Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34118 Publications

Fabrication of Sub-Micron Surface Structures on Copper, Stainless Steel and Titanium using Picosecond Laser Interference Patterning

Bieda, M.; Siebold, M.; Lasagni, A. F.

Picosecond direct laser interference patterning is investigated theoretically and experimentally for the bulk metals copper, stainless steel and titanium. In the past, results on thermal modelling for nanosecond irradiation were reported for pitches in the range of several micrometers. When nanosecond pulses are utilized, the smallest possible pitch on metals is limited by the thermal diffusion length. In this case, the laser patterning process is predominantly determined by heat conduction mechanisms, and pitches less than 1 μm are not feasible. Picosecond laser pulses allow values below 1 μm pitch size on metallic surfaces. The modelling and simulation of DLIP is based on the two-temperature-model and was carried out for a pulse duration of 35 ps at 515 nm wavelength and a laser fluence of 0.1 J cm-2. The subsurface temperature distribution of both electrons and phonons was computed for periodic structures with a pitch of 0.8 μm. The increase in temperature rises for a lower absorption coefficient and a higher thermal conductivity (larger absorption depth) . The distance, at which the maximum subsurface temperature occurs, increases for a small absorption coefficient. High absorption and low thermal conductivity minimizes internal heating and give rise to a pronounced surface micro topography with pitches smaller than 1 μm. Periodic line-like surface structures were produced using two interfering beams on copper, stainless steel and titanium surfaces with a pitch of 0.7 μm using a Yb:YAG-Laser with 515 nm wavelength and a pulse duration of 35 ps.

Publ.-Id: 23485

Stakeholder integration in new product development – A systematic analysis of drivers and firm capabilities

Martin, M. V.; Reinhardt, R.; Gurtner, S.

In this article, we develop a conceptual model of stakeholder integration in new product development (NPD) that (i) explains the drivers of the process and (ii) proposes a framework of capabilities that firms need for successful stakeholder integration. The focus lies on external stakeholders that directly influence the adoption of new products. We conduct a systematic literature review and content analyze a sample of 96 peer-reviewed journal articles. The study is restricted to the medical device industry to enable the use of specific search terms and the consistent categorization of information. We dedicate a section to showing how the framework applies to other settings. The drivers of stakeholder integration are classified into push factors (i.e., expected benefits for the focal firm) and pull factors (i.e., expected benefits for the stakeholders). This study provides an initial model of how stakeholder integration works based on its drivers. In addition, three related stakeholder integration capabilities emerge: stakeholder identification capability, stakeholder interaction capability and stakeholder input integration capability. The paper proposes a description of these capabilities for stakeholder integration in NPD and, thus, contributes to stakeholder theory and research on the management of NPD. The results open new paths for empirical testing and offer practical guidance on how to successfully integrate stakeholders in NPD processes.

Keywords: Stakeholder; New Product Development; Innovation

Publ.-Id: 23484

Smart Kd‑concept for realistic description of sorption processes

Stockmann, M.; Becker, D.; Flügge, J.; Schikora, J.; Noseck, U.; Brendler, V.

Sorption on mineral surfaces is an important retardation process to be considered in safety assessments of both chemotoxic and radioactive waste repositories. Most often conventional conservative concepts with temporally and spatially constant distribution coefficients (Kd‑values) are applied in reactive transport simulations.
This work describes, for the first time, a new methodology, where temporally and spatially variable distribution coefficients, so‑called smart Kd‑values were calculated for a more realistic description of sorption processes. This concept is based on a Bottom-Up approach (Davis 1998) of a competitive mineral-specific sorption of dissolved species on surfaces, combining surface complexation models with ion exchange and precipitation in a quasi-thermodynamic manner. The respective multi-dimensional matrices are computed a-priori to any run of the reactive transport codes (here: r³t, Fein 2004). During the run of such transport codes respective calls to the Kd–matrix with an appropriate averaging deliver parameter-specific Kd–values.
Three computer codes were coupled to form one tool: PHREEQC, UCODE and SIMLAB. This strategy has various benefits: (1) One can calculate smart Kd‑values for a reasonable number of environmental parameter combinations; (2) It is possible to perform uncertainty and sensitivity analysis based on such smart Kd‑matrices; (3) The approach is highly flexible with respect to chemical reactions and environmental conditions; (4) The overall methodology is much more efficient in computing time than a direct coupling of the geochemical speciation code with reactive transport codes.
The capability of this new methodology is demonstrated for the sorption of radioactive waste repository-relevant elements such as U, Am, or Np on a natural sandy aquifer. This served as a proof-of-concept for the new methodology to describe the sorption behavior in dependence of changing geochemical conditions. Results were compared to conservative Kd–values from literature used so far.

Fig 1: Kd histogramm for Am(III) in the upper aquifer of the Gorleben cap rock
Sensitivity and uncertainty analysis for the nuclides revealed the importance of ternary interaction effects, the non-concervatism of some generic distribution coefficients used so far, and the effects of input parameter correlation. Moreover, a ranking of the sensitivity of the environmental parameters nearly always put pH value, dissolved inorganic carbon and the content of matrix cations in the first places. Consequently, the mechanistic processes involving them (and their error distribution functions) should deserve higher attention in future research schemes.
Davis, J. A., Coston, J. A., Kent, D. B., Fuller, C. C. (1998): Application of the surface complexation concept to complex mineral assemblages. Environ. Sci. Technol. 32, 2820-2828.
Fein, E. (2004): Software Package r³t. Model for Transport and Retention in Porous Media. Report GRS-192, Braunschweig.

Keywords: nuclear waste disposal; safety assessment; modelling; thermodynamics; sorption; uncertainty; sensitivity; radionuclides

  • Lecture (Conference)
    DAEF 2016 - 2nd Conference on Key Topics in Deep Geological Disposal – Challenges of a Site Selection Process: Society – Procedures – Safety, 26.-28.09.2016, Köln, Deutschland

Publ.-Id: 23483

Vacancy Defect Complexes in Silicon: Charge and Spin Order

Liu, Y.; Pan, R.; Zhang, X.; Han, J.; Yuan, Q.; Tian, Y.; Yuan, Y.; Liu, F.; Wang, Y.; N'Diaye, A. T.; Arenholz, E.; Chen, X.; Sun, Y.; Song, B.; Zhou, S.

We investigate the interaction between charges and spin order of the defect complex V6 in silicon. The first-principles calculations predict spin resolved band splitting incurred by a neutral V6 yet with no net spin. Therefore, any shift of Fermi level can trigger the spin polarization. Both s and p states contribute local moments in the positively charged V6. The ferromagnetic coupling is only obtained between a positively charged V6 and a neutral one. In silicon after neutron irradiation, magnetism is achieved even at room temperature. The 3s∗3p∗ hybrid states of V6 are probably responsible for the observed long-range magnetic order. Our results unravel the role of charged V6 in inducing magnetism and will be useful in understanding and further manipulating the intrinsic properties of defect complexes in silicon and other semiconductors.

Keywords: defect-induced ferromagnetism; silicon; neutron irradiation; semiconductors; defect complex; charge state


Publ.-Id: 23482

Late Quaternary paleoenvironmental records from the Chatanika River valley near Fairbanks (Alaska)

Schirrmeister, L.; Meyer, H.; Andreev, A.; Wetterich, S.; Kienast, F.; Bobrove, A.; Fuchs, M.; Sierralta, M.; Herzschuh, U.

Perennially-frozen deposits are considered as excellent paleoenvironmental archives similar to lacustrine, deep marine, and glacier records because of the long-term and good preservation of fossil records under stable permafrost conditions. A permafrost tunnel in the Vault Creek Valley (Chatanika River Valley, near Fairbanks) exposes a sequence of frozen deposits and ground ice that provides a comprehensive set of proxies to reconstruct the late Quaternary environmental history of Interior Alaska. The multi-proxy approach includes different dating techniques (radiocarbon-accelerator mass spectrometry [AMS 14C], optically stimulated luminescence [OSL], thorium/uranium radioisotope disequilibria [230Th/U]), as well as methods of sedimentology, paleoecology, hydrochemistry, and stable isotope geochemistry of ground ice.

The studied sequence consists of 36-m-thick late Quaternary deposits above schistose bedrock. Main portions of the sequence accumulated during the early and middle Wisconsin periods. The lowermost unit A consists of about 9-m-thick ice-bonded fluvial gravels with sand and peat lenses. A late Sangamon (MIS 5a) age of unit A is assumed. Spruce forest with birch, larch, and some shrubby alder dominated the vegetation. High presence of Sphagnum spores and Cyperaceae pollen points to mires in the Vault Creek Valley. The overlying unit B consists of 10-m-thick alternating fluvial gravels, loess-like silt, and sand layers, penetrated by small ice wedges. OSL dates support a stadial early Wisconsin (MIS 4) age of unit B. Pollen and plant macrofossil data point to spruce forests with some birch interspersed with wetlands around the site. The following unit C is composed of 15-m-thick ice-rich loess-like and organic-rich silt with fossil bones and large ice wedges. Unit C formed during the interstadial mid-Wisconsin (MIS 3) and stadial late Wisconsin (MIS 2) as indicated by radiocarbon ages. Post-depositional slope processes significantly deformed both, ground ice and sediments of unit C. Pollen data show that spruce forests and wetlands dominated the area. The macrofossil remains of Picea, Larix, and Alnus incana ssp. tenuifolia also prove the existence of boreal coniferous forests during the mid-Wisconsin interstadial, which were replaced by treeless tundra-steppe vegetation during the late Wisconsin stadial. Unit C is discordantly overlain by the 2-m-thick late Holocene deposits of unit D. The pollen record of unit D indicates boreal forest vegetation similar to the modern one.

The permafrost record from the Vault Creek tunnel reflects more than 90 ka of periglacial landscape dynamics triggered by fluvial and eolian accumulation, and formation of ice-wedge polygons and post-depositional deformation by slope processes. The record represents a typical Wisconsin valley-bottom facies in Central Alaska.

Keywords: Permafrost; Interior Alaska; Loess; Cryolithology; Geochronology; Paleoecology; Landscape dynamics


Publ.-Id: 23481

Synthesis and characterization of modified ultrasmall nanoparticles as multimodal imaging agents

Singh, G.; Hunoldt, S.; Licciardello, N.; Stephan, H.; Faramus, A.; de Cola, L.

The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications.[1] The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles[2] (Si NPs) of size <5 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cyanine 5[3] dye was attached selectively to the amine terminated Si NPs. The single domain antibody is also conjugated with the particles for specific targeting of the cancerous tumors via a molecular handle such as PEG-Maleimide, which facilitates the targeting as well as maintains the hydrophilicity of the particles at the same time. Bispidines[4] are to be used as a copper chelator for radiolabeling the particles by 64Cu and could be used for the in vitro and in vivo studies by Positron emission tomography.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

[1] G. J. Cheon, Y. Chang, J. Yoo, J. Cheon, Angew. Chem. 2008, 120, 6355 –6358.
[2] Y. Zhong, F. Peng, F. Bao, S. Wang, X. Ji, L. Yang, Y. Su, S. Lee, Y. He, J. Am. Chem. Soc. 2013, 135, 8350−8356.
[3] K. Viehweger, L. Barbaro, K. P. García, T. Joshi, G. Geipel, J. Steinbach, H. Stephan, L. Spiccia, B. Graham, Bioconjugate Chem. 2014, 25, 1011−1022.
[4] H. Stephan, M. Walther, S. Fähnemann, P. Ceroni, J. Molloy, G. Bergamini, F. Heisig, C. E. Müller, W. Kraus, P. Comba, Chem. Eur. J. 2014, 20, 17011-17018.

  • Poster
    Analytica Conference 2016, 10.-12.05.2016, Munich, Germany

Publ.-Id: 23480

Intrinsic diamagnetism in the Weyl semimetal TaAs

Liu, Y.; Li, Z.; Guo, L.; Chen, X.; Yuan, Y.; Liu, F.; Prucnal, S.; Helm, M.; Zhou, S.

We investigate the magnetic properties of TaAs, a prototype Weyl semimetal. TaAs crystals show diamagnetism with magnetic susceptibility of about −7×10−7 emu/(g Oe) at 5 K. A general feature is the appearance of a minimum at around 185 K in magnetization measurements as a function of temperature, which resembles that of graphite. No phase transition is observed in the temperature range between 5 K and 400 K.

Keywords: Diamagnetism; Weyl semimetal; TaAs; Magnetic susceptibility

  • Journal of Magnetism and Magnetic Materials 408(2016), 73-76
    DOI: 10.1016/j.jmmm.2016.01.100
  • Poster
    33rd International Conference on the Physics of Semiconductors, 31.07.-05.08.2016, Beijing, China

Publ.-Id: 23479

In-beam PET at clinical proton beams with pile-up rejection

Helmbrecht, S.; Enghardt, W.; Fiedler, F.; Iltzsche, M.; Pausch, G.; Tintori, C.; Kormoll, T.

Positron emission tomography (PET) is a means of imaging the β+-activity produced by the radiation field in ion beam therapy and therefore for treatment verification. Prompt Γ-rays that are emitted during beam application challenge the detectors and electronics of PET systems, since those are designed for low and medium count rates. Typical PET detectors operated according a modified Anger principle suffer from multiple events at high rates. Therefore, in-beam PET systems using such detectors rely on a synchronization of beam status and measurement to reject deteriorated data.

In this work, a method for pile-up rejection is applied to conventional Anger logic block detectors. It allows for an in-beam data acquisition without further synchronization.

Though cyclotrons produce a continuous wave beam, the radiation field shaping technique introduces breaks in the application.
Time regimes mimicking synchrotrons as well as cyclotron based ones using double-scattering or pencil beam scanning field shaping at dose rates of 0.5, 1.0 and 2.0 Gy/min were investigated. Two types of inhomogeneous phantoms were imaged. The first one simulates cavity structures, the other one mimics a static lung irradiation.

It could be shown that, depending on the dose rate and the beam time structure, in-beam measurement including a few seconds decay time only, yield images which revealed all inhomogeneities in the phantoms. This technique can be the basis for the development of an in-beam PET system with traditional detectors and off-the-shelf electronics.

Keywords: Positron emission tomography; in-beam PET; Pile up; Proton therapy; Ion beam therapy

Publ.-Id: 23478

Influence of uranium(VI) on the metabolism of plant cells

Sachs, S.; Geipel, G.; Fahmy, K.; Obeid, M. H.; Bok, F.

Detailed knowledge of the radionuclide transfer in the environment including the food chain represents the basis for the reliable assessment of the resulting risk potential for human and wildlife. In order to improve the knowledge of the underlying processes, interaction processes of plants with actinides are studied (e.g., [1-3]). Due to the interaction with heavy metal ions, plants segregate metal chelates into the rhizosphere, store metal chelates in vacuoles or synthesize protective metabolites that can bind metal ions and consequently reduce their availability in the cytoplasm [4].

In the present work we study the interaction of uranium(VI) with canola cell suspensions (Brassica napus) as a function of the uranium(VI) concentration. The influence of uranium(VI) on the cell metabolism is studied by microcalo-rimetry. Our results show that in the presence of uranium(VI) concentrations >100 µM the heat flow generated by the cells is decreased, which indicates a lower metabolic activity of the cells compared to control samples cultivated in the absence of uranium(VI). These results agree to cell viability data measured applying the MTT test [5]. Furthermore, we study the release of plant cell metabolites in consequence of the cell contact with uranium(VI). Focusing on flavonoids, flavonoid glycosides, and phenolic acids, a solid phase extraction method coupled with high-performance liquid chromatography is developed. This method allows the separation and enrichment of cell metabolites from the nutrient medium as well as their fractionation as basis for their further identification. Knowledge of an element’s speciation is crucial for understanding its biochemical and biological behavior. Therefore, the uranium(VI) speciation in the nutrient medium is determined by time-resolved laser-induced fluorescence spectroscopy and calculated by thermodynamic modeling. The objective is to correlate the influence of uranium(VI) on the metabolic activity of the cells with the uranium(VI) speciation in the nutrient medium.

The authors thank J. Seibt, S. Heller, J. Philipp, and S. Gurlit for their technical support.

[1] Günther, A. et al. (2003) Radiochim. Acta 91, 319-328.
[2] Laurette, J. et al. (2012) Environ. Exp. Bot. 77, 96-107.
[3] Geipel, G. et al. (2015) Biometals 28, 529-539.
[4] Weiler, E., Nover, L. (2008) Allgemeine und molekulare Botanik, Thieme, Stuttgart.
[5] Mosmann, T. (1983) J. Immunol. Meth. 65, 55-63.

Keywords: Plants; plant cells; metabolism; interaction; actinides; uranium; microcalorimetry; solid phase extraction; HPLC; speciation; TRLFS

  • Poster
    10th International Biometals Symposium (Biometals 2016), 10.-15.07.2016, Dresden, Germany

Publ.-Id: 23477

Untersuchung zum Einfluss lokaler Strömungszustände auf das Auftreten der Siedekrise

Geißler, T.; Franz, R.; Hampel, U.

Die Effizienz von Verdampfungssystemen hängt maßgeblich von der übertragbaren Wärmestromdichte ab. Eine Leistungssteigerung ist durch das Auftreten der Siedekrise limitiert. Dabei kommt es durch ein abruptes Abfallen des Wärmeübergangskoeffizienten in leistungsbestimmten Systemen zu einem starken Temperaturanstieg der Heizfläche, welcher zu einem Versagen der Strukturelemente führen kann. Sicherheitsmargen sorgen in industriellen Anwendungen für einen ausreichenden Schutz vor diesem kritischen Zustand. Mit einer verlässlichen Vorhersage der Siedekrise können diese Margen allerdings reduziert werden. Durch Experimente mit hochaufgelöster Messung der Wandtemperatur und Bestimmung der Phasenverteilung während des Siedens werden Verdampfungsprozesse besser verstanden und CFD-Modell-Entwicklung unterstützt.

  • Poster
    Jahrestreffen der ProcessNet-Fachgruppe Wärme- und Stoffübertragung, 01.-02.03.2016, Kassel, Deutschland

Publ.-Id: 23475

On the influence of local flow structure on the boiling crisis

Geißler, T.; Franz, R.; Hampel, U.

Nucleate boiling is one of the main heat transfer mechanism in safety analysis of nucleate power plants. Thereby the decision if the boiling crisis is occurs is on central aspect and main purpose of this study. The MORENA experiment is designed to make a contribution towards the understanding of the influence of local two-phase flow structures on the boiling crisis by the help of fast electron beam X-ray tomography (ROFEX) and infrared thermography.

Keywords: heat transfer; boiling crisis; x-ray tomography; MORENA; infrared thermography; CHF

  • Lecture (Conference)
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
  • Contribution to proceedings
    47th Annual Meeting on Nuclear Technology, 10.-12.05.2016, Hamburg, Deutschland
    Proceedings of the 47th Annual Meeting on Nuclear Technology

Publ.-Id: 23474

Mechanism of attenuation of uranyl toxicity by glutathione in Lactococcus lactis

Obeid, M. H.; Oertel, J.; Solioz, M.; Fahmy, K.

Both prokaryotic and eukaryotic organisms possess mechanisms for the detoxification of heavy metals, which are found among distantly related species. We investigated the role of intracellular glutathione (GSH), which in a large number of taxa plays a role in the protection against the toxicity of common heavy metals. Anaerobically grown Lactococcus lactis containing an inducible GSH synthesis pathway was used as a model organism. Its physiological condition allowed study of putative GSH-dependent uranyl detoxification mechanisms without interference from additional reactive oxygen species. By microcalorimetric measurements of the metabolic heat during cultivation, it was shown that intracellular GSH attenuates the toxicity of uranium at a concentration in the range of 10-150 µM. In this concentration range, no effect was observed with copper which was used as a reference for redox-metal toxicity. At higher copper concentrations, GSH aggravated metal toxicity. Isothermal titration calorimetry revealed the endothermic binding of U(VI) to the carboxyl group(s) of GSH, rather than to the reducing thiol group involved in copper interactions. The data indicate that the primary detoxifying mechanism is the intracellular sequestration of carboxyl-coordinated U(VI) into an insoluble complex with GSH. The opposite effects on uranyl and on copper toxicity can be related to the difference in coordination chemistry of the respective metal-GSH complexes, which cause distinct growth phase-specific effects on enzyme metal interactions.

Keywords: calorimetry; radiotoxicity; growth model; metabolic monitoring; toxicology

Publ.-Id: 23473

Electron Dynamics in Silicon−Germanium Terahertz Quantum Fountain Structures

Sabbagh, D.; Schmidt, J.; Winnerl, S.; Helm, M.; Di Gaspare, L.; de Seta, M.; Virgilio, M.; Ortolani, M.

Asymmetric quantum well systems are excellent candidates to realize semiconductor light emitters at far-infrared wavelengths not covered by other gain media. Group-IV semiconductor heterostructures can be grown on silicon substrates, and their dipole-active intersubband transitions could be used to generate light from devices integrated with silicon electronic circuits. Here, we have realized an optically pumped emitter structure based on a three-level Ge/Si0.18Ge0.82 asymmetric coupled quantum well design. Optical pumping was performed with a tunable free-electron laser emitting at photon energies of 25 and 41 meV, corresponding to the energies of the first two intersubband transitions 0 → 1 and 0 → 2 as measured by Fourier-transform spectroscopy. We have studied with a synchronized terahertz timedomain spectroscopy probe the relaxation dynamics after pumping, and we have interpreted the resulting relaxation times (in the range 60 to 110 ps) in the framework of an out-of-equilibrium model of the intersubband electron−phonon dynamics. The spectral changes in the probe pulse transmitted at pump−probe coincidence were monitored in the range 0.7−2.9 THz for different samples and pump intensity and showed indication of both free carrier absorption increase and bleaching of the 1 → 2 transition. The quantification from data and models of the free carrier losses and of the bleaching efficiency allowed us to predict the conditions for population inversion and to determine a threshold pump power density for lasing around 500 kW/cm2 in our device. The ensemble of our results shows that optical pumping of germanium quantum wells is a promising route toward siliconintegrated far-infrared emitters.

Keywords: silicon photonics; quantum wells; chemical vapor deposition; terahertz spectroscopy; pump−probe spectroscopy; germanium

Publ.-Id: 23472

Growth and characterization of multi-crystalline silicon ingots

Schmid, E.; Funke, C.; Behm, T.; Würzner, S.; Pätzold, O.; Galindo, V.; Stelter, M.; Möller, H.-J.

This paper summarizes studies in the field of growth and characterization of multi-crystalline (mc) silicon ingots performed within the Cluster of Excellence "Structure Design of Novel High-Performance Materials via Atomic Design and Defect Engineering (ADDE)". Experimental results on the interaction between impurities, inclusions, dislocations and grain boundaries in multi-crystalline (mc) silicon ingots grown from well-mixed and poorly mixed melts in graphite-containing and graphite free configurations are presented. The ingots were grown in a high-vacuum induction furnace by the vertical Bridgman (VB) method and the degree of impurity mixing within the melt was modified by changing the growth configuration and the growth rate. Vertical and horizontal slices were prepared from the ingots and analyzed by Fourier transform IR spectroscopy, as well as reflected-light and IR transmission microscopy to measure the axial carbon concentration and the distribution of dislocations or inclusions, respectively. The correlation between individual inclusions and dislocations has been investigated by correlative reflected-light/IR transmission and scanning electron microscopy in both setups. The influence of the melt mixing on the segregation of carbon is demonstrated and discussed with respect to the consequences for the formation of inclusions and dislocation clusters in multi-crystalline silicon. Additionally the alignment of dislocations in samples from VB-grown ingots and wafers from edge-defined film-fed (EFG) growth are investigated. Crystallographic orientations of single grains and dislocation structures are analyzed by electron backscatter diffraction and by the "traces on two parallel surfaces" method. The influence of the growth and cooling conditions on the final alignment of dislocations in mc-Si is discussed and explained.

Keywords: multi-crystalline (mc) silicon ingots

  • Contribution to external collection
    Rafaja, David: Functional structure design of new high-performance materials via atomic design and defect engineering (ADDE), Freiberg: Saxonia, 2016, 978-3-934409-68-2, 26-41

Publ.-Id: 23471

Terahertz Near-Field Investigation of a Plasmonic GaAs Superlens

Fehrenbacher, M.

This work presents the first demonstration of a semiconductor based plasmonic near-field superlens, utilizing highly doped GaAs to generate infrared optical images with a spatial resolution beyond the difraction limit. Being easily transferable to other semiconductor materials, the concept described in this thesis can be exploited to realize spectrally adjustable superlenses in a wide spectral range. The idea of superlensing has been introduced theoretically in 2000, followed by numerous publications including experimental studies. The effect initiated great interest in optics, since in contrast to difraction limited conventional optical microscopy it enables subwavelength resolved imaging by reconstructing the evanescent waves emerging from an object. With techniques like scanning near-field optical microscopy (SNOM) and stimulated emission depletion (STED) being already successfully established to overcome the conventional restrictions, the concept of superlensing provides a novel, different route towards high resolution. Superlensing is a resonant phenomenon, relying either on the excitation of surface plasmons in metallic systems or on phonon resonances in dielectric structures. In this respect a superlens based on doped semiconductor benefits from the potential to be controlled in its operational wavelength by shifting the plasma frequency through adjustment of the free carrier concentration.
For a proof of principle demonstration, we investigate a superlens consisting of a highly n-doped GaAs layer (n = 4 x 10^18 cm-3) sandwiched between two intrinsic layers. Recording near-field images of subwavelength sized gold stripes through the trilayer structure by means of SNOM in combination with a free-electron laser, we observe both enhanced signal and improved spatial resolution at radiation wavelengths close to l = 22 µm, which is in excellent agreement with simulations based on the Drude-Lorentz model of free electrons. Here, comparative investigations of a purely intrinsic reference sample confirm that the effect is mediated by the charge carriers within the doped layer. Furthermore, slightly differently doped samples provide indications for the expected spectral shift of the resonance. According to our calculations, the wavelength range to be exploited by n-GaAs based superlenses reaches far into the terahertz region, whereas other semiconductor materials are required to explore the near infrared.

  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-070 2016
    ISSN: 2191-8708, eISSN: 2191-8716


Publ.-Id: 23470

Design Study of a Traveling-Wave Thomson-Scattering Experiment for the Realization of Optical Free Electron Lasers

Steiniger, K.; Albach, D.; Debus, A.; Loeser, M.; Pausch, R.; Roeser, F.; Schramm, U.; Siebold, M.; Bussmann, M.

We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric fi eld of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator fi eld. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses.
An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. In the talk we show how diff raction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser fi eld along the electron trajectory. Furthermore we give tolerance limits on alignment errors to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the scheme.

Keywords: traveling-wave; thomson-scattering; FEL; x-ray; pulse-front tilt; out-of-focus

  • Lecture (Conference)
    DPG-Frühjahrstagung Darmstadt, 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23469

Design Study for an Optical Free-Electron Laser Realized by Traveling-Wave Thomson-Scattering

Steiniger, K.; Albach, D.; Bussmann, M.; Irman, A.; Jochmann, A.; Loeser, M.; Pausch, R.; Röser, F.; Schramm, U.; Debus, A.

We present an experimental setup strategy for the realization of an optical free-electron laser (OFEL) in the Traveling-Wave Thomson-Scattering geometry (TWTS). In TWTS, the electric field of petawatt class, pulse-front tilted laser pulses is used to provide an optical undulator field. This is passed by a relativistic electron bunch so that electron direction of motion and laser propagation direction enclose an interaction angle. The combination of side scattering and pulse-front tilt provides continuous overlap of electrons and laser pulse over meter scale distances which are achieved with centimeter wide laser pulses. An experimental challenge lies in shaping of these wide laser pulses in terms of laser dispersion compensation along the electron trajectory and focusing. The poster shows how diffraction gratings in combination with mirrors are used to introduce and control dispersion of the laser in order to provide a plane wave laser field along the electron trajectory. Furthermore we give limits on alignment tolerances to operate the OFEL. Example setups illustrate functioning and demonstrate feasibility of the design.

Keywords: traveling-wave; Thomson scattering; FEL; x-ray; tilted laser pulse; out-of-focus

  • Lecture (Conference)
    Student Retreat@2. Annual MT Meeting, 07.-08.03.2016, Karlsruhe, Deutschland
  • Poster
    2. Annual MT Meeting, 08.-11.03.2016, Karlsruhe, Deutschland

Publ.-Id: 23468

First evidence of a water soluble Pu(IV) - [Pu6(OH)4O4]12+ - hexanuclear cluster.

Tamain, C.; Dumas, T.; Guillaumont, D.; Hennig, C.; Guilbaud, P.

A singular Pu(IV) hexanuclear cluster [Pu6(OH)4O4]12+ stabilized by DOTA ligands has been structurally characterized for the first time both in the solid state and in water solution using X-ray diffraction, Vis-NIR and X-ray absorption spectroscopies. The cluster solubility in water and its high stability in a relatively large pH range are of the upmost importance for plutonium environmental speciation.

Keywords: Pu(IV); DOTA; SCXRD; EXAFS; UV-Vis

Publ.-Id: 23467

Free - Surface Modelling in the Ribbon Growth on Substrate (RGS)process

Beckstein, P.; Galindo, V.; Gerbeth, G.

The cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. In contrast to other crystallization methods, like e.g. melt spinning or even directional solidification, the RGS process allows high volume manufacturing, better crystallization control and a high material yield due to a substrate driven process. To optimize the application of RGS further, insights from modelling the liquid metal flow are very desirable. We have already conducted extensive numerical investigations in order to study the involved AC magnetic fields. For the RGS technology, these magnetic fields play an essential role in realizing inductive heating and an additional magnetic retention effect.
New simulation results demonstrate the effect of the applied AC magnetic fields on the melt flow of liquid silicon. The focus is thereby devoted to the simulation of the melt surface deformation based on a multi-physical modelling approach in OpenFOAM (foam-extend). Our developed numerical tool allows us to model hydrodynamic and magnetodynamic effects and their interaction. Studies of the time-dependent free-surface flow under the influence of magnetic forces are the key for improving the RGS process as main flow structures and possible instabilities strongly depend on the melt shape.

Keywords: RGS process; OpenFOAM extend; Free-Surface Modelling

  • Poster
    1st German Czechoslovak Conference on Crystal Growth, GCCCG-1 / DKT2016, 16.-18.03.2016, Dresden, Germany

Publ.-Id: 23466

Clinical application of a prompt gamma based in-vivo proton range verification using a knife-edge slit camera

Nenoff, L.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Baumann, M.; Pausch, G.; Richter, C.

To improve the precision and reduce the margins for particle therapy, in-vivo range verification is desirable. In this study, a range verification based on prompt gamma imaging (PGI) was applied to patients and compared with in-room CT data.

  • Poster
    55th Annual Conference PTCOG 55, 22.-28.05.2016, Prague, Czech Republic

Publ.-Id: 23465

First experience from the clinical application of a prompt gamma based proton range verification system in passive scattering mode and sensitivity evaluation compared to active scanning

Nenoff, L.; Priegnitz, M.; Barczyk, S.; Trezza, A.; Golnik, C.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Hotoiu, L.; Prieels, D.; Baumann, M.; Pausch, G.; Richter, C.

After a first clinical application of a prompt gamma knife-edge slit-camera in double scattering (DS) mode, systematic measurements and quantitative analysis of patient data have been started. To investigate the detection sensitivity of the slit camera for range deviations in DS compared to pencil beam scanning (PBS), phantom measurements in both treatment modes with clinically relevant treatment plans have been performed.

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

Publ.-Id: 23464

Multistage bioassociation of uranium to a halophilic archaeon under highly saline conditions

Bader, M.; Müller, K.; Foerstendorf, H.; Drobot, B.; Schmidt, M.; Musat, N.; Swanson, J. S.; Reed, D. T.; Stumpf, T.; Cherkouk, A.

For the final disposal of radioactive waste in a deep geological repository, salt rock is considered as a potential host rock formation. A lot of research has been conducted regarding the physical and geochemical properties and retention suitability of this potential host rock. However, information about the indigenous microorganisms and their impact on the migration behavior of radionuclides in a worst-case scenario – the release of radionuclides – are widely missing in particular. In this work, we studied the interactions between the radionuclide uranium and the extreme halophilic archaeon Halobacterium (Hbt.) noricense. Extensive investigations were performed with an isolate originating from an Austrian salt mine, Hbt. noricense DSM-15987 [1]. Surprisingly, the obtained kinetics of the sorption experiments showed that bioassociation is not only a sorption process; i.e. fast sorption within the first hours until reaching a stable equilibrium state. The obtained kinetics showed a multistage process with a fast sorption phase during the first two hours of exposure. For the next hours an increasing amount of uranium was detectable (ICP-MS) in the supernatant, implying that the sorbed uranium was released from the cells. Subsequently, the amount of bioassociated uranium was found to increase very slowly until a maximum sorption of 80% was reached after 48 h. For more molecular information of these, hitherto unknown, bioassociation processes on archaeal cells, several spectroscopic and microscopic methods were applied. In situ Attenuated Total Reflection Fourier-transform Infrared (ATR FT-IR) spectroscopy provided evidence that uranium simultaneously binds to carboxylic and to phosphate groups within the initial sorption process of uranium to cells of Hbt. noricense DSM-15987. Despite of the high chloride concentration (3 M) required for the experiments and of the resulting quenching effect of chloride on uranium luminescence, we were able to detect weak signals by Laser-induced Fluorescence spectroscopy. The obtained results support the bioassociation kinetics where a higher amount of sorbed uranium was found after 2 hours of exposure time than after 5 hours. From parallel factor analysis, a preference for uranium to carboxylic groups could be verified. Furthermore, the impact of uranium on archaeal cells over time was monitored microscopically, and the viability was proven using the LIVE/DEAD® Bac LightTM Bacterial Viability Kit from Molecular probes. Moreover, it was shown that with increasing uranium concentration the cells tend to form biofilm-like agglomerates. We assume that this effect might reflect a stress reaction to protect the cells from environmental challenges like the presence of uranium. The heavy metal ions could be localized on the cell surface of the halophilic archaeon within the first sorption phase and later on in the biofilm-like agglomerates by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy.
Due to the fact that Hbt. noricense is an archaeon commonly found in salt rock, the kinetics of uranium bioassociation was investigated as well with the Hbt. noricense WIPP strain isolated from the Waste Isolation Pilot Plant (WIPP), NM, USA. The obtained kinetic curve showed the same shape as the one from the Hbt. noricense DSM-15987 strain. Additionally, Hbt. noricense WIPP formed similar but smaller biofilm-like structures. In summary, independent of the origin of both strains, both halophilic archaea obviously interact with dissolved uranium within a unique bioassociation process. This process, including the subsequent biofilm formation, will be investigated in more detail in the near future.
[1] Gruber, C. et al. (2004) Extremophiles, Vol. 8, 431-439.

Keywords: Halophilic archaeon; uranium bioassociation; Halobacterium noricense

  • Lecture (Conference)
    Halophiles (11th International Meeting), 22.-26.05.2016, San Juan, Puerto Rico

Publ.-Id: 23463

Insights into the use of specific metal binding of self-assembling S-layer proteins

Vogel, M.; Drobot, B.; Günther, T.; Lehmann, F.; Weinert, U.; Pollmann, K.; Raff, J.

Most bacteria and all archaea possess as outermost cell envelope surface-layer (S-layer) proteins. These self-assembling proteins form nanostructured lattices with different symmetries, provide regular arranged pores with defined size and possess different kinds of regular arranged functional groups. The formation of stable and functional S-layer lattices via self-assembly on the cell surface, on different technical surfaces as well as interfaces is a dynamic and complex process. Despite the fact that S-layer proteins have been investigated for over 30 years, the full reaction cascade of self-assembly, which includes the role of different bivalent cations such as Ca2+ and Mg2+, are still not fully understood.
Furthermore, S-layers have a number of important intrinsic properties, e.g. they provide cellular wall protection, mediate selective exchange of molecules and therefore function as molecular sieves. Interestingly, S-layers from bacterial isolates recovered from heavy metal contaminated environments have outstanding metal binding properties and are highly stable. They show potential for selective binding of several metals some of them with high affinity. Therefore, three aspects of the metal-interactions with S-layer proteins must be taken into account.
First, S-layers possess different functionalities, e.g. carboxyl-, phosphoryl, hydroxyl groups, binding toxic metals and metalloids, like U and As, unspecifically and by this hinder them to enter the interior of prokaryotic cells. This interaction process is strongly driven by pH-value as the functionalities need to be deprotonated. Second, precious metals like Au and Pd are likewise bound unspecifically to functional groups, but presumably covalently making the binding irreversible unless the S-layer protein is destroyed completely.
Third, some metals are needed for native protein folding of the S-layer protein monomer, self-assembly, and the formation of highly-ordered lattices. These particular metals are bivalent cations such as Ca2+. As known from titration experiments, certain S-layer proteins bind Ca2+ specifically, thereby forming very stable complexes. There are at least two different binding sites for these bivalent cations showing different binding affinities. Important is that these binding sites not only allow selective binding of calcium, but also of chemical-equal elements including the trivalent lanthanides (Eu3+, Tb3+), possessing comparable ionic radii. This was proven by titration and laser fluorescence spectroscopic experiments.
This study shows that the intrinsic properties and physiological functions of the S-layer proteins build the base for its selective metal binding behavior and its potential for fabrication of biohybrid materials. So by combining S-layers with a layer-by-layer technique different materials can be furnished with coatings. The produced biohybrid materials can be directly used as selective metal filter material for the removal or recovery of strategic relevant metals using pH-value as regulating parameter for selective metal binding and also conceivably release.

Keywords: S-layer; metal binding; coatings; biohybrid; lanthanides

  • Lecture (Conference)
    Materials Science and Engineering - MSE 2016 Congress, 27.-29.09.2016, Darmstadt, Deutschland

Publ.-Id: 23462

Nanoparticle guests in lyotropic liquid crystals

Dölle, S.; Park, J. H.; Schymura, S.; Scalia, G.; Lagerwall, J. P. F.

In this chapter we discuss the benefits, peculiarities and main challenges related to nanoparticle templating in lyotropic liquid crystals. We first give a brief bird’s-eye view of the field, discussing di↵erent nanoparticles as well as di↵erent lyotropic hosts that have been explored, but then quickly focus on the dispersion of carbon nanotubes in surfactant-based lyotropic nematic phases. We discuss in some detail how the trans- fer of orientational order from liquid crystal host to nanoparticle guest can be verified and which degree of ordering can be expected, as well as the importance of choosing the right surfactant and its concentra- tion for the stability of the nanoparticle suspension. We introduce a method for dispersing nanoparticles with an absolute minimum of stabi- lizing surfactant, based on dispersion below the Kra↵t temperature, and we discuss the peculiar phenomenon of filament formation in lyotropic nematic phases with a su cient concentration of well-dispersed carbon nanotubes. Finally, we describe how the total surfactant concentration in micellar nematics can be greatly reduced by combining cat- and an- ionic surfactants, and we discuss how nanotubes can help in inducing the liquid crystal phase close to the isotropic–nematic boundary.

Keywords: Nanopartikel; nanoparticles; lyotrope; Flüssigkristalle; lyotropic liquid crystals; Kohlenstoffnanoröhrchen; carbon nanotubes

  • Book chapter
    Lagerwall, Jan P.F., Scalia, Giusy: Liquid Crystals with Nano and Microparticles, London: World Scientific, 2016, 695-722
    DOI: 10.1142/9789814619264_0020

Publ.-Id: 23460

Free-surface dynamics in the Ribbon Growth on Substrate (RGS) process

Beckstein, P.; Galindo, V.; Gerbeth, G.; Schönecker, A.

he cost efficient, high throughput production of metal- and semiconductor alloys is the foundation of many advanced technologies. With the development of the Ribbon Growth on Substrate (RGS) technology, a new crystallization technique is available that allows the controlled, high crystallization rate production of silicon wafers and advanced metal-silicide alloys. Compared to other crystallization methods, such as melt spinning, the RGS process allows better crystallization control, high volume manufacturing and high material yield due to the substrate driven process. In order to optimize RGS further, insights from modelling the liquid metal in the casting frame under electromagnetic fields are very desirable. We performed numerical investigations in order to study the involved AC magnetic fields, which are an essential part of the RGS process to realize a magnetic retention effect. Our simulation results demonstrate the effect of the applied AC magnetic fields on the silicon melt flow. The main focus is thereby devoted to the simulation of the melt surface deformation based on a complex modelling approach. This time-dependent free-surface flow under the influence of magnetic forces is the key for optimizing the RGS process.

Keywords: Ribbon Growth on Substrate; Semi-conductor processing; AC magnetic fields; Magnetic retention; OpenFOAM extensions; COMSOL Multiphysics; Moving mesh; Surface-tracking; Free-surface; Dome-shaping

  • Contribution to proceedings
    8th International Conference on Electromagnetic Processing of Materials, 12.-16.10.2015, Cannes sur Mer, France
    EPM 2015 8th International Conference on Electromagnetic Processing of Materials, St. Martin d'Héres: SIMAPLaboratory, 978-2-9553861-0-1, 167-170
  • Lecture (Conference)
    8th International Conference on Electromagnetic Processing of Materials, 12.-16.10.2016, Cannes sur Mer, France

Publ.-Id: 23459

Translation of a prompt gamma based proton range verification system to first clinical application

Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Golnik, G.; Bombelli, L.; Enghardt, W.; Fiedler, F.; Fiorini, C.; Hotoiu, L.; Janssens, G.; Keitz, I.; Mein, S.; Perali, I.; Prieels, D.; Smeets, J.; Thiele, J.; Vander Stappen, F.; Werner, T.; Baumann, M.

To improve precision of particle therapy, in vivo range verification is highly desirable to reduce range uncertainties and thereby increase the advantage of proton therapy. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically, although proposed 12 years ago. We report on the translational implementation as well as the worldwide first clinical application of prompt gamma imaging (PGI) based range verification. A prototype of a PGI camera was used to measure the prompt gamma depth distribution during proton treatment of a head and neck tumor. Inter-fractional variations of the prompt gamma profile were evaluated and anatomical changes were independently verified.

  • Lecture (Conference)
    ESTRO 35, European society for radiotherapy and oncology, 29.04.-03.05.2016, Turin, Italy

Publ.-Id: 23458

First clinical application of a prompt gamma based in vivo proton range verification using a knife-edge slit camera

Richter, C.; Pausch, G.; Barczyk, S.; Priegnitz, M.; Keitz, I.; Thiele, J.; Smeets, J.; Vander Stappen, F.; Bombelli, L.; Fiorini, C.; Hotoiu, L.; Perali, I.; Prieels, D.; Enghardt, W.; Baumann, M.

To improve precision of particle therapy, in vivo range verification is highly desirable. Methods based on prompt gamma rays emitted during treatment seem promising but have not yet been applied clinically. Here we report on the worldwide first clinical application of prompt gamma imaging (PGI) based range verification.

  • Lecture (Conference)
    ICTR-PHE 2016, International Conference on Translational Research in Radio-Oncology | Physics for Health in Europe, 15.-19.02.2016, Geneva, Switzerland
  • Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)Suppl. 1, S89-S90
    DOI: 10.1016/S0167-8140(16)30184-0

Publ.-Id: 23457

Comparison of SIMS and RBS for depth profiling of silica glasses implanted with metal ions

Lorinčík, J.; Veselá, D.; Vytykáčová, S.; Švecová, B.; Nekvindová, P.; Macková, A.; Mikšová, R.; Malinský, P.; Böttger, R.

Ion implantation of metal ions, followed by annealing, can be used for the formation of buried layers of metal nanoparticles in glasses. Thus, photonic structures with nonlinear optical properties can be formed. In this study, three samples of silicaglasses were implanted with Cu+, Ag+, or Au+ ions under the same conditions (energy 330 keV and fluence 1 × 1016 ions/cm2), and compared to three identical silicaglass samples that were subsequently coimplanted with oxygen at the same depth. All the implantedglasses were annealed at 600 °C for 1 h, which leads to the formation of metal nanoparticles. The depth profiles of Cu,Ag, and Au were measured by Rutherford backscattering and by secondary ion mass spectrometry and the results are compared and discussed.

Keywords: Rutherford backscattering; Secondary ion mass spectroscopy; Gold; Silver; Amorphous metals

Publ.-Id: 23456

A strategy for the qualification of multi-fluid approaches for nuclear reactor safety

Lucas, D.; Rzehak, R.; Krepper, E.; Ziegenhein, T.; Liao, Y.; Kriebitzsch, S.; Apanasevich, P.

CFD-simulations for two-phase flows applying the multi-fluid approach are not yet qualified to provide reliable predictions for unknown flows. Among others, one important reason is the missing agreement within the community on closure models to be used. Considering specific phenomena or not, using different models and adjustable constants, most papers presenting a model validation end up with a good agreement with experimental data. However a case by case selection of models and constants does not help to improve the predictive capabilities of such models. For this reason the definition of baseline models considering all known phenomena that could be important is proposed. In such baseline models all parameter have to be defined, i.e., there are no tuning parameters by definition. Therefore these baseline models have to be applied to many experiments with different complexity. Shortcomings of the models and our physical understanding of the complex flow phenomena have to be identified by detailed analyses on the deviations between experimental data and simulation results. A modification of the baseline model will only be done if it bases on physical considerations and improves the overall performance of the model. This requires a huge effort, but seems to be the only way to improve the situation. In particular more complete experimental data are required. Joint activities on the development of such baseline models are desirable. The paper illustrates this strategy by a baseline model for polydisperse bubbly flows which is presently developed at HZDR.

Keywords: CFD; two-phase flow; multi-fluid; bubbly flow; validation

Publ.-Id: 23455

Terahertz spectroscopy of individual donors in silicon by low-temperature s-SNOM

Lang, D.; Winnerl, S.; Schneider, H.; Li, J.; Clowes, S.; Murdin, B.; Döring, J.; Kehr, S. C.; Eng, L. M.; Helm, M.

Isolated atoms or ions, typically confined in traps, are ideal systems for studying fascinating coherent quantum effects such as photon echoes. Likewise, isolated donor impurity atoms in semiconductors like silicon show a hydrogen-like spectrum, shifted to the far infrared due to the small effective mass and high dielectric constant [1]. Excited Rydberg states are of particular interest for quantum information, because they allow one to prepare long-living microscopic polarization states.

In contrast to previous far-field spectroscopic studies which probed ensembles of many impurities, we aim here at studying individual impurity centers. To this end, low-temperature scattering-type scanning near-field optical microscopy (s-SNOM) is employed and a free-electron laser is used as a precisely tunable terahertz source [2]. Our silicon samples contain different donors (P, Bi) with different defect densities, respectively, and are pre-characterized by conventional Fourier transform infrared spectroscopy.

[1] Greenland et al., Nature 465, 1057 (2010).
[2] Döring et al., Appl. Phys. Lett. 105, 053109 (2014).

Keywords: terahertz; silicon; nanoscopy; s-SNOM; spectroscopy; low-temperature; impurities; free-electron laser

  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland
  • Poster
    Silicon Quantum Information Processing 2016: Towards hybrid quantum circuits, 08.09.2016, Cambridge, United Kingdom

Publ.-Id: 23454

Overview of methodology for spatial homogenization in the Serpent 2 Monte Carlo code

Leppanen, J.; Pusa, M.; Fridman, E.

This paper describes the methods used in the Serpent 2 Monte Carlo code for producing homogenized group constants for nodal diffusion and other deterministic reactor simulator calculations. The methodology covers few-group reaction cross sections, scattering matrices, diffusion coefficients and poison cross sections homogenized in infinite and B1 leakage-corrected critical spectra, as well the calculation of assembly discontinuity factors, pin-power form factors, delayed neutron parameters and total and partial albedos. Also included is a description of an automated burnup sequence, which was recently implemented for the handling of restart calculations with branch variations. This capability enables covering the full range of local operating conditions required for the parameterization of group constants within a single run. The purpose of this paper is to bring the methodological description provided in earlier publications up to date, and provide insight into the developed methods and capabilities, including their limitations and known flaws.

Keywords: Serpent; Monte Carlo; spatial homogenization; group constants; automated burnup sequence


Publ.-Id: 23453

Bipolar resistive switching of p-YMnO3/n-SrTiO3:Nb junctions

Bogusz, A.; Blaschke, D.; Abendroth, B.; Skorupa, I.; Bürger, D.; Schmidt, O. G.; Schmidt, H.

Resistive switching (RS) phenomena of oxides in metal-insulatormetal structures have been widely investigated due to promising applications as a non-volatile memory and in neuromorphic circuits. In our previous works, we have demonstrated unipolar RS of YMnO3-based structures [1]. This work investigates the non-volatile RS switching in Au/YMnO3-/Nb:SrTiO3-/Al structures with (p-YMnO3-)-(n-Nb:SrTiO3-) junctions. The YMnO3- films are deposited by pulsed laser deposition on the (100)-SrTiO3- doped with 0.5 wt.% of Nb substrates and exhibit bipolar RS. Observed RS behavior is assigned to the coupled electronic and ionic processes which depend on the depletion layer extension in the p-n junction. Exploitation of RS in p-n junctions offers additional functionalities of memristive devices, e.g. related to their optical properties.
[1] A. Bogusz et al., AIP Advances 4 (2014), A. Bogusz et al., Adv. Mater. Res. 1101 (2015).

  • Lecture (Conference)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 23452

Nonlinear Terahertz Absorption of Graphene Plasmons

Jadidi, M. M.; König-Otto, J. C.; Winnerl, S.; Sushkov, A. B.; Drew, H. D.; Murphy, T. E.; Mittendorff, M.

Subwavelength graphene structures support localized plasmonic resonances in the terahertz and mid-infrared spectral regimes. The strong field confinement at the resonant frequency is predicted to significantly enhance the light-graphene interaction, which could enable nonlinear optics at low intensity in atomically thin, subwavelength devices. To date, the nonlinear response of graphene plasmons and their energy loss dynamics have not been experimentally studied. We measure and theoretically model the terahertz nonlinear response and energy relaxation dynamics of plasmons in graphene nanoribbons. We employ a terahertz pump − terahertz probe technique at the plasmon frequency and observe a strong saturation of plasmon absorption followed by a 10 ps relaxation time. The observed nonlinearity is enhanced by 2 orders of magnitude compared to unpatterned graphene with no plasmon resonance. We further present a thermal model for the nonlinear plasmonic absorption that supports the experimental results. The model shows that the observed strong linearity is caused by an unexpected red shift of plasmon resonance together with a broadening and weakening of the resonance caused by the transient increase in electron temperature. The model further predicts that even greater resonant enhancement of the nonlinear response can be expected in high-mobility graphene, suggesting that nonlinear graphene plasmonic devices could be promising candidates for nonlinear optical processing.

Keywords: Graphene; plasmons; nonlinear; pump−probe; terahertz

Publ.-Id: 23451

The twofold nature of Coulomb scattering in graphene

König-Otto, J. C.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial non-equilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88meV to suppress efficiently the optical phonon scattering as the photon energy is below the optical phonon energy (~200meV). In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process (see Fig. 1). This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling in which the carrier injection and relaxation dynamics is calculated by solving graphene Bloch equations including orientational phase and energy relaxation in Born-Markov approximation.

[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

  • Poster
    Graphene Week 2016, 13.-17.06.2016, Warszawa, Polska

Publ.-Id: 23450

Slow noncollinear Coulomb scattering in the vicinity of the Dirac point in graphene

König-Otto, J.; Mittendorff, M.; Winzer, T.; Kadi, F.; Malic, E.; Knorr, A.; Berger, C.; de Heer, W. A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

The Coulomb scattering dynamics in graphene in energetic proximity to the Dirac point is investigated by polarization resolved pump-probe spectroscopy and microscopic theory. Collinear Coulomb scattering rapidly thermalizes the carrier distribution in k-directions pointing radially away from the Dirac point. Our study reveals, however, that in almost intrinsic graphene full thermalization in all directions relying on noncollinear scattering is much slower. For low photon energies, carrier-optical-phonon processes are strongly suppressed and Coulomb mediated noncollinear scattering is remarkably slow, namely on a ps timescale. This effect is very promising for infrared and THz devices based on hot carrier effects.

Publ.-Id: 23448

Fast graphene-based hot-electron bolometer covering the spectral range from terahertz to visible

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. J.; Murphy, T. E.; Chatterjee, S.; Kolata, K.; Ohser, J.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

By using broadband absorber materials, bolometric detectors can typically cover an extremely large spectral range. However, since their response relies on the lattice temperature of the employed material, they exhibit slow response times. Hot electron bolometers (HEBs), on the other hand, can be extremely fast, because they exploit a change in device resistance caused by a varying electron temperature. A major drawback of HEBs based on superconductors is the required cooling to very low temperatures. We have developed a detector for room temperature operation, where the broadband absorption of the gapless material graphene is utilized. To this end, a graphene flake grown by chemical vapor deposition (CVD) is transferred to a SiC substrate and coupled to a logarithmic periodic antenna. Fast detection with a rise time of 40 ps is demonstrated for frequencies ranging from 0.6 THz to 390 THz [1]. Interestingly, the detector properties do not deteriorate for wavelength within the Reststrahlen band of SiC (25 – 50 THz). With a noise-equivalent power of 20 µW/Hz½ (800 µW/Hz½) in the near infrared (mid- and far infrared) the detector is capable of recording pulses with energies of the order of 10 pJ (1 nJ). We show that the detector is a versatile device for timing measurements in multi-color ultrafast spectroscopy studies.

Keywords: Detector; graphene; fast detctor; broadband detector

  • Lecture (Conference)
    7th international workshop on terahertz technology and applications, 15.-16.03.2016, Kaiserslautern, Deutschland

Publ.-Id: 23447

Graphene-based fast hot-electron bolometer with bandwidth from THz to VIS

Mittendorff, M.; Kamann, J.; Eroms, J.; Weiss, D.; Drexler, C.; Ganichev, S. D.; Kerbusch, J.; Erbe, A.; Suess, R. S.; Murphy, T. E.; König-Otto, J. C.; Schneider, H.; Helm, M.; Winnerl, S.

We present a fast detector (rise time 40 ps) operating at room temperature that is capable to detect radiation from the THz to visible spectral range (demonstrated wavelengths 500 µm – 780 nm) [1]. The detector consists of a CVD-grown graphene flake contacted by a broadband logarithmic periodic antenna. SiC acts as a substrate material that does not interfere with the detection mechanism in the desired frequency range, even within the Reststrahlen band of SiC (6 – 12 µm). The detector is ideal for timing purposes. Near infrared (mid- and far infrared) pulse energies of the order of 10 pJ (1 nJ) are sufficient to obtain good signal-to-noise ratios. We suggest that the bandwidth is limited by the antenna dimensions (typically several mm) on the long wavelength side and by the bandgap of SiC (380 nm) on the short wavelength side.
[1] M. Mittendorff et al., Opt. Express 23, 28728 (2015).

Keywords: detector; graphene; fast detector; broadband detector

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23446

Noncollinear Coulomb scattering in graphene

König-Otto, J.; Mittendorff, M.; Winzer, T.; Malic, E.; Knorr, A.; Pashkin, A.; Schneider, H.; Helm, M.; Winnerl, S.

Utilizing the anisotropy of the optical excitation in graphene, we reveal the twofold nature of Coulomb scattering in graphene. The initial nonequilibrium charge carrier distribution in graphene created by linearly polarized light possesses a pronounced anisotropy, which has been observed in our recent experiment [1]. In the present study we perform polarization-dependent pump-probe measurements using a photon energy of 88 meV to suppress efficiently the optical phonon scattering. In this case the relaxation dynamics leading to an isotropic distribution is dominated by noncollinear Coulomb scattering. By varying the pump fluence over a range of several orders of magnitudes we are able to successfully control the efficiency of this process. This reveals a surprising twofold nature of Coulomb scattering in graphene: Whereas collinear Coulomb scattering is known to be a very fast process on the fs timescale, noncollinear scattering is remarkably slow, resulting in a thermalization time of several ps in our experiment. Our experimental findings are complemented by the results of microscopic modelling.
[1] M. Mittendorff et al., Nano Lett. 14, 1504 (2014).

Keywords: graphene; ultrafast dynamics; anisotropy

  • Lecture (Conference)
    80. Jahrestagung der DPG und DPG-Frühjahrstagung, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23445

Unusual Coulomb Effects in Graphene

Winnerl, S.

After a brief overview on the ultrafast carrier dynamics in graphene we focus on two Coulomb-mediated effects. The first one is related to the very different scattering times for collinear versus non-collinear scattering. Collinear Coulomb scattering, due to many possibilities to fulfill energy and momentum conservation requirements, is extremely fast (sub-100 fs timescale). Non-collinear scattering, on the other hand, can be surprisingly slow, namely on the scale of a few ps. This observation is in contrast to the common belief that a non-equilibrium carrier distribution in graphene fully thermalizes on a sub-100 fs timescale. We show that polarization resolved pump-probe experiments at low photon energies, i.e. below the optical phonon energy of ~200 meV, allow one to trace the non-collinear Coulomb scattering and to control its efficiency by varying the pump fluence. The second surprising Coulomb effect is the direct observation of strong Auger scattering in Landau quantized graphene. The Auger scattering in this case can efficiently deplete an energy level while that level is optically pumped at the same time. Finally the potential of graphene for photonic and fast optoelectronic devices such as THz sources and detectors will be discussed.

Keywords: graphene; ultrafast dynamics

  • Lecture (others)
    Seminarvortrag im Rahmen des Graduiertenkollegs Electronic Properties of Carbon Based Nanostructures, 22.01.2016, Regensburg, Deutschland

Publ.-Id: 23444

Emittance compensation schemes for a superconducting rf injector

Vennekate, H.; Arnold, A.; Lu, P.; Murcek, P.; Teichert, J.; Xiang, R.

Contemporary particle injector technologies provide different advantages depending on the chosen design. In the case of copper rf injectors these is primarily the high accelerating field, enabling the generation of high charge bunches with very low emittance. However, the cost of that is a comparably low repetition rate. DC guns, on the other hand, can provide higher repetition rates and consequently increased beam currents at lower beam quality, i.e., increased emittance. The concept of a superconducting rf injector offers the opportunity to combine the advantages of both these concepts. However, it demands special concepts for emittance compensation, as the common approach with overlapping magnetic fields during the rf acceleration interferes with the limitations of superconductivity. The ELBE SRF Gun project is one of the most advanced in this field. Gun II, the second SRF injector at the Electron Linear accelerator with high Brilliance and low Emittance (ELBE), introduces new features for emittance compensation which were studied in detail over the last years. One of these methods is the integration of a superconducting solenoid into the cryostat. Another method uses rf focusing by retracting the photocathode’s tip from the last cell of the resonator. This paper discusses both of these schemes by briefly outlining their setups, discussing results of numerical simulations of their impact, and presenting results of initial experimental beam measurements with Gun II.

Keywords: SRF Gun; Solenoid; RF Focusing; Emittance Compensation; Transverse Emittance

Publ.-Id: 23443

Plasmonic efficiency enhancement at the anode of strip line photoconductive terahertz emitters

Singh, A.; Winnerl, S.; König-Otto, J. C.; Stephan, D. R.; Helm, M.; Schneider, H.

We investigate strip line photoconductive terahertz (THz) emitters in a regime where both the direct emission of accelerated carriers in the semiconductor and the antenna-mediated emission from the strip line play a significant role. In particular, asymmetric strip line structures are studied. The widths of the two electrodes have been varied from 2 µm to 50 µm. The THz emission efficiency is observed to increase linearly with the width of the anode, which acts here as a plasmonic antenna giving rise to enhanced THz emission. In contrast, the cathode width does not play any significant role on THz emission efficiency. This is a consequence of the emission being caused by photoexcited electrons while the effect of photoexcited holes is negligible.

Keywords: Terahertz emitters; photoconductivity; plasmonic antenna

Publ.-Id: 23441

A review of thermal processing in the subsecond range: semiconductors and beyond

Rebohle, L.; Prucnal, S.; Skorupa, W.

Thermal processing in the subsecond range comprises modern, non-equilibrium annealing techniques which allow various material modifications at the surface without affecting the bulk. 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 polymers and flexible substrates. It still continues to extend to other material classes and applications, and becomes of interest for an increasing number of users.
In this review we present a short, but comprehensive and consistent picture about the current state of the art of FLA, sometimes also called pulsed light sintering. In the first part we take a closer look to the physical and technological background, namely to the electrical and optical specifications of flash lamps, the resulting temperature profiles and the corresponding implications on process-relevant parameters like reproducibility and homogeneity. The second part briefly considers the various applications of FLA starting with the classical task of defect minimization and ultra-shallow junction formation in Si, followed by further applications in Si technology, namely in the fields of hyperdoping, crystallization of thin amorphous films and photovoltaics. Subsequent chapters cover the topics of doping and crystallization in Ge and silicon carbide, doping of III-V semiconductors, diluted magnetic semiconductors, III-V nanocluster synthesis in Si, annealing of transparent conducting oxides and high-k materials, nanoclusters in dielectric matrices and the use of FLA for flexible substrates.

Keywords: flash lamp annealing; pulsed light sintering; semiconductors

Publ.-Id: 23440

Arguing on entropic and enthalpic first-order phase transitions in strongly interacting matter

Wunderlich, F.; Yaresko, R.; Kämpfer, B.

The pattern of isentropes in the vicinity of a first-order phase transition is proposed as a key for a sub-classification. While the confinement–deconfinement transition, conjectured to set in beyond a critical end point in the QCD phase diagram, is often related to an entropic transition and the apparently settled gas-liquid transition in nuclear matter is an enthalphic transition, the conceivable local isentropes w.r.t. ”incoming” or ”outgoing” serve as another useful guide for discussing possible implications, both in the presumed hydrodynamical expansion stage of heavy-ion collisions and the core-collapse of supernova explosions. Examples, such as the quark-meson model and two-phase models, are shown to distinguish concisely the different transitions.

Publ.-Id: 23439

Laser assisted Breit-Wheeler and Schwinger processes

Nousch, T.; Otto, A.; Seipt, D.; Kämpfer, B.; Titov, A. I.; Blaschke, D.; Panferov, A. D.; Smolyansky, S. A.

The assistance of an intense optical laser on electron-positron pair production by the Breit-Wheeler and Schwinger processes in XFEL fields is analyzed. The impact of a laser beam on high-energy photon collisions with XFEL photons consists in a phase space redistribution of the pairs emerging in the Breit-Wheeler sub-process. We provide numerical examples of the differential cross section for parameters related to the European XFEL. Analogously, the Schwinger type pair production in pulsed fields with oscillating components referring to a superposition of optical laser and XFEL frequencies is evaluated. The residual phase space distribution of created pairs is sensitive to the pulse shape and may differ signifcantly from transiently achieved mode occupations.

Publ.-Id: 23438

Electromagnetic probes of a pure-glue initial state in nucleus-nucleus collisions at energies available at the CERN Large Hadron Collider

Vovchenko, V.; Karpenko, I. A.; Gorenstein, M. I.; Satarov, L. M.; Mishustin, I. N.; Kämpfer, B.; Stöcker, H.

Partonic matter produced at the early stage of ultrarelativistic nucleus-nucleus collisions is assumed to be composed mainly of gluons, but quarks and antiquarks are produced at later times.
The dynamical evolution of this chemically nonequilibrium system is described by the ideal (2+1)–dimensional hydrodynamics with a time dependent (anti)quark fugacity. The equation of state is taken as a linear interpolation of the lattice data for the pure gluonic matter and the chemically equilibrated quark-gluon plasma. The spectra and elliptic flows of thermal dileptons and photons are calculated for central Pb+Pb collisions at the LHC energy. The results are obtained assuming different equilibration times, including the case when the complete chemical equilibrium of partons is reached already at the initial stage. It is shown that a suppression of quarks at early times leads to a significant reduction of the invariant mass spectra of dileptons, but a rather modest suppression of the pT -distributions of direct photons. It is demonstrated that a noticeable enhancements of photon and dilepton elliptic flows might be a good signature of the pure glue initial state.


Publ.-Id: 23437

Spectral caustics in laser-assisted x-ray Compton scattering

Seipt, D.; Surzhykov, A.; Fritzsche, S.; Kämpfer, B.

We study the process of laser-assisted Compton scattering: The Compton scattering of x-rays from an XFEL off electrons that are driven by a relativistically intense short optical laser pulse. The frequency spectrum of the laser-assisted Compton radiation shows a broad plateau in the vicinity of the laser-free Compton line due to a nonlinear mixing between x-ray and laser photons [1]. We observe sharp peak structures in the plateau region. These structures are interpreted as spectral caustics by using a semiclassical analysis of the laser-assisted QED matrix element, relating the caustic peak positions to the laser-driven electron motion [2].

  • Contribution to external collection
    in: Jahresbericht 2015 Helmholtz-Institut Jena (HIJ):, Jena: HIJ, 2016


Publ.-Id: 23436

Bonding structure and morphology of chromium oxide films grown by pulsed-DC reactive magnetron sputter deposition

Gago, R.; Vinnichenko, M.; Hübner, R.; Redondo-Cubero, A.

Chromium oxide (CrOx) thin films were grown by pulsed-DC reactive magnetron sputter deposition in an Ar/O2 discharge as a function of the O2 fraction in the gas mixture (f) and for substrate temperatures, Ts, up to 450 ºC. The samples were analysed by Rutherford backscattering spectrometry (RBS), spectroscopic ellipsometry (SE), atomic force microscopy (AFM), scanning (SEM) and transmission (TEM) electron microscopy, X-ray diffraction (XRD), and X-ray absorption near-edge structure (XANES). On unheated substrates, by increasing f the growth rate is higher and the O/Cr ratio (x) rises from ~2 up to ~2.5. Inversely, by increasing Ts the atomic incorporation rate drops and x falls to ~1.8 . XRD shows that samples grown on unheated substrates are amorphous and that nanocrystalline Cr2O3 (x = 1.5) is formed by increasing Ts. In amorphous CrOx , XANES reveals the presence of multiple Cr environments that indicate the growth of mixed-valence oxides, with progressive promotion of hexavalent states with f. XANES data also confirms the formation of single-phase nanocrystalline Cr2O3 at elevated Ts. These structural changes also reflect on the optical and morphological properties of the films.

Keywords: oxide materials; vapour deposition; atomic scale structure; NEXAFS/XANES

Publ.-Id: 23435

Attachment of hydrophobic particles to the surface of an immersed gas bubble

Lecrivain, G.; Yamamoto, R.; Hampel, U.; Taniguchi, T.

The transport of colloidal particles at the fluidic interface of a binary fluid is of significant importance to the flotation process. Flotation is a separation process in which hydrophobic particles attach to the surface of rising air bubbles while the undesired hydrophilic particles settle down the bottom of the cell to eventually be discharged. Current numerical models developed for the simulation of the particle attachment process are still at an early stage of development. The fine attaching particles have so far been modelled as point particles, thereby neglecting the deformation of the fluidic interface. Here the combination of the smooth profile method with an in-house binary fluid model is suggested to directly simulate the attachment of a single particle to an immersed bubble under various capillary numbers.

Keywords: Froth flotation; Three-phase system; Particle attachment

  • Contribution to proceedings
    81st Annual meeting of the Society of Chemical Engineers Japan, 13.-15.03.2016, Kansai University, Senriyama Campus, Japan
    Proceedings of the 81st Annual meeting of the Society of Chemical Engineers Japan

Publ.-Id: 23434

Proton Beams for Physics Experiments at OncoRay

Helmbrecht, S.; Fiedler, F.; Meyer, M.; Kaever, P.; Kormoll, T.

Purpose: At the OncoRay center in Dresden at proton therapy facility is in operation. The first patient was treated in December 2014. The system is driven by an IBA (IBA Proton Therapy, Louvain-la-Neuve, Belgium) Cyclone 230 isochronous cyclotron with a maximum proton energy of 230 MeV. Patients are treated in one room equipped with a 360° rotating gantry. Besides patient treatment a strong focus is on research. A dedicated experimental room is part of the facility. In the current state of expansion this room is equipped with a fixed beam line. Beam energies between 70 and 230 MeV and currents up to about 120 nA at 230 MeV can be provided.
Materials and Methods: An in house developed control system (figure 1) allows for a parallel operation of the treatment and the experimental beamline. Absolute priority for the treatment room is ensured by the control software.
The beam current is controlled by a dedicated hardware directly. Continuous wave beams as well as pulsed beams with repetition rates up to 333 Hz with variable duty cycles are available. The beam is monitored by means of a segmented ionization chamber. The beam can be activated manually, for a defined time or until a certain charge has been reached at the beam exit. A direct continuance after a beam switch to the treatment room is possible.
Results: The proton therapy system itself is operated by an IBA team, that ensures excellent beam stability and availability. Since only one treatment room is present, experiments can be performed conveniently during the day shifts. Requests from the treatment room cause interruptions of 1-2 min duration in intervals of about 20 min.
Conclusions: In summary, the OncoRay center is equipped with an experimental beamline that combines the reliability and beam quality of a commercial clinical proton therapy system with the flexibility of an in house developed control system whose design parameters are governed by the needs of physical and translational research.

  • Poster
    ICTR-PHE 2016 - International Conference on Translational Research in Radio-Oncology - Physics for Health in Europe, 15.05.2016, Genf, Schweiz
  • Open Access Logo Abstract in refereed journal
    Radiotherapy and Oncology 118(2016)S1, S60-S61
    DOI: 10.1016/S0167-8140(16)30124-4

Publ.-Id: 23433

Comparison of a Separated Flow Response to Localized and Global-type Disturbances

Monnier, B.; Williams, D. R.; Weier, T.; Albrecht, T.

The flow structure and lift response of a separated flow over an airfoil that is subjected to an impulsive type of pitching motion is compared to the response produced by a localized pulse disturbance at the leading edge of an airfoil. Time-resolved PIV data is used to obtain the velocity field on the suction surface of the airfoil. POD analysis shows that the majority of energy is contained within the first four modes. Strong similarities in the shapes of the POD basis functions are found, irrespective of the type of actuation (global or local). The time-varying coefficient of the second POD mode tracks the negative of the lift coefficient in each case. Basis functions from the localized actuation data were projected on the velocity field of the globally actuated flow to obtain a hybrid set of coefficients. The hybrid coefficients matched reasonably well with the coefficients obtained from the original POD analysis for the globally excited flow. Both types of actuation were found to generate very similar Lagrangian flow structures. The results suggest a certain degree of universality in the POD modes/flow structures for the separated flow over an airfoil, irrespective of the type of excitation.


Publ.-Id: 23432

Simulation of liquid metal batteries

Weber, N.; Beckstein, P.; Galindo, V.; Herreman, W.; Landgraf, S.; Nore, C.; Stefani, F.; Weier, T.

The increasing deployment of highly fluctuating renewable energy sources, as e.g. wind and solar power plants, demands for stationary energy storage. Pumped storage hydro power, which is the only technology widely used today, can not be applied in all places; new technologies are therefore required. A promising alternative is the liquid metal battery (LMB). Easy scale-up, low priced raw materials, a simple set-up, long life-time and extremely high current densities make it a promising candidate for grid-scale energy storage. Liquid metal batteries are built as a stable density stratification of two liquid metals, separated by a likewise liquid salt. During discharge, the upper metal will lose electrons; the ion will diffuse through the electrolyte layer and alloy there with the cathode metal. In order to build such batteries cheap, they have to be large; however, this implies currents in the order of kilo-amperes. The battery current and its interaction with magnetic fields may be the source of different instabilities, leading to a fluid flow in the liquid metal battery. Stirring the cathode may be advantageous by mixing or removing reaction products from the salt-cathode interface. However, very strong fluid flow may even wipe away the electrolyte layer and lead to a short-cirucit. This must be avoided.

We present a numerical model implemented in OpenFOAM, coupling the Navier-Stokes equation with Maxwell’s equations. The electric potential is determined by solving a Poisson equation; the current by Ohm’s law and the
magnetic field by Biot-Savart’s law. This model is used to simulate the Tayler instability in the batterie’s anode. A multi-region model, similar to chtMultiRegionFoam, is used to model electro-vortex flow. Finally, a multiphase model, based on multiphaseInterFoam, allows to simulate deformation of the electrolyte layer as well as metal pad rolling, known from aluminium reduction cells.

  • Lecture (Conference)
    11th OpenFOAM Workshop, 26.-30.06.2016, Guimarães, Portugal

Publ.-Id: 23431

Interaction of Eu(III) and Cm(III) with mucin – a key component of the human mucosa

Wilke, C.; Raff, J.; Barkleit, A.; Ikeda-Ohno, A.; Stumpf, T.

Lanthanides (Ln) and actinides (An) could potentially be chemo- and radiotoxic when they are incorporated into the food chain after accidental releases to the environment. This spectroscopic study focuses on the interaction of Ln(III) and An(III) with mucin, one of the essential components of human mucosa, for better understanding of their behaviour in human gastrointestinal tract in case of oral ingestion. The first spectroscopic screening with TRLFS (Time-Resolved Laser-Induced Fluorescence Spectroscopy) revealed mucin as a fundamental binding partner of Eu(III) as well as of Cm(III) in the human gastrointestinal tract. Mucin is an important glycoprotein of the mucosa, working as an important protective barrier on the digestive system and functions. Mucin can interact with metal ions via a variety of their saccharides. This contribution is dedicated to the identification of dominant binding groups of Mucin with Ln(III) and An(III) by spectroscopy (TRLFS, IR, NMR) and thermodynamic calculations

Keywords: lanthanides; actinides; Eu(III); Cm(III); TRLFS; spectroscopy; mucin

  • Contribution to proceedings
    Goldschmidt, 26.06.-01.07.2016, Yokohama, Japan
  • Lecture (Conference)
    Goldschmidt, 26.06.-01.07.2016, Yokohama, Japan

Publ.-Id: 23430

Anisotropic metal growth on phospholipid nanodiscs via lipid bilayer expansion

Oertel, J.; Keller, A.; Prinz, J.; Schreiber, B.; Hübner, R.; Kerbusch, J.; Bald, I.; Fahmy, K.

Self-assembling biomolecules provide attractive templates for the preparation of metallic nanostructures. However, the intuitive transfer of the “outer shape” of the assembled macromolecules to the final metallic particle depends on the intermolecular forces among the biomolecules which compete with interactions between template molecules and the metal during metallization. The shape of the bio-template may thus be more dynamic than generally assumed. Here, we have studied the metallization of phospholipid nanodiscs which are discoidal particles of ~ 10 nm diameter containing a lipid bilayer ~ 5 nm thick. Using negatively charged lipids, electrostatic adsorption of amine-coated Au nanoparticles was achieved and followed by electroless gold deposition. Whereas Au nanoparticle adsorption preserves the shape of the bio-template, metallization proceeds via invasion of Au into the hydrophobic core of the nanodisc. Thereby, the lipidic phase induces a lateral growth that increases the diameter but not the original thickness of the template. Infrared spectroscopy reveals lipid expansion and suggests the existence of internal gaps in the metallized nanodiscs, which is confirmed by surface-enhanced Raman scattering from the encapsulated lipids. Interference of metallic growth with non-covalent interactions can thus become itself a shape-determining factor in the metallization of particularly soft and structurally anisotropic biomaterials.

Keywords: metallization; biotemplate; infrared; FTIR; Raman; SERS; gold nanoparticle

Publ.-Id: 23429

Development of antioxidant COX-2 inhibitors as radioprotective agents for radiation therapy – a hypothesis-driven review

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

Radiation therapy (RT) evolved to be a primary treatment modality for cancer patients. Unfortunately, the cure or relief of symptoms is still accompanied by radiation-induced side effects with severe acute and late pathophysiological consequences. Inhibitors of cyclooxygenase-2 (COX-2) are potentially useful in this regard because radioprotection of normal tissue and/or radiosensitizing effects on tumor tissue have been described for several compounds of this structurally diverse class. This review aims to substantiate the hypothesis that antioxidant COX-2 inhibitors are promising radioprotectants because of intercepting radiation-induced oxidative stress and inflammation in normal tissue, especially the vascular system. For this, literature reporting on COX inhibitors exerting radioprotective and/or radiosensitizing action as well as on antioxidant COX inhibitors will be reviewed comprehensively with the aim to find cross-points of both and, by that, stimulate further research in the field of radioprotective agents.

Keywords: Coxibs; Cyclooxygenases; Normal tissue; NSAIDS; Oxidative stress; Radiation-induced vascular dysfunction; Radioprotection; Radiosensitization; Reactive oxygen/nitrogen species; Tumor models

Publ.-Id: 23428

Improving Performance of Two-Group Interfacial Area Transport Equation Models using Genetic Algorithms and High Resolution Experimental Data

Dave, A.; Manera, A.; Beyer, M.; Lucas, D.

In the two-fluid transport model, the coupling of mass, momentum and energy transfer between phases is highly dependent on interfacial area transfer terms. Several research efforts in the past have been focused on the development of an interfacial area transport equation model (IATE), in order to eliminate the drawbacks of static flow regime maps currently used in best-estimate thermal-hydraulic system codes. The IATE attempts to model the dynamics that are involved in two phase flows by accounting for the different interaction mechanisms affecting bubble transport in the flow.
In general, current IATE models perform poorly in high void fraction flow regimes. As both models depend on closure relations that require empirically determined coefficients, a genetic algorithm is implemented to study their optimization. The preliminary study indicates that improvements are achievable by application of the genetic algorithm.
Optimization of coefficients for an entire set of high-resolution wire mesh sensor (WMS) data provided a single set of optimal coefficients. The application of WMS-optimized coefficients to external tests improved IATE performance for similar hydraulic diameters and provided a neutral change in performance for significantly smaller/larger hydraulic diameters. This is a crucial outcome as an optimized set of coefficients that provide significant improvement for a subset of experimental data – is shown to benefit performance in external data for which the coefficients are not specifically optimized.

Keywords: Interfacial area transport; Optimization; Genetic algorithm

  • Lecture (Conference)
    American Nuclear Society Annual Meeting 2016, 12.-16.06.2016, New Orleans LA, USA
  • Contribution to proceedings
    American Nuclear Society Annual Meeting 2016, 12.-16.06.2016, New Orleans LA, USA
    International Topical Meeting on Advances in Thermal Hydraulics 2016

Publ.-Id: 23427

Evaluating Performance of Two-Group Interfacial Area Transport Equation for Vertical Small and Large Diameter Pipes

Dave, A.; Manera, A.; Beyer, M.; Lucas, D.

In the two-fluid transport model, the coupling of mass, momentum and energy transfer between phases is highly dependent on interfacial area transfer terms. Several research efforts in the past have been focused on the evelopment of an interfacial area transport equation model (IATE), in order to eliminate the drawbacks of static flow regime maps currently used in best-estimate thermal-hydraulic system codes. The IATE attempts to model the dynamics that are involved in two phase flows by accounting for the different interaction mechanisms affecting bubble transport in the flow.
The further development and validation of IATE models has been hindered by the lack of adequate experimental data in regions beyond the bubbly flow regime. At the Helmholtz-Zentrum Dresden Rossendorf (HZDR) experiments utilizing wire mesh sensors have been performed over all flow regimes, establishing a database of high-resolution (in space and time) data. Two sets of data from small and large diameter pipes fitted with wire mesh sensors are utilized in this work. Analysis of flow conditions in the bubbly, churn turbulent and annular flow regimes is presented.
The performance of the Fu-Ishii two-group model is evaluated against small diameter database. Results indicate good performance (< 10% error) for small group 1 bubbles, and poor performance for large group 2 bubbles. The Smith two-group large diameter IATE model is evaluated for the large diameter database. In low void-fraction regimes, the Smith model performs well. In high void-fraction regimes, there is poor group-wise interfacial area prediction – however the total interfacial area is erroneously predicted well as group-wise errors compensate each other. Overall, the study suggests that further efforts and re-evaluation of closure terms are needed in order to extend the range of validity of the IATE models.

Keywords: Interfacial area transport; Validation; Wire mesh sensor; Air-water

  • Lecture (Conference)
    American Nuclear Society Annual Meeting 2016, 12.-16.06.2016, New Orleans LA, USA
  • Contribution to proceedings
    American Nuclear Society Annual Meeting 2016, 12.-16.06.2016, New Orleans LA, USA
    International Topical Meeting on Advances in Thermal Hydraulics 2016

Publ.-Id: 23426

Modellierung von Tayler-Instabilität und Elektrowirbelströmungen in Flüssigmetallbatterien

Weber, N.

Diese Arbeit behandelt numerisch die Fluiddynamik in Flüssigmetallbatterien. Insbesonders die Tayler-Instabilität und Elektrowirbelströmungen werden ausführlich betrachtet. Die Motivation der Untersuchungen besteht zum einen in einer Steigerung von Leistung und Sicherheit und zum anderen in der Senkung von Produktions- und Betriebskosten von Flüssigmetallbatterien.
Es wird ein Lösungsverfahren für zeitabhängige magnetohydrodynamische Strömungen entwickelt und in OpenFOAM implementiert. Die Basisversion des Lösers erlaubt die Analyse einer flüssige Elektrode. Eine Erweiterung dient der Untersuchung des Einflusses von Stromsammler und Zuleitung der Batterie. Simulationen werden vorwiegend für zylindrische, aber auch für quaderförmige Elektrodengeometrien durchgeführt.
Der Hauptteil der Arbeit widmet sich der stromgetriebenen Tayler-Instabilität, die in großen Batterien bei Strömen von einigen Kiloampere auftritt und dort zu einer Strömung in Form von Konvektionszellen führt. Das Auftreten, Wachstum und die Geschwindigkeiten dieser Instabilität werden analysiert und deren Bedeutung für die Batterie diskutiert. Zur Dämpfung bzw. Unterdrückung der Strömung werden eine Reihe von Gegenmaßnahmen vorgestellt und deren praktischer Nutzen bewertet. Der zweite, kürzere Teil der Arbeit befasst sich mit Elektrowirbelströmungen, deren Charakterisierung und ihren Wechselwirkungen mit der Tayler-Instabilität. Die besondere Bedeutung von Elektrowirbelströmungen für die Integrität der Elektrolytschicht sowie ihre Anwendbarkeit für die Verbesserung des Stofftransports in Flüssigmetallbatterien werden hervorgehoben.

Keywords: Tayler Instabilität, Elektrowirbelströmung; Flüssigmetallbatterie

  • Doctoral thesis
    TU Dresden, 2016

Publ.-Id: 23425

Superlattice growth and rearrangement during evaporation induced nanoparticle self-assembly

Josten, E.; Wetterskog, E.; Glavic, A.; Boesecke, P.; Feoktystov, A.; Brauweiler-Reuters, E.; Rücker, U.; Salazar-Alvarez, G.; Brückel, T.; Bergström, L.

Understanding the assembly of nanoparticles into superlattices with well-defined morphology and structure is technologically important but challenging as it requires novel combinations of in-situ methods with suitable spatial and temporal resolution. In this study, we have followed evaporationinduced assembly during drop casting of superparamagnetic, oleate-capped γ-Fe2O3 nanospheres dispersed in toluene in real time with Grazing Incidence Small Angle X-ray Scattering (GISAXS) in combination with droplet height measurements and direct observation of the dispersion. The scattering data was evaluated with a novel method that yielded time-dependent information of the relative ratio of ordered (coherent) and disordered particles (incoherent scattering intensities), superlattice tilt angles, lattice constants, and lattice constant distributions. We find that the onset of superlattice growth in the drying drop is associated with the movement of a drying front across the surface of the droplet. We couple the rapid formation of large, highly ordered superlattices to the capillary-induced fluid flow. Further evaporation of interstitital solvent results in a slow contraction of the superlattice.
The distribution of lattice parameters and tilt angles was significantly larger for superlattices prepared by fast evaporation compared to slow evaporation of the solvent.

Keywords: magnetic nanoparticles; in-situ GISAXS; self-assembly; X-ray scattering; 3D nanoparticle superlattice

Publ.-Id: 23424

Vibrational spectroscopy of Ga+ ion implanted ta-C films

Berova, M.; Sandulov, M.; Tsvetkova, T.; Bischoff, L.; Boettger, R.; Abrashev, M.

In the present work, low energy Ga+ ion beam implantation was used for the structural and optical properties modification of tetrahedral amorphous carbon (ta-C) thin films, using gallium (Ga+) as the ion species. Thin film samples (d~40nm) of ta-C, deposited by filtered cathodic vacuum arc (FCVA), have been implanted with Ga+ at ion energy E = 20 keV and ion doses D=3.1014÷3.1015 cm-2. The Ga+ ion beam induced structural modification of the implanted material results in a considerable change of its optical properties, displayed in a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitisation, as well as to accompanying formation of bonds between the implanted ions and the host atoms of the target, as confirmed by infra-red (IR) and Raman measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of for information archiving, in the area of high-density optical data storage, while using focused Ga+ ion beams.

Keywords: ta-C; ion implantation; Raman; FTIR; spectroscopy

Publ.-Id: 23423

Silicon nanoparticles: a platform towards multimodal imaging

Faramus, A.; Licciardello, N.; Ddungu, J. L. Z.; Singh, G.; Stephan, H.; de Cola, L.

Multimodal imaging combines information from several imaging techniques in order to accurately image and diagnose various medical conditions. A well designed probe can offer imaging prospects using optical imaging, positron emission tomography using a radioactive label and magnetic resonance imaging.[1]
Silicon nanoparticles are an interesting material for biological and medical applications. These nanoparticles combine the low toxicity of silicon and the ultrasmall size (< 5 nm) achievable through wet chemistry techniques.[2] The surface termination of silicon nanocrystals can be functionalized from simple amino acid groups to photoemissive dyes, radiotracers and targeting agents, such as peptides, thus making silicon nanoparticles an interesting platform for targeted multimodal imaging.
After synthesis and purification, the crucial step towards the utilization of silicon nanoparticles as multimodal probes is the modification of the surface. An accurate quantification of the number of available functional groups is both important and a great challenge to determine.
Our research is focused on the surface modification and characterization of silicon nanocrystals and their use as imaging agent in biomedicine.

[1]. Louie A. Multimodality Imaging Probes: Design and Challenges. Chem.Rev. 2010, 110, 3146-3195. Doi:10.1021/cr9003538
[2]. Shiohara A., Lai P.-S., Northcote P, Tilley R.D. Sized controlled synthesis, purification, and cell studies with silicon quantum dots. Nanoscale. 2011, 8, 2040-3364. Doi: 10.1039/C1NR10458F

Keywords: silicon nanoparticle; surface modification; multimodal imaging; biomedical application

  • Lecture (Conference)
    E-MRS spring meeting 2016, 02.-06.05.2016, Lille, France

Publ.-Id: 23422

Improvement of Depth Resolution of VEPAS by Sputtering Techniques

Krause-Rehberg, R.; John, M.; Akhmadaliev, S.; Böttger, R.; Anwand, W.; Wagner, A.

Variable energy positron annihilation spectroscopy (VEPAS) allows to measure depthdependent defect profiles. While the depth resolution is still in the nm range for low positron energies, it broadens strongly at higher penetration energies. The reason is the broad positron implantation profile often described as Makhov profile [1].
To avoid this problem and to determine real defect profiles in a depth of several µm, one can remove the surface step-by-step or continuously by sputtering the surface away, e.g. by low energy Ar ions. Of course, the advantage of VEPAS to have a non-destructing testing tool is lost. However, one gains from relatively sharp depth profile down to several µm and improved defect sensitivity in larger depth.
In the talk details of the sputtering process will be discussed and several examples of photovoltaic CIGS layers and defects after ion implantation in Si will demonstrate the power of this type of defect profiling.

Keywords: VEPAS; Positron annihilation spectroscopy; CIGS; Si; defects; ion implantation

  • Invited lecture (Conferences)
    14th International Workshop on Slow Positron Beam Techniques & Applications, 22.-27.05.2016, Matsue, Japan

Publ.-Id: 23420

Fe doped InAs: what is the exchange interaction?

Yuan, Y.; Hübner, R.; Potzger, K.; Liu, F.; Sawicki, M.; Dietl, T.; Helm, M.; Zhou, S.

Fe doped InAs layers have been prepared by ion implantation and pulsed laser annealing. Fe ions exist in the +3 valence state when located in Indium sites, which indicates that Fe atoms do not introduce free carriers in the InAs layer and only act as the local spins. However, (In, Fe)As or (In, Fe)As codoped with Se (provide free electrons) exhibits typically superparamagnetic behavior, which is proven by both static and dynamic magnetic measurements. This is most probably due to the formation of Fe-rich nanoregions in the InAs matrix, similarly to the case of Cr-doped ZnTe [1]. However, the co-doping by Zn (which introduces free holes) increases both the saturation magnetization and the Curie temperature. A systematic comparison between (In, Fe)As, (In, Fe)As:Zn and (In, Fe)As:Se leads to the re-affirmation of the pd-exchange as the key gradient in dilute ferromagnetic semiconductors [2].

[1]. K. Kanazawa et al., Nanoscale, 6, 14667-14673 (2014)
[2]. T. Dietl et al., Science, 287, 1019-1022 (2000)

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie 2016, 06.-11.03.2016, Regensburg, Germany

Publ.-Id: 23419

Thallium dispersal and contamination in surface sediments from South China and its source identification

Liu, J.; Wang, J.; Chen, Y.; Shen, C.-C.; Jiang, X.; Xi, X.; Chen, D.; Lippold, H.; Wang, C.

Thallium (Tl) is a non-essential element in humans, and it is considered to be highly toxic. In this study, the contents, sources, and dispersal of Tl were investigated in surface sediments from a riverine system (the western Pearl River Basin, China), whose catchment has been contaminated by mining and roasting of Tl-bearing pyrite ores. The isotopic composition of Pb and total contents of Tl and other relevant metals (Pb, Zn, Cd, Co, and Ni) were measured in the pyrite ores, mining and roasting wastes, and the river sediments. Widespread contamination of Tl was observed in the sediments across the river, with the highest concentration of Tl (17.3 mg/kg) measured 4 km downstream from the pyrite industrial site. Application of a modified Institute for Reference Materials and Measurement (IRMM) sequential extraction scheme in representative sediments unveiled that 60 - 90% of Tl and Pb were present in the residual fraction of the sediments. The sediments contained generally lower 206Pb/207Pb and higher 208Pb/206Pb ratios compared with the natural Pb isotope signature (1.2008 and 2.0766 for 206Pb/207Pb and 208Pb/206Pb, respectively). These results suggested that a significant fraction of non-indigenous Pb could be attributed to the mining and roasting activities of pyrite ores, with low 206Pb/207Pb (1.1539) and high 208Pb/206Pb (2.1263). Results also showed that approximately 6 - 88% of Tl contamination in the sediments originated from the pyrite mining and roasting activities. This study highlights that Pb isotopic compositions could be used for quantitatively fingerprinting the sources of Tl contamination in sediments.

Keywords: Tl contamination; Pb isotope; pyrite; binary model

Publ.-Id: 23418

CFD modelling of downward two phase pipe flow

Krepper, E.; Lucas, D.; Rzehak, R.

A widely used approach to model two-phase bubbly flows for industrial applications is the Eulerian two-fluid framework of interpenetrating continua. The loss of small-scale physics caused by the averaging procedure has to be compensated by introduction of closure relations. These concern the momentum exchange between the phases, the effect of the bubbles on the liquid turbulence and bubble breakup and coalescence. The quest for models with a broad range of applicability allowing predictive simulations is an ongoing venture. A set of best available submodels was assembled and validated against different bubbly flow situations (Rzehak and Krepper 2013, 2015). The present contribution deals with two phase downward pipe flow. Experiments were performed at HZDR using an ultrafast X-ray tomographic measurement technique. Gas fraction distribution, gas velocities, and bubble size distributions were measured at different distances from the gas injection. Deduced from the experimental data, in some tests the complexity of the closure problem could be reduced imposing a fixed bubble size distribution. Considering the effect of bubble sizes on the closure relations the agreement of the simulations with the measurements could be improved remarkably.

Keywords: Multiphase flow; CFD; Euler-Eulerian approach; downward flow

  • Lecture (Conference)
    9th International Conference on Multiphase Flow, 22.-27.05.2016, Florenz, Italien
  • Contribution to proceedings
    9th International Conference on Multiphase Flow, 22.-27.05.2016, Florenz, Italien

Publ.-Id: 23417

Mobility and transport of copper(II) influenced by the microbial siderophore DFOB: Column experiment and modelling

Karimzadeh, L.; Lippmann-Pipke, J.; Franke, K.; Lippold, H.

Acid Cu leaching from the European Kupferschiefer ore deposits is a challenge e.g. due to its high carbonate content. In this study, we investigated the transport behaviour of Cu under conditions related to a biohydrometallurgical leaching approach using neutrophil microorganisms in neutral to slightly alkaline solutions. We studied the effect of the microbial siderophore desferrioxamineB (DFOB) as a model leaching organic ligand on Cu mobility in column experiments with kaolinite. The results revealed that DFOB strongly enhances Cu mobility. The breakthrough of Cu occurs considerably earlier in the presence of DFOB than in the absence of the organic ligand. Furthermore, complete elution of Cu was observed at 5 pore volume exchanges faster compared to elution with deionized water. The established geochemical transport model shows good agreement with the experimental data and suggests a maximum efficiency at a Cu to DFOB molar ratio of 1:1. In addition, results of modelling revealed that in the absence of the ligand, a pH increase from 6.5 to 8.5 significantly retarded Cu breakthrough, whereas in the presence of DFOB, Cu breakthrough curves were nearly insensitive to pH changes and close to the breakthrough curve of a non-reactive tracer.

Keywords: Mobility of metals; Microbial siderophore DFOB; Kaolinite; Column experiment; Geochemical modelling

Publ.-Id: 23416

Review of Subcooled Boiling Flow Models

Krepper, E.; Ding, W.

In this chapter the present capabilities of CFD-modelling for wall boiling in industrial applications are described. The basis is the Eulerian two-fluid framework of interpenetrating continua. From the first attempts heat flux partitioning algorithms were used to describe boiling at a heated wall. Based on a mechanistic model representation of the microscopic processes the framework is described by empirical correlations. The developments of the main correlations for the bubble size at detachment and for the nucleation site density are described. Different approaches for the bubble size in the bulk are presented. Further the extension of the conventional heat partitioning model towards the high heat flux will be also stated. Finally an outlook on further model improvement is given.

Keywords: CFD; two phase flow; wall boiling

  • Book chapter
    Guan Heng Yeoh: Handbook of Multiphase Flow Science and Technology, Singapore: Springer, 2017, 978-981-4585-86-6
    DOI: 10.1007/978-981-4585-86-6_20-1

Publ.-Id: 23415

Tuning the structure and crystal habit of mesocrystals using magnetic fields

Wetterskog, E.; Klapper, A.; Disch, S.; Josten, E.; Hermann, R.; Rücker, U.; Brückel, T.; Bergström, L.; Alvarez, G.-S.

A precise control over the meso- and microstructure of ordered and aligned nanoparticle assemblies, i.e., mesocrystals, is essential in the quest of exploiting collective material properties for potential applications. In this work, we produce evaporation-induced self-assembled mesocrystals with different mesostructures and crystal habits based on iron oxide nanocubes by varying the nanocube size and shape, and by applying magnetic fields. A full 3D characterization of the mesocrystals was performed using image analysis, high-resolution scanning electron microscopy and Grazing Incidence Small Angle X-ray Scattering (GISAXS). This enables structural determination of e.g. multi-domain mesocrystals with complex crystal habits, and the quantification of interparticle distances with sub-nm precision. We find a lower size limit for crystallization in the absence of a magnetic field. Mesocrystals of small nanocubes (l = 8.6 – 12.6 nm) are isostructural with a body centered tetragonal (bct) lattice whereas mesocrystals assembly of the largest nanocubes in this study (l = 13.6 nm) additionally form a simple cubic (sc) lattice. The mesocrystal habit can be tuned from a square, hexagonal to star-like and pillar shapes depending on the particle size, shape, and the applied magnetic field strength. Finally, we outline a qualitative phase diagram of the evaporation-induced self-assembled superparamagnetic iron oxide nanocube mesocrystals based on nanocube edge length and magnetic field strength.

Keywords: iron oxide; nanoparticles; magnetic field; assembly; cubes; GISAXS; mesocrystal; superstructure; normal field instability

Publ.-Id: 23414

Micrometer-sized highly ordered 3D nanoparticle superlattices investigated by microresonator ferromagnetic resonance

Josten, E.; Narkowicz, R.; Kakay, A.; Meertens, D.; Banholzer, A.; Bergström, L.; Suter, D.; Brückel, T.; Lenz, K.; Fassbender, J.; Lindner, J.

Magnetic nanoparticles and their assembly into highly correlated structures are of great interest for future applications as e.g. spin-based data storage. These systems are not only distinguished by the obvious miniaturization but by the novel physical properties emerging due to their limited size and ordered arrangement. These superstructures are formed from nanometer-sized building blocks - ordered like atoms in a crystal - which renders them a new class of materials.

Fundamental investigation of magnetic nanostructures represents an important step towards the control and understanding of these systems. Recently, single micrometer-sized 3-dimensional nanoparticle assemblies (so called mesocrystal) became available, exhibiting a high degree of structural order close to that of an atomic crystal. This system provides a good basis for the magnetic investigation of static and dynamic processes inside and of the nanoparticle superstructure.

Microresonators, provide a straightforward method for the investigation of static and dynamic magnetic properties of nm and micrometer sized objects using ferromagnetic resonance (FMR) [1,2]. Due to the much higher filling factor as compared to conventional microwave cavities, they offer several orders of magnitude increased sensitivity. A focused ion beam (FIB) approach is used to isolate an individual 3D mesocrystal from an ensemble [3] and to transfer it into a microresonator loop. The FMR study reveals the dynamic magnetic properties and magnetic anisotropy of the single mesocrystal - an object composed of highly ordered nanoparticles.

Keywords: magnetic nanoparticles; self-assembly; mesocrystals; microresonator; FMR

  • Poster
    603. Wilhelm und Else Heraeus-Seminar, Magnonics, Spin Waves Connecting Charges, Spins and Photons, 06.-08.01.2016, Physikzentrum Bad Honnef, Deutschland
  • Lecture (Conference)
    MMM Intermag, 11.-15.01.2016, San Diego, USA

Publ.-Id: 23413

How to catch the generation Y: Identifying consumers of ecological innovations among youngsters

Gurtner, S.; Soyez, K.

The economic damage of environmental pollution is remarkable, thus protecting the environment has become a pressing issue during the last decades. Consequently, for companies there is an obvious need to consider environmental issues in product development and to understand why consumers adopt ecological innovations. The success of eco-innovations, however, depends on the individual adoption decision of the consumer. Hence, the question arises, why do consumers adopt ecological innovations? By integrating two areas of consumer characteristics, namely environmental consciousness and consumer innovativeness with a special focus of young consumers as the next generation of eco-innovators, the present study provides an answer to this question. Furthermore, we focus on the promising market segment of young consumers as potential agents of change. In total 446 young consumers were surveyed. The results provide insights on what drives eco-innovativeness and thus, how to market new eco-logical products. Structural equation modeling led to the result that joyful consumption is an important antecedent of domain-specific eco-innovativeness. Additionally, a biospheric value orientation leads to higher eco-innovativeness, whereas altruistic values reduce ecoinnovativeness.
The results show that practitioners and product designers have to take into account not only the benefit for nature but also the hedonic component of a new product.

Keywords: consumer innovativeness; new product adoption; eco-innovations; structural equation modeling; generation Y; young consumers

Publ.-Id: 23412

Numerical simulations for the DRESDYN precession dynamo

Giesecke, A.; Gundrum, T.; Stefani, F.; Gerbeth, G.

In a next generation dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation. We will present results from non-linear hydrodynamic simulations with moderate precessional forcing dedicated to the planned experiment.
Our results have been used for flow models in kinematic dynamo simulations in order to determine whether a precession driven flow will be capable to drive a dynamo at experimental conditions and to limit the parameter space within which the occurrence of dynamo action is most promising.

Keywords: dynamo; precession; DRESDYN

  • Lecture (Conference)
    PAMIR 2016 International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italia
  • Contribution to proceedings
    PAMIR 2016 International Conference Fundamental and Applied MHD, 20.-24.06.2016, Cagliari, Italia


Publ.-Id: 23411

Numerical simulations of precession driven flows and their ability to drive a dynamo.

Giesecke, A.; Stefani, F.

In a next generation dynamo experiment currently under development at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) a fluid flow of liquid sodium, solely driven by precession, will be considered as a possible source for magnetic field generation.

In my talk I will present results from hydrodynamic simulations of a precession driven flow in cylindrical geometry. In a second step, the velocity fields obtained from the hydrodynamic simulations have been applied to a kinematic solver for the magnetic induction equation in order to determine whether a precession driven flow will be capable to drive a dynamo at experimental conditions.

It turns out that excitation of dynamo action in a precessing cylinder at moderate precession rates is difficult and future dynamo simulations are required in more extreme parameter regimes where a more complex fluid flow is observed in water experiments which is supposed to be beneficial for dynamo action.

Keywords: dynamo; precession; DRESDYN

  • Invited lecture (Conferences)
    PASC16 - Platform for Scientifik Computing, 08.-10.06.2016, Lausanne, Switzerland


Publ.-Id: 23410

Measurement of isomeric ratios for 89g,mZr, 91g,mMo, and 97g,mNb in the bremsstrahlung end-point energies of 16 and 45-70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; Zaman, M.; Yang, S. C.; Shin, S. G.; Kye, Y.-U.; Massarczyk, R.; John, R.; Junghans, A.; Wagner, A.; Goswami, A.; Cho, M.-H.

The independent isomeric yield ratios of 89g,mZr from the nat Zr(gamma,xn) reactions and those of 91g,mMo and 97g,m Nb from the nat Mo(g,x) reactions with the bremsstrahlung end-point energy of 45 - 70 MeV were determined by an off-line gamma-ray spectrometric technique using the 100 MeV electron linac at the Pohang Accelerator Laboratory, Korea. The isomeric yield ratios of 89g,mZr and 97g,mNb from the nat Zr(g,xn) and nat Mo(gamm,x) reactions at the bremsstrahlung end-point energy of 16 MeV were also determined by the same technique using the 20 MeV electron linac at Helmholtz-Zentrum Dresden-Rossendorf, Germany. The measured isomeric yield ratios of 89g,mZr, 91g,mMo, and 97g,mNb were compared with literature data to examine the role of the Giant Dipole Resonance (GDR). The isomeric yield ratios of the 89g,mZr, 91g,mMo, and 97g,mNb from the above reactions were also calculated by using the computer code TALYS 1.6 and compared with the experimental data to examine the validity of the theoretical model for independent isomeric yield ratio calculations.

Keywords: Photodissociation; Photoactivation; isomeric yield ratios

Publ.-Id: 23409

Multidimensional “smart Kd-matrices” for realistic description of sorption processes

Stockmann, M.; Brendler, V.; Flügge, J.; Noseck, U.

Sorption on mineral surfaces is an important retardation process to be considered in safety assessments of both chemotoxic and radioactive waste repositories. Most often conventional conservative concepts with temporally and spatially constant distribution coefficients (Kd values) are applied in reactive transport simulations.
In this work, the reactive transport program r³t is extended towards a more realistic description of the contaminant migration by implementing pre-computed multidimensional smart Kd matrices that are able to reflect changing geochemical conditions, e.g. caused by climatic changes.
Three computer codes were coupled to form one tool: PHREEQC, UCODE and SIMLAB. This strategy has various benefits: (1) One can calculate smart Kd values for a reasonable numbers of environmental parameter combinations; (2) It is possible to perform uncertainty and sensitivity analysis based on such smart Kd matrices; (3) The approach is highly flexible with respect to chemical reactions and environmental conditions; (4) The overall methodology is much more efficient in computing time than a direct coupling of the geochemical speciation code with the transport code r3t.
The capability of this new methodology is demonstrated for the sorption of repository-relevant radionuclides on a natural sandy aquifer. This proof-of-concept is able to describe the sorption behavior in dependence of changing geochemical conditions quite well.

Keywords: Waste Disposal, Safety Assessment; Smart Kd; Sorption; Radionuclides; Sensitivity and Uncertainty Analysis

  • Lecture (Conference)
    Water-Rock Interaction, 16.-21.10.2016, Évora, Portugal

Publ.-Id: 23408

Metal leaching from Kupferschiefer using bulk and biotechnologically produced organic acids

Kostudis, S.; Bachmann, K.; Kutschke, S.; Pollmann, K.; Gutzmer, J.

The European Kupferschiefer deposits constitute a challenging local resource of base metals such as copper. In order to exploit them both efficiently and environmentally benignly, biotechnological leaching approaches are investigated. Commonly used acidophilic bioleaching is limited by high carbonate content of up to 18 % resulting in an increased pH value of more than 2. Hence, alternative processes such as neutral leaching are tested. We could show that using organic acids in neutral pH range has a higher leaching impact than in acidic milieu.
The paper summarises research results on bioleaching of copper from Kupferschiefer ore in neutral to alkaline environment: Glutamic and citric acid were investigated regarding their leaching performance depending on pH, particle size and temperature. Furthermore the leaching performance of biotechnologically produced citric acid was investigated. For that purpose the yeast Yarrowia lipolytica was grown on raw glycerol, and leaching effect of the cultivation supernatant was ascertained.

  • Lecture (Conference)
    Biohydromet'16, 20.-22.06.2016, Falmouth, United Kingdom

Publ.-Id: 23407

Further insights into the chemistry of the Bi-U-O system

Popa, K.; Prieur, D.; Manara, D.; Naji, M.; Vigier, J.-F.; Martin, P.; Blanco, O. D.; Scheinost, A. C.; Prüssmann, T.; Vitova, T.; Raison, P. E.; Somers, J.; Konings, R. J. M.

Cubic fluorite-type phases have been reported in the UIVO2-Bi2O3 system for the entire compositional range, but an unusual non-linear variation of the lattice parameter with uranium substitution has been observed. In the current extensive investigation of the uranium(IV) oxide - bismuth (III) oxide system, this behaviour of the lattice parameter evolution with composition has been confirmed and its origin identified. Even under inert atmosphere at 800 oC, UIV oxidises to UV/UVI as a function of the substitution degree. Thus, using a combination of three methods (XRD, XANES and Raman) we have identified the formation of the BiUVO4 and Bi2UVIO6 compounds, within this series. Moreover, we present here the Rietveld refinement of BiUVO4 at room temperature and we report the thermal expansion of both BiUVO4 and Bi2UVIO6 compounds.

Keywords: XRD; XANES; XAFS; Raman; lead bismuth eutectic; fast reactor

Publ.-Id: 23406

Simulating spectral detectors - synthetic radiation diagnostics with PIConGPU and ClaRa

Pausch, R.; Debus, A.; Huebl, A.; Irman, A.; Krämer, J.; Steiniger, K.; Widera, R.; Schramm, U.; Bussmann, M.

We present both the in-situ far field radiation diagnostics in the particle-in-cell code PIConGPU and the offline radiation diagnostic code ClaRa. The first was developed to close the gap between simulated plasma dynamics and radiation observed in laser plasma experiments. The second is used to quantitatively simulate radiation observed in e.g. Thomson scattering experiment. Both methods are based on the far field approximation of the Liénard-Wiechert potential. Their predictive capabilities, both qualitative and quantitative, have been tested against analytical models.

We will discuss the advantages of the in-situ approach of PIConGPU over ClaRa that allows predicting both coherent and incoherent radiation spectrally from infrared to x-rays and provides the capability to resolve the radiation polarization and determine the temporal and spatial origin of the radiation. Furthermore, we explain why the direct integration into the highly-scalable GPU framework of PIConGPU allows computing radiation spectra for thousands of frequencies, hundreds of detector positions and billions of particles efficiently.

In this talk we will demonstrate these capabilities on resent simulations of laser wakefield acceleration (LWFA), high harmonics generation during target normal sheath acceleration (TNSA) and Thomson scattering during laser electron interactions.

Keywords: radiation; synthetic diagnostics; spectra; ClaRa; PIConGPU; LWFA; HHG; TNSA; Thomson scattering; GPU; PHOENIX

  • Poster
    2. Annual MT Meeting, 08.-10.03.2016, Karlsruhe, Deutschland

Publ.-Id: 23405

Radiation as synthetic diagnostic in the particle-in-cell code PIConGPU

Pausch, R.; Debus, A.; Huebl, A.; Steiniger, K.; Widera, R.; Bussmann, M.; Schramm, U.

A brief talk starting on how to simulate laser plasma interactions for laser driven accelerators and light sources and conclude on how simulating radiation on top of the laser plasma simulation can give insights for diagnostics in experiments.

Keywords: PIConGPU; laser; plasma; LWFA; radiation; spectra

  • Lecture (Conference)
    Second MT Student Retreat, 07.-08.03.2016, Karlsruhe, Deutschland

Publ.-Id: 23404

The inverse-trans-influence as a general principle of f-block chemistry

Gregson, M.; Lu, E.; Mills, D. P.; Tuna, F.; Mcinnes, E. J. L.; Hennig, C.; Scheinost, A. C.; Mcmaster, J.; Lewis, W.; Blake, A. J.; Kerridge, A.; Liddle, S. T.

Across the periodic table the trans-influence operates, where tightly-bonded ligands selectively lengthen mutually-trans metal-ligand bonds. Conversely, in high oxidation state actinide complexes the inverse-trans-influence (ITI) operates, where normally cis strongly-donating ligands instead reside trans and actually strengthen each other. However, restricted to high valent actinyls and a few uranium(V/VI) complexes, over decades the ITI has had limited scope in an area with few unifying rules. Here, we report cerium, uranium, and thorium bis(carbene) complexes with trans C=M=C cores where characterization data consistently suggest the presence of an ITI. By applying appropriate metal-ligand-matching, this work now demonstrates the occurrence of the ITI beyond high oxidation state 5f metals extended to encompass mid-range oxidation state actinides and lanthanides. Thus, the ITI emerges as an overarching f-block principle.

Keywords: actinides; lanthanides; coordination chemistry; cerium; uranium; thorium; XAFS

Publ.-Id: 23403

99mTc-Cyclopentadienyl Tricarbonyl Chelate-Labeled Compounds as Selective Sigma‑2 Receptor Ligands for Tumor Imaging

Li, D.; Chen, Y.; Wang, X.; Deuther-Conrad, W.; Chen, X.; Jia, B.; Dong, C.; Steinbach, J.; Brust, P.; Liu, B.; Jia, H.

We have designed and synthesized a series of cyclopentadienyl tricarbonyl rhenium complexes containing a 5,6-dimethoxyisoindoline or a 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline pharmacophore as σ2 receptor ligands. Rhenium compound 20a possessed low nanomolar σ2 receptor affinity (Ki = 2.97 nM) and moderate subtype selectivity (10-fold). Moreover, it showed high selectivity toward vesicular acetylcholine transporter (2374-fold), dopamine D2L receptor, NMDA receptor, opiate receptor, dopamine transporter, norepinephrine transporter, and serotonin transporter. Its corresponding radiotracer [99mTc]20b showed high uptake in a time- and dose-dependent manner in DU145 prostate cells and C6 glioma cells. In addition, this tracer exhibited high tumor uptake (5.92% ID/g at 240 min) and high tumor/blood and tumor/muscle ratios (21 and 16 at 240 min, respectively) as well as specific binding to σ receptors in nude mice bearing C6 glioma xenografts. Small animal SPECT/CT imaging of [99mTc]20b in the C6 glioma xenograft model demonstrated a clear visualization of the tumor at 180 min after injection.


Publ.-Id: 23402

PET imaging and biodistribution studies with ultrasmall nanoparticles

Licciardello, N.; Hunoldt, S.; Faramus, A.; Prasetyanto, E. A.; Bergmann, R.; Silvestrini, S.; Maggini, M.; Stephan, H.; de Cola, L.

For the past decade, renally clearable ultrasmall nanoparticles (sub-10 nm size) have attracted enormous attention for biomedical applications[1]. In this direction, ultrasmall silicon nanoparticles (Si NPs) and carbon “quantum” dots (CQDs) are gaining in importance[2, 3]. These quantum-sized particles display tunable photoluminescence, they are highly resistant against photo-bleaching, chemically stable after functionalization and biocompatible. Covalent functionalization of the surface with appropriate bifunctional chelator agents (BFCAs) for radiometals such as 99mTc, 111In, 64Cu, 68Ga enabling SPECT or PET, and simultaneously targeting vector molecules opens the avenue for the development of promising targeted dual-labelled imaging agents.
Here we report on the synthesis and characterization of Si NPs and CQDs (size < 5 nm), containing 64CuII-NOTA for PET imaging. The biodistribution data demonstrate that the 64Cu-labelled particles are rapidly excreted from the body using the renal pathway. In particular, the surface charge of Si NPs and CQDs seems to influence the biodistribution pattern.

Work financially supported by Helmholtz Virtual Institute “Nano-Tracking”, Agreement No. VH-VI-421

[1] B. H. Kim, M. J. Hackett, J. Park, T. Hyeon, Chemistry of Materials 2014, 26, 59-71

[2] Tu, C., X. Ma, A. House, S. M. Kauzlarich, A. Y. Louie, ACS Medicinal Chemistry Letters 2011, 2, 285

[3] Hong, G., S. Diao, A. L. Antaris, H. Dai, Chemical Reviews 2015, 115, 10816–10906

  • Lecture (Conference)
    E-MRS spring meeting 2016, 02.-06.05.2016, Lille, France

Publ.-Id: 23401

Synthesis and characterization of ultrasmall nanoparticles for biomedical applications

Singh, G.; Hunoldt, S.; Faramus, A.; Licciardello, N.; Stephan, H.; de Cola, L.

The synthesis of multimodal imaging agents is indeed a growing field and a lot of research is currently being done in this area because of its wide biomedical applications. The idea behind this research is to prepare a single molecule/nanoparticle which is suitable for two or more imaging techniques and thus can act as a multimodal imaging agent, for example, the combination of optical and nuclear imaging modalities may provide complementary information for improving diagnosis as well as the treatment of diseases. These imaging agents combat the limitations of sensitivity, spatial and temporal resolution and also tissue penetrability. The high hydrophilicity of the nanoparticles and fast renal clearance of the complex from the body are the major highlights.
Amine terminated ultrasmall Silicon nanoparticles of size <4 nm were synthesized by hydrothermal method and purified by dialysis. Sulfo-Cy5 and NOTA-Bn-SCN was attached selectively to the amine terminated Si USNPs. Next step would be the radiolabeling of the particles by 64Cu and could be used for the in vitro and in vivo studies. Bispidines can also be tried as a copper chelator in the complex. Further, we could also attach single domain antibodies via PEG linkers bearing maleimide group.
The substituents after coupling with the USNPs are assumed to act as excellent multimodal imaging agent which can be used for the cancer diagnosis and therapy.

Keywords: multimodal imaging agent; ultrasmall silicon nanoparticles; bispidines

  • Poster
    2nd International Symposium on Nanoparticles/Nanomaterials and Applications, 18.-21.01.2016, Caparica, Portugal

Publ.-Id: 23400

Closure of the Mott gap and formation of a superthermal metal in the Fröhlich-type nonequilibrium polaron Bose-Einstein condensate in UO2+x

Conradson, S.; Durakiewicz, T.; Tayal, A.; Andersson, D.; Bagus, P.; Baldinozzi, G.; Bishop, A.; Boland, K.; Bradley, J.; Byler, D.; Clark, D.; Conradson, D.; Espinosa-Faller, F.; Gilbertson, S. M.; Kas, J.; Kozimor, S.; Kvashnina, K.; Lezama-Pacheco, J.; Martucci, M.; Nordlund, D.; Rehr, J.; Rodriguez, G.; Seidler, G.; Valdez, J.

Mixed valence O-doped UO2+x and photoexcited UO2 containing transitory U3+ and U5+ host a coherent polaronic quantum phase (CPQP) that exhibits the characteristics of a Fröhlich-type, nonequilibrium, phononcoupled Bose-Einstein condensatewhose stability and coherence are amplified by collective, anharmonic motions of atoms and charges. Complementary to the available, detailed, real space information from scattering and EXAFS, an outstanding question is the electronic structure. Mapping the Mott gap in UO2, U4O9, and U3O7 with O XAS and NIXS and UM5 RIXS shows that O doping raises the peak of the U5f states of the valence band by ∼0.4 eV relative to a calculated value of 0.25 eV. However, it lowers the edge of the conduction band by 1.5 eV vs the calculated 0.6 eV, a difference much larger than the experimental error. This 1.9 eV reduction in the gap width constitutes most of the 2–2.2 eV gap measured by optical absorption. In addition, the XAS spectra show a tail that will intersect the occupied U5f states and give a continuous density-of-states that increases rapidly above its constricted intersection. Femtosecond-resolved photoemission measurements of UO2, coincident with the excitation pulse with 4.7 eV excitation, show the unoccupied 5f states of UO2 and no hot electrons. 3.1 eV excitation, however, complements the O-doping results by giving a continuous population of electrons for several eV above the Fermi level. The CPQP in photoexcited UO2 therefore fulfills the criteria prescribed for a nonequilibrium condensate. The electron distributions resulting from both excitations persist for 5–10 ps, indicating that they are the final state that therefore forms without passing through the initial continuous distribution of nonthermal electrons observed for other materials. Three exceptional findings are:
(1) the direct formation of both of these long lived (>3–10 ps) excited states without the short lived nonthermal intermediate;
(2) the superthermal metallic state is as or more stable than typical photoinduced metallic phases; and
(3) the absence of hot electrons accompanying the insulating UO2 excited state. This heterogeneous, nonequilibrium, Fröhlich BEC stabilized by a Fano-Feshbach resonance therefore continues to exhibit unique properties.


Publ.-Id: 23399

Benchmarking PET for geoscientific applications: 3D quantitative diffusion coefficient estimation in clay rock

Lippmann-Pipke, J.; Gerasch, R.; Schikora, J.; Kulenkampff, J.

For the first time ever the diagonal anisotropic effective diffusion coefficient, Deff = (Dxx, Dyy, Dzz), was quantified in a geologic core material in one single object of investigation. That is possible due to the combination of the non-invasive observation of Na+ diffusion in Opalinus clay by means of GeoPET (PET: positron emission tomography) followed by quantitative 3D+t data evaluation by means of finite element numerical modelling (FEM). The extracted anisotropic effective diffusion coefficient parallel (||) and normal (|) to the bedding of the clay rock, Deff =(D||, D|, D||) are comparable to those of earlier experimental studies reported by (Van Loon, et al. 2004. ES&T 38, 5721-5728). They were obtained on the same type of geomaterial (Opalinus clay, Switzerland), but by invasive methods which requires sample aliquots. We consider this study as benchmark for the long-standing development of our GeoPET method. We suggest GeoPET based fluid flow transport visualization combined with computer based process simulation henceforth as gold standard for the effective transport parameter quantification in the geosciences.

Keywords: Benchmarking GeoPET; Ddiffusion; Opalinus clay; FEM simulation

Publ.-Id: 23398

Magnetic storage technology and spintronic applications

Fassbender, J.

Review of magnetic storage technology and spintronic applications

Keywords: magnetic storage; spintronics

  • Lecture (others)
    Invited talk at ICT / Applied Materials, 09.03.2016, München, Deutschland

Publ.-Id: 23397

Ion beam modification of magnetic materials - revisited

Fassbender, J.

In 2009 the Gaede prize was awarded for the ion induced modification and patterning of thin magnetic films. At that time most of the investigations were dealing with the local modification of magnetic anisotropies and exchange bias phenomena. In recent years we could show that also other magnetic properties, e.g. magnetic relaxation processes [1], can be tailored, but also the ferromagnetic state itself can be created [2] or destroyed depending on the material system under investigation. In particular the latter modifications open a route to the creation of nanomagnets [3] and magnonic crystals [4] by local ion irradiation. A current review will be given.
[1] M. Körner et al., Phys. Rev. B 88, 054405 (2013).
[2] R. Bali et al., Nano Lett. 14, 435 (2014).
[3] F. Röder et al., Sci. Rep. 5, 16786 (2015).
[4] B. Obry et al., Appl. Phys. Lett. 102, 202403 (2013).

Keywords: ion beam modification; magnetism

  • Invited lecture (Conferences)
    DPG Spring Meeting, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23396

Petawatt Lasers for Particle Acceleration at the HZDR Dresden

Schramm, U.

Vortrag zum Status der Petawattlaserentwicklung beim Symposium Advanced Concepts for High Peak Power Ultrafast Lasers 2016
der DPG Frühjahrstagung

Keywords: Petawatt Laser

  • Invited lecture (Conferences)
    DPG Frühjahrstagung, 29.02.-04.03.2016, Hannover, Deutschland

Publ.-Id: 23395

Identifying the linear phase of the relativistic Kelvin-Helmholtz instability and measuring its growth rate via radiation

Pausch, R.; Bussmann, M.; Huebl, A.; Steiniger, K.; Widera, R.; Debus, A.

For the relativistic Kelvin-Helmholtz instability (KHI) which occurs at shear interfaces between two plasma streams, we report results on the polarized radiation over all observation directions and frequencies emitted by the plasma electrons from ab-initio kinetic simulations. We find the polarization of the radiation to provide a clear signature for distinguishing the linear phase of the KHI from its other phases. During the linear phase, we predict the growth rate of the KHI radiation power to match the growth rate of the KHI to a high degree. Our predictions are based on a model of the vortex dynamics which describes the electron motion in the vicinity of the shear interface between the two streams. Albeit the complex and turbulent dynamics happening in the shear region, we find excellent agreement between our model and large-scale particle-in-cell simulations. Our findings pave the way for identifying the KHI linear regime and for measuring its growth rate in astrophysical jets observable on earth.

Keywords: Kelvin-Helmholtz instability; KHI; PIConGPU; Astrophysics; radiation; polarization; jets; AGN; SNR


Publ.-Id: 23394

Upconverting Nanophosphors: Preparation Strategies for highly colloidal Stable Particles; International Caparica Congress on Nanoparticles, Nanomaterials and Applications 2016

Nsubuga, A.; Stephan, H.; Hesse, J.

Neodymium containing upconverting nanophosphors (UCNPs)[1] Photon-upconverting nanoparticles (UCNPs) can be excited by near-infrared light and emit visible light(anti-Stokes emission) which prevents autofluorescence and over-heating effect of biological tissues. Due to their unique properties lanthanide-doped inorganic nanoparticles are very appealing particularly in bioimaging. Despite the fast progress in lanthanide-doped upconversion nanoparticles (UCNPs), the preparation of ultrasmall, monodisperse and hydrophilic UCNPs that display intense luminescence is still a challenging issue. Only a few examples of ultrasmall and hydrophilic UCNPs have been reported. [2-4] Information about biodistribution, pharmacokinetics and formation of protein corona is still missing for ultrasmall UCNPs. Therefore the aim of this project is to elaborate and to comprehensively characterize sub-10nm hydrophilic UCNPs. The luminescence properties will be tuned by varying the dopants and relative proportions as well as the fabrication of core-shell particles.
The size and shape of the particles will be influenced by controlling the reaction time and temperature course. To render them watersoluble, a ligand-exchange strategy will be used to replace the oleylamine surface groups by stabilization agents such as PEG-phosphates, O-phospho-L-serine, alendronic, zolendronic and risedronic acid.

Keywords: Upconversion; lanthanide; Sub 10nm particles; surface functionalization; Bio imaging

  • Poster
    2nd International Symposium on Nanoparticles/Nanomaterials and Applications, 18.-21.01.2016, Costa de Caparica, Portugal

Publ.-Id: 23393

Analysis of hydrodynamic effects using ultrafast X-ray tomography with GPU accelerated data acquisition

Bieberle, A.

For effective reconstruction of the ultrafast electron beam X-ray tomography data a new data processing and data management tool is presented. By using multi core CPUs and many core GPUs very fast data processing can be performed.

Keywords: Ultrafast electron beam X-ray tomograph; massive parallel data processing; GPU

  • Lecture (others)
    Workshop on „Parallel Computing for Data Acquisition and Online Monitoring, 07.-08.03.2016, Karlsruhe, Deutschland

Publ.-Id: 23392

Engineering for NEMS with ion beams & flash annealing

Skorupa, W.

Engineering for NEMS with ion beams & flash annealing will be presented based on recent results of the Rossendorf group working for Semiconductor Materials Modification by Ion Beams.

Keywords: NEMS; ion implantation; flash annealing

  • Invited lecture (Conferences)
    Workshop on Ion Implantation - improving the MEMS processes?, 03.03.2016, Erfurt, Germany

Publ.-Id: 23390

Magnetic hydroxyapatite coatings as a new tool in medicine: A scanning probe investigation

Gambardella, A.; Bianchi, M.; Kaciulis, S.; Mezzi, A.; Brucale, M.; Cavallini, M.; Herrmannsdörfer, T.; Chanda, G.; Uhlarz, M.; Cellini, A.

Hydroxyapatite films enriched with magnetite have been fabricated via a Pulsed Plasma Deposition (PPD) system with the final aim of representing a new platform able to disincentivate bacterial adhesion and biofilm formation. The chemical composition and magnetic properties of films were respectively examined by X-ray photoelectron spectroscopy (XPS) and Superconducting Quantum Interference Device (SQUID) measurements. The morphology and conductive properties of the magnetic films were investigated via a combination of scanning probe technologies including atomic force microscopy (AFM), electrostatic force microscopy (EFM), and scanning tunneling microscopy (STM). Interestingly, the range of adopted techniques allowed determining the preservation of the chemical composition and magnetic properties of the deposition target material while STM analysis provided new insights on the presence of surface inhomogeneities, revealing the presence of magnetite-rich islands over length scales compatible with the applications. Finally, preliminary results of bacterial adhesion tests, indicated a higher ability of magnetic hydroxyapatite films to reduce Escherichia coli adhesion at 4 h from seeding compared to control hydroxyapatite films.

Publ.-Id: 23389

Magnetic irreversibility: An important amendment in the zero-field-cooling and field-cooling method

Dias, F. T.; Vieira, V. D.; Nunes, S. E.; Pureur, P.; Schaf, J.; Da Silva, G. F. F.; Gouvea, C. D.; Wolff-Fabris, F.; Kampert, E.; Obrados, X.; Puig, T.; Rovira, J. J. R.

The present work reports about experimental procedures to correct significant deviations of magnetization data, caused by magnetic relaxation, due to small field cycling by sample transport in the inhomogeneous applied magnetic field of commercial magnetometers. The extensively used method for measuring the magnetic irreversibility by first cooling the sample in zero field, switching on a constant applied magnetic field and measuring the magnetization M(T) while slowly warming the sample, and subsequently measuring M(T) while slowly cooling it back in the same field, is very sensitive even to small displacement of the magnetization curve. In our melt-processed YBaCuO superconducting sample we observed displacements of the irreversibility limit up to 7K in high fields. Such displacements are detected only on confronting the magnetic irreversibility limit with other measurements, like for instance zero resistance, in which the sample remains fixed and so is not affected by such relaxation. We measured the magnetic irreversibility, Tirr(H), using a vibrating sample magnetometer (VSM) from Quantum Design. The zero resistance data, Tc0(H), were obtained using a PPMS from Quantum Design. On confronting our irreversibility lines with those of zero resistance, we observed that the Tc0(H) data fell several degrees K above the Tirr(H) data, which obviously contradicts the well known properties of superconductivity. In order to get consistent Tirr(H) data in the H–T plane, it was necessary to do a lot of additional measurements as a function of the amplitude of the sample transport and extrapolate the Tirr(H) data for each applied field to zero amplitude.

Publ.-Id: 23388

Modeling and speciation study of uranium (VI) and technetium (VII) co-extraction with DEHiBA

Moeyaert, P.; Dumas, T.; Guillaumont, D.; Kvashnina, K.; Sorel, C.; Miguirditchian, M.; Dufrêche, P. M. J.-F.

The monoamide DEHiBA (N,N-di-2-ethylhexyl-isobutyramide) is a promising alternative extractant to TBP in order to extract uranium (VI) selectively towards plutonium (IV) and fission products from spent nuclear fuels. Extraction of technetium, present as pertechnetic acid (HTcO4) in the spent fuel solution, by DEHiBA was studied for different nitric acid and uranium concentrations. Uranium (VI) and technetium (VII) co-extraction mechanism with DEHiBA was particularly investigated by different techniques in the present paper to better understand the behavior of technetium in the solvent extraction process. Uranium and technetium distribution ratio were first determined from batch experiments. Based on these data, a thermodynamic model which takes into account deviations from ideality in aqueous phase using the simple solutions concept was developed. The model allowed a good representation of uranium and technetium distribution data, considering the formation of (〖(DEHiBA)_i (HNO_3 )_j (HTcO_4 )〗_k ) ̅ complexes as well as mixed (〖(DEHiBA)〗_2 (UO_2 )(NO_3 )(TcO_4 ) ) ̅ and (〖(DEHiBA)〗_3 (UO_2 )(NO_3 )(TcO_4 )(HNO_3 ) ) ̅ complexes where one pertechnetate anion substitutes one nitrate in the uranium coordination sphere. Combination of complementary spectroscopic techniques (FT-IR and X-ray absorption) supported by theoretical calculations (Density Functional Theory) enabled to fully characterize for the first time the formation of the mixed uranium-technetium specie (〖(DEHiBA)〗_2 (UO_2 )(NO_3 )(TcO_4 ) ) ̅ in organic phase. The structural parameters of this complex are reported in the paper and lead to the conclusion that the pertechnetate group coordinates the uranyl cation in a monodentate fashion in inner coordination sphere. This study also showed how combining a macroscopic study (distribution data acquisition and modeling) with supramolecular investigations (FT-IR and X-ray absorption analysis supported by theoretical calculations) could provide a new insight in the description of solvent extraction mechanism.

Keywords: Monoamides; technetium; uranium; solvent extraction; modeling; speciation


Publ.-Id: 23387

Magnetic Field Induced Relaxation Attenuation of Ultrasound by Jahn–Teller Centers: Application to ZnSe:Cr2+

Zhevstovskik, I. V.; Gudkov, V. V.; Sarychev, M. N.; Zherlitsyn, S.; Yasin, S.; Bersuker, I. B.; Averkiev, N. S.; Baryshnikov, K. A.; Monakhov, A. M.; Korostelin, Y. V.

The influence of magnetic fields on ultrasonic attenuation caused by relaxation in Jahn–Teller centers is studied using chromium ions as Zn Substitute impurities in the ZnSe crystal as an example. The changes of the position and shape of the relaxation peak with the applied magnetic field induction B were observed in the temperature dependence of the ultrasonic attenuation of the shear waves at the frequency of 29.5 MHz propagating along the [110] axis with the polarization vector parallel to the [110] axis. To rationalize the results, a simulation procedure was employed assuming that there are two thermal activation mechanism of relaxation with different relaxation times. One of them emerged with activation energy V0 = 75 K that remains unchanged in the magnetic fields, the other occurs with increasing V0 up to V0 = 106 K at B =14 T.

Publ.-Id: 23386

Anomalous Magnetothermopower in a Metallic Frustrated Antiferromagnet

Arsenijevic, S.; Ok, J. M.; Robinson, P.; Ghannadzadeh, S.; Katsnelson, M. I.; Kim, J. S.; Hussey, N. E.

We report the temperature T and magnetic field H dependence of the thermopower S of an itinerant triangular antiferromagnet PdCrO2 in high magnetic fields up to 32 T. In the paramagnetic phase, the zerofield thermopower is positive with a value typical of good metals with a high carrier density. In marked contrast to typical metals, however, S decreases rapidly with increasing magnetic field, approaching zero at the maximum field scale for T > 70 K. We argue here that this profound change in the thermoelectric response derives from the strong interaction of the 4d correlated electrons of the Pd ions with the shortrange spin correlations of the Cr3+ spins that persist beyond the Néel ordering temperature due to the combined effects of geometrical frustration and low dimensionality.

Publ.-Id: 23385

Dynamical Effects of the Martensitic Transition in Magnetocaloric Heusler Alloys from Direct ΔTad Measurements under Different Magnetic-Field-Sweep Rates

Gottschall, T.; Skokov, K. P.; Scheibel, F.; Acet, M.; Ghorbani Zavareh, M.; Skourski, Y.; Wosnitza, J.; Farle, M.; Gutfleisch, O.

Large magnetocaloric effects can be obtained in Ni-Mn-based Heusler alloys due to the magnetostructural transition between martensite and austenite. This phase transformation proceeds via nucleation and growth. By direct measurements of the adiabatic temperature change ΔTad using different magneticfield-sweeping rates from 0.01 up to 1500 Ts−1, we study the dynamic behavior of the two Heusler compounds Ni50Mn35In15 and Ni45Mn37In13Co5 transforming near room temperature. From these experiments, we conclude that the nucleation process is rather slow in contrast to the relatively fast movement of the phase boundary between martensite and austenite. This is a limiting factor for cooling concepts operating at frequencies beyond 100 Hz. However, the dynamic effects of the transition are negligible in field rates typically used in magnetic refrigeration. These findings are essential considering the suitability of Heusler compounds for energy-efficient solid-state cooling.

Publ.-Id: 23384

High Magnetic Field Study of Elastic Constants of the Cage-structure Compound SmBe13

Mombetsu, S.; Murazumi, T.; Hiura, K.; Yamazaki, S.; Shimizu, Y.; Hidaka, H.; Yanagisawa, T.; Amitsuka, H.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.

Ultrasonic measurements were performed on the cage-structure compound SmBe13. We have investigated the magnetic field-temperature phase diagram of this material by using pulsed magnetic fields. We found that the low-temperature magnetic order is suppressed by a magnetic field of 43 T for H ‖, which is smaller than the estimated value from mean-field approximation assuming the Г8 quartet crystal-electric-field ground state and simple antiferromagnetic order. We found that the elastic constant C44 shows softening below the ordering temperature and has a local minimum below 7 T. These facts suggest that the lowtemperature state is not a simple antiferromagnetically ordered state. In addition, no elastic anomaly due to rattling modes was found in the present measurements.

Publ.-Id: 23383

Narrow-band near-field nanoscopy in the spectral range from 1.3 to 8.5 THz

Kuschewski, F.; von Ribbeck, H.-G.; Döring, J.; Winnerl, S.; Eng, L. M.; Kehr, S. C.

Nano-spectroscopy in the terahertz frequency range remains challenging despite recent technological progress in developing both THz emitter sources and near-field optical microscopy (SNOM). Here we combine scattering-type SNOM with a free-electron laser (FEL) light source, to tune into the 1.3 - 8.5 THz range. A significant portion of this range, namely the frequencies above ~3 THz, is not covered by previously reported near-field microscopy systems. However, it constitutes an indispensable regime where many elementary processes in solids including collective lattice excitations, charge and spin transport occur. Our approach of nano-spectroscopy and nano-imaging provides a versatile analysis of nanostructures as small as 50 nm, hence beating the optical diffraction limit by λ/4600.

Keywords: near-field microscopy; nanoscopy; terahertz

Publ.-Id: 23382

LC-MS supported Studies on the in vitro Metabolism of both Enantiomers of Flubatine and the in vivo Metabolism of (+)-[18F]Flubatine – a Positron Emission Tomography Radioligand for Imaging α4β2-Nicotinic Acetylcholine Receptors

Ludwig, F.-A.; Smits, R.; Fischer, S.; Donat, C. K.; Hoepping, A.; Brust, P.; Steinbach, J.

Both enantiomers of [18F]flubatine are promising radioligands for neuroimaging of α4β2 nicotinic acetylcholine receptors (nAChRs) by positron emission tomography (PET). To support clinical studies in patients with early Alzheimer’s disease, a detailed examination of the metabolism in vitro and in vivo is required. (+)- and (–)-flubatine, respectively, were incubated with liver microsomes from mouse and human in the presence of NADPH. Phase I in vitro metabolites were detected and their structures elucidated by LC-MS/MS. Selected metabolite candidates were synthesized and investigated for structural confirmation. Besides a high level of in vitro stability, the microsomal incubations revealed some species differences as well as enantiomer discrimination with regard to the formation of monohydroxylated products, that was identified as the main metabolic pathway in this assay. Further, after injection of 280 MBq (+)-[18F]flubatine (specific acitivity > 350 GBq/µmol) into a CD-1 mouse, samples were prepared from liver, plasma, and urine after 30 min and investigated by HPLC with radioactivity detection. For structure elucidation of the radiometabolites of (+)-[18F]flubatine formed in vivo, identical chromatographic conditions were applied to LC-MS and radio-HPLC to compare samples obtained in vitro and in vivo. By this correlation we assigned 3 of 4 main in vivo radiometabolites to products exclusively C- or N-hydroxylated at the azabicyclic ring system of the parent molecule.

Keywords: Nicotinic acetylcholine receptors (nAChRs); Flubatine (NCFHEB); Positron emission tomography (PET); Radiometabolites; Liquid chromatography-mass spectrometry (LC-MS); Liver microsomes

Publ.-Id: 23381

Origin of the Zero-Field Splitting in Mononuclear Octahedral MnIV Complexes: A Combined Experimental and Theoretical Investigation

Zlatar, M.; Gruden, M.; Vassilyeva, O. Y.; Buvaylo, E. A.; Ponomarev, A. N.; Zvyagin, S.; Wosnitza, J.; Krzystek, J.; Garcia-Fernandez, P.; Duboc, C.

The aim of this work was to determine and understand the origin of the electronic properties of MnIV complexes, especially the zero-field splitting (ZFS), through a combined experimental and theoretical investigation on five well-characterized mononuclear octahedral MnIV compounds, with various coordination spheres (N6, N3O3, N2O4 in both trans (trans-NO) and cis configurations (cis-N2O4) and O4S2). High-frequency and -field EPR (HFEPR) spectroscopy has been applied to determine the ZFS parameters of two of these compounds, MnLtrans‑N2O4 and MnLO4S2. While at X-band EPR, the axial-component of the ZFS tensor, D, was estimated to be +0.47 cm−1 for MnLO4S2, and a D-value of +2.289(5)cm−1 was determined by HFEPR, which is the largest D-magnitude ever measured for a Mn complex. A moderate D value of −0.997(6) cm−1 has been found for MnLtrans‑N2O4. Quantum chemical calculations based on two theoretical frameworks (the Density Functional Theory based on a coupled perturbed approach (CP-DFT) and the hybrid Ligand-Field DFT (LF-DFT)) have been performed to define appropriate methodologies to calculate the ZFS tensor for MnIV centers, to predict the orientation of the magnetic axes with respect to the molecular ones, and to define and quantify the physical origin of the different contributions to the ZFS. Except in the case of MnLtrans‑N2O4, the experimental and calculated D values are in good agreement, and the sign of D is well predicted, LF-DFT being more satisfactory than CP-DFT. The calculations performed on MnLcis‑N2O4 are consistent with the orientation of the principal anisotropic axis determined by single-crystal EPR, validating the calculated ZFS tensor orientation. The different contributions to D were analyzed demonstrating that the d-d transitions mainly govern D in Mn ion. However, a deep analysis evidences that many factors enter into the game, explaining why no obvious magnetostructural correlations can be drawn in this series of MnIV complexes.

Publ.-Id: 23380

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