Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31828 Publications
Shielding Design of the PANDA Spectrometer at the Munich High-Flux Reactor FRM-II
Noack, K.; Pyka, N.; Rogov, A.; Steichele, E.;
The start-up of the Munich high-flux reactor FRM-II is going on. At the beam tube SR-2 the spectrometer PANDA has been installed. It is a three-axis neutron spectrometer looking onto a slightly under-moderated cold neutron source. For polarization analysis PANDA is equipped with a vertical cryo-magnet producing fields up to 14.5 Tesla at the sample. To get an appropriate shielding of the high-intensity instrument one had to take into account the large cross-section of the primary beam, several restrictions using magnetic materials, limitations in loading the site and, finally, one had to keep the lateral extent of the shielding small to allow for high scattering angles. The shielding has been designed on the base of results which were achieved by the combined use of both the Monte Carlo code MCNP-4B2 and an analytical method based on one-dimensional dose transmission functions.
Keywords: Shielding Design, Neutron/Gamma Transport, High-Flux Reactor FRM-II, PANDA Spectrometer, Monte Carlo Calculations, MCNP Code
  • Lecture (Conference)
    International Conferences ICRS-10/RPS 2004, 09.-14.05.2004, Funchal, Madeira Island Portugal
  • Radiation Protection Dosimetry 115(2005)1-4, 262-267
    DOI: 10.1093/rpd/nci158

Publ.-Id: 6286 - Permalink

Results of TRAMO-Calculations of WWER-1000 Mock-up Experiments in the LR-0 Reactor
Konheiser, J.;
Neutron and gamma fluence results for the VVER-1000 mock-up at the LR0-reactor in Rez, that were calculated with the Monte Carlo Code TRAMO had been compared with measured data. A reasonable agreement between calculation results and experimental data was reached. Additionally, results obtained with different energy group structures were compared.
Keywords: Monte Carlo calculation TRAMO LR-0 mock-up VVER-1000
  • Lecture (others)
    REDOS Progress Meeting, September 3-6 2003, Elena Bulgaria

Publ.-Id: 6285 - Permalink

Creation and evaluation of the VVER-1000 Balakovo-3 ex-vessel dosimetry benchmark for the NEA SINBAD data base
Borodkin, G.; Boehmer, B.; Noack, K.; Khrennikov, N.;
A new neutron dosimetry benchmark of the NEA SINBAD Data Base is described. This full-scale reactor benchmark, based on VVER-1000 ex-vessel neutron activation measurements performed at the Balakovo NPP, Unit 3 (Balakovo-3), is a result of several years of thorough measurements and calculations. With regard to evaluation of measured and calculated results an international intercomparison study played a key role. This interlaboratory comparison produced the reference measured data expressed as end-of-irradiation activities of reaction products of the reactions: 237Np(n,f), 238U(n,f), 93Nb(n,n'), 58Ni(n,p), 54Fe(n,p), 46Ti(n,p) and 63Cu(n,a). A comprehensive analysis of reactor data used for creating the computational models has been performed. Special attention was paid to the analysis of the reliability of the absolute neutron source distributions. Results of calculations performed by various discrete ordinates and Monte Carlo codes have been used for the benchmark evaluation. It turned out that these calculation results are in agreement within 12 % with the reference measured data. The experience gained by creation and evaluation of the full-scale power reactor benchmark is discussed in the paper.
Keywords: neutron activation measurements, fast neutron benchmark, data base, reactor pressure vessel embrittlement, verification of neutron fluence calculations
  • Lecture (Conference)
    ICRS-10 / RPS 2004 Conferences, 09.-14.05.2004, Funchal, Madeira, Portugal

Publ.-Id: 6284 - Permalink

Prasser, H.-M.; Böttger, A.; Zschau, J.; Baranyai, G.; Ezsöl, G.;
  • Lecture (Conference)
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310
  • Contribution to proceedings
    11th International Conference on Nuclear Engineering Tokyo, JAPAN, April 20-23,2003, Proceedings ICONE11-36310

Publ.-Id: 6282 - Permalink

Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models
Dollinger, G.; Neumaier, P.; Bergmaier, A.; Eckstein, W.; Fischer, R.; Hofsaess, H.; Kroeger, H.; Ronning, C.; Jaeger, H. U.;
  • Lecture (Conference)
    European Materials Research Society 2004 Spring Meeting, Symposium J: Synthesis, Characterisation and Advanced Applications of Amorphous Carbon films, contr. J-I.3, 24-28 May 2004, Strasbourg, France

Publ.-Id: 6281 - Permalink

In-situ studies of Shape Memory Alloy (SMA) Ni-Ti thin films
Martins, R. M. S.; Schell, N.; Braz Fernandez, F. M.; Silva, R.;
Ni-Ti thin films (SMA) formed by sputtering have been attracting great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluidic pumps and micromanipulators. Successful implementation of Ni-Ti micro-actuactors requires a good understanding of the relationship among processing, microstructure and proprieties of Ni-Ti thin films. At the ROssendorf BeamLine (ROBL-CRG) at the ESRF, we carried out a series of experiments that clearly illustrate the benefit of in-situ studies, not only during annealing, but also during sputtering. The in-situ annealing experiments, using a Be-dome furnace installed into the six-circle diffractometer of the Materials Research Hutch (MRH) allowed us to determine the kinetics of the phenomena, to identify the sequence of precipitation and to correlate the build-up of the final structure with the processing conditions. The in-situ sputtering experiments during film growth were performed using a magnetron sputter deposition chamber also installed into the six-circle diffractometer [1]. This facility allowed us to follow, almost in “real time”, the structural evolution of the deposited thin film as a consequence of changing deposition parameters.
Keywords: magnetron sputtering, in-situ XRD, real-time structural design, shape memory alloy NiTi
  • Lecture (Conference)
    4th Conference on Synchrotron Radiation in Materials Science (SRMS-4), August 23-25, 2004, Grenoble, France

Publ.-Id: 6280 - Permalink

Real-time and in-situ structural design of functional NiTi SMA thin films
Schell, N.; Martins, R. M. S.; Braz Fernandez, F. M.;
The real-time structural design of magnetron sputtered NiTi SMA (shape memory alloy) thin films is reported. During deposition the phase content was followed in situ by synchrotron x-ray diffraction and controlled by varying the power of co-sputtering NiTi plus Ti for otherwise fixed deposition parameters. This method allows an optimization of the thin film in respect to its functional properties like phase transition temperature or adhesion as well as an understanding of the actual growth process by revealing temporary intermediate growth states (precipitates) and diffusion processes during film growth. The method is neither restricted to the sputter material (NiTi) nor to the controlling parameter (power) chosen, but immediately applicable to a large class of materials as well as general enough for other deposition parameters.
Keywords: magnetron sputtering, in-situ XRD, real-time structural design, shape memory alloy NiTi
  • Applied Physics A 81(2005)7, 1441-1445; DOI: 10.1007/s00339-004-3201-1

Publ.-Id: 6279 - Permalink

Microchanneling Investigation of ß-FeSi2-Structures
Dagkaldiran, Ü.; Grambole, D.; Herrmann, F.; Schreiber, H.-U.; Meijer, J.;
Semiconducting ß-FeSi2 has currently attracted scientific interest, due to the fact that ß-FeSi2 has a direct band gap of 0.8 eV [1,2]. This property makes it a special candidate for e.g. silicon-based micro-LED’s. Single crystalline ß-FeSi2- layers would even open possibilities for devices like micro-laserdiodes. However, the synthesis of these structures is experimentally extremely delicate.

The temperature during implantation, the energy of the beam, the annealing procedures as well as the fluence and current density of the beam, the structure size of the layer etc. are all key process parameters and have to be optimized with respect to one another.

The first micro channeling analyses of FeSi2-structures, which were produced with an ion energy of 800 keV and sample sizes between 70-190 µm in diameters, were carried out. The combination of the two set-ups, the ion projector at the Ruhr University of Bochum and the micro-channeling set-up at the research centre Rossendorf, allows a fast synthesis as well as the analysis of the samples.

The implantation temperature of the samples was varied between 50 – 350 °C. The results show that bulk formation by Ostwald maturing depends on implantation temperature and structure size. Even if the layers do not show the desired crystalline characteristics, the investigations permit to draw conclusions about the damage of the surface layer with consideration of the bulk formation. This is of enormous interest, in order to optimize and model the embedding into a pn-structure as a step towards the development of a LED.

Additional Raman measurements showed clear fingerprints of ß-FeSi2 [3].

[1]: N.E. Christensen;
Electronic structure of ß-FeSi2;
Phys. Rev. B42, 1990, p. 7148-7153

[2]: D. Pankin, F. Eichhorn, E. Wieser, W. Skorupa, W. Henrion, J. Albrecht;
Electrical and optical properties of ß-FeSi2 after Co implantation and annealing;
Nucl. Instrum. Methods Phys. Res. B84, 1994, p. 172-175

[3]: A.G. Birdwell, R. Glosser, D.N. Leong, K.P. Homewood;
Raman investigation of ion beam synthesized ß-FeSi2 ;
J. Appl. Phys., Vol. 89, No. 2, 2001, p. 965- 972
  • Lecture (Conference)
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia

Publ.-Id: 6278 - Permalink

Porous silicon as an intermediate layer for heterojunction solar cells on p-type Si crystalline substrates
Ulyashin, A.; Bilyalov, R.; Carnel, L.; van Nieuwenhuysen, K.; Grambole, D.; Bruck, A.; Scherff, M.; Monakhov, E.; Kuznetsov, A. Y.; Svensson, B. G.; Beaucarne, G.; Poortmans, J.;
The study of the influence of ITO deposition process on the defect formation in the interface region of heterojunctions (HJ) is done. The role of intrinsic a-Si:H and as an alternative a thin porous Si buffer layer is analyzed. It is shown that a thin porous Si as a buffer layer in HJ solar cells leads to the improvement of the HJ solar cells efficiency since this layer serves as a protection one of the Si substrate during the ITO deposition process. By DLTS method it is observed that damages created during the deposition of ITO layer can be essentially suppressed by a thin a-Si:H or thin porous Si buffer layers. In case of porous silicon formation by the electrochemical etching the process is “softer” and this thin intermediate layer has similar properties as a-Si:H concerning the hydrogen concentration and the characteristics of Si-H bonds. This conclusion was derived from the Nuclear Reaction Analysis (NRA) and Raman measurements, which are performed on porous-Si/crystalline Si structures. It is concluded that the main role of a thin porous Si layer in a Si based heterojunction structure is the improvement of the interface properties of HJ solar cells due to a protection of the Si substrate during the depositions of a-Si:H and ITO layers.
Keywords: heterojunction, silicon, passivation
  • Lecture (Conference)
    19th European Photovoltaic Solar Energy Conference, 7 - 11 June, 2004, Paris, France
  • Contribution to proceedings
    19th European Photovoltaic Solar Energy Conference, 07.-11.06.2004, Paris, France, 588

Publ.-Id: 6277 - Permalink

Bonding in hydrogenated diamond-like carbon by Raman spectroscopy
Casiraghi, C.; Piazza, F.; Ferrari, A. C.; Grambole, D.; Robertson, J.;
We study the 514 and 244 nm Raman spectra of a wide variety of hydrogenated amorphous carbons (a-C:H). The hydrogen content can be estimated from the slope of the photoluminescence background (PL) of the spectra measured at 514.5 nm. Generally, the evolution of the sp(2) and sp(3) phases is not independent for as-deposited a-C:H samples. This, in principle, allows us to derive their structural and optical properties just by studying the visible Raman spectra. For highly hydrogenated samples, the PL background overshadows the visible Raman spectra, and UV excitation is the only way to measure a Raman spectrum.

[1] A. C. Ferrari, J. Robertson, Phys. Rev. B 64 (2001) 075414.
[2] T. Schwarz-Selinger, A. von Keudell, W. Jacob, J. Appl. Phys. 86
(1999) 3988
[3] A. C. Ferrari, J. Robertson, M. G. Beghi, C. E. Bottani, R. Ferulano,
R. Pastorelli, Appl. Phys. Lett. 75 (1999) 1893.
  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (Diamond 2004), 12 -17 September 2004, Riva Del Garda, Italy
  • Diamond and Related Materials 14(2005)3 - 7, 1098-1102

Publ.-Id: 6276 - Permalink

Protective diamond-like carbon coatings for future optical storage disks
Piazza, F.; Grambole, D.; Schneider, D.; Casiraghi, C.; Ferrari, A. C.; Robertson, J.;
Diamond-like carbon (DLC) is a promising protective coating for future optical storage technologies. The requirements place conflicting constraints on the nature of the DLC. It must be transparent at 400 nm, hard and wear-resistant, uniform, pinhole-free, have a low stress and be deposited at high rate without a high heat load on a plastic substrate. In order to optimise the films under these constraints, we have studied in detail the band gap, stress, density and Young's modulus of hydrogenated amorphous carbon (a-C:H) films deposited by plasma enhanced chemical vapour deposition using a large area electron cyclotron wave resonance source of 14 in. diameter and a variety of hydrocarbon gas sources. We have been able to produce wear-resistant carbon coatings with a high transparency at 400 nm without damaging the plastic disks. We also show that for these films the refractive index can be used as a rapid empirical means of property correlation.

[1] F. Piazza, D. Grambole, L. Zhou, F. Talke, C. Casiraghi, A.C. Ferrari,
J. Robertson, Diamond Related Mater., in press.
Keywords: Hydrogenated amorphous carbon, ECWR plasma beam source, protective coatings
  • Lecture (Conference)
    15th European Conference on Diamond, Diamond-Like Materials, Carbon Nanotubes, Nitrides & Silicon Carbide (Diamond 2004), 12 -17 September 2004, Riva Del Garda, Italy
  • Diamond and Related Materials 14(2005)3 - 7, 994-999

Publ.-Id: 6275 - Permalink

Micro RBS-channeling measurements to study damage accumulation in silicon by ion implantation
Grambole, D.; Herrmann, F.; Dagkaldiran, Ü.; Meijer, J.;
Ion implantation is the key technology for electrical doping of silicon. There are many studies of the amorphization of silicon by ion implantation. To extend the investigation of the damage accumulation in silicon to very high ion fluxes, Si samples were implanted with 600 keV Si+ ions of a current density of 360 µA/cm² (2.2 x 1015 Si /(s x cm²)) at different substrate temperatures up to a fluence of 1 x 1018 Si/cm² by the Bochum super conducting ion projector [1]. The damage of the Si crystal in the implanted circular areas of 185 µm diameter was investigated by micro RBS-channeling with 3 MeV He ions using the Rossendorf nuclear microprobe. For micro channeling measurements a second chamber with a precisely justified 4-axis goniometer was installed behind the chamber used normally for micro ion beam analysis. It allows to investigate the crystal structure in regions down to a size of about 10 µm, keeping the crystal damage during the analysis in check. For this high Si ion flux a significant dependence of the damage accumulation and of the Si amorphization on the implantation temperature and fluence was observed. It was shown that the model of the current density dependence on the amorphization temperature used also by R.D. Goldberg et al. [2] can not be extrapolated to very high ion current densities.

[1] J. Meijer, A. Stephan, Microelec. Eng. 41/42 (1998) 257
[2] R.D. Goldberg, R.G. Elliman, J.S. Williams, Nucl. Instr. and Meth. B 80/81 (1993) 596
  • Poster
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia

Publ.-Id: 6274 - Permalink

Hydrogen behaviour in novel materials for spintronic: GaFeN codoped with Mg, Si and Al
Turos, A.; Abdul-Kader, A. M.; Podsiadlo, S.; Strojek, B.; Strzalkowski, I.; Grambole, D.;
Hydrogen plays an important role in GaN and related alloys. It is often a part of the growth environment and can be incorporated in GaN during different processing steps. Its behaviour is rather complicated and poorly understood. GaN doped with Fe has currently gained an increasing interest as a suitable magnetic semiconductor for spintronic applications. Here, we report results of the study on GaN doped with Fe and codoped with Mg for deep acceptors, Si for shallow donors and isoelectronic Al. Samples were grown by the chemical transport process in the form of small (~ 0.3 mm) crystallites and subsequently pressed to form platelets. As-grown samples and after annealing in different atmospheres (successively with N2 and NH3) were studied. Hydrogen concentration were determined by NRA using the 15N profiling method. Hydrogen release due to the analysing beam was evaluated using the molecular recombination model. Effective H-release cross-section was found to be the same for all GaFeN samples, independently of codoping. The lowest concentration of hydrogen among as-grown materials was revealed in GaFeN samples. Codoped materials showed higher hydrogen concentration, increasing in the following sequence: Mg, Si and Al. Hydrogen concentration can be substantially reduced by annealing in N2 atmosphere, whereas subsequent annealing in NH3 produces hydrogenation, however, to concentrations below that for pristine samples. The model of these processes has been proposed.
Keywords: Spintronics; Gallium nitride; Hydrogen; Nuclear reaction analysis
  • Lecture (Conference)
    Vth International Conference Ion Implantation and Other Applications of Ions and Electrons, June 14-17, 2004, Kazimierz Dolny, Poland
  • Vacuum 78(2005)2-4, 285-290

Publ.-Id: 6273 - Permalink

Experimentelle Untersuchungen zur reaktionsgetriebenen Druckentlastung
Kryk, H.; Schmitt, W.; Hessel, G.; Tefera, N.;
Die Qualität der Simulationsergebnisse existierender Computercodes zur dynamischen Simulation von Druckentlastungsvorgängen (z.B. SAFIRE/ Vent, BRICK) ist von der Genauigkeit der Untermodelle zur Berücksichtigung von Wärme- und Stofftransport, Reaktionskinetik, Mischphasenthermodynamik sowie Aufwall- und Schaumverhalten abhängig. Die Untersuchungen dienen einer verbesserten Modellierung dieser Teilprozesse unter Berücksichtigung der spezifischen Prozessbedingungen der Druckentlastung. Hierzu sind sowohl reaktionsgetriebene Druckentlastungsexperimente in Rührkesselreaktoren unter prozessnahen Bedingungen als auch zusätzliche Experimente zur Ermittlung von apparate- und prozessspezifischen Parametern durchzuführen. Die Ergebnisse liefern den Prozessdaten-Pool zur Weiterentwicklung und Validierung von Simulationssoftware für Druckentlastungsprozesse in Batch-Reaktoren. Ziel ist die Simulation des Gesamtprozesses vom Reaktionsstart über die hydro- und thermodynamischen sowie die prozesskinetischen Vorgänge während der Druckentlastung bis hin zu Nachreaktionen.
Als Modellprozess wurde die Veresterung von Essigsäureanhydrid mit Methanol gewählt. Zur Berücksichtigung der stofflichen und wärmetechnischen Einflüsse der Reaktion auf den Druckentlastungsprozess wurde ein reaktionskinetisches Modell entwickelt, das die thermischen und chemischen Reaktionsverläufe über weite Temperatur- und Konzentrationsbereiche unabhängig von der Prozessführung wiedergibt.
Hauptgegenstand der experimentellen Untersuchungen sind reaktive Druckentlastungsexperimente unter prozessnahen Bedingungen. Die Experimente werden unter isoperibolen Prozessbedingungen in mantelgekühlten Rührkesselreaktoren aus Glas und Edelstahl durchgeführt. Die Reaktorvolumina betragen 1 bis 10 Liter. Bei Verwendung der Glasreaktoren kann, bedingt durch die Positionierung des kritischen Querschnittes (wechselbare Lochblende) in Höhe des Reaktordeckels, das Einströmverhalten in die Blende mittels High-Speed-Videotechnik beobachtet werden. Zusätzliche elektrische Heizpatronen im Reaktor gestatten die Bestimmung von Wärmeübergangskoeffizienten und anderen Prozess- und Anlagenkennwerten. Die für den Druckentlastungsprozess signifikantesten Signale werden mit einer Abtastrate von max. 200 Hz aufgezeichnet. Zur Ermittlung der dynamischen Phasenanteile in der Druckentlastungsleitung wurde eine spezielle nadelförmige Leitfähigkeitssonde mit integrierter Temperaturmessung entwickelt. Durch Verwendung von Rührkesselreaktoren mit Mantelkühlung in Verbindung mit elektrischen Kalibrierheizungen ist die thermodynamische Charakterisierung des Systems durch Wärmebilanzierung realisierbar. Zur stofflichen Charakterisierung der Reaktionsgemische wird die FTIR-Spektroskopie eingesetzt.
Gegenstand der Präsentation bilden die Versuchsanlagen, die experimentelle Strategien zur Modellierung und Simulation von Druckentlastungsszenarien sowie die konkreten Versuchsabläufe zur Realisierung reproduzierbarer reaktionsgetriebener Druckentlastungsprozesse. Erste Versuchsergebnisse werden gezeigt und ein Ausblick auf weitere experimentelle und modelltheoretische Untersuchungen wird gegeben.

Keywords: Anlagensicherheit, Druckentlastung, chemische Reaktion, Rührkesselreaktor, Modellierung
  • Lecture (Conference)
    7. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit" 04.-05.2004, Köthen, Germany
  • Contribution to proceedings
    7. Fachtagung "Anlagen-, Arbeits- und Umweltsicherheit" 04.-05.2004, Köthen, Germany, CD-ROM

Publ.-Id: 6272 - Permalink

Strömungskontrolle bei Formfüllung mittels Magnetfeldern
Eckert, S.; Galindo, V.; Gerbeth, G.; Witke, W.; Buchenau, D.; Gerke-Cantow, R.; Nicolai, H.-P.; Steinrücken, U.;
Es ist aus theoretischen Überlegungen und praktischen Untersuchungen bekannt, daß beim Feinguß eine in die Form einströmende Schmelze eine in ihrem exakten Zahlenwert unbekannte Maximalgeschwindigkeit (Näherungswert: 0,5 m/s) nicht übersteigen darf. Füllt die Schmelze den Formhohlraum mit einer höheren Geschwindigkeit, ergeben sich Verwirbelungen und Oxideinschlüsse, die sich nachteilig auf die mechanischen Eigenschaften des Gussteils auswirken. Es gibt Hinweise an Gussteilen, die diese Theorien stützen. Da eine Form als oben offener Hohlraum betrachtet werden kann, muß das Metall immer aus einer Höhe eingefüllt werden, die durch die Höhe des Gussteils und zusätzlicher gießtechnischer Anordnungen vorbestimmt ist. Damit resultiert die Maximalgeschwindigkeit der Schmelze am tiefsten Punkt aus den geometrischen und flüssigkeitsdynamischen Gegebenheiten. Eine kontaktlose Regelung der Schmelzströmung, welche durch Einsatz elektromagnetischer Felder realisiert werden kann, ist offensichtlich wünschenswert und vorteilhaft im Vergleich zu mechanischen Lösungen.
Keywords: Feinguss, Formfüllung, Flüssigmetall, elektromagnetische Strömungskontrolle, Magnetfeld
  • Lecture (Conference)
    Deutscher Giessereitag 2004, 03.-04.06.2004, München, Germany
  • Giesserei 92(2005)5, 26-31

Publ.-Id: 6271 - Permalink

Calculations of K+, K- and Phi Production in Near-Threshold Proton-Nucleus Collisions
Barz, H.-W.; Kämpfer, B.; Naumann, L.; Wolf, G.; Zetenyi, M.;
K+, K- and phi meson production in proton-nucleus (pA) collisions has been calculated within a BUU transport model. It is shown that the nucleon-hyperon strangeness transfer channel is essential. The role of three-body reactions has been investigated within the medium.
The mass dependence of phi production is predicted to give important information on the in-medium properties of all three mesons.
  • Acta Physica Hungarica A 22(2005)3-4, 231-237

Publ.-Id: 6270 - Permalink

Modelling of bubble flow in vertical pipes
Krepper, E.; Lucas, D.; Shi, J.;
To qualify CFD codes for two-phase flows, they have to be equipped with constitutive models standing for the interaction between the gaseous and the liquid phases. In case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. Information on the local structure of the flow is also required by 1D thermal-hydraulic codes. Gas-liquid flow in vertical pipes is a very good object for studying the corresponding phenomena. Here, the bubbles move under clear boundary conditions, resulting in a shear field of nearly constant structure where the bubbles rise for a comparatively long time. The evolution of the flow within the pipe depends on a very complex interaction between bubble forces and bubble coalescence and break-up. E.g. the Lift-force, which strongly influences the radial distribution of the bubbles, changes its sign depending on the bubble diameter. Basing on extensive experimental data with a high resolution in space and time the applicability and the limits for the simulation of bubble flow with current CFX-codes are demonstrated, using the simulation of vertical pipe flow with CFX-4 as an example. Using a simplified model, parametric studies can be conducted. They give an indication for necessary improvements of the codes. Finally a possible way for the improvement of the CFD-codes is shown.
Keywords: two phase flow, bubble flow, bubble size, vertical pipe flow, CFD
  • Lecture (Conference)
    Multiphase Flows in Industrial Applications CFX-Germany, FZ-Rossendorf 28.-30.04.03

Publ.-Id: 6269 - Permalink

CFD Modelling of subcooled boiling
Krepper, E.;
Heat transfer and boiling are key phenomena in critical equipment used in power generation facilities. Modelling of boiling in 1D thermal hydraulic codes was state of the art right from the beginning of their development, whereas boiling models in 3D thermal hydraulic codes are far from reaching this level of maturity. In this paper, the boiling model implemented in the CFD code CFX-4 was applied, to analyse several boiling experiments, the results of which are published in literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement with experiments. However, especially in the low pressure region, the steam volume fraction is under predicted. The models implemented in CFX are critically reviewed and compared to alternative solutions. The sensitivity of the calculated results on different parameters are compared. The need for improvements in the model and for further experiments are derived. Main attention should be focused on measuring and modelling of the correct size of the steam bubbles generated.
Keywords: CFD, boiling, experiments
  • Lecture (Conference)
    XIII. AER-Symposium on VVER Physics and Reactor Safety, Dresden, Germany, September 23-26, 2003, Proceedings pp. 819-833
  • Contribution to proceedings
    XIII. AER-Symposium on VVER Physics and Reactor Safety, Dresden, Germany, September 23-26, 2003, Proceedings pp. 819-833

Publ.-Id: 6268 - Permalink

Coupled Fluid-Structure Analysis with EUROPLEXUS Fast Dynamics Software of the CWHTF Experiment
Potapov, S.; Altstadt, E.;
The present paper aims at the validation of modelling capacities of the EUROPLEXUS fast dynamics software in the domain of condensation-induced water hammers and Fluid-Structure Interaction (FSI). Two numerical models of EUROPLEXUS accounting for FSI effects are considered and compared throughout modelling and computation. The first model is a simplified pipeline model using intrinsically coupled pipeline elements. The second FSI model is a mixed model; it contains both pipeline and 3D parts and uses a special interface model between the 3D fluid volume and the shell mesh of the piping. Numerical results are compared with experimental data obtained on the Cold Water Hammer Test Facility (CWHTF) at Forschungszentrum Rossendorf, within the WAHALoads European project. In this experiment water hammer is generated by accelerated water bouncing against a lid flange.

Keywords: Water Hammer Experiment, Fluid-Structure Interaction, EUROPLEXUS fast dynamics software
  • Lecture (Conference)
    6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6), 04.-08.10.2004, Nara, Japan
  • Contribution to proceedings
    6th International Conference on Nuclear Thermal Hydraulics, Operations and Safety (NUTHOS-6), 04.-08.10.2004, Nara, Japan

Publ.-Id: 6267 - Permalink

NIR Spectroscopic Study of the Complexation of Neptunium(V) with Humic Acids: Influence of Phenolic OH Groups on the Complex Formation
Sachs, S.; Bernhard, G.;
The influence of phenolic OH groups on the Np(V) complexation by humic acids was studied at pH 7 and pH 8 under nitrogen atmosphere applying chemically modified humic acids with blocked phenolic OH groups in comparison to their corresponding unmodified humic acids. The studies were performed by near-infrared (NIR) absorption spectroscopy using the metal ion charge neutralization model for evaluation of the experimental data. For all humic acids under investigation comparable complexation constants were determined. However, the studied modified humic acids Aldrich and M42 show significantly lower loading capacities for NpO2+ ions (e.g., pH 7: 7.2 ± 1.1 % and 5.3 ± 1.0 %, respectively) than the corresponding unmodified humic acids (e.g., pH 7: 10.0 ± 1.5 % and 11.2 ± 1.1 %, respectively). This result points to a lower amount of maximal available humic acid ligand sites after blocking of phenolic OH groups. From that, it can be concluded that humic acid phenolic OH groups contribute to the interaction between humic acid and Np(V) under the studied conditions. The comparison of the loading capacities obtained for unmodified and modified Aldrich humic acid at pH 7 and pH 8 shows that the impact of phenolic OH groups on the Np(V) complexation by humic acids is increased with increasing pH value.
Keywords: Humic acid, Synthetic humic acid, Modified humic acid, Phenolic OH groups, Complexation, Neptunium(V)
  • Radiochimica Acta 93(2005), 141-145

Publ.-Id: 6266 - Permalink

In-situ investigations of the amorphous-to-crystalline transformation of ITO films by synchrotron X-ray scattering
Shevchenko, N.; Rogozin, A.; Schell, N.; Cantelli, V.; Vinnichenko, M.; Prokert, F.; Kolitsch, A.;
Amorphous tin-doped indium oxide (ITO) films were grown by reactive pulsed middle frequency dual magnetron sputtering on Si (100) substrates covered with 500 nm SiO2. Changes in the microstructure and the resistivity of the ITO films during annealing in vacuum (p ~ 10-6 mbar) were characterized by in-situ synchrotron XRD analysis and simultaneous four-point probe measurements at ROssendorf Beam Line (ROBL). The in-situ experiments are performed at isothermal (temperature range of 210 - 240 °C) and non-isothermal (T-ramp: 2.5 - 10 K/min) annealing modes.
At non-isothermal annealing the XRD data reveal a rapid crystallization in the temperature range of 240 - 280°C. The heating rate does not influence on the temperature of the crystallization onset (T=240 ± 10 °C).
At isothermal annealing increase of the temperature leads to decrease of the time of crystallization onset and the total time of amorphous-to-crystalline transformation and, therefore the crystallization rate increases. Using the Kolmogorov-Avrami-Johnson-Mehl equation [f ~ 1-exp(-ktn)] for the dependence of the crystalline fraction f on the annealing time, the kinetic parameters of crystallization were determined. On the condition that the coherently diffracting domain size (~65 nm) is smaller than the film thickness (~130 nm) a three-dimensional crystallization process was indicated.
Even in amorphous films the resistivity significantly decreases with increasing temperature, likely by the generation of oxygen vacancies. The rapid crystallization leads to further reduction of the resistivity probably due to Sn donor activation.

Keywords: ITO, crystallization, annealing, in-situ
  • Poster
    The Conference on Synchrotron Radiation in Materials Science (SRMS-4), France, 23-25 August 2004

Publ.-Id: 6265 - Permalink

Ion implantation of NiTi alloy: surface processes and properties
Shevchenko, N.; Pham, M.-T.; Richter, E.; Maitz, M. F.;
The superelastic or memory shape NiTi alloy has big potential for biomedical applications, but due to the high nickel content there are restrictions against it. It has been shown, that ion implantation is a very versatile method to reduce the surface nickel content and modify the structure, by this improve the surface properties for biomaterials applications. The understanding of the mechanism of the Ni depleted layer formation and growth is still limited, but it is a key for achieving control and optimization of the process. The aim of this contribution is to study the surface processes of TiNi alloys during ion implantation, especially the phenomena of Ni depletion of NiTi surface to improve the biocompatibility.
N, O and Ar ion implantation of the NiTi samples was performed by means of plasma immersion ion implantation at different parameters: ion energy (20 - 40 keV and 200 keV), fluence (10 17 - 10 18 cm -2), substrate temperature (RT - 400 °C). The implanted layers were examined by Auger electron spectroscopy, grazing incidence X-ray diffraction analysis and transmission electron microscopy. The corrosion resistance and biocompatibility were investigated by the electrochemical corrosion analysis, cell culture and blood compatibility tests, respectively.
Nickel depleted surface layers of TiOx or TiNx are formed during oxygen or nitrogen implantation, respectively. Below this a nickel enriched zone up to 300 nm is found, with the possible phases Ni4Ti3 and Ni2.67Ti1.33. This indicates a reactive diffusion process as main control mechanism of Ni transport. Finally, any correlation of corrosion, chemical and microstructure properties of modified NiTi surfaces to the biocompatibility are discussed.

Keywords: NiTi, modified surface, ion implantation
  • Poster
    7th International Conference on Modification of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, July 25 -30, 2004

Publ.-Id: 6264 - Permalink

Microstructural and Mechanical Characterization of the Radiation Effects in Model Reactor Pressure Vessel Steels
Ulbricht, A.; Boehmert, J.; Viehrig, H.-W.;
This paper presents results of radiation-induced nanoscal microstructural changes measured by Small-Angle Neutron Scattering (SANS) on ASTM-type reactor pressure vessel (RPV) steels. Five different base metals and one weld metal were investigated. The irradiation was performed in a VVER-type power reactor on 3 different dose levels, maximally 0.14 dpa, at an irradiation temperature of 255 °C. The volume content of the micostructural features measured is correlated with the irradiation hardening and embrittlement.
In every case clear radiation-related hardening, embrittlement and microstrucural effects are proven. Radiation produces nanoscaled scattering defects of a radius between 0 < R < 3 nm with the maximum near R = 1 nm. Fluence and chemical composition do not or hardly change the shape of the size distribution but strongly the volume content. The radiation sensitivity is mainly controlled by the copper content. Copper also increases the A-ratio. There are good correlations between volume content of the nanoscaled radiation defects and the radiation hardening or embrittlement, respectively.
Annealing at 475 °C produces almost full recovery of the mechanical properties. However, the original microstructure of the unirradiated state is not completely reproduced.
Keywords: microstructure, SANS, radiation hardening, radiation embrittlement
  • Lecture (Conference)
    STP 1475: Effects of Radiation on Materials, 22nd Symposium, 08.-10.06.2004, Boston, Massachusetts, United States
  • Journal of ASTM International 2(2005)10, 14, Paper ID JAI12385
  • Contribution to proceedings
    STP 1475: Effects of Radiation on Materials, 22nd Symposium, 08.-10.06.2004, Boston, United States
    STP 1475, West Conshohocken, PA: ASTM International, 978-0-8031-3401-0, 151-164


Publ.-Id: 6263 - Permalink

Ion implanted NiTi surfaces for biomedical applications
Shevchenko, N.; Pham, M.-T.; Richter, E.; Maitz, M. F.;
  • Poster
    16th International Vacuum Congress IVC-16/ ICSS-12/ NANO-8, Venice, Italy, June 28 - July 2, 2004

Publ.-Id: 6262 - Permalink

In situ monitoring of the ITO film structure and properties during annealing
Shevchenko, N.; Rogozin, A.; Vinnichenko, M.; Prokert, F.; Cantelli, V.; Kolitsch, A.; Moeller, W.; Keywords: ITO, in situ, annealing
  • Lecture (Conference)
    16th International Vacuum Congress IVC-16/ ICSS-12/ NANO-8, June 28 - July 2, 2004, Venice, Italy

Publ.-Id: 6261 - Permalink

Ni depletion of a NiTi surface by ion implantation for biomedical applications
Shevchenko, N.; Maitz, M.;
The NiTi alloy is interesting for medical applications because of its either superelastic or memory shape properties. However, clinical acceptance of the alloy still is limited due to its high nickel content.
The aim of this work is to reduce the Ni concentration in a NiTi surface by ion implantation and study the influence on surface stability and biocompatibility.
Modification of the NiTi samples was performed by N or/ and Ar ion implantation at different parameters: ion energy (20 - 40 keV and 200 keV), fluence (10 17 - 10 18 cm -2), substrate temperature (RT - 400 °C). The modified layers were examined by Auger electron spectroscopy, grazing incidence X-ray diffraction analysis and transmission electron microscopy. The corrosion resistance and biocompatibility were investigated by the electrochemical corrosion analysis and cell culture tests with bone forming cells, respectively.
Ion implantation could reduce the surface nickel content down to ~0.5 at%. Below the Ni depleted surface a Ni enriched zone is formed, which indicates an increased mobility either of Ni from the surface to the bulk or of Ti from the sub-surface to the surface. A reactive diffusion mechanism for the nickel depletion in this system is discussed. The corrosion stability increases by this treatment. In preliminary studies with bone forming cells no decrease in biocompatibility was seen by this treatment.

Keywords: NiTi, biocompatibility, ion implantation
  • Lecture (Conference)
    DPG - spring meeting, March 8-12, 2004, Regensburg, Deutschland

Publ.-Id: 6260 - Permalink

Nucleation of calcium phosphate by surface-bound extracellular matrix
Pham, M. T.; Maitz, M.; Reuther, H.; Muecklich, A.; Prokert, F.; Steiner, G.;
The native extracellular matrix (ECM) laid down on silicon and titanium surfaces by osteoblast-like SAOS-2 cells was exposed by selective removing of cells. This type of material surface ECM-Si, ECM-Ti was shown to promote the nucleation of calcium phosphate from a simulated body fluid (SBF). Microscopic and spectroscopic results revealed the effect being associated with a collagen fibre-free extracellular matrix.
Keywords: osteoblasts; extracellular matrix; silicon; titanium; mineralization
  • Journal of Biomedical Materials Research 71A(2004), 16-24.

Publ.-Id: 6259 - Permalink

Application of Advanced Monte Carlo Methods in Numerical Dosimetry
Reichelt, U.; Henniger, J.; Lange, C.;
Many tasks in different sectors of dosimetry are very complex and highly sensitive to changes of the radiation field, e. g. dose estimations in microdosimetry. Often experimental measurements are only available for particular conditions or at single target points. Thus only the simulation of radiation transport is capable of describing the radiation field completely. Different approaches for solving the radiation transport problem as e.g. FEM can be used. In particular the Monte Carlo (MC) method is very useful for high-dimensional problems, and it is accepted as a standard method for this purpose.
Down to sub cellular dimensions the energy deposition by cascades of secondary electrons is the main pathway for damage induction in matter. A high number of interactions is taking place until such an electron is slowed down to thermal energies. For this reason the non-analog Monte Carlo program AMOS has been developed for photon and electron transport. The advanced MC algorithms implemented are able to handle a large number of histories at reasonable performance even for time consuming single scattering models. They facilitate the calculation of photon dose distributions at up to 10^6 points.
Modeling the dose distribution of a 125-I brachytherapy source has proven the high efficiency of this MC approach. Further on results achieved by AMOS for the transport of electrons with low energies (E < 100 keV) in matter with low atomic numbers were compared to measured data from the literature. It has been proven that the program code produces results in rather well agreement to the experiments also for small target structures of about one micrometre. This is especially important for the application to cell irradiation experiments as they are carried out at the FZ Rossendorf. As another example of application a simulation of the whole spectral detector response of an HPGe detector will be presented.
  • Poster
    14 International Conference on Solid State Dosimetry (2004)
  • Radiation Protection Dosimetry 119(2006), 479-482
    DOI: 10.1093/rpd/nci682

Publ.-Id: 6258 - Permalink

Coherent phonons in NdBa2Cu3O7-x single crystals: Optical-response anisotropy and hysteretic behavior
Misochko, O. V.; Lebedev, M.; Georgiev, N.; Dekorsy, T.;
Femtosecond pump-probe measurements of reflection from crystallographic planes are performed to investigate lattice relaxation dynamics in the NdBa2Cu3O7-x high-temperature superconductor. Ultrafast phonon response is examined over a wide temperature range for various orientations of the pump and probe polarization vectors with respect to particular crystallographic axes. The initial phases of coherent phonons are measured, and hysteretic behavior is revealed in the transition between two temperature regions above T-c for the ac plane.
Keywords: coherent phonons, high temperature superconductors
  • Journal of Experimental and Theoretical Physics 98(2004), 341-347

Publ.-Id: 6256 - Permalink

Umklapp process in observation of coherent folded longitudinal acoustic phonons in a GaAs/AlAs long-period superlattice
Mizoguchi, K.; Hino, T.; Nakayama, M.; Dekorsy, T.; Bartels, A.; Kurz, H.; Nakashima, S.;
Coherent folded longitudinal acoustic phonons in a GaAs/AlAs long-period superlattice (SL) have been investigated by using a reflection-type two-color pump-probe technique under the condition that the wave vector of the probe pulse in the sample exceeds the mini-Brillouin zone. The coherent oscillations observed in the time-domain signals indicate the propagation of the phonon wave packet through the whole SL layer. The Fourier transform spectrum of the time-domain signals is compared with the dispersion relation of the folded longitudinal acoustic phonons in the long-period SL calculated using a transfer matrix method on the bases of an elastic continuum model. This comparison indicates that the folded longitudinal acoustic phonons in the long-period SL are observed through the umklapp process.
Keywords: coherent phonons, superlattices, femtosecond, umklapp process
  • Physica E 21(2004), 646-650

Publ.-Id: 6255 - Permalink

Investigation of the Damage Around a Crack Tip in Metals using Small Angle X-ray Scattering
Müller, G.; van Ouytsel, K.; Böhmert, J.; Dolbnya, I.; Bergner, F.;
Structural materials, such as ferritic and austenitic steels and aluminium alloys, as used in the nuclear and aircraft industry are subject to external stresses which may lead to the nucleation of cracks. The damage zone ahead of a crack tip introduced as a result of static deformation was investigated in an Al-2024 and Al-6013 alloy and in a 10 CrMo9 10 reference steel by means of small angle X-ray scattering. A robust parameter, the anisotropy parameter, describing the damage region was developed. Further parameters were exployed. The data, supported by electron microscopy investigations point to large oriented dislocation networks. Finite element calculations show a good correspondence in the shape and size of the damage zone.

Konstruktionswerkstoffe, z.B. ferritische Stähle, austenitische Stähle und Aluminiumlegierungen mit Anwendung in der Kernenergie- und Luftfahrttechnik, sind hohen äußeren Belastungen ausgesetzt, die zur Rissbildung führen können. Die Schädigungszone vor der Spitze von Rissen, die durch quasistatische Belastung in Materialproben der Aluminiumlegierungen Al-2024 und Al-6013 und des warmfesten Stahls 10 CrMo9 10 eingebracht worden waren, wurde mittels Röntgenkleinwinkelstreuung punktweise erfasst und abgerastert. Aus den Streubildern wurden mehrere verschiedene Streuparameter abgeleitet, von denen sich der Anisotropieparameter als besonders robust erwies. Die Ergebnisse deuten, gestützt durch elektronenmikroskopische Untersuchungen, auf grobe orientierte Versetzungsnetzwerke. Finite-Elemente-Rechnungen zeigen eine gute Übereinstimmung hinsichtlich Form und Größe der Schädigungszone.
Keywords: SAXS, Al-alloy, steel, crack, damage, synchrotron radiation, dislocations, microvoids
  • MP Materials Testing 50(2008)4, 191-198

Publ.-Id: 6254 - Permalink

Suitability of drift-flux models, void-fraction evolution and 3D flow pattern visualization during stationary and transient flashing flow in a vertical pipe
Manera, A.; Prasser, H.-M.; van der Hagen, T. H. J. J.;
An assessment of void fraction correlations and drift-flux models applied to stationary and transient flashing flows in a vertical pipe has been performed. Experiments have been carried out on a steam/water loop that can be operated both in forced and natural-circulation conditions. Advanced instrumentation, namely wire-mesh sensors, has been used to obtain a detailed picture of the void-fraction development in the system. On the basis of experimental data collected, three-dimensional flow-pattern visualization was achieved.
Keywords: Drift-flux models, flashing, void fraction, natural circulation
  • Nuclear Technology, 152(2005)1, 38-53

Publ.-Id: 6253 - Permalink

Benchmark of Dynamics Simulation Tool for Molten Salt Reactors
Delpech, M.; Dulla, S.; Garzenne, C.; Kophazi, J.; Krepel, J.; Lebrun, C.; Lecarpentier, D.; Mattioda, F.; Ravetto, P.; Rineiski, A.; Schikorr, M.; Szieberth, M.;
A benchmark of some codes developed for the neutronic analysis of molten-salt reactors is presented. The results of the calculations are compared to the experimental data reported for the Molten Salt Reactor Experiment performed at Oak Ridge National Laboratory in the 60's. Both static and time-dependent situations are considered. The phenomena connected to the motion of the multiplying material are investigated. The results presented show a good agreement among the codes and with the available experimental data, thus providing the adequateness of the computational tools for the simulation of molten-salt system.
Keywords: Molten, Salt, Reactor, MSR, MSRE, Benchmark, Transient
  • Contribution to proceedings
    Proceedings of the international conference GLOBAL 2003, 2182-2187, New Orleans, LA, November 2003

Publ.-Id: 6252 - Permalink

Investigation of flashing-induced instabilities at the CIRCUS test facility using the code ATHLET
Schäfer, F.; Manera, A.;
The CIRCUS test facility has been built to study the start-up phase of a natural-circulation BWR. During the start-up so called flashing-induced instabilities can arise. These instabilities are induced by flashing, due to steam production in the long adiabatic riser section, which is placed above the core to enhance the flow rate. Flashing occurring in the riser causes an unbalance between driving force and pressure losses in the natural-circulation loop, giving rise to flow oscillations.

This paper gives an overview about experimental results and the physics of the instabilities. The thermo-hydraulic code ATHLET is used to investigate the dynamic behavior of the CIRCUS test facility and the results of the calculations are compared with the experimental data.

This work is part of the NACUSP project (Natural Circulation and Stability Performance of BWRs) within the European-Union 5th Framework Programme.
Keywords: BWR, ATHLET, CIRCUS, flow instabilities
  • Lecture (Conference)
    29th International Meeting on Reactor Noise, 17.-19.05.2004, Budapest, Hungary
  • Contribution to proceedings
    29th International Meeting on Reactor Noise, 17.-19.05.2004, Budapest, Hungary, CD-ROM

Publ.-Id: 6251 - Permalink

Untersuchung der Kühlmittelvermischung an der Versuchsanlage ROCOM - Experimente und Modellierung
Prasser, H.-M.; Höhne, T.; Kliem, S.; Rohde, U.; Weiß, F.-P.;
Die experimentellen Arbeiten zur Kühlmittelvermischung in einem Druckwasserreaktor vom Typ KONVOI an der Versuchsanlage ROCOM werden vorgestellt. Weiterhin sind die parallel zu den Experimenten durchgeführten theoretischen Arbeiten zur Anwendung und Validierung des CFD-Codes CFX-4 Bestandteil des Beitrages.
  • Lecture (Conference)
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.57-83
  • Contribution to proceedings
    Fachsitzung "Experimentelle und theoretische Untersuchungen zu Borverdünnungstransienten in DWR" auf der Jahrestagung Kerntechnik 2003, Berlin, 20.-22. Mai 2003, Berichtsheft S.57-83

Publ.-Id: 6249 - Permalink

Fabrication of Schottky barrier MOSFETs on SOI by a self-assembly CoSi2-patterning method
Zhao, Q. T.; Kluth, P.; Winnerl, S.; Mantl, S.;
  • Solid State Electronics 47 (2003) 1183

Publ.-Id: 6248 - Permalink

X-ray studies of Al(x)GA(1-x)As implanted with 1.5 meV As ions
Wierzchowski, W.; Wieteska, K.; Graeff, W.; Turos, A.; Grötzschel, R.;
  • Vacuum 70 (2003) 115

Publ.-Id: 6247 - Permalink

Resistance to high temperature oxidation in B+Si implanted TiN coatings on steel
Werner, Z.; Piekoszewski, J.; Grötzschel, R.; Richter, E.; Szymczyk, W.;
  • Vacuum 70 (2003) 93

Publ.-Id: 6246 - Permalink

Raman and HRTEM investigations of Ge nanocrystals produced by Ge+ ion implantation of SiO2 films and subsequent high pressure annealing
Tyschenko, I. E.; Talochkin, A. B.; Cherkov, A. G.; Zhuravlev, K. S.; Misiuk, A.; Yankov, R. A.; Skorupa, W.;
  • Contribution to external collection
    Proc. SPIE Int. Soc. Opt. Eng. 5136 (2003) 236

Publ.-Id: 6245 - Permalink

Jahresbericht 2003 - Forschung für Mensch und Umwelt
Bohnet, C.; (Editor)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-398 2004


Publ.-Id: 6244 - Permalink

Properties of Ge nanocrystals formed by implantation of Ge+ ions into SiO2 films with subsequent annealing under hydrostatic pressure
Tyschenko, I. E.; Talochkin, A. B.; Cherkov, A. G.; Zhuravlev, K. S.; Misiuk, A.; Yankov, R. A.; Skorupa, W.;
  • Semiconductors 37 (2003) 462

Publ.-Id: 6243 - Permalink

Strong blue light emission from ion implanted Si-SiO2 structures
Skorupa, W.; Rebohle, L.; Gebel, T.; Helm, M.;
  • Contribution to external collection
    in: L. Pavesi et al. (eds.), "Towards the First Silicon Laser", NATO Sciences Series, Kluwer Academic Publishers, Dordrecht, 2003, p. 69

Publ.-Id: 6242 - Permalink

Formation and structure of Sn and Sb nanoclusters in thin SiO2films
Spiga, S.; Franciulli, M.; Ferretti, N.; Boschrini, F.; D'Acapito, F.; Ciatto, G.; Schmidt, B.;

Publ.-Id: 6241 - Permalink

Phase transformation in the near surface layer of carbon steels modified with short intense nitrogen and argon plasma pulses
Sartowska, B.; Piekoszewski, J.; Walis, L.; Kopcewicz, M.; Werner, Z.; Stanislawski, J.; Szymczyk, W.; Prokert, F.;
  • Contribution to proceedings
    Proc. of 9th Int. Seminar on Nitriding Technology (IFHTSE), ed. by A. Nakonieczny, IMP, Warsaw, Poland 2003, p. 227

Publ.-Id: 6240 - Permalink

The feasibility of in-beam PET for accurate monitoring of proton therapy: Results of a comprehensive experimental study
Parodi, K.; Pönisch, F.; Enghardt, W.;
Positron emission tomography is currently the only feasible method for in-situ and non-invasive 3D monitoring of the precision of the treatment in highly conformal ion therapy. Its positive clinical impact has been proven for fractionated carbon ion therapy of head and neck tumours at the experimental facility at the Gesellschaft für Schwerionenforschung Darmstadt (GSI), Germany. Following previous promising experiments, the possible extension of the method to the monitoring of proton therapy has been investigated further in extensive in-beam measurements at GSI. Millimetre accuracy for verification of the lateral field position and for the most challenging issue of range monitoring has been demonstrated in mono-energetic and SOBP proton irradiation of PMMA targets. The irradiation of an inhomogeneous phantom with tissue equivalent inserts in combination with further dynamic analysis has supported the extension of such millimetre precision to real clinical cases, at least in regions of interest for low perfused tissues. All the experimental investigations have been reproduced by the developed modeling rather well. This indicates the possible extraction of valuable clinical information as particle range in-vivo, irradiation field position and even local deviations from the dose prescription on the basis of the comparison between measured and predicted b+-activity distributions. Hence, the clinical feasibility of in-beam PET for proton therapy monitoring is strongly supported.
  • Lecture (Conference)
    Contribution to IEEE NSS 16.-22.10.2004, Rome, Italy
  • Contribution to proceedings
    IEEE Nuclear Science Symposium and Medical Imaging Conference 16-22 October 2004 Rome, Conference Record NSS 43-5

Publ.-Id: 6239 - Permalink

Oxygen exchange and diffusion in the near surface of pure and modified yttria-stabilized zirkonia
de Ri; van Welzenis, R. G.; Brongersma, H. H.; Kreissig, U.;
  • Solid State Ionics 158 (2003) 67

Publ.-Id: 6238 - Permalink

Blood compatibility study of chromium oxide films deposited on stainless steel surfaces by magnetron sputtering
Poperenko, L. V.; Maitz, M. F.; Vinnichenko, M. V.;
  • Functional Materials 10 (2003) 447

Publ.-Id: 6237 - Permalink

TiB and TiB-C coatings deposited by plasma immersion ion implantation and their fretting behavior
Pakrash, B.; Richter, E.; Pattyn, H.; Celis, J. P.;
  • Surface and Coatings Technology 173 (2003) 150

Publ.-Id: 6236 - Permalink

Germanium quantum dots in SiO2: fabrication and characterization
Nylandsted Larsen, A.; Kanjilal, A.; Lundsgaard Hansen, J.; Gaiduk, P.; Cherkashin, N.; Claverie, A.; Normand, P.; Kapelanakis, E.; Tsoukalas, D.; Heinig, K.-H.;
  • Contribution to external collection
    in: Physics, Chemistry and Application of Nanostructures, eds. V.E. Borisenko, S. V. Gaponenko, V. S. Gurin, World Scientific Singapore, 2003, p. 439

Publ.-Id: 6235 - Permalink

Böttger stoneware - authentic or not?
Neelmeijer, C.; Mäder, M.; Pietsch, U.; Ulbricht, H.; Walcha, H.-M.;
  • Contribution to external collection
    in: Ehrenfried Walther von Tschirnhaus Gesamtausgabe, ed. by E. Knobloch, Beiband zum Kolloquium aus Anlass des 350. Geburtstages von E. W. v. Tschirnhaus am 10.4.2001 in Dresden, ed. by D. Hülsenberg, Verlag der Sächsischen Akademie der Wissensc...

Publ.-Id: 6234 - Permalink

Zerstörungsfreie Untersuchung an Hinterglasbildern des 19. Jahrhunderts durch Ionenstrahlanalyse
Neelmeijer, C.; Mäder, M.;
  • Contribution to external collection
    Katalog zur Ausstellung "Hinterglasmalerei in Südbayern im 18. und 19. Jahrhundert", Schloßmuseum Murnau, 14.3.-19.6.2003

Publ.-Id: 6233 - Permalink

Charge trapping in high-dose Ge-implanted and Si-implanted silicon dioxide thin films
Nazarov, A. N.; Osiyuk, I. N.; Tyagulskii, I. P.; Lysenko, V. S.; Gebel, T.; Skorupa, W.;
  • Contribution to external collection
    in: "Silicon Nitride and Silicon Dioxide Thin Insulating Films VII", ed. by R. E. Sah et al., ECS Inc., Pennington USA, v. 2003-02, p. 144

Publ.-Id: 6232 - Permalink

Ion beam characterization and engineering of strain in semiconductor multilayers
Nageswara Rao, S. V. S.; Pathak, A. P.; Siddiqui, A. M.; Avashti, D. K.; Muntele, C.; Dev, B. N.; Muralidharan, R.; Eichhorn, F.; Grötzschel, R.; Turos, A.;

Publ.-Id: 6231 - Permalink

Swift heavy ion mixing in In0.12Ga0.88As/GaAs strained layer superlattice
Nageswara Rao, S. V. S.; Lakshmi, G. B. V. S.; Siddiqui, A. M.; Ghosh, S.; Srivastava, S. K.; Avashti, D. K.; Jain, R. K.; Eichhorn, F.; Pathak, A. P.;
  • Contribution to proceedings
    Proc. of the 44th DAE Solid State Physics Symposium (DAE SSPS'2001) 44 (2003) 505

Publ.-Id: 6230 - Permalink

A time-resolved optical study of the paramagnetic dielectric-ferromagnetic metal transition in La0.7Ca0.3MnO3
Misochko, O. V.; Kaidashev, E. M.; Georgiev, N.; Dekorsy, T.;
The relaxation dynamics of charge carriers in an epitaxial La0.7Ca0.3MnO3 film was studied by the light reflection method with a femtosecond time resolution in a wide temperature range. The relaxation of time-resolved photoinduced reflections was shown to be two-component in the whole temperature range including the paramagnetic dielectric-ferromagnetic metal transition at Tapproximate to150-160 K. The fast relaxation component had a maximum lifetime (tausimilar to500 fs) in the transition region, and its contribution to relaxation increased as temperature decreased. The lifetime of the slow component was minimum (tausimilar to15 ps) in the transition region. In addition, fast oscillations assigned to coherent phonons appeared in photoinduced responses at T<200 K. The dephasing time of these oscillations increased as temperature decreased, whereas their frequency changed insignificantly.
  • J. Exp. Theor. Phys. 97 (2003) 788

Publ.-Id: 6229 - Permalink

Studying in-Medium Hadron Properties with HADES
Salabura, P.; Dohrmann, F.; Grosse, E.; Kaempfer, B.; Kanaki, K.; Kotte, R.; Naumann, L.; Sadovsky, A.; Agakichiev, G.; Agodi, C.; Alvarez-Pol, H.; Balanda, A.; Braun-Munzinger, P.; Chepurnov, V.; Chernenko, S.; Christ, T.; Coniglione, R.; Diaz, J.; Djeridi, R.; Bellia, G.; Belver, D.; Bielcik, J.; Böhmer, M.; Bokemeyer, H.; Boyard, J.; Duran, I.; Eberl., T.; Emeljanov, V.; Fabbietti, L.; Fateev, O.; Fernandez, C.; Finocchiaro, P.; Friese, J.; Fröhlich, I.; Fuentes, B.; Garzon, J.; Gernhäuser, R.; Golubeva, M.; Gonzales, D.; Guber, F.; Hennino, T.; Hlavac, S.; Hoffmann, J.; Holzmann, R.; Ierusalimov, A.; Iori, I.; Jaskula, M.; Jurkovic, M.; Karavicheva, T.; Koenig, I.; Koenig, W.; Kolb, B.; Kotulic-Bunta, J.; Krücken, R.; Kugler, A.; Kühn, W.; Kulessa, R.; Kurepin, A.; Kurtukian-Nieto, T.; Lang, S.; Lehnert, J.; Maiolino, C.; Marin, J.; Markert, J.; Metag, V.; Montes, N.; Mousa, J.; Münch, M.; Müntz, C.; Novotny, J.; Otwinowski, J.; Pachmayer, Y.; Panebratsev, Y.; Pechenov, V.; Perez, T.; Pietraszko, J.; Pleskac, R.; Pospisil, V.; Przygoda, W.; Rabin, N.; Ramstein, B.; Reshetin, A.; Ritman, J.; Rodriguez-Prieto, G.; Roy-Stephan, M.; Rustamov, A.; Sabin-Fernandez, J.; Sailer, B.; Sanchez, M.; Smolyankin, V.; Smykov, L.; Spataro, S.; Spruck, B.; Stroebele, H.; Stroht, J.; Sturm, C.; Sudol, M.; Titov, A.; Tlusty, P.; Toia, A.; Traxler, M.; Tsertos, H.; Vazquez, A.; Volkov, Y.; Wagner, V.; Walus, W.; Winkler, S.; Wisniowski, M.; Wojcik, T.; Wüstenfeld, J.; Zanevsy, Y.; Zumbruch, P.;
HADES is a second generation experiment designed to study dielectron production in proton, pion and heavy ion induced reactions at the GSI accelerator facility in Darmstadt. The physics programme of HADES is focused on in-medium properties of the light vector mesons. In this contribution we discuss relevance of dielectron spectroscopy to the problem of hadron mass origin. We present status of the HADES experiment, demonstrate ists capability to identify rare dielectron signal and show first experimental results obtained from C+C reations at 2 AGeV.
  • Open Access LogoActa Physica Polonica B 35(2004)3, 1119-1125

Publ.-Id: 6228 - Permalink

Cluster coarsening and luminescence emission intensity of Ge nanoclusters in SiO2 layers
Lopez, J. M. J.; Zawislak, F. C.; Behar, M.; Fichtner, P. F. P.; Rebohle, L.; Skorupa, W.;

Publ.-Id: 6227 - Permalink

Behaviour of hydrogen impurity in aluminium alloys during anodizing
Iglesias-Rubianes, L.; Skeldon, P.; Thompson, G. E.; Kreissig, U.; Grambole, D.; Habazaki, H.; Shimizu, K.;
  • Thin Solid Films 424 (2003) 201

Publ.-Id: 6226 - Permalink

Synthesis and size control of Si nanocrystals by SiO/SiO2 superlattices and Er doping
Heitmann, J.; Kovalev, D.; Schmidt, M.; Yi, L. X.; Scholz, R.; Eichhorn, F.; Zacharias, M.;
  • Contribution to external collection
    Mat. Res. Soc. Symp. Proc. 737 (2003) 271

Publ.-Id: 6225 - Permalink

Characteristics of erbium-producing liquid metal ion sources
Ganetsos, T.; Mair, G. L. R.; Aidinis, C. J.; Bischoff, L.;
  • Physica B 340-342 (2003) 1166

Publ.-Id: 6224 - Permalink

14.5% normal-incidence reflectance of Cr/Sc X-ray multilayer mirrors for the water window
Eriksson, F.; Johansson, G. A.; Hertz, H. M.; Gullikson, E. M.; Kreissig, U.; Birch, J.;
  • Optics Letters 28 (2003) 2494

Publ.-Id: 6223 - Permalink

Modification of growth mode of Ge on Si by pulsed low-energy ion-beam irradiation
Dvurechenskii, A. V.; Smagina, J. V.; Zinovyev, V. A.; Grötzschel, R.; Teys, S. A.; Gutakovskii, A. K.;
  • Contribution to external collection
    Proc. of 11th Int. Symp. "Nanostructures: Physics and Technology", St. Petersburg, Russia, June 23-28, 2003, p. 305

Publ.-Id: 6222 - Permalink

Research of coatings containing zirkonium properties on metallic substrate
Deshkovskaya, A. A.; Lynkov, L. M.; Nagibarov, A. V.; Pham, M. T.; Richter, E.;
  • Doklady BGUNP 1 (2003) 57

Publ.-Id: 6221 - Permalink

Gluon Emission of Heavy Quarks: Dead Cone Effect
Thomas, R.; Kämpfer, B.; Soff, G.;
The lowest-order induced soft gluon radiation processes of heavy quarks are considered with the aim to quantify the dead cone effect. The dead cone effect is expected to suppress significantly the energy loss of charm quarks passing an amorphous colour-neutral deconfined medium, as anticipated in recent experiments at RHIC.
Keywords: Induced gluon radiation, energy loss, dead cone
  • Contribution to external collection
    Acta Physica Hungarica A 22(2005), 83

Publ.-Id: 6220 - Permalink

Uran-Aufnahme in Pflanzen - Transferfaktoren und chemische Speziation
Günther, A.;
  • Lecture (others)
    Friedrich-Schiller-Universität Jena, Biologisch-Pharmazeutische Fakultät 18.05.2004, Jena, Germany

Publ.-Id: 6219 - Permalink

Relaxation kinetics in amorphous carbon films: An insight from atomic scale simulation
Belov, A. Y.; Jäger, H. U.;
Using molecular-dynamics (MD) techniques and a hydrocarbon potential of Brenner with an increased C-C interaction range, we investigate kinetics of relaxation processes in tetrahedral amorphous carbon films (ta-C) with high sp3 fractions. The structural models for as-grown non-equilibrium ta-C networks were generated using MD film deposition simulation with ion energy of 80 eV. The results of MD simulations of low temperature annealing show that both film stress and energy behave with annealing time t as a+bexp(-t/t1). This exponential dependency is interpreted in terms of structural transformations in the amorphous carbon networks. It is also shown that the relaxation times for the energy and stress do not coincide, indicating that some atomic rearrangements in the networks may reduce their energy without changing the stress. At the annealing temperature of 1000 K, the relaxation constant t1 for energy was found to be in the range of 0.5-0.7 ns, depending on the simulation parameters. It considerably exceeds an estimate of 10 ps for the thermalization stage of the subplantation model for ta-C film formation from energetic C ions. A decrease in the ta-C energy during the first 10 ps of the simulated annealing is much larger than that predicted by the exponential law with the relaxation constant t1.
Keywords: Tetrahedral amorphous carbon; Intrinsic Stress; Structural relaxation; Molecular Dynamics
  • Thin Solid Films 482(2005)74-78

Publ.-Id: 6218 - Permalink

Bacteria from extreme environments: basis for new technical applications
Raff, J.; Selenska-Pobell, S.;
The Molecular Microbiological Group at the Institute of Radiochemistry, Research Centre Rossendorf nearby Dresden, performs as part of an institute from the Wissenschaftsgemein-schaft Gottfried Wilhelm Leibniz e.V. basic and applied research. Main interests are

- bacterial diversity of soil and water
samples highly contaminated with radionuclides and heavy-metals
- investigation and characterization of
metal-microbe interactions
- development of novel bacteria-based bioremediation strategies for cleaning contaminated wastewater
- use of bacteria or bacterial components as biotemplates for the formation of nanoclusters for biotechnological applications

Bacteria consist of only one single cell, but apart from their simple organisation and their small size they are an unbelievable complex and highly efficient group of creatures. Some bacteria are able to thrive at the most forbidding, uninviting places on Earth: they live in hot springs, in extremely alkaline or acid waters, in muds of marshes or even at the bottom of the ocean. For production of energy they can use different kinds of organic and inorganic matter or sun light. Against this background, investigation of bacteria recovered from extreme environments shows a great promise to discover novel and yet unknown properties of this interesting group of organisms.
  • BioMeT-Magazin (2004), 18

Publ.-Id: 6217 - Permalink

Comparison of TiN and Ti1-xAlxN coatings deposited on Al using plasma immersion ion implantation assisted deposition
Mukherjee, S.; Prokert, F.; Richter, E.; Möller, W.;
TiN and Ti1-xAlxN coatings were deposited on Al substrates using the plasma immersion ion implantation and deposition technique, employing a filtered Ti and Ti0.5Al0.5 cathodic arc in a nitrogen atmosphere. Negative pulsed bias voltages between 0 to –4.0 kV were applied with varying duty cycles, at a constant time-averaged bias. Stress measurements using X-ray diffraction reveal an increase and then a decrease in the intrinsic compressive stress at increasing on-time bias, more pronounced for Ti1-xAlxN coatings. A bias dependent preferred orientation is observed for both the coatings, with [200] being the preferred orientation at higher bias. The hardness always reduces for TiN coatings with increase in bias, whereas for Ti1-xAlxN it shows a reverse trend. The results are qualitatively explained by the role played by Al in Ti1-xAlxN. The results indicate that the peak bias plays a more dominant role than time averaged bias.
Keywords: Plasma immersion ion implantation assisted deposition, titanium nitride, preferred orientation, stress
  • Surface and Coatings Technology 200 (2005)7 2459-2464

Publ.-Id: 6216 - Permalink

Structures and energetics of defects: a comparative study of 3C- and 4H-SiC
Gao, F.; Posselt, M.; Belko, V.; Zhang, Y.; Weber, W. J.;
The structures, formation energies and stable configurations of elementary defects (vacancies, antisite defects and self-interstitials) in 3C- and 4H-SiC are studied using classical molecular dynamics simulation with a recently developed interatomic potential. The defect structures in 3C-SiC are relatively simple, but those in 4H-SiC are more complex. The interstitials between hexagonal and trigonal rings are characteristic for 4H-SiC and other hexagonal polytypes, but not for 3C-SiC. The number of non-equivalent defects in 4H-SiC is much higher than that in 3C-SiC, and a considerable difference is found for some complex and anisotropic defects, in particular for the dumbbells D1Si+Si, D1Si+C and D2Si+C. The lattice deformation beyond the first nearest neighbor shell, which depends strongly on the polytype structure, plays an important role on these effects. However, the polytypism does not have a significant influence on the structure and energetics of the more compact and isotropic defects, such as vacancies and antisite defects. Despite the complexity of defect configurations, the tetrahedral interstitials have very similar properties in 3C- and 4H-SiC because their first, second and third nearest neighbor shells are identical.
Keywords: Defects and defect properties; Computer simulations; 3C- and 4H-SiC

Publ.-Id: 6215 - Permalink

Ultrafast X-ray Computed Tomography with a Linearly Scanned Electron Beam Source
Hampel, U.; Speck, M.; Koch, D.; Menz, H.-J.; Mayer, H.-G.; Fietz, J.; Hoppe, D.; Schleicher, E.; Zippe, C.; Prasser, H.-M.;
We devised and tested a novel computed tomography approach that utilises a scanned electron beam X-ray source to produce fast sequences of tomographic images of transient density distributions. In contrary to classical electron beam tomography we used a linear deflection pattern for the electron beam and a non-annular detector arc to record transmission data of an object from different projection angles. This approach gives the highest achievable axial resolution and is comparatively moderate in effort and costs. For the inverse problem we applied iterative image reconstruction techniques to reconstruct the density distribution from a limited data set. The method has been experimentally tested on static and dynamic phantoms with a frame rate of 1000 images per second and a spatial resolution of approximately 1 mm in plane and axial.
Keywords: high-speed X-ray computed tomography, limited angle reconstruction
  • Flow Measurement and Instrumentation 16 (2005), 65-72

Publ.-Id: 6213 - Permalink

Magnetic field controlled FZ single crystal growth of intermetallic compounds
Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Uhlemann, H.-J.; Fischer, F.; Schultz, L.;
Intermetallic Rare-Earth-Transition-Metall compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of massive single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.
  • Journal of Crystal Growth 275(2005), e1533-e1538

Publ.-Id: 6211 - Permalink

Magnetic field controlled FZ single crystal growth of intermetallic compounds
Hermann, R.; Behr, G.; Gerbeth, G.; Priede, J.; Uhlemann, H.-J.; Fischer, F.; Schultz, L.;
Intermetallic Rare-Earth-Transition-Metall compounds with their coexistence of magnetic ordering and superconductivity are still of great scientific interest. The crystal growth of massive single crystals is very often unsuccessful due to an unfavourable solid-liquid interface geometry enclosing concave fringes. The aim of the work is the contactless control of heat and material transport during floating-zone single crystal growth of intermetallic compounds. This control is provided by a tailored design of the electromagnetic field and the resulting electromagnetically driven convection. Numerical simulations for the determination of the electromagnetic field configuration induced by the RF heater coil and the solution of the coupled heat and hydrodynamic equations were done for the model substance Ni with and without additional magnetic field. As a result, an innovative magnetic two-phase stirrer system has been developed which enables the controlled influence on the melt ranging from intensive inwards/outwards flows to flows almost at rest. The selection of parameters necessary for the desired fluid flow is determined from numerical simulation. The basis for the calculations are the process-related fluid flow conditions which are determined by the mode of heating, heat radiation at the free surface and material parameters. This treatment of the problem leads to the customised magnetic field for the special intermetallic compound. The application of the new magnetic system leads to a distinct improvement of the solid-liquid interface validated on experiments with the model substance Nickel.
  • Lecture (Conference)
    14th "International Conference on Crystal Growth", 09.-13.08.2004, Grenoble, France

Publ.-Id: 6210 - Permalink

Experimental Evidence of Si Nanocluster delta-Layer Formation in Buried and Thin SiO2 Films Induced by Ion Irradiation
Röntzsch, L.; Heinig, K. H.; Schmidt, B.;
Self-aligned Si nanocluster (NC) formation in thin MOSFET gate oxides by means of ion beam mixing and post-irradiation annealing of SiO2-Si interfaces is proven for the first time by cross-section TEM. This study proves a recent prediction based on kinetic Monte Carlo (KLMC) simulations that a delta-layer of tiny Si NCs in SiO2, located 2…3nm apart from the SiO2-Si interface, can be fabricated by ion irradiation [1]. Such a self-aligned NC delta-layer configuration meets the requirements of non-volatile multi-dot floating-gate memory transistors [2], on which immense research effort has been spent in recent years.
By conventional TEM techniques the delta-layer of Si NCs in SiO2 can not be observed due to the low mass contrast between Si and SiO2 and the tininess of the Si NCs which have a mean diameter of 1.5nm. Here we present a method of mass contrast enhancement of such tiny Si NCs by alloying them with Ge. For this purpose, a thin Ge layer was embedded into the oxide far above the SiO2-Si interface, i.e. outside the mixing range of the SiO2-Si interface in order not to interfere with the original Si NC formation process. During post-irradiation annealing, diffusing Ge atoms are captured by the Si NCs due to the strong Si-Ge bond.
Keywords: ion-beam-mixing, SiO2-Si interface, ion irradiation, self-alignment, Si nanocluster, Ge decoration, multi-dot, non-volatile memory
  • Contribution to external collection
    Materials Science in Semiconductor Processing 7(2004), 357-362
    DOI: 10.1016/j.mssp.2004.09.098
  • Lecture (Conference)
    EMRS Spring Meeting, 26.05.2004, Strasbourg, France

Publ.-Id: 6208 - Permalink

Limitations on ultra-thin multilayers: pulsed cathodic arc and computer simulation
Chun, S. Y.; Chayahara, A.; Posselt, M.;
Nanoscale metallic multilayers have been deposited by a pulsed double-cathodic arc deposition with varying thicknesses of each layer from a few to tens of angstroms and examined by cross-sectional transmission electron microscopy (XTEM). TRIDYN computer simulations are performed to get a better understanding of the nanoscale deposition of multilayers during the cathodic arc deposition process. Their results are compared with the experimental data. For the higher ion fluence ( > 1.e16 ions/cm**2 ) and larger bilayer thickness ( > 2 nm), the periodicity of multilayers was good. However, the results of the simulations for the lower ion flux and smaller bilayer thickness reveal that the individual layers are intermixed and diffused. The experimental results are in good agreement with those of simulations that the limit of bilayer period of the ultra-thin multilayers is approximately 2 nm in the present case.
Keywords: Pulsed cathodic arc; Multilayers and computer simulation

Publ.-Id: 6207 - Permalink

Developmental changes in the activity of aromatic amino acid decarboxylase and catechol-O-methyl transferase in pigs: a positron emission tomography study
Brust, P.; Walter, B.; Hinz, R.; Füchtner, F.; Müller, M.; Steinbach, J.; Bauer, R.;
Newborn (7-10 days old) and young (6-8 weeks old) pigs were used to study the metabolism of 6-[F-18]fluoro-L-DOPA (FDOPA) in various brain regions with positron emission tomography (PET). Compartmental modeling of PET data was used to calculate the rate constants for the decarboxylation of FDOPA (k(3)) and for the metabolism of the resulting [F-18]fluoro-dopamine (k(cl)). Whereas general physiological parameters such as cerebral blood flow, cerebral oxygen uptake, arterial blood gases and glucose concentration remained unchanged in young pigs as compared to newborns, a 50-200% increase of k(3) in frontal cortex, striatum and mesencephalon was found. Also a 60% enhancement of k(cl) in the frontal cortex was measured, which is related to changes of the catechol-O-methyl-transferase (COMT) activity and implies a special function of this enzyme in the development of this brain region. In addition, measurement of plasma metabolites of FDOPA with HPLC was performed. The metabolism of FDOPA in young pigs was significantly faster than in newborns. Calculation of the rate constant for O-methylation of FDOPA by COMT revealed a significant elevation of this enzyme activity in young pigs compared to newborns. The increase of AADC and COMT activity with brain development is considered to be associated with special stages of neuronal maturation and tissue differentiation.
Keywords: aromatic amino acid decarboxylase; cerebral blood flow; catechol-0-methyl transferase; development; dopamine; pig; positron emission tomography
  • Neuroscience Letters, 364(2004)3, 159-163

Publ.-Id: 6206 - Permalink

Age-dependent effects of severe traumatic brain injury on cerebral dopaminergic activity in newborn and juvenile pigs
Walter, B.; Brust, P.; Füchtner, F.; Müller, M.; Hinz, R.; Kuwabara, H.; Fritz, H.; Zwiener, U.; Bauer, R.;
There is evidence that the dopaminergic system is sensitive to traumatic brain injury (TBI). However, the age-dependency of this sensitivity has not been studied together with brain oxidative metabolism. We postulate that the acute effects of severe TBI on brain dopamine turnover are age-dependent. Therefore F-18-labelled 6-fuoro-L-3,4-dihydroxyphenylalanine (FDOPA) together with Positron-Emission-Tomography (PET) was used to estimate the activity of the aromatic amino acid decarboxylase (AADC) in the brain of Ill newborn piglets (7-10 days old) and nine juvenile pigs (6-7 weeks old). Six newborn and five juvenile animals were subjected to a severe fluid-percussion (FP) induced TBI. The remaining animals were used as sham operated untreated control groups. Simultaneously, the regional cerebral blood flow (CBF) was measured with colored microspheres and the cerebral metabolic rates of oxygen and glucose were determined. At 1 h after FP-TBI, [F-18]FDOPA was infused and PET sca! nning was performed for 2 h. At 2 h after FP-TBI administration, a second series of measurements of physiological values including CBF and brain oxidative metabolism data had been obtained. Severe FP-TBI elicited a marked increase in the rate constant for fluorodopamine production (k(3)(FDOPA)) in all brain regions of newborn piglets studied by between 97% (mesencephalon) and 143% (frontal cortex) (p < 0.05). In contrast, brain hemodynamics and cerebral oxidative metabolism remained unaltered after TBI. Furthermore, the permeability-surface area product of FDOPA (PSFDOPA) was unchanged. In addition, regional blood flow differences between corresponding ipsi- and contralateral brain regions did not occur after TBI. Thus, it is suggested that severe FP-TBI induces an upregulation off AADC activity of newborn piglets that is not related to alterations in brain oxidative metabolism.
  • Journal of Neurotrauma 21(2004)8, 1076-1089

Publ.-Id: 6205 - Permalink

Messung von Phasen- und Konzentrationsverteilungen in Blasensäulen mit Positronen-Emissions-Tomographie
Zippe, C.; Hoppe, D.; Fietz, J.; Hampel, U.; Hensel, F.; Mäding, P.; Prasser, H.-M.; Zippe, W.;
Schaumbildung in Chemiereaktoren ist eine oft unerwünschte Begleiterscheinung bei mehrphasigen Prozessen und Anlagenstörfällen. Die hier vorgestellte Experimentiertechnik gestattet die berührungslose Messung von Phasen- und Konzentrationsverteilungen mittels PET und wurde für Grundlagenuntersuchungen zum Verhalten von Tensiden bei Schaumbildungs- und Zerfallsprozessen in rohrförmigen Reaktionsgefäßen entwickelt und erprobt.
Keywords: PET, Phasenverteilung, Konzentrationsverteilung, Blasensäule, Chemiereaktor, Anlagenstörfall, Tensidanreicherung

Publ.-Id: 6204 - Permalink

Two-proton small-angle correlations in central heavy-ion collisions: a beam-energy- and system-size-dependent study
Kotte, R.; Alard, J. P.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, M. L.; Caplar, R.; Cordier, E.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gasparic, I.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Herrmann, N.; Hildenbrand, K. D.; Hong, B.; Kecskemeti, J.; Kim, Y. J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kress, T.; Lebedev, A.; Leifels, Y.; Lopez, X.; Merschmeyer, M.; Mösner, J.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; de Schauenburg, B.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Yushmanov, Y.; Zhilin, A.;
Small-angle correlations of pairs of protons emitted in central collisions of Ca + Ca, Ru + Ru and Au + Au at beam energies from 400 to 1500 MeV per nucleon are investigated with the FOPI detector system at SIS/GSI Darmstadt. Dependences on system size and beam energy are presented which extend the experimental data basis of pp correlations in the SIS energy range substantially. The size of the proton-emitting source is estimated by comparing the experimental data with the output of a final-state interaction model which is processing either static Gaussian sources or the one-body phase-space distribution of protons provided by the BUU transport approach. The trends in the experimental data, i.e. system-size and beam energy dependences, are well reproduced by this hybrid model. However, the pp correlation function is found rather insensitive to the stiffness of the equation of state entering the transport model calculations.
Keywords: PACS. 25.70.Pq, 25.75.Gz
  • European Physical Journal A 23(2005), 271
    DOI: 10.1140/epja/i2004-10075-y
  • Lecture (Conference)
    FOPI Collaboration Meeting, 02.04.2004, Darmstadt, Germany

Publ.-Id: 6203 - Permalink

From QCD lattice calculations to the equation of state of quark matter
Peshier, A.; Kaempfer, B.; Soff, G.;
We describe two-flavor QCD lattice data for the pressure at a nonzero temperature and vanishing chemical potential within a quasiparticle model. Relying only on thermodynamic consistency, the model is extended to nonzero chemical potential. The results agree with lattice calculations in the region of a small chemical potential.

Publ.-Id: 6202 - Permalink

Neutral oxorhenium(V) and oxotechnetium(V) complexes with novel amide thioether dithiolate ligands derived from cysteine
Noll, B.; Hilger, C. S.; Leibnitz, P.; Spies, H.;
Summary. Bifunctional ligands able to form neutral complexes with radioactive technetium and rhenium and to couple to biological relevant anchor groups play an important role in the design of new radiopharmaceuticals for diagnosis and therapy. A novel tetradentate amide thioether dithiolate ligand HS-CH2CH2-S-CH2CONH-CH(COOR)CH2SH(H3SNSS) with R = CH3, C10H21 was synthesized that forms stable complexes with technetium and rhenium in oxidation state V. The molecular structures of the rhenium and technetium complexes MO(SNSS) were determined by X-ray structural analysis and show that the metal coordination number is five and the coordination polyhedron is between square-pyramidal and trigonal-bipyramidal. The pendent ester group allows coupling of the chelate unit at biologically relevant anchor groups. As a relevant representative the X-ray structural analysis of the rhenium decylester complex was carried out. The complex formation with Tc at teh n.c.a. level and 186Re at 10-10M level is described.
  • Radiochimica Acta 92(2004)4-6, 271-276

Publ.-Id: 6200 - Permalink

Labelling of biomolecules using 99mTc(III) and 188Re(III) mixed-ligand complexes
Seifert, S.; Künstler, J.-U.; Schiller, E.; Pietzsch, H.-J.; Pawelke, B.; Bergmann, R.; Spies, H.;
The trigonal-bipyramidal Re(III) and Tc(III) mixed-ligand complexes of the general formula [MIII(Ln)(Lm)] (M = Tc, Re; Ln = 2,2‘,2“-nitrilotris-(ethanethiol) NS3 or NS3-COOH; Lm = isocyanide or phosphine) are stable against ligand exchange with cysteine or glutathione and in vitro in incubations with plasma as well as whole blood of rats and represent therefore an alternative to the more unstable ‘3+1‘ Re(V) or Tc(V) complexes concerning the possibilities of designing biologically interesting 99mTc or 188Re labelled compounds1. Improved methods for their preparation are presented. To avoid the unrequested formation of reduced-hydrolysed species of both metals the preparation of complexes is performed in a two-step procedure.
At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand NS3 or its carboxyl derivative NS3-COOH and the monodentate phosphine or isocyanide ligands to the so-called ‘4+1’ complexes. Copper(I) isocyanide complexes are used for preparing the ‘4+1’ complexes. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labelling of interesting molecules. The stability of the 99mTc and 188Re preparations is discussed. The introduction of a carboxyl group into the tetradentate ligand and/or the monodentate ligands enables the conjugation of biomolecules and controlling of lipophilicity.
  • Poster
    ISBOMC’04, Second International Symposium on Bioorganometallic Chemistry; Zürich, 14.-17.07.2004

Publ.-Id: 6199 - Permalink

99mTc and 188Re mixed-ligand complexes at lower oxidation state
Seifert, S.; Künstler, J.-U.; Schiller, E.; Pietzsch, H.-J.; Pawelke, B.; Bergmann, R.; Spies, H.;
Technetium and rhenium mixed-ligand complexes represent an important approach to the development of radiotracers for diagnostic and therapeutic application because of the many possibilities to vary their biobehaviour. The trigonal-bipyramidal Re(III) and Tc(III) complexes of the general formula [MIII(Ln)(Lm)] (M = Tc, Re; Ln = 2,2‘,2“-nitrilotris-(ethanethiol) NS3 or NS3-COOH; Lm = isocyanide or phosphine) are stable against ligand exchange with cysteine or glutathione and in vitro in incubations with plasma as well as whole blood of rats and represent therefore an alternative to the more unstable ‘3+1‘ Re(V) or Tc(V) complexes concerning the possibilities of designing biologically interesting 99mTc or 188Re labelled compounds. Improved methods for their preparation are presented. To avoid the unrequested formation of reduced-hydrolyzed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal ligand NS3 or its carboxyl derivative NS3-COOH and the monodentate phosphine or isocyanide ligands to the so-called ‘4+1’ complexes. Copper(I) isocyanide complexes are used for preparing the ‘4+1’ complexes. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of 188Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labeling of interesting molecules. The stability of the 99mTc and 188Re preparations is discussed. The introduction of a carboxyl group into the tetradentate ligand and/or the monodentate ligands enables the conjugation of biomolecules and controlling of lipophilicity.
  • Invited lecture (Conferences)
    19th KAIF/KNS Annual Conference, 25.-27.04.2004, Seoul, Korea
  • Invited lecture (Conferences)
    Institutskolloquium, The Korea Atomic Energy Research Institute, Hanaro Application Research, 24.04.2004, Daejeon, Republic of Korea,

Publ.-Id: 6198 - Permalink

Structural studies of epitaxial Au nanocrystals in rutile
Eichhorn, F.; Fromknecht, R.;
Besides promising applications for electronic nanostructures or nonlinear optical devices nanocrystalline Au may be used as efficient catalysis material (e.g. chemisorption of CO or hydrocarbons). The catalytic reaction is often very sensitive to the structure and size of the metal crystallites and their crystallographic orientation Both conditions may be controlled by growing the nanocrystals in a single crystalline non-metallic matrix.
Here, Au nanocrystals were generated inside rutile TiO2 by implantation of 260 keV Au ions. The growth in a matrix allows to stabilize the precipitates structurally. Furthermore, no impurities were introduced because of mass separation during the process. However, the host crystal is damaged by the ion impact processes. This damage may be reduced by in situ or post-implantation annealing.
Various x-ray scattering techniques were used for the structural characterization of the material: specular reflection for surface and near-surface studies, diffraction for determination of strain and crystal size, pole figure measurements to reveal the orientation relationship.
In the as-implanted state randomly oriented crystals with a size of 5 … 7 nm as well as crystals oriented in a fibre texture with axis parallel to the rutile surface normal have been obtained. Annealing at 1000 K let the nanocrystals grow to 15 nm; simultaneously the amount of epitaxially oriented Au crystals increases. The orientation relationship is controlled by the crystallographic axis of the rutile matrix surface so that the ensemble of the Au nanocrystals fits to the crystal symmetry of the matrix:
- the surface normal is the two-fold rutile [100] direction:
surface normal - Au < 2 1 1 > || TiO2 < 1 0 0 >
in the surface - Au < 1 1 0 > || TiO2 < 0 0 1 > and Au < 1 1 1 > || TiO2 < 0 1 0 >.
In order to fulfil the two-fold matrix symmetry there are two groups of Au crystallites rotated by 180° each to other around the surface normal.
- the surface normal is the four-fold rutile [001] direction:
surface normal - Au <110> || TiO2 <001>
In order to fulfil the four-fold matrix symmetry there are two groups of Au crystallites rotated by 90° each to other around the surface normal. Each of them is split into two sub-groups rotated by +9.7° and –9.7° around the surface normal from the “ideal” orientation: Au <110> + 9.7° and –9.7° || TiO2 <110 > and Au <100 > + 9.7° and –9.7° || TiO2 <110>.

Keywords: nanocrystals, Au, Rutile, x-ray diffraction, structure
  • Lecture (Conference)
    7th Biennial Conference on High Resolution X-Ray Diffraction and Imaging - XTOP 2004, Prague, Czech Republic, September 7-10, 2004

Publ.-Id: 6197 - Permalink

Herstellung von Nanometer-Strukturen mittels feinfokussiertem Ionenstrahl (FIB)
Mucke, S.;
Feinfokussierte Ionenstrahlen dienen in den Gebieten der Halbleiterindustrie und Materialforschung der Mikro- und Nanostrukturierung. Die vorliegende Arbeit beschäftigt sich mit den beiden Hauptanwendungen von fokussierten Ionenstrahlen, dem Materialabtrag und der ionenstrahlinduzierten Materialabscheidung. Dabei wird die hochauflösende Ionensäule CANION 31Z der Firma Orsay Physics mit Stromdichten von bis zu 10 A/cm2 und mit integriertem Gassystem eingesetzt. Es wird ausführlich auf Anwendungsbeispiele von Fokussierten Ionenstrahlsystemen im Bereich der Industrie und Forschung eingegangen.
Schwerpunktmäßig wird die Abscheidung von Wolfram aus dem Precursorgas W(CO)6 (Wolframhexacarbonyl) auf Si und SiO2 als Substrat untersucht, mit dem Ziel, gut leitfähige Drähte (hier im Sinne von Leiterbahnen) mit minimalem Querschnitt herzustellen. Die Optimierung der Ionenstrahl-Parameter dieser Feinfokussierten Ionenstrahlanlage bezüglich der Abscheidung steht im Vordergrund. Dabei wird ein kurzer Einblick in die Theorie der Schichtentstehung beim Abscheidevorgang gegeben. Untersuchungen der erzeugten Strukturen entsprechend der Schichtqualität und der Strukturabmessungen werden erläutert und die Ergebnisse diskutiert. Es konnten Wolframdrähte mit einer Länge von 20 ... 100 µm, einer Breite von minimal 150 nm und einer Höhe von maximal 600 nm angefertigt werden. Die Zusammensetzung der Drähte in Abhängigkeit der Prozessparameter wurde mittels AES bestimmt. Im optimalen Fall wurden die Schichtanteile zu 80% W, 5% O, 6% C und 9% Ga ermittelt (Angaben in Atomprozent). Der spezifische Widerstand der Wolframdrähte ist im Bereich 150 ... 320 µWcm gemessen worden.
Keywords: Fokussierter Ionenstrahl, MOCVD, Wolfram Nanodrähte, Sputtern
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-402 2004


Publ.-Id: 6196 - Permalink

Stability of melt flow due to traveling magnetic field in a closed ampoule
Grants, I.; Gerbeth, G.;
The linear three-dimensional instability of the flow due to a low frequency traveling magnetic field in a regular cylinder is studied numerically for height-to-diameter ratios in the range [0.5:2.5]. The first instability has the form of a non-rotating azimuthal wave with wave numbers between 1 and 6 depending on the aspect ratio. It is shown that the flow is stable if the Reynolds number is below 290. Even stronger stationary flows may be obtained in a flattened cylinder.
  • Journal of Crystal Growth 269(2004), 630-638

Publ.-Id: 6195 - Permalink

Classical MD study on the the mobility of di- and tri-interstitials
Posselt, M.;
In a recent work [1], a combined simulation method was applied to investigate ion-beam-induced defect formation in silicon. BCA simulations were used to treat the ballistic processes, whereas the subsequent fast relaxation and the first stage of thermally activated processes were described by classical MD calculations. It was found that the metastable defect structure formed immediately after ion impact consists not only of isolated vacancies and self-interstitials but also of complex defects. A more detailed analysis of the results shows, that at elevated implantation temperatures or during the annealing of the defect structures obtained at room temperature, di- and tri-interstitials are formed. In some cases a high mobility of these defects is observed. In agreement with former studies [2,3], the di-interstital is found to move relatively fast. The present contribution deals with systematic investigations on the migration of di- and tri-interstitials. The classical MD simulations allow direct investigations of the motion of defects and its atomic mechanisms. Particular attention is paid to the role of transformations between different modifications of di- or tri-interstitials. These transformations may lead to an substantial increase or decrease of the defect mobility. The present results are compared with the few literature data obtained by tight-binding and density-functional methods which employ mainly static potential energy calculations.
[1] M. Posselt, Mat. Res. Soc. Symp. Proc. 647 (2001) O2.1.1.
[2] G. H. Gilmer, T. Diaz de la Rubia, D. M. Stock, M. Jaraiz, Nucl. Instr. Meth. Phys. Res. B 102 (1995) 247.
[3] M. Hane, T. Ikezawa, G. H. Gilmer, Proc. SISPAD 2000, IEEE Catalog Number 00TH8502, p. 119 , IEEE, Piscataway, 2000.

Keywords: defect diffusion, silicon, simulation, molecular dynamics
  • Lecture (Conference)
    MRS 2004 Spring Meeting, April 12 - 16, 2004, San Francisco, USA

Publ.-Id: 6194 - Permalink

Multiple implantations - experiments and computer simulations
Posselt, M.; Mäder, M.; Lebedev, A.; Grötzschel, R.;
Advanced technologies use successive implantations of p- and/or n-dopants without any intermediate annealing steps. A characteristic example is the engineering of the regions of source, drain, extension and halo. The sequence of the implantations may influence the final distribution of dopants and radiation damage. In particular it affects the as-implanted distribution of dopants if in one or more implantation steps the direction of ion incidence is close to a major crystallographic axis of the silicon substrate. For example, extension implantations are often performed perpendicularly to the wafer surface, i.e. nearly parallel to the [100] axis. The defect production in previous implantations influences the shape of dopant and damage profiles in a subsequent channeling implantation step, since these defects may lead to increased dechanneling. Furthermore, the amorphization dose in a certain implantation step may be affected by the level of radiation damage formed during the previous steps. The present work deals with the simple example of two consecutive implantations in order to demonstrate the effects mentioned above. Two implantation sequences are investigated: (i) 35 keV B followed by 50 keV As into the [100] channel direction, (ii) 50 keV As followed by 35 keV B [100] channeling implantation. The depth profiles of B and As are measured by SIMS. The as-implanted damage is determined by RBS/C. The experimental data can be reproduced by atomistic computer simulations using the Crystal-TRIM code with an improved phenomenological model for damage buildup during multiple implantations. The present results contribute to a better understanding of ion-beam-induced defect formation and to progress in TCAD.

Keywords: ion implantation, silicon, process simulation
  • Lecture (Conference)
    MRS 2004 Spring Meeting, April 12 - 16, 2004, San Francisco, USA

Publ.-Id: 6193 - Permalink

Crack initiation determination for Charpy size 3-point bend specimens by ICFPD method
Dzugan, J.; Viehrig, H.-W.;
The paper deals with the problematic of determination of the crack initiation for three point bend specimens during fracture toughness testing of materials in the upper transition and upper shelf region. In the presented study was developed Induced Current Focussed Potential Drop method for the fracture mechanics tests of Single Edge Notched Bend specimens of Charpy size. The performance of the newly developed technique is shown here. Obtained crack initiation integrals are compared with Stretch Zone Width based crack initiation integrals.
  • Lecture (Conference)
    Fatigue and Fracture Mechanics, 20.-22.04.2004, Zinkovy, Czechia

Publ.-Id: 6192 - Permalink

Dose quantification from in-beam positron emission tomography
Enghardt, W.; Parodi, K.; Crespo, P.; Fiedler, F.; Pawelke, J.; Pönisch, F.;
Positron emission tomography (PET) imaging of the radioactivity distributions induced by therapeutic irradiation is at present the only feasible method for an in-situ and non-invasive monitoring of radiooncology treatments with ion-beams. The clinical implementation of this imaging technlogy at the experimental carbon ion therapy facility at the Gesellschaft für Schwerionenforschung (GSI) at Darmstadt, Germany is outlined and an interactive approach for a PET guided quantification of local dose deviations with respect to the treatment plan is presented.
Keywords: Positron emission tomography, Charged hadron therapy, Ion therapy
  • Radiotherapy and Oncology 73(2004)Suppl. 2, S96-Sp98

Publ.-Id: 6190 - Permalink

Betriebserfahrungen beim Online-Monitoring exothermer chemischer Prozesse mit adaptiven Stoff- und Wärmebilanzen
Schmitt, W.; Hessel, G.; Kryk, H.;
Es wird ein entwickeltes Überwachungssystem vorgestellt, das zum Online-Monitoring sicherheitstechnisch schwieriger chemischer Reaktionen in Rührkesselreaktoren entwickelt wurde. Die Industrieerprobung erfolgte an einer Mehrzweckanlage der Degussa AG.
Betriebserfahrungen und der praktische Nutzen werden am Beispiel des Semibatch-Betriebes eines heterogenen exothermen Hydrierprozesses aufgezeigt und diskutiert.
  • Contribution to external collection
    Fortschritte in Wissenschaft und industrieller Herstellung von Backhefe, Berlin: Versuchsanstalt der Hefeindustrie e.V., 2004, 87-96

Publ.-Id: 6189 - Permalink

Separation control by stationary and time periodic Lorentz forces
Weier, T.; Gerbeth, G.; Mutschke, G.;
Stationary and time periodic wall parallel Lorentz forces in streamwise direction have been used to control the suction side flow
of NACA 0015 and PTL IV hydrofoils. Experimental results, consisting of flow visualizations and force measurements in the low Reynolds number range $Re=0.5 \dots 1.5 \times 10^5$ will be presented.
A stationary Lorentz force may increase lift by two mechanisms: 1) reattaching the separated flow and therefore increasing the critical angle and 2) introducing circulation due to acceleration of the attached suction side flow. Periodic excitation by oscillatory Lorentz forces near the leading edge is able to reattach the separated flow with much less momentum input then required for stationary forcing. However, to increase the maximum lift gain requires a comparable expenditure for both methods. The action of a wall parallel Lorentz force compares well to that of momentum input by blowing.

Keywords: Lorentz force, separation control, periodic addition of momentum
  • Lecture (Conference)
    XXI International Congress of Theoretical and Applied Mechanics, 15 - 21 August 2004, Warsaw, Poland

Publ.-Id: 6186 - Permalink

Electromagnetic control of flow separation by stationary and time periodic forces
Weier, T.; Mutschke, G.; Gerbeth, G.;
Electromagnetic flow control is a viable option, if the fluid in question is electrically conducting. In the case of liquid metals or
semiconductor melts, this control method is being used on an industrial scale. The application of Lorentz forces to fluids of low
electrical conductivity like seawater and other electrolytes is less common, although first efforts date back to the 1950s [1]. The present talk gives a short overview on separation control with steady wall parallel Lorentz forces [2], while the main part reports on recent activities on time periodic forces. The latter topic reveals certain parallels to current aerodynamic research on separation control by oscillatory blowing. The main motivation to investigate time periodic Lorentz forces is that periodic input of momentum has proven to be around two orders of magnitude more efficient than steady blowing [3].

An electromagnetic body force F results from the vector product of current density j and magnetic induction B. For fluids of low
electrical conductivity (10 S/m) as seawater and other electrolytes, the currents due to the induced voltages are generally very low for magnetic fields of moderate strength (1 T). Consequently, the Lorentz force due to these currents is negligible. In order to obtain current densities large enough for flow control purposes it is therefore necessary to additionally apply an electric field.

There are several distinct features, that make the Lorentz force an attractive actuator: momentum is directly generated in the fluid
without associated mass flux; its frequency response is practically unlimited; virtually any excitation wave form might be realized by
feeding the electrodes with appropriate current. On the other hand, efficiency of momentum generation by weak magnetic and strong electric fields is generally small, since Joule losses dominate in electrically low conducting fluids.

For the experiments described in the following, an arrangement of flush mounted electrodes and permanent magnets producing a streamwise wall parallel Lorentz force has been used. The Lorentz force decays exponentially with the wall distance. The characteristic parameter to describe the Lorentz force action on the suction side flow is the effective momentum coefficient cµ. It relates the rms­value of the momentum injected by the Lorentz force to the freestream dynamic pressure multiplied by the foil area. Since the mechanism of periodic forcing is supposed to be connected to shear layer excitation (see [3]), the actuator should be placed near the separation line. A sketch of the NACA 0015 equipped with permanent magnets and electrodes is given in Fig. 1. Flow visualizations on an inclined flat plate (Fig. 2) show, that the otherwise fully separated flow can be reattached in an averaged sense by a time periodic Lorentz force acting near the leading edge. A characteristic feature of the flow are the vortices moving along the plate. F+ is the excitation frequency nondimensionalized by chord length and freestream velocity. Direct force measurements on the stalled NACA 0015 reveal that the maximum lift gain occurs around F+ 1, the forcing effect decays relatively
rapidly for higher frequencies. A specific lift increase at a constant angle of attack and relativ to the value for the separated flow can be obtained by oscillatory forcing with fractions of the momentum input necessary for steady Lorentz forces. In contrast, an equal increase of the maximum lift gain requires a similar expenditure of momentum for both control methods.

Direct numerical simulations (DNS) at lower Reynolds numbers have been performed by using an well-established spectral element method [4]. The results obtained confirm the experimental findings in a qualitative sense. Figure 3 shows a snapshot of velocity contours (gray) and streamtraces of the controlled flow around an hydrofoil of 30o angle of attack at Re = 500, cµ = ...
Keywords: Lorentzf force, separation control, periodic addition of momentum
  • Lecture (Conference)
    13th European Drag Reduction Meeting,17.06.2004, Aussois, France

Publ.-Id: 6185 - Permalink

Seawater Flow Transition and Separation Control
Weier, T.; Albrecht, T.; Mutschke, G.; Gerbeth, G.;
First efforts on using Lorentz forces to control the flow of electrically low conducting fluids date back to the 1950s [1]. The
present talk reports on recent activities to delay transition in flat plate boundary layers and to control separation at hydrofoils by means of streamwise, wall parallel Lorentz forces. The actuator consists of a strip­like arrangement of permanent magnets and electrodes as proposed by [2].

Direct Numerical Simulations (DNS) by means of a spectral element method investigate the stability of a flat plate boundary layer under the influence of the Lorentz force. The evolution of Tollmien­Schlichting waves and proper 3­D disturbances is reported. A
stabilizing effect of the mean profile modification due to the Lorentz forces applied was found, verifying the assumption of [2].

Separation control at hydrofoils is undertaken by means of steady [3] as well as time periodic Lorentz forces. The latter topic reveals certain parallels to current aerodynamic research on separation control by oscillatory blowing. The main motivation for applying time periodic momentum input is that efficiency can be around two orders of magnitude higher than in case of steady blowing [4]. Since the mechanism of periodic forcing is supposed to be connected to shear layer excitation (see [4]), the Lorentz force actuator is placed in the nose region of the NACA 0015 investigated here. Direct force measurements on the stalled NACA 0015 reveal that the maximum lift gain occurs around a nondimensionalized excitation frequency of F+ 1, decaying rapidly for larger frequencies. For stalled hydrofoils, the same lift increase can be obtained by oscillatory forcing with only fractions of the momentum input necessary for steady forcing. In contrast, an equal increase of the maximum lift gain requires a similar expenditure of momentum for both control methods. DNS at lower Reynolds numbers confirm the experimental findings in a qualitative sense.

[1] Resler, E.L., Sears, W.: The prospects for
magneto­aerodynamics. J. Aero. Sci. 25, 235­245, 1958.

[2] Gailitis, A., Lielausis, O.: On a possibility to reduce the
hydrodynamic resistance of a plate in an electrolyte. Applied
Magnetohydrodynamics. Reports of the Physics Institute, 12, 143­146,
1961 (in Russian).

[3] Weier, T., Gerbeth, G., Mutschke, G., Lielausis, O., Lammers, G.:
Control of Flow Separation Using Electromagnetic Forces. Flow,
Turbulence and Combustion, 71, 5-17, 2003.

[4] Greenblatt, D., Wygnanski, I.J.: The control of flow separation by
periodic excitation. Prog. Aero. Sci., 36, 487­545, 2000.
Keywords: Lorentz force, flow control, transition delay, separation control
  • Lecture (Conference)
    International Workshop on "Flow Control by Tailored Magnetic Fields (FLOWCOMAG)", 01.-02.04.2004, Dresden, Germany

Publ.-Id: 6184 - Permalink

Advanced Thermal Processing of Semiconductor Materials by Flash Lamp Annealing
Skorupa, W.; Panknin, D.; Voelskow, M.; Anwand, W.; Gebel, T.; Yankov, R. A.; Paul, S.; Lerch, W.;
The use of flash lamp annealing for processing semiconductor materials is outlined. Specific applications include ultra-shallow junction formation and heteroepitaxial growth of improved quality thin films of cubic silicon carbide. It is demonstrated that flash lamp annealing holds great promise as a technique for fabricating novel devices.
Keywords: flash lamp annealing, ultra shallow junctios, silicon carbide-silicon heteroepitaxy, ion implantation
  • Lecture (Conference)
    Materials Research Society Spring Meeting, Symp.C: Silicon Front-End Junction Formation—Physics and Technology, 12.-16.04.2004, San Francisco, USA
  • Contribution to proceedings
    Materials Research Society Spring Meeting, Symp.C: Silicon Front-End Junction Formation - Physics and Technology, 12.-16.04.2004, San Franzisco, USA
    Proceeding 810(2004), C4.16, C4.16

Publ.-Id: 6183 - Permalink

Contactless inductive flow tomography: theory and experiment
Stefani, F.; Gerbeth, G.; Gundrum, T.;
When a moving electrically conducting fluid is exposed to an applied magnetic field, electrical currents are induced that give rise to an additional magnetic field. The ratio of the induced field to the applied field is determined by the magnetic Reynolds number Rm. If Rm is not too small, the induced field can be measured in the exteriour of the fluid. Applying the imposed magnetic fields in different directions and measuring the respective induced fields one can gather sufficient information to reconstruct, at least approximatively, the velocity structure of the fluid. The theory of such a contactless inductive flow tomography (CIFT) is delineated, and its practical feasibility is demonstrated in a liquid metal experiment. Qualitative as well as quantitative changes of the flow field were resolved by the CIFT method in a reasonable and reproducible way.
  • Lecture (Conference)
    XXI International Congress of Theoretical and Applied Mechanics, 15-21 August 2004, Warsaw, Poland

Publ.-Id: 6182 - Permalink

Inferring flows from magnetic field constraints
Stefani, F.; Gerbeth, G.; Gundrum, T.; Xu, M.;
Examplified by three case studies, we address the problem on how flow structures can be inferred from various magnetic field constraints. At first, we present the contactless inductive flow tomography in which we reconstruct the three-dimensional velocity field from externally measured induced magnetic fields. At second, we reconsider the optimization problem for the sodium flow in the Riga dynamo experiment. The third example concerns the special inverse spectral dynamo problem on how a spherically symmetric alpha^2 dynamo can become oscillatory.
  • Lecture (Conference)
    International Workshop on "Flow Control by Tailored Magnetic Fields (FLOWCOMAG)", 01.-02.04.2004, Dresden, Germany

Publ.-Id: 6181 - Permalink

Nonlinear transition of a flow driven by a rotating magnetic field
Grants, I.; Gerbeth, G.;
Non-normal nonlinear transition of a linearly stable liquid metal flow driven by a rotating magnetic field is simulated numerically. Three dimensional Navier-Stokes equations are solved by a highly accurate spectral methods. Response of the flow to noise is simulated introducing a random body force. We observe four flow regimes. At a low control parameter the flow response does not differ from the response of a fluid at rest. In the second regime the amplitude of response is considerably higher though it scales linearly with the noise amplitude. Nonlinear intermittent outbursts are observed in the third regime. Duration of outbursts increases with noise amplitude until they merge in a continuous series in the fourth regime. We demonstrate that direct numerical simulation of the flow response to random forcing can uncover mechanisms which lead to transition in linearly stable flows.
  • Lecture (Conference)
    XXI International Congress of Theoretical and Applied Mechanics, 15.–21.08.2004, Warsaw, Poland

Publ.-Id: 6180 - Permalink

Investigation of the Fluid Flow Driven by an Alternating Magnetic Field with Ultrasonic Doppler Velocimetry
Cramer, A.; Varshney, K.; Gerbeth, G.;
We report on an experimental study of the influence of technical frequency pulsating magnetic field on a liquid metal volume. Such single-phase a.c. fields are widely used in metallurgy. Ultrasonic Doppler Velocimetry (UDV) has been used to determine the topology of the flow in a liquid metal column contained in a cylindrical vessel. Profile-scan-rates exceeding 25 Hz permit to acquire sequential time series for different radial co-ordinates which in turn allow to map the statistical properties of the flow. Concerning the sensitivity of UDV it was possible to measure values of the velocity down to a few mm/s. Even the flow is no more laminar in this regime almost any industrial situations are more turbulent. Limited by the maximum current which can be supplied to our magnet a range nearly spanning one order of magnitude of the driving magnetic field strength could be investigated. By that scaling laws derived analytically can be checked over a wide parameter range of industrial interest. The characteristic velocity was estimated from the time averaged mean profile in the centre of the container. Here the maximum absolute values of the vertical velocity component are found throughout the whole vessel in the up-stream in the upper half and the downstream in the lower half. Both local maxima scale nearly perfectly linear with the applied magnetic induction. This characteristic is similar to that of classical turbulent shear flows, even here the skin depth is not large compared to the dimension of the bath.
Keywords: MHD, fluid flow, alternating magnetic field, flow measurement techniques, ultrasonic Doppler velocimetry
  • Lecture (Conference)
    International Symposium HES-04 Heating by Electromagnetic Sources, 23.-25.06.2004, Padua, Italy
  • Contribution to proceedings
    International Symposium on Heating by Electromagnetic Sources (ISBN 88-86281-92-7), 23.-25.06.2004, Padua, Italy, 413-420

Publ.-Id: 6179 - Permalink

New possibilities for velocity measurements and model experiments in liquid metal processing
Cramer, A.; Varshney, K.; Gerbeth, G.;
Potential difference probes and ultrasound have been employed to investigate liquid metal flows in cylindrical containers.
The fluid motion was driven by either a rotating or a pulsating magnetic field. Experimental results containing flow mapping and scaling of mean velocities for very small driving forces will be presented. We report on our new MULTIMAG facility which allows for almost any combination of rotating, traveling, pulsating and d.c. magnetic fields in extended geometries for industrially relevant regimes.
  • Lecture (Conference)
    XXI International congress of theoretical and applied mechanics (ICTAM), 15.-21.08.2004, Warsaw, Poland

Publ.-Id: 6178 - Permalink

Directional solidification of Pb-Sn alloys affected by a rotating magnetic field
Eckert, S.; Willers, B.; Michel, U.; Zouhar, G.; Nikritjuk, P. A.; Eckert, K.;
An experimental and numerical study with respect to the influence of a rotating magnetic field (RMF) on the directional solidification of a Pb-Sn alloys is reported. A cylindrical crucible with a diameter of 50 mm was positioned on a water cooled copper chill thus inducing an axial heat transfer from the mold. The electromagnetically driven convection shows a distinct effect on the solidification parameters such as the cooling rate, the temperature gradient or the growth velocity of the liquidus isotherm resulting in significant modifications of the observed macro- and microstructures. The fluid flow promotes the heat transfer rate and decreases the temperature gradients in the melt. Analyzing the columnar-equiaxed transition (CET) a dependence of the CET position and shape on the applied Taylor number was demonstrated. The experiments also revealed that the permanent modification of the fluid volume due to the movement of the solidification front prevents the development of stationary flow pattern as known for the isothermal case.

Keywords: solidification, forced convection, rotating magnetic field, CET, macrosegregation
  • Lecture (Conference)
    XXI International Conference of Theoretical and Applied Mechanics (ICTAM), 15.-21.08.2004, Warsaw, Poland

Publ.-Id: 6177 - Permalink

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