Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Thermal wave measurements on 6H-SiC with a particular emphasis on Al+ and Al+/N+ implanted 6H-SiC was carried out. The 6H-SiC wafers were implanted at different substrate temperatures.

Thermoelectromagnetic convection (TEMC) in a generic configuration is studied experimentally. The experimental results demonstrate that even a moderate temperature gradient can produce distinct convection. When the magnet was positioned close to an isothermal wall with its direction of magnetization parallel to , a relatively stable vortex developed throughout the whole container. Moving the magnet to the center led to a modified distribution of the magnetic field, while, in turn, altered the flow topology into four-vortex structure. Numerical results support the experimental findings.

This final report presents the work done for the numerical prediction of the plunging jet configuration including the air entrainment below the surface by the jet. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. Various drag models are tested and their influence on the gas void fraction below the water level is discussed. For the quantification of the gas entrainment and for the description of the plume geometry diverse measures are developed. The results of simulations are compared with experimental correlations and are discussed with respect to physical plausibility, e.g. in terms of mass conservation, bubble entrainment and the penetration depth of the gas plume below the water level.
If the gas is treated as dispersed phase everywhere in the domain and the grace drag law is applied, the gas entrainment is overestimated substantially. The algebraic interface area density (AIAD) model applies a drag coefficient for bubbles and a drag coefficient for the free surface. If the AIAD model is used for the simulation of impinging jets, the gas entrainment depends on the free surface drag coefficient. The gas entrainment can be controlled (tuned) via this parameter. So the AIAD approach can be used in future for the implementation of models (e.g. correlations) for the gas entrainment, since the physical details of the bubble generation generally can not be resolved in Euler-Euler simulations of large multiphase configurations.

In this work, the use of electrical impedance techniques for multiphase flow measurement has been investigated. Three different impedance sensor systems to quantify and monitor multiphase flows have been developed, implemented and metrologically evaluated. The first one is a complex permittivity needle probe which can detect the phases of a multiphase flow at its probe tip by simultaneous measurement of the electrical conductivity and permittivity at up to 20 kHz repetition rate. Two-dimensional images of the phase distribution in pipe cross section can be obtained by the newly developed capacitance wire-mesh sensor. The sensor is able to discriminate fluids with different relative permittivity (dielectric constant) values in a multiphase flow and achieves frame frequencies of up to 10,000 frames per second. The third sensor introduced in this thesis is a planar array sensor which can be employed to visualize fluid distributions along the surface of objects and near-wall flows. The planar sensor can be mounted onto the wall of pipes or vessels and thus has a minimal influence on the flow. It can be operated by a conductivity-based as well as permittivity-based electronics at imaging speeds of up to 10,000 frames/s. All three sensor modalities have been employed in different flow applications which are discussed in this thesis. The main contribution of this research work to the field of multiphase flow measurement technology is therefore the development, characterization and application of new sensors based on electrical impedance measurement. All sensors present high-speed capability and two of them allow for imaging phase fraction distributions. The sensors are furthermore very robust and can thus easily be employed in a number of multiphase flow applications in research and industry.

Ge-ion implantation in SiC is of interest for fundamental damage studies and hetero-junction device applications. For instance, a thin Ge-implanted layer has already been used as base for hetero-structure bipolar transistors [5]. Germanium is also a widely used solvent in VLS (Vapor-Liquid-Solid) growth technology and shedding more light on the incorporation of Ge in the SiC lattice is of interest [6]. Recently, high dose / high temperature ion-implantations have been done in 4H-SiC samples which, when investigated by RBS (Rutherford Backscattering Spectroscopy) techniques, suggested that up to 50% of the initial dose could be lost for targeted concentrations in the range of 10 to 20%. In this work we present a comparative investigation of the Ge concentration distributions carried out by SIMS and RBS and highlight the effects affecting the depth distribution and measurement results.

The HADES experiment, installed at GSI, Darmstadt, measures di-electron production in A+A, p/pi+N and p/pi+A collisions. Here, the pi0 and eta Dalitz decays have been reconstructed in the exclusive p+p reaction at 2.2 GeV to form a reference cocktail for long-lived di-electron sources. In the C+C reaction at 1 and 2 GeV/u, these long-lived sources have been subtracted from the measured inclusive e+e- yield to exhibit the signal from the early phase of the collision. The results suggest that resonances play an important role in dense nuclear matter.

High quality 3C-SiC nanocrystallites were epitaxially formed on a single crystalline Si surface covered by a 150 nm thick SiO2 capping layer after low dose carbon implantation and subsequent high temperature annealing in CO atmosphere. Carbon implantation is used to introduce nucleation sites by forming silicon-carbon clusters at the SiO2/Si interface facilitating the growth of 3C-SiC nanocrystallites.

Strong decrease in the carrier mobility of the nanometer-thick silicon films imposes a limitation on the application of silicon-on-insulator (SOI) structures in the current silicon planar CMOS technology. The formation of SiGe-heterostructures-on-insulator (SGOI) is a way to increase the hole mobility in the nanometer-scale layers. In this work, we present the results on the interface mediated endotaxial growth of nanometer-thick Ge film from the Ge+-ion implanted SiO2 layer of the SOI structure

This progress report presents the work done for the numerical prediction of the plunging jet configuration. A study case is simulated with both the NURESIM_CFD_1.0.5 code and with CFX-11 and the results for the gas entrainment near the jet are compared. In the frame of an Euler-Euler simulation, the local morphology of the phases has to be considered in the drag model. For example the air is a continuous phase above the water level but bubbly below the water level. In this study the SIMMER model is applied for the drag. This model assumes bubbly flow where the gas void fraction is low and droplets in air, where the gas void fraction is high. The influence of the drag model and particle diameters for droplets and bubbles on the gas entrainment is studied.
For the drag, the Grace law (constant drag coefficient) and the Schiller Naumann law are tested. The particle diameter also has an influence on the drag. A variation of the drag force does not have an obvious effect on the gas entrainment in the simulations performed with the SIMMER model. The gas entrainment is overestimated in all simulations and there is no free parameter inside the SIMMER model which allows an adjustment of the entrainment in the simulation.

The formation of heterostructures-on-insulator is a way to increase the carrier mobility in the nanometer-scale layers. The electron mobility in InSb is about 50 times higher than that in bulk silicon. The formation of Si/InSb on insulator heterostructures may provide an increase of effective electron mobility in the nanometer scale SOI films. In this work, we present the results on the interface mediated endotaxial growth of InSb nanocrystalline phase at the Si/SiO2 bonding interface of silicon-on-insulator (SOI) structure.

The annealing of semiconductor surfaces via pulsed laser melting has been practised since the 70 ' s. During the process a thin surface layer is molten up to a depth of mkm and recrystallises, after the pulse is over, epitaxially on the non molten substrat.
Depending on the segregation coefficient of additionally admixed atoms completely different doping profiles can be achieved. Typical for all pulse irradiation techniques is, that the melting process starts near the surface. The aim of the present work is to overcome this phenomen and to force a buried melting by large area flash lamp irradiation using an additional Ge admixture. The addition of Germanium locally leads to a reduction of the silicon melting temperature so that separated melting in the bulk of silicon can be observed. During cooling down of the sample the buried liquid layer recrystallises epitaxially on the non molten bulk material and for the case of additional doping of the layer special profiles can be observed. Ion implantation at high doses and high energies was used to produce structures with a buried germanium enriched layer. The pulse irradiation was performed at the Rossendorf flash lamp apparatus using intense light pulses with a duration of 20 ms from a field of Xe flash tubes. The energy density at the sample surface was varied within wide limits. For the determination of the Ge profiles after the flash lamp irradiation the RBS technique was used. The microstructure of the recrystallised films was observed by cross sectional TEM. It could be shown that buried melting takes place whereby the width of the molten zone depends on the energy density. Deep facetted melting, typical for virgin silicon material, was not observed.

Ultra-intense lasers are expected to produce, in near future, relativistic electron-positron plasma droplets. Considering the local photon production rate in complete leading order in quantum electrodynamics (QED), we point out that these droplets are interesting sources of gamma ray flashes.

Samples of a precursor for an alumina ceramic reinforced by zirconium dioxide were synthesized. The samples have a uniform structure and are characterized by high ratios of the tetragonal and monoclinic modifications of ZrO2, tlm, after a thermal treatment (1250 degrees C). The structure of samples in the system Al2O3-ZrO2 is formed under conditions favorable for deposition of products of hydrolysis of Al(III) ions on the surface of ZrO2 sol particles in decomposition of urea. The coating of ZrO2 sol particles by products of hydrolysis of Al(III) salts was confirmed by electrophoresis. The size distribution of particles of the in?dividual ZrO2 sol was determined by small-angle X-ray scattering. The structure of the products formed in thermal treatment of samples of mixed oxides Al2O3-ZrO2 was characterized by X-ray phase analysis and scanning electron microscopy. The porosity and specific surface area of a thermally treated sample was determined by measuring nitrogen absorpt!

We present a novel design of flowmeter using a single cylindrical permanent magnet magnetized perpendicularly to its axis about which it can freely rotate, and placed close the duct with liquid metal flow. The electromagetic torque on the magnet caused by the liquid metal flow sets the magnet into rotation. However, the equilibrium rotation rate, which attained at vanishing net electromagnetic torque on the magnet, depends only on the flowrate and geometry of the system while it is independent of the electromagnetic torque itself. A laboratory model of a such flowmeter has been built and tested at a liquid metal flow.

A liquid gallium cylinder is subject to a stable vertical thermal stratification (hot top and cold bottom) and an upward traveling magnetic field (TMF). The instability, which arises due to the combined action of magnetic field and temperature gradient, is investigated experimentally.

This paper describes our investigations into the generation of the electro-vortex flow of a conducting fluid in a plane long layer in the unstable regime. In the context of the present problem we consider the velocity field and the amplitude and frequency of velocity oscillations of this flow. The pressure drop in the channel with inclined ferromagnetic plates induced by both the direct and alternating electrical currents is studied. The obtained results can be used in developing metallurgical devices having the maximum possible stability of the flow-rate.

We analyze numerically the magnetorotational instability (MRI) of a hydrodynamically stable Taylor-Couette flow with a helical external magnetic field in the inductionless approximation defined by a zero magnetic Prandtl number. The Chebyshev collocation method is used to calculate the eigenvalue spectrum for small amplitude perturbations. Besides the convective instability threshold also an absolute one is found implying that this type of MRI might be experimentally observable in a system of sufficiently large but finite axial extension.

The Vertical Gradient Freeze (VGF) method is an important technology for the melt growth of bulk compound semiconductors. The structural perfection of the crystals and the distribution of dopants in the material are closely connected to the conditions of heat and mass transport in the liquid phase. The application of external magnetic fields allows for tailoring the melt flow and, hence, gives the possibility to optimize the quality of the crystals and the yield of the growth process.
In this paper experimental and numerical results are presented, showing the influence of a combined traveling magnetic field (TMF) and steady axial magnetic field (DC) on the VGF growth of semiconducting GaAs and Ge single crystals. The quality of the crystals is characterized in terms of the interface deflection, axial/radial macrosegregation and microsegregation. The numerical simulations of the VGF growth are performed using the commercial code CrysMAS. The TMF melt flow and its influence on the interface deflection as well as the resulting local v. Mises stress are calculated on the basis of a global thermal model of the equipment.

We present a numerical analysis of the free surface liquid metal flow and its three-dimensional linear stability. The flow is driven by an alternating magnetic field in a spinning cylindrical container. The electromagnetic and hydrodynamic fields are fully coupled via the shape of the liquid free surface.

We model numerically the growth of small–diameter single crystals of intermetallic compounds by the floating zone technique using two-phase radio-frequency (RF) electromagnetic heating. An axisymmetric quasi-stationary numerical model is implemented as several coupled computer programs for modeling electromagnetic fields, heat source and force density distributions, heat transfer, and turbulent melt flow. The results of model calculations are presented for the growth of Ni crystals of 2 mm in diameter. It is found that the stable molten zone exists in a very narrow range of inductor currents.

The lesson 4 of the "Short Course on Multiphase Flow Modelling" deals with the simulation of mass and energy exchange between the phases based on the two fluid model approach. After the basic principles the lesson describes the simulation of subcooled boiling and the simulation of cavitation processes.

The lesson 6 of the "Short Course on Multiphase Flow Modelling" describes the practical simulation of the flow in a bubble column. The necessiy of the correct simulation of the momentum exchange between the phases is shown comparing different results with experiments.

A finite-time thermodynamics formalism is proposed to compute mean flow and fluctuation levels of unsteady incompressible flows. The formalism builds upon a Galerkin model framework (see Noack et al., J. Noneqilib. Thermodyn. 33 (2008) 103-148) and is applied to a periodic vortex shedding regime behind a circular cylinder, homogeneous shear turbulence and the Burgers equation.

In thin magnetic films different intrinsic length scales affect the magnetic properties, e.g., the exchange correlation length determined by the exchange constant and the anisotropy of the material or the grain size of polycrystalline materials determined mainly by the growth conditions and substrates used. In the latter case also the intergranular coupling influences the magnetic properties.

Introducing an artificial extrinsic length scale in the range 10 – 100 nm allows an additional degree of freedom to tailor the overall magnetic properties of the material of choice. This length scale is established by means of low energy ion erosion of semiconductor surfaces which lead to a periodically modulated surface (ripple structure). The periodicity and amplitude can easily be varied by means of the ion erosion parameters [1]. Hence upon thin film deposition modulated surfaces and interfaces of the magnetic films result.

Two different examples will be discussed. i) Induced magnetic anisotropies in soft magnetic films deposited on rippled substrates [2]. The microscopic origin can be extrinsic, due to dipolar stray fields, as well as intrinsic, due to spin-orbit coupling phenomena at monoatomic steps. The relative contribution of both microscopic effects to the macroscopically measurable material properties depend sensitively on the introduced ripple wavelength and amplitude. ii) Magnetic properties of hard magnetic CoCrPt-SiO2 perpendicular recording media [3]. Due to a combination of deposition on a modulated surface and post-deposition ion irradiation a predefined number of grains can be exchange coupled to act as one magnetic entity required for bit patterned media. The physical mechanisms will be discussed.

Support of the Deutsche Forschungsgemeinschaft is gratefully acknowledged.

[1] S. Facsko, H. Kurz, T. Dekorsy, Energy dependence of quantum dot formation by ion sputtering, Phys. Rev. B 63, 165329 (2001).
[2] M. O. Liedke, B. Liedke, A. Keller, B. Hillebrands, A. Mücklich, S. Facsko, J. Fassbender, Induced anisotropies in exchange-coupled systems on rippled substrates, Phys. Rev. B 75, 220407(R) (2007).
[3] T. Strache, S. Tibus, F. Springer, H. Rohrmann, M. Albrecht, J. Fassbender, Tuning coercivity in CoCrPt-SiO2 hard disk material, OR15-4, International Conference on Ion Beam Modification of Materials, IBMM08, 31.08.-05.09.2008, Dresden, Germany

We present results of a simulation study on the role of different design parameters for the count rate accuracy of a high resolution gamma ray detector used for transmission tomography. The considered gamma ray tomography system is operated with a Cs-137 isotopic source and a special detector composing 320 single elements, made of LYSO scintillators coupled to APD. Typically, energy resolution of the detector elements (geometry 2mm x 2mm x 24mm) is limited to about 25% which leads to erroneous counting of photons which have been Compton scattered before detection in other parts of the detector and the object. This introduces a linearity error into the tomographic data which leads to artefacts and errors in the reconstructed images. We therefore performed a theoretical analysis with the GATE simulation software. Simulation of the count rate error for the existing configuration shows good agreement with measured detector cross-talk. In the following we assessed different virtual design changes regarding crystal geometry, separation, shielding and arrangement. Results show that further increase in accuracy is possible.

Electron beam X-ray CT is a new technique for a fast measurement of multiphase flows with frame rates of 1000 images per second and more. It gives, in principle, quantitatively accurate images of the flow at high spatial resolution and it is non-intrusive since moderately radiation absorbing vessel walls can be penetrated by X-rays. However, on the road to a technical realisation of such a technique within a computed tomography system many problems have to be solved. As a first prototype for scientific flow measurement studies we devised and built a fast scanned electron beam X-ray tomography scanner. The scanner consists of an electron beam unit that can be operated at up to 150 kV acceleration voltage and up to 65 mA electron beam current, with the required electron optics for beam adjustment, beam focussing and beam deflection unit and a fast circular CZT detector comprising 240 elements of 1.5 mm x 1.5 mm x 1.5 mm active pixel
area. X-ray radiation is produced on a circular water cooled tungsten target The CT system achieves up to 7000 frames per second with a spatial resolution of 1 millimetre. First two-phase flow experiments have been carried out on gas-water flows in bubble columns. On the basis of these data we developed image processing algorithms which enable to extract information on bubble shapes, bubble size distributions and interfacial area density distribution. Further, a vertical test section made of titanium alloy has been installed at the TOPFLOW facility and will be used in the future to study the evolution of two-phase gas-water pipe flow at high pressures and temperatures.

The two-photon quantum well infrared photodetector (QWIP) comprises three equidistant subbands, two of which are bound in the quantum well, and the third state in the continuum. This results in a resonantly enhanced optical nonlinearity, which is by six orders of magnitude stronger than in usual semiconductors. In addition, temporal resolution is only limited by the sub-ps intrinsic time constants of the quantum wells, namely the intersubband relaxation time and the dephasing time of the intersubband polarization. Both properties make this device very promising for quadratic autocorrelation measurements of pulsed mid-infrared sources, including modelocked quantum cascade lasers, radiation obtained by nonlinear optical frequency conversion, and free-electron lasers (FEL).
We have performed autocorrelation measurements of ps optical pulses from the free-electron laser (FEL) facility FELBE at the Forschungszentrum Rossendorf. Using a rapid-scan autocorrelation scheme at a scan frequency of 20 Hz, high-quality quadratic autocorrelation traces are obtained, yielding ratios close to the theoretically expected value of 8:1 between zero delay and large delay for interferometric autocorrelation, and 3:1 for intensity autocorrelation. Thus, two-photon QWIPs provide an excellent new approach to online pulse monitoring of the FEL. In addition, we have investigated the saturation mechanism of the photocurrent signal, which is due to internal space charges generated in the detector. We will also report on room temperature operation of two-photon QWIPs.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

Es handelt sich um einen vertraulichen Bericht, kein Abstract.

Due to the special characteristics of ion beams and delicate treatment situations, i.e. in close vicinity to organs at risk, a three-dimensional, in-vivo and in-situ monitoring of the dose delivery is highly desirable. At present, in-beam PET is the only method meeting these requirements. An in-beam PET system has been implemented for clinical application at the carbon ion therapy facility of the Gesellschaft für Schwerionenforschung (GSI) Darmstadt. So far, more than 400 patients have been monitored with this system. It could be demonstrated that this PET technique is capable of assessing relevant parameters for quality assurance of carbon ion therapy, measuring the particle range in tissue, the position of the irradiated volume with respect to anatomical landmarks, and estimating local deviations between the planned and applied dose. In-beam PET has become a tool providing valuable clinical feedback.
The implementation of the in-beam PET system at the medical beamline at GSI will be described. Clinical results will be shown with examples. Furthermore, the application of in-beam PET for protons, 3-He, 7-Li and 16-O shows promising results and will be presented.

We present experimental evidence for structural trransformation of multiply twinned CuAu nanoparticles to single crystalline morphology by 0.5 keV helium irradiation. This finding is unexpected as the stability of twin boundaries should not be affected by ion-beam induced Frenkel pairs. Molecular dynamics simulations reveal, however, a new transformation mechanism based on transient amorphization of the particle. By comparing with irradiation simulations of elemental nanoparticles, as well as alloyed bulk samples and surface cascades, we show that this transformation route is only present in alloyed particles. Moreover, the observed amorphization is more efficient for twinned than single-crystalline particles. This, together with the fast recrystallization kinetics in CuAu, explains the experimentally observed untwinning process.

It is demonstrated that both the nucleation field and the irreversible switching field of Sm2Co7/Fe exchange spring bilayers is decreased by means of 10 keV He ion irradiation. The reduction is attributed to interfacial mixing and irradiation induced softening of the hard magnetic layer. By lowering the energy to 0.8 keV the ions do not penetrate the hard magnetic layer and consequently no softening is observed. However, although irradiation induced interfacial mixing is still present it is not large enough to create a graded interface layer and the nucleation field decreases. In contrast conventional annealing under appropriate conditions leads to an increase of the nucleation field. This distinct discrepancy can be explained by detailed investigation of the layer structure by x-ray reflectivity measurements.

The wire-mesh sensor is an imaging instrument which is able to generate cross-sectional phase distribution images with high spatial and temporal resolutions, thus being very well suitable for the investigation of multiphase flows. It has successfully been used in several research and industrial applications. In this article, we present the results of the precise simulation analysis of the spatial sensitivity of this device, which support further developments of the image data processing.

no abstract available

no abstract available

Thioarsenic complexes play an important role in regulating arsenic solubility, mobility, and toxicity in sulfidic systems. Despite their importance, there is little consensus on their thermodynamic properties and structural identification. A major focus of current research is the unambiguous identification of the members of the two homologue series of monomeric thioarsenic species that are conceptually postulated to exist under sulfidic conditions, (oxy)thioarsenites and (oxy)thioarsenates. Here we report the unambiguous identification of synthetic mono-, di, and tetrathioarsenate using a combination of X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). As-O and As-S coordination numbers confirmed the structure as the expected mono-, di- and tetrathioarsenate compounds. The As-O bond distances of 1.69 to 1.70 $\AA$ are comparable with those stated for arsenates, and are easily distinguishable from those for arsenites at 1.78 $\AA$. The As-S distances in our standard materials with 2.17 $\AA$ are clearly shorter than those published for arsenite-sulfide minerals with 2.24 to 2.34 $\AA$. As expected, no As-O bonding was determined in tetrahedral tetrathioarsenate, which is fully coordinated to S. As the extent of thiol complexation increases, the position of the absorption-edge shifts systematically and linearly towards lower energies compared to that of arsenate. The structural data for the individual solid and liquid samples, measured at room temperature or at 15 K, did not show obvious differences, suggesting that the aqueous complexes have similar structures as the XRD-identified solids and are stable in natural waters. An interesting observation was made during the titration of the liquid tetrathioarsenate from pH 6 to 3. Below neutral pH, the absorption edge shifted to lower energies by $\sim$2 eV concomitant with an increase of the As-S bond length to 2.28 $\AA$ at pH 3, comparable with those of orpiment and indicative of either thioarsenites (which have been reported to exist in arsenite-sulfide-containing solutions) or colloidal orpiment. As for thioarsenates, the observed complexes also show a linear trend together with arsenite and orpiment, clearly distinguishable from the arsenate-based line. The present data demonstrate that it is possible to differentiate thioarsenates from thioarsenites by XAS. Combined with other recent studies, these data indicate that thioarsenates can be formed in sulfidic solutions under a broad range of conditions.

Under certain conditions ion beam bombardment on semiconductor surfaces leads to well-defined morphological structures in the nanoscale range caused by a self-organization process. Due to the ion impact as a start the surface-adjacent layer is amorphized before a periodical wave-like rippled structure on the surface as well as at the amorphous-crystalline interface is developed. So far we found that the ripple wavelength linearly scales with the ion energy in a range of 5 to 70 keV (50 to 300 nm). Furthermore, we try to evaluate the ripple patterns from the point of homogeneity and uniformity. Therefore, we defined a quality factor for the amplitude and a correlation length for the wavelength to characterize the structures over a larger scale. We used a routine to extract the ripple amplitude from the Atomic Force Microscopy (AFM) images. In order to determine the correlation length we prosecuted Grazing Incidence Small Angle X-Ray Scattering (GISAXS) measurements.
Also, we asked for the mechanisms behind the formation of ripples. The investigation of the amorphous-crystalline interface gives a first hint. The subsurface structure has been identified by both Transmission Electron Microscopy (TEM) and Rutherford backscattering (RBS). Applying two different ion types for the formation of rippled patterns we could identify clear differences in the structure of the amorphous layer.

We prepared conductive, polycrystalline or amorphous Cu1.05Cr0.89 Mg0.05O2 films on a-plane sapphire substrates by pulsed laser deposition under different O2 partial pressure and substrate temperature. Hall measurements were performed to study the majority carrier type in these films. Polycrystalline Cu1.05Cr0.89 Mg0.05O2 is n-type conducting at 290 K, while in amorphous Cu1.05Cr0.89 Mg0.05O2 the type of majority charge carriers changes from electrons to holes at around 270 K. Interestingly, the structure has little influence on the magnetic properties of the films. A clear antiferromagnetic to paramagnetic transition was observed in both polycrystalline and amorphous Cu1.05Cr0.89 Mg0.05O2 films at 25 K. Similar electrical properties to Cu1.05Cr0.89 Mg0.05O2 film were observed for Cu0.96Cr0.95 Mg0.05Mn0.04O2 in dependence on the structure, while only paramagnetic without antiferromagnetic ordering was observed down to 5 K. Large negative magnetoresistance of 27% at 20 K was observed at 6 T in amorphous Cu1.05Cr0.89 Mg0.05O2 film.

We used ab-initio methods in the LDA with pseudo potentials and a plane wave basis to simulate the growth of thin palladium films on the piezo electric oxide PMN (Pb(Mg/Nb)O3). It is known that the palladium ground state is similar to the ground state of ferromagnetic nickel. A magnetic switch of nano-scale dimension might be possible if the palladium ground-state can be forced to get also ferromagnetic. The piezo electric property of PMN oxides can be used to achieve this by an expansion of the lattice constant. First calculations on bulk-Pd with all-electron and pseudo-potential methods lead to different results with respect to the magnetic ground state, but it seems, that the projector augmented wave method PAW describes the magnetism correctly. In PAW calculations pure fcc-palladium films remain non-magnetic during expansion, but a doping with cobalt can help to induce a magnetic state.

It is well known that oblique low and medium energy (typically 0.1 – 100 keV) ion erosion of solid surfaces may lead to the formation of periodic ripple patterns with wavelengths ranging from 10 to 1000 nm. The ripples produced in this way are oriented either parallel or normal to the projection of the ion beam and their wavelength scales with ion energy. These structures have been found on a large variety of materials, such as semiconductors, metals, and insulating surfaces. The formation and early evolution of the ripple patterns can be qualitatively reproduced by a linear continuum equation derived by Bradley and Harper. At longer times, however, nonlinear terms have to be taken into account leading to nonlinear models based on the Kuramoto-Sivashinsky equation.
The evolution of Si(100) surfaces during oblique sub-keV ion sputtering has been studied in-situ and ex-situ by means of surface sensitive X-ray techniques, namely X-ray Reflectivity and Grazing Incidence Small Angle X-ray Scattering (GISAXS), and atomic force microscopy, respectively. The observed morphologies are dominated by nanoscale ripples at short lateral scales but exhibit kinetic roughening at larger distances. The roughening of the surface is found to depend strongly on the angle of incidence and even small changes of only 2° lead to very different roughening dynamics. The obtained experimental results will be compared to predictions of different nonlinear continuum models of ion erosion.

We present superparamagnetic clusters of highly disordered Zn-Co-O created by high fluence Co ion implantation into ZnO (0001) single crystals at low temperatures. This secondary phase cannot be detected by x-ray diffraction but by high-resolution transmission electron microscopy. In contrast to many other secondary phases it shows anomalous Hall effect and thus is a candidate for magneto-electronics applications.

The Rossendorf Beamline as a dedicated X-ray absorption spectroscopy station for actinide research is in operation since 1998. It has served for hundreds of experiments in the past 10 years, ranging from Materials Science to Aquatic and Environmental Chemistry of actinides and other radionuclides. A short overview on research highlights will be given, including the current extensive work on redox processes.
The beamline’s strength is built on the high reliability and flux of the ESRF, which allows to run samples even at very low concentrations of a few ppm, and on the long experience with actinide EXAFS. After 10 years of operation, the beamline is ready to take the next step in order to further lower the concentration limits of XAFS and to extend the array of methods to -XRF, -XAFS and XRD. Essential optical components will be replaced parallel to the upgrade of the ESRF to increase the photon flux by about one order of magnitude to 1012 photons/sec on the sample, and to prepare the microfocus. Additional modifications like easily exchangeable monochromator crystals, additional mirror coatings and a routine quick-XAFS mode will widen the experimental possibilities without sacrificing the user friendly operation of the beamline.
These changes are planned for 2010, and will be installed and commissioned with little loss of beamtime. This is especially important, since the Rossendorf Beamline will continue to provide its facilities to the actinide community within the ACTINET network, in addition to the routine beamtime application paths via ESRF and FZD collaborations.
An overview on the current status of operation modes, technical details, access conditions and user support with advanced data analysis methods is presented, by updating earlier information and summarizing the features most important for prospective users.

Ferritic-martensitic chromium steels are candidate materials for future applications in both Gen-IV and fusion technology. Investigations of related binary Fe-Cr alloys will significantly contribute to the understanding of the behaviour of more complex alloys. The presented SANS results are focused on a Fe-9at.% Cr alloy neutron-irradiated up to a dose of 1.5 displacements per atom (dpa).
We have observed a pronounced increase of scattering intensities for two different irradiation conditions at scattering vectors Q > 0.2 nm-1 for both magnetic (figure (a)) and nuclear scattering. The reason for the increased intensities are irradiation-induced clusters with size distributions presented in figure (b). The A-ratio is about 2.8 for both irradiation conditions. This value is far from a value of 1.45 corresponding to nanovoids as scattering objects. This indicates that the irradiation-induced clusters are different from pure nanovoids and must contain Cr-atoms with the same or very similar average composition for both irradiation conditions. These clusters are interpreted as alpha’-phase. The volume fraction of clusters of this type increases slightly with neutron dose.

Clay minerals play an important role in the retention/retardation of radio-contaminants in the near- and far-fields of a radioactive waste repository. Identifying and quantifying the radionuclide sorption processes occurring at clay/solution interface over a representative range of relevant conditions is indispensable for performance assessment.
Next to hydroxide ions, carbonate is the predominant inorganic ligand in most natural groundwaters and clay porewaters. Actinides are known to form very strong carbonate complexes in solution, which could potentially decrease the metal ion sorption and thus increase the migration rates of actinides. The aim of this study is:
To apply Extended X-Ray Absorbtion Spectroscopy to verify whether or not U(VI)-carbonato ternary complexes form at the montmorillonite surface

The macroscopic sorption data show a significant influence of dissolved carbonate on the sorption of U(VI)) on Na-montmorillonite.
Structural data obtained by EXAFS show unambiguously that U(VI) forms inner-sphere complexes at the montmorillonite surface (splitting of the Oeq shell, Si and Fe shell).
No difference is observed in the absence and the presence of carbonate (no C shell ~ 2.90 Å [1], no Odist shell), indicating that no U(VI)-carbonato ternary complexes
form at the montmorillonite surface.

Formation of minerals at the Earth’s surface can often be directly or indirectly assigned to the activity of microorganisms. Regarding a direct effect, several examples of microbially controlled, extracellular precipitation of minerals have been reported, which typically involve the enrichment of metal ions at the bacterial surface. However, sorption of metal ions to microbial cell walls might also inhibit mineral formation. Here, we present two examples in which interactions between metal ions and bacterial cell walls interfere with the formation of mineral although a promoting effect could be anticipated: the formation of UO2 as a consequence of microbial U reduction and the formation of Mn oxides in the presence of a Mn oxidizing organism. Microbial reduction of U(VI) to U(IV) is expected to result in the precipitation of solid UO2 at neutral pH.
However, EXAFS analyses of samples from incubation experiments with the organism Shewanella putrefaciens revealed that enzymatic reduction of U(VI) did not instantaneously lead to the formation of an UO2 precipitate but that U(IV) was monomerically associated with the bacterial cells. Indications were obtained that U(IV) in this form is very susceptible for reoxidation.
The kinetics of Mn(II) oxidation with and without the organism Pseudomonas putida were studied at pH 7.5 and 8.5.
The rates of Mn2+(aq) consumption in the presence of bacteria were similar at both pH values although the rates of abiotic Mn oxidation, determined in the absence of bacteria, were higher at pH 8.5. XANES analyses showed that the removal of Mn(II) from solution by the bacteria at pH 8.5 was, in contrast to pH 7.5, not caused by Mn oxidation. Consequently, not only enzymatic Mn(II) oxidation but also the abiotic oxidation were inhibited at pH 8.5 in the presence of bacteria. Possible mechanisms for the removal of dissolved Mn(II) by the bacteria and the inhibition of the abiotic oxidation at pH 8.5 will be discussed.

Both Se and Sb exist in nature in a wide range of oxidation states and can be potential hazardous contaminants depending on their speciation and reactivity. While Se typically occurs as oxyanions (SeO3-2 and SeO4-2) in oxic conditions, it can be reduced by FeII containing minerals such as mackinawite (FeS) to Se0 and Se–II [1, 2]. Similarly, Sb occurs in several oxidations states (-III, 0, III, V) and is shown to strongly adsorb to Fe oxide minerals as Sb(OH)6 - and subsequently reduced to the more mobile form Sb(OH)3(aq) [3]. In this study we employed cryogenic-XPS and XAS techniques in order to understand the redox processes involving SeIV and SbV at the surface of mackinawite.
Fe 2p XPS spectrum of pure mackinawite surface revealed presence of both FeII-S and FeIII-S species and the proportion of the latter increased when reacted to SeIV suggesting oxidation of surface FeII. In addition, presence of elemental S at the surface of the reacted sample suggested oxidation of sulfur as well. Corresponding Se K-edge XANES spectra of the reacted sample confirmed reduction of Se with the formation of FeSe. These results suggest that Se reduction is coupled to both S-II/S0 and FeII/FeIII redox half reactions.
Sb 3d spectrum of the reacted sample revealed that SbV was completely reduced to SbIII at the surface of mackinawite.
However, the S 2p spectrum of the reacted sample remained largely unchanged except for a slight increase in surface monosulfide content. This suggests that in contrast to the SeIVmackinawite system, S did not take part in the redox reaction involving SbV. The Fe 2p spectrum, however, showed a distinct shoulder of FeIII-species indicating oxidation of surface FeII. Corresponding Sb K-edge EXAFS of the reacted sample confirmed that the SbIII was coordinated to three sulfur atoms at a distance of 2.5 Å as in Sb2S3, which most likely explains the slight increase in the surface monosulfide content in the S 2p spectrum.
These results demonstrate the importance of surface mediated redox reactions in controlling the fate of toxic
contaminats such as Se and Sb in soil and groundwater.
[1] Charlet et al. (2007) GCA 71, 5731-5749. [2] Scheinost & Charlet (2008) ES&T, online. [3] Scheinost et al. (2006) GCA 70, 3299-3312.

Cement in the Swiss radioactive waste management program is used as a waste matrix for the long-lived intermediate-level waste (ILW) disposal, where Uranium is an important radionuclide. Calcium Silicate Hydrates (C-S-H) are one of the major components of Hardened Cement Paste (HCP). In such a context, the understanding of Uranium uptake processes occurring in cementitious materials is necessary.

U(VI) uptake by C-S-H (CaO/SiO2 = 1.07) in Artificial Cement pore-Water (ACW) and HCP has been investigated using X-Ray Absorption Spectroscopy (XAS) technique in order to determine the chemical environment of sorbed and precipitated U(VI) species in cementitious matrices.

Phase X (CaUO4(H2O)x) and a uranophane (Ca(H3O)2 have been chosen as relevant reference compounds.

Similar coordination environment of U(VI) taken up by C-S-H and HCP
U(VI) sorbed species  a-uranophane-like structure
U(VI) precipitated species  phase-X-like structure
No split equatorial shell is observed
Complementary informations are expected using Time-Resolved Laser Fluorescence spectroscopy (TRLFS)

In order to understand the results of recent dynamo experiments, the behavior of kinematic dynamos in cylindrical geometries is analyzed. Simulations are performed applying a hybrid finite volume/boundary element method that allows a stringent treatment of insulating boundary conditions.

A suitable prescribed velocity field, either analytic or -- more realistic -- from measurement data from water experiments, leads to dynamo action, and a strong influence of boundary conditions and additional (stagnant) fluid layers around the active domain is observed.

An additional source term for dynamo action exists in case of a spatially varying conductivity distribution. A very simple set-up -- serving as a proof of concept -- is given by a steady axial flow in an infinite cylinder with inhomogenous container walls. Such a configuration is sufficient for dynamo action, however, the critical Reynolds number might be too large for the realisation in a simple laboratory-sized experiment.

Similiar effects appear in case of permeability inhomogenities, where increased gradients might also lead to a significant reduction of the critical Reynolds number.

Flow visualization and velocity measurements in a liquid metal flow were performed in order to study the combined action of a rotating and a travelling magnetic field. The combination of both fields, which is not necessarily a linear superposition, may give rise to an inherent three-dimensional constituent of the electromagnetic force distribution. As the Lorentz force may also become time-dependent, a quite intense mixing of metallic melts is achievable.

In the fine chemical and pharmaceutical industry, batch and semi-batch processes are mostly used to produce special chemicals in small amounts. The behaviour of such strongly exothermic processes in stirred tank reactors is characterised by instationarity, non-linearity and a large number of influences which may affect the process safety and efficiency as well. Especially in multi purpose plants, such complex processes are usually controlled by conventional process variables, such as temperatures, pressures, dosing rates etc., but without any knowledge of the crucial parameters of a chemical reaction, the concentration profiles of reactants, products and intermediates. Thus, even experienced operators have difficulties to distinguish allowable from undesired process deviations and to identify the cause of process trends.
Therefore, it is of vital importance to establish industrially applicable methods for an objective detection of the actual process state and for alerting the operators in case of undesired process deviations. To avoid the use of expensive and fragile on-line analytics, a real-time monitoring approach based on adaptive energy and mass balances was developed, and related monitoring systems were tested at pilot scale and industrial applications as well.
Especially, if such a real-time monitoring approach is used as an integral part of a batch information management system (BIMS), the additional data could contribute to the enhancement of the process knowledge as a basis for continuative process optimisation. The additional process information provided by real-time monitoring systems enables application of advanced control strategies up to the point of a safety-oriented fully automated control of complex exothermic batch and semi-batch processes.

The nearest-neighbor coordination and electronic structure in C:Ni(∼30 at.%) nanocomposite films grown by ion beam cosputtering in the temperature range of room temperatue (RT) to 500 °C are investigated by the means of extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge spectroscopy (XANES) and X-ray photoelectron spectroscopy (XPS). The obtained results are correlated with the composite nanostructure published elsewhere and magnetic properties determined by the means of X-ray magnetic circular dichroism (XMCD) and superconducting quantum interference device (SQUID) magnetometry. A combined use of EXAFS, XANES, and XPS shows that a carbidic Ni phase exhibiting only local atomic ordering is formed at low growth temperatures (e200 °C), while ordered carbidic Ni phase forms at ∼300 °C. Further increase in growth temperature results in the formation of face-centered cubic (fcc) Ni with a high degree of crystallinity. On the other hand, Ni incorporation strongly promotes the formation of carbon structures with the prominent peak in C K-edge XANES spectra positioned at 288.5 eV in the whole growth temperature range. The magnetic measurements show no magnetic response for the films grown at RT to 200 °C, superparamagnetic behavior for the film grown at 500 °C with >90% of the Ni atoms in metallic state, and a weak magnetic response for the film grown at 300 °C, indicating the presence of Ni-rich regions within carbon containing Ni nanoparticles with ∼3% of Ni atoms in metallic state.

According to the state of the art nuclear safety analyses related to thermohydraulics are mostly done using so-called system codes. Such one-dimensional codes base on empirical or semi-empirical correlations, which are generally geometry dependent and valid only within a limited range of scales. In principle the validation of such codes requires experimental data obtained for the same geometries, similar scales and flow conditions. In the past such codes were validated and successfully applied to many relevant flow situations. But the transferability to differing flow situations as well as the reliability for flows with pronounced 3D effects as they are observed e.g. in Reactor Pressure Vessel (RPV) is questionably. For this reason there is an interest to apply beside system codes also Computational Fluid Dynamics (CFD) codes for special analyses in future. Presently CFD codes are frequently used in practical applications for single phase flows, e.g. in automobile or aviation industries. Two-phase flow simulations using CFD codes are not yet mature due to the complex interactions between the phases. Closure models are needed to describe mass, momentum and energy transfer between the phases. Such models should consider only local flow parameters, i.e. correlations available for system codes cannot be transferred in general for the use in CFD codes. Such models have to be developed and validated basing on new experimental data with high resolution in space and time. Examples are poly-dispersed bubbly flows which require a multi bubble size modelling or models for separated flows in horizontal or near horizontal channels. TOPFLOW is a unique thermal hydraulic test facility for such two-phase flow studies. Experiments can be carried out for air-water or steam-water two phase flows at pressures up to 7 MPa. For steam production up to 4 MW heating power are available. The TOPFLOW facility is currently prepared for different types of flow experiments in vertical test sections and a large pressure chamber. Unique measurement devices, such as high-pressure wire-mesh sensors and an X-ray scanner are available. They provide CFD like data, which means data in high resolution in space and time. The lecture gives a general overview on the CFD model development and validation for two-phase flows, which is illustrated on the examples of poly-dispersed bubbly flows and Pressurized Thermal Shock (PTS). The experimental capabilities of the TOPFLOW facility and the applied measuring techniques are discussed.

Die Magneto-Rotationsinstabilität (MRI) ist verantwortlich für Turbulenz und Drehimpulstransport in kosmischen Akkretionsscheiben und ermöglicht damit das Wachstum von Sternen und Schwarzen Löchern. Im Vortrag wird das PROMISE-Experiment vorgestellt, mit dem die helikale Variante der MRI erstmalig nachgewiesen worden ist.

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1]. [1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004); [2] all materials prepared by D. Souptel at IFW Dresden; [3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999).

YMnFeO5 is a ferrimagnet below 165 K [1]. Its crystal structure is derived from that of the ferromagnetic and low-temperature ferroelectric YMn2O5 by occupation of the Mn position possessing pyramidal oxygen environment with Fe; the other Mn site is coordinated by oxygen in an octahedral manner. Powder samples for x = 0, 0.25, 0.5, 1 [2] were inspected by X-ray powder diffraction and EXAFS, single crystals (x = 0.07, 0.25) by single-crystal X-ray diffraction methods. The structure data show a significant displacement of Fe within the oxygen pyramid, while the Mn position remains nearly constant with respect to the surrounding oxygen atoms. All-electron density-functional calculations in the LSDA+U approximation for the x = 1 compound [3] are in good agreement with the collinear, commensurate ferrimagnetic ordering of the magnetic moments as proposed in [1].
[1] Munoz, A. et al., Chem. Mater. 16, 4087 (2004);
[2] all materials prepared by D. Souptel at IFW Dresden;
[3] FPLO: Koepernik, K. et al., Phys. Rev. B 59, 1743 (1999)

We present new results from the PROMISE experiment, consisting of a GaInSn alloy confined between differentially rotating cylinders, in the presence of a combined axial and azimuthal (helical) magnetic field. The apparatus has been upgraded to incorporate split-ring end-plates, thereby reducing end-effects. The resulting traveling-wave disturbances are in good agreement with theoretical predictions for the onset of the helical magnetorotational instability.

Interest in magnetoelectric multiferroic materials has increased exponentially over the last ten years, with considerable effort devoted both to combining magnetism and ferroelectricity in a single phase material and in obtaining magnetoelectric coupling between the two phenomena. Progress has been made on both front and a rich array of fundamental phenomena have been revealed in prototypical multiferroics such as bismuth ferrite, BiFeO3. Here we describe a new and previously unanticipated functionality: the observation – using conductive atomic force microscopy – of room temperature electronic conductivity at ferroelectric domain walls in BiFeO3. We explore the origin of the observed conductivity using high resolution transmission electron microscopy and first-principles density functional computations. Our results suggest the possibility of exploiting domain walls as a functional component in novel applications.

We report the clearly observed tunneling magnetoresistance at 5 K in magnetic tunnel junctions with Co-doped ZnO as a bottom ferromagnetic electrode and Co as a top ferromagnetic electrode prepared by pulsed laser deposition. Spin-polarized electrons were injected from Co-doped ZnO to the crystallized Al2O3 and tunnelled through the amorphous Al2O3 barrier. Our studies demonstrate the spin polarization in Co-doped ZnO and its possible application in future ZnO-based spintronics devices.

The origin of magnetic interactions in Diluted Magnetic Semiconductors (DMS) is attracting a great attention as a basic problem on magnetism[1-2]. This subject is still an issue of controversy. In all of these works, the observed ferromagnetism has been attributed to interactions between the magnetic impurities, but the main source has never been associated to magnetically ordered defects. We have reported the different types of magnetic source in case of Fe doped SnO2 powder [3], and the phonon density of states of rutile type structures [4]. Defects in DMS can also contribute to saturation magnetization. Here we have made the thin films of SnO2 implanted with 57Fe and characterized them by 57Fe and 119Sn conversion electron Mössbauer spectrometry (CEMS).

Worldwide, semiconductor spin transfer electronics (spintronics) is of strongly increasing interest. To realize such materials polarized carriers can be injected from a ferromagnetic metal into a diluted magnetic semiconductor (DMS). DMS are “conventional” semiconductors doped with transition metal or rare-earth ions which are diluted within the host matrix and ferromagnetically aligned via an indirect magnetic coupling.

Wide band gap semiconductors like GaN, ZnO, or TiO2 are promising candidates. Doping could be performed by Mn, V, Fe, Co or Ni with concentrations in the range of some %. In the case of 57Fe as doping ion, Mössbauer spectroscopy can be used to investigate how it is built in the host matrix. The 57Fe ion acts both as doping and probe.

In the present study, a survey about Mössbauer spectroscopy as a tool to explore such materials is given. It is very useful however it is insufficient for a full characterization. Other techniques like transmission electron microscopy, Zero-field-cooled/field-cooled SQUID measurements or X-ray diffraction are necessary as complementary methods.

The work reports on experimental features and theoretical studies of swift-heavy-ion-induced shaping of Ge nanospheres into disks. A stack of alternating Ge and SiO2 layers was sputtered on an oxidized Si wafer. The Ge layer thicknesses varied from 2.5 to 7.5 nm. Thermal treatment above the melting temperature of Ge transformed each Ge layer into a layer of Ge nanospheres. With growing Ge layer thickness the mean diameter increases from 8 to 37 nm. Irradiation with low fluences (~1014cm-2) of 38 MeV I7+ shaped medium-sized Ge nanospheres into disks, whereas smaller ones became rod-like and larger ones remained unchanged. At higher fluences, the larger Ge nanospheres shrink due to Ge loss and shape into disks too. A new model is presented and atomistic Monte-Carlo simulations are shown which describe the shaping evolution and the size thresholds for shaping quantitatively. The volume change of Ge upon melting has been identified as driving force.

In burning stellar environments like supernova explosions, the temperatures are high enough for the production of heavy neutron deficient nuclei, the so-called p-nuclei. These are thought to be produced in such explosive scenarios either through chains of photodisintegration reactions on heavy seed nuclei. The modelling of the nucleosynthesis for the p-nuclei is mainly based on statistical model calculations. In this context, the knowledge of the experimental cross sections for the prediction of the p-nuclei abundances is of crucial importance and to forward in this direction we have started and experimental program at the bremsstrahlung facility of the superconducting electron accelerator ELBE of FZ Dresden-Rossendorf . Photodisintegration measurements on the astrophysically relevant p-nuclei 92Mo and 144Sm have been performed via photoactivation technique with bremsstrahlung end-point energies from 10.0 to 16.5 MeV. In particular the (gamma,alpha) reactions of the mentioned nuclei were studied for the first time at different endpoint energies above and close to the threshold. The bremsstrahlung facility and the experimental area are deigned so as to facilitate the studies under optimized background conditions. To probe the fascinating investigations on short-lived nuclei a new pneumatic delivery system has been built recently. First experiments on the short-lived decays following the reaction 144Sm(gamma,n) is discussed. The activation yields from all measurements are compared with calculations using cross sections from recent Hauser-Feshbach models .

Self-ion irradiation was used to simulate the damage caused by fast neutrons in the austenitic stainless steel SS 304 SA, the ferritic/martensitic steel Eurofer’97 and a Fe-9at%Cr model alloy. The irradiation-induced hardness change in the damage layer was evaluated by means of nanoindentation. Three-step irradiations were performed at room temperature and 300°C up to 1 and 10dpa. An irradiation-induced hardness change was shown for all materials. No influence of irradiation temperature could be resolved. Irradiation-induced hardening exhibits different fluence dependencies in Eurofer’97 and Fe-9at%Cr. While the data indicate a saturation-like behaviour for Fe-9at%Cr, a monotonous increase of hardness with fluence up to 10dpa was found for Eurofer’97.

A large-area interdigitated terahertz (THz) emitter based on molecular-beam epitaxy grown GaInAsN with an additional AlGaAs heterostructure is investigated as THz source for excitation wavelengths between 1.1 and 1.5 µm. The optical and electrical properties of the emitter material exhibit absorption up to a wavelength of 1.5 µm and have a resistivity of 550 kΩ cm. Terahertz waves were detected by electro-optical sampling with a bandwidth exceeding 2 THz. Best performance is found for excitation wavelengths below 1.35 µm. Furthermore the emission properties for several excitation powers are investigated showing a linear increase of THz emission.

The formation of ultra-shallow n+ layers by P or As implantation and subsequent rapid thermal annealing (RTA) or flash-lamp annealing (FLA) is investigated. The focus is on diffusion and activation of dopants. RTA leads to considerable broadening of the shallow as-implanted profiles by concentration-dependent diffusion. In contrast, FLA does not cause any diffusion and is therefore a promising method for producing ultra-shallow n+p junctions in Ge. Under present annealing conditions RTA yields maximum activation levels of about 1.1E19 and 6.5E18 for P and As, respectively. The maximum activation achieved by FLA is about 4.0E19 and 2.1E19 for P and As, respectively. Possible mechanisms for diffusion and deactivation of dopants are discussed.

The rate of the hydrogen-burning carbon-nitrogen-oxygen (CNO) cycle is controlled by the slowest process, 14N(p,gamma)15O, which proceeds by capture to the ground and several excited states in 15O. Previous extrapolations for the ground state contribution disagreed by a factor 2, corresponding to 15% uncertainty in the total astrophysical S-factor. At the Laboratory for Underground Nuclear Astrophysics (LUNA) 400 kV accelerator placed deep underground in the Gran Sasso facility in Italy, a new experiment on ground state capture has been carried out at 317.8, 334.4, and 353.3 keV center-of-mass energy. Systematic corrections have been reduced considerably with respect to previous studies by using a Clover detector and by adopting a relative analysis. The previous discrepancy has been resolved, and ground state capture no longer dominates the uncertainty of the total S-factor.

wird nachgereicht

Bacteria are simply organized, but apart from that and their small size they are an unbelievable complex and a highly efficient group of creatures. Some are able to thrive at the most forbidding, uninviting places on Earth, for example in hot springs, in the perpetual ice, in the deep sea or in deserts. For production of energy they can use different kinds of organic and inorganic matter or sun light. Furthermore, they successfully conquer also any other habitats, even so an environment is highly contaminated with toxic substances, like organic solvents, heavy metals and radionuclides. Adaptation and detoxification mechanisms allow them to resist high concentrations of toxic elements without getting sustainably affected. These mechanisms are very prospective for the development of innovative remediation strategies and for other biotechnical applications [1-6].
Within the radio-ecological research on the interaction of bacteria with actinides many reference strains and isolates were investigated for their interaction with heavy metals and radionuclides [7-11]. The studied bacteria possess different strategies to handle high metal concentrations in their environment. Namely, via an immobilization of the metals by biosorption, bioaccumulation inside the cell, biomineralization and biotransformation. In principle, all mentioned strategies are suitable for the development of new materials for bioremediation techniques and the removal of metals. In respect of the development of metal selective and reusable filter materials, several Bacillus and Lysinibacillus isolates from a uranium mining waste pile were preferentially investigated. The cells bind selectively and reversibly uranium on their surface. Furthermore the analyses results in the identification of new so called surface layer (S-layer) proteins, forming the outermost structure on many bacteria. This S-layers are able to bind and detain toxic heavy metals while essential ones may pass. To take advantage of this intelligence intact cells, spores and the S-layer proteins of the bacteria were immobilized in sol-gel ceramics [11, 12] and used for metal binding experiments. Ongoing experiments include also the production of biofilm based materials and the protein immobilization on conventional carriers. Especially the S-layer proteins not only bind heavy metals very selectively but also some precious metals. The superior aim is the development of metal selective filter materials for the removal of heavy metals and in future for the recovery of precious metals from aqueous solutions.

Ackowledgements
We gratefully acknowledge support by the DFG (Biocere, SE 671/1-2) and the BMWi/PTJ (BIOREM, 03EGSSN014).

References
[1] L. Hendrickx and M Mergeay (2007), Curr Opin Microbiol 10(3), 231-237
[2] R. Margesin and F. Schinner F. (2001), Appl Microbiol Biotechnol. 56(5-6) 650-663
[3] G. Antranikian (2005), Adv Biochem Eng Biotechnol, 96, 219-262
[4] M. Kalin et al. (2005), J Environ Radioact. 78(2),151-177
[5] B. Volesky and Z.R. Holan (1995), Biotechnol. Prog. 11, 235-250
[6] J. Raff and S. Selenska-Pobell (2006), Nuclear Engineering International 51(619) 34-36
[7] M. Merroun et al. (2005) Appl. Environ. Microbiol. 71(9): 5532-5543
[8] M. Merroun et al. (2006) Radiochimica Acta 94, 723-729
[9] H. Moll et al. (2008) BioMetals 21, 219-228
[10] H. Moll et al. (2006) Radiochimica Acta 94(2006), 815-824
[11] J. Raff et al. (2003), Chem. Mater. 15, 240-244
[12] K. Pollmann et al. (2006), Biotechn. Adv. 24 (1), 58-68

In this paper we introduce an algorithm for the creation of polyhedral approximations for certain kinds of digital objects in a three-dimensional space. The objects are sets of voxels represented as strongly connected subsets of an abstract cell complex. The proposed algorithm generates the convex hull of a given object and modifies the hull afterwards by recursive repetitions of generating convex hulls of subsets of the given voxel set or subsets of the background voxels. The result of this method is a polyhedron which separates object voxels from background voxels. The objects processed by this algorithm and also the background voxel components inside the convex hull of the objects are restricted to have genus 0. The second aim of this paper is to present some practical improvements to the discussed convex hull algorithm to reduce computation time.

Surface layer proteins (S-layers) form the outer sheet around the cells of many primitive microorganisms. They form two-dimensional paracrystalline arrays with repeating units on the scale of a few nanometers (10-9 m). We have established their utilization as a technology platform for innovative materials. The S-layer of Lysinibacillus sphaericus JG-A12 isolated from a uranium waste pile has been shown to exhibit highly ordered binding sites for various metals such as Pt, Pd, Au, suitable for the formation of regularly distributed nanoclusters of defined sizes. Such bioinorganic materials possess a great potential for the development of novel catalysts, new biomedical and bio¬analytical applications, the assembly of nanometer-scaled electronic devices, optical industry, and storage media. At the Institutes of Radiation Physics, Ion-beam Physics and Materials Research, and the Dresden High Magnetic Field Laboratory, the structure of such nanoparticles and their physical properties are currently analyzed in an interdisciplinary approach.

The electrical conductivity of Pb-Bi alloys of eutectic and near eutectic compositions was investigated in the melting-solidification temperature region. The revealed discrepancies between the heating and cooling curves as well as a hysteresis observed in course of heating-cooling cycles suggest a metastable microheteregenous structure of the Pb-Bi melts.

We report on the implementation of metal nanoparticles as probes for scattering and apertureless near-field optical investigations in the mid-infrared (mid-IR) spectral regime. At these wavelengths, an efficient electric-field confinement is necessary and achieved here through a gold metal nanoparticle of 80 nm in diameter (Au80-MNP) acting as the optical antenna. The Au80-MNP is attached to a standard AFM cantilever used as the spatial manipulator. When approached to a sample surface while being illuminated with an infrared beam, the Au80-MNP produces a considerably improved spatial confinement of the electric field compared to an ordinary scattering AFM tip. We demonstrate here the confinement normal to the sample surface by making use of a sample-induced phonon polariton resonance in a ferroelectric lithium niobate sample. Our experimental findings are in very good agreement with the quasistatic dipole model and show improved optical resolution via well-selected antenna particles.

High magnetic fields are one of the most powerful tools available to scientists for the study, modification, and control of the state of matter. The application of magnetic fields, therefore, has become a commonly used instrument for condensed-matter physics. For the observation of many phenomena very high magnetic fields are essential. Consequently, the demand for the highest possible magnetic-field strengths is increasing. At the Dresden High Magnetic Field Laboratory (HLD), that has just opened its doors for external users, pulsed magnetic fields up to 70 T are available and the ambitious goal of reaching 100 T has been set. Here, I will present the current status of the HLD and discuss some scientific results recently obtained at high magnetic fields. This covers e.g. the clear thermodynamic evidence for the existence of the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state in a layered organic superconductor, the magnetic-field-induced change of the electronic band structure in the metal CeBiPt, and finally the determination of the band- and angle-resolved superconducting coupling strength in a borocarbide superconductor.

The discovery of superconductivity in polycrystalline boron-doped diamond (BDD) synthesized under high pressure and high temperatures [Ekimov, et al. (2004) Nature 428:542–545] has raised a number of questions on the origin of the superconducting state. It was suggested that the heavy boron doping of diamond eventually leads to superconductivity. To justify such statements more detailed information on the microstructure of the composite materials and on the exact boron content in the diamond grains is needed. For that we used high-resolution transmission electron microscopy and electron energy loss spectroscopy. For the studied superconducting BDD samples synthesized at high pressures and high temperatures the diamond grain sizes are ≈1–2 µm with a boron content between 0.2 (2) and 0.5 (1) at %. The grains are separated by 10- to 20-nm-thick layers and triangular-shaped pockets of predominantly (at least 95 at %) amorphous boron. These results render superconductivity caused by the heavy boron doping in diamond highly unlikely.

ZnO is of considerable interest for optoelectronic device applications due to its wide band gap and high exciton binding energy. In spite of decades of study and recent progress in research on ZnO properties, there remained unresolved controversies which are mainly related to native defects formed during crystal growth. Positron annihilation spectroscopy (PAS) is among the methods to tackle this structural issue [1, 2].
ZnO nanostructures, like e.g. nanorods [3] and tetrapods [4], are of special interest for device applications [5, 6]. However, their characterization remains an ongoing challenge.
This talk intends to review our recent efforts and latest achievements in this direction. Results obtained will comprise PAS in the form of Slow Positron Implantation Spectroscopy (SPIS) and Pulsed Low Energy Positron Lifetime Spectroscopy (PLEPS), Nuclear Reaction Analysis (NRA), Atomic Force Microscopy (AFM), conductive AFM (C-AFM), Nuclear Magnetic Resonance (NMR), Electron Spin Resonance (ESR), Photoluminescence (PL) spectroscopy, and latest theoretical investigations of structure-related and positron properties of selected defects.
The fundamental importance of a relationship between fabrication conditions, native defect formation, and resulting optical and electronic properties is demonstrated by getting either inferior (nanorods) or significantly improved (tetrapods) optical properties compared to single crystal samples, depending on the nanostructure fabrication method.

Zinc oxide (ZnO) is an interesting and promising semiconductor material for many potential applications, e.g. in opto-electronics and for sensor devices. However, its p-type doping represents a challenging problem, and the physical reasons of its mostly n-type conductivity are not perfectly clear at present.
Firstly, efforts to achieve p-type conductivity by ion implantation are reviewed, and the creation of a p-n junction by N+ ion implantation with post-implantation annealing is discussed.
Secondly, ways to achieve p-type ZnO nanorods by various growth conditions are presented. Their characterization by electrical, optical and positron annihilation spectroscopy methods will also be included.
Third, the preparation of Schottky contacts on ZnO with the surface pre-treatments of hydrogen peroxide is mentioned in some detail as this is a demand of the device formation process.
Finally, the possible incorporation of hydrogen and nitrogen into structural defects, which can act as trapping sites for positrons, is discussed. This will be discussed in the context of positron experimental and theoretical results and estimated H and N contents in a selected variety of ZnO materials.

While the mechanism by which a kinesin-1 molecule moves individually along a microtubule is quite well understood, the way that many kinesin-1 motor proteins bound to the same cargo move together along a microtubule is not. We have identified a 60-aa-long domain, termed Hinge 1, in kinesin-1 from Drosophila melanogaster that is located between the coiled coils of the neck and stalk domains. Its deletion reduces microtubule gliding speed in multiple–motor assays but not single-motor assays. Hinge 1 thus facilitates the co-operation of motors by preventing them from impeding each other. We have addressed the structural basis for this phenomenon. Video-microscopy of single microtubule-bound full-length motors reveals the sporadic occurrence of high compliance states alternating with longer-lived low compliance states. Deletion of Hinge 1 abolishes transitions to the high compliance state. Based on FTIR, CD, and fluorescence spectroscopy of Hinge 1 peptides, we propose that the low compliance states correspond to an unexpected structured organization of the central Hinge 1 region, whereas the high-compliance state corresponds to the loss of that structure. We hypothesize that strain accumulated during multiple-kinesin motility populates the high compliance state by unfolding helical secondary structure in the central Hinge 1 domain flanked by unordered regions, thereby preventing the motors from interfering with each other in multiple-motor situations.

The static and dynamic magnetic properties, electrical resistivity, specific heat, and magnetoresistance have been studied in EuCu2Si2 single crystals grown by a floating zone method. The magnetic susceptibility exhibits a considerable anisotropy and a steep rise below 10 K for external fields parallel to the c axis but with no evident magnetic ordering in the temperature range of 2–350 K. The data imply a gradual change in the Eu valence as a function of temperature. Electron spin resonance (ESR) measurements reveal a sizeable fraction of stable Eu2+ magnetic moments that interact with conduction electrons and develop quasistatic antiferromagnetic correlations on the ESR timescale. The electrical resistivity and specific heat demonstrate the presence of spin fluctuations and Kondo-like behavior, which apparently competes with the antiferromagnetic order. The analysis of experimental data enables to conclude that the remarkable diversity of the physical properties of EuCu2Si2 results from the variation of lattice parameters as well as of local crystal chemistry as a consequence of the particular preparation route employed for the growth of single crystals and polycrystals.

As-doping of zinc oxide has been approached by ion implantation and chemical vapor deposition. The effect of thermal annealing on the implanted samples has been investigated by using secondary ion mass spectrometry and Rutherford backscattering/channeling geometry. The crystal damage, the distribution of the arsenic, the diffusion of impurities, and the formation of secondary phases is discussed. For the thin films grown by vapor deposition, the composition has been determined with regard to the growth parameters. The bonding state of arsenic was investigated for both series of samples using x-ray photoelectron spectroscopy.

Electron beam CT has until today been exclusively used in cardiac imaging of human beings. As a high cost diagnostic tool with frame rates in the range of 20 Hz it has so far not been considered for small animal imaging. With recent progress in technology an application in this field becomes feasible. Especially perfusion imaging for heart and other organs using iodine based contrast agents may be a target of interest for electron beam CT. We present a small volume ultra fast electron beam CT scanner which was originally developed for process tomography applications and with it preliminary results of a small animal study showing visualization of heart motion and perfusion in a rat. We further discuss the potential of this new technology and novel technological principles which allow fast 3D electron beam imaging of small animals. Included in the discussion is an assessment of radiation effects.

Ultra fast electron beam tomography has been developed as a novel tool for visualisation of fast processes. As in medical electron beam CT this technique is based on the generation of images from radiographs produced with a rapidly scanned electron beam. Thereby an electron beam of sufficiently high power (typically UB=150kV, power up to 10 kW) is scanned across a circular metal target producing X-rays in a small focal spot. With the rotation of the spot around an object radiographs from different viewing angles are produced and subsequently reconstructed to slice images. A fast electron beam scanner at FZD operates with beam sweeping of up to 7 kHz, producing up to 7000 images per second. The X-ray detector used in this device consists of 240 room temperature semiconductor elements operated in current mode. Photon flux at the detector is rather high, being >10^11 ph/s. The detector is sampled with 1 MHz frequency. It is known, that high flux current mode operation poses problems for semiconductor detectors made of CZT and CdTe due to polarization effects and decay time in the few hundred ns range. We have compared both types of detectors regarding their suitability in such an application. The presentation will give an overview on these results and furthermore give an introduction of this new fast imaging technique.

The presentation gives an overview on recent developments in ultra fast electron beam X-ray tomography for process applications. Principles of this new tomographic imaging modality are discussed along with applications in flow measurement. A focus is given on potential extension of the technology towards high power electron beam CT using DC electron LINAC.

The lecture introduces computerized tomography as applied in process and flow diagnostics. In many indutrial fields multiphase flows play a key role in efficiency and safety aspects of indiustrial plants and processes. In the lecture principles of tomographic imaging modalities, such as electrical tomography, gamma and X-ray tomography, electron beam tomography, PET and PEPT are discussed along with exemplary applications in oil industry, chemical industry, nuclear engineering and other industrial and scientific fields.

We demonstrate a production method for self-organized arrays of metal nanoparticles and aligned nanowires. Ion beam-sputtered Si/SiO2 substrates are used as templates for metallic vapor deposition, forming aligned arrays of 5–20 nm silver and cobalt nanoparticles with a period of 35 nm. The 20 nm diameter cobalt nanowires with lengths in excess of a micrometer are produced under appropriate conditions. All processing steps can be integrated into a single vacuum chamber and performed in a matter of minutes at mild temperatures. This inherently scalable technique can be extended to a range of substrate materials, array patterns, and nanoparticle materials.

Flow separation and its control is a persistent topic of fluid dynamic research with large technological importance. Since the early 1990s, separation control by periodic addition of momentum, now commonly termed “active flow control”, has been a subject of intense research. Its main advantage compared to steady actuation is that a control goal, e.g. a specific lift increase, can typically be attained by orders of magnitude smaller momentum input . The significant actuation parameters are mainly the time averaged momentum input and the normalized excitation frequency.
The present lectures discusses the applicability of electromagnetic forces to control separated flows. Simultaneous time resolved force measurements and flow fields obtained by Particle Image Velocimetry on a NACA 0015 are presented. The effects of momentum coefficient, exciatation frequency and -wave-form on the coherent structures and the resulting mean flow are discussed.

Hydrogen pre-implantation performed in addition to helium implantation efficiently shrinks the width of the gettering layer in Si and increases the empty volume fraction as well as the internal surface area per unit volume. The gettering efficiency for oxygen is significantly enhanced compared to the single helium implantation, and the helium implantation dose can be strongly reduced. The gas-filled bubble layer induced by the co-implantation of hydrogen and helium has the highest gettering efficiency for the oxygen accumulation. Direct evidence for oxygen gettering at the internal wall of the cavity is demonstrated by cross-sectional transmission electron microscopy (XTEM).

This talk will focus on several research topics exploiting our free-electron (FEL) and modelocked Ti:Sapphire lasers to investigate semiconductor nanostructures. Pump-probe spectroscopy and two-photon detection is used for time-resolved investigations of intersubband transitions in semiconductor quantum wells and for FEL pulse diagnostics, respectively. Terahertz emitters based on interdigitated metal stripe arrays will also be discussed.

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We report on a two-photon detector based on resonantly enhanced nonlinear absorption between subbands in InGaAs/InAlAs quantum wells and demonstrate its use as a quadratic autocorrelator for mid-infrared pulses. Modified device design allows for device operation at room temperature, which is crucial for applications in practical systems.

Independent poloidal and azimuthal body forces are induced in a liquid metal cylinder by traveling and rotating magnetic fields of different frequencies, respectively. The bulk axial and azimuthal velocities are measured by the ultrasound Doppler method. Particle image velocimetry is used to observe the upper free surface velocity distribution. The transition from the poloidal to the azimuthal body force governed regime occurs at a fixed ratio of the respective force magnitude of around 100. This transition is marked by a formation of a concentrated vortex revealing several similarities to intense atmospheric vortices. The vortex structure is controlled by a relatively weak azimuthal force while the poloidal one holds the main control over the top speed of the top speed of the swirl is mainly governed by the poloidal one. Under a certain force ratio the average axial velocity changes its direction in the vortex core resembling the subsidence in an eye of a tropical cyclone or a large tornado. Multiple moving vortices encircle the vortex core in this regime.

A 1D test solver was developed in recent years for the modeling of two phase bubbly flow in pipe geometry. The solver considers number of bubble classes and calculates bubble-size resolved void fraction profiles in radial direction. A successful implementation was achieved regarding bubble forces models (non-drag forces). Discrepancies appeared when coalescence and breakup rates are significant. These rates depend upon local turbulent values, which are possible reason for shortcomings in calculating coalescence and breakup rates. Originally the test solver is equipped by Sato model (Sato et al. 1981) which accounts for turbulence via shear- and bubble-induced viscosities calculated out of empirical correlations. One-equation for the turbulent kinetic energy was considered. In order to improve the local values of turbulence parameters the existing turbulence model was replaced by two-equation turbulence model. The new model accounts for the bubble-induced turbulence via source term taken from literature. Comparisons between new and old turbulence modeling against experimental data showed better agreement of the new model. The experiments covered wide range of water and air superficial velocities for upward bubbly flow in two pipe’s diameters: 50 mm and 200 mm. Main feature of new calculations is providing values of turbulence parameters for application in coalescence and breakup models. A comparison with CFX 5.7 calculations in 50 mm pipe showed better calculation results when applying the source term. An implementation of the source term into CFX calculations is planned.

The influence of melt convection on the microstructure during solidification of peritectic Nd-Fe-B and Ti-Al alloys has been investigated. Since the magnetic and mechanical properties of these technical relevant materials depend strongly on the microstructure and especially on the volume fraction of the properitectic phase, such investigation is of growing scientific interest. On the basis of numerical simulation of melt convection modes in an inductively heated metallic melt, novel techniques for the modification of the melt convection were developed. This is the forced rotation technique and a modified floating-zone facility equipped with a special designed double coil system enabling the application of additional magnetic fields. The forced rotation technique where the crucible rotates with well defined frequencies leads in accordance to numerical simulation to a strong reduction of the melt convection in dependence on the frequency. The volume fraction of the soft magnetic α-Fe phase could be drastically reduced in comparison to a common induction melting accompanied by a simultaneous reduction of the secondary dendritic arm spacing. The floating-zone facility with the patented double coil system allows the tailoring of the melt convection in a wide range from motion at rest to strong stirring. The microstructure of the investigated Ti-Al alloy changed from dendritic to globulitic morphology under strong stirring whereas the volume fraction of the properitectic phase increases with increasing stirring. The mechanical properties show a significant increased plastic deformation of the samples solidified under strong stirring. The possible reason of the change in morphology is explained as a result of spherical growth under forced convection. The study of the influence of melt convection on the microstructure formation of peritectic alloys showed the feasibility of tailoring the microstructure and the resulting alloy properties by customized melt convection using magnetic fields.

A rotating cylindrical magnetron with a Ti target was sputtered in pure Xe or in a mixture of Xe and N2. The atomic composition of the target surface during sputtering has been investigated by in situ Rutherford backscattering spectrometry. The noble gas atomic ratio at the target surface is around 3.4% or 9.8% for sputtering in pure Xe and with 10% N2 addition, respectively. Energy resolved mass spectrometry reveals that some of the implanted Xe atoms are sputtered from the target. A radiation enhanced diffusion/detrapping/sputtering mechanism is proposed to model the flux of noble gas leaving the target during sputtering

One of the most convenient approaches to observe experimentally the magnetorotational instability (MRI) is to use a magnetized Taylor-Couette setup. The flow of liquid metal between two rotating, concentric cylinders can become unstable in the presence of an external magnetic field. One of the issues which should be addressed when designing such an experiment is the influence of plates enclosing the cylinders from the top and the bottom. In this paper we discuss properties of the boundary layer which arises near these plates. Our primary concern is the importance of this layer in the MRI experiment PROMISE.

The advantageous properties of numerous 3,7-diazabicyclo[3.3.1]nonane (bispidine) derivatives have attracted much attention and caused intensive research efforts in different directions. An attractive goal represents the development of target-specific radiopharmaceuticals. For this purpose, bifunctional chelating agents are needed which have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, hexadentate bispidines 1 – 3 containing pyridine units in C2, C4, N3, and N7 position have been shown to rapidly form stable radiocopper (such as ⁶⁴Cu and ⁶⁷Cu) complexes. Furthermore, the carboxylic groups of ligand 3 provide the possibility for coupling bio-molecules.

Beim Aufspüren von Tumoren und deren Metastasen hat die Positronen-Emissions-Tomographie (PET) entscheidende Fortschritte gebracht. Mit speziellen radioaktiven Substanzen lassen sich Tumore viel früher finden als mit anderen bildgebenden Verfahren. Die PET-Bilder geben – oft in Kombination mit anderen Verfahren wie Computertomographie (CT) oder Magnetresonanztomographie (MRT) – die notwendigen Informationen für eine chirurgische oder externe strahlentherapeutische Behandlung von Tumorerkrankungen. Ihre Grenzen findet die externe Bestrahlung häufig bei der metastasierenden Erkrankung, wobei Tumorzellen über Blut oder Körperflüssigkeit abgeschwemmt werden und an neuen Orten weiter wachsen. In diesen Fällen muss die Behandlungsmethode systemisch sein, d.h. die Tumortherapeutika müssen über die Blutbahnen zu den (zum Teil nicht sichtbaren) Metastasen gelangen. Dies ist bisher der Chemotherapie vorbehalten. Mit Mitteln der internen Radionuklidtherapie sollen künftig die Heilungserfolge insbesondere bei der Bekämpfung solcher Metastasen verbessert werden.

Radiopharmaceuticals based on metallic radionuclides, such as ^64/67Cu, ^99mTc, ^186/188Re and ^86/90Y, are often used for diagnostic and therapeutic purposes. These nuclides are usually enveloped in organic ligands, such as heteromacrocyclic systems. To be effective, the ligands have to show fast metal complexation kinetics, form complexes with high in vitro and in vivo stability and contain a group that can be linked to biomolecules. In this regard, we are developing new ligand scaffolds for copper radionuclides which satisfy these requirements. Ligands – based on hexadentate 3,7-diazabicyclo[3.3.1]nonane I (bispidine) and bis(2-pyridylmethyl) triazacyclononane (DMPTACN) II – are discussed. These derivatives allow the introduction of linker groups, such as carboxylic acids, maleinimide or isothiocyanate, thereby facilitating coupling of targeting molecules.