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31860 Publications
Scintillator-Based High-Throughput Fast Timing Spectroscopy for Real-Time Range Verification in Particle Therapy
Pausch, G.; Petzoldt, J.; Berthel, M.; Enghardt, W.; Fiedler, F.; Golnik, C.; Hueso-González, F.; Lentering, R.; Römer, K.; Ruhnau, K.; Stein, J.; Wolf, A.; Kormoll, T.;
Range verification of particle beams in real time is considered a key for tapping the full potential of radiooncological particle therapies. The novel technique of prompt gamma-ray timing (PGT), recently proposed and explored in first proof-of-principle experiments, promises range assessment at reasonable expense but challenges detectors, electronics, and data acquisition. Energy-selected time distributions have to be measured at very high throughput rates to obtain the statistics necessary for range verification with single pencil beam spots. Clinically applicable systems should provide a time resolution of about 200 ps, to be obtained with large (about 2” diameter) scintillators, detector loads in the few-Mcps range, and data acquisition rates around 1 Mcps, if possible with compact and inexpensive systems. Such requirements can be met best with CeBr3 scintillators read out with conventional photomultiplier tubes, coupled to commercial but customized electronics featuring high-resolution pulse digitization and fast digital signal processing. The paper deduces design parameters from the constraints given by typical treatment conditions, and presents first results obtained with prototype detectors and electronics developed in accordance with the derived specifications.
Keywords: Hadron therapy, proton beams, range monitoring, gamma rays, gamma-ray spectroscopy, gamma ray detectors, fast timing, inorganic scintillators, cerium bromide, photomultipliers, digital signal processing, medical applications
  • IEEE Transactions on Nuclear Science 63(2016)2, 664-672
    DOI: 10.1109/TNS.2016.2527822
  • Lecture (Conference)
    13th International Conference on Scintillators and their Applications (SCINT), 07.-12.06.2015, Berkeley, USA

Publ.-Id: 23130 - Permalink


Review and present status of preparation of thin layer lead photocathodes for e- injectors of superconducting RF linacs
Lorkiewicz, J.; Nietubyc, R.; Sekutowicz, J.; Barlak, M.; Kostin, D.; Kosinska, A.; Barday, R.; Xiang, R.; Mirowski, R.; Grabowski, W.; Witkowski, J.;
Results are reported on using evaporation and UHV arc lead deposition to create thin-layer superconducting Pb photocathodes on niobium wall of electron gun. Evaporated photocathodes were prepared and tested for the first time in 2014. A complete XFEL-type photo-injector with an evaporated photocathode underwent successful quality check at DESY - an acceptable working point was reached. On the other hand poor adhesion to niobium proved to be the most serious shortcoming of the evaporated Pb layers. UHV arc deposition seems to be much more promising in this context as it allows energetic coating. Filtered arc coating lead to creation of uniform, 2 μm thick lead layers with casual spherical extrusions which enhance locally electric field and leads to high dark current. Conditioning in electric field is needed to reduce the field emission effects from these layers to acceptably low value. Using non-filtered UHV lead deposition enabled fast coating up to a thickness above 10 μm. Pb films obtained in this way require further post-processing in pulsed plasma ion beams in a rod plasma injector. In order to reach a sufficiently planar film surface the pulsed heat flow through a lead layer on niobium was modeled and computed.
Keywords: Superconductors ; Coating ; Niobium ; Plasmas ; Electrons ; Ion beams
  • Contribution to proceedings
    XXXVI Symposium on Photonics Applications in Astronomy, Communications, Industry, and High-Energy Physics Experiments, 25.05.2015, Wilga, Poland
    Proceedings of SPIE - The International Society for Optical Engineering, Wilga, 966233
    DOI: 10.1117/12.2205443

Publ.-Id: 23129 - Permalink


Optische Synchronisation am CW-Beschleuniger ELBE
Kuntzsch, M.;
Moderne Experimente in der Kurzzeitphysik erfordern eine hochpräzise Synchronisation der beteiligten Strahlungsquellen, um dynamische Prozesse und atomare Strukturen aufzulösen. Die Komplexität und räumliche Ausdehnung einer linearbeschleuniger-getriebenen Strahlungsquelle wie ELBE verlangt nach neuen Konzepten, um die anspruchsvollen Anforderungen zu erfüllen.
Kernbestandteile der vorliegenden Arbeit sind die Konzeption, der Aufbau und die Inbetriebnahme eines gepulsten optischen Synchronisationssystems zur Verteilung eines Phasenreferenzsignals. Dieses System bildet eine wesentliche Grundvoraussetzung für wissenschaftliche Experimente mit einer Auflösung im Bereich von wenigen zehn Femtosekunden.
Darüber hinaus wurde der Prototyp eines Ankunftszeitmonitors am ELBE-Beschleuniger entwickelt und charakterisiert. Mit diesem Diagnoseelement wurden erstmals Messungen der Elektronenpulsankunftszeit mit einer Auflösung von wenigen Femtosekunden am ELBE-Strahl möglich. Die implementierte Datenanalyse erlaubt einzelpulsaufgelöste Messzyklen mit bisher unerreichter spektraler Bandbreite am kontinuierlichen (CW) Elektronenstrahl. Ferner wurde eine Methode zur Datenerfassung entwickelt, die unter Verwendung der Lockin-Technik besonders rauscharme Messungen hervorbringen kann.
Abschließend wurde der ELBE-Beschleuniger hinsichtlich Ankunftszeit und Energiestabilität umfassend untersucht. Dabei wurden die erweiterten Möglichkeiten, die ELBE als CW-Beschleuniger bietet, ausgeschöpft. Der Fokus lag besonders auf der spektralen Analyse der Störungen bei verschiedenen Kompressionszuständen der Elektronenpulse. Diese methodische Untersuchung wurde sowohl für den thermionischen Injektor als auch für die supraleitende Fotoelektronenquelle durchgeführt.
Die präsentierten Messergebnisse ermöglichen ein erweitertes Verständnis für die wirkenden Störmechanismen während der Elektronenpulspropagation und stellen den Ausgangspunkt für systematische Verbesserungen der Strahlqualität dar. Ein beschriebener Grundlagenversuch belegt, wie der ELBE-Elektronenstrahl in Zukunft aktiv stabilisiert werden kann, um die erforderliche Zeitauflösung zu erreichen. Intrinsische Strahlinstabilitäten können dadurch signifikant reduziert werden.


Experiments in ultra-fast science require a precise synchronization of the interacting light sources to resolve dynamic processes and structures on an atomic scale. The complexity and spatial dimension of an accelerator-driven radiation source need novel concepts to fulfill these requirements.
The main focus of this thesis lies on the conceptual design, realization and commissioning of a pulsed optical synchronization system to distribute phase-stable reference signals. It is a basic prerequisite for scientific experiments with a temporal resolution in the ten femtosecond range.
Based on the synchronization system a prototype of a bunch arrival time monitor has been developed and characterized at ELBE. It enables measurements with few femtosecond accuracy which were done for the first time at ELBE. The implemented data processing scheme allows single pulse resolution measurements at the continuous wave (CW) electron beam at an unprecedented spectral range. A second method based on lockin-amplifier technique has been developed which has the potential for very low noise measurements.
Finally comprehensive energy and timing jitter studies have been performed at ELBE using the unique properties offered by a CW-accelerator. The investigation was mainly focused on spectral analysis of noise components at varying compression states of the electron bunches. This examination has been done for both the thermionic injector and the superconducting photo electron source.
The results presented in this thesis created an extended comprehension of how noise sources are affecting the beam propagating along the accelerator and lead to further improvements of the beam quality. A proof of concept experiment demonstrates how a future feedback scheme can be used to reduce the residual jitter and to achieve the desired temporal resolution. Intrinsic beam instabilities can be lowered significantly by using this technique.
Keywords: Synchronisation, synchronization, ELBE, CW, continous wave, Beschleuniger, accelerator
  • Doctoral thesis
    TU Dresden, 2015
    Mentor: Prof. Dr. Thomas Cowan
    0156 Seiten

Publ.-Id: 23128 - Permalink


Positron Annihilation Study of Vacancy-Type Defects in Al Single Crystal Foils with the Tweed Structures Across the Surface
Kuznetsov, P.; Cizek, J.; Hruska, P.; Anwand, W.; Bordulev, Y.; Lider, A.; Laptev, R.; Mironov, Y.;
The vacancy-type defects in the aluminum single crystal foils after a series of the cyclic tensions were studied using positron annihilation. Two components were identified in the positron lifetime spectra associated with the annihilation of free positrons and positrons trapped by dislocations. With increasing number of cycles the dislocation density firstly increases and reaches a maximum value at N = 10 000 cycles but then it gradually decreases and at N = 70 000 cycles falls down to the level typical for the virgin samples. The direct evidence on the formation of a two-phase system “defective near-surface layer/base Al crystal” in aluminum foils at cyclic tension was obtained using a positron beam with the variable energy.
Keywords: Al single crystal foils, tweed structures, cyclic tension, positron annihilation

Publ.-Id: 23127 - Permalink


TOPFLOW-Experiments on Direct Condensation and Bubble Entrainment
Seidel, T.; Lucas, D.; Beyer, M.;
Direct Contact Condensation between steam and water as well as bubble entrainment below the water surface play an important role in different accident scenarios for light water reactors. One example is the emergency core cooling water injection into a two-phase mixture. It has to be considered for example to evaluate potential pressurized thermal shock phenomena.
This report documents experiments conducted in flat basin inside the TOPFLOW pressure chamber aiming on the generation of a database useful for CFD model development and validation. It comprises 3 different setups: condensation at a stratified flow of sub-cooled water, condensation at a sub-cooled water jet and a combination of both phenomena with steam bubble entrainment. The documentation includes all details on the experimental set up, on experimental conditions (experimental matrices), on the conduction of the experiments, on measuring techniques used and on data evaluation procedures. In addition, selected results are presented.
Keywords: experiment, CFD, two-phase flow, condensation, bubble entrainment
  • Open Access LogoWissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-066 2016
    ISSN: 2191-8708

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Publ.-Id: 23126 - Permalink


Nuclear and optical dual-labelled imaging agents: Design and challenges
Singh, G.; Gott, M.; Pietzsch, H.-J.; Stephan, H.ORC
Over the last two decades, molecular imaging has been established as a valuable technology, aiming at visualization and characterization of biochemical processes on a molecular level in isolated cells, tissues and higher organisms. Within the wide scope of the various imaging techniques, dual-labelled modalities for nuclear (PET, SPECT) and near-infrared fluorescence (NIRF) imaging show promise owing to their comparable detection sensitivity. Novel materials offer excellent prospects for the development of new non-invasive strategies of early diagnosis and efficient monitoring of therapeutic treatments. In the field of cancer medicine, the combination of different imaging techniques such as PET/SPECT and OI for tracking down tumours and metastases, and subsequent image-guided surgery for tumour resection is particularly attractive.
This review focuses on the development of promising dual-labelled agents to be applied in bimodal nuclear/optical imaging, combining radionuclides and fluorescent dyes. The discussion encompasses modular ligands as well as nanoscale systems, including antibodies and their fragments.
  • Open Access LogoNuklearmedizin 55(2016)2, 41-50

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Publ.-Id: 23125 - Permalink


Correlation of electron and laser beam parameters on the spectral shape and bandwidth of laser-Thomson backscattering x-ray beams
Irman, A.; Jochmann, A.; Couperus, J. P.; Bussmann, M.; Debus, A.; Pausch, R.; Schlenvoigt, H.-P.; Kuntzsch, M.; Lehnert, U.; Wagner, A.; Seipt, D.; Sauerbrey, R.; Ledingham, K.; Stöhlker, T.; Thorn, D.; Trotsenko, S.; Cowan, T.; Schramm, U.;
  • Lecture (Conference)
    Novel Light Sources from Laser-Plasma Interactions Workshop, 20.-24.04.2015, Dresden, Germany

Publ.-Id: 23124 - Permalink


Commissioning of LWFA and Laser-Thomson scattering experiments at HZDR
Irman, A.; Couperus, J. P.; Köhler, A.; Zarini, O.; Krämer, J.; Jochmann, A.; Lehnert, U.; Schramm, U.;
Commissioning of laser wakefield acceleration and laser-Thomson backscattering experiments at HZDR is presented.
  • Invited lecture (Conferences)
    Laboratory for Laser- and beam-driven plasma Acceleration Workshop, 23.-24.06.2015, Wismar, Germany

Publ.-Id: 23123 - Permalink


Towards laser wakefield acceleration with external injection at HZDR: current status
Irman, A.;
Progress towards laser wakefield acceleration with external injection is presented.
  • Invited lecture (Conferences)
    2nd EuCARD-2 Annual Meeting, 21.-24.04.2015, Barcelona, Spain

Publ.-Id: 23121 - Permalink


Laser cooling of relativistic heavy-ion beams for FAIR
Winters, D.; Beck, T.; Birkl, G.; Dimopoulou, C.; Hannen, V.; Kühl, T.; Lochmann, M.; Loeser, M.; Ma, X.; Nolden, F.; Nörtershäuser, W.; Rein, B.; Sanchez, R.; Schramm, U.; Siebold, M.; Spiller, P.; Steck, M.; Stöhlker, T.; Ullmann, J.; Walther, T.; Wen, W.; Yang, J.; Zhang, D.; Bussmann, M.;
Laser cooling is a powerful technique to reduce the longitudinal momentum spread of stored relativistic ion beams. Based on successful experiments at the experimental storage ring at GSI in Darmstadt, of which we show some important results in this paper, we present our plans for laser cooling of relativistic ion beams in the future heavy-ion synchrotron SIS100 at the Facility for Antiproton and Ion Research in Darmstadt.
Keywords: laser cooling, storage ring, heavy ion, relativistic, bion beam, sis100, fair

Publ.-Id: 23120 - Permalink


Progress of laser cooling of 12 C 3+ ions at the CSRe
Wang, H. B.; Ma, X.; Wen, W. Q.; Huang, Z. K.; Zhang, D. C.; Hai, B.; Zhu, X. L.; Zhao, D. M.; Li, J.; Ma, X. M.; Yan, T. L.; Mao, R. S.; Zhao, T. C.; Wu, J. X.; Yang, J. C.; Yuan, Y. J.; Xia, J. W.; Loeser, M.; Siebold, M.; Schramm, U.; Boine-Frankenheim, O.; Eidam, L.; Winters, D.; Birkl, G.; Rein, B.; Walther, T.; Bussmann, M.;
We have performed a test run for laser cooling experiments with 12 C 3+ ion beams at an energy of 122 MeV/u at the CSRe with a pulsed laser. During this beamtime a lot of progress have been made. This was the first time we could successfully separate the 12 C 3+ ions and 16 O 4+ ions in the Schottky spectrum with the help of electron cooling. And our newly installed CPM detector worked well during the experiment. We tried to see effects from the interaction of the pulsed laser light with the stored 12 C 3+ ion beams, but no cooling effects could yet be observed.
Keywords: rf bunching, ion beam, storage ring, relativistic

Publ.-Id: 23119 - Permalink


Optimized small animal tumor model for the radiobiological characterization of low-energy laser accelerated protons
Beyreuther, E.; Brüchner, K.; Baumann, M.; Krause, M.; Leßmann, E.; Schmidt, M.; Pawelke, J.;
The long-term aim of developing laser based particle acceleration (protons, heavier ions) towards clinical radiotherapy application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short and ultra-intensive particle beam pulses. Already obtained in vitro data reveal similar effects of laser accelerated versus conventional proton beams on clonogenic cell survival and DNA double-strand breaks. To proceed in the translational chain, these effects have to be further verified by radiobiological experiments in vivo. However, as the proton energies currently available by laser driven acceleration are still too low to penetrate standard tumor models on mouse legs, a small animal tumor model allowing the delivery of a homogeneous 3D dose distribution with low energy protons (<30 MeV) was established. In the present work, the optimization of this small animal model towards its applicability in a full scale radiobiological experiment at a laser driven proton accelerator will be shown.
  • Contribution to proceedings
    25. Symposium „Experimentelle Strahlentherapie und klinische Strahlenbiologie, 12.-13.02.2016, Dresden, Deutschland
    Proceeedings zum 25. Symposium „Experimentelle Strahlentherapie und klinische Strahlenbiologie
  • Poster
    25. Symposium „Experimentelle Strahlentherapie und klinische Strahlenbiologie, 12.-13.02.2016, Dresden, Deutschland

Publ.-Id: 23118 - Permalink


Radiosynthese von [F-18]NS10746- ein neuer Radioligand des α7-nikotinischen Acetylcholin-Rezeptors (α7-nAChR)
Fischer, S.; Sarasamkan, J.; Ludwig, F. A.; Peters, D.; Steinbach, J.; Brust, P.;
Ziel: α7-nAChR-Liganden sind für das Neuroimaging degenerativer und inflammatorischer Prozesse von Interesse. Wir erarbeiteten die Herstellung von 4-[5-(2-[F-18]fluor-phenyl)-[1,3,4]oxadiazol-2-yl]-1,4-diaza-bicyclo[3.2.2]nonane ([F-18]NS10746), einem selektiven α7-nAChR-Radioliganden mit höherer Affinität als [F-18]NS10743.
Methodik: Entwicklung einer Synthese basierend auf der nukleophilen Substitution eines NO2-Präkursors durch [F-18]Fluorid und Übertragung auf eine automatisierte Herstellung.
Ergebnisse: Der NO2-Präkusor (NS14559, 2mg) wurde mit K[F-18]F-K222-K2CO3 in DMF bzw. DMSO (0,75; 1,0ml) bei erhöhten Temperaturen (145 bzw. 155°C) mit Ausbeuten von 12- 20% bzw. 15- 21% (n=7,7) umgesetzt. Parallel zum Zielprodukt wurde, vor allem in DMF, ein F-18- markiertes Folgeprodukt detektiert, welches durch Reaktion von 12-16 min in DMSO ausreichend minimiert werden konnte. Versuche zur Mikrowellen-unterstützten Reaktionsführung (n=15) erbrachten keine Erhöhung der Ausbeute. Die Isolierung von [F-18]NS10746 erfolgte mittels semi-präparativer Gradienten-HPLC (NH4OAcaq /MeCN an RP-Säule, z. B. ReproSil-Pur C18-AQ). Die Zielfraktion wurde auf eine Kartusche (SEP-PAK LIGHT C18) aufgetragen, mit EtOH eluiert und als sterile 10% EtOH/0,9% NaCl-Lösung formuliert. Die Herstellungsprozedur konnte auf das Synthesemodul TRACERlab FX N übertragen werden (RCY: 13-15%, 65- 70 min, n= 5). Das Produkt wurde mit hoher chemischer und radiochemische Reinheit (jeweils > 95%) sowie hoher spez. Aktivität (150- 320 GBq/μmol) erhalten.
Schlussfolgerungen: Es konnte ein Verfahren zur Herstellung von [F-18]NS10746 erarbeitet werden, wobei die Markierungsausbeute geringer war als die von [F-18]NS10743 (p-Fluor-Substitution; 40- 55%). Der Radioligand [F-18]NS10746 wird für laufende In-vitro- und In-vivo- Validierungen bereitgestellt.
  • Poster
    NuklearMedizin2016, 54. Jahrestagung der DGN, 20.-23.04.2016, Dresden, Deutschland

Publ.-Id: 23117 - Permalink


Development update of the PENELOPE laser system
Albach, D.; Siebold, M.; Loeser, M.; Roeser, F.; Schramm, U.;
We present the development status of the PENELOPE laser system currently being under construction at the Helmholtz-Zentrum Dresden-Rossendorf. We will present experimental data for the first amplification stages as well as results for the stretcher-compressor setup. The focus will be set on the main amplifying stages designed to boost the output energy after compression above 150J.
Keywords: laser, diode pumping, DPSSL, amplification, Ytterbium, Penelope
  • Lecture (Conference)
    The 4th Advanced Lasers and Photon Sources, 22.-24.04.2015, Yokohama, Japan

Publ.-Id: 23116 - Permalink


Rectifying filamentary resistive switching in ion-exfoliated LiNbO3 thin films
Pan, X.; Shuai, Y.; Wu, C.; Luo, W.; Sun, X.; Zeng, H.; Zhou, S.; Böttger, R.; Ou, X.; Mikolajick, T.; Zhang, W.; Schmidt, H.;
In this letter, we report the resistive switching properties of ion-exfoliated LiNbO3thin films. After annealing in Ar or in vacuum, electro-forming has been observed on the thin films, and the oxygen gas bubbles can be eliminated by tuning the annealing conditions in order to prevent the destruction of top electrodes. The thin films show rectifying filamentary resistive switching after forming, which is interpreted by a simplified model that the local filament does not penetrate throughout the LiNbO3thin film, resulting in asymmetric contact barriers at the two interfaces. The well controlled electro-forming step and the highly reproducible switching properties are attributed to the more homogeneous distribution of defects in single crystalline materials and the specific geometry of filament.
Keywords: gold, electrodes, mangetization reversal, single crystals, crystal structure

Publ.-Id: 23115 - Permalink


Synthesis, characterization and in vivo evaluation of radiolabeled anti-inflammatory dendritic polyglycerol: A structure – pharmacokinetics relationship
Pant, K.; Gröger, D.; Bergmann, R.; Pietzsch, J.; Stephan, H.; Haag, R.;
Dendritic polyglycerols (dPGs) represent highly biocompatible scaffolds with narrow polydispersity, multivalency and ease of synthesis. The sulfate derivatives (dPGS) in particular, are potent candidates for, e.g., in the development of anti-inflammatory drugs due to their ability to inhibit the L & P selectins. In order to understand the physiological fate of these nano-objects, it is crucial to understand their behavior especially with respect to their absorption, distribution, metabolism and excretion (ADME). Herein, we present the in vivo distribution pattern of the neutral (dPG) as well as the therapeutically active polymer scaffolds using radiolabeling strategies. A novel 3H radiolabeling strategy has been established for these nano-objects which enable to study longer biochemical processes via radio imaging. In parallel, isothiocyanate and/or maleimide-functionalized TACN based CuII-chelating ligands were attached to dPGS derivatives with terminal amine or mercapto groups to allow for performing positron emission tomography (PET) studies using 64Cu (t1/2 = 12.5 h). 1H NMR, DLS and zeta potential measurements have been performed in order to achieve information about the number of chelators, size and charge of the dPGS derivatives. A new titration assay was established to determine the copper loading capacity and to obtain exact numbers of CuII chelators for the dPG derivatives. The 64Cu - conjugates are resistant to transchelation in vitro as well as in vivo. Independent studies in rats & mice show different routes of excretion for neutral dPGs in contrast to their polysulfated analogs. Furthermore, to derive an insight on the pharmacokinetics, effect of size, charge and surface groups have been studied in a range of scaffolds. Uptake mechanism in the cells, protein adsorption profile and cytotoxicity will be discussed. The results from these studies show that these polyglycerols are highly promising candidates for theranostic applications and drug targeting.
  • Poster
    PACIFICHEM 2016, 15.-20.12.2015, Honolulu, USA

Publ.-Id: 23114 - Permalink


Polyglycerol based Nanoparticles as an EGFR specific multimodal imaging agent
Pant, K.; Zarschler, K.; Neuber, C.; Pufe, J.; Pietzsch, J.; Spiccia, L.; Graham, B.; Stephan, H.;
Purpose: Dendritic polyglycerols (dPG) are globular, highly biocompatible macromolecular scaffold which can be synthesized with a broad range of molecular weights and sizes for their desired application.[1] They show a size dependent blood circulation, no protein interactions and a very fast renal clearance.[2] The multiple peripheral groups gives them an advantage of multivalent interactions and thus, multiple moieties for e.g. for PET imaging or optical imaging can be integrated on a single probe for an enhanced resolution leading to an early diagnosis. The purpose of the work was to use these polyglycerols based nanoparticles to attach 64Cu based PET tracer, a dye to the scaffold. For a receptor mediated targeting, a camelid single domain antibody (SdAb) was used which is known to bind to the epidermal growth factor receptors (EGFR).
Experimental description: Dendritic polyglycerol with peripheral hydroxyl groups of a size of 10 kDa and a hydrodynamic volume of 6.5 ± 1.5 nm was prepared in a one pot reaction using ROMBP. Amine groups (9.5%) were introduced to the scaffold for further functionalization. For synthesizing the multimodal agent, the dPG was thiolated using iminothiolane. To the thiolated dPG in a one pot reaction, a maleimide containing DMPTACN based 64Cu chelator, a maleimide containing Cy3 (in vitro) or Cy7 (in vivo) dye were added in a slow monomer type addition. For the targeting unit, the SdAb was attached to the polyglycerol via a maleimide containing PEG linker.
Results: Purification was done using dialysis and several chromatographic techniques. The conjugates were then characterized by UV-Vis, radiometric titrations and microscopy experiments. Radiolabeling was done using 64CuCl2 at physiological conditions with a 99% RCY. Uptake and binding studies were done using A431 and FaDu cell lines using 64Cu labeled conjugate. Confocal scanning laser microscopy was performed for colocalization and internalization studies. In vivo PET and bio distribution studies were done on an A431-tumor mouse model. To confirm receptor specific binding, in vitro as well as in vivo blocking studies were done. The results show a pronounced affinity and active targeting of the dPG multimodal conjugate.
Conclusions: Soft matter nanoparticles based on dendritic polyglycerols are a promising platform for multimodal imaging and theranostics.

Acknowledgements: This study is part of a research initiative “Technologie und Medizin – Multimodale Bildgebung zur Aufklärung des in-vivo Verhaltens von polymeren Biomaterialien” of the Helmholtz-Portfoliothema. Financial support by the Helmholtz Virtual Institute NanoTracking (Agreement Number VH-VI-421) is gratefully acknowledged.

References :
[1] H.Frey, R. Haag; Rev.Mol. Biotechn. 2002, 90, 257-67.
[2] K. Pant, D. Gröger, R. Bergmann, J. Pietzsch, J. Steinbach, B. Graham, L. Spiccia, F. Berthon, B. Czarny, L. Devel, V. Dive, H. Stephan, R. Haag; Bioconjugate Chem. 2015, 26, 906-18
Keywords: Polyglycerols, PET imaging, Nanoparticles, Optical imaging, Antibodies, Multimodality
  • Poster
    2nd International Symposium on Nanoparticles/Nanomaterials and Applications (ISN2A 2016), 18.-21.01.2016, Lisbon, Portugal

Publ.-Id: 23113 - Permalink


Dendritic polyglycerols as dual modal imaging agent for EGF-receptor mediated tumor targeting
Pant, K.; Zarschler, K.; Bergmann, R.; Pietzsch, J.; Stephan, H.;
Dendritic polymers represent a powerful, multifunctional nanoscalic platform for imaging and therapeutic applications. To overcome specific limitations in imaging, having multiple modalities on a single carrier molecule is preferred and also obviates the need to administer several compounds with different pharmacokinetics. In this regard, dendritic polyglycerols (dPG) are globular macromolecules with a narrow size distribution, high degree of branching and high end group functionalities. The great versatility of the dendritic polymers allows to fine tune physico-chemical parameters such as particle size, water solubility, surface charge, chemical functionalities, etc., that are relevant for the successful preparation of theranostic systems. Lower molecular weights (LMW) uncharged dPGs' (2-20kDa) however are known to show no/minimum uptake by the cells and thus represent ideal candidates for receptor mediated targeting. The present work here deals with the development of a dendritic polyglycerol derivative (10kDa,10% NH2 groups) as a dual modal agent for epidermal growth factor receptor (EGFR) specific tumor targeting. In this respect, in a one pot reaction, simultaneously maleimido- bearing fluorescent labels (dye) and macrocyclic chelators for 64Cu (PET tracer) were attached to thiol anchoring groups of the polymeric scaffold. For an EGFR specific targeting, a small camelid single-domain antibody (sdAb) representing a potential recognition agent for EGFR was attached via a PEG linker. Purification of the bioconjugates was achieved using size exclusion chromatography. 64Cu radiolabeling was done under ambient temperature and physiological pH. Binding and uptake studies were performed using A431 and FaDu cell lines using 64Cu-labeled bioconjugates. Confocal laser scanning microscopy was used to study the receptor mediated cellular uptake. The results obtained unveil the potential of dendritic polyglycerols as multimodal platforms for theranostic applications.
  • Lecture (Conference)
    PACIFICHEM 2015, 15.-20.12.2015, Honolulu, USA

Publ.-Id: 23112 - Permalink


Polyoxometalates with potent inhibitory activity at P2X receptors
Spanier, C.; Abdelrahman, A.; Tang, J.; Hausmann, R.; Kortz, U.; Schmalzin, G.; Stephan, H.; Wang, W.; Müller, C. E.;
P2X receptors are trimeric ligand-gated ion channels activated by ATP and permeable for cations such as Na+, K+ and Ca2+. Seven different subunits exist, assembled as homo- or heterotrimers of various stoichiometry.1 Polyoxometalates (POMs) are polynuclear metal-oxo anions of early transition metals in high oxidation states (e. g. W6+, Mo6+, V5+). This class of inorganic metal cluster compounds exhibits great variability with respect to shape, size, charge and composition.2 POMs bear several negative charges and in this respect resemble ATP, which binds to P2X receptors in its negatively charged state. We previously found that certain POMs can inhibit ATP-hydrolyzing ectonucleotidases.2-4 In the present study we investigated whether tungsten-containing POMs can interact with P2X receptors. A series of POMs was investigated for their ability to inhibit ATP-induced calcium influx in recombinant 1321N1 astrocytoma cells stably transfected with P2X receptor subtypes. Several POMs were found to be highly potent inhibitors of P2X receptors exhibiting low nanomolar potency. PEGylation of POMs to increase their metabolic stability was tolerated by the receptors. Structure-activity relationships at P2X receptor subtypes differed from those observed for ecto¬nucleotidases. The majority of POMs were found to be non-cytotoxic at pharmacologically active concentrations.

(1) Coddou, C., Yan, Z., Obsil, T., Huidobro-Toro, J.P., Stojilkovic, S.S. Activation and regulation of purinergic P2X receptor channels. Pharmacol Rev, 2011, 63:641-683
(2) Stephan, H., Kubeil, M., Emmerling, F., Müller, C.E. Polyoxometalates as versatile enzyme inhibitors. Eur. J. Inorg. Chem., 2013, 1585-1594
(3) Müller, C.E., Iqbal, J., Baqi, Y., Zimmermann, H., Röllich, A., Stephan, H. Polyoxometalates – a new class of potent ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) inhibitors. Bioorg Med Chem Lett, 2006, 16:5943-5947
(4) Lee, S., Fiene, A., Li, W., Hanck, T., Brylev, K.A., Fedorov, V.E., Lecka, J., Haider, A., Pietzsch, H.J., Zimmermann, H., Sévigny, J., Kortz, U., Stephan, H., Müller, C.E. Polyoxometalates – potent and selective ecto-nucleotidase inhibitors. Biochem Pharmacol, 2015, 93:171-181
  • Poster
    Purinergic Signaling Symposium, 24.-28.01.2016, Vancouver, Canada

Publ.-Id: 23110 - Permalink


Target development for LWFA experiments at HZDR: Supersonic gas jets and plasma waveguides
Köhler, A.; Messmer, M.; Couperus, J. P.; Zarini, O.; Jochmann, A.; Wolterink, T.; Bastiaens, B.; Boller, K.; Irman, A.; Schramm, U.;
Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. To attain highest possible particle energies in this acceleration scheme, high intensity laser beam must be maintained over distances much longer that the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterized using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulse Ti:Sa laser are evaluated.
The results show a broad, easy to realize parameter window for pressure and time in which high laser transmission of above 75% are achieved.
  • Lecture (Conference)
    Laser Plasma Targetry Workshop, 20.-22.04.2015, Paris, Frankreich

Publ.-Id: 23109 - Permalink


Cyclam propionates: Stable copper(II) chelates for radiopharmaceutical application
Kubeil, M.; Zarschler, K.; Pietzsch, J.; Stephan, H.; Comba, P.;
Due to their ability to form thermodynamically stable complexes with copper(II), ligands based on 1,4,8,11-tetraazacyclotetradecane (cyclam) are important for radiopharmaceutical applications [1]. Of particular interest are ligands that enable the simultaneous introduction of targeting molecules, e.g. peptides and/or fluorescence units, to construct effective radiopharmaceuticals for diagnostic and therapeutic purposes. In this context, 1,4,8,11-tetraazacyclotetradecane-1,4,8,11-tetracetic acid (TETA) is widely used for the development of copper-based target-specific radiopharmaceuticals.

Herein, we present a comprehensive study of CuII-cyclam complexes with propionic acid arms [2]. The influence of the number of pendant arms on structural features of CuII complexes formed as well as the radiopharmacologic properties of 64Cu-complexes are investigated and compared to CuII-TETA. Quite a few parameters (e.g. charge, configuration, lipophilicity) influence the kinetic inertness of the radiocopper complexes and thus may impair the pharmacokinetic properties.
All experiments point to a decrease of complex and in vivo stability with an increasing number of N-substituted propionic acid groups. Altogether, the cyclam mono- and dipropionic acids TE1P and trans-TE2P are ideally suited as chelating agents for 64CuII due to their fast complexation kinetics, their high kinetic inertness in the presence of superoxide dismutase (SOD) and human serum as well as their excellent biodistribution behavior. trans-TE2P has the possibility to use the non-chelating second propionate to introduce additional functions, such as solubilizing, fluorescent and targeting units.


References
1. T. J. Wadas, E. H. Wong, G. R. Weisman, C. J. Anderson, Chem. Rev. 110, 2858 (2010).
2. P. Comba, F. Emmerling, M. Jakob, W. Kraus, M. Kubeil, M. Morgen, J. Pietzsch, H. Stephan, Dalton Trans. 42, 6142 (2013).
  • Lecture (Conference)
    PACHIFICHEM 2015, 15.-20.12.2015, Honolulu, USA

Publ.-Id: 23108 - Permalink


High intensity laser guiding in plasma waveguides created by slow capillary discharge
Messmer, M.; Köhler, A.; Couperus, J. P.; Jochmann, A.; Irman, A.; Schramm, U.;
Laser wakefield acceleration (LWFA) has emerged as a promising concept for the next generation of high energy electron accelerators. To attain highest possible particle energies in this acceleration scheme, high intensity laser beam must be maintained over distances much longer that the Rayleigh length. Therefore laser guiding is necessary to counteract the diffraction induced divergence of the beam.
For this, a plasma channel is created inside a capillary via the concept of slow capillary discharge and characterized using an interferometric method. It is shown that the plasma channel has a refractive index profile suitable for laser guiding. As the first step, the pressure range and the time window in which guiding can occur are determined by guidance of a He-Ne laser. With the gained knowledge, laser guiding capabilities of a pulse Ti:Sa laser are evaluated.
The results show a broad, easy to realize parameter window for pressure and time in which high laser transmission of above 75% are achieved.
  • Lecture (Conference)
    DPG-Frühjahrstagung Wuppertal, 09.-13.03.2015, Wuppertal, Deutschland

Publ.-Id: 23107 - Permalink


Investigation of betatron radiation from laser-wakefield accelerators
Köhler, A.; Couperus, J. P.; Zarini, O.; Debus, A.; Jochmann, A.; Irman, A.; Schramm, U.;
Betatron radiation emitted by accelerated electrons in laser-wakefield accelerators can be used as a diagnostic tool to investigate electron dynamics during the acceleration process. Utilizing a 2D x-ray imaging spectroscopy technique we analyse the spectral dependence of the emitted Betatron pattern which basically represents certain electron beam parameters inside the plasma cavity.
The experiments are carried out with the Draco Ti:Sapphire laser system at HZDR.
Keywords: LWFA Laser-wakefield acceleration Betatron radiation
  • Lecture (Conference)
    DoKDoK, 11.-15.10.2015, Eisenach, Deutschland

Publ.-Id: 23106 - Permalink


Molecular imaging of cancer using bispidine ligands
Stephan, H.; Comba, P.;
The development of multi-functional complexing agents for radiometal nuclides with a view of nuclear medical application represents a field of research that is intensively dealt with and has rapidly been developing. In this context, ligands that form highly stable metal complexes and additionally possess several different functional groups are of particular interest. This enables the simultaneous introduction of targeting, solubilizing and, for example, fluorescent units into the relevant metal complexes.

Ligands based on 3,7-diazabicyclo[3.3.1]nonane (bispidine) form very stable coordination compounds, in particular with CuII. Due to the formation of thermodynamically and kinetically stable CuII complexes, bispidine ligands are well suited for in vivo application in cancer imaging (64CuII) and radiotherapy (64CuII, 67CuII). Since they are also relatively easy to functionalize with multiple modalities, they are ideal chelators for the design of novel multimodal imaging agents. The bispidine scaffold has a number of options for derivatization that permit the introduction of additional functions such as biological vectors and fluorescence molecules.

Here, the important properties of 64CuII-labeled bispidine complexes, e. g. stabilities, ligand exchange kinetics, serum stability, partition coefficients (n-octanol/water) and biodistribution data will be reported. It can be concluded that 64CuII-labeled bispidine derivatives with fluorescent tags have considerable potential for targeted dual imaging using positron emission tomography (PET) and fluorescence imaging.
  • Lecture (Conference)
    PACIFICHEM 2015, 15.-20.12.2015, Honolulu, USA

Publ.-Id: 23105 - Permalink


Radiopharmaceutical Evaluation of Peptide Nucleic Acid Bioconjugates as Complementary System for Tumor Targeting
Stephan, H.;
The search for novel strategies for the diagnosis and therapy of cancer is currently a field of active research. A promising option is the use of a pretargeting approach with the non-natural DNA/RNA analogues Peptide Nucleic Acids (PNAs) as in vivo recognition units. Such a concept overcomes major drawbacks present when conventional monoclonal antibodies (mAbs) are employed as tumor-targeting agents by decoupling the delivery of a tumor-specific mAb from the delivery of the diagnostic or therapeutic radionuclide. In this multistep process an unlabeled, highly specific antibody-PNA conjugate has sufficient time to target the tumor before administering a small, fast-clearing radiolabeled complementary PNA that hybridizes with the antibody-PNA conjugate at the tumor side. Rapid clearance of the radiolabeled PNA significantly reduces radiation exposure of non-target tissues and its small size permits speedy delivery to the tumor, creating excellent tumor/non-tumor ratios. These appealing characteristics allow the rational application of the pretargeting approach for diagnosis as well as therapy of cancer.

Herein a successful tumor pretargeting approach using PNA radiolabeled with clinically available 99mTc and complementary PNA linked to the antibody Cetuximab in murine xenografts will be presented. Importantly, no metabolization and a high specific tumor accumulation of the PNA conjugate were observed.

The results presented in this work are promising in the view of further preclinical studies including internal radiotherapeutic treatment.
  • Lecture (Conference)
    PACIFICHEM 2015, 15.-20.12.2015, Honolulu, USA

Publ.-Id: 23104 - Permalink


Ultrasmall nanomaterials for biomedical applications
Stephan, H.ORC
The field of nanomedicine offers excellent prospects for the development of new non-invasive strategies for the diagnosis and therapy of cancer [1, 2]. A major advantage of nanomaterials (NMs) is their potential to be used as non-invasive diagnostic tools. By combining multiple modalities into a single probe, higher sensitivity can be achieved, leading to deeper insights into different in vitro and in vivo processes. Despite the significant progress that has been made in the field of NMbased cancer diagnostics, our overall understanding of their pharmacokinetics (adsorption, uptake, distribution, metabolism and excretion) is still limited. Detailed investigations of the physicochemical properties and physiological behavior of NMs in biological environments are required to be better able to understand, predict and control their biodistribution.
We are aiming to develop targeted nanomaterials capable of imaging cancer by a combination of positron emission tomography PET, fluorescence optical imaging (OI) and/or magnetic resonance imaging (MRI) to provide a deeper understanding of their interactions in vitro and in in vivo. For the development of any functional nanomaterial to be applied for cancer imaging, it is of utmost importance to evade capture by the mononuclear phagocyte system and to circulate in vivo until reaching the target. It is now well recognized that ultrasmall (< 6 nm), renally-excretable particles are the most appropriate from this point of view, provided that they can be coupled to an efficient targeting vector.
Prototypes of highly-defined narrow-sized NPs have been developed and characterized, e.g. 2 - 4 nm-sized silicon NPs with reactive surface moieties, such as amino and carboxylic acid groups. Ultrasmall superparamagnetic iron oxide (USPIOs), upconverting nanophosphors and dendritic polyglycerol derivatives (< 10 nm) are also available as defined platforms. New assembly strategies, resulting in well-defined surface-attached radiochelates, fluorophores and targeting vectors will be presented. This includes in particular the engineering of zwitterionic-coated “stealth” NPs, leaving only targeting groups directly exposed to the surrounding biological milieu. [3] A small camelid single-domain antibody (sdAb) was chosen as targeting vector of the epidermal growth factor receptor (EGFR) which is overexpressed in a variety of solid tumors. [4]

References:
[1] Ferrari, M. Cancer nanotechnology: opportunities and challenges. Nat. Rev. Cancer 5 (2005) 161-71.
[2] Kim, B. Y.; Rutka, J. T.; Chan, W. C. Nanomedicine. N. Engl. J. Med. 363 (2010) 2434-43.
[3] Pombo García, K.; Zarschler, K.; Barbaro, L.; Barreto, J. A.; O'Malley, W.; Spiccia, L.; Stephan, H.; Graham, B. Zwitterionic-coated "stealth" nanoparticles for biomedical applications: recent advances in countering
biomolecular corona formation and uptake by the mononuclear phagocyte system. Small 10 (2014) 2516-2529.
[4] Zarschler, K.; Prapainop, K.; Mahon, E.; Rocks, L.; Kelly, P. M.; Bramini, M.; Stephan, H.; Dawson, K. A. Diagnostic nanoparticle targeting of the EGF-receptor in complex biological conditions using single-domain antibodies.
Nanoscale 6 (2014) 6046-6056.
  • Invited lecture (Conferences)
    1st International Caparica Christmas Congress on Translational Chemistry, 07.-10.12.2015, Lisbon, Portugal

Publ.-Id: 23103 - Permalink


The influence of microorganisms on the immobilization of radionuclide in subsurface crystalline rock environments
Krawczyk-Bärsch, E.;
In the underground rock characterization facility tunnel ONKALO in Finland, and in the Äspö Hard Rock Laboratory (HRL) in Sweden massive 5–10-mm thick biofilms were observed attached to tunnel walls where groundwater was seeping from bedrock fractures. The main goal of the study was to evaluate the relevance of microbial processes for the immobilization of radionuclides in a deep crystalline repository for high-level radioactive waste. In laboratory experiments the effect of uranium on biofilms was studied on site in the ONKALO tunnel by adding uranium to the fracture water in a self constructed flow cell by using detached biofilm samples. Biofilm specimens collected for transmission electron microscopy studies indicated that uranium in the biofilm was immobilized intracellularly in microorganisms as needle-shaped uranyl phosphate minerals, similar to meta-Autunite (Ca[UO2]2[PO4]2•10-12H2O).
Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) from the Äspö HRL were used for laboratory experiments, in which uranium and neptunium, respectively, were added to the BIOS biofilms. The biofilms were submerged in Äspö groundwater in a flow cell under aerobic conditions. The results showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85% and 95%, respectively. Thermodynamic calculation of the theoretical predominant fields of uranium species showed that the formation of an aqueous uranium carbonate species Ca2UO2(CO3)3 was predicted due to the high concentration of carbonate in the groundwater. Under the given pH conditions the uptake of uranium and neptunium in the BIOS biofilm depends predominantly on the high amount of ferrihydrite, which precipitated onto the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea. Consequently, the combination of the biological material and iron oxides created an abundant surface area for bioaccumulation and adsorption of radionuclides.
Keywords: biofilm, uranium, neptunium, nuclear waste repository
  • Invited lecture (Conferences)
    Teaching module: Interactions of heavy metals with bacteria for bioremediation purposes., 16.06.2015, Granada, Spain

Publ.-Id: 23102 - Permalink


Topological Spin Textures as Emitters for Multidimensional Spin Wave Modes
Sluka, V.; Weigand, M.; Kakay, A.; Schultheiss, K.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.ORC; Raabe, J.; Wintz, S.
The investigation of propagating spin waves is a key topic of magnetism research. For the excitation of spin waves with short wavelengths, it was typically necessary to either use transducers with sizes on the order of the desired wavelengths (striplines or point-contacts) or to generate those spin waves parametrically by a double-frequency spa- tially uniform microwave signal. Only recently, a novel mechanism for the local excitation of spin waves has been discovered, which over- comes the wavelength limit given by the minimum patterning size. This method utilizes the translation of natural topological defects, namely the gyration of spin vortex cores. In the present contribution we will show that in a vortex pair system with uniaxial magnetic anisotropy, spin waves of even different symmetries and dimensionalities can be excited.
Keywords: spin wave, multilayers, dipole-exchange, non-reciprocity
  • Lecture (Conference)
    DPG Frühjahrstagung der Sektion kondensierte Materie, 06.-11.03.2016, Regensburg, Deutschland

Publ.-Id: 23101 - Permalink


Relaxation of excited surface states of thin Ge-implanted silica films probed by OSEE spectroscopy
Zatsepin, A. F.; Buntov, E. A.; Mikhailovich, A. P.; Slesarev, A. I.; Schmidt, B.; von Czarnowski, A.; Fitting, H. J.;
As an example of thin silica films, 30 nm SiO2-Si heterostructures implanted with Ge+ ions (10(16) cm(-2) fluence) and rapid thermally annealed (RTA) at 950 degrees C are studied by means of optically stimulated electron emission (OSEE) in the spectral region of optical transparency for bulk silica. Quartz glass samples were used as references. Experimental data revealed a strong dependence between electron emission spectral features and RTA annealing time. The spectral contributions of both surface band tail states and interband transitions were clearly distinguished. The application of emission Urbach rule as well as Kane and Passler equations allowed to analyze the OSEE spectra at different optical excitation energy ranges and to retrieve the important microstructural and energy parameters. The observed correlations between parameter values of Urbach- and Kane-related models suggest the implantation-induced conversion of both the vibrational subsystem and energy band of surface and interface electronic states.
Keywords: Surface states; Relaxation; Thin films; Ion implantation; Electron emission; Energy structure

Publ.-Id: 23100 - Permalink


Novel implementation of memristive systems for data encryption and obfuscation
Du, N.; Manjunath, N.; Shuai, Y.; Buerger, D.; Skorupa, I.; Schueffny, R.; Mayr, C.; Basov, D.; Di Ventra, M.; Schmidt, O. G.; Schmidt, H.;
With the rise of big data handling, new solutions are required to drive cryptographic algorithms for maintaining data security. Here, we exploit the nonvolatile, nonlinear resistance change in BiFeO3 memristors [Shuai et al., J. Appl. Phys. 109, 124117 (2011)] by applying a voltage for the generation of second and higher harmonics and develop a new memristor-based encoding system from it to encrypt and obfuscate data. It is found that a BiFeO3 memristor in high and low resistance state can be used to generate two clearly distinguishable sets of second and higher harmonics as recently predicted theoretically [Cohen et al., Appl. Phys. Lett. 100, 133109 (2012)]. The computed autocorrelation of encrypted data using higher harmonics generated by a BiFeO3 memristor shows that the encoded data distribute randomly.
Keywords: analog resistive switch, flexible barrier height, BiFeO3, fast and energy-efficient resistive swiching

Publ.-Id: 23099 - Permalink


Electric-field-induced insulator to Coulomb glass transition via oxygen vacancy migration in Ca-doped BiFeO3
Lim, J. S.; Lee, J. H.; Ikeda-Ohno, A.; Ohkochi, T.; Kim, K.-S.; Seidel, J.; Yang, C.-H.;
The BiFeO3 (BFO) is an interesting playground to explore correlated electronic conduction. It is found that a non-rigid polaronic band is created by hole doping as a result of a strong electron-lattice coupling. We also show strong evidence for the disorder-driven formation of a Coulomb glass state. These results can be harmonized in a framework of the spatial inhomogeneity of polaronic charge density, suggesting a unique electronic conduction mechanism applicable to systems with coexistence of strong electron correlation, electron-lattice interaction, and randomness.
Keywords: Material science, insulator, synchrotron, PEEM, XAS, XPS, XRD, characterisation

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Publ.-Id: 23097 - Permalink


Spin-glass behavior of Fe doped InAs prepared by ion implantation and pulsed laser annealing
Yuan, Y.; Cai, H.; Helm, M.; Zhou, S.;
Dilute magnetic semiconductors (DMSs) attracted great interests in the last several decades because of their potential for spintronic device [1]. III-V compounds especially GaAs based DMS has recently emerged as the most popular material for this new technology. However, that the low mobility of holes in p-type DMS limits the potential application in semiconductor spintronic devices. Therefore, the searching for n-type DMS is of interest.
The doping of Fe in InAs is attracting research attentions due to the possibility to fabricate n-type diluted magnetic semiconductors [2, 3]. However, the low solubility of Fe in InAs is the most difficulty to achieve InFeAs DMS. In this work, we obtain Fe doped InAs layers by ion implantation and pulsed laser annealing. This approach has shown success for preparing other III-V based DMSs [4, 5]. The formed InFeAs layers are proved to be epitaxial-like on InAs substrates. The prepared InFeAs layers reveal similar magnetic properties independent of their conductivity types. While the samples are lacking of charactersistics of DMS, they appear to be spin-glass like, revealing such as time-dependent magnetiszation measurements reveal aging and memory effects.
1. T. Dietl et al., Science 287, 1019-1022 (2000)
2. M. Kobayashi et al., Appl. Phys. Lett., 105, 032403(2014)
3. P. Nam Hai et al., Appl. Phys. Lett., 101, 182403 (2012)
4. D. Bürger et al., Phys. Rev. B, 81, 115202 (2010)
5. M. Khalid et al., Phys. Rev. B, 89, 121301(R) (2014)
  • Poster
    ICM 2015, 05.-10.07.2015, Barcelona, Spain

Publ.-Id: 23096 - Permalink


What defines the quantum regime of the free-electron laser?
Kling, P.; Giese, E.; Endrich, R.; Preiss, P.; Sauerbrey, R.; Schleich, W. P.;
The quantum regime of the free-electron laser (FEL) emerges when the discreteness of the momentum of the electron plays a dominant role in the interaction with the laser and the wiggler field. Motivated by a heuristic phase space approach we pursue two different routes to define the transition from the classical FEL to the quantum domain: (i) standard perturbation theory and (ii) the method of averaging. Moreover, we discuss the experimental requirements for realizing a Quantum FEL and connect them to today's capabilities.
Keywords: free-electron laser; quantum regime; Quantum FEL

Publ.-Id: 23094 - Permalink


Quantum theory for the dynamic micro-structure in correlated two-component systems far from equilibrium -- application to x-ray scattering
Vorberger, J.; Chapman, D. A.;
We present a quantum theory for the dynamic structure factors in non-equilibrium, correlated, two-component systems like plasmas or warm dense matter. On this basis, expressions for the local field corrections in non-equilibrium could be determined as well. The polarization function, needed as input for the calculation of the structure factors, is calculated in non-equilibrium based on a perturbation expansion in the interaction strength. To make our theory applicable for x-ray scattering, a generalized Chihara decomposition for the total electron structure factor in non-equilibrium is derived. Examples are given for the special case of equilibrium and for a bump-on-hot-tail distribution as often encountered during laser heating of materials.
Keywords: Plasma kinetic equations, Thermodynamics of plasmas, Strongly-coupled plasmas, Perturbative methods, X-ray and γ-ray measurements, Dielectric properties, Scattering theory (quantum mechanics)

Publ.-Id: 23093 - Permalink


Multiphase CFD activities at Helmholtz–Zentrum Dresden – Rossendorf
Lucas, D.;
Multiphase flows are frequently applied in industrial processes as e.g. in chemical engineering, oil industries or power plants. Reliable predictions of the flow characteristics such as local concentration of species, interfacial area density or heat transfer in gas-liquid flows can contribute to an optimization of the design of corresponding apparatuses and processes. While Computational Fluid Dynamics (CFD) is frequently used for industrial problems in case of single phase flows, it is not yet mature for two-phase flows. The reason is the complex gas-liquid interface. For medium and large scale flow domains it is not feasible to resolve all details of this interface. Averaging procedures have to be applied and in most cases the so-called two- or multi-fluid approach is used. It assumes interpenetrating phases and the information on the interface gets lost by these averaging procedures. This information has to be added to the basic balance equations by so-called closure models. The development and validation of general frameworks as well as closure models is done at Helmholtz-Zentrum Dresden – Rossendorf (HZDR) to obtain tools for reliable predictions of multiphase flow characteristics in medium and large industrial scales.
In this talk the HZDR-strategy for the CFD-model development and validation for multiphase flows with focus on gas-liquid flows is presented.
Keywords: CFD, two-fluid model, iMUSIG, GENTOP
  • Invited lecture (Conferences)
    EVT/Virtuhcon-Seminar, 15.01.2016, Freiberg, Deutschland

Publ.-Id: 23092 - Permalink


Single pairing spike-timing dependent plasticity inBiFeO3 memristors with a time window of 25ms to 125µs
Du, N.; Kiani, M.; Mayr, C. G.; You, T.; Buerger, D.; Skorupa, I.; Schmidt, O. G.; Schmidt, H.;
Memristive devices are popular among neuromorphic engineers for their ability to emulate forms of spike-driven synaptic plasticity by applying specific voltage and current waveforms at their two terminals. In this paper, we investigate spike-timing dependent plasticity(STDP) with a single pairing of one presynaptic voltage spike and one post-synaptic voltage spike in a BiFeO3 memristive device. In most memristive materials the learning window is primarily a function of the material characteristics and not of the applied waveform. In contrast, we show that the analog resistive switching of the developed artificial synapses allows to adjust the learning time constant of the STDP function from 25ms to 125μs via the duration of applied voltage spikes. Also, as the induced weight Change may degrade, we investigate the remanence of the resistance change for several hours after analog resistive switching, thus emulating the processes expected in biological synapses. As the power consumption is a major constraint in neuromorphic circuits, we show methods to reduce the consumed energy per setting pulse to only 4.5 pJ in the developed artificial synapses.
Keywords: BiFeO3 memristor, artificial synapse, single Pairing STDP, memory consolidation, learning window, low-power device

Publ.-Id: 23091 - Permalink


An Energy-Efficient, BiFeO3-Coated Capacitive Switch with Integrated Memory and Demodulation Functions
You, T.; Selvaraj, L. P.; Zeng, H.; Luo, W.; Du, N.; Buerger, D.; Skorupa, I.; Prucnal, S.; Lawerenz, A.; Mikolajick, T.; Schmidt, O. G.; Schmidt, H.;
A capacitive switching behavior is observed in a Si 3 N 4 /p-Si-based metal–insulator–semiconductor (MIS) structure due to the electron tunneling at the Si 3 N 4 /p-Si interface. A BiFeO 3 (BFO) layer is deposited on Si 3 N 4 /p-Si by pulsed laser deposition technique to obtain the memcapacitive effect as the distribution of positive charges in the Si 3 N 4 layer can be stabilized by the polarization charge of the ferroelectric BFO coating layer. The capacitive switching behavior of the Al/BFO/Si 3 N 4 /p-Si/Au MIS structure is also sensitive to both intensity and wavelength of the illumination, which offers the possibility to create a photodetector for both intensity and color detection. Thus, the presented device has the potential application for future information storage and visible light communications. As an example, a photocapacitive demodulator with capability of decoding both wavelength and intensity information of the incident light is demonstrated.
Keywords: analog resistive switch, flexible barrier height, BiFeO3, fast and energy-efficient resistive switching

Publ.-Id: 23089 - Permalink


Sorption of trivalent lanthanides and actinides onto montmorillonite: Macroscopic, thermodynamic and structural evidence for ternary hydroxo and carbonato surface complexes on multiple sorption sites
Marques Fernandes, M.; Scheinost, A. C.; Baeyens, B.;
The credibility of long-term safety assessments of radioactive waste repositories may be greatly enhanced by a molecular level understanding of the sorption processes onto individual minerals present in the near- and far-field. In this study we couple extensive macroscopic sorption experiments to surface complexation modelling and spectroscopic tools including extended X-ray absorption fine structure (EXAFS) and time-resolved laser fluorescence spectroscopies (TRLFS), in order to elucidate the uptake mechanism of trivalent actinides and lanthanides (Ln/AnIII) on montmorillonite in the absence and presence of dissolved carbonate. Based on the experimental sorption isotherms, the previously developed 2SPNE SC/CE sorption model needed to be complemented with an additional surface complexation reaction on to a weak site (ºSWOEu2+) for the carbonate-free system. In the presence of carbonate, the previously published model required refinement by reducing the strong-site capacity and by adding the formation of Ln/AnIII-carbonato complexes both on strong and weak sites. EXAFS spectra collected of selected Am sorption samples and TRLFS spectra of selected Cm sorption samples corroborate the model assumptions by showing the existence of different surface complexation sites and evidencing the formation of Ln/AnIII carbonate surface complexes. In the absence of carbonate and at low loadings, Ln/AnIII form strong innersphere sorption complexes through binding to three Al(O,OH)6 octahedra, most likely by occupying vacant sites in the octahedral layers of montmorillonite, which are exposed on {010} and {110} edge faces. At higher loadings, Ln/AnIII bind to only one Al octahedron, forming a weaker, edge-sharing sorption complex. In the presence of carbonate, we identified a ternary mono-carbonato Ln/AnIII complex binding directly to one Al(O,OH)6 octahedron, thereby revealing that type-A ternary complexes form with one or two carbonato groups pointing away from the surface into the solution phase; these complexes form on weak sites only at the observable concentration range, in line with the small amount of strong-site complexes suggested by the complexation model. When the solubility of carbonates was exceeded, formation of an Am carbonate hydroxide could be identified. The excellent agreement between the thermodynamic model parameters developed by fitting a large set of macroscopic data, and the spectroscopically identified mechanisms, demonstrates the mature state of the 2SPNE SC/CE model for predicting and quantifying the retention of Ln/AnIII elements by montmorillonite-rich clay rocks.
Keywords: Americium Sorption clay rocks montmorillonite TRLFS EXAFS surface complexation modeling

Publ.-Id: 23088 - Permalink


Magnetoelectric effect and phase transitions in CuO in external magnetic fields
Wang, Z.; Qureshi, N.; Yasin, S.; Mukhin, A.; Ressouche, E.; Zherlitsyn, S.; Skourski, Y.; Geshev, J.; Ivanov, V.; Gospodinov, M.; Skumryev, V.;
Apart from being so far the only known binary multiferroic compound, CuO has a much higher transition temperature into the multiferroic state, 230 K, than any other known material in which the electric polarization is induced by spontaneous magnetic order, typically lower than 100 K. Although the magnetically induced ferroelectricity of CuO is firmly established, no magnetoelectric effect has been observed so far as direct crosstalk between bulk magnetization and electric polarization counterparts. Here we demonstrate that high magnetic fields of ≈50 T are able to suppress the helical modulation of the spins in the multiferroic phase and dramatically affect the electric polarization. Furthermore, just below the spontaneous transition from commensurate (paraelectric) to incommensurate (ferroelectric) structures at 213 K, even modest magnetic fields induce a transition into the incommensurate structure and then suppress it at higher field. Thus, remarkable hidden magnetoelectric features are uncovered, establishing CuO as prototype multiferroic with abundance of competitive magnetic interactions.

Publ.-Id: 23086 - Permalink


Room temperature deposition of highly dense TiO2 thin films by Filtered Cathodic Vacuum Arc
Guillen, E.; Heras, I.; Rincon Llorente, G.; Lungwitz, F.; Alcon-Camas, M.; Escobar-Galindo, R.;
A systematic study of TiO2 films deposited by dc filtered cathodic vacuum arc (FCVA) was carried out by varying the deposition parameters in a reactive oxygen atmosphere. The influence of the oxygen partial pressure on film properties is analyzed. Composition was obtained by Rutherford backscattering spectroscopy (RBS) measurements, which also allow us to obtain the density of the films. Morphology of the samples was studied by scanning electron microscopy (SEM) and their optical properties by ellipsometry. Transparent, very dense and stoichiometric TiO2 films were obtained by FCVA at room temperature.
  • Contribution to proceedings
    SPIE Optics + Photonics 2015, 09.-13.08.2015, San Diego, USA
    Proceedings of SPIE 9558
    DOI: 10.1117/12.2189503

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Publ.-Id: 23085 - Permalink


Cyclotron Resonance in InAs/AlSb Quantum Wells in Magnetic Fields up to 45 T
Spirin, K. E.; Krishtopenko, S. S.; Sadofyev, Y. G.; Drachenko, O.; Helm, M.; Teppe, F.; Knap, W.; Gavrilenko, V. I.;
Electron cyclotron resonance in InAs/AlSb heterostructures with quantum wells of various widths in pulsed magnetic fields up to 45 T are investigated. Our experimental cyclotron energies are in satisfactory agreement with the results of theoretical calculations performed using the eight-band kp Hamiltonian. The shift of the cyclotron resonance (CR) line, which corresponds to the transition from the lowest Landau Level to the low magnetic-field region, is found upon varying the electron concentration due to the negative persistent photoconductivity effect. It is shown that the observed shift of the CR lines is associated with the finite width of the density of states at the Landau levels.
Keywords: cyclotron resonance, quantum wells

Publ.-Id: 23083 - Permalink


Magnetic anisotropy and reduced neodymium magnetic moments in Nd3Ru4Al12
Gorbunov, D.; Henriques, M. S.; Andreev, A. V.; Eigner, V.; Gukasov, A.; Fabrèges, X.; Skourski, Y.; Petricek, V.; Wosnitza, J.;
This paper addresses the electronic properties of Nd3Ru4Al123Ru4Al12.We performed magnetization measurements on a single crystal in static and pulsed magnetic fields as well as neutron-diffraction experiments. Nd3Ru4Al12 is a strongly anisotropic uniaxial ferromagnet with a Curie temperature of 39 K. The magnetic moments are aligned collinearly along the [001] axis. The magnetic structure of Nd3Ru4Al12 has orthorhombic symmetry for which the crystallographic Nd site is split into two magnetically inequivalent positions, Nd1 and Nd2. The Nd1 and Nd2 atoms exhibit reduced magnetic moments, 0.95 and 2.66 μB, as compared to the free Nd3+-ion value (3.28 μB). We discuss this finding in terms of crystal-field effects and competing exchange and anisotropy interactions. Since the single-ion mechanism in Nd3Ru4Al12 leads to uniaxial anisotropy and the two-ion mechanism of the actinide analog U3Ru4Al12 is known to lead to planar anisotropy, this paper demonstrates the decisive influence of these different mechanisms on the magnetic anisotropy.

Publ.-Id: 23082 - Permalink


Structural stability study of the mixed La0.7-xLuxEu0.3PO4 solid solutions by Extended X-ray Absorption Spectroscopy
Lozano-Rodriguez, M. J.; Arinicheva, Y.; Holthausen, J.; Neumeier, S.; Scheinost, A. C.;
Monazite and related solid solutions are considered as potential candidates for the immobilization of actinides for the disposal of high-level nuclear waste. Because of their low solubility, high resistance to radiation damage and high chemical flexibility, phosphate materials are matter of study 1. Recently many efforts have been putting to find effective ways to synthesis and characterize lanthanide phosphates through diverse methods3. However, a deeper understanding on structural determinations concerning the local atomic arrangement of surrogate elements, i.e., europium, in phosphates matrices is still in progress. In order to correlate the high chemical flexibility of monazite/xenotime structures with local atomic ordering, mixed La0.7-xLuxEu0.3PO4 solid solutions (x=0, 0.35, 0.5, 0.7) have been study by Extended X-ray Absorption Spectroscopy. La L1, Eu L3 and Lu L3-edges were measured for each phosphate solid solution series. It has been found that for each measured element, the local atomic environment has tendency to adopt an environment closer to monazite or xenotime depending strongly to the x loading. The results obtained by XRPD, XANES and EXAFS are discussed with respect to its chemical flexibility in potential host matrix for sequestering long-lived radionuclides.
Keywords: EXAFS, phosphate solid solutions, monazite, lanthanides
  • Invited lecture (Conferences)
    Scientific Basis for Nuclear Waste Management XXXIX, 02.-06.11.2015, Montpellier, France

Publ.-Id: 23081 - Permalink


Determination of local structure in mixed lanthanoid phosphate solid solutions by X-ray absorption spectroscopy
Lozano-Rodriguez, M. J.; Arinicheva, Y.; Heuser, J.; Kvashnina, K.; Neumeier, S.; Scheinost, A. C.;
In the 21st century, scientific challenges are required for the disposal of high-level nuclear waste in deep geological formations. Ceramic waste forms like monazite and xenotime, are natural lanthanoid phosphate minerals containing U and Th. When light lanthanoids are involved the monazite structure forms; when heavy lanthanoids are present, the xenotime structure predominates. X-ray absorption spectroscopy was carried out to elucidate the structural changes induced by different lanthanoids when mixed lanthanoids phosphates are formed. EXAFS measurements for La1-xEuxPO4 solid solutions around La and Eu, show the flexibility of the monazite structure when two light lanthanoids are hosted. The La-O distances in the first coordination shell and the first metal-metal distances decrease with increasing Eu content; while the Eu-O local coordination remains unchanged. Additionally, HR-XANES shows an increase on the white line in the absorption coefficient with increasing Eu content, suggesting a change in the valence electron distribution. However, EXAFS measurements of Sm1-xTbxPO4 solid solutions around the Sm, show significant differences between low and high Tb content.
Keywords: EXAFS, phosphate solid solutions, lanthanoids
  • Lecture (Conference)
    E-MRS 2015 Spring Meeting, 11.-15.05.2015, Lille, France

Publ.-Id: 23080 - Permalink


Modern Approaches in Ion Beam Analysis - Challenges and ongoing Developments
Heller, R.;
The general trend in technology and science to create, process and analyze small structures on a nm scale or even on an atomic scale leads to new challenges in modern ion beam analysis (IBA). This is accompanied by higher demands on the lateral resolution as well as by the demand on high precision determination of elemental compositions on an atomic depth scale. Further the complexity of processing materials in micro and nano electronics is increasing continuously. Thus elemental analysis is no longer limited to the determination of a few particular atomic species and a division of measurement tasks into „light element in a heavy matrix“ or vise versa becomes obsolete in this way. 

Thinner but more complex layer structures are closely related to an increased sensitivity on external impacts. Even the transport of a sample to the place of analysis under ambient conditions can lead to unwanted (chemical) modifications at the surface. Thus IBA under in-situ conditions has developed into an established method within recent years. Furthermore in technological developments not only the state of a system after processing but the process itself may be of particular interest. “Online” IBA under process conditions is thus more and more desired.

Analysis methods of classical IBA like RBS (Rutherford Backscattering Spectrometry), ERD (Elastic Recoil Detection Analysis), PIXE (Particle Induced X-Ray Emission) or PIGE (Particle Induced Gamma Emission), either applied as broad beam or in terms of a micro probe, can therefore rapidly reach their limits. Even the use of modern magnetic spectrometers with depth resolution of a few nano-meters may in particular situations not be sufficient.

Searching for approaches to all these modern measurement tasks often brings IBA to the physical limits and thus complicates quantitative analysis. This for instance may manifest in energy depended charge fractions of the projectile, deviations from classical Rutherford cross-sections, the modification of the sample by the probing beam, etc. All these effects have to be carefully taken into consideration when interpreting analysis results.

The present contribution will give an overview on the demands and difficulties resulting from the described demands on modern IBA. Ongoing development of new IBA techniques and approaches at the Ion Beam Center at HZDR will be presented and discussed. Those are covering

- the realization of IBA within a Helium ion microscope,
- the unification of different IBA techniques in complex experimental chambers including in-situ capabilities,
- the increase of efficiency of lateral resolved PIXE measurements,
- the controlled implantation of single ions into surfaces with nm precision, as well as
- concepts for a new low-energy ion laboratory.
Keywords: Ion Beam Analysis, IBA, TBS, ERD, PIXE, lateral resolved IBA
  • Invited lecture (Conferences)
    50th Zakopane School of Physics, 18.-23.05.2015, Zakopane, Polen

Publ.-Id: 23079 - Permalink


Carbon:nickel nanocomposite templates - predefined stable catalysts for diameter-controlled growth of single-walled carbon nanotubes
Melkhanova, S.; Kunze, T.; Haluska, M.; Hübner, R.; Keller, A.; Abrasonis, G.; Gemming, S.; Krause, M.;
Carbon: nickel (C:Ni) nanocomposite templates (NCTs) were used as catalyst precursors for diameter-controlled growth of single-walled carbon nanotubes (SWCNTs) by chemical vapor deposition (CVD). Two NCT types of 2 nm thickness were prepared by ion beam co-sputtering without (type I) or with assisting Ar+ ion irradiation (type II). NCT type I comprised Ni-rich nanoparticles (NPs) with defined diameter in an amorphous carbon matrix, while NCT type II was a homogenous C:Ni film. Based on the Raman spectra of more than 600 individual SWCNTs, the diameter distribution obtained from both types of NCT was determined. SWCNTs with a selective, monomodal diameter distribution are obtained from NCT type I. About 50% of the SWCNTs have a diameter of (1.36 ± 0.10) nm. In contrast to NCT type I, SWCNTs with a non-selective, relatively homogeneous diameter distribution are obtained from NCT type II. From both catalyst templates predominantly separated as-grown SWCNTs are obtained. They are free of solvents or surfactants, exhibit a low degree of bundling and contain negligible amounts of MWCNTs. The study demonstrates the advantage of predefined catalysts for diameter-controlled SWCNT synthesis in comparison to in situ formed catalysts.
Keywords: Nanocomposites, single-walled carbon nanotubes, diameter selective growth, predifined stable catalyst templates

Publ.-Id: 23078 - Permalink


Comprehensive real time characterization of AlTiO(x)N(y) thin films at high temperatures
Heras, I.; Guillén, E.; Krause, M.; Wenisch, R.; Lungwitz, F.; Escobar-Galindo, R.;
AlTiN, AlTiO, and AlTiO(x)N(y) thin films were investigated in order to understand the influence of the oxygen to nitrogen ratio on the failure mechanisms at high temperatures. The thin films were deposited by cathodic vacuum arc and characterized in-situ following the methodology proposed for comprehensive environmental testing of optical properties in thin films using the HZDR cluster tool [1].
This multi-chamber material processing and analysis system enables the detailed analysis of the temperature dependence of composition, chemical bonding, and optical properties of thin films. The methodology combines the sequential study of the optical constants by spectroscopic ellipsometry, compositional analysis using ion beam analysis techniques and structure analysis by Raman spectroscopy. All characterizations of AlTiO(x)N(y) thin films were carried out in situ without sample exposure to undefined atmospheres. The samples were heated in vacuum from room temperature to 800°C inside the different chambers and in parallel, to elucidate the influence of the ambience on the degradation process. Moreover, ex-situ annealing in air was performed. Ellipsometry, Raman and ERDA results show the influence of the initial oxygen content in the sample with the inward diffusion of oxygen into the coating and the oxidation resistance at high temperatures.

[1] I. Heras, E. Guillén, R. Wenisch, M. Krause, R. Escobar Galindo, J.L. Endrino - Comprehensive environmental testing of optical properties in thin films. Procedia CIRP. 22 (2014) 271–276
Keywords: In situ analysis, cluster tool, new energy materials, solar-selective coatings
  • Lecture (Conference)
    78th IUVSTA Workshop, 05.-09.10.2015, Braga, Portugal

Publ.-Id: 23077 - Permalink


New energy materials - concepts, structure formation and in situ analysis
Krause, M.;
An overview on the current activities on new energy materials is given. It includes concepts, structure formation, and in situ analysis of nanocomposite materials for solar energy applications.
Keywords: New energy materials, in situ analysis, nanocomposites
  • Lecture (Conference)
    Ehrenkolloquium für Prof. Hans Kuzmany, 10.09.2015, Wien, Österreich

Publ.-Id: 23076 - Permalink


Solar selective coatings based on carbon:transition metal nanocomposites
Heras, I.; Guillén, E.; Krause, M.; Pardo, A.; Endrino, J.-L.; Escobar, R.;
The design of efficient and stable solar selective coatings for Concentrating Solar Power (CSP) central receivers requires a comprehensive knowledge about the incorporated materials. In this work solar selective coatings were grown by filtered cathodic vacuum arc (FCVA) deposition. The complete stacks consist of an infrared reflection layer, an absorber layer of C:ZrC nanocomposites and an antireflection layer. The Carbon-transition metal nanocomposites were studied as absorber materials because they show appropriate optical properties, i.e. high absorption in the solar region and low thermal emittance. Furthermore metal carbides are thermally and mechanically stabile in air at high temperatures. In order to optimize the absorber layer, the metal content was controlled by adjusting the pulse ratio between the two arc sources. The elemental composition of the absorber layers was determined by Ion Beam Analysis. X-Ray diffraction (XRD) measurements show the formation of metal carbides when the metal content is high enough. The optical properties of the deposited coatings were characterized by spectroscopic ellipsometry (SE). The reflectance spectra of the complete selective coating were simulated with the optical software CODE. Bruggeman effective medium approximation (EMA) was employed to average the dielectric functions of the two components which compose the nanocomposite in the absorber layer. Good agreement was found between simulated and measured reflectance spectra of the solar selective multilayer.
Keywords: Solar selective coatings, carbide thin films, high temperature applications, cathodic arc deposition, simulation of optical properties
  • Lecture (Conference)
    SPIE: Optics + Photonics 2015, 09.-13.08.2015, San Diego, United States
  • Contribution to proceedings
    SPIE Optics + Photonics for Sustainable Energy, 09.-13.08.2015, San Diego, USA
    Proceedings Volume 9559, High and Low Concentrator Systems for Solar Energy Applications X
    DOI: 10.1117/12.2189515

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Publ.-Id: 23075 - Permalink


Effect of hydrogen on magnetic properties of Fe60Al40 alloy thin films
Ehrler, J.; Bali, R.; Otalora, C.; Yildirim, O.; Anwand, W.; Trinh, T. T.; Liedke, M. O.; Cornelius, S.; Böttger, R.; Heller, R.; Potzger, K.;
The influence of hydrogen on magnetic properties and defects of metallic thin films based on FeAl alloys was investigated. Therefore, hydrogen ions have been implanted with different fluences into disordered Fe60Al40 thin films. Magneto-optical Kerr effect showed an increase of coercivity with increasing ion fluence. The treatment of paramagnetic Fe60Al40 thin films in a climate chamber, on the other hand, led to an establishment of ferromagnetism. Elastic Recoil Detection Analysis showed no hydrogen in the implanted and climate chamber treated samples. However, positron annihilation measurements suggest storage of hydrogen in vacancies. The origin of ferromagnetism was investigated with further methods.
Keywords: Hydrogen, Defects, Implantation, Climate Chamber, FeAl, MOKE, VSM, RBS, ERD, PAS
  • Poster
    PSI Summer School 2015, 15.-21.08.2015, Zuoz, Schweiz

Publ.-Id: 23074 - Permalink


Magnetohydrodynamic effects in liquid metal batteries
Stefani, F.; Galindo, V.; Kasprzyk, C.; Landgraf, S.; Seilmayer, M.; Starace, M.; Weber, N.; Weier, T.;
Liquid metal batteries (LMBs) consist of two liquid metal electrodes and a molten salt ionic conductor sandwiched between them. The density ratios allow for a stable stratification of the three layers. LMBs were already considered as part of energy conversion systems in the 1960s and have recently received renewed interest for economical large-scale energy storage. In this paper, we concentrate on the magnetohydrodynamic aspects of this cell type with special focus on electro-vortex flows and possible effects of the Tayler instability.
  • Contribution to proceedings
    Liquid Metal Processing & Casting Conference 2015, 20.-24.09.2015, Leoben, Austria
    LMPC 2015 - Proceedings of the 2015 International Symposium on Liquid Metal Processing and Casting, Leoben: ASMET, 978-3-901384-63-9, 347-354
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 143(2016), 012024
    DOI: 10.1088/1757-899X/143/1/012024

Publ.-Id: 23073 - Permalink


Contactless inductive flow tomography: basic principles and first applications in the experimental modelling of continuous casting
Stefani, F.; Eckert, S.; Ratajczak, M.; Timmel, K.; Wondrak, T.;
Contactless inductive flow tomography (CIFT) aims at reconstructing the flow structure of a liquid metal from the magnetic fields measured at various positions outside the fluid body which are induced by the flow under the influence of one or multiple applied magnetic fields. We recap the basic mathematical principles of CIFT and the results of an experiment in which the propeller-driven three-dimensional flow in a cylindrical had been reconstructed. We also summarize the recent activities to utilize CIFT in various problems connected with the experimental simulation of the continuous casting process. These include flow reconstructions in single-phase and two-phase flow problems in the Mini-LIMMCAST model of slab-casting, studies of the specific effects of an electromagnetic stirrer attached to the Submerged Entry Nozzle (SEN), as well as first successful applications of CIFT on the background of a strong electromagnetic brake field. We conclude by discussing some remaining obstacles for the deployment of CIFT in a real caster.
  • Contribution to proceedings
    Liquid Metal Processing & Casting Conference 2015, 20.-24.09.2015, Leoben, Austria
    LMPC 2015 - Proceedings of the 2015 International Symposium on Liquid Metal Processing and Casting, Leoben: ASMET, 978-3-901384-63-9, 339-346
  • Open Access LogoIOP Conference Series: Materials Science and Engineering 143(2016), 012023
    DOI: 10.1088/1757-899X/143/1/012023

Publ.-Id: 23072 - Permalink


Evolution of Crystal Structure During the Initial Stages of ZnO Atomic Layer Deposition
Boichot, R.; Tian, L.; Richard, M.-I.; Crisci, A.; Chaker, A.; Cantelli, V.; Coindeau, S.; Lay, S.; Ouled, T.; Guichet, C.; Chu, M. H.; Aubert, N.; Ciatto, G.; Blanquet, E.; Thomas, O.; Deschanvres, J.-L.; Fong, D. D.; Renevier, H.;
A complementary suite of in situ synchrotron X-ray techniques is used to investigate both structural and chemical evolution during ZnO growth by atomic layer deposition. Focusing on the first 10 cycles of growth, we observe that the structure formed during the coalescence stage largely determines the overall microstructure of the film. Furthermore, by comparing ZnO growth on silicon with a native oxide with that on Al2O3(001), we find that even with lattice-mismatched substrates and low deposition temperatures, the crystalline texture of the films is dependent strongly on the nature of the interfacial bonds.
Keywords: ALD, ZnO, in-situ X-ray scattering

Publ.-Id: 23071 - Permalink


Nickel-Enhanced Graphitic Ordering of Carbon Ad-Atoms During Physical Vapor Deposition
Wenisch, R.; Hübner, R.; Munnik, F.; Gemming, S.; Abrasonis, G.; Krause, M.;
The mechanism of graphitic ordering of atomic C on Ni was investigated at temperatures ranging from room temperature to 550°C. The C/Ni films were prepared by ion beam sputtering. Their structure has been determined by Rutherford backscattering spectrometry/nuclear reaction analysis, X-ray photoelectron spectroscopy, Raman spectroscopy and cross-sectional transmission electron microscopy. A temperature-induced and a Ni-induced enhancement of graphitic ordering is demonstrated. The Ni-effect is responsible for the formation of a bi-layer structure of the C films at higher deposition temperatures. In the bi-layers, C forms graphenic planes parallel to the Ni surface within a thickness range of 1-2 nm. Further deposited C grows preferentially perpendicular to the surface. The results are discussed on the basis of hyperthermal atom deposition, surface diffusion, metal-induced crystallization and dissolution-precipitation. Our findings point to a dominating role of surface diffusion-assisted crystallization in the carbon ordering process.

Publ.-Id: 23070 - Permalink


Quantitative detection of microscopic lithium distributions with neutrons
Neri, G.; Gernhäuser, R.; Lichtinger, J.; Winkler, S.; Seiler, D.; Bendel, M.; Kunze-Liebhäuser, J.; Brumbarov, J.; Portenkirchner, E.; Renno, A. D.; Rugel, G.;
The importance of lithium in the modern industrial society is continuously increasing. Spatially resolved detection of tritium particles from 6Li(n,α)3H nuclear reactions is used to reconstruct microscopic lithium distributions. Samples are exposed to a flux of cold neutrons. Emitted charged particles are detected with a PSD. Introducing a pinhole aperture between target and detector, the experimental setup works like a “camera obscura”, allowing to perform spatially resolved measurements. Tritium detection analysis was successfully used to reconstruct the lithium content in self-organized TiO2-x-C and Si/TiO2-x-C nanotubes electrochemically lithiated, for the first time. Titanium dioxide nanotubes are a candidate for a safe anode material in lithium-ion batteries. Also lithium distributions in geological samples, so called “pathfinder-minerals” containing lithium, like lepidolite from a pegmatite, were analyzed. With this development we present a new precision method using nuclear physics for material science.
Supported by the DFG (GE 2296/1-1).
Keywords: microscopic lithium distribution PNAA
  • Lecture (Conference)
    DPG-Frühjahrstagung des Fachverbandes Physik der Hadronen und Kerne (HK), 14.-18.03.2016, Darmstadt, Deutschland

Publ.-Id: 23069 - Permalink


Multiphase Flow Measurement and Visualization for Fluid Dynamics Research at Helmholtz-Zentrum Dresden-Rossendorf
Schleicher, E.;
The presentation will give a short overview on our research activities in the field of multiphase flow investigations and focus on advanced measurement techniques developed in-house.
The content can be summarized to:
- introduction of HZDR:
o Who we are?
o Where we come from?
o Basic structure of German research organization.
- Institute of fluid dynamics: structure and research topics
- Advanced measurement techniques to create CFG grate data for multiphase flow experiments,
functional principle and application examples of:
o wire-mesh sensors,
o gamma-ray computed tomography,
o ultra-fast X-ray tomography.
  • Lecture (others)
    Institutsseminar bei CSIRO, Melbourne, 17.11.2015, Melbourne, Australien

Publ.-Id: 23068 - Permalink


An algorithm for refined reconstruction of the phase interface for two-phase gas/liquid annular flows using wire-mesh data
Aydin, T. B.; Brito, R.; Schleicher, E.; Pereyra, E.; Sarica, C.;
Wire-Mesh sensors (WMS) are used to measure the instantaneous distributions of the phases with high temporal and spatial resolutions with conducting and non-conducting fluids. The experimental data acquired from WMS can be used in a variety of ways to obtain detailed information on the two-phase flow topology including the quantitative visualization of the phase interface.

The current study explores the applicability of a phase interface identification algorithm for two-phase annular flows. The experimental data used in the development of the algorithm is acquired by a WMS with a 16×16 wires for water/air two-phase annular flow at Tulsa University Horizontal Well Artificial Lift Projects (TUHWALP) in 0.05 m (2-in.), 1° upward inclined pipe. The superficial gas and liquid velocities are set to 26 m/s and 0.075 m/s, respectively.

Initially, the WMS data is transformed from a Cartesian coordinate system (with a mesh size of 16×16) onto a polar coordinate system with a mesh size of (MRF×16)×(MRF×16) using a weighted average interpolation, where MRF is the mesh refinement factor. The interpolated data (defined in the polar coordinate system) enables the identification of the phase interface based on the local liquid holdup profile along the radial direction at a given tangential position using the centre of mass concept.

The data interpolation scheme conserves the liquid mass within the pipe cross-section as the mesh refinement factor is increased. However, large values of the refinement factor yield in outliers in the phase interface coordinates. The significance of these outliers is more pronounced if the WMS measurements are affected by the end effects such as in capacitance based measurements. The current algorithm is also capable of producing satisfactory results under stratified flow conditions.
Keywords: Phase interface reconstruction, two-phase, annular flow, wire-mesh
  • Contribution to proceedings
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland
    Proceedings of the 7th International Symposium on Process Tomography
  • Poster
    7th International Symposium on Process Tomography, 01.-03.09.2015, Dresden, Deutschland

Publ.-Id: 23067 - Permalink


Preparation and characterization of high purity Ti thin films by high power impulse magnetron sputtering deposition
Meško, M.; Munnik, F.; Heller, R.; Grenzer, J.; Hübner, R.; Krause, M.;
The increased ion-to-atom ratio in high power impulse magnetron sputtering (HiPIMS) allows directional deposition and film densification by the bombarding ions [1]. Recently, Andersson et al. showed HiPIMS gasless self-sputtering operation and proposed this method for the synthesis of ultraclean metal coatings through self-ion-assisted deposition [2]. In the present work we investigated Ti thin films prepared by direct current magnetron sputtering (dcMS) and HiPIMS with respect to their element composition, surface roughness, and microstructure. Ti films were deposited on Si/SiO2 substrates at room temperature. The base pressure prior to the two hours depositions was 5x10-5 Pa. The film thicknesses were determined by profilometry after the deposition and are 800 nm and 200 nm for dcMS and HiPIMS respectively. It is shown that Ti thin films prepared by HiPIMS do not suffer from bulk contamination like dcMS films (Fig. 1). In particular, the impurity levels for O, N and C are below the detection limit (0.3 – 0.5 at.%) of elastic recoil detection analysis (ERDA) and the hydrogen content was measured to 0.5 at.% for the HiPIMS case. Compared to the dcMS films, we observed an element specific reduction of impurities by a factor 3- 4 for N and H; and a factor of 20 for O. This suggests the presence of at least two sources of impurities. Unlike in [2], the HiPIMS self-sputtering regime was sustained in Ar gas. The high purity of Ti films can be partly explained by gas rarefaction and the cleaning effect of the bombarding ions. Moreover, densification effects presumably suppress post-deposition oxidation. The compositional effects are correlated with differences in the film microstructure revealed by SEM, XRD and TEM analysis. A more sensitive analytical method is needed to evaluate the actual impurity levels of O, N, and C in the deposited HiPIMS films.
[1] U. Helmersson, M. Lattemann, J. Bohlmark, A. P. Ehiasarian, J. T. Gudmundsson “Ionized physical vapor deposition (IPVD): A review of technology and applications” (2006) Thin Solid Films 513, 1–24
[2] J. Andersson and A. Anders “Gasless sputtering: Opportunities for ultraclean metallization, coatings in space, and propulsion” (2008) Appl. Phys. Lett. 92, 221503
Keywords: HiPIMS, self-sputtering, impurity level, Ti thin films
  • Poster
    6th International Conference on HIPIMS 2015, 10.-11.06.2015, Braunschweig, Deutschland

Publ.-Id: 23066 - Permalink


Carbide Formation and Optical Properties in Carbon: Transition Metal Nanocomposites Thin Films
Heras, I.; Guillen, E.; Krause, M.; Pardo, A.; Endrino, J. L.; Escobar Galindo, R.;
Transition metals with carbon deposited by physical vapor deposition techniques, lead the formation of metal nano-clusters or nanocrystalline metallic carbides embedded in a carbon matrix. Interstitial carbides are stable at high temperature, have high melting points and possess a high reflectivity. In contrast, the resulting carbon: transition metal nanocomposites show optical selective properties such as good absorptance in the visible with high reflectance in the infrared. These properties make them very attractive for applications where high temperature resistant materials with selective optical properties are required.
In this study, carbon: transition metal nanocomposites were grown using a physical vapor deposition system incorporating two pulsed filtered cathodic arc sources, one provided with a graphite cathode and the other with a metallic cathode (Zr, V or Mo). The metal content in the composite was controlled by adjusting the pulse ratio between the two sources, and determined by Rutherford backscattering spectroscopy (RBS) and nuclear reaction analysis (NRA). Comprehensive structure characterization was carried out using a combination of X-ray diffraction (XRD), Raman spectroscopy and high resolution transmission electron microscopy (HRTEM). Optical characterization has been done using both ellipsometry and spectrophotometer measurements in order to obtain the optical constants and the reflectance spectra of the samples.
Together with experimental characterization, a computer program is used to simulate the reflectance spectra of different carbon: transition metal films. Bruggeman effective medium theory was used to average the dielectric functions of the two components which compose the film. According to our simulations, the resulting reflectance of the nanocomposite films is strongly affected by the metal content, independently if it results in metallic nano-clusters or nanocrystalline metallic carbides. Simulated spectra were compared with the measured reflectance of the deposited films obtaining good agreement between simulations and experimental results.
Keywords: Nanocomposites, Optical properties, Carbon
  • Lecture (Conference)
    2015 MRS Spring Meeting & Exhibit, 06.-10.04.2015, San Francisco, United States

Publ.-Id: 23065 - Permalink


Subcritical excitation of the current-driven Tayler instability by super-rotation
Rüdiger, G.; Schultz, M.; Gellert, M.; Stefani, F.;
It is known that in a hydrodynamic Taylor-Couette system, uniform rotation or a rotation law with positive shear (“super-rotation”) is linearly stable. It is also known that a conducting fluid under the presence of a sufficiently strong axial electric-current becomes unstable against nonaxisymmetric disturbances. It is thus suggestive that a cylindrical pinch formed by a homogeneous axial electric-current is stabilized by rotation laws with dOmega/dR ≥ 0. For magnetic Prandtl number Pm not equal 1 and for slow rotation, however, rigid rotation and super-rotation support the instability by lowering the critical Hartmann numbers. This double-diffusive instability of superrotation even exists for toroidal magnetic fields with rather arbitrary radial profiles, the current-free profile B_phi∝1/R included. The sign of the azimuthal drift of the nonaxisymmetric hydromagnetic instability pattern strongly depends on the magnetic Prandtl number. The pattern counterrotates with the flow for Pm ≪ 1 and it corotates for Pm ≫ 1 while for rotation laws with negative shear, the instability pattern migrates in the direction of the basic rotation for all Pm. An axial electric-current of minimal 3.6 kA flowing inside or outside the inner cylinder suffices to realize the double-diffusive instability for super-rotation in experiments using liquid sodium as the conducting fluid between the rotating cylinders. The limit is 11 kA if a gallium alloy is used

Publ.-Id: 23064 - Permalink


Ferromagnetism of nonstoichiometric manganese monosilicides at room temperature
Semisalova, A. S.; Chernoglazov, K. Y.; Perov, N. S.; Gan'Shina, E. A.; Granovsky, A. B.; Zenkevich, A. V.; Zhou, S.; Rylkov, V. V.;
Ferromagnetic Si-Mn alloys attract increasing interest due to their interesting properties - recently it was found that these alloys prepared by PLD method exhibit unusual magnetic characteristics which cannot be adequately interpreted within the framework of available theoretical models. Curie temperature TC in nonstoichiometric Si1-xMnx alloys slightly enriched in Mn (x ~ 0.52-0.55) was shown to be on order of magnitude higher (TC ~ 300 K) in comparison to the stoichiometric MnSi (TC ~ 30 K). The mechanism of high-temperature ferromagnetism is still not clear. The ferromagnetic exchange is associated with the formation of defects with localized magnetic moments coupled via spin fluctuations of itinerant electrons in the host. Also we suppose that structural defects have a strong influence on the formation of metastable phases with enhanced ferromagnetic response. In this contribution the recent experimental results on ferromagnetism of PLD deposited SiMn alloys are summarized.
  • Poster
    DPG Frühjahrstagung (Spring Meeting) of the Condensed Matter Section (SKM), 17.-20.03.2015, Berlin, Germany

Publ.-Id: 23063 - Permalink


Correlations of RBM, G line, and D line frequencies of individual SWCNTs grown from carbon:nickel nanocomposite templates
Melkhanova, S.; Kunze, T.; Haluska, M.; Hübner, R.; Keller, A.; Gemming, S.; Krause, M.;
Carbon:nickel nanocomposite templates were used for CVD growth of separated, individual single-walled carbon nanotubes (SWCNTs) free of solvents or surfactants. The as-grown carbon nanotubes were characterized by laser-energy dependent Raman spectroscopy and atomic force microscopy. Raman spectra showing a single radial breathing mode (RBM) line were analyzed with respect to correlations of RBM, G+ line and D line frequencies for SWCNT diameters covering the range of 0.8 nm to 1.6 nm. Opposite line shifts were found for RBM and G+ lines of the individual SWCNTs. However, the line shifts of the G+ line are smaller than the standard deviation of the G+ position for SWCNTs with almost the same RBM frequency, i.e. 1 1/cm compared to ± 1 1/cm for the whole diameter range. The D line often shows a complex shape including up to three components, which makes the identification of correlations with RBM frequencies possible only in selected cases.
Keywords: Nanocomposites, thin films, carbon nanotubes, Raman spectroscopy
  • Poster
    29th International Winterschool for Electronic Properties of Novel Materials, 07.-14.03.2015, Kirchberg, Austria

Publ.-Id: 23062 - Permalink


Maldistribution susceptibility of monolith reactors: Case study of glucose hydrogenation performance
Schubert, M.; Haase, S.; Lange, R.; Kost, S.; Salmi, T.; Hampel, U.;
In this work an ultrafast electron beam modality was applied for the first time to characterise the gas-liquid Taylor flow inside each channel of an opaque honeycomb monolith structure (65 cpsi) for u_(G,S)=0.1…0.5 m/s and u_(L,S)=0.2 m/s. Significant spatial and temporal deviations in the phase holdup as well as in the gas bubble and liquid slug lengths were found. In order to evaluate the impact of Taylor flow maldistribution on the reactor performance, the data of more than 125,000 unit cells were used to simulate the reactor productivity in the hydrogenation of glucose. The results verify that a monolith reactor solely designed by using superficial velocities and empirical correlations for gas bubble and liquid slug lengths fails significantly in achieving high product selectivity and the desired conversion. The developed methods are a solid base to design and select proper distributors ensuring the favourable flow configurations for specific chemical processes.
Keywords: monolith reactor, Taylor flow, X-ray tomography, reactor modelling, glucose hydrogenation

Publ.-Id: 23061 - Permalink


Controlled immobilization of His-tagged proteins for protein-ligand interaction experiments using Ni2+-NTA layer on glass surfaces
Cherkouk, C.; Rebohle, L.; Lenk, J.; Keller, A.; Ou, X.; Laubec, M.; Neuber, C.; Haase-Kohn, C.; Pietzsch, J.; Skorupa, W.;
Gold surfaces functionalized with nickel-nitrilotriacetic acid (Ni2+-NTA) as self-assembled monolayers (SAM) to immobilize histidine (His)-tagged biomolecules are broadly reported in the literature. However, the increasing demand of using microfluidic systems and biosensors takes more and more advantage on silicon technology which provides dedicated glass surfaces and substantially allows cost and resource savings. Here we present a novel method for the controlled oriented immobilization of His-tagged proteins on glass surfaces functionalized with a Ni2+-NTA layer. Exemplarily, the protein pattern morphology after immobilization on the Ni2+-NTA layer of His6-tagged soluble receptor for advanced glycation endproducts (sRAGE) was investigated and compared to non-oriented immobilization of sRAGE on amino SAM by using scanning electron microscopy (SEM). Moreover, we demonstrated interaction of immobilized sRAGE with three structurally different ligands, S100A12, S100A4, and glycated low density lipoproteins (glycLDL), by means of peak-force tapping atomic force microscopy (PF-AFM). We showed a clear discrimination of different protein-ligand orientations by differential height measurements.
Keywords: His-tagged proteins, glycated low density lipoproteins, microfluidic systems and biosensors, S100 proteins, self-assembled monolayers, soluble receptor for advanced glycation endproducts

Publ.-Id: 23060 - Permalink


Quantitative observation of tracer transport with high-resolution PET
Kulenkampff, J.; Gründig, M.; Zakhnini, A.; Lippmann-Pipke, J.;
Transport processes in natural porous media are typically heterogeneous over various scales. This heterogeneity is caused by the complexity of pore geometry and molecular processes. Heterogeneous processes, like diffusive transport, conservative advective transport, mixing and reactive transport, can be observed and quantified with quantitative tomography of tracer transport patterns. Positron Emission Tomography (PET) is by far the most sensitive method and perfectly selective for positron-emitting radiotracers, therefore it is suited as reference method for spatiotemporal tracer transport observations.
The number of such PET-applications is steadily increasing. However, many aplications are afflicted by the low spatial resolution (3 - 5 mm) of the clinical scanners from cooperating nuclear medical departments. This resolution is low in relation to typical sample dimensions of 10 cm, which are restricted by the mass attenuation of the material. In contrast, our GeoPET-method applies a high-resolution scanner with a resolution of 1 mm, which is the physical limit of the method and which is more appropriate for samples of the size of soil columns or drill cores. This higher resolution is achieved at the cost of a more elaborate image reconstruction procedure, especially considering the effects of Compton scatter. The result of the quantitative image reconstruction procedure is a suite of frames of the quantitative tracer distribution with adjustable frame rates from minutes to months. The voxel size has to be considered as reference volume of the tracer concentration. This continuous variable includes contributions from structures far below the spatial resolution, as far as a detection threshold, in the pico-molar range, is exceeded.
Exemples from a period of almost 10 years (Kulenkampff et al. 2008a, Kulenkampff et al. 2008b) of development and application of quantitative GeoPET-process tomography are shown. Theses examples include differnt transport processes, like conservative flow, reactive transport, and diffusion (Kulenkampff et al, 2015). Such experimental data are complementary to the outcome of model simulations based upon structural µCT-images. The PET-data can be evaluated with respect to specific process parameters, like effective volume and flow velocity distribution. They can further serve as a basis for establishing intermediate-scale simulation models which directly incorporate the observed specific response functions, without requiring modeling on the pore scale at the highest possible spatial resolution.
Kulenkampff, J., Gründig, M., Richter, M., Wolf, M., Dietzel, O.: First applications of a small-animal-PET scanner for process monitoring in rocks and soils. Geophysical Research Abstracts, Vol. 10, EGU2008-A-03727, 2008a.
Kulenkampff, J., Gründig, M., Richter, M., and Enzmann, F.: Evaluation of positron emission tomography for visualisation of migration processes in geomaterials, Physics and Chemistry of the Earth, 33, 937-942, 2008b.
Kulenkampff, J., Gruendig, M., Zakhnini, A., Gerasch, R., and Lippmann-Pipke, J.: Process tomography of diffusion with PET for evaluation anisotropy and heterogeneity, Clay Minerals, accepted 2015, 2015.
  • Lecture (Conference)
    European Geosciences Union General Assembly 2016 (EGU 2016), 17.-22.04.2016, Wien, Österreich

Publ.-Id: 23058 - Permalink


MHD effects in continuous casting and liquid metal batteries
Stefani, F.;
This invited talk gives an overview about the recent activities of the Magnetohydrodynamics Department at HZDR related to continuous casting and liquid metal batteries. Particular focus is laid on the development and first experimental tests of the contactless inductive flow tomography (CIFT) for the continuous casting of steel, and the simulation of various MHD phenomena in liquid metal batteries.
  • Invited lecture (Conferences)
    Liquid metal processing and casting conference, LMPC 2015, 20.-24.09.2015, Leoben, Austria

Publ.-Id: 23057 - Permalink


The DRESDYN project: Theoretical background and planned experiments
Stefani, F.;
The DREsden Sodium facility for DYNamo and thermohydraulic studies (DRESDYN) is a platform for large scale experiments related to geo- and astrophysics as well as to various industrial liquid metal applications. The most ambitious parts of DRESDYN are a homogeneous hydromagnetic dynamo driven solely by precession, and a large Tayler-Couette type experiment for the combined investigation of the magnetorotational instability (MRI) and the Tayler instability (TI). We present recent numerical results on precession driven flows in cylinders and their dynamo action. We also discuss some new theoretical results on various versions of the magnetorotational instability and the Tayler instability, including magnetically triggered instabilities of rotating flows with positive shear. The progress of the construction of the DRESDYN building and of the design of the various experiments is delineated.
  • Invited lecture (Conferences)
    The Dynamo Effect in Astrophysical and Laboratory Plasmas, 07.-09.12.2015, Princeton, USA

Publ.-Id: 23056 - Permalink


Liquid metal experiments on dynamo action, magnetorotational instability and current-driven instabilities
Stefani, F.;
Magnetic fields of planets, stars and galaxies are generated by self-excitation in moving electrically conducting fluids. Once produced, cosmic magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, both effects, i.e. hydromagnetic dynamo action and magnetically triggered flow instabilities, have been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe [1,2]. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability (MRI) was observed in the PROMISE experiment in Dresden-Rossendorf [3]. More recently, the azimuthal MRI was found at the same facility [4]. First evidence of the current-driven Tayler instability in a liquid metal was obtained, too [5].
The lecture gives an overview about liquid metal experiments on dynamo action and magnetically triggered instabilities. It concludes with an overview about future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project [6].

1. Gailitis, A., Lielausis, O., Platacis, E., Gerbeth, G., Stefani, F., Rev. Mod. Phys. 74 (2002), 973-990
2. Stefani, F., Gailitis, A., Gerbeth, G., ZAMM - Z. Angew. Math. Mech. 88 (2008), 930-954
3. Stefani, F. et al., Phys. Rev. Lett. 97 (2006), 184502
4. Seilmayer, M. et al., Phys. Rev. Lett. 113 (2014), 024505
5. Seilmayer, M. et al., Phys. Rev. Lett. 108 (2012), 244501
6. Stefani, F. et al, Magnetohydrodynamics 48 (2012), 103-113
  • Invited lecture (Conferences)
    Russian Conference on Magnetohydrodynamics, 22.-25.06.2015, Perm, Russia

Publ.-Id: 23055 - Permalink


The present status of the DRESDYN project, and some recent theoretical results
Stefani, F.;
Magnetic fields of planets, stars and galaxies are produced by self-excitation in moving electrically conducting fluids. Once produced, cosmic magnetic fields can play an active role in cosmic structure formation by destabilizing rotational flows that would be otherwise hydrodynamically stable. For a long time, hydromagnetic dynamo action and magnetically triggered flow instabilities, have been the subject of purely theoretical investigations. This situation changed in 1999 when the threshold of magnetic-field self-excitation was exceeded in the two liquid sodium experiments in Riga and Karlsruhe. Since 2006, the VKS dynamo experiment in Cadarache has successfully reproduced many features of geophysical interest such as reversals and excursions. In the same year, the helical version of the magnetorotational instability (MRI) was observed in the PROMISE experiment in Dresden-Rossendorf. More recently, the azimuthal MRI was found at the same facility. First evidence of the current-driven Tayler instability in a liquid metal was obtained, too.
The lecture gives a short overview about liquid metal experiments on dynamo action and magnetically triggered instabilities. The main part is devoted to future experiments, including a precession driven dynamo and a large-scale Tayler-Couette experiment to be set-up in the framework of the DRESDYN project at HZDR.
  • Lecture (Conference)
    GdR Dynamo 2015, 08.-12.06.2015, Bangalore, India

Publ.-Id: 23054 - Permalink


Industrial application of radiation
Hampel, U.;
The presentation gives an overview over various diagnostic applications of radiation in industry reaching from thickness gauging, over multiphase flow metering in the oil and gas production to tomographic techniques on industrial plant components, like chemical reactors or distillation units. The talk comprises physical and mathematical fundamentals, technical system designs and data as well as image processing aspects. Different applications on industrial and scientific flow analysis problems are being discussed in detail.
Keywords: gamma radiation, X-ray diagnostics, tomography, industrial processes, multiphase flow
  • Lecture (others)
    PhD Seminar Series, 12.01.2016, Dresden, Deutschland

Publ.-Id: 23053 - Permalink


Protracted fluvial recovery from medieval earthquakes, Pokhara, Nepal
Stolle, A.; Bernhardt, A.; Schwanghart, W.; Andermann, C.; Schönfeldt, E.; Seidemann, J.; Adhikari, B. R.; Merchel, S.; Rugel, G.; Fort, M.; Korup, O.;
River response to strong earthquake shaking in mountainous terrain often entails the flushing of sediments delivered by widespread co-seismic landsliding. Detailed mass-balance studies following major earthquakes in China, Taiwan, and New Zealand suggest fluvial recovery times ranging from several years to decades. We report a detailed chronology of earthquake-induced valley fills in the Pokhara region of western-central Nepal, and demonstrate that rivers continue to adjust to several large medieval earthquakes to the present day, thus, challenging the notion of transient fluvial response to seismic disturbance. The Pokhara valley features one of the largest and most extensively dated sedimentary records of earthquake-triggered sedimentation in the Himalayas, and independently augments paleo-seismological archives obtained mainly from fault trenches and historic documents.
New radiocarbon dates from the catastrophically deposited Pokhara Formation document multiple phases of extremely high geomorphic activity between ~700 and ~1700 AD, preserved in thick sequences of alternating fluvial conglomerates, massive mud and silt beds, and cohesive debris-flow deposits. These dated fan-marginal slackwater sediments indicate pronounced sediment pulses in the wake of at least three large medieval earthquakes in ~1100, 1255, and 1344 AD. We combine these dates with digital elevation models, geological maps, differential GPS data, and sediment logs to estimate the extent of these three pulses, which are characterized by sedimentation rates of ~200 mm yr-1 and peak rates as high as 1,000 mm yr-1. Some 5.5 to 9 km3 of material infilled the pre-existing topography, and is now prone to ongoing fluvial dissection along major canyons. Contemporary river incision into the Pokhara Formation is rapid (120-170 mm yr-1), triggering widespread bank erosion, channel changes, and very high sediment yields of the order of 103 to 105 t km-2 yr-1, which by far outweigh bedrock denudation rates inferred from cosmogenic 10Be inventories in river sands. The rapid infill of about a dozen tributary valleys displaced river channels, and caused them to re-incise into bedrock along steep epigenetic gorges. We conclude that the Pokhara Formation offers a unique archive of medieval earthquakes as well as the associated protracted fluvial response that may have been ongoing for up to 900 years.
Keywords: earthquake, AMS, dating, radiocarbon, Be-10
  • Lecture (Conference)
    European Geosciences Union (EGU) General Assembly, Vienna, Austria, 17.-22.04.2016., 17.-22.04.2016, Wien, Österreich

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Publ.-Id: 23052 - Permalink


Geomorphic legacy of medieval Himalayan earthquakes in the Pokhara Valley
Schwanghart, W.; Bernhardt, A.; Stolle, A.; Hoelzmann, P.; Adhikari, B. R.; Andermann, C.; Tofelde, S.; Merchel, S.; Rugel, G.; Fort, M.; Korup, O.;
The Himalayas and their foreland belong to the world’s most earthquake-prone regions. With millions of people at risk from severe ground shaking and associated damages, reliable data on the spatial and temporal occurrence of past major earthquakes is urgently needed to inform seismic risk analysis. Beyond the instrumental record such information has been largely based on historical accounts and trench studies. Written records provide evidence for damages and fatalities, yet are difficult to interpret when derived from the far-field. Trench studies, in turn, offer information on rupture histories, lengths and displacements along faults but involve high chronological uncertainties and fail to record earthquakes that do not rupture the surface. Thus, additional and independent information is required for developing reliable earthquake histories.
Here, we present exceptionally well-dated evidence of catastrophic valley infill in the Pokhara Valley, Nepal. Bayesian calibration of radiocarbon dates from peat beds, plant macrofossils, and humic silts in fine-grained tributary sediments yields a robust age distribution that matches the timing of nearby M>8 earthquakes in ~1100, 1255, and 1344 AD. The upstream dip of tributary valley fills and X-ray fluorescence spectrometry of their provenance rule out local sediment sources. Instead, geomorphic and sedimentary evidence is consistent with catastrophic fluvial aggradation and debris flows that had plugged several tributaries with tens of meters of calcareous sediment from the Annapurna Massif >60 km away.
The landscape-changing consequences of past large Himalayan earthquakes have so far been elusive. Catastrophic aggradation in the wake of two historically documented medieval earthquakes and one inferred from trench studies underscores that Himalayan valley fills should be considered as potential archives of past earthquakes. Such valley fills are pervasive in the Lesser Himalaya though high erosion rates reduce preservation potential. Further studies may wish to seek such remnants of prehistoric earthquakes using extensive sedimentological work as well as numerical age control.
Keywords: earthquake, Nepal, radiocarbon, AMS, Be-10
  • Lecture (Conference)
    European Geosciences Union (EGU) General Assembly, 17.-22.04.2016, Wien, Österreich

Downloads:

Publ.-Id: 23051 - Permalink


Making SiMn and TiO2 ferromagnetic at room temperature
Semisalova, A. S.; Rylkov, V. V.; Nikolaev, S. N.; Tugushev, V. V.; Zhou, S.; Potzger, K.; Smekhova, A.; Perov, N.; Granovsky, A.;
During the last two decades the enormous efforts were put into the creation, understanding and manipulation of room temperature ferromagnetism (RT FM) in semiconductors. The utilization of spin functionality hand in hand with electrical charge-based electronics opens the wide field of phenomena combining brand-new physics and extensive potential for applications in the next generation logic device and storage. In this talk, recent experimental results on RT FM in Si1-xMnx and Ti1-xCo(V)xO2, the promising materials for hybrid semiconductor spintronics will be reported. Si1-xMnx mosaic (polycrystalline) thin films prepared by pulsed laser deposition exhibit unusual magnetic characteristics - The Curie temperature TC in nonstoichiometric Si1-xMnx alloys (x ~ 0.52-0.55) is one order of magnitude higher (TC ~ 300 K) as compared to stoichiometric MnSi (TC ~ 30 K). The mechanism of the high-temperature FM is still not clear. The FM exchange is associated with the formation of defects with localized magnetic moments coupled via spin fluctuations of itinerant electrons in the host. Also we suppose that structural defects caused, in particular, by small sizes of crystallites have a strong influence on the formation of Si1-xMnx phase with high temperature FM. In case of TiO2, Co and V dopants have been used to create a RT FM dilute magnetic oxide. The study of magnetic, magnetotransport and magneto-optical properties of magnetron sputtered Ti1-xCo(V)xO2–δ (x ∼ 1 at. %) revealed a different mechanism responsible for ferromagnetic response at RT. For Ti1-xVxO2−δ the magnetic properties are determined mainly by structural defects, whereas in Ti1-xCoxO2−δ the magnetic moments of Co play a main role.
  • Invited lecture (Conferences)
    9th International Conference on Magnetic and Superconducting Materials, 01.-3.05.2015, Antalya, Turkey

Publ.-Id: 23050 - Permalink


Approval procedures for clinical trials in the field of radiation oncology
Simon, M.; Habeck, M.; Büttner, D.; Habeck, U.; Nölling, T.; Krause, M.; Brix, G.; Willich, N.; Wenz, F.; Schmidberger, H.; Debus, J.; Baumann, M.;
BACKGROUND AND PURPOSE:

Application of ionizing radiation for the purpose of medical research in Germany needs to be approved by the national authority for radiation protection (Bundesamt für Strahlenschutz, BfS). For studies in the field of radiation oncology, differentiation between use of radiation for "medical care (Heilkunde)" versus "medical research" frequently leads to contradictions. The aim of this article is to provide principle investigators, individuals, and institutions involved in the process, as well as institutional review or ethics committees, with the necessary information for this assessment. Information on the legal frame and the approval procedures are also provided.
METHODS:

A workshop was co-organized by the German Society for Radiation Oncology (DEGRO), the Working Party for Radiation Oncology (ARO) of the German Cancer Society (DKG), the German Society for Medical Physics (DGMP), and the German Cancer Consortium (DKTK) in October 2013. This paper summarizes the results of the workshop and the follow-up discussions between the organizers and the BfS.
RESULTS:

Differentiating between "Heilkunde" which does not need to be approved by the BfS and "medical research" is whether the specific application of radiation (beam quality, dose, schedule, target volume, etc.) is a clinically established and recognized procedure. This must be answered by the qualified physician(s) ("fachkundiger Arzt" according to German radiation protection law) in charge of the study and the treatments of the patients within the study, taking into consideration of the best available evidence from clinical studies, guidelines and consensus papers. Among the important parameters for assessment are indication, total dose, and fractionation. Radiation treatments applied outside clinical trials do not require approval by the BfS, even if they are applied within a randomized or nonrandomized clinical trial. The decision-making by the "fachkundigem Arzt" may be supported on request by an opinion given by the DEGRO Expert Committee for clinical trials.
CONCLUSION:

An important aim for promoting clinical research and patient care in radiation oncology is to further professionalize planning and implementation of clinical trials in this field. Correct assessment, at an early stage, whether a trial needs to be approved by the BfS may reduce unneccesary costs and reduce the time needed for the approval procedure for those trials which need to be assessed by the BfS.

Publ.-Id: 23049 - Permalink


Evaluating the use of optimally respiratory gated 18F-FDG-PET in target volume delineation and its influence on radiation doses to the organs at risk in non-small-cell lung cancer patients
Wijsman, R.; Grootjans, W.; Troost, E. G.; van der Heijden, E. H.; Visser, E. P.; de Geus-Oei, L.-F.; Bussink, J.;
OBJECTIVE:

This radiotherapy planning study evaluated tumour delineation using both optimally respiratory gated and nongated fluorine-18 fluorodeoxyglucose-PET (F-FDG-PET).
METHODS:

For 22 non-small-cell lung tumours, both scans were used to create the nongated and gated (g) gross tumour volumes (GTVg) together with the accompanying clinical target volumes (CTV) and planning target volumes (PTV). The size of the target volumes (TV) was evaluated and the accompanying radiotherapy plans were created to study the radiation doses to the organs at risk (OAR).
RESULTS:

The median volumes of GTVg, CTVg and PTVg were statistically significantly smaller compared with the corresponding nongated volumes, resulting in a median TV reduction of 0.5 cm (interquartile range 0.1-1.2), 1.5 cm (-0.2 to 7.0) and 2.3 cm (-0.5 to 11.3) for the GTVg, CTVg and PTVg, respectively. For the OAR, only the percentage of lung (GTV included) receiving at least 35 Gy was significantly smaller after gating, with a median difference in lung volume receiving at least 35 Gy of 5.7 cm (interquartile range -0.8 to 30.50).
CONCLUSION:

Compared with nongated F-FDG-PET, the TVs obtained with optimally respiratory gated F-FDG-PET were significantly smaller, however, without a clinically relevant difference in radiation dose to the OAR.

Publ.-Id: 23048 - Permalink


Determination of the exchange stiffness in ultrathin magnetic films by magnonic patterning and ferromagnetic resonance
Lenz, K.; Langer, M.; Wagner, K.; Sebastian, T.; Schultheiss, H.; Lindner, J.; Fassbender, J.ORC
In ultrathin films of below 20 nm thickness, it is hardly possible to determine the exchange constant A, since perpendicular standing spin waves (PSSWs) are shifted up to inaccessibly high energies. In this work, a method is presented to analytically determine the exchange stiffness constant D = 2A/MS using ferromagnetic resonance (FMR) and magnonic patterning. Usual FMR measurements, however, are not influenced by the value of D, since no exchange energy is involved in uniform precession. To overcome this problem a coupling mechanism, such as two-magnon scattering (TMS), can be employed to couple exchange dominated in-plane spin waves with the uniform mode.
In our approach lateral magnetic surface patterning was carried out to artificially induce TMS. Subsequent FMR measurements give access to the spin wave spectra of backward volume modes, and thus, to the exchange stiffness constant D.
Keywords: Magnetism, FMR, magnonics
  • Poster
    603. WE-Heraeus Seminar: Magnonics: Spin Waves Connecting Charges, Spins and Photons, 05.-8.1.2016, Bad Honnef, Deutschland

Publ.-Id: 23047 - Permalink


Spontaneous pattern formation on ion irradiated semiconductor surfaces
Facsko, S.; Ou, X.; Wang, X.; Hübner, R.; Grenzer, J.;
Low energy ion irradiation of semiconductor surfaces induces the formation of periodic surface patterns under particular conditions. These nanostructured surfaces exhibit periodici- ties in the range of a few tens to hundreds of nanometers and are promising templates for producing nanostructured thin films [1]. During ion irradiation the surfaces are driven out of equilibrium by continuous creation of displacements in the sub-surface region. At room tem- perature (RT) the accumulation of created displacements leads to amorphization of the irradi- ated semiconductor surfaces. Under these conditions periodic ripple patterns with wave vec- tor parallel to the ion beam direction are observed frequently for ion irradiation at incidence angles between 50° and 70° to the surface normal [2]. At normal incidence dot or hole pat- terns with hexagonal symmetry are observed for specific semiconductors, i.e. GaSb [3], InSb, GaP, or for special irradiation conditions, e.g. Ga+ or Bi3+ irradiation of Ge [4, 5].
In Fig. 1 different patterns on ion irradiated Ge (001) surfaces are shown. Although the Ge (001) surface is thermodynamically stable at all temperature used in the experiments, ion irradiation induces a surface instability which is counterbalanced by surface smoothing via different relaxation mechanisms, e.g. surface diffusion, ion enhanced surface diffusion, sur- face viscous flow, etc. As a result a wavelength selection in the surface roughness manifests itself as a periodic surface pattern. For off-normal angle of incidence ripple patterns are
At higher temperatures than RT, however, point defects created by the displacements in the ion collision cascade can diffuse longer distances, thus, vacancies and interstitial recom- bine or diffuse to the surface more effectively. Eventually, at temperatures higher than the recrystallization temperature, defects in the sub-surface region are annealed or diffuse to the surface before a second ion creates new defects in the same area and the surface remains crystalline. However, the average density of surface vacancies and ad-atoms is much higher than the corresponding densities in thermal equilibrium resulting in a much higher entropy. In this regime, ion irradiation creates an excess of vacancies on the crystalline surface due to sputtering. Thus, the surfaces morphology is determined primarily by vacancy kinetics alt- hough the kinetics of ad-atoms also play an important role.
In this contribution we present investigations of the evolution of Ge surfaces with dif- ferent surface orientation irradiated at temperatures above the recrystallization temperature. The irradiations were done with 1 keV Ar+ ions at normal incidence at temperatures above 250°C which has been established to be the temperature at which the Ge surface remains crystalline even after prolonged irradiation. The samples were cut from epi-ready Ge wafers with (001) and (111) surface orientation. Irradiations were performed in a UHV chamber with a base pressure in the range of 10-8 mbar with a beam from a Kaufman ion source. During irradiation the chamber is flooded with Ar up to a pressure of 3x10-4 mbar. The flux was 1.7x1015 cm-2s-1 and the applied fluence was in the range of 1017 – 1019 cm-2.
The formation of these patterns on crystalline surfaces can be understood in analogy to the formation of 3D structures in homoepitaxy. In molecular beam epitaxy (MBE) the contin- uous deposition of atoms can lead to growth of self-organized 3D nanostructures [5]. One of the possible surface instability, which is responsible for the formation of islands or mounds is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad- atoms to cross terrace steps. Due to this effect the arriving atoms are trapped on a terraces and can again nucleate to form new terraces.
The same mechanism is also active on ion irradiated surfaces when the temperatures is above the recrystallization temperature. In this case bulk defects are dynamically annealed and amorphization is prevented. Now, ion sputtering is creating vacancies on the crystalline surface and the surfaces morphology is determined by vacancy kinetics. The diffusion of va- cancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into 3D erosion. The resulting structures are inverse pyramids which are grow- ing into the surface. The symmetry of these patterns is given by the crystal symmetry. In Fig. 3 zooms of AFM images and the 2D slope distributions of the surface patterns on Ge (001) and Ge (111) are shown, respectively. The detailed facet analysis of the patterns by the 2D slope distribution reveals that on Ge (001) {105} facets with a polar angle of 11° exhibiting a four-fold symmetry are formed, whereas on Ge (111) {356} facets with a polar angle of 15° are formed with a three-fold symmetry. These facets are not know to be thermodynamically stable facets in growth conditions. The {105} facets have only been observed in heteroepi- taxy, where they are stabilize by strain due to the lattice mismatch. In the case of ion erosion no strain is expected [8]. Hence, it can be concluded that these are non-equilibrium facets which are determined by the kinetics of vacancies induce by ion irradiation.
For the description of the pattern formation and evolution in reverse epitaxy a continuum equation can be used which combines the effects of ion irradiation and effective diffusion
currents due to the ES barrier on the crystalline surface. For normal incidence irradiation it is know that smoothing mechanisms dominate thus we can omit an instability term induced by the curvature dependent sputtering or ion induced mass redistribution [9]. By choosing the adequate ES barrier induced surface currents and including also a conserved Kardar-Parisi- Zhang term a remarkable qualitative agreement to the experiments is achieved for both sur- face orientations. Ge (001) and Ge (111), respectively (see Fig. 4) [7].

1. J. Fassbender, T. Strache, M.O. Liedke, D. Marko, S. Wintz, K. Lenz, A. Keller, S. Facsko, I. Monch, J. McCord, New Journal of Physics 11, 125002 (2009).
2. W.L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007).
3. S. Facsko, T. Dekorsy, C. Koerdt, C. Trappe, H. Kurz, A. Vogt, and H.L. Hartnagel, Science 285, 1551 (1999).
4. M. Fritzsche, A. Muecklich, S. Facsko, Appl. Phys. Lett. 100, 223108 (2012).
5. Böttger, K.-H. Heinig, L. Bischoff, B. Liedke, R. Hübner, and W. Pilz, Phys. Status Solidi (RRL), 501 (2013).
6. C. Teichert, Phys. Rep. 365, 335 (2002).
7. X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).
8. X. Ou and S. Facsko, Nucl. Instr. Meth. B 341, 13 (2014).
9. C.S. Madi, E. Anzenberg, K.F. Ludwig, and M.J. Aziz, Phys. Rev. Lett. 106, 066101 (2011).
Keywords: ion induced nanopatterns
  • Invited lecture (Conferences)
    22nd International Conference on Ion-Surface Interactions, 19.-22.08.2015, Moskow, Russia
  • Lecture (Conference)
    8th International Meeting on Recent Developments in the Study of Radiation Effects in Matter, 21.-23.09.2015, Kerteminde, Denmark

Publ.-Id: 23046 - Permalink


Reverse Epitaxy on Semiconductor Surfaces
Facsko, S.; Ou, X.; Hübner, R.; Grenzer, J.; Heinig, K.-H.;
Arrays of semiconductor nanostructures are emerging as building blocks for next generation of electronic and optoelectronic nano-devices. In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instabilities, which is responsible for this kind of growth, is caused by the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms to cross terrace steps [1]. The arriving atoms are trapped on terraces and can again nucleate to form new terraces. This mechanism leads to the growth of pyramidal mounds on the surface with facets corresponding to energetically favored crystal planes. An analogous mechanism is also observed on ion irradiated surfaces. However, ion sputtering leads to the erosion of the surfaces and at room temperature semiconductor surfaces become amorphous. At these conditions various periodic patterns are observed. [2,3] For device fabrication, a crystalline surface of high quality is indispensable.
In this talk, we demonstrate single crystal elemental (Si and Ge) and compound semiconductor (III-V) nanostructure pattern formation based on a “reverse epitaxy” process. Vacancies created during ion beam irradiation at elevated temperature distribute according to the crystallographic anisotropy, which results in an orientation-dependent pattern formation on single crystal semiconductor surfaces. This process shows nicely the equivalence of epitaxy with deposited adatoms and “reverse epitaxy” with ion induced surface vacancies on semiconductors. The formation of these patterns is interpreted as the result of a surface instability due to an Ehrlich-Schwoebel barrier for ion induced surface vacancies. The potential application of reverse epitaxy on fabrication of UUV optical grating and of metallic nanowires will be discussed.

[1] P. Politi, G. Grenet, A. Marty, A. Ponchet, J. Villain, Phys. Rep. 324, 271 (2000).
[2] S. Facsko, T. Dekorsy, C. Koerdt, C. Trappe, H. Kurz, A. Vogt, and H. L. Hartnagel, Science 285, 1551 (1999).
[3] W. L. Chan and E. Chason, J. Appl. Phys. 101, 121301 (2007).
Keywords: ion induced nanopatterns
  • Invited lecture (Conferences)
    8th International Workshop on Nanoscale Pattern Formation at Surfaces, 12.-16.07.2015, Krakow, Poland

Publ.-Id: 23045 - Permalink


First clinical application of a prompt gamma based in vivo proton range verification
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.;
Background and Purpose: 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.
Material and Methods: A prototype of a knife-edge shaped slit camera was used to measure the prompt gamma ray depth distribution during a proton treatment of a head and neck tumor for seven consecutive fractions. Inter-fractional variations of the prompt gamma profile were evaluated. For three fractions in-room control CTs were acquired and evaluated for dose relevant changes.
Results: The measurement of PGI profiles during proton treatment was successful. Based on the PGI information, inter-fractional global range variations were in the range of ±2 mm for all evaluated fractions. This is in agreement with the control CT evaluation showing negligible range variations of about 1.5 mm.
Conclusions: For the first time, range verification based on prompt gamma imaging was applied for a clinical proton treatment. With the translation from basic physics experiments into clinical operation, the potential to improve the precision of particle therapy with this technique has increased considerably.

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Publ.-Id: 23044 - Permalink


Interaction of Highly Charged Ions with Surfaces and Nanomembranes
Facsko, S.; Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Aumayr, F.;
Highly charged ions (HCI) release a large amount of potential energy (the stored ionization energy) when interacting with solids. This energy is deposited into a very small volume directly at the surface via multiple charge exchanges on a fs time scale leading to a highly excited electronic system. Especially ionic crystals have shown a predisposition to potential energy effects due to their low conductivity and their strong electron phonon coupling. On CaF_2 surfaces the formation of hillocks induced by the potential energy of a single highly charged Xe^{q+} ion has been observed for charge states higher than q > 27. The formation of these hillocks can be attributed to local melting [1]. In contrast, on surfaces of KBr one monolayer deep pits are formed by defect mediated desorption also showing a threshold behavior in the pit formation [2].
The interaction of HCI with thin membranes is particularly interesting because the pre-equilibrium interaction regime can be accessed for thicknesses below a few nm. In 1 nm carbon nano membranes (CNM) for instance, holes are produced by the passage of highly charged Xe^{q+} ions [3]. For the formation of these holes a threshold in the potential energy of the HCI exists that depends on the kinetic energy. In order to elucidate the formation mechanism we examined the charge state and the energy loss of the Xe^{q+} ions after their passage through the CNM. Surprisingly, two distinct exit charge distributions were observed [4]. Part of the ions are passing the membrane with almost now charge loss, whereas the other part looses most of their charge. Apparently, the measured charge distribution reflects two different impact parameter regimes. Ions with trajectories far away of any C atom of the membrane can stabilize only few electrons and exit therefore in a high charge state, whereas ions with trajectories close to a C atom can capture a large amount of electrons and exit the membrane in a low charge state. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are practically not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
[1] A. El-Said, R. Wilhelm, R. Heller, S. Facsko, C. Lemell, G. Wachter, J. Burgdorfer, R. Ritter, and F. Aumayr, Phys. Rev. Lett. 109, 117602 (2012).
[2] R. Heller, S. Facsko, R.A. Wilhelm, and W. Moller, Phys. Rev. Lett. 101, 096102 (2008).
[3] R. Ritter, R.A. Wilhelm, M. Stöger-Pollach, R. Heller, A. Mücklich, U. Werner, H. Vieker, A. Beyer, S. Facsko, A. Gölzhäuser, F. Aumayr, Appl. Phys. Lett. 102, 063112 (2013).
[4] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
Keywords: highly charged ions
  • Invited lecture (Conferences)
    MRS Spring Meeting, 06.-10.04.2015, San Francisco, USA

Publ.-Id: 23043 - Permalink


Transition from Pits to Mounds in Ion Induced Patterning of Germanium
Facsko, S.; Ou, X.;
Low energy ion irradiation drives surfaces out of equilibrium by continuous creation of displacements in the sub-surface region. At room temperature the accumulation of displacements leads to the amorphization of the irradiated surfaces and self-organized ripple pattern perpendicular to the ion beam direction are formed for incidence angles higher than 50° [1]. At normal incidence irradiation smoothing dominates and no pattern are observed for low energy ion irradiation. At higher temperatures, point defects created by the displacements in the ion collision cascade can diffuse longer distances, thus vacancies and interstitial recombine more effectively or diffuse to the surface. Finally, at temperatures higher than the recrystallization temperature, all defects in the sub-surface region are annealed before an ion creates new defects and the surface remains crystalline. The average density of surface vacancies and ad-atoms on the surface is, however, much higher than the corresponding densities in thermal equilibrium resulting in a much higher entropy.
In this regime, ion irradiation creates an excess of vacancies on the crystalline surface due to sputtering and the surfaces morphology is determined primarily by their kinetics. The diffusion of vacancies is biased by the Ehrlich-Schwoebel barrier, i.e. an additional barrier for crossing terrace steps, similar to the diffusion barrier of ad-atoms known from growth by molecular beam epitaxy. Consequently, ion sputtering leads to the erosion of 3D structures in a “reverse epitaxy” process. The resulting patterns are arrays of inverse pyramids growing into the Ge surface [1,2]. The morphology of these patterns is given by the crystal symmetry of the surface. Hence, checkerboard patterns appear on the Ge (001) surface Here, we show that the inverse pyramid pattern on Ge(001) surface, which is observed for normal incidence ion irradiation at higher temperatures, turns into a pyramidal mound pattern at incidence angles between 50° and 70° with respect to the surface normal, and finally, into ripple patterns above 80° incidence. All irradiations were performed at 350° C with 1 keV Ar+ at a fluence of 1x1018 cm-2 from a Kaufman ion source.
The observed transition from pit to mound patterns in reverse epitaxy can be understood by assuming a transition from vacancy dominated pattern formation to ad-atom dominated pattern formation. Therefore, at incidence angles above 50° the pattern resemble mound patterns observed in growth. Furthermore, the transition to ripples patterns at higher incidence angles is ascribed to a shadowing instability at these grazing incidence angles.

[1] A. Keller and S. Facsko, Materials 2010, Vol. 3, Pages 4811-4841 3, 4811 (2010).
[2] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).
[3] X. Ou and S. Facsko, Nucl. Instr. Meth. B 341, 13 (2014).
Keywords: ion induced nanostructures
  • Lecture (Conference)
    21st International Workshop on Inelastic Ion-Surface Collisions, 18.-23.10.2015, San Sebastian, Spanien

Publ.-Id: 23042 - Permalink


Pre-equilibrium Dynamics of Highly Charged ions at Surfaces and Carbon Nanomembranes
Facsko, S.; Wilhelm, R.; Gruber, E.; Heller, R.; Aumayr, F.;
The interaction of HCI with thin membranes is particularly interesting because the pre-equilibrium interaction regime can be accessed for thicknesses below a few nm. In 1 nm carbon nano membranes (CNM) for instance, holes are produced by the passage of highly charged Xe$^{q+}$ ions. For the formation of these holes a threshold in the potential energy of the HCI exists that depends on the kinetic energy. In order to elucidate the formation mechanism we examined the charge state and the energy loss of the Xe$^{q+}$ ions after their passage through the CNM. Surprisingly, two distinct exit charge distributions were observed. Part of the ions are passing the membrane with almost now charge loss, whereas the other part looses most of their charge. Apparently, the measured charge distribution reflects two different impact parameter regimes. Ions with trajectories far away of any C atom of the membrane can stabilize only few electrons and exit therefore in a high charge state, whereas ions with trajectories close to a C atom can capture a large amount of electrons and exit the membrane in a low charge state. The different impact parameter regimes are also connected to different energy losses: ions with large impact parameters are practically not stopped, whereas ions in close collisions exhibit high stopping force which is strongly dependent on the incident charge state.
Keywords: highly charged ions
  • Lecture (others)
    Kolloquiumsvortrag, 12.11.2015, Leipzig, Deutschland

Publ.-Id: 23041 - Permalink


Defects in zinc oxide grown by pulsed laser deposition
Ling, F. C. C.; Wang, Z.; Ho, L. P.; Younas, M.; Anwand, W.; Wagner, A.; Su, S. C.; Shan, C. X.;
ZnO films are grown on c-plane sapphire using the pulsed laser deposition method. Systematic studies on the effects of annealing are performed to understand the thermal evolutions of the defects in the films. Particular attention is paid to the discussions of the ZnO/sapphire interface thermal stability, the Zn-vacancy related defects having different microstructures, the origins of the green luminescence (~2.4-2.5 eV) and the near band edge (NBE) emission at 3.23 eV.
Keywords: ZnO, pulsed laser deposition, Zn-vacancy, green luminescence, near band edge emission, positron annihilation spectroscopy

Publ.-Id: 23037 - Permalink


Ferromagnetism of MnxSi1-x (x~0.5) films grown in the shadow geometry by pulsed laser deposition method
Nikolaev, S.; Semisalova, A.; Rylkov, V.; Tugushev, V.; Zenkevich, A.; Vasiliev, A.; Pashaev, E.; Chernoglazov, K.; Chesnokov, Y.; Likhachev, I.; Perov, N.; Matveyev, Y.; Novodvorskii, O.; Kulatov, E.; Bugaev, A.; Wang, Y.; Zhou, S.;
The results of a comprehensive study of magnetic, magneto-transport and structural properties of nonstoichiometric MnxSi1-x (x=0.51-0.52) films grown by the Pulsed Laser Deposition (PLD) technique onto Al2O3(0001) single crystal substrates at T = 340 C are present. A highlight of used PLD method is the non-conventional ("shadow") geometry with Kr as a scattering gas during the sample growth. It is found that the films exhibit high-temperature (HT) ferromagnetism (FM) with the Curie temperature TC ~ 370 K accompanied by positive sign anomalous Hall effect (AHE); they also reveal the polycrystalline structure with unusual distribution of grains in size and shape. It is established that HT FM order is originated from the bottom interfacial self-organizing nanocrystalline layer. The upper layer adopted columnar structure with the lateral grain size >50 nm, possesses low temperature (LT) type of FM order with ТС ~ 46 K and contributes essentially to the magnetization at T < 50 K. Under these conditions, AHE changes its sign from positive to negative at T < 30K. We attribute observed properties to the synergy of distribution of MnxSi1-x crystallites in size and shape as well as peculiarities of defect-induced FM order in shadow geometry grown polycrystalline MnxSi1-x (x~0.5) films.
Keywords: Si-Mn alloys, High-temperature ferromagnetism, Anomalous Hall effect

Publ.-Id: 23036 - Permalink


Modifications of gallium phosphide single crystals using slow highly charged ions and swift heavy ions
El-Said, A. S.; Wilhelm, R. A.; Heller, R.; Akhmadaliev, S.; Schumann, E.; Sorokin, M.; Facsko, S.; Trautmann, C.;
GaP single crystals were irradiated with slow highly charged ions (HCI) using 114 keV 129Xe(33–40)+ and with various swift heavy ions (SHI) of 30 MeV I9+ and 374 MeV–2.2 GeV 197Au25+. The irradiated surfaces were investigated by scanning force microscopy (SFM). The irradiations with SHI lead to nanohillocks protruding from the GaP surfaces, whereas no changes of the surface topography were observed after the irradiation with HCI. This result indicates that a potential energy above 38.5 keV is required for surface nanostructuring of GaP. In addition, strong coloration of the GaP crystals was observed after irradiation with SHI. The effect was stronger for higher energies. This was confirmed by measuring an increased extinction coefficient in the visible light region.
Keywords: GaP; Swift heavy ions; Slow highly charged ions; Nanostructures

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Publ.-Id: 23035 - Permalink


A setup for transmission measurements of low energy multiply charged ions through free-standing few atomic layer films
Smejkal, V.; Gruber, E.; Wilhelm, R. A.; Brandl, L.; Heller, R.; Facsko, S.; Aumayr, F.;
We report the design and testing of a setup for transmission measurements of multiply charged ions through free-standing films with a thickness of a few atomic layers. The in- vestigation thereof can yield deeper insight into charge equilibration and pre-equilibrium stopping phenomena which can ultimately be used to specifically tailor and modify these materials.
Keywords: transmission measurements, highly charged ions, ion surface interaction, graphene, carbon nano membranes, ion charge loss, ion energy loss, equilibrium charge state

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Publ.-Id: 23033 - Permalink


Polarity dependence of Mn incorporation in (Ga,Mn)N superlattices
Tropf, L.; Kunert, G.; Jakieła, R.; Wilhelm, R. A.; Figge, S.; Grenzer, J.; Hommel, D.;
In the context of recent efforts to combine high Mn concentrations in (Ga,Mn)N with a pronounced p- type carrier density, (Ga,Mn)N/GaN:Mg-superlattices have been fabricated using plasma-assisted mole- cular beam epitaxy. Profiles of the dopant atomic densities in the heterostructures are obtained by secondary ion mass spectroscopy. They show an abrupt drop of two to three orders of magnitude in both Mn and Mg concentrations after the first GaN:Mg layer above a critical Mg-flux. Scanning electron microscopy before and after selective etching reveals a polarity inversion from originally Ga-face to N- face GaN in samples in which high Mg fluxes were applied. From our observations, we are able to draw an analogy between the impurity incorporation laws of Mg and Mn.
Keywords: Doping, Molecular beam epitaxy, Nitrides, Magnetic materials

Publ.-Id: 23032 - Permalink


Interaction of multiply charged ions with single layer graphene Part I: Charge exchange and energy loss (Conference Paper)
Smejkal, V.; Gruber, E.; Kralik, M.; Wilhelm, R. A.; Heller, R.; Facsko, S.; Aumayr, F.;
The exit charge state distribution and the energy loss of slow multiply charged ions transmitted through single layers of graphene and 1 nm thick carbon nanomembranes is analyzed.

Publ.-Id: 23031 - Permalink


Imaging-Based Treatment Adaptation in Radiation Oncology
Troost, E. G.; Thorwarth, D.; Oyen, W. J.;
In many tumor types, significant effort is being put into patient-tailored adaptation of treatment to improve outcome and preferably reduce toxicity. These opportunities first arose with the introduction of modern irradiation techniques (e.g., intensity-modulated radiotherapy) combined with functional imaging for more precise delineation of target volume. On the basis of functional CT, MRI, and PET results, radiation target volumes are altered during the course of treatment, or subvolumes inside the primary tumor are defined to enhance the dosing strategy. Moreover, the probability of complications to normal tissues is predicted using anatomic or functional imaging, such as in the use of CT or PET to predict radiation pneumonitis. Besides focusing, monitoring, and adapting photon therapy for solid tumors, PET also has a role in verifying proton-beam therapy. This article discusses the current state and remaining challenges of imaging-based treatment adaptation in radiation oncology.

Publ.-Id: 23029 - Permalink


Is integrated transit planar portal dosimetry able to detect geometric changes in lung cancer patients treated with volumetric modulated arc therapy?
Persoon, L. C.; Podesta, M.; Hoffmann, L.; Sanizadeh, A.; Schyns, L. E.; de Ruiter, B. M.; Nijsten, S. M.; Muren, L. P.; Troost, E. G.; Verhaegen, F.;
BACKGROUND:

Geometric changes are frequent during the course of treatment of lung cancer patients. This may potentially result in deviations between the planned and actual delivered dose. Electronic portal imaging device (EPID)-based integrated transit planar portal dosimetry (ITPD) is a fast method for absolute in-treatment dose verification. The aim of this study was to investigate if ITPD could detect geometric changes in lung cancer patients.
MATERIALS AND METHODS:

A total of 460 patients treated with volumetric modulated arc therapy (VMAT) following daily cone beam computed tomography (CT)-based setup were visually inspected for geometrical changes on a daily basis. Forty-six patients were subject to changes and had a re-CT and an adaptive treatment plan. The reasons for adaptation were: change in atelectasis (n = 18), tumor regression (n = 9), change in pleural effusion (n = 8) or other causes (n = 11). The ITPDs were calculated on both the initial planning CT and the re-CT and compared with a global gamma (γ) evaluation (criteria: 3%\3mm). A treatment fraction failed when the percentage of pixels failing in the radiation fields exceeded 10%. Dose-volume histograms (DVHs) were compared between the initial plan versus the plan re-calculated on the re-CT.
RESULTS:

The ITPD threshold method detected 76% of the changes in atelectasis, while only 50% of the tumor regression cases and 42% of the pleural effusion cases were detected. Only 10% of the cases adapted for other reasons were detected with ITPD. The method has a 17% false-positive rate. No significant correlations were found between changes in DVH metrics and γ fail-rates.
CONCLUSIONS:

This study showed that most cases with geometric changes caused by atelectasis could be captured by ITPD, however for other causes ITPD is not sensitive enough to detect the clinically relevant changes and no predictive power of ITPD was found.

Publ.-Id: 23025 - Permalink


Single organ metastatic disease and local disease status, prognostic factors for overall survival in stage IV non-small cell lung cancer: Results from a population-based study.
Hendriks, L. E.; Derks, J. L.; Postmus, P. E.; Damhuis, R. A.; Houben, R. M.; Troost, E. G.; Hochstenbag, M. M.; Smit, E. F.; Dingemans, A. M.;
PURPOSE:

To analyse the prognostic impact on overall survival (OS) of single versus multiple organ metastases, organ affected, and local disease status in a population based stage IV non-small cell lung cancer (NSCLC) cohort.
METHODS:

In this observational study, data were analysed of all histologically confirmed stage IV NSCLC patients diagnosed between 1 January 2006 and 31 December 2012 registered in the Netherlands Cancer Registry. Location of metastases before treatment was registered. Multivariable survival analyses [age, gender, histology, M-status, local disease status, number of involved organs, actual organ affected] were performed for all patients and for an (18)fluorodeoxyglucose-positron emission tomography ((18)FDG-PET)-staged subgroup.
RESULTS:

11,094 patients were selected: 60% male, mean age 65years, 73% adenocarcinoma. Median OS for 1 (N=5676), 2 (N=3280), and ⩾3 (N=2138) metastatically affected organs was 6.7, 4.3, 2.8months, respectively (p<0.001). Hazard ratio (HR) for 2 versus 1 organ(s) was 1.33 (p<0.001), for ⩾3 versus 1 organ(s) 1.91 (p<0.001). Results were confirmed in the (18)FDG-PET-staged cohort (N=1517): patients with single organ versus 2 and ⩾3 organ metastases had higher OS (8.6, 5.7, 3.8months, HR 1.40 and 2.17, respectively, p<0.001). In single organ metastases, OS for low versus high TN-status was 8.5 versus 6.5months [HR 1.40 (p<0.001)]. (18)FDG-PET-staged single organ metastases patients with low TN-status had a superior OS than those with high TN-status (11.6 versus 8.2months, HR 1.62, p<0.001).
CONCLUSION:

Patients with single organ metastases stage IV NSCLC have a favourable prognosis, especially in combination with low TN status. They have to be regarded as a separate subgroup of stage IV disease.
Keywords: Local disease status; Metastases; Non-small cell lung cancer; Prognosis; Stage IV

Publ.-Id: 23023 - Permalink


Increasing the Therapeutic Ratio of Stereotactic Ablative Radiotherapy by Individualized Isotoxic Dose Prescription
Zindler, J. D.; Thomas, C. R.; Hahn, S. M.; Hoffmann, A. L.; Troost, E. G. C.; Lambin, P.;
To obtain a favorable tradeoff between treatment benefits and morbidity ("therapeutic ratio"), radiotherapy (RT) dose is prescribed according to the tumor volume, with the goal of controlling the disease while respecting normal tissue tolerance levels. We propose a new paradigm for tumor dose prescription in stereotactic ablative radiotherapy (SABR) based on organ-at-risk (OAR) tolerance levels called isotoxic dose prescription (IDP), which is derived from experiences and limitations of conventionally fractionated radiotherapy. With IDP, the radiation dose is prescribed based on the predefined level of normal tissue complication probability of a nearby dose-limiting OAR at a prespecified dose-volume constraint. Simultaneously, the prescribed total tumor dose (TTD) is maximized to the technically highest achievable level in order to increase the local tumor control probability (TCP). IDP is especially relevant for tumors located at eloquent locations or for large tumors in which severe toxicity has been described. IDP will result in a lower RT dose or a treatment scheduled with more fractions if the OAR tolerance level is exceeded, and potential dose escalation occurs when the OAR tolerance level allows it and when it is expected to be beneficial (if TCP < 90%). For patients with small tumors at noneloquent sites, the current SABR dose prescription already results in high rates of local control at low toxicity rates. In this review, the concept of IDP is described in the context of SABR.

Publ.-Id: 23022 - Permalink


Interactive Plasma Simulations on Next Generation Supercomputers for Everybody
Huebl, A.; Widera, R.; Zenker, E.; Worpitz, B.; Burau, H.; Pausch, R.; Grund, A.; Matthes, A.; Garten, M.; Eckert, C.; Debus, A.; Bussmann, M.;
Subject to change: we will cover our fundamental, performance portable building blocks (alpaka) that power kernels in PIConGPU and PMacc. PMacc is our particle-mesh library with reusable, light-weight containers and event scheduling for many/multi-core hardware. Combining our open source libraries with C++ meta-programming and our open data standard suitable for extreme I/O load in HPC (openPMD) we will visualize the whole plasma simulation environment with a live simulation.
Keywords: Simulation, Plasma, LPA, GPU, PIConGPU, HPC, Open
  • Invited lecture (Conferences)
    Swiss Platform for Advanced Scientific Computing (PASC) Conference 2016, 08.-10.06.2016, Lausanne, Schweiz

Publ.-Id: 23021 - Permalink


Functional DNA origami nanostructures for nanoelectronics and Photonics
Teschome, B.; Facsko, S.; Keller, A.; Kerbusch, J.;
Nanodevices based on DNA origami-based nanowires
  • Lecture (Conference)
    Group meeting Aarhus University, 22.05.2015, Aarhus, Denmark

Publ.-Id: 23020 - Permalink


Arrangement and characterization of functional DNA origami nanostructures for nanoelectronics
Teschome, B.; Facsko, S.; Kerbusch, J.; Hübner, R.; Gothelf, K. V.; Keller, A.;
In this work, we will highlight some of results from our work on the arrangement and characterization of functional DNA origami nanostructures for nanoelectronics. First, a new compelling approach to generate ordered arrays of DNA origami nanotubes on topographically patterned Si surfaces will be introduced. Then, the high-yield synthesis of high-density gold nanoparticle (AuNP) arrangements on DNA origami nanotubes with few unbound background nanoparticles will be presented. The high yield of AuNP assembly was achieved by careful control of the buffer concentration and the hybridization time on Si surface. Finally, also the assembly of heterogeneous nanostructures, i.e. 5 nm gold nanoparticles (AuNPs) and 10 nm semiconductor quantum dots (QDs), on a single DNA origami will be demonstrated.
  • Invited lecture (Conferences)
    IHRS NanoNet Annual Workshop 2015, 30.09.-02.10.2015, Lohmen, Germany

Publ.-Id: 23019 - Permalink


Above Room Temperature Ferromagnetism in Dilute Magnetic Oxide Semiconductors
Semisalova, A. S.; Orlov, A.; Smekhova, A.; Gan’Shina, E.; Perov, N.; Anwand, W.; Potzger, K.; Lähderanta, E.; Granovsky, A.;
In this chapter, we will survey early and recent experimental results on magnetic properties of dilute magnetic oxide semiconductors, focusing on TiO2-δ:Co and TiO2-δ:V. Room temperature ferromagnetism was observed in both types of thin film samples fabricated by RF sputtering, but their magnetic properties appeared to be quite different. Magnetic moments in case of TiO2-δ:Co are mostly associated with local polarization of Co ions and induced defects. There is an evidence of intrinsic ferromagnetism in the case of low Co content (<1 at.%). Room temperature ferromagnetism was observed in TiO2-δ:V at V content from 3 up to 18 at.% in the whole resistivity range from 10e-3 up to 10e6 Ω cm. Positron annihilation spectroscopy revealed a correlation between magnetization and concentration of the negatively charged defects in TiO2-δ:V thin films. The origin of room temperature ferromagnetism in these systems is discussed. Besides, the recent research findings in ZnO-based magnetic semiconductors are briefly discussed with focus on defect-induced ferromagnetism.
Keywords: Dilute magnetic oxides; Dilute magnetic semiconductors; Above room temperature ferromagnetism; Defect-induced ferromagnetism; Positron annihilation spectroscopy
  • Book chapter
    Zhukov, A.: Novel Functional Magnetic Materials. Fundamentals and Applications. Springer Series in Materials Science 231, Switzerland: Springer International Publishing, 2016, 978-3-319-26104-1, 187-219
    DOI: 10.1007/978-3-319-26106-5_5

Publ.-Id: 23018 - Permalink


Structure-Correlated Exchange Anisotropy in Oxidized Co80Ni20 Nanorods
Liebana-Vinas, S.; Wiedwald, U.; Elsukova, A.; Perl, J.; Zingsem, B.; Semisalova, A.; Salgueirino, V.; Spasova, M.; Farle, M.;
Rare earth-free permanent magnets for applications in electro-magnetic devices promise better sustainability and availability and lower prices. Exploiting the combination of shape, magnetocrystalline and exchange anisotropy in 3D-metals can pave the way to practical application of nanomagnets. In this context, we study the structural and magnetic properties of Co80Ni20 nanorods with a mean diameter of 6.5 nm and a mean length of 52.5 nm, prepared by polyol reduction of mixed cobalt and nickel acetates. Structural analysis shows crystalline rods with the crystallographic c-axis of the hexagonal close-packed (hcp) phase parallel to the long axis of the Co80Ni20 alloy rods, which appear covered by a thin oxidized face-centered cubic (fcc) shell. The temperature dependence of the surprisingly high coercive field and the exchange bias effect caused by the antiferromagnetic surface oxide indicate a strong magnetic hardening due to alignment of anisotropy axes. We identify a temperature dependent local maximum of the coercive field at T = 250 K, which originates from noncollinear spin orientations in the ferromagnetic core and the antiferromagnetic shell. This might be useful for building four way magnetic switches as a function of temperature.

Publ.-Id: 23017 - Permalink


Discrimination, correlation and provenance of Bed I tephrostratigraphic markers, Olduvai Gorge, Tanzania, based on multivariate analyses of phenocryst compositions
Habermann, J. M.; Mchenry, L. J.; Stollhofen, H.; Tolosana-Delgado, R.; Stanistreet, I. G.; Deino, A. L.;
The chronology of Pleistocene flora and fauna, including hominin remains and associated Oldowan industries in Bed I, Olduvai Gorge, Tanzania, is primarily based on 40Ar/39Ar dating of intercalated tuffs and lavas, combined with detailed tephrostratigraphic correlations within the basin. Although a high-resolution chronostratigraphy has been established for the eastern part of the Olduvai Basin, the western subbasin is less well known due in part to major lateral facies changes within Bed I combined with discontinuous exposure. We address the correlation difficulties using the discriminative power of the chemical composition of the major juvenile mineral phases (augite, anorthoclase, plagioclase) from tuffs, volcaniclastic sandstones, siliciclastic units, and lavas. We statistically evaluate these compositions, obtained from electron-microprobe analyses, applying principal component analysis and discriminant analysis to develop discriminant models that successfully classify most Bed I volcanic units. The correlations resulting from integrated analyses of all target minerals provide a basin-wide Bed I chemostratigraphic framework at high lateral and vertical resolution, consistent with the known geological context, which expands and refines the geochemical databases currently available. Correlation of proximal ignimbrites at the First Fault with medial and distal Lower Bed I successions of the western basin enables assessment of lateral facies and thickness trends that corroborate Ngorongoro Volcano as the primary source for Lower Bed I, whereas Upper Bed I sediment supply is mainly from Olmoti Volcano. Compositional similarity between Tuff IA, Bed I lava, and Mafic Tuffs II and III single-grain fingerprints, together with north- and northwestward thinning of Bed I lava, suggests a common Ngorongoro source of these units. The techniques applied herein improve upon previous work by evaluating compositional affinities with statistical rigor rather than primarily relying on visual comparison of bivariate plots.
Keywords: Olduvai; Ngorongoro fan; Principal component analysis; Discriminant analysis; Chemostratigraphy

Publ.-Id: 23015 - Permalink


Lectures concerning uranium pollution, time-resolved laser-induced fluorescence spectroscopy (TRLFS), and radiometric dating
Baumann, N.;
Within a comprehensive course in Radioecology, 5 special lectures were held in the Department of Applied Radiation and Isotopes, Faculty of Science, Kasetsart University, Chatuchak, Bangkok. Topics of these 5 lectures were “Kinds of radiation and radioactive decay”, “Natural occurring radionuclides and natural radiation”, “Age determination by radioactive decay and mass spectrometry”, “Speciation of radionuclides and time-resolved laser-induced fluorescence spectroscopy (TRLFS)”, and “Uranium as basement of nuclear energy production”. As a precondition for obtaining Credit Points for the students in the audience, a questionnaire was created concerning these 5 topics.
Keywords: Uranium, TRLFS, Radiometric Dating
  • Invited lecture (Conferences)
    Course in Radioecology, Department of Applied Radiation and Isotopes, Faculty of Science, Kasetsart University, 22.-26.02.2016, Chatuchak, Bangkok, Thailand

Publ.-Id: 23014 - Permalink


Single crystal growth, structural characteristics and magnetic properties of chromium substituted M-type ferrites
Shlyk, L.; Vinnik, D. A.; Zherebtsov, D. A.; Hu, Z.; Kuo, C.-Y.; Chang, C.-F.; Lin, H.-J.; Yang, L.-Y.; Semisalova, A. S.; Perov, N. S.; Langer, T.; Pöttgeng, R.; Nemrava, S.; Niewa, R.;
Two different types of fluxes, namely sodium based and chloride based fluxes were used to grow Cr substituted barium and strontium hexaferrite ferrite crystals, (Sr,Ba)Fe12 − xCrxO19 at comparatively low temperatures of about 1300 °C. The sodium based flux led to growth of larger crystals up to 5 mm, but with only minor Cr contents x ≤ 0.07. From the chloride based flux the obtained Cr contents are significantly higher with x = 5.7 (Sr) and x = 3.4 (Ba), however, crystals reach only sizes in the sub-mm range. X-ray absorption spectroscopy data support exclusively isovalent substitution of Fe3+ by Cr3+ even for very low Cr contents. 57Fe Mößbauer spectroscopy reveals Cr to preferentially occupy the six-fold by oxygen coordinated site at 12k and, to a lower degree, 2a and 4f2 in space group P63/mmc. All characteristic magnetic properties drop upon Cr substitution, e. g., the Curie temperature from 728 K for pure BaFe12O19 to 465 K for BaFe8.6Cr3.4O19, the saturation magnetization from 71 emu/g to 29.7 emu/g and the coercive field from 363 Oe to 45 Oe.
Keywords: Hexaferrites; Chromium; Mößbauer; Magnetism

Publ.-Id: 23013 - Permalink


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