Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

In consideration of the practical importance regarding the application of gas–liquid flow in a vertical pipe and the quest towards the development of more robust physical models to accurately predict the essential interfacial parameters of the two-phase flow, comprehensive analysis of the characteristics and phase distribution patterns of such a flow have been performed on both experimental measurements and theoretical predictions. In this first part, analysis of experimental data in a large diameter pipe with an inner diameter of 195.3 mm via the wire-mesh senor measuring technique was presented. The experiments were performed at the TOPFLOW facility of Helmholtz-Zentrum Dresden-Rossendorf. In the present paper, measurements of local interfacial parameters which included the void fraction, volume equivalent bubble diameter, bubble size distribution and interfacial velocities were discussed. Test points covering flow regimes from bubbly to cap to slug to churn-turbulent flow were selected to investigate the flow of different bubble shapes and sizes and the significant bubble coalescence and break-up mechanism throughout the large vertical pipe. The radial and axial evolutions of the local flow structure were interpreted in terms of the classifications of different groups of bubbles (Group-1 and Group-2). In addition, the phase distribution patterns were analyzed through the concept of skewness, which essentially identified two fundamental patterns, namely, wall peak and core peak. In general, Group-1 bubbles being smaller spherical bubbles have shown to exhibit a wall peaking distribution while Group-2 bubbles being larger non-spherical bubbles corresponded to a core peaking distribution. The classification of bubbles that have been performed in this present study can be employed for the development of bubble coalescence and break-up mechanistic kernels and other interfacial force closure models for a two bubble group approach in the context of computational fluid dynamics.

The main objective of this project was to study the interaction processes between An(III)/Ln(III), (representated by Am(III) and Eu(III), respectively), organic model ligands, and Opalinus Clay at elevated temperature (until 80°C). The thermodynamic data (log, ΔG, ΔH and ΔS) for the complexation and sorption processes have been derived and led to an enhancement of the thermodynamic database by data at elevated temperatures.

The complexation of Am(III)/Eu(III) with small organic ligands (pyromellitic, salicylic, lactic, acetic, citric, and tartaric acid) that serve as model ligands for natural organic material, like humic substances or clay organic was investigated by temperature dependent UV-Vis and time-resolved laser-induced fluorescence spectroscopy (TRLFS).
For the first time, the UV-Vis absorption spectroscopy utilizing a Long Path Flow Cell (LPFC) has been established for speciation analysis of Am(III) at trace concentrations. A detection limit of 5*10-9 mol/l-1 Am(III) was determined with an 2 m LPFC.
Several Am(III)/Eu(III)-organic ligand complexes were spectroscopically and thermodynamically characterized. General, all studied complexation reactions are endothermic and driven by entropy.
Furthermore, the interaction of Eu(III) with pyromellitc acid (1,2,4,5-benzene-tetracarboxylic acid) had been studied in detail with additional methods like isothermal titration calorimetry (ITC) and Fourier-transform infrared spectroscopy in combination with density function theory (DFT) calculations. At elevated temperature and higher concentration (> 5 mM Eu(III) and pyromellitic acid) a temperature-dependent polymerization was observed. It had been shown that predominantly chelating coordination with two carboxylic groups in the monomeric complex and monodentate binding of a single carboxylic group in the polymeric complex of the polycarboxylate with Eu(III) occurs.

The sorption of Eu(III) on Opalinus Clay was investigated in absence and presence of the small organic ligands citric and tartaric acid at different temperatures and under synthetic pore water conditions (I = 0.4 M, pH = 7.6) by batch experiments. Time-resolved laser-induced fluorescence spectroscopy was used for analysis of the Eu(III) speciation in the binary system Eu(III)-Opalinus Clay and ternary system Eu(III)-Opalinus Clay-small organic ligand under pore water conditions.
The Eu(III) sorption was found to increase generally with temperature in a considerably endothermic reactions with enthalpies of about 50 kJ/mol 1. In presence of tartrate or citrate the Eu(III) sorption decreases with increasing ligand concentration due to a complex formation of Eu(III) in solution. This complex formation was verified by TRLFS investigations. The detected Eu(III) surface species on Opalinus Clay with a luminescence lifetime of (201  9) µs is no influenced by the presence of the studied organic ligands.

Nowadays, the development of new materials is often associated with specific properties of functionalized nanostructures. X-ray investigations are a very important tool to find the link between the functional (magnetism, luminescence) and the corresponding structural properties (size, orientation etc.) that are generating this function and to explain the underlying physical processes. This knowledge makes it possible to design new materials with specific properties. We report on (in-situ) X-ray studies that are focused on ion-beam sputtering techniques (IBS) creating nanostructures either by ion beam erosion or by sputter deposition processes.
With IBS the roughness of solid surfaces can be modified on lateral scales of a few nanometers to micrometers or even further. In a defined parameter set IBS leads to a surface smoothing, whereas at other parameters the roughness is increased, leading eventually to periodic patterns, i.e. ripple and hexagonal dot patterns. In-situ measurements of the surface roughness during IBS of GaSb surfaces give insight into the detailed mechanisms; especially, if the early time regime is addressed. Modern synchrotron sources give us the possibility to study the nanostructure growth during deposition. A sputtering chamber mounted on a six-circle goniometer allows an insight into the growth of nanostructures using different scattering and diffraction methods. We have investigated the growth of FePt islands incorporated into an Ag matrix. The high brilliance of the synchrotron source had made it possible to obtain a reliable GISAXS signal and to control the cluster morphology during growth even at the initial stage. By depositing 6 nm Ag layer directly on the SiO2 substrate, we obtained well defined FePt clusters. FePt nanoislands have been achieved without degradation of the magnetic properties. We obtained a magnetic asymmetry with magnetic moments preferentially oriented parallel to the layer surface.

We report on the evolution of wave-like nanopatterns induced by Xe+ ion irradiation at high fluences in an energy range between 5 keV and 70 keV. By means of atomic force microscopy a statistical analysis of the ripple amplitude and wavelength was carried out showing that the periodicity and the amplitude of the rippled structures follow a linear dependence on the energy.
However, the evolution of the rippled patterns clearly differs for the lower and higher ion energies. For energies below 25 keV we observed almost no fluence dependence of the wavelength and amplitude in the investigated range of 1...8·1017 cm-2. But for energies above 25 keV and fluences above 1·1017 cm-2 coarsening was found. At energies larger than 50 keV Xe the ripple structures display a saturation regime for fluences higher than 5·1017 cm-2.
Investigations with cross-sectional high resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy revealed the appearance of Xe filled inclusions at ion energies above 25 keV. This result correlates with an almost stable ratio of the ripple wavelength to the ripple amplitude of about 30 occurring above a threshold fluence of 2·1017 cm-2 and above 25 keV.
These results indicate that there is a certain threshold energy and fluence above which a stable form of the investigated wave-like structure is build up. This is possibly caused by the formation of noble gas inclusions at higher ion energies.

For the development of nano-optical devices nano wires (NW) are of emerging interest. One of the most important steps in the fabrication of Si devices is doping using ion beam implantation. However, this may lead to a distortion of the NW’s crystalline structure or even to an amorphization. A subsequent annealing procedure is necessary to recover the crystalline structure. The advantage of implanted Si NW’s is that the electrical conductivities are significantly higher than MBE-grown in-situ doped ones [1]. NW’s of about 100nm in diameter and 100..400 nm in length, nominally undoped, were MBE grown on Si(111) using Au as a growth-initiator. We followed the structural changes of the NW’s caused by implantation and annealing. We used rapid thermal annealing up to a temperature of 1100∘ C of about 30 seconds to remove a possible damage induced by implantation. Diffraction experiments were carried out at the ID01 ESRF beamline using a microfocused X-ray beam in combination with a 2D detector to obtain 3D diffraction patterns. Our experiments have shown that defect structure and form of the investigated NW’s change after implantation and annealing.

The Serpent Monte Carlo (MC) code has been developed since 2004, and publicly distributed since 2009. One of the main applications for the code is the production of homogenized multi-group constants, which can still be considered a relatively unexplored field for the MC method. The calculation techniques required for this task have been implemented and refined during the seven years of Serpent development, with valuable feedback, contribution and new ideas from the user community. This paper presented two such topics: homogenization in leakage-corrected criticality spectrum and group constant generation in reflector regions. The implemented methods were verified and demonstrated by numerical examples. It is concluded that the new methodology improves the results of the deterministic calculation, and paves the way for Monte Carlo based group constant generation.

The natural volcanic glass obsidian is one of the classical objects of archaeometrical analyses. Reliable provenancing by means of its highly specific chemical composition, the “chemical fingerprint”, can provide information about economy, policy and the social system of ancient societies.

Although Mediterranean obsidian have mainly been the focus of characterization since the pioneer work of Cann and Renfrew (1964), provenancing of Central and Eastern Europe obsidian sources attracts increasing attention in the past decades. Fingerprinting of Hungarian and Slovakian obsidian sources is of great interest especially for Central European sites where obsidian has been widely used (Williams-Thorpe et al., 1984, Kasztovszky et al., 2008, Biró, 2009).

The application of three complementary analytical techniques on the same set of raw material samples allows both, a more complete characterization of obsidian sources and a comparison of analytical results. The aim of this multi-methodical approach is to apply three different analytical methods, in particular:

• Instrumental Neutron Activation Analysis (INAA),
• Ion Beam Analysis (IBA) comprising of Particle Induced X-ray Emission (PIXE) and Particle Induced Gamma-ray Emission (PIGE)
• Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS)

to detect a maximum element spectrum and to compare element concentrations determined with at least two analytical techniques. This way a check of self-consistency of analytical results is possible. Furthermore, it allows the identification of a maximum of compositional differences between Hungarian and Slovakian sources by revealing the most characteristic “chemical fingerprint” composed of more than 40 elements.

For this study, NAA, IBA and LA-ICP-MS measurements are scheduled to be applied to 25 raw material samples from sources from Hungary and Slovakia in cooperation with the Natural History Museum Vienna (Hammer, V. and Seemann, R., Department of Mineralogy and Petrography) and the Vienna Lithothek (Trnka, G., Department of Prehistoric and Protohistoric Archaeology).

Up to now, IBA studies have already been carried out using the external 4 MeV proton beam of the 6 MV Tandem accelerator of the Ion Beam Centre of Helmholtz-Zentrum Dresden-Rossendorf. Further NAA investigations will be performed at the TRIGA Mark II 250 kW research reactor of the Atominstitut in Vienna. LA-ICP-MS measurements will be conducted using the Thermo Element 2 ICP-MS coupled to an ArF gas Excimer laser system at the Aberystwyth University.

CANN, J.R. AND RENFREW, C, 1964. The characterization of obsidian and its application to the Mediterranean Region. Proceedings of the Prehistoric Society 30, 111-131.

WILLIAMS-THORPE, O., WARREN, S.E. and NANDRIS, J.G., 1984. The distribution and provenance of archaeological obsidian in central and eastern Europe. Journal of Archaeological Science 11, 183-212.

KASZTOVSZKY, Z., BIRÓ, K., MARKÓ, A. and DOBOSI, V., 2008. Prompt gamma activation analysis for non-destructive characterization of chipped stone tools and raw materials. Journal of Radioanalytical and Nuclear Chemistry 278, 293-298.

BIRÓ, K.T., 2009. Sourcing Raw Materials for Chipped Stone Artifacts: The State-of-the-Art in Hungary and the Carpathian Basin. In: Adams, B. and Blades, B.S. (Eds.) Lithic Materials and Paleolithic Societies (eds B. Adams and B. S. Blades), Wiley & Blackwell, 47-53.

Mit der Entwicklung spezialisierter Feldbusknoten lässt sich eine für den wissenschaftlichen Gerätebau in vielen Fällen sinnvolle Aufteilung zwischen selbst entwickelten und kommerziell verfügbaren Komponenten unter konsequenter Nutzung vorhandener Automatisierungssysteme erreichen. Im Folgenden wird vorgestellt, welche Schritte dabei erforderlich sind und welche Möglichkeiten sich mit diesem Ansatz ergeben.

Enrichment of Cr on both <100> and ½<111> dislocation loops has been reported under ion, electron and neutron irradiation in Fe-xCr with x=9-15 at.%. Cr enrichment in Fe-9,12Cr around edge of loops is predicted by atomistic Monte Carlo simulations. MC simulations indicate that Cr clustering on loops disappears above equilibrium solubility limit (ΔT~100-150K). MD simulations indicate that Cr enrichment at loops enhances their strength in a range of specific loading conditions.

The objectives are to report data for Fe2.5Cr, Fe5Cr, Fe9Cr, Fe12Cr irradiated up to 0.06, 0.6, 1.5 dpa; to calculate nuclear scattering from features reported by Kuksenko et al. based on APT; and to compare with measured nuclear SANS. We have found that the NiSi-enriched clusters observed by APT are not responsible for the observed SANS intensities. Possible sources of the apparent discrepancy between SANS and APT for Fe12Cr are discussed. The dominant source is the overestimation of the Fe fraction in the Cr-rich clusters by APT.

SANS data are presented for as-irradiated, irradiated and annealed, and re-irradiated weld material from units 4, 2, and 1, respectively, of the decommissioned NPP Greifswald. The unirradiated reference condition is represented by a data scatter band obtained for several unirradiated weld materials of the same kind. The effects or irradiation, annealing and re-irradiation are worked out. Comparison of the SANS data with available atom probe data for the same material from unit 4 indicates an apparent discrepancy between both methods. Possible reasons are carefully discussed. The dominant reason is the overestimation of the Fe fraction in the irradiation-induced clusters by APT due to trajectory overlaps.

Full set of nuclear and magnetic SANS data for a number of four Cr levels, three dpa levels each, is presented. The results are given in terms of concentration, size and A-ratio as function of Cr and dpa. A consistent understanding is obtained for Fe12Cr in terms of alpha‘ phase formation. For Fe2.5Cr, Fe5Cr and Fe9Cr, the presence of a second kind of scatterers is indicated, to which impurity elements such as Ni, Si, and C must contribute. The nature of scatterers in Fe2.5Cr, Fe5Cr and Fe9Cr is among the unsolved issues. Candidates are Cr-C-enriched clusters and/or Cr-Si-P-Ni-enriched clusters detected by atom probe tomography. There is an inconsistency between composition reported for APT and composition assumed in the SANS analysis with respect to Cr/Fe-fraction.

In this paper, we report a correction to the model potential of the Ga acceptor in germanium, evidenced by high-magnetic-field photoconductivity measurements. We found that under high magnetic fields the chemical shift of the binding energy of Ga acceptors vanishes, contrary to the results given by the generally accepted theory. To fit our data, we found that the central-cell correction should contain a repulsive part (i.e., it must be bipolar), in contrast to the purely attractive screened point-charge potential widely used in the literature.

The neutronics model of the nodal reactor dynamics code DYN3D developed for 3D analyses of steady states and transients in Light-Water Reactors has been extended by a simplified P3 (SP3) neutron transport option – to overcome the limitations of the diffusion approach at regions with significant anisotropy effects. To provide a method being applicable to reactors with hexagonal fuel assemblies and to furthermore allow flexible mesh refinement, the nodal SP3 method has been developed on the basis of a flux expansion in trigonal-z geometry. In this paper, a verification of the methodology on quasi-pin level is performed by means of a single-assembly test example. The corresponding pin-wise few-group cross sections were obtained by the deterministic lattice code HELIOS. The power distributions were calculated using both the trigonal DYN3D diffusion and SP3 solver and compared to the HELIOS reference solutions. Close to regions with non-negligible flux anisotropies, e.g., caused by the presence of a strong absorbing material, the power distribution calculated by DYN3D-SP3 shows a significant improvement in comparison to the diffusion method.

The setup and idea of the Gamma-induced Positron Spectroscopy (GiPS) using the superconducting LINAC ELBE is presented. Features of a setup using bremsstrahlung to create positrons by pair production as well as the advantages of the characteristics of the ELBE beam will be shown and discussed. The measurement of the positron and positronium lifetime of water at various temperatures is an example for investigation and the connection of theory and experiment and will also show the perfect function of the GiPS setup.

In order to establish links between p-wave pion production in nucleon-nucleon collisions and low energy three-nucleon scattering, an extensive programme of experiments on pion production is currently underway at COSY-ANKE. The final proton pair is measured at very low excitation energy, leading to an S-wave diproton, denoted here as {pp}_s. By using a deuterium target we have obtained data on the differential cross section and analysing power of the quasi-free pol{p}n -> {pp}_s pi^- reaction at 353 MeV. The spectator proton p_sp was either measured directly in silicon tracking telescopes or reconstructed using the momentum of a detected pi^-. Both observables can be described in terms of s-, p-, and d-wave pion production amplitudes. Taken together with the analogous data on the pol{p}p -> {pp}_s pi⁰ reaction, full partial wave decompositions of both processes were carried out.

The Gamma-induced Positron Spectroscopy (GiPS) facility at ELBE (Helmholtz-Zentrum Dresden-Rossendorf) is ideally suited to measure extended volume sample materials like liquids with an information depth of several mm in an appropriate time [1]. Moreover, GiPS allows for studying positron lifetimes and positron momentum within the same experiment and thus allows for realizing Age-Momentum Correlation (AMOC) experiments within a fraction of time needed with conventional setups.

There are still questions about the microscopic structure of liquid water and the behavior of water inside membranes and at boundaries is under vivid investigation.
AMOC experiments revealing additional information about the local environment at the instance of pick-off positron annihilation of o-Ps were performed for water at temperatures between 20°C and 90°C to verify recently reported observations of periodic quantum beats in the AMOC spectra, caused by spin conversion of o-Ps [2]. The radiation effect caused by the use of bremsstrahlung for positron production was also investigated.

Different analysing methods for these spectra with high statistic and quality will be presented. Also the application of common theory for positronium formation and chemical reactions in water will be discussed.

Lead sheets are a basic material to build metal pipes for organ pipes. Mostly lead gets alloyed with tin and in this manner its properties have been seen superior over centuries. But, the classical organ construction (16.-18.century) in the northern parts of Europe comprised the use of alloys with very low (2-3%) or no tin content because of cost reasons. In such cases the lead material shows critical properties regarding the mechanical strength and density. Nowadays, the restoration of organ instruments from this period requires the production of new material to replace corroded material or to substitute missing pipes or other organ parts. An important issue is the engineering of such material by mechanical hammering to increase the density. Microscopic cavities inside the casted material get closed in this way and the mechanical strength gets increased. Up to now there exists only an empirical knowledge about the quality changes due to the hammering treatment within a period of several centuries.
We used the Gamma-induced Positron Spectroscopy (GiPS) setup at ELBE at Helmholtz-Zentrum Dresden-Rossendorf to investigate the porosity of hammered and non-hammered material both for historical material from the 17th century and for newly produced sheet material for the first time to get microscopic information about the effect of the hammering practise. The Gamma-induced Positron Spectroscopy setup at ELBE is worldwide the only suitable setup to investigate solids with an information coming from the whole volume. Results obtained from this are compared with conventional depth resolving Doppler Broadening Spectroscopy measurements using a slow positron beam.

The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. Furthermore, the existing DRACO laser system - a 200TW flash lamped Ti:Sapphire laser is going to be upgraded soon towards the PW-level at short pulse lengths in the range of 25-30fs. Recent laser plasma experiments as well as issues of the laser development are addressed.

The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. Furthermore, the existing DRACO laser system - a 200TW flash lamped Ti:Sapphire laser is going to be upgraded soon towards the PW-level at short pulse lengths in the range of 25-30fs.

With the first demonstration of direct diode-pumped TW lasers with pulse energies of 1 J and more a scaling of this approach for use in PW-class laser systems became feasible. The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. In order to minimize the required pump peak power and therefore the initial costs a broad-band Ytterbium doped laser material with a long fluorescence lifetime (i.e. Yb:glass or Yb:CaF2) is chosen. A total pump peak-power of 1.2 MW is scheduled assuming a pump pulse duration of 2 ms and an envisioned optical-to-optical conversion efficiency of 10% before compression. Pulses as short as 60fs having an energy of 25nJ are generated in a commercial Yb:KGW oscillator at a center wavelength of 1035nm. In order to employ CPA technique the pulses are stretched to 2ns in a grating stretcher having grating constant of 1760 lines per mm. The amplifier-chain consists of a regenerative amplifier and 4 subsequent multipass amplifiers. While the regenerative amplifier produces a gain 40.000 gain narrowing is required to be suppressed by intra-cavity spectral shaping. In free-running mode (unseeded) a bandwidth of 20nm of the regenerative amplifier operating at the mJ level was achieved. A booster amplifier with a gain of 100 and 3 further multipass amplifiers each having a gain of 10-16 are required to achieve the desired pulse energy. Both, multipass amplification to the Joule-level and a small-signal of >40 in a single-disk Yb:CaF2 booster have been demonstrated recently.
For thermal management of the high-energy lasers the active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. In order to maintain both efficiency and repetition rate and to suppress parasitic lasing while scaling the aperture of disk amplifiers a multiple disk approach also employing pump-recycling was proposed. Time-resolved thermal lens investigations on a diode-pumped Yb:CaF2 disk revealed a one order of magnitude less impact on the wavefront abberations compared to a Yb:YAG disk having a similar geometry.
In this paper we introduce the basic design concepts and first experimental proofs of the fully diode-pumped high peak-power laser PEnELOPE.

Diode-pumped lasers and amplifiers using Yb-doped materials have attracted increasing interest in the past years. This is owed to the high achievable efficiency of high energy amplifiers with high repetition rates and their potential to provide ultrafast laser pulses in the sub 100fs range. These properties allow their use in high intensity physics, laser fusion or pump sources for ultra-short Ti:Sa and OPCPA systems. Yb:YAG is one of the most important material for ns pulse generation and amplification with high efficiency also at room temperature. Here we present a joule-class Yb:YAG active mirror amplifier and the time-resolved analysis of its thermal lens. The active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. A pulse energy of 730mJ at a repetition rate of 1Hz was obtained at an optical-to-optical conversion efficiency of 16%. Here a relay-imaging multipass cavity with 4 extraction passes and also 4 pump passes was employed. For seeding a Yb:YAG pre-amplifier with a output energy of 65mJ was used. The disk with an Yb-concentration of 5mol% comprises a thickness 2.5mm and diameter of 12.5mm. At pump energies of 4J and above the small-signal gain was drastically reduced by transverse lasing which was observed as a roll-over of the measured gain and efficiency. In order to get rid of parasitic lasing the doping concentration will be reduced while the thickness is increased such that the optical thickness of the disk remains. Furthermore, a multiple active mirror will be used in a redesigned setup allowing reduced thermal load of each single disk. The thermal lens measurements were compared with a rod type (transversally) cooled disk. At a repetition rate of 10Hz the thermal equilibrium of the disk was attained within the first pump shots while in the case of the rod type cooling serveral seconds were required.

The Research Centre Dresden-Rossendorf is planning to build a fully diode-pumped Petawatt laser based on Ytterbium-doped calcium fluoride. A pulse energy of 200J, a repetition rate of 1Hz and a pulse duration of 200fs after compression are desired. In this project a total pump peak-power of 1.5MW is scheduled assuming a pump pulse duration of 2ms and a targeted optical-to-optical conversion efficiency of 10%. Here we present gain measurements and time-resolved analysis of the thermal lens of different Yb:CaF2 amplifier configurations. The active mirror concept is one of the most promising techniques for room temperature operation of Yb-based lasers providing efficient cooling of the laser material and energy extraction. Therefore, a disk amplifier was compared with a rod laser. A pulse energy of 600mJ at a repetition rate of 1Hz was achieved using a cylindrical rod with a length of 20mm, a diameter of 28mm and an Yb-concentration of 2mol%. For seeding an Yb:YAG pre-amplifier produced pulses with a duration of 6ns. With a 2-disk Yb:CaF2 amplifier comprising of 8 extracting beams and a pump recovery configuration the minimum required pump fluence in order to bleach out re-absorption at the laser wavelength of 1030nm was reduced roughly by a factor of two down to 13J/cm². Furthermore, the thermal lens power was reduced from 5dpt of the rod down to smaller than 0.05dpt for 3mm thin disks at 10Hz.

Here we present first lasing and tunability results of a diode-pumped Yb:SiO₂ multicomponent glass laser. The multicomponent glass consists of 70 mol% SiO₂, 20 mol% Al₂O₃, 9.1 mol% La₂O₃, and a doping level of 0.875 mol% Yb₂O₃. Due to the high contingent of SiO₂ the spectroscopic properties of the multicomponent glass is similar to Yb-doped fused silica glass. The huge advantage of the here presented multicomponent fused silica glass as gain material is its fabrication technique. It can be produced directly out of a glass melt with large active volume and high optical quality.
The Yb-doped multicomponent glass sample in the experiment had a thickness of 1.5 mm and was polished in laser quality. For pumping a fiber coupled laser diode was used with power of 6W at 975nm. The pump absorption was about 60%. In order to increase the pump absorption the non-absorbed pump was re-imaged back into the Yb:SiO₂. The laser cavity was a V-shaped resonator and the folding mirror had a curvature of 200mm. This results in a stable confocal resonator with a beam waist of about 50 µm in the glass and 600 µm on the output coupler. The free running laser wavelength was centered around 1055nm. The slope efficiency results in a value of 32%. The wavelength tunability of the laser cavity was achieved inserting a brewster prism (SF10) in between the folding mirror and the output coupler. At a pump level of 5W the laser had a tuning range from 1010 nm to 1080nm.

We present temperature dependent gain measurements with different Ytterbium doped laser media, such as Yb:YAG, Yb:FP15-glass and Yb:CaF2 in a multi-pass amplifier setup. The temperature of these materials was adjusted arbitrarily between 100K and 300K, while heat removal was realized by transverse cooling. In order to obtain a good beam profile throughout the amplification process, we used an all-mirror based relay imaging setup consisting of a telescope accomplishing a 4f-imaging with a plane mirror in each image plane. The amplification beam is then coupled into the cavity and doing several round trips wandering over the surface of the spherical mirrors. Hence the laser material is placed in one of the image planes, the beam quality of the amplifier was ruled by the intensity profile of the pumping laser diodes consisting of two stacks with 2.5kW peak output power each. Due to the given damage threshold fluence, the output energy of the amplifier was limited to about 1J at a beam diameter of 4.5 mm (FWHM). The seed pulses with a duration of 6 ns were generated in a Yb:FP15-glass cavity dumped oscillator with further amplification up to the 100mJ level by a room temperature Yb:YAG multi pass amplifier. The 1 Hz repetition rate of the system was limited by the repetition rate of the front-end. With Yb:YAG for instance an output energy of 1.1 J with an record high optical to optical efficiency of more than 35% was achieved, which was further increased to 45% for 500 mJ output energy.

For laser performance simulations, optical properties of applied active materials have to be exactly known. Here we report on temperature dependent emission and absorption cross section measurements for Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The temperature of the samples was aligned in steps of 20 K between 100 K and room temperature with a liquid nitrogen driven cryostat. Absorption spectra were obtained with a fiber coupled white light source and fluorescence spectra by excitation with a fiber coupled 10W laser diode at 970 nm. All spectral measurements were performed with a scanning spectrum analyzer, providing a spectral resolution down to 0.05 nm. By applying the McCumber relation in combination with the Fuchtbauer-Ladenburg method, we were able to obtain a valid emission cross section over the whole range of interest from the measured data.

Highly transparent CaF2 has found many applications from the deep UV- to the IR-range. The optical quality and the laser damage threshold are influenced by the purity and the real structure of the crystal. Both properties strongly depend on raw material quality and growth conditions. Production of pure CaF2 single crystals and their characterization are described. The authors´ process enables to produce crystals up to diameters of 425mm with an internal transmittance of higher than 99.7% at 193nm (thickness 100mm) and a homogeneity of refractive index below 1ppm for diameters >200mm. A new approach is the growth of Yb3+ doped CaF2 crystals in such furnaces dedicated to large volumes. The advantage of higher volume is a better homogeneity of the dopant concentration and the diffractive index in the crystal. Critical mechanical properties especially of the doped fluoride have to be taken into account. The growth process has to be adopted carefully to avoid stress, cracks and other crystal defects. Data of refractive index homogeneity and stress birefringence are presented. A comparison of doped and undoped crystals is made and an outlook for further improvement is given. The segregation coefficient of the dopant which is important to be near to one is reported. The ratio Yb3+ /Yb2+ is characterized spectroscopically. Differences between top and bottom of the crystal are shown. Results of the real structure evaluation are presented. The most critical feature for high energy applications which are strength and concentration of small angle grain boundaries are compared with that of undoped crystals.

Since typically low temperatures turn the quasi three level system of Yb:YAG into a four level system much higher efficiencies are expected by cryogenic cooling. Former experiments achieved efficiencies up to 30 % [3], which is below theoretical expectations [1,2]. To increase the efficiency through a better overlap between the pumped area and the seed beam profile, a novel all-reflective relay imaging amplifier has been built. Astigmatism compensation of the setup was achieved by folding the beam pass out of plane. The Yb:YAG crystal was placed in a liqiud nitrogen cooled mount inside a vaccum chamber.
The amplifier design allows to switch between different numbers of passes easily. In a six pass configuration a maximum optical-to-optical efficiency of 46% with a output energy of more than 600 mJ was achieved (s. Figure 1). With a slightly modified setup the output energy was increased to 1.1 J in a eight-pass scheme at a reduced efficiency of 36 %.

It has been shown, that cryogenic cooling of Yb3+-doped media is increasing laser performance significantly[1,2]. The reason for this is the thermal depopulation of the lower laser levels turning the quasi three level extraction scheme into a real four level scheme. By now most of these cryogenic cooled amplifiers aim on liquid nitrogen temperature. For future systems it has to be estimated what is an optimum operation temperature as compromise between laser performance and effort for cooling. This is needed as well from an energetic point of view as from an financial point of view. For this it is necessary to know the basic absorption and emission cross sections in dependence of temperature.
We present measurement of such cross sections in an temperature range from 100K to room temperature for various gain material such as Yb:YAG, Yb:CaF2 and Yb:FP15-glass. The absorption cross sections are calculated from the absorption spectra. The emission cross sections are determined from the absorption and emission spectra employing the Füchtbauer-Ladenburgmethod and theMcCumber relation [3,4]. Additional wavelength dependent gain measurements are used to cross check the validity of the measurements.

Previous works on Ytterbium-doped alcaline-earth fluoride have impressively shown that these materials are suitable for high-peak power operation [1,2] due to their broad emission spectrum comparable with rare-earth doped laser glasses. From the scaling point of view Yb:CaF2 is the most promising material since crystal growth at large sizes with diameters up to 100 mm and more with high optical quality have been demonstrated so far. Also the thermo-mechanical and thermo-optical properties such as the negative thermal lens of Yb:CaF2 are superior for high-average power lasers [3]. Moreover, the high saturation fluence (i.e. 80 J/cm²) pushes the potential energy limit of thin disk lasers by about one order of magnitude compared to oxide laser materials such as Yb:YAG. This means that at a given stored energy parasitic lasing is reduced by a low transverse gain [4]. However, the low single-pass gain of Yb:CaF2 lasers must compensated by a large number of amplifier passes. We built a multi-pass Yb:CaF2 disk amplifier pumped with a diode laser module having a peak power of 16.8 kW (provided by Lastronics GmbH, Germany). A maximum pump energy of 40.3 J at a wavelength of 940 nm was obtained at a pump duration of 2.4 ms while the flat-top shaped pump profile (6 × 6 mm²) was homogenized by a doublet of micro-lens arrays inside the module and imaged into the gain medium. The seed pulses with a duration of 6 ns (FWHM) were generated in a Q-switched Yb:YAG oscillator and then pre-amplified from 400 μJ to 100 mJ at a repetition rate of 1 Hz in a booster Yb:YAG amplifier. For comparison a rod type and a disk Yb:CaF2 amplifier were build and analyzed. While the laser rod with a diameter of 28 mm and a length of 20 mm was 2.2 mol% Yb-doped the doping concentration of the disk with a thickness of 2.7 mm and diameter of 20 mm was 4.5 mol% Yb. In case of the rod a two-side anti-reflection (AR) coating and a highly reflective (HR) mirror was used, whereas the disk was HR-coated from the rear side and glued on a plane copper-mirror for thermal contact. A maximum output pulse energy of 1.2 J at a repetition rate of 1 Hz of the multi-pass Yb:CaF2 amplifier with the rod-type material was measured. Above 1.2 J laser induced damage occurred in the rod volume while at 270 mJ surface damage on the AR-side was observed in the case of the disk. This very low damage resistance of ~1 J/cm² is owed to the surface quality in our specific case and therefore the optical-to-optical conversion efficiency was limited to 1.5%. In the case of the rod type amplifier an efficiency of 4% was obtained. Fig. 1 illustrates the setup and the dynamic of both Yb:CaF2 amplifier configurations. Although the efficiency achieved was limited it becomes obvious that the performance of the disk is improved compared to the rod with regard to the total gain and minimum pump energy in order to bleach out the reabsorption at the laser wavelength of 1030 nm. Future work is now in progress in order to boost the pulse energy and hence the extraction efficiency of the disk Yb:CaF2 amplifier.

Das Papier beschreibt innovative Anwendungen der Informationstechnologie in der Forschung am Helmholtz-Zentrum Dresden-Rossendorf (HZDR). Dazu werden Beispiele aus den Gebieten High Performance Computing, Visualisierung und Virtual Reality sowie Identity Management erläutert, bei denen das HZDR zusammen mit Partnern fortschrittliche Lösungen entwickelt hat.

The objective of this project was the study of basic interaction processes in the systems actinide - clay organics - aquifer and actinide - natural clay - clay organics - aquifer. Thus, complexation, redox, sorption and diffusion studies were performed.
To evaluate the influence of nitrogen, phosphorus and sulfur containing functional groups of humic acid (HA) on the complexation of actinides in comparison to carboxylic groups, the Am(III) and U(VI) complexation by model ligands was studied by UV-Vis spectroscopy and TRLFS. The results show that Am(III) is mainly coordinated via carboxylic groups, however, probably stabilized by nitrogen groups. The U(VI) complexation is dominated by carboxylic groups, whereas nitrogen and sulfur containing groups play a minor role. Phosphorus containing groups may contribute to the U(VI) complexation by HA, however, due to their low concentration in HA they play only a subordinate role compared to carboxylic groups. Applying synthetic HA with varying sulfur contents (0 to 6.9 wt.%), the role of sulfur functionalities of HA for the U(VI) complexation and Np(V) reduction was studied. The results have shown that sulfur functionalities can be involved in U(VI) humate complexation and act as redox-active sites in HA for the Np(V) reduction. However, due to the low content of sulfur in natural HA, its influence is less pronounced.
In the presence of carbonate, the U(VI) complexation by HA was studied in the alkaline pH range by means of cryo-TRLFS (-120°C) and ATR FT-IR spectroscopy. The formation of the ternary UO₂(CO₃)₂HA(II)⁴⁻ complex was detected. The complex formation constant was determined with log β_{0.1 M} = 24.57 ± 0.17.
For aqueous U(VI) citrate and oxalate species, luminescence emission properties were determined by cryo-TRLFS and used to determine stability constants. The existing data base could be validated.
The U(VI) complexation by lactate, studied in the temperature range 7 to 65°C, was found to be endothermic and entropy-driven. In contrast, the complex stability constants determined for U(VI) humate complexation at 20 and 40°C are comparable, however, decrease at 60°C.
For aqueous U(IV) citrate, succinate, mandelate and glycolate species stability constants were determined. These ligands, especially citrate, increase solubility and mobility of U(IV) in solution due to complexation.
The U(VI) sorption onto crushed Opalinus Clay (OPA, Mont Terri, Switzerland) was studied in the absence and presence of HA or low molecular weight organic acids, in dependence on temperature and CO₂ presence using OPA pore water as background electrolyte. Distribution coefficients (K_d) were determined for the sorption of U(VI) and HA onto OPA with (0.0222 ± 0.0004) m³/kg and (0.129 ± 0.006) m³/kg, respectively. The U(VI) sorption is not influenced by HA (50 mg/L), however, decreased by low molecular weight organic acids (> 1×10^-5 M), especially by citrate and tartrate. With increasing temperature, the U(VI) sorption increases both in the absence and in the presence of clay organics.
The U(VI) diffusion in compacted OPA is not influenced by HA at 25 and 60°C. Predictions of the U(VI) diffusion show that an increase of the temperature to 60°C does not accelerate the migration of U(VI). With regard to uranium-containing waste, it is concluded that OPA is suitable as host rock for a future nuclear waste repository since OPA has a good retardation potential for U(VI).

Ausgezeichnet mit dem DFCNA-Sonderpreis 2011 vom Dresdner Fraunhofer-Cluster Nanoanalytik im Rahmen der Vergabe der Dresdner Barkhausen-Poster-Preise

BiFeO₃ thin films have been deposited on Pt/sapphire and Pt/Ti/SiO₂/Si substrates with pulsed laser deposition using the same growth conditions. Au was sputtered as the top electrode. The microscopic structure of the thin film varies by changing the underlying substrate. Thin films on Pt/sapphire are not resistively switchable due to the formation of Schottky contacts at both the top and the bottom interfaces. However, thin films on Pt/Ti/SiO₂/Si exhibit an obvious resistive switching behavior under forward bias. The conduction mechanisms in BiFeO₃ thin films on Pt/sapphire and Pt/Ti/SiO₂/Si substrates are discussed to understand the different resistive switching behaviors.

Resistive switching in oxides has attracted increasing attention due to the potential application for nonvolatile memory devices [1,2]. Resistive switching has been observed usually in a metal-insulator-metal (MIM) capacitor-like structure, which can be set and reset to low resistance state and high resistance state by applying external voltages with opposite polarities. In an asymmetric MIM structure where a Schottky contact and an Ohmic contact are formed at the two interfaces, respectively, it is generally believed that the Schottky interface dominates the bipolar resistive switching behavior.
BiFeO₃ thin films have been grown on Pt/Ti/SiO₂/Si substrates with pulsed laser deposition. RF sputtered Au has been used for the top electrode. The transport properties of the BiFeO₃ thin films have been previously demonstrated to be sensitive to the interface [3]. In the present work, an interface-related resistive switching behavior with large switching ratio of ~300 has been observed in the Au/BiFeO₃/Pt structure [4]. The different polarities of the external voltage induce an electron trapping or detrapping process, and consequently change the depletion layer width below the Au Schottky contact, which is revealed by capacitance-voltage measurements and by long-term low/high resistance state capacitance transient measurements at zero bias. The resistive switching shows a long term retention and non-destructive read-out character, which is proved by pulsed voltage measurements. A dynamic equilibrium process involving the extension of the depletion region can be used to explain the good retention in the Au/BiFeO₃/Pt structure. The present work can help to further understand the physical origin of bipolar switching in BiFeO₃ and in other thin film oxides with electron trapping centers.

[1] K. Terabe et al., Nature 433, 47 (2005).
[2] R. Waser and M. Aono, Nature Mater. 6, 833 (2007).
[3] Y. Shuai et al., J. Appl. Phys., in press.
[4] Y. Shuai et al., Appl. Phys. Lett. 98, 232901 (2011).

Industrial demands for short process times at low cost are steadily increasing. Considerable attention is thereby drawn to ultra-short annealing cycles on the order of just a few milliseconds. Flash Lamp Annealing allows for directed thermal treatment of surfaces within just a few milliseconds without or with drastically reduced thermal stress of the bulk material. Due to the selected wavelength range in the visible and near infrared region the lightpulse is absorbed by the near-surface layers and diffusion into the bulk is limited by the ultrashort time span. Thereby temperatures up to 2000°C are achieved dependent on the energy of the lightpulse and the optical properties of the sample. Cooling takes place by heat conduction into the bulk. To control the annealing process a precise temperature measurement is required that can filter the intense background radiation to obtain the true wafer temperature from its thermal radiation. A new method for temperature measurement will be presented which imposes a modulation on the lamp radiation to extract the true wafer signal.

Dieser Vortrag befasst sich mit der Temperaturmessung in der Kurzzeitausheilung. Dazu werden die besonderen Anforderungen an die Temperaturmessung in Kurzzeitausheilungsprozessen beleuchtet und historische Lösungen vorgestellt, darunter auch die Ripple Pyrometrie. Letztere wird seit Mitte der Neunziger Jahre erfolgreich für Heißprozesse im Sekundenbereich angewandt. Den Autoren ist es gelungen, diese Methode für Prozesse im Millisekundenbereich (Blitzlampenausheilung) umzusetzen. Experimentelle Ergebnisse werden vorgestellt und hinsichtlich ihres Einflusses auf den Gesamtfehler der Messung analysiert.

High dopant concentrations are often a prerequisite condition for the realization of semiconductors with new functionalities. For example, magnetic dopants can be used to fabricate ferromagnetic semiconductors (FMS) [1] or intermediate band semiconductors for solar cells [2, 3]. The main problem for processing these materials is the very low solubility of magnetic dopants in elementary and III-V semiconductors. Therefore, thermodynamical non-equilibrium conditions have to be applied to overcome these limits. Thereby, the diffusion path during processing has to be as short as possible to reduce clustering processes which would result in a deactivation of dopants.
The diffusion barrier Q of standard shallow donor or acceptor dopants in the solid phase
is generally high which results in very low diffusion coefficients. Therefore, during the fast cooling process after PLA, diffusion or hopping of such shallow dopant atoms in recrystallized Si and GaAs has not been considered in detail and no models were developed which quantify interdiffusion processes of dopants for materials with large bulk diffusion barriers Q. However, 3d transition metal dopants in the most important semiconductors have relatively small bulk diffusion barriers Q that result in higher diffusion rates as compared to standard shallow donors. Therefore, the usual assumption that dopants remain fixed on their initial position during PLA processing has to be verified for each type of magnetic dopant in semiconductor spintronics materials.
In this work, we perform a Monte Carlo Study on a three-dimensional diffusion model to evaluate the kinetics of initial clustering in a simple cubic host:dopant system. In a second step, the temperature quenching process during PLA was calculated for the materials GaAs and Si and conclusions about diffusion and clustering of typical 3d transition metal dopants can be drawn with respect to the PLA parameters. For Mn in GaAs we also consider declustering effects that have to be included for strongly diffusing dopants like Mn in Si.

[1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287, 1019 (2000).
[2] A. Luque and A. Marti, Phys. Rev. Lett. 78, 5014 (1997).
[3] J. Olea, M. Toledano-Luque, D. Pastor, G. Gonzáles-Díaz, and I. Mártil, J. Appl. Phys. 104, 016105 (2008).

A new CFD-strategy of a generalized two-phase flow (GENTOP) is presented. The idea of GENTOP combines a multi-field simulation with the recently developed Multiple Size Group (MUSIG) -approach. In the MUSIG-framework, transfers between the different bubble size groups due to bubble coalescence and –breakup are described. By modelling an additional mass transfer between the polydispersed and continuous gas phase, transitions between different gas morphologies can be considered. The continuous gas phase represents the largest gas structures so that for these structures the gas-liquid-interfaces are resolved. This new concept can give a more detailed explanation of complex flow situations, particularly with higher gas fractions, such as the impinging jet being just one application. First results computed by the CFD-code CFX 13.0 are compared to experiments and theoretical data reported in literature.

Transition metal ions (Mn²⁺, Cr³⁺, Fe^2+/3+, V²⁺) as substitutional impurities in cubic crystals play an important role due to their influence on the magneto-optical properties of the virgin crystals. The optical and magnetic properties of commercial MgO(001) single crystals were investigated. The PL spectra of 3d impurity ions (Cr³⁺ and V²⁺) show narrow zero phonon lines with decay times in the range of milliseconds and a broad multiphonon sideband decaying in microseconds. The EPR study exhibits hyperfine components corresponding to Mn atoms and to V atoms located in orthorhombic symmetry. The intensity change of the EPR and PL spectra as well as the variation of the decay time with temperature can be explained by electron-spin lattice relaxation due to the Raman process.

Zinc oxide (ZnO) is regarded as a promising material for optoelectronic devices, due to its electronic properties. Solely, the difficulty in obtaining p-type ZnO impedes further progress. In this connection, the identification and quantification of impurities is a major demand. For quantitative information using secondary ion mass spectrometry (SIMS), so-called relative sensitivity factors (RSF) are mandatory. Such conversion factors did not yet exist for ZnO. In this work, we present the determined RSF values for ZnO using primary (ion implanted) as well as secondary (bulk doped) standards. These RSFs have been applied to commercially available ZnO substrates of different surface termination (a-plane, Zn-face, and O-face) to quantify the contained impurities. Although these ZnO substrates originate from the same single-crystal, we observe discrepancies in the impurity concentrations. These results cannot be attributed to surface termination dependent RSF values for ZnO.

Using the large acceptance apparatus FOPI, we study central and semi-central collisions in the reactions (energies in A GeV are given in parentheses): ⁴⁰Ca+⁴⁰Ca (0.4, 0.6, 0.8, 1.0, 1.5, 1.93), ⁵⁸Ni+⁵⁸Ni (0.15, 0.25, 0.4), ⁹⁶Ru+⁹⁶Ru (0.4, 1.0, 1.5), ⁹⁶Zr+⁹⁶Zr (0.4, 1.0, 1.5), ¹²⁹Xe+CsI (0.15, 0.25, 0.4), ¹⁹⁷Au+¹⁹⁷Au (0.09, 0.12, 0.15, 0.25, 0.4, 0.6, 0.8, 1.0, 1.2, 1.5). The observables include directed and elliptic flow. The data are compared to earlier data where possible and to transport model simulations. A stiff nuclear equation of state is found to be incompatible with the data. Evidence for extra-repulsion of neutrons in compressed asymmetric matter is found.

Evidence is provided by PCS, ultrafiltration and ultracentrifugation that uranium(IV) can form silicate-containing colloids. The particles are generated in near-neutral to slightly alkaline solutions containing background chemicals of geogenic nature (carbonate, silicate, sodium ions). They remain stable in aqueous suspension over years. A concentration of up to 10-3 M of colloid-borne U(IV) was observed which is a concentration much higher than the concentrations of truly dissolved or colloidally suspended waterborne An(IV) species hitherto reported for the near-neutral pH range. The prevailing size of the particles is below 20 nm. Laser Doppler velocimetry reveals that the nanoparticles are stabilized in solution by electrostatic repulsion due to a negative zeta potential caused by the silicate. The isoelectric point of the nanoparticles is shifted toward lower pH values by the silicate. Extended X-ray absorption fine structure (EXAFS) spectroscopy showed that U-O-Si bonds, which increasingly replace the U-O-U bonds of the amorphous uranium(IV) oxyhydroxide with increasing silicate concentrations, make up the internal structure of the colloids.
Keywords: uranium(IV), silicate, colloids, near-neutral pH

It is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. A first non-trivial physical effect related to the double semi-simple eigenvalue was discovered by Hamilton in 1833, who established that it determines a conical singularity of the dispersion surface – the Hamilton’s diabolical point (DP) – that yields a conical ray surface, which is observable in experiments with birefringent crystals as a conical refraction. In the presence of absorption and optical activity the conical singularities of the dispersion surface can transform into branch points that correspond to double eigenvalues with the Jordan block (exceptional points, EPs). This happens because the matrix determining the dispersion relation becomes a non-Hermitian one, for which an EP has a lower codimension than for a DP. In my presentation I will talk about manifestation of the multiple eigenvalues and the singular surfaces associated with them in modern physical applications such as magnetohydrodynamics dynamo and helical magnetorotational instability where the singularities determine non-trivial scaling laws and help to establish important limits for the critical parameters. I will discuss the role of the singularities in dissipation-induced instabilities on the example of the Brouwer’s problem on a heavy particle in a rotating vessel and show its connection to the modern works on crystal optics, wave propagation and rotor dynamics. Finally, I will touch the issue of the geometric phase in non-Hermitian systems.

it is common to consider that generically discrete eigenvalues of an operator are simple. However, in multiparameter operator families multiple eigenvalues are a robust phenomenon. Singular ruled surfaces were studied already by John Wallis, who in 1655 introduced his famous conical wedge known in the modern physical literature under the name of the “double coffee filter”. Later on, due to the efforts of Monge, Catalan, Plücker, Steiner and Cayley, the development of the theory of the ruled surfaces had lead to the formulation of the projective geometry. In XXth century the singular surfaces reappeared again in the form of a powerful singularity theory. In my presentation I will talk about multiple eigenvalues and associated singular surfaces in stability and optimization problems for non-conservative systems. First, I consider circulatory systems without damping that describe stability of columns under follower loads and torques, friction-induced instabilities in rotor dynamics as well as aeroelastic stability problems. I present an algorithm for classification of generic singularities on the stability boundary of a circulatory system and list all generic singularities up to codimension 10. I plot generic singularities on the stability boundary for one-, two-, and three-parameter families of circulatory systems and show how to approximate the boundary near the singularities studying perturbation of simple and multiple eigenvalues. I illustrate the general theory by the examples from robotics, rotor dynamics and structural optimization. In the latter case structural optimization of the m-link Ziegler pendulum will be considered and derivation of optimality conditions as well as the connection of the optimal solutions to singularities on the stability boundary will be discussed. Then, I will study the effect of small dissipation on the stability of circulatory systems. In 1952 Ziegler found that an infinitesimally small amount of damping leads to a finite change in the stability domain of a two-link pendulum loaded by the follower force. In 1956 Bottema resolved this destabilization paradox by means of the Whitney umbrella singularity that as he established exists on the stability boundary of the damped Ziegler’s pendulum. I will talk about extensions of this result to general finite dimensional and continuous circulatory systems as well as to the gyroscopic systems with small damping and non-conservative positional forces. Examples of similar paradoxal phenomena from rotor dynamics, soil mechanics and magnetohydrodynamics will be considered in detail.

Structural optimization of non-conservative systems with respect to stability criteria is a research area with important applications in fluid-structure interactions, friction-induced instabilities, and civil engineering. In contrast to optimization of conservative systems where rigorously proven optimal solutions in buckling problems have been found, for non-conservative optimization problems only numerically optimized designs were reported. The proof of optimality in the non-conservative optimization problems is a mathematical challenge related to multiple eigenvalues, singularities on the stability domain, and non-convexity of the merit functional. We present a study of the optimal mass distribution in a classical Ziegler’s pendulum where local and global extrema can be found explicitly. In particular, for the undamped case, the two maxima of the critical flutter load correspond to a vanishing mass either in a joint or at the free end of the pendulum; in the minimum, the ratio of the masses is equal to the ratio of the stiffness coefficients. The role of the singularities on the stability boundary in the optimization is highlighted and extension to the damped case as well as to the case of higher degrees of freedom is discussed.

In the theory of magnetorotational instability and its modern extensions such as the helical MRI, non-trivial scaling laws between the critical parameters are observed. In case of the standard MRI it is well known that the Reynolds and Hartmann numbers are scaled as Re ∼ Ha² while for the helical MRI Re ∼ Ha³. What is less known is that the thresholds of SMRI and HMRI plotted as surfaces in the space of parameters, possess singularities that determine the scaling laws. Moreover, the two paradoxes of SMRI and HMRI in the limits of infinite and zero magnetic Prandtl number (Pm), respectively, sharply correspond to the singularities on the instability thresholds. In either case, it is the local Plücker conoid structure that explains the non-uniqueness of the critical Rossby number, and its crucial dependence on the Lundquist number. For HMRI, we have found an extension of the former Liu limit Roc ≃ −0.828 (valid for Lu = 0) to a somewhat higher value Ro ≃ −0.802 at Lu = 0.618 which is, however, still below the Kepler value.

Complexation of NpIV with several carboxylates (RCOO–; R = H, CH3, CHR’NH2; R’ = H, CH3, CH2SH) in moderately acidic aqueous solutions were studied by using UV-vis-NIR and X-ray
absorption spectroscopy. As pH increased, all investigated carboxylates initiated formation of watersoluble hexanuclear complexes, Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4, where the neighboring Np atoms are connected by RCOO– syn-syn bridges and the triangular faces of the Np6 octahedron are capped with μ3-O2–/μ3-OH–. The structure information of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 was extracted from the EXAFS data: Np–O2– = 2.22-2.23 Å (coordination number, N = 1.9-2.2), Np–O(RCOO–) and Np–OH– = 2.42-2.43 Å (N = 5.6-6.7 in total), Np···C(RCOO–) = 3.43 Å (N = 3.3-3.9), Np···Np(neighbor) = 3.80-3.82 Å (N = 3.6-4.0), Np···Np(terminal) = 5.39-5.41 Å (N = 1.0-1.2). For the simpler carboxylates, the gross stability constants of Np6(μ-RCOO)12(μ3-O)4(μ3-OH)4 and related monomers, Np(RCOO)(OH)2 +, were determined from the UV-vis-NIR titration data: R = H, log β6,12,–12 = 42.7 ± 1.2, log β1,1,–2 = 2.51 ± 0.05 at I = 0.62 M and 295 K; R = CH3, log β6,12,–12 = 52.0 ± 0.7, log β1,1,–2 = 3.86 ± 0.03 at I = 0.66 M and 295 K.

Nanostructured ferritic oxide dispersion strengthened (ODS) alloy is an ideal candidate for fission/fusion power plant materials, particularly in the use of a first-wall and blanket structure of a next generation reactor. These steels usually contain a high density of Y–Ti–O and Y–Al–O nanoparticles, high dislocation densities and fine grains. The material contains nanoparticles with an average diameter of 21 nm and was treated by several cold rolling procedures, which modify the dislocation density. Structural analysis with HRTEM shows that the chemical composition of the initial Y2O3 oxide is modified to perovskite YAlO3 (YAP) and Y2Al5O12 garnet (YAG). Irradiation of these alloys was performed with a dual beam irradiation of 2.5 MeV Fe+/31 dpa and 350 keV He+/18 appm/dpa. Irradiation causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. Extended SRIM calculations for ODS steel indicate a clear spatial separation between the excess vacancy distribution close to the surface and the excess interstitials in deeper layers of the material surface. The helium atoms are supposed to accumulate mainly in the vacancies. Additionally to structural changes, the effect of the irradiation generated defects on the mechanical properties of the ODS is investigated by nanoindentation. A clear hardness increase in the irradiated area is observed, which reaches a maximum at a close surface region. This feature is attributed to synergistic effects between the displacement damage and He implantation resulting in He filled vacancies. Fine He cavities with diameters of a few nanometers were identified in TEM images.

An oxide dispersion strengthened steel is produced which contains Y-Al-Ti-O nanoparticles with an average diameter of 21 nm. HRTEM analysis shows that the chemical composition of the Y2O3 oxide is modified with perovskite YAlO3 (YAP), Y2Al5O12 garnet (YAG) and Y4Al2O9 monoclinic (YAM) particles. Irradiation of these alloys was performed with a dual ion beam system operating simultaneously with 2.5 MeV Fe+ to 31 dpa and 350 keV He+ to 18 appm/dpa. Ion bombardment causes atomic displacements resulting in vacancy and self-interstitial lattice defects and dislocation loops. TRIM calculations for ODS steel indicate a clear spacial separation between vacancies and self-interstitials at which the vacancy distribution is close to the surface and the interstitials are deposited at a deeper position. The helium atoms mainly accumulate in the vacancies. Fine He cavities with diameters of a few nanometers were identified in HRTEM images. Additionally to structural changes, irradiation generated defects also affect the mechanical properties of the ODS steel. These were investigated by nanoindentation, which is a suitable measuring method as the irradiation damage is created within a thin surface layer. A clear hardness increase in the irradiated depth region was observed, which reaches a maximum close to the surface. This indicates the He condensation in the vacancy dominated region as predicted by the simulations.

Silicon nanowires (Si NWs) have generated enormous scientific interest as building blocks for future nanoelectronics. Due to the quasi-one dimensional structure and a high surface to volume ratio of Si NWs controlled doping to change their electrical properties is challenging. Also, in order to understand the doping mechanism various techniques were used to qualify the spatial distribution and electrical activation of dopant atoms in Si. In our previous work strong surface segregation of implanted phosphorus was found after the rapid thermal annealing (RTA). [1] The studies were carried out for relatively thick Si NWs grown by Molecular Beam Epitaxy (MBE) with a diameter of ~100 nm. However, the preferable size for the future logic application is in the range below 20 nm. This work will also discuss the doping behavior of the thin Si NWs with diameters of sub-20 nanometer fabricated by metal-assisted chemical etching. Electrical characterization of the thin NWs was performed by SSRM of the NW cross section. The issues of the doping of such thin NWs by ion implantation and the diameter dependence of the boron activation in the Si NW are discussed.
[1] Xin Ou et al., Nano Letters, 10 (2010) 171.

Using a pulse power solenoid, we demonstrate efficient capture of laser accelerated proton beams and the ability to control their large divergence angles and broad energy range. Simulations using measured data for the input parameters give inference into the phase-space and transport efficiencies of the captured proton beams. We conclude with results from a feasibility study of a pulse power compact achromatic gantry concept. Using a scaled target normal sheath acceleration spectrum, we present simulation results of the available spectrum after transport through the gantry.

Fresnoite (Ba2TiSi2O8–BTS) thin films were grown on fused quartz, silicon (100), MgO (100), and aplane sapphire by pulsed laser deposition, and crystallized by subsequent thermal or flash lamp annealing. The corresponding texture evolution of the BTS thin films was studied by X-ray diffraction. The preferential (001) texture of the crystallised BTS films was found to be most pronounced on sapphire substrates. The broad photoluminescence band of the BTS thin films depends only weakly on temperature. The intensity of the BTS luminescence can be as high as that of the most efficient oxide scintillator materials. In order to qualify the fresnoite thin films for photonic applications, we demonstrate infrared-laser direct writing in amorphous BTS films which allows a local crystallisation and patterning. A subsequent considerable enhancement of luminescence intensity can be applied for UV-sensitive marking of nearly any object.

Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

Kelvin probe force microscopy (KPFM) [1] is used for the nanoscale characterization of silicon nanowires (NWs). Horizontal NW arrays have been prepared from a silicon-on-insulator (SOI) starting material. After transferring the NW structures into the Si top layer by means of electron-beam lithography and reactive ion etching, the samples have been locally implanted with B and As. Activation of dopants was carried out by a rapid thermal annealing for 5 s at 1000 °C. Athena simulations showed that for the applied implantation and annealing conditions a box-like dopant distribution with comparable concentration of activated dopants can be assumed [2]. Quantitative dopant profiling by means of KPFM is successfully employed to locate the junctions along the B-doped and As-doped Si NWs. In addition, the influence of local intrinsic electric fields [3] is discussed for the investigated SOI structures.
References
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009). [2] S. F. Feste, J. Knoch, S. Habicht, D. Buca, Q.-T. Zhao, S. Mantl, Solid-State Electronics 53, 1257 (2009). [3] C. Baumgart, A.-D. Müller, F. Müller, and H. Schmidt, Phys. Stat. Sol. A 208, 777 (2011).

A different silanization method for SiO₂ surfaces has been raised for Si-based light emitter which are considered as light sources in sensors for the detection of harmful biomolecules. This approach uses a special experimental setup for gas phase silanization (GPS) and is based on the evaporation and deposition in nitrogen atmosphere at normal pressure for 15 minutes with different silane volumes. The light emitter has a SiO₂ passivation layer on the top which was hydrolyzed in an in situ hybridization chamber and catalyzed with MES (2-(N-morpholino)ethanaesulfone acid hydrate) buffer solution. Afterward, the substrates were silanized with the GPS method using the organosilane (3-Aminopropyl)trimethoxysilane (APTMS). Infrared spectroscopy, X-ray spectroscopy and Atomic force microscopy were used to control and characterize the structure of the SiO₂ surface and the APTMS layer. The results demonstrate a successful covalent binding of the coupling agent and the interaction of the deposited molecules with each other. The roughness of the modified surface was investigated by the Atomic force microscopy. The silanized samples show rough and textured surfaces. At last, the suitability of the developed GPS method was verified on light emitters.

In this report we present our recent investigations of rare earth (Ce, Tb) implanted SiO₂ thin films for Down-conversion (DC) as an application for solar cells. Photovoltaic modules (PV) are showing high losses in the ultra violet range of the incident sunlight, because of band gap losses and front layer absorption. DC layers are applied to the front surface of photovoltaic cells to enhance solar cell efficiency

Integration of III-V semiconductors with a silicon technology is crucial for the device performance. In this paper we present investigations of the microstructural, optical and electrical properties of III-V quantum dots (InAs, GaAs, InP and GaP) formed in silicon. The III-V QDs were obtained by means of sequential ion implantation and flash lamp annealing (FLA). Conventional selective etching was used to form the n-III-V/p-Si heterojunction. In case of InAs/Si heterostructures, the current-voltage measurement confirms the heterojunction diode formation with the ideality factor of 4.6. Kelvin Probe Force Microscopy measurements indicate a type-II band alignment of n-type InAs NPs on p-type silicon. The main advantage of our method is its integration with large-scale silicon technology, which also allows applying it for Si-based electronic devices.

The operator product expansion (OPE) for heavy-light-quark pseudoscalar mesons (D -mesons and B -mesons) in medium is determined, both for a moving meson with respect to the surrounding medium as well as for a meson at rest. First of all, the OPE is given in terms of normal-ordered operators up to mass dimension 5, and the mass of the heavy quark and the mass of the light quark are kept finite. The Wilson coefficients of such an expansion are infrared (IR) divergent in the limit of a vanishing light-quark mass. A consistent separation of scales necessitates an OPE in terms of non-normal-ordered operators, which implies operator mixing, where the IR-divergences are absorbed into the operators. It is shown that the Wilson coefficients of such an expansion are IR-stable, and the limit of a vanishing light-quark mass is perfomed. Details of the major steps for the calculation of the Wilson coefficients are presented. By a comparison with previous results obtained by other theoretical groups we have found serious disagreements.

Over the last more than 15 years we have been employing ion beam processing to dope gate-type amorphous silicon dioxide layers grown by thermal oxidation with a variety of species, mostly rare earth elements, to use these layers for the purpose of electroluminescence from a MOS capacitor device based on silicon technology. The main motivation for this work was the integration of optoelectronic functionality into silicon-based electronic circuits as one of the key challenges for future semiconductor applications. Here we report on different rare earth (RE) luminescent centres embedded into the silicon dioxide layer of purpose-designed Metal-Oxide-Silicon-based Light Emitting Devices (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. The electrical and electroluminescence properties of these devices are discussed in respect of possible applications for biosensing. Most of our work was recently published in one of the Springer textbook series [1]. Special devotion will be given in the talk to Akos G.Revesz who died in 2008 [2]. He was one of the pioneers of the physico-chemistry of amorphous silicon dioxide devoted to MOS technology.
[1] L.Rebohle & W.Skorupa “Rare-Earth Implanted MOS Devices for Silicon Photonics”, Springer Series in Materials Science vol.142, 2010
[2] http://www.electrochem.org/dl/interface/sum/sum08/su08_p20-22.pdf

In dieser Arbeit wird ein mikrofluidisches System zum Nachweise von hormonaktiven Substanzen (engl. EDC´s) in wässrigen Lösung vorgestellt. Diese Plattform-Technologie besteht aus vier getrennten mikrofluidischen Einheiten aus Polydimethylsiloxan (PDMS) und Glas, und bietet damit die Möglichkeit einen selektiven Nachweis von mindestens zwei Substanzen pro ein Einweg Chip, dessen Oberfläche mit den jeweiligen Rezeptoren immobilisiert ist. Der Chip selbst enthält eine integrierte Silizium-basierte Lichtquelle. Das Nachweiskonzept basiert auf der direkten Fluoreszenzanalyse. Zur Optimierung der elektrischen Parameter wurden Elektrolumineszenzmessungen (EL) als Funktion der Farbstoffkonzentration( QD800) im Kanal durchgeführt.

Within the current study, experimental investigations and computational fluid dynamics (CFD) simulations were performed to investigate the flow field structure developed under a turbulent liquid jet plunging into a quiescent pool of water. This topic is still challenging for CFD codes. Indeed, the study of turbulence in two-phase bubbly flows is one domain where experimental, numerical, and theoretical work is being extensively done nowadays. A correct description of closure laws for drag, lift, and interfacial forces is of great importance in numerical simulations.
Most critical with respect to CFD is the impact region between the jet and free surface of the liquid pool. Here, a complex interaction between surface waves and turbulence leads to the entrainment of air. These phenomena occur on very small scales. Up to now, it is not possible to resolve all relevant scales in one simulation due to limited computational resources. Therefore in this work, all phenomena above the pool surface and the impact region are excluded and the focus is set on the development of the flow field below the pool surface. The jet is modeled as a two-phase bubbly flow injecting into the pool.
For this purpose, the Particle Image Velocimetry (PIV) was utilized as measuring technique. Velocity fields for both impinging region and recirculation zone developed in the tank below the free surface were quantified and instantaneous and time-averaged velocity fields were obtained. For test cases where air entrainment occurred, only the recirculation region situated outside the bubble plume was quantified.On the other hand, the numerical simulations were performed using ANSYS-CFX 12.0, a commercial CFD package that solves the Navier-Stokes equations via a finite volume method and a coupled solver. The 2D as well as 3D simulation results are presented and compared with experimental results. Comparisons with the experimental data reveal satisfactory predictions of mean flow quantities, obtained by applying proper models of inter-phase momentum transfer.

One-dimensional ZnO nanostructures exhibit technological potential for many device applications, like efficient low-cost ZnO nanorod-polymer solar cells [1]. Conductive atomic-force microscopy (AFM) is a valuable tool for nanometer-scale electrical characterization of such nanorods [2]. Here, we present a complementary study of electrical transport in individual upright standing ZnO nanorods (NRs) grown by thermal evaporation [4] using conductive AFM (C-AFM) and photoconductive AFM (PC-AFM) [5]. Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps measured at different bias voltages applied to the sample contact mode. Further, C-AFM was utilized to determine the local current-to-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. PC-AFM investigations reveal that I-V curves taken from a single upright standing NR under illumination appear more degraded with respect to the non-illuminated state. Using PC-AFM, we also observed persistent photoconductivity from a single ZnO NR. Both phenomena can be attributed to oxygen desorption/re-adsorption from the ZnO NR surface.
Supported by Austrian Science Fund FWF under project # P19636.
[1] E. Greene, et al., Nano Lett. 5, 1231 (2005).
[2] G. Brauer, et al., Phys. Status Solidi C 6, 2556 (2009).
[4] Y. F. Hsu, et al., Appl. Phys. Lett. 92, 133507 (2008).
[5] H. Sakaguchi, et al., Jpn. J. Appl. Phys. 38, 3908 (1999).

The identification of the molecular interactions occurring at solid-liquid interfaces is of great significance to the assessment of the migration behavior of heavy metal ions in the environment. In particular, the dissemination of radioactive metals, such as uranium (U), in soils and groundwater aquifers is determined by sorption and desorption processes at mineral surfaces.
The molecular structures of the sorption complexes are mainly obtained by means of spectroscopic investigations of batch samples. These experiments provide no molecular information about the dynamic processes occurring during complex formation at the solid-liquid interface. However, such information, in particular about the early sorption steps, is expected to improve the understanding of the sorption processes. Therefore, we applied attenuated total reflection Fourier-transform infrared (ATR FT-IR) spectroscopy for in situ studies of the molecular processes at solid-liquid interfaces in real time with time resolution in the sub minute range and under selective conditions approaching near environmental relevant conditions [1].
In this work, we provide vibrational spectroscopic data from binary and ternary sorption systems, namely U(VI)/TiO2 and U(VI)/atm. CO2/ferrihydrite(Fh), respectively. From the binary U(VI)/TiO2-system the subsequent formation of two different surface species was observed [2]. These species were identified as inner and outer sphere uranyl complexes substantiating basic principles of surface complexation modeling which are based on thermodynamic approaches.
The spectral data obtained from in situ sorption experiments of U(VI) onto Fh demonstrate the formation of a unique U(VI) surface species irrespective of the absence or presence of atmospherically derived CO2. In contrast, the surface speciation of the carbonate anions significantly changes upon U(VI) sorption strongly suggesting the formation of ternary surface species. Moreover, the online monitoring of the sorption and desorption reactions allows the analysis of the sorption kinetics. Because of the different reaction rates found for carbonate sorption and desorption reactions on pristine Fh and Fh pretreated with U(VI), it is shown that carbonate sorption is a faster reaction than the sorption of U(VI). From the structural information of the ternary sorption complex derived from the spectroscopic results, molecular structures of the surface species are proposed [3].

References:

[1] Voegelin, A. et al. (2003) Environ. Sci. Technol. 37, 972-978.
[2] Müller, K. et al. (2012) Geochim. Cosmochim. Acta 76, 191-205.
[3] Foerstendorf, H. et al. (2012) Journal of Colloid and Interface Science, submitted.

Conductive probe based atomic force microscopy techniques like conductive atomic-force microscopy (C-AFM) [1,2], photoconductive AFM (PC-AFM) [3, 4], and photo-assisted Kelvin probe force microscopy (PA-KPFM) [5,6] provide an opportunity to study electronic and optoelectronic properties of surfaces and interfaces with nanometer resolution.
Here, we present our results on investigations of: 1) photoconductivity of single upright standing ZnO nanorods (NRs) grown by thermal evaporation [7], and 2) photoresponse in thin organic semiconductor films, namely AnE-PVstat:PCBM blends. The measurements have been performed in ambient or under N2 atmosphere using MFP3D from Asylum Research and in UHV with room temperature AFM/STM from Omicron extended with an external illumination system employing lock-in detection.
First, a novel PC-AFM setup which has been implemented to study the optoelectronic properties of individual upright standing ZnO NRs under illumination from the top will be presented. Using this setup we investigated transient photocurrent behavior and recorded photocurrent spectra from single upright standing ZnO NRs. A persistent photoconductivity from single ZnO NRs for the time intervals up to 1800 s has been observed. Simultaneously, the photoconductivity spectra (Fig. 1) revealed that the minimum photon energy sufficient for photocurrent excitation is 3.1 eV, which is at least 100 mV less than the energy sufficient for the band-to-band excitation. The mechanism of the persistent photoconductivity in ZnO is discussed in the frame of existing theoretical models.
In the second part, the results on investigations of the photoresponse in AnE-PVstat:PCBM blends spin-coated on PEDOT:PSS/ITO/ will be presented. The AnE-PVstat:PCBM blend acts as an active layer where the charge generation (by illumination) and charge separation processes take place. The charge separation in this structure occurs due to the presence of the effective electric field between AnE-PVstat, which serves as a donor, and PCBM which serves as an acceptor. The heterogeneity of the films, in turn, impacts the charge carrier generation, separation, and transport. Here, we analyzed the correlation between the heterogeneity and efficiency of the light-to-electricity conversion for (1:1), (1:2) and (1:3) AnE-PVstat to PCBM blend ratios. The 2D current maps recorded under illumination reveal the regions of high photoresponse for the case of (1:3) blend ratio, which is also confirmed by PA-KPFM and local current-to-voltage characteristics. The results on local photoresponse characterization of the samples with different blend ratios are correlated with the data on the light-to-electricity conversion efficiency obtained macroscopically.

1 S. Kremmer, C. Teichert, E. Pischler, H. Gold, F. Kuchar, and M. Schatzmayr, Surf. Interface Anal. 33, 168-172 (2002).
2 C. Teichert and I. Beinik, in Scanning Probe Microscopy in Nanoscience and Nanotechnology 2, edited by B. Bhushan (Springer, Berlin Heidelberg, 2011), pp. 691-721.
3 H. Sakaguchi, F. Iwata, A. Hirai, A. Sasaki, and T. Nagamura, Jpn. J. Appl. Phys. 38, 3908-3911 (1999).
4 D.C. Coffey, O.G. Reid, D.B. Rodovsky, G.P. Bartholomew, and D.S. Ginger, Nano Letters 7, 738-744 (2007).
5 L. Kronik and Y. Shapira, Surface Science Reports 37, 1-206 (1999).
6 E.J. Spadafora, R. Demadrille, B. Ratier, and B. Grévin, Nano Letters 10, 3337-3342 (2010).
7 Y.F. Hsu, Y.Y. Xi, A.B. Djurišić, and W.K. Chan, Applied Physics Letters 92, 133507 (2008).

One-dimensional ZnO nanostructures exhibit technological potential for many device applications, like efficient low-cost ZnO nanorod-polymer solar cells [1]. Conductive atomic-force microscopy (AFM) is a valuable tool for nanometer-scale electrical characterization of such nanorods [2]. Here, we present a complementary study of electrical transport in individual upright standing ZnO nanorods (NRs) grown by thermal evaporation [4] using conductive AFM (C-AFM) and photoconductive AFM (PC-AFM) [5]. Initially, the electrical properties of the arrays of upright standing ZnO NRs were characterized using two-dimensional current maps measured at different bias voltages applied to the sample contact mode. Further, C-AFM was utilized to determine the local current-to-voltage (I-V) characteristics of the top and side facets of individual upright standing NRs. Further, we pioneered the application of PC-AFM to resolve the photoconductivity spectra measured from a single as-grown ZnO NR. PC-AFM is similar in concept to C-AFM: the sample surface is biased and additionally irradiated from a Xe light source connected to a monochromator. The current through the AFM tip is measured as a function of illumination intensity and/or wavelength. PC-AFM investigations reveal that I-V curves taken from a single upright standing NR under illumination appear more degraded with respect to the non-illuminated state. Analyzing the photoconductivity spectra it has been found that the band gap of ZnO NR is reduced by about 220 meV with respect to the known value of 3.37 eV at room temperature. Using PC-AFM, we also observed persistent photoconductivity from a single ZnO NR. We believe that both phenomena can be attributed to the processes of oxygen desorption/re-adsorption from the ZnO NR surface. Moreover, these observations are in good agreement with theoretical predictions of the influence of oxygen vacancies on the electronic structure of ZnO [6].
Supported by Austrian Science Fund FWF under project # P19636.
[1] E. Greene, et al., Nano Lett. 5, 1231 (2005).
[2] G. Brauer, et al., Phys. Status Solidi C 6, 2556 (2009).
[3] C. Teichert and I. Beinik, in “Scanning Probe Microscopy in Nanoscience and Nanotechnology”, Vol. 2,
Edited by B. Bhushan, (Springer, Heidelberg, 2011).
[4] Y. F. Hsu, Y. Y. Xi, A. B. Djurišić, W. K. Chan, Appl. Phys. Lett. 92, 133507 (2008)
[5] H. Sakaguchi, et al., Jpn. J. Appl. Phys. 38, 3908 (1999).
[6] S. Lany and A. Zunger, Physical Review B 72, 035215 (2005).

Die Magnetfeldwirkung auf die Stahlströmung im kontinuierlichen Stranggussverfahren wurde experimentell an einem verkleinerten Flüssigmetallmodell untersucht. In vorangegangenen Messungen mit dem Ultraschall-Doppler-Verfahren zeigte sich bereits ein Einfluss des Magnetfeldes sowohl auf die gemittelte Strömung als auch auf die zeitlichen Geschwindigkeitsschwankungen. Mittels einer schnelleren Ultraschall-Konfiguration und dem Einsatz von Potentialsonden wurde das Zeitverhalten der Strömung nun näher untersucht und ein Überblick über die ersten Ergebnisse gegeben.

Many organic and oxidizable inorganic substances are main targets for oxidation and destruction during treatment, purification and disinfection of contaminated ground water, waste water, air, soil and waste gas and odor. Uviblox® technology uses the effects of photooxidation and photocatalytical processes by middle and low pressure UV lamps for technical systems. There are many possibilities for combination and optimisation of photooxidation with other technologies like nanotechnologies. Degradation processes can be enforced by nano structures of photocatalysts significantly. Different approaches are strongly pursued in research & development projects like NanoAqua, Fe-NANOSIT and nanoblox. These projects search for different ways of applying and handling the photocatalytical nano particles like TiO₂ and ZnO. Biological surface layers, magnetite, transparent and reflecting materials are tested for suspending nano particle solids as well as for coating fixtures. Research results are very promising and economic application of nano photocatalysts in water and gas phase for purification seems likely. Any presumed ecotoxicity was not found for the examined nanoparticles so far.

Semiconductor nanomaterials have come into the focus of research due to their potential for electronic and optoelectronic applications. Their properties strongly depend on their size, morphology, and dimension. In this work, we concentrate on the electrical and optoelectric properties of individual nanorods (NRs) in arrays of upright standing ZnO NRs. ZnO is a wide band gap semiconductor with potential application in solar cells [1] and gas sensors [2]. The NRs under investigation were grown via thermal evaporation (TE) and via hydrothermal synthesis (HT) [3,4]. In order to investigate such small structures atomic force microscopy (AFM) based methods have been applied. We utilized conventional conductive atomic force microscopy (C-AFM) [5] and additionally realized a photo conductive atomic force microscopy (PC-AFM) [6, 7] setup for our measurements. Examination of the current-to-voltage (I-V) characteristics measured for the top and side facets of individual TE grown NRs yielded Schottky like behavior with different barrier heights and ideality factors for both facet types [8]. The PC-AFM measurements on the top facet of TE grown NRs revealed a clear photo-response upon illumination with white light. Additionally, persistent photo-conductivity could be observed, manifesting itself by a very slow recovery to the initial dark conductivity level after light is switched off. Comparison of the dark and illuminated I-V characteristics revealed an increase in p-type conductivity for the illuminated case. The results will be discussed referring to the current models.

[1] M. Law, L. E. Greene, J. C. Johnson, R. Saykally, P. Yang, Nat. Materials 4, 455 (2005).
[2] H.-J. Lim, D. Y. Lee, Y.-J. Oh, Sensors and Actuators A: Physical 125, 405 (2006).
[3] A.B. Djurisic, Y. H. Leung, Small 2, 944 (2006).
[4] Y. F. Hsu, Y. Y. Xi, A. B. Djurišić, W. K. Chan, Appl. Phys. Lett. 92, 133507 (2008).
[5] C. Teichert, I. Beinik, in Scanning Probe Microscopy in Nanoscience and Nanotechnology, (vol. 2) edited by B. Bhushan (Springer, Heidelberg, 2011).
[6] H. Sakaguchi, F. Iwata, A. Hirai, A. Sasaki, T. Nagamura, Jpn. J. Appl. Phys. 38, 3908 (1999).
[7] D. C. Coffey, O. G. Reid, D. B. Rodovsky, G. P. Batholomew, D. S. Ginger, Nano Lett. 7, 738 820 (2007).
[8] I. Beinik, M. Kratzer, A. Wachauer, L. Wang, R. T. Lechner, C. Teichert, C. Motz, W. Anwand,
G. Brauer, X. Y. Chen, Y. F. Hsu, A. B. Djurišić, J. Appl. Phys. accepted .

For the majority of deep levels studied in n - type conducting ZnO by means of capacitance spectroscopy only the activation energy and the high temperature limit of the electron capture cross - section are known since these quantities can be evaluated easily from the temperature dependence of the trap’s thermal electron emission rate. We focused on the T2 level occuring in pulsed laser deposition grown ZnO thin films. In order to tune the T2 concentration in the samples, we employed different growth and annealing conditions as well as the implantation of oxygen and zinc ions, respectively. The physical properties of T2 were studied by sophisticated deep level transient spectroscopy and photo - capacitance experiments. These experiments revealed a strong dependence of the thermal activation energy, 185meV < Ea < 280meV, on the concentration of T2 in the sample as well as on the electric field (Poole - Frenkel effect). T2 was found to be preferentially generated under zinc rich conditions as both, the implantation of zinc ions and thermal annealing at low oxygen partial pressures increase its concentration. From photo - capacitance transients the photo - ionisation cross - section spectrum was calculated.

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1, 2]. In fluid media the device is placed beneath the dye-labeled sample exciting the dye. This light emission can be recorded by an external detector. It was shown that the silanization of the device surface was successfully based on the covalent binding of the organosilane [3]. The harmlessness of the silanization method to the integrated light emitters was proved by comparing the electroluminescence spectra of Tb-based MOSLEDs before and after silanization. We further showed that the transparency is maintained. Similarly, the human estrogen receptor hERα could be immobilized effectively on the coated surface [3]. We also discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. This lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)
[3] C. Cherkouk, L. Rebohle, W. Skorupa, T. Strache, H. Reuther and M. Helm, Journal of Colloid and Interface Science 337, 375 (2009)

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1,2]. Now we discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. The guiding of the light depends on the geometry and material composition of the waveguide. First waveguides were fabricated through plasma enhanced chemical vapor deposition (PECVD) and optical photolithography with following etching steps. Afterwards the layer thicknesses were analyzed by ellipsometry and the surface roughness via scanning electron microscopy (SEM). However, the investigation of the different waveguides will be allowed through finite element method (FEM) simulations (COMSOL) and experimentally through a setup for the optical transmission measurement. In summary, this lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

[1] L. Rebohle, C. Cherkouk, S. Prucnal, M. Helm, W. Skorupa, Vacuum 83, 24 (2009)
[2] L. Rebohle, T. Gebel, R.A. Yankov, T. Trautmann, W. Skorupa, J. Sun, G. Gauglitz, R. Frank, Optical Materials 27, 1055 (2005)

Failure analysis and optimization of semiconducting devices require knowledge of their electrical properties. Kelvin probe force microscopy (KPFM) is the most promising non-contact electrical nanometrology technique to meet the demands of today‘s semiconductor industry. We present its applicability to locally doped silicon structures. Quantitative dopant profiling by means of KPFM measurements is successfully demonstrated on a conventional static random access memory (SRAM) cell and on cross-sectionally prepared Si epilayers by applying a recently introduced new explanation of the measured KPFM signal [1]. Additionally, the influence of local, carrier-depleted space charge regions and of the electric fields across them is discussed. It is explained how drift and diffusion of injected charge carriers in intrinsic electric fields influence the surface region of the investigated semiconductor and thus may disturb the detected KPFM bias.
[1] C. Baumgart, M. Helm, H. Schmidt, Phys. Rev. B 80, 085305 (2009).

Transition metal oxides are interesting materials with important prospective applications. Planar defects like stacking faults and grain boundaries are often present in such materials and may affect their properties. In particular, it has been recently shown that a zinc oxide (ZnO) single crystal contain a large amount of stacking faults [1]. Furthermore, nanocrystalline materials based on zirconia (ZrO2) are also frequently studied and their characteristics are significantly influenced by grain boundaries [2]. The planar defects just mentioned exhibit free volumes which, in principle, are detectable using positron annihilation spectroscopy. In this contribution, we present a preliminary theoretical study of positron interaction with planar defects in oxides.
First, we examine several stacking faults (SFs) in ZnO, following their structural investigation presented in [3]. It is found that studied SFs represent rather shallow positron traps with the corresponding positron lifetime exceeding the bulk one slightly only. It might be necessary to consider interactions of SFs with other defects (vacancies, impurities) in order to characterize more precisely their effect on materials’ properties, including positron response.
Second, we perform the case study of the Sigma 5 (310) [001] symmetric tilt grain boundary [4,5] in ZrO2. In this case, positrons also localize at the grain boundary, but such localization is affected by the presence of yttrium (Y3+) ions which are often added to zirconia to improve its mechanical properties. The reason is that Y3+ ions influence the charge state of the grain boundary studied.

[1] W. Anwand et al., J. Appl. Phys. 109, 063516 (2011).
[2] J. Čížek et al., Phys. Rev. B 81, 024116 (2010).
[3] Y. Yan et al., Phys. Rev. B 70, 193206 (2004).
[4] Z. Mao et al., J. Am. Ceram. Soc. 85, 1594 (2002).
[5] T. Oyama et al., Phys. Rev. B 71, 224105 (2005).

A variable energy slow positron beam was utilised to investigate depth dependent effects of sintering on the tetragonal yttria stabilised zirconia nanopowders. Positron implantation was combined with the determination of Doppler broadened profiles of annihilation radiation. The results are consistent with recent positron lifetime data showing that sintering at elevated temperatures leads to a disappearance of pores and a significant grain growth, which is demonstrated by a strong suppression of positronium formation and a substantial decrease in concentration of open volume defects at triple points, respectively, with increasing sintering temperature. An existence of a subsurface layer of a relatively high content of defects was shown in sintered samples and tentatively attributed to arise from a diffusion of open volume defects from the sample interior toward the surface or from a sintering-induced surface modification.

Cinnamic acid (phenyl acrylic acid) is an essential constituent of Cinnamon oil, and is well known for its medicinal values. The compound comprises of hydrogen bonded supra molecular structure due to strong hydrogen bonding between the carboxylic groups and other intermolecular hydrogen bonding as well. On the whole it forms a crystalline layered structure in solid state. In order to study its structural organization and orientation of the molecular functional groups it has been our astute interest if we could form thin layers of these molecules on suitable substrates. Thus, thin layer characteristics of cinnamic acid (CINN) on the two commonly used substrates namely: fused quartz plate and on silicon substrate has been attempted and they were subjected to Doppler broadening of positron annihilation radiation (DB) line shape analysis by slow positron beam on the range of 30 – 1200 eV energy to study the near surface properties. While CINN on quartz substrate showed a periodic pattern (the rippled nature) significant from the point of view of the layer structure, as compared to the pure solid state analysis, the results on the pure silicon substrate were not so regular, it is rather apparent that a strong substrate dependent property was noticed with the layer formation . The cause of this effect was also identified through coincidence DB analysis and another complementary technique XPS in corroboration and shall be presented.
The discussion on the organization of CINN on the quartz substrate as revealed from the DB will be presented.

Physical and mechanical properties of Fe-Al alloys are strongly influenced by atomic ordering and point defects. In the present work positron lifetime (LT) measurement combined with slow positron implantation spectroscopy (SPIS) were employed for investigation of quenched-in vacancies in Fe-Al alloys with Al content ranging from 18 to 49 at.%. Interpretation of positron annihilation data was performed using ab-inito theoretical calculations of positron parameters. Quenched-in defects were identified as Fe-vacancies.
It was found that the lifetime of positrons trapped at quenched-in defects increases with increasing Al content due to increasing number of Al atoms surrounding vacancies. The concentration of quenched-in vacancies strongly increases with increasing Al content from ~10e-5 in Fe82Al18 (i.e. the alloy with the lowest Al content studied) up to ~ 10e-1 in Fe51Al49 (i.e. the alloy with the highest Al content studied in this work).

A long term safety assessment of a repository for radioactive waste requires evidence, that all relevant processes, which might have a significant positive or negative impact on its safety, are known and understood. In the case of brine intrusion into the disposal area, it has to be demonstrated, that the initiated chemical reactions don’t lead to an undue release of radionuclides into the biosphere. The starting point for this is to assess the solubility of contaminants in the solutions interacting with the waste. Solubility estimations can either be based on experimental data determined at conditions closely resembling those in the repository or on thermodynamic calculations.
A so called “thermodynamic database” created from experimental data is the basis for thermodynamic model calculations. Several research institutions in Germany are working on an improvement of the thermodynamic database. This work comprises investigations into fundamental thermodynamic data (such as vapour pressures or solubili-ties) as well as the application of sophisticated analytical or spectroscopic tools, which allow insight into aqueous speciation or structural details of surface complexes as basis for correct chemical and thermodynamic models.
Experience teaches that thermodynamic equilibrium calculations performed by different experts readily become difficult to compare and evaluate. This is only in part due to ill-defined (and -documented!) boundary conditions imposed on the calculations, but is frequently related to the use of different thermodynamic data or different conceptual models underlying them. Further difficulties arise by the fact that thermodynamic data used for a calculation actually are strongly interrelated; modification of an individual value without adapting the dependent values leads to “inconsistent” data. If applied in a calculation, this may lead to erroneous results, often unnoticed by the user.
As a result, in different institutions various databases exist that are appropriate for spe-cific tasks. However, they might lead to different results when they are applied to the same problem. This situation is unacceptable, both from a scientific point of view and considering the special public awareness for the final disposal of radioactive waste.
In 2002, a working group of five institutions was established for the creation of a com-mon thermodynamic database for nuclear waste disposal in deep geological formations (HZDR, GRS, TU BAF, KIT, AF-Consult). The common database was named THEREDA: Thermodynamic Reference Database.
It was agreed that the newly created database should be operated jointly by all members of the working group. In the mean term it is intended, that its usage becomes mandatory for geochemical model calculations for nuclear waste disposal in Germany. Furthermore, it was agreed that the new database should be developed along the guidelines long-term usability, easy access, applicability, internal consistency, comprehensiveness, documentation.
Activities within the time for which this report is valid cover a wide range of aspects. At first, a data model had to be designed from scratch which allows for the storage of thermodynamic data, at the same time facilitating export into code-specific parameter files. Creating the data model emphasis was laid upon its long term usage. Thus, a degree of abstraction was chosen which exceeds todays necessities and allows for future extensions. Technically the databank is implemented on a web server. Programs were created, which permit reading and writing access to the data. From the created webpages programs can be called that produce code specific parameter files ready for download upon specific request by the user.
THEREDA can thus be thought of as a databank in conjunction with a suite of peripheral programs, which aims at administrating, processing and extracting data. The data export is intended for the use in programs that calculate thermodynamic equilibria in aqueous solutions at temperatures which are of potential interest for hydrogeochemical systems in general and solutions containing hazardous contaminants like radionuclides or heavy metals in particular. As such, THEREDA is not designed to hold primary experimental data, neither data concerning any liquid other than aqueous solu-tion, e. g. melts or other substances which are stable under conditions beyond those where aqueous solutions may exist. Emphasis is laid on the correct calculation of ex-perimentally determined solubilities and aqueous speciation. Accompanying the above mentioned activities the working group agreed upon guide-lines which are to be followed upon selection and assessment of data. A system of quality assuring measure was set up; this comprises technical aspects relating to the databank as well as criteria determining how data are to be internally reviewed prior to release (auditing). As an external measure of quality assurance an internet forum was established to feedback questions and requirements from realistic problems into the project. A handbook was written to guide users in the handling of THEREDA (for the time being in german only).
Finally, thermodynamic data were entered. They comprise the system of oceanic salts as well as species and solid phase of a variety of radio-toxic and chemo-toxic ele-ments. This piece of work is on-going. At present, benchmark calculations are prepared. The first release of data will cover the system of oceanic salts (apart from C).

The HAVAR alloy was originally developed in the late 1940. It is a high strength, nonmagnetic and corrosion resistant material. One of its applications is in the medical industry, in the process of fluorodeoxyglucose (FDG) production for Positron Emission Tomography (PET). The 18F positron emitting isotope is produced by the reaction 18O(p,n)18F in proton cyclotrons. In Soreq NRC, 25 µm foils of HAVAR are used as a window material for the 18O enriched water targets, contained in Al vessels. With the increasing demand for 18F-FDG, an accelerated production rate is planned, with much higher intense proton beam from the new SARAF accelerator at Soreq NRC [1]. This initiated a research effort to study radiation damage in HAVAR that can predict its radiation hardness in the ~2-4 mA SARAF proton beam.
We measured four 25 µm thick HAVAR samples: cold rolled (CR), cold rolled and heat treated (HT), annealed (AN) and CR irradiated (IR). The latter was a window taken apart from the target 7 years ago after irradiation in the cyclotron to 10MeV protons of total charge 1mA-h. The first three samples were metallurgically characterized by means of Transmission Electron Microscope (TEM). Positron Annihilation Spectroscopy (PAS) measurements were preformed on all four samples. These included Doppler Broadening (DB) and Positron Annihilation Lifetime ( PAL) measurements in the slow positron beam and in the table top lifetime spectrometer at HZDR [2]. We present preliminary results from these PAS measurements, that show clear differences between the four samples. Positron lifetimes of the HAVAR types change between ~80ps for the annealed sample to ~175ps for the irradiated sample. The positron diffusion length changes from (8 ± 1) nm (CR) to (66 ± 1) nm (AN) in these samples. We also compare between the metallurgical characteristics of the different types of HAVAR measured with TEM to PAS results. The PAS measurements show a clear increase of the mean lifetime with the increase of the density of dislocations in the CR sample compared to that of AN HAVAR foils.

[1] L. Weissman et al., "The Status of the SARAF Linac Project", WE102 in Proceedings of Linac 2010, Tsukuba, September 12-17, 2010
[2] W. Anwand, H. - R. Kissener, and G. Brauer, Acta Phys. Pol. A 88, 7 (1995).

Die räumliche Erfassung relevanter Prozessparameter wird bei einer Vielzahl industrieller Anwendungen durch den begrenzten Zugang zum Prozess erschwert. Beispiele sind Reaktoren mit Rührwerken, Bioreaktoren, Fermenter und Schüttgutbehälter. In solchen Behältern ist die Installation von fest angebrachten Sensoren und Kabelverbindungen oft nicht realisierbar oder unerwünscht. Zudem sind räumlich auflösende Apparate, wie Kameras oder Tomografiemesssysteme, meist nicht anwendbar. Daher bietet die Überwachung der räumlichen Verteilung relevanter Prozessparameter ein hohes Potential für die verbesserte Untersuchung und die Optimierung der Anlagen und Prozesse. Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde ein Konzept autonomer Sensorpartikel entwickelt und getestet. Das Messsystem beinhaltet mehrere autonome Sensorpartikel und eine Basiseinheit.

We have demonstrated the feasibility of using ion irradiation to induce ferromagnetism in 4H-SiC. Upon Ne+ ion irradiation to a fluence of 5×10¹⁴ /cm², ferromagnetism is observed up to room temperature, while the virgin sample only shows diamagnetism. Sample characterization by using both Rutherford backscattering/channeling spectrometry and Raman spectroscopy shows defect generation and the partial loss of crystalline structures by ion irradiation. With further increased fluences to reach complete amorphization in SiC, the magnetic moments are still observed. The defect-induced ferromagnetism is stable upon thermal annealing at 1400 °C.

Ultrafast electron beam X-ray computed tomography has seen considerable progress in the last few years. Beginning with a limited-angle approach, single-plane, dual-plane and multi-plane tomography arrangements have been studied. Based on these proofs of principle, a single-plane full-angle tomography system has been built up and was used to image and analyze various two-phase flow scenarios. Lately, the dual-plane tomography has also been realized as a full-angle setup, which is now able to measure phase distributions as well as velocity profiles within the object of interest.
Now, we present a full-angle volumetric X-ray computed tomography setup, which comprises eight circular X-ray source paths distributed on a vertically expanded target and one ring of 320 detector elements surrounding the target. The resulting reverse cone-beam geometry allows three-dimensional reconstruction of the imaged object volume using Feldkamp-type reconstruction algorithms. The electron beam is guided consecutively along all circular source paths, which takes 500 µs per path, while the detector elements simultaneously measure the X-ray projections with 1 MHz sampling rate. This results in 500 discrete source positions per revolution and a volume rate of 250 s-1.
The performance of the setup has been demonstrated in phantom as well as two-phase flow experiments, which revealed detailed structures and flow dynamics in 3-D.

We present exclusive measurements of π⁺, π⁰ and ω production in pp reactions at 1.25 GeV and 2.2 GeV beam kinetic energy, in hadronic and dielectron channels. Using the former, high statistics invariant mass and angular distributions within the HADES acceptance are obtained for π⁺ and π⁰ exclusive production, as well as acceptance corrected distributions, which are compared to a resonance model. The sensitivity of the data to the Δ(1232) production angular distribution and to the contribution of higher lying baryon resonances is shown and an improved parameterization of the data is proposed. Cross sections are extracted especially in the case of pp->ppη at 2.2 GeV (σ=0.142 ± 0.022 mb) for which only old and controversial data existed. Using the dielectron channels, the π⁰ and η Dalitz decay signals could be reconstructed, with yields fully consistent with the hadronic channels. The electron invariant masses and acceptance corrected helicity angle distributions are found in good agreement with model predictions.

Data on inclusive dielectron production are presented for the reaction 2.2 GeV p + p measured with the High Acceptance DiElectron Spectrometer (HADES). Our results supplement data obtained formerly in this bombarding energy regime by DLS and HADES. The comparison with the DLS data for the reaction p + p at 2.09 GeV is shown. The reconstructed e+e− distributions are compared with a simulated pair cocktail, which points to an excess yield of invariant masses at around 0.5 GeV/c². Inclusive cross sections of neutral pion and eta production are obtained as well.

Ion irradiation of semiconductors is a well understood method to tune the carrier concentration in a controlled manner. For dilute magnetic semiconductors (DMS), the free carriers mediate the local magnetic moments and develop the long-range ferromagnetic coupling. Therefore, ion irradiation should provide a tool to engineer the magnetic properties of DMS. In this contribution, we show the possibility of fine tailoring the magnetism of highly conducting virgin GaMnAs films by ion irradiation. With increasing the displacement per atom (ion fluence), the GaMnAs films become more insulating step by step and only paramagnetic at the end. The coercivity can be increased by several times [1]. The approach can be used to tailor GaMnAs films with different coercivities, Curie temperatures (TC) as well as saturation magnetization. On the other hand one can use the approach to understand the conduction and magnetic coupling mechanism [2]. For relatively thick 25nm GaMnAs films with a high TC of 150 K [3] where the electrical gating is difficult due to the large hole concentration, ,we can decrease the hole concentration gradually. We found a linear dependence of Tc with increasing the compensation of holes by ion irradiation. This observation favours a valence band picture of ferromagnetic GaMnAs with high Mn concentrations.
1. L. Li, et al., J. Phys. D 44 099501 (2011);
2. T. E. Winkler, et al., Appl. Phys. Lett. 98, 012103 (2011).
3. Y. Nishitani, et al., Phys. Rev. B 81, 045208 (2010).

Doping of semiconductors is an essential issue for device fabrication. Ion implantation followed by annealing is a well-established method to dope Si and Ge. This approach has been maturely integrated with the IC industry production line. Nowadays, the demands for functional spintronics/photovoltaic materials require a supersaturated doping of semiconductors. For instance, regarding spintronics applications one needs to prepare magnetic semiconductors which are doped with up to 5-10% Mn. 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. Shallow dopants in Si and Ge, mainly the elements from the III or V columns of the periodic table, have been successfully built in by ion implantation and pulsed laser annealing [1]. The carrier concentration can reach values as high as 1021 cm-3. Such a platform combining ion implantation and short-time annealing has been established at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) [2]. In this contribution, we will give an overview of the platform and particularly of its application in the preparation of Mn doped Ge [3, 4].

Reference:

[1] C. W. White, et al., J. Appl. Phys. 51, 738 (1980).
[2] W. Skorupa, et al., J. Electrochemical Soc. 152, G436 (2005).
[3] S. Zhou, et al., Phys. Rev. 81, 165204 (2010).
[4] S. Zhou, et al., Appl. Phys. Lett. 96, 202105 (2010).

Oxide Dispersion Strengthened (ODS) steel is a promising candidate for an application in fission and fusion power plants of a new generation because of its advantageous properties as stability and temperature resistance. A microscopic understanding of the physical reasons of the mechanical and thermal properties as well as the behaviour of the material under irradiation is an important pre-condition for such applications. The investigated ODS FeCrAl alloy “PM2000” has been produced in a powder metallurgical way by means of hot isostatic pressing and hot rolling. Neutron-induced damage at ODS steel was simulated by He+ and Fe2+ co-implantation with energies of 2.5 MeV and 400 keV, respectively, and different fluences. The implantation has been carried out with a dual ion beam which enables a simultaneous implantation of both ion types. Thereby the Fe2+ implantation was used for the creation of radiation defects, and He+ was implanted in order to reproduce He bubbles as they are expected to appear by neutron irradiation. The implantation-induced damage was investigated by depth dependent Doppler broadening (DB) measurements using a variable energy slow positron beam. In addition, as-received, deformed and annealed ODS samples were characterized by DB and positron lifetime measurements for comparison.

Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators, including TiO2 [1] and ZnO [2-5] (see a review by Coey et al. [6]). This kind of observation challenges the conventional understanding of ferromagnetism, which is rather due to spin-split states or bands. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accidence or by mistake. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in TiO2 [1] and SiC [7]. The saturation magnetization rises and falls with increasing the ion fluence due to the interplay between the amount of defects and the crystalline quality. Using electron spin resonance and positron annihilation spectroscopies, one can determine where the unpaired electrons are located and the concentration of defects. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Reference:

[1] S. Zhou, et al., Phys. Rev. B 79, 113201 (2009).
[2] S. Zhou, et al., J. Phys. D 41, 105011 (2008).
[3] K. Potzger, et al., Appl. Phys. Lett. 92, 182504 (2008).
[4] S. Zhou, et al., Appl. Phys. Lett. 93, 232507 (2008).
[5] Q. Xu, et al., Appl. Phys. Lett. 92, 082508 (2008).
[6] J. M. D. Coey, et al., New J. Phys. 12, 053025 (2010).
[7] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).

Uranium and arsenic often co-occur in nature, for example, in acid mine drainage waters. Interaction with arsenic is thus important to understand uranium mobility in aqueous solutions. For the present study, EXAFS spectroscopy was used to investigate the formation and identify the structure of aqueous uranyl arsenate species at pH 2. The nearest U−As distance of 3.39 Å, observed in shock-frozen liquid samples, was significantly shorter than that observed in solid uranyl arsenate minerals. The shorter bond length indicated that the solution contained a bidentate-coordinated species, in contrast to the monodentate coordination in solid uranyl arsenate minerals. The U−As coordination number of 1.6 implied that two uranyl arsenate species with U:As ratios of 1:1 and 1:2 formed in nearly equal proportions and that the hydrated uranyl ion was present only as a minor component. The two uranyl arsenate species could not be differentiated spectroscopically, since their U−As distances were equal. A comparison based on DFT modeling indicated for both the 1:1 and the 1:2 species, that the bidentate arsenates were bound to uranium with one of the binding oxygen atoms being protonated. Based on the present spectroscopic study, the two species that will have to be considered in acidic uranium−arsenic-rich solutions are thus
UO₂H₂AsO₄ ⁺, and UO₂(H₂AsO₄)₂ ⁰.

Positron lifetime measurements and Doppler-broadening spectroscopy were combined to investigate the defect properties during Cu diffusion in Te-doped GaAs. The diffusion of Cu was performed during an annealing step at 1100°C under two different arsenic vapor pressures. The samples were quenched into room temperature water. During a subsequent isochronal annealing experiment, it was found that vacancy clusters were generated and grown, and finally they disappeared. The lifetime results show that, in addition to deep positron traps of vacancy type, positron trapping with a lifetime close to the bulk value of 228 ps occurs. The positron lifetime results give direct evidence of positron localization at shallow traps in GaAs:Te. Due to the Cu contamination during the annealing process, the shallow trap is believed to be the Cu²⁻ _Ga double acceptor. The concentration of shallow traps is determined and found to be in good agreement with the concentration determined by Hall measurement. It decreases up to saturation with increasing annealing. The positron binding energy to these negative nonopen volume trap centers is determined to be 79 meV. It is found to be in agreement with the calculated value.Moreover, coincidence Doppler-broadening spectroscopy shows clearly that Cu atoms are bound in the direct vicinity of the observed vacancy-like defects. Theoretical calculations of momentum distribution predicted that one Cu atom incorporated into a Ga site surrounds the observed open-volume defects.

We investigated the magneto-optical coupling in ferromagnetic thin films (Fe, Ni₂₀Fe₈₀, Co, Ni₈₀Fe₂₀, Ni) in the spectral range from 300 to 1100 nm. We performed Mueller matrix ellipsometry measurements in a magnetic field of arbitrary orientation and magnitude up to 400 mT at room temperature with a set-up vector-magneto-optical generalized ellipsometer (VMOGE). We extracted the magneto-optical dielectric tensor of the ferromagnetic thin films under saturated in-plane magnetization conditions. The off-diagonal elements of the magneto-optical dielectric tensor depend on the net spin polarization and the electronic band structure of the magnetized material. For ferromagnetic Fe, Co, and Ni, the converted magneto-optical dielectric tensor agrees well with reported experimental optical conductivity data. With additional measurements on the magnetization of the ferromagnetic thin films, we extracted the magnetic field independent magneto-optical coupling constant Q, which is a useful parameter for characterization of magneto-optical materials.
Reference: K. Mok et al., Phys. Rev. B 84, 094413 (2011)

Magneto-optical generalized ellipsometry (MOGE) has become extensively important for characterization the magneto-optical response of single and multilayer materials. We setup a Vector-Magneto-Optical Generalized Ellipsometer (VMOGE) in the spectral range from 250 nm to 1100 nm using an octupole magnet, to perform VMOGE measurements of the Mueller matrix in a magnetic field of arbitrary orientation and magnitude up to 0.4 T at room temperature. The VMOGE features a new "field orbit" measurement that can be performed without physically moving the sample, which is useful to study magnetic multilayer or nanostructure samples. An optical model based on the 4 x 4 matrix formalism is required to evaluate and fit the experimental Mueller matrix data. Searching the best match model between experimental and calculated VMOGE data, the magneto-optical dielectric tensor of each layer in a multilayer sample system can be determined. In this work, we investigate the magneto-optical properties of the elemental ferromagnets Co, Fe, and Ni, as well as of NiFe alloys. We extracted the wavelength dependence of the magneto-optical dielectric tensor under saturated magnetization conditions.

The report describes the capabilities of CFD simulatin wall boiling coupled with a population balance model. For the demonstration DEBORA tests were used. Instead of water at high pressure in the DEBORA tests Dichlorodifluoromethane (R12) was used as the working fluid. Similar conditions in terms of the relevant non-dimensional numbers have been realized. This facilitated measurements of radial profiles for gas volume fraction, gas velocity, liquid temperature and bubble size.
Essential for the momentum, mass and energy exchange between the phases is an adequate description of the interfacial area or respectively the bubble size. In the present work a population balance approach coupled to a wall boiling model is used, where bubbles are generated at the wall with a certain size that subsequently evolves due to both condensation / evaporation and coalescence / fragmentation processes. The paper shows the potential of this approach which is able to describe the observed bubble size increase caused by bubble coalescence after leaving the wall as well as the change of gas fraction profile from wall to core peaking with increasing inlet temperature respective decreasing liquid subcooling and consequently enhanced vapour generation.

The influence of the microstructure of the as-deposited cathodic arc evaporated Ti_1-xAl_xN coatings and, in particular, the influence of the intrinsic lattice strains on their thermal stability were investigated by insitu synchrotron high temperature glancing angle X-ray diffraction (HT-GAXRD) experiments up to 850 °C. The microstructure of the as-deposited coatings was adjusted by the bias voltage (UB=−40 V, UB=−80 V and UB=−120 V) and by the [Al]/([Ti]+[Al]) ratio (0.4, 0.5 and 0.6) of the used Ti–Al targets. The microstructure evolution during annealing was described in terms of the phase composition of the coatings, the aluminium content, aluminium distribution and residual lattice strains in fcc-(Ti,Al)N. Independent of the deposition parameters ([Al]/([Ti]+[Al]) ratio and bias voltage), all coatings contained a mixture of fcc-(Ti, Al)N, fcc-AlN and w-AlN after annealing at 850 °C. The [Al]/([Ti]+[Al]) ratio was found to control the amount of fcc-(Ti,Al)N, whereas the bias voltage was mainly responsible for the relative amount of fcc-AlN and w- AlN. Finally, the interplay between lattice strains and the kinetics of the spinodal decomposition of fcc-(Ti, Al)N was illustrated.

Low-temperature (∼450 °C), scalable chemical vapor deposition of predominantly monolayer (74%) graphene films with an average D/G peak ratio of 0.24 and domain sizes in excess of 220 μm² is demonstrated via the design of alloy catalysts. The admixture of Au to polycrystalline Ni allows a controlled decrease in graphene nucleation density, highlighting the role of step edges. In situ, time-, and depthresolved X-ray photoelectron spectroscopy and X-ray diffraction reveal the role of subsurface C species and allow a coherent model for graphene formation to be devised.

Numerical simulations of the kinematic induction equation are performed on a model configuration of the Cadarache von-K\'arm\'an-Sodium dynamo experiment. The effect of a localized axisymmetric distribution of relative permeability mur that represents soft iron material within the conducting fluid flow is investigated. The critical magnetic Reynolds number Rm^c for dynamo action of the first non-axisymmetric mode roughly scales like Rm^c _μ-Rm^c _∞ ∝ μ_r ^-1/2 i.e. the threshold decreases as μ_r increases. This scaling law suggests a skin effect mechanism in the soft iron disks. More important with regard to the Cadarache dynamo experiment, we observe a purely toroidal axisymmetric mode localized in the high permeability disks which becomes dominant for large μ_r.
In this limit, the toroidal mode is close to the onset of dynamo action with a (negative) growth-rate that is rather independent of the magnetic Reynolds number. We qualitatively explain this effect by paramagnetic pumping at the fluid/disk interface and propose a simplified model that quantitatively reproduces numerical results.
The decise role of the high permeability disks for the mode selection in the Cadarache dynamo experiment cannot be inferred from computations using idealized pseudo-vacuum boundary conditions (H ✕ n =0).

1. Introduction

Phosphodiesterase 10A (PDE10A) is a key enzyme that mediates neural signal transduction by regulating intracellular concentration of the cyclic nucleotides adenosine (cAMP) and guanosine monophosphate (cGMP) and is mainly present in brain. Particularly high PDE10A expression and activity was observed in brain regions of dopaminergic and GABAergic neurotransmission. As these relations are not fully understood and PDE10A hypofunction is supposed to correlate with neuropsychiatric disorders such as schizophrenia, obsessive-compulsive disorders, Parkinson’s disease, and Huntington’s disease, there is an ongoing interest in PDE10A as target for molecular imaging by PET.
For the pharmacological treatment of schizophrenia, a highly PDE10A inhibiting, selective and brain penetrable 6,7-dimethoxy-4-pyrrolidinylquinazoline has been designed (Ki=4 nM [1]). Based on this structure we developed fluorine-18 labeled derivatives as potential PET radiotracers for imaging PDE10A in brain [2]. Herein we report on the radiosynthesis and radiotracer properties of the 6-[18F]fluoroethoxy derivative [18F]2 (Figure 1).

2. Materials & Methods

The non-radioactive reference compound 2 and the 7-tosyloxy precursor 1 were prepared in multi-step syntheses, and 2 was screened for its PDE10A inhibitory potency (Ki=32 nM) as well as selectivity in enzyme activity studies [2]. The automated radiosynthesis of [18F]2 was carried out on a TRACERlabTM FX F-N synthesizer. Aqueous n.c.a. [18F]Fluoride was transferred to MeCN via a Chromafix® 30-PS-HCO3 cartridge, dried azeotropically and converted to its K[18F]F-K2.2.2-carbonate complex. Nucleophilic 18F-for-OTs substitution was performed with ~2 mg of 1 in 750 µL MeCN at 85°C within 15 min. Purification of [18F]2 was carried out by SPE (SepPak®Plus C-18, MeCN), followed by semi-preparative RP-HPLC (e.g. on ReproSil-Pur® C18 AQ, 7 µm; 5010 + 15010 mm, 42% MeCN, 20 mM NH4OAc, 4 mL/min; tR=30.3 min). Formulation of [18F]2 was done by SPE, removal of organic eluent and dissolution in physiological saline.
Radioligand stability (EtOH, MeCN, physiological saline and phosphate buffer solution, 40 and 80°C, 5-120 min) and lipophilicity (logD7.0-7.4, shake-flask) were determined. Further characterization in vitro of [18F]2 included the determination of stability in rat plasma (37°C, 30 and 60 min), PDE10A affinity (KD, PDE10A transfected SF21 cells) and autoradiographic imaging of sagittal female rat brain slices, incubated with [18F]2 alone, together with 2 or highly PDE10A-specific MP-10, respectively. Evaluation in vivo of [18F]2 in female CD-1 mice was carried out by the determination of biodistribution and brain uptake as well as metabolism studies and ex vivo brain autoradiography, with validation of specificity by pre-treatment with MP-10 (1mg/kg at 15 min before radiotracer).

Figure 1. Radiosynthesis of [18F]2 and its binding at a sagittal rat brain slice in vitro.

3. Results

Radiosynthesis of [18F]2 resulted in labeling efficiencies of 76-94%, a radiochemical yield of 41.210.3% (n=6, 2 h, based on [18F]F-), a radiochemical purity of ≥99% and specific activities of 80-1030 GBq/mol. [18F]2 remained stable during heating in organic solvents (97% of [18F]2, 120 min, 80°C), and showed moderate stability in aqueous buffer solutions (95% of [18F]2, 60 min, 40°C) and rat plasma (94% of [18F]2, 60 min, 37°C). A logD7.0-7.4 of ~2.5, was determined, and by homologous competition a KD of 24 nM (n=2) was estimated. By autoradiography in vitro, a heterogeneous distribution of [18F]2 in rat brain was observed (Figure 1), which was partially inhibited by MP-10. Biodistribution studies revealed an initial brain uptake of 1.6%ID/g at 5 min p.i.. Striatal uptake at 60 min p.i. was not inhibited by MP-10, which was confirmed by ex vivo autoradiography. Only 41%, 64% and 20% of the radioactivity measured in plasma, brain and liver, respectively, at 30 min p.i. corresponded to parent radioligand. An evidence for slight defluorination was observed because in femur uptake values increased by 25% at 60 min p.i. after removal of the bone marrow.

4. Discussion/Conclusion

A convenient radiosynthesis and satisfactory radiochemical results, as well as moderate lipophilicity and PDE10A affinity initially indicated [18F]2 to be a suitable radiotracer. However, the heterogeneous but non-displaceable binding of [18F]2 in vitro provides evidence for binding affinity to another target. Reasonable high uptake of [18F]2 in mice brain was found, which was non-specific and non-selective. The radioligand stability in vivo is comparably low and the presence of brain metabolites is inappropriate for molecular imaging.
In conclusion, a structural revision of our pharmaceutical lead is needed to improve the in vivo properties and to develop an applicable radiotracer for neuroimaging of PDE10A with PET.

Research Support: European Regional Development Fund (ERDF).

References: [1] Chappie TA, Humphrey JM, Allen MP et al. [2007] J.Med.Chem. 50: 182-185.
[2] Nieber K, Erdmann S, Briel D et al. [2010] Patent Appl. P1014WO.