Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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30708 Publications
Magnetic ground state of the cubic perovskite Ba3NiNb2O9
Yamamoto, S.; Aslan Cansever, G.; Gottschall, T.; Uhlarz, M.; Blum, C. G. F.; Wolter-Giraud, A.; Aswartham, S.; Wurmehl, S.; Herrmannsdörfer, T.; Seiro, S.
We investigated the magnetic spin-1 perovskite Ba3NiNb2O9 by means of complex ac susceptibility measurements at extreme sample conditions. Ba3NiNb2O9 with cubic perovskite structure (Pm-3m) has a random occupation of Nb(66 %)/Ni(33 %) at the center of the cubic perovskite unit cell. Different from the isostoichiometric sister compound, Ba3NiNb2O9 with P-3m1 structure which shows both uud-spin configuration and multiferroicity, the magnetic properties of the investigated system have not been studied below 2 K yet. For our single crystals, we observe a spin freezing transition at around 0.7 K. Furthermore, the peak of 𝜒’ is suppressed by applying an external dc field of 200 mT and 𝜒” shows a sudden onset near the freezing temperature.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28340 - Permalink

Thermal and thermal-Hall conductivity study of SrCu2(BO3)2
Arsenijevic, S.; Dabkowska, H.; Gaulin, B.; Stern, R.; Wosnitza, J.
We present measurements of the thermal and the thermal-Hall conductivity as a function of temperature and magnetic field in the twodimensional dimer spin system SrCu2(BO3)2. The thermal conductivity in zero magnetic field shows a pronounced peak around 4 K which is ascribed to a spin-gap opening. The low-temperature maximum is strongly suppressed by the application of magnetic field. This result implies that the majority of heat is conducted by phonons which interact with the magnetic excitations. Furthermore, a theoretical study predicted a strong thermal Hall signature due to anisotropies originating from the Dzyaloshinskii-Moriya interactions which lead to a topological character of triplon excitations [1]. Our detailed experimental investigation did not reveal such effect disproving the existence of topological transitions in the triplon band structure.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28339 - Permalink

Inverted hysteresis within the antiferromagnetic all-in-allout state of the pyrochlore Nd2Hf2O7
Opherden, L.; Bilitewski, T.; Hornung, J.; Herrmannsdörfer, T.; Samartzis, A.; Islam, A. T. M. N.; Anand, V. K.; Lake, B.; Moessner, R.; Wosnitza, J.
We report the observation of an anisotropic and inverted hysteresis loop in the antiferromagnetic all-in-all-out ordered phase of Nd2Hf2O7 having a negative remnant magnetization. The hysteresis emerges once exceeding a characteristic magnetic-field strength 𝐻(𝑇) below the Neél temperature. The very unusual appearance of a negative remnant magnetization is observed for a field parallel to the [111] and [110] direction. However, for field parallel to [001] no hysteresis can be seen. For this orientation the projection of the field onto all four local spin directions is equal and, hence, both realizations of the all-in-all-out state gaining equal Zeeman energy through a canting of their spins. We show further, that the underlying all-in-all-out phase is established in Nd2Hf2O7 for temperatures below 𝑇𝑁 = 0.48 K and persists up to fields of 0.27 T. We account for the inverted hysteresis in terms of a theory of uncompensated domain-wall spins of spherical Domains forming inside a fully polarized single-domain state.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28338 - Permalink

Electronic structure of the B20 compound CrGe
Klotz, J.; Götze, K.; Bruin, J.; Geibel, C.; Weber, K.; Schmidt, M.; Rosner, H.; Wosnitza, J.
CrGe is a nonmagnetic transition-metal germanide with the B20 noncentrosymmetric cubic structure. In contrast, the isostructural MnGe and FeGe both show a helical spin order. We present dHvA-effect data on CrGe that were obtained employing capacitive torque Magnetometers in a 18 T/30 mK and a 33 T/340 mK system. In combination with our fplo calculations, we provide a detailed picture of the Fermisurface topology of CrGe. Furthermore, by comparing the calculated band structures of CrGe and MnGe, we discuss possible reasons for the absence of magnetic order in CrGe. Finally, our calculations indicate that substituting Ge by As or Sn will not lead to magnetic order.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28337 - Permalink

Reversibility of minor hysteresis loops in magnetocaloric Heusler alloys
Gottschall, T.; Stern-Taulats, E.; Manosa, L.; Planes, A.; Skokov, K. P.; Gutfleisch, O.; Skourski, Y.; Wosnitza, J.
The unavoidable existence of thermal hysteresis in these magnetocaloric materials is one of the central challenges limiting their implementation in cooling devices. Transforming the material in minor loops of the thermal hysteresis, however, allows achieving significant reversible effects even when the hysteresis is relatively large. In this work, we focus on the magnetocaloric properties of Heusler alloys under cycling. We compare thermometric measurements of the adiabatic temperature change in low magnetic fields and pulsed field experiments with calorimetric measurements of the isothermal entropy change when moving in minor hysteresis loops driven by magnetic fields [1, 2].
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berline, Deutschland

Publ.-Id: 28336 - Permalink

Exploring the Quantum Limit of Weyl semimetal candidates
Förster, T.; Klotz, J.; Wosnitza, J.; Shekhar, C.; Yan, B.; Felser, C.
Non-centrosymmetric transition-metal mono-pnictides such as NbAs, NbP and TaAs attracted a lot of attention because their bandstructures show linear non-degenerate band crossings, dubbed Weyl nodes [1,2]. Additionally, for certain magnetic-field orientations, the highest de Haas-van Alphen frequencies observed are smaller than 50 T. For that reason, all bands are expected to be in the quantum limit at fields easily reachable by pulsed magnetic fields. Thus, these semimetals constitute an ideal playground to study the quantum limit by electric transport and magnetic-torque measurements. Our first results for NbP show an unexpected linear increase in magnetic-torque measurements. In our contribution we show the results of our magnetic-torque measurements on NbP, NbAs, TaP and TaAs in pulsed fields up to 70 T.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28335 - Permalink

NMR of the two-dimensional 𝑆 = 1/2 Heisenberg antiferromagnet CuPOF
Dmytriieva, D.; Zhang, Z. T.; Uhlarz, M.; Landee, C. P.; Wosnitza, J.; Kühne, M.
The metal-organic compound [Cu(pz)2(2-OHpy)2](PF6)2 (CuPOF) is a molecular-based analog of the two-dimensional quantum 𝑆 = 1/2 Heisenberg antiferromagnet (2D QHAF) with well-isolated Cu(pz) layers and a very low 𝑘𝐵𝑇𝑁/𝐽 = 0.21 ratio (𝐽/𝑘𝐵 = 6.8 K, 𝑇𝑁 = 1.38 K). We present a focus study of the low-temperature phase transition to long-range order performed via 1H and 31P nuclear magnetic resonance (NMR), as well as high-field magnetometry. A low-temperature Minimum of the temperature-dependent local and uniform magnetizations at 𝑇𝑚𝑖𝑛 indicates a presence of the magnetic order. Within the ordered state, a splitting of the 1H NMR spectra reveals commensurate AF order, presumably of checkerboard type. The phase transition, manifested as a sharp maximum of the temperature-dependent 31P nuclear spin-lattice relaxation rate 1/𝑇1, occurs at temperatures slightly lower than 𝑇𝑚𝑖𝑛, indicating an easy-plane anisotropy as well as a crossover between isotropic and XY behavior.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28334 - Permalink

Exploring the magnetic phase diagram of a metal-organic S = 1 triangular spin system.
Chattopadhyay, S.; Herrmannsdörfer, T.; Kanungo, S.; Zvyagin, S.; Uhlarz, M.; Manna, K.; Schnelle, W.; Sannigrahi, J.; Wosnitza, J.; Patra, R.
We report on magnetic properties of a novel metal-organic S = 1 antiferromagnetic triangular spin compound with isolated Ni2+ triangles entitled as BHAP-Ni3. Specific heat measurements reflect an onset of magnetic correlation at low temperatures without any long-range order down to 300 mK, indicating the presence of an unusual magnetic ground state. ESR measurements performed at 1.5 K advocate this ground state to be a gapped one. Field-dependent magnetization measured on the single crystal shows anisotropic behavior with field applied parallel and perpendicular to the triangle plane. However, a clear plateau-like region is seen in both directions above 8 T which corresponds to half of the fully polarized value of Ni2+ moment. The presence of such half-magnetization plateau is quite unusual in the family of triangular magnets. High-field magnetization measurements using pulsed magnet show another field-induced plateau above 30 T corresponding to the fully polarized state of S = 1 triangles.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28333 - Permalink

High-field ESR studies of the honeycomb-lattice material 𝛼-RuCl3
Ponomaryov, A. N.; Schulze, E.; Wosnitza, J.; Lampen-Kelley, P.; Banerjee, A.; Yan, J. Q.; Bridges, C. A.; Mandrus, D. G.; Nagler, S. E.; Kolezhuk, A. K.; Zvyagin, S.
We present high-field electron spin resonance (ESR) studies of the honeycomb-lattice material 𝛼-RuCl3, a prime candidate to exhibit Kitaev physics. Two modes of antiferromagnetic resonance were detected in the zigzag ordered phase, with magnetic field applied in the 𝑎𝑏 plane. A very rich excitation spectrum was observed in the field-induced Quantum paramagnetic phase. The obtained data are compared with results of recent numerical calculations, strongly suggesting a very unconventional multiparticle character of the spin dynamics in 𝛼-RuCl3. The frequency-field diagram of the lowest-energy ESR mode is found consistent with the behavior of the field-induced energy gap, revealed by thermodynamic measurements. This work was supported by DFG (project ZV 6/2-2).
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie (SKM) gemeinsam mit der European Physical Society (CMD), 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 28332 - Permalink

Magnetoelastic phenomena in antiferromagnetic uranium intermetallics: The UAu2Si2 case
Valiska, M.; Saito, H.; Yanagisawa, T.; Tabata, C.; Amitsuka, H.; Uhlirova, K.; Prokleska, J.; Proschek, P.; Valenta, J.; Misek, M.; Gorbunov, D. I.; Wosnitza, J.; Sechovsky, V.
Thermal expansion, magnetostriction, and magnetization measurements under magnetic field and hydrostatic pressure were performed on a UAu2Si2 single crystal. They revealed a large anisotropy of magnetoelastic properties manifested by prominent length changes, leading to a collapse of the unit-cell volume accompanied by breaking the fourfold symmetry (similar to that in URu2Si2 in the hidden-order state) in the antiferromagnetic state as consequences of strong magnetoelastic coupling. The magnetostriction curves measured at higher temperatures confirm a bulk character of the 50K weak ferromagnetic phase. The large positive pressure change of the ordering temperature predicted from Ehrenfest relation contradicts the more than an order of magnitude smaller pressure dependence observed by the magnetization and specific heat measured under hydrostatic pressure. A comprehensive magnetic phase diagram of UAu2Si2 in magnetic field applied along the c axis is presented. The ground-state antiferromagnetic phase is suppressed by a field-induced metamagnetic transition that changes its character from second to first order at the tricritical point

Publ.-Id: 28330 - Permalink

The Serial Interface Package -- v2.0
Seilmayer, M.ORC
The 'serial' package as an extension to the programming language R enables reading and writing binary and ASCII data to RS232/RS422/RS485 or any other virtual serial interfaces of the computer.
Keywords: serial interface, RS232, RS422, RS485, R
  • Software in external data repository
    Publication year 2018
    Programming language: R
    System requirements: Windows, Mac, Unix
    License: GPL-2
    Hosted on Link to location

Publ.-Id: 28318 - Permalink

Characterization and beneficiation of pyrolyzed black mass from lithium ion batteries
Vanderbruggen, A.; Gilbricht, S.; Möckel, R.; Rudolph, M.
The lithium-ion battery (LiB) market is growing rapidly. Consequently, LiB wastes will increase in the future and LiB components such as Co, Li, but also graphite, are forecast to be critical materials. These critical materials are contained in the black mass produced by LiBs recycling. This original research focuses on graphite beneficiation from cathode lithium metal oxides by flotation. Detailed characterization of the pyrolyzed black mass (inculding MLA, XRF and XRD) shows that the graphite particles are fully liberated from the copper foils, and the organic layer PVDF is removed. Batch flotation shows that pretreatment, such as attritioning, improves process efficiency while preserving the shape of spheriodized graphite. Concentrate impurities mainly comprise fine particles from cathode active materials, which can be removed with desliming and flotation cleaner stages. As an outlook, this reasearch is expected to bring about an innovative and useful process for the recycling industry.
Keywords: Attritionning, black mass, characterization, flotation, graphite, mineral liberation analysis (MLA), pre-treatment, recycling, spent lithium ion battery, surface analysis
  • Poster
    Minerals Engineering International (MEI) conference: Process Mineralogy '18, 19.-21.11.2018, Cape Town, South Africa

Publ.-Id: 28316 - Permalink

Serpent solution of the X2 VVER-1000 benchmark fresh core experiments
Bilodid, Y.; Fridman, E.
The X2 VVER-1000 benchmark describes first 4 fuel cycles of the Khmelnitsky NPP 2nd unit with VVER-1000 reactor as well as some operational transients. The benchmark specifications contain description of the reactor core material, geometry and operational history supplemented by measured operational data and startup experiments. In this work, the hot zero power experiments conducted during the fresh core startup are modelled with the Serpent-2 Monte Carlo code. The numerical results are validated against the available measured core data. The calculated and measured values of a critical boron concentration, temperature reactivity effect, and control rod worth are in a very good agreement while the deviations lay within the measurement uncertainties. Since the power distribution was not measured at the hot zero power state, the obtained Serpent solution could be used as a reference for a deterministic codes verification.
Keywords: X2 benchmark, VVER-1000, Serpent
  • Contribution to proceedings
    PHYSOR 2018: Reactor Physics Paving The Way Towards More Efficient Systems, 22.-26.04.2018, Cancun, Mexico, 1982-1989

Publ.-Id: 28315 - Permalink

Doping issues in silicon nanowires by ion implantation and flash lamp annealing
Berencen, Y.; Prucnal, S.; Wang, M.; Rebohle, L.; Helm, M.; Zhou, S.; Skorupa, W.
Semiconducting nanowires (NWs) hold promises for functional nanoscale devices. Although several applications have been demonstrated in the areas of electronics, photonics and sensing, the doping of NWs remains challenging. Ion implantation is a standard doping method in top-down semiconductor industry, which offers precise control over the areal dose and depth profile as well as allows for the doping of all elements of the periodic table even beyond their equilibrium solid solubility. Yet its major disadvantage is the concurrent material damage. A subsequent annealing process is commonly used for the healing of implant damage and the electrical activation of dopants. This step, however, might lead to the out-diffusion of dopants and eventually the degradation of NWs because of the low thermal stability caused by the large surface–area-to-volume ratio.

In this work, we report on non-equilibrium processing (flash lamps) for controlled doping of drop-casted Si/SiO2 core/shell NWs with shallow- and deep-level dopants below and above their equilibrium solid solubility. The approach lies on the implantation of either shallow-level dopants, such as B and P, or deep-level dopants like Se followed by millisecond flash lamp annealing. In case of amorphization upon high-fluence implantation, recrystallization takes place via a bottom-up template-assisted solid phase epitaxy. Non-equilibrium Se concentrations lead to intermediate-band Si/SiO2 core/shell NWs that have room-temperature sub-band gap photoresponse when configured as a photoconductor device [1]. Alternatively, the formation of a cross-sectional p-n junction is demonstrated by co-implanting P and B in individual NWs at different depth along the NW core.
[1] Y. Berencén, et al. Adv. Mater. Interfaces 2018, 1800101
Keywords: doping, nanowires, semiconductor, silicon, ion implantation, flash lamp annealing
  • Lecture (Conference)
    22nd International Conference on Ion Implantation Technology, 16.-21.09.2018, Würzburg, Deutschland

Publ.-Id: 28313 - Permalink

Advanced doping issues using nonequilibrium processing
Skorupa, W.; Rebohle, L.; Prucnal, S.; Berencen, Y.; Zhou, S.; Helm, M.
In this talk I will introduce with a short view on the background of the transistor invention as a key element driving the topic of semiconductor doping. After that I will discuss examples of advanced doping including ion beam based and other methods: doping and alloying of germanium, hyperdoping of silicon, doping from deposited layers, doping of silicon nanowires, doping from deposited layers. In all cases the experiments were performed in correlation to nonequilibrium thermal processing using flash lamps in the millisecond time range.
Keywords: semiconductor doping, ion beam based methods, flash lamp annealing,
  • Lecture (others)
    Eingeladener Seminarvortrag an der Marie-Curie-Universität Lublin/Polen, 11.10.2018, Lublin, Polen

Publ.-Id: 28311 - Permalink

Dataset on characterization, ion irradiation and nanoindentation of ODS Fe14Cr-based alloys
Bergner, F.

The dataset comprises raw data of the nanoindentation tests and processed data on the ion irradiations and irradiation-induced hardness changes. File formats are excel, word, origin and ascii.

Related publications
Nanoindentation of single- and dual-beam (Fe and He)… (Id 28308) has used this publication of HZDR-primary research data
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-12-04
    DOI: 10.14278/rodare.72


Publ.-Id: 28310 - Permalink

Bonding and stability analysis of tetravalent f-element complexes with mixed N-, O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.
The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands re- flecting natural bonding motifs.
This study shows the different bonding behaviour of tetravalent f-elements with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent inter- actions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are presented. The obtained results are a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the inter- action between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possi- ble to understand the chemical properties of the f-elements and predict yet unknown complexes.
Keywords: Bonding analysis, Theoretical Chemistry, DFT, QTAIM, Actinides
  • Poster
    Symposium on Theoretical Chemistry, 17.-20.09.2018, Halle, Deutschland

Publ.-Id: 28309 - Permalink

Bonding and stability analysis of tetravalent actinide and lanthanide complexes with N,O-donor ligands
Kloditz, R.; Radoske, T.; Patzschke, M.; Stumpf, T.
The contribution of the f-orbitals leads to a very rich chemistry of the f-elements[1] where it is known that this contribution is less important for lanthanides. Of special interest is the influence of these orbitals on the bonding character of actinides and lanthanides with organic ligands reflecting natural binding motifs.
This study shows the different bonding behaviour of tetravalent actinide and lanthanide complexes with Schiff bases, like salen (see Fig. 1) and derivatives, by means of real-space bonding analysis. This includes the popular quantum theory of atoms in molecules (QTAIM), plots of the non-covalent interactions (NCI)[2] and density differences complemented by natural population analysis (NPA). Thermodynamic calculations on the stability of these complexes are done being a direct consequence of the different interaction strengths of the f-elements.
First studies reveal a strong interaction of the actinides, i.e. Th to Pu, with the oxygen of salen characterized by a high electron density concentration between the atoms. In contrast, the interaction between the actinides and the nitrogen of salen is much weaker.
By acquiring knowledge about the different behaviours of bonding and complexation it is possible to understand the chemical properties of the f-elements and predict yet unknown complexes.
Keywords: Bonding, Salen, Actinides, theoretical chemistry, DFT, QTAIM
  • Lecture (Conference)
    International Symposium on Nano and Supramolecular Chemistry, 09.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28307 - Permalink

AER Working Group Meeting on VVER safety analysis - report of the 2018 meeting
Kliem, S.ORC
The AER Working Group D on VVER reactor safety analysis held its 27th meeting in Rossendorf, Germany, during the period 12-13 June, 2018. The meeting was hosted by Helmholtz-Zentrum Dresden-Rossendorf. Altogether 19 participants from nine AER member organizations attended the meeting of the working group D. The co-ordinator of the working group, Mr. S. Kliem, served as the chairperson of the meeting.
The meeting started with a general information exchange about the recent activities in the participating organizations.
The given 13 presentations and the discussions can be attributed to the following topics:
• Safety analyses methods and results
• Code development and benchmarking
• Severe accident analyses
• Future activities
The Working Group decided to include also in future the severe accident analyses into the scope of the activities.
A list of the participants and a list of the handouts distributed at the meeting are attached to the report. The corresponding PDF-files of the handouts can be obtained from the chairperson.
  • Contribution to proceedings
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic
    Proceedings of the 28. Symposium of AER, Budapest: MTA EK Budapest, 9789637351303, 665-671
  • Lecture (Conference)
    28. Symposium of AER, 08.-12.10.2018, Olomouc, Czech Republic

Publ.-Id: 28295 - Permalink

Aerosol particle deposition and resuspension in turbulent air channel flows
Lecrivain, G.; Hampel, U.
The deposition of aerosol graphite particles in a turbulent channel flow obstructed with periodic steps is here investigated et experimentally at Reynolds number Re = 8,000. Particles in the size range d = 1...100µm deposit non-uniformly on the various wall surfaces and eventually form a fairly thick layer of dust. The build-up of the dust layer affects the air flow which in turn affects the deposition rate of the conveyed particles. To numerically reproduce the growth of the dust layer an interdisciplinary study involving the dynamic coupling of fluid simulation, Lagrangian particles, mesh deformation and granular bed is carried out. The numerical results compare well with the experimental data.
  • Invited lecture (Conferences)
    Workshop on particle resuspension, 04.09.2018, Nice, France

Publ.-Id: 28294 - Permalink

Numerical Models for the DRESDYN Precession Dynamo Experiment
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.
More than 100 years ago, Henri Poincare in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

In the present study we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around Rm_c ≈ 430, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precission are able to excite dynamo action when their structure is sufficient complex, i.e. the forcing is sufficient strong.

More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment. Finally, we discuss the role of turbulent flow fluctuations for the occurrence of dynamo action.
Keywords: Dynamo DRESDYN
  • Poster
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA
  • Open Access LogoContribution to proceedings
    AGU Fall Meeting 2018, 09.-14.12.2018, Washington DC, USA

Publ.-Id: 28293 - Permalink

Numerical simulations for the DRESDYN precession dynamo
Giesecke, A.; Vogt, T.; Gundrum, T.; Stefani, F.
More than 100 years ago, Henri Poincar{\'e} in his pioneering study showed that the inviscid base flow in a precessing spheroid is described by a constant vorticity solution, the spin-over mode. Since then there have been repeated discussions whether the geodynamo is driven (or at least influenced) by precession. More recently, precession has also been considered as an important mechanism for the explanation of the ancient lunar dynamo.

Experiments with precessing fluids in cylindrical and in spherical geometry showed that precession indeed is an efficient mechanism to drive substantial flows even on the laboratory scale without making use of propellers or pumps. A precession dynamo experiment is currently under construction within the project DRESDYN (DREsden Sodium facility for DYNamo and thermohydraulic studies) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) in which a precession driven flow of liquid sodium will be used to drive dynamo action.

Here we address related numerical and experimental examinations in order to identify parameter regions where the onset of magnetic field excitation will be possible. Preliminary kinematic dynamo models using a prescribed flow field from hydrodynamic simulations, exhibit magnetic field excitation at critical magnetic Reynolds numbers around ${\rm{Rm}}_{\rm{c}} \approx 430$, which is well within the range of the planned liquid sodium experiment. Our results show that large scale inertial modes excited by precession are able to excite dynamo action when their structure is sufficiently complex, i.e. the forcing is sufficiently strong.
More advanced models that take into account the container's finite conductivity show that boundary conditions may play an important role, but the critical magnetic Reynolds number will still be achievable in the planned experiment.
Keywords: Dynamo DRESDYN
  • Lecture (Conference)
    MHD Days 2018, 26.-29.11.2018, Dresden, Germany

Publ.-Id: 28292 - Permalink

µTRLFS: Spatially-resolved sorption studies of Eu(III) on Eibenstock granite with time-resolved laser fluorescence spectroscopy
Molodtsov, K.; Schymura, S.; Rothe, J.; Dardenne, K.; Krause, J.; Schmidt, M.
Finding a safe long-term repository for high-level nuclear waste is a highly relevant global issue. To that end, the interaction of radionuclides with mineral phases contained in possible host rocks and construction materials must be understood. On a time scale of up to one million years, especially the scenario of a water intrusion into the repository and thus dissolution of radionuclides has to be considered.

To investigate the sorption behaviour of actinides (e.g. Cm(III) and U(VI)O22+) and lanthanides (e.g. Eu(III)), time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method, because of its trace concentration sensitivity and capability to distinguish multiple species in complex systems. On the one hand this method gives the spectral information of the emitted fluorescence light, which allows determining the symmetry and the grade of complexation of the sorbed Ln/An. On the other hand the lifetimes of the excited electronic states provide information about the surrounding quenchers, mainly water. Typically, TRLFS investigations will focus on the interaction of an actinide with one relevant mineral phase. For a real rock formation, e.g. granite, sorption will however be a competitive process involving multiple mineral phases at the same time.

In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS. By doing so, it is possible to separate the multi-phase system into discrete single-phase systems and therefore to make a step beyond model systems by investigating, for example whole natural granite rock with TRLFS. Because of its advantageous fluorescence properties, we use Eu(III) as an analogue for the trivalent actinides Am and Cm. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused laser beam at a wavelength of 394 nm, and scanned through the laser’s focal point by an XYZ-stage with a resolution of approximately 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, F2/F1-band ratios, as well as fluorescence lifetimes.

A combination of spatially-resolved X-ray fluorescence spectroscopy (µXRF) and electron probe microanalysis (EPMA) is used to reveal the mineral phase composition in each point of measurement which can then be correlated to the µTRLFS maps. In addition, these methods provide impurity distributions of e.g. Fe or Mn as additional quenchers. By doing so, µTRLFS mapping of sorption capacity, complexation strength and surrounding quenchers can be correlated to phase distribution mappings and thus provide information about the sorption behaviour of each phase within the complete multi-phase system. The µTRLFS data can be directly compared to single phase TRLFS data of the main granite components quartz, feldspar, and mica. For verification, the Eu(III) distribution obtained from µTRLFS data will be compared to autoradiography images.
Keywords: µTRLFS, europium, sorption, granite
  • Poster
    10th International Conference on f-elements, 03.-06.09.2018, Lausanne, Schweiz
  • Lecture (Conference)
    Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28283 - Permalink

µTRLFS: Spatially- and time-resolved laser fluorescence spectroscopy with Eu(III) as a fluorophore on Eibenstock granite
Molodtsov, K.; Schmidt, M.
Time-resolved laser fluorescence spectroscopy (TRLFS) is a widely used method to obtain information about the surrounding chemical environment of fluorophores with trace concentration sensitivity. This method allows determining the symmetry and grade of complexation of the fluorophore and provides information about the surrounding quenchers, mainly water as well. For highly heterogeneous systems however distinguishing and separating multiple binding species becomes an unsolvable problem. In this study a new method called µTRLFS is introduced, which will add a spatial dimension to TRLFS, giving the possibility to separate a multi-phase system into discrete single-phase systems. Because of its advantageous fluorescence properties we use europium as an analogue for Am(III) and Cm(III) to study the sorption behaviour of granite as a possible host rock for high-level nuclear waste repositories. Spatially resolved sorption experiments with Eu(III) on granite samples from Eibenstock, Germany are presented. These samples are excited by a focused and pulsed UV laser beam, and scanned with a resolution of 20 µm. Through this approach it becomes possible to characterize Eu(III) sorption on single grains of the complex material by mapping fluorescence intensity, band ratios, as well as lifetimes.
Keywords: µTRLFS, europium, sorption, granite
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft Frühjahrstagung, 04.-09.03.2018, Erlangen, Deutschland

Publ.-Id: 28282 - Permalink

Trivalent Actinide Incorporation into Zirconium(IV) oxide – Eu3+ and Cm3+ luminescence spectroscopic studies
Eibl, M.; Shaw, S.; Morris, K.; Hennig, C.; Stumpf, T.; Huittinen, N.
In a final repository for spent nuclear fuel (SNF), the mobilization of actinides from the UO2 matrix is a great concern for safety considerations. The SNF rods are surrounded by zircalloy cladding material, which, similarly to the UO2 waste matrix, has a very low solubility in aqueous solution. Despite the very good corrosion resistance of the cladding material, corrosion and dissolution are expected to occur together with the leaching of radionuclides from the SNF over geological timescales. Therefore, the dissolution of zircalloy and the formation of a corrosion layer mainly composed of zirconia (ZrO2) on the cladding surface may be accompanied by reactions with dissolved, long-lived radionuclides from the SNF matrix.
At ambient conditions zirconium oxide has a monoclinic (m) crystal structure. However, the incorporation of metal cations can stabilize the high-temperature zirconia phases, i.e. the tetragonal (t) and the cubic (c) phases, leading to the formation of stable structures at ambient conditions.[1] Such phase transformation may be expected when actinides from the SNF become incorporated and thus, immobilized within the zirconia corrosion layer.
In the present study the incorporation of aliovalent actinides in zirconia, and their stabilizing influence on the crystal structure, have been investigated. The crystallinity and structural properties of the resultant actinide-doped zirconia solids were investigated with powder x-ray diffraction (PXRD), while the local structure around the incorporated dopant was studied with laser-induced luminescence spectroscopy (TRLFS). Cm3+ and Eu3+ were taken as representatives for the trivalent actinides.
The PXRD results of calcined Eu3+ doped zirconia samples show that a systematic transformation of the monoclinic to the cubic phase via the tetragonal structure occurs as a function of increasing Eu3+ doping (Fig. 1, left) whilst the Eu3+ TRLFS results show a 7F1, 7F2 emission band splitting corresponding to a low symmetry environment despite the cubic bulk symmetry (Fig. 1, middle).

The Cm3+ co-doped luminescence spectra show strong red-shifts of the emission spectra in the cubic bulk system with a peak maximum of 643.9 nm (Fig. 1, right) which have been observed before.[2] Both spectroscopic methods point towards a strongly distorted local structure, caused by the effect of oxygen vacancies and lattice stress induced by the largely oversized dopant ions.
  • Lecture (Conference)
    4th International Workshop on Advanced Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28280 - Permalink

Pressure-tuning of the magnetic properties of the Heusler compound Mn2PtGa
Salazar Mejia, C.; Najak, A. K.; Felser, C.; Nicklas, M.
We report on the pressure-tuning of the magnetic properties of the Heusler alloy Mn2PtGa. At ambient pressure, Mn2PtGa orders ferrimagnetically below TC ≈ 222 K, followed by a first-order ferrimagnetic to antiferromagnetic transition around TFI-AF ≈ 102 K upon cooling. Magnetization measurements up to 1.2 GPa evidence a stabilization of the ferrimagnetic phase, i.e., TC increases while TFI-AF decreases upon application of pressure. The magnetic properties in the ferromagnetic phase are not altered upon increasing pressure. However, the fraction of the ferrimagnetic phase present in the inhomogeneous antiferromagnetic low-temperature phase increases with pressure.


  • Secondary publication expected from 07.11.2019

Publ.-Id: 28279 - Permalink

X-ray visualisation of melt flow effects on dendritic solidification
Shevchenko, N.; Keplinger, O.; Grenzer, J.; Rack, A.; Eckert, S.
X-ray radiography is an effective tool for investigating flow phenomena and solidification processes in opaque metallic alloys. This work is devoted to complex interaction between dendritic growth and melt flow during solidification of Ga-In alloys under natural and forced convection. Natural convection is caused by density variations within the solidifying alloys. Forced convection was produced by electromagnetic stirring. The conventional X-ray radioscopic experiments with sufficient spatial resolution (5-10 µm) deliver simultaneous information of both the dendrite structure and the flow patterns ahead of the solidification front and especially near the mushy zone. Melt convection alters the solutal field near the solidification front leading to different microstructures or even to the formation of freckle defects. The coarsening stage of dendritic structure is characterized by transformation of the sidearm morphology present after growth. The direct investigation of dendritic sidearm evolution during coarsening appears to be rather complex and impose high requirements with respect to the spatial and temporal resolution and sensitivity of the detector. The synchrotron imaging experiments with solidifying Ga-In alloys were performed at the BM20 and ID19 beamlines (ESRF, France) at a spatial resolution of < 1 µm. The present measurements provide real-time in-situ data on three phenomena that are of major importance in coarsening of dendrites: sidearm retraction, pinch-off and coalescence of neighboring sidearms. Using an advanced image analysis of high temporal and spatial resolution experimental data allows us to verify existing microstructural models.
Keywords: X-ray radiography, dendritic growth, melt flow, sidearm evolution
  • Lecture (Conference)
    32nd International Congress on High Speed Imaging and Photonics, 09.-12.10.2018, University of Twente, The Netherlands

Publ.-Id: 28274 - Permalink

In-situ observation of dendritic growth under the influence of electromagnetically driven flow
Shevchenko, N.; Keplinger, O.; Eckert, S.
Many studies have demonstrated that the application of electromagnetic stirring enhances the area of equiaxed grains and reduces the mean grain size (see e.g. [1-2]). It is widely accepted that flow-induced grain refinement and the CET (columnar to equiaxed transition) in metallic alloys is triggered by the appearance of additional dendrite fragments originating from the columnar front. The mechanism for grain multiplication by melt convection is supposed to be complex and is not fully understood until now.
The X-ray radiography was used for an in-situ study of the effect of electromagnetic stirring during the solidification of a Ga-25wt%In alloy in a Hele-Shaw cell [3]. The experimental setup was extended by a magnetic wheel, which allowed for controlled excitation of a melt flow in the liquid phase. The forced flow induces different effects on dendrite morphology, such as the uneven growth of primary trunks or lateral branches, remelting of single dendrites and also of lager dendrite ensembles, freckle formation, changes the inclination angle of the dendrites and leads to an increasing arm spacing. These effects are primarily governed by the convective redistribution of solute. Figure 1 demonstrates an interesting effect of "repairing" of a segregation channel (see the right-hand side part of Fig. 1a) after switching off the magnetic wheel (Fig 1b). It can be seen that an area with equiaxed or fine dendrites was formed instead of a segregation channel. The appearance of small equiaxed grains in the undercooled melt in the segregation pools is triggered by quick redistribution of solute after stopping the magnetic pump.
1. B. Willers et al, Materials Science and Engineering A 402 (2005) 55-65
2. T. Campanella et al, Metallurgical and Materials Transactions A 35 (2004) 3201-3210
3. N. Shevchenko et al, Journal of Crystal Growth 417 (2015) 1-8
Keywords: Electromagnetic stirring, solidification, X-ray radiography, freckle formation, Ga-In alloy
  • Lecture (Conference)
    9th International Symposium on Electromagnetic Processing of Materials (EPM2018), 14.-18.10.2018, Awaji, Hyogo, Japan

Publ.-Id: 28273 - Permalink

Characterization of Isostructural An(IV) Complexes with Hetero-donor Imine Ligands
Radoske, T.ORC; Schöne, S.ORC; Kaden, P.; Ikeda-Ohno, A.ORC; Stumpf, T.
The coordination chemistry of actinides (An) serves as fundamental knowledge for chemical engineering and environmental science related to the nuclear industry.[1] However, as compared with other transition metals, the basic chemistry of An is far less explored. The chemistry of An is complicated by, e.g., various possible oxidation states ranging from II to VII for the early An. One possible approach to understand the chemical nature of the An series is the comparison of isostructural compounds containing different actinides with the same oxidation state.[2,3,4] With this approach, the relative changes observed among the An series could allow us to gain insight into their unique chemical nature, such as electronic properties originating from their f-electron orbitals. One major question remaining in the field of An chemistry is the degree of “covalency” across the An series.[5] In order to study the “covalency” across the An series, one would require to perform a systematic study on a wide series of An, including transuranium (TRU) elements. Nonetheless, precedent studies covering TRU elements are rather scarce. This background motivates us to perform the current study focusing on a systematic comparison of the isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)), which is dominant particularly under anoxic environmental conditions.[1] Synthesis of their compounds and the experiments should be conducted under inert and water-free atmosphere. The ligands used in this study are a hetero-donor imine ligand of salen and its derivatives (Fig. 1). These ligands have a capability to coordinate to metal ions tetradentately and exhibit both the hard- (oxygen) and medium-donor (nitrogen) characters, which could be a simple analog of natural occurring organic molecules. The eightfold coordination, which is often preferred for An complexes, can be readily achieved with these ligands by coordination of two ligand molecules. Salen and its derivatives have also been employed as a framework for catalytic and extraction agents.[6,7]
  • Lecture (Conference)
    Plutonium Futures 2018, 11.09.2018, San Diego, Vereinigte Staaten von Amerika

Publ.-Id: 28271 - Permalink

Actinide Bonding – Comparative Study of Isostructural An(IV) Imine Complexes
Radoske, T.ORC; Kaden, P.; Schöne, S.ORC; Ikeda-Ohno, A.ORC; Stumpf, T.
Because of their unique electronic properties originating from 5f-orbitals, the coordination chemistry of actinides (An) is still an attractive research field in terms not only of nuclear engineering but also of basic chemistry. In particular, the early An show profound complex chemistry due to a wide variety of possible oxidation states ranging from +II to +VII, which is in contrast to the dominant trivalent state for their chemical analog of lanthanides. The aim of our research activities is to gain knowledge about the interaction of An with a variety of hard- and soft-donor ligands, eventually providing a comprehensive understanding of the electronic nature of actinide compounds. The ligands used in this study possess both O- (i.e. hard) and N-donor (soft) containing functionalities (Fig.1) and could also be considered as a simplified model of naturally relevant organic O/N-donor ligands.
A series of single crystals of [AnIV(Lp)2] complexes were synthesized from the tetrachloride compounds of An = Th, U and Np. SC-XRD measurements on the obtained crystals reveal their crystal structures, all showing the eight-fold coordination of the metal centre with the ligands on their primary coordination sphere, forming a trigonal dodecahedral geometry around the metal centre.
1H-NMR spectra of the dissolved complexes [ThIV(Le)2], [UIV(Le)2], [CeIV(Le)2] and the pure ligand in solution were recorded. The observed shifts show unique features when comparing isostructural diamagnetic compounds of lanthanides and actinides, which can not be explained by charge density differences.
  • Lecture (Conference)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 10.07.2018, Dresden, Deutschland

Publ.-Id: 28270 - Permalink

Age and genesis of polymetallic veins in the Freiberg district, Erzgebirge, Germany: constraints from radiogenic isotopes
Ostendorf, J.; Henjes-Kunst, F.; Seifert, T.; Gutzmer, J.
The Freiberg mining district in the Erzgebirge hosts three principal types of polymetallic veins. These are (1) the quartz-bearing polymetallic sulfide type, (2) the carbonate-bearing polymetallic sulfide type, and (3) the barite-fluorite-sulfide type. We investigated the genesis of each vein-type using Rb-Sr sphalerite geochronology, Sm-Nd fluorite geochronology, and Pb, Sr, and Nd isotope systematics of ore and gangue minerals. Field relationships and the Rb-Sr and Pb isotope systematics of sulfides from quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins confirm their close genetic affiliation and yield a combined Rb-Sr errorchron age of 276 ± 16 Ma. The high mean squared weighted deviation (MSWD) value of 42 on the regression is considered to reflect initial isotopic heterogeneity, which is probably related to fluid-rock interaction during the hydrothermal mineralization process. Although some sphalerites from barite-fluorite-sulfide veins have strongly disturbed Rb-Sr isotope systematics, six sphalerites and one co-genetic fahlore yield a robust isochron age of 121.3 ± 4.2 Ma with an MSWD of 2.9. This age is supported by a fluorite Sm-Nd isochron age of 101 ± 18 Ma (MSWD = 1.3). The new ages and radiogenic isotope data place robust constraints on the long-held hypothesis that veins in the Freiberg district formed during two hydrothermal events. The Lower Permian age of first stage quartz-bearing polymetallic sulfide veins and carbonate-bearing polymetallic sulfide veins coincides with post-Variscan crustal reorganization and Rotliegend volcanism. The Mid-Cretaceous age of second stage barite-fluorite-sulfide veins coincides with opening of the North Atlantic Ocean during the break-up of Pangea.
Keywords: Erzgebirge, Freiberg district, Pb isotopesRb-Sr sphalerite dating, Sm-Nd fluorite dating, Vein-type deposit

Publ.-Id: 28268 - Permalink

Observation of charge density waves in free-standing 1T-TaSe2 monolayers by transmission electron microscopy
Börner, P. C.; Kinyanjui, M. K.; Björkman, T.; Lehnert, T.; Krasheninnikov, A. V.ORC; Kaiser, U.
While bulk 1T-TaSe2 is characterized by a commensurate charge density wave (CCDW) state below 473K, the stability of the CCDW state in a 1T-TaSe2 monolayer, although theoretically predicted, has not been experimentally confirmed so far. As charge density waves and periodic lattice distortions (PLDs) always come together, we evaluate the PLD in a 1T-TaSe2 monolayer from low-voltage aberration-corrected high-resolution transmission electron microscopy experiments. To prevent fast degradation of 1T-TaSe2 during exposure to the electron-beam, a 1T-TaSe2/graphene heterostructure was prepared. We also perform the image simulations based on atom coordinates obtained using density functional theory calculations. From the agreement between the experimental and simulated images, we confirm the stability of the CCDW/PLD in a monolayer 1T-TaSe2/graphene heterostructure at room temperature in the form of a 13 13 superstructure. At the same time, we find that in comparison to multi-layer structures, the superstructure is less pronounced.
Keywords: 1T-TaSe2, graphene, TEM, first-principles calculations


  • Secondary publication expected from 25.10.2019

Publ.-Id: 28260 - Permalink

Reversible superdense ordering of lithium between two graphene sheets
Kühne, M.; Börrnert, F.; Fecher, S.; Ghorbani-Asl, M.ORC; Biskupek, J.; Samuelis, D.; Krasheninnikov, A. V.ORC; Kaiser, U.; Smet, J. H.
Many carbon allotropes can act as host materials for reversible lithium uptake1,2, thereby laying the foundations for existing and future electrochemical energy storage. However, insight into how lithium is arranged within these hosts is difficult to obtain from a working system. For example, the use of in situ transmission electron microscopy3–5 to probe light elements (especially lithium)6,7 is severely hampered by their low scattering cross-section for impinging electrons and their susceptibility to knock-on damage8. Here we study the reversible intercalation of lithium into bilayer graphene by in situ low-voltage transmission electron microscopy, using both spherical and chromatic aberration correction9 to enhance contrast and resolution to the required levels. The microscopy is supported by electron energy-loss spectroscopy and density functional theory calculations. On their remote insertion from an electrochemical cell covering one end of the long but narrow bilayer, we observe lithium atoms to assume multi-layered close-packed order between the two carbon sheets. The lithium storage capacity associated with this superdense phase far exceeds that expected from formation of LiC6, which is the densest configuration known under normal conditions for lithium intercalation within bulk graphitic carbon10. Our findings thus point to the possible existence of distinct storage arrangements of ions in two-dimensional layered materials as compared to their bulk parent compounds.
Keywords: Li storage, graphene, TEM, first-principles caclulations


  • Secondary publication expected from 26.05.2019

Publ.-Id: 28259 - Permalink

Epitaxial Mn5Ge3 (100) layer on Ge (100) substrates obtained by flash lamp annealing
Xie, Y.; Yuan, Y.; Wang, M.; Xu, C.; Hübner, R.; Grenzer, J.; Zeng, Y.; Helm, M.; Zhou, S.; Prucnal, S.
Mn5Ge3 thin films have been demonstrated as promising spin-injector materials for germanium-based spintronic devices. So far, Mn5Ge3 has been grown epitaxially only on Ge (111) substrates. In this letter, we present the growth of epitaxial Mn5Ge3 films on Ge (100) substrates. The Mn5Ge3 film is synthetized via sub-second solid-state reaction between Mn and Ge upon flash lamp annealing for 20 ms at the ambient pressure. The single crystalline Mn5Ge3 is ferromagnetic with a Curie temperature of 283 K. Both the c-axis of hexagonal Mn5Ge3 and the magnetic easy axis are parallel to the Ge (100) surface. The millisecond-range flash epitaxy provides a new avenue for the fabrication of Ge-based spin-injectors fully compatible with CMOS technology.
Keywords: Mn5Ge3, epitaxial thin film, ferromagnetism, spintronic devices

Publ.-Id: 28258 - Permalink

First Series of Tetravalent Thorium-, Uranium- and Neptunium-Amidinate Complexes
Schöne, S.ORC; Kaden, P.ORC; Patzschke, M.ORC; Roesky, P. W.ORC; Stumpf, T.; März, J.ORC
Actinides (An) can possess a variety of different oxidation states, which typically range from +III to +VI for the early actinides Th-Cm. They have unique electronic properties originating from the 5f-orbitals, what makes their coordination chemistry a fascinating area of research for both, the nuclear engineering but also for fundamental chemistry. Thorium (Th), uranium (U), neptunium (Np) and plutonium (Pu) can form highly charged cations with the oxidation state of four (An4+), which is the dominant one under reductive conditions. Furthermore, An(IV) are of particular interest for the coordination chemistry because of their strong interaction with ligands.
Hence, the overall aim of our investigations is a deep understanding of the interaction mechanisms between tetravalent An (An(IV)) and ligands bearing soft donor atoms, such as nitrogen (N). Thus, we focused on the synthesis and characterization of a series of An(IV) complexes with the N-donor ligand N,N’-Diisopropylbenzamidine (iPr2BA) both in solution and in solid state.
The structures of the synthesised complex series were determined by single-crystal X-ray diffraction (SC-XRD), showing the An(IV) coordinated by three iPr2BA molecules and one chloro ligand in a monocapped octahedral coordination geometry. This is the very first example of an An(IV) complex series including Np(IV) as a transuranium element with an amidinate ligand. The isostructural complexes allow a direct comparison of the binding situation of the An(IV) across the series. Quantum chemical calculation strongly supported the experimental results to to further study the electronic structure of the complexes.
NMR-spectroscopic investigations of the dissolved complexes in toluene-d8 showed significant chemical shifts due to considerable effects of the paramagnetic metal centres U(IV) and Np(IV) compared to the diamagnetic reference [Th(iPr2BA)3Cl].
Keywords: actinide, amidinate, coordination chemistry, thorium, uranium, neptunium, NMR, SC-XRD
  • Invited lecture (Conferences)
    10th International Conference on f-Elements (ICFE-10), 03.-07.09.2018, Lausanne, Schweiz

Publ.-Id: 28257 - Permalink

Coordination Chemistry of Tetravalent Actinides: Series & Trends
Schöne, S.ORC; Radoske, T.ORC; Kloditz, R.; Köhler, L.; Kaden, P.ORC; Patzschke, M.ORC; Roesky, P. W.ORC; Stumpf, T.; März, J.ORC
The coordination chemistry of actinides (An) using model ligands helps to deeply understand their bonding situation on a molecular level. However, the basic An chemistry is still little explored. Characteristic of An is a huge variety of possible oxidation states, typically ranging from II to VII for early An. A suitable approach to explore the fundamental phico-chemical properties of An is to study a series of isostructural An compounds in the same oxidation state. Observed changes in e.g. the binding situation or magnetic effects among the An series could deliver insight into their unique electronic properties mainly origination from the f-electrons. A question still remaining in An chemistry is the degree of "covalency". However, studies covering TRU elements are rather scarce. Against this background, we are strongly motivated to perform a systematic comparison of isostructural An complexes (Th, U and Np).
In this study we investigate the coordination chemistry of tetravalent actinides (An(IV)) for two major reasons: a) the series of An(IV) is the largest accessible one within the early actinides, and b) the tetravalent state is the dominant one particularly under anoxic conditions. The ligands used in this study range from hard- (oxygen) and medium- (nitrogen) to pure soft-donor (carbon) character, according to Pearsons's HSAB concept. Due to the expected changes in orbital overlap between the metal and ligand, the formed complexes could further provide us a deep insight into the electronic situation of the actinides.
The An(IV) complexes are characterised in solution by NMR-, IR- and UV-vis spectroscopy as well as in the solid-state by SC_XRD. The acquired experimental results are further supported by quantum chemical calculations with a focus on the electronic structure of the complexes.
Keywords: actinide, coordination chemistry, thorium, uranium, neptunium
  • Invited lecture (Conferences)
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-13.07.2018, Dresden, Deutschland

Publ.-Id: 28256 - Permalink

Synthesis and Characterization of U(IV) Imidazol-2-ylidene Complexes
Köhler, L.; März, J.ORC; Patzschke, M.ORC; Kaden, P.ORC; Monkowius, U.ORC
In the field of actinide coordination chemistry, it is assumed that ligands bearing soft donor atoms, according to Pearson’s hard-soft-acid-base concept, such as sulphur, phosphorous or carbon lead to stable complexes. Furthermore, due to the expected strong orbital overlap between the metal and ligand, the formed complexes would provide us a deep insight into the electronic situation of the actinides. However, the majority of published actinide compounds still focusses on complexes with hard donor atoms such as oxygen.
A few examples of actinide-carbene complexes reported in the literature emphasise the remarkable strong σ donor properties of the carbon donor ligands, making the complexes e.g. excellent catalysts in organic synthesis1. Of particular interest are N-heterocyclic carbenes (NHCs) based on an imidazole-2-ylidene backbone, also known as “Arduengo carbenes”. For instance, the stability and electronic properties of these ligands can be easily tuned by synthetic introduction of suitable substituents at the nitrogen atoms.
The aim of this study is the synthesis of tetravalent actinide (An(IV)) complexes with soft-donor carbene ligands according to Figure 1 and the characterisation of the formed complexes in solution by NMR-, IR- and UV-vis spectroscopy as well as the solid-state characterisation with the help of single crystal X-ray diffraction. The acquired experimental results are further supported by quantum chemical calculations to further study the electronic structure of the complexes.
Keywords: actinide, coordination chemistry, carbene, uranium
  • Poster
    ISNSC - 10th International Symposium on Nano and Supramolecular Chemistry 2018, 08.-12.07.2018, Dresden, Deutschland

Publ.-Id: 28255 - Permalink

Coordination Chemistry of Uranium (U(IV) and -(VI)) with Bidentate N-donor Ligands
März, J.ORC; Schöne, S.ORC; Radoske, T.ORC; Patzschke, M.ORC; Stumpf, T.; Ikeda-Ohno, A.ORC
The bidentate N-donor ligands 2,2’-bipyridine (bipy) and 1,10-phenanthroline (phen) have attracted considerable attention in the field of coordination chemistry over the last decades because of their remarkable stability towards a wide variety of transition metals1. The coordination chemistry of uranium (U) has been explored with these N-donor ligands as well with a primary focus on its hexavalent state (U(VI) as UO₂2+). To the contrary, much less attention has been paid for the lower oxidation states, such as a tetravalent state (U(IV)). Here we present a systematic study on the coordination chemistry of U(IV) and -(VI) with bipy and phen under different chemical conditions, such as different solvents and changing the metal / ligand ratio.

In this study we succeeded to obtain a series of U(IV) complexes with U:ligand ratios of 1:1 and 1:2, all of which show an eight-fold coordinated uranium centre. In addition to the ligand, chloro and methanolato ligands are coordinating to the metal centre for charge compensation. Interestingly, the complexation between U(IV) and the ligand does occur even in protic solvents, in which the ligand is expected to be protonated. We also obtained another series of U(VI) complexes with both bipy and phen, underlining the versatile coordination chemistry of uranyl (UO22+). That is, the coordination between uranyl and the ligand depends strongly on the pH of the solvent used. For instance, in media with lower pH mononuclear complexes are formed, showing the uranyl unit in an unusually bent geometry.3 On the other hand, dinuclear uranyl arrangements with hydroxo-brinding are dominated in the media with higher pH, as shown in the right of Fig. 1. As illustrated in Fig. 1, bipy and phen are forming isostructural complexes both with U(IV) and- (VI).
Keywords: uranium, coordination chemistry, N-donor ligand, bipyridine, phenanthroline
  • Lecture (Conference)
    RadChem 2018, 13.-18.05.2018, Mariánské Lázně, Tschechien

Publ.-Id: 28254 - Permalink

Precipitation and dissolution of cement minerals in sandstone: Opportunities and limitations of pore and plug scale flow analysis for reactive transport modelling approaches
Kulenkampff, J.; Karimzadeh, L.; Fischer, C.
Reservoir properties of sandstones are controlled by precipitation and dissolution reactions at the pore walls. Both, the formation and dissolution of cement minerals are responsible for the complex pattern formation of porosity and permeability in reservoir rocks.
At the scale of drilled core sections (plugs), experimental and analytical approaches utilize positron emission tomography (PET) with radiotracers (Kulenkampff et al. 2016). Resulting spatiotemporal concentration distributions provide quantitative insight into fluid flow and diffusion parameters. The sensitivity is in the picomolar range of the utilized radiotracers and the spatial resolution is about 1 mm. Thus, mechanistically-important surface features such as etch pits or growth hillocks and their evolution during reaction are not yet part of the direct analysis of the flow field.
Here, we present an approach based on existing information about the complex crystal surface morphology and rate evolution (Fischer& Luttge 2017). We utilize artificial materials that are produced by 3D printing capabilities. Such an approach using PET analysis of sequences of machined surfaces in flow-through experiments provides quantitative insight into the local stability vs. temporal heterogeneity of fluid flow close to reacting surfaces. The measured flow velocity data from PET are implemented into reactive transport models and compared to existing small-scale calculations. We discuss the resulting size and complexity of surface rate patterns.

Fischer, C. and A. Luttge (2017). Beyond the conventional understanding of water–rock reactivity. Earth and Planetary Science Letters, 457: 100-105
J. Kulenkampff, M. Gründig, A. Zakhnini and J. Lippmann-Pipke (2016): Geoscientific process monitoring with positron emission tomography (GeoPET). Solid Earth, 7: 1217-1231
  • Lecture (Conference)
    Interpore 2018, 14.-17.05.2018, New Orleans, USA

Publ.-Id: 28250 - Permalink

Surface-Functionalized Mesoporous Nanoparticles as Heterogeneous Supports To Transfer Bifunctional Catalysts into Organic Solvents for Tandem Catalysis
Zhang, N.; Hübner, R.; Wang, Y.; Zhang, E.; Zhou, Y.; Dong, S.; Wu, C.
The combination of chemo- and biocatalysts offers a powerful platform to address synthetic challenges in chemistry, particularly in synthetic cascades. However, transferring both catalysts into organic solvents remains technically difficult because of the enzyme inactivation and catalyst precipitation. Herein, we designed a facile approach using functionalized mesoporous silica nanoparticles (MSN) to transfer chemo- and biocatalysts into a variety of organic solvents. As a proof-of-concept, two distinct catalysts, palladium nanoparticles (Pd NPs) and Candida antarctica lipase B (CalB), were stepwise loaded into separate locations of the mesoporous structure, which not only provided catalysts with heterogeneous supports for the recycling but also avoided their mutual inactivation. Moreover, mesoporous particles were hydrophobized by surface alkylation, resulting in a tailor-made particle hydrophobicity, which allowed bifunctional catalysts to be dispersed in eight organic solvents. Eventually, these attractive material properties provided the MSN-based bifunctional catalysts with remarkable catalytic performance for cascade reaction synthesizing benzyl hexanoate in toluene. With a broader perspective, the success of this study opens new avenues in the field of multifunctional catalysts where a plethora of other chemo- and biocatalysts can be incorporated into surface-functionalized materials ranging from soft matters to porous networks for synthetic purposes in organic solvents.
Keywords: multifunctional biocatalyst, mesoporous silica nanoparticles (MSN), palladium nanoparticles, lipase CalB, cascade reaction

Publ.-Id: 28249 - Permalink

Trace element geochemistry of sphalerite in contrasting hydrothermal fluid systems of the Freiberg district, Germany: insights from LA-ICP-MS analysis, near-infrared light microthermometry of sphalerite-hosted fluid inclusions, and sulfur isotope geochemistry
Bauer, M. E.; Burisch, M.; Ostendorf, J.; Krause, J.; Frenzel, M.ORC; Seifert, T.; Gutzmer, J.
The historic silver mining district of Freiberg (Germany) comprises hydrothermal vein-style mineralization of Permian and Cretaceous age. We compare sphalerite compositions with associated ore-forming fluids and constrain the behavior of critical metals such as In, Ge, and Ga in contrasting hydrothermal environments. Fluid inclusion studies reveal that the Permian veins formed due to boiling and cooling of a low-salinity (0 to 6% eq. w[NaCl]) magmatic-hydrothermal fluid at 350 to 230 °C. In contrast, Cretaceous veins formed by mixing of highly saline (17 to 24% eq. w[NaCl + CaCl2] and variable Na/(Na + Ca) ratios) brines at low temperatures (~ 120 °C). Sulfides of the Permian ore stage have a narrow range of δ34SVCDT from − 2.3 to + 0.9‰, while the sulfides of the Cretaceous stage have a large scatter and significantly more negative δ34SVCDT values (− 30.9 to − 5.5‰), supporting the different nature of the hydrothermal systems. Contrasting fluid systems and ore-forming mechanisms correspond to markedly different trace element systematics in sphalerite. Permian sphalerite is significantly enriched in In (up to 2500 μg/g In) relative to two sphalerite generations of Cretaceous veins. The latter have higher Ge (up to 2700 μg/g Ge) and Ga (up to 1000 μg/g Ga) concentrations. The observed trace element systematics of different sphalerite generations imply that In is enriched in high-temperature, low- to intermediate-salinity fluids with a significant magmatic-hydrothermal fluid component, while Ge and Ga are more concentrated in low-temperature, high-salinity crustal fluids with no obvious magmatic-hydrothermal affiliation.
Keywords: Sphalerite, Indium, Germanium, Gallium, Critical metals, EPMA, LA-ICP-MS, Fluid inclusions, Near-infrared light microthermometry, Sulfur isotopes, Geothermometer, Erzgebirge

Publ.-Id: 28247 - Permalink

Indium and selenium distribution in the Neves-Corvo deposit, Iberian Pyrite Belt, Portugal
Carvalho, J. R. S.; Relvas, J. M. R. S.; Pinto, A. M. M.; Frenzel, M.; Krause, J.; Gutzmer, J.; Pacheco, N.; Fonseca, R.; Santos, S.; Caetano, P.; Reis, T.; Goncalves, M.
High concentrations of indium (In) and selenium (Se) have been reported in the Neves-Corvo volcanic-hosted massive sulfide deposit, Portugal. The distribution of these ore metals in the deposit is complex as a result of the combined effects of early ore-forming processes and late tectonometamorphic remobilization. The In and Se contents are higher in Cu-rich ore types, and lower in Zn-rich ore types. At the deposit scale, both In and Se correlate positively with Cu, whereas their correlations with Zn are close to zero. This argues for a genetic connection between Cu, In and Se in terms of metal sourcing and precipitation. However, re-distribution and re-concentration of In and Se associated with tectonometamorphic deformation are also processes of major importance for the actual distribution of these metals throughout the whole deposit. Although minor roquesite and other In-bearing phases were recognized, it is clear that most In within the deposit is found incorporated within sphalerite and chalcopyrite. When chalcopyrite and sphalerite coexist, the In content in sphalerite (avg. 1400 ppm) is, on average, 2–3 times higher than in chalcopyrite (avg. 660 ppm). The In content in stannite (avg. 1.3 wt.%) is even higher than in sphalerite, but the overall abundance of stannite is subordinate to either sphalerite or chalcopyrite. Selenium is dispersed widely between many different ore minerals, but galena is the main Se-carrier. On average, the Se content in galena is ~50 times greater than in either chalcopyrite (avg. 610 ppm) or sphalerite (avg. 590 ppm). The copper concentrate produced at Neves-Corvo contains very significant In (+Se) content, well above economic values if the copper smelters recovered it. Moreover, the high In content of sphalerite from some Cu-Zn ores, or associated with shear structures, could possibly justify, in the future, a selective exploitation strategy for the production of an In-rich zinc concentrate.
Keywords: Neves-Corvo, indium, selenium


Publ.-Id: 28246 - Permalink

Irradiation tests at HZDR
Müller, S. E.ORC; Ferrari, A.ORC
Irradiation tests at HZDR in the framework of the MUSE project are presented
  • Lecture (Conference)
    MUSE meeting, 22.10.2018, Fermilab, USA

Publ.-Id: 28238 - Permalink

FLUKA simulations for the Mu2e experiment
Müller, S. E.; Ferrari, A.
FLUKA simulations for the Mu2e experiment are presented
  • Lecture (Conference)
    MU2E collaboration meeting, 18.10.2018, 18.10.2018, Fermilab, USA

Publ.-Id: 28237 - Permalink

Unconventional trace elements in sphalerite – Clues to fluid origin?
Frenzel, M.ORC; Slattery, A.; Wade, B.; Gilbert, S.; Ciobanu, C. C.; Cook, N. J.; Voudouris, P.
It is well known that the trace element content of sphalerite correlates with the conditions of ore formation (T, fS2). However, the suite of trace elements analysed in geological studies is generally restricted to the chalcophile and siderophile elements (Ag, As, Cd, Co, Fe, Ga, Ge, In, Mn, Sb, Se etc.). This may limit the inferences that can be made about the chemistry of the ore-forming fluids.

We used an integrated analytical approach consisting of electron probe micro-analysis, laser-ablationinductively coupled plasma-mass spectrometry, scanning electron microscopy and transmission electron microscopy to investigate the incorporation of the halogens Cl and Br, as well as the alkali metals Na and K into natural sphalerite from a range of deposits. This allowed us to study element distribution at length scales from >1 mm down to ~1 nm.

We found that Cl, Br, Na and K occur in measurable concentrations (100s to 1000s of ppm) in samples from several deposits. Chlorine occurs as either atomic substitutions in the sphalerite lattice or as a mixture of substitution and nano-inclusions. Unfortunately, analytical limitations mean that an investigation of the nanoscale distribution of Br, Na and K was not possible. However, concentrations of these elements (determined by LA-ICP-MS) correlate with Cl concentrations suggesting that they may be present together
with Cl in the sphalerite lattice.

The levels of trace elements present as atomic substitutions are generally related to the chemistry of the oreforming fluids. Therefore, our findings raise the possibility to measure Cl concentrations as well as Cl/Br ratios in natural sphalerite, and use these measurements to constrain fluid salinity and origin. However, more work will be required to constrain the relevant thermodynamic relationships and improve the detection limits of Cl and Br before such measurements can become a standard tool in economic geology.
  • Lecture (Conference)
    SEG 2018 conference, Keystone, 24.09.2018, Keystone, Colorado, United States of America

Publ.-Id: 28235 - Permalink

Criticality - What makes a raw material critical?
Frenzel, M.; Kullik, J.; Reuter, M.; Gutzmer, J.
A key to the current debate on the supply security of mineral raw materials is the concept of 'criticality'. This presentation provides a brief review of the criticality concept, as well as the methodologies used in its assessment, including a critical evaluation of their validity. Furthermore, it discusses several risks present in global raw materials markets that are not captured by most criticality assessments. The key result is that current assessments of raw material criticality are fundamentally flawed in several ways. This is mostly due to a lack of adherence to risk theory, and highly limits their applicability. Many of the raw materials generally identified as critical may not be critical, meaning that new assessments are urgently required.

While these are important results for policy makers, it is not necessarily clear what their implications are for geoscientific research on critical element deposits, the topic of this session. Therefore, this question will briefly be explored in the second part of the presentation.
  • Invited lecture (Conferences)
    GeoBonn, 05.09.2018, Bonn, Deutschland

Publ.-Id: 28233 - Permalink

The geometallurgical assessment of by-products - Geochemical proxies for the complex mineralogical deportment of indium at Neves-Corvo, Portugal
Frenzel, M.ORC; Bachmann, K.; Carvalho, J. R. S.; Relvas, J. M. R. S.; Pacheco, N.; Gutzmer, J.
Many by-productmetals are classified as critical.However, they are only ofmarginal interest tomanymining companies and are rarely part of detailed resource statements or geometallurgical assessments. As a result, there is a general lack of reliable quantitative data on the mineralogy and spatial distribution of these metals in ore deposits—hampering assessments of future availability.We propose here an innovative approach to integrate by-product metals into geometallurgical assessments. As an example, we use the distribution and deportment of indium at Neves-Corvo, a major European base-metal mine (Cu + Zn), and one of the largest and richest volcanichosted massive sulfide (VHMS) deposits in the world. Based on a combination of bulk-ore geochemistry and mineralogical and microanalytical data, this study is the first to develop a quantitativemodel of indium deportment inmassive sulfide ores, demonstrating how regularities in indium partitioning between different minerals can be used to predict its mineralogical deportment in individual drill-core samples. Bulk-ore assays of As, Cu, Fe, Pb, S, Sb, Sn, Zn, and In are found to be sufficient for reasonably accurate predictions. The movement of indium through the ore processing plants is fully explained by its mineralogical deportment, allowing for specific mine and process planning. The novel methodologies implemented in this contribution for (1) the assessment of analytical uncertainties, (2) the prediction of complex mineralogical deportments from bulk geochemical data, and (3) the modeling of byproduct recoveries from individual mining blocks, are of general applicability to the geometallurgical assessment of many other byproduct metals in polymetallic sulfide ores, including Ga, Ge, Mo, Re, Se, Te, as well as the noble metals.
Keywords: Geometallurgy; By-products; Trace elements; Automated mineralogy; Mineral balances; VMS deposits; VHMS deposits


Publ.-Id: 28231 - Permalink

Simulation-based exergy, thermo-economic and environmental footprint analysis of primary copper production
Abadías Llamas, A.; Reuter, M. A.; Valero Capilla, A.; Torres Cuadra, C.; Peltomäki, M.; Stelter, M.; Valero Delgado, A.; Roine, A.; Hultgren, M.
The transition from a Linear to Circular Economy has become a societal challenge to be tackled. However, the increasing complexity of materials and products increases also the sophistication of the circular economy systems required to deal with them. These systems are very resource consuming, therefore, a rigorous evaluation of the impact of every “actor” in circular economy must be done at design and operation stages to ensure the sustainability of the metal-production value chain.

A circular economy system implies, among others, low consumption of energy and material resources and low production of wastes or pollutant emissions. Its sustainability cannot therefore be evaluated just with one indicator. In this paper, we integrate indicators such as recovery rates, environmental impact indicators, as well as the quantities and qualities of the flows, losses and emissions, quantified through exergy. These must all be considered and evaluated simultaneously to perform a rigorous sustainability analysis.

The challenges of achieving a circular processing system and society are illustrated using a unique copper flowsheet that covers the complete processing chain from ore to refined metal including among others minor elements refining, scrap recycling, residue processing, steam utilization, sulphur capture and power generation in 129 unit operations linked by 289 streams and all the compositional and thermochemical detail. Using a simulation-based approach, two scenarios have been studied and compared: (i) a representative primary copper flowsheet and (ii) excluding all waste treatment processes. This unique simulated flowsheet permits a complete evaluation of various scenarios of all copper related processing options (while any additional unit operations can also be added) and also rigorously permits an allocation of impacts of all flows, products, residues etc. as a function of the complete mineral composition.

This approach to evaluating systems shows how to estimate the true losses from a system and will be a key approach to evaluate the true circularity of the circular economy system.
Keywords: Circular economy Metallurgical process simulation Thermoeconomics Exergy Copper production Life Cycle Assessment (LCA) System design

Publ.-Id: 28230 - Permalink

Materials research in high magnetic fields
Wosnitza, J.
  • Invited lecture (Conferences)
    12th Annual Matsurf Seminar, 05.11.2018, Turku, Finnland

Publ.-Id: 28226 - Permalink

FFLO states in organic superconductors − Modulated order parameter
Wosnitza, J.
  • Invited lecture (Conferences)
    Workshop on “Emergent Phenomena in Strongly Correlated Quantum Matter”, 26.-31.08.2018, Natal, Brasilien

Publ.-Id: 28225 - Permalink

"Superconductivity under Extreme Conditions” (Discussion Leader of this Session)
Wosnitza, J.
  • Invited lecture (Conferences)
    Gordon Research Conference on Conductivity and Magnetism in Molecular Materials, 12.-17.08.2018, Smithfield, USA

Publ.-Id: 28224 - Permalink

Spin-imbalanced superconductivity in layered organic superconductors
Wosnitza, J.
  • Invited lecture (Conferences)
    International Conference on Science and Technology of Synthetic Metals 2018 (ICSM 2018), 01.-06.07.2018, Busan, Korea

Publ.-Id: 28223 - Permalink

Frustrated and low-dimensional magnets in high magnetic fields
Wosnitza, J.
  • Invited lecture (Conferences)
    12th International Conference on Research in High Magnetic Fields (RHMF 2018), 24.-28.06.2018, Santa Fe, USA

Publ.-Id: 28222 - Permalink

Kinetic concepts for quantitative prediction of fluid-solid interactions
Lüttge, A.; Arvidson, R. S.; Fischer, C.; Kurganskaya, I.
In a unique “perspectives” format that examines both past and future, we appraise the field of crystal dissolution kinetics, showing how the last century’s strong progress in experimental discovery has both driven, and been driven by, the tandem evolution of basic theory. To provide context for examining the current state-of-the-art in this critical field, we highlight the key milestones that have punctuated our progress in understanding the dynamics of crystalline surfaces. For crystal growth, these are the energy relations between kinks on stepped surfaces, and the phenomena of screw dislocations sustaining steady state growth at low thermodynamic overstep. For crystal dissolution, the corresponding recognition is the tie between defects, hollow cores, and macroscopic etch pits. These latter relationships have been more recently formalized in the stepwave model, incorporating etch pit nucleation, step generation, and global retreat of the crystal surface: the total dissolution rate. All these conceptual advances contain an assertion of a link, fundamental but often implicit, between mass action and kinetics, where chemical potential is the primary driver of rates of physical process. This link is inherent in many “classical” rate equations, whose parameterization is often the endgame of laboratory observations.
Today, this extant framework serves as the conceptual basis for organizing the data available from a sophisticated suite of analytical and experimental instrumentation. These resources permit ever-increasing resolution of reacting surfaces in breathtaking detail, often under in situ conditions. These direct observations are now further enhanced by powerful computer-driven simulation and numerical modeling, allowing the virtual exploration of complex reaction systems, ranging from isolated single crystals to porous, multiphase networks. Despite the exhilarating breadth and detail of these accomplishments, it is also becoming increasingly apparent that we are moving further, not closer, from the goal of predictive understanding, a goal that is an increasingly vital social responsibility of our science. A major source of this divergence reflects the fact that at key intersecting points of study, our prowess in technical observation has effectively outpaced our theoretical understanding. In confronting the daunting complexity of these systems, we must be careful to first identify major vacancies in theory. Until we resolve these deficits, more observations may be of only limited utility.
In assessing this problem, a major uncertainty is how to properly reconcile thermodynamics, by its very nature a macroscopic formalism, with our current focus on atomic scales of reaction. This may be a problem unique to crystalline materials and their interactions with phases whose components are otherwise mobile. Detailed balancing and related microscopic reversibility, the implicit link referred to above, is often used to form a mechanistic bridge between the macroscopic distribution of energy and microscopic heterogeneity of events in crystal surfaces, but its employment creates two problems: spatial and temporal. First, reaction mechanism is truly atomic in dimension, involving actual, nondegenerate collisions at crystal surface sites, whereas 〖∆G〗_r or ∆μ is macroscopic. Second, the rate at which a crystal surface dissolves reflects both the chemical composition of the ambient fluid and the distribution of surface energy. Reaction towards “equilibrium”, involving the typically slow redistribution of surface energy, may thus inherit topography inconsistent with the computed “driving force”. This reactivity mismatch yields surfaces that evolve over time, producing a heterogeneous distribution of rates. This distribution can be efficiently characterized by rate spectra: the span of non-steady-state rates reflecting diversity of reactive sites established under previous 〖∆G〗_r regimes. We use these spectra as a basic compact variable: a signal that encodes the complex link between site-specific surficial energy distributions, solution and surface chemistry, and the cumulative rate that results. Because this encoding is efficiently captured by numerous surface analytical microscopies (VSI, AFM), this approach permits the testing of hypotheses regarding the probabilistic nature of rate distributions, a process we hope the community will embrace, serving ultimately as a key step forward in establishing useful predictive approaches. We illustrate this potential with a series of case studies that target a range of composition, space, and time scales.

Publ.-Id: 28221 - Permalink

Effects of gamma-alumina nanoparticles on strontium sorption in smectite: additive model approach
Mayordomo, N.; Alonso, U.; Missana, T.
Strontium sorption was analysed in binary mixtures of smectite and γ-alumina nanoparticles under different pH, ionic strength and Sr concentration. The aims were to verify if γ-alumina nanoparticles enhance Sr sorption in smectite and to analyse whether a component additive model satisfactorily described Sr sorption in the mixtures.
In smectite, Sr sorption mainly occurs by cation exchange but surface complexation was also accounted for. In both solids, surface complexation was described with a non-electrostatic model.
The addition of γ-Al₂O₃ nanoparticles to smectite improved Sr uptake under alkaline pH and high ionic strength, and the additive model successfully reproduced experimental data. In contrast, under acid pH and low ionic strength, no sorption improvement was observed upon adding the nanoparticles and the additive model overestimated Sr sorption. The competition of Al(III) ions, coming from γ-Al₂O₃ dissolution, partially explained the differences between data and model. Nevertheless, surface interactions between alumina particles and smectite layers may be shielding the charge, hindering contaminant access to exchangeable sites in smectite.
Keywords: Strontium, smectite, alumina, nanoparticles, sorption modelling, additive model

Publ.-Id: 28214 - Permalink

Is It Here/There Yet? - Real Life Experiences of Generating/Evaluating Extreme Data Sets Around the World
Juckeland, G.ORC; Huebl, A.ORC; Bussmann, M.ORC

Large scale simulations easily produce vast amounts of data that cannot always be evaluated in-situ. At that point parallel file systems come into play, but their per node performance is essentially limited to about the speed of a USB 2.0 thumb drive (e.g. the Spider file system at OLCF provides over 1 TB/s write bandwidth, but with 18000+ nodes of Titan writing simultaneously, this number is reduced to about 50 MB/s per node). Making the most out of such a limited resource requires I/O libraries that actually scale. In addition such libraries also offer on the fly data transformations (e.g. compression) to better utilize the raw I/O bandwidth, albeit, opening a new can of worms by trading compression throughput with compression ratios for performance. We will present a detailed study of I/O performance and various compression techniques at OLCF and compare them against smaller local I/O installations, demonstrating the highest achieved I/O performance for real world applications at OLCF. Furthermore, we demonstrate that the best performing I/O setup can be determined prior to starting the job based on hardware characteristics.
Now that you have your data on disk the clock starts ticking and you are fighting against the deadline until your data will be purged, since most centers only offer the high performing storage spaces on a temporary basis. Extracting all valuable information out of a petabyte sized data set requires parallel processing as well and induces wait times until the resources are available and quite naturally a lot of trial-and-error for the evaluation. The time constraint for keeping the temporary data becomes even more troublesome when trying to compare multiple large simulations that naturally have a delay of multiple days until they are scheduled and write their results. And ideally analysis could embrace the data of multiple simulations of a quarterly accounted, yet year-long computing campaign. Another challenge for actually conducting scientific discoveries comes when utilizing multiple compute sites. This seems to be rather usual for research groups as they will use all the compute clock cycles they
can get wherever that may be. For comparative studies the data sets now need to be available at the same time for analysis, e.g. via archiving solutions or transfer to one location. The achievable transfer bandwidth between data centers is in our experience still much lower than expected. The talk will also present on the experiences of evaluating petabyte sized data sets in such a diverse environment.

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-09-18
    DOI: 10.14278/rodare.70
    License: CC-BY-4.0


Publ.-Id: 28213 - Permalink

Radiosynthesis and preliminary biological evaluation of a novel 18F-labeled MCT1/MCT4 inhibitor for tumor imaging by PET
Sadeghzadeh, M.; Moldovan, R.-P.; Wenzel, B.; Deuther-Conrad, W.; Toussaint, M.; Fischer, S.; Ludwig, F.-A.; Teodoro, R.; Kranz, M.; Spalholz, T.; Gurrapu, S.; Steinbach, J.; Drewes, L. R.; Brust, P.
Aim: Monocarboxylate transporters (MCTs) are integral plasma membrane proteins that bi-directionally transport lactate and ketone bodies and are highly expressed in non-hypoxic regions of human colon, brain, breast, lung and other tumors.[1] Transporter inhibition leads to intracellular lactate accumulation, acidosis and cell death especially in glioma cell lines.[2] Accordingly, MCT1/MCT4 inhibitors are regarded to be of potential clinical use. In the current study a new 18F-labeled MCT1/MCT4 inhibitor was developed for in vivo PET imaging of MCT1/MCT4-overexpressing brain tumors.

Methods: (E)-2-Cyano-3-{4-[(3-fluoropropyl)(propyl)amino]-2-methoxyphenyl}acrylic acid (CAPAA) was synthesized from m-anisidine in three consecutive steps with 50% overall yield. Similar strategy was carried out to synthesize the mesylated precursor for radiosynthesis. Radiosynthesis of [18F]CAPAA was achieved by a two-step reaction, starting with the nucleophilic substitution of fluorine-18 on the alkyl chain using [18F]TBAF followed by removal of the protecting group by TFA at room temperature. [18F]CAPAA was isolated by semi-preparative HPLC eluting with 46% CH3CN/aq. 20 mM NH4HCO2 (Reprosil-Pur C18-AQ column, 250 × 10 mm), purified via Sep-Pak® C18 light cartridge and formulated in 10% EtOH/saline solution. LogD was assessed by the shake-flask method. The average IC50 values for MCT1 and MCT4 were evaluated via [14C]lactate uptake assay on the rat brain cerebrovascular endothelial cell line RBE4. The apparent affinity of [18F]CAPAA (KD) was determined using brain homogenate obtained from female CD1 mouse. The radiotracer metabolism was investigated in female CD1 mice by radio-HPLC of plasma and brain samples obtained at 30 min p.i. Plasma obtained at 60 min p.i. was used to measure the in vivo plasma free fraction.

Results: During radiosynthesis, a radiolabeled intermediate was obtained by an optimized procedure (CH3CN, 50µl of TBAHCO3-, 2-5 GBq of K[18F]F, 100 ̊C, 15 min) with 55-70% yield (n=8, non-isolated) determined by radio-HPLC analysis. Deprotection of tert-Bu group was accomplished with TFA in acetonitrile at r.t. for 15 min with 65-73% yield (n=10, radio-HPLC, non-isolated). The radiotracer was obtained in 42-65% radiochemical yield (RCY) with >98% radiochemical purity (RCP). The radioligand was highly stable in saline and PBS (>95%) up to 60 min. LogD was determined as 0.42 which reveals the tracer has moderate lipophilicity. CAPAA showed high MCT1 and MCT4 inhibition activity (IC50 = 11 and 6.4 nM respectively). [18F]CAPAA binds with an apparent KD value of ~30 nM in a saturable manner to a binding site in the brain of healthy mice. In vivo studies showed >99% of intact tracer in plasma at 30 min p.i. and a free fraction in plasma of ~3% at 60 min p.i.

Conclusions: [18F]CAPAA was achieved in high RCY and RCP and showed considerable in vitro and in vivo stability. Accordingly, the newly developed MCT1/MCT4 radioligand is anticipated to be a useful agent for imaging of tumors by PET. Animal PET imaging on healthy and brain tumor-bearing mice is currently performed.
Keywords: Radiofluorination, MCT1, Tumor imaging
  • Contribution to proceedings
    26. Jahrestagung Arbeitsgemeinschaft Radiochemie und Radiopharmazie (AGRR2018), 20.-22.09.2018, Aachen, Deutschland

Publ.-Id: 28210 - Permalink

Paramagnetic NMR investigations of metal-organic complexes of soft donor ligands and the tetravalent actinides
Schöne, S.ORC; Radoske, T.; Felsner, B.; Köhler, L.; Patzschke, M.ORC; März, J.ORC; Kaden, P.ORC
NMR spectroscopy of metal-organic complexes of the f-element metal ions is often challenging due to additional chemical shifts and enhanced relaxation close to the paramagnetic metal center. These effects originate from electronic interactions between metal and ligand and often result in large additional NMR chemical shifts, compared to isostructural diamagnetic complexes, ob-served on the resonances of the ligands’ nuclei. The major two contributors to these paramag-netic chemical shifts are Fermi-contact shifts (FCS) and pseudo-contact shifts (PCS). FCS are due to delocalization of unpaired electron density in molecular orbitals involving both metal and ligand orbitals and thus report on the bond properties. PCS are originating from distance- and angle-dependent dipolar coupling of electron spins through space and are therefore bearing structural information.

The paramagnetic contributions can be mathematical separated provided that a suitable diamag-netic reference is available in order to subtract non-paramagnetic contributions. For the trivalent actinides no diamagnetic reference in the same series is available in milligram scale. Further-more, all available theories behind mathematical disentangling of contributions to the paramag-netic chemical shift, even for the lanthanide series, omit the influence of spin-orbit effects that might have a sizeable contribution as well. [1,2] Comparing studies of isostructural diamagnetic complexes of both f-element series of tetravalent metal ions (Ce(IV) and Th(IV)) allow for an es-timation of additional influences to the chemical shifts and the effect of contributions usually omitted by commonly used mathematical theories.

With Th(IV) as a diamagnetic reference in the same series, studying paramagnetic metal-organic complexes of the tetravalent actinides (An(IV)) allows to assess the chemical bonding situation via the influences on NMR chemical shifts (via FCS) and additionally allows to exploit the geo-metrical information which can be extracted from dipolar interactions (via PCS). These structural properties of the complexes as derived from PCS contributions can be compared to single crys-tal X-ray diffraction structures enabling a comparison of solution state and solid state structure of the metal-organic complexes under investigation. Herein we report the first results of investiga-tions of N- and N,O-donor ligand complexes of the An(IV) series (Th(IV), U(IV) and Np(IV)).
Keywords: NMR, actinides, paramagnetic, metal organic, Th, U, Np, Pu, Thorium, Uranium, Neptunium, Plutonium, diamagnetic
  • Lecture (Conference)
    ATAS - 4th International Workshop on Advanced Techniques in Actinide Spectroscopy, 06.-09.11.2018, Nice, France

Publ.-Id: 28209 - Permalink

The Unofficial "Green HPCG"
Huebl, A.ORC

An unofficial list of HPC systems, compiled from the HPCG Benchmark and TOP500 in order to explore an alternative metric for the Green500.

Keywords: hpc; manycore; top500; computing; hardware; energy efficiency
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-11-18
    DOI: 10.14278/rodare.68
    License: CC-BY-4.0


Publ.-Id: 28207 - Permalink

FMR Linewidth Variation with Distance from Lateral Antiferromagnet/Ferromagnet Interfaces
Usami, T.; Bali, R.; Lindner, J.; Itoh, M.; Taniyama, T.
B2-ordered FeRh alloys show a fascinating first-order magnetic phase transition from the antiferromagnetic (AFM) to the ferromagnetic (FM) state at around 380 K[1]. Recently, the AFM/FM phase transition and its related phenomena have been extensively studied; the transition temperature can be manipulated by substituting ions[2], introducing disorder via ion irradiation[3], injecting a spin-polarized current[4], and applying an electric field[5]. These experimental demonstrations would provide a fundamental basis for the use of FeRh in practical novel spintronic applications such as magnetic recordings, AFM memory resistors, and magnonic devices. Also, we have shown a long-range propagation of spin waves in a ferromagnetic Fe60Rh40 thin wire, demonstrating that FeRh has its potential of an alternative material for magonics [6]. In this study, we report ferromagnetic resonance (FMR) in the proximity of lateral AFM/FM FeRh interfaces that are generated by Ne+ ion irradiation. From the FMR measurements, we find a unique dependence of linewidth of the FMR spectra as a function of distance between the rf-antenna and the AFM/FM interface.
  • Poster
    Magnetics and Optics Research International Symposium 2018, 07.-10.01.2018, New York, United States of America

Publ.-Id: 28206 - Permalink

Identical pion intensity interferometry in central Au+Au collisions at 1.23A GeV
Adamczewski-Musch, J.; Arnold, O.; Behnke, C.; Belounnas, A.; Belyaev, A.; Berger-Chen, J. C.; Biernat, J.; Blanco, A.; Blume, C.; Böhmer, M.; Bordalo, P.; Chernenko, S.; Chlad, L.; Deveaux, C.; Dreyer, J.; Dybczak, A.; Epple, E.; Fabbietti, L.; Fateev, O.; Filip, P.; Fonte, P.; Franco, C.; Friese, J.; Fröhlich, I.; Galatyuk, T.; Garzon, J. A.; Gernhäuser, R.; Golubeva, M.; Greifenhagen, R.; Guber, F.; Gumberidze, M.; Harabasz, S.; Heinz, T.; Hennino, T.; Hlavac, S.; Höhne, C.; Holzmann, R.; Ierusalimov, A.; Ivashkin, A.; Kämpfer, B.; Karavicheva, T.; Kardan, B.; Koenig, I.; Koenig, W.; Kolb, B. W.; Korcyl, G.; Kornakov, G.; Kotte, R.; Kühn, W.; Kugler, A.; Kunz, T.; Kurepin, A.; Kurilkin, A.; Kurilkin, P.; Ladygin, V.; Lalik, R.; Lapidus, K.; Lebedev, A.; Lopes, L.; Lorenz, M.; Mahmoud, T.; Maier, L.; Mangiarotti, A.; Markert, J.; Maurus, S.; Metag, V.; Michel, J.; Mihaylov, D. M.; Morozov, S.; Müntz, C.; Münzer, R.; Naumann, L.; Nowakowski, K. N.; Palka, M.; Parpottas, Y.; Pechenov, V.; Pechenova, O.; Petukhov, O.; Pietraszko, J.; Przygoda, W.; Ramos, S.; Ramstein, B.; Reshetin, A.; Rodriguez-Ramos, P.; Rosier, P.; Rost, A.; Sadovsky, A.; Salabura, P.; Scheib, T.; Schuldes, H.; Schwab, E.; Scozzi, F.; Seck, F.; Sellheim, P.; Siebenson, J.; Silva, L.; Sobolev, Y. G.; Spataro, S.; Ströbele, H.; Stroth, J.; Strzempek, P.; Sturm, C.; Svoboda, O.; Szala, M.; Tlusty, P.; Traxler, M.; Tsertos, H.; Usenko, E.; Wagner, V.; Wendisch, C.; Wiebusch, M. G.; Wirth, J.; Zanevsky, Y.; Zumbruch, P.
For the first time, identical pion HBT intensity interferometry is investigated for a large heavy ion collision system in the energy region of 1 GeV per nucleon. High-statistics π−π− and π+π+ data are presented for central Au+Au collisions at 1.23A GeV, measured with HADES at SIS18/GSI. The radius parameters, derived from the correlation function depending on relative momenta in the longitudinal-comoving system and parametrized as three-dimensional Gaussian distribution, are studied as function of transverse momentum. A substantial charge-sign difference of the source radii is found, particularly pronounced at low transverse momentum. The extracted Coulomb-corrected source parameters agree well with a smooth extrapolation of the center-of-mass energy dependence established at higher energies, extending the corresponding excitation functions down towards a very low energy. Our data would thus rather disfavour any strong energy dependence of the radius parameters in the low energy region.

Publ.-Id: 28202 - Permalink

High-field ESR in low-dimensional spin systems
Zvyagin, S.
Electron spin resonance (ESR) is traditionally recognized as one of the most sensitive tools for probing magnetic excitations in strongly-correlated spin systems. Among other exchange-coupled spin systems, low-dimensional magnets serve as almost ideal paradigmatic models in quantum magnetism, exhibiting highly unusual ground-state properties and spin dynamics. Here, I review results of our recent high-field ESR studies of some low-dimensional magnets, including quantum spin chains [1], quantum antiferromagnets on triangular lattice [2], Heisenberg spin ladders [3], and quasi-two-dimensional magnets on a honeycomb lattice [4]. In addition, I will give a brief introduction into the high-field ESR facilities at the Dresden High Magnetic Field Laboratory, which allows for multi-frequency ESR experiments in a very broad frequency range (ca 50 GHz - 9 THz) in magnetic fields up to 60 T and above.
  • Invited lecture (Conferences)
    Third Joint Conference of the Asia-Pacific EPR/ESR Society and The International EPR (ESR) Society (IES) Symposium, 23.-27.09.2018, Brisbane, Australia

Publ.-Id: 28200 - Permalink

TEM investigation of irradiation-induced defects in an ion-irradiated Fe-9Cr ODS steel
Vogel, K.; Duan, B.; Heintze, C.; Bergner, F.
Oxide dispersion strengthened (ODS) steels are promising candidate materials for structural components in nuclear power generators. Here we report on our preliminary results of TEM investigations of irradiation-induced defects in an ion-irradiated Fe-9Cr ODS steel. A cross-sectional TEM sample prepared by focused ion beam (FIB) was studied in a FEI Talos F200X transmission electron microscope by imaging under various diffraction conditions in bright- and dark-field mode. The TEM micrographs show a defect-rich band of about 400 nm width. The band is aligned parallel to the specimen surface and its position corresponds to the position of the peaks in the damage and/or injected interstitials profiles. Therefore we conclude that the defects within the band are caused by the ion irradiation. In higher magnified images of the band we observe a large number of defects, which appear as "black dots" showing a high contrast under kinematic bright-field conditions. We assume that these defects are interstitial loops, however this assumption has to be proved by further investigations. Additionally we observe some strongly curved dislocation segments, which will also be a subject of our further TEM studies.
Keywords: Transmission Electron Microscopy, Irradiation-induced defects
  • Poster
    Microscopy of Radiation Damage 2018, 21.-23.03.2018, Oxford, United Kingdom

Publ.-Id: 28199 - Permalink

Effect of Tb for Gd substitution on magnetic and magnetocaloric properties of melt-spun (Gd1-xTbx)3Co alloys
Shishkin, D. A.; Volegov, A. S.; Ogloblichev, V. V.; Mikhalev, K. N.; Gerasimov, E. G.; Terentev, P. B.; Gaviko, V. S.; Gorbunov, D. I.; Baranov, N. V.
The melt-spun (Gd1-xTbx)3Co alloys (0≤x≤1) have been obtained and studied by X-ray diffraction, ac-susceptibility, magnetization in steady and pulse magnetic fields, and NMR measurements. A comparison of the results obtained on melt-spun alloys with their crystalline analogs has revealed a strong impact of amorphization on the magnetic state and magnetocaloric properties. The Gd-rich amorphous (Gd1-xTbx)3Co alloys (x≤0.1) exhibit increased magnetic ordering temperatures in comparison with the crystalline compounds, which is attributed to the appearance of a magnetic moment on Co atoms. The substitution of Tb for Gd results in the growth of the ratio of local anisotropy to exchange. The melt quenching of the (Gd1-xTbx)3Co alloys allows improving their magnetocaloric properties in the temperature range from 80 K up to 170 K.

Publ.-Id: 28198 - Permalink

Cm complexation with aqueous phosphates at elevated temperatures
Huittinen, N.; Jordan, N.; Demnitz, M.; Lösch, H.; Starke, S.; Brendler, V.
Orthophosphate ions (H2PO4-, HPO42-, and PO43-) are ubiquitous in the environment and may originate from the natural decomposition of rocks and minerals (e.g. monazite or apatite), agricultural runoff, or from wastewater treatment plants. Furthermore, the potential use of monazite (LnPO4) ceramics for the immobilization of specific actinide-containing waste streams may become an important source of phosphates in the future [1–2]. Among the inorganic ligands, phosphates are strong complexants and can be expected to influence the speciation of dissolved radioactive contaminants when present in solution. However, very little data is available on the complexation of especially actinides with aqueous phosphates, even though these complexation reactions precede any aqueous synthesis of monazite ceramics and are expected to occur in natural waters as well as in the proximity of monazite-containing high-level waste repositories. The existing data also suffers from an almost systematic absence of independent spectroscopic validation of the stoichiometry of the proposed complexes.
In the present work, time-resolved laser fluorescence spectroscopy (TRLFS) has been employed to study the complexation of the actinide Cm3+ (5×10-7 M) as a function of total phosphate concentration (0–0.5 M Σ(PO4)) in the temperature regime 25–80°C, using NaClO4 as a background electrolyte (0.5–2.1 M). The studies have been conducted in the acidic pH-range ( log[H+] = 1–2.5) to avoid precipitation of solid Cm rhabdophane (CmPO4×nH2O). Under these experimental conditions, the trivalent actinide cation was found to form a complex with the anionic H2PO4- species, i.e. CmH2PO42+ and Cm(H2PO4)2+, depending on the solution pH and the total phosphate concentration, Figure 1.
The complexation reaction occurs at lower total phosphate concentration when increasing the ionic strength or the temperature. Using specific ion interaction theory (SIT) and the Van’t Hoff equation, obtained conditional constants at varying ionic strengths and temperatures have been extrapolated to infinite dilution (logβ0) and values for the enthalpy ΔRH° (assumed constant between 25 to 80 °C) and entropy ΔRS° of reaction have been acquired. The results of the extrapolations are shown exemplarily for the CmH2PO42+ species in Figure 2.
The new thermodynamic data derived in this fundamental study will contribute to a fundamental process understanding necessary to critically assess the environmental fate of actinides in the environment.
  • Lecture (Conference)
    Radiation in the environment – scientific achievements and challenges for the society, 16.-17.04.2018, Helsinki, Finland

Publ.-Id: 28197 - Permalink

Spectroscopic investigations of Cm3+ incorporation in lanthanide orthophosphates
Huittinen, N.; Scheinost, A. C.; Ji, Y.; Kowalski, P. M.; Arinicheva, Y.; Neumeier, S.
Monazites (LnPO4) are envisioned as potential immobilization matrices for high-level radioactive wastes produced e.g. during the nuclear fuel cycle [1–2]. Hydrated rhabdophane (LnPO4×0.67H2O) is a precursor phase during monazite synthesis and a potential solubility-limiting solid phase under nuclear waste storage conditions [3–4]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the radionuclide incorporation process in both the pristine monazite ceramics and their alteration products is required.
In the present study [5] we have combined two spectroscopic methods, (1) time-resolved laser fluorescence spectroscopy (TRLFS) and (2) extended x-ray absorption fine structure spectroscopy (XAFS) with density functional theory-based ab initio calculations to investigate the incorporation of the actinide curium (Cm) in (La,Gd)PO4 monazite and rhabdophane solid phases. Spectroscopic methods allow for direct probing of the dopant and its local environment in host matrices, providing a better understanding of potential lattice defect formations, lattice strain or disordering phenomena, and site population deviances with regard to the composition of the host structure, which may occur in the solid phase upon introduction of the dopant. Ab initio calculations can further deliver descriptions and explanations for spectroscopic findings, thus, contributing to a better understanding of the incorporation processes on a molecular level.
The solid phases were synthesized by addition of phosphoric acid to a solution containing La3+ and Gd3+ in desired relative concentrations and a small amount of the actinide (248Cm), until a white precipitate of La1-xGdxPO4 rhabdophane doped with approximately 50 ppm Cm3+ was obtained. An aliquot of the obtained solid phase was thereafter sintered at 1450°C to acquire the crystalline monazite ceramic. Structural refinement of collected XRD data for both rhabdophane and monazite solids show a linear dependency of lattice parameters as a function of Gd3+ substitution according to Vegard’s law.
Our combined spectroscopic results show that Cm3+ is incorporated in the monazite end-members (LaPO4 and GdPO4) on one specific, highly ordered lattice site. In the intermediate solid solution compositions, an increasing disorder around the Cm3+ dopant can be seen as a result of a broader distribution of possible Cm∙∙∙O bond-lengths in comparison to the end-member compositions with very well-defined nearest neighbour distances. Despite this local structural disordering, homogenous solid solutions were obtained for all synthesized monazite compositions without the formation of dopant clusters that could potentially hamper the performance of the monazite ceramics for the immobilization of minor actinide containing wastes.
The hydrated rhabdophane lattice comprises two different site types that could accommodate the actinide dopant: a 9-coordinated “hydrated” site amounting to two thirds (2/3) of the total number of lanthanide sites in the solid structure, where one coordinating oxygen atom originates from a water molecule, and an 8-fold coordinated “non-hydrated” site (1/3 of available Ln sites) where all oxygen atoms are provided by phosphate groups [4]. Based on our laser spectroscopic investigations, curium incorporation on both site types can be confirmed, however, the site occupancy is not in agreement with the hydrated rhabdophane structure. In contrast, a preferential incorporation of curium on non-hydrated lattice sites can be seen, especially for the La-rich rhabdophane compositions, implying that structural substitution reactions cannot be predicted based on the structure of the host matrix only.
  • Lecture (Conference)
    4th International Workshop on Advanced Techniques in Actinide Spectroscopy (ATAS), 06.-09.11.2018, Nice, France

Publ.-Id: 28196 - Permalink

Inverted hysteresis and negative remanence in a homogeneous antiferromagnet
Opherden, L.; Billitewski, T.; Hornung, J.; Herrmannsdörfer, T.; Samartzis, A.; Islam, A. T. M. N.; Anand, V. K.; Lake, B.; Moessner, R.; Wosnitza, J.
Magnetic remanence—found in bar magnets or magnetic storage devices—is probably the oldest and most ubiquitous phenomenon underpinning the technological applications of magnetism. It is a macroscopic nonequilibrium phenomenon: A remanent magnetization appears when a magnetic field is applied to an initially unmagnetized ferromagnet, and then taken away. Here, we present an inverted magnetic hysteresis loop in the pyrochlore compound Nd2Hf2O7: The remanent magnetization points in a direction opposite to the applied field. This phenomenon is exquisitely tunable as a function of the protocol in field and temperature, and it is reproducible as in a quasiequilibrium setting.


Publ.-Id: 28195 - Permalink

Experimental investigation on the buoyancy-induced flow in a model of the Czochralski crystal growth process
Pal, J.; Franke, S.; Eckert, S.; Gerbeth, G.
Within this paper we present a model experiment focusing on investigations of the flow field in a Czochralski puller. Low melting point liquid metals as GaInSn are an important tool to investigate the flow structure for such industrial processes. The topology of the prevailing thermally-driven convection might be very complex and is mainly determined by the aspect ratio of the liquid volume and the strength of the convection described by the characteristic dimensionless Grashof number. The measurements of the fluid flow have been conducted by means of the ultrasound Doppler velocimetry (UDV) with and without the influence of external magnetic fields. Two kinds of sensor configurations were used to investigate the flow. Firstly, measurements of the radial velocity component by means of single UDV transducers were carried out shortly below the melt surface across the entire diameter of the cylindrical liquid column at various azimuthal angles. Secondly, a vertically arranged UDV array was applied at the side of the cylinder to obtain more detailed information about the radial velocities in the covered meridional plane. The results reveal the complex flow structure of natural convection in a Czochralski crucible which gains in complexity with applied external magnetic fields.
Keywords: Czochralski crystal growth process
  • Lecture (Conference)
    Electromagnetic Processing of Materials 2018, 14.-18.10.2018, Awaji, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012011
    DOI: 10.1088/1757-899X/424/1/012011

Publ.-Id: 28191 - Permalink

Two-dimensional Pd3P2S8 Semiconductors as Photocatalysts for Solar Oxygen Evolution Reaction: A Theoretical Investigation
Jing, Y.; Heine, T.
On the basis of first principles calculations, we propose Pd3P2S8 monolayer and bilayer, two-dimensional semiconductors, whose layered bulk parent crystals are experimentally reported, as promising photocatalysts for the solar-driven oxygen evolution reaction. The monolayer is kinetically and thermodynamically stable and shows a small cleavage energy of 0.35 J m−2, suggesting that it can be prepared by exfoliation from its bulk material, and exhibits a direct band gap of 2.98 eV, which can be engineered by applying strain. The Pd3P2S8 bilayer is an indirect band gap semiconductor with a slightly smaller band gap of 2.83 eV. The photoexcited holes generate favorable driving forces for promoting the specific solar-driven O2 evolution reaction. The extraordinary electronic properties, pronounced light harvesting capability in the visible and ultraviolet regions and active surface sites render the Pd3P2S8 monolayer and bilayer as compelling 2D materials with interesting application potential for photocatalytic and photoelectrocatalytic water splitting.

Publ.-Id: 28188 - Permalink

Cavitation energies can outperform dispersion interactions
He, S.; Biedermann, F.; Vankova, N.; Zhechkov, L.; Heine, T.ORC; Hoffman, R. E.; de Simone, A.; Duignan, T. T.; Nau, W. M.
In this work we prepare Langmuir–Blodgett monolayers with a trifunctional amphiphilic anthraphane monomer. Upon spreading at the air/water interface, the monomers self-assemble into 1 nm-thin monolayer islands, which are highly fluorescent and can be visualized by the naked eye upon excitation. In situ fluorescence spectroscopy indicates that in the monolayers, all the anthracene units of the monomers are stacked face-to-face forming excimer pairs, whereas at the edges of the monolayers, free anthracenes are present acting as edge groups. Irradiation of the monolayer triggers [4 + 4]-cycloadditions among the excimer pairs, effectively resulting in a two-dimensional (2D) polymerization. The polymerization reaction also completely quenches the fluorescence, allowing to draw patterns on the monomer monolayers. More interestingly, after transferring the monomer monolayer on a solid substrate, by employing masks or the laser of a confocal scanning microscope, it is possible to arbitrarily select the parts of the monolayer that one wants to polymerize. The unpolymerized regions can then be washed away from the substrate, leaving 2D macromolecular monolayer objects of the desired shape. This photolithographic process employs 2D polymerizations and affords 1 nm-thin coatings.
Keywords: 2D polymerization; air/water interface; anthracene; fluorescence; photolithography; self-assembled monolayers


  • Secondary publication expected from 16.04.2019

Publ.-Id: 28187 - Permalink

PtTe Monolayer: Two-Dimensional Electrocatalyst with High Basal Plane Activity toward Oxygen Reduction Reaction
Wang, Y.; Li, Y.; Heine, T.
PtTe is a layered bulk material that was discovered in 1897. According to first-principles calculations, it is one of the few layered materials that maintains structure and metallic character when thinned down to the monolayer. Interlayer energy is small enough to allow for chemical exfoliation techniques. Our calculations show that monolayer PtTe is a candidate to substitute Pt electrodes, and we computationally studied its catalytic performance in the oxygen reduction reaction (ORR). Remarkably, the basal plane of a PtTe monolayer exhibits excellent catalytic activity toward ORR, with a positive half-wave potential (∼0.90 V) and a high four-electron reduction pathway selectivity. These characteristics suggest that it outperforms Pt electrodes as catalyst, has a reduced Pt content, high Pt utilization, and a high surface area, and is a promising candidate for fuel cell components.


  • Secondary publication expected

Publ.-Id: 28186 - Permalink

Correction of Geometrical Effects of a Knife-Edge Slit Camera for Prompt Gamma-Based Range Verification in Proton Therapy
Petzoldt, J.; Janssens, G.; Nenoff, L.; Richter, C.; Smeets, J.
Prompt gamma (PG) based range verification can potentially reduce the safety margins in proton therapy. A knife-edge slit camera has been developed in this context using analytical PG simulations as reference for absolute range verification during patient treatment. Geometrical deviations between measurement and simulation could be observed and have to be corrected for in order to improve the range retrieval of the system. A geometrical correction model is derived from Monte Carlo simulations in water. The influence of different parameters is tested and the model is validated in a dedicated benchmark experiment. We found that the geometrical correction improves the agreement between measured and simulated PG profiles resulting in an improved range retrieval and higher accuracy for absolute range verification. An intrinsic offset of 1.4 mm between measurement and simulation is observed in the experimental data and corrected in the PG simulation. In summary, the absolute range verification capabilities of a PG camera have been improved by applying a geometrical correction model.


Publ.-Id: 28183 - Permalink

Experimental Analysis of the effect of column feed pipe configurations on the flow morphology
Döß, A.ORC; Schubert, M.; Hampel, U.
Droplets entrained by the vapor phase can drastically reduce the separation capacity of distillation columns and cause severe corrosion problems, process instabilities as well as higher emissions due to droplet carry-over into the downstream process units.
Intensive interactions between vapor and liquid phases favor droplet formation. Feed pipe and feed inlet are prone positions for such droplet formation, depending on flow rates, phase change and pipe geometry resulting in characteristic morphologies.
Several models are available to predict the flow regime for known liquid and vapor flow rates. However, these models and flow maps are often restricted to fully developed flows in straight pipes of small diameter only and do not account for the effects of various entrance lengths, larger diameters as well as bends found in industry. Thus, an experimental analysis is performed to study the effect of column feed pipe configurations on the evolving flow regime using the wire-mesh sensor technique (Fig. 1). Wire-mesh sensors visualize the dynamic flow structure in the pipe cross-section at high spatiotemporal resolution (1 to 3 mm, up to 10,000 Hz). This work is supported by the Federal Ministry for Economic Affairs and Energy (BMWi) based on a decision by the German Bundestag (FKZ 03ET1395D).
Keywords: Two-phase flow morphology, Horizontal feed pipe, Wire-mesh sensor, Pipe configuration
  • Poster
    ProcessNet-Jahrestagung und 33. DECHEMA-Jahrestagung der Biotechnologen 2018, 10.-13.09.2018, Aachen, Deutschland
    DOI: 10.1002/cite.201855425

Publ.-Id: 28181 - Permalink

Flow morphology in feed pipes: theoretical analysis and experimental investigation
Döß, A.ORC; Schubert, M.; Hampel, U.; Schleicher, E.; Geipel, C.; Mehringer, C.; Flegiel, F.
Efficient separation in distillation columns driven by the thermodynamic non-equilibrium between vapor and liquid phase is achieved by high turbulence as well as large interfacial area. At the same time, intensive interactions between vapor and liquid phases result in the formation of droplets, whose entrainment by the vapor phase may drastically reduce the separation capacity. The feed pipe is a prone position for such droplet formation. Besides the flash evaporation, the evolving flow morphology in the feed pipe is decisive for the droplet generation.The flow morphology in pipes depends on fluid flow rates and properties as well as on the pipe geometry. Several models and flow regime maps for fully developed flows in small pipe diameters exist, relating operating conditions and flow morphology. However, industrial feed pipe configurations with larger diameters and bends are so far not studied.
Thus, an experimental study in feed pipes of 50 mm and 200 mm diameter is performed using the wire-mesh sensor technique (Fig. 1). The wire-mesh sensor visualizes the dynamic flow structure in the pipe cross-section at high spatiotemporal resolution (1 to 3 mm, up to 10,000 Hz). The obtained data are compared with the
state-of the art models to assess their applicability for feed pipes. This project is supported by the Federal Ministry for Economic Affairs and Energy (BMWi) based on a decision by the German Bundestag (FKZ 03ET1395D).
Keywords: Two-phase flow morphology, Horizontal feed pipe, Wire-mesh sensor,
  • Lecture (Conference)
    ACHEMA 2018, Session: TERESA – Droplet entrainment and droplet reduction in mass transfer devices, 11.-15.06.2018, Fankfurt am Main, Deutschland

Publ.-Id: 28179 - Permalink

Ultrasonic measurements of the flow field in foam and froth
Heitkam, S.; Nauber, R.; Richter, T.; Büttner, L.; Czarske, J.; Eckert, K.
In this work, the non-invasive Ultrasound-Doppler velocimetry has been used to measure the velocity distribution inside a liquid foam bulk for the first time. The foam flows upward in a transparent channel. Optical correlation algorithms and conductivity measurement provide reference data. An array of ultrasound transducers is mounted within the channel, sending bursts along the main flow axis and receiving the echoes. The penetration depth equals up to 0.2 meters. With purposely designed flows it is demonstrated, that the velocity uncertainty is below 15 percent and the spatial resolution better than 1 cm. In static experiments, the applicability to particle laden foam and froth has been estimated. These parameters allow for monitoring of industrial processes as well as scientific investigation of three-dimensional foam and froth flow on medium scales.
Keywords: Ultrasound Doppler Velocimetry, Foam flow
  • Lecture (Conference)
    ISUD 11 - 11th International Symposium on Ultrasonic Doppler Methods for Fluid Mechanics and Fluid Engineering, 06.09.2018, Berlin, Germany

Publ.-Id: 28171 - Permalink

Neutron Imaging of Foam and Froth
Heitkam, S.; Lappan, T.; Rudolph, M.; Trtik, P.; Eckert, S.; Eckert, K.
The present contribution reports on the investigation of particle movement and drainage in unsteady foam and froth using Neutron Imaging (NI) (S. Heitkam et al. "Neutron imaging of froth structure and particle motion." Minerals Engineering, vol. 119, pp. 126-129, 2018.)

Froth flotation is one of the major separation processes in mining. Billions of tons per year of ore are treated by flotation worldwide. Despite the industrial relevance, measurement techniques for the observation of particle movement and liquid distribution inside the froth are limited.

In this situation, NI can reveal new insights on the mechanisms in froth flotation. NI is similar to radiography, but X-rays are replaced by neutrons. The neutrons pass through the measurement object, being partially attenuated. Then they hit a scintillator, generating photons that are observed by a high-speed camera. The advantage of NI in froth research is, that some materials (e.g. gadolinium) offer extremely high attenuation of neutrons. And also water attenuates neutrons about 30 times stronger than X-rays.
Keywords: Neutron Imaging, Foam, Froth
  • Lecture (Conference)
    EUFOAM, 10.07.2018, Liege, Belgium

Publ.-Id: 28170 - Permalink

Ultrasonic measurements of the velocity distribution inside foam
Heitkam, S.; Nauber, R.; Büttner, L.; Czarske, J.; Eckert, K.
The flowing behavior of liquid foam and froth is not yet well investigated. One reason for that is, that adequate measurement techniques are scarcely available. Also, industrial foam applications could be improved by monitoring the foam flow in the process.

In this work, the ultrasound Doppler velocimetry is used to measure the velocity distribution inside liquid foam. (Nauber et al. “Ultrasonic measurements of the bulk flow field in foams.”, Physical Review E, vol. 97 (1), pp 013113, 2018). To that end, an array of five ultrasound transducers is positioned inside a foam channel. One transducer sends pulses into the foam and the others receive the echoes. Sound pulses are reflected at moving particles and air-liquid interfaces. The echoes reveal the longitudinal velocity distribution along the beam axis. Multiplexing of the array allows for 2D-1C measurement.
Keywords: Ultrasound Doppler Velocimetry, Foam flow
  • Lecture (Conference)
    EUFOAM, 10.07.2018, Liege, Belgium

Publ.-Id: 28169 - Permalink

Improving the range accuracy in particle therapy: Wrap up of the workshop
Richter, C.
Summary of the workshop results
  • Lecture (Conference)

Publ.-Id: 28167 - Permalink

Improving range accuracy in particle therapy: Introduction of the workshop
Richter, C.
Introduction of the workshop
  • Lecture (Conference)

Publ.-Id: 28166 - Permalink

Hochpräzisions-Strahlentherapie: Mit Protonen gegen Krebs
Richter, C.
  • Invited lecture (Conferences)
    50. Kraftwerkstechnisches Kolloquium, 23.-24.10.2018, Dresden, Deutschland

Publ.-Id: 28165 - Permalink

Neutronen-Imaging von partikelbeladenen Schäumen
Heitkam, S.; Rudolph, M.; Lappan, T.; Sarma, M.; Eckert, S.; Trtik, P.; Lehmann, E.; Vontobel, P.; Eckert, K.
Die Flotation ist ein Trennverfahren mit großer industrieller Bedeutung, beispielsweise in der Gewinnung von Elementen aus Erzen. Dabei werden die Erze gemahlen und in Wasser suspendiert. Durch Zugabe geeigneter oberflächenaktiver Substanzen werden die gewünschten Partikel selektiv hydrophobisiert. Dadurch haften sie an eingebrachten Gasblasen an, werden an die Oberfläche transportiert und dort in sich bildenden Schaum eingelagert. Der Schaum wird abgezogen und man erhält gewünschte Partikel in hoher Konzentration.
Keywords: Neutron Imaging, Froth flotation
  • Lecture (Conference)
    Dechema Jahrestreffen, 06.03.2018, Bremen, Deutschland

Publ.-Id: 28158 - Permalink

Nematicity of correlated systems driven by anisotropic chemical phase separation
Yuan, Y.; Hübner, R.; Birowska, M.; Xu, C.; Wang, M.; Prucnal, S.; Jakiela, R.; Potzger, K.; Böttger, R.; Facsko, S.; Majewski, J. A.; Helm, M.; Sawicki, M.; Zhou, S.ORC; Dietl, T.
The origin of nematicity, i.e., in-plane rotational symmetry breaking, and in particular the relative role played by spontaneous unidirectional ordering of spin, orbital, or charge degrees of freedom, is a challenging issue of magnetism, unconventional superconductivity, and quantum Hall effect systems, discussed in the context of doped semiconductor systems such as Ga1−xMnxAs, CuxBi2Se3, and Ga(Al)As/AlxGa1−xAs quantum wells, respectively. Here, guided by our experimental and theoretical results for In1−xFexAs, we demonstrate that spinodal phase separation at the growth surface (that has a lower symmetry than the bulk) can lead to a quenched nematic order of alloy components, which then governs low-temperature magnetic and magnetotransport properties, in particular the magnetoresistance anisotropy whose theory for the C_2v symmetry group is advanced here. These findings, together with earlier data for Ga1−xMnxAs, show under which conditions anisotropic chemical phase separation accounts for the magnitude of transition temperature to a collective phase or merely breaks its rotational symmetry. We address the question to what extent the directional distribution of impurities or alloy components setting in during the growth may account for the observed nematicity in other classes of correlated systems.


Publ.-Id: 28154 - Permalink

Analytical properties of the gluon propagator from truncated Dyson-Schwinger equation in complex Euclidean space
Kaptari, L. P.; Kämpfer, B.; Zhang, P.
We suggest a framework based on the rainbow approximation with effective parameters adjusted to lattice data. The analytic structure of the gluon and ghost propagators of QCD in Landau gauge is analyzed by means of numerical solutions of the coupled system of truncated Dyson-Schwinger equations. We find that the gluon and ghost dressing functions are singular in complex Euclidean space with singularities as isolated pairwise conjugated poles. These poles hamper solving numerically the Bethe-Salpeter equation for glueballs as bound states of two interacting dressed gluons. Nevertheless, we argue that, by knowing the position of the poles and their residues, a reliable algorithm for numerical solving the Bethe-Salpeter equation can be established.


Publ.-Id: 28153 - Permalink

Towards Measuring Vacuum Birefringence
Schlenvoigt, H.-P.ORC
We will present a design study how one could detect vacuum birefringence when combining an ultra-intense optical laser and an X-ray free electron laser. By means of precision X-ray polarimetry, one may detect the polarization flip of X-ray photons induced by the ultra-strong laser fields as a signature of vacuum birefringence. We will discuss crucial experimental parameters and provide a comprehensive model to study the experimental feasibility.
Keywords: Hibef
  • Lecture (Conference)
    27th Annual International Laser Physics Workshop, 16.-20.07.2018, Nottingham, UK

Publ.-Id: 28151 - Permalink

Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields
Helm, M.
Operating three research infrastructures at one site: electrons & photons, ions, magnetic fields
Keywords: research infrastructure, large-scale facility
  • Invited lecture (Conferences)
    Conference on International Cooperation of Science Centers, 19.10.2018, Huairou, China

Publ.-Id: 28147 - Permalink

Strategien zur Darstellung eines neuen 18F-markierten Adenosin-A2A-Rezeptorliganden zur PET-Bildgebung von Hirntumoren [1]
Lai, T. H.; Schröder, S.; Ludwig, F.-A.; Fischer, S.; Moldovan, R.-P.; Scheunemann, M.; Dukic-Stefanovic, S.; Deuther-Conrad, W.; Brust, P.
Ziel: Auf Grundlage einer Pyrazolo[2,3-d]pyrimidin-Leitverbindung[2] wurden 21 fluorierte Derivate synthetisiert. Basierend auf den dazu ermittelten Affinitäts- und Selektivitätsdaten für den humanen Adenosin-A2A-Rezeptor wurde das potente 4-Fluorbenzyl-Derivat 1 (Ki(A2A) = 5,3 nM; Ki(A1) = 220 nM) für die 18F-Markierung zur Darstellung eines neuen potentiellen A2A Radiotracers ausgewählt. Die gewünschte Position in 1 ist jedoch nicht für eine nukleophile aromatische Substitution gegen [18F]Fluorid aktiviert, sodass die Zielstellung in der Entwicklung einer geeigneten Radiosynthese von [18F]1 besteht.

Methodik: Es wurden drei Strategien zur Radiosynthese von [18F]1 verfolgt. Ausgehend vom Trimethylammonium-Präkursor 2 erfolgte die 18F-Markierung zum [18F]Fluorbenzaldehyd [18F]3. Dieser wurde entweder direkt über eine reduktive Aminierung oder nach Reduktion und anschließender Bromierung über eine Benzylierung mit dem Pyrazolo[2,3-d]pyrimidin-Baustein 4 zu [18F]1 umgesetzt. Parallel dazu wurde die direkte 18F-Markierung des Boronsäurepinacol-Präkursors 5 bearbeitet.

Ergebnisse: Ausgehend von 2 wurde [18F]1 nach der zweistufigen Radiosynthese mit nur 1,5% radiochemischer Ausbeute in der Reaktionsmischung detektiert (Radio-HPLC). Diese konnte mittels der vierstufigen Methode auf 49% gesteigert werden. In beiden Verfahren wurde eine hohe Anzahl an 18F-Nebenprodukten nachgewiesen, welche die Isolierung von [18F]1 mittels semi-präparativer HPLC erschweren. Die direkte 18F-Markierung von 5 führte zu einer radiochemischen Ausbeute von 80-90% an [18F]1 in der Reaktionsmischung (Radio-DC/-HPLC), wobei lediglich ein 18F-Nebenprodukt (< 5%) detektiert wurde.

Schlussfolgerungen: Aufgrund dieser Ergebnisse wird ausschließlich die einstufige Strategie zur Darstellung des neuen potentiellen A2A-Radiotracers [18F]1 ausgehend von 5 weiterverfolgt. Für die geplante biologische Evaluierung (in vitro und in vivo) werden derzeit geeignete Methoden zur Isolierung, Konzentration und Formulierung von [18F]1 erarbeitet.

[1] Allard et al., Immunol. Cell. Biol. 2017, 95(4), 333-339
[2] Gillespie et al., Bioorg. Med. Chem. Lett. 2008, 18, 2924-2929
Keywords: Adenosin A2A Rezeptor, Radiotracer, 18F, PET, Hirntumor
  • Lecture (Conference)
    26. Jahrestagung der AGRR, 20.-22.09.2018, Aachen, Deutschland

Publ.-Id: 28145 - Permalink

1-Dimensional inorganic double helices as candidates for information storage materials
Springer, M.; Kuc, A.; Vankova, N.; Heine, T.ORC
Alkali metal monopnictides contain one-dimensional chains with a double-helical structure. In this work, we report about their possible use as information storage materials. We investigated computationally fundamental properties of hetero- and homocationic systems and ways towards the application. It was shown, that the phosphorous backbone is capable of stabilising cationic chains of different composition and thus allows encoding of information.
  • Poster
    Computational Spectroscopy: Bridging Theory and Experiment, 09.-14.09.2018, Como, Italien
  • Poster
    13th HZDR PhD seminar, Ustí, 05.-07.11.2018, Ustí nad labem, Tschechische Republik

Publ.-Id: 28143 - Permalink

Theoretical and simulation study of ‘Comb’ electron beam and THz generation
Joshi, V.; Lehnert, U.; Karmakar, J.; Kumar, N.; Karmakar, B.; Tripathi, S.; Aryshev, A.; Gosh, S.; Urakawa, J.; Bhandari, R. K.; Kanjilal, D.
A compact accelerator based super-radiant THz source is under development at Inter University Accelerator Centre (IUAC), New Delhi. The facility is based on the principle of pre-bunched Free Electron Laser (FEL) which will produce THz radiation in the range of 0.18 to 3 THz from a modulated electron beam. A photocathode electron gun will generate a short train of micro-bunches (a ‘‘comb’’ beam) driven by a fibre laser system capable of producing multi micro-pulse laser beam with variable separation (‘‘comb’’ laser pulse). Upon acceleration, the electron beam will be injected in to a compact undulator magnet tuned to the same frequency as the separation of the electron micro-bunches. The paper discusses the process of enhancement of super-radiant emission of radiation due to modulation in the comb beam and the conditions required to achieve maximum enhancement of the radiation power. The feasibility study of generating a comb beam at the photocathode and its transport through the beamline while preserving its temporal structure has been reported. To evaluate the characteristics of the radiation emitted from the comb beam, a 𝐶++ based particle tracker and Lienard–Wiechert field solver has been developed. The conceptual understanding of the emission of radiation from comb beam is shown to conform with the numerical results. The code has been used to calculate the radiation pulse energy emitted into the central cone of undulator for various comb beam configurations.
Keywords: linear accelerator; THz; THz source; radiation source; comb beam; pre-bunched beam; radiation emission; undulator radiation; super-radiant emission;


Publ.-Id: 28142 - Permalink

Dissecting spin-phonon equilibration in ferrimagnetic insulators by ultrafast lattice excitation
Maehrlein, S. F.; Radu, I.; Maldonado, P.; Paarmann, A.; Gensch, M.; Kalashnikova, A. M.; Pisarev, R. V.; Wolf, M.; Oppeneer, P. M.; Barker, J.; Kampfrath, T.
To gain control over magnetic order on ultrafast time scales, a fundamental understanding of the way electron spins interact with the surrounding crystal lattice is required. However, measurement and analysis even of basic collective processes such as spin-phonon equilibration have remained challenging. We directly probe the flow of energy and angularmomentum in the model insulating ferrimagnet yttriumiron garnet. After ultrafast resonant lattice excitation, we observe thatmagnetic order reduces on distinct time scales of 1 ps and 100 ns. Temperature-dependentmeasurements, a spin-coupling analysis, and simulations show that the two dynamics directly reflect two stages of spinlattice equilibration. On the 1-ps scale, spins and phonons reach quasi-equilibrium in terms of energy through phonon-induced modulation of the exchange interaction. This mechanism leads to identical demagnetization of the ferrimagnet’s two spin sublattices and a novel ferrimagnetic state of increased temperature yet unchanged total magnetization. Finally, on the much slower, 100-ns scale, the excess of spin angular momentum is released to the crystal lattice, resulting in full equilibrium. Our findings are relevant for all insulating ferrimagnets and indicate that spin manipulation by phonons, including the spin Seebeck effect, can be extended to antiferromagnets and into the terahertz frequency range.
Keywords: THz control, ultra-fast, magnetism

Publ.-Id: 28141 - Permalink

Visualisation of the large scale circulation in Rayleigh-Bénard convection using contactless inductive flow tomography
Wondrak, T.; Stefani, F.; Galindo, V.; Eckert, S.
Rayleigh-Bénard (RB) convection plays an important role in geo- and astrophysics as well as in many metallurgical applications. At sufficiently high values of the Rayleigh number, a large scale circulation (LSC) is formed whose dynamics had turned out to be surprisingly rich. In this paper, the applicability of the contactless inductive flow tomography (CIFT) for the detection of the torsional mode of the LSC is investigated. CIFT enables the three-dimensional reconstruction of flow structures in liquid metals by applying one or more magnetic fields and measuring the flow induced perturbations of those fields outside the melt. Additionally, preliminary measurements of the flow induced magnetic field with a similar sensor arrangement will be presented.
Keywords: flow measurement techniques, Rayleigh-Bénard convection
  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012007
    DOI: 10.1088/1757-899X/424/1/012007

Publ.-Id: 28138 - Permalink

Real-time control of the mould flow in a model of continuous casting in frame of the TOMOCON project
Wondrak, T.; Hampel, U.; Ratajczak, M.; Glavinić, I.; Stefani, F.; Eckert, S.; van der Plas, D.; Pennerstorfer, P.; Muttakin, I.; Soleimani, M.; Abouelazayem, S.; Hlava, J.; Blishchik, A.; Kenjeres, S.
In continuous casting, the flow structure of the liquid steel in the mould and the two-phase distribution in the submerged entry nozzle (SEN) are crucial for the quality of the produced steel. In order to effectively control the flow in the mould by electromagnetic brakes (EMBrs) and the injection of gas into the SEN, even a rough knowledge of the flow structure would be very helpful. In the framework of the TOMOCON project, the contactless inductive flow tomography (CIFT) and the mutual inductance tomography (MIT) will be integrated into a control loop for slab casters. This control loop will be developed and implemented at the Mini-LIMMCAST facility, which is available at the Helmholtz-Zentrum Dresden – Rossendorf. In this paper a short overview of this project will be given.
Keywords: continuous casting, electromagnetic brake, inductive measurement techniques, flow control
  • Lecture (Conference)
    9th international symposium on electromagnetic processing of materials (EPM2018), 14.-18.10.2018, Awaji Yumebutai International Conference Center, Japan
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 424(2018), 012003
    DOI: 10.1088/1757-899X/424/1/012003

Publ.-Id: 28137 - Permalink

All-optical structuring of laser-driven proton beam profiles data sets
Obst-Huebl, L.ORC; Ziegler, T.; Brack, F.-E.; Branco, J.; Bussmann, M.; Cowan, T. E.; Curry, C. B.; Fiuza, F.; Garten, M.; Gauthier, M.; Göde, S.; Glenzer, S. H.; Huebl, A.; Irman, A.; Kim, J. B.; Kluge, T.; Kraft, S.; Kroll, F.; Metzkes-Ng, J.; Pausch, R.; Prencipe, I.; Rehwald, M.; Rödel, C.; Schlenvoigt, H.-P.; Schramm, U.; Zeil, K.

This data repository contains analyzed data files of the shown figures and simulation input files.

Please see the according README.txt files in the individual directories and the original manuscript for guidance.

Manuscript title:
  All-optical structuring of laser-driven proton beam profiles

  Lieselotte Obst, Tim Ziegler, Florian-Emanuel Brack, Joao Branco, Michael Bussmann, Thomas E. Cowan, Chandra B. Curry, Frederico Fiuza, Marco Garten, Maxence Gauthier, Sebastian Göde, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Siegfried H. Glenzer, Axel Huebl, Arie Irman, Jongjin B. Kim, Thomas Kluge, Stephan Kraft, Florian Kroll, Josefine Metzkes-Ng, Richard Pausch, Irene Prencipe, Martin Rehwald, Christian Rödel, Hans-Peter Schlenvoigt, Ulrich Schramm, Karl Zeil

Submitted to:
  Nature Communications (2018)

Responsible for the data repository:
  Lieselotte Obst-Huebl, TU Dresden and HZDR
  Axel Huebl, TU Dresden and HZDR
  Tim Ziegler, TU Dresden and HZDR
  Thomas Kluge, HZDR


Related publications
All-optical structuring of laser-driven proton beam profiles (Id 28155) has used this publication of HZDR-primary research data
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-10-30
    DOI: 10.14278/rodare.65
    License: CC-BY-4.0


Publ.-Id: 28136 - Permalink

Contactless inductive flow tomography for models of continuous casting and crystal growth
Ratajczak, M.; Wondrak, T.ORC; Glavinić, I.; Stefani, F.
Contactless inductive flow tomography (CIFT) enables the reconstruction of the major flow structure in electrically conducting liquids, like molten steel or silicon. It is based on the permeation of the melt by an external primary magnetic field and the subsequent induction of currents, which generate a flow-induced secondary magnetic field. The measured secondary field allows for reconstruction of the flow by solving the underlying linear inverse problem. We present results for the application of CIFT for two lab-scale model experiments of (a) continuous steel casting in the presence of an electromagnetic brake and (b) Czochalski crystal growth with a thermally driven convection. In the first scenario (a), the electromagnetic brake poses the biggest challenge, since its strong static magnetic field of about 300 mT superimposes the flow-induced field of about 100 nT, and the brake’s ferromagnetic parts distort the CIFT excitation field. We show how this can be overcome by simulations and adequate instrumentation using gradiometric induction coil sensors, which enables correct flow reconstructions in this scenario. In the second setup (b) the biggest challenges arise from the long measurement times of up to 12 hours together with thermal expansion and contraction of the setup mounting due to the intrinsic temperature gradient of the melt. Here an optimized experimental construction is necessary to enable successful measurements magnetic field measurements with Fluxgate sensors. The experimental data reveal plausible stationary and transient phenomena in accordance with numerical
flow simulations.
Keywords: metallurgy, contactless inductive flow tomography, magnetic field measurement, flow measurement
  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 839-845
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Publ.-Id: 28135 - Permalink

Numerical aspects of contactless inductive flow tomography for crystal growth
Wondrak, T.ORC; Jacobs, R. T.; Galindo, V.; Stefani, F.
The flow structure of liquid silicon in the crucible for Czochralski (Cz) crystal growth is important for the quality of the silicon crystal. However, the high temperature and the required cleanliness of the melt represent a challenge for any flow measurement device. A promising technique to reconstruct the flow of a conducting liquid is contactless inductive flow tomography (CIFT). The procedure relies on the measurement of the flow induced perturbation of a primary magnetic field and the inversion of the corresponding integral equation system. In this paper, the numerical challenges for the application of CIFT to Cz crystal growth will be investigated. This includes the treatment of the singularities of the integral equation system as well as the selection of appropriate integration techniques. The paper concludes with numerical investigation of the expected flow induced magnetic field for a reversal of the rotation in simple model of a typical crucible.
Keywords: contactless inductive flow tomography, Czochralski crystal growth, flow measurement, liquid metal
  • Contribution to proceedings
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK
    Proceedings of the 9th world congress on industrial process tomography, 978 0 85316 3497, 451-456
  • Lecture (Conference)
    9th world congress on industrial process tomography, 02.-6.9.2018, Bath, UK

Publ.-Id: 28134 - Permalink

Surface nanobubbles on the carbonate mineral dolomite
Owens, C. L.ORC; Schach, E.; Rudolph, M.ORC; Nash, G. R.
Surface nanobubbles are of wide interest to a number of research fields, ranging from mineral processing to metamaterials. Their formation on hydrophobic surfaces has long been confirmed but the factors controlling their size and location are less well understood. In this work we investigate, using non-contact atomic force microscopy, the properties of surface nanobubbles on the mineral dolomite under three aqueous solutions; water, depressant and collector. Nanobubbles were observed under all three conditions, but with the highest density observed under collector conditions. Analysis of the critical angle of the bubbles suggests that the collector does not affect the surface tension of the bubbles, but instead does affect their pinning, consistent with the observed increased density.
Keywords: nanobubbles, flotation, atomic force microscopy

Publ.-Id: 28133 - Permalink

Magnon Transport in Spin Textures
Schultheiss, H.
One of the grand challenges in cutting edge quantum and condensed matter physics is to harness the spin degree of electrons for information technologies. While spintronics, based on charge transport by spin polarized electrons, made its leap in data storage by providing extremely sensitive detectors in magnetic hard-drives, it turned out to be challenging to transport spin information without great losses. With magnonics a visionary concept inspired researchers worldwide: Utilize magnons - the collective excitation quanta of the spin system in magnetically ordered materials - as carriers for information. Magnons are waves of the electrons’ spin precessional motion. They propagate without charge transport and its associated Ohmic losses, paving the way for a substantial reduction of energy consumption in computers.
While macroscopic prototypes of magnonic logic gates have been demonstrated, the full potential of magnonics lies in the combination of magnons with nano-sized spin textures. Both magnons and spin textures share a common ground set by the interplay of dipolar, spin-orbit and exchange energies rendering them perfect interaction partners. Magnons are fast, sensitive to the spins’ directions and easily driven far from equilibrium. Spin textures are robust, non-volatile and still reprogrammable on ultrashort timescales. The vast possibilities offered by combining this toolset of magnetic phenomena, add value to both magnonics and the fundamental understanding of complex spin textures.
I will give an introduction about magnon propagation and manipulation in microstructures with non-collinear spin textures, in particular magnons propagating in nano channels formed by magnetic domain walls. Furthermore, I will address how magnons can be excited in domain wall channels by pure spin currents originating from the spin Hall effect.
[1] K. Wagner, A. Kákay, K. Schultheiss, A. Henschke, T. Sebastian, and H. Schultheiss, Nature Nanotech 11, 432 (2016).
[2] K. Vogt, F. Y. Fradin, J. E. Pearson, T. Sebastian, S. D. Bader, B. Hillebrands, A. Hoffmann, and H. Schultheiss, Nat Comms 5, 3727 (2014).
Keywords: magnonics, spin waves, spin textures, domain walls, auto-oscillations
  • Invited lecture (Conferences)
    Lüscher Seminar, 08.02.2018, Klosters, Schweiz
  • Invited lecture (Conferences)
    Spin Mechanics 5 and Nano MRI 6 workshop, 16.02.2018, Chamonix, Schweiz
  • Invited lecture (Conferences)
    Nano-Magnonics Workshop, 20.02.2018, Kaiserslautern, Deutschland
  • Invited lecture (Conferences)
    International Conference on Microwave Magnetics, 25.06.2018, Exeter, England
  • Invited lecture (Conferences)
    Workshop on Advances in Brillouin Light Scattering, 13.09.2018, Perugia, Italien
  • Invited lecture (Conferences)
    International Advanced School on Magnonics, 20.09.2018, Kyiv, Ukraine

Publ.-Id: 28132 - Permalink

Ultrasmall Nanomaterials for Multimodal Cancer Imaging
Stephan, H.
Ultrasmall nanomaterials (NMs) offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. Provided with special functionalities, NMs allow the simultaneous application of different molecular imaging methods. In the field of cancer medicine, the combination of different imaging techniques such as nuclear (PET: positron emission tomography and SPECT: single-photon emission computed tomography) and near-infrared fluorescence (NIRF) imaging for tracking down tumors and metastases is particularly attractive.
This lecture will focus on the development and application of very small radiolabeled NMs, embracing inorganic particles and soft polymeric structures. Novel strategies will be discussed to develop stealth NMs capable of avoiding biomolecular corona formation and thus evading scavenging of NMs by the mononuclear phagocyte system, leading to eventual accumulation in the liver and spleen.
  • Invited lecture (Conferences)
    Kolloquium, 25.10.2018, Hamburg, Deutschland

Publ.-Id: 28130 - Permalink

Magnon auto-oscillation under zero magnetic field
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.
Magnons are attractive for application in energy efficient information technology, because they propagate without any actual charge currents and they offer high frequencies up to THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a heavy metallic/ferromagnetic bilayer, the spin currents originating from a spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local magnon nano channels [2]. Since domain walls can be moved by electrical currents [3], they are attractive for reprogrammable nano circuits.
A 370 nm wide zigzag structure was fabricated from a Pt/CoFeB bilayer. A domain wall was generated at the apex by magnetic saturation. The magnon intensity on the remanent state was measured by Brillouin light scattering microscopy [4] with applying a dc current. The magnon excitation showed the dc current dependency. Magnons were detected only for positive dc currents. We succeeded to drive magnon auto-oscillation in the domain wall under zero magnetic field by spin transfer torque.

[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).
  • Lecture (Conference)
    9th Joint European Magnetic Conference, 03.-07.09.2018, Mainz, Germany

Publ.-Id: 28122 - Permalink

Magnon auto-oscillation in domain walls
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Awad, A. A.; Hellwig, O.; Fassbender, J.; Schultheiss, H.
Magnons are the fundamental excitations in magnetic materials, and they can transport angular momentum without actual charge currents. Therefore, they are attractive for applications in energy efficient information technology, offering high operating frequencies up to the THz range. Here we present a novel scheme for magnon generation using spin currents and domain walls.
When a charge current is applied to a bilayer consisting of a heavy metal and a ferromagnetic metal, the spin currents originating from the spin Hall effect in the heavy metal apply a spin transfer torque on the magnetization of the ferromagnetic layer. This allows driving efficiently auto-oscillations of magnetization [1]. We focused on domain walls as local nano magnon channels [2]. Since it is possible to move domain walls by electrical currents [3], domain walls are attractive for nano-sized reprogrammable circuits.
A 370 nm wide boomerang structure was fabricated from a Pt/CoFeB bilayer (Fig.1). The sample was magnetized by applying an external magnetic field H. After the saturation, the external magnetic field was set to 0 Oe, and a dc current was applied to the sample. The magnon intensity at the apex of the boomerang structure was measured by Brillouin light scattering microscopy [4]. Figure 2 shows the dc current dependency of the magnon spectrum on the remanent state. Magnons were detected for currents between 3.6 mA and 4.5 mA, while no magnons were observed for any negative dc currents. A domain wall is generated at the apex for the remanent state because of the shape anisotropy of the boomerang structure. We succeeded to excite magnons under zero magnetic field due to the autooscillation of the magnetization by spin transfer torque.

[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et. al., Nat. Nanotech. 11, 432 (2016).
[3] S. S. P. Parkin et. al., Science 320, 190 (2008).
[4] T. Sebastian et. al., Front. Phys. 3, 35 (2015).
  • Lecture (Conference)
    International Conference on Magnetism, 15.-20.07.2018, San Francisco, USA

Publ.-Id: 28121 - Permalink

Magnon auto-oscillation in domain walls by spin transfer torque
Nishida, N.; Hache, T.; Arekapudi, S. S. P. K.; Hellwig, O.; Fassbender, J.; Schultheiss, H.

図1に示すように、PtとCoFeBの二層膜から成る線幅370 nmの折れ線構造を作製し、y方向に着磁した。試料に直流電流を印加し、ブリルアン散乱分光装置を用いて折れ線の頂点におけるマグノン強度を測定した。図2にマグノン強度の電流依存性を示す。図2(a)に示すように、y方向に1.0 kOeの外部磁場を印加した場合には、2.3 mAから5.0 mAの電流値の範囲においてマグノンの励起が検出された。一方、電流の印加方向を反転させるとマグノンは検出されなかった。図2(b)に、y方向に試料を着磁した後に外部磁場を0 kOeにし、残留磁化状態において測定した結果を示す。1.0 kOeの外部磁場を印加した場合と同様に、正の電流を印加した場合のみマグノンの励起が検出された。残留磁化状態では形状磁気異方性により、試料頂点に磁壁が生成される。スピントランスファートルクを用いた磁壁中の磁化の自励発振により、ゼロ磁場下においてマグノンの励起に成功した。

[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).

Magnons are the fundamental excitations in magnetic materials and are attractive for applications in information technology devices. They do not involve charge transport and the associated waste heat and offer high operating frequencies up to the THz range. When a charge current is applied to a bilayer consisting of Pt and a ferromagnetic metal, the spin currents originating from the spin Halle effect in the Pt layer generate a spin transfer torque to the magnetizations in the ferromagnetic layer. This allows to efficiently drive auto-oscillations of magnons[1]. We focused on domain walls as local nano magnon channels[2], and investigated the magnon auto-oscillation in the domain walls.

As shown in Fig. 1, a zigzag structure was fabricated from a Pt/CoFeB bilayer. The width was set to be 370 nm. The sample was magnetized to the y direction and a dc current was applied to the sample. The magnon intensity at the corner was measured by Brillouin Light Scattering microscopy. Figure 2 shows the dc current dependency of the magnon intensity measured at the corner. As shown in Fig. 2(a), in the case that an external magnetic field of 1.0 kOe was applied to the y direction, the magnons were detected when the dc current was between 2.3 mA and 5.0 mA. While there were no magnons in the case of the reversed dc current direction. Figure 2(b) shows the magnon intensity at the remanence state after saturation to y direction. There were also no magnon in the case of the reversed dc current. The domain wall is generated at the corner under the remanence state because of a shape anisotropy. We succeeded to excite magnons under zero magnetic field due to the auto-oscillation of the magnetizations by spin transfer torque.

[1] A. N. Slavin and V. Tiberkevich, IEEE Trans. Magn. 45, 1875 (2009).
[2] K. Wagner et al., Nat. Nanotech. 11, 432 (2016).
  • Poster
    The Physical Society of Japan, 73rd Annual Meeting, 22.-25.03.2018, Noda, Chiba, Japan

Publ.-Id: 28120 - Permalink

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