Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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34122 Publications

10 MeV Proton Irradiation Effect on 4H-SiC nMOSFET Electrical Parameters

Florentin, M.; Alexandru, M.; Constant, A.; Schmidt, B.; Godignon, P.

This work presents the 10 MeV proton irradiation effects on 4H-SiC MOSFETs at different fluences. MOSFETs main electrical parameters, such as the channel mobility (µEFF), threshold voltage (VTH), transconductance (gm) and subthreshold current, were analyzed using the time bias stress instability (BSI) technique. Applying this method allowed us to study the effect of carrier interaction with proton induced defects (traps), whether in the bulk or at the interface. Improvements, such as VTH stabilization in time and a significant increase of the µEFF at high fluencies, have been noticed. We assume that this behavior is connected with the atomic diffusion from the SiO2/SiC interface, towards the epilayer during proton irradiation. These atoms, mainly Nitrogen, may create other bonds by occupying various vacancies coming from Silicon and Carbon’s dangling bond. Therefore, by increasing the number of passivated Carbon atoms, we show that high irradiation proton could be a way to improve the SiO2/SiC interface quality.

Keywords: Silicon carbide; MOSFET devices; proton irradiation

  • Lecture (Conference)
    HeteroSiC-WASMPE, 17.-19.07.2013, Nice, France
  • Materials Science Forum 806(2015), 121-125

Permalink: https://www.hzdr.de/publications/Publ-19144
Publ.-Id: 19144


Deceleration of Ar9+ ions within a tapered glass capillary

Kreller, M.; Zschornack, G.; Kentsch, U.

We report experimental studies of the deceleration of Ar9+ ions within a single tapered glass capillary with an inlet diameter of 1 mm, an outlet diameter of 0.15 mm and a length of 45 mm. In the experiments we have chosen an incident ion energy of q x 8.5 keV (q – ion charge state). The influence of the deceleration potential between entrance and exit of the glass capillary on the intensity of the transmitted ion beam was measured. We detected a transmission of the ion beam up to a deceleration potential of 7 kV. Hence, the ion beam was decelerated and compressed to a diameter of 150 µm without using any additional decelerating lens systems.

Keywords: Ion guiding; Highly charged ion; Tapered macro-capillary; Ion beam deceleration

Permalink: https://www.hzdr.de/publications/Publ-19143
Publ.-Id: 19143


Quantitative imaging of the magnetic configuration of modulated nanostructures by electron holography

Körner, M.; Röder, F.; Lenz, K.; Fritzsche, M.; Lindner, J.; Lichte, H.; Fassbender, J.

Regarding magnetic nanostructures, dipolar stray fields start to evolve with ongoing miniaturization, that grossly alter the magnetic properties. Besides, these fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals.
Hence, a detailed knowledge of the magnetic configuration under geometric confinements on the nanoscale is mandatory.
We present a study of the magnetic fields arising from thin Permalloy films deposited on periodically modulated surfaces (ripples).
These ripples were prepared using a self-organized ion beam erosion process generating modulations on the nanoscale.
Cross-sectional transmission electron holography nowadays offers the necessary sensitivity and nanoscale lateral resolution to probe the magnetic configuration of such rippled films quantitatively.
The imaging allows for an absolute analysis of the local magnetization inside the film as well as the accompanying stray fields outside.
In addition, the evolving stray fields above the sample's surface were investigated by magnetic force microscopy.

Permalink: https://www.hzdr.de/publications/Publ-19142
Publ.-Id: 19142


Two-Magnon Scattering in the Transition from Periodical Perturbations to Magnonic Crystals

Lenz, K.; Körner, M.; Gallardo, R. A.; Banholzer, A.; Facsko, S.; Lindner, J.; Landeros, P.; Fassbender, J.

Two-magnon scattering is a well-known effect e.g. in ferromagnetic resonance (FMR) experiments leading to a linewidth broadening. Available theory so far was based on random defects acting as a dipolar scattering potential. Recently it was shown by Landeros and Mills [1] that this theory can be extended to handle two-magnon scattering in periodically perturbed films, which can be easily created by lithographical patterning. These perturbed films are the intermediate step towards full magnonic crystals.
The extended model allows for analytically calculating the resonance response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments [2,3]. The scattering potential of the defects builds up due to the dipolar stray fields at the edges of the defects. Within the perturbation theory this leads on the one hand to a shift of the resonance peak and on the other hand also to a splitting of the uniform resonance mode. Both effects are clearly visible in the FMR experiments. The mode splitting due to the two-magnon scattering finally is also responsible for the opening of magnonic band gaps in the dispersion relation of magnonic crystals. The splitting can be tailored by the geometric and magnetic sample parameters. Experimental data for magnetically patterned stripe samples as well as for ripple samples [3] is presented and compared to calculations by the analytical model (see e.g. Fig. 1).
This work was supported by the DFG grants FA 314/6-1, FA314/3-2.
[1] P. Landeros and D. L. Mills, Phys. Rev. B 85, 054424 (2012).
[2] R. A. Gallardo, K. Lenz, A. Banholzer, M. Körner, J. Lindner, J. Fassbender, P. Landeros, Phys Rev. B (2013) submitted
[3] M. Körner, K. Lenz, R. A. Gallardo, M. Fritzsche, A. Mücklich, S. Facsko, J. Lindner, P. Landeros, J. Fassbender, Phys. Rev. B (2013) submitted

Keywords: magnonic crystals; two-magnon scattering

  • Poster
    3rd international conference on magnonics 2013, 04.-08.08.2013, Varberg, Schweden

Permalink: https://www.hzdr.de/publications/Publ-19141
Publ.-Id: 19141


Establishment of a small animal tumour model for in vivo studies with low energy laser accelerated particles

Brüchner, K.; Beyreuther, E.; Baumann, M.; Krause, M.; Oppelt, M.; Pawelke, J.

Background: The long-term aim of developing a laser based acceleration of protons and ions towards clinical application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short pulsed particle beams. Recent in-vitro data showed similar effects of laser-accelerated versus “conventional” protons on clonogenic cell survival. As the proton energies currently achieved by laser driven acceleration are too low to penetrate standard tumour models on mice legs, the aim of the present work was to establish a tumour model allowing for the penetration of low energy protons (~ 20 MeV) to further verify their effects in vivo.
Methods: KHT mouse sarcoma cells were injected subcutaneously in the right ear of NMRI (nu/nu) mice and the growing tumours were characterized with respect to growth parameters, histology and radiation response. In parallel, the laser system JETI was prepared for animal experimentation, i.e. a new irradiation setup was implemented and the laser parameters were carefully adjusted. Finally, a proof-of-principle experiment with laser accelerated electrons was performed to validate the tumour model under realistic conditions, i.e. altered environment and horizontal beam delivery.
Results: KHT sarcoma on mice ears expressed a high take rate and showed continuous tumour growth after reaching a volume of ~ 5 mm³. The first irradiation experiment using laser accelerated electrons versus 200 kV X-rays was successfully performed and tumour growth delay was evaluated. Comparable tumour growth delay was found between X-ray and laser accelerated electron irradiation. Moreover, experimental influences, like anaesthesia and positioning at JETI, were found to be negligible.
Conclusion: A small animal tumour model suitable for the irradiation with low energy protons was established and validated at a laser based particle accelerator. For this reason, the translation from in vitro to in vivo experimentation was for the first time realized and an important milestone towards the clinical application of laser driven particle accelerators was achieved.

Permalink: https://www.hzdr.de/publications/Publ-19140
Publ.-Id: 19140


Laser Induced Sponge-like Si in Si-rich Oxides for Photovoltaics

Gundogdu, S.; Sungur Ozen, E.; Hübner, R.; Heinig, K.-H.; Aydinli, A.

We show that a sponge-like structure of interconnected Si nanowires embedded in a dielectric matrix can be obtained by laser annealing of silicon rich oxides (SRO). Due to quantum confinement, the large bandgap displayed by these percolated nanostructures can be utilized as a tandem stage in 3rd generation thin-film solar cells. Well passivated by the SiO2 dielectric matrix, they are expected to overcome the difficulty of carrier separation encountered in the case of isolated crystalline quantum dots. In this study PECVD grown SRO were irradiated by a cw Ar+ laser. Raman spectroscopy has been used to assess the crystallinity of the Si nanostructures and thus to optimize the annealing conditions as dwell times and power densities. In addition, Si plasmon imaging in the transmission electron microscope was applied to identify the sponge-like structure of phase-separated silicon.

Permalink: https://www.hzdr.de/publications/Publ-19139
Publ.-Id: 19139


Neutron transport in hexagonal reactor cores modeled by trigonal-geometry diffusion and simplified P3 nodal methods

Duerigen, S.

The superior advantage of a nodal method for reactor cores with hexagonal fuel assemblies discretized as cells consisting of equilateral triangles is its mesh refinement capability. In this thesis, a diffusion and a simplified P3 (or SP3) neutron transport nodal method are developed based on trigonal geometry. Both models are implemented in the reactor dynamics code DYN3D. As yet, no other well-established nodal core analysis code comprises an SP3 transport theory model based on trigonal meshes. The development of two methods based on different neutron transport approximations but using identical underlying spatial trigonal discretization allows a profound comparative analysis of both methods with regard to their mathematical derivations, nodal expansion approaches, solution procedures, and their physical performance.
The developed nodal approaches can be regarded as a hybrid NEM/AFEN form. They are based on the transverse-integration procedure, which renders them computationally efficient, and they use a combination of polynomial and exponential functions to represent the neutron flux moments of the SP3 and diffusion equations, which guarantees high accuracy.
The SP3 equations are derived in within-group form thus being of diffusion type. On this basis, the conventional diffusion solver structure can be retained also for the solution of the SP3 transport problem.
The verification analysis provides proof of the methodological reliability of both trigonal DYN3D models. By means of diverse hexagonal academic benchmark and realistic detailed-geometry full-transport-theory problems, the superiority of the SP3 transport over the diffusion model is demonstrated in cases with pronounced anisotropy effects, which is, e.g., highly relevant to the modeling of fuel assemblies comprising absorber material.

Keywords: DYN3D; trigonal; triangular; hexagonal; nodal; diffusion; simplified P3; SP3

  • Doctoral thesis
    Karlsruhe Institute of Technology, 2013
    175 Seiten
  • Open Access Logo Wissenschaftlich-Technische Berichte / Helmholtz-Zentrum Dresden-Rossendorf; HZDR-035 2013
    ISSN: 2191-8708, eISSN: 2191-8716

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Permalink: https://www.hzdr.de/publications/Publ-19137
Publ.-Id: 19137


The DYN3D trigonal-geometry diffusion model – verification using the AER-FCM-101 benchmark

Duerigen, S.; Kliem, S.

DYN3D is a three-dimensional nodal diffusion code for steady-state and transient analyses of light-water reactors with square and hexagonal fuel assembly geometries as well as of innovative reactor concepts, which is undergoing continuous development.
In this work, the trigonal-geometry DYN3D diffusion model is verified by means of the AER-FCM-101 benchmark. With increasing trigonal mesh refinement, both effective multiplication factor and power distribution converge well to the extrapolated finite-element reference solution. In addition, a comparison to the hexagonal DYN3D diffusion models HEXNEM1 and HEXNEM2 is given.

Keywords: DYN3D trigonal nodal diffusion triangles AER-FCM-101

  • Contribution to proceedings
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia
    Proceedings of the 23rd Symposium of AER on VVER Reactor Physics and Reactor Safety
  • Lecture (Conference)
    23rd Symposium of AER on VVER Reactor Physics and Reactor Safety, 30.09.-04.10.2013, Štrbské pleso, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-19136
Publ.-Id: 19136


A micro-structured ion-implanted magnonic crystal

Obry, B.; Pirro, P.; Braecher, T.; Chumak, A. V.; Osten, J.; Ciubotaru, F.; Serga, A. A.; Fassbender, J.; Hillebrands, B.

We investigate spin-wave propagation in a microstructured magnonic-crystal waveguide fabricated by localized ion implantation. The irradiation caused a periodic variation in the saturation magnetization along the waveguide. As a consequence, the spin-wave transmission spectrum exhibits a set of frequency bands, where spin-wave propagation is suppressed. A weak modification of the saturation magnetization by 7% is sufficient to decrease the spin-wave transmission in the band gaps by a factor of 10. These results evidence the applicability of localized ion implantation for the fabrication of efficient micron- and nano-sized magnonic crystals for magnon spintronic applications.

Keywords: magnonic-crystal; waveguide; ion implantation

Permalink: https://www.hzdr.de/publications/Publ-19135
Publ.-Id: 19135


Positron annihilation studies of zirconia doped with metal cations of different valence

Prochazka, I.; Cizek, J.; Melikhova, O.; Konstantinova, T. E.; Danilenko, I. A.; Yashchishyn, I. A.; Anwand, W.; Brauer, G.

New results obtained by applying positron annihilation spectroscopy to the investigation of zirconia-based nanomaterials doped with metal cations of different valence are reported. The slow-positron implantation spectroscopy combined with Doppler broadening measurements was employed to study the sintering of pressure-compacted nanopowders of tetragonal yttria-stabilised zirconia (t-YSZ) and t-YSZ with chromia additive. Positronium (Ps) formation in t-YSZ was proven by detecting 3γ-annihilations of ortho-Ps and was found to gradually decrease with increasing sintering temperature. A subsurface layer with enhanced 3γ-annihilations, compared to the deeper regions, could be identified. Addition of chromia was found to inhibit Ps formation. In addition, first results of positron lifetime measurements on nanopowders of zirconia phase-stabilised with MgO and CeO2 are presented.

Keywords: positron annihilation spectroscopy; zirconia-based nanomaterials; positronium formation

Permalink: https://www.hzdr.de/publications/Publ-19134
Publ.-Id: 19134


Technical concepts for the operation of a Cameca 7f-Auto as ion source for the HZDR Super-SIMS

Ziegenrücker, R.; Merchel, S.; Renno, A. D.; Rugel, G.; Akhmadaliev, S.; Wustmann, B.

Super-SIMS - also called Accelerator-SIMS - is an ultrasensitive analytical method (Döbeli et al., 2013; Renno et al., 2013). A Super-SIMS-Set-up is now under installation at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) by connecting a conventional SIMS-source (Cameca 7f-Auto) to a 6 MV tandem accelerator (Akhmadaliev et al., 2013). The operation of a classical SIMS demands strong structural and building technological efforts [Cameca, 2012]. The requirements for the 6 MV tandem accelerator at the HZDR are of the same complexity.

Requirements # Cameca 7f-Auto # 6 MV tandem accelerator
vibrations # very strict # -
temperature | fluctuation # 19°C < T < 23°C|< 1°C•h-1 # max. 25°C
relative humidity | fluctuation # 30% < RH < 75% | < 10%•h-1 # 30%< RH < 75%
spurious magnetic field # < 3•10-7 Tesla # < 10-4 Tesla
vacuum # 10-9 mbar # 10-6 mbar
cooling | fluctuation # 17°C – 19°C | < 1°C•h-1 # 20°C – 25°C
nitrogen # N4.8 # N4.8
compressed air # dry | 5 – 7 bar | 35 – 50 L•min-1 # dry | 5 – 7 bar
uninterruptible power supply # 10 min # only for PC
radiation safety # - # very strict

The original specifications to optimally run both machines are in many cases incompatible. An additional challenge originates from the fact that a pre-acceleration voltage of 30 kV to inject negative secondary ions into the accelerator is needed. To guarantee the compliance with all specifications and safety regulations a specific concept for the housing of the Cameca 7f-Auto following a house-in-house-principle was developed. This concept guarantees the following operational options:
• independent operation of the 6 MV tandem accelerator
• independent operation of the Cameca 7f-Auto
• combined operation as a Super-SIMS by remote control
• operation of the Super-SIMS by remote control from outside the HZDR in the framework of the planned Helmholtz-SIMS network SIGMA
The most critical issue is the complete separation of all electric circuits in- and outside the SIMS housing by an insulating transformer, demanding the supply of electricity, gases, cooling, the intranet broadband network as well as all HVACR (heating, ventilation, air conditioning and refrigeration) without the use of electrically conductive materials. The strong vibrations in the accelerator hall are asking for further precautions. To follow all laboratory specifications for the Cameca instrument, the SIMS will be fixed on a cuboid made of natural gabbro (weight 6.4 t, size: 1.4 m x 1.8 m x 0.86 m) and all peripheral instruments on a frame vibrationally decoupled from the cuboid. This construction ensures the isolation of the SIMS and guarantees the compliance with all high-voltage safety regulations.

References
Döbeli et al., 2013, this meeting.
Renno et al., 2013, this meeting.
Akhmadaliev S., Heller R., Hanf D., Rugel G., Merchel S. (2013) The new 6 MV AMS-facility DREAMS at Dresden. Nucl. Instr. Meth. Phys. Res. B, 294, 5-10.
CAMECA (2012) IMS 7F Auto Installation & Delivery Conditions

Keywords: 6 MV Tandemaccelerator; SIMS; CAMECA 7f-Auto; Super-SIMS; Housing; Gabro; SIGMA

  • Poster
    Seventh Biennial Geo-SIMS Workshop, 20.-22.08.2013, Potsdam, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19133
Publ.-Id: 19133


Application of a new concept for multi-scale interfacial structures to the dam-break case with an obstacle

Hänsch, S.; Lucas, D.; Höhne, T.; Krepper, E.

New results of a generalized concept developed for the simulation of two-phase flows with multi-scale interfacial structures are presented in this paper. By extending the inhomogeneus Multiple Size Group-model, the concept enables transitions between dispersed and continuous gas morphologies, including the appearance and evanescence of one of these particular gas phases. Adequate interfacial transfer formulations, which are consistent with such an approach, are introduced for interfacial area density and drag. A new drag-formulation considers shear stresses occurring within the free surface area.
The application of the concept to a collapsing water column demonstrates the breakup of continuous gas into a polydispersed phase consisting of different bubble sizes. Both resolved free surface structures as well as the entrainment of bubbles and their coalescence and breakup underneath the surface can be described. The simulations have been performed with the CFD-code CFX 14.0 and will be compared with experimental images.
The paper will further investigate the possible improvement of such free surface simulations by including sub-grid information about small waves and instabilities at the free surface. A comparison of the results will be used for a discussion of possible new mass transfer models between filtered free surface areas and dispersed bubble size groups as part of the future work.

Keywords: multi-scale; flow regime transitions; air entrainment; dam-break; MUSIG; AIAD

Permalink: https://www.hzdr.de/publications/Publ-19132
Publ.-Id: 19132


Osteoblast responses to novel titanium-based surfaces produced by plasma- and ion beam technologies

Tsyganov, I.; Lode, A.; Hanke, T.; Kolitsch, A.; Gelinsky, M.

Plasma and ion beam technologies have been proven to be effective approaches for modification of surface properties of different materials. In the present work, structure, phase composition, hydrophilicity and microhardness of titanium oxynitride TiNxOy, and pure and phosphorus ions implanted TiO2 coatings produced by metal plasma immersion ion implantation and deposition were investigated. The mixed, highly amorphous TiN0.4O1.6 surface has maximal hydrophilicity and microhardness. P implantation in a TiO2 layer consisting mainly of rutile phase leads to disorder in the crystal lattice, slight amorphisation, and increasing hydrophilicity as well as microhardness of the surface. To evaluate the correlation between the structure of the layers and their cytocompatibility, the influence of the surfaces on the behavior of osteoblast-like SaOS-2 cells was studied in vitro. The cells were cultured on the three Ti-based coatings, both on the bare surfaces as well as on the surfaces biomineralised from simulated body fluid. No statistically significant differences were observed for cell adhesion to all bare Ti-based surfaces. Cell proliferation and osteogenic differentiation were surface sensitive and showed an opposite effect:
osteogenic differentiation, indicated by an increase of alkaline phosphatase (ALP) activity, on the P-implanted TiO2 and TiNxOy surfaces was reduced whereas the proliferation increased in comparison to TiO2.
Attachment and proliferation of cells were significantly lower on biomineralised surfaces.

Keywords: Plasma and ion beam technologies; cytocompatibility

Permalink: https://www.hzdr.de/publications/Publ-19131
Publ.-Id: 19131


Eph-Rezeptoren und Ephrin-Liganden als molekulare Schnittstelle zwischen Melanomzellen und Tumor-assoziierten inflammatorischen Zellen

Neuber, C.

  • Doctoral thesis
    TU Dresden, Fakultät Mathematik und Naturwissenschaften, 2013
    174 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19130
Publ.-Id: 19130


Magnetic and Structural Properties of Equiatomic FeRh thin films

Heidarian, A.; Potzger, K.; Lindner, J.; Heller, R.; Wilhelm, R.; Grenzer, J.; Reuther, H.; Bali, R.

Equiatomic FeRh thin films with varying thickness have been prepared on MgO (100) substrates via molecular beam epitaxy (MBE). The optimization of the stoichiometry was monitored using XRD, RBS and AES while the magnetic properties were probed using SQUID magnetometry. XRD results evidence a well ordered CsCl-type crystal structure. By increasing the annealing temperature of the films, the structural quality of the films also increases. Moreover, the known first order phase transition at ~350 K from an antiferromagnetic (AF) to a ferromagnetic (FM) state slightly shifts towards higher temperatures. M-H loops of films annealed at 800 ∘C or 850 ∘C recorded at 300 K show an opening, which is likely related to the magnetic field-induced AFM-FM phase transition. Residual low-temperature ferromagnetic moments are of unknown origin, but likely related to strain or diffusion effects at the surface or interface.

Keywords: FeRh thin films; Magnetic properties; Lattice structure; SQUID

  • Poster
    The IEEE Magnetics Society Summer School, 09.-14.06.2013, Assisi, Italy
  • Poster
    Joint European Magnetic Symposia (JEMS 2013), 25.-30.08.2013, Rhodes, Greece
  • Lecture (Conference)
    Deutsche Physikalische Gesellschaft (DPG 2014), 30.03.-04.04.2014, Dresden, Germany
  • Lecture (Conference)
    IEEE International Magnetics Conference (INTERMAG 2014), 04.-08.05.2014, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19129
Publ.-Id: 19129


Atom probe tomography characterization of CrN precipitation in low temperature 15N-enriched plasma nitrided 316L austenitic stainless steel.

Martinavičius, A.; Danoix, R.; Drouet, M.; Abrasonis, G.; Hannoyer, B.; Danoix, F.

Nitriding of austenitic stainless steel (ASS) at moderate temperatures (~400°C) leads to the formation of a modified surface layer which shows increased hardness and induced magnetism, without compromising the corrosion resistance. The exact nature of this layer is still a matter of debate.

In this study, ASS 316L has been plasma nitrided with a mixture of 14N and 15N for 30 min at 400°C. Only a single phase, usually called the S phase or expanded austenite, is detected by X-ray diffraction. Transmission electron microscopy shows a high density of stacking faults and lattice distortions in this S phase, but does not provide any direct information regarding its composition, in particular regarding nitrogen and chromium distributions at the nanometer scale. Atom probe tomography and field ion microscopy reveal the presence of nanometric chromium nitride precipitates, with irregular oblate-spheroid-like shape. The preferential precipitation of chromium nitride at grain boundaries and/or stacking faults is investigated. These observations suggest that incorporation of large amounts of N provides strong driving force for chromium nitride formation, even at such a short nitriding time and rather low temperature.

Because of the presence of silicon and obviously iron in this industrial stainless steel, direct composition measurement of these chromium nitrides, in particular their nitrogen content, is not possible. In order to solve this classical analytical issue, specimens were nitrided using different 14N/15N ratios. Possible N+/Si2+ and N2+/Fe2+ overlaps at 14 and 28 Da respectively are investigated in order to estimate the actual chromium nitride composition. Results will be compared with the one obtained with the newly developed high mass resolution Flextap, potentially allowing N+/Si2+ and N2+/Fe2+ peak discrimination.

  • Poster
    53rd International Field Emission Symposium (IFES 2012), 21.-25.05.2012, Tuscaloosa, Alabama, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19128
Publ.-Id: 19128


Low-energy enhancement of magnetic dipole radiation

Schwengner, R.; Frauendorf, S.; Larsen, A. C.

Magnetic dipole strength functions have been deduced from averages of a large number of M1 transition strengths calculated within the shell model for the nuclides 94Mo, 95Mo, and 90Zr. An enhancement of M1 strength toward low transition energy has been found for all nuclides considered. Large M1 strengths appear for transitions between close-lying states with configurations including proton as well as neutron high-j orbits that re-couple their spins and add up their magnetic moments coherently. The M1 strength function deduced from the calculated M1 transition strengths is compatible with the low-energy enhancement found in (3He,3He') and (d,p) experiments. The present work presents for the first time an explanation of the experimental findings.

Keywords: Magnetic dipole radiation; gamma-ray strength functions; shell model

Permalink: https://www.hzdr.de/publications/Publ-19127
Publ.-Id: 19127


Extending the Range of the Inductionless Magnetorotational Instability

Kirillov, O.; Stefani, F.

The magnetorotational instability (MRI) can destabilize hydrodynamically stable rotational flows, thereby allowing angular momentum transport in accretion disks. A notorious problem for the MRI is its questionable applicability in regions with low magnetic Reynolds number. Using the WKB method, we extend the range of applicability of the MRI by showing that the inductionless versions of the MRI, such as the helical MRI and the azimuthal MRI, can easily destabilize Keplerian profiles if the radial profile of the azimuthal magnetic field is only slightly modified from the current-free profile. This way we further show how the formerly known lower Liu limit of the critical Rossby number connects naturally with the upper Liu limit.

Keywords: MHD waves; magnetorotational instability; accretion disk; WKB approximation; stability

Permalink: https://www.hzdr.de/publications/Publ-19126
Publ.-Id: 19126


Validation of closure models for interfacial drag and turbulence in numerical simulations of horizontal stratified gas-liquid flows

Höhne, T.; Mehlhoop, J.-P.

The development of general models closer to physics and including less empiricism is a long-term objective of the activities of the HZDR research programs. Such models are an essential precondition for the application of CFD codes to the modelling of flow related phenomena in the chemical and nuclear industries. The Algebraic Interfacial Area Density (AIAD) approach allows the use of different physical models depending on the local morphology inside a macroscale multi-fluid framework. A further step of improvement of modelling the turbulence at the free surface is the consideration of sub-grid wave turbulence that means waves created by Kelvin-Helmholtz instabilities that are smaller than the grid size. In fact, the influence on the turbulence kinetic energy of the liquid side can be significantly large. The new approach was verified and validated against horizontal two-phase slug flow data from the HAWAC channel and smooth and wavy 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

Permalink: https://www.hzdr.de/publications/Publ-19125
Publ.-Id: 19125


Ion-irradiation induced damage in Fe-Cr alloys characterized by nanoindentation

Heintze, C.; Bergner, F.; Hernandez Mayoral, M.

Self-ion irradiation in combination with nanoindentation offers the possibility to characterize irradiation damage in a broad range of irradiation temperature and fluence. Nanoindentation results are reported for Fe-2.5at%Cr, Fe-9at%Cr and Fe-12.5at%Cr irradiated at room temperature, 300°C and 500°C. Special features of this work are roughly rectangular damage profiles and exploitation of the full load dependence of hardness. The effects of Cr content, fluence and irradiation temperature are discussed. Hardening features were characterized by means of transmission electron microscopy. A tentative multi-feature hardening model was applied, to this end APT data published for the same alloys ion-irradiated under the same nominal conditions are taken into account.

Keywords: Ion irradiation; nanoindentation; TEM; Fe-Cr-alloys

  • Poster
    Getmat International Workshop, 17.-19.09.2013, Berlin, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19124
Publ.-Id: 19124


Nanoindentation of ion-irradiated Fe-Cr alloys

Heintze, C.; Bergner, F.; Hernandez Mayoral, M.

The structural materials of particular components in nuclear applications like fission or fusion reactors are exposed to high neutron fluxes giving rise to the formation of irradiation-induced defects and subsequent changes of the mechanical properties. Ion-irradiation is a well-recognized tool to simulate damage caused by fast neutron irradiation in a wide range of irradiation temperature and fluence and allows for an efficient screening of potential structural materials for nuclear application due to short irradiation times. The limited depth of penetration of the ions into the material (up to few µm) demands characterization methods suitable for thin layers. In the present work, nanoindentation is applied to deduce the irradiation-induced hardness changes. The approach is based on the generation of an approximately rectangular dpa-profile by means of multi-step irradiations with ions of different energies and the exploitation of the depth dependence of the hardness. Results will be reported for ferritic/martensitic Cr-steels considered as candidate structural materials for future application in Generation IV fission reactors and for Fe-Cr binary alloys with emphasis on the effect of irradiation temperature and fluence. Transmission electron microscopy results on the formation of irradiation-induced defects will be taken into account.

Keywords: ion-irradiation; nanoindentation; TEM; Fe-Cr-alloys

  • Poster
    Nano Measure 2013, 25.-26.06.2013, Warsawa, Polska

Permalink: https://www.hzdr.de/publications/Publ-19123
Publ.-Id: 19123


On the homogenization of the thickness of Cu deposits by means of MHD convection within small dimension cells

Mühlenhoff, S.; Mutschke, G.; Uhlemann, M.; Yang, X.; Odenbach, S.; Fröhlich, J.; Eckert, K.

The influence of magnetohydrodynamic (MHD) convection on the thickness of an electrochemically deposited copper layer along a vertical plane cathode is examined. A magnetic gradient field, that induces a Lorentz force, establishes a vortical motion of the electrolyte which can be oriented either antiparallel or parallel to the natural convection. For the latter case, we show both experimentally and numerically that a sufficiently strong Lorentz force levels the inhomogeneities of the deposit thickness characteristic for deposition under pure natural convection.

Keywords: electrochemical deposition; magnetoelectrochemistry; Lorentz force; forced convection; mass transport; MHD

Permalink: https://www.hzdr.de/publications/Publ-19122
Publ.-Id: 19122


Growth of carbon-tungsten nanocomposites by high power impulse magnetron sputtering from compound targets

Yadav, R. K.; Abrasonis, G.; Munnik, F.; Heller, R.; Hübner, R.; Möller, W.; Neidhardt, J.

High-power impulse magnetron sputtering (HiPIMS, also known as high-power pulsed magnetron sputtering, HPPMS) is a method for physical vapour deposition of thin lms which is based on magnetron sputter deposition. HiPIMS utilises extremely high power densities of the order of kW cm-2 in short pulses (impulses). A distinguishing feature of HiPIMS is its high degree of ionization of the sputtered metal and high rate of molecular gas dissociation. In this poster we present the study on the growth of C-W nanocomposite lms grown in DC (MS) and HiPIMS modes. For deposition, we have used 3 in C and C-W (90 to 10 at%) substrates. In order to prevent arcing, the depositions were carried out with three-pulse sequence followed by a long off-time. Film areal density was determined by Rutherford Backscattering Spectrometry (RBS) and Nuclear Reaction Analysis (NRA). Film microstructure was determined by Raman spectroscopy, X-Ray diraction, and transmission electron microscopy. Film mechanical properties were studied by nanoindentation and scratch test. We got extensive arcing with pure carbon. In contrast, for the compound target we got stable plasma condition with duty cycle as low as 1 %. Deposited films consist of WC nanoparticles embedded in a carbon matrix. From NRA and RBS, the film areal density of tungsten shows a small decrease concomitantly with the duty cycle (transition from pulsed DC to HiPIMS). In contrast, the film areal density of carbon remains constant. This implies that in different sputtering modes like Ar + dominated in the pulsed DC mode or a mixture of Ar/W ions in the HiPIMS mode the average sputtering rate of carbon is not affected. A collisional computer simulation using TRIDYN was carried out to show a considerable sputter yield amplication of carbon when irradiated with a mixture of Ar/W ions. This is in-line with the observed stable carbon film areal density, which can be attributed to the compensation of the change in sputtering ion composition by sputter yield amplication due to W-enrichment of the target surface. Film characterization shows that there is no signicant change between the films grown in DC and HiPIMS modes.

  • Poster
    537th Wilhelm and Else Heraeus Seminar Physics of Ionized and Ion-Assisted PVD: Principles and Current Trends, 26.-28.06.2013, Dreseden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19121
Publ.-Id: 19121


Optical Selectivity Enhancement of Carbon-based nanocomposites: Simulation and Experiments

Guillén, E.; Heras, I.; Abrasonis, G.; Pardo, A.; Krause, M.; Endrino, J. L.

Carbon-based metal nanocomposites have been shown to be good material candidates for applications requiring optical selectivity. However their true potential usage largely depends on the optimization of their composition and microstructure. Diamond Like Carbon with different transition metals were grown on stainless steel and Inconel substrates using pulse filtered cathodic arc deposition from two repetitively pulsed cathodic arc sources with separate macroparticle filters. The influence of several transition metals (Ti, Zr, Cr, W, Mo, V and Nb) on their optical selectivity was investigated. Carbon metal-containing samples were prepared using two cathodic arc sources provided with a carbon cathode and a pure transition metal cathode. Different metal concentrations in the coatings were obtained by varying the average arc current of the metal pulsed cathodic arc source (Imetal). The volume fraction of metal was determined by combined Rutherford Backscattering Spectroscopy (RBS) and Nuclear Reaction Analysis (NRA) measurements. The structure of the deposited films was analyzed by Transmission Electron Microscopy (TEM), X-ray diraction (XRD) and Raman spectroscopy. In this study, the computer simulation program Coating Design (CODE) has been used to calculate optical properties of the different carbon-transition metal nanocomposites. The optical constants of various carbon-based nanocomposites were simulated using a physical model proposed by Bruggeman and Maxwell Garnett which averages the dielectric function of the components of the composite, which allows treating the composite system as an effective medium. The performed simulations allowed calculating the solar absorptance and thermal emittance of the nanocomposites. Varying the nanocomposite material configurations such as layer thickness, volume metal fraction, number of layers and multilayer stack resulted in new configurations that enhance the optical selectivity of these materials. Simulated reflectance was compared with spectrophotometry measurements of the deposited films with good agreement between them.

  • Poster
    537th Wilhelm and Else Heraeus Seminar Physics of Ionized and Ion-Assisted PVD: Principles and Current Trends, 26.-28.06.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19120
Publ.-Id: 19120


Ion induced compositionally modulated ripples during composite film growth: 3D sculpting at the nanoscale

Abrasonis, G.; Krause, M.; Buljan, M.; Mücklich, A.; Fritzsche, M.; Facsko, S.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Baehtz, C.; Shalimov, A.; Gemming, S.

Ion irradiation of multielement surfaces can induce regular compositionally modulated surface roughness nanopattern formation such as ripples or nanodots. This kind of bottom-up nanopatterning can provide means to not only structure the solid surfaces but also to create ordered heterogeneous structures in three dimensions (3D) when performed in growth mode: the compositional surface nanopattern is continuously buried by incoming species while the surface is again restructured due to ion irradiation.
The present work is an experimental demonstration of this concept: 3D ordered nanocomposites are grown via ion induced two dimensional (2D, surface) nanopattern formation during bi-component film growth. The influence of low energy (50-140 eV) assisting Ar+ ion irradiation on the morphology of C:Ni (~ 5 at.% Ni to ~ 30 at.% Ni) thin films will be reported. It will be shown that for certain growth conditions surface ripples form during oblique incidence low energy ion beam assisted deposition of C:Ni films. These surface ripples are compositionally modulated: Ni is located on the crests and carbon in the valleys. The film cross sections show periodic distribution of metal nanoparticles in a carbon matrix with the same periodicity as the surface ripples. As this 3D patterning effect has a physical origin, it can be expected to occur in many material systems. Such an approach holds high potential for the growth of functional nanocomposite films for a wide range of applications.

  • Lecture (Conference)
    International Symposium on Nanoscale Pattern Formation at Surfaces, 26.-30.05.2013, Copenhagen, Denmark

Permalink: https://www.hzdr.de/publications/Publ-19119
Publ.-Id: 19119


Konzeptioneller Entwurf und prototypische Realisierung einer automatisierten Berichtserstellung für statistische Auswertungen des HZDR

Likerski, A.

Die vorliegende Arbeit zeigt, wie innerbetriebliche Berichtserstellungsprozesse durch Unterstützung von IT-Systemen verbessert werden können. Im Speziellen geht es dabei um die prototypische Realisierung eines Berichtssystems am Helmholtz-Zentrum Dresden-Rossendorf e.V., wobei es den Mitarbeitern mithilfe des SharePoint-Add-In der Microsoft Reporting Services möglich ist, Berichte im SharePoint zu erstellen und diese dort zu hinterlegen.
Zur Umsetzung dieser Zielstellung wurde zunächst die Ausgangssituation anhand des Geschäftsprozesses sowie die Quelle der benötigten Informationen analysiert, um daraufhin ein entsprechendes Konzept zu erarbeiten. Dabei wurde eine, dem System zur Datenbeschaffung, nachgelagerte Datenbank erstellt, welche zur Sammlung aller berichtsrelevanten Informationen dienen soll und danach, nach vorheriger Beschreibung verschiedener Möglichkeiten, die oben genannte Realisierung ausgewählt wurde.
Im Anschluss daran wurde eine Kosten-Nutzen-Analyse durchgeführt, welche die Vorteile der durchgeführten Teilautomatisierung verdeutlicht.

Keywords: Reporting Services; Reporting

  • Bachelor thesis
    BA Dresden, 2013
    69 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19118
Publ.-Id: 19118


Special Issue: Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications, Geophysical and Astrophysical Fluid Dynamics, 107, Issue 4 (2013)

Ferriz-Mas, A.; Hollerbach, R.; Stefani, F.; Tilgner, A.; (Editors)

This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.

  • Book (Editorship)
    London, UK: Taylor and Francis, 2013
    98 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19117
Publ.-Id: 19117


GEANT4 Simulationen zur Optimierung einer Compton Kamera für die In-vivo Dosimetrie

Rohling, H.; Enghardt, W.; Hertel, N.; Kormoll, T.; Pausch, G.; Fiedler, F.

Fragestellungen: Zur Qualitätssicherung der Partikelbestrahlungen von Tumorpatienten ist eine nicht-invasive, in-vivo Überwachung wünschenswert. Am OncoRay / TU Dresden / HZDR wird zur Zeit ein Prototyp einer Compton Kamera für die klinische Anwendung entwickelt, die eine solche Überwachung anhand der bildgebenden Messung prompter Gammastrahlung ermöglichen soll [1]. Aufgrund der Vielzahl der zu optimierenden Parameter wie Größe, Abstände und Material der Detektoren, zur Analyse der auftretenden Wechselwirkungen und zur Selektion von Ereignissen sind Monte Carlo Simulationen dabei unerlässlich.

Material und Methoden: Die betrachtete Compton Kamera ist aus einer Streuebene (CZT) und einer Absorberebene (CZT oder LSO) aufgebaut (Abb.1). Das Funktionsprinzip einer Compton Kamera basiert auf der Berechnung des Streuwinkels und damit der Eintreffrichtung des Photons mithilfe der gemessenen Energiedepositionen.
Zur Optimierung des Detektorsystems wurden Simulationen mit dem Monte Carlo Code GEANT4 Version 9.5 [2] durchgeführt. Neben der Untersuchung der Zählraten war die Charakterisierung der auftretenden Ereignisse das Ziel dieser Simulationen. Dabei wird eine koinzidente Energiedeposition in beiden Detektorebenen genau dann als nutzbares Ereignis angesehen, wenn in der Streuebene genau eine Compton Streuung und in der Absorptionsebene eine vollständige Absorption des Photons stattfand. Außer einer Punktquelle wurden Emissionen aus einer kugelförmigen Quelle mit 10 cm Durchmesser simuliert. Verschiedene Abstände des Detektors zur Quelle sowie unterschiedliche Anordnungen von Streuebene zur Absorptionsebene wurden angenommen. Des Weiteren wurden die Simulationen mit experimentellen Daten verglichen. Ferner wurde der Fehler, der durch die Abweichung zwischen simuliertem Schwerpunkt, der dem experimentellen Messpunkt nahe kommt, und dem Ort der Comptonstreuung im Streuer bzw. der Einfallsrichtung im Absorber untersucht.

Ergebnisse: Die Konfiguration aus CZT und LSO weist erwartungsgemäß eine höhere Ansprechwahrscheinlichkeit als der CZT-CZT Detektor auf (Abb.2), außerdem ist die Rate an nutzbaren Ereignissen deutlich höher (Abb.3). Die Abstände zwischen den Detektorebenen und der Abstand zur Quelle haben kaum Einfluss auf die Güte der Ereignisse. Eine Selektion von Ereignissen zur Minimierung des Rauschens anhand der Wechselwirkungstiefe in der Streuebene erscheint sinnvoll.

Zusammenfassung: Es wurden umfassende Simulationen mit GEANT4 zur Bewertung und Optimierung von möglichen Compton Kamera Systemen durchgeführt. Um die Güte der Simulationen zu bewerten wurden die Simulationsergebnisse mit experimentellen Daten verglichen.

Literatur

[1] Kormoll, T.: A Compton Camera for In-vivo Dosimetry in Ion-beam Radiotherapy. Diss.,
Technische Universität Dresden, Mathematik und Naturwissenschaften. Dresden, 2013

[2] Agostinelli, S. et al 2003 GEANT4 - a simulation toolkit Nucl. Instr. Meth. A 506(3) 250-303

  • Poster
    44. Jahrestagung der Deutschen Gesellschaft für Medizinische Physik, 18.-21.09.2013, Köln, Deutschland
  • Abstract in refereed journal
    Medizinische Physik 2013 (2013), 710

Permalink: https://www.hzdr.de/publications/Publ-19116
Publ.-Id: 19116


Introduction

Ferriz-Mas, A.; Hollerbach, R.; Stefani, F.; Tilgner, A.

This Special Issue originates from a Special Session on “Magnetohydrodynamics: Mathematical Problems and Astrophysical Applications” that was held in the framework of the “8th AIMS International Conference on Dynamical Systems, Differential Equations and Applications” at Dresden University of Technology from 25 to 28 May 2010. The Special Issue papers are elaborated and updated versions of several of the review talks.

Permalink: https://www.hzdr.de/publications/Publ-19115
Publ.-Id: 19115


Radio-colouration of diamond: a spectroscopic study

Nasdala, L.; Grambole, D.; Wildner, M.; Gigler, A. M.; Heinschwang, T.; Zaitsev, A. M.; Harris, J. W.; Milledge, J.; Schulze, D. J.; Hofmeister, W.; Balmer, W. A.

We have undertaken a study of the common green or orange-brown spots at the surface of rough diamond specimens, which are caused by alpha particles emanating from radioactive sources outside the diamond. Richly coloured haloes represent elevated levels of structural damage, indicated by strong broadening of the main Raman band of diamond, intense strain birefringence, and up-doming of spots due to their extensive volume expansion. Green radio-colouration was analogously generated through the irradiation of diamond with 8.8 MeV helium ions. The generation of readily visible radio-colouration was observed after irradiating diamond with a parts per thousand yen10(15) He ions per cm(2). The accumulation of such a high number of alpha particles requires irradiation of the diamond from a radioactive source over long periods of time, presumably hundreds of millions of years in many cases. In the samples irradiated with He ions, amorphisation was observed in volume areas where the defect density exceeded 5 x 10(-3) (-3) (or 0.03 dpa; displacements per target atom). In contrast, graphitisation as a direct result of the ion irradiation was not observed. The green colouration transformed to brown at moderate annealing temperatures (here 450 A degrees C). The colour transformation is associated with only partial recovery of the radiation damage. The colour change is mainly due to the destruction of the GR1 centre, explained by trapping of vacancies at A defects to form the H3 centre. An activation energy of similar to 2.4 +/- A 0.2 eV was determined for the GR1 reduction. The H3 centre, in turn, causes intense yellowish-green photoluminescence under ultraviolet illumination. Radio-colouration and associated H3 photoluminescence are due to point defects created by the ions irradiated, whereas lattice ionisation is of minor importance. This is concluded from the depth distribution of the colouration and the photoluminescence intensity (which corresponds to the defect density but not the ionisation distribution pattern). The effect of the implanted He ions themselves on the colour and photoluminescence seems to be negligible, as radio-colouration and H3 emission were analogously produced through irradiation of diamond with C ions. The photoluminescence emission becomes observable at extremely low defect densities on the order of 10(-6) (-3) (or 0.000006 dpa) and is suppressed at moderate defect densities of similar to 5 x 10(-4) (-3) (or similar to 0.003 dpa). Intensely brown-coloured diamond hence does not show the H3 emission anymore. Anneals up to 1,600 A degrees C has reduced considerably irradiation damage and radio-colouration, but the structural reconstitution of the diamond (and its de-colouration) was still incomplete.

Keywords: Diamond; Radiation damage; Radiocolouration; Defect luminescence; Volume swelling

Permalink: https://www.hzdr.de/publications/Publ-19114
Publ.-Id: 19114


Energetic ion-assisted nanocomposite film growth: sculpting matter in 3D at the nanoscale

Abrasonis, G.

Nanostructures dramatically influence materials properties due to size, shape and interface effects. Thus the control over the structure at the nanoscale is a key issue in nanomaterials science. The growth of nanostructured thin films is governed by the atomistic processes at the very surface of the growing film. The interaction range of hyperthermal ions with solid surface is confined to some nanometers. Therefore energetic ion assistance during film deposition is of primary relevance in the context of the thin film nanostructuring.
Our recent activities in the field of ion-assisted physical vapor deposition (PVD) of nanocomposite films will be summarized with the focus on the growth-structure relationship of carbon-transition metal films. This class of materials is relevant in the context of tribology, sensing, fusion, electrochemistry, information storage, spintronics, solar-thermal energy conversion or as metamaterials. We have employed two paradigms involving the use of energetic ions:
• ion assisted PVD (ia-PVD), where the growing film is irradiate with assisting ion beam
• ionized PVD (i-PVD), where the depositing species are energetic ions themselves.
The nanocomposite film growth is determined by surface diffusion assisted phase separation of immiscible species adsorbed from homogeneous mixture in the vapor phase. Ion irradiation intervenes with the interplay of thermodynamic forces and kinetic constraints as a third competing factor and has a dramatic effect on the film morphology. A large variety of structures is observed such as encapsulated nanoparticles, high aspect ratio nanocolumns or self-organized layered 3D nanoparticle arrays (see Fig 1.). In addition, the ion induced atomic mobility is not isotropic, as it would be in the case of thermally excited migration, but conserves to a large extent the initial direction of the incoming ions. Independently of the growth regime, it results in the morphology tilt: metal nanopatterns no longer align with the advancing surface but with the incoming ions. Such effects allow 3D sculpting of nanocomposites which is due to ion irradiation effects and does not require any glancing incidence conditions.
As the observed effects are of physical origin (ion-solid interactions), we believe that the presented results are applicable to other immiscible or partially miscible systems as well. This presents a possible path towards a material design approach based on material system independent tools to sculpt the morphology at the nanoscale in order to match the requirements of a wide range of applications.

  • Invited lecture (Conferences)
    2013 Energy Materials Nanotechnology (ENM Spring), 08.-11.04.2013, Orlando, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19113
Publ.-Id: 19113


Advanced Solar Absorber Coatings Based on Nanocomposites

Heras, I.; Escobar Galindo, R.; Abrasonis, G.; Pardo, A.; Vinnichenko, M.; Endrino, J. L.

The design of an efficient and stable solar selective coating for photo-thermal conversion plants requires a complex study of the materials that composed the coating. The optimal optical properties for those absorber coatings are high solar absorptance in the wavelength range of 0.3 to 2.5 μm which corresponds to solar spectrum under atmospheric conditions and low thermal emittance in the infrared wavelength range.
Carbon-transition metal nanocomposites have been selected as absorber materials because they show appropriate optical properties as well as thermal and mechanical stability at high temperatures. The refractory metal carbide nanoparticles have been experimentally shown to stabilize the surrounding carbon matrix at least up to 700°C.
The computer simulation program CODE has been used to calculate solar absorptance and thermal emittance of various multilayers coatings material combinations of carbon - metal nanocomposites (NCTM). The optical properties of the inhomogeneous composite material were simulated with a physical model proposed by Bruggeman and Maxwell Garnett which average the dielectric function of the components of the composite. This allows treating the composite system as an effective medium.
This contribution compares simulated optical properties for different nanocomposite structural configurations (layer thickness, metal to carbon ratio). The calculated results are in the range of 0.91-0.97 for solar absorptance and 0.02 - 0.07 for thermal emittance at 300K.

  • Poster
    2013 MRS Spring Meeting & Exhibit, 01.-05.04.2013, San Francisco, CA, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19112
Publ.-Id: 19112


Ion Assistance Effects on the Morphology of Carbon-Nickel Composite Films Grown by Physical Vapor Deposition at Various Metal Contents

Abrasonis, G.; Krause, M.; Muecklich, A.; Baehtz, C.; Shalimov, A.; Zschornak, M.; Wintz, S.; Endrino, J. L.; Gemming, S.

Phase separation occurring on the surface of growing films provides unique means to influence the microstructure of composite materials. Here, the influence of ion assistance on the morphology of carbon-nickel nanocomposite thin films for different metal contents is investigated. Carbon-transition metal nanocomposites are relevant in the context of solar-thermal energy conversion, fusion, fuel cells, tribology or sensing. The films were grown by dual ion beam sputtering in a temperature range of RT-300°C. The growing films were irradiated by an assisting Ar ion beam with energies ranging from 50 to 130 eV. It is found that the nickel content drastically influences the morphology of the films: while films with low Ni contents show regular self-organized structures consisting of ordered Ni nanoparticles embedded in the carbon matrix, higher Ni contents predominantly exhibit a columnar morphology. The results are discussed on the basis of the interplay of ion-induced effects and phase separation modes.
Acknowledgements: Funding by the European Union, ECEMP-Project D1, "Nanoskalige Funktionsschichten auf Kohlenstoffbasis", Projektnummer 13857 / 2379 is gratefully acknowledged.

  • Lecture (Conference)
    2013 MRS Spring Meeting & Exhibit, 01.-05.04.2013, San Francisco, CA, United States of America

Permalink: https://www.hzdr.de/publications/Publ-19111
Publ.-Id: 19111


Interference effects in super-radiant THz sources

Asgekar, V.; Geloni, G. A.; Kocharyan, V.; Stojanovice, N.; Michel, P.; Gensch, M.

A new class of linear accelerator (linac) based THz facilities, aiming to provide peak THz fields in the GV/m regime from highly charged, ultra-short relativistic electron bunches is currently studied and developed worldwide. These facilities are based on low emittance, electron beams delivered by a linear radio frequency (RF) driven accelerator followed by one or several magnetic chicanes that act as bunch compressor. THz radiation is then emitted coherently for wavelengths appropriately longer than the longitudinal electron bunch length upon one single pass through any of the typical sources of synchrotron radiation. This allows for an enormous flexibility in the generated spectral, spatial and temporal properties of the THz pulses. Together with the theoretically large scalability and simplicity of these sources, they are discussed as extension of the THz pulses from laser-based THz sources towards extreme transient THz fields and high repetition rates with more than 10 projects currently being pursued worldwide. In this respect it is timely to investigate if current idealized theoretical descriptions can be technically fully realized. As our contribution to this effort, in this paper it is shown by numerical and analytical calculations that the interference effects between different THz radiators, intrinsically emitting in the forward direction of a linac can crucially affect radiation properties.

Keywords: super-radiant THz sources; coherent THz sources

Permalink: https://www.hzdr.de/publications/Publ-19110
Publ.-Id: 19110


Multiphase CFD @ HZDR - Strategy and research topics of the CFD department

Lucas, D.; Montoya, G.

CFD Workshop about the different projects and modelling strategies inside the Computational Fluid Dynamics Department of the Institute of Fluid Dynamics of HZDR, along with a brief introduction of other different institutes such as Resource Ecology, Material Research, Cancer Research, among others.

Keywords: CFD; HZDR; Fluid Dynamics; Workshop

  • Invited lecture (Conferences)
    21st International Conference on Nuclear Engineering (ICONE21), 29.07.-02.08.2013, Chengdu, China

Permalink: https://www.hzdr.de/publications/Publ-19109
Publ.-Id: 19109


Comparison of PHITS, GEANT4, and HIBRAC simulations of depth-dependent yields of beta+-emitting nuclei during therapeutic particle irradiation to measured data

Rohling, H.; Sihver, L.; Priegnitz, M.; Enghardt, W.; Fiedler, F.

For quality assurance in particle therapy, a non-invasive, in-vivo range verification is highly desired. Particle Therapy Positron-Emission-Tomography (PT-PET) is the only clinically proven method up to now for this purpose. It makes use of the beta+-activity produced during the irradiation by the nuclear fragmentation processes between the therapeutic beam and the irradiated tissue. Since a direct comparison of beta+-activity and dose is not feasible, a simulation of the expected beta+-activity distribution is required. For this reason it is essential to have a quantitatively reliable code for the simulation of the yields of the beta+-emitting nuclei at every position of the beam path. In this paper results of the three-dimensional Monte-Carlo simulation codes PHITS, GEANT4, and the one-dimensional deterministic simulation code HIBRAC are compared to measurements of the yields of the most abundant beta+-emitting nuclei for carbon, lithium, helium, and proton beams. In general, PHITS underestimates the yields of positron-emitters. With GEANT4 the overall most accurate results are obtained. HIBRAC and GEANT4 provide comparable results for carbon and proton beams. HIBRAC is considered as a good candidate for the implementation to clinical routine PT-PET.

Permalink: https://www.hzdr.de/publications/Publ-19108
Publ.-Id: 19108


Review of effects of radiation damage on the luminescence emission of minerals, and the example of He-irradiated CePO4

Nasdala, L.; Grambole, D.; Ruschel, K.

The accumulation of structural damage that is created in minerals upon corpuscular irradiation, has two apparently contrarious effects on their luminescence behaviour. First, irradiation may cause the generation of luminescent defect centres, which typically results in broad-band emissions. Such defect emissions are characteristic of low levels of radiation damage. Second, radiation damage depletes in general the luminescence of minerals, which is associated with broadenings and intensity losses of individual emission lines. Minerals that have suffered elevated levels of irradiation hence tend to be virtually non-luminescent. This review paper aims at giving an overview of the possible correlations of radiation damage and emission characteristics of minerals. After a brief, introductory summary of the damage-accumulation process and its causal corpuscular radiation, an array of examples is presented for how internal and/or external irradiation may change appreciably the emission of rock-forming and accessory minerals. As a detailed example for the complexity of changes of emissions upon damage accumulation, preliminary results of a case study of the photoluminescence (PL) of synthetic CePO4 irradiated with 8.8 MeV He ions are presented. Irradiation-induced spectral changes include (i) the initial creation, and subsequent depletion, of a broad-band, defect-related PL emission of orange colour, and (ii) gradual broadenings and intensity losses of PL lines related to electronic transitions of rare-earth elements, eventually leading to gradual loss of their splitting into multiple Stark levels (shown for the 4F3/2 → 4I9/2 transition of Nd3+).

Permalink: https://www.hzdr.de/publications/Publ-19107
Publ.-Id: 19107


Nonconservative Stability Problems of Modern Physics

Kirillov, O. N.

This work gives a complete overview on the subject of nonconservative stability from the modern point of view. Relevant mathematical concepts are presented, as well as rigorous stability results and numerous classical and contemporary examples from mechanics and physics. It deals with both finite- and infinite-dimensional nonconservative systems and covers the fundamentals of the theory, including such topics as Lyapunov stability and linear stability analysis, Hamiltonian and gyroscopic systems, reversible and circulatory systems, influence of structure of forces on stability, and dissipation-induced instabilities. The book serves present and prospective specialists providing the current state of knowledge in the actively developing field of nonconservative stability theory. Its understanding is vital for many areas of technology, ranging from such traditional ones as rotor dynamics, aeroelasticity and structural mechanics to modern problems of hydro- and magnetohydrodynamics and celestial mechanics.

Keywords: Lyapunov stability; mathematical physics; dynamical systems; nonconservative systems; dissipative systems; perturbation theory

  • Book (Authorship)
    Berlin; Boston, Mass.: Walter de Gruyter GmbH, 2013
    429 Seiten

Downloads:

Permalink: https://www.hzdr.de/publications/Publ-19106
Publ.-Id: 19106


The genesis of Zr-Nb-REE mineralisation at Khalzan Buregte (Western Mongolia) reconsidered

Kempe, U.; Möckel, R.; Graupner, T.; Kynicky, J.; Dombon, E.

The genesis of the economic Zr-Nb-REE mineralisation at Khalzan Buregte, Western Mongolia was re-explored by field work, whole rock analysis (chemical composition, quantitative XRD mineral analysis) and by application of various transmitted light and electron microscopic techniques. Coarse-grained bodies, dikes, and volcanics of alkaline, silica-saturated rocks were contemporarily emplaced at subvolcanic to volcanic levels forming four alkaline massifs within the Khalzan Buregte area. The whole rock composition of the weakly altered magmatic rocks ranges from syenite to quartz monzonite and alkaline granite (alkali feldspar syenite to alkali feldspar granite according to mineral composition). Magmatic and hydrothermal processes contributed to the formation of economic concentrations of several high field strength elements (HFSE) as Zr, Hf, Nb, Ta, REE, and Y in the Khalzan Buregte deposit and in the nearby Tsakhir prospect. Magmatism with mixing of at least three melt types and, possibly, the formation of K-feldspar cumulates resulted in a local enrichment of Zr, Nb, and of the light rare earth elements (LREE) in the rocks up to a sub-economic level. There was, however, no significant increase in Y and the heavy rare earth elements (HREE). In contrast, hydrothermal alteration by silica- and carbonate-rich fluids yielded extreme concentrations of Zr, Nb, and LREE. Additionally, one of the late alteration events resulted in economic levels of Y and HREE. These fluids were rich in fluorine. There are new indications for two main alteration events causing ore formation: (1) an early, carbonatite-style and (2) a late by F-rich fluids. Multistage metasomatic alteration resulted in a pronounced chemical and mineralogical heterogeneity of the alteration assemblages. The main hosts of Zr (and Hf) in the ores are zircon and other zirconium silicates (gittinsite, catapleiite-(Ca), and elpidite). Nb (and Ta) is mainly contained in various types of pyrochlore (Khalzan Buregte) and – to a lesser extent – in fergusonite and some other minerals (Tsakhir). A large diversity of REE-bearing minerals includes oxides, fluoro-carbonates, and silicates that concentrate LREE, HREE, and Y.

Keywords: Zr-Nb-REE mineralisation; zirconium silicates; Khalzan Buregte; alkaline rocks; HFSE

Permalink: https://www.hzdr.de/publications/Publ-19105
Publ.-Id: 19105


Hydrodynamic multiplicity in a tubular reactor with solid foam packings

Mohammed, I.; Bauer, T.; Schubert, M.; Lange, R.

Catalytic active open foam packings are promising to enhance the performance of tubular reactors for gas–liquid–solid reactions. In this paper the hydrodynamics of gas–liquid two-phase flow through foam packings in co-current downflow mode of operation are studied experimentally. In particular, the effects of gas and liquid superficial velocities and the pre-wetting mode of the packing (‘LEVEC’ and ‘KAN-LIQUID’) on pressure drop, liquid holdup, and axial liquid dispersion were researched. The experiments revealed multiplicity behavior of the hydrodynamic phenomena in the packed bed. The multiplicity has a significant impact on the forming of upper and lower parameter branches of hydrody- namics. Taking the aforementioned phenomena into account, new correlations are proposed to predict the pressure drop and the total liquid holdup. The occurrence of different flow regimes depending on the foam pore density, namely trickle flow regime and pulse flow regime, was observed. The results can be applied for a better understanding of the heat and mass transfer and overall chemical conversion of tubular reactors with catalytic active foam packings.

Keywords: Solid foam; Liquid holdup; Pressure drop; Axial dispersion; Multiplicity; Pre-wetting mode

Permalink: https://www.hzdr.de/publications/Publ-19104
Publ.-Id: 19104


Photo-neutron reaction cross-section for 93Nb in the end-point bremsstrahlung energies of 12-16 and 45-70 MeV

Naik, H.; Kim, G. N.; Schwengner, R.; Kim, K.; Lee, M. W.; Zaman, M.; Tartari, M.; Sahid, M.; Massarczyk, R.; John, R.; Junghans, A.; Shin, S. G.; Gey, Y.; Wagner, A.; Goswami, A.; Cho, M.-H.

The photo-neutron cross-sections of 93Nb at the end point bremsstrahlung energies of 12, 14 and 16 MeV as well as 45, 50, 55, 60 and 70 MeV have been determined by the activation and the off-line γ-ray spectrometric techniques using the 20 MeV electron linac (ELBE) at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) Dresden, Germany and 100 MeV electron linac at Pohang Accelerator Laboratory (PAL), Pohang, Korea. The 93Nb(γ,xn,x=1-4) reaction cross-sections as a function of photon energies were also calculated using computer code TALYS1.4. The flux-weighted average values were obtained from the experimental and the theoretical (TALYS) values based on mono-energetic photons. The experimental values of present work are in good agreement with the flux-weighted theoretical values of TALYS 1.4 but are slightly higher than the flux-weighted experimental data of mono-energetic photons. It was also found that the theoretical and the experimental values of present work and literature data for the 93Nb(γ,xn) reaction cross-sections increase from the threshold values to a certain energy, where other reaction channels opens. However, the increase of 93Nb(γ,n) and 93Nb(γ,2n) reaction cross-sections are sharper compared to 93Nb(γ,3n) and 93Nb(γ,4n) reaction cross-sections. The sharp increase of 93Nb(γ,n) and 93Nb(γ,2n) reaction cross-sections from the threshold value up to 17-22 MeV is due to the Giant Dipole Resonance (GDR) effect besides the role of excitation energy. After a certain values, the individual 93Nb(γ,xn) reaction cross-sections decrease with increase of bremsstrahlung energy due to opening of other reaction channels.

Keywords: 93Nb(γ; xn; x=1-4) reaction cross-sections; 197Au(γ; n)196Au and 27Al(γ; 2pn)24Na reactions flux monitor; end point bremsstrahlung energy of 12-16 and 45-70 MeV; activation and off-line γ–ray spectrometric technique; TALYS calculation

Permalink: https://www.hzdr.de/publications/Publ-19103
Publ.-Id: 19103


Fully automated radiosynthesis of both enantiomers of [18F]Flubatine under GMP conditions for human application

Patt, M.; Schildan, A.; Habermann, B.; Fischer, S.; Hiller, A.; Deuther-Conrad, W.; Wilke, S.; Smits, R.; Hoepping, A.; Wagenknecht, G.; Steinbach, J.; Brust, P.; Sabri, O.

A fully automatized radiosynthesis of (+)- and (−)-[18F]Flubatine ((+)- and (−)NCFHEB) by means of a commercially available synthesis module (TRACERlab FX FN) under GMP conditions is reported. Radiochemical yields of 30% within an overall synthesis time of 40 min were achieved in more than 70 individual syntheses. Specific activities were approximately 3000 GBq/μmol and radiochemical purity was determined to be at least 97%.

Keywords: Fluorine-18; NCFHEB; Flubatine; α4β2 Nicotinic acetylcholine receptors; GMP; Automation

Permalink: https://www.hzdr.de/publications/Publ-19102
Publ.-Id: 19102


Effect of the metal concentration on the structural, mechanical and tribological properties of self-organized a-C:Cu hard nanocomposite coatings

Pardo, A.; Buijnsters, J. G.; Endrino, J. L.; Gómez-Aleixandre, C.; Abrasonis, G.; Bonet, R.; Caro, J.

The influence of the metal content (Cu: 0–28 at.%) on the structural, mechanical and tribological properties
of amorphous carbon films grown by pulsed filtered cathodic vacuum arc deposition is investigated.
Silicon and AISI 301 stainless steel have been used as substrate materials. The microstructure, composition
and bonding structure have been determined by scanning electron microscopy, combined Rutherford backscattered spectroscopy-nuclear reaction analysis, and Raman spectroscopy, respectively. The mechanical and tribological properties have been assessed using nanoindentation and reciprocating sliding (fretting tests) and these have been correlated with the elemental composition of the films. A self-organized multilayered structure consisting of alternating carbon and copper metal nanolayers (thickness in the 25–50 nm range), whose formation is enhanced by the Cu content, is detected. The nanohardness and Young’s modulus decrease monotonically with increasing Cu content. A maximum value of the Young’s modulus of about 255 GPa is obtained for the metal-free film, whereas it drops to about 174 GPa for the film with a Cu content of 28 at.%. In parallel, a 50% drop in the nanohardness from about 28 GPa towards 14 GPa is observed for these coatings. An increase in the Cu content also produces an increment of the coefficient of friction in reciprocating sliding tests performed against a corundum ball counterbody. As compared to the metal free film, a nearly four times higher coefficient of friction value is detected in the case of a Cu content of 28 at.%. Nevertheless, the carbon–copper composite coatings produced a clear surface protection of the substrate despite an overall increase in wear loss with increasing Cu content in the range 3–28 at.%.

Keywords: Amorphous carbon; Pulsed filtered cathodic vacuum arc deposition; Multilayered a-C:Cu nanocomposite; Mechanical properties; Tribological properties

Permalink: https://www.hzdr.de/publications/Publ-19101
Publ.-Id: 19101


Metabolitenanalytik in der Entwicklung 18F-markierter Tracer für die Positronen Emissions Tomographie (PET)

Ludwig, F.-A.; Hiller, A.

  • Lecture (others)
    Kolloquium des Departments Analytical Chemistry des Helmholtz-Zentrum für Umweltforschung GmbH - UFZ, 14.02.2013, Leipzig, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19100
Publ.-Id: 19100


Flow control during solidification of AlSi-alloys by means of tailored AC magnetic fields and the impact on the mechanical properties

Räbiger, D.; Willers, B.; Eckert, S.

This paper presents an experimental study which in a first stage is focused on obtaining quantitative information about the isothermal flow field exposed to various magnetic field configurations. Melt stirring has been realized by utilizing a rotating magnetic field. In a second step directional solidification of AlSi7 alloys from a water-cooled copper chill was carried out to verify the effect of a certain flow field on the solidification process and on the resulting mechanical properties. The solidified structure was reviewed in comparison to an unaffected solidified ingot. Measurements of the phase distribution, the grain size, the hardness and the tensile strength were realized. Our results demonstrate the potential of magnetic fields to control the grain size, the formation of segregation freckles and the mechanical properties. In particular, time–modulated rotating fields show their capability to homogenize both the grain size distribution and the corresponding mechanical properties.

Keywords: elektromagnetic stirring; mechanical properties; solidification

  • Lecture (Conference)
    The 6th International Conference on Solidification and Gravity, 02.-06.09.2013, Miskolc - Lillafüred, Hungary
  • Materials Science Forum 790-791(2014), 384-389
    DOI: 10.4028/www.scientific.net/MSF.790-791.384
  • Contribution to proceedings
    The 6th International Conference on Solidification and Gravity, 02.-06.09.2013, Miskolc - Lillafüred, Hungary
    Solidification and Gravity VI: Trans Tech Publications, 978-3-03835-093-4, 384-389

Permalink: https://www.hzdr.de/publications/Publ-19099
Publ.-Id: 19099


Implantation Temperature Effects on the Nanoscale Optical Pattern Fabrication in a-SiC:H Films by Ga+ Focused Ion Beams

Tsvetkova, T.; Wright, C. D.; Hosseini, P.; Bischoff, L.; Zuk, J.

This work is related to a novel approach of providing some new generation ultrastable (> 50 years), ultrahigh density (> 1 Tbit/sq.in.) data storage for archival applications. We used ion-implantation to write nanoscale data into hydrogenated amorphous silicon carbide (a-SiC:H) films. Wide bandgap a-SiC:H samples, Ga+ focused ion beam implanted, have been prepared. A range of samples has been focused ion beam patterned under dierent implantation conditions, with emphasis on dierent substrate temperatures (typically from 0C temperature to around room temperature). Some of the room temperature implanted samples were further annealed at +250C in vacuum. The focused ion beam patterned samples were then analysed using near-field techniques, like atomic force microscopy, to define optimum implantation conditions and the resulting consequences for archival data storage applications. The atomic force microscopy analysis of Ga+ focused ion beam implanted a-Si1-xCx:H samples at room temperature and at 0C revealed an increase of both the depth and the width of the individual lines within the focused ion beam written patterns at the lower temperature, as a result of an increased ion beam induced sputtering yield, in good agreement with the previous results for the case of Ga+ broad beam implantation in a-Si1-xCx:H and again suggesting that the best conditions for optical data storage for archival storage applications would be using Ga+ ion implantation in a-SiC:H films with an optimal dose at room temperatures. Similarly, the atomic force microscopy results confirm that no advantage is expected to result from post-implantation annealing treatments.

Keywords: data storage; hydrogenated amorphous silicon carbide; Ga+ focused ion beam

Permalink: https://www.hzdr.de/publications/Publ-19098
Publ.-Id: 19098


Si-based light emitter in an integrated photonic circuit for smart biosensor applications

Germer, S.; Rebohle, L.; Skorupa, W.; Helm, M.

Integrated optics concerns mainly the generation, guiding, and detection of light. Especially bio sensing needs systems that incorporate electronic and photonic devices for the detection of harmful substances, like synthetic estrogens or plasticizers. We present recent developments in the integration of Si-based light emitters into a photonic circuit for a planar optical waveguide-based bio detection system. The growing demand for sensitive biochemical sensors in the environmental control, medicine or process technology results in the development of integrated sensors, which should show a high resolution over a wide concentration regime. In our first approach we deal with the integration of a Si-based light emitting device (LED) into a photonic circuit for the detection of harmful biological substances. Light injection into a waveguide is commonly obtained by using an external source coupled to the waveguide, e.g. an optical fiber via total internal reflection. For simplifying this injection process, we built Si-based LEDs consisting of a metal-oxide-semiconductor (MOS) structure, in which the oxide film contains group-IV and/or rare earth elements, incorporated by ion-beam synthesis [1, 2]. The Si-based LED exhibits strong electroluminescence, tunable from the visible up to the UV region depending on the rare-earth element (e.g. Gd, Tb, Eu, Nd, Er). Currently, the Si-based LEDs are already available and best efficiencies were achieved by Tb or Er implantation with an external quantum and power efficiency of 16% and 0.3%. LOCOS (local oxidation of silicon) processing and an additional layer of SiON were applied to the device to improve the electrical stability and operation time. Our concept bases upon a Si-based photonic circuit which consists of the integrated LED, working as the light source, a newly fabricated dielectric strip-waveguide below a bioactive layer and a receiver. The dielectric strip-waveguide has a Si3N4 or SiON core, in which the light should be guided, and a cladding of SiO2. The receiver should be a photodiode (e.g. Ge, Si). In this work, we focus on the development and characterization of the dielectric waveguides. For theoretical pre-analysis we are using the finite element method by the FlexPDE software for calculating the mode profiles and resonance frequencies according to the cross sections of the structures. The fabrication of the waveguides was done by plasma enhanced chemical vapor deposition (PECVD), photolithography and electron beam lithography. Obtained SEM results enabled an improvement of the fabrication recipe of the waveguides by using an additional Al-masking during the reactive ion etching (RIE). Furthermore, a new measurement setup is built up, which enables transmission measurements and the inspection of the beam profiles as well as the damping factors of the structures in dependence on their cross sections. In future, the theoretical calculations are going to be compared with the experimental results of transmission and beam profiling measurements. Moreover, the Si-based LED should be coupled with the waveguide e.g. by Bragg grating. Finally, this lab-on-a-chip system is showing a high potential to become an all-round applicable integrated sensor system, without using any external light sources or relay lenses, which is why it should be easily portable and customizale.

Keywords: Si-based light emission; dielectric waveguide; biosensor; integrated photonic circuit

  • Poster
    Mircotechnologies, 24.-26.04.2013, Grenoble, Frankreich
  • Contribution to proceedings
    Microtechnologies, 24.-26.04.2013, Grenoble, Frankreich
    Integrated Photonics: Materials, Devices, and Applications II; Proceedings of SPIE Vol. 8768, 876710
    DOI: 10.1117/12.2017275

Permalink: https://www.hzdr.de/publications/Publ-19097
Publ.-Id: 19097


Conditions of magma crystallization in the Henties Bay-Outjo dyke swarm, Namibia: implications for the feeder system of continental flood basalts

Keiding, J. K.; Frei, O.; Renno, A. D.; Veksler, I. V.; Trumbull, R. B.

The Henties Bay-Outjo dyke swarm (HOD) in NW Namibia presents a well-exposed example of the magma feeder system for continental flood basalts. This study uses bulk-rock, mineral and melt inclusion compositions from dyke samples to define pressure-temperature crystallization conditions and thus contribute to understanding the magma plumbing and storage beneath the province. The thermobarometry calculations for near-equilibrium mineral-melt pairs (the latter proxied by whole-rock) indicate olivine crystallization at ~1170 to 1350°C and lower, overlapping, temperatures for clinopyroxene and plagioclase (~1070 to 1210°C) in keeping with the order of crystallization inferred from petrographic observation. The dykes yielding the highest temperatures (>1300 °C) are in a specific region of the HOD near the litho-tectonic boundary of the Neoproterozoic Kaoko and Damara Belts, where magma permeability of the crust may have been enhanced. Pressure estimates from clinopyroxene-melt pairs range from 0 to 10 kbar overall (13 dykes) indicating polybaric crystallization. The lowest pressures are recorded by clinopyroxene oikocrysts intergrown with plagioclase, which likely represent the dyke emplacement depths. Clinopyroxene phenocrysts and plagioclase free oikocryst cores yield a higher range of crystallization pressures at 4-6 kbar, corresponding to mid-crustal depths of 11-17 km. There is no spatial pattern in the pressure variations, suggesting a rather uniform level of magma stagnation and crystallization in all areas of the HOD. Partial crystallization at intermediate depths is consistent with the inference of entrained crystals and with geochemical evidence for crystal accumulation in some of the dykes. Comparison of model magma densities and the crustal density derived from seismic velocity profiles suggest the dyke magmas had positive buoyancy in the lower- and middle crust and near-neutral buoyancy in the upper crust. The depth of magma stagnation or pooling at 11-17 km depth may relate to this or to the brittle-ductile transition in the felsic Damara crust.

Keywords: Etendeka; Namibia; Thermobarometry; Magma plumbing; Dyke swarm

Permalink: https://www.hzdr.de/publications/Publ-19096
Publ.-Id: 19096


Radiolabelling and biodistribution studies of potential radioligands for PET-Imaging of CB2

Günther, R.; Teodoro, R.; Fischer, S.; Moldovan, R.-P.; Lueg, C.; Deuther-Conrad, W.; Wünsch, B.; Brust, P.

The level of expression of cannabinoid receptors type 2 (CB2) in healthy and diseased brain has not been fully elucidated. Furthermore, there is interest in the ultra-localisation of CB2 in brain. Positron emission tomography (PET) is a technique, which allows monitoring of very low amounts of radiolabelled compounds in living organisms. Here, we attached 18F as radiolabel at different sites of N-aryl-oxadiazolyl-propionamides as potential radioligands and investigated it’s influence on affinity and pharmacology of the compounds.

Methods: Compounds were synthesised according to our previously described route (Rühl et al. Org. Med. Chem. Lett. 2012; 2: 32). Affinities towards CB2 and CB1 were determined via competitive radioligand binding assays with XXX as blocking compound. For labelling of 1, a tosylat moiety as selected as optimal leaving group (LG). Labelling at the aromatic ring in 2 was achieved with trimethylammonium as LG. In vivo organ distribution was investigated on CD-1 mice by injection of ~ 300 kBq of radiotracer (in 200 ml isotonic solution) in the tail vein. At various times, the animals were anesthetized, organs of interest dissected and the percentage of injected dose per gram of wet tissue (% ID/g) calculated. Blocking studies were conducted by intraperitoneal pre-injection of 1 mg/kg SR144,528 dissolved in isotonic solution 10 min prior to the radiotracer. All animals were sacrificed at 60 min p.i., and radioactivity uptake was determined.

Results: 1) In both cases, good labelling yields (XX %) could be achieved.
2) The radiolabelled compounds show the same affinity and specificity towards CB2 as the reference compound. 3) The radiotracers undergo strong metabolism but 4) can cross the blood brain barrier (BBB). After five minutes, approximately 2 to 4% of intact radiotracer was found in the plasma. Nevertheless, 36% of 18F1 and 80% of 18F2 could be observed in the brain after 30 minutes. The main metabolite could be identified as the free acid derivative, which has no affinity towards the CB receptors.

Conclusions: The introduction of 18F into the lead structure does not affect the affinity and the selectivity towards the CB2 receptor. The radiotracers cross the BBB. However, the compounds undergo strong metabolism in plasma.

  • Poster
    Cannabinoid Conference, 27.-28.09.2013, Köln, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19095
Publ.-Id: 19095


1-Arylimidazo[1,5-a]chinoxalininhibitoren als Leitsubstanzen zur Entwicklung eines PETTracers für die Phosphodiesterase 10A

Wagner, S.; Scheunemann, M.; Egerland, U.; Fischer, S.; Hoefgen, N.; Steinbach, J.; Brust, P.

Ziel/Aim:
Das Enzym Phosphodiesterase 10A (PDE10A) besitzt eine Schlüsselrolle in der zellulären Signaltransduktion. Das einzigartige Expressionsmuster der PDE10A mit fast ausschließlicher Expression im Striatum macht dieses Enzym zu einem interessanten Target zur Behandlung neurodegenerativer Erkrankungen, die mit einer striatalen Dysfunktion einhergehen, beispielsweise Schizophrenie.1 Molekulare Bildgebung mittels PET würde eine In-vivo-Untersuchung dieses Enzyms und seiner Expression in Zusammenhang mit neurologischen und pathologischen Prozessen erlauben.
Zu hochpotenten und selektiven PDE10A Inhibitoren zählt die Substanzklasse der 1-Arylimidazo[1,5-a]chinoxaline.2 Deren Wirkstoffstruktur wurde als Leitstruktur zur Entwicklung eines F-18 markierten PETTracers für die PDE10A gewählt.

Methodik/Methods:
Verschiedene Referenzverbindungen auf Basis des Imidazo[1,5-a]chinoxalingerüsts wurden durch Derivatisierung mit 2-Fluorpyridinresten hergestellt. Die ortho-Position zum Stickstoff des Pyridinrings wurde gewählt, um die nukleophile Einführung eines F-18 in einer späteren Radiosynthese zu erleichtern und hohe spezifische Aktivitäten zu erzielen. Die Identität und Reinheit der Referenzverbindungen wurden mittels NMR, HRMS und HPLC bestimmt. Die inhibitorische Wirksamkeit auf humane, rekombinante PDE10A wurde in Enzymassays bestimmt.

Ergebnisse/Results:
Das benötigte Imidazo[1,5-a]chinoxalingerüst wurde erfolgreich über eine Mehrstufensynthese ausgehend von 2,6-Difluoranillin hergestellt. Zur Einführung unterschiedlicher 2-Fluorpyridinhaltiger Reste wurde die Palladium-katalysierte Suzuki-Kupplung verwendet. Durch eine Variation in der Reaktionssequenz konnte dieser Rest an unterschiedlichen Positionen des aromatischen Systems eingeführt werden (siehe Abbildung). Die erzielten Referenzverbindungen zeigten in Untersuchungen zur inhibitorischen Wirksamkeit eine hohe Affinität zu PDE10A (IC50 < 10 nM) und erwiesen sich als sehr selektiv für PDE10A im Vergleich zu anderen Phosphodiesterasen. Ein hochaffines Derivat wurde als Leitsubstanz ausgewählt, um ein F-18 markiertes Derivat herzustellen. Zurzeit wird an der organischen Synthese eines geeigneten Präkursors für die Radiosynthese gearbeitet.

Schlussfolgerungen/Conclusions:
Über einen divergenten Syntheseschritt, die Suzuki-Kupplung, wurden unterschiedliche 2-Fluorpyridinsubstituierte Inhibitoren hergestellt. Durch eine Variation der Reaktionssequenz war dies an unterschiedlichen Positionen möglich. Die pharmakologische Evaluierung zeigte, dass alle Referenzverbindungen sehr affin und selektiv sind.

Referenzen/References:
[1] Kehler et. al. Curr. Pharm. Design, 2011, 17, 137-150.
[2] Malamas et. al. J. Med. Chem. 2011,54, 7621-7638.

  • Lecture (Conference)
    21. Jahrestagung der Arbeitsgemeinschaft Radiochemie/Radiopharmazie - AGRR2013, 12.-14.09.2013, Pamhagen, Austria

Permalink: https://www.hzdr.de/publications/Publ-19094
Publ.-Id: 19094


Excitons in strong, narrowband terahertz fields: Rabi splitting and beyond

Helm, M.; Teich, M.; Wagner, M.; Stehr, D.; Winnerl, S.; Schneider, H.; Klettke, A. C.; Chatterjee, S.; Kira, M.; Koch, S. W.

Excitons possess a hydrogen-like internal excitation spectrum with a characteristic energy scale in the THz range. We explore these internal degrees of freedom by using an intense THz free-electron laser to pump the 1s-2p intraexcitonic transition in GaAs and InGaAs multiquantum wells. The induced absorption changes are probed via interband absorption using a near-infrared femtosecond laser. We observe a splitting of the 1s exciton line, which can be explained by the Autler-Townes effect, also called AC Stark or Rabi splitting [1]. The behavior is, however, much more complex than for an ideal two-level system. Since for electric fields in the 10 kV/cm range the Rabi energy is already of the same order of magnitude as the 1s-2p transition energy, we are in fact clearly beyond the validity of the rotating wave approximation. At the highest fields, when also the ponderomotive energy (e2F2/4mw2) approaches the exciton binding energy, signatures of exciton field ionization are observed. Microscopic calculations based on the semiconductor Bloch equations including THz interaction show that the spectra can be reproduced, if the full set of higher exciton states is taken into account [2].
The experiments would not have been possible without the high-quality multiquantum well samples grown and provided to us by A. M. Andrews and G. Strasser (TU Vienna, Austria), and by G. Khitrova and H. M. Gibbs (Univ. Arizona, Tucson, USA), whose contributions are gratefully acknowledged.

Keywords: excitons; Autler Townes; Stark effect; Rabi splitting; terahertz; free electron laser; quantum well

  • Invited lecture (Conferences)
    Fundamental optical processes in semiconductors (FOPS 2013), 12.-16.08.2013, Kodiak, Alaska, USA

Permalink: https://www.hzdr.de/publications/Publ-19092
Publ.-Id: 19092


TRI3DYN – Collisional computer simulation of the dynamic evolution of 3-dimensional nanostructures under ion irradiation

Möller, W.

A computer program is described which allows fully three-dimensional dynamic collisional simulations of ion irradiation effects in particular in nanosystems. The program is based on the well-known TRIDYN code which describes dynamic modifications along one dimension. In a computational volume composed of fixed and equisized voxels, local atomic density changes due to ion implantation or recoil relocation are relaxed to constant predefined atomic volumes. This is accomplished by interaction with neighboring voxels and by material transport from and to the surface. Arbitrary initial system shapes and elemental distribution can be defined as well as a wide range of irradiation conditions including non-uniform beam profiles. The paper addresses details of the involved algorithms, discusses potential artifacts with respect to surface sputtering, broadening of compositional profiles and surface contours. It demonstrates the capabilities of the program on the basis of examples for focused ion beam erosion, self-organized surface pattering, and ion implantation and sputter-shaping of nanostructures.

Keywords: Ion Irradiation; Dynamic Computer Simulation; Binary Collision Approximation; Nanostructures; 3D

Permalink: https://www.hzdr.de/publications/Publ-19091
Publ.-Id: 19091


Extracellular S100A4 as a mediator of metastasis in human melanoma cells

Wolf, S.; Tandler, N.; Haase-Kohn, C.; Lenk, J.; Mosch, B.; Pietzsch, J.

kein Abstract verfügbar

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 116

Permalink: https://www.hzdr.de/publications/Publ-19090
Publ.-Id: 19090


Macrophages modulate prometastatic phenotype of human melanoma cells – role of EphB4, EphB6, and ephrinB2

Neuber, C.; Mosch, B.; Pietzsch, J.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 91

Permalink: https://www.hzdr.de/publications/Publ-19089
Publ.-Id: 19089


Radiosensitization of melanoma cells by a novel triaryl-olefine based selective cyclooxygenase-2 inhibitor containing a nitric oxide-releasing moiety

Bechmann, N.; Tondera, C.; Sehn, F.; Mosch, B.; Kniess, T.; Pietzsch, J.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 91

Permalink: https://www.hzdr.de/publications/Publ-19088
Publ.-Id: 19088


Visualization of cyclooxygenase-2 by confocal laser induced cryofluorescence microscopy at 20 K using a novel autofluorescent inhibitor in amelanotic and melanotic melanoma cells

Tondera, C.; Laube, M.; Wimmer, C.; Kniess, T.; Mosch, B.; Großmann, K.; Pietzsch, J.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 90

Permalink: https://www.hzdr.de/publications/Publ-19087
Publ.-Id: 19087


Macrophage-derived S100A4 modulates invasiveness of melanoma cells

Haase-Kohn, C.; Wolf, S.; Tandler, N.; Mosch, B.; Pietzsch, J.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 90

Permalink: https://www.hzdr.de/publications/Publ-19086
Publ.-Id: 19086


Effects of EphA2 receptor regulation on metastasis of melanoma cells

Mosch, B.; Neuber, C.; Reissenweber, B.; Tandler, N.; Pietzsch, J.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 89

Permalink: https://www.hzdr.de/publications/Publ-19085
Publ.-Id: 19085


Eph receptor and ephrin gene expression and protein synthesis in normoxic and hypoxic human melanoma cell lines

Pietzsch, J.; Reissenweber, B.; Neuber, C.; Mosch, B.

  • Poster
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 88-89

Permalink: https://www.hzdr.de/publications/Publ-19084
Publ.-Id: 19084


Establishment of an EphB4 receptor overexpressing A375 melanoma tumor xenograft model: investigation of melanoma growth, (lymph)angiogenesis, and characterization of EphB4-targeted radiotracers

Neuber, C.; Mamat, C.; Mosch, B.; Bergmann, R.; Pietzsch, J.

  • Lecture (Conference)
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 14

Permalink: https://www.hzdr.de/publications/Publ-19083
Publ.-Id: 19083


Extracellular S100A4 interacts with the receptor for advanced glycation endproducts (RAGE) resulting in prometastatic effects in human melanoma cells

Tandler, N.; Haase-Kohn, C.; Wolf, S.; Mosch, B.; Pietzsch, J.

kein Abstract verfügbar

  • Lecture (Conference)
    8th World Congress of Melanoma, 9th Congress of the European Association of Dermatology (EADO), 7th Interdisciplinary Melanoma/Skin Cancer Meeting, and the 3rd European Post-Chicago Melanoma Meeting, 17.-20.07.2013, Hamburg, Deutschland
  • Abstract in refereed journal
    Journal der Deutschen Dermatologischen Gesellschaft 11(2013), 14

Permalink: https://www.hzdr.de/publications/Publ-19082
Publ.-Id: 19082


Silicon Nanoparticles: From Synthesis, Characterization to Application in Biomedicine

Hsu, C.-W.; Licciardello, N.; Septiadi, D.; Hunoldt, S.; Viehweger, K.; Stephan, H.; de Cola, L.

Silicon Nanoparticles (Si NPs) have been studied for twenty years, and recently they have received a lot of attention because of their potential use in in vitro1and in vivo imaging2,3. Indeed Si NPs have shown no toxicity when uptaken by cells4, and display interesting luminescence properties as well as photo- and electro- stability which are suitable also for photoelectron application.5,6 Here we report on the synthesis of Si NPs via wet chemistry methods either by reducing Si(OMe)4 in reverse micelle1,7 or oxidizing Mg2Si8. The size of Si NPs is 1.6 nm and 3.9 nm, respectively. The Si NPs have been characterized by high resolution transmission electron microscopy (HRTEM), infrared spectroscopy (IR), and their photophysical properties were investigated. The Si NPs exhibit very bright luminescence that is strongly dependent on their size, as already known, and can be functionalized with a variety of groups allowing different solubility and further derivatization. We indeed show that different labels can be covalently attached and even targeting groups can be attached for multimodal bio-imaging. The first experiments in in vivo conditions will be shown to demonstrate the potentiality of these ultrasmall particles.

References
[1] R. D. Tilley, et al. Angew. Chem. Int. Ed. 2005, 44, 4550 -4554.
[2] P. N. Prasad, et al. ACS Nano, 2010, 4, 5131-5138.
[3] P. N. Prasad, et al. ACS Nano, 2011, 5, 413-423.
[4] N. S. Wang, et al. J. Appl. Toxicol. 2009, 29, 52-60
[5] G. A. Ozin, et al. Nano Lett. 2011, 11, 1585-1590.
[6] M. P. M. Jank, et al. small 2011, 7, 2853-2857.
[7] L. De Cola, et al. small, 2008, 4, 1835-1841.
[8] S. M. Kauzlarich, et al. J. Am. Chem. Soc. 1999, 121, 5191-5195.
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  • Poster
    26th International Photochemistry Conference (ICP2013), 21.-26.07.2013, Leuven, Belgium

Permalink: https://www.hzdr.de/publications/Publ-19081
Publ.-Id: 19081


Optimization of the bispidine structure for copper radiopharmaceuticals

Comba, P.; Hunoldt, S.; Morgen, M.; Steinbach, J.; Stephan, H.

Rigid bispidine (3,7-diazabicyclo[3.3.1]nonane) derivatives form very stable complexes, particularly with first row transition metal ions. Furthermore, the bispidine skeleton opens suitable pathways to introduce biomolecules, which are important concerning the pharmaceutical targeting of such complexes. Therefore, bispidines are attractive bifunctional chelating agents for the development of target-specific copper-based radiopharmaceuticals.
In order to optimize the radiopharmaceutical behavior, further bispidine ligands have been developed with different denticity (tetra-, penta- and hexadentate), with pyridine and/or methoxypyridine donor groups and with the possibility to introduce functionalities, such as targeting units and fluorescence labels in view of pharmaceutical targeting and dual labeling (PET and optical imaging).
These ligands and the important properties of their CuII complexes, e. g. stabilities, ligand exchange kinetics, partition coefficients (64Cu: n-octanol/water) and biodistribution studies will be reported.

  • Lecture (Conference)
    XXIV. International Conference on Coordination and Bioinorganic Chemistry (ICCBIC), 02.-07.06.2013, Smolenice, Slovakia

Permalink: https://www.hzdr.de/publications/Publ-19080
Publ.-Id: 19080


Recent Trends in Bioorthogonal Click-Radiolabeling Reactions Using Fluorine-18

Pretze, M.; Pietzsch, D.; Mamat, C.

The increasing application of positron emission tomography (PET) in nuclear medicine has stimulated the extensive development of a multitude of novel and versatile bioorthogonal conjugation techniques especially for the radiolabeling of biologically active high molecular weight compounds like peptides, proteins or antibodies. Taking into consideration that the introduction of fluorine-18 (t1/2 = 109.8 min) proceeds under harsh conditions, radiolabeling of these biologically active molecules represents an outstanding challenge and is of enormous interest. Special attention has to be paid to the method of 18F-introduction. It should proceed in a regioselective manner under mild physiological conditions, in an acceptable time span, with high yields and high specific activities. For these reasons and due to the high number of functional groups found in these compounds, a specific labeling procedure has to be developed for every bioactive macromolecule. Bioorthogonal strategies including the Cu-assisted Huisgen cycloaddition and its copper-free click variant, both Staudinger Ligations or the tetrazine-click reaction have been successfully applied and represent valuable alternatives for the selective introduction of fluorine-18 to overcome the afore mentioned obstacles. This comprehensive review deals with the progress and illustrates the latest developments in the field of bioorthogonal labeling with the focus on the preparation of radiofluorinated building blocks and tracers for molecular imaging.

Keywords: Staudinger ligation; Huisgen click reaction; bioorthogonal; radiolabeling; tetrazine

Permalink: https://www.hzdr.de/publications/Publ-19079
Publ.-Id: 19079


Partikelentstehung und –transport im DWR-Kern

Alt, S.; Kästner, W.; Renger, S.; Seeliger, A.; Kryk, H.; Hoffmann, W.

Bei postulierten Kühlmittelverluststörfällen (KMV) in Druckwasserreaktoren können Korrosionsprozesse an feuerverzinkten Einbauten des Containments auftreten und in Folge dessen einen starken Anstieg der Zinkkonzentration im Kühlmittel bewirken. An Heißstellen wie z.B. an Brennstab-Hüllrohren können sich die Zink-Korrosionsprodukte unter Umständen schichtbildend abscheiden. Neben der Abscheidung von Zinkborat, die bei Kühlmitteltemperaturen von 90 °C beobachtet wurde, kann durch Thermohydrolyse eine Umwandlung in schwerer lösliche Verbindungen bis hin zum Zinkoxid erfolgen und durch anwachsende Ablagerungen die thermofluiddynamischen Prozesse im Kern beeinflussen. Eine Freisetzung von Partikelsystemen mit breitem Größenspektrum, welche sich an Kernkomponenten oder Rückhaltevorrichtungen anlagern können, ist hierbei durch das Abplatzen von Partikelagglomeraten aus den Abscheidungen und im Kern ablaufende Kristallisations- und Umwandlungsprozesse möglich. Nach dem Einsetzen des Korrosionsprozesses erfolgt nachweislich auch nach Entfernung der Korrosionsquellen eine weitere Abscheidung von Zink-Korrosionsprodukten an Heißstellen. Es existiert somit eine Quelle für die Bildung unlöslicher Feststoffe im Primärkreis in der Spätphase eines KMV.
Im Rahmen eines BMWi-Verbundprojektes (FKZ 1501430 und 1501431) werden die physikochemischen Grundlagen und die thermohydraulischen Auswirkungen der Zink-Korrosionsproduktbildung und –ablagerung mit Hilfe von Experimenten an unikalen Versuchseinrichtungen des HZDR bzw. der HS Zittau/Görlitz untersucht.

Keywords: reactor safety; pressurized water reactor; loss-of-coolant accident; LOCA; corrosion; zinc borate

  • Lecture (Conference)
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
  • Contribution to proceedings
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
    Jahrestagung Kerntechnik, Annual Meeting on Nuclear Technology, Documentation CD-ROM

Permalink: https://www.hzdr.de/publications/Publ-19078
Publ.-Id: 19078


Regularization of flow reversals in a MHD Rayleigh-Benard convection

Tasaka, Y.; Igaki, K.; Yanagisawa, T.; Vogt, T.; Eckert, S.

In this paper Rayleigh-Benard convection has been investigated under the influence of a DC magnetic field. Similar configurations can be found in geophysical or steel production. Our group reported recently that spontaneous flow reversals of quasi two-dimensional rolls randomly occur in Rayleigh-Benard convection of liquid metal exposed to a horizontal magnetic field (Yanagisawa, et al., PRE, 2011). In fluid layers with relatively large aspect ratios (see Fig.1 (a)) the convection roll pattern becomes isotropic. However, the rolls are aligned with the magnetic field direction if the Lorentz force becomes comparable to the buoyancy or larger. In our experiment, where the fluid layer has a dimension of 200 * 200 * 40 mm (corresponding to an aspect ratio of 5), the convection pattern can show 3, 4 or 5 rolls regimes depending on the Rayleigh number Ra and the Chandrasekhar number Q. Flow reversals occur spontaneously between these steady states in the Ra-Q parameter space. A new regime has been found in experiments conducted at Chandrasekhar numbers in a magnetic system at HZDR. In this regime the flow reversals occur regularly. The non-dimensional characteristic time of the reversal normalized by circulation time of the roll is around 100, being similar to the characteristic time of the ‘random’ flow reversals reported by Yanagisawa, et al. Detailed observations reveal that movements of each cell toward the reversal start just after the last reversal occurs unlike the random flow reversals.

Keywords: Rayleigh-Benard convection; liquid metal; DC magnetic field; flow measurements; ultrasound Doppler velocimetry

  • Lecture (Conference)
    Bifurcations & Instabilities in Fluid Dynamics - 5th International Symposium, 08.-11.07.2013, Haifa, Israel

Permalink: https://www.hzdr.de/publications/Publ-19077
Publ.-Id: 19077


Neutron total cross section measurements of gold and tantalum at the nELBE photoneutron source

Hannaske, R.; Elekes, Z.; Beyer, R.; Junghans, A.; Bemmerer, D.; Birgersson, E.; Ferrari, A.; Grosse, E.; Kempe, M.; Kögler, T.; Marta, M.; Massarczyk, R.; Matic, A.; Schramm, G.; Schwengner, R.; Wagner, A.

Neutron total cross sections of 197Au and natTa have been measured at the nELBE photoneutron source in the energy range from 0.1 – 10 MeV with a statistical uncertainty of up to 2% and a total systematic uncertainty of 1%. This facility is optimized for the fast neutron energy range and combines an excellent time structure of the neutron pulses (electron bunch width 5 ps) with a short flight path of 7 m. Because of the low instantaneous neutron flux transmission measurements of neutron total cross sections are possible, that exhibit very different beam and background conditions than found at other neutron sources.

  • European Physical Journal A 49(2013), 137
    DOI: 10.1140/epja/i2013-13137-1
  • Lecture (Conference)
    ERINDA 2013 Worskhop, 01.-03.10.2013, Genf, Schweiz
  • Contribution to WWW
    arXiv:1311.1094 [nucl-ex]: http://arxiv.org/abs/1311.1094
  • Contribution to proceedings
    ERINDA 2013 Worskhop, 01.-03.10.2013, Genf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-19076
Publ.-Id: 19076


Asymmetries of azimuthal photon distributions in non-linear Compton scattering in ultra-short intense laser pulses

Seipt, D.; Kämpfer, B.

Non-linear Compton scattering in ultra-short intense laser pulses is discussed with the focus on angular distributions of the emitted photon energy. This is an observable which is accessible easily experimentally. Asymmetries of the azimuthal distributions are predicted for both linear and circular polarization. We present a systematic survey of the influence of the laser intensity, the carrier envelope phase and the laser polarization on the emission spectra for single-cycle and few-cycle laser pulses. For linear polarization, the dominant direction of the emission changes from a perpendicular pattern with respect to the laser polarization at low-intensity to a dominantly parallel emission for high-intensity laser pulses.

Permalink: https://www.hzdr.de/publications/Publ-19075
Publ.-Id: 19075


Equation of State and Viscosities from a Gravity Dual of the Gluon Plasma

Yaresko, R.; Kämpfer, B.

.Employing new precision data of the equation of state of the SU(3) Yang-Mills theory (gluon plasma) the dilaton potential of the gravity dual is adjusted in the temperature range (1 - 10) T_c in a bottom-up approach. The ratio of bulk viscosity to shear viscosity follows then as zeta/eta approx\pi Delta v_s^2 for Delta v_s^2 < 0.2 and achieves a maximum value of 0.95 at Delta v_s^2 approx 0.32, where Delta v_s^2 is the non-conformality measure, while the ratio of shear viscosity to entropy density is known as (4 \pi)^{-1} for the considered special set-up with Hilbert action on the gravity side.

Permalink: https://www.hzdr.de/publications/Publ-19074
Publ.-Id: 19074


PEnELOPE - a diodepumped, high-energy, chirped-pulse laser amplifier

Siebold, M.; Loeser, M.; Albach, D.; Roeser, F.; Schramm, U.

We present principle setup and design parameters of the PENELOPE system. It is scheduled as a direct diode-pumped PW system for laser-plasma experiments. The five-stage chirped pulse amplifier chain with a target pulse energy of 200J is based on Yb:CaF2.

  • Lecture (Conference)
    Advance Lasers and Photon Sources (ALPS), 23.-25.04.2013, Yokohama, Japan

Permalink: https://www.hzdr.de/publications/Publ-19073
Publ.-Id: 19073


A pulsed, high-repetition laser source for laser cooling at storage rings

Siebold, M.

We present an all diode-pumped picosecond solid-state Master-oscillator power-amplifier (MOPA) for extending laser ion-cooling to broad momentum spread applications. The challenge of the system lies in the generation of bandwidth-limited pulses with a pulse duration of 70ps and energies at the 100µJ level. The pulses with a duration of 170fs were generated in a commercial Yb:KGW mode-locked oscillator with a repetition-rate of 50MHz. Inside a subsequent regenerative amplifier with an intra-cavity dielectric grating the pulse bandwidth is reduced by 5 orders of magnitude which corresponds to 20pm at a center-wavelength of 1028nm. The system allows a tuning range between 1028 and 1032nm. Finally, the output is frequency quadrupled (forth harmonic generation) to 257nm, which is in the range of the cw laser lines used for laser-cooling. Due to thermal and damage issues the average power was limited to 50mW in the infra-red at a maximum repetition rate of 500Hz.

Keywords: laser cooling; picosecond pulses; diode-pumping; UV-light generation

  • Lecture (others)
    China-Germany Symposium for ”Laser Cooling at Storage Rings", 06.-10.05.2013, Lanzhou, China

Permalink: https://www.hzdr.de/publications/Publ-19072
Publ.-Id: 19072


High‐energy, Yb:LuAG and Yb:YAG active mirror amplifiers

Loeser, M.

We report the first short-pulse amplification results to several hundred millijoule energies in ceramic Yb:LuAG. We have demonstrated ns-pulse output from a diode-pumped Yb:LuAG disk amplifier at a maximum energy of 580 mJ and a peak optical-to-optical efficiency of 28% at 550 mJ. We also compare our results with Yb:YAG within the same amplifier system based on active mirror design. Previous works reporting on diode-pumped Yb:YAG amplifiers with similar pulse energies or even more than 1 J either demonstrated a maximum optical-to-optical efficiency around 10% or relied on cryogenic cooling, and/or based on bulk material. While cryogenically cooled lasers allow for even higher efficiencies the gain spectrum is narrowed dramatically for both Yb:YAG and Yb:LuAG. Pulses as short as 2 ps, corresponding to a gain bandwidth of about 1 nm, can be amplified at room temperature, whereas at liquid nitrogen temperature the gain bandwidth reduces by about one order of magnitude. Hence, we also studied the spectral response of both materials at room temperature. Although the peak absorbtion cross section of Yb:LuAG around 940 nm is lower compared to Yb:YAG the broader absorption spectrum is more suitable for using pump diodes without wavelength stabilization. Furthermore, we report on CPA-free picosecond amplification to the 100mJ level in Yb:YAG demonstrating the potential of the active mirror approach for efficient energy extraction at low fluences without optical damage or nonlinear effects such as self phase modulation (SPM) or self-focusing.

  • Lecture (Conference)
    Workshop on High-energy class diode-pumped solid-state lasers (HEC-DPSSL), 11.-14.09.2012, Tahoe City, USA

Permalink: https://www.hzdr.de/publications/Publ-19071
Publ.-Id: 19071


Current status of the PEnELOPE project

Siebold, M.

With the first demonstration of direct diode-pumped TW lasers with pulse energies of 1 J and more a scaling of this approach for use in PW-class laser systems became feasible. The Helmholtz-Centre Dresden-Rossendorf is now planning to build a fully diode-pumped Petawatt laser for laser-particle acceleration research. Within the PEnELOPE project (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments) a pulse energy of 150 J, a repetition rate around 1 Hz and a pulse duration of 150 fs after compression are desired. In order to minimize the required pump peak power and therefore the initial costs a broad-band Ytterbium doped laser material with a long fluorescence lifetime (i.e. Yb:glass or Yb:CaF2) is chosen. A total pump peak-power of 1.2 MW is scheduled assuming a pump pulse duration of 2 ms and an envisioned optical-to-optical conversion efficiency of 10% before compression. Pulses as short as 60 fs having an energy of 25 nJ are generated in a commercial Yb:KGW oscillator at a center wavelength of 1035 nm. In order to employ CPA technique the pulses are stretched to 2 ns in a grating stretcher having grating constant of 1760 lines per mm. The amplifier-chain consists of a regenerative amplifier and 4 subsequent multipass amplifiers. While the regenerative amplifier produces a gain 40.000 gain narrowing is required to be suppressed by intra-cavity spectral shaping. At the sub-mJ energy level a bandwidth of 25 nm was achieved out of the regenerative amplifier. Two booster amplifiers with an energy of 100mJ and 1J output were also demonstrated. The full amplifier system will consist of two more multipass amplifiers each having a gain of 10-16 in order to achieve the desired pulse energy.

  • Lecture (others)
    Workshop on High-energy class diode-pumped solid-state lasers (HEC-DPSSL), 11.-14.09.2012, Tahoe City, USA

Permalink: https://www.hzdr.de/publications/Publ-19070
Publ.-Id: 19070


High intensity lasers – new developments and applications.

Siebold, M.

Basics of ultra-short pulse generation and amplication towards high energies are presented. We focussed on scaling issues and applications of high-intensity laser systems. Furthermore, diode-pumping of high energy lasers was discussed.

  • Lecture (others)
    Summer School ”Trends and new developments in Laser Technology, 28.08.2012, Dresden, Germany

Permalink: https://www.hzdr.de/publications/Publ-19069
Publ.-Id: 19069


Efficient Burst Mode Amplifier for Ultra-Short Pulses Based on Cryogenically Cooled Yb3+:CaF2

Koerner, J.; Hein, J.; Liebetrau, H.; Seifert, R.; Kloepfel, D.; Kahle, M.; Loeser, M.; Siebold, M.; Schramm, U.; Kaluza, M. C.

We present a novel approach for the amplification of high peak power femtosecond laser pulses at a high repetition rate. This approach is based on an all-diode pumped burst mode laser scheme. In this scheme, pulse bursts with a total duration between 1 and 2 ms can be generated and amplified, containing between 50 and 2000 individual pulses equally spaced in time. The individual pulses have an initial duration of 350 fs and are stretched to 50 ps in a chirped pulse amplification scheme. The first amplifier stage, which is described in detail in this work, is based on Yb3+:CaF2 cooled to 100 K. In this amplifier, a total output energy in excess of 600 mJ per burst at a repetition rate of 10 Hz is demonstrated. For lower repetition rates the total output energy per burst can be scaled to 915 mJ at longer pump duration. This corresponds to an efficiency as high as 25% from absorbed pump energy to extracted energy. This is – to our knowledge – the highest efficiency, which has so far been demonstrated for a pulsed Yb3+:CaF2 amplifier.

Keywords: Lasers and laser optics; Laser amplifiers; Lasers, pulsed; Lasers, solid-state; Lasers, ytterbium; Ultrafast lasers

Permalink: https://www.hzdr.de/publications/Publ-19068
Publ.-Id: 19068


Interaction of Europium and Nickel with calcite studied by Rutherford Backscattering Spectrometry and Time-Resolved Laser Fluorescence Spectroscopy

Sabau, A.; Pipon, Y.; Toulhoat, N.; Lomenech, C.; Jordan, N.; Moncoffre, N.; Barkleit, A.; Marmier, N.; Brendler, V.; Surblé, S.; Giffaut, E.

This study aims at elucidating the mechanisms regulating the interaction of Eu and Ni with calcite (CaCO3). Calcite powders or single crystals (some mm sized) have been put into contact with Eu or Ni enriched solutions. The concentrations ranged from 10−3 to 10−5 mol.L−1 for Eu and 10−3 mol.L−1 for Ni and the sorption durations ranged from one week to one month. In order to elucidate the retention mechanisms of these elements into calcite, Rutherford Backscattering Spectrometry (RBS) has been carried out. This technique is well adapted to discriminate incorporation processes such as: (i) adsorption or co precipitation at the mineral surfaces or, (ii) incorporation into the mineral structure (through diffusion for instance). Moreover, using the fluorescence properties of Europium, the results have been compared to those obtained by Time-Resolved Laser Fluorescence Spectroscopy (TRLFS) on calcite powders. For the single crystals, complementary SEM observations of the mineral surfaces at low voltage have also been carried out. Results show that Ni accumulates at the calcite surface whereas Eu is also incorporated at a greater depth. Eu seems therefore to be incorporated into two different states in calcite: (i) heterogeneous surface accumulation and (ii) incorporation at depth greater than 160 nm after 1 month of sorption. Ni was found to accumulate at the surface of calcite without incorporation.

Keywords: calcite; europium; nickel; RBS; TRLFS, sorption; incorporation

Permalink: https://www.hzdr.de/publications/Publ-19067
Publ.-Id: 19067


Time-dependent ion heating and ionization dynamics– probing complex plasma dynamics inside solid target with XFEL

Huang, L.; Kluge, T.; Schlenvoigt, H.-P.; Gutt, C.; Li, R.; Yu, W.; Bussmann, M.; Cowan, T. E.

We investigate bulk ion heating in solid CD2-Al-CD2 buried layer targets and ionization dynamics in solid copper target irradiated by ultra-short relativistic laser pulses. The potential techniques such as small angle X-ray scattering, Faraday rotation, and resonant coherent X-ray diffraction imaging to probe relative physical processes in high power laser plasma interactions using X-ray free-electron lasers are also presented.

Keywords: Ion heating; Ionization; XFEL probing

  • Poster
    Kick Off Meeting for the Helmholtz International Beamline for Extreme Fields (HIBEF) at the European XFEL, 02.-05.06.2013, Hamburg, Germany

Permalink: https://www.hzdr.de/publications/Publ-19063
Publ.-Id: 19063


Fluorine containing 6,7-dialkoxybiaryl-based inhibitors for phosphodiesterase 10A: Synthesis and in vitro evaluation of inhibition potency, selectivity and metabolism

Schwan, G.; Asskar, G. B.; Höfgen, N.; Kubicova, L.; Funke, U.; Egerland, U.; Zahn, M.; Nieber, K.; Scheunemann, M.; Sträter, N.; Brust, P.; Briel, D.

Based on the potent phosphodiesterase 10A (PDE10A) inhibitor PQ-10, we have synthesised thirty-two derivatives to determine relationships between their molecular structure and binding properties. Their roles as potential positron emission tomography (PET) ligands as well as the inhibitory potency to PDE10A and other PDEs have been evaluated and the metabolic stability has been determined in vitro. According to our findings, halogenalkyl substituents at position 2 of the quinazoline moiety and/or halogenalkyloxy substituents at position 6 or 7 affect not only the compounds' affinity, but also their selectivity. As a result of substituting the methoxy group for a monofluoroethoxy or difluoroethoxy group (19d and 19c) at position 6 of the quinazoline ring, the selectivity to PDE10A primarily increased compared to PDE3A. The same result was obtained by 6,7-difluoride substitution on the quinoxaline moiety (35). Finally, the fluorinated compounds 16a, 19a-d, 29 and 35 (IC50 PDE10A 11-65 nM) showed the highest inhibitory potential. Further, fluoroethoxy substitution at position 7 of the quinazoline ring improved metabolic stability in comparison to the lead structure, PQ-10.

Permalink: https://www.hzdr.de/publications/Publ-19062
Publ.-Id: 19062


Pattern Formation by Focused Polyatomic Ion Beam Irradiation on GaAs

Bischoff, L.; Böttger, R.; Facsko, S.; Schmidt, B.; Pilz, W.

Surface patterning by ion beams is a well-established technique to create self-organized regular surface patterns. The type of these patterns depends on the ion species, their energy, fluence, target temperature and angle of incidence. Emerging applications of these patterns are under discussion in particular for electronic, photonic and magnetic nano devices. The irradiation of different matter with focused monatomic ions like Ga or Bi is a well-known application. Here, a novel approach is presented, the use of heavy polyatomic Bi2+ and Bi3+ ions, promising high intensity sputtering and new kinds of surface morphology. The ultra-heavy Bi ions emitted from a liquid metal ion source (LMIS) in a mass separated FIB instrument are directed to the GaAs surface. Whereas the irradiation with monatomic Bi-ions at normal incidence creates a deep sputtering crater without any strong pattering or Ga precipitates on the crater bottom which is still known from Ga FIB irradiation. But the much heavier projectiles Bi2+ and Bi3+ lead also to a Ga droplet formation on the GaAs crater base. With increasing projectile mass, i.e. higher deposited energy in the stopping cascade of polyatomic ions more and also smaller Ga droplets are found. The phenomenon of surface evolution investigated for monatomic as well as heavy Au and Bi dimer and trimer ions is presented in dependence of the ion species, the energy, the angle of incidence as well as the target temperature in the range from RT up to 400°C.

Keywords: Surface patterning; GaAs; FIB; LMIS; droplets; angle dependence

  • Lecture (Conference)
    18th International Conference on Surface Modification of Materials by Ion Beams, 15.-20.09.2013, Kusadasi, Izmir, Turkey

Permalink: https://www.hzdr.de/publications/Publ-19060
Publ.-Id: 19060


Angle-dependent sputtering and pattern formation by polyatomic ion irradiation

Bischoff, L.; Schmidt, B.; Böttger, R.; Pilz, W.

The very high erosion rates of heavy projectiles, in particular Bi dimer and trimer ions on different substrates were investigated in relation to the ion incidence angle. In the case of high angle irradiation attended by a ripple structure formation the erosion rate is decreased due to the wide variety of surface angles faced to the beam. On the eroded surfaces very regular, high-amplitude dot and ripple patterns on Ge and Si are formed under the heavy polyatomic ion impacts, which differs significantly from surface mor-phologies formed by monatomic ion irradiation [1]. Dot and ripple heights equal to their wavelengths can be achieved. The Bi2+ and Bi3+ ions are extracted from a liquid metal ion source [2], are mass separated, focused and scanned using a focused ion beam sys-tem. Studies are performed for fluences of 1e14 to 1e17 ions/cm2 in the ion impact angle range from normal to 85°. In Ge hexagonally ordered dot patterns with ~30 nm diameter and nearly the same height are found in the incidence angle range from 0° to 30° for Bi3++ ions [3] followed by a smoothening region up to 60°. Incidence angles from 60° to 80° cause a pronounced ripple structure on the Ge surface. For nearly grazing incidence, shingles perpendicular to the beam direction are found. FIB cross section imaging shows that the slope of the shingles is parallel to the ion incidence direction. The angle-dependent behaviour of pattern formation is summarized in a phase diagram.
[1] R. Böttger, L. Bischoff, K.-H. Heinig, W. Pilz and B. Schmidt, Journal of Vacuum Science and Technology B 30 (2012) 06FF12.
[2] L. Bischoff, W. Pilz, P. Mazarov and A.D. Wieck, Applied Physics A99 (2010) 145.
[3] L. Bischoff, K.-H. Heinig, B. Schmidt, S. Facsko and W. Pilz, Nucl. Instr. and Meth. B 272 (2012) 198.

Keywords: Bi dimer and trimer ions; FIB; liquid metal ion source; germanium; dots; ripple; shingle

  • Lecture (Conference)
    The 17th International Conference on Radiation Effects in Insulators, 30.06.-05.07.2013, Helsinki, Finland

Permalink: https://www.hzdr.de/publications/Publ-19059
Publ.-Id: 19059


Zugang zu potenziellen Metaboliten des σ1-Rezeptorliganden (R)-(+)-Fluspidin durch elektrochemische Oxidation - ein Beitrag zur Entwicklung neuer Radiotracer für die Positronen-Emissions-Tomographie (PET)

Ludwig, F.-A.; Fischer, S.; Hiller, A.; Vetter, D.; Brüning, R.; Wünsch, B.; Steinbach, J.; Brust, P.

Der σ1-Rezeptor kommt hauptsächlich in den Mitochondrien-assoziierten Membranen des endoplasmatischen Reticulums vor1und wird zunehmend als biologisches Target für die Behandlung von Tumoren und neurologischen Erkrankungen, wie Depression, Angstzuständen oder Neurodegeneration, erkannt.2a,2b
Durch die hohe Affinität zum σ1-Rezeptor, die Spezifität gegenüber anderen Rezeptoren sowie weitere pharmakologische Eigenschaften stellt (R)-(+)-Fluspidin einen potenziellen 18F-Tracer für den Einsatz in der Positronen-Emissions-Tomographie (PET) zur bildgebenden Diagnostik o. g. Erkrankungen dar.3 Die Evaluierung eines PET-Tracers erfordert u. a. detaillierte Untersuchungen zu dessen Metabolismus sowie eine Charakterisierung der Metabolite.
Neben der aufwendigen Gewinnung von Metaboliten aus Gewebematerialien oder der chemischen Synthese von potenziellen Metaboliten, hat deren Darstellung mittels elektrochemischer Oxidation eine zunehmende Bedeutung für die Strukturaufklärung von Radiometaboliten erlangt. So können Proben ohne biologische Matrix in vergleichbar kurzer Zeit mit geringem Aufwand hergestellt werden.

Für die Generierung von Metaboliten wurde die in das ROXY-System (Fa. Antec) implementierte elektrochemische Zelle (μPrepCell) mit der Arbeitselektrode Glassy Carbon eingesetzt. Die Umsetzung von (R)-(+)-Fluspidin (50 μM) in Ammoniumformiat-Puffer (20 mM) und 50 % Acetonitril bei pH 7,4 erfolgte bei jeweils konstanter Spannung von 1,0 - 1,4 V und einer Durchflussrate von 50 μl/min. Die Reaktionslösungen wurden off-line mittels HPLC und MS untersucht.

Als Hauptprodukt der elektrochemischen Umsetzung von (R)-(+)-Fluspidin entstand das Desbenzyl-Derivat , welches bereits bei Versuchen mit Leber-Mikrosomen als Metabolit zugeordnet werden konnte.3 Weiterhin konnten vor allem Mono- und in geringerem Ausmaß auch Dioxidationsprodukte des (R)-(+)-Fluspidins nachgewiesen werden. Auch die Substitution des Fluoratoms durch eine Hydroxylgruppe wurde beobachtet.

Es konnte gezeigt werden, dass mit Hilfe der elektrochemischen Oxidation mögliche Metaboliten des (R)-(+)-Fluspidins zugänglich sind. Durch Korrelation mit Daten der Radio-HPLC bietet sich im Rahmen von In-vivo-Studien an Tieren und am Patienten die Möglichkeit, Radiometabolite zu identifizieren, welche mit strukturaufklärenden analytischen Verfahren nicht direkt charakterisiert werden können.
Die elektrochemische Oxidation ist eine effiziente Methode zur Vorhersage der metabolischen Stabilität, die auch in der Entwicklung metabolisch stabiler Radiotracer für PET zunehmenden Einsatz finden kann.

1 Duncan G., Wang L. 2005; Experimental Eye Research 81: 121–122.
2a Cobos E.J. et al. 2008; Curr. Neuropharmacol 6: 344–366.
2b Hayashi T., Su T.P. 2008; Expert Opin. Ther. Targets. 12: 45–58.
3 Fischer S. et al. 2011; Eur. J Nuclear Medicine and Molecular Imaging 38: 540-51.

  • Poster
    ElCheMS 2: 2nd International Workshop on Electrochemistry/Mass Spectrometry, 23.-24.05.2013, Münster, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19058
Publ.-Id: 19058


Diode-pumped Yb:LuAG and Yb:YAG disk laser amplifiers with high pulse energies

Siebold, M.; Loeser, M.; Albach, D.; Roeser, F.; Banerjee, S.; Schramm, U.

Ytterbium-doped garnets are attractive for use in high-energy diode-pumped solid-state lasers due to their spectral and thermal properties. Recently, Yb:LuAG was investigated as a promising candidate for kW thin-disk lasers because of its superior thermal conductivity especially at high doping concentrations compared to Yb:YAG. In this paper we demonstrate high-energy ns-pulse multipass amplification in Yb:YAG and Yb:LuAG towards 500mJ. The study presented here has confirmed that further scaling of both efficiency and pulse energy is possible by a further reduction of Yb-doping level reducing the gain per disk.

  • Contribution to proceedings
    Conference on Lasers and Electro-Optics (CLEO) Europe, 12.-16.05.2013, Munich, Germany
    CLEO/Europe - IQEC 2013: Conference Digest, CA8.1

Permalink: https://www.hzdr.de/publications/Publ-19056
Publ.-Id: 19056


Colloid-borne forms of tetravalent actinides: A brief review

Zänker, H.; Hennig, C.

Tetravalent actinides, An(IV), are usually assumed to be little mobile in near-neutral environmental waters because of their low solubility. However, there are certain geochemical scenarios during which mobilization of An(IV) in a colloid-borne (waterborne) form can not be ruled out. A compilation of colloid-borne forms of tetravalent actinides described so far for laboratory experiments, field experiments and real-world scenarios is given. It is intended to be a knowledge base and a tool for those who have to interpret actinide behavior under environmental conditions. Colloids containing structural An(IV) and colloids carrying adsorbed An(IV) are considered. Their behavior is compared with the behavior of An(IV) colloids observed after the intentional or unintentional release of actinides into the environment. A list of knowledge gaps as to the behavior of An(IV) colloids is provided and items which need further research are highlighted.

Keywords: Tetravalent actinides; groundwater; colloids; nanoparticles; subsurface transport

  • Journal of Contaminant Hydrology 157(2014), 87-105

Permalink: https://www.hzdr.de/publications/Publ-19055
Publ.-Id: 19055


Kalibrierung von Ultraschallsonden für reaktionstechnische Untersuchungen

Mittendorff, T.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) beschäftigt sich unter anderem mit der Untersuchung von verfahrens-technischen Prozessen und fluiddynamischen Phänomenen in Mehrphasenkontaktapparaten.
Die dazugehörige Untersuchung von Mehrphasenströmungen, die Modellentwicklung sowie die Validierung numerischer Berechnungsverfahren erfordern belastbare experimentelle Daten.
Für ein neuartiges Reaktorkonzept mit geneigt rotierendem Festbett soll die Reaktionsführung hinsichtlich der Raum-Zeit-Ausbeute einer Modellreaktion (Hydrierung von α-Methylstyrol zu Cumol) untersucht werden.

Keywords: speed of sound; ultrasonic probe; binary mixtures; chemical reaction engineering

  • Study thesis
    HTW Dresden, 2013
    45 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19054
Publ.-Id: 19054


Experimentelle Untersuchung der flüssig-fest Stoffübertragung in einem geneigt rotierenden Festbettreaktor

Herrmann-Heber, R.

Das Institut für Fluiddynamik im Helmholtz-Zentrum Dresden-Rossendorf (HZDR) beschäftigt sich unter anderem mit der Untersuchung verfahrenstechnischer Prozesse sowie der Entwicklung und Charakterisierung neuer effizienter Mehrphasenkontaktapparate.
Ein solches neuartiges Reaktorkonzept mit dem Ziel der Prozessintensivierung durch periodische Betriebsweise stellt der geneigt rotierende Festbettreaktor dar. Im Gegensatz zum zeitlich-periodischen Reaktorbetrieb erfolgt die Prozessintensivierung hier durch Aufprägung einer örtlichen Periodizität unter ansonsten stationären Betriebsbedingungen. Aus dieser veränderten Betriebsweise ergeben sich in Form von Neigung und Drehzahl zusätzliche Freiheitsgrade bei der Strömungsführung und damit zur Beeinflussung der Reaktorleistung.
Im Rahmen der interdisziplinären Projektarbeit ist ein Verfahren zur experimentellen Untersuchung der flüssig-fest Stoffübertragung im geneigt rotierenden Festbettreaktor umzusetzen. Die Stoffübertragung stellt einen Schlüsselparameter der Makrokinetik heterogener Reaktionssysteme dar und kann somit zur Leistungsbewertung des neuen Reaktorkonzepts herangezogen werden.

Keywords: liquid-solid mass transfer; electrochemical method; fixed bed reactor; rotation; inclination

  • Study thesis
    TU Dresden, 2013
    55 Seiten

Permalink: https://www.hzdr.de/publications/Publ-19053
Publ.-Id: 19053


Overview of diode pumped high energy solid state lasers

Röser, F.; Loeser, M.; Albach, D.; Siebold, M.; Schramm, U.; Sauerbrey, R.

In the past, ultra-short laser pulses with several 100J have been produced by mature flash lamp technologies1, 2. Alternatively, diode-pumped lasers have a great potential for generating peak-powers at higher repetition rates (1-10Hz). Worldwide, several ambitious laser projects e.g. MERCURY3, LUCIA4, GENBU5, HALNA6, DIPOLE7, LIFE8 are developing diode-pumped amplifier systems for output pulses with expected energies of 100J or more.
The Helmholtz-Centre Dresden-Rossendorf (HZDR) is currently building a fully diode-pumped Petawatt laser called PEnELOPE (Petawatt, Energy-Efficient Laser for Optical Plasma Experiments). PEnELOPE is designed for pulse energy of 150J, a repetition rate of 1Hz and pulse duration of 120fs. Additionally, the operational Ti:Sapphire based laser system DRACO (Dresden laser acceleration source9) is currently upgraded (25-30fs, 30J). Both PW-class lasers are designated for laser-plasma and particle acceleration research. While electron acceleration experiments and principles of proton/ion-acceleration are studied with DRACO, PEnELOPE is dedicated to produce laser accelerated proton and ion beams with energies of 100MeV or more which become relevant for future cancer therapy applications

  • Invited lecture (Conferences)
    ICAN final conference CS3, 28.06.2013, CERN, Genf, Schweiz

Permalink: https://www.hzdr.de/publications/Publ-19052
Publ.-Id: 19052


Status Report of ²⁰N(γ,n)¹⁹N Analysis

Röder, M.; for the R3B Collaboration

Summary of the status of the analysis of the ²⁰N(γ,n)¹⁹N reaction.

  • Lecture (Conference)
    R3B Collaboration Meeting, 13.-17.05.2013, Darmstadt, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19051
Publ.-Id: 19051


Linear thermal expansion coefficient determination using in situ curvature and temperature dependent X-ray diffraction measurements applied to metalorganic vapor phase epitaxy-grown AlGaAs

Maaßdorf, A.; Zeimer, U.; Grenzer, J.; Weyers, M.

AlxGa1xAs grown on GaAs is known to be almost perfectly lattice matched with a maximum lattice mismatch of 0.14% at room temperature and even less at temperatures of 700 C–800 C. However, as layer structures for edge-emitting diode lasers exhibit an increasing overall thickness of several microns of AlxGa1xAs, e.g., diode lasers comprising a super-large optical cavity, the accumulated elastic strain energy increases as well. Depending on the growth temperature the formation energy of dislocations can be reached, which is limiting the pseudomorphic growth. In this regard, the thermal expansion coefficient difference between layer and substrate is an important parameter. We utilize in situ curvature measurements during growth of AlxGa1xAs by metal-organic vapour phase epitaxy to determine the thermal expansion coefficient a. The curvature change with increasing layer thickness, as well as with wafer temperature at constant layer thickness is used to assess a. This is compared to ex situ temperature dependent X-ray diffraction measurements to obtain a. All determined values for α are in good agreement, yielding αAlAs = 4.1×10−6 K−1 for a given GaAs linear thermal expansion coefficient of αGaAs = 5.73×10−6 K−1.

Permalink: https://www.hzdr.de/publications/Publ-19050
Publ.-Id: 19050


Retention of U(VI) and Np(V) in bacteriogenic iron oxide-producing biofilms from Äspö HRL (Sweden)

Krawczyk-Bärsch, E.; Schmeide, K.; Bok, F.

At the Äspö HRL (Sweden) Gallionella ferruginea dominated biofilms associated with bacteriogenic iron oxides (BIOS) and groundwater were sampled from an in situ continuous flow cell, which has been installed in a cavity of the main access tunnel at 2200 A site, 300 m below sea level (Anderson & Pedersen, 2003). In laboratory sorption experiments UO2(ClO4)2 and NpO2(ClO4) were added to the BIOS biofilms in groundwater under aerobic conditions adjusting a final U(VI) concentration of 1.9×10-5 M.U(VI) and 3.27×10-5 M Np(V). At the end of the experiments the groundwater/BIOS biofilm samples were ultra centrifuged and the pH and Eh of the supernatants were defined to be 7.52 0.1 and 355 +- 30 mV in the uranium contaminated samples and 7.02 +- 0.1 and 367 +- 30 mV in the neptunium contaminated samples. The analysis showed a substantial decrease of uranium and neptunium in the groundwater of approximately 85 % and 95 %, respectively. Thermodynamic calculation of the theoretical predominant field of uranium species was performed using the analytical data of the uranium-contaminated groundwater. Under the given pH and Eh the formation of the aqueous uranium carbonate species Ca2UO2(CO3)3(aq) is predicted due to the high concentration of carbonate in the groundwater. In the BIOS biofilm the ferrous iron-oxidizing and stalk-forming bacterium Gallionella ferruginea is dominating the sorption process. The stalk represents an organic surface upon which Fe oxyhydroxides can precipitate. Due to the high concentration of ferric iron in the BIOS biofilm the portion of iron oxyhydroxides (ferrihydrite) amounts approximately to 70 wt%. Under the given pH conditions the uptake of U and Np depends predominantly on the high amount of ferrihydrite precipitated onto the stalks. Conclusively, the combination of this biological material and iron oxides creates an abundant surface area for adsorption of radionuclides.

Keywords: biofilms; Gallionella ferruginea; uranium; neptunium; Äspö

  • Contribution to proceedings
    Final Workshop of the Project "Crystalline Rock Retention Processes" (CROCK), 14.-16.05.2013, Karlsruhe, Deutschland
    Final Workshop Proceedings of the Collaborative Project "Crystalline Rock Retention Processes" (7th EC FP CP CROCK), KIT Scientific Reports 7656 (2014), Karlsruhe: KIT Scientific Publishing, 69-76

Permalink: https://www.hzdr.de/publications/Publ-19049
Publ.-Id: 19049


Exploring the hydromagnetic Bermuda triangle between Taylor, Tayler, and Velikhov

Stefani, F.; Galindo, V.; Gerbeth, G.; Gundrum, T.; Kirilllov, O.; Seilmayer, M.; Weber, N.; Weier, T.; Gellert, M.; Rüdiger, G.; Hollerbach, R.

The interaction of rotating fluids and magnetic fields is of fundamental importance for a number of astrophysical processes. The magnetorotational instability (MRI), discovered by Velikhov in 1959, is considered as a viable mechanism for triggering turbulence and angular momentum transport in accretion disks. The Tayler instability (TI), a kink-type current-driven instability, may play an important role in angular momentum transport in stars, and is also discussed as a possible ingredient of an alternative stellar dynamo mechanism.
We start by analyzing the problem of a viscous, resistive, incompressible rotating fluid under the influence of a constant axial magnetic field and an azimuthal field with arbitrary radial dependence. Within the short-wavelength approximation, we focus on the limit of low magnetic Prandtl numbers and explore the various inductionless versions of MRI, and the TI. As a main result, we show that with a slight deviation of the azimuthal magnetic field profile from the current-free 1/r law, the inductionless versions of MRI become capable of destabilizing Keplerian flows. In addition, we present a new 3D integro-differential equation code that allows to study TI for real liquid metal systems.

We further summarize recent results, obtained in various liquid metal experiments, on the helical and the azimuthal MRI, and on the TI. Finally, we discuss the prospects for studying MRI and TI in a combined large scale liquid sodium experiment in the framework of the DRESDYN project.

  • Lecture (Conference)
    International Symposium on Geophysical and Astrophysical Dynamos, 07.-12.07.2013, Ascona, Switzerland

Permalink: https://www.hzdr.de/publications/Publ-19047
Publ.-Id: 19047


Taylor, Tayler, Velikhov: Tailored experiments on the interaction of rotating fluids and magnetic fields

Stefani, F.; Galindo, V.; Gellert, M.; Gerbeth, G.; Gundrum, T.; Hollerbach, R.; Kirillov, O.; Rüdiger, G.; Seilmayer, M.; Weber, N.; Weier, T.

The interaction of rotating fluids and magnetic fields is of crucial interest for the explanation of many astrophysical phenomena. The magnetorotational instability (MRI), discovered by Velikhov in 1959 when studying a magnetized Couette-Taylor flow, is presently considered the most likely mechanism for triggering turbulence and angular momentum transport in accretion disks. The Tayler instability (TI), a kink-type current-driven instability, may play an important role in angular momentum and chemical species transport in stars, and is also discussed as a possible ingredient of an alternative stellar dynamo mechanism.
The last years have seen significant progress in the experimental investigation of both instabilities. We summarize the recent results, obtained in various liquid metal experiments, on the helical and azimuthal versions of MRI, and on the TI. The prospects of studying both instabilities, MRI and
TI, in a combined large scale liquid sodium experiment are discussed in the context of theoretical predictions.

  • Lecture (Conference)
    18th International Couette-Taylor Workshop, 24.-26.06.2013, Enschede, The Netherlands

Permalink: https://www.hzdr.de/publications/Publ-19046
Publ.-Id: 19046


Time-dependent PT-symmetric phase transitions: exactly solvable models and their underlying geometry

Günther, U.

Time-dependent 2×2 matrix Hamiltonians are designed which preserve formal PT-symmetry, pass through an exceptional point and whose evolution matrices can be obtained analytically. These exactly solvable models allow for a full analytical treatment of the underlying geometric deformation features of the eigenspaces (the structures of the eigenvector bundles) including their geometric and algebraic properties. It is shown that a passage through an exceptional point is not sufficient for a time-dependent Hamiltonian to describe a time-dependent PT phase transition. Rather additional singular gauge terms have to be added in order to force a time-dependent eigenvector coalescence of the models. This opens a way to new classes of exactly solvable models. First results in this direction are presented.

Keywords: PT symmetry; non-Hermitian Hamiltonian; PT phase transition; exceptional point; Jordan block; branch point; time evolution; exactly solvable model; fibre bundle; projective Hilbert space; gauge theory

  • Invited lecture (Conferences)
    12th International Workshop on Pseudo-Hermitian Hamiltonians in Quantum Physics, 02.-06.07.2013, Istanbul, Turkey

Permalink: https://www.hzdr.de/publications/Publ-19045
Publ.-Id: 19045


Radiosynthesis and in vivo Evaluation of a 18F-Labelled Styryl-Benzoxazole Derivative for ß-Amyloid Targeting

Ribeiro Morais, G.; Kniess, T.; Bergmann, R.; Gano, L.; Abrunhosa, A.; Santos, I.; Paulo, A.

The formation of β-amyloid deposits is considered a histopathological feature of Alzheimer´s disease (AD). In vivo molecular imaging by means of amyloid-avid radiotracers will allow for an early and conclusive diagnostic of AD. Herein, we describe the radiosynthesis of the radiofluorinated styryl benzoxazole derivative [18F]-[2-[N-methyl-N-(2`-fluoroethyl)-4`-aminostyryl]benzoxazole] ([18F]-1) and its pre-clinical evaluation, including metabolic and biodistribution studies in male Wistar rats. The in vivo biological evaluation of [18F]-1 showed that this new radiotracer has a moderate brain uptake with a slow brain washout and a poor in vivo stability.

Permalink: https://www.hzdr.de/publications/Publ-19044
Publ.-Id: 19044


Measurement of the ²⁰N(γ,n)¹⁹N Reaction Rate for R-Process Nucleosynthesis

Röder, M.; for the R3B Collaboration

In the astrophysical r-process (rapid neutron capture process), that is important for the nucleosynthesis of heavy elements, many neutron-rich nuclei are involved.
The reactions on these exotic nuclei can only be studied with radioactive ion beams since target material cannot be fabricated from them.
One example of these reactions is the ¹⁹N(n,γ)²⁰N reaction that is important in a neutrino-driven wind scenario.
Using ²⁰N as a beam, this reaction was studied at GSI in inverse kinematics via Coulomb-dissociation exploiting the virtual gamma field of a heavy target in the so called s393-experiment.
The experiment was performed at the LAND/R3B setup (Large Area Neutron Detector, Reactions with Relativistic Radioactive Beams) in a kinematically complete measurement, i.e., detecting all particles leaving the nuclear reaction.
The neutrons flying at relativistic velocity were observed by the LAND-detector, the calibration of which plays a crucial role for the above specific reaction.
I will give an overview of the R3B-setup, the calibration of the LAND-detector and a status of the analysis of the ²⁰N(γ,n)¹⁹N reaction.

Keywords: r-process; neutron-rich nuclei; Coulomb-dissociation; radioactive ion beams

  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19043
Publ.-Id: 19043


NeuLAND MRPC-based detector prototypes tested with fast neutrons

Caesar, C.; Aumann, T.; Bemmerer, D.; Boretzky, K.; Elekes, Z.; Gonzalez-Diaz, D.; Hehner, J.; Heil, M.; Kempe, M.; Maroussov, V.; Nusair, O.; Reifarth, R.; Rossi, D.; Simon, H.; Stach, D.; Wagner, A.; Yakorev, D.; Zilges, A.

Recent results from a first irradiation of multi-gap resistive plate chambers with fast neutrons are presented. The counters have been built at GSI and FZD. The experiment was performed at the “The Svedberg Laboratory” (TSL) in Uppsala, Sweden, utilizing a quasi-monoenergetic neutron beam with an energy En=175 MeV. For a 2×4 gap prototype operated at E=100 kV/cm, an efficiency of (0.77 ±0.33)% was measured.

Keywords: multi-gap resistive plate chamber neutron

Permalink: https://www.hzdr.de/publications/Publ-19042
Publ.-Id: 19042


Quasi-cw THz source TELBE: Challenges and Opportunities

Gensch, M.

  • Invited lecture (Conferences)
    FLASH Seminar, 16.07.2013, Hamburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19041
Publ.-Id: 19041


Coherent THz Radiation from linear accelerators and 4th Generation X-ray Light sources: Status, Challenges and Opportunities and applications in biophysics

Gensch, M.

The past fifteen years have seen a rapid development of novel techniques to generate and detect ultra-short and high power THz pulses. The availability of these pulses with electric field strength in the few 10 to 100 MV/m regime has led to a number of exciting experiments in particular in the field of non-linear THz spectroscopy and THz control experiments. One class of these THz generation techniques utilizes highly charged, ultra short electron bunches accelerated to relativistic speed in linear particle accelerators [1]. A variety of different source concepts allows to shape the THz pulses from single cycle/broad band pulses to multicycle/narrow-bandwidth pulses with polarizations ranging from radial to linear. One main attraction of accelerator-based THz originates from the fact that the THz generation process does not take place in a medium but in the ultra-high vacuum of the accelerator, so that the THz pulse energy can hence theoretically much easier up scaled than in any of the table top sources available today. Additionally it could recently be shown that coherent THz radiation can be generated residually and in parallel to the femtosecond X-ray pulses in 4^th Generation X-ray Light sources such as FLASH [2,3,and 4] and LCLS [5]. This opens up the exciting opportunity to perform naturally synchronized THz pump X-ray probe experiments on few femtosecond time scales [2,3,and 5]. An overview over different THz facility projects will be presented and experimental opportunities and challenges will be discussed with an emphasis on potential applications in Biophysics.

  • Invited lecture (Conferences)
    ICS-4 Seminar, 12.07.2013, Juelich, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19040
Publ.-Id: 19040


Morphology studies of Si-SiO2 nanocomposites using energy-filtered transmission electron microscopy

Hübner, R.; Friedrich, D.; Wolf, D.; Liedke, B.; Schmidt, B.; Heinig, K.-H.

Due to significant band gap widening by quantum confinement, Si nanosponge structures embedded in SiO2 formed by spinodal decomposition of metastable silicon-rich silicon oxide are promising, advanced Si absorbers for 3rd generation solar cells. In thermodynamically metastable, silicon-rich oxide, i.e. SiOx with x < 2, high-temperature annealing results in the formation of Si precipitations in a stoichiometric SiO2 matrix. Phase separation of SiOx films with 1.2 ≤ x < 2 (Si excess of up to 40 at.-%) leads to disconnected Si nanoclusters, whereas for x < 1.2 (Si excess larger than 40 at.-%) phase separation results in percolated Si nanostructures with a sponge-like morphology [1].

To reveal such a sponge-like morphology in sputter-deposited SiOx films for x ~ 1 after activation by rapid thermal annealing (RTA), energy-filtered transmission electron microscopy (EFTEM) imaging as well as EFTEM tomography were carried out and the results were compared with kinetic Monte-Carlo (KMC) simulations. To this end, 200 nm thick SiOx layers were prepared at room temperature on p type (100) Si wafers by magnetron sputtering in Ar plasma from two simultaneously operating Si and SiO2 targets. During subsequent RTA in Ar or Ar + 5 % H2 ambient, samples were heated up to 1150 °C and annealed for 30 s. Sponge-like nanostructures were investigated by EFTEM imaging using an image-corrected FEI Titan 80-300 microscope equipped with a Gatan Imaging Filter 863. For EFTEM tomography, a tilt series between ±70° was acquired in steps of 2° in a Philips CM200 FEG microscope with Gatan Imaging Filter 678. The tilt series alignment, i.e. the correction of residual displacements, was carried out using the IMOD software [2], while the tomographic reconstruction of the Si 3D morphology was performed with the Weighted Simultaneous Iterative Reconstruction Technique [3].

The contrast in zero-loss filtered high-resolution TEM images is caused by the coherent superposition of unscattered and elastically scattered electrons within the thin TEM lamella, and hence, related to the projected atomic structure. Consequently, Bragg-oriented Si nanocrystals larger than a minimum size are visible in Figure 1 and indicate phase separation of the SiOx film with subsequent crystallization during RTA. Since large amorphous Si precipitates crystallize preferably, high-resolution TEM images allow the determination of a maximum Si structure size. For small Si structures, however, phase separation is also possible without crystallization. Such amorphous precipitates as well as not Bragg-oriented Si nanocrystals cannot be observed with high-resolution electron microscopy, leading to an underestimation of the Si phase fraction. Therefore, EFTEM analysis is a suitable alternative for Si morphology studies. In particular, valence-band plasmon energy-loss imaging is an appropriate approach, since the Si plasmon peak is, except the zero-loss peak, the most intense feature in the electron energy-loss spectrum. It has a narrow energy distribution of a few eV, and thus, allows to distinguish the Si phase from the SiO2 compound [4]. As shown in Figure 2, the expected sponge-like Si morphology in phase-separated SiOx has been proven by Si plasmon imaging, which particularly shows that Si filaments have diameters of a few nanometers with a narrow size distribution. This finding is in excellent agreement with large-scale simulations based on KMC (Figure 3). Although Si plasmon EFTEM images can show the Si phase distribution in a planar projection, they do not provide three-dimensional information. For example, a superposition of Si nanodots cannot be distinguished from a sponge-like morphology in a 2D projection. Therefore, EFTEM tomography was applied, revealing that the separation of silicon into percolated nanostructures is not obvious (Figure 4). Coarsening of the Si sponge accompanied by a loss of percolation may be the reason. Indeed, longer annealing at 1100 °C for 3 h leads to separated non-spherical nanoclusters [5]. However, an underestimation of the thinnest, presumably amorphous, Si filaments cannot be excluded. Prolonged electron irradiation during acquisition of the EFTEM tilt series might have an influence on the sponge-like morphology, too.

1. T. Müller, K.-H. Heinig, W. Möller, C. Bonafos, H. Coffin, N. Cherkashin, G. Ben Assayag, S. Schamm, G. Zanchi and A. Claverie, Appl. Phys. Lett. 85 (2004), p. 12.
2. J. Kremer, D. N. Mastronarde and J. R. McIntosh, J. Struct. Biol. 116 (1996), p. 71.
3. D. Wolf, A. Lubk and H. Lichte, Ultramicroscopy (2013), submitted.
4. S. Schamm, C. Bonafos, H. Coffin, N. Cherkashin, M. Carradaa, G. Ben Assayag, A. Claverie, M. Tencé and C. Colliex, Ultramicroscopy 108 (2008), p. 346.
5. A. Yurtsever, M. Weyland and D. A. Muller, Appl. Phys. Let. 89 (2006), p. 151920.
6. The authors kindly acknowledge TEM sample preparation by Annette Kunz and Martina Missbach.

Keywords: silicon-rich silicon oxide; EFTEM imaging; EFTEM tomography; KMC simulation

  • Poster
    Microscopy Conference 2013, 25.-30.08.2013, Regensburg, Deutschland
  • Contribution to proceedings
    Microscopy Conference 2013, 25.-30.08.2013, Regensburg, Deutschland

Permalink: https://www.hzdr.de/publications/Publ-19039
Publ.-Id: 19039


Terahertz generation and detection with InGaAs-based large-area photoconductive devices excited at 1.55 µm

Xu, M.; Mittendorff, M.; Dietz, R.; Künzel, H.; Sartorius, B.; Göbel, T.; Schneider, H.; Helm, M.; Winnerl, S.

We report on scalable large-area terahertz emitters and detectors based on In0.53Ga0.47As/In0.52Al0.48As heterostructures for excitation with 1.55 µm radiation. Different geometries involving three different electrode gap sizes are compared with respect to THz emission, bias field distribution and Joule heating. The field distribution becomes more favorable for THz emission as gap size increases while Joule heating exhibits the opposite dependence. Best performance is found for emitters with a gap size of 7.5 µm. The scalable devices are furthermore employed as detectors. The scalable electrode geometry enables spatially integrated detection, which is attractive for specific applications.

Keywords: photoconductive THz emitter; photoconductive THz detector; 1.55 µm excitation

Permalink: https://www.hzdr.de/publications/Publ-19038
Publ.-Id: 19038


Performing kinetic lattice Monte-Carlo simulations of far-from-equilibrium processes on GPUs

Kelling, J.; Heinig, K.-H.

Kinetic Metropolis lattice Monte-Carlo (KLMC) simulations can be applied to study systems without strong external driving forces, for example the evolution of nanostructures. An algorithm allowing nearest neighbor interaction in thermally activated processes has been implemented for GPUs. External driving forces can be modeled by adding appropriate rules to the cellular automaton. Ion-beam induced mixing, which is governed by comparatively long-ranged interactions, leads to far-from-equilibrium processes (defect relaxation) producing disordered structures. A plain implementation of long-range interactions reduces the performance on GPUs substantially. In this talk we present an efficient implementation of long-range ballistic displacements in GPU-KLMC.

  • Lecture (Conference)
    2nd International Symposium “Computer Simulations on GPU”, 27.-29.05.2013, Freudenstadt, Deutschland
  • Lecture (others)
    Wigner RCP Institute Seminar, 30.08.2013, MTA-TTK, Budapest, Hungary

Permalink: https://www.hzdr.de/publications/Publ-19037
Publ.-Id: 19037


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