Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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.

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.

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.

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.

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.

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.

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).

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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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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
them.

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)

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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

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.

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.

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.

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.

no abstract !

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Cathodoluminescence spectra shapes and respective band decay times show no similarity between luminescence centers in different crystal and amorphous modifications of SiO2 and GeO2. On the other hand, the additionally produced red luminescence centers (650 nm) by oxygen implantation into SiO2 layers are of the same nature as in stoichiometric SiO2 and are attributed to the non-bridging oxygen hole center (NBOHC). Moreover, the elevated blue (460 nm) luminescence in Si implanted SiO2 belongs to the silicon related oxygen deficient center (SiODC) as in stoichiometric layers too. Ge implantation into SiO2 and thermal post-annealing leads to a huge violet luminescence (400 nm) with a first rapid decay of t = 24 ns followed by a slow hyperbolic decay with (t)-0.15 ... (t)-0.54. The last 10% show again an exponential decay with a mean life time t = 125 µs. This complex luminescent center is related to the GeODC center formed during the thermal treatment by Ge cluster formation

The full-scale zero power facilitlity V-1000 was build at the Russian Research Centre ?Kurtschatov Institute? for the investigation of neutron-physical parameters of the VVER-1000 core[1]. Two steady-state measurements and two transient experiments at the V-1000 were made available in the frame of EU project VALCO for the valida-tion of three-dimensional neutron kinetic codes. The results of the DYN3D code [2] by using three different libraries of two group constants generated with the cell codes HELIOS [3], CASMO [4] and WIMS [5] are compared with the measurements. The C/E comparisons of the radial power distribution at the axial detector position for the two steady-states with all control rods out of core and with inserted bank 10 are pre-sented in the next section. A single control rod of bank 9 is moved in the core and reverse in the transient experiment 1. The experiment 2 consists of a scram with a delayed motion of one stuck cluster The results of the calculations with the three li-braries are compared with the incore detectors signals and the signals of two ioniza-tion chambers in section 3. The reactivity calculated by inverse point kinetics from the ionization chambers signals and from the calculated core averaged fluxes are pre-sented.

Ge nanocrystals embedded in thermal SiO2 on top of a Si substrate are investigated using Raman spectroscopy and transmission electron microscopy. We observe that the Raman peak frequency of the Ge nanocrystals is strongly affected by compressive stress. In the case of large particles for which the phonon confinement-induced Raman shift can be neglected, the stress is measured taking into account isotopic composition effects induced by the ion implantation process used to produce
the nanocrystals. The stress is proposed to originate from a liquid¿solid phase transition in Ge.

Ion beams are widely used in research and development as well as in different fields of industrial applications, for example for doping of semiconductors in microelectronics. Furthermore, among other techniques ion beams exhibit a great potential for synthesis of new materials as well as for the self-organization of nanostructures. Two of the goals of materials research using ion beams are the ion beam synthesis (IBS) of nanocrystals (NC´s) and the self-organization of NCs under ion irradiation in a solid matrix, for example the formation of semiconducting or metallic NCs in insulating films for applications microelectronics and optoelectronics, respectively.
Semiconducting NCs embedded in the gate oxide of a MOS field effect transistor can be charged/decharged by tunnelling of electrons from/to the Si substrate, caused by an appropriate voltage pulse applied to the gate. There is a difference in the source/drain current for charged and neutral NCs which can be used for the storage of information. The basis of this memory concept is quite simple. However, the fabrication of tiny NCs (~2 nm) placed at the right position within the very thin (< 20 nm) gate oxide is a strong challenge. Different ion beam processes are being developed for realization: i) low energy ion implantation into the thin gate silicon oxide and ii) medium energy ion irradiation through the gate oxide. The two approaches will be described from the physical and technological point of view and experimental results of charge storage behaviour in NC MOS transistors fabricated by the two ion beam processes will be presented.
Another effort is currently devoted to the application of ion beam synthesized metallic NCs in optoelectronics. The fabrication of NCs by IBS requires usually a thermal treatment for phase separation of implanted impurity atoms and for damage annealing. This annealing leads inevitably to broad NC size distribution. Due to the broad size distribution of NCs fabricated by IBS, their size- depending characteristics, e.g. absorption and luminescence, can be obscured. Thus the potential for tailoring of size and size distribution of NCs by IBS is rather limited. It will be shown that size and size distribution can be tailored by high-energy ion irradiation through an ensemble of NCs.
Finally, in the outlook the lecture will address new trends of IBS for nanostructure fabrication, e.g. self-organization at ion implantation into templates and IBS of nanostructures by using focused ion beams (FIB).

The formation and the structural properties of Sn nanocrystals produced by ion implantation in thin SiO2 films was investigated by 119Sn conversion electron Moessbauer spectroscopy (CEMS), x-ray absorption spectroscopy (XAS), and transmission electron microscopy (TEM). Sn ion implantation was performed at 80 keV with a fluence of 1x1016 cm2, positioning the peak of the implantation profile in the middle of the SiO2. The annealing treatments were performed in the temperature range 800–1100 °C by rapid thermal processing. CEMS and XAS provided unique information on the local atomic and electronic environment of Sn in SiO2 allowing a detailed investigation of the effect of different annealing conditions. In the as-implanted state all Sn ions are oxidized (with both Sn2+ and Sn4+ oxidation states present), while annealing induces the formation of beta-Sn nanoclusters. TEM showed that cluster sizes are in the range 7–17 nm. For clusters with average diameter ,10 nm, XAS detected a reduction in coordination number and interatomic distances. Both XAS and CEMS indicate an increase in the static disorder in the metallic clusters. The investigated annealing treatments do not lead to a complete precipitation of Sn atoms in the metallic phase, leaving a fraction of them oxidized.

Ion beams are widely used in research and development as well as in different fields of industrial applications, for example for doping of semiconductors in microelectronics. Furthermore, among other techniques ion beams exhibit a great potential for synthesis of new materials. One of the goals of materials research using ion beams is the ion beam synthesis (IBS) of nanocrystals (NC´s) in a solid matrix, for example the synthesis of semiconducting or metallic NC´s in insulating films.
NC´s embedded in the gate oxide of a MOS field effect transistor can be charged/decharged by tunnelling of electrons from/to the Si substrate, caused by an appropriate voltage pulse applied to the gate. There is a difference in the source/drain current for charged and neutral NCs which can be used for the storage of information. The basis of this memory concept is quite simple. However, the fabrication of tiny NCs (~2 nm) placed at the right position within the very thin (< 20 nm) gate oxide is a strong challenge. Different processes are being developed for realization. Among these, only ion implantation of impurity atoms into the gate oxide followed by their precipitation during subsequent annealing is completely compatible with CMOS technology.
The lecture will first address the fundamentals governing ion beam synthesis NC´s in extremely thin SiO2 layers, with well-controlled size and position tailoring. The results of the fundamental investigations form the base for technology transfer to the production of non-volatile memories. In the frame of national and international R&D projects and in strong collaboration with local microelectronics industries, the viability of a new technology route to memory device fabrication is demonstrated.

kein Abstrakt

Introduction

If a fluid is electrically conductive, its flow may be controlled using electromagnetic forces. Meanwhile, this technique is a recognized tool even on an industrial scale for handling highly conductive materials like liquid metals. However, also fluids of low electrical conductivity as considered in the present study, like sea--water and other electrolytes, permit electromagnetic flow control. Experimental results on the prevention of flow separation by means of a streamwise, wall parallel Lorentz force acting on the suction side of inclined flat plates and hydrofoils will be presented.

Force Configuration
The stripwise arrangement of permanent magnets and electrodes of alternating magnetization direction and polarity shown in Fig. 1 was proposed by Gailitis and Lielausis (1961). It generates a wall parallel force with a maximum value directly at the wall, decaying exponentially with the wall distance. Due to the low electrical conductivity, both electric and magnetic fields have to be applied to generate a Lorentz force of adequate strength. The width of the electrodes is equal to that of the magnets and
determines the penetration of the force into the flow. The ratio of electromagnetic to inertial force can be characterized by the interaction parameter. In analogy to the terminology used in separation control by blowing, one may also define an electrohydrodynamic momentum coefficient.

Results and Discussion
A downstream directed force adds momentum to the flow and accelerates the fluid in the vicinity of the wall. This flow acceleration may be used to counteract the energy loss due to friction and adverse pressure gradients. Actually, a streamwise Lorentz force has already been successfully applied to control the flow around a circular cylinder in Weier et al. (1998). The two inserts in Fig. 2 show the flow around an inclined flat plate. In the lower left photograph, the unforced separated flow is visible, whereas the upper subfigure depicts the fully attached flow under the action of a suction side Lorentz force. The graph indicates that the interaction
parameter, necessary to completely suppress separation, decreases with increasing chord length Reynolds number. The effect of a suction side Lorentz force on lift and drag of NACA--0017--like hydrofoils has been quantified by means of force balance measurements. Depending on the inclination angle, two different effects are observed. At small angles of incidence, a moderate lift increase due to additional circulation is observed. Simultaneously, caused by the added momentum, the drag is decreased. At higher angles of attack, where the unforced hydrofoil would normally stall, a more pronounced lift increase occurs. Fig. 3 shows the lift gained by the suction side Lorentz force at a fixed inclination angle of 17. Here delta CL is the difference of the lift coefficients of the forced and the unforced hydrofoil at the specified chord length Reynolds number. The shape of the curve as well as the total values of the lift gain and the momentum coefficient resemble the behavior found in separation control experiments with steady blowing. In the presentation, a complementary discussion on scaling issues based on experiments with a NACA 0015 hydrofoil will be given.

Proteine zeichnen sich durch eine hohe Suszeptibilität gegenüber dem Angriff reaktiver Sauerstoffspezies (ROS) aus. Die oxidative Modifikation von Proteinen kann zur Veränderung ihrer Struktur und zur Beeinträchtigung ihrer biologischen Funktion führen. Diese Veränderungen sind beim Menschen eng mit der Ätiologie, Manifestation und Progression verschiedener Krankheiten assoziiert. Durch neue Methoden zur Charakterisierung und quantitativen Beschreibung der Bildung und des Metabolismus spezifischer Oxidationsprodukte werden Hinweise auf die Art und Weise der Schädigung sowie Schutzmöglichkeiten des Organismus gewonnen.

We report a combined experimental and theoretical study of the unoccupied electronic states of the neutral molecular organic materials TTF (tetrathiafulvalene) and TCNQ (7,7,8,8-tetracyano-p-quinodimethane) and of the one-dimensional metallic charge transfer salt TTF-TCNQ. The experimental density of states (DOS) is obtained by x-ray absorption near edge spectroscopy (XANES) with synchrotron light and the predicted DOS by means of first-principles density functional theory calculations. Most of the experimentally derived element specific XANES features can be associated to molecular orbitals of defined symmetry. Because of the planar geometry of the TTF and TCNQ molecules and the polarization of the synchrotron light, the energy dependent sigma or pi character of the orbitals can be inferred from angular dependent XANES measurements. The present work represents the state of the art analysis of the XANES spectra of this type of materials and points out the need for additional work in order to elucidate the governing selection rules in the excitation process.

Heat transfer and boiling are key phenomena for power generation facilities. Whereas for 1D thermalhydraulic system codes modeling of boiling was state aof the art from the beginning of their development, the 3D modelling of boiling has not yet reached this maturity. In the paper the boiling model implemented in the CFD-code CFX-4 was applied, to analyse lots of experiments, their results were published in the literature. The validity of the implemented correlations is examined. In many cases the model yields a good agreement to experiments. The modelling of subcooled boiling in the section of a BWR fuel rod element is presented as an application example.

Improved methods are presented for the preparation of ^99mTc and ¹⁸⁸Re mixed-ligand complexes with tetradentate and monodentate ligands of the general formula [M^III(L₁)(L₂)] (M = Tc, Re; L₁ = NS₃ or NS₃-COOH; L₂ = isocyanide or phosphine). To avoid the unrequested formation of reduced-hydrolyzed species of both metals the preparation of complexes is performed in a two-step procedure. At first the Tc(III)- or Re(III)-EDTA complex is formed which reacts in a second step with the tripodal NS₃ ligand and the monodentate isocyanide or phosphine ligand to the so-called ‘4+1’ complex. Copper(I) isocyanide complexes are used for preparing the ‘4+1’ complexes. That facilitates storage stability and allows kit formulations. Moreover, using that stabilized form of isocyanides enables the formation of ¹⁸⁸Re complexes in acidic solution. Only micromolar amounts of the monodentate ligand are needed and that results in high specific activity labeling of interesting molecules. The lipophilicity of complexes can be controlled by introducing a carboxyl group into the tetradentate ligand and/or derivatization of the monodentate ligands. Furthermore, the carboxyl group enables the conjugation of biomolecules. As an example, the neurotensin derivative CN-NT(8-13) was prepared and labeled with ^99mTc according to the ‘4+1’ approach and its behavior in vivo was studied.

Simulations of a real transient of an operating VVER-1000 power plant have been performed using DYN3D-ATLET and DYN3D-RELAP5 code systems in the frame of activities aimed at a validation of the coupled neutronic / thermal-hydraulic codes. The problem chosen for simulation is a main coolant pump (MCP) switching off, when three of the four MCPs of the plant are in operation (transient scenario of the VALCO project). The same nodalization models of the plant (except the core) but two different libraries of macroscopic cross-sections have been used in calculations. Additionally, the compared code systems are based on the different - external and internal - coupling techniques. This paper contains a brief description of the coupled codes and the plant model as well as a comparison between results from simulations.

A one-dimensional code DYN1D-MSR for transient analysis of Molten Salt Reactors – MSR was developed in FZR. The code is based on the well know three-dimensional code DYN3D. The neutron kinetics routines for axial direction calculation from DYN3D are combined with new models of delayed neutrons production and thermal-hydraulic. The results from the Molten salt Reactor Experiment were used to validate the code. After the successful validation several transients typical for the liquid fuel system were analyzed using the design data of the Molten Salt Breeder Reactor. The results of all transients (overcooling of fuel at core inlet, reactivity insertion, and fuel pump coast-down) have shown that the dynamic behavior of MSR is stable when the coefficients of thermal feedback are negative.

For the electron beam diagnostic in the undulator of the ELBE FEL two systems are completed. The first one consists of insertable OTR (Optical Transition Radiation)view screens. The same view screens will be used for the FEL optical resonator alignment. This is why there are very strong requirements on the long-term positioning reproducibility of the view screens. The second system is based on a single moveable YAG (Yttrium Aluminum Garnet activated by Cerium) screen, which can travel within the undulator vacuum chamber such that the electron beam position can be measured at any place in the undulator. Both systems are completed and successfully tested. Results of the tests as well as design ideas are presented. After transporting two undulator units to Rossendorf and installing the stainless steel vacuum chamber the magnetic field has been measured again and adjusted applying the pulsed-wire method. Irregularities of the undulator magnetic field could affect gain and wavelength of the FEL. Such effects were analyzed using numerical simulations.

The goal of our work is to apply the UDV technique for investigations of liquid metal two-phase flows. In the present paper UDV is validated for its capability of measuring both gas and liquid velocities in transparent two-phase flow. The results are discussed with references to the existing knowledge and parallel measurements by Laser Doppler Anemometry (LDA).

Chromium recoil implantation into SAE 1020 steel by nitrogen bombardment

Results from experiments on hybrid plasma immersion ion implantation / nitriding processing of materials

Chromium implantation into ABNT 1020 steel by nitrogen PIII and ion beam recoil

Annealing effects on silicon oxynitride layer synthesized by N plasma immersion ion implantation

Grazing incidence X-ray diffraction of SS304 steel surfaces modified by high and low pressure ion nitriding processes

Nitrogen recoil chromium implantation into construction steel SEA 1020 steel by means of ion beam or plasma immersion ion implantation

The Rossendorf superconducting Electron Linac of high Brilliance and low Emittance (ELBE) delivers an 40 MeV, 1 mA cw-beam for different applications such as bremsstrahlung production, electron channeling, free-electron lasers or secondary particle beam generation. In this energy region in case of collisions of the electron beam with the pipe nearly all beam power will be deposited into the pipe material. Therefore a reliable beam loss monitoring is essential for machine protection at ELBE. Different systems basing on photo multipliers, compton diodes and long ionisazion chambers were studied. The pros and cons of the different systems will be discussed. Ionisazion chambers based on air-isolated RF cables installed some cm away parallel to the beam line turned out to be the optimal solution. The beam shut-off threshold was adjusted to 1 µC integral charge loss during a 100 ms time interval. Due to the favourable geometry the monitor sensitivity varies less than +/- 50 % along the beam line (different shielding conditions).

The energy distribution of the monomer ion species is studied as a function of emitter temperature for a Au82Si18 eutectic liquid metal alloy ion source (LMAIS). Secondary peaks, or shoulders, in the distribution of some of the species are explained in terms of Hornsey's model, which involves the fast movement of the jet in conjunction with a space-charge energy broadening mechanism within the beam. Moreover, the results confirm an earlier conclusion that whereas Au+, Si+ and Si++ are emitted by direct field-evaporation from the liquid surface, Au++ forms by the post ionization of Au+.

Seit mehreren Jahren werden verdünnte Legierungen aus III-V Halbleitern und Stickstoff intensiv untersucht. Eine hervorstechende Eigenschaft dieser Systeme ist die starke Reduktion der Bandlücke mit steigendem Stickstoffgehalt. Neben epitaktischem Wachstum ist Ionenimplantation eine weitere Methode zur Herstellung solcher Materialien.
Wir untersuchen die optischen Eigenschaften und deren Abhängigkeit von den Implantations- und Ausheilbedingungen für GaNxAs1-x (x<0,04). Es zeigt sich, dass unter entsprechenden Bedingungen der von der Implantation verursachte Schaden minimiert und die Bandkantenverschiebung maximiert werden kann. Eine in Photoreflexion beobachtete Bandlückenverschiebung von 63meV konnte bei einer implantierten N-Konzentration von 1% beobachtet werden. Der Einfluss der modifizierten Bandstruktur auf die Ladungsträgerdynamik wird in Femtosekunden zeitaufgelösten pump-probe Experimenten untersucht.

The influence of melt convection on the microstructure formation of Nd-Fe-B alloys, mainly the volume fraction and grain size of the a-Fe phase, has been investigated experimentally using the electromagnetic levitation technique and a specially designed floating-zone arrangement. Samples were subjected to a strong rotation during levitation and compared to fixed samples without additional sample rotation in the levitation facility. A controlled influence on the melt flow is possible via tailored magnetic fields which enable enhancement or suppression of the melt convection using the floating-zone arrangement. A specially designed magnetic two-phase stirrer offers a strong influence on the melt flow in the floating-zone facility. The microstructure pattern, mainly the volume fraction and grain size of the a-Fe phase, vary strongly with the strength of the internal flow motion in both types of experiments. The melt flow in a levitated droplet was studied numerically under the additional effect of a global sample rotation resulting in a strong suppression of internal motions. The electromagnetically driven flow in the inductively heated melt zone of the floating-zone arrangement turned out to be of strong influence on the resulting microstructure. Numerical simulations are essential in order to understand and design the various flow structures.