Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

thermoelectric properties of Si strained along (111) and Si/Ge(111) superlattices are discussed

presentation of the planned activities, pre-requisites and know-how of the newly established Helmholtz Virtual Institute Memeriox

ZnO belongs to the class of wide band gap semiconductors (Eg>3eV), with Eg=3.37eV, and exhibits very interesting optical and electrical properties. Used as a transparent conductive oxide (TCO) electrode in optoelectronic devices [1], ZnO has been developed as a low costs material, an alternative to commonly used and indium tin oxide (ITO). Due to the required transparency, at least in the solar spectral range and a low resistivity, ZnO has to be doped degenerately. While doping with Al leads to the required high carrier concentration [1], alloying with Mg increases the band gap up to 4.5 eV [2]. However, the increase of the conductivity by the increase of the carrier concentration (i.e. reaching the level of N=10^21cm^-3) can lead to a significant increase of the absorption of the light. Therefore, many researches focus on the increase of the electron mobility μ, in accordance with formula ρ=(eNμ)^-1.
The electron mobility is determined by the typical scattering processes in semiconductors, among other the extrinsic scattering on dopants and defects in the film. Since Al doped ZnO and ZnMgO layers, used for transparent electrodes are polycrystalline films, this process can be connected directly with dopants but also with local structure defects as Zn or/and O vacancies, stacking faults and grain boundaries are. These together with the small crystallographic domain size, in the range of 100nm, preferred growing orientation in c axis (perpendicular to the substrate), together with the Al and Mg dopants ionic radius smaller than for Zn [3] (respective crystal radii in tetrahedral coordination are: Al3+ 0.53Å, Mg2+ 0.71Å and Zn2+ 0.74Å), can cause the decrease of the local ordering of the samples.
In this paper we present XAS measurements on the Al doped ZnO and ZnMgO. The XANES spectra were fitted with the simulation program FEFF9 [4]. First results on the Al K edge, see Figure 1, show that the Al substitutes preferably the Zn lattice site in the material. For both dopants, Al and Mg, the spectra show a similar behaviour. The only clearly visible difference, the decrease of the intensity of the first peak for Al and Mg doped ZnO, in comparison to Al doped ZnO, can be attributed to the higher doping level (a similar effect is observed for double Al substitution of ZnO). The comparison of the experimental data with the simulation shows that the measured samples (3 at. % Al doped ZnO and 3 at. % Al doped ZnMgO (6 at.% Mg)) are in the low doping regime, where only single ion doping can be considered. The effect of the expansion of the c axis and the compression of a axis for the growth on glass substrate is also observed.

Acknowledgments: This work was supported by the German Ministry for Economy (AiF Köln).

Reference
[1] K. Ellmer, A. Klein, B. Rechs (Eds.), "Transparent Conductive Zinc Oxide: Basics and Applications in Thin Film Solar Cells", Springer, Berlin (2008)
[2] S. Choopun, R. D. Vispute, W. Yang, R. P. Sharma, T. Venkatesan, H. Shen, “Realization of band gap above 5.0 eV in metastable cubic-phase MgxZn1-xO alloy films” Appl. Phys. Lett. 80 (2002) 1529
[3] R.D. Shannon, “Revised Effective Ionic Radii and Systematic Studies of Interatomic Distances in Halides and Chalcogenides”, Acta Cryst. A32 (1976) 751
[4] J.J. Rehr, J.J. Kas, M.P. Prange, A.P. Sorini, Y. Takimoto, F. Vila, “Ab initio theory and calculations of X-ray spectra”, Comptes Rendus Physique 10 (2009) 548-559

This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits.
Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Regarding photovoltaic applications, we dealt with two aspects: (i) the ion beam doping and thermal processing of so-called dirty silicon demonstrating a distinct improvement of the minority carrier diffusion length compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation
Whereas all these examples base on solid phase processing the more sophisticated approach regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (NanoLett. 11, 2814 (2011)). Moreover a new approach of measuring temperatures in the subsecond time range will be mentioned as well as the interesting field of large area-low cost electronics.

The persistent competition for the cost-effective production of solar cells and displays requires low cost and high throughput production of transparent conductive oxides (TCOs). Nb-doped titania (TiO2:Nb) is a promising novel TCO material for these applications. The results of investigations of TiO2:Nb thin film deposited on large area substrates by sputtering with high deposition rates are reported. As a deposition method we used the direct current sputtering of a 780 mm length substoichiometric oxide tubular target arranged in a rotatable magnetron system in a pilot scale inline sputtering plant. The films were grown on unheated substrates and then thermally annealed at temperatures of 450°C. The influence of the magnetron magnetic field strength and oxygen partial pressure in the sputtering gas on the properties and structure of TiO2:Nb was investigated. A 100 nm thin film deposited on Borofloat® substrate shows after annealing a resistivity of 9.4 x 10-4Ωcm, 82% transmittance in the visible range and a refractive index of ~2.5 (λ=550 nm). The film properties were compared with those of the films grown using a planar oxidic target.

Combining first principles density functional theory and semi-classical Boltzmann transport, the anisotropic Lorenz function was studied for thermoelectric Bi2Te3/Sb2Te3 superlattices and their bulk constituents. It was found that already for the bulk materials Bi2Te3 and Sb2Te3, the Lorenz function is not a pellucid function on charge carrier concentration and temperature. For electron-doped Bi2Te3/Sb2Te3 superlattices large oscillatory deviations for the Lorenz function from the metallic limit were found even at high charge carrier concentrations. The latter can be referred to quantum well effects, which occur at distinct superlattice periods.

Experimental evidence links the receptor tyrosine kinases EphA2 and EphB4 to melanoma progression and metastasis. Another factor contributing to melanoma invasion-metastasis cascade is hypoxia. However, data on the influence of tumor hypoxia on regulation of Eph receptors and their ephrin ligands are scarce. This study aimed at clarifying whether hypoxia influences expression and synthesis of EphA2 and EphB4 and, furthermore, ephrinA1 and ephrinB2, respectively, in four human melanoma cell lines (A375, A2058, MeWo, and MelJuso). In order to investigate Eph/ephrin expression under hypoxic conditions we used cell monolayer cultures as extrinsic hypoxia models and A2058 spheroids as intrinsic hypoxia model. Hypoxic conditions were approved by measurement of VEGF expression and cellular uptake of [18F]fluoromisonidazol ([18F]FMISO). In all models, both VEGF expression and ([18F]FMISO) uptake increased under hypoxic conditions. In normoxia, EphA2, EphB4, ephrinA1, and ephrinB2 expression was detectable in all cell lines showing a substantially varying extent. Protein synthesis of EphA2 was detected in all cell lines and, moreover, of EphB4 in A375 and A2058 cells. However, no effect of experimental hypoxia on Eph/ephrin expression and protein synthesis could be observed. The findings contribute to debating the hypothesis that hypoxia is an important regulator of Eph/ephrin expression in tumors.

The thermoelectric transport properties of Bi2Te3/Sb2Te3 superlattices are analyzed on the basis of first-principles calculations and semi-classical Boltzmann theory. The anisotropy of the thermoelectric transport under electron and hole-doping was studied in detail for different superlattice periods at changing temperature and charge carrier concentrations. A clear preference for thermoelectric transport under hole-doping, as well as for the in-plane transport direction was found for all superlattice periods. At hole-doping the electrical transport anisotropies remain bulk-like for all investigated systems, while under electron-doping quantum confinement leads to strong suppression of the cross-plane thermoelectric transport at several superlattice periods. In addition, insights on the Lorenz function, the electronic contribution to the thermal conductivity and the resulting figure of merit are given.

In relativistically strong laser fields with intensities well above 10^19 W/cm^2, multi-photon emission processes are important in collisions of relativistic electron beams with the laser pulse. We present results on the coherent two-photon process (double Compton scattering) in the presence of strong and short laser pulses, taking into account the finite temporal pulse length exactly for the first time.

In relativistically strong laser fields with intensities well above 10^19 W/cm^2, multi-photon emission processes are important in collisions of relativistic electron beams with the laser pulse. We present results on the coherent two-photon process (double Compton scattering) in the presence of strong and short laser pulses, taking into account the finite temporal pulse length exactly for the first time.

The anisotropic thermoelectric transport properties of bulk silicon strained in the [111]-direction were studied by detailed first-principles calculations focusing on a possible enhancement of the power factor. Electron and hole doping were examined in a broad doping and temperature range. At low temperature and low doping an enhancement of the power factor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. For the thermoelectrically more important high-temperature and high-doping regime a slight enhancement of the power factor was only found under small compressive strain with the power factor overall being robust against applied strain. To extend our findings the anisotropic thermoelectric transport of a [111]-oriented Si/Ge superlattice was investigated. Here, the cross-plane power factor under hole doping was drastically suppressed due to quantum-well effects, while under electron doping an enhanced power factor was found. For this, we state figures of merit of ZT = 0.2 and 1.4 at T = 300 and 900 K for the electron-doped [111]-oriented Si/Ge superlattice. All results are discussed in terms of band structure features.

The dipole strength of the N=50 nucleus 86Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE and using quasi-monoenergetic gamma rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HIgS facility. A high-pressure gas target was used. We identified 42 levels up to an excitation energy of 10.1 MeV. Simulations of gamma-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a recent (gamma,n) experiment at HIgS. The enhanced E1 strength found in the range from 6 to 10 MeV is compared with that in the N = 50 isotones 88Sr, 90Zr, and 92Mo and with predictions of calculations within the quasiparticle-phonon model.

We present mciroscopic theory on the relaxation dynamics in graphene as well as experimental results. The excitation energies ccover the complete infrared spectral range.

At Helmholtz-Zentrum Dresden-Rossendorf ultra-short high-power laser pulses drive sources of electron, ion and X-ray pulses. Close collaboration of experimental and theoretical studies drive the understanding and optimization of these sources for applications such as laser-driven ion beam tumour therapy.
When working close to the experiment fast simulation results and surveys of large parameter spaces are mandatory. We have developed a new code that works on accelerator hardware to return simulation results in hours instead of weeks. These fast response times allow us to add physical effects not yet available in simulation due to time constraints. We present simulations using our code PIConGPU, a particle-in-cell code working on graphic processing units, which show what is in reach of simulations based on modern hardware.
Besides developing new simulation software we work on making numerical and analytical models of laser-driven particle acceleration more realistic in order to better predict the outcome of experiments. This is necessary since our focus lies on optimum control of laser-driven radiation sources for applications. We present results on laser-driven ion acceleration and its applications that show how realistic models influence our experimental strategy.
We end with an outlook on why we see data analysis of large-scale simulations as an integrated part of our joint experimental and theoretical program and how we plan to integrate this into our daily work.

Magnetoelectric coupling allows for manipulating the magnetization by an external electric field or the electrical polarization by an external magnetic field. Here, we propose a mechanism to electrically induce 180 degree magnetization switching combining two effects: the magnetoelectric coupling at a multiferroic interface and magnetic interlayer exchange coupling. By means of first-principles methods, we investigate a ferroelectric layer in contact with a Fe/Au/Fe trilayer. The calculations show that the interface magnetism is strongly coupled to the ferroelectric layer. Furthermore, under certain conditions a reversal of polarization causes a sign reversal of the interlayer exchange coupling which is results in a 180 degree switching of the free layer magnetization. We argue that this magnetoelectric coupling mechanism is very robust and can find applications in magnetic data storage.

Many-core compute architectures such as graphic cards will be the building blocks of next-generation Exaflop computers. With these architectures, complex laser plasma simulations can run on a frames-per-second rate, decreasing the waiting time to get results to hours instead of weeks. Thus, large surveys for optimum acceleration parameters come in reach. This will enable theoreticians and experimentalists to discuss and understand the physics behind particle acceleration scenarios instead of simply adding a few pretty simulation pictures to a publication. When considering future applications of ultra-intense lasers, new physics will have to be taken into account. It is thus not only mandatory to make simulations fast, but to then add new physical effects into the code. This will require new strategies to leverage the power of next-generation supercomputers. We propose potentially successful techniques to get the most out of upcoming HPC systems based on our experience with PIConGPU and show what is already possible today.

We present PIConGPU, an implementation of a three-dimensional fully relativistic particle-in-cell (PIC) code for GPU clusters. PIConGPU can simulate laser matter interaction at relativistic laser intensities, for example to investigate laser particle acceleration schemes.

Recent progress in wave packet dynamics based on the insight of Berry pertaining to adiabatic evolution of quantum systems has led to the need for a new property of a Bloch state, the Berry curvature, to be calculated from first principles. We report here on the response to this challenge by the ab initio community during the past decade. First we give a tutorial introduction of the conceptual developments we mentioned above. Then we describe four methodologies which have been developed for first-principle calculations of the Berry curvature. Finally, to illustrate the significance of the new developments, we report some results of calculations of interesting physical properties such as the anomalous and spin Hall conductivity as well as the anomalous Nernst conductivity and discuss the influence of the Berry curvature on the de Haas–van Alphen oscillation.

With powerful lasers breaking the Petawatt barrier, applications for laser-accelerated particle beams are gaining more interest than ever. Ion beams accelerated by intense laser pulses foster new ways of treating cancer and make them available to more people than ever before. Laser-generated electron beams can drive new compact x-ray sources to create snapshots of ultrafast processes in materials. With PIConGPU laser-driven particle acceleration can be computed in hours compared to weeks on standard CPU clusters. We present the techniques behind PIConGPU, detailed performance analysis and the benefits of PIConGPU for real-world physics cases.

GPUs are one implementation of the many-core architecture that could be an important building block of future Exascale HPC-systems.
I present PIConGPU, an electromagnetic particle-in-cell code for laser-plasma interaction, discussing the important building blocks and techniques implemented in PIConGPU to leverage the power of large-scale GPU clusters.
PIConGPU hints at what to expect in the near-term future of massively-parallel particle-in-cell simulations in terms of parameter surveys, new physics modules and large-scale simulations.

Thomson scattering of high-power laser pulses from relativistic bunches of electrons is a promising technique to deliver ultra-short x-ray pulses of high peak brightness. X-ray pulses in the multi-keV regime are obtainable using few MeV electrons delivered by conventional accelerators.

With laser-accelerated electrons photon energies of several MeV can be reached. We introduce concepts to improve the peak brightness of these beams using high power lasers and compare simulation results to experiment. Analytic models show that long interaction lengths could be obtained by spatio-temporal tayloring of the laser pulse. This Travelling-Wave Thomson Scattering technique would allow to produce narrow-bandwidth X-ray pulses of high peak brightness.

We present recent results on PIConGPU, a charge-conserving 3D relativistic particle-in-cell code running on graphic processors. We discuss best practices on how to implement the particle-in-cell algorithm on this new hardware and run it on large GPU clusters. We show that these codes have become mature enough to be considered for real life applications, delivering fast response time even for large physical problems.

Cooling of ion beams is essential for precision experiments at future storage rings. Laser cooling is one of the most promising techniques to reach high phase space densities at relativistic ion energies for all ion species which provide suitable atomic cooling transitions.

Establishing laser cooling as a standard technique at future storage rings requires laser sources that can address ion beams with large initial velocity spreads.

Without optical diagnostics however, the dynamics of ions at very low temperatures cannot be resolved, as conventional beam diagnostics reach their resolution limits.

We discuss concepts and techniques that pave the way for making laser cooling a reliable tool at future storage rings, some of which can already be tested at the ESR at GSI.

Die genaue Bestimmung der Hyperfeinstrukturaufspaltung (HFS) von hochgeladenen Ionen erlaubt im Abgleich mit theoretischen Berechnungen einen Test der QED. Die Messung an schweren und hochgeladenen Ionen erlaubt einen Test der QED in starken Feldern.

Im Rahmen der LIBELLE (E083)-Kollaboration am Helmholtzzentrum für Schwerionenforschung (GSI) wurden hierzu wasserstoff- und lithium-ähnliches Bismut bei Geschwindigkeiten von β=0.7 im Speicherring ESR gespeichert und mittels Laserspektroskopie untersucht. Nach 12-jähriger Suche wurde nun erstmals der verbotene HFS-Übergang im lithium-ähnlichen Bismut gefunden.

Recent theoretical results have led to a new understanding of how to derive the temperature of hot electrons generated in laser-solid interactions from the laser intensity.

We present new scaling laws for electron temperature with laser intensity. We then focus on the implications of our findings for applications such as laser-driven ion acceleration and laser-driven fusion using buried-layer targets.

The „Helmholtz-Zentrum Dresden-Rossendorf“ (HZDR) research center covers a wide area of fundamental research in the fields of matter, health and energy. In particular for the first domain, a key topic is the behavior of matter in strong fields. The center operates several large-scale facilities of excellent research: The „Dresden High Magnetic Field Laboratory“ (HLD), the accelerator and radiation source ELBE and the high-intensity laser system DRACO.
In view of preparatory research and training for the upcoming x-ray free electron laser XFEL at Hamburg, an initiative was taken in order to combine the expertises of generating ultra-strong magnetic fields, high-power laser-matter interaction, plasma physics, radiation physics and material science. The junction of all of these fields settles exactly at laboratory astrophysics.
We will present our experiences in the individual fields, outline the project and discuss possible experiments.

Spin textures have been an interesting topic of magnetism research for many years. Within this field, magnetic vortices have attracted much attention, due to their non-trivial topology and the various dynamic modes they exhibit. Such a magnetic vortex consists of a planar, flux-closing magnetization curl that turns out of the plane in the central nanoscopic core region. In a single vortex, typically no significant radial magnetization components are present. Recent investigations show that this also holds true for multilayer vortex systems with bilinear interlayer exchange coupling (IEC).
Here we report on pairs of diverging-converging spin vortices occurring in patterned magnetic multilayers (Co/Rh/NiFe). These effective meron states can be understood as a superposition of the topological meron state (defined by a perfectly radial magnetization distribution) and a regular tangential vortex. Using magnetic scanning transmission x-ray microscopy (STXM) we directly image the individual effective merons in both ferromagnetic layers with high lateral resolution. Supporting SQUID measurements and micromagnetic simulations reveal that a significant biqudratic IEC is necessary to stabilize the states observed.

With a half-life of 81.1 Myr, ²⁴⁴Pu could be both the heaviest and the shortest-lived nuclide present on Earth as a relic of the last supernova(e) that occurred before the formation of the Solar System. Hoffman et al. [Nature (London) 234, 132 (1971)] reported on the detection of this nuclide (1.0 × 10⁻¹⁸ g ²⁴⁴Pu/g) in the rare-earth mineral bastnäsite with the use of a mass spectrometer. Up to now these findings were never reassessed. We describe the search for primordial ²⁴⁴Pu in a sample of bastnäsite with the method of accelerator mass spectrometry (AMS). It was performed with a highly sensitive setup, identifying the ions by the determination of their time-of-flight and energy. Using AMS, the stripping to high charge states allows the suppression of any molecular interference. During our measurements we observed no event of ²⁴⁴Pu. Therefore, we can give an upper limit for the abundance of ²⁴⁴Pu in our sample of the mineral bastnäsite of 370 atoms per gram (1.5 × 10⁻¹⁹ g²⁴⁴Pu/g). The concentration of ²⁴⁴Pu in our sample of bastnäsite is significantly lower than the previously determined value.

Chemical environment plays a significant role on the size, shape, or surface composition of nanostructures. Here, the chemical environment effects are studied in the context of core−shell nanoparticle synthesis. The environment driven dynamics and kinetics of Rh/Pd bilayers is investigated by in situ ambient pressure X-ray photoelectron spectroscopy. Thin Rh (∼1.5 nm)/Pd (∼ 1.5 nm) bilayers were grown on thermally oxidized Si substrates. The films were heated in CO or NO environments or heated in vacuum with a subsequent NO/CO cycling. This study demonstrates that not the initial stacking sequence but the chemical environment plays a crucial role in controlling the surface composition. Heating in CO results in a surface enrichment of Pd at ∼200°C and is followed by film dewetting at ∼300 °C. Heating in NO results in progressive oxidation of Rh starting at ∼150 °C, which stabilizes the film continuity up to >∼375 °C. The film rupture correlates with the thermal destabilization of the surface oxide. Heating in vacuum results in a significant increase in surface Pd concentration, and the following NO/CO cycling induces periodic surface composition changes. The quasi-equilibrium states are ∼50% and ∼20% of Rh/(Rh + Pd) for NO and CO environments, respectively. Possible surface composition change and dewetting mechanisms are discussed on the basis of the interplay of thermodynamic (surface/oxide energy and surface wetting) and kinetic (surface oxidation and thermally induced and chemically enhanced diffusion) factors. The results open alternative ways to synthesize supported (core−shell) nanostructures with controlled morphology and surface composition.

There is a possibility that small traces of long-lived superheavy elements (Z ≥ 104) still exist in nature. An ultrasensitive search for such superheavy elements has been conducted at the Maier-Leibnitz Laboratory in Garching (Germany) by means of accelerator mass spectrometry. A sample of raw platinum has been scanned for 13 different masses in the range 292 ≤ A ≤ 310. The masses A = 292 and 298 were scanned in pure osmium and pure lead fluoride, respectively. For each mass, several hours of background-free data were recorded. Since no events could be attributed to superheavy elements, upper limits on their abundances in the sample materials on the order of 10⁻¹⁴–10⁻¹⁶ were established.

Lanthanides have become a useful tool in NMR spectroscopy within the last 40 years. Due to their paramagnetic properties they can be utilized as probes to determine the binding sites of biologically or environmentally relevant organic molecules as they cause significant line broadenings and / or paramagnetic induced shifts.
In our former and actual research we investigate the interactions between actinides and biomolecules, revealing the structure as well as thermodynamic and kinetic behaviour. Lanthanides can easily be used as inactive analogues for trivalent actinides in consequence of their similar chemistry.
We found out that lanthanide ions are able to act as linkers to build up polymeric structures of bifunctional organic acids such as phosphorylated amino acids. For instance, in the case of O-phospho-L-serine the lanthanide ions can serve as a bridge between the carboxylate and the phosphate group of two amino acid molecules to form macromolecules with repetitive units. Solid state NMR spectroscopy was the most feasible tool for structure elucidation, proving that both the phosphate and the carboxylic group are involved in the complexation. By means of 1D and 2D methods it was confirmed that both functional groups lose their protons and, thus, must be the binding sites for the lanthanides, whereas the protons of the amino group are unaffected.
The interactions between the lanthanides (Eu3+, La3+) and the phosphorylated acids can be monitored by solution 31P-NMR spectroscopy and confirmed by dynamic light scattering. After mixing the reactants, colloids are formed immediately. After some minutes up to hours the formed aggregates precipitate. Different temperature, pH and ionic strength conditions may be object of further investigations.

In this work, we report on the changes in structural and magnetic properties of Pt (0.7 nm)/Cr (x nm)/Co (0.5 nm) was observed. Above finding is discussed in the realm of ion beam mixing, leading to the CoCrPt ternary alloy phase formation, after low-energy He+-ion irradiation.

In previous work it has been found that active flow control on a separated shear layer of an airfoil is able to increase lift by 50 percent. It was shown, the effect of control depends on various parameter like amplitude, frequency waveform of the signal. The electromagnetic actuator we use, induces a mainly wall normal body force. As the force amplitude is proportional to the external applied voltage a wide range of time signals can be generated.
Due to the variety of actuating variables present work was focused to study the variation of unique parameters. Our aim is to set up an optimization method including a wide range of variables to find the most effective constellation. In order to reduce the numeric costs for the optimization we use a reduced order model. The model is derived by projecting the Navier-Stokes equation to a basis derived from proper orthogonal decomposition (POD). The POD modes are computed from autocorrelated snapshots of a high fidelity solution (Direct Numerical Simulation or Large Eddy Simulation). To cope with pressure effects due to open boundaries we adopted the approach of Noack et al. (2005). The choice of the snapshots restricts the area of application of the model. For this reason the optimization has to be combined with a trust region method . As there are several references dealing with cylinder wake flow, we validate the approach with the flow past a circular cylinder with Re = 100. In order to work out a suitable strategy for controling separated shear flows we consider the backward-facing step as a simple, but yet characteristic example. As a particular challenge we plan to address the reduced order representation of short forcing peaks and a robust selection of snapshots within the trust region iteration of the optimizer.

The response of a separated flow over a two-dimensional wing to a short duration disturbance from a Lorentz force leading-edge actuator is presented. The transient flow structures and lift force measurements were obtained from PIV measurements. The dependence of the lift response on actuator pulse duration, pulse amplitude, and direction of actuation was documented. The flow structures in the separated shear layer were identified using Finite Time Lyapunov Exponent (FTLE) method. The direction of the actuator pulse had a significant effect on the initial development of the shear layer, but the larger scale envelope of the separated flow had essentially the same response, irrespective of the direction of actuation.

Zur Erfassung räumlich verteilter Parameter in Prozessbehältern wurde das Konzept autonomer Sensorpartikel entwickelt und getestet. Die Sensorpartikel sind auftriebsneutral und bewegen sich frei mit der vorherrschenden Strömung im Prozess. Die integrierte Messelektronik erfasst die Signale der internen Messfühler für die Temperatur, die Eintauchtiefe und die Beschleunigung in einem autonomen und energieeffizienten Messregime. Die Validierung des Messsystems erfolgte unter realen Strömungsbedingungen in einem Versuchsfermenter. Die aufgenommenen Messda-ten und die daraus extrahierten Prozesskenndaten charakterisieren den Zustand des Prozesses und die Strömungsbedingungen.

The magnetorotational instability (MRI) plays a key role for cosmic structure formation by triggering turbulence in the rotating flows of accretion disks that would be otherwise hydrodynamically stable. In the limit of small magnetic Prandtl number, the helical and the azimuthal version of MRI are known to be governed by a quite different scaling behaviour than the standard MRI with a vertical applied magnetic field. Using the short-wavelength approximation for an incompressible, resistive, and viscous rotating fluid we present a unified description of helical and azimuthal MRI, and we identify the universal character of the Liu limit for the critical Rossby number.
From this universal behaviour we are also led to the prediction that the instability will be governed by a mode with an azimuthal wavenumber that is proportional to the ratio of axial to azimuthal applied magnetic field, when this ratio becomes large and the Rossby number is close to the Liu limit.

In order to correlate the size and crystallinity of FePt nanoparticles with their respective electrical and mangeto-electrical properties individual nanoparticles are contacted using electron beam lithography. The particles are prepared from gas phase on electron transparent SiN membranes which allows the transmission electron microscopy of the same nanoparticle which is characterized electrically. This procedure results in junctions, in which single FePt nanoparticles are connected to external leads. These junctions are tested electronically by measuring the current-voltage characteristics at various gate voltages, temperatures and magnetic fields. We observe Coulomb Blockade effects which are in agreement with the dimensions obtained from the TEM studies. The results of the magnetic nanoparticles are compared to measurements taken on Au nanoparticles of similar sizes.

We present a novel device for the separation of microparticles in a single channel, which is made of inversely asymmetric Brownian ratchets. It enables separation into two different fractions with an adjustable threshold and can be modeled with good agreement. This device serves as proof of concept for an extremely compact class of microsieves.

We show statistical measurements of single molecule-metal contacts using the mechanically controllable break junction technique. The measurements are carried out in a solvent, in order to allow in situ binding of the molecules to the metallic contacts during the measurements. Statistics is gathered by opening and closing the junctions repeatedly and recording current-voltage characteristics at various stages of the opening and closing curves. By modeling the data with a single level model we can extract parameters such as the position of the molecular energy level, which carries the current, and the coupling between the metal and the molecule. In first experiments we use this method to characterize di􏰹erent anchoring groups, which mediate the mechanical and electrical coupling between the metallic electrodes and the molecules. We use tolane molecules, which are structurally simple, as model systems for this purpose.

Mittels erweitertem Laser-Doppler-Geschwindigkeitsprofilsensor wurde ein hoch aufgelöste, mehrkomponentige Vermessung von Strömungsfeldern durchgeführt, welche von Plasma- bzw. Lorentzkraft-Aktuatoren angetrieben wurden. Für den Einsatz der Aktuatoren zur aktiven Strömungskontrolle ist ein genaues Verständnis der jeweiligen Wirkungsweise erforderlich, was im Fall des Plasma-Aktuators noch nicht komplett vorliegt. Da Plasma-Aktuatoren im Allgemeinen mittels alternierender Hochspannung betrieben werden, ist eine hohe Zeitauflösung des Messsystems ebenso unabdingbar. Die gewonnen Messergebnisse, welche bis zu 100 mum nahe an der Aktuatoroberfläche gewonnen werden konnten, erlauben schließlich die Berechnung der induzierten Kraft und gewähren daher einen tieferen Einblick in das Funktionsprinzip. Es konnte somit ein wertvoller Beitrag zur Beschreibung des zeitlichen Verlaufs der erzeugten Kraft geleistet werden.

Experimental photoabsorption cross sections for the nuclei 92,94,96,98,100Mo, 88Sr, 90Zr, and 139La are used as an input for calculations of (γ,n), (γ,p), and (γ,α), as well as (n,γ), (p,γ), and (α,γ) cross sections and reaction rates at energies and temperatures relevant for nucleosynthesis network models and transmutation projects. The calculations are performed with the statistical-model code talys. The results are compared with those obtained by using different analytic standard parametrizations of γ-ray strength functions implemented in talys and with an energy-damped double-Lorentzian model. The radiative capture reaction cross sections are enhanced by the pygmy resonances in 88Sr, 90Zr, and 139La.

In this study we investigate the flow structure in a liquid metal cylinder while a bubble driven recirculation flow is superposed with a rotating magnetic field (RMF). The measurements revealed the potential of the RMF to control both the amplitude of the meridional flow and the bubble distribution and to provide an effective mixing in the whole fluid volume. Various periodic flow patterns were observed in a certain parameter range with respect to variations of the magnetic field strength and the gas flow rate.

Visualizations of the solidification process were obtained by means of X-ray radioscopy within a Hele-Shaw cell filled with a Ga-25wt%In alloy. Thermo-solutal convection in the solidifying melt gives rise to the development of vertical segregation channels (“chimneys”). The probability of chimney formation depends sensitively on variations of both the concentration and temperature distribution. A forced melt flow perpendicular to the growth direction accelerates the growth of the secondary dendrite arms on the upstream side and suppresses the development of secondary arms on the downstream side. The primary dendrite arm spacing is increased, whereas the secondary arm spacing remains unaffected. Flow-induced modifications of the local composition were observed within the mushy zone which may contribute to the formation of spacious segregation pattern.

This paper considers the situation where the liquid metal flow with a free surface covered by an oxide layer is driven by a rotating magnetic field. The cylindrical configuration was investigated in an experiment accompanied by numerical simulations. The oxide layer feels the effect of the viscous force arising from the moving liquid beneath and the friction force from the side walls. A complex interaction occurs if both forces are in the same order of magnitude. Our measurements demonstrate that the occurrence of the oxide layer may lead to an unexpected oscillating behaviour of the bulk flow. Our numerical model was shown to be able to reproduce essential features of the phenomenon in a qualitative way.

X-ray irradiation has an influence on metastatic properties of tumor cells. Moreover, metastasis and cellular motility can be modified by EphA2 and EphA3, two members of the Eph receptor/ephrin family of receptor tyrosine kinases. However, a link between X-ray irradiation, Eph receptor expression, and modification of metastasis-relevant cellular properties has not yet been shown.
In this study, we irradiated one pre-metastatic and three metastatic human melanoma cells lines with X-rays and found impairment of cell growth and clonal growth. Regarding adhesion, an irradiation-induced increase paralleled by a decrease in migration was detected in Mel-Juso and Mel-Juso-L3 cells and, in part, also in A375 cells. These results indicate irradiation-induced anti-metastatic effects.
For EphA2 a decrease both in expression and activity at 7 days after irradiation was detected. In contrast, EphA3 was found to be up-regulated in 3 of 4 analyzed cell lines. Analyzing downstream signaling after irradiation decreased Src kinase phosphorylation, but unchanged focal adhesion kinase (FAK) phosphorylation was demonstrated. Our findings indicate that irradiation-induced downregulation of EphA2 and up-regulation of EphA3 in human melanoma cells is associated with anti-metastatic effects. The observed effects are assumed partly to be mediated by regulation of Src and FAK through EphA2.

Lanthanides have become a useful tool in NMR spectroscopy within the last 40 years. Due to their paramagnetic properties they can be utilized as probes to determine the binding sites of biologically or environmentally relevant organic molecules as they cause significant line broadenings and / or paramagnetic induced shifts.
In our former and actual research we investigate the interactions, thermodynamic and kinetic behaviour of actinides and biomolecules. Lanthanides can easily be used as inactive analogues for trivalent actinides in consequence of their similar chemistry.
As one major result, determined by solution and solid state NMR spectroscopy, we have found out that lanthanide ions are able to act as linkers to build up polymeric structures of bifunctional organic acids such as pyromellitic acid [1] or phosphorylated amino acids. For instance, in the case of O-phospho-L-serine the lanthanide ions can serve as a bridge between the carboxylate and the phosphate group of two amino acid molecules to form repetitive macromolecules. The influence of pH and temperature has also been studied.
The results were confirmed by dynamic light scattering and FT-IR spectroscopy as well as by isothermal titration calorimetry and laser-induced fluorescence spectroscopy.
Future investigations will focus on actinides, in particular the trivalent americium ion, possibly showing similar chemical reactions.

[1] A. Barkleit, S. Tsushima, O. Savchuk, J. Philipp, K. Heim, M. Acker, S. Taut, K. Fahmy, Inorg. Chem. 50 (2011), 5451-5459.

The conversion of Z-phenylalanine hydrazide with cyanogen bromide resulted in the formation of the corresponding 2-amino-1,3,4-oxadiazole by spontaneous cyclization of the intermediary cyanohydrazide. The molecular structure of the product was confirmed by single crystal X-ray diffraction. Crystals of the title compound where obtained from a saturated solution in a mixture of petroleum ether and ethyl acetate and belong to the monoclinic space group P21 with unit cell parameters a =
9.8152(2) Å, b = 9.6305(2) Å, c = 9.8465(2) Å, beta = 116.785 (1)°. The asymmetric unit contains one molecule.

We investigate the influence of a nanoscale periodic ripple morphology on the structure and magneto-crystalline anisotropy of thin ferromagnetic (FM) NiFe, Co, and Fe films. The ripples are created by ion beam erosion of the Si substrate. The periodic ripple structures induce a uniaxial magnetic anisotropy (UMA) in the FM films as confirmed by ferromagnetic resonance and magnetooptical Kerr effect measurements. The thickness dependence of the UMA reveals an abrupt transition. For a thin film regime there is a corrugated alignment of the magnetic moments and above a critical thickness one has dipolar interactions due to the sinusoidal surface modulations.

Semiconductor multilayers are a versatile tool in optoelectronics. The III-V/IV heterostructure GaP(001) on Si(001) provides a viable and almost lattice-matched stack making it suitable for device applications such as multi-junction solar cells. One of the main challenges still arises from the efficiency limitation due to symmetry breaking and imperfections at the buried GaP on Si interface. Here, we present a density-functional investigation of the interface using both the pseudopotential plane-wave code ABINIT and the all-electron augmented plane-wave code Wien2K. The study distinguishes between the Ga-rich and the P-rich interface termination of GaP in the (001) plane. Overall insight into the interface characteristics is gained from structural and electronic quantities. At the perfectly flat interface, the P-rich variant is found to exhibit higher stability. This is supported by the investigation of the atom distances and the local electronic system. Further, it could be shown that the impact of the interface is very local and does not reach far into the layers. Depending on the interface termination, the electronic system shows distinct behavior.

Regarding the successful use of strontium titanate with different doping within resistive switching memory cells, the presence of crystallographic defects seems to be an important prerequisite. Standard explanations for resistive switching rely on the redistribution of oxygen vacancies, however, this motion can be enhanced or prevented by higher-dimensional defects. Intrinsic defects in crystalline SrTiO3 include point defects such as oxygen or strontium vacancies, line defects, stacking faults like Ruddlesden-Popper phases and precipitates (TiO2, SrO etc.). Electric formation of the metal/oxide/metal cells is widely used as an initial step to enable resistive switching, but the interaction of the multi-dimensional defects during this treatment remains questionable. This talk will present several measurements that were performed in situ, i.e. during the application of an electric field, to investigate the effects of the electric formation on the real structure.

Gallium phosphide thin films on cheap silicon substrates are a promising III-V/IV heterostructure to be used in optoelectronic devices. As an almost lattice matched system with a band gap difference of 1.14 eV it includes applicability for multi-junction solar cells. The present study concerns discontinuities emerging at the boundaries of a GaP thin layer on a silicon substrate. The optical anisotropy of the (001) interface has been determined by an optical model applied to reflectance anisotropy spectroscopy measurements of the GaP/Si heterostructure. Density-functional calculations of the interface have been performed with both, the pseudopotential plane wave code ABINIT [1] and the all-electron augmented plane wave code Wien2K [2]. The study distinguishes between the Ga-rich and the P-rich interface termination. At the perfectly flat interface, the latter exhibits higher stability as indicated by the work of separation. More complex interface models also consider defects. The calculated density of states projected onto in-plane directions gives an indication for anisotropy. It aims at distinguishing interface termination and defects as origin of the experimentally observed reflectance anisotropy. [1] www.abinit.org [2] www.wien2k.at

no abstract available

The Virtual Institute (VI) „Memriox“ establishes a joint research initiative in the field of ion-tailored oxide-based memristive materials, to be pursued within a novel and unique combination of core competences from the Helmholtz centers Dresden-Rossendorf and Jülich and their university partners in Aachen, Dresden, Freiberg, and Jena. A nanoscale memristive switch may prove the ultimate future non-volatile memory and logic cell with a resistance set directly by electric currents. Thus, the nanoscale memristor has matured to a key player in strategies combining the virtues of the “More Moore” and “More than Moore“ concepts to drive the development of both miniature and functionalized electronic components for a resource-efficient “green“ computing.
Scientifically, the VI aims at stepping beyond the established layer-by-layer control of intrinsic defects during the synthesis of memristive homojunctions. For that purpose, the VI will employ the broad range of ion-beam techniques (HZDR and FSU Jena competence) to induce functionalized one- and two-dimensionally extended memristive nanoregions with high spatial precision. Nano-scale electronic and optical properties and functiona¬lities will be investigated at the partner institutions at the FZJ and the universities in Aachen, Freiberg, and Jena. Applica-bility will be assessed at the NaMlab facility of the TU Dresden. Associated partners at the U.C. San Diego (U.S.A.) and the ETH Zürich (Switzerland) extend the expertise on spectroscopy and simulation.
This combination of the VI partners’ profound, long-term expertise in complementary high-level synthesis, characterization and analysis techniques is unique in the German research area. It provides the ideal framework to explore the spatial limits of memristive elements and their environment hence the VI faces the challenges of the ‘More Moore’ concept, which is still less prominent in basic memristor research. The VI will thus make a significant, qualitatively and quantitatively distinct contribution to cutting-edge science, which aims at quantifying defect-related effects on memristive behavior according to the ‚More Than Moore‘ concept.

Sea ice is a very variable biotope with respect to extension,thickness, porosity or texture. Therefore the basic understanding of brine channel formation in sea ice is important for the interplay between the microbial colonization and their natural habitat. The early phase of brine channel formation in sea ice is considered. The first structures emerging during sea-ice formation are determined by the phase instability of the ice-water system in the presence of salt. We apply a Ginzburg-Landau type approach to describe the phase separation in the two-component system (ice, salt). The free energy density involves two order parameters: one for the hexagonal ice phase with low salinity, and one for the liquid water with high salinity. A gradient dynamics minimizes the free energy with respect to the conservation of the salinity. The resulting model equations are solved numerically in one and two dimensions. The numerical solution shows a short-time behavior of structure formation where the freezing is assumed and a large-time broadening of the structure. A stability analysis provides the phase diagram where brine channels can be formed. In thermodynamics the parameters determine the supercooling or superheating region and the specific heat respectively. The size of the brine channels depends on the salinity and the temperature. With the help of realistic parameters the brine channel distribution is calculated and found in agreement with the measured samples.

Carbon nanotubes (CNTs) are a promising material for novel sensor and interconnect applications. In both cases, the device performance depends strongly on the electronic properties of the tubes. Methods for tuning the electronic structure and especially the band gap are highly desirable. A computational study of cobalt decorated CNTs, by means of density functional theory, reveals that very few cobalt atoms can have a significant impact on the electronic structure, turning semiconducting CNTs into the metallic state. This is further verified by quantum transport simulations. The influence of different amounts of cobalt is also investigated.

Transition metal oxides exhibit many physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. The stoichiometry of transition metal oxides depends on the oxygen partial pressure and changes conductivity and ferroic properties. Ternary/quaternary oxides are discussed, which correlate local defect-induced structure changes with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional theory as basis for more large-scale simulations with effective Hamiltonians. Oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. For Sr/O excess SrO(SrTiO3)n phases with additional SrO planes occur, which change the X-Ray reflectivity. Ion-irradiation triggers additional point defects which can form stable aggregates. In YMn2O5 several antiferromagnetic phases coexist with ferroelectricity; YFeMnO5 exhibits only one commensurable ferrimagnetic phase. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the two compounds and relates them to crystal-field interactions.

Nanostructures influence material properties dramatically due to size, shape and interface effects. Thus the control of the structure at the nanoscale is a key issue in nanomaterials science. The interaction of hyperthermal ions with solids is confined to the nanometer scale. Thus, it can be used to control the morphology evolution during multiphase film deposition. Ion-induced displacements occur in a thin surface layer of the growing film where they increase the atomic mobility for the phase separation. Here the growth-structure relationship of C:Ni (~15 at.%) nanocomposite films grown by oblique incidence (~45) ion beam assisted deposition is reported. The influences of the flux of an assisting Ar+ ion beam (0-140 eV) as well as of an elevated substrate temperature have been studied. The formation of elongated nickel nanoparticles is strongly promoted by the ion beam assistance. Moreover, the metal nanocolumns no longer align with the advancing surface, but with the incoming ions. A window of conditions is established within which the ion assistance leads to the formation of regular composition modulations with a well defined periodicity and tilt. As the dominating driving force for the pattern formation is of physical origin, this approach might be applicable to other immiscible systems.

Transition metal oxides exhibit a wealth of physical phenomena, among them ferroic properties such as ferroelasticity, ferroelectricity and ferromagnetism, or their combination in multiferroics. In addition, transition metal oxides are sensitive to the chemical environment via the oxygen partial pressure or ion irradiation; changes induce stoichiometry deviations, which cause conductivity changes and modify the ferroic characteristics. Ternary and quaternary compounds from the perovskite family will be discussed as examples, which correlate local changes due to point and planar defects with changes of the elastic, polarization and magnetic properties. The microscopic interactions are determined by density functional calculations, which yield the basis for more large-scale simulations with effective Hamiltonian approaches. Under oxygen-poor conditions, oxygen vacancies in SrTiO3 accumulate in an external electric field and reduce the hardness. In an Sr/O-rich environment the phases SrO(SrTiO3)n are formed, which yield a distinct change of the X-ray reflectivity due to the regular arrangement of extrinsic SrO(001) stacking faults. YMn2O5 has a series of complex antiferromagnetic phases in coexistence with ferroelectricity. In YFeMnO5, only one commensurable ferrimagnetic phase was found and ferroelectricity is absent. Based on spin-polarized DFT calculations a Heisenberg model yields the coupling constants of the Fe-substituted and the mangenese-only compounds and relates them to crystal-field interactions. Finally, BiFeO3 will be addressed, which is a rhombohedral multiferroic with several domain wall configurations, which exhibit specific magnetic and conductance properties.

no abstract available

Trickle bed reactors with liquid and gas phase flowing cocurrently downwards at moderate superficial velocities are widely used, e. g. for selective hydrogenation, processing of volatile organic compounds or wastewater treatment [Duduković et. al., 2010]. This reactor type, however, has inherent disadvantages like liquid maldistribution and hence, imperfect wetting of the packing. Furthermore, mass transfer limitations of the gas phase to the active sites of the catalyst through liquid films at the packing surface are another shortcome.

As a new process intensification concept, an inclined fixed bed reactor with superimposed rotation that allows a spatial periodic operation at constant gas and liquid flow rates is proposed. The packing is periodically immersed into the liquid phase that accumulates mainly in the lower part of the reactor cross-section. Inclination angle and rotational speed provide additional degrees of freedom to adjust liquid residence time and periodicity of wetting and draining, respectively.

The present work aims to study the hydrodynamics, i. e. dynamic liquid holdup and pressure drop, in the new reactor concept. These studies comprise variations of reactor inclination (α = 15° - 90°), rotational speed (up to 60 rpm) as well as gas (vG = 0.025 m/s - 0.05 m/s) and liquid (vL = 0.01m/s - 0.05 m/s) superficial velocities. Additional variations, e.g. of packing and packing particle size, liquid viscosity and liquid (water, silicone oil, cumene) will be reported.
The experimental setup consists of a tubular reactor (ID = 0.1 m, L = 1.2 m) with rotary unions. The whole reactor is supported by rollers, driven by a hollow shaft rotary actuator and mounted in an inclinable frame. The gas-liquid distribution patterns are visualized by means of a noninvasive compact γ-ray computer tomography system (CompaCT), which is mounted in the same frame on a rotary stage. The spatial in-plane resolution of the measurement system is 2 mm. The applicability of γ-ray CT for hydrodynamic investigations in packed bed reactors has been demonstrated recently [Bieberle et. al., 2010].

References
1. Bieberle, A., M. Schubert, M. J. da Silva, and U. Hampel, Ind. Eng. Chem. Res., 49, 9445-9453 (2010).
2. Duduković, M. P., F. Larachi, and P. L. Mills, Catal. Rev., 44, 123-246 (2002).

Rieselbettreaktoren unterliegen Limitierungen bei Gaslöslichkeit und Gasphasenstofftransport an den Katalysator, die z. B. durch adiabatischen Betrieb bei hohen Drücken und Temperaturen kompensiert werden. Außerdem führen inhomogene Phasenverteilungen und Benetzungszustände zu verminderter Katalysatorausnutzung sowie zur Ausbildung von Hotspots. Zur Prozessintensivierung wurde u. a. die dynamische Betriebsweise vorgeschlagen, bei der dem Reaktor ein periodisch variierter Flüssigkeitsstrom zugeführt wird. Dadurch können Filmdicke und Benetzungsgrad periodisch variiert und der Zugang der Gasphase an den Katalysator verbessert werden. In Reaktoren im industriellen Maßstab sind jedoch nur geringer Effekte zu erwarten, da die aufgeprägte Periodizität mit der Reaktorlänge abnimmt. Außerdem erfordert die Betriebsweise zusätzliche Aufwendungen für MSR-Technik, Lastwechselkompensation und Schnittstellenmanagement im Anlagenverbund.

Beim neuen Reaktorkonzept führt die Neigung zu einer Phasensegregation und damit jeweils zu einem direkten Zugang beider fluiden Phasen an den Katalysator. Die zusätzlich aufgeprägte Rotation bewirkt eine periodischen Be- und Entnetzung der Katalysatorschüttung. Von Vorteil ist, dass neben der Periodizität auch die Verweilzeit eingestellt werden kann.

Zur Bewertung des neuen Reaktorkonzepts wurden hydrodynamische Untersuchungen bei unterschiedlichen Neigungswinkeln und Reaktordrehzahlen sowie bei verschiedenen Flüssigkeiten und Durchsätzen durchgeführt. Mittels kompakter Gamma-Tomographie sowie Gittersenortechnologie wurden die Zweiphasenströmung hinsichtlich Phasenverteilungen, Strömungsform und Verweilzeitverhalten charakterisiert. Neben dem neuen Reaktorkonzept werden im Beitrag die eingesetzte bildgebende Messtechnik sowie die hydrodynamischen Charakterisierungsmethoden vorgestellt sowie die Ergebnisse zusammengefasst.

Periodic operation of trickle bed reactors (TBR) as a promising process intensification approach has been examined in many studies since more than 2 decades. It has been demonstrated to reduce known limitations and disadvantages of the conventional operation mode of such reactors, i. e. avoiding the formation of hot spots, enhancing liquid maldistribution and boosting poor mass transfer rates. Though widely examined in the academic field, an industrial implementation of periodically operated TBRs is not expected, mostly because of the higher requirements on the upstream peripheral devices in an industrial environment. Additionally, modelling and prediction of the transient behaviour of such reactors remain challenging tasks due to the complex hydrodynamics and related mass and heat transfer resulting from the dynamic mode of operation. As a consequence, alternative reactor concepts with enhanced performance which do not require flow modulation but potentially provide benefits over established configurations need to be studied.

To avoid the problem of shorter residence times arising from the pulse flow regime while maintaining a periodic wetting and draining of the packed bed, a superimposed rotation of the inclined TBR is proposed. This new concept allows process intensification via a spatial periodic mode of operation while feeding with invariant gas and liquid flow rates. Inclination angle and reactor rotational speed provide additional degrees of freedom to adjust liquid residence time and period length (periodicity), respectively.

The objective of this study is the systematic investigation of the influence of inclination and rotation on the gas-liquid mass transfer for selected gas and liquid flow rates. Therefore, oxygen desorption in a reactor (1.6 m length, 0.1 m diameter) with particle packing (4 mm diameter) will be studied and mass transfer coefficients determined. The mass transfer results will also be discussed with respect to flow patterns obtained from tomographic imaging. Furthermore, the results will be compared with experimental data of the conventional TBR configuration as well as with established correlations.

Multi-gap resistive plate chambers (RPCs) are proposed to build the Time-of-Flight wall of the Compressed Baryonic Matter experiment with a time resolution better than 80 ps. The high fluxes expected at the innermost part of the detector, ~20x10³ cm²s^-1, require the development of new materials capable of withstanding such fluxes. At Helmholtz-Zentrum Dresden-Rossendorf, several RPC prototypes of 10x10 cm² and 20x20 cm² have been built with ceramic plates with bulk resistivities in the range of 10⁹-10¹⁰ Ω cm [1]. They have been tested at the superconducting electron accelerator facility ELBE with 30 MeV electrons. We present the characteristics of the ceramic electrodes and the latest results concerning the performance of these prototypes in electron and protons beams up to fluxes of 10⁶ cm^-2 s^-1.

No abstract provided.

We have developed the mechanical controllable break junction technique for the use in liquid environments in order to characterize the electrical properties of single molecules in their solvents. The metallic electrodes, which form the contacts for the molecular structures, are produced on an insulating substrate in order to reduce all spurious effects coming from parallel conduction through the liquid. We present first electrical characterization of such junctions in dry and in liquid environments. The solvents range from aqueous buffer, which will be used for measurements of DNA fragments, to toluene and THF, which are typical solvents for short, conjugated organic molecules.

We report on the fabrication of Nd:GdCOB ridge waveguides by using femtosecond laser micromachining of planar waveguides that were produced by carbon ion irradiation. The guiding properties of the Nd:GdCOB ridge waveguides are investigated. The second harmonic generation (SHG) at 532 nm green laser from ridges in a series of transverse widths is realized. The results show that the optical conversion efficiencies of SHG in the fabricated ridge waveguides are considerably enhanced with respect to the planar waveguide, and the maximum value reaches 11.4% under a pulsed 1064 nm laser pump.

We have studied the thermoelectric properties of porous silicon, a nanostructured, yet single-crystalline form of silicon. Using electrochemical etching, liquid-phase doping, and high-temperature passivation, we show that porous Si can be fabricated such that it has thermoelectric properties superior to bulk Si, for both n- and p-type doping. Hall measurements reveal that the charge carrier mobility is reduced compared to the bulk material which presently limits the increase in thermoelectric efficiency.

Einleitung:

Hochenergetische Positronenstrahler, wie beispielsweise die Isotope I-124 oder Ga-68, besitzen aufgrund ihrer maximalen Zerfallsenergie von 2,1 bzw. 1,9 MeV eine mittlere Reichweite von ~3 mm in Wasser. Bei der Kleintierbildgebung mit hohen räumlichen Auflösungen von 1-2 mm, sind daher der resultierende Ortsauflösungsverlust und die Bildverschmierung besonders dominant. Die direkte Einarbeitung der Positronenreichweite in den Rekonstruktionsalgorithmus kann durch die Faltung der geschätzten Aktivität mit einem Kernel vor der Vorwärtsprojektion erfolgen (Positronen Range - Maximum Likelihood Expectation Maximization, PR-MLEM- lgorithmus). Ziel dieser Arbeit war die Implementierung und Validierung eines solchen Algorithmus verbunden mit einer exakten Kernelbestimmung mittels GATE Monte-Carlo (MC) Simulationen [1]. Zur Vereinfachung des Verfahrens wurden ferner verschiedener Gausskernel verwendet.
Anhand ihrer auflösungsrückgewinnenden Charakteristik und der Generierung von Bildartefakten im Iterationsprozess wurde überprüft, ob und wie genau ein Reichweitenkernel bestimmt werden muss.

Material und Methoden:

Für die exakte Bestimmung des Reichweiten kernels wurden GATE 6.1 Monte-Carlo Simulationen für das Concorde MicroPET Focus 120 gerechnet. Der simulierte Kleintierscanner ist ein stationäres Blockdetektorsystem bestehend aus 12x12 LSOKristallmatrizen angeordnet in 48 axialen Kristallringen und 24 transaxialen Modulen. Die am Gerät gemessene und für die Simulationen verwendete durchschnittliche Energieauflösung beträgt etwa 20%. Das Standardakquisitionsfenster von 350- 650keV wurde beibehalten. Simulationen wurden für eine punktförmige F-18, Ga-68 und I-124 Quelle (d = 1 Pxl = 0,796 mm) in einem kugelförmigen Phantom (d = 146 mm) mit verschiedenen Materialien (Knochen, Lungengewebe, Muskel, PMMA und Wasser) durchgeführt. Über die Reichweitenhistogramme der beiden I-124 und F-18 Quellen innerhalb eines wasseräquivalenten Materials wurden zwei- und dreidimensionale Faltungskerne bestimmt. Die Reichweitenverteilung für I-124 konnte über ein Polynom 6. Grades angenähert werden (Korrelationskoeffizient R=0,9993). Der daraus berechnete Kernel wurde bis zu einer Perzentilen von 95% verwendet. Dies entspricht einer Länge von jeweils 21 Pixeln für jede Dimension. Neben dem exakten Reichweitenkernel wurde ein Gausskernel mit entsprechender Halbwertsbreite σ gebildet. Für diesen wurde σ sowohl unter- als auch überschätzt
(Abb. 1). Der umgesetzte PR-MLEM-Algorithmus verwendet die „Ray Tracing“ Projektoren aus der STIR Library [2]. Bis zur annähernden Konvergenz des Algorithmus werden mindestens 50 Iterationen benötigt. Ab 75 Iterationen erschlechtert sich das Bild aufgrund von Rauschen, weswegen alle Bildrekonstruktionen mit dieser Anzahl an
Iterationen durchgeführt wurde. Die auflösungsrückgewinnende Bildrekonstruktion wurde bei verschiedenen I-124
und F-18 Phantommessungen (Image Quality Phantom nach NEMA NU4-2008 und Schoeppy-Auflösungsphantom) und einer I-124 Mausstudie angewandt. Das Image Quality Phantom besteht, neben einem homogen gefüllten Bereich mit zwei kalten 2 zylindrischen Einschüben, aus fünf heißen Inserts, jeweils mit Durchmessern von 1 bis 5 mm. Das Schoeppy-Auflösungsphantom besitzt fünf Segmente deren mit Aktivität gefüllte Inserts Durchmesser von 1 bis 3 mm in 0,5 mm Schritten besitzen. Die Auflösungsbestimmung erfolgte über die Kantenverschmierung der radialsymmetrischen Zylinderinserts in Polarkoordinatendarstellung (Softwaretool Rover von ABX [3]).

Ergebnisse:

Bei der Verwendung des PR-MLEM-Algorithmus treten im Laufe der Iterationen deutliche Bildartefakte auf. Als Artefakt wird hier eine asymmetrische Verschiebung der Aktivitätsverteilung bezeichnet. Äußere Bereiche im Objekt werden gegenüber innenliegenden überkorrigiert (beispielsweise die Randüberhöhung bei homogen gefüllten Bereichen). Daher können die Korrekturen nicht während des gesamten Iterationsprozesses, sondern nur am Ende angewandt werden. Die Bestimmung der notwendigen Anzahl an Faltungsiterationen erfolgte anhand des Gradienten der Log-
Likelihood Funktion. Ist der unkorrigierte MLEM bereits konvergiert (> 50 Iterationen), so reichen 4-5 Iterationen mit Korrektur um wieder in einen konvergierten Zustand zu gelangen. I-124 Phantommessungen: Bei der Verwendung des exakten I-124 Reichweiten und des äquivalenten Gausskernels mit einer Halbwertsbreite von σ = 3,2 mm entstehen Veränderungen in der Aktivitätsverteilung bereits ab der dritten Faltungsiteration. Bei einem Kernel mit 50% der exakten Halbwertsbreite (Full Width at Half Maximum FWHM) erhöht sich die Iterationsanzahl vor dem Auftreten von
Artefakten auf neun. Bei 25% FWHM (σ = 0,8 mm) können alle 75 Iterationen artefaktfrei gefaltet werden. Wird der Gausskernel überschätzt und σ z. B. auf 6,4 mm verdoppelt, können nur ein bis zwei Faltungsiterationen artefaktfrei durchgeführt werden.
Die höchste Auflösung wird für beide Phantomgeometrien mit der Faltung der letzten neun Iterationen mit einem Kernel von σ = 1,6 mm erreicht, der die tatsächliche FWHM um 50% unterschätzt (Tab. 1). Für das Image Quality Phantom ergibt sich somit am Ø 5 mm Insert eine Auflösungsverbessung von 2,70 mm FWHM gegenüber der unkorrigierten Rekonstruktion von 4,06 mm FWHM. Am Ø 3 mm Insert des Auflösungsphantoms ergibt sich noch eine Verbesserung von ca. 19% (4,11 mm FWHM vor gegenüber 3,34 mm FWHM nach der Korrektur). Dennoch verändert sich hierbei die Aktivitätsverteilung in den äußeren Inserts (Abb. 2 b). Ohne 3 Artefakte kann somit die Auflösung von F-18 nicht erreicht werden, die 2,18 mm FWHM am Ø 3 mm Insert des Auflösungsphantoms beträgt.
Bei einer zu großen Anzahl an Faltungsiterationen (Gausskernels (σ = 3,2 mm) auf alle 75 Iterationen) verschwindet im Auflösungsphantom die Darstellung des Segmentes mit dem geringsten Durchmesser (1 mm) nahezu komplett (Abb. 2 c). Demgegenüber können alle 75 Iterationen artefaktfrei mit einem Gausskernel gefaltet werden, dessen albwertsbreite lediglich 25% der tatsächlichen beträgt (σ = 0,8 mm).
F-18 Phantommessungen: Wird für F-18 der reichweitenäquivalente Gausskernel mit σ = 0,4 mm verwendet, ergibt sich keine Auflösungsverbesserung. Durch die Verdopplung der Halbwertsbreite wird der 1 mm Insert des Image Quality Phantoms deutlicher sichtbar, wobei in der Folge Ringartefakte in der transversalen Ansicht auftreten (Abb. 3).
I-124 Mausstudie: Ohne Korrektur können die beiden Schilddrüsenlappen einer mit I-124 injizierten Maus nicht separiert dargestellt werden (Abb. 4). Wenn hingegen für alle Iterationen ein Gausskernel mit geringer FWHM (σ = 0,8 mm) verwendet wird, ist eine Differenzierung beider Lappen zulasten eines erhöhten Rauschanteils möglich.
Dieser Rauschanteil wird bei Verwendung eines Gausskernels mit doppelter FWHM und bei der Faltung mit dem exakten Kernel aus GATE reduziert und es ergibt sich ein erhöhter Kontrast der Schilddrüse. Dennoch ist keine signifikante Verbesserung der Auflösung erkennbar, so dass die beiden Schilddrüsenlappen nach wie vor nicht
differenziert werden können (Abb. 4 e). Die Verwendung eines 3D Kernels ergibt für den Gauss mit σ = 1,6 mm (50% der tatsächlichen FWHM) leichte Veränderungen der Aktivitätsverteilung im Magen im Vergleich zum 2D Faltungskern (Abb. 5 a-b).
Der exakte 3D Reichweitenkernel aus GATE verstärkt diese Effekte weiter, wodurch die Aktivitätsverteilung im Magen überproportional erhöht wird (Abb. 5 c-d).

Diskussion:

Der exakte I-124 Reichweitenkernel aus GATE und der entsprechende Gausskernel mit σ = 3,2 mm liefern bzgl. der Auflösung und der rekonstruierten Bilder vergleichbare Ergebnisse. Daher ist die genaue Kenntnis der Form des Kernels nicht relevant. Ausschlaggebend ist vielmehr die verwendete Halbwertsbreite. Wird diese
überschätzt, treten bereits nach nur wenigen Faltungsiterationen Artefakte auf. Eine Unterschätzung um 50% (σ = 1,6mm) lieferte für beide Phantomgeometrien die höchste Auflösung ohne deutliche Randüberhöhungen. Bei einer FWHM von nur 25% (σ = 0,8mm) können alle Iterationen ohne Artefakte gefaltet werden und die Definition des Abbruchkriteriums hierfür entfällt. Bei der Anwendung im Rahmen einer I-124 Mausstudie konnte mit diesem Kernel die Auflösung soweit erhöht werden, dass beide Schilddrüsenlappen nun differenzierbar sind.
Aufgrund der geringen Reichweite der F-18 Positronen beträgt die Halbwertsbreite des äquivalenten Gausskernels nur 0,4 mm (entspricht 0,5 Pixel) und kann somit die Auflösung nicht signifikant erhöhen. Der Kontrast und die Auflösung können mit der beschriebenen Entfaltungsmethode für I-124 erhöht werden. Ein Kernel mit nur 25 bzw. 50% FWHM eignet sich hierfür besser als die Verwendung der exakten Reichweite. Dennoch ist aufgrund der Abhängigkeit der Faltung von der örtlich variierenden Aktivitätsverteilung eine absolute Quantifizierung erschwert, da die ktivitätskonzentrationen lokal überschätzt werden.

Literatur:

[1] S. Jan et al.: GATE V6: A major enhancement of the GATE simulation platform
enabling modelling of CT and radiotherapy. Phys. Med. Biol. (56) (2011) 881-901
[2] K. Thielemans et al.: STIR: software for tomographic image reconstruction release
2. Phys. Med. Biol. (57) (2012) 867-883
[3] Rover ROI Visualization, Evaluation and Image Registration. ABX Radeberg:
http://www.abx.de/rover/ 2012

Es ist kein Abstract vorhanden.

Motivated by the fact, that millisecond annealing methods are going to play an important role in an advanced CMOS technology, this investigation of the effects of flash-lamp annealing (FLA) on actual and possible future high-k materials was performed [1]. Employed high-k materials were HfO2, LaYbO3, LaScO3 or LaLuO3.
HfO2 is already used in the industry while LaYbO3, LaScO3 and LaLuO3 are interesting as possible replacements, because of their thermally stable (>800°C) amorphous states with k-values above 20 as well as large bandgaps > 5 eV [2, 3, 4].
The high-k materials were deposited on p-Si by atomic-layer, molecular beam or pulsed laser deposition. Afterwards, FLA was used as a post-deposition annealing technique in which the pulse durations and peak temperatures were varied from 1 to 20 ms and 1000 to 1300°C, respectively. Pt-top and Al-back contacts were created for electrical measurements.
The microstructure of the samples was investigated by electron microscopy, XRD and nuclear methods (RBS, ERD), while the electrical properties were derived from current-voltage and capacitance-voltage measurements. It was found that for example metal-oxide semiconductor capacitors (MOSCAP) containing LaLuO3 can profit from FLA because this oxide remains amorphous and the capacitance is increased. On the other hand, the picture is not so clear for HfO2-MOSCAPs, because their capacitance is reduced and the oxide crystallizes while the leakage current is decreased.

References:

[1] J. C. Gelpey, S. McCoy, D. Camm and W. Lerch, Mater. Sci. Forum 573-574, 257 (2008)
[2] W. Su, L. Yang, B. Li, Appl. Surf. Sci. 257, 2526 (2011)
[3] V. V. Afanas’ev, A. Stesmans, C. Zhao, M. Caymax, T. Heeg, J. Schubert, Y. Jia, D. G. Schlom, and G. Lucovsky, Appl. Phys. Lett. 85, 5917 (2004)
[4] J. Lehmann, N. Shevchenko, A. Mücklich, J.v. Borany, W. Skorupa, J. Schubert, J.M.J. Lopez, S. Mantl, Microelectron. Eng. 88, 1346 (2011)

In an advanced CMOS technology millisecond annealing methods such as flash lamp annealing (FLA) may play an important role [1]. For this reason, we did study the effects of FLA on actual and possible future high-k materials such as HfO2 or LaLuO3. HfO2 is already used in the industry while LaLuO3 is interesting as a possible replacement, because of its thermally stable (~1000°C) amorphous state with a k-value of 32 as well as its large bandgap of 5.2 eV and symmetrical band offsets of 2.1 eV [2].
TiN-capped and uncapped samples were annealed under different conditions with pulse durations ranging from 1 to 20 ms and peak temperatures up to 1300°C. The microstructure was investigated by electron microscopy, XRD and nuclear methods (RBS, ERD) Current-voltage and capacitance-voltage measurements helped to characterize the electrical properties. It was found that metal-oxide semiconductor capacitors containing LaLuO3 can profit from FLA because the oxide remains amorphous and the capacitance is increased. In case of HfO2 the capacitance is decreased and the oxide crystallizes.

References:

[1] J. C. Gelpey, S. McCoy, D. Camm and W. Lerch, Mater. Sci. Forum 573-574, 257 (2008)
[2] J. Lehmann, N. Shevchenko, A. Mücklich, J.v. Borany, W. Skorupa, J. Schubert, J.M.J. Lopez, S. Mantl, Microelectron. Eng. 88, 1346 (2011)

In two dimensional electron gases with parabolic band structure, the Landau level (LL) system is equidistant, hence bleaching of the absorption is strongly suppressed. In contrast to quantum wells in conventional semiconductors the dispersion in graphene is linear for low energies. Due to this linearity the Landau levels are not equidistant and pump-probe measurements are feasible. Additionally a Landau level at zero energy appears. We performed pump-probe measurements on quasi-neutral sheets of rotated multilayer epitaxial graphene in magnetic fields. The free-electron laser FELBE at Dresden-Rossendorf served as radiation source at a constant wavelength of 16.5 µm (photon energy of ~75 meV). The magnetic field was applied perpendicularly to the graphene sheets by a magneto-optical superconducting magnet system, which is able to generate a magnetic field of up to 7T. This combination of photon energy and variable magnetic field allowed us to perform resonant pump-probe measurements at three different Landau level transitions (see inset of Fig: 1): For the transitions LL-1(-2) -> LL2(1) and LL-2(-3) -> LL3(2) we could observe a slight increase of the pump-probe signal while the relaxation time stayed constant. For the transition LL-1(0) -> LL0(1) the amplitude of the pump-probe signal increased by a factor of 2.5, the relaxation time decreased from 20 ps to 5 ps. In fig.1 the signal amplitude is plotted as a function of the square root of the magnetic field. The faster relaxation was contrary to our expectations: Due to the reduced phase space we expected the relaxation time to increase. For further insights into the carrier dynamics we performed measurements with circularly polarized radiation. Therewith it was possible to distinguish between the transitions LL-1->LL0 and LL0->LL1. These measurements revealed complex dynamics involving positive and negative signals with a very fast component and a slow component with an increased relaxation time. We present a model that takes into account Auger-type processes as well as carrier cooling. The model explains the main signatures of the measured signals.

The integration of positron emission tomography (PET) and magnetic resonance imaging (MRI) in a combined PET/MR scanner is attracting much interest. With this new bimodal approach novel functional-anatomical and multiparametric applications become feasible, which can be expected to deliver information beyond that accessible by separately applied modalities. Although the two technologies where initially regarded as inherently incompatible, different solutions have been developed and implemented to realise PET/MR instruments for both small animal and human bimodal imaging. The present review first summarizes the basic options for possible PET/MR designs. A chronological outline describes the evolution from the first ideas, how PET and MR imaging might be combined, over different experimental solutions to the systems recently realized by industry. The BrainPET/MR and the mMR developed by Siemens and the Philips Ingenuity TF PET/MR are characterised and application examples are provided illustrating the features of these instruments. Based on own experiences and those reported in different publications a number of open issues are discussed. Finally a short comparative analysis on the status and perspectives of human PET/MR imaging is given.

After the completion of the experimental program at SIS18 the HADES setup will migrate to FAIR, where it will deliver high-quality data for heavy-ion collisions in an unexplored energy range of up to 8 A GeV. In this contribution, we briefly present the physics case, relevant detector characteristics and discuss the recently completed upgrade of HADES.

This talk reviews the advances that subsecond thermal processing using flash lamps and lasers brings to the processing of the most advanced semiconductor materials, thus enabling the fabrication of novel electronic structures and materials. It will be demonstrated how such developments can translate into important practical applications leading to a wide range of technological benefits. Recently we could demonstrate that germanium and silicon exhibit superconductivity at ambient pressure. Techniques of the state-of-the-art semiconductor processing as ion implantation and FLA were used to fabricate such material based on a highly doped Ga-rich layer at the surface. Moreover we demonstrated that carrier-mediated ferromagnetism can be reached in manganese-implanted and Laser-annealed Ge. Regarding photovoltaic applications, we dealt with two aspects: (i) the thermal processing of so-called dirty silicon demonstrating a distinct improvement of the metal diffusion suppression compared to RTP and furnace treatments, and (ii), for the annealing of CIGS layers millisecond annealing leads to better optical output and lower degradation Whereas all these examples base on solid phase processing the more sophisticated approach of subsecond thermal processing regards on working with the liquid phase at the surface of solid substrates. A very recent example is the controlled formation of III-V nanocrystals (InAs, GaAs) in silicon after ion beam synthesis (Nano Lett. 11 (2011) 2814).

We report on an in-situ and ex-situ X-ray investigations of a self-assembled growth of Ge nanocrystals embedded in a dielectric matrix forming BCC- or FCC-like superstructures. Germanium quantum dots (QD’s) embedded in dielectric matrices like SiO2 [1] or Al2O3 [2] have numerous interesting properties e.g. a strong quantum confinement. They could be used in optoelectronic devices and memory systems. Such a material can be a key element for the development of a new generation of solar cells extending the spectral range for electrical energy generation, either for an up and/or down conversion of the incident photons or simply as one part of a multilayer stack arrangement.

The structural optimization of polycrystalline silicon films is important to improve the electronic properties of microelectronic devices and photovoltaic solar cells, based on thin film silicon. The enlargement of the grain size is of big interest since the fabrication of silicon based thin film devices started. In this work we present results on the lateral dendritic growth in 100nm thin silicon layers which leads to lateral grain sizes in the range of 100µm. The second topic in this field is the manipulation of the grain lattice orientation within the layer which can lead to a uniformly oriented polycrystalline material.

Focused ion beam techniques are one way to modify locally the properties of magnetic thin films. We report on structural investigations of 50 nm thick non-ordered nano-crystalline Permalloy (Ni81Fe19) films modified by 30 keV Ga+ focused ion beam (FIB) irradiation. From the X-ray diffraction (XRD) measurements a considerable crystallite growth and a material texturing towards (111)-direction with a linearly increasing lattice constant was observed. In addition cross-sectional transmission electron microscope (XTEM) images show that crystallites are growing through the entire film at high irradiation fluences.
Extended X-ray absorption fine structure (EXAFS) analysis shows a perfect near-order coordination corresponding to a face-centered (fcc) unit cell for both FeNi and Ga atom surrounding. The structural changes are accompanied by a decrease of saturation polarization with increasing ion fluence. Such behavior is attributed to a simple incorporation of non-magnetic Ga atoms in the Permalloy film.

We present ion beam erosion experiments on Si(001) with simultaneous sputter co-deposition of steel at 660 K. At this temperature the sample remains remains within the crystalline regime during ion exposure and pattern formation takes place by phase separation of Si and iron-silicide. After an ion fluence of F ≈ 5.9 × 1021 ions m−2 investigations by atomic force microscopy and scanning electron microscopy identify sponge, segmented wall and pillar patterns with high aspect ratios and heights of up to 200 nm. Grazing incidence X-ray diffraction and transmission electron microscopy reveal the structures to be composed of polycrystalline iron-silicide. The observed pattern formation is compared to the one in the range from 140 K to 440 K under otherwise identical conditions, where a thin amorphous layer forms due to the ion bombardment.

es hat kein Abstract vorgelegen.

Investigation of the interaction of metals with the biosphere is important not only from an ecological point of view but also from an application oriented one. Biosorption of metals by bacteria was intensively studied. Furthermore, bacterial cell wall components itself e.g. surface layer (S-layer) proteins, lipids and peptidoglycan were intensively studied. Nevertheless, the investigation of their interaction with metals both as molecules and as intact layers on a molecular level remains challenging.
Parts of our investigations concentrated on S-layers. These are the outermost cell envelope of many eubacteria and archaea, forming highly ordered paracrystalline lattices not only on the cell, but also after isolation on various technical surfaces by self-assembling processes. These proteins show remarkable high metal binding capacities.
In our work we used the quartz crystal microbalance with dissipation monitoring (QCM-D) in order to study the layer formation of single cell wall compounds and interaction processes on the nano scale range. This method gives a detailed understanding of biological structure formation and the amount of metal deposition. Within the experiments the influence of surface modification with adhesive promoters e.g. polyelectrolytes was studied in order to make exact statements regarding coating kinetics, layer stability and metal interaction. Subsequent atomic force microscopy (AFM) studies enable the imaging of bio nanostructures and reveal complex information of structural properties.
Aim of these investigations is the assembly of a simplified biological cell wall based on Gram-positive bacteria in order to clarify sorption processes in a complex system.

In this article we show how to produce materials consisting of regularly ordered Ge quantum dots in amorphous alumina matrix with the controllable Ge quantum dot size, shape, spacing, crystalline structure and degree of regularity in the Ge quantum dot ordering. The production of such materials is achievable already at room temperature by magnetron sputtering deposition of a (Ge+Al2O3)/Al2O3 multilayer. The materials show large, size-dependent blueshift of the photoluminescence peak and enhancement in the oscillator strength caused by confinement effects. The materials also show advanced mechanical properties due to alumina matrix, and their internal structure is shown to be highly resistive to irradiation with energetic particles for a large range of the irradiation parameters. The reported materials have excellent potential for application in demanding environments for light harvesting.

We report on the fabrication of pseudomorphic wurtzite Gax Mnx N grown on GaN with Mn concentrations up to 10 % using molecular beam epitaxy. According to Rutherford backscattering the Mn ions are mainly at the Ga-substitutional positions, and they are homogeneously distributed according to depth-resolved Auger-electron spectroscopy and secondary-ion mass-spectroscopy measurements. A random Mn distribution is indicated by transmission electron microscopy, no Mn-rich clusters are present for optimized growth conditions. A linear increase of the c-lattice parameter with increasing Mn concentration is found using x-ray diffraction. The ferromagnetic behavior is confirmed by superconducting quantum-interference measurements showing saturation magnetizations of up to 150 emu/cm3 .

Die vielfältigen Anwendungen transparenter leitfähiger Oxide (TCO), wie zum Beispiel in Flachbildschirmen, Solarzellen und der Beleuchtungstechnik erfordern die Entwicklung neuartiger TCO-Materialien. Darüber hinaus ist der Einsatz der etablierten TCOs, wie Indiumzinnoxid (ITO) oder Fluor dotiertes Zinnoxid (FTO) zukünftig nur bedingt fortzuführen. Die Verwendung von ITO ist aufgrund des kontinuierlich steigenden Indiumpreises sehr kostenintensiv, während der Einsatz von FTO-Dünnschichten aufgrund des hochgradig toxischen Herstellungsprozesses weltweit umstritten ist. Es konnte gezeigt werden, dass Titandioxid dotiert mit Tantal (TTO) vergleichbare elektrische und optische Eigenschaften, verglichen mit den etablierten TCOs aufweist. Eine wesentliche Herausforderung besteht allerdings darin, TTO-Dünnschichten mittels eines industrienahen kostengünstigen Prozess abzuscheiden. Diese Problemstellung wurde gelöst, indem TTO-Schichten mittels eines 2-stufigen Prozesses bestehend aus Sputtern und anschließender thermischer Nachbehandlung abgeschieden wurden. Die dabei erreichten spezifischen Widerstände im Bereich von 0,001 Ohmcm sind für zahlreiche Anwendung ausreichend. Darüber hinaus wurde gezeigt, dass die Kurzzeittemperprozesse eine mögliche Alternative zur konventionellen Nachtemperung sind.

Precise control of single walled carbon nanotube (SWCNT) diameter, chirality, alignment, and intertube arrangement are still remaining challenges in the catalytic chemical vapour deposition (CCVD) synthesis. In this context it has still to be clarified whether a predefined size and shape of the nanoparticles can be stabilized by a suitable matrix material while preserving the catalytic activity of the metal.
For this study Ni nanoparticles were encapsulated in an amorphous carbon matrix by physical vapour deposition. As prepared Ni catalysts were used for CNT fabrication by laser assisted CVD applying either no external carbon source or C₂H₄ gas, and by low pressure CVD applying C₂H₂ or CH₄ as carbon source. The broad range of CNT synthesis conditions indicates the robustness of the embedded Ni particles as a catalyst for carbon nanotube formation. SEM and laser wavelength dependent Raman spectroscopy were used for CNT characterisation. The nickel-SWCNT-interaction was modelled by density functional calculations with the projector augmented plane wave method, utilizing the generalized gradient approximation for the exchange-correlation functional.

Silicon-Germanium is commonly used as a semiconductor material in integrated circuits (ICs) for heterojunction bipolar transistors or as a strain-inducing layer for CMOS transistors. Normally epitaxial methods (e.g., CVD, MBE) are applied to the synthesis of Si1-xGex alloys.
In our contribution we present the fabrication of Si1-xGex alloy by ion-implantation and short-time-annealing. The Ge ions in the fluence range of 3×1016 - 10×1016 cm2 were implanted into monocrystalline (100)-oriented Si wafers covered by 50 nm thermal oxide at an energy of 100 keV. As the consequence, the 50 nm amorphous Ge rich Si layers were obtained. The recrystallization of the implanted layers and the Si1-xGex alloying were carried out by flash lamp annealing or scanning continuous laser annealing in the time scale of 20 ms or 1 s, respectively. Both flash lamp treatment and laser annealing at high energy densities lead to local melting of the germanium rich silicon layer. The recrystallization of the Si1-xGex layer takes place due to millisecond range liquid phase epitaxy. Formation of the high quality monocrystalline Si1-xGex layer was confirmed by μ-Raman spectroscopy, RBS channeling and cross-section TEM investigation. The μ-Raman spectra reveal tree phonon modes located at around 293, 404 and 432 cm-1 corresponding to the Ge-Ge, Si-Ge and Si-Si in the Si1-xGex alloy vibrational modes, respectively. Due to much higher carrier mobility in SiGe layer than in silicon such system can be used for the fabrication of advanced devices.

Die Ionenstrahlanalytik nutzt hochenergetische Ionen zur Material-, Struktur- und Radionuklidanalyse. Sie wird im Rahmen der Ressourcenanalytik eingesetzt, um neue Technologien zur Erkundung, Gewinnung, Nutzung und Recycling von Rohstoffen entlang der Wertschöpfungskette zu entwickeln. Die Projektgruppe Ionenstrahlanalytik am Helmholtz-Institut Freiberg für Ressourcentechnologie (HIF) ist stark methodisch orientiert und entwickelt in interdisziplinären Forschungsprojekten nahezu unikale Analysemethoden unter Einsatz bzw. Eigenbau neuester Technologien. Diese Methoden eröffnen neue und interessante Möglichkeiten der (Ultra-)Spurenelementanalyse. Das HIF ist eine gemeinsame Einrichtung des Helmholtz-Zentrums Dresden-Rossendorf und der TU Bergakademie Freiberg.

Fast neutron reactors have a large potential as sustainable energy source. In particular, Sodium Fast Reactors (SFR) with al closed fuel cycle and potential for minor actinide burning may allow minimization of volume and heat load of high level waste and provide improved use of natural resources (as compared to only 1 % energy recovery in the current once-through fuel cycle, with Thermal Reactors, such as EPR).

Accidental scenarios such as the depressurisation of the primary circuit of high temperature gas cooled pebble bed reactors may lead to the release of fission products via the discharge of radioactive graphite dust. For a detailed source term assessment in such accident scenarios knowledge of the flow mechanics of dust transport in complex coolant circuit components, like pebble beds, recuperator structures and pipe systems is necessary. In this article an experimental study of aerosol deposition in a pebble bed is described. We investigated the deposition of radiolabelled liquid aerosol particles in a scaled pebble bed in an air-driven small-scale aerosol flow test facility under isothermal ambient conditions. The aerosol particles were generated by means of a condensational aerosol generator with potassium-fluoride (KF) condensation nuclei. Particle concentration measurements upstream and downstream of the pebble bed were performed by isokinetic sampling and particle counting. The results agree with typical deposition curves for turbulent and inertia driven particle deposition. Furthermore, positron emission tomography (PET) was performed to visualize and measure particle deposition distributions in the pebble bed. Results of a selected deposition experiment with moderately large particles (daero = 3.5 μm, Re′pb=2200) show that the deposited particles are located in the vicinity of the upstream stagnation points of the pebbles. These findings support the thesis that inertia driven particle deposition is predominating.