Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In reflux cooling, steam generated in the reactor core and water condensed in a steam generator (SG) form a countercurrent flow in a hot leg, which consists of a horizontal pipe, an elbow and an inclined pipe. At Forschungszentrum Dresden-Rossendorf (FZD), both countercurrent air-water and steam-water tests were previously carried out using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility. In this paper, in order to evaluate the effects of fluid properties, numerical calculations for the steam-water CCFL tests at FZD were conducted using the CFD code, FLUENT6.3.26. The numerical calculation region included the reactor vessel simulator, hot leg and SG inlet chamber, in order to avoid uncertainties of boundary conditions at both ends of the hot leg. The VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. The CCFL characteristics calculated by the 2F and VOF models agreed with the steam-water CCFL data at FZD and showed the same trends with the data for fluid properties.

Hexagonal barium ferrites were deposited onto sapphire substrates by radio frequency magnetron sputtering. The composition, microstructure, and magnetic properties of these isotropic thin films were investigated with Rutherford backscattering spectroscopy, X-ray diffraction, atomic force microscopy, magnetic force microscopy and SQUID magnetometry. The intrinsic coercivity of the films reaches about 11.5 kOe at room temperature. The mechanism of the coercivity is proposed to be nucleation in the decoupled single domain nanometer particles as shown by the characteristics of the magnetic domains and the virgin magnetization curves.

Air-water CCFL (countercurrent flow limitation) tests were previously carried out at Kobe University using the 1/5th scale rectangular channel and 1/15th scale circular tube simulating a PWR hot leg. Then numerical calculations for these tests and full-scale PWR conditions were made using the CFD code, FLUENT6.3.26. At Forschungszentrum Dresden-Rossendorf (FZD), similar tests were previously carried out for both air-water and steam-water flows using the 1/3rd scale rectangular channel simulating a PWR hot leg installed in the pressure chamber of the TOPFLOW facility.
In this paper, numerical simulations for the air-water CCFL tests of FZD using FLUENT6.3.26 are presented and compared with the experimental data obtained at Kobe University and FZD. In the calculations, the VOF (volume of fluid) model or two-fluid (2F) model was used. In the 2F model, we used the combination of three correlations on the interfacial friction coefficients as a function of void fractions, which had been validated for the 1/15th and 1/5th scale tests at Kobe University. Calculation parameters were the air flow rates and air inlet locations, which were at the top of the reactor vessel simulator simulating the FZD test facility (inlet 1) and the opposite side of the hot leg junction simulating the test loops at Kobe University (inlet 2). Conclusions were as follows : (1) the calculated CCFL characteristics using the 2F model for the FZD tests agreed well with the 1/15th scale circular tube data obtained at Kobe University and the calculated results for full-scale PWR conditions, which supported the validity of the 1/3rd scale rectangular channel to simulate CCFL in circular tubes; (2) there were no significant differences between the calculated CCFL characteristics with the air inlet 1 and inlet 2, which indicated that the air inlet location did not influence CCFL behavior in a hot leg; and (3) comparison with the FZD data showed that the calculations using the 2F and VOF models overestimated the water flow rates for deflooding.

Bubble condensation plays an important role e.g. in sub-cooled boiling or steam injection into pools. Since the condensation rate is proportional to the interfacial area density, bubble size distributions have to be considered in an adequate modeling of the condensation process. The effect of bubble sizes was clearly shown in experimental investigations done previously at the TOPFLOW facility of FZD. Steam bubbles were injected into a sub-cooled upward pipe flow via orifices in the pipe wall located at different distances from measuring plane. 1 mm and 4 mm injection orifices were used to vary the initial bubble size distribution. Measurements were done using a wire-mesh sensor. Condensation is clearly faster in case of the injection via the smaller orifices, i.e. in case of smaller bubble sizes. Recently the Inhomogeneous MUSIG model was implemented into the CFD code CFX from ANSYS enabling the simulation of poly-dispersed flows including the effects of separation of small and large bubbles due to bubble size dependent lift force inversion. It allows to divide the dispersed phase into size classes regarding the mass as well as regarding the momentum balance. Up to now transfers between the classes in the mass balance can be considered only by bubble coalescence and breakup (population balance). Here an extension of the model is proposed to include the effects due to phase transfer. The paper focuses on the derivation of equations for the extension of the Inhomogeneous MUSIG model and presents some first results for verification and validation.

Systematic investigations of dilepton production are performed at the SIS accelerator of GSI with the HADES spectrometer. The goal of this program is a detailed understanding of di-electron emission from hadronic systems at moderate temperatures and densities. New results obtained in HADES experiments focussing on electron pair production in elementary collisions are reported here. They pave the way to a better understanding of the origin of the so-called excess pairs earlier on observed in heavy-ion collisions by the DLS collaboration and lately confirmed in two measurements of the HADES collaboration using C+C and Ar+KCl collisions. Results of these studies are discussed.

The production of pseudo scalar, Eeta, Eta-prime, and vector, Omega, Rho, Phi, mesons in NN collisions at threshold-near energies is analyzed within a covariant effective meson-nucleon theory. It is shown that a good description of cross sections and angular distributions, for vector meson production, can be accomplished by considering meson and nucleon currents only, while for pseudo scalar production an inclusion of nucleon resonances is needed. The di-electron production from subsequent Dalitz decay of the produced mesons, eta' to gamma gamma^* to gamma e^+e^- and omega to pi gamma^* to pi e^+e^- is also considered and numerical results are presented for intermediate energies and kinematics of possible experiments with HADES, CLAS and KEK-PS.
We argue that the transition form factor omega to gamma^* pi as well as eta' to gamma^* gamma can be defined in a fairly model independent way and the feasibility of an experimental access to transition form factors is discussed.

Dieser Vortrag für Schüler zeigt auf, wie Protonenstrahlanalytik an Atmosphäre erfolgt, welcher Informationsgehalt durch die Kombination von PIGE-PIXE-RBS gewonnen wird und welche typische Fragestellungen damit beantwortrt werden können.

In this talk first experiments of proton acceleration with the Draco laser are presented.

The impact of actinides on living organisms has been the subject of numerous studies since the 1950s. From a general point of view, these studies show that actinides are chemical poisons as well as radiological hazards. Actinides in plasma are assumed to be mainly complexed to transferrin, the iron carrier protein. This paper casts light on the uptake of actinides(IV) (thorium, neptunium, plutonium) by transferrin, focusing on the pH dependence of the interaction and on a molecular description of the cation binding site in the protein. Their behavior is compared with that of iron(III), the endogenous transferrin cation, from a structural point of view. Complementary spectroscopic techniques (UV/Vis spectrophotometry, microfiltration coupled with g spectrometry, and X-ray absorption fine structure) have been combined in order to propose a structural model for the actinide-binding site in transferrin. Comparison of our results with data available on holotransferrin suggests some similarities between the behavior of FeIII and NpIV/PuIV/ NpIV is not complexed at pH <7, whereas at pH ≈7.4 complexation can be regarded as quantitative. This pH effect is consistent with the in vivo transferrin “cycle”. PuIV also appears to be quantitatively bound by apotransferrin at around pH ~7.5, whereas ThIV was never complexed under our experimental conditions. EXAFS data at the actinide edge have allowed a structural model of the actinide binding site to be elaborated: at least one tyrosine residue could participate in the actinide coordination sphere (two for iron), forming a mixed hydroxo–transferrin complex in which actinides are bound with transferrin both through An–tyrosine and through An-OH bonds. A description of interatomic distances is provided.

Plunging jets play an important role in nuclear reactor safety research. In the present paper the case of the strainer clogging issue is considered. Entrained air caused by a plunging jet has an influence of the liquid flow field and on the fibre transport in the sump. In the paper the amount of entrained air is given as an inlet boundary condition according to correlations in the literature and confirmed by own experiments. The influence of entrained air on the fibre deposition pattern at the bottom of a tank and on the mixing procedure for the case of temperature differences between jet and tank water are investigated by Computational Fluid Dynamics (CFD) calculations and compared to experiments.
The presented work is part of a joint research project performed in cooperation between the University of Applied Science Zittau/Görlitz and Forschungszentrum Dresden-Rossendorf. The project deals with the experimental investigation of particle transport phenomena in coolant flow in Zittau and the development of CFD models for its simulation in Rossendorf Whereas an overview and a description of the main concepts of this project are described by Krepper et al. 2008, 2009, the focus of the actual paper is directed on the different aspects of a jet.
The entrained air has a remarkably influence on the generation of swirls und therefore on the transport and deposition of fibres. At least qualitative conclusions concerning main effects, critical regions of fibre deposition and design improvements avoiding undesired fibre deposition can be drawn. The CFD simulation of the sump flow conditions during a real accident scenario over several 1000 seconds however will fail caused by the large computational effort.

Laser-plasma wakefield based electron accelerators are expected to deliver ultrashort electron bunches with and unprecedented peak currents. However, their actual pulse duration has never been directly measured in a single-shot experiment.
We present measurements of the ultrashort duration of such electron bunches by means of THz time-domain interferometry. With data obtained using a 0.5J, 45fs, 800nm laser and a ZnTe-based electro-optical setup we demonstrate the duration of laser-accelerated, quasi-monoenergetic electron bunches (best fit of 32fs (FWHM) with a 90% upper confidence level of 38fs) to be shorter than the drive laser pulse, but similar to the plasma period.

We report on new charge calibrations and linearity tests with high-dynamic range for eight different scintillating screens typically used for detection of relativistic electrons from laser-plasma based acceleration schemes. The absolute charge calibration was done with picosecond electron bunches at the ELBE linear accelerator in Dresden. The lower detection limit in our setup for the most sensitive scintillating screen (KODAK Biomax MS) was 10 fC / mm². The screens showed a linear photon-to-charge dependency over several orders of magnitude. An onset of saturation effects starting around 10 - 100 pC / mm² was found for some of the screens. Additionally, a constant light source was employed as a luminosity reference, to simplify the transfer of a one-time absolute calibration to different experimental setups.

The characterization of the absolute number of electrons generated by laser wakefield acceleration often relies on absolutely calibrated FUJI imaging plates (IP), although their validity in the regime of extreme peak currents is untested. Here, we present an extensive study on the dependence of the sensitivity of BAS-SR and BAS-MS IP to picosecond electron bunches of varying charge of up to 60 pC, performed at the electron accelerator ELBE, making use of about three orders of magnitude of higher peak intensity than in prior studies. We demonstrate that the response of the IPs shows no saturation effect and that the BAS-SR IP sensitivity of 0.0081 photostimulated luminescence per electron number confirms surprisingly well data from previous works. However, the use of the identical readout system and handling procedures turned out to be crucial and, if unnoticed, may be an important error source.

Die Erfindung betrifft ein Verfahren, mit dessen Hilfe Kohlenstoffnanoröhrchen mit definiertem Durchmesser auf einem Substrat in gleichmäßiger Ausrichtung hergestellt werden können. Bei dem erfindungsgemäßen Verfahren wird die Eigenschaft von selbstorganisierenden Molekülen, geordnete Schichten auszubilden, ausgenutzt, um einheitliche Nanopartikel auf einem Trägersubstrat geordnet zu erzeugen und damit Nanokohlenstoffröhrchen mit definierter Anordnung auf diesem Trägersubstrat zu synthetisieren. Dazu bringt man zunächst eine Schicht aus selbstorganisierenden Molekülen auf ein Trägersubstrat auf und erzeugt auf der Schicht aus selbstorganisierenden Molekülen anorganische Nanopartikel. Anschließend wird die Schicht aus selbstorganisierenden Molekülen entfernt, wobei die anorganischen Nanopartikel auf dem Trägersubstrat zurückbleiben und an den Nanopartikeln Nanokohlenstoffröhrchen synthetisiert werden. Mit dem erfindungsgemäßen Verfahren können Kohlenstoffröhrchen mit definierter Größe in hoher Ausbeute und Einheitlichkeit hergestellt werden.

In magnetohydrodynamics ultrasound Doppler velocimetry (UDV) is applied for flow field investigations of liquid metal flows. Thereto, commercial UDV instruments are available. However, their application possibility for multi-dimensional, multi-componential flow mapping with high measurement rates is highly limited since these features cannot be applied simultaneously. Hence, we have developed an ultrasound Doppler velocimeter for measuring the two-dimensional two-componential (2d-2c) flow field of magnetically driven liquid metal. The velocimeter utilizes two identical linear ultrasound Doppler arrays arranged orthogonally to each other to facilitate the 2d-2c flow mapping in a plane of 70 x 70 mm². Each ultrasound array providing a centre frequency of 8 MHz comprises 25 transducer elements each with a piezo element size of 2.5 x 5 mm². In operation two adjacent elements are combined to a square transducer pair of 5 x 5 mm² allowing a small lateral scanning step width of 2.5 mm on the one hand and a low divergence of the ultrasound beam and accordingly a better lateral resolution up to 2 mm on the other hand. To achieve a high temporal resolution concurrently to the high spatial resolution, the measurement is parallelized as much as possible by simultaneous operation of four transducer pairs which are controlled by a special multiplex control unit. The operation principle, design considerations and the characterisation of the ultrasound Doppler array velocimeter will be reported. Flow mapping of a swirling flow in a cubic vessel with GaInSn generated by a rotating magnetic field were performed. Measurement results of a stationary as well as a periodically reversed flow will be presented.

Fluid flow in the mould cavity of the continuous casting process can be controlled by the application of magnetic fields. Experiments have been performed at room temperature using a small-scale experimental set-up with the eutectic alloy GaInSn. The ultrasound Doppler method was applied for measuring the fluid velocity in the mould. An arrangement of 10 transducers was used to determine a two-dimensional distribution of the horizontal velocity component. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the outlet flow from the submerged entry nozzle (SEN) has been studied. Our measurements deliver an authentic reproduction of the location and extension of the emergent jet and disclose the temporal behaviour of the flow inside the jet as well as in the recirculating zones. An important result of our study was the feature that a static magnetic field may give rise to non-steady, non-isotropic large-scale flow perturbations. Likewise, the flow measurements presented here did not confirm the expectation of a smooth reduction of the velocity fluctuations at the nozzle outlet due to the magnetic field. This problem requires further investigation, because the concept of an EMBR in the continuous casting process relies on a reliable damping effect of the applied magnetic field. The combination of liquid metal cold models and the ultrasound Doppler method as a powerful flow measuring technique in liquid metals appears as an important tool for an experimental investigation of such open questions and provides valuable experimental data for the validation of numerical flow simulations.

This presentation considers various situations where the flow inside a liquid metal column is driven by different configurations of AC magnetic fields. The ultrasonic Doppler method has been used to determine profiles of the fluid velocity in the ternary alloy GaInSn. The azimuthal and vertical velocity components have been measured allowing for an analysis of both a swirling flow in the horizontal planes and the flow pattern in the radial-meridional plane. In the first part we consider the transient liquid metal flow which is generated inside a cylindrical container by the discontinuous application of a rotating magnetic field (RMF) and the alternating application of subsequent RMF and TMF pulses, respectively. Such new approaches have been recently suggested for melt stirring during solidification of metal alloys in order to control the heat and mass transfer at the solidification front. The second part is concerned with an RMF-driven flow which is influenced by an oxide layer at the free surface of the metallic melt. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if the both forces are in the same order of magnitude. In that case, our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Finally, we study the combination of a travelling and a rotating magnetic field which may generate a specific flow phenomenon in form of a concentrated vortex with properties similar to a tornado. The travelling magnetic field (TMF) creates an intense converging flow at one end of the cylinder whereas the additionally superimposed rotating magnetic field (RMF) with a substantially different frequency sets the flow into rotation. The angular momentum conservation forces the rotation to intensify towards the centre of the converging flow. This phenomenon may be useful to stir floating particles into the melt.

This paper presents the new experimental facility CONCAST which was designed for modeling fluid flow and transport processes in the continuous casting of steel. The facility operates at temperatures of 200°C - 400°C by using the low melting point alloy SnBi. The main parameters of the facility, including the dimensions of the test sections, will be given. The resultant possibilities with respect to flow investigations in the tundish, in the submerged entry nozzle, and in the mould will be discussed. Over the period of assembling and commissioning the CONCAST facility, the small-scale set-up Mini-CONCAST was employed which uses the alloy GaInSn that is liquid at room temperatures. At this precursory facility an experimental program was started which is focused on quantitative flow measurements in the mould and in the submerged entry nozzle (SEN). The Ultrasound Doppler Velocimetry (UDV) and the Contactless Inductive Flow Tomography (CIFT) were applied to determine the flow structure within the mould. First experimental results will be presented here for a single and a two-phase flow in which argon gas bubbles were injected at the inlet of the SEN. According to the concept of the electromagnetic brake the impact of a DC magnetic field on the emergent jet flow from the SEN has been studied.

Die Erfindung betrifft ein Verfahren zur Reduzierung von Temperaturfluktuationen in Halbleiter- oder Metall-Schmelzen. Das Hauptinteresse gilt vor allem Schmelzen in Kristallzüchtungsprozessen wie Gallium-Arsenid (GaAs), Indium-Phosphid (InP) oder Silizium (Si).
Mit der Erfindung werden große Temperaturfluktuationen in der Schmelze unterdrückt, die den Prozess des Kristallwachstums stören bzw. teilsweise unmöglich machen.
Durch den Einsatz dieses Verfahrens können deutlich größere Schmelzvolumina als heute üblich verwendet werden.

Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagneti-schen Rühren elektrisch leitfähiger Flüssigkeiten (2) unter Verwendung eines in der horizontalen Ebene rotierenden Magnetfeldes RMF (34) und eines dazu in vertikaler Richtung wandernden Magnetfeldes WMF (47).

Die Aufgabe besteht darin, dass unsymmetrische Strömungsstrukturen in mit Schmelzen gefüllten Behältern, insbesondere zu Beginn und während des Ver-laufs der Erstarrung vermieden werden. Außerdem sollen eine effektive Durch-mischung der Flüssigkeit und/oder eine kontrollierte Erstarrung metallischer Le-gierungen unter Vermeidung der Ausbildung von Entmischungszonen im Erstar-rungsgefüge erreicht werden.

Die Lösung besteht darin, dass sowohl das rotierende Magnetfeld RMF (34) als auch das wandernde Magnetfeld WMF (47) diskontinuierlich in Form von zeitlich begrenzten und einstellbaren Periodendauern (TP,RMF,TP,WMF) und abwechselnd zeitlich nacheinander über zugehörige Induktionsspulen (31,32,33;41,42,43,44, 45,46) zugeschaltet werden.

Die Erfindung betrifft ein Verfahren und eine Einrichtung zum elektromagnetischen Rühren von elektrisch leitenden Flüssigkeiten (2,21,22) im flüssigen Zustand und/oder im Zustand des Beginns der Erstarrung der Flüssigkeit (2,21,22) unter Verwendung eines in der horizontalen Ebene eine Lorentzkraft (FL) erzeugenden, rotierenden Magnetfeldes.
Die Aufgabe besteht darin, dass eine intensive dreidimensionale Strömung im In-nern der Flüssigkeit zum Durchmischen im flüssigen Zustand bis in die unmittelbare Umgebung von Erstarrungsfronten erreicht und gleichzeitig eine ungestörte, freie Oberfläche der Flüssigkeit gewährleistet werden. ...

Die Erfindung betrifft eine Flüssigmetall-Ionenquelle (LMIS) zur Erzeugung von Lithiumionenstrahlen, insbesondere das den Emitter benetzende Quellenmaterial einer derartigen Ionenquelle.
Die Erfindung beinhaltet Flüssigmetall-Ionenquellen, deren Emitter mit einer definierten Legierung aus Lithium und einem oder mehreren der Elemente Gallium, Indium und Wismut als Quellenmaterial benetzt ist.
Mit derart ausgestatteten Flüssigmetall-Ionenquellen ist es möglich, langzeitig einen stabilen Ionenstrom, der im ausreichendem Maße aus Lithiumionen besteht, zu erhalten.
Die Bestandteile der Legierung im Zusammenspiel mit dem niedrigen Schmelzpunkt führen dazu, dass keine chemischen Reaktionen mit dem Emitter- und Heizermaterial auftreten sowie die Legierungsoberfläche relativ langsam an Luft korrodiert.

The bis(salicylhydroxamato), bis(benzohydroxamato), and bis(benzoato) complexes of UO22+ in aqueous solution have been investigated in a combined experimental and computational effort using extended X-ray absorption fine structure and UV−vis spectroscopy, and density functional theory (DFT) techniques, respectively. Experimental data indicates 5-fold UO22+ coordination with mean equatorial U−O distances of 2.42 and 2.40 Å for the salicyl- and benzohydroxamate systems, respectively. DFT calculations on microsolvated model systems [UO2L2OH2] indicate UO22+ eta-2-chelation via the hydroxamate and benzoate oxygen atoms in excellent agreement with experimental data; calculated complex stabilities support that UO22+ prefers hydroxamate over carboxylate coordination. The 414 nm absorption band of UO22+ in aqueous solution is blue-shifted to 390 and 386 nm upon complexation by salicyl- and benzohydroxamate, respectively. Calculated time-dependent DFT excitation energies of [UO2L2OH2], however, occasionally fail to reproduce accurately experimental UV−vis spectra, which are dominated by L− -to- UO22+ charge-transfer contributions. We additionally show that the UVI large-core pseudopotential approximation recently developed by some of the authors can routinely be applied for electronic structure calculations not involving uranium 5f occupations significantly different from UVI.

Plutonium and other long-lived radioactive actinides are produced in light water reactors (LWR) using conventional fuel. "Innovative" fuel matrices may reduce the breeding of these nuclides. However, essential LWR safety features have to be preserved, which restricts the possibilities for new fuel-carrying matrices. Respective fuel-assembly and LWR-core safety studies indicate practicable new fuel options for the near future.

Colloid-borne transport of actinides in aquifer systems is a topic of major interest in view of long-term risk assessments for underground radwaste repositories. In particular, complexation with aquatic humic substances can be decisive for the mobility of radiotoxic metals [1,2]. Depending on geochemical parameters, migration can be both enhanced and reduced. The respective conditions need to be identified, and models must be able to describe such complex systems by few parameters. According to the Linear Additive Model [3], total metal adsorption in the presence of humic matter can be calculated by linking parameters for the adsorption of both components and their interaction with each other. The basics of this approach are also implicit in advanced transport models [4].
In our study, the influence of humic acid on metal adsorption onto three clay materials (montmorillonite, illite, Opalinus clay) as a function of pH was investigated for Tb(III) as an analogue of trivalent actinides. 160Tb and 131I-labelled humic acid were used as radiotracers, allowing experiments at very low concentrations to mimic realistic conditions. For all clay materials under study, the presence of humic acid caused an increase in metal adsorption at neutral and acidic pH, i.e., metal desorption from clay barriers in consequence of acidification processes is generally counteracted in the presence of humic matter. Based on the pH-dependences of humic acid adsorption and Tb-humate complexation, this can be qualitatively explained by co-adsorption of humic-bound Tb. Quantitative estimates by means of the Linear Additive Model were, however, not successful.
In equilibrium models (Kd models), it is presumed that reaction rates for adsorption and desorption are both high enough to ensure a steady local equilibrium under flow conditions. Regarding the adsorption of humic substances onto geological materials, however, there is a lack of clarity concerning the dynamic character of this process. Recoveries in column experiments suggest a limited reversibility. In order to gain direct insight into the dynamics of the adsorption-desorption equilibrium, we conducted tracer exchange experiments with 14C-labelled humic acid. A negligible amount of the radiotracer was contacted with equilibrated systems of kaolinite and non-labelled humic acid for different periods of time. Tracer exchange at surface saturation provided evidence of a reversible process, but the time needed until the dynamic equilibrium was quantitatively represented by the tracer turned out to be much longer than the time needed to attain the overall adsorption equilibrium. This discrepancy between exchange kinetics and adsorption kinetics, which is indicative of a very slow desorption rate, has to be taken into consideration when the equilibrium condition is assigned to a maximum flow rate in transport systems.

In order to investigate the two-phase flow behaviour in a complex reactor-typical geometry and to supply suitable data for CFD code validation, a model of the hot leg of a pressurised water reactor was built at Helmholtz-Zentrum Dresden Rossendorf (HZDR). The hot leg model is devoted to optical measurement techniques, therefore, a flat test section design was chosen and equipped with large windows. In order to enable the operation at high pressures, the test section is installed in the pressure chamber of the TOPFLOW test facility of HZDR, which is used to perform the experiments under pressure equilibrium with the inside atmosphere. Counter-current flow limitation (CCFL) experiments were performed, simulating the reflux-condenser cooling mode appearing in small break LOCA scenarios. The fluids used were air and water at room temperature and pressures of up to 3.0 bar, as well as steam and water at pressures of up to 50 bar and the corresponding saturation temperature of 264°C. One selected 50 bar experiment is presented in detail: the observed behaviour is analysed and illustrated by typical high-speed camera images of the flow.

Furthermore, the flooding characteristics obtained from the different experimental runs are presented in terms of the Wallis parameter and Kutateladze number, which are commonly used in the literature. However, a discrepancy was first observed between the air/water and steam/water series. Further investigations show that the steam was probably wet due to heat losses and to liquid entrainment from the heater circuit. Consequently, a correction of the steam measurements was required. The amount of parasitic water was evaluated indirectly over the zero liquid penetration noticed in the CCFL diagram. Finally, the experimental results confirm that the Wallis similarity is appropriate to scale flooding in the hot leg of a pressurised water reactor over a wide range of pressure and temperature conditions.

Feasibility of Compton camera for monitoring of ion beam therapy as well as for recognition of weak radioactive sources in a security interests application was investigated. First reconstruction results are presented.

Die Auflösung von Gips, als ein Vertreter für Minerale mit einer hohen Auflösungsrate, wurde unter wassergesättigten und wasserungesättigten Bedingungen anhand von Batch- und Säulenexperimenten untersucht. Die erhaltenen experimentellen Daten wurden den numerischen Lösungen gegenübergestellt und mit ihnen verglichen. Die Säulenexperimente wurden mit einer Fließgeschwindigkeit des Wassers von υ = 0,015 cm/h durchgeführt. Es zeigte sich, dass unter wasserungesättigten Bedingungen nur ein sehr kleiner Teil der Oberfläche der Körner von 2,2 % als reaktiver Part fungiert. Weiterhin zeigten die Ergebnisse, dass die Auflösung von Gips in der Säule hauptsächlich durch die Darcy-Geschwindigkeit bestimmt wird.

The dissolution of gypsum under water-saturated and unsaturated conditions was studied using batch and column experiments. The experimental results were successfully verified with the use of model calculations. The column experiments were performed with a water flow velocity of 0.015 cm/h. Comparing the dissolution experiments, we conclude that under unsaturated conditions only 2.2 % of the grain surface is chemically reactive. Experiments and calculations show that gypsum dissolution in the columns is mainly determined by the Darcian velocity.

no abstract available

An insulating Zn_0.96Co_0.04O film on a highly conducting Zn_0.99Al_0.01O layer has been deposited on a-plane sapphire substrate by pulsed laser
deposition to study the magnetoresistance (MR) of depleted Co-doped ZnO with low electron concentration (about 1.5x10¹⁷ cm^-3 at 21 K). Au ohmic contact and Pd Schottky contact were deposited on the Zn_0.99Al_0.01O and Zn_0.96Co_0.04O layer, respectively. Positive magnetoresistance (MR) of 30 % with current of 10^-6 A was observed at 5 K. The positive MR decreases drastically at 5 K and changes to negative MR at 50 K with increasing current, which is considered to be due to the bias voltage control of the electron concentration in the Zn_0.96Co_0.04O layer. Our work demonstrates the electrically controllable magnetotransport behavior in insulating ZnO-based diluted magnetic semiconductors.

Purpose: To allow for reproducible rodent positioning using molding in multimodal tomographic imaging (positron emission tomography (PET), magnetic resonance imaging/spectroscopy (MRI/MRS)), minimization of magnetic field inhomogeneity during MRI investigations of peripheral structures, and reproducible positioning for subsequent histological sectioning of the separated tumor.
Materials and Methods: Chemical shift imaging (CSI) studies were carried out using phantoms and NMRI nu/nu mice bearing subcutaneous tumors. For embedding, three different materials were used: i) alginate, ii) gelatin, and iii) a mixture of wheat flour and salt. The animals were placed in an animal chamber including position markers visible by MRI and PET. The frozen embedded explanted tumors were sliced and examined autoradiographically as well as histologically.
Results: Alginate showed a substantial improvement of magnetic field homogeneity and histological sectioning was superior to the other methods. This embedding led to a significant reduction of the full width at half maximum (FWHM) of the water peak in the peripheral rim of the tumor in comparison to the same peak FWHM without embedding (41+-10 Hz vs. 80+-20 Hz).
Conclusions: Our research shows that animal positioning in an imaging chamber together with alginate embedding allows high quality multimodality investigations including coregistration of MRI/MRS, PET, and histological images.

We performed photoluminescence (PL) measurements on Si surface irradiated with 60 keV Ar+ at a fixed ion fluence of E18 ions/cm² for two angles of ion incidence, namely 0° (with respect to surface normal of the sample) and 60°. Periodically modulated ripple morphology is observed for a 60° angle of ion incidence. The ripple microstructure consists of amorphous structure on the rear slope and a comparatively thicker amorphous layer with Ar bubbles on the front slope, whereas a uniformly thick amorphous layer with relatively large bubbles is created under normal bombardment. Room temperature PL of the rippled Si shows a visible band with a peak at ~700 nm and a strong infrared (IR) band having a peak at ~1000 nm. However, the visible PL was very weak and no IR emission was observed for normally irradiated Si.

Understanding of the mechanisms of donor impurity incorporation, its electrical activation and charge carrier transport in transparent conducting oxides (TCO) is required for further improvement of functionality of this class of materials. The present work focuses on investigation of indium oxide (IO), Sn-doped indium oxide (ITO), ZnO, and ZnO:Al (AZO) films grown by reactive pulsed magnetron sputtering (RPMS) with a precise control of the oxygen partial pressure at substrate temperatures, TS, ranging from RT to 550 °C. In order to explore potential advantages of RPMS, the relationship between the deposition parameters and structure, phase composition and physical properties of these TCOs was investigated. The films were characterized by spectroscopic ellipsometry, Hall effect measurements, X-ray diffraction (XRD) and, in case of ZnO and AZO films, by X-ray absorption near edge structures (XANES). The Sn concentration in ITO was determined by Auger analysis, while the Al concentration in ZnO matrix was estimated by elastic recoil detection analysis and Rutherford back scattering.
The comparison of the real-time behavior of the IO and ITO film structure and electrical properties during annealing provides a direct evidence of Sn donor activation (with an estimated efficiency of 40%) in ITO due to amorphous-to-crystalline transition. The ITO film crystallinity always improves with increasing substrate temperature or during isothermal annealing, with the electrical resistivity decreasing. In contrast, the electrical resistivity of AZO films shows a clear minimum at an optimum substrate temperature (200-400 °C), which depends on metal/oxygen flux ratio and correlates with a maximum in crystallinity (grain size). In this case, the highest mobility value of 46 cm2 V-1 s-1 is comparable to the best values achieved in AZO films grown by less cost-efficient techniques. This value is achieved at the free electron density of 6x1020 cm-3 which corresponds to maximum ~30% electrical activation of Al impurity. At higher temperatures, the AZO electrical properties and crystalline quality deteriorate abruptly according to the following mechanism. Increasing TS above its optimum value leads to a higher Al concentration in the AZO films, which exceeds the solubility limit and triggers the formation of an insulating metastable homologous (ZnO)3Al2O3 phase. This phase impedes crystal growth and causes a significant increase of free electron scattering both at grain boundaries and inclusions of this phase. In order to enable the growth of low-resistivity AZO films in a wider range of TS, lower metal/oxygen flux ratios should be used. The proposed approach to minimizing the influence of this undesirable phase may also be applied to other deposition methods of AZO involving high-energy particle bombardment.

This Presentation Gives An Overview On Recent Knowledge An Actinide Coordination, Speciation Complex Formation In Solutions

The availability of 3rd generation synchrotrons in Europe has strongly enhanced the use of Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy to determine the structure of systems that are not accessible with X-ray diffraction or NMR techniques alone. This presentation intends to demonstrate how the combination of EXAFS, UV-Vis and XRD provide insight in the coordination of solution species. The combination of EXAFS and UV-Vis is often successful, because both techniques are sensitive in the same concentration range. Statistical approaches like factor analysis allow the analysis of large series of titration data providing the coordination of the solution species as well as species distribution functions. At the other hand, XRD is nowadays a standard technique to reveal atomic structures of single crystals. However, there is often no link between structures in solution and its solid state structure. The capability of EXAFS to detect both, the near-order structure in solution and solid state, provides the unique opportunity to follow structural modifications during the crystallization process and to use the solid state structure or its modifications to reveal the coordination of metal complexes in solution.

no abstract available

Recently we could demonstrate that advanced SOI material can be treated in advantageous manner regarding USJ formation [1]. Especially, strained Si and SiGe/Si heterostructures on insulator are promising channel materials for future nanoelectronics devices. Their successful integration into new device architectures depends on the ability of forming ultra shallow and ultra steep junctions. We present results for dopant activation in SOI, sSOI, HOI and sHOI [2]. FLA allows complete suppression of diffusion while obtaining sheet resistances lower than 500 Ω/□ in both, SOI and sSOI. Strained and unstrained SiGe heterostructures indicated significant diffusional broadening of Sb implant profiles and low electrical activation. In contrast, B shows higher activation but significant dopant loss in the near surface region. Moreover, we demonstrate that, after diamond and silicon, the third elemental group-IV semiconductor, germanium, exhibits superconductivity at ambient pressure [3]. For the first time, techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material, i.e. a highly Ga-doped Ge (Ge:Ga) layer in near-intrinsic Ge. It is shown that superconductivity can be generated and tailored in the Ge host at temperatures as high as 0.5 K. Results of critical-field measurements demonstrate the quasi-two-dimensional character of superconductivity in the 60 nm thick Ge:Ga layer.

[1] F. Lanzerath, D. Buca, H. Trinkaus, M. Goryll, S. Mantl, J. Knoch, U. Breuer, W. Skorupa, B. Ghyselen, J. Appl. Phys. 104 (2008), 044908

[2] R. A. Minamisava, W. Heiermann, D. Buca, H. Trinkaus, J. Hartmann, W. Skorupa, U. Breuer, B. Ghyselen, S. Mantl, Proc. 215th ECS Meeting, Vol. 19, Issue 1, May 24-29, 2009

[3] T. Herrmannsdörfer, V. Heera, O. Ignatchik, M. Uhlarz, A. Mücklich, M. Posselt, H. Reuther, B. Schmidt, K.-H. Heinig, W, . Skorupa, M. Voelskow, C. Wündisch, R. Skrotzki, M. Helm, J. Wosnitza, Phys. Rev. Lett., 102 (2009) 217003

Surely in closed relation to the invention of the first bipolar transistor, W. Shockley filed also the first patent regarding the doping of semiconductors by ion implantation. Since that time ion beam engineering has been taken a tremendous development getting the dominant doping method of choice in chip technology. Automatically, ion beam engineering took also the move to nanotechnology with the Moore-law based miniaturisation of electronic devices.
In this lecture I will present after a short introduction into the basics of ion-solid interaction with a step-by-step philosophy the move to nanotechnology starting (1) with thinning of functional layers, then (2) moving to the world of nanowires and nanoclusters to reach finally (3) the treatment of materials with single ions. The latter item points already to dimensions of the subnano regime, to atom engineering (or, if you like, picotechnology)!
As well known, ion beam engineering is always closely connected to annealing treatments to remove the radiation-induced damage effects from the ion-treated material. With the transition to nanodimensions there developed, at least in silicon chiptechnology after the year of 2000, a need for shorter and shorter annealing times to keep the needed nanodimensions during the processing of the chips. In this context flash lamp annealing in the millisecond range will be included into the discussion of some of the topics.
The Rossendorf research center with one of the worldwide largest ion beam centers in its walls has developed a large variety of activities in the course of the last years to move its expertise in ion beam processing and short time annealing into the world of nanotechnology. Examples for the different above-mentioned approaches mostly based on Rossendorf activities, that will be touched in the lecture, are:

(1) Superconducting germanium, Doping in SOI-chips, Superthin insulator in SOI
(2) Silicon nanowires, surface patterning for ripples, nanoclusters for silicon-based light emission, diluted magnetic semiconductors (DMS)
(3) Highly charged ions etc.: Can they flatten the path to a quantum computer…?

A cavity layer or nano-bubble layer introduced by He implantation before the oxygen implantation collects the implanted oxygen and increases the oxygen concentration. The average size and density of the oxygen precipitates formed in the initial stage of the Separation-by-implanted-oxygen (SIMOX) process is conform with the size and density of the cavities pre-formed by He implantation and annealing. The gettering ability of the cavity layer for oxygen is directly related to the area of the internal surface of the cavities. A nano-bubble layer accumulates oxygen in a very narrow range occurring between the damage maximum, DP, and the mean projected ion range, RP. Such a nano-bubble layer is most efficient in oxygen gettering due to their larger area of the internal surface and the small size of the oxide precipitates initially formed at the bubbles.

In this work, refractive index and extinction coefficient spectra of germanium nanoclusters - rich SiO2 layers have been determined using variable angle spectroscopic ellipsometry (VASE) in the 2501000 nm range. The samples were produced by Ge+ ion implantation into SiO2 layers on Si substrates and subsequent annealing at temperatures from 700 to 1100 degrees C. It is known from previous investigations of similar samples that the Ge nanoclusterization process starts already at 800 degrees C and spherical Ge nanocrystallites 5-8 nm in diameter are observed in the SiO2 layers after annealing for I h at even higher temperatures of 1000-1100 degrees C. Rutherford backscattering spectrometry (RBS) was employed to measure the Ge atom concentration depth profiles in the studied samples. The RBS results helped us choose realistic models for the VASE analysis which were necessary for a proper interpretation of the VASE data. It has been found that the refraction index value for the SiO2/Si layer increases after Ge implantation. This effect can be explained by a defect-dependent compaction of ion-bombarded layers. A band's tail in the extinction coefficient spectra for all the samples is observed which originates from a strong ultraviolet absorption band at 6.8 eV due to a Germanium Oxygen-Deficiency Center (GeODC) and/or a Ge-E'center in SiO2. The annealing process results in the emergence of weaker extinction coefficient bands in the 400-600 nm region, associated with direct band-to-band transitions in Ge nanostructures. Transformation of these bands, including their blue-shift with the increasing annealing temperature could be explained via a quantum-confinement mechanism, by size and structural changes in Ge nanostructures.

6H-SiC single crystals were implanted with 450 keV Al+-ions to a fluence of 3.4 x 10¹⁵ cm^-2, and in a separate experiment subjected to multiple Al+ implantations with the four energies: 450, 240, 115 and 50 keV and different fluences to obtain rectangular-like depth distributions of Al in SiC. The implantations were performed along [0 0 0 1] channeling and non-channeling ("random") directions. Subsequently, the samples were annealed for 10 min at 1650 degrees C in an argon atmosphere. The depth profiles of the implanted Al atoms were obtained by secondary ion mass spectrometry (SIMS). Following implantation and annealing, the samples were beveled by mechanical polishing. Confocal micro-Raman spectroscopic investigations were performed with a 532 nm wavelength laser beam of a 1 mu m focus diameter. The technique was used to determine precisely the depth profiles of TO and LO phonon lines intensity in the beveled samples to a depth of about 2000 nm. Micro-Raman spectroscopy was also found to be useful in monitoring very low levels of disorder remaining in the Al+ implanted and annealed 6H-SiC samples. The micro-Raman technique combined with sample beveling also made it possible the determination of optical absorption coefficient profiles in implanted subsurface layers.

Unintentionally doped n-type zinc oxide (ZnC) single crystal was implanted by arsenic ions with fluence of 10¹⁴cm^-2 at room temperature followed by post-implantation annealing up to 900 degrees C. Rectifying property was not observed in the As-implanted or the post-implantation annealed samples. Au Schottky contact was fabricated on the samples with the H2O2 pre-treatment. Deep-level transient spectroscopy measurements were performed on the Schottky contacts to study the deep-level defects and their thermal evolution. (C) 2008 Elsevier Ltd. All rights reserved.

Nanostructured thin films are of growing relevance for numerous applications including magnetic recording media[1] and photovoltaics.[2] Control of the film and substrate morphology at the submicron scale enables the fabrication of functional thin films with tailored magnetic,[3,4,5] optical,[6,7] chemical[8,9] or biological properties.[10] Various methods have been utilized to fabricate those nanostructured thin films with well defined morphology. In the past, most of these methods have been based on lithographic techniques such as electron beam,[4] nanosphere,[6] or colloidal lithography,[8] as well as on spontaneous pattern formation during epitaxial growth[5,10] or thermal annealing.[7] However, these methods often suffer from various shortcomings, e.g. low throughput, the need of high temperatures, or a restriction to isotropic patterns. An alternative approach for creating topological nanopatterns on solid surfaces that overcomes these shortcomings uses the self-organized formation of periodic nanopatterns during broad beam ion sputtering.

The complex formation of europium(III) with the zwitterionic form of amino acids (alanine, phenylalanine and threonine) has been studied in aqueous solution. Measurements were performed at I = 0.1 M (NaCl/NaClO4), room temperature and trace metal concentrations in the range of pH 2 to 8 using UV/vis and time-resolved laser-induced fluorescence spectroscopy. While complexation leads to a significant luminescence enhancement in the emission spectrum of the metal ion, absorption in the UV/vis spectrum of the amino acid (AA) decreases. As zwitterionic species (AAH) all three ligands form weak complexes with 1:1 stoichiometry and a general formulae of EuAAH3+ with the metal. The complex stability constants were determined to be log K ~ 1 for all complexes, indicating the negligible contribution of the amino acid side chain to the complex formation reaction.

Die Erfindung betrifft einen dispersionsarmen Ultraschallsensor zur Messung von lokalen Strömungsgeschwindigkeiten in flüssigen Schmelzen bei hohen Temperaturen. Durch die Erfindung soll ein Ultraschallsensor zur Durchführung lokaler kontinuierlicher und zuverlässiger Geschwindigkeitsmessungen in heißen Schmelzen (T > 200°C) geschaffen werden. Erreicht wird das dadurch, dass der dispersionsarme Ultraschallsensor einen mit dem piezoelektrischen Wandler (1) verbundenen Ultraschallwellenleiter (2) aus einem Material enthält, das in einem für den Einsatzfall relevanten Temperaturbereich oberhalb von 200 °C eine geringe akustische Dämpfung aufweist sowie gegenüber der Schmelze chemisch resistent ist und dass die der Schmelze zugewandte Stirnfläche des Ultraschallwellenleiters (2) verschlossen und von der Schmelze benetzbar ist.

Aufgabe der vorliegenden Erfindung ist es, eine Anordnung zur Messung der Temperaturverteilung in einem Messquerschnitt anzugeben, mit der vor allem Flüssigkeits- oder Gasströmungen mit geringerem Aufwand vor allem an Verkabelung und Auswerteelektronik untersucht werden können.
Die Lösung beinhaltet im Wesentlichen, dass ein Gitter von draht- oder stabförmigen elektrischen Leitern, die innerhalb eines Sensorahmens (1) elektrisch gegeneinander und gegen das Erdpotential isoliert in zwei koplanaren Ebenen im Abstand von wenigen Millimetern aufgespannt sind, wobei die elektrischen Leiter der einen Ebene als Anregungselektroden (2) ausgeführt und parallel zueinander orientiert sind, die elektrischen Leiter der anderen Ebene als Empfängerelektroden (3) ausgebildet und ebenfalls parallel zueinander orientiert sind, sowie die Anregungselektroden (2) in einem Winkel größer 0° zu den Empfängerelektroden (3) orientiert sind und somit in der Draufsicht ein Gitter von Kreuzungspunkten bilden und die Anregungselektroden (2) und die Empfängerelektroden (3) in jedem Kreuzungspunkt des Gitters durch einen Festkörper mit temperaturabhänger elektrischer Impedanz elektrisch miteinander verbunden sind.

Der Erfindung liegt die Aufgabe zugrunde, einen mehrfarbig emittierenden Si-basierten Lichtemitter zu realisieren, der einfach aufgebaut und mit nur einer Seltenerde-Dotierung herstellbar ist.
Die Erfindung geht aus von einem Si-basierten Lichtemitter, der aus einem frontseitigen Metallkontakt, einer dielektrischen Schutzschicht, einem Si-Substrat und einer rückseitigen, leitfähigen Kontaktschicht besteht, und beinhaltet im Wesentlichen, dass sich zwischen Si-Substrat (1) und dielektrischer Schutzschicht (4) innerhalb einer dünnen SiO2-Schicht (3), die durch lokale thermische Oxidation innerhalb einer durch eine dickere SiO2-Schicht gebildeten Umgebung erzeugt wurde, Europium-Lumineszenzzentren (5) befinden und dass elektrische Anschlüsse an Metallkontakt (6) und rückseitiger Aluminiumschicht (8) vorgesehen sind, die mit einer Stromquelle zur Beaufschlagung mit einem veränderbaren, über eine wählbare Zeit konstanten Strom verbunden sind.

Aufgabe der Erfindung ist es, eine Anordnung zur Röntgen-Computertomographie anzugeben, die ohne einen axialen Versatz zwischen Brennfleckbahn und Röntgendetektorbogen auskommt.
Die Erfindung beinhaltet, dass der Röntgendetektorbogen (2) und das Target (1) um den Untersuchungsquerschnitt innerhalb einer Bestrahlungsebene angeordnet sind, so dass die vom Elektronenstrahl (3) des Elektronenstrahlerzeugers (6) durch Strahlablenkung erzeugten Röntgenbrennflecke mit den aktiven Detektorelementen innerhalb einer axialen Ebene, der Durchstrahlungsebene (5), liegen, der Röntgendetektorbogen (2) in radialer Richtung hinter dem Target (1) angeordnet ist, so dass jeder von einer Brennfleckposition auf dem Target (1) zu einem Detektorelement des Röntgendetektorbogens (2) gedachter Röntgenstrahl im Bereich der winkelmäßigen Überlappung von Target (1) und Röntgendektorbogen (2) das in Strahlrichtung vor dem Auftreffpunkt auf dem Röntgendektorbogen (2) liegende Target (1) durchdringt, das Target (1) aus einem Targetkörper (7) besteht, der vorzugsweise durch ein Material geringer Kernladungszahl und hohem Wärmespeicher- bzw. Wärmeleitvermögen gebildet wird, auf der dem Elektronenstrahl zugewandten Seite des Targetkörpers (7) eine elektronenbremsende Materialschicht (8) vorzugsweise aus einem hochschmelzenden Material hoher Kernladungszahl aufgebracht ist.

By grazing metal vapor deposition perpendicular to ripples of pre-patterned, oxidized Si surfaces, a chain-like formation of the metal nanoclusters along the ripples have been observed. The structures are located on the slopes which point towards the evaporation source. The self-ordering of metal nanostructure has been observed neither for normal deposition nor for low-angle deposition parallel to the ripple direction. The features of the metal nanostructure depend strongly on the evaporation angle.
In this work, we studied the process of silver deposition on pre-patterned, oxidized Si surfaces by means of 3D lattice kinetic Monte Carlo simulations. The experimentally observed Ag nanostructures could be reproduced. It was shown that the extremely low sticking probability of deposited Ag together with a slope-dependent deposition rate leads to a strongly selective Ag nanocluster nucleation on the surface because
the nucleation rate depends on the square of the adatom concentration.

Das Entsorgungskonzept für radioaktiven Abfall in Deutschland ist die Endlagerung in tiefen geologischen Formationen, um die Menschen und die Umwelt im Allgemeinen vor der Radioaktivität zu schützen. Mithilfe eines Multi-Barrier-Systems bestehend aus geologischen und technischen Barrieren soll der Abfall möglichst lange, isoliert von der Biosphäre, gelagert werden. In Deutschland stehen dazu drei mögliche Wirtsgesteine zur Verfügung (Salz, Granit, Ton). Für Salz gibt es bereits eine breite vorhandene Datenbasis. Derzeit werden die Untersuchungen am Ton intensiviert, um letztendlich zwischen drei Gesteinsformationen bezüglich ihrer Eignung als Endlager wählen zu können. Diese Untersuchungen werden am Beispiel Opalinuston (natürlicher Ton aus Mont Terri, Schweiz) und dem System U(VI) - Huminsäure - Opalinuston näher erläutert. Insbesondere der Einfluss des im Ton enthaltenen Calcits auf die U(VI)- und Huminsäurespeziation wird gezeigt. Dazu werden explizit Ergebnisse von Sorptions- und Diffusionsversuchen vorgestellt.

The role of viscous flow of amorphous Si, Ge, and SiO2 for surface pattern formation under ion irradiation is still a matter of discussions. Strong indications for viscous flow exist for ion energies >10keV. A theoretical treatment of ion-induced surface patterning including viscous flow is extremely difficult because mechanisms of surface patterning like curvature dependent ion erosion and diffusion cannot be separated. Therefore, a program package has been developed which allows a simultaneous treatment of the collision cascades, thermally activated processes and viscous flow. The 3D atom relocation by the collision cascades are calculated in the Binary Collision Approximation, the thermally activated relaxation of energetic atomic configurations as well as diffusive processes are simulated be a very efficient bit-coded kinetic 3D Monte Carlo algorithm, and the viscous flow is taken into account by a crude model allowing distant annihilation of interstitials at the surface. The simulations prove a significant contribution of viscous flow to surface patterning. A comparison of simulated pattern with experimental results will be presented.

The objective of WP2 is the development and testing of redox determination methods using different type of electrodes as well as optodes (optical sensors) in order to provide a broad and solid scientific-technical basis for the application of such. In combination with chemical analysis and associated thermodynamic modeling the redox state of systems (relevant for nuclear waste repositories) is assessed. The overall goals are (i) redox determination methods specifically designed for environmental applications, and (ii) a broader information base for interpretation of system conditions.

Atomistic understanding of surface morphology evolution induced by ion beam sputtering is still strongly limited. Available continuum models cannot explain microscopic processes during ion beam irradiation. Also atomistic simulation cannot describe pattern dynamics in the spatiotemporal scales of experiments.
Therefore, we develop a novel program package which unifies the collision cascade with kinetic Monte-Carlo simulations. The 3D atom relocations were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Low energy (up to 5 keV) ion sputtering simulations have been performed on simulation cell of about 17 million atoms, where irradiation fluence goes up to few 1018 cm^-2. The pattern topography has been study by means of various intensive parameters like incidence angle, ion beam energy, ion fluence, and migration energy of surface defects. Moreover, scaling behaviour of surface roughness and pattern periodicity has been analysed.
Finally, we compare our results with experiments as well as with continuum theory.

Bakterielle Hüllproteine (S-Layer-Proteine) besitzen eine großen technische Anwendbarkeit. Eine ist die als Matrix für die Synthese von photokatalytisch aktiven Nanopartikeln wie ZnO und TiO2. Verwendung finden die mit ZnO oder TiO2 beschichteten Hüllproteine beim Abbau von Arzneimittelrückständen wie Diclofenac in Abwässern unter Anwendung von UV-Licht. Ein besonderes Augenmerk richtet sich auf die Analytik der Abbauprodukte bei der Aufspaltung von Diclofenac. Der folgende Vortrag soll einen Überblick über den Einsatz von HPLC zu Analyse des photokatalytischen Abbaus von Diclofenac geben.

Until now, damage formation and thermally activated relaxation are calculated by different atomistic methods like Binary Collision Approximation (BCA) and kinetic Monte Carlo (kMC), respectively. However, frequently damage formation and relaxation happens simultaneously. Molecular Dynamics (MD), which treats both processes, can not describe them on experimental spatiotemporal scales due to insufficient computer power. Here, an unified BCA-kMC simulation method will be presented and applied to ion-induced mixing and phase separation of intermetallic compounds. In particular we will show the importance of employing these two approaches into one algorithm by studies of two contrary systems. We irradiate Al/Pb with He ions causing ballistic interface mixing. Additionally, creation of Al and Pb clusters can be observed due to the bulk thermal diffusion driving the system to the equilibrium. On the other hand, strongly enhanced intermixing in an ordering compound, like PtCo, after the He irradiation is observed. This effect cannot be understood by purely collisional results alone, and therefore the high miscibility of the system has to be taken into account.

Aiming at a more complete but still efficient atomistic calculation of the action of low-energy ion impacts on surfaces, a novel program package has been developed which unifies the calculation of the collision cascade with kinetic 3D Monte Carlo simulations. The 3D atom relocations by the collision cascade were calculated in the Binary Collision Approximation (BCA), whereas the thermally activated relaxation of energetic atomic configurations as well as diffusive processes were simulated by a very efficient bit-coded kinetic 3D Monte Carlo code.
Here, we analyse the impact of bulk processes like vacancy and interstitial creation, defects annihilation and migration as well as ion erosion on surface morphology. In particular, we prove the importance of a complete description of the ion impacts. Collisional and thermally activated processes occurring simultaneously are important for the ripple formation and propagation. The novel program was applied to ripple formation on Si substrates under 1 keV Ar+ irradiation for fluences up to a few 10¹⁸ cm^-2. Besides the angle of ion incidence, the crucial parameters deciding about ripple coarsening are migration energies of surface defects.
So far, simulation cell sizes of 100x100x50 nm³ with about 17 million atoms allow ripple formation up to 25 nm wavelength, thus direct comparison with experiment can be done.
Additionally, the scaling behaviour of the surface pattern wavelength and roughness has been studied.

The Bradley-Harper model assumes that under ion irradiation surface pattern develop by a competition between surface curvature dependent ion erosion and surface curvature driven diffusion. By our contribution it will be shown that the curvature dependence in Sigmund’s sputter theory is not the only possible origin for surface pattern formation. For instance, very low energy ion irradiation does not create collision cascades which justifies the Bradley-Harper model, but produces rather some defects at the surface.
Therefore, simple surface defect (adatoms, vacancies) production procedures are applied in combination with kinetic 3D Monte Carlo simulations of defect recombination and diffusion. Depending on the model parameters (ion incidence angle, temperature, defect creation,…) ripples perpendicular or parallel to the ion beam or even dots have been found.

We show how surfaces can be mapped onto two-dimensional lattice gases with binary site values, where surface growth/erosion is described by one-dimensional forward/backward migration of dimers, respectively. Using this mapping and a bit-coded numerical algorithm, very efficient simulations on large spatiotemporal scales have been performed. In addition, the bit-coding allows parallel simulations of 32 systems on a single 64-bit CPU core by the use of particular bit-pair (dimer) locations of the 64 bit words for each system. Using this novel mapping and the internal massive parallelization, we provide high-precision scaling results for the Kardar- Parisi-Zhang (KPZ) and Edwards-Wilkinson type of surface growth. The (smoothing/roughening) surface diffusion can be described by the correlated (attracting/repelling) motion of dimers and Mullins diffusion scaling can be simulated. The combination of competing KPZ and Mullins processes enables to generate various surface patterns (dots/ripples) analogously to the nonequilibrium states seen in driven Ising models. The relation of surface roughness and wavelength coarsening and the role of initial conditions (flat/tilted) will be analyzed.

Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presented.

Highly charged ions (HCI) have become an important tool in a wide range of basic and applied research activities. At HITRAP, a project realized by SPARC and other collaborations at GSI, HCI up to bare uranium will be decelerated to low energies enabling, for example, the determination of the g-factor of bound electrons, laser spectroskopy investigations on the hyperfine structure, or high precision measurements of the mass of stable as well as radioactive nuclii. In 2007 the SPARC-EBIT, a room temperature electron beam ion trab (EBIT) of the Dresden EBIT type, was installed at GSI as an offline injector for tests of the beamline components at HITRAP and the chance to carry out experiments without the request of beam time at GSI’s Experimental Storage Ring (ESR). To further improve the viability of the EBIT at this or other research facilities we have carried out general source characterization as well as charge breeding measurements. The results revealed details for a better understanding of the ionization process inside the trap region as well as ways of increasing the number of elements of which HCI can be produced with the EBIT. Furtheron, tests with the more powerful Dresden EBIS-A have started which will lateron be used to evaluate its performance in comparison to the small but highly efficient Dresden EBIT.

The further miniaturization of silicon sensor and actuator devices using highly developed semiconductor technology at the micro- and nanometer level will lead to a new generation of nano-electro-mechanical systems (NEMS). In the contribution a NEMS fabrication technique will be presented which combines high concentration p-type doping of silicon by high resolution writing focused ion beam (FIB) implantation and subsequent anisotropic and selective wet chemical etching. FIB-patterned and chemically etched 3D Si structures with nanoscale features have been fabricated using 30 keV Ga+ ion implantation (CANION 31Mplus) into silicon-on insulator (SOI) device layers followed by an anisotropic etching in KOH/H2O solution [1]. This technology is combined with classical microelectronic techniques, like lithography and broad beam implantation working on a 4 inch wafer to increase the fabrication efficiency especially for the contact areas. Fabrication considerations to achieve free-standing Si nanostructures, like nanowires nanobridges, see Fig. 1, nanocantilevers etc., are discussed and some typical nanostructures with potential NEMS applications, for example as nano-thermometer, gas sensors or solid-state vacuum nano-triodes, see Fig. 2, are shown. Because the selectively etched free-standing nanobeams are in a highly Ga-doped amorphous state their electrical resistance is quite large. For reduction of the beam resistance they were covered with a metal film using electron beam assisted deposition of a 30 nm Pt layer.
Finally, results of temperature-dependent resistance measurements on nanowires, of AC voltage excited nanobeam deflection measurements and of measurements on vacuum nano-triodes are presented, showing the potential for future device applications.

no abstract available

no abstract available

This presentation highlights the role of ion beams for the formation of nanostructures. The focus is on the selforganization of regular surface pattern under low-energy ion irradiation and on the self-patterning of metal deposits on prepatterned silica surfaces. It will be shown that a deep understanding about the atomistic mechanisms involved can be gained from a combination of collision cascade simulations with 3D kinetic Monte-Carlo calculations.

There are many cases of ion beam processing of materials where ion beam mixing with defect generation and thermally activated processes like defect annealing and phase separation occur at the same time. Examples are ion-irradiation-induced surface pattern selforganisation and nanocluster formation during ion irradiation through interfaces. Here, a new 3D program will be presented which combines the TRIM program for collision cascade simulation with a 3D kinetic Monte-Carlo program describing all kind of relaxation processes.

Spherical gold and germanium nanoclusters embedded in silicon dioxide can be shaped into rods and discs by high energy ion irradiation. The experimental work, modelling of the shaping mechanism and computer simulations will be presentd.

Biomolecules for new materials

Technologie-Plattform S-Layer für die Umwelttechnologie

Vorstellung der Arbeiten der Nachwuchsgruppe NanoBio

We show that d+1-dimensional surface growth models can be mapped onto driven lattice gases of d-mers. The Kardar-Parisi-Zhang growth corresponds to one dimensional drift of d-mers perpendicular to the (d − 1)-dimensional ”plane” spanned by the d-mers. This facilitates efficient, bit-coded algorithms with generalized Kawasaki dynamics of spins. Our simulations in d = 2, 3, 4, 5 dimensions provide scaling exponent estimates on much larger system sizes and simulations times published so far, where the effective growth exponent exhibits an increase. We provide evidence for the agreement of some field theoretical predictions and numerics. We show that the (2 + 1)-dimensional exponents conciliate with the values suggested by L¨assig within error margin. The increase of the effective growth exponents suggest a crossover to a different, anisotropic scaling behavior in d = 5 dimensions.

Nanoscaled materials comprised of organic and inorganic components are becoming more and more important in nanotechnology due to the diversity of applications. The use of self-assembling organic systems as part of such a hybrid material, serving as template for the fabrication of arrays of inorganic nanoparticles, is an attractive approach for the development of new materials. Especially the proteinaceous bacterial surface layers (S-layers) that envelop bacterial cells are attractive for fabricating and patterning of nanostructures. These proteins are composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. The regular distributed pores of these paracrystalline arrays work as binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1]. Such arrays are very attractive for technical applications ranging from the development of novel catalysts to biomedical applications, the programmed assembly of nanometre scale electronic devices, and optical industry [2]. Another approach is the embedding of S-layer proteins into ceramics thus producing metal binding functionalized nanocomposites [3].

Aim of a current project is the development of novel biosensors. These biosensors are composed of three compounds:

1) Bacterial surface layer; these proteins are used for the nano-structuring of surfaces such as SiO2-wafers or glass; they provide a huge amount of orientated functional groups that can be used for coupling of molecules to the surface, thus introducing a high level of functionality in a small device
2) Aptamers, working as receptors; aptamers are oligonucleotides that specifically bind chemical compounds via their three-dimensional structure; the aptamers are coupled to S-layers
3) Fluorophores for detection, coupled to S-layers; two fluorophores are used as donor/acceptor pair; appropriate excitation/emission spectra and closest proximity permit FRET; FRET is interrupted when the analyte is binding to the aptamers.

Another project is focused on the development of novel photocatalysts for the degradation of organic pollutants in the environment. In this approach, S-layer proteins are used as matrix for synthesis as well as immobilization of phototcatalytic nanoparticles such as ZnO or TiO2. These materials, composed of S-layer coated carriers (e.g. alumina, mica, glass) and ZnO particles deposited on S-layer proteins, showed an enhanced catalytic activity in comparison to commercial ZnO nanopowder.

[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68
[3] Raff, J. et al. (2003). Chem. Mater. 15, 240-244

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We extend our 2 + 1 dimensional discrete growth model (PRE 79, 021125 (2009)) with a local exchange dynamics of octahedra, which describes surface diffusion. An inverse Mullins-Herring type of roughening process was realized by uphill diffusion of octahedra. By mapping the slopes on particles a two-dimensional, driven, nonequilibrium Ising model emerges in which the (smoothing/ roughening) surface diffusion can be described by the correlated (attracting/repelling) motion of dimers. We show that the pathological problem of freezing due to the short range jumps in a model, where the local height differences are restricted to ±1 can be overcome with the addition of a small external noise. In the limit of vanishing noise we provide numerical evidence for the Mullins-Herring class scaling by surface width scaling and roughness distribution studies. The competition of the inverse Mullins-Herring diffusion with a smoothing deposition which realizes a Kardar-Parisi-Zhang process one can generate different patterns: dots or ripples. We analyze numerically the scaling behavior and wavelength coarsening behavior in these models. In particular we confirm that the Kardar-Parisi-Zhang type of scaling is stable against surface diffusion, hence this is the asymptotic behavior of the Kuramoto-Sivashinsky equation as conjectured by field theory. In case of very strong, normal surface diffusion is added to KPZ we observe smooth surfaces with logarithmic growth, which can describe the mean-field KPZ behavior.

The deep gold mines of the Witwatersrand Basin, South Africa have gained recent attention not only because of investigations of the deep fracture water and associated CH₄- and H₂-rich gases found there, but because of recent reports of deep microbial communities persisting to depths of almost 3 kilometres - an exotic outpost of the Earth's deep biosphere. While shallower fluids in the basin (to approximately 1 km) were found to contain abundant populations of methanogens and sulphate-reducing bacteria, the deepest, oldest, most saline fracture waters in the basin hosted hitherto unrecognized low biomass and low biodiversity chemoautotrophic ecosystems independent from the photosphere. Shallow and deep fluids also show distinct differences in gas and fluid geochemistry. Paleometeoric waters are dominated by hydrocarbon gases with compositional and isotopic characteristics consistent with production by methanogens utilizing the CO₂ reduction pathway. In contrast the deepest, most saline fracture waters contain gases that are dominated by high concentrations of H₂ gas, and CH₄ and higher hydrocarbon gases with isotopic signatures attributed to abiogenic processes of water-rock reaction. The high salinities (up to hundreds of g/L), highly altered delta -¹⁸O and delta² H signatures, and both ³⁶Cl and measurements of co-occurring nucleogenic noble gases for these fracture waters are consistent with extensive water-rock interaction over geologically long time scales in these high rock/water ratio environments. While the ultimate origin of these fluids has been attributed alternately to saline waters that penetrated the crystalline basement, formation water, or hydrothermal fluids in some cases, their delta ¹⁸O and delta ² H isotopic signatures have typically been so profoundly overprinted by the effects of long-term water-rock interaction that, for the most saline end-members, little evidence of their primary composition remains. The key objective of the present study is to further investigate the origin of these fluids by integrating for the first time detailed neon isotope analyses on the dissolved gases. Helium isotopic analysis confirmed that there is no significant mantle-derived component associated with these fluids and gases. Neon isotope results show distinct differences in neon composition that correspond to the different fluid geochemical end-members previously identified. Typical crustal neon signatures (type A) are identified in the paleometeoric waters populated with abundant methanogens. In contrast, the deep more saline fracture waters contain an enriched nucleogenic neon signature unlike any previously reported in crustal fluids. These samples show the highest ²¹Ne/²²Ne ratios (0.160 */- 0.003) ever reported in groundwater. Fluid inclusions in these rocks yield even higher ²¹Ne/²²Ne ratios between 0.219 to 0.515, consistent with an extrapolated 21Ne/22Ne value of 3.3 +/- 0.2 at ²⁰Ne/²²Ne = 0. We show that this enriched nucleogenic neon end-member represents a fluid component that was produced in the fluorine-depleted Archaean formations and trapped in fluid inclusions > 2 Ga ago. The observation of enriched nucleogenic neon signatures in deep fracture water implies the release of this billion year old neon component from the fluid inclusions and its accumulation in exceptionally isolated fracture water systems. The observed association of this Archean neon signature with H₂-hydrocarbon-rich geogases of proposed abiogenic origin dissolved in the same deep groundwater suggests that the fracture systems have also allowed for the accumulation of various products of water-rock reactions throughout geologic times. One of these fracture systems contained the deepest characterised microbial ecosystems on earth - chemolithotrophs eking out an existence at maintenance levels independent from sunlight. Consequently, the enriched nucleogenic neon isotope signature may indicate regions in the Archaean crust where investigations of the deep biosphere might be focused.

In the Cadarache von-Karman-Sodium (VKS) experiment a flow of liquid sodium is driven by two counterrotating impellers located at the top and the bottom of a cylindrical vessel. Dynamo action is obtained at a critical magnetic Reynolds number Rm_c=32. Striking property of the self-generated field is the high degree of axisymmetry. Furthermore, dynamo action is obtained only with impellers made of soft iron with a relative permeability of the order of mu_r ~ 100...1000. So far, no satisfying explanation is available that explains the failure of field generation when using steel impellers. Therefore, the role of the ferromagnetic material to obtain a dynamo, appears to be a critical issue and deserves further experimental and numerical investigations.

Numerical simulations of the kinematic induction equation have been carried out in a cylindrical domain that resembles the VKS setup. In case of a prescribed axisymmetric velocity distribution the resulting magnetic field is always determined by an azimuthal m=1 -- mode. Axisymmetric fields can be obtained applying a (localized) alpha-effect that might arise from the induction action of radially oriented helical outflow trapped between the impeller blades. However, it turns out, that the amplitude of alpha, which is necessary to generate an axisymmetric field, is far above realistic values. Therefore, a simple alpha-omega-model can be ruled out as the single explanation for the dynamo mechanism in the VKS experiment. Additional support of dynamo action stems from the presence of a high permeability domain within the cylindrical domain. In numerical simulations with a non-uniform permeability distribution that resembles the shape of the impeller disk (including the flow driving blades) the axisymmetric field mode is significantly enhanced, whereas the first non-axisymmetric mode remains nearly unaffected. To circumvent the restrictions of Cowling's theorem, still an alpha-effect is required for a growing axisymmetric field. However, the necessary magnitude of alpha is significantly reduced.

Self assembly is a widespread phenomenon in nature. We are working with bacterial surface layer proteins which represent the outermost cell envelope of many bacteria and almost all archaea. Our bacteria were isolated from a uranium mining waste pile and are therefore adapted to high contents of heavy metals. Most of them feature surface layer proteins possessing high metal binding capacities. Bacterial surface layer (S-layer) proteins exhibit self organizing properties combined with the ability to arrange at interfaces. In vitro they form a paracrystalline protein lattice with defined pores and cavi-ties as it can be naturally found on the bacterial surface. Our effort is to use the special properties of these proteins for the design of nano structured and functionalized com-posites. Current workings are focused on catalytic materi-als and sensory layers. We use the self assembling proper-ties for coating various substrates by recrystallizing pro-tein monomers direct on surfaces. The metal binding abil-ities of the lattice can be used for filtering or to form met-al nanoparticles of uniform size and distribution in the pores of the protein layer. The amino acid residues of the protein are suitable for linking further functional mole-cules to the lattice with high density

The investigation of the interactions of radionuclides with the biosphere revealed special adapted bacteria. Some of them were isolated from a uranium mining waste pile. These bacteria are covered with a protein envelope called S-layer as many other bacteria and most of archaea. In these cases, the S-layers bind toxic and radioactive heavy metal ions preventing an uptake and a damage of the cell. The proteins exhibit self assembling properties and form a two dimensional paracrystalline protein lattice. The S-layer can be isolated and dissolved into monomers under the influence of chaotropic agents. The purified proteins are able to recrystallize once the chaotrope is removed. Recrystallization occurs preferably at interfaces, but also in solution and is used in the present study to cover various surfaces with a single layer of highly ordered protein polymers. The protein layer features pores of uniform size and distribution. This lattice is useful for nanostructuring of surfaces. The protein lattice can be used as matrix to form nanoparticles. The different functional groups of the protein are potential binding sites for attaching further functional molecules like enzymes or fluorescence markers. The periodicity of the layer is suitable to immobilize molecules regularly and with high density.
One challenge is the complete coverage of the respective surface in an appropriate time. Another problem is the stability of the produced coating under harsh conditions. We have used AFM analysis on a variety of substrates in order to optimize the substrates pretreatment regarding S-layer coverage and time consumptions. While the recrystallization at cleaned silicon supports is too slow and incomplete, the pretreatment with polyelectrolytes enhances speed of the recrystallization process and allows a complete coverage of surfaces. The generated protein layer shows a thickness of about 9 nm which is in good agreement with data published in literature. These monolayers were used as matrix for the formation of Pt- and Pd-nanoparticles. The proteins are able to bind high amounts of Pt or Pd ions from solution. Subsequent reduction leads to the formation of nanoparticles. Afterwards most of the organic compounds can be removed by UV excitation without heating leaving the nanoparticles well arranged on the surface. Moreover the special properties of the S-layer proteins make them highly interesting to be used as a technology platform for the design of new nano-materials.

The volume, shape and microstructure of solids can be influenced by magnetic fields [1]. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu2 compounds (R = rare earth) [2]. RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magneto-crystalline anisotropy:

the strong rare-earth single ion anisotropy. Due to the pseudohexagonal symmetry of RCu2, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= Giant MagnetoStrain). The variant´s fraction stays unchanged still after ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. This irreversibility shows the potential to construct field controlled actuators or switches. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb0.5Dy0.5Cu2. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu2 was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. Futural preparation and characterization of thin or free-standing films are necessary to contsruct micro-mechanical actuators.
[1] M. Doerr et al.: Adv. Phys. 54 (2005) 1.
[2] S. Raasch et al.: Phys. Rev. B 73 (2005) 64402.

Semiconductor Nanocrystals (NC), consisting only of a few hundred of atoms, are of great interest for new generations of light emitters, nonvolatile memories or high efficiency solar cells [1]. However, it remains a remarkable challenge to achieve a high density (>10¹²cm^-2) of equalsized, small (<5 nm) NC’s of Ge or Si embedded in dielectric films. In this study we present the fabrication of Ge-NC’s by decomposition of GeOx (1< x <2) out of a (GeOx -SiO2) superlattice structure (SL). The SL was grown by dual reactive DC magnetron sputtering from elemental targets. Different Ge/O ratios in the SL structures were realized by the variation of oxygen flow and deposition temperature. Using in-situ x-ray reflectivity and grazing incidence diffraction at the CRG Beamline ROBL at ESRF we studied the deposition of the SL and the Ge NC’s evolution during subsequent annealing. Depending on the GeOx stoichiometry closed nanocrystalline films or separated Ge NC’s with grain or particle sizes between 2-5 nm have been obtained with grazing incidence x-ray diffraction. The size of the NC’s can be tuned with thickness of the GeOx sublayer, its density exceeds 10¹²cm^-2.
[1] A.Rogach (ED.), Semiconductor nanocrystal quantum dots, Springer, Wien 2008, ISBN 978-3211752357

The underlying motivation of this research is the tailored growth of Ge nanocrystals (NC) for photovoltaic applications [1,2]. Of special interest are the study of confinement effects to design bandgap engineered materials enabling light absorption within a wide range of the solar spectrum. In this contribution we enlighten the deposition process of (GeOx-SiO2) superlattice structures (SL) via reactive DC magnetron sputtering and the self-ordered Ge-nanocrystal formation during subsequent annealing. SL structure delivers a reliable method to control the NC size after phase separation. Main attention is directed to define proper deposition conditions for tuning the GeOx composition between elemental Ge (x=0) and GeO2 (x=2) by the variation of the deposition temperature and the oxygen partial pressure. A process window has been found which allows GeOx / SiO2 deposition without changing the oxygen flow during the deposition. The phase separation and Ge NCs formation after subsequent anneling was investigated with in − situ X-ray diffraction, Raman spectroscopy and electron microscopy, confirming the existence of 2-5 nm Ge NCs. As the used technique allows to produce SL stacks with very smooth interfaces (roughness <1 nm), the Ge NC layers could be separated by very thin SiO2 films (d >3 nm) which offers interesting possibilities for charge transport via tunneling.

Semiconductor Nanocrystals (NC), consisting only of a few hundred of atoms, came recently even more into focus, because they might help to increase the efficiency of solar cells for the 3rd generation photovoltaics [1]. This could be mainly achieved by an engineered bandgap size of the material, which allows the light absorption of the complete sunlight spectrum. However, it remains a remarkable challenge to achieve a high density (>10¹² cm^-2) of equal-sized, small (< 5 nm) NC’s of Ge or Si embedded in dielectric films.
In this study we present the fabrication of Ge-NC's by decomposition of GeOx (1 < x < 2) out of a (GeOx -SiO2) superlattice structure (SL). The SL was grown by dual reactive DC magnetron sputtering from elemental targets. Different Ge/O ratios in the SL structures were realized by the variation of oxygen flow and deposition temperature. Using in-situ x-ray reflectivity (XRR) and grazing incidence diffraction (GIXRD) at the CRG Beamline ROBL at ESRF we studied the deposition of the SL and the Ge NC's evolution during subsequent annealing. The formation of Ge NC’s by the GeOx phase separation has been proofed with GIXRD. At 600°C a Ge (111) signal confirmed the existence of Ge NC’s in the size of 2-8 nm. Within the SL stability range, the NC size corresponds approximately to the GeOx sublayer thickness.
[1] Martin A. Green, Third generation photovoltaics, Springer, 2006, ISBN 1437-0379

The volume, shape and microstructure of solids can be influenced by magnetic fields. Much effort is focused on magnetic shape memory (MSM) materials. Recently, the MSM effect has been discovered to occur also in the paramagnetic state, e.g. in RCu2 compounds (R = rare earth). RMSM materials distinguish themselves from conventional MSM materials by the new origin of the magnetoic anisotropy: the strong rare-earth single ion anisotropy. Due to the pseudo-hexagonal symmetry of RCu2, three orientational variants exists, each of them rotated by about 60 deg with respect to the others. Switching these variants by an external field results in a change of the macroscopic shape. The strain is in the order of one percent (= GiantMagnetoStrain). The variants fraction remains unchanged when ramping down the field. The virgin state can be recovered by heating or by a perpendicularly directed field. We present temperature and field dependent measurements of magnetostrain and magentization at the model substance Tb0.5Dy0.5Cu2. The macroscopic characterization of the sample is complemented by a detailed microscopic analysis done by elastic neutron scattering. Although the GMS effect of RCu2 was worked out at single crystals, the principle of this magneto-mechanical coupling phenomenon is also useful for polycrystalline or microscaled applications. The existence of this structural irreversibility shows the potential to construct field controlled actuators or switches.

NURESIM and NURISP are two successive European Projects of the 6th and 7th Framework Program with the objective of building a multi-physics and multi-scale platform for numerical simulation of nuclear reactors. It includes core physics and thermalhydraulics with sensitivity and uncertainty methods and coupling of thermalhydraulics with fuel thermomechanics and neutron kinetics. The NURISP European Collaborative Project (FP7) includes 22 organizations from 14 European countries.
This paper summarizes some achievements and ongoing developments of the platform in Thermal-Hydraulics. Within the NURESIM project the development and validation of two-phase-CFD in open medium addressed mainly Departure from Nucleate Boiling, Dry-Out, Direct Contact Condensation and Pressurized Thermal Shock. Within NURISP, CFD use is now extended to some investigations related to LOCA such as flashing flow, and steam-droplet flow in a core during reflooding. The NEPTUNE-CFD code developed by EDF and CEA and sponsored by AREVA-NP and IRSN was first implemented in the NURESIM platform and The TRansaT code developed by ASCOMP is now also in the platform. New physical models have been developed, validation calculations were performed and NEPTUNE-CFD was benchmarked with commercial codes. DNS–ITM techniques (e.g. Lattice Boltzman Method or DNS of the TransAT code) were also used as numerical experiments to obtain information on smaller scale flow processes.
The paper summarizes the achievements, updates the state of the art in two-phase-CFD, and presents the future activities

Magnetoelastic phenomena of irreversible character were investigated on the rare earth germanides Nd5Ge3 and Gd5Ge3 which are prominent members of the hexagonal R5Ge3 series. Both compounds order antiferromagnetically at 52 K and 76 K, respectively. A strong magnetostructural irreversibility (i.e. a relative length change of about 10^-3 which can be induced by a magnetic field and stays stable after ramping down the field) was detected for both samples by measurements of magnetostriction and thermal expansion using capacitive dilatometry. This transition can be reversed by heating the sample near the ordering temperature. Additional experiments by X-ray and neutron scattering at Gd5Ge3 in order to analyze the effect itself and the structural reversal on an atomistic scale indicate the polymorphic (or metastable) magnetic character (e.g. several propagation vectors (0 0 0.4) and (0.3 0.3 0) were found) which allow to induce strong lattice distortions by an external magnetic field via the magnetoelastic coupling.

Fe ions have been implanted into YSZ(001) single crystals at elevated temperatures. Depending on the fluence not only an increase of α-Fe cluster formation but also the appearance of γ-Fe as well as Fe oxide based secondary phases was observed. The clusters are proposed to consist of a metallic core and an oxide shell. Ferromagnetic hyperfine splitting was detected by Mössbauer spectroscopy and mainly assigned to Fe3+ and α-Fe.

Die Bremsung von Schwerionen mit MeV-Energien bei Bewegung in Materie hängt von deren Energie und Ladungszustand ab. Nach einer durchlaufenen Strecke von ca. 50 nm stellt sich eine energieabhängige Gleichgewichtsverteilung der Ladungszustände ein. Auf dieser Verteilung der Ladungszustände beruhen die tabellierten Werte für das mittlere Bremsvermögen [1], die bei den ionenstrahlanalytischen Verfahren der Rutherford-Rückstreu-Spektrometrie (Rutherford Backs-cattering Spectrometry - RBS) und der elastischen Rückstreuanalyse (Elastic Recoil Detection Analysis - ERDA) zur Berechnung der Streutiefe eingesetzt werden.
Die Verteilung der Ladungszustände der Ionen nach atomaren Stößen unterscheidet sich von der Gleichgewichtsverteilung. Beim Einsatz höchstauflösender magnetischer oder elektrostati-scher Spektrometer zur Charakterisierung ultradünner Schichten betragen die Weglängen der Ionen in der Probe nur wenige Nanometer. Es wird dabei kein Ladungsgleichgewicht erreicht und zur Auswertung der Messdaten müssen die unterschiedlichen Bremsvermögen und die Um-ladungsquerschnitte der einzelnen Ladungszustände berücksichtigt werden.
Experimentelle Daten für den für die Ionenstrahlanalyse interessanten Energiebereich von we-niger als 30 MeV liegen nach unserem Wissen nicht vor. Aus diesem Grunde wurden Brems-vermögen und Umladungsquerschnitte leichter Schwerionen (Bor, Kohlenstoff, Stickstoff, Sau-erstoff und Fluor) an ultradünnen DLC-Kohlenstofffolien (Diamond Like Carbon) im Energiebe-reich von 3-14 MeV für die unterschiedlichen Ladungszustände untersucht. Dazu wurde eine experimentelle Anordnung mit elektrostatischem Analysator, ähnlich der in [2] beschriebenen, verwendet, bei der zwei DLC-Folien hintereinander angeordnet sind. Die erste Folie mit einer Massenflächendichte von 2,0 bzw. 2,7 µg/cm² dient dabei als Stripperfolie. Die Ionen unter-schiedlicher Ladung haben nach dem Passieren dieser Folie eine identische Energieverteilung. In kurzem Abstand folgt eine ultradünne Targetfolie mit einer Massenflächendichte zwischen 0,5 und 0,9 µg/cm². Dies entspricht einer Dicke von ca. 2,5 bis 4,5 nm. Diese Folie ist ausreichend dünn, um Vielfachumladungen zu vermeiden. Zur Bestimmung der Umladungsquerschnitte wur-de, analog der von A. Blažević et al. beschriebenen Methode [3], das Potential der Stripperfolie um 30 kV gegenüber der Targetfolie angehoben.
Die hier gewonnen Ergebnisse fließen in die Verbesserung der Präzision und Richtigkeit der mit hochauflösender RBS und ERDA produzierten Daten ein.

Referenzen
[1] J.F. Ziegler, Nucl. Instr. and Meth. B 219-220 (2004) 1027. URL: http://www.SRIM.org.
[2] W. Jiang et al, Phys. Rev. B 59 (1999) 226.
[3] A. Blažević et al, Phys. Rev. A 61 (2000) 032901.

Ternary Ti–Al–N films were deposited onto Al₂O₃ 0001 substrates by reactive cosputtering from elemental Ti and Al targets and analyzed by in situ and ex situ x-ray scattering, Rutherford backscattering spectroscopy, transmission electron microscopy, and x-ray photoemission spectroscopy. The deposition parameters were set to values that yield Ti:Al:N ratios of 2:1:1 and 4:1:3 at room temperature. 2TiAlN depositions at 675 °C result in epitaxial Ti₂AlN growth with basal planes parallel to the substrate surface. Nominal 4TiAl3N depositions at 675 °C and above, however, yield domain growth of TiN and Ti₂AlN due to Al loss to the vacuum. Depositions at a lower temperature of 600 °C yield films with correct 4:1:3 stoichiometry, but Ti₄AlN₃ formation is prevented, supposedly by insufficient adatom mobility. Instead, an incoherent Ti_n+1AlN_n structure with random twinned stacking sequences n is obtained that exhibits both basal plane orientations parallel and nearly perpendicular to the substrate interface. X-ray photoemission spectroscopy shows that in contrast to stoichiometric nitrides the Al is metallically bonded and hence acts as twinning plane within the Ti_n+1AlN_n stackings. Domains with perpendicular basal plane orientation overgrow those with parallel orientation in a competitive growth mode. The resulting morphology is a combination of smooth-surface parallel-basal-plane-oriented domains interrupted by repeated facetted hillocklike features with perpendicular basal plane orientation.

Present strategies of photovoltaic (PV) industry are strongly directed to lower the fabrication costs and/or to enhance the solar cell efficiency with the overall aim to achieve grid parity in near future. Bandgap engineered materials including semiconductor and metal nanoparticles can contribute to reduce energy conversion losses due to thermalization and missing infrared light absorption. Based on such materials, the European PV roadmap describes a clear route towards solar cells with significantly enhanced efficiencies.

Electronic and magnetic properties of the charge ordered phase of LuFe₂O₄ are investigated by means of x-ray spectroscopic and theoretical electronic structure approaches. LuFe₂O₄ is a compound showing fascinating magnetoelectric coupling via charge ordering. Here, we identify the spin ground state of LuFe₂O₄ in the charge ordered phase to be a 2:1 ferrimagnetic configuration, ruling out a frustrated magnetic state. An enhanced orbital moment may enhance the magnetoelectric coupling. Furthermore, we determine the densities of states and the corresponding correlation potentials by means of x-ray photoelectron and emission spectroscopies, as well as electronic structure calculations.

Sulfate-reducing prokaryotes (SRP) can affect metal mobility either directly by reductive transformation of metal ions, e.g., uranium and chromium, into their insoluble forms or indirectly by formation of metal sulfides. This study evaluated in situ and biostimulated activity of SRP in groundwater influenced soils from a creek bank contaminated with heavy metals and radionuclides within the former uranium-mining district, Ronneburg (Germany). In situ activity of SRP, measured by the 35S-SO₄ ^2-radiotracer method, was restricted to reduced soil horizons with rates 142 ± 20 nmol cm^-3 day^-1. Although concentrations of heavy metals were enriched in the solid phase of the reduced horizons, porewater concentrations were low. XANES measurements demonstrated that ~80% of uranium was present as reduced uranium, but appeared to occur as a sorbed complex. Soil-based dsrAB clone libraries were dominated by sequences most closely affiliated to members of the Desulfobacterales, but also Desulfovibrionales, Syntrophobacteraceae and Clostridiales. ¹³C-acetate and ¹³C-lactate biostimulated soil microcosms were dominated by sulfate and Fe(III) reduction, which was associated with enrichment of similar SRP found using the dsrAB marker in soil and with sequences related to Geobacter. Concentrations of soluble nickel, cobalt, and occasionally zinc declined 100% during anoxic soil incubations. In contrast to other studies, soluble uranium increased in carbon-amended treatments reaching 1407 nM in solution. Our results suggest that (i) contaminated reduced soil with on-going sulfate reduction resulted in in situ metal attenuation and (ii) the fate of uranium mobility is not predictable and may lead to downstream contamination of adjacent ecosystems.

It was demonstrated in a previous paper that the interaction between a thermoelectric current j and an imposed static magnetic field B produced thermoelectromagnetic convection (TEMC). The prominent feature was utilisation of a wall material exhibiting a big difference in the thermoelectric power S in comparison to the fluid. Although high flow velocities were accomplished, the vigour was potentially mitigated by two design issues. Firstly, the side walls parallel to the temperature gradient Grad T were made from the same electrically high conducting material as the isothermal walls. This, in parts, shorts the thermoelectric current. Moreover, these walls might be seen as lowering the degree of the experiment of being generic. Secondly, the field created by a permanent magnet covered only a small fraction of the fluid volume. Again, albeit being mirror symmetric, the three-dimensional distribution of B lowers the degree of being generic.

The present paper reports on an experimental study on TEMC in a square box wherein the necessary Grad T is accomplished by heating and cooling of two opposing side walls, respectively, whereas the other two side walls are electrically non-conducting. An almost two-dimensional distribution of B is applied to a relatively large area of the interface between the fluid and the bottom of the container. The pole shoes of the magnet are specifically designed so as to have a high value of the curl of the Lorentz force, the non-vanishing of which is another pre-requisite for TEMC. Two containers with different bottom materials are build. The ferromagnetic nickel with negative S used in previous work is replaced by isotan in one variant, offering probably the highest absolute value of S among metals. To consider also the counterpart, nichrome with a high positive S is used in the construction of the second container. Ultrasonic Doppler velocimetry is employed to quantify the TEMC flow field. The results of all three configurations are compared and discussed. In addition, first results on more developed turbulent regimes are presented, which could not be reached in the previous setup because of a more limited Delta S x Delta T.

Die am Forschungszentrum Dresden-Rossendorf entwickelte ultraschnelle Röntgen-Computertomographie ist eine nichtinvasive Messmethode, die eine überlagerungsfreie Abbildung von Phasenverteilungen in transienten Zweiphasenströmungen mit bisher unerreichter zeitlicher und räumlicher Auflösung erlaubt. Damit können sicherheitsrelevante Aspekte in technischen Prozessen, beispielsweise aus der Chemie- und Bioverfahrenstechnik, der Mineralölförderung und der Kerntechnik, untersucht sowie CFD-Simulationscodes validiert werden.

In this contribution we review the impact of anionic and cationic substitutions on the electronic properties of bulk ZnO crystals, thin films and ZnO powders. p-type doping is discussed with focus on the anionic substitution of oxygen by nitrogen or phosphorous. n-type doping is exemplarily reviewed for substitution of Zn by group III elements. The impact of isoelectronic substitution of zinc (with Cd or Mg) or of oxygen (with S, Se, Te) on the band gap are also discussed for the respective ternary alloy. The substitution of Zn by the transition metal Mn introduces several electronic levels in the band gap which significantly alter the absorption and emission properties. Further, devices based on substitutional effects in ZnO are reviewed: Schottky diodes (unipolar device) and pn-diodes (bipolar device).

The excited-state proton transfer of 3-hydroxybenzoic acid and 4-hydroxybenzoic acid was studied by time-resolved laser-induced fluorescence spectroscopy with ultra-short laser pulses. The excited-state reactions were identified in aqueous media as a function of the pH value. Apart from the well-known inversion of the ordinary dissociation properties of these compounds, new species were found which exist only in the excited-state resulting from a temporal and reversible annihilation of the aromatic bond system. These species and their reaction mechanisms were detected by their absorption and fluorescence spectra.

Ein Hochtemperatur-Oxidationsschutz von Titanaluminiden kann durch Verwendung des Halogen-Effektes realisiert werden. Fluor erwies sich dabei als am besten geeignet, insbesondere bei termozyklischer Beanspruchung. Unter isothermen wie auch zyklischen Bedingungen ist die schützende Wirkung der sich bildenden Aluminiumoxidschicht für bis zu 4000 h bei 900° - 1050°C experimentell gezeigt werden. Als Technik zur Einbringung der Halogene unter die Metalloberfläche wurde die Beamline-Ionenimplantation intensiv untersucht. Die Größe des Strahlfleckes beträgt nur etwa 10 cm² und bei der komplexen Geometrie der zu Behandelnden Bauteile kann ein einheitlicher Einschusswinkel nicht realisiert werden. Chemische Behandlungen, wie das Tauchen in verdünnter HF-Lösung, sind diffusionsgesteuert und damit weiterstehend unabhängig von der vorliegenden Bauteilgeometrie. Bei der kontrollierten Gasphasenfluorierung wurden die Fluorionen durch die thermische Zersetzung einer einer CFn-Verbindung erzeugt. Bei der am Forschungszentrum Dresden-Rossendorf durchgeführten Plasma-Immersions-Ionenimplantation (PIII) werden die Fluorinen von einem CH2F2/Ar-Plasma bereitgestellt. Die PIII Methode soll als Referenztechnik für die Behandlung komplexer Geometrien eingesetzt werden, da die Parameter genau kontrolliert werden können. Am IKF wurden dazu die Protonen induzierte Gamma-Emission (PIGE) und Rutherford Basckscattering (RBS) am 2.5 MV van de Graaf-Beschleuniger eingesetzt. Mit der PIGE können Fluorkonzentrationen mit einer Genauigkeit besser als 7% gemessen werden.

It is now well-established that TiAl alloys containing Al between about 40 and 55 at.% may be modified by introducing a halogen element, notably F, into their near-surface region (the so-called halogen effect) to protect them against high-temperature environmental degradation. Upon subsequent high-temperature oxidation, the TiAl alloys modified in this way acquire а highly protective alumina scale, and are suitable for advanced automobile, aerospace and power generation applications. Low-Al content (typically < 10 at.%) Ti alloys, however, contain insufficient amounts of Al for the halogen effect to be activated necessitating enrichment with Al of their near-surface region. In this work, both α-Ti and low-Al content Ti alloys have been processed to render them oxidation-resistant in air at temperatures of 600 to 1050°C by promoting the formation of a protective scale. Surface processing has generally involved two steps, namely Al enrichment and introduction of F. The Al enrichment has in turn involved deposition of a thin Al film by magnetron sputtering followed by either Ar ion bombardment or rapid thermal annealing. The introduction of F has been achieved by plasma immersion ion implantation. Analytical techniques such as ERDA, RBS, XRD, SEM and EDX have been used for sample characterization. Under optimized processing conditions the metal samples so modified have shown high-temperature environmental stability comparable to that of standard TiAl (40 < Al < 55 at.%) alloys.

Surfaces of titanium aluminides were treated with fluorine either physically by plasma immersion ion implantation (PIII) or chemically using a F-based polymer. Under optimum conditions of fluorination, both treatments were shown to improve the oxidation resistance of the alloys even in aggressive environments containing sulfur dioxide (0.1 vol. %). No sulfur was detected in the oxide scale although thermodynamic calculations predict the formation of sulfides. The inward diffusion of oxygen and nitrogen was found to be reduced in the presence of SiO2.

No abstract available.

Titanium is a widely used structural material due to its low specific weight, mechanical properties and good corrosion resistance at low temperatures. The melting point (1677°C) is much higher than the maximum operating temperature of about 600°C. Because of increased oxidation rate and environmental embrittlement Ti-Alloys can not be used at higher temperatures. The surface treatment with F gives very good results for TiAl-alloys but has only little or no effect on the oxidation resistance of Ti-alloys. Enrichment of the near-surface zone of Ti-alloys with Al leads to an improvement in the oxidation resistance which, however, is insufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed, and an additional F-treatment gives good results. The fluorine effect on TiAl-alloys leads to the formation of a protective alumina scale. Not only does the scale provide protection against environmental attack, but it also prevents oxygen inward diffusion which causes embrittlement. In this work results of high temperature oxidation tests several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment, single Al-treatment, pure F-treatment and the combination of both. Enrichment with Al has been done by either powder pack process or magnetron sputtering. Fluorine has been introduced using a liquid phase process as well as alternative techniques. Subsequent analyses by SEM and other methods reveal the formation of thinner oxide layer on the combined Al and F treated samples.

Due to its low weight and good corrosion resistance at moderate temperatures, titanium is being currently used in a large number of applications. As a result of increased oxidation rate and environmental embrittlement the maximum operating temperature is only about 600°C while the melting point is much higher (1677°C). The oxidation behaviour can be improved by different methods e.g. Al-enrichment of the surface zone. This leads to an improvement which is, however, not sufficient. The combination of Al-enrichment in the surface zone so that a TiAl-layer is formed plus an additional F-treatment gives the best results because a protective alumina scale is formed. The fluorine effect is known for TiAl-alloys. An alumina scale is found on TiAl-alloys after F-treatment. This alumina scale prevents oxygen inward diffusion which causes embrittlement and protects the material against environ-mental attack. Now this effect is transferred to alloys with a very low Al-content or even no Al at all. These alloys can not form an alumina layer by themselves without any treatment. In this work results of oxidation tests of several Ti-alloys (-Ti, Ti3Al, etc.) are presented without any treatment and with Al-treatment, F-treatment and the combination of both. Aluminium was diffused into the samples by a powder pack process. Fluorine can be applied by several ways e.g. ion implantation or gas phase processes. The formation of a thinner oxide scale on treated samples is revealed by post experimental investigations like metallography. The results are discussed referring to the fluorine effect model for TiAl-alloys.