Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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33407 Publications

Next jump of energy efficiency of photovoltaics technology - not only a vision!

von Borany, J.
Present strategies of photovoltaic (PV) industry are strongly directed to lower the fabrication costs and/or to enhance the solar cell efficiency with the overall aim to achieve grid parity in near future. Bandgap engineered materials including semiconductor and metal nanoparticles can contribute to reduce energy conversion losses due to thermalization and missing infrared light absorption. Based on such materials, the European PV roadmap describes a clear route towards solar cells with significantly enhanced efficiencies.
Keywords: photovoltatics, 3rd generation solar cells, nanostructures
  • Invited lecture (Conferences)
    7th Innovationsforum for Automation, 21.-22.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13640
Publ.-Id: 13640


Charge order, enhanced orbital moment, and absence of magnetic frustration in layered multiferroic LuFe2O4

Kuepper, K.; Raekers, M.; Taubitz, C.; Prinz, M.; Derks, C.; Neumann, M.; Postnikov, A. V.; de Groot, F. M. F.; Piamonteze, C.; Prabhakaran, D.; Blundell, S. J.
Electronic and magnetic properties of the charge ordered phase of LuFe2O4 are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe2O4 is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground state of LuFe2O4 in the charge ordered phase to be a 2:1 ferrimagnetic configuration, ruling out a frustrated magnetic state. An enhanced orbital moment may enhance the magnetoelectric coupling. Furthermore, we determine the densities of states and the corresponding correlation potentials by means of x-ray photoelectron and emission spectroscopies, as well as electronic structure calculations.
  • Physical Review B 80(2009)22, 220409

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Permalink: https://www.hzdr.de/publications/Publ-13639
Publ.-Id: 13639


Microbial Links between Sulfate Reduction and Metal Retention in Uranium- and Heavy Metal-Contaminated Soil

Sitte, J.; Akob, D.; Kaufmann, C.; Finster, K.; Banerjee, D.; Burkhardt, E.-M.; Kostka, J.; Scheinost, A.; Büchel, G.; Küsel, K.
Sulfate-reducing prokaryotes (SRP) can affect metal mobility either directly by reductive transformation of metal ions, e.g., uranium and chromium, into their insoluble forms or indirectly by formation of metal sulfides. This study evaluated in situ and biostimulated activity of SRP in groundwater influenced soils from a creek bank contaminated with heavy metals and radionuclides within the former uranium-mining district, Ronneburg (Germany). In situ activity of SRP, measured by the 35S-SO42-radiotracer method, was restricted to reduced soil horizons with rates 142 ± 20 nmol cm-3 day-1. Although concentrations of heavy metals were enriched in the solid phase of the reduced horizons, porewater concentrations were low. XANES measurements demonstrated that ~80% of uranium was present as reduced uranium, but appeared to occur as a sorbed complex. Soil-based dsrAB clone libraries were dominated by sequences most closely affiliated to members of the Desulfobacterales, but also Desulfovibrionales, Syntrophobacteraceae and Clostridiales. 13C-acetate and 13C-lactate biostimulated soil microcosms were dominated by sulfate and Fe(III) reduction, which was associated with enrichment of similar SRP found using the dsrAB marker in soil and with sequences related to Geobacter. Concentrations of soluble nickel, cobalt, and occasionally zinc declined 100% during anoxic soil incubations. In contrast to other studies, soluble uranium increased in carbon-amended treatments reaching 1407 nM in solution. Our results suggest that (i) contaminated reduced soil with on-going sulfate reduction resulted in in situ metal attenuation and (ii) the fate of uranium mobility is not predictable and may lead to downstream contamination of adjacent ecosystems.
Keywords: heavy metals, Uranium, XANES, Sulfate-reducing bacteria

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Permalink: https://www.hzdr.de/publications/Publ-13638
Publ.-Id: 13638


Macroscopic thermomagnetic convection: A more generic case and optimization

Cramer, A.; Zhang, X.; Gerbeth, G.
It was demonstrated in a previous paper that the interaction between a thermoelectric current j and an imposed static magnetic field B produced thermoelectromagnetic convection (TEMC). The prominent feature was utilisation of a wall material exhibiting a big difference in the thermoelectric power S in comparison to the fluid. Although high flow velocities were accomplished, the vigour was potentially mitigated by two design issues. Firstly, the side walls parallel to the temperature gradient Grad T were made from the same electrically high conducting material as the isothermal walls. This, in parts, shorts the thermoelectric current. Moreover, these walls might be seen as lowering the degree of the experiment of being generic. Secondly, the field created by a permanent magnet covered only a small fraction of the fluid volume. Again, albeit being mirror symmetric, the three-dimensional distribution of B lowers the degree of being generic.

The present paper reports on an experimental study on TEMC in a square box wherein the necessary Grad T is accomplished by heating and cooling of two opposing side walls, respectively, whereas the other two side walls are electrically non-conducting. An almost two-dimensional distribution of B is applied to a relatively large area of the interface between the fluid and the bottom of the container. The pole shoes of the magnet are specifically designed so as to have a high value of the curl of the Lorentz force, the non-vanishing of which is another pre-requisite for TEMC. Two containers with different bottom materials are build. The ferromagnetic nickel with negative S used in previous work is replaced by isotan in one variant, offering probably the highest absolute value of S among metals. To consider also the counterpart, nichrome with a high positive S is used in the construction of the second container. Ultrasonic Doppler velocimetry is employed to quantify the TEMC flow field. The results of all three configurations are compared and discussed. In addition, first results on more developed turbulent regimes are presented, which could not be reached in the previous setup because of a more limited Delta S x Delta T.
Keywords: Thermoelectricity, convection, liquid metal, electromagnetic stirring, static magnetic field
  • Magnetohydrodynamics 45(2009)4, 505-510

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Permalink: https://www.hzdr.de/publications/Publ-13637
Publ.-Id: 13637


Ultraschnelle Röntgen-Computertomographie für die Untersuchung von Zweiphasenströmungen

Bieberle, M.; Fischer, F.; Hampel, U.
Die am Forschungszentrum Dresden-Rossendorf entwickelte ultraschnelle Röntgen-Computertomographie ist eine nichtinvasive Messmethode, die eine überlagerungsfreie Abbildung von Phasenverteilungen in transienten Zweiphasenströmungen mit bisher unerreichter zeitlicher und räumlicher Auflösung erlaubt. Damit können sicherheitsrelevante Aspekte in technischen Prozessen, beispielsweise aus der Chemie- und Bioverfahrenstechnik, der Mineralölförderung und der Kerntechnik, untersucht sowie CFD-Simulationscodes validiert werden.
Keywords: x-ray, computed tomography, ultrafast imaging, flow measurement
  • Poster
    Ideas to Market - Dresdner Materialinnovationen für die Praxis & Verleihung "Dresden Barkhausen Award 2009", 15.01.2010, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13636
Publ.-Id: 13636


Anionic and cationic substitution in ZnO

von Wenckstern, H.; Schmidt, H.; Brandt, M.; Lajn, A.; Pickenhain, R.; Lorenz, M.; Grundmann, M.; Hofmann, D.; Polity, A.; Meyer, B. K.; Saal, H.; Binnewies, M.; Börger, A.; Becker, K.-D.; Tikhomirov, V. A.; Jug, K.
In this contribution we review the impact of anionic and cationic substitutions on the electronic properties of bulk ZnO crystals, thin films and ZnO powders. p-type doping is discussed with focus on the anionic substitution of oxygen by nitrogen or phosphorous. n-type doping is exemplarily reviewed for substitution of Zn by group III elements. The impact of isoelectronic substitution of zinc (with Cd or Mg) or of oxygen (with S, Se, Te) on the band gap are also discussed for the respective ternary alloy. The substitution of Zn by the transition metal Mn introduces several electronic levels in the band gap which significantly alter the absorption and emission properties. Further, devices based on substitutional effects in ZnO are reviewed: Schottky diodes (unipolar device) and pn-diodes (bipolar device).

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Permalink: https://www.hzdr.de/publications/Publ-13635
Publ.-Id: 13635


Excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid

Vulpius, D.; Geipel, G.; Bernhard, G.
The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.
Keywords: 3-Hydroxybenzoic acid 4-Hydroxybenzoic acid Excited-state proton transfer Time-resolved laser-induced fluorescence spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-13634
Publ.-Id: 13634


Vergleich von Fluorierungstechniken zur industriellen Anwendung des Halogeneffekts mit kernphysikalischen Verfahren

Neve, S.; Masset, P. J.; Yankov, R. A.; Zschau, H.-E.; Kolitsch, A.; Dörner, R.; Schütze, M.
Ein Hochtemperatur-Oxidationsschutz von Titanaluminiden kann durch Verwendung des Halogen-Effektes realisiert werden. Fluor erwies sich dabei als am besten geeignet, insbesondere bei termozyklischer Beanspruchung. Unter isothermen wie auch zyklischen Bedingungen ist die schützende Wirkung der sich bildenden Aluminiumoxidschicht für bis zu 4000 h bei 900° - 1050°C experimentell gezeigt werden. Als Technik zur Einbringung der Halogene unter die Metalloberfläche wurde die Beamline-Ionenimplantation intensiv untersucht. Die Größe des Strahlfleckes beträgt nur etwa 10 cm2 und bei der komplexen Geometrie der zu Behandelnden Bauteile kann ein einheitlicher Einschusswinkel nicht realisiert werden. Chemische Behandlungen, wie das Tauchen in verdünnter HF-Lösung, sind diffusionsgesteuert und damit weiterstehend unabhängig von der vorliegenden Bauteilgeometrie. Bei der kontrollierten Gasphasenfluorierung wurden die Fluorionen durch die thermische Zersetzung einer einer CFn-Verbindung erzeugt. Bei der am Forschungszentrum Dresden-Rossendorf durchgeführten Plasma-Immersions-Ionenimplantation (PIII) werden die Fluorinen von einem CH2F2/Ar-Plasma bereitgestellt. Die PIII Methode soll als Referenztechnik für die Behandlung komplexer Geometrien eingesetzt werden, da die Parameter genau kontrolliert werden können. Am IKF wurden dazu die Protonen induzierte Gamma-Emission (PIGE) und Rutherford Basckscattering (RBS) am 2.5 MV van de Graaf-Beschleuniger eingesetzt. Mit der PIGE können Fluorkonzentrationen mit einer Genauigkeit besser als 7% gemessen werden.
  • Contribution to external collection
    in: Jahresbericht 2009 des Instituts für Kernphysik der Goethe-Universität Frankfurt, Frankfurt am Main: Goethe-Universität Frankfurt, 2009

Permalink: https://www.hzdr.de/publications/Publ-13633
Publ.-Id: 13633


Surface modification of Ti and low Al-content Ti alloys for enhanced environmental stability at elevated temperatures

Yankov, R. A.; Kolitsch, A.; von Borany, J.; Munnik, F.; Donchev, A.; Schütze, M.
It is now well-established that TiAl alloys containing Al between about 40 and 55 at.% may be modified by introducing a halogen element, notably F, into their near-surface region (the so-called halogen effect) to protect them against high-temperature environmental degradation. Upon subsequent high-temperature oxidation, the TiAl alloys modified in this way acquire а highly protective alumina scale, and are suitable for advanced automobile, aerospace and power generation applications. Low-Al content (typically < 10 at.%) Ti alloys, however, contain insufficient amounts of Al for the halogen effect to be activated necessitating enrichment with Al of their near-surface region. In this work, both α-Ti and low-Al content Ti alloys have been processed to render them oxidation-resistant in air at temperatures of 600 to 1050°C by promoting the formation of a protective scale. Surface processing has generally involved two steps, namely Al enrichment and introduction of F. The Al enrichment has in turn involved deposition of a thin Al film by magnetron sputtering followed by either Ar ion bombardment or rapid thermal annealing. The introduction of F has been achieved by plasma immersion ion implantation. Analytical techniques such as ERDA, RBS, XRD, SEM and EDX have been used for sample characterization. Under optimized processing conditions the metal samples so modified have shown high-temperature environmental stability comparable to that of standard TiAl (40 < Al < 55 at.%) alloys.
  • Poster
    Surface modification of Ti and low Al-content Ti alloys for enhanced environmental stability at elevated temperatures, 08.-12.06.2009, Strasbourg, France

Permalink: https://www.hzdr.de/publications/Publ-13632
Publ.-Id: 13632


Comparison of fluorination treatments to improve the high temperature oxidation resistance of TiAl alloys in SO2-containing environments

Masset, P. J.; Yankov, R. A.; Kolitsch, A.; Schütze, M.
Surfaces of titanium aluminides were treated with fluorine either physically by plasma immersion ion implantation (PIII) or chemically using a F-based polymer. Under optimum conditions of fluorination, both treatments were shown to improve the oxidation resistance of the alloys even in aggressive environments containing sulfur dioxide (0.1 vol. %). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen was found to be reduced in the presence of SiO2.
  • Lecture (Conference)
    International Conference on PROCESSING & MANUFACTURING OF ADVANCED MATERIALS (THERMEC 2009), 25.-29.08.2009, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-13631
Publ.-Id: 13631


Oxidation resistance improvement of TiAl alloys by the halogen effect in industrial environments

Masset, P. J.; Neve, S.; Zschau, H.-E.; Yankov, R. A.; Kolitsch, A.; Schütze, M.
No abstract available.
  • Poster
    European Congress and Exhibition on Advanced Materials and Processes EUROMAT’09, 07.-10.09.2009, Glasgow, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-13630
Publ.-Id: 13630


Enhancing the resistance of Ti-alloys against environmental high temperature degradation by a combination of Al-enrichment and F-treatment

Donchev, A.; Kolitsch, A.; Schütze, M.; Yankov, R.
Titanium is a widely used structural material due to its low specific weight, mechanical properties and good corrosion resistance at low temperatures. The melting point (1677°C) is much higher than the maximum operating temperature of about 600°C. Because of increased oxidation rate and environmental embrittlement Ti-Alloys can not be used at higher temperatures. The surface treatment with F gives very good results for TiAl-alloys but has only little or no effect on the oxidation resistance of Ti-alloys. Enrichment of the near-surface zone of Ti-alloys with Al leads to an improvement in the oxidation resistance which, however, is insufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed, and an additional F-treatment gives good results. The fluorine effect on TiAl-alloys leads to the formation of a protective alumina scale. Not only does the scale provide protection against environmental attack, but it also prevents oxygen inward diffusion which causes embrittlement. In this work results of high temperature oxidation tests several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment, single Al-treatment, pure F-treatment and the combination of both. Enrichment with Al has been done by either powder pack process or magnetron sputtering. Fluorine has been introduced using a liquid phase process as well as alternative techniques. Subsequent analyses by SEM and other methods reveal the formation of thinner oxide layer on the combined Al and F treated samples.
  • Lecture (Conference)
    European Congress and Exhibition on Advanced Materials and Processing EUROMAT’09, 07.-10.09.2009, Glasgow, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-13629
Publ.-Id: 13629


Combined Al- plus F-treatment of Ti-alloys for improved behaviour at elevated temperatures

Donchev, A.; Kolitsch, A.; Schütze, M.; Yankov, R.
Due to its low weight and good corrosion resistance at moderate temperatures, titanium is being currently used in a large number of applications. As a result of increased oxidation rate and environmental embrittlement the maximum operating temperature is only about 600°C while the melting point is much higher (1677°C). The oxidation behaviour can be improved by different methods e.g. Al-enrichment of the surface zone. This leads to an improvement which is, however, not sufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed plus an additional F-treatment gives the best results because a protective alumina scale is formed. The fluorine effect is known for TiAl-alloys. An alumina scale is found on TiAl-alloys after F-treatment. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environ-mental attack. Now this effect is transferred to alloys with a very low Al-content or even no Al at all. These alloys can not form an alumina layer by themselves without any treatment. In this work results of oxidation tests of several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment and with Al-treatment, F-treatment and the combination of both. Aluminium was diffused into the samples by a powder pack process. Fluorine can be applied by several ways e.g. ion implantation or gas phase processes. The formation of a thinner oxide scale on treated samples is revealed by post experimental investigations like metallography. The results are discussed referring to the fluorine effect model for TiAl-alloys.
  • Poster
    European Federation of Corrosion Workshop, 30.09.-02.10.2009, Frankfurt am Main, Germany
  • Materials and Corrosion 62(2011)7, 695-698
    DOI: 10.1002/maco.201005870

Permalink: https://www.hzdr.de/publications/Publ-13628
Publ.-Id: 13628


Study of the role of sulfur functionalities in humic acids for uranium(VI) complexation

Sachs, S.; Reich, T.; Bernhard, G.
Sulfur containing humic acid model substances have been synthesized to study the role of sulfur functionalities for the complexation behavior of humic acids towards U(VI). Humic acids type M1-S with different sulfur contents (1.9, 3.9, 6.9 wt.-%) were synthesized and characterized. The identity of the sulfur species was determined by X-ray photoelectron spectroscopy (XPS). Reduced sulfur species, such as thiols, dialkylsulfides and/or disulfides, were determined as the dominating sulfur functionalities in the used humic acids. The U(VI) complexation of humic acids with different sulfur contents has been studied by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and TRLFS with ultrashort femtosecond laser pulses (fs-TRLFS) in comparison to a sulfur-free humic acid type M1 (pH 3.80 ± 0.02; I = 0.1 M NaClO4; pCO2 = 10-3.5 atm). For all studied humic acids, similar complexation constants were determined. However, with increasing sulfur contents of the humic acids (>2 wt.-%) an increase of the number of humic acid binding sites for U(VI) was determined which is reflected in increasing U(VI) loading capacities and increasing total humic acid ligand concentrations for U(VI) measured by TRLFS and fs-TRLFS, respectively. This increase of the fraction of humic acid binding sites for U(VI) points to an involvement of reduced sulfur functionalities, such as thiol groups, in the complexation between U(VI) and humic acid. However, for environmentally relevant sulfur contents of humic acids (<2 wt.-%) it can be concluded that, compared to oxygen functionalities, especially carboxylic groups, reduced sulfur functionalities play only a subordinate role for the U(VI) complexation by humic acids in the acidic pH range.
Keywords: Humic acid, humic acid model substances, complexation, sulfur functionalities, uranium(VI), XPS, TRLFS, fs-TRLFS

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Permalink: https://www.hzdr.de/publications/Publ-13627
Publ.-Id: 13627


Spin-dependent transport in C:Co and C:Ni nanocomposite thin films

Zhou, S.; Berndt, M.; Buerger, D.; Abrasonis, G.; Radnoczi, G.; Schmidt, H.; Kolitsch, A.; Helm, M.
Nanocomposites exhibiting spin-dependent transport properties show a potential for applications in spintronics. Carbon:transition metal nanocomposites are of particular interest due to their multifunctionality and easiness to control their morphology, and thus properties. In this contribution, we present the study of magneto-transport properties of C:Co and C:Ni nanocomposites. The films were grown by ion beam co-sputtering on thermally oxidized silicon substrates in the temperature range of 200-500°C. Two major effects have been found for C:Co films: (i) a large anomalous Hall effect amounting to 2 micro-Ohm-cm; (ii) a negative magnetoresistance. Both the field-dependent resistivity and Hall resistivity curves well correspond to the magnetization curve, which suggests a spin-dependent transport in the nanocomposite thin films. A similar effect is also reported for C:Ni nanocomposite films. A correlation is reported between the magneto-transport properties and the film microstructure.
  • Poster
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston MA, USA

Permalink: https://www.hzdr.de/publications/Publ-13626
Publ.-Id: 13626


Analysis of non-protein amino acids as specific markers of protein oxidation: the use of N(O,S)-ethoxycarbonyl ethyl ester and N(O,S)-ethoxycarbonyl trifluoroethyl ester derivatives and GC-MS

Pietzsch, J.; Pietzsch, F.-J.; Kopprasch, S.
Oxidative modification of proteins is widely regarded as a crucial event in the pathogenesis of various inflammatory and metabolic diseases. In this line, a sensitive and specific GC-MS methodology using either N(O,S)-ethoxycarbonyl ethyl amino acid esters (ECEE) or N(O,S)-ethoxycarbonyl trifluoroethyl amino acid esters (ECEE-F3) for rapid and sensitive determination of modified amino acid side chain residues as specific oxidation markers in proteins has been developed.
Both ECEE and ECEE-F3 derivatives are formed by the unlabored reaction of amino acids with ethyl chloroformate plus ethanol or trifluoroethanol plus pyridine. The key steps of the methodology involve enzymatic hydrolysis of target proteins to prevent decomposition of oxidation products during hydrolysis and uniquely rapid derivatization of modified amino acids completing sample preparation for GC within a few minutes in aqueous solution at room temperature. The use of this methodology for assessing (glyc)oxidative damage in low density lipoprotein apolipoprotein B-100 (apoB-100) recovered from human plasma and various inflammatory compartments has been demonstrated. The observations provided quantitative chemical evidence for (glyc)oxidative processes in several inflammatory and metabolic diseases.
  • Trends in Chromatography 5(2009), 15-20

Permalink: https://www.hzdr.de/publications/Publ-13625
Publ.-Id: 13625


Mild glykatierte Lipoproteine > geringer Dichte (LDL) verstärken die Adipogenese von 3T3-L1-Zellen

Neuber, C.; Hoppmann, S.; Pietzsch, J.
Diabetes mellitus Typ 2 (T2D) und Adipositas sind zwei wichtige Facetten des Metabolischen Syndroms. Ein pathobiochemisches Bindeglied zwischen beiden Erkrankungen ist möglicherweise die Bildung glykatierter Lipoproteine geringer Dichte (glykLDL), einer frühen Form der advanced glycation endproducts (AGE). Ziel der Untersuchung war es, zu zeigen, ob und über welche Mechanismen glykLDL im Vergleich zu nativen LDL (nLDL) einen Einfluss auf die Adipogenese ausüben.
Durch Inkubation humaner LDL mit Glukose (200 mmol/L, 37°C, 144 h) konnten glykative Veränderungen am Apolipoprotein B-100 der LDL-Partikel erreicht werden, die vergleichbar zu den bei Patienten mit manifestem T2D in vivo auftretenden Veränderungen von LDL sind. Als Modell für die humane Adipogenese diente die hormoninduzierte Umwandlung muriner 3T3 L1-Präadipozyten zu Zellen, die morphologisch und physiologisch reifen Adipozyten ähneln. Mittels quantitativer RT PCR und Western Blotting wurde der Einfluss glykatierter LDL auf die mRNA Expression und Proteinbiosynthese verschiedener (Prä )Adipozytenmarker sowie potentieller glykLDL Rezeptoren untersucht. Darüber hinaus erfolgten Untersuchungen zur zellvermittelten Aufnahme von Fluor-18-markierten LDL.
Es konnte gezeigt werden, dass glykLDL die Lipideinlagerung, als Zeichen der Differenzierung von Präadipozyten zu Adipozyten, signifikant verstärkten, während es unter dem Einfluss der nLDL zu einer signifikant verminderten Adipogenese kam, die sich tendenziell auch in einer verminderten mRNA-Expression des Adipozytenmarkers PPAR2 zeigte. Als potenzielle Mediatoren der LDL-induzierten Effekte wurden sowohl der LDL-Rezeptor (LDLR), der Rezeptor für AGE (RAGE) als auch verschiedene Scavenger-Rezeptoren (SR) näher charakterisiert. Die Untersuchungen mit Fluor-18-markierten LDL zeigten, dass Präadipozyten etwa zehnmal mehr nLDL bzw. glykLDL internalisierten als Adipozyten, wobei die Bindung und Internalisierung von nLDL etwa um den Faktor zwei über der von glykLDL lag. Dies deutet auf eine verminderte Affinität der glykLDL beispielsweise zum LDLR hin. Obwohl glykLDL in vitro und in vivo Liganden für RAGE sind, spielte RAGE bei der Differenzierung von 3T3-L1-Zellen nur eine untergeordnete Rolle. Die Differenzierung von Präadipozyten zu Adipozyten ging mit einer unveränderten SR-B1- sowie mit einer verminderten LDLR-, RAGE-, CD36- und LOX-1-(lectin like oxidized LDL-1)-Rezeptor-Synthese einher. In Kombination mit den Ergebnissen der Zellaufnahmestudien wird deutlich, dass vorrangig der LDLR, der SR-B1 und möglicherweise auch LOX-1 für die Internalisierung der LDL von Bedeutung sind.
Als mögliche intrazelluläre Mechanismen für die glykLDL-induzierte Stimulation der Lipideinlagerung werden die Aktivierung des NF-κB oder des nukleären Leber-X-Rezeptors (LXR) diskutiert. Aus den Ergebnissen der vorliegenden Arbeit lässt sich schlussfolgern, dass bereits mild glykatierte LDL-Partikel die Adipogenese verstärken.
  • Poster
    25. Jahrestagung der Deutschen Adipositas-Gesellschaft und Herbsttagung der Deutschen Diabetes-Gesellschaft, 05.-07.11.2009, Berlin, D
  • Abstract in refereed journal
    AdipositasSpektrum 5(2009), 67

Permalink: https://www.hzdr.de/publications/Publ-13624
Publ.-Id: 13624


Long lifetimes of quantum-dot intersublevel transitions in the terahertz range

Zibik, E. A.; Grange, T.; Carpenter, B. A.; Porter, N. E.; Ferreira, R.; Bastard, G.; Stehr, D.; Winnerl, S.; Helm, M.; Liu, H. Y.; Skolnick, M. S.; Wilson, L. R.
Carrier relaxation is a key issue in determining the efficiency of semiconductor optoelectronic device operation. Devices incorporating semiconductor quantum dots have the potential to overcome many of the limitations of quantum-well-based devices because of the predicted long quantum-dot excited-state lifetimes. For example, the population inversion required for terahertz laser operation in quantum-well-based devices (quantum-cascade lasers1, 2) is fundamentally limited by efficient scattering between the laser levels, which form a continuum in the plane of the quantum well. In this context, semiconductor quantum dots are a highly attractive alternative for terahertz devices, because of their intrinsic discrete energy levels. Here, we present the first measurements, and theoretical description, of the intersublevel carrier relaxation in quantum dots for transition energies in the few terahertz range. Long intradot relaxation times (1.5 ns) are found for level separations of 14 meV (3.4 THz), decreasing very strongly to 2 ps at 30 meV (7 THz), in very good agreement with our microscopic theory of the carrier relaxation process. Our studies pave the way for quantum-dot terahertz device development, providing the fundamental knowledge of carrier relaxation times required for optimum device design.
Keywords: THz, FEL, Quantum Dots

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Permalink: https://www.hzdr.de/publications/Publ-13623
Publ.-Id: 13623


Experimental investigations on the condensation of steam bubbles injected into sub-cooled water at 1 MPa

Lucas, D.; Beyer, M.; Szalinski, L.
Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modelling of the condensation process. To develop and validate closure models for CFD codes new experimental data are required. The effect of bubble sizes is clearly shown in experimental investigations done at the TOPFLOW facility of FZD. Steam bubbles are injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices are used to vary the initial bubble size distribution. The variation of the distance between the location of the gas injection and the measuring plane allows investigating the evolution of the flow along the pipe. Measurements are done using wire-mesh sensors and thermocouples. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Data on averaged void fraction, radial gas volume fraction profiles, profiles of the gas velocity and bubble size distributions in dependency of the L/D ratio are presented in the paper.
Keywords: bubble condensation, poly-dispersed flow, bubble size, pipe flow, experiment, CFD grade data

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Permalink: https://www.hzdr.de/publications/Publ-13622
Publ.-Id: 13622


Electroluminescence induced by Ge nanocrystals obtained by hot ion implantation into SiO2

Bregolin, F.; Behar, M.; Sias, U.; Reboh, S.; Lehmann, J.; Rebohle, L.; Skorupa, W.
Commonly, electroluminescence (EL) from Ge nanocrystals (Ge NCs) has been obtained by room temperature (RT) Ge implantation into a SiO2 matrix followed by a high temperature anneal. In the present work, we have used a novel experimental approach: we have performed the Ge implantation at high temperature (T-i) and subsequently a high temperature anneal at 900 degrees C in order to grow the Ge NCs. By performing the implantation at T-i=350 degrees C, the electrical stability of the MOSLEDs were enhanced, as compared to the ones obtained from RT implantation. Moreover, by changing the implantation fluence from Phi=0.5 x 10(16) and 1.0 x 10(16) Ge/cm(2) we have observed a blueshift in the EL emission peak. The results show that the electrical stability of the hot implanted devices is higher than the ones obtained by RT implantation. (C) 2009 American Institute of Physics.
Keywords: Electroluminescence Ge nanocluster high temperature implantation
  • Journal of Applied Physics 106(2009)10, 106103

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Permalink: https://www.hzdr.de/publications/Publ-13621
Publ.-Id: 13621


Free-space propagation of radially and azimuthally polarized terahertz Bessel-Gauss beams

Winnerl, S.; Zimmermann, B.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.
Radially polarized Bessel-Gauss beams have interesting properties like smaller spot sizes in the focus as compared to linearly polarized beams, and longitudinal field components. These properties have been studied for
visible and near-infrared beams. In the THz range, radially polarized beams have been studied as plasmonically guided modes on metal wires, so called Sommerfeld modes. Recently a first experiment on free space
propagation of radially polarized beams, generated via velocity mismatched optical rectification in (100)-oriented ZnTe, was reported. Here we present microstructured emitters for radially and azimuthally polarized
beams, study for the first time the divergence of the beams behind the emitter and record transverse and longitudinal components of the beams in the focus.
Keywords: Terahertz, vector beams, Bessel-Gauss beams
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, 14.-19.06.2009, München, Deutschland
  • Contribution to proceedings
    Conference on Lasers and Electro-Optics - European Quantum Electronics Conference, 14.-19.06.2009, München, Deutschland
    Conference Digest of the Conference on Lasers and Electro-Optics - European Quantum Electronics Conference

Permalink: https://www.hzdr.de/publications/Publ-13620
Publ.-Id: 13620


Nachweis von Östrogen- wirkenden Substanzen in wässrigen Lösungen

Cherkouk, C.; Rebohle, L.; Skorupa, W.; Helm, M.
In dieser Arbeit wird ein Sensorkonzept zum Nachweis von Östrogen-wirkenden Substanzen in wässrigen Lösungen vorgestellt. Das Kernstück des Sensors ist eine auf Chipebene integrierte Lichtquelle, die zur Fluoreszenzanalyse der Probe benutzt wird. Dieser Lösungsansatz ermöglicht eine deutliche Reduzierung der Geräteabmessungen, verbunden mit einer entsprechenden Ersparnis an Ressourcen, Energie und Herstellungskosten. Zur Realisierung des gesamten Konzepts wurde ein neues Verfahren entwickelt, das die Chipoberfläche einfach und effizient modifiziert.
Dies ermöglicht das Aufbringen einer an der Chipoberfläche kovalent gebundenen Bio-Schicht, die überwiegend aus APS (N,N´-Bis(3-aminopropyl)-2-butene-1,4-diamine)) Silanegruppen besteht. Der spätere Östrogenrezeptor hER(alpha) soll über funktionelle Aminogruppen adsorbiert werden.
Diese Oberflächenmodifizierung der Chips wurde mittels Infrarot-Spektroskopie (FTIR) charakterisiert. Dabei wurde die stabile Haftung der Silanegruppen durch die als Anker dienenden Methoxygruppen an der Chipoberfläche verifiziert. Weitere Untersuchungen sowohl zur chemischen Zusammensetzung als auch zur Rauhigkeit der Oberfläche wurden mit Hilfe von Röntgen-Photoemissionsspektroskopie (XPS) und der Rasterkraftmikroskopie (AFM) durchgeführt. Schließlich wurde mittels Elektrolumineszenzmessungen die Wechselwirkung zwischen der Si- basierten Lichtemission und dem an den Bio- Schicht adsorbierten Farbstoff getestet.
Keywords: Sensorkonzept , Östrogen-wirkenden, Fluoreszenzanalyse, Bio-Schicht, Silanegruppen, Östrogenrezeptor hER(alpha), Oberflächenmodifizierung
  • Poster
    6. Deutsches BioSensor Symposium in Freiburg (LOC-Lab-on-a-Chip und Point-of-Care Diagnostik), 30.03.-01.04.2009, Freiburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13619
Publ.-Id: 13619


Radiale Moden in THz-Feldern

Hubrich, R.
Die im Forschungszentrum Dresden-Rossendorf entwickelten skalierbaren Emitter liegen nicht nur, wie aus der Literatur bekannten, in linearen Form vor, sondern werden auch mit anderen
Elektrodenstrukturen gefertigt. Durch einen radial-symmetrischen Emitter z.B. wird laut Theorie eine stärkere Fokussierung der THz-Strahlung möglich sein [2]. Ein Schwerpunkt bei
den Untersuchungen liegt in der Ermittlung der Moden bzw. der Strahlungsprofile der radialen Emitterstrukturen. Dabei werden mittels EOS sowohl die transversale, als auch die longitudinale
Komponente des THz-Feldes untersucht. Erstmals wurden dafür in unserer Forschungsgruppe THz-Linsen aus TPX verwendet, die das Strahlprofil weniger deformieren, als herkömmliche
Parabolspiegel.
Keywords: terahertz, emitters, vector beams
  • Lecture (Conference)
    Drittes THz-Frischlinge-Meeting 2009, 07.-10.06.2009, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13618
Publ.-Id: 13618


Photoconductive Emitters and Detectors for Radially and Azimuthally Polarized Terahertz Beams

Winnerl, S.; Zimmermann, B.; Hubrich, R.; Peter, F.; Schneider, H.; Helm, M.
Photoconductive emitters and detectors are reviewed, advantages of scalable devices are discussed and new developements for radially and azimuthally polarized terahertz beams are presented.
Keywords: terahertz, emitters, detectors, vector beams
  • Lecture (Conference)
    GDR-E Workshop "Semiconductor sources and detectors of THz radiation", 16.-17.11.2009, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-13617
Publ.-Id: 13617


On the difference of 3D and 4D in-beam PET for a periodically moving target

Laube, K.; Bert, C.; Chaudhri, N.; Fiedler, F.; Parodi, K.; Rietzel, E.; Saito, N.; Enghardt, W.
no abstract available
Keywords: in-beam PET, moving targets, ion beam therapy
  • Contribution to external collection
    Katrin Große: GSI Scientific Report 2009, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung, 2010, 503-503

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Permalink: https://www.hzdr.de/publications/Publ-13616
Publ.-Id: 13616


The impact of FMISO hypoxic volume on local control after single dose irradiation in FADU HNSCC in nude mice

Schütze, C.; Bergmann, R.; Mosch, B.; Yaromina, A.; Hessel, F.; Krause, M.; Thames, H. D.; Zips, D.; Mäding, P.; Baumann, M.; Beuthien-Baumann, B.
kein Abstract verfügbar
  • Poster
    ICTR 2009 - Fourth International Conference on Translational Research in Radiation Oncology, 11.-13.03.2009, Genf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-13615
Publ.-Id: 13615


Characterization of ZnO nanostructures: A challenge to positron annihilation spectroscopy and other methods

Brauer, G.; Anwand, W.; Grambole, D.; Egger, W.; Sperr, P.; Beinik, I.; Wang, L.; Teichert, C.; Kuriplach, J.; Lang, J.; Zviagin, S.; Cizmar, E.; Ling, C. C.; Hsu, Y. F.; Xi, Y. Y.; Chen, X.; Djurisic, A. B.; Skorupa, W.
ZnO nanostructures are of special interest for device applications.
However, their structural characterization remains an ongoing challenge.
This paper reviews recent efforts and latest achievements in this direction. Results comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects. The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.
  • Physica Status Solidi (C) 6(2009)11, 2556-2560

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Permalink: https://www.hzdr.de/publications/Publ-13614
Publ.-Id: 13614


Radiolabeled Cdk4/6 inhibitors for molecular imaging of tumors

Graf, F.; Köhler, L.; Mosch, B.; Pietzsch, J.
Overexpression of cell-cycle regulating cyclin-dependent kinases 4 and 6 (Cdk4/6) and deregulation of Cdk4/6-pRb-E2F pathway are common aspects in human tumors. The aim of our study was the evaluation of pyrido[2,3 d]pyrimidin-7-one derivatives (CKIA and CKIE) concerning their efficacy and suitability as small molecule Cdk4/6 inhibitors and, after iodine-124 ([124I]CKIA) or fluorine-18 ([18F]CKIE) radiolabeling, as radiotracers for Cdk4/6 imaging in tumors by positron emission tomography (PET).
CKIA and CKIE were analyzed concerning their biological properties (effects on cell growth, cell cycle distribution, Cdk4/6 mediated pRb-Ser780 phosphorylation, mRNA expression of pRb affected genes E2F-1 and PCNA) and radiopharmacological properties (cellular radiotracer uptake and PET studies) using human tumor cell lines HT-29, a colorectal adenocarcinoma cell line, FaDu, a head and neck squamous cell carcinoma cell line, and THP-1, an acute monocytic leukemia cell line, as well as phorbol ester TPA-activated THP-1 cells, as model of tumor-associated macrophages.
CKIA and CKIE were identified as potent inhibitors of Cdk4/6-pRb-E2F pathway due to decreased Cdk4/6 specific phosphorylation at pRb Ser780 and downregulation of E2F-1 and PCNA mRNA expression in HT-29, FaDu and THP-1 tumor cells. This resulted in arrest of these tumor cell lines in G1 phase of the cell cycle and growth inhibition. Otherwise, in non-proliferating TPA-activated THP-1 macrophages no change of cell-cycle distribution after treatment with CKIA and CKIE was observed. Furthermore, TPA-activated THP-1 macrophages showed lower Cdk4 mRNA and protein levels, than other tumor cell lines. In vitro radiotracer uptake studies using [124I]CKIA and [18F]CKIE demonstrated tumor cell uptake, which could be blocked with both nonradioactive CKIA and CKIE. However, THP-1 macrophages showed similar radiotracer uptake like other tumor cells. Preliminary small animal PET studies in mouse tumor xenograft models further analyzed the hypothesis that radiolabeled Cdk4/6 inhibitors are suitable tracers for molecular imaging of tumors
  • Open Access Logo Abstract in refereed journal
    Cancer Microenvironment 2(2009), S185
  • Poster
    5th International Conference On Tumor Microenvironment: Progression, Therapy & Prevention, 20.-24.10.2009, Versailles, France

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Permalink: https://www.hzdr.de/publications/Publ-13613
Publ.-Id: 13613


Irradiation-induced changes in metabolism and metastatic properties of melanoma cells

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.
As it is known that irradiation can influence cellular metabolism it is conceivable that it can induce metabolic changes which lead to a predisposition of certain cells to show enhanced survival, migratory activity and metastasis. The aim of this study was to investigate short term and long term irradiation effects on proliferation and metabolism of melanoma cells in vitro and their ability to form metastases in vivo.
B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation in the range of 1 to 20 Gy. One, two, and three days (short term effects) and, furthermore, 7, 14 and 21 days (long term effects) after treatment cells were analyzed concerning cell growth, proliferation, viability, glucose and amino acid transport. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases.
The analysis of short term effects showed decreased cell growth, viability and arrest in the G2/M phase of the cell cycle while glucose transport is increased. Long term effects involve recovered proliferation, accompanied by increased glucose transport and decreased viability and amino acid transport. In vivo studies showed loss of metastasis immediately after irradiation and reduced metastasis if cells were allowed to recover proliferation before injection.
We conclude that melanoma cells as short term response to irradiation show cell cycle arrest and impairment in growth and viability. Three days after irradiation compensatory mechanisms start, leading to recovered growth within three weeks. Studies concerning metabolic properties indicate that a subpopulation of surviving melanoma cells compensate for the initial irradiation-induced damage possibly by metabolic modulations such as increase in glycolysis. As metastasis in vivo is impaired beyond recovered cell proliferation, the role of adjusted cell metabolism and additional extrinsic factors is strongly suggested.
  • Open Access Logo Abstract in refereed journal
    Cancer Microenvironment 2(2009), S150-S151
  • Poster
    5th International Conference on Tumor Microenvironment: Progression, Therapy & Prevention, 20.-24.10.2009, Versailles, France

Permalink: https://www.hzdr.de/publications/Publ-13612
Publ.-Id: 13612


Changes in metabolism and metastatic properties of melanoma cells after X-ray irradiation

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.
Background: Malignant melanoma has the ability to form metastases at very early stages and in addition to surgical resection treatment involves immunotherapy, chemotherapy and also radiotherapy. As it is known that irradiation can influence cellular metabolism it is conceivable that it can induce metabolic changes which lead to a predisposition of certain cells to show enhanced survival, migratory activity and metastasis. The aim of this study was to investigate short term and long term irradiation effects on metabolism and proliferation of irradiated melanoma cells in vitro and their ability to form metastases in vivo.
Material and methods: B16-F10 melanoma cells were irradiated with different doses of X-ray irradiation in the range of 1 to 20 Gy. One, two, and three days (short term effects) and, furthermore, 7, 14 and 21 days (long term effects) after treatment cells were analyzed concerning cell growth, viability, proliferation, cell cycle distribution, glucose and amino acid transport. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases.
Results: The analysis of short term effects showed decreased cell growth, viability and arrest in the G2/M phase of the cell cycle. Long term effects involve increase in proliferation, cell growth and glucose uptake but still decreased viability and amino acid transport. Our in vivo studies showed no formation of lung metastases when cells were irradiated before injection. If irradiated cells were allowed to recover for 2 weeks before injection, mice again developed lung metastases although to a lesser extent than control mice.
Conclusions: We conclude that melanoma cells as short term response to irradiation show cell cycle arrest and decrease in cell viability, growth and metabolic properties. One to three weeks after irradiation, the re-start of proliferation and recurrence of metabolic properties such as glucose uptake indicate that a subpopulation of surviving melanoma cells compensate for the initial irradiation-dependent damage possibly by metabolic modulations such as increase in glycolysis. Furthermore, in vivo studies reveal that irradiated melanoma cells are able to resume their metastatic potential within two weeks. As lung metastasis is lower when using recovered cells versus untreated cells, the role of additional mechanisms is strongly suggested.
  • Abstract in refereed journal
    European Journal of Cancer 7(2009), 587
  • Poster
    ECCO 15 - 34th ESMO Multidisciplinary Congress, 20.-24.09.2009, Berlin, D

Permalink: https://www.hzdr.de/publications/Publ-13611
Publ.-Id: 13611


Influence of irradiation on the metabolism of melanoma cells and metastasis in mice.

Mosch, B.; Müller, K.; Steinbach, J.; Pietzsch, J.
Irradiation is a powerful tool for the therapy of solid tumors. But often single cells elude this treatment and constitute a basis for recurrence of the primary tumor and formation of metastases. Until today it is unclear which properties enable some cells to this. One possible explanation could be predicted on irradiation-dependent metabolic changes which lead to a predisposition of certain cells to show enhanced survival and migratory activity. The aim of this study was to investigate metabolic properties and proliferation of irradiated melanoma cells in vitro and their ability to form metastases in vivo.
We applied different single-dose X-ray irradiation (200kV X-rays, 0.5mm Cu, ~ 1.2 Gy min-1; 1, 2, 5, 7, 10, and 20 Gy) to murine B16-F10 melanoma cells. At particular times we analyzed cell viability, growth properties and cell cycle distribution. Furthermore, we analyzed the cellular uptake of the radiotracers 2-[18F]fluoro-2-deoxy-D-glucose ([18F]FDG) and 3-O-methyl-[18F]fluoro-L-DOPA ([18F]OMFD), providing information about the glucose and amino acid metabolism before and after irradiation. Additionally, we performed in vivo studies in a syngeneic mouse model to analyze the capability of irradiated melanoma cells to form lung metastases after injection into the tail vein of NMRI mice.
In a dose-dependent manner we detected a decrease in cell viability and cell growth properties starting 3 days after irradiation. Decreased cell growth persists up to 1 week for 5 Gy irradiated cells and up to 2 weeks for 10 Gy irradiated cells. After this periods growth of irradiated cells is comparable to control cells. Cell cycle analyses showed an increase in G2/M phase cells up to 3 days after X-ray followed by an increase in S phase cells 6 days after X-ray. At this point of time uptake of radiotracers was altered inasmuch as [18F]FDG uptake decreased, whereas [18F]OMFD uptake increased. Our in vivo studies showed a loss of lung metastases when cells were irradiated (10 Gy) before injection. If irradiated cells were allowed to recover for 2 weeks before injection, mice again developed lung metastases although to a lesser extent than control mice.
We conclude that irradiation of melanoma cells leads to a dose-dependent decrease in cell viability, growth properties and glucose uptake. Cell cycle analyses suggest an arrest in the G2/M phase. One week after irradiation compensating mechanisms of these effects seems to start as indicated by the uptake of [18F]OMFD, the increase in S phase cells and recovered growth of low-dose (5 Gy) irradiated cells. Two weeks after irradiation cell growth is completely recovered in vitro. Accordingly, in vivo studies reveal that irradiated melanoma cells are able to resume their metastatic potential within two weeks, even though to a lesser extent than before irradiation. The questions why and how some cells modulate their metabolism and thus re-start proliferation and why metastasis is influenced in vivo although growth properties are recovered in vitro, need to be further investigated.
  • Poster
    2nd Workshop on Radiation and Multidrug Resistance via the Tumor Microenvironment, 09.-10.02.2009, Dresden, D

Permalink: https://www.hzdr.de/publications/Publ-13610
Publ.-Id: 13610


Detection and quantification of hypoxia in xenotransplanted human squamous cell carcinoma

Bergmann, R.; van den Hoff, J.; Pietzsch, J.; Strobel, K.; Mosch, B.; Schütze, C.; Brüchner, K.; Hofheinz, F.; Beuthien-Baumann, B.
kein Abstract verfügbar
  • Poster
    World Molecular Imaging Conference, 10.-13.09.2008, Nizza, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-13609
Publ.-Id: 13609


Pre-treatment FMISO hypoxic volume is a significant prognostic factor for local control after irradiation of FaDu HNSCC xenografts

Schütze, C.; Bergmann, R.; Mosch, B.; Yaromira, A.; Hessel, F.; Krause, M.; Thames, H. D.; Zips, D.; Mäding, P.; Baumann, M.; Beuthien-Baumann, B.
Objective: To investigate whether pre-treatment FMISO hypoxic tumour volume (HV) adds significant information about radiotherapy outcome in FaDu human squamous cell carcinoma (hSCC) in nude mice.
Materials and Methods: The hSCC cell line FaDu was transplanted subcutaneously into the hind leg of NMRI nude mice. Seventy animals entered the study at tumour volumes ranging from 165-343 mm³. [18F]fluoromisonidazole ([18F]FMISO)-PET scanning was performed under anesthesia (9% desflurane in 40% oxygen/air) on a dedicated animal PET scanner (MicroPET® P4, CTI Molecular Imaging Inc, measured attenuation correction, 11 MBq 18FMISO i.v., list mode acquisition for 30 min after 210 min p.i). The regions of interest (ROI) include the FMISO positive hypoxic volume, the mean, the maximum concentration (ROVER software, ABX GmbH, Radeberg, Germany). After an initial FMISO-PET (day 0) the tumours were stratified according to the median hypoxic volume (HV) for single dose irradiation with either 25 Gy (tumour control probability, TCP20) or 35 Gy (TCP80) under normal blood flow conditions using 200 kV X-rays (0.5 mm Cu, ~ 1.2 Gy min-1). The endpoint was time to local failure. Five animals are currently still in follow up.
Results: Tumour local control rate after irradiation with 25 Gy was lower than after irradiation with 35 Gy (22% vs. 69%, log rank p<0.0001). HV ranged from 38-353 mm³. Median HV was 112 mm³ (95%CI: 92; 128 mm³). In tumours with HV less than the median, local control was 33% after 25 Gy vs. 82% after 35 Gy (p=0.001) and in tumours with HV above the median 15% after 25 Gy vs. 53% after 35 Gy (p=0.0005). Multivariate Cox analysis revealed a significant effect of hypoxic volume treated either as a continuous (p=0.009) or a dichotomic variable (stratification by median HV) (p=0.039) when corrected for dose and tumour volume effects. Dose had a significant impact on hazard of recurrence (p<0.0005), whereas total tumour volume showed no effect (p=0.5).
Conclusions: Hypoxic volume is a significant predictor of tumour control after irradiation with high single doses in a single tumour line. This supports the hypothesis that pre-treatment FMISO-PET may provide useful information for heterogeneous radiation dose prescription in sub volumes of individual tumours. Confirmatory investigations using other tumour models and fractionated radiotherapy are warranted.
This work was performed within the 6th framework EU-project BioCare, proposal# 505785.
  • Abstract in refereed journal
    Radiotherapy and Oncology 88(2008), S102
  • Poster
    27th conference of the European Society for Therapeutic Radiology and Oncology (ESTRO), 14.-18.09.2008, Göteborg, Schweden

Permalink: https://www.hzdr.de/publications/Publ-13608
Publ.-Id: 13608


Neuronal Aneuploidy in Health and Disease: A Cytomic Approach to Understand the Molecular Individuality of Neurons

Arendt, T.; Mosch, B.; Morawski, M.
Structural variation in the human genome is likely to be an important mechanism for neuronal diversity and brain disease. A combination of multiple different forms of aneuploid cells due to loss or gain of whole chromosomes giving rise to cellular diversity at the genomic level have been described in neurons of the normal and diseased adult human brain. Here, we describe recent advances in molecular neuropathology based on the combination of slide-based cytometry with molecular biological techniques that will contribute to the understanding of genetic neuronal heterogeneity in the CNS and its potential impact on Alzheimer´s disease and age-related disorders
Keywords: alu-repeats, Alzheimer´s disease, cell cycle, cell death, chromosomal mosaicism, in situ hybridisation, laser capture microdissection, neurodegeneration, slide-based cytometry

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Permalink: https://www.hzdr.de/publications/Publ-13607
Publ.-Id: 13607


Grain growth in Ni-Mn-Ga alloys

Thoss, F.; Poetschke, M.; Gaitzsch, U.; Freudenberger, J.; Anwand, W.; Roth, S.; Rellinghaus, B.; Schultz, L.
The influence of annealing temperature and time on grain growth in polycrystalline Ni-Mn-Ga samples near the stoichiometric composition Ni2MnGa was investigated. Grain growth was only observed for compositions with a Ni content below 50 at.%. The existence of constitutional vacancies as a possible origin for the different grain growth behaviour was excluded by positron annihilation spectroscopy (PAS). In order to activate grain boundary motion and hence grain growth in Ni50Mn29Ga21 the samples were annealed and deformed in situ in compression up to various strain levels. A sharp threshold to initiate grain growth is observed between 8% and 10% of compression strain.
Keywords: Magnetically ordered materials, casting, grain boundaries
  • Journal of Alloys and Compounds 488(2009), 420-424

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Permalink: https://www.hzdr.de/publications/Publ-13606
Publ.-Id: 13606


Isotopic Comparative Method (ICM) for the determination of variations of the useful ion yields in boron doped silicon as a function of oxygen concentration in the 0 - 10 at% range

Dupuy, J. C.; Dubois, C.; Prudon, G.; Gautier, B.; Kögler, R.; Akhmadaliev, S.; Perrat-Mabilon, A.; Peaucelle, C.
Specific samples containing O-18 and O-16 are used to measure the variations of the relative ion yields of boron, oxygen and silicon as a function of oxygen concentration. O-18 and O-16 are used to implement an Isotopic Comparative Method (ICM) which allows to correct the matrix effects involved by the presence of a high concentration of oxygen in the sample: the near-flat profile of O-18, measured in the 'dilute', linear regime (weak concentration) is used to calculate the real concentration of O-16. The ion yields of B+, O+, Si+, O- and Si- are measured as a function of the oxygen concentration. For B+ ion yield, the variation is important whereas they are weak for Si-+/- and O-+/- ion yields for the range [0-12 at.%]. This ICM applied to oxygen in silicon can be considered as an interesting complementary method of previous 'O-16 implantation method' and of 'O-18 single marker method'.
Keywords: Secondary ion mass spectrometry, SIMS, Isotopic comparative method, ICM, Oxygen, Silicon, Boron
  • Lecture (Conference)
    SIMS XVII Toronto, Canada, 13.-17.09.2009, Toronto, Canada
  • Surface and Interface Analysis 43(2010)1-2, 137-140
    DOI: 10.1002/sia.3657

Permalink: https://www.hzdr.de/publications/Publ-13605
Publ.-Id: 13605


Carrier profiling of individual Si nanowires by scanning spreading resistance microscopy

Ou, X.; Das Kanungo, P.; Kögler, R.; Werner, P.; Skorupa, W.; Gösele, U.; Wang, X.
Individual silicon nanowires (NWs) doped either by ion implantation or by in-situ dopant incorporation during NW growth were investigated by scanning spreading resistance microscopy (SSRM). The carrier profiles across the axial cross sections of the NWs are derived from the measured spreading resistance values and calibrated by the known carrier concentrations of the connected Si substrate or epi-layer. In case of the phosphorus ionimplanted and subsequently annealed NWs the SSRM profiles revealed a radial core-shell distribution of the activated dopants. The carrier concentration close to the surface of a phosphorus-doped NW is found to be by a factor of 6-7 higher than the value in the core and on average only 25% of the implanted phosphorus is electrically active. In contrast, for the insitu boron-doped NW, the activation rate of the boron atoms is significantly higher than for phosphorus atoms. Some specific features of SSRM experiments of Si NWs are discussed including the possibility of three-dimensional measurements.
Keywords: Nanowires, Silicon, Doping, Scanning Spreading Resistance Microscopy, SSRM

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Permalink: https://www.hzdr.de/publications/Publ-13604
Publ.-Id: 13604


Physics and techniques at high pulsed magnetic fields

Herrmannsdörfer, T.
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    2nd Workshop of the Resonant Scattering and Diffraction Beamline (P09) at PETRA III, 04.11.2009, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13603
Publ.-Id: 13603


Superconductivity in p-doped elemental semiconductors

Herrmannsdoerfer, T.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Muecklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K. H.; Skorupa, W.; Voelskow, M.; Wuendisch, C.; Skrotzki, R.; Helm, M.; Wosnitza, J.
We report the first observation of superconductivity in heavily p-type doped Germanium at ambient-pressure conditions. Using advanced doping and annealing techniques, we have fabricated a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic cubic Ge. Depending on the detailed annealing conditions, we demonstrate that superconductivity can be generated and tailored in the p-doped semiconducting Ge host at temperatures as high as 0.5 K. Critical-field measurements reveal the quasi-two-dimensional character of superconductivity in the ~ 60 nm thick Ge:Ga layer. We find critical magnetic in-plane fields up to about 1T, even slightly larger than the Pauli-Clogston limit. There might be interest in the technological potential of on-chip thin-film superconductivity in a semiconducting environment demonstrated here as our preparation method is compatible with state-of-the-art semiconductor processing used nowadays for the mass production of logic circuits. After its finding in Si [1] and diamond [2], our work adds another unexpected observation of superconductivity in doped elemental semiconductors and in one of the few remaining ‘islands of the periodic table of elements’ on which superconductivity has not been found so far.
  • Invited lecture (Conferences)
    The 9th European Conference on Applied Superconductivity, EUCAS 2009, 13.-17.09.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    Workshop: Noval approaches to pairing and condensation, 03.10.2009, Dresden, Deutschland
  • Invited lecture (Conferences)
    Workshop “Physics and Metrology at Very Low Temperatures", 10.12.2009, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13602
Publ.-Id: 13602


Semiconductor quantum structures for quadratic detection at mid-infrared and THz frequencies

Schneider, H.
There is no abstract.
Keywords: intersubband transition, two-photon detection, terahertz
  • Invited lecture (Conferences)
    Novel Quantum Structure Detectors for Opto-electronic Conversion 2010, 04.-06.01.2010, Sanya, China

Permalink: https://www.hzdr.de/publications/Publ-13601
Publ.-Id: 13601


Ultrafast infrared and Terahertz spectroscopy of semiconductor quantum structures

Schneider, H.
This seminar gives an overview on our recent experimental studies involving ps and fs lasers, including the free-electron laser at FZD. In particular, I briefly discuss nonlinear sideband spectroscopy and time-resolved photoluminescence. Then I will focus on quadratic photocurrent autocorrelation involving intersubband transitions in semiconductor quantum wells at mid-infrared wavelengths, and present our concept for scalable photoconductive Terahertz emitters.
Keywords: intersubband transition, two-photon detection, terahertz
  • Lecture (others)
    Physics Colloquium, Shanghai Jiao Tong University, 30.12.2009, Shanghai, China

Permalink: https://www.hzdr.de/publications/Publ-13600
Publ.-Id: 13600


Fulde-Ferrell-Larkin-Ovchinnikov State in the Organic Superconductor κ-(BEDT-TTF)2Cu(NCS)2

Lortz, R.; Wang, Y.; Demuer, A.; Sheikin, I.; Bergk, B.; Wosnitza, J.; Nakazawa, Y.
extraordinary high and the Pauli limit becomes of importance instead. For this case the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state was theoretically predicted. It is now 55 years that this state is being looked for experimentally. The most promising candidates are layered superconductors such as the organic compound κ-(BEDT-TTF)2Cu(NCS)2. When the field is applied parallel to the layers, the orbital limit exceeds the Pauli limit at 22 T. I will present specific heat and magnetic torque experiments up to 30 T and down to 50 mK. The upper critical field transition changes from second to first-order nature above 21 T, the transition line shows a characteristic upturn and a novel transition line separates an unconventional high-field SC phase from the conventional low-field phase. Additional transitions are observed in slightly tilted angles, suggesting a rich physics with a competition between orbital and Pauli limits. These results provide strong evidence for the FFLO state in κ-(BEDT-TTF)2Cu(NCS)2.
  • Invited lecture (Conferences)
    9th Conference on Materials and Mechanisms of Superconductivity (M2S), 07.-12.09.2009, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-13599
Publ.-Id: 13599


Fermi-Surface Topology of the Iron-Pnictide Compound LaFe2P2

Ignatchik, O.; Bartkowiak, M.; Wosnitza, J.; Blackburn, S.; Pesant, S.; Côté, M.; Seyfarth, G.; Bianchi, A. D.; Capan, C.; Fisk, Z.; Goodrich, R. G.
A thorough knowledge on the electronic band structure of metals is a prerequisite for gaining insight in their electronic properties. This becomes especially true for a better understanding of the occurrence of superconductivity. Here, we present results of a comprehensive de Haas-van Alphen (dHvA) study of LaFe2P2, a non-superconducting parent compound of the recently discovered family of iron-pnictide superconductors. By use of the cantilever torque magnetometry we were able to observe dHvA oscillations in high-quality LaFe2P2 single crystals starting at about 10 T at dilution-refrigerator temperatures. From the angular dependence of the oscillations we find a strongly anisotropic, but three-dimensional Fermi-surface topology. The effective masses of two different bands observed for magnetic fields aligned along the c axis are 1.4 and 1.7 me, where me is the free-electron mass. The dHvA frequencies and the effective masses in-crease considerably when rotating away from the c axis. We compare our results to state-of-the-art band-structure calculations.
  • Poster
    9th Conference on Materials and Mechanisms of Superconductivity, 07.-12.09.2009, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-13598
Publ.-Id: 13598


Thin-film Superconductivity in Ga-doped Germanium

Herrmannsdörfer, T.; Skrotzki, R.; Heera, V.; Ignatchik, O.; Uhlarz, M.; Mücklich, A.; Posselt, M.; Reuther, H.; Schmidt, B.; Heinig, K.-H.; Skorupa, W.; Voelskow, M.; Wündisch, C.; Helm, M.; Wosnitza, J.
We report the first observation of superconductivity in heavily p-type doped germanium at ambient pressure conditions. Using Ga as dopant, we have produced Ge:Ga samples by ion-beam implantation and subsequent short-term (msec) flash-lamp annealing. The combination of these techniques allows for Ga-doping levels up to 6%, not accessible to any other preparation method so far. The superconducting critical parameters strongly depend on the annealing conditions. Transport measurements reveal Tc up to 0.5 K and anisotropic Bc(T) with a linear temperature dependence reflecting the two-dimensional character of the superconducting state in the ~ 60 nm thin Ge:Ga layer. We find critical magnetic in-plane fields even larger than the Pauli-Clogston limit. After its finding in Si [1] and diamond [2], this work reports another unexpected observation of superconductivity in doped elemental semiconductors. Our fabrication techniques are compatible to industrial semiconductor processing and allow for on-chip superconductivity in integrated circuits.
  • Poster
    9th International Conference on Materials and Mechanisms of Superconductivity (M2S), 07.-12.09.2009, Tokyo, Japan

Permalink: https://www.hzdr.de/publications/Publ-13597
Publ.-Id: 13597


Phase-sensitive terahertz spectroscopy with backward-wave oscillators in reflection mode

Pronin, A. V.; Goncharov, Y. G.; Fischer, T.; Wosnitza, J.
In this article we describe a method which allows accurate measurements of the complex reflection coefficient rˆ=|rˆ| ·exp(iφR) of a solid at frequencies of 1–50 cm−1 (30 GHz–1.5 THz). Backward-wave oscillators are used as sources for monochromatic coherent radiation tunable in frequency. The amplitude of the complex reflection (the reflectivity) is measured in a standard way, while the phase shift, introduced by the reflection from the sample surface, is measured using a Michelson interferometer. This method is particular useful for nontransparent samples, where phase-sensitive transmission measurements are not possible. The method requires no Kramers–Kronig transformation in order to extract the sample’s electrodynamic properties (such as the complex dielectric function or complex conductivity). Another area of application of this method is the study of magnetic materials with complex dynamic permeabilities different from unity at the measurement frequencies (for example, colossal-magnetoresistance materials and metamaterials). Measuring both the phase-sensitive transmission and the phase-sensitive reflection allows for a straightforward model-independent determination of the dielectric permittivity and magnetic permeability of such materials.
  • Review of Scientific Instruments 80(2009), 123904

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Permalink: https://www.hzdr.de/publications/Publ-13596
Publ.-Id: 13596


Short-range correlations in quantum frustrated spin system

Sytcheva, A.; Chiatti, O.; Wosnitza, J.; Zherlitsyn, S.; Zvyagin, A. A.; Coldea, R.; Tylczynski, Z.
We report on results of sound-velocity and sound-attenuation measurements in the low-dimensional spin-1/2 antiferromagnet Cs2CuCl4 (TN = 0.6 K), in external magnetic fields up to 15 T, applied along the b axis, and at temperatures down to 300 mK. The experimental data are analyzed with a theory based on exchange-striction coupling resulting in a qualitative agreement between theoretical results and experimental data.
  • Physical Review B 80(2009), 224414

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Permalink: https://www.hzdr.de/publications/Publ-13595
Publ.-Id: 13595


Spatiotemporal observation of transport in fractured rocks

Kulenkampff, J.; Enzmann, F.; Gründig, M.; Mittmann, H.; Wolf, M.
We apply positron emission tomography (PET) with a high-resolution "small-animal" PET-scanner (ClearPET by Raytest, Straubenhardt) for process observation in rocks. Without affecting its physico-chemical properties, the fluid is labelled with the PET-tracer, a positron-emitting isotope. The annihilation radiation from individual decaying tracer atoms is detected with high sensitivity, and tomographic reconstruction of the recorded events yields a quantitative 3D-image of the tracer concentration. Sequential tomograms during tracer injection are used for the spatiotemporal observation of transport.
The raw data have to be corrected, prevalently with respect to background radiation (randoms) and Compton scattering, which is more significant than in common biomedical applications. Although these effects can be considered exactly in principle, we had to develop and apply simplified correction methods for performance reasons. Deficiencies of these correction algorithms generate some artefacts, that cause a lower limit of the tracer concentration in the order of 1 kBq/µl or about 107 atoms/µl, outranging other methods (e.g. nmr or resistivity tomography) by many orders.
A number of injection experiments in different rocks have been conducted with PET-process-tomography. New 3D-visualizations of the process-tomograms in fractured rocks showed strongly localized and complex flow paths and some unexpected deviations from the fractures that are deducible from µCT-images.
At least, the results demonstrate the large discrepancy between the µCT-derived volume and specific surface area and the hydraulic effective parameters, which also can be analyzed quantitatively with this method. Possibly, these discrepancies and the complexity of the process show the limits of parameter determination methods with model simulations based on structural pore-space models - as long as the simulations are not verified by experimental data.
  • Lecture (Conference)
    European Geosciences Union General Assembly 2010, 02.-07.05.2010, Wien, Österreich

Permalink: https://www.hzdr.de/publications/Publ-13594
Publ.-Id: 13594


Nuclear Engineering Handbook - Chapter 1.4: VVER-type reactors of Russian design

Gado, J.; Rohde, U.; (Editors)
The Russian designed VVER-type reactors represent a special kind of pressurised light water reactors. The most important features of the VVER-440 and VVER-1000 reactor series are presented here by the representatives of the Russian design company OKB “GIDROPRESS”, Podolsk, Russian Federation.
Design and basic safety properties are described in details, mentioning the differences between various reactors. VVER-440 and VVER-1000 reactors are presented separately. The successful operational experience of the two series is summarised together with data on decommissioned reactors.
Keywords: VVER-type reactors, pressurized water reactors, basic design, safety features, operation experience, decommissioning
  • Contribution to external collection
    D. G. Cacuci, J. Gado, U. Rohde: Handbook of Nuclear Engineering; Vol.IV - Reactors of Generation III and IV, Chapter 20: VVER-Type Reacctors of Russian Design, Heidelberg: Springer, 2010, 978-0-387-98130-7

Permalink: https://www.hzdr.de/publications/Publ-13593
Publ.-Id: 13593


Prediction of positron emitter distributions produced during 7Li irradiation

Priegnitz, M.; Fiedler, F.; Kunath, D.; Laube, K.; Parodi, K.; Enghardt, W.
No abstract available
  • Contribution to external collection
    in: GSI Scientific Report 2009, Darmstadt: GSI Helmholtzzentrum für Schwerionenforschung GmbH, 2010, 497

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Permalink: https://www.hzdr.de/publications/Publ-13592
Publ.-Id: 13592


Electromagnetic inspection of a two-phase GaInSn/Argon flow

Terzija, N.; Yin, W.; Gerbeth, G.; Stefani, F.; Timmel, K.; Wondrak, T.; Peyton, A.
Adequate control of steel flow through the submerged entry nozzle during continuous casting is essential for maintaining steel cleanliness and ensuring good surface quality in downstream processing. Monitoring the flow in the nozzle presents a challenge for the instrumentation system because of the high temperature environment and the limited access to the nozzle in between the tundish and the mould. We study the distribution of two-phase liquid metal/gas flows by using a laboratory model of an industrial steel caster and an inductive sensor array. The experiments were performed with GaInSn as an analogue for liquid steel, which has similar conductive properties as molten steel and allows the measurements at the room temperature. A scaled (approx. 10:1) experimental rig consisting of a tundish, stopper rod, nozzle and mould was used. Argon gas was injected through the centre of the stopper rod and the behavior of two phase GaInSn/Argon flows was studied. The electromagnetic system used in our experiments to monitor the behavior of two phase GaInSn/Argon flows consisted of an array of 8 equally spaced inductive coils arranged around the object, a data acquisition system and a host computer. The present system operates at 10 kHz and has a capture rate of 10 frames per second. The results showed clearly that the injection of the Argon gas was distinguishable from the continuous flow by observing the appearance of oscillation patterns in the raw signals. These oscillations become more dominant with the increase of the Argon flow. In some cases two main oscillation patterns were present in the raw signals and our results suggested that those patterns are highly correlated with the level height in the mould and with the pressure in the nozzle.
  • Contribution to proceedings
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Germany, 19.-23.10.2009, Dresden, Germany
    6th International Conference on Electromagnetic Processing of Materials EPM 2009, Dresden: FZD, 978-3-936104-65-3, 391-394
  • Lecture (Conference)
    6th International Conference on Electromagnetic Processing of Materials (EPM), 19.-23.10.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-13591
Publ.-Id: 13591


The Impact Ionization MOSFET (IMOS) as Low-Voltage Optical Detector

Schlosser, M.; Iskra, P.; Abelein, U.; Lange, H.; Lochner, H.; Sulima, T.; Wiest, F.; Zilbauer, T.; Schmidt, B.; Eisele, I.; Hansch, W.
The avalanche photodiode (APD) is promoted as an alternative to photomultiplier tubes for optical sensing. When operated in Geiger mode, optically generated electron-hole-pairs trigger an avalanche multiplication, releasing typically about 1E6 charge carriers. However, APDs need operating voltages of about 70 V in order to allow cascaded impact ionization, making them unsuitable for several applications, especially in battery-powered devices. We propose a new device concept based on the vertical Impact Ionization MOSFET (IMOS), which could significantly reduce the operating voltage to about 5 V by using gate control and an additional current-enhancing effect.
Keywords: Impact ionization, MOSFET, Optical Detector
  • Poster
    11th European Symposium on Semiconductor Detectors, NEW DEVELOPMENTS IN RADIATION DETECTORS, 07.-11.06.2009, Wildbad Kreuth, Germany
  • Nuclear Instruments and Methods in Physics Research A 624(2010), 524-527
    DOI: 10.1016/j.nima.2010.05.060

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Permalink: https://www.hzdr.de/publications/Publ-13590
Publ.-Id: 13590


Atomistic simulations of elastic and plastic properties in amorphous silicon

Talati, M.; Albaret, T.; Tanguy, A.
We present here potential-dependent mechanical properties of amorphous silicon studied through molecular dynamics (MD) at low temperature. On average, the localization of elementary plastic events and the co-ordination defect sites appears to be correlated. For Tersoff potential and SW potential the plastic events centered on defect sites prefer 5-fold defect sites, while for modified Stillinger-Weber potential such plastic events choose 3-fold defect sites. We also analyze the non-affine displacement field in amorphous silicon obtained for different shear regime. The non-affine displacement field localizes when plastic events occur and shows elementary shear band formation at higher shear strains.
  • EPL - Europhysics Letters 86(2009), 66005

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Permalink: https://www.hzdr.de/publications/Publ-13589
Publ.-Id: 13589


Temperature Effect on Vibrational Properties of La0.7Sr0.3MnO3

Talati, M.; Jha, P. J.
Temperature dependence of phonons spectra and allied properties of rhombohedral La0.7Sr0.3MnO3 are investigated by using the lattice dynamical method. A tendency of phonon mode to instability causing JT lattice distortion is reflected in a softening of the stretching mode in the phonon dispersion curve of La0.7Sr0.3MnO3 at both 1.6 and 300 K. While the A(1g) mode softens because of gradual decrease in MnO6 rotations, the stretching mode hardens upon reduction in temperature. The distinct features of phonon modes at different temperatures are also reflected in the calculated phonon density of states. Other thermal properties such as specific heat, the Debye temperature, and Gruuneisen parameter are also presented. The decrease in the Debye temperature at 300 K indicates the effect of temperature in lattice softening. Anomalously high value of the Gruneisen parameter points out the presence of anharmonic lattice modes.
Keywords: Phonon dispersion; phonon density of states; colossal magnetoresistance; manganites

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Permalink: https://www.hzdr.de/publications/Publ-13588
Publ.-Id: 13588


Talk on Phase retrieval and differential phase-contrast imaging with low-brilliance x-ray source

Bussmann, M.
In this talk I present the ideas and concepts behind phase contrast imaging with conventional x-ray tubes as presented by F. Pfeifer et al. in their 2006 Nature Physics article (Nature Physics Vol. 2, p. 258-261, April 2006).
Keywords: phase contrast imaging, coherence, grating, x-ray, oncoray journal club
  • Lecture (others)
    OncoRay Journal Club, 07.01.2010, OncoRay, Dresden, Deutscland

Permalink: https://www.hzdr.de/publications/Publ-13587
Publ.-Id: 13587


Role of soft-iron impellers on the mode selection in the VKS dynamo experiment

Giesecke, A.; Stefani, F.; Gerbeth, G.
A crucial point for the understanding of the von-Karman-Sodium (VKS) dynamo experiment is the influence of soft-iron impellers. We present numerical simulations of a VKS-like dynamo with a localized permeability distribution that resembles the shape of the flow driving impellers. It is shown that the presence of soft-iron material essentially determines the dynamo process in the VKS experiment. An axisymmetric magnetic field mode can be explained by the combined action of the soft-iron disk and a rather small $\alpha$-effect parametrizing the induction effects of unresolved small scale flow fluctuations.
Keywords: dynamo VKS simulation permeability magnetohydrodynamics

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Permalink: https://www.hzdr.de/publications/Publ-13586
Publ.-Id: 13586


HTGR Fuel Element Depletion Benchmark: Stage Three Results

Fridman, E.; Shwageraus, E.
Recently, a new numerical benchmark exercise for High Temperature Gas Cooled Reactor (HTGR) fuel depletion was defined. The purpose of this benchmark is to provide a comparison basis for different codes and methods applied for burnup analysis of HTGRs. The benchmark specifications include three different models: (1) an infinite lattice of tristructural isotropic (TRISO) fuel particles, (2) an infinite lattice of fuel pebbles, and (3) prismatic fuel including fuel and coolant channels. In this paper, we present the results of the third stage of the benchmark obtained with MCNP based depletion code BGCore and deterministic lattice code HELIOS 1.9. The depletion calculations were performed for three-dimensional model of prismatic fuel with explicitly described TRISO particles as well as for two-dimensional model in which double heterogeneity of the TRISO particles was eliminated using reactivity equivalent physical transformation (RPT). Generally good agreement in the results of calculations obtained by different methods and codes was observed.
  • Contribution to proceedings
    PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear Renaissance, 09.-14.05.2010, Pittsburgh, Pennsylvania, USA
  • Lecture (Conference)
    PHYSOR 2010 – Advances in Reactor Physics to Power the Nuclear Renaissance, 09.-14.05.2010, Pittsburgh, Pennsylvania, USA

Permalink: https://www.hzdr.de/publications/Publ-13585
Publ.-Id: 13585


HTGR Fuel Element Depletion Benchmark: Stage One Results

Fridman, E.; Shwageraus, E.
Recently, a new numerical benchmark exercise1 for High Temperature Gas Cooled Reactor (HTGR) fuel depletion was defined. The purpose of this benchmark is to provide a comparison basis for different codes and methods applied for burnup analysis of HTGRs.
The benchmark specifications include three different models: (1) an infinite lattice of tristructural isotropic (TRISO) fuel particles, (2) an infinite lattice of fuel pebbles, and (3) prismatic fuel including fuel and coolant channels.
In this summary, we present the results of the first stage of the benchmark.
  • Contribution to proceedings
    2009 ANS Winter Meeting, 15.-19.11.2009, Washington, DC Omni Shoreham Hotel, USA
  • Lecture (Conference)
    2009 ANS Winter Meeting, 15.-19.11.2009, Washington, DC Omni Shoreham Hotel, USA

Permalink: https://www.hzdr.de/publications/Publ-13584
Publ.-Id: 13584


Ultrafast carrier capture in InGaAs quantum posts

Stehr, D.; Morris, C. M.; Talbayev, D.; Wagner, M.; Kim, H. C.; Taylor, A. J.; Schneider, H.; Petroff, P. M.; Sherwin, M. S.
To explore the capture dynamics of photoexcited carriers in semiconductor quantum posts, optical pump terahertz (THz) probe and time-resolved photoluminescence spectroscopy were performed. The results of the THz experiment show that after ultrafast excitation, electrons relax within a few picoseconds into the quantum posts, which act as efficient traps. The saturation of the quantum post states, probed by photoluminescence, was reached at approximately ten times the quantum post density in the samples. The results imply that quantum posts are highly attractive nanostructures for future device applications.
Keywords: quantum post, terahertz probe, ultrafast, relaxation

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Permalink: https://www.hzdr.de/publications/Publ-13583
Publ.-Id: 13583


X-ray investigation of the interface structure of free standing InAs nanowires grown on GaAs [(1)over-bar(1)over-bar(1)over-bar](B)

Bauer, J.; Pietsch, U.; Davydok, A.; Biermanns, A.; Grenzer, J.; Gottschalch, V.; Wagner, G.
The heteroepitaxial growth process of InAs nanowires (NW) on GaAs [(1) over bar(1) over bar(1) over bar](B) substrate was investigated by X-ray grazing-incidence diffraction using synchrotron radiation. For crystal growth we applied the vapor-liquid-solid (VLS) growth mechanism via gold seeds. The general sample structure was extracted from various electron microscopic and X-ray diffraction experiments. We found a closed GaxIn1-xAs graduated alloy layer at the substrate to NW interface which was formed in the initial stage of VLS growth with a Au-Ga-In liquid alloy. With ongoing growth time a transition from this VLS layer growth to the conventional VLS NW growth was observed. The structural properties of both VLS grown crystal types were examined. Furthermore, we discuss the VLS layer growth process.
Keywords: MOVPE GROWTH; WHISKERS; ARRAYS; MECHANISM; STRAIN

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Permalink: https://www.hzdr.de/publications/Publ-13582
Publ.-Id: 13582


Low temperature silicon dioxide by thermal atomic layer deposition: investigation of material properties

Hiller, D.; Zierold, R.; Bachmann, J.; Alexe, M.; Yang, Y.; Gerlach, J. W.; Stesmans, A.; Jivanescu, M.; Müller, U.; Vogt, J.; Hilmer, H.; Löper, P.; Künle, M.; Munnik, F.; Nielsch, K.; Zacharias, M.
SiO2 is the most widely used dielectric material but its growth or deposition involves high thermal budgets or suffers from shadowing effects. The low-temperature method presented here (150 °C) for the preparation of SiO2 by thermal atomic layer deposition (ALD) provides perfect uniformity and surface coverage even into nanoscale pores, which may well suit recent demands in nanoelectronics and nanotechnology. The ALD reaction based on 3-aminopropyltriethoxysilane (APTES), water and ozone provides outstanding SiO2 quality and is free of catalysts or corrosive by-products. A variety of optical, structural and electrical properties are investigated by means of infrared spectroscopy, UV-VIS spectroscopy, secondary ion mass spectrometry, capacitance-voltage- and current-voltage-measurements, electron spin resonance, Rutherford backscattering, elastic recoil detection analysis, atomic force microscopy, and variable angle spectroscopic ellipsometry. Many features, such as the optical constants (n, k), optical transmission and surface roughness (1.5 Å) are found to be similar to thermal oxide quality. Rapid thermal annealing (RTA) at 1000°C is demonstrated to significantly improve certain properties, in particular by reducing the etch rate in hydrofluoric acid, oxide charges and interface defects. Besides a small amount of OH-groups and a few atomic per mille of nitrogen in the oxide remaining from the growth and curable by RTA no impurities could be traced. Altogether, the data point to a first reliable low temperature ALD-growth process for silicon dioxide.

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Permalink: https://www.hzdr.de/publications/Publ-13581
Publ.-Id: 13581


Molecular and Crystal Structures of Plutonyl(VI) Nitrate Complexes with N-Alkylated 2-Pyrrolidone Derivatives: Cocrystallization Potentiality of UVI and PuVI for Uniform MOX Fuel Precursor

Kim, S.-Y.; Takao, K.; Haga, Y.; Yamamoto, E.; Kawata, Y.; Morita, Y.; Nishimura, K.; Ikeda, Y.
Plutonyl(VI) nitrate complexes with N-cyclohexyl-2-pyrrolidone (NCP) and N-neopentyl-2-pyrrolidone (NNpP) were prepared, and their molecular and crystal structures were determined by single crystal X-ray analysis. The obtained compounds have the similar composition, PuO2(NO3)2(NRP)2 (NRP = NCP, NNpP), which are analogous to the corresponding UVI complexes. Both PuO2(NO3)2(NRP)2 complexes show typical structural properties of actinyl(VI) nitrates, i.e., hexagonal-bipyramidal geometry consisting of two NRP molecules and two NO3– ions located in trans positions in the equatorial plane of PuO22+ moiety, Pu=Oax = 1.73 Å, Pu–ONRP = 2.38 Å, Pu–ONO3 = 2.50 Å, and a bond angle between the U–ONRP bond and the carbonyl group of NRP ≈. 135°. The lattice constants and molecular arrangement of PuO2(NO3)2(NCP)2 were completely different from those of UO2(NO3)2(NCP)2. In contrast, these properties of PuO2(NO3)2(NNpP)2 are the same as those of UO2(NO3)2(NNpP)2. These findings provide one of criteria in selection of suitable NRP as a precipitation agent for the spent nuclear fuel reprocessing based on the precipitation method from a viewpoint of crystal engineering.
Keywords: Plutonium nitrate, precipitate, 2-pyrrolidone derivative, reprocessing, single crystal X-ray analysis
  • Crystal Growth & Design 10(2010)5, 2033-2036

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Permalink: https://www.hzdr.de/publications/Publ-13580
Publ.-Id: 13580


Neptunium Carbonato Complexes in Aqueous Solution: An Electrochemical, Spectroscopic, and Quantum Chemical Study

Ikeda-Ohno, A.; Tsushima, S.; Takao, K.; Rossberg, A.; Funke, H.; Scheinost, A.; Bernhard, G.; Yaita, T.; Hennig, C.
The electrochemical behavior and complex structure of Np carbonato complexes, which are of major concern for the geological disposal of radioactive wastes, have been investigated in aqueous Na2CO3 and Na2CO3/NaOH solutions at different oxidation states by using cyclic voltammetry, X-ray absorption spectroscopy, and density functional theory calculations. The end-member complexes of penta- and hexavalent Np in 15 M Na2CO3 with pH = 11.7 have been determined as a transdioxo neptunyl tricarbonato complex. [NpO2(CO3)(3)](n-) (n=5 for Np-V, and 4 for Np-VI). Hence, the electrochemical reaction of the Np-V/VI redox couple merely results in the shortening/lengthening of bond distances mainly because of the change of the cationic charge of Np, without any structural rearrangement. This explains the observed reversible-like feature on their cyclic voltammograms. In contrast, the electrochemical oxidation of Np-V in a highly basic carbonate solution of 2.0 M Na2CO3/1.0 M NaOH (pH > 13) yielded a stable heptavalent Np complex of [(NpO4)-O-VII(OH)(2)](3-), indicating that the oxidation reaction from Np-V to Np-VII in the carbonate solution involves a drastic structural rearrangement from the transdioxo configuration to a square-planar-tetraoxo configuration, as well as exchanging the coordinating anions from carbonate ions (CO32-) to hydroxide ions (OH-).
Keywords: Neptunium, carbonate, redox, EXAFS, structure

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Permalink: https://www.hzdr.de/publications/Publ-13579
Publ.-Id: 13579


Tailoring Magnetic Properties Using Ion Beam Irradiation

Lenz, K.
Magnetism is a collective phenomenon. Hence, local variations on the nanoscale of material properties, which act on the magnetic properties, affect the overall magnetism in an intriguing way. In particular important are the length scales on which a material property changes. These might be related to the exchange length, the domain wall width, a typical roughness correlation length, or a length scale introduced by patterning of the material.
Ion beam erosion can be applied to create well ordered substrate ripples with nanometer periodicity. These artificially created templates serve as a source of a predefined surface morphology and hence allow for the investigation of roughness phenomena. In contrast to that post ion beam irradiation can be used to tailor the magnetic properties of conventional thin films and multilayers. The resulting magnetic properties are neither present in non-implanted nor in homogeneously implanted films. In both cases the magnetic properties depend sensitively on the artificially introduced length scale. Ferromagnetic resonance data of irradiated Py/Ta multilayers as well as Co and Fe thin films on ripple substrates are discussed.
Keywords: FMR, irradiation, ripples, coupling
  • Lecture (others)
    Division seminar of the condensed matter theory group, 15.10.2009, Irvine, CA, USA

Permalink: https://www.hzdr.de/publications/Publ-13578
Publ.-Id: 13578


Spin dynamics in ferromagnets: Gilbert damping vs. two-magnon scattering

Lenz, K.
There exist several quite different damping mechanisms, which might contribute to the magnetic relaxation processes following the dynamic excitation of the spin system by ferromagnetic resonance (FMR). Most of the thin film magnetism community however seems to consider only Gilbert type damping contributions.
Using FMR and microwave frequencies between 1 and 225 GHz I will show how the different relaxation channels, i.e., dissipative, isotropic Gilbert damping G as well as anisotropic two-magnon scattering , are identified and disentangled by frequency and angle dependent FMR. In the case of Fe3Si films the scattering rates due to two-magnon scattering at crystallographic defects for spin waves propagating in [100] and [110] directions, and the Gilbert damping term are determined. Changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influences these relaxation channels.
Finally, for the case of Ne+ irradiated Py/Ta multilayers, I will present how ion beam irradiation can be used to tailor the static and dynamic properties determined by FMR and MOKE.
Keywords: FMR, Gilbert Damping, Two-Magnon Scattering
  • Lecture (others)
    Talk at the electromagnetics group seminar, 13.10.2009, Boulder, Colorado, USA
  • Lecture (others)
    Talk at the Physics Seminar Series, 12.10.2009, Colorado Springs, USA

Permalink: https://www.hzdr.de/publications/Publ-13577
Publ.-Id: 13577


Determination of the Saturation Magnetization from Perpendicular Magnetic Anisotropy Measurements of Ion Irradiated Multilayers

Lenz, K.; Markó, D.; Strache, T.; Kaltofen, R.; Fassbender, J.ORC
Ion beam irradiation and ion implantation of ferromagnetic films is a smart technique to tailor their magnetic properties and structural composition of multilayers or nanostructured samples [1,2]. Metals like Ta are commonly used as seed and cap layers in spintronic devices like Giant Magneto-Resistance sensors as Ta is chemically stable. However, it is known that 12% of Ta intermixing in Py leads to magnetically dead layers of 0.6-1.2 nm in thickness [3]. These dead layers make it impossible to determine the correct magnetic volume, which is needed to obtain the saturation magnetization from the magnetic moment measured e.g. by SQUID. This is especially true for multilayer samples which typically have a large number of interfaces.
Here we present a method to determine the saturation magnetization of Py/Ta multilayers from VNA-FMR (Vector Network Analyzer Ferromagnetic Resonance) and MOKE (Magneto-optical Kerr Effect) measurements even in the case of interfacial mixing due to ion irradiation, where SQUID magnetometry fails due to the unknown magnetic volume. Three sets of Py/Ta thin film multilayer systems were sputter-deposited on a Si/SiO2 substrate: (1xPy) is a single 20 nm thick Py layer, (5×Py) a multilayer of the structure 31 nm Ta/[4 nm Py/1 nm Ta]5/2 nm Ta and (10xPy) a multilayer of 30.5 nm Ta/[2 nm Py/0.5 nm Ta]10/2.5 nm Ta. The overall Py amount was always 20 nm and the total Ta thickness including seed and cap layer corresponds to 38 nm. Finally, the films have been irradiated with Ne ions at 40 keV with ion fluences in the range of 5×1013 to 5×1016 Ne/cm2. FMR shows that the FMR frequency vs. field dependence is significantly influenced by the amount of irradiation and number of interfaces (see Fig 1). At fluences above 2.5×1015 Ne/cm2 a significant decrease of the resonance frequency can be observed for the 1xPy samples. For the three unirradiated samples the FMR frequency decreases with an increasing number of Py/Ta repetitions, i.e. increasing number of interfaces. This decrease will be even more pronounced if larger numbers of interfaces are used. This can be explained by the higher number of neighboring Ta atoms in those cases. The deleterious effect of Ta on the ferromagnetic properties is becoming much stronger reducing the effective ferromagnetic film thickness by creating magnetically dead layers close to the interface [1,3-6]. This reduction of the saturation magnetization is directly linked to the resonance frequency. This allow to determine not only the uniaxial in-plane anisotropy field K2|| but also the saturation magnetization μ0Ms from the FMR frequency vs. field dependence. However, this can only be done, if there is only shape anisotropy but no uniaxial out-of-plane anisotropy as it is the case for our Py/Ta multilayers. From polar MOKE loops μ0Ms can be obtained by determining the perpendicular anisotropy field of the samples as well. This feature proves to be very useful here since SQUID magnetometry suffers from a major drawback: It requires the exact effective Py volume to calculate μ0Ms from the magnetic moment, which becomes more and more difficult to determine due to the increasing interfacial mixing induced by the ion irradiation and thinner Py layers. In our case, polar MOKE and FMR represent suitable alternatives since they allow μ0Ms to be determined without the knowledge of any film thickness. The good agreement with the SQUID data of the non-irradiated samples supports this (see Fig 2). ...
Keywords: FMR. MOKE, Irradiation
  • Lecture (Conference)
    11th Joint MMM-Intermag Conference, 18.-22.01.2010, Washington DC, USA

Permalink: https://www.hzdr.de/publications/Publ-13576
Publ.-Id: 13576


Tailoring the Néel- and Interlayer Exchange Coupling of Fe/Cr/Fe Trilayers using Rippled Substrates

Lenz, K.; Körner, M.; Liedke, M. O.; Strache, T.; Dzenisevich, S.; Keller, A.; Facsko, S.; Fassbender, J.ORC
rtificial antiferromagnets made from magnetically coupled trilayer structures are the basis for all types of spintronic devices like MRAM, GMR sensors etc. For years major effort lay on adjusting the coupling strength by changing the spacer thickness or material. Today, nanostructures offer a different approach as they add additional coupling mechanisms like proximity effects or N\'eel orange-peel coupling to the common interlayer exchange coupling (IEC). By means of ion beam erosion techniques it is possible to create well ordered substrate ripples with nanometer periodicity. They are transferred into the films grown on these rippled substrates. Hence, such ripples are a convenient way to induce N\'eel orange-peel coupling [1] and thus allow for tailoring the magnetic properties [2] as well as the coupling strength by varying the ripple periodicity without adjusting the spacer thickness.

We have investigated the influence of rippled vs. flat Si substrates on the interlayer exchange coupling contributions in polycrystalline Fe (4nm)/Cr ($x$ nm)/Fe (4nm) thin film trilayers ($x$=0--5 nm). The substrate surface was periodically modulated (periods of 23 nm and 37 nm) by Ar$^+$ ion beam erosion. The influence of the resulting surface and interface structure on the magnetic properties has been investigated by longitudinal magneto-optical Kerr effect (MOKE) applying a Stoner-Wohlfarth model on the magnetization reversal loops. Using 23 nm period ripples, we find an orange peel type coupling, predicted by N\'eel's theory superimposed on the IEC. In addition due to the morphology of the magnetic layers, a strong uniaxial magnetic anisotropy is induced.
[1] M. Körner, K. Lenz, M.O. Liedke, T. Strache, S. Dzenisevich, A. Keller, S. Facsko, and J. Fassbender, submitted to Phys. Rev. B.
[2] J. Fassbender, T. Strache, M.O. Liedke, D. Mark\'o, S. Wintz, K. Lenz, A. Keller, S. Facsko, I. M\"onch, and J. McCord, submitted to New. J. Phys.

This work is supported by DFG grant FA 314/6-1.
Keywords: MOKE, orange-peel coupling, Neel coupling, interlayer exchange coupling, ripples
  • Poster
    Advances in Magnetic Nanostructures, 04.-09.10.2009, Vail, Colorado, USA

Permalink: https://www.hzdr.de/publications/Publ-13575
Publ.-Id: 13575


Determination of the Saturation Magnetization from Perpendicular Magnetic Anisotropy Measurements

Lenz, K.; Marko, D.; Strache, T.; Fassbender, J.ORC
Over the last years the modification of magnetic parameters of thin films and multilayers by ion irradiation and implantation has become fashionable. However, especially in multilayer structures ion irradiation can lead to interfacial mixing and thus to a significant reduction of the magnetically active volume, i.e. 'dead' layers. Thus, it can be quite difficult---if not at all impossible---to determine the correct effective magnetic volume, e.g. for measurements of the saturation magnetization by SQUID. Here we show how ferromagnetic resonance (FMR) and magneto-optical Kerr effect (MOKE) measurements can be utilized to determine the saturation magnetization of irradiated Py/Ta multilayers instead and how the magnetic properties change upon irradiation.
We prepared thin films and multilayers of Py/Ta with an overall Py thickness of 20 nm and varying number of Py/Ta stacks and irradiated them with Ne ions at various fluences. FMR, MOKE, and SQUID magnetometry were used for investigation. With both, increasing ion fluences and increasing number of Py/Ta interfaces, a decrease of saturation magnetization and an increase of precessional damping can be observed. The uniaxial anisotropy of the samples is only of small magnitude and remains almost unaffected. There is, depending on the number of interfaces, a critical ion fluence at which ferromagnetic order in the multilayers vanishes.
This work is supported by DFG grant FA 314/3-1.
Keywords: FMR, ion irradiation
  • Poster
    Advances in Magnetic Nanostructures, 04.-09.10.2009, Vail, Colorado, USA

Permalink: https://www.hzdr.de/publications/Publ-13574
Publ.-Id: 13574


Spin wave excitations: coupling and damping effects in ultrathin films

Lenz, K.; Marko, D.; Strache, T.; Fassbender, J.ORC
Spinwave excitations in thin film ferromagnets control several phenomena starting with spin transfer torque/spin pumping effects, magnetic relaxation and damping, to interlayer exchange coupling (IEC) and its temperature dependence. Most of them are accessible by ferromagnetic resonance (FMR).
There exist several quite different damping mechanisms, which might contribute to the magnetic relaxation processes following the excitation of the spin system. Using a broad range of microwave frequencies, I will show how these different relaxation channels, i.e., dissipative isotropic Gilbert damping as well as anisotropic two-magnon scattering, can be identified and disentangled by frequency and angle dependent FMR on Fe3Si Heusler alloys.
Changing the film thickness from 8 to 40 nm and slightly modifying the Fe concentration influences these relaxation channels [1]. Ion beam irradiation can be used to tailor the damping properties of Py/Ta multilayers after sample preparation [2].
FMR can also be used to study the interlayer exchange coupling. For single crystalline Ni/Cu/Co prototype trilayers the IEC’s temperature dependence was investigated [3]. It follows an effective power law AT n, n ≈ 1.5. The results clearly indicate that the dominant contribution to the temperature dependence is due to the excitation of thermal spin waves. This is corroborated by recently developed theory [4].

[1] Kh. Zakeri et al., Phys Rev. B 76, 104416 (2007).
[2] D. Markó, T. Strache, K. Lenz, J. Fassbender, and R. Kaltofen, submitted
[3] S.S. Kalarickal, X.Y. Xu, K. Lenz, W. Kuch, and K. Baberschke, Phys. Rev. B 75, 224429 (2007).
[4] S. Schwieger, J. Kienert, K. Lenz, J. Lindner, K. Baberschke, and W. Nolting, Phys. Rev. Lett. 98, 057205 (2007).
Keywords: Spin waves, Ferromagnetic Resonance, Interlayer exchange coupling
  • Invited lecture (Conferences)
    448. WE-Heraeus-Seminar: Excitement in magnetism: Spin-dependent scattering and coupling of excitations in ferromagnets, 22.-25.11.2009, Ringberg, Deutsch

Permalink: https://www.hzdr.de/publications/Publ-13573
Publ.-Id: 13573


Parallel proximal probe arrays with vertical interconnections

Sarov, Y.; Frank, A.; Ivanov, T.; Zöllner, J.-P.; Ivanova, K.; Volland, B.; Rangelow, I. W.; Brogan, A.; Wilson, R.; Zawierucha, P.; Zielony, M.; Gotszalk, T.; Nikolov, N.; Zier, M.; Schmidt, B.; Kostic, I.
This article presents the fabrication and the characteristics of 8x64, parallel, self-actuated, and independently addressable scanning proximal probes with through-silicon via interconnection passing completely through a silicon wafer. The low-resistance highly doped polysilicon through-wafer electrical interconnects have been integrated with scanning proximal probes (SPPs) to enable back side contacts to the application-specific integrated circuit used as an atomic force microscope control circuitry. Every SPP sensor contains a deflection sensor, thermally driven bimetal (bimorph) actuator, and sharp silicon tip. Dry etching-based silicon on insulator three-dimensional-micromachining technique is employed by the creation of the through-silicon vias and the SPP arrays keeping fully complementary metal-oxide semiconductor compatible process regime. The application of the vertical interconnection technology in large-scale two-dimensional cantilever arrays with off-plane bent cantilevers over the chip’s surface, in a combination with the flip-chip packaging technology allow simultaneous approach and parallel scanning of large areas in noncontact mode.
Keywords: AFM probe array, electrical through wafer interconnect, piezoresistive deflection sensor, thermally driven deflection actuator
  • Journal of Vacuum Science & Technology B 27(2009)6, 3132-3138
    DOI: 10.1116/1.3256662

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Permalink: https://www.hzdr.de/publications/Publ-13572
Publ.-Id: 13572


Electrical Characterisation of USJs in doped Si

Ogiewa, M.; Zier, M.; Schmidt, B.
An adaption of the DHE technique, using a stepwise oxidation, as an alternative to e.g. SRP methods as a tool to determine active carrier concentration and mobility depth profiles is presented. As known from the literature, a reduction of dopand activation as well as a decrease of mobility with increasing implantation dose above the solubility limit is observed. The aim is to combine the effects known from the literature in a model system. For industrial purpose, this enables one to find a “sweet spot” of high mobility and active dopand concentration while minimizing the negative effects of a high implantation dose.
Keywords: ultra-shallow pn-junction, charge carrier concentration and mobility, dopand activation
  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie (SKM), 22.-27.03.2009, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-13571
Publ.-Id: 13571


EFTEM, EELS, and Cathodoluminescence in Si-implanted SiO2 Layers

Fitting, H.-J.; Fitting Kourkoutis, L.; Salh, R.; Schmidt, B.
Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters.
Keywords: Ion implantation, Si nanoclusters

Permalink: https://www.hzdr.de/publications/Publ-13570
Publ.-Id: 13570


Ion-erosion-induced pattern as template for layers with magnetic anisotropy and coupling

Fassbender, J.ORC; Liedke, M. O.; Körner, M.; Markó, D.; Lenz, K.; Facsko, S.
Ion-erosion-induced ripples are perfect template systems to systematically investigate the influence of a periodic surface modulation on magnetic properties like magnetic anisotropy in the case of single magnetic films or interlayer exchange coupling in the case of multilayer systems. One of the key advantages of these ripples is that their periodicity can easily be varied in the range between 20 and 60 nm. This matches exactly the range where magnetic properties can be affected by a surface modulation. Two different examples will be discussed: i.) ripple-induced magnetic anisotropies in soft magnetic Permalloy films [1,2] and ii.) the appearance of roughness induced magnetic coupling, e.g. Neel coupling, in multilayer systems [3]. In both cases a significant influence of the surface and interface modulation on the magnetic properties is observed, which drastically depends on the ripple periodicity itself.
References:
[1] M.O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Phys. Rev. B 75, 220407 (2007).
[2] J. Fassbender, T. Strache, M.O. Liedke, D. Markó, S. Wintz, K. Lenz, S. Facsko, I. Mönch, J. McCord, New J. Phys. in press.
[3] M. Körner, K. Lenz, M.O. Liedke, T. Strache, A. Mücklich, S. Facsko, J. Fassbender, Phys. Rev. B, submitted.
Keywords: magnetism, ion erosion, templates, nanopatterning, magnetic anisotropy, magnetic damping, magnetic coupling
  • Invited lecture (Conferences)
    2009 MRS Fall Meeting, 30.11.-04.12.2009, Boston, USA

Permalink: https://www.hzdr.de/publications/Publ-13569
Publ.-Id: 13569


Designing soft magnetic materials by ion irradiation

McCord, J.; Fassbender, J.ORC
The control of the relevant magnetic material parameters like magnetic anisotropy, saturation magnetization as well as the dynamic magnetic properties in ferromagnetic thin films is of significant importance for applications in spin electronics. Commonly, the magnetic anisotropy in ferromagnetic single or multi-layers is initialized either by applying a magnetic field during film deposition or by annealing a magnetic field, which results in an anisotropy aligned along the applied field direction. Another important magnetic parameter, the saturation magnetization, is mainly determined by the film's composition.
We discuss novel ways of patterning magnetic films in terms of laterally varying magnetic properties. The difference of these hybrid property films with respect to conventional ferromagnetic systems is that the magnetic behaviour is strongly influenced by the direct exchange interaction across the regions of different magnetic behaviour. This makes them comparable to magnetic multilayer structures.
Different samples of anisotropy, exchange bias, and saturation magnetization [4] modulated thin films are prepared by local ion irradiation or implantation [1-5]. The magnetization reversal processes in the two-phase materials exhibit unique features, some of them so far only known from multilayer samples. The main emphasis of the presented work is on the role of the magnetic microstructure in stripe-like magnetic hybrid structures on the overall magnetization properties. Unique effects are derived from magnetic property measurements and magnetic domain imaging.
The presented paths of film preparations provide additional degrees of freedom for the tailoring of magnetic properties and functionality of soft-magnetic thin films. The presented methods allow for a local setting of magnetic properties without irreversible structural and magnetic alterations.

[1] J. Fassbender, J. McCord, Magnetic patterning by means of ion irradiation and implantation, J. Magn. Magn. Mat. 320, 579 (2008)
[2] J. McCord, I. Mönch, J. Fassbender, A. Gerber, E. Quandt, Local setting of magnetic anisotropy in amorphous films by Co ion implantation, J. Phys. D: Appl. Phys. 42, 55006 (2009)
[3] J. McCord, L. Schultz, J. Fassbender, Hybrid soft-magnetic lateral exchange spring films prepared by ion irradiation, Adv. Mat. 20, 2009 (2008)
[4] N. Martin, J. McCord, A. gerber, T. Strache, T. Gemming, I. Mönch, N. Farag, R. Schäfer, J. Fassbender, E. Quandt, L. Schultz, Local stress engineering of magnetic anisotropy in soft magnetic thin films, Appl. Phys. Lett. 94, 62506 (2009)
Keywords: magnetism, ion irradiation, magnetic properties, material modification, patterning, microscopy
  • Invited lecture (Conferences)
    XVIII International Materials Research Congress, 16.-20.08.2009, Cancun, Mexiko

Permalink: https://www.hzdr.de/publications/Publ-13568
Publ.-Id: 13568


Ion Beam Mixing as Basic Technology for a Light-emitting silicon nanocrystal field-effect transistor

Schmidt, B.; Heinig, K.-H.; Beyer, V.; Stegemann, K.-H.
A light emitting field-effect transistor (LEFET) which is based on silicon nanocrystals in the gate oxide is demonstrated. The Si nanocrystals in the gate oxide were optimized for a multi-dot floating-gate nonvolatile memory operation. For this aim, ion irradiation through the MOSFET stack of 50 nm poly-Si/15 nm SiO2/Si substrate was performed with 50 keV Si+ ions. The ion beam mixing of the upper poly-Si/SiO2 interface and the lower SiO2/(001)Si interface leads to Si excess in the gate oxide. Subsequent rapid thermal annealing reforms sharp interfaces and separates the excess Si from SiO2. Adjacent to the recovered interfaces, 3-4 nm thick SiO2 zones denuded completely of excess Si have been found, whereas the more distant tails of excess Si form well-aligned narrow layers of nanocrystals with 2-3 nm diameter. LEFETs with an active gate area of 20x20 µm2 were fabricated as nMOSFET devices in a standard 0.6 µm CMOS process line. An AC voltage was applied to the gate in order to inject charges of both polarities into the lower and upper Si nanocrystal layer from the channel and the poly-Si gate of the transistor, respectively. AC voltage and frequency dependent electroluminescence spectra were recorded in the wavelength region of 400-1000 nm as a function of the annealing conditions. The performance of the LEFETs and further possibilities of optimization of efficient light emission will be discussed.
Keywords: Ion beam mixing, Si/SiO2 interface, Si nanocrystals, electroluminesence, MOS-FFET device
  • Lecture (Conference)
    Ionenstrahltreffen 2009, 06.-08.04.2009, Jena, Germany

Permalink: https://www.hzdr.de/publications/Publ-13567
Publ.-Id: 13567


Ion implantation in AFM cantilever array fabrication

Schmidt, B.; Zier, M.; Potfajova, J.
This paper describes the fabrication of p-type silicon piezoresistive sensing and actuating resistive heater elements monolithically integrated in AFM cantilever arrays using ion implantation for boron doping of all elements including corresponding interconnecting lines between them. Because it has been found that for p-type piezoresistivity the predicted values of the piezoresistive coefficients are approximately two times higher in ultra-shallow boron doped layers with a pn-junction depth < 10 nm than in the silicon p-type bulk material special efforts were done for the realization of ultra-shallow boron profiles using low-energy ion implantation and point defect engineering.
Keywords: Low energy ion implantation, piezoresistor, AFM cantilever array
  • Lecture (Conference)
    54th Internationales Wissenschaftliches Kolloquium, Workshop „PRONANO”,, 10.09.2009, Ilmenau, Germany

Permalink: https://www.hzdr.de/publications/Publ-13566
Publ.-Id: 13566


Bildrekonstruktion für die ultraschnelle Limited-Angle-Röntgen-Computertomographie von Zweiphasenströmungen

Bieberle, M.
Die ultraschnelle Röntgentomographie ist eine Messmethode, die speziell für die Untersuchung von transienten Zwei- und Mehrphasenströmungen entwickelt wurde. Speziell angepasste Bildrekonstruktionsalgorithmen ermöglichen die direkte Rekonstruktion von Phasengrenzflächen.
Keywords: Röntgen, Computertomographie, Zweiphasenströmungen, Messtechnik
  • Lecture (others)
    KOMPOST Doktorandenseminar, 10.12.2009, Dresden, FZD, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13565
Publ.-Id: 13565


Ultrafast electron-beam x-ray computed tomography for multi-phase flow measurement

Bieberle, M.
Ultrafast x-ray computed tomography is an imaging technique that has been optimized for transient flow measurements. Special image reconstruction algorithms enable the direct reconstruction of the physical phases of the investigated two-phase-flows.
Keywords: x-ray tomography, flow measurement, image reconstruction
  • Lecture (others)
    FZD Doktorandenseminar, 16.-18.09.2009, Krögis, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13564
Publ.-Id: 13564


Compositional, structural and morphological modifications of N-rich Cu3N films induced by irradiation with Cu8+ at 42 MeV

Gordillo, N.; Rivera, A.; Grötzschel, R.; Munnik, F.; Güttler, D.; Crespillo, M. L.; Agulló-López, F.; González-Arrabal, R.
N-rich Cu3N films were irradiated with Cu8+ at 42 MeV in the fluence range from 4×1011 to 1×1014 cm-2. The radiation-induced changes in the chemical composition, structural phases, surface morphology and optical properties have been characterised as a function of fluence, substrate temperature and angle of incidence of the incoming ion by means of ion beam analysis (IBA), X-ray diffraction (XRD), atomic force microscopy (AFM), profilometry and Fourier transform IR spectrophotometry (IRFT). IBA techniques reveal a very efficient sputtering of N whose yield (5×103 at/ion) is almost independent of substrate temperature (RT-300ºC) but slightly depends on the incidence angle of the incoming ion. The area density of Cu remains essentially constant within the investigated fluence range. All data suggest an electronic mechanism to be responsible for the N depletion. The release of nitrogen and the formation of Cu2O and metallic Cu are discussed on the basis of existing models.
Keywords: Copper nitride, ion beam modification of materials, ion beam mixing, swift heavy ion irradiation, electronic sputtering.

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Publ.-Id: 13563


Combined effects of humic matter and surfactants on PAH solubility: Is there a mixed micellization?

Lippold, H.
1. Introduction
It has been recognized that solid-liquid distribution and transport of hydrophobic contaminants such as PAH (polycyclic aromatic hydrocarbons) are governed by their interaction with mineral-bound and dissolved humic matter, acting as a sink or a mobilizing agent, respectively. As surface-active compounds, humic substances are often compared to surfactants. Emerging environmental technologies involve a deliberate application of surfactants to enhance the sorption capacity of soils and aquifer materials, or to increase the efficiency of soil washing procedures and pump-and-treat operations for groundwater decontamination. Whereas contaminant binding to humics as well as to surfactants has been extensively studied, there is a notable lack of literature on their combined action in mixed systems. This topic is, however, important because environmental influences of surfactants are inevitably associated with the effects of the ubiquitous natural organics. Since both are amphiphilic, it seems conceivable that mixed micelles can be formed, involving synergistic or antagonistic effects in the solubilization of organic compounds.
In this study, we have examined the joint influence of humic acid and surfactants (cationic, anionic) on the water solubility of pyrene as a representative of PAH, at surfactant concentrations below and above the critical micelle concentration (CMC). In order to detect and characterize interaction processes, we have investigated the octanol-water partitioning of humic acid in the presence of various surfactants, using radiolabelled humic material. In particular, the hypothesis of a micellar nature of dissolved humic substances has been addressed.

2. Materials and Methods: omitted here

3. Results and Discussion
The water solubility of pyrene is increased in the presence of humic acid, which acts as a carrier due to hydrophobic interaction of both components. When adding the cationic surfactant dodecyltrimethylammonium bromide (DTAB), this solubility enhancement was found to be cancelled; the humic colloids were precipitated as a consequence of charge compensation by the organo-cations.
Interestingly, an antagonistic effect was also observed on addition of an anionic surfactant, sodium dodecylsulfate (SDS). While no precipitation was induced in this case, the solubility of pyrene was reduced by half and remained constant on further addition. Only at surfactant concentrations above the CMC, the solubility increased sharply owing to micellar incorporation. The presence of HA did not cause any change in the CMC of SDS, as is normally observed on addition of a second amphiphilic compound. Furthermore, the effects of HA and micellar SDS on pyrene solubility turned out to be strictly additive. Consequently, they are based on distinct processes, occurring independently of each other, i.e., there is no mixed micellization with humic molecules acting as a co-surfactant.
The octanol-water partition ratios of HA changed significantly in the presence surfactants. The partitioning equilibrium was shifted towards the organic phase on addition of cationic surfactants, and towards the aqueous phase on addition of anionic surfactants. Based on these findings, different modes of interaction could be identified, providing an explanation for the decline in pyrene solubilization in systems of HA and SDS. Obviously, a competitive situation arises in the hydrophobic binding of the PAH and the surfactant tail groups. The fact that the pyrene molecules cannot be displaced completely supports the proposition that different binding sites exist in humic colloids: weak near-surface sites and strong inner sites.
The size distribution of the colloids was found to be unaffected by the association with anionic as well as with cationic surfactants. A general micellar character is thus unlikely since a co-aggregation should then entail substantial disruptions and rearrangement processes.

4. Conclusions: omitted here
  • Poster
    15th meeting of the International Humic Substances Society (IHSS 15), 27.06.-02.07.2010, Tenerife, Espana

Permalink: https://www.hzdr.de/publications/Publ-13562
Publ.-Id: 13562


Role of impurities and dislocations for the unintentional n-type conductivity in InN

Darakchieva, V.; Barradas, N. P.; Xie, M.-Y.; Lorenz, K.; Alves, E.; Schubert, M.; Persson, P. O. A.; Giuliani, F.; Munnik, F.; Hsiao, C. L.; Tu, L. W.; Schaff, W. J.
We present a study on the role of dislocations and impurities for the unintentional n-type conductivity in high-quality InN grown by molecular beam epitaxy. The dislocation densities and H profiles in films with free electron concentrations in the low 1017 cm-3 and mid 1018 cm-3 range are measured, and analyzed in a comparative manner. It is shown that dislocations alone could not account for the free electron behavior in the InN films. On the other hand, large concentrations of H sufficient to explain, but exceeding substantially, the observed free electron densities are found. Furthermore, enhanced concentrations of H are revealed at the film surfaces, resembling the free electron behavior with surface electron accumulation. The low-conductive film was found to contain C and it is suggested that C passivates the H donors or acts as an acceptor, producing compensated material in this case. Therefore, it is concluded that the unintentional impurities play an important role for the unintentional n-type conductivity in InN. We suggest a scenario of H incorporation in InN that may reconcile the previously reported observations for the different role of impurities and dislocations for the unintentional n-type conductivity in InN.

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Permalink: https://www.hzdr.de/publications/Publ-13561
Publ.-Id: 13561


Numerical simulation of the insulation material transport in a PWR core under loss of coolant conditions

Höhne, T.; Grahn, A.; Kliem, S.; Rohde, U.; Weiss, F.-P.
In 1992, strainers on the suction side of the ECCS pumps in Barsebäck NPP Unit 2 became partially clogged with mineral wool after a safety valve opened because steam impinged on the thermally-insulated equipment and released mineral wool. This event pointed out that strainer clogging in the course of a loss-of-coolant accident is an issue and induced many investigations to understand and prevent strainer clogging effects.

Modifications of the insulation material, the strainer area and mesh size were carried out in most of the German NPPs. Moreover, back flushing procedures to remove the mineral wool from the strainers and differential pressure measurement were implemented to assure the performance of emergency core cooling during the containment sump recirculation mode.

Nevertheless, it cannot be completely ruled out, that a limited amount of the smaller fractions of insulation material could be transported into the RPV. During a postulated cold leg LOCA with hot leg ECC injection, the fibres 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.

It was the aim of the numerical simulations presented to study where and how many mineral wool fibers are deposited at the upper spacer grid. The 3D, time dependent, multi-phase flow problem was modelled by applying the CFD code ANSYS CFX.

The spacer grids were modeled as a strainer, which completely retains all the insulation material that reaches the uppermost spacer level. There, the accumulation of the insulation material gives rise to the formation of a compressible fibrous layer, the permeability of which to the coolant flow is calculated in terms of the local amount of deposited material and the local value of the superficial liquid velocity.

Before the switch over of the ECC injection from the flooding mode to the sump mode, the coolant circulates in an inner convection loop in the core extending from the lower plenum to the upper plenum. The CFD simulations have shown that after starting the sump mode, the ECC water injected through the hot legs flows down into the core via so-called "brake through channels" located in 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 the fibres are not uniformly deposited over the core cross section.

When the inner recirculation stops later in the transient, insulation material can also be collected in other regions of the core cross section at the level of the upper spacer grids. Nevertheless, with a total of 2.7 kg fiber material deposited at the uppermost spacer level, the pressure drop over the fiber cake is not higher than 8 kPa and all the ECC water could still enter the core. The CFD calculation does not yet include steam production in the core and also does not include re-suspension of the insulation material during reverse flow. This will certainly further improve the coolability of the core.
Keywords: CFD, Fibre, Core, PWR
  • Contribution to proceedings
    18th International Conference on Nuclear Engineering, 17.-21.05.2010, Xi'an, China
  • Lecture (Conference)
    18th International Conference on Nuclear Engineering, 17.-21.05.2010, Xi'an, China

Permalink: https://www.hzdr.de/publications/Publ-13560
Publ.-Id: 13560


Temperature dependence of the crossover between the near-infrared Er and defect-related photoluminescence bands of Ge-rich Er-doped SiO2 layers

Kanjilal, A.; Rebohle, L.; Prucnal, S.; Voelskow, M.; Skorupa, W.; Helm, M.
Temperature-dependent photoluminescence of Ge-rich SiO2 in the presence or absence of Er shows a crossover between defect-related (15–150 K) and Er-related (150–295 K) emission within 1525 and 1440 nm. The origin of the near-infrared defect-related bands is discussed in the light of recombination of localized excitons in luminescence centers at the Ge cluster/SiO2 interface. Time-resolved photoluminescence further enables us to illustrate the observed 1.53 um Er emission above 150 K in terms of a phonon-assisted nonradiative energy-transfer process from the luminescence centers to the Er3+ ions.
Keywords: PL, Er, Ge clusters

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Permalink: https://www.hzdr.de/publications/Publ-13559
Publ.-Id: 13559


Establishing the mechanism of thermally induced degradation of ZnO:Al electrical properties using synchrotron radiation

Vinnichenko, M.; Gago, R.; Cornelius, S.; Shevchenko, N.; Rogozin, A.; Kolitsch, A.; Munnik, F.; Möller, W.
X-ray absorption near edge structure and x-ray diffraction studies with synchrotron radiation have been used to relate the electrical properties of ZnO:Al films to their bonding structure and phase composition. It is found that Al-sites in an insulating metastable homologous (ZnO)3Al2O3 phase are favored above a certain substrate temperature (Ts) leading to deterioration of both the crystallinity and the electrical properties of the films. The higher film resistivity is associated with lower carrier mobility due to increased free electron scattering. Lower metal to oxygen flux ratios during deposition expand the range of Ts at which low-resistivity films are obtained.
Keywords: transparent conductive oxides, Al-doped ZnO, reactive pulsed magnetron sputtering, electrical properties, XANES

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Publ.-Id: 13558


DREAMS - a universal AMS facility based on the 6 MV - TandetronTM at FZD in Dresden

Akhmadaliev, S.; Kolitsch, A.; Merchel, S.; Möller, W.
A new accelerator mass spectrometry (AMS) system has been installed at the Forschungszentrum Dresden-Rossendorf (FZD). The system is based on a 6 MV-TandetronTM accelerator produced by High Voltage Engineering Europe (HVEE). The AMS facility is specified for measurements of 10Be, 14C, 26Al, 36Cl, 41Ca and 129I with isotopic ratios of 10-10 - 10-16 and precision better than 0.3% for 14C/12C.
The system uses a bouncer sequential injector with two Cs-sputter ion sources and a 54°-electrostatic analyser (ESA). On the high-energy site it has a 90°-analysing magnet, Faraday-Cups for stable nuclides, a 35°-ESA, a post-stripper foil, and a 30°-vertical magnet for suppression of interfering species, and gas ionisation chamber for detection of radionuclides [1].
The Cockroft-Walton type high voltage generator provides a terminal voltage of up to 6 MV. The system is additionally equipped with a multipurpose ion injector containing a third Cs-sputter ion source and a duoplasmatron for high-energy ion implantation and ion-beam materials analysis.

[1] M. Arnold et al., accepted for Nucl. Instr. and Meth. B (Proceedings
of IBA-2009).
Keywords: Accelerator mass spectrometry, AMS
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion AMOP (SAMOP), 08.-12.03.2010, Hannover, Deutschland

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Publ.-Id: 13557


Comparison among MCNP-based depletion codes applied to burnup calculations of pebble-bed HTR lattices

Bomboni, E.; Cerullo, N.; Fridman, E.; Lomonaco, G.; Shwageraus, E.
The double-heterogeneity characterising pebble-bed high temperature reactors (HTRs) makes Monte Carlo based calculation tools the most suitable for detailed core analyses. These codes can be successfully used to predict the isotopic evolution during irradiation of the fuel of this kind of cores. At the moment, there are many computational systems based on MCNP that are available for performing depletion calculation. All these systems use MCNP to supply problem dependent fluxes and/or microscopic cross sections to the depletion module. This latter then calculates the isotopic evolution of the fuel resolving Bateman's equations.
In this paper, a comparative analysis of three different MCNP-based depletion codes is performed: Montburns2.0, MCNPX2.6.0 and BGCore. Monteburns code can be considered as the reference code for HTR calculations, since it has been already verified during HTR-N and HTR-N1 EU project. All calculations have been performed on a reference model representing an infinite lattice of thorium-plutonium fuelled pebbles. The evolution of k-inf as a function of burnup has been compared, as well as the inventory of the important actinides.
The k-inf comparison among the codes shows a good agreement during the entire burnup history with the maximum difference lower than 1%. The actinide inventory prediction agrees well. However significant discrepancy in Am and Cm concentrations calculated by MCNPX as compared to those of Monteburns and BGCore has been observed. This is mainly due to different Am-241 (n,γ) branching ratio utilized by the codes.
The important advantage of BGCore is its significantly lower execution time required to perform considered depletion calculations. While providing reasonably accurate results BGCore runs depletion problem about two times faster than Monteburns and two to five times faster than MCNPX.
Keywords: HTR, Pebble-bed, MCNP, Monte-Carlo depletion codes, MCNPX, Monteburns, BGCore
  • Nuclear Engineering and Design 240(2010), 918-924

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Publ.-Id: 13556


Silicon Cluster Aggregation in Silica Layers

Fitting, H.-J.; Fitting Kourkoutis, L.; Salh, R.; Kolesnikova, E. V.; Zamoryanskaya, M. V.; von Czarnowski, A.; Schmidt, B.
Scanning transmission electron microscopy (STEM) in combination with electron energy loss spectroscopy (EELS) and cathodoluminescence (CL) have been used to investigate Si+-implanted amorphous silicon dioxide layers and the formation of Si nanoclusters. The microstructure of the Si doped silica films was studied by energy filtered transmission electron microscopy (EFTEM) in a 200 kV FEI Tecnai F20 TEM. The samples were amorphous, thermally grown 500 nm SiO2 layers on Si substrate doped by Si+ ions with an energy of 150 keV up to an atomic dopant fraction of about 4 at%. A thermal post-annealing leads to formation of silicon clusters with sizes 1-5 nm and concentrations of about 1018 cm-3. Respective cathodoluminescence spectra in the near IR region indicate such structural changes by appearance of an additional band at 1.35 eV as well as additional emission bands in the visible green-yellow region.
Keywords: Si ion implantation, Nanoclusters, Understoichiometric silica, Cathodoluminescence

Permalink: https://www.hzdr.de/publications/Publ-13554
Publ.-Id: 13554


Parallel Hardware-accelerated Particle in Cell (PiC) Physics using MPI, pThreads and CUDA: Implementing a Prototype

Juckeland, G.; Bussmann, M.
Presentation of the parallel communication scheme implemented by PIConGPU
Keywords: particle-in-cell, algorithm, parallel, pic, simulation, gpu, cluster, network, mpi, threads, pthreads, message-passing-interface, laser, plasma
  • Invited lecture (Conferences)
    Herausforderungen des HPC in Deutschland, 29.09.2009, Leogang, Österreich

Permalink: https://www.hzdr.de/publications/Publ-13553
Publ.-Id: 13553


New approaches investigating production rates of in-situ produced terrestrial cosmogenic nuclides

Merchel, S.; Braucher, R.; Benedetti, L.; Bourlès, D.
In-situ produced cosmogenic nuclides have proved to be valuable tools for environmental and Earth sciences. However, accurate application of this method is only possible, if terrestrial production rates in a certain environment over a certain time period and their depth-dependence within the exposed material are exactly known. Unfortunately, the existing data and models differ up to several tens of percent.
Thus, one of the European project CRONUS-EU goals is the high quality calibration of the 36Cl production rate by spallation at independently dated surfaces. As part of fulfilling this task we have investigated calcite-rich samples from four medieval landslide areas in the Alps: Mont Granier, Le Claps, Dobratsch, and Veliki Vrh (330-1620 m, 1248-1442 AD).
For investigating the depth-dependence of the different nuclear reactions, especially, the muon- and thermal neutron-induced contributions, we have analysed mixtures of carbonates and siliceous conglomerate samples - for 10Be, 26Al, and 36Cl - exposed at different shielding depths and taken from a core drilled in 2005 at La Ciotat, France (from surface to 11 m shielding).
AMS of 36Cl was performed at LLNL and ETH, 10Be and 26Al at ASTER.

Acknowledgments: Thanks to V. Alfimov, M. Arnold, G. Aumaître, J. Borgomano, R. Finkel, I. Mrak, and J.M. Reitner.
Keywords: accelerator mass spectrometry, cosmogenic nuclides, TCN
  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Atome, Moleküle, Quantenoptik und Plasmen (AMOP), 08.-12.03.2010, Hannover, Deutschland

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Publ.-Id: 13552


Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern

Wosnitza, J.
es hat kein Abstract vorgelegen!
  • Invited lecture (Conferences)
    Studium Generale "Naturwissenschaft Aktuell", 03.12.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13551
Publ.-Id: 13551


Die Jagd nach dem Feldrekord - Forschung in hohen Magnetfeldern

Wosnitza, J.
Was sind Magnetfelder? Wo findet man sie? Wie erzeugt man sie und zu was sind sie nutze? Antworten auf diese Fragen sollen in dem Vortrag durch Vorstellung der weltweiten Bestrebungen, immer höhere Magnetfelder zu erreichen, gegeben werden. Ähnlich wie z. B. Druck und Temperatur haben magnetische Felder einen tief greifenden Einfluss auf den Zustand und Zustandsänderungen der Materie. Untersuchungen von Materialien in hohen Magnetfeldern sind daher mittlerweile Standard und eine Vielzahl von Anwendungen in unserem täglichen Leben sind ohne Magnetfeldeffekte undenkbar. In der Forschung wird der stetig wachsende Bedarf an möglichst großen Magnetfeldstärken durch Hochfeldlaboratorien abgedeckt. In dem neu aufgebauten Hochfeld-Magnetlabor Dresden sollen demnächst gepulste Magnetfelder bis zu 100 Tesla erzeugt werden. Erste Hochfeldmagnete sind in Betrieb und seit 2007 hat neben der Eigenforschung der Nutzerbetrieb begonnen. Der momentane Status des Labors, die Schwierigkeiten, die zur Erzeugung so hoher Magnetfelder überwunden werden müssen, und exemplarische wissenschaftliche Ergebnisse aus Hochfeldstudien sollen vorgestellt werden.
  • Invited lecture (Conferences)
    Technische Universität München, 13.11.2009, München - Garching, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13550
Publ.-Id: 13550


Research at the new Dresden High Magnetic Field Laboratory

Wosnitza, J.
High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument for condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (Hochfeld-Magnetlabor Dresden, HLD), that in 2007 has opened its doors for external users, pulsed magnetic fields up to 70 T are available and a European record field of 87.2 T have been reached. The laboratory has set the ambitious goal of reaching 100 T on a 10 ms timescale. As a unique feature, a free-electron-laser facility next door allows high-brilliance radiation to be fed into the pulsed field cells of the HLD, thus making possible high-field magneto-optical experiments in the range 3-250 µm. Cryotechniques and different sample probes for a broad range of experimental techniques custom designed for the pulsed magnets are readily available for users. In-house research of the HLD focuses on electronic properties of strongly correlated materials at high magnetic fields. Besides introducing some highlights of the HLD experimental infrastructure, some recent scientific research results will be presented. This includes e.g. the detection of Shubnikov-de Haas oscillations in electron-doped high-temperature superconductors that allowed to unravel a drastic change of the Fermi-surface topology upon doping [1]. Furthermore, pulsed-field experiments at the HLD allowed to observe the field-induced conductance switching in single-walled carbon nanotubes
  • Invited lecture (Conferences)
    6th International Symposium on High Magnetic Field Spin science in 100T, 07.-09.12.2009, Sendai, Japan

Permalink: https://www.hzdr.de/publications/Publ-13549
Publ.-Id: 13549


Optical spectroscopy of superconductors in terahertz frequency range

Pronin, A.
es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Universität Göttingen, 16.11.2009, Göttingen, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13548
Publ.-Id: 13548


Exploring the spin-1/2 frustrated square lattice model with high-field magnetization studies

Tsirlin, A. A.; Schmidt, B.; Skourski, Y.; Nath, R.; Geibel, C.; Rosner, H.
We report on high-field magnetization measurements for a number of layered vanadium phosphates that were recently recognized as spin- 1/2 frustrated square lattice compounds with ferromagnetic nearest-neighbor couplings (J1) and antiferromagnetic next-nearest-neighbor couplings (J2). The saturation fields of the materials lie in the range from 4 to 24 T and show excellent agreement with the previous estimates of the exchange couplings deduced from low-field thermodynamic measurements. The consistency of the high-field data with the regular frustrated square lattice model provides experimental evidence for a weak impact of spatial anisotropy on the nearest-neighbor couplings in layered vanadium phosphates. The variation in the J2 /J1 ratio within the compound family facilitates the experimental access to the evolution of the magnetization curve upon the change in the frustration magnitude. Our results support the recent theoretical prediction by Thalmeier et al. [Phys. Rev. B 77, 104441 (2008)] and give evidence for the enhanced bending of the magnetization curves due to the increasing frustration of the underlying spin system
  • Physical Review B 80(2009), 132407

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Permalink: https://www.hzdr.de/publications/Publ-13547
Publ.-Id: 13547


Interplay of frustration and magnetic field in the two-dimensional quantum antiferromagnet Cu(tn)Cl-2

Orendacova, A.; Cizmar, E.; Sedlakova, L.; Hanko, J.; Kajnakova, M.; Orendac, M.; Feher, A.; Xia, J.; Yin, L.; Pajerowski, D.; Meisel, M.; Zelenak, V.; Zvyagin, S.; Wosnitza, J.
Specific heat and ac magnetic susceptibility measurements, spanning low temperatures (T >= 40 mK) and high-magnetic fields (B <= 14 T), have been performed on a two-dimensional (2D) antiferromagnet Cu(tn)Cl-2 (tn=1,3-diaminopropane=C3H10N2). The compound represents a S = 1/2 spatially anisotropic triangular antiferromagnet realized by a square lattice with nearest-neighbor (J/kB = 3 K), frustrating next-nearest-neighbor (0 < J'/J < 0.6), and interlayer (|J''/J| approximate to 10-3) interactions. The absence of long-range magnetic order down to T = 60 mK in B = 0 and the T-2 behavior of the specific heat for T <= 0.4 K and B >= 0 are considered evidence of a high degree of 2D magnetic order. In fields lower than the saturation field, Bsat = 6.6 T, a specific heat anomaly, appearing near 0.8 K, is ascribed to bound vortex-antivortex pairs stabilized by the applied magnetic field. The resulting magnetic phase diagram is remarkably consistent with the one predicted for a square lattice without a frustrating interaction, expect that Bsat is shifted to values lower than expected. Potential explanations for this observation, as well as the possibility of a Berezinski-Kosterlitz-Thouless (BKT) phase transition in a spatially anisotropic triangular magnet with the collinear Neel ground state, are discussed.
  • Physical Review B 80(2009), 144418

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Publ.-Id: 13546


Effects of two gaps and paramagnetic pair breaking on the upper critical field of SmFeAsO0.85 and SmFeAsO0.8F0.2 single crystals

Lee, H.-S.; Bartkowiak, M.; Park, J.-H.; Lee, J.-Y.; Kim, J.-Y.; Sung, N.-H.; Cho, B. K.; Jung, C.-H.; Kim, J. S.; Lee, H.-J.
We investigated the temperature dependence of the upper critical field [Hc2(T)] of fluorine-free SmFeAsO0.85 and fluorine-doped SmFeAsO0.8F0.2 single crystals by measuring the resistive transition in low static magnetic fields and in pulsed fields up to 60 T. Both crystals show that Hc2(T)’s along the c axis [Hc2c(T)] and in an ab-planar direction [Hc2ab(T)] exhibit a linear and a sublinear increase, respectively, with decreasing temperature below the superconducting transition. Hc2(T)’s in both directions deviate from the conventional one-gap Werthamer-Helfand-Hohenberg theoretical prediction at low temperatures. A two-gap nature and the paramagnetic pair-breaking effect are shown to be responsible for the temperature-dependent behavior of Hc2c and Hc2ab, respectively.
  • Physical Review B 80(2009), 144512

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Publ.-Id: 13545


Modifications in structural and optical properties of Mn-ion implanted CdS thin films

Chandramohan, S.; Kanjilal, A.; Strache, T.; Tripathi, J. K.; Sarangi, S. N.; Sathyamoorthy, R.; Som, T.
In this paper, we report on modifications in structural and optical properties of CdS thin films due to 190 keV Mn-ion implantation at 573 K. Mn-ion implantation induces disorder in the lattice, but does not lead to the formation of any secondary phase, either in the form of metallic clusters or impurity complexes. The optical band gap was found to decrease with increasing ion fluence. This is explained on the basis of band tailing due to the creation of localized energy states generated by structural disorder. Enhancement in the Raman scattering intensity has been attributed to the enhancement in the surface roughness due to increasing ion fluence. Mn-doped samples exhibit a new band in their photoluminescence spectra at 2.22 eV, which originates from the d–d (4T1 → 6A1) transition of tetrahedrally coordinated Mn2+ ions.
Keywords: CdS thin films; Mn-ion implantation; Structural properties; Optical properties

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Publ.-Id: 13544


Ion irradiation of permalloy: From thin magnetic films to lateral exchange spring nanostructures

Strache, T.; Reichel, L.; Wintz, S.; Fritzsche, M.; Mönch, I.; Raabe, J.; Martin, N.; McCord, J.; Körner, M.; Markó, D.; Romstedt, F.; Fassbender, J.ORC
Due to its low coercivity and negligible magnetostriction, permalloy (Ni80Fe20) is one of the most used materials in thin film and micro/nano magnetism. By means of ion irradiation the magnetic properties can be modified [1], and in combination with a lithographically defined mask or the use of a focused ion beam magnetic patterning can be achieved [2]. The changes of the magnetic properties due to ion-solid- interaction must be related to different origins, e.g. direct implantation, surface sputtering and interfacial mixing. Their respective influence depends strongly on the chosen multilayer system as well as on the implantation conditions.
Here we present a systematic study of irradiation of permalloy with common ion species. Special emphasis is put on the separation of the effect of direct implantation from mixing and sputtering. By transferring this knowledge to laterally resolved irradiation, direct exchange coupled magnetic stripes of submicron width are created. The magnetization reversal process of this lateral exchange spring structures depends on the interaction between adjacent soft and hard magnetic stripes. By scaling the stripe sizes down, fundamental questions regarding the maximum domain wall density and the domain–wall interaction may be addressed.

References
[1] J. Fassbender et al., Physical Review B 73, 184410 (2006).
[2] J. McCord et al., Advanced Materials 20, 2090 (2008).
  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 06.-08. April 2009, Friedrich-Schiller-Universität Jena, 06.04.2009, Jena, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13543
Publ.-Id: 13543


Tuning Coercivity in CoCrPt-SiO2 Hard Disk Material

Strache, T.; Tibus, S.; Springer, F.; Rohrmann, H.; Albrecht, M.; Lenz, K.; Fassbender, J.ORC
In order to increase the storage density of modern computer disk drives and to push the superparamagnetic limit to the smallest achievable bit sizes further, smaller grains with even larger magnetic anisotropies are required, which are accompanied by large coercive fields obstructing the writing process. One route to overcome this problem is to independently reduce the coercive field without altering anisotropy and remanence by tailoring the intergranular exchange in granular CoCrPt-SiO2 films. Here we demonstrate that by means of ion implantation of Co and Ne a continuous reduction of the coercive field can be achieved without significant modification of the remaining magnetic parameters. In addition to the magnetization reversal behavior of the entire film investigated by magneto-optic Kerr effect and SQUID magnetometry, also the magnetic domain configuration in the demagnetized state is imaged by magnetic force microscopy.
Keywords: magnetism, ion irradiation, magnetic storage, hard disk, coercivity, anisotropy, magnetic domains
  • Lecture (Conference)
    DPG Spring Meeting of the Condensed Matter Section, March 22-27, 2009, Dresden, Germany, 25.03.2009, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-13542
Publ.-Id: 13542


Hochintensitätslaser und ihre Anwendungen

Bussmann, M.; Kroll, F.
Der Vortrag gibt einen Überblick über die nichtlinearen optischen Effekte die im Aufbau und der Diagnostik hochintensiver Kurzpulslaser eine Rolle spielen sowie über die Anwendungen moderner Hochleistungslaser in der Strahlenphysik.

The talk gives an overview of those nonlinear optical effects which are important for building high-intensity short-pulse lasers and their diagnostics as well as the application of high-power lasers in beam physics.
Keywords: high-intensity lasers, nonlinear optics, diagnostics, ultra-short laser pulses, particle acceleration, beam physics, radiation sources
  • Invited lecture (Conferences)
    Lectures on laser and plasma physics, 16.12.2009, TFH Wildau, Berlin, Germany

Permalink: https://www.hzdr.de/publications/Publ-13541
Publ.-Id: 13541


Di-Electrons from Resonances in Nucleon-Nucleon Collisions

Kaptari, L. P.; Kämpfer, B.
The contribution of the low-lying nucleon resonances P-33(1232), P-11(1440), D-13(1520), and S-11(1535) to the invariant-mass spectra of di-electrons stemming from the exclusive processes pp -> pp e(+)e(-) and pn -> pn e(+)e(-) is investigated within a fully covariant and gauge-invariant diagrammatical approach. We employ, within the one-boson exchange approximation, effective nucleon-meson interactions including the exchange mesons pi, eta, sigma, omega, and rho as well as excitations and radiative decays of the above low-lying nucleon resonances. The total contribution of these resonances is dominant; however, bremsstrahlung processes in pp and, in particular, pn collisions at beam energies of 1-2 GeV are still significant in certain phase-space regions.

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Permalink: https://www.hzdr.de/publications/Publ-13540
Publ.-Id: 13540


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