Publication database - Helmholtz-Zentrum Dresden-Rossendorf

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26319 Publications
Probing high-intensity laser-matter interaction at the Helmholtz International Beamline for Extreme Fields at the European XFEL
Schramm, U.ORC
Abstract: Talk on Probing high-intensity laser-matter interaction at the
Helmholtz International Beamline for Extreme Fields
at the European XFEL

Keywords: Relativistic Laser Plasma, HIBEF
  • Invited lecture (Conferences)
    PWSC 8th Petawatt Scientific Committee and ICUIL 2016, 10.-16.09.2016, Montebello, Canada
Registration No. 24159 - Permalink

In situ bow change of Al-alloy MEMS micromirrors during 248-nm laser irradiation
Mai, A.; Bunce, C.; Hübner, R.; Pahner, D.; Dauderstädt, U.
Abstract: Micromirror based spatial light modulators (SLMs) developed by the Fraunhofer Institute for Photonic Microsystems are well established in microlithography applications. Serving, e.g., as reflective, programmable photomasks in deep-UV mask writers, they enable highly flexible pattern generation. During operation, the micromirror bow significantly impacts contrast and the resolvable feature size of generated patterns. In some situations, MEMS micromirrors tend to change their bow during laser irradiation. A test regime including a characterization unit for the in situ analysis of MEMS micromirror topology has been developed to measure the bow change under various irradiation conditions. Experiments in which SLMs were irradiated by a 1-kHz, 248-nm pulse laser revealed that mirror bowing can occur in both directions (concave and convex). The bowing direction is dependent upon the applied irradiation parameters such as pulse-energy density, pulse number, and the deposited energy. Sustained irradiation at energy densities exceeding a certain limit can potentially become a limiting factor for the resolvable feature sizes of the patterns generated and, therefore, for the usable SLM lifespan.
Keywords: spatial light modulator; micromirror array; micro-(opto)-electro-mechanical-system device; laser; UV; in situ Registration No. 24150 - Permalink

Generation of high charge electron beams by ionization injection
Couperus, J. P.; Köhler, A.; Zarini, O.; Krämer, J.; Pausch, R.; Debus, A.; Hübl, A.; Garten, M.; Bussmann, M.; Irman, A.; Schramm, U.
Abstract: One of the most challenging aspects in Laser wakefield acceleration (LWFA) is controlled injection of electrons into the correct phase of the accelerating field. In the ionization injection scheme this is addressed by adding a small fraction of high Z gas to the accelerating medium. Electrons in the K-shell possess a high ionization threshold which is only reached around the laser maximum, close to the center of the propagation axis. Compared to wave-breaking injection, ionization injection requires relatively low laser intensities and plasma densities, allowing us to drive the wakefield in a more stable way.
We present an extensive experimental parameter study, showing the influence of Nitrogen doping concentration on beam parameters: energy spread, charge & repeatability. We discuss the influence of laser energy and plasma density on maximum reachable energy and conversion efficiency.
We show a regime where our laser system (2.5J on target, 30 fs) generates stable electron beams (252 MeV, +/- 9% shot-to-shot) with narrow bandwidth (36 MeV +/- 11MeV FWHM) and high charge (292 pC +/- 59 pC within 1/e2) electron beams, while retaining a low background.

Keywords: Laser wakefield acceleration, LWFA
  • Poster
    Advanced Accelerator Concepts Workshop (AAC 2016), 02.08.2016, National Harbor, Maryland, USA
Registration No. 24149 - Permalink

High temperature stable TCOs as selective transmitter for solar thermal applications
Lungwitz, F.; Schumann, E.; Guillen, E.; Escobar-Galindo, R.; Gemming, S.; Krause, M.
Abstract: Materials used in the receiver tubes of a solar thermal power plant must exhibit several properties, e.g. high temperature stability, high absorption in the solar region and low thermal emittance. Nowadays, temperatures of up to 450°C and up to 550°C are reached using parabolic trough arrays and solar tower absorbers, respectively, whereas temperatures up to 800°C or higher could be reached if the receiver materials were stable enough. Previous R&D approaches for high temperature solar receiver materials include multilayer coatings deposited by PVD or sol-gel techniques. Here, a new concept for solar-selective coating is presented. A transparent conductive oxide (TCO) is deposited as a solar selective transmitter on a black body absorber to implement both, high absorption (from the black body) in the ultraviolet, visible and near infrared spectral range (300 nm – 2500 nm) as well as high reflectivity (from the TCO) in the infrared (> 2500 nm) in a relative simple material design. Therefore SnO2:Ta and TiO2:Ta thin films are reactively magnetron co-sputtered from tantalum doped and undoped metal targets at high temperatures (400°C - 700°C). By changing dopant concentration, oxygen flux, process pressure and deposition temperature the optical properties of these films can be tailored to meet the requirements of a solar selective transmitter coating. It is also shown that the electrical properties of the TCO, namely charge carrier concentration and mobility, determine the optical behavior. The correlation between structural, optical, and electrical properties is analyzed by Raman Spectroscopy and Spectroscopic Ellipsometry (SE) both at room- and especially (in situ) at hightemperatures simulating the conditions where the functional coating is supposed to operate. Additionally, Rutherford Backscattering Spectroscopy (RBS), X-ray Diffraction (XRD), UV-VIS spectrometry, and Hall Effect measurements are performed. Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged.
Keywords: solar thermal transparent conductive oxide
  • Lecture (Conference)
    15th International Conference on Plasma Surface Engineering, 14.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24146 - Permalink

Introduction into Raman spectroscopy
Krause, M.
Abstract: Fundamentals and new developments in Raman spectroscopy
  • Invited lecture (Conferences)
    Friends2-Workshop: Advanced coating and characterization techniques, 19.-20.09.2016, Dresden-Rossendorf, Deutschland
Registration No. 24142 - Permalink

Comparative study of the deposition of highly reflectant metal thin films by ionized PVD techniques
Rincón Llorente, G.; Guillén Rodríguez, E.; Schumann, E.; Heras Pérez, I.; Mesko, M.; Munnik, F.; Krause, M.; Escobar Galindo, R.
Abstract: The degree of ionization during Physical Vapor Deposition (PVD) plays a critical role on the final surface quality of the deposited coatings. In this work a comparative study of metal thin films (Al, Cu, Ag) deposited by conventional DC-Magnetron Sputtering (DCMS) and highly ionized techniques such as Filtered Cathodic Vacuum Arc (FCVA) and high power impulse magnetron sputtering (HiPIMS) was performed. The final scope of the study is aimed to optimize the deposition parameters to achieve higher specular reflectance as this have a critical influence in the yield of solar plants based on concentrated solar power. In this regard, the optical constants of the deposited films were modeled departing from ellipsometry data. A comparison of the experimental reflectance with that obtained after optical simulation was also carried out. The achieved optical performance of the films was further compared to the structural properties resulting from different deposition techniques. Rutherford Backscattering Spectrometry (RBS) and Elastic Recoil Detection Analysis (ERDA)was applied to explore the potential oxidation of the films during deposition. Surface morphological changes were explored by Scanning Electron Microscopy (SEM). In addition, Atomic Force Microscopy (AFM) measurements at different deposition times allowed exploring the dynamics of the growth mechanism of the films.
Keywords: PVD techniques, Optical properties, Simulation, RBS, AFM
  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24140 - Permalink

Impurity suppression in sputtered metallic thin films using HiPIMS
Mesko, M.; Munnik, F.; Heller, R.; Grenzer, J.; Hübner, R.; Halanda, J.; Gemming, S.; Krause, M.
Abstract: Composition and microstructure of thin films deposited by PVD are often influenced by the presence of residual gas. Therefore, it would be desirable to enable thin film growth without residuals incorporation. Strategies to avoid impurities incorporation are substrate heating, applying substrate bias, and reduction of base pressure to ultra-high vacuum (UHV) conditions. Industrial demand for low temperature and low cost processes often precludes these approaches. More recently, a very important question has been raised regarding high power impulse magnetron sputtering (HiPIMS) to form pure metallic films at low deposition rates and high values of base pressure in the deposition chamber [1].

In this study, HiPIMS was applied for room-temperature deposition of pure metallic thin films of Al, Ti, and Cu. These metals are distinguished by their oxygen affinities and melting temperatures. Deposition of carbon top layers was used to differentiate between residual gas and post-deposition contamination. Elastic recoil detection analysis (ERDA) revealed that HiPIMS produces bulk-impurity-free metallic thin films. The growth of such high-purity metallic thin films can be partly explained by gas rarefaction and the self-cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. Proposed deposition mechanism will be explained in sufficient detail. The compositional effects are correlated with differences in the film microstructure revealed by SEM, XRD, and TEM analyses.

[1] P. Pokorný et al., Plasma Processes Polym. 12, 416 (2015)

Financial support by the EU, grant No. 645725, project FRIENDS2, and the HGF via the W3 program (S.G.) is gratefully acknowledged. This work was also funded by the ERDF, Project CAMBO, ITMS: 2622022079, and by Slovak grant agency VEGA, project no. 1/0503/15

Keywords: HiPIMS, Room temperature PVD, High-purity metallic films, ERDA
  • Poster
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24139 - Permalink

In situ RBS, Raman, and ellipsometry studies of layered material systems at elevated temperatures
Wenisch, R.; Heras, I.; Lungwitz, F.; Janke, D.; Guillén, E.; Heller, R.; Gemming, S.; Escobar Galindo, R.; Krause, M.
Abstract: The detailed knowledge of composition and structure is essential for the understanding of processes and properties of functional materials at elevated temperatures. To ensure materials functionality under in operando conditions, new concepts for analysis and process monitoring are necessary. In this contribution, selected layered material systems were studied in situ at temperatures up to 830°C by Rutherford backscattering (RBS), Raman spectroscopy, and ellipsometry within a cluster tool. Metal induced crystallization (MIC) is a promising technique for hydrogen-free synthesis of two-dimensional materials. Here, Si/Ag bilayers are studied as model system. The Si/Ag layer stacks are annealed at temperatures of 380 to 700°C. simultaneously, depth profiles of the elements are investigated by RBS revealing the diffusion kinetics. The changes in the phase structure and the degree of crystallinity are analyzed by Raman spectroscopy. Both the quick initial nucleation and ensuing growth processes are investigated. MIC is observed for all temperatures under study, while layer exchange occurs only for optimized process conditions.
As an example for high-temperature functional coatings, AlTiOxN1-x thin films were investigated in order to understand the influence of the oxygen to nitrogen ratio on the optical properties and their failure mechanisms at high temperatures. Ellipsometry and RBS results showed the influence of the initial oxygen content in the sample, inward diffusion of oxygen into the coating, and the high temperature stability of AlTiOxN1-x thin films. The low emittance of AlTiOxN1-x, allowed performing in situ RBS analysis at temperature up to 830°C for the first time.
Financial support by the EU, grant No. 645725, project FRIENDS2, and the
HGF via the W3 program (S.G.) is gratefully acknowledged.

Keywords: cluster tool, in situ analysis, RBS, Raman
  • Lecture (Conference)
    Plasma Surface Engineering 2016, 11.-16.09.2016, Garmisch-Partenkirchen, Deutschland
Registration No. 24136 - Permalink

Growth and applications of III-V nanowires on Si substrates
Dimakis, E.
Abstract: III-V semiconductor nanowires have been a subject of intense research over the last 10 years and a plethora of exciting nanoscale phenomena has been unveiled. The peculiar strain relaxation mechanisms in nanowire heterostructures offer the possibility to integrate epitaxially materials with large mismatch of lattice parameters and thermal expansion coefficients. Thus, one can tailor the (opto)electronic properties of nanowire heterostructures using an extended palette of materials compared to traditional thin-film heterostructures. Furthermore, the epitaxial growth of III-V nanowires on lattice mismatched Si substrates is of great interest, because the two complementary technologies can thus be integrated on single multifunctional chips combining the superior electronic and optoelectronic properties of the former with the mature CMOS technology of the latter.
This seminar will be focusing on III-As nanowires grown on Si(111) substrates by molecular beam epitaxy. Starting from the basic description of the vapor-liquid-solid (self-induced) growth of GaAs (InAs) nanowires [1,2], the problem of structural polytypism and its effect on the nanowire optoelectronic and electrical properties will be discussed [3,4] and, finally, the droplet-confined alternate pulsed epitaxy will be proposed as a unique growth mode that offers compatibility with the Si-CMOS processing standards [5]. Finally, the growth and the structural properties of coaxial multishell (In,Al,Ga)As/GaAs nanowires will be discussed, and their application in light emitting diodes or modulation doped heterostructures will be demonstrated [6].

[1] E. Dimakis, J. Lähnemann, U. Jahn, S. Breuer, M. Hilse, L. Geelhaar, and H. Riechert, Cryst. Growth Des. 2011, 11, 4001–4008
[2] A. Biermanns, E. Dimakis, A. Davydok, T. Sasaki, L. Geelhaar, M. Takahasi, and U. Pietsch, Nano Lett. 2014, 14, 6878−6883
[3] P. Schroth, M. Köhl, and J.-W. Hornung, E. Dimakis, C. Somaschini, L. Geelhaar, A. Biermanns, S. Bauer, S. Lazarev, U. Pietsch, T. Baumbach, Phys. Rev. Lett. 2015, 114, 055504
[4] G. Bussone, H. Schäfer-Eberwein, E. Dimakis, A. Biermanns, D. Carbone, A. Tahraoui, L. Geelhaar, P. Haring Bolívar, T. U. Schülli, and U. Pietsch, Nano Lett. 2015, 15, 981−989
[5] L. Balaghi, T. Tauchnitz, R. Hübner, L. Bischoff, H. Schneider, M. Helm, and E. Dimakis, Nano Lett. 2016, 16, 4032−4039
[6] E. Dimakis, U. Jahn, M. Ramsteiner, A. Tahraoui, J. Grandal, X. Kong, O. Marquardt, A. Trampert, H. Riechert, and L. Geelhaar, Nano Lett. 2014, 14, 2604−2609
  • Invited lecture (Conferences)
    Seminar, Institute of Electronic Structure and Laser, Foundation for Research and Technology-Hellas (FORTH), 05.08.2016, Heraklion, Greece
Registration No. 24133 - Permalink

The double role of Ga droplets in the self-catalyzed growth of GaAs nanowires on SiOx/Si(111) substrates
Tauchnitz, T.; Schneider, H.; Helm, M.; Dimakis, E.
Abstract: We have investigated the in-situ surface modification of a SiOx/Si(111) substrate by Ga droplets and its effect on the subsequent self-catalyzed growth of GaAs nanowires. Using a procedure of Ga droplet formation and subsequent re-evaporation prior to the nanowire growth, we found that the number density of nanowires at a given growth temperature can be varied deliberately within four orders of magnitude without affecting the nanowire diameter. A detailed study of the Ga droplet formation in a wide range of substrate temperatures revealed the physical processes that control the number density and size of the droplets.
Keywords: Nanowire; Ga droplets; oxide etching; nanoholes; GaAs; Si substrate
  • Lecture (Conference)
    International Conference on Molecular Beam Epitaxy (MBE 2016), 04.09.2016, Montpellier, France
Registration No. 24131 - Permalink

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.
Abstract: 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
Registration No. 24130 - Permalink

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.
Abstract: 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. Registration No. 24129 - Permalink

Evaluation of E-Waste Processing through Secondary Copper Smelting
Rhamdhani, M. A.; Ghodrat, M.; Brooks, G.; Masood, S.; Corder, G.; Haque, N.; Reuter, M.
Abstract: 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


Registration No. 24125 - Permalink

Digitalizing the Circular Economy: Circular Economy Engineering Defined by the Metallurgical Internet of Things
Reuter, M.
Abstract: 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)


Registration No. 24121 - Permalink

Fast neutron-induced fission at the time-of-flight facility nELBE
Kögler, T.; Beyer, R.; Junghans, A. R.; Müller, S.
Abstract: 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
Registration No. 24120 - Permalink

The case of a rough potential energy surface: Discrepancies between results of NEB and MD calculations
Posselt, M.
Abstract: 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
Registration No. 24117 - Permalink

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
Registration No. 24112 - Permalink

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.
Abstract: 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. Registration No. 24111 - Permalink

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.
Abstract: 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. Registration No. 24109 - Permalink

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.
Abstract: 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. Registration No. 24108 - Permalink

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.
Abstract: 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. Registration No. 24107 - Permalink

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.
Abstract: Thin films of Mn x Si1−x alloys with different Mn concentration $x\approx0.44\text{--}0.63$ 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 $(f = 7\text{--}60\ \text{GHz})$ and magnetic fields $(H = 0\text{--}30\ \text{kOe})$ . For samples with $x\approx0.52\text{--}0.55$ , FMR data show clear evidence of ferromagnetism (FM) with high Curie temperatures $T_\mathrm{C} \sim 300\ \text{K}$ . 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. Registration No. 24100 - Permalink

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.
Abstract: 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 Registration No. 24099 - Permalink

Untersuchungen zu magnetohydrodynamischen Instabilitäten in Flüssigmetallen
Seilmayer, M.
Abstract: 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
Registration No. 24097 - Permalink

Cm3+ incorporation in La1-xGdxPO4 monazites: a TRLFS and XAFS study
Huittinen, N.; Scheinost, A. C.; Wilden, A.; Arinicheva, Y.
Abstract: 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
Registration No. 24096 - Permalink

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.
Abstract: 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 Registration No. 24093 - Permalink

MIR and THz spectroscopy of condensed matter
Helm, M.
Abstract: 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
Registration No. 24090 - Permalink

Common methods of spectral data analysis
Seilmayer, M.
Abstract: 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
    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
Registration No. 24082 - Permalink

Seilmayer, M.
Abstract: This is a wrapper function for image(), which makes reasonable raster plots with nice axis and other useful features.
Keywords: plot function R
  • Software
    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
Registration No. 24081 - Permalink

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.
Abstract: 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 Registration No. 24079 - Permalink

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. F.; Barbrel, B. G.; Döppner, T. H.; Glenzer, S. H. A.
Abstract: 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)]. Registration No. 24077 - Permalink

Phase Shift and Reflection of Spin Waves at Magnetic Domain Walls in Thin Films
Körber, L.; Wagner, K.; Lindner, J.; Fassbender, J.; Schultheiß, H.
Abstract: 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
Registration No. 24076 - Permalink

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.
Abstract: Use of magnetic domains as nano channels for spin wave propagation
  • Lecture (Conference)
    Spin, Waves and Interaction, 31.08.-02.09.2016, Greifswald, Deutschland
Registration No. 24075 - Permalink

Modern Measurement Methods of Brillouin Light Scattering
Osten, J.; Schultheiß, H.; Wagner, K.; Körber, L.; Wehrmann, F.; Hula, T.
Abstract: 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
Registration No. 24074 - Permalink

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.
Abstract: 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 Registration No. 24069 - Permalink

Scalable, multi-GPU photon tracing for the interaction of X-Rays with solid density plasmas
Grund, A.; Huebl, A.ORC; Kluge, T.; Widera, R.; Fortmann-Grote, C.; Bussmann, M.
Abstract: 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
Registration No. 24065 - Permalink

Plasmas, Photons, Open Standards: PIConGPU meets simex_platform through openPMD
Huebl, A.ORC; Kluge, T.; Grund, A.; Fortmann-Grote, C.; Widera, R.; Bussmann, M.
Abstract: 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.

- 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

  • Lecture (Conference)
    EUCALL Annual Meeting, 31.08.-02.09.2016, Dresden, Deutschland
Registration No. 24064 - Permalink

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.
Abstract: 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


Registration No. 24063 - Permalink

Magnetic functionalities for flexible interactive electronics
Makarov, D.
Abstract: 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
Registration No. 24062 - Permalink

In-situ X-ray observations of dendritic solidification under the influence of natural and forced convection
Eckert, S.; Shevchenko, N.; Kepplinger, O.; Sokolova, O.
Abstract: 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
Registration No. 24060 - Permalink

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.
Abstract: 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
Registration No. 24059 - Permalink

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.
Abstract: 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
Registration No. 24058 - Permalink

A mineral liberation study of grain boundary fracture based on measurements of the surface exposure after milling
Leißner, T.ORC; Hoang, D.; Rudolph, M.ORC; Heinig, T.; Bachmann, K.; Gutzmer, J.; Schubert, H.; Peuker, U. A.
Abstract: 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 Registration No. 24056 - Permalink

Tuning the fabrication of nanostructures by low-energy highly charged ions
El-Said, A. S.; Wilhelm, R. A.ORC; Heller, R.; Sorokin, M.; Facsko, S.; Aumayr, F.
Abstract: 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. Registration No. 24053 - Permalink

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.
Abstract: 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


Registration No. 24051 - Permalink

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.
Abstract: 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 Registration No. 24042 - Permalink

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.
Abstract: 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 Registration No. 24040 - Permalink

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.
Abstract: 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.


Registration No. 24039 - Permalink

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.
Abstract: 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.


Registration No. 24038 - Permalink

Holographically emulating sequential versus instantaneous disappearance of vector mesons in a hot environment
Zöllner, R.; Kämpfer, B.
Abstract: 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.


Registration No. 24037 - Permalink

Magnetic properties and giant reversible magnetocaloric effect in the GdCoC2 compound
Meng, L.; Xu, C.; Yuan, Y.; Qi, Y.; Zhou, S.; Li, L.
Abstract: 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. Registration No. 24034 - Permalink

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.
Abstract: 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
Registration No. 24033 - Permalink

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.
Abstract: 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
Registration No. 24032 - Permalink

Semiconductor spectroscopy with infrared and THz free-electron lasers
Schneider, H.
Abstract: 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
Registration No. 24031 - Permalink

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.
Abstract: 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
Registration No. 24030 - Permalink

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.
Abstract: 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 Registration No. 24029 - Permalink

Dynamics of nonequilibrium electrons on neutral center states of interstitial magnesium donors in silicon
Pavlov, S. G.; Deßmann, N.; Pohl, A.; Shuman, V. B.; Portsel, L. М.; Lodygin, А. N.; Astrov, Y. A.; Winnerl, S.; Schneider, H.; Stavrias, N.; van der Meer, A. F. G.; Tsyplenkov, V. V.; Kovalesky, K. A.; Zhukavin, R. K.; Shastin, V. N.; Abrosimov, N. V.; Hübers, H.-W.
Abstract: Subnanosecond dynamics of optically excited electrons bound to excited states of neutral magnesium donor centers in silicon has been investigated. Lifetimes of nonequilibrium electrons have been derived from the decay of the differential transmission at photon energies matching the intracenter and the impurity–to–conduction band transitions. In contrast to hydrogen-like shallow donors in silicon, significantly longer lifetimes have been observed. This indicates weaker two-phonon and off-resonant interactions dominate the relaxation processes in contrast to the single-intervalley-phonon assisted impurity-phonon interactions in the case of shallow donors in silicon.
Keywords: Extrinsic semiconductors, dynamics of electrons from impurities, magnesium doping of silicon Registration No. 24025 - Permalink

Volumetrical Laser Ion Acceleration of Spherical Mass Limited Solid Density Targets
Huebl, A.; Hilz, P.; Schreiber, J.; Kluge, T.; Widera, R.; Bussmann, M.
Abstract: Invited presentation at the LMU group of Jörg Schreiber about the results of the large scale 3D3V simulations for their experiments.
Keywords: Mass Limited Target, Paul Trap, PIConGPU, Simulation, 3D3V, GPGPU, OpenSource
  • Invited lecture (Conferences)
    LMU/MPI QO Munich: Prof. Schreiber Group Meeting (Laser-driven ion acceleration), 18.-20.07.2016, München, Deutschland
Registration No. 24023 - Permalink

Test of Lorentz invariance in β decay of polarized 20Na
Sytema, A.; van den Berg, J. E.; Böll, O.; Chernowitz, D.; Dijck, E. A.; Grasdijk, J. O.; Hoekstra, S.; Jungmann, K.; Mathavan, S. C.; Meinema, C.; Mohanty, A.; Müller, S. E.; Noordmans, J. P.; Nunez Portela, M.; Onderwater, C. J. G.; Pijpker, C.; Timmermans, R. G. E.; Vos, K. K.; Willmann, L.; Wilschut, H. W.
Abstract: Background: Lorentz invariance is key in our understanding of nature, yet relatively few experiments have tested Lorentz invariance in weak interactions.

Purpose: Our goal is to obtain limits on Lorentz-invariance violation in weak interactions, in particular rotational invariance in β decay.

Method: We search for a dependence of the lifetime of 20Na nuclei on the nuclear spin direction. Such directional dependence would be evidence for Lorentz-invariance violation in weak interactions. A difference in lifetime between nuclei that are polarized in the east and west direction is searched for. This difference is maximally sensitive to the rotation of the Earth, while the sidereal dependence is free from most systematic errors.

Results: The experiment sets a limit of 2×10-4 at 90% C.L. on the amplitude of the sidereal variation of the relative lifetime differences, an improvement by a factor 15 compared to an earlier result.

Conclusions: No significant violation of Lorentz invariance is found. The result sets limits on parameters of theories describing Lorentz-invariance violation.

Keywords: Lorentz violation, beta-decay


Registration No. 24020 - Permalink

Laser proton acceleration from liquid crystal films of different thicknesses with ultra-high laser contrast
Obst, L.; Poole, P.; Metzkes, J.; Zeil, K.; Cochran, G.; Kluge, T.; Schlenvoigt, H.-P.; Kraft, S.; Prencipe, I.; Rehwald, M.; Schumacher, D.; Schramm, U.
Abstract: We present results of our experimental campaign on laser proton acceleration, in which liquid crystal film targets of tunable thickness were irradiated with plasma mirror cleaned laser pulses. The data show a significant increase in proton cut-off energy up to 25 MeV for a target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.

The performance of laser based ion acceleration strongly depends on the laser temporal contrast and its effect on the target plasma scale length. Plasma mirror setups have proven to be a valuable tool to improve the temporal contrast by several orders of magnitude, reducing the intensity of pre-pulses that emanate from the laser chain and steepening the rising edge of the main laser pulse. We present recent results obtained at the Titanium Sapphire laser system Draco, delivering 30 fs long laser pulses at an intensity exceeding 10^20 W/cm^2. Our recently commissioned single plasma mirror improves the contrast by four orders of magnitude while reflecting 80% of the initial pulse energy. Its influence on the laser proton acceleration process was studied in a campaign in collaboration with the High Energy Density Physics Group of Ohio State University using their tunable liquid crystal film target source. This device allows an on-demand variation of the target thickness from tens of micrometers down to 10 nm while keeping the target composition constant. The target was positioned under 45 degrees with respect to the incoming laser beam while accelerated protons and ions were monitored in both laser- and target normal direction by means of Thomson Parabolas and Radiochromic Film stacks. Hence, being sensitive to the identification of acceleration regimes beyond the well-known Target Normal Sheath Acceleration, preliminary results display a significant increase in proton cut-off energy when reaching thin targets. Up to 25 MeV could be observed for an optimum target thickness of 10 nm as compared to the few- micron scale reference for this target configuration yielding roughly 12 MeV.

Keywords: laser-driven proton acceleration, high-intensity lasers
  • Lecture (Conference)
    Advanced Accelerator Concepts Workshop 2016, 2.8.2016, National Harbor, Maryland, USA
Registration No. 24018 - Permalink

Superconductivity in Weyl semimetal candidate MoTe2
Qi, Y.; Naumov, P. G.; Ali, M. N.; Rajamathi, C. R.; Schelle, W.; Barkalov, O.; Hanfland, M.; Wu, S.-C.; Shekhar, C.; Sun, Y.; Süß, V.; Schmidt, M.; Schwarz, U.; Pippel, E.; Werner, P.; Hillebrand, R.; Förster, T.; Kampert, E.; Parkin, S.; Cava, R. J.; Felser, C.; Yan, B.; Medvedev, S. A.
Abstract: Transition metal dichalcogenides have attracted research interest over the last few decades due to their interesting structural chemistry, unusual electronic properties, rich intercalation chemistry and wide spectrum of potential applications. Despite the fact that the majority of related research focuses on semiconducting transition-metal dichalcogenides (for example, MoS2), recently discovered unexpected properties of WTe2 are provoking strong interest in semimetallic transition metal dichalcogenides featuring large magnetoresistance, pressure-driven superconductivity and Weyl semimetal states. We investigate the sister compound of WTe2, MoTe2, predicted to be a Weyl semimetal and a quantum spin Hall insulator in bulk and monolayer form, respectively. We find that bulk MoTe2 exhibits superconductivity with a transition temperature of 0.10 K. Application of external pressure dramatically enhances the transition temperature up to maximum value of 8.2 K at 11.7 GPa. The observed dome-shaped superconductivity phase diagram provides insights into the interplay between superconductivity and topological physics.


Registration No. 24017 - Permalink

Commensurate and incommensurate magnetic order in spin-1 chains stacked on the triangular lattice in Li2NiW2O8
Ranjith, K. M.; Nath, R.; Majumder, M.; Kasinathan, D.; Skoulatos, M.; Keller, L.; Skourski, Y.; Baenitz, M.; Tsirlin, A. A.
Abstract: We report the thermodynamic properties, magnetic ground state, and microscopic magnetic model of the spin-1 frustrated antiferromagnet Li2NiW2O8, showing successive transitions at TN1 similar or equal to 18 K and TN2 similar or equal to 12.5 K in zero field. Nuclear magnetic resonance and neutron diffraction reveal collinear and commensurate magnetic order with the propagation vector k = (1/2,0,1/2) below TN2. The ordered moment of 1.8 µB at 1.5 K is directed along [0.89(9), - 0.10(5), - 0.49(6)] and matches the magnetic easy axis of spin-1 Ni2+ ions, which is determined by the scissor-like distortion of the NiO6 octahedra. Incommensurate magnetic order, presumably of spin-density-wave type, is observed in the region between TN2 and TN1. Density-functional band-structure calculations put forward a three-dimensional spin lattice with spin-1 chains running along the [01-1] direction and stacked on a spatially anisotropic triangular lattice in the ab plane. We show that the collinear magnetic order in Li2NiW2O8 is incompatible with the triangular lattice geometry and thus driven by a pronounced easy-axis single-ion anisotropy of Ni2+. Registration No. 24016 - Permalink

Spin transport in tantalum studied using magnetic single and double layers
Montoya, E.; Omelchenko, P.; Coutts, C.; Lee-Hone, N. R.; Hübner, R.; Broun, D.; Heinrich, B.; Girt, E.
Abstract: We report on spin transport in sputter-grown Ta films measured by ferromagnetic resonance. Spin diffusion length and spin mixing conductance are determined from magnetic damping measurements for a varying thickness of Ta layer 0 <= dTa <= 10 nm. The different boundary conditions of single- and double-magnetic-layer heterostructures Py|Ta and Py|Ta|[Py|Fe] allow us to significantly narrow down the parameter space and test various models.We showt hat a common approach of using bulk resistivity value in the analysis yields inconsistent spin diffusion length and spin mixing conductance values for magnetic single- and double-layer structures. X-ray diffraction shows that bulk Ta is a combination of β-Ta and bcc-Ta. However, in the region of significant spin transport, <~ 2 nm, there is an intermediate region of growth where the Ta lacks long-range structural order, as observed by transmission electron microscopy. Thickness-dependent resistivity measurements confirm that the bulk and intermediate regions have significantly different resistivity values. We find that the data can be well represented if the intermediate region resistivity value is used in the analysis. Additionally, the data can be fit if resistivity has the measured thickness dependence and spin diffusion length is restricted to be inversely proportional to resistivity. Finally, we rule out a model in which spin diffusion length is a constant, while the resistivity has the measured thickness dependence.
  • Physical Review B 94(2016), 054416
    Button zum Volltext
Registration No. 24015 - Permalink

TEM investigation of barrier-like anodic oxide films on aluminum
Schneider, M.; Lämmel, C.; Hübner, R.; Gierth, U.; Michaelis, A.
Abstract: The present study focuses mainly on non-electrochemical investigation of thin barrier-like oxide films formed under different pulse frequencies. The TEM investigation principally shows amorphous oxide films, which are dense and free of pores. The various pulse experiments have no influence on these film properties. The oxide growth factor was calculated to 1.06 nmV-1 in all cases. The microstructure (crystallographic orientation, grain boundaries) of the underlying substrate does not affect the oxide films. Independent of the pulse frequency, electrolyte species are not incorporated into the oxide films. The evidenced differences in the filmthickness are caused by intrinsic peculiarities of the high-field mechanism of growing oxide.
Keywords: pulse anodizing; high field mechanism; anodic oxide; aluminum
  • Surface and Interface Analysis 48(2016), 906-912
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Registration No. 24014 - Permalink

Theoretical prediction of mass transfer coefficients in both gas-liquid and slurry bubble columns
Nedeltchev, S.
Abstract: The gas-liquid contact time has been defined in a new way (bubble surface-to-rate of surface formation) and the range of applicability of the penetration theory in both gas-liquid and slurry bubble columns has been examined. In both reactors, the mass transfer coefficients were predicted successfully not only in the homogeneous regime but also in the heterogeneous regime (superficial gas velocities up to 0.08 ms-1).
The results in the article demonstrate the importance of the geometrical characteristics (length and height) of the oblate ellipsoidal bubbles for the accurate calculation of the contact time and thus the volumetric liquid-phase mass transfer coefficient kLa. The gas-liquid interfacial area has been calculated in both reactors in the classical way, i.e. as a function of the gas holdup and inversely proportional to the Sauter-mean bubble diameter. It was found that in the gas-liquid bubble column (0.095 m in ID) the modified penetration theory was applicable to tap water, 9 organic liquids (decalin, nitrobenzene, 2-propanol, 1,4-dioxane, ethanol (99 %), tetralin, xylene, 1,2-dichloroethane, ethylene glycol) and two liquid mixtures (water-glycol and tetralin-ethanol). Tetralin was aerated with both nitrogen and helium, whereas xylene was aerated with hydrogen and helium. The correction factor introduced by Calderbank (1967) was found useful for improving the kLa predictions in 1,2-dichloroethane, ethanol (99 %), xylene(-hydrogen) and toluene-ethanol 97.2 %. In the case of a slurry bubble column, the new approach was found applicable (at low solids concentrations) to four different gas-liquid-solid systems: air-tetralin-Al2O3, air-water-Al2O3, air-water-activated carbon and air-Na2SO4-kieselguhr. It is noteworthy that in some cases (air-water-Al2O3) the new definition of the contact time was found applicable up to solids concentrations of 6.29 %. In the case of a slurry bubble column, it was found that when the theoretical kLa value is multiplied by the inverse value of the correction factor the predictions improve with about 5 %.
Finally, in the slurry bubble column the contact time was defined on the basis of the length of the micro-eddies and the kLa values in both air-water-alumina and air-water-activated carbon systems were successfully predicted. This is also a potentially good approach.

Keywords: New definition of contact time; Penetration theory applicability; Prediction of mass transfer coefficients; Organic liquids; Gas-liquid bubble columns; Slurry bubble columns


Registration No. 24009 - Permalink

Ab initio description of the thermoelectric properties of heterostructures in the diffusive limit of transport
Hinsche, N. F.; Rittweger, F.; Hölzer, M.; Zahn, P.; Ernst, A.; Mertig, I.
Abstract: The scope of this review is to present the recent progress in the understanding of the microscopic origin of thermoelectric transport in semiconducting heterostructures and to identify and elucidate mechanisms which could lead to enhanced thermoelectric conversion efficiency. Based on first-principles calculations a consistent and convenient method is presented to fully describe the thermoelectric properties in the diffusive limit of transport for bulk systems and their associated heterostructures. While fundamentals of the functionality of phonon-blocking and electron-transmitting superlattices could be unveiled, we provide also distinct analysis and ideas for thermoelectric enhancement for two archetypical thermoelectric heterostructures based on inline image and Si/Ge. A focus was on the influence of bulk and interfacial strain, varying charge carrier concentration, temperature, and superlattice periods on the thermoelectric transport properties.
Keywords: super lattices, electronic structure, first principles, transport theory, Boltzmann theory, electric transport, heat transport, thermoelectric transport, uniaxial strain, biaxial strain


Registration No. 24008 - Permalink

Tests of a Compton imaging prototype in a monoenergetic 4.44 MeV photon field—a benchmark setup for prompt gamma-ray imaging devices
Golnik, C.; Bemmerer, D.; Enghardt, W.; Fiedler, F.; Hueso-González, F.; Pausch, G.; Römer, K.; Rohling, H.; Schöne, S.; Wagner, L.; Kormoll, T.
Abstract: The finite range of a proton beam in tissue opens new vistas for the delivery of a highly conformal dose distribution in radiotherapy. However, the actual particle range, and therefore the accurate dose deposition, is sensitive to the tissue composition in the proton path. Range uncertainties, resulting from limited knowledge of this tissue composition or positioning errors, are accounted for in the form of safety margins. Thus, the unverified particle range constrains the principle benefit of proton therapy. Detecting prompt gamma-rays, a side product of proton-tissue interaction, aims at an on-line and non-invasive monitoring of the particle range, and therefore towards exploiting the potential of proton therapy. Compton imaging of the spatial prompt gamma-ray emission is a promising measurement approach. Prompt gamma-rays exhibit emission energies of several MeV. Hence, common radioactive sources cannot provide the energy range a prompt gamma-ray imaging device must be designed for. In this work a benchmark measurement-setup for the production of a localized, monoenergetic 4.44MeV gamma-ray source is introduced. At the Tandetron accelerator at the HZDR, the proton-capture resonance reaction 15N(p , alpha gamma4.439)12C is utilized. This reaction provides the same nuclear de-excitation (and gamma-ray emission) occurrent as an intense prompt gamma-ray line in proton therapy. The emission yield is quantitatively described. A two-stage Compton imaging device, dedicated for prompt gamma-ray imaging, is tested at the setup exemplarily. Besides successful imaging tests, the detection efficiency of the prototype at 4.44MeV is derived from the measured data. Combining this efficiency with the emission yield for prompt gamma-rays, the number of valid Compton events, induced by gamma-rays in the energy region around 4.44MeV, is estimated for the prototype being implemented in a therapeutic treatment scenario. As a consequence, the detection efficiency turns out to be a key parameter for prompt gamma-ray Compton imaging limiting the applicability of the prototype in its current realization.
Keywords: Comptonimaging; Dosimetryconceptsandapparatus; Imagereconstructioninmedical imaging; Instrumentation for hadron therapy


Registration No. 24007 - Permalink

Coulomb dissociation of N-20,N-21
Röder, M.; Adachi, T.; Aksyutina, Y.; Alcantara, J.; Altstadt, S.; Alvarez-Pol, H.; Ashwood, N.; Atar, L.; Aumann, T.; Avdeichikov, V.; Barr, M.; Beceiro, S.; Bemmerer, D.; Benlliure, J.; Bertulani, C.; Boretzky, K.; Borge, M.; Burgunder, G.; Caamano, M.; Caesar, C.; Casarejos, E.; Catford, W.; Cederkall, J.; Chakraborty, S.; Chartier, M.; Chulkov, L.; Cortina-Gil, D.; Crespo, R.; Pramanik, U.; Diaz-Fernandez, P.; Dillmann, I.; Elekes, Z.; Enders, J.; Ershova, O.; Estrade, A.; Farinon, F.; Fraile, L.; Freer, M.; Freudenberger, M.; Fynbo, H.; Galaviz, D.; Geissel, H.; Gernhauser, R.; Gobel, K.; Golubev, P.; Diaz, D.; Hagdahl, J.; Heftrich, T.; Heil, M.; Heine, M.; Heinz, A.; Henriques, A.; Holl, M.; Ickert, G.; Ignatov, A.; Jakobsson, B.; Johansson, H.; Jonson, B.; Kalantar-Nayestanaki, N.; Kanungo, R.; Kelic-Heil, A.; Knobel, R.; Kroll, T.; Krucken, R.; Kurcewicz, J.; Kurz, N.; Labiche, M.; Langer, C.; Le Bleis, T.; Lemmon, R.; Lepyoshkina, O.; Lindberg, S.; Machado, J.; Marganiec, J.; Caro, M.; Movsesyan, A.; Najafi, M.; Nilsson, T.; Nociforo, C.; Panin, V.; Paschalis, S.; Perea, A.; Petri, M.; Pietri, S.; Plag, R.; Prochazka, A.; Rahaman, M.; Rastrepina, G.; Reifarth, R.; Ribeiro, G.; Ricciardi, M.; Rigollet, C.; Riisager, K.; Rossi, D.; Saez, J.; Savran, D.; Scheit, H.; Simon, H.; Sorlin, O.; Stoica, V.; Streicher, B.; Taylor, J.; Tengblad, O.; Terashima, S.; Thies, R.; Togano, Y.; Uberseder, E.; van de Walle, J.; Velho, P.; Volkov, V.; Wagner, A.; Wamers, F.; Weick, H.; Weigand, M.; Wheldon, C.; Wilson, G.; Wimmer, C.; Winfield, J.; Woods, P.; Yakorev, D.; Zhukov, M.; Zilges, A.; Zuber, K.
Abstract: Neutron-rich light nuclei and their reactions play an important role in the creation of chemical elements. Here, data from a Coulomb dissociation experiment on N-20,N-21 are reported. Relativistic
N-20,N-21 ions impinged on a lead target and the Coulomb dissociation cross section was determined in a kinematically complete experiment.
Using the detailed balance theorem, the N-19(n,gamma)N-20 and
N-20(n,gamma)N-21 excitation functions and thermonuclear reaction rates have been determined. The N-19(n,gamma)N-20 rate is up to a factor of 5 higher at T < 1 GK with respect to previous theoretical calculations, leading to a 10% decrease in the predicted fluorine abundance.
Registration No. 24005 - Permalink

Transversal Kerr effect of In1− x Mn x As layers prepared by ion implantation followed by pulsed laser annealing
Gan'Shina, E.; Golik, L.; Kun'Kova, Z.; Bykov, I.; Novikov, A.; Rukovishnikov, A.; Yuan, Y.; Zykov, G.; Böttger, R.; Zhou, S.
Abstract: In1− x Mn x As (x = 6.9%) layers prepared by ion implantation and subsequent pulsed laser annealing have been studied using the magnetooptical transversal Kerr effect (TKE) and spectral ellipsometry. Ellipsometry data reveal the good crystal quality of the layers. The samples show ferromagnetic behaviour below 77 K. Near the absorption edge of the parent InAs semiconductor, large TKE values are observed. In the energy regions of the transitions in the Γ and L critical points of the InAs Brillouin zone, there are several clearly defined structures in the low-temperature TKE spectra. We have calculated the spectral dependences of the diagonal and nondiagonal components of the permittivity tensor (PT), as well as the spectrum of magnetic circular dichroism (MCD) for our samples. A number of extrema in the obtained MCD and PT spectra are close to the energies of transitions in the critical points of the parent semiconductor band structure, which confirms the intrinsic ferromagnetism of the Mn-doped InAs layers. Registration No. 24004 - Permalink

Thermodynamics data of valuable elements relevant to e-waste processing through primary and secondary copper production: a review
Shuva, M. A. H.; Rhamdhani, M. A.; Brooks, G. A.; Masood, S.; Reuter, M. A.
Abstract: Waste of electronics and electrical equipment (WEEE or e-waste) can be viewed as a resource for metals, as it does not only contain the common metals like iron (Fe), aluminium (Al), lead (Pb) and copper (Cu) but also traces of precious and rare elements such as gold (Au), silver (Ag), tin (Sn), selenium (Se), tellurium (Te), platinum (Pt), palladium (Pd), tantalum (Ta), cobalt (Co) and indium (In). The recovery of these trace elements is vital, not just because it has high commercial values, but also for resources efficiency. One of the existing industrial routes for processing of e-waste is through the primary and secondary Cu smelting processes. During these processes, the trace elements are distributed in different phases, i.e. in metal/matte, slag and gas.
Different elements have different thermodynamic properties that govern the partitioning behaviour during the process. There has been a number of studies on the distribution behaviour of the trace elements relevant to primary Cu smelting (extraction of metals from virgin ores). However, there are only limited thermodynamics data relevant to secondary Cu smelting (extraction of metals from secondary/recycled sources). This paper reviews the thermodynamics data relevant for recovering the trace valuable elements from the primary Cu as well as secondary Cu smelting.
These data and knowledge provide the basis for determining the optimum conditions favourable for recovering the trace valuable elements in e-waste through the industrial Cu pyrometallurgical processing.

Keywords: E-Waste, E-Waste processing, WEEE recycling, precious metals, secondary copper Registration No. 24002 - Permalink

Gelatin-based hydrogel degradation and tissue interaction in vivo: insights from multimodal preclinical imaging in immunocompetent nude mice
Tondera, C.; Ullm, S.; Krüger-Genge, A.; Jung, F.; Neffe, A. T.; Lendlein, A.; Klopfleisch, R.; Steinbach, J.; Neuber, C.; Pietzsch, J.
Corresponding author: Pietzsch, J.
Abstract: Hydrogels based on gelatin have evolved as promising multifunctional biomaterials. Gelatin is crosslinked with lysine diisocyanate ethyl ester (LDI) and the molar ratio of gelatin and LDI in the starting material mixture determines elastic properties of the resulting hydrogel. In order to investigate the clinical potential of these biopolymers, hydrogels with different ratios of gelatin and diisocyanate (3-fold (G10_LNCO3) and 8-fold (G10_LNCO8)) molar excess of isocyanate groups) were subcutaneously implanted in mice (uni- or bilateral implantation). Degradation and biomaterial tissue interaction were investigated in vivo (MRI, optical imaging, PET) and ex vivo (autoradiography, histology, serum analysis). Multimodal imaging revealed that the number of covalent net points correlate well with degradation time, which allows for targeted modification of hydrogels based on properties of the tissue to be replaced. Importantly, the degradation time was also dependent on the number of implants per animal. Despite local mechanisms of tissue remodeling no adverse tissue responses could be observed neither locally nor systemically. Finally, this preclinical investigation in immunocompetent mice clearly demonstrated a complete restoration of the original healthy tissue.
Keywords: Autoradiography ex vivo, Biomaterials, Computed tomography, Magnetic resonance imaging, Optical imaging, Positron emission tomography


Registration No. 24001 - Permalink

Synchronized helicity oscillations: A link between planetary tides and the solar cycle?
Stefani, F.; Giesecke, A.; Weber, N.; Weier, T.
Abstract: Recent years have seen an increased interest in the question of whether the gravitational action of planets could have an influence on the solar dynamo. Without discussing the observational validity of the claimed correlations, we ask for a possible physical mechanism that might link the weak planetary forces with solar dynamo action. We focus on the helicity oscillations that were recently found in simulations of the current-driven, kink-type Tayler instability, which is characterized by an m=1 azimuthal dependence. We show how these helicity oscillations can be resonantl excited by some m=2 perturbation that reflects a tidal oscillation. Specifically, we speculate that the 11.07 years tidal oscillation induced by the Venus-Earth-Jupiter system may lead to a 1:1 resonant excitation of the oscillation of the alpha-effect. Finally, in the framework of a reduced, zero-dimensional alpha-Omega dynamo model we recover a 22.14-year cycle of the solar dynamo. Registration No. 23998 - Permalink

Pressure-tank technology for steam-water two-phase flow experiments at elevated pressure and temperature
Hampel, U.; Seidel, T.; Beyer, M.; Szalinski, L.; Lucas, D.
Abstract: In this contribution we describe the TOPFLOW pressure tank as an experimental facility for thermal hydraulics experiments in pressure equilibrium. The facility has been designed for studying steam-water two-phase flows at pressures of up to 50 bar. It enables to run experiments in flow domains of complex shape without paying attention to high difference pressures across the wall. The concept therefore allows us to use thin metal walls or even glass windows to observe flows in complex geometry domains with the help of IR or video camera and to considerably reduce cost and complexity of experimental settings. Several experimental studies have been performed with this technology so far. This includes counter-current flow in a reactor hot-leg mock-up, an experimental study on the thermal hydraulics of emergency core-cooling injection as well as investigations of direct contact condensation phenomena. In the following we give an introduction to the technology, details of design and operation and demonstrate its applicability to fundamental experimental studies on the direct steam condensation at jets and free surfaces.
Keywords: pressure tank technology, high pressure steam-water experiments, pressurized two-phase flow, high-speed videometry, falling jet, contact condensation
  • Contribution to proceedings
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH
  • Lecture (Conference)
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
Registration No. 23996 - Permalink

Ultrafast X-ray tomography for two-phase flow experiments
Hampel, U.; Banowski, M.; Krepper, E.; Szalinski, L.; Beyer, M.; Lucas, D.; Barthel, F.; Wagner, M.; Bieberle, M.
Abstract: Non-invasive tomographic imaging techniques are appropriate tools for the study of two-phase flow in nuclear thermal hydraulic experiments. Ultrafast X-ray tomography developed at Helmholtz-Zentrum Dresden-Rossendorf can scan two-phase flows both fast and with good spatial resolution. In this paper we introduce the tomography scanner system ROFEX and discuss its application to the study of two-phase flow in pipes – a benchmark problem for two-fluid CFD code development.
Keywords: two-phase flow, ultrafast X-ray tomography, gas holdup measurement, image processing, bubble size measurement, CFD code validation
  • Contribution to proceedings
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
    Proceedings of SWINTH
  • Lecture (Conference)
    Specialist Workshop on Advanced Instrumentation and Measurement Techniques for Nuclear Reactor Thermal Hydraulics (SWINTH), 15.-17.06.2016, Livorno, Italy
Registration No. 23995 - Permalink

Millisecond thermal processing using flash lamps for the advancement of thin layers and functional coatings
Skorupa, W.; Schumann, T.; Rebohle, L.
Abstract: Thermal processing in the millisecond range provides advanced, non-equilibrium annealing techniques which allow dedicated material modifications at the surface without affecting the substrate volume below. The process called flash lamp annealing (FLA) is one of the most diverse methods of short time annealing with applications ranging from the classical field of semiconductor doping to the treatment of layers on glass, polymers and other flexible substrates. It still continues to extend to other material classes and applications, and becomes of interest for an increasing number of users. Other phrases for FLA used throughout the literature are intense pulsed light sintering (IPL) or photonic curing. This review presents a short and comprehensive view of the current state of the art of FLA with a focus on functional coatings. After an introduction including historical aspects a look is taken to equipment issues as well as to the pioneering role which semiconductor processing in the framework of advanced chip technology played for the development of short time annealing. Mostly, examples of processing for photovoltaics, including doping aspects, hydrogen engineering, copper indium gallium diselenide (CIGS), silicon crystallisation on glass, and transparent conductive oxides (TCO), including indium tin oxide (ITO), zinc oxide (also Al-doped AZO) as well as inkjet printing for flexible electronics will be presented.
Keywords: flash lamp annealing (FLA), intense pulsed light sintering (IPL), semiconductors, silicon, indium tin oxide (ITO), ink jet printing Registration No. 23994 - Permalink

Radiobiology of pulsed particle beams
Beyreuther, E.
Abstract: Current radiotherapy treatment modalities like Intensity Modulated Radiation Therapy (IMRT) and gated irradiation and new technological developments like laser-driven particle accelerators include the dose delivery by short radiation pulses of high dose rate that overlap in the tumor region. The doses are accumulated over sequent radiation pulses that vary in dose fraction and time structure, which might influence the radiation response of the irradiated tissue.
In order to understand the temporal and fractionation influence of sequent beam delivery basic radiobiological experiments and translational studies to the point of clinical implementation are necessary. Starting with fundamental radiobiological principles, like radiation action and the induction of DNA damage, the lecture will also introduce some standard methods in radiobiological research. On cellular level this includes the colony formation assay as so called “golden standard” to measure the cellular survival and the quantification of molecules involved in the recognition and repair of DNA damage. One step further in the translational research chain, the observation of the radiation induced tumor growth delay on small animals will be explained.
In the second part of the lecture preceding and recent radiobiological experiments with pulsed particle beams will be presented. Beginning in the 1950s, first experiments were carried out mainly to understand the mechanism of radiation action revealing that the radiobiological effect is influenced by dose rates below 1 Gy/min, but not by higher ones. In continuation of these experiments, several studies focusing on different aspects of pulsed radiation were performed during the last two decades.
Parallel to their clinical implementation the radiobiological consequences of the sequent pulse delivery of gating and IMRT techniques were investigated highlighting the overall fraction time as critical parameter. Contrary to the dose rates of < 104 Gy/min applied for these current clinical dose delivery techniques, the laser driven techniques are characterized by pulse dose rates higher than 109 Gy/min. Taking the ultra-high pulse dose rate and other specific properties of laser driven particle beams into account the replacement of conventional accelerators for particle radiotherapy was investigated by several groups worldwide. To sum up, the hitherto performed cell and animal studies disclose that the radiobiological response to laser driven particle beams is not influenced by their ultra-high pulse dose rate.
  • Invited lecture (Conferences)
    Lamelis - Lasers in Medicine and Life Sciences - Summerschool, 07.07.2016, Szeged, Hungary
Registration No. 23990 - Permalink

Magnetic-field and composition-dependent Fermiology in correlated metals
Wosnitza, J.
Abstract: es hat kein Abstract vorgelegen
  • Invited lecture (Conferences)
    Workshop on "Fermi-surface topology and emergence of novel electronic states in strongly correlated systems", 18.07.-01.08.2016, Natal, Brasilien
Registration No. 23989 - Permalink

How To Analyze The Electronic Density - An Introduction To Some Useful Tools
Patzschke, M.
Abstract: Understanding a molecular system is not possible by only doing an electronic structure calculation. The results have to be analysed. In this presentation we will show some useful tools to do that.
Keywords: computational chemistry, ELF/ELI, AIM, NCI
  • Invited lecture (Conferences)
    CSC Spring School 2016, 11.03.2016, Helsinki, Finnland
Registration No. 23988 - Permalink

Understanding and advancing the coordination and redox chemistry of the actinides
Woodall, S.; Natrajan, L.; Kaden, P.; Kerridge, A.
Abstract: Sean Woodall, Louise Natrajan, Peter Kaden and Andrew Kerridge highlight recent advances in the chemistry of actinide elements that have been made possible through the collaborative efforts of industry and academia
Keywords: uranyl, neptunyl, TPIP, NMR, emmission, spectroscopy, theory, Single-crystal, x-ray, Uranium, Neptunium
  • Contribution to external collection
    in: Nuclear Future, Volume 11 issue 6, London: The Nuclear Institute CK International House, 2015, 1745 2058, 21-26
Registration No. 23987 - Permalink

Monitoring Redox Behaviour of Actinide Ions by a Combination of Emission and NMR Spectroscopy
Natrajan, L. S.; Woodall, S. D.; Swinburne, A. N.; Randall, S.; Banik, N.; Adam, C.; Di Pietro, P.; Kaden, P.; Kerridge, A.
Abstract: Europe currently holds a substantial nuclear legacy arising from fission activities, with a large proportion of high activity wastes that pose a radiological threat to natural and engineered environments. The decision to dispose of these high level wastes (following separation) in a suitable geological disposal facility (GDF) has provided some of the most demanding technical, and environmental challenges facing the EU in the coming century. In order to address these issues, we have begun a programme of work to establish a comprehensive understanding of the electronic properties and physical and chemical properties of the radioactive actinide metals using state of the art emission spectroscopic techniques in combination with NMR and computational methods.[1,2]
Our approach to this is to firstly use coordination chemistry to synthesise uranium compounds with ligands that model environmentally complexed species and use optical spectroscopy to understand and map both the chemical and physical behaviour of these species (Figure 1). We have recently established that U(IV) complexes are emissive and will demonstrate that uranium in the +IV and +VI oxidation states can be detected simultaneously at relatively low concentrations. Time gating techniques enable the long lived uranyl(VI) species to be separated from the shorter lived uranium(IV) species. Furthermore, the form of the emission spectra of uranyl(VI) compounds are extremely sensitive to the nature of the ligand bound in the equatorial plane and the complex nuclearity (extent of aggregation), potentially giving a sensitive method of assessing the solution forms of uranium in environmental conditions. We will next discuss how the optical properties of these model compounds can be extended to the trans-uranics and applied to disproportionation reactions and redox events in solution.
Financial support for this research was provided by the UK Engineering and Physical Sciences Research Council (EPSRC) and The Leverhulme Trust. The authors thank the European Commission Euratom FP7 funded project
(no. 269923) EURACT-NMR for support.
1. L.S. Natrajan, Coord. Chem. Rev., 2012, 256, 1583; Coord. Chem. Rev., 2014, 266–267, 171.
2. S.D. Woodall, A.N. Swinburne, N. lal Banik, A. Kerridge, P. Di Pietro, C. Adam, P. Kaden and L.S. Natrajan, Chem. Commun., 2015, 51, 5402.

Keywords: redox, actinide, emission, NMR, spectroscopy, uranium, U(IV), U(VI), uranyl
  • Lecture (Conference)
    Second Joint Student workshop on f-Element Chemistry, 09.-10.06.2015, Karlsruhe, Deutschland
Registration No. 23986 - Permalink

Luminescence spectroscopy of uranium
Steudtner, R.; Drobot, B.; Haubitz, T.; Lehmann, S.; Vogel, M.
Abstract: Luminescence spectroscopy is a powerful tool to study the chemistry of f-elements (actinides – An, lanthanides – Ln) in trace concentration. Manifold operating mode, e.g. steady-state, time-resolved, laser-induced, site-selective, cryogenic, etc. were used to investigate the environmental behavior of An/Ln in various geological and biological systems.
  • Lecture (others)
    Institutskolloquium, 27.07.2016, Karlsruhe, Deutschland
Registration No. 23985 - Permalink

Comparison of Model-free Methods for Paramagnetic Chemical Shifts in Lanthanide and Americium(III) Complexes
Adam, C.; Kaden, P.; Beele, B. B.; Müllich, U.; Geist, A.; Panak, P. J.
Abstract: NMR spectroscopy on paramagnetic compounds is a sensitive and versatile method for structural investigations of metal-organic complexes. Furthermore, separation of the overall observed paramagnetic chemical shift into parts due to covalently transferred electron spin density (Fermi contact shift, FCS) and distance- and angle-dependent dipolar electron-nucleus spin coupling (pseudo contact shift, PCS) yields insights into metal-ligand bonding. The evaluation of the pure FCS allows to determine the share of covalance in this bond. Covalence is thought to be the reason for some ligands’ selectivity for the selective complexation of actinide over lanthanide ions in potential partitioning processes.[1,2]
Since the advent of chemical shift reagents in NMR spectroscopy in 1969, several methods for the separation of FCS and PCS have been developed.[3-6] Modell-free methods rely on calculated values like spin expectation values, geometrical constants and crystal field parameters. All these values are still unknown for actinide compounds. On the other hand, the application of methods requiring a structural modell of the complex is only possible for metal ions with a large magnetic anisotropy, like the heavy lanthanides. As Am(III) has a low magnetic anisotropy, only modell-free methods can be applied to separate the observed paramagnetic shift and to elucidate the bonding in Am(III)-N-donor complexes.
Currently, we evaluate the applicability of several approaches for separation of FCS and PCS in lanthanide complexes and their transferability to actinide compounds. This includes methods based on calculated values as well
as temperature-dependent methods. We will report on our studies on a complete set of 15N-labeled lanthanide nPr-BTP and C5-BPP complexes and discuss the applicability of the methods on actinide complexes.
This work is supported by the German Federal Ministry of Education and Research (BMBF) under contract numbers 02NUK020A and 02NUK020D.
1. C. Adam, B. B. Beele, A. Geist, U. Mullich, P. Kaden and P. J. Panak, Chemical Science, 2015, 6, 1548-1561.
2. C. Adam, P. Kaden, B. B. Beele, U. Müllich, S. Trumm, A. Geist, P. J. Panak and M. A. Denecke, Dalton Trans.,
2013, 42, 14068-14074.
3. C. F. G. C. Geraldes, S. Zhang and A. D. Sherry, Inorg. Chim. Acta, 2004, 357, 381-395.
4. C. Piguet and C. F. G. C. Geraldes, in Handbook on the Physics and Chemistry of Rare Earths, eds. J. K.A. Gschneidner,
J. C. G. Bünzli and V. K. Pecharsky, Elsevier, 2003, vol. Volume 33, pp. 353-463.
5. S. Di Pietro, S. L. Piano and L. Di Bari, Coord. Chem. Rev., 2011, 255, 2810-2820.
6. A. G. Martynov, Y. G. Gorbunova and A. Y. Tsivadze, Dalton Trans., 2011, 40, 7165-7171.

Keywords: NMR, paramagnetic, lanthanide, Americium, chemical shift, BTP, BPP
  • Lecture (Conference)
    Second Joint Student Workshop on f-Element Chemistry, 09.06.-10.07.2015, Karlsruhe, Deutschland
Registration No. 23984 - Permalink

How Theory Can Probe The Chemical Bond: The Case Of Caged U2
Patzschke, M.
Abstract: "Nothing is simple in actinide chemistry" B. Roos
We present results on the intricate changes in An-An bonding in differently sized cages.
Methods used model the compounds are introduced and analysis tools are presented.

Keywords: computational chemistry, ELI, AIM, actinides, endohedral complexes
  • Invited lecture (Conferences)
    15. Koordinierungsgespräch PSI/LES - HZDR/IRE, 28.08.2015, Dresden, Deutschland
Registration No. 23982 - Permalink

Computational chemistry for actinide compounds: examine the U-U bond inside fullerenes
Patzschke, M.
Abstract: Computational chemistry methods to further the understanding of chemical bonds in heavy-metal systems are presented. Results obtained in this manner are presented for U_2 inside various fullerenes and the usefulness of the presented methods demonstrated.
Keywords: computational chemistry, actinides, fullerenes
  • Lecture (others)
    Eingeladener Vortrag Universität Hannover, 13.04.2016, Hannover, Deutschland
Registration No. 23981 - Permalink

How can Theoretical Chemistry contribute to coordination chemistry?
Patzschke, M.
Abstract: We present computational chemistry methods and tools useful in the understanding of coordination compounds, especially for complexes of actinides and technetium.
Keywords: computational chemistry, actinides, technetium
  • Invited lecture (Conferences)
    8th International Workshop on “Coordination Chemistry of Metals with Medical Relevance and Supramolecular Building Blocks“, 26.05.2016, Berlin, Deutschland
Registration No. 23980 - Permalink

Probing the chemical bond: The case of caged U_2
Patzschke, M.
Abstract: We present computational results on the "unwilling" bonding of U2 in fullerenes. We explain the nature of the strong bond to cage and the weak U-U bond.
We show how this An-An bond changes whith cage size. We will show how understanding of this special bonding might help in development of An-An forcefields.

Keywords: computational chemistry, DFT, CASPT2, ELF, AIM, actinides, fullerenes
  • Invited lecture (Conferences)
    GöCH Vortrag Linz, 29.02.2016, Linz, Österreich
Registration No. 23979 - Permalink

Uranyl Spectroscopy - Do We Know Everything?
Patzschke, M.
Abstract: Highly accurate thermodynamic data is necessary to model the behaviour of toxic/radiotoxic species in the environment. We show for the uranyl system, that TRLFS/CW spectroscopy in combination with theory is a powerful tool for such predictions.
Keywords: computational chemistry, TRLFS, PARAFAC
  • Invited lecture (Conferences)
    IX MMQC Mariapfarr Workshop on Theoretical Chemistry, 26.02.2016, Mariapfarr, Österreich
Registration No. 23978 - Permalink

Using ADF in computational actinide chemistry
Patzschke, M.
Abstract: ADF (Amsterdam Density Functional code) is a quantum chemical code that allows computations for molecules containing all elements in the periodic table. We will present its capabilities, demonstrate its usage and instruct the participants to set up their own calculations.
Keywords: computational chemsitry, DFT, actinides
  • Invited lecture (Conferences)
    ThUL school 2105, 28.09.2015, Karlsruhe, Deutschland
Registration No. 23977 - Permalink

Visualising Your Results - An Introduction to VMD
Patzschke, M.
Abstract: Visualising the results of quantum chemical computations is an important part of research. Producing high quality graphics becomes more and more a required skill. We will present the use of the program VMD, show applications and teach students to use it on their own.
Keywords: computational chemistry, visualisation, VMD
  • Invited lecture (Conferences)
    CSC Spring School 2015, 12.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 10.03.2016, Helsinki, Finnland
Registration No. 23976 - Permalink

Quantum Chemistry Workshop - using Orca & Gabedit
Patzschke, M.
Abstract: The capabilities of the qc-code Orca and the versatile GUI gabedit are presented. Calculations with Orca are demonstrated and the students are taught to set up their own calculations.
Keywords: computational chemistry, Orca
  • Invited lecture (Conferences)
    CSC Spring School 2015, 11.03.2015, Helsinki, Finnland
  • Invited lecture (Conferences)
    CSC Spring School 2016, 09.03.2016, Helsinki, Finnland
Registration No. 23975 - Permalink

Planned Projects of the New Theory- Group in Rossendorf
Patzschke, M.
Abstract: We present research projects of the newly established computational chemistry group at the FWO.
Keywords: computational chemistry, actinides
  • Lecture (others)
    Helmholtz-Koordinierungstreffen 2015, 04.03.2015, Jülich, Deutschland
Registration No. 23974 - Permalink

Computational Methods for f-Elements
Patzschke, M.
Abstract: Theoretical chemistry is a comparatively new research area in chemistry. In the last 100 years enormous progress has been made in understanding the electronic structures of molecules. Almost every publication nowadays has a theory section. This means, that all chemists have to understand the basics of quantum chemistry.

The f-elements, and especially the actinides are very challenging to work with in the laboratory, to make matters worse, they are even very challenging to treat computationally. The reason for this is threefold:

1) Each actinide atom adds a lot of electrons to the system and as computational methods get much more time consuming when the amount of electrons in the system is increased, special care has to be taken to make the computations as efficient as possible.
2) Actinides, especially the later ones in low oxidation states contain many unpaired electrons, making many of the actinide-containing species multi-reference cases, where simple computational methods do not work.
3) For heavy elements, the expectation value of the speed of the innermost electrons approaches the speed of light. This means, normal quantum-chemical methods as used for light elements will not work.

In the light of the above mentioned points we will have a look at the methods available in the quantum chemical treatment of f-elements. We will spend some time looking at density-functional theory, the work-horse of computational chemistry. Special care will be taken to explain were this theory excels and what its shortcomings are.

We will then move to so called multi-reference methods, useful for treating actinide systems. Here the difference between static and dynamic correlation will be explained and methods to treat both will be introduced. The concept of an active space will be presented in some detail and guidelines for a successful choice of this active space will be given.

Finally, we will spend some time looking at the fundamental ideas of relativistic quantum chemistry and the effect of relativity on chemical properties. In this part we will also discuss the special requirements relativistic calculations impose.

Keywords: computational chemistry, actinides
  • Invited lecture (Conferences)
    Second Joint Student Workshop on f-Element Chemistry, 09.06.2015, Karlsruhe, Deutschland
Registration No. 23973 - Permalink

Investigating Catalytic Activity with DFT
Patzschke, M.
Abstract: We present computational results for the regioselectivity of the Pauson-Khand reaction and the computationally validated catalytic cycle of the gold(III) catalyzed enynamine – cyclopentadiene cycloisomerisation.
Keywords: computational chemistry, DFT, CASPT2, catalysis
  • Invited lecture (Conferences)
    IXth Workshop on Modern Methods in Quantum Chemistry, 26.02.2015, Mariapfarr, Österreich
Registration No. 23972 - Permalink

DFT in the f-block
Patzschke, M.
Abstract: Computational chemistry has become an important tool. The most popular approaches are based on the electronic density, methods known as DFT calculations. We review the basic principles as well as the applicability to f-element systems.
Keywords: Computational chemistry, DFT, f-elements
  • Invited lecture (Conferences)
    EUFEN 4, 09.04.2015, Lissabon, Portugal
Registration No. 23971 - Permalink

Magnetically induced ring currents in actinide extraction ligand systems
Patzschke, M.
Abstract: Aromaticity is an old concept in chemistry. With newly developed metods, like GIMIC, it is possible to quantify this concept. With this method the ring current induced by an external magnetic field is evaluated (in nA/T), paramagnetic and diamagnetic contributions can be seen and the stabilisation due to aromaticity predicted. We present latest results for some typical actinide extraction ligands like BTP and look on the influence of complexation on these currents.
Keywords: Computational chemistry, actinides, aromaticity
  • Lecture (others)
    Eingeladener Vortrag TU München, 05.02.2015, München, Deutschland
Registration No. 23970 - Permalink

Nanoparticle dispersion in liquid metals by electromagnetically induced acoustic cavitation
Kaldre, I.; Bojarevics, A.; Grants, I.; Beinerts, T.; Kalvans, M.; Milgravis, M.
Abstract: Ceramic nanoparticle dispersion in metallic matrix is a technical challenge to produce class of composite materials-Metal matrix nano-composites (MMNC). Current powder metallurgy has limitations producing these materials. Process is time consuming and dimensions of ingots are limited. Aim of this study is to investigate experimentally the effect of magnetically induced cavitation applied for the purpose of nanoparticle dispersion in liquid metals. We present a contactless electromagnetic method to induce ultrasound and disperse particles in liquid metals by simultaneously applied steady and alternating magnetic fields. The oscillating magnetic force due to the azimuthal induction currents and the axial magnetic field excites power ultrasound in the sample. If the fields are sufficiently high then it is possible to achieve the acoustic cavitation threshold in liquid metals. Cavitation bubble collapses create intense microscale jets, which can break nanoparticle agglomerates and disperse them. Cavitation bubble collapses are known to create microscale jets with a potential to break nanoparticle agglomerates and disperse them. The samples are solidified under the contactless ultrasonic treatment and later analyzed by electron microscopy and energy-dispersive X-ray spectroscopy (EDX). It is observed that SiC nanoparticles are dispersed in an aluminum magnesium alloy, whereas in tin the same particles remain agglomerated in micron-sizedclusters despite a more intense cavitation.
Keywords: Nanaoparticles, Metal matrix composites (MMCs), Cavitation, High magnetic field, Power ultrasound Registration No. 23969 - Permalink

Scalable critical-path analysis and optimization guidance for hybrid MPI-CUDA applications
Schmitt, F.; Dietrich, R.; Juckeland, G.
Abstract: The use of accelerators in heterogeneous systems is an established approach in designing petascale applications. Today, Compute Unified Device Architecture (CUDA) offers a rich programming interface for GPU accelerators but requires developers to incorporate several layers of parallelism on both the CPU and the GPU. From this increasing program complexity emerges the need for sophisticated performance tools. This work contributes by analyzing hybrid MPI-CUDA programs for properties based on wait states, such as the critical path, a metric proven to identify application bottlenecks effectively. We developed a tool to construct a dependency graph based on an execution trace and the
inherent dependencies of the programming models CUDA and Message Passing Interface (MPI). Thereafter, it detects wait states and attributes blame to responsible activities. Together with the property of being on the critical path, we
can identify activities that are most viable for optimization. To evaluate the global impact of optimizations to critical activities, we predict the program execution using a graph-based performance projection. The developed approach has been demonstrated with suitable examples to be both scalable and correct. Furthermore, we establish a new categorization of CUDA inefficiency patterns ensuing from the dependencies between CUDA activities.

Keywords: GPGPU, CUDA, MPI, wait states, critical-path analysis, performance analysis, performance optimization Registration No. 23968 - Permalink

Advanced characterization and optical simulation for the design of solar selective coatings based on carbon:transition metal carbide nanocomposites
Heras, I.; Krause, M.; Abrasonis, G.; Pardo, A.; Endrino, J. L.; Guillén, E.; Escobar-Galindo, R.
Abstract: Solar selective coatings based on carbon transition metal carbide nanocomposite absorber layers were designed. Pulsed filtered cathodic arc was used for depositing amorphous carbon: metal carbide (a-C:MeC, Me = V, Mo) thin films. Composition and structure of the samples were characterized by ion beam analysis, X-ray diffraction, Raman spectroscopy, and transmission electron microscopy. The optical properties were determined by ellipsometry and spectrophotometry. Three effective medium approximations (EMA), namely Maxwell-Garnett, Bruggeman, and Bergman, were applied to simulate the optical behaviour of the nanocomposite thin films. Excellent agreement was achieved between simulated and measured reflectance spectra in the entire wavelength range by using the Bergman approach, where in-depth knowledge of the nanocomposite thin film microstructure is included. The reflectance is shown to be a function of the metal carbide volume fraction and its degree of percolation, but not dependent on whether the nanocomposite microstructure is homogeneous or a self-organized multilayer. Solar selective coatings based on an optimized a-C:MeC absorber layer were designed exhibiting a maximum solar absorptance of 96% and a low thermal emittance of ~5 and 15% at 25 and 600ºC, respectively. The results of this study can be considered as predictive design tool for nanomaterial-based optical coatings in general.
Keywords: Solar selective coatings, Amorphous carbon:transition metal carbides, Effective Medium approximation, Pulsed filtered cathodic vacuum arc, Bergman representation Registration No. 23967 - Permalink

Thermally induced formation of metastable nanocomposites in amorphous Cr-Zr-O thin films deposited using reactive ion beam sputtering
Rafaja, D.; Wüstefeld, C.; Abrasonis, G.; Braeunig, S.; Baehtz, C.; Hanzig, F.; Dopita, M.; Krause, M.; Gemming, S.
Abstract: Successive crystallization ofamorphous Cr-Zr-O thin films, formation of the (Cr,Zr)2O3/(Zr,Cr)O2 nanocomposites and the thermally induced changes in the hexagonal crystal structure of metastable (Cr,Zr)2O3 were investigated by means of in situ high-temperature synchrotron diffraction experiments up to 1100 °C. The thin films were deposited at room temperature by using reactive ion beam sputtering, and contained 3–15 at.% Zr. At low Zr concentrations, chromium-rich (Cr,Zr)2O3 crystallized first, while the crystallization of zirconium-rich (Zr,Cr)O2 was retarded. Increasing amount of zirconium shifted the onset of crystallization in both phases to higher temperatures. For 3 at.% of zirconium in amorphous Cr-Zr-O, (Cr,Zr)2O3 crystallized at 600 °C. At 8 at.% Zr in the films, the crystallization of (Cr,Zr)2O3 started at 700 °C. At 15 at.% Zr, the Cr-Zr-O films remained amorphous up to the annealing temperature of 1000 °C.Metastable hexagonal (Cr,Zr)2O3 accommodated up to ~3 at.% Zr. Excess of zirconium formed tetragonal zirconia, which was stabilized by chromium.
Keywords: Metastable oxides In situ synchrotron diffraction Crystallization Reactive ion beam sputtering Rutherford backscattering spectrometry Registration No. 23966 - Permalink

Evaluation of the enantiomer specific biokinetics and radiation doses of [18-F]-fluspidine – a new tracer in clinical translation for imaging of σ1 receptors
Kranz, M.; Sattler, B.; Wüst, N.; Deuther-Conrad, W.; Patt, M.; Meyer, P. M.; Fischer, S.; Donat, C. K.; Wünsch, B.; Hesse, S.; Steinbach, J.; Brust, P.; Sabri, O.
Corresponding author: Kranz, M.
Abstract: The enantiomers of [18F]-fluspidine, recently developed for imaging of σ1 receptors, exhibit promising and distinct pharmacokinetics which makes them attractive for different clinical questions. To support their clinical translation, human radiation dosimetry of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine was estimated from ex vivo biodistribution and PET/MR imaging in mice after extrapolation to human scale. The results were validated by a first-in-human study where time-dependent activity data of (S)-(-)-[18F]-fluspidine was obtained by PET/CT. The time-activity curves were exponentially fitted and the integral used in OLINDA to calculate organ doses (ODs) and the effective dose (ED). According to different biokinetics of (S)-(-)-[18F]-fluspidine and (R)-(+)-[18F]-fluspidine, the EDs differ significantly with values of 12.9 µSv/MBq and 14.0 µSv/MBq (p<0.025, image-derived data of mice), respectively, as observed by ex vivo biodistribution too. In the human study, the ED was calculated to be 21.0 µSv/MBq. The preclinical dosimetry reveals the ED for [18F]-fluspidine comparable with other 18F-labeled PET imaging agents, despite differences of the EDs due to enantiomer specific kinetics. The first-in-human study confirmed that the radiation risk of (S)-(-)-[18F]-fluspidine imaging is within accepted limits. However, the ED in humans is underestimated when using preclinical imaging for dosimetry which needs to be considered when applying for first-in-human studies.


Registration No. 23965 - Permalink

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