Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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32228 Publications
Experimental studies of contact angle hysteresis phenomena on polymer surfaces — Toward the understanding and control of wettability for different applications
Grundke, K.; Pöschel, K.; Synytska, A.; Frenzel, R.; Drechsler, A.; Nitschke, M.; Cordeiro, A. L.; Uhlmann, P.; Welzel, P. B.;
Contact angle hysteresis phenomena on polymer surfaces have been studied by contact angle measurements using sessile liquid droplets and captive air bubbles in conjunction with a drop shape method known as Axisymmetric Drop Shape Analysis — Profile (ADSA-P). In addition, commercially available sessile drop goniometer techniques were used. The polymer surfaces were characterized with respect to their surface structure (morphology, roughness, swelling) and surface chemistry (elemental surface composition, acid–base characteristics) by scanning electron microscopy (SEM), scanning force microscopy (SFM), ellipsometry, X-ray photoelectron spectroscopy (XPS) and streaming potential measurements.
Heterogeneous polymer surfaces with controlled roughness and chemical composition were prepared by different routes using plasma etching and subsequent dip coating or grafting of polymer brushes, anodic oxidation of aluminium substrates coated with thin polymer films, deposition techniques to create regular patterned and rough fractal surfaces from core–shell particles, and block copolymers. To reveal the effects of swelling and reorientation at the solid/liquid interface contact angle hysteresis phenomena on polyimide surfaces, cellulose membranes, and thermo-responsive hydrogels have been studied. The effect of different solutes in the liquid (electrolytes, surfactants) and their impact on contact angle hysteresis were characterized for solid polymers without and with ionizable functional surface groups in aqueous electrolyte solutions of different ion concentrations and pH and for photoresist surfaces in cationic aqueous surfactant solutions.
The work is an attempt toward the understanding of contact angle hysteresis phenomena on polymer surfaces aimed at the control of wettability for different applications.
Keywords: Contact angle hysteresis Polymer surfaces Morphological and chemical heterogeneity Swelling and reorientation at the solid/liquid interface Different solutes in the liquid

Publ.-Id: 21548 - Permalink


Flow measurements in continuous casting models by means of contactless inductive flow tomography under the influence of electromagnetic brakes
Ratajczak, M.; Wondrak, T.; Stefani, F.; Timmel, K.; Eckert, S.;
Most of the steel in the world is produced by continuous casting, where liquid metal flows from a tundish through a submerged entry nozzle into a copper mould. The mould is cooled by water, so a solid shell starts to form at the mould walls. The resulting steel strand is pulled out of the mould continuously and solidifies completely.
In industry it is well-known that an unstable flow in the mould has negative effects on the resulting steel’s quality. Electromagnetic brakes (EMBr) are expected to dampen instabilities, although their impact on the flow can hardly be examined directly in liquid steel. In spite of the casting method’s economical and industrial importance, only a few simple measurement techniques are available to investigate the actual flow patterns in the mould. A more sophisticated technique for liquid metal flow measurements could help to resolve the open issues in the mould flow.
The contactless inductive flow tomography (CIFT) is a technique that measures the mean global flow of an electrically conducting melt by exposing it to a magnetic excitation field and measuring the flow induced perturbations of that field outside the melt. The velocity profile can then be calculated by solving an inverse problem, using adequate regularization techniques to deal with the non-uniqueness.
We present preliminary results for a physical model of a mould with a rectangular cross-section of 140 × 35 mm 2 in the presence of an EMBr. Additionally we show flow reconstructions for a 400 × 100 mm 2 mould, demonstrating the upward scalability of CIFT.
  • Lecture (Conference)
    3rd International Workshop on Measuring Techniques for Liquid Metal Flows (MTLM2015), 15.-17.04.2015, Dresden, Deutschland

Publ.-Id: 21547 - Permalink


Hyperdoping silicon with selenium: solid vs. liquid phase epitaxy
Zhou, S.; Liu, F.; Prucnal, S.; Gao, K.; Khalid, M.; Baehtz, C.; Posselt, M.; Skorupa, W.; Helm, M.;
Chalcogen-hyperdoped silicon shows potential applications in silicon-based infrared photodetectors and intermediate band solar cells. Due to the low solid solubility limits of chalcogen elements in silicon, these materials were previously realized by femtosecond or nanosecond laser annealing of implanted silicon or bare silicon in certain background gases. The high energy density deposited on the silicon surface leads to a liquid phase and the fast recrystallization velocity allows trapping of chalcogen into the silicon matrix. However, this method encounters the problem of surface segregation. In this paper, we propose a solid phase processing by flash-lamp annealing in the millisecond range, which is in between the conventional rapid thermal annealing and pulsed laser annealing. Flash lamp annealed selenium-implanted silicon shows a substitutional fraction of ≈ 70% with an implanted concentration up to 2.3%. The resistivity is lower and the carrier mobility is higher than those of nanosecond pulsed laser annealed samples. Our results show that flash-lamp annealing is superior to laser annealing in preventing surface segregation and in allowing scalability.
Keywords: Ion implantation, Solid phase epitaxy, Deep level impurity, Si

Publ.-Id: 21546 - Permalink


Ion irradiation and nanoindentation as a screening test for irradiation effects on neutron-irradiated ferritic/martensitic high-Cr steels
Heintze, C.; Akhmadaliev, S.; Altstadt, E.; Bergner, F.;
A combined approach based on ion irradiation and nanoindentation as a screening test procedure for the irradiation response of structural materials foreseen for components exposed to heavy neutron irradiation has been selected and specified in detail. Important constituents of the approach are:
• Design of the ion irradiation experiments using the MD code SRIM and taking into account recommendations according to [1], detailed documentation of the irradiation experiments and the SRIM calculations,
• Nanoindentation testing over a large range of indentation depths (from about 5% to 100% of the thickness of the ion-irradiated layer) to gain information on the indentation size effect and the substrate effect, analysis according to the Oliver-Pharr method [2,3],
• Elimination of the indentation size effect (ISE) based on an unirradiated reference sample of the same material using a suitable model (e.g. [4]), elimination of the substrate effect.

A version of the approach specified above was applied to unirradiated, ion-irradiated and neutron-irradiated 9%Cr F/M steel T91 (MATTER reference material). The findings indicate that the approach based on ion irradiation and nanoindentation is suitable as a screening test for F/M steels exposed to neutron irradiation.

References
[1] R. E. Stoller, M. B. Toloczko, G. S. Was, A. G. Certain, S. Dwaraknath, F. A. Garner, Nucl. Instrum. Methods Phys. Res. B 310 (2013) 75–80.
[2] W. C. Oliver, G. M. Pharr, J. Mater. Res., 7 (1992) 1564–1583.
[3] W. C. Oliver, G. M. Pharr, J. Mater. Res., 19 (2004) 3–20.
[4] W. D. Nix, H. Gao, J. Mech. Phys. Solids, 46 (1998) 411–425.
Keywords: ion irradiation, neutron irradiation, nanoindentation, irradiation hardening, ferritic/martensitic steels, T91
  • Lecture (Conference)
    MATTER - “MATerials TEsting and Rules“ Project Final Workshop, 20.-22.10.2014, Rom, Italy

Publ.-Id: 21544 - Permalink


The Zn-vacancy related green luminescence and donor-acceptor pair emission in ZnO grown by pulsed laser deposition
Wang, Z.; Su, S. C.; Younas, M.; Ling, F. C. C.; Anwand, W.; Wagner, A.;
Low temperature (10 K) photoluminescence study shows that green luminescence (GL) peaked at 2.47 eV and near band edge (NBE) emission at 3.23 eV are introduced in undopd ZnO grown by pulsed laser deposition (PLD) after the 900°C annealing. The NBE emission exhibiting blue shift with increasing temperature is assigned to the transitions of donor-acceptor-pair (DAP)/free-electron-to-acceptor (FA). Positron annihilation spectroscopy (PAS) study shows that the introduction of the GL is correlated with the formation of the Zn vacancy-related defect (VZn). Comparing the transition energies of VZn obtained by the previous first principle calculation [Janotti and Van de Walle, Phys. Rev. B 76, 165202 (2007)], the GL is associated with the transition from the conduction band to the ε(-/2-) state of VZn and the DAP/FA emission involves the acceptor level ε(0/-) of VZn.
Keywords: ZnO, green luminescence, Zn vacancy

Publ.-Id: 21543 - Permalink


Influence of the discharge regime on Ti thin films growth and properties in dc, single pulsed and chopped high power impulse magnetron sputtering
Meško, M.; Heller, R.; Hübner, R.; Krause, M.;
High power impulse magnetron sputtering (HiPIMS) has been becoming an appealing deposition process for synthesis of high quality coatings over the last decade. It utilizes average power similar to the dc magnetron sputtering (DCMS) applied on magnetron target, which is however concentrated in short pulses. This ensures generation of dense plasmas with high fraction of ionized film forming species. Control over the energy and trajectory of ionized sputtered species can lead to the formation of coatings with improved properties. Despite of certain advantages the HiPIMS process has often a lower deposition rate compared to DCMS. This is one reason which hinders the HiPIMS process from further exploration in industrial applications. However more recently it has been shown that deposition rates of Ti thin films can be significantly increased by so called chopped-HiPIMS (c-HiPIMS) technique [1]. In this case a single HiPIMS pulse is decomposed into several individual pulses with microsecond pulse off-times. C-HiPIMS can be especially effective in suppression of thermal spikes on the target. The effect of thermal spikes is most pronounced during long single HiPIMS pulses. It negatively influences mobility of arriving ad-atoms leading to the formation of larger grains and rougher surface of Ti thin films [2]. In present work we compare the density, crystallinity, roughness, and microstructure of Ti thin films prepared by dc, single pulsed, and c-HiPIMS. Much attention has been paid on role of microsecond pulse off-times on Ti thin films properties. Plasma parameters have been measured to supplement our investigations.
References:
[1] P. M. Barker, E. Lewin, and J. Patscheider “Modified high power impulse magnetron sputtering process for increased deposition rate of titanium” J. Vac. Sci. Technol. A 31 (2013) 0606041
[2] F. J. Jing, T. L. Yin, K. Yukimura, H. Sun, Y. X. Leng, and N. Huang “Titanium film deposition by high-power impulse magnetron sputtering: Influence of pulse duration” Vacuum 86 (2012) 2114
Keywords: HiPIMS, Ti thin film, microstructure, plasma parameters
  • Poster
    14th International Conference on Plasma Surface Engineering, 15.-19.09.2014, Garmisch-Partenkirchen, Deutschland

Publ.-Id: 21542 - Permalink


The effect of He on irradiation hardening of Fe-9Cr-based non-ODS and ODS alloys at 300°C
Heintze, C.; Kögler, R.; Bergner, F.; Hernández Mayoral, M.;
The influence of helium on the irradiation hardening and embrittlement of reduced-activation ferritic/martensitic Cr-steels and their oxide dispersion strengthened variants under fusion-relevant irradiation conditions is still a concern. While the fact that He can influence the mechanical properties is well established [1,2], the underlying mechanisms are not fully understood [1,2]. In this work the effect of He and displacements per atom (dpa) on the irradiation-induced hardening of an Fe-9at%Cr alloy, Eurofer97 and an oxide dispersion strengthened variant of Eurofer (ODS-Eurofer) at 300°C was studied. Self-ion irradiation was applied to simulate the neutron-irradiation-induced damage. To separate the effect of helium different irradiation modes were applied. Apart from single-beam irradiations with He or self-ions, only, Helium was implanted prior to (pre-implantation), simultaneously (dual-beam irradiation) or following the (post-implantation) self-ion irradiation. The ion irradiated layer was characterized by means of nanoindentation. We conclude, that:
• there is a significant interaction between dpa and He
• pre-implantation of He followed by self-ion irradiation is not suitable to replace simultaneous irradiations or to simulate neutron irradiation induced damage
• nano-oxides in ODS-Eurofer mitigate the effect of helium on irradiation hardening

[1] H. Trinkaus, B.N. Singh, J. Nucl. Mater. 323 (2003) 229
[2] R. Schäublin, Y.L. Chiu, J. Nucl. Mater. 362 (2007) 152
Keywords: irradiation hardening, ODS, dual-beam, ion irradiation, nanoindentation
  • Poster
    2nd International Workshop on ODS Materials, 26.-27.06.2014, Dresden, Deutschland

Publ.-Id: 21541 - Permalink


Using nature's genius for pollutant detection
Raff, J.; Weinert, U.; Nikolaus, N.; Guenther, T.; Strehlitz, B.; Pollmann, K.;
In all environments single cell organisms such as bacteria are directly affected by changing and sometimes extreme environmental conditions. This includes not only pH, temperature and salinity but also the presence of toxic ions, compounds and complexes. It is thusly essential for these microorganisms to possess a robust and selectively permeable cell surface. For this purpose, many bacteria form a proteinaceous cell envelope, the so called surface layer (S-layer). This cell envelope has different functions in different organisms for example the binding of toxic metals and metalloids to protect cells from being damaged by these elements. On other cells, S-layers may act as immobilization matrix for exoenzymes, as molecular sieve or as ion and molecule trap or they protect the cell from being affected by other bacteria or by lytic enzymes. S-layers are composed of identical protein or glycoprotein monomers, which are able to self-assemble to highly ordered monomolecular layers. They form para-crystalline sheets in suspension, on interfaces and on surfaces. Furthermore, on the surface of such a layer different functional groups are available which can be modified without the loss of its structure. The protein layers are in general mechanically and chemically highly stable. These properties make S-layers very interesting building blocks for the construction of new bioinspired nanomaterials and nanocoatings. Using the two-dimensional protein arrays in combination with layer-by-layer technique different kinds of technical surfaces can be functionalized.
This technique is used to design a new kind of sensory layers which will allow detecting small amounts of analytes with high selectivity. This sensory device will consist of an S-layer coating, a selective receptor and two fluorescence dyes. Aptamers were used as compound specific receptors . These are short, single stranded nucleic acid oligomers that meet the requirements for a more selective and sensitive detection of pollutants in nature, medicine and industry. Aptamers are able to recognize almost all classes of substrates and bind them in analogy to antigen-antibody interactions. By using an in vitro selection and amplification technique aptamers can be developed for pollutants like heavy metals, pharmaceuticals but also for proteins and complex targets like viruses and microbial spores. Currently, several aptamers for different antibiotics have been selected and experiments confirmed their high selectivity for single antibiotics or groups of antibiotics. As third component two fluorescence dyes allowing a FRET as signal transducer system will be coupled onto the S-layer lattice. This setup can be combined in different ways to optimize the sensitivity and selectivity of the sensor. Comparable to the binding of exoenzymes on S-layer carrying cells the three sensor components can also be linked to S-layer coated technical surfaces. In first experiments we coupled the model aptamer, anti-thrombin-aptamer, on S-layer proteins and proved its functionality after being linked to the protein. Furthermore, we modified S-layer proteins with a FRET pair and proved the energy transfer between them. We used a FRET pair containing a green and red fluorescence dye and succeed to detect a FRET between the S-layer linked fluorescence dyes. The FRET efficiency was 40 %. Because of the regular arranged functional groups on the S-layer lattice, coupling of the sensor components can be done in a defined and reproducible way.
In further work we will combine all components, aptamers and fluorescence dyes, on the S layer proteins. The aptamer will bind the specific analyte, affecting also the fluorescence dyes and disturbing FRET because of their close proximity to each other. In result a sensory layer is developed which uses the high specificity of aptamers and fluorescence dyes for an easy detection due to an optical signal. Additionally, in the future other techniques such as phage surface display will be used to select also peptide based binding molecules. Hopefully, this will allow detecting even more and also other kinds of pollutants not being bound by aptamers.
Keywords: S-layer, aptamer, biosensor, FRET
  • Invited lecture (Conferences)
    Rapid Methods Europe 2014, 03.03.-02.04.2014, Noordwijkerhout, Niederland

Publ.-Id: 21540 - Permalink


Transport in mesoscopic conductors
Erbe, A.;
Electronic transport in mesoscopic structures

The size of electrical components has been scaled down by several orders of magnitude during the past decades arriving at structure sizes of only tens of nanometers in modern circuits. Electrical current on the nanocale obeys different laws than in macroscopic conductors. The resistance of macroscopic conductors is described by Ohm’s law, assuming diffusive charge transport carried by the conduction electrons. At small length scales this concept cannot be applied any more, electrons move ballistically at these length scales and transport needs to be described using a scattering approach. We will review the concepts used to describe mesoscopic conductors and give examples for typical structures that can be treated using these concepts.

Molecular electronics

The use of single molecules as active elements in electrical circuits may serve as alternative technology for building integrated circuits on the nanoscale. In this presentation we want to give an overview on various techniques that have been used successfully to contact single molecules and to characterize them electrically. Especially the comparison between different techniques shows that a single measurement is always prone to artifacts originating from the unknown microscopic details of the junctions. It is therefore necessary to perform a statistically relevant number of measurements in order to resolve molecular properties. Using these techniques various properties of the molecules can be studied. Special examples are the influence of conformational changes of the molecules, differences between various coupling endgroups of the molecules, effects of light-irradiation onto the molecular junctions, and the influence of self-organization in DNA nanostructures.
  • Invited lecture (Conferences)
    PIER summer school, 06.-09.10.2014, Hamburg, Deutschland

Publ.-Id: 21539 - Permalink


Introduction to transport in confined geometries an across point contacts
Erbe, A.;
The size of electrical components has been scaled down by several orders of magnitude during the past decades arriving at structure sizes of only tens of nanometers in modern circuits. Electrical current on the nanocale obeys different laws than in macroscopic conductors. The resistance of macroscopic conductors is described by Ohm’s law, assuming diffusive charge transport carried by the conduction electrons. At small length scales this concept cannot be applied any more, electrons move ballistically at these length scales and transport needs to be described using a scattering approach. We will review the concepts used to describe mesoscopic conductors and give examples for typical structures that can be treated using these concepts.
Mechanically controllable breakjunctions (MCBJs) are excellent tools to form stable metallic contacts consisting of single atoms, only. In these devices, a tiny metallic bridge is broken by mechanically bending the underlying substrate. During the breaking, the number of atoms taking part in the conduction is reduced gradually, leading to a step-wise decrease of the conductance of the whole junction. This behavior is understood by taking the atomic orbitals, which contribute to the conductance mechanism, into account1. We will show how the experimental results showing this behavior can be obtained and compared to theoretical predictions. Apart from being a fascinating model system for mesoscopic conductance, MCBJs can be used for making contacts to other nanoscale conductors, such as single molecules. We will give a brief introduction on the transport mechanisms involved in single molecule conductance and show measurements of such systems using MCBJs2.

1. Scheer, E. et al. The signature of chemical valence in the electrical conduction through a single-atom contact. Nature 394, 154–157 (1998).
2. Zotti, L. A. et al. Revealing the Role of Anchoring Groups in the Electrical Conduction Through Single-Molecule Junctions. Small 6, 1529–1535 (2010).
  • Invited lecture (Conferences)
    MAINZ summer school, 25.-29.08.2014, Mainz, Deutschland

Publ.-Id: 21538 - Permalink


Benchmarking of reactive transport visualisation (PET) by numerical modelling with COMSOL Multiphyiscs and PhreeqC
Lippmann-Pipke, J.; Kulenkampff, J.; Lippold, H.; Stuhlfauth, C.; Gerasch, R.; Gründig, M.;
For about a decade we apply positron emission tomography (PET) as molecular imaging modality for non-destructive process visualisation in geological material on laboratory scale [1]. Sequential PETimages directly yield the spatiotemporal concentration distribution of a PET radiotracer (3D+t) in the course of the process, with a resolution of ~1 mm and tracer sensitivity to some ten thousand atoms per 1 mm³ voxel. Our PET data sets are typically complemented by μCT-images. We demonstrated its advantages for elucidating heterogeneous processes on different time scales, conservative and reactive flow experiments, including the transport of nano-particles. We considered our 3D+t data sets as highly valuable for benchmarking of reactive transport modelling results. In the recent past we have consequently gained some experiences in aligning differently complex data sets (up to 3D, (non-)reactive) with available modelling tools. As suitable for aligning our data with well-established transport codes we identified Comsol Multiphysics for the transport process parameter estimation, PhreeqC for the geochemical reaction simulation, as well as couplings of both for reactive transport processes in 2D at the mm to cm scale. Benchmarks in 3D+t have their strength in emphasising on the role of heterogeneity on macroscopic reaction rates. Here, retroactions from geochemical reactions on the effective transport pathways in geological media (dissolution, precipitation, filtration, etc.) cause spatial and temporal variations of their transport properties - processes verifiable by our non-destructive PET method.
We aim at developing into this highest complexity level of reactive transport benchmarking; the backcoupling of reaction on structural transport parameter values (porosity, permeability).
REFERENCES
[1] Kulenkampff, J. et al., 2013. Application of high-resolution positron-emission-tomography for quantitative spatiotemporal process monitoring in dense material. 7. World Congress on Industrial Process Tomography, Krakow, Poland, http://www.isipt.org/worldcongress/7/902.html (free access after registration)
  • Poster
    Interpore Conference, 18.-21.05.2015, Padova, Italy

Publ.-Id: 21537 - Permalink


Development of a Compton Camera for online ion beam range verification via prompt gamma detection
Aldawood, S.; Böhmer, M.; Bortfeldt, J.; Castelhano, I.; Dedes, G.; Lutter, R.; Gernhäuser, R.; Kolff, H. V. D.; Lang, C.; Maier, L.; Petzoldt, J.; Römer, K.; Pausch, G.; Fiedler, F.; Schaart, D. R.; Parodi, K.; Thirolf, P. G.; Auer, M.;
Precise and preferably online ion beam range verification is a mandatory prerequisite to fully exploit the advantages of hadron therapy in cancer treatment. Our aim is to develop an imaging system based on a Compton camera designed to detect prompt gamma-rays induced by nuclear reactions between the ion beam and biological tissue. The Compton camera prototype consists of a stack of six customized double-sided Si-strip detectors (DSSSD, 50x50 mm2,128 strips/side) acting as scatterer, while the absorber is formed by a monolithic LaBr3:Ce scintillator crystal (50x50x30mm3) read out by a position-sensitive multi-anode photomultiplier (Hamamatsu H9500). This camera has the ability to not only detect the scattered photon, but it can also track the scattered Compton electron due to the way of designing and arranging the scatter detectors, and the multi-MeV energy of the incidentprompt gamma-rays[1].Thereflectively wrapped LaBr3:Ce detector was characterized with calibration sources, showing an excellent performance of this crystal. The time resolution was determined to be 273ps and the relative energy resolution at 662 keV was found to be 3.8%.The study of the DSSSD detectors together with the full Compton camera properties are inprogress both in the laboratory as well as at the online facilities.

References
[1] C. Lang et al., Journal of Instrumentation 9 (2014) P01008.
This work is supported by the DFG Cluster of Excellence MAP (Munich-Centre for Advanced Photonics)
Keywords: Compton Camera, range verification, particle therapy
  • Poster
    International Workshop on Range Assessment and Dose Verification in Particle Therapy, 29.-30.09.2014, Dresden, Germany

Publ.-Id: 21536 - Permalink


Entwicklung von Elektromagneten mit kurzen, hohen Strompulsen für die laserbasierte Protonentherapie
Schürer, M.; Herrmannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Sobiella, M.; Pawelke, J.;
  • Poster
    5. Dresdner Medizintechnik Symposium, 01.-03.12.2014, Dresden, Deutschland
  • Contribution to proceedings
    5. Dresdner Medizintechnik Symposium, 01.-03.12.2014, Dresden, Deutschland
    A. Förster, J. Füssel, M. Gelinsky, E. Koch, H. Malberg, W. Vonau (Hrsg.): Biomedizinische Technik – Von der Grundlagenforschung zum Transfer. Reports on Biomedical Engineering, Stuttgart: Steinbeis-Edition, ISBN 978-3-95663-018-7, 94

Publ.-Id: 21535 - Permalink


Turbulent amplification of magnetic fields in laboratory laser-produced shock waves
Meinecke, J.; Doyle, H. W.; Miniati, F.; Bell, A. R.; Bingham, R.; Crowston, R.; Drake, R. P.; Fatenejad, M.; Koenig, M.; Kuramitsu, Y.; Kuranz, C. C.; Lamb, D. Q.; Lee, D.; Macdonald, M. J.; Murphy, C. D.; Park, H.-S.; Pelka, A.; Ravasio, A.; Sakawa, Y.; Schekochihin, A. A.; Scopatz, A.; Tzeferacos, P.; Wan, W. C.; Woolsey, N. C.; Yurchak, R.; Reville, B.; Gregori, G.;
X-ray and radio observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. Field coincident with the outer shock probably arises through a nonlinear feedback process involving cosmic rays. The origin of the large magnetic field in the interior of the remnant is less clear but it is presumably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas9. However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar butt bank formed before the supernova explosion. Here we investigate the possibility that turbulent amplification is induced when the outer shock overtakes dense clumps in the ambient medium. We report laboratory experiments that indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. The experiment also provides a laboratory example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena.

Publ.-Id: 21534 - Permalink


Experimental demonstration of an inertial collimation mechanism in nested outflows
Yurchak, R.; Ravasio, A.; Pelka, A.; Pikuz, S.; Falize, E.; Vinci, T.; Koenig, M.; Loupias, B.; Benuzzi-Mounaix, A.; Fatenejad, M.; Tzeferacos, P.; Lamb, D. Q.; Blackman, E. G.;
Interaction between a central outflow and a surrounding wind is common in astrophysical sources powered by accretion. Understanding how the interaction might help to collimate the inner central outflow is of interest for assessing astrophysical jet formation paradigms. In this context, we studied the interaction between two nested supersonic plasma flows generated by focusing a long-pulse high-energy laser beam onto a solid target. A nested geometry was created by shaping the energy distribution at the focal spot with a dedicated phase plate. Optical and x-ray diagnostics were used to study the interacting flows. Experimental results and numerical hydrodynamic simulations indeed show the formation of strongly collimated jets. Our work experimentally confirms the “shock-focused inertial confinement” mechanism proposed in previous theoretical astrophysics investigations.

Publ.-Id: 21533 - Permalink


Fabrication of highly efficient transparent metal thin film electrodes using Direct Laser Interference Patterning
Eckhardt, S.; Müller-Meskamp, L.; Siebold, M.; Fabián Lasagni, A.;
The demand of highly efficient transparent electrodes without the use of rare earth materials such as indium requires a new generation of thin metallic films with both high transparency and electrical conductivity. For this purpose, Direct Laser interference Patterning was used to fabricate periodic hole-like surface patterns on thin metallic films in order to improve their optical transparency by selective laser ablation of the material and at the same time keeping the electrical properties at an acceptable level.
Metallic films consisting of aluminum and copper with film thicknesses ranging between 5 and 40 nm were deposited on glass substrates and treated with nanosecond and picosecond pulse laser system..In order to analyze the processability of the films, the laser ablation threshold for each material as function of the layer thickness and pulse duration was firstly determined. After analyzing these initial experiments, the samples were structured with a 1.7 μm spatial period hole-like-pattern using three beam direct laser interference patterning. The structural quality of the fabricated structures was analyzed as function laser energy density (laser fluence) using scanning electron microscopy (SEM), atom force microscopy (AFM). Finally, optical and electrical properties of the films were characterized using optical spectroscopy, as well as surface impedance measurements.
Keywords: direct laser interference patterning, metallic thin films, large area surface functionalization
  • Contribution to proceedings
    SPIE Photonics West - LASE, 07.-12.02.2015, San Francisco, USA
    Laser-Based Micro- and Nanoprocessing IX, 9351
    DOI: 10.1117/12.2082537

Publ.-Id: 21532 - Permalink


Realizing a reference setup for irradiation experiments with laser-accelerated proton pulses (at the Draco laser)
Obst, L.; Zeil, K.; Metzkes, J.; Kraft, S.; Schramm, U.;
By focusing an ultra-short high-intensity laser pulse on a solid target, pulses of protons and other positively charged ions with energies of several 10 MeV per nucleon are generated. The properties of these particle beams such as their energy and absolute number are highly dependent on experimental conditions like laser and target parameters. In order to achieve principal comparability between different experimental campaigns at the Draco laser system at the Helmholtz-Zentrum Dresden-Rossendorf, a reference setup for the laser ion acceleration experiment was established. A configuration is sought in which proton beams of reproducible characteristics are generated. To ensure a high stability of the proton spectra, the application of longer focal length parabolas (f ~ 1000 mm) will be tested for this setup, according preparatory studies being presented in this talk.
Keywords: accelerators, laser-driven proton acceleration, high-intensity lasers, beams and electromagnetism
  • Lecture (Conference)
    DPG-Tagung 2014, 17.-21.03.2014, Berlin, Deutschland

Publ.-Id: 21531 - Permalink


Comparative investigation of three dose rate meters for their viability in pulsed radiation fields.
Gotz, M.; Karsch, L.; Pawelke, J.;
Pulsed radiation fields, characterized by microsecond pulse duration and correspondingly high pulse dose rates, are increasingly used in therapeutic, diagnostic and research applications. Yet, dose rate meters which are used to monitor radiation protection areas or to inspect radiation shielding are mostly designed, characterized and tested for continuous fields and show severe deficiencies in highly pulsed fields. Despite general awareness of the problem, knowledge of the specific limitations of individual instruments is very limited, complicating reliable measurements. We present here the results of testing three commercial dose rate meters, the RamION ionization chamber, the LB 1236-H proportional counter and the 6150AD-b scintillation counter, for their response in pulsed radiation fields of varied pulse dose and duration. Of these three the RamION proved reliable, operating in a pulsed radiation field within its specifications, while the other two instruments were only able to measure very limited pulse doses and pulse dose rates reliably.

Publ.-Id: 21530 - Permalink


Laserbasierte Teilchenbeschleunigung und deren Anwendung in der Strahlentherapie
Pawelke, J.;
  • Invited lecture (Conferences)
    Referententagung des Strahlenschutzseminar in Thüringen e.V., 15.-16.03.2013, Heyda, Deutschland

Publ.-Id: 21529 - Permalink


Concept of a compact gantry for laser based proton therapy.
Karsch, L.; Bussmann, M.; Enghardt, W.; Kroll, F.; Masood, U.; Pawelke, J.;
  • Poster
    52th Particle Therapy Cooperative Group (PTCOG) Meeting, 02.-08.06.2013, Essen, Deutschland
  • Contribution to proceedings
    52th Particle Therapy Cooperative Group (PTCOG) Meeting, 02.-08.06.2013, Essen, Deutschland
    Proceedings of the 52th Particle Therapy Cooperative Group (PTCOG) Meeting, 312

Publ.-Id: 21528 - Permalink


Einfluss der Pulslänge auf die Sättigungskorrektur von Ionisationskammern in gepulsten Strahlungsfeldern.
Gotz, M.; Karsch, L.; Pawelke, J.;
  • Lecture (Conference)
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
  • Contribution to proceedings
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
    H. Treuer (Ed.): Medizinische Physik 2013, Deutsche Gesellschaft für Medizinische Physik e. V., ISBN 978-3-9816002-1-6, 318-321

Publ.-Id: 21527 - Permalink


Optimierung der Bestrahlungsplanungsstrategie für laserbeschleunigte Protonen.
Findeisen, A.; Karsch, L.; Masood, U.; Pawelke, J.;
  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
  • Contribution to proceedings
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik (DGMP), 18.-21.09.2013, Köln, Deutschland
    H. Treuer (Ed.): Medizinische Physik 2013, Deutsche Gesellschaft für Medizinische Physik e. V., ISBN 978-3-9816002-1-6, 714-715

Publ.-Id: 21526 - Permalink


Proton therapy in Dresden: present and future
Pawelke, J.;
  • Invited lecture (Conferences)
    International Conference on the Future of Radiation Oncology: Imaging, Dosimetry, Biology and Therapy (7th Berder Workshop), 25.-28.09.2013, Berder Island, France

Publ.-Id: 21525 - Permalink


Review on radiobiological studies using laser driven particle beams:From in vitro experiments to human tumor irradiations on mice
Pawelke, J.;
  • Invited lecture (Conferences)
    International Workshop on Microbeam Probes of Cellular Radiation Response (11th Microbeam Workshop), 03.-04.10.2013, Bordeaux, Frankreich

Publ.-Id: 21524 - Permalink


Development of a compact particle therapy facility with laser- driven ion beams via novel pulse powered gantry systems
Masood, U.; Bussmann, M.; Baumann, M.; Cowan, T. E.; Enghardt, W.; Herrmannsdörfer, T.; Hofmann, K. M.; Kaluza, M.; Karsch, L.; Kroll, F.; Schramm, U.; Schürer, M.; Wilkens, J. J.; Pawelke, J.;
  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 27-28
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Publ.-Id: 21523 - Permalink


A treatment planning study to assess the feasibility and the limitations of laser-driven proton therapy
Hofmann, K. M.; Masood, U.; Pawelke, J.; Wilkens, J. J.;
  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 29
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Publ.-Id: 21522 - Permalink


Wechselwirkung langsamer hochgeladener Ionen mit Ionenkristalloberflächen und ultradünnen Kohlenstoffmembranen
Wilhelm, R. A.;
In der vorliegenden Arbeit wurde die Strukturbildung durch Einzeleinschlag von langsamen hochgeladenen Ionen (v < 5·10^5 m/s, Q < 40) auf Ionenkristalloberflächen und freistehenden amorphen Kohlenstofffolien untersucht. Mittels experimenteller Methoden der Rasterkraft-, Transmissionselektronen- und Heliumionenmikroskopie wurden die in jüngster Zeit gewonnenen Modellbeschreibungen für Nanostrukturbildung an Oberflächen erweitert. Beim Auftreffen eines langsamen hochgeladenen Ions auf die (001)-Oberfläche von KCl können Nanostrukturen mit Ausdehnungen bis zu einigen 10nm entstehen. Die damit verknüpften Desorptionsausbeuten von bis zu 3000 Atomen pro Ion aus der Oberfläche werden vor allem durch die Deposition der potentiellen Energie in sehr oberflächennahe Schichten erklärt. Die kinetische Energie der Ionen wirkt jedoch unterstützend auf die Entstehung und Vergrößerung der Lochstrukturen. Die Entstehung der Strukturen durch die potentielle Energie kann konsistent im Bild der defektinduzierten Desorption erklärt werden.
Für die CaF2(111)-Oberfläche konnte gezeigt werden, dass auch unter ununterbrochenen Ultrahochvakuumbedingungen Nanohügel durch Ionenbeschuss erzeugt werden können. Die Größenverteilung beobachteter Nanohügel ist dabei jedoch um einen Faktor 3 kleiner im Vergleich zu atmosphärenexponierten Proben. Der Einfluss der Atmosphäre auf die beobachteten Strukturgrößen wird diskutiert. Für niedrigere Ladungszustände als nötig für Nanohügelerzeugung wurden ioneninduzierte Kristalldefekte durch nasschemisches Ätzen der Oberfläche nachgewiesen. Diese Tatsache verbindet die Beschreibung der Strukturbildung durch elektronische Anregungen in Alkali- und Erdalkalihaliden.
Für den Durchgang von hochgeladenen Ionen durch 1 nm dicke, freistehende und amorphe Kohlenstofffolien zeigte sich, dass Poren durch Einzelioneneinschlag entstehen, sobald ein Schwellwert von etwa Q = 25 in der Ionenladung überschritten wurde. Erstmalig konnte gezeigt werden, dass sich bei der Transmission der Ionen zwei unterschiedliche Ladungszustandsverteilungen bilden. Die Ausbildung der beiden Verteilungen wird durch einen stark stoßparameterabhängigen Ladungsaustausch beschrieben. Neben dem Einfluss der potentiellen Energie bei der Porenbildung ist auch der Einfluss der kinetischen Energie untersucht worden. Um den Anteil nuklearer und elektronischer kinetischer Energieverluste in Abhängigkeit des Ionenladungszustandes abzuschätzen, wurde ein Modell im Rahmen der Beschreibung statistischer Atome bzw. Ionen aufgestellt. Auf Basis dieses Modells wird der Einfluss der kinetischen Energiedeposition und die damit verbunde- ne Synergie aus potentieller und kinetischer Energie bei der Strukturbildung diskutiert.

The formation of nano-structures due to the impact of individual slow highly charged ions (v < 5 · 105 m/s, Q < 40) on surfaces of ionic crystals and 1 nm thick, freestanding and amorphous carbon membranes is investigated in this work. By an experimental approach using atomic force, transmission elec- tron and helium ion microscopy recent model descriptions for the formation processes of highly charged ion induced nano-structures are expanded. Upon impact of slow highly charged ions on the (001)-surface of KCl pit-like structures with sizes up to a few 10nm are found. The corresponding desorption yields of a few thousand atoms per ion are mainly attributed to the deposition of potential energy in a shallow region near the surface. The kinetic energy has only a minor effect on the formation processes. The structure formation due to potential energy deposition is described consis- tently in the framework of a defect induced desorption model.
For the CaF2(111) surface it is shown, that even without breaking the vac- uum between irradiation and analyses ion induced nano-hillocks are present. However, the sizes of the nano-hillocks are about a factor of 3 smaller than the sizes after exposure to atmosphere. The influence of the atmosphere conditions on the structure sizes is discussed. For lower charge states than needed for nano-hillock formation ion-induced defects are revealed by wet- chemical etching of the exposed surfaces. The existence of defects for lower charge states combines the model descriptions of nano-structure formation by strong electronic excitations for alkali and earth-alkali halide surfaces. Pore formation due to highly charged ion impact on 1 nm thick, freestanding and amorphous carbon films is observed for ions with a charge state above a threshold of about Q = 25. It has been shown for the first time that two distinct exit charge state distributions are formed upon transmission of the ions through the membrane. The formation of the distributions is explained
by a strongly impact parameter dependent charge exchange. Besides the influence of the potential energy on the pore formation also the importance of the kinetic energy is investigated. To distinguish between nuclear and electronic losses in the case of highly charged ions at low velocities a model for charge state dependent energy loss is proposed. Based on the descrip- tion of statistical atoms and ions, respectively, the synergy of potential and kinetic energy upon nano-structure formation is discussed.
  • Doctoral thesis
    TU Dresden, 2014
    Mentor: Prof. Jürgen Fassbender / Dr. Stefan Facsko
    149 Seiten

Publ.-Id: 21521 - Permalink


In vivo dose response to laser driven electron beams
Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Hartmann, J.; Kaluza, M.; Karsch, L.; Krause, M.; Laschinsky, L.; Lessmann, E.; Nicolai, M.; Reuter, M.; Sävert, A.; Schnell, M.; Schürer, M.; Pawelke, J.;
  • Contribution to proceedings
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz
    Proceedings of the Joint Conference in Medical Physics, 191
  • Lecture (Conference)
    Joint Conference in Medical Physics, 07.-10.09.2014, Zürich, Schweiz

Publ.-Id: 21520 - Permalink


Laserbasierte Partikeltherapie.
Pawelke, J.;
Laserbasierte Partikeltherapie.
  • Invited lecture (Conferences)
    Symposium “Innovationen in der Radioonkologie”, 24.09.2014, Dresden, Deutschland

Publ.-Id: 21519 - Permalink


Development of short-pulsed high-field electromagnetic dipoles for laser-based proton therapy
Schürer, M.; Herrmannsdörfer, T.; Karsch, L.; Kroll, F.; Masood, U.; Pawelke, J.;
Introduction
During the last years, the new technology of laser based particle acceleration was developed at such a rate that medical application for cancer therapy becomes conceivable. Promising more compact and economic accelerators, the laser technology however generates intense ultra-short (~ ps) pulsed proton beams with large divergence and broad energy spectrum. Within the German joint research project “onCOOPtics” the clinical applicability of such pulsed proton beams is investigated including the development of a laser accelerator and a suitable beam transport.
Methods
A compact beam transport system was designed enabling an efficient transport of proton pulses from generation to treatment site. The initially divergent proton beam is captured by a cylindrical electromagnet (solenoid), deflected by 45° dipole magnets and formed by quadrupole magnets, whereas the spectrum is shaped by adaptable lead apertures. For realization, electromagnetic dipoles with magnetic fields of up to 10 T are required to deflect up to 220 MeV protons. These field strengths are achieved by in-house developed non-ferrous dipoles that consist of 80 copper coils in 12 layers and are operated at peak currents of up to 20 kA. To handle the high currents and the generated heat the dipoles are externally cooled and operated in 1 ms short pulses synchronized with the laser repetition frequency.
Results
The prototype of a short-pulsed electromagnetic dipole magnet was designed and manufactured. Results of the experimental characterization and first performance tests at a conventional Tandem accelerator are under way.
Conclusion
Pulsed electromagnetic dipoles as crucial components of a compact beam line for laser-accelerated protons are engineered. Following validation of their suitability at a conventional accelerator the dipoles will be implemented and further tested at a laser accelerator. Together with improvement of the dipole the design of quadrupoles will start.
  • Open Access LogoAbstract in refereed journal
    Biomedical Engineering / Biomedizinische Technik 59(2014)Suppl 1, 891
    DOI: 10.1515/bmt-2014-5011
  • Lecture (Conference)
    48. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, 08.-10.10.2014, Hannover, Deutschland
  • Poster
    48. Jahrestagung der Deutschen Gesellschaft für Biomedizinische Technik, Hannover, Germany, 8-10 Oct 2014, 08.-10.10.2014, Hannover, Deutschland

Publ.-Id: 21518 - Permalink


Development of laser-driven proton beam therapy
Masood, U.; Bussmann, M.; Cowan, T.; Enghardt, W.; Herrmannsdörfer, T.; Kaluza, M.; Krause, M.; Pawelke, J.; Sauerbrey, R.; Schramm, U.; Baumann, M.;
  • Open Access LogoAbstract in refereed journal
    Annals of Oncology 25(2014)Suppl 4, iv546-iv547
    DOI: 10.1093/annonc/mdu358.3
  • Lecture (Conference)
    Congress of the European Society for Medical Oncology (ESMO) on “Precision Medicine in Cancer Care”, 26.-30.09.2014, Madrid, Spanien
  • Poster
    Congress of the European Society for Medical Oncology (ESMO) on “Precision Medicine in Cancer Care”, 26.-30.09.2014, Madrid, Spanien

Publ.-Id: 21517 - Permalink


Negative magneto- and electroresistance of silicon films with superconducting nanopreciptates - the role of inelastic cotunneling
Heera, V.; Fiedler, J.; Schmidt, B.; Hübner, R.; Voelskow, M.; Skrotzki, R.; Skorupa, W.;
The electronic transport properties of insulating Si:Ga films with superconducting, Ga-rich nanopreciptates are investigated in dependence on temperature, current, and magnetic field. The large negative magnetoresistance, observed below the critical temperature, can be explained by Cooper pair breaking and subsequent tunneling of the fermionic quasiparticles. Localization due to quantum interferences of bosons or fermions, as recently discussed, seems not to be the reason for the insulating state and the large magnetoresistance. Cooper pair tunneling is blocked by the high Coulomb barrier. The quasiparticles can overcome the barrier by inelastic cotunneling that results in nonlinear current-voltage characteristics and negative electroresistance. Since the experimental results obtained for the Si:Ga film resemble that of many other films with superconducting nanoprecipitates the conclusions drawn here could be quite general.
Keywords: disordered films, superconducting precipitates, insulating state, magnetotransport measurement, negative magnetoresistance, inelastic cotunneling

Publ.-Id: 21516 - Permalink


Comparison study of in vivo dose response to laser driven versus conventional electron beam.
Oppelt, M.; Baumann, M.; Bergmann, R.; Beyreuther, E.; Brüchner, K.; Hartmann, J.; Karsch, L.; Krause, M.; Laschinsky, L.; Leßmann, E.; Nicolai, M.; Reuter, M.; Richter, C.; Sävert, A.; Schürer, M.; Schnell, M.; Woithe, J.; Kaluza, M.; Pawelke, J.;
The long-term goal to integrate laser-based particle accelerators into radiotherapy clinics not only requires technological development of high-intensity lasers and new techniques for beam detection and dose delivery, but also characterization of the biological consequences of this new particle beam quality, i.e. ultra-short, ultra-intense pulses. In the present work, we describe successful in vivo experiments with laser-driven electron pulses by utilization of a small tumour model on the mouse ear for the human squamous cell carcinoma model FaDu. The already established in vitro irradiation technology at the laser system JETI was further enhanced for 3D tumour irradiation in vivo in terms of beam transport, beam monitoring, dose delivery and dosimetry in order to precisely apply a prescribed dose to each tumour in full-scale radiobiological experiments. Tumour growth delay was determined after irradiation with doses of 3 and 6 Gy by laser-accelerated electrons. Reference irradiation was performed with continuous electron beams at a clinical linear accelerator in order to both validate the dedicated dosimetry employed for laser-accelerated JETI electrons and above all review the biological results. No significant difference in radiation-induced tumour growth delay was revealed for the two investigated electron beams. These data provide evidence that the ultra-high dose rate generated by laser acceleration does not impact the biological effectiveness of the particles.

Publ.-Id: 21515 - Permalink


Scaling of TNSA-accelerated proton beams with laser energy and focal spot size
Obst, L.; Zeil, K.; Metzkes, J.; Kraft, S.; Schramm, U.;
By focusing an ultra-short high-intensity laser pulse on a solid target, pulses of protons and other positively charged ions with energies of several 10 MeV per nucleon are generated. The properties of these particle beams such as their energy and absolute number are highly dependent on experimental conditions like laser and target parameters. In order to achieve principal comparability between different experimental campaigns at the Draco laser system at the Helmholtz-Zentrum Dresden-Rossendorf, a reference setup for the laser ion acceleration experiment was established. A configuration is sought in which proton beams of reproducible characteristics are generated. To ensure a high stability of the proton spectra, the application of longer focal length parabolas (f ~ 1000 mm) will be tested for this setup, according preparatory studies being presented in this paper.
Keywords: accelerators, laser-driven proton acceleration, high-intensity lasers, beams and electromagnetism
  • Open Access LogoContribution to proceedings
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland
    IPAC2014 - Proceedings, TUPME033
  • Poster
    IPAC'14 - 5th International Particle Accelerator Conference, 15.-20.06.2014, Dresden, Deutschland

Publ.-Id: 21514 - Permalink


Energetic stability of solute–carbon–vacancy complexes in bcc iron
Bakaev, A.; Terentyev, D.; Zhurkin, E. E.; van Neck, D.;
The strong binding between a vacancy and carbon in bcc iron plays an important role in the evolution of radiation-induced microstructure. Our previous ab initio study points to the fact that the vacancy–carbon (V–C) pair can serve as a nucleus for the solute-rich clusters. Here, we continue the ab initio study by considering the interaction of mixed solute clusters (Mn, Ni and Si) with the V–C pair, and the interaction of typical alloying elements of Fe-based steels (i.e., Mn, Ni, Cu, Si, Cr and P) with di-carbon–vacancy pair (V–C2). We have identified the sequence of growth of Ni, Si and Mn solute-rich clusters nucleating on the V–C pair. The mixed-solute–V–C configurations are found to be less stable clusters than pure-solute–V–C clusters with the energy difference up to 0.22 eV per four atoms. The V–C2 pair is found to be as strong nucleation site for the solute-rich clusters as the V–C pair. Only Si solute atom stands out from the trend showing a weaker affinity to the V–C2 complex by 0.09 eV compared to the attraction to the V–C pair. The overall results point to the importance of taking into account the existence of both V–C and V–C2 complexes in studying the formation of solute-rich clusters in Fe-based steels for nuclear applications.
Keywords: Ferritic steels; Minor alloying elements; Carbon; Solute clusters; Ab initio calculations

Publ.-Id: 21513 - Permalink


The pH dependence of Am(III) complexation with acetate: an EXAFS study
Froehlich, D. R.; Skerencak-Frech, A.; Bauer, N.; Rossberg, A.; Panak, P. J.;
The complexation of acetate with Am(III) is studied as a function of the pH (1–6) by extended X-ray absorption fine-structure (EXAFS) spectroscopy. The molecular structure of the Am(III)–acetate complexes (coordination numbers, oxygen and carbon distances) is determined from the raw k3-weighted Am LIIIedge EXAFS spectra. The results show a continuous shift of Am(III) speciation with increasing pH value towards the complexed species. Furthermore, it is verified that acetate coordinates in a bidentate coordination mode to Am(III) (Am—C distance: 2.82 0.03 A ° ). The EXAFS data are analyzed by iterative transformation factor analysis to further verify the chemical speciation, which is calculated on the basis of thermodynamic constants, and the used structural model. The experimental results are in very good agreement with the thermodynamic modelling.
Keywords: americium; acetate; coordination chemistry; EXAFS; ITFA

Publ.-Id: 21512 - Permalink


A new look at the structural properties of trisodium uranate Na3UO4
Smith, A. L.; Raison, P. E.; Martel, L.; Prieur, D.; Charpentier, T.; Wallez, G.; Suard, E.; Scheinost, A. C.; Hennig, C.; Martin, P.; Kvashnina, K. O.; Cheetham, A. K.; Konings, R. J. M.;
The crystal structure of the trisodium uranate, which forms following the interaction between sodium and hyperstoichiometric urania, has been solved for the first time using powder X-ray and neutron diffraction, X-ray Absorption Near-Edge Structure spectroscopy, and solid state 23Na Multi-Quantum Magic Angle Spinning Nuclear Magnetic Resonance. The compound, isostructural with Na3BiO4, has a monoclinic symmetry, in space group P2~c. Moreover, it has been shown that this structure can accommodate some cationic disorder, with up to 16(2)% sodium on the uranium site, corresponding to the composition -Na3(U1−x,Nax)O4 (0 Keywords: Sodium uranate, X-ray diffraction (XRD), Neutron diffraction, XANES, MQMAS NMR

Publ.-Id: 21511 - Permalink


Pushing the Limits of Ferromagnetic Resonance: Detection of Single sub-100-nm Nanodots
Lenz, K.; Banholzer, A.; Narkowicz, R.; Grebing, J.; Stienen, S.; Lindner, J.; Fassbender, J.ORC
Spintronic devices like MRAM, STNOs, or magnonic crystals are based on various types of magnetic nanostructures. Hence, it is crucial to know their magnetic properties, e.g., to allow for proper simulation for further development. The magnetic characterization in terms of magnetic damping, resonance modes, or magnetic anisotropy of single nanosized objects is very challenging, nevertheless of utmost importance, as otherwise bulk or film parameters need to be used for simulations.
Ferromagnetic resonance (FMR) is in principle the ultimate technique to measure such parameters. Unfortunately, conventional FMR based on resonant cavities and even modern broadband coplanar waveguide FMR lacks the sensitivity to measure single sub-micron-sized nano elements. Usually the detection limit of FMR, i.e. the minimum number of spins, which can be detected, is about 1012 spins for permalloy. Up to now, arrays of such elements had to be prepared to overcome this limit. However, great care on a homogeneous sample preparation has to be taken. For example, already slight inhomogeneities between the array's elements render the individual resonant modes of the nanostructures invisible, due to linewidth broadening.
For the analysis of single nanoobjects a much higher sensitivity is required. Using our recently developed microresonators [1,2] we show how single nanoelements down to sample diameters of 100 nm can be measured.
Taking the signal-to-noise ratio achieved so far into account, we extrapolate the detection limit to 105 spins. The uniform excitation mode as well as various localized modes like e.g. edge modes can be observed. Their state can be visualized with micromagnetic simulations.
References:
[1] A. Banholzer, et al., Nanotechnology 22, 295713 (2011).
[2] R. Narkowicz et al., Rev. Sci. Instrum. 79, 084702 (2008).
Keywords: ferromagnetic resonance, nanostructures, damping, spinwaves, microresonators
  • Lecture (Conference)
    59th Annual Magnetism and Magnetics Materials Conference, 04.-07.11.2014, Honolulu, Hawaii, USA

Publ.-Id: 21510 - Permalink


Light emitting diode based on (In,Ga)As/GaAs coaxial multi-shell nanowires monolithically integrated on silicon
Dimakis, E.; Jahn, U.; Ramsteiner, M.; Tahraoui, A.; Grandal, J.; Trampert, A.; Biermanns-Föth, A.; Pietsch, U.; Riechert, H.; Geelhaar, L.;
We demonstrate the use of III-arsenide nanowires as light emitting diodes (LEDs) monolithically integrated on Silicon. LEDs made of (In,Ga)As/GaAs coaxial multi-shell nanowires were grown catalyst-free directly on Si(111) by molecular beam epitaxy (MBE). The active region consists of a single (In,Ga)As/GaAs quantum well in the radial direction (Fig. 1-a). Correlating the emission properties of the quantum wells (Fig. 1-b) with the growth kinetics on the ( ) side-walls, we were able to identify the optimal growth conditions for coherently strained quantum wells with high-quality interfaces and homogeneous structure (in terms of chemical composition and shell thicknesses) along the nanowire axes. Shell-doping methods were successfully employed for the realization of p- and n-type GaAs shells, while a planarization scheme with transparent ohmic contacts allowed massive biasing in parallel configuration of the free-standing nanowires on the Silicon substrate. Rectifying operation and room-temperature electroluminescence were obtained (Fig. 1-c), proving the great potential of this technology.
  • Invited lecture (Conferences)
    Nanowires 2013, 12.11.2013, Weizmann Institute of Science, Rehovot, Israel

Publ.-Id: 21509 - Permalink


Magnetostatics and Dynamics of Ion Irradiated NiFe/Ta Multilayer Films Studied by Vector Network Analyzer Ferromagnetic Resonance
Markó, D.;
In the present work, the implications of ion irradiation on the magnetostatic and dynamic properties of soft magnetic Py/Ta (Py = Permalloy: Ni80Fe20) single and multilayer lms have been investigated with the main objective of nding a way to determine their saturation magnetization. Both polar magneto-optical Kerr eect (MOKE) and vector network analyzer ferromagnetic resonance (VNA-FMR) measurements have proven to be suitable methods to determine 0MS, circumventing the problem of the unknown eective magnetic volume that causes conventional techniques such as SQUID or VSM to fail. Provided there is no perpendicular anisotropy contribution in the samples, the saturation magnetization can be determined even in the case of strong interfacial mixing due to an inherently high number of Py/Ta interfaces and/or ion irradiation with high uences.
Another integral part of this work has been to construct a VNA-FMR spectrometer capable of performing both azimuthal and polar angle-dependent measurements using a magnet strong enough to saturate samples containing iron. Starting from scratch, this comprised numerous steps such as developing a suitable coplanar waveguide design, and writing the control, evaluation, and tting software.
With both increasing ion uence and number of Py/Ta interfaces, a decrease of saturation magnetization has been observed. In the case of the 10Py samples, an immediate decrease of 0MS already sets in at small ion uences. However, for the 1Py and 5Py samples, the saturation magnetization remains constant up to a certain ion uence, but then starts to rapidly decrease. Ne ion irradiation causes a mixing and broadening of the interfaces. Thus, the Py/Ta stacks undergo a transition from being polycrystalline to amorphous at a critical uence depending on the number of interfaces. The saturation magnetization is found to vanish at a Ta concentration of about 10{15 at.% in the Py layers. The samples possess a small uniaxial anisotropy, which remains virtually unaected by the ion uence, but slightly reduces with an increasing number of Py/Ta interfaces. In addition to magnetostatics, the dynamic properties of the samples have been investigated as well. The Gilbert damping parameter increases with both increasing number of Py/Ta interfaces and higher ion uences, with the former having a stronger in uence. The inhomogeneous linewidth broadening B0 increases as well with increasing number of Py/Ta interfaces, but slightly decreases for higher ion uences.
Keywords: ferromagnetic resonance, FMR, thin films, multilayers, ferromagnetism
  • Doctoral thesis
    TU Dresden, 2010
    Mentor: Jürgen Fassbender
    107 Seiten

Publ.-Id: 21508 - Permalink


From 2D CoCrPt:SiO2 films with perpendicular magnetic anisotropy to 3D nanocones — A step towards bit patterned media
Ball, D. K.;
Due to the ever-increasing worldwide consumption of memory for digital information, new technologies for higher capacity and faster data storage systems have been the focus of research and development. A step towards achieving higher data storage densities for magnetic recording media is the concept of bit patterned media, where the magnetic recording layer is divided up into magnetically isolated bit units. This approach is one of the most promising technologies for increasing data storage densities and could be implemented by nanostructuring the wafer. Therefore, the fabrication of the appropriate nanostructures on a small scale and then be able to manufacture these structures on an industrial scale is one of the problems where science and industry are working on a solution. In addition, the answer to the open question about the influence that patterning on the nano length scale has on the magnetic properties is of great interest.
The main goal of this thesis is to answer the open question, which magnetic properties can be tailored by a modification of the surface texture on the nanometre length scale. For this purpose the following properties: anisotropy, remanence, coercivity, switching field distribution, saturation magnetisation, Gilbert damping, and inhomogeneous linebroadening were compared between planar two dimensional thin ferromagnetic films and three dimensional magnetic structures. In addition, the influences of the tailored morphology on the intergranular or the exchange coupling between the structures, which is called interdot exchange coupling, was investigated. For the ferromagnetic thin films, the focus of the investigations was on the granular CoCrPt:SiO2 and [Co/Pd] layer, which currently are the state-of-the-art material for magnetic data storage media. These materials are characterised by their high coercivity and high perpendicular anisotropy, which has a low spatial distribution in the preferred direction of magnetisation.
In this work the pre-structured GaSb(001) substrate with self-assembled periodic nanocone structures at the surface are used. The preparation by ion beam erosion of these structures is simple, fast, and highly reproducible and therefore this method is particularly beneficial for fundamental research. To compare the 2D thin films with the 3D magnetic structures, besides the pre-structured specimen, planar samples were also fabricated. The first sample series prepared was coated by Py. Due to the fact that the magnetic properties of this material are well-known, it was also possible to do some OOMMF simulations in addition to the VNA-FMR and MOKE measurements.
Afterwards two planar samples with CoCrPt and CoCrPt:SiO2 were prepared. The planar CoCrPt:SiO2 samples were Co+ ion implanted to study the influence of such irradiation on the intergranular and interdot exchange coupling, switching field distribution, and in particular on the spin dynamics. Moreover, both samples were measured by TRMOKE in order to obtain information about the spin dynamics.
Subsequently, the perpendicular storage media materials CoCrPt:SiO2 and [Co/Pd] were deposited on a prestructured GaSb(001) nanocone substrate surface. These sample series were measured by MOKE, SQUID, and vector-VSM. The measurements demonstrate the influence of the periodicity and height of the nanocones on the intergranular and interdot exchange coupling. They also show the reorientation of the magnetization with respect to the curvature of the substrate template and furthermore, the morphology-induced influences on the magnetic domains.
From the comparison between the results for the planar and the pre-structured samples, a decrease of the interdot exchange coupling was observed, which scales together with the periodicity of the nanocone pattern. In addition, it was shown that for all samples with thin magnetic films on nanocones,the magnetization aligns along the curvature of the underlying nanocone structure. For Py on nanocones, planar granular CoCrPt:SiO2, and planar granular CoCrPt, measurements by VNA-FMR and TRMOKE could be carried out, which yielded information about the spin dynamics. The results obtained for both of the planar sample are comparable to values from the literature for the Gilbert damping. The results for the Py samples showed that the commonly used 2D model resonance condition is, in case of a 3D magnetic structure, no longer valid due to the alignment of the magnetisation along the underlying substrate structure and therefore an new model has to be derived.
Keywords: Ferromagnetic resonance, VSM, ferromagnetism, MOKE, nanostructures, spin waves
  • Doctoral thesis
    TU Dresden, 2013
    Mentor: Jürgen Fassbender
    132 Seiten

Publ.-Id: 21507 - Permalink


Method for evaluation of upgrading by liberation and separation
Leißner, T.; Mütze, T.; Atanasova, P.; Bachmann, K.; Peuker, U. A.;
A method is presented for the evaluation of mineral processing by liberation and upgrading. The method bases on the plot of recovery of valuables versus the recovery of gangue (Fuerstenau upgrading curve). The locking curve of a feed material was plotted together with the upgrading curve in a Fuerstenau diagram. The assessment of liberation and upgrading is done by a comparison of surfaces formed by the curves and some characteristic lines of the diagram. This plot allows the calculation of two new quantitative measures for liberation and upgrading.
Both parameters can be combined to a third parameter describing the quality of the whole technical setup for mineral processing by subtracting the upgrading parameter from the liberation parameter. The third parameter shows a positive value in cases of upgrading determined processes, a negative value in cases of liberation affected processes and about zero for processes affected equally by liberation and upgrading. Thus it is easily possible to distinguish between poor results in the mineral processing caused by insufficient liberation or poor results caused by insufficient upgrading. Preliminary results from two case studies, performed on two different ore types, are very promising illustrating the practical use of such an approach.
Keywords: flotation modeling, optimization, process development
  • Contribution to proceedings
    XXVII International Congress on Mineral Processing, 20.-24.10.2014, Santiago de Chile, Chile
    Proceedings of the XXVII International Mineral Processing Congress – IMPC 2014, 1-10

Publ.-Id: 21506 - Permalink


Morphology-Induced Magnetic Phenomena Studied by Broadband Ferromagnetic Resonance
Körner, M.;
In the present work, the influence of the morphology of thin ferromagnetic films on their static as well as dynamic magnetic properties was investigated by means of broadband ferromagnetic resonance (FMR). Using an ion beam erosion process the surface of the substrates was periodically modulated (ripples), where the modulation wavelength is determined by the ion energy. In this way a well-controllable roughness profile evolves ranging from a few ten up to several hundreds of nanometers in wavelength. The substrate’s surface profile in turn is repeated by films grown on top offering an easy and fast approach to investigate morphology influences on the magnetic properties. This work aims on modifications of the magnetic anisotropy as well as the FMR linewidth of the magnetic relaxation process.
Prior to magnetic investigations the existing FMR setup was extended to measure FMR spectra at a fixed microwave frequency while sweeping the external magnetic field. Furthermore, a software toolbox was developed to perform the data processing and evaluation.
Starting with the morphology influence on the magnetic anisotropy 10 nm thin Fe, Co, and Ni81Fe19 (Permalloy Py) films were deposited on rippled Si substrates. Due to Si displacements during ion erosion and natural oxidation the rippled Si substrates exhibit an amorphous surface causing a polycrystalline material growth. This leads to a suppression of magneto-crystalline anisotropy leaving only morphology-induced anisotropy contributions.
Here, a uniaxial magnetic anisotropy (UMA) was observed that aligns its easy axis with the ripple ridges, whereas its strength decays with increasing ripple wavelength for all materials. From thickness-dependent measurements two characteristic regions were determined with competing uniaxial volume and surface anisotropy contributions. Underlined by micromagnetic simulations a dominant volume contribution was found in the thin region accompanied by magnetic moments nearly following the surface corrugation. In the thick region the UMA is controlled by dipolar stray fields at the surface.
In contrast to Si, ion eroded MgO keeps its crystal structure offering epitaxial growth of 10 nm thin single-crystalline Fe films. Consequently, a superposition of morphology-induced UMA and magneto-crystalline cubic anisotropy was observed. The direction of the ripple ridges is predetermined by the incident ion beam, which allows to freely orient the UMA’s direction with respect to the cubic anisotropy, offering a possibility for anisotropy engineering. In comparison to the planar reference case rippled magnetic films exhibit lower intrinsic and extrinsic relaxation contributions.
For the final part, 30 nm Py was grown on rippled Si covering modulation wavelengths l ranging from 27 to 432 nm. Using magnetic force microscopy and holography measurements the dipolar stray fields above and inside the magnetic layer were characterized. For l 222 nm, the stray fields act as scattering centers for spin waves triggering two-magnon scattering (TMS). This causes an apparent line broadening generating distinct peaks in the frequency-dependent linewidth whose position can be tuned by altering l. These effects are understood in the framework of a perturbation theory of spin waves in periodically perturbed films recently presented in the literature. Furthermore, the in-plane angular dependence of the linewidth revealed a two-fold symmetry, which is not present for vanishing TMS at small l.
Keywords: ferromagnetic resonance, ferromagnetism, FMR, thin films, spin waves
  • Doctoral thesis
    TU Dresden, 2013
    Mentor: Jürgen Fassbender
    185 Seiten

Publ.-Id: 21505 - Permalink


Polytypism in GaAs nanowires: determination of the interplanar spacing of wurtzite GaAs by X-ray diffraction
Köhl, M.; Schroth, P.; Minkevich, A. A.; Hornung, J.-W.; Dimakis, E.; Somaschini, C.; Geelhaar, L.; Aschenbrenner, T.; Lazarev, S.; Grigoriev, D.; Pietsch, U.; Baumbach, T.;
In GaAs nanowires grown along the cubic [111]c direction, zinc blende and wurtzite arrangements have been observed in their stacking sequence, since the energetic barriers for nucleation are typically of similar order of magnitude. It is known that the interplanar spacing of the (111)c Ga (or As) planes in the zinc blende polytype varies slightly from the wurtzite polytype. However, different values have been reported in the literature. Here, the ratio of the interplanar spacing of these polytypes is extracted based on X-ray diffraction measurements for thin GaAs nanowires with a mean diameter of 18–25 nm. The measurements are performed with a nano-focused beam which facilitates the separation of the scattering of nanowires and of parasitic growth. The interplanar spacing of the (111)c Ga (or As) planes in the wurtzite arrangement in GaAs nanowires is observed to be 0.66% 0.02% larger than in the zinc blende arrangement.
Keywords: GaAs; nanowires; polytypism; X-ray diffraction; nanofocus

Publ.-Id: 21504 - Permalink


Analyse eines Messplatzes für frequenzaufgelöste magnetooptische Kerr-Effektmessungen (FR-MOKE) sowie dessen Ansteuerung auf der Basis von LabVIEW
Trache, M.;
keines Vorhanden
Keywords: ferromagnetism, ferromagnetic resonance, MOKE, FR-MOKE
  • Diploma thesis
    Wilhelm Büchner Hochschule, 2012
    Mentor: Kilian Lenz
    80 Seiten

Publ.-Id: 21503 - Permalink


Untersuchung der elektrischen und magnetischen Eigenschaften von BiFeO3-Filmen
Noack, H.;
keines vorhanden.
Keywords: ferromagnetism, ferromagnetic resonance, ferroelectrics
  • Diploma thesis
    Wilhelm Büchner Hochschule, 2011
    Mentor: Kilian Lenz
    94 Seiten

Publ.-Id: 21502 - Permalink


Magnetische Charakterisierung dünner Keilschichten mittels frequenzaufgelöstem magnetooptischen Kerr-Effekt
Hoffmann, S.;
Im Rahmen dieser Arbeit wurden erstmalig ein Probensystem aus zwei ferromagnetischen Fe3Si Schichten und einer keilförmigen Magnesiumoxid (MgO) Zwischenschicht, mittels der Kombination von ferromagnetischer Resonanz (FMR) und magnetooptischer Detektion mit Hilfe des Kerr-Effekts (MOKE), am FR-MOKE Aufbau untersucht. An verschiedenen Stellen der Probe wurden frequenzabhängige Messungen durchgeführt, um daraus Rückschlüsse auf die magnetischen Eigenschaften des Materials zu ziehen. Durch den Vergleich mit Literaturwerten konnte gezeigt werden, dass mithilfe dieser Messmethode durchaus zuverlässige Messungen durchgeführt werden können. Anhand der aufgenommen Spektren wurde der Gradient in der Probe nachgewiesen, sowie die Abhängigkeit der Interlagenaustauschkopplung von der Zwischenschichtdicke verdeutlicht.
Keywords: magnetism, ferromagnetic resonance, MOKE, thin films
  • Bachelor thesis
    TU Ilmenau, 2014
    Mentor: Kilian Lenz
    50 Seiten

Publ.-Id: 21501 - Permalink


Impact of strain induced by polymer curing in benzocyclobutene embedded semiconductor nanostructures
Bussone, G.; Dimakis, E.; Grifone, R.; Biermanns, A.; Tahraoui, A.; Carbone, D.; Geelhaar, L.; Schülli, T. U.; Pietsch, U.;
Polymers such as benzocyclobutene are commonly used as embedding materials for semiconductor nanostructures. During the curing process of the polymer up to 250 °C, a significant impact of strain can be induced on the embedded semiconductor material due to different thermal expansion coefficients. This strain has been revealed by X-ray diffraction in free-standing GaAs nanowires grown on a silicon substrate, embedded in a polymer matrix. It will be shown that this strain is released during the X-ray irradiation if additionally an external static electric field is applied.
Keywords: benzocyclobutene; polymer matrix; X-ray diffraction; embedded semiconductor nanostructures; GaAs nanowires; strain

Publ.-Id: 21499 - Permalink


Untersuchung der magnetischen Eigenschaften von Permalloy-Filmen mittels frequenzaufgelöstem magnetooptischen Kerr-Effekt (FR-MOKE)
Rupp, S.;
Im Rahmen dieser Arbeit wurden dünne ferromagnetische Filme aus Permalloy (Ni80Fe20) mit eine Kombination aus ferromagnetischer Resonanz (FMR) und magnetooptischem Kerr-Effekt (MOKE) auf ihre dynamischen Eigenschaften hin untersucht. Das Hauptmerkmal dieser frequenzaufgelösten FR-MOKE Messung lag hierbei auf der Bestimmung der Linienbreite zur Charakterisierung der wirksamen Dämpfung der Magnetiserungspräzession und des g-Faktors für Permalloy. Die Ergebnisse im Einzelnen sind: 1. Die Linienbreite kann im Bereich von 1-25 GHz bestimmt werden. 2. Die Linienbreite steigt mit der Mikrowellenfrequenz f linear an und besitz einen geringen inhomogenen Anteil. 3. Die Amplitude der Lorentzkurve fällt mit 1/f ab. 4. Bestimmung des g-Faktors g=2,085(11), für Permalloy. 5.
Die Dämpfung ist konstant und beträgt alpha=0,007.
Keywords: ferromagnetism, ferromagnetic resonance, thin films, MOKE
  • Bachelor thesis
    nta Naturwissenschaftlich-Technische Akademie Prof. Dr. Grübler gGmbH, 2014
    Mentor: Kilian Lenz
    54 Seiten

Publ.-Id: 21498 - Permalink


Role of liquid indium in the structural purity of wurtzite InAs nanowires that grow on Si(111)
Biermanns, A.; Dimakis, E.; Davydok, A.; Sasaki, T.; Geelhaar, L.; Takahasi, M.; Pietsch, U.;
InAs nanowires that grow catalyst-free along the [111] crystallographic orientation are prone to wurtzite-zincblende polytypism, making the control of the crystal phase highly challenging. In this work, we explore the dynamic relation between the growth conditions and the structural composition of the nanowires using time-resolved X-ray scattering and diffraction measurements during the growth by molecular beam epitaxy. A spontaneous buildup of liquid indium is directly observed in the beginning of the growth process and associated with the simultaneous nucleation of InAs nanowires predominantly in the wurtzite phase. The highly arsenic-rich growth conditions that we used limited the existence of the liquid indium to a short time interval, which is defined as the nucleation phase. After their nucleation, the nanowires grow in the absence of liquid indium, and with a highly defective wurtzite structure. Complementary ex-situ diffuse X-ray scattering measurements and modeling revealed that this structural degradation is due to the formation of densely spaced stacking faults. Thus, high wurtzite phase purity is associated with the presence of liquid indium. This finding implies that pure wurtzite nanowires may be obtained only if the growth is performed under the continuous presence of liquid indium at the growth interface, that is, in the vapor–liquid–solid mode.
Keywords: nanowires; InAs; Si; molecular beam epitaxy (MBE); X-ray diffraction

Publ.-Id: 21497 - Permalink


Two-dimensional electron gas in monolayer InN quantum wells
Pan, W.; Dimakis, E.; Wang, G. T.; Moustakas, T. D.; Tsui, D. C.;
We report in this letter experimental results that confirm the two-dimensional nature of the electron systems in a superlattice structure of 40 InN quantum wells consisting of one monolayer of InN embedded between 10 nm GaN barriers. The electron density and mobility of the two-dimensional electron system (2DES) in these InN quantum wells are 51015cm2 (or 1.251014cm2 per InN quantum well, assuming all the quantum wells are connected by diffused indium contacts) and 420 cm2/Vs, respectively. Moreover, the diagonal resistance of the 2DES shows virtually no temperature dependence in a wide temperature range, indicating the topological nature of the 2DES.

Publ.-Id: 21496 - Permalink


Evolution of polytypism in GaAs nanowires during growth revealed by time-resolved in situ x-ray diffraction
Schroth, P.; Köhl, M.; Hornung, J.-W.; Dimakis, E.; Somaschini, C.; Geelhaar, L.; Biermanns, A.; Pietsch, U.; Bauer, S.; Lazarev, S.; Baumbach, T.;
In III-V nanowires the energetic barriers for nucleation in zinc blende or wurtzite arrangement are typically of similar order of magnitude. As a result, both arrangements can occur in a single wire. Here, we investigate the evolution of this polytypism in self-catalyzed GaAs nanowires on Si(111) grown by molecular beam epitaxy with time-resolved in situ X-ray diffraction. We interpret our data in the framework of a height dependent Markov model for the stacking in the nanowires. This way, we extract the mean sizes of faultless wurtzite and zinc blende segments -- a key parameter of polytypic nanowires -- and their temporal evolution during growth. Thereby, we infer quantitative information on the differences of the nucleation barriers including their evolution without requiring a model of the nucleus.

Publ.-Id: 21495 - Permalink


Status of the ELBE SRF Gun II
Arnold, A.;
As in 2007 the first 3.5 cell superconducting radio frequency (SRF) gun was taken into operation, it turned out that the specified performance has not been achieved. However, to demonstrate the full potential of this new type of electron source, a second and slightly modified SRF gun II was built in collaboration with Thomas Jefferson National Accelerator Facility (TJNAF). We will report on commissioning and first results of the new gun, which includes in particular the characterization of the most important RF properties as well as their comparison with previous vertical test results.
Keywords: superconducting electron injector, SRF gun, ELBE
  • Lecture (others)
    HOPE / SINEMP project meeting, 03.-04.11.2014, Siegen, Deutschland

Publ.-Id: 21494 - Permalink


System Integration and Application of CdZnTe Detectors in a Compton Camera for Medical Use
Fiedler, F.; Enghardt, W.; Golnik, C.; Hueso-Gonzalez, F.; Kormoll, T.; Schumann, A.; Pausch, G.; Petzold, J.; Rohling, H.; Roemer, K.; Schoene, S.;
Ion beams offer advantages over conventional treatment modalities, such as photons. Because of the way ions deposit their energy on their path through tissue they allow for an increased dose deposition in the tumor volume and reduce the collateral damage to the surrounding healthy tissue. However, the range of these particles is sensitive to small density changes in the irradiated volume. Deviations will lead to a misalignment of the deposited dose maximum and the tumor. It is therefore highly desirable to verify the particle range in-vivo and in realtime by means of a detector system independent from the treatment device. One approach is to monitor the prompt gamma-ray emissions from excited nuclei that originate in the interaction of projectile and target nuclei. A Compton camera could be one of the feasible technical solutions for such a monitoring system. To set up a clinical applicable device a comprehensive modelling of the creation of secondary radiation as well as of the detection process is required. Furthermore, a sophisticated reconstruction of the data is essential. This paper will present three different prototypes of such a detector system made of CdZnTe and scintillation detectors. Also we will show measurements on the detector performance as well as reconstructed images of the radiation sources.
Keywords: Compton camera, in-vivo dose imaging, proton therapy, CdZnTe detectors
  • Invited lecture (Conferences)
    IEEE NSS MIC, 21st Symposium on room-temperature Semiconductor and Gamma-Ray detectors, 08.-15.11.2014, Seattle, WA, USA

Publ.-Id: 21493 - Permalink


Broadband, diode pumped Yb-doped fused silica laser
Röser, F.; Loeser, M.; Albach, D.; Siebold, M.; Grimm, S.; Brand, D.; Schwuchow, A.; Langner, A.; Schötz, G.; Schönfeld, D.; Schramm, U.;
We report on the fabrication, optical properties and lasing characteristics of Yb-doped fused silica in bulk volume. The glass rods were manufactured by sintering of Yb-doped fused silica granulates and subsequent homogenization. Samples of various thicknesses containing doping levels of 0.27 mol% and 0.39 mol%, respectively, were investigated. The glass shows a high optical quality with refractive index variations in the 10 ppm range. We successfully demonstrated cw lasing with a maximum optical to optical efficiency of 60 % and slope efficiencies of about 70 % with respect to absorbed pump power for all samples. The laser cavity could be tuned in a wavelength range of 100 nm. The large amplification bandwidth of fused silica was verified by gain distribution measurements in a double-pass amplifier configuration.
Keywords: Lasers, diode-pumped; Lasers, ytterbium; Lasers, solid-state; Laser materials

Publ.-Id: 21492 - Permalink


Comparison of a Separated Flow Response to Localized and Global type Disturbances
Monnier, B.; Williams, D.; Weier, T.; Albrecht, T.;
POD modes and coefficients obtained from an inclined flat plate with Lorentz force actuator are compared to that of a pitching wing model (NACA 0009). The pitching wing model emulates an impulsive disturbance by pitching from 15 deg to 17 deg and then back to 15 deg in a very short time interval. There is also a negative pitching case, 15 deg to 13 then back to 15 deg. The Lorentz force actuator produced a spatially localized disturbance, whereas the pitching wing produces a spatially global disturbance. We found very close similarities in the POD modes and the time-varying coefficients. We also found that POD mode 2 tracks the negative of the lift force in both cases.
Keywords: active flow control, Lorentz force, pitching wing
  • Lecture (Conference)
    53rd AIAA Aerospace Sciences Meeting, 05.-09.01.2015, Kissimmee , Florida, USA
  • Contribution to proceedings
    53rd AIAA Aerospace Sciences Meeting, 05.-09.01.2015, Kissimmee, Florida, USA
    AIAA papers
    DOI: 10.2514/6.2015-1056

Publ.-Id: 21491 - Permalink


Critical exponents and intrinsic broadening of the field-induced transition in NiCl2 · 4SC(NH2)2
Wulf, E.; Hüvonen, D.; Schönemann, R.; Kühne, H.; Herrmannsdörfer, T.; Glavatskyy, I.; Gerischer, S.; Kiefer, K.; Gvasaliya, S.; Zheludev, A.;
The field-induced ordering transition in the quantum spin system NiCl2 · 4SC(NH2)2 is studied by means of neutron diffraction, ac magnetometry, and relaxation calorimetry. The interpretation of the data is strongly influenced by a finite distribution of transition fields in the samples, which was present but disregarded in previous studies. Taking this effect into account, we find that the order-parameter critical exponent is inconsistent with the BEC universality class even at temperatures below 100 mK. All results are discussed in comparison with previous measurements and with recent similar studies of disordered Ni(Cl1−xBrx)2 · 4SC(NH2)2.

Publ.-Id: 21490 - Permalink


Multigap superconductivity in locally noncentrosymmetric SrPtAs: An 75As nuclear quadrupole resonance investigation
Brückner, F.; Sarkar, R.; Günther, M.; Kühne, H.; Luetkens, H.; Neupert, T.; Reyes, A. P.; Kuhns, P. L.; Biswas, P. K.; Stürzer, T.; Johrendt, D.; Klauss, H.-H.;
We report detailed 75As nuclear quadrupole resonance investigations of the locally noncentrosymmetric superconductor SrPtAs. The spin-lattice relaxation studies prove weakly coupled multigap superconductivity. A retardation of the decay in 1/T1T evidences a nodeless (fully gapped) superconducting state on the complex multipocket Fermi surface, which is consistent with an anisotropic s-wave order parameter and with proposed unconventional f-wave and chiral d-wave symmetries. A quantitative analysis of these models favors the unconventional f-wave state.

Publ.-Id: 21489 - Permalink


Nanowire spin torque oscillator driven by spin orbit torques
Duan, Z.; Smith, A.; Yang, L.; Youngblood, B.; Lindner, J.; Demidov, V. E.; Demokritov, S. O.; Krivorotov, I. N.;
Spin torque from spin current applied to a nanoscale region of a ferromagnet can act as negative magnetic damping and thereby excite self-oscillations of its magnetization. In contrast, spin torque uniformly applied to the magnetization of an extended ferromagnetic film does not generate self-oscillatory magnetic dynamics but leads to reduction of the saturation magnetization. Here we report studies of the effect of spin torque on a system of intermediate dimensionality—a ferromagnetic nanowire. We observe coherent self-oscillations of magnetization in a ferromagnetic nanowire serving as the active region of a spin torque oscillator driven by spin orbit torques. Our work demonstrates that magnetization selfoscillations can be excited in a one-dimensional magnetic system and that dimensions of the active region of spin torque oscillators can be extended beyond the nanometre length scale.

Publ.-Id: 21488 - Permalink


Calculation of Electronic Structure and Transport properties of Donor – Acceptor Polymers
Günther, F.; Gemming, S.; Seifert, G.;
Donor-acceptor (DA) polymers have been found to be good materials for organic electronics since they provide interesting features like mechanical flexibility and high impact resistance.
Moreover, they offer the possibility to produce devises by low cost roll-to-roll printing techniques.
Thus, they are highly promising candidates for organic thin-film transistors and solar cells.
For applications, however, these materials should fulfill several demands such as ambient stability, good solubility, and good film-forming properties.
The charge carrier mobility is one of the most important quantities.
In order to analyse the influence of the molecular structure on these properties, we investigate DA polymers using first-principals methods as density functional theory (DFT).
In particular, density functional based tight binding (DFTB) is used to study large systems.

In our study we analyse the electronic structures of the isolated monomers which are the building blocks of the DA polymers, of finite oligomers up to a length of 20 conjugated units, and of infinite long polymers using periodic boundary conditions.
Furthermore, we investigate the morphological properties by studying systems of several polymer chains with different crossing angles and relative shifts.

Using Marcus transfer theory, we then calculated the electronic transport properties based on hopping processes.
Here, we focus on the coupling matrix elements and their dependence on the stacking configuration.
Using a Boltzmann-like approach for evaluating an average value of this quantity, we obtain good agreements to experimental trends.
Especially the dominating transport type is nicely reproduced by our approach.
  • Lecture (others)
    Arbeitsgruppenseminar der Professur für Theoretische Chemie, 20.11.2014, Dresden, Deutschland
  • Lecture (others)
    Seminar der Professur Theorie ungeordneter Systeme, 17.12.2014, Chemnitz, Deutschland

Publ.-Id: 21487 - Permalink


Optical Synchronization and Electron Bunch Diagnostic at the CW-Linac ELBE
Kuntzsch, M.;
no abstract submitted
Keywords: Synchronization ELBE BAM BCM Diagnostic
  • Invited lecture (Conferences)
    DESY MSK Seminar, 09.01.2015, Hamburg, Germany

Publ.-Id: 21486 - Permalink


Optimising the spatial structure of BLN protein models by means of "partial distortion''-quench cycles
Günther, F.; Möbius, A.; Schreiber, M.;
The prediction of the spatial structure of a protein based on its amino acid sequence is a challenging problem.
Corresponding theoretical studies of the protein folding require highly efficient structure optimisation tools.
Here we investigate whether and to what extent the thermal cycling (TC) algorithm [1] is appropriate for determining low energy structures of the BLN protein model by J.D. Honeycutt and D. Thirumalai [2].
In our simulations for 46-, 58-, and 69-bead sequences, the TC algorithm reliably finds the global minimum within reasonable computing time.
In comparison to the multi-start local search and simulated annealing approaches, TC turns out to be far more efficient.

In the present work, the BLN model with rigid bonds is studied in detail for the first time.
Comparing these results to data for the extended model by Berry et al. [3], where stiff springs are substituted for the rigid bonds, we observe several level crossings when varying the spring constant, even for quite hard springs.

[1] A. Möbius et al. , Phys. Rev. Lett. 79 (1997) 4297.
[2] J.D. Honeycutt and D. Thirumalai, Biopolymers 32 (1992) 695.
[3] R.S. Berry et al. , Proc. Natl. Acad. Sci. USA 94 (1997) 9520.
  • Lecture (Conference)
    DPG Spring Meeting 2014, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21485 - Permalink


Handling Domain Decomposition in Massively Parallel Implementations of Stochastic Lattice Models
Kelling, J.; Ódor, G.; Gemming, S.;
Nanopatterning of surfaces and bulk materials is very important from molecular electronics to photovoltaics. But, in order to understand the underlying physics of self-organization, large scale atomistic simulations are crucial. Only stochastic models can bridge the gap from nano to micro, enabling simulations of micron-sized volumes, billions of atoms and study long-time evolution. Random site-selection is essential but can be harmed by domain decomposition in GPGPU. We present solutions by example of a dimer-model for KPZ surface growth.
Keywords: Statistical Physics, Domain Decompostion

Publ.-Id: 21484 - Permalink


Mesoscale magnetism
Hoffmann, A.; Schultheiss, H.;
Magnetic interactions give rise to a surprising amount of complexity due to the fact that both static and dynamic magnetic properties are governed by competing short-range exchange interactions and long-range dipolar coupling. Even though the underlying dynamical equations are well established, the connection of magnetization dynamics to other degrees of freedom, such as optical excitations, charge and heat flow, or mechanical motion, make magnetism a mesoscale research problem that is still wide open for exploration. Synthesizing magnetic materials and heterostructures with tailored properties will allow to take advantage of magnetic interactions spanning many length-scales, which can be probed with advanced spectroscopy and microscopy and modeled with multi-scale simulations. This review highlights some of the current basic research topics in mesoscale magnetism, which beyond their fundamental science impact are also expected to influence applications ranging from information technologies to magnetism based energy conversion.
Keywords: Magnetic soliton; Magnetomechanical coupling; Magnonics; Optical magnetization switching; Permanent magnet; Spin caloritronics; Spin Hall effect; Spin texture; Spin transfer torque

Publ.-Id: 21483 - Permalink


Calculation of Electronic Structure and Transport in Polymers
Günther, F.; Seifert, G.; Luschtinetz, R.; Gemming, S.;
Organic thin-film transistors producible by low-cost roll-to-roll manufacturing processes seem to be highly promising for flexible electronics. Therefore, high mobility semiconducting polymers with ambient stability, good solubility and film-forming properties are needed. Our study is turned to the calculation of the electronic transport properties through polymers consisting of conjugated thiophene based donor units and di-ketopyrrolo-pyrrol based acceptor units. The structure and electronic properties of thiophene-based molecular stacks is studied by means of quantum- mechanical calculations. We demonstrate how the functionalization of thiophenes can increase the dispersion interaction and promote the parallel- stacked arrangement of the molecules, which is essential to get efficient charge transport channels in the direction perpendicular to the plane of the thiophene rings. Moreover, we found that the π-π-stacking is the main driving force in the self-assembly of the molecules in the film. These results are the basis for further studies of the hopping transport properties of this promising organic semiconducting material.
For the description of the electronic transport we apply a Greens function method, including Coulomb and inelastic tunneling to a simple one-particle hopping Hamiltonian by calculating the matrix elements through overlap integrals of orbitals obtained from density-functional calculations.
  • Poster
    XXIII International Materials Research Congress, 17.-21.08.2014, Cancun, Mexico

Publ.-Id: 21482 - Permalink


Transport Calculations for Si4 Clusters with Gold single Atom Contacts
Kelling, J.; Kerbusch, J.; Erbe, A.; Dietsche, R.; Ganteför, G.; Scheer, E.; Zahn, P.; Gemming, S.;
We present results for electronic transport through Si4 clusters contacted by single-atom gold contacts attached to <111> fcc-gold leads. The calculations were performed using density functional theory and the non-equilibrium Green's function approach for transport. The simulation setup mimics contacts in mechanically controllable break-junction experiments, which provide data for comparison.
  • Poster
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 15.-20.03.2015, Berlin, Deutschland

Publ.-Id: 21481 - Permalink


Ab inito study on morphology of donor-acceptor polymers
Günther, F.; Gemming, S.; Seifert, G.;
Donor-acceptor (DA) polymers have been found to be good materials for organic electronics since they provide interesting features like mechanical flexibility and high impact resistance.
Moreover, they offer the possibility to produce devises by low cost roll-to-roll printing techniques. Thus, they are highly promising candidates for organic thin-film transistors and solar cells. For applications, however, these materials should fulfill several demands such as ambient stability, good solubility, and good film-forming properties. The charge carrier mobility is one of the most important quantities.
In order to analyze the influence of the molecular structure on these properties, we investigate DA polymers using first-principals methods as density functional theory (DFT). In particular, density functional based tight binding (DFTB) is used to study large systems.
Starting from isolated monomers being the building blocks of the DA polymers the total energy, the atomic charges, the difference between highest occupied and lowest unoccupied molecular orbitals, and the reorganization energies are calculated.
Furthermore, oligomers up to a length of 100 conjugated units as well as infinite long polymers are considered. Finally, the morphological properties are investigated by studying systems of several polymer chains with different crossing angles and relative shifts.
  • Poster
    IHRS NanoNet Annual Workshop 2014, 29.-30.09.2014, Rathen, Sächsische Schweiz, Deutschland

Publ.-Id: 21480 - Permalink


Structure optimization of BLN protein models combining local-search, evolutionary, and genetic approaches
Günther, F.; Möbius, A.; Schreiber, M.;
Establishing relations between the amino acid sequence of a protein and its spatial structure is a very important and challenging task.
When analysing the forces affecting the protein folding, the investigation of the related free energy landscape is of central importance.
Thereby, to obtain the ground state and low-energy metastable states, highly effcient structure optimization tools are needed.
Here, we study the properties of genetic local-search type optimization approaches, in particular of thermal cycling (TC) [1] and systematic-crossover localsearch (SCLS) algorithms.
For this aim, we focus on the BLN protein model, designed by J.D. Honeycutt and D. Thirumalai [2]. We consider 46-, 58-, and 69-bead sequences from Refs. [2,3]; the 69-bead sequence seems to be the largest BLN model treated in the liteature up to now.
In all these cases, the TC and SCLS algorithms reliably find the global minimum within reasonable computing times.
Both algorithms proved to be far more effcient than multi-start local-search and simulated annealing approaches.
In the present work, to the best of our knowledge, the BLN model with rigid bond lengths is studied in detail for the first time.
We compare our results to the properties of the extended model by Berry et al. [4], in which stiff spring-like bonds are substituted for the rigid bonds:
The hardening of the spring constants causes several level crossings of the metastable states.
For the 46-bead model, this concerns even the ground state.

[1] A. Möbius, A. Neklioudov, A. Diaz-Sanchez, K.H. Hoffmann, A. Fachat, and M. Schreiber, Phys. Rev. Lett. 79 (1997) 4297.
[2] J.D. Honeycutt and D. Thirumalai, Biopolymers 32 (1992) 695.
[3] M.T. Oakley, D.J.Wales, and R.L. Johnston, J. Phys. Chem. B 115 (2011) 11525.
[4] R.S. Berry, N. Elmaci, J.P. Rose, and B. Vekhter, Proc. Natl. Acad. Sci. USA 94 (1997) 9520.
  • Poster
    Conference of Middle European Coorperation in Statistical Physics, 08.-10.04.2014, Coventry, England

Publ.-Id: 21479 - Permalink


Electronic Transport through Au-contacted PEEB
Kelling, J.; Gemming, S.;
Transport through the organic molecule PEEB has been investigated using Density functional Theory (DFT) and the Non-Equilibrium Green's Function (NEGF) approach.
Keywords: electronic transport, molectular electronics, dft
  • Poster
    NanoNet Workshop, 29.-30.09.2014, Rathen, Sächsische Schweiz, Deutschland

Publ.-Id: 21478 - Permalink


Calculation of electronic transport properties through polymeres
Günther, F.; Gemming, S.; Seifert, G.;
Organic thin-film transistors producible by low-cost roll-to-roll manufacturing processes seem to be highly promising for flexible electronics.
Therefore, high mobility semiconducting polymers with ambient stability, good solubility and film-forming properties are needed.
Our study is turned to the calculation of the electronic transport properties through polymers consisting of conjugated thiophene based donor units and di-ketopyrrolo-pyrrol based acceptor units.
Therefore, we use empirical hopping equations such as Marcus transfer theory in order to determine the mobility of holes and electrons.
The parameters required for this are taken from first-principles calculations such as density functional theory and Hartree-Fock approaches.
  • Poster
    DPG Spring Meeting 2014, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21477 - Permalink


EcoMetals - innovative eco-efficient biohydrometallurgy process for the recovery of strategic and rare metals: primary and secondary resources
Kutschke, S.; Bodénan, F.; Schaefer, J.; Guezennec, A.-G.; Janneck, E.; Möckel, R.; Petiot, C.; Pollmann, K.;
The German-French project EcoMetals focuses on metal production from base (copper) and rare metal- bearing primary and secondary resources in Europe. The main objectives are the development of alternative methods in mineral processing involving pretreatment steps, biohydrometallurgical and metal recovery processes, their up scaling and finally the determination of economic and sustainable performances through process integration, life cycle analysis and economic assessment.
German Kupferschiefer dumps and ores from Mansfeld and Lausitz region, Polish Kupferschiefer concentrates and French complex polymetallic deposits will be used as case studies for scientific breakthrough and integrated process demonstration activity.
Keywords: copper, rare metals, black shale, bioleaching
  • Lecture (Conference)
    Biohydrometallurgy '14, 09.-11.06.2014, Falmouth, United Kingdom and Ireland

Publ.-Id: 21476 - Permalink


Recyclingpotenziale von Galliumarsenid
Kutschke, S.; Zeidler, O.; Matys, S.; Pollmann, K.; Scharf, C.;
Zusammenfassung zu Stand der Arbeiten zum Galiumarsenid-Recycling, Darstellung bilogischer und hydrometallurigischer Ansätze
  • Lecture (others)
    21. Kolloquium Abfall & Altlasten aktuell, 11.12.2014, Dresden, Deutschland

Publ.-Id: 21475 - Permalink


Stacked topological spin textures as emitters for multidimensional spin wave modes
Sluka, V.; Weigand, M.; Kakay, A.; Erbe, A.; Tyberkevych, V.; Slavin, A.; Deac, A.; Lindner, J.; Fassbender, J.ORC; Raabe, J.; Wintz, S.
In the present contribution we will show that in a vortex pair system with uniaxial magnetic anisotropy, spin waves of different symmetries and dimensionalities can be excited.
Keywords: vortex spin wave
  • Lecture (Conference)
    IEEE International Magnetics Conference (Intermag), 11.-15.05.2015, Beijing, China

Publ.-Id: 21474 - Permalink


Fast Timing with BGO (and other Scintillators) on Digital Silicon Photomultipliers for Prompt Gamma Imaging
Petzoldt, J.; Roemer, K.; Kormoll, T.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Hueso-Gonzalez, F.; Golnik, C.; Kirschke, T.; Wagner, A.; Pausch, G.;
Particle therapy is supposed to be an advanced treatment modality compared to conventional radiotherapy because of the well-defined range of the ions. Prompt gamma rays, produced in nuclear reactions between ion and nuclei, can be utilized for real-time range verification to exploit the full potential of particle therapy. Several devices have been investigated in the field of Prompt Gamma Imaging (PGI), like Slit and Compton Cameras. The latter need very high detection efficiency as well as good time and energy resolution, requiring a versatile scintillation detector. In positron emission tomography (PET), LSO and LYSO are known for their good timing resolution, while the lower cost alternative BGO shows worse performance. In PGI however, where gamma rays have energies up to 10 MeV, the light output of a scintillator is up to 20 times larger compared to PET with E gamma = 511 keV. This reduces the statistical contribution of the time resolution, which is the dominant part in case of BGO. Thus, BGO could be a reasonable alternative to LSO/LYSO for applications in PGI. Hence, experiments at the ELBE accelerator at Helmholtz-Zentrum Dresden Rossendorf (Germany) were performed using digital silicon photomultiplier (dSiPM) from Philips with monolithic BGO and LYSO crystals and for completeness with GAGG and CeBr3. The time resolution of BGO compared to the faster scintillators will be presented for a wide range of trigger- and validation levels as well as validation lengths of the dSiPM. Timing resolutions below 300 ps were obtained for BGO, while LYSO and CeBr3 achieve about 170 ps.
Keywords: fast timing, digital silicon photomultiplier, particle therapy, range verification
  • Lecture (Conference)
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
  • Contribution to proceedings
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
    Proceedings of 2014 NSS/MIC

Publ.-Id: 21473 - Permalink


In-Vivo Range Verification Based on Prompt Gamma-Ray Timing Measurements
Golnik, C.; Hueso-Gonzalez, F.; Enghardt, W.; Mueller, A.; Fiedler, F.; Kormoll, T.; Ostendorf, R.; Petzold, J.; Roemer, K.; Dendooven, P.; Pausch, G.;
We present a novel approach for real time range verification in particle therapy based on prompt gamma ray timing (PGT) spectroscopy. The measurement approach relies on the fact that high-energy particles need, dependent on their range, a varying transit time through the irradiated material. This transit time is about 1-2 ns in the case of protons with a range of 5-20 cm. Timing spectroscopy of promptly emitted gamma rays, measured with an arrangement resembling a typical time-of-flight (TOF) setup, encode these transit times and thus give a real time access to the particle range. We show that statistical momenta of PGT distributions such as the center of gravity and the variance incorporate the information on the particle range with a millimeter precision, although measurement uncertainties may cover the described effect at first sight. Typical uncertainties are limited by the detector time resolution and the particle bunch spread, and are finally determined by the spectrum stability. In contrast to other prompt gamma imaging techniques, the PGT method is based on straight timing spectroscopy with a single scintillation detector. Therefore, neither passive nor electronic collimation is required. The proposed idea is verified by an analysis of experimental data taken during proton irradiation experiments at the AGOR facility at KVI-CART in Groningen (The Netherlands). The measurement results are in excellent agreement with Monte Carlo based modeling of the experimental setup. We conclude that precise range assessment is feasible within a few seconds of irradiation due to the direct measurement method.
Keywords: particle therapy, range verification, prompt gamma timing
  • Lecture (Conference)
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA

Publ.-Id: 21472 - Permalink


Particle Range Retrieval in Heterogeneous Phantoms with the Prompt Gamma Timing Method at a Clinical Proton Accelerator
Hueso-Gonzalez, F.; Golnik, C.; Berthel, M.; Dreyer, A.; Enghardt, W.; Fiedler, F.; Heidel, K.; Janssens, G.; Kormoll, T.; Petzoldt, J.; Prieels, D.; Priegnitz, M.; Roemer, K. E.; Smeets, J.; Sobiella, M.; Vander Stappen, F.; Wagner, A.; Weinberger, D.; Pausch, G.;
The characteristic dose profile of accelerated ions has opened up new horizons in the context of cancer treatment. However, particle range uncertainties strongly constrain the potential of ion beam therapy. Despite of worldwide efforts, a detector system for range and dose delivery assessment in real-time is not yet available for clinical routine. Complementary to the active- and passively collimated prompt gamma ray imaging systems for range assessment under development in several research centers, the prompt gamma ray timing method has been recently proposed. Based on the measurable transit time of ions through matter, the emission times of prompt gamma rays encode essential information about the depth-dose profile. In a collaboration between OncoRay, Helmholtz-Zentrum Dresden-Rossendorf and IBA, the prompt gamma ray timing method was tested for the first time at a clinical proton accelerator (Westdeutsches Protonentherapiezentrum Essen) with different phantoms. Several fast scintillation detectors were used to acquire prompt gamma ray timing distributions at various geometries and proton energies. From the resulting distributions, particle range differences of around 5 millimeters in heterogeneous phantoms were observed. In conclusion, we proved the feasibility of the prompt gamma ray timing method for range verification in a clinical radiation environment and realistic phantoms, which reassures this novel approach as a promising alternative in the field of prompt gamma based in vivo dosimetry.
Keywords: particle therapy, range verification, prompt gamma timing
  • Poster
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
  • Contribution to proceedings
    2014 IEEE Nuclear Science Symposium and Medical Imaging Conference (2014 NSS/MIC), 08.-15.11.2014, Seattle, USA
    Proceedings of 2014 NSS/MIC

Publ.-Id: 21471 - Permalink


Vacancy controlled spontaneous pattern formation on semiconductor surfaces
Facsko, S.;
In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, 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. The arriving atoms are trapped on a terraces and can again nucleate to form new terraces. 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 periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam.
At temperatures above the recrystallization temperature of the material, 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 primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the surface. The symmetry of these patterns is given by the crystal symmetry. Hence, checkerboard patterns appear on the Ge (001) surface, oriented in the <100> directions (Fig. 1 left). On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve (Fig. 1 right).
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. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved.
Keywords: reverse epitaxy, nanostructures, ion irradiation, self-organized patterning
  • Lecture (others)
    Seminar, 12.11.2014, Stuttgart, Deutschland

Publ.-Id: 21470 - Permalink


Faceting semiconductor surfaces by reverse epitaxy
Facsko, S.; Ou, X.; Helm, M.; Fassbender, J.ORC
In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, 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. The arriving atoms are trapped on a terraces and can again nucleate to form new terraces. 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 periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam.
At temperatures above the recrystallization temperature of the material, 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 primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the surface. The symmetry of these patterns is given by the crystal symmetry. Hence, checkerboard patterns appear for instance on the Ge (001) surface, oriented in the <100> directions. On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve. For high ion fluences the patterns also exhibit facets, which correspond to low index crystal planes.
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. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved.
Keywords: reverse epitaxy, ion irradiation, nanopatterning, nanostructures
  • Invited lecture (Conferences)
    16th International Conference on Thin Films, 13.-16.10.2014, Dubrovnik, Kroatien

Publ.-Id: 21467 - Permalink


Energy Loss and Charge Exchange of Highly Charged Ions in Carbon Nanomembranes
Facsko, S.; Wilhelm, R. A.; Gruber, E.; Ritter, R.; Heller, R.; Aumayr, F.;
During the interaction of highly charged ions with solids the ions potential energy, i.e. the stored ionization energy, is released via multiple charge exchanges on a fs time scale. Thus, HCIs reach charge equilibrium after passing only a few nanometers of the solid. The dependence of the charge state on the stopping force of the ions is therefore not accessible in irradiation experiments with bulk material. In order to investigate this pre-equilibrium regime films of just a few nanometers have to be used.
We examined the charge state and the energy loss of highly charged Xe ions after their passage through 1 nm thick carbon nanomembranes. Surprisingly, two distinct exit charge distributions were observed [1]. Part of the ions are passing the membrane with almost now charge loss, whereas the other part loose 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 enough 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.
The charge distribution and energy loss of Xeq+ ions of different incident charge states up to q=30 will be presented and the implication for the formation of holes in these nanomembranes by the HCIs [2] will be discussed.

[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
[2] 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).
Keywords: highly charged ions, nano membranes, energy loss
  • Lecture (Conference)
    International Conference on Ion Beam Modification of Materials, 15.-19.09.2014, Leuven, Belgien

Publ.-Id: 21466 - Permalink


IBA on a Nanometer Scale by use of a Helium Ion Microscope - Challenges, Achievements and ongoing Progress
Klingner, N.; Heller, R.; von Borany, J.; Facsko, S.; Gnauk, P.;
Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of about 0.3 nm and the ultimate field of depth make them a unique tool in surface imaging. The imaging contrast in such devices is usually generated either by measuring the secondary electron emission yield (SE mode) or the backscattered He ion yield (RBI mode). So far there is no possibility to analyze target compositions (elements) in a quantitative manner.
In the present contribution we will show concepts as well as first preliminary studies on the capability, efficiency and the limits of applying (Rutherford) Backscattering Spectrometry (RBS) within a HIM device to image samples with target mass contrast and to analyze target compositions. In particular, the capability of different kind of particle detectors (Si detector, TOF-setup, electrostatic and magnetic analyzers) with respect to their use for IBA in a HIM will be discussed.
The basic considerations and design studies are accompanied by first He backscat- tering investigations for energies between 1-40 keV using a test facility equipped alternatively with a time-of-flight detector or a classical 70° ESA. For various projectile energies the energy resolution of both detection systems is measured and compared to theoretical estimations. Moreover, we will present an experimental setup which allows to perform quantitative measurements on the secondary electron yield, the absolute backscattering cross sections and the charge fraction of the backscattered particles for ions with low energies in the order from sub keV to 40 keV. These measurements will be one key point on the way to a quantitative IBA within the HIM.
Keywords: Helium Ion Microscope
  • Lecture (Conference)
    21st Ion Beam Analysis, 23.-28.06.2013, Seattle, United States of America

Publ.-Id: 21465 - Permalink


Study of the relationship between zinnwaldite chemical composition and magnetic susceptibility
Chehreh Chelgani, S.; Leißner, T.; Rudolph, M.; Peuker, U. A.;
This study investigates the relationship between chemical analyses and magnetic susceptibility of zinnwaldite through magnetic separation of various size fractions. Statistical analyses were used to increase information about magnetic properties of this mineral as a future source of lithium. Statistical modeling indicated that magnetic susceptibility (as a main factor of magnetic separation) accurately can be predicted based on cations content of zinnwaldite. However the size of particles had a significant effect on magnetic susceptibility. The small difference between the estimated and measured values for the non-linear relationship of this prediction (less than 1 (10−8 m3/kg)) shows that these accurate theoretical techniques can be also applied to estimate magnetic properties of zinnwaldite in other resources, and in-situ analysis.
Keywords: Zinnwaldite Lithium Magnetic Susceptibility Statistical Analysis Chemical Composition

Publ.-Id: 21464 - Permalink


Spontaneous pattern formation on Ge induced by ion irradiation
Facsko, S.; Ou, X.; Böttger, R.; Bischoff, L.; Liedke, B.; Heinig, K. H.;
Ion irradiation of Ge surfaces leads to a variety of morphologies depending on the ion beam parameters. In the energy range of a few hundreds down to a few tens of keV swelling and the formation of sponge like structures is observed [1]. When lowering the energy these porous structures turn into self-organized periodic surface patterns. At off-normal incidence angles well-known ripple patterns with wave vector parallel or perpendicular to the ion beam direction appear, whereas at normal incidence angles hexagonally ordered dot [2] or hole patterns can be formed [3]. The structure size of the patterns is in the range of 10 - 100 nm and, occasionally, a remarkable high degree of ordering is achieved.
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter-playing processes: ion induced surface roughening due to local variation of erosion rate and smoothing via diffusional processes [4]. In addition, atomic relocations on the surface and in the bulk resulting from the collision cascade have been identified as equally important or even dominant [5]. At the atomic level the creation of surface and bulk defects, sputtering, and the influence of the ion beam on kinetic processes in the surface play a decisive role in the morphology evolution.
At high temperature, when amorphization of the Ge surface is prevented, novel crystalline surface patterns are developing during ion irradiation. In this case, regular checkerboard patterns are evolving on the Ge (001) surface with structures oriented along the <100> direction [6]. Moreover, an additional mechanism for pattern formation on Ge has been discovered recently: by very heavy ion irradiation melt pools are induced at the Ge surface by the incident ions. These melt pools can also lead to a surface instability and thus to the formation of periodic dot patterns at normal incidence.
We will present an overview of the different morphologies induced by ion irradiation on Ge surfaces and analyze briefly the dominant formation mechanism.

References
[1] R. Böttger, K.-H. Heinig, L. Bischoff, B. Liedke, and S. Facsko, Appl. Phys. A (2013) 113, 53.
[2] R. Boettger, L. Bischoff, K.-H. Heinig, W. Pilz, and B. Schmidt, J. Vac. Sci. Technol. B (2012) 30, 06FF12.
[3] M. Fritzsche, A. Muecklich, and S. Facsko, Appl. Phys. Lett. (2012) 100, 223108.
[4] R.M. Bradley and J.M.E. Harper, J. Vac. Sci. Technol. A (1988) 6, 2390.
[5] C.S. Madi, E. Anzenberg, K.F. Ludwig, and M.J. Aziz, Phys. Rev. Lett. (2011) 106, 066101.
[6] X. Ou, A. Keller, M. Helm, J. Fassbender, and S. Facsko, Phys. Rev. Lett. (2013) 111, 016101.

Keywords: reverse epitaxy, pattern formation, ion irradiation, Ge
  • Lecture (Conference)
    26th International Conference on atomic collisions in solids, 14.-18.07.2014, Debrecen, Ungarn

Publ.-Id: 21463 - Permalink


Spontaneous pattern formation in reverse epitaxy
Facsko, S.; Ou, X.;
In molecular beam epitaxy (MBE) the continuous deposition of atoms can lead to growth of self-organized 3D nanostructures. One of the possible surface instability, 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 a 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 periodic patterns are observed which are oriented perpendicular or parallel to the ion beam direction or are isotropic dot or hole patterns for normal incidence of the ion beam [2].
At temperatures above the recrystallization temperature of the material, 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 primarily by vacancy kinetics. The diffusion of vacancies is also biased by the ES barrier like the diffusion of ad-atoms. Consequently, the 3D growth turns into a 3D erosion. The resulting structures are inverse pyramids which are growing into the material [3]. The symmetry of these patterns is given by the crystal symmetry of the surface. Hence, checkerboard patterns appear for instance on the Ge (001) surface, oriented in the <100> directions. On the other hand, on the Ge (111) surface facets with a three fold symmetry evolve. For high ion fluences the patterns also exhibit facets, which correspond to low index crystal planes [3].
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. By including also a conserved Kardar-Parisi-Zhang term a remarkable qualitative agreement to the experiments is achieved [3].
[1] P. Politi, G. Grenet, A. Marty, A. Ponchet, J. Villain, Phys. Rep. 324, 271 (2000).
[2] A. Keller, S. Facsko, Materials 3, 4811 (2010).
[3] X. Ou, A. Keller, M. Helm, J. Fassbender, S. Facsko, Phys. Rev. Lett. 111, 016101 (2013).
Keywords: reverse epitaxy, pattern formation, nanostructures, ion irradiation
  • Invited lecture (Conferences)
    5th International Conference on NANO-structures SElf-Assembly, 07.-11.07.2014, Marseille, France

Publ.-Id: 21462 - Permalink


Low energy ion irradiations in material research
Facsko, S.;
The ion beam centre (IBC) of the Helmholtz-Zentrum Dresden-Rossendorf is an European leading user facility primarily dedicated to research and application of ion beam techniques in materials science. The IBC comprises various ion beam facilities (accelerators, ion beam implanters, plasma-based ion beam equipment, focused / highly-charged ion facilities) which provide a wide energy range between 100 eV and 60 MeV. Besides these facilities, structural analysis (electron microscopy and spectroscopy, X-ray scattering techniques) and sample or device processing (under clean-room conditions) are part of the IBC to deliver a “complete” user service.
Special focus of the IBC is material research with low energy ions. Irradiations of surfaces with low energy ions can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. At off-normal angle of incidence between 50° and 70° to the surface normal ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 50° smoothing dominates on elemental materials, like Si and Ge. However, in contrast to irradiations at room temperature pattern formation is observed at normal ion incidence irradiations performed at temperatures above the recrystallization temperature of the material. Depending on the surface orientation checkerboard patterns with two-fold, three-fold, or six-fold symmetry reflecting the crystal structure of the irradiated surface are formed (Fig. 1).
Moreover, low energy highly charged ions are used to create nanostructures on surfaces and in thin membranes by single ion impacts. In this case the release of the potential energy of the ions leads to a local phase transformation of the material. Currently a new facility for highly charged ions is developed to enable controlled single ion implantation with a positioning accuracy of a few nanometers only.
Keywords: ion irradiation, highly charged ions, surface patterning, nanostructures
  • Lecture (others)
    Seminar, 20.06.2014, Cork, Ireland

Publ.-Id: 21461 - Permalink


Energy Loss and Charge Exchange of Highly Charged Ions in Carbon Nanomembranes Nanomembranes
Facsko, S.; Wilhelm, R. A.; Gruber, E.; Heller, R.; Aumayr, F.;
During the interaction of highly charged ions with solids the ions potential energy, i.e. the stored ionization energy, is released via multiple charge exchanges on a fs time scale. Thus, HCIs reach charge equilibrium after passing only a few nanometers of the solid. The dependence of the charge state on the stopping force of the ions is therefore not accessible in irradiation experiments with bulk material. In order to investigate this pre-equilibrium regime films of just a few nanometers have to be used.
We examined the charge state and the energy loss of highly charged Xe ions after their passage through 1 nm thick carbon nanomembranes. Surprisingly, two distinct exit charge distributions were observed [1]. Part of the ions are passing the membrane with almost now charge loss, whereas the other part loose 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 enough 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.
The charge distribution and energy loss of Xeq+ ions of different incident charge states up to q=30 will be presented and the implication for the formation of holes in these nanomembranes by the HCIs [2] will be discussed.

[1] R.A. Wilhelm, E. Gruber, R. Ritter, R. Heller, S. Facsko, F. Aumayr, Phys. Rev. Lett. 112, 153201 (2014).
[2] 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).
Keywords: highly charged ions, nano membranes, energy loss
  • Lecture (others)
    Seminar an der Fakultät für Physik der Universität Bielefeld, 06.06.2014, Bielefeld, Deutschland

Publ.-Id: 21460 - Permalink


Ion Induced Surface Patterning - The Role of Surface Currents
Facsko, S.; Liedke, B.; Ou, X.; Heinig, K. H.;
The formation of these periodic surface patterns during ion irradiation is generally ascribed to the interplay of a sur- face instability, i.e. ion induced roughening, and smoothing mechanisms [2]. Different mechanisms have been proposed for surface roughening: The Bradley-Harper (BH) mecha- nism describes the curvature dependent sputtering whereas the Carter-Vishnyakov (CV) mechanism accounts for mass drift by momentum transfer from the incoming ions. Sur- face smoothing is accomplished by surface diffusion, and surface viscous flow [2].
2.2. ReverseEpitaxy
At temperature above the dynamic recrystallization temper- ature of the material a new kind of pattern is formed on the surface during ion irradiation [3]. At these conditions the surface remains crystalline and an additional surface in- stability appears due to the Ehrlich-Schwoebel (ES) barrier, i.e. an additional diffusion barrier for ad-atoms or vacancies to cross terrace steps. The symmetry of the pattern is now given by the crystalline symmetry of the surface. In Figure 1 patterns on different crystalline Ge surfaces irradiated with 1 keV Ar+ at normal incidence are shown: a checkerboard pattern with four-fold symmetry on the Ge(100) surface ori- ented along h100i crystal directions is visible in the atomic force microscopy (AFM) in Fig. 1a). On the Ge(111) sur- face a pattern with three-fold symmetry is formed by ion irradiation (Fig. 2b).
Keywords: ion irradiation, self-organized patterning, ripples
  • Lecture (Conference)
    20th International Workshop on Inelastic Ion-Surface Collisions, 16.-21.02.2014, Wirrina Cove, Australien

Publ.-Id: 21459 - Permalink


Ion Beam Analysis in a Helium Ion Microscope
Klingner, N.; Heller, R.; Hlawacek, G.; Facsko, S.; von Borany, J.;
Helium ion microscopes (HIM) have become powerful imaging devices within the last decade. Their enormous lateral resolution of below 0.3 nm and the highest field of depth make them a unique tool in surface imaging. So far the possibilities to identify target materials (elements) are rather limited.
In the present contribution we will show concepts as well as preliminary studies on the capability, efficiency and the limits of applying (Rutherford) Backscattering Spectrometry (RBS) within a HIM device to image samples with target mass contrast and to analyze target compositions.
We will present different concepts of how to realize RBS in a HIM and point out mayor challenges and physical limitation.
Keywords: Helium Ion Microscope
  • Poster
    AVS 61st International Symposium & Exhibition, 09.-14.11.2014, Baltimore, United States of America
  • Poster
    19th International Conference on Ion Beam Modification of Materials, 14.-19.09.2014, Leuven, Belgium
  • Lecture (Conference)
    Ionenstrahlen & Nanostrukturen, 20.-22.07.2014, Paderborn, Deutschland
  • Lecture (Conference)
    Ionenstrahlen in Forschung und Anwendung, 13.-14.06.2013, Leipzig, Deutschland
  • Poster
    79. Jahrestagung der DPG und DPG-Frühjahrstagung, 18.03.2015, Berlin, Deutschland
  • Invited lecture (Conferences)
    ZEISS ORION User Meeting, 15.04.2015, Empoli, Italy
  • Poster
    3rd Dresden Nanoanalysis Symposium, 17.04.2015, Dresden, Deutschland
  • Lecture (others)
    PhD Seminar, 31.08.2015, Dresden, Deutschland
  • Lecture (others)
    Zeiss Meeting, 27.01.2015, Dresden, Deutschland
  • Lecture (others)
    Meeting at Ion Microscopy Innovation Center at Carl Zeiss Microscopy LLC, 20.11.2014, Peabody, United States of America
  • Lecture (others)
    Group Meeting at Rutgers University, 19.11.2014, Rutgers, United States of America
  • Poster
    9th PhD seminar, Altenberg, 26.09.2014, Altenberg, Deutschland
  • Lecture (others)
    FWI Internal Meeting, 14.06.2014, Weinböhla, Deutschland
  • Lecture (others)
    8th PhD Seminar, 08.10.2013, Bautzen, Deutschland
  • Lecture (others)
    Annual FWI PhD Seminar, 02.09.2013, Dresden, Deutschland
  • Lecture (others)
    Internal FWI Meeting "Statusklausur", 10.07.2013, Dresden, Deutschland

Publ.-Id: 21458 - Permalink


Bioleaching von Kupferschiefer- ecometals
Kutschke, S.; Dirlich, S.;
Vorstellung des aktuellen arbeitsstands im Projekt Ecometals
  • Lecture (others)
    Treffen des TK Geobiotechnologie, 29.09.2014, Aachen, Deutschland

Publ.-Id: 21457 - Permalink


Seltene Erden in Mikroorganismen
Kutschke, S.;
Bisher galten die Seltenen Erden nicht als biologisch bedeutsam. Forscher des Max-Planck-Instituts für medizinische Forschung entdeckten in dem acidophilen und thermophilen Bakterium Methylacidiphilium fumarolicum kürzlich eine Methanol-Dehydrogenase, die Seltene Erden als Kofaktor benötigt (vgl. Journal Club, BIOspektrum 7/13, S. 762). M. fumarolicum ist dabei in der Lage mehr Seltene Erden aus der Umwelt aufzunehmen, als er zum Überleben benötigt. Möglicherweise speichert er die Metalls in der Zelle. Das könnte ihn für Biomining interessant machen. Seltene Erden sind zwar nicht selten, aber nur an wenigen Stelen existieren abbauwürdige Vorkommen.
  • BIOspektrum 20(2014)1, 99

Publ.-Id: 21456 - Permalink


Efficient and accurate identification of platinum group minerals by a combination of Mineral Liberation Analysis and Electron Probe Microanalyser with a new approach of offline overlap correction of Platinum Group Elements Concentrations
Osbahr, I.; Krause, J.; Bachmann, K.; Gutzmer, J.;
Identification and accurate characterisation of platinum group minerals (PGM) is a very cumbersome procedure due to their grain sizes that are mostly below 10 µm and a light microscopic appearance that is rather inconspicuous. A novel strategy for finding PGM and quantifying their composition was applied by combining a mineral liberation analyser (MLA), a point logging system and an electron probe microanalyser (EPMA).
As a first step the PGM are identified, using the MLA. Grains identified as PGM are then marked and coordinates recorded and transferred to the EPMA. Case studies illustrate that the combination of MLA, point logger and EPMA results in the identification of several times more PGMs than by careful reflected light microscopy. Wavelength dispersive spectrometer analyses of PGM by EPMA require considerable caution due to overlaps of X-rays on both peak and background of almost all PGE and associated elements. X-ray lines suitable for quantitative analyses need to be carefully selected. As peak overlaps cannot be avoided completely, an offline overlap correction based on weight percent proportions has been developed and explained in detail. Results obtained with the procedure proposed in this study attain acceptable totals and atomic proportions, concluding that the applied corrections are appropriate.

Publ.-Id: 21455 - Permalink


Euler-Euler-Modelling of Segregated Flows and Flows with Transitions between Different Flow Morphologies
Höhne, T.;
Stratified two-phase flows are relevant in many industrial applications, e.g. pipelines, horizontal heat exchangers and storage tanks. Special flow characteristics as flow rate, pressure drop and flow regimes have always been of engineering interest. The numerical simulation of free surface flows can be performed using phase-averaged multi-fluid models, like the homogeneous and the two-fluid approaches, or non-phase-averaged variants. The approach shown in this paper within the two-fluid framework is the Algebraic Interfacial Area Density (AIAD) model. It allows the macroscopic blending between different models for the calculation of the interfacial area density and improved models for momentum transfer in dependence on local morphology. An approach for the drag force at the free surface was introduced. The model improves the physics of the existing two fluid approaches and is already applicable for a wide range of industrial two phase flows. A further step of improvement of modelling the turbulence was the consideration of sub-grid wave turbulence (SWT) that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth stratified flow experiments of a different rectangular channel. The results approve the ability of the AIAD model to predict key flow features like liquid hold-up and free surface waviness. Furthermore an evaluation of the velocity and turbulence fields predicted by the AIAD model against experimental data was done. The results are promising and show potential for further model improvement.
Keywords: CFD, horizontal flow, AIAD, two-phase flow, HAWAC, HZDR
  • Book chapter
    Guan Heng Yeoh: Handbook of Multiphase Flow Science and Technology, Singapore: Springer, 2017, 978-981-4585-86-6
    DOI: 10.1007/978-981-4585-86-6_5-1

Publ.-Id: 21454 - Permalink


Diffusion of Carbon Atoms at the Carbon-Nickel Interface During Graphitization
Wenisch, R.; Hübner, R.; Gemming, S.; Munnik, F.; Krause, M.;
Interface dynamics play a crucial role in the Nickel catalyzed synthesis of carbon nanotubes, carbon nanoribbons and graphene. Interface dynamics are studied by deposition of atomic C on Ni at temperatures of 23−550°C.
The obtained films are characterized by transition electron microscopy, Ramanspectroscopy, nuclear reaction analysis and X-ray photoelectron spectroscopy. Bulk diffusion and carbon dissolution are found to be negligible under the chosen experimental conditions leaving surface/interface diffusion as the main graphitization mechanism.
Graphitic ordering starts at ~ 250°C and increases further at temperatures > 500°C. The initial graphitization occurs parallel to the Ni surface. As the growth continues, additional atomic planes turn perpendicular. First results are shown for the Si-Ag system processed under similar deposition conditions.
  • Poster
    International Winterschool on Electronic Properties of Novel Materials, 08.-15.03.2014, Kirchber in Tirol, Österreich

Publ.-Id: 21453 - Permalink


Carbon-Nickel Interface Dynamics During Physical Vapor Deposition
Wenisch, R.; Krause, M.; Hübner, R.; Gemming, S.; Abrasonis, G.;
Interface dynamics play a crucial role in Nickel catalyzed fabrication of carbon nanotubes, carbon nanowires and graphene. Interface dynamics are studied by deposition of atomic C on Ni at temperatures of 23–550°C. The obtained films are characterized by transition electron microscopy, Raman-spectroscopy, nuclear reaction analysis and X-ray photoelectron spectroscopy. Bulk diffusion and solubility are found negligible in the present experiments leaving surface diffusion as the main graphitization mechanism. The presented process may open new avenues for the fabrication of graphene on Ni at low temperatures (< 300°C).
  • Poster
    DPG Früjahrstagung, 30.03.-04.04.2014, Dresden, Deutschland

Publ.-Id: 21452 - Permalink


First experiences with SRF Gun II
Teichert, J.;
The talk presents status and preliminary results of the ELBE SRF gun II.
Keywords: photo injector, superconducting RF, electron source
  • Lecture (others)
    PITZ collaboration meeting, 02.-03.12.2014, Zeuthen, Deutschland

Publ.-Id: 21451 - Permalink


α integrin targeting for radiosensitization of three-dimensionally grown human head and neck squamous cell carcinoma cells.
Steglich, A.; Vehlow, A.; Eke, I.; Cordes, N.;
Integrin cell adhesion molecules play a crucial role in tumor cell resistance to radio- and chemotherapy and are therefore considered attractive targets for cancer therapy. Here, we assessed the role of β1 integrin-interacting α integrin subunits in more physiological three-dimensional extracellular matrix grown head and neck squamous cell carcinoma (HNSCC) cell cultures for evaluating cytotoxic and radiosensitizing potential. α2, α3, α5 and α6 integrins, which are overexpressed in HNSCC according to Oncomine database analysis, were coprecipitated with β1 integrin. More potently than α2, α5 or α6 integrin inhibition, siRNA-based α3 integrin targeting resulted in reduced clonogenic cell survival, induced apoptosis and enhanced radiosensitivity. These events were associated with diminished phosphorylation of Akt, Cortactin and Paxillin. Cell line-dependently, simultaneous α3 and β1 integrin inhibition led to higher cytotoxicity and radiosensitization than α3 integrin blocking alone. Stable overexpression of wild-type and constitutively active forms of the integrin signaling mediator focal adhesion kinase (FAK) revealed FAK as a key determinant of α3 integrin depletion-mediated radiosensitization. Our findings show that α3 integrin is essentially involved in HNSCC cell radioresistance and critical for a modified cellular radiosensitivity along with β1 integrins.
Keywords: FAK; Head and neck cancer; Radiosensitivity; α3 integrin; β1 integrin

Publ.-Id: 21450 - Permalink


Hyperbranched polyglycerols: Biodistribution and structure-compatibility relationships
Pant, K.; Stephan, H.; Bergmann, R.; Pietzsch, J.; Gröger, D.; Haag, R.; Spizzia, L.; Graham, B.;
Dendritic polyglycerols (PG’s) are promising biocompatible scaffolds for drug delivery, targeting and other therapeutic applications due to their low polydispersity, multivalency and convenient large scale one-pot synthesis. In particular, the sulphated polyglycerol derivatives are potent candidates for, e.g., anti-inflammatory drugs due to their ability to inhibit the L & P Selectins [1]. It is therefore crucial to know the physiological fate of these scaffolds in order to establish their suitability for potential biomedical applications. The present work deals with the biodistribution studies of the dendritic polyglycerol sulphate derivatives (dPGS, 10 kDa) using 64Cu (t1/2 = 12.5 h) for tracking them with positron emission tomography (PET). Since PG’s do not have any metal binding sites, coupling of bifunctional chelators (BFCs) capable of binding 64Cu to PG’s is required. A prerequisite for achieving reliable biodistribution data is that the BFCs form stable complexes with 64Cu. For this reason, BFCs based on macrocyclic triazacyclononane containing two pendant pyridyl rings (DMPTACN) [2] (LogCu-L > 25) have been synthesized with maleimide and isothiocyanate coupling groups to enable conjugation to mercapto and amine groups of the polyglycerol derivatives. These conjugates form highly stable radiocopper complexes at room temperature within 5 minutes. The conjugates are resistant to transchelation and are stable in the presence of superoxide dismutase. The biodistribution of the dPGS has been studied in healthy Wistar rats for 72 h. Furthermore, in order to exploit the properties PG’s for further applications, the effect of size, charge and surface groups have been investigated. Cytotoxicity has been studied using a selection of cell lines. The results from these studies show that these polyglycerols are highly biocompatible and potential candidates for theranostics that combine multimodal imaging and drug targeting.

References:
[1] H. Türk et al, Bioconjug. Chem. 2004, 15, 162-167.
[2] G. Gasser et al, Bioconjug. Chem 2008, 19, 719-730
  • Poster
    7th Asian Biological Inorganic Chemistry Conference (AsBIC7), 30.11.-05.12.2014, Gold Coast, Australia

Publ.-Id: 21449 - Permalink


Synthesis and biodistribution of 64Cu and 68Ga radiolabelled dendritic polyglycerol sulfate derivatives
Pant, K.; Stephan, H.; Bergmann, R.; Steinbach, J.; Gröger, D.; Haag, R.;
Dendrimers and their hyper-branched analogues, particularly highly biocompatible polyglycerols, claim an interesting area of research due to their multivalency, simplicity in preparation and large scale one-pot synthesis. They can be modified and functionalized using manifold strategies. Dendritic polyglycerol sulfates (dPGS) are potent substances that serve as candidates for anti-inflammatory drugs [1]. The presence of amino functionalities can be further exploited for the introduction of fluorescent dyes, drugs, radiolabels or any moiety of interest. To achieve detailed information about the in vivo fate of certain compounds, nuclear imaging techniques are the most reliable methodologies. Ex vivo imaging using 35S–isotopic labelling of these macromolecules has already been reported [2]. Positron emission tomography (PET) provides quantitative distribution data in vivo. The convenient detection of the emitted radiation from the radionuclides in combination with the high sensitivity underlines the utility of nuclear imaging techniques. If a metal is used as a radiolabel, the choice of an appropriate bifunctional chelator (BFC) is the crucial point. The BFCs shall permit an easy linkage to the polymers and rapid, unsophisticated, stable labelling.
Herein, protocols for the attachment of BFCs for the positron emitting radionuclides 64Cu (t1/2 = 12.7h) and 68Ga ((t1/2 = 68 min) on dPGS scaffolds are reported. For this reason, derivatives based on 1,4-bis(2-pyridylmethyl)-1,4,7-triazacyclononane (DMPTACN) and 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA) equipped with suitable linker groups have been applied. Efficient radiolabelling procedures have been established (>99% RCY). The stability of the radiolabelled bioconjugates has been studied in presence of strong competing chelators (EDTA/Cyclam) as well as in presence of HSA (human serum albumin), SOD[3] (for Cu-Conjugates) and transferrin (for Ga-conjugates). Furthermore, PET studies using Wistar rats have been performed and discussed.

References
[1] J. Demedde, A. Rausch, M.Weinhart, S. Enders, R. Tauber, K. Licha, M. Schimer, U. Zugel, A. von Bonin, R. Haag, Proc. Natl. Acad. Sci. 107, 19679 (2010).
[2] C. Holzhausen, D. Groger, L. Mundhenk, P. Welker, R. Haag, A. D. Gruber, Nanomed. 9,
  • Lecture (Conference)
    5th EuCheMS Chemistry Congress, 31.08.-04.09.2014, Istanbul, Turkey

Publ.-Id: 21448 - Permalink


Temporal changes in mantle wedge geometry and magma generation processes in the Central Andes: towards linking petrological data to thermomechanical models
Heistek, R.; Brandmeier, M.; Freymuth, H.; Wörner, G.;
Temporal and spatial patterns of Neogene ignimbrite magmatism in the Central Andes were analyzed using GIS and geostatistical modeling. We compiled a comprehensive ignimbrite database using available literature, satellite imagery and geochemical data. 203 individual ignimbrite sheets were digitized in GIS, for which geochemical, isotopic (partly), and geochronological data are available from literature sources and own data (http://www.arcgis.com/home/item.html?id=47038ddc0628473f9f0ce67aa2eff8be). Based on this analysis, we estimate composition, volumes and sources of erupted ignimbrite magmas through space and time for five segments of the Central Andes.
The total erupted ignimbrite magma volume is estimated to be about 31,000 km3 for the past 30 Ma, with the highest average eruption rates (rm) for the northern Puna segment (3.4 km3 Ma-1 km (arc)-1), followed by 0.7 km3 Ma-1 km (arc)-1 for the Altiplano. For Southern Peru, rm is smaller (0.5 km3Ma-1km (arc)-1), which might be due to the lack of knowledge about intra-caldera volumes. Furthermore there is a clear N-S “younging” of ignimbrite pulses. Major pulses of high magma eruption rate occurred at 19-24 Ma (e.g. Oxaya, Nazca Group), 13-14 Ma (e.g. Huaylillas ignimbrites), 6-10 Ma (Altiplano and Puna ignimbrites, e.g. Vilama ignimbrite) and 3-6 Ma (e.g. Atana, Los Frailes, Toconao). In contrast, small volume young ignimbrites from 0-3 Ma (e.g. Lauca-Perez, Purico) do not show the spatio-temporal pattern of eruptions that are documented for the large- volume ignimbrite flare-ups.
Compositional and Sr-O isotopic data indicate that ignimbrite magmas are more crustally derived in younger flare-ups in the Southern Central Andes (up to 50 % crustal melts) compared to older ignimbrites in the north (only up to 20 % crustal melts). This suggests that thermal conditions, juvenile magma production in the mantle, thickness, and/or composition of the crust must have been different along the Central Andes at the time when ignimbrite flare up magmas formed.
The amount of juvenile magmas that entered the crust and the degree and volume of partial melting within the crust can thus in principle be constrained in time and space by these data. Such data are essential in order to understand the thermal evolution of the Andean crust in space and time.
The Miocene large-volume, plateau forming ignimbrites always overly a pronounced unconformity and occur after a time with no magmatism. They are followed, however, by andesitic arc magmatism characterized during the Late Miocene by low angle, large-volume (~2.2 km3 per lava flow) volcanic shields with long single lava flows up to 20 km. These shields are succeeded by younger and more evolved steeply-sided strato-cones that characterize much of the CVZ active volcanic front for Pliocene-Quaternary times. Andesites in such young stratovolcanoes (~0.7 km3 per lava flow) are often characterized by amphibole phenocrysts.
In principle, the transition between these andesite regimes could be due to:
(1) a change in the mantle melting regime from decompression (hot and dry?) to flux melting (wet and lower T?),
(2) different rates in magma production and effusion, and
(3) different P-T-regimes of magma evolution within the crust as is shown by the depletion in HREE and Y from Miocene to Pleistocene volcanic rock caused by a residual garnet after crustal assimilation in a thickened crust.

To understand the shift from andesite shields to stratovolcanoes we studied Miocene to modern Central Andean volcanic rocks that represent different ages but are similar in petrography and composition in order to test differences in processes of magma generation. Based on a survey of ~1300 chemical analyses of lava samples (http://andes.gzg.geo.uni-goettingen.de/) we selected three representative sample types: (1) most mafic samples (50-55 % SiO2), (2) intermediate andesites representing 63 % of the data (55-60 % SiO2), and (3) felsic samples (60-65 % SiO2), all of which were identified before as important endmember magma type in the Central Andes. Using a range of geothermometers, hygrometers and MELTS modelling we show that the P-T parameters at the time of eruption, for a given composition, remained surprisingly constant trough time and throughout the Central Andes (e.g. 975 °C to 985 °C for 2-px thermometry). Moreover, the depth of the last (phenocryst) crystallization of Miocene to Present magmas took place between 9 and 3.5 km throughout Andean history. These observations clearly indicate that estimated temperatures only reflect the late crystallization history at shallow levels and that any distinct regimes of magma formation in the mantle wedge that may have existed are entirely dampened out during the passage through the crust. Density, viscosity and degassing of andesite magmas control the latest stages of ascent and crystallization and these parameters are independent of crustal conditions, subduction geometry and mantle wedge conditions. Therefore, the thickened upper crust not only serves as a chemical filter for mantle wedge magmas but also controls (and synchronizes) P-T conditions of crystallization as recorded in erupted products.
Deep evolution at the level of the magma sources and lower crust, where assimilation and magmatic differentiation takes place, is thus completely decoupled from the shallow processes of late crystallization. Therefore only the rate of effusion, and by implication, magma production and upper crustal stress regime remain as primary factors that may have influenced differences between Miocene and Recent magmatic products.
Since the sequence of distinct magmatic regimes (plateau-ignimbrites, shield andesites and evolved stratovolcanoes) is diachronous during the past 26 Ma of Andean evolution with ages getting younger from N to S. This suggests control by “deeper” processes guided by the geometry of the slab and the thermal evolution of the upper plate during Andean orogeny. As patterns, timing of events, subduction parameters and magma production rates in the mantle wedge change regionally and temporally during ongoing thickening of the Central Andean crust, the upper plate reacts at any given location individually to these changes according to its present thermal state, crustal composition, magmatic history and tectonic stress conditions at that time and space.
We propose that large-volume ignimbrite eruptions occurred in the wake of subduction of the Juan-Fernandez ridge that passed below the Central Andes from N to S during the past 25 Ma. This event resulted in compression, uplift, low angle subduction (flat slab) and fluid release in a first stage, followed by massive inflow and melting of asthenospheric mantle after the passing of the ridge when the slab again steepened rapidly. This in turn caused massive melting within the crust aided by advective heat transport shortly after slab steepening. Differences in chemical and isotopic composition of the large-volume ignimbrites are related to changes in crustal thickness, and its “preconditioning” during the Anden orogeny over time.
The change in effusion rate during the Miocene to Pliocene/Quarternary may be the only parameter that relates to changing angles and/or convergence rates of the slab. Since only convergence rates changed during the last 26 Ma (Sérbier and Solar, 1991), this parameter likely controls magmatic activity (Cagnoicle et al., 2007). In southern Peru, Miocene voluminous magmatic activity correlates with high convergence rates, both decreasing in the last 10 Ma (Sébrier and Soler, 1991).
Previous model predictions for arc magmatism (Sobolev et al., 2006) follows from the comparison between the evolution of tectonic shortening and the evolution of the mantle temperature beneath the magmatic arc. Processing the delamination material throught the asthenospheric wedge by corner flow results in an increasing shortening rate. Simultaneously, the temperature of the asthenospheric wedge beneath the magmatic arc decreases, which in turn should lead to reduced magmatic activity. However, apart from the Puna (Kay and Kay, 1993) and Northern Altiplano (Back and Zandt., 2002; Yuan et al., 2002)) no evidence exists for mantle lithosphere delamination in the Central Andes. Therefore a new model based on our volumes, eruption rates, petrological constraints and the movement of the Juan Fernández ridge should give a better understanding of the controlling factors of arc magmatism.

Back SL, Zandt G (2002) The nature of orogenic crust in the Central Andes. J Geophys Res 107:n doi 10.1029/2000JB000124
Cagnioncle AM, Parmentier EM, Elkins-Tanton LT (2007) Effect of solid flow above a subducting slab on water distribution and melting at convergent plate boundaries. J Geophys Res 112: B09402
de Silva, S., Gosnold, W.D. (2007) Episodic construction of batholiths: Insights from the spatiotemporal development of an ignimbrite flare-up. J. Volcanol. Geotherm. Res. 167: 320–335.
Kay RW, Kay SM (1993) delamination and delamination magmatism. Tectonophysics 219:177 - 189
Sébrier, M., Solar, P. 1991. Tectonics and magmatism in the Peruvian Andes from late Oligocene time to the Present. Geological Society of America 265, 259–278.
Sobolev SV, Babeyko AY, Koulakov I, Oncken O (2006) Mechanism of the Andean orogeny: insight from numerical modeling. In: Oncken O, Chong G, Franz G, Giese P, Götze H-J, Ramos VA, Strecker MR, Wigger P (eds) The Andes – active subduction orogeny. Frontiers in Earth Science Series, Vol 1. Springer-Verlag, Berlin Heidelberg New York, pp 513–536, this volume
Yáñez, G., Cembrano, J., Pardo, M., Ranero, C., Selles, D., 2002. The Challenger–Juan Fernández– Maipo major tectonic transition of the Nazca–Andean subduction system at 33–34 S: geodynamic evidence and implications. Journal of South American Earth Sciences 15, 23‐38.
  • Contribution to proceedings
    GeoMod 2014, 31.07.-05.09.2014, GFZ Potsdam, Germany

Publ.-Id: 21447 - Permalink


From basalt to ryholite: Uniform components and mixing regimes in magma systems of the Central Andes
Wörner, G.; Banaszak, M.; Brandmeier, M.; Heistek, R.;
The major element most mafic compositions of Quaternary to Miocene magmatism in the Andean Central Volcanic Zone are rather variable but present throughout the evolution of the Central Andes in the past 20 Ma. Compositions encompass high-K to medium-K calc-alkaline basaltic andesites (52-55 SiO2 wt%) and have large ranges in major (3.6-9.4 wt% MgO, 4-7 wt% Na2O+K2O, 0.8-1.8 wt% TiO2) and trace element concentrations (9-197 ppm Ni, 501-1944 ppm Sr, 95-257 ppm Zr), as well as trace element ratios (LILE/HFSE: 93>Sr/Y>24; LREE/HREE: 8>La/Yb>63). Such a remarkable variability and the absence of truly primitive lavas in the CVZ since the onset of crustal thickening reflects distinct petrogenetic processes during ascent and evolution of mantle-derived melts traversing exceptionally thick continental crust (70 km).
Our statistical analysis (Polytopic Vector Analysis, PVA) on a on a subset of our large data base of Andean magmas (>1000 samples) which have complete major- and trace element data and isotope compositions shows that the entire compositional space of Central Andean magmas can be described by the three same endmembers: (1) a low-Mg high-Al calc-alkaline basaltic andesite (BA), (2) a incompatible trace element enriched basalt (EB), and 3) a high-K calc-alkaline rhyodacite (RD). A first mixing stage produces a range of hybrid baseline magmas consisting of the EB and BA. These represent typical recharge magmas into more evolved magma chambers at shallower crustal levels. There, a second mixing stage occurs with mixing between the already mixed, mafic (BA+EB) and the silicic RD component, which typically is crystal rich. Mixing proportions between these endmembers vary widely and magma compositions of endmembers and/or hybrids are overprinted by different degrees of magmatic differentiation and crustal assimilation.
These three endmember magmas enclose nearly all Quaternary CVZ lavas in a mixing triangle and accounts for the entire compositional variability of the Quaternary volcanic rocks in the CVZ. A first mixing stage produces hybrid baseline magmas consisting of the EB and BA. The second mixing stage represents shallow crustal magma mixing between the already mixed, mafic (BA+EB) and the silicic RD components. Mixing proportions between these endmembers vary widely and magma compositions of endmembers and/or hybrids are overprinted by different degrees of magmatic differentiation and up to 20% crustal assimilation.
A particular setting is required for andesite lava fields that occur throughout the Central Andes (Huambo, Andagua, Negrillar). These Quaternary lava fields are unrelated to stratovolcanoes and probably reflect direct differentiation of the mafic hybrids towards phenocryst poor pyroxene-andesites without interaction with crystal-rich shallow crustal magmas.
A survey of our data base including older (Pliocene and Miocene) andesites and dacites shows a surprisingly similar compositional pattern.
The BA, EB, and RD endmembers represent distinct magma sources: the mantle wedge, enriched lithospheric mantle, and the continental crust, respectively. Therefore, these endmembers are expected to be ubiquitous in the central Andes and have uniform geochemical character.
These mixed magmas give rise to and are genetically associated with large volume ignimbrite eruptions (ignimbrite “flare-ups” with >3000km3 erupted in 1 Ma) that are hybrids between 20 to 50% of a crustal melting endmember and a mantle component. Further evolution of these silicic magmas towards the thermal minimum results in rather uniform magma compositions smoothing out compositional diversity in the constituent magmas. A rigorous statistical analyses of the ignimbrite compositional data throughout the Central Andes identifies four groups that reflect the assembly of large magma volumes from slightly distinct sources at different P-T-X conditions.
  • Contribution to proceedings
    IMA2014 - 21st General Meeting of the International Mineralogical Association, 01.-05.09.2014, Sandton Convention Centre, Gauteng South Africa, South Africa

Publ.-Id: 21446 - Permalink


Cosmic-ray induced background intercomparison with actively shielded HPGe detectors at underground locations
Szücs, T.; Bemmerer, D.; Reinhardt, T. P.; Schmidt, K.; Takács, M. P.; Wagner, A.; Wagner, L.; Weinberger, D.; Zuber, K.;
The main background above 3MeV for in-beam nuclear astrophysics studies with g-ray detectors is caused by cosmic-ray induced secondaries. The two commonly used suppression methods, active and passive shielding, against this kind of background were formerly considered only as alternatives. In this work the study of the effects of active shielding against cosmic-ray induced events at a medium deep location is performed. Background spectra were recorded with two actively shielded HPGe detectors. The experiment was located at 148m below the surface of the Earth in the Reiche Zeche mine in Freiberg, Germany. The results are compared to data with the same detectors at the Earth's surface, and at depths of 45m and 1400 m, respectively.
Keywords: Nuclear astrophysics, underground physics, active shielding, gamma-ray background, cosmic-ray induced background, germanium detectors

Publ.-Id: 21445 - Permalink


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