Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33413 Publications

Interaction of U(VI) with Some Bioligands or the Influence of Different Functional Groups on Complex Formation

Frost, L.; Osman, A. A. A.; Geipel, G.; Viehweger, K.; Moll, H.; Bernhard, G.
U(VI) released anthropogenically, e.g. through mining activities, can be accumulated for instance in plants and consequently can enter further parts of the food chain. Hence it is of crucial importance to study the interaction of U(VI) with cellular ligands, like glutathione, uric acid and benzoic acid. Glutathione, the most abundant thiol compound of a cell, has a well known affinity for heavy metal ions. It is a precursor for phytochelatin synthesis and thus also a model substance for the study on U(VI) phytochelatin interaction. Uric acid (UA) was investigated as a further ligand being potentially capable of chelate formation with U(VI). It is present e.g. in bio-fluids such as urine and sweat. Benzoic acid occurs naturally free and bound as benzoic acid esters in many plant and animal species. Furthermore it is a model ligand to study the interaction with bacterial siderophores and humic acids.
UV-vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS) were applied to investigate complex formation between U(VI) and glutathione, uric acid and benzoic acid. Additionally one of the four major potential binding sites of glutathione, the thiol group, was blocked by derivatization to assess the coordination chemistry more detailed.
In the U(VI)-glutathione system a 1:1 complex with a large stability constant of 39.07 ± 0.15 (at zero ionic strength) could be identified. On the contrary, in the U(VI)-urate and -benzoic acid systems a comparably weak complexation was found.
What are the structure-related reasons for such a considerable discrepancy in complex stability? Investigating the interaction of U(VI) with glutathione-S-conjugates, no decrease in complex stability in comparison to U(VI) complexation by glutathione was found. Thus here a significant involvement of the thiol group in coordination can be excluded. Since benzoic acid offers one carboxyl functionality but exhibits a very weak U(VI) coordination, for U(VI) complexation by glutathione a chelate-like coordination with an involvement of at least one carboxyl functionality can be assumed. Since uric acid coordinates as a bidentate ligand and is suggested to undergo a chelation with U(VI) as well, specifically by its 7-amine and 6-carbonyl group, it follows that chelate formation must not necessarily result in strong complexation.
In general, these results contribute to a better understanding of the intricate U(VI) interactions in biological systems on a molecular level.
Keywords: U(VI), Glutathione, Uric Acid, Benzoic Acid, Complexation, UV-vis spectroscopy, TRLFS
  • Contribution to proceedings
    Uranium Mining and Hydrogeology VI, 18.-22.09.2011, Freiberg, Deutschland
    The New Uranium Mining Boom, Berlin: Springer, 978-3-642-22121-7, 595-606
  • Lecture (Conference)
    Uranium Mining and Hydrogeology VI, 18.-22.09.2011, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15267
Publ.-Id: 15267


The geochemical fate of Se(IV) in the Boom Clay system - XAS based solid phase speciation

Breynaert, E.; Scheinost, A.; Dom, D.; Rossberg, A.; Vancluysen, J.; Gobechiya, E.; Kirschhock, C.; Maes, A.
For more than 30 years the Boom Clay formation is studied as a reference host formation for methodological research concerning clay-based geological disposal of HLRW in Belgium and Europe. Boom Clay provides good sorption capacity, very low permeability and chemically reducing conditions due to the anoxic conditions and the presence of pyrite and siderite. Performance Assessment calculations have indicated Se79 (t1/2 = 2.95×105 y) to be one of the critical radionuclides for the geological disposal of HLRW [1]. Aqueous selenite [Se(+IV)] and selenate [Se(+VI)] are the dominant species in mildly and strongly oxidizing environments. Under reducing conditions the solubility of Se is theoretically controlled by the formation of sparsely soluble selenium phases such as elemental Se or transition metalselenide salts (e.g. FeSe or FeSe2) [2, 3]. Slow kinetic reactions between the different redox states have been observed [4] and proposed to explain different redox phases observed within a single reducing environment. Se oxyanions, such as SeO4 2- and SeO32-, are generally considered as the most mobile forms of Se [5] and their migration through Boom Clay thus is considered as “worst case scenario”. In order to assess their long-term fate it is imperative to understand the influence of different geochemical phases present in the Boom Clay matrix on selenium speciation and mobility. A multidisciplinary approach combining long-term batch sorption experiments with linear combination XANES and ITFA-based EXAFS analysis on different fractions isolated from Boom Clay batch systems equilibrated with Se(IV), identified Se0 as the dominant in situ solid phase speciation of Se in Boom Clay conditions.
[1] SAFIR-2, 2001. Brussels, Belgium. p. 288. [2] Breynaert, E. et al., ES&T. 42 (10): p. 3595. [3] Scheinost, A.C. et al., J. Contam. Hydrol. 102 p. 228. [4] Masscheleyn, P.H. et al., ES&T. 24 (1): p. 91. [5] Elrashidi, M.A. et al., Soil Science 144 (2): p. 141.
Keywords: selenium redox Boom clay
  • Lecture (Conference)
    Goldschmidt Conference, 13.06.2010, Knoxville, Tennessee, USA
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 74(2010)12, A122

Permalink: https://www.hzdr.de/publications/Publ-15266
Publ.-Id: 15266


Ultraschnelle Elektronenstrahl-Röntgencomputertomographie als Verfahren zur zerstörungsfreien Qualitätskontrolle

Pöpping, U.; Barthel, F.; Tietze, H.; Hampel, U.
Qualitätskontrollen von Nahrungsmitteln haben eine besondere Bedeutung sowohl zur Sicherstellung eines unbedenklichen Verzehrs als auch zur Feststellung der Güte. Neben der Untersuchung von äußeren Qualitätsmerkmalen sowie chemisch-biologischen Analysen spielt dabei auch die Beschaffenheit im Inneren eine wesentliche Rolle. Die Untersuchung hier kann aber in vielen Fällen nur in Stichproben erfolgen, da das Untersuchungsobjekt dazu zerstört werden muss. Zudem ist die Qualitätsprüfung in der Regel auch nur manuell möglich.

Am Institut für Sicherheitsforschung im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) wurde eine ultraschnelle Elektronenstrahl Röntgencomputertomographie entwickelt. Hierbei handelt es sich um ein bildgebendes Messverfahren, bei dem von einem Untersuchungsobjekt bis zu 7.000 Schnittbilder pro Sekunde bei einer räumlichen Auflösung von ca. 1 mm erzeugt werden können. Dabei wird die für die Rekonstruktion von überlagerungsfreien Schnittbildern benötigte Aufnahme von Durchstrahlungsprojektionen aus unterschiedlichen Blickwinkeln nicht durch die mechanische Drehung von Objekt oder Messsystem erreicht, stattdessen wird ein Elektronenstrahl, der den die Röntgenstrahlung emittierenden Brennfleck auf einem ringförmigen Target erzeugt, elektronisch abgelenkt. Auf diese Weise wird die Untersuchung einer großen Stückzahl von Untersuchungsobjekten innerhalb kurzer Zeit möglich.

Erste Untersuchungen haben die prinzipielle Eignung der - ursprünglich für die Messung in mehrphasigen Strömungen entwickelten - Technologie auch zur zerstörungsfreien Qualitätskontrolle gezeigt. Es konnte für verschiedenste Untersuchungsobjekte wie beispielsweise Wallnüsse, Esskastanien aber auch Paprikaschoten die Rekonstruktion des Inneren in einer prinzipiell für die Qualitätssicherung mehr als ausreichender Güte gezeigt werden.

Die Ergebnisse der ersten Studien lassen auf ein großes Potenzial dieser Technologie für dieses Anwendungsfeld schließen. Allerdings liegt die Expertise am HZDR vor allem in der Entwicklung solcher Messsysteme und nicht in der fachlichen Bewertung von Qualitätsmerkmalen von Nahrungsmitteln. Weitere Forschungs- und Entwicklungsarbeiten, die gemeinsam mit einer Forschungseinrichtung mit notwendiger Expertise auf dem Gebiet der Landwirtschaft bzw. des Gartenbaus angestrebt werden, sind vor allem zur erheblichen Verkürzung der notwendigen Rekonstruktionszeit sowie zur Automatisierung dieser Technologie und des Prozesses selbst notwendig.
Keywords: Ultrafast X-ray computed tomography, quality inspection
  • Poster
    47. Jahrestagung der Deutschen Gartenbauwissenschaftlichen Gesellschaft (DGG) und des Bundesverbandes der Hochschulabsolventen/Ingenieure Gartenbau u. Landschaftsarchitektur (BHGL), 23.-26.02.2011, Hannover, Deutschland
  • Contribution to proceedings
    47. Jahrestagung der Deutschen Gartenbauwissenschaftlichen Gesellschaft (DGG) und des Bundesverbandes der Hochschulabsolventen/Ingenieure Gartenbau u. Landschaftsarchitektur (BHGL), 23.-26.02.2011, Hannover, Deutschland
    Ultraschnelle Elektronenstrahl-Röntgencomputertomographie als Verfahren zur zerstörungsfreien Qualitätskontrolle, Hannover: BHGL & DGG, 1613-088X

Permalink: https://www.hzdr.de/publications/Publ-15265
Publ.-Id: 15265


Geogases in the Kaapvaal Craton – Origin and modes of transport

Lippmann-Pipke, J.; Sherwood Lollar, B.; Niedermann, S.; Stroncik, N. A.; Naumann, R.; van Heerden, E.; Onstott, T. C.; Erzinger, J.; Zimmer, M.; Kujawa, C.; Boettcher, M.; Bester, A.; Moller, H.; Reches, Z.
Introduction The deep gold mines of the Witwatersrand Basin, South Africa, have gained recent attention because of reports of deep microbial communities persisting to depths of >3 kilometers - an exotic outpost of the Earth's deep biosphere [1,2]. Prerequisites of such investigations are studies on the age of the deep fracture water [3] and the origin of associated abiogenic CH4- [4] and H2-rich gases [5]. Here we report about insights obtained from two new gas data sets (I, II) with respect to the dynamic of the ultra-deep fluid system [6,7].
Methods (I) The isotopic composition of neon dissolved in deep fracture water and in fluid inclusions of quartz host rock was analyzed, and the results correlated with the isotopic signatures of the biogenic and abiogenic H2- and CH4-rich sample aliquots. (II) In the other project the geogas composition of the free gas was monitored by means of a mass spectrometer and gas sensitive sensors installed just inside the Pretorius Fault Zone at 3.45 km depth in the TauTona Mine. Data from a 4-year observation period are cross-correlated on the minute-by-minute basis with seismic data obtained from a 3-dimensional array of highly sensitive seismometers.
Results (I) Highest ever observed 21Ne/22Ne ratios combined with an anomalous 21Ne/22Ne production ratio imply that the dissolved neon is a 2 Ga metamorphic signal stored in fluid inclusions and accumulating in fracture water since geological times as a result of water rock reaction processes. (II) Geogas concentration variations (4He, H2, CH4, CO2) strongly correlate with seismic signals resulting from mining related blasts and induced earthquakes in the TauTona Mine. The fracture gas permeability of ~ 5*10e-10 m² is estimated on the basis of observed gas flux rates.
Conclusion (I) 21Ne/22Ne ratios may serve as search proxy for regions of the Archean Earth's crust where investigations of the deep biosphere might be focused. (II) Methodological improvements enabled the simultaneous gas geochemical and seismic signal recording in the world deepest operating mine, reflecting the near-field at earthquake focal depths.

[1] Lin et al., Science 2006, 314(5798): 479-482; [2] Chivian et al., Science 2008, 322(5899): 275-278 ; [3] Lippmann et al., GCA 2003, 67(23): 4597-4619; [4] Sherwood Lollar et al., Chem. Geol. 2006, 226(3-4): 328-339; [5] Lin et al., GGG 2005, 6: Q07003; [6] Lippmann-Pipke et al. Chem. Geol., submitted; [7] Lippmann-Pipke et al., Appl. Geol., submitted
  • Invited lecture (Conferences)
    New Horizons for International Investigations into Carbon Cycing in the Deep Crustal Biosphere, 18.-23.01.2011, Bloemfontein, South Africa

Permalink: https://www.hzdr.de/publications/Publ-15264
Publ.-Id: 15264


Vibrational characteristics of outer-sphere surface complexes: example of sulfate ions adsorbed onto metal (hydr)oxides

Müller, K.; Lefèvre, G.
The vibrational characteristics of outer-sphere complexes of sulfate at several mineral oxide – water interfaces were investigated by in situ attenuated total reflection Fourier transform infrared (ATR FT-IR) spectroscopy. In the IR spectra obtained from surface outer-sphere complexes only one peak of the antisymmetric stretching vibrational mode υ3 similar to the free sulfate ion SO42− in aqueous solution is observed. However, on the investigated (hydr)oxide surfaces of Al3+, Ti4+, Fe2+/3+, Cr3+, Ni2+, Ce4+, Cu2+, Y3+, Zn2+, and Nd3+ a shift of up to 14 cm−1 was found, correlated to the polarizing power of the metal cations. A high polarizing power was found to result in a stronger shift of υ3 compared to the aqueous SO42− ion. Furthermore, the impact of the metal oxide structure on the characteristics of the formed outer-sphere complex was negligible, since different Al and Fe (hydr)oxides did not show any changes in the respective IR spectra. A variation of ionic strength (1 – 10-4 M) and pH (6.8 – 3.1) during the formation of SO42− outer-sphere complexes on g-Al2O3 showed that those changes directly influence the surface potential, without modifying the geometry of the outer-sphere complex.

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Permalink: https://www.hzdr.de/publications/Publ-15263
Publ.-Id: 15263


Synthesis and biological evaluation of new [Tc(N)(PS)]-based mixed-ligand compounds useful in design of target-specific radiopharmaceuticas: the 2-methoxyphenylpiperazine dithiocarbamate derivatives as example

Bolzati, C.; Salvarese, N.; Carta, D.; Refosco, F.; Dolmella, A.; Pietzsch, H.-J.; Bergmann, R.; Bandoli, G.
This study presents the first application of a general procedure based on the use of the [Tc(N)Cl(PS) (PPh3)] species (PS is an alkyl phosphinothiolate ligand) for the preparation of Tc(N) target-specific compounds. [Tc(N)Cl(PS)(PPh3)] selectively reacts with an appropriate dithiocarbamate ligand (S^Y) to give [Tc(N)(PS)(S^Y)] compounds. 1-(2-Methoxyphenyl)piperazine, which displays a potent and specific affinity for 5HT1A receptors,
was selected as a functional group and conjugated to the dithiocarbamate unit through different spacers (Ln). [99mTc(N)(PS)(Ln)] complexes were prepared in high yield (more than 90%). The chemical identity of 99mTc complexes was determined by high performance liquid chromatography comparison with the corresponding 99gTc complexes. All complexes were found to be inert toward transchelation with an excess of glutathione and cysteine. No notable biotransformation of the native compound into different species by the in vitro action of the serum and liver enzymes was shown. Nanomolar affinity for the 5HT1A receptor was obtained for [99mTc(N)(PSiso)L3] (IC50 = 1.5 nM); a reduction of the affinity was observed for the other complexes as a function of the shortening of the alkyl chain interposed between the dithiocarbamate and the pharmacophore. Negligible brain uptake was found from in vivo distribution data of [99mTc(N)(PSiso)L3]. The key finding of this study is that the complexes maintained good affinity and selectivity for 5HT1A receptors, and the IC50 value for [99gTc(N)(PSiso)L3] being comparable to the IC50 value found for WAY 100635. This result confirmed the possibility of preparing [99mTc(N)(PS)]-based targetspecific compounds without affecting the affinity and selectivity of the bioactive molecules for the corresponding receptors.
Keywords: Technetium, Phosphinothiolate, Dithiocarbamate, 5HT1A receptor, Brain

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Permalink: https://www.hzdr.de/publications/Publ-15262
Publ.-Id: 15262


[18F]1-(3-fluoropropyl)piperazines as model compounds for the radiofluorination of pyrido[2,3-d]pyrimidines

Grosse-Gehling, P.; Wuest, F. R.; Peppel, T.; Köckerling, M.; Mamat, C.
The visualization of cyclin-dependent kinases (CDKs), which are overexpressed in multiple tumor types, with radiolabeled CDK inhibitors by means of positron emission tomography in vivo is a promising approach for tumor imaging.
Pyrido[2,3-d]pyrimidines belong to a class of inhibitors, which bind with high affinity to CDK4 and CDK6. [18F]1-(3-Fluoropropyl)-4-(4-nitrophenyl)piperazine and [18F]1-(3-fluoropropyl)-4-(4-nitropyridin-3-yl)piperazine represent
structural elements of the appropriate CDK inhibitors and were therefore chosen as model compounds for the incorporation of fluorine-18 into pyrido[2,3-d]pyrimidines. Three methods are known for the preparation of tertiary [18F]3-fluoropropyl-amines:
1) the direct substitution of a good leaving group,
2) the two-step reaction synthesizing a [18F]3-fluoropropyl intermediate,
and 3) the utilization of aziridinium or azetidinium salts. In general, radiofluorinations using azetidinium salts lead to
excellent radiochemical yields in short periods of time. For these reasons we developed a synthesis route to tosylated piperazine precursors and establish a radiolabeling approach based on the incorporation of fluorine-18 into open-chained
tosylates as well as the respective azetidinium spiro compounds to yield the desired radiofluorinated piperazines successfully.
Keywords: Radiofluorination, Spiro compounds, CDK inhibitor, Pyrido[2,3-d]pyrimidines

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Permalink: https://www.hzdr.de/publications/Publ-15261
Publ.-Id: 15261


Radioiodination of humic substances

Franke, K.; Kupsch, H.
The known IODO-GEN™-method [1] was adapted for radiolabeling of humic and fulvic acids with 131I. The water insoluble oxidizing agent 1,3,4,6tetrachloro-3α,6α-diphenylglycoluril (IODO-GEN™) forms an iodous ion species (I+), which undergoes an electrophilic I/H-substitution on aromatic moieties of the humic and fulvic acids. This method offers mild conditions with a lesser extent of oxidative alterations of the target molecule, accompanied by an easy handling due to the virtual water-insolubility of the oxidizing agent. The method was optimized and different techniques were tested for the purification of the radioiodinated humic material. The yield of the labeling procedure varies between 45 and 75% depending on the provenance of the humic material and the applied purification method. A specific activity up to 40 MBq/mg was achieved. Furthermore, the known inherent photo-susceptibility of the iodinated humic substance and the influence of reducing agents were verified. An additional release of 131I up to 20% and up to 35%, respectively were observed.

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Permalink: https://www.hzdr.de/publications/Publ-15260
Publ.-Id: 15260


Twin boundary motion and magnetic domain distribution investigated by optical polarization microscopy

Neudert, A.; McCord, J.
An overview of optical studies of magnetic and structural transformation in magnetic shape memory materials is given. The magnetic domain behavior and the motion of twin boundaries in single crystalline bulk samples of the shape memory alloy NiMnGa are investigated by optical polarization microscopy and magnetic indicator film technique. During stress induced twin boundary motion the magnetization reversal takes place by rotation of magnetization, leading to a total rearrangement of the magnetic domain distribution. Time-resolved studies of twin boundary motion induced by pulsed magnetic fields show that the distance traveled by the twin boundary is enhanced with increasing sample temperature. An overview of these and complementary experiments and the obtained results will be given.
Keywords: magnetic shape memory alloy, optical polarization microscopy, time-resolved microscopy
  • Invited lecture (Conferences)
    International Conference on Ferromagnetic Shape Memory Alloys, 18.-22.07.2011, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15259
Publ.-Id: 15259


The influence of biofilms on the migration of uranium in acid mine drainage (AMD) waters

Krawczyk-Bärsch, E.; Lünsdorf, H.; Arnold, T.; Brendler, V.; Eisbein, E.; Jenk, U.; Zimmermann, U.
The uranium mine in Konigstein (Germany) is currently in the process of being flooded. Huge mass of Ferrovum myxofaciens dominated biofilms are growing in the acid mine drainage (AMD) water as macroscopic streamers and as stalactite-like snottites hanging from the ceiling of the galleries. Microsensor measurements were performed in the AMD water as well as in the biofilms from the drainage channel on-site and in the laboratory. The analytical data of the AMD water was used for the thermodynamic calculation of the predominance fields of the aquatic uranium sulfate (UO2SO4) and UO2++ speciation as well as of the solid uranium species Uranophane [Ca(UO2)(2)(SiO3OH)(2)center dot 5H(2)O] and Coffinite [U(SiO4)(1-x)(OH)(4x)], which are defined in the stability field of pH>4.8 and Eh < 960 mV and pH>0 and Eh<300 mV, respectively. The plotting of the measured redox potential and pH of the AMD water and the biofilm into the calculated pH Eh diagram showed that an aqueous uranium(VI) sulfate complex exists under the ambient conditions. According to thermodynamic calculations a retention of uranium from the AMD water by forming solid uranium(VI) or uranium(IV) species will be inhibited until the pH will increase to >4.8. Even analysis by Energy-filtered Transmission Electron Microscopy (EF-TEM) and electron energy loss spectroscopy (EELS) within the biofilms did not provide any microscopic or spectroscopic evidence for the presence of uranium immobilization. In laboratory experiments the first phase of the flooding process was simulated by increasing the pH of the AMD water. The results of the experiments indicated that the F. myxofaciens dominated biofilms may have a substantial impact on the migration of uranium. The AMD water remained acid although it was permanently neutralized with the consequence that the retention of uranium from the aqueous solution by the formation of solid uranium species will be inhibited.
Keywords: AMD water, Uranium, Biofilm, Ferrovum myxofaciens, microsensor measurement, thermodynamically calculation

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Permalink: https://www.hzdr.de/publications/Publ-15258
Publ.-Id: 15258


Nuclear Astrophysics and Nuclear Transmutation

Wagner, A.
Albeit their quite disjoint research history, the research areas of nuclear astrophysics and transmutation of nuclear waste show striking similarities resembling the same basics in nuclear physics. In both fields, the electromagnetic response function of nuclei and the nuclear level density play a key role in the explosive stellar burning as in the reduction of long-lived actinides produced in nuclear power plants. In the talk, I will present recent results on the electromagnetic strength function in medium-mass nuclei studied at the superconducting electron linear accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf. Neutron-induced reactions on various nuclei, like neutron capture, neutron inelastic scattering are studied at a new neutron time-of-flight facility, as well.
Keywords: nuclear astrophysics transmutation waste electromagnetic response function nuclei level density long-lived actinides neutron capture inelastic scattering nELBE
  • Invited lecture (Conferences)
    Kernphysikalisches Kolloquium, 27.01.2011, Bonn, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15256
Publ.-Id: 15256


Recombinant S-layer production induces disordered cell division in E. coli filaments

Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.
The rod-shaped bacterium Escherichia coli is one of the best studied microorganism with a size of 1.1-1.5 µm x 2.0-6.0 µm. We used E. coli BL21(DE3), one of the most widely used host in genetic engineering, for heterologous expression of surface layer (S-layer) proteins to enable a fast and efficient protein production.
S-layer are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelopes. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as filter materials or patterning structures in nanotechnology.
Surprisingly, the heterologous expression of S-layer proteins of the uranium mining waste pile isolate Lysinibacillus sphaericus JG-A12 induced drastic morphological changes of E. coli BL21(DE3) single cells to filaments and tubes enclosing single cells of >100 µm in length. The S-layer expressing E. coli cultures reached a high optical density and cells showed a high viability as well as strong expression of S-layer proteins. The drastically changed cell morphology was investigated by light microscope, AFM and TEM. Analyses with S-layer-GFP expressing cells, which were stained with DAPI and membrane stain, present a disordered cell division process. Our results give a new insight in the morphology and the cell division process in E. coli induced by recombinant proteins.

Lederer et al. (2010) Heterologous expression of the surface-layer-like protein SllB induces the formation of long filaments of Escherichia coli consisting of protein-stabilized outer membrane. Microbiology 156,3584-95.
  • Poster
    FEMS (Federation of European Microbiological Societies), 26.-30.06.2011, Geneva, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-15255
Publ.-Id: 15255


Recombinant S-layer production induces disordered cell division in E. coli filaments

Lederer, F.; Günther, T.; Raff, J.; Pollmann, K.
The rod-shaped bacterium Escherichia coli is one of the best studied microorganism with a size of 1.1-1.5 µm x 2.0-6.0 µm. We used E. coli BL21 (DE3), one of the most widely used host in genetic engineering, for heterologous expression of surface layer (S-layer) proteins to enable fast and efficient protein production.
S-layer are proteins which cover the outermost of many prokaryotes and are probably the basic and oldest forms of bacterial envelope. These proteins are mostly composed of protein and glycoprotein monomers and have the ability to self-assemble into two-dimensional arrays on interfaces. Several characteristics like their work as molecular sieve, as virulence factor or the protection of the cell from toxic heavy metal ions make S-layer proteins interesting for their usage as ultrafiltration membranes, drug microcontainers, filter materials or patterning structures in nanotechnology.
Surprisingly, the heterologous expression of S-layer proteins of the uranium mining waste pile isolate Lysinibacillus sphaericus JG-A12 induced drastic morphological changes of E. coli BL21 (DE3) single cells to filaments and single cell enclosing tubes of >100 µm in length. The assumed secretion of tube-stabilizing S-layer proteins was investigated with SDS-PAGE and ß-galactosidase assay. These analyses result in a high S-layer appearance without significant ß-galactosidase activity in the supernatant and the periplasm. The origin and composition of filaments and tubes were analysed by membrane stain studies. We identified that filaments in the exponential growth phase form a continuous intracellular space without partitioning. To investigate the mechanism of filament and tube formation we analyzed GFP/S-layer expressing E. coli with DAPI-stain. The staining showed >50 µm long DNA-fibres that cross the filaments and “DNA-free” areas, the latter exhibiting strong GFP-expression. Our results point to a disordered cell division in E. coli filaments which is effected by recombinant S-layer expression.

[1] Lederer et al. (2010) Heterologous expression of the surface-layer-like protein SllB induces the formation of long filaments of Escherichia coli consisting of protein-stabilized outer membrane. Microbiology 156,3584-95.
  • Poster
    VAAM (Jahrestagung der Vereinigung für Allgemeine und Angewandte Mirkobiologie), 03.-06.04.2011, Karlsruhe, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15254
Publ.-Id: 15254


Bulk diffusion induced structural modifications of carbon-transition metal nanocomposite films

Berndt, M.; Abrasonis, G.; Kovacs, G. J.; Krause, M.; Munnik, F.; Heller, R.; Kolitsch, A.; Möller, W.
The influence of transition metal (TM=V,Co,Cu) type on the bulk diffusion induced structural changes in carbon:TM nanocomposite films is investigated. The TMs have been incorporated into the carbon matrix via ion beam co-sputtering, and subsequently the films have been vacuum annealed in the temperature range of 300-700°C. The structure of both the dispersed metal rich and the carbon matrix phases has been determined by a combination of elastic recoil detection analysis, X-ray diffraction, transmission electron microscopy, and Raman spectroscopy. The as-grown films consist of carbidic (V and Co) and metallic (Cu) nanoparticles dispersed in the carbon matrix. Thermal annealing induces surface segregation of Co and Cu starting at >=500°C, preceded by carbide-metal transformation of Co-carbide nanoparticles at ~300°C. No considerable morphological changes occur in C:V films. In contrast to the surface diffusion dominated regime where all the metals enhance the six-fold ring clustering of C, in the bulk diffusion controlled regime only Co acts as a catalyst for the carbon graphitization. The results are consistent with the metal-mediated crystallization mechanism in the C:Co films. The results are discussed on the basis of the metal-carbide phase stability, carbon solubility in metals or their carbides and interface species.

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Permalink: https://www.hzdr.de/publications/Publ-15253
Publ.-Id: 15253


The Dresden High Magnetic Field Laboratory (HLD) - a User Facility for Advanced Pulsed-Field Experiments

Wosnitza, J.; Herrmannsdörfer, T.; Zherlitsyn, S.; Zvyagin, S.
es liegt kein Abstract vor.
  • Invited lecture (Conferences)
    Physical Phenomena at High Magnetic Fields (PPHMF VII), 04.-08.12.2010, Tallahassee, Florida, USA

Permalink: https://www.hzdr.de/publications/Publ-15252
Publ.-Id: 15252


The role of water H-bond imbalances in B-DNA substate transitions and peptide recognition revealed by time-resolved FTIR spectroscopy

Khesbak, H.; Savchuk, O.; Tsushima, S.; Fahmy, K.
The conformational substates BI and BII of the phosphodiester backbone in B-DNA are thought to contribute to DNA flexibility and protein recognition. We have studied by rapid scan FTIR spectroscopy the isothermal BI-BII transition on its intrinsic time scale. Correlation analysis of IR absorption changes occurring within seconds after a reversible incremental growth of the DNA hydration shell identifies water populations w1 (PO2--bound) and w2 (non-PO2--bound) exhibiting weaker and stronger H-bonds, respectively, than those dominating in bulk water. The BII substate is stabilized by w2. The water H-bond imbalance of 3-4 kJ mol-1 is equalized at little enthalpic cost upon formation of a contiguous water network (at 12-14 H2O molecules per DNA phosphate) of reduced n(OH) band width. In this state, hydration water cooperatively stabilizes the BI conformer via the entropically favored replacement of w2-DNA interactions by additional w2-water contacts, rather than binding to BI-specific hydration sites. Such water rearrangements contribute to the recognition of DNA by indolicidin, an antimicrobial 13-mer peptide from bovine neutrophils which, despite little intrinsic structure, preferentially binds to the BI conformer in a water-mediated induced fit. The FTIR spectra resolve sequential steps leading from PO2--solvation to substate transition and eventually to base stacking changes in the complex. In combination with CD-spectral titrations, the data indicate that in the absence of a bulk aqueous phase, as in molecular crowded environments, water relocation within the DNA hydration shell allows for entropic contributions similar to those assigned to water upon DNA ligand recognition in solution.
Keywords: indolicidin netropsin DNA conformation hydration infrared 2D correlation
  • Journal of the American Chemical Society 133(2011), 5834-5842

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Publ.-Id: 15251


Fermi surface of the electron-doped cuprate superconductor Nd2−xCexCuO4 probed by high-field magnetotransport

Kartsovnik, M. V.; Helm, T.; Putzke, C.; Wolff-Fabris, F.; Sheikin, I.; Lepault, S.; Proust, C.; Vignolles, D.; Bittner, N.; Biberacher, W.; Erb, A.; Wosnitza, J.; Gross, R.
We report on the study of the Fermi surface of the electrondoped cuprate superconductor Nd2−xCexCuO4 by measuring the interlayer magnetoresistance as a function of the strength and orientation of the applied magnetic field. We performed experiments in both steady and pulsed magnetic fields on high-quality single crystals with Ce concentrations of x = 0.13–0.17. In the overdoped regime of x > 0.15, we found both semiclassical angledependent magnetoresistance oscillations (AMROs) and Shubnikov–de Haas (SdH) oscillations. The combined AMROs and SdH data clearly show that the appearance of fast SdH oscillations in strongly overdoped samples is caused by magnetic breakdown. This observation provides clear evidence for a reconstructed multiply connected Fermi surface up to the very end of the overdoped regime at x ~ 0.17. The strength of the superlattice potential responsible for the reconstructed Fermi surface is found to decrease with increasing doping level and likely vanishes at the same carrier concentration as superconductivity, suggesting a close relation between translational symmetry breaking and superconducting pairing. A detailed analysis of the high-resolution SdH data allowed us to determine the effective cyclotron mass and Dingle temperature, as well as to estimate the magnetic breakdown field in the overdoped regime.
  • Open Access Logo New Journal of Physics 13(2011), 015001

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Publ.-Id: 15250


High-field ESR in low-dimensional spin systems

Zvyagin, S. A.
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Einladung an die University of Heraklion and the FORTH (Institut für Forschung und Technologie), 10.-15.05.2010, Heraklion, Greece
  • Invited lecture (Conferences)
    2016 Hefei Conference on Novel Phenomena in High Magnetic Fields, 29.10.-01.11.2016, Hefei, China

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Publ.-Id: 15248


Implementation and workflow for PET monitoring of therapeutic ion irradiation: a comparison of in-beam, in-room, and off-line techniques

Shakirin, G.; Braess, H.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Priegnitz, M.; Enghardt, W.
Abstract
An independent assessment of the dose delivery in ion therapy can be performed using positron emission tomography (PET). For that a distribution of positron emitters which appear as the result of interaction between ions of the therapeutic beam and the irradiated tissue is measured during or after the irradiation. Three concepts for PET monitoring implemented in various therapy facilities are considered in this paper. The in-beam PET concept relies on the PET measurement performed simultaneously to the irradiation by means of a PET scanner which is completely integrated into the irradiation site. The in-room PET concept allows measurement immediately after irradiation by a standalone PET scanner which is installed very close to the irradiation site. In the off-line PET scenario themeasurement is performed by means of a standalone PET/CT scanner 10–30 min after the irradiation. These three concepts were evaluated according to image quality criteria, integration costs, and their influence onto the workflow of radiotherapy. In-beam PET showed the best performance. However, the integration costs were estimated as very high for this modality. Moreover, the performance of in-beam PET depends heavily on type and duty cycle of the accelerator. The in-room PET is proposed for planned therapy 5 Present address: Philips Research, HTC11, 5656 AE Eindhoven, The Netherlands.
0031-9155/
Keywords: in-beam PET, PET monitoring, ion therapy, in-vivo dosimetry

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Publ.-Id: 15247


Infrared/terahertz applications in physical sciences

Schneider, H.
Starting with a brief survey on infrared/THz applications and systems, this talk concentrates on specific research opportunities in physics offered by free-electron lasers (FEL) at infrared/THz wavelengths. Unique properties of FEL radiation are (i) continuous spectral tunability at narrow spectral bandwidth, (ii) high power, (ii) spatial coherence, and (iv) short pulse length. Corresponding experimental techniques include linear, nonlinear/high-field, near-field, and time resolved spectroscopy. After describing the free-electron laser facility FELBE at HZDR, a few recent studies in solid-state physics covering these techniques will be reported.
Keywords: mid-infrared and terahertz (THz) spectroscopy, free-electron laser, semiconductor quantum structures
  • Invited lecture (Conferences)
    Free Electron Laser IR to THz Applications Workshop, 28.01.2011, Bangkok, Thailand

Permalink: https://www.hzdr.de/publications/Publ-15246
Publ.-Id: 15246


A Markov chain model of classified atomistic transition states for discrete kinetic Monte-Carlo simulations

Numazawa, S.; Smith, R.
Classical harmonic transition state theory is considered and applied in discrete lattice cells with hierarchical transition levels. The scheme is then used to determine transitions which can be applied in a lattice-based kinetic Monte Carlo (KMC) atomistic simulation model.
The model results in an effective reduction of KMC simulation steps by utilizing a classification scheme of transition levels for thermally activated atomistic diffusion processes. Thermally activated atomistic movements are considered as local transition events constrained in potential energy wells over certain local time periods. These processes are represented by Markov chains of multi-dimensional Boolean valued functions in three dimensional lattice space.
The events inhibited by the barriers under a certain level are regarded as thermal fluctuations of the canonical ensemble and accepted freely.
Consequently, the fluctuating system evolution process is implemented as a Markov chain of equivalence class objects.
It is shown that the process can be characterized by the acceptance of metastable local transitions.
The method is applied to a problem of Au and Ag cluster growth on a rippled surface. The simulation predicts the existence of a morphology dependent transition time limit from a local metastable to stable state for subsequent cluster growth by accretion. Excellent agreement with observed experimental results is obtained.
Keywords: Kinetic Monte-Carlo
  • Physical Review E 84(2011), 046714

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Publ.-Id: 15245


A population balance approach considering heat and mass transfer - experiments and CFD simulations

Krepper, E.; Beyer, M.; Lucas, D.; Schmidtke, M.
Bubble condensation in sub-cooled water is a complex process, to which various phenomena contribute. Since the condensation rate depends on the interfacial area density, bubble size distribution changes caused by breakup and coalescence play a crucial role.
Experiments on steam bubble condensation in vertical co-current steam/water flows have been carried out in an 8m long vertical DN200 pipe. Steam is injected into the pipe and the development of the bubbly flow is measured at different distances to the injection using a pair of wire mesh sensors. By varying the steam nozzle diameter the initial bubble size can be influenced. Larger bubbles come along with a lower interfacial area density and therefore condensate slower. Steam pressures between 1-6.5 MPa and sub-cooling temperatures from 2 to 6 K were applied. Due to the drop of hydrostatic pressure along the pipe, the saturation temperature falls towards the upper pipe end. This affects the sub-cooling temperature and can even cause re-evaporation in the upper part of the test section. The experimental configurations are simulated with the CFD code CFX using an extended MUSIG approach, which includes the bubble shrinking or growth due to condensation or re-evaporation. The development of the vapour phase along the pipe with respect to vapour void fractions and bubble sizes is qualitatively well reproduced in the simulations. For a better quantitative reproduction, reliable models for the heat transfer at high Reynolds number as well as for bubble breakup and coalescence are needed.
Keywords: two phase flow, experiments, CFD, population balance model, bubble coalescence, bubble breakupo, condensation, evaporation

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Publ.-Id: 15244


Biokinetics, metabolism and PET imaging with Cu-64 and Ga-68 labeled ghrelin analogues in rats

Bergmann, R.; Chollet, C.; Pietzsch, J.; Beck-Sickinger, A. G.; Steinbach, J.
Ghrelin is a gastric peptide involved in food intake control, and growth hormone release. Besides its well-defined orexigenic role, ghrelin is likely involved in tumor development and growth. Therefore, non-invasive imaging agents for determining ghrelin receptors are desirable. However, ghrelin receptors are expressed in low level making detection via imaging difficult. The labeling using activated esters like 4-(F-18-fluoro)benzoyl-succinimide (2) was not possible due to the existence of three primary amino groups per peptide. Therefore, human ghrelin1-28 [Lys16(NODAGA)]-ghrelin1-28 and a short ghrelin inverse agonist NODAGA-KwFwLL-NH2 were synthesised on solid-phase. Subsequently, radiolabeling yielded Cu-64- and Ga-68-NODAGA-peptides in high radiochemical purity (>98%) with a specific activity >10 GBq/Gmol. For basic radiopharmacological characterization biodistribution, small animal PET, and metabolite analysis in arterial blood plasma were carried out in Wistar rats with all 4 radiotracers. The ghrelin analogues were in high amounts taken up by the kidneys. The Cu-64- and Ga-68-NODAGA-KwFwLL-NH2 were for the most part hepathobilliary eliminated. The metabolite analysis showed the well-known des acyl ghrelin as the main metabolite in vivo reaching 90% in blood plasma after one hour. On the other site the NODAGAKwFwLL-NH2 peptides were highly stabile; only 5% metabolites were observed after one hour in rat plasma. Interestingly, the biodistribution and kinetics were similar for the pairs of peptide labeled ether with Cu-64 or Ga-68. This shows the small effect of the different ionization of the Ga-68 (neutral) or Cu-64 (one negative charge) NODAGA complexes on the biodistribution. The blood clearance of these peptides was relative low, with about 50% of starting amount after one hour. The high stability and low blood clearance are important prerequisites for further studies of ghrelin receptor imaging. These results indicate that further in vivo evaluation of radiolabeled ghrelin inverse agonists as potential PET tracers for ghrelin receptors is warranted.

Reference: (1) Holst, B., et al. (2003) High constitutive signaling of the ghrelin receptor--identification of a potent inverse agonist. Mol Endocrinol 17, 2201-10. (2) Bergmann, R., et al. (2002) Biodistribution and catabolism of (18)F-labeled neurotensin(8-13) analogs. Nucl Med Biol 29, 61-72.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057
  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-15243
Publ.-Id: 15243


Dual-labeled Cetuximab-based imaging agent for NIR Fluorescence and PET

Bergmann, R.; Zenker, M.; Walther, M.; Pietzsch, H.-J.; Hofheinz, F.; van den Hoff, J.; Pietzsch, J.; Steinbach, J.
Cetuximab (C225) as a chimeric monoclonal antibody specifically targets the epidermal growth factor receptor (EGFR) that often is overexpressed in human malignancies. This phenotype is associated with tumor aggressiveness, treatment resistance, and biological heterogeneity with potential to bypass the blockade of the EGFR signaling pathways. The aim of this work was to prepare and characterize the C225 for near infrared fluorescence (NIRF) and PET imaging using a X-SIGHT Large Stokes Shift Dye (X-SIGHT 670 LSS Dye) and [64Cu]Cu-NOTA as a prerequisite for combination of both imaging methods. C225 was conjugated with the bifunctional chelator 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bz-NOTA) and the X-SIGHT 670 Large Stokes Shift Dye, TFP Ester (XS670). The EGFR-affinity of the immunoconjugate resulted in 94% versus 100% of the unmodified C225 measured with specific enzyme-linked immunosorbent assay (ELISA) on EGFR-positive tumor cell line A431. C225-SCNBz-NOTA was labeled with 64Cu within 30 min with high radiolabeling yield and radiochemical purity. The [64Cu]Cu-NOTA-C225-XS670 showed high accumulation in xenotransplanted squamous cell carcinoma tumors in mice after 24 hours imaged with small animal PET and NIRF. The comparison of both methods in living animals showed the high signal intensity and accumulation of the probe in tumors; however only PET allowed the quantitative characterization of the probe distribution in vivo. The subsequent whole body cryosectioning of the animals into 40 µm sections permitted the direct comparison of the autoradiograms and NIRF images of the tissue cuts. The quantitative comparison of the autoradiograms and the NIRF images after coregistration of the corresponding images yielded a good correlation of the pixel intensities, but the different geometric resolution did not allow a pixel vise comparison. The NIRF images showed a higher differentiation than the autoradiograms. The dual-labeled C225 demonstrated the higher resolution and comparable concentration values of the antibody distribution in whole body cryosections of tumor bearing mice using the combination of 64Cu-radioluminography and NIRF imaging. The dual labeling of antibodies is a promising tool for quantitative evaluation of the long time distribution in animals using NIRF of cryosections beyond the decay of the radionuclide used.

Acknowledgement: This project was partially supported by FP7 project “GIPIO”, Project Reference: 223057
  • Poster
    2010 World Molecular Imaging Congress, 08.-11.09.2010, Kyoto, Japan

Permalink: https://www.hzdr.de/publications/Publ-15242
Publ.-Id: 15242


Multimodality imaging in preclinical cancer research

Bergmann, R.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    4th Bioscan Imaging Users Meeting (European part), 10.10.2010, Vienna, Austria

Permalink: https://www.hzdr.de/publications/Publ-15241
Publ.-Id: 15241


Identification of transport processes in bioirrigated muddy sediments by [18F]fluoride PET (Positron Emission Tomography)

Roskosch, A.; Lewandowski, J.; Bergmann, R.; Wilke, F.; Brenner, W.; Burchert, R.
In aquatic environments transport processes across the sediment–water interface are intensified by bioirrigating macrozoobenthos. Transport processes caused by Chironomus plumosus larvae dwelling in U-tubes were investigated by dynamic small animal Positron Emission Tomography (PET) with [18F]fluoride. Significant tracer transport from the burrows into the sediment was detected; penetration was deeper at the outlet branch of the burrow than at the inlet branch. Hence, advection plays a significant role in exchange between water in the burrows and muddy sediment.

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Permalink: https://www.hzdr.de/publications/Publ-15240
Publ.-Id: 15240


Small animal PET for evaluation of tumor therapy

Bergmann, R.
kein Abstract verfügbar
  • Lecture (others)
    Oncoray Retreat, 28.01.2010, Bautzen, D

Permalink: https://www.hzdr.de/publications/Publ-15239
Publ.-Id: 15239


Biodistribution, -kinetics, metabolic stability, and imaging with radioactive ghrelin analogues

Bergmann, R.
kein Abstract verfügbar
  • Lecture (Conference)
    2nd GIPIO meeting, 02.-03.06.2010, Copenhagen, Danmark

Permalink: https://www.hzdr.de/publications/Publ-15238
Publ.-Id: 15238


Small animal molecular imaging in cancer research

Bergmann, R.
Quantitative small animal imaging plays a key role in preclinical research and drug development. However, no single imaging modality is perfect and sufficient to gain all the necessary morphologic, physiologic, metabolic or genetic information. For instance, optical fluorescence imaging is difficult to quantify - especially in tissue more than a few millimetres in depth within a subject; magnetic resonance imaging of protons (MRI) has superb resolution but low sensitivity, positron emission tomography (PET) has very high sensitivity but poor resolution, single photon emission tomography (SPECT) has good resolution but low sensitivity and X-ray tomography (CT) has good resolution of bones but cannot good resolve tissues. The combination of multiple molecular imaging techniques can therefore offer synergistic advantages over any modality alone. The multimodal approach by combination of the methods and development of multimodal probes is far from trivial and a challenge for the interdisciplinary work and collaboration of scientists.
In the presentation we provide an overview of the small animal imaging in the Forschungszentrum Dresden-Rossendorf, recent developments of probes and applications in multimodal cancer research. We will show examples of quantitative imaging using low and high molecular weight probes and microspheres labeled for PET, SPECT and optical imaging. The especial developed animal bed system helps us to register the 3D data from different dedicated modalities for combining and comparing the methods. The development of imaging probes is embedded a combination of in vitro and ex vivo evaluation of gene expression, cell uptake and binding studies.
The molecular imaging in mouse and rat models allows us to ‘see’ the biological complexities of tumors for the treatment of this disease. This is one of the most exciting and growing areas in our research.
  • Invited lecture (Conferences)
    International workshop on bio-medical applications of micro-PET, 20.-21.09.2010, Seville, Spain

Permalink: https://www.hzdr.de/publications/Publ-15237
Publ.-Id: 15237


Small animal imaging in Cancer Research

Bergmann, R.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Budapest, 28.04.2010, Budapest, Hungary
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Veterinärmedizinische und Pharmazeutische Universität Brno, 27.04.2010, Brno, Czech Republic
  • Invited lecture (Conferences)
    Workshop Molecular Imaging, Karls-University Prague, 26.04.2010, Prague, Czech Republic

Permalink: https://www.hzdr.de/publications/Publ-15236
Publ.-Id: 15236


Multimodality small animal imaging in tumor biology

Bergmann, R.
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Seminar Semmelweis University of Medicine, Faculty of Medicine, Institute of Human Physiology and Clinical Experimental Research, 28.04.2010, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-15235
Publ.-Id: 15235


Synthesis and biological evaluation of novel 4-benzylpiperazine ligands for sigma-1 receptor imaging

Li, Z.-J.; Ren, H.-Y.; Cui, M.-C.; Deuther-Conrad, W.; Tang, R.-K.; Steinbach, J.; Brust, P.; Liu, B.-L.; Jia, H.-M.
We report the synthesis and evaluation of 4-benzylpiperazine ligands (BP-CH3, BP-F, BP-Br, BP-I, and BPNO2) as potential r1 receptor ligands. The X-ray crystal structure of BP-Br, which crystallized with monoclinic space group P21/c, has been determined. In vitro competition binding assays showed that all the five ligands exhibit low nanomolar affinity for r1 receptors (Ki = 0.43–0.91 nM) and high subtype selectivity (r2 receptor: Ki = 40–61 nM; Kir2/Kir1 = 52–94). [125I]BP-I (1-(1,3-benzodioxol-5-ylmethyl)-4-(4-iodobenzyl)piperazine) was prepared in 53 ± 10% isolated radiochemical yield, with radiochemical purity of >99% by HPLC analysis after purification, via iododestannylation of the corresponding tributyltin precursor. The log D value of [125I]BP-I was found to be 2.98 ± 0.17, which is within the range expected to give high brain uptake. Biodistribution studies in mice demonstrated relatively high concentration of radiolabeled substances in organs known to contain r1 receptors, including the brain, lung, kidney, heart, and spleen. Administration of haloperidol 5 min prior to injection of [125I]BP-I significantly reduced the concentration of radioactivity in the above-mentioned organs. The accumulation of radiolabeled substance in the thyroid was quite low suggesting that [125I]BP-I is relatively stable to in vivo deiodination. These findings suggest that the binding of [125I]BP-I to r1 receptors in vivo is specific.

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Permalink: https://www.hzdr.de/publications/Publ-15234
Publ.-Id: 15234


Micro-structured copper electrodeposition in inhomogeneous magnetic fields

Mutschke, G.; Tschulik, K.; Weier, T.; Uhlemann, M.; Bund, A.; Fröhlich, J.

It is well known that in various electrochemical systems the mass transfer and also the morphology and the structure of the electrodeposits can be influenced by the proper application of magnetic fields. One of the main reasons seems to be the convection induced by the resulting magnetic forces. Lorentz forces have been used to tailor the electrodeposition of metals for quite a while. Only recently, an improved understanding of the convection forced was gained that turned out to be more complex than expected, even in simple geometries [1]. Additionally, the influence of magnetic gradient forces on the preparation of micro-structured metal deposits on field-gradient electrodes has been discussed in the literature [2]. These electrodes consist of magnetic elements such as permanent magnets or magnetized ferromagnetic materials which are arranged beneath the surface of the working electrode. Here, however, besides the magnetic gradient force, also the Lorentz force might influence the deposition process. The presentation will summarize new numerical simulations, analytical findings and experimental results in order to discuss the influence of the different magnetic forces involved and will discuss the prospects towards smaller deposition structures [3,4].

[1] G. Mutschke et al., Electrochim. Acta 55 (2010) 1543.

[2] K. Tschulik et al., Electrochem. Comm. 11 (2009) 2241.

[3] G. Mutschke et al., Electrochim. Acta 55 (2010) 9060.

[4] K. Tschulik et al., Electrochim. Acta 56 (2010) 297.

Keywords: Magnetoelectrochemistry, electrodeposition
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-15233
Publ.-Id: 15233


Future aspects of X-ray emission from crystalline undulators at positron channeling

Backe, H.; Krambrich, D.; Lauth, W.; Buonomo, B.; Dabagov, S. B.; Mazzitelli, G.; Quintieri, L.; Lundsgaard Hansen, J.; Uggerhoj, U. I.; Azadegan, B.; Dizdar, A.; Wagner, W.
In connection with ideas to produce undulator-like radiation in the hundreds of keV up to the MeV region by means of positron and electron channeling, there is renewed interest to study various channeling phenomena also experimentally. With electrons experiments have been performed at the Mainz Microtron MAMI to explore channeling-radiation emission by a 4-period epitaxially grown strained layer SiGe undulator. Unfortunately, high quality positron beams of sufficient intensity are not easily accessible. The only serious candidate in Europe seems to be the Beam Test Facility at INFN LNF Frascati, Italy. Some requirements to extend BTF in a facility which is also well suited for positron channeling-radiation experiments will be outlined.
Keywords: undulator radiation, crystal undulator, positron channeling, channeling radiation
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Future aspects of X-ray emission from crystalline undulators at positron channeling, Bologna: Societa Italiana di Fisica, 175-180
  • Nuovo Cimento C 34(2011)04, 175-180
    DOI: 10.1393/ncc/i2011-10983-9

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Permalink: https://www.hzdr.de/publications/Publ-15232
Publ.-Id: 15232


Simulation of axial channeling radiation on a thin Ge single crystal

Azadegan, B.; Dabagov, S. B.; Wagner, W.
Based on classical electrodynamics the radiation emitted by axially channeled electrons has been investigated by means of computer simulations. Using the Doyle-Turner approximation for the atomic scattering factor and taking thermal vibrations of atoms into account, we calculated the two-dimensional continuum potential of the <110> crystallographic axis of a thin Ge single crystal. The trajectories, velocities and accelerations of electrons are obtained by solving the equations of motion in three dimensions, and the spectral-angular distribution of radiation has been calculated in the classical way.
Keywords: axial channeling, channeling radiation, Germanium single crystal
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Simulation of axial channeling radiation on a thin Ge single crystal, Bologna: Societa Italiana di Fisica, 149-156
  • Nuovo Cimento C 34(2011)04, 149-156
    DOI: 10.1393/ncc/i2011-10919-5

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Permalink: https://www.hzdr.de/publications/Publ-15231
Publ.-Id: 15231


Ion erosion induced surface patterning studied by combined trim and kinetic monte-carlo simulations

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.
Understanding of surface morphology evolution induced by ion erosion is still limited. Continuum models cannot explain microscopic processes. On the other hand, so far atomistic simulations could not describe pattern evolution on experimental spatiotemporal scales. Therefore, recently continuum equations were feeded with MD simulation results, which allows the understanding of smoothing mechanisms like an effective mass ‘downhill’ current induced by ballistic drift.

We developed a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. This allows a fully atomistic description on experimental spatiotemporal scales. 3D atom relocations were calculated using the binary collision approximation, whereas the thermally activated relaxation as well as diffusive processes were simulated by a bit-coded kinetic 3D Monte Carlo program. Effects like ballistic mass drift or dependence of local morphology on sputtering yield are automatically included by this approach.

The mechanism of ripple formation induced by a local surface currents is studied. The quantitative description of current vectors for different environmental parameters, and initial surface condition of sinusoidal structure, can be analized in time and space, following the local atomic drift. Different driving forces can be distinguished. Without ion irradiation the mass current vectors are always parallel to the surface plane with down-hill direction. Collision-cascade-induced defects change the mass currents significantly. Up-hill currents induce self-organization for certain obligue ion incidence angles. This driving forces causes patterning even without sputtering events.
Keywords: ripples, ion beam sputtering, pattern formation, kinetic Monte-Carlo, TRIM, crater formation, surface mass current
  • Poster
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-15230
Publ.-Id: 15230


Channeling radiation on quartz stimulated by acoustic waves

Wagner, W.; Azadegan, B.; Büttig, H.; Grigoryan, L. S.; Mkrtchyan, A. R.; Pawelke, J.
The stimulation of channeling radiation by acoustic waves excited in the single crystal has been predicted in early works of the 1980's. Based on quantum calculations, the described experiment aimed at verification of theoretical considerations. Making use of the reverse piezoelectric effect, hypersonic waves of frequency 12 GHz, which corresponds to a dedicated transition between bound states of planar channelled relativistic electrons, were excited in a single-crystal quartz plate. The spectrum of channeling radiation measured under the influence of acoustic waves reveals enhanced radiation intensity. The obtained results are discussed and may be phenomenologically understood assuming electron diffraction on an acoustic superlattice.
Keywords: channeling radiation, quartz single crystal, ultrasound
  • Contribution to proceedings
    4th International Conference Charged and Neutral Particles Channeling Phenomena, Channeling 2010, 03.-08.10.2010, Ferrara, Italy
    Channeling radiation on quartz stimulated by acoustic waves, Bologna: Societa Italiana di Fisica, 133-140
  • Nuovo Cimento C 34(2011)04, 133-140
    DOI: 10.1393/ncc/i2011-10899-4

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Permalink: https://www.hzdr.de/publications/Publ-15229
Publ.-Id: 15229


Ion-beam-induced interface mixing: unified atomistic simulations of collisional and thermal processes

Liedke, B.; Heinig, K.-H.; Facsko, S.; Möller, W.
Ion beam processing of materials at elevated temperature, which can be room temperature for metals, is controlled simultaneously by both, collisional and thermally activated processes. So far, large scale process simulations separate these processes, calculating all collision cascades of the complete ion irradiation in the binary collision approximation like the TRIDYN code, and simulating then the defect relaxation/impurity nucleation by kinetic Monte Carlo.

Here we present and apply a unified computer simulation program package which unifies both programs, i.e. after each calculated 3D collisional cascade some kinetic Monte Carlo steps allow relaxation, diffusion, phase separation etc. in the whole volume. Contrary to molecular dynamics simulations, our approach allows studies on experimental spatiotemporal scales. In this presentation we focus on the evolution of interfaces under ion irradiation, where collisional mixing is in competition with thermally activated diffusion and phase separation. He+ irradiations for two extreme cases were studied: (i) Irradiation of interfaces made by immiscible elements, here Al and Pb. Ballistic interface mixing is accompanied by phase separation. Al and Pb nanoclusters form and show self-ordering (banding) parallel to the interface. (ii) Irradiation of interfaces made by intermetallics forming species, here Pt and Co. Well-ordered layers of phases of intermetallics appear in the sequence Pt/Pt3Co/PtCo/PtCo3/Co, resulting in a stepwise changing Pt/Co concentration depth profile. Novel magnetic properties of such sandwiched phases are predicted and can explain the transition between out of plane and in-plane magnetic anisotropy caused by ion irradiation.
Keywords: interface, mixing, bi-layer, kinetic monte-carlo, KMC, TRIM, TRIDYN, phase transition, crystal ordering
  • Lecture (Conference)
    17th International Conference on Ion Beam Modification of Materials (IBMM 10), 22.-27.08.2010, Montreal, Canada

Permalink: https://www.hzdr.de/publications/Publ-15228
Publ.-Id: 15228


Quantum uncertainties in the energy of transverse oscillations of planar channeled particle

Mkrtchyan, A. R.; Grigoryan, L. S.; Mkrtchyan, A. H.; Khachatryan, H. F.; Wagner, W.; Azadegan, B.
It is shown that quantum uncertainties in the energy of transverse oscillations of planar channeled particle become significant at definite values of the crystal period in the direction of channeling. The possibility of producing superlattices with periodical potential is discussed.
Keywords: channeling radiation, quantum uncertainties
  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Quantum uncertainties in the energy of transverse oscillations of planar channeled particle, Yerevan, Armenia, 978-99941-2-486-2

Permalink: https://www.hzdr.de/publications/Publ-15226
Publ.-Id: 15226


Channeling radiation on quartz influenced by acoustic waves

Wagner, W.; Azadegan, B.; Büttig, H.; Mkrtchyan, A. R.; Grigoryan, L. S.; Pawelke, J.
The influence of acoustic waves excited in a single quartz crystal on the emission of channeling radiation by relativistic electrons has been proved experimentally.
Keywords: channeling radiation, quartz single crystal, ultrasound
  • Contribution to proceedings
    International conference on electrons, positrons, neutrons and X-rays scattering under external influences, 26.-30.10.2009, Yerevan-Meghri, Armenia
    Proceedings of the International conference on electrons, positrons, neutrons and X-rays scattering under external influences, Yerevan, Armenia, 978-99941-2-486-2

Permalink: https://www.hzdr.de/publications/Publ-15225
Publ.-Id: 15225


Warum Ge und Si durch Ionenimplantation zu Supraleitern werden

Fiedler, J.
Es konnte gezeigt werden, dass neben Diamant auch die technologisch relevanten Gruppe-IV-Halbleiter Si und Ge im extrem hochdotierten Zustand supraleitend werden. Am Helmholtz – Zentrum Dresden – Rossendorf ist es erstmalig gelungen, supraleitfähige Ge-Schichten in einem zu Fertigungsverfahren der Mikroelektronik kompatiblen Dotierprozess, bestehend aus Ga-Ionenimplantation und Kurzzeitausheilung, herzustellen. Die hochdotierten Ge-Schichten zeigen intrinsische Supraleitung mit kritischen Temperaturen bis zu 1 K. Eine weitere Erhöhung der Dotierkonzentration und damit der kritischen Temperatur ist aufgrund der begrenzten Löslichkeit von Ga in Ge (1 at.%) sehr schwierig. Um dennoch höhere Sprungtemperaturen zu erreichen, wurden die geringe Löslichkeit von Ga in Si (0.1 at.%) sowie die supraleitenden Eigenschaften von Ga ausgenutzt. In Ga implantiertem Si bilden sich Ausscheidungen, wodurch vergrabene, extrinsisch supraleitende Ga reiche Schichten hergestellt werden können. Die kritische Temperatur ist mit 7 K deutlich höher als in dotiertem Ge.
Die Struktur der Proben wurde mit Rutherford Rückstreuspektrometrie (RBS), Transmissionselektronenmikroskopie (TEM) sowie Sekundärionen-Massenspektrometrie (SIMS) untersucht. Für die elektrische Charakterisierung wurden Temperaturen zwischen 100 mK und 400 K sowie Magnetfelder bis 9 T verwendet. Im Vortrag werden die Grundzüge der Dotierung mittels Ionenimplantation sowie die Ergebnisse elektrischer und struktureller Untersuchung beider Materialsysteme vorgestellt.
  • Lecture (others)
    Institutsseminar SS 2011, Institut für Physik, TU Ilmenau, 18.05.2011, Ilmenau, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15224
Publ.-Id: 15224


ROBL: The first European actinide XAS beamline in its second decade of operation

Scheinost, A. C.; Hennig, C.; Rossberg, A.; Banerjee, D.
The Rossendorf Beamline at ESRF (ROBL) in operation since 1998 [1] is together with the INE Beamline at ANKA and the micro-XAS beamline at SLS one of three dedicated radionuclide XAS beamlines in Europe. ROBL is specialized in handling actinide nuclides up to Cf with a total activity to 185 MBq. The wide energy range (5 to 35 keV) permits to run actinide L1, L2 and L3 edges, important for the investigation of mixed actinide systems. Both the high photon flux (6 1011 ph/s on the sample) and the high-performance fluorescence detection makes ROBL suited for very low concentrations (according to XAS standards,  1 ppm XANES,  20 ppm EXAFS). Research at ROBL encompasses basic actinide chemistry, biogeochemistry, environmental chemistry and materials sciences, with applications for the improvement of nuclear waste repositories, remediation of uranium mining areas and other contaminated sites, development of fourth generation nuclear fuels, minor actinide waste forms and transmutation targets. The ROBL team supports users before, during and after the experiments. Own research specializes on the development of new data analysis tools (statistical tools, wavelets, Monte-Carlo simulations, PDF) as well as on actinide redox chemistry (structure of aqueous and non-aqueous complexes, redox mechanisms at water/mineral interfaces). From 2012 on, a major upgrade of the ROBL optics will further increase photon flux, energy range, and spectral resolution; and reduce spot size and data acquisition time; while maintaining reliable and relatively easy operation.

[1] W. Matz et al., Journal of Synchrotron Radiation 6, 1076-1085 (1999).
Keywords: xafs robl xanes xas synchrotron beamline
  • Invited lecture (Conferences)
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan

Permalink: https://www.hzdr.de/publications/Publ-15223
Publ.-Id: 15223


AcXAS, a reference data base for XAS spectra of actinides and other radionuclides

Scheinost, A. C.; Schmeisser, N.; Denecke, M.; Banerjee, D.; Dardenne, K.; Hennig, C.; Rossberg, A.; Rothe, J.; Daehn, R.
Reference spectra of well characterized samples are crucial for the analysis of x-ray absorption spectra (XAS). In order to avoid that experimentalists have to repeat XAS measurements of standard actinide compounds/species, thereby making more efficient use of costly radionculides, sample preparation, beamtime, radioprotection measures, transport, administration, etc., we are in the process of establishing a public database of actinide XAS reference spectra. The spectra are retrieved from the large data inventory of the three current European radionuclide beamlines, the Rossendorf Beamline at ESRF (France), the INE beamline at ANKA (Germany), and the micro-XAS beamline at SLS (Switzerland), but will also include data from other beamlines. This effort is supported by the European Commission through the ACTINET-I3 project. An overview on data base structure, criteria for data entry and use, as well as on the current status of data will be given.
Keywords: actinides xas xanes exafs data base
  • Poster
    Actinide-XAS 2011, 02.02.2011, Harima Science Garden City, Japan
  • Invited lecture (Conferences)
    ACTINET Plenary Meeting, 01.02.2011, Marcoule, France

Permalink: https://www.hzdr.de/publications/Publ-15222
Publ.-Id: 15222


Probing redox reactions at the mineral/water interface by X-ray absorption spectroscopy: Reduction of Se, Sn, Sb and Pu by Fe(II)-bearing minerals

Scheinost, A. C.
Fe(II)-bearing phases are naturally occuring in most anoxic aquifers, and form also at the surface of corroding steel containers under typical nuclear waste repository conditions. Due to their ability to reduce metal and metalloid contaminants, they are expected to play a key role for the migration behaviour of a wide range of radionuclides, including actinides and fission products. Using X-ray absorption spectroscopy as main tool, we have studied reaction end products, mechanisms and kinetics of redox processes at a range of water/mineral interfaces, including magnetite, green rust, mackinawite, siderite and Fe2+-sorbed clays. Our results show that the electron transport within mineral structures and at the surface is controlling the extent and the kinetics of multi-electron redox reactions. Examples that I will show include: (1) The fast reduction of Se(IV) to Se and Se(-II) nanoparticles, a reaction which was previously thought to be extremely slow. (2) The reduction of Pu(V) to Pu(III), which then forms a highly ordered inner-sphere sorption complex at the 111 face of magnetite, instead of the expected precipitation of PuO2 clusters. (3) The oxidation of Sn(II) to Sn(IV), which then forms inner-sphere sorption complexes, instead of the expected precipitation of SnO2. The results highlight the need for direct spectroscopic investigation of such processes, which are difficult to predict by thermodynamic methods, in order to provide reliable risk assessments.
Keywords: Redox interfaces XAFS XANES
  • Lecture (Conference)
    LES Seminar, 15.03.2011, Villigen, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-15221
Publ.-Id: 15221


Experiments on electromagnetic control of a backward facing step flow

Weier, T.; Wittwer, S.; Albrecht, T.; Gerbeth, G.

The flow over a backward-facing step is a prototype of a separating and reattaching shear flow and has therefore received a considerable amount of interest. We focus here on the excitation of the separated shear layer since it is often understood as the basic mechanism in active flow control. Forcing frequencies and amplitudes are obviously major parameters of influence, but different signal forms can have a profound impact as well, albeit the physical mechanism behind the latter is still not fully understood.

Electromagnetic body forces offer a simple and direct way to provide excitation by different wave forms. Particle image velocimetry measurements have been performed in a free surface electrolyte channel. We will discuss spatial amplification rates in the unforced shear layer, which show a fair agreement with results obtained by others in free shear layers. Compared to the natural flow, forcing near the optimal excitation frequency St=0.012 leads to a much earlier vortex roll-up and, consequently, the reattachment length is reduced. For the first subharmonic of the optimal excitation frequency, vortex roll up starts later but produces larger vortices. Excitation with the relatively high frequency of St=0.03 has only a very small effect on the flow. Keeping the excitation frequency at St=0.012 and increasing the forcing amplitude leads to earlier vortex roll up, larger vortices, and shorter reattachment lengths.

Keywords: flow control, Lorentz force, backward facing step
  • Lecture (Conference)
    Jahrestagung der Gesellschaft für angewandte Mathematik und Mechanik (GAMM 2011), 18.-21.04.2011, Graz, Österreich

Permalink: https://www.hzdr.de/publications/Publ-15220
Publ.-Id: 15220


Elektrische Kontaktierung vertikaler Nanostrukturen

Wieser, M.
Diese Arbeit beschreibt die Herstellung, Kontaktierung und Charakterisierung vertikaler Nanostrukturen in Form von Pfeilern der Höhe 50 nm mit einer elliptischen Querschnittsfläche von 100 × 150 nm. Die hergestellte Gesamtstruktur besteht dabei aus mehreren Metallebenen, so dass der Pfeiler an der Unterseite von einer Grundelektrode und an der Oberseite von einer Deckelektrode kontaktiert wird. Zur Fertigung der Metallebenen wird die Elektronenstrahllithographie mit anschließendem thermischen Bedampfen und Lift-Off genutzt. Die Isolation der Grundelektrode von der obersten Metallebene erfolgt mit einem durch Rotationsbeschichtung aufgetragenen Negativ-Lack aus dem Bereich der Elektronenstrahllithographie, der bei Erwärmung in Siliziumoxid transformiert.
Nach dem Ausarbeiten und Optimieren des Herstellungsprozesses dieser Strukturen sollten erste Nanostrukturen mit integrierter Tunnelbarriere erstellt und charakterisiert werden. Aufgrund von unvorhergesehenen Verzögerungen bei der Herstellung konnten diese Strukturen allerdings nicht fertiggestellt werden, so dass für die Charakterisierungsmessungen auf eine aus einem anderen Projekt bereitgestellte Probe zurückgegriffen werden musste, die einen ähnlichen Strukturaufbau besitzt. Die während der Charakterisierung dieser Probe aufgenommenen Strom-Spannungs-Kennlinien werden mit bekannten quantenmechanischen Tunnelmodellen verglichen.
Keywords: Electrical contacting vertical nanostructures
  • Diploma thesis
    Otto-von-Guericke-Universität Magdeburg, 2010
    79 Seiten

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Permalink: https://www.hzdr.de/publications/Publ-15219
Publ.-Id: 15219


Electrical Contacting of Vertical Nanostructures

Wieser, M.; Grebing, J.; Höwler, M.; Bernert, K.; Schmidt, B.; Fassbender, J.ORC; Erbe, A.
The aim of this new approach is the contacting and characterization of small vertical nanostructures. Therefore, in contrast to conventional lateral contacting a vertical pillar with a height of about 70 nm and an elliptic size of 100 nm × 150 nm is contacted using a bottom electrode, a via with the same height as the pillar and two top electrodes for tipcontacting of measurement devices. The structuring of the different layers is done using electron beam lithography (EBL). A resist layer is used as an insulator between the bottom and the top electrodes. In the center of the pillar an Al2O3 tunnel barrier will be integrated. The current voltage (IV) characteristics of the system will be investigated and compared to the direct tunneling and the Fowler-Nordheim tunneling model. Using this technique we will characterize the electrical properties of oxides with varying thickness.
Keywords: Electrical contacting vertical nanostructures
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15218
Publ.-Id: 15218


3D vector magnetooptical ellipsometry investigations on magnetic thin film samples at room temperature

Mok, K. M.; Schmidt, H.
We present the set-up of a vector-magneto-optical generalized ellipsometer (VMOGE) which allows to perform generalized Mueller matrix ellipsometry in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. Using VMOGE measurements, we measured the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni and extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions via model analysis.
Keywords: Magnetic semiconductors, spin poalrization, magnetooptical response
  • Lecture (others)
    Halbleiterphysik-Seminar (AG Zahn), TU Chemnitz, 21.01.2011, Chemnitz, Germany

Permalink: https://www.hzdr.de/publications/Publ-15217
Publ.-Id: 15217


Magnetic characterization of Bi(Fe1 − xMnx)O3

Xu, Q.; Zhou, S.; Wen, Z.; Wu, D.; Qiu, T.; Xu, M.; Potzger, K.; Schmidt, H.
Bi(Fe1 − xMnx)O3 ceramics (x up to 0.3) were prepared by rapid sintering. Weak ferromagnetism with two magnetic anomalies at low temperatures was observed for Bi(Fe0.95Mn0.05)O3 and Bi(Fe0.9Mn0.1)O3. From temperature-dependent magnetic relaxation measurements, the anomalies at 20 K and 100 K are related to the freezing of cluster spin glass.
Keywords: Multiferroic; Spin glass; Ferromagnetism; Cluster

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Permalink: https://www.hzdr.de/publications/Publ-15216
Publ.-Id: 15216


Synthesis and characterization of nickel cobalt oxide thin films

Calin, G.; Irimia, M.; Scarlat, C.; Purica, M.; Comanescu, F.; Iacomi, F.
p-Type transparent and conductive cobalt–nickel oxide films of 130 nm thickness, have been deposited by spin coating method on glass substrates. The electrical and optical properties of the oxides have been studied as a function of the x=Co/(Co+Ni) ratio. A combination of x-ray diffraction, x-ray photoelectron spectroscopy and Raman spectroscopy was used in order to investigate thin film structures. Thin films of mixed oxides: NiCo2O4, Ni1.71 Co1.29 O4; NiO were obtained for x>0.60. The electrical conductivity of these films reaches a maximum conductivity at this stoichiometry.
Keywords: p-type TCO, structure, optical properties, electrical properties, Raman spectroscopy.
  • Contribution to proceedings
    International Semiconductor Conference (CAS 2010), 11.-13.10.2010, Sinaia, Romania
    Semiconductor Conference (CAS), 2010 International, Sinaia, 978-1-4244-5783-0, 387-390

Permalink: https://www.hzdr.de/publications/Publ-15215
Publ.-Id: 15215


Experimental realisation of homogeneous dynamo action

Giesecke, A.; Stefani, F.; Gerbeth, G.

From the technical point of view the realisation of dynamo action under laboratory conditions is a demanding task because it requires magnetic Reynolds numbers of the order of Rm ~100. So far only three experiments have been able to demonstrate fluid flow driven self-excitation of magnetic fields.

The dynamo experiments in Karlsruhe and Riga, based on an optimized flow geometry, have demonstrated the principal possibility of the magnetic field generation process and its saturation as it occurs e.g. in stars or planets. Both dynamos are characterized by a non-axisymmetric field mode and are theoretically very well understood.

In contrast to this the mechanism responsible for the dynamo process in the von Karman sodium (VKS) experiment is still subject of intense discussion, in particular due to the obscure influence of the flow driving soft iron impellers. Recently, it could be shown numerically that the (localized) high relative permeability of the impellers is responsible for the rather low value of the critical magnetic Reynolds number as well as for the selection of the dominating axisymmetric dynamo mode observed in the experiment (Giesecke et al. 2010, PRL 104). However, to explain a growing axisymmetric field an alpha-effect is required for which the theoretical or experimental justifications remain only vague.

Further progress in the experimental examination of dynamo action is expected from the future dynamo facility that is scheduled at the Helmholtz-Zentrum Dresden-Rossendorf. In order to avoid the influence of internal components or artificial driving mechanisms a precession driven flow of liquid sodium in a cylinder shall provide the necessary energy to exhibit dynamo action. A precession driven dynamo operating in a sphere has been presented by A. Tilgner (2005, Phys. Fl. 17). However, it remains to be shown that precessional flow driving will be possible with sufficient efficiency to overcome the dynamo threshold in a cylindrical geometry as well.

Keywords: Dynamo Simulations Experiments Precession VKS dynamo
  • Lecture (Conference)
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Wien, Oesterreich
  • Contribution to proceedings
    European Geosciences Union General Assembly 2011, 03.-08.04.2011, Vienna, Austria
    Experimental realisation of homogeneous dynamo action

Permalink: https://www.hzdr.de/publications/Publ-15214
Publ.-Id: 15214


Oscillating alpha-square dynamos

Giesecke, A.; Stefani, F.; Gerbeth, G.

A simple way to interpretate the reversal mechanism of the Earth's magnetic field has been achieved in theoretical models based on the interplay between very few magnetic modes.

Motivated by the temporal behavior of elementary multipolar components of the Earth's magnetic field during the last reversal 780ka ago, (Leonhardt & Fabian 2007) the possibility of interacting magnetic modes is examined in a simple mean field model.

Field modes that are suitable canditates to be involved in the reversal process are oscillating eigenfunctions of the linear eigenvalue problem for geodynamo models of alpha2 type.

Regarding the spectrum of the dynamo operator time-dependent solutions arise at so called exceptional points where two stationary modes merge and continue at a single oscillating eigenfunction. In the present model this behavior essentially involves dipolar and octupolar modes. The spectrum exhibits further time-dependent modes of higher order that appear at coupling points of different radial field modes.

In order to couple odd ("dipolar-like") and even ("quadrupolar-like") modes equatorial symmetry breaking is required. However, instead of oscillating eigenfunctions an equatorial asymmetry results in stationary hemispherical dynamos. This behavior can be explained by the approximate dipole-quadrupole degeneration for the unperturbed problem.

More complicated scenarios occur in case of (more realistic) anisotropies of alpha- and beta-effect or through non-linearities caused by the backreaction of the magnetic field (magnetic quenching).

Keywords: Dynamo linear eigenvalue problem alpha-effect reversal geodynamo
  • Lecture (Conference)
    RädlerFest: Alpha Effect and Beyond, 14.-18.02.2011, Stockholm, Sweden

Permalink: https://www.hzdr.de/publications/Publ-15213
Publ.-Id: 15213


Ga ion irradiation induced spin reorientations in Co films

Mazalski, P.; Maziewski, A.; Tekielak, M.; Ferré, J.; Jaworowicz, J.; Mougin, A.; Liedke, B.; Liedke, M. O.; Fassbender, J.ORC
Some years ago, it has been demonstrated that after submitting Pt/Co/Pt films to increasing ion irradiation dose, one observes a decrease of: (i) perpendicular magnetic anisotropy (up to reach a spin reorientation transition (SRT) towards an in-plane magnetisation state); (ii) coercive field; (iii) Curie temperature (see e.g. [1-3]). In thicker Co films, by increasing the Ga ion dose, two successive inverse SRTs take place [4].
Pt(4.5nm)/Co(2.6nm)/Pt(3.5nm) films were deposited by sputtering on a sapphire substrate. 1mm wide strip regions were irradiated by 30 keV Ga ions under different doses D ranging from 2x1013 to 3x1014 Ga ions/cm2. Samples were studied by polar Kerr PMOKE (out-of-plane magnetization component sensitive), magneto-optical microscopy and local scanning magnetometry using a focused light beam. In-plane magnetized domains were studied using longitudinal magneto-optical Kerr effect, LMOKE. Magnetic Force Microscopy (MFM) was used to image domain patterns at higher spatial resolution. TRIDYN simulations were performed to estimate irradiation driven changes of the in-depth ion distributions. The irradiation driven SRTs are illustrated in Fig.1. Magnetization lies in-plane in the non-irradiated (NI) region. When increasing D, two successive SRTs undergo between planar to perpendicular magnetization states, and again back to a planar state (through a canted magnetization state, as shown from the magnetization curve obtained for D=3x1014 Ga ions/cm2).

This work was partly supported by the EU-“Research Infrastructures Transnational Access” program “Center for Application of Ion Beams in Materials Research” under contract no. 025646 and DAAD.

[1] C. Chappert, H. Bernas, et al., Science 280, 1919 (1998)
[2] J. Ferré and J.-P. Jamet, in Handbook on Magnetism and Advanced Materials. Eds H. Kronmüller and S. Parkin Vol. 3, 1710 (2007).
[3] Fassbender and J. McCord, J. Magn. Magn. Mat. 320 (2008).
[4] J. Jaworowicz, A. Maziewski, P.Mazalski, M.Kisielewski, I. Sveklo, M. Tekielak, V. Zablotski, J. Ferré, N. Vernier, A. Mougin, A. Henschke, J. Fassbender, Appl. Phys. Lett., 95, 022502 (2009).
Keywords: irradiation, SRT, TRIDYN
  • Poster
    IV Euro-Asian Symposium “Trends in MAGnetism”: Nanospintronics. EASTMAG – 2010, 28.06.-02.07.2010, Ekaterinburg, Russia

Permalink: https://www.hzdr.de/publications/Publ-15212
Publ.-Id: 15212


Magnetooptical Spectroscopy Of Ga+ Irradiated Pt/Co/Pt Sandwiches

Lišková, E.; Veis, M.; Višpovský, Š.; Maziewski, A.; Mazalski, P.; Ferré, J.; Mougin, A.; Liedke, M. O.; Fassbender, J.ORC
The magnetic properties of ultrathin Pt/Co/Pt sandwiches depend on the interface structure and can thus be controlled by ion irradiation [1]. In the present work, we study the magneto-optic properties by polar Kerr rotation upon Ga+ irradiation of Pt(3.5 nm)/Co(2.6 nm) /Pt(4.5 nm) trilayers which have been sputter deposited on (001) Al2O3 substrates. In Figure 1 the MO spectra at saturation before and after irradiation are compared. The enhanced MO amplitude after irradiation results from an increased thickness of the alloyed PtxCo1-x interface layer [2]. The MO spectra were modeled assuming interface PtxCo1-x layers with a monotonous x gradient using the data of ref. [3]. The curves in Fig. 1 were obtained assuming the structure shown in Fig. 2, i.e., Pt(2.8 nm)/ PtxCo1-x(1.1 nm)/Co(2.3 nm) /PtxCo1-x(1.1 nm)/Pt(4.0 nm) and Pt(1.2 nm)/ PtxCo1-x(4.0 nm)/ Co(1.0 nm)/PtxCo1-x(3.0 nm) /Pt(1.5 nm)/Al2O3 for the non-irradiated sample and the sample irradiated with a dose of 1014 Ga+/cm2, respectively. The changes in the MO spectra after irradiation confirm the expected high sensitivity of the coupled 3d levels of Co and 5d levels of Pt (with high spin-orbit interaction) to the interface geometry [2]. Partially supported by NSF (DMR 0605629 and DMR 0907053), Research Corporation (CC6471), CU-NIST Joint Project and by Ministry of Education, Youth and Sport of the Czech Republic (MSM 6198910016, 0021520834 and ME09045), Grant Agency of Charles University (3146/2008), Czech Science Foundation (P204/10/P346), EU-“Research Infra-structures Transnational Access” program “Center for Appli-cation of Ion Beams in Materials Research” (025646) and DAAD.
[1] J. Jaworowicz et al., Appl. Phys. Lett. 95, 022502 (2009)
[2] D. Weller et al. J. Magn. Magn. Mat. 93, 183 (1991)
[3] S. Visnovsky et al., IEEE Trans Magn. 29, 3390 (1993)
Keywords: irradiation, Co, Pt, MOKE
  • Poster
    IEEE 7th International Symposium on Metallic Multilayers (MML2010), 19.-24.09.2010, Berkeley, CA, USA

Permalink: https://www.hzdr.de/publications/Publ-15211
Publ.-Id: 15211


Influence of Ga+ irradiation on MO spectra of Pt/Co/Pt films

Liskova, E.; Veis, M.; Visnovsky, S.; Mazalski, P.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The magnetic anisotropy of Pt/Co/Pt sandwiches transforms from in-plane to out-of-plane and back as a function of uniform Ga+ ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett. 95 (2009)]. We study the effect of the irradiation on magneto-optical (MO) Kerr spectra between 1 and 5 eV in Pt(5nm)/Co(3.3nm)/Pt(20nm)/Mo(20nm). In the range up to an irradiation fluence of 1e15 ions/cm2 the MO amplitudes gradually increase and at 6e15 ions/cm2 it falls below that of the non-irradiated sample. The results are explained assuming the model system Pt/PtxCo1-x/Co/PtxCo1-x/Pt which accounts for increased PtCo alloy thicknesses at the interfaces. At 6e15 ions/cm2, the reduction in MO amplitudes is explained by the circumstance that a significant part of the sample is ablated and the sandwich reduces to a single alloy layer.
Keywords: irradiation, MOKE
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-15210
Publ.-Id: 15210


Modifications of magnetic properties of Pt/Co/Pt layers induced by Ga irradiations

Gieniusz, R.; Mazalski, P.; Kurant, Z.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The influence of Ga irradiation dose D on the magnetic properties of Pt/Co(d=3.3nm)/Pt trilayers grown by molecular beam epitaxy have been studied by both ferromagnetic resonance (FMR) and magnetooptical magnetometry (PMOKE). A broadening of Co-Pt interfaces induced by irradiation was deduced from X-ray reflectivity. For the nonirradiated sample the magnetisation was in-plane with negligible remanence ThetaR PMOKE hysteresis loops. Increasing D ThetaR(D) displays a maximum in irradiated samples for a dose DM ~ 2,8e14 ions/cm2. FMR study showed a similar behaviour (occurence of a maximum in a function of dose) both effective uniaxial magnetic anisotropy and FMR linewidth. For DM the increase of a uniaxial anisotropy field up to 0.3T was estimated from FMR data. Similar effects have been recently reported for Ga irradiated Co films deposited by sputtering which showed a double spin reorientation [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502].
Keywords: SRT, FMR, irradiation
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-15209
Publ.-Id: 15209


X-ray reflectivity investigations of Ga+ ion irradiated Pt/Co/Pt films

Kanak, J.; Stobiecki, T.; Powroznik, W.; Mazalski, P.; Sveklo, I.; Maziewski, A.; Liedke, M. O.; Fassbender, J.ORC; Wawro, A.; Baczewski, L. T.
The effects of Ga+ ion implantation in MBE grown Mo20nm/Pt20nm/Co3.3nm/Pt5nm films were investigated by low and high angle x-ray diffraction methods. The reflectivity measurements were used for characterization of changes in layer thickness and interface Pt/Co structure upon 30 keV Ga ion irradiation in a fluence range between 0 and 6e15 ions/cm2. The layer stack thickness was found to decrease with increase of Ga+ fluence. Mixing of Pt and Co at interfaces leads to a change of interface roughness of the top layers. The results were compared with high-fluence ion implantation simulations, of the dynamic changes of thickness and composition of layers, obtained using TRIDYN.
Keywords: TRIDYN, irradiation, Co, Pt , SRT
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-15208
Publ.-Id: 15208


Effects of thermal annealing on structural and magnetic properties of thin Pt/Cr/Co multilayers

Tripathia, J. K.; Satpatib, B.; Liedke, M. O.; Guptad, A.; Som, T.
Thermal stability of thin Pt/Cr/Co multilayers and the subsequent changes in their structural, magnetic, and magneto-optical properties are reported. We observe CoCrPt ternary alloy phase formation due to annealing at temperatures about 773 K, which is accompanied by enhancement in the coercivity value. In addition, 360° domain wall superimposed on a monodomain like background has been observed in the pristine multilayer, which changes into a multidomain upon annealing at 873 K
Keywords: Pt/Cr/Co multilayer; Structural property; Magnetic property; Thermal annealing

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Permalink: https://www.hzdr.de/publications/Publ-15207
Publ.-Id: 15207


Quenched-in vacancies in Fe-Al alloys

Melikhova, O.; Cizek, J.; Lukac, F.; Procházka, I.; Kuriplach, J.; Anwand, W.; Brauer, G.
Quenched-in vacancies in Fe-Al alloys with Al content ranging from 24 to 49 at.% were investigated employing two complementary techniques of positron annihilation: slow positron implantation spectroscopy and positron lifetime measurements. It was found that quenched alloys exhibit a very high concentration of vacancies. Although the free positron component cannot be resolved in positron lifetime spectrum in majority of samples, the concentration of quenched-in vacancies can be still determined from the positron diffusion length measured by a variable energy positron beam. The lowest concentration of vacancies was found in a stoichiometric (SM) Fe3Al alloy. The concentration of defects increases with increasing degree of non-stoichiometry with respect to Fe3Al, i.e. in alloys with under-SM and over-SM Al concentration. However, the increase in concentration of quenched-in defects is more pronounced in Al-rich alloys, i.e. alloys containing more than 25 at.% of Al.

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Permalink: https://www.hzdr.de/publications/Publ-15204
Publ.-Id: 15204


Use of superconducting linacs for positron generation: the EPOS system at the Forschungszentrum Dresden-Rossendorf (FZD)

Krause-Rehberg, R.; Jungmann, M.; Krille, A.; Werlich, B.; Pohl, A.; Anwand, W.; Brauer, G.; Butterling, M.; Büttig, H.; Kosev, K. M.; Teichert, J.; Wagner, A.; Cowan, T. E.
Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting LINACbased accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system (ELBE Positron Source) at the Forschungszentrum Dresden-Rossendorf (FZD), is described.

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Publ.-Id: 15203


Surface nanostructures induced by slow highly charged ions

Facsko, S.; Wilhelm, R. A.; El-Said, A. S.; Heller, R.
Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear or electronic sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation in the surface can thus induce various modifications [1]. Recently, it has been shown that hillock structures are formed on CaF2 by HCI due to a localized phase transition [2].
In the case of the alkali halide crystal KBr we observed the formation of nanostructures resulting by desorption of surface atoms from a single ion impact site [3]. For high enough charge states each ion produces a mono-atomic deep pit with a diameter of 10-30 nm (depending on the charge state) on the atomically flat surface. The desorption of such a high amount of material can not be induced by kinetic sputtering alone, which dominates in this kinetic energy regime, but is induced by the excitation due to the potential energy. For a kinetic energy of 40 keV a threshold in the potential energy of the HCI is found for the formation of these structures between Xe15+ and Xe20+ around 3 keV. Above this threshold the volume of the pits and therewith the potential sputtering yield exhibits a linear dependence on the potential energy. However, the kinetic energy also plays an important role. For higher kinetic energies the threshold shifts to lower values of the potential energy.
Keywords: highly charged ions, nanostructures, surface modifications
  • Invited lecture (Conferences)
    EMMI Workshop "Physics prospects at the ESR and HITRAP", 27.-30.06.2010, Eisenach, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15202
Publ.-Id: 15202


SQUID investigations of Ga+ irradiated epitaxial Pt/Co/Pt trilayers

Liedke, M. O.; Shalimov, A.; Fassbender, J.ORC; Mazalski, P.; Maziewski, A.; Wawro, A.; Baczewski, L. T.
Spin reorientation transition in polycrystalline Pt/Co/Pt trilayers, i.e. rotation of the magnetization from an in-plane to out-of-plane orientation and vice versa can be precisely controlled by ion irradiation fluence [J. Jaworowicz et al., Appl. Phys. Lett., 95 (2009) 022502], similarly to the epitaxial Pt/Co/Pt trilayers exposed to 30 keV Ga+ ions in the fluence range of 1014-1016 ion·cm−2. Magnetic properties of a such irradiated system are studied by means of SQUID magnetometry. Zero field cooling and field cooling dependencies and also magnetization reversal curves are measured and analyzed in the frame of the Preisach model. The model explains structural and magnetic modifications occurring due to ion irradiation. A key magnetic properties, i.e. distribution of coercive and interaction fields, reversible and irreversible magnetic contributions are addressed. The interpretation of the results is also supported by the XRD synchrotron studies.
Keywords: SQUID, spin reorientation transition, Co, Pt, magnetization
  • Poster
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-15201
Publ.-Id: 15201


Magnetic anisotropy engineering: ultrathin Fe films on single crystalline rippled surfaces

Liedke, M. O.; Körner, M.; Lenz, K.; Ranjan, M.; Fassbender, S.; Facsko, J.
Ultrathin Fe films exhibit an excellent epitaxial relation to MgO(100) substrates because of a very low lattice mismatch (~3.8%). Due to a cubic symmetry of the Fe crystal an in-plane fourfold magnetic anisotropy is induced. By means of ion erosion coherently aligned single crystalline patterns (ripples) are created at the MgO surface, which induce an additional uniaxial magnetic anisotropy in the afterwards deposited Fe film. The uniaxial magnetic anisotropy direction and strength is controlled by an arbitrarily chosen irradiation direction with respect to the sample plane and the ion energy dependent ripple wavelength, respectively. Thus an ensemble of twofold and fourfold anisotropy is created and analyzed by ferromagnetic resonance and magneto-optic Kerr effect techniques. Theoretical analysis reveals both the anisotropy fields and their directions that are in a perfect agreement with the experiment.
Keywords: magnetic anisotropy, ripples, MgO, Fe, single crystalline, ion erosion
  • Lecture (Conference)
    Joint European Magnetic Symposia, 23.-28.08.2010, Krakow, Poland

Permalink: https://www.hzdr.de/publications/Publ-15200
Publ.-Id: 15200


Ions for Nanotechnology

Kolitsch, A.
The aim of the nanocenter slovakion is its integration into university research (e.g. STU/MtF, materials research), which is highly required by professional public This will enable university to bring its research closer to the needs of industry and shift it to up-to-date topics on one side, and raise funds from private sources in the industry on the other side, which altogether represents a unique chance to train young qualified researchers in the field of contemporary materials research. The activities of the centre will be equally utilised by both in-house and external research and in a wide scale of services oriented on the support in introducing nanostructures using plasma and ion technologies into production processes for external industrial and other users.
The subject of the research, both basic and applied, will be focused on the modification of surface properties, such as hardness, friction, wear, fatigue, adhesion, as well as electrical, magnetic and optical properties, along with corrosion and bio-compatibility using ion beams technologies in the nanometer range. The research will employ the technologies, such as ion implantation (II), ion beam mixing (IBM) and ion beam assisted deposition (IBAD), as well as plasma assisted pulsing, non-pulsing, reactive and non-reactive processes where energetic ions form a decisive component of this process implementation. Highly topical is the research dealing with the development of nanostructures via ion beams.
Typical fields of utilisation are as follows:
• Exposed parts in automotive and mechanical engineering industry (injection nozzles, camshafts, bearings, valves and others);
• Medical and biomedical applications (prosthetics with interesting alloys, even those with the surfaces not sufficiently wear-resistant);
• Surface nitration of stainless steels via ion implantation with the purpose to improve wear resistance of stainless steels while preserving their high corrosion resistance;
• Stents (endoluminal catheter protheses), nano-porous stents for additional controlled administration of drugs, biocompatible and blood-compatible materials, etc. for modern medicine;
• Further possibilities of ion implantation in industry in the fields other than microelectronics, such as precise mechanics, special construction parts of expensive watches;
• High thermal oxidation protection (Ti AL – alloys, turbine construction);
• Mould injection of plastics (improvement of safety in the removing of injection-made plastic parts from the mould, as well as wear protection of highly exposed parts of forming tools);
• Ion implantation of polymers surfaces for the improvement of certain surface properties, such as printability for electric conductivity, biocompatibility, etc.

The important areas of ion beams technology application can be found in the field of ion beam analysis in a nanometer scale as well as in research and industry. Planned procedures are as follows:
• Rutherford Backscattering (RBS)
• Elastic Recoil Detection (ERD)
• Nuclear reaction Analysis (NRA)
• Proton Induced X-ray Emission (PIXE)
• Proton Induced Gamma-ray Emission (PIGE)

They provide a possibility of a non-standard depth profile analysis with high precision of nearly all chemical elements. In special cases, such as hydrogen depth profile analysis or light elements (B, C, N, O) analysis in heavy matrix (steel), they are unequalled when compared to other procedures.
Three groups of devices suggested as basic equipment for various uses of ion implantation are as follows:
• PBII equipment (three machines with various chamber volumes, basic vacuum and pulse voltage);
• Two linear ion implanters in the energetic range up to 500 kV (standard equipment) and 200 kV as a so-called high current implanter;
• 6 MV Tandetron Accelerator with experimental stations for high energy ion implantation and ion beam analysis.

The basic equipment for plasma and ion beam assisted separation processes is as follows:
• IBAD instrumentation with different low energy ion sources;
• Combination of PBII and thin film deposition
• Universal magnetron sputtering application systems with possible reactive middle frequency pulsed dual magnetron sputtering and the possibility of choice for typical plasma diagnostics and thin layers diagnostics.
Along with the implantation processes for micro-electronic development of nano-clusters, nano-wires, and nano-arrays, typical surface processes aiming at nano-scale ordered structures such as surface design created by ion erosion, nano-porosity for bio-medicine usage, blistering, etc., play an important role. Anyway, the magnetic nano-scale order of a structure as an indication of ferro-magnetic phases in non-magnetic materials or magnetic domain configuration using ion beams is of certain interest. Ion-beam-assisted separation process or special reactive processes of magnetron sputtering contributed to a significant achievement in the field of fullerene materials, nano-crystalline highly refracting optical materials or in transparent electrical conductive oxides, which play an important role in solar technology and technology of displays. Coating by super hard substances such as a-C or c-BN is impossible without energetic ions.
Keywords: ion implantation, plasma, ion assisted deposition, plasma based implantation, plasma immersion ion implantation, nanotechnology, hard coatings, doping, accelerator, implanter
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic
  • Invited lecture (Conferences)
    Jahresempfang der Slowakischen Technischen Universität Bratislava, 21.01.2010, Trnava, Slovak Republic

Permalink: https://www.hzdr.de/publications/Publ-15199
Publ.-Id: 15199


Exploring uranyl(VI) photochemistry by DFT calculations (in Japanese)

Tsushima, S.
no abstract for this publication
  • Lecture (Conference)
    Seminar talk at the Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology, 08.03.2011, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-15198
Publ.-Id: 15198


Time-resolved photoluminescence from GaAs/AlGaAs multiquantum wells quenched by pulsed mid-infrared radiation

Zybell, S.; Schneider, H.; Winnerl, S.; Helm, M.
Several groups have demonstrated the suppression of photoluminescence (PL) from semiconductor quantum wells (QWs) by intense midinfrared radiation (MIR). Since most of the previous studies are done on time-integrated PL the ultrafast changes in the radiative state population are not well understood. We present a detailed study on time-resolved PL from an undoped GaAs/AlGaAs QW sample quenched by MIR pulses from a free-electron laser, which was tuned to the intersubband transition (ISBT) energy. At the arrival time of the MIR pulse a clear sharp dip appears in the PL transient. Free carrier absorption and ISBT are the two processes that take place under MIR excitation and result in an abrupt drop of the radiative state population and consequently in an ultrafast quenching of the PL. Performing polarization sensitive measurements, we were able to discriminate the contributions of free carrier absorption from that of ISBT. A quantitative analysis of the PL dip depth and recovery time as a function of MIR fluence was done using a model based on rate equations.
Keywords: time-resolved photoluminescence, semiconductor quantum wells, intersubband transition
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP) und der Sektion Kondensierte Materie (SKM), 13.-18.03.2011, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15197
Publ.-Id: 15197


Voruntersuchungen am HZDR für Filmdickenmessungen an der thermohydraulischen Versuchsanlage KATHY (Karlstein, AREVA NP) mit Gamma-CT

Bieberle, A.; Hoppe, D.; Hampel, U.
Für die Überprüfung des Strömungsregimes im sogenannten Kaminrohr, das in Kernkraftwerken der AREVA NP zur Anwendung kommen soll, müssen zur Überprüfung des Systems im thermohydraulischen Versuchsstand KATHY in Karlstein (AREVA NP) authentische Betriebsszenarien nachgebildet und getestet werden. Grundlage hierfür sind Simulationen und Berechnungen, die mit direkt am Versuchstand gewonnenen Messwerten überprüft werden müssen. Aus diesem Grund soll der mögliche Einsatz des am HZDR entwickelten hochauflösenden Gamma-Computertomographie-Messsystems (Gamma-CT) zur Bestimmung von Wasserfilmdicken überprüft werden.
Keywords: Gamma-CT, Wasser-Dampf Strömung
  • Other report
    HZDR: HZDR, 2011
    20 Seiten

Permalink: https://www.hzdr.de/publications/Publ-15196
Publ.-Id: 15196


Optimierung des Energiefensters für I-124 anhand von Monte-Carlo Simulationen und PET-Messungen an Kleintier- und Human-Tomographen

Sauerzapf, S.; Zakhnini, A.; Behe, M.; Thomas, L.; Axer, M.; Weber, W.; Pietrzyk, U.; Mix, M.
Ziel/Aim:
Die Verwendung des nichtreinen Positronenstrahlers I-124 bietet aufgrund seiner Halbwertszeit von 4,18 Tagen Vorteile bei der Quantifizierung von langsamen biochemischen Prozessen. Nachteilig bei I-124 ist das komplexe Zerfallsschema. Der Anteil an Positronen liegt nur bei 22,8%. Zusätzlich werden koinzidente g -Linien mit Energien emittiert, die innerhalb des am PET-Scanner verwendeten Energiefensters liegen. Ziel dieser Arbeit ist es, das Energiefenster für die PET-Akquisition so zu optimieren, dass ein möglichst geringer Anteil an falschen Koinzidenzen auftritt. Dazu wurden Monte-Carlo Simulationen gerechnet, und Phantome an verschiedenen Kleintier- und Humanscannern gemessen.

Methodik/ Methods:
Die Monte-Carlo Simulationen wurden mit Hilfe von GATE (1) für die Scanner ClearPET (Raytest) und Gemini TF (Philips) sowie für unterschiedliche Phantome durchgeführt. Um die zusätzlich zum Positronenzerfall auftretenden koinzidenten g -Linien im Energiespektrum zu unterscheiden, wurde die I-124 Aktivität nicht als Ionenquelle, sondern alle g -Linien als reine Gammaemitter und die Positronenemission als quasikontinuierliches Energiehistogramm definiert. F-18 wurde als Ionenquelle definiert und als Vergleichsstandard verwendet. Die
Energiespektren wurden für die verschiedenen Bereiche im Phantom hinsichtlich der wahren und gestreuten Koinzidenzen unterschieden. Neben den Messungen mit den o.g. Phantomen für I-124 und F-18 am ClearPET und PET/CT Gemini TF 64 wurden vergleichende Messungen am MicroPET Focus 120 (Concorde) und am ECAT EXACT (Siemens) gemacht.

Ergebnisse/ Results:
Die Simulationen zeigen, dass im Vergleich zu F-18 die I-124 Energiespektren mehr Counts speziell im niederenergetischen Bereich (<350keV) aufweisen. Dies resultiert aus den zusätzlich koinzidenten g -Linien, die als wahre Koinzidenzen gewertet werden. Da die Energieverteilung der g -Linien exponentiell verläuft, wird durch die Wahl einer höheren unteren Energieschwelle (450keV anstatt 250 bzw. 350keV) ein Großteil der falschen
Koinzidenzen herausgefiltert. Die Energieauflösung des PET-Scanners bestimmt dabei die Qualität dieser Maßnahme, was sich in den Phantommessungen an den unterschiedlichen Scannern bestätigt. Besonders deutlich wird dies zwischen dem BGO- und dem LYSOHumanscanner. Durch das engere Energiefenster am Gemini TF wird mit I-124 im Phantom eine auf 10% genaue Quantifizierung sowie annähernd keine Streuanteile in kalten Phantombereichen festgestellt.

Schlussfolgerungen/ Conclusions:
Die Simulationen erlauben eine sehr gute Abschätzung, inwieweit sich bei den PET-Scannern die Akquisition mit dem Isotop I-124 durch Einschränkung des Energiefensters verbessern lässt. Die Phantommessungen zeigen, dass gute quantitative Ergebnisse mit I-124 erreicht werden können.

Literatur:
(1) S. Jan /et al /2004 GATE: a simulation toolkit for PET and SPECT. Phys. Med. Biol. 49
4543–4561
  • Poster
    NuklearMedizin2011, 13.-16.04.2011, Bregenz, Österreich

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Permalink: https://www.hzdr.de/publications/Publ-15195
Publ.-Id: 15195


Surface nanostructures induced by low energy ion sputtering

Facsko, S.
Under special conditions low energy ion sputtering of solid surfaces leads to the formation of regular nanopatterns. These surfaces represent an interesting example of spontaneous pattern formation in non-equilibrium systems exhibiting different features like wavelength coarsening or a transition to spatiotemporal chaos. Different pattern types are observed for different experimental conditions, i.e. wavelike ripple patterns and hexagonally ordered dot arrays under oblique and normal ion incidence, respectively [1]. These patterns have gained increasing interest in recent years as templates for thin film growth.
According to the model of Bradley and Harper (BH) [2], the regular patterns result from the competition between curvature dependent roughening and smoothing of the surface. Since the local erosion rate is higher in the valleys than on crests, the eroded surface is unstable. In the presence of smoothing mechanisms, however, a wave vector selection occurs and a periodic pattern with one spatial frequency is observed. The pattern formation can be described by continuum equations based on the BH model. Several extensions have been proposed in the last years, with the stochastic Kuramoto-Sivashinsky (KS) equation being the most prominent one [3]. However, although most experimental investigations on ion-induced pattern formation were performed under oblique ion incidence, only few theoretical studies focused on the corresponding anisotropic KS (aKS) equation.
We will also present studies of thin film growth on these patterns. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography or as nanoparticles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires. Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Because of the alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [4]. In addition, the magnetic properties of ferromagnetic thin films grown on rippled surfaces are drastically change by the presence of the interface and surface periodic roughness [5].

[1]W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007)
[2]R. Bradley and J. Harper, J. Vac. Sci. Technol. A 6, 2390 (1988)
[3]R. Cuerno and A.-L. Barabási, Phys. Rev. Lett. 74 4746 (1995)
[4] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[5] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).
Keywords: ion sputtering, surface patterns, ripple patterns
  • Lecture (others)
    Birck Nanoscience Center Seminar, 28.04.201, West Lafayette, Indiana, USA

Permalink: https://www.hzdr.de/publications/Publ-15194
Publ.-Id: 15194


Comprehensive study of the p-type conductivity formation in radio frequency magnetron sputtered arsenic-doped ZnO film

Fan, J. C.; Zhu, C. Y.; Yang, B.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Grambole, D.; Skorupa, W.; Wong, K. S.; Zhong, Y. C.; Xie, Z.; Ling, C. C.
Arsenic doped ZnO and ZnMgO films were deposited on SiO2 using radio frequency magnetron sputtering and ZnO–Zn3As2 and ZnO–Zn3As2–MgO targets, respectively. It was found that thermal activation is required to activate the formation of p-type conductivity. Hall measurements showed that p-type films with a hole concentration of ∼ 1017 cm−3 and mobility of ∼ 8 cm2 V−1 s−1 were obtained at substrate temperatures of 400–500 °C. The shallow acceptor formation mechanism was investigated using x-ray photoelectron spectroscopy, positron annihilation, low temperature photoluminescence, and nuclear reaction analysis. The authors suggest that the thermal annealing activates the formation of the AsZn-2VZn shallow acceptor complex and removes the compensating hydrogen center.
Keywords: zinc oxide, positron annihilation, ZnMgO, p-type conductivity, nuclear reaction analysis, XPS, PL, AsZn-2VZn shallow acceptor complex

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Permalink: https://www.hzdr.de/publications/Publ-15193
Publ.-Id: 15193


Time-resolved photoluminescence from undoped GaAs/Al0.35Ga0.65As quantum wells quenched by pulsed midinfrared radiation

Zybell, S.; Schneider, H.; Wagner, M.; Winnerl, S.; Köhler, K.; Helm, M.
There is much interest in the development of ultrafast devices with possible applications in optoelectronics. An important goal consists in ultrafast control of luminescence in light-emitting devices; it is therefore interesting to investigate the effect of abrupt changes in the carrier distribution on the luminescence signal. We present an experimental study of the effects of mid-infrared radiation (MIR) on the photoluminescence (PL) from undoped AlGaAs/GaAs quantum wells. Electron-hole pairs, created by weak near-infrared light pulses, were excited in the system while a delayed MIR pulse induces an ultrafast redistribution of free carriers that results in abrupt quenching of the PL with a subsequent PL recovery. The source of the MIR laser pulses was the free-electron laser facility FELBE at the Forschungszentrum Dresden-Rossendorf. In combination with the synchroscan streak camera, collecting the PL from the electron-hole recombination, it turned out to be a great spectroscopic tool for time-resolved measurements. Using a simple fit function we found PL recovery times between 40 and 150 ps depending on the MIR intensity.
Keywords: quantum wells, time-resolved photoluminescence, streak camera, FELBE
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 22.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15192
Publ.-Id: 15192


Ordered Ag nanocluster structures by vapor deposition on pre-patterned SiO2

Numazawa, S.; Ranjan, M.; Heinig, K.-H.; Facsko, S.; Smith, R.
Highly ordered Ag nanocluster structures have been grown on pre-patterned amorphous SiO2 surfaces by oblique angle physical vapor deposition at room temperature. Despite the small undulation of the rippled surface, the stripe-like Ag nanoclusters are very pronounced, reproducible and well-separated. Computer modeling of the growth has been performed with a lattice-based kinetic Monte-Carlo (KMC) method using a combination of a simplified inter-atomic potential and experimental transition barriers taken from the literature. An effective transition event classification method is introduced which allows a boost factor of several thousand compared to a traditional KMC approach, thus allowing experimental time scales to be modeled. The simulation predicts a low sticking probability for the arriving atoms, millisecond order lifetimes for single Ag monomers and ~1 nm square surface migration ranges of Ag monomers. It is also shown that metal nucleations can trigger even on defect free surfaces. The simulations give excellent reproduction of the experimentally observed nanocluster growth patterns.
Keywords: Kinetic Monte-Carlo, Physical vapor deposition, nanopatterning

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Permalink: https://www.hzdr.de/publications/Publ-15191
Publ.-Id: 15191


Impact of Slow Highly Charged Ions on Insulating Surfaces

Facsko, S.
Surface modifications induced by the irradiation with ions have been investigated for long time. Depending on their energy the ions create a crater resulting from nuclear sputtering or can induce the formation of hillocks at high kinetic energies. For highly charged ions (HCI) the situation is more complex. In addition to their kinetic energy HCI posses also potential energy which is the sum of the ionization energies to create them. This large amount of potential energy is released when interacting with solids and deposited into a small volume close to the surface. The resulting high excitation can thus induce various effects, like secondary electron emission, potential sputtering, and finally also permanent surfaces modifications [1].
Systematic investigations of surface modifications induced by highly charged ion on different materials have revealed many interesting mechanisms. On CaF2 surfaces hillock structures are formed by the impact of HCI due to a localized phase transition [2]. In the case of the alkali halide crystal KBr the formation of nanostructures results from the desorption of surface atoms from a single ion impact site [3]. In both cases a threshold in the potential energy for the formation of the structure has been identified and could be interpreted in the frame of the applied models. However, still a unified picture of these effects is missing.
This work has been supported by the European Project ITSLEIF (RII3#026015).
[1] S. Facsko, R. Heller, A. S. El-Said, W. Meissl and F. Aumayr, J. Phys.: Cond. Matter 21, 2240122 (2009) .
[2] A. S. El-Said, R. Heller, W. Meissl, R. Ritter, S. Facsko, C. Lemell, B. Solleder, I. C. Gebeshuber, G. Betz, M. Toulemonde, W. Moller, J. Burgdorfer and F. Aumayr, Phys. Rev. Lett. 100 237601 (2008).
[3] R. Heller, S. Facsko, R. Wilhelm, and W. Möller, Phys. Rev. Lett. 101, 096102 (2008).
Keywords: highly charged ions, surface modifications,nanostructures
  • Invited lecture (Conferences)
    24th International Conference on ATOMIC COLLISIONS IN SOLIDS ICACS-24, 18.-23.07.2010, Krakow, Polen

Permalink: https://www.hzdr.de/publications/Publ-15190
Publ.-Id: 15190


Ion-Induced Surface Patterns as Templates for Thin Film Growth

Facsko, S.; Ranjan, M.; Keller, A.; Oates, T. W. H.; Faßbender, J.ORC; Möller, W.
Nanostructured thin films are of growing relevance for all kind of applications in photovol-taics, plasmonics, or as magnetic materials. Various methods have been used to fabricate these nanostructured thin films with well defined morphology. Besides the top-down ap-proaches using lithographic methods, bottom-up, self-organized methods have been used ex-tensively in the last years because of their fast and easy way of producing patterns with struc-tures down to 10 nm.
Ion beam sputtering has proven to be a promising way to produce self-organized patterns on various surfaces. Depending on the ion incidence angle hexagonally ordered dot patterns as well as ripple patterns oriented perpendicular or parallel to the ion beam direction are formed during the continuous sputtering (see Fig. 1 left). These patterns are excellent templates for the growth of metal thin films. Depending on the interface energy of the metal film with the substrate the films grow in a conformal way reproducing the surface topography (Fig. 1 right top) or as nanoparticles on the substrate surface (Fig. 1 right bottom). Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles align parallel to the ripples, eventually coalescing and forming nanowires [1].
Metal thin films grown in this way exhibit distinct optical properties due to their localized surface plasmon resonance. Especially for nanoscale optics aligned equidistant chains of metal nanoparticles are favoured. Because of alignment these nanoparticles exhibit a strongly anisotropic plasmonic resonance [2]. In addition, the magnetic properties of ferromagnetic thin films are drastically change by the presence of the interface and surface periodic roughness [3].

[1] T.W.H. Oates, A. Keller, S. Noda, et al., Appl. Phys. Lett. 93 (2008).
[2] T.W.H. Oates, A. Keller, S. Facsko, et al., Plasmonics 2, 47 (2007).
[3] M. O. Liedke, B. Liedke, A. Keller, et al., Phys. Rev. B 75, 220407 (2007).
Keywords: ripple patterns, nanostructured thin films, magnetic films, plasmonic material
  • Invited lecture (Conferences)
    PSE 2010, Twelfth International Conference on Plasma Surface Engineering, 13.-17.09.2010, Garmisch-Partenkirchen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15189
Publ.-Id: 15189


Cross-Coupling Reactions as Valuable Tool for the Preparation of PET Radiotracers

Pretze, M.; Große-Gehling, P.; Mamat, C.
The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of new radiotracers and novel radiolabeling procedures with the most prominent short-lived positron emitters carbon-11 and fluorine-18. Radiolabeling with these radionuclides represents a remarkable challenge. Special attention has to be paid to synthesis time and specific labeling techniques due to the short physical half life of the respective radionuclides 11C (t1/2 = 20.4 min) and 18F (t1/2 = 109.8 min). In the past, numerous transition metalcatalyzed reactions were employed in organic chemistry, even though only a handful of these coupling reactions were adopted in radiochemical practice. Thus, the implementation of modern synthesis methods like cross-coupling reactions offers the possibility to develop a wide variety of novel radiotracers. The introduction of catalysts based on transition metal complexes bears a high potential for rapid, efficient, highly selective and functional group-tolerating incorporation of carbon-11 and fluorine-18 into target molecules. This review deals with design, application and improvement of transition metal-mediated carbon-carbon as well as carbon-heteroatom cross-coupling reactions as a labeling feature with the focus on the preparation of radiolabeled compounds for molecular imaging.
Keywords: cross-coupling; radiolabeling; carbon-11; fluorine-18

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Publ.-Id: 15188


Surface patterning by low energy ion sputtering

Facsko, S.
The morphology of surfaces after erosion by ion sputtering show very different char-acteristics depending on the ion beam parameters and the material properties. The surface exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns, like periodic rip-ples or hexagonally ordered dots [1,2]. The structures of these patterns have small sizes in the range of 10 to 100 nm and show a high degree of ordering. Therefore, they have attracted strong interest recently as templates for nanostructured thin film deposition [3]. On materials whose surface turns amorphous during the ion erosion the formation of the periodic patterns relies on at least two interplaying processes: roughening of the surface due to the local variation of sputtering yield and smoothing via diffusion processes. Therefore, the surface morphology depends strongly on the details of the energy deposition by the incoming ions and on the details of the surface diffusion.
At the atomic level, the atomic sputtering, the creation of surface defects, and the influence of the ion beam on surface diffusion processes play a decisive role for the morphology evolution. In the case of single charged ions, the energy deposition is dissipated mainly kinetically in a collision cascade which leads finally to the emission of the sputtered atoms and the creation of defects.

[1] A. Keller, S. Rossbach, S. Facsko and W. Möller, Nanotechnology 19, 135303 (2008).
[2] S. Facsko et al., Science 285, 1551 (1999), F. Frost et al., Phys. Rev. Lett. 85, 4116 (2000).
[3] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mucklich, S. Facsko and J. Fassbender
Keywords: Nanostructures, ion sputtering, ripple patterns
  • Lecture (others)
    Seminar der Physikfakultät, 25.11.2010, Cosenza, Italia

Permalink: https://www.hzdr.de/publications/Publ-15187
Publ.-Id: 15187


In vitro binding profile and radiosynthesis of a novel 18F-labeled azaspirovesamicol analog as potential ligand for imaging of the vesicular acetylcholine transporter

Wenzel, B.; Hiller, A.; Fischer, S.; Sorger, D.; Deuther-Conrad, W.; Scheunemann, M.; Brust, P.; Sabri, O.; Steinbach, J.
Radiolabeled vesamicol analogues are promising candidates as ligands for the vesicular acetylcholine transporter (VAChT) to enable in vivo imaging of early cholinergic degenerations in brain. The 4-fluorobenzoyl substituted azaspirovesamicol derivative FBASV is one out of six novel vesamicol analogs and demonstrated most appropriate in vitro binding data. 18F-radiolabeling was performed by microwave assisted nucleophilic aromatic substitution of the corresponding nitro precursor and two methods were developed for the purification of [18F]FBASV. Utilizing method A, the remaining nitro precursor was reduced to its corresponding amine, which was separated via semi-preparative HPLC on a conventional RP column. In method B a phenyl column was used for the direct separation of [18F]FBASV and its nitro precursor, resulting in a change of the elution order and better separation parameters. Thus, [18F]FBASV was synthesized with a RCY of 16-18%, a specific activity > 300 GBq/µmol, and a radiochemical purity of > 99.5% suitable for future in vivo studies.
Keywords: azaspirovesamicol, [18F]FBASV, VAChT, PET, 18F-labeling, vesamicol, nitro precursor
  • Journal of Labelled Compounds and Radiopharmaceuticals 54(2011), 426-432
    DOI: 10.1002/jlcr.1891

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Publ.-Id: 15186


Transition metal implanted ZnO: Have we obtained a diluted magnetic semiconductor?

in Chinese
Zhou, S.
Ferromagnetic semiconductor, exhibiting properties of a ferromagnet and a semiconductor simultaneously, is a key material for semiconductor spintronics. To realize diluted ferromagnetic semiconductors, one has to dope semiconductors with transition metal up to several percents. H. Ohno et al. obtained ferromagnetic GaAs:Mn by decreasing the growth temperature in molecular beam epitaxy [1]. In 2000, T. Dietl et al. successfully interpreted the ferromagnetism in GaAs:Mn based on mean-field theory and predicted that p-type wide bandgap semiconductors (ZnO and GaN) can be ferromagnetic above room temperature given the Mn concentration of 5 at.% [2]. This prediction pushed the research on mining for room-temperature ferromagnetic semiconductors as one of the most active topics in the last decade. In this talk, I will present the magnetic and structure properties of transition metal implanted ZnO as well as the opinions from other research groups [3, 4].

1. H. Ohno, et al., Appl. Phys. Lett. 69, 363 (1996).
2. T. Dietl, et al., Science 287, 1019 (2000).
3. K. Potzger, S. Zhou, et al., Appl. Phys. Lett. 88, 052508 (2006).
4. S. Zhou, et al., Phys. Rev. B 77, 035209 (2008).
  • Invited lecture (Conferences)
    Invited talk at Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, 08.11.2010, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-15185
Publ.-Id: 15185


On the role of americium in the reduction process in plutonium-americium oxides

Belin, R. C.; Martin, P. M.; Gavilan, E.; Reynaud, M.; Scheinost, A. C.
Innovative mixed oxide (MOX) (U,Pu)O2-x fuels for sodium fast neutron reactors (SFRs) systems are currently studied within the framework of the fourth generation (GEN-IV) nuclear reactors development. SFRs will be able to burn long-lived minor actinides (MA) such as Americium by adding them homogeneously to the fuel in a small amount (2 to 6%). Because oxygen to metal ratio (O/M) has a direct impact on irradiation performance, a thorough knowledge of its correlation with oxygen potential during manufacturing and especially sintering is of major concern.
A study by Osaka et al. [ ] highlights a conflicting redox behaviour of Am and Pu cations responsible for an unusual oxygen potential vs. O/M ratio relationship in Am-doped MOX. The reason might be that interactions between U and Am predominate and those between Pu and Am can be neglected [ ]. According to the authors, this should result in U being oxidized to a pentavalent state since Am is likely to be trivalent [ ].
We recently performed a coupled X-Ray Diffraction (XRD) and X-Ray Absorption Spectroscopy (XAS) characterization on substoichiometric Am-containing MOX [ ]. Our results show that Am reduction to Am+III is completed before any reduction of Pu is yet observed. Surprisingly, no pentavalent U was evidenced and the behaviour of Am tends to solely influence that of Pu.

In the present work, to go deeper into the underlying phenomenon involved in the correlated redox behavior of Pu and Am, we focused on U-free sub-stoichiometric (Pu,Am)O2-x compounds. Three compositions were prepared via conventional solid-state reaction under Ar/5%H2 (1800K; 50h): (Pu0.992Am0.008)O2-x, (Pu0.9Am0.1)O2-x and (Pu0.8Am0.2)O2-x. XRD and XAS analyses were combined to selectively probe the long-range and the short-range order and the local environment of both cations. In particular, X-ray Absorption Near Edge Structure (XANES) allows to quantitatively determining the oxidation states for each cation. XRD shows a monophasic system for each composition. Interestingly, the variation of the cell parameter vs. Am concentration is not linear.
In the presentation, we shall detail and compare XRD and XAS results. Especially, we will focus on the correlation between Am content, cell parameter and ratios of Am+3/Am+4 and of Pu+3/Pu+4. We believe our results will improve comprehension of the role of Americium in the overall reduction process occuring in Americium-doped MOX fuels. They may also contribute to the development of the chemical thermodynamic models used to describe such materials.
Keywords: americium, plutonium, MOX, nuclear fuel, SFR, XAS, XRD
  • Lecture (Conference)
    GLOBAL 2011, 04.-09.09.2011, Nagoya, Japan

Permalink: https://www.hzdr.de/publications/Publ-15184
Publ.-Id: 15184


CFD simulation of fibre material transport in a PWR under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Weiss, F.-P.
During a postulated cold leg LOCA with hot leg ECC injection, a limited amount of small fractions of the insulation material after passing the sump strainers can enter the upper plenum and can accumulate at the fuel element spacer grids, preferably at the uppermost grid level. This effect might affect the ECC flow into the core and could result in degradation of core cooling. The CFD simulations show that after starting the sump mode, the ECC water injected through the hot legs flows down into the core at so-called “brake through channels” located at the outer core region where the downward leg of the convection role had established. The hotter, lighter coolant rises in the center of the core. As a consequence, the insulation material is preferably deposited at the uppermost spacer grids positioned in the break through zones. This means that at the beginning the fibers are not uniformly deposited over the core cross section.
Keywords: CFD, LOCA, PWR
  • Kerntechnik 76(2011), 39-45

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Publ.-Id: 15183


Structural characterization of thermodynamically predicted U(VI)-tartrate complexes: Combing Factor Analysis with Landweber inversion method

Rossberg, A.; Lucks, C.; Tsushima, S.; Scheinost, A. C.
An intrinsic problem of EXAFS shell fitting is that the radial pair distribution function (PDF) is approximated by Gaussians functions imitating the coordination shells. Different combinations of shells can yield different structures with similar fit quality, thereby making the structural solution non-unique. Even the so-called F-test often does not yield a unique solution. The shell fit analysis of complicated spectra, as in the case of thermodynamically predicted aqueous complexes of U(VI) with tartaric acid, is much more eased if the PDF for the first shells are computed precisely and independently. Solely based on the FEFF scattering theory, the Landweber inverse method [1] yields the PDF for the aqueous mono-, bi- and tri-nuclear U(VI)-tartaric acid complexes without predefined assumptions about the form of the PDF. With this information and density functional theory (DFT) calculations, the spatial structures of the complexes were determined. Depending on the pH the U(VI)-tartaric acid complexes coexist, hence the EXAFS signal is a mixture of the spectral contributions of the complexes. In order to accomplish this special structural analysis we measured an EXAFS pH-series and isolated the spectra of the single complexes from their mixtures by using factor analysis [2].

[1] A. Rossberg, et al., Journal of Synchrotron Radiation, 17, 280-288 (2010).
[2] A. Rossberg, et al., Analytical and Bioanalytical Chemistry, 376, 631-638 (2003).
Keywords: EXAFS, metal complex, inverse method, Landweber iteration
  • Poster
    Actinide XAS 2011, 02.-04.03.2011, Hyogo, Japan

Permalink: https://www.hzdr.de/publications/Publ-15182
Publ.-Id: 15182


Numerical simulations of counter-current two-phase flow experiments in a PWR hot leg model using an interfacial area density model

Höhne, T.; Deen, D.; Lucas, D.
In order to improve the understanding of counter-current two-phase flows and to validate new physical models, CFD simulations of 1/3rd scale model of the hot leg of a German Konvoi PWR with rectangular cross section was performed. Selected counter-current flow limitation (CCFL) experiments at the Helmholtz–Zentrum Dresden–Rossendorf (HZDR) were calculated with ANSYS CFX 12.1 using the multi-fluid Euler–Euler modeling approach. The transient calculations were carried out using a gas/liquid inhomogeneous multiphase flow model coupled with a k-x turbulence model for each phase. In the simulation, the surface drag was approached by a new correlation inside the Algebraic Interfacial Area Density (AIAD) model. The AIAD model allows the detection of the morphological form of the two phase flow and the corresponding switching via a blending function of each correlation from one object pair to another. As a result this model can distinguish between bubbles, droplets and the free surface using the local liquid phase volume fraction value. A comparison with the high-speed video observations shows a good qualitative agreement. The results indicated that quantitative agreement of the CCFL characteristics between calculation and experimental data was obtained. The goal is to provide an easy usable AIAD framework for all Code users, with the possibility of the implementation of their own correlations.
Keywords: Slug flow, CFD, AIAD

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Publ.-Id: 15181


Herstellung und magnetische Charakterisierung von Co-Nanopartikel auf ionenstrahlerodierten Siliziumsubstraten

Buhl, M.; Körner, M.; Fritzsche, M.; Wiesenhütter, U.; Liedke, O.; Fassbender, J.ORC
Co-Nanopartikel wurden auf den selbstorganisierten Ripplen ionenstrahlerodierter Si-Substrate mittels Molekularstrahlepitaxie deponiert. Im Rahmen der Untersuchung sind Substrattemperatur und nominelle Beschichtungsdicke gezielt variiert worden. Mit Hilfe der longitudinalen magneto-optischen Kerr-Effekt Magnetometrie wurde der Einfluss der Ripple-Oberfläche auf das magnetische Verhalten der Co-Partikel analysiert. Die Auswertung der Messergebnisse von normierter remaneter Kerr-Drehung und Koerzitivfeldstärke zeigt eine uniaxiale magnetische Anisotropie. Die leichte Richtung der Magnetisierbarkeit liegt parallel zu den Ripple-Wellenfronten.
Keywords: Ripple, Co-nanoparticle, MOKE, Co-particle, Kerr Effect, Selforganisation, Magnetism, Anisotropy
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM) 2010, 21.-26.03.2010, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15180
Publ.-Id: 15180


The trigonal nodal SP3 method of the reactor code DYN3D

Duerigen, S.; Fridman, E.; Kliem, S.
DYN3D is a 3D nodal diffusion code for steady-state and transient analyses of Light-Water Reactors (LWRs) with square and hexagonal fuel assembly geometries. Currently, several versions of the DYN3D code are available including a multi-group diffusion and a simplified P3 (SP3) neutron transport option for square geometry as well as a multi-group diffusion version for hexagonal geometry.
In this work, the multi-group SP3 method based on a trigonal-z geometry was developed. The method is applicable to the analysis of reactor cores with hexagonal fuel assemblies and allows flexible mesh refinement, which is of particular importance for VVER-type Pressurized Water Reactors (PWRs) as well as for innovative reactor concepts including block type High-Temperature Reactors (HTRs) and Sodium Fast Reactors (SFRs).
In this paper, the theoretical background for the trigonal SP3 methodology is outlined and the results of a preliminary verification analysis are presented by means of two VVER-440 single assembly test examples with different material compositions. The accordant cross sections and reference solutions were produced by the Monte Carlo code SERPENT. The DYN3D results are shown for 2 and 8 energy groups, respectively, and are in good agreement to the reference solutions. The maximum deviation in the nodal power distribution is about 1%.
Keywords: simplified P3, SP3, nodal, trigonal, triangular, hexagonal, DYN3D
  • Contribution to proceedings
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan
  • Lecture (Conference)
    19th International Conference on Nuclear Engineering (ICONE19), 16.-19.05.2011, Chiba, Japan

Permalink: https://www.hzdr.de/publications/Publ-15179
Publ.-Id: 15179


Numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field

Miao, X.; Lucas, D.; Gerbeth, G.
The numerical simulation of the melt flow in the continuous casting process with respect to gas injection and the impact of a DC magnetic field is presented. Numerical calculations were performed by means of the software package CFX with an implemented RANS-SST turbulence model.
Keywords: continuous casting, electromagnetic brake, numerical simulation
  • Lecture (Conference)
    Symposium zur Simulation metallurgischer Strömungen an österreichischen und deutschen Universitäten, 17.-18.06.2010, Kirnitzschtal, Germany

Permalink: https://www.hzdr.de/publications/Publ-15178
Publ.-Id: 15178


Structural characterisation of Er implanted, Ge-rich SiO2 layers using slow positron implantation spectroscopy

Anwand, W.; Kanjilal, A.; Brauer, G.; Wagner, A.; Butterling, M.; Cowan, T. E.; Rebohle, L.; Skorupa, W.
Electroluminescence in SiO2 layers can be created by Ge implantation and a subsequent heat treatment, leading to the formation of Ge nano-particles inside the SiO2. An additional implantation of Er, connected with a further annealing, can lead to an improvement of the luminescent properties. However, the intensity of electroluminescence was found to decrease drastically after exceeding an optimum concentration of the Er doping.
Slow positron implantation spectroscopy (SPIS), both in single (DB) and coincidence (CDB) Doppler broadening mode, was applied to probe processes at a microscopic level which might have an impact on the optical response. It shows that the increasing intensity of the electro-luminescence is connected with a crystalline structure of the SiO2 covering the nano-particles and also with the improved reverse energy transfer process between Er and Ge.
Keywords: Er doped Ge-rich SiO2, electroluminescence, positron annihilation, Doppler broadening, structural changes

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Permalink: https://www.hzdr.de/publications/Publ-15177
Publ.-Id: 15177


Cu diffusion-induced vacancy-like defects in freestanding GaN

Elsayed, M.; Krause-Rehberg, R.; Moutanabbir, O.; Anwand, W.; Richter, S.; Hagendorf, C.
Positron annihilation spectroscopy was employed to elucidate the nature and thermal behavior of defects induced by Cu in freestanding GaN crystals. Cu atoms were intentionally introduced in GaN lattice through thermally activated diffusion from an ultrathin Cu capping layer. During isochronal annealing of the obtained Cu-doped GaN in the temperature range of 450–850 K, vacancy clusters were found to form, grow and finally vanish. Doppler broadening measurements demonstrate the presence of vacancy-like defects across the 600 nm-thick layer below the surface corresponding to the Cu-diffused layer as evidenced by secondary ion mass spectrometry. A more qualitative characterization of these defects was accomplished by positron lifetime measurements. We found that annealing at 450K triggers the formation of divacancies, whereas further increase of the annealing temperature up to 550K leads to the formation of large clusters of about 60 vacancies. Our observations suggest that the formation of these vacancy-like defects in bulk GaN is related to the out-diffusion of Cu.
Keywords: Cu diffusion-induced vacancy-like defects, GaN, positron annihilation spectroscopy
  • Open Access Logo New Journal of Physics 13(2011), 013029

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Permalink: https://www.hzdr.de/publications/Publ-15176
Publ.-Id: 15176


The DRESDYN project at FZD

Gerbeth, G.; Eckert, S.; Gundrum, T.; Stefani, F.
The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is intended to become a platform both for large scale experiments related to geo- and astrophysics as well as for safety and thermohydraulic studies related to liquid metal batteries and sodium fast reactors. The most ambitious parts of DRESDYN are a homogeneous dynamo driven solely by precession and a large Tayler-Couette like experiment for the combined investigation of the magnetorotational instability and the Tayler instability.
In the talk we give a short summary of the previous achievements, and we delineate the next steps for the realization of DRESDYN.
  • Lecture (Conference)
    13th MHD-days, 22.-23.11.2010, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-15175
Publ.-Id: 15175


Experimental and numerical modeling of the steel flow in a continuous casting mould exposed to a transverse DC magnetic field

Timmel, K.; Miao, X.; Lucas, D.; Eckert, S.; 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
  • Lecture (Conference)
    Workshop "Modelling for Material Processing", 16.-17.09.2010, Riga, Latvia

Permalink: https://www.hzdr.de/publications/Publ-15174
Publ.-Id: 15174


How to circumvent the size limitation of liquid metal batteries due to the Tayler instability

Stefani, F.; Weier, T.; Gundrum, T.; Gerbeth, G.
Recently, a new type of battery has been proposed that relies on the principle of self-assembling of a liquid metalloid positive electrode, a liquid electrolyte, and a liquid metal negative electrode. While this configuration has been claimed to allow arbitrary up-scaling, there is a size limitation of such a system due to a current-driven kink-type instability that is known as the Tayler instability. We characterize this instability in large-scale self-assembled liquid metal batteries and discuss various technical means how it can be avoided.

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Publ.-Id: 15173


VGF - type buoyant flow under a Travelling Magnetic Field - Numerical and experimental modelling

Galindo, V.; Niemietz, K.; Paetzold, O.; Gerbeth, G.; Stelter, M.
The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The application of a travelling magnetic field (TMF) allows the temperature and concentration fields to be tailored during growth by introducing an additional melt flow. Detailed knowledge about the flow pattern and stability resulting from the superposition of buoyant and electromagnetic forces is necessary to achieve VGF-TMF growth under optimal convective conditions. Direct measurements of the melt flow in real conditions, however, are extremely difficult because of the enclosed, high-temperature growth environment. In this lecture experimental and numerical modelling of a VGF-type flow under the influence of a TMF are presented. Low-temperature flow experiments at around 70°C were carried out using a GaInSn alloy (melting point: 10.5°C) as the model fluid. Radial heating and cooling of the melt leading to a double vortex buoyant flow like in typical VGF growth, was introduced by means of a model furnace with separately adjustable resistance heaters. The flow was characterized by means of Ultrasonic Doppler Velocimetry (UDV) giving the velocity profile perpendicular to the UDV probe face. The turbulent flow and the temperature distribution in the melt due to the combined action of a travelling magnetic field and the thermal convection were simulated numerically using a finite volume code based on the open source code library OpenFOAM. The k-omega SST RAS turbulence model was used. The distribution of the amplitude of the kinetic energy k, as an expression for the velocity fluctuations, was calculated for different values of the strength and frequency of the applied magnetic field and different heating regimes. The melt flow is systematically studied as a function of axial and radial temperature gradients as well as of strength and frequency of the magnetic field. Particular attention is paid on the effect of the thermal and TMF parameters on the transition to time-dependent melt flow which is a crucial problem in VGF crystal growth. The stability limit is found to be significantly influenced by the mutual interaction of buoyant and TMF-driven flows. It is shown that the TMF-induced flow can be stabilized by natural buoyancy and vice versa, and the conclusions to be drawn for real VGF growth are discussed.
Keywords: crystal growth, vertical gradient freeze, travelling magnetic field
  • Lecture (Conference)
    7. Workshop Angewandte Simulation in der Kristallzüchtung, 23.-24.11.2010, Burghausen, Deutschalnd

Permalink: https://www.hzdr.de/publications/Publ-15172
Publ.-Id: 15172


Bakterien als Lieferanten für neue Recycling-Technologien: Rückgewinnung von Metallen aus Wässern mit neuen Biokompositmaterialien

Pollmann, K.
Potenzial von Bakterien für neue Technologien
  • Invited lecture (Conferences)
    1. Freiberger Ressourcen-Technologie Symposium, 14.-15.02.2011, Freiberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15171
Publ.-Id: 15171


Combination of internal and external irradiation: Binding of the monoclonal EGFR-antibody C225 in irradiated tumors

Koi, L.; Brüchner, K.; Bergmann, R.; Helbig, L.; Steinbach, J.; Baumann, M.; Zips, D.
kein Abstract verfügbar
  • Poster
    European Society for Therapeutic Radiology and Oncology (ESTRO), 12.-16.09.2010, Barcelona, Spain

Permalink: https://www.hzdr.de/publications/Publ-15170
Publ.-Id: 15170


Fundamental and application oriented research on bacterial S-layers from uranium mining waste pile isolates

Weinert, U.; Raff, J.; Günther, T.; Pollmann, K.
Übersicht des Instiutes für Radiochemie und Vorstellung aktueller Forschungsthemen der Nachwuchsgruppe NanoBio
  • Lecture (others)
    Besuch der Arbeitsgruppe von Prof. Betzel, 26.01.2011, DESY Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-15169
Publ.-Id: 15169


Monte-Carlo simulations for timing-system of EPOS at ELBE in Research Centre Dresden-Rossendorf

Butterling, M.; Jungmann, M.; Bondarenko, V.; Sachert, S.; Brauer, G.; Anwand, W.; Krause-Rehberg, R.
Most of the monoenergetic slow-positron beam systems capable for positron lifetime spectroscopy are bunched from a continuous beam (e.g., the PLEPS system in Munich). The EPOS system at the ELBE radiation source will use the original time structure of the 40-MeV electron beam which is utilized for pair production. This is an infinite repetition of very short electron pulses (< 5 ps) with an adjustable repetition rate (typical 77 ns). In both cases, the time structure of the positron beam needs sharpening so that the time focus is located at the sample position. This is realized by the bunching system. Usually, double-slit bunchers are used. They are operated by a sinusoidal RF-voltage. This bunching requires an adjustment according to the final positron energy (0.5...30 keV), since the acceleration of the positrons shifts their time focus. Monte-Carlo simulations were done to investigate the effect of different methods of time focusing. One method is the variation of amplitude of the buncher RF-voltage. Another improvement is the combination of such a buncher voltage variation with a variable drift path acceleration short before the final acceleration which is operated by a DC voltage. Our simulations show that indeed a combination of a buncher variation with a drift path gives the sharpest positron pulses when both devices are supplied with individual voltages for each positron implantation energy.
Keywords: Monte-Carlo simulations for timing-system

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Permalink: https://www.hzdr.de/publications/Publ-15168
Publ.-Id: 15168


Single-magnet rotary flowmeter for liquid metals

Priede, J.; Buchenau, D.; Gerbeth, G.
We present a novel design of a contactless flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis, about which it can freely rotate, and placed close to a duct with a liquid metal flow. The electromagnetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation.
The equilibrium rotation rate, which is attained at a vanishing net electromagnetic torque on the magnet, depends only on the flow rate and the geometry of the system while it is independent of the electromagnetic torque itself.
A laboratory model of such a flowmeter has been built and tested on a liquid metal flow.
  • Journal of Applied Physics 110(2011)3, 034512
    DOI: 10.1063/1.3610440
  • Contribution to proceedings
    8th International pamir Conference on Fundamental and Applied MHD, 05.-09.09.2011, Borgo, Corsica, France
    Proceedings of the 8th International pamir Conference on Fundamental and Applied MHD, 575-579

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Publ.-Id: 15167


Quenched-in vacancies in Fe3Al based alloys: a positron annihilation study

Melikhova, O.; Čížek, J.; Kuriplach, J.; Procházka, I.; Lukáč, F.; Cieslar, M.; Anwand, W.; Brauer, G.
In the present contribution, high-resolution positron lifetime spectroscopy and slow positron implantation spectroscopy are used to characterize defects in Fe75.99Al24.01 and Fe71.98Al28.02 alloys. In order to facilitate defect identification, we also perform a theoretical study of basic vacancy-like defects in three phases of the Fe3Al system: ordered (D03), shortrange ordered (B2) and disordered (A2). Positron characteristics, i.e. positron lifetime and positron binding energy to defects are calculated from the first principles for various defect configurations. The results are discussed in the context of experimental data obtained here and available in literature.
Keywords: Fe-Al alloys, defects, positron annihihaltion spectroscopy

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Publ.-Id: 15166


Contactless electromagnetic phase-shift flowmeter for liquid metals

Priede, J.; Buchenau, D.; Gerbeth, G.
We present a concept and test results of an induction flowmeter for liquid metals.
The flow rate is determined by applying a weak AC magnetic field to a liquid metal flow and measuring the flow-induced phase disturbance in the external electromagnetic field. The phase disturbance is found to be more robust than that of the amplitude used in conventional AC flowmeters. The basic characteristics of this type of flowmeter are analysed using simple theoretical models where the flow is approximated by a solid body motion. Design of such a flowmeter is presented and its test results reported.
  • Measurement Science and Technology 22(2011)5, 055402

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Permalink: https://www.hzdr.de/publications/Publ-15165
Publ.-Id: 15165


Digital positron lifetime: the influence of noise

Krille, A.; Anwand, W.; Krause-Rehberg, R.
In contrast to the world around where everything seems to go digital as soon as possible, positron lifetime spectrometers are kind of a “last sanctuary” for analog measurements. Only a few of the newer spectrometers use the analog-digital-converters directly after the photomultipliers and extract the timing information via computer. Judging from their results it seems as if the current available converters and the timing mathematics are only as good as the conventional analog setup in the timing resolution. As it is decided that EPOS [1] will use digital positron lifetime, we try to find some reasons for limited timing resolution by simulating anode pulses from the photomultipliers and measuring the FWHM. We create pulses similar to current state-of-the-art 4GS/s digitizers but can control the level of noise and the bit-depth independently. We found that especially the noise (that would come from the analog electronics in/before the converters) has a great influence on the timing resolution. Also we try to use lowpass filtering to reduce that influence with great success.
Keywords: digital positron lifetime spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-15164
Publ.-Id: 15164


The sensitivity of a travelling magnetic field driven flow to axial alignment

Cramer, A.; Pal, J.; Koal, K.; Tschisgale, S.; Stiller, J.; Gerbeth, G.
The sensitivity of a flow that is driven by a travelling magnetic field (TMF) with respect to a shift between the axes of the cylindrical liquid metal column and of the TMF was studied both experimentally and by numerical simulation. In the physical modelling, the generation of the TMF comprised six equidistantly spaced cylindrical coils loaded with ac current having a phase shift of 60 degree, respectively, between them. Ultrasound Doppler velocimetry was used to acquire vertical sections of the vertical velocity component along the beam axis in the centre and at various azimuthal positions for a fixed radial coordinate. The measurements are compared to the according flow data from large eddy simulations. These computations were based on the usual approximations to simplify the magnetohydrodynamical equations, which are low frequency and low induction, and on an analytical expression for the Lorentz force considering the shift between the fluid volume and the field. It is shown that even a small shift between the axes may result in a distinct three-dimensional constituent of the flow structure, and thus changing completely the usually assumed axisymmetric torus-type flow.
Keywords: Fluid flows, Magnetic fields, Stirring, Growth from melt
  • Journal of Crystal Growth 321(2011)1, 142-150

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Permalink: https://www.hzdr.de/publications/Publ-15163
Publ.-Id: 15163


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