic and electrochemical properties.
  • Lecture (Conference)
    Interaction'2010 "Radiation interaction with material and its use on technologies 2010", 20.09.10, Kaunas, Lithuania

Publ.-Id: 14785 - Permalink

In-situ Thin Film and Nano Structure Characterization at ROBL
Baehtz, C.; Jeutter, N.; Grenzer, J.; von Borany, J.;
The last few years have seen an increasing interest in in-situ investigations on thin filmor nano structured systems. The advantages of these methods are clear: The (x-ray)investigations are done at the time of the phase or structure formation. Misleading results of ex-situ investigation due to altering or decomposition of the sample were avoided, metastable intermediate states were observed and additionally these experiments are less time consuming.The presented experiments were carried out at Material Research Station of the instrument BM20 at ESRF that is operated by the Forschungszentrum Dresden- Rossendorf. Our experimental station focuses on in-situ studies using different X-Ray diffraction and scattering methods in the energy range of 6 to 30 keV. The experiments can be combined with XRF and electrical resistivity measurements on demand. Two different topics of synthesis and processing are given. First, results on the formation of isolated Ge nano particles with well defined size by disproportion of germanium oxides in a silicondioxid matrix at higher temperatures of corresponding multilayer system were presented. Such materials are potential candidates for solar cells, extending the working spectral range for energy conversion. The size and ordering of the Ge nano crystallite can be controlled by the layer thicknesses as well as growth and annealing temperatures. Different in-situ growth techniques like reactive DC magentron sputtering of Si and RF- sputtering of SiO2 are compared. Secondly, the phase behavior of different metal catalyst onto different buffer layers for the carbon nanotube and graphene synthesis will be shown and discussed. Hereby diffraction experiments under controlled and reactive atmosphere were performed. As shown by in-situ investigations process were characterized on-line and structural as well as functional properties are correlated directly with each other. This increases the comprehension of synthesis and processing of functional materials.
Keywords: synchrotron radiation, in-situ diffraction, magnetron sputtering
  • Lecture (Conference)
    Materials Science and Engineering 2010, 24.-26.08.2010, Darmstadt, Germany

Publ.-Id: 14784 - Permalink

Effects of volume mismatch and electronic structure on the decomposition of ScAlN and TiAlN solid solutions
Höglund, C.; Alling, B.; Birch, J.; Beckers, M.; Persson, P. O. Å.; Baehtz, C.; Czigány, Z.; Jensen, J.; Hultman, L.;
Thin solid films of metastable rocksalt structure (c-) Sc1−xAlxN and Ti1−xAlxN were employed as model systems to investigate the relative influence of volume mismatch and electronic structure driving forces for phase separation. Reactive dual magnetron sputtering was used to deposit stoichiometric Sc0.57Al0.43N (111) and Ti0.51Al0.49N (111) thin films, at 675 °C and 600 °C, respectively, followed by stepwise annealing to a maximum temperature of 1100 °C. Phase transformations during growth and annealing were followed in situ using x-ray scattering. The results show that the as-deposited Sc0.57Al0.43N films phase separate at 1000–1100 °C into nonisostructural c-ScN and wurtzite structure (w-) AlN, via nucleation and growth at domain boundaries. Ti0.51Al0.49N, however, exhibits spinodal decomposition into isostructural coherent c-TiN and c-AlN, in the temperature interval of 800–1000 °C. X-ray pole figures show the coherency between c-ScN and w-AlN, with AlN(0001)|| ScN(001) and AlN(01-10)|| ScN(1-10). First-principles calculations of mixing energy-lattice spacing curves explain the results on a fundamental physics level and open a route for design of novel metastable pseudobinary phases for hard coatings and electronic materials.
Keywords: magnetron sputtering, synchrotron radiation

Publ.-Id: 14783 - Permalink

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