Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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31745 Publications
Structural relation between Si and SiC formed by carbon ion implantation
Eichhorn, F.; Kögler, R.; Mücklich, A.; Schell, N.; Matz, W.;
SiC ion beam synthesis by implantation of C ions into Si is a multiple-step process. In our experiments C ion implantation was performed at TII = RT ... 800 °C to a C concentration in the range of 0.3 to 33.5 at% into Si and SIMOX substrates. SiC phase formation and the related lattice strain were studied by different synchrotron X-ray scattering techniques using ROBL at ESRF Grenoble and by transmission electron microscopy:
1. Low ion fluences result in a Si lattice expansion in the order of 1E-3.
2. Intermediate ion fluences and temperatures generate small SiC pre-cursors with enhanced lattice spacings and reduced strain in the Si lattice.
3. High fluences and temperatures form 3C-SiC crystallites with three types of orientation:
- random-like orientation
- fibre texture with axis parallel to the surface normal with a mean orientation spread of 6°
- high alignment to the Si matrix: SiC<001> || Si<001> and SiC<110> || Si<110> due to a partial coherent growth of SiC in the Si matrix. The orientation spread is in the range from 2° to 5°.
Ion beam synthesis of SiC in Si at elevated temperatures favours the growth of highly oriented crystallites.

Keywords: SiC, Si, ion beam synthesis, X-ray diffraction, texture study, synchrotron X-rays
  • Poster
    E-MRS2001 Spring Meeting, June 5 - 8, 2001, Strasbourg (France)

Publ.-Id: 3724 - Permalink


Der Freie-Elektronen-Laser in Dresden/Rossendorf und seine Anwendungen in der Infrarot-Spektroskopie von Halbleitern und anderen Systemen
Helm, M.;
Am Forschungszentrum Rossendorf wird zur Zeit ein Freie-Elektronen-Laser (FEL) gebaut, der Ende 2001 betriebsfertig sein soll. Mittelfristig soll ein Wellenlängenbereich von 5-200 um überstrichen werden können. Ich möchte einen Überblick über dieses Projekt geben, mit Darstellung der angeschlossenen experimentellen Infrastruktur. Desweiteren möchte ich über die möglichen spektroskopischen Anwendungen sprechen, die im Prinzip alle Systeme mit niederenergetischen Anregungen (10-100 meV) betreffen. Der Schwerpunkt dabei wird, gemäß meines Erfahrungshintergrundes, auf dem Gebiet der Halbleiter-Quantenstrukturen liegen.
Keywords: semiconductors, free-eelctron-laser, infrared spectroscopy
  • Lecture (others)
    Seminarvortrag Universität Giessen (25.01.2001)

Publ.-Id: 3723 - Permalink


Elektronen in künstlichen Halbleiterstrukturen: vom Modellsystem für Quantenmechanik und Festkörperphysik zum Quantenbauelement
Helm, M.;
please contact the author
Keywords: semiconductors quantum structures
  • Lecture (others)
    Kolloquium an der TU Dresden (23.01.2001)

Publ.-Id: 3722 - Permalink


Structure refinement of the silicon carbide polytypes 4H and 6H: unambiguous determination of the refinement parameters
Bauer, A.; Reischauer, P.; Kräusslich, J.; Schell, N.; Matz, W.; Götz, K.;
The atomic positions of the silicon carbide polytypes 6H and 4H differ slightly from an ideal tetrahedron. These small deviations can be investigated by X-ray diffraction of so-called "quasiforbidden" reflectios, which are very sensitive to the extremly small variations in the structure.
Keywords: SiC; atomic structure; synchrotron X-ray diffraction
  • Acta Cryst. A57 (2001) 60-67

Publ.-Id: 3721 - Permalink


Formation of the phases Ti3Al and TiAl by high dose implantation of Aluminium into Titanium
Tsyganov, I. A.; Wieser, E.; Matz, W.; Mücklich, A.; Reuther, H.;
formation of buried intermetallic Ti-Al-phases by high doose Al implantation
Keywords: ion implantation; titanium; X-ray diffraction, TEM, AES
  • Contribution to proceedings
    1st International Congress on Radiation Physics and Chemistry of Condensed Matter, High Current Electronics, and Modifikation of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, Sept. 14 - 29, 2000

Publ.-Id: 3720 - Permalink


Modification of Titanium by ion implantation of Calcium and/or Phosphorus
Tsyganov, I. A.; Wieser, E.; Matz, W.; Reuther, H.; Oswald, S.; Pham, M. T.; Richter, E.;
study of implantation treatment of Ti with Ca and P for improving hydroxylapatite formation
Keywords: ion implantation, hydroxylapatite, X-ray diffraction; AES
  • Contribution to proceedings
    1st International Congress on Radiation Physics and Chemistry of Condensed Matter, High Current Electronics, and Modifikation of Materials with Particle Beams and Plasma Flows, Tomsk, Russia, Sept. 14 - 29, 2000

Publ.-Id: 3719 - Permalink


Rossendorfer Beamline ROBL in Grenoble: Synchrotronstrahlung für Ökologie- und Materialforschung
Matz, W.;
Übersicht über ROBL / ausgewählte Ergebnisse
  • Lecture (others)
    Tag der offenen Tür des FZR, 16. September 2000

Publ.-Id: 3718 - Permalink


Influence of thermal treatment and cyclic plastic deformation on the defect structure in ultrafine-grained nickel
Thiele, E.; Bretschneider, J.; Hollang, L.; Schell, N.; Holste, C.;
Ultrafine-grained nickel samples were submitted to thermal treatment and cyclic plastic deformation in order to investigate the stability of the defect structure. Investigations by means of synchrotron radiation diffraction revealed that the mean volume expansion, long-range and short-range internal strains are diminished in consequence of the cyclic plastic deformation.
Keywords: ultrafine-grained nickel, cyclic plastic deformation, synchrotron X-ray diffraction, internal strains
  • Contribution to proceedings
    In: T. C. Lowe and R. Z. Valiev (eds.) Investigations and Applications of Severe Plastic Deformation, Proceedings of NATO Advanced Research Workshop, Moscow, Aug. 2 - 6 1999; Kluwer Academic Publishers, (2000) 173-178

Publ.-Id: 3717 - Permalink


Change of internal strains in ultrafine-grained nickel due to cyclic plastic deformation
Thiele, E.; Hecker, M.; Schell, N.;
Ultra-fine grained nickel samples were cyclically deformed at room temperature and at 200°C. The mean grain size of about 200 nm, determined by SEM and from the broadening of synchrotron diffraction profiles remained nearly constant, whereas the spectrunm of internal strains changed in consequence of the cyclic deformation. The relation between the profile shape ans asymmetry and the {hkl} reflection type suggests the existence of long range granular stresses in the original ufg samples.
Keywords: ultrafine-grained nickel, cyclic plastic deformation, synchrotron X-ray diffraction, diffraction profile analysis, internals strains and stresses
  • Materials Science Forum 321-324 (2000) 598-603

Publ.-Id: 3716 - Permalink


Characterisation of crystallinity of SiC-surface layers produced by ion implantation
Theodossiu, E.; Baumann, H.; Klimenkov, M.; Matz, W.; Bethge, K.;
Carbon implantations into silicon were carried out in order to form thin surface layers of SiC. Single crystalline <100> silicon samples were implanted with 40 keV 13C ions with a fluence of 3.8x1017 ions/cm2 and subsequently thermally treated under high vacuum conditions at different temperatures using a 20 keV electron beam. The isotope 13C offers the advantage to measure the carbon redistribution caused by the thermal treatment process with the nuclear resonance reaction analysis. The crystallinity of the SiC surface layers is studied by X-ray diffraction and transmission electron microscopy measurements. A polycrystalline 3C-SiC surface layer with a low content of 6H-SiC grains is formed with a thickness of about 70 nm. The analysis of high resolution TEM micrographs from the interface region shows obviously that the 6H-SiC phase coexists with the 3C-SiC modification in SiC layer.



Keywords: ion implantation, silicon carbide, 6H-SiC, NRRA, XRD, TEM
  • Phys. Stat. Sol. (a) 182 (2000) 653-660

Publ.-Id: 3715 - Permalink


X-ray structure characterization of barriers for Cu metallization
Mattern, N.; Hecker, M.; Fischer, D.; Wenzel, C.; Schell, N.; Matz, W.; Engelmann, H.; Zschech, E.;
The possibilities and limitations of X-ray scattering techniques are discussed for the structure analysis of Ta-N barriers for Cu metallization.
Keywords: X-ray diffraction; Ta barriers; synchrotron radiation
  • Microelectronics Reliability 40(2000) 1765-1770

Publ.-Id: 3714 - Permalink


Dissociative water vapour absorption in BaZr0.85Y0.15O2.925/H2O: pressure-compositions isotherms in terms of Fermi-Dirac statistics
Groß, B.; Engeldinger, J.; Grambole, D.; Herrmann, F.; Hempelmann, R.;
Thin films of proton-conducting BaZr0.85Y0.15O2.925 perovskite-type ceramics, prepared in a sol-gel process by multiple dip-coating on silicon single crystal wafers, and powder samples, prepared by the conventional carbonate route, were charged with hydrogen by dissociative water absorption at definite values of water vapour pressures and temperatures. The absolute content of the absorbed hydrogen was determined ex situ at room temperature using the 15N nuclear resonance reaction analysis. From the resulting water vapour pressure-hydrogen composition isotherms the absorption enthalpies and entropy were caculated, using our two site model, based on Fermi-Dirac statistics.
  • Phys. Chem. Chem. Phys., 2000, 2, 297-301

Publ.-Id: 3713 - Permalink


Application of the Tikhonov Regularization Method to the EXAFS analysis of UO2(H2AsO4)2 x H2O
Zayarnaya, T.; Reich, T.; Hennig, C.; Funke, H.;
We consider the possibility to determine structural parameters from partial pair correlation functions (PCF's) for UO2(H2AsO4)2 x H2O assuming that its crystal structure is unknown. Since UO2(HAsO4) x 4H2O is chemically similar to UO2(H2AsO4)2 x H2O, we wanted to investigate whether the scattering characteristics calculated by FEFF-8 for the uranium hydrogen arsenate with a known crystal structure are transferable for the analysis of the uranium dihydrogen arsenate.
The Tikhonov regularization method was applied to solve the inverse ill-posed problem of finding up to three partial PCF's from one EXAFS spectrum of UO2(H2AsO4)2 x H2O. From the U L3-edge EXAFS spectrum, we determined the U-U, U-As, and U-O PCF's. The As-As, As-U, and As-O PCF's were received from the As K-edge EXAFS spectrum. The interatomic distances obtained for the first and in several cases also for the second coordination shell of all pairs are in agreement with recently published crystallographic values. This demonstrates that the Tikhonov regularization method is a powerful tool for the structural analysis of samples for which only chemical information (oxidation state, elemental composition, type of ligands) is known.

* Corresponding author: zayarnaya@imp.uran.ru
  • Lecture (Conference)
    Actinide-XAS-2000 Workshop Proceedings, Grenoble, Sept. 10.-12.2000

Publ.-Id: 3711 - Permalink


EXAFS Study of U(VI) Compounds: A New Approach to Data Analysis
Babanov, Y. A.; Zayarnaya, T.; Reich, T.; Funke, H.;

The regularization method is applied to determine three partial pair correlation functions (PCF) from one EXAFS spectrum. The mathematical procedure is discussed and applied to the EXAFS analysis of UO-2(HAsO4) x 4H2O.
The measurements were performed at the Rossendorf Beamline (ROBL) at the ESRF in Grenoble. The As K-edge and the U L3-edge absorption spectra were recorded in transmission mode at temperatures of 41 K and 15 K, respectively. From the U L3-edge EXAFS spectrum, we obtain the PCF's of the pairs U-U, U-As, and U-O and determine the structural parameters for the first and the second coordination shells of each pair. The PCF's of the pairs As-U, As-As, and As-O are obtained from the As K-edge EXAFS spectrum.










  • Lecture (Conference)
    Actinide-XAS-2000 Workshop Proceedings, Grenoble Sept. 10-12., 2000

Publ.-Id: 3710 - Permalink


Tetraaquatrinitratoeuropium(III) dihydrate
Stumpf, T.; Bolte, M.;
In the title compound, [Eu(NO3)3(H2O)4]·2H2O, the Eu atom is ten co-ordinated by three bidentate nitrates and four water molecules. Furthermore, two water molecules are included in the crystal structure forming a complicated network of hydrogen bonds. [Eu(NO3)3(H2O)4]·2H2O is isostructural with other lanthanide analogues.

Acta Cryst. (2001) E (submitted)
  • Acta Cryst. E

Publ.-Id: 3709 - Permalink


Development of bubble size distributions in vertical pipe flow by consideration of radial gas fraction profiles
Lucas, D.; Krepper, E.; Prasser, H.-M.;
A new method for the prediction of the development of the bubble size distribution along the flow path is presented. It combines models for bubble coalescence and break-up with the calculation of radial gas fraction profiles. This model bases on the assumption of the equilibrium of the forces acting on a bubble perpendicularly to the flow direction. A large number of bubble classes is considered and the radial profile of the liquid velocity is taken into account.

The results of the model are compared with experimental data for a number of gas and liquid volume flow rates. The experiments were performed at a vertical test loop in Forschungszentrum Rossendorf (inner diameter 51.2 mm) using a wire mesh sensor. The sensor enables the determination of void distributions in the cross section of the loop. A special evaluation procedure supplies as well bubble size distributions as local distributions of bubbles within a predefined interval of bubble sizes.
  • Lecture (Conference)
    4th International Conference on Multiphase Flow, New Orleans, May 27 - June 1, 2001, Conference-CD, Paper 378
  • Contribution to proceedings
    4th International Conference on Multiphase Flow, New Orleans, May 27 - June 1, 2001, Conference-CD, Paper 378

Publ.-Id: 3708 - Permalink


Acid Rock Drainage samples from an abandoned Zn-Pb-Ag mine investigated by XAS
Moll, H.; Zaenker, H.; Richter, W.; Brendler, V.; Reich, T.; Hennig, C.; Rossberg, A.; Funke, H.; Kluge, A.;
In the aqueous environment of abandoned ore mines, iron sulphide ore crystals play a key role in the sulphide oxidation and water mineralization process occurring there. Highly miner-alised, red-coloured solutions are formed by weathering of ore particles which causes acid rock drainage (ARD). Major cationic components (>1 g/l) of the ARD solution under study were Zn, Fe, Mg, Al, and Mn. Important minor components were toxic heavy metals, e.g. As, Cu, Pb, and Cd. This XAS investigation deals with the in-situ characterisation of the near-order surrounding of As in ARD solutions containing colloidal particles as well as with the determination of the particle mineralogy. The atomic surrounding of Fe and As in ARD samples is compared to those found in model compounds. The presented study is an example for the broad applicability of X-ray absorption spectroscopy (XAS) techniques to environmental research.
Keywords: XAS, EXAFS, particles, Fe, As, ARD
  • Poster
    11th ESRF Users' Meeting, Grenoble, 16-21 February 2001 Workshop, Satellite to the ESRF Users' Meeting Environmental Studies Using Neutron and Synchrotron Facilities

Publ.-Id: 3707 - Permalink


Ion Beam Synthesis of SiC-Diamond-Heterostructures
Heera, V.;
Both, silicon carbide (SiC) and diamond are wide band gap semiconductors with excellent electronic properties. Unfortunately, there has been only limited success in producing n-type regions in diamond or p-type regions in SiC. On the other hand, n-type doping of SiC by nitrogen (N) implantation and p-type doping of diamond by boron (B) implantation are well-established processes. Therefore, it is an obvious idea to combine the materials in order to exploit this complementary behavior for the fabrication of p-n-heterojunctions or n-type regions in insulating diamond. Preliminary experiments have shown that ion beam synthesis could be a suitable process for the production of SiC-diamond-heterostructures in microscopic regions. There are two ways to achieve these heterostructures: (i) diamond formation by high dose carbon (C) implantation in crystalline SiC and (ii) SiC formation by high dose silicon (Si) implantation in natural diamond. The implantation must be carried out at elevated temperatures (> 700°C) in order to avoid accumulation of implantation damage. Epitaxial, nm-sized diamond or SiC precipitates with spherical or platelike shape, respectively, are formed inside the host crystals by the ion beam synthesis.
Keywords: SiC, diamond, ion implantation, phase formation, ion beam synthesis
  • Compound Semiconductor 7 (2001) No. 3, 43

Publ.-Id: 3706 - Permalink


Three VVER-1000 Tests Suitable for the Validation of Coupled Neutronic / Thermal-hydraulic Codes
Danilin, S.; Ilieva, B.; Khalimonchuk, V.; Mittag, S.; Weiß, F.-P.;
In the first test, carried out in the NPP Balakovo-4 (Russia), one of the two working feed water pumps was turned off at nominal power. The control system automatically reduced the reactor power down to 45 % of the nominal level. The coolant heat-up decreased proportionally to the power reduction. In the secondary circuit, the pumping power of the second feed water pump was increased in order to compensate some part of the missing feed water flow. In the following, the power of the second pump was reduced again to match the decreasing thermal power of the primary circuit. Corresponding changes in the steam generator water levels were observed. - The initiating event for a transient observed in the Zaporoshye-6 VVER-1000 (Ukraine) was the degradation of the turbo-generator power from 1000 MW down to the house load level of 50 MW. The reaction of the core control system and the behaviour of the primary circuit were similar to that in the Balakovo case. Immediately after the drastic reduction of the load level, the turbine started increasing its rotation speed. In order to prevent turbine damage, the steam control valves immediately reduced the steam flow to the turbine. Thus the turbine speed was stabilized, but the main steam header pressure started increasing. The turbine bypass valves were opened reducing the pressure quickly to its previous level. - The third test was carried out in the NPP Kozloduy-6 (Bulgaria). At 90 % of nominal power, two neighbouring main coolant pumps were switched off. The power was reduced to 35 %. Immediately after the transient initiation, the pressure in the primary circuit began to drop. All four pressurizer heaters started working to stabilize pressure. - The data measured in the three tests are useful for the validation of coupled codes.
  • Lecture (Conference)
    NEA/NSC Workshop on the Preservation of Experimental Integral Reactor Physics Data, 18-19 May 2000, Budapest, Hungary

Publ.-Id: 3705 - Permalink


Validation of coupled neutron-kinetic/thermal-hydraulic codes for VVERs
Mittag, S.; Kliem, S.; Weiß, F.-P.; Kyrki-Rajamäki, R.; Hämäläinen, A.; Langenbuch, S.; Danilin, S.; Hadek, J.; Hegyi, G.; Kuchin, A.; Panayotov, D.;
Three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal hydraulic system codes. Under the auspices of the EU's Phare programme, these codes have been validated against real plant transients by the participants from several countries. Data measured during tests in the Balakovo-4 VVER-1000 and the Loviisa-1 VVER-440 have been analysed by the codes. Critical boron concentrations, 3-D core power distributions, time behaviour of total fission power, coolant temperatures and pressures were the main parameters utilised in the validation. Good accuracy of the results was generally achieved, comparable to the measurement accuracy. The confidence in the results of the different code systems has increased and the consequences of certain model changes could be evaluated.
  • Lecture (Conference)
    Proc. of Tenth Symposium of AER on VVER Reactor Physics and Reactor Safety, Moscow, Russia, September 18-22, 2000, 763-781
  • Contribution to proceedings
    Proc. of Tenth Symposium of AER on VVER Reactor Physics and Reactor Safety, Moscow, Russia, September 18-22, 2000, 763-781

Publ.-Id: 3704 - Permalink


19F(p,p'gamma)19F and 18O(p, gamma)19F gamma-ray interferences studied on liquids
Grambole, D.; Neelmeijer, C.; Noll, K.; Herrmann, F.;
The interference effects for the 110 keV and 197 keV gamma-ray lines of the nuclear reactions 19F(p, p'gamma)19F and 18O(p, gamma)19F were studied quantitatively. For this, thick liquid targets were examined by PIGE using an external proton beam of 3.4 MeV energy. Several grades of dilutions were prepared from 76.3% 18O enriched H2O and from 1000 ppm F standard NaF solution. From this, a data base was obtained in order to extrapolate the 110 keV and 197 keV gamma-ray yields of the 18O(p, gamma)19F reaction for a target of water containing 0.2 % 18O. As a result it was obtained that, for fluorine in oxygen-rich materials, the reaction 19F(p, p'gamma)19F allows minimum detection limits of (1.06 ± 0.12) at.ppm and (1.85 ± 0.2) at.ppm for the 110 keV and 197 keV gamma-rays, respectively.
Keywords: PIGE; Fluorine; Oxygen-18; External beam; Liquid target
  • Nuclear Instruments and Methods in Physics Research B 161-163 (2000) 269-274

Publ.-Id: 3703 - Permalink


Verfahren zur Dotierung von Siliziumkarbid-Halbleiterbereichen
Heera, V.;
Der Erfindung liegt die Aufgabe zu Grunde, mit geringerem Aufwand in der Tiefe homogen dotierte SiC-Halbleiterbereiche mit einem schmalen Übergangsbereich zum Substrat zu erzeugen.
  • Patent
    Patentanmeldung 100 62 212.7
  • Patent
    DE 100 62 212 C1

Publ.-Id: 3701 - Permalink


Verfahren zur Herstellung von integrierten Abtastnadeln
Schmidt, B.; Bischoff, L.; Eng, L.;
Aufgabe der Erfindung ist es, ein Verfahren zu schaffen, das die Erzeugung von miniaturisierten, integrierten Abtastnadeln, bestehend aus Support, Biegebalken und hohler Nadelspitze mit und ohne Apertur, erlaubt und die somit bevorzugt für den Einsatz in der SNOM geeignet sind.
  • Patent
    DE 100 57 656 C1
  • Patent
    EP 1 209 689 A2
  • Patent
    EP 1 209 689 B1

Publ.-Id: 3700 - Permalink


Steuereinrichtung für einen Kühlkreislauf
Willschütz, H.-G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Steuereinrichtung für einen Kühlkreislauf vorzuschlagen, die sicher und einfach auch bei einem schweren Störfall eine Kühlung des Reaktordruckbehälters sicherstellt. Dabei soll auf den Einsatz von Fremd-energie verzichtet werden.
  • Patent
    DE 100 41 779 C1
  • Patent
    WO 02/17331 A1

Publ.-Id: 3699 - Permalink


Abstützvorrichtung für Stahlbehälter
Willschütz, H.-G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Abstützvorrichtung vorzuschlagen, mit der eine vertikale Unterstützung des Stahlbehälters im Falle von außergewöhnlich hoher Temperatur und/oder Druck gewährleistet wird, ohne die Kühlung des Stahlbehälters zu beeinträchtigen.
  • Patent
    DE 100 41 778 A1
  • Patent
    WO 02/16821 A2
  • Patent
    De 100 41 778 C2

Publ.-Id: 3698 - Permalink


Einrichtung zur lokalen Bestimmung von Strömungsgeschwindigkeiten
Eckert, S.; Witke, W.; Gerbeth, G.;
Der Erfindung liegt die Aufgabe zugrunde, eine Einrichtung zur Messung von Strömungsgeschwindigkeiten vorzuschlagen, die auch in nichttransparenten Fluiden einsetzbar ist und keinen Einschränkungen bei kleinen Geschwindigkeitswerten, turbulenten Geschwindigkeitsschwankungen, hohen Temperaturen und der Richtung der Strömung unterliegt.
  • Patent
    Patentanmeldung 100 37 331.3
  • Patent
    DE 100 37 331 C1

Publ.-Id: 3697 - Permalink


Schaltungsanordnung zur Erzeugung positiver und negativer pulsförmiger Magnetfelder
Krug, H.; Eckert, D.;
Der Erfindung liegt die Aufgabe zugrunde, insbesondere große Anlagen für positive und negative pulsförmige Magnetfelder mit deutlich geringerem Aufwand herstellen zu können.
Die Erfindung geht aus von einer Schaltungsanordnung, die im Wesentlichen aus einer Kondensatorbatterie, einer Hochfeldspule, einer Schutzdrossel, einem Thyristorschalter, einer Crowbardiode, einem Crowbarwiderstand und mehreren Trennkontakten besteht.
  • Patent
    DE 100 30 566 A1
  • Patent
    DE 100 30 566 C2
  • Patent
    WO 01/98792 A1

Publ.-Id: 3696 - Permalink


Verfahren und Anordnung zur kontaktlosen Bestimmung von räumlichen Geschwindigkeitsverteilungen in elektrisch leitfähigen Flüssigkeiten
Stefani, F.; Gerbeth, G.; Gundrum, T.; Eckert, S.; Cramer, A.;
Der Erfindung liegt die Aufgabe zugrunde, ein Verfahren und eine Anordnung zur Bestimmung von räumlichen Geschwindigkeitsverteilungen in elektrisch leitfähigen Flüssigkeiten vorzuschlagen, die für alle Geschwindigkeitskomponenten reproduzierbare Ergebnisse garantieren und in denen jeglicher Kontakt mit der Flüssigkeit oder den sie einschließenden Wänden vermieden wird.
  • Patent
    Patentanmeldung 100 26 052.7
  • Patent
    DE 100 26 052 C2
  • Patent
    WO 01/90762 A1

Publ.-Id: 3695 - Permalink


Mechanisms of pit coarsening in ion erosion of fcc(111) surfaces: A kinetic 3D lattice Monte-Carlo study
Strobel, M.; Heinig, K.-H.; Michely, T.;
An atomic simulation approach toion erosion of fcc(111) surfaces is presented. In a fully 3D kinetic lattice Monte-Carlo model thermodynamically activated processes like adatom, step-edge or surface vacancy diffusion are combined with ballistic eects due to single ion impacts, i.e. sputtering, adatom and surface vacancy generation. In the course of erosion nucleation of surface vacancy islands, their growth, both laterally and vertically, and subsequent coarsening of these pits is observed. For removal of up to theta = 6 monolayers the evolution of the surface is characterized in terms of the roughness and height-height-correlation function. The simulation results are discussed with respect to low-energy noble gas ion erosion experiments of Pt(111) surfaces [M. Kalff, et al., Surf. Sci., preceding paper]. By explicitly tuning specifc atomic transitions within the simulation it is demonstrated, that forbidden thermal adatom generation does hardly in uence the surface evolution. Suppressed step-edge diffusion, however, considerable slows down pit coarsening and impedes pit shape relaxation, emphasizing the importance of this smoothening process in ion erosion.
  • Surface Science 486 (1-2) Jul 2001 p.136-156

Publ.-Id: 3694 - Permalink


Modeling and XPS Study of Precipitation and Oxidation of Ge in Ge+ implanted SiO2 layers
Borodin, V.; Heinig, K.-H.; Schmidt, B.; Oswald, S.;
During annealing at 950°C in an oxidizing ambient, the redistribution of Ge in Ge+ implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM.
Sputtering depth profiling in conjunction with the x-ray photoelectron spectroscopy analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.
  • Nuclear Instruments and Methods in Physics Research B, 178 May 2001 p. 115-119

Publ.-Id: 3693 - Permalink


Ion irradiation of gold inclusions in SiO2: experimental evidence for inverse Ostwald ripening
Rizza, G.; Strobel, M.; Heinig, K.-H.; Bernas, H.;
When sub mm size gold inclusions in SiO2 are irradiated with MeV gold ions, a ring of nanometer-size clusters is formed in their immediate vicinity. The size, density and radial distribution of these nanoclusters was determined. Our observations are in agreement with a recent prediction that in a driven system, under appropriate ion beam and temperature conditions, the steady-state solute concentration's dependence on precipitate size may be opposite to that expected from the equilibrium Gibbs-Thomson relation. Kinetic Monte-Carlo simulations account for additional experimental results: the irradiation-induced increase in solute concentration can promote nucleation of additional precipitates around the first ring. The latter finding contradicts the usual assumption that ion beam mixing hinders nucleation.
  • Nuclear Instruments and Methods in Physics Research B 178: 78-83 MAY 2001

Publ.-Id: 3690 - Permalink


3D Kinetic Lattice Monte-Carlo Simulations of Ion Erosion of fcc(111) Surfaces
Strobel, M.; Heinig, K.-H.; Michely, T.;
In high-dose ion implantation nanoclusters can be formed in a rather well-controlled manner as a function of implantation parameters like ion fluence, ion flux and substrate temperature. According to our current understanding of ion beam synthesis the evolution of nanoclusters is determined by the competition between ballistic and thermodynamic effects. While standard thermodynamics, i.e. the phase transition from a supersaturated solid-solution to second-phase precipitates via homogeneous nucleation and growth, gives a reasonable explanation for a variety of observed nanostructures, under irradiation conditions ballistic processes can modify the phase-ordering kinetics dramatically. By incorporating collisional mixing with the standard thermodynamical kinetic Monte-Carlo model, analytical predictions of irradiation effects of nanoclusters, e.g. inverse Ostwald ripening, are discussed.
Keywords: Ion erosion, fcc(111) surfaces, Kinetic lattice Monte-Carlo modeling
  • Nuclear Instruments and Methods in Physics Research B 178: 105-108 MAY 2001

Publ.-Id: 3689 - Permalink


Shape evolution of oxidized silicon V-grooves during high dose ion implantation
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The evolution of the shape of oxidized V-grooves on (001) Si under high-dose Ge+ ion irradiation has been studied experimentally as well as theoretically. The shape of the V-grooves changes due to sputtering, re-deposition and swelling. An integro-differential equation has been derived which takes into account these 3 effects. The equation where solved numerically for the experimental conditions. Experimentally, V-grooves where formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2 layer thickness reduction as well as the predicted surface shape change agree nicely with XTEM images. It is shown that sputtered material accumulates at the bottom of the V-grooves. At the same time implanted species accumulate in the bottom region of V-grooves, which can result in the formation of a very thin wire during subsequent annealing.
  • Nuclear Instruments and Methods in Physics Research B 178: 109-114 MAY 2001

Publ.-Id: 3688 - Permalink


Shape evolution of oxidized silicon V-grooves during high dose ion implantation
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The evolution of the shape of oxidized V-grooves on (001) Si under high-dose
Ge+ ion irradiation has been studied experimentally as well as
theoretically. The shape of the V-grooves changes due to sputtering,
re-deposition and swelling. An integro-differential equation has been
derived which takes into account these 3 effects. The equation where solved
numerically for the experimental conditions. Experimentally, V-grooves where
formed by anisotropic etching and dry oxidation. XTEM images of as-oxidized
and as-implanted V-grooves where compared. The theoretically predicted SiO2
layer thickness reduction as well as the predicted surface shape change
agree nicely with XTEM images. It is shown that sputtered material
accumulates at the bottom of the V-grooves. At the same time implanted
species accumulate in the bottom region of V-grooves, which can result in
the formation of a very thin wire during subsequent annealing.
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3687 - Permalink


3D Kinetic Lattice Monte-Carlo Simulations of Ion Erosion of fcc(111) Surfaces
Strobel, M.; Heinig, K.-H.; Michely, T.;
In high-dose ion implantation nanoclusters can be formed in a rather well-controlled manner as a function of implantation parameters like ion fluence, ion flux and substrate temperature. According to our current understanding of ion beam synthesis the evolution of nanoclusters is determined by the competition between ballistic and thermodynamic effects. While standard thermodynamics, i.e. the phase transition from a supersaturated solid-solution to second-phase precipitates via homogeneous nucleation and growth, gives a reasonable explanation for a variety of observed nanostructures, under irradiation conditions ballistic processes can modify the phase-ordering kinetics dramatically.
By incorporating collisional mixing with the standard thermodynamical kinetic Monte-Carlo model, analytical predictions of irradiation effects of nanoclusters, e.g. inverse Ostwald ripening, are discussed.
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3686 - Permalink


Ion irradiation of gold inclusions in SiO2: experimental evidence for inverse Ostwald ripening
Rizza, G.; Strobel, M.; Heinig, K.-H.; Bernas, H.;
When sub mm size gold inclusions in SiO2 are irradiated with MeV gold ions, a ring of nanometer-size clusters is formed in their immediate vicinity. The size, density and radial distribution of these nanoclusters was determined. Our observations are in agreement with a recent prediction that in a driven system, under appropriate ion beam and temperature conditions, the steady-state solute concentration's dependence on precipitate size may be opposite to that expected from the equilibrium Gibbs-Thomson relation. Kinetic Monte-Carlo simulations account for additional experimental results: the irradiation-induced increase in solute concentration can promote nucleation of additional precipitates around the first ring. The latter finding contradicts the usual assumption that ion beam mixing hinders nucleation..
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3685 - Permalink


Inverse Ostwald ripening under ion irradiation
Heinig, K.-H.; Strobel, M.;
The steady-state behavior of plain interfaces and nanoclusters (NCs) under
ion irradiation has been studied analytically as well as by kinetic
Monte-Carlo (MC) simulations. In the two-phase system mixing of A-type atoms
into phase B region leads to a strong increase of the solute concentration
at low irradiation temperatures. For NCs the ion irradiation induced
elevated solute concentration depends on their sizes. The analytical form of
this size dependence is identical to that of NCs in equilibrium, i.e. it is
given by the Gibbs-Thomson relation. However, in contrast to equilibrium,
small NCs have a lower increase in solute concentration than larger ones.
This may result in a dramatically change of the evolution of NC ensembles:
The driven system can get a negative capillarity length for its interfaces
with the consequence of mass transport from large NCs to smaller ones, i.e.
inverse Ostwald ripening is observed. Thus, it is predicted theoretically
that a broad size distribution can be made narrow by ion irradiation. At
conditions not being too far from equilibrium this behavior has been proven
by a computer experiment. The MC simulations predict in addition to the
analytical result that at very high fluxes or low temperatures large NCs can
disintegrate due to the formation of smaller ones by nucleation.

Keywords: Ion irradiation, nanoclusters, non-equilibrium, Ostwald ripening, theory
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3684 - Permalink


Atomistic Study of the Evolution of Nanoclusters in Ion Beam Synthesis
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation is an established tool to synthesize or to modify buried low-dimensional nanostructures (e.g. nanoclusters), which have become the basis of numerous technological applications. According to our current understanding of ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. In this work it is shown, that a sound understanding of the diffusional interaction dynamics of nanoclusters can be achieved by kinetic 3D lattice Monte-Carlo simulations. In particular, the exploitation of the cluster size-concentration dependence (the Gibbs-Thomson relation) under pure thermal or ion irradiation conditions provides a wealth of physical information relevant for ion beam synthesis. Furthermore, evidence is presented, that within a certain parameter window of irradiation conditions collisional mixing induced nucleation of nanoclusters occurs.
Keywords: Ion beam synthesis, nanoclusters, nucleation, Ostwald ripening, collisional mixing, kinetic lattice Monte-Carlo modeling
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3683 - Permalink


Modeling and XPS Study of Pricipitation and Oxidation of Ge in Ge+ implanted SiO2 layers
Borodin, V.; Heinig, K.-H.; Schmidt, B.; Oswald, S.;
During annealing at 950oC in an oxidizing ambient, the redistribution of Ge in Ge+ implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM. Sputtering depth profiling in conjunction with the x-ray photoelectron spectroscopy analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.
Keywords: Germanium, oxidation, silicon dioxide, X-ray photoelectron spectroscopy, modeling
  • Lecture (Conference)
    E-MRS - IUMRS 2000 Spring Meeting, Symposium R: Materials Science with Ion Beams, Strasbourg, France, May 30 - June 2, 2000

Publ.-Id: 3682 - Permalink


Morphology Evolution during Ion Erosion of fcc(111) Surfaces: A 3D Kinetic Lattice Monte-Carlo Study
Strobel, M.; Heinig, K.-H.; Michely, T.;
Ion Erosion ...
  • Lecture (Conference)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000

Publ.-Id: 3681 - Permalink


Nanocluster Evolution under Ion Irradiation
Heinig, K.-H.; Strobel, M.; Rizza, G.;
An ensemble of nanoclusters embedded in a substrate evolves during thermal annealing by coarsening or Ostwald ripening, and, if the concentration of cluster material is sufficiently high, coalescence.
In this contribution it will be shown that by ion irradiation the evolution of nanoclusters can be modified or even dramatically changed. (i) Ion irradiation increases due to collisional detachments of atoms from clusters the steady-state solubility. Thus, cluster evolution is accelerated or happens at lower temperatures. (ii) Collisional detachment of atoms from nanoclusters is more efficient for large clusters than for small ones. This dependence on cluster size is opposite to that predicted by the Gibbs-Thomson law for thermally activated detachment. The "inverse" behaviour results in "Inverse Ostwald Ripening", i.e. a broad size distribution becomes narrower during annealing under ion irradiation. (iii) Under intense ion irradiation large clusters can evaporate and new nanoclusters will nucleate. A steady-state mean size, which is dependent on ion flux and temperature, can be found.
The new results listed above were predicted by an analytical theory and have been proven by kinetic lattice Monte-Carlo simulations and preliminary experiments.

Keywords: Ion irradiation, nanoclusters, annealing, Ostwald ripening, theory, computer simulation
  • Invited lecture (Conferences)
    12th Int. Conf. Ion Beam Modifications of Materials (IBMM2000), Canela, Brazil, September 3 - 8, 2000 (invited)

Publ.-Id: 3680 - Permalink


Synthese und Bearbeitung von Nanostrukturen mit Ionenstrahlen
Heinig, K.-H.;
Unter Ionenbestrahlung laufen in der Festkörperoberfläche Prozesse weitab vom thermodynamischen Gleichgewicht ab. Übliche Prozeßabläufe können umgekehrt werden (z.B. inverses Ostwaldreifen), und geordnete Strukturen können sich ausbilden (z.B. wave-ordered-structures). Im Vortrag werden hierzu experimentelle und theoretische Untersuchungen vorgestellt. Es wird u.a. gezeigt, wie Nanocluster in Ordnungszustände gebracht werden können, die für mikroelektronische und mikrooptsche Anwendungen hochinteressant sind.
Keywords: Ionenstrahlsynthese, Nanocluster, Computersimulation, Thermodynamik
  • Lecture (others)
    Friedrich-Schiller Universität Jena, Physikalisch-Astronomische Fakultät, Vortrag am 17. 11. 2000

Publ.-Id: 3679 - Permalink


Physico-chemical characterization of seaborgium as oxide hydroxide
Hübener, S.; Taut, S.; Vahle, A.; Dressler, R.; Eichler, B.; Gäggeler, H. W.; Jost, D.; Piguet, D.; Türler, A.; Schädel, M.; Jäger, E.; Brüchle, W.; Schimpf, E.; Kirbach, U.; Trautmann, N.; Yakushev, A.;
Seaborgium (element 106) was studied in comparison with tungsten in the O2-H2O(g)/SiO2(s)-system using high-temperature on-line isothermal gas chromatography. The 21-s nuclide 266Sg was produced in the 248Cm + 22Ne reaction at a beam energy of 119 MeV. The reaction products were continuously transported by a He(MoO3)-jet to the chromatography apparatus HITGAS. Group 6 element oxide hy-droxide molecules volatile at temperatures above 1000 K were formed at 1325 K by adding humid oxygen as reactive gas. 266Sg was unambiguously detected after gas chromatographic separation by measuring 266Sg-262Rf mother-daughter a-sf correlations. The experimental results demonstrate the volatility of seaborgium in humid oxygen, presumably as seaborgium oxide hydroxide as typical for both uranium (VI) and the group 6 elements.
Keywords: Seaborgium, group 6 elements, oxide hydroxide, reaction gas chromatography
  • Radiochimica Acta 89 (2001) 737-741

Publ.-Id: 3678 - Permalink


Elastic constants of diamond-like amorphous carbon films: the effect of internal stresses
Belov, A.; Jäger, H.-U.;
The extreme wear resistance and chemical inertness of tetrahedral, or
diamond-like, amorphous carbon (ta-C) make it a promising material for
wear-resistive mechanical coatings. The unique mechanical behaviour of ta-C
is related to the atomic structure of amorphous carbon and atomic scale
modeling becomes a valuable tool to study both growth mechanisms of ta-C
films and their mechanical properties. Here we report results of atomistic
calculations of elastic constants in ta-C films grown by a realistic
computer simulation of ion-beam deposition. The dependence of the elastic
constants on the ion energy is presented. Similar to the real as-grown
nonequilibrium (not annealed) ta-C films, the simulated structures possess
the high internal compressive stress, which can considerably effect on
elastic constants. An approach employed allows for the stress dependence of
elastic constants to be analysed. We demonstrate the variation of elastic
constants as a function of the internal stress, and therefore the
importance of nonlinear elastic properties in amorphous carbon.
Keywords: tetrahedral amorphous carbon, elastic constants, internal stresses
  • Lecture (Conference)
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium C: Protective Coatings and Thin Films

Publ.-Id: 3677 - Permalink


Structures of technetium and rhenium complexes
Leibnitz, P.; Reck, G.; Pietzsch, H.-J.; Spies, H.;
Investigations in the 99mTc chemistry are stimulated by the search for new radiopharmaceuticals for nuclear medical applications. To understand the coordination mode of Tc with various complexing agents, macroscopic studies of technetium coordination chemistry are often performed using the low energy ß-emitting radionuclide 99Tc, which has a much longer half life (t1/2 = 2.12 x 105 years) than 99mTc, in the mg level.
Investigations of Re coordination chemistry are done in conjunction with Tc studies because Re possesses chemical properties similar to those of Tc. For some chemical tasks, Re provides a non-radioactive alternative to work with Tc radioisotopes. In addition, 186Re and 188Re are of great interest to nuclear medicine as they possess nuclear properties favorable for use in therapeutic radiopharmaceuticals.
Our investigations of Tc and Re coordination chemistry are toward this goal. A large series of technetium and rhenium complexes resulted from this studies have been characterized by X-ray crystal structure determinations.
This survey covers the structural investigations performed by P.Leibnitz and G.Reck (BAM) from 1992 till now. It summarizes results obtained in the Rossendorf technetium group and is not intended to compete with the well-written reviews published so far.

Keywords: technetium complexes, rhenium complexes, oxotechnetium(V) complexes, oxorhenium(V) complexes, Tc(III) mixed ligand complexes, Re(III) mixed ligand complexes, X-ray structural analysis
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-311 2001

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Publ.-Id: 3676 - Permalink


Calculation of intrinsic stresses in amorphous carbon films grown by molecular dynamics simulation: from the atomic to the macroscopic scale
Belov, A.; Jäger, H.-U.;
We present a method of calculation and an estimate for the bulk intrinsic stress in nonequilibrium tetrahedral amorphous carbon (ta-C) films grown by a realistic atomic scale simulation of ion-beam deposition. The simulated films have a thickness of a few nanometers and reproduce the important features of the real as grown nonequilibrium (not annealed) structures such as the presence of a steady-state growth region with uniform properties, the large content of sp3 bonded atoms, and the high intrinsic compressive stress, which seriously limits the maximum thickness of films that can be deposited. Using slices from the nearly structurally uniform film region, a 3D periodic model was constructed for the bulk intrinsic stress calculation. Employing empirical interatomic potentials for carbon, atomic stresses as well as the bulk stresses were computed. The obtained value of the compressive stress for the transition from the graphitic-like carbon to ta-C is in a good agreement with experimental data for the stress threshold.
Keywords: tetrahedral amorphous carbon, thin films, intrinsic stress
  • Poster
    E-MRS 2001 SPRING MEETING, June 5-8, 2001, Strasbourg (France), Symposium A: Computational Materials Science Across Time and Length Scales

Publ.-Id: 3675 - Permalink


Erwärmung des Reaktordruckbehälters des Blocks 8 des KKW Greifswald bei der Zerlegung mittels Sägetechnik
Mössner, T.; Altstadt, E.; Böhmert, J.; Weiß, R.;
Die Arbeit untersucht das Erwärmungsverhalten des Reaktordruckbehälters des Blockes 8 des KKW Greifswald bei der Zerlegung in Ringabschnitte mit einer Bandsäge. Mit dem Programm ANSYS wurde dazu ein thermisches Finite-Elemente-Modell erstellt. Dieses Modell ist an Hand vorhandener Temperaturmessdaten abgeglichen worden. Mit dem abgeglichenen Modell wurden abschließend die auftretenden Maximaltemperaturen für den Sägevorgang ermittelt. Diese liegen bei höchstens 200 °C.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf, FZR-310 Januar 2001

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Publ.-Id: 3674 - Permalink


Riga Dynamo Experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
It is widely believed that almost all magnetic fields in a natural
environment are a result of the dynamo process -- field generation in a
moving nearly homogeneous fluid electroconducting material of celestial
bodies. Such are fields of the Earth, most of the planets, Sun, another
stars and even galaxies. The believe is based on the theory and numerical
simulation. Until very recently no direct laboratory experiment was
supporting this important point. We are not going to model in the laboratory
any particular celestial body. Our aim is to demonstrate the very idea -- by
intense stirring in a large volume of good electroconducting liquid one can
generate a magnetic field. As the working fluid we are using 2 qm of molten
sodium -- the best electroconducting liquid available. The fluid part of
celestial bodies is stirred by thermal and other types of natural
convection. In laboratory circumstances such stirring is much too slow.
Hence we are stirring sodium by an outside forced propeller consuming 150kW
of power. The propeller is producing an axisymmetric swirling flow inside a
prolongated annular vessel. When flowrate reaches 0.6 qmps or so the device
starts to generate magnetic field. The field pattern is nonaxisymmetric and
slowly (1.2 --1.5hz) rotates round symmetry axis. The overall rotation is
superimposed by turbulent fluctuations. The generation process is stable in
operational sense and results are reproducible. We report on two experiments
at the Riga dynamo facility. In November 1999, a slowly growing magnetic
field eigenmode was observed for the first time in a liquid metal
experiment. In July 2000, the magnetic field saturation regime was studied.
We sketch also the underlying theory in order to illuminate the background
of the Riga dynamo experiment.

  • Lecture (Conference)
    Lecture at European Geophysical Society, XXVI General Assembly, Nice (France), March 25-30, 2001

Publ.-Id: 3673 - Permalink


Validation of coupled neutron kinetic / thermal-hydraulic codes Part 2: Analysis of a VVER-440 transient (Loviisa-1)
Hämäläinen, A.; Kyrki-Rajamäki, R.; Mittag, S.; Kliem, S.; Weiss, F.-P.; Langenbuch, S.; Danilin, S.; Hadek, J.; Hegyi, G.;
Several three-dimensional hexagonal reactor dynamic codes have been developed for VVER type reactors and coupled with different thermal-hydraulic system codes. Under the auspices of the European Union's Phare programme these codes have been validated against real plant transients by the participants from 7 countries. Two of the collected five transients were chosen for validation of the codes. Part 1 of this article consists of validation against VVER-1000 reactor data. This second part is focussed to validation against measured data of `One turbo-generator load drop experiment' at the Loviisa-1 VVER-440 reactor. The experiment was performed just after plant modernisation and more measured data was available to validation than in normal operation of real plants. Good accuracy of the results was generally achieved comparable to the measurement accuracy. The confidence in the results of the different code systems has increased, and consequences of certain model changes could be evaluated.
  • Annals of Nuclear Energy 29 (2002) 255-269

Publ.-Id: 3672 - Permalink


Syntheses and Crystal Structure Determination of hexacoordinated Silicon-Complexes with Dimethylpyridines
Hensen, K.; Kettner, M.; Stumpf, T.; Bolte, M.;
Halogensilane, HSiCl3, forms with 3,4-dimethylpyridine in aprotic solvents a crystalline 1:2-compound which is stable at room temperature and readily soluble in CHCl3. Colourless crystals of the dicationic complex, [H2Si(3,4-dimethylpyridine)4]2+ 2Cl-×6 CHCl3 (verified by X-ray structure analysis) are obtained by dismutation of HSiCl3(3,4-di-methylpyridine)2 in CHCl3, within one week at room temperature. 29Si-NMR indicates that SiCl4 is generated as a second product. H2SiCl2 with 2,4-dimethylpyridine as well as MeHSiBr2 with 3,5-dimethylpyridine in aprotic solvents form 1:2-compounds stable at room temperature. X-ray structure analysis in both cases establish neutral-complexes with a hexacoordinated silicon atom.

  • Naturforschung 55b 2000 (901-906)

Publ.-Id: 3670 - Permalink


Halogen exchange and expulsion : ligand stabilized dihalogen silicon dications
Hensen, K.; Mayr-Stein, R.; Stumpf, T.; Pickel, P.; Bolte, M.; Fleischer, H.;
The first ligand stabilized SiCl22+ dications were synthesed using N-methylimidazole as co-ordinating ligand. The compounds SiCl4, SiBr2Cl2, and SiH2Cl2 form six-co-ordinated dicationic compounds of almost octahedral symmetry with similar structures which were investigated by single crystal X-ray analysis and density functional calculations. The structures exhibit particularly short dative Si-N bonds of about 1.90 C. Complexes crystallized from the same solvent are isostructural. A different solvent, though, leads to geometrical variations. It was also discovered that the halogen exchange process among mixed silicon tetrahalides occurs under much milder conditions than previously thought and proceeds with considerable speed even without a catalyst.

  • J. Chem. Soc., Dalton Trans. 2000 (473-477)

Publ.-Id: 3669 - Permalink


Template-Directed Self-Assembly of Buried Nanowires and the Pearling Instability
Müller, T.; Heinig, K.-H.; Schmidt, B.;
The fabrication of more and more miniaturized electronic and photonic devices relies on new, ingenious methods for the fabrication of spatially controlled nanostructures. Examples are electronic devices based on semiconducting nanowires and photonic devices based on chains of metallic nanoclusters that guide light by coupled surface plasmons. In this contribution a template-directed ion beam synthesis of nanowires and regular nanocluster chains will be presented. As templates, V-grooves etched in (001)Si and subsequently oxidized are used. High fluence Ge+ implantation is carried out into the SiO2 layer at 70 keV. Thereby, the implanted Ge enriches themselves in the V-groove bottom to a critical amount, which may result in nanowire formation by nucleation, growth and coalescence during subsequent thermal treatment. TEM investigations indicate the formation of a nanowire buried in the SiO2 at the V-groove bottom. Kinetic lattice Monte Carlo simulations of the nanowire formation process were performed in order to understand the phase separation mechanism and results are compared to TEM images. Furthermore, it is shown that even ideal nanowires show a instability and form during long-lasting annealing equal-spaced and equal-sized nanoclusters "nanocluster chains" by self-organization.
Keywords: Nanowires, Ion Beam Synthesis, Pearling Instability, Nanocluster Chains
  • Poster
    European Materials Research Society Spring Meeting E-MRS 2001, Strasbourg, France, June 5-8, 2001
  • Material Scince and Engineering C 19 (2002) 209-213
  • Contribution to WWW
    arXiv:cond-mat/0108371 v1 23 Aug 2001

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Publ.-Id: 3667 - Permalink


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers
Spiga, S.; Ferrari, S.; Fanciulli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.;
In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed
Keywords: ion beam synthesis, nanoclusters, Tin, Antimony, ion implantation, silicon dioxide, Ostwald ripening, nonvolatile memory device
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Publ.-Id: 3666 - Permalink


Kinetics of Ion Beam Synthesis of Sn and Sb Clusters in SiO2 Layers
Spiga, S.; Ferrari, S.; Fanculli, M.; Schmidt, B.; Heinig, K.-H.; Grötzschel, R.; Mücklich, A.; Pavia, G.;
In this work we investigate the ion beam synthesis of Sn and Sb clusters in thin oxides. 80 keV (doses of 0.1-1 x 1016 cm-2) Sn implanation in 85 nm thick SiO2 followed by RTP annealing (800-1000°C for 30-300 under Ar or N2 dry ambient) leads to the formation of two cluster bands, near the SiO2 surface and the Si/SiO2 interface. In addition, big isolated clusters are randomly distributed in the middle of the oxide. Cluster-size distribution and cluster-crystallinty are related to implantation dose and annealing time. Low energy (10-12 kev) Sb and Sn implantation (doses 2-5 x 1015 cm-2) leads to the formation of very uniform cluster-size distribution. Under specific process conditions, only an interface cluster band is observed.
Keywords: ion beam synthesis, nanoclusters, Tin, Antimony, ion implantaion
  • Poster
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials" , Boston, USA, Nov. 27-29, 2000
  • Contribution to proceedings
    Mat.Res.Soc.Symp.Proc. Vol. 647 (2001) O11.23 MRS2000 Fall Meeting, Symposium O: "Ion Beam Processing of Advanced Materials", Boston, USA, Nov. 27-29, 2000

Publ.-Id: 3665 - Permalink


Understanding ion beam synthesis of nanostructures: Modelling and atomistic simulations
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced, which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient in understanding nanocluster evolution. Various aspects of precipitate evolution during implantation, formation of ordered arrays of nanophase domains by focused ion implantation and compound nanocluster synthesis are discussed.
Keywords: ion beam synthesis, nanostructures, nanoclusters, ion implantation, ion beam mixing, Ostwald ripening, kinetic Monte-Carlo simulation
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647 (2001)

Publ.-Id: 3664 - Permalink


Successful nitriding of austenitic stainless steel: On the diffusion mechanism of nitrogen and on the role of the surface oxide layer.
Parascandola, S.; Möller, W.; Williamson, D. L.;
In the first part of this paper we present a quantitative trapping model that includes detrapping to describe the diffusion of nitrogen in austenitic stainless steel during successful nitriding. Calculated nitrogen depth profiles, assuming a diffusion pre-exponential factor D0 = 10-3 cm2/s, a diffusion activation energy Ed = 1.1 eV, and a detrapping activation energy Et2d = 1.45 eV, show good agreement with experimental nitrogen depth profiles
obtained from a sample that has been subsequently nitrided with 14N and 15N. The plausibility of a trapping mechanism is also supported by a number of phenomenological and thermodynamical arguments. In the second part of this paper we present a modelling approach for the evolution of the thickness of the surface oxide layer during successful nitriding. The approach bases on the assumption that the surface oxide layer thickness is completely controlled by the interplay of sputtering and oxidation and differentiates between oxide layer growth limited by diffusion and oxide layer growth limited by the rate of oxygen supply. The applicability of this approach is supported by experimental data obtained by real-time elastic recoil detection analysis during ion nitriding at different combinations of ion energy and oxygen partial pressure.
  • Lecture (Conference)
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan
  • Contribution to proceedings
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan

Publ.-Id: 3663 - Permalink


Understanding ion beam synthesis of nanostructures: Modeling and atomistic simulations
Strobel, M.; Heinig, K.-H.; Möller, W.;
Ion implantation, specified by parameters like ion energy, ion fluence, ion flux and substrate temperature, has become a well-established tool to synthesize buried low-dimensional nanostructures. In general, in ion beam synthesis the evolution of nanostructures is determined by the competition between ballistic and thermodynamic effects. A kinetic 3D lattice Monte-Carlo model is introduced,
which allows for a proper incorporation of collisional mixing and phase separation within supersaturated solid-solutions. It is shown, that for both the ballistically and thermodynamically dominated regimes, the Gibbs-Thomson relation is the key ingredient
in understanding nanocluster evolution. Various aspects of
precipitate evolution during implantation, formation of
ordered arrays of nanophase domains by focused ion implantation
and compound nanocluster synthesis are discussed.
Keywords: ion beam synthesis, nanostructures, nanoclusters, ion implantation, ion beam mixing, Ostwald ripening, kinetic Monte-Carlo simulation
  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting, Symp. O "Ion Beam Synthesis and Processing of Advanced Materials", Nov 27 - Dec 1, 2000, Boston, USA, Invited Talk

Publ.-Id: 3662 - Permalink


Evidence for a Soft Nuclear Equation-of-State from Kaon Production in Heavy Ion Collisions
Sturm, C.; Böttcher, I.; Debowski, M.; Förster, A.; Grosse, E.; Koczon, P.; Kohlmeyer, B.; Laue, F.; Mang, M.; Naumann, L.; Oeschler, H.; Pühlhofer, F.; Schwab, E.; Senger, P.; Shin, Y.; Speer, J.; Ströbele, H.; Surowka, G.; Uhlig, F.; Wagner, A.; Walus, W.;
The production of pions and kaons has been measured in Au+Au collisions at beam energies from 0.6 to 1.5 AGeV with the Kaon Spectrometer at SIS/GSI. The K+ meson multiplicity per nucleon is enhanced in Au+Au collisions by factors up to 6 relative to C+C reactions whereas the corresponding pion ratio is reduced. The ratio of the K+ meson excitation functions for Au+Au and C+C collisions increases with decreasing beam energy. This behavior is expected for a soft nuclear equation-of-state.
Keywords: pion kaon Au+Au collisions K+ meson multiplicity nucleon nuclear equation-of-state.
  • Physical Review Letters 86 (2001) 39

Publ.-Id: 3661 - Permalink


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation
Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.;
Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.
Keywords: Nanostructures, ion implantation, Ostwald ripening. nucleation, ion beam mixing, theory, kinetic lattice Monte-Carlo simulation, nonvolatile memory device
  • Contribution to external collection
    Mat. Res. Soc. Proc. vol. 647(2001) O14.6

Publ.-Id: 3660 - Permalink


Inverse Ostwald Ripening and Self-Organization of Nanoclusters due to Ion Irradiation, (invited talk MRS 2000 Fall Meeting, Boston, USA), Mat. Res. Soc. Proc., vol. 647
Heinig, K.-H.; Schmidt, B.; Strobel, M.; Bernas, H.;
Under ion irradiation collisional mixing competes with phase separation if the irradiated
solid consists of immiscible components. If a component is a chemical compound,
there is another competition between collisional forced chemical dissociation of the
compound and its thermally activated re-formation. Especially at interfaces between
immiscible components, irradiation processes far from thermodynamical equilibrium
may lead to unexpected phenomena. If the formation of nanoclusters (NCs) occurs
during ion implantation, the phase separation caused by ion implantation induced
supersaturation can be superimposed by phenomena caused by collisional mixing.
In this contribution it will be studied how collisional mixing during high-fluence ion
implantation affects NC synthesis and how ion irradiation through a layer of NCs
modifies their size and size distribution. Inverse Ostwald ripening of NCs will be
predicted theoretically and by kinetic lattice Monte-Carlo simulations. The
mathematical treatment of the competition between irradiation-induced detachment
of atoms from clusters and their thermally activated diffusion leads to a Gibbs-
Thomson relation with modified parameters. The predictions have been confirmed by
experimental studies of the evolution of Au NCs in SiO2 irradiated by MeV ions. The
unusual behavior results from an effective negative capillary length, which will be
shown to be the reason for inverse Ostwald ripening. Another unexpected
phenomenon to be addressed is self-organization of NCs in a delta-layer parallel to
the Si/SiO2 interface. Such delta-layers were found when the damage level at the
interface was of the order of 1...3 dpa. It will be discussed that the origin of the delta-
layer of NCs can be assigned to two different mechanisms: (i) The negative interface
energy due to collisional mixing gives rise to the formation of tiny clusters of substrate
material in front of the interface, which promotes heteronucleation of the implanted
impurities. (ii) Collisional mixing in the SiO2 produces diffusing oxygen, which may be
consumed by the Si/SiO2 interface. A thin layer parallel to the interface becomes
denuded of diffusing oxygen, which results in a strong pile up of Si excess. This Si
excess promotes heteronucleation too. Independent of the dominating mechanism of
self-organization of a delta-layer of NCs, its location in SiO2 close to the
SiO2/Si interface makes it interesting for non-volatile memory application.
Keywords: nanostructures; nanoclusters; ion implantation; ion irradiation; Ostwald ripening; nucleation; self-organization; nonequilibrium thermodynamics; theory; kinetic lattice Monte-Carlo simulation; nonvolatile memory device
  • Invited lecture (Conferences)
    Materials Research Society 2000 Fall Meeting; Boston (USA), 27.11.-1.12.2000, invited talk
  • Mat.Res.Soc.Proc. 650 (2001) R9.6

Publ.-Id: 3659 - Permalink


A toy model for inverse dynamo theory
Stefani, F.; Gerbeth, G.;
We consider a simple model of inverse dynamo theory consisting of a spherically symmetric alpha^2-dynamo with unknown radial dependence of alpha. Using an evolutionary strategy, we try to reconstruct this radial dependence of alpha from a finite number of given data, e.g. from a few real or complex eigenvalues and/or from the assumption that the field is confined to the dynamo region. Although for planetary dynamos the direct applicability of our specific model is very limited, the principle of inversion is quite general and might be useful for cosmic dynamos as well as for the emerging laboratory dynamo community.
  • Physics of the Earth and Planetary Interiors 128, No. 1-4 (2001), pp. 109-124

Publ.-Id: 3658 - Permalink


Synthesis of S-([18F]fluoromethyl)-(+)-McN5652 as a potential PET radioligand for the serotonin transporter
Zessin, J.; Eskola, O.; Brust, P.; Bergman, J.; Steinbach, J.; Lehikoinen, P.; Solin, O.; Johannsen, B.;
The present study describes the synthesis of the [18F]fluoromethyl analogue of (+)-McN5652 ([18F]FMe-McN) as a new potential tracer for the serotonin transporter. In vitro binding studies have shown that FMe-McN displays only slightly lower affinity for the serotonin transporter (Ki=2.3 ± 0.1 nM) than (+)-McN5652 (Ki=0.72 ± 0.2 nM). The radiofluorinated tracer [18F]FMe-McN was prepared by reaction of normethyl (+)-McN5652 with the fluoromethylation agent [18F]bromofluoromethane in an overall radiochemical yield of 5 ± 1% (decay-corrected, related to [18F]fluoride) and with high specific radioactivity (200 - 2000 GBq/µmol at the end of synthesis).
Keywords: (+)-McN5652, [18F]fluoromethyl analogue, [18F]bromofluoromethane, serotonin transporter, positron emission tomography
  • Nuclear Medicine and Biology 28 (2001) 857-863

Publ.-Id: 3657 - Permalink


The Rossendorf CYCLONE 18/9 Facility - Four Years Experience in Operation and Maintenance -
Preusche, S.; Füchtner, F.; Steinbach, J.;
Our four years experience in operation and maintenance of the PET cyclotron "CYCLONE 18/9" is given. Improvements at the CYCLONE 18/9 are presented as well as results of the routine radionuclide production.
  • Poster
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands
  • Contribution to proceedings
    CYCLONE 18/9 & 10/5 USER COMMUNITY 3. Workshop, February 04 - 06, 2001, Amsterdam, The Netherlands

Publ.-Id: 3656 - Permalink


Radio fluorination and positron emission tomography (PET) as a new approach to study the in vivo distribution and elimination of the advanced glycation endproducts Nepsilon-carboxymethyllysine (CML) and Nepsilon-carboxyethyllysine (CEL)
Bergmann, R.; Helling, R.; Heichert, C.; Scheunemann, M.; Mäding, P.; Wittrisch, H.; Johannsen, B.; Henle, T.;

After synthesis of fluorine-18 labelled analogues by [18F]fluorobenzoylation at the alpha-amino group, biodistribution and elimination of individual advanced glycation endproducts, namely Nepsilon-carboxymethyllysine and Nepsilon-carboxyethyllysine, was studied in comparison to lysine in rats after intravenous injection using positron emission tomography (PET).
The [18F]radiofluorinated amino acids were fast distributed via the blood, followed by a rapid excretion through the kidneys. Elimination kinetics were similar for both AGEs and lysine. For CML and CEL, but not for lysine, a temporary liver accumulation could be observed, which was not connected with any metabolisation or enterohepatic circulation. No further accumulation in any tissues was observable, indicating that increased tissue levels of CML or CEL, which have been described for certain disorders, are exclusively derived from endogenous origin and should not depend on a dietary intake. Under uremic conditions, however, an impaired kidney function might result in a significant increase of the AGE-load of blood and tissues. PET based on 18F-labelled AGEs proved to be a promising tool to elucidate the physiological fate of post-translationally modified amino acids and to clarify the role of AGEs as possible "glycotoxins".

  • Nahrung/Food 45 (2001) 182-188

Publ.-Id: 3655 - Permalink


Biodistribution and catabolism of 18F-labeled neurotensin(8-13) analogs
Bergmann, R.; Scheunemann, M.; Heichert, C.; Mäding, P.; Wittrisch, H.; Kretzschmar, M.; Rodig, H.; Tourwé, D.; Iterbeke, K.; Chavatte, K.; Zips, D.; Reubi, J. C.; Johannsen, B.;

4-([18F]fluoro)benzoyl-neurotensin(8-13) (18FB-Arg8-Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 1) and two analogs stabilized in one and two positions (18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11- Ile12-Leu13-OH, 2, 18FB-Arg8Psi(CH2NH)Arg9-Pro10-Tyr11-Tle12-Leu13-OH, 3) were synthesized in a radiochemical yield of 25 - 36% and a specific activity of 5 - 15 GBq/mmol. The peptides were evaluated in vitro and in vivo for their potential to image tumors, overexpressing neurotensin receptor 1 (NTR1) by positron emission tomography (PET). All analogs exhibited in vitro binding affinity in the low nanomolar range to NTR1-expressing human tumors, measured by quantitative receptor autoradiography, HT-29 and WiDr cells, and to sections of tumors derived from these cell lines in mice. The radiotracers were internalized in the cells in vitro, and the fluorinated peptides were able to mobilize intracellular Ca2+ of WiDr cells. In in vivo studies in rats and in mice bearing HT-29 cell tumors, only a moderate uptake of the radioligands into the studied tumors was observed, presumingly due to degradation in vivo and fast elimination by the kidneys. In comparison with the other analogs, the specific tumor uptake expressed as tumor-to-muscle relation was highest for the radioligand 3. The blood clearance of 3 was reduced by co-injection of peptidase inhibitors. The catabolic pathways of the radiofluorinated peptides were elucidated. The results suggest that the high binding affinity to NTR1 and the stabilization against proteolytic degradation are not yet sufficient for tumor imaging by PET.

Keywords: Neurotensin analogs, Positron emission tomography, F-18, Receptor binding, Tumor
  • Nuclear Medicine and Biology 29 (2002) 61-72

Publ.-Id: 3654 - Permalink


Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation
Schmidt, B.; Heinig, K.-H.; Mücklich, A.;
The evolution of the mean size and the size distribution of Au nanoclusters (NCs) under high-energy ion irradiation has been studied. Au NCs were synthesized in a 480 nm thick SiO2 layer by 330 keV Au+ implantation and subsequent annealing at T = 1000 °C for 1h in dry O2. XTEM images show a 70 nm thick layer of Au NCs, being centered at the projected ion range Rp(330keV) = 100 nm, having a mean NC size of 5 nm at Rp, and resembling the broad LSW size distribution of diffusion controlled Ostwald ripening. Post-irradiation of the Au NCs by 4.5 MeV gold ions were used in order to tailor their size and size distribution. The high-energy Au+ irradiation were performed at 190...210 °C with a fluence of (0.5...1.0)x1016 cm-2. By the post-irradiation no gold was deposited into the SiO2 layer, the Au+ ions come to rest in the (001)Si substrate at Rp(4.5MeV) = 1 mm. XTEM images of the post-irradiated Au NCs show a strong decrease of their mean size as well as the width of their size distribution. The observed NC evolution under ion irradiation agrees with recent theoretical predictions and kinetic Monte-Carlo simulations.
Keywords: Ion beam synthesis, nanucluster, comuter simulation
  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A

Publ.-Id: 3653 - Permalink


Reflectivity and diffraction study of cross-beam pulsed laser deposited Co/Cu multilayers
Prokert, F.; Noetzel, J.; Schell, N.; Wieser, E.; Matz, W.; Gorbunov, A.;
Co/Cu multilayers were prepared by cross-beam pulsed laser deposition and characterised by high-angle X-ray diffraction as well as specular and off-specular reflection. Using synchrotron radiation at the K-edge energy of Co and Cu to enhance the scattering contrast, the study shows that the roughness of these multilayers is well described by the fractal model of self-affine structures. For the pulsed laser deposited layers an extremely large lateral correlation length, xi, of the vertically correlated interfacial roughness is found (xi >1 µm) which exceeds the xi-value of the uncorrelated roughness by about two orders. The interfaces are very jagged (roughness exponent, h, between 0.15 and 0.3). The root mean square roughness, sigma, of the Cu/Co and Co/Cu interfaces are of the same order compared with the values reported for sputtered layers.
Keywords: Surfaces and interfaces; Multilayers; Reflection spec.; Surface roughness; X-ray diffraction
  • Thin Solid Films, vol. 394 (1-2), (2001) p.164-173

Publ.-Id: 3652 - Permalink


Structure and magnetic properties of Co nanoclusters fabricated by ion beam synthesis in SiO2 films.
Klimenkov, M.; von Borany, J.; Matz, W.; Eckert, D.; Wolf, M.; Müller, K.-H.;
Abstract: Co nanoparticles fabricated by ion beam synthesis in SiO2 films were inve-stigated with TEM and SQUID technique. The variation of the thermal treatment enables the formation of Co nanoclusters of different sizes ranging from 2 to 40 nm. Small nanoclusters of about 2-3 nm are amorphous, whereas clusters above 7 nm show the configuration of cubic Co nanocrystals. Measurements of magnetization at tem-peratures between 2 K and 360 K reveal superparamagnetic behaviour for the small nanoclusters up to 3 nm and ferromagnetism for clusters above 7 nm .
Keywords: cobalt nanoclusters, magnetism, transmission electron microscopy, ion implantation
  • Applied Physics A elektron. Publikation vol.73 (2001) DOI 10.1007/s003330100915
  • Appl. Phys. A 74 (2002)571-575 (Druckversion)

Publ.-Id: 3651 - Permalink


Development of an Apparatus for Seaborgium Studies by High Temperature Gas Chromatography
Vahle, A.; Hübener, S.; Dressler, R.; Grantz, M.;
In preparation for the characterization of Sg as oxide hydroxide a new high temperature gas chromatography apparatus based on the OLGA design was developed. However, the time-consuming recluster step was replaced by direct deposition of species leaving the chromatographic column on metal foils. In test experiments with short-lived Mo isotopes a retention time of 9 s was determined for an isothermal temperature of 1270 K, sufficient to study Sg isotopes.
A model based on the theory of supersonic jet and on simple geometrical considerations reproduces the data of direct condensation experiments quite well.

Keywords: on-line gas chromatography, reaction gas chromatography, direct deposition, molybdenum oxide hydroxide, adsorption
  • Nuclear Instruments and Methods in Physics Research A 481 (2002) 637-645

Publ.-Id: 3650 - Permalink


Ion Beam Synthesis of Ge Nanowires
Müller, T.;
The formation of Ge nanowires in V-grooves has been studied experimentally as well as theoretically. As substrate oxide covered Si V-grooves were used formed by anisotropic etching of (001)Si wafers and subsequent oxidation of their surface. Implantation of 1E17 Ge+ cm^-2 at 70 keV was carried out into the oxide layer covering the V-grooves.
Ion irradiation induces shape changes of the V-grooves, which are captured in a novel continuum model of surface evolution. It describes theoretically the effects of sputtering, redeposition of sputtered atoms, and swelling. Thereby, the time evolution of the target surface is determined by a nonlinear integro-differential equation, which was solved numerically for the V-groove geometry. A very good agreement is achieved for the predicted surface shape and the shape observed in XTEM images. Surprisingly, the model predicts material (Si, O, Ge) transport into the V-groove bottom which also suggests an Ge accumulation there proven by STEM-EDX investigations.
In this Ge rich bottom region, subsequent annealing in N2 atmosphere results in the formation of a nanowire by coalescence of Ge precipitates shown by XTEM images. The process of phase separation during the nanowire growth was studied by means of kinetic 3D lattice Monte-Carlo simulations. These simulations also indicate the disintegration of continuous wires into droplets mediated by thermal fluctuations. Energy considerations have identified a fragmentation threshold and a lower boundary for the droplet radii which were confirmed by the Monte Carlo simulation.
The here given results indicate the possibility of achieving nanowires being several nanometers wide by further growth optimizations as well as chains of equally spaced clusters with nearly uniform diameter.

Keywords: Ion Beam Synthesis, Nanowires, Surface Sputtering, Redeposition, Kinetic Monte Carlo Simulation
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-309 Januar 2001

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Publ.-Id: 3649 - Permalink


Strahlkopplung von Tandetron-Beschleuniger und Ionenimplanter zur Durchführung von Mehrstrahlexperimenten im Forschungszentrum Rossendorf
Tyrroff, H.; Richter, B.; Neumann, W.;
Im Sommer 1999 wurde im Forschungszentrum eine Zweistrahlführung in Betrieb genommen. Dieses System gestattet, Ionenarten aus unterschiedlichen Beschleunigern gleichzeitig in die Experimentierstationen zu lenken. In der Doppelimplantationsstation wird die Zweistrahlführung zur Synthese neuartiger Materialien genutzt. In der Analysestation wird die Zweistrahlführung in Kombination mit einem magnetischen Browne-Buechner-Spektrometer eingesetzt, um komplexe und hochgenaue Materialanalysen durchzuführen. Das System überträgt Ionen des gesamten Teilchen- und Energiespektrums von 3-MV-Tandetron-Beschleuniger und 500-kV-Ionenimplanter mit minimalen Intensitätsverlusten zu den Experimenten. Steuerung und Kontrolle von Beschleunigern, Strahlführung und Experiment erfolgen in einem hierarchischen Rechnernetz. Die hier beschriebene Zweistrahlanlage ist Teil eines Projekts zur umfassenden Kopplung von Basisgeräten des Forschungszentrums.
Keywords: Strahlkopplung, Tandetron-Beschleuniger, Ioneneimplanter, Mehrstrahlexperimente, Doppelimplantation, Oberflächenanalyse, ERD, RBS, Browne-Buechner-Spektrometer, Ionenoptik, Emittanz, Optimierung, magnetische Linsen, elektrostatische Linsen, Ablenkmagneten, Strahlenveloppen, Transmission, Energiebereich, Ionenart, Stromdichte, Strahlkontrolle, Testresultate.
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-308 Januar 2001

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Publ.-Id: 3648 - Permalink


Verification of neutron transport calculations for nonstandard pressure vessel surveillance positions in the VVER-1000 Novovoronesh-5
Böhmer, B.; Konheiser, J.; Brodkin, E.; Egorov, A.; Vikhrov, V.; Zaritsky, S.; Polke, E.;
Activation measurements results at non-standard surveillance positions of the VVER-1000 Novovoronesh-5 have been used to verify neutron fluence calculations for pe-ripheral reactor regions with large flux gradients. Fluence integrals and activities of irradiated detectors and specimens had been calculated by three laboratories using different transport calculation methods: 2D/1D-SN synthesis, 3D-SN and the Monte Carlo method. The results obtained by different calculations and by activation measurements have been compared. The differences between measured and calculated activities as well as between the different calculation results were reasonable. Possible causes of discrepancies are discussed.
Keywords: neutron embrittlement, neutron fluences, neutron transport calculations, activation measurements
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Proceedings pp. 37-42

Publ.-Id: 3647 - Permalink


Intersubband Lasers and Detectors
Helm, M.;
The term “intersubband transitions” has been coined to describe optical transitions between confined electronic states in semiconductor quantum structures. In this lecture I will discuss the basic underlying physics of intersubband transitions in quantum wells and discuss their recent applications for real optoelectronic devices, as there are the quantum cascade laser (QCL) and the quantum well infrared photodetector (QWIP).

Concerning the physics, the basic concept of intersubband transitions appears extremely simple; yet a detailed understanding of all aspects, such as absorption strength and frequency, polarization dependence and linewidth, requires a careful consideration of band structure, many-body physics and electromagnetism.

The first observation of intersubband absorption was reported in 1974 in Si accumulation layers and 1985 in GaAs quantum wells. Since then, intense research has driven the development of high-sensitivity intersubband infrared detectors and focal-plane arrays, which are now commercially available. Intersubband lasers have been realized in 1994 and are now covering a spectral range from 4 to 17 m. I will discuss the physics and performance of these optoelectronic devices, also in comparison to conventional band-gap detectors and lasers.

Keywords: infrared, laser, detector, intersubband
  • Invited lecture (Conferences)
    Invited talk at the "29th Int. School on the Physics of Semiconducting Compounds", Jaszowiec, Poland, June 2000

Publ.-Id: 3646 - Permalink


Miniband absorption in strongly coupled superlattices
Helm, M.;
please contact the author
Keywords: superlattice, infrared
  • Lecture (others)
    Seminarvortrag am Paul-Drude-Insitut für Festkörperelektronik (13.11.2000)

Publ.-Id: 3645 - Permalink


Infrarotspektroskopie von Halbleiterübergittern
Helm, M.;
Ich moechte einen Ueberblick ueber die optischen Eigenschaften von Halbleiteruebergittern im Infrarot- und THz-Spektralbereich geben, die ja im wesentlichen von Inter- und Intraminibanduebergaengen herruehren. Die theoretischen Ueberlegungen werden durch verschiedene experimentelle Resultate illustriert - z.B. Interminibandabsorption und ihre Anwendung zur Analyse der Elektronen Verteilungsfunktion oder thermisches "quenching" der Intraminibandabsorption. Abschliessend diskutiere ich die Erweiterung obiger
Messungen auf Uebergitter mit einem vertikalen elektrischen Feld, d.h. die Untersuchung von Wannier-Stark-Leitern und Bloch-Oszillatoren.
Keywords: superlattice, infrared
  • Lecture (others)
    Seminarvortrag am Institut für Technische Physik der Universität Erlangen (10.11.2000)

Publ.-Id: 3644 - Permalink


Elastic Properties of Diamond-Like Amorphous Carbon Films Grown by Computer Simulation of Ion-Beam Deposition Process
Belov, A.; Jäger, H.-U.;
Atomic-scale calculations were performed for the first time to investigate mechanical
properties of amorphous carbon films grown by a realistic simulation of ion-beam deposition process. The simulated films have a thickness of a few nanometers and reproduce the main structural features of real films, with the bulk content of sp3 bonded atoms varying from 35 to 95%, depending on the ion energy (E = 20-80 eV). Employing empirical interatomic potentials for carbon, the average bulk stresses as well as the atomic-level stress distributions were calculated and analysed. The bulk stresses were found to depend not only on the ion energy, but also on the film quality, in particular, on such structural inhomogeneities as local fluctuations of the sp3 fraction with the depth. The local variation of the bulk stress from the average value considerably increases as the local content of sp2 bonded atoms increases. Elastic constants of amorphous carbon films were also computed using the method of inner elastic constants, which allows for the stress dependence of elastic constants to be analysed. This investigation showed how the Young's modulus varies as a function of the lateral bulk stress in an amorphous film.

Keywords: amorphous carbon, thin films, computer simulation, molecular dynamics, mechanical properties, empirical potentials
  • Contribution to proceedings
    Materials Research Society Symposium Proceedings 648 (2001) P6.53.1-6

Publ.-Id: 3643 - Permalink


RESQUE: Dependence of Test Results from Reconstituted Specimens with Tolerance Deviations and Variation of End Block Materials
Viehrig, H.-W.; Richter, H.; Atkins, T.; van Walle, E.; Scibetta, M.; Valo, M. J.; Wootton, M. R.; Keim, E.; Debaberis, L.; Horsten, M.;
This paper continues the presentation of detailed results of the EU-sponsored RESQUE project. Within the RESQUE project it was planned to determine the dependence of Charpy-V test results on tolerance deviations and different end block materials in reconstituted specimens. The conventional Charpy-V parameters - the total impact energy, lateral expansion and shear fracture appearance - are not significantly affected by the effects of oversized dimensional variability. Disturbing load oscillations arise from some of the geometrical deviations. This influences the characteristic yield load, yield deflection and impact energy at load maximum. In comparison to the existing scatter there is no significant effect of the end block material on the main Charpy parameters and the characteristic loads.
Keywords: reactor pressure vessel steel, reconstituted specimens, stud welding, geometrical deviation, Charpy-V test, Charpy-V parameters, transition temperatures
  • Lecture (Conference)
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.
  • Contribution to external collection
    Small Specimen Test Techniques: Fourth Volume, ASTM STP 1418, M. A. Sokolov, J. D. Landes, and G. E. Lucas, Eds., ASTM International, West Conshohocken, PA, 2002, pp. 477 - 488.

Publ.-Id: 3642 - Permalink


Dose Rate Calculations from Radioactive Vascular Stents: DPK versus exact MC approach
Gorodkov, S.; Möslang, A.; Vladimirov, P.;
Vascular stents activated with radioactive isotopes are planned to be used in clinical practice to prevent restenosis in human coronary arteries after balloon angioplasty. Medical stents are cylindrical meshes and their complex geometry is usually treated for energy dose calculation with approximate dose point kernel(DPK) approach. The important point missed in the DPK approach is the absence of the stent material and, hence, the absence of energy absorption inside the stent. We have performed a comparison between DPK and exact Monte Carlo calculations for some simplified stent models. It appears that DPK approximation significantly overestimates pike dose values especially for the case of gamma-emitting sources. We suggest DPK kernel normalization, which minimizes the difference at relatively far distances, while significant discrepancies near the stent surface still remain.
Keywords: vascular stent radioactive isotope medical application Dose Point Kernel(DPK) Monte Carlo EGS4
  • Poster
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8
  • Contribution to proceedings
    Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation an Applications, Proceedings of the Monte Carlo 2000 Conference, Lisbon, 23.-26. October 2000, pp 467-472, Springer-Verlag Berlin Heidelberg New York, 2001, ISBN 3-540-41795-8

Publ.-Id: 3641 - Permalink


Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) Study of the Sorption of Cm(III) onto Smectite and Kaolinite
Stumpf, T.; Bauer, A.; Coppin, F.; Kim, I. J.;
The surface sorption process of Cm (III) onto smectite and kaolinite was investigated by time-resolved laser fluorescence spectroscopy (TRLFS) in the trace concentration range. We conclude that at low pH Cm(III) is sorbed onto kaolinite and smectite as an outer-sphere complex and retains its complete primary hydration sphere. With increasing pH, inner-sphere adsorption onto kaolinite and smectite occurs via the aluminol edge sites. The same evolution of the Cm(III)-clay surface species as a function of pH was observed for both minerals. Starting at a pH ³ 5, we observe the formation of a ºAl-O-Cm2+(H2O)5 surface complex, which is replaced by a second species at higher pH. The second surface complex may be a monodentate ºAl-O-Cm+(OH)(H2O)4 species or bidentate º(Al-O)2-Cm+(H2O)5 species. The Cm(III)/clay surface complexes are characterised by their emission spectra (peak maxima at 598.8 nm and 603.3 nm) and their fluorescence lifetime (both 110±7 µs). An important result for the mobility and bioavailability of radionuclides is that no incorporation of Cm(III) into the bulk clay structure was observed.
  • Environmental Science and Technology

Publ.-Id: 3640 - Permalink


Messung der Kondensatfilmdicken in einem dampfdurchströmten horizontalen Rohr
Li, W.; Hicken, E. F.; David, P. H.; Prasser, H.-M.; Baldauf, D.; Zschau, J.;
Im Mehrzweck-Thermohydraulik-Versuchsstand NOKO wurde die Wirksamkeit verschiedener passiver Sicherheitssysteme oder deren Komponenten untersucht. Passive Sicherheitssysteme besitzen keine Komponenten, die zur Funktionsfähigkeit Fremdenergie benötigen.
Bei Nachrechnungen der Experimente mit den waagerecht angeordneten Notkondensatorbündeln hatte sich ergeben, dass die verwendeten Rechenprogramme wohl die integral abgeführte Energie gut berechnen können; die lokalen Kondensationsraten auf der Innenseite der Rohre unterschieden sich bei den eingesetzten Programmen beträchtlich voneinander. Daher wurde im Rahmen einer Dissertation die Kondensation von Wasserdampf und eines Wasserdampf-Stickstoff-Gemisches auf der Innenseite eines waagerechten Rohres untersucht. Durch eine entsprechende Instrumentierung war die Dicke des Kondensatfilms sowie dessen Struktur zu ermitteln. In einem besonders instrumentierten Rohr des 2. Notkondensator-Bündels wurden hierzu Nadelsonden eingebaut, deren Eintauchtiefe mit Hilfe von Schrittmotoren verändert werden konnte. Diese beweglichen Nadelsonden wurden im wandnahen Bereich hin und her gefahren, um so die Filmdicke zu registrieren. Zusätzlich waren die Nadelsonden mit Thermoelementen ausgestattet, die gleichzeitig eine Messung der Temperaturverteilung in der Grenzschicht ermöglichten.

Keywords: emergency condenser, passive safety systems, steam condensation, two-phase flow, conductivity probes, heat transfer
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15./17. Mai 2001, Tagungsbericht S. 103-106.

Publ.-Id: 3638 - Permalink


Spectroscopic Study of Cm(III)Sorption onto γ-Alumina
Stumpf, T.; Rabung, T.; Klenze, R.; Geckeis, H.; Kim, J. I.;
The surface sorption of Cm(III) onto aqueous suspensions of alumina is investigated by time-resolved laser fluorescence spectroscopy (TRLFS). The experiment is performed under Ar atmosphere at ionic strength of 0.1 M NaClO4. pH is varied between 2 and 10 and the metal ion concentration between 2.7.10-7 and 4.5.10-5 mol/L. With increasing pH, two Cm(III)-alumina surface species are identified which are attributed to ºAl-O-Cm2+(H2O)5 and ºAl-O-Cm+(OH)(H2O)4. The two curium-alumina surface complexes are characterised by their emission spectra (peak maxima at 601.2 nm and 603.3 nm, respectively) and fluorescence emission lifetime (both 110 µs). In the concentration range investigated, the surface complex formation is not dependent upon the metal ion concentration but only on pH. Also the concentration ratio of the two surface species is found to be independent on the metal ion concentration. No spectroscopic evidence for the presence of "strong" and "weak" sites can be found at different surface coverages.
Keywords: Curium, Alumina, Surface complexation, TRLFS
  • Journal of Colloid and Interface Science 238, 219-224(2001)

Publ.-Id: 3637 - Permalink


Synthesis of Spatially Controlled Nanowires by Ion Implantation in V-Grooves on (001) Si-Surfaces
Müller, T.; Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Möller, W.;
The synthesis of spatially controlled Ge nanowires and nanoclusters by Ge+ ion implantation in oxidized V-grooves on (001) Si surfaces has been studied experimentally as well as theoretically. The V-grooves were prepared by anisotropic wet chemical etching and thermal oxydation. The SiO2-covered V-grooves were implanted with 70 keV Ge+ ions up to a fluence of 1017 cm-2. Ge accumulates within the SiO2 at the bottom of the V-groove which has been proven by analytical TEM (EDX-mapping). Theoretical studies have shown that the Ge accumulation is caused by the V-groove geometry, forward sputtering, and re-deposition. During subsequent annealing the redistributed Ge forms a nanowire by precipitation, ripening and coalesence. Kinetic lattice Monte Carlo simulations of the nanowire formation process show growth instabilities and self-organization phenomena.
Keywords: Ion beam synthesis, nanowires, computer simulation
  • Contribution to proceedings
    Materials Research Society, Symposium Proceedings Ion Beam Synthesis and processing of Advanced Materials Symposium held November 27-29, 2000, Boston, Massachusetts, U.S.A. Mat. Res. Soc. Symp. Proc. vol. 647 (2001) O10.2.1-6

Publ.-Id: 3635 - Permalink


Bericht der Herbsttagung der Studiengruppe für elektronische Instrumentierung vom 25. bis 27. September 2000 im Hahn-Meitner-Institut Berlin
Gabriel, F.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-305 November 2000

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Publ.-Id: 3634 - Permalink


Improving the understanding of ion-beam-induced defect formation and evolution by atomistic computer simulations
Posselt, M.;
The morphology of the as-implanted damage in silicon is investigated using a recently developed combination of time-ordered computer simulations based on the binary collision approximation (BCA) with classical molecular dynamics (MD) calculations. The method is applied to determine the type and the amount of defects formed within the first nanosecond after ion impact. The depth profile and the total number of different defect species (vacancies, interstitials, disordered atoms, etc.) produced on average per incident ion are calculated for B+ (15 keV), P+ (5, 10, 20, 30 keV), and As+ (15 keV) implantations. It is shown that the as-implanted defect structure depends not only on the nuclear energy deposition per ion but also explicitly on the ion mass. Therefore for each ion species the damage morphology exhibits characteristic features. For heavy ions the percentage of extended defects is higher than for light ions. In all cases investigated the number of free or isolated interstitials exceeds the amount of free vacancies. The results obtained allow a microscopic interpretation of the phenomenological model for the as-implanted damage employed in conventional BCA simulations in order to describe the dose dependence of the shape of ion range profiles. They can be also applied to get more realistic initial conditions for the simulation of the defect kinetics during post-implantation annealing.
Keywords: ion implantation, computer simulation, defects
  • Invited lecture (Conferences)
    MRS 2000 Fall Meeting, Boston, USA, November 27 - December 1, 2000 (invited talk)
  • Contribution to external collection
    Mat. Res. Soc. Symp. Proc. Vol. 647 (2001) pp. O2.1.1-O2.1.12

Publ.-Id: 3632 - Permalink


MHD Turbulence Measurements in a Sodium Channel Flow Exposed to a Transverse Magnetic Field
Eckert, S.; Gerbeth, G.; Witke, W.; Langenbrunner, H.;
The influence of a static transverse magnetic field on a turbulent sodium flow in a channel with a
rectangular cross section is investigated. The turbulence has been forced by mechanical means
employing a grid of cylindrical bars. Electric potential probes have been used to determine the
longitudinal component of the liquid velocity. The experiments cover a wide range of the
non-dimensional parameters Hartmann number (Ha < 3000) and the magnetic interaction parameter
(N < 800). Measurements of the turbulence intensity as a function of the magnetic interaction
number N will be presented and discussed. The measured spectra are essentially different from those
predicted according to the theory of two-dimensional turbulence.
Keywords: MHD turbulence, liquid metal channel flow, transverse magnetic field, local velocity, measurements, potential probes, velocity profiles, turbulence intensity, power spectra
  • International Journal of Heat and Fluid Flow, Vol. 22/3, 2001, 358-364

Publ.-Id: 3631 - Permalink


On the results of the Riga dynamo experiments
Gailitis, A.; Lielausis, O.; Platacis, E.; Gerbeth, G.; Stefani, F.;
On 11 November 1999, magnetic field self-excitation was observed for the first time in a hydromagnetic experiment at the Riga dynamo facility. In a second experiment in July 2000, the dynamo behaviour in the kinematic as well as in the saturation regime was studied. We report on the results of both experiments and try to understand the saturation mechanism.
  • Magnetohydrodynamics 37, No. 1/2 (2001) 71-79

Publ.-Id: 3630 - Permalink


Ion-nitriding induced plastic deformation in austenitic stainless steel
Grigull, S.; Parascandola, S.;
Lattice parameter measurements in ion-nitrided surface layers of austenitic stainless steel have been performed using x-ray microbeam diffraction on samples with different nitrogen contents as a function of depth and grain orientation, respectively. The lattice expansion observed in the layers as a result of nitriding is anisotropic due to the presence of elastic strains, but the austenite (fcc) structure is largely retained. Parallel to the layer–substrate interface the expanded lattice is highly relaxed which is, along with significant changes in the surface morphology, indicative of plastic deformation in the nitrided zone.
  • Journal of Applied Physics 88 (2000) 6925

Publ.-Id: 3629 - Permalink


Role of Ion-Beam Processing Time in the Formation and Growth of the High-Nitrogen Phase in Austenitic Stainless Steel
Williamson, D. L.; Wilbur, P. J.; Fickett, F. R.; Parascandola, S.;
A systematic series of AISI 316 stainless steel samples has been prepared as a function of exposure time to a nitrogen ion beam. Times from 15 s to 4 h were selected with other conditions maintained as follows: sample temperature = 410oC; accelerating potential = 700 V; beam current density = 2.0 mA/cm2. Compositional, structural, magnetic, and diffusion properties were studied with a combination of x-ray diffraction, backscatter Mössbauer spectroscopy, magnetic force microscopy, surface profilometry, and glow-discharge optical emission spectroscopy. The only N-containing phase detected for all processing times was the high-N-solid-solution phase, γN, and its maximum N content was found to grow rapidly to a saturation value exceeding 30 at.%. A carbon contamination layer, in the form of a C-solid-solution phase, γC, was detected below the γN, and was found to be introduced during the Ar-ion sputter-cleaning/heating step used prior to exposure to the N-ion beam. This C-rich layer is “pushed” ahead of the incoming N. The γN layer thickness growth can be modeled with a simple diffusion-plus-sputtering equation that yields the effective diffusivity and maximum (sputter-limited) γN layer depth for the given processing conditions. The surface roughness increases with processing time. Anisotropy in the lattice expansion for different lattice planes parallel to the sample surface and varying magnetic properties in the different surface grains are observed. This is likely due to a mixture of residual stress and N-composition variation effects. Ferromagnetic maze-like domain structures are observed on the 1 micron size scale.
  • Lecture (Conference)
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan
  • Contribution to proceedings
    Proceedings of the International Current Status Seminar Thermochemical Surface Engineering of Stainless Steels, 5 - 8 November 2000, Osaka, Japan

Publ.-Id: 3628 - Permalink


Determination of the hyperfine parameters of a-FeSi2 by angle dependent Mössbauer spectroscopy on single crystals
Reuther, H.; Behr, G.; Teresiak, A.;
The hyperfine parameters of the metallic disilicide phase a-FeSi2 at room temperature are determined with high accuracy by conversion electron Mössbauer spectroscopy measurements on a single crystal. It is found that there are two well defined iron environments with different electron densities (isomer shifts 0.202 and 0.257 mm/s, resp.) and different electric field gradients. Both quadrupole splittings are negative (-0.382 and -0.730 mm/s, resp.) and the site occupation for both sites is different.
  • Journal of Physics: Condensed Matter 13 (2001) L225-L229

Publ.-Id: 3627 - Permalink


Investigations of natural convection in large pools during the heating up of the secondary side of an emergency condenser
Krepper, E.; Hicken, E.-F.; Jaegers, H.;
Natural convection is a basic principle for a lot of industrial processes. As an example for the investigation of natural convection phenomena, the paper describes investigations of a passive heat removal system in advanced designs of nuclear power plants. The SWR-1000 concept of Siemens AG includes emergency condensers. In the Research Centre Jülich at the NOKO test facility experiments were performed, to investigate the heat transfer capability under different operation modes. In the last time experiments with detailed instrumentation of thermocouples on the secondary side were performed, to investigate the heating up phenomena in the pool. The paper describes simulations performed in the FZ-Rossendorf using the CFD-code CFX-4 of AEA-Technology and comparisons to the experiments.
Keywords: natural convection, experiments, cfd-simulations
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden 15-17 Mai 2001, Tagungsband S. 99-102
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden 15-17 Mai 2001, Tagungsband S. 99-102

Publ.-Id: 3626 - Permalink


A semi-analytical model for the description of coolant mixing inside the KONVOI reactor pressure vessel during pump start-up
Kliem, S.; Prasser, H.-M.;
The coolant mixing in the downcomer and the lower plenum during pump start-up has been investigated experimentally at the ROCOM test facility. This facility is a 1:5 linearly scaled model of the KONVOI reactor pressure vessel. Transfer functions for a semi-analytical model have been derived from these experiments. The comparison of the model with further experiments and a computational fluid dynamics calculation is presented.
Keywords: Coolant mixing; pump start-up
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht, S. 107-112
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, 15.-17. Mai 2001, Tagungsbericht, S. 107-112

Publ.-Id: 3625 - Permalink


Beziehungen zwischen Mikrostruktur und Zähigkeitseigenschaften von neutronenbestrahlten WWER-Reaktordruckbehälterstählen
Ulbricht, A.; Böhmert, J.; Viehrig, H.-W.;
An 7 Chargen von Druckbehälterstählen russischer Herkunft wurden SANS-Unter-
suchungen im unbestrahlten Zustand, nach Bestrahlung im Reaktor WWER-2
Rheinsberg und nach einer 100-h-Ausheilglühung bei 475 °C durchgeführt. Bestrah-
lung erzeugt in jedem Fall eine erhöhte Kleinwinkelstreuintensität. Die Analyse ihrer
Streuvektorabhängigkeit führt auf Strukturdefekte mit einem mittleren Radius von
ca. 1 nm und einem chargenabhängig variierenden Volumenanteil von 0,03 - 0,71 %. Der Volumenanteil korreliert tendenziell mit der Verschiebung der Sprödbruchüber-
gangstemperatur.
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, Germany, 15.-17. Mai 2001, S. 697-700
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, Germany, 15.-17. Mai 2001, S. 697-700

Publ.-Id: 3624 - Permalink


Verification of the code ATHLET by post-test analysis of two experiments performed at the integral test facility CCTF
Schäfer, F.; Krepper, E.;
In the framework of the external validation of the thermo-hydraulic code ATHLET Mod 1.2 Cycle A, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the japanese test facility CCTF. The experiments C2-04/62 and C2-19/79 simulate a double end break in the cold leg of the PWR with ECC injection into the cold leg and with combined ECC injection into the hot and cold legs. The evaluation of the calculated results shows, that the main phenomena can be calculated in a good agreement with the experiment. Especially the behaviour of the quench front and the core cooling are calculated very well.
Keywords: ATHLET, code validation, experiments
  • Lecture (Conference)
    Annual Meeting on Nuclear Technology, Dresden, May 15-17 2001, p. 87-90
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology, Dresden, May 15-17 2001, p. 87-90

Publ.-Id: 3623 - Permalink


The hydrolysis of uranium(VI) investigated using EXAFS and 17O-NMR
Moll, H.; Reich, T.; Szabó, Z.;
The hydrolysis of uranium(VI) has been the subject of extensive studies since 50 years because uranyl forms strong comlexes with OH- in solution. A comprehensive discussion and review of the thermodynamic data is published in [1]. We investigated the structure of UO22+ as a function of pH with the aid of U LIII-edge EXAFS spectroscopy. The experiments were carried out at beamline BM20. The equipment allows excellent XAS measurements up to high k-values, 17.5 Å-1 in our case.
The speciation of uranium(VI) at a total concentration of 0.05 M in slightly acidic (pH: 3 to 4) solutions is dominated by the two polynuclear complexes (UO2)2(OH)22+ and (UO2)3(OH)5+. Sample A is an example from this pH region, where (UO2)3(OH)5+ is the dominant species. Structure investigations of these polymeric cations in solution at such uranium concentrations are rare. The formation of polynuclear complexes is clearly confirmed by the U-U interaction at 3.81 Å (Figure 1). Approximately 5 oxygen atoms are coordinated in the equatorial plane at 2.41 Å.
In the following pH region from 6 to 11, the U(VI) speciation is dominated by the precipitation of schoepite phases, UO2(OH)2xH2O (sample B). A longer U-U distance of 3.87 Å was measured. Similar U bond lengths of Ë 3.9 Å were found in schoepite phases. Their structure consists of a network of UO2(OH)2 sheets, where the uranyl centers are connected via a double OH bridge.
In the alkaline pH region (sample C and D), monomeric uranium species are formed. As compared to our previous study [2], we were able to extend the k-space region from 15 Å-1 in [2] up to 17.5 Å-1 and thereby to increase the accuracy. The EXAFS measurements confirm the speciation calculations indicating that UO2(OH)42- is the major species at 0.5 M tetramethylammonium hydroxide (TMA-OH). There are two trends in the EXAFS data, the U-Oaxial bond length increases 1.79, 1.81, and 1.83 Å moving from pH 4.1 to 13.7, while the average U-Oequatorial bond length decreases, 2.41, 2.34, 2.26 Å, respectively. This indicates a stronger bonding of equatorial OH groups with increasing pH. Clark et al. have presented spectroscopic evidence for the formation of a penta-hydroxide complex at high TMA-OH concentrations, however with no information about the equilibrium constant [3]. We have tested the hypothesis of Clark et. al. using 17O-NMR spectroscopy with 17O-enriched "yl" oxygens. The spectrum recorded at 258 K (Figure 2) shows only one peak for UO2(OH)42- in 1 M TMA-OH. However, when increasing the hydroxide concentration to 3 M two peaks were obtained, one with the same shift as in the 1 M TMA-OH solution, 1132.2 ppm, the other at 1135.8 ppm presumably due to UO2(OH)53- (Figure 2). To conclude, the complex UO2(OH)42- has a very broad range of existence in strongly alkaline solution. At very high total concentrations of hydroxide [> 1 M TMA-OH], an additional OH- ligand may coordinate in an associative reaction.
  • Contribution to external collection
    ESRF Highlights 2000, 21-22 (2001)

Publ.-Id: 3622 - Permalink


Copper gettering in silicon at half of the projected ion range induced by helium implantation
Peeva, A.; Fichtner, P. F. P.; Da Silva, D.; Behar, M.; Koegler, R.; Skorupa, W.;
Damage has been observed in keV He + ion-implanted Si away from the projected ion range Rp, mainly around Rp/2. Cu gettering has been used for the detection of irradiation defects which are formed during rapid thermal annealing (RTA) of 800°C/10 min. The transmission electron microscopy (TEM) micrographs show no visible defects at Rp/2. The Cu gettering peak at Rp/2 is well known for MeV-ion-implanted and annealed Si (Rp/2 effect). In this study the corresponding effect is observed for low energy implantation of a light ion like He. The mechanism of the cavity formation when He is implanted into silicon and its influence to the implantation induced point defects recombination during subsequent annealing is discussed.
Keywords: Gettering, Ion Implantation, Defects, Helium, Cavities
  • Journal of Applied Physics 91 (2002) 69

Publ.-Id: 3621 - Permalink


The Colloid Chemistry of Acid Rock Drainage Solution from an Abandoned Zn-Pb-Ag Mine
Zänker, H.; Moll, H.; Richter, W.; Brendler, V.; Hennig, C.; Reich, T.; Kluge, A.; Hüttig, G.;
Acid rock drainage (ARD) solution from an abandoned ore mine (pH 2.7, sulfate concentration 411 mMol/L, Fe concentration 93.5 mMol/L) was investigated by photon correlation spectroscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis and X-ray absorption fine structure (EXAFS) spectroscopy. A colloid concentration of $ 1 g/L was found. The prevailing particle size was < 5 nm. The most probable mineralogical composition of the colloidal particles is a mixture of hydronium jarosite and schwertmannite. Conclusions as to the type of binding of arsenic onto the particles are drawn.



Keywords: Key words: acid rock drainage, colloids, iron hydroxy sulfates, arsenic
  • Applied Geochemistry 17 (2002) 633-648

Publ.-Id: 3620 - Permalink


The Modeling of Fuel Rod Behaviour under RIA Conditions in the Code DYN3D
Rohde, U.;
A description of the fuel rod behaviour and heat transfer model used in the code DYN3D for the simulation of reactivity initiated accidents (RIA) is given. The model comprises a detailed description of the heat transfer in the gas gap between fuel and cladding by conduction, radiation and fuel-cladding contact. The gas gap behaviour is modeled in a mechanistic way taking into account transient changes of the gas gap parameters based on given conditions for the steady state. Thermal, elastic and plastic deformations of fuel and cladding are taken into account. Metal-water reaction of the cladding material in the high temperature region is considered. The cladding-coolant heat transfer regime map covers the region from one-phase liquid convection to dispersed flow with superheated steam.
For the validation of the model, experiments on fuel rod behaviour during RIAs performed in Russian and Japanese pulsed ressearch reactors with shortened probes of fresh fuel rods are calculated. Comparisons between calculated and measured results are shown and discussed. Numerical studies concerning the fuel rod behaviour under RIA conditions in power reactors are reported about. It is demonstrated, that the fuel rod behaviour at high pressure and mass flow rate in power reactors is different from the behaviour at low pressure and stagnant flow conditions in the experiments. It is shown that the mechanisms of fuel rod failure known from the literature can be qualitatively reproduced by the DYN3D fuel rod model.
Keywords: nuclear reactors, reactivity initiated accidents, fuel rod behaviour, heat transfer, validation, pulsed research reactors
  • Lecture (Conference)
    Jahrestagung Kerntechnik 2001, Dresden, Deutschland, 15.-17.5.2001, Tagungsband S. 339-344, Inforum Verlags- und Verwaltungsgesellschaft mbH, Bonn 2001
  • Contribution to proceedings
    Jahrestagung Kerntechnik 2001, Dresden, Deutschland, 15.-17.5.2001, Tagungsband S. 339-344, Inforum Verlags- und Verwaltungsgesellschaft mbH, Bonn 2001

Publ.-Id: 3619 - Permalink


Boundary Layer Control by Means of Wall Parallel Lorentz Forces
Weier, T.; Fey, U.; Gerbeth, G.; Mutschke, G.; Lielausis, O.; Platacis, E.;
Lorentz forces can be used to control the near wall flow of low conducting liquids like sea-water. To achieve force densities strong enough to modify the flow, both magnetic and electric fields have to be applied to the fluid. Here, wall parallel Lorentz forces in streamwise direction were used to influence the velocity profile of a flat plate boundary layer as well as the flow around a symmetric hydrofoil. Velocity measurements inside the boundary layer and direct force measurements are given for the flat plate.
At moderate force strength, the mean velocity profile is characterized by a momentum thickness smaller than in the unforced case, whereas at high enough Hartmann numbers a wall jet develops. Additionally, a turbulent, but approximately non-growing boundary layer has been observed. The effect of a suction-side, streamwise Lorentz force on a NACA-0017-like hydrofoil is quantified by means of force balance measurements. Depending on the angle of attack, two different effects are observed. (1) At small angles of incidence, a moderate increase in lift due to additional circulation is observed. Simultaneously, a decrease in drag of the hydrofoil is caused by the momentum added. (2) At higher angles of attack, where the unforced hydrof oil would normally stall, a more pronounced lift increase and a corresponding drag reduction are observed due to separation prevention.
  • Magnetohydrodynamics, Vol. 37, No. 1/2, 177-186, 2001

Publ.-Id: 3618 - Permalink


Post-test analysis of two accident management experiments performed at the Bethsy test facility using the code ATHLET
Schäfer, F.; Krepper, E.; Weiß, F.-P.;
In the framework of the external validation of the thermal-hydraulic code ATHLET Mod 1.1 Cycle D, which has been developed by the GRS, post test analyses of two experiments were done, which were performed at the french integral test facility BETHSY. During the experiment 5.2 C the complete loss of steam generator feedwater was simulated. The depressurization of the primary circuit and high pressure injection is assumed as an emergency measure. During the experiment 9.3 the break of a steam generator U-tube is simulated. The failure of the high pressure injection is assumed. As accident management measures, the depressurization of the steam generator secondary sides and finally of the primary circuit by opening of the pressurizer valve was investigated. The results show, that the code ATHLET is able to describe the complex scenario in good accordance with the experiment. For both tests the safety related statement could be reproduced.
Keywords: accident-management, codes, simulations
  • Lecture (Conference)
    ICONE - Ninth International Conference on Nuclear Engineering, Nice, France, April 8-12 2001, Track 7 (407.pdf on CD-ROM)
  • Contribution to proceedings
    ICONE - Ninth International Conference on Nuclear Engineering, Nice, France, April 8-12 2001, Track 7 (407.pdf on CD-ROM)

Publ.-Id: 3617 - Permalink


Evolution of Ion Beam Synthesized Au Nanoclusters in SiO2 under Ion Irradiation
Schmidt, B.; Heinig, K.-H.; Mücklich, A.;
Au nanoclusters have been synthesized in a 500 nm thick SiO2 layer on (001)Si by 330 keV Au+ implantation of 2x1016 cm-2 and subsequent annealing at T = 1000 °C for 1h in dry oxygen. XTEM images show arround the projected ion range Rp = 100 nm a layer of crystalline Au clusters. At Rp the Au clusters have a mean size of 5 nm and a broad size distribution resembling approximately the LSW distribution of diffusion controlled Ostwald ripening. The Au nanoclusters were subsequently irradiated by 4.5 MeV Au+ ions with a fluence of (0.5...1.0)x1016 cm-2 at 190...210 °C . The high energy Au+ ions come to rest at a depth of 1 µm, i.e. in the Si substrate far below the Au nanoclusters and even below the SiO2 layer. The high energy Au+ irradiation causes a strong decrease of the mean size and of the width of the size distribution of Au nanoclusters. The observed Au nanocluster evolution under ion irradiation agrees qualitatively with recent theoretical predictions and kinitic lattice Monte-Carlo simulations.
Keywords: Nanocluster, Ion beam synthesis, Ostwald ripening
  • Poster
    Proceedings MRS 2000 Fall Meeting, Boston, USA, 27.11.-01.12.2000
  • Contribution to proceedings
    Proceedings MRS 2000 Fall Meeting, Boston, USA, 27.11.-01.12.2000

Publ.-Id: 3616 - Permalink


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