Helmholtz-Gemeinschaft
DRESDEN-concept

Mobile version: On

Publication database - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
Without submitted and only approved publications
Only approved publications

< Seite 1 von 187 >   Gesamtzahl lt. Auswahl: 18644 Title records (100 Title records je Seite)
22956 Publications
Risk management in companies - a questionnaire as an instrument for analysing the the present situation
Stiller, D.; Joehnk, P.
Abstract: The topic risk management receives new impulses in the context of the financial and economic crisis in the years 2007 until 2011 as well as the question whether companies took consequences. The article briefly describes the importance of risk management and then explained the theoretical principles of empirical methods. Excerpts from developed questionnaire will be presented.
Keywords: Industrial management, risk management, ermirical research, qualitative and quantitative survey
  • Contribution to proceedings:
    International Doctoral Seminar 2014, 19.-21.05.2014, Zielona Gora, Poland
    Research Papers Faculty of Materials Science and Technology in Trnava, Vol. 22, 83-88
  • Lecture (Conference):
    International Doctoral Seminar 2014, 19.-21.05.2014, Zielona Gora, Poland
Registration No. 21065

Organotypical vascular model for characterization of radioprotective compounds: Studies on antioxidant 2,3-diaryl-substituted indole-based cyclooxygenase-2 inhibitors
Ullm, S.; Laube, M.; Bechmann, N.; Knieß, T.; Pietzsch, J.
Abstract: Radiotherapy of various cancers is closely associated with increased cardiovascular morbidity and mortality. Arachidonic acid metabolites are supposed to play a key role in radiation-induced vascular dysfunction. This study was designed to evaluate the effects of novel, antioxidative 2,3-diaryl-substituted indole-based selective cyclooxygenase-2 (COX-2) inhibitors (2,3-diaryl-indole coxibs) on radiation-induced formation of arachidonic acid metabolites via COX-2 and oxidant stress pathways in an organotypical vascular model of rat aortic rings. Acute and subacute effects of X-ray radiation (4 and 10 Gy; 1 and 3 days post irradiation) with or without the presence of 1 µM of the 2,3-diaryl-indole coxib 2-[4-(aminosulfonyl)phenyl]-3-(4-methoxyphenyl)-1H-indole (C1) or celecoxib as reference compared to sham-irradiated controls were assessed. The following parameters were measured: metabolic activity of the aortic rings; induction and regulation of COX-2 expression; release of prostaglandin E2 and F2alpha-isoprostane. Irradiation without presence of coxibs resulted in a dose-dependent augmentation of all parameters studied. When aortic rings were exposed to the 2,3-diaryl-indole coxib 1 h before irradiation, metabolic activity was restored and the release of both prostaglandin and isoprostane was inhibited. The latter indicates a direct interaction with oxidant stress pathways. By contrast, celecoxib exhibited only slight effects on the formation of isoprostane. The reduction of radiation-induced vascular dysfunction by antioxidative coxibs may widen the therapeutic window of COX-2 targeted treatment.
Keywords: Aortic ring model, coxibs, prostanoids, normal tissue damage, radiation therapy, adjuvant radioprotective therapy, cardiovascular disease Registration No. 21055

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

Keywords: self-organization, nanopatterning, polyatomic ions, energy deposition
  • Lecture (Conference):
    Workshop Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland
  • Lecture (Conference):
    19th International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, Leuven, Belgium
Registration No. 21053

Experimente mit schnellen Neutronen an der Flugzeit-Anlage nELBE
Beyer, R.
Abstract: Beschreibung der verschiedenen bisher an der Neutronen-Flugzeit-Anlage nELBE durchgeführten Experimente.
Keywords: nELBE, neutron time-of-flight, transmission, inelastic scattering, fission
  • Invited lecture (Conferences):
    Fachbereichsseminar, 19.09.2014, Braunschweig, Deutschland
Registration No. 21052

Frequency-Domain Magnetic Resonance—Alternative Detection Schemes for Samples at the Nanoscale
Möller, M.; Lenz, K.; Lindner, J.
Abstract: Magnetic Resonance in the frequency domain provides a tool to investigate and quantitatively measure many important magnetic key parameters, such like the effective magnetization, magnetic anisotropies, magnetic damping parameters or coupling field strengths. Although it has been widely employed for studying magnetic bulk and thin film samples, the sensitivity of this classical method often suffers from being too low when single nanostructures are of interest. This review discusses Magnetic Resonance as technique, providing an introduction also to non-experts in the field. The theoretical background is discussed on an ‘easy to read’ basis, followed by a brief summary of methods that are capable of investigation spin dynamics within single nanostructures (nearfield microscopy, Brillouin Light Scattering, time-resolved Magneto-optical Kerr-effect). Focusing on frequency-domain approaches we then give a detailed explanation of what we call conventional way of experimentally detecting Magnetic Resonance which is based on the use of microwave cavities. This serves a basis to discuss different approaches to enhance sensitivity within a frequency-domain Magnetic Resonance experiment. As shown this includes either improving the conventional setup itself (microresonators) or using alternative detection routes, such as optical or electrical detection.
Keywords: FMR, ferromagnetic resonance, Kerr effect, MOKE, Microresonators, Magnetism, Magnetic nanostructures Registration No. 21051

Magnetic Bioinspired Hybrid Nanostructured Collagen - Hydroxyapatite Scaffolds Supporting Cell Proliferation and Tuning Regenerative Process
Tampieri, A.; Iafisco, M.; Sandri, M.; Panseri, S.; Cunha, C.; Sprio, S.; Savini, E.; Uhlarz, M.; Herrmannsdörfer, T.
Abstract: A bioinspired mineralization process was applied to develop biomirnetic hybrid scaffolds made of (Fe2+/Fe3+)-doped hydroxyapatite nanocrystals nucleated on self-assembling collagen fibers and endowed with super-paramagnetic properties, minimizing the formation of potentially cytotoidc magnetic phases such as magnetite or other iron oxide phases. Magnetic composites were prepared at different temperatures, and the effect of this parameter on the reaction yield in terms of mineralization degree, morphology, degradation, and magnetization was investigated. The influence of scaffold properties on cells was evaluated by seeding human osteoblast-like cells on magnetic and nonmagnetic materials, and differences in terms of viability, adhesion, and proliferation were studied. The synthesis temperature affects mainly the chemical-physical features of the mineral phase of the composites influencing the degradation, the microstructure, and the magnetization values of the entire scaffold and its biological performance. In vitro investigations indicated the biocompatibility of the materials and that the magnetization of the super-paramagnetic scaffolds, induced applying an external static magnetic field, improved cell proliferation in comparison to the nonmagnetic scaffold. Registration No. 21050

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

Keywords: 242Pu Large-area targets Molecular plating Quantitative deposition yield Registration No. 21049

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

Keywords: point defects, nanoclusters, bcc-Fe, free energy, temperature dependence, Density Functional Theory
  • Lecture (Conference):
    7th International Conference on Multiscale Materials Modeling (MMM 2014), 06.-10.10.2014, Berkeley, USA
Registration No. 21048

Establishing the Fundamental Magnetic Interactions in the Chiral Skyrmionic Mott Insulator Cu2OSeO3 by Terahertz Electron Spin Resonance
Ozerov, M.; Romhanyi, J.; Belesi, M.; Berger, H.; Ansermet, J.-Ph.; van den Brink, J.; Wosnitza, J.; Zvyagin, S. A.; Rousochatzakis, I.
Abstract: The recent discovery of Skyrmionics in Cu2OSeO3 has established a new platform to create and manipulate Skyrmionic spin textures. We use high-field electron spin resonance with a terahertz free-electron laser and pulsed magnetic fields up to 64 T to probe and quantify its microscopic spin-spin interactions. In addition to the previously observed long-wavelength Goldstone mode, this technique probes also the high-energy part of the excitation spectrum which is inaccessible by standard low-frequency electron spin resonance. Fitting the behavior of the observed modes in magnetic field to a theoretical framework establishes experimentally that the fundamental magnetic building blocks of this Skyrmionic magnet are rigid, highly entangled and weakly coupled tetrahedra. Registration No. 21047

Solid phase recrystallization of Si nanowires
Posselt, M.; Liedke, B.; Baldauf, S.
Abstract: Advanced Si and Ge nanowire transistors can be produced by top-down or bottom-up approaches. In order to obtain the desired electrical properties doping of the nanowires is required. Ion implantation is one of the favored methods to introduce dopant atoms in a controlled manner. If relatively high ion fluences are needed the originally single-crystalline nanowire is amorphized. Subsequently, thermal processing must be used to restore the Si or Ge crystal and to activate the dopants electrically. In planar structures a complete restoration can be achieved by solid-phase epitaxial recrystallization, whereas more complex processes take place in nanowires, due to the significant influence of surfaces and interfaces. In order to understand the solid-phase recrystallization in such confined systems molecular dynamics simulations are performed. Partially amorphized nanowires embedded in a matrix as well as free nanowires and nanopillars are considered. In dependence on whether embedded or free nanowires are investigated several phenomena are observed, such as stacking fault and twin formation, random nucleation of separate crystalline grains, as well as edge rounding and necking. The simulation results are in qualitative agreement with experimental findings.
Keywords: Solid phase recrystallization, Si nanowires, Molecular dynamics simulation
  • Poster:
    7th International Conference on Multiscale Materials Modeling (MMM 2014), 06.-10.10.2014, Berkeley, USA
Registration No. 21046

Properties of oxide nanoclusters in ODS ferritic steels: A combined DFT and Monte Carlo simulation study
Devaraj, M.
Abstract: Not available, please contact the author.
Keywords: oxide nanoclusters, ferritic steels, Density Functional Theory, Monte Carlo simulations
  • Lecture (others):
    Seminarvortrag im Department of Mathematical Sciences, Loughborough University, UK, 02.10.2014, Loughborough, UK
Registration No. 21045

Electronic properties of a distorted kagome lattice antiferromagnet Dy3Ru4Al12
Gorbunov, D. I.; Henriques, M. S.; Andreev, A. V.; Gukasov, A.; Petricek, V.; Baranov, N. V.; Skourski, Y.; Eigner, V.; Paukov, M.; Prokleska, J.; Goncalves, A. P.
Abstract: Electronic properties of Dy3Ru4Al12 (hexagonal crystal structure, Dy atoms form distorted kagome nets) are studied on a single crystal by means of magnetization, neutron diffraction, specific heat, and resistivity measurements. The onset of a long-range magnetic order of Dy moments occurs at 7 K through a first-order phase transition. The compound has a noncollinear antiferromagnetic structure with a propagation vector (1/2 0 1/2). The configuration of the Dy moments is consistent with the monoclinic Shubnikov group Cc2/c. The gamma coefficient in the temperature linear term of the specific heat is strongly enhanced to 500 mJ mol-1 K-2 taking into account the localized nature of Dy magnetism. An additional contribution originates from spin fluctuations induced in the 4d subsystem of Ru by the exchange field acting from the Dy 4f moments. In an applied magnetic field Dy3Ru4Al12 displays magnetization jumps along all crystallographic directions. All the metamagnetic transitions are accompanied by large positive magnetoresistance. The maximum effect (125%-140%) is attained for current along the [100] axis and field along the [120] or [001] axes. The large positive effect is explained by changes in the conduction electron spectra through the jumps as the conduction electrons interact with localized magnetic moments. Registration No. 21044

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

Keywords: ion-beam mixing, Ge isotope multilayers, temperature and flux dependence
  • Lecture (Conference):
    19th International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium
Registration No. 21043

Quo vadis?: Ion Beam Engineeering and beyond…
Skorupa, W.
Abstract: There is no doubt that ion beam based research and applications- like all semiconductor-based revolutionary developments of our society- have reached a kind of saturation overlooking the last 60 years when ion implantation started as a child of the early nuclear weapon development. It was the mass separator as a key part of the ion implanter allowing the formation of atomically pure beams. Doping of semiconductor materials with a clear dominance of silicon was the technology driver for the development of ion beam technology. Moreover, the physical and chemical modification of surfaces as well as regions in shallow and deeper regions below the surface of solid materials was the matter of interest for using this efficient tool. At all times, annealing/thermal treatment of ion beam treated materials within different time ranges –from hours down to picoseconds- was a close relative of ion beam engineering. Even flash lamp annealing as one of the annealing methods based on early experiments performed for the simulation of strong optical radiation impact on materials during nuclear weapon attacks. In this talk I will shortly discuss historical and future aspects of ion beam engineering to initiate a discussion on: From nuclear weapons to superchips…, what remains to be done? or, ...what more do people really need? I will extend this lecture to issues that should be of broader interest, but also, to our community!
Keywords: ion beam engineering, flash lamp annealing, ion beam technology
  • Invited lecture (Conferences):
    X-th International Conference Ion Implantation and other Applications of Ions and Electrons, 23.-26.06.2014, , Poland, 23.-26.06.2014, Kazimierz Dolny, Poland
Registration No. 21041

Development and Characterization of a tunable ultrafast X-ray source via Inverse Compton Scattering
Jochmann, A.
Abstract: Ultrashort, nearly monochromatic hard X-ray pulses enrich the understanding of the dynamics and function of matter, e.g., the motion of atomic structures associated with ultrafast phase transitions, structural dynamics and (bio)chemical reactions. Inverse Compton backscattering of intense laser pulses from relativistic electrons not only allows for the generation of bright X-ray pulses which can be used in a pumpprobe experiment, but also for the investigation of the electron beam dynamics at the interaction point.
The focus of this PhD work lies on the detailed understanding of the kinematics during the interaction of the relativistic electron bunch and the laser pulse in order to quantify the influence of various experiment parameters on the emitted X-ray radiation.
The experiment was conducted at the ELBE center for high power radiation sources using the ELBE superconducting linear accelerator and the DRACO Ti:sapphire laser system. The combination of both these state-of-the-art apparatuses guaranteed the control and stability of the interacting beam parameters throughout the measurement.
The emitted X-ray spectra were detected with a pixelated detector of 1024 by 256 elements (each 26μm by 26μm) to achieve an unprecedented spatial and energy resolution for a full characterization of the emitted spectrum to reveal parameter influences and correlations of both interacting beams. In this work the influence of the electron beam energy, electron beam emittance, the laser bandwidth and the energy-anglecorrelation on the spectra of the backscattered X-rays is quantified.
A rigorous statistical analysis comparing experimental data to ab-initio 3D simulations enabled, e.g., the extraction of the angular distribution of electrons with 1.5% accuracy and, in total, provides predictive capability for the future high brightness hard X-ray source PHOENIX (Photon electron collider for Narrow bandwidth Intense X-rays) and potential all optical gamma-ray sources.
The results will serve as a milestone and starting point for the scaling of the Xray flux based on available interaction parameters of an ultrashort bright X-ray source at the ELBE center for high power radiation sources. The knowledge of the spatial and spectral distribution of photons from an inverse Compton scattering source is essential in designing future experiments as well as for tailoring the X-ray spectral properties to an experimental need.
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-055 2014
Downloads:
16 MB PDF
Registration No. 21040

The development of a compact EBIS with integrated ion optics for FIB applications
Schmidt, M.; Zschornack, G.; Gierak, J.
  • Lecture (Conference):
    Condensed Matter in Paris 2014, CMD 25 – JMC 14, 25.08.2014, Paris, France
Registration No. 21039

IMALION – Creation and Low Energy Transportation of Milliampere Metal Ion Beams
Weichsel, T.; Hartung, U.; Kopte, T.; Zschornack, G.; Kreller, M.; Silze, A.
  • Lecture (Conference):
    5th International Particle Accelerator Conference, 16.06.2014, Dresden, Deutschland
Registration No. 21038

Implementation of a Superconducting Electron Beam Ion Source into the HIT Ion Source Testbench
Ritter, E.; Silze, A.; Zschornack, G.; Cee, R.; Haberer, T.; Peters, A.; Winkelmann, T.
  • Lecture (Conference):
    5th International Particle Accelerator Conference, 16.06.2014, Dresden, Deutschland
Registration No. 21037

Eifficient charge-breeding of Helium-6 in an EBIT for precision measurement of the beta-neutrino correlation
Schmidt, M.; Hass, M.; Zschornack, G.; Rappaport, M. L.; Heber, O.; Prygarin, A.; Shachar, Y.; Vaintraub, S.
  • Lecture (Conference):
    14th International Symposium on Electron Beam Ion Sources and Traps (EBIS/T 2014), 20.05.2014, East Lansing, USA
Registration No. 21036

Momentum phase space analysis with charged particle diagnostic devices
Zschornack, G.; Ritter, E.
  • Lecture (Conference):
    DPG-Frühjahrstagung 2014, 17.03.2014, Frankfurt/Main, Deutschland
Registration No. 21035

Electron Beam Ion Sources for Student Education
Zschornack, G.; Ritter, E.
  • Lecture (Conference):
    DPG-Frühjahrstagung 2014, 17.-21.03.2014, Frankfurt/Main, Deutschland
Registration No. 21034

Materials Analysis with Electron Beam Ion Sources
König, J.; Bischoff, L.; Kentsch, U.; Kreller, M.; Pilz, W.; Ritter, E.; Schmidt, M.; Silze, A.; Zschornack, G.
  • Lecture (Conference):
    DPG-Frühjahrstagung 2014, Sektion Mikroproben, 02.04.2014, Dresden, Deutschland
Registration No. 21033

Suppression of tin precipitation in SiSn alloy layers by implanted carbon
Gaiduk, P. I.; Lundsgaard Hansen, J.; Nylandsted Larsen, A.; Bregolin, F. L.; Skorupa, W.
Abstract: By combining transmission electron microscopy and Rutherford backscattering spectrometry, we have identified carbon related suppression of dislocations and tin precipitation in supersaturated molecular-beam epitaxial grown SiSn alloy layers. Secondary ion mass spectrometry has exposed the accumulation of carbon in the SiSn layers after high temperature carbon implantation and high temperature thermal treatment. Strain-enhanced separation of point defects and formation of dopant-defect complexes are suggested to be responsible for the effects. The possibility for carbon assisted segregation-free high temperature growth of heteroepitaxial SiSn/Si and GeSn/Si structures is argued.
Keywords: ion implantation, precipitation, carbon, tin, SiSn alloy, transmission electron microscopy, Rutherford backscattering spectrometry Registration No. 21032

Paramagnetism in neutron irradiated graphite
Wang, Y.; Jenkins, C. A.; Arenholz, E.; Bukalis, G.; Skorpa, W.; Helm, M.; Zhou, S.
Abstract: Defect induced magnetism in carbon based materials has many attractive perspectives in the fundamental understanding of magnetism as well as in future spintronic applications. Graphite has been reported that it can be ferromagnetic after proton irradiation. After that, successive investigation was done for confirming the ferromagnetism in graphite and for finding other carbon based materials to be ferromagnetic. So far although the mechanism of ferromagnetism in carbon-based materials is still an open question, more and more experiments show some common features: First, paramagnetism can be largely enhanced by introducing defects. Second, ferromagnetism only appears under certain defect concentration. Third, defects induced or disturbed electron states play an important role to generate local moments and to establishing the ferromagnetic coupling. In the past most of researchers used ions implantation to introduce defects in graphite or graphene. This technology usually generates defect in the near--surface and it is hard to effectively increasing the total number of defect in the whole matrix. Consequently, the magnetic signal is so weak that confuses the interpretation for the source of the observed ferromagmetism. To obtain more reliable information, thereby to better understand this phenomenon, it is necessary to enhance the total number of defect states and simultaneously keep defect concentration constant when the ferromagnetism appears. So in this contribution we use neutron irradiation to extend defect region in graphite from the near surface region to the whole sample. We present the magnetic properties and X-ray absorption spectroscopy of irradiated graphite.
Keywords: XAS, neutron irradiation, graphite
  • Poster:
    19th international conference on ion beam modification of materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium
Registration No. 21025

Low energy proton radiation impact on 4H-SiC nMOSFET gate oxide stability
Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Millán, J.; Godignon, P.
Abstract: The 4H-SiC MOSFET electrical response to 180 keV proton radiations at three different fluences has been evaluated. For a certain dose, the devices show an improvement of their electrical characteristics likely due to the N and/or H atoms diffusion inside the oxide layer. This work shows that not only the 4H-SiC material is robust to the radiation, but also a MOSFET build on this material can withstand it, and even its electrical performance results improved if submitted to an appropriate fluence.
Keywords: Charge trapping; Mobility; Proton irradiation; SiC MOSFET; Threshold voltage; Time bias stress instability Registration No. 21022

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

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

Keywords: magnetic domains, AMR, Kerr microscope
  • Lecture (Conference):
    IEEE International Magnetics Conference, 04.-08.05.2014, Dresden, Deutschland
  • Lecture (Conference):
    Physikerinnentagung, 16.-19.10.2014, Dresden, Deutschland
Registration No. 21021

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

Keywords: molecular dynamics, kinetic Monte-Carlo, TRIM, TRIDER, surface patterning, ion-beam shaping
  • Invited lecture (Conferences):
    Swift Heavy ions in Materials Engineering and Characterization (SHIMEC 2014), 14.-17.10.2014, New Delhi, India
Registration No. 21019

Investigation of interlayer exchange coupling and magnetic anisotropy of Fe3Si-trilayers using ferromagnetic resonance
Schneider, T.; Hübner, R.; Lenz, K.; Lindner, J.; Fassbender, J.
Abstract: In this thesis, magnetic properties of single Fe3Si-films und trilayer structures are investigated by ferromagnetic resonance. Using this technique, it is possible to determine the magnetic anisotropy energy and interlayer exchange coupling J1 in absolute units. Further on, values for the magnetic anisotropy constants and the g-factor should be confirmed in this work. Due to the use of a broad band setup, it is possible to investigate the linewidth of the measured signals. The measurements are carried out using structures containing two Fe3Si films separated by one MgO-layer. The MgO thickness is varied to obtain two different samples. In one of these samples both layers can be considered as decoupled. In the second sample both layers are coupled due to interlayer exchange coupling (IEC). The main results of this thesis are: (i) The obtained parameters for magnetic anisotropy and the g-factor match former results quite well. (ii) The investigation of the resonance linewidth shows contributions of two-magnon-scattering and inhomogeneous broadening due to the mosaicity. (iii) For both used layer thicknesses the interlayer exchange coupling can always be neglected. (iv) The origin of the uniaxial anisotropy is given by effects at the interfaces between the Fe3Si and MgO or the Fe3Si and GaAs layers.
Keywords: Interlayer exchange coupling, FMR, Fe3Si
  • Invited lecture (Conferences):
    Gruppenseminar AG Wende, 14.01.2014, Duisburg, Deutschland
Registration No. 21016

Taktsynchronisierung und Zeitmessung in einem verteilten Datenerfassungssystem
Födisch, P.; Sandmann, J.; Lange, B.; Kaever, P.
Abstract: Die Zeitmessung mit einem verteilten Datenerfassungssystem erfordert die Synchronisierung der einzelnen Teilsysteme. Eine dedizierte Taktverteilung ist für diese Anwendung eine einfache und präzise Lösung, erfordert aber zusätzlichen Installationsaufwand und bereitet vor allem bei der Skalierung des Gesamtsystems Probleme. Stattdessen können auch die vorhandenen Datenlinks der einzelnen Module für eine Rückgewinnung des Systemtaktes verwendet werden. Hier wird gezeigt, wie mit industriellen Komponenten (FPGA und Gigabit-Ethernet PHY) die Synchronisierung auf eine gemeinsame Taktfrequenz realisiert wird. Der Abgleich der Uhren erfolgt anschließend protokollbasiert über die Ethernet-Schnittstelle. Es werden die hardwareseitigen Anforderungen, die Umsetzung sowie die experimentellen Ergebnisse vorgestellt. Das implementierte System erreicht Genauigkeiten im Sub-Nanosekunden Bereich mit einer 1000BASE-T Punkt-zu-Punkt Verbindung.
  • Contribution to proceedings:
    105. Tagung der Studiengruppe elektronische Instrumentierung im Frühjahr 2014, 10.-12.03.2014, Geesthacht, Deutschland, Hamburg: Verlag Deutsches Elektronen-Synchrotron, 978-3-935702-85-0, 238-242
Downloads:
Proceedings 2014 PDF
Registration No. 21015

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

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

Keywords: InMnAs, Ferromagnetic Semiconductors, Ion implantation
  • Poster:
    International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, leuven, Belgium
Registration No. 21014

Mikrobiologische Verfahren in der Hydrometallurgie
Kutschke, S.; Raff, J.; Pollmann, K.
Abstract: Die Vorbereitung von Erzen zur Verhüttung kann mit hydrometallurgischen Verfahren erfolgen. Dazu zählen Extraktionsverfahren mit wässrigen Lösungen, die Flotation, Sink-Schwimmtrennung und Fällungen. Diese Verfahren finden häufig in äußerst aggressiver Umgebung statt. Für einige dieser Prozesse stehen interessante Alternativen zur Verfügung. Die untersuchten und dargestellten Methoden werden durch Mikroorganismen oder ihre Stoffwechselprodukte unterstützt.
Seit 1980 wird Bioleaching im industriellen Maßstab in Chile eingesetzt. Zur Laugung trägt in diesen Anlagen die Oxidation der sulfidischen Erze durch Acidithiobacillus sp. bei. Oxidische oder carbonatische Erze können auf diesem Weg nicht gelaugt werden. Untersuchungen zeigen, dass in diesen Fällen der Einsatz von Pilzen und Bacillus sp. zur Freisetzung von Metallen aus diesen Erzen beiträgt. Dabei spielen die von Mikroorganismen gebildeten organischen Säuren eine entscheidende Rolle.
Für Sink- Schwimmtrennungen und Fällungen können weitere biologische Komponenten verwendet werden. Zum einen sind es Phagen mit speziell gestalteten Oberflächen. Diese Oberflächen können so konstruiert werden, dass sie spezifisch für einzelne Metalle sind. Durch weitere Variationen der Phagenoberfläche kann die Hydro¬phobi¬zität der mikroskopisch kleinen Partikel an die Anforderungen zum Beispiel einer Flotation angepasst werden. Zum anderen sind es calciumbindende Proteine, die über spezifische und unspezifische Bindungsstellen verfügen und darüber einzelne industrierelevante Metalle sehr selektiv binden können. Die letzten beiden Ideen werden in anderen Bereichen bereits genutzt, zeigen aber auch ein sehr hohes Anwendungspotential bei der Aufbereitung von Erzen.
  • Lecture (Conference):
    Jahrestagung 2013 „Aufbereitung und Recycling“, 13.-14.11.2013, Freiberg, Deutschland
Registration No. 21012

Tilting column and 3D pattern formation during ion beam assisted growth of carbon:nickel nanocomposite films
Krause, M.; Buljan, M.; Möller, W.; Facsko, S.; Zschornak, M.; Wintz, S.; Heller, R.; Endrino, J. L.; Gemming, S.
Abstract: Ion assistance provides unique opportunities to influence the microstructure of growing films due to energy and momentum transfer. Here, ion effects on the microstructure of C:Ni nanocomposite thin films grown at RT to 500°C by ion-beam sputtering with assisting oblique incidence angle Ar+ ion beam irradiation (50 – 130 eV) are studied by SEM, (c)AFM, TEM, GISAXS, and TRI3DYN simulations. Two types of ordered metallic nanostructures in an amorphous carbon matrix are identified and characterized: i) tilted parallel columns [1] and ii) rippled, periodic three-dimensional nanoparticle arrays [2]. For the former one, the tilt angle and diameter of the nanocolumns are controlled by the deposition parameters. Ion-enhanced diffusivity and ion-induced surface drift are responsible for the tilted column microstructure. Complex secondary structures like chevrons with partially epitaxial junctions are grown by sequential deposition. For a given composition of the depositing flux, the transition from the columnar growth to the 3D pattern formation regime as a function of the assisting ion energy is demonstrated. The 3D pattern is attributed to the transfer of compositionally modulated surface ripples into the bulk of the C:Ni thin film. The essential experimental features are reproduced by three-dimensional binary collision computer simulations. This agreement points to ion-induced preferential displacements as the driving force for the 3D pattern formation.
Keywords: Nanocomposites, Ion assistance, pattern formation
  • Poster:
    14th International Conference on Plasma Surface Engineering, 15.-19.09.2014, Garmisch-Partenkirchen, Deutschland
Registration No. 21011

P1311-Anordnung zur schnellen Elektronenstrahl-Röntgencomputertomographie
Barthel, F.
Abstract: Aufgabe der Erfindung ist es, eine Anordnung zur Elektronenstrahl-Röntgen-Computertomographie anzugeben, die ohne die erhebliche axiale Ausdehnung des Elektronenstrahlers auskommt, und weitgehend auf elektronenoptische Strahlführungselemente verzichtet. Die Erfindung umfasst, dass ein Röntgendetektorbogen (6) und das Target (4) um den Untersuchungsquerschnitt innerhalb einer Bestrahlungsebene angeordnet sind, und ein im Elektronenstrahlerzeuger generierter Elektronenstrahl in den Durchflutungsbereich einer oder mehrerer Längsspulen radial eingebracht wird, und durch das Magnetfeld auf eine Kreisbahn gezwungen wird. Durch periodisches Verstellen der Feldstärke wird der Radius der Kreisbahn vergrößert, was dazu führt, dass der Elektronenstrahl das Target (4) in einem tangential wandernden Brennfleck (7) trifft. Vom das Target umgebenden Röntgendetektor(6) werden Durchstrahlungsprojektionen des in der Mitte der Anordnung befindlichen Objekts (8) aufgenommen. Der Elektronenstrahlerzeuger (1) kann sowohl innerhalb als auch außerhalb der Längsspulen (3) angeordnet sein. Darüber hinaus kann die Target- und Röntgendetektorebene mit oder ohne Axialversatz angeordnet sein.
  • Patent:
    DE102013206252A1 - Offenlegung-09.10.2014
Registration No. 21010

Tetrahedral amorphous carbon coatings for friction reduction of the valve train in internal combustion engines
Götze, A.; Makowski, S.; Kunze, T.; Hübner, M.; Zellbeck, H.; Weihnacht, V.; Leson, A.; Beyer, E.; Joswig, J.-O.; Seifert, G.; Abrasonis, G.; Posselt, M.; Fassbender, J.; Gemming, S.; Krause, M.
Abstract: Tetrahedral amorphous carbon (ta-C) is studied as a tribological coating for the valve train’s exhaust camshaft of a combustion engine. The coated camshafts were installed in a non-fired engine, tested in a computerized component test bench under practice-relevant conditions and analyzed for their frictional behavior. A notable reduction of the valve train’s drive torque on the test bench is demonstrated. Namely, on a roller cam system with ta-C coated camshaft the reduction is about 15% in average within the entire engine-map. The ta-C coatings were extensively characterized under laboratory conditions before and after the investigations on the test bench. Mechanistic understanding of the tribological behavior of ta-C coatings under dry or starving lubricated conditions was achieved by atomistic simulations of the tribological contact. Industrial utilization of these results would lead to a significant increase of the energy efficiency of combustion engines.
Keywords: tribological coatings, tetrahedral amorphous carbon (ta-C), combustion engines, atomistic simulations
  • Advanced Engineering Materials 16(2014), 1226-1233
Registration No. 21009

Imaging systems for dose monitoring in particle therapy
Fiedler, F.
Abstract: no abstract available
  • Invited lecture (Conferences):
    Interdisciplinary Symposium ''Precision, Speed and Flexibility: New radiation detection methods for ion beam radiotherapy, 23.-25.10.2014, Heidelberg, Deutschland
Registration No. 21007

Particle Therapy Positron Emission Tomography (PT-PET) for Treatment Verification
Fiedler, F.
Abstract: Radiation therapy is an important treatment modality in cancer therapy. New radiation species, like protons and light ions have the potential of increasing tumor conformality of irradiation. Because of the way these particles deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the damage of the surrounding normal tissue.
High precision radiotherapy treatment requires efficient quality assurance techniques. Even small changes in the irradiated volume will lead to a mismatch of the deposited dose maximum and the tumor. This causes missing dose in the tumor volume and potential damage to normal tissue. Therefore, a treatment verification system is highly desirable. Between 1997 and 2008, the in-beam Positron Emission Tomography (PET) method was used at the GSI Helmholtzzentrum für Schwerionenforschung, Darmstadt, Germany to monitor the dose delivered by 12C beams [1]. This method makes use of the β+-activity produced via nuclear interactions between the therapeutic beam and the patient tissue. The results and experiences of the clinical application of in-beam PET for carbon ions GSI will be shown. Based on this experience several approaches to improve the significance of the result have been studied.
Since the dose delivery is evaluated by means of a comparison between measured and simulated data a reliable prediction of β+-activity is crucial. To model the positron emitter production accurately, cross sections for all possible nuclear reactions occurring in the tissue during irradiation which lead to positron emitters are required. Since these cross sections are available only for a few reaction channels in the required energy range, a novel approach for estimating the positron emitter production from experimental data is introduced [2].
Up to now the comparison of the distributions is performed by well-trained observers (clinicians, physicists). This process is very time consuming and low in reproducibility. Therefore, a semi-automatic method has been developed evaluating the range and including a cavity filling detection algorithm. System inherent uncertainties are handled by means of a statistical approach [3, 4].
The Particle Therapy (PT)- PET method has been approved for static tumors under clinical conditions. However, also for intra-fractionally moving targets, the 4D simulation [5] as well as the 4D reconstruction [6] of PT-PET data has been established. By means of dedicated 4D-PET experiments the results of the comparison between measured and anticipated activities have been investigated.
References
[1] W. Enghardt, et al., Nucl. Instr. Meth A 525, 2004.
[2] M. Priegnitz, et al., IEEE Trans. Nucl. Sci. 59, 2012.
[3] S. Helmbrecht, et al., Phys. Med. Biol. 57, 2012.
[4] P. Kuess, et al., Med. Phys. 39, 2012.
[5] K. Laube, et al., Phys. Med. Biol. 58, 2013.
[6] K.Stützer, Phys. Med. Biol. 58, 2013.
  • Invited lecture (Conferences):
    Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Deutschland
Registration No. 21006

Hyperdoping Si with chalcogen: solid vs. liquid phase epitaxy
Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in Si, the materials were previously only realized by femtosecond or nanosecond laser annealing of implanted Si or bare Si in certain background gases. The high energy density deposited on the Si surface renders it into a liquid phase and the fast recrystallization velocity allows trapping of S/Se/Te into the Si matrix. However, this method encounters a problem of S/Se/Te surface segregation. In this Letter, we propose a solid phase processing by flash lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed Se-implanted Si shows a substitutional rate of more than 70% with the implanted concentration up to 1-2%. The resistivity is lower and the carrier mobility is higher than those of laser annealed samples. Our results show that flash lamp annealing is superior laser annealing in preventing surface segregation and in allowing scalability.
Keywords: Chalcogen elements, pulsed laser annealing
  • Poster:
    E-MRS 2014 FALL MEETING, 15.-18.09.2014, Warsaw, Poland
Registration No. 21003

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


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

Keywords: Ion implantation, deep level impurities
  • Lecture (Conference):
    ION, 23.-26.06.2014, Kazimierz Dolny, Poland
Registration No. 21002

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


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

Keywords: Ion implantation, deep level impurities
  • Poster:
    Deutsche Physikalische Gesellschaft, 30.03.-04.04.2014, Dresden, Germany
Registration No. 21001

Ferromagnetic GaMnP prepared by ion implantation and pulsed laser annealing
Y, Yuan.
Abstract: We present the magnetic, transport and structural properties of GaMnP with different Mn concentrations prepared by ion implantation and pulsed laser annealing. The Curie temperature increases with Mn concentration and the samples show in-plane magnetic anisotropy due to the in-plane compressive strain in the GaMnP layer. Anomalous Hall effect and negative magnetoresistance are observed, indicating the carrier mediated nature of the ferromagnetism in GaMnP. According to the micro-Raman spectroscopy data after pulsed laser annealing the implanted layer has been fully recrystallized and the carrier concentration (hole) increases with Mn concentration.
Keywords: Ferromagnetic semiconductors, GaMnP, Ion Implantation, Pulsed laser annealing
  • Lecture (Conference):
    IEEE International Magnetics Conference, 04.-08.05.2014, Dresden, Germany
Registration No. 21000

Possible defect-induced ferromagnetism in Cr doped SiC single crystals
Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.
Abstract: Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.
Keywords: defect-induced ferromagnetism, SiC, Cr doping, semiconductors
  • Poster:
    The 19th International Conference on Ion Beam Modification of Materials (IBMM 2014), 14.-19.09.2014, Leuven, Belgium
Registration No. 20999

Possible defect-induced ferromagnetism in Cr doped SiC single crystals
Liu, Y.; Zhou, S.; Wang, G.; Wang, S.; Sun, W.; Chen, X.
Abstract: Defect-induced ferromagnetism (FM) was realized in non-magnetic materials, such as highly oriented pyrolytic graphite (HOPG), HfO2, and Li doped ZnO. Recently, such FM was also found in SiC by doping, neutron bombardment and ion implantation. As now SiC crystals are available in microelectronic grade, the good crystallinity makes SiC a kind of potential materials for spin electronics. However, one problem in defect-induced FM in bulk SiC crystals is that the magnetization induced by defects is not strong, which might increase the difficulty for the further study. Here, we demonstrate the enhanced defect-induced FM in Cr doped SiC. The 4H-SiC single crystals were grown by physical vapor transport method. The SiC sample is diamagnetic when the nominal doping density of Cr is below 0.5%, whereas the room-temperature FM reaching 1.5 x 10-3 emu/g is observed in SiC with 1% Cr doping. However, the actual Cr concentrations in magnetic SiC measured by secondary ion mass spectroscopy are nearly equal in both the nominal 0.5% and 1% samples, so Cr doping is not the origin of the FM. After annealing, the decreased magnetization suggests that the FM is closely associated with defects. However, we can not distinguish the defect types by positron annihilation lifetime spectroscopy or photoluminescence. The defects with higher dimensions rather than divacancies are proposed to induce the FM in Cr doped SiC. More efforts are needed to clarify this puzzling phenomenon.
Keywords: defect-induced ferromagnetism, SiC, Cr doping, semiconductors
  • Poster:
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
Registration No. 20998

Ferromagnetic InMnAs prepared by Ion implantation and pulsed laser annealing
Yuan, Y.; Wang, Y.; Khalid, M.; Weschke, E.; Skorupa, W.; Helm, M.; Zhou, S.
Abstract: Ferromagnetic InMnAs has been previously prepared by low temperature MBE. In this contribution, we present an alternative method what combines Mn ion implantation and pulsed laser annealing to achieve In1-xMnxAs (x = 0.04 and 0.08) [1], and to obtain a remarkably high Curie Temperature (TC) up to 80 K compared to InMnAs with the same Mn concentration as prepared by MBE. The advantage of pulsed laser annealing is its high process temperature within the nano-second range, eliminating n-type defects which can decrease its magnetization and TC. The saturation magnetization is ~2.6μB / Mn by consideration of all implanted Mn ions. The out-of-plane [001] is the easy axis displaying a nearly square like hysteresis loop. Our results suggest that InMnAs prepared by ion implantation and pulsed laser annealing shows a promising prospect to get high TC DMS after optimizing the preparation parameters.
Keywords: Ferromagnetic Semiconductors, Ion Implantation, Pulsed laser annealing
  • Poster:
    DPG-Frühjahrstagung, 30.03.-04.04.2014, Dresden, Germany
Registration No. 20996

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

Keywords: Magnetic semiconductors, Ion implantation
  • Invited lecture (Conferences):
    E-MRS 2014 SPRING MEETING, 26.-30.05.2014, Lille, France
  • Invited lecture (Conferences):
    The Moscow International Symposium on Magnetism 2014, 29.06.-03.07.2014, Moscow, Russia
  • Invited lecture (Conferences):
    X-th International Conference - Ion Implantation and Other Applications of Ions and Electrons, 23.-26.06.2014, Kazimierz Dolny, Poland
Registration No. 20993

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

Keywords: titanium, titanium aluminides, high-temperature oxidation protection
  • Lecture (Conference):
    28th International Conference on Surface Modification Technologies (SMT), 16.-18.06.2014, Tampere, Finland
Registration No. 20992

Improvement of the resistance of titanium aluminides to environmental embrittlement
Masset, P. J.; Bleicher, F.; Bortolotto, L.; Geiger, G.; Kolitsch, A.; Langlade, C.; Paul, J.; Pelic, B.; Pyczak, F.; Rafaja, D.; Schumacher, P.; Schütze, M.; Wolf, G.; Yankov, R. A.
Abstract: Aluminum enriched coatings have been developed for titanium aluminide alloys. It has been shown that Metal Organic Chemical Vapor Deposition (MO-CVD) and Physical Vapor Deposition (PVD) processes combined with fluorination of the coating enables to reduce significantly the embrittlement of TiAl alloys through oxidation. Even after oxidation at 900 °C for 100h, the coatings exhibit suitable adhesion and 90 % of the fracture toughness and ductility of the alloy are maintained. Registration No. 20991

Development of new coatings to prevent environmental embrittlement of titanium aluminides
P. Masset; F. Bleicher; L. Bortolotto; G. Geiger; A. Kolitsch; C. Langlade; J. Paul; B. Pelic; F. Pyczak; D. Rafaja; P. Schumacher; M. Schütze; G. Wolf; R. Yankov
Abstract: Abstract: For temperatures above 750°C, TiAl alloys still show insufficient oxidation resistance and suffer from environmental embrittlement. This work focuses on the surface modification of alloys and development of coatings against environmental embrittlement, as well as on testing of mechanical properties after high temperature oxidation. Aluminum enriched coatings (between 50 and 60 at.%) containing alloying elements, i.e. Cr, Nb, Si, Y, to improve the oxidation behavior and the corrosion resistance have been produced by MO-CVD, CVD, PVD and thermal spraying techniques (HVOF, APS), and have subsequently been chemically modified with halogen elements, notably fluorine. The mechanical properties have been studied by means of 4-point bending and tensile tests on coated samples after 100h oxidation at 900 °C in laboratory air. The CVD process combined with fluorine treatment using plasma immersion implantation (PI³) of F offers the best combination to remedy environmental embrittlement. It has been shown in particular that 90% of the initial fracture strain and fracture stress can be maintained.
Keywords: titanium, titanium aluminides, high-temperature oxidation, protective coatings
  • Lecture (Conference):
    TMS 2014, 143rd Annual Meeting & Exhibition, 16.-20.02.2014, San Diego, United States
Registration No. 20988

Protection of Ti-alloys against high temperature environmental attack by a two step process, aluminization + fluorination
A. Donchev; M. Galetz; M. Schütze; R. Yankov; A. Kolitsch
Abstract: Ti-alloys cannot be used at elevated temperatures above approximately 600°C in oxidizing environments. They suffer from accelerated oxidation and oxygen uptake in the subsurface zone, which deteriorates the mechanical properties. The addition of Al (usually < 10%) into standard Ti-alloys is not enough to form a protective alumina layer. Aluminization of technical Ti-alloys and formation of intermetallic Al-rich phases (e.g. TiAl3) change the oxidation behavior from fast and non-protective rutile formation to slow growing alumina kinetics, but only for a limited period of time. A subsequent fluorination of the aluminized components gets the fluorine effect to operate. This is away to improve the resistance of technical Ti-alloys against environmental attack, even for longer service times. In this paper the results of high temperature oxidation tests of several untreated and treated Ti-alloys will be presented and their behavior compared.
Keywords: Environmental embrittlement; Fluorine effect; Oxidation
  • Contribution to proceedings:
    TMS 2014 143rd TMS Annual Meeting 2014, 16.-20.02.2014, San Diego, United States
    TMS 2014 Supplemental Proceedings, 9781118889725, 79-85
    DOI-Link: http://dx.doi.org/10.1002/9781118889879
Registration No. 20987

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

Keywords: pressurized water reactor, loss-off-coolant accident, corrosion, zinc, boric acid, in-vessel effects
  • Lecture (Conference):
    17th WGAMA Meeting, 23.-26.09.2014, Paris, France
Registration No. 20986

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

Keywords: titanium, titanium aluminides, high-temperature oxidation, protective coatings
  • Invited lecture (Conferences):
    Shechtman International Symposium, 29.06.-04.07.2014, Cancun, Mexico
Registration No. 20985

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

Keywords: Plasma Immersion Ion Implantation, High-Temperature Oxidation, TiAl Intermetallics
  • Poster:
    19th International Conference on Ion Beam Modification of Materials (IBMM), 14.-19.09.2014, Leuven, Belgium
Registration No. 20984

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

Keywords: radiation dosimetry; positron emission tomography; (−)-18F-flubatine; nicotinic receptors; α4β2 Registration No. 20983

Velocity measurements of heavy liquid metal flows by the Ultrasound Doppler method
Franke, S.; Eckert, S.; Gundrum, T.; Gerbeth, G.
Abstract: The application of heavy liquid metals as coolant or heat transfer medium in advanced reactor systems demands for a comprehensive knowledge of the flow characteristics. CFD simulations are the main tool to predict the flow behaviour, however, the numerical models have to be validated by experimental data. Flow measurements in hot liquid metals are challenging and the available choice of measuring techniques is rather limited. A great deal of work was done during the last decade to develop suitable measuring principles for applications in metallic melts. The Ultrasound Doppler method can be considered as an attractive technique to obtain real-time velocity profiles in liquid metal flows. Flow measurements in hot metallic melts involve several specific problems, especially the high temperature and the abrasive character of the melt. Furthermore, a sufficient input of acoustic energy into the melt to be measured requires favourable conditions concerning acoustic coupling, transmission and wetting. Moreover, the availability of seeding particles has to be guaranteed to obtain Doppler signals from the fluid. We will present a concept for velocity measurement in a liquid metal channel flow based on high temperature transducer probes in combination with a matched mechanical design of the probe seating. Specific measuring procedure enables us for reliable measurements in a temperature range up to 230°C. The measuring principles are successfully applied at experimental facilities operating with different metal alloys and geometric configurations: At the LIMMCAST (Liquid Metal Model for Continuous Casting) facility of Helmholtz-Zentrum Dresden-Rossendorf we studied the flow profile of a Sn60Bi40 alloy in a circular pipe. Furthermore, the LBE duct flow of the META:LIC loop (Megawatt Target: Lead Bismuth Cooled) at the Institute of Physics in Riga-Salaspils (University of Latvia) was measured. Parametric studies of the velocity profile measurements in the ducts will be presented here. Specific problems arising for the application of the Ultrasound Doppler method in the considered experimental configuration will be discussed.
Keywords: Hot metallic melt flow measurements, Heavy liquid metal coolant, LBE, Ultrasound Doppler velocimetry, LIMMCAST, META:LIC
  • Lecture (Conference):
    SEARCH/MAXSIMA 2014 International Workshop, 07.-10.10.2014, Karlsruhe, Deutschland
Registration No. 20982

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

Keywords: loss-of-coolant accident, pressurized water reactor, corrosion, zinc, zinc borate, chemical effects
  • Lecture (Conference):
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland
  • Contribution to proceedings:
    Annual Meeting on Nuclear Technology 2014, 06.-08.05.2014, Frankfurt, Deutschland
Registration No. 20978

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

Keywords: loss-of-coolant accident, pressurized water reactor, corrosion, zinc, chemical effects
  • Poster:
    46. Kraftwerkstechnisches Kolloquium 2014, 14.-15.10.2014, Dresden, Deutschland
Registration No. 20977

In Situ Tuning the Conductance of Single Molecular Diarylethene Switches
Sendler, T.; Luka-Guth, K.; Wieser, M.; Lokamani, M.; Wolf, J.; Huhn, T.; Scheer, E.; Kerbusch, J.; Gemming, S.; Erbe, A.
Abstract: A major goal of molecular electronics is the development and implementation of molecular electronic devices such as single molecular switches. In this work we present a detailed study of single diarylethene molecules that were in situ switched from their non-conductive to conductive state in the presence of gold nanoelectrodes via controlled light irradiation. The molecules were dissolved in two different solvents and measured with two different side-groups. Histograms of conductance traces were taken and complemented by extracting the relative position of the current carrying molecular level and its level broadening from current-voltage characteristics by means of the single level transport model. The obtained results show a clear light-induced ring forming isomerization, which is almost independent of the side-groups, while electron withdrawing side groups lead to a reduction of conductance, a decrease of the level broadening and an increased difference between the molecular level and the Fermi energy of the metals. Quantum chemical calculations of the light-induced switching processes correlate these observations with the fundamentally different low-lying electronic states of the opened and closed forms and their comparably small modification by the electron-withdrawing substituents.
  • Poster:
    Annual Workshop IHRS NanoNet 2014, 29.-30.09.2014, Lohmen/Bastei, Deutschland
Registration No. 20976

Variability and lower bound of fracture toughness of welds in the ductile to brittle transition regime
Schindler, H.-J.; Kalkhof, D.; Viehrig, H.-W.
Abstract: The reference temperature T0 was measured for both T-S and T-L- specimen orientation in 24 layers across the thickness of the beltline weld of a reactor pressure vessel. It turned out to vary in a bandwidth of more than 40K. Because of a high scatter, no clear pattern of T0 as a function of the thickness position could be recognized. A more detailed analysis revealed that the median of KJc was considerably steeper than predicted by the Master-Curve, which leads to a bias of T0 with respect to the testtemperature relative to T0. By a modified evaluation procedure, the scatter of the reference temperature could be significantly reduced, which enabled the global pattern of T0 to be recognized. By comparing the theoretical lower bound to KJc-data of the used specimens with the individual measured KJc a representative T0 that characterizes the overall toughness behaviour of the weld was determined. It turned out to be about 10 K lower than the maximum local T0.
Keywords: reactor pressure vessel, weld metal, fracture toughness, reference temperature Registration No. 20973

Intra-band dynamics in single InAs/GaAs quantum dots under the influence of strong far-infrared excitation
Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.
Abstract: Inter-band transitions in single quantum dots (QDs) have received a huge amount of scientific interest in the recent past. However, mostly due to technical challenges in dealing with mid- and far-infrared radiation, intra-band transitions have not been explored quite as thoroughly. In this work, we combine micro-photoluminescence (µPL) on low-density annealed InAs/GaAs QDs with additional excitation at intra-band transition energies by pulsed radiation from a free-electron laser (FEL). This scheme enables the probing of the single-dot response in spite of the large diameter of the FEL focus. The investigation of single QDs eliminates undesirable effects such as inhomogeneous broadening which has been observed in previous studies on QD ensembles1–3. In the time domain, the FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. The subsequent recovery is significantly larger than would be expected for simple redistribution. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse. When investigating at the PL spectrum of a single dot, we observe a marked difference caused by the FEL pulse (Fig. 2), which implies a change of the excitonic state of the QD.
  • Lecture (Conference):
    International Conference on Superlattices, Nanostructures and Nanodevices, 03.-08.08.2014, Savannah, United States of America
Registration No. 20972

Intra-band dynamics in single InAs/GaAs quantum dots probed with a free-electron laser
Stephan, D.; Bhattacharyya, J.; Helm, M.; Huo, Y. H.; Schmidt, O.; Rastelli, A.; Schneider, H.
Abstract: Compared to the vast amount of research done in the past on inter-band transitions in single quantum dots (QDs), transitions within the bands have received much less attention. The main reasons for this are most likely the largely non-radiative character of intra-band transitions and the technical difficulties associated with the corresponding mid- and far-infrared radiation. In our contribution, we approach this challenge by combining conventional micro-photoluminescence (µPL) on low-density annealed InAs/GaAs self-assembled QDs with additional excitation at intra-band (i.e. inter-sublevel) transition energies by pulsed radiation from a free-electron laser (FEL). In contrast to previous studies on ensembles of QDs1–3, using single dots eliminates undesirable effects such as inhomogeneous broadening. The FEL pulse leads to an initial decrease in the PL transient (Fig.1), which we attribute to a temporary redistribution of carriers. This is followed by a pronounced recovery, such that the integrated PL is larger than for a reference transient without FEL excitation. By varying the NIR excitation energy, we find that this increase is due to carriers which are initially present close to but not inside the QD (in the wetting layer or in defect states) and which are freed and/or transported to the dot upon incidence of the FEL pulse.
  • Poster:
    8th International Conerence on Quantum Dots, 11.05.-16.10.2014, Pisa, Italia
Registration No. 20971

Optical investigations of GaAsN in high magnetic fields
Eßer, F.; Drachenko, O.; Schneider, H.; Patanè, A.; Hopkinson, M.; Helm, M.
Abstract: Introducing a few hundredths of a percent of nitrogen into a GaAs-based semiconductor leads to dramatic changes of the electronic and optical properties of the original material system. This can be used in order to intentionally tune the semiconductors characteristics. In particular the bandgap of semiconductors like GaAs and InGaAs, can be strongly reduced by slight nitrogen incorporation, which is attractive for applications, in particular for detectors or light sources.

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

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

Keywords: GaAsN, ditute nitrides, effective mass, cyclotron-resonance, magneto-photoluminescence, high magnetic field
  • Poster:
    Optical Properties of Individual Nanowires and Quantum Dots in High Magnetic Field, 24.-26.09.2014, Toulouse, France
Registration No. 20969

5 MeV Proton and 15 MeV Electron Radiation Effects Study on 4H-SiC nMOSFET Electrical Parameters
Alexandru, M.; Florentin, M.; Constant, A.; Schmidt, B.; Michel, P.; Godignon, P.
Abstract: The impact of proton and electron irradiations on the electrical parameters of 4H-SiC nMOSFETs has been investigated by the time bias stress instability method. This study has allowed observing the effect of holes trapped in the gate oxide together with the generated interface traps. Improvements of important electrical parameters, such as the threshold voltage, the effective mobility and the maximum drain current were observed. These improvements could be connected with the Nitrogen and residual Hydrogen atoms diffusion from the SiO2/SiC interface toward the epilayer during irradiation. These atoms are likely to create other bonds by occupying the Silicon and Carbon’s dangling bond vacancies. This way, the number of passivated Carbon atoms is increased, hence improving the SiO2/SiC interface quality.
Keywords: Charge trapping, electron irradiation, mobility, proton irradiation, SiC MOSFET, SiO2/SiC interface, threshold voltage shift, time bias stress instability. Registration No. 20968

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

Keywords: spin Nernst effect, spin caloric, spin orbit coupling, Cu, dilute alloys, thermoelectrics, spin dependent transport
  • Poster:
    Material Science and Engineering conference - MSE 2014, 23.-25.09.2014, Darmstadt, Deutschland
Registration No. 20967

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

[1] E. A. Zibik et al., Nature Mat. 8, 803 (2009).
[2] M. Teich et al., Appl. Phys. Lett. 103, 252110 (2013).
[3] R. Jacob, Nano Lett. 12, 4336 (2012).
[4] S. Winnerl et al., Phys. Rev. Lett. 107, 237401 (2011).
[5] M. Mittendorff et al., Nature Phys. (under review).
  • Invited lecture (Conferences):
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland
Registration No. 20963

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

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

Keywords: Carrier dynamics, ultrafast spectroscopy, graphene
  • Poster:
    Graphene Week, 23.-27.06.2014, Goteborg, Sweden
Registration No. 20962

Time-resolved spectroscopy on Landau-quantized graphene revealing strong Auger scattering
Winnerl, S.; Mittendorff, M.; Wendler, F.; Malic, E.; Knorr, A.; Schneider, H.; Helm, M.
Abstract: The carrier dynamics within the system of Landau levels of index n = -1 to n = 0 and n = 1 in graphene is investigated by pump-probe experiments using circularly polarized terahertz radiation. The study, complemented by microscopic modelling, reveals a pronounced carrier redistribution caused by strong Auger scattering.
Keywords: Carrier dyanmics, ultrafast spectroscopy, graphene, Landau quantization, Auger scattering
  • Lecture (Conference):
    4th EOS Topical Meeting on Terahertz Science & Technology (TST 2014), 11.-14.05.2014, Camogli, Italia
Registration No. 20961

THz spectroscopy of solids using a free-electron laser
Helm, M.
Abstract: I will start describing the Dresden free-electron laser FELBE as an intense, tunable, pulsed and narrowband source of infrared and THz radiation and the unique opportunities it offers for the spectroscopy of low-energy excitations in solids. In particular, the FEL can be used for nonlinear optical experiments, for time-resolved pump-probe studies, and also for near-field microscopy. I will mainly discuss nonlinear experiments on excitons in semiconductor quantum wells and pump-probe studies of the relaxation dynamics in graphene. I will conclude with an outlook on further developments, including the superradiant THz radiation source TELBE.
Keywords: free-electron laser, terahertz, quantum wells, graphene
  • Lecture (others):
    Seminarvortrag am Fritz-Haber-Institut (FHI), Berlin, 20.10.2014, Berlin, Germany
Registration No. 20960

Population dynamics in graphene Landau levels
Helm, M.; Mittendorff, M.; Winnerl, S.; Wendler, F.; Malic, E.; Knorr, A.
Abstract: Population dynamics in graphene Landau levels
Keywords: graphene, Landau levels, population, pump-probe, free-electron laser, Auger scattering
  • Invited lecture (Conferences):
    International Quantum Cascade Lasers School and Workshop 2014, 07.-12.09.2014, Policoro, Italy
Registration No. 20958

Intrinsic Formation of Neptunium Nanoparticles in Presence and Absence of Silica: Formation of Np(IV)-silica Colloids and NpO2 Nanocrystals
Husar, R.; Hübner, R.; Hennig, C.; Weiss, S.; Ikeda-Ohno, A.; Zänker, H.; Stumpf, T.
Abstract: The chemistry of tetravalent actinides An(IV) in aqueous solution is typical of a small highly-charged metal ion with a strong tendency to hydrolize and therefore a low solubility. Disregarding the formation of clusters, nanoparticles and colloids lead to underestimation of the migration behavior. The reaction mechanisms of formation and growth, especially under alkaline and near-neutral environmental conditions are still unexplored. On the way from aqueous species to nanoparticles two fundamental questions in An(IV) chemistry provoke discussion in literature: 1) are hydrolysis and condensation the driving forces toward nano-scaled solids or 2) are formed aggregates ill-defined complex hydroxides, hydrous oxides or highly structured clusters/nanoparticles? Excluding the presence of other oxidation states then An(IV), we performed in situ investigation of the self organised formation of neptunium(IV) aggregates and nanoparticles from aqueous complex precursor under alkaline conditions. The kinetics of the self-assembling of the nanoparticles, their morphology and internal structures were determined. The influence of silica on the formation of highly coordinated NpO2 structure was proved. In particular, former studies confirmed the formation of amorphous silica-containing U(IV) and Th(IV) colloids. Starting from aqueous neptunium(IV) carbonate complexes, we investigated the behavior after dilution in presence and absence of silica by TEM, EXAFS, UV vis spectroscopy, Ultrafiltration and DLS (dynamic light scattering). The formation of nanoparticles was observed. TEM and diffraction pattern show different morphologies and internal structures in dependence of presence or absence of silica.
Keywords: Neptunium, Np(IV), nanoparticles, colloids, An(IV), hydrolysis, neptunium carbonate complex
  • Poster:
    Plutonium Futures 2014 - the science, 07.-12.09.2014, Las Vegas, USA
Registration No. 20956

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

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

Keywords: nuclear, nuclear reactor, molten salt, molten salt reactor, fast reactor, transmutation, nuclear waste management
  • Invited lecture (Conferences):
    Seminar an der RWTH Aachen, 08.07.2014, Aachen, Deutschland
Registration No. 20955

On an optimized neutron shielding for an advanced molten salt fast reactor design
Merk, B.; Konheiser, J.
Abstract: The molten salt reactor technology has gained renewed interest. In contrast to the historic molten salt reactors, the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes significantly more challenging than in historic concepts. One very interesting and innovative result of the most recent EURATOM project on molten salt reactors – EVOL – is the fluid flow optimized design of the inner core vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all core internal structures. On the basis of this new geometry a model for neutron physics calculation is presented and applied for a shielding optimization. Based on these results an optimized shielding strategy is developed for the molten salt fast reactor to keep the fluence in the safety related outer vessel below expected limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system has to be significantly increased and will finally be comparable to a sodium cooled fast reac-tor. The HELIOS results are verified against Monte-Carlo calculations with very satisfactory agreement for a deep penetration problem.
Keywords: fast reactor, molten salt reactor, neutron shielding, neutron transport, HELIOS, optimization
  • Contribution to proceedings:
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan
  • Lecture (Conference):
    PHYSOR 2014 – The Role of Reactor Physics Toward a Sustainable Future, 28.09.-03.10.2014, Kyoto, Japan
Registration No. 20954

Mineral Processing of Lithium-bearing Mica.
Leißner, T.; Rode, S.; Bachmann, K.; Gutzmer, J.; Peuker, U.
Abstract: This contribution deals with the mineral processing of Li-silicate greisen-type ores comprising of quartz, topaz and zinnwaldite (lithium-rich mica). The origin of the greisen-type ores processed is the Ore Mountains(Germany) where it is explored as a potential resource for the production of lithium carbonate. The goal is to develop a process chain for the enrichment of zinnwaldite using dry techniques only. As basis for the investigation the process chain, which historically was used to process the greisen focused on cassiterite and wolframite, is taken and modified towards the zinnwaldite.
Starting with crushed material with particle sizes smaller than 35 millimeters, investigations on different approaches to grinding to liberate mica from gangue are carried out. Concentrates of zinnwaldite are then produced by magnetic separation of size fractions. To assess the success of grinding, classification and separation, mineral liberation analysis and atomic absorption spectroscopy are used. The amount of lithium measured in the sample with atomic absorption spectroscopy was used to calculate the content of zinnwaldite based on its known mineral chemistry. Combined with the particle size distributions, product qualities are determined. Altogether, this allows the thorough evaluation of the success of comminution with focus on following steps of concentration.

Keywords: lithium, zinnwaldite, magnetic separation, mineral liberation analysis
  • Lecture (Conference):
    International Mineral Processing Congress, 24.-28.09.2012, New Delhi, India
Registration No. 20948

Recent advances in structural geology, lithogeochemistry and exploration for VHMS deposits, Kristineberg area, Skellefte District, Sweden.
Jansson, N.; Hermansson, T.; Persson, M.; Berglund, A.; Kruuna, A.; Skyttä, P.; Bachmann, K.; Gutzmer, J.; Chmielowski, R.; Weihed, P.
Abstract: Kristineberg is the largest mine and VHMS deposit in the Palaeoproterozoic Skellefte District, Sweden. The deposit was discovered in 1918, and it has been mined since 1941. Besides the Kristineberg deposit, several other VHMS deposits have been mined in the Kristineberg area. Despite the long history of mining, significant advances are still being made in terms of exploration and understanding the geological framework of the ore bodies. A key to this success has been persistence in exploration and a combination of local and regional scale geological, geophysical and geochemical surveys. Holistic industry-university collaborative research projects have furthermore played an important role in bringing together geologists and geophysicists from different disciplines to tackle the large-scale geological framework. Among other things, these projects have resulted in the first structural geological 3D model of the Kristineberg area, better age constraints on the formation of the deposits, a regional alteration map as well as ongoing work to model alteration in 3D. This contribution summarizes the results of these investigations and recent exploration.
Keywords: Kristineberg, Skellefte District, VHMS, 3D modelling, Exploration
  • Poster:
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden
Registration No. 20947

Alteration in the area of the Kristineberg VHMS deposit, Skellefte district, Sweden.
Bachmann, K.; Gutzmer, J.; Persson, M.; Jansson, N.
Abstract: The Skellefte district in north-central Sweden is one of the most important mining districts in northern Europe. It contains over 85 pyritic Zn-Cu-Au-Ag massive sulphide deposits of which 21 deposits have been mined since 1924 and 4 are still in operation by Boliden Mineral AB. The most productive deposit, the Kristineberg mine, has been operated by Boliden since 1940 with a current annual production of 670,000 t of polymetallic ore containing 3.0 wt.-% Zn, 0.7 wt.-% Cu, 0.4 wt.-% Pb, 1.9 g/t Au and 47 g/t Ag. Alteration of the volcanic rocks around the Kristineberg deposit is very intense. The main aim of this study has been to describe the alteration intensity and to define alteration trends around the Kristineberg deposit. The success of this approach provides a new exploration tool for future exploration in the Skellefte District where alteration renders the recognition of primary volcanic facies difficult.
Keywords: Kristineberg, Skellefte district, VHMS, alteration
  • Poster:
    12th Biennial SGA Meeting: Mineral deposit research for a high-tech world, 12.-15.08.2013, Uppsala, Sweden
Registration No. 20946

Raman spectroscopy – casting (laser) light on microbe – mineral interactions
Kostudis, S.; Kutschke, S.; Pollmann, K.
Abstract: Highly efficient and sustainable mining strategies gain importance due to the fact that available resources of base metals like copper but strategic elements such as gallium and molybdenum as well face a steadily decreasing grade. This issue is enhanced by the increased demand and production amounts of those metal compounds. Biohydrometallurgy – the use of microorganisms or related substances in metal extraction - provides the potential of processing low grade ores efficiently. Thus it is applied yet in some gold and uranium mining.
Also due to strategic reasons mining of regional resources such as the European Kupferschiefer come to the fore. Its complex composition including sulphide rich ores, carbonates and organic compounds challenges biotechnological approaches. Nevertheless promising approaches have been reported. We examine heterotrophic bioleaching of copper from Kupferschiefer ores. To investigate the interactions between mineral surface and microorganisms Raman spectroscopy offers a versatile applicability: Identification of minerals and differentiation of microorganisms is nicely provided and is accompanied by imaging opportunities in a two or even three dimensional manner. Thus biofilms, for example, can be analysed with respect to microbial diversity or preferences of minerals during the attaching process.
  • Poster:
    Microbiology and Infection, 05.-08.10.2014, Dresden, Deutschland
Registration No. 20945

Evaluation of mineral processing by assessment of liberation and upgrading.
Leißner, T.; Mütze, T.; Bachmann, K.; Rode, S.; Gutzmer, J.; Peuker, U.
Abstract: A model is presented to evaluate mineral processing on basis of gangue recovery and valuables recovery. It combines mineralogical limiting curves with upgrading curves in the Fuerstenau diagram. These curves are used to assess mineral liberation and mineral beneficiation compared with the ideal result. Two new parameters (ratio of separation and ratio of liberation) are calculated based on a comparison of areas enclosed by the mineralogical limiting curve, the upgrading curve, the curve representing a total liberation of valuables, and the curve representing a perfect mixture of valuables and gangue.
An assessment of the success of mineral processing is possible using these parameters. The assessment shows whether the quality of a separation product is influenced by the separation process itself or by the achieved liberation of the feed.
A series of experiments on the magnetic separation of a greisen-type ore proves the applicability of this model to mineral processing. SEM-based image analysis and ICP-OES measurements have been used to obtain the necessary data.

Keywords: liberation, upgrading, separation, mineral liberation analysis Registration No. 20944

Discrimination of hematite and magnetite in finely intergrown natural iron ores by automated mineralogy.
Bachmann, K.; Bartzsch, A.; Gutzmer, J.
Abstract: Providing a fast, quantitative characterization of iron ores in terms of liberation, grain sizes and shapes as well as mineral association remains a big challenge. Whilst quantitative mineralogical data are easily attained by QXRD, an automated SEM-EDS based approach is needed for the quantification of relevant microfabric attributes. Two different iron ores were investigated for this study, to illustrate the capabilities and limitations of the latter approach. The first example is a banded-iron formation (BIF) ore from Thabazimbi/RSA, the second ore type studied is a magnetite iron ore from Svappavaaragruvan, c. 50 km east of Kiruna/N-Sweden. The greatest difficulty in the characterization of iron ores is certainly the discrimination between different relevant iron oxides (magnetite, hematite, goethite) that are all of very similar elemental composition – and thus have both very similar backscattered electron (BSE) brightness, as well as almost identical EDS spectra. A principle approach was suggested by Figueroa et al. (2011) by using the Mineral Liberation Analyzer (MLA). The suitability of this method was illustrated on synthetic mixtures. The approach of the present study utilizes the method on thin sections of natural iron ores, which show a fine intergrowth of hematite and magnetite with an unknown composition. For calibration, an in-house magnetite and hematite standard was prepared to further optimize the set-up of the method. A new feature in the MLA suite v.3.1.4 is the capability to define the exact working distance for every single sample separately. Slight variations in the working distance between the different samples and the standard were equalized. The MLA results were compared to bulk chemical data as well as traditional point counting-data by reflected light-microscopy. The results are within a relative error of 5 %. It can be concluded that the method was successfully applied and can be applied to iron ores with complex oxide mineral associations.
  • Poster:
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today - Practical Aspects, 22.-24.09.2014, Leoben, Austria
Registration No. 20943

Li isotopes and geochemistry of Li–F–Sn greisen from the Zinnwald deposit.
Bachmann, K.; Seifert, T.; Magna, T.; Neßler, J.
Abstract: The Sn–W greisen deposits, located in the eastern part of the Variscan metallogenic Erzgebirge province (zinnwaldite Ar–Ar ages between 313 and 315 Ma), are emplaced in highly metamorphosed and/or igneous rocks and typically are associated with post-collisional Li–F-enriched small granitic intrusions. This metallogenic province traditionally belonged to the major source of economic Sn, Ag, U, W, Co and fluorite–barite deposits for central Europe. The Zinnwald/Cínovec Li–Sn greisen deposit is associated with a unique zinnwaldite–quartz–topaz mineralization hosted by an albitized stock-granite.
Li contents and isotope compositions were measured in host albite granites (n=2), greisens (n=3), and a sample from a flat-dipping vein in the Zinnwald deposit, paralleled by individual mineral phases. All investigated bulk rocks have extreme Li contents reaching from 1,600–2,200 ppm in albite-granite, to 3,400–6,200 ppm in greisen-type rocks and to ~8,000 ppm in a vein-type sample, most likely carried by zinnwaldite (15,000–19,200 ppm) and muscovite (9,500–15,700 ppm) whereas albite and quartz, in particular, have significantly lower Li abundances (560–660 and 33–330 ppm, respectively). The high bulk Li contents are very unusual even for chemically evolved granitic systems with the exception of Li-rich pegmatites. Bulk 7Li values are restricted (–1.0 to 0.3 ‰), consistent with late orogenic granites from a larger area of the Erzgebirge Mts.. Zinnwaldite and muscovite carry isotopically heavy Li relative to the corresponding bulk rocks and, at the same time, muscovite always is slightly heavier than zinnwaldite. 7Li values of quartz become progressively heavier from granites through greisens to a vein sample. Zinnwaldite may represent a late-stage ingress of Li-rich fluids/melts rather than indigenous phase of these lithologies because from mass balance considerations and mineral modes, bulk [Li] and 7Li values cannot easily be reconstructed for either sample of the suite.
  • Poster:
    Goldschmidt2014, 08.-14.06.2014, Sacramento, USA
Registration No. 20942

Multifunctional S-layer proteins as building blocks for hybrid materials
Weinert, U.; Günther, T.; Lehmann, F.; Vogel, M.; Suhr, M.; Matys, S.; Bobeth, C.; Kutschke, S.; Pollmann, K.; Raff, J.
Abstract: Nanostructured bio-inorganic hybrid materials are very attractive for technical applications, e.g. nanocatalysts, photocatalytic materials, sensors and filter systems. Self-assembling biomolecules like Surface layer (S-layer) proteins represent a promising tool as hybrid material due to their ability to self-assembly in aqueous solutions and on surfaces. In nature S-layer proteins coat the bacterial and archaeal cells with a highly ordered nanostructure and defined symmetry and fulfill various functions, e.g. protection, binding matrix for exoenzymes and molecular sieves. Isolates, which were taken from a uranium mining waste pile in Saxony, produce S layer proteins to protect themselves from heavy metals and radionuclides. If the S layer proteins are saturated with heavy metals or radio nucleotides, the protein will be rejected and a new one will be produced.

We take advantage of the high affinity to heavy metals to produce hybrid filter materials from micro sieves and S-layers. The so called “S-sieves” will be able to bind heavy and noble metals from aqueous solutions even in low concentration ranges economically.

Another aspect will be the synthesis of Pd, Pt and Au nanoparticles on S-layer proteins. Pd and Au nanoparticles were built in the pores of S-layer proteins. Due to that a surface of nanoparticles of a defined size and regularly arrangement can be constructed. Those surfaces will work as nanocatalysts for many technical applications, e.g. the production of CNTs which has already been demonstrated.

Further work deals with the design of a hybrid materials which will work as photocatalysators for drinking water purification. Especially pharmaceuticals can be disintegrated by radicals. The radicals are formed in sunlight and in presence of the catalytic active ZnO- or TiO2-nanoparticles which are coupled and regularly arranged on S-layer protein interface.

These three examples emphasize the use of S-layer proteins their potential in nanotechnology and will give new prospective in the mentioned techniques.

Keywords: hybrid material, s-layer, nanaoparticles, filter material, nanocatalysts
  • Lecture (Conference):
    Multifunctional S-layer proteins as building blocks for hybrid materials, 23.-25.09.2014, Darmstadt, Deutschland
Registration No. 20939

Bioinspired hybrid nanomaterials based on self-assembling proteins
Weinert, U.; Lederer, F.; Günther, T.; Lehmann, F.; Drobot, B.; Vogel, M.; Pollmann, K.; Raff, J.
Abstract: Many microorganisms like bacteria developed during evolution highly effective mechanisms and structures to survive at the most forbidding, uninviting places on Earth. One example is the binding of heavy metals and actinides by cell surface proteins of uranium mining waste pile isolates. The so called surface layer (S-layer) proteins (Fig. 1a) bind toxic metals and metalloids and thusly protect the cells from being damaged by these elements. On other cells, S-layers may act for example as immobilization matrix for exoenzymes, as molecular sieve or as ion and molecule trap.
These properties and their ability to self-assemble in suspension, on surfaces and at interfaces qualify S-layers as interesting building blocks for the construction of new bioinspired nanomaterials for different technical applications. Using the two-dimensional protein arrays, different kinds of surfaces can be nanostructured and novel bio-inorganic hybrid materials with multiple functions can be produced.
Currently three materials are in the focus: metal filters, catalysts and sensors (Fig. 1b). Biocomposites made of microsieves and S-layers are under development to selectively recover strategic metals from aqueous solutions. S-layer proteins with immobilized and regularly arranged metals or metal oxides are useful for diverse catalytic applications. Furthermore, S-layer coatings combining highly specific receptors like aptamers and stable fluorescence dyes are very promising for the construction of new biosensors for organics or pharmaceuticals.
Basis for those materials and their industrial application is an effective production of S-layer proteins. The latter is possible by the extraction of the S-layers from growing cells or by heterologous expression of the proteins. In bacteria or yeasts expressed S-layers can be genetically engineered with molecular modifications to further combine the outstanding S layer protein characteristics with additional expedient features. Native as well as engineered S-layer proteins have an application potential going far beyond above mentioned applications ranging from the chemical industry, water and environmental technologies to medicine.

Keywords: nanoparticles, filter material, S-layer, biosensors, nanocatalysts
  • Lecture (Conference):
    Biomaterials - Made in Bioreactors, 26.-28.05.2014, Radebeul, Deutschland
Registration No. 20938

Quantum structure THz photonics and spectroscopy at HZDR
Schneider, H.
Abstract: Es gibt kein Abstract.
  • Lecture (others):
    Seminarvortrag, Centre Suisse d'Electronique et Microtechnique SA (CSEM), 19.09.2014, Neuchâtel, Schweiz
Registration No. 20936

Photoinduzierte Dynamik in der ps Zeit- und THz Frequenz-Domäne
Schneider, H.; Schmidt, J.; Teich, M.; Stephan, D.; Fehrenbacher, M.; Franke, C.; Winnerl, S.; Gensch, M.; Seidel, W.; Helm, M.
Abstract: Dieser Vortrag stellt die im Rahmen des BmBF-Verbundprojekts PIDID geschaffenen erweiterten Messmöglichkeiten für den Nutzerbetrieb am Freie-Elektronenlaser (FEL) FELBE vor und beschreibt einige exemplarische Experimente. FELBE erlaubt als einziger FEL in Europa einen quasikontinuierlichen Pulsbetrieb, der bei vielen Experimenten zu erheblichen Vorteilen führt im Hinblick auf die Stabilität sowie das Signal-zu-Rauschverhältnis. Aufgrund der Resonatorlänge beträgt die FEL-Pulsrate hierbei 13 MHz (77 ns Pulsabstand). Innerhalb des PIDID-Vorhabens wurden reduzierte Pulsraten (1 kHz bzw. 100 kHz) realisiert, wie sie zur Untersuchung physikalischer Prozesse mit längeren Zeitkonstanten im Bereich µs bis ms benötigt werden. Hierzu wurde ein optischer Schalter aufgebaut, der auf der hohen Reflektivität eines Elektron-Loch-Plasmas beruht, das mittels synchroner optischer Pulse in einem Germaniumkristall angeregt wurde. Des Weiteren wurden ein Fourier-Spektrometer sowie ein Tieftemperatur-Nahfeldmikroskop aufgebaut, die vorwiegend in Teilprojekten der Projektpartner eingesetzt wurden. Im zweiten Teil des Vortrags werden die wichtigsten Messmöglichkeiten an FELBE anhand einiger ausgewählter Experimente dargelegt.
  • Lecture (Conference):
    Deutsche Tagung für Forschung mit Synchrotronstrahlung, Neutronen und Ionenstrahlen an Großgeräten 2014 (SNI 2014), 21.-23.09.2014, Bonn, Deutschland
Registration No. 20935

Monte-Carlo Simulationen zur Untersuchung der Auswirkungen von Quelländerung im Reaktorkern auf die Excore-Instrumentierung
Konheiser, J.
Abstract: Verschiedene Auswirkungen von möglichen Variationen der Kerngeometrie auf die Signalwerte der Excore-Instrumentierung eines Druckwasserreaktors (DWR) werden in dieser Arbeit gezeigt. Zu diesem Zweck werden Neutronenflüsse für mögliche Brennelementanordnungen mit Hilfe stationären Monte Carlo-Berechnungen außerhalb des Reaktors bestimmt. Typische Daten eines deutschen PWR wurden für die Untersuchungen verwendet.
Unterschiede in den Neutronenflüssen der Excore-Instrumentierung von bis zu 4 % wurden bei Änderungen der Abstände von 1 mm zwischen bestimmten Brennelementen, die im Randbereich des Kerns liegen, berechnet.
Der Grund ist eine verbesserte Moderation von Neutronen, die zu einem höheren Leistung bzw. Neutronenfluss im Randbereich des Kerns führt. Die Folge ist ein höherer Neutronenstrom in Richtung der Excore-Instrumentierung. Dieser Effekt ist Abhängigkeit von Zykluszeitpunkt.
Mögliche Wassertemperaturschwankungen von 1K im Ringspalt, die zu Veränderungen der Wasserdichte und somit des Absorptionsvermögens führen, haben dagegen kaum Auswirkungen auf den Neutronenfluss an der Excore-Instrumentierung.

Effects of possible variations of the core geometry on the signal values of excore instrumentation of a pressure water reactor (PWR) are shown in this work. For this purpose, neutron fluxes outside of the reactor are determined for possible arrangements of fuel assemblies by means of stationary Monte Carlo calculations. Typical data of a German PWR were used for the investigations. Differences in the neutron flux of the excore instrumentation of up to 4% were calculated with changes of the pitch from 1 mm between certain fuel assemblies, which lie in the boundary area of the core. The reason is an improved moderation of neutrons, which results in a higher power and neutron flux in the periphery of the core. The result is a higher neutron flux in the direction of excore instrumentation. This effect is a function of cycle time. Possible water temperature fluctuations of 1 K in the downcomer, which leads to changes in water density and thus in the absorbance, have marginal effect on the neutron flux at the excore instrumentation.

Keywords: excore instrumentation, Monte Carlo calculation, pressure water reactor, neutron flux
  • Article, self-published (no contribution to HZDR-Annual report):
    Forschungszentrum Rossendorf 2014
    INSTITUTBERICHT HZDR\FWO\2014\01
    0056 Seiten
Registration No. 20932

Terahertz spectroscopy of zero- and two-dimensional semiconductor nanostructures with the free-electron laser FELBE
Schneider, H.; Teich, M.; Bhattacharyya, J.; Zybell, S.; Jacob, R.; Winnerl, S.; Helm, M.
Abstract: The free-electron laser facility FELBE in Dresden, a unique source of intense, quasi-cw, nearly transform-limited ps pulses in the mid-infrared and terahertz (THz) regimes, provides unique research opportunities. In high-quality semiconductor quantum wells, we investigate the dynamics of excitons, i.e. two-dimensional, hydrogen-like electron-hole quasi-atoms. Tuning FELBE in resonance with the transition between the excitonic 2s and 2p states (at ca. 2 THz) allows us to study the dynamics of intra-excitonic population transfer. Moreover, strong terahertz pumping results in a characteristic Rabi splitting of the 1s exciton state, which is a manifestation of the intra-excitonic Autler-Townes effect. In semiconductor quantum dots, resonant THz excitation between different sublevels is shown to produce an absorption contrast in aperture-less scattering scanning near-field optical microscopy (s-SNOM). This effect allows us to obtain functional s-SNOM images with deep sub-wavelength resolution, where the contrast originates from far-infrared absorption by single electrons. Quantum dots are also known to have very long electronic relaxation times caused by a reduced phase space for optical phonon scattering. We will report on THz four-wave mixing experiments demonstrating that the associated electronic coherence times approximately equal the population relaxation time at low temperatures. This property makes quantum dots promising for quantum optical applications at THz frequencies.
Keywords: free-electrpn laser
  • Lecture (Conference):
    Science@FELs 2014, 15.-17.09.2014, Villigen, Schweiz
Registration No. 20931

QWIP-Based “Ultrafast” Detectors for QCL Research
Schneider, H.
Abstract: In this talk, I will summarize two approaches for “ultrafast” QWIP-based detection of mid-infrared signals and cover a few examples for practical applications.
  • Invited lecture (Conferences):
    International Quantum Cascade Laser School and Workshop 2014 (IQCLSW2014), 07.-12.09.2014, Policoro (Matera), Italien
Registration No. 20930

Selektive Trennung sehr feiner Partikelsysteme mittels Flüssig/Flüssig-Flotation
Leistner, T.; Müller, M.; Erler, J. V.; Rudolph, M.; Peuker, U. A.
Abstract: Die Vergrößerung des effizienten Anwendungsbereiches von Sortierprozessen in den Bereich feinster Partikelsysteme (0,1 – 10 μm) stellt eine erhebliche Herausforderung für die Forschung dar. Ein möglicher Prozessansatz zur Verbesserung des Sortierergebnisses ist die Flüssig/Flüssig-Flotation. In dieser Studie werden Aussagen bezüglich Anwendbarkeit und Prozessverhalten dieses Ansatzes in Abhängigkeit von ausgewählten Prozessparametern an verschiedenen Modellpartikelsystemen präsentiert.
Keywords: Particle-oil-water emulsions; Phase transfer; Surfactant; Two-liquid flotation; Ultrafine particle separation Registration No. 20927

Efficient and accurate identification of platinum group minerals by a combination of mineral liberation and electron microprobe analysis
Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.
Abstract: Identification and accurate characterization of platinum group minerals (PGM) is a very cumbersome procedure due to grain sizes that are mostly below 10 µm and inconspicuous appearance. A novel strategy on finding and quantifying PGM was applied by combining Mineral Liberation Analyzer (MLA) 650F, point logger (JEOL) and a field emission electron probe micro-analyzer (FE-EPMA, JEOL JXA-8530F). Thin sections from a layered intrusion (UG2) in the Bushveld Complex and from two Uralian-Alaskan-type complexes in the Ural Mountains, Russia, were investigated as case studies.
As a first step the PGM are identified, using the Mineral Liberation Analyzer (MLA). The SPL (Sparse Phase Liberation) mode is the best way to find and identify the PGM with high spatial resolution and great accuracy. For this purpose, a series of back-scattered electron images is collected. Within these images, mineral grains are selected that match or exceed a set grey-scale value. These grains are characterized by collecting EDS spectra. Grains identified as PGMs are then marked and coordinates recorded in a format suitable for the EPMA at the point logger. With these coordinates recorded, the sample can be transferred to the microprobe. Despite their small grain sizes the PGM can be retrieved without any difficulties (deviation from the position logged with the point logger is only a few µm). Case studies illustrate that the combination of MLA, point logger and EPMA results in the identification of 4-5 times more PGMs than by careful reflected light microscopy. This is mainly due to the facts that (a) PGM with grain sizes < 5µm are reliably identified and (b) PGM and closely associated base metal sulfides and sulfosalts are well differentiated with the MLA. Furthermore, identification of PGMs remains unaffected by human error and is efficient with respect to the time spent by the mineralogist on a particular sample.
Despite the efficient identification of PGM grains using MLA, the combination with FE-EPMA bears at least one significant advantage. FE-EPMA allows for the accurate determination of mineral chemical composition by WDS, whereas MLA permits only for EDS spot analyses. WDS analyses of PGM by FE-EPMA requires considerable caution, though, due to overlaps of X-rays on both peak and background of almost all PGE and associated elements (e.g. OsMβ on IrMα and AuMβ on HgMα). It is thus necessary to look carefully at every element and to set peak and backgrounds individually for every element. X-ray lines suitable for quantitative analyses (e.g. Mβ instead of Mα) need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction has been developed in order to correct the interferences afterwards. Results obtained in this study attain acceptable totals and atomic proportions, suggesting that the applied corrections are appropriate.

Keywords: Mineral Liberation Analyser, Electron Microprobe, Pointlogger, Platinum Group Minerals, Overlap corrections
  • Contribution to proceedings:
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Practical Aspects, 21.-24.09.2014, Leoben, Österreich
    EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, Antwerp-Wilrijk, Belgien: European Microbeam Analysis Society eV EMAS, 9789082276909, 303-303
  • Poster:
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today, 21.-24.09.2014, Leoben, Österreich
Registration No. 20926

Abschlussbericht "WTZ Russland - Fluenzberechnungen für Voreilproben beim WWER-440"
Konheiser, J.; Grahn, A.
Abstract: Reactor pressure vessels (RPV) are non-restorable equipment and their lifetime may restrict the nuclear power plant-life as a whole. Surveillance specimen programs for RPV materials are among the most important measures of in-service inspection pro-grams that are necessary for realistic and reliable assessment of the RPV residual lifetime. In addition to the chemical composition of the RPV steel, the radiation pa-rameters (neutron and gamma fluences and spectra) have the most important impact on the RPV embrittlement characteristics.
In this work, different geometric positions which have influence on the radiation conditions of the samples are investigated. Thus, the uncertainties can be determined in the fluence values of surveillance specimens. The fluence calculations were carried out by the codes TRAMO and DORT. This study was accompanied by ex-vessel neutron dosimetry experiments at Kola NPP, Unit 3 (VVER-440/213), which provide the basis for validation of calculated neutron fluences. The main neutron-activation monitoring reactions were 54Fe(n,p)54Mn and 58Ni(n,p)58Co. The activity measurements were carried out by “Scientific and Engineering Centre for Nuclear and Radiation Safety (SEC NRS).
Good agreement between the deterministic and stochastic calculation results as well as between the calculations and the ex-vessel measurements was found. The aver-age difference between measured and calculated values is 5%. The influence of the channels for surveillance specimens and the shielding effect of a baffle rib on the monitors and on the Monte-Carlo calculated results was studied.
For the surveillance specimens in the maximum of the flux, an average flux of around 2.45 * 1012 neutrons/cm2 was calculated for the neutron flux E> 0.5 MeV. The differences in the surveillance specimens could be up to 20% depending on the direction to the core. Discrepancies up to 10% can be caused by the change of the position of the capsules in the irradiation channel. Based on these calculations the lead factor of specimens was determined. The maximum fluence of RPV may be achieved after two cycles.
The calculated maximum gamma flux is around 3.4 * 1012 g/cm2s for E> 1.0 MeV and around 8.4 * 1012 g/cm2s for E> 0.5 MeV, with the largest part of the flux (around 97%) from the neutron reactions. The gamma fluxes in the surveillance specimens are two to three times bigger than the neutron fluxes. Nevertheless, the material damage by the gamma radiation is very small, because the dpa (displacement per atom) cross sections of gamma rays are about two to three orders of magnitude smaller.
In order to exclude the possibility of healing effects of the samples due to excessive temperatures, the heat release in the surveillance specimens was determined based on the calculated gamma fluences. The analytic treatment of the heat conduction equation and simplified SS geometries were adopted to calculate the range of tem-peratures to be expected. The temperature increase of 20 K above the inlet coolant temperature was estimated using a conservative approach. Under comparatively re-alistic conditions, the heating was reduced to less than 5 K.

Keywords: Reactor pressure vessels, Surveillance specimen, fluence calculation, neutron-activation monitors
  • Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-053 2014
Downloads:
2,5 MB PDF
Registration No. 20925

Tomographic imaging of gas holdup distribution in pressurized bubble columns
Bieberle, A.; Schubert, M.; Rollbusch, P.; Becker, M.; Schleicher, E.; Hampel, U.
Abstract: The averaged and radial gas holdup as well as gas phase dynamics and approximate bubble size distribution were studied in a high-pressure bubble column reactor of 4000 mm height and 330 mm diameter. Novel imaging measurement techniques, namely high-resolution gamma-ray computed tomography and wire-mesh sensor, were developed and adapted to the industrial reactor system. The gas phase was nitrogen. Deionized water and cumene were applied as liquid phases. The effect of the superficial gas velocity was studied over a range of 0 to 0.05 m/s at low liquid superficial velocities of 0.008 and 0.018 m/s for operating temperatures and pressures up to 75°C and 18.5 bar, respectively.
Keywords: Bubble column, gas holdup, flow structure, gamma tomography, wire-mesh sensor
  • Poster:
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
  • Lecture (Conference):
    2nd International Symposium on Multiscale Multiphase Process Engineering, 24.-27.09.2014, Hamburg, Deutschland
Registration No. 20924

INTRA r³+ Integration und Transfer der r³ Ergebnisse
Dürkoop, A.
Abstract: Das Poster präsentiert die Arbeiten im Begleitforschungsprojekt INTRA r³+ zur r³ Fördermaßnahme "Innovative Technologien für Ressourceneffizienz.
  • Poster:
    Urban Mining Kongress und r³ Statusseminar 2014, 11.-12.06.2014, Essen, Deutschland
Registration No. 20923

Working with hierarchical databases in R to model geometallurgical data
Matos Camacho, S.; van den Boogaart, K. Gerald
Abstract: For the demands of geometallurgy a vast amount of data in multifaceted shape is needed. There are high resolution images from the MLA, data tables with information on the chemistry of some mineral phases, statistics on the distribution of the grain size, and so on. This data needs to be stored in a database, which reflects the often hierarchical structure of it and is flexible enough to be extended with almost any potential occurring information. We provide a MySQL template for such a database. Finding the desired data there can be a tough task, since queries might be highly complex and confusing. Therefore, we developed an easy accessible R interface for accessing this database.
Keywords: R, geometallurgy, MySQL
  • Lecture (Conference):
    16th Annual Conference of the International Association for Mathematical Geosciences, 17.-20.10.2014, New Delhi, India
Registration No. 20921

Evidence for Deposition of Interstellar Material on the Lunar Surface
Fimiani, L.; Cook, D. L.; Faestermann, T.; Gómez Guzmán, J. M.; Hain, K.; Herzog, G. F.; Knie, K.; Korschinek, G.; Ligon, B.; Ludwig, P.; Park, J.; Reedy, R. C.; Rugel, G.
Abstract: Astronomical observations indicate that one or more supernovae (SN) ocurred in the vicinity of our solar system in the recent past (~10Myr) [1,2]. One possible indication of the arrival of SN (or perhaps AGB) debris locally was the detection of 60Fe/Fe (T1/2 = 2.62 Myr [3]) excesses in a ferroman-ganese crust from the Pacific Ocean [4,5]. Another indication came from the Moon. In a previous study [6] we reported a 60Fe/Fe depth profile constructed with 2 samples of the Apollo 12 core 12025, 4 samples of the Apollo 15 core 15008, 2 samples known as ‘skim’, ‘scoop’ and ‘under boulder’ soil collected near the shade of a small boulder in Station 9 during the Apollo 16 mission (shaded samples), and 5 samples of the deep drill core 60007/6, sampled during the same mission. We complete the previous work by reporting new measurements of 53Mn (T1/2 = 3.7 Myr [7]) in the same samples, including deeper samples of the 12025 core, and by using those measurements for a critical assessment of the 60Fe results. We also determined the activities of 60Fe and 53Mn of 7 samples from 4 iron meteorites; these activities were used to establish reference levels for local production due to galactic cosmic rays.
Keywords: supernova, Fe-60, Mn-53
  • Poster:
    45th Lunar and Planetary Science Conference, 17.-21.03.2014, Houston, USA
Registration No. 20920

Geometallurgy of REE deposits - state of the art
Renno, Axel D.; Gutzmer, J.; Birtel, S.; Atanasova, P.; Bachmann, K.; Matos Camacho, S.; Schulz, B.; Kern, M.; Krause, J.; Munnik, F.
Abstract: Review of the most recent activities of the Helmholtz-Institute Freiberg for Resource Technology in the field of geometallurgy of REE deposits
Keywords: geometallurgy, REE
  • Invited lecture (Conferences):
    Geology to Metallurgy of Critical Rare Earths, 24.-25.03.2014, Penryn, UK
Registration No. 20916

High-Speed PIXE – a new tool for Automated Mineralogy using a Color X-Ray Camera
Renno, A. D.; Buchriegler, J.; Dressler, S.; Hanf, D.; Merchel, S.; Munnik, F.; Nowak, S.; Scharf, O.; Ziegenrücker, R.
Abstract: Methods of automated mineralogy form the analytical backbone of geometallurgy. Most of them exploit the combined imaging and analytical capabilities of optical and scanning electron microscopes. Typical results are „phase maps“ either derived from the distribution of major elements or determined directly. The effective application of such methods for strategic metals which are won as by-products from other metal ores or secondary raw materials is handicapped by the restricted possibilities to determine the spatial distribution of such trace elements like In, Ga, Ge or the rare earth elements (REE). The recently commissioned High-Speed PIXE (Particle Induced X-Ray Emission) setup at the Helmholtz-Institute Freiberg for Resource Technologies will overcome these limitations by using the advantages of PIXE over traditional electron beam based methods like the better peak-background ratio. We use the SLcam® Colour X-ray Camera - a novel pnCCD pixel detector (264×264=69696 pixel) combined with a polycapillary X-ray optics (Scharf et al., 2011) as detector for element specific X-ray radiation. This design allows us the simultaneous determination of trace element distributions on a 12 × 12 mm2 area with a lateral resolution better than 100 μm. First results of geometallurgical applications of this method are presented.
Keywords: PIXE, High-Speed PIXE
  • Lecture (Conference):
    92nd Annual Meeting Deutsche Mineralogische Gesellschaft (DMG) 2014, 21.-24.09.2014, Jena, Deutschland
Registration No. 20914

High field THz sources operating at 100 kHz Repetition rates: Challenges and Opportunities
Gensch, M.
Abstract: Picosecond long transients of electric and magnetic fields in combination with repetition rates in the few 100 kHz to even MHz regime is crucial to understand several recently observed fascinating nonequilibrium phenomena driven by THz excitations. A new class of compact accelerator based THz sources based on super-radiant amplification of radiation from ultra-short electron bunches allows to generate high field THz pulses at unprecedented repetition rates. First measurements at a prototype facility proof the feasibility of the approach and demonstrate already parameters which exceeds laser-based sources by more than 2 orders of magnitude. Results from first pilot experiments aiming at investigating THz driven magnetization dynamics in MnGa, NiO and YIG are discussed and an outlook into the opportunities for High-field THz science at the future TELBE user facility is given.
  • Invited lecture (Conferences):
    Seminar of the Stanford Institute for Materials and Energy Sciences, 12.09.2014, Stanford / SLAC, USA
Registration No. 20913

High-Speed PIXE: Automated Mineralogy using a Color X-Ray Camera
Renno, A. D.; Buchriegler, J.; Hanf, D.; Munnik, F.; Nowak, S.; Scharf, O.; Ziegenrücker, R.
Abstract: Methods of automated mineralogy form the analytical backbone of geometallurgy. Most of them exploit the combined imaging and analytical capabilities of optical and scanning electron microscopes. Typical results are „phase maps“ either derived from the distribution of major elements or determined directly. The effective application of such methods for strategic metals which are won as by-products from other metal ores is handicapped by the restricted possibilities to determine the spatial distribution of such trace elements like In, Ga, Ge or the rare earth elements (REE). The recently comissioned High-Speed PIXE (Particle Induced X-Ray Emission) setup at the Helmholtz-Institute Freiberg for Resource Technologies will overcome these limitations.
We use the SLcam® X-ray Color Camera - a novel pnCCD Pixel detector (264 x 264 = 69696 Pixel) combined with a polycapillary X-ray optic (Scharf et al., 2011) as the detector for the element specific X-ray radiation. This design allows us the simultaneous determination of the trace element distribution on a 12 * 12 mm2 area with a lateral
resolution of about 50 μm. First results of geometallurgical applications of this method are presented.

Keywords: PIXE, High-Speed PIXE
  • Lecture (Conference):
    21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Sandton, South Africa
Registration No. 20912

Electron Microprobe Analysis of REE in Eudialyte Group Minerals: Challenges and Solutions
Atanasova, P.; Krause, J.; Möckel, R.; Osbahr, I.; Gutzmer, J.
Abstract: Alkaline complexes containing eudialyte group minerals (EGM) comprise one of the most promising sources for future rare earth element (REE) supply. Complex mineral chemistry and crystal structure of EGM pose particular challenges for resource analytics and ore characterisation. A combination of qualitative scanning electron microscope (SEM)-based image analysis and quantitative analytical methods like electron microprobe (EPMA) is required. For this purpose polished thick sections are first mapped by the mineral liberation analyzer (MLA) to effectively identify the ore-bearing minerals and mineral associations. Backscattered electron images (BSE images) indicate varying BSE contrast within the EGM crystals. In order to determine the assumed elemental variations, element distribution maps of main (e.g., Zr, Si, Al) and minor (e.g., Ce, Y) elements are obtained by EPMA. These maps illustrate variable and complex zonation patterns within the EGM crystals. Based on the element distribution maps, quantitative analyses are then performed with a field emission electron microprobe JEOL JXA 8530F.
The accurate quantification of the chemical composition of EGM is complicated by both mineralogical and X-ray-specific challenges. These include: 1) structural and chemical variability of EGM composition (e.g., [1-3]); 2) mutual interferences of X-ray lines from major and trace elements, in particular REE elements [4]; 3) the diffusive volatility of light anions as F and Cl and cations such as K and Na; 4) particular instability of EGM under the electron beam.
A novel analytical approach has been developed to account for the above mentioned analytical challenges. Additionally, loss on ignition und differential scanning calorimetry data has been applied to constrain the content and composition of volatiles in the EGM structure. All correction for the overlapping of X-ray lines is processed offline. Preliminary results demonstrate that the parameters mentioned above need to be considered and carefully optimized to perform accurate quantitative analyses on the chemical composition of EGM with the electron microprobe.

Keywords: Electron Mikroprobe, EPMA, rare earth elements, eudialyte
  • Poster:
    EMAS 2014 - 11th EMAS Regional Workshop on Electron Probe Microanalysis of Materials Today - Practical Aspects, 22.-24.09.2014, Leoben, Austria
Registration No. 20910

Commissioning Results of the 2nd 3.5 cell SRF Gun for ELBE
Arnold, A.; Freitag, M.; Murcek, P.; Teichert, J.; Vennekate, H.; Xiang, R.; Kneisel, P.; Ciovati, G.; Turlington, L.
Abstract: As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation, it turned out that the specified performance has not been achieved. However, to demonstrate the full potential of this new type of electron source, a second and slightly modified SRF gun II was built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and first results of the new gun, which includes in particular the characterization of the most important RF properties as well as their comparison with previous vertical test results.
Keywords: superconducting, radio frequency, electron, injector, SRF gun
  • Poster:
    27th Linear Accelerator Conference, LINAC14, 31.08.-05.09.2014, Geneva, Switzerland
Registration No. 20908

Assessments of boundary conditions and requirements for Rare Earth Underground Mining due to presence of NORMs
Barakos, G.; Mischo, H.; Gutzmer, J.
Abstract: Rare earths contain NORMs, such as uranium, thorium and their progeny, like radium and radon. The varying concentrations of NORMs are quite often significant enough to result in occupational and environmental radiation exposures during the mining, milling and processing procedures of rare earths and compounds. Ventilation is the primary technique of controlling ambient concentrations of radon. Fresh air volume flow rates, the distribution of airflow within the mine and the radon emanation rate are primary factors affecting such concentrations. In this paper, it is attempted to determine the factors that may result in radiation risks and evaluate the boundary conditions that will contribute to the restriction or even elimination of radon progeny, with a goal to use the evaluations in order to build an overall assessment tool.
Keywords: Rare Earth Elements, NORMs, Radon, Thoron, Underground Mining, Occupational Safety
  • Contribution to proceedings:
    ERES 2014 - 1st International Conference on European Rare Earth Resources, 04.-07.09.2014, Milos Island, Greece
    ERES 2014 - 1st International Conference on European Rare Earth Resources, Imerovigli, Santorini GR‐84700: Heliotopos Conferences Ltd., 978‐960‐6746‐15‐4
Registration No. 20904

Simulation of aerosol particle deposition and resuspension in high temperature reactors
Lecrivain, G.; Hampel, U.
Abstract: In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase in the primary circuit of the high temperature reactor. Depending on the gas velocity, the solid aerosol particles can either attach to the wall surfaces or be re-entrained in the turbulent flow. Two numerical models developed for the prediction of particle attachment and detachment are presented.
  • Invited lecture (Conferences):
    Seminar / Commissariat à l’énergie atomique / Invited lecture, 20.06.2014, Saclay, France
Registration No. 20903

Simulation of aerosol particle deposition in a high temperature reactor
Lecrivain, G.; Hampel, U.; Hurtado, A.
Abstract: In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase in the primary circuit of the high temperature reactor. Depending on the gas velocity, the solid aerosol particles can either attach to the wall surfaces or be re-entrained in the turbulent flow. Two numerical models developed for the prediction of particle attachment and detachment are presented.
  • Contribution to proceedings:
    Workshop des CFD-Kompetenzverbunds / German CFD Network, 19.-20.03.2014, Garching, Germany
    Proceedings of the German CFD Network
Registration No. 20902
Pages: [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26] [27] [28] [29] [30] [31] [32] [33] [34] [35] [36] [37] [38] [39] [40] [41] [42] [43] [44] [45] [46] [47] [48] [49] [50] [51] [52] [53] [54] [55] [56] [57] [58] [59] [60] [61] [62] [63] [64] [65] [66] [67] [68] [69] [70] [71] [72] [73] [74] [75] [76] [77] [78] [79] [80] [81] [82] [83] [84] [85] [86] [87] [88] [89] [90] [91] [92] [93] [94] [95] [96] [97] [98] [99] [100] [101] [102] [103] [104] [105] [106] [107] [108] [109] [110] [111] [112] [113] [114] [115] [116] [117] [118] [119] [120] [121] [122] [123] [124] [125] [126] [127] [128] [129] [130] [131] [132] [133] [134] [135] [136] [137] [138] [139] [140] [141] [142] [143] [144] [145] [146] [147] [148] [149] [150] [151] [152] [153] [154] [155] [156] [157] [158] [159] [160] [161] [162] [163] [164] [165] [166] [167] [168] [169] [170] [171] [172] [173] [174] [175] [176] [177] [178] [179] [180] [181] [182] [183] [184] [185] [186] [187]