Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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27212 Publications
Applications of the atomic force microscope in flotation research
Babel, B.; Rudolph, M.ORC
Abstract: This abstract gives an overview of the applications of the Atomic Force Microscope (AFM) in flotation research. The AFM, which has a broad application in different disciplines, is a versatile tool to measure surface properties and particle-particle interactions. In the field of mineral processing the AFM can be utilized to gather information of mineral surfaces such as the surface roughness or particle-particle interactions related to separation processes like magnetic separation, triboelectric separation and flotation. In the context of flotation it is possible to measure the hydrophobic interaction between a colloidal probe (CP-AFM) and the mineral surface. One drawback of this technique is the missing link between the hydrophobicity and the chemical composition of the mineral surface, respectively the adsorbed layers. This limitation can be exceeded by the combined utilization of the AFM and Raman Spectroscopy named Tip-Enhanced Raman Spectroscopy (TERS). This surface sensitive technique enables the chemical analysis of thin films with nanometer resolution by the utilization of a plasmonic effect that occurs at the surfaces of noble metal nanoparticles. The aim is the detection of adsorbed flotation reagents on mineral surfaces. The combination of TERS and CP-AFM measurements enables the investigation of the adsorption of flotation reagents on mineral surfaces and their effect on hydrophobicity.

As outlined the application of the AFM in mineral processing can give a deeper understanding of occurring micro processes and thereby a better physical and chemical description of macro processes. Especially TERS offers a better understanding of the adsorption of flotation reagents.

The paper presents fundamental investigations of CP-AFM and TERS on actual mineral specimens (quartz, cassiterite, apatite, calcite, scheelite) which are prepared to achieve a surface roughness of less than 10 nm. The impact of collector and depressant adsorption on the measurement, i.e. hydrophobic interactions with CP-AFM and vibrational spectroscopy with TERS is shown.

Keywords: atomic force microscope, tip-enhanced Raman spectroscopy, flotation
  • Poster
    XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec city, Canada
Registration No. 24909 - Permalink

Understanding actinide reactivity at the water-mineral interface
Stumpf, T.
Abstract: The behaviour of radionuclides in the environment is determined by interfacial reactions such as adsorption, ion exchange and incorporation processes. In literature such processes are often described by operational solid-liquid distribution ratios (Rd values). Distribution ratios are defined as the ratio of the quantity of a radionuclide sorbed per solid mass and the equilibrium concentration of the radionuclide. They are macroscopic parameters which are strictly valid only for the mineral and solute combination in the experimental system. For reliable and trustworthy long-term predictions of radionuclide transport behaviour, interaction mechanisms and processes occurring at the solid-water interface, they need to be understood at the molecular level. This can only be achieved by the application of spectroscopic methods.
In the talk a multi-spectroscopic approach will be presented. We used a combination of microscopy, laser and X-ray based techniques to gain process understanding on a molecular level of the interaction of actinides with mineral surfaces. The derived data are used to improve surface complexation modelling. Therefore, the advanced spectroscopic techniques used in Dresden-Rossendorf are an important contribution to the long-term performance assessment of a nuclear waste disposal.

Keywords: radionuclides, nuclear waste disposal.
  • Invited lecture (Conferences)
    les Journées Nationales de Radiochimie et de Chimie Nucléaire (JNR) 2016, 08.-09.09.2016, Nice, Frankreich
  • Lecture (Conference)
    Frontiers in Environmental Radioactivity 2016, 06.-07.01.2016, London, United Kingdom
Registration No. 24902 - Permalink

Emission spectroscopy for the identification of rare earth elements using laser-induced photoluminescence
Fuchs, M. C.; Gloaguen, R.; Beyer, J.; Jakob, S.; Heitmann, J.
Abstract: We present rare earth element (REE) emission spectra stimulated by lasers with wavelength of 325 nm, 442 nm and 532 nm. Measured spectra represent REE standards in phosphates and fluorides, one set embedded in epoxy resin and one set in form of free-standing single grains. The comparison of emission features from the different specimen allows to evaluate, which emission peaks are robust and unequivocal for REE identification. Results showed that photoluminescence spectroscopy allows successful identification of characteristic emission peaks for Dy3+, Er3+, Eu3+, Gd3+, Nd3+, Sc3+, Sm3+, Tb3+, and Yb3+, when using laser stimulation at 325 nm. However, strong matrix emissions such as from epoxy resin may mask weaker luminescence emissions. In such cases, the adequate choice of longer stimulation wavelength is crucial to suppress the strong matrix emission without loosing the REE luminescence. Using laser stimulation at 442 nm and 532 nm shows promising results, but the optimal laser wavelength seems to be REE-specific and consequently, requires comprehensive analyses.
Keywords: emission spectroscopy, photoluminescence, rare earth elements, exploration, raw materials
  • Lecture (Conference)
    WHISPERS - 8th workshop on hyperspectral image and signal processing, 21.-24.08.2016, Los Angeles, USA
Registration No. 24898 - Permalink

Optimization of the Aeration System in Municipal Wastewater Treatment Plant
Mohseni, E.; Herrmann-Heber, R.; Reinecke, S.; Hampel, U.
Abstract: In Germany wastewater is treated in 10000 plants which use 4.400 GWh of energy per year. From this big figure, up to 70% is consumed in the biological treatment and the portion of only aeration of waste water in activated sludge tank is about 50% of the whole figure. Aeration is the essential part of the process since the microorganisms need to be provided by sufficient amount of oxygen to degrade ammonia. Aerators with flexible membranes located at the bottom of the aeration tank are currently state of the art for this process. However the process suffers from some limitations such as high pressure drop, insufficient mixing and underutilization of oxygen. These are mainly due to scarce knowledge about gas dispersion inside the tank.
Initial bubble size in gas dispersion is of a great importance since it determines the ascent and coalescence rate, macro mixing by turbulence, and oxygen transfer from the bubble to the fluid phase. The initial bubble size is drastically influenced by the type of aerator which is being used in the tank. The typical bubble size generated by flexible membrane aerators has been determined to be between 2-4 mm by Hasanen et al. (Hasanen, 2006). However, this is considerably higher than the optimal bubble size calculated by Motarjemi and Jameson (Motarjemi, 1978) who reported the range of 0.7-1.0 mm for the optimal value for the 95% oxygen transfer to water in 3-6 m tank depth.
A novel approach uses solid perforated stainless steel aerators with fine pores in micro scale for gas dispersion. In this work bubble formation of stainless steel aerators has been experimentally investigated with a high resolution optical measurement technique by means of videometry and the results are compared with membrane aerators. Preliminary results of the stainless steel membrane sparger showed a significant reduction in the bubble size up to 47 % and consequently an increase in bubble residence time in comparison with flexible membranes.
A comprehensive set of experiments have been conducted in which the bubble formation with respect to pore size, pore density, plate thickness, flow rate, membrane surface roughness, and bubble generation frequency have been investigated. Thanks to the state of the art manufacturing technique, very fine pores starting at 30 µm up to 200 µm have been processed which resulted in formation of bubbles in the range down to 1.4 mm diameter.
Current poster, presents the motivation of the project and the purposed approaches toward a solution and the initial results of the preliminary experiments done by means of videometry technique.

Keywords: Bubble Generation, Activated Sludge, Aeration, Biological Wastewater Treatment, Multiphase Flow
  • Poster
    11th HZDR PhD Seminar, 17.-19.10.2016, Oberwiesenthal, Germany
Registration No. 24895 - Permalink

Experimentelle Untersuchung zur Hydrodynamik der Partialoxidation von Isobutan in einem Mikroreaktor
Reichelt, C.
Abstract: Die hydrodynamischen Eigenschaften eines zweiphasigen Gemisches aus Isobutan und Stickstoff wurden in einem Mikroreaktor experimentell untersucht. Dazu wurden eine Hochgeschwindigkeitskamera und eine spezielle Bildanalysesoftware verwendet, mit der Isobutan Gas Strömungen in einer Glaskapillare analysiert und ausgewertet werden konnten. Anhand der erhaltenen Ergebnisse konnten Rückschlüsse auf die Bedingungen der Isobutanoxidation in jenem Reaktor gezogen werden. Ziel war es, den Einfluss der betrachteten Parameter (Eduktströme und Betriebsdruck) auf die Zwei-Phasen-Strömung zu analysieren und zu verstehen. Spezielle Strömungsregime können dabei entscheidende Auswirkungen auf den Stofftransport und somit auf reaktionstechnische Kenngrößen wie Umsatz, Selektivität oder Ausbeute haben. Regelmäßige Taylor-Strömungen zeichnen sich in Mikrokanälen durch besonders gute Stoff- und Wärmetransporteigenschaften aus. Aus diesem Grund wurden die Parameter so gewählt, dass sich dieses Strömungsregime ausbildet. Durch diese Arbeit konnten die Strömungsregime der meisten der bisher durchgeführten Oxidationsexperimente als unregelmäßige Taylor-Strömungen charakterisiert werden. Darüber hinaus konnten die Einflüsse der jeweiligen Versuchsbedingungen auf die charakteristischen Kennzahlen der Taylor-Strömung ermittelt werden. Die Arbeit bietet aufgrund ihrer Ergebnisse eine wichtige Grundlage für die Durchführung der partiellen Oxidation von Isobutan im Mikroreaktor.
Keywords: Isobutan, Zweiphasenprozess, Taylor Flow, Charakteristik
  • Study thesis
    Hochschule für Technik und Wirtschaft Dresden, 2016
    Mentor: Thomas WIllms
    34 Seiten
Registration No. 24893 - Permalink

In-situ spectroscopic identification of actinide(V/VI) sorption complexes at the mineral oxide water interface
Müller, K.ORC
Abstract: For the long-term safety assessment of nuclear waste repositories, neptunium and uranium are two of the most environmentally relevant components of nuclear waste to be considered. Hence, great attention is attracted to their geochemistry and migration behavior. Among the various geochemical processes, the migration of radioactive contaminants in the environment is strongly affected by molecular reactions in aqueous solution and at the solid-water interface, e.g. complexation with organic/inorganic ligands, sorption onto mineral phases, surface precipitation, and colloid formation. A detailed description of these interactions on a molecular level is required for a reliable modeling of the contaminants dissemination in the environment.
In the past decade, vibrational spectroscopy has been developed to a powerful tool for the study of dissolved complexes of heavy metal ions with a variety of inorganic and organic ligands and surface complexes on solid phases. In particular, a combined approach of in situ vibrational, time-resolved laser fluorescence and X-ray absorption spectroscopy potentially provides comprehensive molecular information. A survey of very recent spectroscopic results obtained from geochemical reactions of radionuclides, namely Np(V) and U(VI), is given.

Keywords: actinides, vibrational spectroscopy
  • Lecture (others)
    Institutskolloquium, 29.11.2016, Kyoto, Japan
Registration No. 24892 - Permalink

Colloidal particle at a fluidic interface: a direct numerical simulation
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.
Abstract: Froth flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The “Smooth Profile Method”, a numerical method originally developed at the University of Kyoto for the direct numerical simulation of colloidal particles in monophasic fluids, was here combined with a newly-defined binary fluid model. The change in the trajectory as the particle approaches the fluid–fluid interface, the collision process, and the sliding down the bubble surface were all reproduced and compared remarkably well with on-site microscale experiments.
  • Lecture (Conference)
    NetFlot: Network of Infrastructure (NOI) - Modelling the Flotation Process, 19.-21.10.2016, Krakau, Gliwice, Polkowice, and Wroclaw, Poland
Registration No. 24888 - Permalink

Far-Infrared Nonlinear Optics in Multilayer Epitaxial Graphene
Suess, R. J.; Winnerl, S.; Schneider, H.; Helm, M.; Berger, C.; de Heer, W. A.; Murphy, T. E.; Mittendorff, M.
Abstract: We report terahertz pump-probe experiments on multilayer graphene that measure both reflected and transmitted radiation. The data reveal complex reflection and transmission dynamics which calculations attribute to a transition from interband to intraband processes.
Keywords: graphene, pump-probe spectroscopy, refelection, transmission
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA
Registration No. 24881 - Permalink

Nonlinear Plasmonic THz Absorption in Graphene Ribbons
Mittendorff, M.; Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.
Abstract: We investigate the nonlinear plasmonic absorption in graphene ribbons by THz pump-probe spectroscopy. The optical nonlinearity is increased by more than one order of magnitude, which is in excellent agreement with theoretical calculations.
Keywords: graphene ribbons, plasmonics, nonlinear optics
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-10.06.2016, San Jose, USA
Registration No. 24880 - Permalink

Three-dimensional Induction Mapping of Magnetic Nanoscale Materials by Electron Holographic Tomography
Wolf, D.; Lubk, A.; Lichte, H.
Abstract: Off-axis electron holography (EH) is a powerful TEM technique that provides access to the 2D projections of both the electric potential, i.e., mainly the mean inner potential (MIP) contribution, and the components of the magnetic induction (B-field) that lie perpendicular to the electron beam path.
Currently, 2D magnetic induction maps may be obtained with a spatial resolution of a few nanometer [1,2] and a sensitivity of a few millitesla [2]. Frequently, however, nanomagnetic applications, such as spin valves or magnetic nanowires require a characterization of the 3D magnetic induction distribution.
In the following, we therefore elaborate on how electron holography is combined with electron tomography to electron holographic tomography (EHT) [1,3] in order to retrieve the 3D distribution of the magnetic induction.
As shown in Fig. 1, the tomographic reconstruction of one B-field component starts with acquiring a tilt series of electron holograms that is subsequently reconstructed to obtain a tilt series of phase images. In order to collect data for the crucial separation of electric and magnetic phase shifts, either a tilt series over 360° (Fig. 1), or two tilt series, one before and one after reversing the direction of magnetization in the specimen (e.g., using the TEM objective lens or flipping the sample up-side down in the holder), have to be acquired. Before separation of electric/magnetic phase shifts by computing half of the sum/difference of corresponding image pairs, relative displacements, rotations, and direction dependent magnification changes between the two phase images are corrected. Also, the alignment of the whole tilt series, i.e., an accurate tilt axis determination and subpixel displacements correction, is of crucial importance. Finally, from the aligned tilt series, tomograms of both the electric potential and the B-field component parallel to the tilt axis are reconstructed with tomographic reconstruction algorithms.
Fig. 2 shows two recent EHT studies revealing the B-field within a Co nanowire (NW) [4] and a Co2FeGa Heusler alloy NW [5] both with spatial resolution higher than 10 nm. The reconstructions of the dominant axial component of the magnetic induction exhibit two interesting features for each case: At the Co NW, a small inversion domain at the apex was observed, whereas at the Co2FeGa NW, a
magnetic dead layer of 10 nm width was found. These results were achieved by means of dedicated TEM sample holders for acquisition, in combination with advanced in-house developed software packages for acquisition, alignment and tomographic reconstruction. The powerful approach presented here is widely applicable to a broad range of 3D magnetic nanostructures and may trigger the progress of novel spintronic nonplanar nanodevices. In a next step the reconstruction of all B-field components is envisaged.
References:
[1] P A Midgley and R E Dunin-Borkowski, Nat. Mater. 8 (2009) p. 271.
[2] M Körner, F Röder, K Lenz, M Fritzsche, J Lindner, H Lichte and J Fassbender,
Small 10 (2014) p. 5161.
[3] D Wolf, A Lubk, F Röder and H Lichte, Current Opinion in Solid State and Materials Science 17
(2013) p. 126.
[4] D Wolf et al., Chem. Mater. 27 (2015) p. 6771.

Keywords: magnetic induction, 3D reconstruction, nanostructure, electron holography, electron tomography

Downloads:

Registration No. 24879 - Permalink

Unusual Coulomb scattering processes in graphene
Winnerl, S.
Abstract: Graphene, the two-dimensional allotrope of carbon, is characterized by a gapless linear band structure. This unique band structure is directly related to some unusual phenomena regarding the ultrafast Coulomb dynamics in the material. The understanding of this dynamics is of vital interest, both from a fundamental as well as from an application oriented point of view. The elastic Coulomb scattering is the main mechanism for thermalization of a non-equilibrium carrier distribution.
We investigate the carrier dynamics in a regime, where scattering via optical phonons is strongly suppressed. To this end, time resolved spectroscopy was performed with radiation of photon energies around 75 meV, which is smaller than the optical phonon energy (~200 meV). In polarization resolved experiments using co- and cross-polarized linearly polarized pump and probe beams, respectively, the Coulomb scattering dynamics is investigated. We find a two-fold nature of this process, namely very fast (fs timescale) collinear Coulomb scattering but surprisingly slow (ps-timescale) non-collinear scattering [1].
In the presence of a magnetic field, the linear band structure of graphene splits up into a series of non-equidistant Landau levels. Studying the transitions between the lowest Landau levels in pump-probe and four-wave mixing experiments, we find evidence for strong Auger scattering [2, 3].

[1] J. C. König-Otto, M. Mittendorff, T. Winzer, F. Kadi, E. Malic, A. Knorr, C. Berger, W. A. de Heer, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl, Phys. Rev. Lett. 117, 087401 (2016).

[2] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C. Berger, W. A. de Heer, H. Schneider, M. Helm, and S. Winnerl, Nature Phys. 11, 75 (2015).

[3] J. C. König-Otto, Y. Wang, A. Belyanin, C. Berger, W. A. de Heer, M. Orlita, A. Pashkin, H. Schneider, M. Helm, and S. Winnerl (submitted).

Keywords: graphene, carrier dynamics, Coulomb scattering, Auger scattering, ultrafast spectroscopy
  • Lecture (others)
    MML Workshop at DESY 2016, 14.-16.12.2016, Hamburg, Deutschland
Registration No. 24878 - Permalink

Plasmonic superlens based on doped GaAs
Winnerl, S.; Fehrenbacher, M.; Kuschewski, F.; von Ribbeck, H.-G.; Döring, J.; Kehr, S.; Eng, L. M.; Schneider, H.; Helm, M.
Abstract: Infrared and THz free-electron lasers are interesting sources for near-field investigations as they are tunable in a range where suitable tabletop sources exist only at particular frequencies. The free-electron laser FELBE at Dresden covers the frequency range from 1.3–75 THz with narrowband (~ 1 % spectral width) radiation. We briefly show for the low-frequency region of FELBE (1.3–75 THz) that scattering near-field microscopy can be performed with a constant spatial resolution of 50 nm, which is determined by the diameter of the scattering tip. For the longest wavelength, this corresponds to /4600 [1]. Mainly, we present results on a superlens, which consists of a doped GaAs layer sandwiched between two intrinsic GaAs layers. Superlensing is expected when the condition 〖Re(ε〗_GaAs^doped)=〖-Re(ε〗_GaAs^intrinsic) is met in the spectral vicinity of the plasmonic resonance. Here, the Drude response in the doped layer induces resonant enhancement of evanescent waves accompanied by a significantly improved spatial resolution at radiation wavelengths around 15 THz (see Fig. 1) [2]. The resonance frequency is adjustable by changing the doping concentration. Compared to superlenses based on phononic resonances the plasmonic superlance features a somewhat broader range of the resonant response. Such a tunable superlense consisting of a single semiconductor material is
a versatile device to enhance signal and spatial resolution in near-field imaging of buried structures.

Keywords: near-field microscopy, superlens, plasmonics, free-electron laser
  • Invited lecture (Conferences)
    Samller and Faster: Infrared and Terahertz Spectral-Imaging at the Nanoscale with Synchrotron and Free Electron Laser Sources (SAFE), 01.-02.12.2016, Trieste, Italy
Registration No. 24877 - Permalink

Carrier dynamics in Graphene
Winnerl, S.
Abstract: We review our results ion the carrier dynamics in graphene and present an applacitation example, namely a high-speed ultra-broadband detector.
Keywords: graphene, carrier dynamics, detector
  • Lecture (others)
    4. Workshop of SPP 1459 "Graphene", 25.-29.09.2016, Chemnitz, Germany
Registration No. 24876 - Permalink

Population and polarization dynamics in Landau-quantized graphene - evidence for strong Auger scattering
Winnerl, S.; Mittendorff, M.; König-Otto, J. C.; Wendler, F.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.
Abstract: The linear band structure of graphene results in a non-equidistant spectrum of Landau levels (LLs). While transport phenomena have been widely explored after the discovery of graphene in 2004, the ultrafast optical properties of Landau-quantized graphene have been investigated only recently. Predictions of very strong nonlinearities [1], carrier multiplication [2] and Landau-level gain [3] make the system very interesting both from a fundamental and an application-oriented point of view.
Here we present experiments complemented by microscopic theory on the population and polarization dynamics in the subsystem of Landau levels -1, 0 and 1. To this end, multilayer epitaxial graphene in a magnetic field of ~4 T is excited resonantly by ps-pulses of mid-infrared radiation (photon energy 75 meV). Applying circularly polarized radiation allows one to pump and probe the energetically degenerate LL-1 → LL0 and LL0 → LL1 transitions selectively. In pump-probe experiments using all four combinations of pumping and probing with right and left circularly polarized radiation, a surprising change in sign of the measured signal (i.e. induced transmission instead of induced absorption) is observed in one of these configurations. Our analysis shows that this can be associated with a depletion of the LL0 level, even though this level is optically pumped at the same time. Very efficient Auger scattering is responsible for this depletion [4].
Furthermore, we show a very recent study of the polarization dynamics in Landau quantized graphene by means of degenerate four-wave mixing (FWM) spectroscopy. It is carried out on the same subsystem of Landau levels and utilizes similar values of magnetic field and photon energy as in the pump-probe experiments. However, the two incoming beams are linearly polarized in the FWM experiment. A rapid dephasing of the microscopic polarization on a timescale shorter than the pulse duration (4 ps) is observed and attributed to Auger scattering. The FWM signals show the expected dependences on the power of two incoming beams and on the magnetic field.
The results, both for the population as well as the polarization dynamics, depend crucially on the doping level of the sample. The graphene used in the experiments is almost intrinsic, corresponding to a full LL-1 and empty LL1. The occupation of LL0 of about 0.64 is slightly larger than the half-filling corresponding to intrinsic graphene. We will evaluate the implications of this symmetry breaking on Auger scattering and on the FWM signals. Finally, the implications of our results on the feasibility of a graphene based Landau-level laser, which is tunable by the magnetic field, will be discussed.
The sample was grown by C. Berger and W.A. de Heer. We acknowledge valuable discussions with M. Orlita, M. Potemski, Y. Wang, and A. Belyanin. We are grateful to P. Michel and the FELBE team for their dedicated support.
References
[1] X. Yao and A. Belyanin, Phys. Rev. Lett. 108, 255503 (2012).
[2] F. Wendler, A. Knorr, and E. Malic, Nature Commun. 5, 3703 (2014).
[3] F. Wendler and E. Malic, Sci. Rep. 5, 12646 (2015).
[4] M. Mittendorff, F. Wendler, E. Malic, A. Knorr, M. Orlita, M. Potemski, C.

Keywords: Carrier, dynamics, graphene, Landau quantization, Auger scattering, polarization dynamics, four-wave mixing
  • Invited lecture (Conferences)
    22nd International Conference on High Magnetic Fields in Semiconductor Physics (HMF-22), 24.-29.07.2016, Sapporo, Japan
Registration No. 24875 - Permalink

Long-lived Anisotropy of Photoexcited Graphene Electrons
Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.
Abstract: In polarization resolved pump-probe experiments complemented by microscopic modeling we show that an anisotropic carrier distribution persists on ps timescales. In particular, we evaluate the role of non-collinear Coulomb scattering.
Keywords: Carrier dynamics, graphene, ultrafast spectroscopy, Coulomb scattering
  • Lecture (Conference)
    Conference on Lasers and Electro-Optics (CLEO) 2016, 05.-11.06.2016, San Jose, USA
Registration No. 24873 - Permalink

Surprising Coulomb-scattering effects in graphene revealed by polarization-resolved THz spectroscopy
Winnerl, S.; König-Otto, J. C.; Mittendorff, M.; Pashkin, A.; Schneider, H.; Helm, M.; Winzer, T.; Wendler, F.; Malic, E.; Knorr, A.
Abstract: We present experiments complemented by microscopic theory that highlight surprising Coulomb scattering effects. In particular, we find that non-collinear Coulomb scattering is compa-rably slow, namely on a scale of few ps. For the case of Landau-quantized graphene we find evidence for strong Auger scattering that can deplete a Landau level that is optically pumped at the same time. Both Coulomb effects are relevant for graphene based THz devices.
Keywords: graphene, carrier dynamcis, Coulomb scattering, Auger scattering, Landau quantization
  • Invited lecture (Conferences)
    5th EOS Topical Meeting on Terahertz Science & Technology, 08.-11.05.2016, Pecs, Hungary
Registration No. 24870 - Permalink

Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible
Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.
Abstract: By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: high-speed detector, broadband detector, graphene
  • Lecture (Conference)
    7th internationale Workshop Terahertz Technology and Applications, 15.-16.03.2016, Kaiserslautern, Germany
Registration No. 24869 - Permalink

Radio-U(H)PLC - the search on the optimal flow cell for the gamma-detector
Kniess, T.; Meister, S.; Fischer, S.; Steinbach, J.
Abstract: kein Abstract verfügbar
  • Poster
    18th European Symposium on Radiopharmacy and Radiopharmaceuticals, 07.-10.04.2016, Salzburg, Österreich
Registration No. 24868 - Permalink

A fluorine-18 radiolabelled celecoxib-based PET probe for Cyclooxygenase-2 monitoring - COX-2 affinity, radiosynthesis and in vitro studies
Kniess, T.; Bechmann, N.; Steinbach, J.; Pietzsch, J.
Abstract: kein Abstract verfügbar
  • Abstract in refereed journal
    European Journal of Nuclear Medicine and Molecular Imaging 43(2016)S1, EP844
    Button zum Volltext
  • Poster
    Annual Congress of the European Association of Nuclear Medicine, EANM, 15.-19.10.2016, Barcelona, Spanien
Registration No. 24866 - Permalink

Radiosynthesis of O-3-(2-[18F]fluoroethyl)-L-DOPA ([18F]OFED) – a new fluorine-18 labeled phenylalanine derivative.
Kniess, T.; Schröder, S.; Hoepping, A.; Zessin, J.; Fuechtner, F.; Bergmann, R.; Steinbach, J.
Abstract: kein Abstract verfügbar
  • Abstract in refereed journal
    Journal of Nuclear Medicine 57(2016)S2, 1039
    Button zum Volltext
  • Poster
    Annual Meeting of the Society of Nuclear Medicine and Molecular Imaging, SNMMI, 11.-15.06.2016, San Diego, USA
Registration No. 24862 - Permalink

Automatisierte Radiosynthese von O-2[18F]Fluorethyl-L-DOPA ([18F]OFED) – eine neue 18F-markierte Aminosäure für die Tumor-Diagnostik
Kniess, T.; Schröder, S.; Hoepping, A.; Füchtner, F.; Zessin, J.; Bergmann, R.; Steinbach, J.
Abstract: kein Abstract vorhanden
  • Poster
    Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin 2016, 20.-23.04.2016, Dresden, Deutschland
  • Abstract in refereed journal
    Nuklearmedizin 55(2016)2, P51
    Button zum Volltext
Registration No. 24860 - Permalink

Design, synthesis, radiosynthesis, and biological evaluation of radiofluorinated quinoline derivatives for PET imaging of PDE5A in brain
Liu, J.; Wenzel, B.; Dukic-Stefanovic, S.; Teodoro, R.; Ludwig, F.-A.; Deuther-Conrad, W.; Schröder, S.; Chezal, J.-M.; Moreau, E.; Brust, P.; Maisonial-Besset, A.
Abstract: kein Abstract vorhanden
  • Poster
    EFMC – International Symposium on Medicinal Chemistry 2016, 28.08.2016, Manchester, UK
Registration No. 24857 - Permalink

Local etching of a SiOx layer on Si(111) by Ga droplets and its influence on GaAs nanowire growth
Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.
Abstract: GaAs nanowires (NWs) can be grown epitaxially on Si(111) substrates in the vapour-liquid-solid mode. Typically, Au is used as catalyst, but affects the NW and substrate properties due to contamination. Thus, the self-catalyzed mode appears to be advantageous. The NW growth is initialized by the formation of Ga droplets on the substrate surface, which is normally covered by a thin SiOx layer. The yield of vertical NWs depends on the thickness and the nature of the SiOx, pointing out the complex interaction of the liquid Ga with the SiOx. This work investigates the local etching of a native SiOx on Si(111) by liquid Ga droplets, a mechanism, which is thought to precede the NW nucleation. The droplet formation, the etching process, and their effect on the NW growth were studied as a function of the substrate temperature and the etching time using molecular beam epitaxy. In contrast to previous studies, the oxide etching is distinguished from the subsequent NW nucleation by inserting a thermal annealing step, during which the Ga droplets are evaporated completely from the surface. Finally, the yield of vertical NWs and the NW number density can be controlled just by choosing the appropriate conditions for the oxide etching, independent of those used for the subsequent NW growth.
  • Poster
    DPG Spring Meeting, 06.03.2016, Regensburg, Germany
Registration No. 24855 - Permalink

The effect of deposition processing on structural and luminescent properties of a-SiOC: H thin films fabricated by RF-magnetron sputtering
Vasin, A. V.; Rusavsky, A. V.; Kysil, D. V.; Prucnal, S.; Piryatinsky, Y.; Starik, S. P.; Nasieka, I.; Strelchuk, V. V.; Lysenko, V. S.; Nazarov, A. N.
Abstract: Amorphous silicon oxicarbide thin films (a-SiOC(:H)) were deposited by RF-magnetron sputtering using Si or SiC target in Ar/CH4/O2 flow. Interatomic bonding and light emission properties were analyzed by FTIR in transmission and attenuation total reflection (ATR) mode, Raman scattering and photoluminescence spectroscopy. Comparison of the results obtained by FTIR and ATR allows us to suggest that structural properties of the near-surface region and the bulk of the films are significantly different. The surface layer contains a significant fraction of polymer-like SiOC structural components in the form of Si-O-Si/Si-O-C chains and cages, while bulk of the film is represented by inorganic amorphous SiOx network with amorphous carbon precipitates. Samples with the high fraction of carbon precipitates exhibit white luminescence at room temperature. The origin of strong photoluminescence is discussed.
Keywords: Amorphous silicon oxicarbide thin films; ATR; FTIR; Photoluminescence Registration No. 24853 - Permalink

Untersuchungen zur Partialoxidation von Isobutan in einem Mikroreaktor unter überkritischen Bedingungen.
Huiras, J.
Abstract: Die partielle Oxidation von Isobutan durch Sauerstoff in einem Mikroreaktor wurde im überkritischem Zustand zwischen 135 °C und 145 °C unter Verwendung von di-t-butyl peroxide (DTBP) als Initiator untersucht. Dabei wurden das Verhältnis zwischen Isobutan und Sauerstoff, die Verweilzeit, der Druck, die Initiatorkonzentration und die Temperatur variiert. Ziel war es, die Effizienz des Prozesses durch eine Erhöhung der Selektivität des Produkts t-Butyl hydroperoxide (TBHP) und des Umsatzes zu verbessern. Es war insbesondere zu überprüfen, ob sich der Prozess unter diesen Bedingungen durch die Aufhebung von Stofftransportwiderständen gegenüber dem Zweiphasenprozess bei niedrigeren Temperaturen optimieren lässt. Die Reaktionsprodukte TBHP, Azeton, t-butanol und DTBP wurden mittels GC\MS analysiert. Im Rahmen der Arbeit gelang es die höchsten bisher mit einem Mikroreaktor erzielten Umsätze für die Isobutanoxidation zu erzielen. Jedoch gingen die Umsätze nicht wesentlich über die Umsätze hinaus, die aufgrund des zu erwartenden Temperatureffekts bei der Nutzung von überkritischen Bedingungen zu erwarten waren. Auch war die Umsatzerhöhung nur auf Kosten der Selektivität des TBHP zu erzielen. Die Arbeit bietet jedoch aufgrund Ihrer Ergebnisse eine wichtige Grundlage für weitere Untersuchungen.
Keywords: Isobutanoxidation, überkritischer Prozess, Effizienzoptimierung, t-Butylhydroperoxid, Mikroreaktor
  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    63 Seiten
Registration No. 24852 - Permalink

Time-Resolved Studies of the Light-Induced Insulator-Metal Transition in NbO2 and VO2 Thin Films
Beebe, M.; Klopf, J. M.; Wang, Y.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Lukaszew, R. A.
Abstract: While vanadium dioxide (VO2) is one of the most extensively studied highly correlated materials, there are intriguing similarities and differences worth exploring in another highly correlated oxide, niobium dioxide (NbO2). Both materials exhibit a thermally-induced first-order insulator-metal transition at a material-dependent critical temperature, which is considerably higher in NbO2 than in VO2 – approximately 1080 K and 340 K in bulk, respectively. This transition, evidenced by up to 6 orders of magnitude change in DC and optical conductivities, can also be induced in VO2 via photo-doping on a sub-picosecond timescale. Here, we present the first ultrafast pump-probe studies on the optically-induced transition of NbO2 thin films and the comparison with similar VO2 films. It is observed that NbO2 films transition faster and exhibit significantly faster recovery time than VO2 films of similar thickness and microstructure, showcasing that NbO2 is a promising material for next generation high-speed optoelectronic devices.
Keywords: (240.0310) Thin films; (310.6860) Thin films, optical properties; (310.6845) Thin film devices and applications; (320.7100) Ultrafast measurements; (320.7130) Ultrafast processes in condensed matter, including semiconductors. Registration No. 24851 - Permalink

The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates
Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.
Abstract: We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.
Keywords: Nanowire, Ga droplets, oxide etching, nanoholes, GaAs, Si substrate
  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy, 04.09.2016, Montpellier, France
Registration No. 24850 - Permalink

Optimierung und Validierung der GC/MS-Methode zur Bestimmung der Reaktionsprodukte der Partialoxidation von Isobutan mit Sauerstoff im Mikroreaktor.
Liu, W.
Abstract: Die partielle Oxidation von Isobutan, t-Butyl Hydroperoxid (TBHP) wurde zum ersten Mal als ein Zwei-Phasen-Prozess in einer Kapillare als Mikro Reaktor durchgeführt und analytisch untersucht. Um detaillierte Informationen über Produkte, Ausbeute, Selektivität und Reaktion Wege zu erhalten, mussten die Produkte mittels GC-MS analysiert werden. Zur Trennung der flüssigen Produkte wurde eine GC-MS Methode erstellt, optimiert und validiert, die eine Rxi-5ms-Säule und einen PTV-Injek-tors verwendet. Im Rahmen der Validierung wurden der Konzentrationsfehler wie auch der Mess¬fehler des MS-Signals aus sämtlichen Kalibrierschritten ermittelt sowie die entsprechenden analytischen Normen (z.B. DIN 38402) für die Kalibrierung berücksichtigt. Außerdem wurden statistische Tests auf Trends (nach Neumann), Ausreißer (nach Dixon), Normalverteilung (nach David) etc. durchgeführt. Die flüssigen Produkte wurden mittels MS identifiziert: Als Hauptprodukte traten TBHP, di-t-Butyl-Peroxid (DTBP), t-Butanol (TBA) und Propanone auf. Für die Zielprodukte TBHP und DTBP wurden Korrelationkoeffiuienten von r2 > 0,999, für TBA und Azeton r2 > 0,995 erzielt. Daneben traten Nebenprodukte wie z.B. Methanal, Methanol, Isopropanol, Isobutanol und Isobutanal auf, von denn alle bis auf Methanol und Methanal ebenfalls kalibriert wurden.
Keywords: TBHP, DTBP, Vslidierung, isobutanoxidation
  • Study thesis
    TU-Dresden, 2016
    Mentor: Thomas Willms
    68 Seiten
Registration No. 24849 - Permalink

Fluid dynamics in novel sandwich packings for absorption and distillation
Sohr, J.; Schubert, M.; Hampel, U.
Abstract: Poster zum EMR-Meeting am 21.09.2016 am HZDR
  • Poster
    EMR-Meeting, 21.09.2016, Dresden, Deutschland
Registration No. 24845 - Permalink

X-Ray Photoelectron Study of Ion Implanted Tetrahedral Carbon
Berova, M.; Sandulov, M.; Tsvetkova, T.; Avramova, I.; Boettger, I.; Bischoff, L.
Abstract: Samples of thin film (d~40nm) tetrahedral amorphous carbon (ta-C), deposited by filtered cathodic vacuum arc (FCVA), have been implanted with N+ and Ga+ at ion energy E = 20 keV and ion fluences D = 3.1014÷3.1015 cm-2. This results in optical properties modification, best manifested by a significant shift of the optical absorption edge to lower photon energies, which is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitization, as confirmed by X-ray photo-electron spectroscopy (XPS) measurements. The nonimplanted films show the expected variety of carbon-carbon chemical bonds: three- and fourfold coordinated carbon, while the X-ray results show that ion implantation leads to the introduction of additional disorder in the films. The X-ray photoelectron spectra of the implanted films show that, in addition to the already mentioned changes, the ion bombardment results in an increase of the threefold coordinated as compared to the fourfold coordinated carbon bonds, i.e. increased graphitization of the carbon content in the films. These structural modifications, due to the ion implantation, are the reasons for the observed changes in the optical properties of the films, which could be made use of in the area of high-density optical data storage using focused Ga+ ion beams.
Keywords: tetrahedral amorphous carbon; focused ion beams; optical data storage Registration No. 24844 - Permalink

Synthese neuer Imidazol-Derivate für die Entwicklung eines 18F-PET-Radioliganden zur Bildgebung des Cannabinoid Rezeptors 2 im Gehirn
Hausmann, K.
Abstract: Es ist kein Abstract vorhanden.
  • Master thesis
    Universität Leipzig, 2016
    Mentor: Dr. R.-P. Moldovan
    71 Seiten
Registration No. 24841 - Permalink

Preliminary Studies on the Partial Oxidation of Isobutane with Oxygen in Multiphase Flows.
Lu, X.
Abstract: Oxidation of hydrocarbon is an industrially important reaction. Many valuable chemicals are synthesized by the oxidation of relatively cheap raw materials derived from petroleum. The oxidation of isobutane is one of the most important oxidation oxidation processes. For example, isobutane oxidation can be conducted as the preoxidation in oxirane process to produce propylene oxide and tert.-butanol, in which propylene oxide and TBA are important industrial raw materials and widely used in the syntheses of pharmaceuticals, agrochemicals and other fine chemicals (Qi et al., 2014).
In more recent times, there is more and more interest of researchers in the application of microreactors in chemical engineering because of the opportunities of microreactors in chemical process development and intensification, such as excellent heat and mass transfer (Kashid et al., 2014). In this thesis, the oxidation of isobutane in two-phase flow is investigated in a microreactor (100 m long, 1mm ID). The experiments were carried out under different conditions. The start-up behavior of the oxidation of isobutane has been investigated and discussed. In addition, the effect of temperature, pressure, residence time, oxygen-isobutene ratio, the nitrogen dilution and initiator concentration on the performance of isobutane has also been preliminary investigated and discussed. Furthermore, the rate constant of isobutene oxidation has been calculated for 130 °C.

Keywords: microreactor, isobutane oxidation, two phase flow
  • Diploma thesis
    TU-Dresden, 2016
    Mentor: Thomas WIllms
    89 Seiten
Registration No. 24839 - Permalink

Partikelentstehung und -transport im Reaktorwasser von DWR nach Kühlmittelverluststörfällen (KMV) - Untersuchungen im Labormaßstab
Harm, U.; Kryk, H.; Hampel, U.; Seliger, A.; Renger, S.; Kästner, W.
Abstract: Im Rahmen der nuklearen Sicherheitsforschung des Bundesministeriums für Wirtschaft und Energie (BMWi) erfolgten an der Hochschule Zittau/Görlitz (HSZG) in Kooperation mit der Technischen Universität Dresden (TUD) und dem Helmholtz-Zentrum Dresden-Rossendorf (HZDR) experimentelle und methodische Untersuchungen für die systematische Klärung physiko-chemischer Mechanismen im Kühlmittel und deren Auswirkungen auf thermo-fluiddynamische Prozesse im Reaktorkern, welche während des Sumpfumwälzbetriebes als Langzeitnachkühlung nach Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren (DWR) auftreten können. Durch Korrosionsprozesse an feuerverzinkten Installationen im Sicherheitsbehälter (SHB) von DWR wird Zink in ionischer Form im borierten Kühlwasser gelöst. Die freigesetzten Zink-Ionen werden aus dem Reservoir des Nachkühlmittels im SHB über die Not- und Nachkühlsysteme bis in den Reaktorkern gefördert. Im Reaktor wird das eingespeiste Kühlmittel (KM) aufgeheizt.
Im Fokus generischer Experimente standen Untersuchungen zum Verhalten derart zusam-mengesetzter Fluide unter Berücksichtigung von Temperaturunterschieden zwischen dem Kühlmittelreservoir im SHB und dem Reaktorwasser an den Brennstäben im Reaktorkern. Diese generischen Untersuchungen erfolgten an elektrisch beheizten Stabkonfigurationen, welche die durch Nachzerfallsleistung beheizten Brennstäbe im Kern von DWR nachbildeten. Bei der Aufheizung des zinkhaltigen KM innerhalb solcher Konfigurationen wurden Trübungen durch Kolloidbildung beobachtet, gefolgt von Ausscheidungen partikelförmiger, fester Korrosionsprodukte in Form von Zinkboraten. Diese erschienen in Abhängigkeit von der umgebenden KM- bzw. Staboberflächentemperatur als leicht mobilisierbare, flockenartige Dispersphase oder wiesen schichtenbildenden Charakter auf.
Die temperaturabhängigen Umwandlungen von gelösten Zink-Ionen in feststoffartige Zinkborate bewirkten sowohl Ablagerungen an den Heizstäben als auch an den Abstandshaltern (AH) und führten zu erhöhtem Differenzdruckaufbau über die AH sowie Strömungsumverteilungen in der Stabkonfiguration. In Folge dieser Ablagerungen wurden Änderungen des Wärmetransports vom beheizten Stab ans Fluid nachgewiesen, die eine Aufheizung der Heizstäbe bewirkten und damit sicherheitsrelevanten Charakter hinsichtlich der Nachwärmeabfuhr tragen. Aktuell wird dieses generisch ermittelte Verhalten des Reaktorwassers hinsichtlich der Übertragbarkeit auf sicherheitsrelevante Fragestellungen realer DWR mit Bezug auf anzunehmende Leckgrößen und Nachkühlbedingungen und den daraus resultierenden thermohydraulischen Randbedingungen im Sicherheitsbehälter und im Reaktorkern untersucht. Hierfür werden durch Störfallanalysen die Zustände und Bedingungen abgrenzend ermittelt, bei denen eine Gefährdung der Kernkühlung aus Sicht vorhandener Erkenntnisse zu den physiko-chemischen Effekten eintreten könnte. Wesentliche Untersuchungsschwerpunkte bilden die im SHB von DWR auftretenden chemischen und thermodynamischen Einflüsse auf die Zinkfreisetzung und das Ausfällungs- und Ablagerungsverhalten der Korrosionsprodukte an Heißstellen im Reaktorkern.
Die Untersuchungsergebnisse finden u.a. für die Parametrierung von Simulationscodes sowie in alternativen Modellansätzen Verwendung und dienen der sicherheitstechnischen Einschätzung des DWR-Reaktorverhaltens für verschiedene KMV-Störfallszenarien. Die quantitative Analyse der experimentellen Daten zum zeitlichen Ablauf des Quelle-Senke-Mechanismus der Zinkkorrosion und der Umwandlung des gelösten Zinks in feste Produkte unter realen Störfallbedingungen stellt auf Grund der Komplexität und der gegebenen Rückwirkungen eine Herausforderung dar.
Die Vorhaben werden mit Mitteln des Bundesministeriums für Wirtschaft und Energie (BMWi) unter den Förderkennzeichen 150 1491 und 150 1496 gefördert und fachlich von einer Monitoring Group begleitet, welche sich aus Repräsentanten der Forschungsbetreuung des Projektträgers, Gutachtern, Herstellern und Anlagenbetreibern zusammensetzt.

Keywords: Nuclear energy; Loss of coolant accident; corrosion; zinc release; experiments
  • Contribution to proceedings
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 22.-23.09.2016, Zittau, Deutschland
    Proceedings des Zittauer Kraftwerkschemischen Kolloquiums
  • Lecture (Conference)
    Wasser im Kraftwerk und in der Energietechnik, Zittauer Kraftwerkschemisches Kolloquium, 23.09.2016, Zittau, Deutschland
Registration No. 24838 - Permalink

Direct numerical simulations of particle attachment to solids and deformable surfaces
Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.
Abstract: The present talk deals with the transport and the deposition of micron particles to solid wall surfaces and fluid-fluid interfaces. Various particle-interface models are presented and tested with direct numerical flow simulations. The various micro processes observed during the particle attachment and particle detachment are well captured. The results compare well with those experimentally obtained on-site.
  • Lecture (others)
    Institute seminar, 14.12.2016, Karlsruhe, Germany
Registration No. 24823 - Permalink

Optical components in harsh space environment
Pelizzo, M. G.; Corso, A. J.; Tessarolo, E.; Zuppella, P.; Böttger, R.; Hübner, R.; Della Corte, V.; Palumbo, P.; Taglioni, G.; Preti, G.; Foggetta, L.; Valente, P.; Rancoita, P.; Martucci, A.; Napolitani, E.
Abstract: Space exploration is linked to the development of increasingly innovative instrumentation, able to withstand the operation environment, rich in ion particles and characterized by high temperatures. Future space missions such as JUICE and SOLAR ORBITER will operate in a very harsh and extreme environment-. Electrons and ions are considered among the causes of potential damage of the optical instrumentation and components. Development of hard coatings capable to preserve their optical properties is pivotal. Different coating materials have been exposed to ion irradiation in particle accelerators. Change in optical performances has been observed in the extreme ultraviolet and visible spectral region and structural properties have been analyzed by different techniques. The knowledge of the damage mechanisms and thresholds allows the selection of more promising candidate materials to realize the optical components for the new frontiers space missions. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Keywords: Optical components ; Optical properties ; Particle accelerators ; Particles ; Coating ; Electrons ; Extreme ultraviolet ; Hard coatings ; Ions Registration No. 24821 - Permalink

Mechanical properties and current-carrying capacity of Al reinforced with graphene/BN nanoribbons: a computational study
Kvashnin, D. G.; Ghorbani-Asl, M.; Shtansky, D. V.; Golberg, D.; Krasheninnikov, A. V.ORC; Sorokin, P. B.
Abstract: Record high values of Young’s modulus and tensile strength of graphene and BN nanoribbons as well as their chemically active edges make them promising candidates for serving as fillers in metal-based com- posite materials. Herein, using ab initio and analytical potential calculations we carry out a systematic study of the mechanical properties of nanocomposites constructed by reinforcing an Al matrix with BN and graphene nanoribbons. We consider a simple case of uniform distribution of nanoribbons in an Al matrix under the assumption that such configuration will lead to the maximum enhancement of mechanical characteristics. We estimate the bonding energy and the interfacial critical shear stress at the ribbon/metal interface as functions of ribbon width and show that the introduction of nanoribbons into the metal leads to a substantial increase in the mechanical characteristics of the composite material, as strong covalent bonding between the ribbon edges and Al matrix provides efficient load transfer from the metal to the ribbons. Using the obtained data, we apply the rule of mixtures in order to analytically assess the relationship between the composite strength and concentration of nanoribbons. Finally, we study carbon chains, which can be referred to as the ultimately narrow ribbons, and find that they are not the best fillers due to their weak interaction with the Al matrix. Simulations of the electronic transport properties of the composites with graphene nanoribbons and carbyne chains embedded into Al show that the inclusion of the C phase gives rise to deterioration in the current carrying capacity of the material, but the drop is relatively small, so that the composite material can still transmit current well, if required.
Keywords: nanocomposites, atomistic simulation, mechanical properties Registration No. 24816 - Permalink

Creating nanoporous graphene with swift heavy ions
Vazquez, H.; Ahlgren, E. H.; Ochedowski, O.; Leino, A. A.; Mirzayev, R.; Kozubek, R.; Lebius, H.; Karlusic, M.; Jaksic, M.; Krasheninnikov, A. V.ORC; Kotakoski, J.; Schleberger, M.; Nordlund, K.; Djurabekova, F.
Abstract: We examine swift heavy ion-induced defect production in suspended single layer graphene using Raman spectroscopy and a two temperature molecular dynamics model that couples the ionic and electronic subsystems.We show that an increase in the electronic stopping power of the ion results in an increase in the size of the pore-type defects, with a defect formation threshold at 1.22e1.48 keV/layer. We also report calculations of the specific electronic heat capacity of graphene with different chemical potentials and discuss the electronic thermal conductivity of graphene at high electronic temperatures, suggesting a value in the range of 1Wm?1 K?1. These results indicate that swift heavy ions can create nanopores in graphene, and that their size can be tuned between 1 and 4 nmdiameter by choosing a suitable stopping power.
Keywords: Graphene, ion irradiation, two-temperature model, atomistic simulations Registration No. 24815 - Permalink

Vibrational properties of a two-dimensional silica Kagome lattice
BjöRkman, T.; Skakalova, V.; Kurasch, S.; Kaiser, U.; Meyer, J. C.; Smet, J. H.; Krasheninnikov, A. V.ORC
Abstract: Kagome lattices are structures possessing fascinating magnetic and vibrational properties, but in spite of a large body of theoretical work, experimental realizations and investigations of their dynamics are scarce. Using a combination of Raman spectroscopy and density functional theory calculations, we study the vibrational properties of two- dimensional silica (2D-SiO2), which has a kagome lattice structure. We identify the signatures of crystalline and amorphous 2D-SiO2 structures in Raman spectra and show that, at finite temperatures, the stability of 2D-SiO2 lattice is strongly influenced by phonon−phonon interaction. Our results not only provide insights into the vibrational properties of 2D-SiO2 and kagome lattices in general but also suggest a quick nondestructive method to detect 2D-SiO2.
Keywords: Raman spectroscopy, first-principles calculations, 2D materials Registration No. 24814 - Permalink

Effect of Fluid Dynamics on Separation Efficiency of Sieve Tray
Vishwakarma, Vineet; Schubert, M.; Hampel, U.
Abstract: Sieve trays are popular among vapour-liquid contacting devices in distillation columns due to their versatility and simple construction. Flow and mixing patterns on the trays have strong influence on their mass-transfer efficiency. Plug flow is considered ‘ideal’ whereas flow non-idealities such as liquid channelling, bypassing, re-circulation and stagnant zones are disadvantageous for the tray efficiency. Flow patterns quantified by Schubert et. al. (2016) using wire-mesh sensor are analysed using existing mathematical models for efficiency predictions. A serious loss in efficiency is predicted for the tray with large stagnant zones.

(1) M. Schubert, M. Piechotta, M. Beyer, E. Schleicher, U. Hampel and J. Paschold, ‘An imaging technique for characterization of fluid flow pattern on industrial-scale column sieve trays’, Chemical Engineering Research and Design, vol. 111, pp.138–146, 2016.

Keywords: Distillation Column, Sieve Tray, Tray Efficiency, Flow Non-idealities
  • Poster
    Treffen des Wissenschaftlichen Programmausschusses EMR, 21.-22.09.2016, HZDR, Dresden, Germany
Registration No. 24813 - Permalink

CFD codes benchmark on TOPFLOW-PTS experiment
Mérigoux, N.; Apanasevich, P.; Mehlhoop, J.-P.; Lucas, D.; Raynaud, C.; Badillo, A.
Abstract: In the frame of the European Union NURESAFE project a benchmark test between NEPTUNE_CFD, CFX and TransAT CFD codes on a reference TOPFLOW-PTS experiment was conducted. The work is a part of the work package on multi-scale and multi-physics simulation of Pressurized Thermal Shock (PTS). The article includes a short description of the TOPFLOW-PTS facility and the reference steam-water experiment. Furthermore the boundary and initial conditions for the CFD simulations are presented. The computational grids that are used for the benchmark simulations and the models used are introduced. Finally, the results of CFD calculations are compared with the experimental data and differences between simulations and experiment are discussed.
Keywords: Benchmark tests; Boundary and initial conditions; CFD simulations; Computational grids; European union; Multiphysics simulations; Pressurized thermal shock; Work packages Registration No. 24812 - Permalink

Quantum regime of a free-electron laser: relativistic approach
Kling, P.; Sauerbrey, R.; Preiss, P.; Giese, E.; Endrich, R.; Schleich, W. P.
Abstract: In the quantum regime of the free-electron laser, the dynamics of the electrons is not governed by continuous trajectories but by discrete jumps in momentum. In this article, we rederive the two crucial conditions to enter this quantum regime: (1) a large quantum mechanical recoil of the electron caused by the scattering with the laser and the wiggler field and (2) a small energy spread of the electron beam. In contrast to our recent approach based on nonrelativistic quantum mechanics in a co-moving frame of reference, we now pursue a model in the laboratory frame employing relativistic quantum electrodynamics.
Keywords: Electrodynamics; Free electron lasers; Quantum electronics; Quantum theory

Downloads:

Registration No. 24811 - Permalink

Self-assembly of single Si quantum dots in SiO2
Heinig, K.-H.; Stegemann, K.-H.; von Borany, J.; Facsko, S.; Hlawacek, G.; Hübner, R.; Bischoff, L.; Möller, W.; Prüfer, T.; Xu, X.
Abstract: However, such structures are not small enough to operate at room temperature (RT) quantum devices with switching mechanisms different from CMOS. E.g., the extremely low-power device Single Electron Transistor (SET) works at RT only if the size of the quantum dot is below 5 nm, and if the tunnel distances through SiO2 are a few nm only.
Here we present a directed self-assembly process of a 2-3 nm small single Si dot located in the middle of a SiO2 layer with distances of ~2 nm to the upper and lower Si. The self-assembly occurs by phase separation of metastable SiOx during a heat treatment. The self-assembly becomes directed by constraining and shaping the SiOx volume in such a manner that a single Si quantum dot in the requested position forms. The SiOx is fabricated by collisional mixing of Si atoms from above and below in the SiO2 layer. Two methods to form a local, constrained volume of SiOx are presented: (i) A large-area Si/SiO2/Si layer stack is irradiated with a 2 nm narrow energetic Ne+ beam in a Helium Ion Microscope (HIM), which results in a ~10 nm disk of SiOx in the buried SiO2 layer. (ii) Si pillars (<20 nm) with an embedded SiO2 layer are irradiated with a broad beam of energetic Si+ ions. Method (ii) will be used to fabricate SETs in a CMOS technology.
This work has been funded by the European Union's Horizon 2020 research and under grant agreement No 688072 innovation program.

Keywords: quantum dots, nano-electronics, ion irradiation, ion beam mixing, phase separation
  • Lecture (Conference)
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warszawa, Poland
Registration No. 24808 - Permalink

Hybride 3D Modellierungen im Gifhorner Trog für die Kombination von Übertage und Untertage-Gravimetrie
Götze, H.-J.; Schmidt, S.; Menzel, P.
Abstract: Für die hier dargestellte Studie im Bereich des Gifhorner Trogs wurden neben ca. 500 Messpunkten mit vollständig korrigierten Bougueranomalien ca. 4400 digitalisierte ältere Drehwaagemessungen aus dem beginnenden 20. Jahrhundert verwendet. Mit Hilfe der „alten“ Drehwaagemessungen konnten im Detail dann die Schwerehorizontalgradienten Wxz und Wyz sowie die Krümmungsgrößen der Schwere (WΔ = Wyy – Wxx und 2Wxy) in die 3D-Modellierung integriert werden. Neben den an der Oberfläche gemessenen Anomalien standen auch Untertagemessungen des Schwerefeldes zur Verfügung.
Modelliert wurde mit der hauseigenen Modelliersoftware IGMAS+, die nicht nur die simultane 3D Modellierung von Potentialfeldern (GravMag) ermöglicht, sondern auch deren Gradienten. Ein Vergleich von häufig verwendeten 2D-Modellierungen natürlicher 3D-Strukturen im Untergrund mit 3D-Berechnungen zeigt deutlich, wie groß die Gefahr von Fehlinterpretation eines solchen methodisch fragwürdigen Vorgehens ist. Die Modelldichten können variabel – in Abhängigkeit von den „wahren Geschwindigkeitsverhältnissen“ im Modelliergebiet angegeben werden. Als Beispiel zeigen wir das 3D Dichtemodell der Tiefbohrung KTB zusammen mit der Bohrlochgravimetrie – in Ermangelung anderer, frei zugänglicher Datensätze.
Die vorliegende Modellierung von Detailstrukturen im Gifhorner Trog belegt eindeutig, dass eine hybride 3D Modellierung von Potentialfeldern zusammen mit ihren Gradienten wertvolle Informationen über den Untergrund bis in Tiefen von 5 – 10 km liefert, die gemeinsam mit seismischen Informationen einen erheblichen Mehrwert für die Interpretation darstellen.

Keywords: 3D Potentialfeldmodellierung, Geophysik, Untergrundmodellierung
  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
    DGMK-Tagungsbericht 2016-1, Hamburgf: DGMK, 978-3-941721-64-7, 91-96
Registration No. 24806 - Permalink

Magnetic Nanostructures Designed For Hard Disk Drive Applications
Hellwig, O.
Abstract: Continued progress in hard disk drive areal density for conventional perpendicular magnetic recording (PMR) based on granular media has become increasingly difficult. Although adoption of energy assisted magnetic recording (EAMR), specifically Heat Assisted Magnetic Recording (HAMR) is widely viewed as a promising solution for thermal stability issues, challenges in grain size scaling and managing media noise may limit the rate of progress for EAMR based on granular media. Bit patterned recording (BPR) stands as an attractive alternative to granular media, offering a path to thermally stable recording at high density and significantly reduced media noise by replacing the segregated random grains of PMR media with lithographically defined single domain islands. Figure 1 compares and summarizes basic characteristics of currently used conventional PMR based on granular media and BPR based on pre-defined bits. In my talk I will discuss various choices for BPR magnetic materials, such as Co/Pd and Co/Pt multilayers as well as CoCrPt and FePt L10 alloys. I will highlight advantages and disadvantages of the different magnetic material systems with respect to potential applications in BPR and outline the specific challenges when comparing conventional PMR, BPR and currently emerging HAMR systems.
Keywords: magnetic recording, hard disk drive, perpendicular magnetic recording, bit patterned recording, heat assisted magnetic recording
  • Invited lecture (Conferences)
    International Conference on Solid Films and Surfaces, 28.08.-02.09.2016, Chemnitz, Germany
Registration No. 24805 - Permalink

Karrat Zinc 2016 - Personal field report
Zimmermann, R.ORC
Abstract: Results of the 2016 Karrat fieldwork, 11.08.2016 – 24.08.2016
  • Other report
    Kopenhagen: Geological Survey of Denmark and Greenland, 2016
    224 Seiten
Registration No. 24804 - Permalink

The spatial coefficient of variation in arterial spin labeling cerebral blood flow images
Mutsaerts, H. J.; Petr, J.; Václavů, L.; van Dalen, J. W.; Robertson, A. D.; Caan, M. W.; Masellis, M.; Nederveen, A. J.; Richard, E.; Macintosh, B. J.
Abstract: Macro-vascular artifacts are a common arterial spin labeling (ASL) finding in populations with prolonged arterial transit time (ATT) and result in vascular regions with spuriously increased cerebral blood flow (CBF) and tissue regions with spuriously decreased CBF. This study investigates whether there is an association between the spatial signal distribution of a single post-label delay ASL CBF image and ATT. In 186 elderly with hypertension (46% male, 77.4+-2.5 years), we evaluated associations between the spatial coefficient of variation (CoV) of a CBF image and ATT. The spatial CoV and ATT metrics were subsequently evaluated with respect to their associations with age and sex – two demographics known to influence perfusion. Bland–Altman plots showed that spatial CoV predicted ATT with a maximum relative error of 7.6%. Spatial CoV was associated with age (b=0.163, p=0.028) and sex (b=-0.204, p=0.004). The spatial distribution of the ASL signal on a standard CBF image can be used to infer between-participant ATT differences. In the absence of ATT mapping, the spatial CoV may be useful for the clinical interpretation of ASL in patients with cerebrovascular pathology that leads to prolonged transit of the ASL signal to tissue.
Keywords: Arterial spin labeling, ASL, cerebral blood flow, cerebral hemodynamics, perfusion weighted MRI Registration No. 24801 - Permalink

Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion
Rädecker, P.; Scharf, C.; Zeidler, O.
Abstract: Kooperative Entwicklung ressourceneffizienter Verfahren in der Produktion
Philipp Rädecker, Oliver Zeidler & Prof. Christiane Scharf
Freiberg, 24. November 2016
  • Invited lecture (Conferences)
    Ressourceneffizienz vor Ort Wettbewerbsplus Ressourceneffizienz Angebote für KMU in Sachsen, 24.11.2016, Freiberg, Deutschland
Registration No. 24800 - Permalink

Influence of realignment-induced interpolation errors on the estimation of cerebral blood flow using arterial spin labeling fMRI
Petr, J.ORC; Mutsaerts, H.ORC; de Vita, E.ORC; Shirzadi, Z.; Cohen, S.; Blokhuis, C.; Pajkrt, D.ORC; Hofheinz, F.; van den Hoff, J.; Asllani, I.
Abstract: Purpose/Introduction: The realignment transformation needed for motion correction in fMRI has been shown to have the adverse effect of smoothing the realigned images1. This effect is independent of the accuracy of the estimated motion parameters (it can occur even for accurately estimated motion parameters) and can, in ASL, cause gray-matter (GM) cerebral-blood-flow (CBF) underestimation compared to an acquisition without motion. Here, we investigated the smoothing of the realignment transformation in ASL by creating simulated CBF maps based on T1-weighted (T1w) images and motion parameters obtained from ASL images acquired on patients2.
Methods: ASL data from 66 children (age: 8-18y, median: 12.8y, 34 males) were obtained from the NOVICE study2. This dataset is characterized by a relatively high head motion often associated with scanning children. Images were acquired on Philips 3T Ingenia (pCASL: voxel-size 3x3x6.6mm3, 30 controls/label pairs; T1w: voxel-size 1x1x1mm3).
To simulate ASL time-series that reflect motion from real acquisition, the following processing steps were implemented: (1) T1w-image was co-registered to the first ASL volume and segmented into gray and white-matter posterior probability maps (pGM/pWM) using SPM12. (2) ASL images were realigned with respect to the first volume3 (average motion >1mm or >1° was considered 'high'). (3) The motion-parameters from step 2 were applied to pGM/pWM maps, and the maps were down-sampled to the ASL resolution. This resulted in 60 pGM/pWM volumes mimicking a real ASL acquisition (Fig. 1b). (4) The pGM/pWM maps were realigned to their first respective volume (Fig. 1d) and averaged (Fig. 2d).
Two sets of simulated CBF maps were created: (1) from the pGM/pWM corresponding to the first ASL volume (CBF-static), (2) from the realigned pGMs/pWMs described above (CBF-motion), assuming GM-CBF of 80 mL/min/100g and GM/WM CBF ratio of 3. Local and global GM-CBF values of CBF-motion were compared against the idealized CBF-static case.
Results: Figures 1d and 2d show ‘blurring’ of the realigned pGM in high movement cases. The local GM-CBF in CBF-motion was up to 10% lower than in CBF-static (Fig. 2e); negligible differences (<1%) were seen in relatively low movement cases (Fig. 2f). In all 'high-motion' participants, 4-7% lower global GM-CBF was observed (Fig. 3).
Discussion/Conclusion: Relatively high motion during ASL acquisitions appears to result in a GM-CBF underestimation of 4-7% globally and up to 10% locally. This finding can have important implications in studying patients who tend to move more than their healthy counterparts, which may lead to a GM-CBF underestimation in patients relative to controls.

Keywords: cerebral blood flow, perfusion, arterial spin labeling, motion correction Registration No. 24799 - Permalink

Crystal structure and magnetism of UOsAl
Andreev, A. V.; Danis, S.; Sebek, J.; Henriques, M. S.; Vejpravova, J.; Gorbunov, D. I.; Havela, L.
Abstract: Crystal structure, magnetization, and specific heat were studied on single crystal of uranium intermetallic compound UOsAl. It is a hexagonal Laves phase of MgZn2 type, space group P63/mmc, with lattice parameters a = 536.4 pm, c = 845.3 pm. Shortest inter-uranium distance 313 pm (along the c-axis) is considerably smaller than the Hill limit (340 pm). The compound is a weakly temperature-dependent paramagnet with magnetic susceptibility of ≈1.5*10−8 m3 mol (at T=2 K), which is slightly higher with magnetic field along the a-axis compared to the c-axis. The Sommerfeld coefficient of electronic specific heat has moderate value of γ = 36 mJ mol−1 K−2. Registration No. 24797 - Permalink

Adiabatic physics of an exchange-coupled spin-dimer system: Magnetocaloric effect, zero-Point fluctuations, and possible two-dimensional universal behavior
Brambleby, J.; Goddard, P. A.; Singleton, J.; Jaime, M.; Lancaster, T.; Huang, L.; Wosnitza, H.; Topping, C. V.; Carreiro, K. E.; Tran, H. E.; Manson, Z. E.; Manson, J. L.
Abstract: We present the magnetic and thermal properties of the bosonic-superfluid phase in a spin-dimer network using both quasistatic and rapidly changing pulsed magnetic fields. The entropy derived from a heat-capacity study reveals that the pulsed-field measurements are strongly adiabatic in nature and are responsible for the onset of a significant magnetocaloric effect (MCE). In contrast to previous predictions we show that the MCE is not just confined to the critical regions, but occurs for all fields greater than zero at sufficiently low temperatures. We explain the MCE using a model of the thermal occupation of exchange-coupled dimer spin states and highlight that failure to take this effect into account inevitably leads to incorrect interpretations of experimental results. In addition, the heat capacity in our material is suggestive of an extraordinary contribution from zero-point fluctuations and appears to indicate universal behavior with different critical exponents at the two field-induced critical points. The data at the upper critical point, combined with the layered structure of the system, are consistent with a two-dimensional nature of spin excitations in the system. Registration No. 24796 - Permalink

Luminescence spectroscopy of An/Ln in environmental systems
Steudtner, R.; Drobot, B.; Haubitz, T.; Schernikau, M.; Lehmann, S.; Bader, M.; Vogel, M.
Abstract: Luminescence spectroscopy is a powerful tool to study the chemistry of f-elements (actinides – An, lanthanides – Ln) in trace concentration. Manifold operating mode, e.g. steady-state, time-resolved, laser-induced, site-selective, cryogenic, etc. were used to investigate the environmental behavior of An/Ln in various geological and biological systems.
  • Invited lecture (Conferences)
    ATAS 2016 - International Workshop on Advanced Techniques in Actinide Spectroscopy, 07.-10.11.2016, Richland, USA
Registration No. 24793 - Permalink

Structural and electrical characterization of ALD grown HfO2 thin films
Blaschke, D.; Munnik, F.; Zviagin, V.; Schmidt-Grund, R.; Grundmann, M.; Bogusz, A.; Hübner, R.; Scholz, A.; Schmidt, H.; Zahn, P.; Gemming, S.
Abstract: HfO2 films were grown on 4-inch native SiO2/Si wafers by Atomic Layer Deposition (ALD) from tetrakis(dimethylamido)hafnium and deionized water in a Savannah S100 system. The temperature was varied from 100°C to 350°C in steps of 50 K. All other ALD process parameters were fixed. The resulting HfO2 layers were characterized in terms of thickness homogeneity, growth rate per cycle, surface roughness, crystal structure, stoichiometry, mass density, optical bandgap and index of refraction. Based on the obtained growth rate of HfO2 on SiO2/Si, 25 nm thick HfO2 layers were grown on Pt/Ti/SiO2/Si substrates for electrical characterization. Furthermore, the most important structural properties were compared for the growth of HfO2 on Pt/Ti/SiO2/Si and SiO2/Si substrates.
HfO2 breakdown voltages show a clear decrease with increasing growth temperature, which was correlated to the crystallinity of the films due to the preferred breakdown along grain boundaries. For resistive switching, an amorphous HfO2 layer grown at 150°C was compared to a crystalline one grown at 300°C. Furthermore, resistive switching characteristics were tuned by the use of two different top electrode materials, namely an inert Pt or a reactive Ti/Pt electrode. The contact diameter was 50 μm. In the majority of cases, the resistive switching mode was found to be unipolar. Only the combination of a crystalline HfO2 layer with an inert Pt bottom and a reactive Ti/Pt top electrode led to a “pseudo-bipolar” switching mode with a convertible SET and RESET polarity.

Keywords: HfO2, thin film deposition, ALD, resistive switching
  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Lohmen, Germany
Registration No. 24792 - Permalink

Doping by flash lamp annealing
Prucnal, S.; Rebohle, L.; Skorupa, W.
Abstract: After a short introduction we will highlight processing issues (setup, comparison of annealing methods, relevant requirements for annealing due to doping, diffusion, activation, recrystallization, defect engineering), as well as doping issues for group IV-semiconductors (shallow junctions, hyperdoping, solar cells, superconductivity) and other semiconductors (manganese doping of GaAs for diluted magnetic semiconductors, doping for transparent conductive oxides). Mostly ion implantation serves as a source of dopants, but also diffusion from deposited layers is of growing importance.
Keywords: flash lamp annealing, pulsed light sintering, group IV-semiconductors, doping, diffusion, activation, recrystallization, defect engineering, diluted magnetic semiconductors, transparent conductive oxides Registration No. 24791 - Permalink

Bergbau und Konfliktminerale in Afrika
Sterbik, N.ORC
Abstract: Einerseits sind die Rohstofflieferungen Afrikas für die Versorgung der Weltwirtschaft von Bedeutung, andererseits spielen die Exporte aber auch eine wesentliche Rolle für die Wirtschaft dieser Länder. Die steigende Nachfrage (auch in Schwellenmärkten) und der Preisanstieg für einzelne Rohstoffe könnten eine günstige Gelegenheit für die afrikanischen Bergbauländer darstellen.

In großen Teilen des subsaharischen Afrikas wird der Bergbau jedoch noch in sehr kleinem Maßstab und – aufgrund keiner oder nur geringer Mechanisierung – mit hohem Arbeitsaufwand betrieben. Diese Arbeiten werden allgemein als Einzel- und Kleinbergbau (Artisanal and Small-Scale Mining, ASM) kategorisiert. In Zentralafrika steht der ASM zusätzlich auch mit sogenannten „Konfliktmineralien“ in Verbindung (kurz gesagt, „Konfliktressourcen sind natürliche Ressourcen, deren systematische Ausbeutung und Handel im Kontext eines Konfliktes zu schwersten Menschenrechtsverletzungen, Verletzungen des humanitären Völkerrechts oder Verwirklichung völkerstrafrechtlicher Tatbestände führen kann“ (BICC, 1994)).

Diese Präsentation vermittelt einen Überblick über den Bergbau in Afrika, sowohl über industriellen Bergbau als auch Kleinbergbau, und behandelt das Thema der Konfliktmineralien. Es wird ebenfalls die Verbindung zwischen den beteiligten Akteuren und den Initiativen rund um ASM und Konfliktmineralien aufgezeigt.

Keywords: Bergbau, Kleinbergbau, Afrika, Konflikt-Minerale
  • Invited lecture (Conferences)
    145. Freiberger Kolloquium, 14.04.2016, Freiberg, Germany
Registration No. 24790 - Permalink

A lab scale froth flotation study of tungsten bearing tailings of the Barruecopardo mine (Spain) within the EU Horizon 2020 OptimOre Project
Compañero, R. J.
Abstract: This study was done under the framework of the “OptimOre” project which is part of EU Horizon 2020. Froth flotation is applied for obtaining a pre-concentrate from tailings material sourced from an old mine in the Barruecopardo district, located in the province of Salamanca in Spain. Representative samples from the as-received material were submitted to several characterization analyses: MLA, particle size measurements, contact angle measurements, and ICP-AES. Information from the preceding tests were used to design flotation experiments where five factors: collector type, frother type, depressant addition, pH level, and collector dosage were investigated.

Milling was performed on the feed material before flotation because the starting size was too coarse. The flotation behavior of the material was examined and different factor level combinations resulted in varying degrees of recovery and concentrate grades --- the highest attained averaging 35% and 0.36% W (Enrichment ratio = 14) respectively. Further improvements on these results were targeted and thus the grinding time was increased. The merits of this step in terms of mass collection, grade, and recovery are discussed. Exploratory ideas on the effect of the factor levels investigated were also presented.

Keywords: froth flotation; scheelite; depressant; Barruecopardo
  • Master thesis
    HIF/HZDR, 2016
    Mentor: Sterbik, N.
Registration No. 24789 - Permalink

Back-calculating froth flotation rates of scheelite by size fractions and liberation classes : first results
Sterbik, N.ORC; Rudolph, M.ORC
Abstract: This paper is part of an EU funded collaboration under the Horizon 2020 program on the optimization of mineral processing operations of European tungsten and tantalum complex low-grade ores, called OptimOre. There froth flotation is an important process especially for scheelite. It is a versatile mineral processing method, which still lacks of physical and chemical comprehensive, accurate and internationally recognized models. The work package on froth flotation within OptimOre is thus dedicated to developing improved fundamental flotation models with the help of advanced automated mineralogical analyses of the input and output streams of flotation cells.

Reliable flotation models can be potentially used to simplify and shorten lab testing procedures, better understand and predict ore behavior but also establish the potential recovery and grade of the targeted mineral(s).

A first step in fundamental flotation modelling is to obtain the flotation rates of minerals with respect to their size and liberation. This is achieved by back calculation of recovery rates typically under the assumption of a first-order rate process.

In this paper, froth flotation rates of scheelite are back-calculated by size fractions and liberation classes. Flotation parameters such as reagent regime, cell hydrodynamics and pulp and froth properties are systematically varied in properly designed experiments with measured effects on the bubble surface area flux. Finally these flotation rates are then used to critically assess several existing first principle flotation models (Yoon, Pyke and others), which are compared with each other in terms of applicability and limitations.

The scheelite bearing ore used for the experiments is from the Mittersill deposit (Austria). The particle properties (e.g. liberation, mineral composition) are studied with automated mineralogy (Mineral Liberation Analysis) as well as elemental assays by ICP-MS analyses. Froth flotation tests are conducted with a bottom-driven Magotteaux cell equipped with a bubble cam sizer and froth cam.

Keywords: flotation rates, automated mineralogy, scheelite, size-by-liberation, MLA
  • Poster
    XXVIII International Mineral Processing Congress, 11.-15.09.2016, Québec city, Canada
Registration No. 24788 - Permalink

Technical and Modelling Aspects of Subsecond Thermal Processing with Flash Lamps
Schumann, T.; Rebohle, L.; Skorupa, W.
Abstract: This poster gives an overview of the complex technical aspects of Flash-lamp-annealing-tools for thermal processing in the millisecond range used at the Helmholtz Research Center Dresden-Rossendorf (HZDR). It outlines that Flash Lamp Annealing (FLA) is established as a high-performance alternative to Rapid Thermal Annealing and Furnace Annealing when it comes to treatment of the most advanced thin layer and coating materials, thus enabling the fabrication of novel electronic structures and materials. It shows the unique variety of parameters the HZDR is able to provide for applications ranging from annealing of implanted Si and Ge, transparent conductive oxides, photovoltaic materials, silver and copper inks on various non-metal substrates to exceptional applications (roof tiles, watchcases). It explains, how crucial parameters, such as emission spectrum, energy density, and preheat temperature are monitored to provide a reliable reproducibility. Modelling aspects regarding temperature distribution and heat transport within the millisecond range will also be addressed. Furthermore, a summary will be given of characteristic features of our tools to convey the diversity of the fields of application and the enormous range of possible research.
Keywords: Flash-lamp-annealing, millisecond range thermal processing, modelling aspects, thin layers, novel electronic structures
  • Poster
    SVC (Society of Vacuum Coaters) 59th Annual Technical Conference (TechCon), 09.-13.05.2016, Indianapolis, IN, USA
Registration No. 24787 - Permalink

A lab scale froth flotation study of tungsten-bearing tailings of the Barruecopardo mine (Spain)
Sterbik, N.ORC; Compañero, R. J.; Rudolph, M.ORC
Abstract: The “OptimOre” project, as part of the EU Horizon 2020, proposes the research and development of improved modelling and control technologies of tantalum and tungsten ore processing using advanced sensing and artificial intelligence techniques. The Helmholtz Institute Freiberg for Resource Technology is responsible for the Work Package „Froth flotation”.
Within the frame of the OptimOre project, a lab scale froth flotation study was conducted on the tailings of the Barruecopardo mine (Spain) with scheelite as the main tungsten-bearing mineral and a feed grade of 0,025% tungsten. Barruecopardo is part of the world-class tungsten deposits and is being redeveloped for mining.
The reagent system is the main focus of this study, with an emphasis on the influence of depressant combinations aimed at depressing silicates in the gangue. Two collectors at four dosages, two frothers and four depressant combinations were tested at two different pH.
The results show that a higher pH usually stabilizes the froth regardless of the frother and increases the mass pull but does not impact the tungsten recovery. The depressant combination is highly relevant in grade, as expected, but also in recovery. It can hinder it badly or increase it tremendously. Furthermore, the performance of the first collector without depressant is significantly higher than after adding depressant. On the contrary, the second collector that performed poorly in a depressant-less environment yields the best results in presence of depressants. The presence of sodium carbonate (Na2CO3) enhances that effect. Possible interpretations for these observations are given.

Keywords: flotation; scheelite; depressants
  • Poster
    Tagung Aufbereitung und Recycling, 09.-10.11.2016, Freiberg, Germany
Registration No. 24785 - Permalink

Optik einmal anders
Schultheiss, H.
Abstract: Erstmals konnten Forscher experimentell das Brechungsgesetz für Spinwellen direkt nachweisen.
Keywords: Magnonik, Spinwellen, Magnetisierungsdynamik
  • Physik Journal 15(2016)10, 16-17
    Button zum Volltext
Registration No. 24778 - Permalink

Level-Of-Detail Strategie zur Vereinfachung komplexer Untergrundmodelle - Gifhorner Trog
Menzel, P.; Götze, H.-J.; Schmidt, S.
Abstract: In dieser Präsentation werden Verfahren gezeigt, um triangulierte 3D-Untergrundmodelle für die Berechnung ihres „full tensor gravity“-Effektes zu optimieren. Es handelt sich dabei um zwei etablierte Algorithmen aus der Computergrafik zur Vereinfachung von triangulierten Flächen, sowie um ein drittes, an die Erfordernisse der Potentialverfahren angepasstes, Verfahren. Alle drei Algorithmen erzeugen eine Vereinfachungshierarchie für die initiale 3D-Geometrie. Diese „Level-of-Detail“-Hierarchien erlauben es, verschiedene Modell-auflösungen sukzessive ineinander zu überführen. Ein explizites Vorhalten der vereinfachten Geometrieversionen ist aus diesem Grund nicht notwendig.
Die drei verwendeten „Mesh-Simplification“-Ansätze werden auf ein synthetisches 3D-Modell und auf das triangulierte Untergrundmodell zweier realer Salzstöcke angewendet. Die erzeugten vereinfachten Geometrieversionen werden für ihre Verwendbarkeit zur Berechnung des Effektes in den Komponenten der Schwere und des Schweregradienten-tensors evaluiert. Es wird gezeigt, dass die Ergebnisse aller drei Methoden grundsätzliche für eine Berechnung des „full tensor gravity“-Effektes verwendet werden können. Die Ergebnisse der beiden etablierten Verfahren sind allerdings nur bis zu einem relativ geringen Vereinfachungsgrad verwendbar, wenn eine gegebene Fehlertoleranz nicht überschritten werden soll. Das dritte, angepasste Verfahren erzeugt Geometriemodelle, deren Effekt auch für Modellversionen mit sehr wenigen Dreiecken mit dem Effekt des initialen Modells annähernd übereinstimmt.
Die präsentierten Ergebnisse basieren auf den Arbeiten im DGMK-Projekt 771 und das gezeigte 3D-Modell zweier Salzstöcke im Gifhorner Trog wurde von unseren Projektpartnern zur Verfügung gestellt.

Keywords: Mesh-Simplification, Potentialfeldmodellierung, geometrische 3D Modellierung
  • Lecture (Conference)
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Deutschland
  • Contribution to proceedings
    DGMK/ÖGEW-Frühjahrstagung 2016, Fachbereich Aufsuchung und Gewinnung, 21.-22.04.2016, Celle, Germany
    DGMK-Tagungsbericht 2016-1, Hamburg: DGMK, 978-3-941721-64-7, 97-104
Registration No. 24776 - Permalink

Nickel-Enhanced Graphitic Ordering of Carbon Ad-Atoms during Physical Vapor Deposition
Wenisch, R.; Hübner, R.; Munnik, F.; Gemming, S.; Abrasonis, G.; Krause, M.
Abstract: Compatibility with commonly used substrate materials is of crucial importance for graphene device production. Low-temperature synthesis approaches are needed to cope with this challenge. Therefore it has to be clarified, to which extend physical vapor deposition can be used to produce ordered graphene structures.

In this contribution, the mechanism of graphitic ordering of atomic C on Ni was investigated at temperatures ranging from room temperature to 550 °C. The C/Ni films were prepared by ion beam sputtering. A temperature-induced and a Ni-induced enhancement of graphitic ordering is demonstrated. The Ni-effect is responsible for the formation of a bi-layer structure of the C films at higher deposition temperatures. In the bi-layers, C forms graphenic planes parallel to the Ni surface within a thickness range of 1-2 nm. Further deposited C grows preferentially perpendicular to the surface. The results are discussed on the basis of hyperthermal atom deposition, surface diffusion, metal-induced crystallization and dissolution-precipitation. Our findings point to a dominating role of surface diffusion-assisted crystallization in the carbon ordering process.

Keywords: graphitic carbon, graphene, physical vapour deposition, Raman, TEM
  • Poster
    International Winterschool on Electronic Properties of Novel Materials 2016, 13.-20.02.2016, Kirchberg, Österreich
Registration No. 24775 - Permalink

Helmholtz Institute Freiberg for Resource Technology - Helmholtz-Zentrum Dresden-Rossendorf - Introduction
Kelly, N.
Abstract: Helmholtz Institute Freiberg for Resource Technology
Helmholtz-Zentrum Dresden-Rossendorf
Introduction
  • Lecture (others)
    Meeting FWGM und UIT, 06.01.2017, Freiberg, Deutschland
Registration No. 24774 - Permalink

Magnetic anisotropy of III-Mn-V dilute ferromagnetic semiconductors
Xu, C.; Yuan, Y.; Sawicki, M.; Böttger, R.; Helm, M.; Zhou, S.
Abstract: As one of the most important physical properties of III-Mn-V dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy could be tailored by Mn/hole concentrations and by the lattice strain [1, 2]. Particularly, the crystal symmetry lowering in-plane uniaxial anisotropy still remains one of the most puzzling properties of the DFS family. Using a perturbation method and ab initio computations, Birowska et al. showed that the preferential distribution of Mn along (Ga,Mn)As [11(_)0] can produce bulk uniaxial in-plane and out-of-plane anisotropies [3]. This preferential Mn distribution is due to the fact that the nearest-neighbor Mn pair on the GaAs (001) surface has a lower energy for the [11(_)0] axis than the [110] case. However, such a preferential Mn distribution probably will not occur when the material is not grown in a layer-by-layer mode but by a liquid-phase-epitaxy-like process with the growth speed of meters per second, as for the case of ion implantation and pulsed laser melting (II-PLM) [4]. In this work, three typical III-Mn-V DFSs [(In,Mn)As, (Ga,Mn)As, and (Ga,Mn)P] are obtained through II-PLM. We find that both (Ga,Mn)P and (Ga,Mn)As samples exhibit the easy behavior in plane (as shown in Fig. 1) while the (In,Mn)As one reveals perpendicular magnetic anisotropy (not shown). The latter is attributed to the lattice strain due to lattice mismatch between the film and the substrate. The in-plane uniaxial anisotropy is much weakened for (Ga,Mn)P and (Ga,Mn)As from the magnetic hysteresis at 5 K. However, as shown in the inset to Fig. 1, the anisotropy changes with temperature increasing. More experimental results including magnetic hysteresis at different temperatures will be discussed during the conference.

Figure 1: Magnetic hysteresis along different crystalline axis for (Ga,Mn)P and (Ga,Mn)As with different Mn concentration measured at 5 K. The inset shows the magnetic remanence along different crystalline axis for the corresponding sample.
[1] M. Sawicki et al., Phys. Rev. B 70, 245325 (2004).
[2] C. Bihler et al., Phys. Rev. B 78, 045203 (2008).
[3] M. Birowska, et al., Phys. Rev. Lett. 108, 237203 (2012).
[4] M. A. Scarpulla et al., Appl. Phys. Lett. 82, 1251-1253 (2003).

Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    61st Annual Conference on Magnetism and Magnetic Materials (2016 MMM), 31.10.-04.11.2016, New Orleans, United States of America
Registration No. 24772 - Permalink

The magnetic anisotropy of III-Mn-V ferromagnetic semiconductors prepared by ion implantation and pulsed laser melting
Xu, C.; Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.
Abstract: As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin.

[1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014)
[2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012)
[3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003)
[4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004)
[5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)

Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    European Materials Research Society (E-MRS) 2016 Spring Meeting, 02.-06.05.2016, Lille, France
Registration No. 24771 - Permalink

LWFA and laser-thomson scattering experiments at HZDR
Irman, A.
Abstract: I present recent status of laser wakefield acceleration and laser-thomson scattering experiments at HZDR.
  • Lecture (Conference)
    Laboratory for Laser- and beam-driven plasma Acceleration Workshop, 21.-22.06.2016, Wismar, Germany
Registration No. 24769 - Permalink

New insights into a historical mine site: the Sn-W-Li Zinnwald/Cínovec deposit, eastern Erzgebirge, central Europe
Neßler, J.; Seifert, T.; Gutzmer, J.
Abstract: The historically significant Sn-W-Li Zinnwald/Cínovec deposit is characterised by greisen-type mineralization hosted within the apical portion of a small granite intrusion. Similar to other granitic stocks with Sn-W mineralization in the Erzgebirge, the Zinnwald granite intruded during the post- collisional stage of the late-Variscan (Permo-Carboniferous) magmatic evolution. These small Li-F granite bodies are characterised by the prominent enrichment of incompatible elements (F, Li, Rb, Cs, Sn, Nb, Ta) and the depletion of Ba, P, Sr, Zr, Ti, and Mg [1].
The Zinnwald granite is located in the eastern part of the Erzgebirge-Fichtelgebirge anticline and consists of highly evolved, weakly peraluminous and variably altered albite-Li mica leucogranite of anorogenic- type affiliation. Laterally extensive pegmatitic veins, which are located in the apical part of the granite cupola, represent the dominant source for the historically exploited Sn-W mineralisation, whereas sheet-like, metasomatic greisen ore bodies serve as a major resource for Li due to the abundance of Li- mica (zinnwaldite). This was demonstrated recently by extensive exploration of the Li mineralisation carried out by SolarWorld Solicium GmbH (SWS) during 2011 and 2014 [2].
This contribution aims to present new insights into the architecture, mineralization and geochemistry of the Zinnwald deposit based mainly on recent and historic drill core samples and their analysis by light microscopy and scanning electron microscopy, EPMA, LA-ICP-MS and whole rock ICP-MS. The results indicate an orientation of greisen ore bodies and veins parallel to the granite contact as well as a decrease of mineralization thickness and abundance with depth. While the host granite itself is highly evolved in its composition, progressive greisenization (Fig. 1) is accompanied by a decrease of fractionation indices (e.g. K/Rb from 20 to 8) and increasing contents of incompatible elements. For instance, mean grades of the most abundant quartz-mica-topaz-greisen include 3,700 ppm Li, 70 ppm Cs and 3.1 wt.% F. Fluid-controlled metasomatic processes are inferred from microscopic textures, trace element behaviour and significant tetrad-effect in normalized REE patterns. The chemical composition of Li-mica is similar for various greisenized lithologies of the endo- and exocontact, and Li concentrations range from 1.1 to 2.2 wt.%. Greisenization, which corresponds to the formation of zinnwaldite, follows an incipient stage of quartz-replacement and is spatially related, but not genetically linked, to disseminated Sn-W mineralization. This is demonstrated by the presence of disseminated Sn-W mineralization hosted either by greisen lithologies or by albite granite, which was only moderately affected by greisenization. This, in turn, may require a critical assessment of current metallogenetic models.
References
[1] Seifert, Th., Kempe, U (1994) Beiheft z. European Journal of Mineralogy, 6 (2): 125-172 [2] Neumann, M. et al. (2014) Unpublished resource report, pp. 204
[3] Grunewald, V. (1978) Unpublished report, Geological Archive LfULG - EB 1391, pp. 190
  • Contribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South Africa
    Proceedings of the International Geological Congress, Washington: AGI
Registration No. 24768 - Permalink

Redshifting and harmonic radiation in the nonlinear laser-thomson scattering interaction
Irman, A.
Abstract: Thomson scattering of intense laser pulses from relativistic electrons not only allows for the generation of bright x-ray pulses but also serves as a laboratory for strong field physics and nonlinear interactions. We present high resolution angle and energy resolved measurements on the laser-Thomson x-ray distribution generated by colliding picosecond electron bunches from the ELBE linear accelerator with counter-propagating laser pulses from the 150 TW DRACO Ti:Sapphire laser system. As we increase the laser intensity, the electrons start to move in more complex trajectories resulting to emission of x-ray photons at higher harmonics which extends beyond 24 keV. Furthermore the overall radiation spectrum shows the broadening and redshift effect as predicted in the theory of intense laser-relativistic electron interaction in the classical picture. The amount of scattered photon also increases one order of magnitude to 106 photons per shot in the full opening emission angle.
Keywords: Laser-Thomson scattering, DRACO laser, ELBE accelerator
  • Lecture (Conference)
    17th Advanced Accelerator Concepts Workshop, 31.07.-05.08.2016, National Harbor, Maryland, USA
Registration No. 24767 - Permalink

Phosphate mineralization in the Vergenoeg fluorite deposit (RSA) and its implication for the origin of REE-bearing fluid alteration
Höfig, T. W.; Krause, J.; Kern, M.; Birtel, S.; Gutzmer, J.
Abstract: The Vergenoeg volcanic pipe, located in the central part of the Bushveld Complex (Republic of South Africa), hosts one of the economically most significant fluorite deposits on Earth. Its iron-oxide – fluorite – fayalite assemblage is well known for marked enrichment of rare-earth elements (REE) and phosphate. Previous studies reported the presence of apatite and a number of REE-rich accessory minerals, particularly phosphates [1, 2, 3]. Here we present a systematic study of REE-phosphates (monazite, xenotime) from the hematite-fluorite zone of the Vergenoeg orebody. Links between mineral che mi cal variations, paragenesis, and microstructural aspects are examined. The results are used to elucidate the genesis of REE-phosphate mineralization in the Vergenoeg fluorite deposit.
For this study, both apatite-bearing and apatite-free samples from the hematite-fluorite zone were selected.Scanning electronmicroscopy-based image analysis has been performed in order to identify and spatially map the distribution of rare-earth phosphates as well as rock-forming minerals throughout the samples in polished sections. Subsequently, the mineral chemistry of the phosphates has been determined by means of electron probe microanalysis.
Two major fabric type scan be distinguished:First,fine-grained monazite and xeno time form euhedral pseudomorphs in the presence or absence of apatite. Second, they occur as infill of interstices and microfractures. Mineral associations of monazite with xenotime, iron-oxide, fluorite or their joint assemblage have been identified,applying to every fabric type.The combination of mineral chemistry data and microstructural observations suggests a link between the spatial occurrence of REE-phosphates and their chemical composition. Different mineral associations also have an effect on the chemical composition. In addition, the deportment of certain elements suggests microstructural and mineralogical changes as controlling factors, respectively.
The mineral chemistry of monazite is inline with the monazite-(Ce)of type 2 from Graupner et al. [3]. Xenotime data point to Y-rich compositions, corresponding to the secondary xenotime generation proposed by Graupner et al. [3]. Besides regular monazite, the presence of grains with comparatively low analytical totals between c. 90 wt% and 98 wt% may reflect altered compositions, resulting from hydration under low-temperature conditions giving rise to formation of hydrated monazite (or even rhabdophane) [e.g., 4, 5]. Similarly low analytical totals for xenotime may also represent hydration. Increasing sulfur contents with decreasing analytical totals for both rare-earth phosphates indicate enhanced sulfur activity of the overprinting fluid.
References:

[1]FouriePJ(2000)In:Hydrothermal Iron Oxide Copper Gold & Related Deposits:A Global Perspective: Australian Mineral Foundation, Adelaide, 309–320
[2] Goff BH et al. (2004) Miner Petrol 80: 173–199
[3] Graupner T et al. (2015) Ore Geol Rev 64: 583–601
[4] Krenn E and Finger F (2007) Lithos 95: 130–147 [5] Berger A et al.(2008)Chem Geol 254:238–248
  • Contribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South African
    Proceedings of the International Geological Congress, Washington: American Geoscience Institute
Registration No. 24766 - Permalink

Quantifying the resource potential of flotation tailings storage facilities – the role of geometallurgical characterization
Gutzmer, J.; Osbahr, I.; Leißner, T.; Satgé, L.; Unger, G.; Büttner, P.
Abstract: Flotation is the most widely applied separation process in today’s raw materials industry. Billions of tons of flotation tailings are produced every year. As fine-grained residues these are usually deposited in large-scale tailings storage facilities (TSLs). With recoveries commonly below 90%, a significant portion of the value contained in the primary ore finds its way into such TSLs. In addition, commodities that were not targeted by the primary exploitation process may later become valued products. There are many well-known examples of historic tailings (or other mining-related residues) becoming economically attractive targets of renewed exploitation. Arguably the most prominent of these examples is the recovery of gold and uranium from slimes and sand storage facilities of the Witwatersrand goldfields, South Africa. TSLs are thus best described as large, low-grade anthropogenic ore bodies; they are also a prime example of an urban mine.

Retreatment of tailings offers some significant advantages. Very large tonnages of readily milled material are available at surface. Volume and average grade are usually well-known, thus reducing exploration expenses and technical risk. Added economic benefit may be the release of land previously covered by TSLs for development. There are also environmental benefits as particular components identified as environmental risk may be removed and remaining residues transferred into TSLs that comply with modern environmental legislation.

There are, however, also some tangible risks associated with retreatment of materials from TSLs. Most importantly, the value components that have escaped previous separation efforts are likely to be difficult to concentrate. Reasons for losses are manifold, but may include poor liberation or very fine grain size of ore minerals or complex deportment of target metals into various minerals. Furthermore, ore minerals may experience surface alteration processes whilst contained in TSLs for extended periods of time. Such processes result in the development of surface coatings or even complete transformation of primary ore mineral assemblages into a complex paragenesis of secondary products. Ultimately, such processes lead to a complex overprint of the inherent primary stratification related to tailings deposition by a secondary stratification that resembles supergene oxidation and cementation zones.

Given the above it appears only reasonable that TSFs should be exposed to careful geometallurgical characterization prior to retreatment [1]. This contribution will present two examples from the Ore Mountains, Germany [2]. Two large TSLs were systematically drilled; the tailings materials were subjected to comprehensive characterization. 3D models were constructed for the TSLs based on novel recoverability indices that take into account not only grade, but also other tangible characteristics of the tailings material, such as liberation and grain size of value components. In this manner, opportunities and limitations of intended retreatment can be constrained – and an optimal retreatment strategy developed.

References:
[1] Louwrens E et al. (2015) in: Tailings and mine waste management for the 21st Century, AUSIMM, 99-106
[2] http://www.r3-innovation.de/de/15499
  • Contribution to proceedings
    International Geological Congress, 27.08.-04.09.2016, Cape Town, South Africa
    Quantifying the resource potential of flotation tailings storage facilities – the role of geometallurgical characterization, Washington: American Geosciences Institute
Registration No. 24764 - Permalink

The EIT Raw Materials
Gutzmer, J.
Abstract: Invited lecture - no abstract
  • Lecture (others)
    Annual Graduation Ceremony of Emerald MSc Students, 23.-24.08.2016, Liege, Belgium
Registration No. 24761 - Permalink

A systematic investigation of the magnetic anisotropy of III-Mn-V dilute ferromagnetic semiconductors
Xu, C.; Yuan, Y.; Sawicki, M.; Helm, M.; Zhou, S.
Abstract: As one of the most important physical properties of dilute ferromagnetic semiconductors (DFS), the magnetic anisotropy exhibits a complicated character and its origin is under continuous discussion [1, 2]. From the point of view of application, different magnetic anisotropies could meet various needs of spintronic devices. Due to different physical parameters (e.g. band gap, lattice constant) in various Mn doped III-V DMSs, various magnetic anisotropies are expected and could be tailored by Mn or hole concentrations [3-5]. To investigate this in greater detail, we prepare three typical III-Mn-V DFSs, InMnAs, GaMnAs, and GaMnP by ion implantation and pulsed laser annealing, which is a complementary approach to low-temperature molecular beam epitaxy. We report a systematic investigation on the magnetic anisotropy with the aim to understand its physical origin.

[1]. T. Dietl et al., Rev. Mod. Phys. 86, 187-251 (2014)
[2]. M. Birowska et al., Phys. Rev. Lett. 108, 237203 (2012)
[3]. U. Welp et al., Phys. Rev. Lett. 90, 167206 (2003)
[4]. M. Sawicki et al., Phys. Rev. B 70, 245325 (2004)
[5]. C. Bihler et al., Phys. Rev. B 78, 045203 (2008)

Keywords: Magnetic anisotropy, dilute ferromagnetic semiconductors (DFSs), ion implantation, pulsed laser annealing
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft 2016, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 24760 - Permalink

Das Helmholtz Institut Freiberg für Ressourcentechnologie: Status und Ausblick
Gutzmer, J.
Abstract: No abstract - invited lecture
  • Lecture (others)
    Jahrestagung der Praxispartner, Interdisziplinäres Ökologisches Zentrum, 28.04.2016, Freiberg, Germany
Registration No. 24759 - Permalink

Compositional Data Analysis: introduction and applications (and some practice)
Tolosana-Delgado, R.
Abstract: This lecture will cover the fundamental aspects of compositional data analysis, from brief theoretical concepts to most widely used statistical analysis tools. Concepts will be illustrated with examples from Sediment Provenance Analysis. These will include estimating modal compositions, building confidence regions and drawing them in ternary diagrams, developing supervised classification methods to infer the origin of a sediment out of its (bulk or varietal grain) composition, and establishing regression models to describe compositional linear processes such as comminution and weathering.
Keywords: alr, centered logratio, principal components, sediment provenance, spurious correlation
  • Invited lecture (Conferences)
    Sedimentary Provenance Analysis (short course), 21.-23.09.2016, Göttingen, Deutschland
Registration No. 24757 - Permalink

Comparison of Atomistic Quantum Transport and Numerical Device Simulation for Carbon Nanotube Field-effect Transistors
Fuchs, F.; Zienert, A.; Mothes, S.; Claus, M.; Gemming, S.; Schuster, J.
Abstract: Carbon nanotube field-effect transistors (CNTFETs) are studied using atomistic quantum transport simulation and numerical device simulation. The studied CNTFETs consist of n-doped source- and drain-electrodes with an ideal wrap-around gate. Both the off- as well as the on-currents are described in very good agreement by both methods, which verifies the employed simplified approach in the numerical device simulation. The off-current is strongly dependent on interband tunneling in the studied CNTFETs. Thus, the good agreement between the methods verifies the tunneling model in the numerical device simulator, which can therefore be used to describe other tunneling devices, too. On the basis of the two methods we also discuss the effect of different channel lengths and aggressive gate scaling.
Keywords: carbon nanotube, field-effect transistor, numerical device simulation, atomistic quantum transport simulation
  • Contribution to proceedings
    Simulation of Semiconductor Processes and Devices (SISPAD), 06.-08.09.2016, Nürnberg, Deutschland
    Proceedings of SISPAD: IEEE, 978-1-5090-0818-6
    DOI-Link: http://dx.doi.org/10.1109/SISPAD.2016.7605197
  • Poster
    Simulation of Semiconductor Processes and Devices (SISPAD), 06.-08.09.2016, Nürnberg, Deutschland
Registration No. 24754 - Permalink

Investigation of Carbon Nanotube Field-effect Transistors Using Atomistic Quantum Transport and Numerical Device Simulation
Fuchs, F.; Zienert, A.; Schuster, J.; Mothes, S.; Claus, M.; Gemming, S.
Abstract: Carbon nanotube based field-effect transistors (CNTFETs) are studied by using atomistic quantum transport simulation and numerical device simulation. Atomistic simulations are based on the non-equilibrium Green’s functions formalism, where self-consistent extended Hückel theory is used [1]. We apply a parameter set previously developed in our group to describe contacts between metals and carbon nanotubes with a density functional theory (DFT)-like accuracy [2]. Numerical device simulations based on the effective-mass Schrödinger equation are done for comparison [3] to highlight the strengths but also the limitations of this widely used method.
The studied CNTFETs consist of n-doped source- and drain-electrodes together with an ideal wrap-around gate. Thus, the transistor exhibits Ohmic contacts and is comparable to the one studied experimentally by Lu et al. [4]. Different CNTs with diameters ranging from 0.5 nm (7,0-CNT) to 1.3 nm (16,0-CNT) are compared. For larger diameters, band-to-band tunneling (BTBT) takes place, leading to ambipolar transfer characteristics. For small diameters, however, states within the channel are strongly localized and the BTBT is subsequently suppressed, resulting in very high on/off ratios of about 107 and ideal unipolar transfer characteristics. We investigate how different device parameters influence the device performance and show that the studied CNTFET shows excellent properties for channel lengths down to 8 nm and for a very small gate electrode of only 0.4 nm length. Finally, a comparison between the atomistic model and numerical device simulation is given. We show that the on- and off-currents are described in very good agreement and discuss the differences with respect to the switching behavior.
[1] Calculations performed using Atomistix ToolKit 12.8 (www.quantumwise.com)
[2] Zienert et al., Nanotechnology 25 (2014)
[3] Claus et al., Journal of Computational Electronics 13 (2014)
[4] Lu et al., Journal of the American Chemical Society 128 (2006)

Keywords: carbon nanotubes, numerical device simulation, atomistic quantum transport simulation, electron transport, field-effect transistors
  • Lecture (Conference)
    11th International Symposium on Computational Challenges and Tools for Nanotubes, 28.08.-02.09.2016, Wien, Österreich
Registration No. 24753 - Permalink

An Atomistic Model for Carbon Nanotube Based Field-effect Transistors: Interband Tunneling and Device Scaling
Fuchs, F.; Zienert, A.; Schuster, J.; Gemming, S.
Abstract: We study carbon nanotube based field-effect transistors (CNTFETs) consisting of n-doped source and drain electrodes together with an ideal wrap-around gate. This system is comparable to the one studied experimentally by Lu et al. [1] and is our model for comparing different simulation approaches. In this contribution, we present our results based on a fully atomistic quantum transport model.
Carbon nanotubes (CNTs) with diameters ranging from 0.5 nm to 1.3 nm, which corresponds to the (7,0) CNT and (16,0) CNT, respectively, are studied. We find that in case of thick CNTs, the band-to-band tunneling (BTBT) strongly increases the leakage current in the off-state. This leads to ambipolar transfer characteristics in agreement with experimental results1. Concerning very thin CNTs, the BTBT has not been studied in much detail, yet. We demonstrate that for these kind of CNTs, states within the channel are strongly localized. They do not allow carrier transport and thus suppress the BTBT, which results in ideal unipolar transfer characteristics and on/off ratios of about 107.
We furthermore present a systematic investigation of the relation between device parameters and the resulting transistor characteristics, which can guide future device scaling. Thin CNTs for example allow outstanding device properties even for short channel lengths down to 8 nm. It is crucial to maintain channel control in ultra-scaled transistors. Thus, our studies also elucidate the impact of aggressive gate scaling. Even for a very small gate electrode of only 0.4 nm length, good switching properties can be preserved.
The non-equilibrium Green’s functions formalism together with self-consistent extended Hückel theory is used for the simulations. Thanks to a parameter set previously developed in our group [2], we can describe CNTs with a density functional theory-like accuracy.
[1] Lu et al., Journal of the American Chemical Society 128 (2006)
[2] Zienert et al., Nanotechnology 25 (2014)

Keywords: carbon nanotubes, field-effect transistor, extended Hückel theory, electron transport
  • Poster
    17th International Conference on the Science and Application of Nanotubes and Low-Dimensional Materials (NT16), 28.08.-02.09.2016, Wien, Österreich
Registration No. 24752 - Permalink

Stress Analysis in Semiconductor Devices by Kelvin Probe Force Microscopy
Sheremet, E.; Fuchs, F.; Paul, S. D.; Haas, S.; Vogel, D.; Rodriguez, R. D.; Zienert, A.; Schuster, J.; Reuter, D.; Geßner, T.; Zahn, D. R. T.; Hietschold, M.
Abstract: The determination of built-in strain in semiconductor devices with nanometer spatial resolution and high sensitivity is needed for the characterization of nanoscale electronic devices. Kelvin probe force microscopy (KPFM) is an atomic force microscopy-based method that provides the spatially resolved surface potential at the sample surface, fulfilling the requirements on resolution and sensitivity. The contrast observed in KPFM imaging is often attributed to stress, but there are only a few reports on the application of KPFM for quantitative stress analysis [1]. In this contribution we focus on the application of KPFM for analysis of stress in silicon devices, such as copper through silicon vias and silicon membranes. The experimental results are compared with density functional theory calculations of strained silicon. This work provides critical insights into the quantitative determination of stress at the nanoscale that so far has gone largely unnoticed in the scanning probe microscopy community.
[1] W. Li, D.Y. Li, J. Appl. Phys. 99, 073502 (2006).

Keywords: silicon, kelvin probe force microscopy, density functional theory
  • Poster
    DPG Frühjahrstagung Regensburg, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 24751 - Permalink

Electronic Structure and Transport Properties of Thin Silicon Nanowires
Fuchs, F.; Gemming, S.; Schuster, J.
Abstract: Silicon nanowires (SiNWs) are promising candidates as building blocks for electronic devices. For the simulation of SiNWs, numerical device simulations, based on the silicon bulk band structure, are often used. When the diameter of the wires is reduced, however, atomistic quantum simulations become mandatory at some point. In the present work, thin hydrogen-passivated SiNWs with diameters between 1 and 6 nm are studied by means of density functional theory. It is shown that the band gap approaches the bulk value in the limit of infinitely thick nanowires and increases for thin wires due to quantum confinement. Using a radially resolved density of states it is demonstrated, that the density of states is highest in the nanowire center, where most of the current transport would occur, and decreases near the surface. Comparing the density of states between SiNWs with different diameters, the transition to bulk silicon can be observed. This justifies the use of bulk band structure approximations for thicker SiNWs, but also highlights the need for atomistic quantum simulations in case of thinner ones.
Keywords: silicon nanowire, density functional theory, quantum confinement
  • Lecture (Conference)
    DPG Frühjahrstagung Regensburg 2016, 06.-11.03.2016, Regensburg, Deutschland
Registration No. 24750 - Permalink

Experimentelle Untersuchung zum Stofftransport in einer Blasensäule mittels schneller Röntgentomographie
Ayubi, M.
Abstract: Die Bearbeitung des vorliegenden Beleges umfasste eine Literaturrecherche zur Hydrodynamik und Stofftransport in Blasensäulenreaktoren. Es wurden experimentelle Untersuchungen mit der ultraschnellen Röntgentomographie durchgeführt und anhand der gemessenen Daten hydrodynamische Parameter und Parameter zum Stofftransport extrahiert.
  • Study thesis
    TU Dresden, 2016
    Mentor: Ragna Kipping
    71 Seiten
Registration No. 24749 - Permalink

Investigation of inertial waves inside a liquid metal column by means of electromagnetic fields
Vogt, T.; Räbiger, D.; Eckert, S.
Abstract: In this study, the dynamics of inertial waves inside a cylindrical vessel was studied experimentally. The liquid metal GaInSn was chosen as fluid in order to enable a contactless stimulation of the flow inside the cylinder by means of electromagnetic fields. A rotating magnetic field (RMF) generates a supercritical rotating motion of the liquid. The excitation of the inertial waves is realised by means of periodic field strength modulations and by means of short intense magnetic field pulses. Furthermore, the experiment demonstrates that inertial waves may be excited spontaneously by turbulent structures in the rotating flow. The ultrasound Doppler velocimetry was used to record the flow structure and to identify the inertial waves occurring in the setup.
  • Lecture (Conference)
    International Congress of Theoretical and Applied Mechanics, 21.-26.08.2016, Montreal, Canada
  • Contribution to proceedings
    International Congress of Theoretical and Applied Mechanics, 21.-26.08.2016, Montreal, Canada
Registration No. 24748 - Permalink

Higher wavenumber shift of Pb (Al1/2Nb1/2)O3 substitution in relaxor ferroelectric Pb(Zr0.52Ti0.48)O3-Pb(Zn1/3Nb2/3)O3 ceramics
Zhu, J. J.; Li, C. Q.; Jiang, K.; Zhang, P.; Tong, W. Y.; Liu, A. Y.; Shi, W. Z.; Liu, Y.; Huang, Y. P.; Li, W. W.; Hu, Z. G.
Abstract: We report the lattice dynamics of 0.8Pb(Zr0.52Ti0.48)O3−(0.2−x)Pb(Zn1/3Nb2/3)O3−xPb(Al1/2Nb1/2)O3 (0.8PZT−(0.2−x)PZN−xPAN, 0.02≤x≤0.08) ceramics around morphotropic phase boundary (MPB) by infrared and Raman spectra. The dielectric functions in the wavenumbers range between 50 and 1000 cm−1 were extracted from the factorized oscillator model. The addition of PAN to PZT-PZN system introduces Al3+ ions to the B-site and all of these Raman-active modes in the measured range are related to B-site atoms vibration. The effect of PAN addition leads to infrared and Raman modes shifting to higher wavenumbers, because the atomic weight of Al is smaller than that of Zn. Therefore, the substitution of B-site atom in PZT-PZN system is the dominant reason to influence the frequency shift of infrared and Raman modes.
Keywords: PZT-based ceramics, Morphotropic phase boundary, Dispersion relation, Lattice vibrations, Raman spectroscopy Registration No. 24747 - Permalink

Weakly turbulent Rayleigh-Bénard convection in a horizontal magnetic field
Vogt, T.; Ishimi, W.; Tasaka, Y.; Yanagisawa, T.; Sakurba, A.; Eckert, S.
Abstract: MHD Rayleigh-Bénard convection was studied experimentally using a liquid metal inside a box with square horizontal cross section and aspect ratio five. Systematic flow measurements were performed by means of ultrasound Doppler velocimetry that can capture time variations of instantaneous velocity profiles. Applying a horizontal magnetic field organizes the convective motion into a flow pattern of quasi-two dimensional rolls arranged parallel to the magnetic field. If the Rayleigh number (Ra) is increased over a certain threshold Ra/Q, whereby Q is the Chandrasekhar number, the convection flow undergoes a transition to turbulence. We explore the flow structure in a weakly turbulent convection pattern by means of experiments and by means of numerical simulations.
  • Lecture (Conference)
    10th PAMIR International Conference, 20.-24.06.2016, Cagliari, Italy
  • Contribution to proceedings
    10th PAMIR International Conference, 20.-24.06.2016, Cagliari, Italy
Registration No. 24746 - Permalink

Lithological units and Sn deportment of a compositionally complex skarn ore (Hämmerlein, Erzgebirge, Germany)
Kern, M.; Kästner, J.; Gutzmer, J.
Abstract: The Hämmerlein seam is part of the world class Tellerhäuser deposit in the Erzgebirge, Germany, and represents a compositionally complex polymetallic Sn-In-Zn skarn. Current resources amount to 100000 t Sn at a cut-off grade of 0.2 wt. %. In addition, 2100 t of In and 270000 t of Zn have been estimated [1]. In the late 1970s, 50000 t of ore from the Hämmerlein seam were mined and processed experimentally in a pilot plant, but grade and recovery remained below expectations. Cited reasons for poor recovery the complex mineralogy and variability in grain sizes of valuable minerals [2]. The predicted rise in global Sn consumption and limited availability of high grade deposits [3] render the Tellerhäuser deposit an interesting exploration target [1]

A consortium of German research institutions currently conducts new beneficiation experiments on the Hämmerlein orebody. Determination of the Sn deportment and the characterization of the different lithological (skarn) units are the first steps in this process. For this purpose, three transects in the central part of the Hämmerlein orebody were mapped and a suite of hand specimen collected to represent all relevant lithotypes within the studied part of the orebody. Thin sections were prepared and analyzed using the Mineral Liberation Analyzer (MLA) to obtain quantitative data about mineralogy, mineral grain sizes, intergrowths, and associations. The remaining material of the hand specimen was crushed to 99 % < 250 µm. This granular material was split to produce grain mounts for further mineralogical studies and in order to prepare sample powders for geochemical analysis.

The Hämmerlein skarn orebody can be subdivided into the following three macroscopically distinct lithotypes: 1. magnetite-dominated (40 – 80 wt. % magnetite), 2. sulphide-dominated (> 20 wt. % sphalerite) and 3. silicate-dominated (> 60 wt.% silicates). In the silicate-dominated unit a gradual transition of different silicate minerals enables further discrimination of a chlorite-rich, an amphibole-chlorite-rich, an epidote-pyroxene-rich and a garnet-rich subunit. The hanging and footwall are best described as mica schist and gneiss, respectively.

The primary host mineral for Sn is cassiterite (SnO2) with grain sizes between 1 µm and 1 mm. Some of the cassiterite has fibrous crystal habit. Significant amounts (ca. 1.4 wt. %) of coarse-grained (50 µm to 1 mm) cassiterite is present in the chlorite subunit. The amphibole-chlorite subunit contains an average of 0.3 wt. % cassiterite. Samples from other parts of the Hämmerlein orebody indicate significant amounts of cassiterite in the magnetite- and the sulphide-dominated lithotypes as well.

Stokesite (CaSnSi3O9 ∙ 2H2O) is the second most abundant Sn mineral. It appears in fine-grained aggregates in the amphibole-chlorite subunit and in the magnetite-dominated ore type reaching concentrations of ca. 0.1 wt. %. Notable Sn concentrations were detected by WDX in some examples of titanite (≤ 21 wt. %), epidote (≤ 4.4 wt. %), amphibole (≤ 1.9 wt. %), garnet (≤ 2.3 wt. %), and iron oxides (≤ 2.3 wt. %).

Our preliminary results illustrate that the Sn mineralisation of the Hämmerlein skarn is indeed very complex. Cassiterite dominates, but other minerals (most notably stokesite) do contribute significantly to the deportment. Further studies will aim to quantify the variability of deportment and other resource characteristics, in order to guide mineral processing test work.
  • Lecture (Conference)
    EMC Rimini 2016, 19.-22.09.2016, Rimini, Italien
Registration No. 24745 - Permalink

The Hämmerlein orebody: Lithological units and Sn deportment
Kern, M.; Kästner, J.; Gutzmer, J.
Abstract: The Hämmerlein seam is part of the world class Tellerhäuser deposit in the Erzgebirge, Germany, and represents a compositionally complex polymetallic Sn-In-Zn skarn. Current resources amount to 100 000 t Sn at a cut-off grade of 0.2 wt. %. In addition, 2100 t of In and 270 000 t of Zn have been estimated [1]. In the late 1970s, 50 000 t of ore from the Hämmerlein seam were mined and processed experimentally in a pilot plant, but grade and recovery remained below expectations. Cited reasons for poor recovery the complex mineralogy and variability in grain sizes of valuable minerals [2]. The predicted rise in global Sn consumption and limited availability of high grade deposits [3] render the Tellerhäuser deposit an interesting exploration target [1].
A consortium of German research institutions is conducting new beneficiation experiments on ores from the Hämmerlein orebody. Determination of the Sn deportment and the characterization of the different units are the first step towards successful beneficiation. For this purpose, three transects in the central part of the Hämmerlein seam were mapped and sampled. Thin sections were prepared and analyzed using the Mineral Liberation Analyzer (MLA) to obtain quantitative data about mineralogy, mineral grain sizes, mineral intergrowth and mineral associations. The remaining material was crushed to 99 % < 250 µm and grain mounts were prepared for geochemical analysis and for further MLA studies.
Taking into account the amount of main ore- and/or gangue-forming minerals, following three units of the orebody have been distinguished: 1. magnetite-dominated (40 – 80 wt. % magnetite), 2. sulphide-dominated (> 20 wt. % sphalerite) and 3. silicate-dominated (> 60 wt. % silicates). In the silicate-dominated unit a gradual transition of different silicate minerals enables further discrimination of a chlorite-rich, an amphibole-chlorite-rich, an epidote-pyroxene-rich and a garnet-rich subunit. The hanging and footwall are best described as mica schist and gneiss, respectively. Both are partially overprinted and show skarn features in proximity to the skarn ore body.
Sn-bearing minerals are present in the skarn ore body as well as in the overprinted host rocks. The primary host mineral for Sn is cassiterite (SnO2) with grain sizes between 1 µm and 1 mm. Some of the cassiterite has fibrous crystal habit. Significant amounts (ca. 1.4 wt. %) of coarse-grained (50 µm to 1 mm) cassiterite are present in the chlorite subunit. The amphibole-chlorite subunit contains an average of 0.3 wt. % cassiterite. Additional samples from other parts of the Hämmerlein seam indicate significant amounts of cassiterite in the magnetite and the sulphide ore types as well. Malayaite (CaSnSiO5) is the second most abundant Sn mineral. It appears in fine-grained aggregates in the amphibole-chlorite subunit of the silicate-dominated ore type and in the magnetite-dominated ore type reaching concentrations of ca. 0.1 wt. %. Notable Sn concentrations were detected by EDX in typically Sn-free titanite, epidote and iron oxides. However, the total amount of Sn in these minerals account for less than 10 wt. % of the total Sn content of the deposit.
Our preliminary results illustrates that the Sn mineralisation of the Hämmerlein orebody is indeed very complex. The highest beneficiation potential has cassiterite and maybe malayaite, depending on the concentrations and host unit.
  • Poster
    GOOD Meeting 2016, 16.-18.03.2016, Freiberg, Deutschland
Registration No. 24744 - Permalink

Flash lamp annealing of transparent conducting oxides and other thin films
Rebohle, L.; Schumann, T.; Prucnal, S.; Skorupa, W.
Abstract: This presentation gives a short overview about the technique of flash lamp annealing in general and current activities at HZDR related to this topic. Thereby, the focus is on the possibilities to maximize the UV output of the flash lamp the use for thin semi-transparent films, namely transparent conducting oxides.
Keywords: flash lamp annealing, transparent conducting oxides, zinc oxide
  • Lecture (Conference)
    Treffen der Nutzergruppen Heißprozesse und RTP und Ionenimplantation, 08.-09.12.2016, Erlangen, Deutschland
Registration No. 24743 - Permalink

Thermal spin transfer torque on MgO-based magnetic tunnel junctions using FMR microresonators
Cansever, H.; Fowley, C.; Narkowicz, R.; Kowalska, E.; Aleksandrov, Y.; Yildirim, O.; Titova, A.; Lenz, K.; Lindner, J.; Fassbender, J.; Deac, A. M.
Abstract: MgO-based magnetic tunnel junctions are commonly used in spintronic device applications, such as recent spin transfer torque random access memory (STT-RAM) because of their non-volatility, fast switching and high storage capacity. Spin transfer torque is defined as a spin polarized current flowing through a ferromagnet exerting a torque on the local magnetization. With thermal spin transfer torque (T-STT), thermally excited electron transport is used instead of spin polarized charge current and provides an interesting way of using thermoelectric effects in magnetic storage applications. Our study focuses on fundamental experimental research aimed at demonstrating that thermal gradients can generate spin-transfer torques in MgO-based magnetic tunnel junctions (MTJs). We use microresonators in order to analyze how the ferromagnetic resonance signal corresponding to the free layer of an in-plane MgO-based tunnel junction device is modified in the presence of a temperature gradient across the barrier.
This work is supported by DFG-SPP1538

Keywords: Spin Transfer Torque, MTJ, microresonator, FMR
  • Poster
    SpinCat PhD Workshop Mainz, 18.-19.08.2016, Mainz, Germany
Registration No. 24741 - Permalink

Neue numerische Methoden zur Bearbeitung und 3D-Interpretation von Geodaten und -modellen in interdisziplinarer Forschung
Menzel, P.
Abstract: Anhand allgemeiner und spezifischer Aufgaben und Fragen, die sich aus der Mitarbeit in den beiden Forschungsprojekten AIDA und TiPOT3D ergaben, wird in dieser Arbeit gezeigt, wie Ansätze und Verfahren aus der Geoinformatik die Prozessierung und die Interpretation der Geophysik und hier speziell der Potentialverfahren unterstützen können.
Zuerst wird gezeigt, wie die Kommunikation und Interaktion in interdisziplinären Forschungsprojekten durch Arbeiten mit Schwerpunkt Geoinformatik unterstützt warden kann. Dies erfolgt exemplarisch am BMBF-Verbundprojekt “AIDA - From Airborne Data Inversion to In-Depth Analysis”. Für die interne Projektkommunikation und Interaktion wird das “AIDA-Projekt-Wiki” vorgestellt. Es soll einerseits die Kommunikation innerhalb des Projekts unterstützen und gleichzeitig eine online-basierte Plattformzum Austausch und der Archivierung projektbezogener Daten ermöglichen. Das “AIDAProjekt-Wiki” koordiniert und archiviert die Projektkommunikation und vereinfacht die planerische Organisation von Projekttreffen, Publikationen und Tagungsteilnahmen.
Zusätzlich wurden Schnittstellen für den Austausch der verschiedenen Projektdaten zwischen den Projektteilnehmern bereitgestellt. Anhand zweier Anwendungen wird gezeigt, wie Modellinformationen zwischen verschiedenen Modellrepräsentation konvertiert werden.
Die Evaluierung geologischer 3DUntergrundmodelle mittels Dichte-Modellierungen war eines der Hauptanliegen im BMBF-Verbundprojekt. In AIDA wurde von den Projektpartnern für ein Untersuchungsgebiet in Norddeutschland ein solches 3D Untergrundmodell entwickelt (Bremerhaven-Cuxhavener Rinne mit Informationen und Daten aus Strukturgeologie, Elektro-Magnetik, Gravimetrie, Seismik und Bohrungen). In dieser Arbeit wird gezeigt, wie die Modellgeometrie für die Schweremodellierung aufbereitet und mit Literatur-Dichten für die verschiedenen lithologischen Einheiten vervollständigt wurde. Der berechnete Modellschwereeffekt wird mit den Ergebnissen früherer Arbeiten verglichen.
Der Vergleich mit den residualen Schwerefeldern ergab eine weitgehende Übereinstimmung. Unterschiede werden damit begründet, dass Dichteänderungen innerhalb der oberflächennahen lithologischen Einheiten nicht im Modell abgebildet werden konnten. Später wird ein hier entwickeltes Verfahren zur statistischenAbschätzung unbekannter Verteilungen von Materialparametern imUntergrund abgeleitet und gezeigt, wie diese oberflächennahen Dichten abgeschätzt werden können.
Das Verfahren ermöglicht es, aus der vorhandenen Verteilung der spezifischen Widerstände für die Bremerhaven-Cuxhavener Rinne Aussagen über die relative Verteilung der Dichten im Modellgebiet zu treffen.
Der heutzutage übliche enorm große Datenumfang geophysikalischer Datensätzen erschwert die numerische Verarbeitung oft massiv. Es wird deshalb untersucht, wie Punktdatensätze und/oder triangulierte Netze so optimiert werden können, dass sie trotz erheblich reduziertem Datenumfang für geophysikalische Anwendungen bei der weiter verwendet werden können: CIDRe heißt das in dieser Arbeit entwickelte Verfahren, dass es erlaubt, die Punktmenge von Datensätze so zu reduzieren, dass in Regionen mit geringen Änderungen in den Datenparametern niedrigere Punktdichten erzielt werden als in Regionen mit sich stark änderndenWerten. Anwendungen basieren auf der Auswertung von Datensätzen der Satellitenaltimetrie vor Nord-Chile und Aero-Gradiometer-Messungen in Nord-Norwegen.
Auch eine enorm hohe Anzahl von Dreiecken in einem triangulierten Geometriemodell erschwert die Verwendung dieser Geometrie in der 3D Modellierung und bei der Visualisierung. Um die Dreiecksanzahl dieser Modelle zu reduzieren, werden Verfahren vorgestellt, die hoch aufgelöste triangulierte Modelle vereinfachen und dabei deren “Form” weitgehend erhalten. Hierzu wurden verschiedene Ansätze der “Mesh-Simplification” implementiert und an die Erfordernisse der Schwereberechnung angepasst.
Mit Hilfe dieser Verfahren wird ein sehr hoch aufgelöstes Modell zweier Salzstöcke im Gifhorner Trog, auf nur 5% der initialen Dreiecksanzahl reduziert, ohne dass die Güte der darauf basierenden Schweremodellierung beeinträchtigt wird; d.h. es werden nur Differenzen zwischen den berechneten Schwerefeldkomponenten und -gradienten für das Ausgangsmodell und die vereinfachten Modelle von 1% zugelassen.
3D-Druck ist ein inzwischen weit verbreitetes Mittel zur analogen Repräsentation digitaler 3D Modelle vor allem in der Industrie und den Ingenieurwissenschaften. Es wird untersucht, wie ein 3D-Druck für geophysikalische Anwendungen genutzt warden kann. Beispielhaft wird dies am 3D-Drucker “Ultimaker 2” gezeigt und beschrieben, wie verschiedene 2D und 3D Modelle aus der Gravimetrie für den 3D-Druck aufbereitet werden. Im Rahmen dieser Arbeit wird gezeigt, dass mit analogen Repräsentationen von geophysikalischen Ergebnissen ein hoher kommunikativer Mehrwert erzielt werden kann.
  • Lecture (others)
    Disputation zur Dissertation, 12.09.2016, Kiel, Deutschland
Registration No. 24740 - Permalink

Observation of large magnetocaloric effect in equiatomic binary compound ErZn
Li, L.; Yuan, Y.; Xu, C.; Qi, Y.; Zhou, S.
Abstract: The magnetism, magnetocaloric effect and universal behaviour in rare earth Zinc binary compound of ErZn have been studied. The ErZn compound undergoes a second order paramagnetic (PM) to ferromagnetic (FM) transition at Curie temperature of T C ∼ 20 K. The ErZn compound exhibits a large reversible magnetocaloric effect (MCE) around its own T C. The rescaled magnetic entropy change curves overlap with each other under various magnetic field changes, further confirming the ErZn with the second order phase transition. For the magnetic field change of 0-7 T, the maximum values of the magnetic entropy change (−∆SMmax), relative cooling power (RCP) and refrigerant capacity (RC) for ErZn are 23.3 J/kg K, 581 J/kg and 437 J/kg, respectively. Registration No. 24739 - Permalink

Example of High Power Laser Experiment: High-contrast laser-proton acceleration from condensed hydrogen jet
Zeil, K.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Brack, F.; Metzkes, J.; Kluge, T.; Kraft, S.; Sommer, P.; Loeser, M.; Ziegler, T.; Schramm, U.; Goede, S.; Wolter, S.; Kazak, L.; Gauthier, M.; Curry, C.; Macdonald, M.; Schumaker, W.; Mishra, R.; Ruyer, C.; Fiuza, F.; Roedel, C.; Glenzer, S.
Abstract: The presentation gives an overview of a recent experiments for laser driven proton acceleration with high contrast using a plasma mirror at the high power laser Draco at HZDR, delivering pulses of 30fs and 3J on a cryogenic hydrogen target. Challenges of laser alignment and target preparation will be discussed in detail.
  • Invited lecture (Conferences)
    EUCALL Annual Meeting 2016, 01.09.2016, Dresden, Deutschland
Registration No. 24738 - Permalink

High-contrast laser-proton acceleration from condensed hydrogen jet
Zeil, K.; Obst, L.; Rehwald, M.; Schlenvoigt, H.-P.; Brack, F.; Metzkes, J.; Kluge, T.; Kraft, S.; Sommer, P.; Loeser, M.; Ziegler, T.; Schramm, U.; Goede, S.; Wolter, S.; Kazak, L.; Gauthier, M.; Curry, C.; Macdonald, M.; Schumaker, W.; Mishra, R.; Ruyer, C.; Fiuza, F.; Roedel, C.; Glenzer, S.
Abstract: Demanding applications like radiation therapy of cancer have pushed the development of laser plasma proton accelerators and defined levels of control and necessary proton beam stability in laser plasma experiments. The presentation will give an overview of the recent experiments for laser driven proton acceleration with high contrast using a plasma mirror at the high power laser Draco at HZDR, delivering pulses of 30fs and 3J on target. We present results of an experimental campaign employing a pure condensed hydrogen jet as a renewable target.
  • Lecture (Conference)
    Advanced Accelerator Conference 2016, 01.08.2016, National Harbor, Maryland, USA
Registration No. 24737 - Permalink

New developments in Contactless Inductivee Flow Tomography
Ratajczak, M.; Gundrum, T.; Wondrak, T.; Martin, R.; Stefani, F. (Editors)
Abstract: The contactless inductive flow tomography (CIFT) is a measurement technique that allows for reconstructing the mean global flow of an electrically conducting fluid. This is done by applying a primary magnetic field, measuring the flow induced secondary field outside of the container and solving the underlying inverse problem. A promising candidate for the application of CIFT is the continuous casting of steel, where any means of online flow-monitoring could help improving the process and might as well give new insights to the processes in the casting mould. In this paper we will give an overview of the achievements in tailoring CIFT to models of continuous casting, being in particular (a) a two-phase flow in a slab-mould using Argon injection, (b) a mould with an electromagnetic stirrer around the submerged entry nozzle, and (c) the application to a mould influenced by a strong electromagnetic brake (talk only).
Keywords: contactless inductive flow tomography, continuous casting, two-phase flow, magnetic stirring
  • Lecture (Conference)
    Optimization and Inverse Problems in Electromagnetism, 13.-15.09.2016, Roma, Italia
Registration No. 24736 - Permalink

Measurement of bubble parameters in opaque fluids using ultrasound transit time technique
Richter, T.; Wondrak, T.; Eckert, K.; Odenbach, S.
Abstract: The mapping of the fluid flow and the detection of bubbles is very important for opaque fluids, like liquid metals. In these cases ultrasound techniques can be used. Especially the ultrasound transit time technique (UTTT) possesses advantages for studying the bubble distribution or the contour dynamics. In order to validate UTTT with standard optical methods, we started with experiments of single Argon bubbles rising in water. The trajectory, the diameter, the terminal velocity and the tilting of the bubbles were measured simultaneously with UTTT and with a high speed camera. The results of both measurements techniques showed a good agreement.
After these calibration measurements first experiments of Ar bubbles rising in GaInSn were performed. In these experiments the bubble behavior was investigated for different magnitudes of a DC magnetic field in horizontal direction. The parameters of the bubble as well as the velocity of the bubble and of the wake were recorded simultaneously by UTTT and Ultrasound Doppler Velocimetry (UDV), respectively. The results of these measurements were compared with independent measurements using X-ray radiography, which visualized the entire trajectory of the bubble without an applied magnetic field.
The results of the UTTT measurements are shown in Figure 1). The measured bubble position xB and bubble diameter dB of one bubble are shown without (left) and with an applied magnetic field of 500 mT (right). Without magnetic _eld the bubble shows a zig-zag trajectory with an amplitude larger than 4 mm and the measured bubble diameter alternates during the rise between values of 3.4 mm up to 4.9 mm, which is inflicted by the tilting of the bubble during the zig-zag rise. For an applied magnetic field of 500 mT is the bubble trajectory straightened and the diameters show regular behavior around 5.3 mm. The shapes of the diameter curves without applied field are more irregular, indicating the tilting of an ellipsoidal bubble. The diameter curves with 500 mT have a near parabolic shape, so we can assume that there is nearly no tilting. Independent x-ray measurements on the same vessel visualized also the zigzag rise and a tilting of the bubble. These results are in good agreement with the UTTT data.
  • Lecture (Conference)
    14th Multiphase Flow Workshop - Short Course and Conference, 08.-10.11.2016, Dresden, Deutschland
Registration No. 24734 - Permalink

Ion induced self-organized patterning of crystalline semiconductor surfaces
Facsko, S.ORC; Ou, X.; Engler, M.; Erb, D.; Hübner, R.; Škeren, T.
Abstract: Low energy ion irradiation drives surfaces out of equilibrium by continuous atomic displacements in the sub-surface. At room temperature the accumulation of the created defects leads to surface amorphization and self-organized ripple patterns perpendicular or parallel to the ion beam direction are formed for incidence angles higher than 50°. At temperatures higher than the recrystallization temperature, however, all defects in the sub-surface region are dynamically annealed and the surface remains crystalline. In this regime, ion irradiation creates vacancies and ad-atoms on the crystalline surface due to sputtering and dislocations. The surfaces morphology is now determined by the kinetics of the mobile surface species. Due to the Ehrlich-Schwoebel barrier, i.e. an additional barrier for crossing terrace steps, 3D structures are created in a “reverse epitaxy” process [1].
We will present different kinds of self-organized patterns on crystalline surfaces induced by ion irradiation at elevated temperatures. Depending on the crystalline structure and the surface orientation regular patterns of inverse pyramids with three-fold, four-fold, or six-fold symmetry are observed. Furthermore, on III-V semiconductors with zinc-blende structure extremely regular periodic groove patterns with crystalline facets are produced [2].
Such periodic patterns can be used as templates for the deposition of nanostructured thin films with effective medium properties determined by the morphology, e.g. exhibiting a strong anisotropy.
[1] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).
[2] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).

Keywords: nanopatterning, ion beam irradiation, reverse epitaxy
  • Lecture (Conference)
    E-MRS 2016 Fall Meeting, 19.-22.09.2016, Warsaw, Poland
Registration No. 24733 - Permalink

Properties of Metallic Thin Films Grown On Periodically Corrugated Surfaces
Facsko, S.ORC; Ou, X.; Engler, M.; Erb, D.; Lenz, K.
Abstract: Nanostructured thin films are of growing relevance for all kind of applications in pho-tovoltaics, plasmonics, or as magnetic materials. Various methods have been used to fabricate nanostructured thin films with well defined morphology exhibiting tunable effective properties. Bottom-up, self-organized methods have been used extensively in the last years because of their fast and easy way of producing large-scale patterns with structures down to 10 nm.
Ion beam sputtering has proven to be a promising way to produce self-organized patterns on various surfaces [1]. Depending on the ion beam incidence angle, hex-agonally ordered dot patterns as well as ripple patterns oriented perpendicular or parallel to the ion beam direction are formed during the continuous sputtering. Peri-odically corrugated surfaces can also be obtained via crystal surface reconstruction during annealing. The resulting surfaces provide templates for the growth of nano-patterned thin films. Depending on the surface and interface free energies these films can grow in a conformal way reproducing the surface topography or as nano-particles on the substrate surface. Furthermore, depending on deposition angle, substrate temperature, beam flux, and deposition time, the nanoparticles can align parallel to the ripples, eventually coalescing and forming nanowires, thus tuning the physical properties of these structures via their geometrical dimensions.
Metal thin films grown in this way exhibit distinct optical properties due to localized surface plasmon resonance. Due to their alignment along the ripple structures the nanoparticles exhibit strongly anisotropic plasmonic resonances [2]. Furthermore, the magnetic properties of ferromagnetic thin films grown on rippled or faceted sub-strates are drastically changed by the presence of the periodic structures at the inter-face and on the surface [3].

[1] X. Ou, K.-H. Heinig, R. Hübner, J. Grenzer, X. Wang, M. Helm, J. Fassbender, and S. Facsko, Nanoscale 7, 18928 (2015).
[2] T.W.H. Oates, M. Ranjan, S. Facsko, and H. Arwin, Opt. Express 19, 2014 (2011).
[3] M.O. Liedke, M. Korner, K. Lenz, M. Fritzsche, M. Ranjan, A. Keller, E. Čižmár, S.A. Zvyagin, S. Facsko, K. Potzger, J. Lindner, and J. Fassbender, Phys. Rev. B 87, 024424 (2013).

Keywords: metallic thin films; magnetic properties; optical properties; surface plasmon resonance
  • Invited lecture (Conferences)
    18th International Conference on Solid Films and Surfaces (ICSFS18), 28.08.-2.09.2016, Chemnitz, Deutschland
Registration No. 24731 - Permalink

Defect-induced magnetism in SiC probed by nuclear magnetic resonance
Zhang, Z.; Dmytriieva, D.; Molatta, S.; Wosnitza, J.; Wang, Y.; Helm, M.; Zhou, S.; Kühne, H.
Abstract: We give evidence for intrinsic, defect-induced bulk paramagnetism in SiC by means of 13 C and 29 Si nuclear magnetic resonance (NMR) spectroscopy. The temperature dependence of the internal dipole-field distribution, probed by the spin part of the NMR Knight shift and the spectral linewidth, follows a Curie law and scales very well with the macroscopic DC susceptibility. In order to quantitatively analyze the NMR spectra, a microscopic model based on dipole-dipole interactions was developed. The very good agreement between these simulations and the NMR data establishes a direct relation between the frequency distribution of the spectral intensity and the corresponding real-space volumes of nuclear spins. The presented approach by NMR can be applied to a variety of similar materials and, thus, opens a new avenue for the microscopic exploration and exploitation of diluted bulk magnetism in semiconductors.
Keywords: nuclear magnetic resonance; defect magnetism; SiC
  • Lecture (Conference)
    E-MRS (European Materials Research Society) 2016 Fall Meeting, 18.-22.09.2016, Warsaw University of Technology, Poland
  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Dresden, Germany
Registration No. 24730 - Permalink

Ion Irradiation Assisted Fabrication of Si Quantum Dots for Ultra-Low Power Electronics
Heinig, K. H.; Facsko, S.; Stegemann, K. H.; Pruefer, T.; Xu, X.; Hlawacek, G.; Huebner, R.; Wolf, D.; Bischoff, L.; Moeller, W.; Borany, J.
Abstract: The use of single electron transistors in large-scale integrated circuits promises a further boost for higher integration density and lower power consumption. However, in order to achieve single electron operation at room temperature, quantum dots (QDs) with a few nanometers in diameter and defined tunnel junctions have to be fabricated. A technological route to achieve such requirements is the fabrication of Si QDs embedded in SiO2 by phase separation of metastable SiOx (x<2).
In a CMOS-compatible manner, a Si rich oxide layer is produced by ion beam irradiation through a Si/SiO2/Si stack [1]. Choosing the right thickness of the oxide layer of ~7 nm leads to the formation of QDs in the middle of the layer [2]. The position of the Si QDs formed by the subsequent phase separation can be further controlled by applying geometrical constrains to the self-assembly process. This can be achieved in two ways. Firstly, the Si concentration in the SiO2 is strongly enhanced locally by focused ion beam induced mixing. Secondly, under broad beam irradiation of pillars consisting of Si/SiO2/Si stacks, the local mixing is defined by the pillar diameter. It is predicted by 3D kinetic Monte-Carlo (kMC) simulations that a single Si QD of few nm in diameter is formed in the middle of the SiO2 layer of the pillar structure. The optimal geometries and irradiation condition for fabricating reproducible QDs are explored by means of 3DkMC using input data from dynamic 3D ion collision simulations (TRI3DYN).
We will discuss the underlying principles and the mechanism of Si QD formation by ion induced directed self-assembly and present first results of focused Ne+ ion irradiations of a Si/SiO2/Si layer stack as well as Si+ broad beam irradiations of pillars.
This work is part of the project IONS4SET (Horizon 2020 research and innovation program, Grant Agreement No 688072).
[1] K.-H. Heinig et al., Appl. Phys. A77, 17 (2003).
[2] L. Röntzsch et al., phys. stat. sol.(a) 202, R170(2005).

Keywords: ion irradiation, single electron transistor, Si quantum dots
  • Invited lecture (Conferences)
    20th International Conference on Ion Beam Modification of Materials (IBMM 2016), 30.10.-4.11.2016, Wellington, New Zealand
Registration No. 24729 - Permalink

Die Anwendung von Level-Of-Detail und Mesh-Simplification Strategien zur Vereinfachung komplexer Untergrundmodelle
Menzel, P.; Alvers, M.; Barrio-Alvers, L.; Götze, H.-J.; Schmidt, S.; Plonka, C.
Abstract: Die Interpretation von moderner 2D und 3D Seismik ermöglicht die Abbildung von Untergrundstrukturen mit sehr hoher Auflösung und Genauigkeit. Der große Datenumfang der auf der Grundlage von Messungen kompilierten Strukturmodelle erschwert of deren weitere Verwendung in anderen Modellierverfahren in den Geowissenschaften. Deshalb muss für diese Verfahren evaluiert werden, ob die gegebene geometrische Modellauflösung angemessen ist oder ob sie reduziert werden kann.
Komplexe Untergrundmodelle bestehen häufig aus mehreren komplexen triangulierten Flächen.
Um Anzahl der Dreiecke möglichst informationserhaltend zu reduzieren, werden in diesem Beitrag verschiedene hierarchische Ansätze verwendet und die Ergebnisse bezüglich ihrer Anwendbarkeit für eine Potenzialfeldvorwärtsmodellierung validiert. Die verwendeten Verfahren vereinfachen Dreiecksgitter, indem sukzessive Geometrieelemente aus einer gegebenen Vermaschung entfernt werden. Die Reihenfolge, in der die Elemente entfernt werden, wird dabei durch verschiedene Gewichtungsstrategien bestimmt. Alle verwendeten Verfahren erstellen hierarchische Strukturen, welche es ermöglichen, eine Modellgeometrie kontinuierlich in verschiedenen Auflösungsstufen („Level-Of-Detail“) bereit zu stellen und diese ineinander zu überführen.
Die Anwendung der „Mesh-Simplification“ Ansätze wird sowohl an synthetischen als auch an realen Geometriemodellen demonstriert. Für jedes Modell wurden verschiedenen Varianten der Modellgeometrie in mehreren Auflösungsstufen erzeugt. Sowohl für die niedriger aufgelösten Geometrien als auch für die initialen Modelle werden anschließend der Schwereeffekt und die Schweregradienten mit unserer hauseigenen Modelliersoftware IGMAS+ berechnet und miteinander verglichen.
Es wird gezeigt, dass die initiale Auflösung der gegebenen Modellgeometrie für die Berechnung des Schwere- und Schweregradienteneffektes bezüglich der Genauigkeit der vorhandenen Messdaten häufig nicht notwendig ist. Auch für vergleichsweise niedrig aufgelöste Modellversionen lässt sich ein FTG („full tensor gravity“)-Effekt berechnen, welcher sich kaum vom Effekt des initialen Modells unterscheidet, aber aufgrund der geringeren Dreiecksanzahl sehr viel effizienter berechnet werden kann. Dies gilt insbesondere für die Ergebnisse der „Mesh-Simplification“ Strategien, welche zusätzlich die Positionen der vorhandenen Schweremessungen für die Evaluation der Reihenfolge der Dreiecksgittervereinfachung mit heranziehen.

Keywords: Potentialfeldmodellierung, 3D Visualisierung, 3D Geometrie
  • Lecture (Conference)
    76. Jahrestagung der Deutschen Geophysikalischen Gesellschaft e.V., 14.-17.03.2016, Münster, Deutschland
Registration No. 24728 - Permalink

Purely Antiferromagnetic Magnetoelectric Random Access Memory
Kosub, T.; Kopte, M.; Hübner, R.; Liedke, M.; Lindner, J.; Fassbender, J.; Makarov, D.; Hühne, R.; Schmidt, O. G.; Appel, P.; Shields, B.; Maletinsky, P.
Abstract: Magnetic random access memory schemes employing magnetoelectric coupling to write binary information promise outstanding energy efficiency. We propose and demonstrate a purely antiferromagnetic magnetoelectric random access memory (AF-MERAM) that offers a remarkable 50 fold reduction of the writing threshold compared to ferromagnet-based counterparts, is robust against magnetic disturbances and exhibits no ferromagnetic hysteresis losses. Using the magnetoelectric antiferromagnet Cr2O3, we demonstrate reliable isothermal switching via gate voltage pulses and all-electric readout at room temperature. As no ferromagnetic component is present in the system, the writing magnetic field does not need to be pulsed for readout, allowing permanent magnets to be used.
Based on our prototypes of these novel AF-MERAM elements, we construct a comprehensive model of the magnetoelectric selection mechanism in thin films of magnetoelectric antiferromagnets. We identify that growth induced effects lead to emergent ferrimagnetism, which is detrimental to the robustness of the storage. After pinpointing lattice misfit as the likely origin, we provide routes to enhance or mitigate this emergent ferrimagnetism as desired.
Beyond memory applications, the AF-MERAM concept introduces a general all-electric interface for antiferromagnets and should find wide applicability in purely antiferromagnetic spintronics devices. In particular, the read out of the magnetic state is realized by Zero-Offset Hall [Kosub et al., Phys. Rev. Lett. 115, 097201 (2015)] which can detect the proximity magnetization that developes in metallic electrodes at the boundary of insulating antiferromagnets. This technique possesses considerable applicability to the field of antiferromagnetic spintronics, as it can probe the net magnetization of both metallic and insulating antiferromagnetic thin films.
  • Poster
    SPICE Workshop on Antiferromagnetic Spintronics, 26.-30.09.2016, Mainz, Deutschland
Registration No. 24727 - Permalink

1-D Fe-rich Konbu phase in InAs obtained by Fe ion implantation and pulsed laser melting
Yuan, Y.; Sawicki, M.; Hübner, R.; Potzger, K.; Weschke, E.; Dietl, T.; Helm, M.; Zhou, S.
Abstract: Transition-metal rich semiconductor nanostructures driven by spinodal decomposition are drawing considerable attention due to wide prospects of functionalization [1]. However, the complexity of the magnetic cations aggregation (e.g. the competition between p-d hybridization driven attractive force between magnetic cation, entropy terms, and kinetic barriers) hinders obtaining nano-clusters with the desirable structure. Here, a 1-dimensional (In,Fe)As mixed Konbu phase is tailoring by employing ion implantation and subsequent pulsed laser melting (shown in Fig. 1). These Fe-rich nano-columns are fully commensurate with the InAs host lattice and exhibit an isotropic super-paramagnetic behavior. The XAS/XMCD result shows that Fe atoms with valence +2 and +3 are co-existing and both are spin-polarized. Therefore, it is likely that the magnetism in these Fe-rich nano-columns can be provided via the double exchange mechanism as previously described for the Cr-rich phase in (Zn, Cr)Te [2]. However, it still remains to be clarified why these distinctive structures are formed only in InAs: Fe, but not in other III-Mn-V systems obtained by the same method.

[1]. T. Dietl, et al., Rev. Mod. Phys., 87, 1311-1377 (2015)
[2]. K. Kanazawa, et al., Nanoscale, 6, 14667-14673 (2014)
  • Poster
    Jaszowiec 2016, 20.-24.06.2016, Szczyrk, Poland
Registration No. 24726 - Permalink

Bioflotation with Siderophores
Schrader, S.ORC
Abstract: Siderophores are small organic molecules with a high affinity for binding Fe(III) and the ability to form strong complexes. They are produced by microorganisms to equalize the low bioavailability of iron in their environment.
There already is wide knowledge about siderophores, their different structures and the microorganisms (aerobic bacteria and fungi), that produce them.
The aim of the study is to test for the first time, whether it is possible to use siderophores for flotation processes.
Molecules with similar functional groups from the chemical industry have been applied successfully in flotation processes. The main advantage of using biotechnology for the production of siderophores is the wide natural diversity of the structures.

Keywords: siderophore, flotation, hydroxamates
  • Lecture (others)
    Microbiology Meeting HZDR - TU Bergakademie Freiberg, 07.11.2016, Freiberg, Deutschland
Registration No. 24725 - Permalink

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