Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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Only approved publications

27259 Publications
Charge Collection Efficiency in Segmented Semiconductor Detector Interstrip Region
Alarcon-Diez, V.; Vickridge, I.; Jakšić, M.; Grilj, V.; Schmidt, B.
Abstract: Charged particle semiconductor detectors have been used in Ion Beam Analysis (IBA) for over four decades without great changes in either design or fabrication. However one area where improvement is desirable would be to increase the detector solid angle so as to improve spectrum statistics for a given incident beam fluence. This would allow use of very low fluences opening the way for example to increased time resolution in real-time RBS or analysis of materials that are highly sensitive to beam damage. In order to achieve this goal without incurring the costs of degraded resolution due to kinematic broadening or large detector capacitance, a single-chip segmented detector (SEGDET) was designed and built within the SPIRIT EU infrastructure project. In this work we present the Charge Collection Efficiency (CCE) in the vicinity between two adjacent segments focusing on the interstrip zone. Microbeam Ion Beam Induced Charge (IBIC) was used to perform X-Y mapping of CCE with different ion masses and energies, as a function of detector operating conditions (bias voltage changes, detector housing possibilities and guard ring
configuration). We show the CCE in the active area edge region and have also mapped the charge from the interstrip region, shared between adjacent segments. The results indicate that the electrical extent of the interstrip region is very close to the physical extent of the interstrip and guard ring structure with interstrip impacts contributing less than 8% to the complete spectrum. The interstrip contributions to the spectra can be substantially reduced by an offline anticoincidence criterion through the list mode data analysis, which should also be easy to implement directly in the data acquisition software.

Keywords: silicon detectors, ion beam analysis, segmented detectors
  • Lecture (Conference)
    12th European Conference on Accelerators in Applied Research and Technology (ECAART12), 03.-08.07.2016, Jyväskylä, Finland
Registration No. 24962 - Permalink

MHD turbulence in Keplerian disks with net azimuthal magnetic field - bypass concept of self-sustenance via interplay of linear transient growth and nonlinear transverse cascade
Mamatsashvili, G.
Abstract: We studied the mechanism of the self-sustenance of MHD turbulence in spectrally stable stratified Keplerian disk flows threaded by nonzero net azimuthal magnetic field in the shearing box approximation. For this purpose, we performed direct numerical simulations of (homogeneous, subcritical) turbulence at different aspect ratios of the simulation boxes. Then, we analyzed the turbulence dynamics in Fourier/wavenumber/spectral space based on the simulation data to gain deeper insight into the self-sustaining dynamics of such subcritical MHD turbulence. Specifically, we examined the interplay of linear transient growth of Fourier harmonics and nonlinear processes. In the case of azimuthal field in the shearing box setup, the linear growth of (magnetic) perturbations has a transient nature and is strongly anisotropic in spectral space. This, in turn, leads to anisotropy of nonlinear processes in spectral space and, as a result, the main nonlinear process appears to be not a direct/inverse, but rather a transverse/angular redistribution of harmonics in Fourier space referred to as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by interplay of the linear transient growth and the transverse cascade. The main scheme of this interplay in Keplerian disks was first proposed in Chagelishvili, Zahn, et al. (2003) and then its realization in real flows has been investigated in our recent papers Horton et al. (2010), Mamatsashvili et al. (2014, 2016). This scheme exemplifies the bypass concept of subcritical turbulence in spectrally stable shear flows. Both transient growth and transverse cascade mainly operate at large length scales, comparable to the box size. Consequently, the central, small wavenumber area of Fourier space is crucial in the self-sustenance of the turbulence and is labeled as the vital area. Outside the vital area both transient growth and transverse cascade are of secondary importance - Fourier harmonics are transferred to dissipative scales by the usual nonlinear direct cascade.
Keywords: Nonmodal approach, transient growth, turbulence, accretion disks, transverse cascade
  • Invited lecture (Conferences)
    Seminar at the Paris-Meudon Observatory, 16.-18.11.2016, Paris, France
Registration No. 24947 - Permalink

Nonmodal analysis of helical magnetorotational instability
Mamatsashvili, G.; Stefani, F.
Abstract: The helical and azimuthal magnetorotational instabilities (HMRI), relative of standard MRI, has recently received much attention in connection with liquid metal experiments. Its main advantage is that, being governed by Reynolds and Hartmann numbers, persists at very small magnetic Prandtl numbers (Pm) typical to liquid metals, in contrast to standard MRI. However, its applicability to Keplerian astrophysical discs with similarly small Pm is still not settled and controversial; the main hindering factor is the Liu’s criterion. Aiming to resolve this issue, we carry out nonmodal analysis of HMRI, which allows us to capture its growth at intermediate times due to the non-self-adjointness of shear flows, which can occur even when their modal growth would be absent according to Liu’s criterion.
Keywords: magnetorotationa instability, nonmodal growth, nonnormality, astrophysical Keplerian disks, liquid metals
  • Lecture (Conference)
    GdR dynamo meeting, 27.06.-01.07.2016, Barcelona, Spain
Registration No. 24946 - Permalink

Ultrasound measurements in a physical model of Czochralski crystal growth in a horizontal magnetic field
Pal, J.; Grants, I.; Eckert, S.; Gerbeth, G.
Abstract: A horizontal magnetic field (HMF) may improve conditions in the melt during large silicon single crystal growth by the Czochralski technique. This observation is counter-intuitive as the HMF evidently breaks the rotational symmetry. A previous study has shown that the HMF is not able to significantly delay the Rayleigh-Bénard instability in a rotating cylinder. It has been observed that an oscillating flow sets in soon after the linear onset. Can we expect a stabilizing effect of the HMF in the Czochralski growth? Why the symmetry breaking by the HMF is eventually not so relevant? These are two central questions for our primarily experimental study. Besides, it is also meant as a benchmark for comparison with the numerical codes. To serve the latter purpose the boundary conditions should be preferably well defined. Having this in mind the temperature boundary conditions are defined as follows. An isothermal heating is applied at the bottom of a cylindrical cell filled with GaInSn alloy. The side wall is thermally insulated. An optionally rotating isothermal cooler models the growing crystal. A water-cooled layer of an alkaline solution keeps the rest of the metal surface free from oxides and models the radiation heat loss. The maximum HMF strength is 0.3 T that corresponds to a Hartmann number of about 1200. Velocity profiles are measured by ultrasound Doppler velocimetry.
Keywords: Czochralski crystal growth, Horizontal magnetic field, Ultrasound Doppler velocimetry
  • Lecture (Conference)
    10th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 28.-30.09.2016, Tokyo, Japan
  • Contribution to proceedings
    10th International Conference on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 28.-30.09.2016, Tokyo, Japan
    Proceedings of ISUD10, 9-12
Registration No. 24940 - Permalink

Physical model of Czochralski crystal growth in a horizontal magnetic field
Pal, J.; Grants, I.; Eckert, S.; Gerbeth, G.
Abstract: The horizontal magnetic field (HMF) may improve conditions in the melt during large silicon single crystal growth by the Czochralski technique. This observation is counter-intuitive as the HMF evidently breaks the rotational symmetry. A previous study has shown that the HMF is not able to significantly delay the Rayleigh-Bénard instability in a rotating cylinder [1]. It has been observed [2] that an oscillating flow sets in soon after the linear onset. Can we expect a stabilizing effect of the HMF in the Czochralski growth? Why the symmetry breaking by the HMF is eventually not so relevant? These are two central questions for our primarily experimental study. Besides, it is also meant as a benchmark for comparison with the numerical codes. To serve the latter purpose the boundary conditions should be preferably well defined. Having this in mind the temperature boundary conditions are defined as follows. An isothermal heating is applied at the bottom of a cylindrical cell filled with GaInSn alloy. The side wall is thermally insulated. An optionally rotating isothermal cooler models the growing crystal. A water-cooled layer of an alkaline solution keeps the rest of the metal surface free from oxides and models the radiation heat loss. The maximum HMF strength is 0.3 T that corresponds to a Hartmann number of about 1200. Velocity profiles are measured by ultrasound Doppler velocimetry. Temperatures are monitored in the vicinity of the triple point at the rim of the cooler, at the rim of the cell, inside of the cooler and of the heater. The Nusselt-Grashof number dependency is obtained by controlling the total heat flux injected at the bottom and measuring the temperature difference between the bottom plate and the cooler. The critical cooler rotation rate is determined at which the rotation introduces a significant variation of the velocity field dominated by the HMF-aligned convection rolls.

1. I. Grants, G. Gerbeth, J. Cryst. Growth, 358 (2012), 43-50
2. U. Burr, U. Müller, J. Fluid Mech., 453 (2002), 345-370

Keywords: Czochralski crystal growth, horizontal magnetic field
  • Lecture (Conference)
    1st German Czechoslovak Conference on Crystal Growth, 16.-18.03.2016, Dresden, Deutschland
Registration No. 24939 - Permalink

A few structural remarks on matrix PTQM and beyond
Günther, U.
Abstract: In the first part of the talk, the historical and structural origin of PT-symmetric ix3 quantum models is briefly sketched: the Yang-Lee edge singularities for the distribution of the zeros of the partition function of the 2D Ising model in the complex plane, the close relation to criticality in the complex extended Landau-Ginzburg model for 2nd-order phase transitions, Fisher's infra-red (IR) approximation near criticality by a quantum field theory with ix3 coupling. Recent conceptually puzzling results from operator theoretic investigations of related quantum mechanical toy models with PT-symmetric ix3 couplings are reinterpreted in this phase transition context.
In the second part of the talk, the specific structural features of PT-symmetric matrix models are discussed: hidden group theoretical aspects, Lie triple systems following from Cartan decompositions of the corresponding Lie algebras, projectivization embeddings to resolve singularities at PT phase transitions. Starting from these structural findings for finite-dimensional PT-symmetric matrix setups, possible technically feasible extensions toward infinite-dimensional Hilbert-Schmidt Lie groups, Fredholm groups and PT-symmetry related Hilbert-Schmidt Grassmannians are sketched.

Keywords: PT symmetric quantum systems, phase transitions, 2D Ising model, Landau-Ginzburg model, infra-red limit, criticality, operator theory, group theory, Lie triple systems, projectivization embeddings, Hilbert-Schmidt Lie groups, Fredholm groups, Hilbert-Schmidt Grassmannians
  • Invited lecture (Conferences)
    PHHQP16: Progress in Quantum Physics with Non-Hermitian Operators, 08.-12.08.2016, Kyoto, Japan
Registration No. 24936 - Permalink

From Landau-Ginzburg to PTQM: a few structural remarks
Günther, U.
Abstract: The historical and structural origin of PT symmetric ix3 quantum models is briefly sketched. Open questions are discussed and related possible lines for future research are suggested.

Starting from the Yang-Lee result on the distribution of complex zeros of the partition function for the 2D Ising model the structure and origin of the so called Yang-Lee edge singularities is discussed. The close structural relation to complex extended criticality in the Landau-Ginzburg model of 2nd-order phase transitions is shown and Fisher's result is recalled on the field theoretical infra-red (IR) limit of the fluctuating fields as an effective quantum field theory (QFT) with ix3 coupling. Based on this specific phase-transition related conceptual background of the ix3 model recent operator-theoretic findings and still open puzzles of the corresponding quantum mechanical toy model approximations are interpreted as having their origin in such still operator-theoretically unexplored phase-transition related model peculiarities. Possible strategies for future research are briefly sketched to fill corresponding mathematical and technical gaps.

Keywords: PT quantum systems, 2D Ising model, Yang-Lee edge singularities, IR-limit, Landau-Ginzburg theory of phase transitions, operator theory
  • Invited lecture (Conferences)
    Analytic and algebraic methods in physics XIII, 06.-09.06.2016, Prague, Czech Republic
Registration No. 24935 - Permalink

In-situ synchrotron studies of dendritic growth in solidifying Ga – In alloys
Grenzer, J.; Shevchenko, N.; Roshchupkina, O.; Baehtz, C.; Hoppe, D.; Cantelli, V.; Rack, A.
Abstract: X-ray absorption contrast techniques are an important diagnostic tool to investigate solidification processes in metallic alloys. This work is devoted to an in situ visualization of the dendritic growth during the bottom-up solidification of a Ga-25wt%In alloy under natural convection. The coupling of X-ray imaging with X-ray diffraction techniques provides additionally information of the crystallographic orientation of the growing dendrites.
A main advantage of X-ray radiography is the possibility to study simultaneously solidification phenomena on different length scales delivering information on both: the dendrite structure and the flow patterns especially in the vicinity of solidification front. Melt flow, mainly the convective transport of the solute, induces various effects on the dendrite and grain morphology [5]. All these phenomena depend sensitively on the local conditions like the dendrite arm spacing and orientation, the detachment of side branches, the local direction and intensity of the flow it self [3-5]. A more detailed analysis of these particular processes requires a much better spatial resolution. Using synchrotron radiation the spatial resolution of the radiography experiment was improved by more than a factor of 10 reaching a value of below 1µm. Moreover, using synchrotron radiation, the time to record a tomogram was considerably reduced making it possible to visualize a stable dendrite structure in a melt flow.
An other not sufficiently investigated phenomenon is the orientation selection in dendrite evolution. It was demonstrated that the primary dendrite growth directions can vary continuously between different crystallographic directions as a function of the composition–dependent anisotropy parameters [6]. Therefore a challenging part of this experiment was the combination of two in situ techniques: X-ray radiography and synchrotron X-ray diffraction. X-ray diffraction measurements can help to reconstruct crystallographic orientations of growing dendrites.
The first radiography / diffraction experiments with solidifying Ga-25wt%In alloy were performed at BM20 and ID19 at a spatial resolution of < 0.5 µm. The radiography/ diffraction experiments performed at the beamline BM20 were carried out at an energy of 28.5keV, where as at ID 19 the radiography and tomographic experiments were performed at energies at about 65keV using a filtered undulator spectrum without any additional monochromator.
An existing solidification setup and the solidification cell were improved for synchrotron experiments guaranteeing a stable(~0.1°C) temperature gradient to control the convection inside the cell. The nominal composition of the Ga–25wt%In alloy was prepared from 99.99% Ga and 99.99% In. The alloy was melted and filled into the Plexiglas hele-shaw cell with an area of ~230 x 230 mm2 and inner cell thickness of 150μm. The tomography experiment was carried out using a capillary with an inner diameter of 400µm cell.

Keywords: In-Ga alloy solidification crystal growth
  • Poster
    XTOP 2016 – 13th Biennial Conference on High-Resolution X-Ray Diffraction and Imaging, 04.-08.09.2016, Brno, Czech Republic
Registration No. 24926 - Permalink

Structural changes across the metal-insulator transition in thin epitaxial VO2 films
Grenzer, J.; Facsko, S.; Ou, X.; Ji, Y.
Abstract: Vanadium dioxide (VO2) got much interest in the recent years not only from the fundamental point of view as a correlated electron system but as well as due to its intriguing electrical and optical properties, like the metal-insulator transition (MIT) close to room temperature. This makes VO2 favourable for optoelectronic, switching or even memory devices. The main challenge for device applications is the epitaxial growth of VO2 on suitable substrates. Sapphire seems to be one of the promising substrate candidates for the growth of high quality epitaxial VO2 phases.
Referring to literature, the MIT is directly connected with a change in the crystal structure, namely the transition from the low temperature monoclinic phase (P21/c) to the high temperature tetragonal (rutile) phase (P42/mnm). However, this symmetry change at the transition temperature should be strongly influenced by the epitaxy itself. Comparing our structural investigations and electrical measurements the results indicate that the MIT as observed by the resistance measurement in epitaxial VO2 thin films seems to be not necessary accompanied by a complete monoclinic to rutile phase transformation. A slight lattice distortion causing a possible change in the atomic positions without breaking the existing the epitaxial relationship appears to be sufficient.

Keywords: in-situ X-ray diffraction
  • Poster
    XTOP 2016 – 13th Biennial Conference on High-Resolution X-Ray Diffraction and Imaging, 04.-08.09.2016, Brno, Czech Republic
Registration No. 24924 - Permalink

Tidally synchronized Tayler-Spruit dynamos
Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.
Abstract: The dynamo loop in Tayler-Spruit models for the generation of stellar magnetic fields can only be closed if the kink-type Tayler instability (TI) goes along with some alpha effect. While for large magnetic Prandtl numbers (Pm) some finite alpha can easily result from spontaneous symmetry breaking, low Pm systems show typically a vanishing or an oscillatory alpha effect. If the TI, with its typical m=1 azimuthal dependence, is exposed to an m=2 tidal forcing, we observe a sharp resonance if the tidal frequency equals the frequency of theintrinsic alpha oscillation. In the framework of a very simple alpha-Omega dynamo model we further show that this resonance can lead to synchronization of the dynamo. We also discuss the hypothetical possibility that this mechanism could link the 11.07 year periodicity of the tidally dominant Venus-Earth-Jupiter system with the Hale cycle of the solar magnetic field.
  • Lecture (Conference)
    17th MHD Days, 30.11.-02.12.2016, Göttingen, Germany
Registration No. 24923 - Permalink

Liquid metal experiments on dynamo action and magnetically triggered flow instabilities
Stefani, F.
Abstract: The magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. However, magnetic fields also play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects, i.e. hydromagnetic dynamo action and magnetically triggered flow instabilities, had been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability (MRI) was observed in the PROMISE experiment in Dresden-Rossendorf. More recently, the azimuthal MRI was found at the same facility. First evidence of the current-driven Tayler instability in a liquid metal was obtained, too. The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities. New results from the enhanced PROMISE facility with a strongly symmetrized azimuthal magnetic fields are presented. An outlook on future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project, is also given.
  • Invited lecture (Conferences)
    European GDR Meeting 2016, 27.06.-01.07.2016, Barcelona, Spain
Registration No. 24922 - Permalink

The Tayler instability at low magnetic Prandtl numbers: Chiral symmetry breaking and synchronizable helicity oscillations
Stefani, F.; Galindo, V.; Giesecke, A.; Weber, N.; Weier, T.
Abstract: The current-driven, kink-type Tayler instability (TI) is a key ingredient of the Tayler-Spruit dynamo model for the generation of stellar magnetic fields, but is also discussed as a mechanism that might limit the up-scaling of liquid metal batteries. Here, we focus on the chiral symmetry breaking and the related alpha-effect that would be needed to close the dynamo loop in the Tayler-Spruit model. For low magnetic Prandtl number, we observe intrinsic oscillations of the alpha-effect. These oscillations serve then as the basis for a synchronized Tayler-Spruit dynamo model, which could possibly link the periodic tidal forces of planets with the oscillation periods of stellar dynamos.
  • Contribution to proceedings
    10th PAMIR International Conference - Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italy
    Proceedings of the 10th PAMIR International Conference - Fundamental and Applied MHD, 978-88-90551-93-2, 686-690
Registration No. 24921 - Permalink

Flüssigmetallbatterien als stationäre Speicher - Strömungsmechanische Aspekte
Weier, T.; Barry, L.; Galindo, V.; Gerbeth, G.; Landgraf, S.; Seilmayer, M.; Starace, M.; Stefani, F.; Weber, N.
Abstract: Flüssigmetallbatterien, d.h. elektrochemische Hochtemperaturbatterien mit vollständig flüssigem Inventar, werden derzeit als preiswerte Regelenergiespeicher diskutiert. Das ursprünglich auf kleinere Zellen als Bestandteil thermisch regenerierbarer Systeme gerichtete Konzept soll auf Zellen mit Grundflächen im Quadratmeterbereich übertragen werden.

Eine elektrochemische Zelle mit vollständig flüssigem Inventar hat eine Reihe von Vorteilen: bei gut abgestimmten Dichten von Elektrolyt und aktiven Materialien ist die Batterie selbstassemblierend, eine stabile Dichteschichtung bildet sich aus. Die strukturlosen (flüssigen) Elektroden sind für Alterungserscheinungen unanfällig, versprechen somit gute Zyklierbarkeit, die Kinetik an den flüssig-flüssig Phasengrenzen und die Diffusionsprozesse sind vergleichsweise schnell, was hohe Stromdichten ermöglicht. Als aktive Materialien können breit und ökonomisch verfügbare Ausgangsstoffe eingesetzt werden. Die Ausnutzung positiver Skaleneffekte ist ein wichtiges Mittel zur Kostensenkung und die einfache Skalierbarkeit eine der grundlegenden Annahmen bei der Entwicklung von Flüssigmetallbatterien.

Hohe Stromdichten und große Phasengrenzflächen resultieren jedoch in erheblichen Zellströmen. Diese generieren Magnetfelder und mithin beträchtliche elektromagnetische Kräfte. Das flüssige Inventar der Zelle kann auf diese elektromagnetischen Einwirkungen mit Instabilitäten und elektromagnetisch getriebener Konvektion reagieren. Die Konsequenzen solcher Strömungen und Maßnahmen zu ihrer Begrenzung werden diskutiert und realisierte Flüssigmetallbatterien vorgestellt.

Keywords: Flüssigmetallbatterie, Tayler Instabilität, Elektro-Wirbel-Strömung
  • Invited lecture (Conferences)
    Materialforum Rhein-Main, 22.02.2016, Gelnhausen, Deutschland
Registration No. 24920 - Permalink

Visual observations and charge/discharge behavior of liquid metal cells
Weier, T.; Landgraf, S.; Starace, M.; Stefani, F.; Weber, N.
Abstract: Liquid metal batteries (LMBs) consist of a stable density stratification of a molten alkaline metal on the top, a liquid heavy metal on the bottom and a fused salt mixture sandwiched in between. Initially developed as part of energy conversion systems, today they are considered an inexpensive means for stationary large-scale storage of electrical energy. A special feature of LMBs is their very high current density enabled by the fast kinetics at liquid-liquid interfaces and the rapid mass transfer processes in fluids. Scale-up on the cell level will therefore result in large total currents per cell that might however trigger electromagnetic instabilities and/or generate electro-vortex flows.
To allow for an experimental verification of the numerical predictions, a number of low temperature liquid metal cells were tested in order to optimize operating conditions and material combinations. The final aim is the construction of a larger cell able to generate a considerable current.
Na and Li were tested as negative electrode materials versus a positive electrode made of Bi in both cases. Na has a relatively high solubility in its salts and forms a dark metal fog in the electrolyte. While this enables the visualization of an intense flow in the electrolyte, it also leads to an unwanted electronic conduction and accompanying capacity fading. Li solubility in its salts is much weaker and no metal fog formation was observed. Cycling behavior in the tethered drop cell is considerably more stable for Li than for Na. Estimated current densities based on the immersed surface of the drop exceed 2 A/cm2 by far, both for Na and Li. Electrolytes are varied as well since for the metal combinations mentioned above the melting point of the salt mixture determines the cell operating temperature.

Keywords: liquid metal battery, electrochemical energy storage
  • Poster
    67th Annual Meeting of the International Society of Electrochemistry, 21.-26.08.2016, Den Haag, Niederlande
Registration No. 24919 - Permalink

Dynamics of homogeneous shear turbulence: a key role of the nonlinear transverse cascade in the bypass concept
Mamatsashvili, G.; Khujadze, G.; Chagelishvili, G.; Dong, S.; Jiménez, J.; Foysi, H.
Abstract: To understand the mechanism of the self-sustenance of subcritical turbulence in spectrally stable (constant) shear flows, we performed direct numerical simulations of homogeneous shear turbulence for different aspect ratios of the flow domain with subsequent analysis of the dynamical processes in spectral or Fourier space. There are no exponentially growing modes in such flows and the turbulence is energetically supported only by the linear growth of Fourier harmonics of perturbations due to the shear flow non-normality. This non-normality-induced growth, also known as nonmodal growth, is anisotropic in spectral space, which, in turn, leads to anisotropy of nonlinear processes in this space. As a result, a transverse (angular) redistribution of harmonics in Fourier space is the main nonlinear process in these flows, rather than direct or inverse cascades. We refer to this type of nonlinear redistribution as the nonlinear transverse cascade. It is demonstrated that the turbulence is sustained by a subtle interplay between the linear nonmodal growth and the nonlinear transverse cascade. This course of events reliably exemplifies a well-known bypass scenario of subcritical turbulence in spectrally stable shear flows. These two basic processes mainly operate at large length scales, comparable to the domain size. Therefore, this central, small wave number area of Fourier space is crucial in the self-sustenance; we defined its size and labeled it as the vital area of turbulence. Outside the vital area, the nonmodal growth and the transverse cascade are of secondary importance: Fourier harmonics are transferred to dissipative scales by the nonlinear direct cascade. Although the cascades and the self-sustaining process of turbulence are qualitatively the same at different aspect ratios, the number of harmonics actively participating in this process (i.e., the harmonics whose energies grow more than 10% of the maximum spectral energy at least once during evolution) varies, but always remains quite large (equal to 36, 86, and 209) in the considered here three aspect ratios. This implies that the self-sustenance of subcritical turbulence cannot be described by low-order models.
Keywords: Transient growth, turbulence, bypass concept Registration No. 24916 - Permalink

RLumShiny - A graphical user interface for the R Package ’Luminescence’
Burow, C.; Kreutzer, S.; Dietze, M.; Fuchs, M.; Fischer, M.; Schmidt, C.; Brückner, H.
Abstract: Since the release of the R package ’Luminescence’ in 2012 the functionality of the package has been greatly enhanced by implementing further functions for measurement data processing, statistical analysis and graphical output. Along with the accompanying increase in complexity of the package, working with the command-line interface of R can be tedious, especially for users without previous experience in programming languages. Here, we present a collection of interactive web applications that provide a user-friendly graphical user interface for the ’Luminescence’ package. These applications can be accessed over the internet or used on a local computer using the R package ’RLumShiny’. A short installation and usage guide is accompanied by the presentation of two exemplary applications.
Keywords: R, Software, GUI, Luminescence dating, Abanico Plot, Cosmic Dose Rate
  • Ancient TL 34(2016)2, 22-32
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Registration No. 24915 - Permalink

Collision cascades enhanced hydrogen redistribution in cobalt implanted hydrogenated diamond-like carbon films
Gupta, P.; Becker, H.-W.; Williams, G. V. M.; Hübner, R.; Heinig, K.-H.; Markwitz, A.
Abstract: Hydrogenated diamond-like carbon films produced by C3H6 deposition at 5 kV and implanted at room temperature with 30 keV Co atoms to 12 at.% show not only a bimodal distribution of Co atoms but also a massive redistribution of hydrogen in the films. Resonant nuclear reaction analysis was used to measure the hydrogen depth profiles (15N-method). Depletion of hydrogen near the surface was measured to be as low as 7 at.% followed by hydrogen accumulation from 27 to 35 at.%. A model is proposed considering the thermal energy deposited by collision cascade for thermal insulators. In this model, sufficient energy is provided for dissociated hydrogen to diffuse out of the sample from the surface and diffuse into the sample towards the interface which is however limited by the range of the incoming Co ions. At a hydrogen concentration of ∼35 at.%, the concentration gradient of the mobile unbounded hydrogen atoms is neutralised effectively stopping diffusion towards the interface. The results point towards new routes of controlling the composition and distribution of elements at the nanoscale within a base matrix without using any heat treatment methods. Exploring these opportunities can lead to a new horizon of materials and device engineering needed for enabling advanced technologies and applications. Registration No. 24913 - Permalink

Compositional Calibration
van den Boogaart, K. G.; Tolosana-Delgado, R.; Renno, A. D.
Abstract: An emerging field in the statistics of (geo)chemical data is compositional data analysis. In this field the ratio of concentrations between elements is seen as the essential information, while the absolute concentration is considered irrelevant. E.g. for physical age determination the ratio of concentration of various nuclides is very important, while the absolute concentrations change subject to dilution and depletion processes. In many applications chemical data is rescaled to 100%, or transformed with a log ratio transformation. In both cases the information about the absolute concentration is lost.

The aim of the contribution is to initiate a discussion on how the compositional approach might modify the tasks and methods of metrology. Asking a sligthly different question might lead to different answers. We will consider the calibration of an LA-ICP-MS (laser ablation inductive coupled plasma mass spectrometer), which measures multiple, but not all elements (quasi) simultaneously.

If log ratios are considered the relevant quantity, we should be able to measure them unbiasedly and provide a precision assessment of their measurement. We show that both aspects are problematic, when the log ratio is applied to measurements independently calibrated with respect to absolute standards. The same individual absolute errors can correspond to very different relative errors due to inherent correlation between the counts.

A supplementary concept for a traceable calibration of relative concentrations is introduced and discussed. In the example we use a method based on multivariate Poisson regression for a compositional calibration of LA-ICP-MS measurements. A compositionally calibrated measurement does not carry absolute information, but only relative information about a subset of elements. The concept of a compositional error compatible with the variance concepts in compositional data analysis is introduced. This error can not be computed from classical absolute calibration information of single elements and provides essential information for compositional methods.

In the case of the LA-ICP-MS the absolute amount of material turned into plasma is strongly matrix dependent, while the counting ratios for different elements are much less so. In such cases a relative calibration can guarantee better compositional precision and allows the useage of much loosely matrix-matched standards in a well-defined range of matrix compositions.
  • Lecture (Conference)
    MATHMET 2016 - International Workshop on Mathematics and Statistics for Metrology, 07.-09.11.2016, Berlin, Germany
Registration No. 24912 - Permalink

Filtering lack of microhomogeneity in reference materials for microanalytical methods
van den Boogaart, K. G.; Renno, A. D.; Tolosana-Delgado, R.
Abstract: Homogeneity is a relative property of a sample in relation to the measurement (analytical method), the analyte, and the intended purpose, like the usage as a reference material (RM). The verification of homogeneity is essential to define a RM as fit for purpose. In this context, there have been recent efforts to check the possible superiority of synthetic RMs over natural ones. The assessment of homogeneity is an integral part of these synthesis tests and of the following certification for use as RM. With regard to their spatial variability, five types of microheterogeneity of RMs can be found in the literature, depending on which is the source of heterogeneity that it presents: random, systematic, periodic, nugget and island.

This contribution presents a first attempt towards such tests of microhomogeneity for discussion. In a first step, we define a stochastic random function model that will describe each of the types of microheterogeneity mentioned before. Then, in a quite natural manner a particular sampling strategy for each of them is derived in the second step, with the goal to filter out the undesired source of variability. In the third step, we derive a strategy of characterization of the material, namely a strategy of estimation of the heterogeneity properties of the RM that should be used to certify the reference nature of the material. These the adequacy of these strategies is shown in this contribution by using simulations of the several heterogeneity structures and of the proposed sampling and characterization strategies.

For instance, for the case of a random heterogeneity we may assume that the concentration of the target element is described by a random function (RF). If the covariance function of this RF would be known, the sampling strategy would be to repeat measurements on random positions of a very fine regular grid in such a way that the variance of their average decreases as fast as possible, using as many locations as necessary to ensure that it falls below the method specifications. Finally, the way to characterise the RM would require calibrating the concentration of the target element on a coarser grid, on as many locations as necessary to appropriately set the covariance function, using classical concepts and models of Geostatistics. Similar strategies can be derived for the rest of the heterogeneity structures, like robust methods for nugget heterogeneity or geostatistical concepts related to intrinsic functions of order k for systematic heterogeneity
  • Lecture (Conference)
    MATHMET 2016 - International Workshop on Mathematics and Statistics for Metrology, 07.-09.11.2016, Berlin, Deutschland
Registration No. 24911 - Permalink

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

Electron effective mass enhancement in Ga(AsBi) alloys probed by cyclotron resonance spectroscopy
Pettinari, G.; Drachenko, O.; Lewis, R. B.; Tiedje, T.
Abstract: The effect of Bi incorporation on the conduction band structure of Ga(AsBi) alloys is revealed by a direct estimation of the electron effective mass via cyclotron resonance absorption spectroscopy at THz frequencies in pulsed magnetic fields up to 65 T. A strong enhancement in the electron effective mass with increasing Bi content is reported, with a value of mass ∼40% higher than that in GaAs for ∼1.7% of Bi. This experimental evidence unambiguously indicates a Bi-induced perturbation of the host conduction band states and calls for a deep revision of the theoretical models describing dilute bismides currently proposed in the literature, the majority of which neglect or exclude that the incorporation of a small percentage of Bi may affect the conduction band states of the host material. Registration No. 24901 - 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.
[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


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.
[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

Analytical Electron Microscopy Study to Resolve the Phase Morphology of Organic Solar Cell Blends
Sedighi, M.; Löffler, M.; Röder, F.; Zschech, E.
Abstract: To increase the efficiency of bulk heterojunctions for organic photovoltaic devices, the complicated photon-to-electron conversion process has to be understood in detail. To this aim, one challenge is to resolve the correlation between processing parameters of organic solar cells (OSC), the resulting nanoscale morphology of the absorber layer, and efficiency of the completed device. Here, we present the effect of substrate heating on the morphology of the OSC where the active layer is a blend of two small molecules; ZnPc (ZnC32H18N8) as donor and C60 as acceptor.

Obtaining insights into the morphology of the active layer requires the spatial resolution and a contrast mechanism to discriminate two phases with similar average atomic number. To tackle this challenge, we combine electron microscopy imaging with different analytical techniques; energy dispersive X-ray spectroscopy (EDX) and electron energy loss spectroscopy (EELS) in TEM, as well as Energy selective Backscattered (EsB) imaging in SEM.

We imaged different phases of the donor and acceptor, forming ordered and non-ordered regions, depending on the way the heterojunction is fabricated. To this aim, we fabricated samples at substrate temperatures of 110°C and 150°C, each in two different configurations:

1) Focused ion beam prepared ultrathin lamella of a complete solar cell stack with glass substrate, Indium tine oxide (ITO) electrode, ZnPc:C60 blend of the active layer between electron and hole transport layers and aluminum top electrode.
2) Plane view sample as ZnPc:C60 blend deposited on a TEM grid coated with ITO layer.

It was shown that at a substrate temperature of 110°C, the solar cell device has high efficiency [1]., so we consider this as the optimum substrate temperature.

Since identification of the composition of each phase in the plane view sample is more straight forward, we use the plane view sample to attribute each structure to one component of the blend. SEM images recorded by using secondary electron detector show that, the high temperature sample consists of rod-like features and cube-shaped material in between the rods. By combination of analytical microscopy techniques, we can attribute the rod-like structures to ZnPc.

An energy-selective backscatter (EsB) electron detector in a SEM is used to obtain backscattered contrast of the plane view sample. Due to the atomic number difference between the donor phase and the acceptor phase, (the average atomic number of 8.6 for ZnPc and 6 for the C60) sufficient contrast can be achieved [2].

A clear confirmation for the attribution of the ZnPc phase to the rod-like features and the attribution of C60 to the granular structure in between can be drawn from the investigation of the sample in SEM using EDX and with even higher precision in TEM using an improved EDX system. The chemical mapping of zinc and carbon, proves the correct phase assignment, in both plane view and ultrathin samples, prepared at high temperature. For the sample produced at optimum temperature, a much smaller roughness was observed because of the absence of large ordered regions. Even in the plane view sample, the imaging contrast is low due to less separated phases and smaller domains.

To conclude, we clearly resolved the phase morphology of the interpenetrating network of ZnPc:C60 blends for high and optimum temperature samples in plane view and furthermore we were even able to reveal the morphology from TEM images of cross-section lamellas of the real solar cell stacks.

Since the ideal active layer should have domain sizes at the range of the exciton diffusion length (10-20nm), the sample produced at high temperature does not show the desired microstructure. Due to the domain sizes of ~100 nm there is no closed path for exciton dissociation. In addition to that, the sample shows a quite high roughness.

Authors thank A. G. Cid for SEM images. This work was supported by the German Science Council Center of Advancing Electronics Dresden (cfaed). TEM-EDX results were achieved by funding (support code 03SF0451) through the Helmholtz Energy Materials Characterization Platform (HEMCP) initiated by the Helmholtz Association and the German Federal Ministry of Education and Research (BMBF).

[1] S. Pfuetzner, C. Mickel, J. Jankowski, M. Hein, J. Meiss, C. Schuenemann, C. Elschner, A.A. Levin, B. Rellinghaus, K. Leo and M. Riede, “The influence of substrate heating on morphology and layer growth in C60:ZnPc bulk heterojunction solar cells” Org. Electron., 12 (2010), pp. 435–441
[2] A. G. Cid, M. Sedighi, M. Löffler, W. F. van Dorp and E. Zschech, “Energy-Filtered Backscattered Imaging Using Low-Voltage Scanning Electron Microscopy: Characterizing Blends of C60:ZnPc for Organic Solar Cells”. (DOI: 10.1002/adem.201600063)
  • Poster
    EMRS Fall Meeting 2016, 19.-22.09.2016, Warschau, Polen
Registration No. 24871 - 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

Erstellung einer Benutzeroberfläche in LabVIEW zur Steuerung der Mikroreaktoranlage zur Partialoxidation von Isobutan in flüssiger Phase.
Lu, X.
Abstract: Im Rahmen des Belegs wurde eine graphische Oberfläche unter Labview entwickelt, die zur Durchführung von Steuerungs-, Regelungs- und Messaufgaben für einen im Rahmen des Projektes Helmholtz-Energieallianz entworfenen und aufgebauten Reaktor benötigt wurde.
Keywords: Labview, GUI, MSR software, Mikroreaktor
  • Study thesis
    TU-Dresden, 2014
    Mentor: Thomas Willms
    31 Seiten
Registration No. 24854 - 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

“Reverse Epitaxy” on semiconductor surfaces by low energy ion irradiation
Engler, M.; Ou, X.; Facsko, S.
Abstract: Ion beam irradiation can produce different patterns on semiconductor surface. While the surface is amorphized at low temperatures, the surface remains crystalline above the dynamic recrystallization temperature. Reverse Epitaxy leads to pattern formation, which is driven by diffusion of vacancies and adatoms on the surface, above this temperature. The mechanisms of Reverse Epitaxy epitaxy are quite similar to mound formation in homoepitaxial growth. The surface is destabilized in both cases by an effective uphill diffusion current driven by Ehrlich-Schwoebel barriers. The patterns formed depend of step formation energies, diffusion on terraces, and Ehrlich-Schwoebel barriers, which all are anisotropic. Their anisotropy is determined by the surface symmetry. By changing the surface symmetry the resulting patterns are be changed.
  • Invited lecture (Conferences)
    XI-th International Conference on Ion Implantation and other Applications of Ions and Electrons - ION 2016, 13.06.2016, Kazimierz Dolny, Polska
Registration No. 24848 - 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

Kritische Rohstoffe aus zweiter Hand
Scharf, C.
Abstract: Seit drei Jahren lehre und forsche ich als Professorin für Metallurgie und Recycling der Hochtechnologiemetalle in Freiberg. Mein Team und ich setzen uns für einen nachhaltigen Umgang mit kritischen Metallen und anderen Industriemineralen ein. Wir erforschen neue Verfahren, um beispielsweise Produktionsabfälle zu reduzieren und die Wiederverwertung von Rohstoffen aus Altgeräten zu verbessern. Schlacken, Schlämme, Stäube, Späne oder Abwässer — in der Mineralrohstoff und Metallindustrie gibt es, technisch bedingt, viele Rückstände und damit auch eine große Menge bisher nicht genutzter Wertstoffe. Gemeinsam mit den wiederverwertbaren Stoffen, die in alten Elektrogeräten und sonstigen ausgedienten Produkten stecken, gelten sie inzwischen
als wichtiger Hebel für das Erreichen einer maximalen Ressourceneffizienz in der Kreislaufwirtschaft. Um solche „Rohstoffe aus zweiter Hand“, auch sekundäre Ressourcen genannt, dreht sich die Arbeit meines Forscherteams.
  • Contribution to external collection
    Prof. Roewer: ACAMONTA - Zeitschrift für Freunde und Förderer der Technischen Universität Bergakademie Freiberg, Marienberg: Erzdruck GmbH, 2016, ISSN 2193-309X, 27-28
Registration No. 24842 - 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

Entwicklung eines 18F-markierten Radioliganden zur Bildgebung der Phosphodiesterase 10A im Gehirn durch Positronen-Emissions-Tomographie
Wagner, S.
Abstract: Es ist kein Abstract vorhanden.
  • Doctoral thesis
    Universität Leipzig, 2016
    Mentor: Dr. Matthias Scheunemann
    166 Seiten
Registration No. 24840 - 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

High Magnetic Moment in Ferrimagnetic NiCo2O4 films via He Ion Irradiation
Pandey, P.; Bitla, Y.; Zschornak, M.; Wang, M.; Xu, C.; Grenzer, J.; Gemming, S.; Helm, M.; Chu, Y.-H.; Zhou, S.
Abstract: The spinel NiCo2O4 (NCO) exhibits unique combination of electrical conductivity, infrared transparency, electro catalytic activity, and ferrimagnetic order, which makes it an attractive material for spintronic applications.1 The NCO thin-films electrical and magnetic properties can be manipulated from high temperature ferrimagnetic and metallic to low temperature ferromagnetic and insulating by changing the growth temperature.2 The high quality epitaxial NCO films were grown on MgAl2O4 (100) substrate at ~ 400°C exhibits metallic behavior accompanied by ferrimagnetic order with moment ~ 2 μB/fu.1,2 Here, we report the impact of He-ion irradiation with fluence ranging from 5×1015/cm2 – 3×1016/cm2 on these metallic NCO films. The use of He-ion irradiation results in the coherent control of out-of-plane lattice parameter of these films without changing its in-plane lattice parameter (Figure 1). The comprehensive study of magnetization data reveals the magnetic moment increases drastically to ~ 4 μB/fu (Figure 1). The X-ray absorption spectroscopic study also suggests the possible charge redistribution within the octahedral sites of the NCO films which corroborates well with the increase in the magnetic moment.
  • Poster
    MEMRIOX International Workshop 2016, 25.-27.09.2016, Berghotel Bastei, Germany
Registration No. 24831 - Permalink

Hydrodynamic characterization of a novel external loop airlift inverse semi-fluidized bed reactor packed with loofa particles
Hegeholz, G.; Mohammed, I. H. M.; Schubert, M.
Abstract: In biochemical processes, column reactors replaced the stirred tank reactors for their advantages, like mild agitation. Among different configurations of column reactors airlift reactors constitute attractive systems for bio-catalyzed reactions due to the simple de-sign, low investment and operation costs. The advantages of combined external loop airlift and fluidized bed reactor in the downcomer over three-phase fluidized bed reactor and other configuration of airlift reactors are the unique hydrodynamic properties as it requires lower liquid flow rate for complete suspension of solid and good contact among the phases, easy removal of particles, rapid mixing, and easier scale up. This enables inverse fluidizing of low-density particles in the downcomer zone, characterized by low shear rates.
Keywords: fluidized airlift reactor, riser, downcomer, low-density particles, wire mesh sensor
  • Diploma thesis
    TU Dresden, 2016
    Mentor: Hampel Uwe
Registration No. 24827 - 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


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

Dynamical universality classes of simple growth and lattice gas models
Kelling, J.; Odor, G.; Gemming, S.
Abstract: Large scale, dynamical simulations have been performed for the two dimensional octahedron model, describing Kardar-Parisi-Zhang (KPZ) for nonlinear, or Edwards-Wilkinson (EW) for linear surface growth. The autocorrelation functions of the heights and the dimer lattice gas variables are determined with high precision. Parallel random-sequential (RS) and two-sub-lattice stochastic dynamics (SCA) have been compared. The latter causes a constant correlation in the long time limit, but after subtracting it one can find the same height functions as in case of RS. On the other hand the ordered update alters the dynamics of the lattice gas variables, by increasing (decreasing) the memory effects for nonlinear (linear) models with respect to RS. Additionally, we support the KPZ ansatz in 2+1 dimensions and provide a precise growth exponent value β = 0.2414(2).. We show the emergence of finite size corrections, which occur much earlier than the height saturation.
Keywords: Non-Equilibrium Thermodynamics, Surface Growth, GPU, Kardar-Parisi-Zhang


Registration No. 24802 - 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

Vertebral fractures – An underestimated side-effect in patients treated with radio(chemo)therapy
Pilz, K.; Hoffmann, A.; Baumann, M.; Troost, E.
Abstract: There is no abstract available, since this is an Editorial. Registration No. 24784 - Permalink

Technical feasibility of integrating 7 T anatomical MRI in image‑guided radiotherapy of glioblastoma: a preparatory study
Compter, I.; Peerlings, J.; Eekers, D.; Postma, A.; Ivanov, D.; Wiggins, C.; Kubben, P.; Küsters, B.; Wesseling, P.; Ackermans, L.; Schijns, O.; Lambin, P.; Hoffmann, A.
Abstract: Objectives: The use of 7 Tesla (T) magnetic resonance imaging (MRI) has recently shown great potential for high-resolution soft-tissue neuroimaging and visualization of microvascularization in glioblastoma (GBM). We have designed a clinical trial to explore the value of 7 T MRI in radiation treatment of GBM. For this aim we performed a preparatory study to investigate the technical feasibility of incorporating 7 T MR images into the neurosurgical navigation and radiotherapy treatment planning (RTP) systems via qualitative and quantitative assessment of the image quality.
Materials and methods: The MR images were acquired with a Siemens Magnetom 7 T whole-body scanner and a Nova Medical 32-channel head coil. The 7 T MRI pulse sequences included magnetization-prepared two rapid acquisition gradient echoes (MP2RAGE), T2-SPACE, SPACE-FLAIR and gradient echo sequences (GRE). A pilot study with three healthy volunteers and an anthropomorphic 3D phantom was used to assess image quality and geometrical image accuracy.
Results: The MRI scans were well tolerated by the volunteers. Susceptibility artefacts were observed in both the cortex and subcortical white matter at close proximity to air-tissue interfaces. Regional loss of signal and contrast could be minimized by the use of dielectric pads. Image transfer and processing did not degrade image quality. The system-related spatial uncertainty of geometrical distortion-corrected MP2RAGE pulse sequences was ≤2 mm.
Conclusion: Integration of high-quality and geometrically-reliable 7 T MR images into neurosurgical navigation and RTP software is technically feasible and safe.

Keywords: Ultra-high field MRI, Radiotherapy, Treatment planning, Glioblastoma, Geometrical distortion Registration No. 24783 - 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
  • Lecture (others)
    Meeting FWGM und UIT, 06.01.2017, Freiberg, Deutschland
Registration No. 24774 - Permalink

Radiation oncology in the era of precision medicine
Baumann, M.; Krause, M.; Overgaard, J.; Debus, J.; Bentzen, S. M.; Daartz, J.; Richter, C.; Zips, D.; Bortfeld, T.
Abstract: Technological advances and clinical research over the past few decades have given radiation oncologists the capability to personalize treatments for accurate delivery of radiation dose based on clinical parameters and anatomical information. Eradication of gross and microscopic tumours with preservation of health-related quality of life can be achieved in many patients. Two major strategies, acting synergistically, will enable further widening of the therapeutic window of radiation oncology in the era of precision medicine: technology-driven improvement of treatment conformity, including advanced image guidance and particle therapy, and novel biological concepts for personalized treatment, including biomarker-guided prescription, combined treatment modalities and adaptation of treatment during its course. Registration No. 24773 - 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.
[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.

[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.

[1] Louwrens E et al. (2015) in: Tailings and mine waste management for the 21st Century, AUSIMM, 99-106
  • 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

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