Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32337 Publications
Untersuchung elektromagnetischer Strömungsbeeinflussung in elektrisch leitfähigen Fluiden mit Hilfe von 2d2k/1d3k-Ultraschall-Doppler-Array-Techniken
Lenz, M.; Shirai, K.; Büttner, L.; Csarske, J.; Eckert, S.; Gerbeth, G.;
Die elektromagnetische Strömungsbeeinflussung spielt eine wichtige Rolle in der metallischen Werkstofftechnik. Wichtige potentielle Anwendungsgebiete sind Strömungsoptimierungen für die Herstellung einkristalliner Halbleiterkristalle (450 mm Siliziumwafer) und die Optimierung von Stahlgussprozessen.
Zur Validierung der numerischen Strömungssimulationen verwendet man häufig ein Wassermodell des zugehörigen Prozesses. Dieses ermöglicht prinzipiell den Einsatz von Laserverfahren zur Strömungsvermessung, spiegelt jedoch wegen der unterschiedlichen Eigenschaften von Metallen und Wasser die physikalische Realität nur unzureichend wider.
Zur Strömungsmessung in Metallschmelzen bedient man sich daher häufig der Ultraschall-Messtechnik unter Ausnutzung des Doppler-Effektes. Die Messaufbauten ermöglichen in der Regel die Messung einer Geschwindigkeitskomponente entlang einer Linie.
Zukünftige Messaufgaben wie beispielsweise die Vermessung inkohärenter Strömungsfelder können mit den vorhandenen Messgeräten nicht realisiert werden. Das liegt im wesentlichen an der fehlenden zeitlichen Auflösung der Messsysteme und der langsamen Traversierung.
Der Vortrag präsentiert aktuelle Ergebnisse bei Ultraschallmessungen in der Metallurgie. Dabei wird vorgestellt, wie die Erhöhung der zeitlichen Auflösung und damit die Messung instationärer Felder erreicht werden kann. Beschrieben werden dabei grundsätzliche Erwägungen hinsichtlich der Wandler-Geometrie und des Schallfeldes, Probleme bei der Schallanregung in der Flüssigkeit und Elemente der Signalverarbeitung. Die erreichbare maximale zeitliche und örtliche Auflösung wird theoretisch und experimentell dargelegt.
Keywords: Electromagnetic flow control, Ultrasound Doppler velocimetry, Ultrasound array technique, Flow imaging
  • Lecture (Conference)
    14. Fachtagung “Lasermethoden in der Strömungsmesstechnik",”GALA2006, 05.-07.09.06, Braunschweig, Germany
  • Contribution to proceedings
    GALA-Fachtagung: Lasermethoden in der Strömungsmesstechnik, 05.-07.09.06, Braunschweig, Germany
    Lasermethoden in der Strömungsmesstechnik 14(2006), 3-98056 13-3-X, 5.1-5.9

Publ.-Id: 8499 - Permalink


Electromagnetic flow control in casting and metallurgical processing
Eckert, S.; Galindo, V.; Gerbeth, G.; Willers, B.; Zhang, C.;
Es wird ein Überblick über die Möglichkeiten der elektromagnetischen Strömungskontrolle für Anwendungen in der Giessereitechnik und in der Metallurgie gegeben, namentlich zur Kontrolle der Formfüllung beim Feinguß, zur elektromagnetischen Beeinflussung der Strömungsstruktur in Flüssigmetall-Zweiphasenströmungen sowie bei der Erstarrung von Legierungen unter Magnetfeldeinfluß. Insbesondere wird auf die Bedeutung von Modellexperimenten mit metallischen Modellschmelzen hingewiesen, die einen wesentlichen Beitrag zum Verständnis der Strömungs-vorgänge in praxisrelevanten Anordnungen liefern können. Betrachtet man für die industriellen Anwendungen realistische Parameterbereiche liefern diese Wassermodelle liefern allerdings oft falsche Ergebnisse und sind völlig wertlos für Untersuchungen zur elektromagnetischen Strömungskontrolle.
Keywords: electromagnetic flow control, investment casting, bubble plume, solidification
  • Poster
    MCWASP Conference, Modeling of Casting, Welding and Advanced Solidification Processes XI, 29.05.-02.06.06, Opio, France

Publ.-Id: 8498 - Permalink


Myocardial extraction and subcellular distribution of new types of technetium-labeled fatty acids
Mirtschink, P.; Stehr, S. N.; Heintz, A.; Pexa, A.; Wunderlich, G.; Walther, M.; Pietzsch, H.-J.; Spies, H.; Jung, C.; Kraus, W.; Kropp, J.; Deussen, A.;
SPECT- images performed with radiolabeled fatty acids (FA) allow detailed studies about the heart function, because flow and metabolism are represented. Up to now, only 123iodinated FA are available for myocardial viability diagnostics in some parts of the world, but the application is limited due to serious disadvantages: first, the expensive production of pure 123I requires a cyclotron and second, the radiolabeled FA compounds must be purchased by outside vendors which resulted in disproportional costs and logistical problems. 99mTc, has ideal physical properties for SPECT-imaging (Eγ-= 140 keV), a short half- life of 6 h, and is available through a 99Mo/99mTc generator whenever needed. The development of 99mTc- labeled FA has been a goal of various research groups in the past. Despite many different approaches, no appropriate 99mTc compound with similar myocardial extraction properties as found with BMIPP and DMIPP is available to date. Most previous work in this field has focused on radiometal coordination by use of a polar tetradentate N2S2 chelate with a central oxometal(V) core. We concentrated on the development and experimental evaluation of alternative coordination moieties according to the ‘4+1’ mixed ligand approach to create newly technetium labeled FA with an improved myocardial profile. In the ‘4+1’ donor atom arrangement, 99mTc is coordinated by both a tetradentae ligand and by a monodentate bearing the FA moiety. This system is rather lipophilic and show high stability towards, e.g. challenging SH-agents. While the conventional ‘4+1’ 99mTc FA are built on in the sequence Tc-chelate, alkyl chain (a), carboxyl group (c) ->(Tc-a-c) we also developed and investigated some compounds with a new design according to the sequence carboxyl group (c), alkyl chain, Tc chelate, lipophilic tail (lt) -> (c – a – Tc – lt), transferring the 99mTc chelate from the end- to a more central position of the compound.
  • Lecture (Conference)
    ESRR'06 - European Symposium on Radiopharmacy and Radiopharmaceuticals, 30.03.-02.04.2006, Lucca, Italy
  • Abstract in refereed journal
    Quarterly Journal of Nuclear Medicine and Molecular Imaging 50(2006)Suppl 1, 20-21

Publ.-Id: 8497 - Permalink


Experimental and numerical studies of void fraction distribution in rectangular bubble columns
Krepper, E.; Reddy Vanga, B. N.; Zaruba, A.; Prasser, H.-M.; Lopez De Bertodano, M.;
Bubbly flow is encountered in a wide variety of industrial applications ranging from flows in nuclear reactors to process flows in chemical reactors. The presence of a second phase, recirculating flow, instabilities of the gas plume and turbulence, complicate the hydrodynamics of bubble column reactors.
This paper describes experimental and numerical results obtained in a rectangular bubble column 0.1 m wide and 0.02 m in depth. The bubble column was operated in the dispersed bubbly flow regime with gas superficial velocities up to 0.02 m/s. Images obtained from a high speed camera were used to observe the general flow pattern and have been processed to calculate bubble velocities, bubble turbulence parameters and bubble size distributions. Gas disengagement technique was used to obtain the volume averaged gas fraction over a range of superficial gas velocities. A wire mesh sensor was applied, to measure the local volume fraction at two different height positions. Numerical calculations were performed with an Eulerian-Eulerian two-fluid model approach using the commercial code CFX.
The paper details the effect of various two-fluid model interfacial momentum transfer terms on the numerical results. The inclusion of a lift force was found to be necessary to obtain a global circulation pattern and local void distribution that was consistent with the experimental measurements. The nature of the drag force formulation was found to have significant effect on the quantitative volume averaged void fraction predictions.
Keywords: Bubble column, experiments, wire mesh sensor, high speed video camera CFD, drag bubble forces, non-drag bubble forces

Publ.-Id: 8496 - Permalink


Reconstruction and Corrections in In-Beam PET
Shakirin, G.;
The talk was given during the Siemens In-Beam PET workshop 9-10 May 2006 at OnkoRay, Dresden. The achievements and issues in reconstruction procedure of in-beam PET data were discussed
Keywords: in-beam PET, reconstruction
  • Lecture (Conference)
    Scientific Workshop - In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Publ.-Id: 8495 - Permalink


PET and photon therapy
Möckel, D.;
Challenges for in-beam PET at hard photon beams
Keywords: In-beam PET, hard photons
  • Lecture (Conference)
    Scientific Workshop for In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Publ.-Id: 8494 - Permalink


Mikrostrukurelle Mechanismen der Strahlenversprödung
Altstadt, E.; Böhmert, J.; Ulbricht, A.; Borodin, V. A.; Ganchenkova, M.; Voskoboinikov, R.;
Gegenstand des Vorhabens im Rahmen der WTZ mit Russland ist die Versprödung des Reaktordruckbehälters infolge der Strahlenbelastung mit schnellen Neutronen im kernnahen Bereich.
Um den Einfluss von bestrahlungsinduzierten Gitterdefekten auf die mechanischen Eigenschaften zu ermitteln, wurden analytische Berechnungen zum Einfluss von Hindernissen auf die Beweglichkeit von Versetzungen und damit auf die Ausbildung einer plastischen Zone an der Rissspitze durchgeführt. Es wird demonstriert, dass sich die an der Rissspitze entstehenden Versetzungen an dem Hindernis (bestrahlungsinduzierte Punktdefekte) aufstauen. In Abhängigkeit der Rissbelastung KI und der Entfernung des Hindernisses von der Rissspitze werden die Versetzungsdichte und das durch den Versetzungsstau verursachte Spannungsfeld berechnet.
Mit Hilfe von Experimenten zur Neutronenkleinwinkelstreuung (SANS – small angle neutron scattering) an verschiedenen WWER-Stählen und Modelllegierungen wurden Größenverteilungen und die Volumenanteile der strahleninduzierten Defekte für verschiedene Bestrahlungszustände (Fluenzen, Bestrahlungstemperaturen) ermittelt. Es wurde gezeigt, dass sich die strahleninduzierte Werkstoffschädigung durch Wärmebehandlung weitgehend wieder ausheilen lässt. Nach der thermischen Ausheilung ist der Werkstoff bei erneuter Bestrahlung weniger anfällig für strahleninduzierte Defekte. Die Ergebnisse der SANS-Untersuchungen wurden mit der Änderung der mechanischen Eigenschaften (Härte, Streckgrenze und Sprödbruchübergangstemperatur) korreliert.
Mit der kinetischen Gitter-Monte-Carlo-Methode wurden numerische Sensitivitätsstudien zum Einfluss des Cu-Gehalts auf die Stabilität von Defekt-Clustern durchgeführt. Die Berechnungen zeigen, dass die Anwesenheit von Cu-Atomen zur Bildung von langlebigen Defekten führt. Dabei werden Leerstellen in Cu/Leerstellen-Cluster eingefangen. Leerstellen in reinem Eisen sind bei Bestrahlungstemperaturen von 270 °C dagegen nicht stabil, die Lebensdauer liegt zwischen 0.01 s und 1 s. Die kritische Cu-Konzentration, ab welcher stabile Defekte entstehen, beträgt ca. 0.1 Masseprozent.
Keywords: Reactor pressure vessel, Irradiation induced embrittlement, Small angle neutron scattering, Defect cluster, Dislocation, Monte Carlo Simulation, VVER reactors
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-452 2006

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Publ.-Id: 8493 - Permalink


Primary photoluminescence in as-neutron (electron)-irradiated n-type 6H-SiC
Zhong, Z. Q.; Wu, D. X.; Gong, M.; Wang, O.; Shi, S. L.; Xu, S. J.; Chen, X. D.; Ling, C. C.; Fung, S.; Beling, C. D.; Brauer, G.; Anwand, W.; Skorupa, W.;
Low-temperature photoluminescence spectroscopy has revealed a series of features labeled S1, S2, S3 in n-type 6H-SiC after neutron and electron irradiation. Thermal annealing studies showed that the defects S1, S2, S3 disappeared at 500 °C. However, the well-known D1 center was only detected
for annealing temperatures over 700 °C. This experimental observation not only indicated that the defects S1, S2, S3 were a set of primary defects and the D1 center was a kind of secondary defect, but also showed that the D1 center and the E1, E2 observed using deep level transient spectroscopy
might not be the same type of defects arising from the same physical origin.

Publ.-Id: 8492 - Permalink


Study of the solubility of amorphous and crystalline uranium dioxide by combined spectroscopic methods
Opel, K.; Weiß, S.; Hübener, S.; Zänker, H.; Bernhard, G.;
Colloid formation and solubility of U(IV) in acidic HClO4/NaClO4 solutions are investigated by coulometric titration. Quantification of traces of U(VI) by laser fluorescence spectroscopy proves that the tetravalent state of uranium had been maintained. Laser-induced breakdown detection (LIBD) is applied for the detection of traces of uranium colloids as the pH is increased. The pH values at the onset of colloid formation are used for thermodynamic calculations aimed at determining the solubility products Ksp0 of crystalline and amorphous uranium dioxides. The particle size of the colloids determined by means of LIBD is taken into account since it influences the solubility product. The results indicate the formation of crystalline UO2(cr) at low pH ~ 1 (log Ksp0 = 59.6 ± 1.0) whereas the amorphous hydrous oxide UO2·xH2O(am) is formed at pH ~ 3 (log Ksp0 = -54.4 ± 1.0). Measurements by EXAFS, XRD and REM confirm the occurrence of these different modifications. The obtained solubility products fit well in the known series of solubility products of the other tetravalent actinides.
Keywords: Uranium dioxide, solubility product, colloids, laser-induced breakdown detection
  • Radiochimica Acta 95(2007)3, 143-149

Publ.-Id: 8491 - Permalink


Photovoltaic plants in Saxony: Development, status and perspectives
Rindelhardt, U.; Schlegel, H.-J.;
Purpose
The development and the perspectives of photovoltaic plants (PVP) in Saxony will be described. The development reflects the effects of the different funding instruments as well as the technical progress which has been made during the past 15 years.

Funding as accelerator
The first large step in the PVP installation in Saxony was done with the German 1000-Roofs-Program between 1991 and 1995. In the frame of this program the first 150 PVP were installed with a total power of 450 kW (see Fig.1). A new high light was set when the 100.000-Roofs-Program came into force. More than 450 PVP with a total power of 1,5 MW were connected to the grid. With the EEG (Renewable Energy Act) this development was continued. Starting with 2004 also Megawatt PVP were put into operation, the PVP Espenhain (5 MW power) belongs also today to the world largest PVP.

Technical development
The first PVPs reflect the technical level of the early nineties. The power was limited to 5 kW, and the DC-voltage was restricted to 140 V. Beginning with the year 2000 the mean power of the PVP has been clearly increased. Sonny Boy is the dominating inverter type (with a share of more than 50 %), but the module types vary strongly. An increase in the mean module power has been certainly observed.

Some operation results
A mean annual yield of 750 kWh/kW was found for the first generation of PVP, which was influenced by the low quality of some module types. New systematic monitoring programs were started in 2000. These investigations allowed the evaluation of new built PVP (yields up to 1000 kWh/KW, Fig. 2), but also the long time behaviour of the older PVP could be observed (Figs. 3 and 4).

Conclusions
The development generally confirms the politically decisions for PV funding in Germany. It could be proofed, that new PVPs in Saxony with optimal design and components, respectively, can generate up to 950 kWh/kW in an "average" year.
Keywords: PV plants, Saxony
  • Contribution to proceedings
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Germany
    Proceedings, ISBN 3-936338-20-5, 2719-2722
  • Poster
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Deutschland

Publ.-Id: 8490 - Permalink


Irradiance maps applied for the performance assessment of PV-Systems- a case study for the German federal state of Saxony
Beyer, H. G.; Drews, A.; Rindelhardt, U.;
For the estimation of the expected annual energy gain and the month by month check of the system performance, methods based on irradiance maps published by weather services, both general or dedicated to solar energy application, are in use. Examples for this type of information for Germany are annual and monthly irradiance maps published by the German weather service DWD or the data bank of hourly irradiance data with continuous spatial coverage prepared by the University of Oldenburg and offered as commercial service by the company Meteocontrol. The DWD maps are derived from both, satellite images and ground measurements and are given with a spatial resolution of 1km x 1km. The Oldenburg data bank is basically derived from satellite data only (resolution ~ 5km x 5km), although an option for amelioration by ground station data exists.
To assess the validity of these data sets for the aforementioned tasks, a case study for a region covering the German federal state of Saxony is performed, using data for the years 2004-2005.
Saxony is characterised by a wide variety of topographical features, ranging from flat relief to highly structured mountainous terrain. For this region an independent high quality ground data set given by a dense network operated for agro-meteorological purposes is available. An assessment of the end use accuracy of the irradiance data can by done via a set of monthly yield data of grid connected PVsystems.
The comparison of information on radiation sums is on one hand performed by the monthly analysis of the bias and the rms-error for the data bank versus the ground station data. On the other hand, the quality of the information on the spatial structure of the radiation field that is extractable from the data banks is analysed via the inspection of the a co- and cross-variograms.
For the assessment of the end use accuracy of the data, procedures to derive an estimation of the system yield from irradiance data as developed by the PVSAT2 project are applied for the Oldenburg data set.
A first impression of the reliability of the map data is given by the inter comparison of the annual maps for the year 2004. This shows deviations of up to 40 kWh/m², which presents an relative error of about 4%. Besides a systematic bias of about 20 kWh/m² in favour the Oldenburg data, remarkable differences in the spatial structure of the irradiance field concerning the homogeneity/inhomogeneity within some regions occur.
Thus, to pin down the reliability of the content of the maps it has to be compared to the ground data.
For the Oldenburg data it can be stated that even having a quite low bias for each station on an annual scale, monthly sums can deviate by up to 40%, especially for the winter months. This finding is coherent with the results of the PVSAT project, indicating the general increase of the uncertainties of satellite based estimates in months with low radiation sums.
Concerning the annual end use accuracy, a typical deviation of ? 5% for the estimated annual energy gain of a set PV-systems - chosen for their excellent yield figures - can be stated. Regarding the fact, that the system simulation is base on data sheet information rather than system specific parameters, this result is quite satisfactory. However, as expected remarkable relative deviation for the winter
months are hidden by these annual figures which are dominated by the PV gain in the summer months.
Using the respective results of for sets of both 2004 and 2005 general conclusions on the uncertainties connected to the use of state of the art irradiance information in view of PV application can be draw.
Keywords: photovoltaic, system performance, irradiance maps
  • Contribution to proceedings
    21th European Photovoltaoc Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Germany
    Proceedings, 3-936338-20-5, 2756-2760
  • Poster
    21th European Photovoltaic Solar Energy Conference and Exhibition, 04.-08.09.2006, Dresden, Deutschland

Publ.-Id: 8489 - Permalink


Amorphisation at heterophase interfaces
Gemming, S.; Enyashin, A.; Schreiber, M.;
Heterophase interfaces are boundaries, which join two material types with different physical and chemical nature. Therefore, heterophase interfaces can exhibit a large variety of geometric morphologies ranging from atomically sharp boundaries to gradient materials, in which an interface-specific phase is formed, which provides a continuous change of the structural parameters and thus reduces elastic strains and deformations.

In addition, also the electronic properties of the two materials may be different, e.g. at boundaries between an electronically conducting metal and a semiconductor or an insulating material. Due to the deviations in the electronic structure, various bonding mechanisms are observed, which span the range from weakly interacting systems to boundaries with strong, directed bonding and further to reactively bonding systems which exhibit a new phase at the interface. Thus, both elastic and electronic factors may contribute to the formation of a new, often amorphous phase at the interface. Numerical simulations based on electronic structure theory are an efficient tool to distinguish and quantify these different influence factors, and massively parallel computers nowadays provide the required numerical power to tackle structurally more demanding systems. Here, this power has been exploited by the parallelisation over an optimised set of integration points, which split the solution of the Kohn-Sham equations into a set of matrix equations with equal matrix sizes. In this way, the analysis and prediction of material properties at the nanoscale has become feasible.
Keywords: interface, wetting, density-functional, electronic structure, silicon, Si, titanium, Ti
  • Contribution to external collection
    Karl Heinz Hoffmann, Arnd Meyer: Parallel Algorithms and Cluster Computing - Lecture Notes in Computational Science and Engineering, Berlin - Heidelberg - New York: Springer, 2006, 3-540-33539-0, 235-254

Publ.-Id: 8488 - Permalink


Li-doped Mo6S6 nanowires: elastic and electronic properties
Gemming, S.; Seifert, G.; Vilfan, I.;
Isolated and crystalline Mo6S6 nanowires, doped with Li to form Li2Mo6S6, are investigated with the density-functional techniques. We find that Li atoms "decorate" individual wires at the S-coordinated sites and occupy the interstitial positions between 3 S atoms in crystalline nanowires.
Doping with Li changes the lattice constants by less than 0.1 Angstrom, but it decreases the modulus of elasticity along the wire axis in the crystalline form. Doping raises the Fermi energy but retains the strongly uniaxial metallic character of nanowires, attributed to the Mo(4d) electrons.
Keywords: Nanowires, mechanical properties, electronic properties, density functional theory

Publ.-Id: 8487 - Permalink


C28 fullerites - structure, electronic properties and intercalates
Enyashin, A.; Gemming, S.; Heine, T.; Seifert, G.; Zhechkov, L.;
Mechanical and electronic properties of hypothetical carbon nanostructures, on the basis of C28 building blocks, hyperdiamond and hyperlonsdaleite, have been investigated by DFT-based methods. The low mass density and large internal surface suggest applications as catalyst, nanosieve and ga storage material. We estimate the active volume accessible by H2. Special emphasis is given to tune the properties by endo- and exohedral intercalation with Zn, Ti, and K. While endohedral intercalation with Zn does not affect the overall structure, endohedral Ti intercalation has different consequences on the structural stability of the two allotropes. Exohedral intercalation with K leads to an ionic fullerite phase with metallic conductivity.
Keywords: fullerenes, intercalates, hydrogen storage, electronic structure
  • Physical Chemistry Chemical Physics 8(2006)28, 063AN

Publ.-Id: 8486 - Permalink


Investigations on the stability of the flow characteristics in a bubble column
Lucas, D.; Krepper, E.; Prasser, H.-M.; Manera, A.;
The role of the lift force for the stability of the homogeneous flow regime in a bubble column is investigated. Instabilities caused by the lift force may be one important reason for the transition from homogeneous to heterogeneous bubble column. The lift force acts on rising bubbles in lateral direction, when gradients of the liquid velocity are present. Such gradients may result from circulation cells in the bubble column as well as from local disturbances. Depending on the sign of the lift force such local disturbances in a homogeneous flow may be damped or enhanced. The corresponding feedback mechanism was analysed by means of a linear stability analyses. In the result criteria for stability were obtained for mono-dispersed flow, for a with two bubble size groups and finally with some additional approximations also for the case of N bubble size groups or a given bubble size distribution. In a next step the effects were investigated by CFD calculations. The obtained criteria for stability fit well together with the observed effects in CFD simulations. Recently two different groups confirmed the stability criteria experimentally.
Keywords: Bubble column, stabilty, lift force, CFD
  • Chemical Engineering & Technology 29(2006)9, 1066-1072

Publ.-Id: 8484 - Permalink


The electrical properties of heavily Al-implanted, nanocrystalline and single crystalline SiC layers
Heera, V.; Madhusoodanan, K. N.; Skorupa, W.; Dubois, C.; Romanus, H.;
The electrical properties of heavily Al doped (5x1019 – 1.5x1021 cm-3) single and nanocrystalline 4H-SiC layers on semi-insulating 4H-SiC substrate, prepared by multi-energy, high-fluence Al implantation and subsequent furnace annealing, are investigated by sheet resistance and Hall effect measurements. The reliability of recent results on enhanced acceptor activation in heavily Al doped, nanocrystalline SiC on conductive substrate is evaluated by direct comparison with doped SiC layers on semi-insulating substrate.
Keywords: SiC, p-type doping, Hall effect measurement
  • Poster
    SiC Rundgespräch 2006, 17.-18.07.2006, Kloster Banz, Staffelstein, Deutschland

Publ.-Id: 8483 - Permalink


The integral equation approach to kinematic dynamo theory and its application to dynamo experiments in cylindrical geometry
Xu, M.; Stefani, F.; Gerbeth, G.;
The conventional magnetic induction equation that governs hydromagnetic dynamo action is transformed to an equivalent integral equation system. An advantage of this approach is that the computational domain is restricted to the region occupied by the electrically conducting fluid and to its boundary. This integral equation approach is applied to simulate kinematic dynamos within cylindrical geometry including the von Karman sodium (VKS) experiment and the Riga dynamo experiment. A modified version of this approach is utilized to investigate magnetic induction effects under the influence of externally applied magnetic fields. The computed induced magnetic fields for the VKS experiment show a satisfactory agreement with the experimental results.
  • Contribution to proceedings
    ECCOMAS CFD 2006, European Conference on Computational Fluid Dynamics, 05.-08.09.2006, Egmond aan Zee, The Netherlands
    Proceedings paper 497, Delft: TU Delft, 90-9020970-0
  • Journal of Computational Physics 227(2008), 8130-8144

Publ.-Id: 8482 - Permalink


Reducing the impurity incorporation from residual gas by ion bombardment during high vacuum magnetron sputtering
Rosen, J.; Widenkvist, E.; Larsson, K.; Kreissig, U.; Mraz, S.; Martinez, C.; Music, D.; Schneider, J. M.;
The influence of ion energy on the hydrogen incorporation has been investigated for alumina thin films, deposited by reactive magnetron sputtering in an Ar/O2/H2O environment. Ar+ with an average kinetic energy of ~5 eV was determined to be the dominating species in the plasma. The films were analyzed with x-ray diffraction, x-ray photoelectron spectroscopy, and elastic recoil detection analysis, demonstrating evidence for amorphous films with stoichiometric O/Al ratio. As the substrate bias potential was increased from –15 V (floating potential) to –100 V, the hydrogen content decreased by ~70%, from 9.1 to 2.8 at.%. Based on ab initio calculations, these results may be understood by thermodynamic principles, where a supply of energy enables surface diffusion, H2 formation, and desorption [Rosén et al., J. Phys.: Condens. Matter 17, L137 (2005)]. These findings are of importance for the understanding of the correlation between ion energy and film composition and also show a pathway to reduce impurity incorporation during film growth in a high vacuum ambient.
Keywords: Magnetron sputtering; thin films; impurities; hydrogen
  • Applied Physics Letters 88(2006), 191905

Publ.-Id: 8481 - Permalink


Intense terahertz radiation from a large-area photoconductive device.
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
We present an approach of photoconductive terahertz (THz) generation providing a broad bandwidth and exceptional electric field amplitude. A large-area interdigitated two-electrode structure is applied to a GaAs substrate to offer high electric fields. Photocarriers excited by a Ti:Sapphire oscillator laser with MHz repetition rate are accelerated there, yielding an intense THz output. An appropriate binary mask covers every second electrode interval and carriers are excited in uniform electric field areas only. Hence contrary carrier acceleration and destructive interference is avoided. Due to the periodic nature of the electrode structure, the size of the excitation spot on the photoconductive THz emitter can be varied. This results in a THz beam of variable divergence. By electro-optic sampling the THz radiation is detected and characteristic properties of the THz source are measured. For an excitation spot diameter of about 300 μm, which corresponds to the central wavelength of the THz pulses, the THz generation is most efficient. THz radiation with an average power of 145 µW is generated with an efficiency of 2 × 10^-4 for the conversion from NIR to THz power. Furthermore, the THz radiation has excellent focusing properties. A Gaussian beam profile with a diameter (FWHM) of less than 1.4 of the central wavelength of the THz pulses is found. The THz field amplitude in the center of the focused THz beam is 1.5 kV/cm, which is almost one order of magnitude more of what is achieved with conventional semi-large aperture photoconductive emitters and a similar excitation spot diameter. Exceptionally large signal-to-noise ratios are achieved by modulating the bias voltage in the kHz range and using lock-in technique. We suggest that the THz power can be further improved by a sufficient cooling system, e.g. water cooling. Furthermore the use of LT GaAs instead of semiinsulating GaAs can result in larger THz bandwidth.
Keywords: optical, infrared (IR) spectroscopy, photoconductivity
  • Lecture (Conference)
    MRS Spring Meeting 2006, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 8480 - Permalink


The flow structure of a bubble-driven liquid metal jet in a horizontal magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
Static magnetic fields are known to be suitable for damping mean flow and turbulent motion in an electrically conducting liquid. In this paper, an experimental study is presented considering the influence of a horizontal magnetic field on a bubble-driven flow of a liquid metal. The investigation is focused on the liquid circulation inside a liquid metal column driven by a central jet produced by gas injection. The fluid vessel has a circular cross section and electrically insulating walls. Low gas flow rates were applied resulting in a plume of separated bubbles rising inside a spot around the cylinder axis. This axisymmetric configuration is exposed to a horizontal magnetic field. We present detailed experimental data describing the spatial as well as the temporal structure of the velocity field. Measurements of the vertical and the radial velocity component, respectively, were performed using the ultrasound Doppler velocimetry (UDV) allowing for the first time a complete mapping of the liquid velocity distribution for a bubble-driven liquid metal flow. The magnetic field considerably modified the global and local properties of the flow field compared to an ordinary bubble plume. In the parameter range considered here we did not find a prior flow suppression, but, in fact, a restructuring of the convective motion. The original axisymmetric flow field became anisotropic with respect to the direction of the magnetic field lines. An upwards flow dominated in a plane parallel to the magnetic field, whereas the recirculating motion was enforced in the orthogonal plane. Contrary to usual expectations, the application of a moderate magnetic field (100 < Ha < 400, 1 < N < 10) destabilizes the global flow and gives rise to transient, oscillating flow pattern with predominant frequencies.
Keywords: Gas-liquid flow, Bubble plume, Liquid metal, MHD turbulence, UDV velocity measurement
  • Journal of Fluid Mechanics 575(2007), 57-82

Publ.-Id: 8479 - Permalink


Nonmagnetic to magnetic nanostructures via ion irradiation
Dev, B. N.; Bera, S.; Satpati, B.; Goswami, D. K.; Bhattacharjee, K.; Satyam, P. V.; Yamashita, K.; Liedke, M. O.; Potzger, K.; Fassbender, J.ORC; Eichhorn, F.; Grötzschel, R.
A Pt/C multilayer stack (15 layer-pairs) with Fe impurities was prepared on a glass substrate by the ion sputtering technique. Ion irradiation effects on this multilayer were studied following irradiation with 2 MeV Au ions at fluences from 1 · 1014 to 1 · 1015 ions/ cm2. Irradiation induced atomic displacements in such multilayers have been earlier analyzed by a combined X-ray standing wave (XSW) and X-ray reflectivity (XRR) technique with a depth resolution better than 0.2 nm [S.K. Ghose, B.N. Dev, Phys. Rev. B 63 (2001) 245409; S.K. Ghose, D.K. Goswami, B. Rout, B.N. Dev, G. Kuri, G. Materlik, Appl. Phys. Lett. 79 (2001) 467]. Using the combined XSW-XRR technique ion beam induced preferential movement of Fe from C- to Pt-layers has been detected. At the highest ion fluence Pt layers (containing Fe) break into nanoparticles apparently surrounded by C. Grazing incidence X-ray diffraction (GIXRD) measurements indicate the formation of FePt particles in the irradiated multilayer samples. Results of magnetic force microscopy (MFM) and magneto-optical Kerr effect (MOKE) measurements reveal that while the virgin sample hardly shows any magnetism, the irradiated samples show a soft ferromagnetism with an increasing coercive field with increasing ion fluence. Use of focused ion beam to fabricate ferromagnetic nanodots and their possible uses in spin electronics are discussed.
Keywords: magnetism, ion irradiation
  • Microelectronic Engineering 83(2006), 1721

Publ.-Id: 8478 - Permalink


Secondary structure and Pd(II) coordination in S-layer proteins from Bacillus sphaericus studied by infrared and X-ray absorption spectroscopy
Fahmy, K.; Merroun, M.; Pollmann, K.; Raff, J.; Savchuk, O.; Hennig, C.; Selenska-Pobell, S.;
The S-layer of Bacillus sphaericus strain JG-A12, isolated from a uranium-mining site, exhibits a high metal-binding capacity, indicating that it may provide a protective function by preventing the cellular uptake of heavy metals and radionuclides. This property has allowed the use of this and other S-layers as self-assembling organic templates for the synthesis of nano-sized heavy metal cluster arrays. However, little is known about the molecular basis of the metal protein interactions and their impact on secondary structure. We have studied the secondary structure, protein stability, and Pd(II) coordination in S-layers from the B. sphaericus strains JG-A12 and NCTC 9602 to elucidate the molecular basis of their biological function and of the metal nanocluster growth. Fourier-transform IR-spectroscopy reveals similar secondary structures, containing ~35 % -sheets and little helical structure. pH-induced IR absorption changes of the side chain carboxylates evidence a remarkably low pK < 3 in both strains and a structural stabilisation when Pd(II) is bound. The COO--stretching absorptions reveal a predominant Pd(II)-coordination by chelation / bridging by Asp and Glu residues. This agrees with XANES and EXAFS data revealing oxygens as coordinating atoms to Pd(II). The additional participation of nitrogen is assigned to side chains rather than to the peptide backbone. The topology of nitrogen- and carboxyl-bearing side chains appears to mediate heavy metal-binding binding to the large number of Asp and Glu in both S-layers at particularly low pH as an adaptation to the environment from which the strain JG-A12 has been isolated. These side chains are thus prime targets for the design of engineered S-layer-based nanoclusters.
Keywords: metal binding, FTIR, XANES, EXAFS, nanocluster

Publ.-Id: 8477 - Permalink


Investigation of chemical and grain boundary effects in highly ordered Sr2FeMoO6: XPS and Mössbauer studies
Raekers, M.; Kuepper, K.; Hesse, H.; Balasz, I.; Deac, I. G.; Constantinescu, S.; Burzo, E.; Valeanu, M.; Neumann, M.;
We have studied the oxidation states of Fe and Mo and the presence of grain boundaries in the magneto resistive (MR) compounds Sr2FeMoO6 by means of x-ray photoelectron spectroscopy (XPS), Mössbauer spectroscopy and electrical resistivity measurements. XPS of the Mo 3d and Fe 3s core levels is indicating a mixed valence state involving around 30% Fe3+- Mo5+ and 70% Fe2+- Mo6+ states. Mössbauer studies confirm the presence of a valence fluctuation state and an essential amount of grain boundaries in the present Sr2FeMoO6 crystals. Resistivities and magnetoresistance studies evidenced strong grain boundary effects.
Keywords: Sr2FeMoO6, Double perovskite, Magnetoresistance, X-ray photoelectron spectroscopy, Mössbauer spectroscopy, Electrical resistivity
  • Journal of Optoelectronics and Advanced Materials 8(2006)2, 455-460

Publ.-Id: 8476 - Permalink


Prediction of the evolution of the dispersed phase in bubbly flow problems
Dorao, C. A.; Lucas, D.; Jakobsen, H. A.;
For modeling multi-phase where the disperse phase play a major role for determining the flow structure and inter phase transfer quantities, the size distribution of the particles has to be considered. This can be done by extension of the mass balance equation to a population balance equation. In this work, a least squares spectral method is tested for predicting the evolution of the disperse phase in a vertical two phases bubbly flow. The least squares spectral method consists in minimizing the L2 norm of the residual over the simulation domain. The results are compared with experimental data obtain for two different initial bubble distribution.
Keywords: Two Phase Flow; Vertical Pipe Flow, Bubbly Flow, Population; Balance Equation; Least Squares Spectral Method

Publ.-Id: 8475 - Permalink


Ion beam induced magnetic property modifications
Fassbender, J.ORC
In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.


[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.
Keywords: magnetism, magnetic properties, ion irradiation, ion implantation, ripples
  • Lecture (others)
    Seminarvortrag, 06.06.2006, Halle, Deutschland
  • Lecture (others)
    Seminarvortrag Universitaet Goettingen, 08.12.2006, Goettingen, Deutschland
  • Invited lecture (Conferences)
    Workshop on "Ion beam processing and magnetic properties of semiconductors", 13.02.2007, Leuven, Belgien

Publ.-Id: 8474 - Permalink


Tailoring magnetic properties by ion beams
Fassbender, J.ORC
In recent years the tailoring of magnetic properties by means of ion irradiation techniques has become fashionable. Since the magnetic properties of magnetic multilayers depend sensitively on the mutual interfaces a modification of these interfaces by light ion irradiation leads to a local modification of the magnetic anisotropy, the exchange bias or the interlayer exchange coupling [1]. As an example it will be demonstrated that ion irradiation in an applied magnetic field allows to set the uniaxial anisotropy direction on a micrometer scale in the case of soft magnetic alloys [2]. However, in order to modify the structural and magnetic properties not only light ion irradiation but also ion implantation doping can be used. If, for example, Cr is implanted in thin Permalloy films the Curie temperature and the saturation magnetization can be reduced, which consecutively leads to a decrease of the magnetic anisotropy and an increase of the magnetic damping behavior [3]. The formation of magnetically dead layers at the interfaces to buffer and cap layers can be investigated using Ni implantation [4].
In an alternative route to design magnetic properties periodically modulated substrates are employed. These modulated substrates are created by means of low energy ion erosion. A ripple structure with a typical periodicity of 30 – 50 nm and a ripple height of about 2 nm is created on a Si substrate. Subsequently deposited Permalloy films exhibit a uniaxial anisotropy which is about a factor of 20 larger than conventionally prepared films. If exchange bias bilayers are deposited the interplay between the unidirectional and the ripple-induced uniaxial anisotropy contributions can be investigated.


[1] J. Fassbender, D. Ravelosona, Y. Samson, J. Phys. D 37, R179 (2004).
[2] J. McCord, T. Gemming, L. Schultz, J. Fassbender, M. O. Liedke, M. Frommberger, E. Quandt, Appl. Phys. Lett. 86, 162502 (2005).
[3] J. Fassbender, J. von Borany, A. Mücklich, K. Potzger, W. Möller, J. McCord, L. Schultz, R. Mattheis, Phys. Rev. B, in press.
[4] J. Fassbender, J. McCord, Appl. Phys. Lett., in press.
Keywords: magnetism, magnetic properties, ion irradiation, ion implantation, ripples
  • Lecture (Conference)
    Ionenstrahlphysik und Nanotechnologie, 16.-17.05.2006, Berlin, Deutschland

Publ.-Id: 8473 - Permalink


Comparative characterization of differently grown ZnO single crystals by positron annihilation and Hall effect
Brauer, G.; Anwand, W.; Skorupa, W.; Kuriplach, J.; Melikhova, O.; Cizek, J.; Prochazka, I.; Moisson, C.; von Wenckstern, H.; Schmidt, H.; Lorenz, M.; Grundmann, M.;
High quality ZnO single crystals of dimensions 10 x 10 x 0.3 mm3, grown either using a pressurized melt or a hydrothermal growth approach, have been investigated in their as-received state and are compared regarding their properties revealed by positron annihilation and Hall effect measurements. By positron annihilation performed at room temperature it is found that the pressurized melt grown crystals contain a certain amount of Zn+O divacancies but no Zn vacancies are detected, whereas the hydrothermally grown crystals contain a dominating defect yet unknown in its structure but maybe connected to the Zn vacancy. Furthermore, the influence of an additional refined chemical-mechanical polishing of the crystal surface by a special procedure on the depth distribution of vacancy-type defects is demonstrated. Hall measurements, performed in the temperature range 20 – 325 K, showed that the crystal growth method has a strong influence on the carrier mobility, and the estimated acceptor densities also differ significantly in both types of crystal.
Keywords: zinc oxide, point defects, positron annihilation, Hall effect
  • Contribution to proceedings
    E-MRS 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France
    Superlattices and Microstructures: Elsevier
  • Lecture (Conference)
    E-MRS 2006 Spring Meeting, 29.06.-02.07.2006, Nice, France
  • Superlattices and Microstructures 42(2007), 259-264

Publ.-Id: 8472 - Permalink


Tetrabutylammonium bis(2-amidobenzenethiolato-k2S,N)oxorhenate(V)
Gniazdowska, E.; Kraus, W.; Emmerling, F.; Spies, H.; Stephan, H.;
Bu4N[ReO(abt)2] was obtained via the precursor Bu4N[ReOCl4], its conversion into an ethylene glycol complex as an intermediate and subsequent ligand exchange by H2abt to form the tetrabutylammonium salt of the abt complex in 62 % yield. Elemental analysis, mass, NMR and IR spectra confirm the composition Bu4N[ReO(abt)2]. The crystal structure contains well separated ReO(NHC6H4S)2 anions and Bu4N+ counter cations. The coordinationgeometry of Re is distorted square pyramidal, with an apical Re O bond length of 1.676(5)A°.The dihedral angle between the two benzene rings is 33.75(1)°. These values do not differ
much from those of the corresponding Tc compound.

Publ.-Id: 8471 - Permalink


Nanowire transformation into long-range-ordered nanocluster chains controlled by thermocapillarity
Röntzsch, L.; Heinig, K.-H.;
Capillarity-driven surface-free-energy minimization may lead to morphological changes of nanowires (NWs), e.g. their decay into chains of nanoclusters (NCs) by the Rayleigh instability. At the nano-scale, such capillary effects are more pronounced than in macroscopic systems due to the large surface-to-volume ratio. However, the capillary-driven NW decay is subject to increasing fluctuations with decreasing dimensions. This might prevent the formation of NC chains with long-range order which is needed for potential applications (e.g. in nanophotonics as light guides). We predict a novel method to fabricate long-range-ordered NC chains by decay of NWs under the control of an external temperature field. The prediction is based on the temperature dependence of surface tension causing thermocapillary effects. Surface tension gradients trigger atomic migration from hot to cold regions. Thus, long-range-order of NC chains may be achieved by a weak periodic temperature field along the NW. Such a temp. profile might be realized by a standing surface-plasmon-polariton wave. Here, a feasibility evaluation of the prediction will be presented which is based on computer experiments. The NW decay with and without external temperature fields was examined by kinetic Monte Carlo simulations. Just a small, symmetry-breaking periodic temperature field is needed to control long-range-order. In practice, the field must be stronger than thermally induced fluctuations along the NW, as is discussed.
Keywords: nanowire, Rayleigh instability, thermocapillarity, external field, long-range order, atomistic computer simulation
  • Poster
    EMRS Spring Meeting, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8470 - Permalink


Nanowire synthesis with focused ion beams: predictive atomistic simulations on the fabrication of functional nanowire structures
Röntzsch, L.; Heinig, K.-H.;
Nanowires (NWs) play an important role as basic components of electronic and photonic devices, such as interconnects or surface-plasmon propagators. Here, theoretical studies are presented on reaction pathways of the CMOS-compatible fabrication of metal silicide or semiconductor nanowires (NWs) by focused ion beam (FIB) implantation and subsequent thermal annealing. On realistic time and length scales, the simulation of the whole process is divided into two steps: (i) The spatio-temporal evolution of FIB implantation profiles is calculated by a new computer code including dynamical target changes, local ion erosion etc. The FIB implantation along a straight trace leads to a local and surface-near supersaturation in the substrate. (ii) Post-implantation annealing causes NW formation by self-organization, which is described theoretically by kinetic Monte Carlo simulations. It is demonstrated that the evolution of the FIB implantation profile proceeds in three well-separated stages: (1) Phase separation by nucleation and growth, (2) NW formation by coalescence of nanoclusters, (3) NW surface smoothening. After this evolution, a NW diameter which is several times smaller than the width of the FIB implantation trace (some tens of nanometers) is found. Likewise, components for functional devices involving several NWs, like T- or X-junctions, can be obtained by crossing different FIB traces.
Keywords: nanowire, focused ion beam, ion beam synthesis, computer simualtion, phase separation, self-organization
  • Poster
    EMRS Spring Meeting, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8469 - Permalink


Atomistic Structure of Grain Boundaries determined by first-principles Calculations and Quantitative HRTEM
Gemming, T.; Nufer, S.; Gemming, S.; Kurtz, W.; Marinopoulos, A. G.; Fabris, S.; Elsässer, C.; Rühle, M.;
A combination of transmission electron microscopy (TEM) and local density-functional theory (LDFT) is employed to analyze the microscopic structure of the rhombohedral (-1012) and the prismatic Sigma-3 (10-10) twin interfaces in alpha-alumina. LDFT provides interface energies, atomic and electronic structures for competing structure models. With high-resolution TEM the atomic structure at the interface is imaged quantitatively along two orthogonal zone axes. Electron energy loss spectroscopy in TEM yields the interfacial electronic structure with nano-scale spatial resolution. All experiments confirm the theoretically preferred model for each of the two grain boundaries quantitatively.
Keywords: interface, grain boundary, density-functional theory, DFT, calculation, electronic structure, atomic structure
  • Contribution to proceedings
    DFTEM 2006 - bringing together two communities International Conference on Density Functional Theory and Transmission Electron Microscopy, 21.-23.04.2006, Wien, Austria, Wien: Editio Amici/Physicae et chimicae solidorum amici, 3-902548-00-2, 142-145
  • Poster
    DFTEM 2006 - bringing together two communitites International Conference on Density Functional Theory and Transmission Electron Microscopy, 21.-23.04.2006, Wien, Österreich

Publ.-Id: 8468 - Permalink


Inductionless magnetorotational instability in a Taylor-Couette flow with a helical magnetic field
Priede, J.; Grants, I.; Gerbeth, G.;
We consider the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number (Pm=0). This leads to a considerable simplification of the problem eventually containing only hydrodynamic variables. First, we point out that the energy of any perturbation growing in the presence of magnetic field has to grow faster without the field. This is a paradox because the base flow is stable without the magnetic while it is unstable in the presence of a helical magnetic field without being modified by the latter as it has been found recently by Hollerbach and Rüdiger (Phys. Rev. Lett. {95}, 124501, 2005). We revisit this problem by using a Chebyshev collocation method to calculate the eigenvalue spectrum of the linearized problem. In this way, we confirm that MRI with helical magnetic field indeed works in the inductionless limit where the destabilization effect appears as an effective shift of the Rayleigh line. Second, we integrate the linearized equations in time to study the transient behavior of small amplitude perturbations, thus showing that the energy arguments are correct as well. However, there is no real contradiction between both facts. The linear stability theory predicts the asymptotic development of an arbitrary small-amplitude perturbation, while the energy stability theory yields the instant growth rate of any particular perturbation, but it does not account for the evolution of this perturbation. Thus, although switching off the magnetic field instantly increases the energy growth rate, in the same time the critical perturbation ceases to be an eigenmode without the magnetic field. Consequently, this perturbation is transformed with time and so looses its ability to extract energy from the base flow necessary for the growth.
  • Physical Review E 75(2007), 047303

Publ.-Id: 8467 - Permalink


Synthesis of 18F-labelled biphenyls via Suzuki cross-coupling with 4-[18F]fluoroiodobenzene
Steiniger, B.; Wüst, F.;
The SUZUKI reaction of organoboron compounds with 4-[18F]fluoroiodobenzene has been developed as a novel radiolabelling technique in 18F chemistry. The cross-coupling reaction of p-tolylboronic acid with 4-[18F]fluoroiodobenzene was used to screen different palladium complexes, bases and solvents. Optimised reaction conditions (Pd2(dba)3, Cs2CO3, acetonitrile, 60 °C for 5 minutes) were further applied to the synthesis of various 18F-labelled biphenyls bearing different functional groups. The reaction proceeded in excellent radiochemical yields of up to 94 % within 5 min while showing good compatibility to many functional groups.
  • Journal of Labelled Compounds and Radiopharmaceuticals 49(2006), 817-827
    DOI: 10.1002/jlcr

Publ.-Id: 8466 - Permalink


Simulation of positron distributions for carbon and proton beams
Fiedler, F.;
Challenges for further development in in-beam PET
Keywords: in-beam PET
  • Lecture (Conference)
    Scientific Workshop for In-Beam PET, 09.-10.05.2006, Dresden, Deutschland

Publ.-Id: 8465 - Permalink


Predictive process simulation of the FIB-based fabrication of metallic nanoparticle waveguides
Röntzsch, L.; Heinig, K.-H.;
Chains of metallic nanoparticles may be applied as surface-plasmonpolariton (SPP) waveguides. Moreover, nanoparticle waveguide structures with small bend radii, e.g. L-turns or beam splitting T-junctions, are of technological interest. In this contribution, we present reaction pathways of the fabrication of 1D metallic nanostructures by focused metal ion implantation and subsequent thermal treatment. Nanowires (NWs) as well as structures consisting of metallic nanoparticle chains were found. The search for reaction pathways was performed by kinetic Monte Carlo simulations including realistic focused ion beam (FIB) implantation profiles which were determined by spatially dependent dynamic ion range calculations. During annealing, buried NWs and more complex structures (e.g. T- or X-junctions) form that are embedded in the matrix along the FIB implantation trace. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. During longterm thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, by choosing appropriate geometries and implantation conditions, SPP waveguides based on multiple nanodot chains, e.g. L-turns, X- or T-junctions, might be fabricated by FIB implantation. The simulations were performed for focused Co ion implantation into Si since CoSi2 might be a metallic waveguide material with several advantages: monocrystalline embedding into c-Si with coherent (and defect-free) interfaces, CMOS-compatibility, and surface plasmon resonance in the infrared where Si is transparent.
Keywords: focused ion beam, ion beam synthesis, CoSi2, kinetic Monte Carlo simulation, nanowire, waveguide, surface plasmon polaritons, phase separation
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 8463 - Permalink


Focused-ion-beam-based synthesis of semiconductor nanowires and functional structures – an atomistic computer simulation study
Röntzsch, L.; Heinig, K.-H.;
We present reaction pathways of a novel method of semiconductor nanowire (NW) fabrication using a focused ion beam (FIB). This investigation is based on kinetic Monte Carlo simulations including realistic FIB implantation profiles which were determined by spatially dependent dynamic ion range calculations. A focused implantation of Si or Ge ions into SiO2 along a straight trace leads to local supersaturation of the implanted species in the dielectric substrate. During post-implantation annealing, semiconductor NWs embedded in the dielectric matrix form along the FIB implantation trace. Even complex structures involving several NWs, e.g. T- or X-junctions, may be obtained. The dominating driving force of NW formation is a free energy gain by phase separation and by reduction of high interface curvatures. The diameter of the synthesized NWs is about five times smaller than the width of the FIB implantation trace. During long-term thermal annealing, NWs disintegrate into regular chains of nanodots because of the built-up of long-wavelength interface undulations (Rayleigh instability). Crosses, corners or ends of NWs are subject to a preferential disintegration. Thus, structures suitable for single-electron-transistors may be realized where an isolated nanocluster is located in a tunnel distance from several NW contacts. Moreover, multi-gate NW field effect transistors may be fabricated by crossing FIB traces of different ion fluences.
Keywords: focused ion beam, ion beam synthesis, kinetic Monte Carlo simulation, nanowire, Rayleigh instability
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 8462 - Permalink


Search for reaction pathways of a CMOS-compatible fabrication of nanofluidic channels by means of atomistic computer simulations
Röntzsch, L.; Heinig, K.-H.;
Nanofluidic devices are going to play an important role in miniaturization, automation and parallelization of chemical, biological, or medical systems. At present, the fabrication of microfluidic channel networks requires a large number of sophisticated processing steps. For "lab on a chip" devices, CMOS compatibility is desired in the fabrication process, additionally. In this contribution, we present potential reaction pathways of a nonconventional, however, CMOS-compatible fabrication method of nanofluidic channels and channel networks. The reaction pathways are predicted by Monte Carlo simulations which atomistically describe the evolution of a sample configuration during a thermal treatment. Referring to the "empty space-in-silicon" formation technique (T. Sato et al., Jnp. J. Appl. Phys. 43 (2003) 12.), a Si-(100) substrate is assumed which contains isolated trenches that are arranged in a line. This approach is modified by using trenches of different depths and diameters. During thermal treatment in a low-pressure hydrogen atmosphere, migration of surface atoms leads to an overall surface minimization. Thin trenches decouple quickly from the wafer surface forming buried voids. In a self-organizing manner, neighboring voids may coalesce and, thus, they construct a buried channel. Due to their lower surface-to-volume ratio, thick trenches are more stable. They remain in contact with the wafer surface and, therefore, they may act as vertical supply and drain pipes for the buried channels. In addition, the simulations predict the formation of elementary nanochannel networks such as T-junctions, X-junctions, or Hfilters. The channel surface of the whole active layer can be transformed into SiO2 by postfabrication oxidation.
Keywords: fluidics, silicon on nothing, channels, whormholes, fabrication, surface diffusion, Rayleigh instability
  • Poster
    MRS Spring Meeting, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 8461 - Permalink


Size and position control of chains or arrays of nanoparticles by surface-plasmon-polariton-induced thermocapillarity
Röntzsch, L.; Heinig, K.-H.;
Surface free energy minimization, driven by capillary forces, may lead to morphological changes of wires (e.g. disintegration into a droplet chain which is known as Rayleigh instability) and layers (dewetting). At nano-scale dimensions, capillary effects are much more pronounced than in macroscopic systems due to the large surface-to-volume ratio. On the other hand, capillary-driven self-organization processes are subject to increasing fluctuation with decreasing dimensions, which mostly prevent the formation of regular structures with long-range order. In this contribution, we predict by means of atomistic Monte Carlo simulations a novel method to fabricate size- and position controlled 1D- and 2D-patterns of nanoparticles. Our prediction rests on the temperature dependence of surface tension – the origin of the wellknown thermocapillarity. Uncompensated forces occur due to surface temperature gradients. These forces may have considerable impact in the nanoworld, thus, leading to material transport and structure formation on short time and length scales. A surface tension gradient (also responsible for the Marangoni effect) triggers the biased migration of atoms from hot to cold regions by surface diffusion. A periodic temperature gradient on the surface of a wire or a layer may be achieved by a surface-plasmon-polariton (SPP) wave or even by a SPP wave interference pattern. For SPP excitations with long wavelengths (e.g. by a CO2 laser), sufficiently strong steady-state temperature gradients may be produced. However, pulsed operation might be necessary for shorter wavelengths. We predict by kinetic Monte Carlo simulations that the regularity of nanodroplet chains, that form during a self-organized disintegration of nanowires, might be considerably improved by SPPs. If the SPP wavelength is commensurable with the inherent Rayleigh wavelength of the nanowire disintegration, the SPP-induced temperature undulations control the Rayleigh instability. Thus, a regular and long-range order in nanodroplet size and position may be achieved. Similarly, this principle may be used for the fabrication of regular and long-range 2D nanodroplet patterns, if interference patterns of SPP waves on thin layers are achieved.
Keywords: Thermocapillarity, Rayleigh instability, nanowire, dewetting, patterning, surface plasmon polariton, kinetic Monte Carlo simulation
  • Lecture (Conference)
    MRS Spring Metting, 17.-21.04.2006, San Francisco, USA

Publ.-Id: 8460 - Permalink


On the stability of the boundary layer subject to a wall-parallel Lorentz force
Albrecht, T.; Grundmann, R.; Mutschke, G.; Gerbeth, G.;
The stability of a transitional boundary layer controlled by a wall-parallel, streamwise oriented Lorentz force is investigated by means of direct numerical simulation. Damping of Tollmien-Schlichting waves is observed already at weak control amplitudes.
For a particular control amplitude, similar to homogeneous suction, the initial Blasius layer evolves towards an exponential velocity profile of strongly enhanced stability. Here, intermediate velocity profiles are found to have linear stability properties superior to that of the asymptotic exponential profile. Additional 3-D simulations support the 2-D results as Lorentz force control clearly damps the coherent structures of the transitional flow.
Keywords: MHD, Control, Boundary Layer, DNS, linear stability analysis
  • Physics of Fluids 18(2006), 098103

Publ.-Id: 8459 - Permalink


CFD-simulation of thermalhydraulic benchmark V1000CT2 - analysis with advanced turbulence models
Höhne, T.;
CFD calculations have been performed for the themalhydraulic benchmark V1000CT-2
The numerical grid model was generated with the grid generator IC4C (ICEM-CFD) and the preprocessor ANSYS CFX and contains 4.7 Mio. tetrahedral elements
Different advanced turbulence models were used in the numerical simulation
The best agreement with the Kozloduy experiment at the core inlet shows the DES simulation. Strong fluctuations occur in the downcomer of the RPV.
The results show a clear sector formation of the affected loop at the downcomer, lower plenum and core inlet. The maximum local values of the relative temperature rise in the experiment amount 97.7% and in the calculation 97.3%
Keywords: PWR, VVER-1000, CFD
  • Lecture (Conference)
    V1000CT4 Workshop, 24.-29.04.2006, Pisa, Italy
  • Contribution to proceedings
    V1000CT4 Workshop, 24.-29.04.2006, Pisa, Italy

Publ.-Id: 8458 - Permalink


Elektromagnetische Strömungskontrolle mit wandparallelen Lorentzkräften in schwach leitfähigen Fluiden
Weier, T.;
Die vorliegende Arbeit widmet sich der, vorwiegend experimentellen, Untersuchung der Wirkung wandparalleler Lorentzkräfte in Strömungsrichtung auf Grenzschichtprofile und Körperumströmungen. Die Themen
- Beeinflussung der Grenzschicht an ebenen Platten mit stationären Lorentzkräften
- Kontrolle von Strömungsablösungen an Zylindern und symmetrischen Profilen mit stationären Lorentzkräften
- Beeinflussung von Zylindernachläufen und abgelösten Tragflügelumströmungen mit zeitlich periodischen Lorentzkräften
werden behandelt.
Keywords: Lorentz force, boundary layer control, separation control, active flow control
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-454 2006

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Publ.-Id: 8457 - Permalink


Annual Report 2005 - Institute of Radiopharmacy
Steinbach, J.; Seifert, S.; (Editors)
kein Abstract verfügbar
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-449 2006

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Publ.-Id: 8456 - Permalink


Investigation of FIB assisted CoSi2 nanowire growth
Bischoff, L.; Schmidt, B.; Akhmadaliev, C.; Mücklich, A.;
The ion beam synthesis process of CoSi2 by writing stoichiometric ion implantation and subsequent annealing has been studied. For this a Focused Ion Beam (FIB), equipped with a Co36Nd64 alloy liquid metal ion source, was applied. Si(1 0 0) and (1 1 1) wafers were implanted with 60 keV Co2+ ions in the dose range of 2 × 1016–2 × 1017 cm−2. The implantation parameters, like pixel dwell time, relaxation time, dose rate as well as the pixel overlapping factor were investigated. During subsequent annealing CoSi2 nanostructures with dimensions down to 10 nm have been achieved. To investigate the silicide formation more in detail the annealing process was done in situ in a transmission electron microscope (TEM) on a pre-dimpled and FIB implanted samples of a Si(1 1 1). The formation of the cobalt silicide nano-crystals was monitored by plane-view TEM imaging during a 30 min heat treatment at 600 °C in vacuum.
Keywords: Focused ion beam; Cobaltdisilicide; Ion beam synthesis; Nanowire
  • Microelectronic Engineering 83(2006)4-9, 800-803

Publ.-Id: 8455 - Permalink


Actinides in Biosystems - Complexation Studies with Relevant Bioligands
Glorius, M.; Moll, H.; Bernhard, G.;
Biosystems such as microorganisms, plants, algae’s etc. are influencing for instance the migration of actinides in the environment. It is important to include these processes in the risk assessment of potential high level nuclear waste disposal sites and other affected areas. In general, the overall interaction process of actinides with microbes can be divided into a) direct interaction path ways such as biosorption, bioaccumulation and biotransformation/bioreduction and b) indirect interaction paths such as complexation with released bioligands. The potential of microbes to mobilize actinides by means of the formed bioligands is less investigated.

Our approach is focused on the investigation of selected bioligands having relevant functionalities for a better understanding of the complex actinide interaction processes in biological systems on a molecular level. To achieve this goal a variety of spectroscopic techniques such as time-resolved laser fluorescence spectroscopy (TRLFS) and/or absorption spectroscopy in the ultraviolet-visible-near infrared (UV-vis-NIR) wavelength range will be applied depending on the nature of the actinide element and the bioligand.
This poster gives an overview about our ongoing research in this area by taking three examples: complex formation of curium(III) with adenosine 5’-triphosphate (ATP) [1], curium(III) and amino acids of different functionalities [2], and uranium interactions with molecules containing hydroxamate groups [3].
We want to use this workshop in order to try to answer the question: How can theory help to interpret our experimental results obtained by using spectroscopic methods especially in exploring the structure of the respective aqueous actinide species?

[1] H. Moll, G. Geipel, G. Bernhard, Inorg. Chim. Acta 358 (2005) 2275.
[2] H. Moll, G. Bernhard, Inorg. Chim. Acta (2006) submitted.
[3] M. Glorius, H. Moll, G. Bernhard, manuscript in preparation.

This work was funded by the BMWA under contract number 02E9985.
Keywords: actinides, biosystems, complexation, TRLFS, UV-Vis spectroscopy
  • Poster
    ThUL-Actinet School, 15.-20.05.2006, Lille, Frankreich

Publ.-Id: 8453 - Permalink


New TRLFS Laboratory at the CTU in Prague
John, J.; Filipská, H.; Cernochová, K.; Benes, P.; Geipel, G.; Kubecek, V.; Semelová, M.; Bocan, J.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) is a unique method for direct actinide and lanthanide speciation at low concentrations that is increasingly used for the study of various chemical aspects of actinides and lanthanides in solutions, suspensions or on solid surfaces namely in the framework of environmental studies or problems related to nuclear fuel reprocessing and waste disposals. Early in this year, construction and equipment of a new TRLFS laboratory was finished at the Czech Technical University in Prague, Czech Republic, in collaboration and under the support of Institute of Radiochemistry, Forschungszentrum Rossendorf, Germany. The new set-up comprises:
− Vibrant 355 II (Opotec) tunable laser with optical parametric oscillator, basic range 410 2400 nm, pumped at 355 nm with a Brilliant Nd:YAG pulse laser with SHG 532 nm and THG-355 nm modules and an additional FHG 266 nm module. Independent outlets for 355 nm and 266 nm laser beams. A UV 3 module extends the range down to 355 nm. Variable repetition frequency up to 10 Hz with the lengths of the laser pulse 6-8 ns.
− Cuvette Holder Flash 200 with Temperature Controller TC 101 (Quantum Northwest) and the necessary optical elements for signal collection and focussing.
− MS257 (Oriel) monochromator/spectrograph with 4 gratings (150 l/mm 190 800 nm, blaze 300 nm; 300 l/mm 250-1150 nm, blaze 500 nm; 600 l/mm 280 1200 nm, blaze 500 nm; 1200 l/mm 280-1600 nm, blaze 500 nm), with micrometrically adjustable aperture and optical fibre outlet. The main parameters are: outlet focal length 257,4 mm, resolution 0,1 nm, precision ± 0,1 nm, repeatability ± 0,028 nm.
− iStar 720 (Andor) DH720i-18F-03 intensified CCD camera designed for low-light spectroscopy applications requiring fast gating. The CCD sensor has spectral range of 180-850 nm and it includes a digital delay generator built into the head - the minimum optical gate is 1.6 ns.
Results of the first measurements obtained in the new laboratory for a standard UO22+ – SO42– system will be presented. The future research plans include:
− study of uranium complexation with humic substances,
− study of actinides bonding onto solid surfaces,
− actinides and lanthanides complexation with novel extraction and/or complexing agents relevant for spent nuclear fuel reprocessing or operational decontamination, respectively.
  • Contribution to proceedings
    15th Radiochemical Conference, 23.-28.04.2006, Mariánské Lázne, Czech Republic
    Booklet of abstracts & Conference Programme, Prague: Czech Technical University in Prague, 80-01-03474-7
  • Czechoslovak Journal of Physics 56(2006), D565-D568

Publ.-Id: 8452 - Permalink


Ferromagnetic ZnFe2O4 synthesized by Fe implantation into ZnO
Zhou, S.; Potzger, K.; Reuther, H.; Mücklich, A.; Eichhorn, F.; Schell, N.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Bulk Zinc ferrite (ZnFe2O4) is known to possess a normal spinel structure and is an antiferromagnetic material. However, ferri- or ferro- magnetism has been observed in nanosized ZnFe2O4, which raised the current interest of ZnFe2O4 nanoparticles [1-3]. In this work, crystalline ZnFe2O4 was synthesized by Fe implantation into ZnO at 623 K, following a post thermal annealing. In the as-implanted ZnO sample, a fraction of Fe is in metallic state, and is responsible for the magnetic property. An annealing at 823 K enhanced the Fe particle formation, but Fe nanoparticles were oxidized after an annealing at 1070 K. A further annealing at 1070 K for 3.5 h induced the formation of ZnFe2O4. ZnFe2O4 was identified by x-ray diffraction, transmission electron microscopy and indirectly by room temperature conversion electron Mössbauer spectroscopy. The magnetic property was investigated by superconducting quantum interference device (SQUID) magnetometry (Fig. 1). At 5 K, the sample shows a hysteric loop upon magnetization reversal with a high coecivity of around 400 Oe. The magnetization also was measured as a function of temperature with zero field cooling and field cooling protocol. The zero field cooling curve exhibits a maximum magnetization at a temperature of around 26 K, indicating a nanoparticle magnetic characteristic. The ferromagnetism of ZnFe2O4 can be explained by a partially inverted spinel structure, where Fe ions migrate from octahedral B sites (Fe3+) to tetrahedral A sites (Fe2+), and a strong A-B superexchange interaction produces the ferromagnetic coupling [1-3].

[1] Z. H. Zhou, et al, Appl. Phys. Lett. 79, 3167 (2001).
[2] G. F. Goya, et al, J. Phys.: Condens. Matter 15, 641 (2003).
[3] J. H. Shim, et al, Appl. Phys. Lett. 86, 082503 (2005).
Keywords: Zinc ferrite; Ferromagnetism; Ion implantation; ZnO
  • Poster
    The 4th International Conference on Physics and Applications of Spin Related Phenomena in Semiconductors, 15.-18.08.2006, Sendai, Japan

Publ.-Id: 8451 - Permalink


Mn-silicide nanoparticles formed inside Si using ion implantation
Zhou, S.; Potzger, K.; Zhang, G.; Mücklich, A.; Eichhorn, F.; Grötzschel, R.; Schmidt, B.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
300 keV Mn was implanted into p-Si with a fluence of 1*10ˆ15/cm2, 1*10ˆ16/cm2 and 5*10ˆ16/cm2, respectively, at 620 K. The samples were annealed at 1070 K in N2 ambient for 5 min by rapid thermal annealing. Rutherford backscattering/channeling, transmission electron microscopy and X-ray diraction were applied for structural characterization. Mnsilicide nanoparticles were formed with the size of 5 nm already in the asimplanted samples and grew up to around 30 nm after annealing. Moreover no significant evidence is found for Mn substituting Si sites either in as-implanted or annealed samples. The virgin samples already show a ferromagnetic like behavior, and the moment is slightly increased after implantation (1*10ˆ16/cm2) and annealing by around 0.5 Bohr magneton per Mn. Therefore, the majority of Mn ions formed Mn-silicides, and some are diluted in Si matrix and develop into ferromagnetic coupling. These effects have to be properly considered for the design of Si-based diluted magnetic semiconductors.
[1] M. Bolduc, C. Awo-Aouda, A. Stollenwerk, M. B. Huang, F. G. Ramos, G. Agnello, and V. P. LaBella Phys. Rev. B 71, 033302 (2005).
  • Poster
    DPG Frühjahrstagung 2006, 27.-31.03.2006, Dresden, Germany

Publ.-Id: 8449 - Permalink


Carbon ion implantation into aluminium: Mechanical and tribological properties
Foerster, C. E.; Da, S. S. L. R.; Fitz, T.; Dekorsy, T.; Prokert, F.; Kreissig, U.; Richter, E.; Möller, W.; Lepienski, C. M.; Siqueira, C. J. D.;
Aluminium, carbide nucleation and growing kinetics is correlated to the mechanical properties (hardness and elastic modulus), and to the friction coefficients as a function of carbon ion implantation parameters on aluminium. The microstructure of the modified surface was studied by: a) Elastic Recoil Detection Analysis (ERDA), b) Grazing Incidence X-ray Diffraction analysis (GIXRD) and c) Raman spectroscopy. Hardness and elastic modulus profiles were measured by instrumented nanoindentation technique. Pin-on-disc technique in reciprocal scratch mode was employed to obtain the friction coefficient profile. For low carbon fluences (<= 2 x 10(17) C+ cm(-2)) small size (approximate to 4 nm) embedded Al4C3 precipitates were produced. Higher carbon fluences create an amorphous-like structure. Implantations performed at high substrate temperatures can produce big size precipitate (approximate to 40 nm). Surface hardness increases as a function of carbon fluence resulting in values !
of about 6 GPa (20 times Al bulk value). The hardening mechanisms are associated with dislocations to precipitates bowing and/or cutting processes. Implantation parameters ruled the mechanical properties. Tribological responses are more difficult to correlate to the ion implantations conditions. However, wear is reduced when highly disordered C-C cluster are present.
Keywords: aluminium, Carbon ion implantation, hardness, tribology
  • Surface & Coatings Technology 200(2006)18-19, 5210-5219

Publ.-Id: 8448 - Permalink


Determination and evolution of tunneling distances in Ge nanocrystal based memories
Beyer, V.; von Borany, J.; Klimenkov, M.;
A Ge nanocrystal layer embedded in thin SiO2 was prepared by ion beam synthesis in direct-tunneling distance to the Si substrate. The write performance was investigated in metal-oxide-semiconductor capacitors by means of capacitance measurements. With the experimental data and calculations using a floating-gate-like approach, the distribution of the tunneling oxide thickness dtox can be obtained in high precision confirmed by high-angle annular dark-field scanning transmission electron microscopy imaging. The evolution of dtox during heat treatment is discussed in terms of Ostwald ripening; i.e., dtox increases with annealing time.
Keywords: memory, MOS, nanocrystal, Germanium
  • Applied Physics Letters 89(2006), 193505

Publ.-Id: 8447 - Permalink


Ferromagnetic Gd-implanted ZnO single crystals
Zhou, S.; Potzger, K.; Eichhorn, F.; Helm, M.; Skorupa, W.; Mücklich, A.; Fassbender, J.ORC; Herrmannsdörfer, T.; Bianchi, A.
In order to introduce ferromagnetic properties, ZnO single crystals have been implanted with Gd ions at 180 keV ion energy and two different fluences. Magnetization reversal hysteresis loops have been recorded using a superconducting quantum interference device. The virgin ZnO shows a pure diamagnetic behaviour. Besides the diamagnetic background, weak ferromagnetism has been observed for the as-implanted films. Post-implantation annealing greatly improved the magnetism. For a fluence of 5x10ˆ15 Gd/cm2, post implantation annealing at 820K in vacuum leads to an increase of the saturation moment up to 1.8 Bohr magneton per Gd at exactly 300 K thus excluding Gd, ZnGd or Gd2O3 secondary phases to be formed. The increase of the saturation moment can be explained along with changes in resistivity due to the annealing reported elsewhere. Moreover magnetic domains were observed up to 2 microns by atomic/magnetic force microscope, which again evidenced the formation of diluted magnetic semiconductor.
[1]K. Potzger et al, submitted to J. Appl. Phys. (2005).
[2]S. O. Kucheyev et al. J. Appl. Phys. 93, 2972 (2003).
  • Lecture (Conference)
    DPG Frühjahrstagung 2006, 27.-31.03.2006, Dresden, Germany

Publ.-Id: 8446 - Permalink


Hemocompatibility of low-friction boron-carbon-nitrogen containing coatings
Maitz, M.; Gago, R.; Abendroth, B.; Camero, M.; Caretti, I.; Kreissig, U.;
Mechanical heart valves are exposed to extreme mechanical demands, which require a surface showing not only nonhaemostatic properties, but also wear resistance and low friction. As alternative to different forms of amorphous carbon (a-C), so-called diamondlike carbon (DLC), the suitability of boron carbonitride (BCN) coatings is tested here for hemocompatible coatings. They have similar mechanical properties like a-C surfaces, but superior chemical stability at ferrous substrates or counterparts. BCN films with different nitrogen content were compared with hydrogenated a-C films regarding their mechanical properties, surface energy, adsorption of albumin and fibrinogen, blood platelet adherence, and activation of the contact system of the clotting cascade and kinin system. Similar mechanical properties and biological response have been found in the BCN films with respect to a-C, indicating the potential of these coatings for biomedical applications. The increase in the cryst!
allinity and tribological properties of the BCN samples with a higher incorporation of N was also followed by a lower protein adsorption and low activation of the contact system, but an increased adherence of thrombocytes. (c) 2005 Wiley Periodicals, Inc.
  • Journal of Biomedical Materials Research Part B 77B(2006), 179-187

Publ.-Id: 8445 - Permalink


Wettability and biocompatibility of nitrogen-doped hydrogenated amorphous carbon films: Effect of nitrogen
Yang, P.; Huang, N.; Leng, Y.; Yao, Z.; Zhou, H.; Maitz, M.; Leng, Y.; Chu, P.;
Amorphous carbon films have been applied in biomedical fields as potential biocompatible materials with wettability that can be adjusted by doping with other elements, including F, Si, Ti, O and N. In this study, nitrogen-doped hydrogenated amorphous carbon (a-C:H:N) films were deposited by PIII-D using C2H2 + N-2 gas mixtures. The biocompatibility and anti-thrombotic properties of the films were assessed in vitro. The surface morphology and surface wettability of the films were characterized using atomic force microscopy (AFM) and a contact angle method. The results show no cytotoxicity for all films, and films with appropriate nitrogen doping possess much better endothelial cell growth and anti-thrombotic properties. (c) 2005 Elsevier B.V. All rights reserved.
  • Nuclear Instruments and Methods in Physics Research B 242(2006), 22-25

Publ.-Id: 8444 - Permalink


Speciation of actinides
Geipel, G.;
Actinides under environmental conditions can be found in a sub-µ-molar to the lower millimolar concentration range. However, the direct detection of species under these conditions with conventional spectroscopic techniques is not possible.
By application of very intense light sources, as are available with the different laser systems the excitation of traces of actinides ions becomes possible. Several ions of actinides possess outstanding spectroscopic properties which allow the detection of species also in the lowest concentration range.
For the non-invasive detection of species in solution especially the laser-induced photoacoustic spectroscopy (LIPAS) and in the case of fluorescing species the time-resolved laser-induced fluorescence spectroscopy (TRLFS) are method of first choice. LIPAS is a very sensitive method for absorption spectroscopy and can be applied therefore for all non-fluorescent systems. Compared to conventional UV-VIS spectroscopy up to three orders of magnitude lower detection limits can be achieved. TRLFS is only applicable in systems where the deexcitation takes place via radiative processes with emission of photons. In the series of the lower actinides here the systems containing protactinium(IV), uranium(IV) and uranium(VI) as well as americium(III) and curium(III) have to be named. Due to the extremely high quantum efficiency of curium(III) ions concentrations down to 10-11 mol/L can be observed be TRLFS. On the other hand organic ligands as humic substances are ubiquitous in the nature. The interaction of such compounds with actinides can also studied using the fluorescence properties of the organic ligand. A brief overview for these methods will be given.
Examples for the application of the laser-induced spectroscopic methods we be given. At first examples for the spectroscopy and detection of uranium species in natural waters from mining related to drinking waters will be shown. As special case the determination pure uranyl carbonate species, which are non-fluorescent at room temperature, will be shown. Also the interaction with sulfate, phosphate and arsenate will be touched on. The application of LIPAS will be shown especially for the uranium(IV) phosphate and arsenate systems. As uranium(IV) shows also fluorescence properties some problems with the detection of these species will be summarized. Studies of the interaction of curium and americium with several ligands will also shortly summarized.
Polyelectrolytic organic macromolecules, like humic substances, are important complexing agents towards actinide metal ions. Due to these properties humic substances are possible carriers for the migration of actinides in the environment. The study of the high molecular compounds is very complex. Therefore the investigation of simple model ligands would give a more detailed description of the binding behavior of humic substances. Especially the different bonding of carboxylic and phenolic group and the discrimination between them is of interest to get more detailed information about the complex formation. To study the complex formation of actinides with such organic ligands the TRLFS with ultrashort excitation pulses is a very suitable method.
Keywords: Laser-induced spectroscopy, actinides, organid ligands
  • Invited lecture (Conferences)
    Selected topics on nuclear methods for non-nuclear applications, 27.-30.09.2006, Varna, Bulgaria

Publ.-Id: 8443 - Permalink


Microscopic theory of impurity states in coupled quantum wells and superlattices
Stehr, D.; Helm, M.; Metzner, C.; Wanke, M. C.;
We present a theory of impurity states in quantum wells and superlattices which treats the confining heterostructure potential and the random impurity potential on the same footing. The relevant 3D Hamiltonian is diagonalized exactly in the low-doping regime. The results are used to calculate infrared absorption spectra which contain contributions of impurity and intersubband transitions. We mainly discuss the excited impurity states, which are pinned to higher subbands and are resonant states in the continuum. After a detailed analysis of a coupled quantum well system, we study the transition to a superlattice. In particular, we are able to reproduce existing experimental data on a quadruple quantum well, which had not been understood in the past.
  • Physical Review B 7408(2006)8, 511

Publ.-Id: 8442 - Permalink


Experiments and ANSYS CFX simulations of horizontal air-water channel flow phenomena
Höhne, T.; Vallee, C.;
For the investigation of stratified two-phase flow, two horizontal channels with rectangular cross-section were built at Forschungszentrum Rossendorf. The channels allow the investigation of air/water co-current flows, especially the slug behaviour, at atmospheric pressure and room temperature. The test-sections are made of acrylic glass, so that optical techniques, like high-speed video observation or particle image velocimetry (PIV), can be applied for measurements. The rectangular cross-section was chosen to provide better observation possibilities. Moreover, dynamic pressure measurements were performed and synchronised with the high-speed camera system.
CFD post test simulations of stratified flows were performed using the code ANSYS-CFX. The Euler-Euler two fluid model with the free surface option was applied on grids of minimum 4∙105 control volumes. The turbulence was modelled separately for each phase using the k-ω based shear stress transport (SST) turbulence model. The results compare very well in terms of slug formation, velocity, and breaking. The qualitative agreement between calculation and experiment is encouraging and shows that CFD can be a useful tool in studying horizontal two-phase flow.
Keywords: CFD, Stratified flow, horizontal channel
  • Contribution to proceedings
    Multiphase Flows: Simulation, Experiment and Applications, 26.-29.06.2006, Dresden, Germany
    CD-ROM
  • Lecture (Conference)
    Multiphase Flows: Simulation, Experiment and Applications, 26.06.2006, Dresden, Germany

Publ.-Id: 8441 - Permalink


Modeling of a buoyancy-driven flow experiment at the ROCOM test facility using the CFD-Code ANSYS CFX
Höhne, T.; Kliem, S.; Weiß, F.-P.;
The influence of density differences on the mixing of the primary loop inventory and the Emergency Core Cooling (ECC) water in the downcomer of a Pressurised Water Reactor (PWR) was analyzed at the ROssendorf COolant Mixing (ROCOM) test facility. ROCOM is a 1:5 scaled model of a German PWR, and has been designed for coo¬lant mixing studies. It is equipped with advanced instrumen¬ta¬tion, which delivers high-resolution information for temperature or Boron concen¬tra¬tion fields. This paper presents ROCOM experiments in which water with higher density was injected into a cold leg of the reactor model. Wire-mesh sensors measuring the concentration of a tracer in the injected water were installed in the upper and lower part of the downcomer. An experiment with 5 % of the design flow rate in one loop and 10 % density difference between the ECC and loop water was selected for validation of the CFD software ANSYS CFX. A mesh with two million control volumes was used for the calculations. The effects of turbulence on the mean flow were modelled with a Reynolds stress turbulence model. The results of the experiment and of the numerical calculations show that mixing is dominated by buoyancy effects: At higher mass flow rates (close to nominal conditions) the injected slug propagates in the circumferential direction around the core barrel. Buoyancy effects reduce this circumferential propagation. The ECC water falls in an almost vertical path and reaches the lower down¬comer sen¬sor directly below the inlet nozzle. Therefore, density effects play an important role during natural convection with ECC injection in PWRs. ANSYS CFX was able to predict the observed flow patterns and mixing phenomena quite well.
Keywords: CFD, Boron Dilution, ROCOM
  • atw - International Journal for Nuclear Power 3(2007), 168-174

Publ.-Id: 8440 - Permalink


Flow experiments and VGF growth with a travelling magnetic field
Lantzsch, R.; Galindo, V.; Pätzold, O.; Gerbeth, G.; Stelter, M.;
The status of flow modelling under the influence of a travelling magnetic field for the purpose of melt control in VGF growth of GaAs is summarized. Global heat flux modeling is combined with flow simulation, flow stability analysis, and model experiments using the eutectic melt GaInSn.
  • Lecture (Conference)
    DGKK-Arbeitskreis, 22.03.2006, Erlangen, Germany

Publ.-Id: 8439 - Permalink


Tailoring the microstructure and mechanical properties of Ti-Al alloy using a novel electromagnetic stirring process
Biswas, K.; Hermann, R.; Das, J.; Priede, J.; Gerbeth, G.;
The microstructures and mechanical properties of Ti45Al55 alloys were investigated in terms of the melt convection state during solidification. The samples were subjected to conventional induction melting as well as enhanced melt stirring by application of an external magnetic field using a specially designed floating zone arrangement. The stirred samples showed a significant improvement of the plastic deformability (16.9 %) up to 1137 MPa stress. A strong morphology change from dendritic to spherical shape geometry and an increased properitectic phase fraction was observed after stirring. The possible reasons were explained as result of spherical growth under forced convection, rather than a consequence of fragmentation of dendrite arms. An increase in the semi-coherent interfaces between g/a2 interfaces and the lack of orientation anisotropy of the spherical shape (g+a2) colonies in the stirred sample may contribute to the higher deformability of the stirred samples. Reduced Vickers hardness values of the g-matrix and increased hardness of the (g+a2) lamellar structure in the stirred samples is attributed to redistribution of oxygen and reduced interlamellar g/a2 spacing.
  • Scripta Materialia 55(2006)I2, 1143-1146

Publ.-Id: 8438 - Permalink


Applied MHD at Forschungszentrum Rossendorf – a review of R&D activities on tailored magnetic fields and liquid metal measuring techniques
Gerbeth, G.;
Magnetic fields provide an attractive contact-less influence on the motion of metallic or semiconductor melts and the related heat and mass transfer. An optimal design of the magnetic field is often difficult due to the lack of experimental access to the velocity field in such opaque melts. Several recently developed measuring techniques will be presented which allow an almost complete velocity resolution in metallic melts up to temperatures of about 400C. On this basis a combination of cold liquid metal model experiments with numerical simulations represents a powerful approach, allowing to develop tailored magnetic field systems. Various examples will be presented ranging from crystal growth, aluminum investment casting, thermoelectric effects, melt mixing, metal fiber production, electromagnetic levitation, to metal solidification. In many cases, only a special combination of AC and DC magnetic fields provides an optimal solution for the desired melt flow control.
  • Lecture (others)
    Research Institute of Industrial Science & Technology, 29.03.2006, Pohang, Korea

Publ.-Id: 8436 - Permalink


Effect of melt convection on microstructure evolution of Nd-Fe-B alloys using a forced crucible rotation technique
Biswas, K.; Hermann, R.; Acker, J.; Gerbeth, G.; Priede, J.; Shatrov, V.;
The forced crucible rotation technique has been applied to the solidification of Nd-Fe-B alloys. Specially sealed samples were subjected to well-defined forced rotation during induction heating and solidification. The resulting microstructure of the Nd-Fe-B alloys in consideration of melt convection has been investigated using scanning electron probe microscopy. The determination of the a-Fe volume fraction by measuring the magnetic moment in a vibrating sample magnetometer (VSM) resulted in a distinct reduction of the a-Fe volume fraction in samples with high crucible rotation frequencies. Furthermore, the investigation has been extended the peritectic Ti-Al system. It could be shown that the secondary dendritic arm spacing of the properitectic phase reduces with increasing forced sample rotation frequency.
  • Lecture (Conference)
    DPG-Jahrestagung, 27.-31.03.2006, Dresden, Germany

Publ.-Id: 8435 - Permalink


Influence of energetic ions and neutral atoms on the L10 ordering of FePt films
Cantelli, V.; von Borany, J.; Fassbender, J.ORC; Grenzer, J.
With respect to future magnetic recording materials, the L10-ordering of stoichiometric FePt films (70 nm) deposited on amorphous SiO2 by dc magnetron co-sputtering has been studied. A low deposition rate (0.6 Å/s) and Ar pressure (0.3 Pa) was used. The kinetics of structural A1 - L10 transition and the degree of ordering have been investigated with in-situ X-ray diffraction at the Synchrotron beam line ROBL at ESRF. The transition to almost complete ordered L10 films with an ordering parameter S > 0.8 has been obtained at low temperatures of (320 +/- 20)°C. An additional post-deposition ion irradiation with He ions at RT or at 250°C (50 keV, 1x1015 - 3x1016 cm-2) does not influence this low transition temperature. Theoretical calculations reveal that for our experimental conditions no thermalization of the sputtered atoms and the reflected Ar neutrals in the plasma occur; thus, a considerable fraction of energetic ions and neutrals meet the substrate with energies partly exceeding the displacement threshold. The low transition temperature is explained in the reduction of the activation energy for atomic reordering by point defects which becomes mobile at temperatures higher or equal to 250°C. Using operating conditions with a strong thermalization (deposition at 2 Pa), the FePt film showed an increase of the transition temperature to 400°C and a reduced film density. Finally, the results of first experiments towards patterned L10 ordered FePt layers will be reported.
Keywords: FePt, L10 transition, magnetron sputtering process, ion irradiation
  • Poster
    IBMM 2006, 18.-22.09.2006, Taormina, Italy

Publ.-Id: 8434 - Permalink


Magnetic, structural and electronic properties of Fe implanted GaN
Talut, G.; Reuther, H.; Eichhorn, F.; Mücklich, A.; Potzger, K.;
The request for room-temperature diluted magnetic semiconductors resulted in a large interest in GaN containing transition metals. In contrast to the (Ga,Mn)N-system, the origin of the ferromagnetism in Fe implanted GaN is still not sufficiently investigated. The formation of secondary phases and valence states of Fe play an important role in the discussion of the source of the ferromagnetism.
In this study, the electronic, structural and magnetic properties of p-GaN implanted with Fe+ (1 - 16 · 1016 cm^-2) at 350° C and subsequently annealed at 650° - 1000° C were examined by conversion electron Mössbauer spectroscopy, x-ray diffraction, transmission electron microscopy and magnetometry.
First experiments show ferromagnetic behaviour above room temperature in samples implanted with the highest amount of Fe. First x-ray diffraction and conversion electron M¨ossbauer spectroscopy measurements reveal the creation of alpha-Fe-clusters which are most likely responsible for the ferromagnetism.
Keywords: Spintronics, ferromagnetism, (Ga,Fe)N, Mössbauer, clusters
  • Lecture (Conference)
    DPG - spring meeting of the Division Condensed Matter, EPS - 21st General Conference of the Condensed Matter Division, 26.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8433 - Permalink


Oberflächenmodifikation von Titanlegierungen mit einem niederenergetischen starken Elektronenstrom bei höheren Ausgangstemperaturen
in Russian
Rotstein, V. P.; Günzel, R.; Markov, A. B.; Proskurovskij, D. I.; Pham, M. T.; Richter, E.; Shulov, V. A.;
wird nachgereicht
Keywords: titan alloy, surface modification, elektron beam
  • Fisika i khimiya obrabotki materialov (2006)1, 62-72

Publ.-Id: 8432 - Permalink


Influence of energetic ions on the L10 ordering of FePt films fabricated by magnetron sputtering
Cantelli, V.; von Borany, J.; Grenzer, J.; Fassbender, J.ORC
Due to the high uniaxial anisotropy L10-ordered FePt is currently the most favored candidate for future high density storage applications. With respect to a feasible fabrication technology, it is necessary (i) to produce such films on amorphous substrates, and (ii) to enable a low processing temperature (T<400°C). FePt films deposited at RT only exhibit the face-centered cubic A1-phase. Thus, either deposition or a post-deposition heat treatment at temperatures above typically 500°C is required, in order to achieve the L10-phase. We report on the L10 ordering of stoichiometric FePt thin films fabricated on SiO2/Si substrates by magnetron sputtering at various temperatures (RT - 400°C). Using a low deposition rate of about 0.6 Å/s and an Ar pressure of 0.3 Pa the ion/atom-ratio during deposition is » 1 where the ions exhibit energies of about 20 eV. In addition, FePt films have been irradiated subsequently with He ions of 50 keV and fluencies between 1x1015 and 3x1016 cm−2 for comparison. The kinetics of A1-L10 transition and ordering have been investigated with in-situ X-ray diffraction at the Synchrotron-beamline ROBL at ESRF. L10 ordered FePt films with an ordering parameter S=0.8 have been achieved already for an overall process temperature below 350°C. The results are discussed in terms of ion-assisted activation and segregation which supports the atomic relocation during L10 ordering.
Keywords: FePt, L10 transition, magnetron sputtering, ion irradiation
  • Lecture (Conference)
    DPG - spring meeting of the Division Condensed Matter, EPS - 21st General Conference of the Condensed Matter Division, 26.-31.03.2006, Dresden, Germany

Publ.-Id: 8431 - Permalink


Bakterien - die heimlichen Herrscher unserer Erde
Raff, J.;
Bakterien waren die ersten Lebewesen auf unserem Planeten. Über die Jahrmilliarden haben sie gelernt, sich an jeden noch so unwirtlichen Lebensraum anzupassen und nahezu jede noch so komplexe chemische Verbindung abzubauen. Fälschlicherweise haben sie sich insbesondere als Krankheitserreger einen „Namen“ gemacht. Bei genauerer Beschäftigung mit diesen kleinsten Lebewesen wird nämlich schnell klar, dass es sich dabei nur um Ausnahmeerscheinungen handelt. Nach vorsichtigen Schätzungen kennt man zwar nur etwa 1 % aller Bakterien, aber es ist unumstritten, dass nur durch ihre Aktivität das Leben in seiner heutigen Form möglich geworden ist. Neben ihrem fundamentalen Beitrag zur Entstehung der heutigen Atmosphäre und damit der Grundlage unseren Lebens, sorgen sie außerdem dafür, dass die Kreisläufe der Natur nicht zum Erliegen kommen.
Der Vortrag soll dazu einen Überblick geben und am Beispiel ungewöhnlicher Leistungen sowie besonderer Eigenschaften der Bakterien deren Anwendungspotential vor dem Hintergrund der Arbeiten am Forschungszentrum Rossendorf aufzeigen.
  • Lecture (others)
    Tag des offenen Labors, 20.05.2006, Dresden, Germany

Publ.-Id: 8430 - Permalink


Ion erosion induced ripples as templates for ultrathin magnetic films – ripple-induced anisotropies
Liedke, M. O.; Liedke, B.; Keller, A.; Rossbach, S.; Facsko, S.; Fassbender, J.ORC
The substrate/interface morphology and roughness plays a crucial role for the determination of the magnetic properties of ultrathin films. An anisotropic roughness can easily create magnetic anisotropy contributions of the same symmetry. It will be demonstrated that ion erosion fabricated ripples can be used to tailor the magnetic anisotropy and lead to a dramatic enhancement of the uniaxial magnetic anisotropy of Permalloy by a factor of up to 20.
By means of 500 eV Ar+ ion erosion a rippled Si surface with a well defined periodicity (20 – 60 nm) and peak to valley height (2 – 5 nm) is created. The surface topography is investigated by means of atomic force microscopy. On top of this naturally oxidized surface, first a metallic buffer layer and then a 9 nm thin Permalloy layer is deposited by means of thermal evaporation. Depending on the buffer layer material (Cr, Mn, Pt, Cu) and thickness (0 – 20 nm) the ripple morphology is reproduced to a variable extent by the Permalloy film. The magnetization reversal behavior and the ripple-induced magnetic anisotropies are investigated by means of magneto-optic Kerr effect measurements and correlated to the interface morphology. An easy route for the tailoring of magnetic anisotropies is shown.
Keywords: magnetism, ion erosion, ripples, induced anisotropies
  • Poster
    IBMM 2006, 18.-22.09.2006, Taormina, Italia

Publ.-Id: 8428 - Permalink


Tailoring magnetic properties by implantation doping of thin Ni81Fe19 layers
Fassbender, J.ORC; von Borany, J.; Mücklich, A.; Potzger, K.; Möller, W.; McCord, J.; Schultz, L.; Mattheis, R.
The layer magnetization, the saturation magnetization as well as the magnetic anisotropy and damping behavior of 20 nm thick Ni81Fe19 films have been modified by 30 keV Cr, Ni and Co ion implantation with fluences up to 11016 ions/cm2 ( 5 atom-%). As a function of fluence first an improvement of the (111) fiber texture, then a lattice expansion and finally a partial amorphization of the interface near region of the Ni81Fe19 layer is found. The region of amorphization can be understood quantitatively by the concentration profiles as a function of depth in combination with irradiation induced damage formation. The magnetic properties change correspondingly. Magneto-optic Kerr effect magnetometry and inductive techniques have been used to determine the layer magnetization and the static magnetic anisotropy. A strong reduction of the magnetization with increasing implantation fluence is found. This reduction can be decomposed in a reduction of the active magnetic layer thickness and a reduction of the saturation magnetization. The latter one has been determined by means of pulsed inductive microwave magnetometry. This technique allows in addition the determination of the dynamic anisotropy, the relaxation rate and the magnetic damping constant. A reduction in magnetic anisotropy and a strong increase of the magnetic damping behavior is observed as a function of implantation fluence which is mainly attributed to doping effects. However, also radiation induced damage effects have to be considered in order to fully understand the change in magnetic properties.
Keywords: magnetism, magnetic anisotropy, saturation magnetization, magnetic damping, ion implantation
  • Lecture (Conference)
    IBMM 2006, 18.-22.09.2006, Taormina, Italia

Publ.-Id: 8427 - Permalink


Memory effects in interacting and non-interacting ion beam synthesized nanoparticle systems
Zhang, G.; Potzger, K.; Zhou, S.; Mücklich, A.; Ma, Y.; Fassbender, J.ORC
The magnetic properties of both interacting and non-interacting iron nanoparticle systems were investigated by means of SQUID magnetometry. Both nanoparticle systems were produced by ion beam synthesis. For this purpose Fe+ was implanted into diamagnetic LaAlO3 substrates with a fluence of 6×1016 cm-2 at an energy of 120 keV at either 400°C or 800°C. It is observed that for the lower (higher) temperature a non-interacting (interacting) nanoparticle ensemble is created. The size distribution of the nanoparticles is studied by transmission electron microscopy. The memory effects in these systems were investigated by field-cooling and zero field-cooling magnetization measurements. Both analysis methods should help to settle the controversy whether the interaction between superparamagnetic particles or their size distribution is responsible for the memory effect [1, 2].

[1] Y. Sun et al., Phys. Rev. Lett. 91, 167206 (2003).
[2] R. K. Zheng et al., Phys. Rev. Lett. 93, 139702 (2004).
Keywords: magnetism, memory effects, nanoparticles, ion beam synthesis
  • Poster
    IBMM 2006, 18.-22.09.2006, Taormina, Italia

Publ.-Id: 8426 - Permalink


Laser induced precessional switching in exchange biased NiFe/FeMn bilayers
Weber, M.; Blomeier, S.; Hillebrands, B.; Fassbender, J.ORC
Laser pulse induced field assisted precessional switching in exchange coupled mesoscopic NiFe/FeMn striplines has all-optically been triggered and magneto-optically observed in real time with switching times down to 500 ps. A fast decoupling of the exchange bias bilayer launches coherent precession of the magnetization of the ferromagnetic layer of the exchange bias system. By properly choosing the initial equilibrium orientation the optical unpinning of the bilayer can induce complete magnetization switching. Stroboscopic time domain imaging of the switching event has been realized by a sophisticated synchronization scheme of a magnetic preset pulse and both the optical pump and probe pulses, respectively. The observed laser assisted switching can be well described by the Landau-Lifshitz-Klaasen-van Peppen equation combining precessional and thermally activated spin dynamics.
Keywords: magnetism, magnetization dynamics, all-optical, pump-probe, exchange bias
  • Poster
    21st General Conference of the EPS Condensed Matter Division, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8425 - Permalink


Magnetization reversal in NiFe/FeMn ion irradiated patterns
Candeloro, P.; Blomeier, S.; Beck, A.; Schultheiss, H.; Nembach, H.; Hillebrands, B.; Liedke, M. O.; Fassbender, J.ORC; Reuscher, B.
Recently ion irradiation has been proposed as a patterning tool for different magnetic systems. The increasing interest for this technique is due to the capability of tailoring the magnetic properties without affecting the sample topography. We present a study of the magnetic properties of patterns with different geometries produced by ion irradiatio on a Ni81Fe19/Fe50Mn50 exchange bias bilayer by magneto-optic Kerr effect (MOKE) magnetometry and magnetic force microscopy (MFM). The hysteresis loops measured by MOKE present features evidently related to the irradiated geometries. Moreover they also reveal that the magnetization reversal is not proceeding independently in irradiated and non-irradiated areas. This magnetic coupling is confirmed by MFM images, which clearly show that magnetic domains in irradiated and non-irradiated elements are mutually influencing each other during the reversal process. Comparison with previous studies indicates that the above mentioned coupling dramatically affects the reversal process only when the lateral size of irradiated elements approaches a characteristic coupling length.
Keywords: magnetism, exchange bias, ion irradiation, MOKE, MFM, domains, patterning
  • Poster
    21st General Conference of the EPS Condensed Matter Division, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8424 - Permalink


Diluted magnetic semiconductors created by non-equilibrium processing -new challenges for ion beams
Potzger, K.; Zhou, S.; Zhang, G.; Reuther, H.; Talut, G.; Mücklich, A.; Eichhorn, F.; Schell, N.; Grötzschel, R.; Skorupa, W.; Helm, M.; Anwand, W.; Brauer, G.; Fassbender, J.ORC
Diluted magnetic semiconductors (DMS) are based on common semiconducting material like GaAs, Si, Ge, InP, GaN or ZnO doped with a few percent of a transition or rare earth metal. While early work has been performed mainly by polish groups in the 1970ies and 80ies, DMS have attracted worldwide scientific attention during the last 5 years due to their application potential in spintronics. This was triggered by the discovery of ferromagnetic GaMnAs and the theoretical prediction of room temperature ferromagnetism for ZnO:Mn and GaN:Mn by T. Dietl and H. Ohno [1]. One of the main obstacles while creating a DMS is secondary phase formation. Since solubility limits are rather low, non-equilibrium doping techniques like low temperature film growth are commonly used. On the other hand, ion implantation offers superb possibilities for low temperature doping but is always connected with lattice damage of the target material. Combining ion implantation with another non-equilibrium technique, i.e. rapid thermal annealing, leads to a diluted state while the crystallinity of the target material is restored. This has been shown for Si:Mn [2].
Recently, we investigated the secondary phase formation for Fe,Co and Ni as well as Gd, Tb implanted in ZnO single crystals. We found, that at an implantation temperature of 623 K tiny superparamagnetic nanoparticles are formed in all transition metal (TM) doped samples. These phases can hardly be identified using lab X-ray diffraction (XRD), e.g. in the case of Fe. Only application of high resolution methods like synchrotron XRD, susceptometry, Mössbauer spectroscopy and transmission electron microscopy allows their identification [3]. On the other hand, rare earth implanted samples show a diluted state up to annealing temperatures of 823 K. For both ZnO:Tb and ZnO:Gd a ferromagnetic order was found. Low temperature TM implantation (253 K) leads to a 100% diluted state. The TM-ions however do not couple magnetically that can be caused by the lattice damage introduced due to the implantation. Very rapid thermal processing using flash lamps with 20 ms pulse width leads to a significant recovery of the lattice order, while only a small amount of nanoparticles is created.


Reference
[1] T. Dietl, et al., Science 287, 1019 (2000).
[2] M. Bolduc, et al., Phys. Rev. B 71, 033302 (2005).
[3] K. Potzger, et al., Appl. Phys. Lett. 88, 052508 (2006).
Keywords: diluted magnetic semiconductors, ZnO, ion implantation
  • Lecture (Conference)
    IBMM 2006, 18.-22.9.2006, Taormina, Italy
  • Lecture (Conference)
    EMRS Fall Meeting 2006, 04.-8.9.2006, Warschau, Poland
  • Invited lecture (Conferences)
    Fachbereichsseminar der AG W. D. Brewer, Freie Universität Berlin, 8.11.2006, Berlin, Deutschland
  • Invited lecture (Conferences)
    Fachbereichsseminar der AG B. K. Meyer, Universität Giessen, 2.2.2007, Giessen, Deutschland
  • Invited lecture (Conferences)
    Institutseminar des Physikalischen Instituts der Universität Karlsruhe, 6.11.2006, Karlsruhe, Deutschland

Publ.-Id: 8423 - Permalink


Einfluss der mittleren freien Weglänge von Positronenstrahlern auf das Auflösungsvermögen im 3D Tier-PET Scanner unter Verwendung verschiedener Rekonstruktionsalgorithmen
Höhne, R.; Will, E.; Lüdemann, L.; Ruf, J.; Jaeschke, E.; Felix, R.; Amthauer, H.;
Ziel/Aim:
In klinischen PET Scannern ist das räumliche Auflösungsvermögen durch physikalische Größen wie der Gantry und der Kristallgröße (zur Zeit 4 x 4 mm) limitiert. Dagegen ist im Tier-PET das räumliche Auflösungsvermögen durch eine kleine Gantry und eine geringere Kristallgröße (2 x 2 mm) erhöht, sodaß dem Einfluß der mittleren freien Weglänge der Positronen bei Verwendung unterschiedlicher Nuklide für die Entwicklung neuer PET Radiopharmaka eine erhebliche Bedeutung zukommen könnte.

Methodik/Methods:
Es wurden bei 3 Radionukliden (F-18, O-15, Ga-68) je 2 Phantommessungen durchgeführt. Die Messungen erfolgten mit einem MOSAIC PET Scanner der Firma Philips an dem Tier-PET Phantom 50/106 der Firma BS Industrieelektronik & Medizintechnik. Das Phantom hat insgesamt 298 Kanäle mit Durchmessern in Stufen von 1,0 mm, 1,5 mm, 2,0 mm, 2,5 mm und 3,0 mm. Die Phantommessungen wurden ohne Schwächungskorrektur mit 0,5 mm Auflösung und unterschiedlichen Methoden (3D Ramla, Ramla, Iterativ, Butterworth-FTB, Gaussian-FTB, Hanning-FTB) rekonstruiert. Zuerst wurde das Auflösungsvermögen bei F-18, O-15 und Ga-68 visuell verglichen. Es wurde dann beim kleinsten gemeinsamen Auflösungsniveau jeweils der mittlere Kontrast (Differenzsignal/Hintergrundsignal) für die obengenannten Rekonstruktionen ermittelt.

Ergebnisse/Results:
Visuell konnten mit F-18 noch 1,5 mm Kanäle, mit O-15 und Ga-68 2,0 mm Kanäle aufgelöst werden, es ergab sich kein nennenswerter Unterschied bezüglich der jeweiligen Rekonstruktionsmethode. Die Kontrastermittlung erfolgte daher bei 2,0 mm Kanaldurchmesser. Hingegen wurde beim semiquantitativen Vergleich der verschiedenen Rekonstruktionsverfahren der höchste Kontrast für jedes Nuklid mit 3D Ramla erzielt. Die mittleren Kontraste für die Rekonstruktion mit 3D Ramla lag bei 1,36 für F-18, bei 1,23 für O15 und bei 0,78 für Ga-68.

Schlussfolgerungen/Conclusions:
Die Phantommessungen im Tier-PET zeigen zum einen eine deutliche Abhängigkeit von Auflösung und Kontrast vom jeweiligen Rekonstruktionsverfahren, wobei der Rekonstruktionsparameter 3D Ramla die besten Ergebnisse erzielte. Zum anderen wurde der Einfluss der mittleren freien Weglänge des jeweiligen Isotops auf die Auflösung demonstriert. Beide Einflussgrößen müssen bei der Anwendung eines Tier-PETs für die zu erreichende Auflösung berücksichtigt werden.
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A125

Publ.-Id: 8422 - Permalink


Quantifizierung des Uptake von Rhenium-188-HEDP im trabekuären und kortikalen Knochen sowie in Knochenmetastasen im Tierversuch
Liepe, K.; Geidel, H. H.; Bergmann, R.; Barth, M.; Runge, R.; Kotzerke, J.;
Ziel/Aim:
Die MIRDDOSE Annahme einer 50% zu 50% Verteilung knochenaffiner Radiopharmaka im kortikalen und der trabekulären Knochen sowie einer homogene Anreicherung in den Knochenmetastasen dürfte nicht den reellen Verhältnissen entsprechen.

Methodik/Methods:
Ein Modell zur Induktion von osteoblastischen Knochenmetastasen wurde durch intra-ossäre Injektion von Prostata-Karzinomzellen bei Kopenhagenratten in einer Vorversuchsserie entwickelt. In histologischen Untersuchungen konnte das Vorliegen von osteoblastischen Knochenmetastasen bewiesen und diese szintigraphisch dargestellt werden.

Bei 45 Kopenhagenratten (Alter: 9 ± 2 Monate, Gewicht: 318 ± 22g) wurden jeweils 100.000 R3327 Mat-Ly-Tu Zellen in beide Femura injiziert. Ab dem 12. Tag nach Zellapplikation war makroskopisch ein Tumor gut sichtbar. 17 ± 1 Tage nach Tumorzellapplikation erfolgte die Applikation von 134 ± 53 MBq Re-188-HEDP sowie nachfolgend die Tötung von jeweils 15 Tiere 4, 24 und 48 Stunden. Coronare Gefrierschnitte (Cryopolycut, Leica, 40 #mikro#m dick) wurden autoradiographisch mit einer Auflösung von 0,5 #mikro#m (BAS 500, Fuji) untersucht. Mittels ROI-Technik erfolgte die Bestimmung der Anreicherung des Re-188-HEDP pro mm3. Nachfolgend wurden die Verhältnisse zwischen Tumor und normaler Knochen (T/NT) berechnet, sowie die Verteilung im kortikalen und der trabekulären Knochen quantifiziert.

Ergebnisse/Results:
Es zeigte sich eine Verteilung im kortikalen und der trabekulären Knochen von 33,5% zu 66,5% nach 4h, von 34,6% zu 65,4% nach 24h und von 35,9% zu 64,1% nach 48h (p = 0,788 bis 0,871). In den Knochenmetastasen zeigte sich eine stark inhomogene Anreicherung mit einer minimalen und maximalen T/NT von 3:1 und 14:1 nach 4h, von 5:1 und 14:1 nach 24h sowie von 5:1 und 16:1 nach 48h, der Anstieg über die Zeit ist nicht signifikant. Die maximale Anreicherung in einer Metastase betrug 22:1. Bei erneuter Berechnung der Knochenmarkdosis aus vorliegender Daten einer Rhenium-188-HEDP Therapie beim Menschen, ergab sich bei einer Zugrundelegung einer Verteilung von 35% zu 65% (kortikal zu trabekulär) eine um 135% höhere Dosis als bei einer Verteilung von 50% zu 50%.

Schlussfolgerungen/Conclusions:
Das MIRDOSE Schema unterschätzt die reelle Dosis im Knochenmark. Die stark inhomogene Anreicherung in den Knochenmetastasen führt zu einer inhomogenen Dosisverteilung in den Metastasen, bei Anwendung von Betastrahlern mit einer höheren Beta-Energie lässt sich eine homogenere Dosisverteilung erreichen.
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A112

Publ.-Id: 8421 - Permalink


Automatisierte Koregistrierung von dynamischen FDOPA PET-Studien: Anwendung als Bewegungskorrekturmethode
Hofheinz, F.; Pötzsch, C.; van den Hoff, J.;
Ziel/Aim:
Dynamische PET-Studien mit FDOPA erlauben die Beurteilung des striatalen Dopamin-Uptakes und sind damit ein wichtiges Werkzeug in der Diagnose des Morbus Parkinson. Diese Aufnahmen erfordern typischerweise Akquisitionszeiten von ein bis zwei Stunden während deren die Patientenbewegung nicht vollständig vermieden werden kann. Diese Bewegung kann die Analyse der Tracerkinetik stark beeinträchtigen oder gar unmöglich machen. Ziel dieser Arbeit ist eine routinetaugliche Methode um die Patientenbewegung in den PET-Volumina zu korrigieren. Dazu stellen wir eine Methode zur Bewegungskorrektur vor, die auf der vollautomatischen Koregistrierung der dynamischen Studien beruht.

Methodik/Methods:
Es wurden 33 dynamische FDOPA Studien koregistriert und bezüglich der Effekte der Patientenbewegung untersucht. Die Koregistrierung basiert auf starren Transformationen, wobei die besten Transformationsparameter durch Maximieren der Mutual Information (MI) erhalten werden. Die Maximierung der MI erfolgt mittels der Methode der konjugierten Gradienten. Alle Frames der dynamischen Studien wurden gegen das letzte Frame der jeweiligen Studie vollautomatisch koregistriert. Der FDOPA-Uptake im Striatum wurde in den unkorrigierten und in den korrigierten Daten mit einem Referenz-Tissue Zwei-Kompartment Modell bestimmt. Zum einen wurden aus den dynamischen Studien parametrische Bilder erstellt, aus denen sich der FDOPA-Uptake ermittelt lässt. Zum anderen ergab sich der Uptake aus den Zeitaktivitätskurven der in den parametrischen Bildern festgelegten ROIs. Die Ergebnisse für unkorrigierte und bewegungskorrigierte Bilddaten wurden verglichen.

Ergebnisse/Results:
In 16 der 33 Studien führte die Patientenbewegung zu Artefakten in den parametrischen Bildern und zu einem bis zu 70 % über- bzw. unterbewerteten FDOPA-Uptake im Striatum. Dieser Effekt war auch in den Zeitaktivitätskurven deutlich sichtbar. Die angewandte Koregistrierung vermochte in allen untersuchten Studien die Patientenbewegung zu korrigieren. Das verwendete Programm benötigte ca. 10 min. Rechenzeit je Studie (21 Frames) auf einem durchschnittlichen Computersystem. Studienabhängige Einstellungen von Registrierungsparametern waren hierbei nicht notwendig, was eine zuverlässige Stapelverarbeitung von Serien von Studien erlaubt.

Schlussfolgerungen/Conclusions:
Die robusten Ergebnisse und die einfache Handhabung erlauben einen routinemäßigen Einsatz dieser Bewegungskorrekturmethode.
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A32

Publ.-Id: 8420 - Permalink


Möglicher Einfluss von F-18-3-O-methyl-fluordopa (OMFD) und Positronen-Emissions- Tomographie (PET) auf die Bestrahlungsplanung von Hirntumoren
Beuthien-Baumann, B.; Alheit, H.; Oehme, L.; Winkler, C.; Füchtner, F.; Höpping, A.; Kotzerke, J.;
Ziel/Aim:
Die Bestrahlungsplanung beruht auf einem komplexen Zielvolumenkonzept, dass die Tumorregion erfassen (gross tumor volumen,GTV), subklinische Tumorausdehnung beinhalten und Lagerungsinkonsistenzen zwischen den einzelnen Bestrahlungsfraktionen ausgleichen soll (planning target volumen, PTV). Der Einfluss der OMFD-PET auf die Bestrahlungsplanung von Hirntumoren wurde anhand folgender Fragen untersucht: Wurden mit OMFD-PET Tumorareale angezeigt, die nicht vom konventionell erstellten PTV erfasst wurden? Könnte das Einbeziehen von OMFD-PET in die Bestrahlungsplanung das PTV im Vergleich zur konventionellen Planung potenziell verkleinern?

Methodik/Methods:
Bei 30 Patienten mit malignen Hirntumoren wurde OMFD-PET nach subtotaler Resektion und vor Strahlentherapie durchgeführt. Die PET-Daten und soweit vorhanden prä- und postoperative T1-gewichtete MRT-Studien wurden retrospektiv mit dem Planungs-CT am Bestrahlungsplanungssystem Pinnacle 3 überlagert. Die Tumorareale im PET und Kontrastmittelanreicherung im MRT wurden als einzelne GTV markiert und in das Planungs-CT integriert. Es erfolgte der Vergleich der GTV-OMFD und GTV-MRTprä/post mit dem GTV-konv, das allein auf dem Planungs-CT und der visuellen Bildbeurteilung des MRT beruht.

Ergebnisse/Results:
Bei 28 von 30 Patienten war Tumorgewebe mittels OMFD-PET abgrenzbar. Ein Patient zeigte einen multifokalen Befall, so dass die primär kurative Therapieintention in ein palliatives Konzept geändert wurde. Alle im OMFD-PET abgrenzbaren Tumorregionen waren im konventionell erstellten PTV enthalten. Die mittleren Volumina betrugen 69,2 #±# 42,2ccm für das GTV-konv, 48,0 #±# 43,8ccm für das GTV-MRTprä, 16,8 #±# 15,5ccm für das GTV-MRTpost und 14,8 #±# 12,3ccm für GTV-OMFD. Der differentielle Vergleich der Volumina ergab, dass bei 5 von 29 Patienten mehr als 10 ccm der GTV-OMFD außerhalb des GTV-konv und bei 8 von 26 Patienten außerhalb des GTV-MRTpost lokalisiert waren. Bei 6 von 26 Patienten lagen mehr als 10ccm des GTV-MRTpost außerhalb des GTV-OMFD.

Schlussfolgerungen/Conclusions:
Die funktionelle Bildgebung von Hirntumoren mittels OMFD-PET detektiert relevantes Tumorgewebe außerhalb der im MRT detektierten Tumorregion und erbringt somit wichtige Informationen für die Abgrenzung des GTV für die Bestrahlungsplanung. Multimodale Strahlentherapieplanung beinhaltet das Potential die Hochdosisregion genauer abgrenzen und so möglicherweise die Ausdehnung des PTV begrenzen zu können.
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A71

Publ.-Id: 8419 - Permalink


Effects of oligosaccharide derivatives on the metabolism of tumor cells
Kampfrath, T.; Oswald, J.; Bergmann, R.; Schwenzer, B.;
Ziel/Aim:
This study investigates the effect of oligosaccharide derivatives on proliferation, metabolic activity and apoptosis of cultivated tumor cells. The effect of a complex oligosaccharide derivative of marine origin with anti-tumor activity has been compared with a defined trimeric oligosaccharide based on chitosan.

Methodik/Methods:
The human bladder carcinoma cell line EJ-28 was used as tumor model and compared to the human fibroblast cell line NHDF 6369. For quantification of the glucose metabolism [F-18]FDG-uptake was measured. The starting activity was 60 MBq in 10 ml culture medium. The cells were incubated for one hour. The incorporated activity was measured with a gamma counter. Further we studied the programmed cell death with flow cytometry. Early phase of apoptosis was detected by annexin staining and late phase by propidium iodide staining. The protein kinase inhibitor staurosporine was used as control substance in all experiments.

Ergebnisse/Results:
EJ-28 cells treated for 24 hours with oligosaccharide derivatives and chitosan trimers showed a decreased [F-18]FDG-uptake of about 50% in comparison to the untreated reference. On the other hand NHDF 6369 incubated by these agents showed an increased [F-18]FDG-uptake up to 150%. The protein kinase inhibitor staurosporine decreased the [F-18]FDG-uptake to 10% in both cell lines. Furthermore incubation for 24 hours increased the rate of apoptosis. Oligosaccharide derivatives and chitosan trimer were able to raise the rate of apoptosis in EJ-28 from 7% (6 h incubation) to 60% (24 h incubation). In NHDF 6369 cells the substances induced an increase of apoptosis rates from 15% (6 h) to 40% (24 h). Staurosporine increased the apoptosis rates from 20% (6h) to 65% in EJ-28 and 35% in NHDF 6369 (24h) in both cell lines, respectively.

Schlussfolgerungen/Conclusions:
Our data showed a reduced metabolic activity and increased apoptosis rates of cultivated tumor cells treated with oligosaccharide derivatives and chitosan derived trimers. The effects of chitosan trimers were comparable to the effects of the oligosaccharide derivatives of the marine nature material.
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A87

Publ.-Id: 8418 - Permalink


In vitro Untersuchungen zur Stabilität von Er-169-Citrat-Kolloid
Bergmann, R.; Pinkert, J.;
Ziel/Aim:
Er-169-Citrat-Kolloid (ERMM-1) wird in der Radiosynoviorthese eingesetzt. Die Mechanismen der Retention, des Abstroms und besonders die des lokalen Metabolismus der Kolloide in vivo sind noch nicht komplett verstanden. Deshalb sollte in vitro, unter definierten Bedingungen, ihr Diffusionsverhalten in der Gleichgewichtsdialyse, das Rückschlüsse auf die Größenverteilung der Kolloide und ihre Stabilität zulässt, untersucht werden.

Methodik/Methods:
Geträgertes Er-169-Citrat-Kolloid (fertiges Arzneimittel) und Filtrat des Er-169-Citrat-Kolloid (0,22 µm-Filter), welches die nanokolloidale Fraktion (Durchmesser kleiner 100 nm) enthält, wurden in einem Gleichgewichtsdialysesystem mit Synovia, verschiedenen Elektrolyt- und Pufferlösungen dialysiert (cut off der Membran 10000 Dalton). Die Zeit/Aktivitätsverteilung in den Dialysekompartimenten wurde für die einzelnen Präparationen bis zum Erreichen des Gleichgewichts untersucht. Als Referenzpräparate wurden Tl-201-Chlorid, F-18-FDG und Er-169-Chlorid verwendet.

Ergebnisse/Results:
Das ionische Erbium-169-Chlorid (Negativkontrolle) diffundiert praktisch mit der gleichen Kinetik wie die niedermolekularen Referenztracer. Die kolloidalen Er-169-Citrat Fraktionen zeigen bei Inkubation mit einer dem Plasma vergleichbaren Elektrolytlösung (MEM-Medium nach Dulbecco), humaner Synovia oder phosphathaltigen Puffern eine weitgehend fehlende Dialysierbarkeit, weniger als 0,5% der eingesetzten Aktivität werden dabei im Dialysemedium gefunden. Im Gegensatz dazu kommt es bei Inkubation mit physiologischer Natriumchloridlösung zu einer deutlichen Freisetzung von dialysierbaren Erbium (ca. 62%).

Schlussfolgerungen/Conclusions:
Das Verhalten der Kolloidpräparationen wird in erster Linie durch die Anwesenheit von Phosphationen erklärbar. Auf Grund sehr geringer Löslichkeit von Erbiumphosphat wird bei Inkubation der nanokolloidalen Fraktion mit Synovia und phosphathaltigen Puffern eventuell vorhandenes bzw. sekundär gebildetes ionisches Erbium ausgefällt. Dies führt zur Bildung neuer, sekundärer Erbium-Phosphat-Kolloide bzw. zur Stabilisierung und Wachstum bereits vorhandener Erbium-Citrat-Kolloide. Dieser Mechanismus der Stabilisierung der Kolloide durch Phosphationen scheint hauptsächlich für die Fixierung der Er-169-Aktivität in den Gelenken verantwortlich sein bevor die Kolloide durch die Deckzellen der Synovialis phagozitiert werden.
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A89

Publ.-Id: 8417 - Permalink


Experimentelle Hypoxie induziert eine erhöhte Radiotracer-Aufnahme in primären Endothelzellen in vitro
Oswald, J.; Haase, C.; Bergmann, R.;
Ziel/Aim:
Die Radiotracer-Aufnahme von hypoxischen Arealen in solidem Tumorgewebe ist ein wichtiger Parameter für die Visualisierung von Tumoren mit PET. Das Ziel des vorgestellten Projekts ist die Bewertung von Endothelzellen hinsichtlich ihrer Radiotraceraufnahme unter hypoxischen Bedingungen.

Methodik/Methods:
Verschiedene humane primäre Endothelzellen aus der Nabelschnurvene (HUVEC), der Aorta (HAEC) und der Haut (HDMEC) wurden neben etablierten Tumorzelllinien FaDu und HT-29 verwendet. Experimentelle Hypoxie wurde mit einem speziellen Inkubator (Gasboy, Labotect, Göttingen) erzeugt. Nach 24h Kultivierung unter hypoxischen Bedingungen wurde die Expression der Gene HIF-1#alpha# und VEGF mit PCR analysiert sowie die Aufnahme der Radiotracer [Tc-99m]Sestamibi und [F-18]FDG gemessen.

Ergebnisse/Results:
Unter experimenteller Hypoxie wurde eine verstärkte Expression von HIF-1#alpha# sowie VEGF gemessen. Die Aufnahme von [Tc-99m]Sestamibi, einem Marker für die Intaktheit der Atmungskette, war in allen Zelltypen unter hypoxischen Bedingungen verringert. Die [F-18]FDG Aufnahme unter hypoxischen Bedingungen war sowohl von den verwendeten primären Endothelzellen als auch von Tumorzellen deutlich erhöht.

Schlussfolgerungen/Conclusions:
Primäre Endothelzellen nehmen wie Tumorzellen in Gegenwart von experimentell erzeugter Hypoxie vermehrt den Radiotracer [F-18]FDG auf. In vaskularisierten soliden Tumoren tragen Endothelzellen somit zur Anreicherung von Radiotracern bei und haben einen Einfluss auf die nachfolgende Bildgebung mit PET.
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A79

Publ.-Id: 8416 - Permalink


Charakterisierung der Neurotensin-Rezeptoren als potentielles Target für die Tumordiagnose via Radiomarkierung
Haase, C.; Oswald, J.; Bergmann, R.; Pietzsch, J.;
Ziel/Aim:
Peptidrezeptoren sind auf Grund ihrer gesteigerten Expression im Tumorgewebe für das molekulare Imaging von großem Interesse. Das molekulare und biochemische Verständnis dieser Rezeptoren wird für die Entwicklung repräsentativer Liganden via Radiomarkierung für die Tumordiagnose und Therapie genutzt. Die Charakterisierung der Neurotensin- Rezeptor (NTR) Familie als wichtiges Target für die Tumordiagnose und Therapie ist Gegenstand dieser Arbeit.

Methodik/Methods:
In der vorliegenden Arbeit wurde die Expression der NTR in kultivierten HT-29 (humanes Adenokarzinom) und FaDu ( humanes Plattenepithelkarzinom) Zellen sowie in den entsprechenden xenogenen Tumortransplantaten untersucht. Die mRNA Genexpression wurde mittels real-time PCR mit spezifischen Primern für die drei Rezeptorsubtypen quantifiziert. Die Analyse der Rezeptor-Proteinexpression erfolgte mittels Autoradiographie mit Tritium markierten Neurotensin und immunhistochemisch mit spezifischen Antikörpern gegen NTR1, 2 und 3.

Ergebnisse/Results:
Die Quantifizierung auf mRNA Ebene ergab in den HT-29 und FaDu Zellen eine 3,5fach höhere Expression von NTR3 im Vergleich zu NTR1. Die Expression von NTR3 im Vergleich zu NTR2 war um den Faktor 2,5 erhöht. Die mRNA Rezeptorverteilung in den entsprechenden Tumortransplantaten verhielt sich für NTR3 ähnlich stark wie in den Zellen. Ebenfalls konnte in den Transplantaten eine gesteigerte Expression von NTR1 um das 2fache für die HT-29 Transplantate und das 1,4fache für die FaDu Transplantate beobachtet werden. Auf Proteinebene wurde ein starkes immunpositives Signal für NTR1 in den Zellen und Geweben detektiert. Rezeptorprotein für NTR3 konnte in unseren Untersuchungen nicht nachgewiesen werden.

Schlussfolgerungen/Conclusions:
Aufgrund der hohen Proteinexpression, scheint NTR1 für die Tumordiagnose ein geeignetes Target via Radiomarkierung zu sein. Überdies stellt NTR 1 als G-Protein gekoppelter Rezeptor eine wichtige Funktion bei der intrazellularen Signalübertragung dar und ist zudem ein interessantes Target für die Entwicklung therapeutisch wirksamer Medikamente.
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A83

Publ.-Id: 8415 - Permalink


Catabolism of hypochlorite-modified low density lipoprotein (LDL) in vivo: insights from small animal PET studies
Hoppmann, S.; Steiniger, B.; Haase, C.; Pietzsch, J.;
Ziel/Aim:
Oxidative modification of LDL apolipoprotein (apo) B-100 by myeloperoxidase-generated hypochlorite (HOCL) is regarded as a crucial event in atherogenesis. Recently, HOCl-modified LDL (OCl-LDL) have been shown to be present in human atherosclerotic lesions. On the other hand, data concerning the role of circulating OCl-LDL in the development of atherosclerosis are scarce. One reason for this is the shortage of methods for direct assessment of metabolism of oxidized LDL in vivo. We report an improved methodology for radiolabeling of both native LDL (nLDL) and OCl-LDL with the positron-emitter fluorine-18 (F-18) by N-succinimidyl-4-(F-18)fluorobenzoate (F-18-SFB) and the use of F-18-fluorobenzoylated LDL particles in dynamic PET studies in rats.

Methodik/Methods:
As a model, nLDL were modified in vitro by 3 mM NaOCl. For radiolabeling, pools of chemically and biochemically well characterized human nLDL and OCl-LDL were used. Module-assisted synthesis of F-18-SFB resulted in radiochemical yields of 36±2% (corrected for decay) and purites of >95%.

Ergebnisse/Results:
LDL labeling with F-18-SFB resulted in radiochemical yield of 30±10% (nLDL; corrected for decay) and 10±5% (OCl-LDL), respectively, with specific radioactivity of 50-400 GBq/µmol. Radiolabeling of native and modified LDL using F-18-SFB caused neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality in vitro, respectively. The method was further evaluated with respect to the uptake of F-18-fluorobenzoylated native and modified LDL, respectively, in various human cells. Biodistribution studies in rats revealed high in vivo stability for the fluorine-18-fluorobenzoylated LDL. The metabolic fate of F-18-fluorobenzoylated nLDL and OCl-LDL particles in vivo was delineated by dynamic PET studies using a dedicated small animal positron emission tomograph. Dynamic PET data demonstrated a significantly enhanced catabolism of OCl-LDL when compared with nLDL. The in vivo distribution and kinetics of both native and modified LDL correlated well with the anatomical localization of LDL receptors and scavenger receptors.

Schlussfolgerungen/Conclusions:
F-18-SFB-labeling of LDL and the use of small animal PET provide a valuable tool to discriminate the kinetics and the metabolic fate of both native and oxidized LDL in animal models in vivo.
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A22

Publ.-Id: 8414 - Permalink


Vergleich der Inter-Observer-Variabilität bei manueller und automatischer Volumenbestimmung in der PET
Pötzsch, C.; Hofheinz, F.; van den Hoff, J.;
Ziel/Aim:
In (1) und (2) wurden bereits Verfahren vorgestellt, welche halbautomatisch zur Eingrenzung, Analyse und quantitativen Auswertung dreidimensionaler Strukturen innerhalb von PET-Bildvolumen dienen. Die dort beschriebene Schwellwertanalyse mittels Schwellwert über Untergrund und der damit verbundenen Untergrundsubtraktion, führen bei Phantommessungen zu einer Unsicherheit der Volumenbestimmung von unter 20%.

Das Ziel dieser Arbeit war es, die Inter-Observer-Variabilität(IOV) des Verfahrens anhand klinischer Datensätze zu überprüfen und mit der manuellen Schwellwertanalyse, also der interaktiven Festlegung eines von Benutzern als optimal bewerteten Schwellwertes, zu vergleichen.

Methodik/Methods:
Es wurden PET-Volumendatensätze aus dem Bereich der onkologischen Leberdiagnostik und Phantommessungen ausgewertet. Die Studien enthielten eine verschiedene Anzahl von interessierenden Strukturen (VOIs), die dreimal auf unterschiedliche Weise abgegrenzt werden mussten. Im ersten Schritt sollte der Observer die VOIs mittels der manuellen Methodik abgrenzen, im zweiten Schritt sollte er jede VOI einzeln mittels der automatischen Methode aus (2) abgrenzen und im dritten Schritt sollte er alle gesuchten VOIs gleichzeitig mittels der Methode aus (2) bestimmen. Die Zahl der vorläufig untersuchten VOIs ist n=24 und damit die der Abgrenzungen n=168.

Ergebnisse/Results:
Bei den betrachteten Datensätzen lieferten die in (2) vorgestellten Methoden sehr stabile Ergebnisse. Im Gegensatz dazu schwankten die ermittelten Volumen bei der manuellen Schwellwertanalyse zwischen den einzelnen Observern sehr stark.

Die IOV bei manueller respektiv automatischer Volumenbestimmung konnte im Mittel von ca. 30% auf ca. 10% reduziert werden, wobei das mittlere Volumen vergleichbar mit den Werten der manuellen Bestimmung ist.

Schlussfolgerungen/Conclusions:
Der Vergleich zeigt, dass der Einsatz automatischer Verfahren die IOV im Vergleich zu manuellen Verfahren deutlich reduziert. Prospektiv erscheint die implizierte Möglichkeit zur Standardisierung der PET-unterstützten Zielvolumendefinition von potentieller Bedeutung für die Strahlentherapieplanung.

Literatur/References:
(1) C.Pötzsch; B. Beuthien; J. van den Hoff; Teilautomatisierte Segmentierung zur Quantifizierung von Metastasen bei der FDG-PET; Nuklearmedizin (2003) 42 p. A26

(2) C.Pötzsch; F. Hofheinz; J. van den Hoff; Minimierung der Inter-Observer-Variabilität bei volumetrischen Auswertungen von onkologischen Ganzkörperstudien in der PET; Nuklearmedizin (2005) 44 p. A16
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A42

Publ.-Id: 8413 - Permalink


Entwicklung von Methoden zur echtzeitfähigen Listmodeakquisition an ACS2-basierten PET-Scannern
Langner, J.; Pötzsch, C.; Will, E.; van den Hoff, J.;
Ziel/Aim:
PET-Systeme, die wie der weit verbreitete ECAT Exact HR+ das ACS2 Kontrollsystem nutzen, erlauben es auf Grund von Limitationen der ACS2 Hardware mit nur sehr geringen Raten auf die akquirierten Daten zuzugreifen. Bei den üblicherweise mehreren Gigabyte großen Listmodedaten behindert dies die routinemäßige Auswertung dieser Daten erheblich. In (1) wurden bereits Methoden vorgestellt, die dem entgegenwirken. Um jedoch Korrekturmethoden, wie z.B. eine listmode-basierte Bewegungskorrektur effektiv in die Routine zu überführen, bedarf es weiterer Entwicklungen. Unsere Studie soll daher überprüfen, inwieweit ein echtzeitnaher Zugriff auf Listmodedaten durch Analysen und Hardwareentwicklungen am ACS2 System erreicht werden kann.

Methodik/Methods:
Die Koinzidenzdaten einer PET-Akquisition werden innerhalb des ACS2 Systems über einen extern zugänglichen Datenbus geführt. Dieser aus 32 Datenleitungen bestehende Bus verbindet die verschiedenen Hauptkomponenten des ACS2 und überträgt den Listmodedatenstrom während einer Akquisition. Um einen externen Abgriff dieser Daten zu ermöglichen, ohne jedoch die Standardkomponenten des PET Scanners zu beeinflussen, wurde ein optoelektronisch getrennter Adapter entwickelt. Dieser wurde zusammen mit einem durch digitale Datenakquisitionskarten erweiterten Linux Rechner am ACS2 angeschlossen. Ferner wurde eine Software entwickelt, die die abgegriffenen Daten über eine Netzwerkverbindung für andere Rechner zur Verfügung stellt, aber auch eine unmittelbare Verarbeitung bzw. Sortierung der Listmodedaten in Sinogramme zulässt.

Ergebnisse/Results:
Die entwickelten Methoden erlauben es, auf die Rohdaten eines ACS2 basierten PET-Scanners in Echtzeit zuzugreifen. Zur Verifikation wurden verschiedene Testmessungen bis zur Zählratengrenze des PET-Scanners durchgeführt. Hierbei lag die Drop-out Rate von nicht registrierten Ereignissen unterhalb 0,1%.

Schlussfolgerungen/Conclusions:
Die vorgestellten Methoden erlauben es, mit relativ kostengünstigen Mitteln ACS2-basierte PET-Scanner für einen Echtzeitzugriff auf Listmodedaten umzurüsten. Mit der entwickelten Software ist es möglich, die akquirierten Listmodedaten zeitnah zu bearbeiten und unmittelbar nach der Akquisition für eine Auswertung vorzuhalten. Dies stellt einen wichtigen Fortschritt bei der konsequenten Anwendung von Listmode in der PET dar.

Literatur/References:
(1) Langner J. et al., Entwicklung von Methoden zum beschleunigten Zugriff auf Akquisitionsdaten ACS2-basierter PET-Scanner; Nuklearmedizin 2005; 44; p. A161
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 05.-08.04.2006, Berlin, Germany
  • Abstract in refereed journal
    Nuklearmedizin 45(2006)2, A50

Publ.-Id: 8412 - Permalink


Novel investigations towards bispidine ligands
Juran, S.;
kein Abstract verfügbar
  • Lecture (Conference)
    3rd Supraphone Meeting, 04.-06.05.2006, Lissabon, Portugal

Publ.-Id: 8410 - Permalink


Anwendung von PET für die Kontrolle der Tumortherapie mit leichten Ionen
Fiedler, F.;
Ionenstrahlen erlauben bei der Radiotherapie von Tumoren auf Grund ihrer physikalischen und biologischen Eigenschaften ein höheres Maß an Präzision und Wirksamkeit als konventionell zur Bestrahlung eingesetzte Elektronen- oder Photonenstrahlen. Daher ist ein in-situ Monitoring der Dosisapplikation bei Ionenstrahlen wünschenswert. Gegenwärtig ist dafür nur die in-beam
Positronen-Emissionstomographie (PET) bekannt. Dabei werden zwischen Projektil und Gewebe stattfindende Kernreaktionen, die zur Erzeugung von Positronenemittern führen, genutzt um durch den Nachweis der emittierten g-Strahlung Aussagen zur Reichweite der Teilchen, zur Lage des bestrahlten Feldes und zu anatomischen Veränderungen gegenüber dem Zustand des Patienten zur Zeit der Planung der Bestrahlung zu treffen. In die experimentelle 12C Ionentherapieanlage an der Gesellschaft für Schwerionenforschung (GSI) Darmstadt wurde ein in-beam PET-Scanner integriert und diese Methode erstmals klinisch angewendet. An dieser Anlage wurden seit 1997 über 300 Patienten, vornehmlich mit strahlenresistenten Tumoren im Kopf-Hals Bereich behandelt. Diese Bestrahlungen wurden mit Hilfe von in-beam PET kontrolliert. Gegenwärtig gibt es Bemühungen, in-beam PET auch für andere Ionensorten als 12C nutzbar zu machen.
Keywords: in-beam PET, heavy ion tumor therapy
  • Invited lecture (Conferences)
    Seminar SF4, 25.04.2006, Berlin, Deutschland

Publ.-Id: 8409 - Permalink


Towards highly stable complexes of copper radionuclides with bispidines
Juran, S.; Kraus, W.; Steinbach, J.; Stephan, H.; Walther, M.;
Bispidines (bispidine = 3,7-diazabicyclo[3.3.1]-nonane) show interesting complexation behaviour towards transition metal ions. [1] The stabilities achieved for copper complexes with bispidines – lying in the same range as found for copper complexes of aza macrocycles – offer the possibility to apply such complexes for diagnostic and therapeutic purposes (64/67Cu).
We want to present the synthesis of novel hexadentate bispidine derivatives having pyridine and/or imidazole units as donor groups. Cu(II) complexes of some bispidines have been isolated and the structures were characterised by single-crystal X-ray diffraction analysis. Studies which have been performed to label selected bispidines with 64/67Cu indicate a rapid formation of stable complexes under mild conditions. Chemical approaches to introduce bio-molecules into the bispidine skeleton are discussed.
  • Poster
    1. European Chemistry Congress, 27.-31.08.2006, Budapest, Hungary
  • Contribution to proceedings
    1. European Chemistry Congress, 27.-31.08.2006, Budapest, Hungary, 362

Publ.-Id: 8408 - Permalink


Koordinationschemische Aspekte bei der Entwicklung neuer Chelatsysteme für nuklearmedizinische Anwendungen
Juran, S.;
kein Abstract verfügbar
  • Invited lecture (Conferences)
    Bundesanstalt für Materialforschung und -prüfung, 21.04.2006, Berlin, Germany

Publ.-Id: 8407 - Permalink


In-situ X-Ray Diffraction of GaSb Nanopatterned by Normal Incidence Sputter Erosion
Keller, A.; Facsko, S.; Plantevin, O.; Carbone, D.; Metzger, T. H.; Gago, R.;
Low energy ion erosion of surfaces can lead to the formation of self-organized structures in the range from 10 to 100 nm [1]. Periodic ripple patterns and hexagonally ordered dot arrays can be achieved for oblique and normal incidence, respectively. The evolution of ripple structures on different materials has been studied extensively during the last decades whereas the formation of dots has been discovered only recently [2] and is not fully understood yet.
In the presented work, the evolution of GaSb(001) surface morphology under normal incidence sputtering has been studied in-situ by surface sensitive X-ray techniques. The Grazing Incidence Small Angle X-ray Scattering (GISAXS) and Grazing Incidence Diffraction (GID) measurements have been performed at the beam line ID01 at the ESRF. These techniques were used to study the evolution of the dots for ion energies from 100 to 1000 eV. With GISAXS the morphology and the correlation of the dots is analysed, while in GID information about the crystalline structure (i.e. strain) is added. This way, three regimes are observed and identified as smoothing, pattern formation and increase of lateral order.

[1] M. Navez, D. Chaperot and C. Sella, C. R. Acad. Sci. 254 (1962), 240
[2] S. Facsko et al., Science 285 (1999), 1551
  • Lecture (Conference)
    DPG Frühjahrstagung 2006, 26.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8406 - Permalink


Master Curve approach for embrittled reactor pressure vessel steels
Zurbuchen, C.; Viehrig, H.-W.;
The structural integrity of the reactor pressure vessel (RPV) has to be maintained throughout the operation time of a nuclear power plant (NPP). The fracture toughness of the RPV steel has to be higher than the stress intensity at the crack tip. The present regulatory-based correlative approaches for the determination of fracture toughness of RPV steels are not consistent because they link technological parameters (RTNDT, Charpy-V) and universal fracture toughness lower bound curves. Safety margins as well as probability estimations cannot be quantified. In contrast, a new “Master Curve” (MC) method enables the direct measurement of the fracture toughness with less uncertainty. The MC approach is based on Weibull statistics and models the cleavage failure of a specimen in the lower ductile-to-brittle transition region.
To maximize the Master Curve’s benefits, it should be incorporated in regulatory evaluation or integrity assessment as a long term objective. Before the Master Curve approach can be implemented in codes and regulations, open issues such as influence of irradiation, loading rate effects, loss of constraint, as well as the effects of inhomogeneous material need resolving.
The Research Centre Rossendorf is currently investigating the invariability of the MC shape for “extreme” irradiation, the applicability in case of partial intergranular fracture, annealing effects, and the correlation of MC and Charpy results. Latest results will be presented.
Keywords: Master Curve irradiation cleavage failure intergranular fracture
  • Poster
    JUNIOR EUROMAT 2006, 04.-08.09.2006, Lausanne, Schweiz

Publ.-Id: 8405 - Permalink


Magnetic nanoparticle formation in Fe implanted ZnO
Zhou, S.; Potzger, K.; Mücklich, A.; Reuther, H.; Eichhorn, F.; Schell, N.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
Low temperature doping with transition metals is currently accepted as the “silver bullet” for the creation of diluted magnetic semiconductors (DMS). Among them, ion implantation offers the possibility for doping at almost any temperature. However, tiny, hardly detectable ferromagnetic nanoparticles created due to phase separation already during implantation can wrongly give the impression of a DMS by means of a pronounced integral magnetization. In this work we would like to present systematic investigations on the formation of ferromagnetic nanoparticles due to 57Fe implantation into ZnO single crystals applying several sensitive analysis techniques. At an implantation temperature of 623 K and implantation energy of 180 keV, a distinct dependence of the nanoparticle formation on the Fe ion fluence was observed. Below a fluence of 2x1016 cm-2, all Fe is found in nonmagnetic charged states indicating no -Fe-nanoparticle formation as was confirmed using X-ray diffraction. From a fluence of 2x1016 cm-2, superparamagnetic -Fe-nanoparticles are present. They were evidenced by zero-field cooled (ZFC) and field cooled (FC) magnetization curves, x-ray diffraction and transmission electron microscopy. The superparamagnetic blocking temperatures increase with the implanted fluence. An annealing at 823 K for 15 min enhanced the Fe particle formation, but Fe nanoparticles were oxidized after an annealing at 1073 K for 15 min. A further annealing at 1073 K for 3.5 h induced the formed of ZnFe2O4. In a conclusion, we definitely rule out the formation of a diluted magnetic semiconductor in Fe-implanted ZnO at process temperature above 623 K.
Keywords: II-VI semiconductors, magnetic semiconductors, nanostructured materials, superparamagnetism
  • Poster
    E-MRS IUMRS ICEM 2006 Spring Meeting, 29.05.-02.06.2006, Nice, France

Publ.-Id: 8403 - Permalink


Crystalline Ni nanoparticles as the origin of ferromagnetism in Ni implanted ZnO crystals
Zhou, S.; Potzger, K.; Zhang, G.; Eichhorn, F.; Skorupa, W.; Helm, M.; Fassbender, J.ORC
We report the structural and magnetic properties of ZnO single crystals implanted at 623 K with up to 10 at. % of Ni. As revealed by X-ray diffraction, crystalline fcc-Ni nanoparticles were formed inside ZnO. The magnetic behavior (magnetization with field reversal and with different temperature protocol) of all samples is well explained by a magnetic Ni-nanoparticle system. Although the formation of Ni:ZnO based diluted magnetic semiconductor cannot be ruled out, the major contribution to the magnetic properties stems from crystalline nanoparticles synthesized under these implantation conditions.
Keywords: II-VI semiconductors, magnetic semiconductors, nanostructured materials, superparamagnetism

Publ.-Id: 8402 - Permalink


Jahresbericht 2005
Bohnet, C.; (Editor)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-451 2006

Downloads:

Publ.-Id: 8401 - Permalink


Bubble-wall interactions in a vertical gas-liquid flow: bouncing, sliding and bubble deformations
Zaruba, A.; Lucas, D.; Prasser, H.-M.; Höhne, T.;
The paper presents results of a study on the motion of bubbles rising in upward shear liquid flow in the vicinity of a vertical wall. Bubbles were found to slide along the wall, when their diameter is small. Bubbles could also experience multiple collisions with the wall at certain experimental parameters (geometry of a channel, range of superficial liquid velocity, bubble size, etc). The latter was theoretically predicted by solving the equation of the bubble motion for the lateral direction in the boundary layer of the channel. For this, the available in the literature constitutive models for the interfacial forces acting on a bubble in the vicinity of the wall were used. A simplified 1D model predicting bubble lateral displacement near the wall and taking into account the balance of drag and non-drag forces acting on a bubble was proposed. The numerical results were verified against the experimental ones obtained by non-intrusive high-speed video observations and subsequent image processing.
The experiments on the bubble motion were conducted in a vertical acrylic duct having a square cross-section of 25 cm2 and a height of approximately 1.3 m. Desalinated water and air both taken at the room temperature were used in the experiments. All measurements on the bubble motion were performed at channel heights between 0.8 and 1 m above the gas injection point.
Keywords: Bubbles, bouncing motion, shear liquid flow, interfacial forces, turbulent boundary layer
  • Chemical Engineering Science 62(2007), 1591-1605

Publ.-Id: 8400 - Permalink


Relaxation of slow highly charged ions penetrating a solid surface - energy deposition and reemission
Kost, D.; Facsko, S.;
Highly charged ions carry a large amount of potential energy, which is defined as the sum of the binding energies of all removed electrons. In the case of low velocities of the ions this energy can exceed their kinetic energy.
Approaching the solid surface the ions are neutralized, relaxe to the ground state, and their potential energy is released. Thereby different mechanisms, such as surface sputtering, secondary ion emission, secondary electron emisson and X-ray emission take place [1]. The secondary particles leaving the surface carry only up to 10% of the potential energy.
Using a calorimetric setup [2] we measured the amount of the potential energy which remains in the solid to 85% +/- 10%.
To study the detailed mechanism of the energy retention materials with different electronic structures were investigated: Cu, n-Si, p-Si, SiO2.
We can conclude, that the difference in energy depositon between these materials is below 10%.
The calorimetric results are rounded off with results from energy reemission measurements using electron spectroscopy.
The value of the reemitted energy increases with increasing charge state up to 10%.
[1] A. Arnau et.al.: Surf. Sci. Rep.27, 113 (1997).
[2] U. Kentsch et.al.: Phys. Rev. Lett.87, 10 (2001).
  • Lecture (Conference)
    AKF-Frühjahrstagung 2006 in conjunction with 21st General Conference of the EPS Condensed Matter Division, 27.-31.03.2006, Dresden, Deutschland

Publ.-Id: 8398 - Permalink


Die Zweiquellenanlage des Forschungszentrum Rossendorf - Neue Möglichkeiten für Experimente mit hochgeladenen Ionen
Kost, D.; Facsko, S.; Heller, R.; Schlenk, R.; Wustmann, B.; Zschornack, G.;
Die Rossendorfer Zweiquellenionenstrahlanlage stellt eine weltweit einmalige Kombination aus einer Elektron-Zyklotron-Resonanz-Ionenquelle mit einer bei Raumtemperatur arbeitenden Elektronenstrahl-Ionenquelle, der Dresden EBIT, dar. Die Ionenstrahlen beider Quellen münden in eine gemeinsame Targetkammer und stehen dort für Experimente zur Verfügung. Die erreichbaren Ladungszustände, die Ionenströme sowie die Energien der Ionen aus beiden Quellen unterscheiden sich aufgrund der verschiedenen Wirkungsprinzipien und gewährleisten so ein breites Spektrum an Experimenten. Die Gesamtanlage kann gegenüber der Targetkammer auf ein negatives Potential gebracht werden, wodurch sich die Ionen beider Quellen bis auf Energien unter q*100V abbremsen lassen. Die Untersuchung der Wechselwirkung langsamer hochgeladener Ionen mit Festkörperoberflächen, insbesondere der Einfluss der Potentialenergie der Ionen, ist neben der Ionenquellendiagnostik Gegenstand aktueller Forschungen an der Rossendorfer Zweiquellenanlage.
  • Lecture (Conference)
    Energiereiche Atomare Stöße, 06.-10.02.2006, Riezlern, Östereich

Publ.-Id: 8397 - Permalink


Potential Energy Retention of Slow Highly Charged Ar-Ions in Chemical Clean Silicon Surfaces
Kost, D.; Facsko, S.; Tyrroff, H.; Zschornack, G.; Möller, W.;
Highly charged ions (HCI) carry a large amount of potential energy, which is defined as the sum of the binding energies of all electrons that are removed from the atom. In the case of low velocities of the ions this energy is equal or can exceed the kinetic energy of the ions. Retaining such a large energy in a very small surface area of typically about 1-10nm^2 and in a very short interaction time of typically 5-10fs an enormous power flux of 10^13 W/cm^2 is given. In respect of this, high yields of photons and electrons have been observed, which carry away a fraction of the potential energy. Some experiments give a quantitative estimation of an energy reemission coefficent in the order of only 10%. In our experiment we determine the fraction of the retained potential energy of the ions by a calorimetric measurement.

For improved calorimetric measurements of the retention of the potential energy of highly charged ions a UHV device with a base pressure of p<10^-9mbar was constructed and connected to the 7.5 GHz ECR ion source at the Forschungszentrum Rossendorf. The ECR ion source is equipped with a sector field magnetic separation and a beam deceleration system. The ions are accelerated with a voltage of 5 kV and after beam transport decelerated to final kinetic energies down to 60eVxq.

By using a calorimetric setup the increase of the target temperature is measured during the irradiation with argon ions.
The retained energy of Ar q+ (q= 1 up to 9) ions into the Si(100) surface is determined at kinetic energies between 60 eVxq and 200 eVxq. By extrapolation to zero kinetic energy the retained fraction of the potential energy is obtained.

For absolute calorimetric measurements a small resistive heater is used for the calibration of the calorimetric setup. Using the resistive heater a function between the temperature increase and the deposited electrical power of the heater is obtained. Assuming that the electrical power is equivalent to the retained power of the incident ions the retained power of the ions can obtained from the temperature increase.

By sputtering with Ar+ the silicon surface is cleaned before the measurement. The chemical state of the target surface is controlled by AES using LEED
optics. Once being clean there are no other Auger electron signals in spite of silicon signals detectable over a time of 7 hours.

The obtained retained potential energy of the different charge states of the argon ions is related to the total potential energy. The potential energy retention coefficient results as 0.7 +/- 0.2 and decreases weakly with increasing charge state. This values are compared with earlier measurements [1] on a copper surface. The potential energy retention coefficient for silicon is about three times larger than the results with the copper surface.

[1] U. Kentsch, H. Tyrroff, G. Zschornack, and W. Möller, Retention of the potential energy of multiply charged argon ions incident on copper, Phys. Rev. Lett. 87(10), 4273 (2001).
  • Poster
    International Conference on Photonic, Electronic and Atomic Collisions, 23.-29.07.2003, Stockholm, Schweden

Publ.-Id: 8395 - Permalink


Excursions into reversals
Stefani, F.; Gerbeth, G.; Günther, U.; Xu, M.;
Despite the recent success of fully coupled three-dimensional numerical models of the geodynamo, the very nature of field reversals is still a matter of controversy. A mean-field dynamo model with a spherically symmetric helical turbulence parameter alpha serves us as a sort of minimum dynamo model that exhibits a number of typical reversal features. These include the asymmetry of reversals, the correlation between field strength and interval length, the existence of an inhibition time, and the bimodal field distribution. We identify the existence of a branch point of the spectrum of the non-selfadjoint dynamo operator as the essential ingredient for reversals to happen (Phys. Rev. Lett. 94 (2005), 184506). We present some evidences for a self-tuning mechanism of highly supercritical dynamos that tend to saturate into a reversal-prone state by driving the branch point and its nearby local maximum of the growth rate towards the zero line (Earth Planet. Sci. Lett. 143 (2006), 828-840). The high supercriticality can also explain the typical time-scales of asymmetric reversals (arxiv.org/physics/0601011), without taking resort to a turbulent resistivity. The role of the inner core to increase the ratio of excursions to reversals is discussed in the framework of resonant appearance of branch points in dependence on the wavelength of the dynamo source (arxiv.org/math-ph/0602013).
  • Poster
    10th Symposium of SEDI, 09.-14.07.2006, Prague, Czech Republic

Publ.-Id: 8394 - Permalink


Influence of colloids on uranium transport in nuclear waste repositories and abandoned uranium mines – a critical comparison
Zänker, H.; Ulrich, K.-U.; Opel, K.; Brendler, V.;
It is widely recognized that colloids can influence the migration of toxic and radiotoxic elements such as uranium. There are transport-facilitating and transport-impeding effects caused by colloids.
The most common scenario assumed in performance assessment for nuclear waste repositories is contaminant transport through anoxic aquifers. Only transport-facilitating effects of colloids are usually taken into consideration for this case. For abandoned uranium mines, retarding influences of colloids, apart from mobilizing ones, are also of high interest since they have the potential of causing “natural attenuation” of the environmental hazard.
The formation of colloids containing U(IV) and U(VI) was studied by laboratory experiments and by comparing the results with field experience. It is shown that there may be transport-stimulating effects of colloids on the “immobile” contaminant U(IV) and transport-impeding effects on the “mobile” contaminant U(VI).
A key factor in assessing the impact of colloids in a geochemical setting is the timescale that needs to be taken into account. Very long periods of time must be considered for nuclear waste repositories. Here, the point in time at which a certain colloid-borne contaminant such as uranium reaches the biosphere depends on the moment at which spent fuel container leakage begins, the water flow velocity, the concentration and mobility of potential carrier colloids, the hindrance of colloidal transport by barrier materials, and the persistence (reversibility vs. irreversibility) of the binding of the contaminant onto the colloids. In the case of mines, the phase critical for the environment occurs when the flood water reaches the level where first connections to unprotected surface waters or underground drinking water resources occur. This phase is characterized by the „first flush“ of the mine; the maximum release rate of contaminants such as U from the mine to the environment can be reduced by colloids via the flattening of the release rate profile. Whereas the timescale of critical contaminant release is in the range of centuries for the nuclear waste repositories, it lies in the range of only few years for abandoned uranium mines.
It is primarily the different dynamics of the processes behind these two different timescales that causes the different role of colloids for uranium migration in nuclear waste repositories and in abandoned uranium mines.
Keywords: nuclear waste repositories, abandoned uranium mines, uranium, colloids
  • Lecture (Conference)
    16th Goldschmidt Conference 2006, 27.08.-01.09.2006, Melbourne, Australia
  • Abstract in refereed journal
    Geochimica et Cosmochimica Acta 70(2006)18, A731
    DOI: doi:10.1016/j.gca.2006.06.1314

Publ.-Id: 8393 - Permalink


Calculation of the VVER-1000 Coolant Transient Benchmark using the Coupled Code Systems DYN3D/RELAP5 and DYN3D/ATHLET
Kozmenkov, Y.; Kliem, S.; Grundmann, U.; Rohde, U.; Weiss, F.-P.;
Plant-measured data provided by the OECD/NEA VVER-1000 coolant transient benchmark programme were used to validate the DYN3D/RELAP5 and DYN3D/ATHLET coupled code systems. Phase 1 of the benchmark (V1000CT-1) refers to an experiment that was conducted during the commissioning of the Kozloduy NPP Unit 6 in Bulgaria. In this experiment, the fourth main coolant pump was switched on whilst the remaining three were running normal operating conditions. The experiment was conducted at 27.5 % of the nominal level of the reactor power. The transient is characterized by a rapid increase in the primary coolant flow through the core, and as a consequence, a decrease of the space-dependent core inlet temperature. The control rods were kept in their original positions during the entire transient. The coupled simulations performed on both DYN3D/RELAP5 and DYN3D/ATHLET were based on the same reactor model, including identical main coolant pump characteristics, boundary conditions, benchmark-specified nuclear data library and nearly identical nodalization schemes. In addition to validation of the coupled code systems against measured data, a code-to-code comparison between simulation results has also been performed to evaluate the respective thermal hydraulic models of the system codes RELAP5 and ATHLET.
Keywords: Coupled code systems, 3D neutron kinetics, code validation, code-to-code comparison, VVER-1000 model, coolant transient benchmark, main coolant pump

Publ.-Id: 8392 - Permalink


Atomic-level simulations of ion implantation, defect formation and defect migration
Posselt, M.;
for further information, please contact the author
Keywords: ion implantation, defect formation, defect migration, atomic-level simulations
  • Invited lecture (Conferences)
    Seminar, 05.04.2006, Zürich, Switzerland

Publ.-Id: 8391 - Permalink


Interaction of Cu(II) with dendritic ligands studied by TRLFS
Geipel, G.;
  • Lecture (Conference)
    Supraphone Meeting 2006, 04.-06.05.2006, Lissabon, Portugal

Publ.-Id: 8390 - Permalink


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