Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34121 Publications

Droplet-confined alternate pulsed epitaxy of GaAs nanowires on Si substrates: meeting the typical MBE standards

Tauchnitz, T.; Balaghi, L.; Bischoff, L.; Hübner, R.; Schneider, H.; Helm, M.; Dimakis, E.

We introduce a growth scheme with alternate Ga and As4 pulses for the self-catalyzed growth of free-standing GaAs nanowires on Si(111) substrates. Unlike the conventional growth mode, our scheme offers a wide growth temperature window (450 – 600 °C), low growth rates (down to 1-2 monolayers per As4 pulse), and the ability for defect-free and abrupt growth interruptions, meeting the typical MBE standards. We demonstrate the possibility to grow defect-free zinc blende nanowires in the whole temperature window and to probe the growth dynamics in specially designed experiments.

Keywords: nanowire; self-catalyzed; alternate pulsed epitaxy; GaAs; Si substrate

  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy (MBE 2016), 04.09.2016, Montpellier, France

Permalink: https://www.hzdr.de/publications/Publ-24130
Publ.-Id: 24130


Exciton recombination at crystal-phase quantum rings in GaAs/InxGa1−xAs core/multishell nanowires

Corfdir, P.; Lewis, R. B.; Marquardt, O.; Küpers, H.; Grandal, J.; Dimakis, E.; Trampert, A.; Geelhaar, L.; Brandt, O.; Phillips, R. T.

We study the optical properties of coaxial GaAs/InxGa1-xAs core/multishell nanowires with x between 0.2 and 0.4 at 10K. The evolution of the photoluminescence energy of the InxGa1-xAs quantum well shell with x and shell thickness agrees with the result of 8-band k.p calculations, demonstrating that the shell growth is pseudomorphic. At low excitation power, the photoluminescence from the shell is dominated by the recombination of exciton states deeply localized within the shell. We show that these states are associated with crystal-phase quantum rings that form at polytype segments of the InxGa1-xAs quantum well shell.

Permalink: https://www.hzdr.de/publications/Publ-24129
Publ.-Id: 24129


Functional behavior of the anomalous magnetic relaxation observed in melt-textured YBa2Cu3O7- δ samples showing the paramagnetic Meissner effect

Dias, F. T.; Vieira, V. N.; Garcia, E. L.; Wolff-Fabris, F.; Kampert, E.; Gouvea, C. P.; Schaf, J.; Obrados, X.; Puig, T.; Roa, J. J.

We have studied the functional behavior of the field-cooled (FC) magnetic relaxation observed in melt- textured YBa2Cu3O7- δ(Y123) samples with 30 wt% of Y2Ba1Cu1O5 (Y211) phase, in order to investigate anomalous paramagnetic moments observed during the experiments. FC magnetic relaxation experiments were performed under controlled conditions, such as cooling rate and temperature. Magnetic fields up to 5T were applied parallel to the ab plane and along the c-axis. Our results are associated with the para-magnetic Meissner effect (PME), characterized by positive moments during FC experiments, and related to the magnetic flux compression into the samples. After different attempts our experimental data could be adequately fitted by an exponential decay function with different relaxation times. We discuss our results suggesting the existence of different and preferential flux dynamics governing the anomalous FC paramagnetic relaxation in different time intervals. This work is one of the first attempts to interpret this controversial effect in a simple analysis of the pinning mechanisms and flux dynamics acting during the time evolution of the magnetic moment. However, the results may be useful to develop models to explain this interesting and still misunderstood feature of the paramagnetic Meissner effect.

Permalink: https://www.hzdr.de/publications/Publ-24128
Publ.-Id: 24128


Magneto-acoustic study near the quantum critical point of the frustrated quantum antiferromagnet Cs2CuCl4

Cong, P. T.; Postulka, L.; Wolf, B.; van Well, N.; Ritter, F.; Assmus, W.; Krellner, C.; Lang, M.

Magneto-acoustic investigations of the frustrated triangular-lattice antiferromagnet Cs2CuCl4 were performed for the longitudinal modes c11 and c33 in magnetic fields along the a axis. The temperature dependence of the sound velocity at zero field shows a mild softening at low temperature and displays a small kink-like anomaly at TN. Isothermal measurements at T < TN of the sound attenuation a reveal two closely spaced features of different characters on approaching the material’s quantum-critical point (QCP) at Bs = 8.5 T for B II a. The peak at slightly lower fields remains sharp down to the lowest temperature and can be attributed to the ordering temperature TN(B). The second anomaly, which is rounded and which becomes reduced in size upon cooling, is assigned to the material’s spin-liquid properties preceding the long-range antiferromagnetic ordering with decreasing temperature. These two features merge upon cooling suggesting a coincidence at the QCP. The elastic constant at lowest temperatures of our experiment at 32 mK can be well described by a Landau free energy model with a very small magnetoelastic coupling constant G/kB = 2.8 K. The applicability of this classical model indicates the existence of a small gap in the magnetic excitation spectrum which drives the system away from quantum criticality.

Permalink: https://www.hzdr.de/publications/Publ-24127
Publ.-Id: 24127


A monomeric copper-phosphoramide complex: Synthesis, structure, and electronic properties

Henriques, M. S.; Gorbunov, D. I.; Ponomaryov, A. N.; Saneei, A.; Pourayoubi, M.; Dusek, M.; Zvyagin, S.; Uhlarz, M.; Wosnitza, J.

We report on a novel phosphoramide complex with formula Cu(NO3)2([C5H10N]3PO)2. This complex is the first example of a copper monomeric phosphoric triamide having an octahedral Cu[O]6 coordination environment. Cu(NO3)2([C5H10N]3PO)2 crystallizes in the monoclinic space group P21/n with the Cu atom located at an inversion center, as determined by single-crystal X-ray diffraction. Magnetic measurements along the principal crystallographic directions of the single crystal indicate that the complex is a paramagnet with very low magnetic anisotropy. Electron paramagnetic resonance spectra reveal the presence of two Cu2+ sites and make it possible to extract the hyperfine coupling.

Permalink: https://www.hzdr.de/publications/Publ-24126
Publ.-Id: 24126


Evaluation of E-Waste Processing through Secondary Copper Smelting

Rhamdhani, M. A.; Ghodrat, M.; Brooks, G.; Masood, S.; Corder, G.; Haque, N.; Reuter, M. A.

Wastes of electronics and electrical equipment (WEEE) or simply e-wastes contain many valuable elements that include base metals (Cu, Fe, Pb, Al), precious metals (Au, Ag, Pt, Pd), other metals (Sn, Se, Te, Ta, Co, In, Ru, etc); as well as hazardous elements. Sustainable extraction of the valuable elements from e-waste is challenging due to the complexities of the materials and associated processing routes. There have been a number of processing and extraction techniques developed at laboratory level and few are implemented in industrial practices [1]. The processes implemented at industrial scale are mainly based on an improved combination of traditional extractive metallurgy processes (for example a combined pyrometallurgy, hydrometallurgy and electrometallurgy processes). Although practiced at industry scale, these processes and processing routes are far from optimised. Development of new technologies and/or improvement of the existing practices are still needed. Some of the barriers for improvement include: lack of fundamental knowledge (behaviour of all of these elements, which are governed by their solution thermodynamics); limited sound technoeconomic analyses; as well as limited understanding on the environmental impact of the different processing routes.

Keywords: E-Waste; E-Waste processing; WEEE recycling; precious metals; secondary copper

  • Lecture (Conference)
    8th Annual High Temperature Processing Symposium 2016, 01.-02.02.2016, Melbourne, Australien

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Permalink: https://www.hzdr.de/publications/Publ-24125
Publ.-Id: 24125


Recycling Indices Visualizing the Performance of the Circular Economy

Reuter, M. A.; van Schaik, A.

The EU has adopted an ambitious Circular Economy (CE) package. This action plan aims to "close" the loop of product lifecycles through improved product design, improved collection, recycling, remanufacture and re-use. Through this the EU envisages to bring benefits both environmentally as well as economically. Recycling forms the heart of the CE system; metal and material recycling and metallurgical processing are key enablers. Maximizing the recovery of materials from End-of-Life (EoL) products, while simultaneously lowering the environmental footprint, is a vital outcome. Therefore, designing greener products while also optimizing organisational and technology infrastructures of industrial recycling processing flow sheets are vital. This enables the maximal recovery of materials and also especially strategic elements from EoL products, requiring a deep understanding of the fundamental opportunities and limits and the dynamics of the evolving and agile system. In order to inform the consumer, this paper presents the developed Recycling Index (RI) (analogous to the EU Energy Labels) that includes a new Material-RI.These are based on simulation models that have their roots in minerals and metallurgical processing. It builds on previous work by the authors that visualises and communicate the recycling performance of a product as well as of the individual materials in a clear, easy and transparent manner. It will help to empower the consumer to make informed purchasing decisions. Furthermore, RIs are essential for communicating greener design and efforts to improve resource efficiency by producers and state-of-the art recycling and (metallurgical) processing technology by industry. The RI is an excellent tool to provide insight into possibilities and improvements as well as barriers and limits for CE to policy makers and to close the missing links in the CE.

Keywords: Recycling; Design for Recycling; Recycling Index; Simulation; Calculation methods for recycling rates; Circular Economy

  • World of Metallurgy - Erzmetall 69(2016)4, 201-216

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Permalink: https://www.hzdr.de/publications/Publ-24124
Publ.-Id: 24124


Strategic metal recycling: adaptive metallurgical processing infrastructure and technology are essential for a Circular Economy

Reuter, M. A.; van Schaik, A.

Recycling forms the heart of the Circular Economy (CE) system. Ultimately all products will have to be recycled at their End-of-Life (EoL). Maximizing the recovery of materials and also especially strategic elements from EoL products requires a deep understanding of the fundamental limits and the dynamics of the evolving system, thus an adaptive processing and metallurgical infrastructure is critical to recover all metals and materials. Paramount is the quantification of the “mineralogy”, the complex and interlinked composition of products, to trace and quantify specifically all the losses of materials, metals, alloys, etc. due to thermodynamic and other non-linear interactions. We named this product centric recycling. The recycling potential and performance must be quantified and demonstrated for products, collection systems, waste separation and recovery technologies, and material supply. Emphasis is also placed on informing the consumer through iRE i.e. informing Resource Efficiency in an easy-to-understand way. System Integrated Metal Processing (SIMP) using big-data, multi-sensors, simulation models, metallurgy, etc. links all stakeholders through Circular Economy Engineering (CEE), an important enabler to maximize Resource Efficiency and thus iRE.

Keywords: EoL; CE; CEE

  • Annales des Mines - Responsiabilité & Environnement (2016)82, 62-66

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Permalink: https://www.hzdr.de/publications/Publ-24123
Publ.-Id: 24123


Gold - A Key Enabler of a Circular Economy: Recycling of Waste Electric and Electronic Equipment

Reuter, M. A.; van Schaik, A.

Metals are an essential and critical component of today's society: a moment's reflection on their ubiquitous presence in virtually all energy and material production processes is sufficient to confirm this. Metals play a key role in enabling sustainability through various high-tech applications in society. However, the resources of our planet are limited, as is the strain to which we can subject it in terms of emissions, pollution, and disposal of waste. For these reasons, finding ways to lower the environmental footprint of our collective existence and therefore lowering greenhouse gas and other emissions is a vital priority. The principal theme of this contribution is the maximization of resource efficiency as well as enabling a circular economy (CE) through the recycling of waste electric and electronic equipment, with a focus on precious metals (PMs) (incorporating gold, silver, and the platinum group metals [PGMs]) and the base-metal industry that enables their recycling. The detailed and deep knowledge that is required to systemically fully understand resource efficiency in the context of a CE are discussed and the concepts of design for resource efficiency and design for recycling elaborated on. Specifically, the understanding of product-centric recycling is highlighted, setting it apart from the usual material-centric recycling approaches. The latter focus more on bulk materials and therefore inherently limit the maximal recovery of technologically critical elements in particular, as well as PMs and PGMs. The base metals – principally, copper, cobalt, lead, nickel, tin, and zinc – all play a crucial part in the present society. Increasingly, these are linked in concert to form the crucial carrier metals for the sustainable CE society termed the “web of metals” and “web of products” or, in a more modern paradigm, system integrated metal production–in other words, the process metallurgical Internet of things. This chapter also examines the special and crucial role base metals have in acting as enablers in any recycling efforts, as they also play a key role during recycling, such as copper and lead being the solvent of gold and other PMs and PGMs and release them during refining. Above all, the PMs are key economic enablers for the economic viability of recycling as well as the metallurgical infrastructure (system integrated metal production/Internet of things) that makes it possible to recover PMs and PGMs and their other associated elements.

Keywords: Critical metals; Design for recycling; Furnace technology; Gold; Hydrometallurgy; Internet-of-things; Precious metals; Process metallurgy; Pyrometallurgy; Recycling; System integrated Metal production; WEEE

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Permalink: https://www.hzdr.de/publications/Publ-24122
Publ.-Id: 24122


Digitalizing the Circular Economy: Circular Economy Engineering Defined by the Metallurgical Internet of Things

Reuter, M. A.

Metallurgy is a key enabler of a circular economy (CE), its digitalization the metallurgical Internet of Things (m-IoT). In short: Metallurgy is at the heart of a CE, as metals all have strong intrinsic recycling potentials. Process metallurgy, as a key enabler for a CE, will help much to deliver its goals. The first-principles models of process engineering help quantify the resource efficiency (RE) of the CE system, connecting all stakeholders via digitalization. This provides well-argued and first-principles environmental information to empower a tax paying consumer society, policy, legislators, and environmentalists. It provides the details of capital expenditure and operational expenditure estimates. Through this path, the opportunities and limits of a CE, recycling, and its technology can be estimated. The true boundaries of sustainability can be determined in addition to the techno-economic evaluation of RE. The integration of me tallurgical reactor technology and systems digitally, not only on one site but linking different sites globally via hardware, is the basis for describing CE systems as dynamic feedback control loops, i.e., the m-IoT.

Keywords: digitalization the metallurgical Internet of Things (m-IoT)

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Permalink: https://www.hzdr.de/publications/Publ-24121
Publ.-Id: 24121


Fast neutron-induced fission at the time-of-flight facility nELBE

Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S.

The fast neutron-induced fission cross section of Pu(242) was determined the range of 0.5 MeV and in 10 MeV relative to U(235)(n,f) at the neutron time-of-flight facility nELBE. Using the high spontaneous fission rate of Pu(242) to determine the number of target atoms makes the cross section independent from the detection. Sophisticated neutron transport simulations with Geant 4 and MCNP 6 are used to correct the neutron scattering. The determined relative cross section is in good agreement with current experimental and evaluated data sets.

Keywords: neutron-induced fission cross section; neutron scattering corrections; fast neutrons; nELBE

  • Lecture (Conference)
    ND2016 - International Conference on NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, 11.-16.09.2016, Bruges, Belgien
  • Open Access Logo Contribution to proceedings
    ND 2016 - International Conference on NUCLEAR DATA FOR SCIENCE AND TECHNOLOGY, 11.-16.09.2016, Bruges, Belgien
    EPJ Web of Conferences, Les Ulis Cedex A
    DOI: 10.1051/epjconf/201714611023

Permalink: https://www.hzdr.de/publications/Publ-24120
Publ.-Id: 24120


Temperature Quenching in LAB based liquid scintillator

Sörensen, A.; Junghans, A. R.; Kögler, T.; Wagner, A.; Zuber, K.

This work investigated the effect of temperature changes on the light output of LAB based liquid scintillator in a range from -5°C to 30°C with a-particles and electrons in a small scale setup. Assuming a linear behaviour, a combined negative temperature coefficient of (-0.29+-0.01) % / °C is found. Considering hints for a particle type dependency, electrons show (-0.17+-0.02) % / °C, whereas the temperature dependency seems stronger for a-particles, with (-0.35+-0.03) % / °C. A pulse shape analysis shows increased strength of a slow decay component at lower temperatures, pointing to reduced non-radiative triplet state de-excitations at lower temperatures.

Keywords: lineare Alcyl benzene; temperature quenching

Permalink: https://www.hzdr.de/publications/Publ-24119
Publ.-Id: 24119


Plutonium interaction studies with the Mont Terri Opalinus Clay isolate Sporomusa sp. MT-2.99: changes in the plutonium speciation by solvent extractions.

Moll, H.; Cherkouk, A.; Bok, F.; Bernhard, G.

Since plutonium could be released from nuclear waste disposal sites, the exploration of the complex interaction processes between plutonium and bacteria is necessary for an improved understanding of the fate of plutonium in the vicinity of such a nuclear waste disposal site. In this basic study the interaction of plutonium with cells of the bacterium, Sporomusa sp. MT-2.99, isolated from Mont Terri Opalinus Clay, was investigated anaerobically (in 0.1 M NaClO4) with or without adding Na-pyruvate as an electron donor. The cells displayed a strong pH dependent affinity for Pu. In the absence of Na-pyruvate a strong enrichment of stable Pu(V) in the supernatants was discovered, whereas Pu(IV)-polymers dominated the Pu oxidation state distribution on the biomass at pH 6.1. A pH-dependent enrichment of the lower Pu oxidation states (e.g. Pu(III) at pH 6.1 which is considered to be more mobile than Pu(IV) formed at pH 4) was observed in the presence of up to 10 mM Na-pyruvate. In all cases, the presence of bacterial cells enhanced removal of Pu from solution and accelerated Pu interaction reactions, e.g. biosorption and bioreduction.

Keywords: plutonium; bacteria; Sporomusa sp; biosorption; bioreduction; solvent extractions

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Permalink: https://www.hzdr.de/publications/Publ-24118
Publ.-Id: 24118


The case of a rough potential energy surface: Discrepancies between results of NEB and MD calculations

Posselt, M.

Vacancy migration is studied in a silicon crystal with atomic interactions described by the Kumagai potential [1]. The basic functional form of this potential is very similar to the Tersoff potential. The main improvements concern the values of the elastic constants and the melting temperature. However, the potential energy surface is as rough as in the case of the Tersoff potential. In the ground state the vacancy has the “normal” tetrahedral configuration. The migration in the rugged potential energy landscape leads to peculiarities. Extensive Molecular Dynamics (MD) calculations show that the atomic mechanism of the migration process depends on temperature. The vacancy migration energy changes at about 1000 K: At lower and higher temperatures it is about 0.71 and 0.41 eV, respectively. Investigations on the dominating defect structure show that below about 1000 K the tetrahedral vacancy prevails whereas at higher temperature a modified version of the tetrahedral vacancy, the split vacancy and other configurations become dominant.
Applying the Nudged Elastic Band (NEB) method to the potential energy surface in the ground state, the transition between neighboring tetrahedral vacancy structures was studied. A number of intermediate metastable states were found, amongst them the modified version of the tetrahedral vacancy and the split vacancy. The maximum barrier for the migration between one ground state configuration to another is about 0.9 eV, whereas a barrier of about 0.3 eV is found for the transition from the split to the modified tetrahedral structure. Comparing with the results of MD simulations one may assume that in the high temperature range the vacancy moves mainly between high-energy configurations such as the split and the modified tetrahedral structure. The reason why the vacancy is not very often found in the ground state is not completely clear. Obviously, the free energy landscape at elevated temperature differs strongly from the ground-state energy landscape. Vibrational degrees of freedom may lead to the narrowing of the path to the tetrahedral state while the path between the high energy states may become much broader.
[1] T. Kumagai et al., Comput. Mater. Sci. 39, 457 (2007)

Keywords: molecular dynamics; nudged elastic band method; potential energy surface

  • Poster
    Int. Focus Workshop on Bridging-Time Scale Techniques and their Application in Atomistic Computational Science, 12.-15.09.2016, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-24117
Publ.-Id: 24117


Local Scale-Invariance of the 2+1 dimensional Kardar-Parisi-Zhang model

Kelling, J.; Ódor, G.; Gemming, S.

Local Scale-Invariance theory is tested by extensive dynamical simulations of the driven dimer lattice gas model, describing the surface growth of the 2+1 dimensional Kardar–Parisi–Zhang surfaces. Very precise measurements of the universal autoresponse function enabled us to perform nonlinear fitting with the scaling forms, suggested by local scale-invariance (LSI). While the simple LSI ansatz does not seem to work, forms based on logarithmic extension of LSI provide satisfactory description of the full (measured) time evolution of the autoresponse function.

Keywords: Kardar-Parisi-Zhang; Local Scale-Invariance; Monte-Carlo; GPU

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Permalink: https://www.hzdr.de/publications/Publ-24116
Publ.-Id: 24116


Inter-sublevel dynamics in single InAs/GaAs quantum dots probed by strong terahertz excitation

Stephan, D. R.

In this thesis, the response of single self-assembled quantum dots to strong terahertz pulses is investigated by measuring the emitted photoluminescence spectrally as well as in a time-resolved manner, revealing the dynamics of the system. Experimentally, this is realized by combining the micro-photoluminescence technique with illumination from a free-electron laser, which provides intense, tunable narrow-band terahertz pulses. The photoluminescence is triggered by spectrally tunable near-infrared illumination with a synchronized, mode-locked titanium sapphire laser. The measured transients are evaluated with a rate-equation model, taking into account the precise detector response. These measurements reveal three distinct effects, which appear or are obscured depending on the excitation conditions. Firstly, the conduction band inter-sublevel s-p transition is excited by the THz pulses. However, for strong terahertz intensities, a loss of photoluminescence is observed, which can lead to total depletion at very high intensities. This is attributed to the transfer of charge carriers into the wetting layer. Thirdly, for certain near-infrared energies, the opposite behavior is observed, in which the terahertz pulse causes an increase of photoluminescence. The cause of this effect is the release of previously trapped charge carriers, which is also visible in the photoluminescence spectrum. The source of the additional charge carriers is unambiguously identified as the wetting layer. The obtained data is compared to previous studies, and an overview of the relevant theory is presented. In addition, a description of the custom built experimental setup is given.

Keywords: InAs/GaAs semiconductor quantum dot; time-resolved photoluminescence; micro-photoluminescence; free-electron laser; terahertz excitation; carrier dynamics

  • Book (Authorship)
    München: Verlag Dr. Hut, 2016
    122 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24115
Publ.-Id: 24115


Nodal recurrence after stereotactic body radiotherapy for early stage non-small cell lung cancer: incidence and proposed risk factors

Wink, K. C. J.; van Baardwijk, A.; Troost, E. G. C.; de Ruysscher, D.

Stereotactic body radiotherapy (SBRT) is an alternative to surgery for patients with early stage non-small cell lung cancer (NSCLC) who are inoperable due to comorbid disease or who refuse surgery. SBRT results in an excellent local control rate of more than 90%, which is comparable to surgery, while short and long-term overall toxicity is low. Surgically treated patients are often more extensively staged pre-operatively, e.g. with EBUS, and undergo intra-operative lymph node dissection or sampling. Occult nodal metastases (ONM) detected by lymph node dissection have been shown to increase the incidence of regional recurrence (RR) after surgery, which is associated with poor outcome. In patients undergoing SBRT, however, definite pathological nodal staging is lacking. Therefore, other ways to identify patients at high risk for ONM and RR might be thought for.
The aim of this systematic review is to summarize the incidence of and risk factors for RR after SBRT and compare these to those after surgery.

Keywords: SBRT; SABR; NSCLC; regional recurrence; lymph node; early stage

Permalink: https://www.hzdr.de/publications/Publ-24114
Publ.-Id: 24114


Cyclotron resonance and photoluminescence studies of dilute GaAsN in magnetic fields up to 62 Tesla

Eßer, F.

In this thesis, we investigate optical and electrical properties of dilute nitride semiconductors GaAsN in pulsed magnetic fields up to 62 T. For the most part, the experiments are performed at the Dresden High Magnetic Field Laboratory (HLD).
In the first part of this thesis, the electron effective mass of GaAsN is determined with a direct method for the first time. Cyclotron resonance (CR) absorption spectroscopy is performed in Si-doped GaAsN epilayers with a nitrogen content up to 0.2%. For the CR absorption study, we use the combination of the free-electron laser FELBE and pulsed magnetic fields at the HLD, both located at the Helmholtz-Zentrum Dresden-Rossendorf. A slight increase of the CR electron effective mass with N content is obtained. This result is in excellent agreement with calculations based on the band anticrossing model and the empirical tight-binding method. We also find an increase of the band nonparabolicity with increasing N concentration in agreement with our calculations of the energy dependent momentum effective mass.
In the second part of this thesis, the photoluminescence (PL) characteristics of intrinsic GaAsN and n-doped GaAsN:Si is studied. The PL of intrinsic and very dilute GaAsN is characterized by both GaAs-related transitions and N-induced features. These distinct peaks merge into a broad spectral band of localized excitons (LEs) when the N content is increased. This so-called LE-band exhibits a partially delocalized character because of overlapping exciton wave functions and an efficient interexcitonic population transfer. Merged spectra dominate the PL of all Si-doped GaAsN samples. They have contributions of free and localized excitons and are consequently blue-shifted with respect to LE-bands of intrinsic GaAsN. The highly merged PL profiles of GaAsN:Si are studied systematically for the first time with temperature-dependent time-resolved PL. The PL decay is predominantly monoexponential and has a strong energy dispersion. In comparison to formerly reported values of intrinsic GaAsN epilayers, the determined decay times of GaAsN:Si are reduced by a factor of 10 because of enhanced Shockley-Read-Hall and possibly Auger recombinations.
In the third part of this thesis, intrinsic and Si-doped GaAsN are investigated with magneto-PL in fields up to 62 T. A magneto-PL setup for pulsed magnetic fields of the HLD was built for this purpose. The blue-shift of LE-bands is studied in high magnetic fields in order to investigate its delocalized character. The blue-shift is diminished in intrinsic GaAsN at higher temperatures, which indicates that the interexcitonic population transfer is only active below a critical temperature 20 K < T < 50 K. A similar increase of the temperature has no significant impact on the partially delocalized character of the merged spectral band of GaAsN:Si. We conclude that the interexcitonic transfer of Si-doped GaAsN is more complex than in undoped GaAsN. In order to determine reduced masses of undoped GaAsN and GaAs:Si, the field-induced shift of the free exciton transition is studied in the high-field limit. We find an excellent agreement of GaAs:Si with a formerly published value of intrinsic GaAs which was determined with the same method. In both cases, the reduced mass values are enhanced by 20% in comparison to the accepted reduced mass values of GaAs. The determined GaAsN masses are 1.5 times larger than in GaAs:Si and match the rising trend of formerly reported electron effective masses of GaAsN.

Keywords: dilute nitride; recombination dynamics; effective mass; pulsed magnetic fields; magneto-photoluminescence

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-072 2016
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-24113
Publ.-Id: 24113


Rohstoffe für die Energieversorgung der Zukunft

Angerer, G.; Buchholz, P.; Gutzmer, J.; Hagelten, C.; Herzig, P.; Little, R.; Trauer, R. K.; Welker, F.-W.

  • Book (Authorship)
    München: Acatech, 2016
    198 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24112
Publ.-Id: 24112


Self-Supporting Hierarchical Porous PtAg Alloy Nanotubular Aerogels as Highly Active and Durable Electrocatalysts

Liu, W.; Haubold, D.; Rutkowski, B.; Oschatz, M.; Hübner, R.; Werheid, M.; Ziegler, C.; Sonntag, L.; Liu, S.; Zheng, Z.; Herrmann, A.-K.; Geiger, D.; Terlan, B.; Gemming, T.; Borchardt, L.; Kaskel, S.; Czyrska-Filemonowicz, A.; Eychmüller, A.

Developing electrocatalysts with low cost, high activity, and good durability is urgently demanded for the wide commercialization of fuel cells. By taking advantage of nanostructure engineering, we fabricated PtAg nanotubular aerogels (NTAGs) with high electrocatalytic activity and good durability via a simple galvanic replacement reaction between the in situ spontaneously gelated Ag hydrogel and the Pt precursor. The PtAg NTAGs have hierarchical porous network features with primary networks and pores from the interconnected nanotubes of the aerogel and secondary networks and pores from the interconnected thin nanowires on the nanotube surface, and they show very high porosities and large specific surface areas. Due to the unique structure, the PtAg NTAGs exhibit greatly enhanced electrocatalytic activity toward formic acid oxidation, reaching 19 times higher metal-based mass current density as compared to the commercial Pt black. Furthermore, the PtAg NTAGs show outstanding structural stability and electrochemical durability during the electrocatalysis. Noble metal-based NTAGs are promising candidates for applications in electrocatalysis not only for fuel cells, but also for other energy-related systems.

Permalink: https://www.hzdr.de/publications/Publ-24111
Publ.-Id: 24111


Parallel assessment of hypoxia in tumor and LN metastases increases prognostic value of hypoxia-specific PET imaging in locally advanced head-and-neck cancer - secondary analysis of the DDFMISO-trial

Bandurska-Luque, A.; Löck, S.; Haase, R.; Zöphel, K.; Abolmaali, N.; Seidlitz, A.; Perrin, R.; Richter, C.; Troost, E.; Steinbach, J.

Background: Primary tumor (Tu) hypoxia based on hypoxia-specific PET-imaging is a known prognostic parameter for locally-advanced head-and-neck cancer patients. A secondary analysis of the prospective clinical trial on repeated pre- and per-treatment [18F]fluoromisonidazole (FMISO) PET/CT imaging aimed to assess whether parallel evaluation of the oxygenation status in lymph node metastases (LN) and the Tu increases its prognostic value.
Patients and methods: Patients with LN-positive disease from the trial (NCT00180180, Zips et al. 2012, Seidlitz et al. 2015) were included in this analysis (n=45). The patients were treated with curatively intended radiochemotherapy (RCT). The imaging protocol consisted of FMISO PET/CT at four time points: baseline, week 1, 2 and 5. Delineation of the Tu and LNs was based on pre-treatment FDG PET/CT. Qualitative hypoxia analysis was performed for each Tu and LN using a visual binary scale: hypoxic or normoxic being FMISO uptake higher than or equal to background respectively. Based on this scale two prognostic parameters were defined: Tu hypoxia (patients with a hypoxic Tu, independently of LN oxygenation status) and synchronous Tu- and LN-hypoxia (Tu&LN-hypoxia). In the patients with a large LN (n=15) a quantitative analysis of FMISO PET/CT was performed to validate the qualitative hypoxia scale. The log-rank test and multivariate Cox-regression were used to evaluate the prognostic impact of hypoxia on local control (LC) and loco-regional control (LRC).
Results: Qualitative FMISO assessment (Table 1) confirmed poor LC in patients with Tu hypoxia in week 2 and 5. Detection of synchronous Tu- and LN-hypoxia had a strong negative impact on LC and LRC at all measured time-points. These results were supported by multivariate analysis (for LRC: HR=14.8, p=0.016; HR=8.3, p=0,003 and HR=5.5, p=0,005 at baseline, in week 2 and 5, respectively). Moreover, there was a significant correlation between the qualitative and quantitative FMISO PET/CT parameters (p<0.001; R>0.6-0.8).
Conclusions: Parallel evaluation of tumor and LN hypoxia improved the prognostic information in comparison to primary tumor assessment alone, based on secondary analysis of the Dresden FMISO PET/CT trial. If this prognostic value of synchronous tumor- and LN-hypoxia is confirmed in ongoing prospective clinical trials and show to outperform tumor assessment only, it may become a powerful decision-making parameter useful for dose escalation or combined modality trials.

Keywords: FMISO; tumor and lymph node hypoxia

Permalink: https://www.hzdr.de/publications/Publ-24110
Publ.-Id: 24110


Downscaling Effect on the Superconductivity of Pd3Bi2X2 (X = S or Se) Nanoparticles Prepared by Microwave-Assisted Polyol Synthesis

Roslova, M.; Opherden, L.; Veremchuk, I.; Spillecke, L.; Kirmse, H.; Herrmannsdörfer, T.; Wosnitza, J.; Doert, T.; Ruck, M.

PdBi2S2 and Pd3Bi2Se2 have been successfully prepared in the form of nanoparticles with diameters of ∼50 nm by microwave-assisted modified polyol synthesis at low temperatures. The composition and morphology of the samples have been studied by means of powder X-ray diffraction as well as electron microscopy methods, including X-ray intensity mapping on the nanoscale. Superconducting properties of the as-prepared samples have been characterized by electrical resistivity measurements down to low temperatures (∼0.2 K). Deviations from the bulk metallic behavior originating from the submicrometer nature of the samples were registered for both phases. A significant critical-field enhancement up to 1.4 T, i.e., 4 times higher than the value of the bulk material, has been revealed for Pd3Bi2Se2. At the same time, the critical temperature is suppressed to 0.7 K from the bulk value of ∼1 K. A superconducting transition at 0.4 K has been observed in nanocrystalline Pd3Bi2S2. Here, a zero-temperature upper critical field of ∼0.5 T has been estimated. Further, spark plasma-sintered Pd3Bi2S2 and Pd3Bi2Se2 samples have been investigated. Their superconducting properties are found to lie between those of the bulk and nanosized samples.

Permalink: https://www.hzdr.de/publications/Publ-24109
Publ.-Id: 24109


Field-stepped broadband NMR in pulsed magnets and application to SrCu2(BO3)2 at 54 T

Kohlrautz, J.; Haase, J.; Green, E. L.; Zhang, Z. T.; Wosnitza, J.; Herrmannsdörfer, T.; Dabkowska, H. A.; Gaulin, B. D.; Stern, R.; Kühne, H.

Pulsed magnets generate the highest magnetic fields as brief transients during which the observation of NMR is difficult, however, this is the only route to unique insight into material properties up to the regime of 100 T. Here, it is shown how rather broad NMR spectra can be assembled in a pulsed magnet during a single field pulse by using the inherent time dependence of the field for the recording of field-stepped free induction decays that cover a broad frequency range. The technique is then applied to 11B NMR of the spin-dimer system SrCu2(BO3)2, a magnetic insulator known to undergo a series of field-driven changes of the magnetic ground state. At peak fields of about 54 T at the Dresden High Magnetic Field Laboratory, 11B NMR spectra spanning a total of about 9 MHz width are reconstructed. The results are in good accordance with a change from a high-temperature paramagnetic state to a low-temperature commensurate superstructure of field-induced spin-dimer triplets.

Permalink: https://www.hzdr.de/publications/Publ-24108
Publ.-Id: 24108


Quantum phase transitions and multicriticality in Ta(Fe1-xVx)2

Brando, M.; Kerkau, A.; Todorova, A.; Yamada, Y.; Khuntia, P.; Förster, T.; Burkhard, U.; Baenitz, M.; Kreiner, G.

We present a comprehensive study of synthesis, structure analysis, transport and thermodynamic properties of the C14 Laves phase Ta(Fe1-xVx)2. Our measurements confirm the appearance of spin-density wave (SDW) order within a dome-like region of the x-T phase diagram with vanadium content 0.02 < x < 0.3. Our results indicate that on approaching TaFe2 from the vanadium-rich side, ferromagnetic (FM) correlations increase faster than the antiferromagnetic (AFM) ones. This results in an exchange-enhanced susceptibility and in the suppression of the SDW transition temperature for x < 0.13 forming the dome-like shape of the phase diagram. This effect is strictly related to a significant lattice distortion of the crystal structure manifested in the c / a ratio. At x = 0.02 both FM and AFM energy scales have similar strength and the system remains paramagnetic down to 2 K with an extremely large Stoner enhancement factor of about 400. Here, spin fluctuations dominate the temperature dependence of the resistivity ρ ∝ T3/2 and of the specific heat C/T ∝-log(T) which deviate from their conventional Fermi liquid forms, inferring the presence of a quantum critical point of dual nature.

Permalink: https://www.hzdr.de/publications/Publ-24107
Publ.-Id: 24107


Can enhanced feedback effects and improved breeding coincide in a metal fueled, sodium cooled fast reactor?

Merk, B.; Devan, K.; Bachchan, A.; Paul, D.; Puthiyavinayagam, P.; Srinivasan, G.

Different strategies for the improvement of in core breeding on fuel assembly level are investigated using the HELIOS 2.1 code. An additional key boundary condition is the conservation of the safety related feedback effects of the assembly. It is demonstrated that the insertion of 1/3 of fertile fuel rods into the fuel assembly, while the overall Pu content of the assembly is kept constant, can improve the breeding of fresh Plutonium. A second proposal is the reduction of the Pu content of the assembly compensated by eliminating one ring of the fertile blanket around the core. This method proofs to be very efficient to improve the in core breeding. The consequences on the fuel assembly multiplication factor, the fissile material content, and the pin wise power as well as burnup distribution is analyzed. Additionally, the effect of fine distributed material on breeding as well as on the safety related feedback effects is investigated for both proposals. A clear enhancement of the feedback effects could be proven.

Keywords: nuclear reactors; fast reactors; plutonium breeding; enhanced feedback effects; moderating material

Permalink: https://www.hzdr.de/publications/Publ-24106
Publ.-Id: 24106


Multiscale modeling of bacterial colonies: How pili mediate the dynamics of single cells and cellular aggregates

Pönisch, W.; Weber, C.; Juckeland, G.; Biais, N.; Zaburdaev, V.

Neisseria gonorrhoeae is the causative agent of one of the most common sexually transmitted diseases, gonorrhea. An vital step during the infection process is the formation of microcolonies, agglomerates of up to thousands of cells. The assembly of these colonies is driven by type IV pili, filamentaeous polymers protruding from the surface of the colonies, undergoing cycles of elongation and retraction and forming bonds with each other and a substrate. Here, we present a computer model of individual cells interacting via each other solely by pili. This model allows us to study a wide range of processes, from the motion of individual cells and colonies on a surface, over the dynamics within colonies and how they drive the coalescence of two microcolonies, up to the self-assembly of cells.

Permalink: https://www.hzdr.de/publications/Publ-24105
Publ.-Id: 24105


Structure, composition and magnetism in FeAl alloys

Menendez, E.; Surinach, S.; Baro, M. D.; Liedke, M. O.; Fassbender, J.; Nogues, J.; Sort, J.

Fe1–xAlx alloys with x ranging from roughly 0.35 to 0.5 at. % show an interesting combination of room temperature magnetic and structural properties. Atomically ordered Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) alloys are paramagnetic, while atomically disordered Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) alloys become ferromagnetic [1]. The transition from the paramagnetic to the ferromagnetic state can be accomplished by different means (e.g., deformation or ion irradiation) and, remarkably, fully reversed upon thermal treatment [2]. Fabrication of Fe1–xAlx (0.35 ≤ x ≤ 0.5 at. %) thin films with controlled microstructure, composition and thickness would turn them into potential candidates to be magnetically patterned for the functioning of devices, such as magnetic storage media or magnetoresistive random access memories [3]. An overwiew of this order-disorder transition by either deformation or ion irradiation in bulk samples will be presented. Particular emphasis will be given to magnetic patterning routes by both local deformation and selective ion irradiation. Finally, our recent results on the preparation of thin films with controlled microstructure, composition and thickness will be outlined.

[1] E. Menéndez et al. New J. Phys. 10 (2008) 103030
[2] E. Menéndez et al. Small 5 (2009) 229
[3] R. Bali et al. Nano Lett. 14 (2014) 435

Keywords: magnetism; FeAl; binary alloys

  • Invited lecture (Conferences)
    Frontiers in Materials Processing Applications, Research and Technology, 09.-12.07.2017, Bordeaux, Frankreich

Permalink: https://www.hzdr.de/publications/Publ-24104
Publ.-Id: 24104


Effects of Substrate and Post-Growth Treatments on the Microstructure and Properties of ZnO Thin Films Prepared by Atomic Layer Deposition

Haseman, M.; Saadatkia, P.; Winarski, D. J.; Selim, F. A.; Leedy, K. D.; Tetlak, S.; Look, D. C.; Anwand, W.; Wagner, A.

Aluminum doped zinc oxide (ZnO:Al) thin films were synthesized by atomic layer deposition on silicon, quartz and sapphire substrates and characterized by X-ray diffraction (XRD), high-resolution scanning electron microscopy (SEM), optical spectroscopy, conductivity mapping, Hall-effect measurements and positron annihilation spectroscopy (PAS). XRD showed that the as-grown films are of single-phase ZnO wurtzite structure and do not contain any secondary or impurity phases. The type of substrate was found to affect the orientation and degree of crystallinity of the films but had no effect on the defect structure or the transport properties of the films. High conductivity of 10-3 Ohm cm, electron mobility of 20 cm2/Vs and carrier density of 1020 cm-3 were measured in most films. Thermal treatments in various atmospheres induced a large effect on the thickness, structure and electrical properties of the films. Annealing in a Zn and nitrogen environment at 400 oC for one hour led to a 16% increase in the thickness of the film; this indicates that Zn extracts oxygen atoms from the matrix and forms new layers of ZnO. On the other hand, annealing in a hydrogen atmosphere led to the emergence of an Al2O3 peak in the XRD pattern, which implies that hydrogen and Al atoms compete to occupy Zn sites in the ZnO lattice. Only ambient-air anneal had an effect on film defect density and electrical properties, generating reduction in conductivity and electron mobility. Depth resolved measurements of positron annihilation revealed short positron diffusion lengths and high concentration of defects in all as-grown films. However these defects did not diminish the electrical conductivity in the films.

Keywords: ZnO defects positron annihilation annealing

Permalink: https://www.hzdr.de/publications/Publ-24103
Publ.-Id: 24103


Out-of-plane magnetized cone-shaped magnetic nanoshells

Ball, D. K.; Günther, S.; Fritzsche, M.; Lenz, K.; Varvaro, G.; Laureti, S.; Makarov, D.; Mücklich, A.; Facsko, S.; Albrecht, M.; Fassbender, J.

The geometry of a magnetic nanoobject, namely its shape and dimension determines the complex electromagnetic responses. Here, we address the geometry-induced changes of the magnetic properties of thin ferromagnetic Co/Pd multilayers with out-of-plane magnetic anisotropy deposited on 3-dimensionally curved templates. For this pourpose, arrays of self-assembled cone-shaped nanoobjects with a chracteristic size of either 30 or 70 nm were created in GaSb(001) by the ion erosion technique. The templates are designed in the way that the shape of the cone remains the same for all the samples; namely, we keep the opening angle at about 55º by adjusting the ratio between the cone height and its base diameter to be about 1. In this case, we are able to address the impact of the linear dimensions of the object on the magnetic properties and exclude the impact of the shape from the consideration. Deposition of 15-nm-thick Co/Pd multilayers on top of the cone templates results in the formation of a close-packed array of 2-dimensional magnetic cone-shaped shells. Integral angle-dependent magnetometry measurements demonstrate that local curvature results in the spread of the easy axes of magnetization following the shape of nanocones independent of the linear dimensions of the cone. At the same time different local magnetic domain patterns are observed for samples prepared on 30 and 70 nm large cones. When the thickness of the magnetic shell is only half of the linear dimension of a cone, a clear multidomain state is observed. Remarkably, we find that the neighboring magnetic cone-shaped shells are exchange decoupled when the linear dimension of a cone is 4 times larger compared to the thickness of the magnetic shell. These findings are relevant for the further development of tilted bit patterned magnetic recording media as well as for the emergent field of magnetism in curved geometries.

Keywords: curvilinear magnetism; 2D magnetic shells; self-assembled nanostructures; Co/Pd multilayers; magnetic properties; exchange coupling

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Permalink: https://www.hzdr.de/publications/Publ-24101
Publ.-Id: 24101


Magnetic anisotropy peculiarities of high-temperature ferromagnetic MnxSi1−x (x ≈ 0.5) alloy films

Drovosekov, A. B.; Kreines, N. M.; Savitsky, A. O.; Kapelnitsky, S. V.; Rylkov, V. V.; Tugushev, V. V.; Prutskov, G. V.; Novodvorskii, O. A.; Cherebilo, E. A.; Kulatov, E. T.; Wang, Y.; Zhou, S.

Thin films of MnxSi1-xalloys with different Mn concentration x ≈ 0.44-0.63 grown by the pulsed-laser deposition (PLD) method onto the Al2O3(0001) substrate were investigated in the temperature range 4-300 K using ferromagnetic resonance (FMR) measurements in the wide range of frequencies and magnetic fields . For samples with x ≈ 0.52-0.55, FMR data show clear evidence of ferromagnetism (FM) with high Curie temperatures Tc ∼ 300K. These samples demonstrate the complex and unusual character of magnetic anisotropy described in the frame of phenomenological model as a combination of the essential second-order easy-plane anisotropy contribution and the additional fourth-order anisotropy contribution with the easy direction normal to the film plane. We explain the obtained results by a polycrystalline (mosaic) structure of the films caused by the film-substrate lattice mismatch

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Permalink: https://www.hzdr.de/publications/Publ-24100
Publ.-Id: 24100


Formation of silicon nanocrystals in silicon carbide using flash lamp annealing

Weiss, C.; Schnabel, M.; Prucnal, S.; Hofmann, J.; Reichert, A.; Fehrenbach, T.; Skorupa, W.; Janz, S.

During the formation of Si nanocrystals (Si NC) in SixC1-x layers via solid-phase crystallization, the unintended formation of nanocrystalline SiC reduces the minority carrier lifetime and therefore the performance of SixC1-x as an absorber layer in solar cells. A significant reduction in the annealing time may suppress the crystallization of the SiC matrix while maintaining the formation of Si NC. In this study, we investigated the crystallization of stoichiometric SiC and Si-rich SiC using conventional rapid thermal annealing (RTA) and nonequilibrium millisecond range flash lamp annealing (FLA). The investigated SixC1-x films were prepared by plasma-enhanced chemical vapor deposition and annealed at temperatures from 700 C to 1100C for RTA and at flash energies between 34 J/cm2 and 62 J/cm2 for FLA. Grazing incidence X-ray diffraction and Fourier transformed infrared spectroscopy were conducted to investigate hydrogen effusion, Si and SiC NC growth, and SiC crystallinity. Both the Si content and the choice of the annealing process affect the crystallization behavior. It is shown that under certain conditions, FLA can be successfully utilized for the formation of Si NC in a SiC matrix, which closely resembles Si NC in a SiC matrix achieved by RTA. The samples must have excess Si, and the flash energy should not exceed 40 J/cm2 and 47 J/cm2 for Si0.63C0.37 and Si0.77C0.23 samples, respectively. Under these conditions, FLA succeeds in producing Si NC of a given size in less crystalline SiC than RTA does. This result is discussed in terms of nucleation and crystal growth using classical crystallization theory. For FLA and RTA samples, an opposite relationship between NC size and Si content was observed and attributed either to the dependence of H effusion on Si content or to the optical absorption properties of the materials, which also depend on the Si content.

Keywords: solar cells; flash lamp annealing; Si; SiC

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Permalink: https://www.hzdr.de/publications/Publ-24099
Publ.-Id: 24099


Hydrodynamics of Gas-Liquid Cocurrent Upflow in Oscillating Packed Beds for Offshore Marine Applications

Dashliborun, A. M.; Larachi, F.; Schubert, M.

In this study, the hydrodynamic behavior of inclined stationary and oscillating packed beds with gas-liquid cocurrent upflow mode of operation was investigated. Comprehensive hydrodynamic experiments were carried out using embedded low-intrusive Wire-Mesh Sensors (WMSs) and a hexapod ship motion simulator in order to properly understand the effect of column inclination and movements on gas-liquid flow distribution in the bed cross-section, overall pressure drop, liquid saturation, and pulsing flow inception. Furthermore, liquid residence time and Péclet number estimated by a stimulus-response technique and a macromixing model were presented and discussed with respect to the prevailing flow regimes. The results revealed that the column deviation from the vertical posture and tilting motions significantly alter the hydrodynamics prevailing in the packed bed operating in a concurrent upflow mode. Development of gas-liquid disengagement zones, oscillations in the pressure drop and uniformity factor time series, departure from liquid plug flow character, and delay in the inception of pulsing flow regime were observed as a result of bed inclination and oscillations.

Keywords: Cocurrent upflow packed bed; oscillation; wire mesh sensor; hexapod motion simulator; maldistribution; hydrodynamics

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Permalink: https://www.hzdr.de/publications/Publ-24098
Publ.-Id: 24098


Untersuchungen zu magnetohydrodynamischen Instabilitäten in Flüssigmetallen

Seilmayer, M.

This dissertation, “Studies on magnetohydrodynamic instabilities in liquid metal flows”, focuses on two different experiments in a cylindrical Taylor-Couette (TC) geometry. This fundamental set-up consists of an inner and an outer cylinder, which are mounted concentrically. The different radii are defined by the parameters and . The rotation of both cylinders can be set independently by their angular frequencies and . The gap between them is filled with the fluid whose flow is to be investigated. For an ideal non-viscous fluid, Rayleigh’s criterion states that the flow between two concentric cylinders with infinite length is stable against small perturbations as long as the angular momentum increases outward, [1]. Rayleigh’s criterion can be interpreted in a way that an ideal TC-flow remains laminar if the pressure and centrifugal forces are in a stable equilibrium state.
A more general setting is now introduced with an azimuthal magnetic field being applied to the electrical conducting fluid. For this different situation Michael [2] and Chandrasekhar [3] derived an extended stability criterion only for axisymmetric perturbations which is valid for an ideally conducting and non-viscous fluid. The first experiment described in the present dissertation consists of a TC-setup using the eutectic alloy Ga67In20,5Sn12,5 as working fluid. In addition to the common installation an insulated current on the rotation axis with up to 20 kA generates the necessary magnetic field . Michael’s criterion indicates in that case that the flow is stable with respect to axisymmetric perturbations. However, this does not apply for non-axisymmetric perturbations. It was shown theoretically by Rüdiger et al. [4, 5] that the interaction of an azimuthal magnetic field with a laminar rotational flow may become unstable against non-axisymmetric disturbances. This phenomenon is called Azimuthal Magnetorotational Instability (AMRI). The present work gives the first experimental evidence for AMRI in a liquid metal TC-experiment. It is shown that a hydrodynamically stable flow can be disturbed by an applied current free azimuthal magnetic field . The instability itself is then identified as a travelling wave co-rotating with the cylinders.
The second configuration investigated in this work is characterized by a magnetic field profile proportional to the radius. The basis for such an experiment is the remarkable stability criterion from Tayler [6, 7]. It tells that even an ideal fluid at rest can become unstable against non-axisymmetric disturbances. The Tayler instability (TI) in liquid metals can be considered as the incompressible version of the kink instability that is widely known in plasma physics. The TI-experiment confirms the numerical results given by Rüdiger et al. [8, 9] who calculated the onset for the instability in an incompressible liquid metal column with finite conductivity at round about 3 kA.
Both observed phenomena are strongly related to astrophysical processes in which angular momentum transport plays an essential role. What was missing so far was a clear experimental evidence for the described interaction mechanisms between a rotational flow and a magnetic field. The submitted dissertation reports the analysis and results of the first experiments on the two fundamental instabilities AMRI and TI.

[1] Rayleigh, Proc. R. Soc. London, Ser. A, 93(648), 148‑154, 1917.
[2] D. H. Michael, Mathematika, 1, 45‑50, 1954.
[3] S. Chandrasekhar, Proc.Roy.Soc.-A, 216(1126), 293‑309, 1953.
[4] G. Rüdiger et al. MNRAS, 377(4), 1481‑1487, 2007.
[5] G. Rüdiger et al. Astron. Nachr., 328, 1158‑1161, 2007.
[6] R. J. Tayler, Proc. R. Soc. London, Ser. B, 70(1), 31‑48, 1957.
[7] R. J. Tayler, MNRAS, 161(4), 365‑380, 1973.
[8] G. Rüdiger et al., Astron. Nachr., 332(1), 17‑23, 2011.
[9] G. Rüdiger et al., Astrophys. J., 755(2), 181, 2012.

Keywords: MRI; magnetohydrodynamic instabilities; Azimuthal Magnetorotational Instability; Tayler instability

  • Book (Authorship)
    Dresden: TUDpress, 2016
    261 Seiten

Permalink: https://www.hzdr.de/publications/Publ-24097
Publ.-Id: 24097


Cm3+ incorporation in La1-xGdxPO4 monazites: a TRLFS and XAFS study

Huittinen, N.; Scheinost, A. C.; Wilden, A.; Arinicheva, Y.

Crystalline ceramic materials show promise as potential waste forms for immobilization of high-level radioactive wastes. Especially for the immobilization of trivalent minor actinides (MA) and plutonium, some ceramic materials such as the lanthanide phosphates (LnPO4) crystallizing in the monazite structure have been envisioned as host materials due to their thermal stability, high radiation tolerance, and chemical durability [1]. Thus, for a reliable long-term safety assessment of nuclear waste repositories for conditioned radioactive waste, a fundamental understanding of the MA incorporation process in these envisioned ceramic matrices is required.
In the present study, the incorporation of the minor actinide Cm3+ in a series of La1-xGdxPO4 (x = 0, 0.2, 0.5, 0.8, 1) monazite solid solutions has been investigated using time-resolved laser fluorescence- (TRLFS) and Cm L3-edge x-ray absorption fine-structure spectroscopy (XAFS).
The Cm3+ excitation spectra obtained with the TRLFS method of the pure LaPO4 and GdPO4 end-members (Figure 1) show four well-resolved peaks corresponding to the 4-fold splitting of the Cm3+ ground state. The highly resolved ground-state splitting indicates the presence of only one, very well-defined, crystalline environment for the incorporated Cm3+ cation in the La and Gd monazite end-members. The situation changes when examining the solid solution compositions (La0.8Gd0.2PO4, La0.5Gd0.5PO4, and La0.2Gd0.8PO4) where the complete loss of the splitting fine-structure and the broadening of the excitation peaks indicate a decrease of the short-range order in these solid solutions.
The fitting of the first coordination shell of our Cm L3 XAFS data (Figure 2) for LaPO4, La0.5Gd0.5PO4, and GdPO4, indicate a contraction of the Cm-O distance when going from the larger LaPO4 monazite toward GdPO4 (see Table 1). In addition the Debye-Waller (DW, σ2) factor (which is an indicator for thermal and structural disorder) decreases substantially from 0.0079 Å2 in LaPO4 to 0.004 Å2 in GdPO4, while an increase is observed for the solid-solution composition (0.0112 Å2). The shortening of the Cm···O bond distance can be understood by the decreasing size of the monazite unit cell when going from the larger La3+-bearing host toward the smaller GdPO4. The differences in the DW factors between the monazite end-members can be explained when examining our previously obtained results for Eu3+ incorporation in LnPO4 monazites [2]. Here we could show that a larger mismatch between host and dopant radii causes a larger distortion of the monazite crystal lattice around the trivalent dopant. The cation radii of nine-fold coordinated La3+, Cm3+, and Gd3+ are 121.6 Å [3], 114.6 Å [4], and 110.7 Å [3], respectively. Thus, the larger mismatch of host and dopant radii in Cm3+-doped LaPO4 could explain the larger DW factor than obtained for Cm3+ incorporation in GdPO4. The large DW factor obtained for La0.5Gd0.5PO4 in comparison to the monazite end-members is in concordance with the excitation line broadening observed for the monazite solid solutions in our Cm3+ excitation spectra (Figure 1), implying an increasing disordering of the monazite crystal structure. In our previous work investigating the incorporation of Eu3+ in La1-xGdxPO4 monazites [5], the systematic excitation line broadening could be attributed to and increasing broadening of the Eu∙∙∙O bond distance distribution in the synthetic solid solution series when going from the pure end-members with very well-defined Eu∙∙∙O distances toward the La0.5Gd0.5PO4 composition.

Our spectroscopic results obtained in the present study show that Cm3+ is substituted for the host cation sites in all investigated monazites. Although the spectroscopic data suggest a disordering of the monazite solid solution series due to less explicit Ln∙∙∙O bond distances in the mixed solids, the spectroscopic investigations also imply that no preferential incorporation of dopants on host cation sites with similarly sized cation radii occurs, which is of great importance when considering the performance of monazite materials as immobilization matrices for highly radioactive actinide compounds.

[1] G. R. Lumpkin (2006) “Ceramic waste forms for actinides.” Elements 2: 365-372.
[2] N. Huittinen et al. (submitted) Using Eu3+ as an atomic probe to investigate the local environment in LaPO4 GdPO4 monazite end-members.
[3] R. D. Shannon (1976) Revised effective ionic radii and systematic studies of interatomic distances
in halides and chalcogenides. Acta Cryst. A32, 751–767.
[4] F. H. David and V. Vokhmin (2003) Thermodynamic properties of some tri- and tetravalent actinide aquo ions. New J. Chem., 27, 1627–1632.
[5] N. Huittinen et al. (submitted) Structural incorporation of Eu3+ in La1-xGdxPO4 monazite solid solutions: A combined spectroscopic and computational study.

  • Poster
    9th international conference on nuclear and radiochemistry (NRC9), 29.08.-02.09.2016, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-24096
Publ.-Id: 24096


Hydrous 18F-fluoroethylation – leaving off the azeotropic drying

Kniess, T.; Laube, M.; Steinbach, J.

The study describes the development of a simple and effective method for [18F]fluoroethylation, called as smart [18F]fluoroethylation without azeotropic drying, by elution of a [18F]fluoride loaded QMA column with a K2CO3/K222/acetonitrile solution containing 2% (v/v) water directly to the 1,2-ethylene glycol-bis-tosylate precursor. The method was exemplified on the radiosynthesis of three COX-2 inhibitors with different core structures. In comparison to conventional [18F]fluoroethylation, the reaction time was generally shortened and the radiochemical yield was improved in each case by factor 4-5 by this approach.

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Permalink: https://www.hzdr.de/publications/Publ-24095
Publ.-Id: 24095


Probing structural homogeneity of La1-xGdxPO4 monazite-type solid solutions by combined spectroscopic and computational studies

Huittinen, N.; Arinicheva, Y.; Kowalski, P. M.; Vinograd, V. L.; Neumeier, S.; Bosbach, D.

Here we study the homogeneity of Eu3+-doped La1-xGdxPO4 (x = 0, 0.11, 0.33, 0.55, 0.75, 0.92, 1) monazite-type solid solutions by a combination of Raman and time-resolved laser fluorescence spectroscopies (TRLFS) with complementary quasi-random structure-based atomistic modeling studies. For the intermediate La0.45Gd0.55PO4 composition we detected a significant broadening of the Raman bands corresponding to the lattice vibrations of the LnO9 polyhedron, indicating much stronger distortion of the lanthanide cation site than the PO4 tetrahedron. A distortion of the crystal lattice around the dopant site was also confirmed in our TRLFS measurements of Eu3+ doped samples, where both the half width (FWHM) of the excitation peaks and the 7F2/7F1 ratio derived from the emission spectra increase for intermediate solid-solution compositions. The observed variation in FWHM correlates well with the simulated distribution of Eu∙∙∙O bond distances within the investigated monazites. The combined results imply that homogenous Eu3+-doped La1-xGdxPO4 monazite-type solid solutions are formed over the entire composition range, which is of importance in the context of using these ceramics for immobilization of radionuclides.

Keywords: monazite; solid solution; Eu3+ incorporation; Raman; TRLFS; ab initio; force field simulations

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-24094
Publ.-Id: 24094


Using Eu3+ as an atomic probe to investigate the local environment in LaPO4–GdPO4 monazite end-members

Huittinen, N.; Arinicheva, Y.; Schmidt, M.; Neumeier, S.; Stumpf, T.

In the present study, we have investigated the luminescent properties of Eu3+ as a dopant in a series of synthetic lanthanide phosphates from the monazite group. Systematic trends in the spectroscopic properties of Eu3+ depending on the size of the host cation and the dopant to ligand distance have been observed. Our results show that the increasing match between host and dopant radii when going from Eu3+-doped LaPO4 toward the smaller GdPO4 monazite decreases both the full width at half maximum of the Eu3+ excitation peak, as well as the 7F2/7F1 emission band intensity ratio. The decreasing Ln-O bond distance within the LnPO4 series causes a systematic bathochromic shift of the Eu3+ excitation peak, showing a linear dependence of both the host cation size and the Ln-O distance. The linear relationship can be used to predict the energy band gap for Eu3+-doped monazites for which no Eu3+ luminescent data is available. Finally, mechanisms for metal-metal energy transfer between host and dopant lanthanides have been explored based on recorded luminescence lifetime data. Luminescence lifetime data for Eu3+ incorporated in the various monazite hosts clearly indicated that the energy band gap between the guest ion emission transition and the host ion absorption transition can be correlated to the degree of quenching observed in these materials with otherwise identical geometries and chemistries.

Keywords: Eu3+; Monazite; Incorporation; TRLFS; Luminescence; Quenching

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Permalink: https://www.hzdr.de/publications/Publ-24093
Publ.-Id: 24093


Rotational friction of dipolar colloids measured by driven torsional oscillations

Steinbach, G.; Gemming, S.; Erbe, A.

Despite its prominent role in the dynamics of soft materials, rotational friction remains a quantity that is difficult to determine for many micron-sized objects. Here, we demonstrate how the Stokes coefficient of rotational friction can be obtained from the driven torsional oscillations of single particles in a highly viscous environment. The idea is that the oscillation amplitude of a dipolar particle under combined static and oscillating fields provides a measure for the Stokes friction. From numerical studies we derive a semi-empirical analytic expression for the amplitude of the oscillation, which cannot be calculated analytically from the equation of motion. We additionally demonstrate that this expression can be used to experimentally determine the rotational friction coefficient of single particles. Here, we record the amplitudes of a field-driven dipolar Janus microsphere with optical microscopy. The presented method distinguishes itself in its experimental and conceptual simplicity. The magnetic torque leaves the local environment unchanged, which contrasts with other approaches where, for example, additional mechanical (frictional) or thermal contributions have to be regarded.

Permalink: https://www.hzdr.de/publications/Publ-24091
Publ.-Id: 24091


MIR and THz spectroscopy of condensed matter

Helm, M.

MIR and THz spectroscopy of condensed matter

Keywords: infrared; THz; condensed matter

  • Invited lecture (Conferences)
    Summer School NanoTech Tera-Mir, 29.08.-01.09.2016, Porquerolles, Hyeres, France

Permalink: https://www.hzdr.de/publications/Publ-24090
Publ.-Id: 24090


Adhesion- and stress-related adaptation of glioma radiochemoresistance is circumvented by β1 integrin/JNK co-targeting

Vehlow, A.; Klapproth, E.; Storch, K.; Dickreuter, E.; Seifert, M.; Dietrich, A.; Bütof, R.; Temme, A.; Cordes, N.

Resistance of cancer stem-like and cancer tumor bulk cells to radiochemotherapy and destructive infiltration of the brain fundamentally influence the treatment efficiency to cure of patients suffering from Glioblastoma (GBM). The interplay of adhesion and stress-related signaling and activation of bypass cascades that counteract therapeutic approaches remain to be identified in GBM cells. We here show that combined inhibition of the adhesion receptor β1 integrin and the stress-mediator c-Jun N-terminal kinase (JNK) induces radiosensitization and blocks invasion in stem-like and patient-derived GBM cultures as well as in GBM cell lines. In vivo, this treatment approach not only significantly delays tumor growth but also increases median survival of orthotopic, radiochemotherapy-treated GBM mice. Both, in vitro and in vivo, effects seen with β1 integrin/JNK co-inhibition are superior to the monotherapy. Mechanistically, the in vitro radiosensitization provoked by β1 integrin/JNK targeting is caused by defective DNA repair associated with chromatin changes, enhanced ATM phosphorylation and prolonged G2/M cell cycle arrest. Our findings identify a β1 integrin/JNK co-dependent bypass signaling for GBM therapy resistance, which might be therapeutically exploitable.

Keywords: β1 integrin; JNK; radiochemoresistance; GBM stem-like cells; orthotopic GBM mouse model

Permalink: https://www.hzdr.de/publications/Publ-24089
Publ.-Id: 24089


Head and neck cancer cell radiosensitization upon dual targeting of c-Abl and beta1-integrin

Koppenhagen, P.; Dickreuter, E.; Cordes, N.

Integrin-mediated cell adhesion to extracellular matrix (ECM) critically contributes to cancer cell therapy resistance and DNA double strand break (DSB) repair. c-Abl tyrosine kinase has been linked to both of these processes. Based on our previous findings indicating c-Abl hyperphosphorylation on tyrosine (Y) 412 and threonine (T) 735 upon beta1-integrin knockdown, we hypothesized c-Abl tyrosine kinase as an important mediator of beta1-integrin signaling for radioresistance. In a panel of 8 cell lines from different solid cancer types grown in 3D laminin-rich ECM cultures, we targeted beta1 integrin with AIIB2 (mAb) and c-Abl with Imatinib with and without X-ray irradiation and subsequently examined clonogenic survival, residual DSBs, protein expression and -phosphorylation. Single or combined treatment with AIIB2 and Imatinib resulted in cell line-dependent cytotoxicity. Intriguingly, a subgroup in this cell line panel responding to AIIB2/Imatinib treatment with higher radiosensitization relative to both single treatments was identified. Likewise, AIIB2/Imatinib co-treatment elicited a significantly higher number of residual DSBs than controls, which was accompanied by decreased Ku70 expression and enhanced ATM S1981 phosphorylation. Mechanistically, c-Abl was located in the beta1-integrin/JNK signaling axis and abrogated AIIB2/Imatinib-related radiosensitization when exogenously overexpressed in either wildtype or constitutively activated form. Our data generated in more physiological 3D cancer cell culture models indicate c-Abl as important determinant of radioresistance and DNA repair downstream of beta1-integrin. For solid cancers, c-Abl phosphorylation status might be an indicator for reasonable Imatinib application as adjuvant for conventional radio(chemo)therapy.

Keywords: beta1-integrin; c-Abl; Imatinib; ionizing radiation; DNA-repair

Permalink: https://www.hzdr.de/publications/Publ-24088
Publ.-Id: 24088


Theranostic mercury part 2: Production of 197(m)Hg via the 197Au(d,2n) reaction

Lebeda, O.; Walther, M.; Preusche, S.; Pietzsch, H.-J.; Steinbach, J.

The access to no-carrier-added 197(m)Hg using proton irradiation of gold targets and subsequent product separation was recently reported. One of the limiting factors of the large-scale production of this theranostic radionuclide is rather low yield of the 197Au(p,n)197(m)Hg reaction. In contrast, significantly larger cross-sections have been reported for 197Au(d,2n) reaction. In spite of somewhat larger linear energy transfer of deuterons in gold, the latter reaction seems to result in larger achievable activity of 197(m)Hg. We have, therefore, explored its potential for the 197(m)Hg production in a pilot experiment.

Keywords: no-carrier-added 197(m)Hg; theranostic; cross-section; deuteron

  • Lecture (Conference)
    16th International Workshop on Targetry and Target Chemistry (WTTC16), 29.08.-01.09.2016, Santa Fe, USA

Permalink: https://www.hzdr.de/publications/Publ-24087
Publ.-Id: 24087


Theranostic mercury part 1: A new Hg/Au separation by a resin based method

Walther, M.; Lebeda, O.; Preusche, S.; Pietzsch, H.-J.; Steinbach, J.

The production and separation of no-carrier-added 197(m)Hg for imaging and therapy research based on the 197Au(p,n)197(m)Hg reaction was recently reported. However, large-scale production requires the development of a rapid, reliable method for Hg/Au separation. Ideally, a solid phase sorbent is used to bind at least one of the two metal ions reversibly, allowing for the product elution into a small volume. Di(2-ethylhexyl)orthophosphoric acid (HDEHP) im-pregnated onto an inert support as the so called LN resin (LaNthanides) was examined for this application.

Keywords: no-carrier-added 197(m)Hg; therapy; Hg/Au separation

  • Lecture (Conference)
    16th International Workshop on Targetry and Target Chemistry (WTTC16), 29.08.-01.09.2016, Santa Fe, USA
  • Contribution to proceedings
    16th International Workshop on Targetry and Target Chemistry, WTTC 2016, 29.08.-01.09.2016, Santa Fe, United States, 978-073541517-1
    DOI: 10.1063/1.4983554

Permalink: https://www.hzdr.de/publications/Publ-24086
Publ.-Id: 24086


Development of a F-18-labeled Diaryl-Substituted Dihydropyrrolo[3,2,1-hi]indole as Potential Probe for Functional Imaging of Cyclooxygenase-2 with PET

Gassner, C.; Neuber, C.; Laube, M.; Bergmann, R.; Kniess, T.; Pietzsch, J.

High COX-2 expression is associated with tumor progression and poor treatment response. Imaging of functional COX-2 expression by PET would provide beneficial information for theranostics. Here we describe precursor synthesis and radiolabeling attempts of (dihydro)pyrrolo[3,2,1-hi]indoles [18F]DHPI and [18F]PI, two novel tricyclic COX-2 inhibitors. Contrary to [18F]PI, [18F]DHPI was accessible by [18F]fluorination under mild basic conditions and McMurry cyclization. Radiopharmacological evaluation was performed in vitro by investigating cellular uptake in human COX-2-positive cells, and in vivo in rats and A2058-melanoma xenograft mice, by focusing on metabolic stability and tumor uptake. To assess COX-2 specificity, blocking experiments with celecoxib were performed. Despite of high COX-2 selectivity and metabolic stability, [18F]DHPI did not show COX-2-dependent cell and tissue uptake, in part explained by high unspecific binding. Since appropriate lipophilicity is a prerequisite for targeting intracellularly localized COX-2, future efforts should focus on use of longer-lived radionuclides and/or targeted delivery systems.

Keywords: Cancer; Malignant melanoma; Molecular imaging; Radiochemistry; Selective cyclooxygenase-2 inhibitors; Tumor xenograft models

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  • Secondary publication expected

Permalink: https://www.hzdr.de/publications/Publ-24085
Publ.-Id: 24085


A Guide on Spectral Methods Applied to Discrete Data in One Dimension

Seilmayer, M.; Ratajczak, M.

Spectral analysis in conjunction with discrete data in one and more dimensions can become a challenging task, because the methods are sometimes difficult to understand. This paper intends to provide an overview about the usage of the Fourier transform, its related methods and focuses on the subtleties to which the users must pay attention. Typical questions, which are often addressed to the data, will be discussed. Such a problem can be the issue of frequency or band limitation of the signal. Or the source of artifacts might be of interest, when a Fourier transform is carried out. Another topic is the issue with fragmented data. Here, the Lomb-Scargle method will be explained with an illustrative example to deal with this special type of signal. Furthermore, a challenge encountered very often is the time-dependent spectral analysis, with which one can evaluate the point in time when a certain frequency appears in the signal. The information to solve such problems and to answer this questions is spread over many disciplines ranging from mathematics, electrical engineering, economic science to astrophysics. The goal of the first part of this paper is to collect the important information about the common methods to give the reader a guide on how to use these for application on one-dimensional data. The second part of this paper will then address the two- and more-dimensional data. The introduced methods are supported by the 'spectral' package, which has been published for the statistical environment R prior this article.

Keywords: spectral analysis; Fourier transform; Hilbert transform; R; spectral

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Permalink: https://www.hzdr.de/publications/Publ-24083
Publ.-Id: 24083


Common methods of spectral data analysis

Seilmayer, M.

Fourier and Hilbert transforms are utilized to perform several types of spectral analysis on the supplied data. Also gapped and irregularly spaced data can be processed. A user friendly interface helps to interpret the results.

Keywords: spectral analysis; Fourier transform; Hilbert transform; R

  • Software in external data repository
    Publication year 2016
    Programming language: R
    System requirements: Windows, Linux, MacOS, R (>= 2.15.0)
    License: GPL-2 (Link to license text)
    Hosted on CRAN: Link to location

Permalink: https://www.hzdr.de/publications/Publ-24082
Publ.-Id: 24082


rasterImage

Seilmayer, M.

This is a wrapper function for image(), which makes reasonable raster plots with nice axis and other useful features.

Keywords: plot function; R

  • Software in external data repository
    Publication year 2016
    Programming language: R
    System requirements: Windows, Linux, MacOS, R (>= 2.15.0)
    License: GPL-2 (Link to license text)
    Hosted on CRAN: Link to location

Permalink: https://www.hzdr.de/publications/Publ-24081
Publ.-Id: 24081


Progress of the Felsenkeller shallow-underground accelerator for nuclear astrophysics

Bemmerer, D.; Cavanna, F.; Cowan, T. E.; Grieger, M.; Hensel, T.; Junghans, A. R.; Ludwig, F.; Müller, S. E.; Rimarzig, B.; Reinicke, S.; Schulz, S.; Schwengner, R.; Stöckel, K.; Szücs, T.; Takács, M. P.; Wagner, A.; Wagner, L.; Zuber, K.

Low-background experiments with stable ion beams are an important tool in order to put the understanding of stellar hydrogen, helium, and carbon burning on a solid experimental foundation. The pioneering work in this regard has been done by the LUNA collaboration at Gran Sasso, using a 0.4 MV accelerator. In the present contribution, the status of the project for a higher-energy underground accelerator is reviewed. Two tunnels of the Felsenkeller underground site in Dresden, Germany, are currently being refurbished for the installation of a 5 MV high-current Pelletron accelerator. Construction work is on schedule and expected to complete in August 2017. The accelerator will provide intense, 50μA, beams of 1H+, 4He+, and 12C+ ions, enabling research on astrophysically relevant nuclear reactions with unprecedented sensitivity.

Keywords: Felsenkeller; underground nuclear astrophysics

  • Open Access Logo Contribution to proceedings
    Nuclei in the Cosmos XVI, 20.-24.06.2016, Niigata, Japan
    Proceedings of the 14th International Symposium on Nuclei in the Cosmos (NIC2016) JPS Conf. Proc. 14, 021106 (2017), 021106
    DOI: 10.7566/JPSCP.14.021106
  • Contribution to WWW
    arXiv Preprint-Server: http://arxiv.org/pdf/1609.05819v1.pdf

Permalink: https://www.hzdr.de/publications/Publ-24079
Publ.-Id: 24079


The surface reactions of U(VI) on γ-Al2O3 In situ spectroscopic evaluation of the transition from sorption complexation to surface precipitation

Müller, K.; Foerstendorf, H.; Rossberg, A.

Aluminates, representing an essential component of clay minerals, play a decisive role in regulating the mobility of contaminants in rock and soil formations, in particu-lar due to their tendency to form coatings on mineral surfaces [1].
In this work, U(VI) sorption on γ-Al2O3 is comparatively investigated using in situ vibrational and X-ray absorption spectroscopy. The focus was set to micromolar U(VI) concentrations and a variety of environmentally relevant sorption parameters in order to resolve discrepancies reported earlier [2-4].
Time-resolved (TR) IR spectroscopic sorption experiments at the alumina-water in-terface evidence the formation of three different species as a function of surface loading (c.f. Fig.): a monomeric carbonate complex, an oligomeric surface complex and a surface precipitate. These results are confirmed by IR experiments performed at different flow rates, pH values, ionic strengths, U(VI) concentrations, and in inert gas atmosphere. Results of EXAFS experiments of batch samples are consistent to these findings [5].

  • Poster
    3rd International Workshop on Advanced Techniques in Actinide Spectroscopy, 07.-10.11.2016, Richland, USA

Permalink: https://www.hzdr.de/publications/Publ-24078
Publ.-Id: 24078


High resolution x-ray Thomson scattering measurements from cryogenic hydrogen jets using the linac coherent light source

Fletcher, L. B.; Zastrau, U. B.; Galtier, E. A.; Gamboa, E. J. A.; Goede, S. A.; Schumaker, W. A.; Ravasio, A. A.; Gauthier, M. A.; Macdonald, M. J. A.; Chen, Z. A.; Granados, E. A.; Lee, H. J. A.; Fry, A. A.; Kim, J. B. A.; Roedel, C. A.; Mishra, R. A.; Pelka, A. F.; Kraus, D.; Barbrel, B. G.; Döppner, T. H.; Glenzer, S. H. A.

We present the first spectrally resolved measurements of x-rays scattered from cryogenic hydrogenjets in the single photon counting limit. The 120 Hz capabilities of the LCLS, together with a novelhydrogen jet design [J. B. Kimet al., Rev. Sci. Instrum. (these proceedings)], allow for the ability torecord a near background free spectrum. Such high-dynamic-range x-ray scattering measurementsenable a platform to study ultra-fast, laser-driven, heating dynamics of hydrogen plasmas. Thismeasurement has been achieved using two highly annealed pyrolytic graphite crystal spectrometers tospectrally resolve 5.5 keV x-rays elastically and inelastically scattered from cryogenic hydrogen andfocused on Cornell-SLAC pixel array detectors [S. Herrmannet al., Nucl. Instrum. Methods Phys.Res., Sect. A718, 550 (2013)].

Permalink: https://www.hzdr.de/publications/Publ-24077
Publ.-Id: 24077


Phase Shift and Reflection of Spin Waves at Magnetic Domain Walls in Thin Films

Körber, L.; Wagner, K.; Lindner, J.; Fassbender, J.; Schultheiß, H.

Investigating the transmission of magneto-static surface waves through 180° Néel walls using micromagnetic simulations.

Keywords: spin waves; phase shift; micromagnetic simulation; reflection; domain wall

  • Poster
    Spin, Waves and Interactions, 31.08.-02.09.2016, Greifswald, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24076
Publ.-Id: 24076


Magnetic domain walls as reconfigurable spin-wave nano-channels

Wagner, K.; Kakay, A.; Schultheiß, K.; Henschke, A.; Sebastian, T.; Lindner, J.; Fassbender, J.; Schultheiß, H.

Use of magnetic domains as nano channels for spin wave propagation

  • Lecture (Conference)
    Spin, Waves and Interaction, 31.08.-02.09.2016, Greifswald, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24075
Publ.-Id: 24075


Modern Measurement Methods of Brillouin Light Scattering

Osten, J.; Schultheiß, H.; Wagner, K.; Körber, L.; Wehrmann, F.; Hula, T.

Explanation of different measurement methods of BLS: phase, time, wavevector, frequency and spacial resolved

Keywords: BLS

  • Poster
    Spins, Waves and Interactions, 31.08.-02.09.2016, Greifswald, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24074
Publ.-Id: 24074


The role of automated mineralogy in geometallurgy: two case studies

Birtel, S.; Kern, M.; Heinig, T.; Gutzmer, J.

SEM-based automated mineralogy is well established as a key tool in geometallurgical assessments, as it provides quantitative data on mineralogy and microstructure. It is widely used to improve the recovery of those constituents (ore minerals) that contain the major products (metals) of existing or planned mining operations and processing plants. Less common, however, is the use of automated mineralogy to study the presence and distribution of possible by-product or even penalty constituents. In this contribution, we present the results of two case studies that reveal the benefit of application of automated mineralogy to define beneficiation potential for economically significant by-products in large operations. Systematic plant surveys were carried out at one fluorite mine and one porphyry copper deposit. For the fluorite deposit, the plant survey was combined with an assessment of the undisturbed feed material.
Case study 1: For the recovery of REE as a potential by-product in a fluorite mine, blocks were sampled before mining, the material was subsequently followed through the flotation plant, sampling all crucial steps. Samples illustrate that the material from the tailings stream, i.e., the material being considered as waste, is strongly enriched in the two dominant REE-bearing minerals contained in the ore: monazite and xenotime. These REE-bearing minerals are well liberated, thus leading to the conclusion that it may be feasible to produce a REE concentrate as a by-product by only slight modification of the current flow sheet.
Case study 2 focused on the improvement of Mo recovery of a world-class porphyry copper deposit. Samples were taken systematically from the flotation plant also considering residence times. Particular flotation stages accounting for significant Mo losses due to bad molybenite liberation were identified. Lab-scale flotation tests were carried out to improve Mo recovery. Results indicate a clear influence of grain shape, grain size and residence time on the recovery.

Keywords: automated mineralogy; by products; REE; process optimization

  • Contribution to proceedings
    3rd international Seminar on geometallurgy, Editors: Regina Baumgartner, Adam Johnston, 11.-13.12.2016, Lima, Peru
    GEOMET 2016, 3rd International Seminar on Geometallurgy, Santiago, Chile: Gecamin, 978-956-9393-68-6, 58-59
  • Lecture (Conference)
    3rd international Seminar on Geometallurgy, 11.-13.12.2016, Lima, Peru

Permalink: https://www.hzdr.de/publications/Publ-24073
Publ.-Id: 24073


An Electrochemical and Photoelectron Spectroscopy Study of a Low Temperature Liquid Metal Battery Based on an Ionic Liquid Electrolyte

Lalau, C.-C.; Dimitrova, A.; Himmerlich, M.; Ispas, A.; Weier, T.; Krischok, S.; Bund, A.

We report the design of a low-temperature liquid metal battery (LMB). Li and Ga as the negative and positive electrode, respectively, are used in combination with a room temperature ionic liquid as an electrolyte. 1 mol/L lithium bis(trifluoromethylsulfonyl)imide (Li[TFSI]) in 1-butyl-1-methylpyrrolidinium bis (trifluoromethylsulfonyl)imide ([BMP][TFSI]) is chosen as electrolyte. The battery operates at 220 °C which is a relatively low temperature for a LMB and shows good electrochemical performance at low current density. The cells were cycled for more than 600 h and achieved a round-trip Coulombic efficiency close to 100% and an average voltage efficiency of 66% resulting in an overall energy efficiency of 65%. At higher current densities, however, the system showed up to 75% irreversible capacity loss after three cycles. To understand the origin of this strong deterioration, we characterized the surface and the bulk properties of the Ga cathode using X-ray Photoelectron Spectroscopy. Especially at higher current densities a decomposition of the electrolyte was found. The chemical changes that occurred and the elemental distribution at the Ga cathode are analyzed based on XPS measurements at different stages of the battery charge/discharge cycling.

Keywords: liquid metal battery; ionic liquids

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Permalink: https://www.hzdr.de/publications/Publ-24072
Publ.-Id: 24072


Depth profiled ion implantation doping using an energy filter based on Si membrane

Akhmadaliev, S.; Krippendorf, F.; Bezerra, E. B. D.; von Borany, J.; Csato, C.; Rüb, M.; Zowalla, A.

An important step during fabrication of modern semiconductor devices is doping of the material by means of ion implantation. For some applications in power or optoelectronics also special non-Gaussian shaped buried implantation profiles are required. The conventional way to create accurate shaped doping profiles by using multiple implantations of mono-energetic ions with subsequent thermal annealing is quite time consuming. An alternative approach is the application of an ion beam exhibiting the desired energy and flux distribution. For applications of less accuracy metallic foils with various thicknesses have been applied as energy filters (EF). A relatively new method is a filter made of micro-mechanically manufactured silicon membranes with modulated thickness which changes the energy of the initially mono-energetic ion beam from an accelerator and converts quasi-Gaussian shaped implantation profile into the specified one [1]. An example of such an EF shown in Fig.1 which can be used for homogeneous buried box-like doping profiles covering a doping depth of several micrometers. The ions with equal energies Eo will have different energies after the filter depending on the local thickness of the material and the resulting ion ranges are in different depth in the substrate.
There are some challenges by using this technique. Besides the reliable and reproducible fabrication of the energy filter, aspects like thermal stability, ion beam sputtering or geometrical constrains have to be considered. Another difficulty of this method is the monitoring of the ion flux after the EF in order to control the implanted dose. A Faraday cup setup cannot be directly applied because of the recharging of the ions by the EF and their undefined charge state after the filter, so the process needs precise calibration for each ion type and energy. A Si EF fabricated at Ernst-Abbe Hochschule was calibrated and taken for the doping of 4” wafers using the wafer-handler with the mechanical scanning system at 3 MV tandem accelerator at HZDR [2]. The experiments deliver promising results and demonstrate the possibility of application this method for doping purposes.
References
[1] M. Rüb, DE Patent App, 2012, DE102011075350 A1
[2] C. Csato et al., Nucl. Instr. Meth. B 365 (2015) 182

Keywords: SiC; energy filter; ion implantation

  • Lecture (Conference)
    ECAART-12, The 12th European Conference on Accelerator in Applied Research and Technology, 03.-08.07.2016, Jyväskylä, Finnland

Permalink: https://www.hzdr.de/publications/Publ-24071
Publ.-Id: 24071


Kommissionierung von Bestrahlungsplanungsalgorithmen und -systemen mittels eines Systemtestphantoms

Geyer, P.; Schellhammer, S.; Feiks, S.; Debbih, Y. D.

Fragestellungen: Die Empfehlungen der Strahlenschutzkommission „Physikalisch-technische Qualitätssicherung in der Strahlentherapie – Vorschläge zur Prüfung des gesamten Behandlungssystems“ aus dem Jahr 2010 fanden inzwischen ihren Eingang in die novellierten Fassungen der Strahlenschutzverordnung und der Richtlinie Strahlenschutz in der Medizin. Allerdings gibt es bisher eine Vorgaben zum Umfang zu prüfender Parameter, deren Toleranzen und für entsprechende Phantome. Ein solches Phantom für den Test des Gesamtsystems sollte auch für Teilaufgaben im Rahmen der Kommissionierung von Bestrahlungsplanungssystemen geeignet sein.

Material und Methoden: Das in der Klinik entwickelte und gefertigte Phantom ist modular aufgebaut (Abb. 1). Ein PMMA-Grundkörper enthält Strukturen für geometrische Messungen und beinhaltet vier quaderförmige Inhomogenitäten (Lungenmaterial Gammex 455, RW-3, Wasser und PMMA) mit jeweils dem Querschnitt 5 x 5 cm2. Mittels Bohrungen können Dosismessungen im Grundkörper und den Inhomogenitäten erfolgen. Das Phantom wurde mit einem CT-Thoraxprotokoll (130 kV, 90 eff. mAs) am Somatom Emotion (Siemens) mit 3 mm Schichtdicke untersucht. Die Bestrahlungsplanung erfolgte einmal im OTP Masterplan (Version 4.3.0.410, Elekta) mit dem bereits früher implementierten Collapsed-Cone-Algorithmus (Dichtematrix 1x1x1 mm3, Dosismatrix 1x2x1 mm3). Parallel wurde im Rahmen der Kommissionierung des Monte-Carlo-Algorithmus im IPlan RTDose (Version 4.1.4, BrainLab) geplant (Varianz 1 %, dose to water, accuracy optimiert, 2,4x2,4x2,0 mm3 Ortsauflösung). Berechnet wurden rechteckige Felder von anterior der Abmessungen 2x30 cm2, 4x30 cm2 und 5x30 cm2 für jeweils X6 und X15 des Oncor-160 (Siemens), die sich über alle Inhomogenitäten erstrecken. Die Messungen erfolgten mit den Ionisationskammern Semiflex 31006 (0,3 cm3) und PinPoint 31003 (0,015 cm3, beide PTW). Die Ankopplung der PinPoint an die Semiflex, sowie erforderliche Korrekturen erfolgten gemäß den DIN 6809-8 (Entwurf 03/2014) und 6800-2 (2008). Verglichen werden die in den zwei Planungssystemen berechneten Dosiswerte mit den gemessenen Dosen in den Inhomogenitäten und im PMMA-Grundkörper (Isozentrumsmesspunkt), wobei die Feldbreiten 4 und 5 cm mit der Semiflex und die 2-cm-breiten Felder mit der PinPoint gemessen wurden. Die PinPoint-Messungen im Lungeneinsatz wurden bezüglich des abweichenden Materials des Differenzvolumens zur Semiflex korrigiert.
Hier nicht dargestellt werden die Ergebnisse für eine Vielzahl anderer Felder und Berechnungen von Dosis-Volumen-Histogrammen
für die konturierten inhomogenen Einsätze.

Ergebnisse: Für Messpunkte in der Isozentrumsebene (alle in Abb.2 oder 3 nicht mit fokusnah oder fokusfern bezeichneten Punkte) weichen alle gemessenen und berechneten Dosiswerte maximal um 1 % voneinander ab, eine Ausnahme bildet das Lungenmaterial, wo feldgrößen-, energieabhängig und abhängig vom Planungssystem bis zu 5 % Abweichungen gefunden wurden (Abb. 2, 3). Vor allem für einen fokusfernen Messpunkt im RW-3 wird für das schmalste Feld die Dosis von beiden Planungssystemen um bis zu 4 % überschätzt. Ursachen hierfür können Artefakte durch Metallmarker im Phantom sein. Die gefundenen Dosisabweichungen in der Isozentrumsebene (außer für Lunge) liegen innerhalb des Messunsicherheitsbudgets von ≤ 2 %.
Für die (nahezu) Punktdosismessungen zeigte sich kein Genauigkeitsvorteil für einen der zwei Rechenalgorithmen bzw. eines der Planungssysteme.

Zusammenfassung: Das verwendete Phantom ermöglicht die Bestimmung von Datensätzen, die parallel für die Kommissionierung von Planungssystemen und den Systemtest verwendet werden können. Dabei sind auch Bewertungen in Grenzbereichen des Anwendungsspektrums, hier z.B. zur Applikation kleiner Felder in Inhomogenitäten möglich. Die gefundenen Abweichungen bilden die Grundlage für die Toleranzbereiche in unserem Systemtest.

  • Lecture (Conference)
    47. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP) e. V., 07.-10.09.2016, Würzburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24070
Publ.-Id: 24070


Resistive switching behavior in single crystal SrTiO3 annealed by laser

Pan, X.; Shuai, Y.; Wu, C.; Luo, W.; Sun, X.; Yuan, Y.; Zhou, S.; Ou, X.; Zhang, W.

Single crystal SrTiO3 (STO) wafers were annealed by XeCl laser (λ = 308 nm) with different fluences of 0.4 J/cm2, 0.6 J/cm2 and 0.8 J/cm2, respectively. Ti/Pt electrodes were sputtered on the surface of STO wafer to form co-planar capacitor-like structures of Pt/Ti/STO/Ti/Pt. Current-Voltage measurements show that the leakage current is enhanced by increasing laser fluence. Resistive switching behavior is only observed in the sample annealed by laser with relatively high fluence after an electro-forming process. The X-ray photoelectron spectroscopy measurements indicate that the amount of oxygen vacancies increases with the increase of laser fluence. This work indicates resistive switching appears when enough oxygen vacancies are generated by the laser, which form conductive filaments under an external electric field.

Keywords: Resistive switching; Laser annealing; SrTiO3

Permalink: https://www.hzdr.de/publications/Publ-24069
Publ.-Id: 24069


Probing chemical bonding in uranium dioxide by means of high-resolution x-ray absorption spectroscopy

Butorin, S.; Modin, A.; Vegelius, J.; Kvashnina, K.; Shuh, D.

A systematic x-ray absorption study at the U 3d, 4d and 4f edges of UO2 was performed and the data were analyzed within framework of the Anderson impurity model. By applying the highenergy-resolution uorescence-detection (HERFD) mode of x-ray absorption spectroscopy (XAS) at the U 3d3/2 edge and by doing the XAS measurements at the shallower U 4f levels, fine details of the XAS spectra were resolved due to reduced core-hole lifetime broadening. These allowed for more efficient analysis of the electronic structure at the U sites and characterization of the chemical bonding and degree of the 5f localization in UO2. The results support the covalent character of UO2 and refute the claims about rather ionic bonding in this compound, made in some publications.

Permalink: https://www.hzdr.de/publications/Publ-24068
Publ.-Id: 24068


Direct measurement of low-energy 22Ne(p,γ)23Na resonances

Depalo, R.; Cavanna, F.; Aliotta, M.; Anders, M.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Bruno, C. G.; Caciolli, A.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; Gyürky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.

Background: The 22Ne(p,γ)23Na reaction is the most uncertain process in the neon-sodium cycle of hydrogen burning. At temperatures relevant for nucleosynthesis in asymptotic giant branch stars and classical novae, its uncertainty is mainly due to a large number of predicted but hitherto unobserved resonances at low energy.
Purpose: A new direct study of low energy 22Ne(p,γ)23Na resonances has been performed at the Laboratory for Underground Nuclear Astrophysics (LUNA), in the Gran Sasso National Laboratory, Italy.
Method: The proton capture on 22Ne was investigated in direct kinematics, delivering an intense proton beam to a 22Ne gas target. γ rays were detected with two high-purity germanium detectors enclosed in a copper and lead shielding suppressing environmental radioactivity.
Results: Three resonances at 156.2 keV (ωγ = (1.48 ± 0.10) · 10−7 eV), 189.5 keV (ωγ = (1.87±0.06)·10−6 eV) and 259.7 keV (ωγ = (6.89±0.16)·10−6 eV) proton beam energy, respec- tively, have been observed for the first time. For the levels at Ex = 8943.5, 8975.3, and 9042.4 keV excitation energy corresponding to the new resonances, the γ-decay branching ratios have been precisely measured. Three additional, tentative resonances at 71, 105 and 215 keV proton beam energy, respectively, were not observed here. For the strengths of these resonances, experimental upper limits have been derived that are significantly more stringent than the upper limits reported in the literature.
Conclusions: Based on the present experimental data and also previous literature data, an updated thermonuclear reaction rate is provided in tabular and parametric form. The new reaction rate is significantly higher than previous evaluations at temperatures of 0.08-0.3 GK.

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Permalink: https://www.hzdr.de/publications/Publ-24067
Publ.-Id: 24067


Origin of stardust unveiled by the new LUNA rate of the 17O(p,α)14N reaction

Lugaro, M.; Karakas, A. I.; Bruno, C. G.; Aliotta, M.; Nittler, L. R.; Bemmerer, D.; Best, A.; Boeltzig, A.; Broggini, C.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Formicola, A.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gyürky, C. G. G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Scott, D. A.; Straniero, O.; Strieder, F.; Szücs, T.; Takács, M. P.; Trezzi, D.

Stardust grains recovered from meteorites provide high-precision snapshots of the isotopic compositions resulting from nuclear reactions in the stars in which they formed. Establishing their stellar sites of origin, however, often proves difficult. One long-standing problem is that a large fraction of meteoritic stardust is predicted to have originated from the late evolutionary phase of stars with initial mass between roughly 4 and 8 solar masses, however, no grains have been found with an isotopic composition that matches that expected in these stars. This problem points to serious gaps in our understanding of the lifecycle of stars and dust in the Galaxy. Here we show that the new, increased rate of the 17O + p → 14N + α nuclear reaction, based on a recent underground experiment, produces 17O/16O isotopic ratios that match those observed in a population of stardust grains, provided that the burning occurs at relatively high temperatures (60–80 million K). These are the temperatures achieved at the base of the convective envelope during the late evolutionary phase of 4 to 8 solar mass stars, which reveals them as the site of origin of the grains. This result provides the first direct evidence that these stars contributed to the dust inventory from which the Solar System formed.

Permalink: https://www.hzdr.de/publications/Publ-24066
Publ.-Id: 24066


Scalable, multi-GPU photon tracing for the interaction of X-Rays with solid density plasmas

Grund, A.; Huebl, A.; Kluge, T.; Widera, R.; Fortmann-Grote, C.; Bussmann, M.

We present the scientific workflow using our performance portable, open source, 3D3V particle-in-cell (PIC) code PIConGPU and its X-Ray tracing prototype ParaTAXIS to model the interaction of XFEL type X-Rays with solid density plasmas. With an open and modern software environment, our infrastructure is already suited for the largest available supercomputers today and key numerical and methodical challenges have been solved towards first simulations of upcoming pump-probe experiments at the European XFEL.

Keywords: EUCALL; SIMEX; XFEL; GPU; photon beamline; ParaTAXIS; PIConGPU; x-ray scattering

  • Poster
    EUCALL Annual Meeting 2016, 31.08.-02.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24065
Publ.-Id: 24065


Plasmas, Photons, Open Standards: PIConGPU meets simex_platform through openPMD

Huebl, A.; Kluge, T.; Grund, A.; Fortmann-Grote, C.; Widera, R.; Bussmann, M.

Technische Aspekte des Datenaustauschs SIMEX XFEL Wavefronts -> XRT/PIConGPU via openPMD, die wir zusammen erstellt haben und aktueller Stand der Photon-Plasma Streuung der dann anschließenden HPC Simulation auf unserer Seite.

Topics:
- SIMEX Platform: Short intro functional parts, PIConGPU = interaction
- SIMEX Platform: Wavefronts to Photon Picture
- openPMD: why, what, how
- status XRT (PIConGPU photon scattering code prototype)
- typical HPC size of a PIConGPU simulation for dense targets
- continuous integration (simex platform & PIConGPU)
- maybe some future ideas such as successful docker-ization of
PIConGPU for our "relatively fixed" beamline

Keywords: PIConGPU; GPU; EUCALL; SIMEX; openPMD; XFEL

  • Lecture (Conference)
    EUCALL Annual Meeting, 31.08.-02.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24064
Publ.-Id: 24064


Induced conductivity in sol-gel ZnO films by passivation or elimination of Zn vacancies

Winarski, D. J.; Anwand, W.; Wagner, A.; Saadatkia, P.; Selim, F. A.; Allen, M.; Wenner, B.; Leedy, K.; Allen, J.; Tetlak, S.; Look, D. C.

Undoped and Ga- and Al- doped ZnO films were synthesized using sol-gel and spin coating methods and characterized by X-ray diffraction, high-resolution scanning electron microscopy (SEM), optical spectroscopy and Hall-effect measurements. SEM measurements reveal an average grain size of 20 nm and distinct individual layer structure. Measurable conductivity was not detected in the unprocessed films; however, annealing in hydrogen or zinc environment induced significant conductivity (~10^-2 Ohm cm) in most films. Positron annihilation spectroscopy measurements provided strong evidence that the significant enhancement in conductivity was due to hydrogen passivation of Zn vacancy related defects or elimination of Zn vacancies by Zn interstitials which suppress their role as deep acceptors. Hydrogen passivation of cation vacancies is shown to play an important role in tuning the electrical conductivity of ZnO, similar to its role in passivation of defects at the Si/SiO2 interface that has been essential for the successful development of complementary metal–oxide–semiconductor (CMOS) devices. By comparison with hydrogen effect on other oxides, we suggest that hydrogen may play a universal role in oxides passivating cation vacancies and modifying their electronic properties.

Keywords: ZnO conductivity sol-gel hydrogen passivation defects positron annihilation

Permalink: https://www.hzdr.de/publications/Publ-24063
Publ.-Id: 24063


Magnetic functionalities for flexible interactive electronics

Makarov, D.

The flourishing and eagerness of portable consumer electronics necessitates functional elements to be lightweight, flexible, and even wearable [1,2]. Next generation flexible appliances aim to become fully autonomous and will require ultra-thin and flexible navigation modules, body tracking and relative position monitoring systems. Such devices fulfill the needs of soft robotics [3], functional medical implants [4] as well as epidermal [5], imperceptible [6] and transient [7] electronics. Key building blocks of navigation and position tracking devices are the magnetic field sensors.
We developed the technology platform allowing us to fabricate high-performance shapeable, namely, flexible [8-10], printable [11-13], stretchable [14-16] and even imperceptible [17] magnetic sensorics. The technology relies on smart combination of thin inorganic functional elements prepared directly on flexible or elastomeric supports. The unique mechanical properties open up new application potentials for smart skins, allowing to equip the recipient with a “sixth sense” providing new experiences in sensing and manipulating the objects of the surrounding us physical as well as digital world [10,17].
Combining large-area printable and flexible electronics paves the way towards commercializing the active intelligent packaging, post cards, books or promotional materials that communicate with the environment and provide the respond to the customer. Realization of this vision requires fabrication of printable electronic components that are flexible and can change their properties in the field of a permanent magnet [12]. For this concept, we fabricated high performance magnetic field sensors relying on the giant magnetoresistive (GMR) effect, which are printed at pre-defined locations on flexible circuitry and remain fully operational over a temperature range from -10°C up to +95°C, well beyond the requirements for consumer electronics [13]. Our work potentially enables commercial use of high performance magneto-sensitive elements in conventional printable electronic industry, which, although highly demanded, had not yet been possible.
In this talk, I will review the recent advances in the field of shapeable magnetic sensorics and emergent applications of this novel technology.

Keywords: flexible electronics; magnetic field sensorics

  • Invited lecture (Conferences)
    Special seminar, Institute of Physics, Johannes Gutenberg-Universität Mainz, 29.08.2016, Mainz, Germany

Permalink: https://www.hzdr.de/publications/Publ-24062
Publ.-Id: 24062


Evidence of trivalent Am substitution into U3O8

Caisso, M.; Roussel, P.; Den Auwer, C.; Picart, S.; Hennig, C.; Scheinost, A. C.; Delahaye, T.; Ayral, A.

U3O8 is considered to be the most stable phase for uranium oxide. Its structural properties must be accurately understood in order to foresee and manage aspects such as its leaching behavior when spent nuclear fuel is stored in an oxidative environment. Moreover, as fuel irradiation causes the formation of fission products and activation products such as plutonium and minor actinides, it is probable that U3O8 will be mixed with other chemical elements under real conditions of oxidation. The storage issue can be extended to americium transmutation, where the irradiated compounds are mixed oxides composed of uranium and americium. This study thus focused on determining the structural properties of a solid solution containing uranium and trivalent americium (U/Am ratio = 90/10), and synthetized so as to obtain conventional U3O8 oxide. This paper presents the possibility of combining trivalent americium with uranium in a U3O8 mixed oxide for the first time, despite the high valence and atomic ratio differences, and proposes novel structural arrangements. XRD measurements reveal americium substitution in U3O8 uranium cationic sites, leading to phase transformation into a U3O8 high temperature structure and general lattice swelling. XANES and EXAFS experiments highlight an excess of U+VI organized in uranyl units as the main consequence of accommodation.

Keywords: americium; transmutation; U3O8

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Permalink: https://www.hzdr.de/publications/Publ-24061
Publ.-Id: 24061


In-situ X-ray observations of dendritic solidification under the influence of natural and forced convection

Eckert, S.; Shevchenko, N.; Kepplinger, O.; Sokolova, O.

The directional solidification of Ga–25wt%In alloys within a Hele-Shaw cell was investigated by means of X-ray radioscopy. This diagnostic technique offers a visual access to opaque metal alloys and enables a basic, intuitional understanding of the complex interplay between melt flow and dendritic growth. Natural convection occurs during a bottom up solidification because lighter solute is rejected at the solid-liquid interface leading to an unstable density stratification. Forced convection was produced by a rotating wheel with two parallel disks containing at their inner sides a set of permanent NdFeB magnets with alternating polarization. The direction of forced melt flow is almost horizontal at the solidification front whereas local flow velocities in the range between 0.1 and 1.0 mm/s were achieved by controlling the rotation speed of the magnetic wheel.
Melt flow induces various effects on the grain morphology primarily caused by the convective transport of solute. Our observations show a facilitation of the growth of primary trunks or lateral branches, suppression of side branching, dendrite remelting and fragmentation. The manifestation of all phenomena depends on the dendrite orientation, local direction and intensity of the flow.
The forced flow eliminates the solutal plumes and damps the local fluctuations of solute concentration. It provokes a preferential growth of the secondary arms at the upstream side of the primary dendrite arms, whereas the high solute concentration at the downstream side of the dendrites can inhibit the formation of secondary branches completely. Moreover, the flow changes the inclination angle of the dendrites and the angle between primary trunks and secondary arms.

Keywords: solidification; melt flow; dendritic growth; fragmentation; segregation

  • Invited lecture (Conferences)
    16th International Conference on Liquid and Amorphous Metals (LAM-16), 05.-09.09.2016, Bonn-Bad Godesberg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24060
Publ.-Id: 24060


Reactive transport modelling based on velocity fields obtained on drill core scale

Lippmann-Pipke, J.; Karimzadeh, L.; Blanc, P.; Eichelbaum, S.; Schymura, S.; Rogóż, T.; Frühwirt, K.; Kulenkampff, J.

The objective of the EU project BioMOre is the development of new technological concepts for in situ recovering metals from deep European Kupferschiefer deposits using controlled stimulation of pre-existing fractures in combination with in-situ bioleaching. Considerable parts of the project are leaching experiments on lab scale and on small field scale at a selected location in an existing copper mine, as well as the related reactive transport odelling tasks including the required backcoupling from chemical reactions on the hydrodynamics as well as the upscaling. These tasks shall assist in the optimization of the bio-leaching efficiency, stimulating processes, as well as the environmental impact and sustainability assessment. Here we introduce our most recent technical advancement. It allows us to accomplish two tasks in one line of action: The extraction of effective hydrodynamic parameters in 3D for downstram modelling, and the upscaling from molecular process observations to reactive transport simulations on drill core scale.
For more than a decade a spatiotemporal visualization tool for transport process observations in dense material by means of PET (positron emission tomography) was developed [1-5]. Such quantitative GeoPET images are xceptionally sensitive to displacements of pico molar tracer quantities detected within 1 mm grids on laboratory/drill core scale. Now we reached a strategic milestone: A custom made image analysis algorithm is capable of quantitatively extracting velocity and porosity fields from such GeoPET image time series, even if the 4D image information includes discontinuous flow patterns (due to bottle neck effect related detection limits) and localized image artifacts. We present our approach with the aid of a) the data set with which the algorithm was validated, and b) provide an outlook for its application in the context of this EU project: the bio-leaching of Kupferschiefer.
From an observed fluid flow process in a dense core material by means of GeoPET (Fig. 1 left) the effective porosity and velocity field is extracted by our image analyis algorithm and this data is used in a forward numerical transport simulation and compared with the original fluid flow process (Fig. 1 right). Next steps will be the evaluation of non-reactive flow process observations in fractured calciferous sandstone from the Kupferschiefer ore deposit (Fig. 2), and the respective porosity and velocity field extraction for 3D reactive transport modelling in fracture and porous matrix by means of iCP [6] - an interface coupling the finite element based code COMSOL Multiphysics® with the geochemical code PhreeqC.

  • Lecture (Conference)
    IMWA 2016 - Annual Conference of the International Mine Water Association, 14.07.2016, Leipzig, Germany
  • Contribution to proceedings
    IMWA 2016 - Annual Conference of the International Mine Water Association, 14.07.2016, Leipzig, Germany
    Mining Meets Water – Conflicts and Solutions, Freiberg: Medienzentrum of TU Bergakademie Freiberg, 978-3-86012-533-5, 1219-1220

Permalink: https://www.hzdr.de/publications/Publ-24059
Publ.-Id: 24059


Analysis of the characteristics of hot particles related to environmental fate and interaction with living organisms

Johansen, M. P.; Child, D. P.; Collins, R. N.; Hotchkis, M. A. C.; Howell, N. A.; Payne, T. E.; Mokhber-Shahin, L.; Ikeda-Ohno, A.

The radiological residues at the former British weapons testing sites at Maralinga, Emu and the Monte Bello Islands often occur in particulate form (so called hot particles). Large numbers of these particles were emitted from nuclear and non-nuclear tests. For example each square meter in a plume that extends for tens of kilometres at the Taranaki site (Maralinga) can contain more than 3000 readily identifiable particles. The physical and chemical characteristics of these particles affect their mobility and availability for uptake into living organisms. When they contain long-lived radionuclides (e.g. 239Pu) these particles may slowly weather, and thus provide a persistent source of ionic forms, or smaller particles, for many thousands of years.

Here we present a status on a range of methods being used at ANSTO to evaluate the physical and chemical characteristics of particles gathered from Australian sites. Methods include gamma spectrometry, autoradiography, high sensitivity Accelerator Mass Spectrometry analysis (AMS), leaching studies, and synchrotron-based X-ray fluorescence microscopy/spectroscopy. We focus on some of the practical issues involved when gathering and working with hot particles, as well as challenges in determining speciation and its influence on radioecological outcomes. We discuss data gaps and recommendations for current and future use of analysis methods in radioecological studies in Australia and the wider international community.

Keywords: Actinides; plutonium; environmental fate; bioavailability; nuclear weapons tests; Australia

  • Lecture (Conference)
    The South Pacific Environmental Radioactivity Association (SPERA) Conference 2016, 07.09.2016, Sanur, Indonesia

Permalink: https://www.hzdr.de/publications/Publ-24058
Publ.-Id: 24058


Improved direct measurement of the 64.5 keV resonance strength in the 17O(p,alpha)14N reaction at LUNA

Bruno, C. G.; Scott, D. A.; Aliotta, M.; Formicola, A.; Best, A.; Boeltzig, A.; Bemmerer, D.; Broggini, C.; Caciolli, A.; Cavanna, F.; Ciani, G. F.; Corvisiero, P.; Davinson, T.; Depalo, R.; Di Leva, A.; Elekes, Z.; Ferraro, F.; Fülöp, Z.; Gervino, G.; Guglielmetti, A.; Gustavino, C.; GyÜrky, G.; Imbriani, G.; Junker, M.; Menegazzo, R.; Mossa, V.; Pantaleo, F. R.; Piatti, D.; Prati, P.; Somorjai, E.; Straniero, O.; Strieder, F.; SzÜcs, T.; Takács, M. P.; Trezzi, D.

The 17O(p,α)14N reaction plays a key role in various astrophysical scenarios, from asymptotic giant branch stars to classical novae. It affects the synthesis of rare isotopes such as 17O and 18F, which can provide constraints on astrophysical models. A new direct determination of the ER = 64.5 keV resonance strength performed at the Laboratory for Underground Nuclear Astrophysics accelerator has led to the most accurate value to date, ωγ = 10.0 ± 1.4stat ± 0.7syst neV, thanks to a significant background reduction underground. The (bare) proton partial width of the corresponding state at Ex = 5672 keV in 18F is Γp = 35±5stat ±3syst neV. This width is about a factor of 2 higher than previously estimated thus leading to a factor of 2 increase in the 17O(p,α)14N reaction rate at astrophysical temperatures relevant to shell hydrogen-burning in red giant and asymptotic giant branch stars. The new rate implies lower 17O/16O ratios, with important implications on the interpretation of astrophysical observables from these stars.

Permalink: https://www.hzdr.de/publications/Publ-24057
Publ.-Id: 24057


A mineral liberation study of grain boundary fracture based on measurements of the surface exposure after milling

Leißner, T.; Hoang, D.; Rudolph, M.; Heinig, T.; Bachmann, K.; Gutzmer, J.; Schubert, H.; Peuker, U. A.

Minerals can be liberated by random fracture of particles into smaller fragments or by detachment along phase boundaries. These two mechanisms represent borderline cases. When ores get comminuted the liberation of minerals is achieved to some extent by both mechanisms. This article describes a method to determine the extent of transgranular and intergranular fracture based on 2-dimensional analysis of surface exposure of minerals.
The approach uses the unbiased surface information like of phase specific surface area (PSSA), phase specific free surface (PSFS) and phase specific locked surface (PSLS) of minerals and their change with comminution. The parameters are discussed related to the normalized grain size, which is the ratio of mineral grain size in the product to mineral grain size in the unbroken material. Finally, the amount of transgranular and intergranular fracture on surface exposure can be calculated using the phase specific surface parameters.
A sedimentary rock (apatite ore), an igneous rock (nepheline-syenite) and an artificial material (copper slags) were ground to different fineness. Based on the mineral liberation analysis (MLA) of feed and products, the extent of phase boundary fracture on the surface exposure of the minerals is studied.

Keywords: Mineral liberation Analysis; preferential breakage; transgranular fracture; intergranular fracture; random fracture; grain boundary fracture

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Permalink: https://www.hzdr.de/publications/Publ-24056
Publ.-Id: 24056


JEMS2016: Magnetism in curved geometries

Makarov, D.

While conventionally magnetic films and structures are fabricated on flat surfaces, the topology of curved surfaces has only recently started to be explored and leads to new fundamental physics as well as applied device ideas. In particular, novel effects occur when the magnetization is modulated by curvature providing a new degree of freedom that leads to new magnetization configurations (see for instance [1,2]) and is predicted to have major implications on the spin dynamics due to topological constraints for instance in circular tubes and rolls [3].
Advances in this novel field solely rely on the understanding of the fundamentals behind the modifications of magnetic responses of 3D-curved magnetic thin films. The lack of an inversion symmetry and the emergence of a curvature induced effective anisotropy and Dzyaloshinskii-Moriya interaction are characteristic of curved surfaces [4-6], leading to curvature-driven magnetochiral effects [7-9] and topologically induced magnetization patterning [6, 10], including unlimited domain wall velocities in hollow tubes [3], chirality symmetry breaking [6-9] and Cherenkov-like effects for magnons [11]. In addition to these rich physics, the application potential of 3D-shaped objects is currently being explored as magnetic field sensorics for magnetofluidic applications [12], spin-wave filters [13], magneto-encephalography devices [14] and high-speed racetrack memory devices [3]. To this end, the initially fundamental topic of the magnetism in curved geometries strongly benefited from the input of the application-oriented community, which among others explores the shapeability aspect of the curved magnetic thin films. These activities resulted in the development of the family of shapeable magnetoelectronics [15], which already includes flexible [16], printable [17], stretchable [18] and even imperceptible [19] magnetic field sensorics.
These recent developments starting from the theoretical predictions to the fabrication and characterization of 3D-curved magnetic thin films and their application potential are in the focus of this talk.

Keywords: Curved magnetic thin films; rolled technology

  • Invited lecture (Conferences)
    The 8th Joint European Magnetic Symposia (JEMS2016), 21.-26.08.2016, Glasgow, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-24055
Publ.-Id: 24055


Validation of the DYN3D-Serpent code system for SFR cores using selected BFS experiments. Part I: Serpent calculations.

Rachamin, R.; Kliem, S.

A comparative study has been performed to evaluate the prediction capability of the DYN3D-Serpent code system for sodium fast reactor (SFR) cores. In this study, the calculation system was tested against the BFS-73-1 and BFS-62-3A experiments conducted at the Russian Institute of Physics and Power Engineering (IPPE). These experiments were designed for full-scale modeling of SFR cores, and for validation of codes and nuclear data. The study was performed in two parts. The first part is aimed at developing and validating a 3D full-core heterogeneous model of each of the experiments using the Serpent Monte-Carlo code (MC) code. This part meant as a first step towards the use of the Serpent MC code as a tool for preparation of homogenized group constants, and as a reference solution for code-to-code comparison with the DYN3D code. The second part is devoted to the homogenized group constants generation procedure and the DYN3D steady-state calculations. This paper covers the first part of the study. The experiments were simulated using the Serpent MC code, and the basic neutronic characteristics were evaluated and compared against experimental values. The calculated results agreed well with the measured values on most of the neutronic characteristics. It suggests that the Serpent MC code can reliably be used for the preparation of homogenized group constants and as a reference solution for code-to-code verification with the DYN3D code.

Keywords: SFR; critical assembly; BFS experiments; validation; Serpent and DYN3D

Permalink: https://www.hzdr.de/publications/Publ-24054
Publ.-Id: 24054


Tuning the fabrication of nanostructures by low-energy highly charged ions

El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Sorokin, M.; Facsko, S.; Aumayr, F.

Slow highly charged ions were utilized recently for the creation of monotype surface nanostructures (craters, calderas or hillocks) in different materials. In the present study, we report on the ability of slow highly charged xenon ions (129XeQ+) to form three different types of nanostructures on LiF (100) surface. By increasing the charge state from Q = 15 to Q = 36, the shape of the impact induced nanostructures changes from craters to hillocks crossing an intermediate stage of caldera structures. The dimensional analysis of the nanostructures reveals an increase of the height up to 1.5 nm as a function of the potential energy of the incident ions. Based on the evolution of both the geometry and size of the created nanostructures, defect-mediated desorption and the development of a thermal spike are utilized as creation mechanisms of the nanostructures at low and high charge states, respectively.

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Permalink: https://www.hzdr.de/publications/Publ-24053
Publ.-Id: 24053


Reactivity of t-butyl hydroperoxide and t-butyl peroxide towards reactor materials measured by a microcalorimetric method at 30 °C.

Willms, T.; Kryk, H.; Oertel, J.; Lu, X.; Hampel, U.

To investigate the oxidation of isobutane to t-butyl hydroperoxide (TBHP) for the first time as a two-phase process in a micro reactor in a broad range of flow rates (isobutane flow rate: 15 to 188 µl/min, oxygen: 0.1 to 1.5 ml/min), temperatures (75 to 150 °C) and pressures (25 to 100 bar), a study has been performed to select the most appropriate construction materials for the experimental facility, especially for the microreactor but also for fittings, sealings, sensors, pumps, tubes, the sampling unit etc. TBHP, as most hydroperoxides, is quite reactive and reacts with most metals, polymers, acids and bases. Therefore, the most suitable materials had to be determined to minimize losses of TBHP in the initiator pump and in the reaction mixture of the sample at ambient temperature. As TBHP ¬¬decom¬poses very slowly under such conditions, a microcalorimetric method (TAM) has been used to measure the heat production of TBHP in contact with selected materials at 30 °C. Among those materials various metals e.g. copper, gold, silver, zinc, aluminum, titanium, tantalum, normal steel, hastelloy C276, hastelloy C-2000, V4A steel as well as semiconductors like silicon and silicon carbide have been tested. Furthermore, several polymers like nitrile butyl rubber, PEEK, silicone, Chemraz® and PTFE have been studied. Moreover, the role of metals and metal ions as catalysts for the decomposition of TBHP and DTBP is discussed. The experiments showed that silver and copper are the most reactive metals of the investigated substances and silicon the most suitable coating material for the reactor. The most stable polymers were found to be PEEK, Tedlar, Chemraz® and PTFE.

Keywords: Reactivity; reactor materials; micro calorimetry; t-butyl hydroperoxide; di-t-butyl peroxide

  • Lecture (Conference)
    GEFTA-Jahrestagung 2016 - Polymeranwendungen der ultraschnellen Kalorimetrie, 14.-16.09.2016, Halle, Deutschland
  • Open Access Logo Journal of Thermal Analysis and Calorimetry 128(2017)1, 319-333
    DOI: 10.1007/s10973-016-5860-5
  • Contribution to proceedings
    GEFTA-Jahrestagung 2016 - Polymeranwendungen der ultraschnellen Kalorimetrie,, 14.-16.09.2016, Halle (Saale), Deutschland
    Proceedings der GEFTA-Jahrestagung 2016

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Permalink: https://www.hzdr.de/publications/Publ-24052
Publ.-Id: 24052


ZnO Luminescence and scintillation studied via photoexcitation, X-ray excitation, and gamma-induced positron spectroscopy

Ji, J.; Colosimo, A. M.; Anwand, W.; Boatner, L. A.; Wagner, A.; Stepanov, P. S.; Trinh, T. T.; Liedke, M. O.; Krause-Rehberg, R.; Cowan, T. E.; Selim, F. A.

The luminescence and scintillation properties of ZnO single crystals were studied by photoluminescence and X-ray-induced luminescence (XRIL) techniques. XRIL allowed a direct comparison to be made between the near-band emission (NBE) and trap emissions providing insight into the carrier recombination efficiency in the ZnO crystals. It also provided bulk luminescence measurements that were not affected by surface states. The origin of a green emission, the dominant trap emission in ZnO, was then investigated by gamma-induced positron spectroscopy (GIPS) - a unique defect spectroscopy method that enables positron lifetime measurements to be made for a sample without contributions from positron annihilation in the source materials. The measurements showed a single positron decay curve with a 175 ps lifetime component that was attributed to Zn vacancies passivated by hydrogen. Both oxygen vacancies and hydrogen-decorated Zn vacancies were suggested to contribute to the green emission. By combining scintillation measurements with XRIL, the fast scintillation in ZnO crystals was found to be strongly correlated with the ratio between the defect luminescence and NBE. This study reports the first application of GIPS to semiconductors, and it reveals the great benefits of the XRIL technique for the study of emission and scintillation properties of materials.

Keywords: luminescence scintillation ZnO photoluminescence X-ray-induced luminescence XRIL gamma-induced positron spectroscopy GIPS defect spectroscopy

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Permalink: https://www.hzdr.de/publications/Publ-24051
Publ.-Id: 24051


Insights into the structure and thermal stability of uranyl aluminate nanoparticles

Chave, T.; Le Goff, X.; Scheinost, A. C.; Nikitenko, S. I.

Ultrasonically assisted hydrolytic precipitation of U(VI) in the presence of mesoporous alumina followed by thermal treatment of solid precursor allowed to obtain crystallized uranyl aluminate (URAL) nanoparticles (NPs) dispersed in alumina matrix. Effect of U(VI) concertation and calcination temperature on the yield of URAL NPs was studied using XRD, XAFS and HRTEM techniques. At 800°C, URAL NPS (d≈5 nm) are formed only for low uranium loading of about 5 wt% whereas for higher content of uranium, larger U3O8 NPs (d≈20 nm) were identified as a principal uranium specie. At 500°C, URAL NPs are formed even for 25 wt% of uranium. U LIII edge EXAFS spectra pointed out that uranyl cation in URAL is coordinated by bidentate aluminate groups. Presumably URAL is formed during the heating of 2UO3·NH3·2H2O/AlO(OH) precursor. However, high temperature and larger content of uranium promote URAL transformation to more thermodynamically stable U3O8 oxide. This process is accompanied by uranium NPs growing via Ostwald ripening mechanism.

Keywords: uranium oxide; nanoparticles; EXAFS; HRTEM

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Permalink: https://www.hzdr.de/publications/Publ-24050
Publ.-Id: 24050


Proteine als neue Bausteine für funktionalisierte Textilverbunde

Sallat, M.; Raff, J.

Ziel eines Forschungsvorhabens war es, neue Möglichkeiten der Oberflächenfunktionalisierung textiler Fasern bzw. Flächengebilde durch die Applikation bakterieller Hüllproteine, sogenannter S-Layer-Proteine, zu erarbeiten. Aufgrund der intrinsischen Eigenschaft dieser Proteine, sich auch nach Isolation in Abhängigkeit von den Randbedingungen in äußerst regelmäßiger Form auf Oberflächen verschiedenster Materialien zu reorganisieren, eröffnen sich neue Wege bei der Nano- und Mikrostrukturierung von Textilien. Auf Basis dieser Strukturierung wurde untersucht, ob und in welcher Form sich prinzipiell ausgewählte Funktionalitäten (antimikrobielle Wirksamkeit, katalytische Aktivitäten, Hydrophilie/Hydrophobie) auf Vliesstoffen erzielen lassen und ob ausgewählte Effekte (Hydrophilie/Hydrophobie, Oleophobie) intensiviert werden können.

Im Rahmen der Arbeiten wurden Vliesstoffe unterschiedlicher chemischer Basis (PP, PE/PP, PET, PA/PET) mit S-Layer-Proteinen beschichtet und anschließend
- mit Silbernanopartikeln antimikrobiell ausgerüstet,
- mit Palladiumnanopartikeln katalytisch aktiviert,
- mit Carbonsäure- bzw. Polyurethanverbindungen chemisch hydrophiliert,
- mit Fluorcarbonen oleophobiert und
- mit wasserbasierten Polyurethan-Dispersionen beschichtet.

Aus den im Beitrag dargestellten Ergebnissen dieser Grundlagenarbeiten lassen sich nun weitere erfolgversprechende Entwicklungsarbeiten im Hinblick auf mögliche industrielle Anwendungen ableiten. Erwähnt seien in diesem Zusammenhang z. B. die Verbesserung der Verklebbarkeit textiler Oberflächen (Hotmelt-Kaschierung) oder die Funktionalisierung textiler Filtermedien zur Adsorption von Schadstoffen (Atemluftfiltration, Wasseraufbereitung).

Keywords: Textil; S-Layer; Funktionalisierung

  • Lecture (Conference)
    24. Neues Dresdner Vakuumtechnisches Kolloquium, 29.-30.09.2016, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-24049
Publ.-Id: 24049


Bacterial S-layer proteins and their interaction with radionuclides

Raff, J.; Vogel, M.; Drobot, B.; Schmoock, C.; Moll, H.; Barkleit, A.; Börnick, H.; Worch, E.; Stumpf, T.

Bacterial surface-layer (S-layer) proteins form the outermost cell envelope of many bacteria and all archaea. These proteins are able to self-assemble in highly regular layers forming an oblique, square or hexagonal lattice on the entire cell. This layer protects especially bacteria living in extreme habitats against diverse harmful environmental influences. In case of uranium mining waste pile isolates belonging to the genera Lysinibacillus and Bacillus it was proven that the S-layers act as scavenger for reactive oxygen species probably formed by either radiolysis of water or Fenton reaction. The inactivation of the radicals is achieved by intermolecular crosslinking of tyrosine residues of the protein monomers. Furthermore, these S-layers have a variety of free functional groups such as carboxyl, hydroxyl and amino groups determined by potentiometric titration. These groups form at least two different calcium binding sites being important for the self-assembly of the protein and are responsible for the selective binding of toxic elements. Additionally, S-layer proteins are posttranslationally modified with sugar residues, phosphate, sulfate or sulfoxide groups. While hexavalent uranium is bound by several surface exposed functional groups, it is easily released at acidic pH and thusly do not affect strongly cell metabolism. However, the trivalent curium substitutes calcium and is only released at pH 2.0 or below. Interestingly, metabolism relevant metals such as Mn, Fe, Co, Ni, Cu, Zn were not bound by the proteins. These examples demonstrate that radionuclides can specifically interact with the biosphere affecting significantly their behaviour even in natural environments.

Keywords: Radionuclides; S-layer

  • Invited lecture (Conferences)
    Frontiers in Environmental Radioactivity, 06.-07.01.2016, London, United Kingdom

Permalink: https://www.hzdr.de/publications/Publ-24048
Publ.-Id: 24048


Investigating the removal of particles from the air/water-interface – Modelling detachment forces using an energetic approach

Knüpfer, P.; Fritzsche, J.; Leistner, T.; Rudolph, M.; Peuker, U. A.

and removing a particle from an interface requires a high force. The capillary force affects at the particle and causes an interfacial deformation during detachment. In this study the detachment force of hydrophilic and hydrophobic particles is measured via CP-AFM. In order to calculate the detachment force, a simple analytical model is developed and compared with the classical capillary force model. The new model is grounded on an energetic approach in compliance to the interfacial deformation and wetting of the particle. A model spring is assumed for both sub-processes and the force affects onto these two springs. The calculated force in the new model referred to goes better with experimental values than the capillary force model which does not consider interfacial deformation.

Keywords: AFM; capillary force; detachment force; energy of adhesion; interfacial deformation; spring model

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Permalink: https://www.hzdr.de/publications/Publ-24047
Publ.-Id: 24047


WissKom2016: Der Schritt zurück als Schritt nach vorn – Macht der Siegeszug des Open Access Bibliotheken arbeitslos? 7. Konferenz der Zentralbibliothek, Forschungszentrum Jülich

Reschke, E.

Vom 14. bis 16. Juni 2016 fand die nunmehr siebente WissKom statt. Die Zentralbibliothek des Forschungszentrum Jülich hatte wieder eingeladen und in gewohnter Perfektion die Tagung organisiert. An drei Tagen wurde zum Themenfeld Modernes Bibliothekswesen und zeitgemäße Informationsversorgung unter besonderem Augenmerk auf den Open Access Transformationsprozess im wissenschaftlichen Publikationswesen vorgetragen und diskutiert. Neue Aufgabenfelder für wissenschaftliche Bibliotheken im vielgestaltigen Prozess der Neuorientierung wurden vorgestellt. Das umfasste den Wandel im Publikationsprozess selbst, Nachweissysteme für Publikationen, Repositorien, Open Access Grün und Zweitveröffentlichung, Forschungsdaten und Fragen der Wissenschaftsevaluierung.

Keywords: Wisskom; Open Access; Libray

  • b.i.t.online 19(2016)5, 459-460
  • Open Access Logo b.i.t.online 19(2016)5, 458-466

Permalink: https://www.hzdr.de/publications/Publ-24046
Publ.-Id: 24046


Physicochemical Properties of Aminated Butyl-Nanocrystals in Correlation to the Flotation Response of Quartz

Hartmann, R.; Rudolph, M.; Laitinen, O.; Sirviö, J. A.; Liimatainen, H.; Illikainen, M.

The increasing complexity of the ores composition worldwide calls for suitable collectors with specific properties, such as selectivity, wettability, and in regard to environmental regulations, biodegradability. Therefore, collectors have to satisfy many features to improve the efficiency of flotation processes. Cellulose nanocrystals gain more and more interest due to the versatile preparation routes which enable the integration of specific functional groups and components with different degrees of hydrophobicity within the molecular structure. Consequently, cellulose nanocrystals can be employed in flotation processes as depressant or collector molecules, respectively. Nonetheless, the usage of cellulose nanocrystals is still limited due to a lack of the characterization of nanocrystal-mineral interactions and the change of the surface wetting properties of minerals after adsorption phenomena between nanocrystals and minerals. In these studies, butyl-amine cellulose nanocrystals (BAC) and quartz are used as standard model to investigate physicochemical properties of both, BAC and quartz, and examine the applicability of BAC in flotation processes. Therefore, the particle size and size distribution, surface charge distribution and electrophoretic mobility of BAC and quartz are measured. Based on this, the adsorption isotherm of BAC on quartz is established. For the determination of the surface free energy, the inverse gas chromatography (iGC) technique as well as the contact angle method are applied and compared. Finally, flotation experiments in bench-scale prove the efficiency of BAC to be used in flotation processes.

Keywords: cellulose nanocrystals; quartz; surface charge distribution; electrophoretic mobility; adsorption; surface free energy; flotation

  • Contribution to proceedings
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016 - Conference Proceedings, Quebec: CIM/ICM, 978-1-926872-29-2

Permalink: https://www.hzdr.de/publications/Publ-24045
Publ.-Id: 24045


Treatment of once rejected material – investigating the recovery of cassiterite from tailings disposals using different flotation methods

Leistner, T.; Leißner, T.; Möckel, R.; Osbahr, I.; Rudolph, M.; Peuker, U. A.

Tin-mining activities have taken place in the region of the German Erzgebirge (Ore Mountains) for over hundreds of years up until the late 1980s. For long times, gravity separation processes used to be the main beneficiation approach in those mining districts to recover cassiterite, the main tin-bearing mineral. Since for fine and very fine particles these approaches might not represent effective techniques, much valuable material could not be recovered and reported to tailings, where it was subsequently disposed. Thus, there are substantial amounts of cassiterite still present in these disposals, most of it as very fine particles with already high degrees of liberation. That fact brings these disposals into focus for potential reprocessing using beneficiation approaches, which are more sensitive to fine and very fine particles.

In this paper we present results concerning the laboratory-scale treatment of material from exemplary heaps of the former Altenberg and Ehrenfriedersdorf mining sites using various flotation methods. The material used is previously classified into different size ranges. Conventional froth flotation is applied to the fine particles (20µm – 100µm). For the very fine particle (< 20µm), special emphasis is put on oil-assisted flotation methods, including oil agglomeration flotation and two-liquid flotation. Therefore, an aliphatic oil phase of alkane basis is used to either selectively aggregate or collect the cassiterite particles. Recovery and flotation performance results are presented with respect to different process parameters: various collectors (e.g. sulphosuccinamates, phosphonic acids) and depressants (e.g. sodium fluorosilicate, oxalic acid) regime, oil dosage, oil/pulp agitation time and pulp density. Furthermore, the oil/particle aggregation behavior is analyzed via particle image analysis and, additionally, collector adsorption characteristics are investigated by contact angle measurements, zeta potential analysis and infrared spectroscopy. The data obtained is correlated with the testwork results achieved in order to interpret the flotation response of very fine cassiterite particles.

Keywords: tailing reprocessing; flotation methods; cassiterite; very fine particle processing; oil-assisted flotation

  • Contribution to proceedings
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016 - Conference Proceedings, Quebec: CIM/ICM, 978-1-926872-29-2

Permalink: https://www.hzdr.de/publications/Publ-24044
Publ.-Id: 24044


Investigations on Mineral Liberation by Transgranular and Intergranular Fracture after Milling

Leißner, T.; Hoang, D. H.; Rudolph, M.; Heinig, T.; Bachmann, K.; Schubert, H.; Peuker, U. A.

In comminution minerals can be liberated by random fracture of particles into smaller fragments or by detachment along phase boundaries. These two mechanisms represent borderline cases. When ores get crushed and milled the liberation of minerals is achieved to some extent by both mechanisms. This article describes a method to determine the extent of transgranular and intergranular fracture of minerals based on 2-dimensional liberation analysis from automated mineralogy.
The approach uses the non-biased surface information like phase specific surface area (PSSA), phase specific free surface (PSFS) and phase specific locked surface (PSLS) of minerals and their change through comminution. The parameters are discussed related to the normalized grain size, which is the ratio of mineral grain size of the milled product to mineral grain size of the feed material. Finally the amount of transgranular and intergranular fracture can be calculated using the phase specific surface parameters.
An apatite ore (sedimentary origin), a rare earth mineral containing nepheline-syenite and a porphyry-copper ore (both igneous origin) were ground to different fineness using a ball mill. Based on the mineral liberation analysis (MLA, device FEI Quanta 650 MLA-FEG) of feed and products, the extent of phase boundary fracture on the surface exposure of the minerals is studied.
It is found, that the extent of transgranular and intergranular fracture on surface exposure differs for different types of ores. For sedimentary rocks, intergranular fracture (detachment) plays a major role in the liberation of the minerals (cf. Fig. 1 a). Surface exposure of minerals from the nepheline-syenite (cf. Fig. 1, b) has to be discussed more differentiated. Feldspar shows a small percentage of detachment on surface exposure whereas the aegirine is liberated in equal proportions by both mechanisms.
The presented method of liberation analytical calculations using phase specific surface information will be useful for the better understanding of ore specific fracture events with different comminution strategies. Consequently, it will lead to a more economical way to successfully liberate minerals by the energy intense processes of comminution.

Keywords: Mineral liberation analysis; preferential breakage; transgranular fracture; intergranular fracture; random fracture; grain boundary fracture

  • Contribution to proceedings
    IMPC 2016 - XXVIII International Mineral Processing Congress, 11.-15.09.2016, Quebec, Canada
    IMPC 2016 - Conference Proceedings, Quebec: CIM/ICM, 978-1-926872-29-2

Permalink: https://www.hzdr.de/publications/Publ-24043
Publ.-Id: 24043


Activation cross sections of longer-lived radionuclides produced in germanium by alpha particle irradiation

Takács, S.; Takács, M. P.; Ditrói, F.; Aikawa, M.; Haba, H.; Komori, Y.

The cross sections of alpha particles induced nuclear reactions on natural germanium were investigated by using the standard stacked foil target technique, the activation method and high resolution gamma spectrometry. Targets with thickness of about 1 μm were prepared from natural Ge by vacuum evaporation onto 25 μm thick polyimide (Kapton) backing foils. Stacks were composed of Kapton-Ge-Ge-Kapton sandwich target foils and additional titanium monitor foils with nominal thickness of 11 μm to monitor the beam parameters using the natTi(α,x)51Cr reaction. The irradiations were done with Eα = 20.7 and Eα = 51.25 MeV, Iα = 50 nA alpha particle beams for about 1 h. Direct or cumulative activation cross sections were determined for production of the 72,73,75Se, 71,72,74,76,78As, and 69Ge radionuclides. The obtained experimental cross sections were compared to the results of theoretical calculations taken from the TENDL data library based on the TALYS computer code. A comparison was made with available experimental data measured earlier. Thick target yields were deduced from the experimental cross sections and compared with the data published before.

Keywords: Alpha particle irradiation; Natural germanium target; Cross sections; 72,73,75Se, 71,72,74,76,78As and 69Ge excitation functions; TENDL comparison

Permalink: https://www.hzdr.de/publications/Publ-24042
Publ.-Id: 24042


Incorporation of thorium in the zircon structure type through the Th1-xErx(SiO4)1-x(PO4)x thorite-xenotime solid solution

Mesbah, A.; Clavier, N.; Lozano-Rodriguez, J.; Szenknect, S.; Dacheux, N.

Pure powdered compounds with a general formula Th1-xErx(SiO4)1-x(PO4)x belonging to the zircon-xenotime were successfully synthesized under hydrothermal conditions (250°C, 7 days) as recently reported for the preparation of coffinite. Therefore a thorough combined PXRD, EDS, EXAFS, μ-Raman and FTIR analyses showed the formation of solid solution in agreement with the Vergard’s law. Moreover, the examination of the local structure shows that the Th-O distances remain close to those found in ThSiO4. Whereas, the Er-O distances show big decrease from 2.38(14) Å to 2.34(7) Å when increasing the erbium content from x = 0.2 to x = 1. The variation of the local structure also affects the PO4 3- groups that are surely distorted in the structure.

Keywords: xenotime; monazite; EXAFS; actinides; phosphate

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Permalink: https://www.hzdr.de/publications/Publ-24041
Publ.-Id: 24041


Thermodynamics Behavior of Germanium During Equilibrium Reactions between FeOx-CaO-SiO2-MgO Slag and Molten Copper

Reuter, M. A.; Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S.

The distribution ratio of germanium (Ge), (Formula presented.) during equilibrium reactions between magnesia-saturated FeOx-CaO-SiO2 (FCS) slag and molten copper has been measured under oxygen partial pressures from 10−10 to 10−7 atm and at temperatures 1473 to 1623 K (1200 to 1350 °C). It was observed that the Ge distribution ratio increases with increasing oxygen partial pressure, and with decreasing temperature. It was also observed that the distribution ratio is strongly dependent on slag basicity. The distribution ratio was observed to increase with increasing optical basicity. At fixed CaO concentration in the slag, the distribution ratio was found to increase with increasing Fe/SiO2 ratio, tending to a plateau at (Formula presented.) = 0.8. This behavior is consistent with the assessment of ionic bond fraction carried out in this study, and suggested the acidic nature of germanium oxide (GeO2) in the slag system studied. The characterisation results of the quenched slag suggested that Ge is present in the FeOx-CaO-SiO2-MgO slag predominantly as GeO2. At 1573 K (1300 °C) and (Formula presented.) = 10−8 atm, the activity coefficient of GeO2 in the slag was calculated to be in the range of 0.24 to 1.50. The results from the current study suggested that less-basic slag, high operating temperature, and low oxygen partial pressure promote a low Ge distribution ratio. These conditions are desired for maximizing Ge recovery, for example, during pyrometallurgical processing of Ge-containing e-waste through secondary copper smelting. Overall, the thermodynamics data generated from this study can be used for process modeling purposes for improving recovery of Ge in primary and secondary copper smelting processes.

Keywords: Engineering controlled terms: Copper; Germanium; Germanium oxides; Iron oxides; Magnesia; Oxygen; Partial pressure; Pyrometallurgy; Secondary recovery; Slags; Temperature; Thermodynamics; Distribution ratio; Equilibrium reactions; High operating temperature; Low oxygen partial pressure; Oxygen partial pressure; Pyrometallurgical processing; Secondary copper smelting; Thermodynamics data

Permalink: https://www.hzdr.de/publications/Publ-24040
Publ.-Id: 24040


Hydrodynamic modeling of a pure-glue initial scenario in high-energy hadron and heavy-ion collisions

Vovchenko, V.; Pang, L.-G.; Niemi, H.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stoecker, H.

Partonic matter produced in the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, and quarks and antiquarks are produced at later times. The comparable hydrodynamic simulations of heavy-ion collisions for (2+1)-flavor and Yang-Mills equations of state performed by using three different hydrodynamic codes are presented. Assuming slow chemical equilibration of quarks, the spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy of √sNN=2.76 TeV. It is shown that a suppression of quarks at early times leads to a significant reduction of the yield of the thermal dileptons, but only to a rather modest suppression of the pT-distribution of direct photons. It is demonstrated that an enhancement of photon and dilepton elliptic flows might serve as a promising signature of the pure-glue initial state. Calculations based on Bjorken hydrodynamics suggest that collisions of small systems at intermediate energies available at RHIC or future FAIR facilities may show stronger effects associated with initial pure gluodynamic evolution.

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Permalink: https://www.hzdr.de/publications/Publ-24039
Publ.-Id: 24039


Vacuum particle-antiparticle creation in strong fields as a field induced phase transition

Smolyansky, S. A.; Panferov, A. D.; Blaschke, D. B.; Juchnowski, L.; Kämpfer, B.; Otto, A.

The features of vacuum particle creation in an external classical field are studied for simplest external field models in 3+1 dimensional QED. The investigation is based on a kinetic equation that is a nonperturbative consequence of the fundamental equations of motion of QED. The observed features of the evolution of the system apply on the qualitative level also for systems of other nature and therefore are rather general. Examples from cosmology and condensed matter physics illustrate this statement. The common basis for the description of these systems are kinetic equations for vacuum particle creation belonging to the class of integro-differential equations of non-Markovian type with fastly oscillating kernel. This allows to characterize processes of this type as belonging to the class of field induced phase transitions.

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Permalink: https://www.hzdr.de/publications/Publ-24038
Publ.-Id: 24038


Holographically emulating sequential versus instantaneous disappearance of vector mesons in a hot environment

Zöllner, R.; Kämpfer, B.

Descent extensions of the soft-wall model are used to accommodate two variants of Regge trajectories of vector meson excitations. At non-zero temperatures, various options for either sequential or instantaneous disappearance of vector mesons as normalisable modes are found, thus emulating deconfinement at a certain temperature in the order of the (pseudo-) critical temperature of QCD. The crucial role of the blackness function, which steers the thermodynamic properties of the considered system, is highlighted.

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Permalink: https://www.hzdr.de/publications/Publ-24037
Publ.-Id: 24037


The Link Between the Local Bubble and Radioisotopic Signatures on Earth

Feige, J.; Breitschwerdt, D.; Wallner, A.; Schulreich, M. M.; Kinoshita, N.; Paul, M.; Dettbarn, C.; Fifield, K. L.; Golser, R.; Honda, M.; Linnemann, U.; Matsuzaki, H.; Merchel, S.; Rugel, G.; Steier, P.; Tims, S. G.; Winkler, S. R.; Yamagata, T.

Traces of 2-3 Myr old 60Fe were recently discovered in a manganese crust and in lunar samples. We have found that this signal is extended in time and is present in globally distributed deep-sea archives. A second 6.5-8.7 Myr old signature was revealed in a manganese crust. The existence of the Local Bubble hints to a recent nearby supernova-activity starting 13 Myr ago. With analytical and numerical models generating the Local Bubble, we explain the younger 60Fe-signature and thus link the evolution of the solar neighborhood to terrestrial anomalies.

Keywords: supernova; AMS; radionuclide; local bubble; deep-sea samples; interstellar medium; accelerator mass spectrometry

  • Open Access Logo Contribution to proceedings
    14th International Symposium on Nuclei in the Cosmos XIV, 19.-24.06.2016, Toki Messe, Niigata, Japan
    Proceedings of the 14th International Symposium on Nuclei in the Cosmos XIV, JPS Conf. Proc. 14 (2017): JPS (Japan Physical Society) Conference Proceeding, 010304
    DOI: 10.7566/JPSCP.14.010304

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Permalink: https://www.hzdr.de/publications/Publ-24036
Publ.-Id: 24036


Moments-based ultrasound visual servoing: from mono to multi-plane approach

Nadeau, C.; Krupa, A.; Petr, J.; Barillot, C.

This paper presents a new image-based visual servoing approach to control a robotic system equipped with an ultrasound imaging device. The presented method allows an automatic positioning of the probe with respect to an object of interest. Moments-based image features are computed from three orthogonal ultrasound images to servo in-plane and out-of plane motions of the system. An efficient segmentation method, based on graph cut strategy, is proposed to extract the object contour in each image plane. Simulation results demonstrate that this approach improves upon techniques based on a single 2D US image in terms of probe positioning. Our method was also validated from robotic experiments performed on an ultrasound phantom with the use of a motorized 3D probe that provides the three US images.

Keywords: Visual servoing; ultrasound images; graph cut segmentation; moment features

Permalink: https://www.hzdr.de/publications/Publ-24035
Publ.-Id: 24035


Magnetic properties and giant reversible magnetocaloric effect in the GdCoC2 compound

Meng, L.; Xu, C.; Yuan, Y.; Qi, Y.; Zhou, S.; Li, L.

The crystal structure, magnetic properties and magnetocaloric effect (MCE) of GdCoC2 have been studied. The compound crystallizes in an orthorhombic CeNiC2-type structure which belongs to Amm2 space group. A giant reversible MCE is observed in GdCoC2 accompanied by a second-order paramagnetic to ferromagnetic (PM-FM) phase transition around the Curie temperature ~15 K. For the magnetic field change of 0-5 T, the maximum values of the magnetic entropy change (-ΔSMmax), relative cooling power (RCP), and refrigerant capacity (RC) are 28.4J/kg K, 566 J/kg and 369 J/kg, respectively. The present results indicate that the GdCoC2 compound is a promising candidate for low temperature magnetic refrigeration.

Keywords: GdCoC2 compound; magnetocaloric effect; magnetic properties; magnetic refrigeration

Permalink: https://www.hzdr.de/publications/Publ-24034
Publ.-Id: 24034


Raman scattering at terahertz frequencies enabled by an infrared free electron laser

Pavlov, S.; Dessmann, N.; Zhukavin, R. K.; Shastin, V.; Hübers, H.-W.; Pohl, A.; Redlich, B.; van der Meer, A. F. G.; Winnerl, S.; Schneider, H.; Ortega, J.-M.; Prazeres, R.; Abrosimov, N. V.

In the last decade the use of infrared free electron laser facilities enabled observation of inelastic light (Raman) scattering in THz frequency range. Raman-active intracenter donor transitions in silicon fall into the THz range and serve as outgoing resonances in electronic Stokes scattering. At photon fluxes above 1E24 photon/cm2/s donor-related Raman stimulated emission occurs in the range 4.2-6.5 THz from natural and isotopically enriched silicon crystals with various dopants while the free electron laser wavelength was varied between 18 and 41 mkm (7.5-16.5 THz). Study of dynamics of the observed emission shows a transient picosecond-micropulse mode that indicates on significantly larger Raman gain realized in THz Raman silicon lasers. This research has been partly supported by the EC CALIPSO project for the Transnational access to the European FELs and Synchrotron facilities as well as joint German-Russian program "Research on technological advances of radiation sources of photons and neutrons based on accelerators and neutron sources in cooperation with research organizations and universities of the Federal Republic of Germany" (InTerFEL project, BMBF No. 05K2014 and the Russian Ministry of Science and Education (No. RFMEFl61614X0008).

Keywords: terahertz; infrared; free-electron laser; Raman scattering

  • Lecture (Conference)
    2016 International Conference "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-24033
Publ.-Id: 24033


Exciton dynamics in semiconductor quantum wells and single quantum dots studied with a THz free-electron laser

Schneider, H.; Stephan, D.; Zybell, S.; Winnerl, S.; Bhattacharyya, J.; Eßer, F.; Helm, M.

Excitons in III-V semiconductors are Coulomb-bound electron-hole pairs which are analogous to two-dimensional hydrogen atoms with terahertz (THz) binding energies. In semiconductor quantum wells (QW), confinement into the plane of the QW gives rise to essentially two-dimensional excitons, thus giving rise to a different symmetry and higher binding energy. In quantum dots (QD), three-dimensional confinement leads to discrete electronic and excitonic states, such that the system becomes similar to a trapped atom.
Using intense, spectrally narrow terahertz (THz) pulses from the free-electron laser (FEL) facility FELBE in Dresden, Germany, we have investigated the population dynamics between exciton states in III-V QWs and single QDs. To this end, carriers are optically injected by picosecond near-infrared optical pulses, which leads to a population of the lowest excitonic level. Using narrowband THz pulses provided by the free-electron laser at HZDR, excitons are resonantly excited into higher levels. Time-dependent photoluminescence (TDPL) measurements based on a streak camera system and on time-correlated photon counting, respectively, then allow us to study the transient population of dipole-allowed higher excitonic levels and to access the relaxation dynamics of these quasi-particles.
In QWs, the most prominent transition is from the 1s ground state into the 2p excited state (using hydrogen notation). While the 2p state is "optically dark", rapid scattering from the 2p into the 2s state occurs. TDPL originating from the 1s and 2s exciton states thus provides a unique signature which allows us to explore the relaxation dynamics involving 1s, 2s, and 2p excitons. Now turning to QDs, single QDs rather than QD ensembles should be investigated in order to prevent strong inhomogeneous broadening. We have therefore developed a micro-TDPL setup with a probe volume significantly below 1 µm^3 and high quantum efficiency to become sensitive to one single QD. In particular, we investigate the dynamics of the s-to-p inter-sublevel transition, which occurs in the range 13-20 meV for the QDs under study. Resonant excitation with a THz pulse, which is applied at about 0.7 ns time delay after interband excitation, causes an instantaneous reduction of the ground state TDPL. The signal recovers within about 100 ps towards a value which depends on the near-infrared excitation energy. In particular, qualitatively different behavior has been observed and analyzed using a phenomenological rate equation for interband excitation of the GaAs matrix, the InGaAs wetting layer, and quasi-resonant excitation of the QD.
Acknowledgements: We thank L. Schneebeli, C.N. Böttge, M. Kira, and S.W. Koch (Marburg, Germany) for fruitful discussions and collaboration.

Keywords: quantum well; exciton; terahertz; free-electron laser

  • Invited lecture (Conferences)
    International Workshop on "Terahertz Science, Nanotechnologies and Applications", 16.-22.07.2016, Erice, Italien

Permalink: https://www.hzdr.de/publications/Publ-24032
Publ.-Id: 24032


Semiconductor spectroscopy with infrared and THz free-electron lasers

Schneider, H.

This talk reviews some recent spectroscopic studies on semiconductor structures carried out using the mid-infrared and terahertz (THz) free-electron laser facility FELBE in Dresden, Germany. Its intense, nearly transform-limited picosecond pulses, which can also be combined with synchronous pico- or femtosecond pulses from near-infared tabletop lasers, provide unique research opportunities to advance our knowledge on the interaction of intense mid-infrared and THz fields with materials and devices.

Keywords: Semiconductor spectroscopy; infrared; terahertz; free-electron laser

  • Invited lecture (Conferences)
    2016 International Conference on "Synchrotron and Free electron laser Radiation: generation and application" (SFR-2016), 04.-07.07.2016, Novosibirsk, Russia

Permalink: https://www.hzdr.de/publications/Publ-24031
Publ.-Id: 24031


Overcoming the diffraction limit with a GaAs-based plasmonic superlens

Fehrenbacher, M.; Winnerl, S.; Döring, J.; Kehr, S. C.; Eng, L. M.; Huo, Y. H.; Schmidt, O. G.; Yao, K.; Liu, Y.; Helm, M.; Schneider, H.

We report a semiconductor-based superlens for sub-diffraction-limited near-field imaging at mid-infrared wavelengths. The superlens is based on a sequence of intrinsic and doped GaAs layers. Resonant enhancement of evanescent waves is accomplished here by exploiting the Drude response of a highly doped n-GaAs layer. Operation as a near-field superlens is validated by utilizing an aperture-less scattering near-field optical microscope (s-SNOM), which allows us to probe the image plane of the superlens with sub-wavelength resolution.
In our experiments, gold stripes underneath the GaAs superlens are imaged by the s-SNOM. The s-SNOM comprises an atomic-force microscope (AFM), the tip of which is illuminated by mid-infrared radiation from a free-electron laser (FEL). Imaging results reveal sub-wavelength resolution better than λ/6 at the resonant wavelength of λ = 22.0 µm. In excellent accordance with the Drude-Lorentz model, the resonant wavelength for superlensing can easily be adjusted by changing the doping concentration. Our approach thus reveals a simple and versatile superlens implementation for infrared nanospectroscopy. Detector issues specific for s-SNOM will also be addressed.
[1] M. Fehrenbacher, S. Winnerl, H. Schneider, J. Döring, S. C. Kehr, L. M. Eng, Y. Huo, O. G. Schmidt, K. Yao, Y. Liu, M. Helm, Nano Lett. 15, 1057 (2015)

Keywords: Scattering near-field optical microscopy; s-snom; superlens; GaAs; sub-diffraction-limited

  • Lecture (Conference)
    Quantum Structured Infrared Photodetector International Conference (QSIP 2016), 12.-17.06.2016, Tel Aviv, Israel

Permalink: https://www.hzdr.de/publications/Publ-24030
Publ.-Id: 24030


The South Um Mongul Cu-Mo-Au prospect in the Eastern Desert of Egypt: From a mid-Cryogenian continental arc to Ediacaran post-collisional appinite-high Ba-Sr monzogranite

Abd El-Rahman, Y.; Gutzmer, J.; Said, A.; Hofmann, M.; Gärtner, M.; Linnemann, U.

The South Um Mongul prospect is a Cu-Mo-Au porphyry system. It is covered by porphyritic dacite and hornblende gabbro. Both units are intruded by monzogranite, which encloses xenoliths of both units. Using LA-ICP-MS U-Pb zircon method, the dacite is dated at ca. 773 ± 6.9 Ma, while the gabbro and the monzogranite are dated at 603 ± 3.5 and 558 ± 4.6 Ma, respectively. The dacite age is consistent with the mid-Cryogenian subduction-related magmatic stage and the gabbro-monzogranite age is comparable to the Ediacaran post-collisional magmatic stage during the evolution of the Arabian-Nubian Shield. The dacite is akin to high-K I-type granitoids and its primitive mantle-normalized trace element patterns show negative Nb anomalies and enrichment in LILE (large ion lithophile elements), Th and U over HFSE. These geochemical characteristics are similar to those of felsic magma formed in a subduction-related tectonic setting. The high La/Ybcn (7.2–30.9), Nb/Yb (2.63–4.41) and Th/Yb (2.07–3.04) ratios of the dacite are comparable to continental rather than oceanic arc systems. Its low Sm/Yb ratios (1.84–3.13) support the primitive nature of the crust beneath the continental arc and derivation from a garnet-free lower crustal source. The dacite has low Sr/Y ratios (5–9) and its Eu/Eu⁎ ratios range from 0.66 to 0.83. Similar to dacite, the primitive mantle-normalized trace element patterns of the post-collisional suite show a subduction-related geochemical signature. However, the gabbro is characterized by Th/Ta ratios (3.4–14.8), which are comparable with the within-plate tectonic setting. The subduction-related geochemical signature is inherited from long subduction history beneath the Arabian-Nubian Shield. Both the gabbro and monzogranite are characterized by high Ba (404–590 ppm and 936–1590 ppm, respectively) and Sr (611–708 ppm and 624–793 ppm, respectively) contents, which make them analogous to the Caledonian appinite-high Ba-Sr granite assemblage. The formation of these rocks is related to the Ediacaran lithospheric erosion accompanying slab break-off. This process induced asthenospheric upwelling, which led to partial melting of the lithosphere previously metasomatised by subducted sediments involving carbonates impregnated by hydrothermal barite. Melting of this lithosphere led to the formation of the hornblende gabbro. Underplating by the mafic magma led to melting of the lower crust and the formation of high Ba-Sr monzogranite in the area. The high Sm/Yb (2.94–4.19) and Sr/Y (52–74) ratios of the monzogranite may indicate the presence of garnet in the melted amphibolitic lower crust. The higher Sr/Y ratios, lower HFSE (high field strength elements) contents and the absence of pronounced Eu anomalies in monzogranite relative to dacite suggest the productive nature of the post-collisional magma relative to the continental arc magma in this prospect.

Keywords: Appinite; Arabian-Nubian Shield; Continental arc; High Ba-Sr granite; Neoproterozoic; Post-collisional porphyry copper

Permalink: https://www.hzdr.de/publications/Publ-24029
Publ.-Id: 24029


Long-term diffusion of U(VI) in bentonite: Dependence on density

Joseph, C.; Mibus, J.; Trepte, P.; Müller, C.; Brendler, V.; Park, D. M.; Jiao, Y.; Kersting, A. B.; Zavarin, M.

As contribution to the safety assessment of nuclear waste repositories, U(VI) diffusion through the potential buffer material MX-80 bentonite was investigated at three clay dry densities over 6 years. Synthetic MX 80 model pore water was used as background electrolyte. Speciation calculations showed that Ca2UO2(CO3)3(aq) was the main U(VI) species. The in- and out-diffusion of U(VI) was investigated separately. U(VI) diffused about 3 mm, 1.5 mm, and 1 mm into the clay plug at ρ = 1.3, 1.6, and 1.9 g/cm3, respectively. No through-diffusion of the U(VI) tracer was observed. However, leaching of natural uranium contained in the clay occurred and uranium was detected in all receiving reservoirs. As expected, the effective and apparent diffusion coefficient, De and Da, decreased with increasing dry density. The Da values for the out-diffusion of natural U(VI) were in good agreement with previously determined values. Surprisingly, Da values for the in-diffusion of U(VI) were about two orders of magnitude lower than values obtained in short-term in-diffusion experiments reported in the literature. As potential reasons for this behavior, changes of the U(VI) speciation within the clay (precipitation, reduction) or changes of the clay porosity and pore connectivity with time were evaluated. By application of Archie’s law and extended Archie’s law, it was estimated that a significantly smaller effective porosity must be present for the long-term in-diffusion of U(VI). The results suggest that long-term studies of key transport phenomena may reveal additional processes that can directly impact long-term repository safety assessments.

Keywords: nuclear waste repository; MX-80; clay; uranium; speciation; extended Archie’s law

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Permalink: https://www.hzdr.de/publications/Publ-24028
Publ.-Id: 24028


The effect of microstructural heterogeneity on pore size distribution and permeability in Opalinus Clay (Mont Terri, CH): insights from an integrated study of laboratory fluid flow and pore morphology from BIB-SEM images

Philipp, T.; Amann-Hildenbrand, A.; Laurich, B.; Desbois, G.; Littke, R.; Urai, J. L.

Opalinus Clay (OPA) is considered as potential host rock for the deep-geological disposal of radioactive waste. One key-parameter in long-term storage prediction is permeability. In this study we investigated microstructural controls on permeability for the different facies of OPA. Permeability and porosity were determined under controlled pressure conditions. In addition, the pore space was investigated by SEM, using high quality surfaces prepared by Broad Ion Beam milling (BIB). Water permeability coefficients range from 1.6×10-21 to 5.6×10 20 m². Helium pycnometer porosities range between ~21% and ~12%. The sample with the highest helium porosity (shaly facies) is characterized by the lowest permeability, and vice versa (carbonate-rich sandy facies). This inverse behavior deviates from the generally reported trend of increasing permeability with increasing porosity, indicating that parameters other than porosity affect permeability. Visible porosities from SEM images revealed that 67-95% of the total porosity resides within pores smaller than the SEM detection limit. Pore sizes follow a power law distribution with characteristic power law exponents (D), strongly differing among the facies. The carbonate-rich sandy facies contains a network of much larger pores (D(shaly)~2.4, D(carbonate-rich)~2.0), because of the presence of load-supporting sand grains that locally prevent clay compaction, being responsible for a higher permeability.

Keywords: Opalinus Clay; permeability; porosity; BIB-SEM; microstructure; pore size distribution

  • Geological Society Special Publication 454(2017)1, 85
    DOI: 10.1144/SP454.3

Permalink: https://www.hzdr.de/publications/Publ-24027
Publ.-Id: 24027


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