Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32180 Publications
Romanian ancient gold objects provenance studies using micro-beam methods: the case of Pietroasa hoard
Constantinescu, B.; Bugoi, R.; Cojocaru, V.; Voiculescu, D.; Grambole, D.; Herrmann, F.; Ceccato, D.;
Five fragments of ancient gold objects belonging to Pietroasa “Cloşca cu Puii de Aur” (“The Golden Brood Hen with Its Chickens”) Romanian hoard were analyzed using the micro-PIXE (Particle Induced X-ray Emission) technique. The purpose of the study was to gain some more knowledge regarding the metal provenance by determining the presence of PGE (Platinum Group Elements) and other high-temperature melting point trace elements (Ta, Nb, Cr) at a micrometric scale. Ta and Nb inclusions (micrometeric areas of composition different from the surroundings) on two samples and Pd inclusions on one sample were found. The measurements led to some conclusions for the possible gold ore sources of Pietroasa treasury: the South-Ural Mountains, Nubia (Sudan) and/or Anatolian deposits and Roman imperial coins.
Keywords: micro-PIXE, archaeometry, gold, PGE, inclusions, provenance.
  • Lecture (Conference)
    9th International Conference on Nuclear Microprobe Technology and Applications (ICNMTA-2004), Sept. 13 -17 2004, Cavtat, Dubrovnik, Croatia
  • Nuclear Instruments and Methods in Physics Research B 231(2005), 541-545

Publ.-Id: 6663 - Permalink


High-efficient wire sawing of GaAs-wafers by utilization of crack nucleation mechanisms
Hammer, R.; Kleinwechter, A.; Jurisch, M.; Schaper, M.; Bergner, F.;
One of the big challenges for wire sawing of semiconductor wafers is warp and waviness, which are mainly caused by wire deflection during cutting process. Therefore, lapping or grinding steps are often used to improve quality but accompanied by additional material losses. The mechanisms of a high quality wire sawing process for compound semiconductors will be presented here. The commonly accepted model for out-of-plane deviation of wires during wire sawing process was expanded by including intrinsic forces in addition to commonly considered technological ones, which are determined by material properties of the semiconductor used. For this the concept of a critical cutting depth for ductile-brittle-transition underlying cutting and grinding processes of brittle materials has been revised. Both Vickers hardness tests and single scratching tests were used to study the ductile-brittle-transition in greater detail. It was found that mainly two types of cracks (called A- and B-cracks) nucleate in GaAs, which are characterized by different threshold loads for their appearance. The effect is related to the existence of two types of dislocations with different PEIERLS-barriers, which dominate in III-V compounds, the 600 a- and b-dislocations. The micro crack nucleation is assisted by pile-ups of these dislocations, which leads to different crack initiation probabilities n for A- and B-cracks at a given load with nA > nB. This effect causes a significant dependence of the critical penetration depth for ductile-brittle-transition from the direction of a moving indenter in scratching tests. This critical penetration depth and the corresponding critical load determines measurable constraint forces, which act on the wire during the sawing process. Under certain well-defined conditions these constraint forces maintain the wire in a stable position perpendicular to the cutting direction, i. e. the out-of-plane-deviation of the wires is near to zero and, consequently, warp and bow will be minimal. This context has been proven by wire sawing experiments at a industrial multi-wire saw and by optical flatness measurements of GaAs-wafers. The result of this investigation was verified in a high efficient wire sawing technology for mass production of 150-mm-GaAs-wafers. Commonly used technological steps like lapping or surface grinding are no longer necessary and, in consequence, the material losses are reduced. Furthermore, the feed rates could be increased up to 400 percent compared to standard wire sawing of GaAs with improved geometrical parameters of the wafers.
Keywords: GaAs wafer, Wire sawing, Waviness, Cracking
  • Poster
    19th Annual Meeting of the American Society of Precision Engineering (ASPE), Orlando, Florida, October 24-29, 2004
  • Contribution to proceedings
    Proceedings of the 19th Annual Meeting of the American Society of Precision Engineering (ASPE), 24.-29.10.2004, Orlando, Florida, United States

Publ.-Id: 6662 - Permalink


Uranyl Sorption Onto Gibbsite Studied by Time-Resolved Laser-Induced Fluorescence Spectroscopy (TRLFS)
Baumann, N.; Brendler, V.; Arnold, T.; Geipel, G.; Bernhard, G.;
Time-resolved laser-induced fluorescence spectroscopy (TRLFS) was combined with batch experiments to study the sorption of uranium(VI) onto gibbsite (γ-Al(OH)3). The experiments were performed under ambient conditions in 0.1 M NaClO4 solution in the pH range from 5.0 to 8.5 using a total uranium concentration of 1 x 10-5 M, and a solid concentration of 0.5 g/40 mL. Two uranyl surface species with fluorescence lifetimes of 330 ± 115 ns and 5600 ± 1640 ns, respectively, were identified. The first species was dominating the more acid pH region whereas the second one became gradually more prominent towards higher pH values. The fluorescence spectra of both adsorbed uranyl(VI) surface species were described with six characteristic fluorescence emission bands situated at 479.5 ± 1.1, 497.4 ± 0.8, 518.7 ± 1.0, 541.6 ± 0.7, 563.9 ± 1.2, and 585.8 ± 2.1 nm. The surface species with the short-lived fluorescence lifetime of 330 ns is attributed to a bidentate mononuclear inner-sphere surface complex in which the uranyl(VI) is bound to two reactive OH- groups at the broken edge linked to one Al. The second surface species with the significant longer fluorescence lifetime of 5600 ns was attributed to small sorbed clusters of polynuclear uranyl(VI) surface species. The longer fluorescence lifetime of the long-lived uranyl surface species at pH 8.5 is explained with the growing average size of the adsorbed polynuclear uranyl surface species.
  • Journal of Colloid and Interface Science 290(2005)2, 318-324

Publ.-Id: 6661 - Permalink


Detection of Adsorbed U(VI) Surface Species on Muscovite by TRLFS
Arnold, T.; Baumann, N.; Brendler, V.; Geipel, G.;
Spectroscopic evidence for two adsorbed uranium(VI) surface species on edge surfaces of a muscovite platelet was obtained by Time-resolved Laser-induced Fluorescence Spectroscopy (TRLFS). In contrast, no fluorescence signal was obtained on the basal plane surfaces clearly indicating that U(VI) sorption on muscovite predominantly takes place at the edge surfaces. TRLFS spectra of adsorbed U(VI) surface species on gibbsite are very similar and show that U(VI) sorption on muscovite occurs on aluminol sites of the edge surfaces.
  • Lecture (Conference)
    SORPO Workshop, 25.-26.03.2004, Karlsruhe, Germany
  • Contribution to proceedings
    SOPRO Workshop, 25.-26.03.2004, Karlsruhe, Germany; FZKA Report 6986, 3-6

Publ.-Id: 6660 - Permalink


Actinide Speciation Based on EXAFS Spectroscopy: From Shell Fitting to MCTFA
Rossberg, A.; Scheinost, A.;
Abstract:
  • Lecture (Conference)
    Actinide-XAS-2004, 14.-16.09.2004, Berkeley, United States
  • Contribution to proceedings
    Actinide-XAS-2004, 14.-16.09.2004, Berkeley, United States
    Proceedings

Publ.-Id: 6659 - Permalink


Annual Report 2003 - Institute of Safety Research
Weiß, F.-P.; Rindelhardt, U.; (Editors)
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-407

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Publ.-Id: 6657 - Permalink


Determination of RBE of 10 kV and 25 kV X-rays
Panteleeva, A.; Enghardt, W.; Lessmann, E.; Pawelke, J.; Wagner, W.; Dörr, W.;
X-rays in the range ~10 – 50 keV are widely applied in the diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). However, the published data about their relative biological effectiveness (RBE) allow up to now no definitive conclusions about the action on different biological systems. Moreover, the biological effects depend on the spectral distribution of the photon source. In order to study this dependence, the RBE of 10 kV and 25 kV X-rays has been determined relative to 200 kV X-rays by X-ray tube irradiation.
The studies were carried out on the mouse fibroblasts NIH/3T3 and the human mammary epithelial cells MCF-12A. For the soft X-rays irradiation, a tungsten-anode X-ray tube operated at 10 kV (no filtration) or at 25 kV (0.3 mm Al filtration) was used. The reference irradiation was performed with a 200 kV X-ray tube with 0.5 mm Cu filter. The dose rate for all irradiations was in the range 0.3 – 1.9 Gy/min. The spectral dose distribution of all radiation qualities was also determined. Cell survival was studied after irradiation with 0.5 – 10 Gy by the clonogenic assay. Chromosomal damage was assessed by the cytokinesis-block micronucleus (MN) test in the dose range 0.2 – 5 Gy. In addition, first results for the RBE determination by chromosomal aberrations induction in MCF-12A, will be presented.
The cell survival data were fitted to the linear-quadratic model, resulting in an RBE value of 1.1 – 1.3 at the 10% survival level, depending on the used radiation quality and cell line. For both cell lines, an increase of RBE was found with decreasing dose after 10 kV X-rays, whereas a decrease of RBE of 25 kV rays was observed. The MN test results for the fraction of binucleated cells (BNC) with MN and the number of MN per BNC were fitted to a quadratic dependence, resulting in an RBE of 1.1 – 1.4.
The data obtained in the present work are in good agreement with observations of other authors as well as with theoretical predictions for this photon energy range. However, the detailed RBE dependence on photon energy can be determined only at a monochromatic X-ray source. Currently, the installation of an intensive, tunable, quasi-monochromatic source for cell irradiation in the energy range 10 – 100 keV is under progress at the ELBE accelerator at Forschungszentrum Rossendorf. The experimental verification of the theoretical calculation of the spectral distribution and intensity of this novel photon source will be presented.

Keywords: soft X-rays, cell survival, micronucleus, chromosomal aberrations, ELBE
  • Poster
    33rd Annual Meeting of the ESRB, 2004, Book of Abstracts, Self Publishing, p. 220,
  • Contribution to proceedings
    33rd Annual Meeting of the ESRB, 2004, Central European Journal of Occupational and Environmental Medicine 10(2004)Suppl., 150

Publ.-Id: 6656 - Permalink


Sorption of Am(III) onto 6-Line-Ferrihydrite and its alteration products: Investigation by EXAFS
Stumpf, S.; Stumpf, T.; Fanghänel, T.; Dardenne, K.; Hennig, C.; Klenze, R.;
For the long-term performance assessment of nuclear waste repositories, knowledge concerning the interactions of actinide ions with mineral surfaces is imperative. The mobility of released radionuclides is strongly dependent on the sorption/desorption processes at mineral surfaces and their incorporation into the mineral frame. Hydrous iron oxides (ferrihydrite) are globally of great importance in the environment. Upon heating pure ferrihydrite converts to crystalline goethite and hematite. In the presence of di- or trivalent metal ions the transformation is affected leading to the promotion of one crystal formation over the other and incorporation of these ions. This Study deals with the question if released Am(III) can be immobilized by sorption onto 6-line-ferrihydrite. Moreover it is studied what happens if ferrihydrite transforms to a more crystalline phase.
Keywords: Am(III), Sorption, Ferrihydrite, EXAFS
  • Poster
    Actinide-XAS-2004 Berkeley/USA 14.-16.09.2004
  • Contribution to proceedings
    Actinide-XAS-2004, 14.-16.09.2004, Berkeley, United States
    Proceedings

Publ.-Id: 6655 - Permalink


Determination of RBE of 10 kV and 25 kV X-rays for cell survival and micronuclei induction
Panteleeva, A.; Enghardt, W.; Lessmann, E.; Pawelke, J.; Wagner, W.; Dörr, W.;
The data about relative biological effectiveness (RBE) of low-energy X-rays as well as the RBE dependence on photon energy allow no definitive conclusions about their action on living cells. X-rays in the range ~10 – 50 keV are widely applied in the diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was determined for cell survival and micronuclei induction in mouse fibroblasts NIH/3T3 and human mammary epithelial cells MCF 12A. The RBE was found to be in the range from 1.0 to 1.4, depending on the used radiation quality, cell line and the biological endpoint. However, the detailed RBE dependence on photon energy can be determined only at a monochromatic X-ray source. A tunable, quasi-monochromatic X-ray source in the energy range 10 – 100 keV based on the channeling of a relativistic electron beam in a diamond crystal is under construction at the ELBE accelerator at Forschungszentrum Rossendorf. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution.
Keywords: cell survival, micronucleus, soft X-rays
  • Lecture (Conference)
    GBS 2004 : 7. Jahrestagung der Gesellschaft für Biologische Strahlenforschung ; 31. 03 - 2. 04 2004, Darmstadt, Germany
  • Contribution to proceedings
    GBS 2004 : proceedings der 7. Jahrestagung der Gesellschaft für Biologische Strahlenforschung ; 31. 03 - 2. 04 2004, Darmstadt, Germany, p. 36

Publ.-Id: 6654 - Permalink


Determination of RBE of low-energy X-rays at ELBE
Panteleeva, A.; Enghardt, W.; Lessmann, E.; Pawelke, J.; Wagner, W.; Dörr, W.;
The precise determination of the relative biological effectiveness (RBE) of low-energy X-rays is important because of their wide application in diagnostic radiology (particularly mammography) and radiotherapy (e. g. brachytherapy). The RBE of both 10 kV and 25 kV X-rays relative to 200 kV X-rays by X-ray tube irradiation was found to be in the range from 1.0 to 1.4, depending on the used
radiation quality, cell line and the biological endpoint. In order to study in detail the RBE dependence on photon energy, the investigations will be continued at a monochromatic X-ray source. The installation of an intensive, tunable, quasi-monochromatic source in the energy range 10 - 100 keV is currently under progress at the ELBE accelerator at Forschungszentrum Rossendorf. X-rays are produced by channeling of a relativistic electron beam in a diamond crystal. The status of the commissioning of the radiation source will be presented, such as the experimental verification of the theoretical calculation of the spatial energy and intensity distribution. Furthermore, a monochromator, designed to minimize the contribution of the background radiation to the dose in the cell target, will be presented.
Keywords: ELBE, RBE, soft X-rays, cells
  • Lecture (Conference)
    DPG-Frühjahrstagung VI, 2004

Publ.-Id: 6653 - Permalink


Electronic properties and viscosity of liquid Pb-Sn alloys
Plevachuk, Y.; Sklyachuk, V.; Yakymovych, A.; Willers, B.; Eckert, S.;
Electrical conductivity, thermopower and vsicosity of liquid Pb-Sn alloys are investigated in a wide temperature range. The revealed discrepancies between heating and cooling curves of temperature dependencies of some electrophysical and structural-sensitive properties as well as a hysteresis observed in the course of heating-cooling cycles suggest a metastable microheterogeneous structure of the Pb-Sn melts.
Keywords: Material data, Thermophysical properties, Eutectic
  • Journal of Alloys and Compounds 394(2005), 63-68

Publ.-Id: 6652 - Permalink


The mass spectrum of a tin liquid metal ion source
Bischoff, L.; Mair, G. L. R.; Mair, A. W. R.; Et, A.;
Tin is an important metal with new potential applications regarding the fabrication of novel devices. In this work the mass spectrum of a tin liquid metal ion source (LMIS) is studied in detail. Sn++ was found to dominate in the beam both over Sn+ and over cluster ions. By studying the behaviour of the relative intensities of Sn+ and Sn++, as a function of emission current, the conclusion is reached that both Sn+ and Sn++ are emitted as a result of direct field-evaporation from the liquid surface. Cluster ions form by ion impact-aided droplet disintegration.

Publ.-Id: 6650 - Permalink


Round Robin: measurement of H implantation distributions in Si by elastic recoil detection
Boudreault, G.; Elliman, R.; Grötzschel, R.; Et, A.;
A 200 mm amorphised Si wafer was implanted with 6-keV H+ ions at a nominal fluence of 5 x 10(16) atoms/cm(2). The uniformity of the implant was better than 2% over the wafer. Samples of the wafer were analysed for absolute H fluence by nuclear reaction analysis and elastic recoil detection (ERD) analysis, including both helium and heavy ion beams, using various types of detector (Si with range foil, time of flight ERD, and a position-sensitive gas ionisation DeltaE-E detector), various ion beams (He, Cl, Cu, I, Au) and independent analytical procedures. The results are compared and the inter-lab reproducibility is evaluated. The surface H, unstable under heavy ion beams, was resolved and accounted for throughout the analysis. Estimates of total combined uncertainties are about 6% for all participants, but the inter-lab reproducibility of the measurements was found to be 2.2%. Correct quantification of the H data from the gas ionisation detector is demonstrated. The uncertain! ty budget is discussed in detail.
  • Nuclear Instruments and Methods in Physics Research B 222(2004)3-4, 547-566

Publ.-Id: 6649 - Permalink


Evidence for a narrow resonance at 1530 MeV/c(2) in the K(0)p-system of the reaction pp ->Sigma(+)K(0)p from the COSY-TOF experiment
Cosy-Tof-Collaboration; Abdel-Baryd, M.; Abdel-Samad, S.; et. al.;
The hadronic reaction pp --> Sigma(+)K(0)p was measured exclusively at a beam momentum of 2.95 GeV/c using the TOF detector at the COSY storage ring. A narrow peak was observed in the invariant mass spectrum of the K(0)p-subsystem at 1530 +/- 5 MeV/c(2) with a significance of 4-6 standard deviations, depending on background assumptions. The upper limit of 18 +/- 4 MeV/c(2) (FWHM) for its width is given by the experimental resolution. The corresponding total cross section is estimated to be about 0.4 +/- 0.1 (stat) 0.1 (syst) mub. Since a resonance in this subsystem must have strangeness S = + I we claim it to be the Theta(+) state for which very recently evidence was found in various experiments. (C) 2004 Elsevier B.V. All rights reserved.

Publ.-Id: 6648 - Permalink


Gamma and X-Ray tomography for transient two-phase flows and other instrumentation developed by Rossendorf
Prasser, H.-M.;
First subject of the paper is a gamma-tomography setup for imaging a periodically changing density field. It is based on a time-resolved acquisition of the detector signals. The system consists in a 5 Ci source of Cs-137 and a detector arc with 64 BGO scintillation crystals coupled with photo-multipliers. It was used to visualize the gas fraction distribution within the impeller of an axial turbo-pump operating at about 1500 rpm, that delivered a gas-liquid mixture. The detectors operated in pulse mode. The pulses were counted by several banks of 64 counters activated in a successive order - each for a period of 100 µs. The counting procedure is restarted in the first bank after each full rotation of the impeller. After a measuring time of typically 3 -6 min, projections of the density distribution inside the object are acquired in a rotation-angle resolved manner. This allowed to afterwards reconstruct the void fraction distribution inside the rotating impeller structure by applying filtered back-projection algorithms. In a second application, the tomography system was applied to a hydraulic clutch (coupling). These measurements showed the distribution of the hydraulic liquid inside both semi-filled working wheel of the clutch at different slip ratios. An advanced detector system with a total number of 320 crystals is under construction. This will allow to increase the resolution from now about 7 mm to about 2-3 mm inside the measuring plane.
In the field of X-ray tomography, the status of the development of an ultra-fast system based on a scanning electron beam is presented. An electron beam is linearly deflected over a tungsten target with a frequency of 1 kHz. X-rays generated by the traveling focus penetrate the object and arrive at a detector line placed behind the object. The detectors are read-out with a sufficiently high speed in order to obtain projections of the density distribution in different projecting directions, which change thanks to the scanning. First results showing tomographic image sequences of a phantom consisting of small spheres kept in arbitrary motion in a cylindrical test box will be presented. Moving spheres of 3 mm diameter with cylindrical holes of 1 mm diameter were resolved at a framing rate of 1 kHz. For the experiments, an electron beam of a 150 kV gun with a current of 5 mA together with a line of 64 CdZnTe detectors working in current mode with a sampling frequency of 100 kHz for each detector (total data rate: 6.4 MHz) were used. It is planned to continue this development in direction towards an application in two-phase flow experiments.
A second application of X-rays concerns a cone-beam tomography of a stirred vessel reactor. In this case, time-averaged gas fraction distributions produced by a gassing stirrer were visualized using a standard X-ray tube and a 2D detector array. The rotation of the fluid inside the reactor was used to obtain the projections necessary for the 3D reconstruction.
The paper will furthermore present a summary of other kinds of two-phase instrumentation developed in the Research Center Rossendorf. Examples are: (1) local void probes based on impedance measurements, that are equipped with a micro-thermocouple substituting the traditional electrode applied to non-adiabatic gas-liquid flows, (2) the use of high-speed video imaging together with image processing techniques for bubble-column studies, (3) the developments of an optical tomograph and other optical sensors.

Keywords: two-phase flow, gamma tomography, X-ray tomography, local void probes, optical tomography, image processing
  • Lecture (Conference)
    Advances in the Modeling Methodologies of Two-Phase Flows S, 24.-26.11.2004, Lyons, France

Publ.-Id: 6647 - Permalink


Wire-mesh sensors: an experimental tool for two-phase CFD model development and code validation
Prasser, H.-M.;
The Institute of Safety Research of the Forschungszentrum Rossendorf, Germany, has developed electrode-mesh sensors, which allow the measurement of the electrical conductivity distribution in a flow duct. This can be used either for the detection of the gaseous phase in a gas-liquid flow or for mixing studies in single phase flow, when the components have different electric conductivities. Two grids of crossing wires are placed into the flow closely behind each other. The wires of the first plane (transmitter plane) are supplied with pulses of a driving voltage in a successive order. The data acquisition is done by measuring the electrical currents arriving at the second grid (receiver wires). After the last transmitter electrode has been activated, a two-dimensional matrix is available that reflects the conductivities at crossing points of the electrodes of the two grids. Sequences of these 2D distributions are recorded with a rate of up to 10 kHz.
Due to the high measuring rate each bubble is mapped in several successive instantaneous frames. This allows to obtain bubble size distributions as well as bubble-size resolved gas fraction profiles beside the visualisation and the calculation of profiles of the time-averaged void fraction. Two sensors placed behind each other can furthermore be used for bubble velocity measurements using cross-correlation techniques. Sensors with three layers of electrode grids can be used for the measurement of the velocity of individual bubbles.
The sensor is widely used to study the evolution of the flow pattern in an upwards air-water flow. The experiments aim at closure equations describing forces acting on bubbles as well as coalescence and fragmentation frequencies for the implementation in CFD-codes. The largest sensor used until now has a circular measuring cross-section of about 200 mm diameter and is equipped with two grids of 64 wires. Therefore, the spatial resolution is 3 mm, the measuring frequency is 2.5 kHz. In the meanwhile, a sensor of this kind has been constructed and successfully used in a hot steam-water flow at 70 bar and 286 °C. Experiments were carried out at a vertical test channel of 195 mm inner diameter, in which the distance between gas/steam injection and sensor can be varied in a wide range. Results will be presented.
Some other prominent examples of the application of wire-mesh sensors will be given, like (1) the use of two wire-mesh sensors at the CIRCUS test facility of the University of Delft in the Netherlands for boiling water reactor stability studies, (2) the visualization of cavitation at fast-acting cut-off valves at the Pilot Plant Pipework test facility of Fraunhofer UMSICHT, Oberhausen, (3) the visualization of the flow structure behind a closing globe valve at TU Munich, and finally (4) mixing studies in single-phase flow at the ROCOM test facility in Rossendorf, which are aimed at the mixing of deborated slugs during boron dilution transients. Results will be discussed on basis of animated data visualizations for all examples.
The accuracy and the effect of the wire grids to the flow were investigated using a sensor built into a transparent channel. The comparison with the frames of a high-speed video camera have shown that the sensor acts as a bubble fragmenting obstacle. Nevertheless it was be proved, that the sensor signal represents the bubble geometry present in the upstream flow.

Keywords: two-phase flow, wire-mesh sensor, gas fraction, gas velocity, bubble size measurement, coolant mixing, boron dilution
  • Lecture (Conference)
    Advances in the Modeling Methodologies of Two-Phase Flows S, 24.-26.11.2004, Lyons, France

Publ.-Id: 6646 - Permalink


Development of a Mineral-Specific Sorption Database for Surface Complexation Modeling (Final Report and Manual)
Brendler, V.; Richter, A.; Nebelung, C.; Vahle, A.;
RES³T - the Rossendorf Expert System for Surface and Sorption Thermodynamics - is a digitized thermodynamic sorption database, implemented as a relational database. It is mineral-specific and can therefore also be used for additive models of more complex solid phases such as rocks or soils. An integrated user interface helps users to access selected mineral and sorption data, to extract internally consistent data sets for sorption modeling, and to export them into formats suitable for other modeling software. Data records comprise of mineral properties, specific surface area values, characteristics of surface binding sites and their protolysis, sorption ligand information, and surface complexation reactions. An extensive bibliography is also included, providing links not only to the above listed data items, but also to background information concerning surface complexation model theories, surface species evidence, and sorption experiment techniques.
The RES³T database is intended for an international use. This requires high standards in availability, consistency and actuality. Therefore the authors of the database decided to couple the database onto an authorization tool.

Keywords: sorption, database, mineral, RES3T, surface complexation, MS Access
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-409 2004

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Publ.-Id: 6644 - Permalink


Structure modifications in silicon irradiated by ultra-short pulses of XUV free electron laser
Peika, J. B.; Andrejczuk, A.; Reniewicz, H.; Schell, N.; Krzywinski, J.; Sobierajski, R.; Wawro, A.; Zytkiewicz, Z. R.; Klinger, D.; Juha, L.;
Structural modifications of solid Si (0 0 1) targets exposed to the XUV TESLA free electron laser radiation were studied. The samples were irradiated with the photon energy centered at 14 eV, in short pulses of only 80 fs and of peak power up to 1 GW. The FEL beam was focused on sample surfaces to microspots of size 10–100 small mu, Greekm. The energy density in the spots varied from below the ablation threshold up to far above this threshold. The structural modifications induced with the irradiation were studied by AFM, Nomarski contrast microscopy and by X-ray diffraction methods. A variety of morphological structures created in the damaged areas was found. The maps of the X-ray diffracted intensity distribution recorded around chosen spots on the Si surface made it possible to probe the damage distribution range around the spots. The observed features are related to the FEL irradiation fluencies applied.
Keywords: Semiconductors; Laser processing; XUV free electron laser; Material modification; Ablation; Silicon
  • Poster
    Proceedings of the E-MRS 2003 Fall Meeting, Warsaw, Poland, 15-19 September 2003
  • Contribution to proceedings
    Proceedings of the E-MRS 2003 Fall Meeting, Warsaw, Poland, 15-19 September 2003

Publ.-Id: 6643 - Permalink


The mechanism in efficient silicon light-emitting diodes
Sun, J. M.; Dekorsy, T.; Skorupa, W.; Schmidt, B.; Mücklich, A.; Helm, M.;
Light emission from silicon is one of the hot topics of temporary semiconductor physics and technology. Recent papers report encouraging electroluminescence efficiencies observed from bulk silicon diodes prepared by boron implantation. This report deals with a detailed analysis of the mechanism in light emission from silicon pn diodes prepared by boron implantation. From low-temperature electroluminescence spectra in combination with structural analysis, we obtain evidence that the light emission is strongly related to the locally enhanced boron doping spikes produced by ion implantation and subsequent annealing, which act as potential minima for holes and barriers for electrons. The doping spikes are able to capture spatially indirect bound excitons with a low recombination rate, thus effectively suppressing the fast non-radiative recombination at defects. The captured indirect bound excitons are thermally released to free electron-hole pairs at elevated temperature; therefore contribute to an increase of the band edge electroluminescence. A model containing rate equations of bound excitons and free excitons gives a very well description on the anomalous temperature dependence, which was observed in the efficient silicon light emitting diodes.
Keywords: Electroluminescence, silicon pn diode, bound excitons
  • Contribution to proceedings
    Vth International Conference, Ion Implantation and Other Applications of Ions and Electrons, 14.-17.06.2004, Kazimierz Dolny, Poland

Publ.-Id: 6640 - Permalink


Efficient silicon light emitting diodes by boron implantation: The mechanism
Sun, J. M.; Dekorsy, T.; Skorupa, W.; Mücklich, A.; Schmidt, B.; Helm, M.;
Experiments and theoretical modeling are presented on the origin of efficient electroluminescence from boron implanted Si-LEDs. At low lattice temperatures two bound exciton traps created by high dose boron implantation were observed in the most efficient LEDs with external power efficiency above 0.12%. The temperature dependence of the correlation between the EL intensity from free and bound excitons is analyzed by a rate equation model. This analysis reveals that the bound excitons have a unique characteristic of a low recombination rate. The enhancement of EL from free electron-hole pairs with increasing temperature is due to the thermal activation of carriers from bound exciton traps.
Keywords: silicon pn junction, electroluminescence, bound excitons, rate equations, and temperature dependence.
  • Optical Materials 27(2005)5, 1041-1045

Publ.-Id: 6638 - Permalink


On the mechanism of electroluminescence excitation in Er-doped SiO2 containing silicon nanoclusters
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Nazarov, A. N.;
The effect of the density of silicon nanoclusters on both electroluminescence (EL) and photoluminescence (PL) of Er3+ ions in indium-tin oxide/SiO2:Er/n-type silicon metal-oxide-semiconductor structures was studied by co-implantation of excess silicon into a 200 nm SiO2 layer with a concentration in the range of 1-15 %. Contrary to the PL, the EL from both the green and infrared peaks of Er3+ shows a dramatic quenching when the average distance between the silicon clusters decreases below 3 nm. In addition, electric-field-induced quenching of the photoluminescence from silicon clusters and Er3+is observed. These results indicate that the EL excitation process of Er3+ ions is governed by the direct impact excitation by hot electrons. An increase of the silicon nanocluster density cause direct tunneling of electrons between silicon clusters, thus reducing the population of energetic hot electrons for impact excitation of Er3+ ions.
Key words: Erbium, electroluminescence, impact excitation, silicon dioxide, nanoclusters.

Keywords: electroluminescence, Erbium, silicon, nanoclusters, metal-oxide-semiconductor
  • Optical Materials 27(2005)5, 1050-1054

Publ.-Id: 6636 - Permalink


Dileptons and Open Charm: Probes of Chiral Restoration
Gallmeister, K.; Kaempfer, B.; Zschocke, S.;
We summarize the status of electromagnetic probes of strongly interacting matter produced in relativistic heavy-ion collisions at CERN-SPS with respect to indications of chiral symmetry restoration. Explorative results for studying the open charm dynamics at BNL-RHIC are presented.
Keywords: medium modifications, chiral symmetry, heavy-ion collisions
  • Contribution to external collection
    High Energy Physics, ICHEP 2004, Proceedings of the 32nd Internationale Conference, 16.-22. 08.2004, Beijing, China, 381-384

Publ.-Id: 6635 - Permalink


In-situ GIXRD characterization of the crystallization of Ni-Ti sputtered thin films
Martins, R. M. S.; Silva, R. J. C.; Braz Fernandes, F. M.; Pereira, L.; Gordo Paulo, R.; Maneira Manuel, J. P.; Schell, N.;
The Ni-Ti system is the most popular of the SMA’s because of its large recovery force, a transformation temperature near room temperature and a good oxidation resistance. Although the transformation frequency is low (mainly limited by thermal inertia), a thin film of Ni-Ti coupled with silicon for heat dissipation can produce cycling frequencies much larger than the typical macrosize structures. The thin films can be electrically driven using joule heating, and they demonstrate fast cooling rates because of their large surface-to-volume ratio. The control of film composition and properties has proven difficult in sputter-deposited films, and a deeper study of deposition techniques is needed. Furthermore, the as-deposited films show an amorphous structure and thus have to be heat treated to induce crystallization in order to have the shape memory effect. In the present study, thin films have been prepared by dc and rf magnetron sputtering. The crystallization of these films has been studied by in-situ grazing incidence X-Ray diffraction (GIXRD), allowing us to establish a correlation between the deposition conditions and the tendency for crystallization.
Keywords: shape memory alloy, Nitinol, thin films, X-ray diffraction
  • Poster
    Materials Science Forum 455-456 (2004) 342-345
  • Contribution to external collection
    Materials Science Forum 455-456 (2004), 342-345

Publ.-Id: 6634 - Permalink


Scaling of self-similar long fatigue crack growth in aluminium alloys
Bergner, F.;
Propagation of long fatigue cracks in thin-sheet wrought aluminium alloys at constant stress ratio and constant stress amplitude (DK range from about 10 MPa m1/2 to well below instability) is considered. The crack growth rates of aluminium alloys with strength-controlling precipitates that cannot be sheared by dislocations nearly coincide at a particular value of DK and increasingly diverge for increasing values of DK. The characteristic quantities specified by the point to which the fatigue crack growth curves converge are related to the shear modulus and the slip band spacing.
Keywords: Fatigue crack growth, Aluminium alloys, Dislocations
  • Materials Science and Engineering A 400-401(2005), 422-425
  • Poster
    International Conference on the Fundamentals of Plastic Deformation 'Dislocations 2004', La Colle-sur-Loup, France, September 13-17, 2004

Publ.-Id: 6632 - Permalink


Interactions of the native and engineered S-layer of Bacillus sphaericus JG-A12 with U, Pd, and other metals
Pollmann, K.; Raff, J.; Merroun, M.; Schnorpfeil, M.; Fahmy, K.; Selenska-Pobell, S.;
The cells of the uranium mining waste pile isolate B. sphaericus JG-A12 are enveloped by a highly ordered paracrystalline protein surface layer (S-layer) with a square lattice structure (1). The protein consists of 1238 amino acids, contains three N terminal S-layer homologous (SLH) domains and is, in contrast to the other Bacillus S-layers studied up to date, phosphorylated. A comparative analysis of the amino acid sequence of the JG-A12 S-layer protein with those deposited in the GeneBank demonstrated that the SLH domains of JG-A12 possess an unique structure. However, particular parts of the central and of the C-terminal domains of the protein share high identity with some of the known B. sphaericus S-layers (2). The latter is an indication that the JG-A12 S-layer protein gene was subjected to late evolutionary events via lateral genetic transfer and rearrangements.
The interactions of the purified and re-crystallized S-layer with U (VI) and Pd (II) were studied by using x-ray and infrared spectroscopic analyses. The results of these analyses show that U(VI) is coordinated to both phosphate and carboxyl groups of the S-Layer whereas Pd(II) was bound mainly by carboxyl groups. This is in accordance to our finding that the protein is phosphorylated and also that aspartate and glutamate rich stretches are distributed in its C-terminal domain which is supposed to build the S-layer lattice pores. The latter are involved in the complexation and also in the deposition of the metals. The infrared spectroscopic analysis indicated in addition that the deposition of the Pd complexes stabilizes the structure of the protein.
In our former work the S-layer of B. sphaericus JG-A12 was successfully used for the construction of sol-gel Si02 bio-ceramics for remediation of uranium contaminated waters (3). In addition, the S-layer of another B. sphaericus strain, which is closely related to the JG-A12, was used as a template for deposition of metallic Pd nanoclusters (4). Such nanoclusters are of great importance for the development of novel catalysts and biosensors for the industry.
In this work we apply genetic engineering of the S-layer of B. sphaericus JG-A12 in order to extend its capability to interact with other metals of industrial interest.
  • Lecture (Conference)
    Biotechnology 2004, 17.-22.10.2004, Santiago de Chile, Chile
  • Contribution to proceedings
    Biotechnology 2004, 17.-22.10.2004, Santiago de Chile, Chile
    Proceedings

Publ.-Id: 6631 - Permalink


Analysis and engineering of the S-layer protein of Bacillus sphaericus JG-A12 and potential technological applications
Pollmann, K.; Raff, J.; Merroun, M.; Fahmy, K.; Mikeehenko, I.; Creamer, N.; Macaskie, L.; Selenska-Pobell, S.;
Uranium mining waste isolate B. sphaericus JG-A12 is capable of selective and reversible accumulation of U, Cu, Pb, Al, and Cd from the U waste waters [1]. The cells of this strain are enveloped by a surface protein layer (S-layer), which differs significantly in its primary structure from the other B. sphaericus S-layers studied up to date [2]. The highly ordered crystalline S-layers are one of the most common cell envelope structures of bacteria and archaea [3]. Most of them are composed of identical protein monomers which possess the ability to self-assemble into two-dimensional paracrystalline lattices. The highly regular structure of the S-layers with many pores of identical size offers good binding sites for different kinds of molecules and also nucleation sites for formation of metal nanoclusters or minerals.
We demonstrate that the purified and recrystallized S-layer of B. sphaericus JG-A12 is capable to bind effectively Pd(II) from salt solutions. EXAFS and IR spectroscopic analyses demonstrate that the Pd atoms are bound to the carboxyl groups of the S-layer. In accordance to this we found aspartate and glutamate rich stretches in the C-terminal domain of the S-layer which are possibly responsible for the deposition of Pd in the pores of the protein lattices. The deposition of Pd complexes stabilizes the protein structure. In presence of reducing agents deposited Pd is reduced to metallic nanoclusters. The latter is in agreement with the studies on another S-layer [4].
We demonstrate also that Pd nanoclusters are formed on the intact cells of B. sphaericus JG-A12 via a two step process consisting of biosorption (I) and of consequent metal reduction (II) in the presence of molecular H2 as an electron donor. The metallic nature of the clusters was confirmed by EXAFS and their size was estimated to be about 9-10 Ǻ. TEM analysis showed that the clusters are localized at specific sites of the bacterial cell wall, indicating the primary role of the S-layer in their formation. The Pd nanoclusters deposited at the cells of B. sphaericus JG-A12 show catalytic activity comparable to commercial ones.
Genetic engineering of the S-layer is applied for optimizing its capability to form Pd nanoclusters with increased catalytic activity and also in order to extend its binding capacity to other metals of industrial interest.
  • Poster
    Biotechnology 2004 - Konferenz, Santiago de Chile, 17.10.-22.10.2004
  • Poster
    2nd Max Bergmann Symposium, 17.-18.02.2005, Dresden, Deutschland
  • Contribution to proceedings
    Biotechnology 2004, 17.-22.10.2004, Santiago de Chile, Chile

Publ.-Id: 6630 - Permalink


Bacterial Diversity in the Uranium Mill-Tailings Gittersee as Estimated via a 16S rDNA Approach
Satchanska, G.; Golovinski, E.; Selenska-Pobell, S.;
Bacterial diversity in a soil sample collected from a uranium mill-tailings called Gittersee and situated near the city of Dresden, Germany, was analysed by using a culture-independent 16S rDNA approach exploiting PCR amplification primers 7F and 1513R. The results were compared with those obtained earlier analysing the same sample by using another primer pair, namely 43F-1404R (Selenska-Pobell et al., 2002). The two 16S rDNA approaches demonstrated that Proteobacteria were the most predominant group in the sample, followed by Citophaga/Flavobacterium/ Bacteroides and by Gram positive bacteria with low and also with high G+C content. Moreover, a large number of the 16S rDNA sequences from the two libraries were identical or almost identical. However, the ratio between the bacterial groups represented in them differed significantly.
The 7F-1513R primer set retrieved in addition to the above mentioned 16S rDNA sequences also such of green non-sulfur bacteria and sequences of representatives of the AD1 and the OP11 divisions. The latter indicates that the 7F-1513R primer set seems to be more reliable in analyses of bacterial diversity.
  • Comptes Rendues de l'Academie bulgare des Sciences 58(2005)9, 1105-1112

Publ.-Id: 6629 - Permalink


Bog ground aquifer system as a natural analogue for future redox conditions in flooded underground mines
Abraham, A.; Baraniak, L.; Bernhard, G.;
To characterize the future redox milieu caused by natural degradation of wood in flooded mines, the aquifer of a highland bog ground was studied as a natural analogue site. Going from the surface to a depth of one meter in the bog water, the redox potential measured with a platinum electrode changes from 593 mV to -95 mV. From the depth-water analyses of bog gas extracted from the ground, an Eh value of -119 +/- 5 mV could be calculated. Methane and hydrogen sulfide were found in the gas, characterizing the strongly reducing condition in the bog ground. From that, the conclusion for the future mine situation can be drawn that uranium(VI) and arsenic(V) will be reduced and precipitated as U(OH)4 and As2S3. In that way, decontamination of the mine water takes place as a consequence of a natural attenuation process.
  • Journal of Radioanalytical and Nuclear Chemistry, 261(2004)3, 597-604

Publ.-Id: 6627 - Permalink


On the development of the <111> fiber texture in nanocrystalline gold during growth and annealing
Andreasen, K. P.; Schell, N.; Jensen, T.; Petersen, J. H.; Jensen, M. S.; Chevallier, J.; Bøttiger, J.;
The evolution during growth and subsequent annealing of the <111> fiber texture in magnetron-sputtered nanocrystalline Au films has been studied experimentally using X-ray diffraction with synchrotron radiation. To quantitatively investigate this fiber texture, grain orientation distributions were recorded in situ during growth and during subsequent annealing using Bragg-Brentano geometry. The (111) diffraction intensity was measured as a function of the sample tilt chi, the tilt axis lying at the intersection of the film surface and the scattering plane. As a quantitative measure of the texture, we used the width of the orientation distibutions. The grain-orientation distributions narrowed during annealing. The activation energy for the process behind this texture change was found to be 0.64 ± 0.05 eV, close to the activation energy for grain boundary self-diffusion in nanocrystalline Au. This and the narrowing of the grain orientation distributions led us to suggest that the observed changes in texture originated from grain rotations and not from grain growth. Grain growth did not take place at the lower temperatures, where changes in orientation distributions were observed.
Keywords: texture development, Au-nanocrystals, magnetron sputtering
  • Poster
    Materials Research Society Symposium 2004
  • Contribution to proceedings
    Materials Research Society Symposium Proceedings 788(2003), L11-50

Publ.-Id: 6626 - Permalink


The structure and the corresponding mechanical properties of magnetron sputtered TiN–Cu nanocomposites
Andreasen, K. P.; Jensen, T.; Petersen, J. H.; Chevallier, J.; Bottiger, J.; Schell, N.;
The present paper describes experimental studies of the structure and the corresponding mechanical properties of TiN–Cu nanocomposites synthesised by reactive magnetron sputtering. By X-ray diffraction, the crystalline phases appearing, the texture, the grain size and the microstrain were studied as a function of the deposition temperature and the substrate bias voltage. In addition, the nanostructure was studied by cross-section transmission electron microscopy and the surface orphology by scanning electron microscopy. At low deposition temperatures, a two-phase structure consisting of a fcc TiN phase and a highly disordered crystalline or amorphous Cu-rich phase was formed. Increasing the deposition temperature, a fcc Cu phase was observed in addition to the crystalline TiN phase. The texture varied with the deposition temperature, and the grain size increased and the microstrain decreased with rising deposition temperature. The mechanical properties were measured by nanoindentation. For the nanocomposites Ti41N46Cu13, Ti43N46Cu11 and Ti43N49Cu8, hardness values of 25, 35 and 40 GPa, respectively, were measured.
Keywords: TiN–Cu; Nanocomposites; Magnetron sputtering; X-ray diffraction; Transmission electron microscopy; Nanoindentation
  • Surface and Coating Technology 182(2004), 268-275

Publ.-Id: 6625 - Permalink


Influence parameters of martensitic transformation during low cycle fatigue for steel AISI 321
Grosse, M.; Kalkhof, D.; Keller, L.; Schell, N.;
The volume fraction of martensite continuously increases with the fatigue cycle number. Consequently, the martensite amount can be used for indication of the low cycle fatigue state. Following an exponential decay function, the martensite volume fraction decreases with increasing temperature. No influence of the load frequency was found. The initial material state plays an important role for the martensite formation rate. The amount of martensite formed is much higher after cold-rolling than after solution annealing as final manufacturing process. The martensite shows a fibre texture in the annealed material. The (I 10) planes are preferentially oriented parallel and perpendicular to the loading direction. In the cold-rolled material no significant preferred orientation of this phase was found. The martensite is concentrated in the centre of the specimens. The shape of the distribution seems to be independent on the martensite amount.
Keywords: Martensitic transformation; Austenite; Martensite; Low cycle fatigue

Publ.-Id: 6624 - Permalink


Uncertainty and sensitivity analysis of a VVER-1000 start-up experiment using the coupled code DYN3D/ATHLET and the statistical code package SUSA
Kliem, S.; Mittag, S.; Langenbuch, S.;
The transition from the application of conservative models to the use of best-estimate models raises the question about the uncertainty of the obtained results. This question becomes especially important, if the best-estimate models should be used for safety analyses in the field of nuclear engineering. Different methodologies were developed to assess the uncertainty of the calculation results of computer simulation codes. One of them is the methodology developed by Gesellschaft fuer Anlagen- und Reaktorsicherheit (GRS) which uses the statistical code package SUSA. In the past, this methodology was applied to the calculation results of the advanced thermal hydraulic system code ATHLET. In the frame of the recently finished EU FP5 funded research project VALCO, that methodology was extended and successfully applied to different coupled code systems, including the uncertainty analysis for neutronics. These code systems consist of a thermal hydraulic system code and a 3D neutron kinetic core model. One of the code systems applied was ATHLET coupled with the Rossendorf kinetics code DYN3D. Two real transients at NPPs with VVER-type reactors documented within the VALCO project were selected for analyses. One of them was a test with the switching-off of one of two main feed water pumps at the VVER-1000 Balakovo-4 NPP. The current paper is dedicated to the different steps of the use and implementation of the GRS methodology to coupled code systems and to the assessment of the results obtained in the calculations of the VVER-1000 transient by the DYN3D/ATHLET code.

Based on the relevant physical processes in the transient, a list of possible sources of uncertainties was compiled. Besides control parameters like control rod movement and thermal hydraulic parameters like secondary side pressure, mass flow rates, and pressurizer heater performance, different neutron kinetic parameters were included into the list of possible sources of uncertainties. These are the burn-up state of the core, the control rod efficiency for different control rod groups and the coefficients for Doppler and moderator density feed back. By use of the SUSA package, sets of input data with statistical variation of the relevant parameter values were generated for a large number of runs of the coupled code. New tools were developed for the automated implementation of the varied input parameters into the different input decks of the DYN3D/ATHLET code. The same concerns the extraction of result parameters from the output data of the calculations and statistical analysis of these results. Time-dependent rank correlation coefficients were calculated showing the influence of the varied parameters on the output parameter under investigation. The most interesting output parameters are the physical parameters for which experimental data are available. First of all, these are the core power, upper plenum pressure, loop temperatures and steam generator levels. The calculation results allowed also the determination of time-dependent tolerance intervals for given coverage and confidence. The comparison of the experimental data, the (best-estimate) reference solution and the tolerance intervals showed how the agreement between experiment and calculation could be quantified. In most of the cases the tolerance intervals include the experimental curves. A compiled list of the most important input parameters based on the rank correlation coefficients shows, which input parameters and models are responsible for the deviations. This list gives indications for further model improvements and code developments.
  • Lecture (Conference)
    14. AER Symposium, 13.-17.09.2004, Helsinki, Finnland
  • Contribution to proceedings
    14. AER Symposium, 13.-17.09.2004, Helsinki, Finnland, Proceedings, 503-516

Publ.-Id: 6623 - Permalink


Experimental study of a single bubble motion in a liquid metal column exposed to a DC magnetic field
Zhang, C.; Eckert, S.; Gerbeth, G.;
The motion of single Argon bubbles rising in the eutectic alloy GaInSn under the influence of a DC longitudinal magnetic field was examined. The magnetic field strength was chosen up to 0.3 T corresponding to magnetic interaction parameters N of 1.5. The experiments were carried out in the following parameter range: 2500 < Re < 5500, 2 < Eo < 7, Mo = 2.4?10-13. The liquid metal was in a cylindrical container at rest. Bubble and liquid velocities were measured using Ultrasonic Doppler Velocimetry (UDV). The measured bubble terminal velocity showed oscillations indicating a zig-zag movement of ellipsoidal bubbles. Whereas for small bubbles (de ? 4.6 mm) an increase of the drag coefficient with increasing magnetic interaction parameter was observed, the application of the magnetic field reduces the drag coefficient of larger bubbles (de ? 5.4 mm). The measurements revealed a distinct electromagnetic damping of the bubble induced liquid velocity leading to more rectilinear bubble trajectories. Moreover, significant modifications of the bubble wake structure were observed. Raising of the magnetic field strength causes an enlargement of the eddies in the wake. The Strouhal number St decreases with increasing magnetic interaction parameter.
Keywords: Single bubble, Liquid metal, Magnetic field, Terminal velocity, Drag coefficient, Bubble wake, Ultrasound Doppler Velocimetry
  • International Journal of Multiphase Flow 31(2005), 824-842

Publ.-Id: 6622 - Permalink


Below-band gap electroluminescence related to doping spikes in boron-implanted silicon pn diodes
Sun, J. M.; Dekorsy, T.; Skorupa, W.; Schmidt, B.; Mücklich, A.; Helm, M.; (Editors)
The origin of two luminescence bands with maxima around 1.05 eV and 0.95 eV is studied in silicon pn diodes prepared by boron implantation. The two peaks are related to the formation of p-type doping spikes on a nanometer scale. These doping spikes are generated by long-time thermal activation of preformed boron clusters. The peak with a larger binding energy stems from spatially indirect excitons bound to doping spikes in a strained environment, while the peak with a lower binding energy is related to doping spikes without strain. The doping spikes are able to capture spatially indirect bound excitons with a low recombination rate, thus effectively suppressing the fast non-radiative recombination at defects. This effect leads to an efficient room temperature electroluminescence in silicon light-emitting diodes prepared by boron implantation.
Keywords: silicon, light-emitting diode, elecroluminesencce, bound excitons, ion implantation, boron.

Publ.-Id: 6621 - Permalink


Spectroscopic Ellipsometry Characterization of ITO Films Prepared by Reactive MF Dual Magnetron Sputtering: Effect of Substrate Temperature
Vinnichenko, M.; Rogozin, A.; Shevchenko, N.; Kreissig, U.; Kolitsch, A.; Möller, W.;
The reactive middle frequency (MF) dual magnetron sputtering is a favorable process for industrial applications. Production of low resistivity (~10^-4 Ohm*cm) ITO films by this method requires their heat treatment. The ITO film formation and evolution at elevated substrate temperatures is not properly addressed because the phase diagram of this material is not known. Thus, in situ spectroscopic ellipsometry (SE) was applied to characterize the growth of ITO films at heated substrates (Ts=RT-510 °C). The results of in situ and ex situ SE were compared with the film resistivity, stoichiometry (elastic recoil detection analysis) and structure (X-ray diffraction).
The in situ SE indicates formation of the rough film with graded optical properties. This grading is stronger for the films deposited without substrate heating. The free electron parameters were determined from parameterization of the film optical constants in Drude-Lorentz approach. Their behavior with increasing Ts agrees with concomitant resistivity dependence, measured by the four point probe method. Thus, in situ SE monitoring of the free electron parameters provides a tool for real-time contactless characterization of the growing film resistivity. Quantitative characterization of the resistivity by SE requires further improvement of the optical model. The existence of the resistivity grading through the film thickness was indicated by this method for the growth without heating. At heated substrates this grading vanishes after deposition of ~50 nm layer and homogeneous film start growing. The films grown at the Ts=400 C have resistivity of 1.2*10^-4 Ohm*cm that is comparable with the best results achieved with ceramic targets. The SE data analysis demonstrated that improvement of the film resistivity with increasing Ts is mainly due to enhancement of the free electron mobility. It is accompanied by improvement of the film stoichiometry, changes of texture and crystallinity.

Keywords: tin doped indium oxide, in situ spectroscopic ellipsometry, thin film growth
  • Lecture (Conference)
    International Conference on Metallurgical Coatings and Thin Films, April 19-24, 2004, San Diego, CA, USA

Publ.-Id: 6620 - Permalink


Plasma influence on the properties and structure of indium tin oxide films produced by reactive middle frequency pulsed magnetron sputtering
Rogozin, A.; Vinnichenko, M.; Shevchenko, N.; Kolitsch, A.; Möller, W.; (Editors)
Reactive pulsed magnetron sputtering was used to produce conductive and transparent tin-doped indium oxide (ITO) films with low thickness inhomogeneity. Due to the parallel operation of two magnetrons, the deposition system allows in situ investigations of the plasma influence on the film properties. The distribution of the film resistivity, refractive index, structure and stoichiometry along the substrate are presented and related to the spatial distribution of the plasma flow escaping the magnetrons, and the substrate temperature. A higher plasma flow likely causes a localized relaxation of the distorted In–O bonds in amorphous phase which prevails in ITO films prepared at unheated substrates. This leads to a decrease of the film resistivity due to free electrons density and mobility enhancement. The free electron density increase is caused likely by generation of oxygen vacancies. Deposition on a heated substrate (Ts /Tm=0.3) leads to a change of the film growth mode due to enhanced surface diffusion of the adatoms which results in a textured low resistivity film. This also causes significant improvements of the homogeneity of the film properties that is important for ITO applications.
Keywords: Indium tin oxide; Plasma processing and deposition; Electrical properties and measurements; Optical properties
  • Thin Solid Films 496(2)(2006)197-204, doi:10.1016/j.tsf.2005.08.273

Publ.-Id: 6619 - Permalink


Efficient ultraviolet electroluminescence from a Gd-implanted silicon metal-oxide-semiconductor device
Sun, J. M.; Skorupa, W.; Dekorsy, T.; Helm, M.; Rebohle, L.; Gebel, T.;
Strong ultraviolet electroluminescence with an external quantum efficiency above 1% is observed from an indium-tin oxide/SiO2:Gd/Si metal-oxide-semiconductor structure. The SiO2:Gd active layer is prepared by thermal oxidation followed by Gd+ implantation and annealing. The electroluminescence spectra show a sharp peak at 316 nm from the 6P7/2 to 8S7/2 transition of Gd3+ions. Micrometer sized electroluminescent devices are demonstrated.
Keywords: Ultravoilet, Electroluminescence, Gd, silicon, metal-oxide-semiconductor

Publ.-Id: 6618 - Permalink


Design and operation of strain-compensated InGaAs/AlAs/InP quantum cascade lasers emitting at 3.7-4.2 micrometer
Semtsiv, M. P.; Ziegler, M.; Dressler, S.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.;
not available
Keywords: quantum cascade laser, infrared, intersubband transition
  • Lecture (Conference)
    6th Int. Conference on Mid-Infrared Optoelectronics Materials and Devices (MIOMD-VI), 27 June-2 July 2004, St. Petersburg, Russia

Publ.-Id: 6617 - Permalink


In situ speciation of U(IV) and U(VI) aqueous complexes with a newly developed spectro-electrochemical cell
Hennig, C.; Tutschku, J.; Rossberg, A.; Scheinost, A.; Bernhard, G.;
Natural aquatic and terrestrial environments exert large variations in redox state due to oxygen diffusion on one hand and microbial processes on the other hand. Actinides with their large number of oxidation states are especially susceptible to these redox changes, forming a large number of aqueous complexes which may greatly differ by solubility and mobility. These complexes are often difficult to investigate due to their thermodynamic metastability. Therefore, we developed a new spectro-electrochemical cell, which allows to study the structure and speciation of aqueous actinide complexes in-situ by X-ray absorption spectroscopy (XAS), while applying and maintaining a constant potential.

While in-situ investigations by combining electrochemical cells with XAS are not new, the prevention of any gas-releasing electrode reaction due to the special safety regulations for actinides required a new electrochemical approach. We used an Ag metal electrode as anode, where Ag+ is released and precipitates as AgCl. The cell itself consists of a double confinement following the safety regulations for the use of radioactive materials at the ESRF. The cell body and the windows are machined from one piece of chemically resistant material, which is closed by air-tight cover plates.

First U L3-edge XAS spectra have been obtained from aqueous solutions of U(VI) and U(IV) in the presence of different ligand systems. The reduction of U(VI) to U(IV) was performed by applying a constant potential for several hours. Independent UV/vis measurements of the solutions were performed in order to verify that uranium was completely reduced. A quantitative analysis of the uranium redox species during the reduction procedure was performed by iterative transformation factor analysis of the XANES spectra. Finally, EXAFS measurements were used to solve the structure of the uranium redox species.
  • Lecture (Conference)
    Actinide-XAS-2004, 14.-16.09.2004, Berkeley, United States
  • Contribution to proceedings
    Actinide-XAS-2004, 14.-16.09.2004, Berkeley, United States
    Proceedings

Publ.-Id: 6616 - Permalink


Strain-compensated AlAs/(In,Ga)As heterostructures for short wavelength intersubband absorption and laser emission
Semtsiv, M. P.; Ziegler, M.; Dressler, S.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.;
We have investigated intersubband transitions in strain-compensated AlAs/(In,Ga)As heterostructures, demonstrating both absorption and quantum-cascade laser emission at short wavelengths. Short-wavelength optical transitions in such structures are associated with a number of challenges in both the growth and design, including managing the internal strain and designing around indirect valleys. We achieve absorption peaks at wavelengths as short as 1.7 micrometer in fully strain-compensated AlAs/(In,Ga)As structures. Quantum cascade lasers based on similar heterojunctions exhibit laser emission as short as 3.7 micrometer. These lasers exhibit low-temperature threshold current densities of 860 A/cm2 in pulsed mode and output power as high as 6W per facet (12W total). At room temperature, the threshold current density is 4.5 kA/cm2 and the maximum power 240 mW per facet.
Keywords: infrared, intersubband absorption, quantum cascade laser, semiconductor quantum wells
  • (Proceedings of MBE 2004) Journal of Crystal Growth 278(2005)1-4,526-531
  • Lecture (Conference)
    Int. Conf. on Molecular Beam Epitaxy (MBE 2004), Aug. 22-27, 2004, Edinburgh, UK

Publ.-Id: 6615 - Permalink


EPOS - intensive Positronenquelle für die Materialforschung
Krause-Rehberg, R.; Brauer, G.; Leipner, H. S.;
Materialforschung mit Positronen ist eine anerkannte Spezialrichtung der Halleschen Physik. In Kooperation zwischen dem Großforschungszentrum Rossendorf und dem Interdisziplinären Zentrum für Materialwissenschaften der Martin-Luther-Universität Halle-Wittenberg befindet sich eine hochintensive Positronenquelle im Aufbau. Nach Fertigstellung wird das Labor als ein europäisches Kompetenzzentrum für Materialforschung mit Positronen auch externen Nutzern zur Verfügung stehen.
Keywords: Positron, Materialforschung,Defekte, ELBE-Quelle, MLU Halle-Wittenberg, FZ Rossendorf
  • scientia halensis 2(2004), 13-14

Publ.-Id: 6614 - Permalink


Influence of the lift force on the stability of a bubble column
Lucas, D.; Prasser, H.-M.; Manera, A.;
This work investigates the role of the lift force in the transition from homogeneous to heterogeneous bubble column. On rising bubbles the lift force acts in a lateral direction, when gradients of the liquid velocity are present. Non-uniform liquid velocity fields may be induced if the gas fraction is not equally distributed, e.g. caused by local disturbances. This feedback mechanism is studied in the paper. It was found, that a positive lift coefficient (small bubbles) stabilizes the flow, while a negative coefficient (large bubbles) leads to unstable gas fraction distributions, and thus it favours the appearance of a heterogeneous bubble column regime. The turbulent dispersion force has always a stabilizing action, i.e. it partially compensates the destabilisation induced by a negative lift coefficient. A stability analysis for a mono-dispersed system nevertheless showed, that influence of the lift force is much larger, compared to the influence of the turbulent dispersion force, if only bubble induced turbulence is considered. Thus the stability condition is practically the positive sign of the lift force coefficient. The extension of the analysis to two bubbles classes, from which one being small enough to have a positive lift coefficient, results in a minimum fraction of small bubbles needed for stability. Finally a generalized criterion for N bubble classes and for a continuous bubble size distribution is given.
Keywords: Bubble columns, Bubble, Stability, Modelling, Lift force, Turbulence
  • Chemical Engineering Science 60(2005)13, 3609-3619

Publ.-Id: 6613 - Permalink


Modification of Textile Mats with Calixarenes – Separation of Uranium from Mine and Seepage Waters
Jansen, K.; Buschmann, H.-J.; Schmeide, K.; Schollmeyer, E.;
More than 40 years of uranium production in Germany left abandoned equipment and mine wastes, which have to be disposed to avoid the release of contaminants into the biosphere. The separation of uranium(VI) from aqueous solution by calixarenes by means of solvent extraction has been described in literature. Calixarenes are macrocyclic ligands formed by the base inducted condensation reaction of para-substituted phenols and formaldehyde. Substituents at the hydroxyl groups control the selectivity of the ligand for the complexation of uranium(VI) ions.
The present work describes the development of a textile filter material for the separation of uranium(VI) from mine and seepage water using uranophile calixarenes. These ligands are permanently fixed on a textile substrate by a process comparable to a disperse dying procedure. For this purpose the calixarenes are statistically functionalized by spacer groups. The filter materials are especially applicable for the remediation of uranium contaminated waters at low concentration levels.
Keywords: calixarene, uranium, extraction, filter
  • Contribution to proceedings
    1st International Textile, Clothing and Design Conference – Magic World of Textiles (Z. Dragcevic, ed.). Faculty of Textile Technology University of Zagreb, Zagreb 2002, p. 692-697

Publ.-Id: 6612 - Permalink


Functionalization of Synthetic Polymers by Supramolecular Compounds: Immobilization of Calix[n]arenes on Polyester
Schollmeyer, E.; Jansen, K.; Buschmann, H.-J.; Schmeide, K.;
Calix[n]arenes are macrocyclic molecules synthesized by the base induced reaction of para-substituted phenols and formaldehyde. These ligands are known to form complexes with suitable guest substances. The selectivity of the calix[n]arenes is influenced by their size and functional groups. The present paper describes the preparation and application of calix[6]arene derivatives statistically functionalized with 1-alkyl groups at the upper rim. The separation of copper(II), nickel(II), cobalt(II) and uranium(VI) from aqueous solutions has been investigated by solvent extraction, as well as by using calix[6]arene-finished polyester felt. Uranium(VI) separation was studied as a function of pH value and uranium(VI) concentration. Furthermore, the recycling of calix[6]arene finished polyester felts loaded with uranium(VI) ions by elution with different solvents was examined. The suitability for the remediation of uranium contaminated water especially at low concentration levels was shown.
Keywords: Filter, extraction, preconcentration, copper, cobalt, nickel, uranium, calix[n]arene
  • Contribution to external collection
    K.L. Mittal: Polymer Surface Modification: Relevance to Adhesion 3, Zeist: VSP, 2004, 353-366

Publ.-Id: 6611 - Permalink


Separation Control at Hydrofoils using Lorentz forces
Mutschke, G.; Gerbeth, G.; Albrecht, T.; Grundmann, R.;
Lorentz forces originating from surface-mounted actuators of permanent magnets and electrodes in weakly conducting fluids like seawater can be used to control flow separation at hydrofoils. The numerical results presented here are based on direct numerical simulation in the laminar flow regime, limited to Reynolds numbers of about 500. Control by steady forcing at the suction side and by oscillatory forcing near the leading edge of the foil is investigated in the post-stall regime.

By applying a strong enough steady control, separation can be completely suppressed. Oscillatory forcing always has to compete with the natural shedding process, lock-in behavior may occur. Lift-optimum control for strong amplitudes is found in a frequency band around the natural shedding frequency. In terms of the momentum coefficient describing the control effort, appropriate excitation frequencies in relation to the natural vortex shedding frequency allow for a more effective lift control than steady forcing.
  • European Journal of Mechanics B 25(2006)2, 137-152

Publ.-Id: 6610 - Permalink


Validation of coupled neutronic/thermal-hydraulic codes for VVER reactors - final report - FIKS-CT-2001-00166
Mittag, S.; Grundmann, U.; Kliem, S.; Kozmenkov, Y.; Rindelhardt, U.; Et, A.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-408

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Publ.-Id: 6609 - Permalink


CFD-Simulation of a Boron Dilution Transient During Start-Up of the Coolant Pump in the 1:5 Scaled VVER-1000 Reactor Model
Höhne, T.; Bezrukov, Y.; Kabanova, L.;
During so called boron dilution transients at pressurized water reactors too weakly borated water might enter the reactor core. This can be the case e.g. during re-start of the first main coolant pump after a deborated slug has formed for instance in the loop seal of the cold leg during stop of coolant circulation under Small Break Loss of Coolant Accident (SBLOCA) conditions. The deboration results in the insertion of positive reactivity and possibly leads to a power excursion. This scenario was studied in the 1:5 scaled VVER-1000 reactor model at OKB “Gidropress”.

The deborated slug was modeled by water with lower temperature entering during the start-up of the coolant pump the hot water inside the Reactor Pressure Vessel (RPV). The experiments were repeated 5-6 times to get statistically independent results. The mass flow rate was varied in a series of experiments studying Reynolds-number effects.

The 3-D computational fluid dynamics (CFD) codes provide an effective tool for mixing calculations. In recent years, the rapid development of both the software and the computers has made it feasible to study the coolant mixing in sufficient detail and to perform the calculations for transient conditions. The experiment with the final mass flow rate of 175 m³/h was taken for CFD-validation. The CFD-Code used was CFX-5.

The geometric details of the construction internals inside the RPV have a strong influence on the flow field and on the mixing. Therefore, an exact representation of the cold leg, the inlet region, the spacer in the downcomer, the elliptical perforated plate and the complicated structures in the lower plenum were modeled in detail. Some parts of the lower plenum internals were modeled using resistance coefficients. The computational grid contained 2.5 Mio. tetrahedral elements. The inlet boundary conditions (velocity, temperature) were set at the cold leg. As an initial guess of the turbulent kinetic energy and the dissipation rate the medium intensity was used. The outlet boundary conditions were pressure controlled. As in the experiment, the temperature differences for describing the boron dilution processes were used. A constant temperature at the RPV walls was assumed.

In the VVER-1000 reactor, the same characteristic flow pattern is observed in the case of the start-up of one pump like for Western type PWR. Due to a strong momentum insertion into the flow at the inlet nozzle, also a horizontal component of the flow is generated in the upper part of the downcomer. The injected flow is distributed into two main jets, the minimum boron concentration at the core inlet appears at two outer regions of the core inlet near the affected loop. The experiment and the CFX calculation showed that for the given slug volume a rather good mixing of the slug and the ambient coolant occur.

A comparison of measured and calculated degree of mixing is performed. Reasons for deviation and directions of further model improvements are discussed.

Keywords: Boron Dilution, CFD, Turbulence, PWR
  • Lecture (Conference)
    14th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-17.09.2004, Espoo, Finland
  • Contribution to proceedings
    14th Symposium of AER on VVER Reactor Physics and Reactor Safety, 13.-17.09.2004, Espoo, Finland, Proceedings, S.581-593

Publ.-Id: 6608 - Permalink


Validation of Trio_U for Transient Accident Scenarios – Numerical Studies of the ROCOM Buoyancy Driven Test Case Simulating ECC Injection During Natural Convection in PWR
Höhne, T.; Bieder, U.;
For the validation of the Trio_U code an experiment with constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop water was taken. For this study a LES approach was used for mesh sizes between 340000 – 1.7 mil-lion control volumes. As a result in the experiment as well as in the calculation the ECC water only partly mixes with ambient coolant in the cold leg. A stratified flow is developing during the injection. In the downcomer a momentum driven flow field is still present at the begin-ning, after this the ECC water propagates downwards the downcomer below CL 1. Trio_U calculations show a good qualitative agreement with the experiment, while at local positions some differences in the concentration field occur.

The obtained results can be used for further studies of the core behaviour using coupled thermo-hydraulic-neutron-kinetic code systems.

Keywords: Turbulence, boron dilution transients, LES, TRIO_U
  • Other report
    Note technique SMTH/LDTA N° 2003-079, CEA Grenoble, August 2004

Publ.-Id: 6607 - Permalink


In situ characterization of phase formation during high-energy oxygen ion implantation in molybdenum
Bohne, Y.; Shevchenko, N.; Prokert, F.; von Borany, J.; Rauschenbach, B.; Möller, W.;
A special designed high-temperature vacuum chamber for in situ X-ray diffraction (XRD) measurements was used to study kinetics of structural phase formation and transformation in molybdenum during oxygen ion implantation and post-annealing treatment. Oxygen ions with an energy of 1.5 MeV were implanted in polycrystalline molybdenum up to a fluence of 3×1018 O+/cm2 at different temperatures (160°C - 700°C). Subsequently, implanted samples were annealed up to 700°C for in situ studying during synthesis of buried oxide layers. Complementary, Transmission Electron Microscopy (TEM) and sputter Auger Electron Spectroscopy (AES) were employed to receive depth dependent information concerning the crystal structure and the elemental composition. The formation of different molybdenum oxides during oxygen implantation and post-implantation annealing process could be observed by in situ x-ray analysis. The XRD spectra of samples implanted at 160°C show that MoO3 and/or Mo4O11 precipitates have been formed, whereas implantation in the temperature range 300°C - 700°C preferably leads to the MoO2 phase formation.
Keywords: : In situ XRD, ion implantation, molybdenum, phase formation
  • Abstract in refereed journal
    Abstract Book of the ECAART8 (8th European Conference on Accelerators in Applied. Research and Technology), September 20-24, 2004, Paris, France
  • Nuclear Instruments and Methods in Physics Research B 240(2005)1-2, 157-161

Publ.-Id: 6605 - Permalink


Laboratory astrophysics as exemplified by the Riga dynamo experiment
Gailitis, A.; Lielausis, O.; Platacis, E.; Stefani, F.; Gerbeth, G.;
It has been proposed to investigate the magnetorotational instability at a large scale liquid sodium facility. This sort of laboratory astrophysics is encouraged by the recent successful dynamo experiments. We report on our experiences with the Riga dynamo experiment where magnetic field self-excitation is achieved in a cylindrical vessel filled with approximately 2 cube meters of liquid sodium which can reach flow velocities up to 20 m/s. The main experimental results on the kinematic and the saturation regime are compared with numerical modelling. Some focus is also laid on the spectra of the magnetic field and the pressure.
  • Contribution to external collection
    MHD COUETTE FLOWS: Experiments and Models, AIP Conference Proceedings 733(2004), 35-44

Publ.-Id: 6604 - Permalink


MRI in Taylor-Dean flows
Stefani, F.; Gerbeth, G.;
The magnetorotational instability (MRI) can destabilize hydrodynamically stable flows which are characterized by an angular momentum that is increasing with the radius and by an angular velocity that is decreasing with radius. Its astrophysical importance comes from the fact that the Kepler flow shows exactly such a behaviour. In order to investigate MRI in a laboratory experiment, the Taylor-Couette flow has been proposed as a substitute for the Kepler flow. In this paper we consider the Taylor-Dean flow as another example of a flow profile which can exhibit the necessary radial dependence. Taylor-Dean flows are a combination of the traditional Taylor-Couette flow with an additional flow that is produced by an azimuthal force. Special focus is laid on the case that the Taylor-Couette part of the flow is a rigid body rotation and the magnitude of the Dean flow is adjusted in such a way that in the outer part of the flow the conditions for MRI are fulfilled. Based on the dispersion relation derived by Ji, Kageyama and Goodman, in combination with some preliminary global instability analysis, we give some first estimates for the physical parameters of a Taylor-Dean MRI experiment with liquid sodium.
  • Contribution to external collection
    MHD COUETTE FLOWS: Experiments and Models, AIP Conference Proceedings 733 (2004), 100-113

Publ.-Id: 6603 - Permalink


Suppression of Random Coincidences during In-Beam PET Measurements.
Crespo, P.; Barthel, T.; Frais-Kölbl, H.; Griesmayer, E.; Heidel, K.; Parodi, K.; Pawelke, J.; Enghardt, W.;
In-beam positron emission tomography (PET) is currently the only method for an in-situ monitoring of charged hadron therapy. However, in-beam PET data, measured at beams with a sub-microsecond-microstructure due to the accelerator radiofrequency (RF), are highly corrupted by random coincidences arising from prompt gamma-rays following nuclear reactions as the projectiles penetrate the tissue. Therefore, since random-correction techniques from conventional PET cannot be applied, at the clinical in-beam PET at the therapy facility at the Gesellschaft fuer Schwerionenforschung (GSI) Darmstadt merely events registered in the pauses (2-3s) between the beam macropulses (< 2s) are reconstructed. Image statistics may increase up to 50% if coincidences acquired during the macropulse, but out of the micropulses, are taken into account. Two methods for suppressing the micropulse-induced random coincidences have been successfully tested at GSI with carbon ion beams. They rely on the synchronization of the gamma-gamma-coincidences measured by the positron camera with the time microstructure of the beam, either by using the RF-signal from the accelerator or the signal of a thin diamond detector placed in the beam path in front of the target. Time and energy correlated spectra, first-measured during the macropulses, together with the corresponding tomographic images of the beta+ activity induced by the beam in a phantom, clearly confirm the feasibility of the proposed random supression methods.
  • Lecture (Conference)
    IEEE Nuclear Science Symposium and Medical Imaging Conference,18.-23.10.2004, Rome, Italy
  • Contribution to proceedings
    IEEE Nuclear Science Symposium and Medical Imaging Conference, 18.-23. 10.2004, Rome, Italia, Conference Record N 45-6, Book of abstract p. 127-128

Publ.-Id: 6602 - Permalink


FE-simulation of the viscoplastic behaviour of different RPV steels in the frame of in-vessel melt retention scenarios
Altstadt, E.; Willschuetz, H.-G.; Mueller, G.;
Abstract – Assuming the hypothetical scenario of a severe accident with subsequent core meltdown and formation of a melt pool in the reactor pressure vessel (RPV) lower plenum of a Light Water Reactor (LWR) leads to the question about the behav-ior of the RPV. One accident management strategy could be to stabilize the in-vessel debris configuration in the RPV as one major barrier against uncontrolled release of heat and radio nuclides.
To get an improved understanding and knowledge of the melt pool convection and the vessel creep and possible failure processes and modes occurring during the late phase of a core melt down accident the FOREVER-experiments (Failure Of REactor VEssel Retention) have been performed at the Division of Nuclear Power Safety of the Royal Institute of Technology Stockholm. These experiments are simulating the behavior of the lower head of the RPV under the thermal loads of a convecting melt pool with decay heating, and under the pressure loads that the vessel experiences in a depressurization scenario. The geometrical scale of the experiments is 1:10 com-pared to a common LWR.
Accompanying the experiments metallographical and numerical work is performed at the Forschungszentrum Rossendorf. An axisymmetric Finite Element model is devel-oped based on the multi-purpose code ANSYS®. To describe the viscoplastic defor-mation a numerical creep data base (CDB) is developed where the creep strain rate is evaluated in dependence on the current total strain, temperature and equivalent stress. In this way the use of a single creep law, which employs constants derived from the data for a limited stress and temperature range, is avoided. For an evalua-tion of the failure times a damage model according to an approach of Lemaitre is ap-plied. The microstructural investigations give insight to the material state of the vessel wall at different positions. This can be compared with the numerical damage value calculated in the Finite Element Model.
This paper deals with the experimental, numerical, and metallographical results of the creep failure experiment EC-FOREVER-4, where the American pressure vessel steel SA533B was applied for the lower head. For comparison the results of the experi-ment EC-FOREVER-3B, build of the French 16MND5 steel, are discussed, too. Em-phasis is put on the differences in the viscoplastic behaviour of different heats of the RPV steel. For this purpose, the creep tests in the frame of the LHF/OLHF experi-ments are reviewed, too. As a hypothesis it is stated that the sulphur content could be responsible for differences in the creep behaviour.

Keywords: Finite-Element-Method, In-vessel melt retention, Light water reactor, Severe accident scenarios, Creep
  • Lecture (Conference)
    MPA-Seminar, 05.07.2004, Stuttgart, Germany
  • Contribution to proceedings
    MPA-Seminar, 05.-07.10.2004, Stuttgart, Germany, Proceedings pp. 33.1-33.12

Publ.-Id: 6601 - Permalink


Efficient light emitting diodes based on nanoscale silicon
Helm, M.; Sun, J.; Potfajova, J.; Winnerl, S.; Dekorsy, T.; Skorupa, W.; Schmidt, B.; Mücklich, A.;
After giving an overview about various approaches for silicon based light emitters, we will present our results on Si light emitting diodes prepared by high-dose boron implantation. The electroluminescence (EL) increases with temperature, resulting in a wall-plug efficiency of 0.1% at room temperature. Extensive low-temperature EL measurements allow us to put forward a model, which is based on the interplay between free excitons/carriers and excitons localized at nanoscale boron doping spikes. Finally, we demonstrate an electrically driven resonant-cavity LED based on silicon.
Keywords: silicon, luminescence, implantation, microcavity
  • Physica Status Solidi (c) 2 (2005) 2941-2946

Publ.-Id: 6600 - Permalink


Efficient light emitting devices based on nanoscale silicon
Helm, M.;
Recently some remarkable advances concerning silicon based light emission have been reported. This has triggered the hope that a practical Si based light source may soon become reality. Several approaches are pursued by research groups worldwide: porous Si, Si nanocrystals and Er3+ in SiO2, Er3+ doped Si, Si/Ge quantum cascade structures, and also more “conventional” Si pn diodes. I will give a survey on some of these approaches and then concentrate on Si pn diodes, fabricated by high-dose boron implantation.

In these structures the electroluminescence (EL) increases with temperature, resulting in a wall-plug efficiency of 0.1% at room temperature. Extensive low-temperature EL measurements allow us to put forward a model, which is based on the interplay between free excitons/carriers and excitons localized at nanoscale boron doping spikes, similar to delta-doped layers produced by MBE. Within this model we are able to explain the EL dependence on current and temperature, as well as an electrical bistability occurring at low temperature. Finally, we have fabricated what is, to our knowledge, the first electrically driven resonant-cavity LED based on silicon.

Keywords: silicon, luminescence, implantation, microcavity
  • Invited lecture (Conferences)
    Invited talk at the International Conference on Superlattices, Nanostructures, and Nanodevices (ICSNN'04), July 19-23, 2004, Cancun, Mexico

Publ.-Id: 6599 - Permalink


LEDs und Laserdioden: die Lichtrevolution
Winnerl, S.;
Leuchtdioden (LED, engl.: light emitting diode) und Laserdioden haben bereits vielfältigen Einzug in unser Alltagsleben gefunden, beispielsweise im CD- und DVD-Spieler. In dem Vortrag werden die Funktionsweisen von LEDs und Laserdioden erklärt, insbesonder wird erklärt, wie die verschiedenen Farben erreicht werden und warum gerade die Farbe Blau so wichtig ist. Unterschiedliche Konzepte für Weißlichtquellen auf der Basis von LEDs werden vorgestellt. Die Wirkungsgrade von LEDs werden diskutiert und ein Ausblick auf die Palette von Anwendungen wird geboten.
Keywords: LED, Laserdiode
  • Lecture (others)
    Lehrertag, Forschungszentrum Rossendorf, 2004, Dresden, Deutschland

Publ.-Id: 6598 - Permalink


Die Stoppuhren der Forschung: Femtosekundenlaser
Winnerl, S.;
Nach einer kurzen Darstellung des Laserprinzips wird erklärt, wie in einem Titan-Saphir-Laser durch passeive Modenkopplung ultrakurze Lichtpulse erzeugt werden. Weiterhin wird gezeigt, wie mit Hilfe von nichtlinearen optischen Effekten eine Veränderung der Laserwellenlänge möglich ist. Als typisches Beispiel des Einsatzes von Kurzpuls-Lasern in der Forschung wird die Anrege-Abfrage-Technik vorgestellt. Abschließend werden praktische Beispiele vom Einsatz von Kurzpuls-Lasern in der physikalischer Forschung, Materialbearbeitung und Medizintechnik gezeigt.
Keywords: Ultraschnelle Prozesse, Femtosekundenlaser
  • Lecture (others)
    Lehrertag, Forschungszentrum Rossendorf, 2004, Dresden, Deutschland

Publ.-Id: 6597 - Permalink


LEDs und Laserdioden: die Lichtrevolution
Winnerl, S.;
Die faszinierende Erfolgsgeschichte von Leuchtdioden (engl.: light emitting diode, LED) und Laserdioden wird vorgestellt. Es wird erklärt, wie Licht unterschiedlicher Farbe mit LEDs erzeugt wird und welche besondere Rolle blaue LEDs spielen. Neben weißen Leuchtdioden, die ein hohes Potential für zukünftige Alltagsbeleuchtung besitzen, werden auch aktuelle Forschungsergebnisse zu siliziumbasierenden LEDs diskutiert.
  • Lecture (others)
    Lange Nacht der Wissenschaften, 2004, Dresden, Deutschland

Publ.-Id: 6596 - Permalink


THz-time-domain spectroscopy of doped semiconductor superlattices
Winnerl, S.; Dreyhaupt, A.; Dekorsy, A.; Helm, M.;
The search for Bloch gain in doped semiconductor superlattices is still a field of considerable interest. Our approach is to obtain the dynamic conductivity of doped biased GaAs/AlGaAs superlattices by measuring the transmission in the terahertz frequency range. We present experimental results on the electric transport in a wide temperature range and preliminary results for the THz transmission through superlattice mesa elements.
Keywords: Bloch gain, seminconductor superlattice, THz spectroscopy
  • Lecture (others)
    Workshop on Quantum Heterostructures and THz Electronics, 2004, Regensburg, Deutschland

Publ.-Id: 6595 - Permalink


Time-domain THz spectroscopy of electronic excitations in GaAs/AlGaAs superlattices
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
We investigate the electronic properties of weakly and more strongly coupled n-doped GaAs/AlGaAs superlattices by time domain spectroscopy in the low frequency range from 0.5 to 3.5 THz. The sample properties are modulated either by applying an AC voltage via a gate electrode or by injecting a vertical current. The transmission signal is detected at the frequency of the modulation voltage with a lock-in amplifier leading to a signal-to-noise ratio superior compared to conventional FTIR spectroscopy in this frequency range. We will discuss the observation of inter-miniband transitions, confined donor transitions, plasmon excitations and the measurement of intra-miniband THz conductivity in a wide range of lattice temperatures.
Keywords: THz time-domain spectroscopy, semiconductor superlattice, interminiband-transition, intra-miniband THz conductivity
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Halbleiterphysik, HL 9.2, Regensburg 2004

Publ.-Id: 6594 - Permalink


Large-area high-power THz emitter based on interdigitated electrodes
Dreyhaupt, A.; Winnerl, S.; Dekorsy, T.; Helm, M.;
We present a planar large-area photoconductor based on GaAs for impulsive generation of THz radiation. The device consists of an interdigitated electrode metal-semiconductor-metal structure (MSM) with 5 µm electrode spacing. The MSM structure is masked by an opaque metallization layer isolated from the MSM electrodes in a way that optical excitation takes place only in regions with unidirectional electric field. Constructive interference of the THz emission from accelerated carriers leads to amplitudes that are 104 times higher than from the same MSM structure without second metallization layer.
Keywords: THz emmitter
  • Lecture (Conference)
    The Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics (IRMMW2004/THz2004); Karlsruhe
  • IEEE Conference digest IRMMW2004/THz2004

Publ.-Id: 6593 - Permalink


THz emission from GaSb samples with modified surface stoichiometry
Winnerl, S.; Dekorsy, T.; Helm, M.;
The optimization of emitters for THz radiation pulses has gained a lot of interest in recent years. They can be based on accelerating charge carriers, which are photoexcited by fs-laser pulses in the surface field of a semiconductor. We studied the THz emission from GaSb samples that were annealed at different temperatures in the range from 300 °C to 700 °C. Without annealing, no THz emission was observed under fs excitation at 800 nm. This is consistent with the fact, that for GaSb no surface states in the band gap have been found [1]. The THz emission was strongest for the annealing temperature of 450 °C with amplitudes comparable to that of an InGaAs emitter. We attribute the THz emission to a surface field caused by decomposition of the surface of the annealed samples. The decomposition is confirmed by measuring the surface stoichiometry using Auger electron spectroscopy. We suggest that the decrease of THz intensity for the higher annealing temperatures is due to a lowering of the carrier mobility. Our experiment demonstrates the possibility to modify materials for THz emission in a very simple way.

[1] P.W. Chey, I.A. Babalado, T. Sukegawa, and W.E. Spicer, Phys. Rev. Lett. 35, 1602 (1975).
  • Lecture (Conference)
    DPG Frühjahrstagung, Fachverband Halbleiterphysik, HL 4.4, 2004, Regensburg, Deutschland

Publ.-Id: 6592 - Permalink


Structural analysis of ion irradiated polycrystalline NiFe/FeMn exchange bias systems
Blomeier, S.; Mcgrouther, D.; Mcvitie, S.; Chapman, J. N.; Weber, M. C.; Hillebrands, B.; Fassbender, J.ORC
Structural investigations of the ion irradiated polycrystalline NiFe/FeMn exchange bias bilayer system were carried out by means of transmission electron microscopy. Key structural parameters like average grain size, lattice constant, and texture, as well as their dependence upon ion irradiation could be determined. For this purpose, a detailed analysis of a series of bright field images, dark field images, and diffraction patterns was performed. Also in this context, a previously established model was tested which ascribes changes in the magnetic properties upon irradiation with 5 keV He+ to the creation of point defects within the antiferromagnetic layer and to the intermixing between the ferromagnetic and antiferromagnetic layers. The obtained results indirectly support this model by excluding the aforementioned structural parameters as a possible source of the observed changes of the magnetic properties.
Keywords: magnetism, exchange-bias, ion irradiation, ion implantation, focused ion beam, TEM
  • European Physical Journal B 45(2005), 213

Publ.-Id: 6591 - Permalink


All-optical probe of magnetization dynamics in exchange biased bilayers on the picosecond time-scale
Weber, M. C.; Nembach, H.; Blomeier, S.; Kaltofen, R.; Schumann, J.; Carey, M.; Fassbender, J.ORC
All-optical control of the magnetization of polycrystalline exchange bias bilayer systems is achieved using short picosecond laser pulses. Due to the photoexcitation, the spin temperature across the interface between the ferromagnetic and antiferromagnetic layer is elevated, resulting in a collapse of the interfacial exchange coupling. Thus, within the first 10 ps, a fast reduction of both the exchange bias field and the coercive field is observed for three different exchange bias systems comprising both different ferromagnets and antiferromagnets. The fast thermal unpinning is followed by a slower heat diffusion dominated relaxation process, which strongly depends on the thermal conductivity of the used buffer layers and substrates. The fast optical unpinning can be understood in terms of an internal anisotropy pulse field capable of triggering ultrafast precessional magnetization dynamics of the ferromagnetic layer, which makes heat-assisted coherent magnetization rotation feasible.
Keywords: magnetism, exchange bias, magnetic films, pump-probe, time-resolved techniques
  • European Physical Journal B 45(2005)2, 243-248

Publ.-Id: 6590 - Permalink


THz emission from GaSb samples with modified surface stoichiometry
Winnerl, S.; Sinning, S.; Dekorsy, T.; Helm, M.;
We prepared efficient THz emitters based on photoexcited (fs-laser pulses) carriers in GaSb. Annealing (range 300 °C - 700 °C) provided a simple way for optimization. This is due to a surface field caused by a decomposition of the surface induced by the annealing. The decomposition is confirmed by Raman spectroscopy.
Keywords: THz emission, GaSb, Raman spectroscopy
  • Lecture (Conference)
    The Joint 29th International Conference on Infrared and Millimeter Waves and 12th International Conference on Terahertz Electronics (IRMMW2004/THz2004), 28.09.-1.10.2004, Karlsruhe, Deutschland
  • IEEE Conference digest IRMMW2004/THz2004

Publ.-Id: 6588 - Permalink


Detecting irradiation induced damage in RPV steels by SANS
Ulbricht, A.; Bergner, F.;
It is well known that reactor pressure vessel steels suffer a degradation of the mechanical properties caused by neutron irradiation. Unfortunately, the ultra-fine microstructural features produced by irradiation cannot be directly detected by means of microscopic imaging techniques. Indirect evidence can, however, be obtained on the basis of Positron Annihilation Spectroscopy (PAS) and Small-Angle Neutron Scattering (SANS). The latter method has the advantage of high sensitivity to particle sizes from less than 1 to more than 10 nm in conjunction with integrating over a macroscopic volume (Fig. 1). Volume integration is important, because the difference between SANS intensities for neutron-irradiated material and unirradiated reference becomes independent of local fluctuations of both composition and microstructure. Furthermore, both size distribution and volume fraction of irradiation-induced defects can be calculated from measured SANS intensities. The ratio of SANS intensities for magnetic and nuclear scattering reveals also information on the composition of defects. In the Institute of Safety Research at the Forschungszentrum Rossendorf SANS experiments on Reactor Pressure Vessel (RPV) steels have been systematically and successfully designed, performed and analysed for a period of more than 10 years. In the present paper a short overview of the main results obtained by the Rossendorf group is given. Some open questions are summarized. On the other hand, one will not be able to obtain optimum information on the basis of a single experimental technique alone in most cases. From this viewpoint, supplementary experimental methods and numerical simulation techniques are considered.

Keywords: Small-angle neutron scattering, Neutron irradiation, Reactor pressure vessel steel
  • Lecture (Conference)
    30th MPA-Seminar in conjunction with 9th German-Japanese Seminar 'Safety and Reliability in Energy Technology', 06.-07.10.2004, Stuttgart, Germany
  • Contribution to proceedings
    Proceedings of the 30th MPA-Seminar in conjunction with 9th German-Japanese Seminar 'Safety and Reliability in Energy Technology', 06.-07.10.2004, Stuttgart, Germany, MPA-Seminar, Stuttgart, (2004)1, 10.1-10.13

Publ.-Id: 6587 - Permalink


Increased terahertz emission from thermally treated GaSb
Winnerl, S.; Sinning, S.; Dekorsy, T.; Helm, M.;
We report on the terahertz emission from GaSb surfaces with modified surface stochiometry. While very weak emission is observed from virgin GaSb wafers, the emission is significantly increased by a single thermal treatment of the wafers. Optimum emission is observed for 500 °C thermal annealing. The reason for the THz emission is a surface electric field induced by thermal decomposition of the surface as corroborated by Raman spectroscopy.
Keywords: Terahertz emission, Raman spectroscopy, surface field, GaSb

Publ.-Id: 6586 - Permalink


Recents Developments in Nuclear Safety Research
Weiß, F.-P.;
The presentation starts from sustainability considerations of different energy carries like oil, hoard cool, or nuclear energy.
It is highlighted, that in terms of sustainability nuclear energy suffers from the danger of proliferation of weapons grade material, the maximum damage of a conceivable severe accident, and the extremely long isolation period of the nuclear waste in the final disposal. Discussing the safety analysis of so called boron dilution transients in PWRs, the behaviour of the reactor pressure vessel during a severe core melt accident, and the possibilities of the transmutation of long lived radio-nuclides it is shown how modern nuclear safety research can contribute to improved sustainability performance of nuclear energy.
  • Invited lecture (Conferences)
    Conference on Multi-Phase Flow: Simulation Experiment and Application, 28.-30.06.2004, Dresden, Germany

Publ.-Id: 6585 - Permalink


Boron dilution Transients in PWRs
Weiß, F.-P.; Kliem, S.;
Boron 10 is a strong thermal neutron absorber. As boric acid solved in the coolant of PWRs, it is used to compensate the excess reactivity of the reactor especially at the beginning of the fuel cycle. Therefore, an inadvertent or even unavoidable reduction of the boron concentration means an increase of reactivity that might result in a power excursion, a so called boron dilution transient.
The reactivity increase depends on the of mixing of the underborated water with the coolant inventory in the downcomer (DC) and lower plenum (LP) where the boron concentration is still on the normal high level.
After introducing the different boron dilution scenarios, results of the latest PKL (Primärkreislauf test facility at FANP) experiments will be presented aiming at the assessment of the maximum slug volume for the different safety injection cases. Moreover, the ROCOM (Rossendorf Coolant Mixing) tests will be discussed that were performed to study mixing phenomena inside the reactor pressure vessel (RPV) and which provided typical boron concentration profiles at the core entrance for the different flow regimes. These experiments are used to develop and validate calculation models for boron mixing. Such models are needed to get information about realistic time dependent boron concentration profiles over the cross section of the core entrance. The obtained concentration profiles are used as boundary conditions for coupled neutronic / thermal-hydraulic core calculations to show whether recriticality of the shut down reactor is reached and how high the maximum power peak can be. The results of such calculations will be presented proving that these deborated slugs can cause prompt criticality. Nevertheless, due to the fast Doppler feedback no core damage occurs even with the maximum slug volume of 36m³ .
  • Book (Authorship)
    Unterrichtsmaterial für die Frederic Joliot/Otto Hahn Summer School, Karlsruhe,August 20-29, 2003

Publ.-Id: 6584 - Permalink


Boron dilution Transients in PWRs
Weiß, F.-P.;
Boron 10 is a strong thermal neutron absorber. As boric acid solved in the coolant of PWRs, it is used to compensate the excess reactivity of the reactor especially at the beginning of the fuel cycle. Therefore, an inadvertent or even unavoidable reduction of the boron concentration means an increase of reactivity that might result in a power excursion, a so called boron dilution transient.
The reactivity increase depends on the of mixing of the underborated water with the coolant inventory in the downcomer (DC) and lower plenum (LP) where the boron concentration is still on the normal high level.
After introducing the different boron dilution scenarios, results of the latest PKL (Primärkreislauf test facility at FANP) experiments will be presented aiming at the assessment of the maximum slug volume for the different safety injection cases. Moreover, the ROCOM (Rossendorf Coolant Mixing) tests will be discussed that were performed to study mixing phenomena inside the reactor pressure vessel (RPV) and which provided typical boron concentration profiles at the core entrance for the different flow regimes. These experiments are used to develop and validate calculation models for boron mixing. Such models are needed to get information about realistic time dependent boron concentration profiles over the cross section of the core entrance. The obtained concentration profiles are used as boundary conditions for coupled neutronic / thermal-hydraulic core calculations to show whether recriticality of the shut down reactor is reached and how high the maximum power peak can be. The results of such calculations will be presented proving that these deborated slugs can cause prompt criticality. Nevertheless, due to the fast Doppler feedback no core damage occurs even with the maximum slug volume of 36m³ .
  • Lecture (Conference)
    Vortrag zur Frederic Joliot/Otto Hahn Summer School, Karlsruhe, August 20-29, 2003

Publ.-Id: 6583 - Permalink


Charged pion production in 9644Ru + 9644Ru collisions at 400A and 1528 A MeV
Hong, B.; Kim, Y. J.; Herrmann, N.; Stockmeier, M. R.; Alard, J. P.; Andronic, A.; Barret, V.; Basrak, Z.; Bastid, N.; Benabderrahmane, L.; Caplar, R.; Crochet, P.; Dupieux, P.; Dzelalija, M.; Fodor, Z.; Gobbi, A.; Grishkin, Y.; Hartmann, O. N.; Hildenbrand, K. D.; Kecskemeti, J.; Kirejczyk, M.; Koczon, P.; Korolija, M.; Kotte, R.; Kress, T.; Lebedev, A.; Leifels, Y.; Lopez, X.; Mangiarotti, A.; Merschmeyer, M.; Neubert, W.; Pelte, D.; Petrovici, M.; Rami, F.; Reisdorf, W.; Schüttauf, A.; Seres, Z.; Sikora, B.; Sim, K. S.; Simion, V.; Siwek-Wilczynska, K.; Smolyankin, V.; Stoicea, G.; Tyminski, Z.; Wagner, P.; Wisniewski, K.; Wohlfarth, D.; Xiao, Z. G.; Yushmanov, I.; Zhilin, A.;
We present the transverse momentum and rapidity spectra of charged pions in central Ru + Ru collisions at 400A and 1528A MeV. The data exhibit enhanced productions at low transverse momenta compared to the expectations from the thermal model that includes the decay of Delta(1232)-resonances and thermal pions. Modification of the Delta-spectral function and the Coulomb interaction are necessary to describe the detailed shape of the transverse momentum spectra. Within the framework of the thermal model, the freeze-out radii of pions are similar at both beam energies. The IQMD model also reproduces the shapes of the transverse momentum and rapidity spectra of pions, but the predicted absolute yields are larger than in the measurements, especially at lower beam energy.
  • Physical Review C 71(2005), 034902

Publ.-Id: 6582 - Permalink


Prüfung duktiler Werkstoffe mit dem Small Punch Test
Kuna, M.; Abendroth, M.;
Der Small Punch Test (SPT) ist ein Kleinstprobenversuch, der sich zur Bestimmung des aktuellen lokalen Materialzustandes in technischen Anlagen unter Betriebsbedingungen eignet. Dieser Artikel stellt ein kombiniertes experimentell-numerisches Verfahren zur Identifikation von Verfestigungs- und Versagenseigenschaften duktiler Werkstoffe aus dem SPT vor. Ein schädigungsmechanisches Materialmodell dient zur Beschreibung des Probenverhaltens.
Die Einflüsse der Parameter des schädigungsmechanischen Materialmodells auf das Versuchsergebnis werden anhand von FEM-Simulationen des SPT dargestellt. Neuronale Netze werden mit diesen Simulationen trainiert und stellen so einen generalisierten Zusammenhang zwischen Materialparametern und Versuchsergebnis dar, der in einem Optimierungsalgorithmus zur Identifikation der unbekannten schädigungsmechanischen Materialparameter benutzt wird. Die identifizierten Materialparameter lassen sich auf andere Probengeometrien übertragen und ermöglichen eine Vorhersage von bruchmechanischen Werkstoffkennwerten.
Keywords: Small Punch Test, Schädigungsmechanik, Parameteridentifikation, Neuronale Netze
  • Materialprüfung 47 2005)1-2, 45-54

Publ.-Id: 6580 - Permalink


The effect of atomic hydrogen flow on electrical resistance of the transition metal films
Kagadei, V.; Nefyodtsev, E.; Proskurovsky, D.; Romanenko, S.; Shevchenko, V.; Grambole, D.; Groetzschel, R.; Herrmann, F.; Ivanov, Y.;
On using of nuclear reaction analysis, X-ray analysis, electron microscopy, the mechanisms of structure and phase composition change of thin vanadium films at treatment in a flow consisting of molecular and atomic hydrogen (AH) have been studied. A comparative analysis on regularities of the film saturation with hydrogen and its resistance changing was carried out. It has been settled that the resistance dependence on hydrogen concentration in the case of thin film hydrogenised in AH flow differs from the analogous dependence for the bulk material hydrogenised in an atmosphere of molecular hydrogen in the conditions of thermodynamic equilibrium. Nevertheless, the found peculiarities of thin film resistance dependence on hydrogenation time, the same as in the case of bulk material, are determined by formation of vanadium hydride -phase in the film. It is shown that with transient metal films it is possible to measure AH flow densities under reduced pressure of gas (10-1 to 10-3 Pa). The principle of measurement is based on dependence analysis of the film resistance increment determined by hydrogen solubilization in the film versus exposure time in AH flow. The suggested measurement method is characterized by high selectivity to AH allowing measurement of partial density of atomic flow over the range from 5×1013 up to 1016 at /cm²/s in a mixed atomic–molecular flow. The sensor made on the basis of this method can find applications in microelectronic techniques where semiconductor treatment by atomic hydrogen flows is employed.
Keywords: Gas sensor; Atomic hydrogen; Electrical conductivity
  • Sensors and Actuators A 113(2004), 293-300

Publ.-Id: 6579 - Permalink


Determination of ductile material properties by means of the small punch test and neural networks
Abendroth, M.; Kuna, M.;
This Paper compares two different methods for the identifikation of ductile properties of materials using the small punch test to measure the material response under loading. The finite element method is used to calculate the load displacement curve of the punch depending on the parameters of a hardening law. Via systematical variation of the material parameters a data base is built up, which is used to train neural networks. The second method allows the indentification of material parameters by using a conjugate directions algorithm, which minimizes the error between an experimental load displacement curve and one calculated by the network function.
Keywords: small punch test, damage mechanics, neural networks, parameter identifikation, finite elements

Publ.-Id: 6578 - Permalink


Deformation-induced small-angle scattering contrast in aluminium alloys
Bergner, F.; Müller, G.; Ulbricht, A.; van Ouytsel, K.; Blank, C.; Bras, W.; Dewhurst, C.;
Small-angle neutron scattering experiments have been performed on a homogeneously deformed specimen (uniform elongation 18.5%) of commercial thin-sheet wrought aluminium alloy AA 6013 (Al-Mg-Si-Cu) aged at room temperature. Comparisons with undeformed material revealed characteristic deformation-induced anisotropy of the two-dimensional X-ray and neutron scattering pattern, which can be interpreted as being due to deformation-induced arrangements of preferentially aligned dislocation segments. The results turn out to be helpful for the understanding of anisotropic small-angle X-ray scattering patterns obtained from the crack-tip plastic zone of cracked specimens of the aluminium alloy AA 6013 tempered at 190°C to maximum hardness.
Keywords: Small-angle X-ray scattering, Small-angle neutron scattering, Aluminium alloys, Plasticity
  • Nuclear Instruments and Methods in Physics Research B 23(2005), 92-97
  • Poster
    4th Conference on Synchrotron Radiation in Materials Science (SRMS4), 23.-25.08.2004, Grenoble, France

Publ.-Id: 6577 - Permalink


Centrality Dependence of Thermal Parameters Deduced from Hadron Multiplicities in Au + Au Collisions at sqrt{s_{NN}} = 130\ GeV
Cleymans, J.; Kämpfer, B.; Kaneta, M.; Xu, N.;
We analyse the centrality dependence of thermal parameters deduced from hadron multiplicities in Au + Au collisions at sqrt{s_{NN}} = 130\ GeV. While the chemical freeze-out temperature and chemical potentials are found to be roughly centrality-independent, the strangeness saturation factor gamma_S increases with participant number towards unity, supporting the assumption of equilibrium freeze-out conditions in central collisions.
Keywords: strangeness, heavy ion collisions, statistical model
  • Physical Review C 71(2005), 054901

Publ.-Id: 6576 - Permalink


Above room temperature operation of short wavelength (lambda=3.8 µm) strain-compensated In0.73Ga0.27As–AlAs quantum-cascade lasers
Semtsiv, M. P.; Ziegler, M.; Dressler, S.; Masselink, W. T.; Georgiev, N.; Dekorsy, T.; Helm, M.;
We demonstrate the design and implementation of a broad-gain and low-threshold (Jth = 860 A/cm2 at 8 K) quantum-cascade laser emitting between 3.7 and 4.2 µm. The active region design is based on strain-compensated In0.73Ga0.27As–AlAs on InP. Laser operation in pulsed mode is achieved up to a temperature of 330 K with maximum single-facet output peak powers of 6 W at 8 K and 240 mW at 296 K. The temperature coefficient T0 is 119 K.
Keywords: QCL, quantum cascade laser, room temperature, low-threshold, strain-compensated, InGaAs, AlAs

Publ.-Id: 6575 - Permalink


Syntheses of 18F-Labeled Acyclic Purine and Pyrimidine Nucleosides Intended for Monitoring Gene Expression
Grote, M.; Noll, S.; Noll, B.;
  • Lecture (Conference)
    6th International Conference on Nuclear and Radiochemistry, 29.08.-03.09.2004, Aachen, Germany
  • Lecture (Conference)
    European Symposium on Radiopharmacy and Radiopharmaceuticals, 09.-12.09.2004, Danzig, Poland

Publ.-Id: 6574 - Permalink


Mikromilieu und Hypoxie im Bild
Baumann, M.; Krause, M.; Eicheler, W.; Petersen, C.; Zips, D.; Beuthien-Baumann, B.; Kotzerke, J.; Laniadao, M.; Herrmann, T.;
Der prätherapeutischen Identifikation prognosebestimmender Parameter des Tumormikromilieus, z. B. dem Ausmaß der Hypoxie kommt eine besondere Bedeutung für die Individualisierung der Tumortherapie zu. Entsprechende Informationen können heute grundsätzlich durch die biologisch-funtionelle Bildgebung zur Verfügung gestellt werden. Ein wesentliches Problem sämtlicher bildgebender Verfahren ist jedoch, dass nicht zwischen klonogenen, also rezidivfähigen, und nicht -klonogenen Zellen unterschieden werden kann. Klonogene Zellen machen oft nur einen verschwindend kleinen Anteil aller Zellen im Tumor aus und können ausschließlich durch funktionell-tumorbiologische Methoden erfasst werden. Voraussetzung für die Entwicklung und Validierung funktioneller Bildgebungsmethoden ist daher die Integration von Methoden der Strahlen- und Tumorbiologie mit bildgebenden Untersuchungensverfahren. Diese Integration setzt den Aufbau und die gezielte Förderung entsprechender fachübergreifender Gruppen voraus. Bisherige Ergebnisse zur funktionellen Bildgebung des Tumormikromilieus, die anhand eines Beispiels illustriert werden, zeigen eine hohe Relevanz für unser Verständnis der Biologie von Krebserkrankungen. Es besteht wenig Zweifel daran, dass in der Zukunft die Integration der funktionellen Bildgebung in die Krebsbehandlung, z. B. in die computergeschützte Strahlentherapieplanung, wesentliche Impulse für die Verbesserung der Therpaie krebskranker Patienten bieten wird.
  • Nova Acta Leopoldina NF 89, Nr. 337 (2004) 119-125

Publ.-Id: 6573 - Permalink


SANS-Untersuchungen zur Charakterisierung von Strahlendefekten in RDB-Stählen nach Bestrahlung, Ausheilung und Wiederbestrahlung
Ulbricht, A.; Bergner, F.;
Bekanntlich bewirkt das Strahlungsfeld schneller Neutronen in der Umgebung des Reaktorkerns eine Verschlechterung der mechanischen Eigenschaften des Druckbehälters. Zur Vertiefung des Verständnisses und zur quantitativen Beschreibung der Zusammenhänge zwi-schen Gefüge, mechanischen Eigenschaften und Strahlenbelastung wurden an Reaktor-druck-behälter-(RDB)-Stählen Strukturuntersuchungen mit Neutronen-Kleinwinkelstreuung (SANS) durchgeführt. Dazu wurden Proben aus verschiedenen Chargen von west- und ost-europäischen RDB-Stählen verwendet, die im Rahmen des Bestrahlungsprogramms am ehemaligen Proto-typ-Reaktor WWER-2 in Rheinsberg oder der Versprödungsüberwachungsprogramme laufender WWER-Reaktoren (u.a. in Loviisa, Finnland) bestrahlt worden sind.
Die bestrahlungsbedingten Strukturveränderungen sind abhängig vom Stahltyp. Charakteristische Parameter der Strahlendefekte, wie Anzahldichte, Größenverteilung und Volumen-gehalt wurden bestimmt und mögliche Defektzusammensetzungen abgeschätzt. Es zeigte sich, dass mit zunehmender Strahlenbelastung für einen bestimmten Stahltyp der Gehalt an Defekten nicht proportional ansteigt, wobei die Größenverteilung nahezu unverändert bleibt. Defektradien bis 3 nm treten auf. Das Maximum der Größenverteilung liegt bei 1 nm. Zudem kann sich mit der Bestrahlungszeit auch die mittlere Zusammen-setzung der Punktdefekt-agglomerate aus Leer-stellen und Fremdatomen ändern. Kupferverunreinigungen im Stahl beeinflussen die Clusterbildung am stärksten. Reine Kupfer-ausschei-dungen wurden nicht beobachtet.
Eine Wärmebehandlung über 400 °C reduziert den Anteil an Defekten, aber stabilisiert kupferreiche Cluster.
Erstmals wurden SANS-Untersuchungen an nach einer Ausheilwärmebehandlung (475 °C / 100 h) wiederbestrahltem RDB-Stahl durchgeführt. Die Defekterzeugung war im zweiten Bestrahlungszyklus wesentlich geringer. Auch die Zusammensetzung der neuen Strahlendefekte wich von der des ersten Bestrahlungszustandes ab.
  • Poster
    Deutsche Neutronenstreutagung, 1.-3. September 2004, Dresden

Publ.-Id: 6572 - Permalink


Heating effect on steady and unsteady horizontal laminar flow of air past a circular cylinder
Shi, J.-M.; Gerlach, D.; Breuer, M.; Biswas, G.; Durst, F.;
Extensive numerical experiments were carried out to study the effect of cylinder heating on the characteristics of the flow and heat transfer in a two-dimensional horizontal laminar flow of air past a heated circular cylinder for the range of Reynolds numbers $0.001 \le Re \le 170$. The fluid was treated as incompressible (density is independent of the pressure) while the variation of the fluid properties with temperature was taken into account. By including the transient density term of the continutiy equation, which was neglected in a previous study by Lange et al.(IJHMT, 41(22), 1998), we were able to predict correctly the vortex shedding frequency at various overheat ratios using an incompressible flow solver. The effect of dynamic viscosity and density variations on the flow dynamics occurring with the cylinder heating was analyzed separately. Another emphasis of the work was to investigate the physical mechanism behind the ``effective Reynolds number'' concept widely applied in engineering correlations. Similarity was discovered for the distribution of the local dimensionless viscous force, the vorticity and the Nusselt number at the cylinder surface and the pressure force in the rear part of the cylinder. Two characteristic temperatures, T_{ef\!f} = T_\infty + 0.28(T_W-T_\infty) for the flow dynamics and T_{f} = T_\infty + 0.5(T_W-T_\infty) for the heat transfer, were identified.
Keywords: heat transfer, forced convection, vortex shedding, local similarity, characteristic temperature

Publ.-Id: 6571 - Permalink


In-situ conformational analysis of fibrinogen adsorbed on Si surfaces
Tunc, S.; Maitz, M. F.; Steiner, G.; Vázquez, L.; Pham, M. T.; Salzer, R.;
Fibrinogen is a major plasma protein. Previous investigations of structural changes of fibrinogen due to adsorption are mostly based on indirect evidence after its desorption, whereas our measurements were performed on fibrinogen in its adsorbed state. Specific enzyme linked immunosorption experiments showed that the amount of adsorbed fibrinogen increased as the surface became more hydrophobic. AFM investigations revealed the trinodular shape of fibrinogen molecules adsorbed on hydrophilic surfaces, whereas all of the molecules appeared globular on hydrophobic surfaces. The distribution of secondary structures in adsorbed fibrinogen was quantified by in-situ FTIR analysis. Substrates of identical chemical bulk composition but different surface hydrophobicity permit direct comparison among them. Adsorption properties of fibrinogen are different for each degree of hydrophobicity. Although there is some increase of turn structure and decrease of β-sheet structure, the secondary structure of adsorbed fibrinogen on hydrophilic surface turned out to be rather similar to that of the protein in solution phase with a major α-helix content. Hydrophilic surfaces exhibit superior blood compatibility as required for medical applications.
Keywords: Silizium, Protein, Fibrinogen, Adsorption, Konformation, AFM, FTIR
  • Colloids and Surfaces B: Biointerfaces, 42(2005)3-4, 219-225

Publ.-Id: 6569 - Permalink


Experimental Evidence of Si Nanocluster delta-Layer Formation in the Vicinity of Ion-Irradiated SiO2-Si Interfaces
Röntzsch, L.; Heinig, K. H.; Schmidt, B.; Mücklich, A.;
Predictions on formation and self-alignment of Si nanocrystals (NCs) at ion-irradiated SiO2-Si interfaces have been proven by cross-section transmission electron microscopy (TEM). The model is based on ion-mixing of SiO2-Si interfaces resulting in a region of SiOx (x<2). During annealing, the interface restores and in the tail of the mixing profile Si excess precipitates and forms a self-aligned layer
of Si NCs in SiO2. This Si NC delta-layer structure can hardly be observed by conventional TEM techniques due to the very low mass contrast of tiny Si NCs embedded in SiO2. Here, a contrast enhancing method is presented based on alloying of these Si NCs with Ge. For this purpose, a thin Ge layer is embedded into the oxide sufficiently far from the interface mixing range, thus, preventing interference with the Si precipitate formation. During annealing, diffusing Ge monomers attach to the Si NCs, mainly due to the energetically favored Si-Ge bond, resulting in Si1-xGex NCs with an enhanced mass contrast in TEM.
Keywords: SiO2-Si interface; ion irradiation; phase separation; silicon; nanocrystal; self-alignment
  • Poster
    14th International Conference on Ion Beam Modification of Materials, 05.-10.09.2004, Monterey, USA
  • Nuclear Instruments and Methods in Physics Research B 242(2006), 149-151

Publ.-Id: 6565 - Permalink


Renormalization of the Two-Photon Vacuum Polarization and the Self Energy Vacuum Polarization for a Tightly Bound Electron
Zschocke, S.; Plunien, G.; Soff, G.;
The renormalization method of Bogoljubov-Parasuik-Hepp-Zimmermann (BPHZ) is used in order to derive the renormalized energy shift due to the gauge invariant Källén-Sabry diagram of the two-photon vacuum polarization (VPVP) as well as the self energy vacuum polarization S(VP)E beyond the Uehling approximation. It is outlined, that no outer renormalization is required for the two-photon vacuum polarization and that only the inner renormalization has to be accomplished. It is shown that the so-called nongauge invariant sourious term is absent for a wide class of vacuum polarization (VP) diagrams if one applies the widely used sherical expansion of bound and free-electron propagator. This simplifies significantly calculations in bound state quantum electrodynamis. As one result of our paper the use of the BPHZ-approach in bound state QED is established.

Publ.-Id: 6564 - Permalink


An Electromagnetic Undulator for the Far Infrared at ELBE
Dekorsy, T.; Fahmy, K.; Grosse, E.; Michel, P.; Seidel, W.; Wolf, A.; Wünsch, R.;
The parameters of an envisaged undulator at the radiation source ELBE for the production of IR radiation up to 150 microns are presented.
  • Poster
    Poster, 26th Int. Free-Electron Laser Conf. and 11th FEL Users Workshop, Trieste, 29.08.-3.09.2004
  • Open Access LogoContribution to proceedings
    26th International Free-Electron Laser Conference and 11th FEL Users Workshop, 29.08.-03.09.2004, Trieste, Italy
    Proceedings of the 26th International Free-Electron Laser Conference and 11th FEL Users Workshop, 389-391

Publ.-Id: 6563 - Permalink


Ion-induced stress relaxation during the growth of cubic boron nitride thin films
Abendroth, B.;
  • Open Access LogoWissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-406

Downloads:

Publ.-Id: 6560 - Permalink


Modification of magnetic thin films and nanostructures by ion irradiation and implantation
Fassbender, J.ORC
He ion irradiation in an applied magnetic field allows to tailor the magnetic properties of thin films and nanostructures after preparation due to structural phase transformations, interfacial mixing, chemical ordering and magnetic ordering. Some examples for the case of exchange bias films, soft magnetic films and FePt nanoparticles will be demonstrated.
In addition ion implantation can be used for the doping of magnetic materials to modify the Curie temperature, the saturation magnetization or the magnetic damping behavior of ferromagnetic films. First results of these ion implantation studies will be presented.
Keywords: magnetism, magnetic films, nanoparticles, ion irradiation, ion implantation
  • Lecture (others)
    Seminar talk: Hitachi Almaden, San Jose, USA, 08.10.2004

Publ.-Id: 6557 - Permalink


Maßgeschneiderte magnetische Materialien – neue Wege durch Ionenbestrahlung
Fassbender, J.ORC
Aufgrund der reduzierten Dimensionen in ultradünnen magnetischen Schichten und Nanopartikeln hängen die magnetischen Eigenschaf-ten, wie z. B. magnetische Anisotropien und Austauschkopplung, empfindlich von der Grenzflächen- bzw. Oberflächenmorphologie ab. Zusätzlich werden chemisch geordnete intermetallische Verbindungen zunehmend anwendungsrelevant. In beiden vorgenannten Bereichen bietet die Ionenbestrahlung eine exzellente Möglichkeit nach der Prä-paration die magnetischen Eigenschaften gezielt auf einer lokalen Skala zu beeinflussen. Somit lässt sich eine rein magnetische Na-nostrukturierung ohne Veränderung der Oberflächentopographie reali-sieren.
Der Vortrag gibt eine Übersicht über die neuen Möglichkeiten mit Hilfe der Ionenbestrahlung künstliche magnetische Strukturen herzustellen und ordnet diese im Bezug auf deren Anwendungsrelevanz ein.

Keywords: magnetism, ion irradiation
  • Lecture (others)
    Physikalisches Kolloquium TU Dresden

Publ.-Id: 6556 - Permalink


Reflectivity characterization of ion irradiated exchange bias FeMn-FeNi films
Solina, D.; Liedke, M. O.; Tietze, U.; Fassbender, J.ORC; Schreyer, A.
X-ray reflectivity, neutron reflectivity studies and Magneto-Optic Kerr Effect measurements (MOKE) have been carried out on thermally evaporated FeMn-FeNi exchange biased films before and after ion irradiation by helium ions. MOKE shows that ion irradiation reduces the exchange bias characteristics of the samples with increased dose. Modelling of the reflectivity data infers that atoms from the buffer layer are displaced by the ions and imbedded into the substrate material. The correlation between these strong structural modifications by irradiation with the reduction of the exchange bias will be discussed.
Keywords: magnetism, magnetic films, exchange bias, x-ray diffraction, neutron scattering
  • Journal of Magnetism and Magnetics Materials 286(2005), 225

Publ.-Id: 6555 - Permalink


Analysis of theNi81Fe19/Fe50Mn50 exchange bias system with a varying Cu spacer thickness and position for partial decoupling
Liedke, M. O.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
In order to study the role of the exchange interaction at and near the interface, Ni81Fe19/Fe50Mn50 bilayers have been studied, which have an intervening layer of varying thickness and position in the antiferromagnetic Fe50Mn50 layer. The role of the intervening layer is to generate partial exchange decoupling. As a result, samples were obtained, where in one in-plane direction the position of the intervening layer varies from the interface to the top surface of the Fe50Mn50 layer at a constant intervening layer thickness, and in the other in-plane direction the intervening layer thickness varies. Two-dimensional maps of the resulting exchange bias field and the coercive field were obtained from magneto-optic Kerr effect magnetometry measurements. The role of the position and strength of the partial decoupling within the antiferromagnetic layer on the exchange bias effect and the coercive field is discussed.
Keywords: magnetism, magnetic films, exchange bias, antiferromagnets, exchange coupling
  • Journal of Magnetism and Magnetic Materials 290-291(2005)1, 588-590

Publ.-Id: 6554 - Permalink


Modified Gilbert Damping due to Exchange Bias in NiFe/FeMn Bilayers
Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
A picosecond all-optical pump-probe technique is used to investigate magnetization dynamics and magnetic damping behaviour in the Ni81Fe19/Fe50Mn50 exchange bias system. Within the laser excitation the spin temperature is elevated resulting in a collapse of the exchange bias field. Thus, a fast anisotropy field pulse is launched which triggers the magnetization precession. The extracted Gilbert damping increases linearly with the exchange bias field magnitude which can be understood taking local fluctuations of the interfacial exchange coupling as an additional dissipation mechanism into account.
Keywords: magnetism, magnetic films, exhange-bias, magnetic damping, pump-probe, time-resolved
  • Journal of Applied Physics 97(2005), 10A701

Publ.-Id: 6552 - Permalink


Real time temperature dynamics in exchange biased bilayers upon laser excitation
Weber, M.; Nembach, H.; Hillebrands, B.; Fassbender, J.ORC
A hot spin and phonon gas in exchange biased metallic bilayers is induced by an 8.5 ps laser excitation. The spin-lattice temperature dynamics is sensed in real time by the time evolution of the exchange bias field on the picosecond timescale. A calibration with temperature dependent quasistatic Kerr measurements explains a pump pulse induced temperature increase of about 100°C at the interface. Upon photoexcitation the exchange coupling across the interface between the ferromagnetic and antiferromagnetic layer is reduced within the first 10 ps, leading to a reduction of the bias field to about 50% of its initial value. The fast thermal unpinning of the exchange coupling is followed by a heat diffusion dominated recovery with a relaxation time on the order of 160 ps. A heat transport analysis reveals the diffusivity of the studied bilayer system.
Keywords: magnetism, magnetic films, time-resolved MOKE, exchange-bias, pump-probe
  • IEEE Transactions on Magnetics 41(2005)3, 1089-1092

Publ.-Id: 6551 - Permalink


Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high- and low- pressure ion nitriding processes
Ueda, M.; Gomes, G.; Abramof, E.; Reuther, H.;
Ion nitriding is an important surface modification technique used routinely in the advanced technology industries aiming at producing high added value components with increased hardness and wear resistance. To further improve the performance of critical-part components, new methods for surface strengthening are being developed with success, like plasma immersion ion implantation (PIII) and hybrid surface treatments combining PIII and ion nitriding. In particular, a combination of high-pressure (40 Pa), high-temperature (up to 450 degreesC) glow discharge nitriding with low-pressure (8 x 10(-2) Pa) ion nitriding was implemented. Analysis of the SS304 samples treated by this hybrid method was carried out using the technique of grazing incidence X-ray diffraction (GIXRD) and the results were supported by both normal XRD and AES (Auger electron spectroscopy) measurements. Depending on the particular conditions of the treatment and the depth probed, mixed phases Of gamma(N), and gamma were measured. The improvement in hardness of the obtained surfaces (up to a factor of 2.7) was also in accordance with the results of other analysis.

Publ.-Id: 6550 - Permalink


Surface modification of metal alloys by plasma immersion ion implantation and subsequent plasma nitriding
Kostov, K. G.; Ueda, M.; Lepiensky, A.; Soares, P. C.; Gomes, G. F.; Silva, M. M.; Reuther, H.;
Thermal or radiation enhanced diffusion of nitrogen are extensively utilized for the surface hardening of metallic components. Plasma-immersion ion implantation (PIII) is a newly developed technology, which provides ion implantation at moderate energy (10-50 keV), and thereby allowing penetration depths deeper than the surface oxide barrier. The damage caused by ion implantation together with the surface sputtering may create favorable boundary conditions for an efficient subsequent diffusive treatment such as nittiding. Surface modification of aluminum alloy 5052, Ti6A14V alloy and steels (AISI 304 and H13) by a combination of PIII and plasma nitriding (PN) has been investigated. Nitrogen ions were implanted into specimens at 15 W and then ion nitrided at low pressure with bias of - 800 V. Compared to the untreated samples the hardness of Ti6Al4V alloy and AISI 304 steel could be improved significantly. The hardness of H13 steel can be increased by 20+ACU- using a duplex process with 4-h nitriding time. X-ray diffraction (XRD) results have shown some structural modification of the metallic samples and formation of a double-layer structure in AISI 304, treated by PIII and PN. Nitrogen depth profile of the same stainless steel sample, obtained by Auger electron spectroscopy (AES), shows two rather well-defined nitrogen enriched regions with different N contents: high (25-30 at.+ACU-) in a surface layer and medium (similar to 10+ACU-) in a subsurface layer.

Publ.-Id: 6549 - Permalink


Use of low energy and high frequency PBII during thin film diposition to achieve relief of intrinsic stress and microstructural changes
Bilek, M. M. M.; Mckenzie, D. R.; Möller, W.;
In this paper, we describe the use of plasma based ion implantation (PBII) together with physical vapour deposition (PVD) to achieve low intrinsic stress and influence the microstructure of coatings. A model is proposed to explain the physical mechanisms responsible for observed changes in stress. The model is compared with other available models and all are tested against data obtained using a cathodic vacuum arc in background gas to deposit aluminium nitride, titanium nitride and carbon in the presence of high voltage pulsed bias on the substrate. In all three systems, application of PBII resulted in large reductions in intrinsic stress as the voltage and frequency of the pulses was increased. We observed a trade off between applied bias voltage and pulsing frequency. The crystalline systems, aluminium nitride and titanium nitride showed changes in preferred orientation in PBII treated films. An important conclusion of significance to industry is that even relatively low energy (0.5¿5 keV) ion implantation can be effectively employed to achieve stress relief.
Keywords: Intrinsic stress; Plasma immersion ion implantation; Deposition

Publ.-Id: 6548 - Permalink


Stability of the N=50 shell gap in the neutron-rich Rb, Br, Se, and Ge isotones
Zhang, Y. H.; Podolyàk, Z.; de Angelis, G.; Gadea, A.; Ur, C.; Lunardi, S.; Marginean, N.; Rusu, C.; Schwengner, R.; Kröll, T.; Napoli, D. R.; Menegazzo, R.; Bazzacco, D.; Farnea, E.; Lenzi, S.; Martinez, T.; Axiotis, M.; Tonev, D.; Gelletly, W.; Langdown, S.; Regan, P. H.; Valiente Dobon, J. J.; von Oertzen, W.; Rubio, B.; Quintana, B.; Medina, N.; Broda, R.; Bucurescu, D.; Ionescu-Bujor, M.; Iordachescu, A.;
The low- and medium-spin states of the N = 50 neutron-rich, 3787Rb, 3585Br, 3484Se and 3282Ge isotones have been populated in deep-inelastic processes produced by the interaction of 460 MeV 82Se ions with a 192Os target. The subsequent gamma decay has been investigated at the Laboratori Nazionali di Legnaro using the GASP gamma-ray detector array. The comparison of the experimentally observed excited states with shell-model calculations performed with and without neutron degrees of freedom has allowed the investigation of the role of the neutron-core breaking excitations and therefore of the N = 50 shell gap. The inclusion of neutron configurations in the shell-model calculations results in an improved agreement between the experimental and calculated level energies at medium and high spin. These results highlight the considerable contribution of neutron-core particle-hole excitations across the N = 50 shell gap to the level configurations. The overall agreement of the measured excited states with the shell-model predictions is indicative of the persistence of the N = 50 shell gap down to Z = 32.
Keywords: nuclear shell model; gamma-ray spectra; deep inelastic heavy ion reactions; nuclei with mass number 190 to 219; nuclear spin; nuclear energy level transitions; high spin states; nuclei with mass number 59 to 89

Publ.-Id: 6547 - Permalink


Ion Irradiation through SiO2/Si-interfaces: Non-conventional Fabrication of Si Nanocrystals for memory applications
Schmidt, B.; Heinig, K.-H.; Röntzsch, L.; Müller, T.; Stegemann, K.-H.; Votintseva, E.;
Si nanocrystals for multi-dot floating-gate memories have been produced by non-conventional ion beam synthesis (IBS). Due to ion beam mixing irradiation with 1015-1016 Si+ cm-2 at 50-100 keV through 50 nm poly-Si and 15 nm SiO2 on (001)Si results in a considerable Si excess within the oxide. At the upper and lower interfaces of the gate oxide, this ion irradiation forms a metastable SiOx (x < 2) composition. Post-irradiation RTA thermal treatment leads to phase separation into Si and SiO2. Adjacent to the recovering interfaces, narrow SiO2 zones become denuded of excess Si. More distant excess Si precipitates as Si NCs in the gate oxide. MOSFET characteristics in terms of write/erase voltage, duration of the programming time, endurance and retention have been evaluated.
Keywords: nanocluster, ion irradiation, phase separation, non-volatile multi-dot floating-gate memory
  • Lecture (Conference)
    14th Int. Conf. on Ion Beam Modification of Materials (IBMM 2004), September 5-11, 2004, Monterey, California, USA
  • Nuclear Instruments and Methods in Physics Research B 242(2006)1-2, 146-148

Publ.-Id: 6546 - Permalink


Nitrogen Transport in the Primary Circuit of a VVER during a LOCA occurring under Plant Cool-down Conditions
Prasser, H.-M.; Baranyai, G.; Böttger, A.; Ezsöl, G.; Guba, A.; Perneczky, L.; Toth, I.; Zschau, J.;
The paper presents the results of a thermal hydraulic experiment conducted at the PMK-2 test facility in the frame of the IMPAM-VVER project. The test was dedicated to a scenario assuming a loss-of-coolant event dur-ing the cool-down phase of the plant, when neither core flooding tanks nor safety injections systems are available by an automatic action. This may lead to core heat-up in case of a larger LOCA. The assumed break size in the test was 30%. The experiment has shown that an overheat of the fuel rod cladding occurs. Finally, one of four lines of the low pressure ECC injection system is sufficient to handle the situation and to cool down the reactor safely. A speciality of the scenario is the fact that the primary circuit is pressurised with nitrogen. In the course of the transient, non-condensable gas can enter the primary circuit from the pressurizer during the blow-down phase. In order to study the transport of the nitrogen along the primary circuit, the test facility PMK-2 was equipped with a novel type of probe: a local void probe equipped with an integrated micro-thermocouple. The new probes delivered a global picture of the process. Nitrogen coming from the pressurizer after its depletion enters the circuit via the surge line and turns first in the direction of the main coolant flow towards the steam generator and finally towards the break in the cold leg. However, nitrogen is also moving in the opposite direc-tion and reaches the reactor outlet and enters even the upper plenum of the reactor closely after the main circulation pump has stopped. RELAP5 was found to be able to predict the behaviour of the non-condensable gas in the primary circuit. Despite of some delay in the prediction of the time of the appearance of the gaseous phase in the begin of the process, most details of the transient were reproduced by the calculation with a good accuracy.
Keywords: pressurized water reactors, loss-of-coolant transients, VVER, nitrogen transport, void probes, RELAP
  • Kerntechnik 69(2004)4, 167

Publ.-Id: 6545 - Permalink


Long-time operation of a modified Cs sputter ion source 860-C
Friedrich, M.; Tyrroff, H.;
The modified Rossendorf Cs sputter ion source 860-C presented at the SNEAP 2002 [1] was opened in July 2004 for maintenance after 4100 operation hours. The main reason for this first source opening after its installation in July 2002 was a short circuit of the sputter voltage due to material deposition on the cathode insulator. Beside the long lifetime the modification of the source has resulted in a reduced erosion of the spherical ioniser and in a concentrated deposition of the sputtered material on the front side of the additional shielding electrode and on the cathode-shielding electrode. After cleaning all inner source parts can be reused in the ion source.

[1] M. Friedrich and H. Tyrroff, Nucl. Instr. and Meth. B 201 (2003) 645.

Keywords: Ion sources; Negative ions; Electrostatic accelerators
  • Lecture (Conference)
    SNEAP-2004, Hamilton/Ontario, Canada
  • Contribution to external collection
    Proceedings of SNEAP-2004, Hamilton/Ontario, Canada, 2005 (auf CD)

Publ.-Id: 6544 - Permalink


RBS with high depth resolution using small magnetic spectrometers
Grötzschel, R.; Klein, C.; Mäder, M.;
The increasing importance of ultra-thin layers for novel technologies demands quantitative analysis techniques with a depth resolution of atomic monolayers, which can be obtained for RBS and ERDA by magnetic spectrometers.

We operate at the 3 MV Tandetron accelerator a magnetic spectrometer consisting of an UHV scattering chamber and a simple dipole magnet with circular field boundaries (Browne¿Buechner spectrometer). Since in many cases of high resolution ion beam analysis the samples must be prepared in situ in UHV, the chamber with a base vacuum of 4 × 10-10 mbar is equipped with an ion sputter gun and two low rate e-beam evaporators for in situ layer deposition. A RHEED system is used to check the surface reconstruction and monitor the layer growth. Samples are transferred, together with a BN heater, to the precision 5-axes channelling goniometer. The magnet with a mean radius of 0.65 m is mounted vertically and can be positioned either at 35.5° or 144.5°. The backward position offers the advantage of a high mass resolution, but the Rutherford cross sections are a factor of about 100 lower than at the forward angle, which is the preferred position if kinematically possible.

At the 5 MV tandem accelerator a QQDS magnetic spectrometer is being installed. The facilities for in situ sample preparation in UHV are similar. These spectrometers are described in detail and recent applications are discussed.

Publ.-Id: 6542 - Permalink


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