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35810 Publications

Colloid-borne uranium in an abandoned uranium mine in the stage of flooding

Ulrich, K.-U.; Zänker, H.; Jenk, U.

Abandoned uranium mines which underwent or just undergo flooding may represent a severe source of radioactive contaminants against groundwater, surface water, and the atmosphere. The uranium mines operated until 1990 in Saxony and Thuringia left a total void volume of more than 100 million m3 to be flooded. Prognosis of radionuclide emission via the water path needs detailed knowledge about the hydrological regime of the mine and the speciation of the contaminants. The adsorption of radionuclides on colloidal phases may stimulate or delay their transport and migration. Neglecting the colloidal phases may have the following consequences on environmental hazard prognosis:
a) The radionuclide is fully mobile, i.e. it is not adsorbed onto solid phases: colloidal transport is irrelevant and the model description is correct.
b) The radionuclide is regarded as fully mobile in the model, but it adsorbs on colloids which aggregate and settle (‘natural attenuation’): the prognosis is too pessimistic.
c) The radionuclide is regarded as immobile in the model due to adsorption on the host rock, but in part it adsorbs on colloids which are transported: the prognosis is too optimistic.
Based on their chemical and colloidal composition, mine waters usually range between the following water types:
i) Type ‘acid pore water’ (acid rock or mine drainage, sometimes called ‘yellow boy’): Very acidic (pH 1-3) and usually anoxic waters with a high salt loading.
ii) Type ‘bulk water’: Near-neutral, oxic or suboxic waters with a moderate salt loading, typically represented by gallery or adit water.
Mine flooding is accompanied with a transition of type (i) into type (ii) water, which is crucial for colloid-chemical processes changing the partitioning of heavy metals and radionuclides. Due to pH increase and access of oxygen, colloids of Fe(III) and Al compounds are formed known to adsorb trace metals.
To assess the uranium migration in the stage of flooding and afterwards, we performed neutralization experiments by mixing acid floodwater from an uranium mine with oxic groundwater from an aquifer above the mine and studied the formation and composition of colloids as well as the adsorption of uranium onto these colloids by using spectroscopic methods.

Keywords: mine flooding; acid mine drainage; groundwater; neutralization experiment; uranium mobility; adsorption; colloids; ironoxyhydroxides; ferrihydrite; tangential flow ultrafiltration; XAFS spectroscopy

  • Contribution to external collection
    Qaim, S.M., Coenen, H.H. (Eds.), Advances in Nuclear and Radiochemistry, Extended Abstracts of NRC 6, Schriften des Forschungszentrums Jülich, Reihe Allgemeines und Interdisziplinäres 3(2004), 645-647
  • Lecture (Conference)
    Sixth International Conference on Nuclear and Radiochemistry (NRC 6), 29.08.-03.09.2004, Aachen, Germany

Publ.-Id: 6052

Capability of SCM and RES3T Database for Blind Predictions

Richter, A.; Brendler, V.

The paper presents the general strategy and an example for the current blind predictive capabilities of surface complexation models (SCM) and the respective database RES3T - the "Rossendorf Expert System for Surface and Sorption Thermodynamics"[1]. The approach for the elucidation of numerical data includes the collection of the mineral surface characteristics, the selection of reliable data records, the extrapolation to infinite dilution, the normalization to a reference site density and the averaging of selected thermodynamic data records.
The copper(II) sorption onto goethite was chosen as system illustrating the blind predictive capabilities. To keep the number of parameters at a minimum, the Diffuse Double Layer model was selected accounting for electrostatics. The calculations were performed with FITEQL code [2].
The model prediction represents the experimental values for the adsorbed amount of Cu(II), expressed as conventional distribution coefficients KD as required by most performance assessment software, within one order of magnitude or better.

  • Lecture (Conference)
    SOPRO 2004, 25.-26.03.2004, Karlsruhe, Germany
  • Contribution to proceedings
    SOPRO 2004, 25.-26.03.2004, Karlsruhe, Germany
    Proceedings, 127-131

Publ.-Id: 6051

Multi-Dot Floating-Gates in MOSFETs for Nonvolatile Memories - Their Ion Beam Synthesis and Morphology

Müller, T.; Bonafos, C.; Heinig, K.-H.; Tencé, C.; Coffin, H.; Cherkashin, N.; Ben Assayag, G.; Schamm, S.; Zanchi, G.; Colliex, C.; Möller, W.; Claverie, A.

Scalability and performance of current flash memories can be improved substantially by novel devices based on Multi-Dot Floating Gate MOSFETs. The multi-dot layer in the very thin gate oxide can be fabricated CMOS-compatibly by ion beam synthesis (IBS). Here, we present both experimental and theoretical studies on IBS of multi-dot layers consisting of Si nanocrystals (NCs). The NCs are produced by ultra low energy Si ion implantation, which causes a high Si supersaturation in the shallow implantation region. During post-implantation annealing, this su-persaturation leads to phase separation of the excess Si from the SiO₂. Till now, the study of this phase separation suffered from the weak z contrast between Si and SiO₂ phases in Transmission Electron Microscopy (TEM). Here, this imaging problem is solved by Energy Filtered Scanning Transmission Electron Microscopy (EFSTEM). Additionally, kinetic lattice Monte Carlo simula-tions of Si phase separation have been performed and compared with EFSTEM images. It has been predicted theoretically that the morphology of the multi-dot Si floating gate changes with increasing ion fluence from isolated, spherical NCs to percolated spinodal Si pattern. These pat-tern agree remarkably with EFSTEM images. However, the predicted fluence for spinodal pattern is lower than the experimental one. Because oxidants of the ambient atmosphere penetrate into the as-implanted SiO₂, a substantial fraction of the implanted Si is lost due to oxidation.

Publ.-Id: 6050

Angewandte Medieninformatik: Workshop Digitale Fotografie

Joehnk, P.

  • Lecture (others)
    Hochschule Anhalt, Köthen, Fachbereich Informatik gehalten am 20.1.2004

Publ.-Id: 6049

Control of Separated Flows by Time Periodic Lorentz Forces

Weier, T.; Gerbeth, G.

Electromagnetic, i.e. Lorentz forces, may be used to influence the flow of electrically conducting fluids. The present paper investigates the application of time periodic Lorentz forces to the control of the suction side flow on a NACA 0015 hydrofoil.
Experimental results, consisting of flow visualizations and force measurements, characterizing the control effect in the low Reynolds number range of 10^4 < Re < 10^5, are presented. A comparison of the forcing effect with stationary Lorentz forces on one hand and conventional oscillatory blowing on the other hand is given as well.

  • European Journal of Mechanics B23(2004)6, 835-849

Publ.-Id: 6048

Non-normal nonlinear transition to turbulence in a magnetically driven swirling flow

Grants, I.; Gerbeth, G.

It is well-known that several shear flows become turbulent far below their linear stability limit. The transition to turbulence is triggered by unavoidable finite-amplitude disturbances. Although all infinitesimal disturbances eventually decay, their amplitude can grow temporarily. The lower limit of the control parameter when the amplitude of disturbances can grow initially is called limit of energetical instability [1]. As a rule, this limit considerably underestimates the threshold when the transition to turbulence is observed experimentally in various shear flows. Only recently certain clues of theoretical prediction of the phenomenon of non-linear non-normal transition have been found [2]. However, a routine method to predict this so-called non-normal non-linear transition is still a challenge.
We consider the flow of an electrically conducting melt driven by a rotating magnetic field (RMF) in a cylindrical cavity. Our numerical analysis evidenced that the intermittency route may take place also for this example of a rotating flow [3]. A pronounced flow sensitivity and additional unstable saddle type steady solutions have been detected at control parameters several times below the critical value for the onset of linear axisymmetric instability. The presence of such additional solutions is a sign of a possible non-linear non-normal transition due to finite perturbations despite the linear stability of the basic flow.
We present experimental and numerical results for the transition to turbulence in the RMF driven flow in a cylindrical cavity. The experimental approach is based on a non-invasive examination of the sensitive flow field by hanging the cavity on a torsion wire [4]. Under carefully prepared, clean conditions the occurrence of first flow oscillations was observed at a control parameter close to the linear stability threshold. If an artificial perturbation like a thermocouple was installed at the inner cavity wall, the transition was observed at a considerably lower forcing in the linearly stable parameter range. Examples of the typically intermittent onset of transition will be given. The numerical results will comprise the linear stability analysis based on a highly accurate spectral method and, in particular, the investigation of additional unstable steady solutions. Current evidence suggests that the lowest possible control parameter for the non-linear transition may be reasonably associated with the first bifurcation of such solutions. Indeed, a good quantitative agreement was found between experiments and numeric for the value of this global stability threshold.
Further results will be presented for the linear as well as global stability limits if the RMF driven flow in the cylinder is additionally exposed to a heating from below or a superimposed steady magnetic field. The latter typically delays the transition. The stability analysis of such flows is of particular interest in crystal growth technologies from the melt, for which the occurrence of a turbulent flow should often be prevented.

[1] D. D. Joseph, Stability of Fluid Motions Vol. I, Springer, Berlin, 1976.
[2] S. Grossmann, The onset of shear flow turbulence, Rev. Mod. Phys. 72, 603, 2000.
[3] I. Grants, G. Gerbeth, Stability of axially symmetric flow driven by a rotating magnetic field in a cylindrical cavity, J. Fluid Mech. 431, 407, 2000.
[4] I. Grants, G. Gerbeth, Experimetal study of non-normal nonlinear transition to turbulence in a rotating magnetic field driven flow, Phys. Fluids 15, 2803, 2003.

  • Lecture (Conference)
    10th European Turbulence Conference, 29.06.-02.07.2004, Trondheim, Norway
  • Contribution to proceedings
    10th European Turbulence Conference, 29.06.-02.07.2004 Trondheim, Norway, H.I. Andersson, P.-A. Krogstad (Eds.): Advances in Turbulence X, 161-164

Publ.-Id: 6047

Depth profiling of ZrO2/SiO2/Si stacks - a TOF-SIMS and computer simulation study

Ignatova, V. A.; Conard, T.; Möller, W.; Vandervorst, W.; Gijbels, R.

This study is dedicated to a better understanding of the processes occurring under ion bombardment of ultra-thin ZrO2/SiO2/Si gate dielectric stacks. Complex-shaped depth profiles were obtained by using TOF-SIMS with dual beam (500 eV for sputtering and 10 keV for analysis) Ar+ ions. The SIMS intensities of all the elements depend critically on the amount of oxygen at any moment of the sputtering process. Increased intensity is observed at the surface and at the ZrO2/SiO2 interface. A long tail of the Zr signal is present in the Si substrate, even after the second (SiO2/Si) interface, and a double bump structure in the 90Zr and ZrO dimer is observed, which is more pronounced with increasing thickness of the interfacial SiO2 layer.

Computer simulations using the dynamic Monte Carlo code (TRIDYN) are performed in order to distinguish the ion-bombardment-induced effects from changes in the ionization degree. The original code is extended with simple models for the ionization mechanism and for the molecular yield during sputtering. Oxygen preferential sputtering at the surface and ballistic transport of Zr towards and through the interface are clearly demonstrated, but there is also evidence that due to recoil implantation oxygen gets piled-up near the ZrO2/SiO2 interface.

Publ.-Id: 6046

Intrinsic stress and preferred orientation in TiN coatings deposited on Al using plasma immersion ion implantation assisted deposition

Mukherjee, S.; Prokert, F.; Richter, E.; Möller, W.

TiN coatings were deposited on Al substrates using the plasma immersion ion implantation and deposition (PIIIAD) technique, employing a filtered Ti cathodic arc in a nitrogen atmosphere. Negative pulsed bias voltages between 0 to –4.0 kV were applied with varying duty cycles, at a constant time-averaged bias. Stress measurements using X-ray diffraction reveal an increase and then a decrease in the intrinsic compressive stress at increasing on-time bias. A bias dependent preferred orientation of TiN is observed i.e., {111}, {200} and {220} at low bias and predominantly {200} at higher bias. The hardness reduces from 29 GPa at lower bias to 20 GPa at higher bias. Thus, the time averaged energy of ion bombardment does not uniquely determine the properties of the growing coating, which can be adjusted by the on-time substrate bias applied for very short durations. A subplantation model of stress development is applied to explain the results.

Publ.-Id: 6045

Neptunium(V) sorption onto granite and its mineral constituents in the absence and presence of humic acid

Schmeide, K.; Bernhard, G.

The sorption of neptunium(V) onto granite and its main mineral constituents quartz, orthoclase, albite, biotite, and muscovite is studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. Furthermore, the effect of humic acid on the neptunium(V) sorption is studied applying a 14C-labeled synthetic humic acid (type M42) for the experiments. The data suggest that the neptunium sorption onto granite is affected by both the pH and the presence of organic material. In the absence of humic acid, the neptunium sorption starts between pH 7 and pH 8 and increases with increasing pH value. Due to addition of humic acid the neptunium sorption onto granite is decreased in the neutral to alkaline pH range, which is attributed to complexation of neptunium by humic acid in solution. Thus, in this pH range the neptunium mobility is increased by humic substances. The neptunium(V) sorption onto granite and onto its mineral constituent biotite is nearly equal, suggesting that the sorption of neptunium(V) is controlled by the minor amount of biotite which, however, is reactive.

Keywords: neptunium; humic acid; sorption; reduction

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Wissenschaftliche Berichte FZKA 6969, Forschungszentrum Karlsruhe, Karlsruhe 2004, 85-94

Publ.-Id: 6044

Comparative Study of Charge Trapping in High-Dose Si and Ge-Implanted Al/SiO2/Si Structures

Nazarov, A.; Skorupa, W.; Osiyuk, I. N.; Tjagulskii, I. P.; Lysenko, V. S.; Yankov, R. A.; Gebel, T.

We have studied the trapping of negative and positive charge in Si-implanted SiO2 layers of Al/SiO2/Si-based devices during high-field electron injection from the Si substrate under conditions typically used for obtaining electroluminescence. The location, capture cross-section and concentration of negatively and positively charged traps have been determined in dependence on the time of heat treatment by rapid thermal annealing (RTA). A comparison between the results obtained from Si- and Ge-implanted oxide layers has been made. It has been shown that in the case of Si-rich oxides an increase in the RTA time leads to the formation of hole and electron traps of high concentration, both of which are located within the oxide. For Ge-rich oxide layers, however, the hole traps are found primarily in the vicinity of the SiO2/Si interface while the electron traps are present within the oxide. The nature of these traps has been discussed.

Keywords: charge trapping; ion implantation; silicon; germanium; electroluminescence; silicon dioxide; trapping cross section

  • Journal of the Electrochemical Society 152(2005)2 F20

Publ.-Id: 6042

Comparison of two HSV1-tk-based approaches for PET of cardiac transgene expression

Miyagawa, M.; Simoes, M. V.; Städele, C.; Haubner, R.; Reder, S.; Lehner, T.; Noll, S.; Noll, B.; Grote, M.; Gambhir, S. S.; Gansbacher, B.; Schwaiger, M.; Anton, M.; Bengel, F. M.

Objectives: PET imaging of cardiac reporter gene expression holds promise for noninvasive monitoring of gene therapy. Two approaches based on herpesviral thymidine kinase gene(HSV1-tk) habe been applied. Wild-type HSV1-tk was imaged with 2´-fluoro-2´-deoxy-5[124I]-iodo-arabinofuranosyluracil([124I]FIAU), and mutant HSV1-sr39tk was imaged with 9-[4-[18F]-fluoro-3-(hydroxymethylbutyl)guanine([18F]FHBG).
Methods: Adenovirus expressing wild-type HSV1-tk(Adtk), mutant HSV1-sr39tk (Adsr39tk), or control gene (AdLacZ) were directly injected into myocarcardium of 24 rats and 8 pigs. Two days later, dynamic PET imaging was performed for 120 min after injection of [124I]FIAU or [18F]FHBG with a clinical scanner. Imaging with [13N]-ammonia was performed to identify cardiac regions of interest. Pig hearts were sliced into 5 short-axis slices for ex vivo imaging, and regional tracer uptake was analyzed.
Results: For [124I]FIAU, the largest difference of cardiac uptake between Adtk rats and controls was found at 10-30 min after injection (1.7±0.25 vs 0.87±0.22 %dose/ml, p=0.035). No difference was observed at later imaging times due to [124I]FIAU washout. For [18F]FHBG, difference between Adsr39tk rats and controls continuously increased over time and was largest at 105-120 min (1.45±0.45 vs 0.35±0.05 %dose/ml, P=0.0066). Global cardiac reporter probe kinetics in rats was confirmed by regional myocardial analysis in pigs. Transgene expression was specifically visualized by both approaches. Highest target/background ratio of [124I]FIAU in Adtk infected myocardium was 1.50±0.20 vs 2.64±0.49 for [18F]FHBG in Adsr39tk infected areas (P=0.01). In vivo results of rats were confirmed by ex vivo counting and autoradiography. In vivo segmental reporter probe uptake in pigs correlated well with those in ex vivo images.
Conclusions: Both combinations were feasible for PET of cardiac transgene expression in different species. Specific probe kinetics suggests different myocardial handling of pyrimidine ([124I]FIAU) and acycloguanosine ([18F]FHBG) derivatives. Results are in favour of [18F]FHBG because of continuous accumulation over time and higher imaging contrast.

  • Lecture (Conference)
    51st Annual Meeting, Society of Nuclear Medicine Philadelphia, 19.-23.06. 2004, Philadelphia, USA

Publ.-Id: 6041

Coexpression of Herpesviral Thymidine Kinase Reporter Gene for Nonivasive Monitoring of Therapeutic Gene Transfer - In Vivo- and Initial In Vivo-Evaluation

Anton, M.; Wittermann, C.; Haubner, R.; Simoes, M.; Reder, S.; Essien, B.; Wagner, B.; Henke, J.; Erhardt, W.; Noll, S.; Hackett, N. R.; Crystal, R. G.; Schwaiger, M.; Gansbacher, B.; Bengel, F. M.

Background: Coexpression of a reporter gene and therapeutic gene may allow for non-invasive monitoring of cardiac gene therapy. We sought to evaluate the usefulness of an adenoviral vector expressing mutant herpesviral thymidine kinase reporter gene(HSV1-sr39tk) and VEGF121 in independent expression cassettes(Ad4tk).
Methods and Results: Accumulation of [14C]FIAU and [18F] FHBG as reporter probes, and VEGF secretion into medium were determined for Ad4tk-infected H9c2 rat cardiac cells in vitro. Tracer uptake increased with increasing vector concentration and over time, and was comparable to cells infected with adenovirus expressing only wild-type HSV1-tk(reporter probe: [14C]FIAU) or mutant HSV1-sr39tk(reporter probe: [18F]FHBG). No significant uptake was observed in uninfected cells or cells infected with adenovirus expressing VEGF alone. With increasing vector concentration, Ad4tk-infected cells increasingly released VEGF into medium. VEGF production correlated significantly with cellular reporter uptake (r=.98). In an initial in vivo experiment, Ad4tk and control vector were injected directly into two separate myocardial areas of a healthy pig following thoracotomy. Two days later, PET imaging was performed using [124I]FIAU, allowing for specific visualization of the area of Ad4tk injection. Identification of regional reporter gene expression was accompanied by significant increase of plasma VEGF concentration.
Conclusion: The usefulness of a vector coexpressing HSV1-tk and VEGF for noninvasive imaging of the expression of a therapeutic transgene has been demonstrated for the first time. This approach may allow for in vivo monitoring of cardiac angiogenesis gene therapy in the future.
Condensed Abstract: Usefulness of an adenoviral vector(Ad4tk) expressing mutant herpesviral thymidine kinase reporter gene and VEGF121 was evaluated. Accumulation of radiolabelled reporter probes increased for Ad4tk-infected rat cardiac cells with increading vector concentration and over time, and was comparabel to cells expressing reporter gene alone. No significant uptake was observed in cells expressing VEGF alone. VEGF production after Ad4tk-infecion correlated significantly with reporter probe uptake in vitro. In vivo, PET yielded specific visualization of Ad4tk injection area in a pig. This approach may allow for noninvasive monitoring of cardiac angiogenesis gene therapy.

Keywords: imaging; gene therapy; radioisotopes; reporter genes; VEGF

  • Journal of Nuclear Medicine 45(2004)10, 1743-1746

Publ.-Id: 6040

Positron Emission Tomography of Cardiac Transgene Expression - Comparison of two Approaches Based on Herpesviral Thymidine Kinase Reporter Gene

Miyagawa, M.; Anton, M.; Haubner, R.; Simoes, M. S.; Städele, C.; Erhardt, W.; Reder, S.; Lehner, T.; Wagner, B.; Noll, S.; Noll, B.; Grote, M.; Gambhir, S. S.; Gansbacher, B.; Schwaiger, M.; Bengel, F. M.

Background: PET imaging of reporter gene expression holds promise for noninvasive monitoring of gene therapy. Previously, two approaches based on the herpes simplex virus type 1 thymidine kinase gene(HSV1-tk) have been applied to the heart. Wild-type HSV1-tk was imaged with [124I]-fluoro-deoxy-iodo-arabinofuranosyluracil(FIAU) and mutant HSV1-sr39tk with [18F]-fluoro-hydroxymethylbutyl-guanine(FHBG), but a direct comparison has not yet been performed.
Methods and Results: In H9c2 cardiac cells, in vitro FIAU accumulation was superior to FHBG following infection with adenovirus expressing wild-type HSV1-tk(Adtk), while FHBG uptake was superior to FIAU using adenovirus expressing mutant HSV1-sr39tk(Adtk). Subsequent in vivo studies employed dynamic PET two days after intramyocardial vector injection. FIAU was used after Adtk infection. Highest cardiac uptake compared to negative controls occurred at 10-30min after tracer injection. Specific uptake disappeared at later times due to FIAU washout. FHBG was used after Adsr39tk infection. Specific tracer uptake continuously increased over time and was highest vs controls at latest imaging times(105-120min). Global cardiac reporter probe kinetics in rats were confirmed by regional analyses in pigs. Transgene expression was specifically visualized by both approaches. Highest traget/backgrounde ratio of FIAU in Adtk infected pig myocardium was 1.50±0.20 vs 2.64±0.49 for FHBG in Adsr39tk infected areas(P=0.01). In vivo results were confirmed by ex vivo counting and autoradiography.
Conclusions: Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression in different species. Specific probe kinetics suggest different myocardial handling of pyrimidine(FIAU) and acycloguanosine(FHBG) derivatives. Results are in favour of FHBG and mutant HSV1-sr39tk because of continuous accumulation over time and higher imaging contrast.
Condensed Abstract: Two approaches for PET imaging of cardiac reporter gene expression based on herpesviral thymidine kinase gene (HSV1-tk) were compared in small and large animals. Using wild-type HSV1-tk, dynamically imaged with [124I]-fluoro-deoxy-iodo-arabinofuranosyluracil (FIAU), highest myocardial FIAU uptake occurred early after injection, but tracer washout was observed at later times. Using mutant HSV1-sr39tk, imaged with [18F]-fluoro-hydroxymethylbutyl-guanine (FHBG), specific uptake increased over time and was highest at late imaging. Both reporter gene/probe combinations were feasible for noninvasive imaging of cardiac transgene expression, but results are in favour of FHBG because of continuous accumulation over time and higher imaging contrast.

Keywords: imaging; genes; gene therapy; HSV1-tk radioisotopes

  • Journal of Nuclear Medicine 45(2004) 11, 1917-1923

Publ.-Id: 6039

Influence of humic acid on the neptunium(V) sorption onto granite and its mineral constituents

Schmeide, K.; Bernhard, G.

To evaluate the influence of humic substances upon the extent of neptunium(V) sorption by granite, the sorption of neptunium(V) on granite in the absence and presence of humic acid was studied under anaerobic conditions as a function of pH in a series of batch equilibrium experiments. The neptunium and humic acid sorption onto the mineral constituents of granite (quartz, orthoclase, albite, biotite, and muscovite) was also studied to identify the mineral component which dominates the sorption of neptunium and humic acid on granite. The study showed that the neptunium sorption is affected by both the pH and the presence of humic acid. An increased mobility of neptunium was found between pH 7 and pH 11 in the presence of humic acid. As dominating mineral phase in the granite for the neptunium sorption, biotite was identified.

Keywords: neptunium; humic acid; sorption; reduction

  • Poster
    International workshop on sorption processes at oxide and carbonate mineral water interfaces - SOPRO 2004, Karlsruhe, 25.-26.03.04
  • Contribution to external collection
    in: Wissenschaftliche Berichte FZKA 6986, Karlsruhe: Forschungszentrum Karlsruhe, 2004, 132-136

Publ.-Id: 6038

Investigation of thick 3C-SiC films re-grown on thin 35nm "Flash Lamp Annealed" 3C-SiC

Ferro, G.; Panknin, D.; Stoemenos, J.; Balloud, C.; Camassel, J.; Polychroniadis, E.; Monteil, Y.; Skorupa, W.

We report on the formation of thick 3C-SiC films on 3C-SiC/Si substrates which were produced by flash lamp processing (FLP). Employing a three step process, firstly a 35nm thick 3C-SiC film on a <100>-Si substrate is deposited which is followed, secondly by FLP. This leads to a melting of the SiC/Si interface region within 20ms followed by epitaxial solidification. Then, in a third step, this film is used as a seed for the deposition of a second, 3 µm thick, 3C-SiC layer. This newly developed process including FLP is called FLASiC (Flash LAmp supported deposition of Silicon Carbide). Compared with standard 3 µm thick layers directly grown on silicon, both transmission electron microscopy and low temperature photoluminescence evidence improvement of the re-grown material.

Keywords: 3C-SiC; flash lamp annealing; epitaxy; TEM; LTPL

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 313-316

Publ.-Id: 6037

Formation of 3C-SiC films embedded in SiO2 by sacrificial oxidation

Panknin, D.; Godignon, P.; Mestres, N.; Polychroniadis, E.; Stoemenos, J.; Ferro, G.; Pezoldt, J.; Skorupa, W.

The formation of SiC on Insulator (SiCOI) using a tool wet sacrificial oxidation is studied. The wet oxidation in 3C-SiC is very anisotropic strongly depended on the defect density, especially the inversion domain boundaries (IDBs). The SiCOI structure was realized by depositing of 35 nm thick 3C-SiC film on (100)-Si substrate by APCVD subsequently the film was annealed by flash lamps. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After radiation two zones can be distinguished, upper and lower, exhibiting high and low defect density, respectively. The highly defected upper zone was etched by wet sacrificial oxidation at 1150°C for 16 min. forming a 50nm thick oxide layer on the top of a good quality, 20nm thick, 3C-SiC film. In parallel, a buried oxide layer having a mean thickness of 44nm was formed by oxidation of the Si substrate through existing channels created in the SiC by the preferential wet oxidation of the IDBs which touch the SiC/Si interface. Through the oxided channels the Si substrate is oxided fast forming a continuous buried oxide layer realizing the SiCOI structure.

Keywords: 3C-SiC; SiCOI; flash lamp annealing

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 1515-1518

Publ.-Id: 6036

Flash lamp supported deposition of 3C-SiC (FLASiC) - a promising technique to produce high quality cubic SiC layers

Skorupa, W.; Anwand, W.; Panknin, D.; Voelskow, M.; Ferro, G.; Monteil, Y.; Leycuras, A.; Pezoldt, J.; Mcmahon, R.; Smith, M.

The production of cubic SiC (3C-SiC) layers in device quality through the epitaxial growth on (100)-Si wafers has remained a challenging task yet. Recently, it was demonstrated that the use of Flash Lamp Processing (FLP) can support the production of high quality 3C-SiC layers in a promising manner. The FLASiC team organized within a project of the V. Framework of the European Community is currently extending this early work as a broader approach with the following main aspects: a) Development of the epitaxial process including FLP, b) Development of a prototype equipment for the FLP, and c) Demonstrating the improved quality at dedicated devices. In this talk a short overview will be given regarding the latest advancements of this new approach.

Keywords: +3C-SiC; flash lamp annealing epitaxy; microstructure; modelling

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 175-180

Publ.-Id: 6035

Structural characterization of thin 3C-SiC films annealed by flash lamp process

Polychroniadis, E.; Stoemenos, J.; Ferro, G.; Monteil, Y.; Panknin, D.; Skorupa, W.

The formation of 3C-SiC epitaxially grown on Si wafers is still a considerable problem. Due to the 20% misfit between Si and 3C-SiC the defect density in the film is very high. the partial melting and subsequent recrystallization of the film by the flash lamp process can improve the quality of the thin 3C-SiC films. In this paper the microstructure of the annealed and partially recrystallized 35 nm thick films is studied by transmission electron microscopy. The films were grown by APCVD using Silane and Propane. The flash lamp annealing system consists of Xe lamps powered by discharging capacitors producing pulses of 20 ms. After irradiation almost free of defects 3C-SiC trapezoidal protrusions (TPs) are formed at the lower part of the film. In the uppermost part of the film the defect density was also reduced. The good quality of the TPs is shown by high resolution cross-section TEM observations. The good quality of the films was also confirmed by Plane View TEM observations of the moiré patterns in the as grown and annealed films. Moiré patterns are formed when the electron beam penetrates both the Si and the SiC lattices and are very sensitive to any lattice distortion or defects.

Keywords: 3C-SiC; flash lamp annealing; epitaxy; microstructure

  • Poster
    ICSCRM 2003, held in Lyon, France
  • Materials Science Forum 457-460(2004), 351-354

Publ.-Id: 6034

Examination of the charge storage of Si- and Ge nanoclusters in SiO2 films by scanning probe techniques

Beyreuther, E.; Beyer, R.; Beyer, V.; von Borany, J.; Weber, J.

Embedded Si or Ge nanoclusters in SiO2 films might be a future alternative to conventional floating gate memories. Si or Ge implanted 20nm SiO2 layers were annealed to generate nanoclusters with sizes of 3-4 nm. The charge storage of the implanted layers was studied by scanning capacitance microscopy (SCM) and electrostatic force microscopy (EFM). Local charge injections were accomplished by a biased conductive tip.
The amount of the injected charge was estimated from the shifts of the local dC/dV curves acquired with scanning capacitance spectroscopy (SCS). The SCS data were compared with CV-measurements on planar MOS structures. The decay of the SCM- and EFM-contrasts was monitored and the retention time was determined.

  • Poster
    DPG Frühjahrstagung des Arbeitskreises Festkörperphysik (AKF) 2003 Dresden, 24.-28. März 2003

Publ.-Id: 6032

Ladungsrelaxation in MOS-Strukturen mit Ge Nanoclustern

Beyer, R.; Beyer, V.; von Borany, J.; Weber, J.

Mittels Kapazitästransientenspektroskopie (DLTS) wurde die Umladung von Grenzflächen- und Isolatorzuständen in MOS-Strukturen mit eingebetteten Ge-Nanoclustern untersucht. Die Clusterbildung in den 20 nm dicken SiO2-Schichten erfolgte durch Ionenstrahlsynthese, wobei Ge mit verschiedenen Dosen (5x10^15, 1.5x10^16 cm^-2) und Energien (12, 18 keV) implantiert wurde und die Proben bei 950°C/1050°C in N2-Atmosphäre getempert wurden. TEM-Messungen zeigen die Bildung und Verteilung der Nanocluster im SiO2. Die DLTS-Messungen ergaben eine signifkante Abhängigkeit der Zustandsdichte an der Si-SiO2-Grenzfläche von den Ausheilparametern. Ein Trapniveau ~0.32 eV oberhalb der Valenzbandkante des Siliziums wurde in allen implantierten Proben gefunden. Durch Variation der elektrischen Anregungspulse kann der Beitrag der langsam relaxierenden grenzflächennahen Oxidzustände separiert und die für die Clusterumladung relevante Tunneloxidschicht an der Interface charakterisiert werden.

  • Lecture (Conference)
    DPG Frühjahrstagung des Arbeitskreises Festkörperphysik (AKF) 2003 Dresden, 24.-28. März 2003

Publ.-Id: 6031

Comparison of the Charge Storage Properties of Ion Beam Sythesized Si and Ge Nanoclusters in Thin Gate Oxides

Beyer, V.; von Borany, J.; Knobloch, K.; Mücklich, A.

Semiconductor nanoclusters (NCs) embedded in thin gate dielectrics are of fundamental interest for future integrated memory concepts. In this contribution we compare the properties of Ge and Si NCs embedded in thin SiO2 films (d = 20 nm) with respect to their charge storage behaviour. Those NCs were prepared by ion beam synthesis combining low energy ion implantation (6-18 keV, 5x1015-2x1016cm-2) with subsequent rapid thermal processing (950 or 1050°C, 30-120 s) choosing identical ion ranges and peak concentrations for both elements. Electrical characterization based on CV, IU, pulsed Ct and It measurements were performed at MOS capacitors. The investigations reveal significant differences for Ge and Si NC containing gate oxides. Ge NCs near the Si/SiO2 interface are characterized by fast charging / decharging and a flatband voltage shift of several volts. In contrast, Si implanted oxides show memory effects with a smaller flatband voltage shift, but considerably improved data retention. In both cases charging is possible for electrical field strength of 4-6 MV/cm, well below the Fowler-Nordheim tunnelling region. The varying electrical properties correlate with differences in the spatial distribution of ion beam synthesized Ge and Si NC in thin SiO2 films, which were investigated by XTEM and RBS. The change of spatial distribution during annealing is due to different thermodynamics of NC evolution and chemical processes especially in thin SiO2 films.

  • Lecture (Conference)
    E-MRS 2003 Spring Meeting / Strasbourg (Frankreich), 10.-13. Juni 2003
  • Lecture (Conference)
    EUROMAT 2003 Lausanne (Schweiz), 01.-05. September 2003

Publ.-Id: 6029

Charge Storage Behavior of Ion Beam Synthesized Au Nanocrystals

Beyer, V.; Müller, T.; von Borany, J.; Heinig, K.-H.

Studies of semiconductor nanocrystals (NC’s) in the MOS gate oxide received much interest due to their potential application in non-volatile memory devices. However, the detailed charge storage mechanism is still under discussion. Defect-based charge trapping at NC surfaces is hard to distinguish from storage in the conduction band of NC’s. For metal NC’s in SiO2 the situation is different. Charge traps at the Au/SiO2 interface are assumed to be negligible at first sight. In this contribution, Au NC’s serve as a model system for the charge storage phenomena in NC containing gate oxides with a thickness of less than 40 nm. For the present study, Au NC’s were synthesized by low-energy ion implantation followed by annealing. The formation of well-separated NCs (4..5 nm diameter) were observed by X-TEM studies. Additionally, a zone denuded of NC’s forms at the interface. Thus, the formed NC-layer has the right distance from the Si/SiO2 interface for charging by direct electron tunneling. On prepared MOS capacitor structures, charge storage behavior was successfully demonstrated by capacitance-voltage measurements.

  • Poster
    Jahrestagung der Deutschen Physikalischen Gesellschaft DPG, 24.-28. März 2003, Dresden

Publ.-Id: 6028

Interaction Processes of Tetravalent Actinides in the System Humic Acid / Quartz Sand / Solution

Krepelova, A.; Mibus, J.; Sachs, S.; Nebelung, C.; Bernhard, G.

In the present work the influence of HA on the interaction of tetravalent actinides onto quartz sand was investigated in batch and column experiments. HA can affect the sorption of actinides onto mineral surface as a complexing ligand for cations in solutions, and as an adsorbent by modifying the properties of the mineral surface.
Batch experiments were performed with Th(IV) as stable tetravalent actinide element. Column experiments were carried out with uranium which is less stable in the tetravalent state under laboratory conditions. Results of the U(IV) migration were compared to the U(VI) migration.
HA shows a pH-dependent influence on the Th(IV) sorption onto quartz sand. At pH < 4 HA may immobilize Th(IV) due to HA sorption and/or precipitation onto the surface. Between pH 4 and pH 5 the Th(IV) sorption is decreased in the presence of HA which can be attributed to the formation of dissolved Th(IV)-humate complexes. For higher pH values a comparable effect is assumed. The experimental proof was not possible by the performed batch experiments.
From the column experiments it can be concluded that HA affects the migration of both U(IV) and U(VI). In the presence of HA U(VI) is significantly mobilized. A similar effect is supposed for U(IV). This is in accordance with the results of the batch experiments.

  • Poster
    SOPRO 2004, 25.-26.3.2004, Karlsruhe, Germany
  • Contribution to proceedings
    SOPRO 2004, International Workshop on Sorption Processes at Oxide and Carbonate Mineral Water Interfaces, 25.-26.03.2004, Karlsruhe, Germany
    Book of extended abstracts, 75-79

Publ.-Id: 6027

Perspectives for biotechnological applications of the uranium mining waste pile isolate Bacillus sphaericus JG-A12

Merroun, M.; Raff, J.; Pollmann, K.; Hennig, C.; Rossberg, A.; Foerstendorf, H.; Scheinost, A.; Selenska-Pobell, S.

The strain Bacillus sphaericus JG-A12 was isolated from a uranium mining waste pile near the town of Johanngeorgenstadt. The most prominent properties of this strain are reversible and selective binding of U, Cu, Pb, Al and Cd and the presence of a surface layer protein as outermost cell wall component. Mass spectroscopical, colorimetric and phosphor specific staining methods showed phosphorylation of the S-layer protein. EXAFS analysis and Infrared spectroscopy of the uranium complexes formed by the cells and S-layer of this bacterium demonstrated that this metal is coordinated to carboxyl and phosphate groups. In this work we present analysis of Pd nanoclusters formed on the cells of B. sphaericus JG-A12 in the presence of H2 as a reducing agent. These nanoclusters are interesting for the development of bionanocatalysts and biosensors. Further, by embedding cells, spores or S-layers using sol-gel techniques bioceramics particles were produced. These bioceramics can be used for bioremediation of heavy metal contaminated waters.

  • Lecture (Conference)
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6026

Microbial diversity in uranium contaminated soils

Geißler, A.; Tzvetkova, T.; Selenska-Pobell, S.

Contamination of soils with heavy metals and radionuclides is a severe environmental problem. Bacteria are involved in migration and detoxification of a large number of toxic metals due to their ability to interact with and to biotransform them. Total DNA was extracted from soils of one uranium mining waste pile near the town of Johanngeorgenstadt (Germany) and of one uranium mill tailings near Shiprock, NM in the USA. Universal bacterial, archael and also Geobacter-specific primers were used to construct 16S rDNA libraries. We found that natural microbial communities at the two uranium wastes differed significantly. Alpha-Proteobacteria and representatives of the Holophaga/Acidobacterium phylum were predominant in the U mining waste pile, whereas the Shiprock U mill tailings was occupied mainly by Bacillales, Gamma-Proteobacteria and Green non-sulfur bacteria. The most related sequences to ours in the GenBank were those of not yet cultured bacteria or archaea. Representatives of the genus Geobacter were identified in the U waste pile by using Geobacter-specific primers and in the U mill tailings by both Geobacter-specific and universal primers. Because these bacteria are able to reduce and immobilize a large number of heavy metals, we are performing a quantification of them via Real time PCR. Efforts to cultivate some bacterial isolates from the U wastes are in progress in our laboratory.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

  • Poster
    VAAM-2004 vom 28.03-31.03.04 in Braunschweig
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6025

Bacterial diversity in waters at the Siberian deep-well monitoring site Tomsk-7

Nedelkova, M.; Selenska-Pobell, S.

Bacterial diversity was studied in water samples collected at depths of 290 to 324 m from the Siberian deep-well radioactive waste disposal site S15 near the Russian city of Tomsk by using the 16S rDNA retrieval. Bacterial clone libraries were constructed for the DNA isolated from the biomass collected on filters with a pore size of 0.45µm and 0.22µm. Comparative analyses of the two libraries revealed significant differences in the predominant bacterial groups and in the species composition. In the 0.45µm clone library a dominance of Dechlorosoma spp. was found, whereas in the 0.22µm library populations of Chrysobacterium spp. belonging to Cytophaga/Flavobacterium/ Bacteroides (CFB) group were predominant. Many of the identified 16S rDNA sequences were affiliated to uncultured members of different bacterial lineages. Effort to culture some of them is in progress in our laboratory.
In addition, using CFB-specific primers and applying semi-nested PCR a clone library was generated for the total DNA extracted from the same site. Our previous study of this DNA, applying universal bacterial primers, indicated a presence of relatively small CFB population there. The estimation of the real amount and the significance of this bacterial group via real-time PCR is also in progress.

VAAM-2004 vom 28.03-31.03.04 in Braunschweig

  • Poster
    VAAM-2004 vom 28.03-31.03.04 in Braunschweig
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany
  • Contribution to external collection
    Tsang, C. F.; Apps., J. A.: Developments in Water Science, Underground Injection Science and Technology, Amsterdam: Elsevier, 2005, 0-444-52068-6, 521-536

Publ.-Id: 6024

Molecular analysis of the S-layer protein of the uranium mining waste pile isolate Bacillus sphaericus JG-A12

Pollmann, K.; Raff, J.; Schnorpfeil, M.; Fahmy, K.; Selenska-Pobell, S.

Cells of the uranium mining waste pile isolate Bacillus sphaericus JG-A12 are capable of selective and reversible accumulation of heavy metals.
The cells of B. sphaericus JG-A12 are enveloped by a surface-layer (S-layer). S-layers, which are composed of identical protein monomers with the ability to self-assemble into two-dimensional crystalline arrays, are one of the most commonly observed surface structures of archaea and bacteria.
In case of the strain JG-A12 our analyses showed that the S-layer is capable of binding metals. Thus, it is probable that the S-layer contributes to heavy metal resistance.
Sequence analyses showed, that the S-layer proteins of B. sphaericus JG-A12 and its closest relative, B. sphaericus NCTC9602, possess an unusual high identity of the N-terminus and the central domain, whereas the C-terminal parts differ significantly between the two strains. Further, both strains contain a second truncated S-layer gene-like copy which is possibly encoded by large plasmids. These results indicate a horizontal transfer of parts of the gene between different strains.
The S-layer proteins show a high content of aspartate and glutamate, especially in the C-terminal part. IR analyses demonstrated that the carboxylgroups of these residues are involved in Pd-binding.

VAAM 2004
Braunschweig 28.03.-31.03.2004

  • Lecture (Conference)
    VAAM 2004, 28.3.-31.3.2004, Braunschweig, Germany
  • Contribution to proceedings
    VAAM 2004, 28.-31.03.2004, Braunschweig, Germany

Publ.-Id: 6023

Models for the forces acting on bubbles in comparison with experimental data for vertical pipe flow

Lucas, D.; Shi, J.-M.; Krepper, E.; Prasser, H.-M.

As a consequence of the averaging process constitutive models for the interaction between the phases are required in the multi-fluid modelling. For the simulation of bubbly flows this concerns models for the forces acting on bubbles. Detailed experimental data for vertical pipe flow, obtained by an advanced wire-mesh sensor, were used to assess such models for a wide range of combinations of superficial velocities. A simplified one-dimensional model, which considers a number of bubble classes is used for the prediction of radial gas fraction profiles from a given (measured) bubble size distribution. A comparison of these profiles with the measurements allows the evaluation of the models for the non-drag forces. In contrast to common CFD codes the simplified model also allows to consider the extension of the bubbles. This is important, if large bubbles or slugs occur. A good agreement is achieved for liquid superficial velocities up to 1 m/s using the lift- and wall force models from Tomiyama and the Favre averaged drag model for the turbulent dispersion force. For larger liquid superficial velocities an intermediate peak occur in the measured radial gas fraction profile, which cannot be reproduced by the available models.

Keywords: two-phase flow; modelling; bubble forces; vertical pipe flow

  • Lecture (Conference)
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy
  • Contribution to proceedings
    3rd International Symposium on Two-Phase Flow Modelling and Experimentation, 22.-24.09.2004, Pisa, Italy, paper ha04

Publ.-Id: 6022

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern ermöglicht. In Anrege-Abfrage Experimenten ist damit die Zeitskala zugänglich, in der sich wichtige elementare Wechselwirkungen abspielen. In Halbleiter Quantenstrukturen können durch fs-Laserpulse z.B. kohärente elektronische Wellenpakete präpariert werden, deren Untersuchung die Überprüfung elementarer Vorhersagen zur Existenz von Bloch Oszillationen erlaubt. Desweiteren werde ich auf Beiträge zur technologischen Weiterentwicklung des Feldes, wie die Realisierung des kompaktesten fs-Lasers auf Festkörperbasis, und dessen Anwendungen eingehen.

  • Lecture (others)
    Physikalisches Kolloquium, Universität Konstanz, Januar 2004, Konstanz, Deutschland

Publ.-Id: 6021

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie eröffnet. Über nichtlinear-optische Prozesse lassen sich ultrakurze optische Pulse in nahezu jeden Frequenzbereich konvertieren. Insbesondere im niederenergetischen Terahertz Bereich (1 THz entspricht 4 meV) erlaubt dies die zeitaufgelöste Spektroskopie von wichtigen Elementaranregungen in Festkörpern.
In Anrege-Abfrage Experimenten an Halbleitern und Halbleiter Quantenstrukturen ist somit die Zeitskala zugänglich, in der sich Elektron-Elektron Wechselwirkungen, Elektron-Phonon Streuung und Kohärenzzerfall abspielen. So lassen sich zum Beispiel kohärente elektronische Wellenpakete präparieren, die mit einer kohärenten Intrabandpolarisationen verbunden sind. Diese Intrabandpolarisation ist von Interesse für die Erzeugung elektrisch abstimmbarer THz Emission von Bloch Oszillationen in Halbleiter-Übergittern.
Zukünftige Perspektiven der Femtosekunden Spektroskopie werden im Hinblick auf die Untersuchung von Halbleiter-Nanostrukturen diskutiert.

  • Lecture (others)
    Universität Stuttgart, Dezember 2003

Publ.-Id: 6020

Reliability test of a PAL spectrometer - selected results on Fe

May-Tal Beck, S.; Brauer, G.; Anwand, W.; Berant, Z.; Shahal, O.; Ganor, M.; Israelashwily, I.

A positron lifetime spectrometer for defect studies in bulk, with time resolution of 185 +-7 ps, is described. Its reliability, tested on 4N Fe samples in various states, is demonstrated. For comparison, the same samples are studied also by Slow Positron Implantation Spectroscopy.

Keywords: defects; iron; positron lifetime spectroscopy; slow positron implantation spectroscopy

  • Contribution to external collection
    Material Science Forum 445-446 (2004), 495-497

Publ.-Id: 6019

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern eröffnet. Über nichtlineare optische Prozesse lassen sich ultrakurzen optischen Pulse in nahezu jeden Frequenzbereich konvertieren. Insbesondere im niederenergetischen Terahertz Bereich erlaubt dies die Entwicklung von zeitaufgelöster Spektroskopie mit hoher Empfindlichkeit.
In Anrege-Abfrage Experimenten an Halbleitern ist somit die Zeitskala zugänglich, in der sich wichtige elementare Prozesse, wie zum Beispiel Elektron-Phonon Streuung und Kohärenzzerfall, abspielen. In Halbleiter Quantenstrukturen können durch die Anregung mit Femtosekunden Pulsen kohärente elektronische Wellenpakete präpariert werden, die mit kohärenten Interband- und Intrabandpolarisationen verbunden sind. Die Dephasierungszeit der Intrabandpolarisation ist von Interesse für die auf Bloch Oszillationen basierende THz Emission aus Übergittern. Besonders interessant sind Untersuchungen für den Resonanzfall, wenn die Frequenz der Intrabandpolarisation auf die LO Phononfrequenz abgestimmt wird.

  • Lecture (others)
    Universität Regensburg, Mai 2003

Publ.-Id: 6018

Hydrogen-induced defects in niobium studied by positron annihilation spectroscopy

Cizek, J.; Prochazka, I.; Kuzel, R.; Becvar, F.; Cieslar, M.; Brauer, G.; Anwand, W.; Kirchheim, R.; Pundt, A.

Changes of the defect structure of niobium induced by hydrogen loading are presented in this work. The evolution of the microstructure with increasing hydrogen concentration was studied by X-ray diffraction and two complementary techniques of positron annihilation spectroscopy (PAS). A comparison of PAS results with theoretical calculations revealed that complexes consisting of a vacancy, surrounded likely by four hydrogen atoms, were introduced into the samples due to hydrogen loading.

Keywords: hydrogen; niobium; vacancies

  • Contribution to external collection
    Materials Science Forum, 445-446 (2004), 60-62
  • Journal of Alloys and Compounds 404-406(2005), 580-583

Publ.-Id: 6017

Fluence dependence and thermal stability of defects in helium-implanted cubic zirconia

Saude, S.; Grynszpan, R. I.; Anwand, W.; Brauer, G.; Grob, J. J.; Le Gall, Y.

Slow positron implantation spectroscopy investigations of yttria-stabilized cubic zirconia implanted with 50 keV He ions detect, at 60% of the projected range, a concentration of defects maximum, which may constitute a barrier for the diffusion of helium towards the surface. The Doppler broadening lineshape dependence on the fluence suggests a change in the nature of defects above 4 x 10**16 ions/cm**2, with an enhancement of the trapping efficiency. These defects evolve into large bubbles by Ostwald ripening after annealing at temperatures higher than 573 K, as suggested by their distribution narrowing. Above 973 K, a breaking-up of the bubbles occurs, with He release and diffusion towards the surface and eventual out-gassing.

Keywords: ion implantation; zirconia; radiation effects; positrons

Publ.-Id: 6016

Femtosekunden Spektroskopie an Quantenstrukturen

Dekorsy, T.

Die Entwicklung von modengekoppelten Lasersystemen, die optische Pulse im Femtosekunden Bereich (1 fs=10-15 s) emittieren, hat neue Möglichkeiten in der zeitaufgelösten Spektroskopie von Festkörpern ermöglicht. In Anrege-Abfrage Experimenten ist damit die Zeitskala zugänglich, in der sich die wichtigsten elementaren Wechselwirkungen, zum Beispiel Elektron-Phonon Kopplung und Kohärenzzerfall, abspielen. Über nichtlineare optische Prozesse lassen sich diese ultrakurzen optischen Pulse in nahezu jeden Frequenzbereich vom niederenergetischen Terahertz Bereich bis ins UV konvertieren, was die Entwicklung neuer spektroskopischer Anwendungen ermöglicht.

In Halbleiter Quantenstrukturen können durch die Anregung mit Femtosekunden Pulsen kohärente elektronische Wellenpakete präpariert werden, deren Untersuchung die Überprüfung elementarer Vorhersagen der Quantenmechanik in Festkörpern zur Existenz von Bloch Oszillationen ermöglicht. Desweiteren werde ich auf Beiträge zur technologischen Entwicklung des Feldes, wie die Realisierung des kompaktesten Femtosekunden Lasers auf Festkörperbasis, und dessen Anwendungen eingehen.

  • Lecture (others)
    Universität Paderborn, März 2003

Publ.-Id: 6015

Electroluminescence from silicon pn diodes

Dekorsy, T.

The indirect band gap of silicon makes this material an inherently bad light emitter. However, since silicon is the key material of electronics, there is a tremendous effort for realizing silicon based light emitters in order to take full advantage of silicon process technology. The different routes pursued so far include porous silicon, 2 dimensional silicon nanostructures, silicon nanocrystals in a SiO2 matrix [1], Er3+ doped silicon, and silicon-germanium quantum cascade lasers.
Recently, the light emission from bulk silicon received considerable interest [2,3]. We pursue a similar route for preparing silicon pn-diodes via high-dose boron implantation. Under forward bias these diodes emit electroluminescence close beneath the silicon bandgap. The origin of the electroluminescence is based on high local boron concentration, which leads to the localization of holes at doping spikes similar as observed in delta doped layers produced by MBE. The relevance of excitons bound at the B doping spikes on the electrical [4] and optical properties will be discussed with respect to the prospects of obtaining efficient room temperature light emitters.

[1] L. Pavesi, et al., Optical gain in silicon nanocrystals, Nature 408, 440 (2000).
[2] W.L. Ng et al., An efficient room temperature silicon based light emitting diode, Nature
410, 192 (2001).
[3] M.A. Green et al., Efficient silicon light-emitting diodes, Nature 412, 805 (2001).
[4] J. Sun et al, Bound-exciton-induced current bistability in a silicon light-emitting diode, Appl. Phys. Lett. 82, 2823 (2003).

Keywords: silicon based light emission; pn diodes; boron implantation

  • Lecture (others)
    Seminarvortrag, Gruppe Prof. J. Feldmann, LMU München, Juni 2003

Publ.-Id: 6014

Vergleich der ELBE - FELs mit Table Top Lasersystemen

Dekorsy, T.

not available

  • Lecture (others)
    ELBE Palaver, Forschungszentrum Rossendorf, Juli 2003

Publ.-Id: 6013

Mehr Licht...aus Silizium

Dekorsy, T.

not available

  • Lecture (others)
    Festkolloquium anläßlich des 60. Geburtstages von Prof. H. Kurz, RWTH Aachen, Dezember 2003

Publ.-Id: 6012

Ultra-fine grained copper prepared by high pressure torsion: spatial distribution of defects

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

High-purity bulk ultra-fine grained (UFG) metals of grain size of " 100 nm and of no porosity can be produced by high-pressure torsion (HPT) technique. In the present contribution a study of spatial distribution of defects in HPT made UFG copper is reported. Positron annihilation spectroscopy (slow-positron implantation, lifetime and Doppler broadening spectroscopies) was utilized together with transmission electron microscopy, x-ray diffraction and microhard-ness measurements to investigate lateral distributions as well as depth profiles of defects.
Two types of defects were identified: dislocations situated in distorted regions along grain boundaries and microvoids of size comparable to 3-5 vacancies inside grains. No lateral changes in grain size and mean dislocation density were observed. Close to the specimen sur-face, the mean coherent domain size was found to be 80±20nm and it slightly increased with depth. As a consequence, a decrease in volume fraction of distorted regions takes place, which results in a decrease of the mean dislocation density with depth. These changes were observed at depths below 35 mm. At higher depths, the mean dislocation density tends to independence of depth. Contrary to lateral behavior of dislocations, concentration of microvoids was found to vary with distance from center of the specimen disk.

Keywords: High-pressure torsion; ultra-fine grained copper; spatial distribution of defects; positron annihilation

  • Contribution to external collection
    Proc. Second Int. Conf. on Nanomaterials by Severe Plastic Deformation: Fundamentals - Processing - Applications, Vienna 2002, eds. M.J. Zehetbauer, R.Z. Valiev (Wiley, Weinheim, 2003) pp. 407-412

Publ.-Id: 6010

Electroproduction of Strangeness on 3,4He

Dohrmann, F.; Abbott, D.; Ahmidouch, A.; Ambrozewicz, P.; Armstrong, C. S.; Arrington, J.; Asaturyan, R.; Assamagan, K.; Avery, S.; Bailey, K.; Baker, O. K.; Beedoe, S.; Bitao, H.; Breuer, H.; Brown, D. S.; Carlini, R.; Cha, J.; Chant, N.; Christy, E.; Cochran, A.; Cole, L.; Collins, G.; Cothran, C.; Crowder, J.; Cummings, W. J.; Danagoulian, S.; Duncan, F.; Dunne, J.; Dutta, D.; Eden, T.; Elaasar, M.; Ent, R.; Ewell, L.; Fenker, H.; Fortune, H. T.; Fujii, Y.; Gan, L.; Gao, H.; Garrow, K.; Geesaman, D. F.; Gueye, P.; Gustafsson, K.; Hafidi, K.; Hansen, J. O.; Hinton, W.; Jackson, H. E.; Juengst, H.; Keppel, C.; Klein, A.; Koltenuk, D.; Liang, Y.; Liu, J. H.; Lung, A.; Mack, D.; Madey, R.; Markowitz, P.; Martoff, C. J.; Meekins, D.; Mitchell, J.; Miyoshi, T.; Mkrtchyan, H.; Mohring, R.; Mtingwa, S. K.; Mueller, B.; O'Neill, T. J.; Niculescu, G.; Niculescu, I.; Potterveld, D. H.; Price, J. W.; Raue, B. A.; Reimer, P. E.; Reinhold, J.; Roche, J.; Roos, P.; Sarsour, M.; Sato, Y.; Savage, G.; Sawafta, R.; Segel, R. E.; Semenov, A. Y.; Stepanyan, S.; Tadevosian, V.; Tajima, S.; Tang, L.; Terburg, B.; Uzzle, A.; Wood, S.; Yamaguchi, H.; Yan-1, C.; Yan-2, C.; Yuan, L.; Zeier, M.; Zeidman, B.; Zihlmann, B.

The A(e,e'K+)X reaction has been investigated at Jefferson Laboratory. Data were taken for Q{2} approx 0.35 rm GeV2 at a beam energy of 3.245 rm
GeV for 1H,3He and 4He targets. Missing mass spectra are fitted with Monte Carlo simulations taking into account the production of Lambda and Sigma0 hyperon production off the proton, and Sigma- off the neutron. Models for quasifree production are compared to the data, excess yields close to threshold are attributed to FSI. Evidence for Lambda-hypernuclear bound states is seen for 3,4He targets. This is the first time that the electroproduction of these hypernuclei has been observed.

Keywords: Electroproduction; Strangeness; Hyperons; Hypernuclear boundstates

  • Contribution to external collection
    Proceedings of HYP2003

Publ.-Id: 6008

Lateral and depth distribution of defects in ultra fine grained copper prepared by high pressure torsion

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

Ultra-fine grained copper prepared by high-pressure torsion has been studied by means of positron annihilation techniques (slow positron implantation spectroscopy,conventional positron lifetime and Doppler broadening measurements) combined with transmission electron microscopy, X-ray diffraction and microhardness measurements. Dislocations in distorted regions along grain boundaries and microvoids of size 3-4 vacancies inside grains were identified and their lateral distribution and depth profile were investigated in detail. The concentrationof microvoids has been found to decrease with depth and to vary slightly with the distance from specimen axis, being lowest in the centre of the specimen disc. No position dependence of the concentration of dislocations was observed.

Keywords: ultra-fine grained copper; high-pressure torsion; dislocations; microvoids; slow positron implantation spectroscopy; positron lifetime; Doppler broadening

  • J. Metastable Nanocryst. Mater. 17 (2003) 23-28

Publ.-Id: 6006

Sampling and Characterization of Rock Material from Uranium Mining Waste Rocks for Study and Modeling of Release and Migration of Uranium

Sachs, S.; Benes, P.; Vopalka, D.; Stamberg, K.; Mibus, J.; Bernhard, G.; Bauer, A.

To study the effects of humic substances on the leaching and migration of uranium from uranium mining waste a natural rock material was sampled from a uranium rock pile situated in the mining region Schlema/Alberoda (Saxony, Germany). This report describes the sampling and characterization of the <1 mm grain size fraction of the rock material. The main focus is on the characterization of the sampled material with regard to its elemental and mineralogical composition and its amount of uranium that is accessible from the rock material by leaching processes.

Keywords: Uranium; migration; humic substances; uranium mining; rock pile; rock material; characterization

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte, FZKA 6969, Karlsruhe 2004, 73-84

Publ.-Id: 6005

Spatial distribution of defects in ultra-fine grained copper prepared by high pressure torsion

Cizek, J.; Prochazka, I.; Brauer, G.; Anwand, W.; Kuzel, R.; Cieslar, M.; Islamgaliev, R. K.

A study of ultra-fine grained copper produced by high-pressure torsion is presented. Positron annihilation spectroscopies (slow-positron implantation, lifetime and Doppler broadening spectroscopies), transmission electron microscopy, X-ray diffraction spectroscopy and micro-hardness measurements have been employed in order to identify defects and their spatial dis-tribution, i.e. lateral distribution and depth profile, in the specimens. Two types of defects could be identified: dislocations in the distorted regions along grain boundaries and micro-voids of size of 3-4 vacancies inside the grains. No change in grain size as a function of the distance from the center of the sample disk was observed. The mean coherent domain size close to the surface was found to be 80 ± 20 nm and it slightly increases with depth. The con-centration of microvoids has been found to decrease with depth and it slightly varies with the distance from the center of the disk, being lowest in the center. No position dependence of the concentration of dislocation was observed.

Keywords: High-pressure torsion; ultra-fine grained copper; spatial distribution of defects; positron annihilation spectroscopy

  • phys.stat.sol.(a) 195 (2003) 335-349

Publ.-Id: 6004

Metallographical and Numerical Investigation of the EC-FOREVER-4 Test

Willschütz, H.-G.; Altstadt, E.; Mueller, G.; Boehmert, J.; Sehgal, B. R.

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 behavior 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) are currently underway 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 compared to a common LWR.
Accompanying the experiments metallographical and numerical work is performed at the Forschungszentrum Rossendorf. An axisymmetric Finite Element model is developed based on the multi-purpose code ANSYS/Multiphysics®. First the temperature field within the melt pool and within the vessel wall is evaluated. The transient structural mechanical calculations are then performed applying a creep model which takes into account large temperature, stress and strain variations. For a failure prediction it is necessary to introduce a damage measure. This is done according to a model proposed by Lemaitre. The microstructural investigation gives an 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 experiment EC-FOREVER-3B are discussed, too.

Keywords: metallographic investigations; creep; crack; RPV; vessel failure

  • Lecture (Conference)
    International Congress on Advances in Nuclear Power Plants (ICAPP '04),13.-17.06.2004, Pittsburgh, PA, United States
  • Contribution to proceedings
    International Congress on Advances in Nuclear Power Plants (ICAPP '04),13.-17.06.2004, Pittsburgh, PA, United States, Proceedings on CD-ROM, paper 4006

Publ.-Id: 6003

Depth resolved investigations of boron implanted silicon

Sztucki, M.; Metzger, T. H.; Milita, S.; Berberich, F.; Schell, N.; Rouviere, J. L.; Patel, J.

We have studied the depth distribution and structure of defects in boron implanted silicon (001). Silicon wafers were implanted with a boron dose of 6e15 ions/cm2 at 32 keV and went through different annealing treatments. Using diffuse X-ray scattering at grazing incidence and exit angles we are able to distinguish between different kinds of defects (point defect clusters and extrinsic stacking faults on {111} planes) and to determine their depth distribution as a function of the thermal budget. Cross-section transmission electron microscopy was used to gain complementary information.
In addition we have determined the strain distribution caused by the boron implantation as a function of depth from rocking curve measurements.

Keywords: Diffuse X-ray scattering; Transmission electron microscopy; Ion implantation; Defects

Publ.-Id: 6002

The nanostructure evolution during and after magnetron deposition of Au films

Schell, N.; Jensen, T.; Petersen, J. H.; Andreasen, K. P.; Bottiger, J.; Chevallier, J.

The evolution of the nanostructure of magnetron sputtered Au films has been experimentally studied. At a synchrotron-radiation beam line, during growth and subsequent annealing, in-situ X-ray diffraction has been carried out to follow the texture, the grain size, the microstrain and lattice-plane distances. With Bragg–Brentano geometry, only (111) grains, having a (111) plane parallel to the film surface, have been observed, while, with glancing incidence and exit X-ray diffraction, (111)* grains, having one of their (111) planes perpendicular to the film surface, have also been observed. Both during growth and subsequent annealing, the (111) texture changed, and some (111)* grains recrystallized and/or the orientation of the grains changed. The microstrain decreased drastically during the first few minutes of growth (300 A) while, simultaneously, the size of the coherently diffracting domains increased. Subsequently, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off. Initially, during the first few minutes of annealing, a large decrease in the microstrain was observed simultaneously with a dramatic rise of the size of the coherently diffracting domains. After this initial annealing period, as during film growth, the microstrain became constant, and the rate of increase of the size of coherently diffracting domains leveled off.
The activation energy for the initial growth of the coherent diffracting domains was found to be Q=(0.25 +/- 0.03) eV, and the activation energy for normal grain growth was found to be Q=(0.99 +/- 0.04) eV.
Finally, the thin-film stress was followed during growth and subsequent annealing. A tensile contribution to the stress was observed during island coalescence.

Keywords: Nanocrystalline Au; Nanostructure; In-situ X-ray diffraction; Growth; Magnetron sputtering

  • Contribution to HZDR-Annual report
    ERSF Highlights 2003 (2004) 39-40
  • Thin Solid Films 441 (2003) 96-103


Publ.-Id: 6001

On the development of texture during growth of magnetron-sputtered CrN

Schell, N.; Petersen, J.; Bottiger, J.; Mücklich, A.; Chevallier, J.; Andreasen, K. P.; Eichhorn, F.

During growth of CrN films deposited by reactive magnetron sputtering, the development of the microstructure, especially the texture, was studied.By ex-situ Bragg–Brentano X-ray diffraction measurements, the texture, the grain size and the microstrain were measured as a function of film thickness.In addition, in-situ Bragg–Brentano X-ray diffraction and reflection measurements were carried out with synchrotron radiation, including measurements where the dynamic development of the microstructure was followed in real-time. Below a transition deposition temperature of approximately 550°C, it was found that the <002> preferred orientation dominated, while a mixture of <111> and <002> preferred orientations was found above the transition temperature. The development of texture with film thickness was controlled by a recrystallization mechanism.With increasing film thickness, the grain size increased while the microstrain decreased.The real-time measurements with synchrotron radiation revealed that several different dynamic processes took place both during and after depositions.After a long-time interruption of the growth,major changes in the texture were observed.

Keywords: Texture development; CrN; Magnetron sputtering

  • Thin Solid Films 426 (2003) 100-110

Publ.-Id: 6000

In situ high temperature synchrotron-radiation diffraction studies of silicidation processes in nanoscale Ni layers

Rinderknecht, J.; Prinz, H.; Kammler, T.; Schell, N.; Zchech, E.; Wetzig, K.; Gessner, T.

The formation of nickel silicides has been studied by X-ray diffraction experiments using synchrotron radiation (SR). A high temperature chamber was used to investigate the phase formation and transition processes under quasi-static conditions at temperatures from 200 to 650 °C. Samples with different dopants, several metal layer thicknesses as well as samples with and without a 150 A TiN capping layer on single-crystal (001) and polycrystalline silicon substrates were examined. While n-type dopants like P and As had no significant impact on the silicidation processes, boron decreased the range of thermal stability of the low-resistivity phase NiSi. A TiN capping layer shifts both these formation and transition temperatures to higher values.

Keywords: Nickel silicide; Phase formation; Transition temperatures; Dopants; Capping layer

  • Microelectronic Engineering 70 (2003) 226-232

Publ.-Id: 5999

Analysis of the biaxial strain state of Al-doped c-BN films using diffraction experiments with synchrotron radiation

Linss, V.; Halm, T.; Hoyer, W.; Richer, F.; Schell, N.

Thin films of cubic-boron nitride with a small amount of aluminum were produced by rf magnetron sputtering of a h-BN target and an additional Al ring-shaped electrode. Then the strain state of the biaxially stressed films was measured using synchrotron X-ray diffraction and the lattice spacing that unstressed films would have was calculated for different amounts of aluminum. This unstressed lattice spacing gets larger with increasing Al-amount. There is much evidence that the aluminum atoms are substitutionally incorporated at boron sites. This article provides an insight into the method of determining the unstressed lattice spacing using a slightly changed sin2_psi method.

Keywords: Cubic boron nitride (c-BN); Al-doping; Unstressed lattice spacing; Synchrotron radiation; sin2_psi-method

  • Vacuum 70 (1) (2003) 1-9

Publ.-Id: 5998

Dynamo experiments: where we stand and where we go

Stefani, F.; Gerbeth, G.; Gailitis, A.; Lielausis, O.; Platacis, E.

It was a nice coincidence that, after years of preparations, the liquid sodium dynamo facilities in Riga and Karlsruhe had become operative nearly simultaneously at the end of 1999. Since those pioneering times, there have been many additional runs in either place, yielding a wealth of reproducible data on the kinematic as well as on the saturated regime. The accompanying numerical work has got some maturity and shows, by now, a reasonable correspondence with the experimental results. The results of the two experiments are complementary rather than redundant as they cover the paradigmatic cases of a large scale dynamo (Riga) and a mean-field dynamo (Karlsruhe). With the main focus on the results and the interpretation of the Riga dynamo experiment, we give a summary of what has been achieved so far and what is left for future dynamo experiments. In particular, we demonstrate that the saturation mechanism of the Riga dynamo experiment is already a non-trivial one as it relies heavily on the change of the flow structure due to the back-reaction of the self-excited magnetic field. We comment on the envisioned dynamo experiments in non-rotating and rotating spheres and ask what geodynamo simulation could learn from

  • Abstract in refereed journal
    Geophysical Research Abstracts 6(2004), 02933
  • Invited lecture (Conferences)
    European Geosciences Union, 1st General Assembly, 25.-30.04.2004, Nice, France

Publ.-Id: 5996

Relaxation kinetics in amorphous carbon films: an insight from atomic scale simulation

Belov, A. Y.; Jäger, H. U.

Depending on temperature, thermodynamically favoured structural relaxations in as-deposited tetrahedral amorphous carbon (ta-C) films can either essentially retain the content of sp3 bonded atoms or result in a transition to a graphitic phase with dominating sp2 bonding. The structural relaxation occurs at low temperatures (less than ~ 600 °C) and is accompanied by reduction of the grown-in film stress. The most recent NMR spectroscopy investigation [1] shows that the structural changes in highly tetrahedral a-C films due to low-temperature annealing don't reduce to simple sp3-to-sp2 or sp3-to-sp2 conversions and have more complicated nature than it was previously believed. We present results of long-term simulated annealing studies of the relaxation processes in ta-C using molecular dynamics with a modified Brenner potential for C-C interactions and the structural models of as-deposited (unrelaxed) ta-C generated by an ion-beam film deposition simulation [2]. It is shown that during low-temperature annealing the potential energy and stress of the as-deposited ta-C films are released with only minor changes in the short-range order and density. It is demonstrated that as a result of annealing the volumes of sp3 atoms decrease, which is consistent with experiment [1]. It is also found that the change of potential energy with annealing time can be fit by an exponential function, which enables to analyze the relaxation kinetics in as-deposited ta-C, in particular, to obtain the dependence of the relaxation time on annealing temperature.
[1] T.M. Alam, T.A. Friedmann, P.A. Schultz, D. Sebastiani, Phys. Rev. B 67, 245309 (2003)
[2] H.U. Jäger, A.Yu. Belov, Phys. Rev. B 68, 024201 (2003)

  • Lecture (Conference)
    European Materials Research Society 2004 Spring Meeting, Symposium J : Synthesis, Characterisation and AdvancedApplications of Amorphous Carbon films, 24-28 May 2004, Strasbourg France, contr. J-V.6

Publ.-Id: 5995

Hydrogen bonding and structural order in hydrogenated amorphous silicon prepared with hydrogen-diluted silane

Danesh, P.; Pantchev, B.; Antonova, K.; Liarokapis, E.; Schmidt, B.; Grambole, D.; Baran, J.

A study of the structural development of hydrogenated amorphous silicon (a-Si :H) during plasma-enhanced chemical vapour deposition with hydrogen-diluted silane has been carried out with focus on the variations in the hydrogen bonding configuration and in the amorphous silicon network with increasing film thickness. In addition, the hypothesis of a high fraction of non-bonded (molecular) hydrogen in a-Si :H has been tested. The total hydrogen concentration and its silicon-bonded fraction have been estimated by means of nuclear reaction analysis and infrared spectroscopy, respectively. It has been shown that the presumable molecular hydrogen is not detectable within the limits of the measurement accuracy of the methods used. The hydrogen concentration is uniformly distributed along the growth direction, and the infrared absorption modes at 2000 and 2100 cm-1 are not affected by increasing the film thickness. Raman spectroscopy has been used to follow the variations in the structure of the silicon network. The increase in the film thickness leads to an improved ordering of the amorphous network on the short and medium range scale for films deposited at low substrate temperatures. In films deposited at high substrate temperatures, the tendency of structural improvement has been detected only on the medium range scale.

Keywords: H:a-Si; NRA; Raman spectroscopy; hydrogen bonding

  • Journal of Physics D 37(2004), 249-254

Publ.-Id: 5993

Effect of post-hydrogenation on the structural properties of amorphous silicon network

Pantchev, B.; Danesh, P.; Liarokapis, E.; Schmidt, B.; Schmidt, J.; Grambole, D.

Post-hydrogenation of magnetron sputtered amorphous silicon films has been carried out with the aim to study the effect of hydrogen interaction with amorphous silicon network on its short and medium range order. Raman spectroscopy has been used to study the variations in the amorphous structure. Nuclear reaction analysis (NRA) has been used to determine the total amount and depth distribution of the penetrated hydrogen atoms. The concentration of the silicon-bonded hydrogen and the bonding configurations have been established by means of infrared (IR) transmission measurements. The values of hydrogen concentration evaluated by NRA and IR spectroscopy coincide within the measurement accuracy, suggesting that the hydrogen diffusion proceeds via interaction with the host silicon atoms. This interaction is accompanied by a rearrangement of the strained Si-Si bonds which leads to an improvement of the amorphous network.

Keywords: amorphous silicon; post-hydrogenation; hydrogen depth distribution; Raman spectroscopy

Publ.-Id: 5990

NIR Spectroscopic Study on the Influence of Phenolic OH Groups on the Neptunium(V) Humate Complex Formation

Sachs, S.; Bernhard, G.

We investigated the influence of phenolic OH groups on the Np(V) complexation by humic acids at pH 7 and pH 8. The studies were performed by near-infrared (NIR) absorption spectroscopy applying unmodified and chemically modified humic acids with blocked phenolic/acidic OH groups. The experimental data were evaluated with the metal ion charge neutralization model. For all humic acids under investigation comparable complexation constants were determined. However, compared to the original humic acids, modified humic acids with blocked phenolic/acidic OH groups show significant lower loading capacities for Np(V) under the applied experimental. This result indicates a lower amount of maximal available humic acid ligand sites for the complexation of Np(V). Thus, it can be concluded that humic acid phenolic/acidic OH groups contribute to the interaction between humic acid and Np(V) under the studied conditions.

Keywords: Humic substances; Humic acids; Actinides; Complexation; Neptunium

  • Contribution to external collection
    Humic Substances in Performance Assessment of Nuclear Waste Disposal : Actinide and Iodine Migration in the Far-Field. Second Technical Progress Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte, FZKA 6969, Karlsruhe 2004, 61-71

Publ.-Id: 5989

Some metallurgical applications of magnetic fields. The role of model experiments and velocity measuring techniques.

Gerbeth, G.

Magnetic fields provide the possibility of a tailored flow control for metallurgical and crystal growth processes. Two examples will be presented: the application of a specially shaped steady magnetic field in the melt extraction process of thin metallic fibres, and the control of the flow filling process in the investment casting of aluminium alloys. The role of cold model experiments and the development of velocity measuring techniques for metallic melts will be stressed. As a final example, velocity measurements in a liquid metal switcher will be presented.

  • Lecture (Conference)
    Coventry University, 12.01.2004, Coventry, Great Britain

Publ.-Id: 5988

Differentiation between recurrent tumor or radiation necrosis in a child with anaplastic ependymoma after chemotherapy and radiation therapy

Beuthien-Baumann, B.; Hahn, G.; Winkler, C.; Heubner, G.

Background: In patients after treatment for malignant brain tumors, a clear distinction between tumor recurrence and radiation necrosis can be challenging. This case report describes the diagnostic workup in child with anaplastic ependymoma and inconclusive MRI (magnetic resonance imaging) and PET (positron emission tomography) findings.
Case Report: 1.5 years after resection, hyperfractionated radiotherapy and chemotherapy of an anaplastic ependymoma in the right parietal region, the cranial MRI of an 11-year-old girl showed multiple small contrast-enhanced lesions in the frontal cortex. In the following months, these lesions increased in number and size and neurologic symptoms developed. Diagnostic workup included repeated MRI scans, PET with an 18F-amino acid and 18F-fluorodexyglucose (FDG), as well as a brain biopsy.
Results: Amino acid PET, performed when the lesions were still small, showed multiple small areas of mild uptake in close correlation to the MRI lesions. Although not typical, this result was suspicious of tumor seeding, the more since the lesions appeared in gray matter areas outside the high-dose-rate irradiation field. A biopsy, performed 6 months later when the clinical appearance worsened, showed no tumor tissue. FDG PET, performed after the size and number of the lesions has increased, showed no intensely increased glucose metabolism, a high-grade recurrent tumor was therefore very unlikely. In the following months, the clinical picture stabilized.
Conclusion: The final interpretation of the lesions was multiple focal radiation necrosis based on perfusion abnormalities after chemotherapy and conformal hyperfractionated radiotherapy, probably due to an individually enhanced of the cerebral vessels.

Keywords: Anaplastic ependymoma; Magnetic resonance imaging; Positron emission tomography; Hyperfractionated radiotherapy; Radiation necrosis

  • Strahlentherapie Onkologie (2003) 179: 819-822

Publ.-Id: 5987

Core response of a PWR to a slug of under-borated water

Kliem, S.; Rohde, U.; Weiß, F.-P.

A parameter study, incorporating stationary and transient core calculations, was carried out for a hypothetical boron dilution event in a pressurized water reactor, using the 3D neutron kinetics core model DYN3D in combination with a fast running semi-analytical coolant mixing model. It was assumed that a slug of deborated water was formed in one of the loops, due to a secondary-to-primary steam generator leakage during outage. It was further assumed that this slug is not recognised and that the first main coolant pump is started, in preparation to returning to power. At the initiation of pump start-up, the reactor is still in the cold and deeply sub-critical state. By varying the initial slug volume, it was found in stationary calculations that, for the given core configuration, slugs of less than 14 m³ do not lead to re-criticality. Transient core calculations with larger slug volumes show a significant reactivity insertion and over-criticality. However, according to the calculations, even an over-criticality of about 2 $ did not lead to safety-relevant consequences. The power excursion is mitigated and stopped by Doppler feedback. The influence of the cross- section library on the course of the transient was investigated, applying an alternative library. Differences in the global core parameters lead to quantitative differences in the time and height of the power excursion. In addition, it is shown that numerical diffusion has to be suppressed in order to describe the boron transport correctly, especially at low flow velocities. Otherwise the neutron kinetic core behaviour cannot be correctly modelled.

Publ.-Id: 5986

EXAFS Study on the Neptunium(V) Complexation by Various Humic Acids under Neutral pH Conditions

Sachs, S.; Schmeide, K.; Reich, T.; Brendler, V.; Heise, K. H.; Bernhard, G.

The structure of Np(V) humic acid (HA) complexes at pH 7 was studied by extended x-ray absorption fine structure analysis (EXAFS). For the first time, the influence of phenolic OH groups on the complexation of HA and Np(V) in the neutral pH range was investigated using modified HAs with blocked phenolic OH groups and Bio-Rex70, a cation exchange resin having only carboxyl groups as proton exchanging sites.
The formation of Np(V) humate complexes was verified by near-infrared (NIR) spectroscopy. Axial Np-O bond distances of 1.84 - 1.85 Å were determined for the studied Np(V) humate complexes and the Np(V)-Bio-Rex70 sorbate. In the equatorial plane Np(V) is surrounded by about 3 oxygen atoms with bond lengths of 2.48 - 2.49 Å. The comparison of the structural parameters of the Np(V) humates with those of Np(V)-Bio-Rex70 points to the fact that the interaction between HA and Np(V) in the neutral pH range is dominated by carboxylate groups. However, up to now a contribution of phenolic OH groups to the interaction process cannot be excluded completely. The comparison of the obtained structural data for the Np(V) humates to those of Np(V) carboxylates and Np(V) aquo ions reported in the literature indicates that humic acid carboxylate groups predominantly act as monodentate ligands. A differentiation between equatorial coordinated carboxylate groups and water molecules using EXAFS spectroscopy is impossible.

Keywords: Neptunium(V); Humic acid; Complexation; EXAFS; NIR absorption spectroscopy; Structure

  • Radiochimica Acta 93(2005), 17-25

Publ.-Id: 5985

Factors affecting the specific activity of [18F]fluoride from a water target

Füchtner, F.; Preusche, S.; Mäding, P.; Steinbach, J.

  • Contribution to proceedings
    15th International Symposium on Radiopharmaceutical Chemistry (ISRC), Sydney, Australia, 10.-14.08.2003; J. Label. Comds. Radiopharm. 46 (2003) S218
  • Poster
    10th Workshop on Targetry and Target Chemistry, Medison, 13.-15.08.2004
  • Lecture (Conference)
    10th Workshop on Targetry and Target Chemistry, 13.-15.08.2004, Madison, USA

Publ.-Id: 5983

Changes in brain metabolism associated with remission in unipolar major depression

Holthoff, V.; Beuthien-Baumann, B.; Zündorf, G.; Triemer, A.; Lüdecke, S.; Winiecki, P.; Koch, R.; Füchtner, F.; Herholz, K.

Objective: Functional brain correlates of remission in patients with major depressive disorder (MDD) are measured with positron emission tomography (PET) and 18F-fluorodeoxyglucose.
Method: Glucose metabolism was measured in patients (n = 41) with moderate to severe MDD during acute depression and in the remitted state defined as a period of asymptomatic condition over 12 weeks. Data analyses used a region-of-interest (ROI) approach and statistical parametric mapping (SPM).
Results: There were significant decreases in metabolism upon remission with respect to the baseline scan in left prefrontal, anterior temporal and anterior cingulate cortex and bilateral thalamus (SPM analysis) and bilateral putamen and cerebellum (SPM and ROI analyses). There was a significant asymmetriy in prefrontal and anterior cingulate cortex metabolism with lower metabolism in the left hemisphere that persisted despite clinical remisson.
Conclusion: These findings support the hypothesis that selective monoamine reuptake inhibition leads to an attenuation of a brain circuit that mediates depressive symptomatology.

Keywords: depressive disorder; tomography; emission-computed; limbic system; frontal lobe; cerebellum

  • Acta Psychiatrica Scandinavica 110(2004), 184-194

Publ.-Id: 5982

Impact of asymmetric intrauterine growth restriction on organ function in newborn piglets

Bauer, R.; Walter, B.; Brust, P.; Füchtner, F.; Zwiener, U.

  • European Journal of Obstetrics and Gynecology and Reproductive Biology 110 (2003) S40-S49

Publ.-Id: 5981

An accurate method for correction of head movement in PET

Bühler, P.; Just, U.; Will, E.; Kotzerke, J.; van den Hoff, J.

A method is presented to correct positron emission tomography (PET) data for head motion during data acquisition. The method is based on simultaneous acquisition of PET data in list mode and monitoring of the patient's head movements with a motion tracking system. According to the measured head motion, the line of response (LOR) of each single detected PET event is spatially transformed, resulting in a spatially fully corrected data set. The basic algorithm for spatial transformation of LORs is based on a number of assumptions which can lead to spatial artifacts and quantitative inaccuracies in the resulting images. These deficiencies are discussed, demonstrated and methods for improvement are presented. Using different kinds of phantoms the validity and accuracy of the correction method is tested and its applicability to human studies is demonstrated as well.

  • IEEE Transaction on Medical Imaging 23(2004)9, 1176-1185
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 30(2003), S174/116
  • Lecture (Conference)
    European Association of Nuclear Medicine Annual Congress 2003, Amsterdam, 23.-27.08.2003

Publ.-Id: 5980

Teilautomatisierte Segmentierung zur Quantifizierung von Metastasen bei der FDG-PET

Pötzsch, C.; Beuthien-Baumann, B.; van den Hoff, J.

  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A26

Publ.-Id: 5979

Nutzbarmachung der List-Mode Akquisition an der PET-Kamera ECAT EXACT HR+

Just, U.; Will, E.; Beuthien-Baumann, B.; Bühler, P.; van den Hoff, J.

  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A93

Publ.-Id: 5978

Korrektur bewegungsbedingter Fehlortung individueller Koinzidenzereignisse in der PET

Bühler, P.; Just, U.; Will, E.; Zührl, K.; Kotzerke, J.; van den Hoff, J.

  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A26
  • Lecture (Conference)
    41. Jahrestagung der DGN, 2.-5. April 2003, Essen

Publ.-Id: 5977

Untersuchung des Glukosestoffwechsels bei Patienten mit HIV-Infektion unter hochaktiver antiretroviraler Therapie (HAART) mittels quantitativer dynamischer FDG-PET

van den Hoff, J.; Börner, A.; Behrens, G.; Meyer, G. J.; Knapp, W. H.

  • Abstract in refereed journal
    In: Nuklearmedizin als Paradigma molekularer Bildgebung, ed. I Brink, S Högerle, E Moser, p. 16, Blackwell Verlag, Berlin (2002)

Publ.-Id: 5976

Dynamische 15O-H2O-PET zur Erzeugung quantitativer 3D-Polar-Maps der Myokardperfusion

van den Hoff, J.; Fricke, H.; Wielepp, P.; Burchert, W.

  • Abstract in refereed journal
    Nuklearmedizin (2003) 42 p. A27

Publ.-Id: 5975

P0316 - Anordnung zur Röntgentomographie milt einem elektronisch abgelenkten Elektonenstrahl

Prasser, H.-M.; Hampel, U.

Aufgabe der Erfindung ist es, eine Anordung zur schnellen Tomographie mit elektronisch abgelenktem Elektronenstrahl vorzuschlagen, die es ermöglicht, Projektionen der Dichteverteilung eines zeitlich veränderlichen Messobjekts aus einer genau definierten Messebene zu ermitteln, deren Orientierung im Raum sich bei Veränderung der Durchstrahlungsrichtung während des Messzyklus nicht ändert.

  • Patent
    DE 103 56 601 A1
  • Patent
    DE 103 56 601 B4 - 2008.11.27

Publ.-Id: 5974


Dekorsy, T.; Helm, M.; Georgiev, N.; Künzel, H.

Es wird ein Quantenkaskadenlaser mit einer Emissionswellenlänge unterhalb von 3,4 um und oberhalb von 1,5 um vorgeschlagen.

  • Patent
    DE 103 55 949 A1
  • Patent
    EP 1536531

Publ.-Id: 5973

P0313 - Verfahren zur Erzeugung verbesserter heteroepitaktischer gewachsener Siliziumkarbidschichten auf Siliziumsubstraten

Skorupa, W.; Panknin, D.; Ferro, G.; Gebel, T.; Yankow, R.

Aufgabe der Erfindung ist ein Verfahren, mit dem es möglich ist, die in der unteren Schicht vorhandenen gewünschten Eigenschaften der mit Lichtimpulsen behandelten Substrate für den weiteren Prozess verwertbar zu machen und die Welligkeit der Schicht zu verringern oder zu vermeiden.

  • Patent
    DE 103 44 986 A1
  • Patent
    WO 2005/031825 A1
  • Patent
    DE 103 44 986 B4 - 23. Okt. 2008

Publ.-Id: 5971

3-O-Methyl-6-[18F]Fluoro-L-DOPA and its Evaluation in Brain Tumour Imaging

Beuthien-Baumann, B.; Bredow, J.; Burchert, W.; Füchtner, F.; Bergmann, R.; Alheit, H.-D.; Reiss, G.; Hliscs, R.; Steinmeier, R.; Franke, W.-G.; Johannsen, B.; Kotzerke, J.

  • European Journal of Nuclear Medicine and Molecular Imaging (2003) 30: 1004-1008

Publ.-Id: 5970

Synthesis and Characterization of [11C]SMe-ADAM as a Potential Radiotracer for Imaging the Serotonin Transporter with PET

Zessin, J.; Kretzschmar, M.; Pawelke, B.; Bergmann, R.; Deuther-Conrad, W.; Brust, P.; Wüst, F.; Steinbach, J.; Johannsen, B.

  • Poster
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5969

Sex Differences in the Uptake of [18F]FMe-McN in Rat Brain

Marjamäki, P.; Eskola, O.; Haaparanta, M.; Grönroos, T.; Fagerholm, V.; Bergman, J.; Lehikoinen, P.; Savisto, N.; Zessin, J.; Solin, O.

  • Lecture (Conference)
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5968

Comparison of [11C](+)-MCN5652 and S-([18F]Fluoromethyl)-(+)-MCN5652 for PET Imaging of the Serotonin Transporter

Brust, P.; Zessin, J.; Solin, O.; Steinbach, J.

  • Lecture (Conference)
    15th International Symposium on Radiopharmaceutical Chemistry, Sydney, Australia, 2003

Publ.-Id: 5967

S-[18F]fluoromethyl-(+)-McN5652, a PET Tracer for the Serotonin Transporter: Evaluation in Rats

Marjamäki, P.; Zessin, J.; Eskola, O.; Grönroos, T.; Haaparanta, M.; Bergman, J.; Lehikoinen, P.; Forsback, S.; Brust, P.; Steinbach, J.; Solin, O.

The [18F]fluoromethyl analog of (+)-McN5652 ([18F]FMe-NcN) for imaging serotonin transporter (SERT) with positron emission tomography (PET) has recently been synthesized. We describe here the biological evaluation of [18F]FMe-NcN in rats. Biodistribution studies of [18F]FMe-McN in rat brain ex vivo after an intravenous injection showed a high accumulation of radioactivity in the regions rich in SERT, such as raphe nuclei, hypothalamus, thalamus, substantia nigra, locus coeruleus, and amygdala. Region-to-cerebellum ratios reached a muximum value of 9 in raphe nuclei within 3.5 h after administration. The specificity and selctivity of [18F]FMe-McN binding to SERT was studied by preinjecting blocking doses of serotonin, norepinephrine, and dopamine transporter inhibitors. Fluoxetine, a specific inhibitor for SERT, decreased the specific binding of [18F]FMe-McN in raphe nuclei by 91 plus minus 4 %; in other regions rich in SERT, similar results were obtained GBR12909 and nisoxetine, selective inhibitors for dopamine transporter (DAT) and norepinephrine transporter (NET), respectively, showed no significant effects on the uptake of [18F]FMe-McN. Our studies show that [18F]FMe-McN has a clear potential as a tracer for studies with PET or SERT function in humans.

Keywords: [18F]FMe-(+)-McN5652; serotonin transporter; positron emission tomography; 18F

  • Synapse (2003) 47: 45-53

Publ.-Id: 5966

18F-Labelling of the CCR1 antagonist ZK811460 for the diagnosis of the Alzheimer´s disease

Mäding, P.

  • Lecture (others)
    Technical Exchange Meeting on Alzheimer Imaging, Berlin, 30.10.2003

Publ.-Id: 5965

Investigation of the Complexation and the Migration Behavior of Actinides and Non-Radioactive Substances with Humic Acids under Geogenic Conditions - Complexation of Humic Acids with Actindies in the Oxidation State IV Th, U, Np

Sachs, S.; Schmeide, K.; Brendler, V.; Krepelova, A.; Mibus, J.; Geipel, G.; Heise, K.-H.; Bernhard, G.

Objective of this project was the study of basic interaction and migration processes of actinides in the environment in presence of humic acids (HA). To obtain more basic knowledge on these interaction processes synthetic HA with specific functional properties as well as 14C-labeled HA were synthesized and applied in comparison to the natural HA Aldrich. One focus of the work was on the synthesis of HA with distinct redox functionalities. The obtained synthetic products that are characterized by significantly higher Fe(III) redox capacities than Aldrich HA were applied to study the redox properties of HA and the redox stability of U(VI) humate complexes. It was confirmed that phenolic OH groups play an important role for the redox properties of HA. However, the results indicate that there are also other processes than the single oxidation of phenolic OH groups and/or other functional groups contributing to the redox behavior of HA. A first direct-spectroscopic proof for the reduction of U(VI) by synthetic HA with distinct redox functionality was obtained.
The complexation behavior of synthetic and natural HA with actinides (Th, Np, Pu) was studied. Structural parameters of Pu(III), Th(IV), Np(IV) and Np(V) humates were determined by X-ray absorption spectroscopy (XAS). The results show that carboxylate groups dominate the interaction between HA and actinide ions. These are predominant monodentately bound. The influence of phenolic OH groups on the Np(V) complexation by HA was studied with modified HA (blocked phenolic OH groups). The blocking of phenolic OH groups induces a decrease of the number of maximal available complexing sites of HA, whereas complex stability constant and Np(V) near-neighbor surrounding are not affected.
The effects of HA on the sorption and migration behavior of actinides was studied in batch and column experiments. Th(IV) sorption onto quartz and Np(V) sorption onto granite and its mineral constituents are affected by the pH value and the presence of HA. HA exhibits a significant influence on the transport of U(IV) and U(VI) in a laboratory quartz sand system.
In order to provide the basis for a more reliable modeling of the actinide transport, the metal ion complexation with HA has to be integrated into existing geochemical speciation codes. Within this project the metal ion charge neutralization model was embedded into the geochemical modeling code EQ3/6. In addition to that, a digital data base was developed which covers HA complexation data basing on the charge neutralization model.

Keywords: Humic Substances; Humic Acids; Model Substances; Redox Properties; Actoinides; Thorium; Uranium; Neptunium; Plutonium; Complexation; Structure; Sorption; Migration; Repository; Modeling; Data Base

  • Other report
    Final Report, BMWA Project No. 02 E 9299
  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf, FZR-399 2004
    ISSN: 1437-322X
  • Other report
    In: C.M. Marquardt (Ed.): Investigations on the Complexation Behaviour of Humic Acids and their Influence on the Migration of Radioactive and Non-radioactive Substances under Conditions Close to Nature. Final Report, Forschungszentrum Karlsruhe, Wissenschaftliche Berichte FZKA 6999, Karlsruhe 2004


Publ.-Id: 5964

18F-markierte Corticosteroide als Liganden für die Darstellung von Glucocorticoidrezeptoren (GR) im Gehirn mittels PET

Wüst, F.

  • Lecture (others)
    Gemeinsames Institutskolloquium der Klinik und Poliklinik für Nuklearmedizin und des Instituts für Interdisziplinäre Isotopenforschung Leipzig, 23.10.2003

Publ.-Id: 5962

Fraktografie an radioaktiven Proben mit der Abdrucktechnik

Müller, G.

Die direkte Fraktografie auf Bruchflächen von bestrahlten oder radioaktiv kontaminierten Proben ist nur an speziell für einen solchen Einsatz dedizierten Rasterelekt-ronenmikroskopen (REM) möglich. Eine Alternative bietet die Anwendung der Abdrucktechnik, mit deren Hilfe auch fraktografische Untersuchungen an herkömmli-chen REMs durchgeführt werden können. Die Methode muss genügend Details wie-dergeben, unter den Bedingungen einer heißen Zelle handhabbar sein und im Endabdruck kontaminationsfrei arbeiten.

Abdrucktechniken werden von einschlägigen Firmen vorzugsweise auf der Basis von Folien angeboten. Für rauhe, duktile Bruchflächen sind sie ungeeignet. Auch die Verwendung von Filmmaterialien und Wachsen ist unter den gegebenen Bedingungen nicht geeignet. Am erfolgreichsten erweist sich ein einstufiger Negativ-Abdruck mit duktilen, additionsvernetzenden Silikonen.

Dieses Verfahren wurde an Bruchflächen von Proben aus Reaktordruckbehälterstäh-len und -schweißmetall erfolgreich getestet. Zielstellung war vor allem der Nachweis von interkristallinen Bruchanteilen an vorzugsweise spröd und duktil gebrochenen Charpy-Proben. An den unbestrahlten RDB-Stählen A 533-B Cl. 1 und 15 CrMoV2 sowie dem Schweißmetall 10 CrMnNiMo2 konnte ein relativ großer Anteil interkristallinen Bruchs nachgewiesen werden. Die Anwendung des Verfahrens auf bestrahlte Proben des Schweißmetalls 10 CrMnNiMo2 erbrachte, je nach der Zähig-keit der Proben, differierende Anteile an transkristallinem Spalt- und Wabenbruch und nur sehr vereinzelten interkristallinen Bruch.

Keywords: Abdrucktechnik; Bruchfläche; Provil Novo; Reaktordruckbehälterstähle; radioaktiv; kontaminiert

  • Lecture (Conference)
    Sonderbände der Praktischen Metallographie, Band 35, Fortschritte in der Metallographie, S. 371-376, Sonderdruck und Internetbericht durch Fa. Heraeus Kulzer GmbH & Co. KG
  • Contribution to external collection
    Sonderbände der Praktischen Metallographie, Band 35, Fortschritte in der Metallographie, S. 371-376, Sonderdruck und Internetbericht durch Fa. Heraeus Kulzer GmbH & Co. KG


Publ.-Id: 5961

Comment on "Identification of lattice vacancies on the two sublattices of SiC"

Kuriplach, J.; Brauer, G.; Anwand, W.; Skorupa, W.

no abstract !

Keywords: silicon carbide; positron annihilation; defects

Publ.-Id: 5958

Percolation of Electron Tunneling between Si Nanocrystals Synthesized in Thin SiO2 Films by Ion Implantation

Müller, T.; Heinig, K.-H.

The controlled fabrication of a narrow layer of Si nanocrystals (NCs) in thin SiO2 films for multi-dot non-volatile memories (NC memory) is still a considerable materials issue, which will be addressed in this contribution. The synthesis of NCs by Si+ implantation of SiO2 followed by a thermal treatment aims at an optimum NC density. A NC density being as high as possible is required in order to achieve a substantial threshold voltage shift of the MOS transistor. On the other hand, the advantages of the NC memory, as good scalability and data retention, are lost at too high NC densities. Then NC’s charge can spread over neighboring NCs by direct e- tunneling, i.e. due to electrical in-plane percolation paths. One single oxide defect could discharge several electrically percolated NCs.
This contribution is devoted to the trade-off between these two optimization routes. The Si NC formation by nucleation, growth and Ostwald ripening in low-energy Si+ implanted SiO2 is predicted by kinetic lattice Monte Carlo simulations. On the basis of these simulations, the dependence of the Si NC density, the distribution of the NC spacing as well as the threshold for extended electron tunneling paths are predicted. Thus, process conditions could be identified, where NCs align in narrow layer at high density but are sufficiently electrically isolated.

  • Poster
    Fall Meeting of the Materials Research Society, December 1-5, 2003, Boston, USA

Publ.-Id: 5957

Comparison of Kinetic MC Simulations and EFSTEM Observations of Phase Separation in Si Implanted Thin SiO2 Films

Müller, T.; Heinig, K.-H.; Bonafos, C.; Coffin, H.; Ben Assayag, G.; Schamm, S.; Zanchi, G.; Claverie, A.; Colliex, C.; Tencé, C.

Studies on the ion beam synthesis of narrow Si nanocrystal (NC) layers in thin SiO2 films are presented. Very low-energy Si+ implantation into gate oxides for MOS transistors followed by thermal annealing allows for the fabrication of novel Si NC floating gate based non-volatile charge storage devices.
Small and isolated Si NCs at high density are required to obtain a large threshold voltage shift of the memory transistor. However, former work shows that the characterization of the Si NCs embedded in SiO2 by conventional Transmission Electron Microscopy (TEM) is difficult. It requires careful con-siderations and special imaging conditions [1] due to the weak contrast be-tween Si and SiO2 .
In this contribution, Energy Filtered Scanning Transmission Electron Micros-copy (EFSTEM) investigations on the morphology of phase separated Si in SiO2 are presented, which overcome the contrast limitations of the conven-tional TEM. Furthermore, a comparison of the observed Si pattern with pre-dictions of kinetic lattice Monte Carlo (MC) simulations [2] is performed. The Si precipitates were synthesized by 1 keV Si+ implantation into 10 nm thick SiO2 and by furnace annealing in N2 (or N2 + O2). Varying fluences from 5E15 to 2E16 Si+ cm-2 were used in order to adjust the Si excess in the SiO2. For these conditions, dynamical binary collision simulations (TRIDYN) of high-fluence implantation were combined with kinetic Monte Carlo simula-tions of NC formation by phase separations. For low Si excess, NCs are pre-dicted to form by nucleation, growth and Ostwald ripening. On the other hand, at high Si excess, phase separation proceeds via spinodal decomposition, were elongated NCs are found in our computer experiment. At even higher flu-ences, structural percolation occurs and a random connected Si mesh forms. Thus, the morphology of the phase separated Si changes with increasing ion fluence from isolated, spherical NCs to percolated structures as observed by EFSTEM. The pattern of the phase separated Si predicted by kinetic Monte Carlo simulations and observed by Electron Microscopy agree remarkably well.

  • Lecture (Conference)
    Fall Meeting of the Matrials Research Society 2003, December 1-5, Boston, USA

Publ.-Id: 5955

Range and mixing distributions of low-energy carbon ions as a base for subplantation growth models

Dollinger, G.; Neumaier, P.; Bergmaier, A.; Görgens, L.; Eckstein, W.; Fischer, R.; Hofsäss, H.; Jäger, H. U.; Kröger, H.; Ronning, C.

Subplantation was early recognised as being the basic process in low-energy ion growth of diamondlike materials and has also to be considered for the description of bias enhanced diamond nucleation. A number of theories modelling the evolution of diamondlike phases have been proposed. However, the precise details of the subplantation and relaxation processes remain unclear. The problem in testing the complex models is that experimental information other than film structure versus ion energy is missing to a large extent. Mixing and range distributions of low-energy carbon ions are ideal data to model diamond-like film growth. Here we present measurements of range and mixing distributions for carbon ions at energies in the relevant energy range between 12 eV and 692 eV in carbon. The substrates are grown at the identical energies using 12C ions by mass separated ion beam deposition. Less than a monolayer of 13C was implanted each for the range distributions and as a marker layer for the mixing profiles. The 13C depth profiles are measured by high-resolution elastic recoil detection (ERD). These data are directly compared to calculations based on the binary collision approximation (TRIDYN) and to molecular dynamics (MD) simulations which consider atomic interactions on a time scale up to 15 ps including the thermal spike phase. Additionally, mixing distributions are derived from a transport calculation based on the measured range distributions. The measured range profiles show bimodal structures for energies below 200 eV which are significantly broader than the calculated profiles.The mixing profiles are also significantly broader than respective TRIDYN and MD calculations at these low energy. However, mixing profiles are in good agreement with transport calculations based on the measured range profiles showing the relevance of the measured range structures. Three reasons for the observed differences between the measured and theoretical range and mixing distributions are discussed in the paper: thermal induced self diffusion during thermal spike, mobility solely of the deposited ion after the collisional stage and a 3-dimensional surface structure of the carbon films on atomic scale. The experiment allows a crucial test for models of the subplantation scheme and may serve as input for improved calculations.

  • Invited lecture (Conferences)
    MRS 2003 Fall Meeting, Dec. 1 - 5, Boston, USA; Symp.R: Radiation Effects and Ion Beam Processing of Materials; contr. R12.1, invited talk

Publ.-Id: 5954

Conserved high-affinity ligand binding and membrane association in the native and refolded extracellular domain of the human glycine receptor alpha 1 subunit

Breitinger, U.; Breitinger, H.-G.; Bauer, F.; Fahmy, K.; Glockenhammer, D.; Becker, C.-M.

  • Journal of Biological Chemistry 279(2004)4, 1627-1636

Publ.-Id: 5953

Analysis of buoyancy driven coolant mixing by using the code TRIO_U

Höhne, T.; Bieder, U.

A generic investigation of the influence of density differences between the primary loop inventory and the ECC water on the mixing in the downcomer was made at the ROCOM Mixing Test Facility at Forschungszentrum Rossendorf (FZR). For the validation of the Trio_U code an experiment with 5% constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop inventory was taken. Trio_U is a CFD code developed by the CEA France, aimed to supply an efficient computational tool to simulate transient thermal-hydraulic single -phase turbulent flows encountered in the nuclear systems as well as in the industrial processes. For this study, a LES approach was used for mesh sizes between 1–2 million control volumes. The study showed, that density effects play an important role during natural convection with ECC injection in pressurized water reactors. Further-more it was important to point out, that Trio_U is able to cope the main flow and mixing phenomena.

Keywords: Boron Dilution; COOLANT MIXING; ROCOM Test FACILITY; Computational Fluid Dynamics; LES; Trio_U

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 25.-27.05.2004, 2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 25.-27.05.2004, 2004, Düsseldorf, Germany, CD-ROM

Publ.-Id: 5952

Validation of TRIO_U – Numerical Simulations of a ROCOM Buoyancy Driven Test Case

Höhne, T.; Bieder, U.; Prasser, H.-M.; Kliem, S.

A generic investigation of the influence of density differences between the primary loop inventory and the ECC water on the mixing in the downcomer was made at the ROCOM Mixing Test Facility at Forschungszentrum Rossendorf (FZR)/Germany.
ROCOM is designed for experimental coolant mixing studies over a wide variety of possible scenarios. It is equipped with advanced instrumentation, which delivers high-resolution information characterizing either temperature or boron concentration fields in the investigated pressurized water reactor.
For the validation of the Trio_U code an experiment with 5% constant flow rate in one loop (magnitude of natural circulation) and 10% density difference between ECC and loop water was taken.
Trio_U is a CFD code developed by the CEA France, aimed to supply an efficient computational tool to simulate transient thermal-hydraulic single-phase turbulent flows encountered in the nuclear systems as well as in the industrial processes. For this study a LES approach was used for mesh sizes according to between 300000 – 2 million control volumes.
The results of the experiment as well as of the numerical calculations show, that a streak formation of the water with higher density is observed. At the upper sensor, the ECC water covers a small azimuthal sector. The density difference partly suppresses the propagation of the ECC water in circumferential direction. The ECC water falls down in an almost straight streamline and reaches the lower downcomer sensor position directly below the affected inlet nozzle. Only later, coolant containing ECC water appears at the opposite side of the downcomer.
The study showed, that density effects play an important role during natural convection with ECC injection in pressurized water reactors. Furthermore it was important to point out, that Trio_U is able to cope the main flow and mixing phenomena.


  • Lecture (Conference)
    12th International Conference on Nuclear Engineering, 25.-29.05.2004, Washington D.C., United States
  • Contribution to proceedings
    12th International Conference on Nuclear Engineering, 25.-29.05.2004, Washington D.C., United States, Book of Abstracts, S. 278

Publ.-Id: 5951

Radiation enhanced silicon self-diffusion and the silicon vacancy at high temperatures

Bracht, H.; Fage, J. P.; Zangenberg, N.; Nylandsted, A. L.; Haller, E. E.; Lulli, G.; Posselt, M.

We report proton radiation enhanced self-diffusion (RESD) studies on Si-isotope heterostructures. Self-diffusion experiments under irradiation were performed at temperatures between 780 0C and 872 0C for various times and proton fluxes. Detailed modeling of RESD provides direct evidence that vacancies at high temperatures diffuse with a migration enthalpy of HmV = (1.8±0.5 eV) significantly more slowly than expected from their diffusion at low temperatures, which is described by HmV < 0.5 eV. We conclude that this diffusion behavior is a consequence of the microscopic configuration of the vacancy whose entropy and enthalpy of migration increase with increasing temperature.

Keywords: defects; silicon; vacancy; interstitial; diffusion; ion implantation

  • Physical Review Letters 91 (2003) 245502

Publ.-Id: 5950

Monte-Carlo-Methoden für den Elektronentransport mit Einzelstreumodellen

Reichelt, U.; Henniger, J.; Enghardt, W.

Die Abbremsung eines Elektrons bis zu seiner vollständigen Thermalisierung ist durch eine sehr große Anzahl von Wechselwirkungen gekennzeichnet. Deshalb basieren Monte-Carlo-Algorithmen für den Elektronentransport derzeit noch fast ausschließlich auf der Anwendung von zwei Mehrfachstreumodellen. Die Vielfachstreutheorie nach MOLIERE versagt bei kleinen räumlichen Strukturen und Dichtesprüngen. Das Modell nach GOUDSMIT-SAUNDERSON führt für diese Fälle praktisch zum Einzelstreumodell und erfordert dabei aber einen enormen numerischen Aufwand.
An dieser Stelle soll ein Monte-Carlo-Algorithmus vorgestellt werden, der genuin auf Einzelstreuakten basiert. Die Strahlverfolgung (ray tracing) sowie das Erheben von Stichproben für freie Weglängen und Eigenschaften der Streuteilchen müssen mit effektiven numerischen Verfahren behandelt werden. Insbesondere die stark anisotropen Streuprozesse erschweren dieses Anliegen erheblich.
Diese Methodik ist ins Transportprogramm AMOS implementiert. Ein Vergleich mit experimentell bestimmten Daten und anderen Transportrechnungen zeigt zufriedenstellende Übereinstimmungen.

Keywords: Strahlungstransport; Einzelstreumodell; Monte-Carlo-Algorithmus

  • Lecture (Conference)
    68. Physikertagung der Deutschen Physikalischen Gesellschaft 2004, Frühjahrstagung der Arbeitskreise Atome, Moleküle, Quantenoptik und Plasmen (AMOP)

Publ.-Id: 5949

Measurements of gamma and neutron flux spectra in iron-water configurations

Böhmer, B.; Grantz, M.; Hansen, W.; Hinke, D.; Konheiser, J.; Noack, K.; Mehner, H.-C.; Stephan, I.; Unholzer, S.

Neutron and gamma spectra were measured behind and inside of modules consisting of variable iron and water slabs which were installed in radial beams of the zero-power training and research reactors AKR of the Technical University Dresden and ZLFR of the University of Applied Sciences Zittau/Görlitz. The applied NE-213 scintillation spectrometer allowed the measurement of gamma and neutron fluence spectra in the energy regions 0.3 - 10 MeV for photons and 1.0 - 20 MeV for neutrons. Measurements with thermoluminescence dosemeters (TLD) between slabs supplied additional information about the space distribution of energy integrated fluxes. The paper describes the experiments and presents some important results of the measurements. They will be compared with the results of transport calculations made by means of MCNP and TRAMO in another paper.

Keywords: neutron spectra; gamma spectra; spectrum measurements; coupled neutron/gamma transport calculations; NE-213 scintillation spectrometer; TLD-measurements

  • Kerntechnik 68 (2003) 5-6

Publ.-Id: 5948

Theorien und Experimente zum hydromagnetischen Dynamoeffekt

Stefani, F.

Die Magnetfelder von Planeten, Sternen und Galaxien entstehen hauptsächlich durch Selbsterregung in strömenden elektrisch leitfähigen Fluiden. Falls die Strömung stark genug ist und ein gewisses Mass an Schraubenförmigkeit aufweist, können die unter der Wirkung eines angenommenen Magnetfeldes induzierten elektrischen Ströme genau jenes Magneteld reproduzieren. Die Theorie hydromagnetischer Dynamos wird anhand der Induktionsgleichung sowie eines äquivalenten Integralgleichungssystems auf Basis des Biot-Savart-Gesetzes skizziert. Der Schwerpunkt des Vortrages liegt auf dem experimentellen Nachweis des Effektes, der Ende 1999 nahezu zeitgleich an zwei Natriumanlagen in Riga und Karlsruhe erfolgte. Die Ergebnisse des Rigaer Experimentes werden ausführlicher dargestellt und mit numerischen Resultaten verglichen.

  • Lecture (others)
    Physikalisches Kolloquium, Brandenburgische Technische Universität Cottbus, 13. 01.2004, Cottbus, Germany

Publ.-Id: 5947

Free-Electron Lasers in Physics

Dekorsy, T.

The topic of this chapter is a survey on the main applications of free-electron lasers (FELs) in physical sciences. The merits of FELs are discussed with respect to other available laser sources. For the wavelength ranges, where FELs contributed significantly to advances in physical sciences, specific examples of the research with FELs are given.

Keywords: free-electron lasers; applications of FELs; spectroscopy; time-resolved

  • Contribution to external collection
    Encyclopedia of Modern Optics, Eds. B.D. Guenther and D.G. Steel, Elsevier (2004), 164-169

Publ.-Id: 5946

Light-emitting silicon pn diodes

Dekorsy, T.; Sun, J.; Skorupa, W.; Schmidt, B.; Helm, M.

We report on the electrical and optical characteristics of silicon light-emitting pn diodes. The diodes are prepared by ion implantation of boron at high doses and subsequent high-temperature annealing. Under forward bias, the diodes emit infrared electroluminescence close below the bandgap of bulk Si. We present a rate equation model for bound excitons, free excitons and free carriers which successfully describes the electrical and optical behaviour of the diodes at low temperatures. Especially an electrical bistability observed below 50 K is shown to be based on the interplay of bound excitons, free excitons, and free carriers in the active area of the diodes. The ionization of bound excitons is the origin of an improved electroluminescence from the diodes
at higher lattice temperatures.

Keywords: silicon based optoelectronics; light emission; pn diode; ion implantation

  • Applied Physics A 78(2004), 471-475

Publ.-Id: 5945

Discussion of the Behaviour of Different RPV-Steels in Vessel Creep Failure Experiments

Willschütz, H.-G.; Müller, G.; Altstadt, E.

Considering the hypothetical core melt down scenario for a light water reactor the failure mode of the reactor pressure vessel (RPV) has to be investigated to deter-mine the loadings on the containment. Experimental and numerical work is performed worldwide to get insights about possible consequences. To validate the developed computational tools numerical simulations of Lower Head Failure experi-ments like OLHF or FOREVER are conducted.
An interesting question to be solved in this frame is the reason for the different shape of the failure site even under comparable loading conditions and for the same material: In some experiments like LHF-7 and EC-FOREVER-3B a rough crack surface was found at the failure site while in others like OLHF-1 a rather ductile behaviour was observed resulting in nearly blade-like edges on both sides of the vessel opening.

Keywords: lower head failure experiments; LHF; OLHF; FOREVER; creep failure; FEM simulation

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, CD-ROM 519-522

Publ.-Id: 5944

Fluid-Structure Interaction Investigations for Pipelines

Altstadt, E.; Carl, H.; Weiß, R.

The influence of the fluid-structure interaction on the magnitude fo the loads on pipe walls and support structures is not yet completely understood. In case of a dynamic load caused by a pressure wave, the stresses in pipe walls, especially in bends, are different from the static case.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Forschungszentrum Rossendorf; FZR-393 Dezember 2003
    ISSN: 1437-322X


Publ.-Id: 5943

Characterization of Radiation Effects in Reactor Pressure Vessel Steels by means of Small Angle Neutron Scattering

Ulbricht, A.; Böhmert, J.

The influence of deleterious elements on the microstructural evolution in materials due to neutron irradiation was investigated by small angle neutron scattering experiments.
The study compares properties of ASTM and VVER RPV steels after different exposure levels.

Keywords: SANS; RPV steel; radiation defect

  • Lecture (Conference)
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany
  • Contribution to proceedings
    Annual Meeting on Nuclear Technology 2004, 25.-27.05.2004, Düsseldorf, Germany, CD-ROM pp. 515-518,

Publ.-Id: 5942

Kolloidgetragene Schadstoffe in oxischen Bergwerkswässern

Zänker, H.; Ulrich, K.-U.; Jenk, U.; Moll, H.; Richter, W.

Ausgehend von drei grundsätzlichen Fällen werden die Konsequenzen der Vernachlässigung des kolloidgetragenen Transports von toxischen und radiotoxischen Schadstoffen in stillgelegten Bergwerken für die Prognose der Auswirkungen der Bergwerke auf die Umwelt diskutiert. Zunächst werden Messungen zur Bestimmung des Kolloidinventars in einem typischen "sauren Porenwasser" (Lettenwasser Freiberg) und einem typischen "Bulk-Wasser" (Stollenwasser Rothschönberg) beschrieben. Sodann wird ein Neutralisationsversuch vorgestellt, bei dem innerhalb von fünf Tagen 6 Liter sauerstoffarmes saures Flutungswasser aus einem Uranbergwerk mit etwa 100 Liter oxischem Grundwasser aus einem in der Nähe gelegenen Grundwasserleiter gemischt wurden, um die Flutung der Grube unter oxischen Bedingungen (Begasung mit Sauerstoff) bis in ihr Endstadium zu simulieren. Der Versuch zeigt, dass ab pH > 4 zunehmende Mengen des in dem Flutungswasser enthaltenen Urans in einen kolloidgetragenen Zustand übergehen. Die Natur der Uranbindung in den Kolloiden wird auf spektroskopischem Wege (Tieftemperatur-EXAFS an der Rossendorfer Beamline ROBL der ESRF in Grenoble) noch direkt bestimmt.

Keywords: Kolloide; Bergwerke; Uran; Flutung

  • Poster
    Jahrestagung der Wasserchemischen Gesellschaft in der GDCh, Bad Saarow, 17. - 19. Mai 2004
  • Contribution to proceedings
    Jahrestagung Wasserchemische Gesellschaft, 17.-19.05.2004, Bad Saarow, Deutschland
    Kurzreferate, Wächtersbach: PM-GrafikDesign, 3-936028-24-9, 181-185

Publ.-Id: 5941

Imaging Si Nanoclusters in Thin SiO_2 Layers by XTEM using Contrast Enhancing Decoration with Ge

Röntzsch, L.; Heinig, K. H.; Schmidt, B.

The Multidot Nano-flash Memory suggested by Tiwari [APL69(1996)1232] is a promissing candidate for succeeding the common Floating Gate Flash Memory.

Its most challenging configurational feature is a layer of insulated Si nanoclusters (NCs) within the oxide of a MOS-like structure.

Here, we present experimental evidence that the theoretical concept predicting the self-organization of delta-layers of Si NCs at ion irradiated interfaces is valid (cf. Heinig [APA77(2003)17]).

In this approach of ``bottom-up" structuring, unconventionally, a 15nm thin buried SiO_2 layer, which is enclosed by a 50nm poly-Si capping layer and the Si substrate, is irradiated with Si ions. Ion impact drives the system to a state far from thermodynamic equilibrium, i.e. the local composition of the target is modified to a degree unattainable in common processes. A region of SiO_x (x<2) -- where x is a function of depth -- is formed which is not stable.

During annealing, the system relaxes towards equilibrium, i.e. phase separation (via spinodal decomposition and nucleation) sets in. Within a certain time window of annealing, the structure of the system matches with a structure similar to the Multidot Memory device, the principal character of which is a 2D layer of Si nanoclusters of (d~3nm) which is embedded in a 3D SiO_2 matrix at a distance of ~3nm from the Si substrate.

The experimental handicap that tiny Si NCs (d<3nm) which are embedded in SiO_2 are not visible in common XTEM is resolved by a novel method which applies Ge as contrast enhancing element in TEM studies of tiny Si NCs.

Keywords: Ion Irradiation; Si Nanoclusters; Ge decoration; Multidot Flash Memory

  • Poster
    Conference contribution to Trends in Nanotechnology, Sept. 2003, Salamanca, Spain

Publ.-Id: 5939

Velocity measuring techniques at FZR and status of MULTIMAG

Galindo, V.; Cramer, A.; Eckert, S.; Gerbeth, G.

A review will be given on the present status of the facility MULTIMAG and the possibilities to measure local velocities in metal or semiconductor melts. The use of MULTIMAG or the measuring techniques for applications in crystal growth modeling will be discussed.

  • Lecture (Conference)
    Use of magnetic fields in crystal growth, Workshop, Riga (Lettland), 5.-6.12.2003

Publ.-Id: 5938

In vivo Measurement of the Serotonin Transporter with (S)-([18F]fluoromenthyl)-(+)-McN5652

Brust, P.; Hinz, R.; Kuwabara, H.; Hesse, S.; Zessin, J.; Pawelke, B.; Stephan, H.; Bergmann, R.; Steinbach, J.; Sabri, O.

The radiolabeled serotonin transporter (SERT) ligand [11C](+)-McN5652 has recently been used in clinical positron emission tomography (PET) studies for SERT imaging. However, this radioligand offers disadvantages in routine clinical settings because of its short radioisotope half-life (eg PET facilities within hospitals without a cyclotron need to acquire such radioligands from distant cyclotron units for clinical use). S-([18F]fluoromenthyl)-(+)-McN5652 ([18F](+)-FMe-McN5652) is an analogue which has been synthesized newly, and has a significant longer radioisotope half-life. In the porcine brain, it demonstrates the same characteristic distribution pattern of serotonin-uptake sites like the 11C-labeled congener with the highest binding in the midbrain and thalamus and the lowest in the cerebellum and occipital cortex. It shows a 30 % higher blood-brain transfer and a slower peripheral metabolism than [11C](+)-McN5652. Rather uniform brain binding was observed after injection of the pharmacologically inactive radiolabeled enantiomer, or after pretreatment with the highly selective SERT inhibitor citalopram. The norepinephrine uptake inhibitor maprotiline did not show any inhibitory effect. Using a one-tissue compartment model (K1, k´´2) or a two tissue compartment model (K1, k4) with or without constraints for calculation, the regional binding parameters of [11C](+)-McN5652 and [18F](+)-FMe-McN5652 are highly correlated among each other and with the SERT density, as determined by in vivo binding of [3H]citalopram. Using constraints to correct for the free fraction and nonspecific binding of the radiotracers, a considerable increase of the midbrain-occipital cortex ratios with higher values for [18F](+)-FMe-McN5652 compared to [11C](+)-McN5652 was revealed. It is concluded that [18F](+)-FMe-McN5652 has better features than [11C](+)-McN5652 for SERT imaging with PET.

Keywords: serotonin transporter; receptor imaging; positron emission tomography; kinetic modeling; [18F](+)-FMe-McN5652; citalopram

  • Neuropsychopharmacology (2003) 28, 2010-2019

Publ.-Id: 5937

Local flow structures in liquid metals measured by ultrasonic Doppler velocimetry

Cramer, A.; Zhang, C.; Eckert, S.

Ultrasound Doppler velocimetry (UDV) has been successfully applied to measure local velocities in mercury and the eutectic alloy InGaSn. Two different kinds of magnetic fields established the fluid motion in a cylindrical vessel. For both, the rotating and the traveling field, agreement with expectations from theory and local measurements employing different techniques was achieved.
The deliverance of a profile by UDV instead of one value at one fixed co-ordinate, typical for almost any other method, allowed for the determination of the topology in a plane covered by the ultrasonic beam while the sensor was traversed. These area-wide results are, by nature, time averaged respectively mean velocities.
The range of flow regimes regarding the magnitude of velocity which is detectable by means of the Doppler procedure begins already in the turbulent region. For the case of the rotating magnetic field spectral distributions of time series of velocity signals measured at different positions in the fluid volume will be presented.

  • Flow Measurement and Instrumentation 15(2004), 145-153

Publ.-Id: 5936

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