Publications Repository - Helmholtz-Zentrum Dresden-Rossendorf

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29792 Publications
Anomalous Hall effect in fully compensated half-metallic Mn₂RuₓGa thin films
Fowley, C.; Rode, K.; Lau, Y. C.; Thiyagarajah, N.; Betto, D.; Borisov, K.; Atcheson, G.; Kampert, E.; Wang, Z.; Yuan, Y.; Zhou, S.; Lindner, J.; Stamenov, P.; Coey, J. M. D.; Deac, A. M.
High-field magnetotransport is investigated in thin films of half-metallic ferrimagnet Mn₂RuₓGa. A non-vanishing Hall signal is observed over a broad temperature range, spanning the compensation temperature (155K), where the net magnetic moment is strictly zero, the Hall conductivity is 6673 Ohm⁻¹ m⁻¹ and the coercivity exceeds 9T. Molecular field modelling is used to determine the intra- and inter-sublattice exchange constants and from the spin-flop transition we infer the anisotropy of the electrically active sublattice to be 216 kJm⁻³ and predict the magnetic resonances
frequencies. Exchange and anisotropy are comparable and hard-axis applied magnetic fields result in a tilting of the magnetic moments from their collinear ground state. Our analysis is applicable to collinear ferrimagnetic half-metal systems.
Keywords: Ferrimagnetism, Magnetotransport, Half-metals, Anomalous Hall effect, Magnetic anisotropy, Exchange interaction
  • Invited lecture (Conferences)
    Intermag 2018, 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 27502 - Permalink


Features of magnetization behavior in the rare-earth intermetallic compound (Nd0.5Ho0.5)2Fe14B
Kostyuchenko, N. V.; Tereshina, I. S.; Gorbunov, D. I.; Tereshina-Chitrova, E. A.; Andreev, A. V.; Doerr, M.; Politova, G. A.; Zvezdin, A. K.
The crystal-electric field parameters are determined for the (Nd0.5Ho0.5)2Fe14B compound by analyzing experimental magnetization curves obtained in magnetic fields up to 60 T. The values of the crystal-field parameters B20, B40, B60, B44, B64 are 56.3, −73.2, −10.74, −8.9, 0 cm−1 for Nd3+ ion and 312.38, −176.78, 89.2, −88.43, 0 cm−1 for Ho3+ ion. The transition from the ferri- to the field-induced ferromagnetic state has been studied in detail.

Publ.-Id: 27501 - Permalink


Magnetic and magnetocaloric properties of single Crystal (Nd0.5Pr0.5)2Fe14B
Politova, G. A.; Tereshina, I. S.; Gorbunov, D. I.; Paukov, M. A.; Andreev, A. V.; Grechishkin, R. M.; Rogacki, K.
In this work the magnetic and magnetocaloric properties of a (Nd0.5Pr0.5)2Fe14B single crystal have been investigated in a wide range of temperatures and magnetic fields. Magnetic phase transition temperatures (spin-reorientation transition (SRT) at TSR = 73 K and Curie point at Tc = 570 K) were determined together with the values of saturation magnetization Ms and magnetocrystalline anisotropy constants K1 and K2. In the vicinity of a spin-reorientation magnetic phase transition, the value of the magnetocaloric effect was determined as an isothermal magnetic entropy change (DSM). The universal curve of ΔS´(ʘ) around TSR under various magnetic field changes has been constructed by using a phenomenological procedure. It is found that this approach is applicable to materials with a second-order spin-reorientation phase transition.

Publ.-Id: 27500 - Permalink


Complex magnetic order in the kagome ferromagnet Pr3Ru4Al12
Henriques, M. S.; Gorbunov, D. I.; Andreev, A. V.; Fabrèges, X.; Gukasov, A.; Uhlarz, M.; Petricek, V.; Ouladdiaf, B.; Wosnitza, J.
In the hexagonal crystal structure of Pr3Ru4Al12, the Pr atoms form a distorted kagome lattice, and their magnetic moments, are subject to competing exchange and anisotropy interactions.We performed magnetization, magnetic-susceptibility, specific-heat, electrical-resistivity, and neutron-scattering measurements. Pr3Ru4Al12 is a uniaxial ferromagnet with TC = 39 K that displays a collinear magnetic structure (in the high-temperature range of the magnetically ordered state) for which the only crystallographic position of Pr is split into two sites carrying different magnetic moments. A spin-reorientation phase transition is found at 7 K. Below this temperature, part of the Pr moments rotate towards the basal plane, resulting in a noncollinear magnetic state with a lower magnetic symmetry. We argue that unequal RKKY exchange interactions competing with the crystal electric field lead to a moment instability and qualitatively explain the observed magnetic phases in Pr3Ru4Al12.

Publ.-Id: 27499 - Permalink


Bethe‐Strings: Exotische Anregungen in Spinsystemen
Wang, Z.; Loidl, A.
Hans Bethe sagte 1931 in einer fundamentalen Arbeit die Existenz von stark gebundenen Zuständen von Quasiteilchen voraus. Nun konnte eine internationale Kooperation erstmals derartige Bethe‐Strings in einem Kristall nachweisen.
Keywords: Spin Kette, Quasiteilchen, String Erregungen, Hans Bethe

Publ.-Id: 27497 - Permalink


Stability and instability of hydromagnetic Taylor–Couette flows
Rüdiger, G.; Gellert, M.; Hollerbach, R.; Schultz, M.; Stefani, F.
Decades ago S. Lundquist, S. Chandrasekhar, P. H. Roberts and R. J. Tayler first posed questions about the stability of Taylor–Couette flows of conducting material under the influence of large-scale magnetic fields. These and many new questions can now be answered numerically where the nonlinear simulations even provide the instability-induced values of several transport coefficients. The cylindrical containers are axially unbounded and penetrated by magnetic background fields with axial and/or azimuthal components. The influence of the magnetic Prandtl number Pm on the onset of the instabilities is shown to be substantial. The potential flow subject to axial fields becomes unstable against axisymmetric perturbations for a certain supercritical value of the averaged Reynolds number (with Re the Reynolds number of rotation, Rm its magnetic Reynolds number). Rotation profiles as flat as the quasi-Keplerian rotation law scale similarly but only for Pm >> 1 while for the instability instead sets in for supercritical Rm at an optimal value of the magnetic field. Among the considered instabilities of azimuthal fields, those of the Chandrasekhar-type, where the background field and the background flow have identical radial profiles, are particularly interesting. They are unstable against nonaxisymmetric perturbations if at least one of the diffusivities is non-zero. For Pm << 1the onset of the instability scales with Re while it scales with Rm for Pm >> 1. Even superrotation can be destabilized by azimuthal and current-free magnetic fields; this recently discovered nonaxisymmetric instability is of a double-diffusive character, thus excluding Pm=1 . It scales with Re for Pm -> 0 and with Rm for Pm -> infinity.
The presented results allow the construction of several new experiments with liquid metals as the conducting fluid. Some of them are described here and their results will be discussed together with relevant diversifications of the magnetic instability theory including nonlinear numerical studies of the kinetic and magnetic energies, the azimuthal spectra and the influence of the Hall effect.

Publ.-Id: 27496 - Permalink


Reply to “Comment on Methodological accuracy of image-based electron density assessment using dual-energy computed tomography” [Med. Phys. 44, 2429-2437 (2017)]
Möhler, C.ORC; Wohlfahrt, P.ORC; Richter, C.; Greilich, S.ORC
To the editor,
In his recent letter, Dr. Bouchard expressed his concern that our article on electron density (ED) assessment with dual-energy computed tomography (DECT) contained “some errors and speculative arguments”. We are aware that any study — no matter how carefully conducted — can exhibit erroneous aspects. In this case, however, we concluded that most of the statements and additional data provided by Dr. Bouchard in fact support the key findings of our paper, while other points raised can be attributed to a different use of concepts and to occasional overinterpretation. We therefore firmly reject his assertion. In this reply we provide our response to the criticism
raised:
Keywords: dual-energy CT, electron density, proton therapy

Publ.-Id: 27492 - Permalink


Microresonator-ferromagnetic resonance investigation of thermal spin-transfer torque in Co2FeAl/MgO/CoFeB magnetic tunnel junctions
Cansever, H.ORC; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.ORC; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.
Similar to electrical currents flowing through magnetic multilayers [1,2], thermal gradients applied across the barrier of a magnetic tunnel junction may induce pure spin currents and generate ‘thermal’ spin-transfer torques large enough to induce magnetization dynamics on the free layer [3, 4]. The relation of spin current, charge current and heat current was theoretically described by Bauer et al. using Onsager’s reciprocity rule [5]. According to Onsager’s law, spin currents can be produced by bias voltages or thermal gradients and investigated in terms of spin-Seebeck effect in magnetic multilayers.
First, Hatami et al. theoretically studied the spin-Seebeck effect in spin-valves and introduced the concept of thermal spin-transfer torques. They predicted that the thermally induced spin current creates an imbalance on the interface between non-magnetic and ferromagnetic layers due to collisions (electron-electron and electron-phonon interactions) [3]. Thermal spin-transfer torques were studied experimentally within asymmetric Co/Cu/Co nanowire spin-valves which exhibit switching field changes under varying a.c. currents causing Joule heating [6]. In magnetic tunnel junctions, it was theoretically predicted that temperature differences of around 10 K over an ultrathin barrier (1 nm) can create magnetization dynamics in Fe/MgO/Fe magnetic tunnel junctions [4]. The spin-Seebeck effect has been studied on CoFeB/MgO/CoFeB magnetic tunnel junctions using different heating methods such as Joule heating, heating with Peltier elements, as well as laser heating [8-14]. Recently, it was shown that using Co2FeAl as a reference layer improves tunneling magneto-Seebeck (TMS) in magnetic tunnel junctions [7].
Here, we describe a novel experimental approach and setup to observe effects of thermal gradients within magnetic tunnel junctions with Heusler compounds by using the microresonator ferromagnetic resonance (µR-FMR) method under laser heating. Initially, microresonators (shown in figure 1) were introduced by Narkowicz et al. for electron paramagnetic resonance (EPR) experiments to achieve optimal sensitivity for small objects [8]. Detecting the FMR signal of nano- to micron-sized samples in conventional cavities (cm3) is not possible, due to the too small ferromagnetic volume, and therefore low filling factor. A planar microresonator, by definition, is a two-dimensional structure, its diameter can be tailored to match the order of the sample’s size (shown as a black ellipse in the microresonator loop in figure 1). Two stubs are attached to the inductive loop. The capacitive radial stub in first approximation may be viewed as an element to tune the loop to the operation frequency, while the rectangular stub matches the structure to the 50 Ω impedance of the microstrip feedline.

Figure 1: Layout of a planar microresonator with simulated electric field distribution at the resonance frequency. The inset shows the current and magnetic field distribution (out-of-plane direction) in the loop containing a sample (black ellipse).
We investigated magnetic tunnel junctions (MTJs) fabricated out of Co2FeAl/MgO/CoFeB stacks. The sample and microresonator fabrication consist of multiple steps of lithography, ion etching and lift-off processes. The sample is finally patterned into a 6x9 µm2 elliptical shape using electron beam lithography (EBL) and ion beam etching is used to etch down the sample to the substrate. Microresonators are then fabricated around the sample using UV lithography. For laser heating, a continuous-wave (CW) laser at 532 nm wavelength and with tunable power up to 33 mW is focused on the sample.
“Hot-FMR” measurements were performed on unpatterned multilayers between 300 K and 450 K (figure 2) to understand the effect of global heating. It is clearly seen that the FMR signal of Co2FeAl exhibits a shift with increasing temperature. As seen in the inset graph, it is difficult to quantify the changes for the CoFeB signal, due to its small intensity. Subsequent, measurements in the presence of a thermal gradient were performed on 6x9 µm2 MTJs, integrated into microresonator loops with an inner diameter of 20 µm. The MTJs were submitted to laser irradiation, up to a maximum power of 33 mW. Unlike the Hot-FMR measurements, the resonance field and linewidth did not show clear changes with increasing laser power. The results suggest that the laser power is neither sufficient to induce magnetization dynamics via thermal gradients across the barrier, nor lead to significant changes of the magnetic parameters due to global heating of the sample.
Figure 2: FMR spectra of the extended films of Co2FeAl / MgO / CoFeB measured in the in-plane direction at different temperatures
As a conclusion, the effect of a global temperature change on the resonance frequency and linewidth of Co2FeAl was analyzed. With regards to the µR-FMR results, higher laser power is needed to induce magnetization dynamics. Moreover, the lateral heat transport might reduce the vertical thermal gradients, thus similar measurements on smaller structures are required.
This study was funded by the German Research Foundation (DFG) via priority program SpinCaT (SPP 1538). We thank H. Schultheiss for helping with the optical part of the experimental setup and S. Zhou for giving the access to the VSM setup.
[1] J.C. Slonczewski, J. Magn. Magn. Mater. 159, L1, (1996).
[2] L. Berger, Phys. Rev. B 54, 9353, (1996).
[3] M. Hatami, G.E.W. Bauer, Q. Zhang and P.J. Kelly, Phys. Rev. Lett. 99, 066603 (2007).
[4] X. Jia, K. Xia and G.E.W. Bauer, Phys. Rev. Lett. 107, 176603 (2011).
[5] G.E.W. Bauer, E. Saitoh and B.J. van Wees, Nature Mater. 11, 391, (2012).
[6] H. Yu, S. Granville, D.P. Yu and J.-Ph. Ansermet, Phys. Rev. Lett. 104, 146601 (2010).
[7] A. Boehnke, U. Martens, C. Sterwerf, A. Niesen, T. Huebner, M. von der Ehe, M. Meinert, T. Kuschel, A. Thomas, C. Heiliger, M. Münzenberg M, Nature Communications 8,(1),1626, (2017).
[8] R. Narkowicz, D. Suter and R. Stonies, J. Magn. Reson.175, 275 (2005).
Keywords: thermal spin transfer torque, ferromagnetic resonance, microresonator, magnetic tunnel junctions
  • Lecture (Conference)
    INTERMAG 2018 Singapore, 23.-27.04.2018, Singapore, Singapore

Publ.-Id: 27490 - Permalink


Strain and order-parameter coupling in Ni-Mn-Ga Heusler alloys from resonant ultrasound spectroscopy
Salazar Mejia, C.; Born, N.-O.; Schiemer, J. A.; Felser, C.; Carpenter, M. A.; Nicklas, M.
Resonant ultrasound spectroscopy and magnetic susceptibility experiments have been used to characterize strain coupling phenomena associated with structural and magnetic properties of the shape-memory Heusler alloy series Ni50+xMn25−xGa25 (x=0, 2.5, 5.0, and 7.5). All samples exhibit a martensitic transformation at temperature TM and ferromagnetic ordering at temperature TC, while the pure end member (x=0) also has a premartensitic transition at TPM, giving four different scenarios:
Tc > TPM > TM, TC > TM without premartensitic transition, TC ≈ TM, and TC < TM. Fundamental differences in elastic properties, i.e., stiffening versus softening, are explained in terms of coupling of shear strains with three discrete order parameters relating to magnetic ordering, a soft mode, and the electronic instability responsible for the large strains typical of martensitic transitions. Linear-quadratic or biquadratic coupling between these order parameters, either directly or indirectly via the common strains, is then used to explain the stabilities of the different structures. Acoustic losses are attributed to critical slowing down at the premartensite transition, to the mobility of interphases between coexisting phases at the martensitic transition, and to mobility of some aspect of the twin walls under applied stress down to the lowest temperatures at which measurements were made.

Publ.-Id: 27478 - Permalink


Investigating spin-transfer torques induced by thermal gradients in magnetic tunnel junctions by using micro-cavity ferromagnetic resonance
Cansever, H.; Narkowicz, R.; Lenz, K.; Fowley, C.; Ramasubramanian, L.; Yildirim, O.; Niesen, A.; Huebner, T.; Reiss, G.; Lindner, J.; Fassbender, J.; Deac, A. M.
Similar to electrical currents flowing through magnetic multilayers, thermal gradients applied across the
barrier of a magnetic tunnel junction may induce pure spin-currents and generate ‘ thermal’ spin-transfer torques large enough to induce magnetization dynamics in the free layer. In this study, we describe a novel experimental approach to observe spin-transfer torques induced by thermal gradients in magnetic multilayers by studying their ferromagnetic resonance response in microwave cavities
. Utilizing this approach allows for measuring the magnetization dynamics on micron/nano-
sized samples in open-circuit conditions, i.e. without the need of electrical contacts. We performed first
experiments on magnetic tunnel junctions patterned into 6×9μm2 ellipses from Co2FeAl/MgO/CoFeB stacks. We conducted microresonator ferromagnetic resonance (FMR) under focused laser illumination to induce thermal gradients in the layer stack and compared them to measurements in
which the sample was globally heated from the backside of the substrate. Moreover, we carried out
broadband FMR measurements under global heating conditions on the same extended films the
microstructures were later on prepared from. The results clearly demonstrate the effect of thermal
spin-torque on the FMR response and thus show that the microresonator approach is well suited to
investigate thermal spin-transfer-driven processes for small temperatures gradients, far below the
gradients required for magnetic switching
Keywords: thermal spin transfer torque, microresonator, ferromagnetic resonance, magnetic tunnel junction

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  • Secondary publication expected from 14.05.2019

Publ.-Id: 27477 - Permalink


Magnetocaloric materials for refrigeration near room temperature
Waske, A.; Gruner, M. E.; Gottschall, T.; Gutfleisch, O.
This article overviews the current status of magnetocaloric materials for room-temperature refrigeration. We discuss the underlying mechanism of the magnetocaloric effect and illustrate differences between fi rst- and second-order type materials starting with gadolinium as a reference system. Beyond the key functional properties of magnetocaloric materials, the adiabatic temperature, and entropy change, we briefl y address the criticality of the most promising materials in terms of their supply risk. Looking at practical applications, suitable geometries and processing routes for magnetocaloric heat exchangers for device implementation are introduced.

Publ.-Id: 27476 - Permalink


Spatially Nonuniform Superconductivity in Quasi-Two-Dimensional Organic Charge-Transfer Salts
Wosnitza, J.
In the following, a brief overview on the recently found robust experimental evidence for the existence of the Fulde–Ferrell–Larkin–Ovchinnikov (FFLO) state in layered organic superconductors is given. These electronically quasi-two-dimensional (2D) clean-limit superconductors are ideally suited for observing FFLO states. Applying a magnetic field parallel to the layers suppresses orbital effects and superconductivity is observed beyond the Pauli paramagnetic limit. Both, thermodynamic as well as microscopic experimental data show the existence of an additional high-field low-temperature superconducting state having a one-dimensionally modulated order parameter.

Publ.-Id: 27475 - Permalink


Fermi-surface topology of the heavy-fermion system Ce2PtIn8
Klotz, J.; Götze, K.; Green, E. L.; Demuer, A.; Shishido, H.; Ishida, T.; Harima, H.; Wosnitza, J.; Sheikin, I.
Ce2PtIn8 is a recently discovered heavy-fermion system structurally related to the well-studied superconductor CeCoIn. Here we report on low-temperature de Haas–van Alphen-effect measurements in high magnetic fields in Ce2PtIn8 and Pr2PtIn8. In addition, we performed band-structure calculations for localized and itinerant Ce-4f electrons in Ce2PtIn8. Comparison with the experimental data of Ce2PtIn8 and of the 4f -localized Pr2PtIn8 suggests the itinerant character of the Ce-4f electrons. This conclusion is further supported by the observation of effective masses in CePtIn8, which are strongly enhanced with up to 26 bare electron masses.

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  • Secondary publication expected

Publ.-Id: 27474 - Permalink


Crystal-field effects in the kagome antiferromagnet Ho3Ru4Al12
Gorbunov, D. I.; Nomura, T.; Ishii, I.; Henriques, M. S.; Andreev, A. V.; Doerr, M.; Stöter, T.; Suzuki, T.; Zherlitsyn, S.; Wosnitza, J.
In Ho3Ru4Al12, the Ho atoms form a distorted kagome lattice. We performed magnetization, magnetic-susceptibility, specific-heat, and ultrasound measurements on a single crystal. We find that the magnetic and magnetoelastic properties of Ho3Ru4Al12 result from an interplay between geometric frustration and crystalelectric-field (CEF) effects. The Ho atoms order antiferromagnetically at TN = 4.5 K with reduced magnetic moments. In applied field, the magnetization shows anomalies that can be explained by CEF level crossings. We propose a CEF level scheme for which the ground-state doublet and the first two excited singlets at about 2.7 K form a quasiquartet. Indirect interlevel transitions allow for a quadrupolar interaction. This interaction explains well changes in the elastic shear modulus C44 as a function of temperature and magnetic field.

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  • Secondary publication expected

Publ.-Id: 27473 - Permalink


Search for multipolar instability in URu2Si2 studied by ultrasonic measurements under pulsed magnetic field
Yanagisawa, T.; Mombetsu, S.; Hidaka, H.; Amitsuka, H.; Cong, P. T.; Yasin, S.; Zherlitsyn, S.; Wosnitza, J.; Huang, K.; Kanchanavatee, N.; Janoschek, M.; Maple, M. B.; Aoki, D.
The elastic properties of URu2Si2 in the high magnetic field region above 40 T, over a wide temperature range from 1.5 to 120 K, were systematically investigated by means of high-frequency ultrasonic measurements. The investigation was performed at high magnetic fields to better investigate the innate bare 5f -electron properties, since the unidentified electronic thermodynamic phase of unknown origin, the so-called “hidden order” (HO), and associated hybridization of conduction and f electrons (c-f hybridization) are suppressed at high magnetic fields. From the three different transverse modes we find contrasting results; both the Γ4(B2g) and Γ5(Eg) symmetry modes C66 and C44 show elastic softening that is enhanced above 30 T, while the characteristic softening of the Γ3/B1g) symmetry mode (C11 - C12)/2 is suppressed in high magnetic fields. These results underscore the presence of a hybridization-driven Γ3(B1g) lattice instability in URu2Si2. However, the results from this work cannot be explained by using existing crystalline electric field schemes applied to the quadrupolar susceptibility in a local 5f2 configuration. Instead, we present an analysis based on a band Jahn-Teller effect.

Publ.-Id: 27472 - Permalink


Data for publication
Kluge, T.ORC; Rödel, M.; Metzkes, J.; Pelka, A.; Garcia, A. L.; Prencipe, I.; Rehwald, M.; Nakatsutsumi, M.; Mcbride, E. E.; Schönherr, T.; Garten, M.; Hartley, N. J.; Zacharias, M.; Erbe, A.; Georgiev, Y. M.; Galtier, E.; Nam, I.; Lee, H. J.; Glenzer, S.; Bussmann, M.; Gutt, C.; Zeil, K.; Rödel, C.; Hübner, U.; Schramm, U.; Cowan, T. E.

Raw data, lineouts and fits for the publication

  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-05-09
    DOI: 10.14278/rodare.23

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Publ.-Id: 27465 - Permalink


Synthesis and structural characterization of the first neptunium based metal-organic frameworks incorporating {Np6O8} hexanuclear cluster
Martin, N. P.ORC; März, J.; Feuchter, H.; Duval, S.; Roussel, P.; Henry, N.; Petricek, V.; Ikeda-Ohno, A.ORC; Loiseau, T.ORC; Volkringer, C.ORC
Successful synthesis of the first transuranium Metal-Organic Frameworks (MOFs) involving neptunium(IV) (Np(IV) is reported. These compounds were obtained from the controlled hydrolysis of Np(IV) in the presence of dicarboxylate ligands. The final structures contain the [Np6O4(OH)4(H2O)6]12+ unit, which were never cristallized before with tetravalent neptunium
Keywords: actinides, neptunium, metal-organic frameworks, carboxylate, coordination chemistry, structure, X-ray diffraction

Publ.-Id: 27442 - Permalink


Flow Measurements in a Liquid Metal Model for Continuous Casting of Steel
Schurmann, D.; Willers, B.; Eckert, S.; Hackl, G.; Nitzl, G.
Poster for the Graduate Student Poster Contest of the AISTech 2018 Conference in Philadelphia, USA.
Related publications
Gyro Nozzle – An innovative Submerged Entry Nozzle Design… (Id 27128) is supplemented by this publication
  • Poster
    AISTech 2018, 07.-10.05.2018, Philadelphia, USA

Publ.-Id: 27436 - Permalink


Origin and Manipulation of Stable Vortex Ground States in Permalloy Nanotubes
Zimmermann, M.; Gerhard-Meier, T. N.; Dirnberger, F.; Kákay, A.; Decker, M.; Wintz, S.; Finizio, S.; Josten, E.; Raabe, J.; Kronseder, M.; Bougeard, D.; Lindner, J.; Back, C. H.
We present a detailed study on the static magnetic properties of individual permalloy nanotubes (NTs) with hexagonal cross-sections. Anisotropic magnetoresistance (AMR) measurements and scanning transmission X-ray microscopy (STXM) are used to investigate their magnetic ground states and its stability. We find that the magnetization in zero applied magnetic field is in a very stable vortex state. Its origin is attributed to a strong growth-induced anisotropy with easy axis perpendicular to the long axis of the tubes. AMR measurements of individual NTs in combination with micromagnetic simulations allow the determination of the magnitude of the growth-induced anisotropy for different types of NT coatings. We show that the strength of the anisotropy can be controlled by introducing a buffer layer underneath the magnetic layer. The magnetic ground states depend on the external magnetic field history and are directly imaged using STXM. Stable vortex domains can be introduced by external magnetic fields and can be erased by radio-frequency magnetic fields applied at the center of the tubes via a strip line antenna.
Keywords: Nanotube, anisotropic magnetoresistance, permalloy, vortex, ground state

Publ.-Id: 27435 - Permalink


Functional thiols as repair and doping agents of defective MoS2 monolayers
Förster, A.; Gemming, S.; Seifert, G.
Recent experimental and theoretical studies indicate that thiols (R-SH) can be used to repair sulfur vacancy defects in MoS2 monolayers (MLs). This density functional theory (DFT) study investigates how the thiol repair mechanism process can be used to dope MoS2 MLs. Fluorinated thiols as well as amine-containing ones are used to p- and n-dope the MoS2 ML, respectively. It is shown that functional groups are only physisorbed on the repaired MoSS2 surface. This explains the reversible doping with fluorinated thiols.
Keywords: 2D materials, desnsity functional theory, DFT, defects, thiols, repair, doping, tuning

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  • Secondary publication expected from 17.05.2019

Publ.-Id: 27430 - Permalink


Freisetzung und Rückhaltung von Radionukliden in Systemen mit Zementphasen, Zuschlagstoffen und Tongestein.
Wolter, J.-M.; Philipp, T.; Schmeide, K.; Schymura, S.; Huittinen, N.; Stumpf, T.
Leaching experiments of uranium(VI) and Cm(III) doped calcium-silicate-hydrate (CSH) phases with various calcium to silicon ratios were carried out in NaCl, NaCl/Na2SO4, NaCl/NaHCO3 and NaHCO3 containing solutions to study the time-dependent release of Ca, Si, U and Cm. Potential changes of the U(VI) and Cm(III)-CSH binding induced by leaching were monitored with time-resolved laser-induced fluorescence spectroscopy (TRLFS), infrared spectroscopy (IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and powder X-ray diffraction (PXRD).
Furthermore, investigations of the Eu(III) sorption on Ca-bentonite in the presence of high ionic strengths and superplasticizer were carried out.
Additionally, the U(VI) binding to the Ca-bentonite surface in the hyper-alkaline pH region was studdied with EXAFS.
Keywords: Cm(III), U(VI), Eu(III), TRLFS, IR, EXAFS, PXRD, CSH, Ca-bentonite, NaCl, Na2SO4, NaHCO3, CaCl2
  • Lecture (others)
    6. Workshop des BMWi-Verbundvorhabens “Geochemische Radionuklidrückhaltung an Zementalterationsphasen (GRaZ)“, 25.-26.04.2018, Karlsruhe, Deutschland

Publ.-Id: 27425 - Permalink


Phytotoxicity of tin mine waste and accumulation of involved heavy metals in common buckwheat (Fagopyrum esculentum Moench)
Franzaring, J.; Damsohn, W.; Fangmeier, A.; Schlosser, S.; Kurz, H.; Büttner, P.
Extraction and processing of cassiterite (SnO2) left large tailings with high concentrations of tin, tungsten, molybdenum and lithium. Information on the phytotoxicity of mine waste is important with regard to ecological hazards. Exposure studies help to identify plants useful for the stabilization of waste tips and the phytomining of metals. A greenhouse study was performed using a dilution series of mine waste and four crops, a halophytic and a metallophytic species to derive dose response curves. Based on effective doses for growth reductions, sensitivity increased in the following order: maize > common buckwheat > quinoa > garden bean. Element analyses in different species and compartments of common buckwheat grown in a mixture of standard soil and 25% of the mine waste showed that only low levels of the metals were taken up and that transfer to seed tissues was negligible. As indicated by soil metal levels prior to and after the experiment, only lithium and arsenic proved to be plant available and reached high levels in green tissues while seed levels were low. The experiment confirmed differences in the uptake of metals with regard to elements and species. Common buckwheat is a suited candidate for cultivation on metal polluted soils. © 2018 Taylor & Francis Group, LLC.
Keywords: bioaccumulationdose-response, curvessoil, contaminationsoil, reclamation

Publ.-Id: 27420 - Permalink


Controlled Nickel Silicidation of Silicon Nanowires for Fabrication of Reconfigurable Field Effect Transistors
Khan, M. B.; Deb, D.; Georgiev, Y. M.; Prucnal, S.; Voelskow, M.; Erbe, A.
Physical scaling down of field effect transistors (FET) is reaching its end. To meet the consistent demand for faster, smaller and energy efficient transistors, new concepts which include new materials, new architectures, new computation principles and enhanced functionality are under research. Focus of this work is to fabricate devices with enhanced functionality, the so called reconfigurable FET (RFET) which can be configured as p- or n-channel FET. These FETs are realized by fabricating silicon nanowires (SiNWs) on Si on insulator (SOI) substrates. These NWs are subsequently nickel silicided at both ends to form
Si-NiSi2-Si Schottky junctions. Control over silicide length is important to scale Si channel and to have symmetric contacts on both sides of nanowires. Focus of our recent work is achieve this control over silicidation by using flash lamp annealing (FLA). Comparison between silicidation using flash lamp annealing (FLA) and rapid thermal annealing (FLA) along with the resulting electrical characteristics of these devices will be presented at the conference.
  • Poster
    DPG, 2018, 18.-23.03.2018, Berlin, Germany

Publ.-Id: 27418 - Permalink


Profiling of RT-PICLS Code
Kelling, J.; Juckeland, G.ORC

It was observed, that the RT-PICLS code ran by FWKT on the hypnos cluster was producing an unusual amount of system load, according to Ganglia metrics. Since this may point to an IO-problem in the code, this code was analyzed more closely.

RT-PICLS was run with additionally provided input data on 64 CPU cores (AMD Opteron) in a single node of the hypnos cluster. Score-P 4.0 with IO-tracing support was used for profiling and tracing of the application. A developer version of Vampir 9.2 [3] enabled graphical analysis of the traces.

Different file systems were evaluated for storing the output:

  • bigdata: the high-performance file system of the cluster based on GPFS.
  • nfs: a loop-mounted EXT4 image mounted to the current compute node via NFS.
  • scr: the local scratch file-system of the compute node.
  • tmpfs: a virtual filesystem, physically located in the main memory of the compute node.

The trace files that were used to compile the referenced report are collected in this upload.

Keywords: Scorep; Vampir; Tracing; Profiling
Related publications
Profiling of RT-PICLS Code (Id 25474) is a supplement to this publication
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-04-25
    DOI: 10.14278/rodare.15
    License: CC-BY-4.0

Downloads:

Publ.-Id: 27417 - Permalink


Time-delayed multiple shocks
Kraus, D.
Time-delayed multiple shocks
  • Invited lecture (Conferences)
    Workshop on Dynamic Laser Compression Experiments at the HED instrument at European XFEL, 12.-14.09.2016, Hamburg, Deutschland

Publ.-Id: 27416 - Permalink


Structural transitions in shock-compressed (hydro) carbon(s)
Kraus, D.
Structural transitions in shock-compressed (hydro) carbon(s)
  • Invited lecture (Conferences)
    Workshop on High Pressure, Planetary and Plasma Physics, 14.-16.09.2016, Hamburg, Deutschland

Publ.-Id: 27415 - Permalink


Phase separation of hydrocarbons at conditions relevant to planetary interiors and the first shock in ICF
Kraus, D.
Phase separation of hydrocarbons at conditions relevant to planetary interiors and the first shock in ICF
  • Invited lecture (Conferences)
    4th High Power Laser Workshop, 03.-04.10.2016, Menlo Park, USA

Publ.-Id: 27414 - Permalink


Diagnostics of shock-compressed matter at X-ray facilities
Kraus, D.
The combination of pulsed high-energy lasers with highly brilliant X-ray sources has started to provide unprecedented in situ diagnostics of dynamically compressed materials. Combining various diagnostic techniques will be crucial in order to obtain an improved understanding of the extreme states of matter that are investigated in such experiments. This talk will discuss diagnostics that are planned for HPLF at ESRF in the context of other X-ray facilities that also provide high-energy laser systems.
  • Invited lecture (Conferences)
    2nd Workshop on "Studies of dynamically compressed matter with X-rays", 29.-30.03.2017, Grenoble, Frankreich

Publ.-Id: 27413 - Permalink


X-ray scattering and diffraction from samples driven by ultra-intense lasers
Kraus, D.
The combination of X-ray free electron lasers and ultra-intense optical lasers promises unprecedented opportunities to investigate matter at most extreme pressures and temperatures on ultra-short timescales, particularly accessing and resolving non-equilibrium dynamics. Recent experiments at LCLS and SACLA have demonstrated this great potential, but also identify certain technical challenges that need to be addressed for high-precision experiments. This talk will discuss exemplary X-ray diffraction and X-ray scattering results obtained with ultra-intense optical lasers at LCLS and SACLA.
  • Invited lecture (Conferences)
    Workshop on High Intensity Laser Science at the HED instrument at the European XFEL, 05.-06.04.2017, Hamburg, Deutschland

Publ.-Id: 27412 - Permalink


In situ investigation of nanodiamonds formed in shock compressed plastics
Kraus, D.
In situ investigation of nanodiamonds formed in shock compressed plastics
  • Invited lecture (Conferences)
    5th High-Power Laser Workshop, 27.-28.09.2017, Menlo Park, USA

Publ.-Id: 27411 - Permalink


Experimental Investigation of Diamond Precipitation inside Giant Planets
Kraus, D.; Vorberger, J.; Pak, A.; Hartley, N. J.; Fletcher, L. B.; Frydrych, S.; Galtier, E.; Gamboa, E. J.; Gericke, D. O.; Glenzer, S. H.; Granados, E.; Macdonald, M. J.; Mackinnon, A. J.; Mcbride, E. E.; Nam, I.; Neumayer, P.; Roth, M.; Saunders, A. M.; Schuster, A. K.; Sun, P.; van Driel, T.; Doeppner, T.; Falcone, R. W.
The effects of hydrocarbon reactions and diamond precipitation on the internal structure and evolution of icy giant planets like Neptune and Uranus have been discussed for more than three decades. Inside these celestial bodies, gravity compresses mixtures of light elements to densities of several grams per cubic centimeter while the temperature reaches thousands of kelvins resulting in thermal energies on the order of chemical bond energies and above. Under these conditions, simple hydrocarbons like methane, which are highly abundant in the atmospheres, are believed to undergo structural transitions that release hydrogen from deeper layers and may lead to compact stratified cores. Indeed, the isentropes of Uranus and Neptune intersect a temperature-pressure regime where first polymerization occurs, whereas in deeper layers, a phase separation into diamond and hydrogen may be possible. Here we show experimental evidence for this phase separation process obtained by in situ X-ray diffraction from polystyrene (C8H8)n samples dynamically compressed to conditions around 150 GPa and 5000 K, which resembles the environment ~10,000 km below the surfaces of Neptune and Uranus [1]. Our findings demonstrate the necessity of high pressures for initiating carbon-hydrogen demixing and imply that diamond precipitation may require ~10x higher pressures than previously suggested by static compression experiments. In addition to their relevance for planetary modelling, by showing the formation of nanodiamonds from laser-irradiated plastic, our results identify a possible method to produce diamond nanoparticles for material science and industrial applications.
  • Invited lecture (Conferences)
    55th European High Pressure Research Group Meeting, 04.-08.09.2017, Poznan, Polen

Publ.-Id: 27409 - Permalink


Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions
Kraus, D.
The effects of hydrocarbon reactions and diamond precipitation on the internal structure and evolution of icy giant planets such as Neptune and Uranus have been discussed for more than three decades. Inside these celestial bodies, simple hydrocarbons such as methane, which are highly abundant in the atmospheres, are believed to undergo structural transitions that release hydrogen from deeper layers and may lead to compact stratified cores. Indeed, from the surface towards the core, the isentropes of Uranus and Neptune intersect a temperature–pressure regime in which methane first transforms into a mixture of hydrocarbon polymers, whereas, in deeper layers, a phase separation into diamond and hydrogen may be possible. Here we show experimental evidence for this phase separation process obtained by in situ X-ray diffraction from polystyrene, PET ant PMMA samples dynamically compressed to conditions around 150 GPa and 5,000 K; these conditions resemble the environment around 10,000 km below the surfaces of Neptune and Uranus. Our findings demonstrate the necessity of high pressures for initiating carbon–hydrogen separation and imply that diamond precipitation may require pressures about ten times as high as previously indicated by static compression experiments. Our results will inform mass–radius relationships of carbon-bearing exoplanets, provide constraints for their internal layer structure and improve evolutionary models of Uranus and Neptune, in which carbon–hydrogen separation could influence the convective heat transport. In addition to their relevance for planetary modelling, by showing the formation of diamonds that are possibly a few nanometers in size from laser-irradiated plastic, our results may identify a new method to produce diamond nanoparticles for material science and industrial applications.

*We acknowledge support by the U.S. DOE under awards DE-FG52-10NA29649 and DE-NA0001859 as well as the Helmholtz Association under award VH-NG-1141.
  • Invited lecture (Conferences)
    APS March Meeting, 05.-09.03.2018, Los Angeles, USA

Publ.-Id: 27406 - Permalink


Formation of diamonds in laser-compressed hydrocarbons at planetary interior conditions
Kraus, D.
High-energy laser systems can be used to mimic extreme states of matter, as found in the interior of various celestial bodies, in the laboratory. Combining such laser systems with extremely bright X-ray sources, particularly X-ray free electron lasers (XFELs), allows for studying exotic physical processes in real-time. This includes high-pressure phase separation reactions, such as diamond precipitation from liquid hydrocarbons, which has been predicted to happen deep inside Neptune and Uranus, and many other interesting phenomena.

At the Linac Coherent Light Source (LCLS), we obtained experimental results from hydrocarbon samples that were laser-compressed to the extreme pressure and temperature conditions found in the deep interiors of such ‘icy’ giant planets [1]. The extreme brightness of the XFEL source enables unprecedented in situ snapshots of the induced chemical reactions and shows that diamond nucleation is initiated on sub-nanosecond timescales at ~150 GPa and ~5000 K. Combining several X-ray and optical diagnostic methods, we obtain high-quality constraints for theoretical models of the involved physical processes: X-ray diffraction records the formation of solid diamond structures, Small angle X-ray scattering determines the size distribution of the growing nanodiamonds while spectrally resolved X-ray scattering provides an absolute scale for the diffraction pattern giving the absolute amount of the reacting material that undergoes species separation. Optical velocimetry is used to characterize and optimize the laser-driven compression waves and optical reflectometry indicates that the isolated hydrogen produced by the phase separation reaction is in a metallic state. All these diagnostics can be used with single-shot quality in the same experiment and provide unprecedented insights into the nanosecond kinetics of chemical reactions at extreme pressures and temperatures.

Besides underlining the general importance of chemical processes inside giant planets, our results
will inform mass-radius relationships of carbon-bearing exoplanets, provide constraints for their internal layer structure and improve evolutionary models of Uranus and Neptune, where carbon-hydrogen separation could significantly influence the convective heat transport. Finally, our experiments may identify a new method to produce diamond nanoparticles for material science and
industrial applications.

[1] D. Kraus et al., Nature Astronomy 1, 606-611 (2017)
  • Invited lecture (Conferences)
    European XFEL Users Meeting, 22.-25.01.2018, Hamburg, Deutschland

Publ.-Id: 27405 - Permalink


A Maximum-Likelihood Timing Resolution Estimation algorithm for TOF-PET
Nikulin, P.ORC; Lougovski, A.; Hofheinz, F.ORC; Maus, J.ORC; van den Hoff, J.ORC
Timing resolution in time-of-flight (TOF) PET is known to be to a different extend count-rate dependent, while using the actual timing resolution during TOF-PET image reconstruction is crucial for achieving high contrast recovery. However, a count-rate dependent TOF-resolution calibration procedure is usually not provided by the vendor. We therefore developed such a procedure which is compatible with clinical routine and is also applicable retrospectively to existing data.

We propose a novel Maximum-Likelihood Timing Resolution Estimation algorithm that maximizes likelihood by updating activity image and TOF-kernel width alternately. For activity update TOF-MLEM was used and quadratic surrogate based maximization of the likelihood was performed to update timing resolution.

The algorithm was integrated into our previously developed reconstruction tool THOR, see ref. (1), and evaluated using the Philips Ingenuity TF PET/MR scanner and phantom and patient studies covering a large range of count-rates. Studies were grouped by imaging protocol ("brain" and "whole-body", covering different transaxial fields of view). Within each group a linear dependency of timing resolution on count-rate was observed which is in correspondence with reports by other groups. The timing resolution degradation value approaches 150 ps (~25% of initial TOF-kernel width) for clinical relevant count-rates. No difference in estimated timing resolution between the study groups was encountered.

Our preliminary results indicate that the proposed algorithm is capable of realistic timing resolution estimation. The timing resolution of the Philips Ingenuity TF PET/MR degrades rapidly with count-rate. This should be accounted for during image reconstruction.

(1) A. Lougovski, F. Hofheinz, J. Maus, et al., Physics in Medicine and Biology 59(3), 561 (2014)
Keywords: PET, MLEM, MLTRE, image reconstruction, TOF-PET, calibration, TOF-resolution
  • Poster
    56. Jahrestagung der Deutschen Gesellschaft für Nuklearmedizin, 18.-21.04.2018, Bremen, Deutschland

Publ.-Id: 27403 - Permalink


Characterization of the cesium sputter ion source for the new Felsenkeller 5 MV underground accelerator
Ludwig, F.; Koppitz, M.; Bemmerer, D.; Zuber, K.
In order to determine the cross section of the ¹²C(α,γ)¹⁶O reaction at astrophysically relevant energies, an accelerator with a stable and intensive ¹²C ion beam in an ultra low background environment is needed. For this purpose a 134-MC-SNICS cesium sputter ion source is going to be part of the Felsenkeller shallow underground accelerator facility. To determine the characteristics of this ion source overground tests were undertaken at HZDR. The contribution will report on long time measurements of the ion current and the beam emittance.
  • Lecture (Conference)
    DPG Frühjahrstagung, 26.02.-02.03.2018, Bochum, Deutschland

Publ.-Id: 27402 - Permalink


Prognostische Relevanz von FDG-PET/CT-basierten Biomarkern bei Kopf-Hals-Tumoren: Total Lesion Glycolysis (TLG) übertrifft klinische Parameter
Weidt, D.; Spanier, G.; Meier, J.; Hofheinz, F.; Reichert, T.; Hellwig, D.; Grosse, J.
Ziel/Aim:
Ziel der retrospektiven Studie war die Evaluation der prognostischen Relevanz der FDG-PET/CT-basierten Biomarker maximaler und mittlerer SUV (SUVmax, SUVmean), metabolisches Tumorvolumen (MTV) und total lesion glycolysis (TLG) im Primarius bei Erstdiagnose eines oralen Plattenepithelkarzinoms (OSSC). Der Einfluss auf das Gesamtüberleben (OS) wurde mit etablierten Prognoseparametern verglichen.

Methodik/Methods:
Einschluss von 127 Patienten mit zwischen 2006 und 2013 bioptisch gesichertem OSCC und präoperativer FDG-PET/CT (3 MBq/kg Körpergewicht, Start 60 min p.i., Biograph 16, Siemens). Messung von SUVmax, SUVmean, MTV (Schwellenwert: 41% SUVmax) und TLG im Primarius mittels ROVER (ABX, Radebeul). Berechnung des OS nach Kaplan-Meier. Analyse prognostischer Parameter mit uni-/multivariater Cox-Regression.

Ergebnisse/Results:
In der Nachbeobachtung starben 52 (41%) der Patienten (Status aller Patienten über mindestens 36 Monate bekannt). Das mediane OS war länger bei geringerem MTV (≤5,3 ml: >95 Monate; >5,3 ml: 59 Monate; p=0,006) oder TLG (≤38,7 g: 95 Monate; >38,7 g: 47 Monate; p<0,001). SUVmax und SUVmean hatten keinen Einfluss auf das OS (p>0,05). Die univariate Cox-Regression identifizierte MTV (Hazard Ratio [HR]=2,260, p=0,005), TLG (HR=2,808, p=0,001), Lymphknoten (LK)-Status (HR=2,234, p=0,005) und UICC-Stadium (HR=2,095, p=0,021) als Prognosefaktoren, nicht jedoch Geschlecht, Alter (>60 J), oder Tabak-/Alkoholabusus. Multivariat erwiesen sich nur MTV (HR=1,991, p=0,019) und TLG (HR=2,808, p=0,001) als unabhängige Prognosefaktoren.

Schlussfolgerungen/Conclusions:
MTV und TLG des Primarius sind Prognosefaktoren für das OS bei Patienten mit Erstdiagnose eines OSCC. TLG ist der stärkste unabhängige Prognosefaktor für das OS und übertrifft etablierte klinische Parameter.
  • Lecture (Conference)
    Jahrestagung der DGN, 19.-21.04.2018, Bremen, Deutschland

Publ.-Id: 27394 - Permalink


Assessment of in vivo PET quantification accuracy using image derived arterial blood SUVs
Maus, J.ORC; Hofheinz, F.; Apostolova, I.; Kreissl, M. C.; Kotzerke, J.; van den Hoff, J.
Aim: Accurate calibration is a prerequisite for SUV quantification in PET and usually performed via phantom measurements. However, such a calibration is only valid for the used phantom since attenuation and scatter correction limitations affect quantification accuracy (QA) in-vivo. In recent studies in-vivo QA was assessed using bladder image vs. urine samples comparisons and showed a systematic underestimate of SUVs when relying on phantom-based calibration. A notable disadvantage of this approach is that it requires additional effort, making it unattractive for clinical use. The goal of this work was evaluation of an alternative method utilizing image-derived arterial blood SUVs (BSUV) averaged over a sufficiently large number of subjects.

Methods: We analyzed 681 patient scans from 3 sites which underwent routine 18F-FDG PET/CT or PET/MR. BSUVs were determined in the descending aorta using a roughly cylindrical ROI (delineated in the attenuation image and spatially transferred to PET). Minimum ROI volume was 5 mL and a safety margin used to avoid partial volume effects. Mean BSUVs, standard deviation (SD), and standard error of the mean (SEM) were computed for subgroups corresponding to 3 scanner calibrations of each site (9 subgroups, n=54–100). Intra- and inter-site variability was computed.

Results: Relative SD (SEM) of BSUV in the subgroups ranged 14.3%–20.7% (2.8%–4.8%). BSUV-differences between intra-site groups were 1.8%–6.4% and mostly (5/6) insignificant. Inter-site BSUV-differences were significant and much larger (12.6%–25.1%, P<0.001).

Conclusions: Due to low inter-site BSUV-variability, group-averages can be computed with high statistical accuracy (<5%) in groups of ~70 patients and used for comparison of relative in-vivo QA. For multi-center trials this method can reveal inter-site differences at the 10% level and might even be used to calibrate image data between sites.
Keywords: PET; quantification; blood SUV; standardization; multicenter; in vivo
Related publications
Monitoring scanner calibration using the image derived… (Id 27358) is supplemented by this publication

Publ.-Id: 27391 - Permalink


An Overview of High Energy Density Sciences in HiBEF Project
Huang, L. G.
This talk will give an overview of high energy density (HED) researches in the frame of Helmholtz International Beamline for Extreme Fields (HiBEF) project leading by the Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The HiBEF user consortium is aiming to contribute and operate different experimental setups at the HED beamline of the European XFEL with worldwide unique ultrashort and extremely bright X-ray flashes.
Three main kinds of HED experiments including relativistic laser solid targets interactions to understand the plasma heating and ionization dynamics, high energy long pulse laser shocked warm dense matters to understand the stellar structures, intense XFEL-matter interactions to understand the effect of crystal structure on the rapidly melting and heating process performed by our group at LCLS and SACLA will be reviewed in this talk. All these experiments take advantages of the ultra-short and intense coherent XFEL beam as a probe to achieve nanometer and femtosecond resolutions simultaneously. Furthermore, to design and under the HED experiments, we will also present the theoretical and simulation studies based on the particle-in-cell (PIC) code, atomic collisional- radiative code and density function theory (DFT) code.
Keywords: High Energy Density; HiBEF; XFEL; High Power Laser; High Energy Laser.
  • Invited lecture (Conferences)
    The 3rd International symposium series on High Power Laser Science and Engineering, 09.-13.04.2018, Suzhou, China

Publ.-Id: 27388 - Permalink


Activation of acceptor levels in Mn implanted Si by pulsed laser annealing
Li, L.; Bürger, D.; Shalimov, A.; Kovacs, G. J.; Schmidt, H.; Zhou, S.
In this paper, we report the magnetic and electrical properties of Mn implanted nearly intrinsic Si wafers after subsecond thermal treatment. Activation of acceptors is realized in pulsed laser annealing (PLA) films with a free hole concentration of 6.29  ×  10^20 cm−3 while the sample annealed by rapid thermal annealing (RTA) shows n-type conductivity with a much smaller free electron concentration in the order of 10^15 cm−3. Ferromagnetism is probed for all films by a SQUID magnetometer at low temperatures. The formation of ferromagnetic MnSi1.7 nanoparticles which was proven in RTA films can be excluded in Mn implanted Si annealed by PLA.

Downloads:

  • Secondary publication expected from 19.03.2019

Publ.-Id: 27387 - Permalink


Importance of austenitization temperature and ausforming on creep strength in 9Cr ferritic/martensitic steel
Vivas, J.; Capdevila, C.ORC; Altstadt, E.ORC; Houska, M.; San-Martin, D.
Small Punch Creep technique was used as a screening procedure to evaluate the creep properties of different microstructures developed in a thermomechanical simulator. The goal seek was to generate alternative microstructures in a conventional ferritic-martensitic G91 steel grade which boost thermal stability at temperatures as high as 700ºC. The developed microstructures allow studying the effect of the austenitization temperature optimized by thermodynamic calculations and the ausforming on the creep strength and ductility. The improvement in creep strength recorded was attributable to a higher number density of MX precipitates. By contrast, these microstructures showed an important reduction in creep ductility.
Keywords: Small Punch Creep Tests; MX nanoprecipitates; creep ductility; ausforming; creep resistant steels

Downloads:

  • Secondary publication expected from 01.05.2019

Publ.-Id: 27383 - Permalink


The multi-purpose electron accelerator ELBE and its applications, with a focus on THz spectroscopy
Helm, M.
I will introduce the superconducting electron accelerator ELBE (Electron Linear accelerator with high Brilliance and low Emittance) as a source for different types of secondary radiation, including low- (meV) and high- (MeV) energy photons, positrons and neutrons. Being a solid-state spectroscopist, I will then focus on research we have performed using the terahertz free-electron laser FELBE. Here the high peak power can be employed for nonlinear optical experiments in the THz range, whereas the picosecond pulse structure enables time-resolved studies of relaxation processes.
Keywords: electron accelerator, free electron laser, THz spectroscpy
  • Lecture (others)
    Kolloquium am Max-Planck-Institut für Plasmaphysik (IPP), 19.04.2018, Munich, Germany

Publ.-Id: 27382 - Permalink


Agile Software Development using GitLab and GitLab CI
Juckeland, G.ORC; Frust, T.ORC
This talk presents how the GitLab Community Edition installation at HZDR is used to map components of agile programming and also motivates why most scientific programming is agile.
  • Lecture (Conference)
    SEI-Tagung 2018, 16.-18.04.2018, Dresden, Deutschland

Publ.-Id: 27373 - Permalink


Superior electrical conduction of a water repelling 3D interconnected nano-network
Dhal, S.; Das, P.; Rajbhar, M. K.; Chatterjee, S.; Möller, W.; Chatterjee, S.; Ramgir, N.
A three-dimensional (3D) network of interconnected nanowires of functional materials possesses huge potential for device fabrication since it hinders sluggish interfacial charge carrier transport owing to reduced contact resistance. In the present work, the formation of a highly porous 3D interconnected nano-network by Na+ ion irradiation is demonstrated. The mechanism of solid junction formation at very low energy is established using the results obtained from TRI3DYN computer simulation studies. The formation of a 3D interconnected network resulted in a significant improvement in the electrical conduction as compared to that observed for the pristine nanotube mesh. Further, contact angle measurement shows a transition from "superhydrophilic" nature, as observed for pristine nanotubes, to "superhydrophobic" nature for the 3D nano-network. The superhydrophobicity of the 3D nano-network is expected to find application in miniaturized electronic devices, wherein water condensation and related effects such as short-circuits and erroneous signal output can be significantly minimized.

Publ.-Id: 27370 - Permalink


Nanofabrication activities at HZDR
Georgiev, Y. M.ORC
During this talk I will first briefly introduce the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the Institute of Ion Beam Physics and Materials Research as well as the Ion Beam Centre as a user facility run by the Institute.

Next, I will present some of the equipment available at the nanofabrication facility in Rossendorf (NanoFaRo), in particular electron beam lithography (EBL) systems as well as tools for thin film deposition and reactive ion etching (RIE), paying special attention on their capabilities.

I will then go through the most important nanofabrication projects, both internal and external, run lately at NanoFaRo, including top-down fabrication and electrical characterisation of silicon (Si) nanowire (NW) reconfigurable field effect transistors (RFETs) together with detailed study of nickel (Ni) silicidation of Si NWs; top-down fabrication of a large number of gratings with different periodicity on 2 µm thick Si membranes for laser targets; electrical contacting of randomly distributed nanostructures (bottom-up grown VO2 and hyperdoped Si NWs, DNA origami, flakes of 2D materials, etc.); top-down fabrication of four-terminal Si NW test devices for modulation doping experiments; nanopatterning of polymer brushes by reactive writing with EBL; bevel formation by EBL and RIE for dopant/conductance profiling of thin films and NWs by conductive atomic force microscopy (C-AFM); top-down fabrication of Si NWs hyperdoped with selenium (Se) as well as of plasmonic antennas on Si hyperdoped with tellurium (Te); fabrication and electrical characterisation of FETs on 2D materials, etc. Concluding this part of my talk, I will draw your attention to some highlights of our activities, focussing mostly on processes for high-resolution patterning as well as on high-precision electrical contacting of randomly distributed nanostructures.

Finally, I will discuss possibilities for collaboration between HZDR and UCC/Tyndall in the field of our activities.
Keywords: nanofabrication, electron beam lithography, reactive ion etching, silicon nanowires, reconfigurable field effect transistors, nickel silicidation, silicon gratings, silicon membranes, laser targets, DNA origami, 2D materials, conductive atomic force microscopy, hyper doped silicon nanowires, plasmonic antennas
  • Lecture (others)
    Seminar of the School of Chemistry, University College Cork, 22.03.2018, Cork, Ireland

Publ.-Id: 27368 - Permalink


Group IV Semiconductor Nanowires for Sensing and Nanoelectronic Applications
Georgiev, Y. M.ORC
During the last decade, semiconductor nanowires (NWs) have received significant academic and commercial attention due to their attractive electrical and mechanical properties and large surface area to volume ratios. They have a variety of possible applications including nanoelectronics, nanophotonics, photovoltaics, sensorics, etc. Among all semiconductor NWs the ones based on group IV materials have the added value of being the most silicon (Si) compatible. This would allow their relatively easy integration into the existing semiconductor technology platform.

In my talk I will first present the NWs that we are working with. These include top-down fabricated Si and germanium (Ge) NWs having widths down to 6-7 nm as well as bottom-up grown alloyed germanium-tin (Ge1-xSnx) NWs with x = 0.07-0.1, diameters of 50-70 nm and lengths of 1 to 3 µm. In the future we plan to work also with alloyed SiGe and SiGeSn NWs with varying content of the different materials.

I will next discuss the innovative devices that we are targeting, namely junctionless nanowire transistors (JNTs) and reconfigurable field effect transistors (RFETs). In particular, we are interested in Si JNTs for sensing application as well as in Ge and GeSn JNTs for digital logic. Concerning RFETs, we are currently working on Si RFETs and commencing activities on Ge RFETs. In the future we are planning to work also on GeSn RFETs.

Finally, I will pay a special attention to a novel device that we recently invented: group IV heterostructure band-to-band tunnel FET (TFET). We are planning to fabricate this device with a scalable and fully CMOS compatible process and expect it to demonstrate high Ion together with low Ioff and hence steep subthreshold slopes.
Keywords: semiconductor nanowires, nanoelectronics, silicon, germanium, germanium-tin, junctionless nanowire transistors, reconfigurable field effect transistors, heterostructure band-to-band tunnel field effect transistors
  • Lecture (others)
    Science Meets Industry, 08.03.2018, Dresden, Germany

Publ.-Id: 27367 - Permalink


Formation of a new type of {U38} cluster based on a controlled release of water via esterification reaction
Martin, N. P.ORC; Volkringer, C.ORC; Henry, N.; Trivelli, X.; Stoclet, G.; Ikeda-Ohno, A.ORC; Loiseau, T.ORC
A new strategy for the synthesis of large poly-oxo cluster bearing 38 tetravalent uranium atoms {U38} has been developed by controlling the water release from the esterification reaction between carboxylic acid and alcohol. The molecular entity [U38O56Cl40(H2O)2(ipa)20]·(ipa)x (ipa = isopropanol) was crystallized from the solvothermal reaction of the mixture of UCl4 and benzoic acid in isopropanol at temperature ranging from 70 to 130°C. Its crystal structure reveals the molecular assembly of the UO2 fluorite-like inner core {U14} with oxo groups bridging the uranium centers. The {U14} core is further surrounded by six tetrameric sub-units of {U4} to form the {U38} cluster. Its surface is decorated by either bridging- and terminal chloride anions or terminal isopropanol molecules. Another synthesis using the same reactant mixture at a room temperature resulted in the crystallization of discrete dinuclear complex [U2Cl4(bz)4(ipa)4] (bz = benzoate), in which each uranium center is coordinated by two chlorine atoms, four oxygen atoms from carboxylate groups and two additional oxygen atoms from isopropanol. The slow production of water released from the esterification of isopropanol allows the formation of the giant cluster with oxo bridges linking the uranium atoms at a temperature above 70°C, whereas no such oxo groups are present in the dinuclear complex formed at a room temperature. The kinetic of {U38} crystallization as well as the ester formation are analyzed and discussed. SAXS experiments indicate that the {U38} species are not dominant in the supernatant, but hexanuclear entities which are closely related to the [U6O8] type are formed.
Keywords: Actinides, uranium, cluster, polymer, coordination, solid-state chemistry, structure characterisation, solution speciation

Publ.-Id: 27366 - Permalink


Bentonite – a natural source for sulfate-reducing bacteria
Matschiavelli, N.; Kluge, S.; Cherkouk, A.
In order to analyze the potential influence of natural occuring microorganisms within the bentonite on the properties of the bentonite barrier, we set up microcosm-experiments. Two different Bavarian bentonites (a natural and an industrial one) were supplied with an anaerobic, synthetic Opalinus-clay pore water solution under an N2/CO2-atmosphere and were incubated for one year at 30 °C and 60 °C. To some set ups organics (acetate or lactate) or H2 were supplemented. During the incubation time samples were analyzed for several biogeochemical parameters and the evolution of microbial community.
Our results clearly demonstrate, that natural occuring microbes affect geochemical parameters. Set ups containing the industrial bentonite supplemented with lactate or H2 show the most striking effects. The respective batches were dominated (up to 81 %) by Desulfosporosinus spp. after 6 months – spore-forming, strictly anaerobic, sulfate-reducing organisms, able to survive under very harsh conditions. Concomitantly, an increase of ferrous iron and a simoultaneous decrease of ferric iron was observed as well as a decrease in sulfate – alterations that could effect different properties of and reactions within the barrier system of an HLW.
Keywords: Bentonite, sulfate-reduction, Desulfosporosinus spp.
  • Lecture (Conference)
    MIND-Project Annual Meeting 2018, 07.-09.05.2018, Lausanne, Switzerland

Publ.-Id: 27362 - Permalink


Shibboleth-Authenticator for Invenio
Frust, T.ORC

The shibboleth-authenticator module for Invenio provides web browser single sign-on via the SAML protocol. It is based on the python3-saml module and supports the usage of multiple identity providers at the same time.


Related publications
Invenio Shibboleth-Authenticator (Id 26045) is identical to this publication
  • Software in the HZDR data repository RODARE
    Publication date: 2018-04-18
    DOI: 10.14278/rodare.13
    License: GPL-3.0

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Publ.-Id: 27360 - Permalink


Monitoring scanner calibration using the image derived arterial blood SUV in whole-body FDG-PET
Maus, J.ORC; Hofheinz, F.; Apostolova, I.; Kreissl, M. C.; Kotzerke, J.; van den Hoff, J.
Background:
The current de facto standard for quantification of tumor metabolism in oncological whole-body PET is the standardized uptake value (SUV) approach. SUV determination requires accurate scanner calibration. Residual inaccuracies of the calibration lead to biased SUV values. Especially, this can adversely affect multicenter trials where it is difficult to ensure reliable cross-calibration across participating sites. The goal of the present work was the evaluation of a new method for monitoring scanner calibration utilizing the image-derived arterial blood SUV (BSUV) averaged over a sufficiently large number of whole-body FDG-PET investigations.

Data of 681 patients from three sites which underwent routine 18F-FDG PET/CT or PET/MR were retrospectively analyzed. BSUV was determined in the descending aorta using a three-dimensional ROI concentric to the aorta’s centerline. The ROI was delineated in the CT or MRI images and transferred to the PET images. A minimum ROI volume of 5 mL and a concentric safety margin to the aortic wall was observed. Mean BSUV, standard deviation (SD), and standard error of the mean (SE) were computed for three groups of patients at each site, investigated 2 years apart, respectively, with group sizes between 53 and 100 patients. Differences of mean BSUV between the individual groups and sites were determined.

Results: SD (SE) of BSUV in the different groups ranged from 14.3 to 20.7% (1.7 to 2.8%). Differences of mean BSUV between intra-site groups were small (1.1–6.3%). Only one out of nine of these differences reached statistical significance. Inter-site differences were distinctly larger (12.6–25.1%) and highly significant (P<0.001).

Conclusions: Image-based determination of the group-averaged blood SUV in modestly large groups of whole-body FDG-PET investigations is a viable approach for ensuring consistent scanner calibration over time and across different sites. We propose this approach as a quality control and cross-calibration tool augmenting established phantom-based procedures.
Keywords: PET; Quantification; Blood SUV; Standardization; Multicenter; In vivo
Related publications
Assessment of in vivo PET quantification accuracy using… (Id 27391) is a supplement to this publication

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  • Secondary publication expected

Publ.-Id: 27358 - Permalink


Massive Parallel Computing on GPU Architectures
Frust, T.ORC
Graphics processing units (GPU) have evolved to massively parallel processors for general-purpose computing during the last couple of years. They are now available in small and energy-efficient embedded systems, too. This talk gives a brief overview about GPU computing and introduces the NVIDIA Jetson platform as an example for a GPU powered embedded system.
Keywords: GPU; Embedded systems; Parallel computing
  • Lecture (others)
    TOMOCON Kick-Off Meeting, 18.04.2018, Technische Universtität Dresden, Deutschland

Publ.-Id: 27357 - Permalink


Research Data Management
Frust, T.ORC
The importance of research data and research data management (RDM) in the research lifecycle is growing. This talk provides an overview about data management in research projects. The goal is to make research data FAIR (Findable, Accessible, Interoperable and Retrievable) by starting early with a Data Management Plan (DMP) and making research data available in appropriate data repositories.
Keywords: Data Management; Data Management Plan; FAIR; RODARE; Zenodo
  • Lecture (others)
    TOMOCON Kick-Off Meeting, 18.04.2018, Technische Universität Dresden, Deutschland

Publ.-Id: 27356 - Permalink


Liquid metal batteries - activities at the Helmholtz-Zentrum Dresden - Rossendorf
Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Stefani, F.; Weber, N.
The talk will provide an overview of the liquid metal battery (LMB) related activities at Helmholtz-Zentrum Dresden - Rossendorf (HZDR) with a focus on magnetohydrodynamic aspects of future large scale LMBs. High current densities in the range of 4 up to 130 kA/m-2, as typical for LMBs, together with cells of large cross section will result in substantial currents accompanied by considerable magnetic fields. Thus electromagnetically driven flows and instabilities should be of concern for large enough installations, especially when the thin electrolyte layers necessitated by the limited open circuit voltages are taken into account. Beneficial effects of mild electromagnetically driven flows are to be expected for the cathodes were mixing should improve cell performance.
Keywords: liquid metal batteries, magnetohydrodynamics, Tayler instability, sloshing
  • Lecture (others)
    Seminar, 12.04.2018, Cambridge, United Kingdom

Publ.-Id: 27354 - Permalink


Liquid metal batteries - stationary storage for fluctuating renewable energy sources
Weier, T.; Horstmann, G. M.; Landgraf, S.; Nimtz, M.; Stefani, F.; Weber, N.
Liquid metal batteries are introduced as a potential means to future economic large-scale electricity storage indispensable for energy systems with high penetration of fluctuating sources. The talk will concentrate on the role of electrodynamics and fluid mechanics in the design of large single cells, discussing a few instability mechanisms that should be taken into account.
Keywords: liquid metal batteries, magnetohydrodynamics, instabilities
  • Invited lecture (Conferences)
    Battery Application and Energy Storage, 11.04.2018, London, United Kingdom

Publ.-Id: 27353 - Permalink


Layer-by-Layer assembly of heparin and peptide-polyethylene glycol conjugates to form hybrid nanothin films of biomatrices
Thomas, A. K.; Wieduwild, R.; Zimmermann, R.; Lin, W.; Friedrichs, J.; Bickle, M.; Fahmy, K.; Werner, C.; Zhang, Y.
We investigated the utility of a heparin/peptide-polyethylene glycol conjugate system to build Layer-by-Layer (LbL) structures, to assemble tailored multilayer-biomatrices for cell culture. The LbL assembly balances the advantages of polyelectrolyte systems and protein-based systems. Human umbilical vein endothelial cells showed distinct responses to: the film thickness and structure; the presence, density and spatial arrangement of a cell adhesion ligand within the nanothin film; and the pretreatment of the film with morphogens. The LbL technique presents a versatile tool for modifying cell culture substrates with defined and diverse biochemical and structural features, for investigating cell-material interactions.
Keywords: extracellular matrix, layer-by-layer, nano thin, heparin, biomimetic, Fourier transform infrared

Publ.-Id: 27352 - Permalink


Influence of thin film morphology and stacking sequence on Ni-catalyzed graphitization of thin amorphous carbon films
Janke, D.; Wenisch, R.; Munnik, F.; Julin, J.; Hübner, R.; Gemming, S.; Rafaja, D.; Krause, M.
Metal-induced crystallization with layer exchange (MIC w LE) reduces the crystallization temperature of group 14 elements significantly. This is especially interesting for device fabrication on substrates with limited thermal stability. In this contribution, MIC w LE is applied on Ni and C thin film stacks with different stacking sequences. The influence of the thin film morphology and stacking on the layer exchange degree αLE and the graphitic ordering is studied comprehensively in situ and ex situ.
During annealing of the thin films at up to 700 °C, film morphology and stacking sequence had a significant impact on αLE, showing an incomplete LE for the C/Ni stack. The highest αLE of 96%, determined by RBS and ERDA, was achieved for the smoothest samples and Ni/C stacking sequence. Raman spectroscopy and TEM demonstrated the formation of 2D crystalline carbon structures independently of the stacking sequence, while the degree of graphitic ordering increased with decreasing surface roughness. The simultaneous occurrence of LE and graphitization has been demonstrated in situ by RBS and Raman, giving insights into mechanism responsible for carbon crystallization in this system.
Keywords: metal-induced crystallization, layer exchange, amorphous carbon, Rutherford backscattering spectrometry, Raman spectroscopy, elastic recoil detection
  • Poster
    International Winterschool on Electronic Properties of Novel Materials, 17.-24.03.2018, Kirchberg in Tirol, Österreich

Publ.-Id: 27337 - Permalink


Data set to illustrate advanced process-synchronized computed tomography for the investigation of periodic processes
Bieberle, A.; Neumann, M.

This data set contains raw data and data read-in routines used for the publication:
"Advanced process-synchronized computed tomography for the investigation of periodic processes"

Object of investigation: A centrifugal pump that impeller rotates at 1480 rpm and that is operated in gas-liquid two phase flow.
Used CT imaging system: HireCT (high resolution gamma-ray computed tomography) scanner of the HZDR

Keywords: Tomographic imaging, synchronized data acquisition, multiphase flow, centrifugal pump
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-04-12
    DOI: 10.14278/rodare.7
    License: CC-BY-4.0

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Publ.-Id: 27335 - Permalink


Fabrication of Y128-and Y36-cut lithium niobate single-crystalline thin films by crystal-ion-slicing technique
Shuai, Y.; Gong, C.; Bai, X.; Wu, C.; Luo, W.; Böttger, R.; Zhou, S.; Tian, B.; Zhang, W.
Y128- and Y36-cut single-crystalline lithium niobate (LN) thin films are fabricated by the crystal-ion-slicing (CIS) technique onto LN substrates. The conditions for the successful exfoliation of submicron-thick LN thin films are independent of the wafer orientation used in the present work. Wafer bonding using benzocyclobutene (BCB) is adopted to transfer LN thin films onto substrates, instead of the generally used hydrophilic bonding, which does not need a strict surface polishing process before the bonding. A noncontact polishing method involving low-energy Ar+ irradiation is adopted to treat the sliced LN thin films. The atomic force microscopy result shows that the surface roughness of the LN thin film is reduced from 10.6 to 6.4nm.
Keywords: Lithium niobate, Crystal-ion-slicing, ion implantation

Publ.-Id: 27334 - Permalink


Heavy doping of CdTe single crystals by Cr ion implantation
Popovych, V. D.; Böttger, R.; Heller, R.; Zhou, S.; Bester, M.; Cieniek, B.; Mroczka, R.; Lopucki, R.; Sagan, P.; Kuzma, M.
Implantation of bulk CdTe single crystals with high fluences of 500 keV Cr+ ions was performed to achieve Cr concentration above the equilibrium solubility limit of this element in CdTe lattice. The structure and composition of the implanted samples were studied using secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) to characterize the incorporation of chromium into the host lattice and to investigate irradiation-induced damage build-up. It was found that out-diffusion of Cr atoms and sputtering of the targets alter the depth distribution and limit concentration of the projectile ions in the as-implanted samples. Appearance of crystallographically oriented, metallic α-Cr nanoparticles inside CdTe matrix was found after implantation, as well as a strong disorder at the depth far beyond the projected range of the implanted ions.
Keywords: CdTe; Ion implantation; Doping; Irradiation-induced damage; Rutherford backscattering spectrometry; Secondary ion mass spectrometry

Publ.-Id: 27333 - Permalink


Luminescence in the Visible Region from Annealed Thin ALD‐ZnO Films Implanted with Different Rare Earth Ions
Ratajczak, R.; Guziewicz, E.; Prucnal, S.; Łuka, G.; Böttger, R.; Heller, R.; Mieszczynski, C.; Wozniak, W.; Turos, A.
Epitaxial ZnO thin films grown by atomic layer deposition on GaN/Al2O3 substrates are implanted with Yb, Dy, and Pr ions to a fluence of 5 x 10^14 at cm^2 and subseq uently anneals at 800 oC using a rapid thermal annealing (RTA) system. Structural prope rties of implanted and anneale d ZnO films and the optical respo nse are evaluated by channeling Rutherford backscattering (RBS/c) and photoluminescence spectroscopy (PL), respectively. RTA leads to a partial removal of the post-implantation defects with simultaneous native defects transformation and optical activation of RE ions. It is found that two groups of defects: defects formed during implantation process and native defects, play an important role in the luminescence in the visible region. The room temperature PL spectra obtained from annealed ZnO:RE films do not show sharp PL lines from transitions within the RE 4f shell, but show near band gap emission and defect related emission, which energy emission is controlled by the RE atoms. It suggests a presence of RE-related complexes that are formed during high-temperature annealing in oxygen atmosphere. The excitonic and defect emission modified by RE ions create an optical response of the system resulting in a specific color of the emitted light.
Keywords: ZnO, ALD, Luminescence, Rare Earth Ions, Ion Implantation

Publ.-Id: 27332 - Permalink


Improving depth resolutions in positron beam spectroscopy by concurrent ion-beam sputtering
John, M.; Dalla, A.; Ibrahim, A. M.; Anwand, W.; Wagner, A.; Böttger, R.; Krause-Rehberg, R.
The depth resolution of mono-energetic positron annihilation spectroscopy using a positron beam is shown to improve by concurrently removing the sample surface layer during positron beam spectroscopy. During ion beam sputtering with argon ions, Doppler-broadening spectroscopy is performed with energies ranging from 3 keV to 5 keV allowing for high-resolution defect studies just below the sputtered surface. With this technique, significantly improved depth resolutions could be obtained even at larger depths when compared to standard positron beam experiments which suffer from extended positron implantation profiles at higher positron energies. Our results show that it is possible to investigate layered structures with a thickness of about 4 microns with significantly improved depth resolution. We demonstrated that a purposely generated ion-beam induced defect profile in a silicon sample could be resolved employing the new technique. A depth resolution of less than 100 nm could be reached.
Keywords: positron annihilation spectroscopy ion-beam sputtering

Publ.-Id: 27328 - Permalink


Magnetic properties of Co/Ni grain boundaries after annealing
Coutts, C.; Arora, M.; Hübner, R.; Heinrich, B.; Girt, E.
Magnetic and microstructural properties of <111> textured Cu/Nx[Co/Ni] films are studied as a function of the number of bilayer repeats N and annealing temperature. M(H) loop measurements show that coercivity, Hc, increases with annealing temperature and that the slope of the saturation curve at Hc has a larger reduction for smaller N. An increase of the magnetic anisotropy (Ku) to saturation magnetization (Ms) ratio after annealing Nx[Co/Ni] with N < 15 only partially describes the increase to Hc. Energy-dispersive X-ray spectroscopy analyses performed in scanning transmission electron microscopy mode across cross-sections of as-deposited and annealed Cu/16x[Co/Ni] films show that Cu diffuses from the seed layer into grain boundaries of Co/Ni. Diffusion of Cu reduces exchange coupling (Hex) between the magnetic grains and explains the increase in Hc. Additionally, the difference in the slope of the M(H) curves at Hc between the thick (N = 16) and thin (N = 4) magnetic multilayers is due to Cu diffusion more effectively decoupling magnetic grains in the thinner multilayer.

Publ.-Id: 27327 - Permalink


Increased evidence for the prognostic value of late-treatment FDG-PET uptake in non-tumor affected oesophagus in irradiated patients with oesophageal carcinomas
Li, Y.; Hofheinz, F.; Furth, C.; Lili, C.; Hua, W.; Ghadjar, P.; Zschaeck, S.
Purpose: 18F-fluorodeoxyglucose (FDG) uptake within irradiated non-tumor affected oesophagus (NTO) at re-staging positron emission tomography (PET) is a potential surrogate to measure radiation induced inflammation (RIF). RIF itself was shown to be of high prognostic relevance in patients undergoing preoperative radiochemotherapy (RCT) for locally advanced oesophageal cancer. We assessed the prognostic relevance of NTO uptake in an independent cohort of patients treated with definitive RCT.

Methods: Seventy-two patients with oesophageal squamous cell carcinomas treated with curative intent definitive RCT were retrospectively evaluated. All patients underwent pre-treatment and re-staging FDG-PET after 40-50 Gray radiation dose. Standardized uptake values (SUVmax/SUVmean), metabolic tumor volume (MTV) and relative changes between pre-treatment and re-staging PET (∆SUVmax/∆SUVmean) were determined within tumor and NTO. Univariate Cox regression with respect to overall survival (OS), local control (LC), distant metastases (DM) and treatment failure (TF) was performed. Independence of parameters was tested in multivariate Cox regression.

Results: ∆SUVmax NTO and MTV were prognostic factors for all investigated clinical endpoints (OS, LC, DM, TF). Inclusion of clinical and PET tumor parameters in multivariate analysis showed ∆SUVmax NTO as an independent prognostic factor. Furthermore, multivariate analysis of ∆SUVmax NTO with previously published cutoffs from the preoperatively treated patients revealed ∆SUVmax NTO as independent prognostic factor for OS (HR=1.88, p=0.038), TF (HR=2.11, p=0.048) and DM (HR=3.02, p=0.047).

Conclusions: NTO-related tracer uptake during course of treatment in patients suffering from esophageal carcinoma was proven to be of high prognostic relevance. Thus, metabolically activity of NTO measured by ∆SUVmax NTO is a potential candidate for future treatment individualization (i.e. organ preservation).
Keywords: oesophageal cancer; definitive radiochemotherapy; re-staging; response assessment; normal tissue; side effects; inflammation; FDG PET

Publ.-Id: 27325 - Permalink


Bubble column with internals: Comparative hydrodynamic analysis of narrow and pilot-scale columns
Möller, F.; Kipping, R.; Hampel, U.; Schubert, M.
Bubble columns are widely applied reactors in the chemical process industry due to their excellent heat and mass transfer properties as well as their simple design and easy manufacturing without any moving part. Fischer-Tropsch and methanol syntheses are typical processes carried out in such columns. Most of the involved reactions are highly exothermic and require an efficient heat removal, for example, via internal tube bundle heat exchangers. Heat exchangers, with up to 60 m2 m-3 surface area, can be installed as dense tube bundles covering up to 60 % of the cross-sectional area, which accordingly, alter hydrodynamics, flow patterns, mixing and mass transfer significantly.
Therefore, this study aims at revealing the influence of common tube bundle layouts, i.e. triangular and square pitches, at various tube diameters at approx. 25 % cross-sectional area coverage. The studies were carried out using narrow and pilot-scale bubble columns with 100 and 400 mm diameter, respectively, operated with air and water. Ultrafast X-ray tomography as well as wire-mesh sensors were applied to study the columns’ hydrodynamics as well as the flow in individual sub-channels. In particular, holdup and bubble size distributions were measured and compared for both columns. Furthermore, it is discussed to which extend hydrodynamic parameters, such as radial holdup profiles and gas velocity profiles etc., can be utilized for scale-up purposes based on hydrodynamic similarity at both reactor scales.
  • Poster
    Jahrestreffen der ProcessNet Fachgruppen MPH, WSUE, CFD, HTT, AuW, KRI, PMT, 06.-09.03.2018, Bremen, Deutschland

Publ.-Id: 27319 - Permalink


Quantification: there is more to worry about than good scanner hardware and reliable calibration
Kotzerke, J.; van den Hoff, J.
Positron emission tomography (PET) is "an analytical imaging technology developed to use compounds labelled with positron-emitting radioisotopes as molecular probes to image and measure biochemical processes of mammalian biology in vivo" [1]. One outstanding feature of the PET technology is the ability to perform absolute quantification of regional perfusion, metabolism, and function [2]. There are clinical demands for quantification regarding description of biodistribution, dosimetry, intra- and inter-individual comparisons, and setup of age- and gender-specific (normal) databases. Notably, FDG PET allows diagnosis, differential diagnosis, assessment of prognosis, and patient stratification in malignant disease. Moreover, image guided therapy has been proven to improve tumour delineation and irradiation field definition regarding protection of normal tissue and dose escalation on tumour tissue [3]. After initial assessment, follow-up investigations describe the effect of therapy and influence therapeutic management regarding continuation or change of modality and intensification or de-escalation of therapy. In addition to qualitative description and quantification of tracer uptake or uptake changes during follow-up, more sophisticated kinetic modelling and analysis may be applied. However, reliability and significance of all derived numbers is influenced by technical factors and biological processes.

Publ.-Id: 27318 - Permalink


Intrinsic Charge Dynamics in High-Tc AFeAs (O,F) Superconductors
Charnukha, A.; Pröpper, D.; Zhigadlo, N.  D.; Naito, M.; Schmidt, M.; Wang, Z.; Deisenhofer, J.; Loidl, A.; Keimer, B.; Boris, A.  V.; Basov, D.  N.
We report the first determination of the in-plane complex optical conductivity of 1111 high-Tc superconducting iron oxypnictide single crystals PrFeAs(O,F) and thin films SmFeAs(O,F) by means of conventional and microfocused infrared spectroscopy, ellipsometry, and time-domain THz transmission spectroscopy. A strong itinerant contribution is found to exhibit a dramatic difference in coherence between the crystal and the film. Using extensive temperature-dependent measurements of THz transmission, we identify a previously undetected 2.5-meV collective mode in the optical conductivity of SmFeAs(O,F), which is strongly suppressed at Tc and experiences an anomalous T-linear softening and narrowing below T∗≈110  K≫Tc. The suppression of the infrared absorption in the superconducting state reveals a large optical superconducting gap with a similar gap ratio 2Δ/kBTc≈7 in both materials, indicating strong pairing.

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Publ.-Id: 27316 - Permalink


Calorimetry techniques for ultra-intense laser-plasma experiments
Molodtsova, M.; Ferrari, A.; Laso Garcia, A.; Metzkes-Ng, J.; Irman, A.; Lutz, B.; Prencipe, I.; Sobiella, M.; Stach, D.; Weinberger, D.; Cowan, T. E.
With ultra-high intensity short pulse lasers generating plasma, new extreme states of matter can be created, and new concepts for particle acceleration, material science, and fusion energy can be explored. A critical component is the characterization of relativistic electrons that are accelerated and transported in the material of the target, generating ultra-intense bremsstrahlung.
Measuring the bremsstrahlung spectrum is a crucial aspect of plasma diagnostics. In this work it is showed how calorimetric techniques, based on longitudinally resolved measurements of energy deposition, are especially suitable for the reconstruction of the photon spectra and how electron dynamics can be studied.
Multi-layered scintillator calorimeters with different readouts are under development at Helmholtz-Zentrum Dresden-Rossendorf for this purpose. Prototypes have been tested at the ELBE facility both at the gELBE beamline with a well-known bremsstrahlung spectrum and in a laser-plasma environment at DRACO.
  • Lecture (Conference)
    DPG Spring Meeting 2018 of the Section on Atomic, Molecular, Plasma Physics and Quantum Optics (SAMOP), 05.-09.03.2018, Erlangen, Germany

Publ.-Id: 27315 - Permalink


In situ structural study of the surface complexation of lead(II) on the chemically mechanically polished hematite (1-102) surface
Qiu, C.; Majs, F.; Eng, P.; Stubbs, J.; Douglas, T.; Schmidt, M.; Trainor, T.
A structural study of the surface complexation of Pb(II) on the (View the MathML source) surface of hematite was undertaken using crystal truncation rod (CTR) X-ray diffraction measurements under in situ conditions. The sorbed Pb was found to form inner sphere (IS) complexes at two types of edge-sharing sites on the half layer termination of the hematite (View the MathML source) surface. The best fit model contains Pb in distorted trigonal pyramids with an average Pbsingle bondO bond length of 2.27(4) Å and two characteristic Pb-Fe distances of 3.19(1) Å and 3.59(1) Å. In addition, a site coverage model was developed to simulate coverage as a function of sorbate-sorbate distance. The simulation results suggest a plausible Pb-Pb distance of 5.42 Å, which is slightly larger than the diameter of Pb’s first hydration shell. This relates the best fit surface coverage of 0.59(4) Pb per unit cell at monolayer saturation to steric constraints as well as electrostatic repulsion imposed by the hydrated Pb complex. Based on the structural results we propose a stoichiometry of the surface complexation reaction of Pb(II) on the hematite (1-102) surface and use bond valence analysis to assign the protonation schemes of surface oxygens. Surface reaction stoichiometry suggests that the proton release in the course of surface complexation occurs from the Pb-bound surface O atoms at pH 5.5.
Keywords: Pb(II); Hematite; Crystal truncation rod

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  • Secondary publication expected from 03.04.2019

Publ.-Id: 27312 - Permalink


Advanced Analysis of Liquid Dispersion and Gas-Liquid Mass Transfer in a Bubble Column with Dense Vertical Internals
Möller, F.; Macisaac, A.; Lau, Y. M.; Schleicher, E.; Hampel, U.; Schubert, M.
The influence of dense vertical tube bundles in a batch bubble column reactor of 100 mm diameter and 1100 mm clear liquid height on liquid dispersion and gas-liquid mass transfer was studied. In particular, the effects of different tube patterns (triangular and square pitch), tube diameters (8 and 13 mm) and bottom end designs (flat and U-tube) having a tube diameter-to-pitch ratio of approx. 1.3 were investigated.
Dispersion coefficients were determined based on conductive tracer experiments recorded via wire-mesh sensors (WMS) with up to 90 measurement points distributed in the column’s cross-section in between the tubes. The gas-liquid mass transfer coefficient was determined via fast-responding oxygen needle probes. Tube pitch and pattern were identified as the most crucial design parameters for the extent of liquid dispersion. We found that particularly the U-tube bottom end design induces large liquid circulation patterns, which enhance dispersion. The presence of internals decreases the k_l a value as a consequence of turbulence damping, which is also confirmed by lower k_l values (e.g. 0.6 × 10-3 m s-1 for the empty BCR and 0.25 × 10-3 m s-1 for the square pitch with 8 mm tubes at 0.05 m s-1 superficial gas velocity), whereas the pitch is the most decisive design parameter. The U-tube bottom end design was identified as the most beneficial configuration with respect to liquid mixing and gas-liquid mass transfer.
Keywords: Bubble column, Heat exchanger internals, Gas-liquid mass transfer, 2D dispersion model, Wire-mesh sensor

Publ.-Id: 27309 - Permalink


Organische Chemie XI - Chemie der Carbonylverbindungen
Mamat, C.
Nachdem wir uns sehr ausführlich über Verbindungen unterhalten haben, die Kohlenstoff-Kohlenstoff-Mehrfachbindungen enthalten (Alkene, Alkine, Aromaten), wollen wir zu Verbindungsklassen und funktionellen Gruppen kommen, bei denen Kohlenstoff-Heteroatom-Doppelbindungen existieren. Das sind insbesondere Aldehyde, Ketone, Carbonsäuren und deren Derivate. Im Gegensatz zu den nichtaktivierten C=C-Doppelbindungen sind diese Kohlenstoff-Heteroatom-Doppelbindungen bereits durch die Unterschiede in den EN-Werten aktiviert. Wir finden ein elektronegatives Zentrum am Heteroatom (Sauerstoff, Stickstoff oder Schwefel) und ein elektropositives Zentrum am Kohlenstoff. Somit ist die Regioselektivität bei nucleophilen bzw. elektrophilen Angriffen vorgegeben. Wenn beispielsweise Nucleophile an diese Doppelbindung angreifen, werden sie spezifisch an den Kohlenstoff gebunden, wohingegen die Elektrophile den Sauerstoff angreifen. Neben der Carbonylgruppe, in der der Sauerstoff über eine Doppelbindung gebunden ist gibt es auch carbonylanaloge Verbindungen mit Stickstoff oder Schwefel, wobei die Elektronegativitätsdifferenz und damit die Polarisierung der Doppelbindung in der Richtung O > N > S abnimmt.
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0049 Seiten

Publ.-Id: 27302 - Permalink


Organische Chemie X - Aromatische Substitution
Mamat, C.
In den vergangenen Heften haben wir uns ausführlich über die Reaktionen an gesättigten und ungesättigten Kohlenstoffatomen unterhalten, wobei wir die aromatischen Vertreter geflissentlich ausgelassen haben. Außerdem haben wir geschaut, welche Effekte diese Aromaten bzw. aromatische Reste wie Phenylgruppen auf die Stabilität von Zwischenstufen wie Carbanionen, Carbokationen oder Radikalen ausüben und welche Konsequenzen sich aus diesem Einfluss dann auf die Reaktivität und /oder (Regio-)Selektivität der Derivate ergeben.
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0035 Seiten

Publ.-Id: 27301 - Permalink


Organische Chemie IX - Additionsreaktionen
Mamat, C.
Additionen sind die mit Abstand wichtigsten Reaktionen von ungesättigten Verbindungen (Alkenen, Alkinen, aber auch Carbonylverbindungen). Formal handelt es sich dabei um die Umkehrung der Eliminierungsreaktionen. Additionsreaktionen können radikalisch oder ionisch verlaufen. Im Falle eines ionischen Verlaufs können wir noch zwischen einem elektrophilen oder einem nucleophilen ersten Angriff auf die Doppelbindung unterschieden. Der vierte Typ umfasst die große Gruppe der Cycloadditionen. Diese pericyclischen Reaktionen kommen ohne geladene Teilchen aus und verlaufen meist konzertiert. Somit sind vier Typen von Additionen an die Doppelbindung zu unterscheiden.
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0051 Seiten

Publ.-Id: 27300 - Permalink


Organische Chemie VIII - Eliminierungen
Mamat, C.
Wir haben schon aus den Studienheften der Organischen Chemie I erfahren, dass Eliminierungsreaktionen am sp3- oder sp2-hybridisierten Kohlenstoff die Umkehrung von Additionsreaktionen sind. Sie treten damit als Konkurrenzreaktion zu den nucleophilen Substitutionen auf und führen generell zu ungesättigten Verbindungen (Alkenen oder Alkinen). Dabei müssen zwei σ-Bindungen gebrochen werden. Aus den beteiligten sp3-hybridisierten Kohlenstoffatomen werden sp2-hybridisierte gebildet und als Konsequenz daraus bilden sich nach Abspaltung aus sp2-hybridisierten Kohlenstoffatomen sp-hybridisierte, die an der jeweiligen Mehrfachbindung beteiligt sind. Neben der σ-Bindung zwischen den beteiligten Kohlenstoffatomen wird nun eine oder zwei π-Bindungen ausgebildet. Dabei entstehen kleine, stabile Moleküle wie z. B. Halogenwasserstoff (HCl, HBr), Wasser, CO2 und andere als eliminierte Nebenprodukte.
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0030 Seiten

Publ.-Id: 27299 - Permalink


Organische Chemie VII - Radikalische und nucleophile aliphatische Substitution
Mamat, C.
Nachdem wir uns ausführlich mit den wichtigsten Stoffklassen und funktionellen Gruppen in der organischen Chemie beschäftigt haben, wollen wir nun im zweiten Teil noch einmal auf die Reaktionen und ihre Mechanismen schauen. Diese Mechanismen sind wichtige Werkzeuge, um zu verstehen, warum Reaktionen funktionieren oder auch nicht. Oder warum das eine Produkt gebildet wird und das andere nicht. Oftmals haben wir auch Konkurrenzsituationen, wie die Eliminierung bei der nucleophilen Substitution oder auch zwei (oder mehrere) reaktive Zentren, an denen die Reaktion prinzipiell ablaufen könnte. In solchen Situationen werden wir sehen, dass eine Steuerung möglich ist, je nachdem wie die Reaktionsbedingungen gewählt werden. Ein weiterer wichtiger Faktor wird durch die Kinetik der Reaktionen beschrieben. Sie gibt ebenfalls Auskunft darüber, ob und wie Reaktionen ablaufen. Wenn das alles nicht hilft, gibt es die Möglichkeit, funktionelle Gruppen, die nicht reagieren sollen, mit Schutzgruppen vor der Reaktion zu blockieren. Damit wird ebenfalls eine regioselektive Reaktion erreicht.
  • Book (Authorship)
    Heidelberg: Springer Verlag, 2018
    0040 Seiten

Publ.-Id: 27298 - Permalink


Charge Carrier Dynamic in Ga1-xMnxAs Studied by Resistance Noise Spectroscopy
Lonsky, M.; Teschabai–Oglu, J.; Pierz, K.; Sievers, S.; Schumacher, H. W.; Yuan, Y.; Böttger, R.; Zhou, S.; Müller, J.
We report on electronic transport measurements of the magnetic semiconductor Ga1-xMnxAs, whereby the defect landscape in various metallic thin films (x = 6%) was tuned by He-ion irradiation. Changes in the distribution of activation energies, which strongly determine the low-frequency 1/f-type resistance noise characteristics, were observed after irradiation and can be explained by deep-level traps residing in the As sublattice. Various other kinds of crystalline defects such as, for instance, Mn interstitials, which possibly form nanoscale magnetic clusters with a fluctuating spin orientation, also contribute to the 1/f noise and can give rise to random telegraph signals, which were observed in films with x = 7%. In addition, we neither find evidence for a magnetic polaron percolation nor any features in the noise near the Curie temperature.

Publ.-Id: 27295 - Permalink


Hybrid plasma wakefield acceleration: Concept & preliminary results
Kurz, T.ORC; Heinemann, T.; Knetsch, A.; Couperus, J. P.; Köhler, A.; Zarini, O.; Hidding, B.; Assmann, R.; Bussmann, M.; Osterhoff, J.; Schramm, U.; Martinez De La Ossa, A.; Irman, A.
Plasma wakefield accelerators can be driven by either a powerful laser pulse (LWFA) or a high-current charged particle beam (PWFA). We combine both acceleration methods in a staged setup to efficiently exploit the advantages of each scheme. We present preliminary results of a proof of concept-experiment at the DRACO laser facility at Helmholtz-Zentrum Dresden-Rossendorf (HZDR). The LWFA stage (1st stage) generates ultra relativistic electron beams with peak currents exceeding 20kA via self truncated inonization injection (STII) out of a 3mm super sonic dopant (He+N) gas jet. These beams are sent into the second 3mm dopant (H+He) gas jet, driving plasma wakefields in the non-linear bubble regime. Thereby, injected electrons induced by the field ionization form a second electron beam (witness) that ideally exeeds the driving bunch (driver) quality in terms of energy and brightness.
  • Lecture (Conference)
    DPG - Frühjahrstagung, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27292 - Permalink


Production and Characterization of the 163Ho Source for the ECHo Project
Wendt, K.; Düllmann, C. E.; Kieck, T.; Dorrer, H.; Mokry, C.; Rugel, G.; Wiescher, F.; Merchel, S.ORC; Forstner, O.
The ECHo (Electron Capture in Holmium Experiment) collaboration aims at measuring the electron neutrino mass by recording the spectrum following electron capture of 163Ho using metallic magnetic calorimeters. The radioisotope 163Ho (t1/2 = 4570 a) is produced by neutron capture from enriched 162Er in the Institute Laue-Langevin high-flux nuclear reactor. After chemical separation the important step of embedding the sample into the 180x180 𝜇m2 Au-absorbers of the ECHo detectors is carried out by laser mass spectrometric techniques. The application of multi-step resonance ionization at the 60 kV RISIKO mass separator of Mainz University ensures highest efficiency and unrivalled elemental and isotopic selectivity for ultra-pure 163Ho ion implantation with sub-millimeter beam spot. The efficiency and stability of the laser ion source and the implantation process is permanently monitored and improved to minimize any losses of the precious sample material, while an in-situ deposition of gold by parallel pulsed laser deposition (PLD) ensures a homogeneous 163Ho/Au layer production and prevents disturbing sputter effects. To screen the purity of the source from production up to use besides a number of more conventional analytical techniques accelerator mass spectrometry (AMS) of Ho at the AMS-facility of the Helmholtz-Zentrum Dresden-Rossendorf is under development to address the very low content in the 10 or lower region of the radiocontaminating isotope 166mHo (t1/2 = 1200 a).
Keywords: AMS, Holmium, electron capture, mass separator,
  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.03.2018, Darmstadt, Deutschland

Publ.-Id: 27288 - Permalink


High Speed, High Resolution Imaging Spectrometers Based on pnCCDs for XRF and XRD Applications
Strüder, L.; Hartmann, R.; Holl, P.; Ihle, S.; Huth, M.; Schmidt, J.; Thamm, C.; Kanngießer, B.; Baumann, J.; Renno, A. D.ORC; Grenzer, J.; Radtke, M.; Abhoud, A.; Pietsch, U.; Soltau, H.
For many years pnCCDs have been well known as X-ray detectors for spectroscopic imaging in many fields of science: X-Ray Fluorescence analysis (XRF), X-ray Diffraction (XRD) with light sources in large accelerator facilities as well as with laboratory light sources or with X -rays from celestial sources in X-ray astronomy. A brief introduction in GEXRF (Grazing Emission XRF) measurements with a laboratory laser produced plasma source will be given, PIXE (Particle Induced X-ray Emission) measurements and D2XRF (Double Dispersive X -Ray Fluorescence) and Slicing experiments with pnCCDs coupled to polycapillary optics performed at the BESSY synchrotron will be shown. Energy - dispersive Laue diffraction with ultra - hard X-rays for the analysis of defects in metals will conclude the overview of spectroscopic X-ray imaging measurements in the field of structure and dynamics of matter. pnCCDs are radiation detectors on high resistivity 450 μm thick fully sensitive silicon [1]. They are back-illuminated devices with an ultra-thin, homogeneous radiation entrance window, enabling the proper detection of X-rays up to 30 keV with high quantum efficiency. As all pnCCDs are equipped with a fully column parallel readout, frame rates on more than 1200 frames per second are achieved, keeping the read noise level at 3 electrons (rms). Some of the key performance figures are (1) a quantum efficiency above 90% from 1 keV up to 10 keV, (2) single photon counting capability starting at only 30 eV, (3) extreme radiation hardness due to the avoidance of active MOS structures, and (4) energy resolution of 130eV (FWHM) at 6 keV and 37 eV (FWHM) at 90 eV. These properties have enabled a variety of spectacular measurements. (a) GEXRF: By combining a highly brilliant laser produced plasma (LPP) source with a scanning - free setup, grazing emission X-ray fluorescence (GEXRF) measurements in the soft X - ray range were realized [2]. The detector, a pnCCD, was operated in a single photon counting mode in order to utilize its energy dispersive properties. GEXRF profiles of the Ni - Lα line of a carbon - nickel multilayer sample, which displays a lateral (bi-)layer thickness gradient, were recorded at several positions. Simulations of theoretical profiles predicted a prominent intensity dip at emission angles between 5° and 12°, depending strongly on the bi-layer thickness of the sample (see Fig.1). This information was used to retrieve the bi - layer thickness gradient. The results are in good agreement with values obtained by X-ray reflectometry, conventional X-ray fluorescence and transmission electron microscopy measurements and serve as proof of principle for the suggested GEXRF setup. (b) PIXE: The unique properties pnCCDs, coupled to polycapillary X-ray optics, allows a fast position resolved overview over a large detection area with first results visible in real time. The maximum field of view exceeds 1 cm2 and the spatial resolution approaches a few microns when using sub-pixel algorithms by centroiding the signal charge cloud in the pixel structure [3] .
The device has been used as an X-ray detector at the PIXE beamline at the Helmholtz-Zentrum Dresden Rossendorf (see Fig. 2). In addition to the above measurements (c) D2XRF and Slicing experiments performed at the BESSY synchrotron will be presented (see Fig. 3) as well as (d) Energy Dispersive Hard X-ray Laue Diffraction measurements at the ESRF.
Keywords: pnCCD, High-Speed PIXE
  • Contribution to proceedings
    Microscopy and Microanalysis 2016, 24.07.2016, Columbus, USA
    Proceedings of Microscopy and Microanalysis 2016, 100-101
    DOI: 10.1017/S14319276

Publ.-Id: 27286 - Permalink


Development of an efficient high-current ion source for Accelerator Mass Spectrometry
Hofsäss, H.; Bregolin, F.; Yordanov, D.; Rugel, G.; Akhmadaliev, S.; Merchel, S.ORC; Feige, J.
A new efficient negative ion source for Accelerator Mass Spectrometry (AMS) is being built to quantify the ratios of long-lived cosmogenic radionuclides in micrometeorites. Measuring these extremely small ratios is at the technological limits of present AMS systems. The new source is designed specifically to provide a higher AMS detection sensitivity by having an optimal ion-optics design, incorporating new concepts for the construction and operation of the Cs ionizer, optimized Cs ion beam currents and Cs vapor transport, as well as the operation with higher cathode voltages than usual. Moreover, its design is modular providing ease of access and simplifying maintenance while providing better mechanical stability. Several source parameters can be controlled and measured during operation to achieve a better source performance. The new source will consist of a auto-aligning modular ionizer, a Cesium supply with active temperature control of the supply tubes, a novel shroud for the Cs supply and a cathode operated at up to -20 kV cathode bias. The design is optimized using COMSOL ion optics simulations, including space charge effects, thermal transport simulations as well as detailed sputter simulations. The authors would like to thank the Federal Ministry of Education and Research of Germany for its financial support (project 05K2016), and the HZDR's Ion Beam Center for its essential contribution to the realization of this project.
Keywords: AMS, micrometeorite
  • Lecture (Conference)
    Workshop on Ion and Particle Beams (Ionenstrahl Workshop), 24.-25.03.2018, Darmstadt, Deutschland

Publ.-Id: 27282 - Permalink


Experimental investigation of three-dimensional bubbly two-phase pipe flows
Neumann, M.; Bieberle, A.; Krepper, E.; Hampel, U.
Modelling gas-liquid two-phase flow is a topic of constant relevance in nuclear thermal hydraulics. Gas-disperse two-phase flows occur in e.g. fuel elements in the reactor core, in pipes and components during pressure loss, sudden reflooding or other events. Due to the deformable gas-liquid interface and the complexity of heat, mass and momentum transfer across the interface, gas-liquid two-phase flow is very difficult to model and simulate. On the device scale it is common to use Euler/Euler multi-fluid approaches for CFD simulations, which require a good number of empirical correlations as closure models. Such models are commonly derived from experiments. Validation of the correctness of predictive simulations then also requires experiments, which must be simplified to a degree to allow provision of CFD-grade experimental data but complex enough to resemble real flow situations. The latter calls especially for investigations on flow fields in more complex three-dimensional domains, which are prototypical for e.g. bends, valves, T-junctions and rod bundles.
In this contribution the experimental investigation of generic three-dimensional two-phase flows will be presented. Experiments were performed at a vertical test section at the Transient Two-Phase Flow (TOPFLOW) facility at Helmholtz-Zentrum Dresden – Rossendorf (HZDR). The test section is a pipe with an inner diameter of 54 mm and a length of 5000 mm with a flow constriction at half lengths. For the latter a ring shaped diaphragm and a half-moon shaped diaphragm have been investigated. Experiments were performed for a wide range of superficial gas and liquid velocities in the bubbly flow regime. Besides conventional measurement techniques for mass flow rates, temperatures and pressure, the ultrafast X-ray tomography scanner ROFEX for the determination of bubble dynamics, as well as a specifically adapted thermal anemometer probe for determination of liquid velocities is employed. The two-phase flow in such geometry exhibits certain important structures. In the narrow obstacle passage the flow accelerates with accordingly high shear stress being visible in large bubble deformation and break-up. Downstream a dead zone with recirculation develops and bubbles are being captured, which is associated with increased gas hold-up and bubble coalescence. The high resolution measurements allow for the first time to study the two-phase dynamics in detail and disclose velocity distributions along with gas phase and bubble size data as a function of time and space.
Keywords: two-phase flow, three-dimensional flow field, ultrafast X-ray tomography, thermal anemometry
  • Lecture (Conference)
    17th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-17), 03.-08.09.2017, Xi'an, China

Publ.-Id: 27279 - Permalink


Synthesis and radiofluorination of novel fluoren-9-one based derivatives for the imaging of α7 nicotinic acetylcholine receptor with PET
Teodoro, R.; Scheunemann, M.; Wenzel, B.; Peters, D.; Deuther-Conrad, W.; Brust, P.
By structure-activity relationship studies on the tilorone scaffold, the ‘one armed’ substituted dibenzothiophenes and the fluoren-9-ones were identified as the most potential α7 nAChR ligands. While the suitability of dibenzothiophene derivatives as PET tracers is recognized, the potential of fluoren-9-ones is insufficiently investigated. We herein report on a series of fluoren-9-one based derivatives targeting α7 nAChR with compounds 8a and 8c possessing the highest affinity and selectivity. Accordingly, with [18F]8a and [18F]8c we designed and initially evaluated the first fluoren-9-one derived α7 nAChR selective PET ligands. A future application of these radioligands is facilitated by the herein presented successful implementation of fully automated radiosynthesis.
Keywords: α7 nAChR PET Radiofluorination Fluoren-9-one Dibenzothiophenes

Publ.-Id: 27271 - Permalink


Quantitative Measurement of Interaction between Solidification and Convection in Ammonium-Chloride Solutions
Anders, S.; Noto, D.; Eckert, S.
An experimental investigation of double-diffusive convection with simultaneous crystallisation in ammonium-chloride solutions will be presented. Measurements were performed in a transparent Hele-Shaw with controlled thermal boundary conditions. The flow field of the liquid was measured by PIV. Using thermochromic liquid crystals, the temperature field inside the fluid was established. PTV was used to determine the size-evolution and the trajectories of the salt crystals. Alternating lighting methods and digital image filtering allow for simultaneous operation of PIV, PTV and temperature field measurement. This enables a quantitative study of the interplay of convection regimes and solidification processes like columnar and equiaxed crystallization, chimney-formation and remelting.
Keywords: Iron Snow, PTV, PIV, TLC, Multiphase Flow, Solidification, Double-diffusive Convection
  • Lecture (Conference)
    Symposium zur Simulation Metallurgischer Prozesse 2018, 30.01.-02.02.2018, Feuerkogel, Österreich

Publ.-Id: 27268 - Permalink


Applied Mineralogy for Resource Efficiency of Platinum Metals - Towards a Geometallurgical Model
Bachmann, K.; Menzel, P.; Tolosana-Delgado, R.; Gutzmer, J.
A geometallurgical model allows to predict parameters relevant for mineral beneficiation in a spatial domain. Therefore, we need a basic understanding of the geolocial architecture which can be provided by 3D geological models. Additionally, a tailored sample selection and characterization is crucial. This may include drill core logging data, whole rock geochemistry, modal mineralogies, micro-textures and mineral association as well as mineral chemistry data. In a next step, it is necessary to integrate the data into a spatial context and to derive process-relevant paramters. Finally, the development of domains with similar mineral beneficiation characteristics as well as geostatistical interpolation of relevant parameters onto a 3D geometry is possible.
  • Invited lecture (Conferences)
    Joint AMREP & DST-CIMERA Symposium, 14.-15.03.2018, Johannesburg, South Africa

Publ.-Id: 27266 - Permalink


Regge Trajectories of Radial Meson Excitations: Exploring the Dyson-Schwinger-- Bethe-Salpeter Approach
Greifenhagen, R.; Kämpfer, B.; Kaptari, L. P.
The combined Dyson-Schwinger and Bethe-Salpeter equations in rainbow-ladder approximation are used to search for Regge trajectories of mesons in the pseudo-scalar and vector channels. We focus on the often employed Alkofer-Watson-Weigel kernel which is known to deliver good results for the ground state meson spectra; it provides linear Regge trajectories in the JP=0− channel.

Publ.-Id: 27261 - Permalink


Impact of Dipolar Interaction on Superfluid Spin Transport
Schneider, T.; Barsukov, I.; Smith, A.; Upadhyaya, P.; Liu, Y.; Fan, Y.; Wang, K.; Macdonald, A.; Tserkovnyak, Y.; Krivorotov, I. N.
Ferromagnetic easy-plane system are theoretically excepted to support a long-range coherent transport flow, normally referred as spin superfluid. However, the influence of local dipole-dipole interaction on these states are not fully investigated. Here, the present a detailed micromagnetic study of the superfluid flow in a easy-plane ferromagnetic in the presence of local dipole-dipole interactions.
  • Lecture (others)
    Spintronics group seminar, 15.03.2018, Irvine, CA, USA
  • Lecture (others)
    Group seminar Prof. Tserkovnyak, 19.03.2018, Los Angeles, USA

Publ.-Id: 27260 - Permalink


Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings
Li, Z.; Klopf, J. M.; Wang, L.; Yang, K.; Lukaszew, R. A.
Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD) and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.

Publ.-Id: 27254 - Permalink


CMOS‐compatible controlled hyperdoping of silicon nanowires
Berencén, Y.; Prucnal, S.; Möller, W.; Hübner, R.; Rebohle, L.; Böttger, R.; Glaser, M.; Schönherr, T.; Yuan, Y.; Wang, M.; Georgiev, Y. M.; Erbe, A.; Lugstein, A.; Helm, M.; Zhou, S.; Skorupa, W.
Hyperdoping consists of the intentional introduction of deep‐level dopants into a semiconductor in excess of equilibrium concentrations. This causes a broadening of dopant energy levels into an intermediate band between the valence and the conduction bands. Recently, bulk Si hyperdoped with chalcogens or transition metals is demonstrated to be an appropriate intermediate‐band material for Si‐based short‐wavelength infrared photodetectors. Intermediate‐band nanowires can potentially be used instead of bulk materials to overcome the Shockley–Queisser limit and to improve efficiency in solar cells, but fundamental scientific questions in hyperdoping Si nanowires require experimental verification. The development of a method for obtaining controlled hyperdoping levels at the nanoscale concomitant with the electrical activation of dopants is, therefore, vital to understanding these issues. Here, this paper shows a complementary metal‐oxide‐semiconductor (CMOS)‐compatible technique based on nonequilibrium processing for the controlled doping of Si at the nanoscale with dopant concentrations several orders of magnitude greater than the equilibrium solid solubility. Through the nanoscale spatially controlled implantation of dopants, and a bottom‐up template‐assisted solid phase recrystallization of the nanowires with the use of millisecond‐flash lamp annealing, Se‐hyperdoped Si/SiO2 core/shell nanowires are formed that have a room‐temperature sub‐bandgap optoelectronic photoresponse when configured as a photoconductor device.
Keywords: Flash lamp annealing, hyperdoping, intermediate band, ion implantation, nanowires

Publ.-Id: 27251 - Permalink


Core-Shell Structuring of Pure Metallic Aerogels towards Highly Efficient Platinum Utilization for the Oxygen Reduction Reaction - Kern-Schale-Strukturierung rein metallischer Aerogele für eine hocheffiziente Nutzung von Platin für die Sauerstoffreduktion
Cai, B.; Hübner, R.; Sasaki, K.; Zhang, Y.; Su, D.; Ziegler, C.; Vukmirovic, M. B.; Rellinghaus, B.; Adzic, R. R.; Eychmüller, A.
The development of core-shell structures remains a fundamental challenge for pure metallic aerogels. Here we report the synthesis of PdxAu-Pt core-shell aerogels composed of an ultrathin Pt shell and a composition-tunable PdxAu alloy core. The universality of this strategy ensures the extension of core compositions to Pd transition-metal alloys. The core-shell aerogels exhibited largely improved Pt utilization efficiencies for the oxygen reduction reaction and their activities show a volcano-type relationship as a function of the lattice parameter of the core substrate. The maximum mass and specific activities are 5.25 A mgPt-1 and 2.53 mA cm-2, which are 18.7 and 4.1 times higher than those of Pt/C, respectively, demonstrating the superiority of the core-shell metallic aerogels. The proposed core-based activity descriptor provides a new possible strategy for the design of future core-shell electrocatalysts.
Die Entwicklung von rein metallischen Aerogelen mit Kern-Schale-Strukturen ist nach wie vor eine grundlegende Herausforderung. Hier stellen wir die Synthese von PdxAu-Pt-Kern-Schale-Aerogelen vor, welche aus einer ultradünnen Pt-Schale und einem Kern aus einer PdxAu-Legierung mit einstellbarer Zusammensetzung bestehen. Die universelle Synthesestrategie ermöglicht eine Erweiterung der Kern-Zusammensetzung hin zu Pd-Übergangsmetall-Legierungen. Die Kern-Schale-Aerogele zeigen eine stark verbesserte Nutzungseffizienz von Pt in der Sauerstoffreduktion und ihre Aktivitäten folgen einem vulkanförmigen Verlauf bezüglich der Gitterparameter des Kern-Substrats. Mit einer maximalen massenbezogenen bzw. spezifischen Aktivität von 5.25 A mgPt-1 und 2.53 mA cm-2, welche 18.7- bzw. 4.1-mal höher sind als die für Pt/C, zeigt sich die Überlegenheit dieser metallischen Kern-Schale-Aerogele. Die vorgeschlagene kernbasierte Aktivitätsabhängigkeit liefert eine neue mögliche Strategie für den Entwurf zukünftiger Kern-Schale-Elektrokatalysatoren.
Keywords: aerogels, electrocatalysis, core-shell structures, oxygen reduction reaction, sol-gel processes - Aerogele, Elektrokatalyse, Kern-Schale-Strukturen, Nanostrukturen, Sol-Gel-Prozess

Publ.-Id: 27248 - Permalink


Detecting and quantifying the relativistic Kelvin-Helmholtz instability in interstellar jets via radiation observable on Earth
Pausch, R.; Bussmann, M.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Debus, A.
We present a microscopic model of the radiation emitted during the relativistic Kelvin-Helmholtz instability (KHI) and validate our findings with particle-in-cell simulations at unprecedented spatial resolution and size that including complete far-field radiation spectra.

The KHI is expected in shear flow regions of astrophysical plasma jets, which are significant sites for particle acceleration and radiation. We demonstrate that the emitted polarized radiation can be used to identify and characterize the microscopic plasma dynamics of a KHI light-years away. We have simulated the radiation of the KHI using the particle-in-cell code PIConGPU. With this code's synthetic radiation diagnostic, based on Liénard-Wiechert potentials, quantitative predictions of the far field radiation for hundreds of observation directions and a frequency range covering 3 orders of magnitude were performed on the TITAN cluster at Oak Ridge National Laboratory. The simulation showed that the time-dependent changes in the radiation polarization and power correlate directly with the stages of the KHI. This allows identifying the linear growth phase of the KHI and quantifying its characteristic growth rate as predicted by our microscopic model.
Keywords: Kelvin Helmholtz instability, Particle-in-cell, PIConGPU, radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27244 - Permalink


In-situ synthetic radiation diagnostics for laser wakefield acceleration
Pausch, R.; Debus, A.; Huebl, A.; Schramm, U.; Steiniger, K.; Widera, R.; Bussmann, M.
We present recent results of LWFA simulations including in-situ radiation diagnostics performed with the particle-in-cell code PIConGPU. Our results demonstrate the power provided by synthetic radiation diagnostics to determine the laser-plasma dynamics with regard to applications in experiments.

PIConGPU is currently one of the fastest 3D3V particle-in-cell codes and provides an in-situ radiation diagnostic based on Liénard-Wiechert potentials. This synthetic diagnostic is capable of quantitatively predicting the spectrally and directionally resolved far-field radiation of billions of macro-particles by an in-situ implementation in the PIC cycle. Among other things, the code enables resolving the spatial origin and temporal evolution of the radiation, determine the polarization, quantifying both coherent and incoherent radiation simultaneously and covering a frequency range from infrared to x-rays.

The talk briefly introduces the technical background of computing the radiation in-situ on GPUs. Its main focus, however, is the characteristic radiation of LWFA that allows identifying the various stages of the laser-plasma dynamics. Possible applications of these radiation signatures in laboratory experiments will be discussed.
Keywords: Laser Wakefield Accelerator, Particle-in-cell, radiation
  • Lecture (Conference)
    DPG-Frühjahrstagung Würzburg, 19.-23.03.2018, Würzburg, Deutschland

Publ.-Id: 27243 - Permalink


The prognostic value of FMISO-PET-based synchronous tumor and lymph node hypoxia outperforms that of tumor hypoxia only in patients with advanced stage HNSSC – secondary analysis of Dresden FMISO trail
Bandurska-Luque, A.; Löck, S.; Haase, R.; Richter, C.; Zöphel, K.; Perrin, R.; Seidlitz, A.; Zschaeck, S.; Appold, S.; Krause, M.; Steinbach, J.; Kotzerke, J.; Zips, D.; Baumann, M.; Troost, E.
Purpose: Primary tumor (Tu) hypoxia based on hypoxia-PET is a known prognostic parameter for locally-advanced head-and-neck squamous cell carcinoma (HNSCC) patients. This secondary analysis of the prospective clinical trial [1] on repeat [18F]fluoromisonidazole (FMISO) PET/CT before and during radiochemotherapy (RCT) compared the prognostic value of synchronous Tu and lymph node metastases (LN) hypoxia with that of hypoxia only determined in Tu.

Methods: Forty-five LN-positive patients with 103 LNs were included in this analysis. FMISO-PETs were performed at baseline, week 1, 2 and 5 of RCT. Based on a qualitative scale, Tu and LN were independently categorized as hypoxic or normoxic, being FMISO uptake higher than or equal to background, respectively. Two prognostic parameters were defined: Tu-hypoxia (patients with a hypoxic Tu, independent of the LN oxygenation status) and synchronous Tu-and-LN-hypoxia. In fifteen patients with a large LN (n = 21) a quantitative analysis of FMISO PET was performed to validate hypoxia scale and to correlate with regional control (RC). Log-rank, uni- and multivariate Cox test were used to assess the parameters’ prognostic impact on locoregional control (LRC), RC and time to progression (TTP).

Results: Synchronous Tu-and-LN-hypoxia was a strong adverse prognostic factor for LRC and TTP at all time-points (p ≤ 0.005) whereas Tu-hypoxia only was significantly associated with poor LRC in week 2 and 5 (p ≤ 0.004) and with short TTP in week 1, 2 and 5 (p ≤ 0.043). The quantitative FMISO parameters correlated with RC. There was a significant correlation between the qualitative and quantitative FMISO parameters (R > 0.6–0.8).

Conclusions: FMISO-based synchronous hypoxia in the primary tumor and lymph node metastases holds strong prognostic information in HNSCC patients outperforming that based on primary tumor hypoxia only. Confirmation in ongoing prospective trials is intended before introducing in personalized radiation oncology.
  • Lecture (Conference)
    33. Deutscher Krebskongress 2018, 21.-24.02.2018, Berlin, Deutschland

Publ.-Id: 27241 - Permalink


Dose-dependent changes after proton and photon irradiation in zebrafish model
Brunner, S.; Tőkés, T.; Szabó, E. R.; Szabó, I. Z.; Polanek, R.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.
Purpose/Objective: The laser-driven ionizing (LDI) beams have unique property of ultra-high dose rate, ultra-short pulses and carry the potential toward special clinical application. Our aim was to establish an in vivo zebrafish model for radiobiological research on later LDI radiation.
Material/methods: 24 hours post-fertilization (hpf) zebrafish (Danio rerio) embryos were irradiated at the University Proton Therapy Dresden with escalated doses (5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve, at the plateau and at the middle of Spread Out Bragg Peak, and with reference 6 MV photon beams from a clinical linac (n=96 in each group). The experiment was 3 times repeated under the same conditions. On the 3th (96 hpf) and 4th (120 hpf) days after irradiation morphological malformations were documented (photo) and determined quantitatively. Two independent observers measured the length of the embryos, the degree of the yolk sac edema and the diameter of the eyes. Additionally, we have detected the DNA double-strand breaks immunohistochemically (gamma-H2AX foci) after 30 min of the irradiation at the two positions of the proton (mSOBP and plateau) and photon beams, at 5 Gy dose level.
Results: Dose-dependent organ developmental deteriorations could be detected morphologically at >10 Gy dose levels. The length of the embryo and the size of the eyes reduced, while the yolk sac edema increased significantly in dose dependent degree after 10 Gy, 15 Gy, 20 Gy and 30 Gy irradiation, at both developmental stages. At 5 Gy dose irradiation we have found significant elevation in the number of DNA double-strand breaks, as compared to the unirradiated control groups. Furthermore, data showed that after proton irradiation the degree of the DNA damage was higher, as compared to the photon irradiation.
Conclusion: We could establish a reliable quantitative morphological analysis of dose-dependent organ malformations using an in vivo vertebrate system. The zebrafish embryo model proved to be appropriate for complex evaluation of the irradiation-caused damages, molecular changes and for comparison of the biological effects of different radiation qualities. We could define the optimal parameters for future radiobiological experiments with the LDI beams.
Supported by: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund. The project has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no 654148 Laserlab-Europe and by the German BMBF, grant no. 03Z1N511.
  • Open Access LogoAbstract in refereed journal
    Radiotherapy and Oncology 127(2018)1, S588
  • Poster
    37. ESTRO Meeting, 20.-24.04.2018, Barcelona, Spain

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  • Secondary publication expected

Publ.-Id: 27240 - Permalink


Development of zebrafish embryo model for radiobiology research at ELI-ALPS on laser driven hadron beams
Szabó, E. R.; Tőkés, T.; Polanek, R.; Szabó, Z.; Brunner, S.; Czifrus, S.; Fenyvesi, A.; Biró, B.; Beyreuther, E.; Pawelke, J.; Hideghéty, K.
Purpose/objective: High power lasers provide the basis of particle acceleration, but at the actual status of the development, low energy, limited size beams with special properties (ultrahigh dose rate, pulsed mode) are available under technical conditions for radiobiology experiments. Our main aim was to introduce, optimize and validate a vertebrate system for in vivo experiments to study the biological effects of novel hadron beams.
Material/methods: Series of zebrafish embryos in different ages (from 1 hour post-fertilization (hpf) to 72 hpf), in different holders varying the number/well were prepared. For irradiation we used fission neutron (0, 1.25, 1.875, 2, 2.5 Gy), cyclotron-based neutron (0, 2, 4, 6.8, 8.12, 10.28 Gy) and proton (0, 5, 10, 15, 20 and 30 Gy) at two positions along the proton depth-dose curve (PDDC): at the plateau and at the middle of Spread Out Bragg Peak (mSOBP), furthermore, with reference linear accelerator photon (0, 5, 10, 15, 20 Gy) beam (n=96 in each group), repeated several times (≥3). Thereafter, survival, any type of organ developmental disturbance (pericardial edema, spine curvature, shortening of the body length and micro-opthalmia) were detected each days up to 7 post irradiation days (pid). Histological evaluation (size of the eye, brain necrosis, intestinal changes, liver vacuolization, hyper eosinophilic necrotic muscle-fibers) and molecular changes were evaluated with RT-PCR method at certain time points post irradiation.
Results: A higher vulnerability and radiation sensitivity could be observed at earlier stages of the embryogenesis (1-12 hpf). The LD50 was determined with the well reproducible survival curves, resulting in RBE between 10 and 4.8 for the 1MeV and 14MeV neutrons and the Relative Biological Effectivity (RBE) around 1.1-1.4 for proton sources at the two positions respectively. The morphological distortions shown close correlation to the dose delivered and their evaluation on the 4th pid exhibited a good agreement to the survival derived RBE. The gravity of the histopathological changes on the basis of semi-quantitative analysis corresponded well to the macro morphological abnormalities (eye layer disorganization, degree of brain necrosis, increased numbers of the goblet cells in the gastrointestinal tract, and muscle fibrosis).
Conclusion: Numerous features of the zebrafish embryo model makes it amenable for large scale of radiobiological investigations. On the basis of our experimental series the optimal embryonal age (hpf), radiation setup and observation time points for assessment of the different biological endpoints could be established. The defined parameters proved to be suitable for reliable RBE determination.

Acknowledgement: The ELI-ALPS project (GINOP-2.3.6-15-2015-00001) is supported by the European Union and co-financed by the European Regional Development Fund, and by the German BMBF, grant nos. 03ZIK445 and 03Z1N511. The project has received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no 654148 Laserlab-Europe.
  • Poster
    37. ESTRO Meeting, 20.-24.04.2018, Barcelona, Spain
  • Abstract in refereed journal
    Radiotherapy and Oncology 127(2018)Suppl1, S586

Publ.-Id: 27239 - Permalink


Hazard statements: looking for alternatives to toxicity evaluation using LCA
Rodriguez-Garcia, G.; Braun, J.; Peters, J.; Weil, M.
Life Cycle Assessment is a methodology for the evaluation of potential hazards to the environment and to human health. It can be used for decision support when selecting materials for a product. It is a detailed method that can become very labor intensive. As alternatives, we introduce here two methodologies for ranking products and materials according to their safety: Both methods are built on two pieces of European legislation. Hazard Traffic Lights is a qualitative visual way to quickly identify potential hazards. Total Hazard Points is a quantitative method for weighting the different hazards related to a product. It is based on the method developed for the German Environmental Agency (UBA), but its scope includes all materials and hazards, rather than a selection of them. As a case study, we evaluated the 9 batteries described in the UBA study and compared our results with those presented there. In our opinion, batteries are in general terms more hazardous in the UBA study. This is due to more thorough identification of hazards –including some potentially more significant – and the inclusion of all the potential hazards of a material. Since not all the materials present in the battery were quantified, both sets of results should be considered an underestimation of the possible hazard.

Publ.-Id: 27237 - Permalink


AMS of 93 Zr: Passive absorber versus gas-filled magnet
Hain, K.ORC; Deneva, B.; Faestermann, T.; Fimiani, L.; Gómez-Guzmán, J. M.; Koll, D.; Korschinek, G.; Ludwig, P.; Sergeyeva, V.; Thiollay, N.
Two different isobar separation techniques were tested for the detection of the long-lived fission product 93Zr (T1/2T1/2 = 1.64 ·· 106 a) using Accelerator Mass Spectrometry (AMS), i.e. a passive absorber and a gas-filled magnet, respectively. Both techniques were used in combination with a Time-of-Flight path for the identification of the stable neighboring isotopes 92Zr and 94Zr. The passive absorber was represented by a stack of silicon nitride foils for high flexibility regarding the thickness for optimal isobar separation. Ion beams with a large variety of energies, between 80 and 180 MeV, were provided for this experiment by the tandem accelerator at the Maier-Leibnitz Laboratory in Garching, Germany. With these beams, the stopping powers of 93Zr and 93Nb as a function of energy were determined experimentally and compared to the results obtained with the simulation program SRIM. Considerable discrepancies regarding the energy dependence of the two stopping power curves relative to each other were found. The lowest detection limit for 93Zr achieved with the passive absorber setup was 93Zr/Zr = 1 ·· 10−10. In comparison, by optimizing the gas-filled magnet set-up, 93Nb was suppressed by around six orders of magnitude and a detection limit of 93Zr/Zr = 5 ·· 10−11 was obtained. To our knowledge, these results represent the lowest detection limit achieved for 93Zr until now.
Keywords: 93Zr; AMS; Gas-filled magnet; Passive absorber

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Publ.-Id: 27236 - Permalink


Non-covalently Assembled Electroconductive Hydrogel
Xu, Y.; Yang, X.ORC; Thomas, A. K.; Patsis, P. A.; Kurth, T.; Kräter, M.; Eckert, K.ORC; Bornhäuser, M.; Zhang, Y.
Crosslinking biomolecules with electroconductive nanostructures through noncovalent interaction can result in modular networks with defined biological functions and physical properties such as electric conductivity and viscoelasticity. Moreover, the resulting matrices can exhibit interesting features caused by the dynamic assembly process, such as self-healing and molecular ordering. In this paper, we present a physical hydrogel system formed by mixing peptide-polyethylene glycol and poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS). This combinatorial approach, which uses different modular building blocks, could lead to high tunability on aspects of rheology and electrical impedance. The proposed physical hydrogel system is characterized by both a self-healing ability and injectability. Interestingly, the formation of hydrogels at relatively low concentrations led to a network of closer molecular packing of PEDOT nanoparticles, reflected by the enhanced conductivity. The biopolymer system can be used to develop 3D cell cultures with incorporated electric stimuli, as evidenced by its contribution to the survival and proliferation of encapsulated mesenchymal stromal cells and their differentiation upon electrical stimulation.
Keywords: self-assembling, PEDOT:PSS, peptide, electroconductive hydrogel, 3D cell

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  • Secondary publication expected from 12.04.2019

Publ.-Id: 27229 - Permalink


Results of the stationary measurements at COSMEA-I facility - CT part
Bieberle, A.; Boden, S.; Beyer, M.; Hampel, U.

At the COSMEA-I facility cross-sectional distributions of the condensated steam is measured at five different positions along a slightly inclined condensator-tube using adapted conventional CT imaging technique based on X-ray. This data set contains the reconstructed raw data of the CT imaging scans.

Keywords: Passive heat transfer; Conventional CT imaging; Reconstructed raw data of the CT imaging scan
  • Reseach data in the HZDR data repository RODARE
    Publication date: 2018-03-20
    DOI: 10.14278/rodare.3

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Publ.-Id: 27228 - Permalink


Molekulare Bildgebung in der Onkologie mittels Positronen-Emissions-Tomographie
Derlin, T.; Grünwald, V.; Steinbach, J.; Wester, H.-J.; Ross, T. L.
Hintergrund: Mit der Positronenemissionstomographie (PET) steht ein Verfahren in der klinischen Bildgebung zur Verfügung, dass bei Durchführung als Hybridverfahren mit Computertomographie (CT) oder Magnetresonanztomographie (MRT) die simultane Erfassung anatomischer und molekularer Informationen ermöglicht. Die PET besitzt eine hohe Sensitivität zur Detektion von Tumormanifestationen. Unterschiedliche Radiopharmaka dienen der Charakterisierung verschiedener Stoffwechselprozesse oder der Analyse der Expression von Rezeptoren, Enzymen und weiteren molekularen Zielstrukturen.
Methode: Selektive Literaturrecherche in PubMed unter Bezug auf nationale und internationale Leitlinien sowie systematische Übersichtsarbeiten und Metaanalysen.
Ergebnisse: Etablierte PET Radiopharmaka wie 2-[18F]Fluor-2-desoxyglukose ([18F]FDG) erlauben die Darstellung physiologischer Prozesse auf molekularer Ebene und können entscheidende Informationen für die klinische Versorgung liefern. Für die PET stehen in zunehmendem Umfang neben gut erforschten und evaluierten auch neuere Radiopharmaka zur nicht-invasiven Phänotypisierung von Tumorerkrankungen zur Verfügung, beispielsweise zur Analyse der Expression des prostataspezifischen Membranantigens (PSMA) oder von Chemokinrezeptoren (z.B. CXCR4) auf Tumorzellen.
Schlussfolgerung: Die PET stellt einen wichtigen Bestandteil diagnostischer Algorithmen in der Onkologie dar, kann die Präzision der Diagnostik verbessern und helfen, die Therapie zu individualisieren. Eine zunehmende Anzahl an PET Radiopharmaka erweitert die verfügbaren Bildgebungsoptionen. Viele Radiopharmaka erlauben neben der nicht-invasiven Analyse der Expression therapeutisch relevanter
Zielstrukturen auch eine nachfolgende zielgerichtete Radionuklidtherapie.

Publ.-Id: 27227 - Permalink


Experimental Signals for Broxen Axial Symmetry in Excited Heavy Nuclei From The Valley of Stability
Grosse, E.; Junghans, A. R.
An increasing number of experimental data indicates the breaking of axial symmetry in many heavy nuclei already in the valley of stability:
Multiple Coulomb excitation analysed in a rotation invariant way, gamma transition rates and energies in odd nuclei, mass predictions, the splitting of Giant Resonances (GR), the collective enhancement of nuclear level densities and Maxwellian averaged neutron capture cross sections. For the interpretation of these experimental observations, the axial symmetry breaking shows up in nearly all heavy nuclei as predicted by Hartree–Fock–Bogoliubov (HFB) calculations; this indicates a nuclear Jahn–Teller effect.
We show that nearly no parameters remain free to be adjusted by separate fitting to level density or giant resonance data, if advance information on nuclear deformations, radii etc. are taken from such calculations with the force parameters already fixed. The data analysis and interpretation have to include the quantum mechanical requirement of zero point oscillations and the distinction between static vs. dynamic symmetry breaking has to be regarded.
  • Open Access LogoContribution to proceedings
    XXIV Nuclear Physics Workshop “Marie and Pierre Curie”, Kazimierz Dolny, Poland, September 20–24, 2017., 20.-24.09.2017, Kazimierz Dolny, Polen
    Acta Physica Polonica B, Vol. 11, No. 1-37
    DOI: 10.5506/APhysPolBSupp.11.37

Publ.-Id: 27226 - Permalink


Diffusion of oxygen in bcc Fe under the influence of other foreign atoms
Wang, X.; Posselt, M.; Faßbender, J.
First-principle calculations and kinetic Monte Carlo simulations are applied to investigate the diffusion of oxygen in bcc Fe under the influence of other foreign atoms, such as Al, Si, P, S, Ti,, Cr, Mn, Ni, Y, and Mo. In the first part of this work jumps of oxygen in pure bcc Fe, between first-, second-, and third-neighbor octahedral interstitial sites were investigated by DFT. It is found that a second-neighbor jump consists of two consecutive first-neighbor jumps and that the barrier of the third-neighbor jump is too high to be relevant. In the second part DFT was applied to determine the modified migration barriers, i.e. for the oxygen jump between the first and the second neighbor of a foreign atom, etc. It is found that Si, P, Ni and Mo influence the migration barriers of oxygen only slightly. Al and Cr cause moderate changes, while S, Ti, and Y lead to strong modifications. With the exception of Y the migration paths are first-neighbor jumps between (modified) octahedral sites with (modified) tetrahedral sites as saddle points. Y changes some migration paths considerably. Using the migration barriers calculated by DFT the diffusion coefficient of oxygen was determined by kinetic Monte Carlo simulations considering a dilute iron alloy. In general the foreign atoms cause a reduction of the mobility of oxygen compared to that in pure bcc Fe. The strongest decrease is obtained for the foreign atoms S, Ti, and Y.
Keywords: Diffusion, oxygen, bcc Fe, Density Functional Theory, Kinetic Monte Carlo simulations
  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deutschland

Publ.-Id: 27225 - Permalink


Structure and energetics of Y-Ti-O nanoclusters in bcc Fe
Vallinayagam, M.; Posselt, M.; Faßbender, J.
In this research project the nature of yttria-based oxide nanoclusters in a bcc Fe matrix is investigated by DFT calculations. The main goal of these studies is the better understanding of the nucleation as well as the structure and composition of the clusters.
In the first part of the work three types of structures are considered: (i) clusters consisting of parts of the bixbyite (Y2O3) or pyrochlore (Y2Ti2O7) structure embedded in bcc Fe, (ii) clusters with Y, Ti, and O on substitutional sites, and (iii) clusters with of Y, Ti, on substitutional sites and O on octahedral interstitial sites of the bcc lattice. Simulation cells containing different structures but the same composition of atoms (Fe, Y, Ti, O) are compared. It is found that the energetics of three different structure types, i.e. their total binding energy, is very similar. This modifies the statement of Barnard et al. [1] who only considered the first type of structure and concluded that this is the most favorable. Further, more stable cluster structures are constructed using another model with the nanocluster core similar to the metal monoxide structure. Also the binding energy of monomers like O, Y, Ti, and the vacancy to the cluster are studied. O and the vacancy are strongly attracted by the nanoclusters, while the interaction with metal atoms is weaker.
[1] L. Barnard et al. Acta Mater. 60 935 (2012)
Keywords: Density Functional Theory, Y-Ti-O nanoclusters, bcc Fe
  • Poster
    DPG-Frühjahrstagung und EPS-CMD27, 11.-16.03.2018, Berlin, Deustchland

Publ.-Id: 27224 - Permalink


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