Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

Radiotherapy of various cancers is closely associated with increased cardiovascular morbidity and mortality. Arachidonic acid metabolites are supposed to play a key role in radiation-induced vascular dysfunction. This study was designed to evaluate the effects of novel, antioxidative 2,3-diaryl-substituted indole-based selective cyclooxygenase-2 (COX-2) inhibitors (2,3-diaryl-indole coxibs) on radiation-induced formation of arachidonic acid metabolites via COX-2 and oxidant stress pathways in an organotypical vascular model of rat aortic rings. Acute and subacute effects of X-ray radiation (4 and 10 Gy; 1 and 3 days post irradiation) with or without the presence of 1 µM of the 2,3-diaryl-indole coxib 2-[4-(aminosulfonyl)phenyl]-3-(4-methoxyphenyl)-1H-indole (C1) or celecoxib as reference compared to sham-irradiated controls were assessed. The following parameters were measured: metabolic activity of the aortic rings; induction and regulation of COX-2 expression; release of prostaglandin E₂ and F_2alpha-isoprostane. Irradiation without presence of coxibs resulted in a dose-dependent augmentation of all parameters studied. When aortic rings were exposed to the 2,3-diaryl-indole coxib 1 h before irradiation, metabolic activity was restored and the release of both prostaglandin and isoprostane was inhibited. The latter indicates a direct interaction with oxidant stress pathways. By contrast, celecoxib exhibited only slight effects on the formation of isoprostane. The reduction of radiation-induced vascular dysfunction by antioxidative coxibs may widen the therapeutic window of COX-2 targeted treatment.

The manganese induced magnetic, electrical and structural modification in InMnP epilayers, prepared by Mn ion implantation and pulsed laser annealing, are investigated in the following work. All samples exhibit clear hysteresis loops and strong spin polarization at the Fermi level. The degree of magnetization, the Curie temperature and the spin polarization depend on the Mn concentration. The bright-field transmission electron micrographs show that InP samples become almost amorphous after Mn implantation but recrystallize after pulsed laser annealing. We did not observe an insulator-metal transition in InMnP up to a Mn concentration of 5 at.%. Instead all InMnP samples show insulating characteristics up to the lowest measured temperature. Magneotresistance results obtained at low temperatures support the hopping conduction mechanism in InMnP. We find that the Mn impurity band remains detached from the valence band in InMnP up to 5 at.% Mn doping. Our findings indicate that the local environment of Mn ions in InP is similar to GaMnAs, GaMnP and InMnAs, however, the electrical properties of these Mn implanted III-V compounds are different. This is one of the consequences of the different Mn binding energy in these compounds.

Bi and Au ions of a few tens of keV deposit a high energy density into the collision cascade volume of due to (i) their high mass and (ii) their low projected range. At higher energies, this density becomes diluted as the cascade volume increases super-linearly with ion energy.
Compared to monatomic ions, polyatomic ions deposit a much higher energy density. This is sufficient to form a pool of a localized, almost classical melt in a semiconductor surface lasting up to half of a nanosecond. Local melting and resolidification by single polyatomic ion impacts is proven by molecular dynamics calculations.
Well-ordered, self-organized dot patterns on Si and Ge surfaces have been found after heavy polyatomic ion irradiation, which can be attributed to the impact-induced local transient melting. The kinetics of localized melt pools leads to a generic, Bradley-Harper-type partial differential equation for the surface evolution. Whereas so far the mechanisms of ion-induced surface pattern evolution are assumed to be surface curvature dependent ion erosion or ion-momentum-induced mass drift of surface atoms, for heavy polyatomic ions we have identified a completely different mechanism.
The local melting and quenching process is so far from equilibrium that particularities of phase diagrams like the Bi state in Si or Ge are frozen into the nanostructure of the resolidified volume. This opens the possibility to study extremely fast solid-liquid phase transitions.

Beschreibung der verschiedenen bisher an der Neutronen-Flugzeit-Anlage nELBE durchgeführten Experimente.

Magnetic Resonance in the frequency domain provides a tool to investigate and quantitatively measure many important magnetic key parameters, such like the effective magnetization, magnetic anisotropies, magnetic damping parameters or coupling field strengths. Although it has been widely employed for studying magnetic bulk and thin film samples, the sensitivity of this classical method often suffers from being too low when single nanostructures are of interest. This review discusses Magnetic Resonance as technique, providing an introduction also to non-experts in the field. The theoretical background is discussed on an ‘easy to read’ basis, followed by a brief summary of methods that are capable of investigation spin dynamics within single nanostructures (nearfield microscopy, Brillouin Light Scattering, time-resolved Magneto-optical Kerr-effect). Focusing on frequency-domain approaches we then give a detailed explanation of what we call conventional way of experimentally detecting Magnetic Resonance which is based on the use of microwave cavities. This serves a basis to discuss different approaches to enhance sensitivity within a frequency-domain Magnetic Resonance experiment. As shown this includes either improving the conventional setup itself (microresonators) or using alternative detection routes, such as optical or electrical detection.

A bioinspired mineralization process was applied to develop biomirnetic hybrid scaffolds made of (Fe₂₊/Fe₃₊)-doped hydroxyapatite nanocrystals nucleated on self-assembling collagen fibers and endowed with super-paramagnetic properties, minimizing the formation of potentially cytotoidc magnetic phases such as magnetite or other iron oxide phases. Magnetic composites were prepared at different temperatures, and the effect of this parameter on the reaction yield in terms of mineralization degree, morphology, degradation, and magnetization was investigated. The influence of scaffold properties on cells was evaluated by seeding human osteoblast-like cells on magnetic and nonmagnetic materials, and differences in terms of viability, adhesion, and proliferation were studied. The synthesis temperature affects mainly the chemical-physical features of the mineral phase of the composites influencing the degradation, the microstructure, and the magnetization values of the entire scaffold and its biological performance. In vitro investigations indicated the biocompatibility of the materials and that the magnetization of the super-paramagnetic scaffolds, induced applying an external static magnetic field, improved cell proliferation in comparison to the nonmagnetic scaffold.

For measurements of the neutron-induced fission cross section of 242Pu, large-area (42 cm2) 242Pu targets were prepared on Ti-coated Si wafers by means of constant current density molecular plating. Radiochemical separations were performed prior to the platings. Quantitative deposition yields (495%) were determined for all targets by means of alpha-particle spectroscopy. Layer densities in the range of 100–150 μg/cm2 were obtained. The homogeneity of the targets was studied by radiographic imaging.
A comparative study between the quality of the layers produced on the Ti-coated Si wafers and the quality of layers grown on normal Ti foils was carried out by applying scanning electron microscopy and energy dispersive X-ray spectroscopy. Ti-coated Si wafers resulted clearly superior to Ti foils in the production of homogeneous 242Pu layers with minimum defectivity.

Ferritic Fe and Fe-Cr alloys are basic structural materials of present and future nuclear fission and fusion reactors. The formation of the micro- and nanostructure of these alloys and the structural evolution under irradiation is essentially influenced by the interaction between solutes, vacancies and self-interstitials. These processes take place in different alloys such as reactor-pressure-vessel and oxide-dispersion-strengthened steels. The understanding of the nanostructure of those materials and of its radiation-induced evolution is indispensable for nuclear reactor safety. First-principle calculations based on the Density Functional Theory (DFT) are a very useful method to get atomistic insights into the interactions between solutes, vacancies and self-interstitials in bcc Fe. Traditionally, formation and binding energies of these species are investigated at T=0 and these data are further used in calculations on larger length and time scales such as in kinetic Monte Carlo simulations and Rate Theory.
The main objective of present work is the determination of the temperature-dependent free formation and binding energy of selected point defects and their clusters in bcc Fe. For this purpose DFT is used to obtain the corresponding vibrational free energies within the framework of the harmonic approximation. The substitutional solutes Cu, Y and Ti, the interstitial solute atom O, the vacancy as well as small clusters consisting of solute atoms and vacancies are considered. The results are compared with theoretical data obtained by other authors and discussed in relation to experimental solubility data. It is found that the free energies show a significant dependence on temperature. This must be taken into account in multiscale simulations that use DFT input data.

The recent discovery of Skyrmionics in Cu₂OSeO₃ has established a new platform to create and manipulate Skyrmionic spin textures. We use high-field electron spin resonance with a terahertz free-electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. In addition to the previously observed long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency electron spin resonance. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this Skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra.

Advanced Si and Ge nanowire transistors can be produced by top-down or bottom-up approaches. In order to obtain the desired electrical properties doping of the nanowires is required. Ion implantation is one of the favored methods to introduce dopant atoms in a controlled manner. If relatively high ion fluences are needed the originally single-crystalline nanowire is amorphized. Subsequently, thermal processing must be used to restore the Si or Ge crystal and to activate the dopants electrically. In planar structures a complete restoration can be achieved by solid-phase epitaxial recrystallization, whereas more complex processes take place in nanowires, due to the significant influence of surfaces and interfaces. In order to understand the solid-phase recrystallization in such confined systems molecular dynamics simulations are performed. Partially amorphized nanowires embedded in a matrix as well as free nanowires and nanopillars are considered. In dependence on whether embedded or free nanowires are investigated several phenomena are observed, such as stacking fault and twin formation, random nucleation of separate crystalline grains, as well as edge rounding and necking. The simulation results are in qualitative agreement with experimental findings.

Not available, please contact the author.

Electronic properties of Dy₃Ru₄Al₁₂ (hexagonal crystal structure, Dy atoms form distorted kagome nets) are studied on a single crystal by means of magnetization, neutron diffraction, specific heat, and resistivity measurements. The onset of a long-range magnetic order of Dy moments occurs at 7 K through a first-order phase transition. The compound has a noncollinear antiferromagnetic structure with a propagation vector (1/2 0 1/2). The configuration of the Dy moments is consistent with the monoclinic Shubnikov group C_c2/c. The gamma coefficient in the temperature linear term of the specific heat is strongly enhanced to 500 mJ mol^-1 K^-2 taking into account the localized nature of Dy magnetism. An additional contribution originates from spin fluctuations induced in the 4d subsystem of Ru by the exchange field acting from the Dy 4f moments. In an applied magnetic field Dy₃Ru₄Al₁₂ displays magnetization jumps along all crystallographic directions. All the metamagnetic transitions are accompanied by large positive magnetoresistance. The maximum effect (125%-140%) is attained for current along the [100] axis and field along the [120] or [001] axes. The large positive effect is explained by changes in the conduction electron spectra through the jumps as the conduction electrons interact with localized magnetic moments.

The availability of highly enriched stable isotopes enables the preparation of isotopically controlled semiconductors. By means of crystalline (c-Ge) and preamorphized (a-Ge) germanium isotope multilayer structures we investigated the temperature and flux dependence of ion-beam induced self-atom mixing. Low,intermediate,and high temperature regions with different mixing behavior are identified after Ga implantation at 310 keV and various temperatures. In the first region (0K - 470K) the amount of mixing in c-Ge and a-Ge is very similar, an increasing mixing with increasing temperature is observed. Region 2 (470K - 540K) reveals a strong drop of mixing in c-Ge whereas the mixing in a-Ge still increases with temperature. In region 3 (570K and above) the mixing in a-Ge drops to the level of c-Ge. Within region 2 no significant structural change occurs during implantation suggesting an efficient annealing of the radiation damage. In addition we performed Focused-Ion-Beam (FIB) implantations with 60 keV Si ions into Ge using two different fluxes at two different temperatures. The experimental results indicate that the annealing of radiation damage is not only temperature but also flux dependent.
Molecular dynamics simulations with a Stillinger-Weber type potential are used to study the self-atom mixing observed in the experiment. It is found that the dominant mechanisms of mixing are thermal spikes formed by transferring kinetic energy of the incident ion to the lattice. If the transferred energy is high enough,locally molten regions are created in which the atoms can move more freely compared to the lattice atoms. With increasing temperature the thermal spikes last longer and the mixing increases. This is in accord with the experimentally observed mixing behavior in region 1. Differences between the mixing in a-Ge and c-Ge in region 2 are related to the initial crystal structure. Qualitative agreement is achieved with molecular dynamics simulations.

Magnetization reversal processes were investigated in iron-aluminum (Fe60Al40) alloy films of 40 nm thickness by employing magnetometry and magnetic domain imaging using magneto-optical longitudinal and polar effects. The films were initially chemically ordered and weakly ferromagnetic, and a large increase in the saturation magnetization was induced due to disorder magnetization induced by Ne+-ion irradiation. Three different sample geometries were investigated; a) continuous film; b) homogenously irradiated wire; and c) magnetic stripe-patterned wire. Specific magnetization reversal mechanism were identified for the different sample geometries.

There is no doubt that ion beam based research and applications- like all semiconductor-based revolutionary developments of our society- have reached a kind of saturation overlooking the last 60 years when ion implantation started as a child of the early nuclear weapon development. It was the mass separator as a key part of the ion implanter allowing the formation of atomically pure beams. Doping of semiconductor materials with a clear dominance of silicon was the technology driver for the development of ion beam technology. Moreover, the physical and chemical modification of surfaces as well as regions in shallow and deeper regions below the surface of solid materials was the matter of interest for using this efficient tool. At all times, annealing/thermal treatment of ion beam treated materials within different time ranges –from hours down to picoseconds- was a close relative of ion beam engineering. Even flash lamp annealing as one of the annealing methods based on early experiments performed for the simulation of strong optical radiation impact on materials during nuclear weapon attacks. In this talk I will shortly discuss historical and future aspects of ion beam engineering to initiate a discussion on: From nuclear weapons to superchips…, what remains to be done? or, ...what more do people really need? I will extend this lecture to issues that should be of broader interest, but also, to our community!

Ultrashort, nearly monochromatic hard X-ray pulses enrich the understanding of the dynamics and function of matter, e.g., the motion of atomic structures associated with ultrafast phase transitions, structural dynamics and (bio)chemical reactions. Inverse Compton backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses which can be used in a pumpprobe experiment, but also for the investigation of the electron beam dynamics at the interaction point.
The focus of this PhD work lies on the detailed understanding of the kinematics during the interaction of the relativistic electron bunch and the laser pulse in order to quantify the influence of various experiment parameters on the emitted X-ray radiation.
The experiment was conducted at the ELBE center for high power radiation sources using the ELBE superconducting linear accelerator and the DRACO Ti:sapphire laser system. The combination of both these state-of-the-art apparatuses guaranteed the control and stability of the interacting beam parameters throughout the measurement.
The emitted X-ray spectra were detected with a pixelated detector of 1024 by 256 elements (each 26μm by 26μm) to achieve an unprecedented spatial and energy resolution for a full characterization of the emitted spectrum to reveal parameter influences and correlations of both interacting beams. In this work the influence of the electron beam energy, electron beam emittance, the laser bandwidth and the energy-anglecorrelation on the spectra of the backscattered X-rays is quantified.
A rigorous statistical analysis comparing experimental data to ab-initio 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential all optical gamma-ray sources.
The results will serve as a milestone and starting point for the scaling of the Xray flux based on available interaction parameters of an ultrashort bright X-ray source at the ELBE center for high power radiation sources. The knowledge of the spatial and spectral distribution of photons from an inverse Compton scattering source is essential in designing future experiments as well as for tailoring the X-ray spectral properties to an experimental need.

By combining transmission electron microscopy and Rutherford backscattering spectrometry, we have identified carbon related suppression of dislocations and tin precipitation in supersaturated molecular-beam epitaxial grown SiSn alloy layers. Secondary ion mass spectrometry has exposed the accumulation of carbon in the SiSn layers after high temperature carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. The possibility for carbon assisted segregation-free high temperature growth of heteroepitaxial SiSn/Si and GeSn/Si structures is argued.

A quaternary alloying concept comprising the addition of 1-5 at% Fe to Al_0.7Cr_0.3 targets for cathodic arc evaporation at 550 °C is investigated regarding its influence on promoting singe-phase α-(Al,Cr)₂O₃ film growth. Based on detailed X-ray diffraction and transmission electron microscopy studies we can show that the α-phase fraction correlates with the incorporated Fe content and increases with increasing film thickness at the expense of the cubic phases.

Chemoradiotherapy with nimorazole: Factors influencing local tumor control

no abstract available

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The aqueous speciation of selenium(IV) was elucidated by a combined approach applying quantum chemical calculations, infrared (IR), Raman, and 77Se NMR spectroscopy. The dimerization of hydrogen selenite (HSeO3−) was confirmed at concentrations above 10 mmol L–1 by both IR and NMR spectroscopy. Quantum chemical calculations provided the assignment of vibrational bands observed to specific molecule modes of the (HSeO3)22– ion. The results presented will provide a better understanding of the chemistry of aqueous Se(IV) which is of particular interest for processes occurring at mineral/water interfaces.

Background: The transcription factor hypoxia-inducible factor-1 (HIF-1) pathway plays an important role in tumor response to cytotoxic treatments. We investigated the effects of a novel small molecule inhibitor of mitochondrial complex I and hypoxia-induced HIF-1 activity BAY-87-2243, on tumor microenvironment and response of human squamous cell carcinoma (hSCC) to clinically relevant fractionated radiotherapy (RT) with and without concomitant chemotherapy.
Methods: When UT-SCC-5 hSCC xenografts in nude mice reached 6 mm in diameter BAY-87-2243 or carrier was administered before and/ or during RT or radiochemotherapy with concomitant cisplatin (RCT). Local tumor control was evaluated 150 days after irradiation and the doses to control 50% of tumors (TCD50) were compared between treatment arms.
Tumors were excised at different time points during BAY-87-2243 or carrier treatment for western blot and immunohistological investigations.
Results: BAY-87-2243 markedly decreased nuclear HIF-1 alpha expression and pimonidazole hypoxic fraction already after 3 days of drug treatment. BAY-87-2243 prior to RT significantly reduced TCD50 from 123 to 100 Gy (p=0.037). Additional BAY-87-2243 application during RT did not decrease TCD50. BAY-87-2243 before and during radiochemotherapy did not improve local tumor control.
Conclusions: Pronounced reduction of tumor hypoxia by application of BAY-87-2243 prior to RT improved local tumor control. The results demonstrate that radiosensitizing effect importantly depends on treatment schedule. The data support further investigations of HIF-1 pathway inhibitors for radiotherapy and of predictive tests to select patients who will benefit from this combined treatment.

Defect induced magnetism in carbon based materials has many attractive perspectives in the fundamental understanding of magnetism as well as in future spintronic applications. Graphite has been reported that it can be ferromagnetic after proton irradiation. After that, successive investigation was done for confirming the ferromagnetism in graphite and for finding other carbon based materials to be ferromagnetic. So far although the mechanism of ferromagnetism in carbon-based materials is still an open question, more and more experiments show some common features: First, paramagnetism can be largely enhanced by introducing defects. Second, ferromagnetism only appears under certain defect concentration. Third, defects induced or disturbed electron states play an important role to generate local moments and to establishing the ferromagnetic coupling. In the past most of researchers used ions implantation to introduce defects in graphite or graphene. This technology usually generates defect in the near--surface and it is hard to effectively increasing the total number of defect in the whole matrix. Consequently, the magnetic signal is so weak that confuses the interpretation for the source of the observed ferromagmetism. To obtain more reliable information, thereby to better understand this phenomenon, it is necessary to enhance the total number of defect states and simultaneously keep defect concentration constant when the ferromagnetism appears. So in this contribution we use neutron irradiation to extend defect region in graphite from the near surface region to the whole sample. We present the magnetic properties and X-ray absorption spectroscopy of irradiated graphite.

Today: Limits in simulating stratified & segregated two phase flow
Algebraic Interfacial Area Density Model (AIAD)
Free Surface Drag
Turbulence Damping
Sub-grid wave turbulence (SWT)
Verification and Validation is going on – more experimental data are required for the validation

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The 4H-SiC MOSFET electrical response to 180 keV proton radiations at three different fluences has been evaluated. For a certain dose, the devices show an improvement of their electrical characteristics likely due to the N and/or H atoms diffusion inside the oxide layer. This work shows that not only the 4H-SiC material is robust to the radiation, but also a MOSFET build on this material can withstand it, and even its electrical performance results improved if submitted to an appropriate fluence.

AMR depends on the angle between applied current and the direction of the internal magnetization. The influence of magnetic domains on the AMR is still not fully understood. Therefore it is important to observe the domain structure while measuring the AMR. To observe the domain structure Kerr microscopy based on the magneto-optical Kerr effect was applied. For measuring the AMR during imaging, the sample holder was equipped with electrical contacts in four-point style.The investigated permalloy films are stripe patterned by Implantation.The implantation leads to a lower saturation magnetization in the implanted stripes compared to the non-implanted ones. Our measurements show a clear correlation between AMR and the magnetic domain structur.

Here we present how simultaneous anisotropic magnetoresistance (AMR) and Kerr microscopy measurements of patterned samples can be applied to develop new types of magnetic sensors. One observes that the AMR has a minmum value if the magnetization is perpendicular to the current and a maximum value if parallel. Without patterning Permalloy the resistance shows a symmetric behavior. By introducing a certain stripe structure it was possible to achieve a sinusoidal resistance.

Chemical groups of surface layer (S-layer) proteins were chemically modified in order to evaluate the potential of S-layer proteins for the introduction of functional molecules.
S-layer proteins are structure proteins that self-assemble to regular arrays on surfaces. One general feature of S layer proteins is their high amount of carboxylic and amino groups. These groups are potential targets for linking functional molecules thus producing reactive surfaces.
In this work these groups were conjugated with the amino acid tryptophan. In another approach, SH-groups were chemically inserted in order to extend the spectrum of modifiable groups. The amount of modifiable carboxylic groups was further evaluated by potentiometric titration in order to evaluate the efficiency of S-layer proteins to work as matrix for bioconjugations. The results proved that S-layer proteins can work as matrizes for the conjugation of different molecules. The advantage of using chemical modification methods over genetic methods lies in its versatile usage enabling the attachment of biomolecules as well as fluorescence dyes and inorganic molecules. Together with their self-assembling properties S-layer proteins are suitable as targets for bioconjugates, thus enabling a nanostructuring and bio-functionalization of surfaces which can be used for different applications like biosensors, filter materials or (bio)catalytic surfaces.

Modeling of ion-beam induced processes includes ion beam – solid interactions as well as solid state physics. Thus, a rather broad field of physics has to be considered which can be approached using a large variety of modeling techniques. Atomistic models of ion-induced materials modification can be classified as follows: (i) including the ion-induced collision cascade, molecular dynamics (MD) simulations provide the most accurate way to simulate a single or a few ion impacts. The predictive power of MD simulations depends on the accuracy of the interatomic potentials in the wide energy range from meV to keV. (ii) For energetic ions, with the Binary Collision Approximation (BCA) properties like the ion range can be predicted with similar precision like with MD, but thermally activated processes following the collision cascade cannot be simulated; (iii) kinetic Monte-Carlo (KMC) simulations can be used very efficiently and with an acceptable accuracy for modelling of diffusion, relaxation and precipitation of defects and impurities.
Here we will address all of three types of atomistic simulations: (i) With our recently developed TRIDER program, which unifies the BCA and KMC methods [1], low-energy irradiation of a-Si surface has been accurately simulated, in particular the rotation of self-organized surface ripples with the angle of ion incidence. (ii) The BCA, KMC and MD simulation methods have been employed to study the surface stability of Ge and Si under irradiation with heavy ion. [2]. KMC simulations show that the hole-like and sponge-like morphologies results from the vacancy kinetics. The origin of dot-like patterns after irradiation with poly-atomic ions or at elevated substrate temperatures has been revealed by a model based on TRIM and MD simulations: Single ion impacts induce tiny, short-living melt pools. Each meltpool generates a local surface minimization which leads, together with the high ion erosion rate, to a pronounce surface instability. (iii) Swift-heavy-ions change drastically the shape of spherical nanoparticles embedded in silica: Metal clusters become rods, whereas e.g. Ge clusters form to discs. [3]. A model has been developed which is based on transient melting of the nanoparticles by single ion hits, and the volume change of the metal/Ge upon this phase transition. Our KMC program has been modified to simulate the ion-induced shape evolution of different elements for different ion species, energies and fluences even quantitatively, where finally just one fit parameter describes all experiments.
References:
1. Liedke, B.; Heinig, K.-H.; Möller, W.; Nucl. Instr. Meth. B 316, 56 (2013)
2. Böttger, R.; Heinig, K.-H.; Bischoff, L.; Liedke, B.; Facsko, S.; Appl. Phys. A 113, 53 (2013)
3. Schmidt, B.; Heinig, K.-H.; Mücklich, A.; Akhmadaliev,; Nucl. Instr. Meth. B 267, 1345 (2009)

The micro reactor, the principal structure and components of the lab facility and the most important challenges of its construction are presented. As a proof of functionality, the first two-phase flow oxidation experiment of isobutane to t-Butyl hydroperoxide (TBHP) in a micro reactor was accomplished. Challenges of the gas chromatographic analytics (GC) of the reaction are discussed.
The chromatogram of the reaction mixture obtained by the first experiment has been interpreted.
Furthermore a device has been developed to allow the analysis of the gaseous products in a high pressure steel crucible for Differential scanning calorimetry (DSC).
It has been used to analyze the gases resulting from the decomposition of TBHP at higher temperatures by GC.

Im Rahmen dieser Arbeit wurden Einzelfilme und Dreifachlagen bestehend aus Fe3Si mittels ferromagnetischer Resonanz untersucht. Das Hauptaugenmerk lag hierbei auf der Bestimmung der Interlagenaustauschkopplungskonstanten J1 . Außerdem sollen g-Faktor und Anisotropiekonstanten bestätigt werden. Hierbei kann aufgrund des breitbandigen Aufbaus auf die Linienbreite der Signale über einen großen Frequenzbereich eingegangen werden. Bei dem verwendeten Probensystemen Fe3Si/MgO/Fe3Si/MgO/GaAs(001) wurde die Dicke der MgO-Schicht variiert, um einerseits den Einfluss der verschiedenen Lagen aufeinander und andererseits das gekoppelte Verhalten zu untersuchen. Dabei konnte festgestellt werden: (i) Die in dieser gemessenen Parameter stimmen gut mit vorher bestimmten überein. (ii) Das dynamische Verhalten wird durch Zwei-Magnonen-Streuung und Einflüsse der Mosaizität geprägt. (iii) Die Kopplungkonstante J1 wurde bei beiden verwendeten MgO-Zwischenschichtdicken bestimmt. (iv) Der Ursprung der uniaxialen Anisotropie ist durch Grenzflächeneffekte zwischen Fe3Si/GaAs und Fe3Si/MgO bedingt.

In this thesis, magnetic properties of single Fe3Si-films und trilayer structures are investigated by ferromagnetic resonance. Using this technique, it is possible to determine the magnetic anisotropy energy and interlayer exchange coupling J1 in absolute units. Further on, values for the magnetic anisotropy constants and the g-factor should be confirmed in this work. Due to the use of a broad band setup, it is possible to investigate the linewidth of the measured signals. The measurements are carried out using structures containing two Fe3Si films separated by one MgO-layer. The MgO thickness is varied to obtain two different samples. In one of these samples both layers can be considered as decoupled. In the second sample both layers are coupled due to interlayer exchange coupling (IEC). The main results of this thesis are: (i) The obtained parameters for magnetic anisotropy and the g-factor match former results quite well. (ii) The investigation of the resonance linewidth shows contributions of two-magnon-scattering and inhomogeneous broadening due to the mosaicity. (iii) For both used layer thicknesses the interlayer exchange coupling can always be neglected. (iv) The origin of the uniaxial anisotropy is given by effects at the interfaces between the Fe3Si and MgO or the Fe3Si and GaAs layers.

Die Zeitmessung mit einem verteilten Datenerfassungssystem erfordert die Synchronisierung der einzelnen Teilsysteme. Eine dedizierte Taktverteilung ist für diese Anwendung eine einfache und präzise Lösung, erfordert aber zusätzlichen Installationsaufwand und bereitet vor allem bei der Skalierung des Gesamtsystems Probleme. Stattdessen können auch die vorhandenen Datenlinks der einzelnen Module für eine Rückgewinnung des Systemtaktes verwendet werden. Hier wird gezeigt, wie mit industriellen Komponenten (FPGA und Gigabit-Ethernet PHY) die Synchronisierung auf eine gemeinsame Taktfrequenz realisiert wird. Der Abgleich der Uhren erfolgt anschließend protokollbasiert über die Ethernet-Schnittstelle. Es werden die hardwareseitigen Anforderungen, die Umsetzung sowie die experimentellen Ergebnisse vorgestellt. Das implementierte System erreicht Genauigkeiten im Sub-Nanosekunden Bereich mit einer 1000BASE-T Punkt-zu-Punkt Verbindung.

Due to the great potential application in spintronic device, III-Mn-V dilute magnetic semiconductors (DMS) have drawn significant attention during the past two decades. Although of the model member GaMnAs (mostly be prepared by low-temperature molecule beam epitaxy: LTMBE) have been comprehensively investigated, the challenge for preparing other DMS such as InMnAs still exists. Therefore, the understanding about the full family III-Mn-V DMS is far from satisfaction. Ferromagnetic DMS GaMnAs and GaMnP were firstly obtained alternatively by Mn ion implantation and pulsed laser annealing [1, 2], a method rather than LTMBE. The Mn concentration and depth could be controlled through implanting fluence and implanting energy, respectively. When annealing under pulsed laser, due to high temperature gratitude, the large regrowth velocity could trap Mn atoms into the substitutional sites, which is quite effective to obtain high quality laser with less defects which can act as double donors and be harmful to ferromagnetism.
We prepared ferromagnetic InMnAs with different Mn concentrations by ion implantation and pulsed laser annealing. The formation of an epitaxial InMnAs on InAs substrates was proved by Rutherford Backscatting/Channeling and X-ray diffraction. The Curie temperature could be as high as around 75 K when the Mn concentration is around 8%. The out-of-plane direction is the easy axis, originating from the compreassive strain along the perpendicular direction, as expected from the case of GaMnAs [3, 4]. The perpendicular anisotropy is particularly useful for exploiting spintronics functionalities, such as current induced magnetization switching.

[1] M. A. Scarpulla et al. Phys. Rev. Lett., 95, 207204 (2005)
[2] M. A. Scarpulla et al. Appl. Phys. Lett., 82, 1251 (2003)
[3] Shengqiang Zhou et al. APEX, 5, 093007 (2012)
[4] K. W. Edmonds et al. Phys. Rev. Lett., 96 117207 (2006)

Application of laser-induced methods allow the direct determination of uranium speciation at extremely low concentrations. First tunable solid state laser in an actinide chemistry lab was installed in 1993 in Dresden-Rossendorf under Heino Nitsche’s directorship. Later the installation of the first fs-laser system allowed us to study the interaction of organic compounds with actinides.
U(VI) released anthropogenically, e.g. through mining activities, can be accumulated for instance in plants and consequently can enter further parts of the food chain. Uranium as a redox-active heavy metal can cause also various redox imbalances in plant cells.
Recently we have shown that uranium can be taken up by plant cells. Fractionation studies showed that the uranium was present in nearly all cell compartments.
One of the major remaining questions concerns to the ways of uranium uptake. Recently published work proposed that the uranium uptake is influenced by the iron uptake. As it is known that the iron uptake occurs via reduction of the iron(III) into iron(II), we conclude that uranium uptake should also by accompanied by a redox process.
The evaluation of Laser-Induced Photoacoustic Spectra (LIPAS) in the wavelength range 620 nm to 680 nm gave evidence for the formation of both reduced oxidation states in the media studied. The uranium(V) is assigned to an absorption at around 637 nm, while uranium(IV) absorbs light at ~660 nm.

Die Vorbereitung von Erzen zur Verhüttung kann mit hydrometallurgischen Verfahren erfolgen. Dazu zählen Extraktionsverfahren mit wässrigen Lösungen, die Flotation, Sink-Schwimmtrennung und Fällungen. Diese Verfahren finden häufig in äußerst aggressiver Umgebung statt. Für einige dieser Prozesse stehen interessante Alternativen zur Verfügung. Die untersuchten und dargestellten Methoden werden durch Mikroorganismen oder ihre Stoffwechselprodukte unterstützt.
Seit 1980 wird Bioleaching im industriellen Maßstab in Chile eingesetzt. Zur Laugung trägt in diesen Anlagen die Oxidation der sulfidischen Erze durch Acidithiobacillus sp. bei. Oxidische oder carbonatische Erze können auf diesem Weg nicht gelaugt werden. Untersuchungen zeigen, dass in diesen Fällen der Einsatz von Pilzen und Bacillus sp. zur Freisetzung von Metallen aus diesen Erzen beiträgt. Dabei spielen die von Mikroorganismen gebildeten organischen Säuren eine entscheidende Rolle.
Für Sink- Schwimmtrennungen und Fällungen können weitere biologische Komponenten verwendet werden. Zum einen sind es Phagen mit speziell gestalteten Oberflächen. Diese Oberflächen können so konstruiert werden, dass sie spezifisch für einzelne Metalle sind. Durch weitere Variationen der Phagenoberfläche kann die Hydro¬phobi¬zität der mikroskopisch kleinen Partikel an die Anforderungen zum Beispiel einer Flotation angepasst werden. Zum anderen sind es calciumbindende Proteine, die über spezifische und unspezifische Bindungsstellen verfügen und darüber einzelne industrierelevante Metalle sehr selektiv binden können. Die letzten beiden Ideen werden in anderen Bereichen bereits genutzt, zeigen aber auch ein sehr hohes Anwendungspotential bei der Aufbereitung von Erzen.

Ion assistance provides unique opportunities to influence the microstructure of growing films due to energy and momentum transfer. Here, ion effects on the microstructure of C:Ni nanocomposite thin films grown at RT to 500°C by ion-beam sputtering with assisting oblique incidence angle Ar+ ion beam irradiation (50 – 130 eV) are studied by SEM, (c)AFM, TEM, GISAXS, and TRI3DYN simulations. Two types of ordered metallic nanostructures in an amorphous carbon matrix are identified and characterized: i) tilted parallel columns [1] and ii) rippled, periodic three-dimensional nanoparticle arrays [2]. For the former one, the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Ion-enhanced diffusivity and ion-induced surface drift are responsible for the tilted column microstructure. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. For a given composition of the depositing flux, the transition from the columnar growth to the 3D pattern formation regime as a function of the assisting ion energy is demonstrated. The 3D pattern is attributed to the transfer of compositionally modulated surface ripples into the bulk of the C:Ni thin film. The essential experimental features are reproduced by three-dimensional binary collision computer simulations. This agreement points to ion-induced preferential displacements as the driving force for the 3D pattern formation.

Aufgabe der Erfindung ist es, eine Anordnung zur Elektronenstrahl-Röntgen-Computertomographie anzugeben, die ohne die erhebliche axiale Ausdehnung des Elektronenstrahlers auskommt, und weitgehend auf elektronenoptische Strahlführungselemente verzichtet. Die Erfindung umfasst, dass ein Röntgendetektorbogen (6) und das Target (4) um den Untersuchungsquerschnitt innerhalb einer Bestrahlungsebene angeordnet sind, und ein im Elektronenstrahlerzeuger generierter Elektronenstrahl in den Durchflutungsbereich einer oder mehrerer Längsspulen radial eingebracht wird, und durch das Magnetfeld auf eine Kreisbahn gezwungen wird. Durch periodisches Verstellen der Feldstärke wird der Radius der Kreisbahn vergrößert, was dazu führt, dass der Elektronenstrahl das Target (4) in einem tangential wandernden Brennfleck (7) trifft. Vom das Target umgebenden Röntgendetektor(6) werden Durchstrahlungsprojektionen des in der Mitte der Anordnung befindlichen Objekts (8) aufgenommen. Der Elektronenstrahlerzeuger (1) kann sowohl innerhalb als auch außerhalb der Längsspulen (3) angeordnet sein. Darüber hinaus kann die Target- und Röntgendetektorebene mit oder ohne Axialversatz angeordnet sein.

Tetrahedral amorphous carbon (ta-C) is studied as a tribological coating for the valve train’s exhaust camshaft of a combustion engine. The coated camshafts were installed in a non-fired engine, tested in a computerized component test bench under practice-relevant conditions and analyzed for their frictional behavior. A notable reduction of the valve train’s drive torque on the test bench is demonstrated. Namely, on a roller cam system with ta-C coated camshaft the reduction is about 15% in average within the entire engine-map. The ta-C coatings were extensively characterized under laboratory conditions before and after the investigations on the test bench. Mechanistic understanding of the tribological behavior of ta-C coatings under dry or starving lubricated conditions was achieved by atomistic simulations of the tribological contact. Industrial utilization of these results would lead to a significant increase of the energy efficiency of combustion engines.

Flashing flow is an important industrial phenomenon present in many contexts. In flashing flow, a liquid boils in response to a depressurization. CFD is used to simulate the complex two-phase nature of flow, but nucleation is frequently neglected in these simulations. In this work, 3 models for wall nucleation in flashing flow are tested and compared against experimental data. The models are implemented as source terms at the walls only, consistent with experimental observations. The model proposed by Blinkov et al. (1993) is found to provide the best agreement with no parameter fitting. Axial properties and mass flow can be well predicted, but matching the radial profiles requires the addition of a bulk heterogeneous nucleating term, which is small in comparison to wall nucleation and has little impact on average properties but has a large effect on the vapour structure. Additionally, other effects such as coalescence influencing bubble size should be taken into account, since radial distribution of the vapour phase depends directly on the bubble size.

no abstract available

Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding normal tissue.
High precision radiotherapy treatment requires efficient quality assurance techniques. Even small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to normal tissue. Therefore, a treatment verification system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany to monitor the dose delivered by 12C beams [1]. This method makes use of the β+-activity produced via nuclear interactions between the therapeutic beam and the patient tissue. The results and experiences of the clinical application of in-beam PET for carbon ions GSI will be shown. Based on this experience several approaches to improve the significance of the result have been studied.
Since the dose delivery is evaluated by means of a comparison between measured and simulated data a reliable prediction of β+-activity is crucial. To model the positron emitter production accurately, cross sections for all possible nuclear reactions occurring in the tissue during irradiation which lead to positron emitters are required. Since these cross sections are available only for a few reaction channels in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced [2].
Up to now the comparison of the distributions is performed by well-trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. Therefore, a semi-automatic method has been developed evaluating the range and including a cavity filling detection algorithm. System inherent uncertainties are handled by means of a statistical approach [3, 4].
The Particle Therapy (PT)- PET method has been approved for static tumors under clinical conditions. However, also for intra-fractionally moving targets, the 4D simulation [5] as well as the 4D reconstruction [6] of PT-PET data has been established. By means of dedicated 4D-PET experiments the results of the comparison between measured and anticipated activities have been investigated.
References
[1] W. Enghardt, et al., Nucl. Instr. Meth A 525, 2004.
[2] M. Priegnitz, et al., IEEE Trans. Nucl. Sci. 59, 2012.
[3] S. Helmbrecht, et al., Phys. Med. Biol. 57, 2012.
[4] P. Kuess, et al., Med. Phys. 39, 2012.
[5] K. Laube, et al., Phys. Med. Biol. 58, 2013.
[6] K.Stützer, Phys. Med. Biol. 58, 2013.

Für eine verlässliche Beschreibung des Migrationsverhaltens von Radionukliden in der Umwelt ist unter anderem eine genaue Kenntnis der molekularen Prozesse an Mineraloberflächen in Aquiferen unverzichtbar. Unter den spektroskopischen Methoden, die sich auf diesem Forschungsfeld etabliert haben, hat sich die in situ Infrarotspektroskopie für Untersuchungen von Grenzflächenprozessen gelöster Schwermetallionen an festen Mineralphasen als besonders wertvoll erwiesen, da aus den schwingungsspektroskopischen Daten komplementäre Informationen auf molekularer Ebene erhalten werden. In diesem Vortrag soll ein Überblick über aktuelle Ergebnisse der Sorptionsreaktionen von Uran(VI) und Selen(VI) an Metalloxiden gegeben werden.
Mit Hilfe der in situ IR Spektroskopie lassen sich die Sorptions- und Desorptionsprozesse in Echtzeit unter umweltrelevanten Bedingungen untersuchen und somit können Rückschlüsse über die Art der Oberflächenkomplexe über die Reversibilität der Sorptionsreaktionen gezogen werden. Für das Uran wurde beispielsweise eine signifikant unterschiedliche Oberflächenkomplexierung an verschiedenen eisenhaltigen Mineralphasen beobachtet. Zudem lassen sich die Bildung ternärer Oberflächenkomplexe des Urans mit Carbonat- oder Phosphatliganden beobachten, womit weitere Einblicke in den Ablauf komplexerer Sorptionsprozesse gewonnen werden.
Das Selenatanion (Se^VIO₄ ²⁻) zeigt generell schwache, überwiegend elektrostatische Wechselwirkungen (Physisorption) mit Mineralphasen im neutralen pH Bereich. Es hat sich jedoch gezeigt, dass diese Wechselwirkungen, die sog. außersphärische Komplexierung, auf verschiedenen Arten von Oberflächenkomplexen basieren kann. Auf Grund der hohen Selektivität der IR Spektroskopie bezüglich der Molekülsymmetrie, zeigen die Sorptionsexperimente des Se(VI) mit verschiedenen Mineralphasen die Bildung zweier unterschiedlicher Arten außersphärischer Komplexe.

Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in Si, the materials were previously only realized by femtosecond or nanosecond laser annealing of implanted Si or bare Si in certain background gases. The high energy density deposited on the Si surface renders it into a liquid phase and the fast recrystallization velocity allows trapping of S/Se/Te into the Si matrix. However, this method encounters a problem of S/Se/Te surface segregation. In this Letter, we propose a solid phase processing by flash lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed Se-implanted Si shows a substitutional rate of more than 70% with the implanted concentration up to 1-2%. The resistivity is lower and the carrier mobility is higher than those of laser annealed samples. Our results show that flash lamp annealing is superior laser annealing in preventing surface segregation and in allowing scalability.

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration [1, 2]. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell [3]. In the present work, we use ion implantation combined with short-time annealing to realize hyperdoping of Ti and chalcogens in Si. The structural, electrical and optical properties were determined by X-raydiffraction and Rutherford backscattering spectroscopy/channeling, electrical transport measurement and Raman spectroscopy. Analysis shows that the implanted Si layer can be recrystallized by both flashlamp and pulsed laser annealing. Ti ions mainly occupy the interstitial sites, while S and Se ions substitute the Si in the lattice. The consequent changes in electrical properties are also observed.

[1] J. Olea, G. González-Díaz, D. Pastor, I. Mártil, A. Martí, E. Antolín, and A. Luque, J. Appl. Phys. 109, 063718 (2011).
[2] Brion P. Bob, Atsushi Kohno, Supakit Charnvanichborikarn, Jeffrey M. Warrender, Ikurou Umezu, Malek Tabbal, James S. Williams, and Michael J. Aziz J. Appl. Phys. 107, 123506 (2010)
[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).

Impurities play an important role in determining the electrical, optical and structural properties of semiconductors. It has been proposed that deep level impurities, such as Titanium (Ti) or chalcogens in Si, can induce an impurity band inside the bandgap at high enough doping concentration [1, 2]. The insertion of an impurity band can enhance the absorption at a broader wavelength range and leads to applications in the so-called intermediate band solar cell [3]. In the present work, we use ion implantation combined with short-time annealing to realize hyperdoping of Ti and chalcogens in Si. The structural, electrical and optical properties were determined by X-raydiffraction and Rutherford backscattering spectroscopy/channeling, electrical transport measurement and Raman spectroscopy. Analysis shows that the implanted Si layer can be recrystallized by both flashlamp and pulsed laser annealing. Ti ions mainly occupy the interstitial sites, while S and Se ions substitute the Si in the lattice. The consequent changes in electrical properties are also observed.

[1] J. Olea, G. González-Díaz, D. Pastor, I. Mártil, A. Martí, E. Antolín, and A. Luque, J. Appl. Phys. 109, 063718 (2011).
[2] Brion P. Bob, Atsushi Kohno, Supakit Charnvanichborikarn, Jeffrey M. Warrender, Ikurou Umezu, Malek Tabbal, James S. Williams, and Michael J. Aziz J. Appl. Phys. 107, 123506 (2010)
[3] A. Luque and A. Martí, Phys. Rev. Lett. 78, 5014 (1997).

We present the magnetic, transport and structural properties of GaMnP with different Mn concentrations prepared by ion implantation and pulsed laser annealing. The Curie temperature increases with Mn concentration and the samples show in-plane magnetic anisotropy due to the in-plane compressive strain in the GaMnP layer. Anomalous Hall effect and negative magnetoresistance are observed, indicating the carrier mediated nature of the ferromagnetism in GaMnP. According to the micro-Raman spectroscopy data after pulsed laser annealing the implanted layer has been fully recrystallized and the carrier concentration (hole) increases with Mn concentration.

Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.

Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.

The soil particles collected at a former British nuclear test site in Australia were investigated by synchrotron-based X-ray fluorescence microscopy (XFM), in order to determine the chemical speciation of radioactive nuclides retained in the particles. The results demonstrate that the particles contain a high concentration of Pu which derives from the original nuclear bomb material. The outcomes of this study would have a potential impact on the safety and environmental assessment associated with the former nuclear test sites.

Ferromagnetic InMnAs has been previously prepared by low temperature MBE. In this contribution, we present an alternative method what combines Mn ion implantation and pulsed laser annealing to achieve In1-xMnxAs (x = 0.04 and 0.08) [1], and to obtain a remarkably high Curie Temperature (TC) up to 80 K compared to InMnAs with the same Mn concentration as prepared by MBE. The advantage of pulsed laser annealing is its high process temperature within the nano-second range, eliminating n-type defects which can decrease its magnetization and TC. The saturation magnetization is ~2.6μB / Mn by consideration of all implanted Mn ions. The out-of-plane [001] is the easy axis displaying a nearly square like hysteresis loop. Our results suggest that InMnAs prepared by ion implantation and pulsed laser annealing shows a promising prospect to get high TC DMS after optimizing the preparation parameters.

We perform a local stability analysis of rotational flows in the presence of a constant vertical magnetic field and an azimuthal magnetic field with a general radial dependence. Employing the short-wavelength approximation we develop a unified framework for the investigation of the standard, the helical, and the azimuthal version of the magnetorotational instability, as well as of current-driven kink-type instabilities. Considering the viscous and resistive setup, our main focus is on the case of small magnetic Prandtl numbers which applies, e.g., to liquid metal experiments but also to the colder parts of accretion disks. We show that the inductionless versions of MRI that were previously thought to be restricted to comparably steep rotation profiles extend well to the Keplerian case if only the azimuthal field slightly deviates from its current-free (in the fluid) profile. We find an explicit criterion separating the pure azimuthal inductionless magnetorotational instability from the regime where this instability is mixed with the Tayler instability. We further demonstrate that for particular parameter configurations the azimuthal MRI originates as a result of a dissipation-induced instability of the Chandrasekhar's equipartition solution of ideal magnetohydrodynamics.

241Am is one of the most hazardous actinide isotopes present in the spent fuel Transmutation in fast neutrons reactors :

conversion of highly radioactive elements into short-lived isotopes
Dramatic reduction of the nuclear waste inventory (< 300 years)
Two strategies :
Homogeneous transmutation : Incorporation of MA in low concentration (<5%) to the conventional MOX fuel Am-MOX, Np-MOX, etc.
Heterogeneous transmutation : Incorporation of MA in high concentration (5-30%) in dedicated assemblies at the core periphery
(U,Am)O2, (Pu,Am)O2, etc.

Ferromagnetic semiconductors have been under intensive investigation during the last decade. Until now, III-Mn-V based compound semiconductors are the only well accepted class of materials. The prototype ferromagnetic semiconductor GaMnAs has revealed a variety of unique features induced by the combination of its magnetic and semiconducting properties. To prepare ferromagnetic semiconductors, one needs to dope the host with up to 5-10% Mn, which is far beyond the solid solubility of Mn in III-V compounds. As a non-equilibrium process, ion implantation can introduce enough dopants as required. However, the activation of dopants remains challenging due to the clustering of implanted ions during post-annealing. The solubility limit is a fundamental barrier for dopants incorporated into a specific semiconductor. On the other hand, one notes that the solubility limit in the liquid phase is generally much larger than that in the solid phase. Short-time annealing in the millisecond or nanosecond regime allows the epitaxial growth from a liquid phase. The mature development and commercialization of ion implantation promise the versatility. The approach combining ion implantation and pulsed laser melting allows us to prepare ferromagnetic semiconductors covering the full spectrum of III-V compound semiconductors. We have successfully synthesized ferromagnetic Mn doped III-V from InAs and GaAs to InP and GaP with different bandgaps. The results of magnetization, magnetic anisotropy, resistivity, anomalous Hall effect, magnetoresistance and x-ray magnetic circular dichroism obtained from the synthesized samples confirm the intrinsic origin and the carrier-mediated nature of the ferromagnetism. Moreover, in different III-V hosts we observe distinct differences regarding the magnetic anisotropy and conduction mechanism which are related with the intrinsic parameters such as the lattice mismatch, energy gap and the acceptor level of Mn. These results could allow a panorama-like understanding of III-V:Mn based ferromagnetic semiconductors.
[1] D. Bürger, S. Zhou, et al., Phys. Rev. B 81, 115202 (2010).
[2] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).
[3] S. Zhou, et al., Appl. Phys. Express 5, 093007 (2012).
[4] M. Khalid et al., Phys. Rev. B., 89, 121301(R) (2014).
[5] Y. Yuan, et al, IEEE Tran. Magn., in press (2014).

Ti and its alloys with Al are a class of lightweight materials, which find extensive use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their poor oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
We have developed a technique for protecting the above-mentioned materials against high-temperature environmental degradation (oxidation and embrittlement). In the case of TiAl alloys of an Al content of about 40 to 60 at.% , the technique has involved a single step, i.e. plasma immersion ion implantation (PIII) of fluorine, making use of the so-called “fluorine effect”. Optimum process parameters have been established under which the F-implanted TiAl alloys acquire a stable, adherent and highly protective alumina scale upon subsequent high-temperature oxidation in air. The extent of oxidation protection has been evaluated by testing F-implanted TiAl samples either isothermally or under conditions of thermal cyclic oxidation at temperatures ranging from 900° to 1050°C, and for times as long as 6000 hours. Results from characterization by elastic recoil detection analysis (ERDA), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray analysis (EDX) and Rutherford backscattering spectrometry (RBS) have proven the possibility of forming a protective alumina scale on both laboratory coupons and machine components such as jet turbine blades and turbochargers. In the case of Ti and low-Al-content Ti-Al alloys, e.g. Ti3Al, the technique has involved two steps, namely Al enrichment (aluminization) of the material’s near-surface, and introduction of F by PIII to activate the fluorine effect. Under optimized process conditions, the Ti and Ti3Al samples so modified have shown marked environmental stability at temperatures as high as 700°C and for extended oxidation times due to the presence of a protective alumina layer.

Aluminum enriched coatings have been developed for titanium aluminide alloys. It has been shown that Metal Organic Chemical Vapor Deposition (MO-CVD) and Physical Vapor Deposition (PVD) processes combined with fluorination of the coating enables to reduce significantly the embrittlement of TiAl alloys through oxidation. Even after oxidation at 900 °C for 100h, the coatings exhibit suitable adhesion and 90 % of the fracture toughness and ductility of the alloy are maintained.

Advances in the chemical, crystallographic and isotopic characterization of geological and environmental materials can often be ascribed to technological improvements in analytical hardware or to innovative approaches to data acquisition and/or its interpretation. This biennial review addresses key laboratory methods that form much of the foundation for analytical geochemistry; again this contribution is presented as a compendium of laboratory techniques. We highlight advances that have appeared since January 2012 and which are of particular significance for the chemical and isotopic characterization of geomaterials. Prominent scientists from the selected analytical fields present publications they judge to be particular noteworthy, providing background information about the method and assessing where further opportunities might be anticipated. In addition to well established technologies such as thermal ionization mass spectrometry and plasma emission spectroscopy, this publication also presents new or rapidly growing methods such as electron backscattered diffraction analysis and atom probe tomography – a very sensitive method providing atomic scale information.

The purpose of this presentation is to demonstrate the capability of the Serpent Monte Carlo code to generate few-group constants for existing and innovative reactor systems

Abstract: For temperatures above 750°C, TiAl alloys still show insufficient oxidation resistance and suffer from environmental embrittlement. This work focuses on the surface modification of alloys and development of coatings against environmental embrittlement, as well as on testing of mechanical properties after high temperature oxidation. Aluminum enriched coatings (between 50 and 60 at.%) containing alloying elements, i.e. Cr, Nb, Si, Y, to improve the oxidation behavior and the corrosion resistance have been produced by MO-CVD, CVD, PVD and thermal spraying techniques (HVOF, APS), and have subsequently been chemically modified with halogen elements, notably fluorine. The mechanical properties have been studied by means of 4-point bending and tensile tests on coated samples after 100h oxidation at 900 °C in laboratory air. The CVD process combined with fluorine treatment using plasma immersion implantation (PI³) of F offers the best combination to remedy environmental embrittlement. It has been shown in particular that 90% of the initial fracture strain and fracture stress can be maintained.

Ti-alloys cannot be used at elevated temperatures above approximately 600°C in oxidizing environments. They suffer from accelerated oxidation and oxygen uptake in the subsurface zone, which deteriorates the mechanical properties. The addition of Al (usually < 10%) into standard Ti-alloys is not enough to form a protective alumina layer. Aluminization of technical Ti-alloys and formation of intermetallic Al-rich phases (e.g. TiAl3) change the oxidation behavior from fast and non-protective rutile formation to slow growing alumina kinetics, but only for a limited period of time. A subsequent fluorination of the aluminized components gets the fluorine effect to operate. This is away to improve the resistance of technical Ti-alloys against environmental attack, even for longer service times. In this paper the results of high temperature oxidation tests of several untreated and treated Ti-alloys will be presented and their behavior compared.

Within the framework of German nuclear safety research, generic experimental investigations were carried out at HZDR and the Hochschule Zittau/Görlitz aiming at the elucidation of physicochemical and thermo hydraulic mechanism of corrosion product formation, which may occur during the sump circulation operation after loss-of-coolant accidents in pressurized water reactors.
The contact of the boric acid containing coolant with hot-dip galvanized steel containment internals causes corrosion of the corresponding materials resulting in dissolution of the zinc coating. As main result of batch experiments, decreasing solubility of zinc corrosion products in boric acid solutions with increasing temperature was found. Thus, the formation and deposition of solid corrosion products cannot be ruled out if zinc containing coolant is heated up due to its recirculation into hot regions within the cooling circuit. Generic corrosion and deposition experiments at a lab-scale test facility proved that dissolved zinc, formed at low temperatures in boric acid solution by zinc corrosion, may turn into solid deposits of zinc borates when contacting heated zircaloy surfaces during the heating of the coolant. The results obtained at lab-scale were confirmed by generic experiments at semi-technical scale using a 3x3 heating rod configuration including spacer segments as well as a 16x16 (8x8 heated) fuel rod dummy.
Experiments regarding the corrosion kinetics of zinc-coated components were not subject of the study. Therefore, a quantitative transferability of the results to postulated PWR-LOCA is not given so far.

Titanium and its alloys with aluminum are lightweight structural materials, which find ever-increasing use in a number of advanced aerospace, automotive and power generation applications. These materials, however, are limited in applicability by their inadequate oxidation resistance at elevated temperatures (> 500°C for Ti, and > 750°C for TiAl).
This talk reviews recent advances in using state-of-the-art techniques for surface engineering of Ti, Ti-base alloys and γ-TiAl intermetallics, with a view to rendering them resistant to high-temperature environmental oxidation and oxygen embrittlement.
The first part of the talk covers the surface modification of Ti and low-Al-content Ti-base alloys by using combined techniques involving either aluminization followed by plasma immersion ion implantation (PIII) of fluorine or formation of a surface barrier coating by magnetron sputter co-deposition of Ti and Al followed by vacuum annealing and PIII of F.
The second part focuses on the direct surface treatment of γ-TiAl by PIII of F. Such type of fluorination enables the F-implanted alloy surface to develop a stable, adherent and highly protective alumina scale upon subsequent oxidation in air at temperatures in excess of 1000°C for extended exposure times.
The last part deals with the fabrication of protective TiAl coatings using a two-step coating scheme. First, an Al-rich TiAl layer is formed on the γ-TiAl alloy by either MO-CVD, PVD or thermal spraying. Then the TiAl layer is treated by PIII of F. The resulting coatings are tested for oxidation resistance, oxygen embrittlement, and retention of mechanical properties. A combination of an Al-rich CVD coating and treatment by PIII of F gives the best results. An example is also given of a thermal barrier coating whose structure comprises, instead of a bond coat, a thin alumina layer formed by PIII of F and subsequent high-T oxidation. The results of these studies have been helpful in understanding the oxidation behavior of the surface-engineered alloys from both a scientific and a technological standpoint.

Low-Al content Ti-base alloys and TiAl intermetallics are attractive lightweight materials for advanced medium-temperature (500°-750°C) structural applications including components such as jet engine and industrial gas turbine blades, turbocharger rotors and automotive engine valves. However, envisaged service temperatures are in the range of 750° to 1050°C at which these alloys are prone to both destructive oxidation and oxygen embrittlement. Therefore, development of surface-engineering techniques for preventing high-T environmental damage is critical in exploiting the advantages of the TiAl alloys to their fullest extent.
We propose two techniques for protecting candidate Ti-base and TiAl alloys from high-temperature (>750°C) oxidation environments. The first technique involves a single step, namely treating the alloys directly by plasma immersion ion implantation (PIII) of fluorine using a mixture of CH2F2+6.25% Ar as the precursor gas. This technique is applicable to TiAl alloys of an Al content of ~ 45 to 55 at.%. The F implant dose has been found to depend critically on the gas flow rate ratio (GFRR, i.e. CH2F2/Ar) while the resulting F depth profiles show dependence on both the GFRR and the alloy material. Optimum implantation conditions have been established under which the F-implanted alloy surface is able to form a highly protective Al2O3 film upon subsequent oxidation in air. Oxidation resistance has been evaluated by thermal gravimetric analysis (TGA) at temperatures as high as 1050°C for extended exposure times.
The alternative technique is applicable to low-Al-content Ti-base alloys (< 40 at.% Al). It involves the fabrication of a barrier coating in a three-step process, namely formation of a Ti+Al layer by magnetron co-sputtering of Ti and Al followed by vacuum annealing to form a gamma-TiAl coating and, finally, PIII of fluorine. The coating so formed has been shown to prevent further oxidation of the base material at elevated temperatures.

(−)-¹⁸F-flubatine is a promising tracer for neuroimaging of nicotinic acetylcholine receptors (nAChRs), subtype α4β2, using PET. Radiation doses after intravenous administration of the tracer in mice and piglets were assessed to determine the organ doses (ODs) and the effective dose (ED) to humans. The results were compared with subsequent clinical investigations in human volunteers.
Methods:
Twenty-seven female CD1 mice (weight ± SD, 28.2 ± 2.1 g) received intravenous injection of 0.75 ± 0.33 MBq of (−)-¹⁸F-flubatine. Up to 240 min after injection, 3 animals per time point were sacrificed and the organs harvested, weighed, and counted in a γ counter to determine mass and activity, respectively. Furthermore, whole-body PET scans of 5 female piglets (age ± SD, 44 ± 3 d; weight ± SD, 13.7 ± 1.7 kg) and 3 humans (2 men and 1 woman; age ± SD, 59.6 ± 3.9 y; weight ± SD, 74.3 ± 3.1 kg) were obtained up to 236 min (piglets) and 355 min (humans) after injection of 186.6 ± 7.4 and 353.7 ± 10.2 MBq of (−)-¹⁸F-flubatine, respectively, using a PET/CT scanner. The CT was used for delineation of the organs. Exponential curves were fitted to the time–activity-data, and time and mass scales were adapted to the human anatomy. The ODs were calculated using OLINDA/EXM (version 1.0); EDs were calculated with the tissue-weighting factors of ICRP103.
Results:
After the injection of (−)-¹⁸F-flubatine, there were no adverse or clinically detectable pharmacologic effects in any of the subjects. The highest activities after injection were found in the kidneys, urinary bladder, and liver. The urinary bladder receives the highest OD in all investigated species, followed by the kidneys and the liver for animals and humans, respectively. On the basis of mouse, piglet, and human kinetic data, the projected human ED of (−)-¹⁸F-flubatine was estimated to be 12.5 μSv/MBq in mice, 14.7 ± 0.7 μSv/MBq in piglets, and 23.4 ± 0.4 μSv/MBq in humans.
Conclusion:
As has been demonstrated for other PET radiotracers, preclinical (i.e., animal-derived) dosimetry underestimates the ED to humans, in the current case of (−)-¹⁸F-flubatine by 34%–44%.

The application of heavy liquid metals as coolant or heat transfer medium in advanced reactor systems demands for a comprehensive knowledge of the flow characteristics. CFD simulations are the main tool to predict the flow behaviour, however, the numerical models have to be validated by experimental data. Flow measurements in hot liquid metals are challenging and the available choice of measuring techniques is rather limited. A great deal of work was done during the last decade to develop suitable measuring principles for applications in metallic melts. The Ultrasound Doppler method can be considered as an attractive technique to obtain real-time velocity profiles in liquid metal flows. Flow measurements in hot metallic melts involve several specific problems, especially the high temperature and the abrasive character of the melt. Furthermore, a sufficient input of acoustic energy into the melt to be measured requires favourable conditions concerning acoustic coupling, transmission and wetting. Moreover, the availability of seeding particles has to be guaranteed to obtain Doppler signals from the fluid. We will present a concept for velocity measurement in a liquid metal channel flow based on high temperature transducer probes in combination with a matched mechanical design of the probe seating. Specific measuring procedure enables us for reliable measurements in a temperature range up to 230°C. The measuring principles are successfully applied at experimental facilities operating with different metal alloys and geometric configurations: At the LIMMCAST (Liquid Metal Model for Continuous Casting) facility of Helmholtz-Zentrum Dresden-Rossendorf we studied the flow profile of a Sn60Bi40 alloy in a circular pipe. Furthermore, the LBE duct flow of the META:LIC loop (Megawatt Target: Lead Bismuth Cooled) at the Institute of Physics in Riga-Salaspils (University of Latvia) was measured. Parametric studies of the velocity profile measurements in the ducts will be presented here. Specific problems arising for the application of the Ultrasound Doppler method in the considered experimental configuration will be discussed.

Because of the flexibility between the tri- and tetravalent oxidation states, cerium (Ce) is known to be the only rare earth element (REE) forming a stable pure stoichiometric dioxide compound (CeO2). Owing to this chemical specificity along with the highest natural abundance of Ce among all REEs, the application of CeO2 has spread over a variety of fields. More recently, CeO2 has been employed as nanoparticles with many technological applications, which include the catalysts for harmful gas treat-ment the water gas shift reaction, electrodes for solid oxide fuel cells and a medical use as an artificial superoxide dismutase. These versatile and still emerging applications of CeO2 still require a simpler and more efficient synthetic strategy, particularly for manufacturing CeO2 nanoparticles.
The hydrolysis of tetravalent cerium (Ce(IV)) is a primary step of many wet syntheses for fabricating CeO2 nanoparticles, although all the reported synthetic methods require additional processes, such as heating, adding organic solvents or calcination, subsequent to the initial hydrolysis step to finally yield CeO2 nanoparticles. This means that understanding of the hydrolysis mechanism of Ce(IV) would be beneficial to developing a new concept for the efficient production of CeO2 nanoparticles. Based on this background, this study focuses on the systematic investigation of the hydrolysis behaviour of Ce(IV) using synchrotron-based X-ray techniques (X-ray absorption spectroscopy (XAS) and high en-ergy X-ray scattering (HEXS)), dynamic light scattering (DLS) and transmission electron microscopy (TEM).

The liquid residence time and backmixing in an inclined rotating tubular fixed bed reactor, operated with gas-liquid co-current downflow, are studied experimentally. This novel reactor concept is introduced to extent the process intensification strategies of chemical multiphase reactors. The intermittent catalyst immersion due to rotation induces a continuous refreshment of the liquid at the catalyst surface and enhances the access of the gas phase to the catalyst in the drained section of the fixed bed. Depending on the inclination angle and rotational velocity, different flow regimes are observed. In particular, the flow regimes with stratified gas-liquid flow can be utilized to enhance the performance of the reactor for heterogeneous catalytic reactions.
The backmixing study is based on the method of the imperfect tracer pulse and the propagation of the tracer is measured by low-intrusive wire-mesh sensors. Compared to conventional trickle bed reactors, the liquid residence time and axial dispersion are increased by the inclination and rotation. The effects of reactor inclination angle and rotational velocity as well as of particle size and liquid superficial velocity on the liquid backmixing in the inclined rotating tubular fixed bed reactor are shown in detail.

During loss-of-coolant accidents (LOCAs) in pressurized water reactors (PWRs), coolant spilling from the leak in the primary cooling circuit is collected in the reactor sump and recirculated to the reactor core by low pressure injection pumps as part of the emergency core cooling system. The long-term contact of the boric acid containing coolant with hot-dip galvanized steel containment inter-nals (e.g. grating treads, channels, supporting grids of sump strainers) may cause corrosion of the corresponding materials influencing the cooling water chemistry due to dissolution of the zinc coating. Experimental investigations regarding the solubility of Zn corrosion products in boric acid solutions resulted in a decreasing solubility with increasing temperature. Thus, the formation of solid (i.e. particulate) corrosion products cannot be ruled out if the Zn containing coolant is heated up due to its recirculation into hot zones.
During lab-scale experiments, significant amounts of solid corrosion products have been found as deposited layers on hot surfaces as well as in the form of deposits at tubes, fittings and retaining components depending on formation temperature and hydrodynamic conditions. The solid corrosion products were identified as zinc borates. Depending on their forming temperature, different zinc borate compounds may occur having different physicochemical properties.
Although the kinetics of the processes obtained at lab-scale are not transferable to those proceeding during a PWR LOCA due to their dependency on the corroding surface area as well as on the local thermal hydraulics, the results give an insight into physicochemical processes, which might occur in case of zinc corrosion in cooling circuits.

Im Rahmen der Reaktorsicherheitsforschung erfolgten an der Hochschule Zittau/Görlitz in Kooperation mit dem Helmholtz-Zentrum Dresden-Rossendorf experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen und deren Auswirkungen auf thermo-fluiddynamische Prozesse, welche während des Sumpfumwälzbetriebs nach Kühlmittelverluststörfällen in einem Kernkraftwerk ablaufen können, falls in boriertem Kühlmittel (KM) gelöstes Zink in Kernbereiche höherer Temperatur (Hot-Spots) gelangt. Das im KM befindliche Zink kann hierbei im Vorfeld durch die Korrosion feuerverzinkter Bauteile freigesetzt werden.
In den Untersuchungen im halbtechnischen Maßstab wurden die physiko-chemischen Mechanismen und der Temperatureinfluss analysiert. Gleichzeitig wurden Auswirkungen dieser Prozesse auf das thermo-fluiddynamische Verhalten in einer Heizstabkonfiguration (3x3-Anordnung mit für Druckwasserreaktoren (DWR) typischen Zirkaloy-Hüllrohren) mit Abstandshaltern erfasst. Im Fokus der Untersuchungen stand dabei das Verhalten derart zusammengesetzter Fluide an beheizten Konfigurationen, die im Kern von DWR auftreten können.
Die durchgeführten Untersuchungen tragen generischen Charakter und liefern Aussagen zum Löslichkeitsverhalten von Zink in borsäurehaltigem KM sowie zur Bildung fester Korrosionsprodukte und den daraus folgenden Auswirkungen.

A major goal of molecular electronics is the development and implementation of devices such as single-molecular switches. Here, measurements are presented that show the controlled in situ switching of diarylethene molecules from their nonconductive to conductive state in contact to gold nanoelectrodes via controlled light irradiation. Both the conductance and the quantum yield for switching of these molecules are within a range making the molecules suitable for actual devices. The conductance of the molecular junctions in the opened and closed states is characterized and the molecular level E0 , which dominates the current transport in the closed state, and its level broadening Γ are identified. The obtained results show a clear light-induced ring forming isomerization of the single-molecule junctions. Electron withdrawing side-groups lead to a reduction of conductance, but do not influence the efficiency of the switching mechanism. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by electron-withdrawing substituents. This full characterization of a molecular switch operated in a molecular junction is an important step toward the development of real molecular electronics devices.

CFD simulations using the Euler-Euler approach are performed to model the gas-liquid bubbly flow in a helical static mixer. The model validation work was based on experiments, which are carried out in a column of diameter 0.08 m packed with helical static mixer elements (length 80 mm / diameter 80 mm). Measurements of gas volume fractions, gas velocities and bubble size distributions by in-house developed ultrafast X-ray electron beam tomography were taken at several planes within the mixer elements (Rabha et al. 2014).
The predicted axial and radial gas phase distribution considering different mono-disperse bubble sizes (3, 5.8 and 8 mm) are studied and validated against the experimental results. The dependency of non-drag forces on the bubble size was considered. Consequently, the bubble size dependent effects of the non-drag forces on the flow and on the cross sectional gas volume fraction distribution are shown.
Despite obvious shortcomings of the models for this application, some conclusions on the suitability of certain mixer designs for gas-liquid dispersion may be drawn already. The swirling flows created by the twist and turn of the helical mixer elements, which in turn pushes the lighter phase towards the center of the pipe is well predicted and validated. Further investigations have to consider the bubble size distribution e.g. by a population balance model to accurately predict the dispersion of the gas phase within and downstream the helical static mixer.

Das Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) fokussiert sich auf interdisziplinäre und technologieorientierte Projekte zur energie- und ressourceneffizienten Nutzung von Hochtechnologierohstoffen aber auch die Nutzung von anderen Metallen und ihren Nebenprodukten. Seit 2011 haben die AHK Chile und das ihr angegliederte Kompetenzzentrum für Bergbau und Rohstoffe gemeinsam mit dem HIF sehr erfolgreich mehrere geeignete chilenische Partner aus Industrie und Forschung identifiziert und erste Projektanbahnung unterstützt. Hierzu zählt unter anderem ein BMBF gefördertes Projekt mit der Codelco Tochter IM2. Besuche bei Projektpartnern und Veranstaltungen wie den Deutsch-Chilenischen Wirtschafstagen, dem Länderworkshop Chile der Vereinigung Rohstoffe und Bergbau e.V. oder den Freiberger Innovationstagen bieten gute Gelegenheiten für persönliche Gespräche. Dies wird komplementiert durch einen regelmäßigen E-Mail-Austausch zu aktuellen Entwicklungen. Dabei profitieren die Wissenschaftler des HIF stark vom großen Engagement des Kompetenzzentrums auch in der Begleitung der Projekte.

The reference temperature T0 was measured for both T-S and T-L- specimen orientation in 24 layers across the thickness of the beltline weld of a reactor pressure vessel. It turned out to vary in a bandwidth of more than 40K. Because of a high scatter, no clear pattern of T0 as a function of the thickness position could be recognized. A more detailed analysis revealed that the median of KJc was considerably steeper than predicted by the Master-Curve, which leads to a bias of T0 with respect to the testtemperature relative to T0. By a modified evaluation procedure, the scatter of the reference temperature could be significantly reduced, which enabled the global pattern of T0 to be recognized. By comparing the theoretical lower bound to KJc-data of the used specimens with the individual measured KJc a representative T0 that characterizes the overall toughness behaviour of the weld was determined. It turned out to be about 10 K lower than the maximum local T0.

Inter-band transitions in single quantum dots (QDs) have received a huge amount of scientific interest in the recent past. However, mostly due to technical challenges in dealing with mid- and far-infrared radiation, intra-band transitions have not been explored quite as thoroughly. In this work, we combine micro-photoluminescence (µPL) on low-density annealed InAs/GaAs QDs with additional excitation at intra-band transition energies by pulsed radiation from a free-electron laser (FEL). This scheme enables the probing of the single-dot response in spite of the large diameter of the FEL focus. The investigation of single QDs eliminates undesirable effects such as inhomogeneous broadening which has been observed in previous studies on QD ensembles1–3. In the time domain, the FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. The subsequent recovery is significantly larger than would be expected for simple redistribution. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse. When investigating at the PL spectrum of a single dot, we observe a marked difference caused by the FEL pulse (Fig. 2), which implies a change of the excitonic state of the QD.

Compared to the vast amount of research done in the past on inter-band transitions in single quantum dots (QDs), transitions within the bands have received much less attention. The main reasons for this are most likely the largely non-radiative character of intra-band transitions and the technical difficulties associated with the corresponding mid- and far-infrared radiation. In our contribution, we approach this challenge by combining conventional micro-photoluminescence (µPL) on low-density annealed InAs/GaAs self-assembled QDs with additional excitation at intra-band (i.e. inter-sublevel) transition energies by pulsed radiation from a free-electron laser (FEL). In contrast to previous studies on ensembles of QDs1–3, using single dots eliminates undesirable effects such as inhomogeneous broadening. The FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. This is followed by a pronounced recovery, such that the integrated PL is larger than for a reference transient without FEL excitation. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse.

Introducing a few hundredths of a percent of nitrogen into a GaAs-based semiconductor leads to dramatic changes of the electronic and optical properties of the original material system. This can be used in order to intentionally tune the semiconductors characteristics. In particular the bandgap of semiconductors like GaAs and InGaAs, can be strongly reduced by slight nitrogen incorporation, which is attractive for applications, in particular for detectors or light sources.

Even though a lot of effort has been made on the investigation of the effective mass in GaAsN, it is rather challenging to describe the and stucture and in particular the effective mass of this system. We investigate a series of GaAsN samples and make use of high magnetic fields in combination with THz radiation from a free-electron laser, which provides a unique approach in order to find the source of previous inconsistencies. Cyclotron resonance spectroscopy is probably the most direct way to measure the effective mass, but has never been applied before to GaAsN bulk. We compare the results of this method with those of magneto-photoluminescence (PL), which is more commonly applied to dilute nitrides.

Our cyclotron resonance spectroscopy results indicate that the effective mass is not very much affected by the nitrogen doping, in contrast to previous reports (e.g. [1–4]) based on magneto-PL. In our PL investigations in magnetic fields up to 61 T, the observed blueshift of the PL spectrum indicates a similar increase of the effective mass, as reported before in e.g. [1–4]. We will discuss the significance of the particular method and argue that some assumptions have to be reconsidered.

The impact of proton and electron irradiations on the electrical parameters of 4H-SiC nMOSFETs has been investigated by the time bias stress instability method. This study has allowed observing the effect of holes trapped in the gate oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage, the effective mobility and the maximum drain current were observed. These improvements could be connected with the Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of passivated Carbon atoms is increased, hence improving the SiO2/SiC interface quality.

The spin Nernst effect describes the occurrence of a spin current perpendicular to an applied thermal gradient and the spin quantization axis in a non-magnetic material. To quantify the effect, the spin Nernst angle will be defined in a more general way than in ref. [1]. This allows for a clear separation of the transverse spin current into two opposite contributions proportional to the spin Hall angle and the spin Nernst angle, respectively. Qualitative trends for Cu alloys with 3d, 4d and 5d defects extending a resonant scattering model by Fert and Levy [2] will be presented.
The work was partially supported by the Initiative and Networking Fund of the German Helmholtz Association, Helmholtz Virtual Institute MEMRIOX (VH-VI-442) and the DFG Priority Program 'Nanostructured Thermoelectrics' (ZA264/3-2).

In Traveling-Wave Thomson-Scattering (TWTS) a high-power laser pulse is scattered off a relativistic electron pulse to produce radiation from EUV to Angstrom wavelength. TWTS employs a side-scattering geometry where laser and electron propagation direction enclose an angle to become independent of the Rayleigh length limit for the maximum interaction distance in standard head-on Thomson scattering geometries. For optimum spatial overlap in TWTS geometries the laser pulse features a pulse-front tilt. In this way, the electrons interact with all parts of the laser pulse and brilliances as well as photon scattering efficiencies are by orders of magnitude larger than in standard head-on geometries.
Interaction distances in TWTS are long enough for operation of a free-electron laser.
We show how TWTS experiments can be designed, present experimental parameters for TWTS FELs and discuss experimental challenges in their realization.

Resistive switching devices with Nb2O5 as a switching layer are treated with argon ion irradiation, which generates defects in the oxide layer that support the electroforming step. To distinguish between the effects of layer thinning by sputtering and that of defect generation, devices with different thicknesses of deposited oxide are investigated. It is found that the defect-rich interfaces allow the formation of thick oxides at low forming voltages, and therefore, the effects of the ion irradiation are comparable to the use of reactive electrodes.

[¹⁸F]NS10743, a promising and highly competitive α7 nAChR radioligand has been synthesised so far by microwave irradiation using a manual single-mode device followed by a palladium-catalyzed reduction of remaining nitro-precursor for HPLC separation purposes. For further preclinical and clinical use, regulated production of [¹⁸F]NS10743 by fully automated radiosynthesis is a crucial requirement. Therefore, we chose a commercial synthesis module and developed the automated radiosynthesis of [¹⁸F]NS10743. Besides evaluation of several radiosynthesis procedures, we performed an extensive HPLC study for quantitative separation of [¹⁸F]NS10743 from the corresponding nitro precursor. After implementation of the optimised procedure on a TRACERlabTM FX F-N synthesis module, [¹⁸F]NS10743 was obtained in high radiochemical purity (≥ 99%) with an overall radiochemical yield of 32.27% (n=3). The specific activities at the end of the synthesis were 571±17 GBq/µmol (n=3).

Der mittlere Infrarot- und Terahertz-Bereich bietet Zugang zu einer Vielzahl von faszinierenden Effekten in Halbleiter-Quantenstrukturen, da in diesem Spektralbereich eine Vielzahl von elementaren und kollektiven Anregungen wie z. B. Phononen, Plasmonen und Intersubbandübergängen liegen. Der Freie-Elektronen-Laser FELBE ist durchstimmbar im Bereich von 1 – 80 THz und liefert einen kontinuierlichen Zug von intensiven, schmalbandigen Pikosekundenpulsen, die sich ideal für nichtlineare Spektroskopie und resonante Anregung eignen. Wir zeigen exemplarisch Experimente an zweidimensionalen und nulldimensionalen Systemen und diskutieren sie hinsichtlich spektraler, zeitlicher und räumlicher Auflösung. Insbesondere wird die Ladungsträgerdynamik in selbstorganisierten Halbleiter-Quantenpunkten sowie Spektroskopie an einzelnen Quantenpunkten gezeigt [1-3]. Weiterhin stellen wir Resultate zur Ladungsträgerdynamik in Graphen vor [4,5]. Die Untersuchungen geben wichtige Einblicke in das Verhalten von Ladungsträgern auf kurzen Zeitskalen, insbesondere zu ihrer Phasenkohärenz, ihrer Wechselwirkung untereinander und ihrer Wechselwirkung mit Phononen. Neben der grundlegenden Bedeutung ist die Kenntnis er Kurzzeitdynamik wichtig für die Entwicklung zukünftiger optoelektronischer Bauelemente wie Detektoren, Strahlungsquellen und Elementen zur Informationsspeicherung in Quantencomputern.

[1] E. A. Zibik et al., Nature Mat. 8, 803 (2009).
[2] M. Teich et al., Appl. Phys. Lett. 103, 252110 (2013).
[3] R. Jacob, Nano Lett. 12, 4336 (2012).
[4] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[5] M. Mittendorff et al., Nature Phys. (under review).

In the energy region between –1 eV and 1 eV the band structure of graphene is in good approximation described by identical isotropic Dirac cones for electrons and holes, respectively. Therefore, optical properties for interband excitations are typically considered to be isotropic for photon energies below 2 eV. However, our pump-probe experiments at a photon energy of 1.6 eV reveal a pronounced anisotropy in both the excitation characteristics and the subsequent relaxation dynamics. The anisotropy with 2-fold symmetry is induced by the linear polarization of the pump radiation. We compare the experimental results with calculations based on the density matrix formalism and show that optical phonons are mainly responsible for reaching an isotropic carrier distribution.
In the experiments, carried out on multilayer epitaxial graphene, the angle between the polarization of pump and probe beam was varied. Pumping and probing with parallel polarization resulted in two times larger pump-induced transmission as compared to pumping and probing with orthogonal polarization [1]. The initial relaxation after the transmission maximum is faster in the parallel polarization configuration. For time delays larger than 150 fs the induced transmission is similar for the two polarization configurations, indicating that an isotropic carrier distribution is reached. The observed anisotropy in the induced transmission is direct evidence for an anisotropic carrier distribution in k-space. This anisotropy has been predicted by theory [2]. Carriers are preferentially excited in directions perpendicular to the polarization vector of the pump beam. Microscopic modelling, which describes the experimental finding well, allows us to attribute the fast initial relaxation to collinear carrier-carrier scattering. Scattering via optical phonons is mainly responsible for reaching an isotropic distribution.
The results are of fundamental importance as they concern an aspect of the carrier dynamics that has escaped experimental observation so far, despite the large number of publications describing near-infrared pump-probe experiments on graphene. With respect to applications our findings may enable all-optical switches that react differently to pulses of different polarization direction.

References
[1] M. Mittendorff, T. Winzer, E. Malic, A. Knorr, C. Berger, W.A. de Heer, H. Schneider, and M. Helm, Nano Lett. (2014) dx.doi.org/10.1021/nl404730y.
[2] M. Malic, T. Winzer, and A. Knorr, Appl. Phys. Lett. 101, 221115 (2012).

The carrier dynamics within the system of Landau levels of index n = -1 to n = 0 and n = 1 in graphene is investigated by pump-probe experiments using circularly polarized terahertz radiation. The study, complemented by microscopic modelling, reveals a pronounced carrier redistribution caused by strong Auger scattering.

I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. I will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.

Complex biogeochemical processes are essential in various subsurface ecosystems (like in soils and rock formations), and are relevant for e.g. effective bioleaching of metals from various ores. For an improved mechanistic understanding of biogeochemical processes a non-invasive detection method of present microorganisms in a given geological sample is crucial. Ideally, microorganisms from all kingdoms should be determined in a single step (and may be later differentiated from DNA or cell degradation). Furthermore, microbial responses to changes of the physical or chemical conditions of the system such as flow regime, pH, and nutrient concentrations could be addressed non-invasively.
Our strategy for in-situ identification of microorganism in geological samples is to use labeled antimicrobial peptides (AMPs) as selectively binding agents. In the nuclear medical sciences, this strategy is successfully applied for the identification and visualization of bacterial infections in humans [1]. We aim at tagging the AMPs first with fluorescent dyes, in a later step with the radionuclide ¹⁸F for imaging with positron emission tomography (PET).
For our study, AMPs are selected based on their ability to bind to the cells of the tested bacterial strains in sub-lethal concentrations while their sorption to matrix compounds is minimal. We show that AMPs readily interact with microorganisms commonly found in soils such as Pseudomonas fluorescence and Lysinibacillus sphaericus. We aim at labeling the AMPs by means of established, commercial crosslinkers.
In combination with our GeoPET method [2-4] ¹⁸F-radiolabeled AMPs were an extremely useful agent for the in-situ visualization of microorganisms also in opaque geological environments. Radiolabeled AMPs could be used for the visualization of growth and dispersal of microbial communities in such environments.

Population dynamics in graphene Landau levels

UV-vis absorption spectroscopy proves itself as an convenient method for in-situ monitoring the formation and growth of waterborne An(IV) nanoparticles. Dilution of pure aqueous Np(CO3)56- species in ultrapure water leads to the dynamic self-assembling of NpO2 nanocrystals, monitored among others at absorbance 742 nm.

Nowadays, various state-of-the-art spectroscopic techniques (e.g., X-ray spectroscopies, laser-induced and vibrational spectroscopy, etc.) are available to investigate chemical interactions of actinides (An) on a molecular level. Old-fashioned (or conventional) UV-vis absorption spectroscopy is often underestimated as a powerful tool to investigate the chemistry of An, including An(IV) colloids. The present study spotlights the application of UV-vis absorption spectroscopy to studying the colloid system of An(IV). The chemistry of An(IV) in aqueous solution is typical of a small and highly-charged metal ion with a strong hydrolysis tendency leading low solubility, which often result in the underestimation of the migration behavior of An(IV) on the geological disposal of radioactive wastes. The formation mechanisms of An(IV) colloids?, especially under alkaline and near-neutral conditions relevant to the actual environment, are still unexplored even to date. One important issue to be addressed in An(IV) colloid chemistry is the chemical identification of An(IV) colloids. That is, are the colloids formed ill-defined hydroxide precipitate or hydrous oxides, or highly structured clusters/nanoparticles? In order to characterize An(IV) colloids, we investigated in-situ the aggregation of neptunium(IV) colloids formed under ambient aqueous alkaline conditions. The kinetics of the aggregation of Np(IV) colloids and the formation of Np(IV) nanoparticles were tracked by UV-vis absorption spectroscopy, and their morphology and internal structures were further investigated by transmission electron microscopy (TEM). In this study, we demonstrate that UV-vis absorption spectroscopy is an unique and powerful tool for in-situ monitoring of the hydrolysis reaction of Np(IV) and associated colloid/nanoparticle formation. The obtained results will be further discussed by combining with TEM and X-ray absorption spectroscopy.

The chemistry of tetravalent actinides An(IV) in aqueous solution is typical of a small highly-charged metal ion with a strong tendency to hydrolize and therefore a low solubility. Disregarding the formation of clusters, nanoparticles and colloids lead to underestimation of the migration behavior. The reaction mechanisms of formation and growth, especially under alkaline and near-neutral environmental conditions are still unexplored. On the way from aqueous species to nanoparticles two fundamental questions in An(IV) chemistry provoke discussion in literature: 1) are hydrolysis and condensation the driving forces toward nano-scaled solids or 2) are formed aggregates ill-defined complex hydroxides, hydrous oxides or highly structured clusters/nanoparticles? Excluding the presence of other oxidation states then An(IV), we performed in situ investigation of the self organised formation of neptunium(IV) aggregates and nanoparticles from aqueous complex precursor under alkaline conditions. The kinetics of the self-assembling of the nanoparticles, their morphology and internal structures were determined. The influence of silica on the formation of highly coordinated NpO2 structure was proved. In particular, former studies confirmed the formation of amorphous silica-containing U(IV) and Th(IV) colloids. Starting from aqueous neptunium(IV) carbonate complexes, we investigated the behavior after dilution in presence and absence of silica by TEM, EXAFS, UV vis spectroscopy, Ultrafiltration and DLS (dynamic light scattering). The formation of nanoparticles was observed. TEM and diffraction pattern show different morphologies and internal structures in dependence of presence or absence of silica.

Salzschmelzenreaktoren besitzen eine lange Historie, zurückgehend auf mehrere Experimente am Oak Ridge Mational Laboratory, die bereits in den 50er und 60er Jahren stattfanden. Das bekannteste hiervon ist das Molten Salt Reactor Experiment (MSRE). Das Konzept des Salzschmelzenreaktors verschwand danach aus dem wissenschaftlichen Fokus. Um die Jahrtausendwende wurde das Konzept dann von russischer und von europäischer Seite wieder aufgegriffen. Zusätzlich wurde das Konzept des Salzschmelzenreaktors im Rahmen des Generation IV International Forums (GIF) als eines der 6 Reaktorkonzepte verankert.
Mit Hinblick auf das Ziel Sustainability des GIF hat sich bereits nach kurzer Zeit eine Verschiebung des Konzeptes für Salzschmelzenreaktoren ergeben. Derzeit untersuchte Reaktoren sind als sogenannte schnelle Systeme ausgelegt und besitzen in im Gegensatz zum MSRE keine Graphitstrukturen innerhalb des Reaktorkerns. Salzschmelzenreaktoren mit schnellem Neutronenspektrum eigenen sich aber nicht nur zur Energieproduktion, sondern sind auch als Transmutationssystem von Interesse und bieten für diesen speziellen Einsatz diverse Vorteile.
Im Vortrag werden die wichtigsten Unterschiede von Reaktoren mit festem Brennstoff (z. B. Sodium Cooled Fast Reactor) und Reaktoren mit flüssigem Brennstoff analysiert und diskutiert. Darauf aufbauend werden die spezifischen Vorteile von Salzschmelzenreaktoren für die Transmutation hergeleitet und die spezifischen Herausforderungen erörtert. Ein besonderer Blick gilt auch den Konsequenzen die sich durch das veränderte Neutronenspektrum, im Vergleich zum MSRE, ergeben.
Abschließend werden ausgewählte neueste wissenschaftliche Ergebnisse zu Salzschmelzenreaktoren vorgestellt. Es wird ein kurzer Einblick in die Ergebnisse der deutschen P&T Studie gegeben und die daraus resultierenden Konsequenzen auf eventuelle zukünftige Forschungsarbeiten zu Salzschmelzenreaktoren beleuchtet.

An overview on the history of molten salt reactors and the projects of the last years is given. The major advantages of molten salt reactors in the view of transmutation are discussed and evaluated in comparison with sodium cooled fast reactors. Finally some scientific highlights are given for the application of molten salt reactors under the bounday conditions of the nuclear ophase out decission in Germany.

The molten salt reactor technology has gained renewed interest. In contrast to the historic molten salt reactors, the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes significantly more challenging than in historic concepts. One very interesting and innovative result of the most recent EURATOM project on molten salt reactors – EVOL – is the fluid flow optimized design of the inner core vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all core internal structures. On the basis of this new geometry a model for neutron physics calculation is presented and applied for a shielding optimization. Based on these results an optimized shielding strategy is developed for the molten salt fast reactor to keep the fluence in the safety related outer vessel below expected limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system has to be significantly increased and will finally be comparable to a sodium cooled fast reac-tor. The HELIOS results are verified against Monte-Carlo calculations with very satisfactory agreement for a deep penetration problem.

The 'Energiewende' in Germany has put some questions on the future of the P&T research. The Bundesministerium für Wirtschaft Energie and the Bundesministerium für Bildung und Forschung have launched a study in 2012 to answer these questions on a broad scientific basis. A major point during the discussions was the so-called last transmuter problem. This requires special attention in the case of the nuclear phase out, since transmutation of transuranium isotopes is only attractive under the phase out condition when this problem can be solved. Recently, a solution has been proposed, the so-called twofold operation cycle using a molten salt fast reactor.
Based on this proposal a simulation for the burning of the 170t TRUs remaining in Germany after the phase out as efficient as possible. A salt configuration based on the MOSART composition is used which is able to carry the required amount of TRUs for the fertile free operation. The requested number of reactors, the required operation time and the expected TRU leftovers are determined. Finally, a general discussion is added which major R&D topics would have to be envisaged for the realization of P&T in a molten salt fast reactor.