Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

A distributed electron cyclotron resonance (DECR) plasma reactor powered by a microwave generator operating at 2.45 GHz (800 W) was used to deposit (t)a-C:H thin films at RT on <100> Si substrates RF biased within the range 25 < |Vo| < 600 V. C2H2 was used as precursor. The plasma pressure was varied within the range 0. 1 < P < 1 .5 mTorr. The films were analysed using spectroscopic ellipsometry (SE) and Fourier transform infrared (FTIR) spectroscopy. The hydrogen content NH and the density of the films were determined from nuclear reaction analysis (NRA) using the resonance at 6.385 MeV of the reaction: 15N + 1H ---> 12C + 4He + Gamma. Positron annihilation spectroscopy was used to detect the porosity. The evolutions of NH as a function of the substrate ion current density n+ and as a function of Vo show that the hydrogen incorporation results from the competition between chemisorption and deposited energy density related effects. The increase of the hydrogen incorporation leads to a decrease in the film density and a lower deposition rate. The porosity of the films deposited at low pressure (~ 0. 1 mTorr) with Vo = - 80 V has been detected. The comparison between results of SRIM-2000 simulations and the evolution of NH as a function of Vo shows that the porosity and the hydrogen content are not correlated. The absorption of oxygen and nitrogen for the low density films has been detected from the observation of the 3250-4000 cm-1 infrared (IR) band.

Until recently, the existence of oscillatory mean-field dynamos of the alpha^2-type with spherically symmetric and isotropic alpha was an open question. We find such dynamos by means of an evolutionary strategy, and we illustrate the spectral properties of the corresponding dynamo operators.

Alloying by high dose ion implantation of iron into magnesium and aluminum

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The encapsulation of active centres is a widespread principle used in biological systems. So, enzymes may wrap certain substrates leading to the complete shielding from the environment. Currently, dendrimers are considered to be applicable as artificial encapsulating systems which can effectively bind guest molecules. In principle, dendrimers can accommodate different kind of guests, such as anionic species, metal ions, and neutral substrates. Furthermore there is the possibility to graft biomolecules on the periphery of dendrimers, by which in particular the biodistribution can be influenced. These unique structural features and properties make dendrimers attractive as candidates for imaging and therapeutic purposes. In this nexus, the encapsulation of radionuclides by dendritic boxes^[1] (I) and the fixation by dendrons^[2] (II) seems to be promising concepts.

We report on preliminary results of binding pertechnetate and perrhenate by polypropyleneamine dendrimers. Lipophilic urea-containing dendrimers are efficient carriers for these anions. We could shown that the polyamine skeleton is suitable for binding some anions inside of the dendrimer.
The concept of dendritic encapsulation in view of the development of highly stable metallodendrimers is discussed. Some examples for potential copper- and rhenium-containing dendrimers are presented.

[1] J. F. G. A. Jansen, E. W. Meijer, E. M. M. de Brabander-van den Berg: The dendritic box: Shape-selective liberation of encapsulated guests, J. Am. Chem. Soc. 1995, 117, 4417-18.
[2] S. Hecht, J.M.J. Frechet: Dendritic encapsulation of function: Applying nature's site isolation principle from biomimetics to materials science, Angew. Chem. Int. Ed. Engl. 2001, 40, 74-91.

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Diamond-like carbon is a system of rather high disorder as it has a wide optical absorption tail and a high density of paramagnetic defects. The defect density
remains high even in DLCs containing 30-60% hydrogen, so hydrogen does not appear to passivate defects well unlike in a-Si:H. To investigate the role of hydrogen
on the disorder in DLCs we have investigated the effect of low concentrations of hydrogen on the disorder in ta-C, by introducing 10(-6)-10(-3) mbar hydrogen into
the deposition of ta-C by filtered cathodic vacuum are (FCVA), which corresponds to 0.1-15 at.% hydrogen in the films. Higher pressures of hydrogen reduces the
ionisation leading to sp(2) bonding, and ultimately the thermalisation of the plasma leads to nanotubes and fullerenes. The deposited ta-C:H films were investigated by
electron energy loss spectroscopy (EELS), Raman spectroscopy, optical measurements, electronic transport and N-15 resonant nuclear reaction analysis. Plasma
characterisation with a retarding field analyser showed that the ion current density remains nearly unchanged in the pressure range used to deposit the films. Raman
measurements indicate the onset of clustering of sp(2) sites when the hydrogen pressure exceeds 2 x 10(-4) mbar. We find that small amounts of hydrogen increase
the optical gap up to 2X10(-6) mbar hydrogen pressure, and then the band gap decreases continuously. The absorption tail sharpens by the addition of hydrogen, as
measured by photothermal deflection spectroscopy (PDS) and thus confirms the Raman measurements that suggest that the order in the material increases with
increasing hydrogen content. (C) 2001 Elsevier Science B.V. All rights reserved.

Hüllproteinschichten (S-Layer) sind Protein- oder Glykoproteinschichten auf der Oberfläche vieler Bakterien und Archaea. Sie können als Gitter mit schräger, tetragonaler oder hexagonaler Symmetrie vorliegen. Die Funktion dieser äußersten Zellwandkomponente ist nicht einheitlich und nur teilweise näher untersucht. So können diese zum Beispiel als Schutzhülle, Molekularsieb oder Ionenfalle fungieren oder der Formerhaltung dienen. In neueren Arbeiten konnte gezeigt werden, dass die Hüllproteinschichten verschiedene Metalle binden und in einigen Fällen die Bildung von Nanoclustern ermöglichen. Unter den Aspekten der Wechselwirkungen von Hüllproteinen mit Schwermetallen und der Entwicklung möglicher Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden Hüllproteine von Bakterien untersucht, die von Schwermetall und Radionuklid belasteten Umgebungen isoliert wurden. Dazu wurde ein Hüll-protein eines Bakteriums aus einer Uranabfallhalde isoliert und strukturell sowie molekularbiologisch analysiert.
Im Rahmen der vorgelegten Arbeit wurden mehrere Haldenisolate der Gattung Bacillus hinsichtlich der Existenz von Hüllproteinen untersucht. Dies erfolgte mit Hilfe einer neu entwickelten Methode zum schnellen Nachweis von Hüllproteinen auf Gram-positiven Bakterien. Dabei wird das Peptidoglycan der Zellwand mit Lysozym verdaut und auf diese Weise die Proteinschicht von der Zellwand gelöst. Die freien Schichten können somit im Transmissionselektronenmikroskop oder Atomkraftmikroskop direkt nachgewiesen werden. Es wurde gefunden, dass nur das Isolat Bacillus sphaericus JG-A12 eine Hüllproteinschicht mit tetragonaler Symmetrie und einer Gitterkonstante von 12,5 nm besitzt. Die (135±5) kDa schweren Hüllproteinmonomere sind nicht glykosyliert, weisen aber zwei verschieden stabil gebundene Phosphorspezies auf. Mittels molekularbiologischer Analysen konnten Teile der Hüllproteingene von B. sphaericus JG-A12 (Base 1 bis 1497 des strukturkodierenden Teils des Gens) und des nächst verwandten Referenzstamms B. sphaericus NCTC 9602 (Base 1 bis 579 des strukturellen Teils des Gens) entschlüsselt werden. Beide Hüllproteine besitzen N-terminal drei S-Layer homologe Domänen und weisen in den Aminosäuren 1-182 nur sehr geringe Identitäten zu bereits entschlüsselten Hüllproteinen anderer B. sphaericus Stämme auf. Dem gegenüber ergeben sich hohe Identitäten für die Aminosäuren 183-320 für Hüllproteine mit tetragonaler Symmetrie (Hüllproteine der B. sphaericus Stämme P-1 und CCM 2177) und sehr niedrige für das Hüllprotein mit schräger Symmetrie (Hüllprotein von B. sphaericus WHO 2362).

Im Hinblick auf katalytische Anwendungen oder der Entwicklung von Bioremediationsverfahren auf der Basis immobilisierter Biokomponenten wurden die Wechselwirkungen von Hüllproteinen mit verschiedenen Metallen untersucht. Es konnten direkte Wechselwirkungen von Palladium, Platin und Uran mit den Hüllproteinen von B. sphaericus JG-A12 und NCTC 9602 nachgewiesen werden. Die Ergebnisse zeigen für beide Proteine eine Komplexierung von Platin über CO- und NH-Gruppen der Peptidbindungen und über COOH- und OH-Gruppen. Das Hüllprotein von B. sphaericus JG-A12 komplexiert Palladium über NH-Gruppen der Peptidbindung und COOH-Gruppen, während das von B. sphaericus NCTC 9602 Palladium sowohl über CO-Gruppen der Peptidbindungen als auch über COOH- und OH-Gruppen bindet. Die Komplexierung von Uran erfolgt vorrangig über NH-Gruppen der Peptidbindungen aber auch über OH- sowie zwei verschiedene PO4-Gruppen. Um eine Anwendung der metallbindenden Eigenschaften von Hüllproteinen im Rahmen von Bioremediationsprozessen zu ermöglichen, wurden diese mittels Sol-Gel-Technik in einer SiO2-Matrix immobilisiert und die Sorption und Desorption von Uran und Kupfer untersucht. Zum Vergleich wurden intakte Zellen und Sporen immobilisiert und in die Untersuchungen mit einbezogen. Die biologisierten Keramiken (Biocere) binden 2,7-42fach mehr Uran und Kupfer als andere zur Sanierun...

Energiereiche Neutronenstrahlung verursacht in Materialien Schädigungen, die zum Verlust ihrer mechanischen Festigkeit führen. Ein solcher Effekt ist die Neutronenversprödung. Für Komponenten, die sich innerhalb bzw. nahe des Kerns eines Spaltreaktors befinden, ist sie der wichtigste Schädigungsmechanismus. Für den Druckbehälter ist sie von besonderer Sicherheitsrelevanz. Da sich die Schädigung mit fortlaufender Bestrahlung akkumuliert, ergibt sich aus Sicherheitsgründen für eine Komponente eine maximal zulässige Strahlungsfluenz, der sie ausgesetzt werden darf. Bei vielen Druckwasserreaktoren ist der Materialzustand des Druckbehälters sogar entscheidend für die zulässige Betriebsdauer des Reaktors. Daher ist einerseits die Monitorierung der Strahlungsbelastung für sicherheitsrelevante Komponenten mit Hilfe geeigneter Messungen und Berechnungen eine notwendige Voraussetzung für den sicheren Betrieb eines Kernreaktors und andererseits die Entwicklung und Verifikation solcher Mess- und Berechnungsmethoden eine wichtige Aufgabe der Reaktorsicherheitsforschung. Die möglichst zuverlässige Bestimmung der Strahlungsbelastung für kernnahe Komponenten, darunter insbesondere des Druckbehälters, zu ermöglichen, ist das Ziel des Fachgebiets "Reaktordosimetrie". Seine Bearbeitung auf hohem wissenschaftlich-technischen Niveau ist daher eine notwendige Voraussetzung für zuverlässige Integritätsbewertung und Gewährleistung von Komponentensicherheit.

Nach dem Zusammenbruch des Ostblocks ist die Sicherheitsproblematik der Druckbehälter der russischen Kernreaktoren vom Typ WWER weltweit ins Blickfeld der Öffentlichkeit gerückt und zum Gegenstand zahlreicher Forschungsprojekte geworden. Da in diesem Falle die Strahlenschädigung im Vergleich zu anderen Effekten wesentlich größer ist, hat insbesondere die Reaktordosimetrie dadurch neue Impulse erfahren. Mit der Neugründung des Forschungszentrums Rossendorf aus dem ehemaligen ZfK Rossendorf wurde auch ein Teil der reaktordosimetrischen Arbeiten zu WWER-Reaktoren übernommen und im Institut für Sicherheitsforschung parallel zur entsprechenden Materialforschung fortgeführt. Bisher wurden hier die wichtigsten Teilgebiete bearbeitet: Fluenzmessung, Fluenzberechnung und Spektrumsjustierung. Im Vortrag werden der erreichte Stand dargelegt, dieser mit dem internationalen Niveau verglichen und Ansätze für Weiterentwicklungen aufgezeigt.

Early evidence that small technetium compounds may be subject to active transport processes was provided by the historical serependipitous finding that pertechnetate was handled by the sodium-iodide symporter in the thyroid gland. The pertechnetate ion can mimic the iodide ion, despite its different nature and geometry.
Starting from this observation ^99mTc radiotracers are designed for probing and imaging a distinct biochemical reaction of diagnostic relevance. Such biochemical reactions are transmembrane processes, binding reactions, enzymatic conversions, possibly redox reactions, etc., and key proteins or enzymes are the targets of the ^99mTc diagnostic agents. "Bioactivity" is therefore required in the sense of the ^99mTc species being able to participate in the biochemical reaction of interest, being bound or processed.
Keeping the artificiality of technetium in the human body in mind, the feasibility of biochemical Tc-99m probes can only be based on imperfection of the target specificity, on the tolerance of the target molecule towards a substrate mimic that accidentally fits the target molecule to some extent, despite its different chemical nature. This will be examplified by the development of ^99mTc ligands for brain receptors.
The possibility of using biochemical ^99mTc probes for various CNS receptors is due to the tolerance of the target molecules towards metal-based mimics. As the high in-vitro affinities to various neuroreceptors in the nanomolar and subnanomolar range indicate, molecular recognition of complex technetium molecules has become possible.
However, one main issue in developing CNS receptor imaging agents remains the very low or totally absent brain uptake. After two decades of research into brain ^99mTc perfusion agents it has now become feasible for certain technetium complexes to cross the blood-brain barrier. In contrast, a suitable combination of a high receptor affinity with a sufficient brain uptake was not achieved. Systematic studies of model technetium compounds with various logP and pKa values provided rules for selected homologous series of complexes but did not really help to tackle the problem. Since a wide variety of chemically diverse compounds, among them lipophilic cations such as ^99mTc MIBI, ^99mTc tetrofosmin or Q-series compounds, may be actively transported out of the cell by P-glycoprotein, it might also affect the transport of potentially receptor-binding ^99mTc agents.

To conclude, approaches to specific small technetium radiopharmaceutical tracers have not changed much in recent years. From a coordination chemistry point of view, the design of new ^99mTc radiopharmaceuticals starts conceptually with the modification of the coordination environment around the metal with a variety of chelators. Diversity of the chelate unit is needed, and considerable research has consequently been devoted to designing improved and new chelate types, resulting in a flourishing technetium chemistry. New impetus has come in particular from the progress made in technetium(I) chemistry.
Although this knowledge explosion in the technetium chemistry has been translated into targeted radiopharmaceutical research activity the number of newly launched Tc-99m radiopharmaceuticals is stagnant, at least in a short-term perspective. The development of biochemically specific, small technetium and rhenium complexes remains therefore a challenging, rewarding and often frustrating activity.

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Inhalt

• Material: Halbleiter-Heterostrukturen aus SiC in Si, Diamant in SiC, SiC in Diamant
• Ionenstrahlsynthese: Ionenverteilung im Material, Strahlenschäden, Temperatur-behandlung bei und nach Implantation
• Bedeutung der Synchrotronstrahlung für die Materialforschung, Rossendorfer Beamline an der ESRF Grenoble
• Materialcharakterisierung wie Phasen-bildung, Kristallitgröße und -orientierung, Gitterdeformation in Matrix und Kristallit mittels diverser Röntgenmethoden
• Ausblick: simultane Doppelimplantation

CFD codes are more and more used for practical applications as the design and optimization of technical facilities, e.g. in process industry or in nuclear power plants. For most cases this limited to single phase flows. To qualify CFD codes for two-phase flows, they have to be equipped with constitutive laws describing the interaction between the gaseous and the liquid phases. In the case of bubble flow this particularly concerns the forces acting on the bubbles and bubble coalescence and break-up. To obtain detailed experimental data, an electrode wire-mesh sensor was used, which enables the measurement of the phase distribution with high reso-lution in space and in time. Air-water flow at ambient conditions in a vertical pipe (51.2 mm inner diameter) is investigated to have well defined boundary condi-tions. Local bubble size distributions are calculated from the data. The measure-ments were done in different distances from the gas injection device. As a result the development of bubble size distributions and the development of the radial gas fraction profiles can be studied. It was found, that the bubble size distribution as well as local effects determine the transition from bubble flow to slug flow. The data are used for the development of a model, which predicts the development of the bubble size distribution and the transition from bubble flow to slug flow in case of stationary flow in a vertical pipe.

Oxidized LDL (oxLDL) is a key mediator in atherogenesis and a marker of coronary artery disease (CAD). Type 2 diabetes is associated with excessive cardiovascular morbidity and mortality. Because atherogenesis starts before diabetes is diagnosed, we investigated whether circulating oxLDL levels are increased in impaired glucose tolerance (IGT). OxLDL levels were measured in 376 subjects with normal glucose tolerance (NGT), 113 patients with IGT, and 54 patients with newly diagnosed type 2 diabetes. After correction for age and BMI, serum levels of oxLDL were significantly increased in IGT versus NGT subjects (P = 0.002). OxLDL levels were not associated with the following parameters of the oxidative/antioxidative balance in the blood: total antioxidant capacity, urate-to-allantoin ratio, and circulating phagocyte oxygenation activity. In stepwise multivariate analysis, LDL cholesterol (P < 0.0005) and triglycerides (P < 0.0005) were the strongest predictors of circulating oxLDL levels, followed by HDL cholesterol (P = 0.003), 2-h postchallenge C-peptide (P = 0.011), fasting free fatty acids (P = 0.013), and serum paraoxonase activity (P = 0.035). The strong correlation of oxLDL with LDL cholesterol and triglycerides indicates that LDL oxidation in IGT is preferentially associated with dyslipidemia. OxLDL increase may explain the high atherogenic potency of dyslipidemia in the prediabetic

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
A more detailed analysis shows that several stages should be considered corresponding to different dominating processes on very different time scales. For investigation of the film growth in the short time impact stage molecular dynamics was used. For this purpose the empirical interaction potential of Brenner was modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) was quantitatively analysed in dependence on particle energy and temperature.
The results of the impact stage represent the input data for the long time diffusion stage. Based on continuum mechanics a simplified model for the further film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

Range distributions of carbon ions deposited onto tetrahedral amorphous carbon films at kinetic energies between 22 eV and 692 eV are measured utilizing high-resolution elastic recoil detection. These data are compared to range calculations based on binary collision approximation as well as to classical molecular dynamics simulations. Asymmetric range profiles, differences in mean ion ranges and increased range straggling compared to theories are attributed due to self diffusion during thermal spike and have to be considered in subplantation growth models.

The extremely broad structural variability of carbon films is based on the competition of trigonal sp² bonds leading to layered structures (as in graphite) and tetrahedral sp³ bonds leading to three-dimensional networks (as in diamond). These complementary structures may be combined in amorphous carbon films as they are produced by highly activated ion or plasma beams. Amorphous films with up to 80% diamond bonds and corresponding hardness has been realized in this way. The necessary deposition conditions are qualitatively well known: high particle energy, low deposition temperature, not too grazing incidence.
To understand the film growth on a quantitative level molecular dynamics has been used. For this purpose the empirical interaction potential of Brenner has been modified to describe film formation by hyperthermal species. By optimised codes and long-time calculations of several months, it was for the first time possible to simulate the stationary growth of carbon films of several nanometer thickness. The film structure (interface, diamond-like bulk film, graphitic top layer) has been quantitatively analyzed in dependence on particle energy and temperature.
Based on these fundamental studies a simplified model for the film formation has been developed. It describes the formation of the different carbon structures (characterized by the density or the corresponding sp² : sp³ ratio) as a competition of subplantation and relaxation, so it becomes possible to quantify the influence of more complex technological parameters like beam energy distribution and thermal transport. The characteristic tendencies extracted from these technological maps are discussed and compared to experimental results.

The corrosion of metals is associated both with a release of ions and changes in optical surface properties. In this study these two effects were correlated by a potentiodynamic corrosion test and in situ probing of the surface by ellipsometry. The studies were carried out with stainless steel AISI 304 and 316 in phosphate buffered saline (PBS) and in Dulbecco's Modified Minimal Essential Medium (DMEM) at pH 7.4. In both media 304 steel is more susceptible to corrosion than 316 grade. The 316 steel shows higher corrosion potential and higher corrosion current density in PBS than in DMEM, for 304 steel this behavior is vice versa. Ellipsometry demonstrated a higher sensitivity than potentiodynamics to surface modification in the cathodic area. In DMEM the removal of a surface layer at negative voltage and a further repassivation with increasing voltage was characteristic. In PBS a surface layer started to grow immediately. X-ray photoelectron spectra of this layer formed in PBS are consistent with iron phosphate. Its formation is inhibited in DMEM; the presence of aminoacids is discussed as the reason.

The morphological evolution of nanostructures on semiconductor surfaces eroded by low-energy ion beams has gained particular interest recently as a possible way to generate regular, ordered, and highly dense quantum dots. Generally, the erosion by ion beams increases the surface roughness, which under certain sputter conditions can turn to periodic surface structures. At normal incidence of the ion beam hexagonally arranged dot patterns appear on the eroded surface. The diameter of these structures is in the range of 15 - 80 nm depending on ion energy with a density up to 2x10^11cm^-2.
After an initial stage of irradiation the temporal evolution of the dot pattern can be described by a stochastic continuum equation. In the case of crystalline semiconductor surfaces rapid amorphization and variation in stoichiometry takes place. As the erosion process proceeds nanoscale dot structures appear at the surface, which are remarkable well ordered and grow up to an aspect ratio of nearly unity. We present the temporal evolution of dot pattern formation on GaSb (100) surfaces during Ar+ ion sputtering. The characteristic length of the dot pattern is determined as a function of ion energy, ion current density, and sample temperature.

Ion beam deposition of carbon films was studied by molecular-dynamics simulations. Using an analytic hydrocarbon potential of Brenner with an increased C-C interaction cutoff value, deposition of films with a thickness of up to 10 nm was simulated for ion energies E_ion =10-80 eV, and for substrate temperatures T_s ranging from 100 to 900 K. The bulk properties of the computed tetrahedral amorphous carbon (ta-C) films as well as structure and roughness of their sp² -rich surface layers agree qualitatively with experiment. At low ion energies and low substrate temperatures, the sp³ fraction in the films increases with ion energy, resulting in a highly sp³ -bonded ta-C with a high compressive stress for E_ion >30 eV. This trend remains also at room temperature, however with lower sp³ content and stress.
In agreement with experiment the simulations predict a sharp transition from ta-C to graphitic carbon as T_s exceeds a critical temperature T_c . The calculated transition temperature T_c is a bit too low (T_c ~100 ^oC for E_ion =40 eV). For the ion energies E_ion ≤ 80 eV, the incidence atom is predicted to come to rest in the sp² -rich surface layer. A time-resolved analysis of the film formation shows that atom subplantation leads generally to a highly tetrahedral structure, but above T_c the kinetic energy of the atoms is sufficiently large to overcome the barrier in cohesive energy between ta-C and the more stable graphite-like films.

The complexation of uranium(VI) by humic and fulvic acids was studied to obtain information on the binding of uranium(VI) onto functional groups of humic substances. For this, various natural and synthetic humic acids were chemically modified resulting in humic acids with blocked phenolic OH groups. Both from the original and from the modified humic substances, solid uranyl humate complexes were prepared at pH 2. FTIR and extended X-ray absorption fine structure (EXAFS) spectroscopy were applied to study the chemical modification process of humic substances, to study the structure of uranyl humate complexes and to evaluate the effect of individual functional groups of humic substances (carboxylic and phenolic OH groups) on the complexation of uranyl ions. The results confirmed the predominant blocking of phenolic OH groups in the modified humic acids. These modified humic acids are suitable model substances to study the role of phenolic OH groups of humic acids in dependence on pH. By EXAFS spectroscopy, identical structural parameters were determined for all uranyl humates. Axial U-O bond distances of 1.78 Å were determined. In the equatorial plane approximately five oxygen atoms were found at a mean distance of 2.39 Å. The blocking of phenolic OH groups of humic acids did not change the near-neighbor surrounding of uranium(VI) in uranyl humate complexes. Thus, the results confirmed that predominantly humic acid carboxylate groups are responsible for binding of uranyl ions and that the influence of phenolic OH groups is insignificant under the applied experimental conditions. The carboxylate groups are monodentate coordinated to uranyl ions.

The test facility ROCOM (Rossendorf Coolant Mixing Model) has been built for the investigation of coolant mixing processes in the reactor pressure vessel of pressurised water reactors (PWR). ROCOM is a 1:5 model of the German PWR KONVOI and has been designed for a wide range of different mixing scenarios. ROCOM disposes of four loops with fully controllable coolant pumps. The test facility is operated with demineralised water. For the investigation of mixing, tracer solution (water labelled with salt) is injected into the facility. The transient distribution of the electrical conductivity is is measured at different positions of the flow path by means of wire-mesh sensor technique with high resolution in space and time. The measured conductivity is transformed into a dimensionless mixing scalar.
The mixing at quasi-stationary conditions (constant loop mass flow rates) has been investigated in the presented experiments. That concerned nominal operation conditions, the operation with a reduced number of loops and the investigation of cold-water transients with running pumps and conditions of developed natural circulation. In special experimental series, the reproducibility of the results at identicla boundary conditions within the confidence intervalls has been shown. Further, the influence of various factors on the mixing has been investigated. This included the pressure losses at the core bottom plate, the global coolant flow level and the influence of the loop flow rate on the perturbed sector at the core inlet. An analysis of the measurement error of the used measurement technique completes the report.

A combination of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy, Transmission Electron Microscopy (TEM) and Energy-Dispersive X -ray (EDX) was used to conduct a molecular and atomic analysis of the uranium complexes formed by A. ferrooxidans. The results demonstrated that this bacterium accumulates uranium as phosphate compounds. We hypothesize that the poly P-bodies of A. ferrooxidans may play a role in detoxification of those part of uranium which is uptaken by the cells.

BACKGROUND: Titanium oxides are known to be good hemocompatible, therefore they are suggested as coatings for blood contacting implants. But little is known about the influence of physical characteristics like crystal structure, roughness and electronic state on the activation of blood platelets and the blood clotting cascade. METHODS: Titanium oxide films were produced by metal plasma deposition and implantation in form of rutile, crystalline and nanocrystalline anatase + brookite and amorphous TiO2. The redox potential was reduced by implantation of chromium ions, the electronic band gap of the semiconductive oxide was shifted by ion implantation of the electron donor phosphorous. Hemocompatibility was determined by measuring the adhesion of blood platelets, their P-selectine expression, and of the blood clotting time on these samples. RESULTS: The crystalline titanium oxides had a slightly higher activation of the clotting cascade but lower platelet adhesion than nanocrystalline and amorphous titanium oxides. The surface roughness below 50 nm had no obvious effect. Both, implantation of phosphorous or chromium ions, strongly reduced the activation of the clotting cascade, but only the phosphorous implanted surface also showed a reduced platelet activation, whereas platelet adhesion and activation was strongly increased on the chromium implanted surfaces. CONCLUSION: Phosphorous doping of rutile TiO2 can increase its hemocompatibility, both concerning blood platelets and blood clotting cascade, but the biochemical mechanism has to be worked out.

This work reports the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: (i) conventional method of doping by implanting with N into an ion beam synthesized SiC layer and (ii) a novel method based on pre-doping (with N and P) of the Si wafers before the ion beam synthesis of SiC. For the N implantation the electrical data show a p-type overcompensation of the SiC layers for both doping methods used. The structural (XRD) and in-depth (SIMS, Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N ion implantation damage, and therefore, the need for further optimization of their thermal processing. In contrast, the P-doped SiC layers always show n-type conductivity. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the undoped material. Our electrical data, together with the absence of additional stress related to P-implant suggest that this technique could be suitable to avoid effects related to the ion implantation damage in the SiC lattice, although the electrical activation of P in the SiC is about one order of magnitude lower than in Si.

This work reports preliminary data on the ion beam synthesis of n-doped SiC layers. For this, two approaches have been studied: i) doping by ion implantation (with N) of ion beam synthesized SiC layers and ii) ion beam synthesis of SiC in previously doped (with P) Si wafers. In the first case, the electrical data show a p-type overcompensation of the SiC layer in the range of temperatures between -50°C and 125 °C. The structural (XRD) and in-depth (SIMS; Spreading Resistance) analysis of the samples suggest this overcompensation to be induced by p-type active defects related to the N-ion implantation damage, and therefore the need for further optimization of their thermal processing. In contrast, the p-doped SiC layers always show n-type doping. This is also accompanied by a higher structural quality, being the spectral features of the layers similar to those from the not doped material. Electrical activation of P in the SiC lattice is about one order of magnitude lower than in Si. These data constitute, to our knowledge, the first results reported on the doping of ion beam synthesized SiC layers.

Benchmark calculations for the validation of the coupled neutron kinetics/thermohydraulic code complex DYN3D-ATHLET are described. Two benchmark problems concerning hypothetical accident scenarios with leaks in the steam system for a VVER-440 type reactor and the TMI-1 PWR have been solved. The first benchmark task has been defined by FZR in the frame of the international association "Atomic Energy Research" (AER), the second exercise has been organised under the auspices of the OECD. While in the first benchmark the break of the main steam collector in the sub-critical hot zero power state of the reactor was considered, the break of one of the two main steam lines at full reactor power was assumed in the OECD benchmark. Therefore, in this exercise the mixing of the coolant from the intact and the defect loops had to be considered, while in the AER benchmark the steam collector break causes a homogeneous overcooling of the primary circuit. In the AER benchmark, each participant had to use its own macroscopic cross section libraries. In the OECD benchmark, the cross sections were given in the benchmark definition. The main task of both benchmark problems was to analyse the re-criticality of the scrammed reactor due to the overcooling.
For both benchmark problems, a good agreement of the DYN3D-ATHLET solution with the results of other codes was achieved. Differences in the time of re-criticality and the height of the power peak between various solutions of the AER benchmark can be explained by the use of different cross section data. Significant differences in the thermohydraulic parameters (coolant temperature, pressure) occurred only at the late stage of the transient during the emergency injection of highly borated water. In the OECD benchmark, a broader scattering of the thermohydraulic results can be observed, while a good agreement between the various 3D reactor core calculations with given thermohydraulic boundary conditions was achieved. Reasons for the differences in the thermohydraulics were assumed in the difficult modelling of the vertical once-through steam generator with steam superheating.
Sensitivity analyses which considered the influence of the nodalisation and the impact of the coolant mixing model were performed for the DYN3D-ATHLET solution of the OECD benchmark. The solution of the benchmarks essentially contributed to the qualification of the code complex DYN3D-ATHLET as an advanced tool for the accident analysis for both VVER type reactors and Western PWRs.

VALCO is an EU FP5 project on transient analysis code validation for VVER type reactors that continues the work of the former EU Phare project SRR1/95. Twelve organisations from nine East and West European countries are participating. For the validation of coupled neutronic / thermal-hydraulic codes that are used in VVER safety analyses, five measured transients from different VVER-440 and VVER-1000 plants have been documented. Two of them have been chosen for validation calculations. First results of an ATHLET / DYN3D calculations for a MCP trip measured in the Kozloduy-6 VVER-1000 are presented. Uncertainty analysis applying the SUSA methodology developed at GRS to coupled-code calculations for VVER will be performed. To validate the stand-alone three-dimensional neutronic codes together with the applied two-group diffusion parameters independently from thermohydraulic feedback, the analysis of measurements in the V-1000 zero-power facility (KI Moscow), which is a full-scale VVER-1000 mock-up, is going to be performed. Preliminary results of DYN3D steady-state calculations using a HELIOS two-group data library and albedo coefficients calculated by the transport code MARIKO are compared to measurement data.

Thin films of semiconducting iron disilicide (ß-FeSi2)with up to 8 at.% Cr addition grown on Si(001) and Si(111) substrates were studied by spectroscopic ellipsometry as well as transmission and reflection measurements at room temperature. The dielectric function was deduced in the interband spectral range. In molecular beam epitaxy (MBE) preparation part of the Fe atoms were substituted by Cr during deposition. For a low Cr amount in the doping range up to about 0.4 at.%, Cr was found to modify epitaxial growth on Si(111) substrates with a change in dominating ß-FeSi2 grain orientation. Higher amounts of Cr lead to the precipitation of CrSi2, which was detected optically and confirmed by x-ray diffraction measurements and a deterioration of film morphology. Furthermore, ß-FeSi2 thin films were implanted with Cr and subsequently annealed at varios temperatures. In these samples also CrSi2 was detected. The results suggest that it is impossible to produce ß-(Fe(1-x)Cr(x))Si2 alloys by MBE or ion implantation.

Diamondlike amorphous carbon (DLC) is a transparent hard material approaching crystalline diamond in hardness and elastic modulus. The main issue restricting applications of this very promising material is a high compressive stress in DLC films after growth. I present recent results of atomic scale calculations of growth and mechanical properties of DLC films performed in collaboration with H.-U. Jaeger. The following topics are discussed:

- the nature of intrinsic stresses in DLC films;
- the dependence on the intrinsic stresses on the film deposition parameters;
- the effect of the intrinsic stresses on the second-order elastic constants of amorphous carbon.

The atomic models of DLC films are prepared by direct molecular dynamics simulation of ion-beam deposition. Similar to real as-deposited films, the simulated films have a high content of tetrahedrally coordinated atoms and large intrinsic compressive stresses in the region of steady-state growth. The stress in the region of steady-state growth is calculated as an average of atomic-level stresses derived from an empirical interatomic potential. The origin of the intrinsic stress in DLC films is discussed on the basis of the structural changes due to thermal annealing simulated by molecular dynamics method. We propose that the high stress in DLC films can be
related to local defects in amorphous carbon networks. The dependence of the second-order elastic contants of amorphous carbon on the intrinsic stress is examined by the method of homogeneous deformation. We nonlinear effects are shown to become appreciable at the stress values typical of as-deposited DLC films.

Der Vortrag berichtete über unsere Simulationen zur Ionenstrahlabscheidung von
Diamant-ähnlichen Kohlenstoffschichten. Zuerst wurden die typischen Resultate
einer Rechnung vorgestellt. Danach wurden der sp³-Gehalt der Filme,
ihre Dichte, die Bindungsenergie der Atome und die Struktur der Graphit-ähnlichen Filmoberfläche erläutert.

Three different methods for measuring the depth distribution of dopants in 4H-SiC have been investigated: (1) Spreading Resistance Profiling (SRP), (2) Scanning Capacitance Microscopy(SCM) and (3) Scanning Electron Microscopy (SEM). The investigated samples included p- and n-type epitaxial layers grown by vapor phase deposition with doping concentrations of 10E16 - 10E20 cm-3. Also p+n implanted profiles using a combination of Al and B multi-energy implantation were studied. All techniques were able to provide doping profiles qualitatively corresponding to Secondary Ion Mass Spectrometry (SIMS) data. The SRP results suggest a lower limit of the p-doping concentration below which the ohmic contact between the probe tip and sample become more Schottky-like. The magnitude of the SCM signal corresponds well to the chemical doping profile except in the depleted region surrounding the metallurgical junction of the p+n structure.

In einem mehrjährigen umfangreichen Bestrahlungsprogramm wurden in den Bestrahlungskanälen des Reaktors WWER-2 des KKW Rheinsberg Druckbehälterstahlproben bestrahlt. Das Programm diente der Erweiterung der Datenbasis zur Bewertung der Strahlenversprödung von Reaktordruckbehälterstählen. Zur Ermittlung der Neutronenbelastung wurden die Bestrahlungskapseln mit Neutronenaktivierungsdetektoren bestückt. Der Bericht enthält die Beschreibung des Typs, des Aufbaues und der Zusammensetzung der Neutronenfluenzmonitore, ihre Anordnung im jeweiligen Experiment, die Auswerteprozedur nach der Bestrahlung und gibt eine zusammenfassende Übersicht über die gemessenen und spektrumsjustierten Neutronenfluenzen für alle 8 Einzelexperimente des Bestrahlungsprogrammes Rheinsberg II. Die Ergebnisse der neutronendosimetrischen Messungen sind konsistent mit den Ergebnissen der Neutronenfeldrechnungen und ergeben in Verbindung mit diesen zuverlässigen Daten über die Neutronenbelastung der in den Bestrahlungsexperimenten neutronen-exponierten Materialproben.

A mass selected focused ion beam is employed for the fabrication of plasmonic structures applying different techniques. So the local implantation of equidistant gold-dots of some ten nm diameter in a silicon or SiO2 target will be studied. Also the local growth of Au-dots after a FIB pre-treatment is a promising approach due to the low adhesion of Au on Si and SiO2 surfaces. Dots or columns can also be achieved by sputtering small holes in a thin film and filling them with noble metals. A new approach is the local ion beam synthesis of CoSi2 nano-structures after cobalt-FIB implantation and annealing. An additional possibility is the growth of metal structures in a FIB aided CVD process using a certain precursor metal-organic gas.

An alternative approach for the fabrication of SiCOI material based on ion beam synthesis technique IBS is presented. Combining IBS with wafer bonding, high crystalline quality ß-SiC layers with low residual strain, have been successfully transferred onto oxidized Si wafers, obtaining SiCOI structure with abrupt SiC/SiO2 interfaces and low surface roughness.

Combining He ion irradiation and thermal mobility below 600K, we both trigger and control the transformation from chemical disorder to order in thin films of an intermetallic ferromagnet (FePd). Kinetic Monte Carlo simulations show how the initial directional short range order determines order propagation. Magnetic ordering perpendicular to the film plane was achieved, promoting the initially weak magnetic anisotropy to the highest values known for FePd films. This post-growth treatment should find applications in ultrahigh density magnetic recording.

Many recent conferences on ion beam processing of materials have concentrated on process optimisation, with comparatively less effort on understanding basic science features. It seemed timely to reverse this trend, and focus on ion beams as a tool for probing the basic materials processes and properties or for exploring the more fundamental aspects of nonequilibrium modifications induced by irradiation.

Symposium O, "Ion Beam Synthesis and Processing of Advanced Materials",was held November 27-29 at the 2000 MRS Fall Meeting in Boston, Massachusetts, USA. 116 papers were presented in fourteen sessions including two poster sessions. The sessions were well attended and the discussion were lively.

Auf der Basis von Nanostrukturen gibt es völlig neue Funktionsprinzipien und
Bauelementekonzeptionen für die Elektronik und Optik. Es wird gezeigt, dass
der Ionenstrahl als etabliertes Werkzeug der Mikroelektronik auch bei der
Züchtung (Ionenstrahlsynthese) und Zähmung (Eigenschaftsänderung)
von Nanostrukturen ein technologiefreundliches Verfahren ist. Es müssen
Selbstorganisationsphänomene verstanden und eingesetzt werden, die bei der
Prozeßführung weitab vom thermodynamischen Gleichgewicht auftreten.
Hierzu gehören die inverse Ostwald-Reifung unter Ionenbestrahlung, die Ordnung von Präzipitaten bei der Phasenseparation und die Pearling-Instabilität. Zwei Anwendungen werden vorgestellt: Die Entwicklung eines nichtflüchtigen Halbleiterspeichers (nvRAM) und die Lichtleitung in Goldclusterketten für die Nanooptik (Plasmonics).

The control of the MOSFET channel by nanoclusters within the gate oxide, which are charged/decharged due to direct e--tunneling, provides a conceptually very simple non-volatile memory. The development of reliable processes for the production of the required nanocrystals on an industrial scale is a big challenge to current research. The two processes being favored at present are the self-organization of nanocluster-delta-layers after ion implantation [1] and the deposition of Si aerosols [2]. Here, we present an alternative process taking advantage of the well-known self-assembling of Ge quantum dots on (001)Si [3,4] in combination with chemical reduction of GeO2 by Si during thermal treatment [5]. Using process simulations it will be studied, how, in comparison to pure thermal treatment, ion-irradiation induced detachment of Si monomeres from the Si/SiO2 interface accelerates the Ge precipitation due to the GeO2+Si --> SiO2+Ge reaction. For our study it was assumed that self-assembled Ge nanoclusters on Si [3,4] were covered by a Si layer, and, finally, oxidized under special conditions [5] which suppresses Ge segregation. The resulting thin gate oxide with embedded GeO2 clusters is the starting point of our kinetic Monte-Carlo simulations. In an fcc-cell of about 256000 lattice points having periodic boundary conditions in the interface plane, Ising-model-like interactions in the two-component system (Si and Ge) and the reaction GeO2+Si-->SiO2+Ge are taken into account. Additionally, according to ion beam mixing estimated by TRIM calculations, atomic displacements of Si bulk and nanocluster atoms have been considered.
[1] K.H.Heinig, B.Schmidt,.M.Strobel, H.Bernas, Mat.Res.Soc.Proc. v.650(2001).
[2] H. Atwater, J.W. De Blauwe et al., Mat.Res.Soc.Proc. v.638(2001).
[3] F. Jensen, J.W. Petersen, S.Y. Shiryaev, A.N. Larsen, Nanotechn. 7, 117 (1996).
[4] O.Pchelyakov, Y.Bolkhovityanov, A.Dvurechenskii, Thin Solid Films 367, 75 (2000).
[5] Y.-C.King, T.-J.King, C.Hu, Int.Electron Dev. Meeting Technical Digest (1998), 115.

The control of the MOSFET channel by nanoclusters within the gate oxide, which are charged/decharged due to direct e--tunneling, provides a conceptually very simple non-volatile memory. The development of reliable processes for the production of the required nanocrystals on an industrial scale is a big challenge to current research. The two processes being favored at present are the self-organization of nanocluster-delta-layers after ion implantation [1] and the deposition of Si aerosols [2]. Here, we present an alternative process taking advantage of the well-known self-assembling of Ge quantum dots on (001)Si [3,4] in combination with chemical reduction of GeO2 by Si during thermal treatment [5]. Using process simulations it will be studied, how, in comparison to pure thermal treatment, ion-irradiation induced detachment of Si monomeres from the Si/SiO2 interface accelerates the Ge precipitation due to the GeO2+Si --> SiO2+Ge reaction. For our study it was assumed that self-assembled Ge nanoclusters on Si [3,4] were covered by a Si layer, and, finally, oxidized under special conditions [5] which suppresses Ge segregation. The resulting thin gate oxide with embedded GeO2 clusters is the starting point of our kinetic Monte-Carlo simulations. In an fcc-cell of about 256000 lattice points having periodic boundary conditions in the interface plane, Ising-model-like interactions in the two-component system (Si and Ge) and the reaction GeO2+Si-->SiO2+Ge are taken into account. Additionally, according to ion beam mixing estimated by TRIM calculations, atomic displacements of Si bulk and nanocluster atoms have been considered.
[1] K.H.Heinig, B.Schmidt,.M.Strobel, H.Bernas, Mat.Res.Soc.Proc. v.650(2001).
[2] H. Atwater, J.W. De Blauwe et al., Mat.Res.Soc.Proc. v.638(2001).
[3] F. Jensen, J.W. Petersen, S.Y. Shiryaev, A.N. Larsen, Nanotechn. 7, 117 (1996).
[4] O.Pchelyakov, Y.Bolkhovityanov, A.Dvurechenskii, Thin Solid Films 367, 75 (2000).
[5] Y.-C.King, T.-J.King, C.Hu, Int.Electron Dev. Meeting Technical Digest (1998), 115.

Nanoclusters (N) can be generated by ion implantation of impurity atoms into a host matrix and subsequent phase separation of the impurity phase from the matrix during annealing. This is a CMOS technology compatible process, which has great potential for applications. However, a serious problem arises: The NCs have a broad size distribution, which obscures the size dependent characteristics of the NCs.
Here, we show that irradiation of NCs with high-energy ions can be used to overcome this problem. During irradiation, the collisional mixing at the NC-matrix interfaces competes with phase separation. A negative interface tension can be the consequence, which can only be understood in terms of non-equilibrium thermodynamics. The negative interface tension leads to unexpected results: The system will evolve towards a state of maximal surface area!! Thus, a flat interface
becomes instable. Here, we focus on the Gibbs-Thomson relation with a negative interface tension, where we find an increasing solute concentration with increasing NC size. This is inverse to equilibrium behavior. Consequently, we find inverse Ostwald-ripening, e.g. small NCs grow at the expense of large ones. This can be used for the fabrication of monodisperse NCs. These theoretical predictions have been verified by kinetic MC simulations and by ion irradiation of Au NCs in a SiO2 matrix.

no abstract delivered frm author

We aim at a deeper understanding of how thermodynamic systems that have been driven far-from-equilibrium by ion implantation or irradiation may either relax towards equilibrium (in which case self-organisation phenomena are observed frequently), or - alternatively - be driven into stationary nonequilibrium states (where dissipative structures may develop). The far-from-equilibrium states having a high supersaturation and/or specific interface energy relax by nucleation, growth and coarsening. The stationary states are driven by irradiation damage (dpa/sec) and shows new phenomena like inverse Ostwald ripening. Kinetic 3D lattice Monte Carlo simulations were applied succesfully to predict routes of far-from-equilibrium processing of tailored quantum dots and wires for electronic and photonic applications.

Metal and semiconductor nanostructures embedded in insulators, in particular in SiO2, attract at present much interest due to their potential application in microelectronics (nanocluster memories), optoelectronics (luminescence from Si nanocrystals) and photonics (plasmonic devices using Au nanoclusters). The nanostructures can be synthesized by ion implantation and modified by ion irradiation. Thereby, radiation effects in the matrix as well as in the nanostructures induce self-organisation phenomena, which might allow to control, e.g., the spatial and size distribution of nanoclusters.
Two different regimes of self-organization will be discussed: (i) Relaxation regime: Ion implantation of impurity atoms may produce extremely supersaturated solid solutions. During subsequent annealing this far-from-equilibrium state relaxes towards equilibrium by phase separation (nucleation, growth) and minimization of interface energy (Ostwald ripening, coalescence). Self-organization phenomena (e.g. pattern formation during phase separation, Rayleigh or pearling instability during interface minimization) have been found. (ii) Driven system: Interfaces or compounds like SiO2 can be driven into a steady state far from equilibrium by ion irradiation. The steady state is established by a competition between collisional mixing, diffusion and re-formation of the compound. For driven systems a theoretical study and atomistic computer simulations of radiation effects like the nanocluster d-layer formation and ''inverse'' Ostwald ripening will be presented.

no abstract delivered from author

The evolution of diffusively interacting nanoclusters is investigated by combined atomistic (kinetic lattice Monte Carlo method based on the nearest-neighbor Ising model) and mean-field (numerical integration of the governing reaction-diffusion equations) simulations. By expressing Monte Carlo parameters in terms of macroscopic thermodynamic quantities a well-defined interface between both methods is derived. Based on extensive Monte Carlo studies of the Gibbs-Thomson equation an explicit expression for the intrinsic capillary length is presented. Starting with
high-temperature quenches, the evolution of nanoclusters is first studied by the atomistic model. The observed transient dynamics of coarsening is explained uniquely on the basis of the ratio of the capillary length to the mean cluster size. Using input data from the atomistic model, Ostwald ripening is also studied in parallel with the mean-field model. In a detailed study, the similarities and differences of both approaches are discussed and explained in terms of their statistical and deterministic natures. It is demonstrated that in contrast to the commonly applied linearized version of the Gibbs-Thomson relation in the mean-field approach only the use of the full exponential form provides a reasonable matching with the atomistic model.

During annealing at 950°C in an oxidizing ambient, the redistribution of Ge in Ge+-implanted SiO2 layer is influenced by the germanium oxidation. Crystalline clusters precipitate immediately after sample heating. During the annealing an oxidation front proceeds into the layer, consuming crystalline clusters and leaving behind glassy precipitates barely visible by XTEM. Sputtering depth profiling in conjunction with the X-ray photoelectron spectroscopy (XPS) analysis was applied in order to identify the chemical state of both the precipitated Ge and that dissolved in the silicon dioxide matrix. For a reliable interpretation of the measured data, modeling of the physical processes involved in the depth profiling XPS technique was performed. It is shown that the depth profiling by ion beam sputtering causes collisional mixing of the subsurface region, which modifies the XPS signal. The results indicate possible improvement of the depth profiling XPS method to be used in future experiments.

Ion nitriding of Al has been performed by a nitrogen reactive ion beam using a hot filament ion source. The N incorporation has been determined at different beam voltage from 0.4 kV to 2.4 kV with an ion current density of 0.2 mA/cm2, and a substrate temperature of 350°C. For this purpose, the beam has been characterised in terms of ion flux, ion composition and energy distribution using an energy selective mass spectrometer and a Faraday cup. From the beam parameters, N loss due to sputtering and backscattering has been calculated as a function of the ion energy using dynamic binary collision computer simulations. The total amount of incorporated N measured by Nuclear Reaction Analysis (NRA) is consistent with the incident N fluence and the N loss obtained from the simulation. A discrepancy is observed for a beam voltage lower than 0.8 kV due to the stationary surface oxide layer reducing the rate of nitrogen incorporation during ion nitriding of Al.

Die Strahlenversprödung von Druckbehältermaterialien heutiger Kernreaktoren, die durch die anliegenden Neutronen- und Gammafelder verursacht wird, ist meistens durch die Neutronen dominiert. Durch experimentelle Befunde ist aber belegt, dass unter bestimmten Umständen die Gammastrahlung nicht zu vernachlässigen ist und sogar den Hauptbeitrag liefern kann. Die Materialforschung konnte bis heute nicht klären, mit welcher Effektivität beide Strahlungsarten zur Versprödung beitragen.
Im Bericht sind die wesentlichen Ergebnisse, die im Vorhaben Nr. 150 1221 der Reaktorsicherheitsforschung erziellt wurden, dargelegt. Es hatte das Ziel, den aktuellen Kenntnisstand der Materialforschung aufzuarbeiten und auf dessen Grundlage für jeweils zwei russische und deutsche Reaktortypen den Einfluss der Gammastrahlung auf die Versprödung ihrer Druckbehälter abzuschätzen. Die notwendigen Neutronen/Gamma-Fluenzberechnungen wurden mit den SN-Programmen DORT/ANISN unter Verwendung der Gruppendatenbibliothek
BUGGLE-96T und mit dem Monte-Carlo-Code MCNP4C mit den Kerndaten aus der Bibliothek ENDF/B-VI Rev. 3 durchgeführt. Beide Programm- und Datenpakete stellen den heutigen Entwicklungsstand der reaktordosimetrischen Fluenzberechnungen dar. Aus den erzielten Ergebnissen wurden die Konsequenzen für die Bewertung der Druckbehälterversprödungen abgeleitet, Fehlerbetrachtungen dazu durchgeführt und der Einfluss der Gammastrahlung auf reaktordosimetrische Messungen ausgewiesen.

Phase analysis on ion treated surfaces by conversion electron
Mössbauer spectroscopy

Electron microscopy in the Research Center Rossendorf

Surface investigations by Auger electron and X-ray induced
photoelectron spectroscopy

Experimental results and a model for the prediction of the transition from bubble to slug flow within a vertical pipe are presented. The mechanism of the transition is discussed. Local effects as well as the bubble size distribution have to be considered for an appropriate modelling of the development of the flow pattern.

Experimental results concerning the development of the flow pattern for air-water flow in a vertical pipe of 51.2 mm inner diameter are presented. The data were obtained by a wire-mesh sensor. This allows a high resolution in space and time. 99 combinations of air and water superficial velocities were investigated in up to 10 different distances between the gas injection device and the sensor.

A series of different dendrons for the encapsulation of ^99mTc and ¹⁸⁸Re have been synthesised, "3+1" mixed ligand ^99mTc complexes with dendritic polyether thiols as monodendate ligands have been prepared. Challenge experiments with glutathione showed a remarkable enhancement of stability with increasing number of dendron generation. To achieve better solubility behaviour oligoethyleneoxy- and sugar-substituted dendrons are developed. In this case 2-aminobenzenethiol is introduced as chelating unit. Molecular modeling calculations point to an almost complete shielding of the radionuclide by use of second generation dendrons.

Boron nitride films are grown by ion beam assisted deposition (IBAD). Si cantilevers are used as substrates. Intrinsic stress data are derived from dynamic simultaneous measurement of cantilever bending and film thickness during growth. The cantilever bending was measured with a two-beam laser deflection system for real time measurement of the stress in thin films during processing. The curvature of the cantilever, laser reflectivity, quartz thickness monitoring and real time spectroscopic ellipsometry data are recorded simultaneously. Instantaneous stress knowledge with a depth resolution in the nanometer scale provide detailed information on growth processes. The layer sequence of interfacial turbostratic BN layer/mixed (t-BN+c-BN) transition layer/cubic BN can be clearly identified in the instantaneous stress data. The measured stress depends sensitively on fluctuations in the boron evaporation rate which in turn cause variations in the ion/atom arrival ratio. The global stress in turbostratic and cubic boron nitride films is studied during annealing up to 670°C. It is observed that the stress relaxation starts when the deposition temperature is exceeded. It is demonstrated that the intrinsic stress of cubic boron nitride films can be relaxed during growth by simultaneous medium energy implantation. For simultaneous implantations with an ion energy of several keV it is shown that the stress in the growing film can be reduced below 2 GPa, resulting in high quality c-BN.

Early evidence that small technetium compounds may be subject to active transport processes was provided by the historical serependipitous finding that pertechnetate was handled by the sodium-iodide symporter in the thyroid gland. The feasibility of using biochemical ^99mTc probes for various targets such as enzymes and particularly receptors is due to the tolerance of the target molecules towards metal-based mimics. As the high in-vitro affinities to various neuroreceptors in the nanomolar and subnanomolar range indicate, molecular recognition of complex technetium molecules has become possible. One main issue in developing CNS receptor imaging agents remains the very low or totally absent brain uptake.
The general approach to specific small technetium radiopharmaceutical tracers has not changed much in recent years. Despite substantial progress in technetium chemistry, the number of newly launched ^99mTc radiopharmaceuticals is stagnant, at least in a short-term perspective. The development of biochemically specific, small technetium and rhenium complexes remains therefore a challenging, rewarding and often frustrating activity.

CN layers were gr own on polished Si (100 )wafers by the ion beam assisted deposition (IBAD technique at temperatures varying between 200 and 600°C . A Kaufman type ion source fed by Ar and N₂ was applied together with an e-beam heated evaporation source of graphite for the deposition of the CN layers.The composition and chemical bonding state of elements were studied by X-rayphotoelectron spectroscopy.The N-content varied in the range of 8 –16 at.% and showed a decrease with the increase of deposition temperature.The broad C1s and N1s XPS lines manifested several bonding states.The elative intensities of the component peaks varied with the preparation conditions.The two main components of the N1s peak situated at BE s 398.2 eV and 400.6 eV were assigned to sp² (C –N =C )and sp³ (N –C )type bonding states,espectively.The stability of the sp³ states was higher than that of the sp² ones, because the intensityof the 398.2 eV component decreased preferentially with increasing deposition temperature.A post-deposition treatment with low energy ion beam resulted in a significant increase in N₂ ⁺ the overall N-content on the surface,with a preferential increase in the concentration of sp² type nitrogen.

Boron nitride films are grown by ion beam assisted deposition (IBAD). Si cantilevers are used as substrates. Intrinsic stress data are derived from dynamic simultaneous measurement of cantilever bending and film thickness during growth. The cantilever bending was measured with a two-beam laser deflection system for real time measurement of the stress in thin films during processing. The curvature of the cantilever, laser reflectivity, quartz thickness monitoring and real time spectroscopic ellipsometry data are recorded simultaneously. Instantaneous stress knowledge with a depth resolution in the nanometer scale provide detailed information on growth processes. The layer sequence of interfacial turbostratic BN layer/mixed (t-BN+c-BN) transition layer/cubic BN can be clearly identified in the instantaneous stress data. The measured stress depends sensitively on fluctuations in the boron evaporation rate which in turn cause variations in the ion/atom arrival ratio. The global stress in turbostratic and cubic boron nitride films is studied during annealing up to 670°C. It is observed that the stress relaxation starts when the deposition temperature is exceeded. It is demonstrated that the intrinsic stress of cubic boron nitride films can be relaxed during growth by simultaneous medium energy implantation. For simultaneous implantations with an ion energy of several keV it is shown that the stress in the growing film can be reduced below 2 GPa, resulting in high quality c-BN.

Novel Tc-labelled receptor ligands for the serotonin 5HT_1A receptor have been synthesized and biologically evaluated. The complexes consist of a Tc chelate unit with the metal at the oxidation state +5 or +3 and 1-(2-methoxyphenyl)-piperazine or 2-(1-piperazino)phenol as receptor-targeting domain. Tc chelate and receptor targeting moiety are linked by an alkylspacer of various chain length. Re was used as Tc surrogate for complete chemical characterization and in vitro receptor-binding studies. All complexes display subnanomolar affinities for the 5-HT_1A receptor but also high affinities for the alpha1-adrenergic receptor. Biodistribution studies in rats show initial brain uptakes between 0.2% ID and 0.6% ID five minutes post injection. In vitro autoradiographic studies in rat brain and post-mortem human brain indicate the accumulation of the Tc-99m complexes in areas which are rich in 5-HT_1A receptors and additionally in areas rich in alpha1-adrenergic receptors.

The uptake of the ^99mTc(V) DMS ester complexes [^99mTcO(DMSA/DMSEt)]^- (B), [^99mTcO(DMSEt)₂]^- (C), and [^99mTcO(DMSA/DMSEt₂)]^- (D) in comparison with ^99mTcO(DMSA)₂]^- (A) by tumour-bearing nude mice was evaluated. From former biodistribution studies was known, that ^99mTc(V)DMSA already loses its bone affinity when one ester group is introduced into the complex molecule. Now we found that the tumour uptake is maintained also in complexes which contain one or two non-hydrolysable ester functions. Preliminary biodistribution studies showed similar uptake into the human squamous cell carcinoma (FaDu) as well as into the human colonic cell carcinoma (HT29) of nude mice. The low bone accumulation of B, C and D results in excellent tumour to bone ratios of approx. 3:1 for the ester complexes compared to approx. 1:2 for complex A.

Detailed knowledge of the nature of uranium complexes formed after the uptake by plants is an essential prerequisite to describe the migration behavior of uranium in the environment. This study focuses on the determination of uranium speciation after uptake of uranium by lupine plants. For the first time, time-resolved laser-induced fluorescence spectroscopy and X-ray absorption spectroscopy were used to determine the chemical speciation of uranium in plants. Differences were detected between the uranium speciation in the initial solution (hydroponic solution and pore water of soil) and inside the lupine plants. The oxidation state of uranium did not change and remained hexavalent after it was taken up by the lupine plants. The chemical speciation of uranium was identical in the roots, shoot axis, and leaves and was independent of the uranium speciation in the uptake solution. The results indicate that the uranium is predominantly bound as uranyl(VI) phosphate to the phosphoryl groups. Dandelions and lamb's lettuce showed uranium speciation identical to lupine plants.

Nanoindentation techniques have been used to investigate the mechanical properties such as hardness and Young's modulus of carbon nitride films deposited on Si (111) substrates using Ion Beam Assisted Deposition (IBAD) process with varying the deposition parameter. For the lower and higher deposition temperatures, two different types of load displacements behaviour of the loading regime has been found. At a certain temperature limit, the elastic modulus values are dropping significantly down. To estimate the film-only properties of these composites, a simple energy model has been used. For comparison, a Hertzian contact analysis of the load-displacement curves at low loads and direct modulus measurements by laser sound velocity technique were performed. The film thickness was estimated using optical profilometry and the nitrogen content of these films was determined using Electron Energy Loss Spectroscopy (EELS), X-ray induced Photoelectron Spectroscopy (XPS) and Elastic Recoil Detection Analysis (ERDA) techniques. The highest nitrogen content at deposition temperatures between 200 and 400 °C occurs for a Nitrogen-to-Carbon (N/C) transport ratio of 1.2. The film microstructure investigated, using Transmission Electron Microscopy/Selected Area Electron Diffraction (TEM/SAD) exhibits more crystallinity at higher deposition temperatures.

In an attempt to develop new technetium-based radiopharmaceuticals for the non-invasive diagnosis of oxidative myocardial metabolism, rhenium model compounds according to the ‚3+1' mixed ligand approach as well as the organometallic tricarbonyl-design were synthesized. The geometrical impact of different chelates on the integrity of the fatty acid head structure was determined by single crystal X-ray analyses. To evaluate the diagnostic potential of the analogous Technetium-99m compounds, fatty acid complexes of the ‚3+1' mixed ligand type were prepared on n.c.a.-level and studied in the isolated constant-flow-perfused guinea pig heart model; compared to established [¹²³I]Iodine-labelled fatty acid radiotracers, the tested Technetium-99m derivatives showed a specific, however significantly lower myocardial extraction rate.

The sputter ion source HVEE 860-C has shown after an operation time of some thousands hours significant erosion of inner source parts. This is caused by Cs ions generated at hot surfaces outside of the spherical ioniser surface.
The calculated trajectories of these ions and the erosion patterns show an excellent correspondence. The suppression of the disturbing ions has resulted in increased lifetimes of the ion source and an improved focus of the primary Cs ions on the sputter target.

The master curve approach is a new concept for a fracture mechanics-based integrity assessment of pressurized engineering construction. It permits the determination of fracture toughness properties with small-size specimens under quasi-static loading conditions. The transfer of the quasi-static master curve approach to dynamical loading like Chapry impact testing would be expedient but is not trivial. In principle, the master curve approach seems to be applicable for dynamic loading. The detailed statistical analysis of the results, however, shows several shortcomings. The test temperature affects significantly the reference temperature, To. With small Charpy-size specimens valid values are only obtained if tested within the upper part of the lower shelf region. Approximately, the experimental results are compatible to the Weibull-distribution of the master curve concept.

MOCVD grown epitaxial layers of In0.53Ga0.47As/InP were implanted with 1.5 MeV Se ions or 1.0 MeV Si ions at room temperature and at liquid nitrogen temperature. A wide range of ion doses exceeding 10(15) ions/cm(2) was applied. White beam synchrotron section and projection topography as well as rocking curve measurements were used for the characterisation of samples. The aim of the experiment was the evaluation of the dose dependence of ion implantation induced strain and the determination of amorphisation threshold. It was found that the implantation performed at room temperature did not cause lattice amorphisation even for highest applied doses, i.e. 2 x 10(15) Se/cm(2). The strain induced by 1.5 MeV Se ions implantation at room temperature increases with the ion dose and reaches its maximum for 3 X 10(14) ions/cm(2). Further increase of the dose resulted in the decrease of the strain. Ion implantation performed at liquid nitrogen temperature led to amorphisation of the sample at doses of the order of 10(13) ions/cm(2). The amorphisation manifested itself in the significant decrease of the implanted layer maximum in the rocking curve. A strain modulation fringes characteristic for non-monotonic strain profiles were observed in some Bragg-case section topographs. (C) 2001 Elsevier Science BY All rights reserved.

Pd¯Ti alloy surface layers in Ti formed by N- and Ar-pulse plasma alloying of Pd films deposited by pulse erosion of Pd electrode tips were studied by RBS, XRD, SIMS, and gravimetric analysis. Layers of a thickness up to 2 m and concentration up to 40% Pd at the surface were obtained. Pd is present as a solute in hcp Ti and as TiPd and TiPd3 phases. The Pd profiles follow Gaussian distribution although no simple theoretical model can account for this behavior.

In the present contribution, we report experimental results on the formation of He-induced cavities in Cz grown (1 0 0) Si samples implanted with 40 keV He⁺ ions to a fluence of 1×10¹⁶ cm^-2 at four implantation temperatures, 77, 133, 233 and 300 K, and submitted to rapid thermal annealing at 1073 K for 600 s. The as-implanted samples were analyzed by Rutherford backscattering/channeling spectrometry (RBS/C) and the annealed ones by transmission electron microscopy (TEM). The results obtained show that the characteristics of the produced cavity systems depends significantly on the implantation temperature. A correlation between the dynamic annealing behavior and the bubble nucleation process is proposed.

Characterization of multilayer thin films optical filters using RBS

The lattice site of implanted tellurium in gallium nitride heteroepitaxial films grown on sapphire substrates has been studied. GaN samples were implanted with 400 keV 130Te ions at 300 °C. The ion dose was 1.5×1015 cm-2. The samples were analysed with Rutherford backscattering spectrometry channelling using 2.0 MeV 4He ions. The maximum Te concentration was 0.2 at.%. Based on measured channelling angular scans for Ga and Te along the 0001 and 101 axial directions, analysed by comparison with Monte Carlo simulations, it was concluded that in the as-implanted sample about 70% of Te atoms were on the Ga atom lattice sites, slightly displaced. The measured 101 scan showed no evidence of substitutional Te on N lattice site. The post-implantation annealing at 900 °C was found to decrease the substitutional fraction of Te while little recovery of the host lattice was observed. This indicates an interaction process between Te atoms and implantation-induced lattice defects. No migration of Te during annealing at 900 °C was observed. In addition, the effect of misfit dislocations in the host lattice on the channelling yield was visible in the 101 angular scan measured at a 47° tilt angle.}

The aim of this study was to obtain information about the sorption mechanism of uranium(VI) in chlorite systems. Chlorite is a main mineralogical constituent of phyllite and therefore found in tailings related to the former uranium mining activity in Saxony and Thuringia/Germany. It is also a common subsolidus alteration product in granites and therefore important for risk assessment of high level waste in granitic environments. Alteration of the ferrous chlorite leads to a release of iron, followed by precipitation as ferrihydrite, goethite or hematite. The altered chlorite as well as the ferric iron precipitates affect the uranium migration by sorption processes.

Samples for Extended X-ray Absorption Fine Structure (EXAFS) analyses were prepared under ambient conditions using 200 mg of a ferrous iron chlorite (grain size 2 to 6.3 µm, [Mg_5,5Al_2,48Fe²⁺ _3,02Fe³⁺ _0,94)[(Si_5,33Al_2,66)O₂₀(OH)₁₆], from Flagstaff Hill, California), dispersed in 1000 ml of 0.01 N NaClO₄ solution. The initial uranium(VI) concentrations were set to 1x10^-5 M at approximately pH 6.5. The uranium(VI) was added to the first sample immediately after pH adjustment, allowing no time for alteration reactions. Uranium(VI) was added to the second and third sample allowing an alteration period of 2 and 6 months, respectively. The pH was not adjusted during the alteration. After a sorption period of 6 hours for the first and approx. 60 hours for the second and third sample, the suspensions were centrifuged and the sorption samples were prepared as wet pastes for EXAFS measurements.

Extended X-ray Absorption Fine Structure (EXAFS) is a well-established spectroscopic method to identify the local coordination of uranium. EXAFS spectra were recorded at room temperature in fluorescence mode at the Rossendorf beamline (ROBL) at the ESRF in Grenoble. The measured EXAFS oscillations were fitted using the EXAFSPAK program. The theoretical phase shifts and backscattering amplitudes were calculated with FEFF8.
Two axial oxygens at a distance of 1.79 Å to the uranium atom were found, suggesting that uranium(VI) reduction to uranium(IV) is not the dominant sorption mechanism. The low mean distance of the equatorial oxygen's of 2.32 to 2.36 Å and the high Debye-Waller factors are typical for an inner-sphere surface complexation. No magnesium, aluminum, silicon, or iron backscatterers at distances of 3 to 4 Å , which would indicate a bidentate or monodentate surface complexation, were observed. On the basis of these results it was not possible to attibute the adsorbed uranium to different crystallographic sites (edges versus basal plane sites) including secondary iron sites.
However, a simulation of EXAFS spectra shows a destructive interference of aluminum (or magnesium) and iron EXAFS contributions in bidentate coordination of uranium(VI) on metal octahedras.

A thin-layer reference material for surface and near-surface analytical methods was produced and certified. The surface density of the implanted Sb layer was determined by Rutherford backscattering spectrometry (RBS), instrumental neutron activation analysis (INAA), and inductively coupled plasma isotope dilution mass spectrometry (ICP-IDMS) equipped with a multi-collector. The isotopic abundances of Sb (121Sb and 123Sb) were determined by multi-collector ICP-MS and INAA. ICP-IDMS measurements are discussed in detail in this paper. All methods produced values traceable to the SI and are accompanied by a complete uncertainty budget. The homogeneity of the material was measured with RBS. From these measurements the standard uncertainty due to possible inhomogeneities was estimated to be less than 0.78% for fractions of the area increments down to 0.75 mm2 in size. Excellent agreement between the results of the three different methods was found. For the surface density of implanted Sb atoms the unweighted mean value of the means of four data sets is 4.811016 cm-2 with an expanded uncertainty (coverage factor k=2) of 0.091016 cm-2. For the isotope amount ratio R (121Sb/123Sb) the unweighted mean value of the means of two data sets is 1.435 with an expanded uncertainty (coverage factor k=2) of 0.006.

Energy spectra of protons channeling along the (0001) axis of several SiC polytype crystals, (namely 4H, 6H, 15R, 21R) in the energy region E_p=1.7-2.5 MeV, in the backscattering geometry, were taken and analyzed. Computer simulations based on the assumption that the dechanneling of protons follows an exponential law are in very good agreement with the measured spectra. The obtained results for the two crucial channeling parameters, ?, the mean channeling distance, and, a, the ratio of the stopping powers in the aligned and random mode are compared for the different structures and an attempt is made to explain the occuring similarities as well as the differences, in order to evaluate the use of SiC polytypes as substrates in implantations and thin film depositions. An attempt is also made to correlate the results from the present work to the ones obtained in the past for simpler crystallographic structures, namely Si <100> and Si <111>, as well as more complex ones, such as SiO₂ (c-axis).

Energy spectra of protons channeling along the optical axis (c-axis) of a quartz crystal in the energy region E_p=1.7¯2.5 MeV in the backscattering geometry were taken and analyzed. Computer simulations based on the assumption that the dechanneling of protons follows an exponential law are in good agreement with the measured spectra, yielding electronic stopping powers for the specific crystal orientation that vary between 2.35 and 1.74 eV/Å, respectively, for the energy interval in consideration. The results are compared with the ones obtained in the past for simpler crystallographic structures, namely Si <1 0 0> and Si <1 1 1>, and an attempt is made to explain the occurring similarities as well as the differences.

Energy spectra of protons channeling along the (0 0 0 1) axis of several SiC polytype crystals (namely 4H, 6H, 15R, 21R) in the energy region E_p=1.7¯2.5 MeV, in the backscattering geometry, were taken and analyzed. Computer simulations based on the assumption that the dechanneling of protons follows an exponential law are in very good agreement with the measured spectra. The obtained results for the two crucial channeling parameters, , the mean channeling distance, and, , the ratio of the stopping powers in the aligned and random mode are compared for the different structures and an attempt is made to explain the occurring similarities as well as the differences, in order to evaluate the use of SiC polytypes as substrates in implantations and thin film depositions. An attempt is also made to correlate the results from the present work to the ones obtained in the past for simpler crystallographic structures, namely Si(1 0 0) and Si(1 1 1), as well as more complex ones, such as SiO₂ (c-axis).

A calcium phosphate layer was deposited on the surface of AISI 316 stainless steel by immersion in a solution, supersaturated for calcium and phosphorous ions. The substrates were pre-modified by ion implantation of Ca and P in order to induce nuclei for calcium phosphate growth on the surface. The reactivity of these surfaces towards crystal growth in aqueous solution was examined by Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, Scanning Electron Microscopy and Energy Dispersive X-ray Spectroscopy. They showed that the deposited layer was a mixture of hydroxyapatite and other calcium phosphates.

Die Grundlagen der zeitaufgelösten Spektroskopie an Halbleitern und Halbleiterheterostrukturen mit dem Freie-Elektronen Laser
an ELBE werden erläutert mit Schwerpunkt auf der Dynamik von Intersubbandübergängen. Neben Anrege-Abfrage Experimenten mit einer Wellenenlänge (degenerate pump-probe) liefern Mehrfarben-Experimente mit synchronisierten Femtosekunden Lasern zusätzliche wichtige Informationen über elektronische Nichtgleichgewichts-Verteilungsfunktionen. Desweiteren werden die Techniken des Vier-Wellen Mischens und des spektralen Lochbrennens diskutiert, die bei der Beantwortung von Fragen nach inhomogenen/homogenen Verbreiterungen von Übergängen wichtig sind.

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Eine vorhandene Elektronenstrahl-Schweißanlage soll mit geringstem technischen Zusatzaufwand zur Röntgen-Tomographie eingesetzt werden. Im Vakuum der Schweißanlage werden dafür neben einer geeigneten Anode für den Elektronenstrahl nur eine einfache Vorrichtung zum Drehen des Untersuchungsobjektes und insbesondere nur ein einziger Detektor für die Röntgenstrahlung untergebracht. Die zur tomographischen Bildrekonstruktion benötigte Information soll allein aus der Messgröße dieses Detektors gewonnen werden.

Ion bombardment causes atomic collisions and the displacement of target atoms. The subsequent athermal and rapid thermal relaxation processes lead to a (meta)stable defect structure which can still be changed by thermal activation. The initial stage of defect formation occurs on very small time and length scales and is therefore hardly accessible by available experimental methods. Therefore, atomistic computer simulations are employed to investigate these processes and to determine the (meta)stable defect structure formed. The knowledge of details of this damage state, e.g. of type and amount of defects, can contribute to a better understanding of ion implantation and ion-assisted layer deposition.
In this talk, a combined atomistic simulation method is used to study a relatively simple case, the defect formation by a single ion impact in bulk silicon. The procedure allows the effective calculation of the total number and the depth distribution of different defect species (isolated vacancies and self-intersitials as well as more complex defects) formed on average per incident ion. Furthermore, it enables investigations on the temporal evolution of the defect structure up to several 100 ps after ion impact, and on the influence of the target temperature on this process.

Ion implantation is considered to be a very suitable means for selective electrical doping of SiC. However, ion irradiation produces defects which can prevent the electrical activation of the implanted dopants. The understanding of ion-beam-induced defect generation and evolution in SiC is therefore extremely important. It consists of three stages: (i) atomic displacements during ballistic processes, (ii) formation of metastable defects after fast relaxation of the crystalline lattice, and (iii) long-term thermally induced defect rearrangement, migration, recombination and reduction. The present work deals with elementary processes occurring in the first two stages. Classical molecular dynamics (MD) simulations using a modified Tersoff potential are performed to investigate the conditions for defect formation by a single Si or C primary knockon atom (PKA) at T = 300 K. The threshold PKA energy for defect formation as well as the resulting defect configuration and its formation energy are determined. This study is limited to cases where the PKA starts parallel or antiparallel to the [0001] direction, which is identical to [111] in the cubic 3C-SiC. However, certain general results obtained are also valid for other examples. In contrast to previous publications, the more detailed investigations performed in this work reveal, that for a well-defined start direction neither for a Si nor for a C PKA a fixed threshold PKA energy for defect formation exists. Instead, a transition region having a width of 2.5 – 20 eV is found in which the probability for defect formation increases from 0 to 1. Moreover, for the same PKA energy and start direction, different defect configurations may be obtained. Both results are due to the fact that lattice vibrations influence the dynamics of atomic displacement and relaxation processes, in particular its initial conditions. Most of the defects found are different configurations of single pairs of vacancies (V) and self-interstitials (I). Since the lattice structure of 4H-SiC is more complicated than that of 3C-SiC, a greater variety of different defect types is found in this polytype. At 300 K the probability for overcoming the energetic barriers for V-I recombination or between different metastable defect states is very small. Therefore, within 20 – 50 ps after the PKA is started, present MD simulations do not yield a further transformation of the defect configurations formed by fast relaxation processes.

Investigations of ion-beam-induced defect formation by classical molecular dynamics simulations are determined decisively by the quality of the interatomic potentials employed. Potentials of Tersoff and Brenner type are presently considered the best to describe structural and defect properties of SiC. However, their repulsive part does not agree well with state-of-the-art potentials used in atomic collision physics. The subject of the present work is therefore the improvement of the repulsive interaction in the Tersoff and Brenner type potentials, in order to enable a better description of ballistic and athermal processes occuring during ion bombardment of SiC. At small interatomic distances the pair part of these potentials is replaced by the well-tested ZBL potential. An exponential spline function is employed to connect the ZBL potential with the two-body part of the Tersoff or Brenner potential, in the region between some ten and zero eV. The resulting pair potential and its first derivative must be continuous and monotonic over the whole range of repulsive interaction. The improvements introduced are tested by comparing the energies for repulsive interactions in Si-Si, Si-C, and C-C dimers with corresponding results obtained by ab-initio DFT calculations using the DMOL code. The second modification introduced into the Tersoff and Brenner type potentials concerns their three-body part. Its contribution to the total potential is reduced for small interatomic separations at which the interaction between two atoms should be independent of their coordinations to the other neighbor atoms. This is realized in such a manner that the total potential and its derivative remain continuous and monotonic in the region where the reduction of the three-body part is performed.

Silicon carbide is a promising material for applications in special electronic devices. Ion implantation is considered to be the best means to introduce dopants into SiC in a controlled manner. However, ion irradiation produces defects which can prevent the electrical activation of the implanted dopants. The understanding of ion-beam induced defect formation and evolution in SiC is therefore very important. A peculiarity of SiC is the occurence of polytypism. It can be illustrated by different stacking sequences of layers formed by SiC4 (or CSi4) tetrahedra. Wafers available for technological applications are either 4H or 6H-SiC single crystals, i.e. polytypes with hexagonal symmetry. The present work deals with structure and energetics of elementary defects in 4H-SiC. Based on the lattice structure and symmetry, a classification of potential vacancies, antisite defects and interstitials is given. In comparison with the cubic polytype 3C-SiC which was already studied in detail a considerably higher number of nonequivalent defect sites is found. The stability, formation energy, and structural details of the potential defects is investigated by classical MD simulations using a recently developed interatomic potential of Brenner type. Most of the potential defects are found to be stable. Many of them show a similar structure and formation energy. In these cases the first and the second nearest neighbor atoms of the defect site are identical.

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Der Beitrag stellt Ergebnisse zum Wasserstoffdiffusionsverhalten, zur Wasserstofflöslichkeit und zum Einfluss des Wasserstoffs auf die mechanischen Eigenschaften von unterschiedlichen unbestrahlten Druckbehälterstählen vor. Sie beziehen sich auf solche Bedingungen, die denen im DWR nahe kommen. Die Wasserstoffdiffusion und -löslichkeit wurde durch Permeationsexperimente und Beladungsversuche ermittelt. Zur Charakterisierung des Einflusses von Wasserstoff auf Festigkeit und Zähigkeit wurden Zugversuche mit Dehnraten von 10-6...10-4/s im Temperaturbereich von 25-250°C nach elektrolytischer Wasserstoffvorbeladung und bei gleichzeitiger Wasserstoffbeladung mit kathodischen Stromdichten von -0.5 bis -5 mA/cm2 im simulierten Reaktordruckwasser durchgeführt. Mit Wasserstoff vorbeladene Charpy-Proben wurden im instrumentierten Kerbschlagbiegeversuch bei Prüftemperaturen bis 323 K geprüft.

Titanium atoms were alloyed into a polycrystalline alindum substrate using various number of intense pulses consisting of plasma of the working gas and vapor and low energy ions of Ti erode from elecctrodes of the rod plasma injector type generator. Analyses of phase composition and of structural properties, as well as computer simulations of thermal evolution brought to the conclusion that increase of number of pulses leads to decrease of melting temperature of the top layer of the substrate. The erosion of the electrode material occurs during the last phase of the discharge via the vacuum arc mechanism.

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The knowledge of the flow in metallic and semiconducting melts is important for a number of industrial problems. Optical methods cannot be applied due to the opaqueness of those fluids. Ultrasonic methods have problems with wetting and thermal stability when applied in hot metallic melts. Evidently, contactless methods for velocity determination would be highly desirable. In some applications even a coarse knowledge of the flow topology and the direction of the main eddies would be of high value. We study the possibility of velocity reconstruction in electrically conducting fluids from external measurements of different induced magnetic fields. It is shown that for a reliable velocity reconstruction the effect of the electric potential at the fluid boundary on the induced magnetic field should be taken into account.

In the aqueous environment of abandoned ore mines, iron sulfide ore crystals em-bedded in clay play a key role in the sulfide oxidation process and water mineraliza-tion process occurring there. Highly mineralized, red-coloured solutions are formed by weathering of ore particles which causes acid rock drainage (ARD) that can be extremely acidic. The access of ARD solutions to the bulk waters of a mine is a major factor influencing the composition of mining effluents. Very little is known about the speciation of heavy and toxic metals and about the mineralogy of the colloidal parti-cles of such ARD solutions. In particular the colloid-chemistry of such waters is little understood. However, colloids can significantly influence the properties of ARD solu-tions.
Acid rock drainage (ARD) solution from an abandoned ore mine (pH 2.7, sulfate con-centration 411 mMol/L, Fe concentration 93.5 mMol/L) was investigated by photon correlation spectroscopy, centrifugation, filtration, ultrafiltration, scanning electron microscopy, ICP-MS, AAS, ion chromatography, TOC analysis, and X-ray absorption (XAS/EXAFS) spectroscopy. A colloid concentration of m 1 g/L was found. The pre-vailing particle size was < 5 nm. Fe, As and Pb were the metal constituents of the colloidal particles. According to EXAFS spectroscopy, the most probable mineralogi-cal composition of these particles is a mixture of hydronium jarosite (HFe3(SO4)2(OH)6) and schwertmannite (ideally Fe8O8(OH)6SO4). A small amount of a relatively coarse precipitate was formed in the ARD solution during the months af-ter sampling. The colloid particles are obviously an intermediate in the precipitate formation process. Our results suggest that the arsenate is bound to the colloid parti-cles by the formation of a bidentate binuclear inner-sphere surface complex. How-ever, the transformation of the colloidal material to the more aggregated long-term precipitate results in the incorporation of the arsenate into the interior of the iron hy-droxy sulfate crystal structures. Pb seems to occur as anglesite (PbSO4).

The paper describes a novel silicon detector with improved linearity characteristics for energetic electrons up to 50 keV. The modified pn-junction detector structure contains a buried implanted n(+)-layer (N~1-5E15 cm-3) in the n-type Si substrate which is attributed by a near-surface high-field region in the depletion zone. To enable a high-field region of several micrometers depth high-energy ion implantation with 31P ions of 10-30 MeV has been used. The corresponding electric field distribution of the novel detector is characterized by a constant electric field strength of 10-50 kV/cm from the surface down to the depth of the buried implanted layer. Detectors with considerable improved linearity up to electron current densities of 20 A/cm2 have been fabricated, which have been tested at the e-beam writer SB 350 of Leica Microsystems Lithography for electrons of 50 keV.

Coating with titanium oxides is a promising method to improve the blood compatibility of materials to be used for medical implants. Ti oxide layers were deposited on oxidised Si from a plasma produced by cathodic arc evaporation under addition of oxygen to the ambient near the substrate. In dependence on the deposition parameters amorphous and nanocrystalline structures, crystalline layers composed of anatase and brookite as well as layers dominated by the rutile phase have been obtained. The activation of the plasmatic clotting cascade was only minimally influenced by the crystal size and the crystallite structure of the titanium oxide films. As a trend, amorphous, nanocrystalline and fine-grained layers show higher clotting times than well crystallized rutile films. Ion implantation of Cr or P strongly the clotting time.
Contrasting tendencies in the dependence of clotting time and platelet adhesion on the microstructure of the Ti oxide have been stated, however for P+-doped rutile both, enhanced clotting time and improved platelet adhesion, are observed. Platelet adherence and activation always show similar trends.

Die folgenden 5 Beiträge dokumentieren die Ergebnisse der Sektionen "Thermo- und Fluiddynamik" (Sektion 2), "Brennelemente und Kernbauteile" (Sektion 5), "Forschungsreaktoren" (Sektion 9), "Fortschrittliche Reaktorkonzepte, Energiesysteme - Energiewirtschaft" (Sektion 10) und "Werkstoffe, Herstellung und Betriebsverhalten" (Sektion 12).