Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

"Online First" included
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Only approved publications

35810 Publications

Evidence for Fulde-Ferrell-Larkin-Ovchinnikov states in layered organic superconductors

Wosnitza, J.

  • Invited lecture (Conferences)
    12th Japanese-German Symposium Emergent Phenomena in Novel Quantum Phases of Condensed Matter, 14.-17.07.2012, Izu, Japan

Publ.-Id: 18351

Tracking ore mineral characteristics from mine to concentrate: The fate of electrum at the Cavanacaw gold deposit, Northern Ireland

Birtel, S.; Wunderlich, I.; Gutzmer, J.

A systematic geometallurgical assessment was carried out to follow changes of mineral composition and microfabric following the ore extracted from two ore blocks at the Cavanacaw Au Mine through the beneficiation process. SEM-based image analysis was used to carry out the investigation on the finely disseminated Au ores. A general assessment quickly reveals that the beneficiation plant suffers only little loss to the tailings. Despite this positive assesment results illustrate that there are some losses that appear to be systemic: Large electrum grains (>16 µm ecd) are abundant in the original uncrushed material only make a minor contribution to the final concentrate. Due to the ductile behaviour of electrum, fracturing of larger electrum grains into smaller grain sizes appears unlikely – it is thus concluded that these particles may be captured in the plant during processing.
Our results reveal that sulphide-rich veins are typically higher in grade than the final concentrate. This results from processing a mixture of high-grade ore and low-grade wall rock. To reduce processing costs it might be considered to introduce an early stage of optical sorting

Keywords: gold; MLA; mineral processing; geometallurgy

  • Open Access Logo Contribution to proceedings
    12th SGA Biennial Meeting, 12.-15.08.2013, Uppsala, Sweden
    Mineral deposit Research for a high-tech world Proceedings, Volume 1, Sweden: Elanders Sverige AB, 978-91-7403-207-9, 306-309
  • Lecture (Conference)
    12th SGA Biennial Meeting, 12.08.-15.11.2013, Uppsala, Sweden
  • Lecture (Conference)
    Workshop on Advanced Analysis Techniques in Process Mineralogy, 03.02.2014, Lulea, Sweden

Publ.-Id: 18350

Competing exchange interactions in Co-doped ZnO: Departure from the superexchange picture

D'Ambrosio, S.; Pashchenko, V.; Mignot, J.; Ignatchik, O.; Kuzian, R.; Savoyant, A.; Golacki, Z.; Grasza, K.; Stepanov, A.

We report the results of a comprehensive study of the exchange interactions in Co-doped ZnO using inelastic neutron scattering, electron paramagnetic resonance, and magnetic property measurements. In particular, we observe an unprecedentedly strong spatial anisotropy of the two nearest-neighbor exchanges, J((1)) = -25.6 +/- 0.3 K and J((2)) = -8.5 +/- 0.4 K, along with the distant-neighbor J values of ferromagnetic sign. We argue that the superexchange mechanism alone cannot account for the obtained data and we suggest that an additional mechanism leading to a strong ferromagnetic spin coupling is responsible for these findings. We also discuss the origin of this ferromagnetic mechanism.

Publ.-Id: 18349

Spin dynamics of S = 1/2 Heisenberg chains with a staggered transverse field: electron spin resonance studies

Zvyagin, S. A.

This article is a review of the recent achievements in experimental studies of magnetic excitations in the copper pyrimidine dinitrate [PM-Cu(NO3)(2)(H2O)(2)](n) (PM = pyrimidine), an S = 1/2 antiferromagnetic chain material with an alternating g-tensor and the Dzyaloshinskii-Moriya interaction, by means of high-field electron spin resonance (ESR). Due to this alternation, in the 1D critical regime this material exhibits a field-induced gap. The excitation spectrum is formed by solitons and their bound states, breathers, and can be effectively described using the sine-Gordon model. With increasing temperature, the soliton-breather regime can be suppressed, resulting in a substantial evolution of ESR parameters. These changes can be described using a new theoretical concept recently proposed for S = 1/2 AF chains with a staggered transverse field. High magnetic field induces a transition into the spin-polarized state with the excitation spectrum formed by magnons. Nonmonotonous behavior of the field-induced gap is observed in vicinity of the saturation field. Experimental data are compared with results of existing theoretical approaches, revealing excellent agreement with predictions.

Publ.-Id: 18348

Magnetic excitations in the spin-1 anisotropic antiferromagnet NiCl2-4SC(NH2)2

Psaroudaki, C.; Zvyagin, S. A.; Krzystek, J.; Paduan-Filho, A.; Zotos, X.; Papanicolaou, N.

The spin-1 anisotropic antiferromagnet NiCl2-4SC(NH2)2 exhibits a field-induced quantum phase transition that is formally analogous to Bose-Einstein condensation. Here we present results of systematic high-field electron spin resonance (ESR) experimental and theoretical studies of this compound with a special emphasis on single-ion two-magnon bound states. In order to clarify some remaining discrepancies between theory and experiment, the frequency-field dependence of magnetic excitations in this material is reanalyzed. In particular, a more comprehensive interpretation of the experimental signature of single-ion two-magnon bound states is shown to be fully consistent with theoretical results. We also clarify the structure of the ESR spectrum in the so-called intermediate phase.

Publ.-Id: 18347

Soliton-magnon crossover in spin-1/2 Heisenberg chains

Zvyagin, S.

Copper pyrimidine dinitrate ([PM-Cu(NO3)2(H2O)2]n, PM = pyrimidine) is a spin-1/2 antiferromagnetic chain material with alternating g-tensor and Dzyaloshinskii-Moriya interactions, whose spin dynamics can be described using the effective sine-Gordon model. Due to the presense of alternating staggered magnetization, this material exhibits a field-induced spin gap, formed by first breather. Here, we report on electron spin resonance (ESR) studies of this material in magnetic fields up to 64 T. In particular, a minimum of the gap in the vicinity of the saturation field Hsat = 48.5 T associated with a transition from the quantum disordered sine-Gordon (with soliton-breather elementary excitations in the magnetic excitation spectrum) to a spin-polarized state (with excitation spectrum formed by magnons) has been observed. This interpretation is fully confirmed by the quantitative agreement over the entire field range of the experimental data with the DMRG calculations for spin-1/2 Heisenberg chain with a staggered transverse field [1]. Such a behavior appears to be a general feature of the high-field excitation spectrum of quantum spin-1/2 chain systems with alternating g-tensor and/or Dzyaloshonskii-Moriya interactions

  • Invited lecture (Conferences)
    JEMS 2012 - Joint European Magnetic Symposia, 13.09.2012, Parma, Italy

Publ.-Id: 18345

High density plasma instabilities in intense laser irradiation

Kluge, T.; Cowan, T.; Huang, L.; Metzkes, J.; Schramm, U.; Gutt, C.; Schlenvoigt, H.-P.; Bussmann, M.

High energy electron channel formation in solid targets is discussed on two exemplary PIC simulations. The feasibility of SAXS diagnostics in laser accelerated plasma physics is discussed on the basis of scattering at high density plasma waves.

  • Lecture (Conference)
    33rd International Workshop on Physics of High Energy Density in Matter, 13.-18.01.2013, Hirschegg, Österreich
  • Lecture (Conference)
    77. Jahrestagung der DPG und DPG-Frühjahrstagung, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18344

Coexistence of ferromagnetism and superconductivity in single-nanostructures

Herrmannsdörfer, T.

  • Invited lecture (Conferences)
    PNI in-house workshop on "Magnetism and highly correlated electron systems", 11.06.2012, Freising, Deutschland

Publ.-Id: 18343

Electron Spin Resonance in High Magnetic Fields

Zvyagin, S.

  • Invited lecture (Conferences)
    Dynamics and Transport in Quantum Magnets LOTHERM, Summer School 2012, 05.06.2012, Ljubljana, Slovenia

Publ.-Id: 18340

The Rossendorf Beamline at ESRF: A Pooled Facility of ACTINET-I3

Scheinost, A. C.

Overview on experimental possibilities and Joint Research Projects performed at The Rossendorf Beamline during ACTINET-I3

Keywords: XAS

  • Invited lecture (Conferences)
    2nd ACTINET-I3 Plenary Meeting, 23.-24.01.2013, Avignon, France

Publ.-Id: 18339

AcXAS: Actinide Reference X-ray Absorption Spectroscopy Database

Scheinost, A. C.; Schmeisser, N.; Banerjee, D.; Rossberg, A.; Denecke, M.; Dardenne, K.; Rothe, J.; Daehn, R.

Why do we need an Actinide Reference X-Ray Absorption Spectroscopy Database?
The team
The concept
The work status

Keywords: XAS; actinides

  • Invited lecture (Conferences)
    2nd ACTINET Plenary Meeting, 23.-24.01.2013, Avignon, France

Publ.-Id: 18338

Nanostructures by mass-separated FIB

Bischoff, L.; Böttger, R.; Philipp, P.; Schmidt, B.

The introduction of mass-separated systems in the field of focused ion beams significantly increases the area of application in nanotechnology due to the availability of a broad spectrum of ions with the same advantages compared to classical Ga instruments. A short description of the configuration of a mass-separated FIB tool is given as well as the fundamentals of alloy liquid metal ion sources. Examples of application include patterned tailoring of functional surfaces and ion-induced phase transformation in thin layers, in particular the Si nanowire fabrication by FIB implantation and subsequent wet-chemical, anisotropic etching and the FIB lithography of thin ta-C films. Furthermore, the ion beam synthesis of CoSi2 nanostructures by Co-FIB writing and annealing, and the modification of surface morphology by various mono- and polyatomic projectiles in a broad energy- and temperature range in different materials are described and discussed.

Keywords: mass-separated focused ion beam; alloy liquid metal ion source; ExB filter; Si nanowire; ion beam synthesis; CoSi2 nanostructures; ta-C films; self-organized surface morphology; polyatomic ions

  • Book chapter
    Zhiming Wang: “FIB Nanostructures” Springer Series in Materials Science Lecture Notes on Nanoscale Science and Technology, Peking, Berlin: Springer, 2013, 978-3-319-02874-3

Publ.-Id: 18337

Scanning Tunnelling Spectroscopy of FIB-induced Local Phase Changes in Tetrahedral Amorphous-Carbon

Klein, F.; Philipp, P.; Bischoff, L.; Mühl, T.

Ion irradiation of tetrahedral amorphous-carbon leads to both an ion implantation and a local phase change of the carbon. The latter is equivalent to an increase of the carbon sp2/sp3 bond ratio. It is caused by the deposition of the ion energy and leads to an increased electrical conductivity. We perform spatially resolved scanning tunneling spectroscopy in order to investigate the impact of different ion species (Ga, Si, Ge, Au). A direct contribution of the implanted metal will be carefully considered.

Keywords: tetrahedral amorphous-carbon; ion implantation; spatially resolved STM

  • Poster
    DPG Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18336

Watching the quantum race of electrons

Schütte, B.; Bauch, S.; Frühling, U.; Wieland, M.; Gensch, M.; Ploenjes, E.; Gaumnitz, T.; Azima, A.; Bonitz, M.; Drescher, M.

When a photon of sufficient high energy hits an atom it may kick out an electron. Quantum mechanics predicts that the electron behaves like a wave that runs away from the atom. If the photon energy was chosen right then a second electron (Auger electron) may be liberated from the atom, racing behind the first one. We were able to detect how this second electron overtakes the first one within only a few femtoseconds (1 fs = 10-15 seconds) and observe the dynamic exchange of energy between the two electrons when they are passing each other.

Keywords: THz; X-ray; pump probe; femtosecond; super-radiant THz sources

  • Open Access Logo Contribution to external collection
    in: DESY - Photon Science 2012: Highlights, Hamburg: DESY, 2013, 48-49

Publ.-Id: 18335

Interaction of energetic ultraheavy ions with surfaces

Bischoff, L.; Böttger, R.; Heinig, K.-H.; Facsko, S.

Energetic ultraheavy polyatomic ions like Bi3++ and Bi2+ produce very dense collision cascades in surface layers. Compared to monatomic ion impacts, which do not overlap in space and time within the heat relaxation time, the simultaneous impact of a few atoms in the same point can cause very different effects. Here, we report on FIB irradiation with fluences up to 1017 cm−2 using a liquid metal ion source. Using ultraheavy ions, a significantly increased sputter yield of Ge has been found, which can be attributed to thermal processes. Another, more striking feature is the dramatic difference in the surface morphologies caused by monatomic and ultraheavy ion irradiation. For instance, the well-known spongy surface layer forms on Ge upon 20 keV Bi+ irradiation, whereas normal incidence Bi3++ irradiation with the same energy per atom results in hexagonally ordered dot pattern having an aspect ratio of about one. Similar pattern have been found on Si by ultraheavy ion irradiation, but only under substantial substrate heating. And, in hot Ge substrates, normal incidence monatomic Bi+ ions produce no longer Ge sponge but also dot pattern. A crude thermal analysis of the experiments shows that the considered dot pattern formation is associated with a critical energy density deposited by an ion close to the surface. A more comprehensive model on this pattern formation will be presented in a subsequent talk by K.-H. Heinig.
R. Böttger, L. Bischoff, K.-H. Heinig, et al. JVST B30 (2012)06FF12

Keywords: ultraheavy polyatomic ions; bismuth; liquid metal ion source; germanium; sponge; dot pattern

  • Invited lecture (Conferences)
    DPG Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18334

Account of the intratrack radiolytic processes for interpretation of the AMOC spectrum of liquid water

Zvezhinskiy, D.; Butterling, M.; Stepanov, S.; Krause-Rehberg, R.; Wagner, A.

Recent development of the Gamma-induced Positron Spectroscopy (GiPS) setup significantly extends applicability of the Age-Momentum Correlation technique (AMOC) for studies of the bulk samples. It also provides many advantages comparing with conventional positron annihilation experiments in liquids, such as extremely low annihilation fraction in vessel walls, absence of a positron source and e+ annihilations in it. We have developed new approach for processing and interpretation of the AMOC-GiPS data based on the diffusion recombination model of the intratrack radiolytic processes. This approach is verified in case of liquid water, which is considered as a reference medium in the positron and positronium chemistry.

Keywords: Gamma-induced Positron Spectroscopy; Age-Momentum Correlation; Positronium Chemistry

  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, Great Britain
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012057
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012057

Publ.-Id: 18333

Optimization of growth parameters of TiO2 thin films using a slow positron beam

Butterling, M.; Anwand, W.; Cornelius, S.; Potzger, K.; Smekhova, A.; Vinnichenko, M.; Wagner, A.

TiO2 thin films grown on fused silica were investigated using positron Doppler broadening spectroscopy at the slow-positron-beam SPONSOR at the Helmholtz-Zentrum Dresden-Rossendorf.
Effects of changes in different parameters like temperature or oxygen flow during film deposition on positron sensitive parameters have been investigated and first results will be presented.

Keywords: Slow Positron; Doppler Broadening Spectroscopy; Thin Films

  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012073
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012073
  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, Great Britain

Publ.-Id: 18332

Si nanowire networks for 3rd generation solar cells

Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Bulutay, C.; Keles, U.; Aydinli, A.

Large-scale self-structuring by spinodal decomposition of metastable SiO is a very promising synthesis process of novel nanostructured Si absorbers for 3rd generation solar cells [1]. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP) and laser annealing. When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x)Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo accelerated by Massive Parallel Programming on NVIDIA graphic cards using a CUDA code. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gaps of sponge have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners.

Keywords: nanocomposite; silicon; silica; sponge; sputter deposition; solar cell; band gap; atomistic simulations

  • Invited lecture (Conferences)
    4th International Conference on Nanostructure Selfassembly (NANOSEA2012), 25.-29.06.2012, Margherita di Pula, Sardinia/Italy

Publ.-Id: 18331

Networks of Si nanowires in SiO2 for solar cells

Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Keles, U.; Bulutay, C.; Aydinli, A.

In Si-based thin film solar cells the a-Si:H or nanocrystalline absorber layer can be replaced by a network of Si nanowires (Si nanosponge) embedded in SiO2[1]. The Si nanosponge is formed by spinodal decomposition of metastable SiO layers which have been deposited by different techniques, sputtering, CVD and e-beam evaporation. The spinodal decomposition has been activated by Rapid Thermal Processing and laser annealing. When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x) Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gap of sponges have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners. [1] BMBF-TÜBITAK project “RainbowEnergy”, coordinators K.-H. Heinig and A. Aydinli

Keywords: nanocomposite; silicon; silica; sponge; solar cell; sputter deposition; laser annealing; band gap; atomistic simulations

  • Lecture (Conference)
    E-MRS Spring Meeting 2012, Symp. A, 14.-18.05.2012, Strasbourg, Frankreich

Publ.-Id: 18330

Morphology of Ge surfaces after Bi, Bi2 and Bi3 ion impacts: holes, dots and sponge

Heinig, K.-H.; Böttger, R.; Bischoff, L.; Liedke, B.; Urbassek, H.; Anders, C.

Outline: (1) Motivation; (2) Patterns after normal Bi_n^+ and Bi_n^++ impacts; (3) Patterns after normal Bi_1^+ and Bi_1^++ impacts; (4) Different regions in the T-E_i phase diagram --> driving forces; (5) MD simulations; (6) kMC simulations; (7) Predictions of damped KS equation; (8) Conclusions

Keywords: polyatomic ions; ion-solid interaction; surface morphology; self-organization

  • Lecture (Conference)
    Workshop Ionenstrahlphysik, 10.-11.07.2012, Augsburg, Germany

Publ.-Id: 18329

Surface Patterning of Ge and Si by Heavy Ion and Cluster Impacts: Experiments, Atomistic Simulations and Theory

Heinig, K.-H.; Böttger, R.; Liedke, B.; Bischoff, L.; Anders, C.; Urbassek, H.

The driving forces for pattern formation on surfaces by ion irradiation have been under discussion for many years. Bradley and Harper published a straightforward derivation of a partial differential equation based on the surface curvature dependent sputtering, which describes some features. Later on, ion impact induced viscous flow and a mass drift in the amorphous surfaces layer caused by the impinging ions where discussed. Only a few years ago it became obvious that on semiconductor surfaces the formation of many of the beautiful patterns are dominated by contaminations with metals. Thus, a discussion started, whether the pattern formation is induced by preferential sputtering of one of the components or by driving forces like phase separation. Additionally, the kinetics of the collision-induced defects in a sub-surfaces layer can produce instabilities resulting in surface pattern. In order to identify the dominating driving forces at least for Ge and Si surface patterning by heavy ion (Bi) and cluster (Bi3) impacts of a few to a few tens of keV, experimental Focussed Ion Beam (FIB) and broad-beam studies were combined with computer experiments (MD and kinetic Monte Carlo simulations) and theoretical studies, e.g. of the damped Kuramoto-Sivashinsky equation. A detailed comparison between experiments, simulations and PDE solutions of the surfaces evolution of specificmorphologies is a powerful approach for a deeper understanding of this kind of self-organization of structures. In this abstract for each approach, experiment, simulation and theory, an example is presented. Experiments cover a wide range of ion energies and fluences. The atomistic simulations study the influence of the ion collision cascades on the pattern formation via defect kinetics. And finally, relations of this defect kinetics to parameters of the damped Kuramoto-Sivashinsky equation are studied.

Keywords: ion-solid interaction; self-organization; surface pattern; theory; kinetic Monte Carlo simulation

  • Lecture (Conference)
    19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19), 16.-21.09.2012, Frauenchiemsee, Germany

Publ.-Id: 18328

Near-surface depth profiling of solids by mono-energetic positrons

Ganguly, B. N.; Brauer, G.; (Editors)

This work reflects the wide and fascinating range of fields to which positrons have made important contributions. This covers, in particular, the development of low-energy (eV-keV) beams of essentially mono-energetic positrons, in the late 1960s, which opened the door to an even wider range of fundamental and technological studies: from surface physics to polymer films. The volume offers some background knowledge on the extent to which positrons have influenced and contributed to work in numerous fields.

Keywords: mono-energetic positrons; near-surface depth profiling; advances in techniques

  • Book (Authorship)
    Durnten-Zurich: Trans Tech Publications Ltd, 2012
    296 Seiten

Publ.-Id: 18327

Cerebral blood flow quantification in the rat: a direct comparison of arterial spin labeling MRI with radioactive microsphere PET

Bos, A.; Bergmann, R.; Strobel, K.; Hofheinz, F.; Steinbach, J.; van den Hoff, J.

Arterial spin labeling magnetic resonance imaging (ASL-MRI) has been recognised as a valuable method for non-invasive assessment of cerebral blood flow but validation studies regarding quantification accuracy by comparison against an accepted gold standard are scarce, especially in small animals. We have conducted the present study with the aim of comparing ASL flow-sensitive alternating inversion recovery (FAIR)-derived unidirectional water uptake (K1) and 68Ga=64Cu microsphere (MS)-derived blood flow (f ) in the rat brain.
In 15 animals, K1 and f were determined successively in dedicated small animal positron emission tomography and MR scanners. The Renkin-Crone model modified by a scaling factor was used for the quantification of f and K1.
Below about 1 mL/min/mL, we obtain an approximately linear relationship between f and K1. At higher flow values, the limited permeability of water at the blood brain barrier becomes apparent. Within the accessed dynamic flow range (0.2 to 1.9 mL/min/mL), the data are adequately described by the Renkin-Crone model yielding a permeability surface area product of .1.53 ± 0.46/ mL/min/mL.
The ASL-FAIR technique is suitable for absolute blood flow quantification in the rat brain when using a one-compartment model including a suitable extraction correction for data evaluation.

Trial registration
24-9168.21-4/2004-1 (registered in Freistadt Sachsen, Landesdirektion Dresden)

Keywords: Arterial spin labeling; Cerebral blood flow; Positron emission tomography; Kinetic modeling; Blood brain barrier

Publ.-Id: 18326

Velocity Measurement Using ROFEX Ultrafast Dual Plane X-ray CT Imaging

Barthel, F.; Hoppe, D.; Hampel, U.

Ultrafast electron beam X-ray computed tomography was developed at HZDR as a powerful imaging tool to observe two phase flows in several industrial applications, such as pipe flow that cannot be accessed by optical techniques. The ROssendorf Fast Electron beam X-ray Tomograph (ROFEX) combines advantages of non-invasive conventional CT systems, with a very high temporal and spatial resolution. This CT system is specially designed for investigations at a vertical test section at TOPFLOW (Transient two phase flow test facility) at HZDR. As a step forward recently ultrafast dual plane X-ray CT imaging was implemented, using new fast double ring X-ray detector electronics and a dual source path target in the ROFEX scanner. For the first time measurements of velocities in gas/water and steam/water flow are possible without any influence to the flow itself. The system provides pairs of slice images with an axial distance of 11mm at frame rates of up to 8000 kHz in time multiplex mode on both CT imaging planes. Thus one can assess the velocity of the interfacial area in the flow using cross correlation algorithm in two corresponding slice images. Beside parameters like phase fraction distribution, bubble sizes and interfacial areas, measurement of gas fraction velocity is possible for the first time non-invasively. From these data one can estimate slip between gas and liquid phase and calculate volumetric gas fraction. Furthermore CFD (Computational Fluid Dynamics) models can be enhanced providing parameters for calculations of bubble forces such as drag force or lift force, which influence shape and flow of bubbles. In chemical engineering applications like catalytic packaging or monolith ceramics it is possible to assess the residence time as well.

Keywords: velocity measurements; electron beam X-ray CT; dual plane CT

  • Lecture (Conference)
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
  • Contribution to proceedings
    6th International Symposium on Process Tomography, 26.-28.03.2012, Cape Town, South Africa
    Proceedings of 6th International Symposium on Process Tomography

Publ.-Id: 18325

Si Nanocrystal Networks by Si/SiO2 Phase Separation in SiOx Thin Films for Third Generation Solar Cells

Gündoğdu, S.; Özen, E. S.; İlday, S.; Heinig, K.-H.; Turan, R.; Aydinli, A.

Si/SiO2 phase separation in Silicon rich oxides is a very promising synthesis process of novel nanocrystaline Si (nc-Si) structures for 3rd generation thin-film solar cells. The incorporation of larger band gap nanocrystaline silicon into the solar cell structure can be utilized to improve the single band gap silicon solar cells efficiency by allowing a better use of the solar spectrum. We present cw laser annealing of Si-rich oxide thin films with varying Si content to obtain nc-Si embedded in silica. Silicon nanocrystals in the form of a nanocrystaline network (sponge-like) are particularly interesting for their percolated structure. Calculations show that considerable Si band gap widening due to quantum confinement in the nanocrystals network is expected. Beside this wide band gap, sponge-like Si has another potential advantage of suppressing the carrier recombination loss mechanism by electrically percolated nanostructures. SiOx thin films with x<2 were obtained by plasma enhanced chemical vapour deposition (PECVD). Hydrogen or nitrogen diluted silane (SiH4) gas was used as the Si source and two different precursor gasses, N2O and CO2, were used for oxygen incorporation. Fine tuning the Si excess in SiOx and optimizing the annealing conditions is pursued to control the inter-nanocrystal distance to generate a network of Si nanocrystals. The network formation depends critically on the precise control of composition during deposition. In the case of SiOx films, it is expected that the network is formed upon phase separation when the stoichiometry parameter of the initial SiOx film is x ~ 1 [1]. Nevertheless, in the case of PECVD grown Si-rich oxides, different elements such as nitrogen, carbon and especially hydrogen can be present in the films. A detailed elemental study has been performed to determine the precise composition of the films using ion beam techniques as elastic recoil detection analysis (ERDA) and Rutherford back scattering (RBS), as well as X-Ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FTIR) and ellipsometry. The presence of hydrogen in PECVD grown samples makes ERDA an essential technique for compositional analysis although it is an expensive and hard to reach method. We have compared the ERDA data of different sets of samples with XPS, FTIR and ellipsometry analysis within the scope of listing a number of correlations between them and, further to be able to obtain the compositional information with these more accessible techniques. After the characterisation of the as-grown samples, the role of the composition in phase separation, as well as the laser irradiation parameters have been investigated and hydrogen has been identified as a key parameter for the Si/SiO2 phase separation. This research is supported by BMBF-TÜBITAK project "RainbowEnergy". [1] T. Muller et al, Applied Physics Letters, 85, 2373 (2004).

Keywords: Phase separation; SiOx; nuclear analysis; layer deposition

  • Lecture (Conference)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18324

The recovery procedure of pin-by-pin fields of power distribution in the core of VVER type reactor for the program BIPR-8. Verification calculations

Gordienko, P.; Kotsarev, A.; Lisorkin, M.; Kozmenkov, Y.; Kliem, S.

Reconstruction of power distribution gives a means to check the compliance with design limits in steady-state calculations and to take account of power distribution deformation from one fuel element to another in transient calculations with use of spatial kinetics model. In calculation of reactivity accidents, its application makes it possible to avoid the additional conservatism derived from nodal calculation of power distributions. The resulting description of distribution behavior is expected to be used in thermal and mechanical calculation of fuel assemblies in transients.
The reconstructed power distributions will be used to calculate power densities in all fuel elements in the reactor core with use of BIPR-8 calculation code [1]. Verification calculations have been carried out by comparing the data of element-by-element power distribution in one cassette calculated with use of PERMAK [2] and BIPR-8 codes to test the method used and a new nodule of BIPR-8 where the method is implemented.

  • Contribution to proceedings
    22nd Symposium of Atomic Energy Research (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
    Proceedings of the 22nd AER Symposium, Budapest: MTA Energoatom, 9789635086276, 177-191

Publ.-Id: 18323

The first comparison of the seventh AER Dynamic Benchmark problem results obtained by RELAP5-3D and DYN3D/ATHLET computing codes

Bencik, M.; Hadek, J.; Kozmenkov, Y.; Kliem, S.

The paper gives the first comparison of the 7th three-dimensional AER dynamic benchmark calculation results received with the codes RELAP5-3D (ÚJV) and DYN3D/ATHLET (HZDR). This benchmark was defined by A. Kotsarev, M. Lizorkin and R. Petrin at the 20th AER Symposium in Hanassari (Finland). It is focused on investigation of transient behavior in a VVER-440 nuclear power plant. Its initiating event is the opening of the main isolation valve and re-connection of the loop with its main circulation pump in operation. A water slug with lower temperature of 100 K enters the core which leads to a reactor power excursion. The activation of the reactor scram is caused by the corresponding power level signal. As a result of the scram, the turbines are turned-off by closure of the turbine isolation valves. All main circulation pumps remain in operation. Each participant had to use its own developed input plant data deck and parameterized library of macroscopic cross sections. The VVER-440/213 plant is at the end of the first fuel cycle and in hot full power conditions. The initial reactor power tuning and burnup calculations were performed with the code DYN3D by both participants. The first part of paper contains a brief description of RELAP5-3D and DYN3D/ATHLET system codes, their NPP input decks and reactor core models. The second part shows the comparison of important global and local time dependent parameters. The trends of main calculated parameters are very close. The calculated nuclear and thermal-hydraulic phenomena like reactor power, cold leg mass flow rates, cold and hot leg coolant temperatures, upper plenum pressure, pressurizer water level and steam generator powers agree quite well.

  • Contribution to proceedings
    22nd Symposium of Atomic Energy Research (AER) on VVER Reactor Physics and Reactor Safety, 01.-05.10.2012, Pruhonice, Czech Republic
    Proceedings of the 22nd AER Symposium, Budapest: MTA Energoatom, 9789635086276, 653-675

Publ.-Id: 18322

Spectroscopic Ellipsometry Studies of nc-Si/a-Si and nc-Si/SiOx Systems: Optical Characterization of Crystallization

Nogay, G.; İlday, S.; Turan, R.; Heinig, K.-H.; Friedrich, D.

Third generation solar cells are expected to utilize the quantum size effect occurring in the semiconductor quantum dots fabricated in an appropriate matrix. A promising and well-studied material system is the Si nanocrystals fabricated in an oxide matrix such as SiO2. In spite of extensive research efforts on this material system, a successful device realization has not been possible due to the difficulties in the device fabrication and the electronic transport in the dielectric matrix that forms an insulating medium for the charge transport. In order to overcome the problems related to the electronic transport while not losing the quantum size effect, the use of a sponge-like nanostructure has recently been proposed. Si nanosponge is composed of tiny interconnected Si nanostructures embedded in an oxide matrix. These nanostructures form an interconnected quantum structure where the charge transport does not require the tunneling current which needs well positioned quantum dots. The band gap of the material can still be engineered by process parameters for tandem solar cell fabrication. Sinanosponge is then a promising candidate for the fabrication of third generation photovoltaic (PV) solar cells. In this work, Si-nanosponge structures were fabricated successfully in a SiOx matrix in a wide range of x values (0

Keywords: phase separation; SiO; silicon; Raman; Ellipsometry; PV cell

  • Lecture (Conference)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18321

Overcoming challenges to the formation of high-quality polycrystalline TiO2:Ta transparent conducting films by magnetron sputtering

Neubert, M.; Cornelius, S.; Fiedler, J.; Gebel, T.; Liepack, H.; Kolitsch, A.; Vinnichenko, M.

The work is focused on understanding the physical processes responsible for the modification of the structure, electrical and optical properties of polycrystalline TiO2:Ta films formed by annealing of initially amorphous films grown by DC magnetron sputtering of electrically conductive ceramic targets. It is shown that fine tuning of the oxygen content during deposition of amorphous TiO2:Ta films is critical to achieving low resistivity and high optical transmittance after annealing. Increasing the total pressure during magnetron sputter deposition is shown to decrease the sensitivity of the annealed films to the oxygen flow variation during deposition of the initially amorphous layers. Polycrystalline anatase TiO2:Ta films of low electrical resistivity (ρH=1.5×10-3 Ω cm), high free electron mobility (µH=8cm²/Vs) and low extinction (k550nm=0.006) are obtained in this way at a total pressure of 2 Pa. The dependence of the polycrystalline film electrical properties on the oxygen content is discussed in terms of Ta dopant electrical activation/deactivation taking into account the formation of compensating defects at different oxygen pressures. The temperature-dependent transport of the polycrystalline anatase TiO2:Ta films is investigated showing the dominant role of the optical phonon scattering in the case of films with an optimum Ti/O ratio.

Keywords: TCO; transparent; conductive; oxide; TiO2; titania; tantalum; polycrystalline; sputter; annealing

  • Journal of Applied Physics 114(2013), 083707
    Online First (2013) DOI: 10.1063/1.4819088

Publ.-Id: 18320

The German-Turkish project RainbowEnergy: A Si-based nanocomposite absorber for thin film PV cells

Heinig, K.-H.; Aydinli, A.; Turan, R.; Hauschild, D.

Si-based thin film PV cells suffer from a rather low efficiency. This leads to a relative small market share, although their module prices are comparably low. RainbowEnergy aims at a novel nanostructured Si-based thin film PV cell absorber, which increases the efficiency substantially without increasing the module costs. Large-scale patterning by spontaneous self-structuring during spinodal decomposition of metastable SiO is a
promising synthesis process of nanostructured Si absorbers for 3rd generation thin-film solar cells. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP, several seconds), very Rapid Thermal Processing (vRTP, dwell time tens of msec), and laser annealing. If after phase separation SiOx --> 0.5SiO2 + (1-0.5x)Si the volume fraction of Si exceeds ~30%, then Si forms a percolated nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on kinetic Monte-Carlo. As the wire diameters coarsens with time of heat treatment like d~t1/3, and because the Si bandgap opens for nmstructures by quantum confinement, a band gap engineering for PV cell optimization becomes feasible. It will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way with industrial partners

Keywords: solar cells; nanocomposite; silicon; thin film; laser annealing; kinetic Monte Carlo simulations

  • Invited lecture (Conferences)
    Solar Electricity Conference & Exhibition (SOLARTR-2), 07.-09.11.2012, Antalya, Turkey

Publ.-Id: 18319

Development of recombinant receptor tyrosine kinase ligands for diagnostics and therapy of tumors based on radionuclides

Pietzsch, D.; Mosch, B.; Pietzsch, J.

Several receptor tyrosine kinases, like the epidermal growth factor receptor (EGFR) play a critical role in tumors and, therefore, are promising targets for tumor imaging and tumor therapy. The present work aims at development of novel recombinant EGF analogs as potential radioligands or receptor-targeted components for functionalization of nanoparticles. This approach uses selective alteration of protein structure by unnatural amino acids, which amenables the protein for both radiolabeling and functionalization by the Click-chemistry.

Material and methods
The structural alteration of the recombinant protein is possible by supplementation based incorporation, because E. coli tRNA can not differ between methionine and azidohomoalanine. So these two amino acids can be exchanged during protein biosynthesis. Therefore, azidohomolalanine was added into methionine-free medium during cultivation of transformed bacteria. Vectors with both GST-tag and His-tag and corresponding methods for purification were tested and first experiments for the Click reaction of the structurally modified protein with biotinylated alkynes, fluorescence dye-labeled and 18F labeled alkynes were realised.

Results and conclusion
The purification of the GST fusion protein only resulted in the unmodified protein, but not in the azido-functionalised protein. Subsequently, native purification of a His-tagged EGF was established and the incorporation of azides into the target protein could be demonstrated by Click reaction with an alkyne. Ongoing work focuses on optimization of this approach. Afterwards, the purified and labeled proteins will be tested concerning their pharmacological properties as potential radioligands or targeted components of functionalized nanoparticles.

  • Lecture (Conference)
    Sixth Berder meeting "Nanomedicine in Oncology", 26.-29.09.2012, Berder Island, France
  • Contribution to proceedings
    Sixth Berder meeting "Nanomedicine in Oncology", 26.-29.09.2012, Berder Island, France
    Proceedings of Sixth Berder meeting "Nanomedicine in Oncology", Paris, 12-13

Publ.-Id: 18318

Experimental hypoxia does not influence gene expression and protein synthesis of Eph receptors and ephrin ligands in human melanoma cells in vitro.

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

Eph receptor tyrosine kinases and their ephrin ligands are supposed to play important roles in melanoma progression and metastasis. Moreover, hypoxia is known to contribute to melanoma metastasis. In this study, the influence of experimental hypoxia on expression and synthesis of EphA2 and EphB4, and their corresponding ligands ephrinA1, ephrinA5, and ephrinB2 was systematically studied in four human melanoma cell lines in vitro. Melanoma cell monolayer and spheroid cultures were used as both extrinsic and intrinsic hypoxia models. Hypoxic conditions were confirmed by analyzing HIF-1α/-2α expression, VEGF expression, and cellular uptake of [18F]fluoromisonidazol. In normoxia, EphA2, EphB4, ephrinA1, ephrinA5, and ephrinB2 expression was detectable in all cell lines with varying extent. Considerable protein synthesis of EphA2 was detected in all cell lines. However, no effect of experimental hypoxia on both Eph/ephrin expression and protein synthesis was observed. This contributes critically to debating the hypothesis that hypoxia regulates the Eph/ephrin system in melanoma.

Publ.-Id: 18317

Si nanowire networks embedded in SiO2 formed by spinodal decomposition of SiO – a novel absorber material for 3rd generation solar cells

Heinig, K.-H.; Schmidt, B.; Mücklich, A.; Liedke, B.; Kelling, J.; Friedrich, D.; Hauschild, D.; Stegemann, K.-H.; Keles, U.; Bulutay, C.; Aydinli, A.

Large-scale patterning by spontaneous self-structuring during spinodal decomposition of metastable SiO is a very promising synthesis process of novel nanostructured Si absorbers for 3rd generation thin-film solar cells [1]. The SiO layers have been produced by different techniques, sputtering, CVD and e-beam evaporation. Spinodal decomposition has been activated by Rapid Thermal Processing (RTP, several seconds) and very Rapid Thermal Processing (vRTP, dwell time tens of msec). When the volume fraction of Si exceeds ~30% after the phase separation SiOx-->0.5SiO2+(1-0.5x)Si, then Si forms a nanowire network. Energy-Filtered Transmission Electron Microscopy (EFTEM) studies show that nanowires have diameters of a few nanometers with a narrow distribution. This is in excellent agreement with large-scale simulations based on bit-coded kinetic Monte-Carlo. There is a considerable Si band gap widening due to quantum confinement in the nanowire network. As the wire diameter coarsens with time of heat treatment like d~t0.33, the band gap of the Si nanosponge can be optimized for solar cell application. Using an atomistic pseudopotential method, the band gap of sponges have been studied. Finally it will be shown that up-scaling of the nanotechnology described above to large-scale PV cell production is under way by industrial partners.

Keywords: solar cells; nanocomposite; silicon; nanowire; band gap; laser annealing; sputter deposition; kinetic Monte Carlo simulations

  • Invited lecture (Conferences)
    E-MRS Spring Meeting 2012, Symp. Y, 14.-18.05.2012, Srasbourg, France

Publ.-Id: 18316

Ion-beam synthesis of magnetic semiconductors

Potzger, K.

This review focuses on current research on the topic of ion beam based approaches for the fabrication of magnetic semiconductors. Among them, classic semiconductors such as Si, Ge, GaAs as well as solid–gas compounds such as ZnO or GaN doped with transition metals are currently in the focus of research. Those are considered to be basic materials for future spintronics devices. In the review also possible pitfalls leading to misinterpretation of the data obtained will be discussed.

Keywords: Ion implantation; Diluted magnetic semiconductors

Publ.-Id: 18315

Kinetic Monte Carlo Simulations at Spatiotemporal Scales of Experiments

Heinig, K.-H.

In comparison with MD, the kinetic Monte Carlo (kMC) method allows the treatment of much larger systems for much longer time periods on the atomistic level. Implementing the kMC method as a stochastic probabilistic cellular automaton according to the definition of Steven Wolfram, the simulations can be performed with many-body potentials projected onto a lattice, and a bit-coding makes the calculations extremely fast. Additionally, by Massively Parallel Programming (MPP) using NVIDIA graphic cards with CUDA programming, we accelerated kMC simulations by almost two orders of magnitude. Other than for finite element and MD codes, MPP cannot be straightforward implemented for the stochastic probabilistic Markov chain of kMC. We have extended the recently by Tobias Preis developed MPP method (Ising model with spin-flip kinetics) to much more complex conservative cellular automata with Kawasaki exchanges. Based on these methodological developments, we present large-scale simulations on the self-organization of surface nanopatterns under ion irradiation and on the scaling behavior of nanosponge formation.

Keywords: kinetic Monte Carlo simulations; program code development; massive parallel programming; CUDA; scaling phenomena

  • Invited lecture (Conferences)
    International Workshop on "Beyond Molecular Dynamics: Long Time Atomic-Scale Simulations", 26.03.2012, Dresden, Germany

Publ.-Id: 18314

Inactivation of HNSCC Cells by 90Y-Labeled Cetuximab Strictly Depends on the Number of Induced DNA Double-Strand Breaks

Saker, J.; Kriegs, M.; Zenker, M.; Heldt, J.-M.; Eke, I.; Pietzsch, H.-J.; Grénman, R.; Cordes, N.; Petersen, C.; Baumann, M.; Steinbach, J.; Dikomey, E.; Kasten-Pisula, U.

Radioimmunotherapy is considered to have great potential for efficient and highly specific treatment of tumors. The aim of this study was to determine the efficacy of radioimmunotherapy when using 90Y-labeled cetuximab and to determine to what degree induction and repair of DNA double-strand breaks (DSBs) are decisive for this approach.
Methods: This study was performed with 9 cell lines of squamous cell carcinoma of the head and neck (HNSCC) differing strongly in epidermal growth factor receptor (EGFR) expression. The radionuclide 90Y was coupled by the chelator trans-cyclohexyl-diethylene-triaminepentaacetic acid (CHX-A"-DTPA)/linker construct to the EGFR-directed antibody cetuximab to yield 90Y-Y-CHX-A"-DTPA-cetuximab with a specific activity of approximately 1.2 GBq/mg. EGFR expression was determined by immunofluorescence and Western blotting, cetuximab binding by fluorescence-activated cell sorter analysis, the number of DSBs by immunofluorescence staining Gamma-H2AX/53BP1-positive repair foci, and cell survival by colony formation.
Results: For the 9 HNSCC cell lines, cetuximab binding correlated with the amount of EGFR present in the cell membrane (r2 = 0.967, P < 0.001). When cells were exposed to 90Y-Y-CHX-A"-DTPA-cetuximab, the number of induced DSBs increased linearly with time (r2 = 0.968, P 5 0.016). This number was found to correlate with the amount of membranous EGFR (r2 = 0.877, P = 0.006). Most DSBs were repaired during incubation at 37C, but the small number of remaining DSBs still correlated with the amount of membranous EGFR (24 h: r2 = 0.977, P < 0.001; 48 h: r2 = 0.947, P < 0.001). Exposure to 90Y-Y-CHX-A"-DTPA-cetuximab also resulted in efficient cell killing, whereby the extent of cell killing correlated strongly with the respective number of remaining DSBs (r2 = 0.989, P < 0.001) and with the amount of membranous EGFR (r2 = 0.967, P < 0.001). No cell killing was observed for UTSCC15 cells with low EGFR expression, in contrast to the strong reduction of 86% measured for UTSCC14 cells showing a strong overexpression of EGFR.
Conclusion: 90Y-YCHX-A"-DTPA-cetuximab affected cell survival through the induction of DSBs. This treatment was especially efficient for HNSCC cells strongly overexpressing EGFR, whereas no effect was seen for cells with low levels of EGFR expression. Therefore, EGFR-directed radioimmunotherapy using 90Y-YCHX-A"-DTPA-cetuximab appears to be a powerful tool that can be used to inactivate tumors with strong EGFR overexpression, which are often characterized by a pronounced radioresistance.

Keywords: targeted radioimmunotherapy; EGFR; 90Y-Y-CHXA"-DTPA-cetuximab; double-strand breaks; cell inactivation

Publ.-Id: 18313

Structured electrodeposition in magnetic gradient fields

Uhlemann, M.; Tschulik, K.; Gebert, A.; Mutschke, G.; Fröhlich, J.; Bund, A.; Yang, X.; Eckert, K.

Electrodeposition in superimposed magnetic gradient fields is a new and promising method of structuring metal deposits while avoiding masking techniques. The magnetic properties of the ions involved, their concentrations, the electrochemical deposition parameters, and the amplitude of the applied magnetic gradient field determine the structure generated. This structure can be thicker in regions of high magnetic field gradients. It can also be free-standing or inversely structured. The complex mechanism of structured electrodeposition of metallic layers in superimposed magnetic gradient fields was studied by different experimental methods, by analytical methods and by numerical simulation and will be discussed comprehensively.

Keywords: Electrochemistry; Electrolysis; Magnetohydrodynamics; Metal deposition; Magnetic fields; Magnetic forces; Electrolyte convection

Publ.-Id: 18312

3D Neutronic and Thermal-Hydraulic Analysis of High Conversion Th-U233 PWR core

Baldova, D.; Fridman, E.

This paper presents the development of a high conversion Th-U233 fuel cycle that is considered for current generation of Pressurized Water Reactors (PWRs). The proposed core design consists of 193 typical 17x17 PWR fuel assemblies. Each fuel assembly is subdivided into two regions designated as seed and blanket. The central seed region, which has high U233 content, serves as a neutron supplier for the peripheral blanket region. The blanket region, which consists mostly of Th232, acts as a U233 breeder. The pins dimensions and U233 content in each region were optimized to achieve maximal fissile inventory ratio (FIR) at discharge, taking into account the target fuel cycle length of 12 months and 3-batch reloading scheme. In this study, 3D core model of a high conversion Th-U233 PWR core is developed and analyzed in order to assess the fuel cycle performance and evaluate maximum achievable power density level of the proposed design.

Keywords: Th-U233 fuel cycle; fissile inventory ratio (FIR); thermal-hydraulic analysis

  • Lecture (Conference)
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea
  • Open Access Logo Contribution to proceedings
    2013 International Congress on Advances in Nuclear Power Plants (ICAPP '13), 14.-18.04.2013, Jeju, Korea

Publ.-Id: 18311

Atomistic simulations of Au-silica nanocomposite film growth

Khan, S. A.; Heinig, K.-H.; Avasthi, D. K.

The growth of Au-silica nanocomposite film is simulated in the framework of kinetic three dimensional lattice Monte Carlo simulations considering the basic phenomena in the deposition process. In case of co-sputter deposition, the growth kinetics of nanoparticles has been studied taking into consideration the effect of the energetic sputtered species reaching the surface of the film during deposition. Formation of Au nanorod like structures are predicted under certain growth conditions particularly when surface diffusion assisted phase separation plays the dominant role and bulk kinetics is frozen. The observed dependence of the Au nanoparticle size on Au/silica ratio is in agreement with the experimental results.

Keywords: Nanocomposite; sputter deposition; Au-silica; kinetic Monte-Carlo simulations

Publ.-Id: 18310

High conversion Th-U233 fuel cycle for current generation of PWRs

Baldova, D.; Fridman, E.

This paper assesses the basic possibility of achieving a high conversion Th-233U fuel cycle that can be used for the current generation of Pressurized Water Reactors. The main fuel assembly design, describe in this paper, follows the RTF SBU design. A 17 x 17 heterogeneous PWR fuel assembly, which can ensure high conversion, was considered. Such heterogeneous fuel assembly geometry consists of central 233U based seed region and a large 232Th based blanket region. The fuel pins in the seed region has a standard PWR pins dimensions. However, the fuel pins in the blanket region was enlarged in order to reduce the moderation to fuel ratio and facilitated the resonance neutron absorption in blanket. This paper describes the 2D neutronics analysis of the proposed fuel assembly. The main analysis was performed with the deterministic lattice transport code HELIOS. The obtained results were conformed using the continuous-energy Monte-Carlo code Serpent. The fuel cycle length was evaluated by applying Non-Linear Reactivity Model to the results of fuel assembly burnup calculations. The 233U content was adjusted to achieve fuel cycle length of 18 months and maximum fissile inventory ratio (FIR). The results of the analysis have been shown that for the heterogeneous seed-blanket (SB) fuel assembly, a FIR of about 0.94 can be achieved.

Keywords: High Conversion Fuel Cycle; Fissile Inventory Ratio; Seed-blanket fuel assembly

  • Lecture (Conference)
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
  • Open Access Logo Contribution to proceedings
    Jahrestagung Kerntechnik, 22.-24.05.2012, Stuttgart, Deutschland
    Proceedings Jahrestagung Kerntechnik

Publ.-Id: 18309

Vortrag zur Mitgliederversammlung der DGVC 2012

Härting, H.-U.

Im ersten Teil des Beitrags wird eine kurze Vorstellung des HZDR gegeben. Es wird weiterhin auf die Arbeit des Instituts für Fluiddynamik eingegangen,
mit den Schwerpunkten auf der Abteilung für Experimentelle Thermofluiddynamik sowie der Mitarbeit von Studenten an aktuellen Forschungsthemen.
Im zweiten Teil des Beitrags wird das Forschungsvorhaben „Geneigt rotierender Festbettreaktor“ vorgestellt sowie Hintergründe und Zwischenergebnisse

Keywords: HZDR; Institut für Fluiddynamik; Geneigt rotierender Festbettreaktor

  • Lecture (others)
    Mitgliederversammlung Dresdner Gesellschaft für Verfahrenstechnik und Chemieingenieurwesen e.V. 2012, 22.06.2012, Dresden, Deutschland

Publ.-Id: 18308

Plasmon resonance tuning in Ag nanoparticles arrays grown on ripple patterned templates

Ranjan, M.; Facsko, S.; Fritzsche, M.; Mukherjee, S.

A bottom-up approach to grow highly ordered self-assembled silver nanoparticles arrays on ripple patterns produced by low energy ion irradiation is reported. The advantage of this approach over other self-assembling or lithographic methods is the flexibility to tune the array periodicity down to 20 nm with inter-particle gaps as low as 5 nm along the ripples. The silver nanoparticle arrays grown on these rippled surfaces are optically anisotropic, i.e. they exhibit a direction dependent shift in their localised surface plasmon resonance. The reason for the observed anisotropy is a direction dependent plasmonic field coupling. In this way the capability to tune the plasmon resonance by varying the ripple wavelength is demonstrated.

Keywords: Ag nanoparticles; plasmonic properties; ion induced ripple paterns

Publ.-Id: 18307

X-ray absorption near-edge structure of hexagonal ternary phases in sputter-deposited TiAlN films

Gago, R.; Soldera, F.; Hübner, R.; Lehmann, J.; Munnik, F.; Vázquez, L.; Redondo-Cubero, A.; Endrino, J. L.

Titanium aluminium nitride (TiAlN) coatings have been grown by reactive (Ar/N2) direct-current magnetron sputtering from a Ti50Al50 compound target. The film composition has been quantified by ion beam analysis showing the formation of Al-rich nitrides (Ti/Al~0.3), with stoichiometric films for N2 contents in the gas mixture equal or above ~25%. The surface morphology of the films has been imaged by atomic force microscopy, showing very smooth surfaces with roughness values below 2 nm. X-ray and electron diffraction patterns reveal that the films are nanocrystalline with a wurzite (w) structure of lattice parameters larger (~2.5%) than those for w-AlN. The lattice expansion correlates with the Ti/Al ratio in stoichiometric films, which suggests the incorporation of Ti into w-AlN. The atomic environments around Ti, Al and N sites have been extracted from the X-ray absorption near-edge structure (XANES) around Ti2p, Al1s and N1s edges, respectively. The analysis of the XANES spectral lineshape and comparison with reported theoretical calculations confirm the formation of a ternary hexagonal phase.

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

Publ.-Id: 18306

Pipetting Nanowires: In Situ Visualization of Solid-State Nanowire-to-Nanoparticle Transformation Driven by Surface Diffusion-Mediated Capillarity

Toimil-Molares, M. E.; Röntzsch, L.; Sigle, W.; Heinig, K.-H.; Trautmann, C.; Neumann, R.

The most interesting applications of nanotubes include their use as storage media for atoms and small molecules, as nanoscale capsules for chemical reactions, and as nanopipettes for material delivery. The geometrical transformation of metallic copper nanowires, confined in graphitic coating, into crystalline nanoparticles of up to tenfold increased diameter is reported. In situ transmission electron microscopy images at 500 °C, recorded as movies, provide an exceptional real-time visualization of Cu draining out of the carbon coating. The solid content of the carbon tube is effectively evacuated over micrometer distances towards the open end, transforming each nanowire into a single monocrystalline, facetted Cu particle. Kinetic Monte Carlo simulations propose that this dramatic morphological transformation is driven by surface diffusion of Cu atoms along the wire/tube interface, thus minimizing the total free energy of the system.

Keywords: Nanowires; Capillarity; Swift Heavy Ions; kinetic Monte Carlo Simulations; Carbon Nanotubes; TEM

Publ.-Id: 18305

The LIMMCAST Program at HZDR: Modelling of Fluid Flow and Transport Phenomena in the Continuous Casting Process

Gerbeth, G.; Eckert, S.; Stefani, F.; Timmel, K.; Wondrak, T.

Model experiments with low melting point liquid metals are an important tool to investigate the flow structure and related transport processes in melt flows relevant for metallurgical applications.We present the new experimental facility LIMMCAST for modelling the continuous casting process of steel using the alloy SnBi at temperatures of 200-400°C. The parameters of the facility and the dimensions of the test sections will be given, and the possibilities for flow investigations in tundish, submerged entry nozzle and mould will be discussed. In addition, the smaller set-up Mini-LIMMCAST will be presented, which works with the room-temperature liquid alloy GaInSn. The main value of cold metal laboratory experiments consists in the capabilities to obtain quantitative flow measurements with a reasonable spatial and temporal resolution. New ultrasonic and electromagnetic techniques for measuring the velocity in liquid metal flows came up during the last decade allowing for a satisfying characterisation of flow quantities in the considered temperature range up to 400°C. First results from LIMMCAST and Mini-LIMMCAST will be presented covering the following phenomena: fully contactless electromagnetic tomography of the flow in the mould, flow monitoring by a multitude of ultrasonic sensors, and analysis of the flow in the mould under the influence of an electromagnetic brake: intensification of the flow turbulence contrary to the expected flow damping, injection of argon bubbles through the stopper rod: occurrence of pressure oscillations.

Keywords: Continuous casting; liquid metal model; mould flow; flow measurements; two-phase flow; magnetic flow tomography; ultrasound Dopplermethod

  • Journal of Iron and Steel Research International 19(2012)Suppl.1-1, 1-8
  • Invited lecture (Conferences)
    7th International Conference on Electromagnetic Processing of Materials (EPM2012), 22.-26.10.2012, Peking, China

Publ.-Id: 18304

Two-Magnon Excitations: From Periodical Perturbations to Magnonic Crystals

Lenz, K.

Two-magnon scattering is a well-known effect e.g.\ in ferromagnetic resonance 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 \emph{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 response function of 1D and 2D periodically perturbed ferromagnetic films in almost perfect agreement to FMR experiments as I will show. A striking feature e.g.\ is the mode splitting due to the two-magnon scattering which opens magnonic band gaps. This splitting can be tailored by the geometric and magnetic sample parameters.

This work was supported by the DFG grants FA 314/6-1, FA314/3-2.

  • Invited lecture (Conferences)
    DPG-Frühjahrstagung der Sektion Kondensierte Materie, 10.-15.03.2013, Regensburg, Deutschland

Publ.-Id: 18303

Frequency and field control of the magnetic relaxation in 2D magnonic crystals

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

We present a method of changing the magnetic damping by more than 500% in 2D magnonic crystals. These magnonic crystals have been prepared either by direct nanopatterning of the magnetic layer using electron beam lithography or by nanostructuring the substrates prior to deposition by ion beam erosion.
It was shown theoretically that magnetic defect structures lead to an increased magnetic damping due to two-magnon scattering [1]. This two-magnon scattering contribution to the magnetic relaxation can be easily determined e.g. from frequency dependent ferromagnetic resonance measurements (FMR) [2]. It is characterized by a non-linear but monotonous increase of the resonance linewidth with excitation frequency. Recent extension of this theory to films with a periodic defect structure, like 2D magnonic crystals, shows that the two-magnon scattering increases the damping only at certain frequencies related to the structural dimensions [3].
This in turn means that by slightly changing the excitation frequency by a few GHz two-magnon scattering enhanced damping can be switched on and off in addition to the intrinsic Gilbert damping that is always present. The frequency where this happens can be preselected by the periodicity of the magnonic crystal [3,4]. Moreover, it is possible to control the damping by the direction of the in-plane magnetic field. For application in spintronic devices it could be very interesting to have a selectively higher or lower damping at certain frequencies. In conventional materials only a monotonous increase of damping with frequency is achievable.
This work was supported by the DFG grant FA 314/6-1.

  • Lecture (Conference)
    12th Joint MMM-Intermag Conference, 14.-18.01.2013, Chicago, USA

Publ.-Id: 18302

Ion implantation techniques for silicon based photovoltaics and light emitters

Lipp Bregolin, F.; Sias, U. S.; Behar, M.; Prucnal, S.; Rebohle, L.; Skorupa, W.

The broad adoption of ecologically friendly and cost-effective renewable energy sources and the continuous advances of the information technology industry are two of the most relevant topics in the current needs of our modern society.
The ion implantation techniques are very powerful tools and will continue to play an important part in the achievement of such goals.
In the present work, two main issues will be addressed. The first one covers the continuous search for efficient and durable silicon based light emitters for fully integrated silicon photonics. The second is the use of new processing techniques for solar cell technologies, where cost reduction is the everlasting ambition.
The light emitters made by hot ion implantation show strong enhancement of the photoluminescence intensities in comparison with the ones implanted at room temperature. In the case of photovoltaics, the plasma immersion ion implantation combined with millisecond flash lamp annealing of Solar-grade mc-Si are used for texturization and dopant activation. This approach shows very encouraging results for the fabrication of the emitter at a low thermal budget, decreasing the overall production costs.
By correlating the results of a number of experimental techniques, a qualitative explanation for the influence of the ion implantation and further fabrication parameters on the characteristics of each system is presented.

Keywords: ion implantation; light emitter; photoluminescence; electroluminescence; silicon photonics; photovoltaics; solar cells

  • Invited lecture (Conferences)
    ION 2012 - Ion implantation and other applications of ions and electrons, 25.-28.06.2012, Kazimierz Dolny, Poland,, Polska

Publ.-Id: 18301

Comments on “Comparative Study With New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy”

van den Hoff, J.; Hofheinz, F.

Phantom measurements with glass inserts in a hot background are still used frequently for calibration and performance assessment of volume delineation algorithms in PET. Taking as an example the recent paper by Shepherd et al.: Comparative Study with New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy (IEEE Trans Med Imaging. 2012 Jun 4. [Epub ahead of print]), we demonstrate that this is not a valid approach due to the discontinuity introduced in the background by the cold walls of the glass inserts. We, moreover, emphasize that in order to define a sensible ground truth for performance assessment of contouring algorithms in patient data it is necessary to average over a sizable number of experienced observers and lesions in order to compensate for the substantial inter-observer variability.

Publ.-Id: 18300

Investigation of resistive switching in YMnO3 thin films grown by PLD technique.

Bogusz, A.

Multiferroic materials are promising candidates for creation of a new generation of memory devices. This work investigates electrical properties of YMnO3 thin films, reported as resistive switching material. Thin YMnO3 films (<200 nm) were grown by pulsed laser deposition on Si substrates with Pt bottom electrode at 800°C and varying partial pressure of oxygen. Characterization of as-grown samples by X-ray diffraction and scanning electron microscopy was followed by determination of electrical properties of films in metal-insulator-metal (MIM) configuration. Results indicate the unipolar resistive switching of all of YMnO3 films with high resistance ratio (>10000) of high over low resistance state. Switching mechanism is ascribed to the structural transitions within the film upon applied current.

  • Lecture (others)
    Topical problems in theoretical physics, 28.11.2012, Chemnitz, Germany

Publ.-Id: 18299

Epitaxial growth of SrTiO3 (0 0 1) films on multilayer buffered GaN (0 0 0 2) by pulsed laser deposition

Luo, W. B.; Jing, J.; Shuai, Y.; Zhu, J.; Zhang, W. L.; Zhou, S.; Gemming, S.; Du, N.; Schmidt, H.

SrTiO3 films were grown on CeO2/YSZ/TiO2 multilayer buffered GaN/Al2O3 (0 0 0 1) substrates with and without the YBa2Cu3 O7−x (YBCO) bridge layer by pulsed laser deposition (PLD). The deposition process of the buffer layers was in situ monitored by reflection high-energy electron diffraction. The crystallographical orientation of the heterostructure was studied by x-ray diffraction (XRD). With the introduction of the YBCO (0 0 1) layer, the STO (0 0 1) film was epitaxially grown on the GaN substrate. There were three sets of inplane domains separated from each other by 30° in both STO and YBCO buffer layers. The epitaxial relationship was STO (0 0 2)[1 1 0]∥YBCO(0 0 1)[1 1 0]∥CeO2(0 0 2)[0 1 0]∥YSZ (0 0 2)[0 1 0]∥GaN(0 0 0 1)[1 1 -2 0] according to XRD results. By comparing the orientation of STO grown on GaN with and without the YBCO top buffer layer, the surface chemical bonding was found to be a very important factor in determining the orientation relationship of STO.

Publ.-Id: 18298

Study of Neutron Induced Defects in Ceramics using the GiPS Facility

May-Tal Beck, S.; Butterling, M.; Anwand, W.; Beck, A.; Wagner, A.; Brauer, G.; Israelashvili, I.; Hen, O.

There has been an increased interest in defects within structural materials motivated by future fission and fusion reactor needs. While reactor steels are extensively studied, much more research effort is needed in order to understand radiation damage in ceramic materials and its effect on their macroscopic characteristics (1).
Sapphire – the single crystal of Al2O3, is a candidate material to serve in diagnostic systems for burning plasma experiments (2), due to its transparency to a wide range of wavelengths (200-5000 nm), high melting temperature (~2300K) and hardness close to that of a diamond. Its optical and electronic properties are expected to be affected by the harsh radiation environment.
The family of ceramics that contains Boron is another interesting group of materials for the nuclear industry, mainly due to high cross sections for thermal neutron capture in Boron, which produce helium inside the material. The much higher neutron flux expected in future reactors can cause swelling of materials and macroscopic cracks formation. Helium is also considered to be one of the most interesting challenges for fusion reactors, due to alpha particles production in the D-T reaction. Materials that will be used as first wall, matrices for Li, or coating materials, will suffer from high radiation damage.
The sensitivity of Positron Annihilation Spectroscopy (PAS) methods to point defects makes them perfect tools to study radiation damage in its first stages of creation.
Especially, Positron Annihilation Lifetime Spectroscopy (PALS) is sensitive to size and concentration of the point defects and Coincidence Doppler Broadening (CDB) can probe changes in defect characteristics as well as in electron momenta in the lattice We present first results of Sapphire and Boron Carbide (B4C) samples investigated at the Gamma Induced Positron Spectroscopy (GiPS) facility at the HZDR (3). Unirradiated Sapphire and B4C samples were measured, as well as neutron irradiated samples, to a fluence of 6x10E18 n/cm2 and ~10E15 n/cm2 for the Sapphire and B4C samples, respectively. In the GiPS facility, four pairs of detectors, each consisting of BaF2 and HPGe detectors, allow to measure PALS, DB and to use the correlated information to measure also CDB and Age-Momentum Correlation (AMOC). Results from these measurements will be discussed.
[1] Workshop on Advanced Computational Materials Science: Application to Fusion and Generation IV Fission Reactors, Washington, D.C. 31 March – 2 April 2004.
[2] D.M. Duffy, Phil. Trans. R. Soc. A 368 (2010) 3315-3328.
[3] M. Butterling et al., Phys. Status Solidi A 207 (2010) 334-337.

Keywords: neutron induced defects; ceramics; gamma-radiation induced positron spectroscopy

  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012076
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012076

Publ.-Id: 18297

Vacancy-induced hardening in Fe-Al alloys

Lukac, F.; Cizek, J.; Prochazka, I.; Jiraskova, Y.; Janickovic, D.; Anwand, W.; Brauer, G.

Iron aluminides are perspective materials for high temperature structural applications due to a high mechanical strength and excellent corrosion resistance. Hardness of Fe-Al alloys shows non-trivial dependence on chemical composition and thermal treatment of samples and cannot be fully explained by consideration of intermetallic phases formed according to the equilibrium phase diagram of Fe-Al system. Hardening caused by quenched-in non-equilibrium vacancies was proposed to explain rise of hardness in quenched Fe-Al alloys [1].
In the present work the concentration of quenched-in vacancies in Fe-Al alloys with various Al content cAl ranging from 18 to 49 at.-% was determined by means of two techniques of positron annihilation spectroscopy (PAS): (i) positron lifetime spectroscopy was employed for investigation of samples with vacancy concentration less than 2 x 10-4 at.-1 representing a limit for saturated positron trapping; (ii) in samples containing more vacancies than 2 x 10-4 at.-1, the vacancy concentration was determined using back-diffusion measurement of monoenergetic slow positrons. It has been demonstrated that both these methods give mutually consistent results [2].
Non-equilibrium vacancies were detected in all alloys studied after quenching from 1000°C. The concentration of quenched-in vacancies strongly increases with increasing Al content from 10-5 at.-1 in the alloy with cAl = 18 at.-% up to 10-1 at.-1 in the alloy with cAl = 49 at.-%. Comparison of the vacancy concentration and the Vickers microhardness measured on quenched samples revealed that hardness indeed increases with increasing concentration of quenched-in vacancies. In alloys with cAl > 30 at.-% the concentration of quenched-in vacancies exceeds 10-4 at.-1 and the hardness was found to be proportional to square root of the vacancy concentration in agreement with solution hardening model proposed by Chang et al. [1]. Subsequent annealing of samples at 520 °C causes recovery of quenched-in vacancies. This is accompanied by a drop of microhardness, but only in alloys where the initial concentration of quenched-in vacancies was least 10-4 at.-1. Hence, vacancies have a measurable effect on hardness of Fe-Al alloys when their concentration becomes 10-4 at.-1 or higher.
[1] Y. A. Chang et al., Intermetallics 1, 107 (1993).
[2] J. Čížek et al., Physica B (2012) doi:10.1016/j.physb.2011.12.122.

Keywords: Fe-Al alloys; vacancy-induced hardening; positron annihilation spectroscopy

  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012025
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012025

Publ.-Id: 18296

Flash lamp annealing of Tungsten surfaces marks a new way to optimized slow positron yields

Anwand, W.; Butterling, M.; Johnson, J. M.; Reuther, H.; Wagner, A.; Skorupa, W.; Brauer, G.

Tungsten is often used as a positron moderator in mono-energetic positron beams [1] with 22Na positron sources. Therefore, mono-crystalline W foils with a thickness of about 2 μm are commonly used. The efficiency of such tungsten moderators strongly depends on the heat treatment of the tungsten foils. Currently, the annealing of such thin foils is mostly done at temperatures of about 2000 oC under vacuum conditions with a considerable difficulty. For this reason, a new method was sought to quickly anneal W foils to produce manageable, low-cost moderators with a high efficiency suitable for mono-energetic positron beams.
Flash lamp annealing (FLA) offers a chance for the optimization of the moderator properties. With FLA, the surface of a W foil can be heated above the melting point (3422ºC) in 1 to 3 ms without melting the whole volume. The heat treatment was carried out in an Ar flow. In this way, a surface cleaning and a considerably longer positron diffusion length could be reached.
Conventional poly-crystalline W foils with a thickness of 9 μm + 25% and heat treated by FLA were characterized by Auger electron spectroscopy, scanning electron microscopy and slow positron implantation spectroscopy and then tested as positron moderators. First promising results obtained with these W foils will be presented and it will be shown that this technique is applicable to tungsten meshes too.
[1] P.G. Coleman, Positron Beams and their applications, World Scientific Publishing, Singapore, 2000

Keywords: Tungsten foils; positron moderation; Flash Lamp Annealing

  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012072
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012072

Publ.-Id: 18295

Defect studies of ZnO films prepared by pulsed laser deposition on various substrates

Melikhova, O.; Cizek, J.; Kuzel, R.; Novotny, M.; Bulir, J.; Lancok, J.; Anwand, W.; Brauer, G.; Connolly, J.; Mccarthy, E.; Krishnamurthy, S.; Mosnier, J.-P.

The quality of ZnO thin films was characterized in this work by slow positron implantation spectroscopy (SPIS) combined with X-ray diffraction (XRD). The ZnO films were grown by pulsed laser deposition (PLD) on three different substrates: sapphire (0001) single crystal, MgO (100) single crystal and amorphous fused silica (FS). Films deposited on all substrates exhibit wurtzite ZnO structure and are characterized by an average crystallite size 20 - 100 nm.
Microstructure of ZnO films is strongly influenced by substrate. XRD investigations revealed that ZnO films deposited on sapphire (0001) and MgO (100) single crystalline substrates exhibit local epitaxy, i.e. a well-defined relation between film crystallites and the substrate. On the other hand, the film deposited on FS substrate exhibits (0002) fiber texture with random lateral orientation of crystallites in the plane of substrate. The films deposited on single crystalline substrates exhibit narrow XRD (0002) rocking curves with the half-widths (FWHM) of 1.3° and 1.2° for the film deposited on sapphire (0001) and MgO (100) substrate, respectively. On the other hand, the film deposited on amorphous FS substrate exhibits significantly wider XRD (0002) rocking curve having half width of 10°. Hence, the mosaic spread of planes is relatively small for the films grown on single crystalline substrates while it is substantial for the film grown on amorphous FS substrate. The half width of the XRD rocking curve is often used as a measure of quality of epitaxial thin films. However, half width of the rocking curve is a measure of the perfection of the structural relationship but is not directly correlated with the density of defects in the film. SPIS investigations revealed that ZnO films deposited on MgO and sapphire single crystalline substrates exhibit significantly higher density of defects than the film deposited on amorphous FS substrate despite the fact that half width of rocking curve exhibits opposite behaviour. In ZnO film deposited on the amorphous FS substrate the mismatch between atomic positions in the substrate and in the film is to some extend compensated for by many differing orientations (tilting) of the ZnO crystallites. As a consequence, the density of misfit dislocations in ZnO crystallites is relatively low and positrons are trapped predominantly at open volume misfit defects at the interfaces between the crystallites. On the other hand, ZnO films deposited on MgO and sapphire single crystalline substrates exhibit local epitaxy. In these cases, the lattice mismatch between the film and the substrate is accumulated mainly by misfit dislocations.

Keywords: ZnO films; pulsed laser deposition; X-ray diffraction; slow positron implantation spectroscopy; structure; defects

  • Poster
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012018
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012018

Publ.-Id: 18294

PGB pair production at LHC and ILC as a probe of the topcolor-assisted technicolor models

Liu, G.; Zhang, H.; Zhou, P.

The topcolor-assisted technicolor (TC2) model predicts some light pseudo goldstone bosons (PGBs), which may be accessible at the LHC or ILC. In this work we study the pair productions of the charged or neutral PGBs at the LHC and ILC. For the productions at the LHC we consider the processes proceeding through gluon-gluon fusion and quark-antiquark annihilation, while for the productions at the ILC we consider both the electron-positron collision and the photon-photon collision. We find that in a large part of parameter space the production cross sections at both colliders can be quite large compared with the low standard model backgrounds. Therefore, in future experiments these productions may be detectable and allow for probing TC2 model.

Publ.-Id: 18293

First experiments with the MePS

Jungmann, M.; Krause-Rehberg, R.; Anwand, W.; Butterling, M.; Wagner, A.; Cowan, T. E.

The MePS system (Mono-energetic Positron Spectroscopy) is located in the Helmholtz Center Dresden-Rossendorf (HZDR) [1]. It is one of the installations at ELBE (Electron Linac for beams with high Brilliance and low Emittance) which supplies a 40-MeV electron beam [2]. MePS makes use of the excellent time structure of the primary electron beam of ELBE (repetition frequency up to 26 MHz; bunch length < 5ps) to produce a pulsed, intense slow-positron positron beam to allow positron lifetime spectroscopy.
In autumn 2011 the system was completed and tested. A new moderator was successfully installed (tungsten meshes on a tungsten foil). Moreover, the accelerator stage together with a sample chamber was added. At a rather low primary electron beam current of 48 μA (maximum current: 1 mA) a count rate of 9400 cps was obtained in a BaF2/PMT detector close to the sample. In order to avoid spurious signals which are in other systems often obtained by positrons being reflected from the sample surface, a bended tube (45°) was added between accelerator and sample chamber. Although up to now no chopper stage is in use, the signal to background ratio is 104. However, a chopper will be used in the future to improve this ratio and the time resolution which is now only about 500 ps.
The MePS system has been used to study the pore system of a series of low-k dielectric layers

Keywords: Mono-energetic Positron Spectroscopy; intense positron source; electron linac

  • Lecture (Conference)
    16th International Conference on Positron Annihilation (ICPA-16), 19.-24.08.2012, Bristol, UK
  • Open Access Logo Journal of Physics: Conference Series 443(2013), 012088
    Online First (2013) DOI: 10.1088/1742-6596/443/1/012088

Publ.-Id: 18292

PET measurements of liquid aerosol deposition in pebble beds

Barth, T.; Ludwig, M.; Kulenkampff, J.; Gründig, M.; Hampel, U.; Lippmann-Pipke, J.; Bieberle, A.

The deposition and resuspension behavior of carbonaceous dust in the primary circuit of a High Temperature Reactor (HTR) is a tremendous safety issue for the assessment of Design Basis Accidents. In this work the deposition of 18F labeled monodisperse aerosol particles in a pebble bed is recorded by means of Positron Emission Tomography (PET) in order to explore the particle behavior in this geometry. Our feasibility study gives first insights into the temporal and a fully 3D spatial distribution of the particle deposits in a pebble bed obtained by PET.
An air driven small scale test facility is used for the generation of a particle laden turbulent flow field through a model pebble bed. Its Reynolds numbers cover the range typically found in a HTR pebble bed. The results of total pressure drop measurements over the pebble bed with respect to Reynolds number show relatively good agreement to literature which assumes the correct fluid mechanic downscaling of the facility.
A condensational aerosol generator was charged with KF condensation nuclei labeled with 18F. The aerosols are made of DEHS and are injected far upstream from the pebble bed. Concentration measurements upstream and downstream of the pebble bed were performed by means of isokinetic sampling and a condensational particle counter. The results agree with typical deposition curves related to turbulent and inertia driven particle deposition.
A small portion of the initially applied activity was detected in the field of view of the scanner. The longitudinal, slice-wise activity distribution shows an exponential digression of deposited particles in downstream direction. In a deposition experiment in the inertia impact regime, PET image quality allows to conclude that the deposited particles are located in the vicinity of the upstream located stagnation points

Keywords: high temperature reactor; pebble bed; particle deposition; positron emission tomography

  • Contribution to proceedings
    6th International Topical Meeting on High Temperature Reactor Technology, 28.10.-01.11.2012, Tokyo, Japan

Publ.-Id: 18291

Periodic Nanoscale Patterns Induced by Ion Irradiation: Ripples, Dots, and Holes

Facsko, S.

The morphology of surfaces after irradiation with low en- ergy ions (E < 50 keV) exhibits a variety of character- istics depending on the ion beam parameters and the ma- terial properties. Surfaces exposed to the ion beam can turn atomically smooth, stochastically or self-affine rough, or can evolve towards regular self-organised patterns. The structure size of these patterns is in the range of 10 to 100 nm and occasionally a high degree of ordering is achieved. Therefore, they have attracted interest recently as templates for nanostructured thin films or for structuring films by an erosive process [1].
On materials which turn amorphous during ion irradiation the formation of periodic patterns relies on at least two inter- playing processes: surface roughening due to local variation of erosion rate and smoothing via diffusional processes. In addition, atomic relocations on the surface and in the bulk resulting from the collision cascade have been identified as equally important. Therefore, the surface morphology de- pends on the details of the energy deposition by the incom- ing ion beam and on the details of surface and bulk diffu- sion. At the atomic level sputtering, the creation of surface and bulk defects, and the influence of the ion beam on sur- face diffusion processes play a decisive role for the mor- phology evolution.
surface normal and at room temperature produces ripple patterns oriented perpendicular to the ion beam direction. Higher incidence angles can lead to ripple patterns oriented parallel to the ion beam direction. Normally, coarsening of the ripple pattern with ion fluence is observed. In addition, the order increases with fluence up to 1 × 1018 cm−2 .
At normal incidence or for incidence angles smaller than 50◦ smoothing dominates on elemental materials. However, additional surface instabilities can exist due to the presence of a second atomic species on the surface. Hexagonally or- dered dot or hole patterns are thus observed at normal ion incidence on compound materials, like III-V semiconduc- tors, or on Si and Ge surfaces with concurrent deposition or implantation of foreign atoms [2, 3].

Keywords: ion induced nanopatterns; Ge nanostructures

  • Lecture (Conference)
    19th International Workshop on Inelastic Ion-Surface Collisions (IISC-19), 16.-21.09.2012, Frauenchiemsee, Deutschland

Publ.-Id: 18290

Ion Induced Patterns on Crystalline Ge Surfaces

Facsko, S.; Ou, X.; Mücklich, A.

Low energy ion irradiations of surfaces can induce the formation of patterns with periodicities in the range of tens to hundreds of nanometers. These patterns have been used as templates for growing thin films with interesting anisotropic properties resulting from the modulation of their interface and surface [1].
At off-normal angle of incidence between around 55° and 70° and at room temperature ripple patterns oriented perpendicular to the ion beam direction are observed. At normal incidence or for incidence angles smaller than 55° smoothing dominates on elemental materials, like Si and Ge. However, additional surface instabilities can exist due to the presence of a second atomic species on the surface. Furthermore, on crystalline surfaces anisotropic diffusion or kinetic restrictions can also lead to additional instabilities.
We studied ion induced pattern formation on Ge surfaces with 1 keV Ar+ at elevated temperature. In contrast to irradiations at room temperature we found pattern formation even at normal ion incidence. Similar to the case of ion irradiated crystalline metal surfaces a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier [2]. Depending on the surface orientation checkerboard or isotropic hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface are observed (see Fig. 1a, b).

Keywords: ion induced nanopatterning; Ge nanostructures

  • Poster
    25th International Conference on Atomic Collisions in Solids (ICACS 25), 21.-25.10.2012, Kyoto, Japan

Publ.-Id: 18289

Ion irradiation of Ge: from sponge-like structure to periodic pattern formation

Facsko, S.; Fritzsche, M.; Ou, X.; Böttger, R.; Bischoff, L.

Ion irradiation of materials can lead to swelling and the formation of sponge like structures. Especially Ge is susceptible to ion induced swelling for ions with energies in the range of 10 keV to 100 MeV. At lower ion energy, however, surface nanopattern can be produced by ion irradiation. These structures show periodicities in the range of a few tenths to hundreds of nanometers and are promising templates for producing nanostructured thin films. Periodic ripple patterns are observed frequently for ion irradiation at incidence angles greater than 55° to the surface normal. At normal incidence dot or hole patterns with hexagonal symmetry are observed only under special irradiation conditions.
We studied the formation of hexagonally arranged hole patterns on Ge(001) surfaces induced by irradiation with a scanned focused Ga+ ion beam (FIB) at normal incidence. Hole patterns with characteristic length of about 50 nm are observed in a narrow energy range of 4 - 6 keV (Fig. 1a). These patterns are independent of ion flux in a range of several orders of magnitude. In addition, the patterns induced by FIB irradiations were compared to broad beam Ga+ irradiations at the same ion energy. No differences were found demonstrating that FIB irradiations with a large overlap of the scanned beam are identical to conventional broad beam irradiations. Using heavy ions, like Bi dimers and trimers, in a mass separated FIB regular hexagonally ordered dot patterns are formed instead at normal incidence (Fig. 1b).
Furthermore, ion induced pattern formation on Ge surfaces with 1 keV Ar+ at normal incidence and higher temperature was studied. Similar to the case of ion irradiated crystalline metal surfaces on the crystalline Ge surface a new instability appears at higher temperature due to the Ehrlich-Schwoebel barrier. In this case, we observe regular checkerboard or hole patterns with the symmetry of the patterns reflecting the crystal structure of the irradiated surface (see Fig. 1c).

Keywords: ion induced nanopatterning; Ge nanostructures

  • Invited lecture (Conferences)
    18th International Conference on Ion Beam Modification of Materials (IBMM-18), 02.-07.09.2012, Qingdao, China

Publ.-Id: 18288

Anisotropic surface enhanced Raman scattering in nanoparticle and nanowire arrays

Ranjan, M.; Facsko, S.

Silver nanoparticles and nanowires self-aligned on pre-patterned rippled substrate are presented as active surface enhanced Raman scattering (SERS) substrates. The reported inter-particle gap of 5 nm and array periodicity of 35 nm are much lower than current lithographic limits. The observed anisotropy in SERS and surface plasmon resonance in such arrays is attributed to different plasmonic field enhancement along and across the chains of nanoparticles not due to shape anisotropy. For nanoparticle arrays higher SERS intensity is found along the particle chain, but for nanowire arrays higher SERS intensity is found for excitation across the wires. Higher intensity across nanowire arrays supports the argument that the SERS phenomenon is due to electromagnetic field enhancement (hot-junctions) caused by localized surface plasmon resonance across the nanowires having a 35 nm gap. The effect of inter-particle gap, ordering, and aspect ratio on field enhancement is demonstrated. Higher SERS intensity is observed in aligned elongated nanoparticles compared to aligned spherical, non-ordered nanoparticles, or aligned nanowires. Aligned silver scattering more strongly than aligned gold nanowires.

Keywords: Ag nanoparticles; ion induced ripple paterns; surface enhanced plasmon resonance

Publ.-Id: 18287

The Helmholtz beamline at the European XFEL - Ultra-bright, ultra-fast, and coherent hard X-ray pulses for laser plasma science

Schramm, U.; Cowan, T.

Status of the Helmholtz beamline project at the European XFEL: Ultra-bright, ultra-fast, and coherent hard X-ray pulses for laser plasma science

  • Invited lecture (Conferences)
    33rd International Workshop on Physics of High Energy Denisty in Matter, 13.-16.01.2013, Hirschegg, Österreich

Publ.-Id: 18286

Neutron shielding studies on an advanced molten salt fast reactor design

Merk, B.; Konheiser, J.

The molten salt reactor technology has gained some new interest, but the current projects are based on designing a molten salt fast reactor. Thus the shielding becomes more challenging than in historic concepts. One very interesting and innovative result of the EVOL project is the fluid flow optimized design of the inner reactor vessel using curved blanket walls. The developed structure leads to a very uniform flow distribution. The design avoids all internal structures. Based on this new geometry a model for neutron physics calculation is presented. The major steps are: the modeling of the curved geometry in the unstructured mesh neutron transport code HELIOS and the determination of the real neutron lfux and power distribution for this new geometry. The developed model is then used for the determination of the neutron fluences in the inner and outer wall of the system and for developing an optimized shielding strategy for the molten salt fast reactor to keep the fluence in the safety related outer vessel below the limit values. A lifetime of 80 years can be assured, but the size of the core/blanket system will be comparable to a sodium cooled fast reactor.

Keywords: molten salt reactor; molten salt; fast reactor; nuclear power; nuclear reactor; advanced shielding; neutron transport; HELIOS

Publ.-Id: 18285

On the major DYN3D developments for fast reactor design and transient analysis

Merk, B.; Kliem, S.

Due to the French project ASTRID [1], the European CP-ESFR [2] project, and the MYRRHA/FASTEF project [3], the research work on fast reactors has got a new push in Europe. Additionally to this European projects a strong project is growing in Russia based on the lead cooled fast reactor design BREST [4]. Following this trend, the Institute of Resource Ecology at the Helmholtz-Zentrum Dresden-Rossendorf has decided to start several projects dedicated to fast reactor technology [5], among them the extension of the well validated LWR core simulator DYN3D.
The new developments, first validation results, and the next strategic steps for the adaption of the code for the improved simulation of fast reactor cores are presented.

Keywords: DYN3D; fast reactors; fast reactor design; fast reactor safety

  • Contribution to proceedings
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
    Jahrestagung Kerntechnik 2013
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland

Publ.-Id: 18284

Fine distributed moderating material to the enhance feedback effects in LBE cooled fast reactors

Merk, B.

Problem of small feedback effects in fast reactors and some onsets to enhance the negative feedback effects have been discussed last year in an IAEA meeting in Vienna [[1]]. Small negative feedback effects are a common problem in all fast reactors. Especially in lead and lead bismuth eutectic (LBE) cooled reactors this problem is evident, due to the hard neutron spectrum. This hard neutron spectrum is caused by the very weak moderation effect in the heavy coolant even compared to sodium and appears due to the significantly higher atomic mass of lead.
A side view to the community of sodium cooled reactors (SFR) indicates a possible solution for the enhancement of one important negative feedback effect, the fuel temperature effect. The use of moderating material to improve the fuel temperature effect and the sodium void reactivity has already been discussed and investigated in detail for SFR with metallic fuel [[2]]. The concept of zirconium-hydride (ZrH) pins in reactors with metallic fuel has even been investigated before in several publications [[3]], [[4]], [[5]], [[6]]. A first test was already published for the use of ZrH in MOX fuelled, but steam cooled fast reactors [[7]]. In the last time, a new proposal has been analyzed. The negative feedback effects in a sodium cooled fast reactor are significantly enhanced by the introduction of fine distributed moderating material. The absolute value of the fuel temperature effect is significantly increased in combination with a decrease of the positive coolant effect by adding fine distributed moderating material, either in a layer inside the cladding or in the wire wrapper. The study has been focused in the first step on the choice of the ideal moderating material [[8]], [[9]] and in a second step on the optimization of the placing of the zirconium hydride to limit the influence on power distribution and burnup [[10]], [[11]].
The thermal stability of the hydrogen bearing compound is of paramount importance for the use of moderating material in a heavy liquid metal cooled fast reactor (HLMR) where significantly higher temperatures can be accepted during transients than in a SFR. Possible hydrogen bearing materials have already been discussed in a textbook on metal hydrides [[12]] and the effects in SFR has already been analyzed and published [13].
In this work it is demonstrated, that the concept of enhanced feedback coefficients is transferable to LBE cooled fast reactors. The demonstration is based on the fuel assembly design of the CDT project. The effect of the moderating material on the neutron spectrum, on the kinf, and on the fuel temperature feedback and the coolant feedback is shown, discussed and compared to SFRs.

Keywords: fast reactor; moderating material; fast reactor core design; Yttrium hydride; zirconium hydride; liquid metal cooled reactor; lead

  • Contribution to proceedings
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland
    Jahrestagung Kerntechnik 2013
  • Lecture (Conference)
    Jahrestagung Kerntechnik, 14.-16.05.2013, Berlin, Deutschland

Publ.-Id: 18283

Polarization of a stored beam by spin-filtering

Augustyniak, W.; Barion, L.; Barsov, S.; Bechstedt, U.; Benati, P.; Bertelli, S.; Carassiti, V.; Chiladze, D.; Ciullo, G.; Contalbrigo, M.; Dalpiaz, P.; Dymov, S.; Engels, R.; Erwen, W.; Fiorini, M.; Gaisserde, M.; Gebel, R.; Goslaswski, P.; Grigoriev, K.; Guidoboni, G.; Kacharava, A.; Khoukaz, A.; Kulikov, A.; Kleines, H.; Langenberg, G.; Lehrach, A.; Lenisa, P.; Lomidze, N.; Lorentz, B.; Macharashvili, G.; Maier, R.; Marianski, B.; Martin, S.; Mchedlishvili, D.; Merzliakov, S.; Meshkov, I.; Meyer, H.; Mielke, M.; Mikirtychiants, M.; Mikirtychiants, S.; Nass, A.; Nekipelov, M.; Nikolaev, N.; Nioradze, M.; Oellers, D.; Papenbrock, M.; Pappalardo, L.; Pesce, A.; Polyanskiy, A.; Prasuhn, D.; Rathmann, F.; Sarkadi, J.; Smirnov, A.; Seyfarth, H.; Shmakova, V.; Statera, M.; Steffens, E.; Stein, H.; Stockhorst, H.; Straatman, H.; Stroher, H.; Tabidze, M.; Tagliente, G.; Thorngren-Engblom, R.; Trusov, S.; Trzcinski, A.; Valdau, Y.; Vasiliev, A.; von Wurtemberg, K.; Weidemann, C.; Wustner, P.; Zupranski, P.

The PAX Collaboration has successfully performed a spin-filtering experiment with protons at the COSY-ring. The measurement allowed the determination of the spin-dependent polarizing cross section, that compares well with the theoretical prediction from the nucleon-nucleon potential. The test confirms that spin-filtering can be adopted as a method to polarize a stored beam and that the present interpretation of the mechanism in terms of the proton-proton interaction is correct. The outcome of the experiment is of utmost importance in view of the possible application of the method to polarize a beam of stored antiprotons. (C) 2012 Elsevier B.V. All rights reserved.

Publ.-Id: 18282

Optical study of superconducting Ga-rich layers in silicon

Fischer, T.; Pronin, A. V.; Skrotzki, R.; Herrmannsdörfer, T.; Wosnitza, J.; Fiedler, J.; Heera, V.; Helm, M.; Schachinger, E.

We performed phase-sensitive terahertz (0.12–1.2 THz) transmission measurements of Ga-enriched layers in silicon. Below the superconducting transition T c middle = 6.7 K we find clear signatures of the formation of a superconducting condensate and of the opening of an energy gap in the optical spectra. The London penetration depth λ(T ) and the condensate density ns = λ2(0)/λ2(T ) as functions of temperature demonstrate behavior typical for conventional superconductors with λ(0) = 1.8 μm. The terahertz spectra can be well described within the framework of Eliashberg theory with strong electron-phonon coupling: the zero-temperature energy gap is 2Δ(0) = 2.64 meV and 2Δ(0)/kBTc = 4.6, consistent with the amorphous state of Ga. At temperatures just above Tc, the optical spectra demonstrate Drude behavior.

Publ.-Id: 18281

Thermodynamic properties of CoCr2O4: specific heat and magnetic entropy

Uhlarz, M.; Pronin, A. V.; Wosnitza, J.; Prokhorov, A. S.; Bush, A. A.

We present the temperature dependence of the specific heat of CoCr2O4 between 2.08 K and 306 K in zero magnetic field. The lattice component can be described by the Komada–Westrum model with a characteristic temperature ΘKW = 541 K. The entropy of the magnetic component amounts to 33.51 J mol-1 K-1 at T = 298.15 K, in good agreement with the magnetic entropy of Co2+ and Cr3+ ions with completely quenched orbital moments. We compare our results with data available in literature.

Publ.-Id: 18280

Γ3-Type Lattice Instability and the Hidden Order of URu2Si2

Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Akatsu, M.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Maple, M. B.

We have performed ultrasonic measurements on single-crystalline URu2Si2 with pulsed magnetic fields, in order to check for possible lattice instabilities due to the hybridized state and the hidden-order state of this compound. The elastic constant (C11 - C12)/2, which is associated with a response to the Γ3-type symmetry-breaking (orthorhombic) strain field, shows a three-step increase at H ≥ 35 T for H || c at low temperatures, where successive meta-magnetic transitions are observed in the magnetization. We discovered a new fact that the absolute change of the softening of (C11 - C12)/2 in the temperature dependence is quantitatively recovered at the suppression of hybridized-electronic state and the hidden order in high-magnetic field for H || c associated with the successive transitions. The present results suggest that the Γ3-type lattice instability, is related to both the emergence of the hybridized electronic state and the hidden-order parameter of URu2Si2. On the other hand, magnetic fields H || [100] and [110] enhance the softening of (C11 - C12)/2 in the hidden order phase, while no step-like anomaly is observed up to 68.7 T. We discuss the limitation of the localized-electron picture for describing these features of URu2Si2 by examination of a crystalline electric field model in terms of mean-field theory.

Publ.-Id: 18279

Particle deposition study in a horizontal turbulent duct flow using optical microscopy and particle size spectrometry

Barth, T.; Lecrivain, G.; Hampel, U.

A new technique based on optical microscopy and particle size spectrometry is here presented to investigate deposition of aerosol particles. Micron-sized monodisperse liquid particles were injected in a horizontal duct flow. The turbulent flow field was recorded using Particle Image Velocimetry. The airborne particle size and number concentration was determined by isokinetic sampling in combination with an Aerodynamic Particle Sizer (APS). The surface deposited particles were counted by means of optical microscopy, which was found to be a robust and simple recording method. The particle deposition velocity was directly determined out of the number of deposited particles detected by the microscope and the airborne particle number concentration recorded by the APS. The present results show good agreement with similar studies and prove the potential of optical microscopy for the detection of wall deposited particles in comparison to the more complex and expensive methods such as fluorescence based wet chemistry or neutron activation techniques.

Keywords: Particle deposition; turbulent flow; optical microscopy; aerodynamic particle sizer; particle image velocimetry

Publ.-Id: 18278

Spectroscopic study of americium(III) complexes with nitrogen containing organic model ligands

Raditzky, B.; Sachs, S.; Schmeide, K.; Barkleit, A.; Geipel, G.; Bernhard, G.

For the first time, the complexation of Am(III) with low molecular weight nitrogen containing aromatic model ligands, representing structural building blocks of humic acid, has been investigated using time-resolved laser-induced fluorescence spectroscopy (TRLFS). The complex formation with anthranilic acid and picolinic acid was studied at pH 3.8 and 6.0 at an ionic strength of 0.1 M (NaClO4) and room temperature. At pH 3.8, where both investigated ligands occur as zwitterionic species, a 1:1 Am(III) picolinate complex is formed with a stability constant of log β11 = 3.81 ± 0.44. The Am(III) complexation with anthranilic acid in its zwitterionic form seems to be hindered, due to electrostatic repulsion between the protonated amino group and the metal ion. With both ligands, Am(III) complexes could be identified at pH 6.0, where the fully deprotonated species of anthranilic acid and picolinic acid occur. Under the given experimental conditions, a 1:1 Am(III) anthranilate complex with log β11 = 3.70 ± 0.11 is formed. For the Am(III) picolinate system 1:1 and 1:2 complexes with log β11 = 3.83 ± 0.22 and log β12 = 7.34 ± 0.04, respectively, were identified. For comparison, the complex formation of Am(III) was also studied with phthalic acid as an example for the interaction of Am(III) with carboxylic groups.

Keywords: americium(III); complexation; nitrogen containing model ligands; anthranilic acid; picolinic acid; phthalic acid; UV-Vis; TRLFS

Publ.-Id: 18277

Semiconductor nanocrystals embedded in high-k matarials

Brenner, F.; Haas, S.; Schneider, F.; Klemm, V.; Schreiber, G.; von Borany, J.; Heitmann, J.

The combination of high-k materials and nanocrystalline semiconductors leads to remarkable properties for various applications. The phase separation of ZrGeO and ZrSiO films in superlattice geometries were investigated. In case of the Si containing films, round-shaped clusters within a crystalline ZrO2 matrix have been observed after annealing at 1000 °C.
The appearance of nanocrystalline Si could not be shown, whereas amorphous clusters within the crystalline ZrO2 matrix were formed. For the Ge containing films, the formation of Ge nanocrystals was observed after annealing at 650 °C. In both material systems the ZrO2 matrix crystallized in the tetragonal phase.

Keywords: nanocrystals; high-k materials; multilayers

  • Invited lecture (Conferences)
    221st Meeting of Electrochemical Society, Symposium Advanced Nanomaterials and Processing, 06.-10.05.2012, Seattle, USA

Publ.-Id: 18276

Corrosion behaviour of Ti-48Al-2Nb-2Cr alloys

Pelic, B.; Rafaja, D.; Masset, P. J.; Seifert, H. J.; Bortolotto, L.; Schütze, M.; Wolf, G.; Loeh, I.

γ-TiAl intermetallics are attractive materials for high-temperature structural applications in the aerospace and automobile industries. However, they show environmental embrittlement at elevated temperatures that is mainly related to their low high-temperature corrosion resistance. One way how to improve the high-temperature corrosion resistance is the deposition of protective coatings on the surface of the base material. In this study, samples of a Ti-Al alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) were covered by physically vapour deposited (PVD), by metalorganic chemically vapour deposited (MOCVD) and by high-velocity oxy-fuel (HVOF) sprayed coatings. All coatings were based on the Ti-Al alloys and contained different amounts of alloying elements. The corrosion experiments were performed in molten salts containing 75 wt.% Na2SO4 and 25 wt.% NaCl at 850ºC up to 336 h. Both, PVD and CVD protected coatings reduced the changes in the mass of the samples over the corrosion time. Still, the formation of TiO2 could not be avoided, as it was confirmed by glancing-angle X-ray diffraction experiments.

Keywords: TiAl alloys; coatings; CVD; PVD; HVOF; high temperature oxidation/corrosion

Publ.-Id: 18275

Helmholtz Institut Freiberg für Ressourcentechnologie stellt sich vor: Spurenelemente für eine gesunde Wirtschaft

Birtel, S.

Präsentation über die Arbeitsfelder und Struktur des HIF vor allem Bewerbungsmöglichkeiten für Studenten, insbesondere Ingenieure, Geowissenschaftler

Keywords: Jobmöglichkeiten; Ingenieure; Geowissenschaftler

  • Lecture (others)
    ORTE Freiberg, 10.01.2013, Freiberg, Deutschland

Publ.-Id: 18274

Nanopattering on crystal Ge surfaces

Ou, X.; Grenzer, J.; Facsko, S.

In contrast to the nanopattering on amorphous semiconductor surfaces by ion irradiation, nanostructures on crystal Ge surfaces are created by irradiation under the temperatures above the recrystallization temperature. The temperature, fluence and orientation dependence on the nanopattens formation are demonstrated in this talk.

Keywords: irradiation; nanopattern; crystal Ge surface

  • Lecture (others)
    Forschergruppe 845 project workshop, 07.-08.11.2012, Dresden, Germany

Publ.-Id: 18273

Nano structure induced by ion beam sputtering

Ou, X.; Grenzer, J.; Facsko, S.

Horizontal silicon nanowires arrays on insulator fabricated by ion irradiation and Nano-dot and nano-hole pattern on Si generated by metal incorporation during the ion beam sputtering

Keywords: irradiation; nanopatterning

  • Lecture (others)
    Forschergruppe 845 project workshop, 07.-08.02.2012, Kaiserslautern, Germany

Publ.-Id: 18272

Crystallization of the high-dose hydrogen ion implanted silicon-on-insulator layers under millisecond pulse annealing

Tyschenko, I. E.; Volodin, V. A.; Voelskow, M.; Cherkov, A. G.; Popov, V. P.

Crystallization of the silicon-on-insulator films implanted with high dose of hydrogen ions was investigated under pulse millisecond annealing. Three-phase structure, consisted of the silicon nanocrystals, amorphous silicon, and hydrogen bubbles, was observed from the as-implanted samples. It was shown that the nanocrystal structure of the films is remained under pulse annealing up to 1000◦C. As pulse annealing temperature was increased, the nanocrystal diameter incrased from 2 to 5 nm, and the naoncrystal fraction rose to 70%. From the analysis of the crystalline-phase growth activation energy, it was speculated about the atomic hydrogen diffusion as limiting factor of the crystallization of the highly-hydrogenated ( 50 at%) silicon films.

Keywords: Crystallisation; SOI; hydrogen; pulse annealing

  • Fizika i Tekhnika Poluprovodnikov 47(2013)5, 591-596

Publ.-Id: 18270

Basic structures of integrated photonic circuits for smart biosensor applications

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

Integrated optics concerns mainly the generation, guiding, and detection of light. Especially biosensing needs systems that incorporate electrical, electronic, and photonic devices for the detection of harmful substances, like synthetic oestrogens or plasticizers. We present here recent developments in the integration of our Si-based light emitter into a photonic circuit for a planar optical waveguide-based biodetection system.

Keywords: biosensor; waveguide; silanization; organosilane; photonic crystals

  • Poster
    DOKDOK 2012, 07.-11.10.2012, Oppurg, Deutschland
  • Lecture (Conference)
    Optics & Optoelectronics, 15.-18.04.2013, Prag, Tschechien
  • Contribution to proceedings
    Optics&Optoelectronics, 15.-18.04.2013, Prag, Tschechien
    Optical Sensors 2013; Sprocceings of SPIE Vol 8774, 87740P
    DOI: 10.1117/12.2014920

Publ.-Id: 18269

Si-based light emitters in integrated photonic circuits for smart biosensor applications

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

In this report we present our recent developments for utilizing the Si-based light emitter consisting of a MOS structure for the detection of organic pollutants. In the latest approach the light emitters are intended to serve as light sources in smart biosensors [1, 2]. Now we discuss our concept of an integrated light emitter and a receiver in a dielectric waveguide structure below the bioactive layer for the detection of harmful substances, like synthetic estrogens or plasticizer in drinking water. Optical properties of waveguides, e.g. the transmission, are very sensitive to changes of the effective refraction index, which might be induced by the immobilization of biomolecules on the waveguide surface or in cavity structures, e.g. photonic crystals. The guiding of the light depends on the geometry and material composition of the waveguide. First waveguides were fabricated through plasma enhanced chemical vapor deposition (PECVD) and optical photolithography with following etching steps. Afterwards the layer thicknesses were analyzed by ellipsometry and the surface roughness via scanning electron microscopy (SEM). However, the investigation of the different waveguides will be allowed through finite element method (FEM) simulations (COMSOL) and experimentally through a setup for the optical transmission measurement.
In summary, this lab-on-a-chip system provides fast light transmission without using of any additional lenses and achieves further portability and miniaturization.

Keywords: biosensor; waveguide; silanization; organosilane; photonic crystals

  • Lecture (Conference)
    DPG-Frühjahrstagung der Sektion AMOP (SAMOP), 12.-16.03.2012, Stuttgart, Deutschland

Publ.-Id: 18268

Experimental observation of fine structures in laser-driven proton beams from micrometer thick targets

Metzkes, J.; Kluge, T.; Bussmann, M.; Kraft, S. D.; Zeil, K.; Cowan, T. E.; Schramm, U.

  • Lecture (Conference)
    33rd International Workshop on Physics of High Energy Density in Matter, 14.-18.01.2013, Hirschegg, Österreich

Publ.-Id: 18267

Optical Afterburner for a SASE FEL

Golz, T.; Riedel, R.; Al-Shemmary, A.; Foerst, M.; Tavella, F.; Gensch, M.; Schneidmiller, E. A.; Yurkov, M. V.; Stojanovic, N.

The radiation produced by a Self-Amplified Spontaneous Emission Free Electron Laser (SASE FEL) leaves a specific energy pattern over the length of the radiating electrons. This pattern, the SASE Fingerprint, leads to a spikey energy structure modulation on the order of the coherence length on the electron bunches. Using a dispersion section and an additional radiator this modulation can be used to recreate the SASE pulse envelope in a different wavelength regime (optical afterburner radiation) [1].
Using this unique feature, at the Free Electron Laser in Hamburg (FLASH) we demonstrated that the pulse duration of an XUV FEL can be obtained using standard laser diagnostics (i.e. FROG). Cross correlation with a multitude of different methods show best agreement down to several femtoseconds. [2]
Future development reaches from online pulse duration measurement to amplification and jitter-free pump probe experiments.


[1] E.L. Saldin, E.A. Schneidmiller and M.V. Yurkov, Phys. Rev. ST Accel. Beams 13, 030701 (2010)
[2] T. Golz, Thesis: Pulse duration measurements at 4th generation X-ray light sources – Frequency Resolved Optical Gating at FLASH (2012)

  • Poster
    Frühjahrstagung der Deutschen Physikalischen Gesellschaft, 04.-08.03.2013, Dresden, Deutschland

Publ.-Id: 18266

[18F]Flubatine, a promising radiotracer for the imaging of α4β2 nicotinic acetylcholine receptors (nAChRs) – development from chemistry to the clinic

Hoepping, A.; Smits, R.; Fischer, S.; Hiller, A.; Patt, M.; Wenzel, B.; Deuther-Conrad, W.; Funke, U.; Sattler, B.; Steinbach, J.; Sabri, O.; Brust, P.

Objectives: The availability of the α4β2 subtype of nicotinic acetylcholine receptors (nAChRs) is impaired in various neurodegenerative diseases, in particular Alzheimer's disease (AD). Immunological findings in brain tissue from AD patients reveal a distinct reduction of α4β2 nAChR. Furthermore, first imaging data obtained by PET indicate a significant reduction of this nAChR subtype already in patients affected by mild cognitive impairment (MCI) that convert later on to AD. The novel radiotracer [18F]flubatine, a homoepibatidine derivative, presents several advantages over other existing α4β2 nAChR-targeting radiotracers like high affinity in vitro and fast kinetics in mice and pig [1,2]. Here we present the development of a suitable labelling precursor along with the radiochemistry and further evaluation of [18F]flubatine for application in humans.
Methods: Starting from inexpensive starting materials enantiomerically pure trimethylammonium precursors with a Boc protecting group were developed [3]. In a two-step radiosynthesis either (–)-[18F]flubatine or (+)-[18F]flubatine is prepared via nucleophilic aromatic radiofluorination followed by cleavage of the Boc-protecting group (Fig. 1). The reference compounds were tested for toxicity in the Wistar rat. Human dosimetry was performed with both enantiomers, and a first-in-man study started comparing healty volunteers with AD patients.

Figure 1. Radiosynthesis of (–)-[18F]flubatine.
Results: The optimized labeling procedure was successfully transferred to a TRACERlabTM FX F-N automated synthesizer for clinical production of [18F]flubatine. For routine application 0.8 mg of trimethylammonium precursor was labeled in acetonitril at 100°C for 20 min. Complete deprotection of the Boc-protecting group succeeded with 1M HCl (80°C, 3 min). Purification was done on semi preparative HPLC. [18F]flubatine was formulated in sterile saline containing up to 10% ethanol for intravenous bolus administration. Overall decay-corrected radiochemical yield was XX ± X % (n = 4) and the radiochemical purity >99% after 40 min. A specific radioactivity of 3000 GBq/μmol was obtained. Dosimetry studies in healthy human volunteers indicate that effective doses of < 10 mSv/300 MBq (-)-[18F]flubatine are compatible with application in routine clinical studies. First human data show that (-)-[18F]flubatine exhibits fast kinetics and that 15 min scan time, starting at 90 min p.i., is already sufficient for visual analysis.

Conclusions: We developed an optimized, reliable and validated procedure for the preparation of both enantiomers of [18F]flubatine with excellent radiochemical parameters. In particular, the fast kinetics of (-)-[18F]flubatine makes this radiotracer a valuable tool for the quantitaitve imaging of α4β2 nAChR in human brain.

Acknowledgements: Supp. by German Federal Ministry Education & Research (01EZ0823).
References: [1] Sabri O. J Nucl Med 2011; 52 (Suppl. 1):1267. [2] Brust P. et al.: Synapse 2008; 62(3):205-18. [3] Patent Application DE 2011080118062700

  • Poster
    The 20th International Symposium on Radiopharmaceutical Sciences (ISRS2013), 12.-17.05.2013, Jeju, South Korea
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 56(2013), S281-S281

Publ.-Id: 18264

Experimental study of slug characteristics - Implications to sand erosion

Kesana, N. R.; Vieira, R.; Schleicher, E.; Mclaury, B. S.; Shirazi, S. A.; Hampel, U.

Sand erosion is a severe problem that many oil and gas producers have to deal with. Therefore, it is desirable to have a model that can predict erosion for various operating conditions. Predicting erosion is a complex problem due to the number of parameters that are involved. The complexity of predicting erosion increases when producing or transporting multiphase fluids through pipelines. It is well known that the characteristics of multiphase flow affect sand erosion in the pipelines. This work specifically concentrates on measuring multiphase-slug characteristics using a measurement technique based on wire-mesh sensor. A 16 x 16 dual wire-mesh sensor is installed before a standard 76.2 mm (3-inch) bend for a horizontally oriented pipe. The distance by which the dual Wire Mesh Sensors are separated is 32 mm. The local void fraction is extracted where horizontal and vertical wires of the sensor intersect, utilizing the differences in conductance between two different fluids. The fluids used in these multiphase experiments were air and either water or water-CMC mixture to increase the liquid viscosity. Experiments were conducted, where superficial gas velocity ranged from 9.1 m/s to 35 m/s, and superficial liquid velocity was 0.76 m/s. Three different liquid viscosities (1 cP, 10 cP and 40 cP) were used for performing the experiments. The void fraction data obtained using the dual Wire Mesh Sensors is utilized to achieve the interfacial velocities of the liquid slug. Further analysis of the data is conducted to obtain other slug characteristics such as the liquid slug body length distribution, and frequency of the slugs. Additionally, liquid slug fronts and slug tails were identified. The differences in the characteristics of slug flow and pseudo-slug flow are addressed. Finally, the slug characteristics were utilized in order to enhance the understanding of sand particle impact velocities with the pipe wall in the horizontal pipelines.

Keywords: Solid particle erosion; Multiphase slug flow; Wire Mesh Sensor

  • Contribution to proceedings
    ASME 2013 Fluids Engineering Division Summer Meeting - FEDSM 2013, 07.-11.07.2013, Incline Village, Nevada, United States
    ASME 2013 Fluids Engineering Division Summer Meeting Volume 1C: ASME, 978-0-7918-5556-0

Publ.-Id: 18263

Surface functionalization for technical applications using bacterial S-layers

Pollmann, K.; Günther, T.; Suhr, M.; Weinert, U.; Kutschke, S.; Lehmann, F.; Raff, J.

Self-assembling biomolecules are very attractive for the development of applications that are based on self-organising nanostructures. Especially the use of highly ordered proteins is an attractive approach and offer new possibilities to functionalize surfaces. In our group we use the proteinaceous paracrystalline bacterial surface layers (S-layers) that envelop bacterial cells as nanostructures for the design of materials with novel properties. These proteins are mostly composed of protein monomers with the ability to self-assemble into two-dimensional arrays on interfaces and surfaces. These features are used for the nano-patterning of various technical surfaces. The regular distributed pores of these paracrystalline arrays are binding sites for various metals and offer ideal structures for the formation of regular distributed metallic nanoclusters of a defined size [1, 2]. In addition, the proteins can be regularly modified with organic groups, thus adding additional defined functions to the nanocoatings.
Here we present our work on the functionalization of various technical surfaces using different natural bacterial S-layers. Currently we develop different applications that are based on these coatings. Examples are biosorptive materials that are of interest for a broad range of industrial applications such as bioremediation and metal recovery. Other applications include sensory layers that are based on an assembly of S-layers, aptamers and fluorophores, and catalytic surfaces that use immobilized inorganic nanoparticles as catalytic compound.
[1] Wahl, R. et al. (2001). Adv. Materials 13, 736-740
[2] Pollmann, K. et al. (2006). Biotechnol. Adv. 24, 58-68

  • Lecture (Conference)
    EURO BioMAT 2013 - European Symposium on Biomaterials and Related Areas, 23.-24.04.2013, Weimar, Deutschland

Publ.-Id: 18262

Direct Numerical Simulation of Moderate-Reynolds-Number Flows in Periodic Arrays of Spheres

Tang, Y.; Kriebitzsch, S. H. L.; Peters, E. A. J. F.; van der Hoef, M. A.; Kuipers, J. A. M.

Simulations with an iterative immersed boundary method (IBM) are performed to obtain the drag force in the gas-solid flows at intermediate Reynolds number (Re). To validate the method, we first computed the steady flow around a single sphere at low Reynolds number (Re=0.1) and compared with the Stokes solution. Then, the flow was computed for Re=100, with the results compared with a reference solution by Zhang & Prosperetti (2005). Subsequently, numerous simulations were done for the flows past a face-centred-cubic (FCC) array at Re=100 with the solid volume fraction (ϕ) varying from 0.1 to close-packed limit. From the results obtained from various different diameter to grid size ratios, we extrapolate a resolution-free dimensionless drag force and formulate a fit of the drag as a function of ϕ. Furthermore, an effective diameter as a function of the resolution was determined from this fit and the simulation data. Finally we show for Re=100 and ϕ=[0.1,0.4], the reliable predictions of the mean drag in random arrays are obtained if one applies the effective diameter. Simulation results as presented in this work can be used to formulate an improved drag correlation, which is required by simulations at larger scales in a multi-scale modelling framework.

Keywords: direct numerical simulation; immersed boundary method; multi-scale modelling; drag force; spheres

  • Contribution to proceedings
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea
  • Lecture (Conference)
    8th International Conference on Multiphase Flow 2013 (ICMF), 26.-31.05.2013, Jeju, Korea

Publ.-Id: 18261

On the effect of carbon nanotubes on properties of liquid crystals

Schymura, S.; Scalia, G.

Liquid crystals (LCs) with their fluidity and selforganization are attractive hosts for the dispersion and manipulation of macro- and nanoparticles, allowing the realization of their ordered assemblies. In addition, new functional materials can be created thanks to the particle properties. Among the nanoparticles, carbon nanotubes (CNTs) stand out for their exceptional electrical, thermal and mechanical properties. While LCs can be used for manipulating CNTs, the nanotube properties are attractive also for influencing and tuning LC properties. In this paper, we discuss different aspects of the CNT–LC combination, briefly introducing their dispersion and interaction and then, more extensively, evaluating their effect on selected properties of LCs relevant for display-related applications. We show that some previously reported improvements cannot be considered an intrinsic feature of CNT-doped LCs. In addition, we were also able to follow locally the Frederiks transition of CNT-doped LCs by Raman spectroscopy, revealing the direct effect of bundles of CNTs on LC reorientation.

Keywords: carbon nanotubes; liquid crystals

Publ.-Id: 18260

Synthesis and preliminary evaluation of novel [(Cp-R)M(CO)3] (M = Re, 99mTc) complexes as potent sigma-2 receptor ligands

Li, D.; Wang, X.; Deuther-Conrad, W.; Chen, X.; Cui, M.; Steinbach, J.; Brust, P.; Liu, B. L.; Jia, H. M.

Objectives: Sigma-2 (σ2) receptors have been proposed to be the progesterone receptor membrane component 1 [1]. Progress in cancer biology has revealed that (σ2) receptors are over-expressed in many types of cancer [2]. The expression of (σ2) receptors is assumed to be a suitable biomarker of cellular proliferation in solid tumors [3]. In our previous work, we used PB28 as lead compound to design novel 99mTc cyclopentadienyl tricarbonyl complex as putative agent for (σ2) receptor tumor imaging [4]. In this abstract, RHM-1, another (σ2) receptor selective ligand, was used as lead compound to design novel [(Cp-R)M(CO)3] (M = Re, 99mTc) complexes as potent (σ2) receptor ligands. Synthesis and preliminary evaluation of these complexes are reported.

Methods: The synthetic routes of 99mTc labeled complexes and the corresponding rhenium complexes are shown in Scheme 1. The affinities of the rhenium complexes towards (σ1) and (σ2) receptors were investigated by in vitro competition binding assays.

Scheme 1. Reagents and conditions: (a) 4-bromobutanoyl chloride, CH2Cl2, AlCl3, 0 °C to rt, 4 h; (b) 6-bromohexanoyl chloride, CH2Cl2, AlCl3, 0 °C to rt, 4 h; (c) 6,7-dimethoxy-1,2,3,4-tetrahydroisoquinoline, KI, toluene, TEA, 115 °C, 5 h; (d) 5,6-dimethoxyisoindoline, KI, toluene, TEA, 115 °C, 5 h; (e) 99mTcO4 -, Mn(CO)5, DMF, 140 °C, 1 h.

Results: In vitro competition binding assays showed that rhenium complexes exhibited moderate to high affinity for σ2 receptors and moderate subtype selectivity. Ki values of complex 2a towards σ1 and σ2 receptors were 121 ± 9.55 nM and 20.9 ± 0.23 nM, respectively. Ki values of complex 2c towards σ1 and σ2 receptors were 28.0 ± 9.35 nM and 9.13 ± 3.06 nM, respectively. [99mTc]5a and [99mTc]5c were prepared with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the corresponding ferrocene precursors. The log D values of [99mTc]5a and [99mTc]5c were determined to be 2.60 ± 0.06 and 2.56 ± 0.08, respectively. Biodistribution and inhibition studies are in progress.

Conclusions: These results are encouraging for further exploration of Tc-labeled probes for σ2 receptor imaging in vivo.

Acknowledgements: Supported by NSFC (21071023).

References: [1] Xu J, et al (2011) Nat Commun, DOI 10.1038/ncomms 1386. [2] Megalizzi V, et al (2012) Med Res Rev, 32, 410-27. [3] Mach RH, et al (2009) Cent Nerv Syst Agents Med Chem, 9, 230-45. [4] Chen X, et al (2012) Bioorg Med Chem Lett, 22, 6352-57.

  • Poster
    The 20th International Symposium on Radiopharmaceutical Sciences - ISRS2013, 12.-17.05.2013, Jeju, South Korea
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 56(2013), S383-S383

Publ.-Id: 18259

Synthesis and biological evaluation of two novel 99mTc cyclopentadienyl tricarbonyl complexes for sigma-1 receptor imaging

Wang, X.; Li, Y.; Deuther-Conrad, W.; Li, D.; Cui, M.; Steinbach, J.; Brust, P.; Liu, B. L.; Jia, H. M.

Objectives: Sigma-1 (σ1) receptors represent a distinct class of intracellular membrane proteins. The σ1 receptors are believed to be linked to a number of human diseases, including brain disorders, tumors and heart failure [1-3]. There are considerable interests in the development of 99mTc radiopharmaceuticals for imaging σ1 receptors using SPECT because of the routine availability of 99mTc radioisotope in hospitals and its ideal nuclear decay properties. We report the design, synthesis and biological evaluation of two novel 99mTc cyclopentadienyl tricarbonyl complexes for sigma-1 receptor imaging.

Methods: The synthetic routes of 99mTc labeled complexes and the corresponding rhenium complexes are shown in Scheme 1 [4]. The biological properties of the complexes were investigated by in vitro competition binding assays, biodistribution and inhibition studies in ICR mice.

Scheme 1. Synthetic routes of 99mTc labeled complexes and the corresponding rhenium complexes. Reagents and conditions: (a) 1, KI, toluene, TEA, 115 ºC, 4 h; (b) 2, KI, toluene, TEA, 115 ºC, 4 h; (c) 99mTc O4 -, Mn(CO)5Br, DMF, 140 ºC, 1 h.

Results: In vitro competition binding assays showed that rhenium complex 5 exhibited nanomolar affinity for σ1 receptors (Ki = 6.77 ± 4.56 nM) and low subtype selectivity (σ2 receptor: Ki = 26.7 ± 0.42 nM; Kiσ2/Kiσ1 = 3.94). Rhenium complex 6 possessed low nanomolar affinity for σ1 receptors (Ki = 2.11 ± 1.36 nM) and moderate subtype selectivity (σ2 receptor: Ki = 30.7 ± 3.83 nM ; Kiσ2/Kiσ1 = 14.5). [99mTc]9 and [99mTc]10 were prepared in 59 ± 2% and 62 ± 5% isolated radiochemical yields with radiochemical purity of >99% via double-ligand transfer (DLT) reaction from the corresponding ferrocene precursors. The log D values of [99mTc]9 and [99mTc]10 were determined to be 2.53 ± 0.09 and 2.24 ± 0.02, respectively. Biodistribution studies in mice revealed high initial brain uptakes of [99mTc]9 and [99mTc]10 with 1.95 ± 0.09 %ID/g and 2.94 ± 0.41 %ID/g at 2 min postinjection, respectively. The brain-to-blood ratios of [99mTc]10 were high with 3.02, 2.89, and 3.18 at 30 min, 1 h, and 4 h postinjection, respectively. Administration of haloperidol 5 min prior to injection of [99mTc]10 significantly reduced the radiotracer uptake in brain and spleen by 40-50% at 1 h postinjection, suggesting that the binding of [99mTc]10 to σ receptors was specific in vivo.

Conclusions: These findings suggest that [99mTc] warrants further investigation as putative sigma-1 receptor imaging agent.

Acknowledgements: Supported by NSFC (21071023).

References: [1] Hayashi T, et al (2011) Expert Opin Ther Targets, 15, 557-77. [2] Megalizzi V, et al (2012) Med Res Rev 32, 410-27. [3] Ito K, et al (2012) Cardiovasc Res, 93, 33-40. [4] Chen X, et al (2012) Bioorg Med Chem Lett, 22, 6352-57.

  • Lecture (Conference)
    The 20th International Symposium on Radiopharmaceutical Sciences - ISRS2013, 12.-17.05.2013, Jeju, South Korea
  • Abstract in refereed journal
    Journal of Labelled Compounds and Radiopharmaceuticals 56(2013), S77-S77

Publ.-Id: 18258

Feasibility of estimation of brain volume and 2-deoxy-2-F-18-fluoro-D-glucose metabolism using a novel automated image analysis method: Application in Alzheimer's disease

Musiek, E. S.; Saboury, B.; Mishra, S.; Chen, Y.; Reddin, J. S.; Newberg, A. B.; Udupa, J. K.; Detre, J. A.; Hofheinz, F.; Torigian, D.; Alavi, A.

The development of clinically-applicable quantitative methods for the analysis of brain fluorine-18 fluoro desoxyglucose-positron emission tomography (18F-FDG-PET) images is a major area of research in many neurologic diseases, particularly Alzheimer’s disease (AD). Region of interest visualization, evaluation, and image registration (ROVER) is a novel commercially-available software package which provides automated partial volume corrected measures of volume and glucose uptake from 18F-FDG PET data. We performed a pilot study of ROVER analysis of brain 18F-FDG PET images for the first time in a small cohort of patients with AD and controls. Brain 18F-FDG-PET and volumetric magnetic resonance imaging (MRI) were performed on 14 AD patients and 18 age-matched controls. Images were subjected to ROVER analysis, and voxel-based analysis using SPM5. Volumes by ROVER were 35% lower than MRI volumes in AD patients (as hypometabolic regions were excluded in ROVER-derived volume measurement ) while average ROVER- and MRI-derived cortical volumes were nearly identical in control population. Whole brain volumes when ROVER-derived and whole brain metabolic volumetric products (MVP) were significantly lower in AD and accurately distinguished AD patients from controls (Area Under the Curve (AUC) of Receiver Operator Characteristic (ROC) curves 0.89 and 0.86, respectively). This diagnostic accuracy was similar to voxel-based analyses. Analysis by ROVER of 18F-FDGPET images provides a unique index of metabolically-active brain volume, and can accurately distinguish between AD patients and controls as a proof of concept. In conclusion, our findings suggest that ROVER may serve as a useful quantitative adjunct to visual or regional assessment and aid analysis of whole-brain metabolism in AD and other neurologic and psychiatric diseases.

Keywords: 18F-FDG - PET; ROVER - Metabolic volume; Whole brain metabolism; Alzheimer’s disease

  • Hellenic Journal of Nuclear Medicine 15(2012), 190-196

Publ.-Id: 18257

Exploratory prospective trial of hypoxia-specific PET imaging during radiochemotherapy in patients with locally advanced head-and-neck cancer

Zips, D.; Zöphel, K.; Abolmaali, N.; Perrin, R.; Abramyuk, A.; Haase, R.; Appold, S.; Steinbach, J.; Kotzerke, J.; Baumann, M.

Purpose: To explore in a prospective trial the prognostic value of hypoxia imaging before and during radiochemotherapy in patients with locally advanced head and neck cancer.
Patients and methods: Twenty-five patients with stage III/IV head and neck cancer were investigated with [18F]-fluoromisonidazole (FMISO) PET/CT at four time points during radiochemotherapy (baseline, 8–10 Gy, 18–20 Gy,50–60 Gy). FMISO PET/CT image parameters were extracted including maximumtumour-to-background (TBRmax) and thresholded volume at different TBR ratios. CT volume and baseline FDG-PET/CT image parameters were also included. Parameters at all time points were investigated for their prognostic value with the local-progression-free-survival endpoint (LPFS). Significance was evaluated with multivariate Cox (including clinical parameters) and Log-rank tests.
Results: FMISO-image parameters were found to have a strong association with the LPFS endpoint, and were strongest at the week 1 and 2 time points (p = 0.023–0.048 and 0.042–0.061 respectively on multivariate Cox). Parameters measured at baseline were only significant on univariate analysis. None of the clinical parameters, and also FDG- or CT-delineated volumes, were significantly associated with LPFS.
Conclusion: This prospective, exploratory study demonstrated that FMISO-PET/CT imaging during the initial phase of treatment carries strong prognostic value. FMISO-PET/CT imaging at 1 or 2 weeks during treatment could be promising way to select patients that would benefit from hypoxia modification or dose-escalated treatment. A validation study is on-going.

Keywords: [18F]-misonidazole-PET; Head-and-neck cancer; Radiotherapy

Publ.-Id: 18256

Innovative Technologien für Ressourceneffizienz - Strategische Metalle und Mineralien

Dürkoop, A.

Um die Versorgung mit metallischen Rohstoffen für Deutschland zukünftig nachhaltig zu sichern, hat das BMBF im Jahr 2012 die r3-Fördermaßnahme mit dem Fokus auf strategische Metalle und Mineralien ins Leben gerufen. Die bisher bewilligten r3-Verbundprojekte sowie das koordinierende Helmholtz-Institut Freiberg für Ressourcentechnologie wurden in der Präsentation vorgestellt.

Keywords: Rohstoffeffizienz; Strategische Metalle und Mineralien

  • Invited lecture (Conferences)
    BMBF Branchendialog Nanotechnologien und Neue Materialien für Ressourceneffizienz, 06.12.2012, Berlin, Deutschland

Publ.-Id: 18255

Additional constraints may soften a non-conservative structural system: Buckling and vibration analysis

Lerbet, J.; Kirillov, O.; Aldowaji, M.; Challamel, N.; Nicot, F.; Darve, F.

The effect of additional kinematic constraints on eigenfrequencies of non conservative systems presenting a non symmetric stiffness matrix is investigated with the use of the second order work criterion. It is shown that there are always additional constraints that may soften structural systems, from both buckling and vibration points of view. The steps for building such constraints are given, consequences on stability are discussed and several illustrating examples are presented.

Keywords: Stability; Vibrations; Non-conservative problems; Constrained systems; Second-order work criterion

Publ.-Id: 18254

Neue Technologien für mehr Rohstoffeffizienz

Dürkoop, A.

Seit Sommer 2012 forschen bundesweit mehr als 100 Unternehmen, Forschungseinrichtungen und Behörden in der BMBF-Fördermaßnahme r3 „Innovative Technologien für Ressourceneffizienz – Strategische Metalle und Mineralien“ mit dem Ziel, die Effizienz für nicht energetische Rohstoffe nachhaltig zu steigern. Alle bisher gestarteten r3-Verbundprojekte zielen darauf ab, wirtschaftsstrategisch wichtige Metalle wie z.B. Indium, Germanium, Gallium und seltene Erden, aber auch Industrieminerale wie Flussspat zukünftig effizienter zu gewinnen, zu recyceln, aber auch effizienter in Produkten zu verwenden. So werden diese Metalle und Mineralien vor allem für die Herstellung von Hightech-Produkten wie Computern, Mobiltelefonen und Energiesparlampen aber auch für Dauermagnete in Windkraftanlagen benötigt. Zwar werden diese Ressourcen zurzeit nicht in großen Mengen verwendet, sind dafür aber wirtschaftsstrategisch von großer Bedeutung. Dabei sind diese Rohstoffe zunehmend schlechter verfügbar und führen somit zu steigenden Produktionskosten. Da die Versorgungslage für diese strategischen metallischen Rohstoffe unsicher ist, könnte es zu Versorgungsengpässen im Rohstoffimportland Deutschland kommen. Nur mit einer sicheren Rohstoffversorgung können in Deutschland auch zukünftig Hightech-Produkte produziert und entwickelt werden.

Keywords: Strategische Metalle; Rohstoffeffizienz; Recycling

  • GAIA - Ökologische Perspektiven für Wissenschaft und Gesellschaft 22/1(2013), 62-64

Publ.-Id: 18253

Serpent Monte-Carlo Code: An Advanced Tool for Few-Group Cross Section Generation

Fridman, E.

Serpent is a continuous-energy Monte Carlo (MC) reactor physics code recently developed at VTT Technical Research Centre of Finland(1). Serpent can be used for 2D fuel lattice calculations as well as for 3D full core simulations.Serpent is especially designed to generate homogenized constants for deterministic 3D core analysis. For any region of interest the code automatically calculates homogenized few-group cross sections, group-to-group scattering matrices, diffusion coefficients, assembly discontinuity factors, kinetics parameters, etc.
The capability to generate homogenized few-group constants can be considered as one of the most attractive features of Serpent. Being a MC code, Serpent is capable of handling complex geometries without any major approximations and can be used for producing cross section data for virtually any fuel or reactor type. The demonstration of the Serpent capability to generate few-group cross sections for different reactor systems is the main topic of this paper.

Keywords: Serpent; Monte Carlo; few-group cross section generation

  • atw - International Journal for Nuclear Power 58(2013)3, 156-157

Publ.-Id: 18252

Doping of nanostructure and defect engineering by ion beam implantation and irradiation

Ou, X.

This talk will give a brief introduction of my recent works on application of ion implantation and ion irradiation on doping of nanostructure and on defect engineering for nanostructure fabrication and nuclear materials.
Doping of vertical Si nanowires (NWs) is demonstrated here by multi energy ion implantation. The doping behavior of the individual Si NWs was investigated by SSRM. A strong surface segregation of the implanted P in Si was found during the subsequent annealing process, and deactivation of the P also was excepted at the NW surface. A diameter dependence of the local resistivity of the NW cross sections RS increases as the NW diameter decreases and this tendency is significantly enhanced as the diameter is below 25 nm.
The resistive switching (RS) of functional oxide thin films has attracted tremendous interest recently due to its promising application as building blocks in non-volatile memory devices. This work reports a low cost and effective approach to tune the resistive switching behavior of BiFeO3 films which have been deposited by pulsed laser deposition and irradiated with low energy Ar+ ions. Due to the preferential sputtering of BiFeO3 films, oxygen vacancies as well as the surface morphology can be tuned by low energy irradiation in a controllable way to enhance the RS performance.
The dual beam facility in Rossendorf is used for the investigation of the radiation damage in yttria-stabilized zirconia (YSZ) created either by simultaneous implantation of Zr+ & He+ or by separate single beam implantation. The results show that the excitation by the additional Zr+ implantation can activate and enhance the out diffusion of the simultaneously implanted helium. The release of helium.from YSZ substrate, instead to be trapped by implantation induced vacancies generated by the heavy Zr+ ions, avoids the formation and growth of He bubbles.

Keywords: doping and defect engineering

  • Lecture (others)
    Lecture given in Beihang University and Perking University, 28.09.2012, Beijing, China

Publ.-Id: 18251

Control of Coulomb-mediated excitonic 2s emission by an external magnetic field

Bhattacharyya, J.; Zybell, S.; Winnerl, S.; Schneebeli, L.; Böttge, C. N.; Breddermann, B.; Kira, M.; Koch, S. W.; Helm, M.; Schneider, H.

We report on time-resolved photoluminescence (PL) studies of exciton dynamics in undoped GaAs quantum wells in the presence of an external magnetic field. Subsequent to pulsed interband excitation, the photogenerated excitons are manipulated by applying time-delayed THz pulses from the free-electron laser (FEL) FELBE at the Helmholtz-Zentrum Dresden-Rossendorf. Simultaneous time and wavelength resolved spectroscopy using a synchroscan streak camera allows us to investigate the emitted PL with high detection efficiency [1]. If the FEL photon energy is tuned into resonance with the intra-excitonic 1s-2p transition, the PL originating from the 1s exciton is suppressed by the incident THz pulse and subsequently recovers to a value higher than the reference trace. Furthermore, the THz pulse leads to pronounced enhancement of the PL intensity at the energy of the excitonic 2s and 2p states. Since radiative recombination is dipole forbidden for the 2p state, this PL contribution is attributed to 2s emission [2], thus confirming earlier theoretical predictions of efficient Coulomb scattering between the nearly degenerate 2s and 2p states which allows for rapid 2p-2s population transfer [3].
In this presentation, we demonstrate the efficient manipulation of the 2p-2s scattering efficiency via an external magnetic field, which tunes the 2s and 2p exciton energies from resonant to non-resonant since these energies change differently with magnetic field. This leads to efficient suppression of the THz induced 2s PL signal upon increasing the magnetic field from 0 T to 2.5 T. These results demonstrate that the underlying Coulomb-mediated 2p-2s scattering process can be magnetically controlled. Our experiments confirm theoretical calculations which will also be discussed.

Keywords: semiconductor quantum well; exciton; time-resolved photoluminescence; free-electron laser; intra-excitonic transition

  • Poster
    International Workshop on Optical Terahertz Science and Technology 2013, 01.-05.04.2013, Kyoto, Japan

Publ.-Id: 18250

Colloidal Stability of Carbon Nanotubes - A Matter of Modification

Schymura, S.; Weiß, S.; Zänker, H.; Franke, K.

The implications of a carbon nanotube (CNT) release into the environment are majorly influenced by the colloidal stability of the CNTs in surface or ground waters. Main factors for this stability are the degree of oxidation of the CNTs and the presence of natural organic matter (NOM) such as fulvic or humic acids. Pristine CNTs show very low dispersion stability in water and quickly aggregate and sediment.
However covalent and/or non-covalent modification of the CNTs through, for example, natural oxidation processes or adsorption of NOM can considerably alter their colloidal stability, thereby affecting the fate of the CNTs upon release. For this study samples of different types of CNTs, multi wall as well as single wall CNTs, were modified covalently by a microwave assisted oxidative treatment and non-covalently by dispersion in the presence of fulvic acid. The colloidal stability of the so modified CNTs was investigated using dynamic light scattering methods to follow the aggregation and sedimentation of the CNTs as well as establishing the ζ potential of the modified CNTs in waters of different ionic strength.
The colloidal stability of the modified CNTs in distilled and low ionic strength water or in the presence of fulvic acid can exceed months. This has implications for their transport behavior upon release into the environment. A transport of CNTs in surface and ground waters can be expected under certain conditions.

Keywords: carbon nanotubes; colloidal stability; modification

  • Poster
    NanoNature Clustertreffen 2013, 14.-15.01.2013, Frankfurt a. Main, Deutschland

Publ.-Id: 18249

Radiolabelling of silver and titania nanoparticles as a tool for sensitive detection of nanoparticle release from surface coatings

Hildebrand, H.; Franke, K.; Gibson, N.; Cydzik, I.; Simonelli, F.; Bulgheroni, A.; Holzwarth, U.; Bilz, E.; Freyer, A.

Engineered nanoparticles (NPs) such as silver and titania are widely used in consumer products e.g. as functional additives in surface coatings. Due to aging or abrasion of these nanocomposites, particle release becomes likely and further transport e.g. in environmental systems could be assumed. For conventional nanocomposites, accurate and sensitive detection and quantification of NP release is still a challenge due to the fact that released fractions might be small but nevertheless significant. The application of radiotracers provides the excellent option of “visibility”, traceability and quantification of NPs in complex media. Therefore, different radiolabelling strategies for engineered nanopowders (TiO2 P 25, Evonic Industries, dp = 21 nm; Ag0, Sigma Aldrich, dp < 100 nm) were established using a diffusive introduction of 110mAg radionuclides (t1/2 = 250 d) into Ag0-NPs (Hildebrand & Franke, 2012) and 44Ti radionuclides (t1/2 = 63 a) into TiO2-NPs through a low-temperature annealing procedure. Another radiolabelling strategy is the direct activation of Ag0 and TiO2 nanopowders that was done via proton irradiation using a Scanditronix MC40 cyclotron (Abbas et al. 2010, Holzwarth et al. 2012).
Both methods were tested with respect to radiolabelling yield, achievable activity concentration, pH-dependent stability of the radiolabelling and the influence on NP properties. Results obtained show an appropriate selection of radiolabelling methods suitable for different experimental conditions for NP release studies.

Abbas K, Cydzik I, Del Torchio R, Farina M, Forti E, Gibson N, Holzwarth U, Simonelli F, Kreyling W (2010) J Nanopart Res 12:2435–2443.
Holzwarth U, Bulgheroni A, Gibson N, Kozempel J, Cotogno G, Abbas K, Simonelli F, Cydzik I (2012) J Nanopart Res 14:880.
Hildebrand H and Franke K (2012) J Nanopart Res 14:1142.

  • Poster
    3. Clustertreffen NanoCare / NanoNature, 14.-15.01.2013, Frankfurt am Main, Deutschland

Publ.-Id: 18248

ELBE SRF Gun Testing Status

Kneisel, P.; Arnold, A.; Murcek, P.; Teichert, J.; Michel, P.; Lu, P.; Vennekate, H.; Xiang, R.; Kamps, T.; Will, I.

A status report on the fabrication, treatment, and testing of the new SRF gun cavities is given.

Keywords: niobium cavity; photo injector; superconducting radio-frequency

  • Lecture (Conference)
    TESLA Technology Collaboration (TTC) Meeting, 05.-08.11.2012, Newport News, USA

Publ.-Id: 18247

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